Image forming apparatus and method for controlling the image forming apparatus

Abstract

To adjust the amount of toner adhered onto recording paper within a target adhesion amount range despite the presence of unevenness in density.SOLUTION: In an image forming apparatus 100, a first detector 19 is used to measure the densities of a plurality of toner patches formed on an image carrier 16 by an image process unit 10. A second detector 32 is used to measure the density profile in a main scanning direction of an image for density unevenness measurement formed on a recording medium S by the image process unit 10. A control unit 20 calculates a correction amount for a target amount of toner adhered onto the recording medium S based on the difference between a representative value of the density according to the density profile and a density value extracted from the density profile at a detection position of the first detector 19. The control unit determines an image forming condition corresponding to a target toner adhesion amount corrected in accordance with the correction amount based on the densities of the plurality of toner patches formed in different image forming conditions.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to an image forming apparatus and a control method for an image forming apparatus, and more particularly to adjusting the amount of toner adhesion on a recording sheet. [Background technology]

[0002] In an image forming apparatus using a roller charging method, the outer film of the photoconductor wears away with use. This wear is suppressed by the transfer of the lubricant contained in the toner to the photoconductor. However, if the amount of lubricant transferred to the photoconductor is not uniform in the main scanning direction, the amount of wear in the film thickness of the photoconductor differs in the main scanning direction. This difference in the film thickness of the photoconductor in the main scanning direction causes a change in density in the main scanning direction of the toner images formed on the photoconductor and the intermediate transfer belt, and causes a change in density in the main scanning direction of the image formed on the recording paper.

[0003] Usually, an image forming apparatus is provided with an IDC (Image Density Control) sensor (e.g., a reflective photosensor) at the end in the main scanning direction to adjust the amount of toner adhesion. The IDC sensor detects the density of the adjustment pattern formed on the photoconductor or intermediate transfer belt, and image forming conditions such as the development bias are adjusted based on the detected density. However, if the density of the toner image formed on the photoconductor and intermediate transfer belt changes in the main scanning direction as described above, the image forming conditions adjusted based on the detected density at the attachment position of the IDC sensor may not be appropriate. As a result, the amount of toner adhesion on the recording paper does not fall within the target range, and the toner density on the recording paper becomes too high or too low.

[0004] JP 2020-013039 A (Patent Document 1) discloses a method for correcting the above-mentioned density change in the main scanning direction by changing the light amount of the exposure beam of the developer. Specifically, a chart for measuring density unevenness is first printed on an inspection sheet, and the printed chart is optically read by a scanner to obtain a density profile that associates each position in the main scanning direction with the toner density. Next, the light amount of the exposure beam of the developer is adjusted so as to cancel out the obtained density profile. At this time, the beam light amount is kept unchanged at a reference position determined on the photoconductor drum and corresponding to the density detection position by the IDC sensor.

[0005] The image forming apparatus disclosed in JP 2019-158910 A (Patent Document 2) includes two IDC sensors for detecting the reflection density of the toner patterns formed on the front and rear sides in the main scanning direction. The control unit adjusts the amount of toner adhesion by adjusting the image formation conditions using the average value of the detection values ​​of the two IDC sensors. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2020-013039 A [Patent Document 2] JP 2019-158910 A Summary of the Invention [Problem to be solved by the invention]

[0007] In the method of Patent Document 1 (JP 2020-013039 A) mentioned above, the density corresponding to the reference position, which is the mounting position of the IDC sensor, is left unchanged, and the density at other positions is corrected by the amount of light beam. Therefore, if the density at the reference position is significantly different from the density at other positions, the uneven density may not be corrected by the amount of light beam. As a result, the amount of toner adhesion on the recording paper may not fall within the target range.

[0008] In the image forming apparatus of the above Patent Document 2 (JP Patent Publication 2019-158910 A), an IDC sensor is provided on each of the front and rear sides in the main scanning direction. Therefore, when the toner concentration on the intermediate transfer belt increases or decreases uniformly in the main scanning direction, the toner adhesion amount can be appropriately adjusted by using the average value of the two IDC sensors. However, when the toner concentration profile does not increase or decrease uniformly, the toner adhesion amount cannot be appropriately adjusted by using the average value of the two IDC sensors.

[0009] The present disclosure has been made in consideration of the above problems. An object of one aspect of the present disclosure is to adjust the toner adhesion amount on a recording sheet to within a target adhesion amount range even when density unevenness exists on a photoconductor or an intermediate transfer belt. [Means for solving the problem]

[0010] An image forming apparatus according to an embodiment includes an image processing unit, Multiple The image processing unit includes a first detector, a second detector, and a control unit. The image processing unit forms a toner image on an image carrier by electrophotography, and transfers the formed toner image onto a recording medium. Multiple The first detector is used to measure the density of a plurality of toner patches formed on the image carrier by the image processing unit. , are located at different positions in the main scanning direction. The second detector is used to measure the density profile in the main scanning direction of the image for measuring density unevenness formed on the recording medium by the image processing unit. The control unit determines a representative value of density according to the density profile based on the density profile of the image for measuring density unevenness. Multiple First detector Each and a density value extracted at the detection location. The control unit selects the first detector corresponding to the concentration value closest to the representative concentration value from among the plurality of concentration values ​​extracted from the concentration profile at the respective detection positions of the plurality of first detectors. The control unit calculates the representative concentration value and , from the concentration profile at the detection position of the selected first detector The control unit calculates a correction amount for the target toner adhesion amount on the recording medium based on the difference from the extracted density value. Measure using the first detector selected , The measured densities of multiple toner patches areThe control unit converts the toner adhesion amount onto the recording medium into the toner adhesion amount on the recording medium, thereby determining the correspondence relationship between the image forming conditions and the toner adhesion amount. the above Image forming conditions corresponding to the target toner adhesion amount corrected by the correction amount are determined. An image forming apparatus according to another embodiment includes an image processing unit, a plurality of first detectors, a second detector, and a control unit. The image processing unit forms a toner image on an image carrier by electrophotography and transfers the formed toner image onto a recording medium. The plurality of first detectors are used to measure the density of a plurality of toner patches formed on the image carrier by the image processing unit, and are arranged at different positions in the main scanning direction. The second detector is used to measure a density profile in the main scanning direction of an image for measuring density unevenness formed on the recording medium by the image processing unit. The control unit determines a representative value of density according to the density profile and a density value extracted at each detection position of the plurality of first detectors based on the density profile of the image for measuring density unevenness. The control unit calculates a correction amount of a target toner adhesion amount on the recording medium for each of the plurality of first detectors based on a difference between the representative value of density and a density value extracted from the density profile at each detection position of the plurality of first detectors. The control unit measures the densities of the toner patches formed under different image forming conditions using each of the multiple first detectors, and converts the densities of the toner patches measured for each of the multiple first detectors into toner adhesion amounts on the recording medium, thereby determining a correspondence relationship between the image forming conditions and the toner adhesion amounts for each of the multiple first detectors. The control unit determines image forming conditions corresponding to the target toner adhesion amounts corrected by the correction amount for each of the multiple first detectors based on the determined correspondence relationship. The control unit determines final image forming conditions by averaging the image forming conditions determined for each of the multiple first detectors.

[0011] In one embodiment, the second detector is a line image sensor disposed between the transfer roller and the fuser of the image processing section.

[0012] In one embodiment, the second detector is included in a scanner that optically reads the image formed on the recording medium after fusing.

[0013] In one embodiment, the different image forming conditions are obtained by changing one or more of the beam amount of an exposure device, the charging bias, the developing bias, and the speed ratio between the developing roller and the photoreceptor.

[0014] In one aspect, the control unit adjusts the beam light amount of the exposure unit of the image processing unit so as to suppress the unevenness in density based on the density profile of the unevenness in density measurement image. The control unit determines a representative value of density and a density profile of the unevenness in density measurement image measured after adjusting the beam light amount of the exposure unit. Multiple First detector Each The density value extracted at the detection position is determined, and the target toner adhesion amount is corrected based on the representative density value and the extracted density value.

[0015] In one embodiment, the representative value of density is an average value of a density profile in the main scanning direction.

[0019] moreover In another embodiment, a method for controlling an image forming apparatus is provided, the image forming apparatus includes an image processing unit that forms a toner image on an image carrier by electrophotography and transfers the formed toner image onto a recording medium, and a toner image forming unit that is used to measure the densities of a plurality of toner patches formed on the image carrier by the image processing unit. , a plurality of images arranged at different positions in the main scanning directionThe apparatus includes a first detector, a second detector used to measure a density profile in the main scanning direction of an image for measuring density unevenness formed on a recording medium by an image processing unit, and a control unit. The control unit determines a representative value of density according to the density profile based on the density profile of the image for measuring density unevenness. Multiple First detector each determining an extracted concentration value at the detection location; A control unit selects a first detector corresponding to a concentration value closest to a representative value of the concentration from among a plurality of concentration values ​​extracted from the concentration profile at each detection position of the plurality of first detectors; The control unit determines the representative value of the concentration , from the concentration profile at the detection position of the selected first detector A step of calculating a correction amount for a target toner adhesion amount on a recording medium based on a difference from the extracted density value; and a step of calculating the densities of a plurality of toner patches formed under different image forming conditions by a control unit. Measure using the first detector selected , The measured densities of multiple toner patches are determining a correspondence relationship between the image forming conditions and the toner adhesion amount by converting the image forming conditions and the toner adhesion amount onto the recording medium; and the above and determining an image forming condition that corresponds to the target toner adhesion amount corrected by the correction amount. In yet another embodiment, a method for controlling an image forming apparatus is provided. The image forming apparatus includes an image processing unit that forms a toner image on an image carrier by electrophotography and transfers the formed toner image onto a recording medium, a plurality of first detectors that are used to measure the densities of a plurality of toner patches formed on the image carrier by the image processing unit and that are arranged at different positions in the main scanning direction, a second detector that is used to measure the density profile in the main scanning direction of an image for measuring density unevenness formed on the recording medium by the image processing unit, and a control unit. The control method includes a step in which the control unit determines, based on a density profile of the density unevenness measurement image, a representative value of density corresponding to the density profile and a density value extracted at each detection position of the multiple first detectors; a step in which the control unit calculates a correction amount for a target toner adhesion amount on a recording medium for each of the multiple first detectors based on a difference between the representative value of density and a density value extracted from the density profile at each detection position of the multiple first detectors; a step in which the control unit determines a correspondence relationship between the image formation conditions and the toner adhesion amount for each of the multiple first detectors by measuring the densities of multiple toner patches formed under different image forming conditions using each of the multiple first detectors and converting the densities of the multiple toner patches measured for each of the multiple first detectors into toner adhesion amounts on the recording medium; a step in which the control unit determines, based on the determined correspondence relationship, image formation conditions corresponding to the target toner adhesion amount corrected by the correction amount for each of the multiple first detectors; and a step in which the control unit determines final image formation conditions by averaging the image formation conditions determined respectively for the multiple first detectors. Effect of the Invention

[0020] According to each of the above-described embodiments, even if there are density unevenness on the photoconductor or intermediate transfer belt, the amount of toner adhered to the recording paper can be adjusted to fall within a target range. [Brief description of the drawings]

[0021] [Figure 1] 1 is a cross-sectional view conceptually illustrating an example of the overall configuration of an image forming apparatus 100. FIG. [Diagram 2] 2 is a block diagram showing a configuration of a control unit 20 of the image forming apparatus 100 in FIG. [Diagram 3] 10 is a flowchart showing a procedure for measuring a concentration profile and calculating a representative concentration value. [Figure 4] 13 is a diagram showing an example of a measurement image 26A of a density profile formed on a recording sheet S. FIG. [Diagram 5]1 is a diagram showing a recording paper S placed on a platen 32A of a scanner 32. FIG. [Figure 6] FIG. 13 is a diagram showing an example of measuring the density profile for a black density profile measuring image 26A. [Figure 7] FIG. 7 is a diagram for explaining a calculation procedure for a correction amount for a target adhesion amount in the numerical example of FIG. 6. [Figure 8] 10 is a flowchart showing a procedure for adjusting the amount of adhered toner. [Figure 9] 13 is a diagram showing an example of an image 26B for adjusting the toner adhesion amount formed on the intermediate transfer belt 16. FIG. [Figure 10] FIG. 11 is a diagram showing the correspondence relationship between the amount of adhered black toner and the developing bias. [Figure 11] FIG. 11 is a diagram showing an example of an image 26B for adjusting the toner adhesion amount formed on the intermediate transfer belt 16 in the image forming apparatus according to the second embodiment. [Figure 12] 11 is a flowchart showing a first procedure for measuring a density profile and calculating a density representative value in an image forming apparatus according to a second embodiment. [Figure 13] 13 is a flowchart showing a second procedure for measuring a density profile and calculating a density representative value in the image forming apparatus of the second embodiment. [Figure 14] 13 is a flowchart showing a second procedure for adjusting the amount of toner adhesion in the image forming apparatus according to the second embodiment. [Figure 15] FIG. 11 is a block diagram showing a configuration of an image forming apparatus according to a third embodiment. [Figure 16] 13 is a flowchart showing a procedure for measuring a density profile and calculating a density representative value in an image forming apparatus according to a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Each embodiment will be described in detail below with reference to the drawings. The components, types, combinations, shapes, and relative arrangements of the components described below are not intended to be limited to those unless otherwise specified. For example, the image forming device 100, which is a color printer equipped with a scanner 32, will be described below as an example, but the image forming device 100 of the present disclosure is not limited to a color printer. For example, the image forming device 100 may be a monochrome printer. The image forming device 100 may also be a multi-functional peripheral (MFP) including a monochrome printer, a color printer, and a FAX. In the following description, the same or corresponding parts are given the same reference symbols, and the description may not be repeated.

[0023] <Embodiment 1> [Overall configuration of image forming device] Fig. 1 is a cross-sectional view conceptually showing an example of the overall configuration of an image forming apparatus 100. Fig. 2 is a block diagram showing the configuration of a control unit 20 of the image forming apparatus 100 in Fig. 1.

[0024] 1 and 2, image forming apparatus 100 includes an image processing unit 10, a control unit 20, a scanner 32, an operation panel 28, an exposure amount adjustment unit 29, a charging bias application unit 30, and a developing bias application unit 31. These components will be described below.

[0025] The image processing unit 10 uses an electrophotographic method to form an image using four colors (yellow, magenta, cyan, and black) of toner on the recording paper S. Here, the direction of the arrow shown in Fig. 1 is the transport direction (sub-scanning direction) of the recording paper S, and the direction perpendicular to this transport direction (i.e., the direction perpendicular to the paper surface) is the main scanning direction.

[0026] As shown in FIG. 1, the image processing unit 10 includes charging rollers 11Y, 11M, 11C, and 11K, photoconductors 12Y, 12M, 12C, and 12K, exposure devices 13Y, 13M, 13C, and 13K, developing rollers 14Y, 14M, 14C, and 14K, primary transfer rollers 15Y, 15M, 15C, and 15K, an intermediate transfer belt 16, a secondary transfer roller 17, a fixing device 18, and an IDC sensor 19 (e.g., a reflective photosensor).

[0027] In the image processing unit 10, components with a "K" after the reference number are related to the generation of a black toner image. Components with a "Y" after the reference number are related to the generation of a yellow toner image. Components with an "M" after the reference number are related to the generation of a magenta toner image. Components with a "C" after the reference number are related to the generation of a cyan toner image.

[0028] Hereinafter, the charging rollers 11Y, 11M, 11C, and 11K are also collectively referred to as charging rollers 11. The photoconductors 12Y, 12M, 12C, and 12K are also collectively referred to as photoconductors 12. The exposure devices 13Y, 13M, 13C, and 13K are also collectively referred to as exposure device 13. The developing rollers 14Y, 14M, 14C, and 14K are also collectively referred to as developing rollers 14. The primary transfer rollers 15Y, 15M, 15C, and 15K are also collectively referred to as primary transfer rollers 15.

[0029] The photoconductors 12 are each uniformly charged by the charging rollers 11. Thereafter, a light beam is irradiated from the exposure device 13 in accordance with input image data, so that an electrostatic latent image in accordance with the image data is formed on each surface of the photoconductor 12. The light beam is scanned in the main scanning direction.

[0030] The developing roller 14 is disposed opposite the photoreceptor 12. The developing roller 14 causes the toner adhering to its surface to adhere to the photoreceptor 12, and develops a toner image corresponding to the electrostatic latent image on the photoreceptor 12. More specifically, each electrostatic latent image formed on the photoreceptor 12 is developed by the developing roller 14 receiving a supply of toner of each color, yellow (Y), magenta (M), cyan (C), and black (K).

[0031] The developed toner images are sequentially transferred onto an intermediate transfer belt 16 by a primary transfer roller 15. The intermediate transfer belt 16 functions as an image carrier that carries the toner images. The recording paper S is transported to a secondary transfer roller 17, and the toner images transferred onto the intermediate transfer belt 16 are transferred all at once onto the recording paper S by the secondary transfer roller 17. The toner images are then fixed onto the recording paper S by a fixing device 18. In this disclosure, the recording paper S is more generally referred to as a recording medium.

[0032] The IDC sensor 19 as a first detector detects the reflection density of the toner image on the intermediate transfer belt 16. When the amount of light projected onto the measurement object is I0 and the amount of light reflected from the measurement object is I, the reflection density D is expressed as follows: D = -log(I / I0) … (1) As will be described later, the IDC sensor 19 is used to adjust the amount of toner adhesion.

[0033] The above describes an example of the configuration of the image processor 10 in the case of a horizontal tandem type secondary transfer system. However, the configuration and arrangement of various elements such as the photoconductor, charger, exposure device, developer, transfer unit, and fixing unit are not limited to those shown in Fig. 1, and other configurations and arrangements may be used. For example, the image processor 10 may be of a direct transfer system.

[0034] Scanner 32 is a flatbed scanner that optically reads an image of a document placed on document table 32A. Specifically, scanner 32 includes a light source and a line image sensor (both not shown), and detects light emitted from the light source and reflected by the surface of the document by the line image sensor as a second detector. The line image sensor is also called a linear image sensor. For example, a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor) image sensor can be used as a sensor element constituting the line image sensor.

[0035] The operation panel 28 shown in FIG. 2 is a user interface that allows the user to input various setting values. For example, the operation panel 28 includes a plurality of input keys and a touch panel. The touch panel is an electronic component that combines a display device such as a liquid crystal panel or an organic EL (Electro-Luminescence) panel with a position input device such as a touch pad. The control unit 20 receives instructions from the user or a service person by inputting the input keys or touching the touch panel. The control unit 20 also displays messages for the user on the touch panel.

[0036] The exposure amount adjustment unit 29 adjusts the amount of light beam from the exposure unit 13 in accordance with a command from the control unit 20. The charging bias application unit 30 applies a charging bias of a designated voltage value to the charging roller 11 in accordance with a command from the control unit 20. The developing bias application unit 31 applies a developing bias of a designated voltage value to the developing roller 14 in accordance with a command from the control unit 20.

[0037] [Control unit configuration example] As shown in FIG. 2, the control unit 20 includes, as basic components, a CPU (Central Processing Unit) 21, a communication interface (I / F) unit 22, a ROM (Read Only Memory) 23, and a RAM (Random Access Memory) 24.

[0038] The CPU 21 reads out the programs stored in the ROM 23 and executes the commands contained in the programs. The ROM 23 stores programs for controlling the operation panel 28, the exposure amount adjustment unit 29, the charging bias application unit 30, the developing bias application unit 31, etc., as well as programs for executing the toner adhesion amount adjustment described below. The RAM 24 is used as a work memory for the CPU 21 when executing the programs. The communication I / F unit 22 is an interface for connecting to a LAN (Local Area Network), such as a LAN card or a LAN board.

[0039] The control unit 20 includes, as additional components, a toner adhesion amount calculation unit 25, an image data memory unit 26, a table memory unit 27, a concentration profile memory unit 33, a concentration representative value calculation unit 34, a target adhesion amount correction amount determination unit 35, a toner adhesion amount adjustment unit 36, an image formation condition determination unit 37, and a target adhesion amount memory unit 38.

[0040] Among the above additional components, the storage units 26, 27, 33, and 38 are realized by rewritable nonvolatile memories such as flash memories. The ROM 23 may be configured as a rewritable nonvolatile memory for realizing the above storage units. The other components 25, 34 to 37 may be realized by a microcomputer including a CPU and a memory, by a Field Programmable Gate Array (FPGA), or by a dedicated circuit such as an Application Specific Integrated Circuit (ASIC). When these functions are realized by a microcomputer, they may be realized by executing a program using the above-mentioned CPU 21.

[0041] The functions of the above additional components 25 to 27 and 33 to 38 will be briefly described below, and will be described in more detail later with reference to FIGS.

[0042] Based on the reflection density of the toner image input from the IDC sensor 19, the toner adhesion amount calculation unit 25 calculates the toner adhesion amount on the intermediate transfer belt 16 corresponding to the reflection density. Furthermore, the toner adhesion amount calculation unit 25 may calculate the toner adhesion amount on the recording paper S corresponding to the reflection density of the toner image based on the transfer efficiency of the secondary transfer. The toner adhesion amount calculation unit 25 may determine the toner adhesion amount on the intermediate transfer belt 16 or the recording paper S by referring to a conversion table that indicates the relationship between the reflection density and the toner adhesion amount on the intermediate transfer belt 16 or the recording paper S, which is determined in advance through experiments. The above conversion table is stored in the table storage unit 27 and is read out by the toner adhesion amount calculation unit 25.

[0043] The toner adhesion amount calculation unit 25 further calculates the toner adhesion amount on the recording paper S corresponding to the image density based on the image density on the recording paper S detected by the scanner 32. At this time, the toner adhesion amount calculation unit 25 may calculate the toner adhesion amount on the intermediate transfer belt 16 corresponding to the image density based on the transfer efficiency of the secondary transfer. Alternatively, the toner adhesion amount calculation unit 25 may determine the toner adhesion amount on the recording paper S or the intermediate transfer belt 16 by referring to a conversion table that indicates the relationship between the image density and the toner adhesion amount on the recording paper S or the intermediate transfer belt 16, which is determined in advance through experiments. The above conversion table is also stored in the table storage unit 27 and is read out by the toner adhesion amount calculation unit 25.

[0044] The image data storage unit 26 stores image data of a density profile measurement image 26A (see FIG. 4) and image data of a toner adhesion amount adjustment image 26B (see FIG. 9) together with the respective image forming conditions. In this disclosure, the density profile measurement image 26A may simply be referred to as a measurement image 26A or as a density unevenness measurement image 26A.

[0045] The table storage unit 27 stores the above-mentioned relationship between reflection density and toner adhesion amount and the relationship between image density and toner adhesion amount. The table storage unit 27 further stores image formation conditions for obtaining a target toner adhesion amount on the recording paper S (hereinafter also referred to as a "target adhesion amount" in this specification).

[0046] Specifically, the table memory unit 27 stores image formation conditions such as the beam light amount of the exposure device 13, the charging bias applied to the charging roller 11, the developing bias applied to the developing roller 14, and the speed ratio θ between the developing roller 14 of the developing device and the photosensitive member 12 (also simply referred to as "developing θ"), corresponding to the target adhesion amount.

[0047] The density profile storage unit 33 stores, for each color, an actual density profile in the main scanning direction when a uniform image is formed on the recording paper S under predetermined image forming conditions. The density profile is generated by reading, with the scanner 32, the recording paper S on which the image 26A for measuring the density profile is formed.

[0048] The density representative value calculation unit 34 calculates a representative value of density that represents the image density distribution in the main scanning direction based on the density profile stored in the density profile storage unit 33. The representative value may be an average value, a median value, a mode value, or the like. For example, when calculating the average value, the density data of the total number of data points obtained by multiplying the image resolution (dpi: dots per inch) by the width (inches) in the main scanning direction is averaged.

[0049] The target adhesion amount storage unit 38 stores a target toner adhesion amount (i.e., target adhesion amount) on the recording paper S, which is set to provide an appropriate shade according to the paper quality. The target adhesion amount correction amount determination unit 35 determines the correction amount of the target adhesion amount. Specifically, the correction amount determination unit 35 calculates the correction amount of the target adhesion amount based on the difference between the toner adhesion amount converted from the density representative value and the toner adhesion amount converted from the image density at the detection position by the IDC sensor 19.

[0050] The toner adhesion amount adjustment unit 36 ​​adjusts the image forming conditions through the image forming condition determination unit 37 so as to obtain a target toner adhesion amount after correction using the above correction amount. Specifically, the image forming condition determination unit 37 causes the image process unit 10 to form an image 26B for adjusting the toner adhesion amount under various image forming conditions, and detects the reflection density of the toner image formed on the intermediate transfer belt 16 by the IDC sensor 19. The image forming condition determination unit 37 determines the image forming conditions for obtaining the corrected target adhesion amount based on the relationship between the toner adhesion amount corresponding to the detected reflection density and the image forming conditions.

[0051] [Measurement of concentration profile and calculation of representative concentration value] 3 is a flowchart showing a procedure for measuring a density profile and calculating a representative density value. The measurement of the density profile and the calculation of the representative density value are performed prior to the adjustment of the toner adhesion amount, which will be described later with reference to FIG.

[0052] 3, in step S101, CPU 21 of control unit 20 starts measurement of a concentration profile and calculation of a concentration representative value.

[0053] In the next step S102, the CPU 21 reads out image data of the density profile measurement image 26A (density unevenness measurement image 26A) and the specified image forming conditions from the image data storage unit 26. Under the image forming conditions, the CPU 21 causes the image processor 10 to form the measurement image 26A on each of the photoconductors 12Y, 12M, 12C, and 12K. Details of the measurement image 26A will be described later with reference to FIG.

[0054] In the next step S103, the CPU 21 controls the image processor 10 to transfer the toner image of the measurement image 26A from each photoconductor 12 onto the intermediate transfer belt 16. In the next step S104, the CPU 21 controls the image processor 10 to transfer the toner image of the measurement image 26A from the intermediate transfer belt 16 onto the recording paper S and fix it.

[0055] FIG. 4 is a diagram showing an example of a measurement image 26A of a density profile formed on a recording paper S. The measurement image 26A is a belt-shaped pattern formed so as to have a uniform density for each color of yellow (Y0), magenta (M0), cyan (C0), and black (K0). The gradation (shade level) of the belt-shaped pattern is not completely solid, but is set to a specific value suitable for detecting a density profile. Each belt-shaped pattern extends in the main scanning direction A from the vicinity of one end of the recording paper S to the vicinity of the other end. This makes it possible to detect the density profile in the main scanning direction A and the image density at the detection position of the IDC sensor 19.

[0056] Returning to FIG. 3, in the next step S105, the CPU 21 displays a message on the operation panel 28 to cause the user or serviceman to place the recording paper S on which the measurement image 26A has been formed in a predetermined position on the document table 32A of the scanner 32.

[0057] Fig. 5 is a diagram showing the recording paper S placed on the platen 32A of the scanner 32. As shown in Fig. 5, the recording paper S is placed on the platen 32A so that the front surface on which the measurement image 26A is formed faces the platen 32A.

[0058] 3, in the next step S106, the CPU 21 causes the scanner 32 to read the measurement image 26A for each color formed on the recording paper S. The output value of the scanner 32 corresponds to the intensity of the reflected light from the measurement image 26A on the recording paper S.

[0059] Instead of the scanner 32, a light source and a line image sensor (neither shown) may be provided on the transport path of the recording paper S between the secondary transfer roller 17 and the fixing unit 18 in Fig. 1. In this case, the measurement image 26A before fixing is optically read by the line image sensor. Alternatively, a light source and a line image sensor may be provided on the transport path of the recording paper S between the fixing unit 18 and the paper output tray.

[0060] After step S106, the processes from steps S107 to S110 and the processes from steps S106A to S110A are executed in parallel.

[0061] First, in step S106A, CPU 21 extracts the scanner output value for each color at the detection position of IDC sensor 19 from the output value of scanner 32.

[0062] In the next step S107, CPU 21 creates a density profile for each color in the main scanning direction A by converting the output value of scanner 32 into image density. That is, the output value of scanner 32 corresponding to the intensity of reflected light is converted into a pixel value indicating the optical density level of each pixel. Note that a conversion table indicating the relationship between the output value of scanner 32 and image density may be created in advance for each color, and CPU 21 may perform the conversion process from the output value of scanner 32 to image density based on this conversion table. In this case, the conversion table is stored in table storage unit 27 in advance.

[0063] In addition to step S107, in step S107A, CPU 21 converts the scanner output value for each color at the detection position of IDC sensor 19 into image density.

[0064] In the next step S108, the CPU 21 stores the image density profile measured for each color in the main scanning direction A in the density profile storage unit 33. Additionally, in step S108A, the CPU 21 stores the image density for each color at the detection position of the IDC sensor 19 in the density profile storage unit 33.

[0065] In the next step S109, the CPU 21 causes the density representative value calculation unit 34 to calculate a representative value of the image density for each color from the density profile for each color stored in the density profile storage unit 33. The representative value of the image density is a value that represents the image density distribution in the main scanning direction, and may be an average value, a median value, a mode value, or the like.

[0066] Fig. 6 is a diagram showing an example of measuring the density profile for the black density profile measuring image 26A. The distribution of image density versus position in the main scanning direction is shown by a solid line. As shown in Fig. 6, the average value as a representative value of image density is 1.44. Also, the image density value at the detection position of the IDC sensor 19 in the main scanning direction A is 1.50.

[0067] 3, in the next step S110, the CPU 21 causes the toner adhesion amount calculation unit 25 to convert the calculated representative value of the density distribution into the toner adhesion amount on the recording paper S or the intermediate transfer belt 16. The toner adhesion amount calculation unit 25 may perform this conversion process by referring to a conversion table that is stored in advance in the table storage unit 27 and indicates the relationship between the image density and the toner adhesion amount on the recording paper S or the intermediate transfer belt 16.

[0068] Additionally, in step S110A, CPU 21 causes toner adhesion amount calculation unit 25 to convert the image density value at the detection position of IDC sensor 19 into the toner adhesion amount on recording paper S or intermediate transfer belt 16. In this case, toner adhesion amount calculation unit 25 may perform this conversion process by referring to a conversion table stored in advance in table storage unit 27.

[0069] In the next step S111, the CPU 21 causes the target adhesion amount correction amount determination unit 35 to calculate a correction amount for the target adhesion amount for each color based on the difference between the toner adhesion amount converted from the concentration representative value and the toner adhesion amount converted from the image density value at the detection position by the IDC sensor 19.

[0070] FIG. 7 is a diagram for explaining a calculation procedure for the correction amount of the target adhesion amount in the numerical example of FIG.

[0071] As described with reference to FIG. 6, in the density profile of black, the average value as the representative value of the image density is 1.44. Also, the image density value at the detection position of the IDC sensor 19 is 1.50. As shown in FIG. 7, the toner adhesion amount α converted from the representative density value is 3.71 [g / m 3 The toner adhesion amount β converted from the image density value at the detection position of the IDC sensor 19 is 4.01 [g / m 3 Furthermore, by subtracting the representative value α of the toner adhesion amount from the toner adhesion amount β at the detection position of the IDC sensor 19, the toner adhesion amount difference is calculated as 0.30 [g / m 3 When the toner adhesion amount α converted from the concentration representative value is equal to the target adhesion amount, the calculated toner adhesion amount difference (β-α) is equal to the correction amount of the target adhesion amount. When the toner adhesion amount α converted from the concentration representative value is different from the target adhesion amount, the correction amount of the target adhesion amount is obtained by converting the calculated toner adhesion amount difference into a value corresponding to the target adhesion amount.

[0072] [Adjusting the amount of toner adhesion] Next, a procedure for adjusting the toner adhesion amount by the toner adhesion amount adjustment unit 36 ​​in Fig. 2 will be described. The toner adhesion amount adjustment unit 36 ​​adjusts the image formation conditions through the image formation condition determination unit 37 so as to obtain a target toner adhesion amount after correction using the correction amount calculated in the above procedure.

[0073] 8 is a flowchart showing the procedure for adjusting the toner adhesion amount. In step S201, the CPU 21 of the control unit 20 starts up the toner adhesion amount adjustment unit 36 ​​when a predetermined start-up condition is satisfied based on the operating state of the image forming apparatus 100 or on an instruction from a user or a serviceman inputted to the operation panel 28.

[0074] In the next step S202, the toner adhesion amount adjustment unit 36 ​​reads out the toner adhesion amount adjustment image 26B (hereinafter simply referred to as "adjustment image 26B") and its image forming conditions from the image data storage unit 26. The image data storage unit 26 stores a plurality of image forming conditions for each color so that images of a plurality of different densities can be obtained. The image forming condition determination unit 37 causes the image processor 10 to form the adjustment image 26B on the photoconductors 12Y, 12M, 12C, and 12K under each image forming condition. Details of the adjustment image 26B will be described later with reference to FIG. 9.

[0075] In the next step S203, the image forming condition determination unit 37 controls the image processor 10 to transfer the toner image of the adjustment image 26B from each photoconductor 12 onto the intermediate transfer belt 16.

[0076] FIG. 9 is a diagram showing an example of a toner adhesion amount adjustment image 26B formed on the intermediate transfer belt 16. As shown in FIG.

[0077] As shown in FIG. 9, the adjustment image 26B includes a plurality of rectangular images (also referred to as "toner patches") formed at one end (front side) in the main scanning direction A at a detection position of the IDC sensor 19. Specifically, the adjustment image 26B includes black toner patches K1-K4, magenta toner patches M1-M4, cyan toner patches C1-C4, and yellow toner patches Y1-Y4. The image forming conditions are changed so that the density of the black toner patches K1-K4 increases in that order. The same is true for the toner patches of other colors. These toner patches are formed to be aligned in the transport direction B.

[0078] Returning to FIG. 8, in the next step S204, the image forming condition determination unit 37 uses the IDC sensor 19 to measure the reflection density of the adjustment image 26B (i.e., each of the toner patches K1 to K4, M1 to M4, C1 to C4, and Y1 to Y4) formed on the intermediate transfer belt 16.

[0079] In the next step S205, the toner adhesion amount calculation unit 25 converts the measured reflection density of the adjustment image 26B into the toner adhesion amount of the adjustment image 26B (i.e., each of the toner patches K1 to K4, M1 to M4, C1 to C4, and Y1 to Y4) on the intermediate transfer belt 16. Furthermore, the toner adhesion amount calculation unit 25 may convert the toner adhesion amount of the adjustment image 26B on the intermediate transfer belt 16 into the toner adhesion amount of the adjustment image 26B on the recording paper S based on the transfer efficiency of the secondary transfer. In this conversion operation, the toner adhesion amount calculation unit 25 may determine the toner adhesion amount on the intermediate transfer belt 16 or the recording paper S from the reflection density of the adjustment image 26B by referring to a table representing the relationship between the reflection density stored in advance in the table storage unit 27 and the toner adhesion amount on the intermediate transfer belt 16 or the recording paper S.

[0080] In the next step S206, the image forming condition determination unit 37 corrects the target adhesion amount to a value corresponding to the measured density profile by using the correction amount of the target adhesion amount on the recording paper S calculated in step S111 of FIG. 3.

[0081] In the next step S207, the image forming condition determination unit 37 determines image forming conditions so as to achieve the corrected target adhesion amount, using the correspondence between the image forming conditions and the toner adhesion amount of the adjustment image 26B obtained in step S205. The image forming condition determination unit 37 stores the determined image forming conditions and the corresponding corrected toner adhesion amount in the target adhesion amount storage unit 38. Hereinafter, the above steps S206 and S207 will be described in more detail with reference to FIG.

[0082] FIG. 10 is a diagram showing the correspondence relationship between the amount of black toner adhesion and the developing bias. FIG. 10 shows an example in which the developing bias, one of the image forming conditions, is changed. In the following, the target adhesion amount γ and its correction amount δ, as well as the toner adhesion amounts Ak1 to Ak4 of the toner patches K1 to K4, will be described as values ​​on the recording paper S. These toner adhesion amounts may also be values ​​on the intermediate transfer belt 16. As already explained, the toner adhesion amount on the recording paper S can be converted to the toner adhesion amount on the intermediate transfer belt 16 by dividing it by the secondary transfer efficiency.

[0083] The image forming condition determination unit 37 corrects the target adhesion amount γ by the correction amount δ calculated in step S111 in FIG. 3 (step S206 in FIG. 9). Specifically, when the toner adhesion amount converted from the image density at the detection position of the IDC sensor 19 is larger than the toner adhesion amount converted from the representative density value in the main scanning direction, the correction amount δ becomes a positive value. In this case, the target adhesion amount γ is corrected to a larger value by adding the absolute value |δ| of the correction amount. Conversely, when the toner adhesion amount converted from the image density at the detection position of the IDC sensor 19 is smaller than the toner adhesion amount converted from the representative density value in the main scanning direction, the correction amount δ becomes a negative value. In this case, the target adhesion amount γ is corrected to a smaller value by subtracting the absolute value |δ| of the correction amount.

[0084] The image forming condition determination unit 37 generates black toner patches K1, K2, K3, and K4 as the toner adhesion amount adjustment image 26B with the development biases Vdc1, Vdc2, Vdc3, and Vdc4, respectively (steps S202 and S203 in FIG. 9). The image forming condition determination unit 37 converts the reflection densities of the toner patches K1, K2, K3, and K4 measured by the IDC sensor 19 into toner adhesion amounts Ak1, Ak2, Ak3, and Ak4 on the recording paper S, respectively (step S205 in FIG. 9). Note that the development biases Vdc1 to Vdc4 used when forming the adjustment image 26B are set to values ​​smaller than the development bias Vdc0 corresponding to the target adhesion amount γ so that the IDC sensor 19 can accurately detect the difference in reflection density according to the image forming conditions.

[0085] As described above, by converting the reflection density into the amount of toner adhesion (step S205 in FIG. 9), the correspondence relationship between the image forming conditions (developing bias in the case of FIG. 10) and the amount of toner adhesion on the recording paper S (or on the intermediate transfer belt 16) is obtained. Specifically, the image forming condition determination unit 37 may obtain an approximation formula showing the relationship between the amount of toner adhesion and the image forming conditions (developing bias). In the case of FIG. 10, the relationship between the amount of toner adhesion and the developing bias is given by an approximation curve G or an approximation straight line G.

[0086] The image forming condition determination unit 37 determines the image forming conditions corresponding to the corrected target adhesion amount based on an approximation formula that represents the relationship between the toner adhesion amount and the image forming conditions. In the case of Fig. 10, the development bias corresponding to the original target adhesion amount γ is obtained as Vdc0. The development bias corresponding to the corrected target adhesion amount γ+|δ| or γ-|δ| is obtained as Vdc0+ or ​​Vdc0-, respectively.

[0087] [Modification of the first embodiment] In the first embodiment, the IDC sensor 19 is disposed at a position for detecting the reflection density of the toner image on the intermediate transfer belt 16, but it may be disposed at a position for detecting the reflection density of the toner image on the photoreceptor 12. In the present disclosure, the intermediate transfer belt 16 and the photoreceptor 12 may be collectively referred to as an image carrier for carrying a toner image.

[0088] 10, the case where the development bias is changed among the image forming conditions is described, but other image forming conditions may be changed. For example, one or more of the exposure amount of the exposure device 13, the charging bias applied to the charging roller 11, the developing bias applied to the developing roller 14, and the speed ratio θ (development θ) between the developing roller 14 and the photoconductor 12 of the developing device may be changed.

[0089] In the first embodiment, the image processing unit 10 is described as employing a secondary transfer method in which the intermediate transfer belt 16 is used. However, the measurement of the density profile, the calculation of the representative density value, and the adjustment of the toner adhesion amount described in the first embodiment are also applicable to a direct transfer method in which the intermediate transfer belt 16 is not used.

[0090] [Advantages of the First Embodiment] According to the image forming apparatus 100 of the first embodiment, a correction amount for a target toner adhesion amount is determined based on a representative value of the density profile of the density unevenness measuring image 26A formed on the recording paper S and a density value extracted from the density profile at the detection position of the IDC sensor 19. Then, image forming conditions are determined so that the corrected target toner adhesion amount is obtained. Therefore, even if the toner image is not uniform in the main scanning direction and has density unevenness, the toner adhesion amount on the recording paper can be adjusted to within the range of the target adhesion amount.

[0091] <Embodiment 2> In the second embodiment, a case where two or more IDC sensors 19 are provided will be described. As an example, a case where one IDC sensor 19f is provided on the front side in the main scanning direction and one IDC sensor 19r is provided on the back side in the main scanning direction in the image processing unit 10 in Fig. 1 will be described. Further IDC sensors may be provided at different positions in the main scanning direction.

[0092] The rest of the configuration of the image forming apparatus is similar to that described in FIG. 1 and FIG. 2 in the first embodiment, and therefore description thereof will not be repeated.

[0093] [Example of an image for adjusting the amount of toner adhesion] FIG. 11 is a diagram showing an example of an image 26B for adjusting the toner adhesion amount formed on the intermediate transfer belt 16 in the image forming apparatus according to the second embodiment.

[0094] As shown in FIG. 11, the adjustment image 26B includes a plurality of rectangular toner patches formed at one end (front side) in the main scanning direction A, and a plurality of rectangular toner patches formed at the other end (rear side) in the main scanning direction A. Specifically, the adjustment image 26B on the front side includes black toner patches Kf1-Kf4, magenta toner patches Mf1-Mf4, cyan toner patches Cf1-Cf4, and yellow toner patches Yf1-Yf4. The image forming conditions are changed so that the density of the black toner patches Kf1-Kf4 increases in that order. The same is true for the toner patches of other colors. These toner patches are formed to be aligned in the transport direction B, and their reflection densities are detected by the front IDC sensor 19f.

[0095] Similarly, the rear adjustment image 26B includes black toner patches Kr1-Kr4, magenta toner patches Mr1-Mr4, cyan toner patches Cr1-Cr4, and yellow toner patches Yr1-Yr4. The image forming conditions are changed so that the densities of the black toner patches Kr1-Kr4 increase in that order. The same is true for the toner patches of other colors. These toner patches are formed aligned in the transport direction B, and their reflection densities are detected by the rear 19r.

[0096] The specific procedures for measuring the density profile, calculating the representative density value, and adjusting the toner adhesion amount are described below. Two methods for carrying out these procedures are described below. In method 1, an IDC sensor 19 is selected such that the image density value at the detection position of the IDC sensor 19 is closest to the representative density value, and the toner adhesion amount is adjusted using the selected IDC sensor 19. In method 2, the toner adhesion amount is adjusted for each IDC sensor 19, and the final image formation conditions are determined by averaging the image formation conditions determined for each IDC sensor 19. The following description will be given with reference to the drawings.

[0097] [Measurement of concentration profile and calculation of representative concentration value (Method 1)] FIG. 12 is a flowchart showing a first procedure for measuring a density profile and calculating a density representative value in the image forming apparatus according to the second embodiment.

[0098] The flowchart in Fig. 12 is obtained by changing steps S106A-S108A, S110A, and S111 in the flowchart in Fig. 3 to steps S106B-S108B, S110B, and S111B, respectively, and adding step S109B between step S108B and step S110B. Since the other steps in Fig. 12 are the same as those in Fig. 3, the same or corresponding steps are given the same reference characters and description thereof will not be repeated.

[0099] 12, in step S106B, CPU 21 extracts scanner output values ​​for each color at the detection positions of IDC sensors 19f, 19r from the output values ​​of scanner 32 for measurement image 26A in FIG.

[0100] In the next step S107B, the CPU 21 converts the scanner output values ​​for each color in the IDC sensors 19f, 19r into image density. In the next step S108B, the CPU 21 stores the image density for each color in the IDC sensors 19f, 19r in the density profile storage unit 33.

[0101] In the next step S109B, the CPU 21 selects the IDC sensor 19 provided at a position that provides the image density closest to the density representative value calculated in step S109. For example, when the image density at the detection position of the IDC sensor 19r is closest to the density representative value among the image densities at the detection positions of the IDC sensors 19f and 19r, the IDC sensor 19r is selected. Since the selection of the IDC sensor 19 is performed for each color, the IDC sensor 19 selected for each color may differ.

[0102] In the next step S110B, CPU 21 causes toner adhesion amount calculation unit 25 to convert the image density at the detection position of IDC sensor 19 selected for each color into the toner adhesion amount on recording paper S or intermediate transfer belt 16. Toner adhesion amount calculation unit 25 may perform this conversion process by referring to a conversion table stored in advance in table storage unit 27.

[0103] In the next step S111B, the CPU 21 causes the target adhesion amount correction amount determination unit 35 to calculate a correction amount for the target adhesion amount for each color based on the difference between the toner adhesion amount converted from the concentration representative value and the toner adhesion amount converted from the image density at the detection position by the selected IDC sensor 19.

[0104] [Target adhesion weight correction (Method 1)] Using the correction amount of the target adhesion amount calculated according to the above procedure, the target adhesion amount is adjusted according to the procedure of the flowchart in Fig. 8. However, in step S204 in Fig. 8, the image forming condition determination unit 37 measures the reflection density of the adjustment image 26B (i.e., the toner patch of each color) formed on the intermediate transfer belt 16 by using the IDC sensor 19 selected for each color. In the next step S205, the image forming condition determination unit 37 converts the reflection density measured by the selected IDC sensor 19 into the toner adhesion amount. The other steps in Fig. 8 are similar to those in the first embodiment, and therefore the description will not be repeated.

[0105] [Measurement of concentration profile and calculation of representative concentration value (Method 2)] Fig. 13 is a flowchart showing a second procedure for measuring a density profile and calculating a density representative value in the image forming apparatus of the second embodiment. The flowchart of Fig. 13 is obtained by changing steps S106A-S108A, S110A, and S111 in the flowchart of Fig. 3 to steps S106C-S108C, S110C, and S111C, respectively. Since the other steps in Fig. 13 are the same as those in Fig. 3, the same or corresponding steps are given the same reference characters and description thereof will not be repeated.

[0106] 13, in step S106C, CPU 21 extracts scanner output values ​​for each color at the detection positions of IDC sensors 19f, 19r from the output values ​​of scanner 32 for measurement image 26A in FIG.

[0107] In the next step S107C, the CPU 21 converts the scanner output values ​​for each color in the IDC sensors 19f, 19r into image density. In the next step S108C, the CPU 21 stores the image density for each color in the IDC sensors 19f, 19r in the density profile storage unit 33.

[0108] In the next step S110C, the CPU 21 causes the toner adhesion amount calculation unit 25 to convert the image densities at the detection positions of the IDC sensors 19f, 19r into the toner adhesion amounts on the recording paper S or the intermediate transfer belt 16. The toner adhesion amount calculation unit 25 may perform this conversion process by referring to a conversion table stored in advance in the table storage unit 27.

[0109] In the next step S111C, the CPU 21 causes the target adhesion amount correction amount determination unit 35 to calculate a correction amount for the target adhesion amount for each color for each of the IDC sensors 19f, 19r based on the difference between the toner adhesion amount converted from the concentration representative value and the toner adhesion amount converted from the image density at the detection position by the IDC sensor 19.

[0110] [Target adhesion weight correction (Method 2)] FIG. 14 is a flowchart showing a second procedure for adjusting the toner adhesion amount in the image forming apparatus according to the second embodiment.

[0111] In step S201C, the CPU 21 of the control unit 20 starts up the toner adhesion amount adjusting unit 36 ​​when a predetermined start-up condition is satisfied based on the operating state of the image forming apparatus 100 or based on an instruction from a user or a serviceman via the operation panel 28.

[0112] In the next step S202C, the toner adhesion amount adjustment unit 36 ​​reads out the toner adhesion amount adjustment image 26B and its image forming conditions from the image data storage unit 26. The image forming condition determination unit 37 causes the image processor 10 to form the adjustment image 26B on the photoconductors 12Y, 12M, 12C, and 12K under each image forming condition. An example of the adjustment image 26B has already been described with reference to FIG.

[0113] In the next step S203C, the image forming condition determination unit 37 controls the image processor 10 to transfer the toner image of the adjustment image 26B from each photoconductor 12 onto the intermediate transfer belt 16.

[0114] In the next step S204C, the image forming condition determination unit 37 uses each of the IDC sensors 19f, 19r to measure the reflection density of the corresponding adjustment image 26B formed on the intermediate transfer belt 16. That is, the IDC sensor 19f on the front side of Fig. 11 measures the reflection density of each of the toner patches Kf1-Kf4, Mf1-Mf4, Cf1-Cf4, and Yf1-Yf4. The IDC sensor 19r on the back side of Fig. 11 measures the reflection density of each of the toner patches Kr1-Kr4, Mr1-Mr4, Cr1-Cr4, and Yr1-Yr4.

[0115] In the next step S205C, the toner adhesion amount calculation unit 25 converts the reflection density of the adjustment image 26B measured for each IDC sensor 19 and for each color into the amount of toner adhesion on the intermediate transfer belt 16 or the recording paper S. In this conversion operation, the toner adhesion amount calculation unit 25 may determine the amount of toner adhesion on the intermediate transfer belt 16 or the recording paper S converted from the reflection density of the adjustment image 26B by referring to a table that indicates the relationship between the reflection density and the amount of toner adhesion on the intermediate transfer belt 16 or the recording paper S, which is stored in advance in the table storage unit 27.

[0116] In the next step S206C, the image forming condition determination unit 37 corrects the target adhesion amount for each IDC sensor 19 and for each color on the recording paper S, using the correction amount for the target adhesion amount calculated for each IDC sensor 19 and for each color in step S111C of Figure 13, so that the target adhesion amount becomes a value corresponding to the measured density profile.

[0117] In the next step S207C, the image forming condition determination unit 37 uses the relationship between the image forming conditions of the adjustment image 26B and the toner adhesion amount to determine the image forming conditions for each IDC sensor 19 and for each color so as to achieve the corrected target adhesion amount.

[0118] In the next step S208C, the image forming conditions determined for each IDC sensor 19 are averaged to determine and store the final image forming conditions for each color.

[0119] [Effects of the second embodiment] According to the image forming apparatus of embodiment 2, by providing multiple IDC sensors 19 at different positions in the main scanning direction, the correction amount for the target toner adhesion amount and the image forming conditions corresponding to the corrected target adhesion amount can be more appropriately determined.

[0120] <Embodiment 3> In the third embodiment, the amount of light of the beam irradiated from the exposure device 13 is changed in the main scanning direction so as to suppress uneven density in the main scanning direction. This allows the toner adhesion amount adjustment described in the first embodiment to be performed while suppressing uneven density in the main scanning direction as much as possible. Note that the second embodiment may also be combined with the third embodiment. This will be described in detail below with reference to the drawings.

[0121] [Configuration of image forming device] Fig. 15 is a block diagram showing the configuration of an image forming apparatus according to embodiment 3. Fig. 15 shows in detail the functional configuration of a control unit 20 of the image forming apparatus.

[0122] The control unit 20 in Fig. 15 differs from the control unit 20 in Fig. 2 in that it further includes a density unevenness correction unit 39. Based on the measured density profile for each color in the main scanning direction, the density unevenness correction unit 39 reduces the amount of light at main scanning positions where the image density is relatively high for each color, and increases the amount of light at main scanning positions where the image density is relatively low. In this way, the density unevenness correction unit 39 reduces density unevenness in the main scanning direction. When exposing actual image data, the exposure unit 13 offsets the beam light amount by the amount of light increased or decreased as described above.

[0123] Other points in FIG. 15 are similar to those in FIG. 2, so the same or corresponding parts are given the same reference characters and descriptions thereof will not be repeated.

[0124] [Measurement of concentration profile and calculation of representative concentration value] FIG. 16 is a flowchart showing a procedure for measuring a density profile and calculating a density representative value in the image forming apparatus according to the third embodiment.

[0125] The flowchart in Fig. 16 differs from the flowchart in Fig. 3 in that steps S301 and S302 are added. The flowchart in Fig. 16 further differs from the flowchart in Fig. 3 in that the execution order is changed so that step S301 is executed after steps S108 and S108A, and steps S109, S110A and thereafter are executed if the result of step S301 is NO.

[0126] 16, the CPU 21 stores the image density profile measured for each color in the main scanning direction A in the density profile storage unit 33. Additionally, in step S108A, the CPU 21 stores the image density for each color at the detection position of the IDC sensor 19 in the density profile storage unit 33. Thereafter, the CPU 21 advances the process to step S301.

[0127] In step S301, the CPU 21 determines whether or not to execute density unevenness correction by the density unevenness correction unit 39. For example, when the amount of change in the density profile (for example, the difference between the maximum and minimum values ​​of the image density) exceeds a predetermined threshold, the CPU 21 causes the density unevenness correction unit 39 to execute density unevenness correction. Alternatively, the CPU 21 may cause the density unevenness correction unit 39 to execute density unevenness correction only once.

[0128] If the CPU 21 determines to execute density unevenness correction (YES in step S301), in the next step S302, the density unevenness correction unit 39 adjusts the beam light amount of the exposure unit 13 so as to eliminate the density unevenness. After that, the CPU 21 returns the process to step S102, and causes the image processor 10 after the beam light amount adjustment to form the measurement image 26A of the density profile.

[0129] On the other hand, if the CPU 21 determines not to execute the density unevenness correction (NO in step S302), the CPU 21 advances the process to steps S109 and after and S110A.

[0130] Specifically, in step S 109 , the CPU 21 causes the density representative value calculation unit 34 to calculate a representative value of the image density for each color from the density profile for each color stored in the density profile storage unit 33 .

[0131] In step S110, the CPU 21 causes the toner adhesion amount calculation unit 25 to convert the calculated representative value of the image density into the toner adhesion amount on the recording paper S or the intermediate transfer belt 16. Additionally, in step S110A, the CPU 21 causes the toner adhesion amount calculation unit 25 to convert the image density at the detection position of the IDC sensor 19 into the toner adhesion amount on the recording paper S or the intermediate transfer belt 16.

[0132] In the next step S111, the CPU 21 causes the target adhesion amount correction amount determination unit 35 to calculate a correction amount for the target adhesion amount for each color based on the difference between the toner adhesion amount converted from the concentration representative value and the toner adhesion amount converted from the image density at the detection position by the IDC sensor 19.

[0133] Other points in FIG. 16 are similar to those in FIG. 3, so the same or corresponding steps are given the same reference characters and the description will not be repeated.

[0134] [Adjusting the amount of toner adhesion] The target adhesion amount is adjusted according to the procedure in the flowchart of FIG. 8 using the correction amount of the target adhesion amount calculated according to the above procedure and the beam light amount of the exposure device 13 after adjustment.

[0135] [Effects of the third embodiment] According to the image forming apparatus of the third embodiment, the light beam amount of the exposure device 13 is changed in the main scanning direction so as to suppress uneven density of the toner image in the main scanning direction. After that, the correction amount of the target toner adhesion amount is determined, so that the toner adhesion amount on the recording paper can be adjusted to be within the target adhesion amount range and the amount of fluctuation in the toner adhesion amount in the main scanning direction can be suppressed.

[0136] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of this application is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0137] 10 image processing unit, 11 charging roller, 12 photoconductor, 13 exposure unit, 14 developing roller, 15 primary transfer roller, 16 intermediate transfer belt, 17 secondary transfer roller, 18 fixing unit, 19 IDC sensor, 20 control unit, 21 CPU, 22 communication I / F unit, 23 ROM, 24 RAM, 25 toner adhesion amount calculation unit, 26 image data storage unit, 26A density profile measurement image (density unevenness measurement image), 26B toner adhesion amount adjustment image, 27 table storage unit, 28 operation panel, 29 exposure amount adjustment unit, 30 charging bias application unit, 31 developing bias application unit, 32 scanner, 33 density profile storage unit, 34 density representative value calculation unit, 35 correction amount determination unit, 36 toner adhesion amount adjustment unit, 37 image formation condition determination unit, 38 target adhesion amount storage unit, 39 density unevenness correction unit, 100 Image forming device, A main scanning direction, B transport direction, C1 to C4, K1 to K4, M1 to M4, Y1 to Y4 toner patches, S recording paper.

Claims

1. an image processing unit that forms a toner image on an image carrier by electrophotography and transfers the formed toner image onto a recording medium; a plurality of first detectors arranged at different positions in a main scanning direction and used for measuring densities of a plurality of toner patches formed on the image carrier by the image processing unit; a second detector used for measuring a density profile in a main scanning direction of the density unevenness measuring image formed on the recording medium by the image processing unit; A control unit. the control unit determines, based on the density profile of the density unevenness measuring image, a representative value of density according to the density profile and density values ​​extracted at the respective detection positions of the plurality of first detectors; the control unit selects a first detector corresponding to a concentration value closest to the representative value of the concentration from among a plurality of concentration values ​​extracted from the concentration profile at each detection position of the plurality of first detectors; the control unit calculates a correction amount for a target toner adhesion amount on the recording medium based on a difference between the representative value of the density and a density value extracted from the density profile at the selected detection position of the first detector; and the control unit measures densities of a plurality of toner patches formed under different image forming conditions using the selected first detector, and converts the measured densities of the plurality of toner patches into toner adhesion amounts on the recording medium, thereby determining a correspondence relationship between the image forming conditions and the toner adhesion amounts; The control unit determines the image forming condition corresponding to the target toner adhesion amount corrected by the correction amount based on the determined correspondence relationship.

2. an image processing unit that forms a toner image on an image carrier by electrophotography and transfers the formed toner image onto a recording medium; a plurality of first detectors arranged at different positions in a main scanning direction and used for measuring densities of a plurality of toner patches formed on the image carrier by the image processing unit; a second detector used for measuring a density profile in a main scanning direction of the density unevenness measuring image formed on the recording medium by the image processing unit; A control unit. the control unit determines, based on the density profile of the density unevenness measuring image, a representative value of density according to the density profile and density values ​​extracted at the respective detection positions of the plurality of first detectors; the control unit calculates a correction amount of a target toner adhesion amount on the recording medium for each of the first detectors based on a difference between the representative value of the density and a density value extracted from the density profile at each detection position of the first detectors; and the control unit measures densities of a plurality of toner patches formed under different image forming conditions using each of the plurality of first detectors, and converts the densities of the plurality of toner patches measured for each of the plurality of first detectors into amounts of toner adhesion on the recording medium, thereby determining a correspondence relationship between the image forming conditions and the amounts of toner adhesion for each of the plurality of first detectors; the control unit determines, based on the determined correspondence relationship, the image forming condition corresponding to the target toner adhesion amount corrected by the correction amount for each of the plurality of first detectors; The control unit determines a final image formation condition by averaging the image formation conditions determined for each of the first detectors.

3. 3. The image forming apparatus according to claim 1, wherein the second detector is a line image sensor provided between a transfer roller and a fixing unit of the image processing unit.

4. 3. The image forming apparatus according to claim 1, wherein the second detector is included in a scanner that optically reads the image formed on the recording medium after fixing.

5. The image forming apparatus according to any one of claims 1 to 4, wherein the different image forming conditions are obtained by changing one or more of the beam light amount of an exposure device, a charging bias, a developing bias, and a speed ratio between a developing roller and a photosensitive member.

6. the control unit adjusts a beam amount of an exposure unit of the image processing unit so as to suppress density unevenness based on the density profile of the density unevenness measuring image; The control unit determines a representative value of density and a density value extracted at each detection position of the plurality of first detectors based on the density profile of the density unevenness measurement image measured after adjusting the beam light amount of the exposure device, and corrects the target toner adhesion amount based on the representative value of density and the extracted density value.

7. 7. The image forming apparatus according to claim 1, wherein the representative value of density is an average value of the density profile in the main scanning direction.

8. A control method for an image forming apparatus, comprising: The image forming apparatus includes: an image processing unit that forms a toner image on an image carrier by electrophotography and transfers the formed toner image onto a recording medium; a plurality of first detectors arranged at different positions in a main scanning direction and used for measuring densities of a plurality of toner patches formed on the image carrier by the image processing unit; a second detector used for measuring a density profile in a main scanning direction of the density unevenness measuring image formed on the recording medium by the image processing unit; a control unit; The control method includes: a step of the control unit determining, based on the density profile of the density unevenness measuring image, a representative value of density according to the density profile and density values ​​extracted at each detection position of the plurality of first detectors; a step of the control unit selecting a first detector corresponding to a concentration value closest to the representative value of the concentration from among a plurality of concentration values ​​extracted from the concentration profile at each detection position of the plurality of first detectors; a step of the control unit calculating a correction amount for a target toner adhesion amount on the recording medium based on a difference between the representative value of the density and a density value extracted from the density profile at the selected detection position of the first detector; the control unit measures densities of a plurality of toner patches formed under different image forming conditions using the selected first detector, and converts the measured densities of the plurality of toner patches into toner adhesion amounts on the recording medium, thereby determining a correspondence relationship between the image forming conditions and the toner adhesion amounts; The control unit determines, based on the determined correspondence relationship, the image forming condition that corresponds to the target toner adhesion amount corrected by the correction amount.

9. A control method for an image forming apparatus, comprising: The image forming apparatus includes: an image processing unit that forms a toner image on an image carrier by electrophotography and transfers the formed toner image onto a recording medium; a plurality of first detectors arranged at different positions in a main scanning direction and used for measuring densities of a plurality of toner patches formed on the image carrier by the image processing unit; a second detector used for measuring a density profile in a main scanning direction of the density unevenness measuring image formed on the recording medium by the image processing unit; a control unit; The control method includes: a step of the control unit determining, based on the density profile of the density unevenness measuring image, a representative value of density according to the density profile and density values ​​extracted at each detection position of the plurality of first detectors; a step of the control unit calculating a correction amount of a target toner adhesion amount on the recording medium for each of the first detectors based on a difference between the representative value of the density and a density value extracted from the density profile at each detection position of the first detectors; the control unit measures densities of a plurality of toner patches formed under different image forming conditions using each of the plurality of first detectors, and converts the densities of the plurality of toner patches measured for each of the plurality of first detectors into amounts of toner adhesion on the recording medium, thereby determining a correspondence relationship between the image forming conditions and the amounts of toner adhesion for each of the plurality of first detectors; determining, by the control unit, the image forming condition corresponding to the target toner adhesion amount corrected by the correction amount for each of the plurality of first detectors based on the determined correspondence relationship; and determining a final image formation condition by the control unit averaging the image formation conditions determined for each of the first detectors.

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