Image forming device

Abstract

To provide an image formation apparatus which can select a type to be adjusted even in an operation mode of collectively performing adjustment of the plurality of types.SOLUTION: An image formation apparatus 100 includes a printer 300 which forms an image on a sheet P and a reader 200 which reads the image formed on the sheet P. The image formation apparatus 100 can collectively perform adjustment of a plurality of types to a plurality of characteristics of the printer 300. The image formation apparatus 100 generates a test chart by causing the printer 300 to form a test image for each type to be collectively adjusted on the sheet. The image formation apparatus 100 collectively performs adjustment on the basis of the reading result of the test chart by the reader 200. The type of adjustment to be collectively performed can be selected by a user.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus having a function for adjusting print conditions and a function for diagnosing image defects. [Background technology]

[0002] Electrophotographic image forming apparatuses have the function of generating a test chart and adjusting print conditions and diagnosing image defects based on the results of reading the test chart using a reader. Adjustments to print conditions include, for example, tone correction, in-plane density unevenness correction, print position adjustment, and transfer output adjustment (secondary transfer voltage adjustment). Image defects include the occurrence of dots, streaks, and the like. A test chart is formed by printing a test image on a sheet according to the adjustment and diagnosis details.

[0003] Gradation correction will be described as an example of adjusting printing conditions using a test chart. The gradation characteristics (density characteristics) of an image formed on a sheet by an image forming apparatus vary due to various factors. For example, gradation characteristics vary due to changes in environmental conditions such as temperature and humidity in the location where the image forming apparatus is installed, and due to changes in the parts of the image forming apparatus over time. For this reason, the image forming apparatus performs calibration to maintain the gradation characteristics. In the calibration, a test image is first formed on a sheet to generate a test chart for gradation correction. The image forming apparatus obtains the image density of the test image by reading the test chart with a reading device. The image forming apparatus creates a correction table so that the obtained image density becomes the target density. During image formation, gradation correction is performed using this correction table. A correction table is prepared for each type of sheet (basis weight, presence or absence of coating, whether or not it is recycled paper).

[0004] Patent Document 1 proposes a method for reducing the user's workload during calibration by continuously creating multiple test charts and continuously reading them using an automatic document feeder. Patent Document 2 proposes a method for collectively performing transfer output adjustment and print position adjustment, which require adjustment for each sheet type, on the same type of sheet. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2019-92034 [Patent Document 2] Japanese Patent Application Publication No. 2019-66721 Summary of the Invention [Problem to be solved by the invention]

[0006] In Patent Document 1, it is possible to perform gradation correction for screens with multiple resolutions (line rulings) at the same time. However, Patent Document 1 does not disclose performing multiple types of adjustments at the same time. In Patent Document 2, it is possible to perform multiple types of adjustments at the same time. Multiple types of adjustments are performed in a batch adjustment mode. However, depending on the state of the image forming apparatus and the user's purpose, unnecessary adjustments may be performed in the batch adjustment mode. For example, if gradation correction and in-plane density unevenness correction are performed but print position adjustment is not necessary, the batch adjustment mode will perform gradation correction, in-plane density unevenness correction, and print position adjustment. This results in wasted adjustment time due to unnecessary adjustments and an increase in the number of unnecessary test charts.

[0007] SUMMARY OF THE INVENTION In view of the above problems, it is a primary object of the present invention to provide an image forming apparatus that allows the user to select the type of adjustment to be made even in an operation mode in which multiple types of adjustment are made simultaneously. [Means for solving the problem]

[0008] The image forming apparatus of the present invention comprises: an image forming means for forming an image on a sheet; Involves forming a test image Multiple adjustment items and used to form the test image. Multiple paper types The adjustment items and paper types are listed in the table. The adjustment method is characterized by having a display means for displaying a selection screen for selection, and a control means for controlling the image forming means so as to form a test image to be used for the selected adjustment item on a sheet of the selected paper type. [Effects of the Invention]

[0009] According to the present invention, even in an operating mode in which multiple types of adjustments are performed at once, by selecting the type of adjustment to be performed, unnecessary adjustments can be avoided depending on the state of the image forming device and the user's purpose. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram illustrating the configuration of an image forming apparatus. [Figure 2] (a) and (b) are explanatory diagrams of a document scanner. [Figure 3] (a) to (d) are explanatory diagrams of the ADF. [Figure 4] FIG. [Figure 5] 10 is a flowchart showing a tone correction process. [Figure 6] 10A to 10C are diagrams illustrating examples of screens displayed during tone correction processing. [Figure 7] FIG. 10 is a diagram illustrating a test chart used for tone correction. [Figure 8] 10A and 10B are explanatory diagrams of a test chart for correcting density unevenness. [Figure 9] FIG. 4 is an explanatory diagram of a print position adjustment chart. [Figure 10] FIG. 10 is an explanatory diagram of a method for detecting the amount of misalignment of a printing position. [Figure 11] FIG. 10 is an explanatory diagram of a transfer output adjustment chart. [Figure 12] (a) and (b) are explanatory diagrams of a test chart for point-indication image diagnosis. [Figure 13] FIG. 10 is a diagram illustrating the relationship between the detected position of a streak and the cause of the streak. [Figure 14] FIG. 10 is an explanatory diagram of a double-sided reading correction chart. [Figure 15] FIG. 10 is a view showing an example of an operation screen for setting an operation mode. [Figure 16] FIG. 10 is a diagram showing an example of an execution acceptance operation screen. [Figure 17] 10 is a flowchart showing the processing of the image forming apparatus in a collective adjustment mode. [Figure 18] 10(a) to 10(c) are explanatory diagrams of an adjustment process that does not require a test chart. [Figure 19] 10A and 10B are diagrams illustrating examples of an execution acceptance operation screen according to the second embodiment. [Figure 20] 10A and 10B are flowcharts illustrating processing by an image forming apparatus in a collective adjustment mode according to a second embodiment. [Figure 21] FIG. 10 is an explanatory diagram of an example of changing a preselected adjustment item. [Figure 22] FIG. 13 is a view showing an example of an execution acceptance operation screen according to the third embodiment. [Figure 23] FIG. 13 is a view showing an example of an execution acceptance operation screen according to the fourth embodiment. [Figure 24] FIG. 2 is an explanatory diagram of the configuration of a print head. [Figure 25] (a) and (b) are explanatory diagrams of a rod lens array. [Figure 26] (a) and (b) are illustrations of a single rod lens in a fallen position. [Figure 27] FIG. 10 is a diagram illustrating a test chart for correcting vertical unevenness of a print head. [Figure 28] FIG. 10 is a diagram illustrating a test chart for correcting density unevenness caused by factors other than the print head. DETAILED DESCRIPTION OF THE INVENTION

[0011] An embodiment of the present invention will be described with reference to the drawings.

[0012] (First embodiment) 1 is a configuration diagram of an image forming apparatus according to this embodiment. The image forming apparatus 100 includes a reader 200, which is a reading device that reads an image from an original, and a printer 300 (printing device) that forms an image on a sheet P. The reader 200 includes a document scanner 210 and an automatic document feeder (hereinafter referred to as an "ADF: Auto Document Feeder") 220. The document scanner 210 is provided above the printer 300, and the ADF 220 is provided above the document scanner 210. The reader 200 reads an image printed on an original 101 and transmits image data representing the read image to the printer 300. The printer 300 can perform printing (image formation) on the sheet P based on the image data acquired from the reader 200.

[0013] In the figure, the sheet conveyance direction by the printer 300 is the PX direction, and the direction perpendicular to the PX direction is the Y direction. The paper feed direction of the ADF 220 is the SX2 direction, and the movement direction of the first mirror unit 104a and the second mirror unit 104b of the document scanner 210 is the SX1 direction.

[0014] The reader 200 reads an image of an original document fed by the ADF 220 and an image of an original document 101 placed on a platen glass 102 provided on the ADF 220 side of the document scanner 210. The document scanner 210 includes an image sensor 105 and a reader image processing unit 108. The reader image processing unit 108 converts an electrical signal generated by the image sensor 105 by reading the original document 101 into image data and transmits the image data to the printer 300.

[0015] The printer 300 includes a printer control unit 109. The printer control unit 109 acquires image data from a reader image processing unit 108 of the document scanner 210. The printer control unit 109 controls the process of forming an image on a sheet P based on the acquired image data. The printer 300 includes an image forming unit 10, which is an electrophotographic image forming engine that generates an image based on the image data. The image forming unit 10 includes four units for generating images of each color: yellow (Y), magenta (M), cyan (C), and black (K). The printer 300 includes an intermediate transfer belt 31 and a fixing unit 40. Note that by using only the black unit, the printer 300 can also be used for monochrome printing.

[0016] As shown in Figure 1, the image forming unit 10 has four photosensitive drums 11 corresponding to the colors yellow, magenta, cyan, and black, in that order from left to right. Around each photosensitive drum 11, a roller-shaped charger 12, an exposure device 13, a developing device 14, a primary transfer device 17, a drum cleaner 15, etc. are arranged. Below, the procedure for forming a black toner image will be explained as a representative of the four colors. The procedures for forming toner images of the other colors are similar.

[0017] When image formation begins, the photosensitive drum 11 rotates in the direction of the arrow. The charger 12 uniformly charges the surface of the photosensitive drum 11. The exposure unit 13 exposes the surface of the photosensitive drum 11 to laser light modulated according to image data obtained from the printer control unit 109, forming an electrostatic latent image. The developer 14 develops the electrostatic latent image by attaching toner to it, forming a toner image. The primary transfer unit 17 primarily transfers the toner image formed on the photosensitive drum 11 to the intermediate transfer belt 31. The drum cleaner 15 removes toner remaining on the photosensitive drum 11 after the primary transfer, thereby preparing the photosensitive drum 11 for the formation of the next image. The drum cleaner 15 in this embodiment is configured to contact a cleaning blade made of an elastic material against the surface of the photosensitive drum 11.

[0018] The exposure device 13 scans the surface of the photosensitive drum 11 in the Y direction with a laser beam. Therefore, the Y direction is the main scanning direction when the printer 300 forms an image. The main scanning direction of the reader 200 and the main scanning direction of the printer 300 are the same Y direction.

[0019] The intermediate transfer belt 31 is suspended between three rollers 34, 36, and 37 and rotates clockwise in the figure. The intermediate transfer belt 31 is an image carrier that carries the toner images transferred from the photosensitive drums 11, and transports the toner images toward the rollers 34 as it rotates. A full-color toner image is formed by superimposing the toner images of each color transferred from the photosensitive drums 11 onto the intermediate transfer belt 31. The rollers 34 and the secondary transfer device 27, which are positioned across the intermediate transfer belt 31, form a secondary transfer unit. A transfer cleaner 35 is provided between the rollers 36 and across the intermediate transfer belt 31.

[0020] The sheet P is fed from the paper feed cassette 20 or the manual feed tray 25. When the sheet P is fed from the paper feed cassette 20 or the manual feed tray 25, it is transported along the transport path to the registration roller pair 23. The registration roller pair 23 temporarily stops the transported sheet P and corrects any skew of the sheet P with respect to the transport direction. The registration roller pair 23 sends the sheet P to the secondary transfer unit in accordance with the timing at which the toner image carried on the intermediate transfer belt 31 is transported to the secondary transfer unit. The secondary transfer device 27 transfers (secondary transfer) the toner image on the intermediate transfer belt 31 to the sheet P. The transfer cleaner 35 removes any toner remaining on the intermediate transfer belt 31. This makes the intermediate transfer belt 31 ready for the next image to be formed.

[0021] The sheet P onto which the toner image has been transferred is transported to the fixing device 40 by the secondary transfer device 27. The fixing device 40 fixes the toner image onto the sheet P. The fixing device 40 fixes the toner image onto the sheet P, for example, by heating, melting, and pressurizing the toner image. In this way, an image is formed on the sheet P. The sheet P on which the image has been formed is discharged onto a discharge tray 64 by discharge rollers 63.

[0022] (document scanner) FIG. 2 is an explanatory diagram of the document scanner 210. FIG. 2(a) shows the configuration of the document scanner 210. FIG. 2(b) is a view of the document scanner 210 as seen from the ADF 220 side. The document scanner 210 includes a first mirror unit 104a, a second mirror unit 104b, an image sensor 105, a lens 115, a motor 116, a document size detection sensor 113, and a home position sensor 106 within its housing. The first mirror unit 104a includes a document illumination lamp 103 and a first mirror 107a. The second mirror unit 104b includes a second mirror 107b and a third mirror 107c. The first mirror unit 104a and the second mirror unit 104b are driven by the motor 116 and are movable in the SX1 direction.

[0023] The document scanner 210 can perform image reading in a first reading mode in which the document 101 transported by the ADF 220 is read, and in a second reading mode in which the document 101 placed on the document platen glass 102 is read. The first reading mode is sometimes called "skimming reading" or "ADF reading." The second reading mode is sometimes called "fixed reading" or "document platen reading."

[0024] The first reading mode has two types of reading methods: a sheet-through method and a fixed document method. In the sheet-through method, the rotation of the motor 116 causes the first mirror unit 104a and the second mirror unit 104b to move to a flow-reading position and stop there. The flow-reading position is a reading position when an image is read from the original 101 being transported by the ADF 220. While the ADF 220 is transporting the original 101 onto the platen glass 102, the image sensor 105 reads the image of the original 101. While the image is being read, the first mirror unit 104a and the second mirror unit 104b remain stopped at the reading position.

[0025] The document scanner 210 turns on the document illumination lamp 103 and irradiates the light onto the reading surface (the surface on which an image is printed) of the document 101. The first mirror 107a, the second mirror 107b, and the third mirror 107c deflect the reflected light (image light) of the light irradiated onto the document 101 and guide it to the lens 115. The lens 115 forms an image of the image light on the light receiving surface of the image sensor 105. The image sensor 105 converts the image light into an electrical signal. The reader image processing unit 108 acquires the electrical signal from the image sensor 105 and generates image data. During image reading, the first mirror unit 104a, the second mirror unit 104b, the image sensor 105, and the reader image processing unit 108 operate as described above. This image reading operation is the same regardless of the reading mode or reading method.

[0026] In the fixed original method, the ADF 220 transports the original 101 onto the platen glass 102 and stops the original 101 at a predetermined position on the platen glass 102. The first mirror unit 104a and the second mirror unit 104b read the image of the original 101 while moving in the SX1 direction by the motor 116. After the image has been read, the ADF 220 resumes transporting the original 101 and discharges it.

[0027] In the second reading mode, the motor 116 rotates, causing the first mirror unit 104a and the second mirror unit 104b to temporarily move to a home position where the home position sensor 106 is located. A single document is placed on the document glass 102 with its reading surface facing the document glass 102, and its position is fixed by the ADF 220. The document scanner 210 turns on the document illumination lamp 103 and irradiates the reading surface of the document 101 with light. As the first mirror unit 104a and the second mirror unit 104b move in the SX1 direction, the first mirror 107a, the second mirror 107b, and the third mirror 107c deflect the image light from the document 101 and guide it to the lens 115. The lens 115 focuses the image light on the light-receiving surface of the image sensor 105. The image sensor 105 converts the image light into an electrical signal. The reader image processing unit 108 acquires the electrical signal from the image sensor 105 and generates image data.

[0028] The document scanner 210 can detect the size (document size) of the original 101. The document scanner 210 of this embodiment detects the original size before reading an original image. The document scanner 210 first illuminates the edge of the original 101 with the original illumination lamp 103 and reads the reflected light from the original 101 with the image sensor 105. The image sensor 105 is, for example, a line sensor in which multiple photoelectric conversion elements are arranged in the Y direction. The image sensor 105 reads a predetermined number of lines. The line direction is perpendicular to the SX1 direction. The width (length in the Y direction) of the original 101 is obtained based on the reading results (electrical signals) of the predetermined number of lines by the image sensor 105. Because the image sensor 105 is configured with multiple photoelectric conversion elements arranged in the Y direction, the Y direction is the main scanning direction when the reader 200 reads an image. The SX direction is the sub-scanning direction perpendicular to the main scanning direction when the reader 200 reads an image.

[0029] Furthermore, the length of the original 101 (length in the SX1 direction) is detected based on the detection result of the original size detection sensor 113. At least one original size detection sensor 113 is arranged at a predetermined position in the SX1 direction inside the housing of the document scanner 210, and detects the presence or absence of the original 101 on the original platen glass 102 at that position. The original size detection sensor 113 is, for example, an infrared sensor, and is capable of outputting the presence or absence of the original 101 in binary. Based on the detection result of the original size detection sensor 113, it can be determined whether the length of the original 101 is longer than the position of the original size detection sensor 113. If it is desired to accurately detect the length of the original 101, multiple original size detection sensors 113 are arranged.

[0030] Based on the width and length of the document 101 thus detected, it is determined which of a plurality of predetermined standard sizes the document 101 is in. Also, based on the width and length of the document 101, it is determined in what orientation (portrait reading, landscape reading) the document 101 is placed on the document platen glass 102.

[0031] As shown in FIG. 2B, the platen glass 102 has a document size label 1230 arranged on its outer periphery, and a document alignment mark 1231 provided at a reference abutment portion on the far side in the Y direction. The document 101 is placed so that its apex abuts against the document alignment mark 1231. The document alignment mark 1231 serves as the reference for standard-sized documents. The document size detection sensor 113 of this embodiment is arranged on the Y direction side of the platen glass 102, at a position slightly farther from the document alignment mark 1231 than the length of an A4-sized document. Therefore, the document size detection sensor 113 cannot detect documents 101 of A4, B5, A5, or B6 sizes, but can detect documents 101 of A3, B4, A4R, and B5R sizes.

[0032] (ADF) FIG. 3 is an explanatory diagram of the ADF 220. FIG. 3(a) is an external perspective view of the ADF 220. FIG. 3(b) is an internal configuration diagram of the ADF 220. FIG. 3(c) is a view of a document stacking unit 301 (described later) seen obliquely from above. FIG. 3(d) is an internal configuration diagram of the document stacking unit 301 (described later). The ADF 220 includes the document stacking unit 301, a document feed unit 304, a document transport unit 308, and a reverse discharge unit 313.

[0033] The document stacking unit 301 has a document tray 302. The document tray 302 can hold one or more documents 101 on its stacking surface. The document tray 302 functions as a paper feed unit. The document stacking unit 301 is provided with a document indicator 303 that lights up when a document 101 is loaded on the document tray 302. The documents 101 loaded on the document tray 302 are transported one by one onto the document glass 102 by a document feed unit 304, pass over the document glass 102, and are discharged by a reversing document discharge unit 313 to a document discharge tray 321 of the reversing document discharge unit 313.

[0034] In the document feed unit 304, a pickup roller 306, a feed roller 307, and a pair of registration rollers 305 are provided along a transport path for the document 101. The pickup roller 306 is a roller that is rotatable and can move up and down. When feeding documents, the pickup roller 306 descends to contact the topmost document 101 in the stack of documents stacked on the document tray 302 and transports the document 101. The feed roller 307 transports the document 101 transported by the pickup roller 306 to the pair of registration rollers 305. The pickup roller 306 and the document feed roller 307 feed the document 101 one sheet at a time. The pair of registration rollers 305 is stopped when the leading edge of the document 101 reaches the pair of registration rollers 305. This is to correct any skew of the document 101. After correcting the skew, the pair of registration rollers 305 starts rotating and transports the document 101 to the document transport unit 308.

[0035] The document transport unit 308 includes a transport belt 309, a drive roller 310, a driven roller 311, and a plurality of pressure rollers 312. The document transport unit 308 transports the document 101 in the SX1 direction using the transport belt 309. The transport belt 309 is stretched across the drive roller 310 and the driven roller 311. The transport belt 309 is further pressed against the document glass 102 by the pressure rollers 312. The transport belt 309 transports the document 101 that has entered between the transport belt 309 and the document glass 102 by frictional force. As a result, the document 101 is transported on the document glass 102.

[0036] In the fixed document method of the first reading mode, the conveyor belt 309 stops when the document 101 reaches the reading position. After the document 101 is read by the first mirror unit 104a and the second mirror unit 104b, the conveyor belt 309 conveys the document 101 to the reverse discharge section 313. In this case, the first mirror unit 104a and the second mirror unit 104b read the stopped document 101 while moving in the SX1 direction.

[0037] In the sheet-through method of the first reading mode, even when the original 101 reaches the reading position, the conveyor belt 309 does not stop but continues to convey the original 101. In this case, the first mirror unit 104a and the second mirror unit 104b remain stopped and read the original 101 being conveyed. In other words, the original 101 is scanned by moving the original 101 instead of moving the first mirror unit 104a and the second mirror unit 104b.

[0038] The reversing and discharging unit 313 includes a reversing roller 314, a pair of conveying rollers 315, a reversing flapper 316, a discharging flapper 317, and a reversing roller 318. The reversing and discharging unit 313 reverses the original 101 conveyed from the original conveying unit 308, and discharges the original 101 onto a discharge tray 321 of a discharge stacking unit 320.

[0039] When the original 101 conveyed by the conveyor belt 309 of the original conveying section 308 enters the reverse discharge section 313, it is picked up by the reverse flapper 316 and conveyed to the reverse roller 314. The original 101 is sandwiched between the reverse roller 314, which rotates in a CCW (Counter Clock Wise) direction, and the opposing reverse roller 318, and conveyed to the pair of conveying rollers 315. When the rear end of the original 101 passes the discharge flapper 317, the discharge flapper 317 rotates in a CW (Clock Wise) direction. The reverse roller 314 also rotates in the CW direction. As a result, the original 101 is switched back and conveyed to the discharge tray 321 of the discharge stacking section 320.

[0040] When the image on the back side of the original 101 is read using the ADF 220, the original 101 is scanned on its front side, then inverted, and then scanned on its back side. This type of reading method is called "duplex inverted reading." After scanning the front side of the original 101, for example, the original 101 is transported from the original transport unit 308 to the inverted paper discharge unit 313, where the front and back sides are inverted. The inverted paper discharge unit 313 rotates the inverted rollers 314 in the counterclockwise direction after discharging a portion of the original 101 onto the paper discharge tray 321 in the same manner as when discharging. As a result, the original 101 enters the original transport unit 308 from the inverted paper discharge unit 313 with its front and back sides inverted, and the back side is scanned.

[0041] The ADF 220 may be configured to include a reading unit at a position facing the document scanner 210 across the transport path of the original 101. The reading sensor includes a light source that irradiates the original with light, and a reading sensor that receives light reflected by the original and generates image data. In such a configuration, the front side of the original 101 is read by the document scanner 210, and the back side is read by the reading unit. In this case, the original 101 does not need to be turned over by the reversing discharge unit 313. This method of simultaneously scanning the front and back sides of the original 101 while skimming is called "simultaneous double-sided reading."

[0042] (Document size detection by ADF) As shown in Fig. 3(c), a pair of regulating members 332 that can slide in the width direction (Y direction) of the original 101 are arranged on the original tray 302 of the original stacking unit 301. The regulating members 332 have the function of aligning the position in the width direction of the original 101 when it is fed by regulating both ends in the width direction of the original 101 placed on the original stacking unit 301 (original tray 302). The pair of regulating members 332 can move symmetrically in the width direction of the original 101, and regulate the original position so that the center in the width direction of the original 101 being fed is the feeding center.

[0043] The document stacking unit 301 is provided with a document width sensor 333 that can detect the position of the regulating member 332 (FIG. 3(d)). The document width sensor 333 detects the position of the regulating member 332 that moves according to the width of the document 101, thereby detecting the widthwise size of the document 101 placed on the document tray 302.

[0044] A plurality of (two in this embodiment) document length detection sensors 334a and 334b ​​are arranged in the document feed direction (SX2 direction) in document stacking unit 301. Document length detection sensors 334a and 334b ​​detect the presence or absence of document 101 on document stacking unit 301 (document tray 302). Based on the detection results of each of document length detection sensors 334a and 334b, the size of document 101 in the document feed direction (SX2 direction) is detected.

[0045] Based on the detection results of the document width sensor 333 and document length detection sensors 334a and 334b, the size and orientation (portrait or landscape) of the document placed on the document stacking unit 301 can be detected.

[0046] (Printer control unit) FIG. 4 is an explanatory diagram of the printer control unit 109. A CPU (Central Processing Unit) 401, which controls the overall operation of the image forming apparatus 100, the reader 200, and a semiconductor laser 410 are connected to the printer control unit 109. A memory 402 and an operation unit 400 are connected to the CPU 401. The memory 402 includes a read-only memory (ROM) and a random access memory (RAM), and stores control programs and various data for controlling the operation of the image forming apparatus 100. The CPU 401 controls the operation of the image forming apparatus 100 by executing the control programs stored in the memory 402. The operation unit 400 is a user interface including an input device and an output device. The input device includes key buttons such as a start key, a stop key, and a numeric keypad, as well as a touch panel. The output device includes a display and a speaker. In addition to the reader image processing unit 108 described above, the reader 200 includes a reader control unit 413. The reader control unit 413 controls the operation of each unit of the reader 200.

[0047] The printer control unit 109 includes a color processing unit 403, a gradation control unit 411, a dither processing unit 407, a PWM (Pulse Width Modulation) unit 408, and a laser driver 409. The printer control unit 109 converts each image data of green (G), red (R), and blue (B) into a PWM signal, and controls the light emission of a semiconductor laser 410 based on this PWM signal. The semiconductor laser 410 is provided in the exposure unit 13, and emits laser light that irradiates the photosensitive drum 11.

[0048] Image data output from the reader image processing unit 108 of the reader 200 is input to a color processing unit 403. The color processing unit 403 performs image processing and color processing on the input image data so that a desired output result (image) can be obtained if the output characteristics of the printer 300 were ideal. The color processing unit 403 expands the number of gradations of the image data from 8 bits to 10 bits to improve accuracy. The color processing unit 403 includes a lookup table, LUTid 404. The LUTid 404 is a luminance-density conversion table that converts luminance information contained in the image data into density information. The color processing unit 403 converts the luminance information of each of the R, G, and B image data into density information of each of the Y, M, and C image data using the LUTid 404. The Y, M, and C image data are input to a gradation control unit 411.

[0049] The gradation control unit 411 corrects the gradation characteristics of the image data acquired from the color processing unit 403 using correction conditions according to the type of sheet on which the image is formed. To this end, the gradation control unit 411 includes a UCR (Under Color Remove) unit 405 and a gamma correction unit 406 including a lookup table, LUTa. The gradation control unit 411 performs gradation correction on the Y, M, C, and K image data so as to obtain the desired output result (image) in accordance with the actual output characteristics of the printer 300. The UCR unit 405 limits the sum of the image data levels by restricting the integrated value (sum) of the image data for each pixel to be equal to or less than a specified value. If the sum exceeds the specified value, the UCR unit 405 performs under color removal (UCR), which replaces a specified amount of C, M, and Y image data with K image data, thereby reducing the sum of the image data levels.

[0050] The gamma correction unit 406 corrects the density characteristics (gamma characteristics) of the image data using LUTa. LUTa is a 10-bit conversion table (tone correction conditions) for correcting the density characteristics. The gradation characteristics of the image formed on the sheet of the printer 300 fluctuate due to environmental fluctuations and component wear. The gradation characteristics of the image also differ depending on the type of sheet. The CPU 401 updates LUTa by performing tone correction, thereby maintaining the gradation characteristics of the image at predetermined gradation characteristics. The printer 300 forms an image on the sheet P according to the image data corrected by the gamma correction unit 406. The memory 402 may store LUTa for each sheet type. The CPU 401 reads from the memory 402 the LUTa corresponding to the sheet type specified by the operation unit 400 and sets it in the gamma correction unit 406. LUTa is used when forming an image in accordance with copying an original or a print job from a host computer, but is not used when performing tone correction. The tone-corrected Y, M, C, and K image data is input to a dither processing unit 407 .

[0051] The dither processing unit 407 performs dither processing (halftone processing) on ​​the 10-bit image data for each of Y, M, C, and K after gradation correction, and converts it into a 4-bit signal. The PWM unit 408 performs pulse width modulation on the dithered signal to generate a PWM signal that is a control signal for the exposure unit 13. The PWM signal is input to a laser driver 409. The laser driver 409 controls the light emission of a semiconductor laser 410 in accordance with the PWM signal.

[0052] (Adjusting the characteristics of the image forming device) The image forming apparatus 100 can use a test chart to adjust the characteristics (printing conditions) of the printer 300 and perform image diagnosis. The image forming apparatus 100 reads the test chart with a reader 200 and performs characteristic adjustment and image diagnosis based on the read results. By adjusting the characteristics, multiple types of printing conditions are adjusted, such as gradation correction, in-plane density unevenness correction, print position adjustment, and transfer output adjustment (secondary transfer voltage adjustment). By image diagnosis, image defects such as dot / streak image diagnosis and double-sided reading color correction are diagnosed. The test chart is created by forming image data on a sheet P according to the type of characteristic adjustment or image diagnosis.

[0053] (tone correction) Gradation correction is performed when there is a decrease in the density or color reproducibility of an image formed by the printer 300. Gradation correction is performed by reading a test chart for gradation correction formed by the printer 300 with the reader 200, and creating an LUTa for correcting the density characteristics (γ characteristics) based on the reading results.

[0054] Fig. 5 is a flowchart showing the tone correction process. Fig. 6 is a view showing an example of a screen displayed on the display of the operation unit 400 during the tone correction process. Fig. 7 is a view showing an example of a test chart used for tone correction.

[0055] The CPU 401 acquires a signal indicating whether the user has selected the ADF reading or the platen reading reading mode from the operation unit 400 (S501). If the user has selected the ADF reading, the CPU 401 operates in the first reading mode. If the user has selected the platen reading, the CPU 401 operates in the second reading mode. FIG. 6(a) shows an example of an operation screen 700a when a reading mode is selected. The CPU 401 displays the operation screen 700a on the display of the operation unit 400. The operation screen 700a displays a button 701a that allows the user to select the ADF reading and a button 701b that allows the user to select the platen reading. The user selects the reading mode by selecting either the button 701a or the button 701b using the operation unit 400. The CPU 401 acquires a signal indicating the selected reading mode from the operation unit 400.

[0056] When the reading mode is selected, the CPU 401 sets the image formation conditions in the printer 300, and the printer 300 creates a test chart for gradation correction, as shown in FIG. 7 (S502). To do this, the CPU 401 sends a density signal of the test image for creating the test chart to the dither processing unit 407. At this time, LUTa is not used. When multiple test charts are required, the printing operation differs depending on whether the reading mode selected in S501 is ADF reading or platen reading. In the case of ADF reading, multiple test charts are printed consecutively. In the case of platen reading, printing of the test chart and platen reading are repeated for each sheet.

[0057] As shown in FIG. 7, test charts 801a and 801b include test images consisting of 10 gradations for each of the colors Y, M, C, and K. The 10-gradation images are formed, for example, by density signals of 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 100% for each color. The dithering processor 407 can apply multiple halftoning processes. For example, the dithering processor 407 has a low-line-count screen (160 lpi to 180 lpi) and a high-line-count screen (250 lpi to 300 lpi). Test chart 801a is a test chart to which a low-line-count screen has been applied. Test chart 801b is a test chart to which a high-line-count screen has been applied. The low-line-count screen is applied to prints, and the high-line-count screen is applied to copies. If the printer 300 has the capability to form images with three or more different screen rulings, the number of types of test charts may also be three or more. For the sake of convenience, the number of test charts formed when performing gradation correction is assumed to be one. In other words, the gradation correction process shown in FIG. 5 is performed for each screen for which the user performs gradation correction.

[0058] After creating the test chart, the CPU 401 reads the test chart using the reader 200 in accordance with the reading mode (S503).

[0059] When the reading mode is ADF reading, the CPU 401 displays a message prompting the user to place the test chart on the document tray 302 of the ADF 220 on the display of the operation unit 400. FIG. 6B shows an example of such a message screen 700b. The message screen 700b displays a message prompting the user to place the test chart on the document tray 302 and a button 701c for instructing the user to start reading. After placing the test chart on the document tray 302, the user presses the button 701c on the operation unit 400 to instruct the user to start ADF reading. This causes the CPU 401 to acquire an instruction to start reading by ADF reading from the operation unit 400.

[0060] When the CPU 401 receives the reading start instruction, it instructs the reader 200 to perform ADF reading. The reader 200 transports the test chart using the ADF 220 and reads the test chart using the document scanner 210. The reader image processing unit 108 of the document scanner 210 transmits image data including a luminance signal representing the reading result of the test chart to the printer control unit 109. If there are multiple test charts, the document scanner 210 continuously reads the multiple test charts continuously transported by the ADF 220. The reader image processing unit 108 continuously transmits image data including a luminance signal representing the reading result of the continuously read test charts to the printer control unit 109.

[0061] When the reading mode is platen reading, the CPU 401 displays a message prompting the user to place the test chart on the platen glass 102 on the display of the operation unit 400. FIG. 6C shows an example of such a message screen 700c. The message screen 700c displays a message prompting the user to place the test chart on the platen glass 102 and a button 701c instructing the user to start reading. The user opens the ADF 220 to expose the platen glass 102, and places the test chart on the platen glass 102 with the side on which the test image is formed facing the platen glass 102. The user then presses the button 701c on the operation unit 400 to instruct the user to start platen reading. As a result, the CPU 401 receives an instruction to start reading by platen reading from the operation unit 400.

[0062] When the CPU 401 receives the instruction to start reading, it instructs the reader 200 to read the document platen. The reader 200 reads the test chart on the document platen glass 102 using the document scanner 210. The reader image processing unit 108 of the document scanner 210 sends image data including a luminance signal representing the reading result of the test chart to the printer control unit 109. If there are multiple test charts, the document scanner 210 reads each test chart placed on the document platen glass 102. The reader image processing unit 108 sends image data including a luminance signal representing the reading result of each read test chart to the printer control unit 109.

[0063] The CPU 401 acquires a density signal of the test image based on the read result (luminance signal) (S504). The CPU 401 converts the luminance signal into a density signal using the LUTid 404 of the color processing unit 403. This allows density signals to be obtained for each of the 10 gradation images. The CPU 401 may switch the table of the LUTid 404 of the color processing unit 403 depending on the type of sheet used for the test chart.

[0064] The CPU 401 creates LUTa based on the density signal used to generate the test image and the density signal obtained from the reading result of the test chart (S505). The CPU 401 stores the created LUTa in the memory 402. The tone correction process is performed in this manner.

[0065] (In-plane density unevenness correction) In-plane density unevenness correction is performed to correct uneven image density within the area where an image is formed on the sheet P. Density unevenness in the main scanning direction (Y direction) of the printer 300 occurs due to, for example, uneven charging caused by deterioration of the charger 12 that charges the surface of the photosensitive drum 11, uneven exposure of laser light by the exposure device 13, or uneven development by the developer 14.

[0066] When correcting such density unevenness in the main scanning direction, a test chart for correcting density unevenness is created. FIG. 8 is an explanatory diagram of a test chart for correcting density unevenness. FIG. 8(a) shows an example of an A4-sized test chart 810. FIG. 8(b) shows an example of an A3-sized test chart 811. In both test charts 810 and 811, a band-shaped test image is formed in the main scanning direction (Y direction) using 50% density signals for each of the colors yellow, magenta, cyan, and black. The band-shaped test image is formed so that the main scanning direction is the longer side of the band, regardless of the sheet size.

[0067] It is recommended that the test charts 810, 811 for correcting density unevenness be read by setting them so that the main scanning direction (Y direction) of the test charts 810, 811 is parallel to the SX1 or SX2 direction of the reader 200. This is because the image sensor 105 has photoelectric conversion elements arranged in a line in the main scanning direction, and the characteristics of the photoelectric conversion elements vary depending on the position in the Y direction. By reading the test charts 810, 811 with the main scanning direction set to the SX1 or SX2 direction of the reader 200, the reader 200 can suppress differences in characteristics due to the position of the photoelectric conversion elements of the image sensor 105. Note that if the effect of differences in characteristics due to the position of the photoelectric conversion elements of the image sensor 105 is small, there is no need to limit the reading direction of the test charts 810, 811 for correcting density unevenness.

[0068] Density unevenness correction is performed by feedback correcting the exposure amount of laser light in the main scanning direction (Y direction) so as to cancel out density unevenness in the main scanning direction (Y direction) detected from the reading result of the test chart for density unevenness correction. Reading of the test chart for density unevenness correction is performed by the reader 200 in ADF reading (first reading mode) or platen reading (second reading mode), similar to gradation correction.

[0069] (Print position adjustment) Print position adjustment is performed when misalignment of the print position occurs due to sheet expansion / contraction, cutting accuracy, or sheet storage conditions. The amount of misalignment of the print position depends heavily on the physical properties of the sheet being printed. For this reason, it is preferable to adjust the print position according to the type of sheet.

[0070] 9 is an explanatory diagram of a print position adjustment chart, which is a test chart for adjusting the print position. Image data of the print position adjustment chart 601 is stored in memory 402. When printing the print position adjustment chart 601, the CPU 401 reads the image data of the print position adjustment chart 601 from memory 402 and transfers it to the printer control unit 109.

[0071] The print position adjustment chart 601 is configured by forming marks 620 at predetermined positions on the front and back of the sheet. In this embodiment, a total of eight marks 620 are formed on the four corners of both sides of the print position adjustment chart 601. The marks 620 are formed in a color that has a large difference in reflectance with respect to the color of the sheet. For example, black marks 620 are formed on a white sheet.

[0072] An image 610 for identifying the transport direction during reading and an image 612 for identifying the front and back are printed on the front side of the print position adjustment chart 601. An image 611 for identifying the transport direction during reading and an image 613 for identifying the front and back are printed on the back side of the print position adjustment chart 601. That is, when aligning images on both sides, the images 610 and 612 are printed on the front side of the print position adjustment chart 601, and the images 611 and 613 are printed on the back side. When adjusting the position of an image on one side, the images 610 and 612 are printed on the front side of the print position adjustment chart 601.

[0073] Images 610 and 611 for identifying the transport direction of the print position adjustment chart 601 only need to be printed when the print position adjustment chart 601 is read using ADF reading, and do not need to be printed when the print position adjustment chart 601 is read using fixed reading. The images 610 and 611 are arrows that allow the user to identify the transport direction of the print position adjustment chart 601. Images 612 and 613 are characters that allow the user to identify the front and back sides of the print position adjustment chart 601.

[0074] When the marks 620 are formed in ideal positions, they are formed at a position a predetermined distance from the sheet edge of the print position adjustment chart 601. By measuring the positions of the marks 620 printed on the front side of the print position adjustment chart 601, the amount of misalignment of the print position on the front side of the sheet is detected. By measuring the positions of the marks 620 printed on the back side of the print position adjustment chart 601, the amount of misalignment of the print position on the back side of the sheet is detected. By measuring the relative positions of each mark 620 printed on both sides of the print position adjustment chart 601, the amount of misalignment of the print position on the back side relative to the print position on the front side, or the amount of misalignment of the print position on the front side relative to the print position on the back side, is detected.

[0075] When adjusting the print position using the print position adjustment chart 601, distances a to j on the front side and distances k to r on the back side are measured to determine the position of the mark 620. Distance a is the length of the print position adjustment chart 601 in the sub-scanning direction, and distance b is the length of the print position adjustment chart 601 in the main scanning direction. The ideal lengths of distance a and distance b are registered in advance in the image forming apparatus 100. Distances c to r are each the length from the mark 620 to the nearest edge of the print position adjustment chart 601.

[0076] There are two methods for measuring the distances a to r: manual measurement and automatic measurement. In the manual measurement method, the user actually measures the lengths of the distances a to r by placing a ruler on the print position adjustment chart 601. The user inputs the actually measured lengths into the image forming apparatus 100 using the operation unit 400. In the automatic measurement method, the print position adjustment chart 601 is read (scanned) by the reader 200. The CPU 401 analyzes image data that is the reading result of the print position adjustment chart 601 and detects the density difference for each pixel of the read image. The CPU 401 detects the edge of the print position adjustment chart 601 and the edge of the mark 620 (i.e., the boundary between the background of the print position adjustment chart 601 and the mark 620) from this density difference. The CPU 401 calculates the distances a to r based on the detected edge of the print position adjustment chart 601 and the edge of the mark 620.

[0077] 10 is an explanatory diagram of a method for detecting the amount of misalignment of the print position from the measured distances a to r. In this embodiment, a calculation table 1300 is used to detect the amount of misalignment of the print position. The calculation table 1300 is stored in the memory 402. The CPU 401 calculates the amount of misalignment of the print position based on the calculation table 1300.

[0078] The calculation table 1300 is defined by measurement values ​​1310, ideal values ​​1311, and print position misalignment amounts 1312 for the "lead position," "side position," "main scanning magnification," and "sub scanning magnification" on the front and back sides of the print position adjustment chart 601. The print position misalignment amount 1312 is expressed by a conversion formula using the measurement values ​​1310 and the ideal values ​​1311.

[0079] The measurement value 1310 of the "lead position" on the surface of the print position adjustment chart 601 is calculated from the actual measurement values ​​of distances c and e in Figure 9 using the conversion formula shown in the calculation table 1300. The lead position is the average value of the distance from the edge of the print position adjustment chart 601 at the beginning of the sheet transport direction to the corresponding mark 620. The measurement value 1310 of the "side position" on the front surface of the print position adjustment chart 601 is calculated from the actual measurement values ​​of the distances f and j in Fig. 9 using the conversion formula shown in the calculation table 1300. The side position is the average value of the distance from the edge of the print position adjustment chart 601 on the left side in the sheet transport direction to the corresponding mark 620. As shown in the calculation table 1300, the ideal values ​​1311 for the "lead position" and "side position" are each 1 cm. That is, the marks 620 are ideally printed at positions 1 cm away from the corresponding edges of the print position adjustment chart 601.

[0080] The measured value 1310 of the "main scanning magnification" on the surface of the print position adjustment chart 601 is calculated from the actual measured values ​​of the distances b, d, f, h, and j in Fig. 9 using the conversion formula shown in the calculation table 1300. The main scanning magnification is the average value of the distances between the marks 620 aligned on the same scanning line in the main scanning direction. The measured value 1310 of the "sub-scanning magnification" on the surface of the print position adjustment chart 601 is calculated from the actual measured values ​​of the distances a, c, e, g, and i in Fig. 9 using the conversion formula shown in the calculation table 1300. The sub-scanning magnification is the average value of the distances between marks 620 lined up on the same scanning line in the sub-scanning direction. As shown in the calculation table 1300, the ideal value 1311 of the "main scanning magnification" is a value obtained by subtracting 2 [cm] from the sheet length 512 in the main scanning direction of each sheet registered in advance in the image forming apparatus 100. Similarly, the ideal value 1311 of the "sub scanning magnification" is a value obtained by subtracting 2 [cm] from the sheet width 512 in the sub scanning direction of each sheet registered in advance in the image forming apparatus 100.

[0081] The positional deviation amount 1312 on the back side of the print position adjustment chart 601 is calculated using the same conversion formula as for the front side.

[0082] As shown in the calculation table 1300, the misalignment amount 1312 of the print position for each of the "lead position," "side position," "main scanning magnification," and "sub scanning magnification" is calculated using the corresponding measurement value 1310 and ideal value 1311. The misalignment amount 1312 of the print position for the "lead position" and "side position" is calculated by subtracting the ideal value 1311 from the measurement value 1310 (unit: [mm]). The misalignment amount 1312 of the print position for the "main scanning magnification" and "sub scanning magnification" is calculated by subtracting the ideal value 1311 from the measurement value 1310 and dividing the result by the ideal value 1311 (unit: [%]). The misalignment amount 1312 of the print position calculated as above is saved in the memory 402 as sheet attribute data.

[0083] (Transfer output adjustment) Transfer output adjustment (secondary transfer voltage adjustment) is performed when a transfer defect occurs during secondary transfer. In transfer output adjustment, the transfer output (secondary transfer voltage) is adjusted based on the results of reading a test chart for transfer output adjustment by a reader 200. A secondary transfer voltage is applied to the secondary transfer device 27 during secondary transfer, and the toner image on the intermediate transfer belt 31 is transferred to the sheet P by the electric field generated by the secondary transfer voltage. The optimal voltage value for the secondary transfer voltage varies depending on the physical characteristics (surface properties, sheet resistance) of the sheet onto which the toner image is transferred. For this reason, it is preferable to adjust the secondary transfer voltage according to the type of sheet.

[0084] 11 is an explanatory diagram of a transfer output adjustment chart, which is a test chart for adjusting the transfer output. Image data of a test image of the transfer output adjustment chart 830 is stored in memory 402. When generating the transfer output adjustment chart 830, the CPU 401 reads the image data of the transfer output adjustment chart 830 from memory 402 and transfers it to the printer control unit 109.

[0085] The transfer output adjustment chart 830 has a test image 830a formed on the front side of the sheet, and a test image 830b formed on the back side of the sheet. Each test image 830a, 830b is composed of seven patch images: patch images of 100% density signals for yellow (Y), magenta (M), cyan (C), and black (K), and patch images of red (R), green (G), and blue (B). The red patch image is composed of a yellow image and a magenta image each formed with a 100% density signal, which are overlapping. The green patch image is composed of a yellow image and a cyan image each formed with a 100% density signal, which are overlapping. The blue patch image is composed of a magenta image and a cyan image each formed with a 100% density signal, which are overlapping.

[0086] The seven-color patch images are each formed using five levels (-2, -1, 0, +1, +2) of secondary transfer voltage values. The five levels of secondary transfer voltage are, for example, 2000 [V], 2250 [V], 2500 [V], 2750 [V], and 3000 [V]. Here, test images 830a and 830b are formed by changing the secondary transfer voltage at the same level on the front and back sides of transfer output adjustment chart 830, but the level of the secondary transfer voltage may also be changed on the front and back sides.

[0087] The test images 830a and 830b on both sides of the transfer output adjustment chart 830 are read by the reader 200 using ADF reading (first reading mode) or platen reading (second reading mode). The reader 200 obtains the luminance value of each patch image by reading the transfer output adjustment chart 830. In this embodiment, the secondary transfer voltage level at which the average luminance value of each of yellow, magenta, cyan, black, red, green, and blue is smallest is set as the transfer output adjustment value. Note that the adjustment values ​​may be different for the front and back sides. Furthermore, instead of the average luminance values ​​of yellow, magenta, cyan, black, red, green, and blue, the comparison may be weighted by color.

[0088] (Point and muscle imaging diagnosis) The point / indication image diagnosis is performed when determining whether the cause of an image defect such as a point or a streak occurring in an image formed on a sheet is the reader 200 or the printer 300.

[0089] 12 is an explanatory diagram of a test chart for point and indication image diagnosis used in "image defect diagnosis including detection of ADF reading streaks." A test chart 820 for image diagnosis includes a white background 821 where no image is formed, and strip-shaped test images 822, 823, 824, and 825 formed with 50% density signals of each of the colors yellow, magenta, cyan, and black.

[0090] Fig. 12(a) illustrates a test chart 820 for point-indication image diagnosis in which test images 822, 823, 824, and 825 are formed on an A4 sheet. In this test chart 820, the test images 822, 823, 824, and 825 are formed so that the long sides of the strips are parallel to the Y direction. Fig. 12(b) illustrates a test chart 820 for point-indication image diagnosis in which the test images 822, 823, 824, and 825 are formed on an A4R sheet. In this test chart 820, the test images 822, 823, 824, and 825 are formed so that the short sides of the strips are parallel to the Y direction. When reading the test chart 820 for point / indication image diagnosis, whether the test chart is A4 or A4R, it is preferable that the test chart 820 be set in the document tray 302 with its longitudinal direction (the long side of the sheet) parallel to the Y direction.

[0091] When determining whether or not there is an ADF streak, if a streak is detected both before the test chart 820 is transported to the reading position of the reader 200 and in the white background 821 of the test chart 820, the streak will be detected regardless of whether or not there is a test chart 820. In this case, it is determined that the streak is caused by the reader 200. If a streak is not detected before the test chart 820 is transported to the reading position of the reader 200, but is detected in the white background 821 of the test chart 820, it is determined that the streak is not caused by the reader 200 but is in the white background 821 of the test chart 820. In this case, it is determined that the streak is caused by the printer 300. Figure 13 is an explanatory diagram of the relationship between the streak detection position and the cause of the streak.

[0092] In order to distinguish between streaks caused by the reader 200 and streaks caused by the printer 300, it is preferable to perform image diagnosis on a wider reading area (Y direction) of the reader 200. For this purpose, the test chart 820 is set with its longitudinal direction (long side of the sheet) parallel to the Y direction.

[0093] (Double-sided scanning color correction) The double-sided reading correction is performed for the purpose of adjusting the read colors on the front and back sides of the sheet when parts of the reader 200 are replaced or maintenance is performed.

[0094] FIG. 14 is an explanatory diagram of a double-sided reading correction chart, which is a test chart for double-sided reading correction. The test image of the double-sided reading color correction chart 850 is composed of patch images of different densities for each color: yellow (Y), magenta (M), cyan (C), black (K), red (R), green (G), and blue (B). In this embodiment, the patch images have five gradations of density signals: 20%, 40%, 60%, 80%, and 100%. The test image includes 35 patch images. The double-sided reading color correction chart 850 of this embodiment is a two-sheet test chart in which test images are printed consecutively on one side of two sheets.

[0095] The double-sided reading correction is performed as follows. The printer 300 creates two double-sided reading color correction charts 850 by successively forming test images on one side of the same type of sheet. One of the two double-sided reading color correction charts 850 is set in the document tray 302 of the ADF 220 with the side on which the test image is formed facing up. Next, the other double-sided reading color correction chart 850 is set in the document tray 302 with the side on which the test image is formed facing down. The two double-sided reading color correction charts 850 are set in the document tray 302 one on top of the other.

[0096] The two double-sided reading color correction charts 850 are successively read using the ADF (first reading mode). This obtains the luminance values ​​of the patch images of each of the two double-sided reading color correction charts 850. A coefficient is derived to correct the reading result of one of the double-sided reading color correction charts 850 so that the luminance values ​​of the patch images of the first double-sided reading color correction chart 850 and the second double-sided reading color correction chart 850 are close to each other. This coefficient is stored in memory 402 as a double-sided reading color correction coefficient and is used for double-sided reading color correction.

[0097] (Bulk adjustment mode) The above-described adjustments and image diagnostic processes can be executed collectively by user instruction. The operating mode in which the processes are executed collectively is called a "collective adjustment mode." In this embodiment, even when the user instructs execution of the collective adjustment mode, the type (item) of correction to be performed can be selected, thereby preventing the execution of adjustments or image diagnostic processes of types not intended by the user.

[0098] 15 is a view showing an example of an operation screen for setting the operation mode of image forming apparatus 100. This operation screen 770 is displayed on the display of operation unit 400. By selecting a button displayed on operation screen 770 using operation unit 400, the user can instruct image forming apparatus 100 to execute a process associated with the selected button.

[0099] When the collective adjustment button 771 on the operation screen 770 is selected, the display on the operation unit 400 switches to an execution acceptance operation screen for accepting execution of collective adjustment. When the gradation correction button 772 or the print position adjustment button 773 on the operation screen 770 is selected, the display on the operation unit 400 switches to an operation screen for individually performing gradation correction or print position adjustment using the method described above.

[0100] Fig. 16 is a view showing an example of an execution reception operation screen. Execution reception operation screen 750 includes an adjustment item selection button 751a for selecting whether or not to perform adjustment for each adjustment item, a batch adjustment execution button 752 for instructing the execution of batch adjustment, and a paper type to be adjusted button 753 for selecting the type of sheet to be adjusted. Fig. 17 is a flowchart showing the processing of image forming apparatus 100 in batch adjustment mode.

[0101] When the collective adjustment button 771 is selected from the operation screen 770 in Fig. 15, the CPU 401 displays the execution acceptance operation screen 750 in Fig. 16 on the display of the operation unit 400. When the collective adjustment execution button 752 is selected, the CPU 401 acquires information on the sheet type currently selected by the paper type button 753 (S551). This determines the sheet type to be adjusted in the collective adjustment mode.

[0102] In this embodiment, plain paper is preset as the sheet to be adjusted. This is because plain paper is assumed to be the most frequently used sheet in the image forming apparatus 100 of this embodiment. The preset sheet may be the most frequently used sheet type according to the print history of the image forming apparatus 100, or the most frequently used sheet type in the most recent month. When performing collective adjustments on sheets of a type other than the preset type, the user can operate the paper type button 753 to change to a sheet type other than the preset type (recycled paper, thin paper, thick paper, coated paper, etc.). In other words, when performing collective adjustments using a preset type (for example, plain paper), the user operation of selecting a sheet can be omitted. Note that if there are no adjustments to be changed depending on the sheet type, the paper type button 753 is not displayed. Furthermore, adjustment items to be collectively adjusted may be set according to the sheet type.

[0103] After the type of sheet to be adjusted in the batch adjustment mode is determined, the CPU 401 acquires information on the adjustment item selected by the adjustment item selection button 751a at that time when the batch adjustment execution button 752 on the execution reception operation screen 750 is selected (S552), thereby determining the adjustment item to be adjusted in the batch adjustment mode.

[0104] In the example of FIG. 16, three adjustment items, "in-plane density unevenness correction," "tone correction: print," and "tone correction: copy," are preset. These preset adjustment items are adjustment items that can cause changes in image quality due to changes in environmental conditions such as temperature and humidity in the installation location of image forming apparatus 100, and changes over time in parts of printer 300. These adjustment items need to be adjusted periodically. These three adjustment items are preset to reduce the number of adjustment item selection operations by the user during regular maintenance work.

[0105] Here, "◯" in FIG. 16 indicates that adjustment will be performed, and "-" indicates that adjustment will not be performed. The user can cancel the execution of an adjustment item from the batch adjustment by deselecting it using the adjustment item selection button 751a, and can add the execution of that adjustment item to the items for batch adjustment by selecting it using the adjustment item selection button 751a. A "-" is displayed for items that have been canceled, and an "◯" is displayed for items that have been added. If the items to be batch adjusted are not to be changed, the user can omit the operation of selecting the adjustment items to be batch adjusted.

[0106] After the adjustment items are selected, the CPU 401 receives an instruction to execute the batch adjustment by selecting the batch adjustment execution button 752 on the execution reception operation screen 750 (S553). Upon receiving the execution instruction, the CPU 401 generates a test chart by continuously printing test images corresponding to the selected adjustment items on the selected type of sheet (S554). In this embodiment, a test chart 810 for density unevenness correction, a test chart 801a for gradation correction for printing, and a test chart 801b for gradation correction for copying are generated. The test images of the test charts 810, 801a, and 801b are all printed on A4-sized plain paper with the long side of the A4 paper in the Y direction (A4 portrait orientation).

[0107] Alternatively, the test images may be printed in a different orientation, with the test image of test chart 810 in A4 portrait orientation and the test images of test charts 801a and 801b in an orientation (A4R) where the short side of the A4 size is parallel to the Y direction. Alternatively, the sizes of the sheets to be printed may be different, with test chart 811 generated on an A3-sized sheet and test charts 801a and 801b generated on A4-sized sheets. The order in which test charts for each adjustment item are generated may be arbitrary. However, if the paper type button 753 is displayed on the execution reception operation screen 750, the test chart is generated on a sheet of the selected type. In other words, in this embodiment, all sheets used for test charts in the batch adjustment mode are the same type.

[0108] The generated test charts 810, 801a, and 801b are all placed on the document tray 302 of the ADF 220. When the CPU 401 receives an instruction to start reading from the operation unit 400, it reads all of the test charts 810, 801a, and 801b consecutively by ADF reading (S555). The batch adjustment mode is an adjustment mode in which multiple types of test charts are generated at once and read consecutively, thereby reducing the workload during adjustment compared to adjusting multiple types individually. In the batch adjustment mode, by using ADF reading, it is possible for the user to perform only one operation to read multiple types of test charts for adjustment.

[0109] Note that ADF reading can be performed continuously even if test charts of multiple paper sizes are loaded on the document tray 302. Therefore, it is not necessary to align the reading directions of the test charts when loading them. However, when the test chart 810 is included in the test charts generated in the collective adjustment mode, it is preferable that the test chart 810 be placed on the document tray 302 so that the PX direction is the SX2 direction, as described above. Furthermore, when the test chart 820 for image diagnosis is included in the test charts generated in the collective adjustment mode, it is preferable that the test chart 820 be placed on the document tray 302 so that the longitudinal direction (long side) is parallel to the Y direction.

[0110] Based on the results of reading the test charts 810, 801a, and 801b, the CPU 401 reflects the adjustment results for each adjustment item through the above-described process (S556). This completes the adjustment process for one or more adjustment items in the batch adjustment mode.

[0111] As described above, in the image forming apparatus 100 of this embodiment, the user can select the items to be adjusted collectively, and can adjust only the necessary items. Furthermore, by setting the adjustment items in advance, it is possible to omit the user's operation of selecting the items. Furthermore, by setting in advance the type of sheet to be used to create the test chart, it is also possible to omit the user's operation of selecting the sheet type.

[0112] (Second embodiment) The configuration of the image forming apparatus 100 of the second embodiment is the same as that of the first embodiment. In the first embodiment, in the collective adjustment mode, only the adjustment items selected by the user from multiple types of adjustment items using test charts are executed, thereby performing collective adjustment of only the adjustments required by the user. In contrast, in the second embodiment, a case will be described in which some adjustments in the collective adjustment mode do not require a test chart. In adjustments that do not require a test chart, adjustments are made based on the detection results of a test image formed on the intermediate transfer belt 31 detected by a sensor. In the second embodiment, adjustment items that do not require a test chart are added. For example, tone correction and color misalignment adjustment that do not use a test chart are added as adjustment items. FIG. 18 is an explanatory diagram of adjustment processing that does not require a test chart.

[0113] 18(a) is an explanatory diagram of a sensor that detects a test image formed on the intermediate transfer belt 31. This sensor 900 is an optical sensor that can detect a test image 904 using specularly reflected light and diffusely reflected light. The sensor 900 detects a test image for gradation correction using specularly reflected light. The sensor 900 detects a test image for color misregistration adjustment using diffusely reflected light. The sensor 900 is provided, for example, near the intermediate transfer belt 31, downstream of the multiple image forming units 10 in the rotation direction of the intermediate transfer belt 31.

[0114] The sensor 900 includes a light-emitting unit 901 that irradiates a test image 904 on the intermediate transfer belt 31, a light-receiving unit 902 that receives specularly reflected light from the test image 904, and a light-receiving unit 903 that receives diffusely reflected light from the test image 904. The light-emitting unit 901 includes a light-emitting element such as an LED (Light Emitting Diode). The light-receiving units 902 and 903 include light-receiving elements such as photodiodes.

[0115] The light-emitting unit 901 emits light such that the optical axis is at a 45-degree angle with respect to the normal to the intermediate transfer belt 31. The light-receiving unit 902 is positioned to receive the specularly reflected light of the light emitted from the light-emitting unit 901 by the intermediate transfer belt 31. The light-receiving unit 902 receives the specularly reflected light from the surface (base) of the intermediate transfer belt 31 and the test image 904, and outputs an output signal having a value corresponding to the amount of specularly reflected light received. The density of the test image 904 is detected based on the value of the output signal. The light-receiving unit 903 is positioned to receive the diffusely reflected light of the light emitted from the light-emitting unit 901 by the intermediate transfer belt 31. The light-receiving unit 903 receives the diffusely reflected light from the surface (base) of the intermediate transfer belt 31 and the test image 904, and outputs an output signal having a value corresponding to the amount of specularly reflected light received. The presence or absence of the test image 904 is determined based on a change in the value of the output signal. The position of the test image is detected based on the presence or absence of the test image 904.

[0116] (tone correction) FIG. 18(b) illustrates a test image for tone correction when a test chart is not used. This test image includes multiple patch images with different gradations for each of the colors yellow, magenta, cyan, and black. In this embodiment, 10-level patch images 905Y1, 905Y2, 905Y3, ... 905K8, 905K9, and 905K10 are formed for each color using density signals in 10 gradations ranging from 10% to 100% in 10% increments. The density of each patch image 905Y1, 905Y2, 905Y3, ... 905K8, 905K9, and 905K10 is detected based on the result of receiving specularly reflected light (output signal value) by the light receiving unit 902 of the sensor 900. For example, a table showing the relationship between the output signal value and the density value is prepared in advance, and the density corresponding to the output signal value is detected by referring to the table. Based on the density of each of the detected patch images 905Y1, 905Y2, 905Y3, . . . 905K8, 905K9, 905K10, tone correction is performed by generating and updating LUTa that corrects tone similarly to the tone correction described above.

[0117] (Color misalignment adjustment) FIG. 18(c) illustrates a test image for adjusting color misalignment when a test chart is not used. This test image includes vertical line patch images 906Y, 906M, 906C, and 906K and diagonal line patch images 907Y, 907M, 907C, and 907K. Patch images 906Y, 906M, 906C, and 906K are straight lines extending in the main scanning direction. Patch images 907Y, 907M, 907C, and 907K are straight lines inclined at a predetermined angle (e.g., 45°) with respect to the main scanning direction. Patch images 906Y and 907Y are yellow images. Patch images 906M and 907M are magenta images. Patch images 906C and 907C are cyan images. Patch images 906K and 907K are black images.

[0118] Patch images 906Y, 906M, 906C, and 906K are used to measure the amount of color misregistration correction between colors in the sub-scanning direction. The amount of color misregistration correction between colors in the main scanning direction is measured from the relative distances from patch images 906Y, 906M, 906C, and 906K to patch images 907Y, 907M, 907C, and 907K. Color misregistration is corrected by adjusting the relative positions of the yellow, magenta, cyan, and black images based on the measured amounts of color misregistration in the sub-scanning direction and main scanning direction.

[0119] FIG. 19 is an example view of an execution acceptance operation screen of the second embodiment. In FIG. 19(a), an adjustment item using the sensor 900 has been added to the execution acceptance operation screen of the first embodiment (see FIG. 16). The types of adjustment item selection button 751b1 include "○" indicating that adjustment will be performed and "-" indicating that adjustment will not be performed, as well as "▲ (triangle)" indicating that adjustment will be performed using the sensor 900. As shown in FIG. 19(b), "sheet use" and "sheet not use" are displayed side by side, but only one of these may be displayed. In this embodiment, "tone correction: print" is an adjustment that uses a sheet, and "tone correction: copy" is an adjustment that does not use a sheet. Furthermore, "color misalignment adjustment" is an adjustment that does not use a sheet.

[0120] Fig. 20 is a flowchart showing the processing of the image forming apparatus 100 in the collective adjustment mode of the second embodiment. Fig. 20(a) and Fig. 20(b) differ only in the order of processing. The processing for selecting the sheet type, selecting the adjustment items, and receiving an instruction to perform adjustment is the same as the processing from S551 to S553 in Fig. 17 (S561 to S563).

[0121] In the process of FIG. 20(a), upon receiving an instruction to perform adjustment, the CPU 401 performs adjustment using the sensor 900 before generating a test chart (S564). The CPU 401 reflects the results of the adjustment using the sensor 900. Thereafter, the CPU 401 generates a test chart (S565). Therefore, adjustment using the test chart can be performed after reflecting the adjustment using the sensor 900. For example, if density unevenness correction is performed after gradation correction using the sensor 900, density unevenness correction using the density unevenness correction test charts 810 and 811 can be performed at a density suitable for density unevenness correction. Therefore, the accuracy of density unevenness adjustment is improved compared to when gradation correction is not performed. Thereafter, the CPU 401 reads the test chart in the same manner as in S554 to S556 of FIG. 17 and performs various processes to reflect the adjustment results based on the read results (S565 to S567).

[0122] In the process of FIG. 20(b), upon receiving an instruction to perform adjustment, the CPU 401 generates and reads a test chart through processes similar to S554 and S555 of FIG. 17 before performing adjustment using the sensor 900 (S565, S566). Then, the CPU 401 performs adjustment using the sensor 900 through processes similar to S564 of FIG. 20(a) (S564). Therefore, the last operation performed by the user when performing the batch adjustment mode is to input an instruction to read the test chart using the ADF. The process of FIG. 20(b) can reduce the user's time compared to the process of FIG. 20(a) by the time it takes the CPU 401 to perform adjustment using the sensor 900. Then, the CPU 401 performs a process to reflect the adjustment results based on the read results (S567), similar to S556 of FIG. 17.

[0123] In the image forming apparatus 100 of this embodiment as described above, it is possible to select adjustments that do not require a test chart as part of the adjustments performed in the batch adjustment mode in the first embodiment. This makes it possible to reduce the number of test charts in the batch adjustment mode. Furthermore, when adjustments using the sensor 900 are performed after the test chart is generated, it is possible to shorten the time required for the user to perform adjustments using the sensor 900 in the batch adjustment mode.

[0124] (Third embodiment) The configuration of the image forming apparatus 100 of the third embodiment is the same as that of the first embodiment. Unlike the first embodiment, the third embodiment presents the user with an optimal combination of adjustment items for the collective adjustment mode by changing the adjustment items pre-selected by the adjustment item selection button 751a shown in Fig. 16 according to the state of the image forming apparatus 100. Fig. 21 is an explanatory diagram of an example of changing the pre-selected adjustment items.

[0125] Case_A is an adjustment item that is preferably performed in the collective adjustment mode when the image forming apparatus 100 is initially installed. In this case, it is preferable that all adjustments are performed in the collective adjustment mode. Therefore, when the image forming apparatus 100 is initially installed, the combination of adjustment items in Case_A is pre-selected.

[0126] Case_B is an adjustment item that is preferably performed in the collective adjustment mode when the user performs regular maintenance work. In-plane density unevenness and gradation are susceptible to changes over time as the image forming apparatus 100 is used, changes in environmental conditions, and the like, and therefore need to be adjusted through regular maintenance. Therefore, when the user performs regular maintenance work, the combination of adjustment items in Case_B is pre-selected. However, in the case of Case_C and Case_D described below, the order of priority is Case_C, then Case_D.

[0127] Case_C shows adjustment items for which "tone correction: print" has been adjusted within a certain period of time before the screen transitions to the batch adjustment mode execution reception operation screen 750. In this case, since there is no need to adjust again from the previous adjustment, the items excluding "tone correction: print" are selected from the adjustment items shown in Case_B. Note that the criteria for determining that there is no need to adjust again from the previous adjustment are the elapsed time since the previous adjustment, changes in environmental conditions, and a combination of the elapsed time and changes in environmental conditions. In this embodiment, adjustment items that have been adjusted within one week of the previous adjustment are excluded from the items that are pre-selected.

[0128] Case_D is an adjustment item when there is no copy job history during a certain period before the screen transitions to the batch adjustment mode execution reception operation screen 750. Some users may not use the copy function of the image forming apparatus 100 from a security standpoint. In this case, there is no need to perform "Gradation correction: Copy" in "Batch adjustment mode." In this embodiment, when there is no copy job history during the three months, "Gradation correction: Copy" is excluded from the items that are pre-selected as adjustment items.

[0129] Case_E is an adjustment item that is preferably performed in the batch adjustment mode when a new type of sheet is used. This is set because, as mentioned above, the print position and transfer output vary greatly depending on the characteristics of the sheet. When the user selects a new type of sheet that has not yet been adjusted using the paper type button 753 on the execution reception operation screen 750, "print position adjustment" and "transfer output adjustment" are added to the pre-selected items.

[0130] Case_F is an adjustment item that is preferably performed in the collective adjustment mode when replacing parts of the image forming apparatus 100 or performing maintenance work. "Double-sided reading color correction" is set because it is an adjustment function of the image forming apparatus 100, as described above. "Dot / streak image diagnosis" is set because dust or other particles may fall into the reading position of the reader 200 during maintenance work. Therefore, when parts or setting values ​​related to the reader 200 are changed, "Dot / streak image diagnosis" and "Double-sided reading color correction" are added to the pre-selected items.

[0131] The method of showing the user the optimal combination of collective adjustment modes is not limited to changing the adjustment items pre-selected by the adjustment item selection button 751a. Fig. 22 is a view showing an example of an execution acceptance operation screen according to the third embodiment. This execution acceptance operation screen 750 displays recommended selection items (adjustment items) in the adjustment item selection button 751d. Furthermore, this execution acceptance operation screen 750 may also display selection reasons 755 for the recommended adjustment items.

[0132] In the image forming apparatus 100 of this embodiment as described above, recommended adjustment items are pre-selected according to the state of the image forming apparatus 100. This makes it easier for the user to select adjustment items to be performed in the batch adjustment mode. This also reduces the amount of work required for the user to change adjustment items.

[0133] (Fourth embodiment) The configuration of the image forming apparatus 100 of the fourth embodiment is the same as that of the first embodiment. Fig. 23 is a view showing an example of an execution acceptance operation screen of the fourth embodiment. Unlike the first embodiment, in the fourth embodiment, it is possible to select multiple types of sheets to be adjusted in the collective adjustment mode for each adjustment item shown in the adjustment item selection button 751c.

[0134] Differences from the processing of the first embodiment will be described. In the fourth embodiment, in the processing of S552 of the image forming apparatus 100 in the collective adjustment mode shown in FIG. 17, the CPU 401 can collectively select three types of sheet to adjust in "Gradation Correction: Printer": plain paper, thick paper, and recycled paper. In the processing of S554, the CPU 401 generates a test chart collectively by printing test images on multiple types of sheets. In this case, the sheet types may be different. This is because the ADF 220 can perform the same ADF reading even with different sheet types. Furthermore, it is preferable to print test images collectively for each sheet type and then switch the sheet type. This is because the image formation conditions differ depending on the sheet type, and the test chart generation time can be shortened by reducing the number of times the image formation conditions are switched.

[0135] In the image forming apparatus 100 of the present embodiment as described above, it is possible to perform adjustments on multiple types of sheets collectively in the batch adjustment mode, thereby reducing the burden on the user when performing adjustments on multiple types of sheets.

[0136] (Fifth embodiment) The image forming apparatus of the fifth embodiment forms an image using a print head as the exposure device 13. When the exposure device 13 is a print head, unlike the density unevenness correction of the first embodiment, the density unevenness correction in the Y direction is divided into "print head vertical unevenness correction" and "density unevenness correction due to factors other than the print head" and is performed separately. These density unevenness corrections can be selected and performed individually in the collective adjustment mode.

[0137] (Print head vertical unevenness correction) Print head vertical unevenness correction is a function that corrects vertical unevenness in density of image forming apparatus 100 caused by the print head. The following describes print head vertical unevenness correction. Unlike the density unevenness correction of the first embodiment, print head vertical unevenness correction is a process that identifies the position of streaks caused by the print head in advance and corrects only the streaks caused by the print head during density unevenness correction.

[0138] Correction of print head vertical unevenness is an adjustment unique to the image forming apparatus 100 configured to use the exposure unit 13 as the print head. Here, the print head is an exposure unit equipped with a light-emitting element array in which light-emitting elements such as LEDs are arranged in a row corresponding to each pixel, and a rod lens array. The image forming apparatus 100 using the print head 130 drives each light-emitting element of the print head 130 based on image data, causing the print head to output light based on the image data. The light output from the light-emitting elements is imaged on the surface of the photosensitive drum 11 by the rod lens. As a result, the photosensitive drum 11 is exposed based on the image data. The exposure position is moved by moving the photosensitive drum 11 and the print head relative to each other in the sub-scanning direction, and an electrostatic latent image is formed on the photosensitive drum 11.

[0139] In the image forming apparatus 100 that uses a print head, stripe-like unevenness (vertical unevenness) running in the sub-scanning direction may occur. The cause of the vertical unevenness will be explained below.

[0140] 24 is an explanatory diagram of the configuration of the print head. The print head 130 includes an LED array 1301, which is an array of light-emitting elements, a printed circuit board 42, and a rod lens array 44 that focuses light emitted from the LED array 1301 on the photosensitive drum 11. The printed circuit board 42 supports the LED array 1301 and includes a circuit device for supplying various signals that drive and control the LED array 1301. The LED array 1301 consists of multiple LEDs arranged in the Y direction, and the light intensity of each LED varies and changes over time.

[0141] FIG. 25 is an explanatory diagram of the rod lens array 44. As shown in FIG. 25(a), the rod lens array 44 includes a plurality of gradient index plastic rod lenses (rod lenses 46) that function as imaging lenses. In this embodiment, the gradient index plastic rod lenses are cylindrical plastic rods whose refractive index varies concentrically from the center to the periphery. The rod lens array 44 focuses light emitted from each LED of the LED array 1301 onto the photosensitive drum 11. The rod lens array 44 focuses incident light using the distribution of refractive index rather than the shape. As shown in FIG. 25(b), the rod lenses 46 are regularly arranged at predetermined intervals with their optical axes aligned.

[0142] One or more of the rod lenses 46 constituting the rod lens array 44 may deviate from a predetermined position or angle. Figure 26 is an illustration of a state in which one rod lens 46 has fallen over.

[0143] As shown in Figures 26(a) and 26(b), if the rod lens 46b tilts and deviates from its intended position or angle, the rod lens array 44 may not exhibit its intended optical performance. That is, if the rod lens 46 is tilted (tilted) like the rod lens 46b, the light passing through the rod lens 46b does not form an image at the intended position. As a result, at position W in the figure, the light forms an image, resulting in a denser dot density than intended, resulting in a thin streak. Conversely, at position B in the figure, the dot density is sparser than intended, resulting in a dark streak. This results in vertical unevenness in the vicinity of the tilted rod lens 46b. Furthermore, even if the rod lens 46 is not physically deviated from its intended position or angle, the refractive index distribution within the rod lens 46 varies. If the refractive index deviates from the desired value, the optical performance specification will not be met, resulting in vertical unevenness as described above.

[0144] In other words, unevenness caused by the rod lens array 44 can be corrected by identifying positions where vertical unevenness is likely to occur by measuring the characteristics in advance, such as at the time of shipping from the factory, and then correcting only the vertical unevenness that occurs in the corresponding positions. In this way, vertical unevenness can be corrected separately from density unevenness caused by factors other than the rod lens array 44.

[0145] On the other hand, as mentioned above, the LED array 1301 has variations in light intensity and changes over time for each LED. Variations in light intensity for each LED and changes over time are one of the causes of vertical unevenness. For this reason, correction must be made for each LED.

[0146] 27 is an example diagram of a test chart 840 for correcting vertical print head unevenness. The test image of the test chart 840 for correcting vertical print head unevenness includes band-shaped patch images of yellow (Y), magenta (M), cyan (C), and black (K), and an image of an arrow 841. The band-shaped patch images have a density signal of 50% for each color. The arrow 841 is formed to establish a correspondence between the position of the print head 130 in the Y direction and the position of the test chart 840 in the Y direction. The arrow 841 corresponds to the position of each LED in the LED array 1301.

[0147] Correction of vertical print head unevenness is performed based on the results of reading test chart 840 for correcting vertical print head unevenness. By performing feedback correction of the light emission amount of print head 130 only at positions in the Y direction that are previously targeted for correction based on the results of reading test chart 840 for correcting vertical print head unevenness, it is possible to correct only vertical unevenness caused by rod lens array 44. By performing feedback correction of the light emission amount of print head 130 on an LED-by-LED basis in LED array 1301, variations in the light amount and changes over time in LED array 1301 are corrected on an LED-by-LED basis. Note that, like tone correction, reading of test chart 840 is performed by reader 200 using ADF reading (first reading mode) or platen reading (second reading mode).

[0148] (Corrects density unevenness caused by factors other than the print head) Figure 28 is an example of a test chart 845 for correcting density unevenness caused by factors other than the print head 130. The difference from the test chart 840 shown in Figure 27 is that a mark 846 has been added to distinguish the test chart.

[0149] In correcting density unevenness caused by factors other than the print head 130, density unevenness in the Y direction caused by factors other than the print head 130 is corrected by feeding back so as to change the signal value of the image data for each position in the Y direction. In other words, even if the same signal value of the image data is set in the Y direction, when forming an image, the signal value of the image data in the Y direction is corrected to reflect the results of correcting density unevenness caused by factors other than the print head 130, and image formation is performed.

[0150] In the fifth embodiment, unlike the first embodiment, adjustments using the collective adjustment mode are performed by dividing "in-plane (density) unevenness correction" into "print head vertical unevenness correction" and "density unevenness correction due to factors other than the print head" and performing them separately. In the first embodiment, "correction of in-plane (density) unevenness" corrects density unevenness in the Y direction caused by the image forming unit 10 including the exposure device 13. In contrast to this, in the fifth embodiment, "correction of print head vertical unevenness" can correct only density unevenness in the Y direction caused by the print head 130. "Correction of density unevenness due to factors other than the print head" can correct density unevenness in the Y direction caused by the image forming unit 10 other than the print head 130.

[0151] As described above in the first to fifth embodiments, the image forming apparatus 100 can perform multiple adjustments collectively in the collective adjustment mode by selecting appropriate adjustment items and operating in the collective adjustment mode. This allows the user to perform only the adjustments they need while maintaining usability.

Claims

1. an image forming means for forming an image on a sheet; a display means for displaying a selection screen for selecting an adjustment item and a paper type from a table consisting of a plurality of adjustment items involving the formation of a test image and a plurality of paper types to be used in the formation of the test image; and a control means for controlling the image forming means so as to form a test image used for the selected adjustment item on a sheet of the selected paper type. Image forming device.

2. the image forming apparatus further comprises a reading unit for reading an image on a sheet; The control means adjusts the selected adjustment item based on a reading result of a test image used for the selected adjustment item read by the reading means.

2. The image forming apparatus according to claim 1.

3. the reading means reads the test image to be used for the selected adjustment item from the sheet while conveying the sheet on which the test image is formed.

3. The image forming apparatus according to claim 2.

4. The reading means comprises a document table, an image sensor that reads a document placed on the document table, a tray on which the document is placed, and a transport means that transports the document from the tray so that the document on the tray can be read by the image sensor.

3. The image forming apparatus according to claim 2.

5. the image forming means forms a test image for each of the selected paper types regardless of the selected adjustment items.

2. The image forming apparatus according to claim 1.

6. The selection screen is a screen that displays a combination of the selected adjustment items and the paper type selected for each of the adjustment items.

2. The image forming apparatus according to claim 1.

7. the plurality of adjustment items include density unevenness correction for suppressing unevenness in density of the image to be formed by the image forming unit, 2. The image forming apparatus according to claim 1.

8. the plurality of adjustment items include gradation correction for adjusting gradation characteristics of the image to be formed by the image forming means, 2. The image forming apparatus according to claim 1.

9. The gradation correction further includes gradation correction for printing and gradation correction for copying.

9. The image forming apparatus according to claim 8.

10. the plurality of adjustment items include a print position adjustment for adjusting a print position of an image to be formed on a sheet by the image forming means, 2. The image forming apparatus according to claim 1.

Images