Image forming apparatus

Abstract

To make it possible to execute an appropriate type of calibration for suppressing unevenness of an image.SOLUTION: Provided is an image forming apparatus that includes an image forming unit and a control unit for controlling the operation of the image forming unit. The image forming unit includes: an image bearing member that rotates around a rotation shaft; exposure means for exposing the image bearing member to form a latent image on a surface of the image bearing member; and developing means for developing the latent image with a developer to form a developer image. The control unit, in a first correction mode, measures unevenness of the image in both a first direction parallel to a rotation axis and a second direction orthogonal to the first direction, and corrects the image forming condition of the image forming unit on the basis of the measurement result in the first and second directions; in a second correction mode, measures unevenness of the image in one of the first and second directions, and corrects the image forming condition of the image forming unit on the basis of the measurement result in the one direction.SELECTED DRAWING: Figure 8

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus. [Background technology]

[0002] The quality of an image formed by an electrophotographic image forming apparatus is affected by various factors such as fluctuations in temperature and humidity, deterioration of components over time, and variations in dimensions and performance during manufacture. For example, if the sensitivity of a photoconductor, the amount of light from an exposure laser, the charging voltage, or the developing voltage is nonuniform, or if there is aberration in the lens of an optical system, unevenness in density or color appears in the output image.

[0003] Patent Document 1 discloses an image forming apparatus that suppresses density unevenness by forming a test pattern having a band-shaped pattern extending in the main scanning direction on a sheet and adjusting image forming conditions based on a read image obtained by optically reading the formed test pattern. Patent Document 2 discloses an image forming apparatus that measures unevenness in the developer on a photoconductor and adjusts image forming conditions in accordance with the rotation cycle of the developing roller based on the measurement results in order to reduce periodic density unevenness in the sub-scanning direction caused by resistance unevenness in the circumferential direction of the developing roller. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2011-191416 A [Patent Document 2] Patent No. 3825184 Summary of the Invention [Problem to be solved by the invention]

[0005] Both the image forming apparatus described in the cited document 1 and the image forming apparatus described in the cited document 2 perform calibration to correct unevenness in only one of the directions. Therefore, in order to correct unevenness in both the main scanning direction and the sub-scanning direction, one calibration must be completed before the other calibration is performed, which means that the user must be confined in front of the image forming apparatus for a long time. On the other hand, depending on the image quality desired by the user, there are cases where it is not necessary to perform calibration to correct unevenness in both the main scanning direction and the sub-scanning direction.

[0006] An object of the present invention is to provide an image forming apparatus capable of performing an appropriate type of calibration for suppressing unevenness in an image. [Means for solving the problem]

[0007] According to one aspect, there is provided an image forming apparatus comprising an image forming unit and a control unit that controls operation of the image forming unit, wherein the image forming unit comprises an image carrier that rotates around a rotation axis, a charging means that charges the image carrier, an exposure means that exposes the charged image carrier to form a latent image on a surface of the image carrier, and a developing means that develops the latent image on the surface of the image carrier with a developer to form a developer image, wherein in a first correction mode, the control unit measures image unevenness in both a first direction parallel to the rotation axis and a second direction perpendicular to the first direction, and corrects image formation conditions of the image forming unit based on the measurement results in the first direction and the second direction, and in a second correction mode, measures image unevenness in one of the first direction and the second direction, and corrects image formation conditions of the image forming unit based on the measurement results in the one direction.

[0008] According to the present invention, it is possible to perform an appropriate type of calibration for suppressing unevenness in an image. [Brief description of the drawings]

[0009] [Figure 1]FIG. 1 is a schematic diagram illustrating an example of a configuration of an image forming apparatus according to an embodiment. [Diagram 2] FIG. 2 is a block diagram showing an example of the configuration of a printer controller according to an embodiment. [Diagram 3] FIG. 4 is an explanatory diagram showing an example of the configuration of a first test pattern used for measuring image unevenness in the main scanning direction. [Figure 4] 10A and 10B are explanatory views of measurement of density for each partial region using a scanned image of the first test pattern. [Diagram 5] 1 is a graph showing an example of a brightness-density curve. [Figure 6] FIG. 11 is an explanatory diagram showing an example of the configuration of a second test pattern used for measuring image unevenness in the sub-scanning direction. [Figure 7] 10A and 10B are explanatory views of measurement of density for each partial region using a scanned image of a second test pattern. [Figure 8] FIG. 11 is an explanatory diagram of an example of the configuration of a GUI for allowing a user to select a correction mode. [Figure 9] 10 is a flowchart showing an example of a flow of processing executed in a main scanning correction mode. [Figure 10] 10 is a flowchart showing an example of a flow of processing executed in a sub-scanning correction mode. [Figure 11] 10 is a flowchart showing an example of a flow of processing executed in a batch correction mode. [Figure 12] 10 is a flowchart showing an example of the flow of an exposure control process when an image forming job is executed. [Figure 13] FIG. 13 is a schematic diagram showing an example of the configuration of an image forming apparatus according to a first modified example. [Figure 14] 10 is a flowchart showing an example of a flow of processes executed in a sub-scanning correction mode of a first modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, the embodiments will be described in detail with reference to the attached drawings. Note that the following embodiments do not limit the invention according to the claims. Although the embodiments describe a number of features, not all of these features are essential to the invention, and the features may be combined in any manner. Furthermore, in the attached drawings, the same reference numbers are used for the same or similar configurations, and duplicated descriptions are omitted.

[0011] <1. Example of the configuration of an image forming device> 1 is a schematic diagram showing an example of the configuration of an image forming apparatus 100 according to an embodiment. In this specification, an example in which the image forming apparatus 100 is a digital multifunction peripheral will be mainly described. However, the technology according to the present disclosure is not limited to this example and can be applied to any type of image forming apparatus, such as a copier, a printer, or a facsimile.

[0012] 1, the image forming apparatus 100 includes a scanner unit 110, a printer unit 120, and an operation unit 130. The scanner unit 110 optically reads an original document and generates read image data. The printer unit 120 forms an image on a sheet (also called a recording material) based on, for example, the read image data generated by the scanner unit 110 or print image data received from an external device (not shown) via a network. The operation unit 130 provides a user interface for interaction between the image forming apparatus 100 and a user.

[0013] (1) Printer unit The printer unit 120 has image forming units 10Y, 10M, 10C, and 10K. The image forming units 10Y, 10M, 10C, and 10K form toner images (developer images) of yellow (Y), magenta (M), cyan (C), and black (K), respectively. The image forming units 10Y, 10M, 10C, and 10K may have the same configuration. Therefore, in the following description, the image forming units 10Y, 10M, 10C, and 10K are collectively referred to as the image forming unit 10 by omitting the alphabets at the end of the symbols representing the color components. The same applies to the symbols of the internal components of the image forming unit 10.

[0014] The photoconductor 1 is an image carrier (e.g., an aluminum cylinder) that rotates around a rotation axis (counterclockwise in the figure). The charger 2 is a charging means that is applied with a charging voltage (e.g., a negative bias voltage) and charges the photosensitive layer on the surface of the photoconductor 1 to a uniform negative potential. The exposure unit 3 is an exposure means that exposes the charged surface of the photoconductor 1 to light to form an electrostatic latent image on the surface of the photoconductor 1. The exposure unit 3 may be, for example, a laser scanner, and writes each line of the latent image on the surface of the photoconductor 1 by scanning the surface of the photoconductor 1 in a first direction parallel to the rotation axis of the photoconductor 1 and emitting a laser beam according to input image data input from the printer controller 150. In the following description, the first direction parallel to the rotation axis of the photoconductor 1 is also called the main scanning direction, and the second direction perpendicular to the first direction (parallel to the sheet conveying direction) is also called the sub-scanning direction. The developing device 4 is a developing means that develops the electrostatic latent image on the surface of the photoreceptor 1 with toner as a developer to form a toner image. The toner image is carried by the photoreceptor 1 and transported to a primary transfer position where the photoreceptor 1 and intermediate transfer belt 11 come into contact. A primary transfer voltage (e.g., a positive bias voltage) is applied to the primary transfer roller 7, which transfers the toner image on the surface of the photoreceptor 1 to the intermediate transfer belt 11. The toner images of the four photoreceptors 1 are superimposed and transferred to the intermediate transfer belt 11, forming a color image on the intermediate transfer belt 11 that includes four color components: yellow, magenta, cyan, and black.

[0015] The intermediate transfer belt 11 is stretched around a tension roller 51, a drive roller 52, and an opposing roller 53. The intermediate transfer belt 11 rotates clockwise in the drawing in response to the rotation of the drive roller 52, and transports the toner image to a transfer nip between the opposing roller 53 and a secondary transfer roller 65.

[0016] The cassette 60 contains a stack of sheets. The pickup roller 61 picks up a sheet from the cassette 60 and feeds it to the conveying path. The separation roller 62 separates the sheet from the stack of sheets. The conveying roller 63 conveys the separated sheet along the conveying path to the registration roller 64. The registration roller 64 sends the conveyed sheet to the transfer nip in accordance with the timing when the toner image on the intermediate transfer belt 11 reaches the transfer nip. The secondary transfer roller 65 is applied with a secondary transfer voltage, transfers the toner image on the intermediate transfer belt 11 to the sheet by the secondary transfer voltage, and conveys the sheet to the fixing device 20 further downstream. The belt cleaner 54 collects the toner remaining on the intermediate transfer belt 11 after passing through the transfer nip.

[0017] The fixing unit 20 heats and presses the sheet onto which the toner image has been transferred, thereby fixing the toner image to the sheet. After the toner image has been fixed, the sheet is discharged to the outside of the image forming apparatus 100 by a discharge roller 66.

[0018] The printer controller 150 controls the overall operation of the printer unit 120 including the image forming sections 10Y, 10M, 10C, and 10K described above. In particular, an example of the configuration of the printer controller 150 related to measurement and correction of image unevenness will be described in more detail later.

[0019] Although an example in which a toner image is indirectly transferred from each photoconductor 1 to a sheet via intermediate transfer belt 11 has been described here, the toner image may be directly transferred from each photoconductor 1 to a sheet. Also, although an example in which a color image is formed using toners of multiple colors has been described here, the technology according to the present disclosure is also applicable to an image forming apparatus that forms a monochrome image using toners of a single color.

[0020] (2) Scanner unit The scanner unit 110 includes a document tray 111, a light emitting unit 112, an image sensor 113, an image processing circuit 114, and a scanner controller 115. The light emitting unit 112 irradiates light onto the bottom surface of a document placed on the document tray 111 while moving left and right in the figure. The light reflected by the bottom surface of the document is guided through an optical system that may include a mirror, a lens, etc., and forms an image on the imaging surface of the image sensor 113. The image sensor 113 optically reads the bottom surface of the document to generate read image data, and outputs the generated read image data to the image processing circuit 114. The image processing circuit 114 performs image processing, such as noise removal and resolution conversion, on the read image data. The scanner controller 115 controls the operation of the scanner unit 110 described above.

[0021] Although an example in which scanner unit 110 reads a document placed on document tray 111 has been described here, the technology according to the present disclosure is not limited to such an example. For example, scanner unit 110 may have an ADF (Auto-Document Feeder) mechanism and be capable of reading a document transported along a transport path.

[0022] (3) Operation unit The operation unit 130 has a display 132 and an input device 134. The display 132 displays a graphical user interface (GUI) generated by the printer controller 150, as described later. The input device 134 may include, for example, one or more buttons, a keypad, and a switch, and accepts operation input by a user. The display 132 and the input device 134 may be integrally configured as a touch panel.

[0023] <2. Printer controller configuration example> 2 is a block diagram showing an example of the configuration of printer controller 150 according to an embodiment. Only components related to measurement and correction of mura are shown here, and other components that printer controller 150 may have are omitted. Referring to FIG. 2, printer controller 150 includes a CPU 151, a ROM 152, a RAM 153, a non-volatile memory 154, an image processing unit 155, a scanner interface (I / F) 156, an operation I / F 157, a bus 159, and an exposure control unit 160.

[0024] The CPU (Central Processing Unit) 151 is a processor that controls the overall function of the printer controller 150. The ROM (Read-Only Memory) 152 stores in advance computer programs to be executed by the CPU 151. The RAM (Random Access Memory) 153 provides the CPU 151 with a temporary storage area for calculations. The non-volatile memory 154 is a storage unit that stores various data that can be referenced or updated by the CPU 151. The image processing unit 155 performs various image processing on input image data of an image forming job (e.g., a copy job or a print job) executed in the printer unit 120. The image processing performed by the image processing unit 155 may include, for example, rasterization, color conversion, resolution conversion, and binarization. The scanner I / F 156 is an interface for connecting the printer controller 150 to the scanner unit 110. The operation I / F 157 is an interface for connecting the printer controller 150 to the operation unit 130.

[0025] The exposure control unit 160 controls exposure of the photoconductor 1 by the exposure unit 3 of each image forming unit 10. In this embodiment, the exposure control unit 160 has a so-called shading function, and can variably control the amount of laser light (also called laser power (LPW)) emitted from the exposure unit 3 during a scanning period of one line in the main scanning direction. Referring to FIG. 2, the exposure control unit 160 includes a light amount control circuit 161, a PWM modulation circuit 162, and a pattern generation circuit 163.

[0026] When an image forming job is executed, the light amount control circuit 161 variably controls the light amount of the laser light emitted from the exposure device 3 of each image forming unit 10 so that image unevenness is suppressed in both the main scanning direction and the sub-scanning direction. For example, the non-volatile memory 154 stores initial profile data indicating the measurement result of image unevenness caused by manufacturing errors, and / or profile data updated by a correction process described later. The profile data may indicate, for example, a correction amount of the light amount for canceling the unevenness (uniformizing the density between the partial regions) determined for each partial region of the image. The light amount control circuit 161 adds the correction amount indicated by the profile data to a reference value to calculate a desired light amount for each partial region, and instructs the PWM modulation circuit 162 to the value of the calculated light amount. The PWM modulation circuit 162 performs pulse width modulation (PWM) on the drive signal (pulse signal) output to the exposure device 3 according to the value of the light amount instructed by the light amount control circuit 161. Specifically, for pixels for which the input image data indicates that light is on, the PWM modulation circuit 162 supplies the exposure device 3 with a pulse signal having a duty ratio corresponding to the value of the light amount instructed by the light amount control circuit 161. The conversion from the value of the light amount to the duty ratio can be performed, for example, using a look-up table (LUT) that is determined in advance and stored in a memory. In the conversion, tone correction such as gamma correction may be performed based on the relationship between the output level of the laser and the density of the image. When a pixel is exposed to light, the larger the duty ratio of the laser light is, the longer the exposure time is, and the larger the dot is formed. If the size of the dot formed in a certain partial area is large, the area gradation in that partial area, i.e., the density of the image, is high. When the exposure device 3 exposes the photoconductor 1 through such exposure control, a latent image expressing an image corresponding to the input image data is formed on the surface of the photoconductor 1 in a form in which unevenness is suppressed.

[0027] The size of the partial regions may be any size depending on the required resolution of correction. For example, if the maximum width of an image that can be formed by the image forming apparatus 100 in the main scanning direction is about 330.2 mm, this maximum width may be divided into 14 partial regions, and the size of the partial regions in the main scanning direction may be set to about 23.59 mm. Also, if the length of the outer periphery of the photoconductor 1 in the sub-scanning direction is 300 mm, this length may be divided into 10 partial regions, and the size of the partial regions in the sub-scanning direction may be set to about 30.0 mm.

[0028] <3. Measuring unevenness and calculating the amount of correction> Unevenness in an image formed by the image forming apparatus 100 can occur not only due to manufacturing errors, but also due to fluctuations in environmental factors and deterioration of components over time. In order to accurately capture and suppress such unevenness, the printer controller 150 has a measurement function for measuring the unevenness and a correction function for correcting the operating conditions of the image forming unit 10 (hereinafter referred to as image forming conditions) based on the unevenness measurement results. Specifically, in this embodiment, the CPU 151 functions as a measurement unit 171 and a correction unit 172.

[0029] The measurement unit 171 can measure image unevenness in the main scanning direction and in the sub-scanning direction. The correction unit 172 corrects the image forming conditions of the image forming unit 10 based on the results of the measurement by the measurement unit 171. In this embodiment, the image forming conditions corrected by the correction unit 172 include the amount of laser light emitted by the exposure device 3. In other embodiments, the image forming conditions corrected by the correction unit 172 may include other conditions, such as a charging voltage, a developing voltage, or a transfer voltage.

[0030] In this embodiment, the measurement of image unevenness in the main scanning direction and the measurement of image unevenness in the sub-scanning direction are both performed by optically reading an image of a test pattern formed on a sheet.

[0031] FIG. 3 is an explanatory diagram of an example of the configuration of a first test pattern 80 used to measure image unevenness in the main scanning direction. The first test pattern 80 has four rectangular regions 81, 82, 83, and 84 corresponding to four color components C, M, Y, and K, respectively. Each of the rectangular regions 81, 82, 83, and 84 is a strip-shaped region extending across the entire width of the paper P in the main scanning direction D1, and occupies a certain length in the sub-scanning direction D2. The rectangular region 81 is formed uniformly, for example, with a cyan signal value of 40% by the image forming unit 10C. The rectangular region 82 is formed uniformly, for example, with a magenta signal value of 40% by the image forming unit 10M. The rectangular region 83 is formed uniformly, for example, with a yellow signal value of 40% by the image forming unit 10Y. The rectangular region 84 is formed uniformly, for example, with a black signal value of 40% by the image forming unit 10K.

[0032] The pattern generation circuit 163 of the exposure control unit 160 stores a configuration of a first test pattern 80 that is defined in advance. The pattern generation circuit 163 controls the image forming units 10Y, 10M, 10C, and 10K to form an image of the first test pattern 80 on the sheet P in response to an instruction from the measurement unit 171. When the image of the first test pattern 80 is formed on the sheet P, the user sets the sheet P in the scanner unit 110 to read the image of the first test pattern 80. The scanner unit 110 optically reads the image of the first test pattern 80 on the sheet P, generates a read image of the first test pattern 80, and outputs the read image data to the measurement unit 171.

[0033] FIG. 4 is an explanatory diagram of the measurement of the density of each partial region using the read image IM1 of the first test pattern 80. Referring to FIG. 4, in the read image IM1, the rectangular region 81 is divided into 14 partial regions 81a to 81n in the main scanning direction D1. The measurement unit 171 calculates the average luminance value for each of these partial regions 81a to 81n, and further converts the average luminance value into a density level of cyan. The graph in FIG. 5 shows an example of a luminance-density curve that represents the relationship between the luminance value (read luminance value) and the density level in the read image. The horizontal axis of the graph represents the read luminance value, and the vertical axis represents the density level, and the ranges of both the read luminance value and the density level are 0 to 255. Such a luminance-density curve is determined in advance for each color component, and is stored in the non-volatile memory 154 in, for example, an LUT format. The measurement unit 171 converts the average luminance value of each of the partial regions 81a to 81n into a density level using the luminance-density curve (or its LUT). Furthermore, the measurement unit 171 calculates the difference in density level (hereinafter referred to as density difference) from a reference value (for example, the average density level over the entire rectangular region 81, or a target value of the density level) for each of the partial regions 81a-81n. The density difference for each partial region calculated in this way represents image unevenness in the main scanning direction D1 (here, for the cyan component). Similarly, for other color components, the measurement unit 171 measures image unevenness in the main scanning direction D1 using the read luminance values ​​of partial regions 82a-82n of rectangular region 82, partial regions 83a-83n of rectangular region 83, and partial regions 84a-84n of rectangular region 84.

[0034] The correction unit 172 converts the density difference for each partial region of each color component calculated by the measurement unit 171 into a correction amount of the light amount. For example, if the index of the partial regions arranged in the main scanning direction D1 is x (x ∈ {a, b, ..., n}), the index of the color component is c (c ∈ {Y, M, C, K}), and the density difference of the partial region x of the color component c is Δd c,x Then, the concentration difference Δd c,x The correction amount ΔL is calculated according to the following formula: c,x can be converted to: ΔL c,x = round(Δd c,x ×N c ) (1) Here, N c is a conversion coefficient that determines how much the amount of laser light of color component c (the pulse width or duty ratio of the drive signal, or the laser power) is changed in response to density fluctuations. round() represents a function that rounds off the argument. Conversion coefficient N c The value of may be predetermined and stored in the non-volatile memory 154. As an example, N c = 200, in which case the concentration difference Δd c,x = 0.01, the correction amount ΔL c,x = 2. Note that the method of converting the density difference into the correction amount is not limited to the method using formula (1). For example, a linear or nonlinear conversion formula different from formula (1) may be adopted, or a conversion method using a look-up table may be adopted. Furthermore, when calculating the density difference for each partial region, the median value of the luminance values ​​or some other statistical value may be used instead of the average luminance value for each partial region.

[0035] FIG. 6 is an explanatory diagram of an example of the configuration of a second test pattern 90 used to measure image unevenness in the sub-scanning direction. The second test pattern 90 has four rectangular regions 91, 92, 93, and 94 corresponding to four color components C, M, Y, and K, respectively. Each of the rectangular regions 91, 92, 93, and 94 has a certain width in the main scanning direction D1 and a certain length in the sub-scanning direction D2. The length of each rectangular region in the sub-scanning direction D2 corresponds to the outer periphery of the photoconductor 1. The rectangular region 91 is formed uniformly, for example, with a cyan signal value of 40% by the image forming unit 10C. The rectangular region 92 is formed uniformly, for example, with a magenta signal value of 40% by the image forming unit 10M. The rectangular region 93 is formed uniformly, for example, with a yellow signal value of 40% by the image forming unit 10Y. The rectangular region 94 is formed uniformly, for example, with a black signal value of 40% by the image forming unit 10K.

[0036] The pattern generation circuit 163 of the exposure control unit 160 stores the configuration of the second test pattern 90 defined in advance. The pattern generation circuit 163 controls the image forming units 10Y, 10M, 10C, and 10K to form an image of the second test pattern 90 on the sheet P in response to an instruction from the measurement unit 171. At this time, the home position of the rotation angle of the photoconductor 1 is aligned to coincide with the writing line of the second test pattern 90 so that there is no deviation in the correspondence between the rotation phase of the photoconductor 1 and the position of the second test pattern 90 in the sub-scanning direction D2. When the image of the second test pattern 90 is formed on the sheet P, the user sets the sheet P in the scanner unit 110 and causes the scanner unit 110 to read the image of the second test pattern 90. The scanner unit 110 optically reads the image of the second test pattern 90 on the sheet P, generates a read image of the second test pattern 90, and outputs the read image data to the measurement unit 171.

[0037] FIG. 7 is an explanatory diagram of the measurement of the density for each partial region using the read image IM2 of the second test pattern 90. Referring to FIG. 7, in the read image IM2, the rectangular region 91 is divided into ten partial regions 91a to 91j in the sub-scanning direction D2. The measurement unit 171 calculates the average luminance value for each of these partial regions 91a to 91j, and converts the average luminance value into a density level of cyan, for example, by the method described in relation to FIG. 5. Furthermore, the measurement unit 171 calculates the density difference from the reference value for each of the partial regions 91a to 91j. The density difference calculated in this way for each partial region represents the unevenness of the image in the sub-scanning direction D2 (here, for the cyan component). Similarly, for other color components, the measurement unit 171 measures the unevenness of the image in the sub-scanning direction D2 using the read luminance values ​​of the partial regions 92a to 92j of the rectangular region 92, the partial regions 93a to 93j of the rectangular region 93, and the partial regions 94a to 94j of the rectangular region 94.

[0038] In the sub-scanning direction D2, the correction unit 172 converts the density difference for each partial region of each color component calculated by the measurement unit 171 into a correction amount of the light amount, as in the main scanning direction D1. For example, the index of the partial regions arranged in the sub-scanning direction D2 is y (y∈{a,b,...,j}), the index of the color component is c (c∈{Y,M,C,K}), and the density difference of the partial region y of the color component c is Δd c,y Then, the concentration difference Δd c,y The correction amount ΔL is calculated according to the following formula: c,y can be converted to: ΔL c,y = round(Δd c,y ×N c ) (2) It should be noted again that the method of converting the density difference into the correction amount is not limited to the method using equation (2).

[0039] The amount of correction used by the light amount control circuit 161 to control the amount of light for each partial region of the input image is determined by identifying each partial region by indexes x and y, and expressing the amount of correction as ΔL c,x,y Then, the correction amount ΔL in the main scanning direction and the sub-scanning direction is as follows: c,x , ΔL c,y It may be the sum of ΔL c,x,y = ΔL c,x + ΔL c,y (3) In formula (3), index x represents the position of the partial region in the main scanning direction D1, and index y represents the phase (with respect to the rotation of the photoconductor 1) of the partial region in the sub-scanning direction D2. Furthermore, the light amount used for exposure for each partial region (for example, the value of the light amount instructed to the PWM modulation circuit 162) is calculated by multiplying the reference light amount commonly set in advance by a correction amount ΔL c,x,y It may be the sum of.

[0040] The non-volatile memory 154 stores in advance initial profile data indicating, for example, the measurement results (results measured at the factory) of image unevenness caused by manufacturing errors. The initial profile data typically includes the following two types of data: First initial profile data... indicates the measurement results of image unevenness in the main scanning direction for each color component at the manufacturing stage of the image forming apparatus 100 (for example, the correction amount for each of 14 partial regions aligned in the main scanning direction). Second initial profile data...shows the measurement results of image unevenness in the sub-scanning direction for each color component at the manufacturing stage of the image forming apparatus 100 (for example, the correction amount for each of 10 partial regions aligned in the sub-scanning direction).

[0041] Furthermore, the non-volatile memory 154 stores profile data indicating the latest measurement results of the measurement of image mura performed by the measurement unit 171. The profile data typically includes the following two types of data: First profile data: This indicates the latest measurement results of image unevenness in the main scanning direction for each color component (for example, the amount of correction for each of 14 partial regions aligned in the main scanning direction). · Second profile data: This indicates the latest measurement results of image unevenness in the sub-scanning direction for each color component (for example, the amount of correction for each of 10 partial areas aligned in the sub-scanning direction). Each time measurement is performed by the measurement unit 171, the correction unit 172 updates the profile data stored in the non-volatile memory 154 with the latest measurement results.

[0042] <4. Batch correction mode and individual correction mode> As described above, the unevenness in the main scanning direction and the unevenness in the sub-scanning direction are measured using separate test patterns. If these measurements could be performed together by calling a single function, the effort required for the user would be reduced, but if unevenness in both directions were always measured, time efficiency would decrease. For example, a user who looks at a printed image and determines that there is room for improvement only in the unevenness in the sub-scanning direction may wish to remeasure only the unevenness in the sub-scanning direction, and vice versa.

[0043] In this embodiment, the image forming apparatus 100 provides a batch correction mode and an individual correction mode in order to meet such needs and improve the efficiency of executing a function for suppressing image unevenness. In the batch correction mode (first correction mode), the measurement unit 171 measures image unevenness in both the main scanning direction and the sub-scanning direction, and the correction unit 172 corrects the image forming conditions of the image forming unit 10 based on the measurement results in the main scanning direction and the sub-scanning direction. In the individual correction mode (second correction mode), the measurement unit 171 measures image unevenness in one of the main scanning direction and the sub-scanning direction, and the correction unit 172 corrects the image forming conditions of the image forming unit 10 based on the measurement results in the one direction.

[0044] The individual correction mode is typically further divided into two correction modes. One is a main scanning correction mode in which image unevenness is measured only in the main scanning direction. The other is a sub-scanning correction mode in which image unevenness is measured only in the sub-scanning direction. In this embodiment, the operation unit 130 provides a user with a graphical user interface (GUI) that allows the user to select one of the collective correction mode, the main scanning correction mode, and the sub-scanning correction mode. The correction unit 172 corrects the image forming conditions of the image forming unit 10 in the correction mode selected by the user via this GUI.

[0045] Fig. 8 is an explanatory diagram of an example of the configuration of a GUI for allowing a user to select a correction mode. The unevenness correction screen 200 shown in Fig. 8 is generated by, for example, the measurement unit 171 and displayed on the display 132 of the operation unit 130. Alternatively, the unevenness correction screen 200 may be displayed on a display of a user terminal connected to the image forming apparatus 100 via a communication I / F not shown in Fig. 2. The unevenness correction screen 200 includes three mode selection buttons 211, 212, and 213, a pattern output button 221, and two read buttons 222 and 223.

[0046] The mode selection button 211 is a button for selecting a collective correction mode, the mode selection button 212 is a button for selecting a main scanning correction mode, and the mode selection button 213 is a button for selecting a sub-scanning correction mode.

[0047] When any of the correction modes is selected by the user, the pattern output button 221 is enabled. The pattern output button 221 is a button for starting output of one or more test pattern images corresponding to the selected correction mode. When the pattern output button 221 is operated in a state where the collective correction mode is selected, the image forming units 10Y to 10K form an image of the first test pattern on a first sheet, and then an image of the second test pattern on a second sheet under the control of the printer controller 150. When the pattern output button 221 is operated in a state where the main scanning correction mode is selected, the image forming units 10Y to 10K form an image of the first test pattern on a sheet under the control of the printer controller 150. When the pattern output button 221 is operated in a state where the sub-scanning correction mode is selected, the image forming units 10Y to 10K form an image of the second test pattern on a sheet under the control of the printer controller 150.

[0048] When the formation of the image of the test pattern is completed, one or both of the read buttons 222 and 223 are enabled. In the batch correction mode or the main scanning correction mode, when the user sets a sheet on the document tray 111 and operates the read button 222, reading of the image of the first test pattern is started, measurement of unevenness in the main scanning direction and calculation of the correction amount are performed. In the batch correction mode or the sub-scanning correction mode, when the user sets a sheet on the document tray 111 and operates the read button 223, reading of the image of the second test pattern is started, measurement of unevenness in the sub-scanning direction and calculation of the correction amount are performed.

[0049] The process flows in the main scanning correction mode, sub-scanning correction mode, and collective correction mode will be described below with reference to Figures 9 to 11. In each flow chart, the process steps are abbreviated as 'S'.

[0050] (1) Main scanning correction mode FIG. 9 is a flowchart showing an example of the flow of processing executed by the printer controller 150 in the main scanning correction mode.

[0051] In the main scanning correction mode, first, in S111, the image forming units 10Y to 10K form an image of a first test pattern generated by the pattern generating circuit 163 in response to the operation of the pattern output button 221 on a sheet.

[0052] Next, in S113, the scanner unit 110 optically reads the sheet on which the first test pattern is formed to generate a first read image in response to the operation of the read button 222. The scanner controller 115 outputs read image data representing the first read image to the printer controller 150.

[0053] Next, in S115, the measurement unit 171 measures image unevenness in the main scanning direction using the first read image. More specifically, the measurement unit 171 calculates an average luminance value of the first read image for each of a plurality of partial regions aligned in the main scanning direction, converts the calculated average luminance value into a density level, and calculates the difference of the density level from the reference value (i.e., the density difference).

[0054] Next, in S117, correction unit 172 determines the amount of correction for each partial region based on the density difference for each partial region calculated by measurement unit 171. Note that, although not shown in detail in Fig. 9 for simplicity of explanation, the measurement of unevenness in S115 and the determination of the amount of correction for each partial region in S117 can be repeated for each of the four color components.

[0055] Next, in S119, the correction unit 172 updates the first profile data stored in the non-volatile memory 154 so as to reflect the amount of correction determined in S117. Then, the processing in FIG.

[0056] As can be seen from Fig. 9, in the main scanning correction mode, image unevenness in the sub-scanning direction is not measured, and only image unevenness in the main scanning direction is newly measured. When correction is performed in the main scanning correction mode, the image forming units 10Y to 10K form images under image formation conditions corrected based on the latest measurement result in the main scanning direction and the past measurement result in the sub-scanning direction indicated by the second profile data when executing a job thereafter. When measurement in the sub-scanning direction has not been performed, second initial profile data indicating the measurement result in the sub-scanning direction at the manufacturing stage of the device may be used instead of the second profile data.

[0057] (2) Sub-scanning correction mode FIG. 10 is a flow chart showing an example of the flow of processing executed by the printer controller 150 in the sub-scanning correction mode.

[0058] In the sub-scanning correction mode, first, in S121, the image forming units 10Y to 10K form an image of the second test pattern generated by the pattern generation circuit 163 on a sheet in response to the operation of the pattern output button 221. At this time, the image forming units 10Y to 10K align the home positions of the rotation angles of the photoconductors 1Y to 1K, respectively, with the writing start line of the second test pattern 90.

[0059] Next, in S123, the scanner unit 110 optically reads the sheet on which the second test pattern is formed to generate a second read image in response to the operation of the read button 223. The scanner controller 115 outputs read image data representing the second read image to the printer controller 150.

[0060] Next, in S125, the measurement unit 171 measures the unevenness of the image in the sub-scanning direction using the second read image. More specifically, the measurement unit 171 calculates an average luminance value of the second read image for each of a plurality of partial regions aligned in the sub-scanning direction, converts the calculated average luminance value into a density level, and calculates the difference of the density level from the reference value (i.e., the density difference).

[0061] Next, in S127, correction unit 172 determines the amount of correction for each partial region based on the density difference for each partial region calculated by measurement unit 171. Note that, although not shown in detail in Fig. 10 for simplicity of explanation, the measurement of unevenness in S125 and the determination of the amount of correction for each partial region in S127 can be repeated for each of the four color components.

[0062] Next, in S129, the correction unit 172 updates the second profile data stored in the non-volatile memory 154 so as to reflect the amount of correction determined in S127. Then, the processing in FIG.

[0063] As can be seen from Fig. 10, in the sub-scanning correction mode, image unevenness in the main scanning direction is not measured, and only image unevenness in the sub-scanning direction is newly measured. When correction is performed in the sub-scanning correction mode, the image forming units 10Y to 10K form images under image formation conditions corrected based on the past measurement results in the main scanning direction indicated by the first profile data and the latest measurement results in the sub-scanning direction when executing a job thereafter. When measurement in the main scanning direction has not been performed, first initial profile data indicating the measurement results in the main scanning direction at the manufacturing stage of the device may be used instead of the first profile data.

[0064] (3) Batch correction mode FIG. 11 is a flowchart showing an example of the flow of processing executed by the printer controller 150 in the collective correction mode.

[0065] In the collective correction mode, first, in S131, the image forming units 10Y-10K form an image of a first test pattern generated by the pattern generation circuit 163 on a first sheet in response to the operation of the pattern output button 221. Next, in S132, the image forming units 10Y-10K form an image of a second test pattern generated by the pattern generation circuit 163 on a second sheet. At this time, the image forming units 10Y-10K align the home positions of the rotation angles of the photoconductors 1Y-1K, respectively, with the writing start line of the second test pattern 90.

[0066] Next, in S133, the scanner unit 110 optically reads the sheet on which the first test pattern is formed to generate a first read image in response to the operation of the read button 222. The scanner controller 115 outputs read image data representing the first read image to the printer controller 150.

[0067] Next, in S135, the measurement unit 171 measures image unevenness in the main scanning direction using the first read image. Next, in S137, the correction unit 172 determines the correction amount (the main scanning direction component) for each partial region based on the density difference measured using the first read image. Note that, although not shown in detail in FIG. 11, S135 and S137 can be repeated for each of the four color components.

[0068] Next, in S143, the scanner unit 110 optically reads the sheet on which the second test pattern is formed to generate a second read image in response to the operation of the read button 223. The scanner controller 115 outputs read image data representing the second read image to the printer controller 150.

[0069] Next, in S145, the measurement unit 171 measures image unevenness in the sub-scanning direction using the second read image. Next, in S147, the correction unit 172 determines the correction amount (sub-scanning direction component) for each partial region based on the density difference measured using the second read image. Note that, although not shown in detail in FIG. 11, S145 and S147 can be repeated for each of the four color components.

[0070] Next, in S148, the correction unit 172 updates the first profile data stored in the non-volatile memory 154 so as to reflect the amount of correction determined in S137. Also, in S149, the correction unit 172 updates the second profile data stored in the non-volatile memory 154 so as to reflect the amount of correction determined in S147. Then, the processing in FIG. 11 ends.

[0071] (4) Exposure control processing FIG. 12 is a flowchart showing an example of the flow of an exposure control process executed by the printer controller 150 when an image forming job is executed.

[0072] 12, first, the process branches in S151 depending on whether or not measurement in the main scanning direction has been performed. If measurement in the main scanning direction has been performed, in S152 the correction unit 172 reads out the first profile data updated last time from the non-volatile memory 154 and outputs it to the light intensity control circuit 161. If measurement in the main scanning direction has not been performed, in S153 the correction unit 172 reads out the first initial profile data from the non-volatile memory 154 and outputs it to the light intensity control circuit 161.

[0073] Next, the process branches in S154 depending on whether or not measurement in the sub-scanning direction has been performed. If measurement in the sub-scanning direction has been performed, in S155 the correction unit 172 reads out the second profile data updated last time from the non-volatile memory 154 and outputs it to the light intensity control circuit 161. If measurement in the sub-scanning direction has not been performed, in S156 the correction unit 172 reads out the second initial profile data from the non-volatile memory 154 and outputs it to the light intensity control circuit 161.

[0074] Next, in S157, the light amount control circuit 161 calculates the amount of light to be used for exposure for each partial region of the image based on the amount of correction in the main scanning direction indicated by the first (initial) profile data and the amount of correction in the sub-scanning direction indicated by the second (initial) profile data. The calculation of the amount of light here can be performed as described above using equation (3). Although not shown in detail in the figure, the calculation of the amount of light to be used for exposure can be repeated for each partial region during scanning in the main scanning direction for each line of the image and scanning in the sub-scanning direction over multiple lines.

[0075] Next, in S158, the light amount control circuit 161 sequentially instructs the PWM modulation circuit 162 on the light amount values ​​calculated in S157, thereby controlling the exposure device 3 to expose the photoconductor 1 with the corrected light amount and form an electrostatic latent image corresponding to the input image data on the surface of the photoconductor 1. Then, through the development of the electrostatic latent image, the transfer of the toner image, and the fixing of the toner image on the sheet, an image is formed on the sheet with density and color with reduced unevenness in both the main scanning direction and the sub-scanning direction.

[0076] <5. Modifications> (1) First Modification In the above-described embodiment, an example has been described in which the measurement of image unevenness is performed using the read images of the first test pattern and the second test pattern in both the main scanning direction and the sub-scanning direction, respectively. However, the technology according to the present disclosure is not limited to such an example. For example, the image unevenness may be measured by detecting the potential of the photoconductor 1 using a potential sensor disposed in each image forming unit 10. The measurement of unevenness using a potential sensor may be applied to either the main scanning direction or the sub-scanning direction, but in this section, an example in which the image unevenness in the sub-scanning direction is measured using a potential sensor will be described as a first modified example.

[0077] Fig. 13 is a schematic diagram showing an example of the configuration of an image forming apparatus 300 according to a first modified example. Referring to Fig. 13, the image forming apparatus 300 includes a scanner unit 110, a printer unit 120, and an operation unit 130 similar to those shown in Fig. 1. However, the image forming sections 10Y, 10M, 10C, and 10K of the printer unit 120 include potential sensors 5Y, 5M, 5C, and 5K, respectively. Each potential sensor 5 is disposed facing the surface of the photoconductor 1 of the same image forming section 10, and is a detection unit that detects the potential of the charged photoconductor 1.

[0078] In the first modified example, measuring image unevenness in the main scanning direction by the measuring unit 171 includes measuring image unevenness in the main scanning direction using a read image based on optical reading of a first test pattern formed on a sheet, as in the above-described embodiment. On the other hand, measuring image unevenness in the sub-scanning direction by the measuring unit 171 includes causing the potential sensor 5 to detect the potential of the photoconductor 1 on which a latent image pattern for unevenness measurement is formed, and measuring image unevenness in the sub-scanning direction based on the distribution of the detected potential of the photoconductor 1.

[0079] In the first modified example, the flow of the process executed by printer controller 150 in the main scanning correction mode may be similar to the flow described using FIG.

[0080] FIG. 14 is a flow chart showing an example of the flow of processing executed by the printer controller 150 in the sub-scanning correction mode.

[0081] In the sub-scanning correction mode, first, in S221, in response to a user's operation of the GUI, the measurement unit 171 causes the charger 2 to charge the surface of the photoconductor 1 to a uniform potential, and causes the exposure unit 3 to form a latent image pattern for unevenness measurement on the surface of the photoconductor 1. At this time, the home position of the rotation angle of the photoconductor 1 is aligned with the writing start line of the latent image pattern.

[0082] Next, in S223, the measurement unit 171 causes the potential sensor 5 to detect the potential of the photoconductor 1 while rotating the photoconductor 1, and measures the distribution of the potential in the sub-scanning direction based on the sensor data acquired from the potential sensor 5.

[0083] Next, in S225, the measurement unit 171 calculates the difference in average potential from the reference value (that is, the potential difference) for each of the partial regions aligned in the sub-scanning direction based on the distribution of the measured potential.

[0084] Next, in S227, the correction unit 172 determines a correction amount for each partial region based on the potential difference for each partial region calculated by the measurement unit 171. For example, the correction unit 172 may convert the potential difference for each partial region into a correction amount for the amount of light using a predetermined linear or nonlinear conversion formula similar to equation (2), or a lookup table. Note that, although not shown in detail in FIG. 14 for simplicity of explanation, S221 to S227 may be repeated for each of the four color components.

[0085] Next, in S229, the correction unit 172 updates the second profile data stored in the non-volatile memory 154 so as to reflect the amount of correction determined in S227. Then, the processing in FIG.

[0086] The flow of the process executed by the printer controller 150 in the collective correction mode may be the same as the flow described using Fig. 11. However, in this modification, the formation of the pattern image on the second sheet in S132 is omitted, and S143 to S147 are replaced with S221 to S227 in Fig. 14.

[0087] Generally, the causes of image unevenness in the sub-scanning direction are various, such as rotational shake or sensitivity unevenness of the image carrier, resistance unevenness in the developer, or transfer unevenness in the transfer roller. However, the most significant factor in image unevenness is usually the unevenness in the potential of the image carrier. Therefore, by adopting a configuration in which the unevenness in the potential of the image carrier is measured using a potential sensor as in this modified example, it is possible to avoid consumption of developer and reduce costs, and to reduce the effort required for forming and reading an image on a sheet, thereby making the work more efficient.

[0088] (2) Second modified example In the above-described embodiment, an example has been described in which the image forming conditions of the image forming unit 10 for suppressing image unevenness are corrected by adjusting the light amount of the exposure device 3 in both the main scanning direction and the sub-scanning direction. However, the technology according to the present disclosure is not limited to such an example.

[0089] In the second modified example, the correction of the image forming conditions to suppress image unevenness may be performed by adjusting at least one of the charging voltage of the charger 2 and the developing voltage of the developer 4. For example, in the main scanning direction, the amount of light of the exposure unit 3 may be adjusted so as to suppress image unevenness, and in the sub-scanning direction, the DC component of at least one of the charging voltage of the charger 2 and the developing voltage of the developer 4 may be adjusted so as to suppress image unevenness. In this case, the profile data in the sub-scanning direction may indicate the amount of correction of the voltage for each partial region, rather than the amount of correction of the light amount for each partial region.

[0090] <6. Summary> Various embodiments and modifications of the technology according to the present disclosure have been described in detail above with reference to FIGS. 1 to 14. In the above-described embodiment, in the image forming apparatus, A first correction mode in which image unevenness is measured in both a first direction (main scanning direction) and a second direction (sub-scanning direction) and image formation conditions are corrected based on the measurement results; and A second correction mode in which image unevenness is measured in one of the first and second directions, and the image formation conditions are corrected based on the measurement results. According to this configuration, it is possible to select whether to accurately measure compound unevenness in two directions in the first correction mode, or to quickly measure unevenness in only one direction in the second correction mode, depending on the situation. Therefore, it is possible to perform an appropriate type of calibration for suppressing unevenness in an image, and the efficiency of executing functions is improved.

[0091] In the above-described embodiment, A third correction mode may also be provided in which image unevenness is measured in the other of the first and second directions, and the image formation conditions are corrected based on the measurement results. With this configuration, it becomes possible to select, depending on the situation, whether to accurately measure compound unevenness in two directions, quickly measure unevenness in the first direction only, or quickly measure unevenness in the second direction only. In other words, more options are provided for calibration to suppress image unevenness, and an appropriate type can be selected from among them.

[0092] In the above-described embodiment, a user interface may be provided to allow a user to select one of the above-described correction modes. With this configuration, the user can flexibly select a desired balance between image quality and productivity, which are in a trade-off relationship, according to his or her needs.

[0093] In the above-described embodiment, when correction is performed in the second correction mode, an image may be formed under image forming conditions corrected based on the latest measurement result in one of the first and second directions and the past measurement result in the other direction. With this configuration, unevenness can be suppressed to the maximum extent based on the latest measurement result in one direction, while also sufficiently suppressing unevenness in the other direction as long as the unevenness does not fluctuate significantly, thereby forming an image of good quality. When measurement of image unevenness in the other direction has not been performed, unevenness can also be suppressed in the other direction by using data indicating the measurement result obtained at the manufacturing stage before the shipment of the device.

[0094] The above-mentioned embodiment and modified examples may be combined with each other in any manner. For example, in the first modified example, an example was described in which the measurement of image unevenness is performed using a read image of a test pattern in the first direction and using a potential sensor in the second direction. However, the measurement of image unevenness may be performed using a potential sensor in the first direction and using a read image of a test pattern in the second direction. When the image unevenness is measured using a read image of a test pattern formed on a sheet, the image unevenness that appears on the sheet due to the combined influence of various factors can be comprehensively captured and suppressed through density measurement. On the other hand, when the image unevenness is measured using a potential sensor, the consumption of developer can be reduced, and the user's effort in handling the sheet can be reduced, thereby making the work more efficient.

[0095] Also, a part of the process described above as being performed when the correction function is executed may be performed when the job is executed. Similarly, a part of the process described above as being performed when the job is executed may be performed when the correction function is executed. As an example, when the correction function is executed, a measurement result indicating a density difference or potential difference for each partial region may be stored as profile data, and a correction amount of the image forming conditions may be calculated based on the density difference or potential difference for each partial region when the job is executed. As another example, when the correction function is executed, the correction amounts (or density difference or potential difference) in the main scanning direction and the sub-scanning direction may be added, or the light amount for exposure, which is the sum of the reference light amount and the total correction amount, may be calculated, and the calculation result may be stored as profile data.

[0096] <7. Other embodiments> The above-mentioned embodiment can also be realized in the form of a process in which a program for realizing one or more functions is supplied to a system or device via a network or a storage medium, and one or more processors in a computer of the system or device read and execute the program. It can also be realized by a circuit (e.g., ASIC) for realizing one or more functions.

[0097] The invention is not limited to the above-described embodiments, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, the following claims are appended to apprise the public of the scope of the invention. [Explanation of symbols]

[0098] 100, 300: image forming apparatus, 1: photoconductor (image carrier), 2: charger (charging means), 3: exposure device (exposure means), 4: developer (developing means), 5: potential sensor (detection means), 10: image forming section, 80: first test pattern (first pattern), 90: second test pattern (second pattern), 110: scanner unit, 120: printer unit, 130: operation unit, 150: printer controller (control means), 154: non-volatile memory (storage section), P: sheet

Claims

1. An image forming unit; A control unit that controls an operation of the image forming unit; Equipped with The image forming unit includes: an image carrier that rotates around a rotation axis; A charging means for charging the image carrier; an exposure unit for exposing the charged image carrier to light to form a latent image on the surface of the image carrier; a developing means for developing the latent image on the surface of the image carrier with a developer to form a developer image; having In the first correction mode, the control unit measuring unevenness in an image in both a first direction parallel to the rotation axis and a second direction perpendicular to the first direction; correcting an image forming condition of the image forming unit based on the measurement results in the first direction and the second direction; In the second correction mode, measuring unevenness of an image in one of the first direction and the second direction; correcting the image forming conditions of the image forming unit based on the measurement result in the one direction; Image forming device.

2. In the third correction mode, the control unit measuring unevenness of the image in the other of the first direction and the second direction; correcting the image forming conditions of the image forming unit based on the measurement result in the other direction; The image forming apparatus according to claim 1 .

3. The image forming apparatus according to claim 2 , wherein the control unit corrects the image forming conditions of the image forming unit in a correction mode selected by a user from among the first correction mode, the second correction mode, and the third correction mode.

4. The image forming apparatus includes: a storage unit configured to store first profile data indicating a measurement result in the first direction and second profile data indicating a measurement result in the second direction; Further equipped with When the correction is performed in the second correction mode, the image forming unit forming an image under image formation conditions corrected based on a latest measurement result in the one direction of the first direction and the second direction and a past measurement result indicated by profile data corresponding to the other direction of the first direction and the second direction; The image forming apparatus according to claim 1 .

5. When the image forming unit performs the correction in the second correction mode, if the measurement of the unevenness of the image in the other direction of the first direction and the second direction has not been performed, forming an image under image forming conditions corrected based on the latest measurement result in one of the first direction and the second direction and the measurement result in the other direction obtained during a manufacturing stage of the image forming apparatus; The image forming apparatus according to claim 4 .

6. The control unit measures image unevenness in the first direction, controlling the image forming unit to form on a sheet an image of a first pattern used for measuring in the first direction; measuring image unevenness in the first direction using a read image of the first pattern obtained by optically reading an image of the first pattern on the sheet; The image forming apparatus of claim 1 .

7. The control unit measures the unevenness of the image in the second direction, controlling the image forming unit to form on a sheet an image of a second pattern used for measuring in the second direction; measuring image unevenness in the second direction using a read image of the second pattern obtained by optically reading an image of the second pattern on the sheet; The image forming apparatus according to claim 6 .

8. The image forming apparatus includes: A detection means for detecting the potential of the charged image carrier; Further equipped with The control unit measures the unevenness of the image in the second direction, measuring image unevenness in the second direction based on the distribution of the potential of the image carrier detected by the detection unit; The image forming apparatus according to claim 6 .

9. The control unit corrects the image forming conditions of the image forming unit, adjusting the amount of light from the exposure means so as to suppress image unevenness in both the first direction and the second direction; The image forming apparatus of claim 1 .

10. The control unit corrects the image forming conditions of the image forming unit, adjusting the amount of light of the exposure means so as to suppress unevenness in the image in the first direction; adjusting at least one of a charging voltage in the charging means and a developing voltage in the developing means so as to suppress unevenness in the image in the second direction; The image forming apparatus of claim 1 .

Images