JP5794471B2 - Control apparatus, image forming apparatus, and control method - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, and a printer, and a control device and a control method used therefor.

  In an image forming apparatus that forms a toner image by an electrophotographic method, if the environment such as temperature and humidity changes or if a continuous printing operation is performed over a long period of time, the toner adhesion amount per unit area with respect to the toner image is increased. It may change and change the image density. In a color image forming apparatus that forms a color image, when the toner adhesion amount fluctuates for each of a plurality of primary colors, the color tone of the multi-order color (for example, the L * value and the a * value in the L * a * b * color system) (b * value combination) is disturbed. Specifically, colors reproduced by the color image forming apparatus are roughly classified into primary colors and multi-order colors. The primary color is a color expressed by only one type of toner. For example, in a configuration using four types of toners of yellow (Y), magenta (M), cyan (C), and black (K), it is expressed by only one of Y, M, C, and K toners. The color to be performed is the primary color. In contrast, a multi-order color is a color expressed using two or more types of toner. Multi-order colors are reproduced by superimposing a plurality of primary color toner images. However, if the amount of toner attached to each primary color toner image fluctuates, the color tone of the multi-order color toner image is determined by the superposition of these primary color toner images. Will be disturbed.

Therefore, in Patent Document 1 and Patent Document 2, an image forming apparatus is proposed that periodically performs the following processing for each primary color of Y, M, C, and K. That is, a tone reproduction curve TRC (Tone Reproduction Curve) indicating the relationship between the input density value and the output density value of the primary color image data is stored in the data storage unit. If the input density value is corrected and output according to the gradation reproduction curve TRC, it is possible to form a primary color toner image with a good reproduction of the original color tone. If it changes, the reproduction accuracy of the primary color will decrease. Therefore, at a regular timing, a test print is performed to form a test toner image of a specific multi-order color on a recording sheet, and the color of the test toner image on the test print paper is measured with a spectrometer and the original color. The difference is calculated. Then, based on the difference and the current gradation reproduction curve TRC, a correction amount necessary for matching the color measurement result with the original color is obtained. Then, the gradation reproduction curve TRC is corrected based on the correction amount. By periodically performing such processing for Y, M, C, and K, it is possible to form a multi-color toner image having a stable color tone over a long period of time.

  However, in such a configuration, since the test print paper that outputs the test toner image is discharged separately from the print paper that outputs the image based on the user's command, the user is forced to sort them out. Since such a sorting operation is very laborious, it is not practical to employ a configuration that outputs a test toner image.

  Accordingly, the present inventors are developing the following image forming apparatus. That is, first, an area search process is performed for searching for a colorimetric adaptation area suitable for colorimetry from the image indicated by the image information acquired by data reception from an external device or image reading based on a user instruction. carry out. In addition, among all the regions of the multi-color toner image actually formed based on the image information, a plurality of colorimetric adaptive regions specified by the region search process are respectively measured by a spectrometer to obtain a plurality of colorimetric results. . The data storage means stores tone reproduction curves TRC for Y, M, C, and K, respectively, as control parameters. Based on the gradation reproduction curve TRC and a result obtained by obtaining a difference from the original color for each of a plurality of color measurement results, a curve correction amount for further reducing the color difference is determined. Then, the gradation reproduction curve TRC is corrected based on the determined curve correction amount. Such processing is performed for Y, M, C, and K, respectively. In such a configuration, the test print paper is output by appropriately correcting the gradation reproduction curve TRC based on the result of colorimetric measurement of the colorimetric adaptation region of the print paper image output based on the user's command. Therefore, it is possible to accurately reproduce multi-order colors. Therefore, it is possible to form a multi-color toner image having a stable color tone over a long period of time without forcing the user to sort test prints.

  However, the image forming apparatus under development still has room for improvement as follows. In other words, an image output based on a user command may have an uneven color distribution. In an image with a biased color distribution, color measurement results cannot be obtained for a specific color tone, so the tone reproduction curve location corresponding to that color tone cannot be properly corrected, and the color tone reproducibility can be corrected. May worsen.

  So far, the problem that occurs in the image forming apparatus that corrects the gradation reproduction curve TRC as the control parameter has been described. However, the same problem may occur in the following image forming apparatus. In other words, the image forming apparatus aims to stabilize color reproducibility by correcting control parameters different from the gradation reproduction curve, such as development bias and latent image writing intensity.

  The present invention has been made in view of the above background, and an object of the present invention is to provide the following image forming apparatus, and a control device and a control method used therefor. That is, an image forming apparatus capable of accurately reproducing multi-order colors over a long period of time without forcing the user to sort test print papers or degrading the reproducibility of colors that could not be measured. Etc.

In order to achieve the above object, the present invention provides a plurality of different primary elements on the surface of one image carrier based on image information obtained by data reception from an external device or image reading based on a user command. Image forming means for forming a color toner image or forming different primary color toner images on the surfaces of a plurality of image carriers, and the one image carrier or the plurality of image carriers. A plurality of primary color toner images formed on the surface of the one image carrier or the surfaces of the plurality of image carriers while the endlessly moving surface of the surface endless movable body faces the surface. Transfer means for obtaining a multi-color toner image by transferring the primary color toner images formed respectively on the surface of the surface endless moving body or a recording sheet held on the surface, and the transfer means By Mounted on an image forming apparatus including a colorimetric unit for measuring a multi-color toner image transferred to a recording sheet, and controls the drive of the image forming unit and the transfer unit or executes predetermined arithmetic processing A region search process for searching for a colorimetric adaptation region suitable for color measurement from an image indicated by the image information, and a multi-order formed based on the image information. A plurality of primary colors formed by the image forming unit after performing a color measurement process for obtaining a plurality of color measurement results by measuring a plurality of the color measurement adaptive regions in the color toner image respectively. A gradation reproduction curve representing a relationship between an input density value and an output density value stored in advance for each toner image; a result of obtaining a difference from an original color for each of the plurality of color measurement results; and the gradation on the basis of the reproduction curve And correction amount determination processing for determining the correction amount of the tone reproduction curve to smaller the difference, the correction amount determination process based on the correction amount determined by by correcting the tone reproduction curve multicolor the improvement in color reproduction accuracy of the toner image carried out and FIG Ru compensation processing, and, at the correction amount determination processing, it is determined whether there is no bias in color distribution on the plurality of color measurement result, deviation If there is a gradation pattern image composed of a plurality of test toner images having different toner adhesion amounts per unit area for each of a plurality of primary colors, a surface pattern of the surface endless moving body is formed on each surface. Processing for detecting the toner adhesion amount per unit area with respect to the toner image by the toner adhesion amount detection means, processing for converting the detection result into color information, and adding the conversion result to the actual color measurement result data group as a color measurement result The correction amount is determined after performing the processing.

In the present invention, for the reason described below, multi-colors can be applied over a long period of time without forcing the user to sort test print papers or degrading the reproducibility of colors that could not be measured. It can be reproduced with high accuracy.
Instead of forming a test toner image for multi-color measurement on test print paper and performing color measurement, the output image is measured based on a user instruction, and the control parameters are set based on the color measurement result. to correct. Thus, the control parameter is appropriately corrected based on the color measurement result without generating test print paper. In addition, if there is a lack of color distribution in the output image based on the user's command and the color measurement result is insufficient for a specific color, prior to the control parameter correction, the following Process. That is, for each of the primary colors, a gradation pattern image is formed on the surface of the surface endless moving body, and the toner adhesion amount with respect to each test toner image in the gradation pattern image is detected by the toner adhesion amount detection means. Each detected result is converted into color information. Then, the conversion result is added as a color measurement result to the data group of the actual color measurement result. As a result, the color measurement result of the color that is insufficient by actual color measurement alone is supplemented with the result of converting the toner adhesion amount detection result for the gradation pattern image into color information, so that the color that could not be measured. Avoid reproducibility degradation. In such a configuration, it is possible to appropriately correct the control parameters without generating test print paper or deteriorating the reproducibility of colors that could not be measured. Multi-colors can be accurately reproduced over a long period of time without impairing the user or degrading the reproducibility of colors that could not be measured.

1 is a schematic configuration diagram illustrating a main part of a printer according to an embodiment. FIG. 2 is an enlarged configuration diagram illustrating an image forming unit of the printer. FIG. 3 is an enlarged configuration diagram illustrating a toner adhesion amount detection sensor of the printer. FIG. 2 is a block diagram showing electrical connection of each unit in the printer. FIG. 3 is a block diagram showing a relationship between a main circuit in the pre-controller of the printer and various processes performed in the calculation unit. The flowchart which shows a part of process flow in control regularly implemented by the calculating part. The schematic diagram which shows an example of the image represented by the image information provided from a user. The schematic diagram which shows the color measurement adaptation area | region searched from the same image and it. The figure which shows an example of the histogram produced in the color distribution bias determination process implemented by the calculating part. The enlarged schematic diagram which shows the gradation pattern image formed by the colorimetric data supplement process implemented by the calculating part. The characteristic view which shows each gradation reproduction curve and correction amount (delta) of time t and t + 1. The schematic diagram which shows the relationship between each primary color of Y, M, C, and K and the density | concentration in four-dimensional color space. The graph which shows an example of the gradation reproduction curve TRC control point and the fluctuation amount. The graph which shows a monotone increasing concave function.

Hereinafter, an embodiment of an image forming apparatus to which the present invention is applied will be described.
First, a basic configuration of the image forming apparatus according to the embodiment will be described. The image forming apparatus according to the embodiment is a color production printer that realizes color on-demand printing that outputs a large amount of color documents such as bills at high speed. Such a color production printer is used when, for example, invoices and receipts for tens of millions of telephone charges are issued in about one week. In such a situation, continuous printing is performed (in other words, several hundreds of high-speed prints are continuously operated in units of several tens of hours per minute).

  FIG. 1 is a schematic configuration diagram illustrating a main part of a color production printer 100 (hereinafter simply referred to as a printer 100) according to an embodiment. FIG. 1 shows only an image forming process part (process engine part) using an electrophotographic process for performing exposure, charging, development, transfer, and fixing in the entire printer 100. In addition to the components shown in FIG. 1, the printer 100 includes a paper feeding device that supplies a recording sheet 115 as a recording material, a manual tray for manually feeding the recording sheet 115, and an image-formed recording. A paper discharge tray or the like (none of which is shown) for discharging the sheet 115 is provided.

  The printer 100 is provided with an endless belt-shaped intermediate transfer belt 105 which is a surface endless moving body. The intermediate transfer belt 105 is endlessly moved in the counterclockwise direction in the figure by the rotational drive of the support roller 112 having a function as a drive roller while being stretched around the four support rollers 112, 113, 114, and 119. .

  Of the entire area in the circumferential direction on the front surface (outer loop surface) of the intermediate transfer belt 105, yellow (Y), cyan (C), magenta (M), black ( Four image forming units 103Y, 103C, 103M, and 103K for each color of K) are provided. The image forming units 103Y, 103C, 103M, and 103K have substantially the same configuration except that the toner colors used are different. Note that the subscripts Y, C, M, and K added to the end of the reference numerals indicate members and devices for Y, C, M, and K.

  The image forming units 103Y, 103C, 103M, and 103K include drum-shaped photoreceptors 101Y, 101C, 101M, and 101K, developing devices 102Y, 102C, 103M, and K, a charging device that uniformly charges the photoreceptor. . In the loop of the intermediate transfer belt 10, primary transfer rollers 106 Y, C, M, and K are disposed at positions facing the photoconductors 101 Y, C, M, and K via the belt so that the belt is exposed to light. The body 101Y, C, M, K is pressed. As a result, primary transfer nips for Y, C, M, and K in which the photoconductors 101Y, C, M, and K abut on the intermediate transfer belt 105 are formed.

  Above the intermediate transfer belt 105, toner bottles 104Y, 104C, M, and K for storing Y, C, M, and K toners to be supplied into the developing devices 102Y, 102C, 102M, and 102K are disposed. .

  The charging devices of the image forming units 103Y, 103C, 103M, and 103K uniformly charge the surfaces of the photoreceptors 101Y, 101C, 101M, and 101K as image carriers to the same polarity as the toner charging polarity. In the figure, as an example of the charging device, a charging brush roller to which a charging bias is applied is shown in contact with or close to the photosensitive members 101Y, 101C, 101M, 101K, but other devices such as a scorotron charger are also shown. You may use the charging device of the structure.

  A latent image writing unit 200 is provided below the image forming units 103Y, 103C, M, and K. The latent image writing unit 200 drives a semiconductor laser (not shown) based on image information sent from an external personal computer or the like and emits Y, M, C, K writing light Lb. The writing light Lb is deflected in the main scanning direction by a polygon mirror (not shown) to optically scan the photosensitive members 101Y, 101C, 101M, and 101K as latent image carriers. As a result, electrostatic latent images for Y, C, M, and K are written on the surfaces of the uniformly charged photoreceptors 101Y, C, M, and K. The light source is not limited to the semiconductor laser, and may be, for example, an LED (light emitting diode).

  Hereinafter, the configuration of the image forming units 103Y, 103C, 103M, and 103K will be described with reference to FIG. The four image forming units 103Y, 103C, 103M, and 103K have substantially the same configuration except that the color of the toner to be used is different, and FIG. 2 shows only one of the four. ing. The suffix (Y, C, M, K) at the end of the code is omitted without limiting which color unit. In the following description, the suffixes (Y, C, M, K) at the end of the reference numerals are omitted.

  The image forming unit 103 includes a charging device 301 for charging the photosensitive member 101, a developing device 102, a photosensitive member cleaning device 311, and the like around the photosensitive member 101. In the loop of the intermediate transfer belt 105, a primary transfer roller 106 is disposed at a position facing the photoconductor 101 through the belt. Instead of the primary transfer roller 106, a conductive brush shape or a non-contact corona charger may be employed.

  The charging device 301 is of a contact charging type employing a charging roller, and uniformly charges the surface of the photoconductor 101 by applying a voltage in contact with the photoconductor 101. As the charging device 301, a non-contact charging type using a non-contact scorotron charger or the like can be used.

  The developing device 102 contains a developer (not shown) containing a magnetic carrier and a nonmagnetic toner. As the developer, a one-component developer may be used. The developing device 102 can be broadly divided into a stirring unit 303 and a developing unit 304 provided in the developing case. In the agitation unit 303, a two-component developer (hereinafter simply referred to as “developer”) is conveyed while being agitated and supplied onto a developing sleeve 305 as a developer carrier.

  The stirring unit 303 is provided with two parallel screws 306. Between these two screws 306, a partition plate 309 is provided for partitioning so that both ends communicate with each other. In addition, a toner density sensor 418 for detecting the toner density of the developer in the developing device 102 is attached to the developing case 308 that houses the developing sleeve 305, the two screws 306, and the like. On the other hand, in the developing unit 304, the toner in the developer attached to the developing sleeve 305 is transferred to the photoreceptor 101.

  The developing unit 304 is provided with a developing sleeve 305 that faces the photoreceptor 101 through the opening of the developing case, and a magnet (not shown) is fixedly disposed in the developing sleeve 305. A doctor blade 307 is provided so that the tip approaches the developing sleeve 305. In the present embodiment, the distance at the closest portion between the doctor blade 307 and the developing sleeve 305 is set to 0.9 [mm]. In the developing device 102, the developer is conveyed and circulated while being stirred by two screws 306, and is supplied to the developing sleeve 305. The developer supplied to the developing sleeve 305 is drawn up and held by a magnet. The developer pumped up by the developing sleeve 305 is conveyed as the developing sleeve 305 rotates, and is regulated to an appropriate amount by the doctor blade 307. The regulated developer is returned to the stirring unit 303.

  The developer thus transported to the developing area facing the photoconductor 101 is brought into a spiked state by a magnet and forms a magnetic brush. In the developing region, a developing electric field for moving the toner in the developer to the electrostatic latent image portion on the photoreceptor 101 is formed by the developing bias applied to the developing sleeve 305. As a result, the toner in the developer is transferred to the electrostatic latent image portion on the photosensitive member 101, and the electrostatic latent image on the photosensitive member 101 is visualized to form a toner image. The developer that has passed through the developing region is transported to a portion where the magnetic force of the magnet is weak, thereby leaving the developing sleeve 305 and being returned to the stirring unit 303. When the toner concentration in the stirring unit 303 becomes light by repeating such an operation, the toner concentration sensor 418 detects this, and the toner is supplied to the stirring unit 303 based on the detection result.

  The photoconductor cleaning device 311 includes a cleaning blade 312 made of polyurethane rubber, for example, which is disposed so that the tip of the cleaning blade 312 can be pressed against the photoconductor 101. In this embodiment, in order to improve the cleaning performance, a conductive fur brush 310 that contacts the photoconductor 101 is also used. A bias is applied to the fur brush 310 from a metal electric field roller (not shown), and the tip of a scraper (not shown) is pressed against the electric field roller. The toner removed from the photoconductor 101 by the cleaning blade 312 and the fur brush 310 is accommodated in the photoconductor cleaning device 311 and collected by a waste toner collecting device (not shown).

  The photoconductor 101 is driven to rotate in the clockwise direction in the drawing at a predetermined linear velocity. The developing sleeve 305 is rotationally driven in a counterclockwise direction in the drawing at a predetermined linear velocity. The surface of the photosensitive member 101 is uniformly charged to, for example, −700 V by the charging device 301, and the potential of the electrostatic latent image written by optical scanning by the latent image writing unit 200 is about −120 [V]. The developing bias applied to the developing sleeve 305 is −470 [V], so that a developing potential of 350 [V] acts between the electrostatic latent image and the developing sleeve 305. Such process conditions are changed as appropriate according to the result of the potential control.

  In the image forming unit 103, the surface of the rotationally driven photoconductor 101 is uniformly charged by the charging device 301. Then, based on image information from the print controller 410 (see FIG. 4), the latent image writing unit 200 performs optical scanning with the writing light Lb to write an electrostatic latent image on the surface of the photoconductor 101. The electrostatic latent image is developed by the developing device 102 to become a primary color toner image having a primary color of Y, M, C, or K. This primary color toner image is primarily transferred from the surface of the photoreceptor 101 to the front surface of the intermediate transfer belt 105 in the primary transfer nip. The transfer residual toner adhering to the surface of the photoconductor 101 after passing through the primary transfer nip is removed by the photoconductor cleaning device 311.

  In FIG. 1 described above, the image forming units 103Y, 103C, 103M, and 103K form Y, C, M, and K toner images on the surfaces of the photoconductors 101Y, 101C, M, and K by the process described above. To do. These Y, C, M, and K toner images are primarily transferred while being superimposed on the front surface of the intermediate transfer belt 105 at the primary transfer nip for Y, M, C, and K. As a result, a four-color superimposed toner image is formed on the front surface of the intermediate transfer belt 105.

  Outside the loop of the intermediate transfer belt 105, a secondary transfer roller 108 that is in contact with a place where the intermediate transfer belt 105 is wound around the support roller 112 and forms a secondary transfer nip is formed. It is arranged. A secondary transfer bias having a polarity opposite to the charging polarity of the toner is applied to the secondary transfer roller 108. A pair of registration rollers is disposed below the secondary transfer nip, and this feeds the recording sheet 115 toward the secondary transfer nip at a timing synchronized with the four-color superimposed toner image of the intermediate transfer belt 105. . A four-color superimposed toner image on the intermediate transfer belt 105 is secondarily transferred onto the recording sheet by the action of the secondary transfer bias and the nip pressure on the recording sheet that has entered the secondary transfer nip. The four-color superimposed toner image is combined with the white color of the recording sheet 115 to become a full-color toner image. A scorotron charger or the like may be used instead of the secondary transfer roller 108.

  Above the secondary transfer roller 108 in the figure, a fixing device 111 is provided for fixing the full color toner image transferred onto the recording sheet 115 to the recording sheet 115. The fixing device 111 has a configuration in which a pressure roller 118 is pressed against a heating roller 117. In addition, the fixing device 111 is a color measurement unit that performs color measurement using a full-color toner image formed on the recording sheet P after passing through the fixing nip formed by the contact between the heating roller 117 and the pressure roller 118 as a test target. The spectrometer 109 is provided. Examples of the spectrometer 109 include those disclosed in Japanese Patent Application Laid-Open No. 2005-315883.

  A belt cleaning device 110 is disposed outside the belt loop. The belt cleaning device 110 is in contact with a portion where the intermediate transfer belt 105 is wound around the support roller 113 in the circumferential direction. Then, the toner adhering to the intermediate transfer belt 105 after passing through the secondary transfer nip is removed.

  Of the entire area of the intermediate transfer belt 105 in the circumferential direction, the toner adhesion amount detection sensor 120 is disposed in a region around the support roller 112 and downstream of the secondary transfer nip in the belt movement direction. It faces the front surface through a predetermined gap. The toner adhesion amount detection sensor 120 receives a reflected light amount corresponding to the toner adhesion amount with respect to a test toner image included in the gradation pattern image when a gradation pattern image to be described later passes directly under the toner adhesion amount detection sensor 120. To do.

  FIG. 3 is an enlarged configuration diagram illustrating the toner adhesion amount detection sensor 120. In the figure, the toner adhesion amount detection sensor 120 includes an LED 120a as a light emitting element, a regular reflection type light receiving element 120b, a diffuse reflection type light receiving element 120c, and the like. In addition, you may use a laser light emitting element etc. instead of LED as a light emitting element. Further, as the regular reflection type light receiving element 120b and the diffuse reflection type light receiving element 120c, phototransistors are used, but it is also possible to use a photodiode or an amplifier circuit.

  The infrared light emitted from the LED 120 a passes through the transparent detection window 120 d and then reaches the test toner image formed on the front surface of the intermediate transfer belt 105. A part of the infrared light is specularly reflected on the surface of the test toner image to become specularly reflected light, and then retransmits through the detection window 120d and is received by the specular reflection type light receiving element 120b. The regular reflection type light receiving element 120b outputs a voltage corresponding to the amount of received light. This output value is input to a main body control unit, which will be described later, and converted into digital data by an A / D conversion circuit. The other part of the infrared light is diffusely reflected on the surface of the test toner image to become diffusely reflected light, and then retransmits through the detection window 120d and is received by the diffuse reflection type light receiving element 120c. The diffuse reflection type light receiving element 120c outputs a voltage corresponding to the amount of received light. This output value is also converted into digital data by the main body control unit (not shown).

  FIG. 4 is a block diagram showing the electrical connection of each part in the printer 100. The printer 100 includes a main body control unit 406 that functions as a control device. The main body control unit 406 controls image forming operations using an electrophotographic process by driving and controlling the respective units. The main body control unit 406 rewrites various data with a ROM (Read Only Memory) 405 that stores in advance fixed data such as a computer program via the bus line 409 in the calculation unit 402 that executes various calculations and drive control of each unit. A RAM (Random Access Memory) 403 that functions as a work area to be freely stored is connected. Note that the arithmetic unit 402 includes a CPU (Central Processing Unit) and the like.

  The main body control unit 406 also includes an A / D conversion circuit 401 that converts information from the toner adhesion amount sensor 120, the spectrometer 109 as a color measurement unit, the toner density sensor 418, the temperature / humidity sensor 417, and the like into digital data. The A / D conversion circuit 401 is connected to the arithmetic unit 402 via the bus line 409.

  Connected to the main body control unit 406 is a print controller 410 that processes image data sent from a PC (Personal Computer) 411, a scanner 412, a FAX (Facsimile) 413, etc., and converts it into exposure data. The main body control unit 406 is connected to a drive circuit 414 that drives a motor and a clutch 415. Further, the main body control unit 406 forms an image on the engine unit (the image forming units 103Y, 103C, 103M, K, the primary transfer device 106, the latent image writing unit 200, the secondary transfer roller 108, and the fixing device 111). A high voltage generator 416 that generates a voltage required for the operation is also connected.

  Receiving the print command, the calculation unit 402 of the main body control unit 406 executes image formation control processing using an electrophotographic process by following the computer program stored in the ROM 405. More specifically, the calculation unit 402 of the main body control unit 406 drives the motor and the clutch 415 via the drive circuit 414, and the support roller 112 is driven to rotate, so that the intermediate transfer belt 105 is driven to rotate. At the same time, the arithmetic unit 402 of the main body control unit 406 is an engine unit (image forming unit 103, primary transfer device 106, latent image) using an electrophotographic process via a drive circuit 414 and a high voltage generator 416. The writing unit 200, the secondary transfer roller 108, and the fixing device 111) are driven.

  The arithmetic unit 402 drives the motor and the clutch 415 via the drive circuit 414 in accordance with the timing at which the four-color superimposed toner image formed on the intermediate transfer belt 105 enters the secondary transfer nip as described above. Then, the recording sheet 115 is supplied by controlling a paper feeding device (not shown). The recording sheet 115 supplied from the paper feeding device is fed between the intermediate transfer belt 105 and the secondary transfer roller 108, and the secondary transfer roller 108 causes the composite toner image on the intermediate transfer belt 105 to be transferred onto the recording sheet 115. Secondary transfer is performed. Thereafter, the recording sheet 115 is conveyed to the fixing device 111 while being attracted to the secondary transfer roller 108, and heat and pressure are applied by the fixing device 111 to perform a toner image fixing process. The recording sheet 115 that has passed through the fixing device 111 is discharged and stacked on a discharge tray (not shown). The transfer residual toner remaining on the intermediate transfer belt 105 after the secondary transfer is removed by the belt cleaning device 110.

  FIG. 5 is a block diagram showing the relationship between the main circuit in the pre-controller 410 and various processes performed in the arithmetic unit 402. When printing is performed by the printer 100 according to information from the PC 411, print information including image data is transmitted from the PC 411 using a printer driver installed in the PC 411. When the print controller 410 receives print information including image data (RGB system) transmitted from the PC 411, the print controller 410 performs predetermined processing on the image data and then outputs it to the engine unit. Specifically, first, in the 3D-LUT processing unit 410a, image data expressing the color tone in the R (red) G (green) B (blue) method is converted into C (cyan) M (magenta) Y (yellow) method. To convert the image data into color data. Next, the converted image data is subjected to UCR (Under Cover Removal) processing or GCR (Grey Component Replacement) processing by the UCR / GCR processing unit 410b, and four colors Y, C, M, and K are obtained. Obtain decomposed image data. The values of the color separation image data are corrected to values according to the characteristics of the engine unit by the input value correction processing unit 410c.

The input value correction processing unit 410c stores tone reproduction curves TRC (Tone Reproduction Curve) for Y, C, M, and K. The gradation reproduction curve TRC is an input density value of color separation image data (dot area ratio of the input image in the case of a halftone image) C _In and a primary color image formed by the engine unit according to the input density value C _In . It is a curve which shows the relationship with output density value _DOut . Ideally, the relationship between the input density value C _In and the output density value D _Out is a proportional relationship, but in practice, it is nonlinear. Therefore, in the gradation correction, a straight line connecting the lowest output density (0) and the highest density is used as an ideal characteristic, and an ideal output density value D _Out for the input density value C _{In is} obtained from the ideal characteristic. An input density value necessary to realize the value D _Out is obtained, and this is output as a corrected density value. By correcting the tone reproduction curve TRC for Y, C, M, and K stored in the input value correction processing unit 410c that performs such processing as necessary, the image forming performance is changed due to environmental fluctuations or the like. Even in the engine section that has been lost, it is possible to form a multi-color toner image with excellent reproducibility.

  The Y, C, M, and K color separation image data corrected by the input value correction processing unit 410c is converted into data for reproducing a halftone by the halftone processing unit 410d, and then output to the engine unit. .

Next, a characteristic configuration of the printer according to the embodiment will be described.
As shown in FIG. 5, the calculation unit 402 performs area search processing, parameter correction processing, correction amount determination processing, color distribution bias determination processing, colorimetric data supplement processing, colorimetry processing, sampling color database construction processing, and the like. To do.

  FIG. 6 is a flowchart showing a part of the processing flow in the control periodically performed by the arithmetic unit 402. In this processing flow, when a print command is issued by the user, the printed sheet count value T is reset to zero (step 1: hereinafter, step is denoted as S). Then, the processes from S3 to S14 are repeated until all pages are output (until Yes in S2).

  In S3 to S14, first, the print sheet count value T is incremented by one (S3), and then image forming processing is performed (S4). This image forming process is a process for forming an image for one page on one recording sheet. After completing the image forming process, after performing the area search process for searching the colorimetric adaptive area suitable for colorimetry from the image based on the image data of the page on which the image forming process has been performed, A colorimetric process is performed to measure the colorimetric adaptive area specified by the area search process in the entire area of the recording sheet on which the image is formed (S6). Colorimetry is performed by the spectrometer 109 facing the image fixing surface of the recording sheet after passing through the fixing device 111. The color measurement by the spectrometer 109 is performed on the entire area of the recording sheet, and the result is sent to the main body control unit 406 and temporarily stored in the RAM 403. The color measurement process is a process of extracting and storing only the color measurement results corresponding to the color measurement adaptive area from the color measurement results of all areas.

After completing the color measurement process, the arithmetic unit 402 inputs the original color and the color measurement result in association with each other in the sampling color database stored in the RAM 403 (S7), and the printed sheet count value T for determining whether divisible by a predetermined period constant P ₀ (S8). The periodic constant P ₀ is a numerical value for determining the timing for performing correction on the Y, C, M, K tone reproduction curve TRC stored in the pre-controller 410 as a control parameter. The gradation reproduction curve TRC is corrected every time the same number of prints as the periodic constant P ₀ are performed. S9 to S14 are flows for correcting the gradation reproduction curve TRC. Therefore, the flow of S9 to S14 is performed only when it is determined in S8 that it is divisible, and when it is determined that it is not divisible, the control flow is looped to S2.

  In S9 to S14, the arithmetic unit 402 first reads data from the sampling database (S9). Then, after analyzing the color distribution based on a plurality of color measurement results input to the sampling database, it is determined whether the color distribution is biased (S10: color distribution bias determination processing). Next, when it is determined that there is no bias (N in S10), the color measurement result read from the sampling database, the original color, and the current tone reproduction curve for each color of Y, C, M, and K, respectively. Based on the above, the curve correction amount is determined (S12: correction amount determination processing). On the other hand, if it is determined that it is biased (Y in S10), after the colorimetric data supplement process for supplementing the colorimetric data is performed (S11), the supplemented colorimetric data and the sampling database are read. A curve correction amount is determined based on the color measurement result, the original color, and the current gradation reproduction curve (S12: correction amount determination process). After that, after correcting the gradation reproduction curve TRC based on the determined curve correction amount for each of Y, C, M, and K (S13: parameter correction processing), the sampling database is cleared (S14), and the control flow is performed. To S2.

  In the area search process (S5), based on the color-separated image data of Y, C, M, and K sent from the UCR / GCR processing unit 410b of the pre-controller 410, the multi-order expressed by the color-separated image data. A search is made as to which of the entire areas of the color image is to be a colorimetric adaptive area that is a colorimetric target.

  The search for the colorimetric adaptation region is performed as follows. That is, a pixel at a predetermined position in the pixel matrix represented by the image information is set as a target pixel, and a region having a predetermined size centered on the target pixel is extracted as a partial region. For example, in the first extraction, for example, the pixel in the 21st column and the 21st row from the upper left in the pixel matrix having a resolution of 200 dpi is the pixel of interest, and a pixel of about 41 mm × 41 pixels having a size of about 5 mm square. An area is extracted as a partial area (corresponding to a square of 61 pixels on one side at 300 dpi). And the flatness which shows the flatness of the light and dark as the whole partial area is calculated, referring the pixel value (C, M, Y, K) of each pixel in the extracted partial area.

  As the flatness, those obtained by various calculation methods can be used. As a first example of flatness, one obtained by the following calculation method can be cited. That is, first, the variance of each pixel is obtained for C, M, Y, and K, respectively. Then, the sum of the variances with a negative sign is obtained as the flatness in the partial region.

  As a second example of flatness, a determinant of a variance-covariance matrix can be given. Specifically, for C, M, Y, and K, the variance and covariance at each pixel in the partial area are obtained. Next, a 4 × 4 variance-covariance matrix is constructed in which variance is arranged in the diagonal component and covariance is arranged in the non-diagonal component, and the determinant thereof is calculated. Then, a value obtained by adding a negative sign to the value of the determinant may be obtained as the flatness. This is because the spread of the distribution in the CMYK space can be evaluated by using the determinant of the variance-covariance matrix. Compared to the flatness of the first example described above, the color spread between different components can be evaluated.

  As a third example of flatness, one using color frequency characteristics can be cited. Specifically, the Fourier transform is performed using each pixel value in the partial region, and the sum of the squares of the absolute values of the Fourier coefficients of the specific frequency is obtained. A flatness is obtained by adding a negative sign to this sum. A plurality of frequencies can be used for the specific frequency. In the flatness of the first example, there is a case in which a flat region cannot be identified for an image subjected to halftone processing due to the influence of the pattern of halftone processing. On the other hand, in the flatness of the third example, the flatness excluding the influence of halftone processing can be calculated by using the sum of squares of the absolute values of the Fourier coefficients of the specific frequency. The flatness is not limited to the first to third examples described so far, and a known flatness calculation technique can be used.

  When computing unit 402 obtains the flatness of the extracted partial area, it next determines whether or not all partial areas have been extracted (whether or not extraction of partial areas has been completed for all areas of the image). . If it is determined that there is a partial area that has not yet been extracted, the position of the target pixel is shifted by one pixel in the right direction, and an area of about 5 mm square of 41 pixels × 41 pixels centered on it is obtained. Extract as a partial area. Similarly, the flatness of the color of the extracted partial area is calculated. Thereafter, when extracting the third, fourth, fifth,..., Nth partial area, the position of the target pixel is shifted by one pixel to the right. After shifting the position of the pixel of interest in the column direction from the right end of the matrix to the 21st position, the position of the pixel of interest in the column direction is returned from the left end of the matrix to the right to the 21st position. At the same time, the position in the row direction is shifted downward by one pixel. Thereafter, the process of shifting the position of the target pixel to the right by one pixel is repeated. As described above, the position of the target pixel is sequentially shifted like raster scanning to cover the entire area of the image.

  Instead of shifting the target pixel by one pixel, each partial area may be extracted so that the edges of the extracted partial areas do not overlap each other. For example, after extracting a partial region having a size of 41 pixels × 41 pixels centered on the pixel of interest in the 21st column and the 21st row, 41 pixels × centering on the pixel of interest in the 62nd column and the 62nd row A partial region having a size of 41 pixels is extracted.

  When extracting partial areas from all areas of the image and calculating flatness, the best flatness is identified from all the partial areas, and the flatness is superior to the specified standard flatness. It is determined whether or not. If it is excellent, the partial area is set as a colorimetric adaptation area suitable for colorimetry.

By such an area search process (S5), for example, in the case of an image as shown in FIG. 7, for example, 27 colorimetric adaptive areas A _{1 to} A ₂₇ shown in FIG. 8 are searched. .

In the color measurement process (S6), the color (L ^* a ^* b ^* ) of the color measurement adaptive area specified in the area search process is measured, and the color measurement data is stored in the sampling color database in the RAM 403. This sampling color database includes sampling position / color: S ^(t) , L ^* a ^* b ^* target value: R ^(t) , and output image measurement value: M ^(t) for the ^t-th output image. save. By measuring colors of a plurality of toner images and storing each colorimetric data in a sampling color database, it is possible to use a large amount of image information from a color with a high density to a color with a low density. Therefore, it is possible to maintain the smoothness of the gradation reproduction curve and suppress the variation in the difference from the ideal gradation reproduction curve. For this reason, it is possible to prevent occurrence of a discontinuity in gradation that can be visually recognized or color variation that can be visually recognized before and after correction.

In the t-th output image, the sampling position / color: S ^(t) , L ^* a ^* b ^* target value: R ^(t) , and output image measurement value: M ^(t) will be outlined below.
For sampling position / color: S ^(t) , N ^(t) sampling positions / colors: S ^(t) determined for the output image at the t-th image in the region search processing are expressed by the following equation ⁽ 1 ^). It is represented by (1) and stored in the sampling color database.

Here, (x _i ^(t) , y _i ^(t) ) is the i-th sampling position (coordinates of the center point of measurement) on the output image at time t, (c _i ^(t) , m _i ^{( t)} , y _i ^(t) , k _i ^(t) ) are CMYK concentrations in the corresponding digital data.

^Further, L ^* a * ^{b *} target ^values: For ^{R (t), L} * a as determined with reference to the sampling position from the original image data (RGB) recorded in the ^{S (t)} by the pre-controller 410 ^* B ^* Target value R ^(t) is expressed by the following equation (2), which is sent to the calculation unit 402 and stored in the sampling color database.

Equation 2
Is an L ^* a ^* b ^* target value obtained by converting RGB values at the i-th sampling position (x _i ^(t) , y _i ^(t) ) on the output image at time t.

Measurement of the output image: for M ^(t), the S ^(t) measured value M ^(t) obtained by the colorimetric processing with reference to the sampling position recorded in the next few 4 expression (3 ) And stored in the sampling color database.

(L _i ^(t) , a _i ^(t) , b _i ^(t) ) in Expression 4 is the i-th sampling position (x _i ^(t) , y _i ^{(t )} on the output image at time t. ⁾ ) L ^* a ^* b ^* measured value.

In the color distribution bias determination process (S10), based on the sampling colors S (t), S (t−1)..., S (t−P ₀ +1) of the acquired colorimetric data, Y, M, Examine the distribution of C and K. For example, for C, the distribution is calculated by removing values of other Y, M, and K components. Similarly, with respect to Y, M, and K, distributions are calculated by removing values of other monochrome components. Then, a histogram indicating the color distribution of each color is created based on the calculation results.

  FIG. 9 is a diagram illustrating an example of a histogram created in the color distribution bias determination process (S10). In this example, 16-level density distribution histograms of 1 to 16 are created for each of the colors Y, C, M, and K, and the presence or absence of color deviation is determined based on the histogram. More specifically, if there are colorimetric results at densities of 1 to 16 for all of Y, C, M, and K, it is determined that there is no color deviation. In this regard, if there is a density range where the colorimetric result is zero for any one color, it is determined that the color deviation is “present”. In the example shown in the figure, since the color measurement result is zero in the density regions 13 and 14 in M, it is determined that there is a color deviation, and the color measurement data supplement process (S11) is executed.

  In the colorimetric data supplement process (S11), first, a gradation pattern image as shown in FIG. 10 is formed on the front surface of the intermediate transfer belt 105, for example. In the example of the gradation pattern image shown in FIG. 10, each of Y, C, M, and K has a gradation pattern composed of five test toner images having different toner adhesion amounts per unit area. Each of the 20 test toner images included in the gradation pattern image detects the toner adhesion amount per unit area as it passes directly under the toner adhesion amount detection sensor 120 as the intermediate transfer belt 105 moves endlessly. Is done. As a method for converting the output voltage from the regular reflection light receiving element 120b and the diffuse reflection light receiving element 120c in the toner adhesion amount detection sensor 120 into the toner adhesion amount per unit area, for example, one described in JP-A-2006-139180 Can be illustrated.

After the toner adhesion amount of each test toner image is calculated in this way, each toner adhesion amount is converted into an L * a * b * value that is color information of an image output on the recording sheet. As a conversion method, for example, as shown in the following Table 1, a method using a data table indicating the relationship between the toner adhesion amount and the L * a * b * value can be exemplified.

The data converted from the toner adhesion amount to the L * a * b * value is subjected to the following data processing and stored in the sampling color database. That is, first, the printed sheet count value t is incremented by 1 (t = t + 1), and then the above mathematical formula 1 for the sampling position / color: S ^(t) is constructed as follows. That is, the total number of test toner images in the gradation pattern image formed on the intermediate transfer belt 105 is treated as N ^(t) in the above equation ⁽ 1 ⁾ . In the example of the gradation pattern image shown in FIG. 10, N ^(t) = 20. (X _i ^(t) , y _i ^(t) ) in Equation 1 is treated as dummy data and is not used. (C _i ^(t) , m _i ^(t) , y _i ^(t) , k _i ^(t) ) in the mathematical formula 1 is a C, M, Y, K test formed on the intermediate transfer belt 105. This corresponds to the C, M, Y, and K image densities of the toner image. Of the four elements, the corresponding primary color element is set as the density of the gradation pattern, and the other three elements are set to zero.

  Next, the target color of the output on the recording sheet corresponding to the Y, M, C, K density of the gradation pattern image Y, M, C, K test toner image formed on the intermediate transfer belt 105 is set to the above. Treated as a mathematical expression of Formula 2. Then, the toner adhesion amount is set to the L * a * b * value corresponding to the C, M, Y, K density of the C, M, Y, K test toner image of the gradation pattern image formed on the intermediate transfer belt 105. The converted value is treated as the mathematical formula of the above formula 4. By such data processing, the amount of adhesion to the test toner image of each color formed on the intermediate transfer belt 105 is handled as colorimetric data and stored in the sampling color database.

In the correction amount determination process (S12), the correction amount is determined as follows. That is, it is assumed that the densities (area ratios) of the primary colors C, M, Y, and K are quantized from 0 to L−1. However, 0 is blank, L-1 is solid, for example, L is 256. The gradation reproduction curve is expressed by functions τ _c , τ _m , τ _y , and τ _k as shown in the following equation (4) that is determined independently for each primary color of CMYK.

The output of the gradation reproduction curve for inputs 0 (blank) and L-1 (solid) is fixed at 0 and L-1, respectively. The set values representing the tone reproduction curves for the CMYK primary colors at time t are denoted by τ _c ^(t) , τ _m ^(t) , τ _y ^(t) , τ _k ^(t) . Now, the fluctuation amounts δ _c , δ _m , δ _y , δ _k of the set values representing the gradation reproduction curve are determined by the following equation (5) by “TRC control”.

Then, each set value representing the gradation reproduction curve at time t + 1 is determined as shown in the following equation (6).

  FIG. 11 is a characteristic diagram showing gradation reproduction curves and correction amount δ at times t and t + 1. This figure shows an example of the gradation reproduction curves τ (t) and τ (t + 1) and the variation δ at times t and t + 1 when L = 256.

For C, M, Y, K data (c, m, y, k), the measured value on the paper at time t is (L, a, b). After the set value representing the gradation reproduction curve is changed only by the fluctuation amounts δ _c , δ _m , δ _y , δ _k , the estimated value at time t + 1

Is given by the following equation (7).

Equation (7) in Equation 9

Is a partial differential coefficient with respect to the C, M, Y, K concentration (c, m, y, k) of each component of L ^* a ^* b ^* , that is, the C, M, Y, K concentration (c, m, y). , K) is a Jacobian matrix that collects the amount of change of each component of L ^* a ^* b ^* when each component is slightly changed. This matrix may be obtained from the data of the colorimetric values of the multi-order color toner image when the input values of C, M, Y, and K are variously changed.

The data recorded in the sampling color database, C, M, Y, K digital data space _{^{(dS (t) (c i}} (t), m i (t), y i (t), k i (t)) Clustering is performed on the component), and tone reproduction curve TRC control is started using the cluster average of C, M, Y, K (digital data) and L ^* a ^* b ^* (target value / measured value). In order to suppress the influence of in-plane color variation and measurement error due to the eccentricity of the photoreceptor, the values of C, M, Y, and K are divided into cells, and the gradation reproduction curve TRC control point is represented at the center of each cell. Let me calculate. In addition, if there is a lot of data in the cell, the error is canceled out, so the reliability becomes high. Introduce a mechanism to give reliability to the cell according to the number of data in the cell.

As shown in FIG. 12, for each of the primary colors C, M, Y, and K, the density (0 to L-1) is divided into Q equal parts (Q is a divisor of L) in a C, M, Y, and K four-dimensional space. consider the Q ⁴ pieces of the cell (four-dimensional length legislative body). FIG. 12 shows cell division and center points of C, M, Y, and K concentrations. In this example, the CM space is divided into Q = 4. The gradation reproduction curve TRC control point is represented by the center point (black circle) of each cell. The cell P (q _c , q _m , q _y , q _k ) is expressed by the following mathematical formula 11.

The center of the cell P (q _c , q _m , q _y , q _k ) is given by the following equation (10).

For a sampling color in which the values of C, M, Y, and K are in the cell P (q _c , q _m , q _y , q _k ), the gradation reproduction curve TRC variation is expressed as the cell P (q _c , q It is calculated by representing the lattice point (10) corresponding to the center point of _{m 1} , q _y , q _k ). FIG. 13 is a graph showing an example of the gradation reproduction curve TRC control point and the fluctuation amount when L = 256 and Q = 16.

Sampling color S for the past P ₀ image data (t = t ₀ , t ₀ −1,..., t−P ₀ +1) held in the sampling color database after printing of the t _0th sheet. ^{(t), L * a *} b * target value ^{R (t),} using a colorimetric value ^{M (t)} of the output image, the tone reproduction curve TRC variation of 4Q pieces, the following number 13 formula ( 11).

The evaluation function J of the following expression (12) using this as a variable is defined.

Here, the following formula 15 represents the maximum integer equal to or less than x.

The first term on the right-hand side of the evaluation function J in the equation (12) in Equation 14 is a term for minimizing the error between the target value and the estimated value at time t + 1. The second term is a term for smoothing the fluctuation amount with respect to the set value representing the gradation reproduction curve TRC, and the square of the second derivative (discrete form) of the fluctuation amount with respect to the setting value representing the gradation reproduction curve TRC. It is sum. Δ that minimizes the evaluation function J of Equation (12) in Expression 14 is calculated as follows.

Further, in the equation (13) of the equation 16, the Jacobian matrix of the following equation (14) of the equation 17 is calculated using the value of the equation (15) of the equation 18.

Formula of the following equation 19 ^{(transposition} of ^T is a matrix) is, C at time t, M, Y, K data _{^{(c i (t), m}} i (t), y i (t), k i (t) ) Represents the deviation between the measured value and the target value.

  If Q in this equation is selected to be sufficiently large (for example, Q = 16), it can be used as an estimated value of the deviation between the measured value and the target value for C, M, Y, K in Equation (15) of Equation 18. it can. Further, in minimizing the evaluation function J of the equation (12) of the equation 14, the weight to the center point of the cell increases as the number of data in the cell increases.

w (t−t ₀ ) is a weight variable for weighting the data so that the contribution of the more recent data becomes larger. When t = t ₀ + 1 → t = t ₀ + T, a function is selected so that w (t) increases monotonously. For example, a monotonically increasing concave function as shown in FIG. 14 (a function in which the derivative approaches 0 or a convex function as t increases) (c = 0 in FIG. 14) may be used. .07, t ₀ = 100).

w (t−t ₀ ) = 1−exp (−c (t−t ₀ )) (16)
Where c is a positive integer (about 10 / T)

Since the minimization problem of the equation (12) in the equation 14 is a quadratic form with respect to δ _c (c), δ _m (m), δ _y (y), and δ _k (k), the standard optimum It is possible to solve by the calculation method. Further, the values of δ _c (c), δ _m (m), δ _y (y), and δ _k (k) other than those in Expression (17) of the following Expression 20 are calculated by interpolation.

In the parameter correction process (S13), the corrected gradation reproduction curve is converted into the following based on the correction amount determined in the correction amount determination process (S12) and the setting value (current TRC) of the gradation reproduction curve TRC. It updates like Formula (18) of Formula 21.

  As described above, the calculation method using the gradation reproduction curve TRC variation of the center point of the hypercube in the CMYK four-dimensional space that can be obtained by dividing the density level by Q has the following advantages. That is, since the measurement data can be averaged, the influence of in-plane color variation and measurement error due to the eccentricity of the photosensitive drum can be canceled. Therefore, the accuracy of control can be improved, and at the same time the smoothness of the gradation reproduction curve can be maintained and fluctuations can be suppressed rapidly. Therefore, it is possible to prevent gradation discontinuity that can be visually recognized or color fluctuation that can be visually recognized.

  Further, the control points of the gradation reproduction curve TRC control can be arranged uniformly and the calculation time can be reduced. Regardless of the image data, 4Q quantities may be calculated for CMYK (for example, Q is 16).

  So far, an example of a printer that corrects the tone reproduction curve TRC as a control parameter to stabilize the color tone reproducibility has been described. However, the tone reproduction curve TRC such as the developing bias and the optical writing intensity to the photosensitive member has been described. The present invention can also be applied to an image forming apparatus that achieves stabilization of color tone reproducibility by correcting control parameters different from those in FIG.

What has been described above is merely an example, and the present invention has a specific effect for each of the following modes.
[Aspect A]
A plurality of different 1's on the surface of one image carrier (for example, a photoreceptor) based on image information acquired by receiving data from an external device such as a PC 411 or FAX 413 or reading an image by a scanner 412 based on a user's command. Image forming means (for example, image forming units 103Y, 103M, 103C, and 103K) for forming a primary color toner image or forming different primary color toner images on the surfaces of a plurality of image carriers; Formed on the surface of the one image carrier while the surface of the surface endless moving body (for example, the intermediate transfer belt 105) is opposed to the surface of the one image carrier or the plurality of image carriers. A plurality of primary color toner images formed, or primary color toner images respectively formed on the surfaces of the plurality of image carriers, on the surface of the surface endless moving body; Is a transfer unit that obtains a multi-color toner image by superimposing on the recording sheet held on the surface, and a color measurement unit that measures the multi-color toner image transferred to the recording sheet by the transfer unit (For example, a spectrometer 109), and a control device (for example, the main body control unit 406) that controls the drive of the image forming unit and the transfer unit and executes predetermined arithmetic processing. And an area search process for searching for a colorimetric adaptation area suitable for colorimetry from the image indicated by the image information, and a plurality of multi-color toner images formed based on the image information. Each of the colorimetric adaptation regions is subjected to colorimetry processing for obtaining a plurality of colorimetric results by colorimetry by the colorimetry unit, and then stored in advance for each of the plurality of primary color toner images formed by the image forming unit. A predetermined algorithm representing the relationship between the output color being set and the set value of the control parameter of the imaging means, the result of obtaining the difference from the original color for each of the plurality of colorimetric results, and the current of the control parameter And a correction amount determination process for determining a correction amount of the control parameter for reducing the difference based on the set value, and the control parameter is corrected based on the correction amount determined by the correction amount determination process. Control parameter correction processing for improving the color reproduction accuracy of the multi-color toner image, and in the correction amount determination processing, it is determined whether or not the plurality of color measurement results have no color distribution bias. If there is a deviation, a gradation pattern image composed of a plurality of test toner images each having a different toner adhesion amount per unit area for each of a plurality of primary colors is transferred to the surface endless transfer. A process of forming a toner adhesion amount per unit area for each test toner image by a toner adhesion amount detection means (for example, toner adhesion amount detection sensor 120) and a process of converting the detection result into color information. The correction amount is determined after performing the process of adding the conversion result as the color measurement result to the data group of the actual color measurement result.

[Aspect B]
Aspect B is the control device of aspect A, in which the area search process and the colorimetric process are performed for a plurality of pieces of image information individually corresponding to a plurality of pages, and the colorimetric results are stored in data storage means. Then, in the correction amount determination process, the correction amount is determined based on the result of storing a plurality of colorimetric results for the images of the plurality of pages. . With such a configuration, it is possible to suppress the occurrence of a situation in which the colorimetric data supplement processing must be performed as compared with the case where the correction amount is determined based on the colorimetry result of only one page.

[Aspect C]
In aspect C, a plurality of primary color toner images different from each other are formed on the surface of one image carrier based on image information obtained by data reception from an external device or image reading based on a user instruction. Or image forming means for forming different primary color toner images on the surfaces of a plurality of image carriers, and surface endless movement with respect to the surface of the one image carrier or the plurality of image carriers. A plurality of primary color toner images formed on the surface of the one image carrier, or primary color toners formed on the surfaces of the plurality of image carriers, with the endless moving surface of the body facing each other The image was transferred onto the recording sheet by the transfer unit, and the transfer unit obtained by superimposing and transferring the image onto the surface of the surface endless moving body or the recording sheet held on the surface to obtain a multi-color toner image In the image forming apparatus, comprising: a colorimetric unit that measures a color toner image; and a control unit that controls driving of the image forming unit and the transfer unit and executes predetermined calculation processing. A toner adhesion amount detection means for detecting a toner adhesion amount per unit area with respect to a primary color test toner image formed on the surface of the body is provided, and the control device according to aspect A or aspect B is used as the control means. It is characterized by this.

101: Photoconductor (image carrier)
103Y, M, C, K: Image forming unit (image forming means)
105: Intermediate transfer belt (surface endless moving body)
106Y, M, C, K: primary transfer roller (part of transfer means)
108: Secondary transfer roller (part of transfer means)
109: Spectrometer (colorimetric means)
106: Main body control unit (control device)
120: Toner adhesion amount detection sensor (toner adhesion amount detection means)
411: PC (external device)
413: FAX (external device)

JP 2002-033935 A JP 2004-229294 A

Claims (4)

Based on image information acquired by data reception from an external device or image reading based on a user command, a plurality of different primary color toner images are formed on the surface of one image carrier, or a plurality Image forming means for forming different primary color toner images on the surface of the image carrier;
A plurality of primary colors formed on the surface of the one image carrier while the endlessly moving surface of the surface endless moving body faces the surface of the one image carrier or the plurality of image carriers. A toner image or a primary color toner image formed on the surface of each of the plurality of image carriers is superimposed and transferred onto the surface of the surface endless moving body or a recording sheet held on the surface. Transfer means for obtaining a multi-color toner image;
A colorimetric means for measuring the color toner image transferred to the recording sheet by the transfer means;
Mounted in an image forming apparatus comprising:
A control device for controlling the drive of the image forming means and the transfer means, or for executing predetermined arithmetic processing;
An area search process for searching for a colorimetric adaptation area suitable for colorimetry from the image indicated by the image information;
After performing a color measurement process that obtains a plurality of color measurement results by measuring each of the plurality of color measurement adaptive regions in the multi-color toner image formed based on the image information by a color measurement unit,
A gradation reproduction curve representing the relationship between the input density value and the output density value stored in advance for each of the plurality of primary color toner images formed by the image forming means, a result of obtaining a difference between the color, and the based on the tone reproduction curve, the correction amount determination processing for determining the correction amount of the tone reproduction curve to smaller the difference,
The improved correction to the color reproduction accuracy of the multi-color toner image the tone reproduction curve to implement compensation process and Ru FIG based on the correction amount determined by the correction amount determination processing,
and,
In the correction amount determination process, it is determined whether or not there is a color distribution bias in the plurality of color measurement results. If there is a bias, the toner adhering to each unit area for each of the plurality of primary colors. Forming a gradation pattern image composed of a plurality of test toner images having different amounts on the surface of the surface endless moving body, and detecting a toner adhesion amount per unit area with respect to each test toner image by a toner adhesion amount detection unit; A control device for performing the process of converting the detection result into color information and the process of adding the conversion result to the data group of the actual color measurement result as the color measurement result, and then determining the correction amount . The control device according to claim 1,
For each of a plurality of pieces of image information individually corresponding to a plurality of pages, the area search process and the colorimetric process are performed, and the colorimetric result is stored in a data storage unit. The control apparatus determines the correction amount based on a result of storing a plurality of color measurement results for each of the images of the plurality of pages. Based on image information acquired by data reception from an external device or image reading based on a user command, a plurality of different primary color toner images are formed on the surface of one image carrier, or a plurality Image forming means for forming different primary color toner images on the surface of the image carrier;
A plurality of primary colors formed on the surface of the one image carrier while the endlessly moving surface of the surface endless moving body faces the surface of the one image carrier or the plurality of image carriers. A toner image or a primary color toner image formed on the surface of each of the plurality of image carriers is superimposed and transferred onto the surface of the surface endless moving body or a recording sheet held on the surface. Transfer means for obtaining a multi-color toner image;
A colorimetric means for measuring the color toner image transferred to the recording sheet by the transfer means;
In an image forming apparatus comprising: a control unit that controls driving of the image forming unit and the transfer unit or executes predetermined arithmetic processing;
Providing a toner adhesion amount detection means for detecting a toner adhesion amount per unit area with respect to a primary color test toner image formed on the surface of the surface endless moving body;
An image forming apparatus using the control device according to claim 1 or 2 as the control means. Based on image information acquired by data reception from an external device or image reading based on a user command, a plurality of different primary color toner images are formed on the surface of one image carrier, or a plurality Image forming means for forming different primary color toner images on the surface of the image carrier;
A plurality of primary colors formed on the surface of the one image carrier while the endlessly moving surface of the surface endless moving body faces the surface of the one image carrier or the plurality of image carriers. A toner image or a primary color toner image formed on the surface of each of the plurality of image carriers is superimposed and transferred onto the surface of the surface endless moving body or a recording sheet held on the surface. Transfer means for obtaining a multi-color toner image;
A colorimetric means for measuring the color toner image transferred to the recording sheet by the transfer means;
Used in an image forming apparatus comprising:
In a control method for controlling the drive of the image forming means and the transfer means or executing a predetermined calculation process,
An area search step for searching for a colorimetric adaptation area suitable for colorimetry from the image indicated by the image information;
A plurality of colorimetric adaptation regions in a multi-color toner image formed based on the image information are measured by a colorimetric means to obtain a plurality of colorimetric results, respectively,
A gradation reproduction curve representing the relationship between the input density value and the output density value stored in advance for each of the plurality of primary color toner images formed by the image forming means, a result of obtaining a difference between the color, the based on the tone reproduction curve, the correction amount determination step of determining a correction amount of the tone reproduction curve to smaller the difference,
The improvement of color reproduction accuracy of correcting the multi-color toner image the tone reproduction curve to implement and FIG Ru compensation process based on the correction amount determined by the correction amount determination step,
and,
In the correction amount determination step, it is determined whether or not there is a color distribution bias in the plurality of colorimetric results. If there is a bias, toner adhesion per unit area with respect to each of the plurality of primary colors. Forming a gradation pattern image composed of a plurality of test toner images having different amounts on the surface of the surface endless moving body, and detecting a toner adhesion amount per unit area with respect to each test toner image by a toner adhesion amount detection unit; Performing the step of converting the detection result into color information and the step of adding the conversion result to the data group of the actual color measurement result as the color measurement result, and then determining the correction amount .