JP4720375B2 - Color matching method of formed image and image forming apparatus - Google Patents

Description

  The present invention relates to a formed image color matching method and an image forming apparatus, and more particularly, to a formed image color matching method and image when forming an image on a recording medium with a toner image formed by toner adhesion to an electrostatic latent image. The present invention relates to a forming apparatus.

  In copiers and printers, the number of devices capable of outputting multicolor images has been increasing, and in order to achieve higher speed, an image forming device equipped with a plurality of image forming mechanisms (image forming engines) in one device has been developed. It is known (see, for example, Patent Document 1).

In an image forming apparatus, in order to form a high-quality image, image processing that suppresses variations in color and density unevenness is necessary. For example, an image forming system that reads a plurality of formed images with the same detection device and matches colors has been proposed (for example, see Patent Document 2). In addition, an image processing apparatus that suppresses variations in color and density unevenness in the surface of a recording medium has been proposed (see, for example, Patent Document 3).
Japanese Patent Laid-Open No. 3-151238 JP 2002-369006 A JP 2002-135610 A

  However, in an image forming apparatus equipped with a plurality of image forming mechanisms in one apparatus, in order to form a high-quality image, not only image processing that suppresses variations in color and density unevenness on a recording medium, It is necessary to consider differences between mechanisms. For example, in an image forming apparatus equipped with a plurality of image forming mechanisms in one apparatus, it is necessary to consider the following three types of variations.

  The first variation is color unevenness or density unevenness on the same recording medium. The second variation is color unevenness or density unevenness that depends on changes over time. The third variation is a variation between image forming mechanisms depending on a variation for each equipped image forming mechanism. If these three types of variations are not taken into consideration, an image forming apparatus with high quality output cannot be obtained.

  The present invention has been made in consideration of the above facts, and provides a formed image color matching method and an image forming apparatus capable of improving the image quality of an image forming apparatus equipped with a plurality of image forming engines in one apparatus. The purpose is to do.

In order to achieve the above object, the present invention exposes a charged image carrier to form an electrostatic latent image based on an input image signal, and attaches toner to the electrostatic latent image on the image carrier. In an image forming apparatus including a plurality of image forming engines that form a toner image on the image carrier and transfer the toner image to a recording medium directly or via an intermediate transfer body to form an image on the recording medium. A method for color matching a formed image by each image forming engine, wherein a toner image is formed by a first image signal for forming a single color image having a predetermined density, and the toner amount of the toner image formed on the image carrier Alternatively, a first amount of toner image of the toner image transferred onto the intermediate transfer member is detected, and the input image signal is adjusted so that the detected toner amount becomes a predetermined toner amount corresponding to the predetermined density. Process, and In each of the image forming engines, the toner amount detection position in the first step is detected by the second image signal for forming the same color image of a predetermined density in a predetermined direction and a predetermined density on the recording medium as unevenness detection. A density distribution of an image formed in a predetermined direction formed in a region including a corresponding position on the recording medium is detected, and the toner amount of the first step in the main scanning direction is detected with the predetermined direction as the main scanning direction. A second step of adjusting the input image signal to each image forming engine so that a density distribution by each image forming engine is substantially uniform in the main scanning direction with reference to a detection position ; As a detection of the color difference between the engines in each, a third image signal for forming a color image composed of a plurality of color patches of a predetermined density and different colors on the recording medium is used. The density of each color patch included in the color image formed on the recording medium is detected, and the input image signal to each image forming engine is detected so that the density of each color patch by each image forming engine substantially matches. And a third step of adjusting.

  The color matching method for formed images of the present invention enables color matching of formed images by each image forming engine in an image forming apparatus having a plurality of image forming engines. This image forming engine irradiates a light beam by an exposure unit or the like based on an input image signal while rotating an image carrier whose peripheral surface is uniformly charged with a predetermined polarity by a charging unit. An electrostatic latent image is formed, and the electrostatic latent image on the image carrier is developed by a developing unit to form a toner image. The formed toner image is transferred to a recording medium directly or via an intermediate transfer member to form an image on the recording medium.

  In the first step, a toner image is formed by a first image signal for forming a monochrome image having a predetermined density. The toner amount of the formed toner image, that is, the toner amount of the toner image formed on the image carrier or the toner image transferred onto the intermediate transfer member is detected. By adjusting the image signal so that the detected toner amount becomes a predetermined toner amount corresponding to the predetermined density, the toner amount can be adjusted so as to form a monochrome image having a predetermined density. The difference can be suppressed and the change with time can be eliminated.

  For example, when a toner image is formed, the toner image is executed based on a predetermined toner amount characteristic indicating a relationship between an image signal and a toner amount of a toner image to be formed by the image signal. The toner amount characteristic includes an exposure amount characteristic indicating the relationship between the image signal and the exposure amount or a gradation characteristic indicating the relationship between the input gradation and the output gradation for adjusting the gradation of the image signal. Therefore, in the first step, based on a predetermined toner amount characteristic (exposure amount characteristic or gradation characteristic) indicating the relationship between the image signal and the toner amount of the toner image to be formed by the image signal, the first step is performed. The toner amount of the toner image formed by the image signal may be detected, and the toner amount characteristic may be adjusted so that the detected toner amount becomes a predetermined toner amount corresponding to the predetermined density.

  In the second step, the same color image having a predetermined density and a predetermined density is formed on the recording medium in a predetermined direction as unevenness detection in each of the image forming engines by the second image signal for forming on the recording medium. As for the formed same color image, the density distribution of the image in the predetermined direction is detected. The image signal for each image forming engine is adjusted from the detected density distribution so that the density distribution by each image forming engine becomes substantially uniform. As a result, uneven color and uneven density for each image forming engine are eliminated.

  For example, when forming an image, it is executed based on a predetermined density characteristic indicating the relationship between the image signal and the density of the image to be formed by the image signal. The density characteristic includes a characteristic obtained through the exposure characteristic indicating the relationship between the image signal and the exposure amount or the gradation characteristic indicating the relationship between the input gradation and the output gradation for adjusting the gradation of the image signal. is there. Accordingly, in the second step, a predetermined direction predetermined as unevenness detection in each of the image forming engines based on a predetermined density characteristic indicating a relationship between the image signal and the density of the image to be formed by the image signal. And the same color image of a predetermined density is formed on the recording medium by a second image signal for forming on the recording medium, and the density distribution of the formed image in a predetermined direction is detected, and each of the image forming engines The density characteristic may be adjusted in the predetermined direction with respect to each image forming engine so that the density distribution due to the above becomes substantially uniform.

  In the third step, in each image forming engine, a color image composed of a plurality of color patches having different densities and having a predetermined density is recorded by a third image signal for forming on a recording medium as detection of a color difference between the engines. Formed on the medium. In the formed color image, the density of each color patch included in the color image is detected. The image signal for each image forming engine is adjusted so that the density of each color patch by each image forming engine substantially matches the detected density of the color patch. As a result, the color difference between the image forming engines can be reduced.

  Even in the adjustment in the third step, the density characteristic may be adjusted as described above.

  Each image forming engine of the image forming apparatus is provided with a detecting means for detecting the toner amount, and each image forming engine in which the detection sensitivity of each detecting means used in the first step is formed by the same image signal. Can be adjusted so that the toner amounts of the toner images substantially coincide with each other.

  In the adjustment of the toner amount, the exposure amount and the image signal may be directly adjusted. However, by adjusting the sensitivity of the detection means for detecting the toner amount, it can be reflected in subsequent image formation only by adjusting the detection means. .

  For example, the detection means for detecting the nominal amount of the toner image has detection sensitivity, and the detection result varies depending on the detection sensitivity. Since the detection sensitivity may change depending on the amount of toner, it is preferable to predetermine the detection characteristics. Therefore, the detection characteristic may be adjusted by setting in advance as detection characteristics indicating the relationship between the image signal and the detected value of the toner amount of the toner image formed by the image signal.

In the second step, the same color image can be formed in a region including a position on the recording medium corresponding to the toner amount detection position in the first step. By including the same position for the first step and the second step, it is possible to easily take cooperation between the steps.

  In the second step, a plurality of the same color images formed on the recording medium are formed at different positions in a direction intersecting a predetermined direction of unevenness detection with different densities for each of a plurality of colors including a single color and a combination of the single colors. be able to.

  The same color image may be formed in any color, but by forming each of a plurality of colors including a toner color (single color) and a combination of the single color with different densities, image formation can be performed a small number of times. Adjustment is possible. Further, by forming a plurality of positions at different positions intersecting the predetermined direction of unevenness detection, detection and adjustment under different conditions can be performed while maintaining the directionality of the unevenness detection direction.

  The detection of the density distribution of the image in the second step and the detection of the density of each color patch in the third step can be detected by the same measuring means.

  The detection of the second configuration and the detection of the third step are performed separately and independently, but when individual sensors are used for each, standardization is required between them. Therefore, by detecting with the same measuring means, the detection result can be shared, and cooperation between processes can be easily achieved.

  Preferably, the second step is performed after the first step is completed, and the third step is performed after the second step is completed.

  When adjusting the color difference between the image forming engines, it is preferable that the individual adjustments of the image forming engines have been completed. For this reason, it is preferable to execute the third step after the first step and the second step are completed. Further, in the adjustment of each image forming engine, since the image is formed after the toner image is formed, it is preferable that the adjustment for detecting the toner amount is completed before the adjustment for detecting the density of the formed image. . For this reason, it is preferable to perform a 2nd process after the 1st process is complete | finished.

The color matching method of the formed image can be realized by the following image forming apparatus. Specifically, based on the input image signal, the charged image carrier is exposed to form an electrostatic latent image, and toner is attached to the electrostatic latent image on the image carrier, thereby allowing the image carrier In an image forming apparatus having a plurality of image forming engines that form a toner image on the recording medium and transfer the toner image to a recording medium directly or via an intermediate transfer member to form an image on the recording medium. A toner image is formed by the first image signal for forming, and the toner amount of the toner image formed on the image carrier or the toner amount of the toner image transferred onto the intermediate transfer member is detected and detected. A first adjusting means for adjusting the input image signal so that the toner amount becomes a predetermined toner amount corresponding to the predetermined density; and a predetermined direction for detecting unevenness in each of the image forming engines; Predetermined dark In the region including the position on the recording medium corresponding to the detection position of the toner amount of the first adjusting means on the recording medium by the second image signal for forming the same color image on the recording medium. And detecting the density distribution of the formed image in a predetermined direction, and using the predetermined direction as the main scanning direction, the respective toner amounts in the first step in the main scanning direction with respect to the detection position of the toner amount in the first step as a reference. Second adjustment means for adjusting the input image signal to each image forming engine so that a density distribution by the image forming engine is substantially uniform, and detection of a color difference between the engines in each of the image forming engines. Each color pattern included in the color image formed on the recording medium by the third image signal for forming on the recording medium a color image having a predetermined density and a plurality of different color patches. Detecting a concentration of Ji includes a third adjusting means for adjusting an image signal to be the input said for each image forming engine so that the concentration of each color patch is substantially coincident by the respective image forming engines.

  In the image forming apparatus, each of the image forming engines is provided with detection means for detecting the toner amount, and the detection sensitivity of each of the detection means used for the first adjustment means is formed by the same image signal. The toner amount of the toner image in each image forming engine can be adjusted so as to substantially match.

In the image forming apparatus, the second adjustment unit can form the same color image in an area including a position on the recording medium corresponding to the toner amount detection position of the first adjustment unit.

  In the image forming apparatus, in the second adjustment unit, the same color image formed on the recording medium has a different density for each of a plurality of colors including a single color and a combination of the single colors, and a direction intersecting a predetermined direction of unevenness detection. A plurality can be formed at different positions.

  In the image forming apparatus, the second measuring unit can detect the density distribution of the image and the third adjusting unit can detect the density of each color patch by the same measuring unit.

  In the image forming apparatus, it is preferable that the second adjustment unit is executed after the end of the first adjustment unit, and the third adjustment unit is executed after the end of the second adjustment unit.

  According to the present invention, an amount of toner detected from a toner image for forming a single color image is adjusted to be a toner amount corresponding to a predetermined density, and the same color image for forming the same color image of a predetermined density is used. The detected density distribution is adjusted so that each image forming engine is substantially uniform, and the density of the color patches detected from the color image to form a color image composed of a plurality of color patches of a predetermined density and different colors is substantially the same. Since each image forming engine is adjusted as described above, it is possible to eliminate temporal changes, to eliminate color unevenness and density unevenness, and to reduce the color difference between the image forming engines.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

  In the image forming apparatus applied in this embodiment, an electrophotographic engine composed of a photoreceptor, a charging device, an exposure device, a developing device, a transfer device, a cleaning device, a fixing device, and the like is arranged in series in four colors of YMCK. Two color marking engines (hereinafter referred to as image forming engines) are arranged in parallel, paper is supplied to both image forming engines from the same paper tray, and the paper output from each image forming engine is output to one place. Is. In the present embodiment, variations in color and density between the two image forming engines are reduced.

(Image forming device)
FIG. 2 shows an example image forming apparatus 10 according to an embodiment of the present invention. The image forming apparatus 10 includes two image forming engines 12 and 14. A computer 24 is connected to the image forming engines 12 and 14 via an image data processing device 16. The image data processing device 16 receives image data output for image formation from the computer 24, processes the image data, and outputs it to either or both of the image forming engines 12, 14. The image data processing device 16 is connected to an unevenness correction device 18 and a color correction device 20 (details will be described later). The correction device 18 and the color correction device 20 are connected to an image detection sensor 22. Further, the image forming apparatus 10 is provided with a paper tray 26 for storing paper as a recording medium.

  Here, the image forming engine 12 and the image forming engine 14 have substantially the same configuration. Next, the image forming engine 12 will be described. The image forming engine 14 having the same configuration as the image forming engine 12 is denoted by the same reference numeral, and detailed description thereof is omitted. In order to avoid confusion between the image forming engine 12 and the image forming engine 14, the image forming engine 12 is denoted by the symbol “A” and the image forming engine 14 is denoted by the symbol “B” for distinction notation. To do.

  The image forming engine 12 includes YMCK four-color photoconductors. The YMCK four-color photoconductors have a configuration (so-called tandem configuration) that is arranged in that order independently in the transport direction.

  A charging device 44A for charging the outer peripheral surface of the photoreceptor 34A is provided above the photoreceptor 34A in charge of the Y color. An exposure device 32A is provided above the charging device 44A. The exposure device 32A is connected to the image data processing device 16 via the laser control device 30A, and is configured to receive image data of an image to be formed. The exposure device 32A modulates one or a plurality of laser beams emitted from the light source in accordance with the image to be formed, and deflects the laser beam in the main scanning direction, so that the axis of the photosensitive member 34A is on the outer peripheral surface of the photosensitive member 34A. Scan in parallel. As a result, an electrostatic latent image is formed on the outer peripheral surface of the photoreceptor 34A.

  A developing device 36A is disposed on the side of the photoreceptor 34A. The developing device 36A stores Y toner. Further, on the opposite side of the developing device 36A across the photoconductor 34A, a cleaning device 46A having a function of discharging the outer peripheral surface of the photoconductor 34A and a function of removing unnecessary toner remaining on the outer peripheral surface is provided. ing.

  An endless belt-like intermediate transfer member 42A is provided substantially below the photosensitive member 34A. The intermediate transfer member 42A is wound around a roller 39A, and is arranged so that the outer peripheral surface is in contact with the outer peripheral surface of the photosensitive member 34A. The roller 39A is rotated by a driving force of a motor (not shown), and moves the intermediate transfer member 42A in the direction of arrow h in FIG.

  A primary transfer device 38A is provided on the opposite side of the photoreceptor 34A across the intermediate transfer body 42A, and the toner image formed on the outer peripheral surface of the photoreceptor 34A is imaged on the intermediate transfer body 42A by the primary transfer device 38A. Transferred to the forming surface. When the toner image formed on the outer peripheral surface of the photoconductor 34A is transferred to the intermediate transfer body 42A, the region carrying the transferred toner image on the outer peripheral surface of the photoconductor 34A is the cleaning device 46A. Is cleaned by.

  The configuration in charge of each of the other colors included in the image forming engine 12, that is, the three colors of MCK other than the Y color, is the same as that of the Y color, and thus detailed description thereof is omitted. In the following description, when each of the four colors of YMCK is described individually, it is represented with a notation indicating a color. For example, when the exposure apparatus 32A is described as being in charge of Y color, it is described as an Y color exposure apparatus 32AY, and when it is described as being in charge of M color, it is described as an M color exposure apparatus 32AM, and is described as being in charge of C color. In this case, it is expressed as a C color exposure device 32AC, and when it is described as K color charge, it is expressed as a K color exposure device 32AK.

  A toner amount detection sensor 48A is provided on the downstream side of the K color photoconductor 34AK in charge of K color. The toner amount detection sensor 48A detects the toner amount of each color transferred to the intermediate transfer body 42A. The toner amount detection sensor 48A is connected to the laser control device 30A and the image data processing device 16 via the arithmetic device 50A.

  A secondary transfer device 40A is provided on the opposite side of the roller 39A across the intermediate transfer body 42A. A paper tray 26 is provided on the left side of FIG. 2 of the secondary transfer device 40A. A large number of sheets P as recording materials are stored in the sheet tray 26 in a stacked state. A take-out conveyance roller 54 for taking out is disposed on the right side of the paper tray 26 in FIG. 2, and a roller 39A is provided downstream in the first take-out direction (D1 direction in FIG. 2) of the paper P by the take-out conveyance roller 54. And the secondary transfer device 40A is positioned. The paper P located in the uppermost position in the stacked state is taken out from the paper tray 26 by the rotation of the take-out transport roller 54, and the direction of the take-out transport roller 54 operated by a control signal from the image data processing device 16 The sheet P is conveyed in a first take-out direction (in the direction of arrow D1 in FIG. 2) or a second take-out direction (in the direction of arrow D2 in FIG. 2) by a switching mechanism (not shown).

  A fixing device 52A and a merging / conveying roller 56 are sequentially provided on the downstream side of the secondary transfer device 40A in the sheet conveying direction. In the fixing device 52A, after the toner image transferred onto the paper P is fixed, the toner image is conveyed by the merging / conveying roller 56 to the image detection unit 23 including the image detection sensor 22. The merging / conveying roller 56 is conveyed in the first take-out direction (in the direction of arrow D1 in FIG. 2) and the second take-out direction (in the direction of arrow D2 in FIG. 2), and in each of the image forming engine 12 and the image forming engine 14. The sheet P on which the image is formed is merged and guided to the same image detection unit 23.

  The image detection sensor 22 of the image detection unit 23 detects the color and density of the image formed on the paper P. The image detection sensor 22 is connected to the image data processing device 16 via the unevenness correction device 18 and is connected to the image data processing device 16 via the color correction device 20.

  The unevenness correction device 18 is a device for correcting unevenness in color and density of an image formed on P. Image data processing is performed based on the detection result of the image detection sensor 22 when the test chart image is formed. A correction amount for adjusting a parameter relating to the unevenness of the device 16, that is, a characteristic indicating a relationship between a pixel position on the image and a color or density is output to the image data processing device 16. The color correction device 20 is a device for correcting the color difference between the image forming engines of the images formed on the paper P by the image forming engine 12 and the image forming engine 14. , 14 is a correction for adjusting a parameter relating to a color difference between the image forming engines, that is, a color characteristic for each image forming engine, according to a detection result (difference or the like) of the image detection sensor 22 when the test chart image is formed by each of The amount is output to the image data processing device 16.

  On the other hand, a guide roller 58 is provided on the downstream side in the second take-out direction of the paper P by the take-out conveyance roller 54 (the direction of arrow D2 in FIG. 2). The guide roller 58 is for guiding the paper P conveyed in the second take-out direction (the direction of arrow D2 in FIG. 2) to the roller 39B of the image forming engine 14 and the secondary transfer device 40B. A fixing device 52B and a conveyance roller 60 are sequentially provided on the downstream side of the secondary transfer device 40B in the sheet conveyance direction. The conveyance roller 60 conveys the paper P after being fixed by the fixing device 52B to 56.

  Next, the formation of a color image by the first image forming engine 12 will be briefly described. The first image forming engine 12 synthesizes (superimposes) color images (toner images) independently formed on the respective YMCK four-color photoconductors on the intermediate transfer body 42A and transfers them onto the paper P. Fixing is performed by the fixing device 52A. That is, the exposure device 32AY scans the photosensitive member 34AY with a laser beam modulated on the outer peripheral surface of the photosensitive member according to Y image data representing a Y image among color images to be formed. The image is transferred to the intermediate transfer member 42A synchronized with the rotation.

  The Y image (toner image) already formed on the intermediate transfer body 42A reaches the M color photoconductor 34AM by the rotation of the intermediate transfer body 42A. The output of the M image data representing the M image is controlled by the laser control device 30A, and the exposure device 32AM is controlled so that the positions of the Y image and the M image coincide. As a result, the M image is stacked on the Y image which is a toner image. This process is sequentially performed for each of the C image and the K image.

  Thus, Y, M, C, and K toner images are sequentially formed on the intermediate transfer member 42A so as to overlap each other by rotation thereof, and a full-color toner image is formed on the intermediate transfer member 42A. Will be formed.

  The toner image formed on the intermediate transfer member 42A is taken out from the paper tray 26 by the take-out conveying roller 5 and transferred to the paper P conveyed in the first take-out direction (the direction of arrow D1 in FIG. 2). Transcribed by 40A. The sheet P on which the toner image has been transferred is melted and fixed by the fixing device 52A, and then conveyed to the image detection unit 23, where the image is viewed, and then discharged out of the image forming apparatus 10. And placed on a paper discharge tray (not shown).

(Color / density correction)
FIG. 1 shows a flow of processing for reducing variations in color and density of the image forming apparatus 10 according to the embodiment of the present invention. The process of reducing the variation in color and density includes a correction process for reducing the change with time by stabilizing the toner amount, a correction process for reducing the density unevenness of the color unevenness and the color distribution by equalizing the density distribution, And three types of correction processing including correction processing for reducing the color difference between the image forming engines.

  The first correction process for reducing the change over time due to the stabilization of the toner amount is executed by the processes in steps 100 to 106 in FIG. Next, a second correction process for reducing unevenness in color unevenness by uniformizing the color distribution and density distribution is executed by the processing in steps 108 to 120. Then, the third correction process for reducing the color difference between the image forming engines is executed by the processes in steps 122 to 128.

  These correction processes may be executed by the image data processing device 16 according to an instruction from the computer 24 by an operator, or may be directly executed by the image data processing device 16. Note that image data and various data for forming a test chart to be described later may be stored in the image data processing device 16 in advance or may be input from the computer 24.

(First correction process)
First, in the first correction process, in step 100, a monochrome toner image is created. That is, each single color of Y, M, C, and K is used as a primary color, and each of the toner images is created on the intermediate transfer member 42A. In this process, the image data processing device 16 outputs the test chart image data stored in the built-in memory 17 to form a toner image.

  As shown in FIG. 3, for example, a toner amount detection toner image 62 is formed as a test chart between images created on the paper P. In the example of FIG. 3, an example in which a total of eight toner cells 62 </ b> S that form toner images having a density of 80% and 20% for each color of YMCK is shown. The image data for forming the toner amount detection toner image 62 by the eight toner cells 62S may be stored in advance in the built-in memory 17 of the image data processing device 16 or read from the computer 24.

  Next, in step 102 in FIG. 1, the toner amount of each of the formed toner images 62 (eight toner cells 62S) is detected by the toner amount detection sensor 48A, and a difference value from the target toner amount is calculated. These processes are executed by the arithmetic device 50A. The arithmetic device 50A includes a built-in memory 51A. The built-in memory 51A has a target toner amount for each toner image formed by the image data for forming the toner image 62 for detecting the toner amount. Stored in advance. Therefore, the arithmetic unit 50A detects the toner amount of each color read from the built-in memory 51A and the toner amount detected by the toner amount detection sensor 48A (in the example of FIG. 3, the toner amount of the toner cell 62S having the density of 80% and 20%). And calculate the difference.

  In the next step 106, gradation correction is executed using the difference value of the calculation result in step 104. The gradation correction processing in step 106 is at least one of the adjustment processing of the exposure amount to each photosensitive member by the laser control device 30A and the gradation correction parameter changing processing in the image processing performed in the image data processing device 16. is there.

  FIG. 11 shows the concept of the correction process in step 106. As shown in FIG. 11A, the gradation characteristic 70 indicating the relationship between the gradation of the image data set at the present time and the toner amount is determined from the gradation of the image data output from the image data processing device 16. This is the relationship up to the toner amount detected by the amount detection sensor 48A. Therefore, if there is a difference value in the calculation result of step 104, the gradation characteristic 70 may be adjusted. Specifically, the value of the image data output from the image data processing device 16 may be increased or decreased, or the exposure amount of the light beam emitted from the laser control device 30A may be increased or decreased. In the adjustment of the gradation characteristic 70, for example, for each of the single colors of YMCK, the toner amount of the toner cell 62S having a density of 80% (dot 74) and the toner amount of the toner cell 62S having 20% (dot 72) are obtained (FIG. 11). (See (B)), and after obtaining the characteristic 76 passing through either of them, a process for obtaining the characteristic 78 passing through both of them (see FIG. 11C) is conceivable.

  For example, in the example of FIG. 3, toner images having a YMCK single color and densities of 80% and 20% are created. The toner amount detection sensor 48A detects the toner amount of these toner images, adjusts the laser exposure amount so that the 80% toner amount becomes a predetermined amount, and in that state, the 20% toner amount becomes the predetermined amount. As described above, the tone correction parameter of the image processing is changed.

  Therefore, the processing in step 106 is performed by setting image processing parameters for increasing or decreasing the value of the image data output from the image data processing device 16 and the light emitted from the laser control device 30A for the difference value of the calculation result in step 104. By setting either or both of the parameter settings for increasing / decreasing the exposure amount of the beam, the toner amount of the primary color (YMCK single color) on the intermediate transfer body 42A is adjusted to a target amount.

  In this adjustment, the image data processing device 16 may process image processing parameter adjustment based on the difference value output from the arithmetic device 50A, and the image data processing device 16 may adjust the exposure amount of the laser control device 30A. You may control to be performed. Further, the arithmetic device 50A may directly adjust the laser control device 30A according to an instruction from the image data processing device 16.

  In the above, the adjustment based on the detection result of the toner amount detection sensor 48A has been described. However, the processing of Step 100 to Step 106 is repeated, and the toner amount of the primary color (YMCK single color) on the intermediate transfer body 42A becomes the target toner amount. You may adjust so that it becomes.

  Similar processing is also executed in the image forming engine 14.

  Here, in executing the first correction process, it is preferable that the sensitivity of the toner amount detection sensors 48A and 48B of each image forming engine is calibrated in advance as follows.

  As shown in FIG. 4, a toner amount detection toner image 62 is created in an area to be transferred to the paper P as an output image creation area, and the toner amount is detected by a toner amount detection sensor 48A. The detected toner image is transferred and fixed on the paper P, and the image detection sensor 22 detects the color and density of the image. This is performed by both image forming engines 12 and 14. Even if the target toner image on the intermediate transfer body 42A is different in color and density on the paper P between the two image forming engines, it is reflected in the target value of the toner amount in the arithmetic unit 50A.

  Specifically, the calibration processing routine shown in FIG. 10 is executed in the image data processing device 16. First, in step 200, by outputting the image data of the test chart, a toner amount detection toner image 62 is created in an area to be transferred to the paper P as an output image creation area. In the next step 202, the toner amount is detected by the toner amount detection sensor 48A, and in the next step 204, processing for transferring and fixing the detected toner image on the paper P is executed. In the next step 206, the image detection sensor 22 detects the color and density of the test chart image fixed on the paper P. In the next step 208, it is determined whether or not an image forming engine that has not been subjected to the above process remains. If the determination is negative, the process returns to step 200 to execute the process on the image forming engine that has not been completed. If the result in Step 208 is negative, the difference between the image forming engines is calculated in Step 210 for the detection result in Step 206. If the difference value is within the predetermined allowable range (Yes in Step 212), End the routine. On the other hand, if the result in Step 212 is negative, in Step 214, an image forming engine that is outside the allowable range is determined. In step 214, the image forming engine having a value farthest from a predetermined reference value can be determined, the order of YMCK colors can be determined, or a predetermined specific color can be determined. In the next step 216, a process for adjusting the toner amount table, that is, the above-described gradation characteristic 70 is executed so that the difference value obtained in step 210 is reduced for the image forming engine determined in step 214. As a result, for each image forming engine, the color and density on the paper P as the target toner image on the intermediate transfer body 42A match in each image forming engine.

(Second correction process)
When the first correction process is completed as described above, the process proceeds to the second correction process. First, in step 108, a composite color image (test chart) in the main scanning direction is formed on the paper P. The test chart may be an image of a primary color, a secondary color, or a tertiary color, which will be described later.

  As shown in FIG. 5, for example, a main scanning distribution detection image 64 for color / density unevenness detection is formed on a sheet P as a test chart. In the example of FIG. 5, an example in the case of forming the pattern cell 64S for forming a pattern image having a uniform density distribution in the main scanning direction is shown. The main scanning distribution detection image 64 includes a plurality of pattern cells 64S that are continuous. In the present embodiment, it is composed of a single color and a plurality of colors formed by each of the four colors of YMCK toner. In the example of FIG. 5, four primary colors that are single colors of YMCK and a combination of a plurality of colors, three secondary colors formed with two types of toners, Y and M, Y and M, and M and C, and A total of 16 pattern cells 64S (bands) in the main scanning direction are formed, which are composed of one tertiary color (gray) formed of YMC toner and have an image with a density of 80% and 20% for each color. Has been. The image data for forming the main scanning distribution detection image 64 by these pattern cells 64S may be stored in advance in the built-in memory 17 of the image data processing device 16 or read from the computer 24.

  In the next step 110, color / density unevenness in the main scanning direction in the test chart formed as the main scanning distribution detection image 64 is detected by the image detection sensor 22 for each color pattern cell 64S, and the next step 112 is detected from the detection result. The unevenness correction process for calculating the correction pattern and performing the process on the image data is executed. These processes are executed by the unevenness correction device 18. The unevenness correction device 18 calculates a correction pattern so that the color or density distribution of each color formed on the paper P and detected by the image detection sensor 22 is uniform over the position in the main scanning direction. This correction pattern represents the characteristic of the correction amount for making the color or density distribution uniform when it is not uniform (flat). For example, the unevenness correction device 18 obtains a difference between the detection amount of the image detection sensor 22 read from an image having a density of 80% and 20% for each color and the color or density value at a predetermined position in the main scanning direction. The correction parameter of the predetermined image data corresponding to the difference value is output to the image data processing device 16. The value of the correction parameter is stored in the built-in memory 19 of the unevenness correction device 18 as a table.

  In this case, it is preferable to perform the above correction based on the detection position of the toner amount detection sensor 48A in the main scanning direction. For example, as shown in FIG. 6, when the toner amount detection sensor 48A is located at the center of the main scanning direction, the entire color is matched with the color at the center of the main scanning direction. The same applies to the concentration.

  As shown in FIG. 7, it is assumed that the toner color detection sensor 48A is matched to the overall average color and density without matching the color and density at the position of the toner amount detection sensor 48A. In this case, when the shape of the color unevenness is different between the two image forming engines 12 and 14, the color and density after the unevenness correction are shifted between the engines. In order to solve this, as shown in FIG. 6, it is preferable to perform the above correction based on the detection position of the toner amount detection sensor 48A in the main scanning direction.

  In the image forming engine provided in the image forming apparatus 10 of the present embodiment, that is, a color engine having a structure in which each of a plurality of color toners is individually and sequentially stacked, the toner image formed on the intermediate transfer member once has another color. A phenomenon called retransfer that is peeled off by the photosensitive member when passing through the transfer device is likely to occur. Since the toner of the uppermost layer is peeled off in the retransfer phenomenon, for example, when forming a monochromatic toner image of only Y color, the Y color toner is peeled off by the retransfer phenomenon in the C primary transfer device 38AC. In addition, when an R color toner image formed of Y and M colors is formed, a retransfer phenomenon occurs only in the upper M color toner by the passage of the C primary transfer device 38AC, and does not occur in the Y color. Therefore, the color unevenness due to the retransfer phenomenon is different between the primary color toner image, the secondary color toner image, and the tertiary color toner image.

  For this reason, in the present embodiment, as shown in FIG. 5, a band (pattern cell 64S) is formed for each of the primary color, the secondary color, and the tertiary color. Further, since the retransfer phenomenon is expected to change depending on the amount of toner on the intermediate transfer member, the pattern cell 64S is created with a plurality of densities. In the present embodiment, as an example, the case where the pattern cell 64S having a density of 80% and 20% is formed for each color is shown. However, the present invention is not limited to this, and three or more kinds of densities may be used. .

  When the process of correcting the density distribution to be uniform in the main scanning direction is completed as described above, the process proceeds to step 114, and it is determined whether or not the unevenness correction process in the sub-scanning direction is executed. This determination may be instructed by an input device (not shown) or by an input signal from the computer 24, or may be set in advance. The unevenness correction process in the sub-scanning direction is almost the same as the unevenness correction process in the main scanning direction described above. That is, when correcting the color unevenness in the sub-scanning direction (paper transport direction), an image may be formed on the paper using the test chart shown in FIG.

  First, in step 116, a composite color image (test chart: sub-scanning distribution detection image 66) in the sub-scanning direction shown in FIG. In the example of FIG. 8, an example in the case of forming the pattern cell 66S for forming a pattern image having a uniform density distribution in the sub-scanning direction is shown. Note that the color of the pattern cell formed on the test chart may be any of a primary color, a secondary color, and a tertiary color.

  In the next step 118, color / density unevenness in the sub-scanning direction in the test chart formed as the sub-scanning distribution detection image 66 is detected by the image detection sensor 22 for each color pattern cell 66S, and the next step 120 is detected from the detection result. The unevenness correction process for calculating the correction pattern and performing the process on the image data is executed. That is, the unevenness correction device 18 calculates a correction pattern so that the color or density distribution of each color formed on the paper P and detected by the image detection sensor 22 is uniform over the position in the sub-scanning direction. The predetermined correction parameters for the image data are output to the image data processing device 16.

  In addition, in order to avoid variation due to the position of the image detection sensor 22, when detection is desired at the same location of the image detection sensor 22, one band (pattern cell 66S) is formed on one sheet of paper. A number of sheets may be output.

  In the above description, the case where the non-uniformity correction in the sub-scanning direction is processed after the non-uniformity correction in the main scanning direction has been described, but the order may be either or only one. When both corrections are performed, it is preferable to process the correction in the sub scanning direction after the correction in the main scanning direction. This is because each color can be arranged in the main scanning direction as shown in FIG. 8 by performing the sub-scanning after equalizing the position in the main scanning direction.

(Third correction process)
When the first correction process and the second correction process are completed as described above, the process proceeds to the third correction process. First, in step 122, a composite color image (test chart) for the main scanning direction and the sub-scanning direction is formed on the paper P for each of the image forming engines 12 and 14.

  As shown in FIG. 9, for example, a composite distribution detection image 68 for detecting color / density unevenness in the surface of the paper P is formed on the paper P as a test chart. In the example of FIG. 9, an example in which a plurality of unit pattern cells 68S having a predetermined distance in the main scanning direction and the sub-scanning direction are formed vertically and horizontally is shown. The unit pattern cell 68S is associated with data so that the densities of Y color, M color, and C color are independently changed to form primary to tertiary colors on the paper.

  In addition, in the composite distribution detection image 68 in which the unit pattern cells 68S of primary colors to tertiary colors are formed, the image data of at least the adjacent unit pattern cells 68S have the same color in order to suppress uneven distribution in the paper P. It is preferable to set so as not to become. The image data for forming the composite distribution detection image 68 by the unit pattern cells 68S may be stored in advance in the built-in memory 17 of the image data processing device 16, or may be read from the computer 24.

  In the next step 124, the correspondence between the position, color and density of the pattern cells 64S of each color arranged in the main scanning direction and the sub-scanning direction in the test chart formed as the composite distribution detection image 68 is determined by the image detection sensor. 22 to detect. In this case, the image forming engine 12 or 14 is grasped together. Thereby, it is possible to detect the color and density image of the composite distribution detection image 68 formed by each image forming engine for each position of the unit pattern cell 68S.

  The image detection sensor 22 used for detection in the third correction process uses the same image detection sensor 22 used in the second correction process. In other words, the image correction sensor 22 is shared in the second correction process and the third correction process.

  In the next step 126, from each of the composite distribution detection image 68 formed by the image forming engine 12 and the composite distribution detection image 68 formed by the image forming engine 14, the color and density are determined for each position of the unit pattern cell 68S. Find the difference between In the next step 128, processing for correcting the color difference between the image forming engines based on the difference value obtained in step 126 is executed. This process is executed by the color correction apparatus 20. The color correction device 20 calculates a difference for the color or density of each color corresponding to the position of the unit pattern cell 68S detected by the image detection sensor 22 from the paper P on which the composite distribution detection image 68 is formed by each image forming engine. At the same time, the color difference between the image forming engines 12 and 14 is obtained from the obtained difference value. The color difference here is a difference in color distribution (for example, Gamut) of an image formed by the image forming engine 12 and means a color tendency. Therefore, a predetermined correction parameter value for correcting the color tendency of the image forming engine 12 or the image forming engine 14 is obtained from the calculation result of step 126, and the result is output to the image data processing device 16. The image data processing device 16 corrects the color tendency of the image forming engine 12 or 14 based on the input correction parameter value, thereby making the image data uniform between the image forming engines 12 and 14. Can be output. As a result, the color difference between the plurality of image forming engines can be reduced. The correction parameter values are stored in advance in the built-in memory 21 of the color correction apparatus 20 as a table.

  As described above, according to the present exemplary embodiment, the first correction process causes the detected toner amount to be a predetermined toner amount corresponding to the predetermined density based on the detected density value of the toner image formed by the monochrome image having the predetermined density. Therefore, the machine difference with respect to the toner amount can be suppressed, and the change with time can be eliminated.

  Further, the second correction process can correct the density distribution by each image forming engine from the same color or density distribution formed in the main scanning direction and the sub-scanning direction, so that each image formation Color unevenness and density unevenness with respect to the engine can be eliminated.

  Further, the third correction process detects the color difference between the image forming engines and corrects the color of the image formed by each image forming engine so as to substantially match from the detected color density. The color difference between them can be reduced.

  In the above-described embodiment, the first correction process, the second correction process, and the third correction process are sequentially performed in order to adjust the color and density of the image forming engine and the color difference between the image forming engines. Although processed, it is most preferable to perform in this order. This is because, when adjusting the color difference between the image forming engines, it is preferable that each individual adjustment of the image forming engine is completed, and therefore, after the first correction process and the second correction process are completed. This is because it is preferable to execute the third correction process. Further, in the adjustment of each image forming engine, since the image is formed after the toner image is formed, it is preferable that the adjustment for detecting the toner amount is completed before the adjustment for detecting the density of the formed image. Therefore, it is also preferable to execute the second correction process after the first correction process is completed. However, the present invention is not limited to the above order, and the object of the present invention is achieved by executing the first to third correction processes.

6 is a flowchart showing a flow of processing for reducing variations in color and density of the image forming apparatus according to the embodiment of the present invention. 1 is a block diagram showing a schematic configuration of an example of an image forming apparatus according to an embodiment of the present invention. FIG. 7 is an explanatory diagram of a toner amount detection toner image used in a first correction process. It is explanatory drawing of the toner image for toner amount detection used by the calibration process utilized for a 2nd correction process. It is explanatory drawing of the main scanning distribution detection image used by a 2nd correction process. FIG. 10 is an explanatory diagram of correction based on a detection position reference of a toner amount detection sensor in a second correction process. FIG. 12 is an explanatory diagram of correction at a position other than the detection position of the toner amount detection sensor in the second correction process. It is explanatory drawing of the subscanning distribution detection image used by a 2nd correction process. It is explanatory drawing of the composite distribution detection image used by a 3rd correction process. It is a flowchart which shows the flow of the calibration process performed in an image data processing apparatus. FIG. 10 is an image diagram showing a concept of correction processing in step 106, (A) is a characteristic diagram showing a relationship between gradation and toner amount, (B) is a conceptual diagram showing a relationship between the property and detection value, and (C) is a characteristic diagram. It is explanatory drawing of adjusting.

Explanation of symbols

P ... paper 10 ... image forming device 12 ... image forming engine 14 ... image forming engine 16 ... image data processing device 18 ... unevenness correction device 20 ... color correction device 22 ... image detection sensor 24 ... computer 42A ... intermediate transfer member 50A ... calculation apparatus

Claims (10)

Based on the input image signal, the charged image carrier is exposed to form an electrostatic latent image, and a toner image is formed on the image carrier by attaching the toner to the electrostatic latent image of the image carrier. A method for color matching of formed images by each image forming engine in an image forming apparatus having a plurality of image forming engines that are formed and transfer the toner image to a recording medium directly or via an intermediate transfer member to form an image on the recording medium Because
A toner image is formed by a first image signal for forming a monochrome image of a predetermined density, and the toner amount of the toner image formed on the image carrier or the toner amount of the toner image transferred on the intermediate transfer member And a first step of adjusting the input image signal so that the detected toner amount becomes a predetermined toner amount corresponding to the predetermined density;
In each of the image forming engines, the toner amount detection position in the first step is determined by a second image signal for forming the same color image in a predetermined direction and with a predetermined density on the recording medium as unevenness detection. In the region including the position on the recording medium corresponding to the image, and detecting the density distribution of the formed image in a predetermined direction, and using the predetermined direction as the main scanning direction, the toner amount of the first step in the main scanning direction A second step of adjusting the input image signal to each image forming engine so that the density distribution by each image forming engine becomes substantially uniform in the main scanning direction with reference to the detected position of
In each of the image forming engines, as a detection of a color difference between the engines, a color image composed of a plurality of color patches having a predetermined density and different colors is formed on the recording medium by a third image signal for forming on the recording medium. A third step of detecting the density of each color patch included in the formed color image and adjusting the input image signal to each image forming engine so that the density of each color patch by each image forming engine substantially matches Color matching method including and.   Each image forming engine of the image forming apparatus is provided with a detecting unit for detecting the toner amount, and each image forming unit is formed by the same image signal with the detection sensitivity of each detecting unit used in the first step. 2. The color matching method according to claim 1, wherein the toner amount of the toner image in the engine is adjusted so as to substantially match.   In the second step, the same color image formed on the recording medium is composed of a single color and a combination of the single colors, a single color is a primary color, a secondary color is a combination of two single colors, and a single color is a combination of three colors. 3. A primary color, a secondary color, and a tertiary color are formed at a different density and at a plurality of different positions in a direction intersecting with a predetermined direction of unevenness detection. The color matching method described in 1.   4. The detection of the density distribution of the image in the second step and the detection of the density of each color patch in the third step are detected by the same measuring means. 5. The color matching method described in 1.   The said 2nd process is performed after completion | finish of said 1st process, and said 3rd process is performed after completion | finish of said 2nd process, The any one of Claim 1 thru | or 4 characterized by the above-mentioned. Color matching method. Based on the input image signal, the charged image carrier is exposed to form an electrostatic latent image, and a toner image is formed on the image carrier by attaching the toner to the electrostatic latent image of the image carrier. In an image forming apparatus including a plurality of image forming engines that form and transfer the toner image to a recording medium directly or via an intermediate transfer member to form an image on the recording medium.
A toner image is formed by a first image signal for forming a monochrome image of a predetermined density, and the toner amount of the toner image formed on the image carrier or the toner amount of the toner image transferred on the intermediate transfer member First adjusting means for adjusting the input image signal so that the detected toner amount becomes a predetermined toner amount corresponding to the predetermined density;
The first adjusting means on the recording medium by a second image signal for forming the same color image in a predetermined direction and with a predetermined density on the recording medium in a predetermined direction as unevenness detection in each of the image forming engines The toner in the first step is formed in an area including the position on the recording medium corresponding to the detection position of the toner amount, detects the density distribution of the formed image in the predetermined direction, and sets the predetermined direction as the main scanning direction. A second adjustment for adjusting the input image signal to each image forming engine so that a density distribution by each image forming engine is substantially uniform in the main scanning direction with reference to a detection position of the amount in the main scanning direction Means,
In each of the image forming engines, as a detection of a color difference between the engines, a color image composed of a plurality of color patches having a predetermined density and different colors is formed on the recording medium by a third image signal for forming on the recording medium. A third adjustment that detects the density of each color patch included in the formed color image and adjusts the input image signal to each image forming engine so that the density of each color patch by each image forming engine substantially matches. Means,
An image forming apparatus including:   Each of the image forming engines of the image forming apparatus is provided with a detecting means for detecting the amount of toner, and each image formed by the same image signal has a detection sensitivity of each detecting means used for the first adjusting means. The image forming apparatus according to claim 6, wherein the toner amounts of the toner images in the forming engine are adjusted so as to substantially coincide with each other.   In the second adjusting means, a plurality of the same color images formed on the recording medium are formed at different positions in a direction intersecting with a predetermined direction of unevenness detection with different densities for each of a plurality of colors including a single color and a combination of the single colors. The image forming apparatus according to claim 6, wherein the image forming apparatus is an image forming apparatus.   9. The detection of the density distribution of the image by the second adjustment unit and the detection of the density of each color patch by the third adjustment unit are detected by the same measurement unit. 2. The image forming apparatus according to item 1.   The said 2nd adjustment means is performed after completion | finish of the said 1st adjustment means, and the said 3rd adjustment means is performed after completion | finish of the said 2nd adjustment means, The any one of Claim 6 thru | or 9 characterized by the above-mentioned. The image forming apparatus described in the item.

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