JP4609110B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to a so-called multi-beam type image forming apparatus that forms an image with a plurality of light beams. More specifically, the present invention relates to an image forming apparatus that performs registration correction by controlling a plurality of polygon motors.

  2. Description of the Related Art Conventionally, multi-beam type image forming apparatuses have been provided with laser devices that can emit a plurality of laser beams having different optical systems. For example, a tandem color image forming apparatus includes a photoreceptor unit corresponding to each color of cyan (C), magenta (M), yellow (Y), and black (K) and a laser device corresponding to each. Yes. Further, each laser device of each color has a polygon mirror and a polygon motor for rotating the polygon mirror.

  In such an image forming apparatus, as a method of correcting the positional deviation in the sub-scanning direction in the image forming system of each color, for example, a deviation in units of one scanning pitch is conventionally a sub-scanning count, and a smaller deviation is determined by a polygon phase. There was a correction method (for example, refer to Patent Document 1). However, there is some variation in the synchronization signal (main scanning image request signal) of each color in the sub-scanning direction due to, for example, uneven rotation of the polygon motor or variations in each control. For this reason, when the synchronization signal of the reference color and the dependent color is set at a very close timing, there is a possibility that a deviation of nearly one line may occur suddenly due to the fluctuation.

On the other hand, Patent Document 2 discloses a technique for performing phase control so that the timing at which the sub-scanning synchronization signal is turned on does not fall within the fluctuation range of the time difference between the output signals of the light beam detection means. According to the technique described in this document, the fluctuation range is grasped by grasping the time difference of the output signal by a plurality of measurements. Further, when the fluctuation range exceeds the delay time of the sub-scanning synchronization signal with respect to the output signal in the reference color, the rotational phase is shifted by that amount. As a result, the occurrence of a shift near one line is prevented.
Registration No. 3282353 JP-A-9-274156

  However, in the image forming apparatus described in Patent Document 2, the above-described fluctuation range is grasped by measurement. Therefore, it cannot be said that the actual output signal does not deviate beyond the fluctuation range. If the output signal is output beyond the measured variation range, there is still a problem that a shift of nearly one line may occur.

The present invention has been made to solve the problems of the conventional image forming apparatus described above. That it is an object, even if the registration correction is to provide an image forming apparatus without the risk of large deviation in the sub-scanning direction is suddenly generated.

An image forming apparatus according to the present invention, which has been made for the purpose of solving this problem, receives a plurality of image forming units and an overlapping transfer of raw images sequentially from the plurality of image forming units while moving, and transfers the overlapping images to a transfer material And a transfer material sensor for detecting the supplied transfer material , and each image forming unit rotates the photosensitive member and a polygon mirror that scans the beam in the main scanning direction toward the photosensitive member by rotating. And a SOS sensor that receives the beam reflected by the polygon mirror before the photosensitive member is irradiated, and a main scanning synchronization signal output unit that outputs a main scanning synchronization signal based on light reception by the SOS sensor. An image forming apparatus in which an ideal phase difference with respect to a reference phase of rotation of a polygon mirror of a plurality of image forming units is set for each image forming unit based on a sub-scanning resist amount When the ideal phase difference set by the setting unit and the phase difference setting unit is within the preset prohibition region that is a region including the reference phase, the ideal phase difference of the polygon mirror is set prohibition region Based on the ideal phase difference for each image forming unit that has been set again, and rotation of the polygon mirrors of multiple image forming units before starting image formation The phase difference of the rotation of each polygon mirror other than the reference color with respect to the phase of the rotation of the polygon mirror of the reference color after the phase adjustment control by the phase control unit is set in advance , if present were in forbidden region is narrower space than setting prohibited regions comprises a reference phase, a phase re-controller to perform the phase adjustment control by the phase control unit again, a plurality of image A count setting unit that sets the number of main scanning synchronization signals between image forming start timings of the forming unit for each image forming unit based on the sub-scanning resist amount, and after phase alignment control by the phase control unit or the phase re-control unit The main scanning synchronization signal of the reference color in the image forming apparatus has a pre-start counter group for counting each of the number of images set up for each of the plurality of image forming units after the transfer material sensor detects the transfer material. Then, after each phase of the image forming unit of the plurality of image forming units is controlled by the phase control unit or the phase re-control unit, the first counter unit after the start of counting for each of the plurality of image forming units is completed. The process starts with a main scanning synchronization signal of the image forming unit .

According to the image forming apparatus of the present invention, for each image forming unit, an elementary image is formed on the photoconductor according to the beam scanned by the polygon mirror, and the elementary image is superimposed and transferred to the transfer body. Here, an ideal phase difference with respect to the reference phase of the polygon mirror for each image forming unit is set by the phase difference setting unit for sub-scanning registration correction at the time of superimposing transfer. Here, if the ideal phase difference set was in setting prohibited area, the phase difference resetting unit is reset to the boundary position of the setting prohibition region. In other words, each phase difference is prevented from entering the reference phase or the range of fluctuation of the phase difference due to driving unevenness or various variations of each part of the image forming unit. This eliminates the possibility that the positional relationship between the reference phase and the phase difference is suddenly reversed.

Further, when the phase difference after the phase matching control by the phase control unit is within the existence prohibition region narrower than the setting prohibition region , the phase re-control unit performs the phase matching control again. That is, the positional relationship between the phase after the phase matching control and the reference phase is set so as not to be less than the detection variation. This prevents the positional relationship between the reference phase and the phase after phase matching control from being reversed. Therefore, even if registration correction is performed, there is no possibility that a large shift in the sub-scanning direction suddenly occurs.
As the reference phase, the rotation phase of one polygon mirror among the plurality of image forming units may be used. In that case, such a phase difference setting is unnecessary for the image forming unit.

Furthermore, the image forming apparatus of the present invention includes a resist detection unit that detects a sub-scanning resist amount that is a positional deviation amount in the sub-scanning direction of a pattern formed on the transfer body by a plurality of image forming units .

Further, in the present invention, phase difference resetting unit, it is preferable to perform the resetting of the ideal phase difference while maintaining the code of the ideal phase difference to be set again.
In such a case, even when the phase difference is ideally reset, the positional relationship with the reference phase does not change. Therefore, a large shift in the sub-scanning direction does not occur.

Further, in the present invention, phase difference resetting unit, while reversing the sign of the ideal phase difference to be set again to reconfigure the ideal phase difference, set by the count setting unit for an image forming unit corresponding to the ideal phase difference It is desirable to change the number of main scanning synchronization signals.
In such a case, when the ideal phase difference is reset, the positional relationship with the reference phase changes. Here, the count setting unit sets the number of main scanning synchronization signals based on the sub-scanning registration amount, and when the ideal phase difference is reset, the number of main scanning synchronization signals is changed. Therefore, there is no possibility that a large shift in the sub-scanning direction occurs.

Further, in the present invention, phase difference resetting unit, the ideal phase difference to be set again, to reconfigure the boundary position of the setting prohibition region.
For this reason , it is reset to a position that is relatively close to the ideal phase difference set by the phase difference setting unit and that is not within the setting prohibited area. That is, it is set to the closest position within a range where there is no possibility of large deviation.

Further, in the present invention, the size of the setting prohibition regions, when the rotational speed of the polygon mirror is double speed is set prohibition region setting unit rotational speed is set to one half the size of the case is a normal speed It is desirable to have
In such a case, the setting prohibition area is set in an appropriate range in both the high definition mode and the low definition mode.

According to the image forming apparatus of the present invention, even if the registration correction, a possibility that a large deviation in the sub-scanning direction is suddenly generated is eliminated.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the best mode for embodying the present invention will be described in detail with reference to the accompanying drawings. In this embodiment, the present invention is applied to a tandem type color printer.

  The color printer 100 according to this embodiment is a tandem full-color copying machine, and includes image forming units 101C, 101M, 101Y, and 101K for each color arranged in parallel as shown in FIG. Each of the image forming units 101C, 101M, 101Y, and 101K includes photosensitive drums 102C, 102M, 102Y, and 102K, laser recording units 103C, 103M, 103Y, and 103K, and peripheral devices (charging device, developing device, transfer device, Cleaner device etc. Furthermore, the color printer 100 also includes a registration sensor 105, a TOD sensor 106, a transfer belt 112, and a control unit 130.

  Each of the image forming units 101 </ b> C, 101 </ b> M, 101 </ b> Y, and 101 </ b> K forms an image on the transfer belt 112. The laser recording units 103C, 103M, 103Y, and 103K expose the photosensitive layers of the photosensitive drums 102C, 102M, 102Y, and 102K, and write electrostatic latent images. The registration sensor 105 detects a correction image (resist pattern) formed on the transfer belt 112. The TOD sensor 106 detects the transferred transfer material S. The control unit 130 controls each unit of the color printer 100.

  In order to form a color image in the color printer 100, first, electrostatic latent images are written on the photosensitive layers of the photosensitive drums 102C, 102M, 102Y, and 102K by the image forming units 101C, 101M, 101Y, and 101K. This is visualized as a toner image. Next, the toner images of these colors are sequentially transferred to the same position on the transfer belt 112 and superimposed. The superimposed toner images are transferred to the transfer material S, whereby a color image is formed. Here, registration correction is performed in order to superimpose toner images of the respective colors without deviation. That is, at the time of non-image formation or the like, a resist pattern is formed by each of the image forming units 101C, 101M, 101Y, and 101K and detected by the resist sensor 105. From the detection timings of the resist patterns of the respective colors, set values for resist correction such as the main scanning position, the sub scanning position, and the main scanning magnification are calculated.

  Next, the laser recording units 103C, 103M, 103Y, and 103K for each color will be described with reference to FIG. The laser recording units 103C, 103M, 103Y, and 103K for the respective colors have the same configuration. Here, the laser recording unit 103C will be described as an example. As shown in FIG. 2, the laser recording unit 103C includes a laser device 1C, a collimator lens 2C, a polygon mirror 3C, an fθ lens 4C, and a polygon motor 5C. In FIG. 2, in addition to the laser recording unit 103C, the photosensitive member 102C irradiated with the laser beam, the SOS sensor 6C for detecting the scanning start timing, and the vicinity of the tip of the scanning region of the photosensitive member 102C are provided. A reflecting mirror 7C is also shown.

  According to the laser recording unit 103C, the divergent light emitted from the laser device 1C is converted into a parallel laser beam by the collimator lens 2C and is irradiated onto the polygon mirror 3C. The laser beam deflected by the polygon mirror 3C is scanned onto the photosensitive drum 102C through the fθ lens 4C. At this time, the polygon mirror 3C is rotated at a high speed by the polygon motor 5C, and the photosensitive drum 102C is driven to rotate in synchronization with the scanning of the laser beam. Further, the laser beam deflected by the polygon mirror 3C is reflected by the reflection mirror 7C and guided to the SOS sensor 6C immediately before being irradiated onto the photosensitive member 102C. The SOS sensor 6C detects the light reception timing of the laser beam, and a synchronization signal in the main scanning direction is generated based on the timing.

  Next, the control unit 130 of the color printer 100 will be described. As shown schematically in FIG. 3, the control unit 130 includes a microcomputer 30, a clock generation circuit 31 that drives the microcomputer 30, and a dot clock that generates a dot clock signal (DCLK_C / M / Y / K). Circuits 32C, 32M, 32Y, and 32K. The microcomputer 30 receives signals from the registration sensor 105 and the TOD sensor 106 and controls the laser recording units 103C, 103M, 103Y, and 103K for each color and the image memory 34. In addition, various devices and sensors for controlling the operation of the color printer 100 are connected to the microcomputer 30.

  Although not shown in FIG. 2, the laser recording unit 103C also includes an LD driver 33C for driving and controlling the laser device 1C. As shown in FIG. 3, the microcomputer 30 receives the signal (SOS_C) from the SOS sensor 6C from the laser recording unit 103C and controls the LD driver 33C and the polygon motor 5C. Although cyan has been described here, the same applies to other colors. In the following, the internal configuration and various signals for other colors will be shown by changing the subscript C to M / Y / K.

  The microcomputer 30 outputs an image request signal (TOD) and a main scanning image request signal (HSYNC_C / M / Y / K) for each color to the image memory 34. The image memory 34 is equipped with a counter group 40 including a plurality of mutually independent counters. These counters are used to count HSYNC_C / M / Y / K using the TOD signal as a trigger. As a result, the image data of each color is output to the LD driver 33C or the like by combining the sub-scanning resist and the main scanning resist. Here, for example, the HSYNC_C signal is a main scanning synchronization signal generated based on the SOS_C signal output from the laser recording unit 103C.

  As the counter group 40, a total of eight counters (first counter to eighth counter) are provided here. The signals counted by these counters, the start trigger, and the event at expiration are set as shown in FIG. That is, the first counter counts HSYNC_C using the HSYNC_C signal after the fourth counter expires as a trigger, and when it expires, the cyan image region ends. The second counter counts HSYNC_M using the HSYNC_M signal after the fifth counter expires as a trigger, and when it expires, the magenta image area ends. The third counter counts HSYNC_Y by using the HSYNC_Y signal after the sixth counter expires as a trigger, and when it expires, the yellow image area ends.

  The fourth counter counts HSYNC_K with the HSYNC_K signal after the TOD signal as a trigger, and when it expires, the start of the cyan image area is permitted. The fifth counter counts HSYNC_K using the HSYNC_K signal after the TOD signal as a trigger, and when it expires, the start of the magenta image area is permitted. The sixth counter counts HSYNC_K using the HSYNC_K signal after the TOD signal as a trigger, and when it expires, the start of the yellow image area is permitted. The seventh counter counts HSYNC_K with the HSYNC_K signal after the TOD signal as a trigger, and when it expires, the black image area starts. The eighth counter counts HSYNC_K when the seventh counter expires as a trigger, and when it expires, the black image region ends.

  Next, the image forming timing of each color in the color printer 100 will be described with reference to the time chart of FIG. In the color printer 100 of this embodiment, when an image formation instruction is input, first, Poly_Rem_C / M / Y / K is used to rotate the polygon motor 5C / M / Y / K of each laser recording unit 103C / M / Y / K. The K signal is activated. When the rotational speed of the polygon motor 5C / M / Y / K becomes a constant speed, the LD_EN_C / M / Y / K signal is activated and the laser device 1C / M / Y / K is activated. As a result, the SOS_C / M / Y / K signal is output from the laser recording unit 103C / M / Y / K, and the microcomputer 30 generates the HSYNC_C / M / Y / K signal in response to the output.

  When the HSYNC_C / M / Y / K signal is output, the phase control of the polygon motors 5C / M / Y / K for each color is performed as necessary before starting the image formation. This phase control will be described later. Thus, the printing preparation of the laser recording unit 103C / M / Y / K is completed. On the other hand, the transfer material S is fed at a predetermined timing by predicting the time until preparation is completed, and a TOD signal is output when it reaches the position of the TOD sensor 106.

  Thereafter, the color printer 100 uses the counters of the counter group 40 to sequentially form images of each color. With the TOD signal as a trigger, the fourth to seventh counters start counting the HSYNC_K signal. When the fourth counter expires, cyan image data is output in synchronization with the next HSYNC_C signal, and image formation is started. At the same time, the count of the first counter is started, and when the first counter expires, the cyan image region ends.

  Similarly, when the fifth counter expires, magenta image data is output in synchronization with the second counter. Similarly, when the sixth counter expires, yellow image data is output in synchronization with the third counter. Similarly, when the seventh counter expires, black image data is output in synchronization with the eighth counter. As a result, toner images of the respective colors are formed on the photosensitive drums 102C, 102M, 102Y, and 102K of the respective colors, and are superimposed on the transfer belt 112.

  Next, correction of misregistration of each color in the sub-scanning direction will be described. For this correction, first, the amount of misalignment of each color with respect to the reference color is detected, and each set value for correction is determined. For this purpose, a resist pattern of each color is formed on the transfer belt 112 and detected by the resist sensor 105. The ideal sub-scanning resist position for each color obtained from the detection timing of each color resist pattern is divided by the period of the HSYNC signal. The resulting quotient is corrected by the number of HSYNC signals, and the remainder is corrected by the phase of the polygon mirror. In correcting the phase, the phase control process which is the point of the present invention is used. Here, black is the reference color and the HSYNC_K signal is the reference signal. Hereinafter, the number of HSYNC signals used for this correction is referred to as a sub-scan count.

  Therefore, first, as shown in FIG. 6, the prohibited area and the peripheral area are set with reference to the phase position of the reference color. The ideal phase of each dependent color obtained by the above processing is set outside the range including the prohibited area and the peripheral area. In other words, if the ideal phase determined for registration correction falls within this range, there may be a shift of one line in the sub-scanning direction due to variations in each part. Invite. This is because there is a risk of crossing the reference phase due to such inevitable variations. An area including the prohibited area and the peripheral area corresponds to a setting prohibited area.

  If the ideal phase of each subordinate HSYNC signal calculated from the registration detection result is within the range including the forbidden area and the peripheral area, the ideal phase is corrected as shown in FIG. . In the first method, the ideal phase is reset to the peripheral region boundary on the negative side if the ideal phase is on the negative side of the reference HSYNC and on the positive side if the ideal phase is on the positive side. This peripheral region boundary is a boundary outside the peripheral region. In this case, it is not necessary to change the sub-scan count. In the second method, when the ideal phase is temporally the negative side of the reference HSYNC, the reference phase is reset to the peripheral region boundary on the positive side beyond the reference HSYNC. In this case, the sub-scan count for the corresponding color is subtracted. Further, when the ideal phase is temporally on the + side of the reference HSYNC, it is reset to the peripheral region boundary on the − side beyond the reference HSYNC. In this case, the sub-scan count for the corresponding color is added. As a resetting method, any method may be used in consideration of other conditions.

  Specifically, this prohibited area is set in consideration of setup, hold time, and transmission system variations when the image memory 34 receives the HSYNC signal. For example, the HSYNC_K signal may have a latching clock period of about 30 ns on the negative side, and the positive side may have a latching clock period of about 1030 ns added to the transmission path variation. The peripheral area is set in consideration of variations in detection and control of the phase amount between the HSYNC_K signal of the reference color and the HSYNC signal of the subordinate color. For example, the clock period for detecting the HSYNC signal is 1 μs and the variation in the phase control of the polygon mirror is 1 μs, which is about 2 μs.

  For example, as shown in the lower part of FIG. 6, when the ideal phase of the HSYNC_C / M / Y signal of the dependent color is set in the peripheral region on the negative side of the prohibited region, according to the first method, It is reset to the-side as in 1. According to the second method, it is reset to the + side as in Example 2. In the case of Example 2, the sub-scan count is further subtracted by 1. The Poly_CLK signal of the polygon mirror of the corresponding color is controlled according to the ideal phase reset as described above. The phase control method may be a conventional one.

  Further, the phase controlled with respect to the ideal phase set in this way is not necessarily arranged completely equal to the set ideal phase. This is also because a slight deviation may occur due to variations in each part. The phase as a result of this phase correction control may be arranged in the peripheral area, but is not arranged in the prohibited area. If the phase resulting from the phase control is again within the prohibited area due to variations in each part, etc., the phase control is performed again. Since the ideal phase is set outside the range of the forbidden area and the peripheral area, the phase can be rearranged so as not to fall within the range of the forbidden area by starting over. Here, the prohibited area corresponds to the existence prohibited area.

  Next, the image forming process performed by the control unit 130 will be described with reference to the flowcharts of FIGS. First, the main routine of the control unit 130 will be described with reference to FIG.

  This process is executed when the color printer 100 is turned on. First, RAM, each timer, etc. are initialized (S101). Next, an internal timer that defines the length of one routine is set (S102). Next, a peripheral area setting process is performed (S103). This process is a process for setting the size of the peripheral area in accordance with the mode of the color printer 100, and the contents thereof will be described later.

  Next, a resist detection process is performed (S104). This process is a process for calculating a set value for registration correction, and the contents thereof will be described later. Next, phase control processing is performed (S105). This process is a process of performing phase control based on the set value calculated in the resist detection process and resetting the set value when necessary, the details of which will be described later. The process of S105 is performed in the “phase control section” in FIG.

  Next, image memory processing is performed (S106). That is, a signal requesting image data is output to the image memory 34. Next, print processing is performed (S107). Further, other processing is performed (S108), and it is confirmed whether or not the internal timer has ended (S109). If it has not ended (S109: No), it waits as it is. When the counting of the internal timer is completed (S109: Yes), the process returns to S102 and the internal timer is set again.

  Next, the surrounding area setting processing routine will be described with reference to FIG. When this process is started, first, it is determined whether or not the color printer 100 is set to the high-definition mode (S201). When the high-definition mode is set (S201: Yes), the rotation speed of the polygon motor is set to double speed (S202). Further, in this case, the size of the peripheral area is set to ½ of the normal size (S203), the process is terminated, and the process returns to the main routine. On the other hand, when the high-definition mode is not set (S201: No), the rotation speed of the polygon motor is set to the normal speed (S204). Further, the size of the peripheral area is also set to the standard (S205), this process is terminated, and the process returns to the main routine.

  Next, the resist detection processing routine will be described with reference to FIG. When this process is started, it is first determined whether or not this correction process needs to be executed (S301). It is not necessary to calculate this set value every time. If the time has not passed since the previous set value was calculated (S301: No), this process is terminated and the process returns to the main routine.

  Alternatively, if it is determined that it is necessary to execute it now (S301: Yes), the image forming units 101C, 101M, 101Y, and 101K for each color are driven to print a resist pattern (S302). Next, the printed resist pattern is detected by the resist sensor 105, and the distance between the resist patterns is measured from the detection result (S303). Further, based on the measured distance or the like, the quotient and the remainder of the sub-scanning resist position for each color are calculated (S304). Then, based on the result of S304, the sub-scan count value and the polygon phase value are set (S305), and this process is terminated and the process returns to the main routine.

  Next, the phase control processing routine will be described with reference to FIG. When this processing is started, first, it is determined whether or not the phase set by the registration detection processing routine is within the range of the prohibited region and the peripheral region (S401). If it is not within the range of the forbidden area and the peripheral area (S401: No), the process proceeds to S404 because it can be left as it is.

  Alternatively, when the phase set by the registration detection processing routine is within the range of the prohibited area and the peripheral area (S401: Yes), the phase is reset to the boundary of the peripheral area (S402). Further, if it is necessary to correct the sub-scan count by resetting S402, the sub-scan count is reset (S403). Next, phase control of the corresponding polygon is performed according to the set sub-scan count and phase (S404).

  Then, the phase of the phase-controlled polygon is detected (S405). It is determined whether or not the phase is within the prohibited region (S406). If it is outside the prohibited area (S406: Yes), this is sufficient, and this process is terminated and the process returns to the main routine. On the other hand, if it is within the prohibited region (S406: No), the process returns to S404 and the phase control is performed again.

As described above in detail, according to the color printer 100 of this embodiment, the prohibited area and the peripheral area are set in advance based on the phase of the reference color. In these regions, the phase of the dependent color is prevented from being set. In addition, it is prevented that the phase of the dependent color exists in the prohibited area. Therefore, the occurrence of phase indefiniteness is prevented even if there is an unexpected large variation. Furthermore, when the phase of the subordinate color enters in these areas, it is corrected outside the area. Thus, even if registration correction is performed, there is no possibility that a large shift in the sub-scanning direction suddenly occurs.

In addition, this form is only a mere illustration and does not limit this invention at all. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof.
For example, the reference color is not limited to black. That is, the reference signal is not limited to the HSYNC_K signal.
Further, the sizes of the prohibited area and the peripheral area are examples, and may be appropriately set depending on the device.
For example, although the present invention is applied to the color printer 100 in this embodiment, the present invention is not limited to this. That is, even if it is a copier, a scanner, a FAX, a word processor, etc., it can be applied as long as it is an electrophotographic image forming apparatus. In addition, the present invention can be applied to any image forming apparatus that forms an image with a plurality of light beams having different optical systems.

1 is a schematic configuration diagram illustrating a device configuration of a color printer according to an embodiment. It is a schematic block diagram which shows the apparatus structure regarding a laser recording part. It is a block diagram which shows schematic structure of a control part. It is a table | surface which shows the count signal and start / end timing of each counter. It is a time chart which shows the processing timing of a control part. It is explanatory drawing which shows the example of the range of a prohibition area | region and a periphery area | region. It is a flowchart which shows the main routine of the process by a control part. It is a flowchart which shows a surrounding area setting process routine. It is a flowchart which shows a resist detection process routine. It is a flowchart which shows a phase control processing routine.

Explanation of symbols

3C, 3M, 3Y, 3K Polygon mirror 30 Microcomputer 100 Color printer 101C, 101M, 101Y, 101K Image forming unit 102C, 102M, 102Y, 102K Photosensitive drum 112 Transfer belt 130 Control unit

Claims (4)

A plurality of image forming units, a transfer body that sequentially receives and transfers the primary images from the plurality of image forming units while moving, and a transfer material sensor that detects the supplied transfer material And each image forming unit rotates a photosensitive member, a polygon mirror that rotates to scan the beam in the main scanning direction toward the photosensitive member, and a beam reflected by the polygon mirror is applied to the photosensitive member. In an image forming apparatus having an SOS sensor that receives the beam before irradiation and a main scanning synchronization signal output unit that outputs a main scanning synchronization signal based on light reception by the SOS sensor ,
A resist detection unit that detects a sub-scanning resist amount that is a positional deviation amount in a sub-scanning direction of a pattern formed on the transfer body by the plurality of image forming units;
A phase difference setting unit for setting an ideal phase difference with respect to a reference phase of rotation of the polygon mirror of the plurality of image forming units for each image forming unit based on the sub-scanning resist amount;
If the ideal phase difference set by the phase difference setting unit is within a preset prohibition region that is a region including a reference phase, the ideal phase difference of the polygon mirror is set to the boundary of the prohibition region. A phase difference resetting unit for resetting the position again,
A phase control unit that performs phase alignment control of rotation of polygon mirrors of the plurality of image forming units before starting image formation based on the ideal phase difference for each set image forming unit;
The phase difference of the rotation of each polygon mirror other than the reference color with respect to the rotation phase of the polygon mirror of the reference color after the phase matching control by the phase control unit is set in advance from the setting prohibition area including the reference phase. A phase re-control unit for performing phase matching control by the phase control unit again when it is within the existence prohibition region which is a narrow region ;
A count setting unit that sets the number of main scanning synchronization signals between image formation start timings of the plurality of image forming units for each image forming unit based on a sub-scanning resist amount;
After the transfer material sensor detects a transfer material, a reference color main scanning synchronization signal after phase matching control by the phase control unit or the phase re-control unit is sent to the count setting unit for each of the plurality of image forming units. up to the number that is set to, possess a start before counter group for counting respectively,
After the image formation of each of the plurality of image forming units, after the phase matching control by the phase control unit or the phase re-control unit, the pre-start counter group finishes counting each of the plurality of image forming units. Starting from the first main scanning synchronization signal of the image forming unit. The image forming apparatus according to claim 1,
Before SL-position phase difference resetting unit, an image forming apparatus which is characterized in that the resetting of the ideal phase difference while maintaining the code of the ideal phase difference to be set again. The image forming apparatus according to claim 1 ,
Before Symbol phase difference re-setting unit,
Resetting the ideal phase difference while reversing the sign of the ideal phase difference to be reset,
An image forming apparatus, wherein the number of main scanning synchronization signals set by the count setting unit is changed for an image forming unit corresponding to the ideal phase difference. The image forming apparatus according to claim 1,
The size of the setting prohibition region, when the rotational speed of the polygon mirror is double speed is to have a set prohibition region setting unit that sets one-half of the size of the case where the rotational speed is the normal speed An image forming apparatus.

Images