JP4923767B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

  An image formed by an electrophotographic method is likely to cause uneven density and streaks, and it is difficult to maintain density uniformity. For this reason, an image forming apparatus that employs an electrophotographic system is equipped with various mechanisms relating to devices and means for correcting density non-uniformity. For example, the image forming apparatus disclosed in Patent Document 1 is equipped with a lookup table that records density correction parameters for each pixel position of the main scanning line, and for each pixel position obtained by interpreting the job. A series of image signals are corrected using the parameters of the lookup table and then supplied to the image forming engine.

On the other hand, instead of ensuring the uniformity of density by image signal processing as in Patent Document 1, the image forming engine such as the developing potential (dark potential, light potential, developing bias potential) and the amount of toner supplied to the developing device is used. A mechanism for maintaining the uniformity of density by controlling the physical quantity that determines the driving state has been proposed, and this mechanism is called “process control” (Patent Document 2).
JP-A-6-003911 JP-A-5-303254

In order to surely prevent the occurrence of density unevenness, it is most desirable to mount a combination of image signal processing and process control. However, when a mechanism according to both of these systems is mounted on an image forming apparatus and individually driven, there is a problem that the image quality of a so-called highest density portion becomes unstable.
This problem will be described with reference to FIG. In the figure, the horizontal axis indicates the image forming position in the main scanning direction of the image forming apparatus, and the vertical axis indicates the density. A chain line x indicates a density detection position of a sensor that supports process control, and a mark “◯” indicates an ideal value of density set for the position. As is well known, the image signal supplied to the image forming engine represents pixel density as a predetermined bit string. For example, if the bit string representing the density of one pixel is 8 bits (1 byte), 256 levels of density from 0 to 255 can be expressed. This means that according to the image signal processing, the density unevenness of the so-called highest density portion (density 100%) can be made uniform only in the direction of decreasing the density. Since there is an upper limit to the density that can be represented by the image signal transmitted from the upper unit, in order to make the density of all the pixel addresses of the main scanning line uniform, there is a variation in a certain range below the upper limit. This is because the average density and the lowest value in the range must be taken as the ideal density value. On the other hand, the process control has a structure that controls a physical quantity that determines the driving state based on the detection result of the density of the patch formed in the image forming engine. Therefore, for the area of the highest density portion, if the density of the patch formed by the image forming engine based on the image signal that has undergone correction signal processing falls below the allowable range of the highest density portion set in the process control, the density correction is performed. For this reason, the density correction process by the image signal process may not be reflected well in the output result.
The present invention has been devised under such a background, and a mechanism capable of performing good density correction by linking image signal processing and a process controller while reliably preventing deterioration in image quality at the highest density portion. The purpose is to provide.

An image forming apparatus according to a preferred embodiment of the present invention includes an image carrier and a unit driven according to a series of xerographic processes including charging, exposure, and development, and a toner corresponding to an image signal supplied thereto An image forming unit that is a unit that forms an image on the image carrier, and the density of the formed toner image is discretely read over a first reading width parallel to the main scanning line, and the read density is indicated. A first reading unit that acquires a density value group and a density of the formed toner image are read over a second reading width that is narrower than the first reading width, and a density value indicating the read density is acquired. The second reading means and the second reading means each time the second reading means obtains the density value of the toner image formed by the image forming means based on the patch image signal including the highest density image. Its darkness is within the allowable range A process for controlling a physical quantity that determines the drive content of the image forming means so as to keep the density value within the permissible density range when it is judged whether or not the value falls within the permissible density range The toner image is formed on the image forming unit based on a test pattern image signal including a control unit and a highest density image having the same width in the main scanning direction as the toner image that can be formed by the image forming unit. A density correction parameter for correcting the image signal so that the density value approaches the ideal value, and an image supplied to the image forming unit. A correction unit that corrects a signal using a density correction parameter calculated by the calculation unit; and the image formation based on the test pattern image signal. Stage to the lowest value of the density value group in the maximum density of the image obtained by reading the first reading means, the toner image formed is, the density of the image of the maximum density at the reading position of the second reading means And an execution control unit that causes the calculation unit to execute calculation of the density correction parameter after switching the actual value and causing the process control unit to execute the control of the physical quantity.

  The image forming means includes a charging means for charging the image holding member, an exposure means for exposing the charged image holding member with light modulated in accordance with an image signal to form a latent image, and a latent image formed thereon. A developing unit that develops toner on the image carrier, and the process control unit includes a charging potential of the charging unit, an exposure amount of the exposure unit, a toner supply amount of the developing unit, or a developing bias of the developing unit. A physical quantity that determines one or more of them may be controlled.

  According to the present invention, it is possible to perform good density correction in which the image signal processing and the process controller are linked while reliably preventing the deterioration of the image quality in the highest density portion.

(First embodiment)
A first embodiment of the present invention will be described.
FIG. 2 is a schematic hardware configuration diagram of the image forming apparatus according to the present embodiment.
As shown in the figure, the image forming apparatus includes a paper tray 11, a paper transport path 12, an intermediate transfer belt 13, a transfer unit 14, a fixing unit 15, an image reading unit 16, an image forming engine 30, an image signal input unit 50, A correction processing unit 60 and a process control unit 80 are included.

  The paper tray 11 stores a plurality of sheets cut to a predetermined size such as A4, and the stored sheets are picked from the paper tray 11 one by one, and the transfer unit 14, the fixing unit 15, and the image reading unit 16 are moved. The paper is sequentially transported on a paper transport path 12 connected to the paper discharge port via.

  The image forming engine 30 is a unit in which modules that are driven according to a series of xerographic processes including charging, exposure, and development are integrated. Yellow (hereinafter referred to as “Y”), magenta (hereinafter referred to as “M”). Toner images corresponding to image signals of respective colors of cyan (hereinafter referred to as “C”) and black (hereinafter referred to as “K”) are formed on the intermediate transfer belt 13. Details of the image forming engine 30 and its driving contents will be described later.

  The transfer unit 14 forms a nip portion by sandwiching the intermediate transfer belt 13 and the paper transport path 12 between the peripheral surfaces of the main drive roll and the backup roll charged to a predetermined potential. When the belt surface of the intermediate transfer belt 13 on which the toner images of the respective colors are superimposed by the image forming engine 30 is carried into the nip portion together with the paper in the paper transport path 12, the toner image is received by the action of the main roll. The image is transferred from the intermediate transfer belt 13 to a sheet.

  The fixing unit 15 forms a nip portion by sandwiching the sheet conveyance path 12 between the peripheral surfaces of a heating roll having a heat source and a pressure roll. When the sheet on which the toner image has been transferred by the transfer unit 14 is carried into the nip portion, the toner image is fixed to the sheet by receiving the heating action by the heating roll and the pressing action by the pressure roll.

  The image reading unit 16 is a sensor array in which a plurality of sensors are arranged. The image reading unit 16 is provided on the downstream side of the fixing unit 15 with the field of view directed toward the paper conveyance path 12. The sensors constituting the image reading unit 16 are arranged in parallel with the main scanning line of the toner image formed on the paper by each image forming engine 30, and the reading width is approximately equal to the line width of the main scanning line. The same. Therefore, the image reading unit 16 reads the density of the toner image over the main scanning line width by each of the sensors, and acquires density value groups each indicating the read density.

The image signal input unit 50 supplies the image signal YMCK of each color of YMCK obtained by interpreting the job to the correction processing unit 60 and the process control unit 80.
The correction processing unit 60 includes a correction arithmetic circuit 61, an image signal conversion table 62, a selector 63, and a test pattern generation circuit 64.

  The image signal conversion table 62 has a matrix structure in which the reference field can be uniquely specified according to the pixel address in the main scanning direction and the density value of the pixel address. A density correction parameter is stored in each field constituting the image signal conversion table 62. The density correction parameter is a parameter that determines a coefficient to be applied during signal processing of the image signal input from the image signal input unit 50.

  When the image signal YMCK of the raster data of each color obtained by interpreting the job is supplied from the image signal input unit 50 to the correction processing unit 60, the correction arithmetic circuit 61 of the correction processing unit 60 causes each of the image signal conversion tables 62 to be displayed. Using the density correction parameter, the image signal YMCK is subjected to signal processing for density correction, and the image processed signal Y′M′C′K ′ is supplied to the image forming engine 30 via the selector 63. The Upon receiving the supply of the image signals Y′M′C′K ′, the image forming engine 30 forms toner images corresponding to the supplied image signals on the intermediate transfer belt 13, and the toner images are further transferred to the transfer unit 14. Will be transferred to the paper.

  FIG. 3 is a diagram illustrating an example of signal processing using the image signal conversion table 62 and the density correction parameter of the table 62. In the image signal conversion table 62 shown in the figure, a specific density correction parameter is prepared for each pixel address in the main scanning direction from 0 to 7000. The correction calculation circuit 61 indicates the density correction parameter of this table 62. The signal processing for applying the respective coefficients is sequentially performed on the image signals of the respective pixel addresses.

  In addition, the correction processing unit 60 performs the toner image formation by the image forming engine 30 when the number of times reaches a predetermined value (for example, 1000 times) or based on a user's instruction to transition to the calibration mode. Transition from the normal output mode to the calibration mode. When the mode is changed to the calibration mode, a plurality of rectangular images having the same width in the main scanning direction as the toner image that can be formed by the image forming engine 30 and in which each density is gradually changed from the highest density to the lowest density are displayed. An image signal of raster data arranged in the scanning direction (hereinafter, this image signal is appropriately referred to as a “test pattern image signal”) is supplied from the test pattern generator to the image forming engine 30 via the selector 63, and the test is performed. The density correction parameter of the image signal conversion table 62 is rewritten according to the deviation between the actual density value and the ideal value of the toner image formed by the image forming engine 30 based on the pattern image signal.

  Rewriting of the density correction parameter is performed by the correction arithmetic circuit 61. More specifically, first, the correction calculation circuit 61 acquires a density value group obtained by the image reading unit 16 reading the density of the toner image on the paper over the main scanning line width. Then, the density value for each pixel address is specified based on the acquired density value group, and after calculating the difference between the density value and the ideal value of the density for each pixel address, the difference is absorbed. The coefficient is sequentially recorded in the image signal conversion table 62 as a new density correction parameter.

In FIG. 2, the process control unit 80 is a unit provided for suitably controlling a physical quantity that determines the driving state of the image forming engine 30.
FIG. 4 is a diagram showing a detailed configuration of the image forming engine 30 and the process control unit 80. As shown in the figure, the process control unit 80 includes a dot counter 81, a signal selector 82, a patch signal generation unit 83, a potential control controller 84, and a development control controller 85. The image forming engine 30 includes a charger 32, a potential sensor 33, an exposure device 34, a developing device 35, a transfer device 36, a toner concentration sensor 37, a cleaner 38, and the like. In addition to the laser driver 39, the charger power supply 40, and the developing bias power supply 41, an environmental sensor 42 that detects the temperature and humidity in the unit and supplies a temperature and humidity signal indicating the detected value to the potential controller 84 is provided.

The image forming engine 30 is driven according to a xerographic process to form a toner image corresponding to the image signal on the intermediate transfer belt 13. The driving procedure is as follows.
First, the charger 32 has a charging roller, and the surface of the photosensitive drum 31 is charged by rotating the charging roller in the same direction as the photosensitive drum 31 by receiving a voltage supply from the charger power supply 40. Charge uniformly to the same potential as the roller. At this time, the potential sensor 33 detects the potential of the surface of the photosensitive drum 31 that has been charged by the charger 32 and supplies a surface potential signal indicating the detected potential to the potential controller 84 of the process control unit 80. It has become.

When the surface of the photosensitive drum 31 is charged, the laser beam whose light intensity is modulated under the control of the laser driver 39 is scanned from the exposure unit 34 to form an electrostatic latent image.
When the electrostatic latent image is formed, the developing device 35 develops toner on the electrostatic latent image. The developing device 35 includes a developing roller and a toner cartridge. The toner loaded in the toner cartridge is supplied into the developing device and stirred with the developer to frictionally charge the toner. The charged toner is supplied to the developing roller rotated in the same direction as the photosensitive drum 31, and the charged toner leaves the developing roller and adheres to the exposure area on the photosensitive drum 31, The electrostatic latent image is developed as a toner image.

  The developed toner image is transferred to the intermediate transfer belt 13 by the transfer unit 36. The transfer device 36 has a transfer roller charged to a predetermined potential. Then, when the intermediate transfer belt 13 is carried into a nip portion where the transfer roller and the peripheral surfaces of the photosensitive member are in contact with each other, the intermediate transfer is received by the action of the potential difference between the transfer roller and the photosensitive drum 31. The toner image is transferred onto the surface of the belt 13. At this time, the toner density sensor 37 reads the density at the density detection point substantially at the center of the main scanning line of the toner image, and supplies a toner density signal indicating the read density to the development control controller 85 of the process control unit 80. Here, as compared with the image reading unit 16 described above, the toner density sensor 37 does not have a plurality of sensors arranged side by side, so that the reading width is naturally narrower than that of the image reading unit 16. .

After the transfer, the remaining toner on the surface of the photosensitive drum 31 is removed by the cleaner 38.
The surface of the intermediate transfer belt 13 onto which the toner image has been transferred is conveyed to the transfer unit 14 via the subsequent image forming engine 30 and the like, and the toner image is transferred onto the paper by the transfer unit 14. The sheet on which the toner image has been transferred is conveyed to the fixing unit 15 where the toner image is fixed on the sheet.

  Next, each part constituting process control will be described in detail. As described above, the process control unit 80 is a unit that controls the physical amount that determines the driving state of the image forming engine 30. Specifically, the exposure amount by the exposure unit 34, and the charger 32 from the charger power source 40. The voltage supplied to the charging roller, the voltage supplied from the developing bias power supply 41 to the developing roller of the developing device 35, and the amount of toner supplied from the toner cartridge of the developing device 35 to the developing device are controlled. The control of the former three of these four physical quantities is performed by the potential controller 84 based on the signals supplied from the environment sensor 42 and the potential sensor 33, whereas the remaining one control is the toner density sensor. Based on the signal supplied from 37, the development controller 85 carries out. The details of the behavior of both controllers will be explained step by step.

  First, the potential controller 84 supplies the surface potential from the potential sensor 33 each time an image signal is supplied from the selector 63 of the correction processing unit 60 to the image forming engine 30 and a toner image is formed according to the xerographic process. A quantity signal and a temperature / humidity signal are respectively acquired from the environment sensor 42. Based on the acquired signals, the deviation between the actual value and the ideal value of the exposure amount of the laser diode of the exposure device 34, the voltage of the charging roll of the charger 32, and the voltage of the developing bias power supply 41 is calculated. Is supplied to each of the laser driver 39, the charger power supply 40, and the developing bias power supply 41.

  On the other hand, the development controller 85 supplies the image signal generated by the patch signal generator 83 of the process controller 80 (hereinafter, this image signal will be referred to as “patch image signal” as appropriate) to the image forming engine 30. After the toner image is formed, the density value of the toner image detected by the toner density sensor 37 is fed back to the toner supply amount of the developing unit 35.

  More specifically, the development controller 85 supplies an image selection signal to the signal selector 82 when the dot count value supplied from the dot counter 81 reaches the trigger threshold value set for itself. This trigger threshold is a value corresponding to the total number of pixels in the image forming area of the number of output sheets (for example, 30 sheets) that requires calibration of the toner supply amount of the developing device 35.

  When the image selection signal is supplied to the signal selector 82, the patch image signal generated by the patch signal generation unit 83 is supplied to the image forming engine 30 via the selector 82. The patch image signal is an image signal of raster data in which a plurality of rectangular images each having a density that gradually changes from the highest density to the lowest density are arranged in the sub-scanning direction. However, unlike the test pattern image signal described above, the width in the main scanning direction of the rectangular image indicated by the raster data of the patch image signal is limited to a narrow range around the density detection point of the toner density sensor 37.

  The image forming engine 30 supplied with the patch image signal is driven according to a xerographic process to sequentially form toner images of rectangular images of respective densities corresponding to the patch image signal on the photosensitive drum 31. The density of these toner images is read by the toner density sensor 37 and supplied to the development controller 85 as a toner density signal. The development controller 85 calculates the deviation between the actual density value at the density detection point and the ideal density value stored in its own memory based on the toner density signals sequentially supplied from the toner density sensor 37. It is determined whether or not it falls within a preset allowable range. When it is determined that the allowable range has been exceeded, a control signal that compensates for the deviation is supplied to the developing device 35, and the amount of toner supplied from the toner cartridge to the developing device is increased or decreased. For example, a control signal for increasing the toner supply amount is supplied if the actual value of the density at the density detection point is below the lower limit of the allowable range, and a control signal for decreasing the toner supply amount is supplied if it exceeds the allowable range. .

Here, when the image forming apparatus according to the present embodiment shifts to the calibration mode, the test pattern image signal is continuously supplied to the image forming engine 30 twice. Then, development control is performed on the lowest density value signal indicating the lowest density value of the density value group obtained by causing the image reading unit 16 to read the toner image formed by the image forming engine 30 upon receiving the first test pattern image signal. The actual density value at the density detection position of the toner density detection sensor of the development controller 85 is switched to the lowest density value indicated by the lowest density value signal. Then, the density obtained by supplying the second test pattern image to the image forming engine 30 and causing the image reading unit 16 to read the toner image formed by the image forming engine 30 in response to the supply of the test pattern image signal. The density correction parameter is rewritten based on the value group. This is because the accuracy of density correction in the highest density portion is ensured by linking the density correction unit and the process control unit 80 in this manner.

  This principle will be specifically described with reference to FIG. In the figure, the horizontal axis indicates the image forming position in the main scanning direction of the image forming apparatus, and the vertical axis indicates the density. A chain line x indicates a density detection position of the toner density sensor 37, and a mark “◯” indicates an ideal value of the density of the highest density portion (density 100%) stored in the memory of the development controller 85.

  In the figure, the development controller 85 controls the toner amount of the developing unit 35 so that the deviation between the ideal value of the density of its own memory and the actual value of the density at the density detection position of the toner density detection sensor is within an allowable range. ing. Therefore, for the toner image formed by the image forming engine 30 that has been supplied with the first test pattern image signal, the toner density at the density detection position matches the ideal value, but at a different position on the main scanning line. The density does not always match the ideal value. In the example of the figure, it can be seen that the density on the left side of the density detection position is inclined lower than the ideal value, and the density on the right side of the density detection position is inclined higher than the ideal value.

  Next, after supplying the first test pattern image signal to the image forming engine 30, a density value group obtained by causing the image reading unit 16 to read the toner image formed by the image forming engine 30 based on the image signal. The actual value of the density at the density detection position of the toner density detection sensor of the development controller 85 is switched to the lowest value, the density value indicated by “◎” at the left end of the main scanning line in the example of the drawing. Thereafter, the toner amount of the developing unit 35 is controlled so that the deviation between the ideal value and the minimum value of the density value group obtained by the image reading unit 16 is within an allowable range.

  In this state, a second test pattern image signal is supplied to the image forming engine 30, and a density value group obtained by causing the image reading unit 16 to read the toner image formed by the image forming engine 30 based on the image signal is obtained. Based on this, the density correction parameter is rewritten. Thereafter, in the normal mode, the supply of the signal processed image signals Y′M′C′K ′ to the image forming engine 30 is resumed. As described in the background section, according to the density correction signal processing, the density unevenness of the highest density part can be uniformed only in the direction of decreasing the density, but when the first test pattern image signal is supplied. Since the actual value of the highest density at the density detection position of the toner density detection sensor in the development controller 85 is set to the lowest density in the plane, the image forming engine 30 is formed based on the image signal Y′M′C′K ′. A situation where the maximum density of the toner image is less than the ideal value can be avoided, and good correction accuracy can be ensured.

  According to the present embodiment, the correction processing unit 60 that performs signal processing on the image signal to correct the density and the process control unit 80 that controls the physical quantity that determines the driving state of the image forming engine 30 are preferably linked together. The accuracy of density correction in the highest density part can be increased. With reference to FIG. 6, the advantageous effect compared with the prior art is confirmed. According to the prior art, the ideal value in which the density of the highest density portion (density 100%) of the toner image formed by the image forming engine 30 based on the image signal that has undergone the signal processing by the correction processing unit 60 is set in the process control unit 80. According to the present embodiment, the density of the highest density portion of the toner image formed by the image forming engine 30 based on the image signal that has undergone the signal processing by the correction processing unit 60 is different from that of FIG. And the ideal value set in the process control unit 80 can be matched, and the density correction by the process control unit 80 can be performed (FIG. 6B).

(Second Embodiment)
A second embodiment of the present invention will be described.
Since the hardware schematic configuration of the image forming apparatus according to the present embodiment is the same as that shown in FIG. 2, the description thereof will be omitted.
FIG. 7 is a diagram illustrating a detailed configuration of the image forming engine 30 and the control unit. In the first embodiment shown in FIG. 4, a minimum density value signal indicating the minimum density value of the density value group obtained by causing the image reading unit 16 to read the toner image is supplied to the development control controller 85 of the process control unit 80. It was like that. On the other hand, in this embodiment, the table value corresponding to the highest density portion of the image signal conversion table 62 corresponding to the position of the rectangular image generated by the patch signal generation unit of the process control unit 80 is used as the image signal conversion table signal. The signal is supplied to the patch signal generation unit 83 of the process control unit 80.

  In this embodiment, the dot area ratio of the rectangular image of the highest density portion of the patch image signal generated by the patch signal generation unit 83 corresponds to the highest density value of the image signal conversion table 62 corresponding to the position. Match table values. In this way, the accuracy of density correction in the highest density portion is also secured by linking the correction processing unit 60 and the process control unit 80 together.

  This principle will be specifically described with reference to FIG. In the figure, the horizontal axis indicates the image forming position in the main scanning direction of the image forming apparatus, the vertical axis indicates the density, x indicates the density detection position of the toner density sensor 37, and a circle indicates the highest level of the development controller 85. The actual value of the density in the density part is shown.

  In the figure, the development controller 85 controls the toner amount of the developing unit 35 so that the deviation between the ideal value of its own memory and the actual value of the density at the density detection position of the toner density detection sensor is within an allowable range. . Therefore, for the toner image formed by the image forming engine 30 that has been supplied with the first test pattern image signal, the toner density at the density detection position matches the ideal value, but at a different position on the main scanning line. The density does not always match the ideal value. In the example of the figure, it can be seen that the density on the left side of the density detection position is inclined lower than the ideal value, and the density on the right side of the density detection position is inclined higher than the ideal value.

Next, the highest corresponding to the recording position of the rectangular image in the image signal conversion table 62 obtained by causing the image reading unit 16 to read the toner image formed by the image forming engine 30 upon receiving the first test pattern image signal. The halftone dot area ratio of the rectangular image of the highest density part (density 100%) of the patch image signal is switched to the image signal conversion table value of the density part. Then, running in the normal mode, the developing control controller 85, the the toner image formed with the concentration after switched will perform control so as to determine the deviation of the tolerance, good correction accuracy Is secured.

(Other embodiments)
The present invention can be modified in various ways.
In the above embodiment, the number of times the process control unit 80 is controlled in the calibration mode is two times. However, this may be performed three times or more in order to improve the correction accuracy. Further, the number of times of supplying the test pattern image signal for rewriting the density correction parameter by the correction processing calculation unit is two times, but this may be performed three times or more.
In the above embodiment, the toner density signal obtained by the toner density sensor 37 reading the toner image is supplied to the development controller 85, and the development controller 85 controls the toner supply amount according to the density indicated by the toner density signal. It was like that. On the other hand, the sensing result of the toner density sensor 37 is supplied as the exposure amount by the exposure device 34, the voltage supplied from the charger power supply 40 to the charging roller of the charger 32, and the developing bias power supply 41 to the developing roller of the developing device 35. It may be fed back to control of another physical quantity that determines the driving state of the image forming engine 30 such as a voltage to be used. This modification can be realized by supplying the toner concentration signal of the toner concentration sensor 37 to the potential controller 84.

It is a figure which shows the conventional problem. It is a hardware schematic block diagram of an image forming apparatus. It is a figure which shows the signal processing using an image signal conversion table. It is a figure which shows an image formation engine and a process control part (1st Embodiment). It is a figure which shows the principle of 1st Embodiment. It is a figure which shows the effect of 1st Embodiment with respect to a prior art. It is a figure which shows an image formation engine and a control part (2nd Embodiment). It is a figure which shows the principle of 2nd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Paper tray, 12 ... Paper conveyance path, 13 ... Intermediate transfer belt, 14 ... Transfer unit, 15 ... Fixing unit, 16 ... Image reading part, 30 ... Image formation engine, 31 ... Photosensitive drum, 32 ... Charger, 33 ... Potential sensor, 34 ... Exposure device, 35 ... Developer, 36 ... Transfer device, 37 ... Toner density sensor, 38 ... Cleaner, 39 ... Laser driver, 40 ... Charger power supply, 41 ... Development bias power supply, 42 ... Environment Sensor 50... Image signal input unit 60. Correction processor 61. Correction arithmetic circuit 62. Image signal conversion table 63. Selector 64 Test pattern generation circuit 80 Process control unit 81 Dot counter , 82 ... Signal selector, 83 ... Patch signal generation unit, 84 ... Potential controller, 85 ... Development controller

Claims (2)

An image carrier,
Image forming means for driving according to a series of xerographic processes including charging, exposure, and development, and for forming a toner image corresponding to an image signal supplied to the image holding member;
First reading means for discretely reading the density of the formed toner image over a first reading width parallel to the main scanning line and acquiring a density value group indicating the read density;
A second reading unit that reads the density of the formed toner image over a second reading width narrower than the first reading width, and acquires a density value indicating the read density;
Each time the second reading unit obtains the density value of the toner image formed by the image forming unit based on the patch image signal including the image with the highest density, the density value falls within a preset density allowable range. And a process control unit that controls a physical quantity that determines the driving content of the image forming unit so that the density value falls within the allowable density range when it is determined that the density value does not fall within the allowable density range. ,
Based on the test pattern image signal including the highest density image having the same width in the main scanning direction as the toner image that can be formed by the image forming means, the image forming means forms a toner image, and the density value of the toner image is determined. Calculating means for calculating density correction parameters for correcting the image signal so that the first reading means obtains the density value to approach the ideal value;
A correction unit that corrects an image signal supplied to the image forming unit using a density correction parameter calculated by the calculation unit;
The second reading means to the lowest value of the density value group in the highest density image obtained by causing the first reading means to read the toner image formed by the image forming means based on the test pattern image signal. An execution control unit that switches the actual value of the density of the highest density image at the reading position and causes the process control unit to execute the control of the physical quantity, and then causes the calculation unit to calculate a density correction parameter. An image forming apparatus provided. The image forming apparatus according to claim 1 .
The image forming unit includes:
Toner is developed on the charging means for charging the image holding body, the exposure means for exposing the charged image holding body with light modulated according to the image signal to form a latent image, and the image holding body on which the latent image is formed. Having developing means,
The process control means includes
An image forming apparatus that controls a physical quantity that determines one or more of a charging potential of the charging unit, an exposure amount of the exposure unit, a toner supply amount of the developing unit, or a developing bias of the developing unit.

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