Image forming apparatus

Abstract

To provide an image forming apparatus that prevents a reading error caused by a user's operation mistake.SOLUTION: An image forming apparatus 100 creates test images on sheets to create test charts with image forming units 120, 130, 140, 150. The test charts are loaded on an ADF unit 220 to be read by a document scanner 210. The image forming apparatus 100 determines whether the test charts are correctly loaded on the ADF unit 220, and determines whether to start reading of the test charts with the document scanner 210 based on a result of the determination.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an image forming apparatus having a function of adjusting printing conditions and a function of diagnosing image defects.

Background Art

[0002] An electrophotographic image forming apparatus has a function of adjusting printing conditions and diagnosing image defects by generating a test chart and reading the test chart with a reading device. Examples of adjusting printing conditions include maximum density correction, gradation correction, density unevenness correction within a plane, alignment correction (front and back registration adjustment), vertical unevenness adjustment of a print head (adjustment of a light emitting unit), transfer output adjustment (secondary transfer voltage adjustment), and the like. Examples of image defects include dots, streak images, and the like. The test chart is formed by printing a test image corresponding to the adjustment content and the diagnosis content on a sheet.

[0003] As an example of adjusting printing conditions using a test chart, gradation correction will be described. The gradation characteristics (density characteristics) of an image formed on a sheet by an image forming apparatus vary due to various factors. For example, the gradation characteristics change due to changes in environmental conditions such as temperature and humidity at the installation location of the image forming apparatus, or due to changes in components of the image forming apparatus over time. Therefore, the image forming apparatus executes calibration to maintain the gradation characteristics. In calibration, first, a test image is formed on a sheet to generate a test chart for gradation correction. The image forming apparatus acquires the image density of the test image by reading the test chart with a reading device. The image forming apparatus creates a correction table such that the acquired image density becomes the target density. During image formation, gradation correction is performed using this correction table. The correction table is prepared for each type of sheet (basis weight, presence or absence of coating, whether it is recycled paper, etc.).

[0004] Patent Document 1 proposes a method to reduce the user's workload during calibration by reading a test chart using an automatic document transport device. Patent Document 2 proposes a method to improve user-friendliness by determining whether or not the sheet to be used for calibration is set in the cassette before the test chart is generated. Both are technologies to improve work efficiency during calibration. Patent Document 3 proposes a technology that, when sequentially scanning multiple documents of different sizes and performing copying, determines whether or not the sheet corresponding to the document size is set in the cassette and selects whether to continue or stop scanning the documents. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2016-111628 [Patent Document 2] Japanese Patent Publication No. 2016-103063 [Patent Document 3] Japanese Patent Publication No. 2003-134287 [Overview of the project] [Problems that the invention aims to solve]

[0006] When using a test chart to adjust print conditions or diagnose image defects, the user is required to manually place the test chart into the scanner. Because this process involves human intervention, errors are possible. For example, the user may place a document other than the test chart into the scanner. Alternatively, the user may instruct the scanner to read the test chart without properly positioning it.

[0007] Thus, operational errors include errors in the type of document placed in the scanner and errors in how the document is placed. If the document is a test chart and is placed in the designated position, no operational errors will occur. Even if the document is a test chart, if it is not placed in the designated position, a reading error will occur due to an operational error. If the document is not a test chart and is a different size from the test chart, a reading error will occur due to an operational error regardless of whether it is placed in the designated position or not. If the document is not a test chart and is the same size as the test chart, a reading error will occur due to an operational error regardless of whether it is placed in the designated position or not.

[0008] If a reading error occurs, the image forming apparatus instructs the user to read the test chart again. In other words, if the test chart is not properly set in the reading apparatus, the image forming apparatus will perform the image reading process once and then have the user repeat the process, resulting in wasted work. Therefore, there is a need for technology that prevents reading errors caused by user mistakes and improves work efficiency.

[0009] In view of the above problems, the primary objective of the present invention is to provide an image forming apparatus that prevents reading errors caused by user errors. [Means for solving the problem]

[0010] The present invention provides an image forming apparatus comprising an image forming means for forming an image on a sheet, and a sheet above A reading means for reading the image, An acquisition means for acquiring paper size information relating to the size of the sheet on which the test image is to be formed, and based on the paper size information acquired by the acquisition means By the aforementioned image forming means The aforementioned Test image form , the aforementioned test In response to the instruction to start reading the image The reading means The test image is read, and the image forming means is calibrated based on the reading result of the test image read by the reading means. Control means and The control means includes a start-read button operated to give the instruction to start reading, and a detection means for detecting document size information corresponding to the size of the sheet read by the reading means, wherein the control means prevents the start-read button from issuing the instruction to start reading if the paper size information and the document size information are different. It is characterized by the following: Another image forming apparatus of the present invention is characterized by comprising: an image forming means for forming an image on a sheet; a reading means for reading an image on a sheet; an acquisition means for acquiring paper size information relating to the size of a sheet on which the test image is to be formed; a control means for forming the test image by the image forming means based on the paper size information acquired by the acquisition means, causing the reading means to read the test image in response to an instruction to start reading the test image, and performing calibration of the image forming means based on the reading result of the test image read by the reading means; a detection means for detecting document size information corresponding to the size of the sheet read by the reading means; and a display means for displaying a start-read button to give the instruction to start reading when the paper size information and the document size information match, and not displaying the start-read button when the paper size information and the document size information do not match. [Effects of the Invention]

[0011] According to the present invention , YuReading error caused by user's operation mistake Prevent can be stopped 。

Brief description of the drawings

[0012] [Figure 1] Configuration diagram of the image forming apparatus. [Figure 2] (a), (b) are explanatory diagrams of the document scanner. [Figure 3] Explanatory diagram of original size determination. [Figure 4] (a) to (d) are explanatory diagrams of the ADF unit 220. [Figure 5] Explanatory diagram of original size determination. [Figure 6] Explanatory diagram of the printer control unit. [Figure 7] Flowchart representing calibration processing. [Figure 8] (a) to (c) are exemplary diagrams of the screens displayed on the display. [Figure 9] Exemplary diagram of a test chart. [Figure 10] Flowchart representing calibration processing. [Figure 11] (a), (b) are exemplary diagrams of the screens displayed on the display. [Figure 12] (a) to (d) are exemplary diagrams of the screens displayed on the display. [Figure 13] (a) to (c) are flowcharts representing calibration processing. [Figure 14] Explanatory diagram for determining whether to start reading. [Figure 15] (a) to (f) are exemplary diagrams of the state when the test chart is set on the original tray. [Figure 16] Relationship diagram between the set state of the test chart and the reading result. [Figure 17] (a) to (f) are exemplary diagrams of the state when the test chart is set on the platen glass. [Figure 18] (a), (b) are exemplary diagrams of the notification screen. [Figure 19] (a) and (b) are explanatory diagrams of test charts for correcting density unevenness. [Figure 20] Diagram illustrating the determination of whether or not to start reading. [Figure 21] A diagram showing the relationship between the test chart's setup status and the reading results. [Figure 22] (a) and (b) are explanatory diagrams of test charts for diagnostic imaging. [Figure 23] Diagram showing the relationship between muscle detection location and muscle-related causes. [Figure 24] Diagram illustrating the determination of whether or not to start reading. [Modes for carrying out the invention]

[0013] Embodiments of the present invention will be described with reference to the drawings.

[0014] (Image forming apparatus) Figure 1 is a diagram of the configuration of the image forming apparatus according to this embodiment. The image forming apparatus 100 comprises a reader 200, which is a reading device that reads an image from a document (sheet), and a printer 300 that forms an image on the sheet. The reader 200 comprises a document scanner 210 and an automatic document feeder (hereinafter referred to as "ADF unit") 220. The document scanner 210 is mounted on the printer 300, and the ADF unit 220 is mounted on the document scanner 210. The reader 200 reads the image printed on the document 101 and transmits an image signal representing the read image to the printer 300. The printer 300 can perform image forming processing on the sheet based on the image signal acquired from the reader 200.

[0015] In the figure, the sheet transport direction by the image forming apparatus 100 is defined as the PX direction, and the direction perpendicular to the PX direction is defined as the Y direction. The paper feeding direction of the ADF unit 220 is defined as the SX2 direction, and the direction in which the first mirror unit 104a and the second mirror unit 104b of the document scanner 210 move is defined as the SX1 direction.

[0016] The reader 200 reads documents fed by the ADF unit 220 or documents 101 placed on the document glass 102 located on the ADF unit 220 side of the document scanner 210. The document scanner 210 is equipped with a reader image processing unit 108. The reader image processing unit 108 converts the electrical signals generated by reading the documents 101 into image signals and transmits them to the printer 300.

[0017] The printer 300 includes a printer control unit 109 inside. The printer control unit 109 acquires an image signal from the reader image processing unit 108 of the document scanner 210. The printer control unit 109 forms an image on the sheet based on the acquired image signal. For image formation, the printer 300 includes image forming units 120, 130, 140, 150, an exposure unit 110, a transfer belt 111, and a fuser 114.

[0018] Image forming units 120, 130, 140, and 150 differ only in the color of the image they form, and perform the same operations with the same configuration. Image forming unit 120 forms a yellow (Y) image. Image forming unit 130 forms a magenta (M) image. Image forming unit 140 forms a cyan (C) image. Image forming unit 150 forms a black (K) image. Here, the configuration of image forming unit 120 will be described, and the configurations of the other image forming units 130, 140, and 150 will not be described.

[0019] The image forming unit 120 comprises a photosensitive drum 121, a charger 122, a developer 123, a transfer blade 124, and a surface potential meter 125. The photosensitive drum 121 is a drum-shaped photoreceptor having a photosensitive layer on its surface. The photosensitive drum 121 rotates clockwise in the figure. The charger 122 uniformly charges the surface of the rotating photosensitive drum 121 to a predetermined potential. An electrostatic latent image is formed on the surface of the photosensitive drum 121 when the charged surface is scanned by a laser beam from the exposure unit 110. The exposure unit 110 is controlled by the printer control unit 109 to irradiate the photosensitive drum 121 with a laser beam. The exposure unit 110 scans the photosensitive drum 121 in the Y direction. Therefore, the Y direction is the main scanning direction. The printer control unit 109 modulates the laser beam emitted from the exposure unit 110 with a PWM (Pulse Width Modulation) signal based on the image signal. The developing unit 123 develops the electrostatic latent image with a developer of the corresponding color (yellow in this case) (for example, toner) to form a toner image on the surface of the photosensitive drum 121.

[0020] The transfer blade 124 is positioned with a transfer belt 111 in between it and the photosensitive drum 121. The transfer belt 111 transports the sheet from the paper feed cassette 152. The transfer belt 111 discharges electricity to transfer the toner image formed on the photosensitive drum 121 to the sheet being transported by the transfer belt 111. This forms a yellow toner image on the sheet.

[0021] Similarly, a magenta toner image is formed on the photosensitive drum 131 of the image forming unit 130, a cyan toner image is formed on the photosensitive drum 141 of the image forming unit 140, and a black toner image is formed on the photosensitive drum 151 of the image forming unit 150. The magenta toner image formed on the photosensitive drum 131 is transferred so as to be superimposed on the yellow toner image on the sheet. The cyan toner image formed on the photosensitive drum 141 is transferred so as to be superimposed on the yellow and magenta toner images on the sheet. The black toner image formed on the photosensitive drum 151 is transferred so as to be superimposed on the yellow, magenta, and cyan toner images on the sheet. By superimposing and transferring the toner images of each color, a full-color toner image is formed on the sheet.

[0022] The sheet on which the full-color toner image has been formed is transported to the fuser 114 by the transfer belt 111. The fuser 114 fixes the transferred toner image to the sheet. The fuser 114 fixes the toner image to the sheet by, for example, heating, melting, and pressurizing the toner image. As a result, an image is formed on the sheet. The sheet with the formed image is discharged from the printer 300.

[0023] Furthermore, the surface potential meters 125, 135, 145, and 155 of each image forming unit 120, 130, 140, and 150 measure the surface potential of the photosensitive drums 121, 131, 141, and 151. The contrast potential is adjusted according to the measurement results from the surface potential meters 125, 135, 145, and 155.

[0024] (Document scanner) Figure 2 is an explanatory diagram of the document scanner 210. Figure 2(a) shows the configuration of the document scanner 210. Figure 2(b) is a view of the document scanner 210 from the ADF unit 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.

[0025] The document scanner 210 can perform image scanning in two modes: a first scanning mode in which it scans the original document 101 transported by the ADF unit 220, and a second scanning mode in which it scans the original document 101 placed on the document glass 102. The first scanning mode is sometimes called "swiping scan" or "ADF scan." The second scanning mode is sometimes called "fixed scan" or "document glass scan."

[0026] The first scanning mode offers two scanning methods: sheet-through and document-fixed. In the sheet-through method, the motor 116 rotates, causing the first mirror unit 104a and the second mirror unit 104b to move to the slide-reading position and stop. The slide-reading position is the reading position when the ADF unit 220 reads an image from the document 101 while it is being transported. While the ADF unit 220 is transporting the document 101 on the document glass 102, the image sensor 105 reads the image from the document 101.

[0027] The document scanner 210 turns on the document illumination lamp 103 to illuminate the reading surface (the side with the image printed on it) of the document 101. The first mirror 107a, the second mirror 107b, and the third mirror 107c deflect the reflected light (image light) from 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 an image signal. 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 in this manner. This reading operation is the same regardless of the reading mode or reading method.

[0028] In the document-fixed method, the ADF unit 220 transports the document 101 onto the document glass 102 and stops the document 101 at a predetermined position on the document glass 102. The first mirror unit 104a and the second mirror unit 104b move in the SX1 direction by the motor 116 and read the image of the document 101. After reading the image, the ADF unit 220 resumes transporting the document 101 and ejects it.

[0029] In the second scanning mode, the motor 116 rotates, causing the first mirror unit 104a and the second mirror unit 104b to move to the 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 unit 220. The document scanner 210 turns on the document illumination lamp 103, illuminating 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 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 an electrical signal from the image sensor 105 and generates an image signal.

[0030] The document scanner 210 can detect the size (document size) of the original document 101. In this embodiment, the document scanner 210 detects the document size before reading the document image. First, the document scanner 210 illuminates the edge of the original document 101 with the document illumination lamp 103 and reads the reflected light from the original document 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 direction of the lines is orthogonal to the SX1 direction. Based on the reading results (electrical signals) of the predetermined number of lines of the image sensor 105, the width (length in the Y direction) of the original document 101 can be obtained.

[0031] Furthermore, the length of the document 101 (length in the SX1 direction) is detected based on the detection result of the document size detection sensor 113. At least one document size detection sensor 113 is placed at a predetermined position in the SX1 direction inside the housing of the document scanner 210, and it detects the presence or absence of the document 101 on the document glass 102 at that position. The document size detection sensor 113 is, for example, an infrared sensor and is capable of outputting the presence or absence of the document 101 as a binary value. Based on the detection result of the document size detection sensor 113, it is possible to determine whether the length of the document 101 is longer than the position of the document size detection sensor 113. If it is necessary to accurately detect the length of the document 101, multiple document size detection sensors 113 are arranged.

[0032] Based on the detected width and length of the document 101, it is determined which of several predetermined standard sizes the document 101 is. Furthermore, based on the width and length of the document 101, it is also determined which orientation (vertical or horizontal reading) the document 101 is placed on the document glass 102.

[0033] As shown in Figure 2(b), the document glass 102 has document size labels 1230 arranged around its outer perimeter, and a document alignment mark 1231 is provided at the reference abutment point on the far side in the Y direction. The document 101 is placed so that its vertex abuts against the document alignment mark 1231. The reference for standard-sized documents is the document alignment mark 1231. In this embodiment, the document size detection sensor 113 is positioned on the Y-side of the document glass 102 at a position slightly further than the length of an A4-sized document from the document alignment mark 1231. For this reason, the document size detection sensor 113 cannot detect A4, B5, A5, and B6-sized documents 101, but can detect A3, B4, A4R, and B5R-sized documents 101.

[0034] Figure 3 is an explanatory diagram of the document size determination process. The document size is determined from the combination of the width of the document 101 (document detection width), which is determined from the electrical signal that is the detection result (reading result) of the image sensor 105, and the detection result (presence or absence of a document) of the document size detection sensor 113. Figure 3 shows this combination.

[0035] The electrical signal output from the image sensor 105 determines which of the four groups the document to be detected belongs to. Specifically, based on the document detection width, it is determined whether the document 101 belongs to the first group (B5R, B6), the second group (A4R, A5), the third group (B5, B4), or the fourth group (A4, A3). However, the document detection width alone is insufficient for distinguishing between groups. The detection result (presence or absence of a document) from the document size detection sensor 113 enables distinction within each group. For example, if the size of the document to be detected is determined to belong to the fourth group based on the document detection width, and the detection result from the document size detection sensor 113 indicates the presence of a document, then the size of the document to be detected is determined to be A3 in portrait orientation. If the document is not present, then the size of the document to be detected is determined to be A4 in landscape orientation. If the document does not belong to any of these categories, it is determined to be a non-standard size.

[0036] (ADF unit) Figure 4 is an explanatory diagram of the ADF unit 220. Figure 4(a) is an external perspective view of the ADF unit 220. Figure 4(b) is an internal configuration diagram of the ADF unit 220. Figure 4(c) is a view of the document stacking section 301, described later, from diagonally above. Figure 4(d) is an internal configuration diagram of the document stacking section 301, described later. The ADF unit 220 comprises a document stacking section 301, a document feeding section 304, a document transport section 308, and a reversed paper output section 313.

[0037] 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 documents 101 are placed in the document tray 302. Documents 101 placed in the document tray 302 are transported one by one onto the document glass 102 by the document feed unit 304, pass over the document glass 102, and are discharged into the paper output tray 321 of the reverse paper output unit 313 by the reverse paper output unit 313.

[0038] The document feeding unit 304 is equipped with a pickup roller 306, a feed roller 307, and a pair of registration rollers 305 along the transport path of the document 101. The pickup roller 306 is a rotatable and vertically movable roller. When feeding, the pickup roller 306 descends and contacts the topmost document 101 in the stack of documents loaded in the document tray 302, and transports the document 101. The feed roller 307 transports the document 101 that has been transported by the pickup roller 306 to the pair of registration rollers 305. The documents 101 are transported one by one by the pickup roller 306 and the feed roller 307. The pair of registration rollers 305 stops when the leading edge of the document 101 reaches it. This is to correct the skew of the document 101. After the skew correction, the pair of registration rollers 305 starts rotating and transports the document 101 to the document transport unit 308.

[0039] The document transport unit 308 comprises 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 over the drive roller 310 and the driven roller 311. Furthermore, the transport belt 309 is 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.

[0040] In the first scanning mode's document fixing method, the transport belt 309 stops when the document 101 reaches the scanning position. After the document 101 is scanned by the first mirror unit 104a and the second mirror unit 104b, the transport belt 309 transports the document 101 to the inverted paper output unit 313. In this case, the first mirror unit 104a and the second mirror unit 104b scan the stationary document 101 while moving in the SX1 direction. In the sheet-through method of the first scanning mode, the transport belt 309 does not stop even when the document 101 reaches the scanning position, and continues to transport the document 101. In this case, the first mirror unit 104a and the second mirror unit 104b remain stationary and scan the document 101 while it is being transported. In other words, scanning of the document 101 is performed by the document 101 moving instead of the first mirror unit 104a and the second mirror unit 104b moving.

[0041] The inverting paper output unit 313 includes an inverting roller 314, a transport roller pair 315, an inverting flapper 316, a paper output flapper 317, and an inverting roller 318. The inverting paper output unit 313 inverts the front and back sides of the document 101 transported from the document transport unit 308 and discharges it to the paper output tray 321 of the paper output stacking unit 320.

[0042] The document 101, transported by the transport belt 309 of the document transport unit 308, is picked up by the reversing flapper 316 and transported to the reversing roller 314 when it enters the reversing paper discharge unit 313. The document 101 is held between the reversing roller 314, which rotates in CCW (Counter Clock Wise), and the opposing reversing roller 318, and transported to the transport roller pair 315. When the rear end of the document 101 passes the paper discharge flapper 317, the paper discharge flapper 317 rotates in CW (Clock Wise). The reversing roller 314 also rotates in CW. As a result, the document 101 is transported in a switchback manner and discharged into the paper discharge tray 321 of the paper discharge stacking unit 320.

[0043] (Document size detection by ADF unit) As shown in Figure 4(c), the document tray 302 of the document stacking unit 301 is equipped with a pair of regulating members 332 that can slide in the width direction of the document (Y direction, a direction perpendicular to the document transport direction). The regulating members 332 have the function of aligning the width direction position of the document during feeding by regulating both ends in the width direction of the document placed on the document stacking unit 301 (document tray 302). The pair of regulating members 332 are movable symmetrically in the width direction of the document, and regulate the position of the document so that the center of the width direction of the document being fed becomes the feeding center.

[0044] The document stacking section 301 is provided with a document width sensor 333 capable of detecting the position of the regulating member 332 (Figure 4(d)). The document width sensor 333 detects the width of the document placed on the document tray 302 by detecting the position of the regulating member 332, which moves according to the width of the document.

[0045] Multiple (two in this embodiment) document length detection sensors 334a and 334b ​​are arranged in the document feeding direction (SX2 direction) of the document stacking section 301. The document length detection sensors 334a and 334b ​​detect the presence or absence of a document 101 on the document stacking section 301 (document tray 302). Based on the detection results of the respective document length detection sensors 334a and 334b, the size of the document 101 in the document feeding direction (SX2 direction) is detected.

[0046] Based on the detection results of the document width sensor 333 and the document length detection sensors 334a and 334b, the size and orientation (whether it is fed vertically or horizontally) of the document placed on the document stacking unit 301 can be detected. Figure 5 is an explanatory diagram of the document size determination. The size of the document placed on the document stacking unit 301 (document tray 302) is determined from the combination of the detection results from the document width sensor 333 and the document length detection sensors 334a and 334b. Figure 5 shows the combination of the document detection width in the width direction of the document in the document stacking unit 301, which is the detection result of the document width sensor 333, and the detection results of the document length detection sensors 334a and 334b ​​(presence or absence of the feeding direction (SX2 direction) of the document placed on the document stacking unit 301). Note that the document length detection sensors 334a and 334b ​​output a binary value indicating the presence or absence of a document.

[0047] The detection result of the document width sensor 333 is used to determine which of the four groups the document to be detected, from the first to the fourth group, belongs to. That is, based on the document detection width, it is determined whether the document 101 belongs to the first group (B5R, B6), the second group (A4R, A5), the third group (B5, B4), or the fourth group (A4, A3). However, the document detection width alone is not sufficient to distinguish within each group. The detection result of the document length detection sensor 334b ​​(presence or absence of a document) enables distinction within each group. For example, if the size of the document to be detected, 101, is determined to belong to the fourth group based on the document detection width, and the detection result of the document length detection sensor 334b ​​indicates that a document is present, then the size of the document to be detected, 101, is determined to be A3 in portrait orientation. If there is no document, then the size of the document to be detected, 101, is determined to be A4 in landscape orientation. If the document length detection sensor 334a indicates that a document is present, but the document does not belong to any of the other determination results, then it is determined that the document is not a standard size. Furthermore, if the document length detection sensor 334a does not detect a document, it is determined that there is no document.

[0048] As described above, the detection of the document size of the document 101 placed on the document glass 102 and the document size of the document 101 placed on the document tray 302 is performed by the reader 200. The reader 200 performs the document size detection process in response to instructions from the printer 300. The document size detection result is transmitted from the reader 200 to the printer 300.

[0049] (Printer control unit) Figure 6 is an explanatory diagram of the printer control unit 109. The printer control unit 109 is connected to a CPU (Central Processing Unit) 401, memory 402, reader 200, and semiconductor laser 410, which comprehensively control the operation of the image forming apparatus 100. The memory 402 is equipped with ROM (Read Only Memory) and RAM (Random Access Memory) 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.

[0050] The CPU 401 is connected to the operation unit 400. The operation unit 400 is a user interface equipped with input and output devices. The input devices include key buttons such as a start key, stop key, and numeric keypad, as well as a touch panel. The output devices include a display and a speaker. In addition to the reader image processing unit 108 described above, the reader 200 is equipped with a reader control unit 413. The reader control unit 413 performs the document size determination process described above. The semiconductor laser 410 is installed inside the exposure unit 110 and emits a laser beam that irradiates the photosensitive drums 121, 131, 141, and 151.

[0051] The printer control unit 109 comprises a color processing unit 403, a gradation control unit 411, a dithering processing unit 407, a PWM unit 408, and a laser driver 409. The printer control unit 109 converts the R, G, and B image signals into PWM signals and controls the emission of the semiconductor laser 410 based on these PWM signals.

[0052] The image signal output from the reader image processing unit 108 of the reader 200 is input to the color processing unit 403. The color processing unit 403 performs image processing and color processing on the input image signal so that the desired output result (image) can be obtained if the output characteristics of the printer 300 are ideal. The color processing unit 403 expands the number of gradations of the image signal from 8 bits to 10 bits for improved accuracy. The color processing unit 403 is equipped with a lookup table called LUTid 404. LUTid 404 is a luminance-density conversion table that converts the luminance information contained in the image signal into density information. The color processing unit 403 uses LUTid 404 to convert the luminance information of the R, G, and B image signals into density information of the Y (yellow), M (magenta), C (cyan), and K (black) image signals. The Y, M, C, and K image signals are input to the gradation control unit 411.

[0053] The gradation control unit 411 corrects the gradation characteristics of the image signal acquired from the color processing unit 403 using correction conditions corresponding 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 γ correction unit 406 including a lookup table called LUTa. The gradation control unit 411 performs gradation correction of the Y, M, C, and K image signals so that the desired output result (image) can be obtained in accordance with the actual output characteristics of the printer 300. The UCR unit 405 limits the sum of the image signal levels by regulating the integrated value of the image signal at each pixel. If the sum exceeds a specified value, the UCR unit 405 performs under-color removal (UCR) processing, which replaces a predetermined amount of C, M, and Y image signals with a K image signal, thereby reducing the sum of the image signal levels.

[0054] The γ correction unit 406 corrects the density characteristics (γ characteristics) of the image signal using LUTa. LUTa is a 10-bit conversion table (gradation correction condition) for correcting density characteristics. As described above, the gradation characteristics of the image formed by the printer 300 on the sheet vary depending on environmental changes and wear and tear of parts. Also, the gradation characteristics of the image differ depending on the type of sheet. The CPU 401 updates LUTa by performing calibration to maintain the image's gradation characteristics at a predetermined level. The printer 300 forms an image on the sheet according to the image signal corrected by the γ correction unit 406. Memory 402 may store LUTa for each type of sheet. The CPU 401 reads the LUTa corresponding to the sheet type specified by the operation unit 400 from memory 402 and sets it in the γ correction unit 406. LUTa is used when forming an image according to copying a document or a print job from a host computer, but it is not used when performing calibration. The Y, M, C, and K image signals after gradation correction are input to the dithering processing unit 407.

[0055] The dithering unit 407 performs dithering (halftone processing) on ​​the 10-bit Y, M, C, and K image signals after gradation correction, converting them into 4-bit signals. The PWM unit 408 performs pulse width modulation on the dithered signal to generate a PWM signal, which is the control signal for the exposure unit 110. The PWM signal is input to the laser driver 409. The laser driver 409 controls the emission of the semiconductor laser 410 according to the PWM signal.

[0056] (calibration) Calibration is performed using a test chart generated by printer 300. This section describes how to generate LUTa through calibration.

[0057] The CPU 401 supplies a predetermined image signal (density signal) to the dithering unit 407 to create a test chart for gradation correction, forming a test image on a sheet. The sheet on which the test image is formed is the test chart. The reader 200 reads the test chart and transmits the image signal (luminance signal), which is the reading result, to the color processing unit 403. The color processing unit 403 uses LUTid 404 to convert the R (red), G (green), and B (blue) luminance signals into Y, M, C, and K density signals. Here, Y is converted to the density signal value of each color using the luminance value of B, C to the luminance value of B, and M and K to the luminance value of G. The LUTid 404 may change the table used for conversion depending on the type of test chart sheet. The above color processing performed by the color processing unit 403 during calibration is different from the color processing performed when a normal document is scanned.

[0058] Next, CPU 401 creates LUTas so that the density signals acquired via reader 200 match the density signals used to form the test image. LUTas are created separately for each YMCK color.

[0059] As described above, the reader 200 can read document images using both ADF reading (first reading mode) and document glass reading (second reading mode). The reader 200 may read the test image printed on the test chart using either ADF reading or document glass reading. ADF reading may be preferred because it places less workload on the user compared to document glass reading.

[0060] Figure 7 is a flowchart illustrating the calibration process. Figure 8 is an example of the screen displayed on the control unit 400 during the calibration process. Figure 9 is an example of a test chart used for calibration.

[0061] The CPU 401 receives instructions from the control unit 400 indicating whether the user has selected ADF reading or platen reading (S501). If the user selects ADF reading, the CPU 401 operates in the first reading mode. If the user selects platen reading, the CPU 401 operates in the second reading mode. Figure 8(a) shows an example of the operation screen 700a when a reading mode is selected. The CPU 401 displays the operation screen 700a on the display of the control unit 400. The operation screen 700a displays a button 701a that allows selection of ADF reading and a button 701b that allows selection of platen reading. The user selects a reading mode by selecting either button 701a or button 701b using the control unit 400. The CPU 401 then receives information from the control unit 400 indicating the selected reading mode. The CPU 401 determines the selected reading mode (S502).

[0062] If ADF reading is selected (S502:Y), the CPU 401 sets the first image forming conditions to the printer 300 and sends a density signal of a test image to the dithering unit 407 to create a test chart for gradation correction. This causes the CPU 401 to have the printer 300 create a test chart (S503). In this case, LUTa is not used.

[0063] As shown in Figure 9, test charts 801a and 801b each contain a test image consisting of 10 gradations for each color, Y, M, C, and K. The 10-gradation image is formed, for example, by density signals of 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 100% for each color. The dithering unit 407 may be capable of applying multiple halftone processing. For example, the dithering unit 407 may have a low-line screen (160 lpi (lines per inch) to 180 lpi) and a high-line screen (250 lpi to 300 lpi). Test chart 801a is a test chart to which a low-line screen is applied. Test chart 801b is a test chart to which a high-line screen is applied. Note that the low-line screen is applied to photographic images, etc., and the high-line screen is applied to text, etc. If the printer 300 has the capability to form images with three or more different line counts, the number of test charts may also be three or more. For the sake of explanation, the number of test charts is assumed to be one.

[0064] After the test chart is created, the CPU 401 uses the reader 200 to operate the ADF unit 220 and perform ADF reading (S504). To do this, the CPU 401 displays a message on the display of the operation unit 400 prompting the user to place the test chart on the document tray 302 of the ADF unit 220. Figure 8(b) illustrates 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 that instructs the user to start reading.

[0065] After the user places the test chart on the document tray 302, they press button 701c on the control unit 400 to initiate ADF reading. The CPU 401 then receives the instruction to start reading via ADF from the control unit 400. Upon receiving the instruction to start reading, the CPU 401 instructs the reader 200 to perform ADF reading. The reader 200 transports the test chart using the ADF unit 220 and reads the test chart using the document scanner 210. The reader image processing unit 108 of the document scanner 210 transmits a brightness signal representing the reading result of the test chart to the printer control unit 109.

[0066] If document glass scanning is selected (S502:N), the CPU 401 sets the second image formation conditions to the printer 300 and sends a density signal of a test image to the dithering unit 407 to create a test chart for gradation correction. This causes the CPU 401 to cause the printer 300 to create a test chart (S511). LUTa is not used in this case. The test image for the test chart is the same as shown in Figure 9, and is the same as in the case of ADF scanning.

[0067] After the test chart is created, the CPU 401 performs a document scanning operation using the reader 200 (S512). To do this, the CPU 401 displays a message on the display of the control unit 400 prompting the user to place the test chart on the document glass 102. Figure 8(c) 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 document glass 102 and a button 701c that instructs the user to start scanning.

[0068] The user opens the ADF unit 220 to expose the document glass 102 and places the test chart on the document glass 102 with the side showing the test screen facing the document glass 102. The user then presses button 701c on the control unit 400 to instruct the start of document glass scanning. The CPU 401 receives the instruction to start scanning via document glass scanning from the control unit 400. Upon receiving the instruction to start scanning, the CPU 401 instructs the reader 200 to scan the document glass. The reader 200 reads the test chart on the document glass 102 using the document scanner 210. The reader image processing unit 108 of the document scanner 210 transmits a brightness signal representing the reading result of the test chart to the printer control unit 109.

[0069] When the test chart is read by processing S504 and S512, the CPU 401 acquires the density signal of the test image based on the reading result (luminance signal) (S505). The CPU 401 converts the luminance signal into a density signal using the LUTid 404 of the color processing unit 403. This provides a density signal for each of the 10 grayscale images. The CPU 401 may also switch the table of the LUTid 404 of the color processing unit 403 depending on the type of sheet used for the test chart.

[0070] The CPU 401 creates a LUTa (S506) based on the density signal used to generate the test image and the density signal obtained from the reading of the test chart. The CPU 401 stores the created LUTa in memory 402. When the test image is formed on a single sheet and there is a single test chart, the calibration process is performed in the manner described above.

[0071] If the test images are formed on two sheets and there are two test charts, the calibration process is performed as follows. Figure 10 is a flowchart showing the calibration process in this case. The same steps as in Figure 7 are given the same step numbers. The explanation of the same steps is omitted. Figures 11 and 12 are illustrative diagrams of the screens displayed on the display of the operation unit 400 during the calibration process.

[0072] As described above, the dithering unit 407 may have multiple screens, each with a different line count. The gradation characteristics of images formed with different line counts can vary significantly. In such cases, a LUTa is created for each line count. However, it is difficult for the user to determine which screen with which line count should be calibrated. This is because it is difficult for the user to understand which line count is applied to images such as text, lines, and photographs, and which is applied to copies, etc. Therefore, when there are multiple screens with different line counts, the user's burden is reduced by performing calibration on all screens with different line counts at once. Calibration with two test charts is applied in such cases.

[0073] When ADF reading is selected as the reading mode (S502:Y), the CPU 401 uses the printer 300 to create two test charts 801a and 801b consecutively (S901). The CPU 401 displays the message screen 700d, as illustrated in Figure 11(a), on the display of the control unit 400. The message screen 700d displays a message prompting the user to confirm that there are two or more sheets in the paper cassette 152, a message indicating that two test charts will be created consecutively, and a button 701d to instruct the user to start printing. After confirming that there are two or more sheets in the paper cassette 152, the user presses button 701d on the control unit 400 to instruct the user to start printing. The CPU 401 then receives the instruction to start printing from the control unit 400.

[0074] When CPU 401 receives a print start command, it sets a first screen in dithering unit 407 and sends a density signal of a test image to dithering unit 407 to create a test chart for gradation correction. Dithering unit 407 uses the first screen to convert the 10-bit density signal to a 4-bit density signal. Printer 300 creates test chart 801a based on the 4-bit density signal. Next, CPU 401 sets a second screen in dithering unit 407 and sends a density signal of a test image to dithering unit 407 to create a test chart for gradation correction. Dithering unit 407 uses the second screen to convert the 10-bit density signal to a 4-bit density signal. Printer 300 creates test chart 801b based on the 4-bit density signal.

[0075] After the test charts are created, the CPU 401 uses the reader 200 to operate the ADF unit 220 and perform an ADF read on the two test charts 801a and 801b (S902). To this end, the CPU 401 displays a message on the display of the operation unit 400 prompting the user to place the two test charts 801a and 801b on the document tray 302 of the ADF unit 220. Figure 11(b) shows an example of such a message screen 700e. The message screen 700e displays a message prompting the user to place the test chart 801b of the second screen on top of the test chart 801a of the first screen on the document tray 302, and a button 701c to start reading. The printer 300 may also print a message or mark on the test charts 801a and 801b indicating which screen is applied.

[0076] After the user places the test chart on the document tray 302, they press button 701c on the operation unit 400 to instruct the start of ADF reading. The CPU 401 then receives the instruction to start reading via ADF reading from the operation unit 400. Upon receiving the instruction to start reading, the CPU 401 instructs the reader 200 to perform ADF reading. The reader 200 transports the test charts 801a and 801b in succession using the ADF unit 220, and the document scanner 210 reads the test charts 801a and 801b in succession. The reader image processing unit 108 of the document scanner 210 transmits a brightness signal representing the reading result of the test charts 801a and 801b to the printer control unit 109.

[0077] When the scanning mode is set to document glass scanning (S502:N), the CPU 401 creates the first test chart 801a using the printer 300 (S911). The CPU 401 displays the message screen 700f, as illustrated in Figure 12(a), on the display of the control unit 400. The message screen 700f displays a message prompting the user to confirm that two or more sheets are stored in the paper cassette 152, a message indicating that the first test chart is being created, and a button 701d to instruct the user to start printing. After confirming that two or more sheets are stored in the paper cassette 152, the user instructs the user to start printing by pressing the button 701d on the control unit 400. The CPU 401 then receives the instruction to start printing from the control unit 400.

[0078] When CPU 401 receives a print start command, it sets the first screen in the dithering unit 407 and sends a density signal of a test image to the dithering unit 407 to create a test chart for gradation correction. Dithering unit 407 uses the first screen to convert the 10-bit density signal into a 4-bit density signal. Printer 300 creates the first test chart 801a based on the 4-bit density signal.

[0079] After the first test chart 801a is created, the CPU 401 has the reader 200 perform a document glass scan of the first test chart 801a (S912). To do this, the CPU 401 displays a message on the display of the operation unit 400 prompting the user to place the test chart on the document glass 102. Figure 12(b) shows an example of such a message screen 700g. The message screen 700g displays a message prompting the user to place the first test chart 801a on the document glass 102, and a button 701c that instructs the user to start scanning.

[0080] The user opens the ADF unit 220 to expose the document glass 102 and places the first test chart 801a on the document glass 102 with the side showing the test screen facing the document glass 102. The user then presses button 701c on the control unit 400 to start document glass scanning. The CPU 401 receives the instruction to start scanning via document glass scanning from the control unit 400. Upon receiving the instruction to start scanning, the CPU 401 instructs the reader 200 to scan the document glass. The reader 200 uses the document scanner 210 to scan the first test chart 801a on the document glass 102. The reader image processing unit 108 of the document scanner 210 transmits a brightness signal representing the scanning result of the first test chart 801a to the printer control unit 109.

[0081] Next, the CPU 401 creates a second test chart 801b using the printer 300 (S913). The CPU 401 displays the message screen 700h, as illustrated in Figure 12(c), on the display of the control unit 400. The message screen 700h displays a message indicating that a second test chart is being created, and a button 701d to instruct the user to start printing. The user instructs the user to start printing by pressing the button 701d on the control unit 400. The CPU 401 then receives the instruction to start printing from the control unit 400.

[0082] When CPU 401 receives a print start command, it sets a second screen in dithering unit 407 and sends a density signal of a test image to dithering unit 407 to create a test chart for gradation correction. Dithering unit 407 uses the second screen to convert the 10-bit density signal to a 4-bit density signal. Printer 300 creates a second test chart 801b based on the 4-bit density signal.

[0083] After the creation of the second test chart 801b, the CPU 401 has the reader 200 perform a document glass scan of the second test chart 801b (S914). To this end, the CPU 401 displays a message on the display of the operation unit 400 prompting the user to place the test chart on the document glass 102. Figure 12(d) illustrates such a message screen 700i. The message screen 700i displays a message prompting the user to place the second test chart 801b on the document glass 102, and a button 701c that instructs the user to start scanning.

[0084] The user opens the ADF unit 220 to expose the document glass 102 and places the second test chart 801b on the document glass 102 with the side showing the test screen facing the document glass 102. The user then presses button 701c on the control unit 400 to start document glass scanning. The CPU 401 receives the instruction to start scanning via document glass scanning from the control unit 400. Upon receiving the instruction to start scanning, the CPU 401 instructs the reader 200 to scan the document glass. The reader 200 uses the document scanner 210 to scan the second test chart 801b on the document glass 102. The reader image processing unit 108 of the document scanner 210 transmits a brightness signal representing the scanning result of the second test chart 801b to the printer control unit 109.

[0085] Once the reading of the two test charts 801a and 801b is complete, the CPU 401 acquires the density signal of the test image based on the reading results (luminance signal) (S505). The CPU 401 creates LUTa based on the density signal used to generate the test image and the density signal obtained from the reading results of the test charts (S506). The CPU 401 creates LUTa' based on the reading results of test chart 801a and creates LUTa'' based on the reading results of test chart 801b. Here, we have described an example of forming two test charts 801a and 801b, but calibration can also be performed using three or more test charts. For each additional test chart, processes S913 and S914 are added.

[0086] (Decision to start reading the test chart) In this embodiment, before reading the test chart, it is determined whether the test chart is correctly set, and based on the determination result, it is decided whether or not the reader 200 should start reading the test chart. Specifically, the reader 200 is permitted to read the test chart only if the test chart is correctly set. "The test chart is correctly set" means that the test chart, which is a sheet on which the test image is printed, is placed in the correct position on the document tray 302 or the document glass 102. By allowing the reader 200 to read the test chart only when it is correctly set, the occurrence of test chart reading errors is suppressed. In other words, the decision on whether or not to start reading the test chart is made by determining whether or not the test chart is correctly set before reading it. Figure 13 is a flowchart showing the calibration process including the decision on whether to start reading.

[0087] Figure 13(a) is a flowchart illustrating the process of determining whether or not to start reading the test chart before receiving the instruction to start reading the test chart. The CPU 401 acquires information representing the sheet size (paper size) selected by the user when creating the test chart (S101). This section describes the case where the user selects an A4 size sheet. As mentioned above, the user selects whether to perform ADF reading (first reading mode) or document glass reading (second reading mode) of the test chart before creating it. The CPU 401 displays a screen for selecting the paper size on the display of the operation unit 400, for example, after the reading mode has been selected on the operation screen 700a in Figure 8(a). This allows the user to select the paper size of the sheet to be used for the test chart from the paper size selection screen after selecting the reading mode. The orientation of the sheet may also be selected when selecting the paper size. In this case, the CPU 401 also acquires information representing the orientation of the sheet.

[0088] The CPU 401 creates a test chart using a sheet of paper size selected by the user (S102). The CPU 401 stores the paper size of the sheet used to create the test chart in memory 402. If a sheet orientation has also been selected, information representing the sheet orientation is also stored in memory 402. As described above, after the test chart is created, the test chart is read using the reading mode selected by the user. To do this, the user inputs a reading start command using the operation unit 400. If ADF reading (first reading mode) is selected, the CPU 401 displays a message on the operation unit 400's display prompting the user to set the test chart in the document tray 302 and adjust the spacing of the regulating members 332. If platen reading (second reading mode) is selected, the CPU 401 displays a message on the operation unit 400's display prompting the user to place the test chart using the document alignment marks 1231 on the platen glass 102 as a reference.

[0089] The CPU 401 detects the document size (size of the set test chart) using the reader 200 (S103). In ADF reading (first reading mode), the reader control unit 413 continuously updates the document size detection result based on the detection result of the document width sensor 333 while the document length detection sensors 334a and 334b ​​are detecting the document. This is to adjust the position of the regulating member 332 to set the test chart in the correct position when the user places the test chart on the document stacking unit 301. In document glass reading (second reading mode), the reader control unit 413 detects the document size at the timing when the reader 200 is closed. This is because the opening and closing operation of the reader 200 is performed when the user sets the test chart on the document glass 102.

[0090] CPU 401 compares the paper size of the test chart created in process S102 (obtained in process S101) with the document size detected in process S103, and determines whether the paper size and document size match based on the comparison result (S104). If they match, CPU 401 determines that the test chart is set correctly and that it is possible to start reading. If they do not match (S104:N), CPU 401 will repeat processes S103 and S104 until the paper size of the test chart matches.

[0091] Figure 14 is an explanatory diagram for determining whether or not to start scanning. In this example, the test chart is created using an A4-sized sheet. Therefore, CPU 401 determines that the paper size and the document size match if the document size detected by reader 200 is A4 or A4R, and determines that the paper size and the document size do not match if the document size is anything other than A4 or A4R. If the test chart is created using an A3-sized sheet, CPU 401 determines that the paper size and the document size match only if the document size detected by reader 200 is A3.

[0092] Figure 15 is an example of the state when a test chart is placed in the document tray 302 during ADF scanning. Figure 16 is a diagram showing the relationship between the state of the test chart placed in the document tray 302 and the scanning result. Here, the example uses a test chart created using an A4 size sheet.

[0093] Figure 15(a) shows the case when the test chart is set correctly. The test chart is set so that the center of the width direction of the document being fed aligns with the center of the test chart. The pair of regulating members 332 have moved to a position that matches the width of the document on the test chart. In this case, the CPU 401 determines that the test chart is ready to be read. Figure 15(b) shows the case when the test chart is set in the horizontal reading direction (R direction). In this case, since the detected document size is the same as the size of the created test chart, the CPU 401 determines that the test chart is ready to be read.

[0094] Figure 15(c) shows the case where the test chart is set on the front side in the width direction. In this case, the test chart is not set correctly, and the size of the created test chart does not match the size of the detected document, so the CPU 401 determines that the test chart cannot be read. This prevents a reading error. Figure 15(d) shows the case where the test chart is set at an angle to the transport direction. In this case, the test chart is not set correctly, and the size of the created test chart does not match the size of the document, so the CPU 401 determines that the test chart cannot be read. This prevents a reading error.

[0095] Figure 15(e) shows the case where a different document from the created test chart is loaded, and the detected document size is different from the paper size of the test chart. In this case, the CPU 401 determines that the test chart cannot be started to read. This prevents a reading error. Figure 15(f) shows the case where a different document from the created test chart is loaded, and the detected document size matches the paper size of the test chart. In this case, the CPU 401 determines that the test chart can be started to read. However, a reading error occurs after the document is read.

[0096] Figure 17 is an example of the state when the test chart is set on the document glass 102 during document scanning.

[0097] Figure 17(a) shows the case when the test chart is set correctly. The edge of the test chart is placed on the document alignment mark 1231 on the reference abutment at the back of the document glass 102. In this case, the CPU 401 determines that the test chart is ready to be read. Figure 17(b) shows the case when the test chart is set horizontally (R-orientation). In this case, since the detected document size is the same as the size of the created test chart, the CPU 401 determines that the test chart is ready to be read.

[0098] Figure 17(c) shows a case where the edge of the test chart is not aligned with the document alignment marks 1231. In this case, the CPU 401 determines that the test chart cannot be read because it is not set correctly. This prevents a reading error. If document scanning is performed in this state, the first mirror unit 104a and the second mirror unit 104b will only move to the A4 size position because the test chart is A4. As a result, only a portion of the test chart will be read, and a reading error will occur. Figure 17(d) shows a case where the test chart is set at an angle. Even if the user sets the test chart correctly, this condition can occur if the test chart is tilted due to wind when closing the reader 200. In this case as well, the CPU 401 determines that the test chart cannot be read. This prevents a reading error.

[0099] Figure 17(e) shows the case where a different document than the created test chart is loaded, and the detected document size is different from the paper size of the test chart. In this case, the CPU 401 determines that the test chart cannot be started to read. This prevents a reading error. Figure 17(f) shows the case where a different document than the created test chart is loaded, and the detected document size matches the paper size of the test chart. In this case, the CPU 401 determines that the test chart can be started to read. However, a reading error occurs after the document is read.

[0100] If the paper size of the test chart matches the detected document size (S104:Y), the CPU 401 determines that the reader 200 can begin reading the test chart (S105). As a result, the CPU 401 switches the button 701c, which instructs the start of reading and is included in the message screens 700b and 700c in Figures 8(b) and 8(c), from a grayed-out state to a pressable state. Alternatively, the CPU 401 switches the display from a message screen that does not include the button 701c to a message screen that includes the button 701c. This switches the display from a state where the user cannot instruct the start of reading the test chart to a state where they can.

[0101] When the button 701c, which instructs the start of reading, is pressed and a reading start command is input, the CPU 401 controls the operation of the reader 200 to perform the test chart reading process (S106). In the first reading mode, the CPU 401 performs ADF reading, and in the second reading mode, it performs document glass reading. Based on the reading results of the test chart, the CPU 401 performs the above calibration and completes the adjustment of the print conditions (S107).

[0102] Figure 13(b) is a flowchart showing the process of determining whether or not to start reading the test chart when an instruction to start reading is received. The same steps as in Figure 13(a) are assigned the same step numbers. The explanation of the same steps as in Figure 13(a) is omitted.

[0103] In the S102 process, the CPU 401 created the test chart. When the button 701c, which instructs the start of scanning, is pressed and the CPU 401 receives the instruction to start scanning (S201), it executes the S103 process to detect the document size by the reader 200. If the paper size of the test chart created in the S102 process does not match the document size detected in the S103 process (S104:N), the CPU 401 determines that scanning cannot be started. In this case, the CPU 401 notifies the user that the test chart is not properly set in the reader 200 (S111).

[0104] Figure 18 is an example of the notification screen displayed on the display of the operation unit 400 in this case. Figure 18(a) shows an example of the notification screen when ADF reading (first reading mode) is selected. This notification screen includes a notification that the test chart is not properly set in the document tray 302 of the ADF unit 220, an instruction to reposition the test chart on the document tray 302, and an instruction to adjust the regulating member 332, etc. Figure 18(b) shows an example of the notification screen when platen reading (second reading mode) is selected. This notification screen includes a notification that the test chart is not properly set on the platen glass 102, an instruction to reposition the test chart on the platen glass 102, and an instruction to set the test chart by abutting it against the document alignment mark 1231.

[0105] After notification, CPU 401 repeatedly performs the processes from S201 onward until the paper size of the test chart created in process S102 matches the document size detected in process S103. To this end, after the notification process in S111, CPU 401 displays a screen on the display of the operation unit 400 that includes a button 701c instructing the user to start scanning. When the user presses this button 701c using the operation unit 400, the processes from S201 onward are performed. Note that the notification in S111 may be performed using output devices such as sound or lamp indicators, in addition to displaying a notification screen on the display.

[0106] Figure 13(c) is a flowchart showing the process of deciding to start reading the test chart when an instruction to start reading is received. Figure 13(c) is an example in which the order of processes S201 and S103 in Figure 13(b) is reversed. The individual processes are the same, so their explanation is omitted.

[0107] Conventionally, it was necessary to determine reading errors from the test chart reading results, and especially when reading using the ADF unit 220, time was wasted until a reading error occurred due to the test chart not being set correctly. In contrast, the image forming apparatus 100 of this embodiment determines whether or not to start reading by determining whether or not the test chart is set correctly before starting to read the test chart. Since reading cannot be started if the test chart is not set correctly, reading errors caused by an incorrectly set test chart can be prevented. The image forming apparatus 100 can prevent the wasted effort of rereading the test chart due to reading errors. In other words, the effects shown in Figure 16 can be obtained.

[0108] (Other examples of when to start reading the test chart) In the process for determining when to start reading the test chart described above, the readability of the test chart is determined by whether the paper size of the sheet used for the test chart matches the document size detected by the reader 200. However, depending on the type of print conditions adjusted by the test chart, the orientation of the test chart when it is read by the reader 200 may be limited. In this case, the orientation of the placed test chart is included in the criteria for determining whether the paper size and document size match.

[0109] For example, during printing, the photosensitive drums 121, 131, 141, and 151 are scanned in the main scanning direction (Y direction) by the laser beam. In this process, density unevenness may occur in the main scanning direction. Density unevenness in the main scanning direction can be caused by, for example, uneven charging due to deterioration of the charger 122 that charges the photosensitive drums 121, 131, 141, and 151, uneven exposure of the laser beam by the exposure unit 110, or uneven development by the developer unit 123.

[0110] When correcting density unevenness in the main scanning direction, a test chart for density unevenness correction is created. Figure 19 is an explanatory diagram of the test chart for density unevenness correction. Figure 19(a) shows an example of an A4-sized test chart 810. Figure 19(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) with 50% density signals for each color: yellow, magenta, cyan, and black. Regardless of the sheet size, the band-shaped test image is formed so that the main scanning direction is the length of the band.

[0111] The reading of test charts 810 and 811 for density uniformity correction is performed with the main scanning direction (Y direction) of test charts 810 and 811 set 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 differ depending on their position in the Y direction. By reading the test charts 810 and 811 with the main scanning direction aligned to the SX1 or SX2 direction of the reader 200, the difference in characteristics due to the position of the photoelectric conversion elements of the image sensor 105 can be suppressed.

[0112] The decision to start reading such a test chart is made in the same way as the process in S104 of Figure 13. That is, the CPU 401 determines whether or not to start reading the test chart by determining whether or not the paper size of the test chart created in the process of S102 matches the original document size detected in the process of S103. At this time, the CPU 401 adds the orientation of the original document as a condition for determining whether or not the size matches. Figure 20 is an explanatory diagram of the decision on whether or not to start reading. The orientation of the original document is added as a condition for determining whether or not the size matches. In Figure 20, if the paper size is A4, reading can only be started if the original document size is A4R. In the case where the paper size is A4 and the original document size is A4, the paper size and original document size match, but reading cannot be started because the orientation of the original document is incorrect. This is the difference between Figure 20 and Figure 14. In Figure 20, if the paper size is A3, reading can only be started if the original document size is outside the standard size. When the paper size is A3, the correct placement of the test chart 811 is on the document glass 102 so that a portion of it extends beyond the document glass. Therefore, when performing density unevenness correction using the A3 size test chart 811, ADF reading (first reading mode) is not possible, and only document glass reading (second reading mode) is possible.

[0113] Figure 21 shows the relationship between the test chart placement in the document tray 302 and the scanning result. In this example, the orientation of the document is added to the criteria for determining whether the document size matches (how the document is placed). Therefore, as shown in Figure 21, it is possible to prevent scanning errors when the test chart is in an incorrect position and scanning orientation, even when adjusting for density unevenness in the main scanning direction (Y direction), which has limitations on the scanning orientation of the test chart.

[0114] (Other examples of when to start reading the test chart) This section describes an example of preventing reading errors by positioning the test chart so that its longest side (the longest side of the sheet) is parallel to the Y-direction of the reader 200, regardless of the test chart's orientation.

[0115] For example, in the case of "image defect diagnosis including detection of ADF reading lines," the test chart is placed so that its longitudinal direction is parallel to the Y direction of the reader 200. Figure 22 is an explanatory diagram of the test chart for image diagnosis used in "image defect diagnosis including detection of ADF reading lines." The test chart 820 for image diagnosis includes a white area 821 where no image is formed, and band-shaped test images 822, 823, 824, and 825 formed with 50% density signals of each color: yellow, magenta, cyan, and black. Figure 22(a) illustrates the test chart 820 for image diagnosis formed on an A4 sheet. Figure 22(b) illustrates the test chart 820 for image diagnosis formed on an A4R sheet.

[0116] When reading the test chart 820 for diagnostic imaging, regardless of whether the test chart is A4 or A4R, the test chart 820 must be set with its long side (the longer side of the sheet) parallel to the Y direction.

[0117] When determining the presence or absence of ADF reading streaks, if streaks are detected both before the test chart 820 is transported to the reader 200's reading position and on the white area 821 of the test chart, then streaks will be detected regardless of the presence or absence of the test chart 820. In this case, it is determined that the streaks are caused by the reader 200. If no streaks are detected before the test chart 820 is transported to the reader 200's reading position, but streaks are detected on the white area 821 of the test chart 820, then it is determined that the streaks are on the white area 821 of the test chart 820 and not caused by the reader 200. In this case, it is determined that the streaks are caused by the image forming apparatus 100. Figure 23 is a diagram illustrating the relationship between the streak detection location and the cause of the streaks.

[0118] To differentiate between streaks caused by the reader 200 and those caused by the image forming apparatus 100, image diagnosis is performed on a wider reading area (Y direction) of the reader 200. For this purpose, the test chart 820 is set with its longitudinal direction (the long side of the paper) parallel to the Y direction. In other words, reading is permitted only when the test chart 820 is set in the reader 200 in A4 size.

[0119] Figure 24 is an explanatory diagram for determining whether or not reading can be started. In the case of the ADF test chart 820 for diagnostic imaging, which includes the reading lines of the ADF, reading can only be started if the original document size is A4, regardless of whether the paper size is A4 or A4R. This makes it possible to prevent reading errors when the diagnostic imaging test chart 820 is placed in any other position.

[0120] As described above, the image forming apparatus 100 of this embodiment determines whether the test chart is correctly set before performing the test chart reading operation when adjusting the print conditions using the test chart. This prevents reading errors caused by user mistakes in reading the test chart to the reader 200. As a result, it becomes possible to improve the efficiency of the adjustment work using the test chart.

Claims

1. Image forming means for forming an image on a sheet, A reading means for reading the test image on the sheet, An acquisition means for acquiring paper size information relating to the size of the sheet on which the test image is to be formed, A control means that forms the test image using the image forming means based on the paper size information acquired by the acquisition means, causes the reading means to read the test image in response to an instruction to start reading the test image, and performs calibration of the image forming means based on the reading result of the test image read by the reading means, A start-read button operated to give the instruction to start reading, The device includes a detection means for detecting document size information corresponding to the size of the sheet read by the reading means, The control means is characterized by preventing the start of reading from being initiated by the start of reading button if the paper size information and the document size information are different. Image forming apparatus.

2. Image forming means for forming an image on a sheet, A reading means for reading the test image on the sheet, An acquisition means for acquiring paper size information relating to the size of the sheet on which the test image is to be formed, A control means that forms the test image using the image forming means based on the paper size information acquired by the acquisition means, causes the reading means to read the test image in response to an instruction to start reading the test image, and performs calibration of the image forming means based on the reading result of the test image read by the reading means, A detection means for detecting document size information corresponding to the size of the sheet read by the reading means, The device is characterized by having a display means that displays a start-read button for issuing a reading start instruction when the paper size information and the document size information match, and does not display the start-read button when the paper size information and the document size information do not match. Image forming apparatus.

3. The control means is characterized in that, if the paper size information and the document size information are different, it controls the system to a state where it cannot instruct the start of reading even if the start of reading button is pressed. The image forming apparatus according to claim 1.

4. The invention further comprises a display means for displaying the reading start button, The control means is characterized in that, if the paper size information and the document size information are different, it grays out the start reading button displayed on the display means. The image forming apparatus according to claim 1.

5. The reading means is characterized by comprising a document tray on which the sheet on which the test image is formed is placed, and a reading unit that reads the test image on the sheet placed on the document tray, An image forming apparatus according to any one of claims 1 to 4.

6. The reading means comprises a mounting tray on which the sheet on which the test image is formed is placed, a transport unit for transporting the sheet placed on the mounting tray, a paper output tray from which the sheet transported by the transport unit is discharged, and a reading unit for reading the test image on the sheet, characterized in that the sheet is transported from the mounting tray by the transport unit and the test image on the sheet is read by the reading unit. An image forming apparatus according to any one of claims 1 to 4.

7. The reading means comprises a stopper member against which a sheet placed on the document table is pressed, and a sensor that detects the presence or absence of a sheet at a detection position located in a predetermined direction away from the stopper member, The detection means is characterized by detecting the document size information based on the detection result of the sensor and the reading result of the reading unit. The image forming apparatus according to claim 5.

8. The reading means is, A restricting member is provided on the aforementioned mounting tray and is slidable in a first direction, and restricts the end of the sheet placed on the aforementioned mounting tray in the first direction, A first sensor for detecting the position of the regulating member in the first direction, A second sensor is provided on the aforementioned tray for detecting the presence or absence of a sheet placed on the aforementioned tray, The aforementioned mounting tray is provided with a third sensor located at a position different from the second sensor in a second direction intersecting the first direction, which detects the presence or absence of a sheet placed on the aforementioned mounting tray. The detection means is characterized by detecting the document size information based on the detection result of the first sensor, the detection result of the second sensor, and the detection result of the third sensor. The image forming apparatus according to claim 6.

9. The aforementioned paper size information is characterized by being user-instructed information that indicates the selection result of a size chosen by the user from among multiple options. An image forming apparatus according to any one of claims 1 to 8.

10. The calibration is characterized by being a control that adjusts the density of the image formed by the image forming means. An image forming apparatus according to any one of claims 1 to 9.

11. The calibration is characterized by being a control that suppresses density unevenness in the image formed by the image forming means. An image forming apparatus according to any one of claims 1 to 9.

12. The calibration is characterized by being a control for diagnosing image defects in the image formed by the image forming means. An image forming apparatus according to any one of claims 1 to 9.

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