Image forming device

Abstract

To provide an image forming device that can form an image with a stable image quality while maintaining productivity.SOLUTION: An image forming device is provided with: image forming parts (220, 221, 222 and 223) that form images on an image carrier on the basis of an image formation condition; and a controller 300 that can perform pre-emptive real-time multiple-tone correction control in which accuracy is high and a processing time is long relatively and image density prediction control in which accuracy is low and a processing time is short relatively, in contrast to the image formation condition. The controller 300 executes the pre-emptive real-time multiple-tone correction control when execution of the pre-emptive real-time multiple-tone correction control is validly set in a printing job, and executes the image density prediction control unless the execution of the pre-emptive real-time multiple-tone correction control is validly set in the printing job.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus such as a printer, a copying machine, or a multifunction machine. [Background technology]

[0002] Image forming devices are subject to short-term fluctuations due to variations in the installation environment or the internal environment of the device, as well as long-term fluctuations due to changes in components and developers over time, which can cause the image density and gradation of output images to deviate from their ideal states. To address these fluctuations, image forming devices adjust image formation conditions as needed to restore the image density and gradation to their ideal states. This process of appropriately correcting image density and gradation to stabilize image quality is generally referred to as calibration. Conventionally, calibration is performed by forming a test image with a uniform image density on an image carrier, such as paper, a photoreceptor, or an intermediate transfer body, measuring the image density of the test image, comparing it with a target value, and appropriately adjusting and correcting the image formation conditions based on the comparison results.

[0003] In recent years, there has been an increasing demand for stable image quality as well as improved usability, particularly for improved productivity through reduced standby and downtime. There is also a strong demand for calibration to stabilize image quality to be performed in a shorter time. Patent Document 1 discloses a technology related to shortening the calibration time. In Patent Document 1, in order to shorten the control time required for creating and measuring a test image, the correlation between fluctuations in the external environment and fluctuations in the test image is modeled, thereby instantly predicting image density.

[0004] Patent Document 2 discloses a printing system that reads an image on paper using an inline sensor. This printing system is capable of real-time multi-tone correction control. Real-time multi-tone correction control is a process in which a printing device prints a test image for gradation correction as an interrupt while processing a print job, reads the test image with an inline sensor, and feeds back the read results to the image formation conditions. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2017-37100 A [Patent Document 2] Japanese Patent Publication No. 2022-178634 Summary of the Invention [Problem to be solved by the invention]

[0006] Real-time multi-tone correction control is only effective for a limited number of print jobs and is not performed for print jobs for which it is not effective. As a result, images formed for print jobs for which real-time multi-tone correction control is not effective suffer from poor image quality stability. Even for print jobs for which real-time multi-tone correction control is effective, it is better to perform calibration more frequently to ensure image quality stability, but performing calibration too frequently reduces productivity.

[0007] SUMMARY OF THE INVENTION In view of the above problems, it is a primary object of the present invention to provide an image forming apparatus that forms images with stable image quality while maintaining productivity. [Means for solving the problem]

[0008] The image forming apparatus of the present invention is characterized by comprising: an image forming means for forming an image on an image carrier based on image forming conditions; a correction means for performing a first correction process with relatively high accuracy and a long processing time for the image forming conditions, and a second correction process with relatively low accuracy and a short processing time; and a control means for causing the correction means to execute the first correction process and the second correction process based on predetermined settings. [Effects of the Invention]

[0009] According to the present invention, it is possible to form images with stable image quality while maintaining productivity. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is an explanatory diagram of an image forming apparatus. [Figure 2] FIG. 1 is a diagram illustrating the configuration of an image forming apparatus. [Figure 3] 10A and 10B are diagrams illustrating examples of setting screens. [Figure 4] FIG. 10 is a diagram illustrating an example of a tone correction chart. [Figure 5] FIG. [Figure 6] 10 is a flowchart showing a process for obtaining a basic signal value and a basic image density. [Figure 7] An explanatory diagram of potential control using two-point electrical control. [Figure 8] FIG. 10 is a diagram illustrating a patch image. [Figure 9] 10 is a graph showing the relationship between image density and exposure intensity. [Figure 10] FIG. 4 is an explanatory diagram of a tone correction table. [Figure 11] 10 is a flowchart showing a process for creating a composite correction LUT. [Figure 12] FIG. 10 is an explanatory diagram of a synthesis correction LUT creation process. [Figure 13] FIG. 10 is an explanatory diagram of a synthesis correction LUT creation process. [Figure 14] FIG. 10 is an explanatory diagram of a synthesis correction LUT creation process. [Figure 15] 10 is a flowchart showing a process for obtaining an image density value. [Figure 16] 10 is a flowchart showing a process for obtaining a predicted image density value. [Figure 17] 10 is a flowchart showing a process for creating an image density prediction model in advance. [Figure 18] 10 is a flowchart showing a printing process according to a print job. [Figure 19] FIG. [Figure 20] FIG. [Figure 21] 10 is a flowchart showing a printing process according to a print job. DETAILED DESCRIPTION OF THE INVENTION

[0011] A preferred embodiment of the present invention will be described below with reference to the accompanying drawings. While this embodiment will be described using an electrophotographic system, the characteristic aspects of control, particularly the matters described in the claims, also apply to inkjet printers, dye-sublimation printers, and other printers, and the problems can be solved using the methods described below. Therefore, we assert that the above claims also apply to each image forming apparatus.

[0012] (Configuration of image forming device) 1 is an explanatory diagram of an image forming apparatus. The image forming apparatus 100 includes a controller 300, an operation panel 191, an external memory 181, and an image forming engine 101. A host computer 301 is connected to the image forming apparatus 100. The image forming apparatus 100 and the host computer 301 are connected via a predetermined interface, such as a network, serial communication, or parallel communication.

[0013] The controller 300 controls the overall operation of the image forming apparatus 100. To this end, the controller 300 includes a host I / F unit 302, an input / output buffer 303, an input / output I / F unit 311, and a memory I / F unit 312. The controller 300 includes a first central processing unit (CPU) 313, a storage 304, a random access memory (RAM) 309, and a read only memory (ROM) 380. The controller 300 also includes a raster image processor (RIP) unit 314, a color processing unit 315, a tone correction unit 316, a pseudo halftone processing unit 317, and an engine I / F unit 318. These components of the controller 300 are connected to a system bus 319, enabling mutual data transmission and reception.

[0014] The host I / F unit 302 controls communication with the host computer 301. The input / output I / F unit 311 controls communication with the operation panel 191. The operation panel 191 is a user interface equipped with an input interface and an output interface. The input interface includes various key buttons, a touch panel, etc. The output interface includes a display, a speaker, etc. A user can input print instructions, correction process execution instructions, etc. to the image forming apparatus 100 via the input interface of the operation panel 191. A user can check the operating status and notifications of the image forming apparatus via the output interface of the operation panel 191. The input / output I / F unit 311 accepts instructions, etc. input via the operation panel 191, and outputs various information via the operation panel 191. The memory I / F unit 312 controls communication with the external memory 181. The external memory 181 is used to store print data and various information about the image forming apparatus 100. The input / output buffer 303 temporarily stores data transmitted and received by the host I / F unit 302 , the input / output I / F unit 311 , and the memory I / F unit 312 .

[0015] The first CPU 313 starts up by executing a boot program stored in the ROM 380, and controls the operation of the image forming apparatus 100 by executing a computer program (control program) stored in the storage 304. The RAM 309 provides a work area for the first CPU 313 when it executes the computer program. The RAM 309 is used for control code, calculations required for data interpretation and printing, and print data processing. The storage 304 stores control data in addition to the control program. The storage 304 stores computer programs that, when executed by the first CPU 313, function as an image information generation unit 305, a maximum density condition determination unit 306, a predicted density calculation unit 307, and a gradation correction table generation unit 308. The storage 304 is a large-capacity storage device such as an HDD (Hard Disk Drive) or an SSD (Solid State Drive).

[0016] An image information generation unit 305 generates various image objects according to data acquired from the host computer 301. A maximum density condition determination unit 306 adjusts the maximum density of the image density. A predicted density calculation unit 307 predicts the image density based on detection results (signal values) from a sensor 340 (described later) provided in the image forming engine 101. A gradation correction table generation unit 308 generates a gradation correction table (γLUT (Look Up Table)) used for gradation correction of the image. A RAM 309 includes a table storage unit 310 that temporarily stores the processing results of the maximum density condition determination unit 306, the predicted density calculation unit 307, and the gradation correction table generation unit 308.

[0017] The RIP unit 314 generates image data by expanding the image object generated by the image information generation unit 305 into a bitmap image. The color processing unit 315 performs multidimensional color conversion processing on the image data. The gradation correction unit 316 performs gradation correction on the image data for each color component after the color conversion processing based on a γLUT corresponding to each color component. The pseudo-halftoning processing unit 317 performs pseudo-halftoning processing such as a dither matrix or error diffusion method on the image data after the gradation correction.

[0018] The image data processed by the RIP unit 314, color processing unit 315, gradation correction unit 316, and pseudo-halftone processing unit 317 is transmitted to the image forming engine 101 via an engine I / F unit 318. The image forming engine 101 forms an image based on the image data acquired from the controller 300.

[0019] The image forming engine 101 includes a second CPU 102, a sensor 340, a timer 350, a counter 360, and an image density sensor 230. The second CPU 102 controls the image forming process (printing process) on paper by the image forming engine 101 based on image formation conditions. Signal values ​​output from the sensor 340, the timer 350, and the counter 360 are used in the image density prediction process by the predicted density calculation unit 307. The sensor 340 is an environmental sensor provided, for example, inside the image forming apparatus 100, that detects the environmental conditions (temperature, humidity, etc.) of the image forming apparatus 100. The timer 350 is used to measure, for example, the time between prints and the time left since the previous print. The counter 360 is used, for example, to count the number of printed sheets of paper and the number of times toner is replenished. In this way, the sensor 340, the timer 350, and the counter 360 are detection units that detect the environmental conditions of the image forming apparatus 100, and the signal values ​​output from each unit indicate changes in the environmental conditions during image formation. The image density sensor 230 will be described later.

[0020] When printing a test image for calibration, the image data (test image data) generated by the controller 300 on the RAM 309 is used for printing.

[0021] 2 is a configuration diagram of image forming apparatus 100. Image forming apparatus 100 includes a housing 201 that houses image forming engine 101 and controller 300. Image forming engine 101 includes various mechanisms for image formation in addition to the configuration described in FIG. 1. Printing process processing (e.g., image formation processing, paper feeding processing, etc.) performed by each mechanism for image formation is controlled by second CPU 102. An operation panel 191 is provided on top of housing 201.

[0022] The mechanisms for image formation in this embodiment include an optical processing mechanism 110, a fixing processing mechanism 120, a paper feeding processing mechanism 130, and a transport processing mechanism 140. The optical processing mechanism 110 forms an electrostatic latent image, visualizes the electrostatic latent image, and transfers the visualized image to paper S. The fixing processing mechanism fixes the transferred visualized image to paper S. The paper feeding processing mechanism feeds paper S. The transport processing mechanism transports the fed paper S.

[0023] The optical processing mechanism 110 includes a plurality of image forming units 220, 221, 222, and 223, an intermediate transfer body 252, and a secondary transfer roller 251. The plurality of image forming units 220, 221, 222, and 223 have the same configuration and are used to form images of different colors. In this embodiment, the image forming unit 220 is used to form images of yellow (Y). The image forming unit 221 is used to form images of magenta (M). The image forming unit 222 is used to form images of cyan (C). The image forming unit 223 is used to form images of black (K).

[0024] Each of the image forming units 220, 221, 222, and 223 includes a photosensitive drum 205, a charger 211, a laser scanner 207, and a developing unit 212. The photosensitive drum 205 is a photosensitive member having a photosensitive layer on its surface, and rotates counterclockwise in the drawing around the drum axis. The charger 211 uniformly charges the surface of the rotating photosensitive drum 205. The laser scanner 207 irradiates the charged surface of the photosensitive drum 205 with laser light, thereby forming an electrostatic latent image on the surface of the photosensitive drum 205.

[0025] The laser scanner 207 includes a laser output unit 208 and a reflecting mirror 209. The laser output unit 208 includes a light source that outputs laser light, a laser driver that controls the on / off of the laser light output from the light source based on image data acquired from the controller 300, and a rotary polygon mirror. The laser light output from the light source is reflected by the rotary polygon mirror and the reflecting mirror 209 and irradiates the surface of the photosensitive drum 205. At this time, as the rotary polygon mirror rotates, the laser light repeatedly moves in one direction. As the laser light moves in one direction, the irradiation position of the laser light on the surface of the photosensitive drum 205 moves in one direction. As a result, an electrostatic latent image for one line is formed on the surface of the photosensitive drum 205.

[0026] In this embodiment, the direction in which the irradiation position of the laser beam on the surface of the photosensitive drum 205 moves is the axial direction of the photosensitive drum 205. Therefore, the axial direction of the photosensitive drum 205 is the main scanning direction. As the laser beam repeatedly moves in the main scanning direction and the photosensitive drum 205 rotates, an electrostatic latent image of multiple lines is repeatedly formed on the surface of the photosensitive drum 205. As a result, an electrostatic latent image that spreads in the main scanning direction and a sub-scanning direction that intersects the main scanning direction is formed on the surface of the photosensitive drum 205.

[0027] The developing device 212 visualizes the electrostatic latent image into a toner image using a developer of the corresponding color (toner in this case). As a result, a yellow toner image is formed on the photosensitive drum 205 of the image forming unit 220. A magenta toner image is formed on the photosensitive drum 205 of the image forming unit 221. A cyan toner image is formed on the photosensitive drum 205 of the image forming unit 222. A black toner image is formed on the photosensitive drum 205 of the image forming unit 223.

[0028] The toner image on each photosensitive drum 205 is transferred onto an intermediate transfer body 252 to which a voltage of the opposite polarity to that of the toner image is applied. The intermediate transfer body 252 is an endless belt-like image carrier that rotates clockwise in the figure. Transfer is performed sequentially according to the relationship between the position of each photosensitive drum 205 and the rotation speed of the intermediate transfer body 252, so that the toner images of each color are transferred and superimposed onto the intermediate transfer body 252. In this way, a full-color toner image is carried on the intermediate transfer body 252. When a black-and-white image is formed, only the image forming unit 223 that forms a black image operates, and the black image is transferred onto the intermediate transfer body 252. The intermediate transfer body 252 conveys the transferred toner image to the secondary transfer roller 251 by rotating.

[0029] An image density sensor 230 is disposed near the intermediate transfer body 252, downstream of the image forming unit 223 in the rotation direction of the intermediate transfer body 252. The image density sensor 230 is a reading device that reads a test image for calibration carried on the intermediate transfer body 252. The reading result of the test image by the image density sensor 230 is used for calibration to adjust the image density and gradation of the image formed by the image forming engine 101.

[0030] The paper feed processing mechanism 130 includes a storage case 210 that stores paper sheets S. The paper feed processing mechanism 130 feeds the paper sheets S stored in the storage case 210 one by one and transports them to the transport processing mechanism 140. The transport processing mechanism 140 transports the paper sheets S fed from the paper feed processing mechanism 130 to the secondary transfer roller 251. At that time, the transport processing mechanism 140 corrects any skew of the paper sheets S and transports the paper sheets S to the secondary transfer roller 251 in accordance with the timing at which the toner image carried on the intermediate transfer body 252 is transported to the secondary transfer roller 251.

[0031] The secondary transfer roller 251 presses the paper S against the intermediate transfer body 252, and at the same time, a voltage of the opposite polarity to that of the toner is applied to the secondary transfer roller 251. As a result, the secondary transfer roller 251 transfers all of the toner images of each color carried by the intermediate transfer body 252 onto the paper S. The secondary transfer roller 251 transports the paper S onto which the toner images have been transferred to the fixing process mechanism 120.

[0032] The fixing process mechanism 120 includes a fixing device 260. The fixing device 260 has two rollers, at least one of which has a heat source. The fixing device 260 sandwiches and conveys the paper S, onto which the toner image has been transferred, between the two rollers. The two rollers heat and press the toner image with the heat source, thereby melting and fixing the toner image to the paper S. This results in an image being printed on one side of the paper S. In the case of single-sided printing, the paper S is discharged from the fixing device 260 to the paper discharge section 280.

[0033] In the case of double-sided printing, the paper S is transported again to the secondary transfer roller 251 via the reversing section 270. The printing side of the image on the paper S is reversed by the reversing section 270, and the toner image is transferred to the other side by the secondary transfer roller 251. The toner image is then fixed on the paper S by the fixing device 260, and the paper S is discharged to the paper discharge section 280. Printing on the paper S is carried out in this manner.

[0034] (Real-time multi-tone correction control) A colorimetric unit 240 for detecting a test image formed on paper S is provided downstream of the fixing unit 260 (reversing unit 270 in FIG. 2). Hereinafter, paper S on which a test image for gradation correction is formed will be referred to as a "gradation correction chart." Colorimetric unit 240 reads the gradation correction chart in response to a color detection operation instruction input from operation panel 191. Colorimetric unit 240 includes an inline sensor as a reading unit. Based on the detection results of the test image by colorimetric unit 240, controller 300 executes correction jobs such as image density correction, gradation correction, and multi-order color correction. Controller 300 can also execute correction jobs based on the detection results of the test image by image density sensor 230. Controller 300 changes image formation conditions according to the detection results of the test image. Image formation conditions are changed in two ways, as described below.

[0035] The first method is a method of creating a gradation correction chart by interrupt processing while a print job is being executed, and performing calibration. In this method, a sheet S (gradation correction chart) on which only a test image is formed is generated by interrupting the print job, and becomes the subject of color measurement by the colorimetric unit 240. The process of printing the gradation correction chart is an interrupt job for the original print job. Note that the paper discharge unit 280 may be provided with a separate paper discharge tray for discharging the gradation correction chart so that the measured gradation correction chart does not get mixed in with the paper S on which the image has been printed in the print job. This first method is called "interrupt-type real-time multi-tone correction control," and is sometimes abbreviated to "interrupt type."

[0036] The second method is a method of performing calibration by forming a test image in the margin of paper S on which an image from a print job has been printed. With this method, a test image can be printed on each sheet of paper and the color can be measured. In this case, the position where the test image is formed is the margin of paper S, which is outside the area where the image from the print job is printed. The second method is called "margin-utilizing real-time multi-tone correction control," and is sometimes abbreviated to "margin-utilizing type."

[0037] Since either the first method or the second method is selected, the test image formation position may be the same regardless of the method. In this case, the test image formation position is the margin of the paper S even in the first method.

[0038] The correction job in this embodiment is a job that prints only a test image, so the following will describe the interrupt-type tone correction control, and will omit a description of the margin-utilizing tone correction control.

[0039] 3A and 3B are diagrams illustrating setting screens for performing image adjustment. Fig. 3A shows an example of a setting screen 410 displayed on the display of operation panel 191. Controller 300 executes a program stored in ROM 380 to display setting screen 410 on operation panel 191. Controller 300 uses setting screen 410 to accept input of settings for image forming apparatus 100. Setting screen 410 has an adjustment tab 411, and the contents of the tab selected by the user are displayed.

[0040] The setting screen 410 has an adjustment tab 411. The adjustment tab 411 includes an adjustment item setting field 412 and an adjustment method setting field 413. The adjustment item setting field 412 is a display field for setting items for adjustment processing performed by the image forming apparatus 100. In the adjustment item setting field 412, check boxes for "Front and back image position" and "Gradation" are displayed so that they can be selected. The user selects both the check boxes for "Front and back image position" and "Gradation".

[0041] The adjustment item selected in the adjustment item setting field 412 is set and executed as an adjustment item for the image forming apparatus 100. Note that "Gradation" in the adjustment item setting field 412 refers to the real-time multi-tone correction function described above. Also, "Front and back image position" in the adjustment item setting field 412 refers to the front and back registration adjustment function that adjusts the position of images printed on the front and back of paper. Note that a detailed explanation of "Front and back image position" will be omitted.

[0042] The adjustment method setting field 413 is a display field for setting the adjustment method for the adjustment item selected in the adjustment item setting field 412. Here, radio buttons for "margin use type" 414 and "interrupt type" 415 are displayed selectably in the adjustment method setting field 413, and an example is shown in which "interrupt type" 415 has been selected by the user. In interrupt type real-time multi-tone correction control, the interval at which the gradation correction chart is inserted (interrupt interval) can be set. Therefore, when "interrupt type" 415 is selected, an interrupt interval setting screen is displayed on the display of the operation panel 191.

[0043] FIG. 3(b) illustrates an interrupt interval setting screen 420. The user can set the interrupt interval of the gradation correction chart using the setting screen 420. The interrupt interval is expressed as the number of sheets of paper S on which an image is formed. The setting screen 420 displays a setting field 421 that displays the interrupt interval (set number of sheets), increase / decrease keys 422 that increase / decrease the interrupt interval, and an OK button 416. The user inputs a predetermined interrupt interval using the increase / decrease keys 422 while checking the value in the setting field 421, and presses the OK button 416. This sets the interrupt interval, and the display on the operation panel 191 switches to the setting screen 410.

[0044] By pressing the OK button 416 on the setting screen 410, the settings made on the setting screen 410 (including the interruption interval) are input to the controller 300. The controller 300 saves the settings (adjustment item, adjustment method (interruption type in this case), and interruption interval of the gradation correction chart) in the RAM 309. This allows the controller 300 to create a gradation correction chart and perform interruption-type real-time multi-tone correction control every time the number of printed sheets reaches the number of sheets specified by the interruption interval.

[0045] 4 is an example diagram of a gradation correction chart. The color measurement unit 240 has two in-line sensors 551 and 552 provided at positions corresponding to both ends of the gradation correction chart 500 in a direction perpendicular to the transport direction of the gradation correction chart 500. The test image printed on the gradation correction chart 500 includes gradation patches 510 to 540. The gradation patches 510 to 540 are arranged at both ends of the gradation correction chart 500 in a direction perpendicular to the transport direction of the gradation correction chart 500, depending on the reading positions of the in-line sensors 551 and 552. The printing positions of the gradation patches 510 to 540 are in a marginal area of ​​the paper provided outside a print guaranteed area 501, which is an area in which an image corresponding to a print job can be printed.

[0046] The gradation patch 510 is, for example, a yellow image. The gradation patch 520 is, for example, a magenta image. The gradation patch 530 is, for example, a cyan image. The gradation patch 540 is, for example, a black image. The colors of the gradation patches 510 to 540 are not limited to these. The gradation patches 510 to 540 are each made up of a total of 10 patch images with image densities ranging from 10% to 100% in 10% increments. Note that the gradation patches may be printed inside the print guaranteed area 501.

[0047] (Predicted concentration calculation section) 5 is an explanatory diagram of the predicted density calculation unit 307. The predicted density calculation unit 307 acquires various signal values ​​from a sensor 340, a timer 350, and a counter 360 provided in the image forming apparatus 100 (image forming engine 101). The predicted density calculation unit 307 also acquires image forming conditions 370 from the image forming engine 101, such as the current exposure intensity LPW of the laser light output from the laser scanner 207 and the charging potential Vd of the photosensitive drum 205 by the charger 211.

[0048] The predicted density calculation unit 307 executes image density prediction control, which predicts image density from these various signal values ​​and current image formation conditions 370. To this end, the predicted density calculation unit 307 has an input signal value processing unit 320 and a density prediction unit 330. The various signal values ​​and current image formation conditions 370 are input to the input signal value processing unit 320. The input signal value processing unit 320 has a signal value storage unit 321 and a difference calculation unit 322. The signal value storage unit 321 stores basic signal values ​​(basic signal values). The difference calculation unit 322 calculates the difference between the input signal value and the basic signal value stored in the signal value storage unit 321.

[0049] The signal values ​​processed by the input signal value processing unit 320 are input to the density prediction unit 330. The density prediction unit 330 has a density storage unit 331 and a prediction function unit 332. The density storage unit 331 stores a basic image density (basic image density). The prediction function unit 332 predicts the image density based on the signal values ​​input from the input signal value processing unit 320.

[0050] The prediction function unit 332 has an image density prediction model that calculates the image density change amount of the basic image density from the signal value. The prediction function unit 332 calculates the current predicted image density by adding the image density change amount calculated from the image density prediction model to the basic image density stored in the density storage unit 331. Details of the image density prediction model will be described later. Acquisition of the basic signal value and acquisition of the basic image density will also be described later.

[0051] The predicted image density calculated by the predicted density calculation unit 307 is transmitted to a gradation correction table generation unit 308. Based on the acquired predicted image density, the gradation correction table generation unit 308 creates a γLUT (Look Up Table) to be input to a gradation correction unit 316. The gradation correction method will be described later.

[0052] (basic signal value and basic image density) A method for acquiring the base signal value and base image density will now be described. FIG. 6 is a flowchart showing the process for acquiring the base signal value and base image density. The base signal value and base image density value are acquired during automatic gradation correction control that is performed periodically using an image printed on paper S. In this embodiment, an example will be described in which a potential sensor that measures the potential on the surface of the photosensitive drum 205 is used, but the present invention is not limited to this.

[0053] When automatic tone correction control is started in response to a user instruction, the controller 300 starts a potential control process. The controller 300 performs potential control before the image forming engine 101 forms an image on the paper S, and determines the target charging potential VdT, grid bias Y, and developing bias Vdc (S601). The potential control process determines each potential according to the environmental conditions (including temperature and humidity conditions) in which the image forming apparatus 100 is installed.

[0054] In this embodiment, the image forming engine 101 performs potential control called two-point electrification. FIG. 7 is an explanatory diagram of potential control using two-point electrification. "Vd1" indicates the charge potential under the first charging condition (grid bias Y=400 [V]), and "Vl1" indicates the exposed portion potential (potential of the electrostatic latent image portion) formed with the standard laser power at that time. "Vd2" indicates the charge potential under the second charging condition (grid bias Y=800 [V]), and "Vl2" indicates the exposed portion potential formed with the standard laser power at that time. The contrast potentials Cont1 and Cont2 when the grid bias Y is 400 [V] and 800 [V], respectively, are calculated using the following equations (1) and (2). Cont1=Vd1-Vl1 …(1) Cont2=Vd2-Vl2 …(2)

[0055] Here, the increase ContΔ in contrast potential when the charging potential fluctuates by 1 [V] is calculated by the following equation (3) based on the results of equations (1) and (2). ContΔ=(Cont2-Cont1) / (Vd2-Vd1) …(3)

[0056] A sensor 340 is provided inside the image forming apparatus 100. The sensor 340 measures environmental conditions such as temperature and humidity inside the image forming apparatus 100. The image forming engine 101 determines the environmental conditions (e.g., absolute moisture content) inside the image forming apparatus 100 based on the measurement results of the sensor 340. The image forming engine 101 references a target contrast potential ContT corresponding to the environmental condition from a pre-registered environmental table. The relationship between the target contrast potential ContT and the increase amount ContΔ of the contrast potential is calculated using the following equation (4): ContT = Cont1 + X · ContΔ …(4)

[0057] By calculating the parameter X that satisfies the relationship of equation (4), the target charging potential VdT (hereinafter also referred to as "target potential") is calculated from the following equation (5). VdT = Vd1 + X … (5)

[0058] The amount of change VdΔ in the charge potential when the grid bias changes by 1 [V] is calculated by the following equation (6). VdΔ=(Vd2-Vd1) / (800-400) …(6)

[0059] The grid bias Y that gives the target potential VdT is calculated by the following equation (7). VdT=400+Y·VdΔ …(7)

[0060] In equation (7), the charge potential change amount VdΔ is calculated using equation (6), and the target potential VdT is calculated using equation (5). Therefore, by substituting the known potentials from equations (5) and (6), the grid bias Y that satisfies the relationship in equation (7) can be finally determined.

[0061] The above process determines the target potential VdT and grid bias Y according to the environmental conditions. The development bias Vdc has a specified potential difference from the target potential VdT and is calculated by subtracting the specified potential from the determined target potential VdT. Subsequent image formation is performed using the determined development bias Vdc. Note that although the potential on the surface of each photosensitive drum 205 is negative, the negative sign is omitted here to make the calculation process easier to understand. The potential control process of S601 is performed as described above.

[0062] The controller 300 causes the image forming engine 101 to print a patch image on the paper S using the grid bias Y and development bias Vdc determined by the potential control (S602) to adjust the maximum toner application amount. In an image forming apparatus 100 that prioritizes productivity, it is possible to omit the following process and adjust the maximum toner application amount using only potential control. However, because the colorant charge retention amount in the developer 212 and the toner / carrier mixture ratio change depending on the environment and the passage of time, control using only potential has low accuracy. Therefore, in this embodiment, multiple patch images are formed with the exposure intensity LPW changed in several stages, and the exposure intensity LPW used for normal image formation is determined.

[0063] After determining the grid bias Y and the development bias Vdc, the image forming apparatus 100 forms five patch images ((1) to (5)) for each of the colors black, cyan, yellow, and magenta shown in FIG. 8 to adjust the maximum toner application amount. Note that the number of patch images is not limited to this. The five patch images are formed under different exposure intensities LPW. Patch image (1) has exposure intensity LPW1, patch image (2) has exposure intensity LPW2, patch image (3) has exposure intensity LPW3, patch image (4) has exposure intensity LPW4, and patch image (5) has exposure intensity LPW5. The laser power increases sequentially from exposure intensity LPW1 to exposure intensity LPW5. Exposure intensity LPW3 corresponds to the standard laser power used for potential control.

[0064] The patch images printed on the paper S are colorimetrically measured by the colorimetry unit 240. The controller 300 detects the image density of each patch image based on the colorimetry results of the patch images measured by the colorimetry unit 240 (S603). FIG. 9 is a graph showing the relationship between the image density detected from each patch image and the exposure intensity LPW. The amount of applied toner can be adjusted by controlling the exposure intensity LPW in accordance with a density target value (hereinafter also referred to as the "maximum applied amount target density value") that targets the detected image density.

[0065] After completing the adjustment of the maximum toner application amount, the controller 300 next performs gradation correction. The controller 300 uses the previously determined grid bias Y, development bias Vdc, and exposure intensity LPW as image formation conditions, and causes the image forming engine 101 to print an image pattern for gradation correction with 64 gradations for each color on the paper S (S604). Note that the number of gradations is not limited to this.

[0066] The image pattern printed on the paper S is colorimetrically measured by the colorimetry unit 240. The controller 300 detects the image density based on the colorimetry result of the image pattern by the colorimetry unit 240 (S605). The controller 300 performs interpolation and smoothing processes on the image density obtained from the image pattern to obtain the engine gamma characteristic for the entire density range. The controller 300 uses the obtained engine gamma characteristic and a preset gradation target to create a gradation correction table for converting an input image signal into an output image signal (S606).

[0067] 10 is an explanatory diagram of the gradation correction table. The controller 300 creates the gradation correction table by performing an inverse conversion process on the engine gamma characteristic so that the engine gamma characteristic matches the gradation target. The gradation correction table ensures that the image density on the paper S matches the gradation target across the entire density range.

[0068] The controller 300 causes the image forming engine 101 to form a plurality of toner image patterns on the intermediate transfer body 252 under the same image forming conditions as those for the image pattern for gradation correction (S607). The controller 300 detects the image density of the toner image pattern based on the detection result of the toner image pattern on the intermediate transfer body 252 by the image density sensor 230 (S608). The controller 300 stores the detected image density value in the density storage unit 331 as the basic image density (target density) on the intermediate transfer body 252 (S609). In this embodiment, after the gradation correction table is created, toner image patterns of 10 gradations for each color are formed on the intermediate transfer body 252. The image density value of the toner image pattern detected by the image density sensor 230 is stored in the density storage unit 331 as the basic image density.

[0069] The controller 300 performs the automatic tone correction as described above, and stores the basic signal value obtained when the basic image density is acquired in the signal value storage unit 321 (S610). This basic signal value is, for example, various signal values ​​of the sensor 340, the timer 350, and the counter 360, as well as image formation conditions such as the levels of the grid bias Y, the development bias Vdc, and the exposure intensity LPW.

[0070] In this embodiment, the image density prediction model is a model for predicting the image density on the intermediate transfer body 252, and therefore the basic image density value is the image density value measured on the intermediate transfer body 252. For example, if the image density prediction model is a model for predicting the image density on paper S, the basic image density value is the image density measured on paper S. The basic image density can be selected appropriately depending on which image carrier (paper S, intermediate transfer body 252, photosensitive drum 205) the image density prediction model is to handle, and is not limited to the above.

[0071] (LUT creation) A method for reflecting image density values ​​in an LUT will be described. During automatic gradation correction performed in response to a user instruction, a gradation correction table (hereinafter referred to as a "basic correction LUT") is generated in accordance with the engine γ characteristics so as to achieve a preset gradation target (hereinafter referred to as a "gradation LUT"). Then, basic image density values ​​of 10 gradations for each color are acquired. After automatic gradation correction, the controller 300 reflects the initial correction LU in the input image data and sends it to the image forming engine 101. The image forming engine 101 forms an image based on the input image data acquired from the controller 300. By correcting the engine γ characteristics using the initial correction LUT, an image is formed in which the image density has been corrected to match the target gradation LUT.

[0072] Fig. 11 is a flowchart showing the process of creating a composite correction LUT, and Figs. 12, 13, and 14 are explanatory diagrams of the process of creating a composite correction LUT.

[0073] The controller 300 acquires predicted image density values ​​(S1101). The controller 300 plots the acquired predicted image density values ​​for each gradation level and creates an image density curve (dashed line) for the predicted image density values ​​indicated by the white circles in FIG. 12 (S1102). The controller 300 performs inverse conversion to correct the image density curve of these predicted image density values ​​to the initial image density curve, and creates a correction LUT indicated by the long dashed line in FIG. 13 (S1103). The controller 300 combines the correction LUT and the initial correction LUT to create a combined correction LUT as indicated by the long two-dot chain line in FIG. 14 (S1104). The combined correction LUT is reflected in the output image. The image density curve may be created using a commonly used approximation method, such as an approximation formula connecting 10 points.

[0074] (Normal image density calculation) FIG. 15 is a flowchart showing the process of acquiring the current image density value of the image forming apparatus 100 during normal image density correction control.

[0075] When the image forming apparatus 100 is started, the controller 300 acquires an input signal value from the image forming apparatus 100 (S1501). The input signal value includes information from the sensor 340, timer 350, and counter 360 of the image forming engine 101, such as the environmental conditions at the time of start-up, the time of leaving the apparatus, and the number of times toner has been replenished, as well as information on the image forming conditions at the time of image formation.

[0076] The controller 300 forms a plurality of toner image patterns on the intermediate transfer body 252 under image forming conditions corresponding to the acquired input signal values ​​(S1502). In this embodiment, the toner image patterns are toner image patterns with 10 gradations for each color, but are not limited to this. The controller 300 detects the image density from the detection results of the toner image patterns on the intermediate transfer body 252 by the image density sensor 230 (S1503). The controller 300 acquires the image density value (γ characteristic) at the time of correction based on the detected image density. Note that the image density may be detected from the colorimetric result of the colorimetric unit 240 of the image printed on the paper S, rather than from the detection results of the image formed on the intermediate transfer body 252.

[0077] (Calculation of predicted image density) 16 is a flowchart showing the process of acquiring a predicted image density value. Here, the process of predicting the image density when the image forming apparatus 100 is started up in a state where the basic signal value and basic image density have been acquired in advance will be described.

[0078] When the image forming apparatus 100 is started, the controller 300 acquires input signal values ​​from the image forming apparatus 100 (S1601). The input signal values ​​include information on the environmental conditions of the sensor 340, timer 350, and counter 360 of the image forming engine 101 at the time of start-up, the time left standing, the number of toner replenishments, etc., and information on the image forming conditions at the time of image formation.

[0079] The controller 300 extracts a difference value between the acquired input signal value and a basic signal value stored in advance in the signal value storage unit 321 (S1602). The controller 300 substitutes the extracted difference value into an image density prediction model formula created in advance and stored in the density storage unit 331 (S1603). As a result, the controller 300 calculates a difference value between the current image density and the basic image density as a predicted value (image density fluctuation predicted value) (S1604). The controller 300 calculates the current predicted image density value from the sum of the image density fluctuation predicted value and the basic image density value, and acquires the gamma characteristic (S1605).

[0080] (Image density prediction model) The image density prediction model is obtained by mathematically formulating experimental results using information correlated with fluctuations in image density as input signal values ​​and image density information as output information. The input signal values ​​are the same as the input signal values ​​acquired in S1501 of FIG. 15 or S1601 of FIG. 16. The input signal values ​​include information on the temperature and humidity detected by sensor 340 at the time of startup of image forming apparatus 100, the amount of time the image forming apparatus 100 has been left unused as measured by timer 350, the number of times the image forming apparatus 100 has been replenished and the number of times the image forming apparatus 100 has been idled as measured by counter 360, and the image formation conditions before the image forming apparatus 100 was left unused. FIG. 17 is a flowchart showing the process of creating an image density prediction model in advance.

[0081] The controller 300 acquires environmental conditions and image density as measurement data (input signal values) (S1701). Here, environmental conditions include the toner concentration in the developer during printing, the temperature and humidity of various locations, the toner concentration in the developer during the previous printing, and the time since the previous printing. These are environmental conditions that can be obtained when the image forming apparatus 100 is started up. Image formation conditions include the charging potential Vd on the photosensitive drum 205, the exposure intensity LPW, and the development contrast Vcont. Multiple patterns of variation in environmental conditions and image formation conditions are prepared, and the image density is obtained from images printed under each of these patterns. The image is carried on one of the image carriers, such as the paper S, the photosensitive drum 205, or the intermediate transfer body 252, and the image density is detected using the colorimeter 240 or the image density sensor 230.

[0082] The controller 300 classifies the acquired measurement data into identification data and verification data (S1702). From the measurement data, the controller 300 calculates fluctuation amounts that represent environmental fluctuations, image formation condition changes, and image density fluctuations, based on the initially acquired measurement data (S1703). The controller 300 creates a linear function model by curve fitting the identification data with a linear function equation that uses each environmental condition and each image formation condition as input variables and image density for each gradation as output variables (S1704).

[0083] The following describes a case where the charging potential Vd during printing, the exposure intensity LPW, the toner concentration in the developer, and the environmental temperature are used as input signal values, but the input signal values ​​are not limited to these. Also, here, a linear function model with up to four inputs for the environmental conditions obtained from the sensor 340 will be described, but even when five or more inputs of environmental conditions or image formation conditions are used, a linear function model can be created by performing similar processing.

[0084] Input variable x after t seconds i(t) , the exposure intensity fluctuation during printing x 1(t) , charging potential fluctuation x 2(t) , fluctuation in toner concentration in the developing unit x 3(t) , environmental temperature fluctuation x 4(t) Let the input variable x i(t) The following linear function model is created to predict the output variable from the combination of the following: The linear function model (one-input model) predicted from one type of input variable is the image density fluctuation y ^ i(t) The linear function model (two-input model) predicted from two types of input variables is ^ ij(t) The linear function model (three-input model) predicted from three types of input variables is ^ ijk(t) The linear function model (four-input model) predicted from four types of input variables is ^ ijkl(t) is.

[0085]

number

[0086] For each of these input models, for each combination of (i), (i,j), (i,j,k), and (i,j,k,l) ​​(i,j,k,l=1 to 4), the output variable is the measured data y (t) The curve fitting method is, for example, to fit the coefficients (a i ), (a ij1 ,a ij2 ), (a ijk1 ,a ijk2 ,a ijk3 ), (a ijkl1 ,a ijkl2 ,a ijkl3 ,a ijkl4 ) is calculated as the sum of squares of the prediction error S expressed by the following equation. The coefficient (a i ), (a ij1 ,a ij2 ), (a ijk1 ,a ijk2 ,a ijk3 ), (a ijkl1 ,a ijkl2 ,a ijkl3 ,a ijkl4 ) to explore.

[0087]

number

[0088] The controller 300, which has created the linear function model, calculates the prediction error of the linear function model created in the process of S1704 using the verification data (S1705). The controller 300 calculates the predicted value y of the image density fluctuation using each linear function model under the environmental conditions and image forming conditions of the verification data. ^ i(t) ,y ^ ij(t) ,y ^ ijk(t) , y ^ ijkl(t) The controller 300 calculates these predicted values ​​and the measured value y of the density fluctuation of the verification data.(t) For comparison, the sum of squares S of the prediction errors is also calculated here.

[0089] The controller 300 compares the prediction errors for the combinations of input variables and determines the image density prediction model from the optimal combination of input variables and the linear function model (S1706). In this embodiment, the sum of the squared sum of the prediction errors calculated using the identification data and the squared sum of the prediction errors calculated using the verification data is evaluated, and the linear function model that provides the optimal combination of input variables taking both the identification data and the verification data into consideration is determined as the image density prediction model. Alternatively, the squared sums of the prediction errors calculated using the verification data may be compared, and the linear function model with the smallest value may be determined as the image density prediction model.

[0090] In this embodiment, the input variable is x 1(t) It was a simple example like this, but x 1(t) ×x 2(t) By preparing the products and quotients of environmental conditions or image formation conditions such as those listed above, it is possible to consider complex models. For example, a prediction model can be considered by creating input variables that can express changes in toner charge amount taking into account the toner concentration in the developer and the time it has been left standing. For simplicity, only curve fitting based on the initially acquired measurement data has been explained here, but a prediction model with even smaller errors can be obtained by performing curve fitting based on each measurement data and evaluating the prediction accuracy by the sum of all prediction errors.

[0091] (Interrupt-type real-time multi-tone correction control and image density prediction control) 18 is a flowchart showing the printing process according to a print job. In this printing process, whether interrupt-type real-time multi-tone correction control or image density prediction control is performed is determined according to the conditions of the print job.

[0092] When the controller 300 receives a print job instructing image formation, it stores data related to the print job in the storage 304 (S1801). The controller 300 determines whether the received print job includes a correction job for which interrupt-type real-time multi-tone correction control is enabled (S1802). Whether interrupt-type real-time multi-tone correction control is enabled depends on, for example, the selection of "interrupt type" 415 on the setting screen 410 of FIG. 3A and paper information such as paper type and size. FIG. 19 is an explanatory diagram of paper information. In FIG. 19, interrupt-type real-time multi-tone correction control is disabled for A5-sized thin paper, plain paper, and thick paper, as well as for paper types such as colored paper, recycled paper, embossed paper, vellum paper, envelopes, and letterhead. In this case, interrupt-type real-time multi-tone correction control is disabled even if "interrupt type" 415 is selected on the setting screen 410. If "Interrupt type" 415 is selected and the paper used in the print job is set to paper information for which interrupt type real-time multi-tone correction control is valid, it is determined that the print job is one for which interrupt type real-time multi-tone correction control is valid. Note that in this embodiment, whether or not it is valid is determined based on the paper information, but this determination may also be made using other print job settings, environmental conditions, etc. as parameters.

[0093] If the accepted print job is a print job for which interrupt-type real-time multi-tone correction control is enabled (S1802: Y), the controller 300 sets the print count N, which indicates the number of prints by the print job, to 1 and stores it in the RAM 309 (S1803). The controller 300 then executes printing processing for the Nth page (S1804).

[0094] The controller 300 determines whether the print count N has reached the number of sheets in the interrupt interval (S1805). The interrupt interval is set by the user on the setting screen 420 in FIG. 3(b). The interrupt interval setting is saved in RAM 309. The controller 300 makes this determination by comparing the interrupt interval saved in RAM 309 with the print count N.

[0095] If the print count N has reached the number of sheets in the interrupt interval (S1805: Y), the controller 300 executes interrupt-type real-time multi-tone correction control (S1806). When the interrupt-type real-time multi-tone correction control ends, the controller 300 initializes the print count N to 0 (S1807). If the print count N has not reached the number of sheets in the interrupt interval (S1805: N), or if the print count N has been initialized, the controller 300 determines whether printing of all pages specified in the print job has been completed (S1808). If printing of all pages has been completed (S1808: Y), the controller 300 ends the print job (S1809). If printing of all pages has not been completed (S1808: N), the controller 300 increments the print count N by 1 (S1810) and repeats the processing from S1804 onwards.

[0096] If the accepted print job is not a print job for which interrupt-type real-time multi-tone correction control is valid (S1802: N), the controller 300 sets the print count N of the print job to 1 and stores it in the RAM 309 (S1811). The controller 300 executes the print process for the Nth page (S1812).

[0097] The controller 300 determines whether the print number count N has reached the number of sheets in the execution interval of the image density predictive control (S1813). FIG. 20 is a view showing an example of a setting screen for setting the execution interval of the image density predictive control. The user can set the execution interval of the image density predictive control using a setting screen 2000. The setting screen 2000 displays a setting field 2001 that displays the execution interval (set number of sheets), increase / decrease keys 2002 that increase / decrease the execution interval, and an OK button 2003. The user inputs a predetermined execution interval using the increase / decrease keys 2002 while checking the value in the setting field 2001, and presses the OK button 2003. This sets the execution interval of the image density predictive control. The execution interval of the image density predictive control is stored in RAM 309. As a result, the controller 300 performs the image density predictive control every time the number of printed pages reaches the number of sheets in the execution interval of the image density prediction.

[0098] If the print count N has reached the number of sheets in the execution interval of image density predictive control (S1813: Y), the controller 300 executes image density predictive control (S1814). If the print count N has not reached the number of sheets in the execution interval of image density predictive control (S1813: N), or if image density predictive control has been executed, the controller 300 determines whether printing of all pages specified in the print job has been completed (S1815). If printing of all pages has been completed (S1815: Y), the controller 300 ends the print job (S1809). If printing of all pages has not been completed (S1815: N), the controller 300 increments the print count N by 1 (S1816) and repeats the processing from S1812 onwards.

[0099] As described above, printing processing is performed with control branching between interrupt-type real-time multi-tone correction control and image density prediction control. By correcting the image formation conditions using interrupt-type real-time multi-tone correction control, highly accurate correction of image quality is performed. By correcting the image formation conditions using image density prediction control, correction that stabilizes image quality is performed without reducing productivity. In this way, it is possible to perform appropriate image quality correction according to the print job settings.

[0100] (Variation) As described above, interrupt-type real-time multi-tone correction control reduces image quality stability when the execution interval is long, and affects productivity when the execution interval is short (high interrupt frequency). In this modified example, image density prediction control is performed between the execution of interrupt-type real-time multi-tone correction control and the execution of the next interrupt-type real-time multi-tone correction control, thereby achieving image quality stability while maintaining productivity.

[0101] (Image density prediction control during non-execution period of interrupt-type real-time multi-tone correction control) 21 is a flowchart showing the print processing of a print job including such processing. Image density prediction control is performed during a period when interrupt-type real-time multi-tone correction control is not being performed.

[0102] When the controller 300 receives a print job that instructs image formation, it stores data related to the print job in the storage 304 (S2101). The controller 300 compares the execution interval of the image density prediction control with the interrupt interval of the interrupt-type real-time multi-tone correction control (S2102).

[0103] If the execution interval of the image density predictive control is shorter than the interrupt interval of the interrupt-type real-time multi-tone correction control (S2102: Y), the controller 300 sets the print number counts M and N to 1 and stores them in the RAM 309 (S2103). The print number count M represents the number of prints by a print job and is a count value of the number of prints for executing the interrupt-type real-time multi-tone correction control. The print number count N represents the number of prints by a print job and is a count value of the number of prints for executing the image density predictive control. If the execution interval of the image density predictive control is shorter than the interrupt interval of the interrupt-type real-time multi-tone correction control, the image density predictive control is performed more frequently than the interrupt-type real-time multi-tone correction control. In other words, the image density predictive control is performed between the execution of the interrupt-type real-time multi-tone correction control and the execution of the next interrupt-type real-time multi-tone correction control. The print number counts M and N are set to perform each control at the respective intervals.

[0104] The controller 300 executes printing processing for the page (S2104). After the printing processing, the controller 300 determines whether the print number count N for image density predictive control has reached the number of sheets in the execution interval of image density predictive control (S2105). If it has not reached that number (S2105: N), the controller 300 increments the print number count N for image density predictive control by 1 (S2106). If it has reached that number (S2105: Y), the controller 300 executes image density predictive control (S2107). When the image density predictive control ends, the controller 300 sets the print number count N for image density predictive control to 1 (S2108).

[0105] After updating the print count N, the controller 300 determines whether the interrupt print count M has reached the interrupt interval count (S2109). If it has not reached that count (S2109: N), the controller 300 increments the interrupt print count M by 1 (S2110). If it has reached that count (S2109: Y), the controller 300 executes interrupt real-time multi-tone correction control (S2111). When the interrupt real-time multi-tone correction control ends, the controller 300 sets the interrupt print count M to 1 (S2112).

[0106] After updating the print count M, the controller 300 determines whether printing of all pages specified in the print job has been completed (S2113). If printing of all pages has been completed (S2113: Y), the controller 300 ends the print job. If printing of all pages has not been completed (S2113: N), the controller 300 repeats the processing from S2104 onwards.

[0107] If the execution interval of the image density prediction control is longer than the interrupt interval of the interrupt-type real-time multi-tone correction control (S2102: N), the controller 300 sets the print count M for the interrupt-type real-time multi-tone correction control to 1 and stores it in the RAM 309 (S2115). The controller 300 executes the print process for the Mth page (S2116). If the execution interval of the image density prediction control is longer than the interrupt interval of the interrupt-type real-time multi-tone correction control, the interrupt-type real-time multi-tone correction control, which can perform relatively high-precision gradation correction, is executed more frequently than the image density prediction control. Therefore, there is no need to execute the image density prediction control, which has relatively low accuracy of gradation correction, so the print count N is not set.

[0108] The controller 300 determines whether the interrupt type print number count M has reached the number of sheets in the interrupt interval (S2117). If it has reached it (S2117: Y), the controller 300 executes the interrupt type real-time multi-tone correction control (S2118). When the interrupt type real-time multi-tone correction control ends, the controller 300 sets the interrupt type print number count M to 1 (S2119). If it has not reached it (S2117: N), the controller 300 increments the interrupt type print number count M by 1 (S2120).

[0109] After updating the print count M, the controller 300 determines whether printing of all pages specified in the print job has been completed (S2115). If printing of all pages has been completed (S2115: Y), the controller 300 ends the print job. If printing of all pages has not been completed (S2115: N), the controller 300 repeats the processing from S2116 onwards.

[0110] As described above, in the processes of S2103 to S2112, image density prediction control is performed between the execution of interrupt-type real-time multi-tone correction control and the execution of the next interrupt-type real-time multi-tone correction control, thereby achieving both productivity maintenance and image quality stability.

[0111] As described above, the image forming apparatus 100 of this embodiment is capable of executing a first correction process, such as interrupt-type real-time multi-tone correction control, which has relatively high accuracy and a long processing time, and a second correction process, such as image density prediction control, which has relatively low accuracy and a short processing time. The image forming apparatus 100 executes the first correction process and the second correction process according to predetermined settings. The predetermined settings include print job settings, paper information used in the print job, and execution intervals for the first correction process and the second correction process. The image forming apparatus 100 can appropriately correct image formation conditions by selectively using the first correction process and the second correction process according to these predetermined settings. This allows the image forming apparatus 100 to stabilize the image quality of output images while maintaining productivity.

Claims

1. an image forming means for forming an image on an image carrier based on image forming conditions; a correction unit that can perform a first correction process with relatively high accuracy and a long processing time and a second correction process with relatively low accuracy and a short processing time for the image forming conditions; and a control means for causing the correction means to execute the first correction process and the second correction process based on a predetermined setting. Image forming device.

2. a reading means for reading a test image for correcting the image forming conditions formed on the image carrier; a prediction unit for predicting the reading result of the test image, the correction means corrects the image forming conditions based on the reading result of the test image by the reading means as the first correction process, and corrects the image forming conditions based on the result of the prediction by the prediction means as the second correction process.

2. The image forming apparatus according to claim 1.

3. the control means causes the correction means to execute the first correction process if execution of the first correction process is enabled in a print job that instructs image formation, and causes the correction means to execute the second correction process if execution of the first correction process is not enabled.

3. The image forming apparatus according to claim 1.

4. the control means, when execution of the first correction process is enabled in the print job, causes the correction means to execute the first correction process if information on a paper used in the print job is set to enable execution of the first correction process.

4. The image forming apparatus according to claim 3.

5. the control means causes the correction means to execute the second correction process if the execution of the first correction process is set to be valid in the print job and the execution of the first correction process is set to be invalid for the information on the paper used in the print job.

5. The image forming apparatus according to claim 4.

6. The present invention is characterized in that the present invention further comprises a setting means for validating execution of the first correction process.

4. The image forming apparatus according to claim 3.

7. the first correction process is performed at a predetermined first interval; the second correction process is performed at predetermined second intervals; When the second interval is smaller than the first interval, the control means causes the correction means to perform the second correction process and then the first correction process.

3. The image forming apparatus according to claim 1.

8. The control means causes the correction means to perform the first correction process when the second interval is greater than the first interval.

8. The image forming apparatus according to claim 7.

9. Further comprising setting means for setting the first interval and the second interval.

8. The image forming apparatus according to claim 7.

10. further comprising a detection means for detecting an environmental condition; The prediction means makes the prediction based on the environmental conditions.

3. The image forming apparatus according to claim 2.

11. the prediction means makes the prediction based on the environmental conditions and current image forming conditions. The image forming apparatus according to claim 10.

Images