JP2005205613A - Image forming apparatus, image forming method and program therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which can effectively utilize an output range of an exposure means. <P>SOLUTION: This printer 10 comprises the exposure means for irradiating a photoconductor with light while performing scanning in a main scanning direction and a sub-scanning direction, an uneven density correcting means for controlling the exposure means so as to eliminate unevenness in density of an output image, and an exposure level control means for controlling the entire exposure in the main scanning direction to a desired level in accordance with an electric potential detected in a predetermined electric-potential detecting position in the main scanning direction of the photo conductor. The uneven density correcting means eliminates unevenness in density by relatively changing the exposure on the basis of reference exposure which is set at an end in the main scanning direction. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus capable of correcting density unevenness.

For example, Patent Document 1 automatically controls the intensity of a light beam to a predetermined intensity level in advance and corrects the intensity of the light beam within one main scan so as to correct density unevenness in the image area. When the image carrier is irradiated and the correction amount is changed, the intensity of the light beam at a predetermined portion of the image area or the average value of the intensity of the light beam in the main scanning direction is substantially the same before and after the change. Thus, an image forming apparatus that changes the intensity level is disclosed. Thereby, for example, it is possible to prevent the image density in the vicinity of the central portion of the image region having the highest visibility from being changed by changing the correction amount.
JP 2002-086800 A

  The present invention has been made from the above-described background, and an object thereof is to provide an image forming apparatus that effectively utilizes the output range of an exposure unit.

[Image forming apparatus]
In order to achieve the above object, an image forming apparatus according to the present invention is an image forming apparatus for forming an image, and exposure means for irradiating light to a photoconductor while scanning in a predetermined scanning direction; Density unevenness detecting means for detecting density unevenness of the image, density unevenness correcting means for controlling the exposure means to change the exposure amount based on the density unevenness detected by the density unevenness detecting means, and in the scanning direction Based on the potential detection means for detecting the potential of the photoconductor at a predetermined detection position, the potential detected by the potential detection means and the detection position of this potential, the exposure amount at a position different from the detection position is predetermined. Exposure level control means for controlling the exposure means so as to fall within the range.

  The image forming apparatus according to the present invention is an image forming apparatus that forms an image, and corrects uneven density of an image by exposing means for irradiating light to a photoconductor while scanning in a predetermined scanning direction. The exposure amount at the at least one end of the scanning range of the exposure unit is within a predetermined range based on the density unevenness correction unit that controls the exposure unit and the exposure amount that is irradiated so as to correct the density unevenness. Exposure level control means for controlling the exposure means so as to change the overall exposure amount by the exposure means.

  Preferably, the exposure level control means sets a reference exposure amount at at least one end of the scanning range of the exposure means based on the potential detected by the potential detection means and this detection position, The density unevenness detection unit controls the exposure unit to relatively change the exposure amount in the scanning direction with reference to the reference exposure amount set at the end of the scanning range by the exposure level control unit.

  Preferably, it further includes synchronization signal detection means for detecting light emitted to the predetermined position by the exposure means as a synchronization signal for image writing, and the exposure means detects the synchronization signal detected by the synchronization signal detection means. The exposure level control means determines the timing at which an image is written on the photoconductor, and the exposure level control means is configured so that an exposure amount at a predetermined position where a synchronization signal is detected by the synchronization signal detection means falls within a predetermined range. Control the exposure means.

  Preferably, the exposure level control means controls the exposure means so that an exposure amount at least at a predetermined position where the synchronization signal is detected becomes an exposure level detectable by the synchronization signal detection means.

  Preferably, the exposure unit exposes the photosensitive member while scanning in the main scanning direction and the sub-scanning direction, and the density unevenness correcting unit corrects the density unevenness in the main scanning direction and the sub-scanning direction. The exposure level control means controls the exposure amount irradiated by the exposure means and the potential detected by the potential detection means when only the density unevenness in the main scanning direction is corrected by the density unevenness correction means. And a reference exposure amount for the end portion in the main scanning direction is set based on the detected position.

  Preferably, the density unevenness correcting unit corrects the density unevenness in the sub-scanning direction by changing the reference exposure amount set by the exposure level control unit according to the density unevenness in the sub-scanning direction.

  Preferably, the exposure level control unit changes the overall exposure amount so that an exposure amount irradiated so as to correct density unevenness is equal to or less than a maximum exposure amount that can be exposed by the exposure unit.

Preferably, the apparatus further includes output control means for controlling the amount of light irradiated by the exposure means so as to fall within a desired range, and the exposure level control means is configured so that the exposure amount irradiated so as to correct density unevenness. The overall exposure level is changed so that the amount of light can be controlled by the output control means at a predetermined accuracy or higher.
Preferably, the exposure level control means is configured such that an exposure amount at at least one end of a scanning range of the exposure means obtained from a detection value by the potential detection means so as to obtain a desired potential is the maximum exposure amount. The overall exposure amount is changed so as to be 30% or more.

  Preferably, the change amount of the exposure amount by the density unevenness correction unit is uniformly adjusted over the entire main scanning direction of the exposure unit so that the exposure amount irradiated to correct the density unevenness falls within a predetermined range. And a correction amount adjusting means.

  Preferably, when the exposure amount irradiated to correct the density unevenness exceeds a predetermined range, it further includes an excess amount calculation means for calculating an excess amount at a position exceeding the range, and the correction amount adjustment The means adjusts the change amount of the exposure amount by the density unevenness correction means equally over the entire main scanning direction in accordance with the excess amount calculated by the excess amount calculation means.

  An image forming apparatus according to the present invention is an image forming apparatus that forms an image, and includes an exposure unit that irradiates light to a photoconductor while scanning in a main scanning direction and a sub-scanning direction; Density unevenness correction means for controlling the exposure means to correct unevenness, and the exposure amount change amount by the density unevenness correction means so that the exposure amount irradiated to correct density unevenness falls within a predetermined range, And a correction amount adjusting unit that adjusts uniformly over the entire main scanning direction.

  Preferably, the correction amount adjustment unit uniformly changes the exposure amount changed by the density unevenness correction unit over the entire sub-scanning direction so that the exposure amount irradiated to correct the density unevenness falls within a predetermined range. Adjust to.

  Preferably, the apparatus further includes a history storage unit that stores an adjustment history of the change amount by the correction amount adjustment unit.

  Preferably, the correction amount adjusting means is provided on the condition that when the amount of change by the density unevenness correcting means is uniformly reduced, the exposure amount irradiated to correct the density unevenness falls within a predetermined range. Gradually restore the reduced amount of change.

[Image forming method]
The image forming method according to the present invention is an image forming method in which an image is formed by exposing a photosensitive member while scanning in a predetermined scanning direction, and the potential of the photosensitive member is detected at a predetermined detection position in the scanning direction. Based on the detected potential and the detection position of this potential, a reference exposure amount is set at a position different from the detection position, density unevenness of the image is detected, and according to the detected density unevenness The exposure amount is relatively changed with reference to the set reference exposure amount.

[program]
The program according to the present invention includes a step of detecting the potential of the photosensitive member at a predetermined detection position in the scanning direction in an image forming apparatus that forms an image by exposing the photosensitive member while scanning in the predetermined scanning direction. And a step of setting a reference exposure amount at a position different from the detection position based on the detected potential and a detection position of the potential, a step of detecting density unevenness of the image, and a density unevenness detected. In response, the image forming apparatus is caused to execute a step of changing the exposure amount relative to the set reference exposure amount.

  According to the image forming apparatus of the present invention, the output range of the exposure unit can be effectively utilized.

Embodiments of the present invention will be described below.
First, the printer apparatus 10 to which the present invention is applied will be described.
FIG. 1 is a diagram illustrating a configuration of a tandem type printer device (image forming apparatus) 10.
As shown in FIG. 1, the printer device 10 includes an image reading unit 12, an image forming unit 14, an intermediate transfer device 16, a plurality of paper trays 17, a paper conveyance path 18, a fixing device 19, a controller 20, an image processing device 24, and A user interface device (UI device) 28 is included. The printer device 10 has a function as a full-color copying machine using the image reading device 12 and a function as a facsimile in addition to a printer function for printing image data received from a personal computer (not shown). It may be a multifunction machine. In this embodiment, the tandem type printer device 10 provided with a plurality of photosensitive drums 152 will be described as a specific example. However, the present invention is not limited to this, and for example, only one photosensitive drum 152 is provided. It may be a rotary type printer device provided.

First, the outline of the printer device 10 will be described. Above the printer device 10, an image reading device 12, a controller 20, an image processing device 24, and a UI device 28 are arranged. The image reading device 12 reads an image displayed on the document and outputs it to the controller 20. The controller 20 uses image data input from the image reading device 12 or image data input from a personal computer (not shown) or the like via a network line such as a LAN, and usage input via the UI device 28. Each component of the printer device 10 is controlled in accordance with an instruction from the user, and the input image is printed. The image processing device 24 performs image processing such as gradation correction and sharpness correction on the image data input via the controller 20, and outputs the image data to the image forming unit 14.
Below the image reading device 12, a plurality of image forming units 14 are arranged corresponding to the colors constituting the color image. In this example, the first image forming unit 14Y, the second image forming unit 14M, and the third image forming corresponding to each color of yellow (Y), magenta (M), cyan (C), and black (K). The unit 14 </ b> C and the fourth image forming unit 14 </ b> K are horizontally arranged at a certain interval along the intermediate transfer device 16. The intermediate transfer device 16 rotates an intermediate transfer belt 160 as an intermediate transfer member in the direction of an arrow A in the drawing, and these four image forming units 14Y, 14M, 14C, and 14K receive images input from the image processing device 20. A toner image of each color is sequentially formed based on the data, and the plurality of toner images are transferred (primary transfer) to the intermediate transfer belt 160 at a timing when they are superimposed on each other. The order of the colors of the image forming units 14Y, 14M, 14C, and 14K is not limited to the order of yellow (Y), magenta (M), cyan (C), and black (K). ), Yellow (Y), magenta (M), and cyan (C).

  The sheet conveyance path 18 is disposed below the intermediate transfer device 16. The recording paper 32a or 32b supplied from the first paper tray 17a or the second paper tray 17b is transported on the paper transport path 18 and is transferred onto the intermediate transfer belt 160 in a multiplex manner. Are transferred together (secondary transfer), and the transferred toner image is fixed by the fixing device 37 and discharged to the outside.

Next, each configuration of the printer device 10 will be described in more detail.
As shown in FIG. 1, the image reading unit 12 displays a platen glass 124 on which a document is placed, a platen cover 122 that presses the document on the platen glass 124, and an image of the document 30 placed on the platen glass 124. And an image reading device 130 for reading. The image reading apparatus 130 illuminates a document placed on the platen glass 124 with a light source 132, and reflects a reflected light image from the document into a full-rate mirror 134, a first half-rate mirror 135, and a second half-rate mirror. Scanning exposure is performed on an image reading element 138 made of a CCD or the like via a reduction optical system consisting of 136 and an imaging lens 137, and the color material reflected light image of the original 30 is given a predetermined dot density (by this image reading element 138. For example, it is configured to read at 16 dots / mm).

  The image processing device 24 performs predetermined image processing such as shading correction, document position shift correction, brightness / color space conversion, gamma correction, frame deletion, color / moving editing, and the like on the image data read by the image reading unit 12. Apply processing. The color material reflected light image of the original read by the image reading unit 12 is, for example, original reflectance data of three colors of red (R), green (G), and blue (B) (each 8 bits), By image processing by the image processing device 24, it is converted into original color material gradation data (raster data) of four colors of yellow (Y), magenta (M), cyan (C), and black (K) (8 bits each). .

The first image forming unit 14Y, the second image forming unit 14M, the third image forming unit 14C, and the fourth image forming unit 14K are arranged and formed in parallel at a certain interval in the horizontal direction. The configuration is almost the same except that the color of the image is different. Accordingly, the first image forming unit 14Y will be described below. The configuration of each image forming unit 14 is distinguished by attaching Y, M, C, or K.
The image forming unit 14Y forms an electrostatic latent image by an optical scanning device 140Y that scans a laser beam in accordance with image data input from the image processing device 24, and a laser beam scanned by the optical scanning device 140Y. And an image forming apparatus 150Y.

The optical scanning device 140Y modulates the semiconductor laser 142Y according to the yellow (Y) image data, and emits the laser light LB (Y) from the semiconductor laser 142Y according to the image data. The laser beam LB (Y) emitted from the semiconductor laser 142Y is applied to the rotary polygon mirror 146Y via the first reflection mirror 143Y and the second reflection mirror 144Y, and is deflected and scanned by the rotary polygon mirror 146Y. The light is irradiated onto the photosensitive drum 152Y of the image forming apparatus 150Y via the second reflecting mirror 144Y, the third reflecting mirror 148Y, and the fourth reflecting mirror 149Y.
The image forming apparatus 150Y includes a photosensitive drum 152Y as an image carrier that rotates at a predetermined rotation speed in the direction of arrow A, and primary charging as a charging unit that uniformly charges the surface of the photosensitive drum 152Y. For example, a developing device 156Y for developing an electrostatic latent image formed on the photosensitive drum 154Y, and a cleaning device 158Y. The photosensitive drum 152Y is uniformly charged by the scorotron 154Y, and an electrostatic latent image is formed by the laser beam LB (Y) irradiated by the optical scanning device 140Y. The electrostatic latent image formed on the photosensitive drum 152Y is developed with yellow (Y) toner by the developing unit 156Y and transferred to the intermediate transfer device 16. Residual toner, paper dust, and the like adhering to the photosensitive drum 152Y after the toner image transfer process are removed by the cleaning device 158Y. In addition, a potential detection sensor 202Y is disposed in the vicinity of the photosensitive drum 152Y. The potential detection sensor 202 detects the potential (image potential) of the electrostatic latent image formed on the surface of the photosensitive drum 152Y under the control of the controller 20, and outputs the detected image potential to the controller 20. To do. The image potential detected by the potential detection sensor 202 is used to control the exposure amount for the photosensitive drum 152Y.
The other image forming units 14M, 14C, and 14K also form magenta (M), cyan (C), and black (K) toner images in the same manner as described above, and intermediately transfer the formed toner images of the respective colors. Transfer to device 16.

The intermediate transfer device 16 is wound around the drive roll 164, the first idle roll 165, the steering roll 166, the second idle roll 167, the backup roll 168, and the third idle roll 169 with a constant tension. The intermediate transfer belt 160 (image carrier) is provided, and the drive roll 164 is rotationally driven by a drive motor (not shown), whereby the intermediate transfer belt 160 is driven to circulate at a predetermined speed in the direction of arrow A. The intermediate transfer belt 160 is formed into an endless belt shape by, for example, forming a flexible synthetic resin film such as polyimide in a band shape and connecting both ends of the synthetic resin film formed in the band shape by welding or the like. It is a thing.
Further, the intermediate transfer device 16 has a first primary transfer roll 162Y, a second primary transfer roll 162M, a third primary transfer roll 162C, and a first primary transfer roll 162Y at positions facing the image forming units 14Y, 14M, 14C, and 14K, respectively. 4 primary transfer rolls 162K, and the toner images of the respective colors formed on the photosensitive drums 152Y, 152M, 152C, and 152K are multiplex-transferred onto the intermediate transfer belt 160 by the primary transfer rolls 162. The residual toner adhering to the intermediate transfer belt 160 is removed by a cleaning blade or a brush of a belt cleaning device provided downstream of the secondary transfer position.
A toner image reading sensor 204 is disposed in the vicinity of the intermediate transfer belt 160. The toner image reading sensor 204 optically reads the toner image transferred to the intermediate transfer belt 160 and outputs the read toner image to the controller 20. The toner image read by the toner image reading sensor 204 is used for detecting the amount of misalignment of each color toner image and detecting the density of the toner image (used for toner supply control).

In the paper transport path 18, a first paper feed roller 181a and a second paper feed roller for taking out the first recording paper 42a or the second recording paper 42b from the first paper tray 17a or the second paper tray 17b. 181b, a pair of paper transport rollers 182 and a registration roll 183 that transports the recording papers 42a and 42b to the secondary transfer position at a predetermined timing.
In addition, a secondary transfer roll 185 that is in pressure contact with the backup roll 168 is disposed at the secondary transfer position on the paper transport path 18, and each color toner image transferred onto the intermediate transfer belt 16 is Secondary transfer is performed on the recording paper 42 a or 42 b by the pressing force and electrostatic force of the secondary transfer roll 185. The recording paper 42 a or 42 b on which the toner image of each color is transferred is transported to the fixing device 19 by the two transport belts 186.
The fixing device 19 melts and fixes the toner to the recording paper 42a or 42b by performing a heating process and a pressurizing process on the recording paper 42a or 42b on which the toner images of the respective colors are transferred.
Further, a carry-out path 187 is provided downstream of the fixing device 19, and an image reading sensor 206 is disposed in the vicinity of the carry-out path 187. The image reading sensor 206 reads an image from the recording paper 42 conveyed through the carry-out path 187 and outputs the read image to the controller 20. The image read by the image reading sensor 206 is used for detecting density unevenness in the output image and measuring the color balance after fixing.

FIG. 2 is a diagram illustrating a mechanism for synchronizing the writing timing of image data by the image processing device 24 with the scanning timing by the optical scanning device 140.
As shown in FIG. 2, two pickup mirrors 212a and 212b are disposed at both ends of the irradiation position of the laser beam deflected and scanned by the polygon mirror 146Y. The first pickup mirror 212a is disposed in the vicinity of the laser beam scanning start end (SOS: Start Of Scan). The laser beam picked up by the first pickup mirror 212a is detected as an SOS signal by the SOS sensor 214Y. The second pickup mirror 212b is disposed in the vicinity of the end of scanning end (EOS: End Of Scan) of the laser beam. The laser beam picked up by the second pickup mirror 212b is detected as an EOS signal by the EOS sensor 216Y. The printer device 10 detects laser light at least one of the scanning start side end (that is, the writing start position) and the scanning end side end, and detects the scanning timing in the main scanning direction by the polygon mirror 146Y. The scanning timing and the output timing of the image data by the image processing device 24 are synchronized.

[background]
Next, the background of the present invention and the outline of the present invention will be described.
3 and 4 are diagrams illustrating a correction profile in the main scanning direction for correcting density unevenness.
As illustrated in FIG. 3, the printer device 10 detects the density unevenness of the output image based on the image read by the image reading sensor 206 (FIG. 1), and performs main scanning so as to cancel the detected density unevenness. A light irradiation pattern (correction profile) that changes the exposure amount within the range or the sub-scanning range is generated. The optical scanning device 140 changes the amount of light to be irradiated (exposure amount) according to the generated correction profile to reduce density unevenness in the output image.
This density unevenness includes sensitivity unevenness of the photosensitive drum 152 (FIG. 1), exposure amount unevenness of the optical scanning device 140, distance fluctuation between the photosensitive drum 152 and the developing sleeve formed by the developing unit 156, or primary transfer or It occurs due to transfer unevenness in the secondary transfer. Accordingly, the density unevenness fluctuates due to an environmental change, a change with time of each component, and the like, and the printer apparatus 10 needs to change the correction profile accordingly (in this example, from “previous correction profile” to “ Change to "This correction profile").
On the other hand, the printer device 10 changes the amount of exposure by the optical scanning device 140 based on the potential detected by the potential detection sensor 202 in order to keep the image density of the output image substantially constant. The potential detection sensor 202 detects the image potential near the center of the photosensitive drum 152 in the main scanning direction in order to detect the density of the output image. Therefore, the printer apparatus 10 changes the overall exposure amount (exposure level) so as to keep the image potential at the center in the main scanning direction substantially constant.
As described above, the printer device 10 changes the exposure amount by the optical scanning device 140 from different viewpoints of eliminating density unevenness and equalizing image density. For this reason, an exposure amount that exceeds the maximum exposure amount that can be output by the optical scanning device 140 may be required, as in “current correction profile A” in FIG. 3.

  In addition, as illustrated in FIG. 4, the printer device 10 determines the overall exposure level based on the image potential detected at the potential detection position by the potential detection sensor 202, and further determines the exposure amount according to the correction profile. Is changed, the light amount becomes insufficient at the detection position (end in the main scanning direction) of the SOS sensor 214 (FIG. 2) or the EOS sensor 216 (FIG. 2), and the SOS signal or EOS signal may not be detected.

Therefore, the printer apparatus 10 according to the present embodiment adjusts the overall exposure level in the main scanning direction and the sub-scanning direction with reference to the end portion in the main scanning direction (position other than the potential detection position), and this end. The exposure amount is adjusted according to the correction profile with reference to the portion.
As a result, as long as the amount of light that can be detected by the SOS signal is guaranteed, the printer device 10 can make maximum use of the output range (exposure amount fluctuation range) of the optical scanning device 140.
The density unevenness correction is realized by a change in relative exposure amount in the main scanning direction and the sub-scanning direction, and the absolute exposure amount does not cause a problem. The overall image density can be adjusted by data processing of image data, development processing, transfer processing, and the like. For this reason, as in “current correction profile B” illustrated in FIG. 3, the exposure amount is small except at the end portion in the main scanning direction (center portion), and even if it falls below the detection lower limit light amount of the SOS signal, there is no problem. .

[Embodiment]
Next, this embodiment will be described more specifically.
FIG. 5 is a diagram illustrating a functional configuration of the image processing device 24.
As illustrated in FIG. 5, the image processing apparatus 24 includes a test pattern generation unit 240, an I / O control unit 242, a screen processing unit 244, an image correction unit 246, a timing control unit 248, a write control unit 250, and an output control unit. 252, a density unevenness correction unit 260, a density unevenness calculation unit 262, a correction amount calculation unit 264, a correction amount adjustment unit 266, and an exposure level control unit 270.
Each of the above components included in the image processing device 24 may be realized in software by a CPU, a memory, a program, or the like, or may be realized in hardware by an ASIC or the like.

The test pattern generation unit 240 generates test pattern image data under the control of the controller 20, and outputs the generated test pattern image data to the screen processing unit 244. This test pattern is read by the potential detection sensor 202 (FIG. 1), the toner image reading sensor 204 (FIG. 1) or the image reading sensor 206 (FIG. 1) to detect the image potential, detect the image displacement, or , And used for toner image density detection (control of toner supply from the toner cartridge to the developing device).
The I / O control unit 242 acquires image data of an input image input from the image reading unit 12 or the client terminal via the controller 20, and outputs the acquired image data to the screen processing unit 244.

The screen processing unit 244 performs screen processing on the input image data, converts multi-value image data into binary image data, and outputs the converted image data to the image correction unit 246. .
The image correction unit 246 performs image processing such as gradation correction (including density correction) and sharpness correction on the input image data, and outputs the processed image data to the writing control unit 250.
The timing control unit 248 generates a synchronization signal for controlling the writing timing of the image data based on the SOS signal input from the SOS sensor 214 (FIG. 2), and sends the generated synchronization signal to the writing control unit 250. Output.

The writing control unit 250 controls the optical scanning device 140 (FIG. 1) to form an electrostatic latent image on the surface of the photosensitive drum 152 (FIG. 1). Specifically, the writing control unit 250 corresponds to the image data (binary pattern) for one main scanning line input from the image correction unit 246 in synchronization with the synchronization signal input from the timing control unit 248. A pulse signal is generated, and the generated pulse signal is output to the optical scanning device 140.
The output control unit 252 performs control so that the laser light amount output from the optical scanning device 140 becomes a desired output level. Note that there is a lower limit to the amount of laser light that can be controlled by the output control unit 252. The lower limit of the laser light amount is, for example, approximately 30% of the maximum light amount that can be output by the optical scanning device 140, and the printer device 10 has an exposure amount that is larger than the lower limit (approximately 30% of the maximum light amount). It is desirable to adjust the correction profile.

  The density unevenness correction unit 260 detects density unevenness based on the image read by the image reading sensor 206, creates a correction profile according to the detected density unevenness, and outputs the correction profile to the writing control unit 250. The writing control unit 250 locally changes the exposure amount by the optical scanning device 140 in the main scanning direction and the sub-scanning direction according to the correction profile input from the density unevenness correction unit 260. Here, “locally changing the exposure amount” means changing the exposure amount relatively within the main scanning range or the sub-scanning range. On the other hand, “changing the exposure amount as a whole” means changing the exposure amount of the entire main scanning range or the entire sub-scanning range uniformly. For example, when changing the exposure amount uniformly (exposure amount A case where the level is changed) and a case where the exposure amount is uniformly changed at a constant rate.

Specifically, the density unevenness correction unit 260 includes a density unevenness calculation unit 262, a correction amount calculation unit 264, and a correction amount adjustment unit 266. The density unevenness calculation unit 262 detects image density unevenness based on the image data input from the image reading sensor 206, and outputs the detected density unevenness amount to the correction amount calculation unit 264.
The correction amount calculation unit 264 calculates a correction amount having a phase opposite to the density unevenness based on the density unevenness amount input from the density unevenness calculation unit 262, and the correction amount adjustment unit 266 uses the calculated correction amount as a correction profile. Output for.
The correction amount adjustment unit 266 determines whether or not the correction profile input from the correction amount calculation unit 264 falls within a predetermined range. If the correction profile does not fit, the correction amount adjustment unit 266 performs adjustment so that the correction profile falls within this range.

The exposure level control unit 270 makes the potential of the electrostatic latent image formed on the photosensitive drum 152 (FIG. 1) substantially constant according to the image potential input from the potential detection sensor 202 (FIG. 1). The output level (exposure level) of the optical scanning device 140 is controlled (hereinafter referred to as exposure level control processing). The writing control unit 250 adjusts the output level of the optical scanning device 140 in accordance with the control by the exposure level control unit 270 and makes the overall density of the output image substantially constant.
Further, the exposure level control unit 270 sets a reference exposure amount that is a reference for density unevenness correction processing. That is, the density unevenness correction unit 260 cancels the density unevenness of the output image by changing the exposure amount relative to the reference exposure amount set at the default position by the exposure level control unit 270.

FIG. 6 is a diagram illustrating an example of a region unit in which the correction amount is set by the density unevenness correction unit 260.
As illustrated in FIG. 6, the surface of the photosensitive drum 152 is divided into six parts in the main scanning direction, and “0” to “5” are sequentially assigned from the writing position, and one round is divided into 16 parts in the sub-scanning direction. Thus, “0” to “15” are assigned to the sub-scanning direction (that is, the rotation direction of the photosensitive drum 152).
The density unevenness correction unit 260 of this example uses exposure unit increase / decrease data (a rate of increase / decrease based on the exposure amount at the reference position) with the region unit in the main scanning direction “0” and the sub-scanning direction “0” as the reference position. Set for each area.

FIG. 7 is a diagram illustrating a test pattern formed on the photosensitive drum 152 and a position where the test pattern is detected.
As illustrated in FIG. 7, the optical scanning device 140 (FIG. 1) corresponding to each color corresponds to the electrostatic latent image of the corresponding color patch 422 and the electrostatic latent images of the plurality of misregistration patches 424. To be written in the non-printing area of the photosensitive drum 152. The non-printing area is an area (so-called inter-image) other than an area (printing area) where an output image (image printed on recording paper) is formed. The size of the non-printing area is common to the image forming units 14 and corresponds to the non-printing area on the intermediate transfer belt 160 (FIG. 1).

The color patch 422 is read on the photosensitive drum 152 by the potential sensor 202 (FIG. 1) and used to detect the image potential, and the density is detected on the intermediate transfer belt 160 by the toner image reading sensor 204 (FIG. 1). Used to control the toner supply amount. Therefore, each color patch 422 is formed in a substantially central portion (region other than the end portion) in the main scanning direction that has a large influence on the visibility of the output image, and the potential sensor 202 and the toner reading sensor 204 are substantially in the center in the main scanning direction. This color patch 204 is detected by the unit.
The misregistration patch 424 is read on the intermediate transfer belt 160 by the toner image reading sensor 204 and used to detect misregistration.
It should be noted that the density unevenness of the output image is detected based on a full-halftone test image printed on the recording paper 42. The entire halftone test image is read by the image reading sensor 206 or the image reading unit 12 in a state of being formed on the recording paper 42.

As described above, the test pattern (color patch 422, misregistration patch 424, etc.) formed on the photosensitive drum 152 is for the purpose of improving the image quality of the output image. , Regions other than the end in the main scanning direction).
The exposure level control unit 270 then determines the reference position (that is, the end in the main scanning direction) based on the positional relationship between the test pattern reading position (that is, the detection position of the color patch 422) and the end in the main scanning direction. ) Is set.

FIG. 8 is a flowchart of exposure amount setting processing (S10) by the printer apparatus 10.
As shown in FIG. 8, in step 100 (S100), the controller 20 (FIG. 1) instructs the image processing device 24 to adjust the exposure amount for the purpose of correcting density unevenness.
A test pattern generation unit 240 (FIG. 5) in the image forming apparatus 24 generates image data of a test pattern (such as a color patch 422) and outputs it to the screen processing unit 244. The screen processing unit 244 (FIG. 5) performs screen processing on the image data (test pattern) input from the test pattern generation unit 240 and outputs it to the image correction unit 246. The image correction unit 246 (FIG. 5) performs image correction processing such as gradation correction on the image data (test pattern) input from the screen processing unit 244, and outputs it to the writing control unit 250. The writing control unit 250 (FIG. 5) controls each optical scanning device 140 (FIG. 1) to write a test pattern in the non-printing area (FIG. 7) of the photosensitive drum 152.
The test pattern written on the photosensitive drum 152 is developed into a toner image by the developing unit 156 and transferred to the intermediate transfer belt 160.

In step 110 (S110), the potential detection sensor 202 (FIG. 1) detects the potential of the test pattern (that is, the image potential) written on the photosensitive drum 152, and uses the detected image potential as the exposure level control unit 270. (FIG. 5) is output.
In step 120 (S120), the exposure level control unit 270 determines a target exposure amount at the detection position of the image potential based on the image potential input from the potential detection sensor 202. In this example, the detection position of the image potential (that is, the arrangement position of the potential detection sensor 202) is 42% from the left end (upstream side in the scanning direction) of the region unit in the main scanning direction “3” illustrated in FIG. A specific example is the case of the position.

In step 130 (S130), the image reading sensor 206 (FIG. 1) reads the entire halftone test image printed on the recording paper 42, and the image data of the read test image is used as the density unevenness correction unit 260 (FIG. 5). ).
The density unevenness calculation unit 262 in the density unevenness correction unit 260 calculates the density unevenness in each region unit based on the image data of the test image input from the image reading sensor 206, and the calculated density unevenness is a correction amount calculation unit. H.264 is output.
In step 140 (S140), the correction amount calculation unit 264 creates a correction profile that cancels out the density unevenness based on the density unevenness in each region unit input from the density unevenness calculation unit 262. The created correction profile is the exposure amount increase / decrease rate set for each region unit, and the optical scanning device 140 increases / decreases the exposure amount according to the increase / decrease rate set for each region unit. become.

In step 150 (S150), the exposure level control unit 270 determines from the detection position to the reference position (ie, the main position in FIG. 6) based on the correction profile created by the correction amount calculation unit 254 and the detection position of the image potential. The amount of correction up to the scanning direction “0” (unit of area) is calculated for each main scanning line.
For example, when the correction profile of each area unit in the main scanning directions “0” to “3” is “−5%”, “−4%”, “+ 3%”, and “+ 3%”, respectively, the exposure level The control unit 270 calculates the correction amount as follows.
(Correction amount) = (− 5%) + (− 4%) + (+ 3%) + (+ 3%) * 0.42 = −4.7%

In step 160 (S160), the exposure level control unit 270, based on the target exposure amount set for the detection position of the image potential and the correction amount (-4.7%) from the detection position to the reference position, An exposure amount at the reference position (that is, a reference exposure amount) is calculated. Specifically, the exposure level control unit 270 calculates the reference exposure amount using the following formula.
(Reference exposure amount) = (target exposure amount at detection position) / {100+ (correction amount from detection position to reference position)} * 100
For example, when the target exposure amount set at the image potential detection position is 800,
(Reference exposure) = 800 / (100-4.7) * 100 = 839.45
Thus, the exposure level control unit 270 sets the exposure amount (839.45) as the reference exposure amount with respect to the reference position.

  In step 170 (S170), the exposure level control unit 270 determines that the reference exposure amount is within a predetermined allowable range (that is, the minimum exposure amount that the SOS sensor 214 can detect and the maximum exposure amount that the optical scanning device 140 can output). Or less). When the reference exposure amount is outside the allowable range, the printer apparatus 10 proceeds to the process of S180, and when the reference exposure amount is within the allowable range, the process (S10) is ended.

In step 180 (S180), the exposure level control unit 270 changes the reference exposure amount so as to fall within the allowable range, and sets the changed reference exposure amount.
As described above, when the reference exposure amount and the correction profile are set, the writing control unit 250 sets the reference exposure amount (in the main scanning direction “0” and the sub-scanning direction “0”) set by the exposure level control unit 270. The image data of the input image is written on the photosensitive drum 152 while increasing or decreasing the exposure amount according to the correction profiles in the main scanning direction and the sub-scanning direction with reference to the exposure amount in the region unit. In other words, the printer 10 uses the exposure amount set at the reference position by the exposure level control unit 270 as a reference, and the correction profile in the sub-scanning direction (that is, the main scanning direction “0” and the sub-scanning directions “0” to “0” to “ The exposure amount at the writing position is determined according to the increase / decrease amount set in the area unit of 15 ”, and the exposure amount is changed according to the correction profile in the main scanning direction with reference to the exposure amount at the writing position, Perform main scanning.

As described above, the printer apparatus 10 according to the present embodiment sets the reference exposure amount at the end portion (detection position of the SOS signal) in the main scanning direction, and performs density unevenness correction using the reference exposure amount as a reference. The exposure amount required for detecting the SOS signal is ensured.
Further, the printer device 10 can freely change the overall exposure level as long as the exposure amount necessary for detecting the SOS signal is ensured, and can effectively utilize the output range of the optical scanning device 140.

[Limit processing]
Next, as a result of applying the reference exposure amount and the correction profile by the printer device 10, the correction amount adjustment method when the exposure amount exceeds the allowable range (the range from the minimum exposure amount to the maximum exposure amount of the optical scanning device 140) ( Limit processing) will be described.
The printer device 10 according to the present embodiment adjusts the correction amount (for example, the increase / decrease rate of the correction profile) in the image unevenness correction substantially equally in the main scanning direction, the sub-scanning direction, or both with reference to the reference exposure amount. Specifically, the correction amount adjusting unit 266 uniformly reduces the correction amount in the density unevenness correction in the main scanning direction and the entire sub-scanning direction so that the reference exposure amount does not change.
As described above, the printer device 10 reduces the correction amount of the density unevenness correction uniformly for the entire image area, thereby preventing the image quality degradation caused by the incomplete application of the density unevenness correction from being locally revealed. .

FIG. 9 is a diagram schematically illustrating a correction amount adjustment method (upper limit processing) when the exposure amount exceeds the maximum exposure amount of the optical scanning device 140.
As shown in FIG. 9, the correction amount adjusting unit 266 uniformly reduces the relative change amount of the exposure amount based on the reference exposure amount (that is, the absolute value of the increase / decrease rate of the correction profile). In this example, the correction amount adjusting unit 266 reduces the exposure amount exceeding the reference exposure amount at the same ratio for the entire image so as not to exceed the maximum exposure amount, and at the same time, reduces the exposure amount below the reference exposure amount to the image. It will increase at the same rate for the whole. Thereby, the printer apparatus 10 prevents the brightness of the entire image from changing.
In this case, the correction amount adjustment unit 266 adjusts the exposure amount of the region unit that most exceeds the maximum exposure amount to a value that is smaller than the maximum exposure amount by a predetermined buffer amount.
The correction amount adjustment unit 266 specifies the region unit that most exceeds the maximum exposure amount, calculates the excess amount of the specified region unit, and subtracts the calculated excess amount from the absolute value of the density unevenness correction amount. Thus, the correction amount limit processing may be realized. At that time, by subtracting the excess amount from the absolute value of the correction amount of density unevenness correction, the absolute value may become a negative value. In this case, the correction amount adjustment unit 266, for example, calculates the absolute value. “0”.

FIG. 10 is a flowchart showing correction amount adjustment processing (S20) when the exposure amount exceeds the maximum exposure amount.
As shown in FIG. 10, in step 200 (S200), the correction amount adjustment unit 266 applied the reference exposure amount set by the exposure level control unit 270 and the correction profile created by the correction amount calculation unit 264. In this case, the exposure amount in the whole area unit is calculated.
In step 210 (S210), the correction amount adjustment unit 266 detects the maximum exposure amount from the calculated exposure amounts for all regions.

  In step 220 (S220), the correction amount adjustment unit 266 determines whether or not the maximum exposure amount exceeds the allowable range (that is, the maximum exposure amount that can be output by the optical scanning device 140). When the maximum exposure amount exceeds the allowable range, the printer device 10 proceeds to the process of S230, and when the maximum exposure amount is within the allowable range, the process (S20) ends.

In step 230 (S230), the correction amount adjustment unit 266 calculates a difference value (excess amount) between the maximum exposure amount and the upper limit of the allowable range (that is, the maximum exposure amount of the optical scanning device 140). The adjusted exposure amount is calculated from the excess amount and the predetermined buffer amount.
Further, the correction amount adjusting unit 266 calculates an adjustment ratio based on the maximum exposure amount and the adjusted exposure amount.
Specifically, the correction amount adjustment unit 266 calculates the adjustment ratio using the following equation.
(Adjustment ratio) = {(Exposure after adjustment) − (Reference exposure)} / {(Maximum exposure) − (Reference exposure)} * 100

  In step 240 (S240), the correction amount adjustment unit 266 determines whether or not the exposure amount setting process is accompanied by gradation correction. If the exposure amount setting process is not accompanied by gradation correction, the correction amount adjustment unit 266 determines that the exposure amount setting process is not performed. If the exposure amount setting process is accompanied by tone correction, the process proceeds to S270. Here, the exposure amount setting process with gradation correction is based on the potential setup for controlling the charging condition and the exposure condition so that the image potential and the charging potential become the target potential, and the gradation detected by the test pattern. This is a setup including gradation control for adjusting the gradation conversion coefficient applied by the image correction unit 246. Since the gradation control is performed based on the formed test pattern, it is possible to correct density unevenness that cannot be corrected by adjusting the exposure amount.

  In step 250 (S250), the correction amount adjustment unit 266 compares the calculated excess amount (difference value between the maximum exposure amount and the maximum exposure amount of the optical scanning device 140) with a predetermined adjustment unit, and exceeds it. When the amount is larger than the adjustment unit, the process proceeds to S260, and when the excess amount is equal to or less than the adjustment unit, the process proceeds to S270. Here, the adjustment unit is a unit for adjusting the correction amount by one exposure amount setting process, as will be described later.

  In step 260 (S260), each time the exposure level control process is performed by the exposure level control unit 270 so that the image potential becomes the target potential, the correction amount adjustment unit 266 performs an exposure amount change amount (unit of adjustment unit). That is, the density unevenness correction amount) is adjusted. Specifically, the correction amount adjustment unit 266 changes the exposure amount when the reference exposure amount is used as a reference (that is, the correction amount for density unevenness) so that the maximum exposure amount is decreased by a predetermined adjustment unit. The absolute value of is reduced by the same ratio as a whole. As described above, when printing is in progress, the printer 10 reduces density unevenness correction in a continuously printed image by gradually reducing the density unevenness correction amount each time exposure level control processing is performed. Make volume fluctuations inconspicuous.

  In step 270 (S270), the correction amount adjustment unit 266 decreases the absolute value of the density unevenness correction amount by the calculated adjustment ratio in the exposure amount setting process with gradation correction. As described above, when the absolute value of the density unevenness correction amount is decreased, the density unevenness correction by the density unevenness correction unit 260 becomes insufficient. This is because the gradation conversion coefficient used by the image correction unit 246 is adjusted. Therefore, the density unevenness of the output image is eliminated.

  In step 280 (S280), when the absolute value of the density unevenness correction amount is decreased, the correction amount adjustment unit 266 stores the fact and the decrease amount in a memory (not shown) as an adjustment history. . This adjustment history is used when restoring the decrease in the density unevenness correction amount.

FIG. 11 is a diagram schematically illustrating a correction amount adjustment method (lower limit processing) when the exposure amount is less than the minimum exposure amount of the optical scanning device 140. FIG. 11A illustrates the sub-scanning direction. FIG. 11B illustrates an adjustment method in the main scanning direction.
As shown in FIG. 11, the correction amount adjustment unit 266 makes a relative change amount of the exposure amount based on the reference exposure amount (that is, correction) so that the exposure amount in all the region units is equal to or larger than the minimum exposure amount. The absolute value of the rate of increase / decrease of the profile is reduced evenly. Thereby, the printer apparatus 10 prevents the brightness of the entire image from changing.

Further, as shown in FIG. 11A, the correction amount adjustment unit 266 corrects density unevenness in the sub-scanning direction (that is, in the unit units of the main scanning direction “0” and the sub-scanning directions “0” to “15”). When the correction amount is adjusted, the correction amount is adjusted so that it does not fall below the minimum exposure amount (in this case, the minimum exposure amount necessary for detecting the SOS signal) for all the sub-scanning positions.
On the other hand, as shown in FIG. 11B, the correction amount adjustment unit 266 allows the amount of exposure less than the minimum exposure amount in units other than the writing position when adjusting the correction amount of density unevenness correction in the main scanning direction. Thus, the correction amount is not adjusted.
That is, the printer device 10 according to the present embodiment performs only the adjustment in the sub-scanning direction when adjusting the correction amount for density unevenness correction with respect to the minimum exposure amount.

FIG. 12 is a flowchart showing a correction amount adjustment process (S22) when the exposure amount falls below the minimum exposure amount. It should be noted that among the processes in this figure, the same reference numerals are assigned to the processes that are substantially the same as those shown in FIG.
As shown in FIG. 12, in step 215 (S215), the correction amount adjustment unit 266 detects the minimum exposure amount from the calculated exposure amounts for all regions.

  In step 225 (S225), the correction amount adjustment unit 266 determines whether or not the minimum exposure amount is below the allowable range (that is, the minimum exposure amount necessary for detecting the SOS signal). When the minimum exposure amount falls below the allowable range, the printer apparatus 10 proceeds to the process of S230, and when the maximum exposure amount is within the allowable range, the process (S22) ends.

In step 235 (S235), the correction amount adjustment unit 266 calculates a difference value (excess amount) between the minimum exposure amount and the lower limit of the allowable range (that is, the minimum exposure amount necessary for detecting the SOS signal), An adjusted exposure amount is calculated from the calculated excess amount and a predetermined buffer amount.
Further, the correction amount adjusting unit 266 calculates an adjustment ratio based on the minimum exposure amount and the adjusted exposure amount.
Specifically, the correction amount adjustment unit 266 calculates the adjustment ratio using the following equation.
(Adjustment ratio) = {(Reference exposure)-(Adjusted exposure)} / {(Reference exposure)-(Minimum exposure)} * 100

  Thereafter, the printer apparatus 10 adjusts the correction amount of the density unevenness correction so that the minimum exposure amount falls within the allowable range by substantially the same processing as S240 to S270 shown in FIG.

[Reset processing]
Next, when the allowable range of the exposure amount is widened by the printer device 10 (for example, when the photosensitivity of the photosensitive drum 152 is improved and the maximum exposure amount is increased as the internal temperature increases), the limit is reached. A return method (reset process) for returning the correction amount suppressed in the process will be described.

FIG. 13 is a diagram schematically illustrating a return method (reset process) when the maximum exposure amount of the optical scanning device 140 increases.
As illustrated in FIG. 13, when the correction amount adjustment unit 266 detects an increase in the maximum exposure amount, the correction value adjustment unit 266 equalizes the absolute value of the density unevenness correction amount by a predetermined amount (for example, a ratio corresponding to the adjustment unit) for all region units. Increase to. Therefore, the exposure amount spreads upward and downward around the reference exposure amount by this return processing. The reset process is performed in the main scanning direction and the sub scanning direction. Specifically, the reset process in the main scanning direction is performed when the maximum exposure amount is relatively increased with reference to the reference exposure amount, and is reset in the sub-scanning direction (that is, in units of areas in the main scanning direction “0”). Processing is performed when the minimum exposure amount (exposure amount capable of detecting the SOS signal) is relatively lowered with reference to the reference exposure amount.

FIG. 14 is a flowchart of the correction amount return processing (S30) by the correction amount adjustment unit 266.
As shown in FIG. 14, in step 300 (S300), when the correction amount adjustment unit 266 detects that the allowable range has been expanded, an adjustment history (density unevenness correction amount in limit processing) stored in a memory (not shown). (Decrease amount of absolute value). Hereinafter, the decrease amount read out as the adjustment history is referred to as “suppression amount”.
In step 310 (S310), the correction amount adjusting unit 266 determines whether or not the density unevenness correction amount remains adjusted (suppressed) based on the read adjustment history, and performs density unevenness correction. If the correction amount remains suppressed, the process proceeds to S320, and the return processing is performed when the correction amount for density unevenness correction is not suppressed, or once it has been suppressed but is completely recovered thereafter. (S30) is terminated.

  In step 320 (S320), the correction amount adjustment unit 266 determines whether or not there is a predetermined buffer between the current exposure amount and the allowable range. If there is no buffer larger than the predetermined amount, the process proceeds to S360.

  In step 330 (S330), the correction amount adjustment unit 266 determines whether or not the exposure amount setting process is accompanied by gradation correction. If the exposure amount setting process is not accompanied by gradation correction, the correction amount adjustment unit 266 determines that the exposure amount setting process is not performed. If the exposure amount setting process is accompanied by tone correction, the process proceeds to S360.

  In step 340 (S340), the correction amount adjustment unit 266 compares the suppression amount read as the adjustment history with a predetermined adjustment unit, and when the suppression amount is larger than the adjustment unit, the process proceeds to S350. If the suppression amount is equal to or smaller than the adjustment unit, the process proceeds to S360. In other words, when the suppression amount is equal to or less than the predetermined value (adjustment unit), the printer device 10 does not return the density unevenness correction amount until the exposure amount setting process with gradation correction is performed.

  In step 350 (S350), the correction amount adjustment unit 266 restores the correction amount of density unevenness by an adjustment unit every time exposure level control processing is performed. Specifically, the correction amount adjustment unit 266 changes the exposure amount when the reference exposure amount is used as a reference (that is, density unevenness so that the maximum absolute value of the density unevenness correction amount increases by a predetermined adjustment unit. The absolute value of the correction amount) is increased at the same ratio as a whole. As described above, when printing is in progress, the printer 10 restores the density unevenness correction amount little by little every time exposure level control processing is performed, thereby correcting density unevenness in continuously printed images. Make volume fluctuations inconspicuous.

In step 360 (S360), the correction amount adjustment unit 266 calculates a difference value between the maximum value of the current exposure amount and the upper limit of the allowable range, and a predetermined ratio (greater than 0) with respect to the calculated difference value. The return amount is determined by multiplying by a value less than 1. This ratio is set so that density fluctuation and color fluctuation are not affected by restoration of the correction amount of density unevenness correction.
The correction amount adjustment unit 226 increases the absolute value of the density unevenness correction amount by the determined return amount in the exposure amount setting process with gradation correction.

  In step 370 (S370), when the correction amount adjustment unit 266 returns the absolute value of the density unevenness correction amount, the correction amount is subtracted from the suppression amount (decrease amount) stored as the adjustment history. Then, the adjustment history stored in the memory (not shown) is updated.

  As described above, the correction amount adjustment unit 266 returns the suppressed density unevenness correction amount when the allowable range of the exposure amount is expanded.

1 is a diagram illustrating a configuration of a tandem type printer apparatus (image forming apparatus) 10. FIG. FIG. 6 is a diagram for explaining a mechanism for synchronizing image data writing timing by the image processing device 24 with scanning timing by the optical scanning device 140. It is a figure which illustrates the correction profile (when exceeding the maximum exposure amount) for the main scanning direction for correcting density unevenness. It is a figure which illustrates the correction profile (when it is less than the detection lower limit light quantity of a SOS signal) for the main scanning direction for correct | amending density unevenness. 3 is a diagram illustrating a functional configuration of an image processing device 24. FIG. FIG. 6 is a diagram exemplifying a region unit in which a correction amount is set by a density unevenness correction unit 260. FIG. 6 is a diagram illustrating a test pattern formed on the photosensitive drum 152 and a position where the test pattern is detected. 6 is a flowchart of exposure amount setting processing (S10) by the printer device 10; It is a figure which illustrates typically the adjustment method of the correction amount in case an exposure amount exceeds the maximum exposure amount of the optical scanning device 140. FIG. It is a flowchart which shows the adjustment process (S20) of the correction amount when the exposure amount exceeds the maximum exposure amount. It is a figure which illustrates typically the adjustment method of the amount of correction | amendment when an exposure amount is less than the minimum exposure amount of the optical scanning apparatus 140, (A) demonstrates the adjustment method of a subscanning direction, (B) An adjustment method in the main scanning direction will be described. It is a flowchart which shows the adjustment process (S22) of correction amount when an exposure amount is less than the minimum exposure amount. It is a figure which illustrates typically the return method when the maximum exposure amount of the optical scanning device 140 becomes large. It is a flowchart of the correction amount return processing (S30) by the correction amount adjustment unit 266.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Printer apparatus 14 ... Image forming unit 16 ... Intermediate transfer apparatus 17 ... Paper tray 18 ... Paper conveyance path 19 ... Fixing device 24 ... Image processing apparatus 202 ... Potential detection sensor 204... Toner image reading sensor 206... Image reading sensor 240... Test pattern generation unit 242... I / O control unit 244 ... Screen processing unit 246. ... Timing control unit 250 ... Write control unit 252 ... Output control unit 260 ... Density unevenness correction unit 262 ... Density unevenness calculation unit 264 ... Correction amount calculation unit 266 ... Correction amount Adjustment unit 270 ... Exposure level control unit

Claims (18)

An image forming apparatus for forming an image,
Exposure means for irradiating the photosensitive member with light while scanning in a predetermined scanning direction;
Density unevenness detecting means for detecting density unevenness of the image;
Density unevenness correcting means for controlling the exposure means to change the exposure amount based on the density unevenness detected by the density unevenness detecting means;
A potential detecting means for detecting a potential of the photosensitive member at a predetermined detection position in the scanning direction;
An exposure level control means for controlling the exposure means so that an exposure amount at a position different from the detection position falls within a predetermined range based on the potential detected by the potential detection means and the detection position of the potential; An image forming apparatus. An image forming apparatus for forming an image,
Exposure means for irradiating the photosensitive member with light while scanning in a predetermined scanning direction;
Density unevenness correcting means for controlling the exposure means to correct image density unevenness;
Based on the exposure amount irradiated so as to correct the density unevenness, the overall exposure amount by the exposure unit is set so that the exposure amount at at least one end of the scanning range of the exposure unit falls within a predetermined range. An image forming apparatus comprising: an exposure level control unit that controls the exposure unit to change. The exposure level control means sets a reference exposure amount at at least one end of the scanning range of the exposure means based on the potential detected by the potential detection means and the detection position;
2. The density unevenness detection unit controls the exposure unit to relatively change an exposure amount in a scanning direction with reference to a reference exposure amount set at an end of a scanning range by the exposure level control unit. The image forming apparatus described in 1. Synchronization signal detecting means for detecting the light emitted to the predetermined position by the exposure means as a synchronization signal for image writing;
The exposure unit determines a timing for writing an image on the photoconductor based on the synchronization signal detected by the synchronization signal detection unit;
The image forming apparatus according to claim 1, wherein the exposure level control unit controls the exposure unit such that an exposure amount at a predetermined position where the synchronization signal is detected by the synchronization signal detection unit falls within a predetermined range. The image formation according to claim 4, wherein the exposure level control unit controls the exposure unit so that an exposure amount at least at a predetermined position where the synchronization signal is detected becomes an exposure level detectable by the synchronization signal detection unit. apparatus. The exposure means exposes the photoreceptor while scanning in the main scanning direction and the sub-scanning direction,
The density unevenness correcting unit controls the exposure unit to correct density unevenness in the main scanning direction and the sub-scanning direction,
The exposure level control means detects the exposure amount irradiated by the exposure means when the density unevenness correction means corrects only density unevenness in the main scanning direction, the potential detected by the potential detection means, and this detection. The image forming apparatus according to claim 3, wherein a reference exposure amount for an end portion in the main scanning direction is set based on the position. The density unevenness correcting unit corrects the density unevenness in the sub-scanning direction by changing the reference exposure amount set by the exposure level control unit according to the density unevenness in the sub-scanning direction. Image forming apparatus. The exposure level control unit changes the overall exposure amount so that an exposure amount irradiated so as to correct density unevenness is equal to or less than a maximum exposure amount that can be exposed by the exposure unit. The image forming apparatus according to any one of the above. Output control means for controlling the amount of light irradiated by the exposure means to fall within a desired range;
The exposure level control means changes an overall exposure level so that an exposure amount irradiated so as to correct density unevenness is not less than a light amount that can be controlled by the output control means with a predetermined accuracy or more. The image forming apparatus according to any one of 1 to 8. The image forming apparatus according to claim 9, wherein the exposure level control unit changes the overall exposure amount so that an exposure amount irradiated so as to correct density unevenness is 30% or more of the maximum exposure amount. . Correction amount adjustment that adjusts the exposure amount change amount by the density unevenness correction unit evenly over the entire main scanning direction of the exposure unit so that the exposure amount irradiated to correct the density unevenness falls within a predetermined range. The image forming apparatus according to claim 1, further comprising: means. When the exposure amount irradiated so as to correct density unevenness exceeds a predetermined range, it further has an excess amount calculation means for calculating an excess amount at a position that most exceeds this range,
The correction amount adjustment unit adjusts the exposure amount change amount by the density unevenness correction unit evenly throughout the main scanning direction according to the excess amount calculated by the excess amount calculation unit. Image forming apparatus. An image forming apparatus for forming an image,
Exposure means for irradiating the photosensitive member with light while scanning in the main scanning direction and the sub-scanning direction;
Density unevenness correcting means for controlling the exposure means to correct image density unevenness;
Correction amount adjusting means for adjusting the exposure amount change amount by the density unevenness correcting means uniformly over the entire main scanning direction so that the exposure amount irradiated to correct the density unevenness falls within a predetermined range. Forming equipment. The correction amount adjustment unit adjusts the exposure amount change amount by the density unevenness correction unit uniformly over the entire sub-scanning direction so that the exposure amount irradiated to correct the density unevenness falls within a predetermined range. Item 14. The image forming apparatus according to any one of Items 11 to 13. The image forming apparatus according to claim 11, further comprising a history storage unit that stores an adjustment history of a change amount by the correction amount adjustment unit. The correction amount adjusting means reduces the change on condition that the exposure amount irradiated to correct the density unevenness falls within a predetermined range when the change amount by the density unevenness correcting means is uniformly reduced. The image forming apparatus according to claim 11, wherein the amount is gradually restored. An image forming method for forming an image by exposing a photoconductor while scanning in a predetermined scanning direction,
Detecting the potential of the photoconductor at a predetermined detection position in the scanning direction;
Based on the detected potential and the detection position of this potential, a reference exposure amount is set at a position different from the detection position,
Detect density unevenness in the image,
An image forming method in which an exposure amount is relatively changed based on a set reference exposure amount in accordance with detected density unevenness. In an image forming apparatus that forms an image by exposing a photoreceptor while scanning in a predetermined scanning direction.
Detecting the potential of the photoreceptor at a predetermined detection position in the scanning direction;
Setting a reference exposure amount at a position different from the detection position based on the detected potential and a detection position of the potential;
Detecting density unevenness in the image;
A program for causing the image forming apparatus to execute a step of relatively changing an exposure amount based on a set reference exposure amount based on the detected density unevenness.

Images