Image forming device

Abstract

To provide an image forming apparatus that prevents a reduction in accuracy of adjusting geometrical characteristics due to a reduction in the number of samples and performs image formation.SOLUTION: An image forming apparatus has: a printer that forms an image on a sheet; an image sensor C1 that reads the sheet on which a test image is formed; an image processing unit 260 that derives an adjustment value for adjusting the geometrical characteristics of an image formed by the printer based on results of reading performed by the image sensor C1; and a printer controller 103 that causes the printer to form the test image, causes the image sensor C1 to read the sheet on which the test image is formed, and controls the geometrical characteristics of the image formed by the printer based on the adjustment value derived by the image processing unit 260. The image processing unit 260 determines abnormal data from the reading results and derives the adjustment value based on a prescribed number of reading results excluding the reading result determined to be the abnormal data.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus such as a copying machine, a multifunction machine, or a printer. [Background technology]

[0002] In recent years, the market for on-demand image forming devices has been expanding. For example, electrophotographic image forming devices are becoming more popular in the offset printing market. Inkjet image forming devices have also been expanding their market share, thanks to their large format, low initial cost, and ultra-high speed. However, market expansion is not easy, and the image quality (hereafter referred to as "image quality") of the previous image forming devices that dominated the market must be maintained. To maintain image quality, the image forming conditions when the image forming device forms an image on a sheet are appropriately corrected.

[0003] Image quality includes factors such as gradation, graininess, in-page uniformity, character quality, and color reproduction (including color stability), but another important factor is "front-to-back register accuracy." Front-to-back register accuracy is the accuracy with which the images on the front and back of a sheet are aligned. The deviation in the position (printing position) of each image on the front and back of the sheet (deliverable) is called "front-to-back misalignment." With offset printing presses, front-to-back register accuracy is adjusted by skilled technicians before printing, and front-to-back misalignment is kept to around 0.1 to 0.2. However, adjusting front-to-back register accuracy takes time and requires skilled techniques.

[0004] Electrophotographic image forming devices using toner are widely known as digital printing devices that meet the needs of high-mix, short-run printing. Image forming devices fix toner to a sheet using heat and pressure. This can cause the sheet to shrink after printing on the first side, resulting in misalignment between the first and second sides, i.e., misalignment between the front and back. Furthermore, cut-sheet image forming devices, including the electrophotographic image forming devices mentioned above, provide highly accurate and stable print positioning through sheet registration. Because registration is typically performed based on one edge of a rectangular sheet, variations in front-to-back register accuracy from sheet to sheet are influenced by the accuracy of the sheet's cutting and deformation.

[0005] Factors that determine sheet shape, including sheet cutting accuracy and deformation, include the length of each side of the sheet, as well as perpendicularity and parallelism. Sheet shape varies depending on differences in sheet cutting lots and the surrounding environment. Front-to-back register accuracy is affected by the sheet shape. Therefore, in order to provide front-to-back register accuracy equivalent to offset printing with an image forming device that handles cut sheets, it is necessary to adjust geometric characteristics such as print position, magnification, and distortion every time the sheet cutting lot or the surrounding environment changes. Adjusting the geometric characteristics corrects for front-to-back misalignment. This process is called "front-to-back register."

[0006] Patent Document 1 discloses an image forming device that reads a sheet on which a test image is printed multiple times and calculates the amount of adjustment for the print position using only the read results that are below a threshold set according to variations in the conveyance of the sheet during reading.Patent Document 2 discloses an image forming device that automatically interrupts and executes print position adjustment at intervals after printing a predetermined number of sheets during a job. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2018-004954 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-221582 Summary of the Invention [Problem to be solved by the invention]

[0008] Differences in the surface properties of sheets (embossed paper, label paper, etc.) can cause false positives in the scan results of test images. If false positive scan results are not excluded as abnormal data, they will affect the accurate calculation of adjustment values. Conventionally, the test image is scanned multiple times and scan results that fall below a threshold are used to reduce the scan error in the scan results used to calculate adjustment values. However, using only scan results that fall below the threshold reduces the number of scan result samples used to calculate the adjustment amount. This reduces the number of samples for paper shape errors and image shape errors between pages, reducing the adjustment accuracy of geometric characteristics such as image position adjustment.

[0009] In view of the above-mentioned problems, an object of the present invention is to provide an image forming apparatus that forms an image while suppressing a decrease in the accuracy of adjusting geometric characteristics due to a decrease in the number of samples. [Means for solving the problem]

[0010] The image forming apparatus of the present invention includes an image forming means for forming a test image for position detection on a sheet, a transport means for transporting the sheet from the image forming means, a reading means for reading the sheet on which the test image has been formed while being transported by the transport means, a detection means for detecting position information of the test image on the sheet based on the reading result of the sheet by the reading means, a determination means for determining whether the position of the test image on the sheet is within a predetermined range based on the reading result of the sheet by the reading means, and a control means for controlling the position and shape of an image to be formed on the sheet by the image forming means based on the position information corresponding to the reading results of a predetermined number of sheets for which the determination means has determined that the position of the test image is within the predetermined range, excluding the reading results for which the determination means has determined that the position of the test image is not within the predetermined range. death , When a first mode in which the image and the test image are formed on the same sheet is executed, the control means controls the position and shape of the image to be formed on the sheet by the image forming means based on the position information of the test image on the specified number of sheets for which it has been determined by the determination means that the test image has been formed within the specified range; and when a second mode in which the test image is formed on a sheet different from the sheet on which the image is to be formed is executed, the control means determines, from the reading results of the specified number of sheets, the reading result for which it has been determined by the determination means that the test image has been formed within the specified range, and controls the position and shape of the image to be formed on the sheet by the image forming means based on the position information of the test image on the sheet corresponding to the determined reading result. It is characterized by: [Effects of the Invention]

[0011] According to the present invention, it is possible to suppress a decrease in the accuracy of adjusting geometric characteristics due to a decrease in the number of samples. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram illustrating the configuration of an image forming apparatus. [Figure 2] FIG. [Figure 3] 10(a) and 10(b) are explanatory diagrams of a reading unit. [Figure 4] FIG. 10 is an explanatory diagram of an adjustment sheet used for interrupt adjustment. [Figure 5] FIG. 10 is an explanatory diagram of an adjustment sheet used for real-time adjustment. [Figure 6] FIG. [Figure 7] 10A and 10B are diagrams illustrating an example of an operation screen. [Figure 8] FIG. [Figure 9] 10 is a flowchart showing front and back registration processing during interrupt adjustment. [Figure 10] 10 is a flowchart showing front-to-back registration processing during real-time adjustment. [Figure 11] 10A and 10B are explanatory diagrams of the position of the adjustment sheet in the adjustment unit. [Figure 12] (a) and (b) are explanatory diagrams of the position of the job sheet in the adjustment unit. [Figure 13] FIG. 10 is a diagram illustrating a false detection of a test image. [Figure 14] 10 is a flowchart showing a process for calculating geometric adjustment values ​​during interruption adjustment. [Figure 15] 10 is a flowchart showing a process for calculating geometric adjustment values ​​during real-time adjustment. [Figure 16] 10A and 10B are explanatory diagrams of a method for searching for a sheet edge and a patch image. DETAILED DESCRIPTION OF THE INVENTION

[0013] An embodiment of the present invention will be described below with reference to the drawings. In this embodiment, a method for solving the above-mentioned problems using an electrophotographic laser beam printer will be described. While the explanation will be given using an electrophotographic system, the characteristic points of control, particularly the matters described in the claims, also apply to inkjet printers and dye-sublimation printers, which have similar problems due to image fixing using a thermal drying method, and the problems can be solved using the method described below. Therefore, we assert that the above claims also apply to each image forming apparatus.

[0014] (Image forming device) 1 is a configuration diagram of an image forming apparatus according to this embodiment. The image forming apparatus 1 according to this embodiment is composed of a printer 100, an adjustment unit 400, and a finisher 600. The printer 100 forms an image on a sheet 110 by electrophotography. The printer according to this embodiment may be an inkjet printer or a dye-sublimation printer.

[0015] The printer 100 includes, within a housing 101, mechanisms that constitute an engine unit for image formation, and a controller (described below) that controls the operation of each mechanism. An operation panel 180 is provided on top of the housing 101. The operation panel 180 is a user interface, and includes an input device that accepts instructions from a user, and an output device that displays screens such as an operation screen. The mechanisms that make up the engine unit include a mechanism that forms an image (image forming mechanism), a mechanism that transfers an image to a sheet 110 (transfer mechanism), a mechanism that feeds the sheet 110 (feed mechanism), and a mechanism that fixes the image on the sheet 110 (fixing mechanism).

[0016] The image forming mechanism includes four image forming units 120, 121, 122, and 123 corresponding to the colors of yellow (Y), magenta (M), cyan (C), and black (K). The image forming units 120, 121, 122, and 123 form images of the corresponding colors. The image forming units 120, 121, 122, and 123 have the same configuration, except for the colors of the images they form. Here, the configuration of the image forming unit 120 will be described, and descriptions of the configurations of the other image forming units 121, 122, and 123 will be omitted.

[0017] The image forming unit 120 includes a photosensitive drum 105, a charger 111, a laser scanner 107, and a developing unit 112. The photosensitive drum 105 is a drum-shaped photosensitive member having a charging layer on its surface, and rotates around the drum axis. The charger 111 uniformly charges the surface of the rotating photosensitive drum 105. The laser scanner 107 scans the photosensitive drum 105 with laser light modulated based on image data representing the image to be formed. The laser scanner 107 includes a light-emitting unit 108 that scans the photosensitive drum 105 with laser light emitted from a semiconductor laser in one direction (the drum axis direction), and a reflection mirror 109 that reflects the laser light from the light-emitting unit 108 toward the photosensitive drum 105. The direction in which the laser scanner 107 scans the photosensitive drum 105 (the depth direction in the figure) is the main scanning direction.

[0018] After being charged, the photosensitive drum 105 is scanned with a laser beam, forming an electrostatic latent image on its surface according to image data. The developing unit 112 develops the electrostatic latent image formed on the photosensitive drum 105 with a developer. This forms an image on the surface of the photosensitive drum 105, in which the electrostatic latent image is visualized. A yellow image is formed on the photosensitive drum 105 of image forming unit 120. A magenta image is formed on the photosensitive drum 105 of image forming unit 121. A cyan image is formed on the photosensitive drum 105 of image forming unit 122. A black image is formed on the photosensitive drum 105 of image forming unit 123. The photosensitive drum 105 and the developing unit 112 are detachable from the housing 101.

[0019] The transfer mechanism includes an intermediate transfer body 106 and a transfer roller 114. Images are sequentially transferred onto the intermediate transfer body 106 in a superimposed manner from the photosensitive drums 105 of image forming units 120, 121, 122, and 123. In this embodiment, the intermediate transfer body 106 rotates clockwise in the drawing, and images are transferred in the order of image forming unit 120 (yellow), image forming unit 121 (magenta), image forming unit 122 (cyan), and image forming unit 123 (black). An image density detection sensor 117 is provided downstream of image forming unit 123 in the rotation direction of the intermediate transfer body 106 for detecting image density from an image for image density detection formed on the intermediate transfer body 106.

[0020] The image transferred to the intermediate transfer body 106 is transported to a transfer roller 114 by the rotation of the intermediate transfer body 106. An image formation start position detection sensor 115 for determining the transfer position onto the sheet 110 is provided upstream of the transfer roller 114 in the rotation direction of the intermediate transfer body 106. The transfer roller 114 presses the sheet 110 against the intermediate transfer body 106 and at the same time applies a bias with reverse characteristics to the image on the intermediate transfer body 106, thereby transferring the image from the intermediate transfer body 106 to the sheet 110.

[0021] The feeding mechanism includes a paper feed cassette 113 that stores sheets 110, a transport path along which the sheets 110 are fed, and various rollers for transporting the sheets 110 along the transport path. The sheets 110 are fed from the paper feed cassette 113, and an image is transferred and fixed onto the sheets 110 as they are transported along the transport path, and the sheets are then ejected to the outside of the housing 101. In this embodiment, multiple paper feed cassettes 113 are provided, and paper can be fed from any of the paper feed cassettes 113. The sheets 110 stored in the respective paper feed cassettes 113 may be of the same type or different types.

[0022] To achieve this, the sheet 110 is first fed from a paper feed cassette 113 and conveyed along a conveyance path to a transfer roller 114. A paper feed timing sensor 116 for adjusting the timing of conveying the sheet 110 is provided along the conveyance path from the paper feed cassette 113 to the transfer roller 114. The timing at which the sheet 110 is conveyed to the transfer roller 114 is adjusted based on the timing at which the image formation start position detection sensor 115 detects the image on the intermediate transfer body 106 and the timing at which the paper feed timing sensor 116 detects the sheet 110. In this way, the image is transferred from the intermediate transfer body 106 to a predetermined position on the sheet 110.

[0023] The sheet 110 onto which the image has been transferred is transported to a fixing mechanism. The fixing mechanism of this embodiment includes a first fixing device 150 and a second fixing device 160. The first fixing device 150 includes a fixing roller 151 for heating the sheet 110 in order to thermocompress the image onto the sheet 110, a pressure belt 152 for pressing the sheet 110 against the fixing roller 151, and a post-fixing sensor 153 for detecting completion of fixing. The fixing roller 151 is a hollow roller that has an internal heater and is configured to rotate to transport the sheet 110. The post-fixing sensor 153 detects the sheet 110 after the image has been fixed.

[0024] The second fixing device 160 is disposed downstream of the first fixing device 150 in the conveying direction of the sheet 110, and is used to add gloss to the image on the sheet 110 that has been fixed by the first fixing device 150, and to ensure fixation. The second fixing device 160 has a fixing roller 161, a pressure roller 162, and a post-fixing sensor 163. The fixing roller 161 has the same configuration as the fixing roller 151 and functions in the same way. The pressure roller 162 functions in the same way as the pressure belt 152. The post-fixing sensor 163 functions in the same way as the post-fixing sensor 153. The second fixing device 160 performs a fixing process on the sheet 110 in the same way as the first fixing device 150.

[0025] The second fixing device 160 may not be used depending on the type of sheet 110 and the contents of the image forming process. The conveying path 130 is provided to convey the sheet 110 that has been subjected to the fixing process by the first fixing device 150 without passing through the second fixing device 160. For this reason, a flapper 131 is provided downstream of the first fixing device 150 in the conveying direction of the sheet 110 to guide the sheet 110 to either the second fixing device 160 or the conveying path 130.

[0026] The sheet 110 that has passed through either the second fixing device 160 or the conveying path 130 may be discharged as is or may be conveyed to the conveying path 135. For this reason, a flapper 132 is provided after the conveying path after the second fixing device 160 and the conveying path 130 join together. The flapper 132 guides the sheet 110 to either the conveying path 135 or a discharge path 139. The sheet 110 that has been guided to the discharge path 139 is discharged to the outside of the housing 101 with the side on which the image has been formed (first side) facing upward.

[0027] The conveying path 135 is a path along which the sheet 110 is conveyed to a reversing path 136 used to reverse the front and back sides of the sheet 110. A reversing sensor 137 that detects the sheet 110 is provided in the reversing path 136. When the reversing sensor 137 detects the trailing edge of the sheet 110, the conveying direction of the sheet 110 is reversed in the reversing path 136. The sheet 110, whose conveying direction has been reversed, is conveyed to either the conveying path 135 or the reversing path 138. For this purpose, a flapper 133 is provided at the branch point between the conveying path 135 and the reversing path 138. When the sheet 110 is conveyed to the conveying path 135, the sheet 110 is guided to the conveying path 135 by the flapper 133, reversed (with the side on which the image is formed facing downward), and discharged to the outside of the housing 101. When the sheet 110 is conveyed to the reversing path 138, the sheet 110 is guided to the reversing path 138 by the flapper 133. The sheet 110 guided to the reversing path 138 is reversed upside down and conveyed again to the transfer roller 114. As a result, an image is formed on the back side (second side) of the sheet 110.

[0028] (adjustment unit) 2 is a configuration diagram of the adjustment unit 400. The adjustment unit 400 is provided at a subsequent stage of the printer 100, and receives the sheet 110 after image formation that is discharged from the printer 100. The adjustment unit 400 has two conveyance paths: a through path 430 and a discharge path 432. A branching flapper 422 is provided at the branch point between the through path 430 and the discharge path 432. A reading unit 500 is provided in the through path 430, upstream of the branching flapper 422 in the conveyance direction of the sheet 110. The reading unit 500 reads the image formed on the sheet 110 received from the printer 100.

[0029] The through path 430 is provided with, in order from the upstream side in the conveyance direction of the sheet 110, a conveyance roller 401, a reading unit 500, a branching flapper 422, and a discharge roller 406. The discharge path 432 is provided with conveyance rollers 415, 416, and 417, and a discharge roller 418, with the branching flapper 422 as a base point. When the sheet 110 passes through the through path 430, the branching flapper 422 moves to the upper position. The sheet 110 that has passed through the through path 430 is discharged from the adjustment unit 400 to the outside (finisher 600) by the discharge roller 406. The finisher 600 discharges the sheet 110 to tray 601 or tray 602 (see FIG. 1). The finisher 600 may perform post-processing such as binding or bookbinding on the sheet 110. When the sheet 110 is conveyed to the discharge path 432, the branching flapper 422 moves to the lower position. The sheet 110 conveyed to the discharge path 432 is discharged onto a fixed tray 431 by a discharge roller 418 .

[0030] In this way, the discharge destination of the sheet 110 can be switched by the branching flapper 422. The sheet 110 transported to the finisher 600 passes through the through path 430. The image on the sheet 110 used for front-to-back registration is read by the reading unit 500 and the sheet is discharged to the fixed tray 431 via the discharge path 432. Note that the sheet 110 on which an image is formed according to a job is sometimes called a "job sheet," and the sheet 110 used for front-to-back registration is sometimes called an "adjustment sheet." The job sheet is transported to the finisher 600 via the through path 430.

[0031] By discharging the job sheet and the adjustment sheet separately, it is possible to prevent the adjustment sheet from being mixed in with the job sheets. The adjustment sheet is unnecessary for the user. If an adjustment sheet is mixed in with the job sheets, work must be done to remove the adjustment sheet. Therefore, discharging the job sheet and the adjustment sheet separately is effective in improving the efficiency of the user's work.

[0032] (Reading unit) Fig. 3 is an explanatory diagram of the reading unit 500. Fig. 3(a) is a cross-sectional view of the reading unit 500. Fig. 3(b) is a top view of the reading unit 500. The reading unit 500 includes conveying rollers 501, 502, and 503, reading sensors C1 and C2, glasses 5041 and 5042, biasing rollers 511, 512, 513, and 514, and sheet detection sensors 521 and 522.

[0033] Conveying rollers 501, 502, and 503 convey the sheet 110. The sheet 110 is conveyed by the conveying roller 501, conveying roller 502, and conveying roller 503 in this order. Reading sensors C1 and C2 detect the edges of the conveyed sheet 110 and read the printed image. The reading sensors C1 and C2 are optical sensors such as a CIS (Contact Image Sensor). The reading sensor C1 reads the image on the back side of the sheet 110. The reading sensor C2 reads the image on the front side of the sheet. The reading sensors C1 and C2 read the image line by line continuously, with the direction perpendicular to the conveying direction of the sheet 110 being the main scanning direction. The conveying direction of the sheet 110 is the sub-scanning direction.

[0034] Sheet detection sensors 521 and 522 detect the conveyed sheet 110. The operation timing of reading sensor C1 is determined depending on when sheet detection sensor 521 detects the sheet 110. The operation timing of reading sensor C2 is determined depending on when sheet detection sensor 522 detects the sheet 110. Note that sheet detection sensor 521 may be located anywhere between the receiving opening through which adjustment unit 400 receives sheet 110 from printer 100 and the reading position of reading sensor C1. Sheet detection sensor 522 may be located anywhere between the reading position of reading sensor C1 and the reading position of reading sensor C2. Alternatively, sheet detection sensor 522 may not be provided, and the operation timing of reading sensor C2 may be determined depending on when sheet detection sensor 521 detects the sheet.

[0035] The reading sensor C1 irradiates the sheet 110 being conveyed with light through the glass 5041 and receives the reflected light through the glass 5041, thereby detecting the edge of the sheet 110 and reading an image. The urging rollers 511 and 512 are arranged opposite the reading sensor C1 and urge the sheet 110 toward the reading sensor C1. The urging rollers 511 and 512 are arranged with a predetermined gap between them and the glass 5041. In other words, the urging rollers 511 and 512 are not nipped with the glass 5041. The urging rollers 511 and 512 are positioned closer to the glass 5041 than the nip line N connecting the nip portions of the conveying rollers 501, 502, and 503. This causes the sheet 110 to pass near the glass 5041, i.e., the focal position of the reading sensor C1. When the reading sensor C1 is a CIS, the focal depth of the CIS is shallow, so the sheet 110 needs to be biased to the vicinity of the focal position of the reading sensor C1.

[0036] The reading sensor C2 irradiates the sheet 110 with light through the glass 5042 and receives the reflected light through the glass 5042 to detect the edge of the sheet 110 and read the image. The biasing rollers 513 and 514 are positioned opposite the reading sensor C2 and bias the sheet 110 toward the reading sensor C2. The biasing rollers 513 and 514 are positioned with a predetermined gap between them and the glass 5042. In other words, the biasing rollers 513 and 514 are not nipped with the glass 5042. The biasing rollers 513 and 514 are positioned closer to the glass 5042 than the nip line N. This allows the sheet 110 to pass toward the glass 5042, i.e., near the focal position of the reading sensor C2. If the reading sensor C2 is a CIS, the focal depth of the CIS is shallow, so the sheet 110 needs to be biased toward the focal position of the reading sensor C1.

[0037] The reading unit 500 configured as described above can read the edge of the sheet 110 and the image formed on the sheet 110 while conveying the sheet 110 with conveyance rollers 501, 502, and 503. Based on the reading result, the distance from the edge of the sheet 110 to the image is detected. Geometric adjustments, such as adjustment of the formation position (printing position) of the image on the sheet 110, are performed based on the distance from the edge of the sheet 110 to the image. Note that the arrangement of the reading sensor C1, the glass 5041, and the urging rollers 511 and 512 and the arrangement of the reading sensor C2, the glass 5042, and the urging rollers 513 and 514 may be reversed. That is, the arrangement of the reading sensor C2, the glass 5042, and the urging rollers 513 and 514 may be arranged upstream, and the arrangement of the reading sensor C1, the glass 5041, and the urging rollers 511 and 512 may be arranged downstream.

[0038] (Adjustment sheet) In the case of interrupt adjustment, which interrupts a print job to adjust geometric characteristics, a test chart such as the one shown in FIG. 4 is used. FIG. 4 is an explanatory diagram of a sheet 110 (adjustment sheet) used in interrupt adjustment. The adjustment sheet is created by printing test images consisting of four patch images 820 near the four corners of the sheet 110. The patch image 820 on the leading edge of the sheet 110 in the conveyance direction is printed at a position that is a distance L from the leading edge of the sheet 110 in the conveyance direction. The patch image 820 on the trailing edge of the sheet 110 in the conveyance direction is printed at a position that is a distance L from the trailing edge of the sheet 110 in the conveyance direction. Let V be the conveyance speed of the sheet 110, T1 be the timing at which the reading sensor detects the sheet edge, and T2 be the timing at which the reading sensor detects the edge of the patch image 820. The distance L is expressed as L = (T2 - T1) / V. In this case, either reading sensor C1 or reading sensor C2 can be used.

[0039] In the case of real-time adjustment in which geometric characteristics are constantly adjusted, a test chart such as that shown in FIG. 5 is used. FIG. 5 is an explanatory diagram of a sheet 110 (adjustment sheet) used for real-time adjustment. On the adjustment sheet, patch images 820 are formed in the same positions as on the adjustment sheet used for interrupt adjustment in FIG. 4. That is, the adjustment sheet is created by printing a test image made up of four patch images 820 near the four vertices of the sheet 110. The shaded area is the area where an image according to the print job is formed. In other words, the adjustment sheet used for real-time adjustment is configured such that patch images 820 are formed on a job sheet on which an image has been formed according to the print job.

[0040] The patch image 820 on the leading edge side of the sheet 110 in the conveying direction is printed at a position that is a distance L from the leading edge of the sheet 110 in the conveying direction. The patch image 820 on the trailing edge side of the sheet 110 in the conveying direction is printed at a position that is a distance L from the trailing edge of the sheet 110 in the conveying direction. The distance L is expressed as L=(T2-T1) / V.

[0041] (controller) 6 is an explanatory diagram of a controller that controls the operation of the image forming apparatus 1. The printer 100 includes a printer controller 103 and an engine control unit 312. The printer controller 103 comprehensively controls the operation of the image forming apparatus 1. The engine control unit 312 controls the operation of each mechanism that constitutes the engine unit for image formation, thereby controlling the image formation process on the sheet 110.

[0042] The printer controller 103 is connected to the operation panel 180, acquires instructions input through the operation panel 180, and displays various screens on the operation panel 180, such as the operation screen shown in FIG. 7. The printer controller 103 includes a print job library 700, a paper library 900, and an image shape correction unit 320. The print job library 700 and the paper library 900 are linked together. Here, for example, a print job including image data transferred from a personal computer, which is an external device, is stored in the print job library 700. In the following description, an image formed by the image forming apparatus 1 based on a print job is referred to as a "user image." The user image is an image that is different from a predetermined test image.

[0043] The print job library 700 stores print jobs input from the operation panel 180. The print job library 700 stores information for each print job, such as the dimensions of the sheet used for printing (paper size) and the number of pages to be printed. The paper library 900 stores information such as geometric characteristics for each type of sheet usable by the printer 100. The geometric characteristics are updated using geometric adjustment values ​​(described below) acquired from the adjustment unit 400. The information stored in the paper library 900 also includes information such as the sheet name, basis weight, and surface texture entered from the operation panel 180. The image shape correction unit 320 acquires information on the geometric characteristics of the sheet used in the print job from the paper library 900. The image shape correction unit 320 corrects the geometric characteristics of the image data, such as the image shape and print position, according to the acquired geometric characteristic information. The image data corrected by the image shape correction unit 320 is sent to the engine control unit 312.

[0044] The engine control unit 312 is connected to the post-fixing sensors 153 and 163, the reversing sensor 137, the flappers 131 and 132, the drive motor 311, and the like. The drive motor 311 is a drive source that drives various rollers that transport the sheet 110 within the printer 100. The engine control unit 312 forms an image on the sheet 110 using the various mechanisms of the engine unit in accordance with print instructions including image data from the printer controller 103. At this time, the engine control unit 312 controls the operation of the flappers 131 and 132, the drive motor 311, and the like based on the detection results of the post-fixing sensors 153 and 163, the reversing sensor 137, and the like, thereby controlling the transport of the sheet 110.

[0045] The adjustment unit 400 is connected to the printer 100 so as to be able to communicate with it. The adjustment unit 400 includes a communication unit 250, a control unit 251, and an image processing unit 260. The control unit 251 is connected to conveyance motors M401 to M405, a flapper switching motor 423, sheet detection sensors 521 and 522, and reading sensors C1 and C2. The image processing unit 260 is connected to the reading sensors C1 and C2.

[0046] The communication unit 250 is a communication interface with the printer 100 (printer controller 103). The communication unit 250 receives data from the printer controller 103 and transmits it to the control unit 251 and the image processing unit 260. The communication unit 250 receives data from the control unit 251 and the image processing unit 260 and transmits it to the printer controller 103. For example, the communication unit 250 receives an operation instruction from the printer controller 103 and transmits it to the control unit 251, and obtains geometric adjustment values ​​(described later) from the image processing unit 260 and transmits them to the printer controller 103.

[0047] The control unit 251 operates in accordance with operation instructions received from the printer controller 103, and controls the operations of the conveying motors M401 to M405, the flapper switching motor 423, and the reading sensors C1 and C2. The conveying motors M401 to M405 are drive sources for the conveying rollers 401, 415, 416, 417, 501, 502, and 503, the discharge rollers 406 and 418, and the urging rollers 511, 512, 513, and 514 in the adjustment unit 400. The conveying motors M401 to M405 drive and control these rollers in accordance with instructions from the control unit 251, thereby conveying the sheet 110.

[0048] The flapper switching motor 423 controls the switching of the branch flapper 422 in response to instructions from the control unit 251. The operation instructions that the control unit 251 acquires from the printer controller 103 include information indicating whether the image to be formed on the delivered sheet 110 is a user image corresponding to the print job or a test image. When a user image corresponding to the print job is to be formed on the delivered sheet 110 (when the sheet is a job sheet), the control unit 251 controls the flapper switching motor 423 to move the branch flapper 422 to the upper position. When a test image is to be formed on the delivered sheet 110 (when the sheet is an adjustment sheet), the control unit 251 controls the flapper switching motor 423 to move the branch flapper 422 to the lower position. When a user image and a test image corresponding to the print job are to be formed on the delivered sheet 110, the control unit 251 controls the flapper switching motor 423 to move the branch flapper 422 to the upper position.

[0049] The reading sensors C1 and C2 read an image from the sheet 110 in response to instructions from the control unit 251. When the sheet to be passed is an adjustment sheet or a sheet on which a user image and a test image are to be formed, the control unit 251 instructs the reading sensors C1 and C2 to read an image. The control unit 251 is also connected to the sheet detection sensors 521 and 522, and instructs the reading sensors C1 and C2 to read an image on the sheet 110 in response to the timing when the sheet detection sensors 521 and 522 detect the sheet 110. The reading sensors C1 and C2 transmit the results of reading the sheet 110 to the image processing unit 260.

[0050] The image processing unit 260 operates in accordance with instructions received from the printer controller 103, and generates geometric adjustment values ​​for adjusting the geometric characteristics of the image formed by the printer 100 based on the results of reading the sheet 110 by the reading sensors C1 and C2. The geometric characteristics include, for example, the shape and print position of the image formed on the sheet 110. The image processing unit 260 stores the generated geometric adjustment values ​​in the paper library 900 of the printer controller 103 via the communication unit 250.

[0051] The process of adjusting geometric characteristics by the controller of the image forming apparatus 1 will be described. Here, the case of adjusting the print position as the geometric characteristic will be described. The adjustment of the geometric characteristics is performed by interrupt adjustment or real-time adjustment. In the case of interrupt adjustment, the adjustment of the geometric characteristics is performed by forming images on a predetermined number of sheets 110. In other words, the adjustment of the geometric characteristics is performed periodically by interrupting the print job each time the number of sheets 110 passed through the image forming apparatus 1 reaches a predetermined number. In the case of real-time adjustment, the adjustment of the geometric characteristics is always performed when images are formed on the sheets 110.

[0052] An adjustment sheet 801 shown in FIG. 8 is used to adjust the geometric characteristics during interrupt adjustment. The adjustment sheet 801 is created each time a periodic condition is met (each time the number of sheets 110 passed through reaches a predetermined number). The predetermined number, which is a condition for periodically creating the adjustment sheet 801, is determined based on, for example, user instruction information. The printer controller 103 acquires user instruction information related to the periodic condition for periodically creating the adjustment sheet 801, which is input from the operation panel 180, and determines the predetermined number based on the user instruction information. An adjustment sheet 804 shown in FIG. 8 is used to adjust the geometric characteristics during real-time adjustment. The adjustment sheet 804 has a test image such as that shown in FIG. 5 formed on both sides of the sheet 110 together with a user image.

[0053] Printer controller 103 displays print job list screen 1001, shown in FIG. 7(a), on operation panel 180 based on the print jobs stored in print job library 700. The user selects "print position adjustment" button 1002 from list screen 1001 using operation panel 180. This causes printer controller 103 to display a print position adjustment screen, shown in FIG. 7(b), on operation panel 180.

[0054] The user can instruct the printer controller 103 to perform interrupt adjustment by checking "Read and adjust adjustment sheet every certain number of sheets" 1105 on the print position adjustment screen using the operation panel 180. When the interrupt adjustment is instructed, the printer controller 103 instructs the engine control unit 312 to form an adjustment sheet for front and back registration. In response to this instruction, the engine control unit 312 creates an adjustment sheet 801 for every predetermined number of sheets.

[0055] The user can instruct the printer controller 103 to perform real-time adjustment by checking "Always read and adjust adjustment sheet" 1106 on the print position adjustment screen using the operation panel 180. When the real-time adjustment is instructed, the printer controller 103 instructs the engine control unit 312 to form an adjustment sheet for front and back registration. In response to this instruction, the engine control unit 312 overwrites the patch image 820 on the user image to create the adjustment sheet.

[0056] 8, a test image 802 consisting of four patch images 820 is formed on the front and back surfaces of the sheet 110 as shown in FIG.

[0057] The reading unit 500 of the adjustment unit 400 continuously reads the patch images 820 on both sides line by line using the reading sensors C1 and C2 while conveying the adjustment sheet 801 using conveying rollers 501, 502, and 503. The image processing unit 260 acquires the reading results for each line from the reading sensors C1 and C2 and stitches them together to generate read images of both sides of the adjustment sheet 801.

[0058] The image processing unit 260 detects the vertex coordinates (X01, Y01) to (X31, Y31) of the sheet and the coordinates (X41, Y41) to (X71, Y71) of the patch image 820 from the read image of the front side (test image 802) of the adjustment sheet 801. The image processing unit 260 detects the vertex coordinates (X02, Y02) to (X32, Y32) of the sheet and the coordinates (X42, Y42) to (X72, Y72) of the patch image 820 from the read image of the back side (test image 803) of the adjustment sheet 801.

[0059] The image processing unit 260 measures the amount of distortion of the image on the front side, deviation of the printing position, etc. based on the detected vertex coordinates (X01, Y01) to (X31, Y31) and coordinates (X41, Y41) to (X71, Y71). The image processing unit 260 measures the amount of distortion of the image on the back side, deviation of the printing position, etc. based on the detected vertex coordinates (X02, Y02) to (X32, Y32) and coordinates (X42, Y42) to (X72, Y72). The image processing unit 260 also measures the deviation of the printing position on the front and back sides according to the printing positions on each side.

[0060] Based on the measurement results of the amount of image distortion, misalignment of printing position, and misalignment of printing position on the front and back sides, the image processing unit 260 derives geometric adjustment values ​​for each of the front and back sides that enable the image shape correction unit 320 to correct the image shape. The geometric adjustment values ​​include parameters such as lead position, side position, magnification, perpendicularity, and rotation amount. The geometric adjustment values ​​for the front and back sides derived by the image processing unit 260 are sent to the paper library 900 of the printer controller 103 via the communication unit 250. The paper library 900 stores the acquired geometric adjustment values ​​for the front and back sides as parameters for image formation for the front and back sides. The geometric adjustment values ​​are derived for each type of sheet 110 and stored in the paper library 900.

[0061] Like the adjustment sheet 801 used during interrupt adjustment, the adjustment sheet 804 used during real-time adjustment is also read by the reading unit 500, and geometric adjustment values ​​are derived from the read results by the image processing unit 260. The method of deriving the geometric adjustment values ​​during real-time adjustment is the same as that during interrupt adjustment. These geometric adjustment values ​​are also derived for each type of sheet 110 and stored in the paper library 900.

[0062] An adjustment sheet 801 during interrupt adjustment read by the reading sensors C1 and C2 is discharged to the fixed tray 431 via a discharge path 432. An adjustment sheet 804 during real-time adjustment read by the reading sensors C1 and C2 is delivered to the finisher 600 via a through path 430.

[0063] The image shape correction unit 320 transmits the image data adjusted based on the geometric adjustment values ​​to the engine control unit 312. The engine control unit 312 forms an image on the sheet 110 based on the adjusted image data. The image formed in this manner has its geometric characteristics, such as image position and distortion, adjusted, and is formed on both sides of the sheet 110 with high-precision front and back registration.

[0064] By updating the geometric adjustment values, the geometric characteristics of the image formed on the sheet 110 are maintained at an optimum with high precision. In this embodiment, the geometric adjustment values ​​are updated not only at predetermined times during a print job, but also before the print job starts. That is, the adjustment sheet 801 is created by interrupting the print job and is also created before the print job starts.

[0065] (Front and back registration) FIG. 9 is a flowchart showing front and back registration processing during interrupt adjustment by the image forming apparatus 1. FIG. 10 is a flowchart showing front and back registration processing during real time adjustment by the image forming apparatus 1. FIG. 11 is an explanatory diagram of the position of the adjustment sheet 801 in the adjustment unit 400 during interrupt adjustment. FIG. 12 is an explanatory diagram of the position of the adjustment sheet 804 in the adjustment unit 400 during real time adjustment. The image forming apparatus 1 accepts a print job and starts processing. When the "Adjust Print Position" button 1002 on the list screen 1001 in FIG. 7(a) is selected, the image forming apparatus 1 performs front and back registration by interrupt adjustment or real time adjustment.

[0066] The process for interrupt adjustment will be described. The branching flapper 422 in the adjustment unit 400 moves to the lower position to guide the sheet 110 to the discharge path 432 (S1130). The printer controller 103 selects the type of sheet for which front-to-back registration is to be performed according to the print job being executed. The printer controller 103 instructs the engine control unit 312 to create an adjustment sheet 801. Upon receiving this instruction, the engine control unit 312 forms test images 802 and 803 on the front and back sides of the sheet 110 to create the adjustment sheet 801 (S1131). The printer 100 passes the created adjustment sheet 801 to the adjustment unit 400 (S1132). Figure 11(a) shows how the adjustment sheet 801 is passed from the printer 100 to the adjustment unit 400.

[0067] The control unit 251 of the adjustment unit 400 drives the conveyance rollers 401, 501, 502, and 503 using the conveyance motors M401 to M405 to convey the adjustment sheet 801. As a result, the adjustment sheet 801 passes the reading position of the reading unit 500. When the adjustment sheet 801 passes the reading position of the reading unit 500, the test images 802 and 803 formed on both sides of the adjustment sheet 801 are read by the reading sensors C1 and C2 (S1133). At this time, the control unit 251 starts reading and measuring the back side of the adjustment sheet 801 with the reading sensor C1 after a predetermined time has elapsed since the sheet detection sensor 521 detected the leading edge of the adjustment sheet 801. In addition, the control unit 251 starts reading and measuring the front side of the adjustment sheet 801 with the reading sensor C2 after a predetermined time has elapsed since the sheet detection sensor 522 detected the leading edge of the adjustment sheet 801.

[0068] As described above, the image processing unit 260 derives geometric adjustment values ​​based on the results of reading the adjustment sheet 801 by the reading sensors C1 and C2, and stores the values ​​in the paper library 900 (S1134). The derivation of the geometric adjustment values ​​completes the print position adjustment for front-to-back registration. Once the print position adjustment is complete, the control unit 251 drives the conveyance rollers 415, 416, and 417 and the discharge rollers 418 using the conveyance motors M401 to M405 to discharge the adjustment sheet 801 onto the fixed tray 431 (S1135). FIG. 11(b) shows the adjustment sheet 801 being conveyed along the discharge path 432 by the conveyance rollers 415, 416, and 417 and the discharge rollers 418.

[0069] When the sheet 110 (job sheet) or the adjustment sheet 801 is discharged, the printer controller 103 determines whether the image forming process on the final sheet has been completed (S1136). If the image forming process on the final sheet has not been completed (S1136: N), the image forming apparatus 1 repeats the processes from S1002 onwards. If the image forming process on the final sheet has been completed (S1136: Y), the image forming apparatus 1 ends the front and back registration process.

[0070] The processing for real-time adjustment will be described. The branching flapper 422 in the adjustment unit 400 moves to the upper position to guide the sheet 110 to the through path 430 (S1130). The printer controller 103 instructs the engine control unit 312 to create an adjustment sheet 804. Upon receiving this instruction, the engine control unit 312 forms the user image and test images 805 and 806 on the sheet 110 (S1231). The printer 100 passes the created adjustment sheet 804 to the adjustment unit 400 (S1232). Figure 12(a) shows how the adjustment sheet 804 is passed from the printer 100 to the adjustment unit 400.

[0071] The control unit 251 of the adjustment unit 400 drives the conveyance rollers 401, 501, 502, and 503 using the conveyance motors M401 to M405 to convey the adjustment sheet 804. As a result, the adjustment sheet 804 passes the reading position of the reading unit 500. When the adjustment sheet 804 passes the reading position of the reading unit 500, the reading sensors C1 and C2 read the test images 805 and 806 formed on both sides of the adjustment sheet 804 (S1233). At this time, the control unit 251 starts reading and measuring the back side of the adjustment sheet 804 with the reading sensor C1 after a predetermined time has elapsed since the sheet detection sensor 521 detected the leading edge of the adjustment sheet 804. In addition, the control unit 251 starts reading and measuring the front side of the adjustment sheet 804 with the reading sensor C2 after a predetermined time has elapsed since the sheet detection sensor 522 detected the leading edge of the adjustment sheet 804.

[0072] As described above, the image processing unit 260 derives geometric adjustment values ​​based on the results of reading the adjustment sheet 804 by the reading sensors C1 and C2, and stores the geometric adjustment values ​​in the paper library 900 (S1234). The derivation of the geometric adjustment values ​​completes the print position adjustment for front-to-back registration. Once the print position adjustment is complete, the control unit 251 drives the discharge rollers 406 using the conveyance motors M401 to M405 to discharge the adjustment sheet 804 to the finisher 600 (S1235). FIG. 12(b) shows how the adjustment sheet 804 is discharged to the finisher 600 by the discharge rollers 406. The finisher 600 discharges the adjustment sheet 804 to tray 601 or tray 602.

[0073] When the adjustment sheet 804 is discharged, the printer controller 103 determines whether the image forming process on the final sheet has been completed (S1236). If the image forming process on the final sheet has not been completed (S1236: N), the image forming apparatus 1 repeats the processes from S1002 onwards. If the image forming process on the final sheet has been completed (S1236: Y), the image forming apparatus 1 ends the front and back registration process.

[0074] (Detection of false positives on test images) The image forming apparatus 1 of this embodiment automatically adjusts the geometric characteristics by reading adjustment sheets 801 and 804 using an in-line reading unit 500. In the case of interrupt adjustment, the image forming apparatus 1 creates an adjustment sheet 801 and adjusts the geometric characteristics every time a predetermined number of job sheets are created. In the case of real-time adjustment, the image forming apparatus 1 adjusts the geometric characteristics every time a user image is formed using an adjustment sheet 804 in which test images 805 and 806 are overwritten on the user image.

[0075] FIG. 13 is an explanatory diagram of erroneous detection of a test image. As described above, when patch image 820 is printed in the correct position, the distance from the edge of sheet 110 to patch image 820 is L. When patch image 820 is printed a predetermined distance close to the edge of sheet 110, the distance from the edge of sheet 110 to patch image 820 is L1. In this case, the deviation of the print position from the correct position is ΔL1 = L - L1. When patch image 820 is printed a predetermined distance away from the edge of sheet 110, the distance from the edge of sheet 110 to patch image 820 is L2. In this case, the deviation of the print position from the correct position is ΔL2 = L - L2. The deviations of the print position, ΔL1 and ΔL2, are used as thresholds for identifying erroneous detection of the test image. The threshold ΔL1 is used to determine abnormal data when the print position is shifted toward the edge of the sheet. The threshold value ΔL2 is a threshold value for determining abnormal data when the print position is shifted to the opposite side from the edge of the sheet.

[0076] The image processing unit 260 measures the distance from the sheet edge to the patch image 820 based on the results of reading the adjustment sheets 801 and 804 (patch image 820) by the reading sensors C1 and C2. The image processing unit 260 calculates the difference ΔL between the measured distance from the sheet edge to the patch image 820 and the distance from the sheet edge to the patch image 820 when the patch image 820 is formed in a normal position. The image processing unit 260 compares the difference ΔL with thresholds ΔL1 and ΔL2. If the comparison result is |ΔL1|<ΔL or |ΔL2|<ΔL, the image processing unit 260 determines that the reading result is a false positive (abnormal data) and decides not to use this reading result in calculating the geometric adjustment value. In other words, reading results for which the difference ΔL is greater than the threshold ΔL1 or threshold ΔL2 are excluded from the samples used to calculate the geometric adjustment value. This prevents a decrease in the accuracy of the geometric adjustment value due to the sudden occurrence of abnormal data. Here, it is assumed that false detection occurs under the following conditions:

[0077] · Misdetection of patch images due to the surface properties of the sheet 110 (embossed paper, label paper, etc.): If the surface of the sheet 110 is uneven, the print position of the patch image may not be measured correctly. False detection due to changes in sheet size caused by variations in cutting, etc.: The margins may become extremely small or large due to changes in the shape of the sheet as it passes through, which can prevent accurate detection of the sheet edges and result in false detection. False detection due to image defects (black streaks, white streaks) caused by dust or other foreign matter at the reading position of the reading unit 500: False detection may occur due to image defects (black streaks, white streaks) that result in the white streaks being determined to be the edge of the sheet, or the black streaks being determined to be missing from the edge of the sheet.

[0078] (Calculation method of geometric adjustment value) 14 is a flowchart showing the process of calculating geometric adjustment values ​​during interrupt adjustment. This process corresponds to S1134 in FIG.

[0079] The image processing unit 260 measures the distance from the edge of the sheet 110 to the patch image 820 based on the reading result of the adjustment sheet 801. The image processing unit 260 calculates the difference ΔL between the measurement result and the distance from the edge of the sheet to the patch image 820 when the patch image 820 is formed in a normal position (S1301). The image processing unit 260 compares the calculated difference ΔL with thresholds ΔL1 and ΔL2 (S1302). If the difference ΔL is greater than the thresholds ΔL1 and ΔL2 (S1302: N), the image processing unit 260 adds information indicating a reading error to the reading result (S1304). After adding the information indicating a reading error to the reading result, the image processing unit 260 increments the number of samples of the reading result by 1 (S1303). If the difference ΔL is smaller than the threshold ΔL1 and the threshold ΔL2 (S1302: Y), the image processing unit 260 increments the number of samples of the read result by 1 (S1303). The image processing unit 260 repeats the processes of S1301 to S1304 until the number of samples of the read result reaches a predetermined number (S1305: N).

[0080] When the number of samples of the read result reaches a specified value (S1305: Y), the image processing unit 260 calculates geometric adjustment values ​​based on the read result to which information indicating a read error is not added (S1306). The image processing unit 260 stores the calculated geometric adjustment values ​​in the paper library 900 (S1307). The printer controller 103 adjusts the print position of the image by affine transformation or the like based on the geometric adjustment values ​​stored in the paper library 900. The image processing unit 260 repeats the processes of S1301 to S1307 until the job is completed (S1308: N). When the job is completed (S1308: Y), the image processing unit 260 terminates the calculation process of the geometric adjustment values ​​during interrupt adjustment. This process reduces the number of samples of the read result used to calculate the geometric adjustment values.

[0081] 15 is a flowchart showing the process of calculating geometric adjustment values ​​during real-time adjustment. This process corresponds to S1234 in FIG.

[0082] The image processing unit 260 measures the distance from the edge of the sheet 110 to the patch image 820 based on the reading result of the adjustment sheet 801. The image processing unit 260 calculates the difference ΔL between the measurement result and the distance from the edge of the sheet to the patch image 820 when the patch image 820 is formed in a normal position (S1401). The image processing unit 260 compares the calculated difference ΔL with thresholds ΔL1 and ΔL2 (S1402). If the difference ΔL is greater than the thresholds ΔL1 and ΔL2 (S1402: N), the image processing unit 260 rejects the reading result and returns to the calculation process of the difference ΔL in S1401. If the difference ΔL is smaller than the thresholds ΔL1 and ΔL2 (S1402: Y), the image processing unit 260 increments the number of samples of the reading result by 1 (S1403). Image processing unit 260 repeats the processes of S1401 to S1403 until the number of samples of the read result reaches a predetermined specified number (S1404: N).

[0083] When the number of samples of the read results reaches a specified value (S1404: Y), the image processing unit 260 calculates a geometric adjustment value based on the specified number of read results (S1405). The image processing unit 260 stores the calculated geometric adjustment value in the paper library 900 (S1406). The printer controller 103 adjusts the print position of the image by affine transformation or the like based on the geometric adjustment value stored in the paper library 900. The image processing unit 260 repeats the processes of S1401 to S1406 until the job is completed (S1407: N). When the job is completed (S1407: Y), the image processing unit 260 real time The calculation process for the geometric adjustment value during adjustment is terminated. In this process, the number of samples of the read results used to calculate the geometric adjustment value is maintained at a specified number without decreasing the number of samples of the read results. This stabilizes the accuracy of the geometric adjustment value.

[0084] (Method of searching for sheet edge and patch image) 16 is an explanatory diagram of a method for searching for the sheet edge and the patch image 820. Here, the reading results by the reading sensor C1 will be described, but the sheet edge and the patch image 820 are similarly searched for by the reading sensor C2.

[0085] The reading sensor C1 reads the sheet 110 (adjustment sheet) being conveyed. The read image 1203 is the reading result of the reading sensor C1. The read image 1203 includes a black background image 1204 that is the background and an image 1205 of the sheet 110. The image processing unit 260 determines the change in color from black to white in the read image 1203 pixel by pixel in the main scanning direction, and when it detects a white width Lb of a predetermined length, it detects the pixel at the start position of the width Lb as the edge of the sheet 110. In other words, because the background image 1204 is black, the image processing unit 260 determines that the edge of the sheet 110 is the pixel where the color changed from black to white, as a predetermined number of white pixels (width Lb) continuing in the main scanning direction from the pixel where the color changed from black to white.

[0086] After detecting the end of the sheet 110, the image processing unit 260 searches for the end of the patch image 820. The image processing unit 260 determines, pixel by pixel in order in the main scanning direction, the change in black-and-white color from the end of the sheet 110 in the read image 1203, and detects the position where the change from white to black occurs as the patch image 820. The image processing unit 260 calculates the distance L from the end of the sheet 110 to the patch image 820.

[0087] When dust 1202 adheres to the reading position of the reading sensor C1, a white streak image 1206 appears in the read image 1203. Let the length of the streak image in the main scanning direction be the dust width La. The dust width La is the assumed width of the streak image 1206 caused by the dust 1202. Let the assumed fluctuation amount be ΔL’(L - Lb) from the distance L and the width Lb of white with a predetermined length. It is preferable that the predetermined width Lb is larger than the dust width La (Lb > La). This is because when the predetermined width Lb is smaller than the dust width La (Lb < La), the streak image 1206 may be misrecognized as the end of the sheet 110.

[0088] The image forming apparatus 1 of the present embodiment as described above selects the reading result so that sudden abnormal data is not included when reading the test image in the adjustment of the geometric characteristics during the job. Specifically, the image forming apparatus 1 excludes the reading result outside the range set by the threshold value from the adjustment of the geometric characteristics. Also, the image forming apparatus 1 calculates the geometric adjustment value when the number of samples of the reading result reaches the specified value. Therefore, the image forming apparatus 1 can perform the adjustment of the geometric characteristics with high precision while preventing the decrease in the number of samples.

[0089] Although the configuration in which the reading sensors C1 and C2 are provided in the adjustment unit 400 has been described for the image forming apparatus 1 of the present embodiment, the reading sensors C1 and C2 may be provided in the printer 100. For example, the reading sensors C1 and C2 may be provided on the conveyance path 135. In this case, the printer 100 has a tray provided at the rear end of the reverse path 136. The printer 排出パス139から排出する。100 discharges the adjustment sheet 801 used for interrupt adjustment to the tray and discharges the adjustment sheet 804 used for real-time adjustment from the discharge path 139.

Claims

1. an image forming means for forming a test image for position detection on a sheet; a conveying means for conveying the sheet from the image forming means; a reading means for reading the sheet on which the test image is formed while being conveyed by the conveying means; a detecting means for detecting position information of the test image on the sheet based on a result of reading the sheet by the reading means; a determining unit that determines whether the position of the test image on the sheet is within a predetermined range based on the result of reading the sheet by the reading unit; a control means for controlling the position and shape of an image to be formed on a sheet by the image forming means based on the position information corresponding to a predetermined number of read results for which the determination means has determined that the position of the test image is within the predetermined range, excluding the read results for which the determination means has determined that the position of the test image is not within the predetermined range; when a first mode in which the image and the test image are formed on the same sheet is executed, the control means controls the position and shape of the image to be formed on the sheet by the image forming means based on the position information of the test image on the predetermined number of sheets on which it has been determined by the determination means that the test image has been formed within the predetermined range; When a second mode is executed in which the test image is formed on a sheet different from the sheet on which the image is to be formed, the control means determines, from the reading results of a specified number of sheets, the reading result in which the determination means has determined that the test image is formed within the predetermined range, and controls the position and shape of the image to be formed on the sheet by the image forming means based on the position information of the test image on the sheet corresponding to the determined reading result. Image forming device.

2. the control means controls the position and shape of the image to be formed on the sheet by the image forming means using the adjustment value; The control means updates the adjustment value based on the position information corresponding to the predetermined number of read results for which the determination means has determined that the position of the test image is within the predetermined range, excluding read results for which the determination means has determined that the position of the test image is not within the predetermined range from read results newly read by the reading means after the adjustment value was last updated.

2. The image forming apparatus according to claim 1.

3. the control means has a counter that counts the number of sheets for which the position of the test image is determined by the determination means to be within the predetermined range, excluding the number of sheets for which the position of the test image is determined by the determination means to be outside the predetermined range, When the number of sheets counted by the counter reaches the predetermined number, the control means determines that the reading results of the predetermined number of sheets, for which the position of the test image is determined to be within the predetermined range by the determination means, have been obtained.

2. The image forming apparatus according to claim 1.

4. The image forming means forms the image and the test image on the same sheet.

2. The image forming apparatus according to claim 1.

5. the image forming means forms the test image every time a specified number of sheets are imaged while continuously forming images on a plurality of sheets in the second mode; 2. The image forming apparatus according to claim 1.

6. The printing method further comprises: receiving means for receiving user instruction information indicating the specified number of sheets; 6. The image forming apparatus according to claim 5.

7. The test image is formed at each of the four corners of the sheet.

2. The image forming apparatus according to claim 1.

Images