JPH11212315A - Image quality compensation device for image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To execute a control action for compensating image quality by selecting an area where a test patch image formed in order to always maintain the formed image quality to a fixed condition is stably formed. SOLUTION: In order to maintain the image quality to the fixed condition and image by the test patch image 19 is formed. By detecting the density of the image 19, the developing bias voltage of one of process means, for example, the developing device 4(4a-4d) being the density control means arranged in a image forming device by which the reference (standard) image quality can be obtained is controlled. A test image is formed at the whole circumference of a transfer drum 5 on the fixed condition by toner. Then, density of the test image is detected by a density detection sensor 16. Based on the detected result, the area where the test patch image is formed is selected by a CPU 6. As the reference of this selection, the area where toner concentration exhibits an excellent value is selected so that the forming action of the test patch image is stabilized. Thus, the control action for compensating the image quality is more enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine (including a digital copying machine) or a printer employing an electrophotographic system, in particular, preventing deterioration of image quality.
The present invention relates to an image quality compensating device in an image forming apparatus that can always compensate for stable image quality.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine or a laser printer adopting an electrophotographic system, several methods have been proposed and put into practice in order to prevent image quality deterioration due to aging or the like. I have.

When an image forming apparatus always reproduces an image under the same conditions, that is, forms an image, the image quality state gradually deteriorates. The deterioration of the image quality is caused by a change over time, for example, the chargeability of a photosensitive member as a recording medium changes according to the number of times of image formation, so that an initial image density cannot be obtained. In addition, the image quality is deteriorated in which the toner adheres to an area where the toner or the like should not adhere on the base (background). Therefore, as a simple method for solving the deterioration of image quality, the number of image formations is counted, and the charging potential on the photosensitive member is compensated in a predetermined state such that the voltage supplied to the charging means is controlled according to the count. Things.

In order to improve the above simple method, the potential charged on the photosensitive member is actually measured, and the voltage supplied to the charging means is controlled in accordance with the measurement result.
Keeping the potential charged on the photoconductor constant at all times,
There is a method for compensating image quality. According to this method, the photoconductor can always be kept at a constant potential, so that the compensation accuracy is further improved as compared with the method of controlling the number of image formation.

However, when a toner image is actually formed on a photoreceptor, the toner density may not be in the initial density state, or unnecessary toner may adhere to the background area.

Therefore, a method for further stabilizing the image quality state has been proposed and put into practice.
A test patch image (image for density detection) for a test is formed directly on the photoconductor, and the density of the test patch image is detected. This detection result is compared with a predetermined reference density value, and according to the comparison result, an image forming condition capable of forming a test patch image having a reference image density, for example, the charging unit described above, Is the amount of light from the exposure lamp,
The developing bias of the developing device is controlled.
That is, the control of the exposure amount, the developing bias, and the like may be performed to prevent unnecessary toner from adhering to the background area as described above.

According to the above method, not only the deterioration of the photoconductor, but also the image density of the toner formed on the photoconductor changes according to environmental changes such as changes in temperature and humidity.
Since such a change can be dealt with, it is very advantageous in that more stable image quality can be compensated.

Further, in order to form a color image, an image forming apparatus is configured to sequentially overlap toner images of respective colors when a toner image formed on a photoreceptor is transferred onto a sheet such as plain paper as a transfer material. Because of the necessity of transfer to a transfer position, a method of winding the sheet and providing a transfer drum for transporting the sheet to a transfer position has been proposed and implemented. Further, there is an image forming method in which an intermediate transfer medium is provided, and toner images of respective colors formed on a photoreceptor are sequentially superimposed on the intermediate transfer medium and transferred, and then re-transferred onto a sheet at once. .

In an image forming apparatus for obtaining such a color image, a test toner patch image formed on a photoconductor is transferred onto a transfer drum (including an intermediate transfer medium) in contact with the photoconductor. The density formed by reading the reflected light is detected. According to the result of the density detection, the control of the charging voltage to be supplied to the charging means and the control of the developing bias are performed so that the density becomes the reference density as described above, so that the image quality is compensated. I have. According to this method, the density can be detected in a state in which the toner image formed on the photoconductor is transferred while the toner image is actually formed on the sheet, so that more excellent image quality compensation can be performed.

As a method of performing such image quality compensation,
For example, it is described in JP-A-6-11935. That is, a toner image (test patch image) having a predetermined gradation formed on the photoconductor is transferred to a transfer drum or the like, the density of the transferred toner image is detected, and whether the detected density is the reference density is determined. Is determined, and the charging potential, the developing bias voltage, and the like are controlled in accordance with the result to control the reference density.

[0011]

Problems to be Solved by the Invention
According to the technical disclosure described in Japanese Patent Publication No. 35-35, in order to perform image quality compensation, a test patch image is formed before image formation using a time period during which image formation is not performed, and the formed test patch image is formed. The image forming state is confirmed by detecting the density of the patch image and the like, and the setting conditions of the process means for forming the image in comparison with the reference image density, such as a charger, a developing bias voltage of a developing device, etc., are controlled. I have. As a result, stable image quality can always be compensated.

However, fluctuations in the nip width between the transfer drum (including a belt or the like) that comes into contact with the photoreceptor and the intermediate transfer medium and the like, uneven resistance values of the transfer drum and the intermediate transfer medium, the transfer drum and the intermediate transfer medium Due to factors such as scratches and dirt on the surface of the surface, accuracy of the outer diameter of the transfer drum, etc., the transfer efficiency, particularly the transfer state, varies depending on each part on the surface of the transfer drum or the intermediate transfer medium, and the transfer is performed on that part The toner density of the test patch image is greatly affected. Therefore, if the toner density changes in the portion where the test patch image is formed, it is not possible to accurately grasp the image forming state.

For example, in a case where the image density in a region where a test patch image is formed is reduced although the image density actually formed becomes high as a whole and image quality such as fog is lowered. Erroneously controls to further increase the image density. As a result, a stable image quality state cannot be maintained.

The present invention provides a method for stabilizing image quality that solves the above problems, and in particular, provides an image quality compensating device that enables a test patch image to be formed with high accuracy and thereby stabilizes the image quality state. The purpose is to do.

That is, an object of the present invention is to form a test patch image and perform image quality compensation according to the image.
An object of the present invention is to stabilize the detection state of the test patch image to perform more accurate image quality compensation.

It is another object of the present invention to specify (select) a region where a test patch image is formed favorably, and at the same time, to enable the best image quality compensation for judging a good condition.

[0017]

In an image quality compensating apparatus for achieving the above-mentioned object of the present invention, an image for forming an image with a desired toner image on a toner image forming medium through various process means is provided. In the forming apparatus, image quality compensation is performed by controlling one or more conditions of various process means for forming the toner image, and a density determined on the toner image forming medium in order to perform image quality compensation. Forming a test patch image by detecting the density of the test patch image, and forming the test patch image in image quality compensation control by setting and controlling the conditions of the process means in comparison with a reference density. Before selecting the area for forming the test patch image on the toner image forming medium, a test toner for a test under a certain condition is arranged around the entire circumference of the toner image forming medium. An image is formed, the toner image is detected by a density detection sensor, an area suitable for forming a test patch image is selected based on the detection result, and a test is performed on the area of the selected toner image forming medium. Forming a patch image,
The setting condition of the process means is controlled based on the density detection.

That is, as a region for forming a test patch image for performing image quality compensation, a toner image forming medium, for example, a photoreceptor, and a transfer for transferring a toner image formed on the photoreceptor to a sheet attracted to a transfer drum, etc. A test toner image is formed under constant conditions on the entire circumference of a transfer belt and the like that finally transfers a toner image formed on a drum and a photoreceptor from an intermediate transfer member (for example, a transfer belt) to a sheet. At this time, differences occur even when the toner image formation state is constant, due to differences in the characteristics of the photoconductor, the transfer drum, the transfer belt, and the like, resistance values, and other factors. This difference can be easily grasped from the output state of the density detection sensor. Therefore, the characteristics of the photoconductor, the transfer drum, or the intermediate transfer body, which is the toner image forming medium, can be easily recognized according to the detection result. Therefore, if the area where the output result of the density by the good toner image is obtained is selected as the formation area of the test patch image, as a result, the accuracy in the control of the image quality compensation is improved. In particular, the test patch image is formed in a state where the toner image is formed stably and the image quality of the toner image is improved, and as a result, the image quality compensation control according to the density detection can be performed accurately.

Therefore, in the image quality compensating apparatus having the above-described configuration, the invention according to claim 2 is arranged so that the entire area of the toner image forming medium is selected in order to select a forming area of the toner image forming medium for forming the test patch image. The image pattern for the test to be formed is a dot-shaped or linear-shaped pattern so that a density difference due to the amount of toner adhered is generated. In this case, a change in density is very likely to occur, and a good area suitable for forming a test patch image can be reliably and accurately selected, and therefore, more accurate image quality compensation can be performed. Here, when the pattern image is a linear pattern, it is conceivable that the direction of the linear pattern largely depends on the density detection. That is, if a linear pattern is formed in the direction of the rotating axis, the density change due to rotation unevenness in the density detection becomes large, and accurate density detection cannot be performed. On the other hand, if the direction of the linear pattern is formed so as to be orthogonal to the direction of the rotation axis, the influence of the density change due to the rotation unevenness is reduced.

In the image quality compensating apparatus according to the third aspect of the present invention, when selecting the area of the toner image forming medium for forming the test patch image,
If an area where the toner image is good and the density is high is selected, the state of formation of the toner image is naturally stable, and good results can be obtained.

Further, according to a fourth aspect of the present invention, there is provided an image quality compensating apparatus having the above structure, wherein a density detecting sensor for detecting the density of at least a test toner image formed on the toner image forming medium is provided with a reflection type light sensor. The angle formed by the tangent of the toner image forming medium at the light irradiation point and the optical axis for light irradiation is 45 to 80.
°. By doing so, in the density detection of the toner image of the test image, the difference in the detection result when a density difference occurs increases. Thereby, the selection of the area for forming the test patch image becomes more accurate. For example, as shown in FIG. 9, the output difference due to the difference in density increases, and a good area can be easily selected, and it can be expected that this selection will be more accurate.

In the image quality compensating apparatus having the above-mentioned structure, the invention according to claim 5 is such that the density of the test toner image formed on the toner image forming medium is lower than the toner density at the time of performing normal image formation. It is characterized by being formed as described above. This is because if a test toner image is formed with a high density at the time of actually forming an image, a difference in density change cannot be detected. That is, the output state at high density tends to be saturated. Therefore, if a test toner image is formed at a low level, a density difference due to a difference in characteristics or the like of a region where the toner image is formed tends to occur. Therefore, a large output difference can be obtained by detecting the density difference. for that reason,
This is a very effective means in selecting a good area for forming a test patch image.

In the image quality compensating apparatus having the above-mentioned structure, the invention according to claim 6 forms a test toner image all around the toner image forming medium, and selects a test patch image forming area. In this case, a test patch is formed for image quality compensation control, and the test patch is formed before the image quality compensation is performed. If you do this,
When the state of image formation changes, a good test patch image can be formed in a state where image quality changes, and stable image quality compensation control can be performed by this. The timing may be a time when initial image formation is performed on condition that the power is turned on, when the process means of the image forming apparatus body is replaced, when the number of times of image formation exceeds a certain number, or when image formation is stopped due to further trouble. , Select a point in time after which trouble can be resolved and the image forming operation can be resumed,
If the formation area of the test patch image is selected by grasping the characteristics and the like of the toner image forming medium, the image quality state can naturally be controlled so as to meet the determined reference image quality. This makes it possible to always stabilize the image quality state in response to various changes.

Further, in the image quality compensating apparatus having the above-described structure, the invention according to claim 7 is an image compensating apparatus according to claim 7, wherein an image is detected in accordance with a density detection state when a test toner image is formed on the entire circumference of the toner image forming medium. If extraction is performed including a continuous area to be formed and used, the extracted area is set as an image formation area, other unextracted areas are set as non-image areas, and the subsequent image formation processing is performed. In addition, the image can be formed in a stable area when the image is formed. Therefore, by performing image quality compensation together, compensation control with further improved image quality can be performed.

In the image quality compensating apparatus having the above-described structure, the invention according to claim 8 is characterized in that the toner image forming medium is constituted by a transfer medium onto which a formed toner image is transferred. When a toner image is transferred to a transfer medium in a selected area of the medium where a test patch image is formed, transfer is performed under a plurality of different transfer conditions, and the density of the toner image transferred at this time is detected. It is characterized in that the transfer condition of the region with the highest density in the detection result is set as one image quality compensation condition.

In such a configuration, particularly in an apparatus capable of transferring a test toner image to another transfer medium, the transfer conditions for transferring the toner image to the transfer medium, for example, the conditions under which the transfer voltage is set to the best condition. Can be set. That is, in order to transfer the formed toner image to the transfer medium, it is determined in advance so that it can be performed under the optimum condition setting, and this may be fixed. The optimum state changes due to other factors such as a change in the surrounding environment. It can be easily recognized that the state of the toner image at the time of transferring this change is the highest, that is, the transfer condition is optimal. For this reason, the transfer conditions are optimized, and more suitable image quality compensation control can be performed.

[0027]

Embodiments of the present invention will be described below in detail with reference to the drawings. 1 to 7 are diagrams for explaining an embodiment for image quality compensation according to the present invention.

First, the image forming apparatus will be described with reference to FIG. 2, but in the present embodiment, a color printer will be described. However, the present invention is not limited to this color printer, and it goes without saying that the present invention can be applied to all image forming apparatuses employing the electrophotographic system.
In addition, FIG. 2 illustrates a transfer drum system in which, when a toner image formed on a photosensitive member, which is a toner image forming medium (recording medium), is transferred onto a sheet, the transfer is performed while the sheet is being attracted. However, the present invention is not limited to such a method.

(Structure of Image Forming Apparatus) The main body of the image forming apparatus rotationally drives a drum-shaped photosensitive member 1 as a recording medium for forming a toner image in the direction of an arrow. The photoreceptor 1 is first uniformly charged to a specific polarity by a charger (charging means) 2, and then is exposed to a laser beam from a laser scanning unit (LSU) 3, whereby the photosensitive member 1 is electrostatically charged in accordance with an image. A latent image is formed. Developing units 4a, 4b, 4c, and 4d, which are developing devices capable of developing four colors of yellow, cyan, magenta, and black (black), are sequentially arranged downstream of the laser beam exposure position. In this case, one developing unit is selectively driven for each exposure to perform development.

The toner image formed on the photoreceptor 1 by the developing unit is transferred onto a sheet of plain paper or the like that is attracted and held by a transfer drum 5 that is driven to rotate at the same peripheral speed as the photoreceptor 1. That is, the transfer drum 5 is rotationally driven by the motor (29) that drives the photoconductor 1, and is rotated in the direction of the arrow in the figure. The transfer drum 5 has a CPU as a control unit for performing an image forming operation and image quality compensation according to the present invention.
6, the D / A converter 7c and the transfer high-voltage power supply 8c
An arbitrary voltage can be applied.

As shown in FIG. 3, details of the structure of the transfer drum 5 are as follows. The surface of the transfer drum 5 has a thickness of about 30 to 300 μm, for example, about 75 μm, which is a high resistance layer of PVDF (polyvinylidene fluoride). A semiconductive foam layer having a uniform thickness of 3 to 7 mm, for example, a semiconductive foam layer 5b made of hydrin rubber or the like having a thickness of about 5 mm is formed under the body layer 5a. In the lower part, a conductive base 5 made of an aluminum cylinder or the like having a thickness of about 5 mm
c is provided, and is constituted by three layers of each of these layers.

Therefore, the base 5c of the transfer drum 5 described above
The sheet is electrostatically attracted to the surface layer 5a of the transfer drum 5 by applying a predetermined voltage to the transfer drum 5.
That is, the sheet fed from the sheet feeding cassette 9 is wound around the transfer drum 5 by the roller 10. At this time, the roller 10 is grounded, that is, grounded, and the sheet is electrostatically attracted to the surface of the transfer drum 5 by a potential difference from the voltage supplied to the transfer drum 5.
Then, the sheet is conveyed to a position facing the toner image formed on the photoreceptor 1, that is, a transfer area.

The toner image formed on the photosensitive member 1 is
Area where the photoconductor 1 contacts the transfer drum 5 (transfer area)
Is transferred to the sheet on the transfer drum 5. At this time,
As described above, by applying a predetermined voltage to the base 5c of the transfer drum 5, the toner image on the photoconductor 1 is transferred onto the sheet on the surface of the transfer drum 5. Then, the toner that has not been transferred is removed by the photoconductor cleaner 11 after the transfer, and unnecessary charges are removed from the surface of the photoconductor 1 by the discharging lamp 12. Thus, image formation using the next color toner or the next color image formation can be started.

In the above-described image forming apparatus, when the image forming operation is started, the photosensitive member 1 is uniformly charged by the charger 2 and then converted by the laser scanning unit 3 into image data from an image processing device or the like (not shown). An image based on light is written based on the image. That is, the semiconductor laser 15 is turned on and off in accordance with the image data via the CPU 6, and the light beam at this time is scanned in the direction of the rotation axis of the photoconductor 1 via the laser scanning unit 3 to form an optical image. Written. In this case, since the image portion (the portion where the toner adheres) is written by the laser, the potential on the photoreceptor 1 becomes almost zero.

The image data is a signal of only one color obtained by color separation of a desired full-color image. In this case, since there are four colors, for example, writing to the photoreceptor 1 is first performed using black image data, and thereafter, image data is formed in the order of yellow, magenta, and cyan.

Next, the electrostatic latent image formed on the photoreceptor 1 is
It is sent to the developing positions of the developing units 4a, 4b, 4c, 4d. In this case, as described above, the developing tank unit
A shutter (not shown) between the opening of the developing unit and the photoconductor 1 other than the image data of the color is closed, so that the developer is not conveyed to the surface of the magnet roller. Alternatively, a shutter made of an elastic member is pressed against the surface of each developing roller constituting the developing unit, and control is performed so that the developer is not conveyed. Then, a predetermined developing bias voltage (V1) is applied to each of the developing units 4a, 4b, 4c, and 4d from the supply source of the developing bias voltage from the CPU 6 via the D / A converter 7b, that is, from the high voltage circuit 8b. The voltage causes the toner to adhere to the electrostatic latent image formed on the photoconductor 1.

The toner image formed in this way is rotated to a transfer position, that is, a position where the photoconductor 1 and the transfer drum 5 are in contact with each other in synchronization with the sheet wound electrostatically on the transfer drum 5 and wound. In addition, the image is electrostatically transferred onto the sheet by the transfer voltage applied to the transfer drum 5.

The sheet on which the toner image has been transferred is transferred to the transfer drum 5 in order to transfer the toner image of the color formed on the photoreceptor 1 in a manner superimposed on the previously formed toner image.
The toner image of the next color formed on the photoreceptor 1 is sequentially transferred by the rotation of.

On the other hand, the toner image is transferred from the photosensitive drum 1 to the transfer drum 5.
After transfer to the upper sheet, remove the remaining toner
In step 1, the residual charge is removed by the charge removing lamp 12, and as described above, an image forming process of the next color is started with a different color.

The toner image transferred onto the sheet by repeating these steps in this manner, after four colors or three colors (yellow, magenta, and cyan) are superimposed on each other,
3, the fixing unit 1 is separated from the transfer drum 5.
4 and is heated and fixed, and then discharged to a discharge tray 17.

(Image Quality Compensation Control) Next, image quality compensation control for controlling the image density formed on a sheet to a predetermined reference density in the above image forming apparatus will be described.

Normally, in the stage before the above-described image forming operation is started, for example, in a start-up state after the power of the image forming apparatus is turned on, or in a standby state in which the image forming apparatus main body is at rest, etc. Automatically forms a test patch image for image quality compensation, and in accordance with the density of the test patch image, the charger 2 and the developing units 4a, 4
One or a plurality of correction control of the setting conditions of the image forming (process) means such as the developing bias voltages b, 4c, and 4d are performed.

Therefore, the density determined on the photoreceptor 1
That is, a test patch image is formed with toner under predetermined conditions, transferred to the transfer drum 5, and its density is detected. Then, based on the detected concentration, a comparison with a reference concentration is performed, and the above-described process control conditions are set so that the reference concentration is obtained. That is, the image forming conditions of the processing means are automatically adjusted so as to obtain the image quality state. There is at least one means for this process,
There are cases where multiple items are adjusted at the same time.

Therefore, when a test patch image is formed, a toner image (test patch image) is transferred to the transfer drum 5, and a change in the characteristic of the toner density (toner adhesion density or the like) of the test patch image is detected. In this case, apart from the image forming operation, the sheet is not wound around the transfer drum 5 and the toner image formed on the photoconductor 1 is transferred to the transfer drum 5.
It is transferred directly to the surface.

In order to measure the toner density, the light emitting unit 16a and the light receiving unit 16b face the transfer drum 5.
A toner density sensor (density detection sensor) 16 is provided, and the density signal detected by the density detection sensor 16 is
The CPU 6 takes in the data via the D / A converter 18a. The CPU 6 compares (comparisons) the input detection density with a preset reference density, and controls the voltage supplied to the charger 2 according to the comparison result. For that purpose, the control signal is output to the high voltage circuit 8a. Alternatively, in order to control the developing bias voltage, the D / A converter 7b
Each of the developing units 4a, 4b,
The developing rollers 4c and 4d are supplied to the respective developing rollers.

Further, the CPU 6 controls the above-described density detection sensor 16 in accordance with the timing of forming a test patch image.
The drive control by the light emitting unit 16a can also be performed via the D / A converter 7a in order to perform the density detection by the D / A converter 7a. This controls the amount of light output by the light emitting unit 16a.

In the above-described configuration, an example for forming a test patch image and a setting condition of a developing bias voltage to be supplied to the developing units 4a, 4b, 4c, and 4d in accordance with the detection of the formed test patch image. An example of the control will be described with reference to a control procedure (flow chart) in FIG. As a result, it is possible to form an image with image quality compensation that meets the reference image quality.

First, the surface of the photoreceptor 1 is uniformly charged by the charger 2. For example, three test patch images are formed so as to have different densities. Therefore, it is a color printer, and each developing unit 4a, 4b, 4c, 4
Test patch images corresponding to the color d are formed, and three test patch images are formed on each of them. In this case, in the developing unit of the color for forming the first test patch image, three kinds of different developing bias voltages are set, and the density is controlled so as to be different.

Thus, the photosensitive member 1 is uniformly charged, and the laser scanning unit 3 irradiates a test patch image, that is, a laser beam. For example, as the test patch image (19), a portion where toner is adhered to the uniformly charged surface of the photoreceptor 1 as shown in FIG. 5A is formed in a dot shape, or as shown in FIG. FIG. Further, the image of the test patch is not limited to the image shown in FIG. Therefore, the laser beam is applied to the portion where the toner is to be attached. Then, after the exposure with such an image pattern is performed, the test patch image 1 is set under the above-described setting condition of the developing bias voltage by the developing unit.
9 is created.

In order to form the first color test patch image 19, when developing the photoreceptor 1 after exposure, as described above, the developing bias voltage is changed to change the toner with three types of densities. An image, that is, a test patch image 19 made of a specific color toner is formed. For example,
Developing is performed by changing the initial developing bias voltage (V1) up and down to ± 50 V (n1). Then, the developed test patch image is transferred onto the transfer drum 5 by a transfer voltage from the high-voltage unit 8c at the transfer unit.

Although the toner image based on the test patch image is directly transferred to the transfer drum 5, the transfer voltage (voltage supplied via the high-voltage power supply 8 c) at this time is applied to the transfer drum 5 in a normal image forming operation. The transfer voltage is set lower than the transfer voltage when the sheet is wound and transferred.
That is, the direct transfer to the transfer drum 5 is usually smaller than the transfer via the sheet, because the gap is very small, and its characteristics are different from those of the toner transfer by charge polarization to the back surface of the sheet. When the transfer is attempted at the transfer voltage of, the electric field is too strong, and the image may be disturbed due to retransfer when the transfer is performed (when the transfer drum 5 is separated from the photoconductor 1). It is lowered to eliminate this.

Therefore, the transfer voltage is set to, for example, 2.0 to 0.8 kV when transferring to a sheet, and the transfer voltage is set to 0.8 kV or less when transferring the test patch image to the transfer drum 5. Transfer is performed. Thereby, the same transfer as the case where the transfer is performed on the sheet can be performed, and the transfer efficiency in a state where the transfer is substantially performed on the sheet can be obtained.

When the toner image 19 of each color by the test patch image is formed on the transfer drum 5 as described above, the density of this image 19 is detected by the density detection sensor 16 as shown in FIG. 2 (n2). The detection result is sent to the CPU 6, and the CPU 6 executes the following control.

For example, a yellow test patch image 19
Is formed, the developing bias voltage of the developing unit 4a includes a standard value, and ± 50
V is set to three types. Assuming that the standard value is -400 V, -350 V, -400 V (standard value), -4
Set to 50V and develop. With this developing bias voltage,
For example, an image pattern as shown in FIG. 5A is exposed through the laser scanning unit 3 and developed to form a test patch image 19 on the surface of the photoconductor 1. The test patch image 19 developed with the yellow toner at that time is transferred to the transfer drum 5 under the above-described transfer voltage application condition, and reaches the position facing the density detection sensor 16 to perform density detection.

Developing with the above three types of developing bias voltages,
The density values (output voltage) detected by the density detection sensor 16 after the transfer are represented by S1, S2, and S3 (S1 <S
2 <S3). As described above, in the case of the color test patch image 19, the higher the output value of the sensor 16, the higher the formed image density. Here, the values of the respective detected densities are in the relationship of S1 <S2 <S3 (n3).
Then, the following control is performed assuming that the formed test patch image is normal.

Therefore, there is a difference in the density detected by the test patch image 19 formed according to each developing bias voltage. Then, it is checked whether the target value for performing the image quality compensation, that is, the reference density (for example, STD) for keeping the image quality constant is between the detected minimum (S1) and the maximum value (S3) (n4). ). If the target value STD is within the above-described range, for example, a straight line approximation is performed from S1, S2, and S3 where the density is detected. This state is illustrated in FIG. That is, it is obtained by S = a · DVB + b. Here, DVB is a developing bias voltage.

Therefore, the respective density values S1, S2 and S3 are obtained from the following equations by an approximation method based on the three detected density values.
A and b so that the developing bias voltage approximates
Can be requested.

S1 = a · DVB1 + b (DVB1 = −450V) S2 = a · DVB2 + b (DVB2 = −400V) S3 = a · DVB3 + b (DVB3 = −350V) In this approximation, a known method may be used. The above a and b are obtained, and the target concentration (target value) is set to STD.
, The developing bias V1 that satisfies STD = a · V1 + b
Ask for. That is, V1 is calculated as V1 = (STD−
b) / a is easily obtained (n5).

Accordingly, by setting three different developing bias voltages and forming the test patch images 19 with the respective densities, the values of the above-mentioned values a and b are obtained, whereby the reference density (STD) is reduced. Obtained developing bias voltage V
1 can be obtained. In this case, three points (S
As shown by the linear approximation of (1, S2, S3), the developing bias voltage V1 for the target density STD can be easily obtained.

The above-mentioned developing bias voltage is obtained according to the density detection based on the test patch image for each color. Then, the obtained developing bias voltage (V1) is stored in the storage unit (n6) because it is used in the next image forming operation. Further, hereinafter, the obtained developing bias voltage V
1 is defined as a target standard developing bias voltage (V0). Then, the test patch image 19 of the next color is transferred to the transfer drum 5, and the developing bias voltage V1 is sequentially obtained based on the density detection, and the setting conditions of the developing units 4a, 4b, 4c, and 4d as the process means, that is, The developing bias voltage is set.

If there is a large difference in the developing bias voltage with respect to the surface potential of the photoreceptor 1, a phenomenon in which the carrier adheres to the surface of the photoreceptor due to the potential difference, or fogging of the ground occurs. There are cases.
That is, this is a phenomenon in which the toner adheres to an area of the photoconductor 1 where no image is formed.

Therefore, regarding the developing bias voltage,
In performing the control, there is a limit value. For example, when the developing bias voltage (V0) at which the target density can be obtained in the initial stage is limited to ± 100 V above and below the developing bias voltage (V0), when a correction voltage exceeding the value is required, the above-described case is required. A phenomenon may occur. for that reason,
What is necessary is just to keep it below the limit value.

In setting the phenomenon bias voltage V1 based on the test patch image, the voltage corresponding to the target density is set to V0 (DVB2), and the developing bias voltages DBV1 and DBV3 are set at ± 50 V (n1). . As a result, a test patch image can be formed with high accuracy while suppressing carrier rise and fog. This is because, in the control flow of FIG. 4, if the target reference density (target value) at n4 is not in the range between the detected density values S1 and S3, the target density (STD) is equal to the detected density value S1 or Determine which of S3 is outside (n10)
In each case, the standard developing bias voltage (V
0) is increased or decreased by 50 V (n11 or n12), the standard developing bias voltage (V0) is changed, and the process returns to step n1 as described above to execute control for forming three types of test patch images.

In the test patch image formed at this time, the target value (STD) also has the minimum and maximum densities S1 to S3.
If it is not within the range, the standard value of the developing bias voltage is similarly changed again, and it is confirmed whether the changed value exceeds the upper or lower limit of the developing bias voltage. Alternatively, the developing bias voltage V1 is set within the lower limit. As a result, it is possible to perform development in which the rise of the carrier or the like is eliminated. This is not directly related to the present invention.

As described above, the test patch image 19 for image quality compensation is formed on the transfer drum 5 in FIG. 2, and the developing bias voltage (V1) corresponding to the density detection of the formed test patch image 19 is set. The control of the condition setting to be adjusted is performed before the image forming operation is performed, and the image forming operation can always be performed under a condition in which a stable image quality is compensated by a good determined density. This is because the image density formed can be accurately detected not only with the aging of the photoreceptor 1 and the like but also with the environmental change, so that a stable image quality can be obtained.

(One Embodiment of the Present Invention) An embodiment for stably forming a test patch image according to the present invention will be described below.

FIG. 1 is an overall block diagram showing a control circuit configuration for controlling color image formation by the image forming apparatus shown in FIG. 2 and controlling image quality compensation by density control according to the present invention. . Here, the same parts as those shown in FIG. 2 are denoted by the same reference numerals.

In FIG. 1, an I / O port 22 is connected to the semiconductor laser 15 through a laser control block 28, a synchronous sensor 33 of a polygon mirror arranged in the laser scanning unit 3, and the photoconductor 1 and the transfer drum 5 through a motor driver 23. Drive pulse motor 29, high voltage power supply 8a for charger 2, transfer drum home position detection sensor 2
4 respectively.

The transfer drum home position detection sensor 24 detects the home position of the transfer drum 5 as shown in FIG.
In addition, it is provided to recognize the entire circumference of the transfer drum 5 in order to control the position where the test patch image is formed. In addition, the timing for winding the sheet, the timing for separating the sheet, and the like are obtained based on the detection signal of the home position.

The home position of the transfer drum 5 is
As shown in FIG. 7, a detection piece 51 provided in a protruding state on a flange portion 50 for rotatingly holding the transfer drum 5 is provided, and this detection piece 51 is detected by a photo sensor (home position sensor) 24. ing.

In FIG. 1, the 8-bit D / A converters 7a, 7b and 7c provide the light quantity of the light emitting portion 16a of the density detection sensor 16, the output of the high voltage source 8b for the developing bias voltage, and the high voltage power supply for the transfer voltage. 8c are individually controlled. The density detection output of the light receiving section 16b of the density detection sensor 16 is supplied to an 8-bit A / D converter 18a.
The detection output 1 is connected to an 8-bit A / D converter 18b, and the CPU 6 reads the received light amount (density) and humidity. The timer 30 is configured to interrupt the CPU 6 at regular intervals, and easily determines the rotational position of the transfer drum 5 according to how much time has elapsed since the detection signal of the home position detection sensor 24 of the transfer drum 5. Can be detected. This allows, as explained earlier,
It is possible to control the timing of the attraction and separation of the sheet, the timing of the transfer position of the test patch image 19 to the transfer drum 5, and the like.

The ROM 31 stores control of the image forming apparatus, control (program) for forming a test patch image, various control parameters, parameters for correcting the value detected by the toner density sensor 16, and the like. The RAM 32 is used for storing a work area or the like for executing a program.

(Explanation of Control Operation of Image Quality Compensation) In order to perform image quality compensation according to the present invention, first, an area of the transfer drum 5 for forming the test patch image 19 is selected. That is, the transfer drum 5 does not always have the same characteristics, that is, the same transfer of the toner image, over the entire circumference in the rotation direction. Therefore, an area where the transfer state of the transfer drum 5 is stable is selected, and the image quality is compensated by forming the test patch image 19 in the selected area. In particular, the test patch image formed on the photoconductor 1 is transferred to a selected area.

Therefore, in order to grasp the transfer state of the toner image on the transfer drum 5 and to recognize its characteristics, a test image is formed on the entire circumference of the transfer drum 5 using the toner formed under the same conditions. Therefore, a test image is formed on the photoreceptor 1 with uniform toner, and the test image is transferred to the entire circumference (one rotation) of the transfer drum 5 according to the detection by the home position sensor 24. At this time, the toner image to be formed is a dot or linear pattern as shown in FIG. 5, and such an image pattern is uniformly charged on the photosensitive member 1.
The semiconductor laser 15 is driven and controlled on the surface, and is exposed through the laser scanning unit 3.

By forming the pattern as shown in FIG. 5, the density difference due to the characteristics of the test image formed on the transfer drum 5 and other factors is well reflected. That is,
In the case of a pattern image that is entirely solid, a change in density is unlikely to occur. However, a dot-shaped or line-shaped pattern has a small difference in density change, and a large output difference in density detection. Therefore, the density change in the state of being transferred to the transfer drum 5 is improved, and the characteristics and the like can be accurately recognized.

In the case of the above-mentioned linear pattern, if it is formed in a direction perpendicular to the axis on which the transfer drum 5 is rotated, it is less susceptible to uneven rotation of the transfer drum 5 and the like. Can be formed. This allows
The characteristics of the transfer drum 5 can be accurately recognized without reflecting the density difference for detecting the test image of the toner due to the rotation unevenness.

When a toner image is formed by the dot pattern shown in FIG. 5A, the dot toner image formed on the photosensitive member 1 varies. If the toner image is transferred to the transfer drum 5, the toner image is transferred in a dispersed state, and the density cannot be detected satisfactorily. Therefore, it is necessary to form a dot-like test image in a stable state without a variation state.

For this reason, when forming a test image according to the pattern shown in FIG. 5A, the charging potential of the photosensitive member 1 is adjusted so that the toner image during development is not dispersed. For example, in FIG. 8, small-diameter dots (cleaning field: absolute value of VO−DVB) between the charging potential (VO) of the photoconductor 1 and the developing bias voltage (DVB) of the developing device 4 are variously changed. (Approximately 45 μm). In this figure,
If possible, use an area with less dispersion. for that reason,
By setting an area where the cleaning field is small, variation in dots is small and a good test image or the like can be formed. Thereby, concentration detection can be performed accurately.

The difference between the developing bias voltage and the charging potential of the photosensitive member 1 is 200 V or more in absolute value at the time of image formation, and the charging potential for charging the photosensitive member 1 is reduced so as to be preferably lower than 200 V. As described above, a favorable dot-shaped test image can be formed.

Even when a test image for selecting an area where such a test patch image is to be formed is formed on the entire circumference of the transfer drum 5, it is preferable that the density is lower than that in normal image formation. This can be performed by controlling the developing bias voltage of the developing device 4 or reducing the amount of laser light. Also, the photoconductor 1 by the charger 2
Can be controlled so that the toner adhesion amount is reduced. As a result, a clear image can be formed without lowering the resolution even in an image using a small amount of toner. In particular, when the density is high, the density difference does not appear, and it is difficult to recognize the difference as a slight difference in the characteristics of the transfer drum 5.

As described above, a test image having a uniform density is transferred (formed) over the entire circumference of the transfer drum 5. At this time, as described when the test patch image is transferred to the transfer drum 5, when the transfer drum 5 is separated from the photoconductor 1, retransfer in which the toner transferred to the transfer drum 5 is returned to the photoconductor 1 is performed. In order to prevent the occurrence of the
It is also important to reduce the voltage supplied to c so that transfer can be performed efficiently.

Thus, the density of the image formed on the entire circumference of the transfer drum 5 is detected by the density detection sensor 16. In this case, by detecting the home position of the transfer drum 5 by the home position sensor 24, the CPU 6 recognizes the detected density corresponding to each position of the entire circumference to be rotated. That is, from the time when the home position sensor 24 detects the home position, the density detection sensor 1
In step 6, the density of the image in the rotation direction can be sequentially detected. For this reason, the image density state over the entire circumference of the transfer drum 5 is recognized, and it is possible to easily grasp at what position and what kind of transfer state.

The detected density of the entire circumference of the transfer drum 5 is stored together with the position of the transfer drum 5. For this storage, for example, the RAM 32 is used. And CP
U6 extracts (selects) an area where the density area is stable over the entire circumference of the transfer drum 5. The stable region is a region where the image density is high (dark), that is, a portion where the transfer efficiency is good. If an area where this image density is stable is selected, a test patch image 19 is formed in this area. In particular, if the test patch image 19 is transferred to the transfer drum 5, the image state is stable and a good test patch image 19 can be formed. Therefore, image quality compensation can be stabilized.

Therefore, if a region where the above-mentioned density region is stabilized is selected, its position, that is, the test patch image 19 is selected.
Is stored in the RAM 32. Based on the stored contents, the position of the test patch image formed on the photoreceptor 1 is controlled, and the image can be accurately transferred to the above-described selected area of the transfer drum 5. As described above, the sensor 24 determines the home position of the transfer drum 5 at the home position of the transfer drum 5 (51).
It is needless to say that the detection can be performed easily by recognizing the rotation angle of the transfer drum.

As described above, since it is considered that the area having the highest transfer efficiency stored in the RAM 32, that is, the place where the most stable toner image can be obtained, a test patch image for performing image quality compensation is formed at that position. . As a result, a stable and good test patch image can be obtained, and the accuracy of image quality compensation can be dramatically improved.

Then, when the formation area of the test patch image 19 on the transfer drum 5 is selected, this is stored in the storage means such as the RAM 32, and when the timing for performing the image quality compensation control is reached, as described in FIG. For example, adjustment control of, for example, a developing bias voltage for performing image quality compensation is performed. As a result of this control, a condition of the developing bias voltage, that is, a voltage value is set, and this is determined as a standard value at the time of image formation, and a color image is formed.

(Another Mode Using One Embodiment of the Present Invention) At this time, as described with reference to FIG. 4, three areas are required to form a test patch image. for that reason,
It is also possible to select three locations apart from areas where transfer efficiency and the like are high and toner density is high. However, it is preferable to select a continuous area where three different test patch images 19 are continuously formed in consideration of simplification of control and the like. In this way, the control is simplified, and the conditions for forming the test patch image can be made constant, so that more precise control can be performed.

Here, the transfer state of the entire circumference of the transfer drum 5,
In other words, if the characteristics and the like are recognized and stored in the RAM 32 or the like, the area having high transfer efficiency is used to hold the sheet by suction, and image formation can be performed using this area. That is, the region where the transfer efficiency is poor is omitted.
By using a continuous area where the transfer efficiency is good, an image forming process can be performed in that area. By doing so, the image quality can naturally be kept good, and the image quality can be compensated satisfactorily.

That is, in the area stored in the RAM 32, a continuous stable area is extracted. Then, an area in which one sheet can be sucked and held is set in the most efficient area. After the setting, the sheet is sucked and held in the set area, and the start position of the leading end of forming the toner image on the photoreceptor 1 is controlled so as to coincide with the held area. .

(Another Aspect Utilizing One Embodiment of the Present Invention) When the toner image is transferred to the transfer drum as described above, the toner image formed on the photosensitive member 1 is once transferred to the transfer drum 5 side. Thus, it has been described that when the photoconductor 1 is about to move away from the transfer drum 5, retransfer occurs in which the transferred toner image is transferred to the photoconductor 1 side. Therefore, control is performed such that the toner image is transferred in a region where the characteristics such as transfer efficiency are good, and the voltage to be transferred at that time is changed stepwise. Then, by detecting the toner image transferred to the transfer drum 5 by the density detection sensor 16, it is possible to easily know the transfer voltage having the best transfer efficiency.

Therefore, a toner image for transfer voltage recognition is formed on the photosensitive member 1. This image may have a pattern as shown in FIG. The toner image formed in such a pattern is transferred to the transfer drum 5. At this time, the CPU 6
In, the high voltage circuit 8c is controlled so that a plurality of voltages supplied to the base 5c of the transfer drum 5 are changed stepwise. The plurality of stepwise voltages may be set arbitrarily.
It is preferable to form a plurality of upper and lower transfer voltages with respect to an efficient transfer voltage at which the transfer state at the beginning is most stable. The timing of changing the transfer voltage can be easily recognized by grasping the rotation angle of the transfer drum 5 based on the detection of the home position sensor 24.

In this case, the voltage supplied to the transfer drum 5 is controlled so as to be kept lower than the voltage value when the toner image is transferred onto the sheet. In other words, the initial optimal voltage value to be transferred onto the sheet is set low, and a plurality of stepwise voltage differences are provided above and below this to perform the transfer.

When the transfer is completed, the transfer drum 5
The density of the toner image for transfer voltage recognition formed thereon is detected by the density detection sensor 16, which is input to the CPU 6. At this time, the region with the highest density can be grasped by the CPU 6. Therefore, the transfer voltage in the region having the highest density is confirmed, and thereafter, control in image formation is performed based on the transfer voltage. Therefore, a transfer voltage that does not perform retransfer at the time of image formation is controlled by the transfer drum 5 to perform stable image formation.

As described above, in order to perform image quality compensation, a toner image is formed on the entire circumference of the transfer drum 5 before the test patch image 19 is formed on the surface of the transfer drum 5. Then, by detecting the density of the formed toner image,
A stable area of the transfer drum 5 can be selected. A test patch image 19 is formed in the selected area, its density is detected, and a developing bias voltage and the like are set by comparison with a reference density. Thereafter, by performing image formation with this developing bias voltage, stable image quality based on the reference density can be compensated.

When performing the transfer to the transfer drum 5,
It is also possible to control the transfer voltage to the most efficient state. By performing the transfer voltage setting control together with the development bias voltage control, it is possible to perform high-precision compensation control with more stable image quality. Moreover, even when this is performed alone, image quality compensation can be effectively performed while maintaining good transfer efficiency.

(Embodiment of Detecting Density of Toner Image) In order to detect the density of the toner image formed on the transfer drum 5, FIG.
As shown in FIG. 7, a density detection sensor 16 which is a reflection type infrared light sensor is provided so as to face the transfer drum 5. In this case, they are simply arranged facing each other in FIG. In this arrangement, the detection of the density of the toner image is greatly affected. Therefore, an actual example for detecting this concentration detection satisfactorily and stably will be described below.

The role of the density detection sensor 16 is not only to simply detect the density of the toner image, but also to obtain an output difference that sufficiently detects the density difference between various test patch images and test images formed. It is important to Therefore, as shown in an example in FIG. 9, as an arrangement position of the density detection sensor 16, an angle formed between a tangent c of the transfer drum 5 and a light incident axis d of the density detection sensor 16 with respect to the detection point is It is set to be 45 to 85 °.

The density detecting sensor 16 irradiates the surface of the transfer drum 5 with light from the light emitting section 16a, and receives the reflected light, particularly irregularly reflected light, at the light receiving section 16b. FIG. 10 shows a density detection state in which the detected toner density is variously changed. FIG. 10 shows the result of detecting the density of the toner image by variously changing the arrangement angle of the density detection sensor 16, that is, the angle state as shown in FIG. Then, the relationship between the output difference due to the density difference and the angle is shown by variously changing the density of the toner image.

Therefore, as can be understood from FIG. 10, the arrangement angle (deg) of the density detection sensor 16 is, for example, 20 to
When toner images of each density are detected when the angle is changed to 90 °, the area where the detected value is most different is the area e of 45 to 80 °. In FIG. 10, as a method of changing the density of the toner image, the density of the toner image is changed by variously changing the developing bias voltage as described above.

If the angle of the density detecting sensor 16 is set and arranged within the above-described range, a large difference occurs in the detection value due to the difference in various densities, and thus accurate density detection can be performed. At the same time, it is possible to perform good detection when performing density detection using a test patch image formed by providing three types of density differences and a test image formed to select an area for forming an area of the test patch image. Also.

Further, in the case where density detection is performed by forming dots or linear patterns as shown in FIG. 5, since the amount of toner adhesion is particularly reduced,
It can be said that it is convenient to accurately detect the concentration.

Further, in the case of a dot or linear pattern as shown in FIG. 5, the output value of the density detection sensor 16 is also reduced as a whole. To compensate for this, by increasing the light emission output from the light emitting section 16a of the sensor 16, the absolute value of the output value of the density detection sensor 16 is increased, and the output difference of the sensor due to the difference in the amount of adhered toner is more easily output. Can be. In particular, as compared with the case where the pattern used in image quality compensation is not the one shown in FIG. 5 but an image formed entirely for density detection, the pattern shown in FIG. By increasing the output light from the element 16a, a result larger than the output difference as shown in FIG. 9 can be obtained.

By obtaining such an output value of the density detection sensor 16, the image quality compensation control can be performed more accurately. In other words, this is a result that density detection can be accurately performed, and a detection output that can reliably grasp a density change can be easily obtained.

(Other Embodiments) In the image forming apparatus described above, the sheet is suction-held on the transfer drum 5 and
The toner image is transferred to a transfer area facing the photoconductor 1 to transfer the toner image. In this case, since the test patch image 19 is formed in the same state as when the toner image is transferred to the sheet, the image quality such as the image density is easily detected on the actual sheet, and the image quality for stabilizing this image quality is obtained. Compensation can be made.

The present invention is not limited to the image forming apparatus using such a method.
Of course, the present invention can also be applied to an image forming apparatus of a system in which the toner on the intermediate transfer medium is finally transferred to a sheet. An example is shown in FIG.

In FIG. 11, the image forming apparatus transfers a toner image formed on a photosensitive member 1 formed in a drum shape to a sheet P via a transfer belt 5-1 as an intermediate transfer medium. ing. The transfer belt 5-1 as an intermediate transfer medium is provided so as to be stretched by, for example, four rollers 52, and comes into contact with the photoconductor 1 in the area of one roller 52a. Further, the transfer roller 53 is brought into pressure contact with the sheet P at the position of another roller 52c to transfer the sheet P. The other roller 52b is a driving roller, and the roller 51d is a driven roller, and is provided to stretch the transfer belt 50.

A transfer voltage for transferring the toner image formed on the surface of the photoreceptor 1 is applied to the roller 52a by the high voltage circuit 5.
The supply is controlled via the control unit 4. The transfer voltage for transferring the toner image to the sheet P via the high voltage circuit 55 is also controlled by the transfer roller 53.

The photosensitive member 1 is not shown in the figure, but as shown in FIG. 2, a portion for exposing a light image from a charger and a laser irradiating device, and a developing device 56 for four colors in a color image forming apparatus. Etc. are arranged facing each other. Therefore, the toner image of the first color is formed on the photoconductor 1, and the toner image is transferred to the transfer belt 5-1. Then, a toner image of the next color is formed on the photoconductor 1, and is transferred onto the transfer belt 5-1 so as to overlap with the toner image of the preceding color. This is repeated for each color, and a four-color or three-color toner image is sequentially superimposed on the transfer belt 5-1 to form a color image. This color image is transferred onto the sheet P appropriately conveyed at a time by the action of the transfer roller 53.

The transferred sheet P is fixed with a color toner image via a fixing roller 14 as shown in FIG. 2 and is discharged onto a discharge tray 17 as a color image.

On the other hand, the photoreceptor 1 has a cleaning unit for removing remaining unnecessary toner that has not been transferred to the transfer belt 5-1 on the surface thereof, and a next charge removal unit for removing (removing) remaining charged charges. Provided for image formation. The transfer belt 5-1 is also provided with a cleaning unit for removing the remaining unnecessary toner after transferring the toner image onto the sheet P.
1 are provided so as to be able to come and go.

As described above, a color image or a single-color toner image is formed on the sheet P by the transfer belt 5-1.
Is formed through. Therefore, in order to perform image quality compensation according to the present invention, a test patch image is formed on the transfer belt 5-1. By detecting the density of the test patch image, the developing bias voltage of the developing device 56 is set and controlled via the power supply circuit 57. For this reason, a reflection type toner density detection sensor 58 is disposed opposite to an appropriate position of the transfer belt 5-1. The toner density detection sensor 58 has the same configuration as the density detection sensor 16 shown in FIG. 2, and is arranged in the angle range shown in FIG.

Before forming a test patch image on the transfer belt 5-1 to perform image quality compensation, in the present invention, an area of the transfer belt 5-1 where a test patch image is formed is selected. Therefore, first, a toner image having the same density on the transfer belt 5-1 under the same conditions, that is, a test image is transferred to the transfer belt 5-1.
Formed all around. The density of the toner image formed on the entire circumference is detected by the density detection sensor 58 and stored.

In the storage result, the transfer drum 5-1
Can be grasped, and its characteristics and the like can be sufficiently grasped. Then, an area having excellent transfer conditions, particularly a stable area having a high toner density is selected. A test patch image is formed in the selected area. In this test patch image, as shown in FIG. 4, for example, a test patch image in which the developing bias voltage is variously changed and a density difference occurs is formed. In this case, three types of test patch images having different densities are formed, the density is detected by the density detection sensor 58, and the optimum value of the developing bias voltage is set in comparison with the reference density. Used when forming. By performing such image quality compensation according to the control procedure shown in FIG. 4, good control can always be performed.

Also in the image forming apparatus shown in FIG. 11, the characteristics and the like of the transfer belt 5-1 as the intermediate transfer body are grasped, and a stable area for transferring the test patch image is selected. , A test patch image is formed on the image, and image quality compensation control can be performed. In addition, the various controls described in the above-described embodiment can be similarly performed. For example,
The control includes setting and controlling the optimum state of the transfer voltage, control for forming a test image, and the like.

(Alternative Embodiment) The above image forming apparatus includes:
By transferring the toner image formed on the surface of the photoreceptor 1 to another medium, the image quality state, in particular, the image quality including the transfer state of the toner image is detected, and depending on how the image quality differs from the reference, Control of the process means to match the reference image quality,
For example, it controls the developing bias voltage and the like. Therefore, detection for image quality compensation can be performed on the premise that the toner image formed on the photoconductor 1 is finally transferred to a sheet, so that more accurate image quality compensation can be expected.

However, the transfer drum 5 and the transfer belt 5-1
In an image forming apparatus provided with a transfer medium such as described above, the excellent image quality compensation control described in the above-described embodiment can be performed. However, in the case where the toner image formed on the photoreceptor 1 having no transfer medium is directly transferred to a sheet, the sheet serves as a transfer medium, and image density compensation is performed by detecting the density of the test patch image transferred to the sheet. Can also be performed. In this case, the sheet is wasted.

Therefore, it is possible to detect the toner density of the test patch image formed on the photosensitive member 1 and perform image quality compensation. As a result, the density of the test patch image formed on the photoconductor 1 is directly detected, and various setting controls of the process means are performed so that the detected density becomes the reference density.
This control includes, for example, a developing bias voltage, a charging potential by a charger, and light amount control by exposure.

FIG. 12 shows the state of the processing means provided around the photosensitive member 1 shown in FIG. The same members and portions having the same functions as those in FIG. 2 are denoted by the same reference numerals. In FIG. 12, a density detection sensor 60 for detecting the density of the toner image formed on the photoconductor 1 is arranged to face the photoconductor 1. The density detection sensor 60 is an infrared reflection type sensor that irradiates light, receives reflected light (irregularly reflected light), and detects density.

In this density detecting sensor 60, FIG.
As described above, the light emission driving control is performed based on the control signal from the CPU 6, and the detection value of the light received from the toner image on the photoconductor 1 is sent to the CPU 6. Thereby, the state of the formed toner density is grasped. Also, the CPU 6
As shown in FIG.
9 is performed.

In this image forming apparatus, as shown in FIG. 2, a method of transferring a toner image onto a sheet attracted to a transfer drum 5 is used.
There is also an image forming apparatus in which a sheet is directly fed and transferred to a transfer area where the sheet contacts. In this case, in order to obtain a color image, the sheet after transfer is once passed through a fixing device,
In order to transfer the toner image of the next color, control is performed so that the toner image is sent again to the transfer area.

In FIG. 12, in order to perform image quality compensation, a test patch image is formed on the photosensitive member 1, and the density of the test patch image is detected by the density detection sensor 60. The detected value is sent to the CPU 6, where the control is performed, for example, by setting a developing bias voltage (DVB) so as to obtain the reference density in comparison with the reference density, so as to obtain an image with a constantly determined stable density. , Thereby performing image quality compensation.

Therefore, the area of the photoconductor 1 on which the test patch image is formed is selected. Therefore, the photoconductor 1
A toner image, in particular, a test image is formed on the entire circumference under a constant condition. The density of the test image is detected for the entire circumference by the density sensor 60, and this value is stored. Then, the most efficient area is selected. That is, a stable area for forming a toner image is selected.

Next, in order to perform image quality compensation control, a test patch image is formed in the area of the photosensitive member 1 selected as described above. Then, the procedure for forming the test patch image and the setting control of the processing means by detecting the formed density, for example, the setting control of the developing bias voltage are performed by the control shown in FIG.

As described above, when there is no transfer medium other than the sheet, a test patch image is formed on the photosensitive member 1 and compensation control for setting the condition of the process means is performed to perform image quality compensation. I have to. At this time, a test image is formed on the entire circumference under the same conditions in order to grasp the characteristics of the entire circumference of the photoconductor 1, and the characteristics are grasped by detecting the density. Then, a stable area of the photoreceptor 1 is selected, a test patch image is formed in the area, and one process condition or a plurality of process conditions of various process means capable of obtaining a reference image quality are set. By performing image formation under the specified conditions, it is possible to compensate for a certain image quality.

As described above, when forming an image with toner, the density state of the toner image is detected in order to perform image quality compensation. To detect this density state, a test patch image is formed, and image quality compensation control is performed to set the condition of the process means that becomes the reference density value in comparison between the density detection value of the test patch image and the reference density value. . Therefore, it is very important to form a test patch image. In other words, if a test patch image cannot be formed in a stable state,
The image quality compensation control is not stable, and the control is largely shifted. According to this, a fixed image quality cannot be compensated.

Therefore, in the present invention, a morphological medium (toner image forming medium) for forming a toner image, for example, the transfer drum 5 shown in FIG. 2 in one embodiment, and a transfer medium in another embodiment (FIG. 11) In the belt 5-1 and another embodiment (FIG. 12), the characteristics of the photoreceptor 1, particularly the formation state of the toner image, are grasped over the entire area. As one means for ascertaining this, a toner image is formed on the entire circumference of the toner image forming medium under the same conditions, and the density of the toner image is detected. From this detection result, an area where toner is favorably formed is selected.

In the toner forming medium, a test patch image for image quality compensation control is formed in a selected area where toner is well formed, and the density of the test patch becomes the reference density by comparing the density detection value with the reference density value. Set process conditions. Thereby, stable image quality compensation can be performed.

(Timing for Performing Image Quality Compensation) Here, at the timing for performing control for image quality compensation as shown in FIG. 4, a test image is naturally formed on the entire circumference of the toner image forming medium according to the present invention. Thereafter, the process is performed after a specific area is selected from the density detection of the test image. Therefore, the following state can be considered as the timing for forming the toner image on the entire circumference of the toner image forming medium and grasping the characteristics of the toner image forming medium.

The first timing is performed when the power of the image forming apparatus is turned on and when the image forming operation is started. For this, it is necessary to turn on the power after the image forming apparatus has been left, and to set process conditions in order to perform an image forming operation. Thereby, the image forming operation can be stabilized.

In this case, particularly, the image forming apparatus falls into a trouble state, and the image cannot be formed. Then, after the trouble is cleared, the power is turned on. At this time, it is best to form a test patch image and perform image quality compensation. Therefore, it is preferable to form a test image on the entire circumference of the toner image forming medium in advance, select a good area based on the test image, and perform image quality compensation by forming a test patch image in the selected area. This trouble includes sheet jam, no toner, and the like.

As the second timing, it is best to form a test patch image at the timing of exchanging the photoreceptor 1 and exchanging various process means, and to perform stable image quality compensation. For this reason, it is preferable that the image quality compensation control of the present invention is performed using the startup period of the image forming apparatus after the replacement. This is because the image quality is deviated from the reference image quality by replacement. Therefore, it is important to compensate for a certain image quality, not limited to the exchange of the process means, and the above-described control of the present invention is executed at the timing of the exchange or the like.

The third timing is periodically performed, for example, when the number of image forming operations reaches a predetermined number. In this case, the image quality may change due to a change over time. Therefore, the number of times of image formation (the number of sheets) is set before the image quality changes, and when the number of times of image formation reaches the predetermined number, the above-described control for image quality compensation according to the present invention is executed. Although this has a trade-off with the life of the photosensitive member 1 and the like, stable image quality can be compensated by sequentially performing the replacement before the replacement. In addition, it is also possible to set a certain period, for example, a period of one day, one week, and perform the operation every time.

The fourth timing is performed according to a change in the surrounding environment. That is, the image quality may be affected by an environmental change at the position where the image forming apparatus is installed. By performing the image quality compensation control of the present invention by detecting such an environment change, the image quality compensation control can be performed without being affected by the environment change.

As an example, a humidity sensor 21 is provided in the image forming apparatus as shown in FIG. 2, and a detection output from the humidity sensor 21 is sent to the CPU 6. At this time, if the CPU 6 confirms that the detected humidity state has changed significantly from the previous humidity state, the control according to the present invention, that is, the characteristics of the entire circumference of the toner image forming medium is grasped, and a good area selection is performed. Is performed, and a test patch image is formed in this area.

Thus, when the image quality state largely changes due to the humidity change, it is possible to set the condition of the processing means for compensating for a constant image quality state. Therefore, image formation can be performed with stable image quality, that is, in a state where the image quality matches the reference image quality.

As another timing, when the setting of the developing bias voltage is controlled by forming a test patch image as shown in FIG. 4, the developing bias voltage is different from the value obtained when the previous condition setting was performed. This is a case where there is a large deviation. That is, it is unlikely that a large change will occur. For this reason, a case where the area for forming the test patch image is not good may be considered. In particular, the toner forming medium is damaged,
This may be due to adhesion (filming) of toner or the like.

Therefore, a good area is selected by detecting the density of the toner formed on the entire circumference of the toner image forming medium. This makes it possible to form a good test patch image by avoiding an area where toner formation is not good, such as a damaged area. This enables more stable image quality compensation control.

In this case, in the case of forming a color image, a developing bias voltage for each color is set. Therefore, even when the developing bias voltage of one color is significantly different from the developing bias voltages of the other colors, it is considered that the formation of the test patch image is affected by some factor. Therefore, if such a situation occurs, it can be said that it is preferable to grasp the characteristics of the toner image forming medium and perform control for selecting the formation area of the test patch image as described above.

Note that, although described later, in the embodiment of the present invention, the developing bias voltage DVB is set to a negative value,
Although it is specified to raise or lower this, it is only to raise (higher) or lower (lower) the absolute value. Further, in the description of the present embodiment, the process bias is mainly set to control the condition setting of the developing bias voltage. However, the present invention is not limited to this. For example, it is possible to control the charging potential of the photoconductor, which is well known in the art.

Further, in a copying machine that forms an image of an original or the like on the photoreceptor 1, the image density is controlled by controlling the amount of exposure for irradiating the original or controlling the amount of laser light in laser irradiation. Can be corrected. Therefore, the light amount may be corrected and controlled.

[0141]

According to the image quality compensating device of the image forming apparatus according to the present invention, when setting the conditions of the process means for maintaining the image quality in a constant state, the characteristics and the like of the toner image forming medium are sufficiently grasped. In particular, by selecting a region where a test patch image is to be formed and forming a test patch image in that region, more accurate image quality compensation control is possible.

In selecting an area of the toner image forming medium, an area in which the toner formation state is particularly good is selected, a test patch image can be formed well, and a comparison with the reference density can be made well. Image quality compensation accuracy can be improved.

In addition, by grasping the characteristics of the entire circumference of the toner image forming medium and selecting an area having good characteristics to form an image, it is possible to easily obtain better image quality. And the image quality compensation is further improved.

In addition, when the toner image forming medium is formed on a transfer medium or the like, the optimum conditions for the transfer conditions can be known at the same time, and image quality compensation for good transfer can be performed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a control circuit configuration of an entire image forming apparatus including image quality compensation control of the image forming apparatus of the present invention.

FIG. 2 is a diagram for explaining a structure of an image forming apparatus and a configuration in image quality compensation control of the present invention.

3 is a cross-sectional view illustrating a configuration example of a transfer drum included in the image forming apparatus in FIG.

FIG. 4 is a flowchart showing a control procedure for setting a condition of a developing bias voltage of a developing device which is a process unit for image quality compensation according to the present invention.

5A and 5B show examples of a test patch image for compensating image quality according to the present invention and an image pattern of a test image for grasping the characteristics of a toner image forming medium, in which FIG. () Is a diagram showing a linear pattern.

FIG. 6 is a graph showing a relationship between a detected density of a test patch image and a developing bias voltage for image quality compensation according to the present invention, and a straight line for obtaining a developing bias voltage based on a reference density indicated by a linear approximation method based on the plot. FIG.

FIG. 7 is a perspective view showing an example for detecting a home position of a transfer drum.

FIG. 8 is a characteristic diagram showing a relationship between a difference between a charging potential of a photoconductor and a developing bias potential and a degree of variation of formed dot pixels.

FIG. 9 is a diagram for explaining an example of the arrangement of a density detection sensor for detecting a toner density of a test image or the like formed to perform image compensation according to the present invention.

FIG. 10 is a characteristic diagram showing a relationship between an arrangement angle of a density detection sensor and an output value as a result of toner density detection in FIG.

FIG. 11 is a diagram illustrating a configuration of an image forming apparatus according to another embodiment for executing the image quality compensation control of the present invention.

FIG. 12 is a diagram illustrating a configuration of an image forming apparatus according to another embodiment for executing the image quality compensation control of the present invention.

[Explanation of symbols]

 Reference Signs List 1 photoconductor (toner image forming medium) 2 charger 3 laser scanning unit 4 developing unit (developing means) 5 transfer drum (toner image forming medium / transfer medium) 6 CPU (control device) 8b high voltage circuit (supply of developing bias voltage) Source) 8c High voltage circuit (transfer voltage supply source) 10 Sheet pressure contact roller (ground roller) 15 Semiconductor laser 16 Density detection sensor 18a A / D converter 18b A / D converter 19 Test patch image 21 Humidity sensor 24 Home position sensor 5-1 Transfer belt (toner image forming medium / transfer medium) 58 Density detection sensor 60 Density detection sensor STD Reference image density TD Reference toner mixing ratio V1 Development bias voltage after setting conditions DVB Development bias voltage DVB2 Standard development bias voltage

 ──────────────────────────────────────────────────続 き Continued on front page (72) Inventor Hiroaki Yoshida 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) Inventor Yuka Sakagami 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside the corporation

Claims (8)

[Claims] An image forming apparatus for forming an image with a desired toner image on a toner image forming medium via various processing means controls one or more conditions of the various processing means for forming the toner image. In order to perform image quality compensation, a test patch image having a predetermined density is formed on the toner image forming medium in order to perform image quality compensation, and the density of the test patch image is detected. In image quality compensation control in which the condition of the process means is set and controlled in comparison with the density, before forming the test patch image, when selecting an area where the test patch image is formed on the toner image forming medium, A test toner image is formed on the entire circumference of the toner image forming medium under certain conditions, the toner image is detected by a density detection sensor, and based on the detection result, Selecting an area suitable for forming a stop patch image, forming a test patch image in the selected area of the toner image forming medium, and controlling the setting conditions of the process means based on the density detection thereof. Image quality compensating device of an image forming apparatus. 2. A method for selecting a formation area of a toner image forming medium on which a test patch image is to be formed, wherein a test image pattern formed on the entire circumference of the toner image forming medium has a density difference due to an amount of toner adhered. 2. The image quality compensating apparatus for an image forming apparatus according to claim 1, wherein the image forming apparatus has a dot-shaped or linear pattern. 3. The image according to claim 1, wherein, when selecting the area of the toner image forming medium on which the test patch image is formed, an area where the toner image is good and the density is high is selected. An image quality compensation device for the forming device. 4. A density detecting sensor for detecting the density of at least a test toner image formed on the toner image forming medium is a reflection type optical sensor, and the arrangement angle of the sensor is set at a toner irradiation point at a light irradiation point. 2. The image quality compensating device for an image forming apparatus according to claim 1, wherein an angle formed between a tangent line of the image forming medium and an optical axis for irradiating light is 45 to 80 [deg.]. 5. The image according to claim 1, wherein the density of the test toner image formed on the toner image forming medium is lower than the toner density when normal image formation is performed. An image quality compensation device for the forming device. 6. A test toner image is formed on the entire periphery of the toner image forming medium, and a test patch image forming area is selected at the timing of forming a test patch for image quality compensation control and performing image quality compensation. 2. The image quality compensating apparatus for an image forming apparatus according to claim 1, wherein the test patch image is formed in a selected area before the timing. 7. According to a density detection state when a test toner image is formed on the entire circumference of the toner image forming medium, extraction is performed including a continuous area used for image formation, and the extracted area is imaged. 2. The image quality compensating apparatus for an image forming apparatus according to claim 1, wherein the image forming apparatus is set as a forming area, and other non-extracted areas are set as non-image areas, and the subsequent image forming processing is performed. 8. The toner image forming medium is a transfer medium to which a formed toner image is transferred, and the toner image is transferred to a transfer medium in a selected area of the transfer medium where a test patch image is formed. At the time of transfer, the transfer was performed under a plurality of different transfer conditions, the density of the toner image transferred at this time was detected, and the transfer condition of the region with the highest density in the detection result was set as one image quality compensation condition. 2. The image quality compensating device for an image forming apparatus according to claim 1, wherein: