JP6528572B2 - Image forming device - Google Patents

Description

  The present invention relates to an image forming apparatus such as a printer and a copying machine, and more particularly to an image forming apparatus that executes an image stabilization operation such as color misregistration correction and density correction of a color image.

  For example, a tandem-type color image forming apparatus arranges image forming units for respective colors mainly including a photosensitive drum and a transfer unit along an intermediate transfer belt, and in each of the image forming units, the photosensitive drum is light from a light source After exposure scanning with a beam to form a latent image, the latent image is developed with toner to form a toner image, and then these are multi-transferred onto the intermediate transfer belt, and each color toner image after multi-transfer is recorded It is configured to be collectively transferred onto the sheet.

In such an image forming apparatus, an image stabilization operation is performed in order to prevent deterioration of the image quality of the reproduced image after printing due to deterioration with time of the photosensitive drum, developer, etc., and temperature and humidity fluctuations around the apparatus. There are many things to do.
The image stabilization operation includes resist correction, density correction, and the like.
With registration correction, in order to prevent color misregistration of each color toner image, for example, a resist pattern of each color is formed on each of a plurality of areas spaced at regular intervals in the belt circulation direction on the intermediate transfer belt by an imaging unit for each color. The position of the resist pattern of each color is detected by the optical sensor, the amount of positional deviation of each color is determined based on the detection result, and the image forming position (writing position) of each color is corrected from the determined amount of positional deviation. It is a thing.

Density correction means that, for example, a gradation density pattern is formed on the intermediate transfer belt for each color by an image forming unit for each color, the density of each density pattern is detected by an optical sensor, and each color is selected based on the detection result. The density of the reproduced image is corrected.
The correction control is executed, for example, when the number of printed sheets reaches a predetermined value, or when a predetermined start-up condition such as when the variation amount of temperature and humidity in the apparatus exceeds a predetermined value.

JP, 2010-217602, A

The optical sensor described above comprises a light emitting portion that emits light toward the circumferential surface of the intermediate transfer belt, and light reflected from a resist pattern or a density pattern formed on the circumferential surface of the intermediate transfer belt among the light emitted from the light emitting portion Alternatively, a light receiving unit that detects transmitted light is provided, and each pattern is detected by photoelectrically converting the amount of the detected reflected light or transmitted light.
The amount of light emitted from the light emitting unit is likely to change with time due to, for example, deterioration of the light source of the light emitting unit or adhesion of dust or floating toner to the light source in the apparatus. If the light emission amount of the light emitting portion fluctuates every time the image stabilization operation is performed, even if the same pattern is formed on the intermediate transfer belt before and after the fluctuation, the light amount of reflected light or transmitted light from the pattern fluctuates. Therefore, each pattern on the intermediate transfer belt can not be detected with high accuracy.

Therefore, usually, at the beginning of the image stabilization operation, sensor adjustment is performed to adjust the light emission amount of the light emitting unit to an appropriate value. Specifically, in the sensor adjustment, the bare surface area of the circumferential surface of the intermediate transfer belt is irradiated with the light from the light emitting unit, the reflected light or the transmitted light is detected by the light receiving unit, and the detected light quantity falls within the predetermined range. As described above, the adjustment is performed by adjusting the light emission amount of the light emitting unit.
If resist correction and density correction are performed after this sensor adjustment, the detection accuracy of the resist pattern and density pattern can be improved, but since it takes a certain amount of time for sensor adjustment, the entire image stabilization operation from the start to the end The image stabilization operation time will be long.

  The image stabilization operation is performed when a predetermined start condition such as when the number of prints reaches a predetermined value is satisfied as described above. For example, if a predetermined start condition is satisfied during print job execution, the job may be interrupted, and the job may be resumed after execution of the image stabilization operation. In such a case, the longer the image stabilization operation time, the lower the productivity of the job. Therefore, it is desirable that the image stabilization operation time be shortened as much as possible.

  The present invention has been made in view of the above problems, and provides an image forming apparatus capable of shortening the overall image stabilization operation time while improving the pattern detection accuracy by sensor adjustment. It is an object.

In order to achieve the above object, an image forming apparatus according to the present invention forms toner images of different colors on a plurality of photosensitive members by an image forming unit, and rotates the respective color toner images on an intermediate transfer member rotating An image forming apparatus for transferring each color toner image after the transfer onto a sheet after multiple transfer onto the sheet, and controlling the image forming means in the rotational direction on the bare surface of the peripheral surface of the intermediate transfer member. After forming a resist pattern of each color for performing a resist correction for correcting the displacement of the formation position of each color toner image in each of a plurality of first regions spaced by a predetermined distance, the second on the circumferential surface of the intermediate transfer member Control means for forming a density pattern of each color for performing density correction of a toner image in an area, light emitted from the light emitting portion toward the intermediate transfer member, light reflected from the intermediate transfer member or transmitted from the light Sen to detect light And image stabilization means for performing the resist correction and the density correction in this order on the basis of the detection result of the resist pattern and the density pattern detected by the sensor on the peripheral surface of the intermediate transfer member, and the image stabilization The light emission unit is configured to emit the light based on the detection result of the first bare surface area located downstream of the first area at the most downstream side in the rotation direction among the plurality of first areas on the circumferential surface of the intermediate transfer member. A determination unit configured to determine whether the light emission amount of the unit is within a range in which the resist pattern can be detected; and if the determination result by the determination unit is affirmative, the plurality of The intermediate transfer is performed between the time when the resist pattern formed in the first region in the most downstream direction in the rotational direction is detected and the density pattern formed in the second region is detected. Wherein not one of the resist patterns formed in the circumferential surface, wherein the first bare surface area determines the light emission amount of the light emitting portion based on a detection result of the sensor of another bare surface area, determined light emission amount The first sensor adjustment for causing the light emitting unit to emit light is executed, and in the negative case, the formation timing of the resist pattern and the density pattern on the intermediate transfer member by the control means is predetermined than in the positive case. By delaying the time, another second bare surface region is secured between the first bare surface region and the most downstream first region, and the resist pattern formed in the most downstream first region is further secured. Before the start of detection by the sensor, the light emission amount of the light emitting unit is determined based on the detection signal of the secured second bare surface area by the sensor, and the light emission unit emits light by the determined light emission amount To perform a second sensor adjustment .

  Here, the determination unit further determines that the light emission amount of the light emitting unit can detect both the resist pattern and the density pattern based on the detection result of the first bare surface area by the sensor. If it is determined that the light emission amount of the light emitting unit is within a range in which both the resist pattern and the density pattern can be detected, The execution of both the one sensor adjustment and the second sensor adjustment may be prohibited.

  Further, the control means forms both the resist pattern and the density pattern only when a predetermined first condition is satisfied, and when the predetermined second condition different from the first condition is satisfied, The image forming means is controlled to form a resist pattern of the same color as the resist pattern on each of the plurality of first regions on the circumferential surface of the intermediate transfer member, and the density pattern is not formed. When the resist pattern is formed by satisfying the second condition, a third bare surface area located downstream of the most downstream first area among the plurality of first areas on the circumferential surface of the intermediate transfer member Based on the detection result by the sensor, it is determined whether the light emission amount of the light emitting unit is within the range where the formed resist pattern can be detected, and the image stabilization unit When the second condition is satisfied, the resist correction of the same method as the resist correction is performed, the density correction is not performed, and the judgment result of the judging means when the second condition is satisfied is If negative, only the sensor adjustment of the same method as the second sensor adjustment may be performed, and if the determination result is positive, only the sensor adjustment of the same method as the first sensor adjustment may be performed. .

Furthermore, the image stabilization means emits light with the same amount of light emission as the amount of light emission determined in the previous sensor adjustment to the light emitting portion when the first bare surface area is detected by the sensor. It is also possible to give an instruction on the amount of light emission.
In the image forming apparatus according to another aspect of the present invention, toner images of different colors are formed on each of a plurality of photosensitive members by image forming means, and the respective color toner images are multiply transferred onto a rotating intermediate transfer member. After that, the image forming apparatus transfers each color toner image after the transfer onto a sheet, wherein the image forming means is controlled to set a predetermined interval in the rotational direction on the bare surface of the peripheral surface of the intermediate transfer member. After forming a resist pattern of each color for performing resist correction for correcting displacement of the formation position of each color toner image in each of the plurality of opened first regions, the toner is formed in the second region on the circumferential surface of the intermediate transfer member. Control means for forming a density pattern of each color for performing density correction of the image, light from the light emitting portion toward the intermediate transfer member, and detection of reflected light or transmitted light of the light from the intermediate transfer member Sensor and the above An image stabilization unit that executes the resist correction and the density correction in this order based on the detection result of the resist pattern and the density pattern by the sensor on the peripheral surface of the transfer member, the image stabilization unit further comprising Between the time when the resist pattern formed in the first area in the most downstream side in the rotational direction of the plurality of first areas is detected by the sensor and the density pattern formed in the second area is detected The amount of light emission of the light emitting unit is determined based on the detection result of the sensor on the bare surface area where none of the resist patterns are formed on the peripheral surface of the intermediate transfer member, and the light emitting unit is made to emit light perform sensor adjustment to the bare surface regions, wherein the intermediate transfer member peripheral surface, each set of two first regions adjacent to the rotational direction A bare surface area existing between one first area and the other first area of any one set, or a bare surface area existing between the uppermost stream first area and the second area It is characterized in that it is the said bare surface area in.

In the image forming apparatus according to still another aspect of the present invention, toner images of different colors are formed on each of a plurality of photosensitive members by image forming means, and the respective color toner images are multiplexed on a rotating intermediate transfer member An image forming apparatus for transferring each color toner image after transfer to a sheet after transfer, wherein the image forming means is controlled to set a predetermined interval in the rotational direction on the bare surface of the peripheral surface of the intermediate transfer member. After forming resist patterns of each color for performing resist correction for correcting the displacement of the formation position of each color toner image in each of the plurality of first areas opened, the second area on the circumferential surface of the intermediate transfer member Control means for forming density patterns of respective colors for performing density correction of a toner image, light emitted from a light emitting portion toward the intermediate transfer member, and light reflected or transmitted from the intermediate transfer member of the light With a sensor to detect An image stabilization unit that executes the resist correction and the density correction in this order based on the detection result of the resist pattern and the density pattern by the sensor on the circumferential surface of the intermediate transfer member, the image stabilization unit comprising Between the time when the resist pattern formed in the first area in the most downstream side in the rotational direction of the plurality of first areas is detected by the sensor and the density pattern formed in the second area is detected The amount of light emission of the light emitting unit is determined based on the detection result of the sensor on the bare surface area where none of the resist patterns are formed on the peripheral surface of the intermediate transfer member, and the light emitting unit is made to emit light perform sensor adjustment to further the image stabilizing means, said at sensor adjustment, reflected light or moisture from the bare surface regions of the intermediate transfer body Based on the detection result by the sensor until the light reaches the target value, the light emission amount of the light emission portion is determined by executing the light emission amount control that instructs the light emission portion to change the light emission amount. In controlling the light emission amount, one of the first region and the other first region of any one of the two sets of first regions adjacent in the rotational direction on the circumferential surface of the intermediate transfer member If the light emission control is being performed at the end of the detection of the bare surface area by the sensor, the light emission control is temporarily interrupted, and the circumferential surface of the intermediate transfer member is more than the one set. A bare surface area existing between one first area and another first area of another set located on the upstream side, or a bare surface area existing between the uppermost first area and the second area In this case, the bare surface area is at the detection position of the sensor. Upon reaching, with respect to the light-emitting from the light emission amount at the point of interruption it is characterized in that an instruction to resume the interrupted though light emission amount control as is resumed.

In the image forming apparatus according to still another aspect of the present invention, toner images of different colors are formed on each of a plurality of photosensitive members by image forming means, and the respective color toner images are multiplexed on a rotating intermediate transfer member An image forming apparatus for transferring each color toner image after transfer to a sheet after transfer, wherein the image forming means is controlled to set a predetermined interval in the rotational direction on the bare surface of the peripheral surface of the intermediate transfer member. After forming resist patterns of each color for performing resist correction for correcting the displacement of the formation position of each color toner image in each of the plurality of first areas opened, the second area on the circumferential surface of the intermediate transfer member Control means for forming density patterns of respective colors for performing density correction of a toner image, light emitted from a light emitting portion toward the intermediate transfer member, and light reflected or transmitted from the intermediate transfer member of the light With a sensor to detect An image stabilization unit that executes the resist correction and the density correction in this order based on the detection result of the resist pattern and the density pattern by the sensor on the circumferential surface of the intermediate transfer member, the image stabilization unit comprising Furthermore, from the detection of the resist pattern formed in the first region of the plurality of first regions in the most downstream direction of the rotation direction by the sensor to the detection of the density pattern formed in the second region In the meantime, the light emitting amount of the light emitting portion is determined based on the detection result by the sensor of the bare surface area on which the resist pattern is not formed on the peripheral surface of the intermediate transfer member, and the light emitting portion perform sensor adjustment to emit light, said control means, said in the intermediate transfer body circumferential surface, of the two first area included in the plurality of first regions The resist patterns of the respective colors formed in the first region on the downstream side and the resist patterns of the respective colors formed in the first region on the upstream side have one cycle of the intermediate transfer member of the same color. It is characterized in that it is formed on the intermediate transfer member so as to be formed at a distant position for half a period of time.

According to the above configuration, in the configuration in which the resist pattern is formed on each of the plurality of first regions spaced in the rotational direction on the intermediate transfer body, for example, the most downstream region of the plurality of first regions The sensor adjustment can be performed using the bare surface area where the resist pattern is not formed between the adjacent area and the area.
As a result, the sensor adjustment can be performed in parallel with the resist pattern detection operation from the start to the end of the resist correction. Therefore, the sensor adjustment is performed first as in the prior art, and after the end, the resist correction and the density correction are performed. The entire image stabilization operation time can be shortened as compared with the configuration in which the above are sequentially executed.

FIG. 1 is a diagram showing an entire configuration of an MFP according to a first embodiment. FIG. 2 is a diagram showing a configuration of a control unit of the MFP. FIG. 2 is a diagram showing a configuration of a detection sensor provided in the MFP. It is a flowchart which shows the content of the stabilization request | requirement determination processing. It is a figure which shows the content of the correction control performed about each of three types of image stabilization operation | movement. FIG. 6 is a view showing an example of forming various toner patterns formed on the circumferential surface of the intermediate transfer belt when long stabilization is performed. It is an enlarged view of a resist pattern formed in a resist amendment field. (A) is a figure which shows the example of formation of the various toner patterns formed in the peripheral surface of an intermediate transfer belt, when performing 2nd short stabilization, (b) performs 3rd short stabilization FIG. 6 is a view showing an example of formation of various toner patterns formed on the circumferential surface of the intermediate transfer belt in the case where It is a flowchart which shows the processing content of image stabilization operation | movement. It is a flow chart which shows the contents of the subroutine of pattern formation timing directions processing. It is a flowchart which shows the content of the subroutine of a registration correction (+ IDC sensor adjustment) process. FIG. 14 is a flowchart showing the processing content of the image stabilization operation according to Embodiment 2. FIG.

Hereinafter, an embodiment of an image forming apparatus according to the present invention will be described by taking a tandem-type multifunctional multifunction device (hereinafter, referred to as “MFP (Multiple Function Peripheral)) as an example.
Embodiment 1
[MFP Overall Configuration]
FIG. 1 is a diagram showing the entire configuration of the MFP 1, and FIG. 2 is a diagram showing the configuration of the control unit 7 of the MFP 1. FIG. 1 schematically shows an example of the sensor input parameter 10 and the control output parameter 12 in the engine control unit 30 of the control unit 7 shown in FIG.

  As shown in FIG. 1, the MFP 1 is provided with a scanner unit 2 and a print unit 3, and is a copy job for reading an original image and printing the image on a recording sheet, sent from an external terminal via a network such as LAN. The MFP is a multi-function multifunction peripheral capable of executing a print job for printing an image of the data on a recording sheet, and a fax job for performing facsimile communication with an external facsimile apparatus.

The scanner unit 2 is a known device for reading an image of a set document to obtain image data. The printing unit 3 forms an image by an electrophotographic method or the like, and in this case, includes an image processing unit 4, a feeding unit 5, a fixing unit 6, and a control unit 7.
The image processing unit 4 includes image forming units 20Y, 20M, 20C, and 20K corresponding to respective reproduction colors of yellow (Y), magenta (M), cyan (C), and black (K), and a print head 26. , The intermediate transfer belt 27 and the like.

The intermediate transfer belt 27 is stretched around a driving roller 271 and a driven roller 272, and is driven to circulate in an arrow B direction.
The image forming units 20Y to 20K are disposed in series at predetermined intervals along the downstream side from the upstream side in the belt traveling direction so as to face the intermediate transfer belt 27, and each of them is detachable from the apparatus main body. Exchange of is possible.

The image forming unit 20 Y includes a photosensitive drum 21 as an image carrier, a charging unit 22 disposed around it, a developing unit 23, and a primary transfer opposing the photosensitive drum 21 with the intermediate transfer belt 27 interposed therebetween. A roller 24 and a cleaner 25 are provided. This configuration is the same for the other image forming units 20M to 20K, and the reference numerals are omitted in the figure.
The print head 26 deflects the laser beams emitted from the four laser diodes 34 (FIG. 2) and the respective laser diodes for reproduction color, and the surfaces of the photosensitive drums 21 of the image forming units 20Y to 20K. And a scanning lens (not shown) for exposing and scanning in the main scanning direction.

  The feeding unit 5 conveys the sheet feeding cassettes 51 and 52 for storing the recording sheets S, feeding rollers 53 and 54 for feeding the recording sheets S in the sheet feeding cassettes 51 and 52 one by one, and the fed recording sheets S. A pair of transport rollers 55, a pair of timing rollers 56 for timing to feed the recording sheet S to the secondary transfer position 571, and a secondary transfer pressed against the driven roller 272 with the intermediate transfer belt 27 at the secondary transfer position 571. The roller 57 is provided. The fixing unit 6 includes a heater (not shown) and is maintained at a predetermined fixing temperature.

[Configuration of control unit 7]
The control unit 7 includes an engine control unit 30 and a print controller 40 as shown in FIG. 2, and both can exchange data such as signals with each other. The engine control unit 30 mainly controls the image forming operation in the printing unit 3 and controls the image forming units 20Y to 20K, etc. A pattern forming unit 301 for forming the patterns 630, 640 and the like (FIG. 6), and an image stabilization control unit 302 for executing an image stabilization operation.

The print controller 40 controls the document image reading operation in the scanner unit 2. Further, the input of the operation panel 8 is received, and communication with an external terminal such as the PCs 91 to 93 and facsimile communication with an external facsimile machine via a FAX interface (IF) 47 are performed.
In a storage unit (not shown) in the print controller 40, image data of various toner patterns 630, 640 and the like (FIG. 6) formed in an image stabilization operation described later is stored. When the engine control unit 30 requests the print controller 40 for the image data, the data is sent to the engine control unit 30.

  In such a configuration, for example, upon receiving a copy job execution instruction, the following processing is executed. That is, reading of the document image is started by the scanner unit 2. The read image signal is sent to the print controller 40 of the control unit 7. The print controller 40 acquires the color shift correction amount and the gradation correction table data (FIG. 1) sent from the engine control unit 30 as control output parameters. The control output parameter is obtained in order to set the image quality of the formed image to a certain level or more in the image stabilization operation, and is stored in advance in the backup memory 38.

  The print controller 40 converts the image signal read by the scanner unit 2 into image data of each reproduction color, develops the image data in the RAM 44, and performs necessary correction based on control output parameters such as a color shift correction amount. In the case of printing an image in a print job or a fax reception job, necessary correction is similarly performed on an image signal from an external terminal such as the PC 91 or a facsimile machine. Further, when it is instructed by the user to save the image data related to the job, the image data is stored in the HDD 45.

  The engine control unit 30 receives the image data corrected by the print controller 40 as CCD read data which is one of the sensor input parameters, and performs correction processing based on the LD light quantity as a control output parameter and the gamma correction data in the image data. To generate a drive signal for the laser diode 34 for each color. The generated drive signals drive the respective laser diodes 34 of the print head 26, and laser beams are emitted from the respective laser diodes 34 respectively.

  In each of the imaging units 20Y to 20K, after the photosensitive drum 21 rotating in the direction of arrow A is cleaned by the cleaner 25, the surface of the photosensitive drum 21 charged and uniformly charged by the charging unit 22 is printed. The latent image is formed by exposure by the laser beam from the head 26, and the formed latent image is developed by the developing unit 23 with toner. For each of the image forming units 20Y to 20K, a voltage based on the charging bias output parameter is supplied to the charging unit 22 from the charging grid high voltage power supply 31 (FIG. 2), and the developing bias 23 is supplied with the developing bias high voltage power supply 32 (FIG. ) Provides a voltage based on the development bias output parameter.

  The primary transfer voltage from the transfer high voltage power supply 33 is applied to the primary transfer roller 24 for each of the image forming units 20Y to 20K, and the developed toner images of the respective colors are photoreceptors by the action of the electric field of the primary transfer roller 24. The toner is primarily transferred from the drum 21 onto the intermediate transfer belt 27. At this time, the image forming operation of each color is performed at a shifted timing so that the toner image is transferred in an overlapping manner at the same position on the intermediate transfer belt 27. The respective color toner images on the intermediate transfer belt 27 move to the secondary transfer position 571 by the traveling of the intermediate transfer belt 27.

The recording sheet S is fed from the sheet feeding cassette selected by the control unit 7 through the timing roller pair 56 from the feeding unit 5 in accordance with the movement timing of each color toner image onto the intermediate transfer belt 27. The recording sheet S is conveyed while being sandwiched between the intermediate transfer belt 27 and the secondary transfer roller 57, which are circulated.
A secondary transfer voltage from the transfer high voltage power supply 33 is applied to the secondary transfer roller 57, and the secondary transfer roller 57 electrostatically acts on the intermediate transfer belt 27 at the secondary transfer position 571 by the action of the electric field by the secondary transfer roller 57. The color toner images are collectively secondarily transferred onto the recording sheet S.

The recording sheet S which has passed the secondary transfer position 571 is conveyed to the fixing unit 6, where the toner image is heated and pressed to be fixed on the recording sheet S, and then discharged to the outside by the discharge roller pair 58. Ru. The residual toner remaining on the intermediate transfer belt 27 without being secondarily transferred to the recording sheet S among the color toner images on the intermediate transfer belt 27 is removed by the cleaner 28.
Although the printing operation of the color image has been described above, the MFP 1 can selectively print not only the color mode but also the monochrome mode, for example, an image of only the black color. In the monochrome mode, only the black image forming unit 20K is driven to primarily transfer the black toner image to the intermediate transfer belt 27, and the toner image is secondarily transferred to the recording sheet S. Be done.

  The cumulative number of printed recording sheets is managed by the backup memory 38. Specifically, the print controller 40 instructs the engine control unit 30 to print one sheet of recording sheet S after the image stabilization operation is performed until the next image stabilization operation is performed. Every time it is executed, the current cumulative print number stored in the backup memory 38 is incremented by "1" to update the cumulative print number, and the current cumulative print number is set to 0 at the start of the next image stabilization operation. Make it reset. This makes it possible to know whether the accumulated number of prints from the end of the previous image stabilization operation to the present has reached the predetermined number for which the image stabilization operation should be performed.

The operation panel 8 is provided at an easy-to-operate position on the front surface of the scanner unit 2. In addition to a copy start key for instructing copy start and a key for selecting a print mode, operation panel 8 displays a touch panel displaying a message screen indicating the status of MFP 1, for example, that job execution is possible. The liquid crystal display unit of the formula is provided.
The surface of the intermediate transfer belt 27 is at a position downstream of the image forming unit 20 K in the belt traveling direction of the intermediate transfer belt 27 and upstream of the secondary transfer position 571 around the intermediate transfer belt 27. An IDC sensor 35 is disposed to face each other.

The IDC sensor 35 is formed by arranging two detection sensors 35a and 35b (FIG. 6) at predetermined intervals on one straight line in the main scanning direction (direction orthogonal to the belt traveling direction B). 6 shows the positional relationship between the intermediate transfer belt 27 and the detection sensors 35a and 35b when the intermediate transfer belt 27 is viewed in the direction of arrow D in FIG.
The detection sensor 35a is a reflective optical sensor including a light emitting unit 351 including a light source such as a light emitting diode as shown in FIG. 3 and a light receiving unit 352 including a light receiving element such as a photodiode. The image stabilization control unit 302 of the engine control unit 30 instructs the light emitting unit 351 on a light emission duty ratio (Dty) indicating a light emission amount. The light emitting unit 351 emits light Lt of the light emission amount according to the light emission duty ratio instructed from the image stabilization control unit 302 of the engine control unit 30 by PWM control. The detection sensor 35b also has the same configuration as the detection sensor 35a, and each detection sensor individually outputs a detection signal.

  Returning to FIG. 1, an in-machine temperature / humidity detection sensor 36 for detecting the temperature / humidity in the apparatus is disposed in the apparatus and in the vicinity of the timing roller pair 56. In addition, a PH temperature detection sensor 37 is disposed in the vicinity of the optical path of the laser beam from the print head 26 to each of the photosensitive drums 21 of the imaging units 20Y to 20K. The signals from these sensors are sent to the engine control unit 30 as one of the sensor input parameters 10 respectively.

The image stabilization control unit 302 of the engine control unit 30 receives the detection signal from the IDC sensor 35, and determines the formation position, density, and the like of various toner patterns formed on the bare surface of the circumferential surface of the intermediate transfer belt 27. To detect.
Further, based on detection signals from the in-machine temperature / humidity detection sensor 36 and the PH temperature detection sensor 37, the in-machine temperature / humidity near the secondary transfer position 571 and the temperature (PH temperature) around the print head 26 are detected. Then, the image stabilization control unit 302 of the engine control unit 30 executes the image stabilization operation for maintaining the level of the image quality of the reproduced image at a certain level or more with respect to the print controller 40 based on the detection result of each sensor. Is executed to determine whether or not to request.

[Stabilization request judgment processing]
FIG. 4 is a flowchart showing the contents of the stabilization request determination process. This determination process is executed by the image stabilization control unit 302 of the engine control unit 30 each time it is read out by the main routine (not shown) at predetermined intervals.
There are three types of image stabilization operations, long stabilization, short stabilization, and resist, each of which is selectively executed when a predetermined start condition is satisfied.

As shown in the figure, it is determined whether a new item is attached to the printing unit 3 (replaced with a new unit) for any of the image forming units 20Y to 20K (step S1). The determination of the attachment of the new unit is performed by detecting that the user has input information to that effect via the operation panel 8, for example, but another method may be used.
If it is determined that the new unit has been installed ("Yes" in step S1), long stabilization is requested (step S2), and the process returns. Details of the long stabilization operation will be described later.

If it is determined that the new unit has not been installed ("No" in step S1), it is determined whether or not there has been a change in the cabin environment from the previous image stabilization operation (step S3). Here, the previous image stabilization operation means the latest one among long stabilization, short stabilization, and resist executed in the past.
Here, if the difference ΔH between the temperature and humidity inside the machine at the time of the previous image stabilization operation and the temperature and humidity inside the machine at present is more than a predetermined value for each of temperature and humidity It is determined that there is no change in the cabin environment. The internal temperature and humidity at the time of the previous image stabilization operation are those stored in the backup memory 38 at the time of the previous execution of the image stabilization operation.

If it is determined that there is a change in the environment inside the aircraft ("Yes" in step S3), long stabilization is requested (step S4), and the process returns.
If it is determined that there is no change in the environment inside the machine ("No" in step S3), whether the cumulative number of prints J from the end of the previous image stabilization operation to the present has reached the predetermined number J1 for image stabilization operation It is determined whether or not it is (step S5). The cumulative print count J from the end of the previous image stabilization operation is stored in the backup memory 38.

If it is determined that the cumulative number of printed sheets has reached the predetermined number ("Yes" in step S5), short stabilization is requested (step S6), and the process returns. Details of the short stabilization operation will be described later.
If it is determined that the cumulative number of printed sheets has not reached the predetermined number ("No" in step S5), it is determined whether there has been a change in PH temperature from the previous image stabilization operation (step S7). Specifically, it is determined whether the difference between the PH temperature at the time of the previous image stabilization operation and the current PH temperature is equal to or greater than a predetermined value ΔT. The PH temperature at the time of the previous image stabilization operation is the one stored in the backup memory 38 at the time of the previous execution of the image stabilization operation.

If it is determined that there has been a change in PH temperature ("Yes" in step S7), a resist is requested (step S8), and the process returns. Details of the resist will be described later.
If it is determined that there is no PH temperature change ("No" in step S7), the process returns without making an image stabilization request (step S9).
Thus, each of the long stabilization, short stabilization, and resist has different start conditions, specifically, long stabilization is the first condition (such as replacement of a new unit), and short stabilization is the second condition (the accumulated number of printed sheets). ), Is required when the resist satisfies the third condition (PH temperature change).

  When the print controller 40 receives an execution request for the image stabilization operation from the engine control unit 30, for example, if the job is being executed, the interruption of the job and the execution of the requested image stabilization operation are sent to the engine control unit 30. To direct. The image stabilization control unit 302 of the engine control unit 30 executes job interruption, an image stabilization operation, and the like based on an instruction from the print controller 40.

[Long Stabilization, Short Stabilization, Resist Content]
FIG. 5 is a diagram showing the contents of three types of image stabilization operations, that is, the contents of correction control performed for each of long stabilization, short stabilization, and resist, and FIG. 6 is a case where long stabilization is performed. FIG. 6 is a view showing an example of formation of various toner patterns formed on the bare surface of the circumferential surface 27 a of the intermediate transfer belt 27. The image stabilization operation is executed by the image stabilization control unit 302, and various toner patterns are formed by the pattern forming unit 301.

[About long stabilization]
As shown in FIG. 5, long stabilization is an image stabilization operation in which base surface detection (IDC sensor adjustment), maximum attached amount adjustment, LD light amount adjustment, resist correction, and γ correction are performed in this order. Here, base surface detection (IDC sensor adjustment) indicates that the IDC sensor adjustment may or may not be performed depending on the result of the base surface detection. This is the same for short stabilization and resist respectively.

In the base surface detection, for each of the detection sensors 35a and 35b of the IDC sensor 35, light is emitted toward the bare surface area where the toner pattern is not formed on the peripheral surface 27a of the intermediate transfer belt 27 from the light emitting portion 351. The reflected light Lb (FIG. 3) is detected by the light receiving unit 352, and it is determined whether the detected light amount of the reflected light falls within a predetermined range.
Specifically, the light emission duty ratio (described later) determined by the IDC sensor adjustment at the time of the previous image stabilization operation is instructed to the light emitting unit 351. Thereby, the light emitting unit 351 emits light of a light emission amount according to the value of the instructed light emission duty ratio.

The light receiving unit 352 outputs, as a detection signal, a voltage according to the amount of light received from the bare surface area of the intermediate transfer belt 27 among the light emitted from the light emitting unit 351.
Assuming that the output voltage of the light receiving unit 352 is a detection value E, if the relationship of threshold th1 <detection value E ≦ threshold th2 is satisfied, it is determined that the light amount of the reflected light is within a predetermined range If not, it is determined that the light amount of the reflected light does not fall within the predetermined range. As the threshold values th1 and th2, values suitable for the apparatus configuration are determined in advance by experiments and the like.

In the base surface detection, while the intermediate transfer belt 27 rotates, the base surface detection area (naked surface area) 61 on the intermediate transfer belt 27 shown in FIG. Portions shown by marks) are executed while passing through 99a, 99b.
The IDC sensor adjustment is a process that is executed when it is determined that the amount of reflected light detected for at least one of the detection sensors 35a and 35b does not fall within the predetermined range in the base surface detection. .

  The IDC sensor adjustment is performed between the base surface detection area 61 and the maximum adhesion amount adjustment area 63 on the upstream side of the peripheral surface 27a of the intermediate transfer belt 27 shown in FIG. Is executed while passing through the detection positions 99a, 99b of the detection sensors 35a, 35b. The IDC sensor adjustment area 62 is the same bare surface area as the base surface detection area 61.

  Specifically, while the IDC sensor adjustment area 62 is passing through the detection positions 99a and 99b of the detection sensors 35a and 35b, the image stabilization control unit 302 emits the light emission units for each of the detection sensors 35a and 35b. The irradiation of the light from 351 is continued, and the detection voltage E of the reflected light by the light receiving unit 352 is monitored, and the light emitting unit 351 is monitored so that the light amount of the reflected light becomes a target value within the predetermined range. On the other hand, switching of the light emission duty ratio (Dty) is instructed to change the light quantity of the light emitted from the light emitting unit 351. Hereinafter, although one detection sensor is demonstrated, the same process is performed also about the other detection sensor.

More specifically, the detection voltage of the light emitting unit 351 when the light amount of the reflected light becomes the above target value is set in advance as the target voltage F.
Then, the image stabilization control unit 302 first instructs the light emitting unit 351 to have a reference value, for example, 16%, as the light emission duty ratio (Dty) of PWM control. As a result, the light emitting unit 351 emits light of a light emission amount according to the light emission duty ratio (= 16%). If the detection value E of the light receiving unit 352 at this time matches the target voltage F, the light emitting amount of the light emitting unit 351 is determined to have a light emitting duty ratio of 16%.

  When the detection value E of the light receiving unit 352 is lower than the target voltage F, the image stabilization control unit 302 raises the light amount step, in this case, the light emission duty ratio. More specifically, until the detection value E of the light receiving portion 352 becomes equal to or higher than the target voltage F, the light emission duty ratio is increased by one step, for example, 16% at fixed time intervals. For example, starting from the first 16%, 32%, 48%, and so on. As a result, the light emission amount of the light emitting unit 351 is increased by one step at a time according to the one step.

If the detection value E of the light receiving unit 352 matches the target voltage F while the light emission duty ratio is increased by one step, the image stabilization control unit 302 emits 32% of the light emission duty ratio at that time, for example. Decide on the amount of luminescence of 351.
When the detection value E of the light receiving unit 352 exceeds the target voltage F by raising the light emission duty ratio by one step, the image stabilization control unit 302 sets the light emission duty ratio one step at a time, for example, 8 Lower by%.

For example, if the light emission duty ratio when the detection value E of the light receiving unit 352 exceeds the target voltage F is 48%, the condition is 40%, 32%, and so on. As a result, the light emission amount of the light emitting unit 351 is reduced by one step at a time according to the one step.
If the detection value E of the light receiving unit 352 matches the target voltage F while the light emission duty ratio is lowered by one step, the image stabilization control unit 302 emits 40% of the light emission duty ratio at that time, for example. Decide on the amount of luminescence of 351.

  When the detection value E of the light receiving unit 352 falls below the target voltage F by decreasing the light emission duty ratio by one step, the image stabilization control unit 302 again increases the light emission duty ratio by one step every predetermined time, For example, increase by 4%. For example, if the light emission duty ratio when the detection value E of the light receiving unit 352 falls below the target voltage F is 40%, the condition is 44%, 48%, and so on. As a result, the light emission amount of the light emitting unit 351 is increased by one step at a time according to the one step.

  As described above, when the detection value E of the light receiving unit 352 exceeds the target voltage F by raising the light emission amount of the light emitting unit 351 step by step, the light emission amount of the light emitting unit 351 is decreased next by one step When the detection value E of the light receiving unit 352 falls below the target voltage F, light emission amount control is repeated by repeatedly increasing the light emission amount of the light emitting unit 351 step by step. At that time, when the light emission amount of the light emitting portion 351 changes from rising to falling and when it changes from falling to rising, the next one-step light amount change width is reduced to half of the previous one, that is, light emission duty Change the ratio between 16%, 8%, 4%, 2% and 1%. This light emission amount control is called binary sort. As a result, the light amount of the reflected light approaches the above-described target value.

  The light emission duty ratio switches in order, for example, from 16% to 32%, 48%, 40%, 44%, 42%, 41% by the increase or decrease of the light emission duty ratio by one step. When the light amount of the reflected light matches the target value, the image stabilization control unit 302 determines 41% as the light emission amount of the light emitting unit 351. When the final 1% increase / decrease is performed and the light amount of the reflected light does not match the target value, the light emission duty ratio at that time is determined as the light emission amount of the light emitting unit 351. Note that the light emission duty ratio value at start (16%), one-step increase / decrease width (such as 8% and 4%) etc. are not limited to the above values, and suitable values may be selected according to the device configuration. It is decided beforehand.

  The light emission amount of the light emitting unit 351 is determined by the value of the light emission duty ratio of PWM by the above light emission amount control, which is the IDC sensor adjustment. When the value of the light emission duty ratio Dty determined by the IDC sensor adjustment is stored in the backup memory 38 as a control variable of the light emitting unit 351 and the IDC sensor 35 is used at each adjustment after the next maximum adhesion amount adjustment Is read by the engine control unit 30, and the light emitting unit 351 is controlled to emit light at that value. The light emission duty ratio data stored in the backup memory 38 is updated each time the IDC sensor adjustment is performed.

  The maximum adhesion amount adjustment is formed by forming the high density patterns 630 and 631 (FIG. 6) in the maximum adhesion amount adjustment area 63 on the intermediate transfer belt 27 by causing the laser diode 34 to emit light with the maximum light amount. The image forming conditions such as the charging voltage and the developing bias voltage are appropriately set for each image forming unit so that the density when the patterns 630 and 631 are detected by the IDC sensor 35 becomes the density previously determined as the maximum density. To adjust.

  The pattern 630 is a pattern in which four high density solid toner patches 63 K of K color are sequentially arranged at intervals along the belt circumferential direction B as shown in FIG. The pattern 631 is a pattern in which high-density solid toner patches 63Y, 63M, and 63C of Y, M, and C colors are sequentially arranged one by one along the belt circumferential direction B. The patterns 631 are formed to be aligned in four along the belt winding direction B.

  The data of the patterns 630 and 631 are read from the storage unit in the print controller 40, and the pattern forming unit 301 of the engine control unit 30 reads the image forming units 20Y to 20K of the printing unit 3 based on the read data. The image processing unit 4 (image forming unit) including the image forming unit is controlled to form the patterns 630 and 631 on the circulating intermediate transfer belt 27 in a predetermined form (number, position, etc.) for each color. The same applies to the following other patterns, resist patterns, gradation patterns, and the like.

The patterns 630 and 631 of the respective colors formed on the circumferential surface 27a of the intermediate transfer belt 27 are broken lines in the figure when passing through the detection positions 99a and 99b of the detection sensors 35a and 35b by the circumferential travel of the intermediate transfer belt 27. Is detected on the detection lines 39a, 39b of
Assuming that the amount of light emitted from the light emitting unit 351 of the detection sensors 35a and 35b is constant, the amount of absorption of light from the light emitting unit 351 into the pattern increases as the density of the pattern increases. The amount of reflected light decreases. Conversely, as the density of the pattern becomes lighter, the amount of absorption of light from the light emitting portion 351 into the pattern decreases, and the amount of light reflected from the pattern increases. The detection sensors 35a and 35b output signals of voltages according to the amount of light of the reflected light from the patterns 630 and 631 of the respective colors as detection signals indicating the density of the respective patterns. The same is true for other types of patterns.

The image stabilization control unit 302 reduces the density by the difference from the maximum density if the detected density is higher (or lower) than the target maximum density for each color based on the output voltage of the detection sensors 35a and 35b (or Update values such as charging voltage and developing bias voltage so as to increase).
Data of the image forming conditions such as the charging voltage adjusted by the maximum adhesion amount adjustment are stored as a control variable in the backup memory 38, and the print after image stabilization is performed at each adjustment at each adjustment after the next LD light amount adjustment. It is read out at the time of operation and controlled so that pattern formation, printing operation and the like are executed under the conditions. The image forming condition data stored in the backup memory 38 is updated each time the maximum attached amount adjustment is performed.

The patterns 630 and 631 formed on the intermediate transfer belt 27 are removed from the intermediate transfer belt 27 by the cleaner 28 when passing through the cleaner 28 by the circumferential movement of the intermediate transfer belt 27 after detection by the detection sensors 35 a and 35 b. Be done. The same applies to the other patterns described later.
The LD light amount adjustment changes the light emission amount and dot density of the laser diode 34, and the multi-tone K color pattern 640 (FIG. 6) and the Y to C color pattern 641 (FIG. 6) The density of each of the formed patterns 640 and 641 is detected by the IDC sensor 35 so that the density of each of the detected patterns 640 and 641 becomes the defined density of each color. The amount of light emission of the 1-dot laser diode 34 is adjusted for each color.

  The pattern 640 is a pattern in which four solid toner patches 64K of K color are sequentially arranged at intervals along the belt winding direction B as shown in FIG. On the other hand, the pattern 641 is a pattern in which solid toner patches 64Y, 64M and 64C of Y, M and C colors are sequentially arranged along the belt winding direction B one by one. The patterns 641 are formed to be aligned in four along the belt winding direction B.

  The data of the light emission amount of the laser diode 34 adjusted by the LD light amount adjustment is stored in the backup memory 38 as a control variable, and read out at the time of printing operation after image stabilization at each correction after the next registration correction, It is controlled such that the pattern formation, the printing operation and the like are executed under the conditions. The light emission amount data stored in the backup memory 38 is updated each time the LD light amount adjustment is performed.

  In the resist correction, Y to K linear resist patterns 71Y to 71K and 72Y to 72K are formed in the resist correction area 65 on the bare surface of the circumferential surface 27a of the intermediate transfer belt 27, and the formation positions of the respective resist patterns are Detected by the IDC sensor 35, detect the amount of positional deviation of each color from the detection result, and based on the detected amount of positional deviation of each color, the image writing start position in the main scanning direction and subscanning direction of Y to K It is to adjust.

  FIG. 7 is an enlarged view of the resist pattern formed in the resist correction area 65. The resist correction area 65 is a pattern forming area 70a on the intermediate transfer belt 27 from the downstream side to the upstream side in the belt circumferential direction B, A non-pattern formation area (blank area) 70b, a pattern formation area 70a, and a non-pattern formation area 70b are divided, and a resist pattern is formed in the pattern formation area (first area) 70a and is formed in the non-pattern formation area 70b. It is supposed not to be.

  Of the two pattern formation areas 70a, in the pattern formation area 70a on the downstream side, the resist pattern 71K for K color and the resist pattern 71C for C color from the downstream side to the upstream side of the belt circulation direction B on the detection line 39b. M resist pattern 71M, Y resist pattern 71Y, K resist pattern 71K, C resist pattern 71C ... Y resist pattern 71Y, K resist pattern 72K, C resist pattern A resist pattern 72M for 72C and an M color, and a resist pattern 72Y for a Y color are formed in this order along the circumferential direction B of the belt at an interval.

Each of the resist patterns 71Y to 71K is a line pattern parallel to a direction (corresponding to the main scanning direction) orthogonal to the belt circulating direction B, and is a direction parallel to the belt circulating direction B (corresponding to the sub scanning direction). Is used to detect the amount of misalignment of each color.
On the other hand, each of the resist patterns 72Y to 72K is a line pattern inclined at an angle of 45 ° with respect to the belt winding direction B, and is used to detect the amount of positional deviation of each color in the main scanning direction.

  If four resist patterns 71K of K color are defined as first, second, third and fourth resist patterns 71K in order from the downstream side to the upstream side, between the first resist pattern 71K and the third resist pattern 71K Of the second resist pattern 71K and the fourth resist pattern 71K in the design of the circumferential surface of the photosensitive drum 21 of the image forming unit 20K. Four resist patterns 71K are formed by the image forming unit 20K at a timing determined in advance so that the distance between them becomes the size of the photosensitive member half cycle D.

  The same applies to the resist patterns 71Y to 71C of the other colors. For example, if four Y-color resist patterns 71 Y are defined as the first, second, third, and fourth resist patterns 71 Y in the order from the most downstream to the most upstream, the first resist pattern 71 Y and the third resist pattern 71 Y are defined. And the distance between the second resist pattern 71Y and the fourth resist pattern 71Y is equal to half the circumference of the photosensitive drum 21 of the image forming unit 20Y. At this timing, four resist patterns 71Y are formed by the imaging unit 20Y. The diameters (one round length) of the photosensitive drums 21 of the image forming units 20Y to 20K are all the same.

The reason why the two resist patterns of the same color are formed with a distance of the photosensitive member half circumference D in this way is as follows.
That is, for each photosensitive drum, the rotation axis ideally coincides with the center of the photosensitive drum from the viewpoint of preventing the occurrence of color misregistration, but in an actual product, it is slightly within the tolerance range. There are things that are eccentric. When the rotation axis is eccentric, while the photosensitive drum makes one revolution (in one cycle), velocity unevenness occurs in the circumferential direction on the circumferential surface of the photosensitive drum, but this velocity unevenness is in one cycle In many cases, the speed fluctuation is similar to a sinusoidal curve, in which the period of time faster than the original circumferential speed and the time of slowing alternately appear one by one.

  In the case where a period in which the speed unevenness becomes fast and a period in which the speed unevenness is alternately appear in one cycle, an interval of half cycle (= 180 °) which is a half of one cycle, that is, an interval of photosensitive drum half circumference D occurs. If two resist patterns of the same color are formed on the photosensitive drum at predetermined time intervals, one of the first and second resist patterns is faster than the original circumferential speed. It is more likely that it will be formed and the other will be formed in the later part.

Assuming that the distance between the first resist pattern and the second resist pattern is much shorter than half the photosensitive member circumference D, for example, one quarter of the circumference (= 90 °), the distance between the two resist patterns is short. In addition, there are many biases such that both are formed in the high speed part, one is formed in the high speed part, and the other is formed in the low speed part.
In this case, the speed variation of the photosensitive drum is the same every time the resist correction is performed, depending on which portion of one rotation on the photosensitive drum two resist patterns are formed on, Of the speed fluctuations, resist correction is performed based on the detection results of two resist patterns that are affected only by acceleration or deceleration, or resist is detected based on the detection results of two resist patterns that are hardly affected by speed fluctuation. Correction is performed, and stable color shift correction can not be performed.

  On the other hand, if it is assumed that the distance between two resist patterns is half the photosensitive drum circumference D as in the present embodiment, both resist patterns have only the influence of acceleration or deceleration of the speed fluctuation at every resist correction. There is almost no reception. As a result, two resist patterns can be formed in such a state that the eccentricity of the rotary shaft is canceled by offsetting the acceleration and deceleration with respect to the original circumferential speed, and stable color shift correction can be performed. it can.

In this embodiment, for example, two sets of two resist patterns 71K separated by half a photosensitive drum distance D for K color are made one set, and two sets are formed in the figure, and the average of their detection values By doing so, the influence of the eccentricity of the drum rotation shaft is avoided as much as possible during color misregistration correction.
Instead of the above, a large number of resist patterns of the same color may be formed on one photosensitive drum over one rotation, but in this case, for each image stabilization operation And consume a large amount of toner for forming a resist pattern. Therefore, it is desirable that the number of resist patterns formed be such that the amount of positional deviation of each color in the sub scanning direction can be detected as accurately as possible while suppressing the toner consumption as much as possible. In this embodiment, four resist patterns are formed for one color.

  On the other hand, in the resist pattern 72K, the distance from the second resist pattern 71K is the size of one rotation of the photosensitive member (= 2 × D), and the distance from the second resist pattern 71C is the photosensitive member 1 in the resist pattern 72C. The resist pattern 72M has a size corresponding to the circumference, the distance from the third resist pattern 71M is a size corresponding to one rotation of the photosensitive body, and the resist pattern 72Y has a distance from the third resist pattern 71Y to the photosensitive body 1 It is formed at a predetermined timing so as to become the size of the circumference.

  As a result, after formation of resist patterns 71Y to 71K for detecting displacement amounts in the sub scanning direction on the photosensitive drum for each color, after one rotation of the photosensitive drum, the formation position and rotation of the resist patterns 71Y to 71K Resist patterns 72Y to 72K for detecting the amount of positional deviation in the main scanning direction are formed at the same position in the direction. As a result, it is possible to detect the amount of positional deviation in the sub-scanning direction and the main scanning direction without being affected as much as possible by the uneven speed due to the eccentricity of the photosensitive drum.

Although the resist patterns 71Y to 71K and 72Y to 72K formed on the detection line 39b have been described above, similar resist patterns 71Y to 71K and 72Y to 72K are formed on the detection line 39a.
Of the two pattern formation areas 70a, the resist patterns 71Y to 71K and 72Y to 72K having the same shape and size as the pattern formation area 70a on the downstream side also have the same number and the same positional relationship as the pattern formation area 70a on the upstream side. It is formed to be

  Here, the distance from the K-color resist pattern 71K of the downstream pattern formation area 70a to the K-color resist pattern 71K of the upstream pattern formation area 70a in the belt circumferential direction B is the circumferential surface of the intermediate transfer belt 27. It is formed at a predetermined timing so as to have a size of a half of the one circumferential length (half of the transfer belt). The same applies to each of the resist patterns 71Y to 71C of Y to C colors other than the K color.

A position where two resist patterns of the same color are separated by a transfer belt half turn G along the belt winding direction B (a position shifted by a half cycle when one turn of the intermediate transfer belt 27 is one cycle) The reason for forming it is the same as the reason why two resist patterns of the same color are formed at positions separated by a half circumference D on the photosensitive drum described above.
That is, as for the intermediate transfer belt 27, as in the case of the photosensitive drum, the unevenness of the peripheral speed occurring in the intermediate transfer belt 27 is generally alternated between a period in which the speed increases with respect to the original peripheral speed and a period in which it is delayed. In many cases, the speed fluctuation as shown in FIG. For this reason, if two resist patterns of the same color are formed with an interval of G for transfer belt half circumference G (formed at a position shifted by half cycle), both of the two resist patterns will be for speed unevenness This is because there is almost no bias that is affected by the deceleration, and stable resist correction can be performed.

Since the length of one round of the intermediate transfer belt 27 is considerably longer than the length of one round of one photosensitive drum, a blank (naked surface) in which no resist pattern is formed at all between the two pattern formation areas 70a. An area arises, and this bare area becomes a non-patterned area 70b. Hereinafter, the non-patterned region 70b may be referred to as a bare surface region 70b.
In the resist correction of the present embodiment, the pattern formation processing is performed such that one bare surface area 70b is continuous to one pattern formation area 70a. Thereby, the bare surface area 70b is set on the upstream side so as to be continuous with the upstream side pattern formation area 70a.

  The resist patterns 71Y to 71K and 72Y to 72K of the respective colors formed on the circumferential surface 27a of the intermediate transfer belt 27 pass the detection positions 99a and 99b of the detection sensors 35a and 35b as the intermediate transfer belt 27 circulates. Is detected. When each resist pattern (linear pattern) passes the detection positions 99a and 99b, the detection sensors 35a and 35b output, as detection signals, voltage signals of peak shapes corresponding to the line widths.

  Based on the detection results of the resist patterns 71Y to 71K by the detection sensors 35a and 35b, the distance in the sub-scanning direction to the formation positions of the resist patterns 71Y to 71C of the other colors is determined based on the formation position of the K resist pattern 71K. The amount of positional deviation in the sub-scanning direction is calculated from the difference between the determined distance and the original distance in the state where no color deviation has occurred. Specifically, since the distances between the first and third patterns and the second and fourth patterns are determined for each area, the difference between the average value of these and the original distance is determined.

Further, the distance between the patterns is obtained for each color from the detection signals of the resist patterns 72Y to 72K, and the difference of the distance of each color is set as the positional deviation amount in the main scanning direction. The positional deviation amount data in the sub-scanning direction and the main scanning direction is stored in the backup memory 38 as a control variable of the image formation timing (image writing position), and read out at the time of printing operation after image stabilization.
That is, the address of the image data is changed so that the positional deviation in the main scanning direction and the sub scanning direction is eliminated by using the read out positional deviation amount data at the time of printing operation, each of the imaging units 20Y to 20K. Then, image writing position correction is performed to correct the writing position of the corresponding color toner image on the photosensitive drum 21 for each pixel, and control is performed so that color misregistration does not occur at the time of color image formation. The positional deviation amount data stored in the backup memory 38 is updated each time registration correction is performed.

  The γ correction is a type of gradation correction, and for each color, a density (gradation) pattern 66K showing gradation based on data of a predetermined gradation pattern (input image) representing a plurality of, for example, 256 gradations. 661 (FIG. 6) are formed in the γ correction area 66 on the bare surface of the circumferential surface 27 a of the intermediate transfer belt 27 by changing the light emission amount and dot density of the laser diode 34.

  The gradation pattern 66K is a solid gradation pattern of K color toner as shown in FIG. 6, and is formed so that two gradation patterns 66K are arranged at intervals along the belt winding direction B. On the other hand, the gradation pattern 661 is a pattern in which solid gradation patterns 66Y, 66M and 66C of toners of Y, M and C are sequentially arranged one by one along the belt winding direction B. The gradation patterns 661 are formed so as to be arranged in two along the belt winding direction B.

The gradation pattern of each color formed on the circumferential surface 27a of the intermediate transfer belt 27 is detected when it passes the detection positions 99a and 99b of the detection sensors 35a and 35b as the intermediate transfer belt 27 travels. The detection sensors 35a and 35b output, as a detection signal, a signal of a voltage corresponding to the density of the detected gradation pattern of each color.
The image stabilization control unit 302 generates a γ table indicating the correspondence between the density of the input image and the density of the actual output image for each color based on the output voltages of the detection sensors 35a and 35b. The generated data of the γ table is stored as a control variable in the backup memory 38 and read out at the time of printing after image stabilization.

Then, at the time of printing operation, the light quantity and the dot density of the laser diode 34 are controlled to improve the tone reproducibility so that the densities of the input image and the output image coincide with each other based on the γ table for each color. . The data of the γ table stored in the backup memory 38 is updated each time the γ correction is performed.
As described above, long stabilization is an image stabilization operation in which the maximum adhesion amount adjustment, the LD light amount adjustment, the resist correction, and the γ correction are performed in this order after the IDC sensor adjustment, and are shown by steps S1 and S3 in FIG. As such, when the imaging unit is replaced with a new one, it is executed when there is a change in the environment inside the machine.

  When the imaging unit is replaced with a new one, it is not known whether the imaging process such as charging, exposure and development by the new imaging unit can always ensure the image quality more than a certain level, and the environment inside the machine For example, fluctuations in temperature and humidity are likely to affect the imaging process, leading to a reduction in the image quality of the formed image. Therefore, when the imaging unit is replaced with a new one or when there is a change in the inside environment of the machine, all the stabilization sequences (IDC sensors) for the correction are performed in order to properly correct all the conditions of the imaging process. Long stabilization including adjustment (gamma correction) is performed.

  The predetermined value indicating the difference between the temperature and the humidity used in the determination of step S3 in FIG. 4 is affected by the change in temperature and humidity when the temperature and humidity change is equal to or more than the predetermined value. It is a value assumed to lead to image quality deterioration due to color shift, deterioration of density, gradation reproducibility and the like due to change in sensitivity of the drum, warp of the optical member, etc. Data of a predetermined value is stored in storage means such as a ROM.

Moreover, in long stabilization, after the adjustment of the IDC sensor, the maximum attached amount adjustment and the LD light amount adjustment are performed. This is because the density of the solid patterns 630, 640 and the like obtained by adjusting the maximum adhesion amount and the LD light amount can not be accurately detected by the IDC sensor 35 when the IDC sensor adjustment is not performed.
In the long stabilization, the resist correction is performed after the maximum adhesion amount adjustment and the LD light amount adjustment. If the resist pattern is formed on the intermediate transfer belt 27 in a state in which the maximum adhesion amount adjustment and the LD light amount adjustment are not performed, the density of the formed resist pattern becomes extremely low and can not be detected by the IDC sensor 35 It is likely to occur, and to prevent this.

[About short stabilization]
Referring back to FIG. 5, the short stabilization is an image stabilization operation that performs base surface detection, IDC sensor adjustment, resist correction, and γ correction, and the maximum adhesion amount adjustment and LD light amount adjustment included in long stabilization are described. Not run.
The short stabilization is executed when the cumulative number of printed sheets reaches a predetermined number as shown in steps S5 and S6 of FIG. When the cumulative number of prints reaches the specified number, changes in gradation may occur due to fluctuations in the sensitivity characteristics of the photosensitive drum, but all process conditions (charging, exposure, development, etc.) are corrected as in the in-machine environment. It is not necessary to do it. Therefore, in the short stabilization, only tone correction related to tone and resist correction for preventing color misregistration are performed.

The predetermined number of sheets J1 used in the determination of step S5 shown in FIG. 4 is color misregistration, deterioration of gradation reproducibility, etc., when the cumulative number of printed sheets J becomes equal to or more than the predetermined number of sheets J1. And is a value assumed to lead to image quality deterioration due to the above. The data of the predetermined number J1 is stored in storage means such as a ROM.
The processing contents of each of the base surface detection to γ correction included in the short stabilization are basically the same as each of the base surface detection to γ correction of long stabilization, and the bare surface of the circumferential surface 27 a of the intermediate transfer belt 27 The number of resist patterns and the number of gradation patterns of each color formed on the top, the positional relationship, etc. are the same, but in the case of short stabilization, the base surface detection result (value of the detection voltage of the light receiving portion 352) to be executed first Therefore, long stabilization is different in that any of the following first to third short stabilizations is selectively performed.

  That is, first, it is determined from the base surface detection result whether or not the IDC sensor adjustment is necessary. This determination is performed based on whether the relationship of threshold th1 <detection value E ≦ threshold th2 is satisfied, where E is the value of the detection voltage of the light receiver 352 acquired at the time of base surface detection. Specifically, it is determined that the IDC sensor adjustment is unnecessary when this relationship is satisfied, and it is determined that the IDC sensor adjustment is necessary when this relationship is not satisfied.

If it is determined that the IDC sensor adjustment is necessary, it is determined from the base surface detection result whether or not the IDC sensor 35 can detect a resist pattern.
Here, the detectable state of the resist pattern means that the light emission amount of the light emitting unit 351 is within a range where it is assumed that the resist pattern can be detected with a certain accuracy or more, and the undetectable state of the resist pattern This means that the amount of light emitted from the light emitting portion 351 is largely changed from the expected value to the extent that the resist pattern can not be detected with a certain precision or more due to environmental fluctuation or deterioration with time.

Here, when the relationship of threshold th0 <detection value E ≦ threshold th1 is satisfied, it is determined that the resist pattern can be detected, and the relationship of detection value E ≦ threshold th0 or threshold th2 <detection value E is satisfied. If the resist pattern is detected, it is determined that the resist pattern can not be detected.
If the IDC sensor 35 determines that the resist pattern can not be detected, after the base surface detection, the IDC sensor adjustment, the resist correction, and the γ correction are performed in this order. Thereby, registration correction and γ correction can be performed using the IDC sensor 35 after IDC sensor adjustment. This short stabilization is called first short stabilization.

FIG. 8A is a view showing a formation example of various toner patterns formed on the circumferential surface 27 a of the intermediate transfer belt 27 when the first short stabilization is performed.
As shown in FIG. 8A, in the first short stabilization, the base surface detection area 61, the IDC sensor adjustment area 62, the resist correction area 65, and the γ correction area 66 are formed on the circumferential surface 27a of the intermediate transfer belt 27. Set in order.

  The base surface detection area 61 is an area from the reference position Qa on the intermediate transfer belt 27 to a position Q1 separated by a predetermined distance L1 on the upstream side in the belt winding direction B. The IDC sensor adjustment area 62 is an area from the position Q1 to a position Q2 upstream from the position Q1 by a predetermined distance L2. The registration correction area 65 is an area from the position Q2 to a position Q3 upstream from the position Q2 by a predetermined distance L3. The γ correction area 66 is an area from the position Q3 to a position Q4 upstream by a predetermined distance L4. The size of each region, the number of resist patterns of each color and the number of gradation patterns, the positional relationship, and the like are the same as in the case of long stabilization.

As the intermediate transfer belt 27 circulates, while the base surface detection area 61 and the IDC sensor adjustment area 62 on the intermediate transfer belt 27 pass the detection positions 99a and 99b of the IDC sensor 35 in this order, the intermediate transfer belt is detected by the IDC sensor 35 27 bare surfaces are detected, and based on this detection result, after base surface detection, IDC sensor adjustment is performed.
After the light emission amount of the light emitting unit 351 of the IDC sensor 35 is properly adjusted by the IDC sensor adjustment, the adjustment is performed while the registration correction area 65 and the γ correction area 66 pass the detection positions 99a and 99b of the IDC sensor 35 in this order. A resist pattern and a gradation pattern on the intermediate transfer belt 27 are detected by the IDC sensor 35 which emits light with a later light emission amount. Based on this detection result, registration correction and γ correction are performed. Each detection method is the same as long stabilization.

On the other hand, if it is determined that the IDC sensor adjustment is necessary and that the IDC sensor 35 is in the detectable state of the resist pattern, after base surface detection, the resist correction is started without performing the IDC sensor adjustment, and this resist correction is The IDC sensor adjustments are made in parallel during the run, followed by the γ correction. This short stabilization is called second short stabilization.
When performing the second short stabilization, the pattern formation unit 301 is arranged so that the resist correction area 65 and the γ correction area 66 follow the base surface detection area 61 without the intervention of the IDC sensor adjustment area 62. The respective writing start timings of the resist pattern and the gradation pattern are generally advanced earlier than in the case of the first short stabilization.

FIG. 8B is a view showing a formation example of various toner patterns formed on the circumferential surface 27 a of the intermediate transfer belt 27 when the second short stabilization is performed.
As shown in FIG. 8B, in the second short stabilization, a base surface detection area 61, a registration correction area 65, and a γ correction area 66 are set in this order on the circumferential surface 27a of the intermediate transfer belt 27.

  The area from the reference position Qa on the intermediate transfer belt 27 to a position Q1 separated by a predetermined distance L1 on the upstream side in the belt winding direction B is the base surface detection area 61, and is separated from the position Q1 by a predetermined distance L3 on the upstream side The area up to the position Q5 is the resist correction area 65, and the area up to the position Q6 away from the position Q5 by the predetermined distance L4 is the γ correction area 66. The distances L1, L3 and L4 are the same as the distances L1, L3 and L4 in the first short stabilization of FIG. 8A.

As compared with the first short stabilization shown in FIG. 8A, the second short stabilization shown in FIG. 8B does not have the IDC sensor adjustment area 62, so the IDC sensor adjustment with respect to the reference position Qa is performed. The resist correction area 65 and the γ correction area 66 are generally positioned (shifted) downstream by the distance L 2 of the area 62.
That is, when performing the second short stabilization, the pattern forming unit 301 sets the writing start timing of each of the resist pattern and the gradation pattern to the intermediate transfer belt 27 with respect to the case where the first short stabilization is performed. Pattern formation control is performed to switch to a timing earlier by a belt movement time Tz corresponding to the distance L2 of the circumferential surface 27a.

  In this pattern formation control, the timing at which the resist pattern and the gradation (density) pattern are formed on the intermediate transfer belt 27 when executing the second short stabilization (in other words, each pattern on each photosensitive drum 21) If writing start timing is considered as a reference, in the first short stabilization, the base surface is delayed by a predetermined time Tz from the timing of the reference due to the second short stabilization, as shown in FIG. 8A. Another control called "IDC sensor adjustment area 62" is inserted into the second bare surface area between the detection area 61 (first bare surface area) and the most downstream pattern formation area 70a (first area). be able to.

8B, the bare surface of the intermediate transfer belt 27 is detected by the IDC sensor 35 while the base surface detection area 61 passes the detection positions 99a and 99b of the IDC sensor 35 due to the circumferential traveling of the intermediate transfer belt 27. Base surface detection is performed based on this detection result.
Subsequently, while the resist pattern of each color formed in the downstream pattern forming area 70 a in the resist correction area 65 on the intermediate transfer belt 27 passes the detection positions 99 a and 99 b of the IDC sensor 35 in order, the IDC sensor 35 Each resist pattern is detected by

Next, while the bare surface area 70b between the two pattern formation areas 70a passes the detection positions 99a and 99b of the detection sensors 35a and 35b, the IDC sensor 35 detects the bare surface area of the intermediate transfer belt 27. Ru. The IDC sensor adjustment is performed based on the detection result of the bare surface area.
That is, the IDC sensor adjustment is performed using the bare surface area 70b between the two pattern formation areas 70a spaced by a predetermined distance in the circumferential direction on the intermediate transfer belt 27.

Next, while the resist pattern of each color formed in the pattern formation area 70a on the upstream side in the resist correction area 65 sequentially passes through the detection positions 99a and 99b of the IDC sensor 35, each resist pattern is detected by the IDC sensor 35 Be done. The resist correction is performed based on the detection result of the resist pattern of each color formed in the two pattern formation regions 70a.
If the adjustment of the IDC sensor is not completed based on the detection result of the IDC sensor 35 while the downstream bare surface area 70b passes the detection positions 99a, 99b of the detection sensors 35a, 35b, the adjustment is temporarily performed. During interruption, the IDC sensor adjustment is resumed while another (upstream) bare surface area 70b passes the detection position 99a, 99b of the detection sensor 35a, 35b.

The value of the duty ratio for the light emitting unit 351 at the time of interruption is temporarily stored, and the amount of light emission of the light emitting unit 351 is adjusted by changing the duty ratio one step at a time from the stored value when restarting. .
As described above, in the second short stabilization, the gradation pattern formed in the γ correction area 66 after the IDC sensor adjustment starts detecting the downstream bare surface area 70 b on the intermediate transfer belt 27 by the IDC sensor 35. It takes place before the start of the detection of Before the start of the detection of the gradation pattern, the light emission duty ratio indicating the light emission amount after the adjustment of the IDC sensor is instructed to the light emission unit 351, and light emission by the light emission amount instructed from the light emission unit 351 is started.

After completion of registration correction and IDC sensor adjustment performed in parallel with this, the gradation pattern of each color formed in the γ correction area 66 on the intermediate transfer belt 27 passes the detection positions 99a and 99b of the IDC sensor 35 In the meantime, γ correction of each color is performed based on the detection result of the gradation pattern of each color detected by the IDC sensor 35 after IDC sensor adjustment.
8 (a) and 8 (b), in the first short stabilization shown in FIG. 8 (a), the IDC sensor adjustment area 62 is interposed between the base surface detection area 61 and the resist correction area 65. In the second short stabilization shown in FIG. 8B, the IDC sensor adjustment area 62 does not intervene between the base surface detection area 61 and the resist correction area 65.

  As a result, the length of the belt winding direction B in the entire area from the base surface detection area 61 to the γ correction area 66 is the second short stabilization shown in FIG. It becomes shorter by ΔL (= L2) than 1 short stabilization. In the second short stabilization, the entire time of the short stabilization which is required from the start of the base surface detection to the end of the γ correction is shortened as the second short stabilization is reduced by the ΔL.

That is, when the IDC sensor 35 can detect the resist pattern at the start of short-circuit stabilization, the IDC sensor adjustment does not have to be completed before the start of the resist correction, and the resist on the intermediate transfer belt 27 Also in the correction area 65, there is a bare surface area 70b that can be used when performing IDC sensor adjustment.
From this, in the second short stabilization, resist correction is performed based on the result of detection of each resist pattern of the pattern formation region 70a by the IDC sensor 35 without executing IDC sensor adjustment before the start of resist correction, and The IDC sensor adjustment is performed based on the result of detection of the bare surface area 70 b by the IDC sensor 35.

  On the other hand, if it is determined that the IDC sensor adjustment is not necessary, the IDC sensor adjustment area 62 is unnecessary, so on the circumferential surface 27a of the intermediate transfer belt 27 as in the case of the second short stabilization shown in FIG. Next to the base surface detection area 61, a resist correction area 65 and a γ correction area 66 are set, and after the base surface detection, the resist correction and the γ correction are performed in this order, but naked as in the second short stabilization. IDC sensor adjustment is not performed using the surface area 70b. This image stabilization operation is called third short stabilization. In the third short stabilization, the processing load of the CPU of the control unit 7 can be reduced by the amount of unnecessary execution of the IDC sensor adjustment.

  In the second short stabilization shown in FIG. 8B, the IDC sensor adjustment is performed while the downstream bare surface region 70b on the intermediate transfer belt 27 passes the detection positions 99a and 99b of the IDC sensor 35. If not completed, the adjustment is temporarily suspended, and the IDC sensor adjustment is resumed while the upstream bare surface area 70b passes through the detection positions 99a and 99b of the IDC sensor 35, but the present invention is limited thereto. Absent.

The adjustment of the IDC sensor is completed from the start of the registration correction to the start of the γ correction, and the γ correction may be performed by the IDC sensor 35 after the adjustment.
For example, the IDC sensor adjustment can be performed only while the upstream bare surface region 70b of the two bare surface regions 70b shown in FIG. 8B passes the detection positions 99a and 99b of the IDC sensor 35.

In addition, when the IDC sensor adjustment can be completed only in the downstream bare surface region 70b, the timing to start formation of the gradation pattern of the γ correction region 66 is set without setting the upstream bare surface region 70b. It is also possible to adopt a configuration to accelerate the start of the γ correction.
[About resist]
Returning to FIG. 5, the resist is an image stabilization operation that performs base surface detection, IDC sensor adjustment, and registration correction, and maximum adhesion adjustment, LD light amount adjustment, and γ correction are not performed for long stabilization.

  The resist is executed when there is a PH temperature change from the previous image stabilization operation as shown in step S7 of FIG. When the PH temperature fluctuates, the image writing position of each color may fluctuate due to the warp of the lens in the print head 26 or the like, but it is not necessary to adjust the maximum adhesion amount, the LD light amount, and the γ correction. Therefore, in the resist, maximum adhesion amount adjustment, LD light amount adjustment, base surface detection excluding γ correction, IDC sensor adjustment, and registration correction for preventing color misregistration are performed.

Therefore, when performing the resist, the pattern formation unit 301 does not set the maximum adhesion amount adjustment area 63, the LD light quantity adjustment area 64, and the γ correction area 66 shown in FIG. 6 (does not form these patterns) The image forming units 20Y to 20K and the like are controlled so that only the resist pattern of the resist correction area 65 is formed next to the IDC sensor adjustment area 62.
Also in this resist, it is determined whether the IDC sensor adjustment is necessary or not based on the base surface detection result. Specifically, when the relationship of threshold th0 <detection value E ≦ threshold th2 is satisfied, it is determined that the IDC sensor adjustment is not necessary, and this relationship is not satisfied, that is, detection value E ≦ threshold th0 or threshold th2 < When the relationship of the detection value E is satisfied, it is determined that the IDC sensor adjustment is necessary. This judgment is the same as in the case of short stabilization. Thereby, the detection of the resist pattern on the intermediate transfer belt 27 can be started by the IDC sensor 35 after the completion of the IDC sensor adjustment.

The predetermined value .DELTA.T used in the determination of step S7 shown in FIG. 4 above is assumed to cause a fluctuation in the image writing position due to the warp of the lens in the print head 26 or the like when the PH temperature change becomes equal to or more than the predetermined value .DELTA.T. It is a value, which is obtained in advance from experiments and the like, and stored in storage means such as a ROM.
[Process content of image stabilization operation]
FIG. 9 is a flow chart showing the processing contents of the image stabilization operation, and when the print controller 40 instructs the engine control unit 30 to execute long stabilization, short stabilization, or resist, the engine It is executed by the image stabilization control unit 302 of the control unit 30.

  As shown in the figure, the image stabilization control unit 302 instructs the light emitting unit 351 of the IDC sensor 35 to obtain an initial light emission amount (step S10). The instruction of the initial light emission amount reads the value of the light emission duty ratio Dty determined by the adjustment of the IDC sensor at the previous image stabilization operation from the backup memory 38, and the read light emission duty ratio Dty It is performed by outputting to 351. The light emitting unit 351 emits light of a light emission amount corresponding to the value of the light emission duty ratio Dty received from the image stabilization control unit 302.

  Then, it is determined whether execution of long stabilization has been instructed (step S11). If it is determined that execution of the long stabilization has been instructed ("Yes" in step S11), base surface detection is performed (step S12). At the time of this base surface detection, light has already been emitted from the light emitting portion 351 toward the circumferential surface 27a of the intermediate transfer belt 27 in the above step S10.

It is determined whether the detected value E of the light reflected from the bare surface portion of the circumferential surface 27a of the intermediate transfer belt 27 and detected by the sensor 35 at the time of base surface detection is larger than the threshold th1 and not larger than the threshold th2. (Step S13).
If it is determined that the relationship of threshold th1 <detection value E ≦ threshold th2 is not satisfied ("No" in step S13), after performing IDC sensor adjustment (step S14), maximum adhesion amount adjustment (step S15), LD The light amount adjustment (step S16), the registration correction (step S17), and the γ correction (step S18) are sequentially performed to end the image stabilization operation.

If it is determined that the relationship of threshold th1 <detection value E ≦ threshold th2 is satisfied (“Yes” in step S13), step S14 is skipped (not performed), and the process proceeds to step S15.
If it is determined that the execution of the short stabilization is instructed instead of the long stabilization ("No" in step S11, "Yes" in S19), base surface detection is performed (step S20). This base surface detection is performed by the same method as the base surface detection of step S12.

Pattern formation timing instruction processing is executed based on the detection value E detected by the sensor 35 at the time of base surface detection (step S21).
FIG. 10 is a flow chart showing the contents of a subroutine of pattern formation timing instruction processing.
As shown in the figure, the image stabilization control unit 302 determines whether the relationship of threshold th0 <detection value E ≦ threshold th2 is satisfied (step S71).

  If it is determined that this relationship is not satisfied (“No” in step S71), the base surface detection area 61 and the IDC sensor adjustment area 62 are formed as shown in FIG. A reference resist pattern write start timing Ta determined in advance so as to form resist patterns of the respective colors of the resist correction area 65 on the intermediate transfer belt 27 later is instructed to the pattern forming portion 301 (step S72), and the process returns. . The pattern forming unit 301 starts writing on the photosensitive drum 21 a resist pattern made of a toner image of the color for each color based on the instructed reference timing Ta.

  On the other hand, if it is determined that the above relationship is satisfied ("Yes" in step S71), the base surface is determined as shown in FIG. 8 (b) to execute the second short stabilization or the third short stabilization. The pattern forming portion 301 is instructed to start the resist pattern writing start timing Tb earlier by the time Tz than the reference, which is predetermined so that the resist pattern of the resist correction region 65 is formed on the intermediate transfer belt 27 after the detection region 61. (Step S73) and return. The pattern forming unit 301 starts writing the resist pattern of the color on the photosensitive drum 21 for each color based on the instructed timing Tb. Thereby, the formation positions of the resist patterns of the respective colors on the intermediate transfer belt 27 are shifted downstream by the distance L2 shown in FIG. 8 compared to the formation positions at the reference timing Ta, and the IDC sensor of the resist pattern 35 Start detection earlier.

The image stabilization control unit 302 acquires the detection result of the resist pattern by the IDC sensor 35 in anticipation of this delay, and based on the acquired detection result of the IDC sensor 35, resist correction, IDC sensor adjustment, γ correction, etc. I do.
In the above description, the presence or absence of the IDC sensor adjustment area 62 is switched by making the formation start timing of the resist pattern different between the first short stabilization and the second and third short stabilization. I can not. It may be possible to switch between the case where the IDC sensor adjustment area 62 is interposed and the case where it is not interposed between the base surface detection area 61 and the resist correction area 65 in the short stabilization.

For example, as in the case of each toner pattern such as a resist pattern, data in which the density of all pixels in each area is 0 (data indicating non-printing) is also used as the image data for the base surface detection area 61 and the IDC sensor adjustment area 62 ) Can be prepared in advance.
Specifically, when performing the first short stabilization, each image data of the base surface detection area, the IDC sensor adjustment area, the resist pattern, and the gradation pattern is prepared for the first short stabilization. The image data of each of the base surface detection area, the IDC sensor adjustment area, the resist pattern, and the gradation pattern is read out, and an image forming operation is performed in each of the image forming units 20Y to 20K based on the read image data. In this image forming operation, no pattern is formed on each of the base surface detection area 61 and the IDC sensor adjustment area 62 on the intermediate transfer belt 27, and the entire area becomes a non-image area (blank area).

  Similarly, when the image data of the base surface detection area, the resist pattern, and the gradation pattern are separately prepared for the second and third short circuit stabilization, and the second or third short circuit stabilization is performed. In each of the image forming units 20Y to 20K, an image forming operation is performed based on the read image data of the base surface detection area, the resist pattern, and the gradation pattern. In this image forming operation, no pattern is formed in the base surface detection area 61 on the intermediate transfer belt 27, and the entire area becomes a non-image area (blank area).

When the first short stabilization is performed, the image stabilization control unit 302 detects the detection results of the base surface detection area 61, the IDC sensor adjustment area 62, the resist correction area 65, and the γ correction area 66 by the IDC sensor 35. Are acquired in this order, and base surface detection, IDC sensor adjustment, resist correction, etc. are executed.
In addition, when the second short stabilization is executed, the detection results of the base surface detection area 61, the resist correction area 65, and the γ correction area 66 by the IDC sensor 35 are acquired in this order to detect the base surface, resist Execute correction (+ IDC sensor adjustment) etc.

Returning to FIG. 9, in step S22, it is determined whether the relationship of threshold th1 <detection value E ≦ threshold th2 is satisfied.
If it is determined that the relationship of threshold th1 <detection value E ≦ threshold th2 is not satisfied (“No” in step S22), it is determined whether the relationship of threshold th0 <detection value E ≦ threshold th1 is satisfied (step S23).

  When it is determined that the relationship of threshold th0 <detection value E ≦ threshold th1 is satisfied (“Yes” in step S23), the light emission amount of the light emitting unit 351 of the IDC sensor 35 can detect the resist pattern and the gradation (density) Assuming that the pattern is in an undetectable range, after performing registration correction (+ IDC sensor adjustment) (step S27), execute γ correction (step S26) and end the image stabilization operation (second short stability) ).

FIG. 11 is a diagram showing the contents of a subroutine of registration correction (+ IDC sensor adjustment) processing.
As shown in the figure, the detection results of the resist patterns 71Y to 71K, 72Y to 72K formed in the downstream pattern forming area 70a on the intermediate transfer belt 27 by the IDC sensor 35 are acquired and stored (step S81) .

  Here, after the position Q1 passes the detection positions 99a and 99b of the IDC sensor 35 based on the position Q1 (FIG. 8B) which is the most downstream end of the pattern formation area 70a on the downstream side, the pattern formation area 70a The output signal (voltage) of the IDC sensor 35 is acquired until the position Q11 (FIG. 8 (b)) which is the most upstream end of the IDC reaches the detection positions 99a and 99b of the IDC sensor 35.

Assuming that the time obtained by dividing the distance (predetermined value) from the position Q1 to the position Q11 in the direction opposite to the belt winding direction B by the peripheral speed Va (constant value: design value) of the intermediate transfer belt 27 is t1 The time when time t1 has elapsed since the detection of the position Q1 by 35 can be set as the time when the position Q11 reaches the detection positions 99a and 99b of the IDC sensor 35.
The detection that the reference position Q1 has reached the detection positions 99a and 99b of the IDC sensor 35 is, for example, the detection position of the reference position Q1 at the IDC sensor 35 from the timing when writing of the resist pattern to the photosensitive drum starts. The time until reaching 99a, 99b is determined in advance by experiments, etc., and that the determined time has elapsed from the write start timing can be performed by clocking with a timer (not shown) or the like.

Subsequently, the detection result of the downstream bare surface area 70b on the intermediate transfer belt 27 by the IDC sensor 35 (detection result of the light amount of the reflected light from the bare surface area 70b) is acquired, and the IDC sensor adjustment is performed based on the detection result. Is executed (step S82).
As described above, the IDC sensor adjustment changes the light emission duty ratio Dty stepwise from 16% of the reference, for example, 16%, 32%, 48%, 40%, etc., as described above. It is done by instructing.

  When the light amount of the reflected light from the bare surface area 70b reaches the target value during stepwise switching of the light emission duty ratio Dty, the value of the light emission duty ratio Dty at that time is stored in the backup memory 38 as a control variable of the light emitting unit 351. Stored. This completes the IDC sensor adjustment. Then, when the IDC sensor 35 is used at the time of the next γ correction, the value of the light emission duty ratio Dty is read, and the light emission of the light emitting unit 351 is performed with the read light emission duty ratio Dty.

  Regarding the acquisition of the detection result of the downstream bare surface area 70b by the IDC sensor 35, the position Q11 (FIG. 8B) which is the most downstream end of the bare surface area 70b passes the detection positions 99a and 99b of the IDC sensor 35. To obtain the output signal (voltage) of the IDC sensor 35 from when the position Q12 (FIG. 8 (b)) which is the most upstream end of the bare surface area 70b reaches the detection position 99a, 99b of the IDC sensor 35 It is done by doing.

  Assuming that the time obtained by dividing the distance (predetermined value) from the position Q11 to the position Q12 in the direction opposite to the belt winding direction B by the circumferential speed Va of the intermediate transfer belt 27 is t2, the reference position by the IDC sensor 35 The point in time when the time (t1 + t2) has elapsed since the detection of Q1 can be determined as the point in time when the position Q12 reaches the detection positions 99a, 99b of the IDC sensor 35, that is, the detection of the downstream bare surface area 70b is completed.

Therefore, the signal output from the IDC sensor 35 during the time from the detection of the position Q1 by the IDC sensor 35 until the time (t1 + t2) elapses from reaching the time t1 The detection result of the surface area 70 b by the IDC sensor 35 can be used.
If it is determined that the detection by the IDC sensor 35 of the downstream bare surface area 70b has ended ("Yes" in step S83), it is determined whether the IDC sensor adjustment has ended at that point (step S84).

When the light amount of the reflected light from the downstream bare surface region 70b does not reach the target value at the end of detection of the downstream bare surface region 70b, that is, in the middle of stepwise switching of the light emission duty ratio Dty It is determined that the IDC sensor adjustment has not ended.
If it is determined that the IDC sensor adjustment is completed ("Yes" in step S84), the process proceeds to step S87. On the other hand, if it is determined that the IDC sensor adjustment has not ended ("No" at step S84), the IDC sensor adjustment is interrupted (step S85), and the value of the light emission duty ratio Dty at that interruption time is stored ( Step S86) The process proceeds to step S87. Specifically, for example, when the IDC sensor adjustment is interrupted when the light emission duty ratio Dty is switched from 16% to 32% and then to 48%, the value of the light emission duty ratio Dty at the time of the interruption (= 48%) Is stored.

In step S87, the detection results of the resist patterns 71Y to 71K and 72Y to 72K formed in the upstream pattern forming region 70a on the intermediate transfer belt 27 by the IDC sensor 35 are acquired.
At the time of detection of this resist pattern, the light emission amount of the light emitting unit 351 is controlled to be the same as the light emission amount at the time of the first base surface detection, regardless of whether the IDC sensor adjustment is completed or not. This is because the resist patterns formed in the upstream and downstream pattern forming regions 70 a on the intermediate transfer belt 27 are detected under the same conditions with respect to the light emission amount of the light emitting unit 351.

  The detection result of the IDC sensor 35 in step S87 is obtained after the position Q12 (FIG. 8B), which is the most downstream end of the upstream pattern formation area 70a, passes the detection positions 99a and 99b of the IDC sensor 35. By obtaining the output signal (voltage) of the IDC sensor 35 until the position Q13 (FIG. 8B), which is the most upstream end of the pattern formation area 70a, reaches the detection positions 99a and 99b of the IDC sensor 35. To be done.

  Assuming that the time obtained by dividing the distance (predetermined value) from the position Q12 to the position Q13 in the direction opposite to the belt winding direction B by the peripheral speed Va of the intermediate transfer belt 27 is t3, the detection of the position Q1 by the IDC sensor 35 When the time (t1 + t2) has elapsed, when the position Q12 reaches the detection positions 99a and 99b of the IDC sensor 35, when the time (t1 + t2 + t3) elapses from the detection of the position Q1 by the IDC sensor 35, the position Q13 takes IDC It can be when the detection positions 99a, 99b of the sensor 35 are reached.

Therefore, the signal output from the IDC sensor 35 during the time from the detection of the position Q1 by the IDC sensor 35 to the time (t1 + t2 + t3) after the elapsed time from (t1 + t2) reaches the upstream side on the intermediate transfer belt 27 It can be set as the detection result by the IDC sensor 35 of the resist pattern formed in the pattern formation area 70a.
In step S88, the detection results of the resist pattern of the downstream pattern formation region 70a stored in step S81 by the IDC sensor 35 and the IDC sensors of the resist pattern in the upstream pattern formation region 70a acquired in step S87. Based on the detection result by 35, as described above, the misregistration amounts in the main scanning direction and the sub scanning direction of each color toner image are calculated, and data of the calculated misregistration amount is used as a control variable of the image writing position as a backup memory. Make it memorize in 38. Thus, the registration correction is completed.

In the next step S89, it is determined whether or not the IDC sensor adjustment has been suspended in step S85. If it is determined that the IDC sensor adjustment has not been interrupted ("No" in step S89), the process returns.
On the other hand, if it is determined that the IDC sensor adjustment is suspended ("Yes" in step S89), the light emission duty ratio Dty for the light emitting unit 351 is switched to the value of the light emission duty ratio Dty stored in step S86. The light emitting unit 351 is caused to emit light with the value of the light emission duty ratio Dty switched to start acquisition of the detection result of the upstream bare surface region 70b on the intermediate transfer belt 27 by the IDC sensor 35, and the acquired IDC Based on the detection result of the sensor 35, the interrupted IDC sensor adjustment is restarted (step S90).

  When the light emission duty ratio Dty stored at the time of interruption is 48%, for example, the start of restart of IDC sensor adjustment is 48% to 40% of the light emission duty ratio Dty. This is done by resuming the instruction to switch in stages. Thereby, the light emission amount of the light emitting unit 351 is switched to the light emission amount according to the instructed light emission duty ratio, and the reflected light from the bare surface area 70b approaches the target value.

  The detection result of the bare surface area 70b on the upstream side on the intermediate transfer belt 27 by the IDC sensor 35 is obtained at the position Q13 (FIG. 8B) at the most downstream end of the bare surface area 70b. IDC sensor 35 after passing detection position 99a, 99b until position Q5 (FIG. 8 (b)) which is the most upstream end of bare surface area 70b reaches detection position 99a, 99b of IDC sensor 35 This is performed by acquiring an output signal (voltage) of

  Assuming that the time obtained by dividing the distance (predetermined value) from the position Q13 to the position Q14 in the direction opposite to the belt winding direction B by the peripheral speed Va of the intermediate transfer belt 27 is t4, the reference position by the IDC sensor 35 When time (t1 + t2 + t3) has elapsed since detection of Q1, when position Q13 reaches the detection positions 99a and 99b of IDC sensor 35, and when time (t1 + t2 + t3 + t4) elapses, position Q14 becomes detection position 99a and 99b of IDC sensor 35 It can be determined that it has arrived.

Therefore, the signal output from the IDC sensor 35 during the time (t1 + t2 + t3 + t4) after the elapsed time from the detection of the position Q1 by the IDC sensor 35 reaches (t1 + t2 + t3) is the upstream side on the intermediate transfer belt 27 It can be set as the detection result of the bare surface area 70b.
If it is determined that the detection by the IDC sensor 35 of the upstream bare surface area 70b on the intermediate transfer belt 27 is completed ("Yes" in step S91), the IDC sensor adjustment is ended (step S92), and the process returns. . When the detection of the upstream bare surface region 70b by the IDC sensor 35 is completed, if the adjustment of the light emission amount from the light emitting unit 351 is still continued by the switching of the light emission duty ratio, The light emission duty ratio is stored in the backup memory 38 as a control variable of the light emitting unit 351.

  Returning to FIG. 9, when it is determined in step S23 that the relationship of threshold th0 <detection value E ≦ threshold th1 is not satisfied (“No” in step S23), the light emission amount of the light emitting unit 351 of the IDC sensor 35 is a resist pattern. Is within the undetectable range, and after IDC sensor adjustment is performed (step S24), registration correction and .gamma. Correction are performed in this order (steps S25 and S26), and the image stabilization operation is ended (first process) Short stabilization).

  Further, when it is determined that the relationship of threshold th1 <detection value E ≦ threshold th2 is satisfied (“Yes” in step S22), the light emission amount of the light emitting unit 351 of the IDC sensor 35 corresponds to the resist pattern and the gradation (density) pattern. The resist correction and the .gamma. Correction are performed in this order (steps S25 and S26), assuming that both are within the detectable range (steps S25 and S26), and the image stabilization operation is ended (third short stabilization). In this case, IDC sensor adjustment is not performed.

The above-mentioned resist correction in step S25 is the same processing as long stabilization resist correction (step S17), and the IDC sensor 35 in the bare surface area 70b is in the process of the resist correction (+ IDC sensor adjustment) in step S27. IDC sensor adjustment will not be performed based on the detection result by.
If it is determined that the execution of the resist has not been instructed but the short stabilization has been made ("No" in step S19), base surface detection is performed (step S28). This base surface detection is performed by the same method as the base surface detection of step S12.

It is determined whether the detected value E detected by the sensor 35 at the time of base surface detection is larger than the threshold th0 and smaller than or equal to the threshold th2 (step S29).
If it is determined that the relationship of threshold th0 <detection value E ≦ threshold th2 is satisfied (“Yes” in step S29), it is assumed that the light emission amount of light emitting unit 351 of IDC sensor 35 is within the detectable range of resist pattern. After performing the registration correction (step S31), the image stabilization operation is ended.

On the other hand, if it is determined that the relationship of threshold th0 <detection value E ≦ threshold th2 is not satisfied (“No” in step S29), the light emission amount of the light emitting unit 351 of the IDC sensor 35 falls within the range where the resist pattern can not be detected. If IDC sensor adjustment is performed (step S30), registration correction is performed (step S31), and the image stabilization operation is ended.
As described above, in the present embodiment, when the relationship of threshold th0 <detection value E ≦ threshold th1 is satisfied in short-circuit stabilization, registration correction and IDC sensor adjustment are performed in parallel. As a result, in the short stabilization that is one of the image stabilization operations, it is possible to shorten the entire image stabilization operation time while improving the pattern detection accuracy by the IDC sensor adjustment.
Second Embodiment
In the first embodiment, the threshold th0 for determining whether or not each of the resist pattern and the gradation pattern can be detected by the IDC sensor 35 in the long stabilization and the short stabilization and the resist as different types of image stabilization operations. In the second embodiment, different threshold values are used in different types of image stabilization operations, and this embodiment differs from the first embodiment in this respect. Hereinafter, in order to avoid duplication of explanation, the explanation shall be omitted about the same contents as Embodiment 1.

  FIG. 12 is a flowchart showing the processing content of the image stabilization operation in the configuration using different threshold values for long stabilization and resist, respectively, which is executed by the control unit 7. 6 is formed by the pattern forming unit 301 on the intermediate transfer belt 27 when the execution of the long stabilization is instructed, and when the resist is instructed by the pattern forming unit 301. It is assumed that only the resist pattern of the resist correction area 65 is formed next to the IDC sensor adjustment area 62 shown in FIG.

As shown in the figure, the light emission amount is instructed to the light emitting unit 351 of the IDC sensor 35 (step S50). This instruction is performed by the same method as step S10.
Then, it is determined whether or not the execution of the resist has been instructed (step S51). If it is determined that execution of long stabilization is instructed instead of resist ("No" in step S51), base surface detection is performed (step S52).

It is determined whether the detection value E of the sensor 35 at the time of base surface detection is equal to or greater than the threshold th1 (step S53).
If it is determined that the relationship of threshold value th1 ≦ detection value E is not satisfied (“No” in step S53), after performing IDC sensor adjustment (step S54), maximum adhesion amount adjustment, LD light amount adjustment, resist correction, γ The correction is performed in this order (steps S55 to S58), and the image stabilization operation is ended.

In long stabilization, the light emission amount of the light emitting part 351 of the IDC sensor 35 needs to be in a range where it can detect both the density pattern such as maximum attached amount adjustment and γ correction and the resist pattern. If the relationship of the value E is not satisfied, it is not within this range as described above, and it is necessary to perform IDC sensor adjustment.
If it is determined that the relationship of threshold value th1 ≦ detection value E is satisfied (“Yes” in step S53), maximum adhesion amount adjustment to γ correction is sequentially performed without performing IDC sensor adjustment (steps S55 to S58 ), End the image stabilization operation. The above-mentioned base surface detection to γ correction is the same processing as the base surface detection to γ correction of long stabilization in the first embodiment.

On the other hand, when it is determined that the execution of the resist has been instructed ("Yes" in step S51), base surface detection is performed (step S59).
It is determined whether the detection value E of the sensor 35 at the time of base surface detection is equal to or greater than the threshold th0 (step S60).
If it is determined that the relationship of threshold th0 ≦ detection value E is not satisfied (“No” in step S60), after IDC sensor adjustment is performed (step S61), registration correction is performed (step S62), the image End the stabilization operation.

In the resist, the light emission amount of the light emitting portion 351 of the IDC sensor 35 may be at least within the range where the resist pattern can be detected, but if the relationship of threshold th0 ≦ detection value E is not satisfied, as described above. Because it is not within the range, it is necessary to perform IDC sensor adjustment.
If it is determined that the relationship of threshold th0 ≦ detection value E is satisfied (“Yes” in step S60), registration correction is performed without performing IDC sensor adjustment (step S62), and the image stabilization operation is performed. finish. The above-mentioned base surface detection to resist correction is the same processing as the resist base surface detection to resist correction in the first embodiment.

In the second embodiment, when it is determined that the IDC sensor adjustment is unnecessary based on the detection value E of the IDC sensor 35 at the time of base surface detection, the IDC sensor adjustment is not performed. In comparison, the time required for the entire image stabilization operation can be shortened.
Further, the threshold value for determining the necessity of the IDC sensor adjustment is made different according to the type of the image stabilization operation. That is, if the type of the image stabilization operation is different, the necessary range of the light emission amount of the light emitting unit 351 of the IDC sensor 35 is also different. As described above, in long stabilization, the light emission amount of the light emitting portion 351 needs to be within a detectable range of both a solid density pattern such as maximum attached amount adjustment and γ correction and a linear resist pattern. , The threshold is th1. On the other hand, in the resist, the threshold value is set to th0 (<th1) because it is sufficient if the linear resist pattern is within a detectable range.

Assuming that one threshold value is shared for all different types of image stabilization operations, for example, if only threshold value th1 is used, if long stabilization or resist satisfies the relationship of detection value E <threshold value th1, then IDC sensor calibration will always be performed.
However, in the resist, if the relationship of threshold th0 <detection value E <threshold th1 is satisfied, the execution of the IDC sensor adjustment is essentially unnecessary. Therefore, if only the threshold th1 is used, unnecessary IDC sensor adjustment may be performed.

  Alternatively, for example, in the case of using only the threshold th0, the IDC sensor adjustment is not necessarily performed if the relationship of the threshold th0 <the detection value E is satisfied, even in the long stabilization or the resist. However, in long stabilization, if the relationship of threshold th0 <detection value E <threshold th1 is satisfied, the execution of the IDC sensor adjustment is essentially necessary. Therefore, when only the threshold th0 is used, the necessary IDC sensor adjustment may not be performed.

  On the other hand, by setting the threshold value for determining the necessity of IDC sensor adjustment to a different value suitable for the image stabilization operation for each different type of the image stabilization operation as in the second embodiment. It does not occur that unnecessary IDC sensor adjustment is not performed or required IDC sensor adjustment is not performed as in a configuration in which one threshold value is shared. Therefore, it becomes possible to optimally execute each of the different types of image stabilization operations.

The invention according to the second embodiment can be expressed as follows.
That is, (1) Toner images of different colors are formed on each of a plurality of photosensitive members (photosensitive drum 21) by an image forming unit (such as the image forming unit 20Y), and the intermediate color transfer image is rotated. An image forming apparatus for transferring each color toner image after transfer onto a sheet (recording sheet S) after multiple transfer onto a body (intermediate transfer belt 27), which has the following configurations (a) to (f): It is characterized by having. Here, (a) is a control means, (b) is a sensor, and (c) is an image stabilization means.

  The control means of (a) controls the image forming means to perform a first predetermined image stabilization operation (long stabilization) for maintaining the image quality of each color toner image formed to a predetermined level or more. One pattern (patterns 631, 641, 71Y to 71K, etc.) and a second predetermined pattern (patterns 71Y to 71K, etc.) used for a second image stabilization operation (resist) different from the first image stabilization operation And B. are selectively formed on the bare surface of the peripheral surface of the intermediate transfer member, and corresponds to the pattern forming portion 301.

The sensor (b) is a sensor that emits light from a light emitting unit (light emitting unit 351) toward the intermediate transfer member and detects reflected light or transmitted light of the light from the intermediate transfer member, and an IDC sensor It corresponds to 35.
The image stabilization means of (c) uses the sensor of the first pattern on the peripheral surface of the intermediate transfer member when a predetermined execution condition (such as an environmental change) for the first image stabilization operation is satisfied. Based on the detection result, when the first image stabilization operation is performed and a predetermined execution condition (PH temperature change or the like) for the second image stabilization operation is satisfied, the peripheral image on the intermediate transfer body The second image stabilization operation is performed based on the detection result of the second pattern by the sensor, and corresponds to the image stabilization control unit 302.

  (D) Then, the image stabilization means forms the first pattern on the peripheral surface of the intermediate transfer body before the detection of the first pattern by the sensor in the first image stabilization operation. The first base surface detection is performed by the sensor to detect the bare surface area (base surface detection area 61) located downstream of the area in the rotation direction (step S52), and the detection result and a predetermined first threshold (th1) And a first determination unit (step S53) that determines whether the light emission amount of the light emitting unit is within a range in which the first pattern can be detected.

  (E) Further, the image stabilization means forms the second pattern on the peripheral surface of the intermediate transfer body before the detection of the second pattern by the sensor in the second image stabilization operation. The second base surface detection is performed by the sensor for detecting the bare surface area (base surface detection area 61) located downstream of the area in the rotational direction (step S59), and the detection result is different from the first threshold A second determination unit (step S60) that determines whether the light emission amount of the light emitting unit is within a range where the second pattern can be detected, based on the magnitude relationship with a predetermined second threshold (th0); Equipped with

  (F) If the determination result of the corresponding determination means is negative for each of the first and second image stabilization operations, the image stabilization means ("No" in step S53, step Before the detection by the sensor of the pattern used for the image stabilization operation, “No” in S60, based on the detection result by the sensor of the bare surface area (IDC sensor adjustment area 62) of the peripheral surface of the intermediate transfer body The light emission amount of the light emission unit is determined, the light emission unit is caused to emit light with the determined light emission amount, and then the sensor adjustment (steps S54 and S61) for detecting the pattern is executed. Does not execute the sensor adjustment ("Yes" at step S53, "Yes" at step S60), and the detection of the pattern by the sensor (steps S55 to S58) S62) carried out.

Further, (2) the first image stabilization operation is an image stabilization operation including a resist correction for correcting a displacement of the formation position of each color toner image and a density correction for the toner image, and the second image stabilization operation It is also possible that the conversion operation is the image stabilization operation of only the registration correction.
The present invention is not limited to the image forming apparatus, and may be an execution method of the image stabilization operation in the image forming apparatus. Furthermore, the method may be a program executed by a computer. The program according to the present invention may be, for example, a magnetic tape, a magnetic disk such as a flexible disk, a DVD-ROM, a DVD-RAM, a CD-ROM, an optical recording medium such as a CD-R, an MO, or a PD, and a flash memory recording medium. It can be recorded in various computer readable recording media, etc., and may be produced, transferred, etc. in the form of the recording media, and various wired and wireless networks including the Internet in the form of programs. It may be transmitted and supplied via broadcasting, telecommunication lines, satellite communication, etc.

[Modification]
As mentioned above, although this invention was demonstrated based on embodiment, of course, this invention is not limited to the above-mentioned embodiment, The following modified examples can be considered.
(1) In the first embodiment, although the short stabilization to be performed is determined to be any one of the first to third short stabilization based on the result of the base surface detection, it is not limited to this.

  For example, in a device configuration in which the amount of light emitted from the light emitting unit 351 does not significantly change to such an extent that the resist pattern can not be detected between the previous short stabilization operation and the current short stabilization operation. In stabilization, processing to perform resist correction (+ IDC sensor adjustment) and γ correction without base surface detection, that is, even if “Yes” in step S 19 in FIG. 9 is followed by steps S 27 and S 26 in this order. good.

  In addition, in the case where the relationship of threshold value th1 <detection value E ≦ th2 is satisfied (“Yes” in step S22), the IDC sensor adjustment is not performed, but the present invention is not limited thereto. For example, in order to further improve the detection accuracy of the toner pattern by the IDC sensor 35 each time short-circuit stabilization is performed, the relationship of threshold th0 <detection value E ≦ threshold th2 is satisfied after base surface detection in step S20. In this case, the resist correction (+ IDC sensor adjustment) of step S27 and the γ correction of step S26 may be performed in this order.

  (2) In the above embodiment, a configuration example in which the so-called reflection type optical sensor in which the light receiving unit 352 receives the light emitted from the light emitting unit 351 and reflected from the intermediate transfer belt 27 is used for the IDC sensor 35 Although explained, it is not limited to this. Any sensor such as a resist pattern or a gradation pattern formed on the circumferential surface 27 a of the intermediate transfer belt 27 and a bare surface area of the intermediate transfer belt 27 may be used. For example, it is also possible to use a so-called transmission type optical sensor in which the light receiving unit 352 receives the light transmitted from the intermediate transfer belt 27 of the light emitted from the light emitting unit 351.

In addition, although the IDC sensor 35 includes the two detection sensors 35a and 35b arranged at intervals in the main scanning direction, the present invention is not limited to this. For example, only one detection sensor may be provided.
(3) In the above embodiment, a configuration example in which the light emission amount of the light emission unit 351 is changed by control to instruct the duty ratio indicating the light emission amount to the light emission unit 351 has been described. The configuration is not limited to the above method as long as the configuration is possible, and another control method may be used.

  In addition, light emission in which the light emission amount of the light emitting unit 351 is changed stepwise so that the light amount of the reflected light Lb from the bare surface area of the intermediate transfer belt 27 among the light Lt emitted from the light emitting unit 351 becomes a target value. Although binary sort was used as a method of quantity control, it is not limited to this. Any method may be used as long as it can control to change the light emission amount of the light emitting unit 351 so that the light amount of the reflected light Lb becomes the target value.

(4) In the above embodiment, two patterns of linear resist patterns 71Y to 71K of respective colors spaced apart from each other in the belt winding direction B (rotational direction) are formed at predetermined intervals in the same direction. Although the region 70a is formed in each of the regions 70a, the number of pattern formation regions 70a is not limited to two, and may be two or more.
In the short-circuit stabilization, when two or more (plural) pattern formation areas 70a exist, a set of two pattern formation areas adjacent in the belt winding direction B among the plurality of pattern formation areas, for example, the upstream side from the downstream side When each pattern formation region is referred to as a first region A, B, C, ... toward the side, any one of a pair of A and B, a pair of B and C on the upstream side of this, etc. The bare surface area 70b existing between one first area and the other first area of one set can be used for IDC sensor adjustment.

Also, instead of this, the bare surface region 70b in the case where the bare surface region 70b exists between the uppermost stream pattern formation region 70a (first region) and the γ correction region 66 (second region) It can also be used for adjustment.
Furthermore, in the short stabilization, although the bare surface area 70b is used to perform the IDC sensor adjustment, the present invention is not limited thereto. Of the plurality of pattern formation areas 70a (first area), after the resist patterns 71Y to 71K formed in the pattern formation area 70a on the most downstream are detected by the IDC sensor 35, in the γ correction area 66 (second area) Detection of a bare surface area on which no resist pattern is formed on the peripheral surface 27a of the intermediate transfer belt 27 by the IDC sensor 35 until the formed density patterns 66C and 66K are detected by the IDC sensor 35 IDC sensor adjustments can be made based on the results.

For example, in the case where the length in the belt circumferential direction of the bare surface area existing between the uppermost resist pattern 71Y and the most downstream resist pattern 72K shown in FIG. 7 has a size that allows the IDC sensor adjustment to be performed. The bare surface area can be used for IDC sensor adjustment as a bare surface area in which any resist pattern is not formed.
(5) In the above embodiment, although γ correction as an example of density correction is performed after resist correction (+ IDC sensor adjustment) in short circuit stabilization, the present invention is not limited to this. The maximum adhesion amount adjustment and the LD light amount correction can also be regarded as one of the density corrections in the sense of optimizing the density of the reproduced image.

  In this case, after registration correction (+ IDC sensor adjustment), either or both of maximum adhesion amount adjustment and LD light amount correction may be executed in order or γ 3 in place of γ correction. it can. In addition to the maximum adhesion amount adjustment, the LD light amount correction, and the γ correction, if there is an image stabilization operation for correcting the density of the reproduced image, the image stabilization operation can be executed as the density correction.

  (6) In the above embodiment, two resist patterns of the same color are formed on the circumferential surface 27a of the intermediate transfer belt 27 at positions separated by the transfer belt half circumference G along the circumferential direction of the belt. It is not restricted to this. For example, when the circumferential speed unevenness occurring in the intermediate transfer belt 27 is faster than the original circumferential speed and the period in which the circumferential speed unevenness occurs periodically alternates with each other, the intermediate transfer belt 27 is separated by a distance equivalent to the half cycle. You can also

(7) In the above embodiment, an example using an MFP as an image forming apparatus according to the present invention has been described, but the present invention is not limited to this.
Toner images of different colors are formed on each of a plurality of photosensitive members (photosensitive drum, photosensitive belt, etc.) for each color by image forming means including image forming units 20Y to 20K, and the respective color toner images are rotated. Image forming apparatus such as a printer, copier, facsimile apparatus, etc. configured to transfer each color toner image after the transfer to a sheet such as paper after multiple transfer onto an intermediate transfer body (intermediate transfer belt, intermediate transfer drum, etc.) The device is generally applicable to devices having a function of performing an image stabilization operation.

  Further, the shape, size, number, and positional relationship between adjacent patterns of each toner pattern such as the resist pattern and density pattern described above, the base surface detection area 61, the IDC sensor adjustment area 62, the resist correction area 65, and the like. The size of the area (belt circumferential length, etc.) is not limited to the above, and the pattern shape, the number, the size of each area, etc. suitable for the apparatus configuration are previously determined for each image forming apparatus.

  Further, the contents of the above embodiment and the above modification may be combined as much as possible.

  The present invention is applicable to an image forming apparatus that performs an image stabilization operation.

1 MFP
DESCRIPTION OF SYMBOLS 4 Image process part 7 Control part 20Y, 20M, 20C, 20K Imaging unit 27 Intermediate transfer belt 27a Peripheral surface of intermediate transfer belt 35 IDC sensor 61 Base surface detection area (bare surface area)
62 IDC sensor adjustment area (bare area)
66Y, 66M, 66C, 66K density pattern 70a resist pattern formation area 70b bare surface area of the peripheral surface of the intermediate transfer belt 71Y, 71M, 71C, 71K, 72Y, 72M, 72C, 72K resist pattern 301 pattern forming part 302 image stabilization Control unit 351 Light emitting unit 352 Light receiving unit

Claims (7)

Toner images of different colors are formed on each of a plurality of photosensitive members by image forming means, and the color toner images are multiply transferred onto a rotating intermediate transfer member, and then the color toner images after transfer are formed on a sheet. An image forming apparatus for transferring
The image forming means is controlled to correct the deviation of the formation position of the toner image of each color in each of a plurality of first regions spaced by a predetermined interval in the rotational direction on the bare surface of the peripheral surface of the intermediate transfer member Control means for forming a density pattern of each color for performing density correction of a toner image in a second region on the circumferential surface of the intermediate transfer body after forming a resist pattern of each color for performing resist correction;
A sensor that emits light from a light emitting unit toward the intermediate transfer body, and detects reflected light or transmitted light of the light from the intermediate transfer body;
An image stabilization unit that executes the resist correction and the density correction in this order based on the detection result of the resist pattern and the density pattern on the circumferential surface of the intermediate transfer member by the sensor;
Equipped with
The image stabilization means is
Wherein the intermediate transfer member peripheral surface, on the basis of the detection result of the sensor of the first bare surface area that Sons downstream of the first region of the rotation direction downstream of the plurality of first regions, the light emitting portion A determination means for determining whether the amount of light emission of the light emission is within the range where the resist pattern can be detected ;
If the determination result of the previous SL judgment means is affirmative, by said sensor, said plurality of said second region from the direction of rotation downstream of the resist pattern formed in the first region is detected in the first region Before the detection of the density pattern formed on the surface of the intermediate transfer member, the resist pattern is not formed on the peripheral surface of the intermediate transfer body, and the sensor of the bare surface region different from the first bare surface region is used. Determining the amount of light emission of the light emitting unit based on the detection result, and performing a first sensor adjustment to cause the light emitting unit to emit light with the determined amount of light emission ;
In the negative case, the first bare surface area and the most downstream area are delayed by delaying the formation timing of the resist pattern and the density pattern on the intermediate transfer member by the control means for a predetermined time than in the positive case. The second bare surface area is further secured between the first area and the second bare surface area, and the second bare surface area secured before the start of detection by the sensor of the resist pattern formed on the most downstream first area. determining the light emission amount of the light emitting portion based on a detection signal from the sensor surface area, it determined light emission amount in images forming apparatus you and performing a second sensor adjustment Ru is emitting the light emitting portion. The judging means
Furthermore, based on the detection result of the first bare surface area by the sensor, it is determined whether the light emission amount of the light emitting unit is within a range in which both the resist pattern and the density pattern can be detected.
The image stabilization means is
If it is determined that the light emission amount of the light emitting unit is within the range in which both the resist pattern and the density pattern can be detected, execution of both the first sensor adjustment and the second sensor adjustment is performed. The image forming apparatus according to claim 1 , wherein the image forming apparatus is prohibited. The control means
Both the resist pattern and the density pattern are formed only when a predetermined first condition is satisfied, and when the predetermined second condition different from the first condition is satisfied, the image forming unit is controlled to Forming a resist pattern of the same color as that of the resist pattern on each of the plurality of first regions on the circumferential surface of the intermediate transfer member, without forming the density pattern;
The judging means
When the resist pattern is formed by satisfying the second condition, a third bare surface existing downstream of the most downstream first region of the plurality of first regions on the circumferential surface of the intermediate transfer member Based on the detection result of the region by the sensor, it is determined whether the light emission amount of the light emitting unit is within a range in which the formed resist pattern can be detected.
The image stabilization means is
When the second condition is satisfied, the resist correction of the same method as the resist correction is performed, and the density correction is not performed.
Furthermore, if the determination result of the determination means when the second condition is satisfied is negative, only the sensor adjustment of the same method as the second sensor adjustment is executed, and if the determination result is positive, the image forming apparatus according to claim 1 or 2, characterized in that to perform only the sensor adjustment in the same way as the first sensor adjustment. The image stabilization means is
At the time of detection of the first bare surface area by the sensor, instructing the light emitting unit to emit light with the same light emission amount as the light emission amount determined at the time of the previous sensor adjustment The image forming apparatus according to any one of claims 1 to 3 , characterized in that Toner images of different colors are formed on each of a plurality of photosensitive members by image forming means, and the color toner images are multiply transferred onto a rotating intermediate transfer member, and then the color toner images after transfer are formed on a sheet. An image forming apparatus for transferring
The image forming means is controlled to correct the deviation of the formation position of the toner image of each color in each of a plurality of first regions spaced by a predetermined interval in the rotational direction on the bare surface of the peripheral surface of the intermediate transfer member Control means for forming a density pattern of each color for performing density correction of a toner image in a second region on the circumferential surface of the intermediate transfer body after forming a resist pattern of each color for performing resist correction;
A sensor that emits light from a light emitting unit toward the intermediate transfer body, and detects reflected light or transmitted light of the light from the intermediate transfer body;
An image stabilization unit that executes the resist correction and the density correction in this order based on the detection result of the resist pattern and the density pattern on the circumferential surface of the intermediate transfer member by the sensor;
Equipped with
The image stabilization means is
Furthermore, from the detection of the resist pattern formed in the first region of the plurality of first regions in the most downstream direction of the rotation direction by the sensor to the detection of the density pattern formed in the second region In the meantime, the light emitting amount of the light emitting portion is determined based on the detection result by the sensor of the bare surface area on which the resist pattern is not formed on the peripheral surface of the intermediate transfer member, and the light emitting portion Adjust the sensor to make
The bare surface area is
In the circumferential surface of the intermediate transfer member, a bare surface existing between one first region and the other first region of any one of two sets of first regions adjacent in the rotational direction region, or images forming device you being a corresponding bare surface region when Hadakamen region resides between the second region and the first region of the most upstream. Toner images of different colors are formed on each of a plurality of photosensitive members by image forming means, and the color toner images are multiply transferred onto a rotating intermediate transfer member, and then the color toner images after transfer are formed on a sheet. An image forming apparatus for transferring
The image forming means is controlled to correct the deviation of the formation position of the toner image of each color in each of a plurality of first regions spaced by a predetermined interval in the rotational direction on the bare surface of the peripheral surface of the intermediate transfer member Control means for forming a density pattern of each color for performing density correction of a toner image in a second region on the circumferential surface of the intermediate transfer body after forming a resist pattern of each color for performing resist correction;
A sensor that emits light from a light emitting unit toward the intermediate transfer body, and detects reflected light or transmitted light of the light from the intermediate transfer body;
An image stabilization unit that executes the resist correction and the density correction in this order based on the detection result of the resist pattern and the density pattern on the circumferential surface of the intermediate transfer member by the sensor;
Equipped with
The image stabilization means is
Between the time when the resist pattern formed in the first area in the most downstream side in the rotational direction of the plurality of first areas is detected by the sensor and the density pattern formed in the second area is detected The amount of light emission of the light emitting unit is determined based on the detection result of the sensor on the bare surface area where none of the resist patterns are formed on the peripheral surface of the intermediate transfer member, and the light emitting unit is made to emit light Make sensor adjustment,
Furthermore, the image stabilization means
In the sensor adjustment, an instruction to change the light emission amount to the light emitting unit based on the detection result by the sensor until the reflected light or the transmitted light from the bare surface area of the intermediate transfer member reaches a target value The light emission amount of the light emitting unit is determined by execution of the light emission amount control to be performed,
At the time of controlling the light emission amount, one of the first region and the other first region of any one of the sets of two first regions adjacent in the rotational direction on the circumferential surface of the intermediate transfer member And if the light emission control is being performed at the end of the detection of the bare surface area by the sensor, the light emission control is temporarily interrupted,
In the circumferential surface of the intermediate transfer member, a bare surface area existing between one first area and another first area of another set located upstream of the one set, or the uppermost first area In the case where a bare surface area is present between the second area and the second area, when the bare surface area reaches the detection position of the sensor, light emission resumes from the light emission amount at the interruption time to the light emitting unit. images forming device you characterized by instructing the interruption to have a light emission amount control resumes as. Toner images of different colors are formed on each of a plurality of photosensitive members by image forming means, and the color toner images are multiply transferred onto a rotating intermediate transfer member, and then the color toner images after transfer are formed on a sheet. An image forming apparatus for transferring
The image forming means is controlled to correct the deviation of the formation position of the toner image of each color in each of a plurality of first regions spaced by a predetermined interval in the rotational direction on the bare surface of the peripheral surface of the intermediate transfer member Control means for forming a density pattern of each color for performing density correction of a toner image in a second region on the circumferential surface of the intermediate transfer body after forming a resist pattern of each color for performing resist correction;
A sensor that emits light from a light emitting unit toward the intermediate transfer body, and detects reflected light or transmitted light of the light from the intermediate transfer body;
An image stabilization unit that executes the resist correction and the density correction in this order based on the detection result of the resist pattern and the density pattern on the circumferential surface of the intermediate transfer member by the sensor;
Equipped with
The image stabilization means is
Furthermore, from the detection of the resist pattern formed in the first region of the plurality of first regions in the most downstream direction of the rotation direction by the sensor to the detection of the density pattern formed in the second region In the meantime, the light emitting amount of the light emitting portion is determined based on the detection result by the sensor of the bare surface area on which the resist pattern is not formed on the peripheral surface of the intermediate transfer member, and the light emitting portion Adjust the sensor to make
The control means
Of the two first areas included in the plurality of first areas on the circumferential surface of the intermediate transfer member, a resist pattern of each color formed in the first area on the downstream side and a first area on the upstream side are formed. Forming a resist pattern of each color on the intermediate transfer body so that the same colors are formed at positions separated by a half cycle when one cycle of the intermediate transfer body is one cycle. images forming device you characterized.

Images