Image forming device for controlling image density in main scanning direction

Abstract

The present invention discloses an image forming device for controlling the image density in the main scanning direction, the image forming device comprising: an image forming unit having a photosensitive component, an exposure unit, and a developing unit having a developing sleeve; and a controller configured to obtain read data related to a first test image, a second test image, and a third test image formed by the image forming unit on the same sheet, and adjust the density of the image formed by the image forming unit in the main scanning direction based on the read data. The first interval between the first test image and the second test image is different from the second interval between the second test image and the third test image. Each of the first interval and the second interval is different from an integer multiple of the circumference of the photosensitive component and is different from an integer multiple of the circumference of the developing sleeve.

Description

Technical Field

[0001] The present invention relates to an image forming apparatus for controlling image density in a main scanning direction. Background Art

[0002] In an image forming apparatus using an electrophotographic method, an image is formed by scanning a photosensitive member with a laser beam. In an electrophotographic print engine, a laser scanner first irradiates a photosensitive drum charged by a charger with a laser beam based on an image signal to form an electrostatic latent image on the photosensitive drum. Then, the electrostatic latent image formed on the photosensitive drum is developed with a toner to form a toner image on the photosensitive drum, and the toner image is transferred to a sheet and melted and thermally fixed by a fixing device, thereby forming an image on the sheet.

[0003] In such an image forming apparatus, charging unevenness due to deterioration of a charger configured to charge a photosensitive drum, exposure unevenness of a laser scanner configured to write a latent image on the photosensitive drum, and development unevenness of a developing device configured to develop the latent image formed on the photosensitive drum may occur. These unevennesses may cause density unevenness in the main scanning direction (sheet width direction orthogonal to the sheet conveying direction) of an image to be formed.

[0004] Japanese Patent Application Laid-Open No. 2004-163216 proposes a technique of outputting a sheet on which a pattern image extending in a main scanning direction is printed as a test print, reading density at different positions in the pattern image by a handheld densitometer, and correcting density unevenness in the main scanning direction.

[0005] Japanese Patent Application Laid-Open No. 2007-264364 also proposes a technique in which a plurality of pattern images are arranged in a sub-scanning direction and density unevenness in a main scanning direction is corrected by adding density unevenness in the sub-scanning direction.

[0006] In an image forming apparatus using an electrophotographic method, density unevenness may occur due to a rotating component such as a photosensitive drum. That is, periodic density unevenness may occur in the sub-scanning direction. This means that, in consideration of the inclination of density in the main scanning direction (spatial brightness and darkness of density in the main scanning direction), portions with an inclination of density (portions with brightness and darkness) and portions with no inclination of density (portions without brightness and darkness) are periodically generated in the sub-scanning direction.

[0007] For example, if the density unevenness is caused by a photosensitive drum having a diameter of 30 mm, the density unevenness as described above occurs at a pitch of about 94 mm (≈30 mm×π) in the sub-scanning direction of the sheet. If the density unevenness is caused by a developing sleeve having a diameter of 25 mm, the density unevenness occurs at a pitch of about 79 mm (≈25 mm×π). If multiple causes overlap, the density unevenness occurs in multiple pitches.

[0008] When correcting the above-mentioned uneven density by the technology of Japanese Patent Application Laid-Open No. 2004-163216 or Japanese Patent Application Laid-Open No. 2007-264364, there is a difference in correction accuracy between the correction result using the pattern image formed in the portion with inclined density and the correction result using the pattern image formed in the portion with non-inclined density.

[0009] As disclosed in Japanese Patent Application Laid-Open No. 2007-264364, even in the case where there are a plurality of pattern images of the same color in the sub-scanning direction, the intervals between the pattern images of the same color and the period of density unevenness in the sub-scanning direction may overlap or approach each other. In this case, even if a plurality of pattern images of the same color are used, all of these pattern images are created in a portion where the density is inclined or a portion where the density is not inclined. As described above, in the conventional technology, it is not possible to accurately perform density unevenness correction in the main scanning direction. Summary of the invention

[0010] According to an embodiment of the present invention, an image forming apparatus includes:

[0011] An image forming unit configured to form an image, the image forming unit comprising:

[0012] Rotating photosensitive components;

[0013] an exposure unit configured to expose the photosensitive member to form an electrostatic latent image on the photosensitive member; and

[0014] A developing unit having a developing sleeve that carries toner and rotates, configured to develop an electrostatic latent image on a photosensitive member using the toner on the developing sleeve; and a controller configured to:

[0015] Controlling an image forming unit to form a first test image, a second test image, and a third test image at different positions in a direction orthogonal to a main scanning direction on the same sheet, wherein the first test image, the second test image, and the third test image are used to adjust the density of an image having a predetermined color formed by the image forming unit in the main scanning direction;

[0016] acquiring read data related to the first test image, the second test image, and the third test image on the same sheet, the read data being output from the reading device; and

[0017] adjusting the density of an image having a predetermined color formed by an image forming unit in a main scanning direction based on the read data,

[0018] wherein a first interval between the first test image and the second test image in a direction orthogonal to the main scanning direction is different from a second interval between the second test image and the third test image in a direction orthogonal to the main scanning direction,

[0019] wherein each of the first interval and the second interval is different from an integral multiple of the circumference of the photosensitive member, and

[0020] Here, each of the first interval and the second interval is different from an integral multiple of the circumference of the developing sleeve.

[0021] Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a block diagram showing an example of the configuration of the image forming apparatus according to the present embodiment.

[0023] Figure 2 is a view showing an example of a software configuration of the image forming apparatus.

[0024] Figure 3 is a view showing a configuration example of a printer image processing unit.

[0025] Figure 4 is a view showing a part of the internal configuration of the printer engine.

[0026] Figure 5 is a cross-sectional view of an example of an image forming portion of a printer engine.

[0027] Figure 6 is a flow chart illustrating an example of main scan shadow processing.

[0028] Figure 7 : is a view showing an example of a test pattern for correcting main scanning shading according to the first embodiment.

[0029] Figure 8 is a graph showing density measurement results before density unevenness correction in the first embodiment.

[0030] Fig. 9 : is a diagram showing density measurement results before density unevenness correction in the first embodiment.

[0031] Fig.10 : is a diagram showing the density difference result before density unevenness correction in the first embodiment.

[0032] Fig.11 : is a diagram showing the calculation result of the required correction amount for each band area in the first embodiment.

[0033] Fig.12 : is a diagram showing the exposure correction level at the time of density unevenness correction in the first embodiment.

[0034] Fig.13 is a graph showing density measurement results after density unevenness correction in the first embodiment.

[0035] Fig.14 : is a diagram showing density measurement results after density unevenness correction in the first embodiment.

[0036] Fig.15 is a diagram showing density measurement results after conventional density unevenness correction.

[0037] Fig.16 is a diagram showing density measurement results after conventional density unevenness correction.

[0038] Fig.17 is a view showing an example of a test pattern used for density unevenness correction in the second embodiment.

[0039] Fig.18 : is a diagram showing an example of band intervals of respective colors of a test pattern for density unevenness correction in the second embodiment.

[0040] Fig.19 1 is a diagram showing an example of an output image in which periodic density unevenness is generated in the sub-scanning direction. DETAILED DESCRIPTION

[0041] {First embodiment}

[0042] In this embodiment, a laser beam printer using an electrophotographic method will be used to describe a method for solving the above-mentioned problem. However, as long as an electrophotographic method is used, a printer other than a laser beam printer may be used. For example, the printer may be an LED printer.

[0043] <Image Forming Apparatus>

[0044]

Hardware Configuration

[0045] Figure 1 1 is a block diagram showing an example of the configuration of the image forming apparatus according to the present embodiment. Figure 1As shown, in the image forming apparatus 100 , a scanner 101 as an image input device and a printer engine 102 as an image output device are electrically connected inside the image forming apparatus 100 .

[0046] The scanner 101 is connected to the device I / F 117 via a scanner image processing unit 118. The printer engine 102 is connected to the device I / F 117 via a printer image processing unit 119. The scanner image processing unit 118 performs control of reading image data. The printer image processing unit 119 performs control of print output.

[0047] The image forming apparatus 100 is connected to a LAN 10 and a public line 104 through a network I / F 111 and a modem 112, which will be described later. The image forming apparatus 100 performs control to input and output image information and device information via the LAN 10 and the public line 104.

[0048] The CPU 105 is a central processing unit configured to control the image forming apparatus 100. The RAM 106 is a system work memory for operating the CPU 105 and an image memory for temporarily storing input image data. The ROM 107 is a boot ROM and stores a boot program of the system.

[0049] The HDD 108 is a hard disk drive, and stores system software and input image data used for various processes. It should be noted that other storage devices such as a solid state drive (SSD) may be provided in place of or in combination with the hard disk drive.

[0050] The console unit I / F 109 is an interface to a console unit 110 having a display screen capable of displaying image data, and outputs operation screen data to the console unit 110. The console unit I / F 109 is also used to transmit information input from the console unit 110 to the CPU 105 by an operator.

[0051] The network I / F 111 is implemented by, for example, a LAN card, etc., and is connected to the LAN 10 to input and output information to and from an external device (not shown). The modem 112 is connected to the public line 104 and inputs and outputs information to and from an external device (not shown). The above units are arranged on a system bus 113.

[0052] The image bus I / F 114 is an interface for connecting the system bus 113 and the image bus 115 for high-speed transmission of image data, and is a bus bridge for converting data structures. A raster image processor (RIP) unit 116, a device I / F 117, an image editing image processing unit 120, an image compression unit 103, an image expansion unit 121, and a color management module (CMM) 130 are connected to the image bus 115.

[0053] The RIP unit 116 expands the page description language (PDL) code into image data. The device I / F 117 connects the scanner 101 and the printer engine 102 via the scanner image processing unit 118 and the printer image processing unit 119 to perform synchronous / asynchronous conversion of image data. The scanner image processing unit 118 performs various processes such as correction and editing on the image data input from the scanner 101. The printer image processing unit 119 performs image processing such as gamma correction and halftone processing according to the image data to be printed out by the printer engine.

[0054] The image editing image processing unit 120 performs various image processing such as rotation, color processing, binary conversion, and multi-value conversion of image data. When the image data is once stored in the HDD 108, the image compression unit 103 encodes the image data processed by the RIP unit 116, the scanner image processing unit 118, and the image editing image processing unit 120 by a predetermined compression method.

[0055] When image data compressed by the HDD 108 is processed by the image editing image processing unit 120 as needed and when image data is image-processed by the printer image processing unit 119 and output by the printer engine 102, the image expansion unit 121 decodes and expands the compressed and encoded data.

[0056] The CMM 130 is a dedicated hardware module that performs color conversion processing (also referred to as color space conversion processing) on ​​image data based on a profile and calibration data. Here, the profile is information such as a function for converting color image data represented by a device-dependent color space into color image data represented by a device-independent color space (e.g., Lab color space). The calibration data is data for correcting the color reproduction characteristics of the scanner 101 and the printer engine 102.

[0057]

Software Configuration

[0058] Figure 2 1 is a diagram showing an example of the software configuration of the image forming apparatus 100. When the CPU 105 loads a program stored in the ROM 107 or the HDD 108 into the RAM 106 as necessary and executes the program, Figure 2 The software modules shown are run.

[0059] The job control processing unit 201 controls each software module to control all jobs generated in the image forming apparatus 100 , such as copying, printing, scanning, and fax transmission and reception.

[0060] The network processing unit 202 is a module configured to control communication with the outside performed mainly via the network I / F 111, and controls communication with each device on the LAN 10. The UI processing unit 203 mainly controls the console unit 110 and the console unit I / F 109. The fax processing unit 204 controls a fax function. The FAX processing unit 204 performs FAX reception / transmission via the modem 112.

[0061] The device information transmission processing unit 205 is a software module configured to transmit device information to a predetermined external device by the network processing unit 202 based on an instruction of the job control processing unit 201. The device information includes information indicating the capability and characteristics of the image forming apparatus 100, such as the type (color / monochrome) of the printer engine 102, the resolution of the printer engine 102, the printing speed of the printer engine 102, the processing time of the color conversion processing unit 209, and the output profile. The device information acquisition processing unit 206 is a software module configured to transmit a device information acquisition request to a predetermined external device by the network processing unit 202 based on an instruction of the job control processing unit 201.

[0062] The print processing unit 207 controls the image editing image processing unit 120, the printer image processing unit 119, and the printer engine 102 to perform print processing of the designated image based on the instruction of the job control processing unit 201. The print processing unit 207 receives information of image data, image information (size, color mode, resolution, etc. of image data), layout information (offset, scaling, imposition, etc.), and output paper information (size, printing direction, etc.) from the job control processing unit 201. The print processing unit 207 controls the image compression unit 103, the image expansion unit 121, the image editing image processing unit 120, and the printer image processing unit 119 to perform appropriate image processing on the image data. In addition, the print processing unit 207 controls the printer engine 102 to print the image data on the designated paper.

[0063] The scanning processing unit 210 controls the scanner 101 and the scanner image processing unit 118 to read the original on the scanner 101 based on the instruction from the job control processing unit 201. The scanning processing unit 210 scans the original on the platen of the original scanner 101 and inputs the image as digital data. The color information of the input image is notified to the job control processing unit 201. In addition, the scanning processing unit 210 controls the scanner image processing unit 118 to perform appropriate image processing, such as image compression, on the input image, and then notifies the job control processing unit 201 of the input image after the image processing.

[0064] The color conversion processing unit 209 performs color conversion processing on an instruction image based on an instruction of the job control processing unit 201 , and notifies the job control processing unit 201 of the image after the color conversion processing.

[0065] The RIP processing unit 211 performs PDL interpretation based on the instruction of the job control processing unit 201 , and performs rendering by controlling the RIP unit 116 to perform development of a bitmap image.

[0066]

Image data processing flow

[0067] By the above configuration, the image processing system of the present embodiment receives a print job from the LAN 10 and performs a print operation. First, as described above, the PDL data transmitted from the external device via the LAN 10 is received by the network I / F 111 and input to the RIP unit 116 from the image bus I / F 114. The RIP unit 116 interprets the received PDL data and converts the PDL data into code data that can be processed by the RIP unit 116. In addition, the RIP unit 116 performs rendering based on the converted code data. The page data rendered by the RIP unit 116 is compressed by the image compression unit 103 of the subsequent stage and sequentially stored in the HDD 108.

[0068] According to the instruction from the job control processing unit 201, the compressed data stored in the HDD 108 is read out in the printing operation, and the image expansion unit 121 performs expansion processing of the compressed data. The image data expanded by the image expansion unit 121 is input to the printer image processing unit 119 via the device I / F 117.

[0069]

Printer image processing unit

[0070] Next, a process flow of image data input to the printer image processing unit 119 will be described based on the above-described configuration. Figure 330 is a diagram showing a configuration example of the printer image processing unit 119. The printer image processing unit 119 includes a color conversion unit 301, a density step correction unit 302, a γ correction circuit 309, a halftone processing unit 304, a page buffer memory 306, and an inter-drum delay memory controller 305.

[0071] The color conversion unit 301 converts image data from brightness values ​​(RGB, YUV, etc.) to density values ​​(CMYK, etc.), and converts the input image data into a color space corresponding to color components that can be printed by the printer engine 102 at the subsequent stage.

[0072] The density step correction unit 302 converts the multi-value image data converted into density values ​​by the color conversion unit 301 into signal values ​​for density step correction in the same page. The density step correction unit 302 has a one-dimensional table for changing the same input / output signal as the γ correction circuit 309 of the subsequent stage, and performs step correction (density level difference correction) by multiplying the density value by a step correction coefficient according to the position in the page based on the one-dimensional table.

[0073] The γ correction circuit 309 (hereinafter referred to as "γLUT 309") converts the density signal of the image data whose density steps have been corrected by the density step correction unit 302 into a signal value for reproducing the density by the printer engine 102. The γLUT 309 is a table for converting an input / output signal generated according to the γ characteristic of the printer engine 102. In the present embodiment, the γ correction is performed based on the pre-stored γLUT 309. However, the γLUT 309 may be created using a known gradient control or the like, and the γ correction may be performed based on the created γLUT 309.

[0074] The halftone processing unit 304 performs halftone processing on the image data corrected by the γLUT 309, and converts the image data into image data in which each color component of one pixel is represented by two values ​​(1 bit). Halftone processing generally includes a dithering method and an error diffusion method. In the present embodiment, the halftone processing may be any one method. The halftone processing is not limited to the above method, but other methods may be used.

[0075] The binary image data generated by the conversion processing in the halftone processing unit 304 is separated for each color component of each pixel in the image data by the inter-drum delay storage controller 305 and temporarily stored in the page buffer memory 306. The inter-drum delay storage controller 305 reads the data of the corresponding color component at the timing when the video data request signal (VREQ_* (* is any one of Y / M / C / K)) corresponding to each color component sent from the printer engine 102 is input. For each color component, the video data request signal is VREQ_Y, VREQ_M, VREQ_C, and VREQ_K. In this case, the exposure timing of the photosensitive drums 1401, 1402, 1403, and 1404 corresponding to the respective color components differs according to the distance from the upstream to the downstream from the photosensitive drums 1401, 1402, 1403, and 1404 arranged in the printer engine 102, so that the timing of reading out the data of the respective color components also differs. The read color component data is output to the printer engine 102.

[0076]

Printer Engine Operation

[0077] Next, the operation when the color component data output from the printer image processing unit 119 is input to the printer engine 102 will be described. Figure 4 1 is a view showing a part of the internal configuration of the printer engine 102. The printer I / F 1201 issues VREQ_* (* is one of Y / M / C / K), which is a video data request signal for requesting data of each color component when the printer engine 102 is ready for a printing operation. The printer I / F 1201 receives color component data sequentially transmitted from the printer image processing unit 119. The color component data received by the printer I / F 1201 is input to the pulse width modulation circuit 1203.

[0078] The pulse width modulation circuit 1203 generates a pulse signal (drive signal) for driving the Y laser driver 1212, M laser driver 1213, C laser driver 1214, and K laser driver 1215 of the subsequent stage based on the input actual color component data, and sends the pulse signal to the respective laser drivers 1212, 1213, 1214, and 1215. The laser drivers 1212, 1213, 1214, and 1215 corresponding to the respective color components drive the laser exposure devices corresponding to the respective color components based on the pulse signal received from the pulse width modulation circuit 1203.

[0079] Figure 51402 is a cross-sectional view showing an example of an image forming portion of a printer engine 102. The printer engine 102 is a so-called electrophotographic printer engine. The printer engine 102 includes photosensitive drums (photosensitive members) 1401, 1402, 1403, and 1404, charging rollers (chargers) 1205Y, 1205M, 1205C, and 1205K configured to charge the surfaces of the photosensitive drums 1401, 1402, 1403, and 1404, and a Y laser exposure device 1406Y, an M laser exposure device 1406M, a C laser exposure device 1406C, and a K laser exposure device 1406K configured to charge the surfaces of the photosensitive drums 1401, 1402, 1403, and 1404. The charged surfaces of the photosensitive drums 1401, 1402, 1403 and 1404 are exposed, the developing devices 1416, 1417, 1418 and 1419 are configured to develop the electrostatic latent images formed on the surfaces of the photosensitive drums 1401, 1402, 1403 and 1404 by exposing them with colorants, and the primary transfer devices 1408, 1409, 1410 and 1411 are configured to transfer the developed colorant images to the intermediate transfer belt (image bearing component) 1412. The toner supply containers 1407Y, 1407M, 1407C, 1407K filled with toners of various colors are driven by motors 1208, 1209, 1210, 1211, and 1212 controlled by the Y toner supply controller 1204, the M toner supply controller 1205, the C toner supply controller 1206, and the K toner supply controller 1207 to supply the toners of various colors to the developing devices 1416, 1417, 1418, and 1419. The printer engine 102 of the present embodiment includes toners of a plurality of color components (e.g., yellow (Y), magenta (M), cyan (C), and black (K)), and can form a toner image having the plurality of color components on the intermediate transfer belt 1412. Hereinafter, the image forming portion of yellow (Y) will be mainly described, but the image forming portions of magenta (M), cyan (C), and black (K) of the other color components have the same configuration. In the present embodiment, the printer engine 102 is an image forming apparatus using a four-color tandem engine of YMCK, but the present invention is not limited thereto.

[0080] The printer engine 102 includes a photosensitive drum 1401 having a diameter of, for example, 32 mm, a charging roller 1205Y having a diameter of, for example, 10 mm, a Y laser exposure device 1406Y, a developing device 1416, and a primary transfer device 1408 as an image forming portion for yellow (Y). The printer engine 102 includes a secondary transfer device 1413, a fixing device 1414, a cleaning device 1415, and an image density sensor 400.

[0081] The Y laser exposure device 1406Y is driven by the Y laser driver 1212, and irradiates the photosensitive drum 1401 with laser light (exposure light) to form an electrostatic latent image on the photosensitive drum 1401. The developing device 1416 develops the electrostatic latent image on the photosensitive drum 1401 with toner. The primary transfer device 1408 transfers the visualized toner image onto the intermediate transfer belt (intermediate transfer member) 1412 (primary transfer). The secondary transfer device 1413 transfers the toner image formed on the intermediate transfer belt 1412 onto a sheet (recording medium) serving as an image bearing member (secondary transfer).

[0082] The fixing device 1414 fixes the toner image transferred onto the sheet. The cleaning device 1415 removes transfer residual toner remaining on the intermediate transfer belt 1412 after the secondary transfer. The image density sensor 400 measures the density of the patch image formed on the intermediate transfer belt 1412.

[0083] The developing device 1416 is provided with a developer container for accommodating a developer in which toner particles (toner) and magnetic carrier particles (carrier) are mixed as a two-component developer. The first screw 1420 mixes the toner particles with the magnetic carrier particles. The second screw 1421 conveys the toner particles. A developing sleeve 1422 having a diameter of, for example, 13 mm is provided close to the photosensitive drum 1401, rotates as the photosensitive drum 1401 rotates, and carries the developer in which the toner and the carrier are mixed. The developer carried on the developing sleeve 1422 contacts the photosensitive drum 1401, and the electrostatic latent image on the photosensitive drum 1401 is developed.

[0084] Although the printer engine 102 Figure 5 There is also a conveying unit (not shown) configured to convey a print sheet in addition to the illustrated configuration, but the description thereof is omitted in the embodiment.

[0085] In the above configuration of the printer engine 102, in the case of printing yellow, the photosensitive drum 1401 is exposed by the Y laser exposure device 1406Y driven by the Y laser driver 1212 to form an electrostatic latent image on the photosensitive drum 1401. The formed electrostatic latent image is visualized as a toner image by the yellow toner carried on the developing sleeve 1422 in the developing device 1416, and the visualized toner image is transferred onto the intermediate transfer belt 1412 through the primary transfer device 1408.

[0086] In this way, the respective color components of magenta, cyan, and black are similarly developed by the respective developing devices 1417, 1418, and 1419, and are visualized as toner images on the photosensitive drums 1402, 1403, and 1404, respectively. The visualized toner images are sequentially transferred by the primary transfer devices 1409, 1410, and 1411 in synchronization with the toner images of the color components transferred immediately before, and a final toner image formed of the toner images of the four colors is formed on the intermediate transfer belt 1412. The toner image formed on the intermediate transfer belt 1412 is transferred to a sheet by the secondary transfer device 1413. The fixing device 1414 fixes the toner image to the sheet.

[0087]

Main Scan Shadow

[0088] Next, correction of density unevenness in the main scanning direction (hereinafter referred to as “main scanning shading”) will be described. Figure 6 1 is a flowchart showing an example of main scan shadow processing. The processing of the flowchart is implemented by the CPU 105 loading and executing a program stored in the ROM 107 or the HDD 108 in the RAM 106 as needed. For example, the processing may be performed by the job control processing unit 201 or by another software module (not shown).

[0089] First, when the main scanning shading process starts, the CPU 105 controls the print processing unit 207 to output a test pattern image for correcting the density in the main scanning direction (S101). The details of the test pattern image in the embodiment will be described later.

[0090] The CPU 105 instructs the user through the display screen of the console unit 110, and the user performs an operation of reading a sheet on which a test pattern image is formed by using the scanner 101. In response to the operation, the scanner 101 reads the sheet and outputs read data related to the test pattern image to the CPU 105. The CPU 105 acquires the read data related to the test pattern image and measures the density of the test pattern image based on the read data (S102). Next, the CPU 105 calculates the density distribution in the main scanning direction according to the density measured in S102, and determines the shading correction amount to eliminate density unevenness (S103). A method of determining the density unevenness correction amount will be described in detail later.

[0091] Next, the CPU 105 controls so that the shading correction amount of each color component determined in S103 is sent to the printer engine 102 via the printer image processing unit 119 and is set (S104). As shading correction methods, a method of changing the modulation degree of pulse width modulation (PWM) of a laser beam according to a scanning position and a method of changing the modulation degree of laser beam intensity according to a scanning position are both known, but are not limited to these two methods. For example, in the case of changing the modulation degree of pulse width modulation of a laser beam according to a scanning position, the shading correction amount of each color component determined in S103 is sent to the pulse width modulation circuit 1203 and stored in a memory (not shown) of the pulse width modulation circuit 1203. Therefore, the pulse width modulation circuit 1203 changes the modulation degree of pulse width modulation of the laser beam according to the scanning position based on the shading correction amount of each color component when printing. As a result, the density unevenness in the main scanning direction is corrected.

[0092]

Test pattern

[0093] Next, we will refer to Figure 7 Describes the test pattern used to correct for main scan shadows. Figure 7 1 is a view showing an example of a test pattern for correcting main scanning shading according to the first embodiment. Although the cyan test pattern is used as an example for explanation here, the same technical effect can be obtained for other color components using the same test pattern.

[0094] In the first embodiment, the test pattern is formed on a sheet of A4 size (210 mm×297 mm). The main scanning direction and the sub-scanning direction (the conveying direction (moving direction) of the intermediate transfer belt 1412) when forming the test pattern are as follows: Figure 5 As shown by the arrows in . The main scanning direction and the sub-scanning direction are orthogonal to each other. The size of the sheet on which the test pattern is formed is not limited to the A4 size. According to the first embodiment, the image forming device 100 forms a test pattern on a sheet, and causes the scanner 101 to read the test pattern on the sheet. Thus, information about the density of the test pattern is acquired. However, the test pattern may be formed on the sheet, and the image density of the test pattern on the sheet may be measured, for example, by an external colorimeter.

[0095] like Figure 7 As shown, the test pattern of the first embodiment includes a plurality of band images (patterns) extending in the main scanning direction. In order to demonstrate the technical effect of the first embodiment, there need to be a variety of intervals between the band images (intervals between adjacent band images in the sub-scanning direction). In the test pattern of the first embodiment, the number of band images is three. However, the number of band images formed on a sheet is not limited to the number of the first embodiment.

[0096] As an example, Figure 7It is shown that three band images are arranged in the test pattern, and the interval between the first band and the second band (the interval between the center positions of the band images) is 30 mm, and the interval between the second band and the third band is 50 mm. The concentration unevenness is detected from the concentration of multiple areas (concentration measurement points) of the test pattern in the main scanning direction. In the test pattern of the first embodiment, for example, the concentration of five areas of area A, area B, area C, area D and area E is obtained in the main scanning direction. CPU 105 obtains the concentration of each area from the read data of scanner 101. The number of areas divided in the main scanning direction is not limited to this. The size of the band image is 20 mm×280 mm, but the size of the band image is not limited to this.

[0097] The reason why various intervals of band images are required is that, as described above, density unevenness having a periodicity in the sub-scanning direction tends to occur in the image forming apparatus 100 using the electrophotographic method. Fig.19 Describe the example.

[0098] Fig.19 This is a view in which an output image printed on an A3 size specific sheet is scanned by the scanner 101 and density unevenness is expressed in light and dark. Special image processing is performed to clarify density unevenness. Fig.19 An image is shown as an example of an output image in which the density fluctuates periodically in the sub-scanning direction and density unevenness occurs in the main scanning direction.

[0099] The periodic density unevenness that appears in the output image occurs particularly at the period corresponding to the circumferential length of the photosensitive drum 1403, the developing sleeve 1422, and the charging roller 1205C. For example, Fig.19 The image is a mixture of unevenness of about 40 mm period and unevenness of about 102 mm period. In the imaging forming device 100 of the first embodiment, the diameter of the developing sleeve 1422 is 13 mm, and the diameter of the photosensitive drum 1403 is 32 mm. Therefore, the circumference of the developing sleeve 1422 is about 41 mm (≈13 mm×π), and the circumference of the photosensitive drum 1403 is about 101 mm (≈32 mm×π), and these values ​​are close to the uneven periods of about 40 mm and about 102 mm described above (basically consistent). Therefore, it is believed that the developing sleeve (rotating component) 1422 causes unevenness of about 40 mm period, and the photosensitive drum (rotating component) 1403 causes unevenness of about 102 mm period.

[0100] Hereinafter, a test pattern necessary for performing shading correction on an image having such periodic unevenness to reduce density unevenness in the main scanning direction will be considered.

[0101] First, consider the case where a band image of one color is used as the correction test pattern of pattern 1. When a place where density unevenness is strongly generated in the main scanning direction (for example Fig.19 The density to be measured is different when a band image is formed in a place where the density unevenness is not strongly generated (solid line part and dotted line part in the figure) and when a band image is formed in a place where the density unevenness is not strongly generated in the main scanning direction. Therefore, the shadow correction amount varies depending on the place where the band image is formed. When a band image is formed in a place where the density unevenness is strongly generated, the shadow correction amount is determined to correct the density unevenness. Therefore, the density deviation amount is suppressed in a place where the density deviation amount is originally large, and the density deviation is large due to excessive correction amount in a place where the density deviation amount is originally small.

[0102] Next, as Pattern 2, consider the case where two or more band images (including two band images) are provided at equal intervals in one color. In this case, when the density suddenly tilts in a certain part, the correction amount can be averaged, or, depending on the processing method, the correction amount can be optimized by processing such as removing unexpected parts. On the other hand, for the periodic density unevenness in the sub-scanning direction, the correction amount is significantly different between the case where the interval of the band images is basically consistent with the period (or an integer multiple of the period) and the case where the interval of the band images is basically inconsistent with the period, and Pattern 2 has the same tendency as Pattern 1.

[0103] Finally, pattern 3, as in the first embodiment, considers a correction test pattern having three or more band images of one color and a plurality of band image intervals. In this case, since the intervals between the band images change, all the band images are substantially inconsistent with the periodic density unevenness in the sub-scanning direction like pattern 1 or pattern 2. The test pattern of the first embodiment has a plurality of different intervals so that the intervals between adjacent band images include intervals that do not correspond to an integral multiple of the circumference of the photosensitive drum 1403, the charging roller 1205C, and the developing sleeve 1422. Therefore, appropriate correction can be performed without excessively correcting the density unevenness in the main scanning direction.

[0104] As described above, the main scanning shading correction test pattern of the first embodiment has been described as a test pattern having three band images of one color and two kinds of intervals. However, the main scanning shading correction test pattern is not limited thereto. The main scanning shading correction test pattern may have a greater number of band images and a greater variety of intervals. The main scanning shading correction test pattern may be formed as three or more band images of one color, and the intervals of the three or more band images in the sub-scanning direction may be two or more kinds of intervals that do not intersect with each other (the common divisor is only one). For example, in Figure 7In the example, the interval between the first belt and the second belt can be 30 mm, and the interval between the second belt and the third belt can be 49 mm, so that the two intervals formed by the three belt images have a non-intersecting relationship (the common divisor of 30 and 49 is only 1). Therefore, all the belt images are basically inconsistent with the periodic density unevenness in the sub-scanning direction.

[0105] [How to determine the amount of shading correction]

[0106] Next, explain Figure 6 That is, a method for correcting density unevenness in the main scanning direction of the image forming apparatus 100 will be described. As correction methods, there are known methods of changing the modulation degree of PWM modulation of the laser beam according to the scanning position and changing the modulation degree of the laser beam intensity according to the scanning position, but the correction method is not limited to these two methods.

[0107] exist Figure 6 In the main scanning shading correction chart output in step S101, as shown in FIG. Figure 7 As shown in FIG. 1 , the area is divided in the main scanning direction, and the density measurement is performed for each band in each area. An example of the measurement result is shown in FIG. Figure 8 and Fig. 9 shown. Figure 8 is a graph showing an example of the result of measuring the density of the test pattern in step S102 . Fig. 9 is a view showing an example of a result of measuring the density of the test pattern in step S102 .

[0108] Next, the average concentration of each band is calculated, and the concentration difference ΔDens of each area relative to the average concentration is calculated. An example of the calculation result is shown in Fig.10 shown. Fig.10 : is a diagram showing the density difference result before density unevenness correction in the first embodiment.

[0109] Next, the required correction amount of the density difference result is calculated. The required correction amount is calculated by the following Expression 1.

[0110] (Required correction amount) = -(ΔDens×(correction coefficient N)) … Expression 1

[0111] The correction coefficient N in Expression 1 is a coefficient used to determine how much the level of the PWM modulation of the laser beam and the modulation degree of the laser beam intensity changes relative to the concentration difference. For example, when the correction coefficient N=100, the level of the modulation degree changes to "1" when the concentration difference ΔDens is "0.01". In the first embodiment, the correction coefficient N is set to 200 (N=200). The correction coefficient N is not limited to this. It should be noted that in this case, the rounded value of the calculation result on the right side of Expression 1 is calculated as the required correction amount, but Expression 1 is not limited to this. Fig.11 : is a diagram showing the calculation result of the required correction amount for each band area in the first embodiment.

[0112] Next, the exposure correction level in each area is determined according to the required correction amount in each area in each band calculated as described above. The exposure correction level is calculated as the average of the density difference results for each band in the same area. Fig.12 : is a diagram showing the exposure correction level at the time of density unevenness correction in the first embodiment.

[0113] In the first embodiment, the exposure correction level is calculated as the average value of each area, but the exposure correction level is not limited to this. For example, the exposure correction level may be a median value or a value obtained by other statistical processing. Therefore, by calculating the modulation degree of the exposure level required for correction and adjusting the exposure level, the density unevenness in the main scanning direction can be corrected.

[0114] Next, the technical effect of correcting density unevenness using the main scanning shadow pattern as in the first embodiment will be described. Fig.13 and Fig.14 The density measured in each area of ​​each band when the same test pattern is output again after correction as described above is shown. Fig.13 is a graph showing density measurement results after density unevenness correction in the first embodiment. Fig.14 : is a diagram showing an example of density measurement results after density unevenness correction in the first embodiment.

[0115] like Figure 8 and Fig. 9 As shown, the density measurement results before the main scanning shading correction according to the first embodiment are as follows.

[0116] Maximum concentration Dmax = 0.83

[0117] Minimum concentration Dmin=0.72

[0118] Concentration difference ΔD=0.11

[0119] Concentration gradient in each band: first band = 0.11, second band = 0.03, third band = 0.05

[0120] On the other hand, Fig.13 and Fig.14 As shown, the density measurement results after the main scanning shading correction according to the first embodiment are as follows.

[0121] Maximum concentration Dmax = 0.795

[0122] Minimum concentration Dmin = 0.73

[0123] Concentration difference ΔD=0.065

[0124] Concentration gradient in each band: first band = 0.055, second band = 0.025, third band = 0.03

[0125] It can be seen that through the main scanning shading correction of the first embodiment, the density unevenness in the main scanning direction is reduced.

[0126] As a first comparative example, Fig.15 Shown are density results after correction in the case where the intervals of the bands are formed at equal intervals and main scanning shading is performed using a test pattern formed at a position where the density gradient is large.

[0127] Fig.15 : is a view showing density measurement results (first comparative example) after conventional density unevenness correction. Density measurement results (first comparative example) obtained when main scanning shading is performed using a test pattern formed at a position with a large density gradient by conventional density unevenness correction are as follows.

[0128] Maximum concentration Dmax = 0.8

[0129] Minimum concentration Dmin=0.71

[0130] Concentration difference ΔD=0.09

[0131] Concentration gradient in each band: first band = 0, second band = 0.08, third band = 0.08

[0132] It can be seen from the measurement results of the first comparative example that, although appropriate correction is performed in one area, excessive correction is performed in another area, so the effect of the correction is small.

[0133] As a second comparative example, Fig.16 Shown are density results after correction in the case where main scanning shading is performed by using a test pattern formed at a position where the density gradient is small and the intervals of bands are formed at equal intervals.

[0134] Fig.16: is a view showing density measurement results (second comparative example) after conventional density unevenness correction. Density measurement results (second comparative example) obtained when main scanning shading is performed using a test pattern formed at a position where the density gradient is small by conventional density unevenness correction are as follows.

[0135] Maximum concentration Dmax = 0.82

[0136] Minimum concentration Dmin = 0.73

[0137] Concentration difference ΔD=0.09

[0138] Concentration gradient in each band: first band = 0.08, second band = 0, third band = 0.03

[0139] It can be seen from the density measurement results of the second comparative example that, although appropriate correction is performed in one area, correction is insufficient in another area, so the effect of the correction is small.

[0140] As described above, in a test pattern for correcting density unevenness in the main scanning direction, density unevenness in the main scanning direction is corrected by using a test pattern having three or more band images for density measurement in the sub-scanning direction and having two or more intervals between the band images and the band images. In this way, the test pattern is composed of three or more band images of monochrome components, and the intervals between adjacent band images include intervals that are integer multiples of the circumference of the rotating parts (photosensitive parts, charging rollers, developing sleeves) in the image forming part. Therefore, it is possible to prevent the density unevenness periodically generated in the sub-scanning direction due to the rotating parts in the image forming part from coinciding with all the forming positions of each band image in the test pattern for the main scanning shadow. Therefore, even in the case where density unevenness periodically occurs in the sub-scanning direction, density unevenness correction in the main scanning direction can be performed with high precision.

[0141] {Second embodiment}

[0142] In the first embodiment, in a test pattern for correcting uneven density in the main scanning direction, a monochrome (monochromatic component) test pattern is used in which three or more band images for density measurement are arranged in the sub-scanning direction and the intervals between the band images are two or more. Then, a configuration for setting the shadow correction amount using a monochrome test pattern for a color component that requires a main scanning shadow is described. In a second embodiment, a case where four colors of Y, M, C, and K are used as test patterns will be described. The image forming device 100, the flowchart in the main scanning shadow, and the correction method described in the first embodiment are the same in the second embodiment, so their description is omitted.

[0143]

Test picture

[0144] Will refer to Fig.17 A main scanning shading correction test pattern according to the second embodiment is described. Fig.17 2 is a view showing an example of a test pattern for correcting main scanning shading according to the second embodiment. Here, as an example, a test pattern in which four band images of each color are arranged in the sub scanning direction will be described, but the test pattern is not limited thereto.

[0145] In the image forming apparatus 100 of the first embodiment, the test pattern is formed on a sheet of A4 size (210 mm×297 mm). The main scanning direction and the sub-scanning direction (the conveying direction (moving direction) of the intermediate transfer belt 1412) when forming the test pattern are as follows: Fig.17 As shown by the arrow in FIG. The size of the sheet forming the test pattern is not limited to the A4 size.

[0146] like Fig.17 As shown in FIG. 1 , the test pattern includes 16 band images in total, which are arranged in the order of Y→M→C→K→M→Y→K→C→M→Y→C→K→Y→M→C→K from the top in the conveying direction. In the test pattern, four band images are arranged in the sub-scanning direction for each monochrome component among a plurality of color components, and the arrangement order is such that the intervals of the band images of the same color component become multiple.

[0147] Fig.18 Shows the intervals between band images of respective colors. Fig.18 : is a table showing an example of a band interval for correcting each color of a test pattern in a main scanning shadow according to the second embodiment.

[0148] from Fig.18 As can be seen in FIG. 1 , the interval of the band image is set for each color so that the interval from the first band to the second band, the interval from the second band to the third band, and the interval from the third band to the fourth band are different from each other. The band image is 10 mm×280 mm, but the band image is not limited thereto. In the test pattern of the second embodiment, three or more patterns are arranged in the sub-scanning direction for each monochrome component among the plurality of color components, and the arrangement order is such that the interval of the pattern of the same color component in the sub-scanning direction becomes multiple.

[0149] As described in the first embodiment, in the image forming apparatus 100 using the electrophotographic method, periodic density unevenness tends to occur in the sub-scanning direction. Therefore, in the case of correcting the density unevenness in the main scanning direction using one or two band images of each color in the sub-scanning direction, it is easily affected by the period of the sub-scanning direction, and even if there are three or more band images, if the intervals between the band images are the same, it is also easily affected by the period of the sub-scanning direction. Therefore, if a correction test pattern formed by arranging band images as shown in the second embodiment is used, even in the case of periodic generation of strong and weak density unevenness in the sub-scanning direction, the influence of the strong and weak density unevenness is reduced, and appropriate density unevenness correction can be performed for all colors.

[0150] In the second embodiment, it has been described that the band images in the correction pattern are arranged in the order of Y → M → C → K → M → Y → K → C → M → Y → C → K → Y → M → C → K. However, this is not limited to this, and the same technical effect can be obtained if the band images of each color are arranged in such a manner that there are multiple intervals between them.

[0151] In the second embodiment, it has been described that the band images of all colors (in this case, four colors of YMCK) in the correction pattern are arranged in the area of ​​one A4 size sheet, but the correction pattern is not limited to this. For example, a test pattern formed in the area on a plurality of A4 size sheets may be used, and the same technical effect may be obtained if there are multiple intervals between the band images of each color.

[0152] Further, even in the case of a two-color or three-color correction pattern, the same technical effect can be obtained if there are various intervals between the band images of the respective colors. The CPU 105 performs the following steps using the correction pattern in which the band images of the color components for the main scanning shadow are arranged. Figure 6 For example, in the case of performing the main scanning shading of two colors Y and C, the CPU 105 performs the main scanning shading processing as shown in FIG. 105 using the correction chart in which the two colors Y and C are arranged in the correction pattern. Figure 6 For an image forming apparatus configured to form an image using five or more color components, correction patterns of five or more colors may be used.

[0153] As described above, according to the embodiment, even in the case where density unevenness is periodically generated in the sub-scanning direction, it is possible to correct density unevenness in the main scanning direction with high accuracy.

[0154] The structure and content of the above-mentioned various data are not limited thereto, and it goes without saying that the structure and content of the various data are varied according to the use and purpose. Although the first and second embodiments have been described above, the present invention can be implemented as, for example, a system, an apparatus, a method, a program or a storage medium. More specifically, the present invention can be applied to a system including a plurality of devices, or can be applied to a device including one device. In addition, the combination of the above-mentioned embodiments is also included in the present invention.

[0155] (Other embodiments)

[0156] The embodiments of the present invention may also be implemented by providing software (program) for performing the functions of the above-described embodiments to a system or device via a network or various storage media, and a computer or a central processing unit (CPU) or a microprocessing unit (MPU) of the system or device reads and executes the program.

[0157] While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

Claims

1. An image forming device, comprising: An image forming unit configured to form an image, the image forming unit comprising: Rotating photosensitive components; an exposure unit configured to expose the photosensitive member to form an electrostatic latent image on the photosensitive member; and a developing unit having a developing sleeve that carries toner and rotates, and configured to develop the electrostatic latent image on the photosensitive member with the toner on the developing sleeve; and A controller configured to: Controlling an image forming unit to form a first test image, a second test image, and a third test image at different positions in a direction orthogonal to a main scanning direction on the same sheet, wherein the first test image, the second test image, and the third test image are used to adjust the density of an image having a predetermined color formed by the image forming unit in the main scanning direction; acquiring read data related to the first test image, the second test image, and the third test image on the same sheet, the read data being output from the reading device; and adjusting the density of an image having a predetermined color formed by an image forming unit in a main scanning direction based on the read data, wherein a first interval between the first test image and the second test image in a direction orthogonal to the main scanning direction is different from a second interval between the second test image and the third test image in a direction orthogonal to the main scanning direction, wherein each of the first interval and the second interval is different from an integral multiple of the circumference of the photosensitive member, and Here, each of the first interval and the second interval is different from an integral multiple of the circumference of the developing sleeve.

2. The image forming apparatus according to claim 1, wherein: The image forming unit further includes a charging roller configured to charge the photosensitive member, and Here, each of the first interval and the second interval is different from an integral multiple of the circumference of the charging roller.

3. The image forming apparatus according to claim 1, wherein: The controller controls the image forming unit to form a fourth test image having a predetermined color at a position different from the first test image, the second test image, and the third test image in a direction orthogonal to the main scanning direction on the same sheet, and Here, in a direction orthogonal to the main scanning direction, a third interval between the third test image and the fourth test image is different from each of the first interval and the second interval.

4. The image forming apparatus according to claim 1, wherein: The controller controls the image forming unit to form a fourth test image, a fifth test image, and a sixth test image at different positions in a direction orthogonal to the main scanning direction on the same sheet, wherein the fourth test image, the fifth test image, and the sixth test image are used to adjust the density of an image having other colors different from the predetermined color formed by the image forming unit in the main scanning direction, wherein the fourth test image is formed between the first test image and the second test image in a direction orthogonal to the main scanning direction, wherein the fifth test image is formed between the second test image and the third test image in a direction orthogonal to the main scanning direction, wherein a third interval between the fourth test image and the fifth test image in a direction orthogonal to the main scanning direction is different from a fourth interval between the fifth test image and the sixth test image in a direction orthogonal to the main scanning direction, wherein each of the third interval and the fourth interval is different from an integral multiple of the circumference of the photosensitive member, and Here, each of the third interval and the fourth interval is different from an integral multiple of the circumference of the developing sleeve.

5. The image forming apparatus according to claim 1 , wherein the first interval is a distance from a center of the first test image in a direction orthogonal to the main scanning direction to a center of the second test image in a direction orthogonal to the main scanning direction, and in, The second interval is a distance from the center of the second test image in the direction orthogonal to the main scanning direction to the center of the third test image in the direction orthogonal to the main scanning direction.

6. The image forming apparatus according to claim 1, wherein: The controller adjusts the density of an image formed by the image forming unit in the main scanning direction by controlling the intensity of exposure light with which the exposure unit exposes the photosensitive member based on the read data.

7. The image forming apparatus according to claim 1, wherein: A length direction of each of the first test image, the second test image, and the third test image is equal to the main scanning direction.

8. An image forming device, comprising: An image forming unit configured to form an image, the image forming unit comprising: Rotating photosensitive components; an exposure unit configured to expose the photosensitive member to form an electrostatic latent image on the photosensitive member; and a developing unit having a developing sleeve that carries toner and rotates, and configured to develop the electrostatic latent image on the photosensitive member with the toner on the developing sleeve; and A controller configured to: Controlling an image forming unit to form a first test image of different colors, a second test image of different colors, and a third test image of different colors at different positions in a direction orthogonal to a main scanning direction on the same sheet, wherein the first test image, the second test image, and the third test image are used to adjust the density of an image formed by the image forming unit in the main scanning direction, and each of the first test image, the second test image, and the third test image includes yellow, magenta, cyan, and black images formed at different positions in a direction orthogonal to the main scanning direction; acquiring read data related to the first test image, the second test image, and the third test image on the same sheet, the read data being output from the reading device; and adjusting the density of an image formed by the image forming unit in the main scanning direction based on the read data, The color sequences of the first test image, the second test image, and the third test image are different from each other, and the intervals of the same colors of the first test image, the second test image, and the third test image are different from each other.

9. The image forming apparatus according to claim 8, wherein: The controller controls the image forming unit to form a fourth test image of a different color at a position different from the first test image, the second test image, and the third test image in a direction orthogonal to the main scanning direction on the same sheet, so as to adjust the density in the main scanning direction; and The fourth test image includes yellow, magenta, cyan and black images formed at different positions in a direction orthogonal to the main scanning direction.

10. The image forming apparatus according to claim 8, wherein an interval between images of the same color of the first test image and the second test image is different from an integral multiple of a circumference of the photosensitive member, and in, An interval between images of the same color of the first test image and the second test image is different from an integral multiple of the circumference of the developing sleeve.

11. The image forming apparatus according to claim 10, wherein: The image forming unit further includes a charging roller configured to charge the photosensitive member, and The interval between the first test image and the second test image of the same color is different from an integral multiple of the circumference of the charging roller.

12. The image forming apparatus according to claim 10, wherein: The interval between the same-color images of the first test image and the second test image is the distance between the respective centers of the same-color images in the direction orthogonal to the main scanning direction.

13. The image forming apparatus according to claim 8, wherein: The controller adjusts the density of an image formed by the image forming unit in the main scanning direction by controlling the intensity of exposure light with which the exposure unit exposes the photosensitive member based on the read data.

Images