Image forming apparatus and control program

Abstract

To provide an image forming apparatus that can prevent excessive correction without impairing the followability of correction to color change.SOLUTION: An image forming apparatus 100 comprises: an image forming unit 20 that forms a patch for correction by using toner; a measuring unit 50 that measures the color, density or amount of toner attached to the patch for correction; a calculation unit that calculates a reference correction amount based on a measured value from the measuring unit 50 so as to adjust the density of the patch for correction to a target value; and a correction unit that corrects an image formation condition for the image forming unit 20 by a first correction amount smaller than the reference correction amount.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an image forming apparatus and a control program. [Background technology]

[0002] In order to stabilize the color of printed matter during continuous printing, a color correction technique is known in which the image forming conditions (hereinafter also referred to as "image forming conditions") of an image forming unit are corrected based on the amount of change in color on paper. For example, Japanese Patent Laid-Open Publication No. 2013-218034 (Patent Document 1) discloses an image forming apparatus that corrects the image forming conditions in stages. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-218034 Summary of the Invention [Problem to be solved by the invention]

[0004] In the image forming apparatus disclosed in JP 2013-218034 A, the image forming conditions are corrected in stages until the correction amount reaches the "target correction amount" detected from the adjustment patch image. This prevents extreme color changes and does not impair the ability of the correction to follow color fluctuations. However, because the image forming conditions are ultimately corrected by the "target correction amount," there is a possibility that the correction may be overcorrected due to the influence of density unevenness in the adjustment patch image.

[0005] The present disclosure provides an image forming apparatus and a control program that can suppress overcorrection without impairing the ability to correct for color variations. [Means for solving the problem]

[0006] An image forming apparatus according to one aspect of the present disclosure includes an image forming unit that forms a correction patch using toner, a measurement unit that measures the color, density, or amount of toner adhesion of the correction patch, a calculation unit that calculates a standard correction amount based on the measurement value of the measurement unit so that the density of the correction patch becomes a target value, and a correction unit that corrects the image creation conditions of the image forming unit by a first correction amount that is smaller than the standard correction amount.

[0007] Preferably, the image forming apparatus further includes a determination unit that determines the first correction amount in accordance with a planned number of calculations of the reference correction amount during a period from when the correction patch is formed until the image-forming conditions are corrected.

[0008] Preferably, the determination unit determines, as the first correction amount, a value obtained by dividing the reference correction amount by the expected number of calculations.

[0009] Preferably, in the initial stage of continuous printing, the determination unit determines, as the first correction amount, a value greater than a value obtained by dividing the reference correction amount by the expected number of calculations.

[0010] Preferably, when the reference correction amount exceeds a threshold, the first correction amount is the sum of a second correction amount determined for an intra-threshold correction amount that is the threshold portion of the reference correction amount and a third correction amount determined for an extra-threshold correction amount that is the threshold portion of the reference correction amount. The image forming apparatus further includes a determination unit that determines the second correction amount based on the intra-threshold correction amount and a planned number of calculations of the reference correction amount during a period from when the correction patch is formed to when the image-forming conditions are corrected, and determines the third correction amount as a value obtained by subtracting the previous extra-threshold correction amount from the current extra-threshold correction amount.

[0011] Preferably, the image forming apparatus is switchable from an image formation mode to an unevenness measurement mode for measuring uneven density of the correction patch, and further includes a first setting unit that sets a threshold value based on a measurement value of the measurement unit in the unevenness measurement mode.

[0012] Preferably, the image forming unit forms the target value calculation patch multiple times at the beginning of continuous printing. The measurement unit measures the density of the target value calculation patch each time. The image forming apparatus further includes a second setting unit that sets a representative value of the densities of the target value calculation patch multiple times as the target value.

[0013] Preferably, the size of the target value calculation patch is larger than the size of the correction patch.

[0014] Preferably, the image forming apparatus further includes an adjusting unit that adjusts the first correction amount determined by the determining unit in accordance with a change in a factor that affects color.

[0015] Preferably, the factors include the coverage of the image.

[0016] Preferably, the image forming apparatus further includes a developing unit, and the factors include the charge amount of the toner in the developing unit.

[0017] Preferably, the factors include the waiting time between the end of a previous print and the start of a current print.

[0018] Preferably, the factors include the temperature within the imaging device.

[0019] Preferably, the factors include humidity within the imaging device.

[0020] A control program executed by a computer according to another aspect of the present disclosure causes the computer to form a correction patch using toner, measure the color, density, or toner adhesion amount of the correction patch, calculate a standard correction amount based on the measurement value so that the density of the correction patch becomes a target value, and correct the image formation conditions by a first correction amount that is smaller than the standard correction amount. [Effects of the Invention]

[0021] According to the present disclosure, overcorrection can be suppressed without impairing the ability of correction to follow color variations. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a diagram illustrating an overview of an image forming apparatus according to a first embodiment. [Figure 2] FIG. 2 is a diagram for explaining correction patches according to the first embodiment. [Figure 3] FIG. 3 is a diagram for explaining a target value calculation patch according to the first embodiment. [Figure 4] FIG. 2 is a diagram illustrating an example of a hardware configuration of the image forming apparatus according to the first embodiment. [Figure 5] FIG. 10 is a diagram illustrating a color correction method B1. [Figure 6] FIG. 10 is a diagram showing changes in color when color correction is performed by method B1. [Figure 7] FIG. 10 is a diagram illustrating a color correction method B2. [Figure 8] FIG. 10 is a diagram showing changes in color when color correction is performed by method B2. [Figure 9] 4A to 4C are diagrams for explaining a color correction method performed by the image forming apparatus according to the first embodiment. [Figure 10] FIG. 10 is a diagram showing changes in color when color correction is performed by method A. [Figure 11] FIG. 2 is a diagram for explaining an outline of a color correction process performed by the image forming apparatus according to the first embodiment. [Figure 12] 5A to 5C are diagrams for explaining an example of correction of image-forming conditions by the image forming apparatus according to the first embodiment. [Figure 13] FIG. 4 is a diagram showing an example of a change in development potential in the first embodiment. [Figure 14] 10 is a flowchart showing a procedure for color correction performed by the image forming apparatus according to the first embodiment. [Figure 15] FIG. 11 is a diagram showing an example of a first correction amount in the second embodiment. [Figure 16] FIG. 11 is a diagram for explaining an outline of a color correction process performed by an image forming apparatus according to a third embodiment. [Figure 17]This is a diagram for explaining the outline of the color correction process by the image forming apparatus in Embodiment 4. [Figure 18] This is a diagram for explaining the method of calculating the first correction amount in Embodiment 4. [Figure 19] This is a diagram showing an example of various correction amounts shown in FIG. 18.

Embodiments for Carrying Out the Invention

[0023] Hereinafter, embodiments and modified examples according to the present disclosure will be described with reference to the drawings. In the following description, the same parts and components are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed descriptions thereof will not be repeated. Note that the embodiments and modified examples described below may be selectively combined as appropriate.

[0024] [Embodiment 1] [A. Outline of the Image Forming Apparatus]

[0025] Referring to FIGS. 1 to 3, the outline of the image forming apparatus in Embodiment 1 will be described.

[0026] FIG. 1 is a diagram showing the outline of the image forming apparatus in Embodiment 1. Referring to FIG. 1, the image forming apparatus 100 in Embodiment 1 includes a paper feeding unit 10, an image forming unit 20, an operation panel 30, a measurement unit 50, and a processor 70.

[0027] The paper feeding unit 10 feeds out the sheets of paper SH stored therein one by one to the conveyance path 5. The image forming unit 20 forms an image on the sheet of paper SH using toner. The image includes at least one of a user-specified image specified by the user, a correction patch, and a target value calculation patch. Details of the correction patch and the target value calculation patch will be described later, but these are gradation patches for each color. The operation panel 30 is a touch panel in which an input device and a display device are integrated. The operation panel 30 receives various setting information of the image forming apparatus 100 and notifies various information.

[0028] The measurement unit 50 is a reflective optical sensor incorporating a light-emitting element such as a light-emitting diode and a light-receiving element such as a photodiode. During the target value calculation period, the measurement unit 50 measures the density of a target value calculation patch formed on the paper SH and outputs the measurement results to the processor 70. The processor 70 sets a target value for color correction based on the measurement results of the measurement unit 50. Furthermore, during the color correction period after the target value calculation period ends, the measurement unit 50 measures the density of a correction patch formed on the paper SH and outputs the measurement results to the processor 70. The processor 70 corrects the image-forming conditions of the image forming unit 20 based on the measurement results of the measurement unit 50. In the following description, correcting the image-forming conditions of the image forming unit is also referred to as "applying correction" or "applying a correction amount."

[0029] The measurement unit 50 may measure the color of a correction patch or a target value calculation patch formed on the paper SH. The measurement unit 50 may also measure the amount of toner attached to a correction patch or a target value calculation patch formed on the paper SH. In the following description, the measurement unit 50 is assumed to measure the density of a correction patch or a target value calculation patch formed on the paper SH.

[0030] Image forming section 20 includes imaging unit 15Y that forms a yellow toner image, imaging unit 15M that forms a magenta toner image, imaging unit 15C that forms a cyan toner image, imaging unit 15K that forms a toner image of a key plate, a secondary transfer device 27, a cleaning device 28, and a fixing device 29. In the following description, when there is no need to distinguish between imaging unit 15Y, imaging unit 15M, imaging unit 15C, and imaging unit 15K, they will be referred to as "imaging units 15."

[0031] Imaging unit 15Y includes a photoconductor 21Y, a charging device 22Y, an exposure device 23Y, a developing device 24Y, and a primary transfer device 25Y. Imaging unit 15M includes a photoconductor 21M, a charging device 22M, an exposure device 23M, a developing device 24M, and a primary transfer device 25M. Imaging unit 15C includes a photoconductor 21C, a charging device 22C, an exposure device 23C, a developing device 24C, and a primary transfer device 25C. Imaging unit 15K includes a photoconductor 21K, a charging device 22K, an exposure device 23K, a developing device 24K, and a primary transfer device 25K.

[0032] In the following description, when there is no need to distinguish between photoconductors 21Y, 21M, 21C, and 21K, they will be referred to as "photoconductors 21." When there is no need to distinguish between charging devices 22Y, 22M, 22C, and 22K, they will be referred to as "charging devices 22." When there is no need to distinguish between exposure devices 23Y, 23M, 23C, and 23K, they will be referred to as "exposure devices 23." When there is no need to distinguish between developers 24Y, 24M, 24C, and 24K, they will be referred to as "developers 24." When there is no need to distinguish between primary transfer devices 25Y, 25M, 25C, and 25K, they will be referred to as "primary transfer devices 25."

[0033] The image forming apparatus 100 forms an image as follows. First, the charging device 22 applies a negative charge to the entire photoconductor 21. Next, the exposure device 23 irradiates the negatively charged photoconductor 21 with laser light based on printing data. The printing data includes image data of a user-specified image and image data of a correction patch. A positive charge is generated in the areas irradiated with the laser light, and negative charges are eliminated. As a result, a latent image of the printing data is formed on the photoconductor 21. Next, the developing device 24 supplies negatively charged toner to the photoconductor 21. As a result, the toner adheres to areas of the photoconductor 21 that do not have a negative charge, making the latent image visible. In other words, a toner image based on the printing data is formed on the photoconductor 21.

[0034] Next, the primary transfer device 25 transfers the toner image formed on the photoreceptor 21 onto the intermediate transfer belt 26. As the intermediate transfer belt 26 rotates, the toner images of each color are superimposed on the intermediate transfer belt 26. As a result, a toner image based on the printing data is formed on the intermediate transfer belt 26.

[0035] A secondary transfer device 27 transfers the toner images of each color superimposed on the intermediate transfer belt 26 onto the paper SH. A cleaning device 28 collects toner that remains on the intermediate transfer belt 26 without being transferred to the paper SH. A fixing device 29 applies heat and pressure to the paper SH onto which the toner image has been transferred, fixing the toner image to the paper SH. This completes the formation of the image on the paper SH, after which the paper SH is discharged onto the paper output tray 18.

[0036] It should be noted that the image forming apparatus 100 is not limited to a color machine, but may also be a monochrome machine.

[0037] 2 is a diagram illustrating correction patches according to Embodiment 1. The correction patches P are gradation patches for each color used for color correction of yellow, magenta, cyan, and the key plate.

[0038] Correction patch P1 is a yellow gradation patch. Correction patch P2 is a magenta gradation patch. Correction patch P3 is a red gradation patch. Correction patch P4 is a green gradation patch. Correction patch P5 is a cyan gradation patch. Correction patch P6 is a black gradation patch. Correction patch P7 is a blue gradation patch. Correction patch P8 is a process ink (Process Bk) gradation patch.

[0039] In the following description, when there is no need to distinguish between correction patches P1, P2, P3, P4, P5, P6, P7, and P8, they will be referred to as "correction patches P." In the example shown in Fig. 2, all of the correction patches P used for color correction of yellow, magenta, cyan, and the key plate are formed on one sheet of paper SH.

[0040] The paper SH is transported in the direction of the arrow in the figure. The paper SH is ultimately cut along cutting lines CR1 and CR2. The correction patches P are formed in an area of ​​the paper SH on which the user-specified image I is formed that will ultimately be discarded, i.e., an area outside the cutting lines CR1 and CR2.

[0041] The correction patches P are repeatedly formed during continuous printing. For example, the correction patches P may be formed on every sheet SH of continuous printing, or may be formed every other sheet of continuous printing.

[0042] The correction patches P may be formed on a sheet of paper different from the sheet of paper SH on which the user-specified image I is formed. Also, if all of the correction patches P cannot fit on one sheet of paper SH, the remaining correction patches P may be formed on the next sheet of paper SH.

[0043] 3 is a diagram for explaining the target value calculation patches according to Embodiment 1. The target value calculation patches Q are gradation patches for each color used to calculate the target value in color correction.

[0044] The target value calculation patch Q1 is a yellow gradation patch. The target value calculation patch Q2 is a magenta gradation patch. The target value calculation patch Q3 is a red gradation patch. The target value calculation patch Q4 is a green gradation patch. The target value calculation patch Q5 is a cyan gradation patch. The target value calculation patch Q6 is a black gradation patch. The target value calculation patch Q7 is a blue gradation patch. The target value calculation patch Q8 is a process ink gradation patch.

[0045] In the following description, when there is no need to distinguish between target value calculation patch Q1, target value calculation patch Q2, target value calculation patch Q3, target value calculation patch Q4, target value calculation patch Q5, target value calculation patch Q6, target value calculation patch Q7, and target value calculation patch Q8, they will be referred to as "target value calculation patches Q." In the example shown in Fig. 3, all of the target value calculation patches Q used to calculate target values ​​in color correction for yellow, magenta, cyan, and the key plate are formed on one sheet of paper SH.

[0046] The paper SH is transported in the direction of the arrow in the figure. The paper SH is ultimately cut along cutting lines CR1 and CR2. The target value calculation patch Q is formed in an area of ​​the paper SH on which the user-specified image I is formed that will ultimately be discarded, i.e., an area outside the cutting lines CR1 and CR2.

[0047] The target value calculation patches Q are formed multiple times at the beginning of continuous printing by the image forming unit 20. For example, the target value calculation patches Q may be formed on all sheets of paper SH at the beginning of continuous printing, or may be formed on every other sheet of paper SH at the beginning of continuous printing.

[0048] The target value calculation patches Q may be formed on a sheet of paper different from the sheet of paper SH on which the user-specified image I is formed. Also, if all of the target value calculation patches Q cannot fit on one sheet of paper SH, the remaining target value calculation patches Q may be formed on the next sheet of paper SH.

[0049] Furthermore, the size of the target value calculation patch Q may be the same as the size of the correction patch P, or may be larger than the size of the correction patch P. When the size of the target value calculation patch Q is larger than the size of the correction patch P, the influence of density unevenness of the target value calculation patch Q can be suppressed, and the accuracy of the target value is improved.

[0050] In this embodiment, the target value calculation patch Q is formed three times at the initial stage of continuous printing, and the target value in color correction is set based on the density of the target value calculation patch Q from the first time to the third time.

[0051] <B. Hardware Configuration Example of Image Forming Apparatus 100> FIG. 4 is a diagram showing an example of the hardware configuration of the image forming apparatus in Embodiment 1. In addition to the above-described paper feeding unit 10, image forming unit 20, operation panel 30, measurement unit 50, and processor 70, the image forming apparatus 100 further includes a communication interface 40, a memory card interface 60, a memory 80, and a storage 90. The paper feeding unit 10, image forming unit 20, operation panel 30, communication interface 40, measurement unit 50, memory card interface 60, processor 70, memory 80, and storage 90 are electrically connected via a bus 99.

[0052] The communication interface 40 is responsible for data exchange between the image forming apparatus 100 and an external device. The external device is, for example, a terminal device used by the user. As an example, the communication interface 40 receives the image data of the user-specified image I from the external device.

[0053] The processor 70 is configured, for example, by a CPU (Central Processing Unit) or an MPU (Micro-Processing Unit). The memory 80 is configured, for example, by a volatile storage device such as a DRAM (Dynamic Random Access Memory) or an SRAM (Static Random Access Memory). The storage 90 is configured, for example, by a non-volatile storage device such as an SSD (Solid State Drive) or a flash memory. The storage 90 stores a program 91. The program 91 includes computer-readable instructions for controlling the image forming apparatus 100. The program 91 includes a "control program" in this disclosure. The processor 70 implements various processes according to this embodiment by expanding the program 91 stored in the storage 90 into the memory 80 and executing it.

[0054] The storage 90 further stores the calculated estimated number of times NT, which will be described later.

[0055] The program 91 is provided by being stored in a storage medium such as the memory card 60A. The program 91 is read from the memory card 60A by the memory card interface 60 and installed in the image forming apparatus 100.

[0056] Program 91 may be provided not as a standalone program but as part of an arbitrary program. In this case, the program 91 cooperates with the arbitrary program to realize the processing according to the present embodiment. Even if the program does not include some of the modules, it does not deviate from the spirit of image forming apparatus 100 according to the present embodiment. In addition, some or all of the functions provided by program 91 may be realized by dedicated hardware.

[0057] Alternatively, instead of installing the program 91 stored in the memory card 60A in the image forming apparatus 100, a program downloaded from a distribution server or the like may be installed in the image forming apparatus 100.

[0058] <C. Problems of Color Correction> Referring to FIGS. 5 to 8, problems of color correction will be described.

[0059] FIG. 5 is a diagram showing a color correction method B1. The method B1 is an example of a color correction method to be compared with the color correction method by the image forming apparatus 100 in the first embodiment.

[0060] The sheet SHn (n is an integer of 1 or more) indicates the nth sheet during continuous printing. In the following description, when the sheet SHn is not distinguished, it is referred to as "sheet SH". The sheet SH is conveyed in the direction of the arrow in the figure. [[ID=十六]]

[0061] [[ID=十七]] In the example shown in FIG. 5, a correction patch P and a user-specified image I are formed on the first sheet SH1. Also, in the example shown in FIG. 5, only the user-specified image I is formed on the sheets SH from the second sheet to the twenty-sixth sheet. In FIG. 5, the correction patch P formed on the first sheet SH1 is referred to as the "first correction patch P".

[0062] In the method B1, a correction amount is calculated based on the density of the correction patch P for one time, and the image forming conditions of the image forming unit are corrected by the correction amount. Specifically, the correction amount is calculated so that the measured density of the correction patch P for one time becomes the target value.

[0063] As an example, when the first correction patch P is formed, first, the density of the correction patch P is measured. Next, a correction amount is calculated so that the density of the correction patch P becomes the target value. Next, the image forming conditions of the image forming unit are corrected by the correction amount.

[0064] 5, the timing at which correction is applied for the first time after the formation of the first correction patch P is the timing at which image formation starts on the twelfth sheet of paper (sheet of paper SH13 in the figure) after the formation of the first correction patch P. That is, in the example shown in FIG. 5, for the twelfth and subsequent sheets of paper after the formation of the first correction patch P, images are formed under image creation conditions corrected by the correction amount calculated based on the first correction patch P. Even when the technology described in Patent Document 1 is applied, for example, after the formation of the first correction patch P, the image creation conditions are corrected in stages at the timing of image formation on the twelfth to fourteenth sheets of paper (sheets of paper SH13, SH14, and SH15 in the figure), and an image is formed on the fifteenth sheet of paper (sheet of paper SH16 in the figure) under image creation conditions corrected by the correction amount calculated based on the first correction patch P.

[0065] A change in color when color correction is performed using method B1 will be described with reference to Fig. 6. Fig. 6 is a diagram showing a change in color when color correction is performed using method B1.

[0066] Color R1 indicates the color when the first correction patch P is formed. Color R2 indicates the color when an image is formed on the fifth sheet of paper (sheet of paper SH6 shown in FIG. 5) after the first correction patch P is formed. Color R3 indicates the color when an image is formed on the tenth sheet of paper (sheet of paper SH11 shown in FIG. 5) after the first correction patch P is formed. Color R4 indicates the color when an image is formed on the fifteenth sheet of paper (sheet of paper SH16 shown in FIG. 5) after the first correction patch P is formed, when color correction is not performed. Color R5 indicates the color when an image is formed on the twentieth sheet of paper (sheet of paper SH21 shown in FIG. 5) after the first correction patch P is formed, when color correction is not performed. Color R6 indicates the color when an image is formed on the twenty-fifth sheet of paper (sheet of paper SH26 shown in FIG. 5) after the first correction patch P is formed, when color correction is not performed.

[0067] Color R4α indicates the color when an image is formed on the 15th sheet of paper (sheet of paper SH16 shown in FIG. 5) after the first correction patch P is formed when color correction is performed using method B1. Color R5α indicates the color when an image is formed on the 20th sheet of paper (sheet of paper SH21 shown in FIG. 5) after the first correction patch P is formed when color correction is performed using method B1. Color R6α indicates the color when an image is formed on the 25th sheet of paper (sheet of paper SH26 shown in FIG. 5) after the first correction patch P is formed when color correction is performed using method B1.

[0068] As described above, for the 12th and subsequent sheets of paper after the first correction patch P is formed, images are formed under imaging conditions corrected by the correction amount calculated based on the first correction patch P. Therefore, the color when image formation is performed on the 15th sheet of paper after the first correction patch P is formed is color R4α, the color when image formation is performed on the 20th sheet of paper after the first correction patch P is formed is color R5α, and the color when image formation is performed on the 25th sheet of paper after the first correction patch P is formed is color R6α. Color R4α is the color when color R4 is corrected by color difference D1. Color R5α is the color when color R5 is corrected by color difference D1. Color R6α is the color when color R6 is corrected by color difference D1. Color difference D1 is the color difference between color R1 when the first correction patch P is formed and the target color.

[0069] In the example shown in FIG. 6, the corrected colors R4α and R6α deviate significantly from the target colors, resulting in overcorrection. Overcorrection occurs because the density of the correction patch P varies with each pass. However, because correction is applied when forming an image on the 15th sheet of paper after the first correction patch P is formed, the time from when the first correction patch P is formed to when the correction is applied is shorter than in method B2, which will be described later. Thus, method B1, in which the correction amount is calculated based on the density of a single correction patch P so that the density of that correction patch P matches the target value, provides good correction responsiveness to color variations, but there is a possibility of overcorrection due to the influence of density unevenness in the correction patch P.

[0070] 7 is a diagram showing color correction method B2, which is another example of a color correction method to be compared with the color correction method by image forming apparatus 100 according to the first embodiment.

[0071] Sheet SHn (n is an integer greater than or equal to 1) indicates the nth sheet of paper in continuous printing. As mentioned above, when there is no need to distinguish between sheets SHn, they will be referred to as "sheet SH." Sheet SH is transported in the direction of the arrow in the figure.

[0072] In the example shown in Fig. 7, correction patches P and user-specified images I are formed on the first sheet SH1, the sixth sheet SH6, and the eleventh sheet SH11. Also, in the example shown in Fig. 7, only the user-specified image I is formed on the second to fifth, seventh to tenth, and twelfth to twenty-sixth sheets SH. In Fig. 7, the correction patches P formed on the first sheet SH1 are referred to as "first correction patches P," the correction patches P formed on the sixth sheet SH6 are referred to as "second correction patches P," and the correction patches P formed on the eleventh sheet SH11 are referred to as "third correction patches P."

[0073] In method B2, the correction amount is calculated based on the densities of three correction patches P, and the image forming conditions of the image forming unit are corrected by the calculated correction amount. Specifically, the correction amount is calculated so that the average value of the densities of the three measured correction patches P becomes the target value.

[0074] As an example, when the first correction patch P is formed, the density of the correction patch P is first measured. Then, when the second correction patch P is formed, the density of the correction patch P is measured. Then, when the third correction patch P is formed, the density of the correction patch P is measured. Next, a correction amount is calculated so that the average value of the densities of the three measured correction patches P becomes the target value, and the image creation conditions of the image forming unit are corrected by the correction amount.

[0075] 7, the timing at which correction is applied for the first time after the formation of the first correction patch P is the timing at which image formation starts on the 22nd sheet of paper (sheet of paper SH23 in the figure) after the formation of the first correction patch P. In other words, in the example shown in Fig. 7, for the 22nd sheet of paper and onwards after the formation of the first correction patch P, images are formed under image creation conditions corrected by the correction amount calculated based on the first to third correction patches P.

[0076] A change in color when color correction is performed using method B2 will be described with reference to Fig. 8. Fig. 8 is a diagram showing a change in color when color correction is performed using method B2.

[0077] Color R1 indicates the color when the first correction patch P is formed. Color R2 indicates the color when an image is formed on the fifth sheet of paper (sheet of paper SH6 shown in FIG. 7) after the first correction patch P is formed. In other words, color R2 indicates the color when the second correction patch P is formed. Color R3 indicates the color when an image is formed on the tenth sheet of paper (sheet of paper SH11 shown in FIG. 7) after the first correction patch P is formed. In other words, color R3 indicates the color when the third correction patch P is formed. Color R4 indicates the color when an image is formed on the fifteenth sheet of paper (sheet of paper SH16 shown in FIG. 7) after the first correction patch P is formed. Color R5 indicates the color when an image is formed on the twentieth sheet of paper (sheet of paper SH21 shown in FIG. 7) after the first correction patch P is formed.

[0078] Color R6 indicates the color when an image is formed on the 25th sheet of paper (sheet of paper SH26 shown in FIG. 7) after the first correction patch P is formed when color correction is not performed. Color R6α indicates the color when an image is formed on the 25th sheet of paper (sheet of paper SH26 shown in FIG. 7) after the first correction patch P is formed when color correction is performed using method B2.

[0079] As described above, for the sheets after the 22nd sheet after the first correction patch P is formed, images are formed under imaging conditions corrected by the correction amount calculated based on the correction patches P from the first to the third. Therefore, the color when forming an image on the 25th sheet after the first correction patch P is formed is color R6α. Color R6α is a color obtained by correcting color R6 by color difference D4. Color difference D4 is the average value of color difference D1 between color R1 at the time of forming the first correction patch P and the target color, color difference D2 between color R2 at the time of forming the second correction patch P and the target color, and color difference D3 between color R3 at the time of forming the third correction patch P and the target color.

[0080] As shown in FIG. 8, the corrected color R6α is the target color, and overcorrection does not occur. On the other hand, since correction has not yet been applied when forming an image on the 15th sheet after the first correction patch P is formed, the time from when the first correction patch P is formed until correction is applied is longer than that of method B1. Thus, in method B2 in which the correction amount is calculated based on the densities of the three correction patches P, while overcorrection is suppressed, the followability of correction to color variation decreases.

[0081] As described above, in the color correction methods (method B1, method B2) compared with the color correction method by the image forming apparatus 100 in Embodiment 1, it has been difficult to achieve both ensuring the followability of correction to color variation and suppressing overcorrection. That is, suppressing overcorrection without impairing the followability of correction to color variation is an issue in color correction.

[0082] <D. Color Correction by Image Forming Apparatus 100> Referring to FIGS. 9 to 14, the color correction by the image forming apparatus 100 in Embodiment 1 will be described.

[0083] (d1: Method of Color Correction) FIG. 9 is a diagram for explaining the method of color correction by the image forming apparatus in Embodiment 1. In the following description, the method of color correction by the image forming apparatus 100 is referred to as "method A".

[0084] 9, sheet SHn (n is an integer equal to or greater than 1) indicates the nth sheet of paper in continuous printing. As mentioned above, when there is no need to distinguish between sheets SHn, they will be referred to as "sheet SH." Sheet SH is transported in the direction of the arrow in the figure.

[0085] 9, the first sheet SH1, the sixth sheet SH6, and the eleventh sheet SH11 have target value calculation patches Q and user-specified images I formed thereon. The sixteenth sheet SH16, the twenty-first sheet SH21, the twenty-sixth sheet SH26, the thirty-first sheet SH31, the thirty-sixth sheet SH36, and the forty-first sheet SH41 have correction patches P and user-specified images I formed thereon. The second to fifth, seventh to tenth, twelfth to fifteenth, seventeenth to twentieth, twenty-second to twenty-fifth, twenty-seventh to thirty-first, thirty-second to thirty-fifth, and thirty-seventh to fortieth sheets SH have only the user-specified image I formed thereon.

[0086] In this embodiment, the target value calculation patch Q formed on the first sheet of paper SH1 is referred to as the "first target value calculation patch Q," the target value calculation patch Q formed on the sixth sheet of paper SH6 is referred to as the "second target value calculation patch Q," and the target value calculation patch Q formed on the eleventh sheet of paper SH11 is referred to as the "third target value calculation patch Q."

[0087] In addition, in this embodiment, the correction patch P formed on the 16th sheet of paper SH16 is referred to as the "first correction patch P," the correction patch P formed on the 21st sheet of paper SH21 is referred to as the "second correction patch P," the correction patch P formed on the 26th sheet of paper SH26 is referred to as the "third correction patch P," the correction patch P formed on the 31st sheet of paper SH31 is referred to as the "fourth correction patch P," the correction patch P formed on the 36th sheet of paper SH36 is referred to as the "fifth correction patch P," and the correction patch P formed on the 41st sheet of paper SH41 is referred to as the "sixth correction patch P."

[0088] In this embodiment, the target value calculation patch Q is formed three times during the target value calculation period. During the target value calculation period, the densities of the first to third target value calculation patches Q are measured by the measurement unit 50, and a representative value of the densities of the first to third target value calculation patches Q is set as the target value. The representative value may be an average value or a median value.

[0089] In this embodiment, color correction is performed by Method A based on the target value set during the target value calculation period and the density of the correction patch P formed during the color correction period. In detail, in Method A, a reference correction amount is calculated each time a correction patch P is formed so that the density of the correction patch P becomes the target value, and the image creation conditions of the image forming unit 20 are corrected by a first correction amount that is smaller than the reference correction amount. The target value is a representative value of the densities of the target value calculation patches Q from the first to third times. The first correction amount is a value obtained by dividing the reference correction amount by the planned number of calculations NT (see FIG. 4).

[0090] The planned number of calculations NT is the planned number of times a reference correction amount is calculated during the period from when the correction patch P is formed until the image-forming conditions are corrected. In the example shown in FIG. 9, the reference correction amounts calculated during the period from when the first correction patch P is formed until the image-forming conditions are corrected are the reference correction amount calculated based on the first correction patch P, the reference correction amount calculated based on the second correction patch P, and the reference correction amount calculated based on the third correction patch P. Therefore, in the example shown in FIG. 9, the planned number of calculations is 3. In the example shown in FIG. 9, the image-forming conditions of the image forming unit 20 are corrected by one-third of the reference correction amount calculated based on each correction patch P.

[0091] As an example, when a first correction patch P is formed, a first correction amount is determined, and the image-forming conditions of the image forming unit 20 are corrected by the first correction amount. Specifically, when the first correction patch P is formed, the density of the correction patch P is first measured. Next, a reference correction amount is calculated so that the density of the correction patch P becomes a target value. Next, one-third of the reference correction amount is determined as the first correction amount. Next, the image-forming conditions of the image forming unit 20 are corrected by the first correction amount. In the example shown in FIG. 9 , the timing at which the first correction amount calculated based on the first correction patch P is applied is the timing at which image formation on the twelfth sheet of paper (sheet of paper SH28 in the figure) begins after the first correction patch P is formed. Therefore, on the fifteenth sheet of paper (sheet of paper SH31 in the figure) after the first correction patch P is formed, an image is formed under image-forming conditions that are corrected by the first correction amount calculated based on the first correction patch P from the image-forming conditions when the first correction patch P was formed.

[0092] When the second correction patch P is formed, a first correction amount is determined again, and the image-forming conditions of the image forming unit 20 are corrected by the first correction amount. Specifically, when the second correction patch P is formed, first, the density of the correction patch P is measured. Next, a reference correction amount is calculated so that the density of the correction patch P becomes the target value. Next, one-third of the reference correction amount is determined as the first correction amount. Next, the image-forming conditions of the image forming unit 20 are corrected by the first correction amount. In the example shown in FIG. 9 , the timing at which the first correction amount calculated based on the second correction patch P is applied is the timing at which image formation starts on the 17th sheet of paper (sheet SH33 in the figure) after the first correction patch P is formed. Therefore, on the 20th sheet of paper (sheet SH36 in the figure) after the first correction patch P is formed, an image is formed under image-forming conditions that are corrected from the most recent image-forming conditions by the first correction amount calculated based on the second correction patch P. That is, on the 20th sheet of paper (sheet of paper SH36 in the figure) after the first correction patch P is formed, an image is formed under image creation conditions that are corrected from the image creation conditions when the first correction patch P was formed by the first correction amount calculated based on the first correction patch P and the first correction amount calculated based on the second correction patch P.

[0093] When the third correction patch P is formed, the first correction amount is determined again, and the image-forming conditions of the image forming unit 20 are corrected by the first correction amount. Specifically, when the third correction patch P is formed, the density of the correction patch P is first measured. Next, a reference correction amount is calculated so that the density of the correction patch P becomes the target value. Next, one-third of the reference correction amount is determined as the first correction amount. Next, the image-forming conditions of the image forming unit 20 are corrected by the first correction amount. In the example shown in FIG. 9 , the timing at which the first correction amount calculated based on the third correction patch P is applied is the timing at which image formation starts on the 22nd sheet of paper (sheet SH38 in the figure) after the first correction patch P is formed. Therefore, on the 25th sheet of paper (sheet SH41 in the figure) after the first correction patch P is formed, an image is formed under image-forming conditions that are corrected from the most recent image-forming conditions by the first correction amount calculated based on the third correction patch P. That is, on the 25th sheet of paper (sheet of paper SH41 in the figure) after the first correction patch P is formed, an image is formed under image-forming conditions that are corrected from the image-forming conditions at the time of forming the first correction patch P by the first correction amount calculated based on the first correction patch P, the first correction amount calculated based on the second correction patch P, and the first correction amount calculated based on the third correction patch P.

[0094] Thereafter, each time a correction patch P is formed, a standard correction amount is calculated so that the density of the correction patch P becomes the target value, one-third of the standard correction amount is determined as the first correction amount, and the image forming conditions of the image forming unit 20 are corrected by the first correction amount.

[0095] A change in color when color correction is performed by method A will be described with reference to Fig. 10. Fig. 10 is a diagram showing a change in color when color correction is performed by method A.

[0096] Color R1 indicates the color when the first correction patch P is formed. Color R2 indicates the color when an image is formed on the fifth sheet of paper (sheet of paper SH21 shown in FIG. 9) after the first correction patch P is formed. In other words, color R2 indicates the color when the second correction patch P is formed. Color R3 indicates the color when an image is formed on the tenth sheet of paper (sheet of paper SH26 shown in FIG. 9) after the first correction patch P is formed. In other words, color R3 indicates the color when the third correction patch P is formed.

[0097] Color R4 indicates the color when an image is formed on the 15th sheet of paper (sheet of paper SH31 shown in FIG. 9) after the first correction patch P is formed, when color correction is not performed. Color R5 indicates the color when an image is formed on the 20th sheet of paper (sheet of paper SH36 shown in FIG. 9) after the first correction patch P is formed, when color correction is not performed. Color R6 indicates the color when an image is formed on the 25th sheet of paper (sheet of paper SH41 shown in FIG. 9) after the first correction patch P is formed, when color correction is not performed.

[0098] The color R4α indicates the color when an image is formed on the 15th sheet of paper (sheet of paper SH31 shown in FIG. 9) after the first correction patch P is formed when color correction is performed using method A. That is, the color R4α indicates the color when the fourth correction patch P is formed when color correction is performed using method A. The color R5α indicates the color when an image is formed on the 20th sheet of paper (sheet of paper SH36 shown in FIG. 9) after the first correction patch P is formed when color correction is performed using method A. That is, the color R5α indicates the color when the fifth correction patch P is formed when color correction is performed using method A. The color R6α indicates the color when an image is formed on the 25th sheet of paper (sheet of paper SH41 shown in FIG. 9) after the first correction patch P is formed when color correction is performed using method A. That is, the color R6α indicates the color when the sixth correction patch P is formed when color correction is performed using method A.

[0099] As described above, on the 15th sheet of paper after the first correction patch P is formed (sheet of paper SH31 in the figure), an image is formed under image-forming conditions that have been corrected from the image-forming conditions when the first correction patch P was formed by the first correction amount calculated based on the first correction patch P. On the 20th sheet of paper after the first correction patch P is formed (sheet of paper SH36 in the figure), an image is formed under image-forming conditions that have been corrected from the image-forming conditions when the first correction patch P was formed by the first correction amount calculated based on the first correction patch P and the second correction patch P. On the 25th sheet of paper after the first correction patch P is formed (sheet of paper SH41 in the figure), an image is formed under image-forming conditions that have been corrected from the image-forming conditions when the first correction patch P was formed by the first correction amount calculated based on the first correction patch P, the second correction patch P, and the third correction patch P.

[0100] Therefore, the color when an image is formed on the 15th sheet of paper after the first correction patch P is formed is color R4α, the color when an image is formed on the 20th sheet of paper after the first correction patch P is formed is color R5α, and the color when an image is formed on the 25th sheet of paper after the first correction patch P is formed is color R6α. Color R4α is the color when color R4 is corrected by color difference D5. Color difference D5 is one-third of the color difference between color R1 when the first correction patch P is formed and the target color. Color R5α is the color when color R5 is corrected by color differences D5 and D6. Color difference D6 is one-third of the color difference between color R2 when the second correction patch P is formed and the target color. Color R6α is the color when color R6 is corrected by color differences D5, D6, and D7. The color difference D7 is one-third of the color difference between the color R3 when the correction patch P is formed for the third time and the target color.

[0101] As shown in FIG. 10, no overcorrection occurs, and the corrected color R6α is the target color. Furthermore, since the correction is applied when forming an image on the 15th sheet of paper after the first correction patch P is formed, the time from when the first correction patch P is formed to when the correction is applied is shorter than in the above-described method B2. Thus, in method A, in which the color is corrected by a first correction amount that is smaller than the reference correction amount, overcorrection can be suppressed without impairing the responsiveness of the correction to color fluctuations. In other words, the color correction method by image forming apparatus 100 in embodiment 1 can suppress overcorrection without impairing the responsiveness of the correction to color fluctuations.

[0102] 9 and 10, the planned number of calculations NT is three, but the planned number of calculations NT is not limited to three and may be two or more. The planned number of calculations NT depends on the processing capacity of the image forming apparatus 100. Specifically, the processing capacity refers to the capacity for processing to measure the density of the correction patches P, calculate the correction amount, change the image forming conditions of the image forming unit 20, and the like.

[0103] (d2: Overview of color correction process) 11 is a diagram for explaining an overview of color correction processing by the image forming apparatus according to Embodiment 1. Image forming apparatus 100 includes measurement unit 50, storage 90, image forming unit 20, calculation unit 151, determination unit 152, correction unit 153, and second setting unit 154. Calculation unit 151, determination unit 152, correction unit 153, and second setting unit 154 are realized by processor 70 executing program 91.

[0104] During the target value calculation period, the measurement unit 50 measures the density of the target value calculation patches Q formed on the conveyed paper SH. In the present embodiment, the measurement unit 50 measures the density of the first target value calculation patches Q, the density of the second target value calculation patches Q, and the density of the third target value calculation patches Q. When the second setting unit 154 acquires the measurement values ​​of the densities of the first to third target value calculation patches Q from the measurement unit 50, it sets a representative value of the densities of the first to third target value calculation patches Q as the target value TG. The representative value may be an average value or a median value. The target value TG is saved in the storage 90.

[0105] During the color correction period, the measurement unit 50 measures the density of the correction patch P formed on the conveyed paper SH.

[0106] When the calculation unit 151 obtains the measurement value of the density of the correction patch P from the measurement unit 50, it obtains the target value TG from the storage 90 and calculates a standard correction amount ST based on the measurement value so that the density of the correction patch P becomes the target value TG.

[0107] The determination unit 152 determines the first correction amount CA1 according to the planned number of calculations NT of the reference correction amount ST during the period from when the correction patch P is formed to when the image creation conditions are corrected. In detail, when the determination unit 152 acquires the reference correction amount ST from the calculation unit 151, it acquires the planned number of calculations NT from the storage 90 and calculates the first correction amount CA1 using the following formula 1.

[0108] (First correction amount CA1)=(Reference correction amount ST) / (Scheduled number of calculations NT) (Equation 1)

[0109] When the correction unit 153 acquires the first correction amount CA1 from the determination unit 152, it corrects the image formation conditions of the image forming unit 20 by the first correction amount CA1. In detail, the correction unit 153 outputs an instruction to correct the image formation conditions to the image forming unit 20 so that the image formation conditions of the image forming unit 20 are corrected by the first correction amount CA1. The image forming unit 20 corrects the image formation conditions in accordance with the correction instruction, and forms an image under the corrected image formation conditions.

[0110] FIG. 12 is a diagram illustrating an example of correction of image-forming conditions by the image forming apparatus according to the first embodiment. Referring to FIG. 12, "current value Pv" in the diagram indicates the density of the correction patch P measured by the measurement unit 50. For example, assume that the density of the correction patch P measured by the measurement unit 50 is 10 percent higher than the target value TG. In such a case, the correction unit 153 issues a correction instruction to the image forming unit 20 to reduce the development potential of the developer 24 by 10 percent. The correction unit 153 may also correct the gamma curve to match the gradation curve. The correction unit 153 may also correct data in a 3D-LUT (Three-Dimensional Look-Up Table) as gradation data. The 3D-LUT is stored in the storage 90.

[0111] FIG. 13 is a diagram showing an example of a change in development potential in the first embodiment. In FIG. 13, "patch No." indicates the mth (m is an integer equal to or greater than 1) correction patch P. FIG. 13 shows the "development potential Vc" when the correction patch P is formed each time, the "reference correction amount ST" calculated based on the density of the correction patch P each time, and the "first correction amount CA1" calculated based on the reference correction amount ST. In the present embodiment, since the planned number of calculations NT is set to three, the first correction amount CA1 is one-third the value of the reference correction amount ST.

[0112] 9, in the present embodiment, the first correction patch P to which application of the first correction amount CA1 begins is the fourth correction patch P. Therefore, the development potential Vc when the second correction patch P is formed and the development potential Vc when the third correction patch P is formed remain the same as the development potential Vc (−500 V) when the first correction patch P was formed.

[0113] The fourth correction patch P is formed under image creation conditions corrected by the first correction amount CA1 calculated based on the density of the first correction patch P. Therefore, the development potential Vc (-503.3 V) when the fourth correction patch P is formed is a value corrected from the most recent development potential Vc (-500 V) by the first correction amount CA1 (-3.3 V) calculated based on the density of the first correction patch P.

[0114] Furthermore, the fifth correction patch P is formed under image creation conditions corrected by the first correction amount CA1 calculated based on the density of the second correction patch P. Therefore, the development potential Vc (-509.3 V) when the fifth correction patch P is formed is a value corrected from the most recent development potential Vc (-503.3 V) by the first correction amount CA1 (-6.0 V) calculated based on the density of the second correction patch P.

[0115] Furthermore, the sixth correction patch P is formed under image creation conditions corrected by the first correction amount CA1 calculated based on the density of the third correction patch P. Therefore, the development potential Vc (-518.8 V) when the sixth correction patch P is formed is a value corrected from the most recent development potential Vc (-509.3 V) by the first correction amount CA1 (-9.5 V) calculated based on the density of the third correction patch P.

[0116] Furthermore, the seventh correction patch P is formed under image creation conditions corrected by the first correction amount CA1 calculated based on the density of the fourth correction patch P. Therefore, the development potential Vc (-526.9 V) when the seventh correction patch P is formed is a value corrected from the most recent development potential Vc (-518.8 V) by the first correction amount CA1 (-8.1 V) calculated based on the density of the fourth correction patch P.

[0117] (d3: Processing procedure) 14 is a flowchart showing the procedure of color correction processing by the image forming apparatus according to Embodiment 1. The color correction processing shown in FIG.

[0118] In step S1, the processor 70 determines whether or not a correction patch P or a target value calculation patch Q has been detected. The processor 70 determines that a correction patch P or a target value calculation patch Q has been detected when a measurement result is received from the measurement unit 50. If a correction patch P or a target value calculation patch Q has been detected (YES in step S1), the processor 70 proceeds to step S2.

[0119] In step S2, processor 70 determines whether or not it is a target value calculation period. If it is a target value calculation period (YES in step S2), processor 70 proceeds to step S3. On the other hand, if it is not a target value calculation period (NO in step S2), processor 70 proceeds to step S5.

[0120] In step S3, the processor 70 determines the target value TG and stores it in the storage 90.

[0121] In step S4, processor 70 determines whether printing is continuing. If printing is continuing (YES in step S4), processor 70 returns the process to step S1. On the other hand, if printing is not continuing (NO in step S4), processor 70 ends the color correction process.

[0122] In step S5, the processor 70 calculates a reference correction amount ST.

[0123] In step S6, the processor 70 determines a first correction amount CA1.

[0124] In step S7, the processor 70 instructs the image forming unit 20 to correct the image forming conditions so that the image forming conditions of the image forming unit 20 are corrected by the first correction amount CA1.

[0125] After step S7, processor 70 proceeds to step S4.

[0126] In this way, in the image forming apparatus 100 according to the first embodiment, the imaging conditions of the image forming unit 20 are corrected by the first correction amount CA1, which is less than the reference correction amount ST. Furthermore, the first correction amount CA1 is calculated based on the density of one correction patch P. This allows color correction to be performed at an early stage, and also makes it possible to suppress the effects of density unevenness in the correction patch P. Therefore, the image forming apparatus 100 according to the first embodiment can suppress overcorrection without impairing the ability of the correction to follow color variations.

[0127] The target value TG for color correction may be calculated during test printing performed before the start of continuous printing. When the target value TG for color correction is calculated during test printing performed before the start of continuous printing, the image forming unit 20 first forms target value calculation patches Q multiple times during test printing. Next, the measurement unit 50 measures the density of the target value calculation patches Q for each test printing. Next, the second setting unit 154 acquires the density of the target value calculation patches Q for each test printing from the measurement unit 50 and sets a representative value of the acquired densities as the target value TG. When the target value TG for color correction is calculated during test printing performed before the start of continuous printing, the correction patches P may be formed on the first sheet of paper in the continuous printing.

[0128] [Embodiment 2] In the first embodiment, a case has been described in which the value obtained by dividing the reference correction amount ST by the planned number of calculations NT is determined as the first correction amount CA1. In the second embodiment, a case will be described in which, at the beginning of continuous printing, a value greater than the value obtained by dividing the reference correction amount ST by the planned number of calculations NT is determined as the first correction amount CA1. Note that the image forming apparatus in the second embodiment has the same hardware configuration as the image forming apparatus 100 described with reference to FIG. 4, and therefore the same components are denoted by the same reference numerals, and description thereof will not be repeated.

[0129] Here, a description will be given of the differences between the color correction process by image forming apparatus 100 in embodiment 2 and the color correction process by image forming apparatus 100 in embodiment 1. The difference between the color correction process by image forming apparatus 100 in embodiment 2 and the color correction process described with reference to Fig. 11 is the formula used by determination unit 152 to calculate first correction amount CA1.

[0130] In the second embodiment, when the determination unit 152 acquires the reference correction amount ST from the calculation unit 151, the determination unit 152 calculates the first correction amount CA1 using the following Equation 2.

[0131] (First correction amount CA1)=(Standard correction amount ST) / (Scheduled number of calculations NT)×(Increase rate Z) (Equation 2)

[0132] The processing procedure of image forming apparatus 100 in the second embodiment is the same as the processing procedure described with reference to FIG. 14, and therefore, description thereof will not be repeated here.

[0133] Fig. 15 is a diagram showing an example of the first correction amount in the second embodiment. In Fig. 15, "patch No." indicates the mth (m is an integer equal to or greater than 1) correction patch P. Fig. 15 shows the "development potential Vc" when forming each correction patch P, the "reference correction amount ST" calculated based on the density of each correction patch P, the "increase rate Z," and the "first correction amount CA1" calculated based on the reference correction amount ST. Note that in this embodiment as well, the expected number of calculations NT is set to three.

[0134] 15, in this embodiment, the "increase rate Z" is set to a value greater than 1.0 at the beginning of continuous printing, for example, from the start of continuous printing until the start of formation of the third correction patch P, and thereafter the "increase rate Z" is set to 1.0. As a result, in this embodiment, the first correction amount CA1 calculated from the correction patch P formed at the beginning of continuous printing is determined to be a value greater than the value obtained by dividing the reference correction amount ST by the planned number of calculations NT, and the first correction amount CA1 calculated from the correction patch P formed after the end of the initial period of continuous printing is determined to be the value obtained by dividing the reference correction amount ST by the planned number of calculations NT.

[0135] In detail, the first correction amount CA1 (-4.0V) calculated based on the density of the first correction patch P is one-third of the standard correction amount ST (-9.9V) calculated based on the density of the first correction patch P multiplied by the increase rate Z (1.2).

[0136] In addition, the first correction amount CA1 (-6.6V) calculated based on the density of the second correction patch P is one-third of the standard correction amount ST (-18.0V) calculated based on the density of the second correction patch P multiplied by the increase rate Z (1.1).

[0137] In addition, the first correction amount CA1 calculated based on the density of the correction patch P from the third time onwards is a value obtained by multiplying one-third of the standard correction amount ST calculated based on the density of the correction patch P by the increase rate Z (1.0).

[0138] In this way, in the early stage of continuous printing, the determination unit 152 determines a value greater than the value obtained by dividing the standard correction amount ST by the planned number of calculations NT as the first correction amount CA1.

[0139] Generally, color tends to fluctuate in the early stages of continuous printing because of changes in the speed at which toner in the developing unit 24 is replaced, the charge amount of the toner in the developing unit 24, and the temperature and humidity inside the image forming apparatus 100.

[0140] For example, if the user-specified image I is different between the previous continuous printing and the current continuous printing, the image coverage, which indicates the amount of toner consumed, will be different between the previous continuous printing and the current continuous printing. Therefore, the image coverage is likely to change at the beginning of the continuous printing. When the image coverage changes, the speed at which the toner in the developing unit 24 is replaced changes. When the speed at which the toner in the developing unit 24 is replaced slows, the charge amount of the toner in the developing unit 24 increases, changing the developability and resulting in color fluctuations.

[0141] Furthermore, at the beginning of continuous printing, the developer starts to be stirred in the developing unit 24, which tends to increase the charge amount of the toner in the developing unit 24. When the charge amount of the toner in the developing unit 24 increases, the developability changes, resulting in color fluctuations.

[0142] Furthermore, in the early stages of continuous printing, the temperature and humidity inside the image forming apparatus 100 are likely to change due to an increase in the fixing temperature and switching of the operation of the cooling fan inside the image forming apparatus 100. When the temperature and humidity inside the image forming apparatus 100 change, the color fluctuates.

[0143] In the second embodiment, in the early stage of continuous printing when color is likely to fluctuate, a value greater than the value obtained by dividing the standard correction amount ST by the expected number of calculations NT is determined as the first correction amount CA1. Therefore, the image forming apparatus 100 in the second embodiment can improve the responsiveness of correction to color fluctuations.

[0144] 15, the increase rate Z at the beginning of continuous printing is set to a larger value the earlier the calculation timing of the first correction amount CA1, but the increase rate Z at the beginning of continuous printing may be set to a uniform value regardless of the calculation timing of the first correction amount CA1. If the increase rate Z at the beginning of continuous printing is set to a larger value the earlier the calculation timing of the first correction amount CA1, the ability of correction to follow color fluctuations is improved.

[0145] [Embodiment 3] In the first embodiment, the case where the first correction amount CA1 is determined by dividing the reference correction amount ST by the planned number of calculations NT has been described. In the third embodiment, the case where the first correction amount CA1 is adjusted in response to changes in factors that affect color during continuous printing will be described.

[0146] Fig. 16 is a diagram for explaining an overview of color correction processing by an image forming apparatus according to Embodiment 3. Image forming apparatus 100A according to Embodiment 3 has a hardware configuration similar to that of image forming apparatus 100 described with reference to Fig. 4, and therefore the same components are denoted by the same reference numerals and description thereof will not be repeated.

[0147] On the other hand, the color correction process by image forming apparatus 100A in embodiment 3 differs from the color correction process by image forming apparatus 100 in embodiment 1. Here, differences between the color correction process by image forming apparatus 100A in embodiment 3 and the color correction process by image forming apparatus 100 in embodiment 1 will be described. Note that the processing procedure of image forming apparatus 100A in embodiment 3 is the same as the processing procedure described with reference to Fig. 14, and therefore the description thereof will not be repeated here.

[0148] The color correction process by image forming apparatus 100A in the third embodiment differs from the color correction process described with reference to Fig. 11 in that image forming apparatus 100A further includes adjustment unit 155A. Adjustment unit 155A is realized by processor 70 executing program 91.

[0149] The adjustment unit 155A adjusts the first correction amount CA1 determined by the determination unit 152 in accordance with changes in factors that affect color. That is, the adjustment unit 155A adjusts the first correction amount CA1 calculated by the determination unit 152 using the above formula 1 in accordance with changes in factors that affect color. The adjustment unit 155A outputs the adjusted first correction amount CA1α to the correction unit 153. Upon acquiring the adjusted first correction amount CA1α, the correction unit 153 corrects the image formation conditions of the image forming unit 20 by the adjusted first correction amount CA1α.

[0150] Factors that affect color include at least one of the following: image coverage, the amount of charge on the toner in the developer 24, the waiting time between the end of the previous print and the start of the current print, the temperature within the image forming apparatus 100A, and the humidity within the image forming apparatus 100A.

[0151] As an example, if the coverage of the user-specified image I changes during continuous printing, the adjustment unit 155A increases the first correction amount CA1. In detail, the adjustment unit 155A compares the coverage of the image when the correction patch P is formed with the coverage of the image when the first correction amount CA1 calculated based on the density of the correction patch P is applied, and the larger the difference between the two coverages, the larger the first correction amount CA1 is increased.

[0152] As another example, the image forming apparatus 100A may be provided with a device for measuring the charge amount of the toner in the developing device 24, and the adjustment unit 155A may increase the first correction amount CA1 when the charge amount of the toner in the developing device 24 increases during continuous printing.

[0153] As another example, image forming apparatus 100A may be provided with a device that measures the waiting time from the end of the previous print until the start of the current print, and adjustment unit 155A may increase first correction amount CA1 as the waiting time becomes longer.

[0154] As another example, a device for measuring the temperature inside image forming apparatus 100A may be provided in image forming apparatus 100A, and adjustment unit 155A may increase first correction amount CA1 when the temperature changes significantly during continuous printing.

[0155] As another example, a device for measuring the humidity inside image forming apparatus 100A may be provided in image forming apparatus 100A, and adjustment unit 155A may increase first correction amount CA1 when the humidity changes significantly during continuous printing.

[0156] It should be noted that the extent to which the first correction amount CA1 is increased is set in advance in image forming apparatus 100A to a value determined based on experimental results.

[0157] Generally, when the coverage of the user-specified image I changes, the color is likely to fluctuate. Furthermore, when the charge amount of the toner in the developing device 24 increases, the developability changes, and the color is likely to fluctuate. Furthermore, the longer the standby time, the more likely it is that the charge amount of the toner in the developing device 24 will change, and the temperature and humidity inside the image forming apparatus 100A will change. When the charge amount of the toner in the developing device 24 or the temperature and humidity inside the image forming apparatus 100A changes, the color is likely to fluctuate.

[0158] In this way, in the third embodiment, the first correction amount CA1 is adjusted in response to changes in factors that affect color. Therefore, according to the image forming apparatus 100A in the third embodiment, it is possible to improve the responsiveness of the correction to color variations.

[0159] [Embodiment 4] In the first embodiment, a case has been described in which the value obtained by dividing the reference correction amount ST by the planned number of calculations NT is determined as the first correction amount CA1. In the fourth embodiment, a case will be described in which the sum of a second correction amount determined for an in-threshold correction amount among the reference correction amounts ST and a third correction amount determined for an out-of-threshold correction amount among the reference correction amounts ST is determined as the first correction amount CA1.

[0160] 17 is a diagram for explaining an overview of color correction processing by an image forming apparatus according to Embodiment 4. Image forming apparatus 100B according to Embodiment 4 has a hardware configuration similar to that of image forming apparatus 100 described with reference to FIG. 4, and therefore the same components are denoted by the same reference numerals and description thereof will not be repeated.

[0161] On the other hand, image forming apparatus 100B in embodiment 4 differs from image forming apparatus 100 in embodiment 1 in that it is switchable from an image formation mode to an unevenness measurement mode for measuring density unevenness of correction patches P. Also, the color correction process performed by image forming apparatus 100B in embodiment 4 differs from the color correction process performed by image forming apparatus 100 in embodiment 1. Here, the differences between the color correction process performed by image forming apparatus 100B in embodiment 4 and the color correction process performed by image forming apparatus 100 in embodiment 1 will be described.

[0162] The color correction process by image forming apparatus 100B in the fourth embodiment differs from the color correction process described with reference to Fig. 11 in that image forming apparatus 100B includes determination unit 152B instead of determination unit 152, and further includes first setting unit 156B. Determination unit 152B and first setting unit 156B are realized by processor 70 executing program 91.

[0163] In the unevenness measurement mode, the measurement unit 50 measures the density of the correction patch P every time a sheet SH on which the correction patch P is formed is conveyed, and outputs the measurement value to the first setting unit 156B. As a result, the first setting unit 156B acquires a plurality of measurement values.

[0164] The first setting unit 156B sets a threshold value TH for the reference correction amount ST based on the measurement value of the measurement unit 50 in the unevenness measurement mode. The threshold value TH is set according to the range of the reference correction amount ST that is expected to vary due to density unevenness of the correction patch P.

[0165] As an example, the first setting unit 156B identifies the density of the correction patch P that has the largest difference from the target value TG based on the multiple measurement values ​​acquired from the measurement unit 50, and calculates a correction amount such that the density of the correction patch P becomes the target value TG. The first setting unit 156B stores the correction amount in the storage 90 as a threshold value TH.

[0166] By setting the threshold value TH in this way, if the reference correction amount ST calculated by the calculation unit 151 is within the threshold value TH, it can be determined that the cause of the color variation is density unevenness of the correction patch P. If the reference correction amount ST calculated by the calculation unit 151 is within the threshold value TH, it can be said that the reference correction amount ST is a correction amount for the color variation caused by density unevenness of the correction patch P.

[0167] On the other hand, if the reference correction amount ST calculated by the calculation unit 151 exceeds the threshold value TH, it can be determined that the causes of the color variation include density unevenness of the correction patch P and factors other than the density unevenness of the correction patch P. If the reference correction amount ST calculated by the calculation unit 151 exceeds the threshold value TH, the threshold value TH portion of the reference correction amount ST can be said to be a correction amount for color variation due to density unevenness of the correction patch P, and the portion of the reference correction amount ST that exceeds the threshold value TH can be said to be a correction amount for color variation due to factors other than density unevenness of the correction patch P.

[0168] Factors other than uneven density of correction patch P include at least one of image coverage, the charge amount of toner in developer 24, the waiting time between the end of the previous print and the start of the current print, the temperature within image forming device 100B, and the humidity within image forming device 100B.

[0169] When the determination unit 152B acquires the reference correction amount ST from the calculation unit 151, the determination unit 152B first acquires the planned calculation count NT and the threshold value TH from the storage 90. Next, the determination unit 152B calculates a second correction amount CA2 and a third correction amount CA3, and determines the sum of the second correction amount CA2 and the third correction amount CA3 as the first correction amount CA1.

[0170] The processing procedure of image forming apparatus 100B in the fourth embodiment is the same as the processing procedure described with reference to FIG. 14, and therefore the description thereof will not be repeated here.

[0171] Next, a method for calculating the first correction amount CA1 by the determination unit 152B will be described with reference to Fig. 18 and Fig. 19. In the present embodiment, the planned number of calculations NT is also set to three. Fig. 18 is a diagram for explaining a method for calculating the first correction amount in the fourth embodiment. Fig. 19 is a diagram showing an example of the various correction amounts shown in Fig. 18.

[0172] 18, "reference correction amount ST1" indicates the reference correction amount calculated based on the density of the first correction patch P, "reference correction amount ST2" indicates the reference correction amount calculated based on the density of the second correction patch P, and "reference correction amount ST3" indicates the reference correction amount calculated based on the density of the third correction patch P. In the following description, when there is no need to distinguish between the reference correction amount ST1, the reference correction amount ST2, and the reference correction amount ST3, they will be referred to as "reference correction amount ST."

[0173] 19, "patch No." indicates the mth (m is an integer greater than or equal to 1) correction patch P. Fig. 19 shows the "reference correction amount ST," "intra-threshold correction amount Wc," "second correction amount CA2," "current extra-threshold correction amount Uc," "previous extra-threshold correction amount Up," "third correction amount CA3," and "first correction amount CA1," all calculated based on the density of the correction patch P each time.

[0174] 18 and 19, the reference correction amount ST1 is 3.0 V, the reference correction amount ST2 is 12.0 V, and the reference correction amount ST3 is 14.0 V. In addition, in FIGS.

[0175] 18 and 19, the intra-threshold correction amount Wc indicates a correction amount of the reference correction amount ST that is within the threshold value TH. When the reference correction amount ST is within the threshold value TH, the determination unit 152B determines the reference correction amount ST to be the intra-threshold correction amount Wc. On the other hand, when the reference correction amount ST exceeds the threshold value TH, the determination unit 152B determines the threshold value TH to be the intra-threshold correction amount Wc.

[0176] In the examples shown in FIGS. 18 and 19, the intra-threshold correction amount Wc in the reference correction amount ST1 is 3.0V, the intra-threshold correction amount Wc in the reference correction amount ST2 is 6.0V, and the intra-threshold correction amount Wc in the reference correction amount ST3 is 6.0V.

[0177] The determination unit 152B determines the second correction amount CA2 based on the intra-threshold correction amount Wc and the expected calculation count NT. The second correction amount CA2 is a correction amount determined for the intra-threshold correction amount Wc among the reference correction amounts ST. As an example, the determination unit 152B calculates the second correction amount CA2 using the following Equation 3.

[0178] (Second correction amount CA2)=(intra-threshold correction amount Wc) / (planned number of calculations NT) (Equation 3)

[0179] 18 and 19, the second correction amount CA2 calculated based on the first correction patch P is 1.0 V. The second correction amount CA2 calculated based on the second correction patch P and the second correction amount CA2 calculated based on the third correction patch P are both 2.0 V.

[0180] The non-threshold correction amount refers to the amount of correction that exceeds the threshold value TH of the reference correction amount ST. The current non-threshold correction amount Uc refers to the non-threshold correction amount calculated based on the density of the current correction patch P. If the reference correction amount ST is within the threshold value TH, the determination unit 152B determines the current non-threshold correction amount Uc to be zero. On the other hand, if the reference correction amount ST exceeds the threshold value TH, the determination unit 152B calculates the current non-threshold correction amount Uc using the following equation 4.

[0181] (Current out-of-threshold correction amount Uc) = (Standard correction amount ST) - (Threshold value TH) (Equation 4)

[0182] In the examples shown in Figures 18 and 19, the current out-of-threshold correction amount Uc for the reference correction amount ST1 is zero V, the current out-of-threshold correction amount Uc for the reference correction amount ST2 is 6.0 V, and the current out-of-threshold correction amount Uc for the reference correction amount ST3 is 8.0 V.

[0183] The previous extra-threshold correction amount Up indicates the extra-threshold correction amount calculated based on the density of the previous correction patch P. When calculating the first correction amount CA1 based on the first correction patch P, the determination unit 152B determines the previous extra-threshold correction amount Up to be zero. Furthermore, when calculating the first correction amount CA1 based on the second or subsequent correction patch P and the previous standard correction amount ST is within the threshold value TH, the determination unit 152B also determines the previous extra-threshold correction amount Up to be zero.

[0184] In the examples shown in Figures 18 and 19, the previous out-of-threshold correction amount Up for the reference correction amount ST1 is zero V, the previous out-of-threshold correction amount Up for the reference correction amount ST2 is zero V, and the previous out-of-threshold correction amount Up for the reference correction amount ST3 is 6.0 V.

[0185] The determination unit 152B calculates the third correction amount CA3 using the following equation 5. The third correction amount CA3 is a correction amount determined for the extra-threshold correction amount out of the reference correction amount ST.

[0186] (Third correction amount CA3) = (current out-of-threshold correction amount Uc) - (previous out-of-threshold correction amount Up) (Equation 5)

[0187] In the examples shown in Figures 18 and 19, the third correction amount CA3 in the reference correction amount ST1 is zero V, the third correction amount CA3 in the reference correction amount ST2 is 6.0 V, and the third correction amount CA3 in the reference correction amount ST3 is 2.0 V.

[0188] The determination unit 152B calculates the first correction amount CA1 using the following equation 6.

[0189] (1st correction amount CA1)=(2nd correction amount CA2)+(3rd correction amount CA3)...(Formula 6)

[0190] In the examples shown in Figures 18 and 19, the first correction amount CA1 calculated based on the first correction patch P is 1.0 V, the first correction amount CA1 calculated based on the second correction patch P is 8.0 V, and the first correction amount CA1 calculated based on the third correction patch P is 4.0 V.

[0191] As described above, in the fourth embodiment, the second correction amount CA2 determined for the intra-threshold correction amount Wc among the reference correction amounts ST is a value smaller than the intra-threshold correction amount Wc. The intra-threshold correction amount Wc is a correction amount for color fluctuations due to density unevenness of the correction patch P. Because the second correction amount CA2 is a value smaller than the intra-threshold correction amount Wc, overcorrection is suppressed.

[0192] Furthermore, the third correction amount CA3 determined for the extra-threshold correction amount among the standard correction amounts ST is the value obtained by subtracting the previous extra-threshold correction amount Up from the current extra-threshold correction amount Uc. The extra-threshold correction amount is a correction amount for color fluctuations due to factors other than density unevenness of the correction patch P. The third correction amount CA3 determined for the extra-threshold correction amount does not further subtract the value obtained by subtracting the previous extra-threshold correction amount Up from the current extra-threshold correction amount Uc, but rather uses the value obtained by subtracting the previous extra-threshold correction amount Up from the current extra-threshold correction amount Uc as is, thereby preventing a loss of correction responsiveness to color fluctuations.

[0193] Moreover, the third correction amount CA3 is not the current extra-threshold correction amount Uc, but the value obtained by subtracting the previous extra-threshold correction amount Up from the current extra-threshold correction amount Uc, thereby suppressing overcorrection.

[0194] In the above description, the threshold value TH is set based on the measurement value of the measurement unit 50 in the unevenness measurement mode, but the threshold value TH determined based on experimental results may be set in advance in the image forming apparatus 100B. When the threshold value TH is set in advance in the image forming apparatus 100B, the image forming apparatus 100B may not be able to switch from the image formation mode to the unevenness measurement mode.

[0195] Also, at the beginning of continuous printing, the determination unit 152B may determine a value greater than the value obtained by dividing the intra-threshold correction amount Wc by the planned number of calculations NT as the second correction amount CA2.

[0196] [Other embodiments] The second and third embodiments may be combined.

[0197] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0198] 5 transport path, 10 paper feed unit, 15, 15C, 15K, 15M, 15Y imaging unit, 18 paper output tray, 20 image forming unit, 21, 21C, 21K, 21M, 21Y photoconductor, 22, 22C, 22K, 22M, 22Y charging device, 23, 23C, 23K, 23M, 23Y exposure device, 24, 24C, 24K, 24M, 24Y developing unit, 25, 25C, 25K, 25M, 25Y primary transfer device, 26 intermediate transfer belt, 27 secondary transfer device, 28 cleaning device, 29 fixing device, 30 operation panel, 40 communication interface, 50 measurement unit, 60 memory card interface, 60A memory card, 70 processor, 80 memory, 90 storage, 91 program, 99 Bus, 100, 100A, 100B image forming apparatus, 151 calculation unit, 152, 152B determination unit, 153 correction unit, 154 second setting unit, 155A adjustment unit, 156B first setting unit, A, B1, B2 method, CA1 first correction amount, CA2 second correction amount, CA3 third correction amount, CR1, CR2 cutting line, D1, D2, D3, D4, D5, D6, D7 color difference, I user-specified image, NT planned calculation count, P, P1, P2, P3, P4, P5, P6, P7, P8 correction patch, Pv current value, Q, Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8 target value calculation patch, R1, R2, R3, R4, R5, R6 Color, SH, SH1, SH6, SH11, SH13, SH16, SH21, SH23, SH26, SH28, SH31, SH33, SH36, SH38, SH41, SHn Paper, ST, ST1, ST2, ST3 Reference correction amount, TG Target value, TH Threshold value, Uc Current out-of-threshold correction amount, Up Previous out-of-threshold correction amount, Vc Development potential, Wc In-threshold correction amount, Z Increase rate.

Claims

1. an image forming unit that forms correction patches using toner; a measurement unit that measures the color, density, or amount of toner attached to the correction patch; a calculation unit that calculates a reference correction amount based on the measurement value of the measurement unit so that the density of the correction patch becomes a target value; a correction unit that corrects the image forming conditions of the image forming unit by a first correction amount that is smaller than the reference correction amount; a determination unit that determines the first correction amount in accordance with a planned number of calculations of the reference correction amount during a period from when the correction patch is formed until when the image-forming conditions are corrected.

2. The image forming apparatus according to claim 1 , wherein the determination unit determines a value obtained by dividing the reference correction amount by the planned number of calculations as the first correction amount.

3. The image forming apparatus according to claim 1 , wherein the determination unit determines, at an early stage of continuous printing, as the first correction amount, a value greater than a value obtained by dividing the reference correction amount by the planned number of calculations.

4. An image forming apparatus, an image forming unit that forms correction patches using toner; a measurement unit that measures the color, density, or amount of toner attached to the correction patch; a calculation unit that calculates a reference correction amount based on the measurement value of the measurement unit so that the density of the correction patch becomes a target value; a correction unit that corrects the image forming conditions of the image forming unit by a first correction amount that is smaller than the reference correction amount, When the reference correction amount exceeds a threshold value, the first correction amount is a sum of a second correction amount determined for an intra-threshold correction amount, which is the threshold portion of the reference correction amount, and a third correction amount determined for an extra-threshold correction amount, which is the portion of the reference correction amount that exceeds the threshold value, The image forming apparatus further includes a determination unit that determines the second correction amount based on the intra-threshold correction amount and a planned number of calculations of the reference correction amount during a period from when the correction patch is formed to when the image forming conditions are corrected, and determines the third correction amount as a value obtained by subtracting the previous extra-threshold correction amount from the current extra-threshold correction amount.

5. the image forming apparatus is switchable from an image forming mode to an unevenness measurement mode for measuring uneven density of the correction patch; The image forming apparatus according to claim 4 , further comprising a first setting unit that sets the threshold value based on the measurement value of the measurement unit in the unevenness measurement mode.

6. the image forming unit forms target value calculation patches multiple times at the beginning of continuous printing; the measurement unit measures the density of the target value calculation patch each time, 6. The image forming apparatus according to claim 1, further comprising a second setting unit that sets a representative value of the densities of the target value calculation patches obtained multiple times as the target value.

7. 7. The image forming apparatus according to claim 6, wherein the size of the target value calculation patch is larger than the size of the correction patch.

8. The image forming apparatus according to any one of claims 1 to 3, further comprising an adjustment unit that adjusts the first correction amount determined by the determination unit in accordance with a change in a factor that affects color.

9. The image forming apparatus according to claim 8 , wherein the factors include image coverage.

10. the image forming apparatus further includes a developing unit, 9. The image forming apparatus according to claim 8, wherein the factors include a charge amount of the toner in the developing unit.

11. 9. The image forming apparatus according to claim 8, wherein the factors include a waiting time from the end of a previous print until the start of a current print.

12. The image forming apparatus according to claim 8 , wherein the factors include a temperature inside the image forming apparatus.

13. The image forming apparatus according to claim 8 , wherein the factors include humidity within the image forming apparatus.

14. A control program executed by a computer, the control program causing the computer to: forming a correction patch using toner; measuring the color, density, or amount of toner attached to the correction patch; calculating a reference correction amount based on the measured value of the color, density, or toner adhesion amount of the correction patch so that the density of the correction patch becomes a target value; correcting the image forming conditions for image formation by a first correction amount that is smaller than the reference correction amount; determining the first correction amount in accordance with a planned number of calculations of the reference correction amount during a period from when the correction patch is formed until when the image-forming conditions are corrected.

15. A control program executed by a computer, the control program causing the computer to: forming a correction patch using toner; measuring the color, density, or amount of toner attached to the correction patch; calculating a reference correction amount based on the measured value of the color, density, or toner adhesion amount of the correction patch so that the density of the correction patch becomes a target value; correcting the image forming conditions for image formation by a first correction amount that is smaller than the reference correction amount; When the reference correction amount exceeds a threshold value, the first correction amount is a sum of a second correction amount determined for an intra-threshold correction amount, which is the threshold portion of the reference correction amount, and a third correction amount determined for an extra-threshold correction amount, which is the portion of the reference correction amount that exceeds the threshold value, the control program further causes the computer to determine the second correction amount according to the intra-threshold correction amount and a planned number of calculations of the reference correction amount during the period from when the correction patch is formed to when the image creation conditions are corrected, and to determine the third correction amount as a value obtained by subtracting the previous extra-threshold correction amount from the current extra-threshold correction amount.

Images