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 generating a test chart and reading the test chart by a reading device to adjust printing conditions, diagnose image defects, etc. For adjusting printing conditions, for example, there are maximum density correction, gradation correction, in-plane density unevenness correction, alignment correction (front-back registration adjustment), vertical unevenness adjustment of a print head (adjustment of a light emitting unit), transfer output adjustment (secondary transfer voltage adjustment), etc. Image defects include dots, streak images, etc. The test chart is formed by printing a test image corresponding to the adjustment content and 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 the temperature and humidity at the installation location of the image forming apparatus, and changes in components of the image forming apparatus over time. Therefore, the image forming apparatus performs 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. At the time of 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 or not).

[0004] Patent Document 1 proposes a method of reducing the user's workload during calibration by reading a test chart using an automatic document feeder. Patent Document 2 proposes a method of improving user-friendliness by determining whether a sheet used for calibration is set in a cassette before generating a test chart. Both are technologies for improving workability during calibration. Patent Document 3 proposes a technology for determining whether a sheet corresponding to the document size is set in a cassette when sequentially reading a plurality of documents with different sizes and performing copy processing, and selecting whether to continue or stop reading the document.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] When adjusting print conditions or diagnosing image defects using a test chart, it is necessary for the user to set the test chart in the reading device. Since this work involves human hands, there is a possibility of work errors. For example, the user may set a document other than the test chart in the reading device. Also, the user may give an instruction to read without correctly setting the test chart in the reading device.

[0007] Such operation errors include errors in the type of document set in the reading device and errors in the way of setting the document. When the document is a test chart and is set in the fixed position, no operation error occurs. Even if the document is a test chart but is not set in the fixed position, a reading error will occur due to the operation error. When the document is other than the test chart and has a size different from that of the test chart, a reading error will occur due to the operation error regardless of whether it is set in the fixed position. When the document is other than the test chart and has the same size as the test chart, a reading error will occur due to the operation error regardless of whether it is set in the fixed position.

[0008] When a reading error occurs, the image forming apparatus instructs the user to read the test chart again. That is, when the test chart is not correctly set in the reading device, the image forming apparatus will cause the user to perform the operation again after performing the image reading process once, resulting in wasted work. Therefore, a technology is required to prevent reading errors caused by the user's operation errors and improve the work efficiency.

[0009] In view of the above problems, the main object of the present invention is to provide an image forming apparatus that prevents reading errors caused by the user's operation errors.

Means for Solving the Problems

[0010] The image forming apparatus of the present invention includes an image forming means for forming an image on a sheet, a placing means on which the sheet is placed, a reading means for reading an image of the sheet placed on the placing means, forming a test image on the sheet by the image forming means to create a test chart, and when the test chart is placed on the placing means, determining whether the test chart is correctly placed on the placing means, and a control means for determining whether the reading means can start reading the test chart.

Effects of the Invention

[0011] According to the present invention, by determining whether the test chart is correctly set before reading the test chart, it is possible to judge whether the reading means can start reading, thereby preventing reading errors caused by user operation mistakes. Therefore, the work efficiency can be improved.

Brief Description of the Drawings

[0012]

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

[0014] (Image forming apparatus) FIG. 1 is a configuration diagram of the image forming apparatus according to the present embodiment. The image forming apparatus 100 includes 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 includes a document scanner 210 and an automatic document feeder (hereinafter referred to as the "ADF unit") 220. The document scanner 210 is provided on the printer 300, and the ADF unit 220 is provided 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 conveyance direction of the sheet by the image forming apparatus 100 is defined as the PX direction, and the direction orthogonal to the PX direction is defined as the Y direction. Also, the paper feed 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 the document fed by the ADF unit 220 and the document 101 placed on the document glass 102 provided on the ADF unit 220 side of the document scanner 210. The document scanner 210 includes a reader image processing unit 108 inside. The reader image processing unit 108 converts the electrical signal generated by reading the document 101 into an image signal and transmits it to the printer 300.

[0017] The printer 300 includes a printer control unit 109 inside. The printer control unit 109 acquires the 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. The printer 300 includes an image forming unit 120, 130, 140, 150, an exposure unit 110, a transfer belt 111, and a fixing unit 114 for image formation.

[0018] The image forming units 120, 130, 140, 150 only differ in the color of the image they form and perform the same operations with the same configuration. The image forming unit 120 forms a yellow (Y) image. The image forming unit 130 forms a magenta (M) image. The image forming unit 140 forms a cyan (C) image. The image forming unit 150 forms a black (K) image. Here, the configuration of the image forming unit 120 will be described, and the descriptions of the configurations of the other image forming units 130, 140, 150 will be omitted.

[0019] The image forming unit 120 includes a photosensitive drum 121, a charger 122, a developing unit 123, a transfer blade 124, and a surface potentiometer 125. The photosensitive drum 121 is a drum-shaped photoreceptor having a photosensitive layer on its surface. The photosensitive drum 121 rotates in the clockwise direction in the figure. The charger 122 uniformly charges the surface of the rotating photosensitive drum 121 to a predetermined potential. When the charged surface of the photosensitive drum 121 is scanned with a laser beam by the exposure unit 110, an electrostatic latent image is formed on the surface. 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 becomes 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 (e.g., toner) of a corresponding color (here, yellow) to form a toner image on the surface of the photosensitive drum 121.

[0020] The transfer blade 124 is disposed with the transfer belt 111 sandwiched therebetween and the photosensitive drum 121. The transfer belt 111 conveys a sheet from the paper feed cassette 152. The transfer belt 111 transfers the toner image formed on the photosensitive drum 121 to the sheet conveyed by the transfer belt 111 by performing discharge. As a result, a yellow toner image is formed 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 overlap the yellow toner image on the sheet. The cyan toner image formed on the photosensitive drum 141 is transferred so as to overlap the yellow and magenta toner images on the sheet. The black toner image formed on the photosensitive drum 151 is transferred so as to overlap the yellow, magenta, and cyan toner images on the sheet. By overlapping 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 is formed is conveyed to the fixing device 114 by the transfer belt 111. The fixing device 114 fixes the transferred toner image to the sheet. The fixing device 114 fixes the toner image to the sheet, for example, by heating and melting the toner image and applying pressure. Thus, an image is formed on the sheet. The sheet on which the image is formed is discharged outside the printer 300.

[0023] Note that the surface potential meters 125, 135, 145, and 155 of the respective image forming units 120, 130, 140, and 150 measure the surface potentials of the photosensitive drums 121, 131, 141, and 151. The contrast potential is adjusted according to the measurement results by 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 as seen 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, an original size detection sensor 113, and a home position sensor 106 inside the housing. The first mirror unit 104a includes an original 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 reading in a first reading mode for reading the original 101 conveyed by the ADF unit 220 and a second reading mode for reading the original 101 placed on the platen glass 102. The first reading mode may be called "continuous reading" or "ADF reading". The second reading mode may also be called "fixed reading" or "platen reading".

[0026] There are two types of reading methods in the first reading mode: the sheet-through method and the original fixing method. In the sheet-through method, when the motor 116 rotates, the first mirror unit 104a and the second mirror unit 104b move to the continuous reading position and stop. The continuous reading position is the reading position when reading an image from the original 101 being conveyed by the ADF unit 220. While the ADF unit 220 is conveying the original 101 on the platen glass 102, the image sensor 105 reads the image of the original 101.

[0027] The document scanner 210 turns on the document illumination lamp 103 to irradiate light onto the reading surface (the surface on which the 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 by 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. When reading an image, the first mirror unit 104a, the second mirror unit 104b, the image sensor 105, and the reader image processing unit 108 operate in this way. This operation during reading is the same regardless of the reading mode or reading method.

[0028] In the document fixing method, the ADF unit 220 conveys the document 101 onto the document table glass 102 and stops the document 101 at a predetermined position on the document table glass 102. The first mirror unit 104a and the second mirror unit 104b read the image of the document 101 while moving in the SX1 direction by the motor 116. The ADF unit 220 resumes the conveyance of the document 101 after image reading and discharges it.

[0029] In the second reading mode, when the motor 116 rotates, the first mirror unit 104a and the second mirror unit 104b move to the home position where the home position sensor 106 is located once. One document is placed on the document table glass 102 with the reading surface facing the document table glass 102 side, and its position is fixed by the ADF unit 220. The document scanner 210 turns on the document illumination lamp 103 and irradiates light onto the reading surface of the document 101. The first mirror unit 104a and the second mirror unit 104b deflect the image light from the document 101 by the first mirror 107a, the second mirror 107b, and the third mirror 107c and guide it to the lens 115 while moving in the SX1 direction. 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.

[0030] The document scanner 210 can detect the size of the document 101 (document size). The document scanner 210 of the present embodiment detects the document size before reading the document image. The document scanner 210 first irradiates the edge of the document 101 with the document illumination lamp 103, and reads the reflected light from the document 101 with the image sensor 105. The image sensor 105 is, for example, a line sensor in which a plurality of 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 document 101 can be obtained.

[0031] Also, based on the detection result of the document size detection sensor 113, the length (length in the SX1 direction) of the document 101 is detected. At least one document 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 document 101 on the document table glass 102 at that position. The document size detection sensor 113 is, for example, an infrared sensor, and can output the presence or absence of the document 101 in binary values. 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. When it is desired to accurately detect the length of the document 101, a plurality of document size detection sensors 113 are arranged.

[0032] Based on the width and length of the document 101 detected in this way, it is determined which of a plurality of predetermined standard sizes the document 101 is. Also, based on the width and length of the document 101, it is also determined in which orientation (vertical reading, horizontal reading) the document 101 is placed on the document table glass 102.

[0033] As shown in Fig. 2(b), on the outer periphery of the platen glass 102, a document size label 1230 is arranged, and a document alignment mark 1231 is provided at the reference abutting portion on the back side in the Y direction. The document 101 is placed so that its vertex abuts on the document alignment mark 1231. The reference for the standard size document is the document alignment mark 1231. The document size detection sensor 113 of the present 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-size document. Therefore, the document size detection sensor 113 cannot detect documents 101 of A4, B5, A5, and B6 sizes, but can detect documents 101 of A3, B4, A4R, and B5R sizes.

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

[0035] Based only on the electrical signal output from the image sensor 105, it is determined to which of the first group to the fourth group the document 101 to be detected belongs. That is, based on the document detection width, it is determined whether the document 101 is in the first group of B5R and B6, the second group of A4R and A5, the third group of B5 and B4, or the fourth group of A4 and A3. However, only the document detection width cannot distinguish within each group. The detection result (presence or absence of the document) by the document size detection sensor 113 enables distinction within each group. For example, when it is determined based on the document detection width that the size of the document 101 to be detected belongs to the fourth group, if the detection result of the document size detection sensor 113 indicates that there is a document, it is determined that the size of the document 101 to be detected is A3 for vertical feeding. If there is no document, it is determined that the size of the document 101 to be detected is A4 for horizontal feeding. In addition, if it does not belong to any of the determination results, it is determined that it is not a standard size.

[0036] (ADF Unit) FIG. 4 is an explanatory diagram of the ADF unit 220. FIG. 4(a) is an external perspective view of the ADF unit 220. FIG. 4(b) is an internal configuration diagram of the ADF unit 220. FIG. 4(c) is a view of the document loading unit 301 described later as seen from obliquely above. FIG. 4(d) is an internal configuration diagram of the document loading unit 301 described later. The ADF unit 220 includes a document loading unit 301, a document feeding unit 304, a document conveying unit 308, and a duplex discharging unit 313.

[0037] The document loading unit 301 has a document tray 302. The document tray 302 can load one or more documents 101 on the loading surface. The document tray 302 functions as a paper feeding unit. The document loading unit 301 is provided with a document indicator 303 that lights up when a document 101 is loaded on the document tray 302. The document 101 loaded on the document tray 302 is conveyed one by one onto the document table glass 102 by the document feeding unit 304, passes over the document table glass 102, and is discharged to the discharge tray 321 of the duplex discharging unit 313 by the duplex discharging unit 313.

[0038] In the document feeding unit 304, a pickup roller 306, a paper feeding roller 307, and a registration roller pair 305 are provided along the conveyance path of the document 101. The pickup roller 306 is a rotatable and vertically movable roller. When feeding paper, the pickup roller 306 descends and contacts the topmost document 101 in the stack of documents loaded on the document tray 302 and conveys the document 101. The paper feeding roller 307 conveys the document 101 conveyed by the pickup roller 306 to the registration roller pair 305. By the pickup roller 306 and the paper feeding roller 307, the documents 101 are conveyed one by one. The registration roller pair 305 stops when the leading edge of the document 101 arrives. This is to correct the skew of the document 101. After skew correction, the registration roller pair 305 starts rotating and conveys the document 101 to the document conveying unit 308.

[0039] The original document conveyance unit 308 includes a conveyance belt 309, a driving roller 310, a driven roller 311, and a plurality of pressing rollers 312. The original document conveyance unit 308 conveys the original document 101 in the SX1 direction using the conveyance belt 309. The conveyance belt 309 is stretched between the driving roller 310 and the driven roller 311. Further, the conveyance belt 309 is pressed against the platen glass 102 by the pressing rollers 312. The conveyance belt 309 conveys the original document 101 that has entered between the conveyance belt 309 and the platen glass 102 by frictional force. Thereby, the original document 101 is conveyed on the platen glass 102.

[0040] In the original document fixing method of the first reading mode, when the original document 101 reaches the reading position, the conveyance belt 309 stops. After the original document 101 is read by the first mirror unit 104a and the second mirror unit 104b, the conveyance belt 309 conveys the original document 101 to the reverse paper discharge unit 313. In this case, the first mirror unit 104a and the second mirror unit 104b read the stopped original document 101 while moving in the SX1 direction. In the sheet-through method of the first reading mode, even when the original document 101 reaches the reading position, the conveyance belt 309 does not stop and continues to convey the original document 101. In this case, the first mirror unit 104a and the second mirror unit 104b read the original document 101 being conveyed while remaining stopped. That is, the scanning of the original document 101 is performed by the movement of the original document 101 instead of the movement of the first mirror unit 104a and the second mirror unit 104b.

[0041] The reverse paper discharge unit 313 includes a reverse roller 314, a pair of conveyance rollers 315, a reverse flapper 316, a paper discharge flapper 317, and a reverse roller 318. The reverse paper discharge unit 313 reverses the front and back of the original document 101 conveyed from the original document conveyance unit 308 and discharges it to the paper discharge tray 321 of the paper discharge stacking unit 320.

[0042] The original document 101 conveyed by the conveyance belt 309 of the original document conveyance unit 308 is scooped up by the reverse flapper 316 and conveyed to the reverse roller 314 when entering the reverse paper discharge unit 313. The original document 101 is sandwiched between the reverse roller 314 rotating in the CCW (Counter Clock Wise) direction and the reverse roller 318 facing it, and is conveyed to the pair of conveyance rollers 315. When the trailing edge of the original document 101 passes through the paper discharge flapper 317, the paper discharge flapper 317 rotates in the CW (Clock Wise) direction. Also, the reverse roller 314 rotates in the CW direction. As a result, the original document 101 is conveyed in a switchback manner and discharged to the paper discharge tray 321 of the paper discharge stacking unit 320.

[0043] (Original document size detection by ADF unit) As shown in FIG. 4(c), a pair of regulating members 332 slidable in the width direction (Y direction, the direction orthogonal to the conveyance direction of the original document) of the original document are arranged on the original document tray 302 of the original document stacking unit 301. The regulating members 332 have a function of aligning the positions in the width direction during feeding by regulating both end portions in the width direction of the original document placed on the original document stacking unit 301 (original document tray 302). The pair of regulating members 332 are movable symmetrically in the width direction of the original document, and regulate the position of the original document so that the center in the width direction of the fed original document becomes the feeding center.

[0044] An original document width sensor 333 capable of detecting the position of the regulating member 332 is provided in the original document stacking unit 301 (FIG. 4(d)). The original document width sensor 333 detects the size in the width direction of the original document placed on the original document tray 302 by detecting the position of the regulating member 332 that moves according to the width of the original document.

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

[0046] Based on the detection results of the original document width sensor 333 and the original document length detection sensors 334a and 334b, it is possible to detect the size and orientation (whether it is vertical feeding or horizontal feeding) of the original document placed on the original document loading unit 301. FIG. 5 is an explanatory diagram of original document size determination. From the combination of each detection result from the original document width sensor 333 and the original document length detection sensors 334a and 334b, the size of the original document placed on the original document loading unit 301 (original document tray 302) is determined. FIG. 5 shows the combination of the original document detection width in the width direction of the original document on the original document loading unit 301, which is the detection result of the original document width sensor 333, and the detection results of the original document length detection sensors 334a and 334b (the presence or absence in the feeding direction (SX2 direction) of the original document placed on the original document loading unit 301). Note that the original document length detection sensors 334a and 334b output the presence or absence of the original document in a binary value.

[0047] Based only on the detection result of the original document width sensor 333, it is determined to which of the first group to the fourth group the original document 101 to be detected belongs. That is, based on the original document detection width, it is determined whether the original document 101 is any of the first group of B5R and B6, the second group of A4R and A5, the third group of B5 and B4, and the fourth group of A4 and A3. However, only the original document detection width cannot distinguish within each group. The detection result (presence or absence of the original document) by the original document length detection sensor 334b enables distinction within each group. For example, when it is determined based on the original document detection width that the size of the original document 101 to be detected belongs to the fourth group, if the detection result of the original document length detection sensor 334b is that there is an original document, it is determined that the size of the original document 101 to be detected is vertical feed A3. If there is no original document, it is determined that the size of the original document 101 to be detected is horizontal feed A4. Note that if the original document length detection sensor 334a detects an original document and does not belong to any of the determination results, it is determined that it is not a standard size. Also, when the original document length detection sensor 334a does not detect the original document, it is determined that there is no original document.

[0048] The detection of the document size of the document 101 placed on the platen glass 102 and the detection of the document size of the document 101 placed on the document tray 302 as described above are performed by the reader 200. The reader 200 performs document size detection processing in response to an instruction from the printer 300. The detection result of the document size is transmitted from the reader 200 to the printer 300.

[0049] (Printer control unit) FIG. 6 is an explanatory diagram of the printer control unit 109. A CPU (Central Processing Unit) 401, a memory 402, a reader 200, and a semiconductor laser 410 for comprehensively controlling the operation of the image forming apparatus 100 are connected to the printer control unit 109. The memory 402 includes a ROM (Read Only Memory) and a RAM (Random Access Memory), and stores a control program for controlling the operation of the image forming apparatus 100 and various types of data. The CPU 401 controls the operation of the image forming apparatus 100 by executing the control program stored in the memory 402.

[0050] An operation unit 400 is connected to the CPU 401. 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 numeric keys, and a touch panel. The output device includes a display and a speaker. In addition to the above-described reader image processing unit 108, the reader 200 includes a reader control unit 413. The reader control unit 413 performs the above-described document size determination processing. The semiconductor laser 410 is provided in 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 includes a color processing unit 403, a gradation control unit 411, a dither processing unit 407, a PWM unit 408, and a laser driver 409. The printer control unit 109 converts each of the R, G, and B image signals into a PWM signal, and controls the light emission of the semiconductor laser 410 based on this PWM signal.

[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 a desired output result (image) can be obtained when 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 accuracy improvement. The color processing unit 403 includes a LUTid404 which is a look-up table. The LUTid404 is a luminance-density conversion table that converts the luminance information included in the image signal into density information. The color processing unit 403 converts the luminance information of each of the R, G, B image signals into the density information of the Y (yellow), M (magenta), C (cyan), K (black) image signals by means of the LUTid404. The Y, M, C, 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. For this purpose, the gradation control unit 411 includes a UCR (Under Color Remove) unit 405 and a γ correction unit 406 which is a look-up table LUTa. The gradation control unit 411 performs gradation correction of the Y, M, C, K image signals so that a desired output result (image) can be obtained in accordance with the actual output characteristics of the printer 300. The UCR unit 405 restricts the integrated value of the image signal at each pixel to limit the sum of the image signal levels. When the sum exceeds a specified value, the UCR unit 405 performs an under color removal process (UCR) of replacing a predetermined amount of the C, M, Y image signals with the K image signal to reduce the sum of the image signal levels.

[0054] The gamma correction unit 406 corrects the density characteristic (gamma characteristic) of the image signal using LUTa. LUTa is a 10-bit conversion table (tone correction condition) for correcting the density characteristic. As described above, the tone characteristic of the image formed by the printer 300 on the sheet varies depending on environmental changes and component wear. Also, the tone characteristic of the image differs depending on the type of sheet. The CPU 401 updates LUTa by executing calibration and maintains the tone characteristic of the image at a predetermined tone characteristic. The printer 300 forms an image on the sheet according to the image signal corrected by the gamma correction unit 406. The memory 402 may hold LUTa for each type of sheet. The CPU 401 reads out from the memory 402 the LUTa corresponding to the type of sheet specified by the operation unit 400 and sets it in the gamma correction unit 406. LUTa is used when forming an image according to a copy of a document or a print job from a host computer, but is not used when executing calibration. The Y, M, C, and K image signals after tone correction are input to the dither processing unit 407.

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

[0056] (Calibration) Calibration is performed using a test chart generated by the printer 300. Here, a method for generating LUTa by calibration will be described.

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

[0058] Next, the CPU 401 creates a LUTa so that the density signal acquired via the reader 200 matches the density signal used to form the test image. The LUTa is created for each color of YMCK.

[0059] As described above, the reader 200 can read a document image in both reading modes of ADF reading (first reading mode) and platen reading (second reading mode). The reader 200 may read the test image printed on the test chart in either ADF reading or platen reading. Since ADF reading places less burden on the user compared to platen reading, ADF reading may be prioritized.

[0060] FIG. 7 is a flowchart showing the calibration process. FIG. 8 is an exemplary diagram of a screen displayed on the display of the operation unit 400 during the calibration process. FIG. 9 is an exemplary diagram of a test chart used for calibration.

[0061] The CPU 401 acquires an instruction indicating which reading mode, ADF reading or platen reading, the user has selected, from the operation unit 400 (S501). When the user selects ADF reading, the CPU 401 operates in the first reading mode. When the user selects platen reading, the CPU 401 operates in the second reading mode. FIG. 8(a) illustrates an operation screen 700a at the time of reading mode selection. The CPU 401 causes the operation screen 700a to be displayed on the display of the operation unit 400. Buttons 701a for selecting ADF reading and 701b for selecting platen reading are displayed on the operation screen 700a. The user selects a reading mode by selecting either button 701a or button 701b using the operation unit 400. The CPU 401 will acquire information representing the selected reading mode from the operation unit 400. The CPU 401 determines the selected reading mode (S502).

[0062] When ADF reading is selected (S502: Y), the CPU 401 sets the first image forming conditions in the printer 300 and transmits a density signal of a test image for creating a test chart for gradation correction to the dither processing unit 407. Thereby, the CPU 401 causes the printer 300 to create a test chart (S503). At this time, the LUTa is not used.

[0063] As shown in FIG. 9, test charts 801a and 801b each include a test image consisting of 10 gradations for each of the colors 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 processing unit 407 may be applicable to a plurality of halftone processes. For example, the dithering processing 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). The test chart 801a is a test chart to which a low-line screen is applied. The 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 and the like, and the high-line screen is applied to characters and the like. When the printer 300 has the ability to form an image with three or more line numbers, the number of test charts may also be three or more. Here, for convenience of explanation, the number of test charts is set to one.

[0064] After creating the test chart, the CPU 401 operates the ADF unit 220 by the reader 200 to perform ADF reading (S504). For this purpose, the CPU 401 displays, on the display of the operation unit 400, a message prompting the user to place the test chart on the document tray 302 of the ADF unit 220. FIG. 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 for instructing the start of reading.

[0065] After the user places the test chart on the document tray 302, the user presses the button 701c with the operation unit 400 to instruct the start of ADF reading. Thereby, the CPU 401 acquires an instruction to start reading by ADF reading from the operation unit 400. When the CPU 401 acquires the reading start instruction, the CPU 401 instructs the reader 200 to perform ADF reading. The reader 200 conveys the test chart by the ADF unit 220 and reads the test chart by the document scanner 210. The reader image processing unit 108 of the document scanner 210 transmits a luminance signal representing the reading result of the test chart to the printer control unit 109.

[0066] When platen reading is selected (S502: N), the CPU 401 sets the second image formation condition in the printer 300 and transmits a density signal of a test image for creating a test chart for gradation correction to the dither processing unit 407. Thereby, the CPU 401 causes the printer 300 to create a test chart (S511). At this time, the LUTa is not used. The test image of the test chart is as illustrated in FIG. 9 and is the same as in the case of ADF reading.

[0067] After creating the test chart, the CPU 401 executes platen reading by the reader 200 (S512). For this purpose, the CPU 401 displays, on the display of the operation unit 400, a message prompting the user to place the test chart on the platen glass 102. FIG. 8(c) illustrates 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 for instructing the start of reading.

[0068] The user opens the ADF unit 220 to expose the platen glass 102, and places the test chart on the platen glass 102 with the surface on which the test screen is formed facing the platen glass 102 side. Then, the user presses the button 701c with the operation unit 400 to instruct the start of platen reading. As a result, the CPU 401 acquires an instruction to start reading by platen reading from the operation unit 400. When the CPU 401 acquires the reading start instruction, it instructs the reader 200 to perform platen reading. The reader 200 reads the test chart on the platen glass 102 by the document scanner 210. The reader image processing unit 108 of the document scanner 210 transmits a luminance signal representing the reading result of the test chart to the printer control unit 109.

[0069] When the test chart is read by the processes of S504 and S512, the CPU 401 acquires a 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 LUTid404 of the color processing unit 403. Thereby, density signals for each of the 10 gradation images are obtained. Note that the CPU 401 may switch the table of the LUTid404 of the color processing unit 403 according to the type of sheet used for the test chart.

[0070] The CPU 401 creates a 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 (S506). The CPU 401 stores the created LUTa in the memory 402. When the test image is formed on one sheet and the test chart is one sheet, the calibration process is performed as described above.

[0071] When the test image is formed on two sheets and there are two test charts, the calibration process is performed as follows. FIG. 10 is a flowchart showing the calibration process in this case. The same steps are assigned to the same processes as those in the process of FIG. 7. The description of the same process is omitted. FIGS. 11 and 12 are exemplary views of the screen displayed on the display of the operation unit 400 during the calibration process.

[0072] As described above, the dither processing unit 407 may have a plurality of screens with different line numbers. The gradation characteristics of the images formed between different line numbers may be significantly different. In such a case, LUTa is created for each line number. However, it is difficult for the user to determine which line number screen should be calibrated. This is because it is difficult for the user to grasp the line number applied to images such as characters, lines, and photos and the line number applied to copying, etc. Therefore, when having a plurality of line number screens, by performing calibration collectively for all line number screens, the burden on the user is reduced. The calibration in the case of two test charts is applied to such a case.

[0073] When ADF reading is selected in the reading mode (S502: Y), the CPU 401 continuously creates two test charts 801a and 801b by the printer 300 (S901). The CPU 401 displays the message screen 700d illustrated in FIG. 11(a) on the display of the operation unit 400. The message screen 700d displays a message prompting confirmation that two or more sheets are stored in the paper feed cassette 152, a message indicating that two test charts are continuously created, and a button 701d for instructing print start. After the user confirms that two or more sheets are stored in the paper feed cassette 152, the user presses the button 701d by the operation unit 400 to instruct print start. Thereby, the CPU 401 acquires an instruction for print start from the operation unit 400.

[0074] When the CPU 401 receives an instruction to start printing, it sets the first screen in the dithering unit 407 and transmits the density signal of the test image for creating the test chart for tone correction to the dithering unit 407. The dithering unit 407 converts the 10-bit density signal into a 4-bit density signal using the first screen. The printer 300 creates a test chart 801a based on the 4-bit density signal. Next, the CPU 401 sets the second screen in the dithering unit 407 and transmits the density signal of the test image for creating the test chart for tone correction to the dithering unit 407. The dithering unit 407 converts the 10-bit density signal into a 4-bit density signal using the second screen. The printer 300 creates a test chart 801b based on the 4-bit density signal.

[0075] After creating the test charts, the CPU 401 operates the ADF unit 220 by the reader 200 to perform ADF reading on the two test charts 801a and 801b (S902). For this purpose, the CPU 401 displays a message prompting the user to place the two test charts 801a and 801b on the original document tray 302 of the ADF unit 220 on the display of the operation unit 400. FIG. 11(b) illustrates 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 original document tray 302, and a button 701c for instructing the start of reading. Note that the printer 300 may print a message or mark indicating which screen was applied on the test charts 801a and 801b.

[0076] After the user places the test chart on the document tray 302, the user presses the button 701c with the operation unit 400 to instruct the start of ADF reading. As a result, the CPU 401 acquires an instruction to start reading by ADF reading from the operation unit 400. When the CPU 401 acquires the instruction to start reading, the CPU 401 instructs the reader 200 to perform ADF reading. The reader 200 continuously conveys the test charts 801a and 801b by the ADF unit 220, and the document scanner 210 continuously reads the test charts 801a and 801b. The reader image processing unit 108 of the document scanner 210 transmits a luminance signal representing the reading result of the test charts 801a and 801b to the printer control unit 109.

[0077] When the platen reading is selected as the reading mode (S502: N), the CPU 401 creates the first test chart 801a with the printer 300 (S911). The CPU 401 displays a message screen 700f illustrated in FIG. 12(a) on the display of the operation unit 400. The message screen 700f displays a message prompting confirmation that two or more sheets are stored in the paper feed cassette 152, a message indicating that the first test chart is being created, and a button 701d for instructing the start of printing. After the user confirms that two or more sheets are stored in the paper feed cassette 152, the user presses the button 701d with the operation unit 400 to instruct the start of printing. As a result, the CPU 401 acquires an instruction to start printing from the operation unit 400.

[0078] When the CPU 401 acquires the instruction to start printing, the CPU 401 sets the first screen in the dither processing unit 407 and transmits a density signal of a test image for creating a test chart for gradation correction to the dither processing unit 407. The dither processing unit 407 converts a 10-bit density signal into a 4-bit density signal using the first screen. The printer 300 creates the first test chart 801a based on the 4-bit density signal.

[0079] After creating the first test chart 801a, the CPU 401 causes the reader 200 to perform platen reading of the first test chart 801a (S912). To this end, the CPU 401 displays, on the display of the operation unit 400, a message prompting the user to place the test chart on the platen glass 102. FIG. 12(b) illustrates such a message screen 700g. The message screen 700g displays a message prompting the user to place the first test chart 801a on the platen glass 102 and a button 701c for instructing the start of reading.

[0080] The user opens the ADF unit 220 to expose the platen glass 102, and places the first test chart 801a on the platen glass 102 with the surface on which the test screen is formed facing the platen glass 102 side. Then, the user presses the button 701c with the operation unit 400 to instruct the start of platen reading. Thereby, the CPU 401 acquires an instruction to start platen reading from the operation unit 400. When the CPU 401 acquires the instruction to start reading, it instructs the reader 200 to perform platen reading. The reader 200 reads the first test chart 801a on the platen glass 102 by the document scanner 210. The reader image processing unit 108 of the document scanner 210 transmits a luminance signal representing the reading result of the first test chart 801a to the printer control unit 109.

[0081] Next, the CPU 401 causes the printer 300 to create the second test chart 801b (S913). The CPU 401 displays, on the display of the operation unit 400, a message screen 700h illustrated in FIG. 12(c). The message screen 700h displays a message indicating that the second test chart is being created and a button 701d for instructing the start of printing. The user presses the button 701d with the operation unit 400 to instruct the start of printing. Thereby, the CPU 401 acquires an instruction to start printing from the operation unit 400.

[0082] When the CPU 401 receives an instruction to start printing, it sets the second screen in the dithering unit 407 and transmits a density signal of a test image for creating a test chart for gradation correction to the dithering unit 407. The dithering unit 407 converts a 10-bit density signal into a 4-bit density signal using the second screen. The printer 300 creates the second test chart 801b based on the 4-bit density signal.

[0083] After creating the second test chart 801b, the CPU 401 causes the reader 200 to perform platen reading of the second test chart 801b (S914). To this end, the CPU 401 displays, on the display of the operation unit 400, a message prompting the user to place the test chart on the platen glass 102. FIG. 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 platen glass 102 and a button 701c for instructing the start of reading.

[0084] The user opens the ADF unit 220 to expose the platen glass 102, and places the second test chart 801b on the platen glass 102 with the surface on which the test screen is formed facing the platen glass 102 side. Then, the user presses the button 701c with the operation unit 400 to instruct the start of platen reading. As a result, the CPU 401 obtains an instruction to start reading by platen reading from the operation unit 400. When the CPU 401 obtains the reading start instruction, it instructs the reader 200 to perform platen reading. The reader 200 reads the second test chart 801b on the platen glass 102 by the document scanner 210. The reader image processing unit 108 of the document scanner 210 transmits a luminance signal representing the reading result of the second test chart 801b to the printer control unit 109.

[0085] When the reading of the two test charts 801a and 801b is completed, the CPU 401 acquires the density signal of the test image based on the reading result (luminance signal) (S505). The CPU 401 creates a 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 (S506). The CPU 401 creates a LUTa' based on the reading result of the test chart 801a and creates a LUTa" based on the reading result of the test chart 801b. Here, an example of forming two test charts 801a and 801b has been described, but calibration may also be performed using three or more test charts. Each time the number of test charts increases by one, the processes of S913 and S914 are added.

[0086] (Judgment of start of reading of test chart) In the present embodiment, before reading the test chart, it is determined whether the test chart is correctly set, and based on the determination result, it is determined whether the reader 200 can start reading the test chart. Specifically, the reader 200 is permitted to read the test chart only when the test chart is correctly set. "The test chart is correctly set" means that the test chart, which is a sheet printed with the test image, is placed at the correct position on the document tray 302 or the document table glass 102. By permitting the reader 200 to read the test chart only when it is correctly set, the occurrence of a test chart reading error is suppressed. That is, by determining whether the test chart is correctly set before reading the test chart, it is determined whether the reading of the test chart can start. FIG. 13 is a flowchart showing the calibration process including the determination of the start of reading.

[0087] FIG. 13(a) is a flowchart showing the process of determining whether the reading can start at the timing before receiving the instruction to start reading the test chart. The CPU 401 acquires information representing the size of the sheet (paper size) selected by the user when creating a test chart (S101). Here, the case where the user selects an A4-sized sheet will be described. As described above, before creating the test chart, the user selects whether to perform ADF reading (first reading mode) or platen reading (second reading mode) of the test chart. The CPU 401 displays, for example, on the display of the operation unit 400, a screen for selecting the paper size after the reading mode has been selected on the operation screen 700a in Fig. 8(a). As a result, the user can continue to select the paper size of the sheet to be used for the test chart from the screen for selecting the paper size after selecting the reading mode. Also, the orientation of the sheet may 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 the sheet of the paper size selected by the user (S102). The CPU 401 stores the paper size of the sheet used for creating the test chart in the memory 402. If the orientation of the sheet is also selected, the information representing the orientation of the sheet is also stored in the memory 402. As described above, after the test chart is created, the test chart is read in the reading mode selected by the user. For this purpose, the user inputs a read start instruction using the operation unit 400. When ADF reading (first reading mode) is selected, the CPU 401 displays on the display of the operation unit 400 a message prompting to set the test chart on the document tray 302 and adjust the interval of the regulating member 332. When platen reading (second reading mode) is selected, the CPU 401 displays on the display of the operation unit 400 a message prompting to place the test chart on the platen glass 102 with reference to the document alignment mark 1231.

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

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

[0091] FIG. 14 is an explanatory diagram for determining whether reading can start. Here, the test chart is created using an A4-sized sheet. Therefore, the CPU 401 determines that the paper size and the document size match when the document size detected by the reader 200 is A4 or A4R, and determines that the paper size and the document size do not match when it is other than A4 and A4R. Note that when the test chart is created using an A3-sized sheet, the CPU 401 determines that the paper size and the document size match only when the document size detected by the reader 200 is A3.

[0092] FIG. 15 is an exemplary view of a state when a test chart is set on the document tray 302 during ADF reading. FIG. 16 is a relational diagram between the setting state of the test chart on the document tray 302 and the reading result. Here, the case where the test chart is created using an A4-sized sheet is taken as an example.

[0093] FIG. 15(a) shows the case where the test chart is set correctly. The test chart is set so that the center in the width direction of the document to be fed coincides with the center of the test chart. The pair of regulating members 332 has moved to the size position of the document width of the test chart. In this case, the CPU 401 determines that the test chart is ready for reading. FIG. 15(b) shows the case where 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 created test chart, the CPU 401 determines that the test chart is ready for reading.

[0094] FIG. 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 since the created test chart does not match the detected document size, the CPU 401 determines that the test chart is not ready for reading. Therefore, a reading error is prevented in advance. FIG. 15(d) shows the case where the test chart is set inclined with respect to the conveyance direction. In this case, the test chart is not set correctly, and since the created test chart does not match the document size, the CPU 401 determines that the test chart is not ready for reading. Therefore, a reading error is prevented in advance.

[0095] FIG. 15(e) shows a case where a manuscript different from the created test chart is set and the detected manuscript 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 for reading. Therefore, a reading error is prevented in advance. FIG. 15(f) shows a case where a manuscript different from the created test chart is set and the detected manuscript size matches the paper size of the test chart. In this case, the CPU 401 determines that the test chart can be started for reading. However, after the manuscript is read, a reading error occurs.

[0096] FIG. 17 is an exemplary view of a state when a test chart is set on the platen glass 102 during platen reading.

[0097] FIG. 17(a) shows a case where the test chart is correctly set. The paper edge of the test chart is placed in alignment with the manuscript alignment mark 1231 at the reference abutting portion on the back side of the platen glass 102. In this case, the CPU 401 determines that the test chart can be started for reading. FIG. 17(b) shows a case where the test chart is set in a horizontal orientation (R orientation). In this case, since the detected manuscript size is the same as the size of the created test chart, the CPU 401 determines that the test chart can be started for reading.

[0098] Figure 17(c) shows a case where the edge of the test chart paper is not aligned with the registration mark 1231. In this case, since the test chart is not set correctly, the CPU 401 determines that the test chart cannot be read. Therefore, a reading error is prevented. If the platen reading is performed in this state, since the test chart is A4 size, the first mirror unit 104a and the second mirror unit 104b only move up to the size position of A4. Therefore, only a part of the test chart is read, and a reading error occurs. Figure 17(d) shows a case where the test chart is set at an angle. This state may occur because the test chart is tilted by wind or the like when the user closes the reader 200 even if the test chart is set correctly. In this case as well, the CPU 401 determines that the test chart cannot be read. Therefore, a reading error is prevented.

[0099] Figure 17(e) shows a case where a document different from the created test chart is set 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 read. Therefore, a reading error is prevented. Figure 17(f) shows a case where a document different from the created test chart is set 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 read. However, after the document is read, a reading error occurs.

[0100] When the paper size of the test chart matches the detected manuscript size (S104: Y), the CPU 401 determines that the test chart can be started to be read by the reader 200 (S105). As a result, the CPU 401 switches, for example, the button 701c for instructing the start of reading included in the message screens 700b and 700c in FIGS. 8(b) and 8(c) from the grayed-out state to the pressable state. Alternatively, the CPU 401 switches the display from a message screen that does not include the button 701c for instructing the start of reading to a message screen that includes the button 701c. Thereby, the display switches from a state where the user cannot instruct the start of reading the test chart to a state where the user can instruct it.

[0101] When the button 701c for instructing the start of reading is pressed and a start-of-reading instruction is input, the CPU 401 controls the operation of the reader 200 to perform a test chart reading process (S106). The CPU 401 executes ADF reading in the case of the first reading mode and platen reading in the case of the second reading mode. The CPU 401 executes the above calibration based on the reading result of the test chart to complete the adjustment of the printing conditions (S107).

[0102] FIG. 13(b) is a flowchart showing a process of determining whether reading can be started at the timing when an instruction to start reading the test chart is received. The same steps as those in the process of FIG. 13(a) are assigned the same step numbers. The description of the same process as that in FIG. 13(a) is omitted.

[0103] The CPU 401 that created the test chart in the process of S102, when the button 701c for instructing the start of reading is pressed and a start-of-reading instruction is received (S201), executes the manuscript size detection process by the reader 200 in S103. When the paper size of the test chart created in the process of S102 does not match the manuscript size detected in the process of S103 (S104: N), the CPU 401 determines that reading cannot be started. In this case, the CPU 401 notifies the user that the test chart is not correctly set in the reader 200 (S111).

[0104] FIG. 18 is an exemplary view of a notification screen displayed on the display of the operation unit 400 in this case. FIG. 18(a) exemplifies the notification screen when ADF reading (first reading mode) is selected. This notification screen includes a notification that the test chart is not correctly set on 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 and the like. FIG. 18(b) exemplifies the notification screen when platen reading (second reading mode) is selected. This notification screen includes a notification that the test chart is not correctly 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 butting it against the document alignment mark 1231.

[0105] After the notification, the CPU 401 repeatedly performs the processes after S201 until the paper size of the test chart created in the process of S102 matches the document size detected in the process of S103. For this purpose, after the notification process of S111, the CPU 401 displays a screen including a button 701c for instructing the start of reading on the display of the operation unit 400. When the user presses this button 701c with the operation unit 400, the processes after S201 are performed. Note that the notification in S111 may be performed using an output device such as voice or lamp display in addition to the display of the notification screen on the display.

[0106] FIG. 13(c) is a flowchart showing a process of determining the start of reading at the timing when an instruction to start reading the test chart is received. FIG. 13(c) is an example in which the order of the processes of S201 and S103 in FIG. 13(b) is reversed. Since the individual processes are the same, the description is omitted.

[0107] Conventionally, since it was necessary to determine a reading error from the reading result of the test chart, especially when reading using the ADF unit 220, time was wasted until the test chart was not set correctly and a reading error occurred. In contrast, the image forming apparatus 100 of the present embodiment determines whether or not the test chart can be started 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, it is possible to prevent a reading error caused by the test chart not being set correctly. The image forming apparatus 100 can prevent waste of re-reading the test chart due to a reading error. That is, the effect as shown in FIG. 16 can be obtained.

[0108] (Another example of determination of start of reading of test chart) In the above determination process of the start of reading of the test chart, whether or not the start of reading of the test chart can be performed is determined based on whether or not 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 reading the test chart with the reader 200 may be limited. In this case, the orientation of the placed test chart is included in the determination condition for the match between the paper size and the document size.

[0109] For example, during printing, the photosensitive drums 121, 131, 141, 151 are scanned in the main scanning direction (Y direction) by a laser beam. At this time, density unevenness may occur in the main scanning direction. The density unevenness in the main scanning direction is caused by, for example, charging unevenness due to deterioration of the charger 122 that charges the photosensitive drums 121, 131, 141, 151, exposure unevenness of the laser beam by the exposure device 110, or development unevenness by the developing device 123.

[0110] When correcting the density unevenness in the main scanning direction like this, a test chart for density unevenness correction is created. FIG. 19 is an explanatory diagram of the test chart for density unevenness correction. FIG. 19(a) illustrates a test chart 810 of A4 size. FIG. 19(b) illustrates a test chart 811 of A3 size. In any of the test charts 810 and 811, in the main scanning direction (Y direction), a strip-shaped test image formed by density signals of 50% of each color of yellow, magenta, cyan, and black is formed. The strip-shaped test image is formed such that the main scanning direction is the longitudinal direction of the strip regardless of the size of the sheet.

[0111] The reading of the test charts 810 and 811 for density unevenness correction is performed by setting the main scanning direction (Y direction) of the test charts 810 and 811 to be parallel to the SX1 direction or the SX2 direction of the reader 200. This is because the image sensor 105 has photoelectric conversion elements arranged linearly 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 and 811 with the main scanning direction of the test charts 810 and 811 being the SX1 direction or the SX2 direction of the reader 200, the characteristic differences due to the positions of the photoelectric conversion elements of the image sensor 105 can be suppressed.

[0112] The determination of the start of reading such a test chart is performed in the same manner as the process of S104 in FIG. 13. That is, the CPU 401 determines whether the paper size of the test chart created in the process of S102 matches the document size detected in the process of S103, and determines whether it is possible to start reading the test chart. At this time, the CPU 401 adds the orientation of the document to the determination condition for size matching. FIG. 20 is an explanatory diagram of the determination of whether reading can start. The orientation of the document is added to the determination condition for size matching. FIG. 20 shows that when the paper size is A4, reading can start only when the document size is A4R. When the paper size is A4 and the document size is A4, although the paper size and the document size match, since the orientation of the document is incorrect, reading start is made impossible, which is different from the case of FIG. 14 in FIG. 20. FIG. 20 shows that when the paper size is A3, reading can start only when the document size is outside the standard size. When the paper size is A3, it is correct to set the test chart 811 on the document table glass 102 so that a part thereof protrudes from the document table. Therefore, when density unevenness correction is performed using the test chart 811 with a paper size of A3, reading by ADF reading (first reading mode) becomes impossible, and only reading by document table reading (second reading mode) is possible.

[0113] FIG. 21 is a relational diagram of the set state of the test chart on the document tray 302 and the reading result. In this example, the orientation of the document is added to the determination condition (the way the document is placed) for matching the document size. Therefore, as shown in FIG. 21, it is possible to prevent a reading error from occurring when it is in the "standard position and the reading orientation is incorrect" with respect to adjustments such as density unevenness correction in the main scanning direction (Y direction) where there is a limitation on the reading orientation of the test chart.

[0114] (Another example of the determination of the start of reading the test chart) Here, an example of preventing the occurrence of a reading error by placing the test chart so that the longitudinal direction (the long side of the sheet) of the test chart is parallel to the Y direction of the reader 200 regardless of the orientation of the test chart will be described.

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

[0116] When reading the test chart 820 for image diagnosis, regardless of whether the test chart is A4 or A4R, the test chart 820 needs to be set in an orientation where its longitudinal direction (the long side of the sheet) is parallel to the Y direction.

[0117] When determining the presence or absence of an ADF reader streak, if streaks are detected both before the test chart 820 is conveyed to the reading position of the reader 200 and in the blank area 821 of the test chart, streaks will be detected regardless of the presence or absence of the test chart 820. In this case, it is determined that streaks are generated due to the reader 200. If no streaks are detected before the test chart 820 is conveyed to the reading position of the reader 200 and streaks are detected in the blank area 821 of the test chart 820, it is determined that there are streaks not in the blank area 821 of the test chart 820 but due to the reader 200. In this case, it is determined that the streaks are due to the image forming apparatus 100. FIG. 23 is a diagram showing the relationship between such streak detection positions and the causes of streaks.

[0118] In order to distinguish between streaks caused by the reader 200 and streaks 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 in an orientation where its longitudinal direction (the long side of the paper) is parallel to the Y direction. That is, reading start is permitted only when the test chart 820 is set to the reader 200 as A4.

[0119] FIG. 24 is an explanatory diagram for determining whether reading can start. In the case of the test chart 820 for image diagnosis including the reading unit of the ADF, regardless of whether the paper size is A4 or A4R, reading can start only when the original size is A4. This makes it possible to prevent a reading error when the test chart 820 for image diagnosis is placed in any other way.

[0120] As described above, when adjusting the print conditions using the test chart, the image forming apparatus 100 according to the present embodiment determines whether the test chart is correctly set before performing the reading operation of the test chart. This can prevent a reading error due to a user's work mistake in the difference that causes the test chart to be read by the reader 200. Therefore, it is 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; mounting means on which the sheet is mounted; reading means for reading an image of the sheet mounted on the mounting means; control means for creating a test chart by forming a test image on the sheet by the image forming means, and when the test chart is mounted on the mounting means, determining whether the test chart is correctly mounted on the mounting means, and determining whether the reading means can start reading the test chart based on the result; characterized in that it comprises: an image forming apparatus.

2. The control means permits the reading means to start reading the test chart when the test chart is correctly mounted on the mounting means. The image forming apparatus according to claim 1.

3. When the control means determines that the reading means cannot start reading the test chart, the control means notifies that the test chart is not correctly mounted on the mounting means. The image forming apparatus according to claim 1 or 2.

4. The control means does not permit the reading means to start reading the test chart until the test chart is correctly mounted on the mounting means. The image forming apparatus according to any one of claims 1 to 3.

5. storage means for storing a first size of the sheet used for creating the test chart; size detecting means for detecting a second size of the sheet mounted on the mounting means; comprising The control means determines whether the test chart is correctly mounted on the mounting means based on a comparison result between the first size and the second size. The image forming apparatus according to any one of claims 1 to 4.

6. The control means determines that the test chart is correctly mounted on the mounting means when the first size and the second size match. The image forming apparatus according to claim 5.

7. The storage means stores information representing the first size and the orientation of the sheet when the test chart was created, The size detecting means detects the second size and the orientation of the sheet mounted on the mounting means, The control means determines whether the test chart is correctly placed on the placement means based on the comparison result between the first size and the second size, the information indicating the orientation of the sheet stored in the storage means, and the orientation of the sheet placed on the placement means. The image forming apparatus according to claim 5 or 6.

8. The placement means is a platen glass on which a sheet is placed with its position fixed, and has a first sensor for detecting the presence or absence of a sheet placed on the platen glass. The size detection means detects the second size of the sheet placed on the platen glass based on the reading result of a predetermined number of lines by the reading means and the detection result of the first sensor. The image forming apparatus according to any one of claims 5 to 7.

9. The placement means is a document tray provided in a conveyance device that conveys a sheet to the reading position of the reading means. The document tray is provided with a pair of regulating members slidable in a direction orthogonal to the conveyance direction of the sheet, and a plurality of second sensors arranged along the conveyance direction of the sheet for detecting the presence or absence of the sheet. The size detection means detects the second size of the sheet placed on the document tray based on the position of the regulating members and the detection results of the plurality of second sensors. The image forming apparatus according to any one of claims 5 to 8.

10. When the control means determines that reading can start, it forms a test image for gradation correction on the sheet by the image forming means to create the test chart, and performs gradation correction based on the result of reading the test chart by the reading means. The image forming apparatus according to any one of claims 1 to 9.

11. When the control means determines that reading can start, it forms a test image for density unevenness correction on the sheet by the image forming means to create the test chart, and corrects the density unevenness based on the result of reading the test chart by the reading means. The image forming apparatus according to any one of claims 1 to 9.

12. The control means creates the test chart by forming a test image for image diagnosis on the sheet by the image forming means, and when it is determined that the reading can be started, determines the cause of an image defect based on the result of having the reading means read the test chart. The image forming apparatus according to any one of claims 1 to 9.

Images