JP4136351B2 - Color image forming apparatus and processing method in color image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrophotographic color image forming apparatus such as a color printer or a color copying machine, and more particularly to control of density-gradation characteristics thereof.
[0002]
[Prior art]
In recent years, color image forming apparatuses employing an electrophotographic system such as a color printer or a color copying machine, an ink jet system, and the like have been required to improve the output image quality. In particular, the gradation of the density and its stability have a great influence on the judgment of the quality of an image given by a human.
[0003]
However, in the color image forming apparatus, the density of the obtained image fluctuates when there are fluctuations in each part of the apparatus due to environmental changes or long-term use. In particular, in the case of an electrophotographic color image forming apparatus, even if a slight environmental change occurs, the density may change and the color balance may be lost. Therefore, it is necessary to have a means for always maintaining a constant density-gradation characteristic. . Therefore, the absolute humidity measured by the temperature / humidity sensor is provided for each color toner with gradation correction means such as several kinds of exposure amounts and development biases according to the absolute humidity, development bias, and lookup table (LUT). Based on the above, the process condition at that time and the optimum value for gradation correction are selected. In addition, a toner patch for density detection is created on the intermediate transfer member, drum, etc. with toner of each color so that a constant density-gradation characteristic can be obtained even if fluctuations occur in each part of the apparatus, and the unfixed toner patch Is detected by a density detection sensor for unfixed toner (hereinafter referred to as a density sensor), and the density control is performed by feeding back process conditions such as exposure amount and development bias based on the detection result, thereby obtaining a stable image. It is configured as follows.
[0004]
However, density control using the density sensor detects patches by forming patches on an intermediate transfer member, drum, etc., and controls changes in image color balance due to subsequent transfer to a transfer material and fixing. Not done. The color balance also changes depending on the transfer efficiency in transferring the toner image to the transfer material, and heating and pressurization by fixing. This change cannot be dealt with by density control using the density sensor.
[0005]
[Related technologies]
Therefore, on the transfer material, a gray patch of black (K) and a process gray patch in which cyan (C), magenta (M), and yellow (Y) are mixed are formed, and after fixing, the colors of both patches are relatively compared. A color image forming apparatus provided with a sensor (hereinafter referred to as a color sensor) for detecting the color of the patch on the transfer material, which can output a CMY mixing ratio at which the process gray patch is achromatic, can be considered.
[0006]
In this color image forming apparatus, the detected result is converted into an exposure amount and process condition of the image forming unit, a color matching table for converting the RGB signal of the image processing unit into the color reproduction range of the color image forming device, and the RGB signal into a CMYK signal. By feeding back to a color separation table to be converted, a calibration table for correcting density-gradation characteristics, etc., the density or chromaticity of the final output image formed on the transfer material can be controlled.
[0007]
Although it is possible to detect the output image of the color image forming apparatus with an external image reading device or a colorimeter / densitometer and perform the same control, the method using the color sensor is completely controlled within the printer. Is excellent in terms of This color sensor uses, for example, three or more light sources having different emission spectra such as red (R), green (G), and blue (B) as light emitting elements, or the light emitting element emits white light (W). And three or more types of filters having different spectral transmittances such as red (R), green (G), and blue (B) are formed on the light receiving element. As a result, three or more different outputs such as RGB output can be obtained.
[0008]
[Problems to be solved by the invention]
However, in order to perform control using a color sensor, a patch must be formed on the transfer material, which consumes the transfer material and toner. Therefore, the implementation frequency cannot be increased very much. There is a need to perform effective density or chromaticity control with a small number of implementations.
[0009]
  The present invention has been made under such circumstances. In a color image forming apparatus, a color sensor is used by combining a color sensor and a density sensor.Image input / outputReduce consumption of transfer materials by reducing the number of times characteristic control is performedFor the purpose. Also,Conventional using only a concentration sensorImage input / outputCompared to characteristic control, it is superior in that it considers the gray balance of the tertiary color.Image input / outputIt is intended to enable characteristic control to be performed inside one color image forming apparatus.The
[0010]
[Means for Solving the Problems]
  In order to achieve the above object, in the present invention, a color image forming apparatus is configured as follows.
  A color having first detection means for detecting the density of an unfixed patch and second detection means for detecting the color of a patch after fixing formed on a transfer material, and correcting input / output characteristics of an image An image forming apparatus,
  Based on the detection results of both the density of the unfixed patch detected by the first detection unit and the color of the patch on the fixed transfer material detected by the second detection unit, the input / output characteristics Has correction means to correctAnd
The correction unit calculates a deviation of the black input / output characteristics from the target based on the density detection result of the unfixed patch by black detected by the first detection unit, and uses the calculation result, The input / output characteristics of the black are corrected so as to return to the target,
And a forming unit for forming a gray patch reflecting the input / output characteristics of the black after correction by the correcting unit and a process gray patch mixed with cyan, magenta, and yellow on the transfer material,
The correcting means detects the gray color of the process gray patch based on the color of each patch after fixing formed on the transfer material formed by the forming means detected by the second detecting means. Cyan, magenta, and yellow gradations that are the same as the chromaticity of the patch are calculated, and input / output characteristics of cyan, magenta, and yellow are corrected based on the calculation results.A color image forming apparatus.
[0034]
【Example】
Example 1
FIG. 1 is a cross-sectional view illustrating an overall configuration of a “color image forming apparatus” according to a first embodiment. As shown in the figure, this apparatus is a tandem color image forming apparatus that employs an intermediate transfer member 27 that is an example of an electrophotographic color image forming apparatus. The color image forming apparatus includes an image forming unit shown in FIG. 1 and an image processing unit (not shown).
[0035]
First, processing in the image processing unit will be described. FIG. 2 is an explanatory diagram illustrating an example of processing in the image processing unit of the color image forming apparatus. In step 221, a color matching table prepared in advance converts a RGB signal representing the color of an image sent from a personal computer or the like into a device RGB signal (hereinafter referred to as DevRGB) that matches the color reproduction range of the color image forming apparatus. Convert. In step 222, the DevRGB signal is converted into a CMYK signal, which is the color of the toner color material of the color image forming apparatus, using a color separation table prepared in advance. In step 223, the CMYK signal is converted into a C′M′Y′K ′ signal obtained by correcting the density-gradation characteristics by using a calibration table for correcting the density-gradation characteristics specific to each color image forming apparatus. Convert. In step 224, the exposure time Tc, Tm, Ty, Tk of the scanner units 24C, 24M, 24Y, 24K corresponding to the C'M'Y'K 'signal is converted by a PWM (Pulse Width Modulation) table.
[0036]
Next, the operation of the image forming unit in the electrophotographic color image forming apparatus will be described with reference to FIG. The image forming unit forms an electrostatic latent image with exposure light that is turned on based on the exposure time converted by the image processing unit, develops the electrostatic latent image to form a single color toner image, and converts the single color toner image A multi-color toner image is formed by superimposing, and the multi-color toner image is transferred to the transfer material 11 and the multi-color toner image on the transfer material 11 is fixed. Photoconductors (22Y, 22M, 22C, 22K) for each station, injection charging means (23Y, 23M, 23C, 23K) as primary charging means, toner cartridges (25Y, 25M, 25C, 25K), developing means (26Y, 26M, 26C, and 26K), an intermediate transfer member 27, a transfer roller 28, a cleaning unit 29, a fixing unit 30, a density sensor 41, and a color sensor 42.
[0037]
The photosensitive drums (photoconductors) 22Y, 22M, 22C, and 22K are configured by applying an organic optical conductive layer to the outer periphery of an aluminum cylinder, and are rotated by the driving force of a driving motor (not shown) being transmitted. Rotates the photosensitive drums 22Y, 22M, 22C, and 22K in the counterclockwise direction in accordance with the image forming operation.
[0038]
As the primary charging means, four injection chargers 23Y, 23M, 23C, and 23K for charging the yellow (Y), magenta (M), cyan (C), and black (K) photoreceptors are provided for each station. In configuration, each injection charger is provided with a sleeve 23YS, 23MS, 23CS, 23KS.
[0039]
Exposure light to the photosensitive drums 22Y, 22M, 22C, and 22K is sent from the scanner units 24Y, 24M, 24C, and 24K, and the electrostatic latent images are selectively exposed by exposing the surfaces of the photosensitive drums 22Y, 22M, 22C, and 22K. An image is formed.
[0040]
As developing means, in order to visualize the electrostatic latent image, four developing devices 26Y, 26M for developing yellow (Y), magenta (M), cyan (C), and black (K) for each station, Each developing device is provided with a sleeve 26YS, 26MS, 26CS, and 26KS. Each developing device is detachably attached.
[0041]
The intermediate transfer member 27 is in contact with the photosensitive drums 22Y, 22M, 22C, and 22K, and rotates clockwise when forming a color image. The intermediate transfer member 27 rotates in accordance with the rotation of the photosensitive drums 22Y, 22M, 22C, and 22K. The toner image is transferred. Thereafter, a transfer roller 28 to be described later comes into contact with the intermediate transfer member 27 to sandwich and convey the transfer material 11, and the multicolor toner image on the intermediate transfer member 27 is transferred to the transfer material 11.
[0042]
The transfer roller 28 contacts the transfer material 11 at the position 28a while the multicolor toner image is transferred onto the transfer material 11, and is separated to the position 28b after the printing process.
[0043]
The fixing unit 30 melts and fixes the transferred multi-color toner image while conveying the transfer material 11, and as shown in FIG. 1, the fixing roller 31 for heating the transfer material 11 and the transfer material 11 are fixed to the fixing roller. A pressure roller 32 is provided for pressure contact with 31. The fixing roller 31 and the pressure roller 32 are formed in a hollow shape, and heaters 33 and 34 are incorporated therein, respectively. That is, the transfer material 11 holding the multicolor toner image is conveyed by the fixing roller 31 and the pressure roller 32, and heat and pressure are applied to fix the toner on the surface.
[0044]
After the toner image is fixed, the transfer material 11 is discharged to a discharge tray (not shown) by a discharge roller (not shown) and the image forming operation is finished.
[0045]
The cleaning unit 29 cleans the toner remaining on the intermediate transfer member 27. The waste toner after the four-color multicolor toner image formed on the intermediate transfer member 27 is transferred to the transfer material 11 is: Stored in a cleaner container.
[0046]
The density sensor 41 is arranged toward the intermediate transfer body 27 in the color image forming apparatus of FIG. 1 and measures the density of the toner patch formed on the surface of the intermediate transfer body 27. An example of the configuration of the density sensor 41 is shown in FIG. An infrared light emitting element 51 such as an LED, a light receiving element 52 such as a photodiode or Cds, an IC (not shown) that processes received light data, and a holder (not shown) that accommodates these elements.
[0047]
The light receiving element 52 a detects the intensity of irregularly reflected light from the toner patch 64, and the light receiving element 52 b detects the intensity of regular reflected light from the toner patch 64. By detecting both the regular reflection light intensity and the irregular reflection light intensity, it is possible to detect the density of the toner patch 64 from a high density to a low density. An optical element such as a lens (not shown) may be used for coupling the light emitting element 51 and the light receiving element 52.
[0048]
FIG. 4 shows an example of a density-gradation characteristic control patch pattern formed on the intermediate transfer member 27. Monochromatic gradation patches 65 of unfixed K toner are arranged. Thereafter, gradation patches of C, M, and Y toner single colors (not shown) are continuously formed. The density sensor 41 cannot distinguish the color of the toner on the intermediate transfer member 27. Therefore, a gradation patch 65 of single color toner is formed on the intermediate transfer member 27. Thereafter, the density data is fed back to a calibration table for correcting the density-gradation characteristics of the image processing unit and each process condition of the image forming unit.
[0049]
Further, the density sensor 41 uses a conversion table for converting the detected density into a color difference with a specific paper type, and converts the color difference with a specific paper type only for C, M, Y, and K single color patches and outputs the result. Some things can be done. When the density sensor can output the color difference with a specific paper type in addition to the density, instead of controlling the density-gradation characteristics of each of C, M, Y, and K, C, M, Y, and K The color difference-gradation characteristics with each specific paper type may be controlled. In this case, it is only necessary to change the density of the density-gradation characteristic control described so far to a color difference from a specific paper type. By controlling the color difference-gradation characteristics of each of C, M, Y, and K with specific paper types, it is possible to obtain gradation characteristics that are more in line with human visual characteristics.
[0050]
The color sensor 42 is disposed toward the image forming surface of the transfer material 11 downstream from the fixing unit 30 in the transfer material conveyance path in the color image forming apparatus of FIG. 1, and after the fixing formed on the transfer material 11. The RGB output value of the color of the mixed color patch is detected. By disposing the image inside the color image forming apparatus, it becomes possible to automatically detect the fixed image before discharging it to the paper discharge unit.
[0051]
FIG. 5 shows an example of the configuration of the color sensor 42. The color sensor 42 includes a white LED 53 and a charge storage sensor 54a with an RGB on-chip filter. The white LED 53 is incident at an angle of 45 degrees with respect to the transfer material 11 on which the patch after fixing is formed, and the intensity of irregularly reflected light in the 0 degree direction is detected by the charge storage sensor 54a with an RGB on-chip filter. The light receiving portion of the charge storage type sensor 54a with RGB on-chip filter is a pixel independent of RGB like 54b.
[0052]
The charge storage sensor of the RGB on-chip filter charge storage sensor 54 may be a photodiode. Several sets of three RGB pixels may be arranged. Further, a configuration in which the incident angle is 0 degree and the reflection angle is 45 degrees may be employed. Furthermore, you may comprise by LED which emits RGB three colors, and a sensor without a filter.
[0053]
Here, FIG. 6 shows an example of a patch pattern for density-gradation characteristic control after fixing formed on the transfer material 11. The patch pattern for density-gradation characteristic control is a gray gradation patch pattern that is the center of the color reproduction range and is a very important color for achieving color balance. It is composed of a gray gradation patch 61 of black (K) and a process gray gradation patch 62 in which cyan (C), magenta (M), and yellow (Y) are mixed, and 61a and 62a, 61b and 62b, 61c. And 62c, a gray tone patch 61 and a CMY process gray tone patch 62 with K having a close chromaticity are arranged in pairs in a standard color image forming apparatus. The RGB output value of this patch is detected by the color sensor 42.
[0054]
If an absolute white reference is provided, absolute chromaticity can be calculated.
[0055]
Further, since the RGB output value changes continuously with respect to the gradation, the RGB output value of a certain gradation and the adjacent gradation is detected by performing mathematical processing such as primary approximation or secondary approximation. It is possible to calculate an estimated value of the RGB output value between the gradation levels. Even when there is no absolute white reference and absolute chromaticity cannot be calculated, a gray patch with K of a certain degree of gradation can be obtained by relatively comparing the RGB output values of the gray gradation patch with K and the CMY process gray gradation patch. It is possible to calculate the mixing ratio of the CMY three colors of the process gray patch in which the three CMY colors are mixed so that the chromaticity is substantially the same.
[0056]
That is, when the output of the means for detecting the color of the patch after fixing formed on the transfer material is an output of three different colors, the output of three different colors of the process gray patch and the three different colors of the gray patch by black Are the same, it is determined that the absolute chromaticity of both patches is equal.
[0057]
FIG. 7 is a flowchart showing control of density-gradation characteristics combining the color sensor 42 and the density sensor 41 in this embodiment. Since the control using the color sensor consumes a transfer material, the number of executions is limited compared to the control using the density sensor. Therefore, as shown in FIG. 7, first, density-gradation characteristic control (hereinafter referred to as color mixing control) using a color sensor and a density sensor is performed in step 101 (shown as S101 in the figure, hereinafter the same), and thereafter In steps 102 to 104, density-gradation characteristic control using only the density sensor (hereinafter referred to as single color control) is performed a predetermined number of times, and the process returns to color mixing control again.
[0058]
As shown in FIG. 7, the mixed color and single color control is performed between normal printing operations. When the color image forming apparatus is turned on, a predetermined number of images are formed, a predetermined environmental change is detected, or a consumable. It is automatically executed at a preset timing such as at the time of replacement, or when the user desires to execute the control, it is executed manually by the user. The predetermined number of times of monochrome control is set in advance. When a change in the status of the color image forming apparatus such as power-on, environmental fluctuation, or replacement of consumables occurs, the color mixture control may be returned to even if the predetermined number of times has not been reached.
[0059]
FIG. 8 is a flowchart showing details of density-gradation characteristic control combining the color mixture control and the single color control.
[0060]
In step 111, a target of density (gradation) characteristics of black (K) is set in advance. This target is set when the image processing unit of the color image forming apparatus is designed or shipped.
[0061]
From this point on, the color image forming apparatus is installed. Steps 112 to 117 correspond to color mixing control.
[0062]
In step 112, a K gradation patch is formed on the intermediate transfer member, and the density is detected by the density sensor.
[0063]
In step 113, a deviation between the detected density-gradation characteristics of the K gradation patch and the density-gradation characteristics target set in step 111 is calculated, and the density-gradation characteristics of the image processing unit are corrected. Update the calibration table to return to the target.
[0064]
The calibration table update method in step 113 will be described with reference to FIG. For example, in a color image forming apparatus with 255 gradations, the actually obtained density sensor output is lower than that for a density target with a gradation degree of 100, and in order to obtain the same density, the gradation degree must be 160. I understand that. Therefore, the calibration table may be updated so that K100 is converted to K′160. This operation is performed at a plurality of gradations, and the calibration table is updated. In FIG. 9, the gradation and the target density are in a linear relationship, but need not be linear.
[0065]
Next, in step 114, a density-gradation characteristic control pattern after fixing, in which a gray gradation patch by K and a CMY process gray gradation patch are formed on the transfer material, is output, and after passing through the fixing device 30, the color sensor 42 detects the RGB output of the patch. At the time of forming the gray patch, only the calibration table updated in step 113 is used for K. C, M, and Y are not used.
[0066]
In step 115, the RGB output is continuously changed with respect to the gradation level from the RGB output values of the gray gradation patch by C detected in step 114 and the CMY process gray gradation patch. The C, M, and Y gradations of the CMY process gray in which the chromaticity of the gray patch by K is the same are calculated. Even if the chromaticities do not become exactly the same, an allowable color difference may be set in advance and determined to be the same within the range of the color difference.
[0067]
In step 116, the C, M, and Y calibration tables are created using the C, M, and Y gradations calculated in step 115. The method to create is as follows. For example, when the C, M, and Y gradations of the CMY process gray having the same chromaticity as the gray patch of K having a gradation of 100 created in step 114 are C140, M120, and Y80, the C calibration table The M calibration table is created to convert M100 to M′120, and the Y calibration table is created to convert Y100 to Y′80, so that C100 is converted to C′140. The same processing is performed for gray patches of other gradations, and C, M, and Y calibration tables are created.
[0068]
In step 117, using the C, M, Y calibration table created in step 116, an unfixed density-gradation characteristic control patch pattern by C, M, Y single-color gradation patches is formed on the intermediate transfer member. The density is detected by the density sensor, and the detected density-gradation characteristic is set as a target of the density-gradation characteristic of each color of C, M, and Y.
[0069]
Steps 118 to 119 correspond to monochromatic control. A normal printing operation is entered between steps 117 and 118.
[0070]
In step 118, C, M, Y, and K single-color gradation patches are formed on the intermediate transfer member, and the density is detected by the density sensor.
[0071]
In step 119, the deviation from the K density-gradation characteristic target set in step 111 and the C, M, Y density-gradation characteristic target created in step 116 is calculated, and the calibration table for each color is selected as the target. Update to return. The updating method is the same as the updating procedure of the K calibration table performed in step 113 for all the colors C, M, Y, and K.
[0072]
A normal printing operation is entered between steps 119 and 120, and it is determined whether the single color control has been performed a predetermined number of times since the previous color mixture control was performed in step 120 until the present. If it has been performed a predetermined number of times, the process returns to step 112. If it has not been performed a predetermined number of times, the process returns to step 118.
[0073]
Even when the single color control has not been performed a predetermined number of times, when there is a change in the status of the color image forming apparatus such as power-on, environmental fluctuation, replacement of consumables, etc., the process returns to the color mixing control in step 112. May be.
[0074]
If the density sensor can output the color difference with a specific paper type in addition to the density, instead of controlling the density-tone characteristics, the color difference-tone characteristics with a specific paper type can be controlled. good. In this case, all the densities in this control may be changed to color differences from a specific paper type. By doing so, it is possible to obtain gradation characteristics more in line with human visual characteristics.
[0075]
If the color sensor is capable of outputting absolute chromaticity, in step 115 the absolute chromaticity of the gray patch by K and the CMY process gray is used, and C, M, Y of the process gray having the same chromaticity are used. Each gradation may be calculated.
[0076]
As described above, according to the present embodiment, a color sensor and a density sensor are used, and by combining color mixing control and single color control, efficient density-gradation characteristics that suppress the consumption of a transfer material and toner as much as possible. This control can be performed in one color image forming apparatus. Further, by matching the density-gradation characteristics of C, M, Y with the density-gradation characteristics of K, the gray balance is stabilized, and even if an environmental change or the like that changes the density-gradation characteristics occurs, the C, M , Y, and K, the density-gradation characteristics fluctuate. Therefore, it is possible to provide a color image forming apparatus that hardly changes in hue and has excellent color reproducibility.
[0077]
(Example 2)
FIG. 10 is a flowchart illustrating details of color difference-gradation characteristic control with respect to a specific paper type in which the color mixture control and the single color control are combined in the second embodiment. The density sensor outputs the color difference from a specific paper type in addition to the density, and the output of the color sensor is absolute chromaticity. The K calibration table updated at the beginning of the color mixture control is updated to the K level formed on the transfer material. The difference from the first embodiment is that the absolute chromaticity of the tone patch is detected by a color sensor.
[0078]
In step 131, a target of color difference-gradation characteristics with a specific paper type of black (K) is set in advance. This target is set when the image processing unit of the color image forming apparatus is designed or shipped.
[0079]
From this point on, the color image forming apparatus is installed. Steps 132 to 137 correspond to color mixing control.
[0080]
In step 132, a K gradation patch is formed on the transfer material, and the absolute chromaticity is detected by the color sensor. The patch may be a patch in which an unfixed density-gradation characteristic control patch pattern 65 is fixed.
[0081]
In step 133, using the absolute chromaticity of the detected K gradation patch and the chromaticity of a specific paper type that is known, the color difference-tone characteristics of the specific paper type and the specific paper type set in step 131 The difference between the color difference and the gradation characteristic with respect to the target is calculated, and the K calibration table for correcting the color difference and the gradation characteristic with the specific paper type of the image processing unit is updated so as to return to the target.
[0082]
The calibration table update method in step 133 will be described with reference to FIG. For example, in a color image forming apparatus with 255 gradations, the color difference obtained from the actually obtained color sensor output is lower than that for a color difference target with a gradation of 100. To obtain the same color difference, the gradation is set to 160. I understand that I have to. Therefore, the calibration table may be updated so that K100 is converted to K′160. This operation is performed at a plurality of gradations, and the calibration table is updated. In FIG. 11, the gradation and the target color difference are in a linear relationship, but need not be linear.
[0083]
Next, in step 134, a density-gradation characteristic control pattern after fixing, in which a gray gradation patch by K and a CMY process gray gradation patch are formed on a transfer material, is output, and after passing through the fixing device 30, the color sensor At 42, the absolute chromaticity of the patch is detected. At the time of forming the gray patch, only the calibration table updated in step 133 is used for K. C, M, and Y are not used.
[0084]
In step 135, by using the fact that the chromaticity continuously changes with respect to the gradation degree from the absolute chromaticity of the gray gradation patch by C detected in step 134 and the CMY process gray gradation patch, The C, M, and Y gradations of the CMY process gray having the same chromaticity as the gray patch by K are calculated. Even if the color difference does not become exactly the same, an allowable color difference difference may be set in advance and determined to be the same within the range of the color difference difference.
[0085]
In step 136, the C, M, and Y calibration tables are created using the C, M, and Y gradations calculated in step 135. The method to create is as follows. For example, when the C, M, and Y gradations of the CMY process gray having the same chromaticity as the gray patch of K having a gradation of 100 created in step 134 are C140, M120, and Y80, the C calibration table The M calibration table is created to convert M100 to M′120, and the Y calibration table is created to convert Y100 to Y′80, so that C100 is converted to C′140. The same processing is performed for gray patches of other gradations, and C, M, and Y calibration tables are created.
[0086]
In step 137, using the C, M, Y calibration table created in step 136, an unfixed density-gradation characteristic control patch pattern by C, M, Y single-color gradation patches is formed on the intermediate transfer member. The color difference with the specific paper type is detected by the density sensor, and the color difference-tone characteristics with the specific paper type detected are the color difference-tone characteristics with the specific paper type of each color of C, M, Y. Set the target.
[0087]
Steps 138 to 139 correspond to monochromatic control. A normal printing operation is entered between steps 137 and 138.
[0088]
In step 138, C, M, Y, and K single-color gradation patches are formed on the intermediate transfer member, and a color difference from a specific paper type is detected by the density sensor. In step 139, the color difference from the specific paper type of K set in step 131 to the gradation characteristic target and the color difference from the specific paper type of C, M, Y created in step 136 from the gradation characteristic target. The deviation is calculated, and the calibration table for each color is updated to return to the target. The updating method is the same as the updating procedure of the K calibration table performed in step 133 for all the colors C, M, Y, and K.
[0089]
A normal printing operation is entered between steps 139 and 140, and it is determined whether the single color control has been performed a predetermined number of times since the previous color mixing control was performed in step 140 until the present. If it has been performed a predetermined number of times, the process returns to step 132. If it has not been performed a predetermined number of times, the process returns to step 138.
[0090]
Even when the single color control has not been performed a predetermined number of times, when a change in the status of the color image forming apparatus such as power-on, environmental change, or replacement of consumables occurs, the process returns to the color mixing control in step 132. May be.
[0091]
As described above, according to the present embodiment, by using a color sensor and a density sensor and combining color mixture control and single color control, in addition to the effects of the first embodiment, the first gradation characteristic control of black is performed. By using the color sensor and controlling the gradation characteristics based on the color difference from the specific paper type, not the density, it is possible to implement controls that are more suited to human visual characteristics, making it difficult for hue changes to occur and color reproduction. A color image forming apparatus having excellent properties can be provided.
[0092]
(Example 3)
FIG. 12 is a flowchart illustrating details of density-gradation characteristic control in which the color mixture control and the single color control are combined in the third embodiment. The target of density-gradation characteristics determined at the time of designing or shipping the image processing unit is not black (K) but one of cyan (C), magenta (M), and yellow (Y) However, this is different from the first and second embodiments.
[0093]
In step 151, a density-gradation characteristic target for any one of cyan (C), magenta (M), and yellow (Y) is set in advance. This target is set when the image processing unit of the color image forming apparatus is designed. Hereinafter, in order to simplify the description, a case where a C target is determined will be described. Even when M and Y targets are determined, the procedure is the same if C is replaced with M or Y.
[0094]
From this point on, the color image forming apparatus is installed. Steps 152 to 157 correspond to color mixing control.
[0095]
In step 152, a C gradation patch is formed on the intermediate transfer member, and the density is detected by a density sensor.
[0096]
In step 153, a deviation between the detected density-gradation characteristics of the gradation patch of C and the target of the density-gradation characteristics set in step 151 is calculated to correct the density-gradation characteristics of the image processing unit. Update the calibration table to return to the target. The update procedure is the same as in the first embodiment.
[0097]
  Next, in step 154, a density-gradation characteristic control pattern after fixing in which a gray gradation patch by K and a CMY process gray gradation patch are formed on the transfer material is output, and after passing through the fixing device 30, the color sensor 42 detects the RGB output of the patch. When forming a gray patch,COnly the calibration table updated in step 153 is used. K, M, and Y are not used.
[0098]
In step 155, the RGB output is continuously changed with respect to the gradation degree from the RGB output values of the gray gradation patch by C detected in step 154 and the CMY process gray gradation patch. The C, M, and Y gradations of the CMY process gray in which the chromaticity of the gray patch by K is the same are calculated. Even if the chromaticities are not exactly the same, an allowable output difference may be set in advance and determined to be the same within the range of the color difference.
[0099]
In step 156, M, Y, and K calibration tables are created using the C, M, and Y gradations calculated in step 155. The method to create is as follows. For example, if the C, M, and Y gray levels of the CMY process gray, which have the same chromaticity as the gray patch with K of gray level 100 created in step 154, are C 140, M 120, and Y 80, the K calibration table. The M calibration table is created to convert M120 to M′140, and the Y calibration table is created to convert Y80 to Y′140, so that K100 is converted to K′140. The same processing is performed for patches of other gradations, and calibration tables for M, Y, and K are created.
[0100]
In step 157, using the M, Y, K calibration table created in step 156, an unfixed density-gradation characteristic control patch pattern using M, Y, K single-color gradation patches is formed on the intermediate transfer member. The density is detected by a density sensor, and the detected density-gradation characteristics are set as targets for the density-gradation characteristics of each of the colors M, Y, and K.
[0101]
Steps 158 to 159 correspond to monochromatic control. A normal print operation is entered between steps 157 and 158.
[0102]
In step 158, C, M, Y, and K single-color gradation patches are formed on the intermediate transfer member, and the density is detected by the density sensor.
[0103]
In step 159, the deviation from the C density-gradation characteristic target set in step 151 and the M, Y, K density-gradation characteristic target created in step 156 is calculated, and the calibration table for each color is selected as the target. Update to return. The update method is the same as the C calibration table update procedure performed in step 153 for any color of C, M, Y, and K.
[0104]
A normal printing operation is entered between steps 159 and 160, and it is determined whether the single color control has been performed a predetermined number of times since the previous color mixture control was performed in step 160. If it has been performed a predetermined number of times, the process returns to step 152. If it has not been performed a predetermined number of times, the process returns to step 158.
[0105]
Even when the single color control has not been performed a predetermined number of times, when there is a change in the status of the color image forming apparatus such as power-on, environmental fluctuation, replacement of consumables, etc., the process returns to the color mixing control in step 152. May be.
[0106]
If the density sensor can output the color difference with a specific paper type in addition to the density, instead of controlling the density-tone characteristics, the color difference-tone characteristics with a specific paper type can be controlled. good. In this case, all the densities in this control may be changed to color differences from a specific paper type. By doing so, it is possible to obtain gradation characteristics more in line with human visual characteristics.
[0107]
If the color sensor can output the absolute chromaticity, in step 155, using the absolute chromaticity of the gray patch by K and the CMY process gray, the C and M of the process gray having the same chromaticity are used. , Y may be calculated.
[0108]
Further, in the update of the C calibration table in steps 152 to 153, as described in the second embodiment, the C gradation patch is formed on the transfer material, and the absolute chromaticity is detected by the color sensor. It may be updated by calculating a color difference-gradation characteristic shift between the C color difference-gradation characteristic target set in step 1 and the detected patch and predetermined paper.
[0109]
As described above, according to the present embodiment, by using a color sensor and a density sensor and combining color mixture control and single color control, in addition to the effects of the first and second embodiments, the initially set density-gradation Setting the characteristic target to one of C, M, and Y instead of K is effective when the measurement accuracy of the density sensor or color sensor is better for C, M, and Y than for K, and the change in hue is effective. It is possible to provide a color image forming apparatus that does not easily occur and has excellent color reproducibility.
[0110]
Example 4
FIG. 13 is a flowchart illustrating details of density-gradation characteristic control in which the color mixture control and the single color control are combined in the fourth embodiment. The difference from the first embodiment is that the target of density-gradation characteristics of cyan (C), magenta (M), yellow (Y), and black (K) is determined in advance.
[0111]
In step 171, targets for density-gradation characteristics of C, M, Y, and K are set in advance. This target is set when the image processing unit of the color image forming apparatus is designed or shipped.
[0112]
From this point on, the color image forming apparatus is installed. Steps 172 to 177 correspond to color mixture control.
[0113]
In step 172, a K gradation patch is formed on the intermediate transfer member, and the density is detected by the density sensor.
[0114]
In step 173, a deviation between the density-gradation characteristics of the detected K gradation patch and the target of the density-gradation characteristics set in step 171 is calculated, and the density-gradation characteristics of the image processing unit are corrected. Update the calibration table to return to the target. The updating method is the same as in the first embodiment.
[0115]
Next, in step 174, a density-gradation characteristic control pattern after fixing, in which a gray gradation patch by K and a CMY process gray gradation patch are formed on the transfer material, is output, and after passing through the fixing device 30, the color sensor 42 detects the RGB output of the patch. When forming a gray patch, K uses the calibration table updated in step 173. C, M, and Y also use a calibration table at the time of design or at that time.
[0116]
In step 175, the RGB output of the gray gradation patch detected by K and the CMY process gray gradation patch detected in step 174 is continuously changed with respect to the gradation. The C, M, and Y gradations of the CMY process gray in which the chromaticity and the chromaticity of the gray patch by K are the same are calculated. Even if the chromaticities do not become exactly the same, an allowable color difference may be set in advance and determined to be the same within the range of the color difference.
[0117]
In step 176, the C, M, and Y calibration tables are updated using the C, M, and Y gradations calculated in step 175. The method of updating is as follows. For example, suppose that the C, M, and Y gray levels of CMY process gray, which have the same chromaticity as a gray patch with a gray level of K at the time of designing the image processing unit, are designed to be C 140, M 120, and Y 80. On the other hand, it is assumed that the C, M, and Y gray levels of the CMY process gray having the same chromaticity as the gray patch with K of gray level 100 are C135, M125, and Y90 based on the calculation result of step 175. In this case, the C calibration table converts C140 to C'135, the M calibration table converts M120 to M'125, and the Y calibration table converts Y80 to Y'90. Create as you want. The same processing is performed for gray patches of other gradations, and the C, M, and Y calibration tables are updated.
[0118]
In step 177, using the C, M, Y calibration table updated in step 176, an unfixed density-gradation characteristic control patch pattern using C, M, Y single-color gradation patches is formed on the intermediate transfer member. The density is detected by the density sensor, and the detected density-gradation characteristics are set as the density-gradation characteristics targets for the C, M, and Y colors.
[0119]
Steps 178 to 179 correspond to monochromatic control. A normal printing operation is entered between steps 177 and 178.
[0120]
In step 178, C, M, Y, and K single-color gradation patches are formed on the intermediate transfer member, and the density is detected by the density sensor.
[0121]
In step 179, the deviation from the K density-gradation characteristic target created in step 171 and the C, M, Y density-gradation characteristic target updated in step 176 is calculated, and the calibration table for each color is selected as the target. Update to return. The update method is the same as the update procedure of the K calibration table performed in step 173 for all the colors C, M, Y, and K.
[0122]
A normal printing operation is entered between steps 179 and 180, and it is determined whether the single color control has been performed a predetermined number of times since the previous color mixing control was performed in step 180. If it has been performed a predetermined number of times, the process returns to step 172. If it has not been performed a predetermined number of times, the process returns to step 178.
[0123]
Even when the single color control has not been performed a predetermined number of times, when there is a change in the status of the color image forming apparatus such as power-on, environmental fluctuation, replacement of consumables, etc., the process returns to the color mixing control in step 172. May be.
[0124]
If the density sensor can output the color difference with a specific paper type in addition to the density, instead of controlling the density-tone characteristics, the color difference-tone characteristics with a specific paper type can be controlled. good. In this case, all the densities in this control may be changed to color differences from a specific paper type. By doing so, it is possible to obtain gradation characteristics more in line with human visual characteristics.
[0125]
If the color sensor is capable of outputting absolute chromaticity, C, M, and Y of the process gray having the same chromaticity are obtained in step 175 using the absolute chromaticity of the gray patch by K and the CMY process gray. Each gradation may be calculated.
[0126]
As in the second embodiment, in steps 172 and 173, a gray patch of K may be formed on the transfer body, and the calibration table of K may be updated.
[0127]
As described above, according to the present embodiment, a color sensor and a density sensor are used, and by combining color mixing control and single color control, efficient density-gradation characteristics that suppress the consumption of a transfer material and toner as much as possible. This control can be performed in one color image forming apparatus. In addition, by adjusting to the density-gradation characteristics of K, the gray balance is stabilized, and even if there is an environmental change that changes the density-gradation characteristics, the C-, M-, Y-, and K-density-gradation characteristics together. Therefore, it is difficult for the hue to change, and by setting the target of C-, M-, and Y-density / gradation characteristics in advance, a color image with good single-color gradation characteristics and excellent color reproducibility can be obtained. A forming apparatus can be provided.
[0128]
【The invention's effect】
  As described above, according to the present invention, the color sensor is used by combining the color sensor and the density sensor.Image input / outputReduce consumption of transfer materials by reducing the number of times characteristic control is performedbe able to. Also, Using only the concentration sensorImage input / outputCompared to characteristic control, it is superior in that it considers the gray balance of the tertiary color.Image input / outputThe characteristic control can be performed inside one color image forming apparatus.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing the overall configuration of Example 1
FIG. 2 is a flowchart showing processing in the image processing unit.
FIG. 3 is a diagram showing the configuration of a density sensor
FIG. 4 is a diagram showing a patch pattern for density-gradation characteristic control.
FIG. 5 is a diagram illustrating a configuration of a color sensor.
FIG. 6 is a diagram showing a density-gradation characteristic control patch pattern formed on a transfer material.
FIG. 7 is a flowchart showing control of density-gradation characteristics by combining a color sensor and a density sensor.
FIG. 8 is a flowchart showing details of density-gradation characteristic control combining color mixture control and single color control in the first embodiment.
FIG. 9 is a diagram for explaining a calibration table update procedure of the image processing unit;
FIG. 10 is a flowchart showing details of color difference-gradation characteristic control from a predetermined sheet, which combines color mixture control and single color control in the second embodiment
FIG. 11 is a diagram for explaining a calibration table update procedure of the image processing unit;
12 is a flowchart showing details of density-gradation characteristic control combining color mixture control and single color control in Embodiment 3. FIG.
FIG. 13 is a flowchart showing details of density-gradation characteristic control combining color mixture control and single color control in Embodiment 4.
[Explanation of symbols]
11 Transfer material
22 Photoconductor, Photosensitive drum
26 Developing means
27 Intermediate transfer member
30 Fixing device
41 Concentration sensor
42 Color sensor
61 Gray tone patch in black
62 Process Gray Tone Patch
63 Patch pattern for density-tone characteristics control after fixing formed on transfer material
64 single color unfixed gradation patch
65 Patch pattern for controlling density-tone characteristics formed on an intermediate transfer member without fixing

Claims (10)

A color having first detection means for detecting the density of an unfixed patch and second detection means for detecting the color of a patch after fixing formed on a transfer material, and correcting input / output characteristics of an image An image forming apparatus,
Based on the detection results of both the density of the unfixed patch detected by the first detection unit and the color of the patch on the fixed transfer material detected by the second detection unit, the input / output characteristics Having correction means for performing correction,
The correction unit calculates a deviation of the black input / output characteristics from the target based on the density detection result of the unfixed patch by black detected by the first detection unit, and uses the calculation result, The input / output characteristics of the black are corrected so as to return to the target,
And a forming unit for forming a gray patch reflecting the input / output characteristics of the black after correction by the correcting unit and a process gray patch mixed with cyan, magenta, and yellow on the transfer material,
The correcting means detects the gray color of the process gray patch based on the color of each patch after fixing formed on the transfer material formed by the forming means detected by the second detecting means. A color image forming apparatus that calculates cyan, magenta, and yellow gradations that are the same as the chromaticity of a patch, and corrects input / output characteristics of cyan, magenta, and yellow based on the calculation result. The forming unit, after performing the correction to return to the target , forms a gray patch reflecting the black input / output characteristics of the correction unit and the process gray patch on the transfer material. The color image forming apparatus according to claim 1. Wherein the first detection means, a color image forming apparatus according to claim 1 or 2, characterized in that it is constituted by an infrared light emitting means and light receiving means. The first detection means for detecting the density of the unfixed patch and the second detection means for detecting the color of the patch after fixing formed on the transfer material, the undecided detected by the first detection means. A color image forming apparatus that corrects input / output characteristics based on both detection results of a density of a patch of a patch and a color of a patch on a transfer material after fixing detected by the second detection unit;
Based on the detection result of the black unfixed patch detected by the first detection means and the target of the black input / output characteristic determined in advance, the black input / output characteristic is corrected to return to the target. First correction means;
Forming means for forming, on the transfer material, a gray patch reflecting the input / output characteristics of the black after correction by the first correction means, and a process gray patch in which cyan, magenta and yellow are mixed;
Based on the color of each patch after fixing formed on the transfer material formed by the forming means detected by the second detecting means, the chromaticity of the process gray patch is the chromaticity of the gray patch by black Color image formation, comprising: second correction means for determining gradation levels of cyan, magenta, and yellow that are the same, and correcting input / output characteristics of cyan, magenta, and yellow based on the obtained results apparatus. It said forming means, the first continues to correction by the correction means, a color image forming equipment according to claim 4, characterized in that formed on the transfer material the process gray patch. A color having first detection means for detecting the density of an unfixed patch and second detection means for detecting the color of a patch after fixing formed on a transfer material, and correcting input / output characteristics of an image A processing method in an image forming apparatus, comprising:
Based on the detection results of both the density of the unfixed patch detected by the first detection unit and the color of the patch on the fixed transfer material detected by the second detection unit, the input / output characteristics have a correction step of performing correction,
The correction step calculates a deviation of a predetermined black input / output characteristic from the target based on the density detection result of the unfixed patch by black detected by the first detection unit, and uses the calculation result, The input / output characteristics of the black are corrected so as to return to the target,
And a forming step of forming, on the transfer material, a gray patch reflecting the input / output characteristics of the black after correction in the correction step, and a process gray patch in which cyan, magenta, and yellow are mixed,
The correction step is based on the color of each patch after fixing formed on the transfer material formed in the forming step, which is detected by the second detection unit, and the chromaticity of the process gray patch is a gray color based on black. Processing in a color image forming apparatus characterized by calculating cyan, magenta, and yellow gradations that are the same as the chromaticity of a patch, and correcting input / output characteristics of cyan, magenta, and yellow based on the calculation results Method. The forming step includes forming a gray patch reflecting the input / output characteristics of black in the correction step and the process gray patch on the transfer material following the correction to return to the target. The processing method in the color image forming apparatus according to claim 6 , wherein: 8. The processing method in the color image forming apparatus according to claim 6 , wherein the first detection unit includes an infrared light emitting unit and a light receiving unit. The first detection means for detecting the density of the unfixed patch and the second detection means for detecting the color of the patch after fixing formed on the transfer material, the undecided detected by the first detection means. Color image forming apparatus having a correction step for correcting input / output characteristics based on both detection results of the density of the patch of the arrival and the color of the patch on the transfer material after fixing detected by the second detection means A processing method in which
Based on the detection result of the black unfixed patch detected by the first detection means and the target of the black input / output characteristic determined in advance, the black input / output characteristic is corrected to return to the target. A first correction step;
Forming a gray patch reflecting the input / output characteristics of the black after correction in the first correction step and a process gray patch in which cyan, magenta, and yellow are mixed on the transfer material;
Based on the color of each patch after fixing formed on the transfer material formed by the forming step detected by the second detection means, the chromaticity of the process gray patch is the chromaticity of the gray patch by black. A color image forming method, comprising: a second correction step of obtaining gradation levels of cyan, magenta, and yellow that are the same, and correcting input / output characteristics of cyan, magenta, and yellow based on the obtained results. Processing method in the apparatus. 10. The processing method of a color image forming apparatus according to claim 9 , wherein, in the forming step, the process gray patch is formed on a transfer material following the correction in the first correction step.

Images