Image forming apparatus, method for controlling image forming apparatus, and program

Abstract

To provide a mechanism that can easily detect a front end and a rear end of a sheet used in performing positioning of an image regardless, for example, of a size and the like of the sheet.SOLUTION: An image forming apparatus 100 can perform positioning of an image. The image forming apparatus 100 comprises: reading means that acquires a read image of a chart for adjustment 601, while moving the chart for adjustment 601 in one direction; reading means that acquires a length in one direction of the chart for adjustment 601; and calculation means that calculates an adjustment amount used for the positioning. The calculation means includes: extraction means that extracts a pair of a front end 606 and a rear end 609 of the chart for adjustment 601 from the read image; and determination means that, on the basis of the length in one direction of the chart for adjustment 601 and a distance between the pair of the front end 606 and the rear end 609, determines whether to adopt the pair of the front end 606 and the rear end 609 as the front end 606 and the rear end 609 of the chart for adjustment 601 used in calculating the adjustment amount.SELECTED DRAWING: Figure 8A

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus, a control method for an image forming apparatus, and a program. [Background technology]

[0002] In printing devices (image processing devices) that form an image on a sheet, devices having a function of adjusting the formation position of an image on a sheet (hereinafter referred to as "print position adjustment") have been conventionally known. Print position adjustment enables high-precision print position alignment, for example, when performing double-sided printing that requires alignment of both sides of the paper. This is because in printing devices, differences in paper transport characteristics occur depending on various conditions such as the size, basis weight, and material of the paper, which leads to minute differences in the print position. For this reason, print position adjustment needs to be performed for each paper used in the printing device. In addition, when fixing heat is generated during printing on the front side of the paper, the shrinkage rate of the paper changes, for example, depending on the moisture absorption of the paper. In this case, it affects the print position on the back side of the paper.

[0003] In the print position adjustment, a sheet of paper to be adjusted that has a "predetermined mark" printed thereon (hereinafter referred to as an "adjustment chart") is used. Then, the amount of misalignment of the print position is detected based on the relative positions of the marks on the adjustment chart and the edge of the adjustment chart. The amount of misalignment of the print position is stored as a print parameter. From this point on, when printing is performed on the same paper as the paper to be adjusted, the print parameter is referenced and the position is adjusted so that the amount of misalignment of the print position is offset (cancelled). This results in a printout with an accurate print position. The relative position of the mark is detected, for example, by acquiring a read image of the adjustment chart with an image reading device. This detection requires paper edge position information on the read image. The paper edge position information is acquired by detecting the paper edge of the adjustment chart based on the luminance difference between the background and the adjustment chart in the image reading device. Generally, the background color is white, and the color of the adjustment chart near the edge of the paper is also white. In this case, the brightness of both becomes close, which may result in difficulty in detecting the paper edge and in subsequent accurate position adjustment. In Patent Document 1, multiple candidates for the paper edge are detected, and the distance between the opposing paper edges is compared with the size of the adjustment chart, and the accurate paper edge position can be detected according to the comparison result. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2022-18079 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in Patent Document 1, the longer the paper length is, particularly in the case of long paper, the greater the variation in the distance between the opposing paper edges, which may make it difficult to accurately detect the paper edge position. Factors that cause the distance between the paper edges to vary depending on the paper length include, for example, variations in the paper feed amount due to roller transport and variations in paper size reduction due to fixing, etc. Furthermore, if the paper edge position cannot be accurately detected, there is a risk that the subsequent print position adjustment cannot be performed accurately.

[0006] The present invention has been made in view of the above problems, and has an object to provide a mechanism for easily detecting the leading and trailing edges of a sheet used when adjusting the position of an image, regardless of, for example, the size of the sheet. [Means for solving the problem]

[0007] In order to achieve the above-mentioned object, the image forming apparatus of the present invention is an image forming apparatus capable of forming an image on a sheet and adjusting the position of the image on the sheet prior to the image formation, and is characterized in that it comprises: an image forming means for forming an adjustment image used for the position adjustment on the sheet to obtain an adjustment chart; a reading means for acquiring a read image of the adjustment chart while moving the adjustment chart relatively in one direction; an acquisition means for acquiring the length of the sheet in the one direction; and a calculation means for calculating an adjustment amount used for the position adjustment based on the adjustment image included in the read image, wherein the calculation means comprises: an extraction means for extracting from the read image at least one pair of a leading end located in front of the movement direction of the adjustment chart and a trailing end located behind the movement direction; and a determination means for determining whether or not the pair of leading and trailing ends should be the leading and trailing ends of the sheet used when calculating the adjustment amount, based on the length of the sheet in the one direction acquired by the acquisition means and the distance between the leading and trailing ends of the pair extracted by the extraction means. Effect of the Invention

[0008] According to the present invention, the leading edge and trailing edge of a sheet used when adjusting the position of an image can be easily detected regardless of, for example, the size of the sheet. [Brief description of the drawings]

[0009] [Figure 1] 1 is a block diagram showing a hardware configuration of an image forming apparatus according to a first embodiment. [Diagram 2] FIG. 2 is a vertical sectional view showing the internal structure of the image forming apparatus. [Diagram 3] FIG. 13 is a diagram showing an interface screen for an operator to perform editing or the like on a paper library. [Figure 4] FIG. 13 is a diagram showing an interface screen for an operator to edit paper attributes. [Diagram 5] FIG. 13 is a diagram showing an example of contents stored in a paper library. [Figure 6] FIG. 13 is a diagram showing an example of an adjustment chart used for adjusting a print position. [Figure 7] FIG. 13 is a diagram showing the distance from the edge of each mark on the adjustment chart. [Figure 8A] 13 is a flowchart showing a process for measuring the relative positions of marks. [Figure 8B] 13 is a diagram showing the relationship between the measured value of the length of the adjustment chart in the sub-scanning direction and the specified value of the adjustment chart when the diameter of each roller of the image reading unit varies over time. FIG. [Figure 9] FIG. 2 is a diagram for explaining the position of a paper edge. [Figure 10] 5 is a schematic diagram showing a state in which an adjustment chart is read by an image reading unit; FIG. [Figure 11] 8B is a flowchart showing a vertical paper edge extraction process (the same applies to step S805) executed in step S804 (subroutine) of the flowchart shown in FIG. 8A. [Figure 12] 13 is a schematic diagram showing the positional relationship between an upper left ROI image and an upper right ROI image when extracting an upper left vertical edge and an upper right vertical edge. FIG. [Figure 13]11. FIG. 12 is a flowchart showing a paper edge candidate extraction process carried out in step S1103 (subroutine) in the flowchart of FIG. [Figure 14] FIG. 13 is a diagram illustrating an example of a Hough table. [Figure 15] 13 is a schematic diagram showing an example of extraction of a plurality of paper edge candidates; FIG. [Figure 16] 11 is a flowchart showing an optimum edge pair determination process executed in step S1104 (subroutine) of the flowchart shown in FIG. [Figure 17] 13A to 13C are diagrams illustrating an example of a specific operation in the optimum paper-side pair determination process in the left-right direction. [Figure 18] 8B is a flowchart showing a horizontal paper edge extraction process (the same applies to step S808) executed in step S807 (subroutine) of the flowchart shown in FIG. 8A. [Figure 19] 13 is a schematic diagram showing the positional relationship between an upper left ROI image and a lower left ROI image when detecting an upper left horizontal edge and a lower left horizontal edge of the paper. FIG. [Figure 20] 13A to 13C are diagrams illustrating an example of a specific operation in the optimum paper-edge pair determination process in the up-down direction. [Figure 21] FIG. 4 is a sequence diagram showing a process executed between an operator, an image forming apparatus, and a host computer. [Figure 22] 8B is a flowchart showing a horizontal paper edge extraction process (the same applies to step S808) executed in step S807 (subroutine) of the flowchart shown in FIG. 8A in the second embodiment. [Figure 23] 13 is a schematic diagram showing the positional relationship between an upper left ROI image and a lower left ROI image when detecting an upper left horizontal edge and a lower left horizontal edge of the paper. FIG. [Figure 24] 13 is a schematic diagram showing the positional relationship between an upper left ROI image and a lower left ROI image when detecting an upper left horizontal edge and a lower left horizontal edge in the third embodiment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Each embodiment of the present invention will be described in detail below with reference to the drawings. However, the configurations described in each of the following embodiments are merely examples, and the scope of the present invention is not limited by the configurations described in each embodiment. For example, each part constituting the present invention can be replaced with any configuration that can exert a similar function. In addition, any configuration may be added. In addition, any two or more configurations (features) of each embodiment can be combined.

[0011] <<First embodiment>> The first embodiment will be described below with reference to FIGS. 1 to 21.

[0012] <Hardware configuration of image forming device> FIG. 1 is a block diagram showing a hardware configuration of an image forming system according to a first embodiment. As shown in FIG. 1, the image forming system 1000 has an image forming apparatus 100 and a host computer 101, which are communicably connected to each other via a communication line 102. The number of image forming apparatuses 100 and host computers 101 in the image forming system 1000 is not limited to one, and may be more than one. The communication on the communication line 102 is communication via a LAN, a WAN, or the like. The host computer 101 is, for example, an information processing device such as a personal computer, a tablet terminal, or a smartphone. The host computer 101 can obtain input information from a user and create a print job to be sent to the image forming apparatus 100.

[0013] The image forming apparatus 100 includes a controller 110, an operation panel 120, a paper size acquisition unit (acquisition means) 121, an image reading unit (reading means) 130, a print position measurement unit (calculation means) 131, a paper feed unit 140, and an image forming unit (image forming means) 150. The controller 110 is communicably connected to the operation panel 120, the image reading unit 130, the paper feed unit 140, and the image forming unit 150 via a system bus 116. The controller 110 performs various data processing and controls the operation of the image forming apparatus 100. The operation panel 120 accepts various operations from a user using a touch panel method. The paper size acquisition unit 121 acquires the size and position adjustment amount of the print paper from a paper library by operating the operation panel 120, as described later. The image reading unit 130 scans an original document using an optical sensor while moving the document, and acquires the scanned image data. In this embodiment, the image reading unit 130 is an external reading device such as an ADF, but is not limited thereto. For example, the image reading unit 130 may have an in-line sensor or the like that can move relative to the original document while the original document remains in its position. The print position measuring unit 131 acquires the relative coordinates of the print position based on an image of an adjustment chart (print position adjustment chart), as described later. The paper feed unit 140 is a paper feed device that is composed of multiple paper feed stages. Each paper feed stage can store various types of printing paper. Each paper feed stage can separate only the topmost sheet of paper stored in that paper feed stage and convey it to the image forming unit 150. The image forming unit 150 prints image data on the printing paper to obtain a print result 160.

[0014] The controller 110 includes an I / O control unit 111, a ROM 112, a RAM 113, a CPU 114, and a HDD 115, which are connected to each other via a system bus 116 so as to be able to communicate with each other. The I / O control unit 111 controls communication between the controller 110 and the communication line 102. The ROM 112 is a ROM that stores various control programs. The control programs include, for example, programs for causing a computer to execute each unit and each means (a control method for the image forming apparatus) of the image forming apparatus 100. The RAM 113 reads out and records the control programs stored in the ROM 112. The CPU 114 executes the control programs read out to the RAM 113, and comprehensively controls image signals and various devices. The RAM 113 also functions as a main memory for the CPU 114, and functions as a work memory. The HDD 115 temporarily or long-term holds large amounts of data such as image data and print data. The control programs and the OS (operating system) are stored in the HDD 115 in addition to the ROM 112. The controller 110 may also include a nonvolatile random access memory (NVRAM). In this case, the NVRAM can store printing device mode setting information input from the operation panel 120.

[0015] <Structure and operation of image forming apparatus> FIG. 2 is a vertical cross-sectional view showing the internal structure of the image forming apparatus. The image forming apparatus 100 shown in FIG. 2 is configured to be capable of forming an image on a sheet P and adjusting the position of the image on the sheet P prior to the image formation. The image forming apparatus 100 has a housing 201. The housing 201 has built-in mechanisms for constituting an engine section, an engine control section for controlling each printing process (e.g., paper feeding process, etc.) by each mechanism, and a control board storage section for storing a printer controller. The image reading section 130 has a document table 230, a pickup roller 231, a conveying roller (conveying means) 232, a roller 233, a light source 234, a reading section (second reading section) 235, a reading section (first reading section) 236, a paper discharge roller 238, and a paper discharge roller 239. One or more documents 237 (e.g., an adjustment chart 601 described later) can be placed on the document table 230. The original 237 is sent to the reading path one by one by the pickup roller 231. Then, the original 237 is conveyed (moved) in one direction by the conveying roller 232 on the path. The original 237 reaches the original reading position while passing through the path. At this original reading position, the image information added to the front side of the original 237 is read by the light source 234 and the reading unit 236 (reading process). After that, the image information added to the back side of the original 237 is read by the reading unit 235. The original 237 from which the image information on both sides has been read is discharged by the paper discharge roller 238 and the paper discharge roller 239. The image forming apparatus 100 may have a mechanism for inverting the original during conveyance. In this case, both sides of the original can be read.

[0016] The printer engine unit includes an optical processing mechanism, a fixing processing mechanism, a sheet P feed processing mechanism, and a transport processing mechanism. The optical processing mechanism forms an electrostatic latent image on the photosensitive drum 205 by scanning with a laser beam, visualizes the electrostatic latent image, transfers the visualized image to the intermediate transfer body 252 in a multi-layered manner, and transfers the multi-layered transferred color image onto the sheet P. The fixing processing mechanism fixes the toner image transferred onto the sheet P.

[0017] The optical processing mechanism includes a photosensitive drum 205, a laser scanner unit 207, a rotating polygon mirror 208, a reflecting mirror 209, a primary charger 211, and a developing unit 212. The laser scanner unit 207 includes a laser driver that drives a laser beam emitted from a semiconductor laser to turn on and off in response to image data supplied from a controller 110. The laser beam emitted from the semiconductor laser is deflected in the scanning direction by the rotating polygon mirror 208. The laser beam deflected in the main scanning direction is guided to the photosensitive drum 205 via the reflecting mirror 209, and exposes the photosensitive drum 205 in the main scanning direction. The electrostatic latent image formed on the photosensitive drum 205 by the scanning exposure with the laser beam, which is charged by the primary charger 211, is visualized into a toner image by the toner supplied by the developing unit 212. The visualized toner image on the photosensitive drum 205 is then transferred (primary transfer) onto an intermediate transfer body 252 to which a voltage having the opposite characteristics to that of the toner image is applied. When forming a color image, each color can be sequentially formed on the intermediate transfer body 252 from the Y (yellow) station 220, the M (magenta) station 221, the C (cyan) station 222, and the K (black) station 223. This allows a full-color visible image to be formed on the intermediate transfer body 252. In addition, the optical processing mechanism conveys the sheet P fed from the transfer material storage 210, presses the sheet P against the intermediate transfer body 252 with the transfer roller 251, and applies a bias with the opposite characteristics to the toner to the transfer roller 251. As a result, the visible image formed on the intermediate transfer body 252 is transferred (secondary transfer) to the sheet P conveyed in synchronization with the conveying direction (sub-scanning direction) of the sheet P by the paper feed processing mechanism. After the secondary transfer, the sheet P passes through the fixing device 260, whereby the toner transferred onto the sheet P is heated and melted, and fixed as an image on the sheet P. In the case of double-sided printing, the sheet passes through the reversing section 270, switches back, and is introduced again into the transfer section 240. As a result, the back side image is transferred to the sheet P. Thereafter, the sheet P passes through the fixing device 260 in the same manner as above, whereby the toner image on the sheet P is heated and fixed, and the sheet is discharged.

[0018] <Paper library editing interface> The paper used for printing in the image forming apparatus 100 is managed by the operator on a database as a paper library. The paper library is stored in the HDD 115 or the RAM 113. The paper library is read and written by each software as necessary. FIG. 3 is a diagram showing an interface screen for the operator to perform editing and the like for the paper library. The interface screen 300 shown in FIG. 3 is displayed on the operation panel 120. The interface screen 300 includes a paper list 310 in which the papers stored in the paper library are listed. In the paper list 310, items 311, 312, 313, 314, and 315 indicating paper attributes are set for each paper. The item 311 is the paper name of the paper. The paper name is a name that allows the paper to be identified, and is specified by the operator, etc. The item 312 is the paper length in the sub-scanning direction of the paper. The item 313 is the paper length in the main scanning direction of the paper. The item 314 is the basis weight of the paper. Item 315 is the surface quality of the paper. Here, "surface quality" is an attribute that represents the physical characteristics of the paper surface, such as "coated" in which the surface is coated to increase glossiness, or "embossed" in which minute irregularities are formed on the surface. In addition, by touching a portion of the paper list 310 on the operation panel 120 where any paper is displayed, the paper can be selected. The selected paper is highlighted (inverted). In FIG. 3, "XYZ Paper, Color 81" is displayed as an example of this highlighted display. In addition, if the number of types of paper recorded in the paper library is greater than the number of types of paper that can be displayed collectively in the paper list 310, a scroll bar 317 is used. By operating the scroll bar 317, all types of paper recorded in the paper library can be checked, and any paper can be selected from among them.

[0019] The interface screen 300 includes an add new button 320, an edit button 321, a delete button 322, and a print position adjustment button 323. The add new button 320 is a button for adding a new paper to the paper library. The edit button 321 is a button for editing the paper attributes of the paper selected in the paper list 310. By operating the add new button 320 or the edit button 321, the interface screen 400 shown in FIG. 4 is displayed. The delete button 322 is a button for deleting the paper selected in the paper list 310 from the paper library. The adjust print position button 323 is a button for adjusting the print position for the paper selected in the paper list 310.

[0020] FIG. 4 is a diagram showing an interface screen for an operator to edit paper attributes. The interface screen 400 shown in FIG. 4 is displayed on the operation panel 120. The interface screen 400 includes a text box 401, a text box 402, a text box 403, a text box 404, a combo box 405, an edit end button 420, and a cancel button 421. The paper name can be input in the text box 401. The paper length in the sub-scanning direction can be input in the text box 402. The paper length in the main scanning direction can be input in the text box 403. The basis weight can be input in the text box 404. Input to the text boxes 401 to 404 is performed, for example, by using the numeric keypad or a software keyboard of the operation panel 120. In the combo box 405, one can be selected and specified from a list of surface properties that are registered in advance in the image forming apparatus 100 and can be supported. By operating the edit end button 420, the paper attributes input at the time of the operation are confirmed and saved in the paper library. Thereafter, the interface screen 400 is closed, and the screen returns to the interface screen 300. The paper attribute editing process can be stopped by operating the cancel button 421. After operating the cancel button 421, the interface screen 400 is also closed, and the screen returns to the interface screen 300.

[0021] <Storage contents of the paper library> FIG. 5 is a diagram showing an example of the contents stored in the paper library. The paper library 500 shown in FIG. 5 is saved as digital information such as XML or CSV. The paper library 500 includes paper 501, paper 502, paper 503, paper 504, paper 505, paper 506, paper 507, and paper 508. The paper library 500 also includes items 511, 512, 513, 514, 515, 521, and 522 indicating paper attributes for each paper. Item 511 is the paper name of the paper. Item 512 is the paper length in the sub-scanning direction of the paper. Item 513 is the paper length in the main scanning direction of the paper. Item 514 is the basis weight of the paper. Item 515 is the surface property of the paper. Item 520 is the amount of print position deviation with respect to the surface of the paper. Item 521 is the amount of print position deviation with respect to the back surface of the paper. Here, the "print position deviation amount (adjustment amount)" represents the amount of position deviation from the ideal print position, and in this embodiment, is composed of the items of lead position, side position, main scanning magnification, and sub-scanning magnification.

[0022] During actual printing, the image forming apparatus 100 adjusts the amount of print position deviation based on these print position deviations so that the image is printed at the ideal print position, that is, adjusts to offset (cancel) the amount of print position deviation. The lead position is the amount of print position deviation in the sub-scanning direction relative to the paper. The side position is the amount of print position deviation in the main scanning direction relative to the paper. The lead position is adjusted by changing the print start position of the image starting from the leading edge of the paper in the paper transport direction. The side position is adjusted by changing the print start position of the image starting from the edge of the paper on the left side in the paper transport direction. These print position deviation amounts are calculated by printing an adjustment chart on which a predetermined mark is arranged and detecting the position of the mark on the adjustment chart. The initial values ​​of these print position deviation amounts are 0 for each item. In addition, when paper information has just been newly registered in the paper library, or when paper has been registered but the print position has not been adjusted, the initial values ​​are used. The sub-scanning direction magnification is the deviation of the image length in the sub-scanning direction (magnification relative to the ideal length). The main scanning direction magnification is the deviation of the image length in the main scanning direction (magnification with respect to the ideal length).

[0023] <Adjustment chart> FIG. 6 is a diagram showing an example of an adjustment chart used for print position adjustment. The adjustment chart 601 shown in FIG. 6 is obtained by forming an adjustment image used for position adjustment on a rectangular sheet P, such as A size or B size, by the image forming unit 150 after the print position adjustment process starts (image forming process). Then, in the above-mentioned reading process, a read image of the adjustment chart 601 can be acquired while moving the adjustment chart 601 in one direction. Marks 602 to 605 are attached to the adjustment chart 601 as print adjustment images at specific positions. In the configuration shown in FIG. 6, the mark 602 is attached to the upper left corner, the mark 603 is attached to the upper right corner, the mark 604 is attached to the lower left corner, and the mark 605 is attached to the lower right corner. Also, the marks 602 to 605 are attached to both sides of the adjustment chart 601, that is, the front side and the back side. Note that FIG. 6 shows the state of the front side of the adjustment chart 601. If the print positions of the marks 602 to 605 are ideal, then the marks 602 to 605 are arranged on both sides of the adjustment chart 601 so as to be printed at positions a certain distance away from each corner (four corners) of the sheet P. In contrast, if the print positions of the marks 602 to 605 are misaligned, the amount of misalignment of the print positions can be detected by measuring the distance (relative position) from the edge of the paper. Note that the shapes of the marks 602 to 605 are square in this embodiment, but are not limited thereto and may be, for example, rectangular or circular.

[0024] FIG. 7 is a diagram showing the distance of each mark from the edge of the adjustment chart. Like FIG. 6, FIG. 7 shows the front side of the adjustment chart 601. Distance A is the distance from the front end (front edge) 606 located in front of the adjustment chart 601 (sheet P) in the transport direction to the mark 602. Distance B is the distance from the left end (left edge) 607 located on the left side of the adjustment chart 601 in the transport direction to the mark 602. Distance C is the distance from the front end 606 of the adjustment chart 601 to the mark 603. Distance D is the distance from the right end (right edge) 608 located on the right side of the adjustment chart 601 in the transport direction to the mark 603. Distance E is the distance from the rear end (rear edge) 609 located behind the adjustment chart 601 in the transport direction to the mark 604. Distance F is the distance from the left end 607 of the adjustment chart 601 to the mark 604. Distance G is the distance from the rear end 609 of the adjustment chart 601 to the mark 605. Distance H is the distance from the right end 608 of the adjustment chart 601 to the mark 605. If the print positions of the marks 602 to 605 are ideal, then distances A to H are each set to 10 mm. The amount of print position deviation in the sub-scanning direction is calculated by the print position measurement unit 131 based on the marks 602 to 605 included in the image 1004, specifically based on the distance from the front end 606 or the rear end 609 of the adjustment chart 601 to each mark (calculation step).

[0025] <Print position measurement unit operation> The calculation of distances A to H will be described. FIG. 8A is a flowchart showing a process for measuring the relative position of the marks. FIG. 8B is a diagram showing the relationship between the measured value of the length of the adjustment chart in the sub-scanning direction and the designated value of the adjustment chart when the diameter of each roller of the image reading unit changes over time. FIG. 9 is a diagram for explaining the position of the paper edge of the adjustment chart. FIG. 10 is a schematic diagram showing the reading state of the adjustment chart in the image reading unit. As shown in FIG. 9, the adjustment chart 601 has an upper left vertical paper edge 607U, an upper left horizontal paper edge 606L, an upper right vertical paper edge 608U, an upper right horizontal paper edge 606R, a lower left vertical paper edge 607D, a lower left horizontal paper edge 609L, a lower right vertical paper edge 608D, and a lower right horizontal paper edge 609R. The upper left vertical paper edge 607U is the upper part of the left end 607. The upper left horizontal paper edge 606L is the left part of the front end 606. The mark 602 is located near the upper left vertical edge 607U and the upper left horizontal edge 606L. The upper right vertical edge 608U is the upper part of the right end 608. The upper right horizontal edge 606R is the right part of the front end 606. The mark 603 is located near the upper right vertical edge 608U and the upper right horizontal edge 606R. The lower left vertical edge 607D is the lower part of the left end 607. The lower left horizontal edge 609L is the left part of the rear end 609. The mark 604 is located near the lower left vertical edge 607D and the lower left horizontal edge 609L. The lower right vertical edge 608D is the lower part of the right end 608. The lower right horizontal edge 609R is the right part of the rear end 609. The mark 605 is disposed near the lower right vertical edge 608D and the lower right horizontal edge 609R.

[0026] As shown in FIG. 8A, in step S801, the CPU 114 of the image forming apparatus 100 operates the image reading unit 130 to obtain a read image of the adjustment chart 601. As described above, the image reading unit 130 is an ADF. As shown in FIG. 10A, the image reading unit 13 conveys the adjustment chart 601 in the direction of the arrow 1002. During this conveyance, the adjustment chart 601 passes over the reading unit 235. This allows the reading unit 235 to obtain a read image of the adjustment chart 601. FIG. 10A shows, as an example, a state in which the adjustment chart 601 having a paper length of 720 [mm] in the sub-scanning direction is read by the reading unit 235. In the image reading unit 13, the adjustment chart 601 is not necessarily conveyed parallel to the conveying direction, that is, the direction of the arrow 1002, depending on various conditions such as the attitude of the adjustment chart 601 on the document table 230. 10(a), it is assumed that the adjustment chart 601 is conveyed in a state inclined with respect to the direction of the arrow 1002. In this case, as shown in FIG 10(b), the read image 1003 acquired by the reading unit 235 includes an image (read image) 1004 of the adjustment chart 601 inclined with respect to the top, bottom, left, and right of the read image 1003.

[0027] Also, the measured value of the length of the image 1004 in the sub-scanning direction may vary from the specified value of the adjustment chart 601. The relationship between the change in roller diameter and the measured value of the length of the image 1004 in the sub-scanning direction will be described. Here, slippage between the conveying roller 232 and the adjustment chart 601 is not considered. The roller diameter of the conveying roller 232 varies within the range of the allowable tolerance, so there are individual differences in the roller diameter. In addition, the conveying roller 232 wears over time and the roller diameter changes. Even if the conveying roller 232 having such a roller diameter rotates at a predetermined rotation speed to convey the adjustment chart 601, the conveying amount of the adjustment chart 601 varies due to the individual difference in the roller diameter and the change in the roller diameter over time. Therefore, there is a risk that the measured value of the length of the image 1004 in the sub-scanning direction will not be the same as the specified value of the adjustment chart 601. This can be expressed as a speed change. The conveying speed v [mm / sec] of the adjustment chart 601 passing over the reading unit 235 is calculated by the following formula (1).

[0028]

number

[0029] φ [mm] is the roller diameter of the conveying roller 232, and n [rpm] is the rotation speed of the conveying roller 232. As is clear from the formula (1), the conveying speed v of the adjustment chart 601 is proportional to the roller diameter φ when the rotation speed n of the conveying roller 232 is constant. In addition, the actual reading resolution dpi of the image reading unit 130 is ADF is calculated using the following formula (2).

[0030]

number

[0031] l [msec / line] is the time required for the reading unit 235 to read one line, and indicates the performance of the reading unit 235. In practice, the reading resolution dpi can be adjusted by adjusting the rotation speed n of the roller and changing the conveying speed v of the adjustment chart 601. ADFcan be set to a target value such as 300 [dpi] or 600 [dpi]. For example, when φ=15 [mm] and l=0.5 [msec / line], the reading resolution dpi can be set to 215.6 [rpm] by adjusting the rotation speed n. ADF 300 [dpi]. Also, as is clear from formula (2), when l [msec / line] does not change from the start to the end of reading in the image reading unit 130 and the rotation speed n is fixed, the actual l [msec / line] is inversely proportional to the change in the roller diameter φ. In this embodiment, when the rotation speed n is fixed in advance, the roller diameter φ varies due to individual differences, and the target reading resolution dpi ADF This assumes a case where the

[0032] The number of pixels y [px] in the sub-scanning direction of the adjustment chart 601 (image 1004) in the read image 1003 acquired by the image reading unit 130 is calculated by the following formula (3).

[0033]

number

[0034] psize [mm] is a designated value for the length in the sub-scanning direction of the adjustment chart 601. When psize is determined in advance, the size of the pixel number y is expressed in dpi. ADF . As a result, when the rotation speed n and l [msec / line] are constant, the number of pixels y is inversely proportional to the change in the roller diameter φ, as described above. Also, the larger the number of pixels y, the more the length of the scanned image 1003 in the sub-scanning direction changes. Therefore, as the roller diameter φ increases, the actual scanning resolution dpi of the image scanning unit 130 ADF When the roller diameter φ becomes smaller, the length of the adjustment chart 601 on the scanned image 1003 becomes shorter. Conversely, when the roller diameter φ becomes smaller and the scanning resolution dpi ADFbecomes higher, the length of the adjustment chart 601 also becomes longer. For the above reasons, when the roller diameter φ changes, the length of the adjustment chart 601 is inversely proportional to the roller diameter φ. In FIG. 10, an example is given in which the adjustment chart 601 with a paper length of 720 [mm] is conveyed and read by the image reading unit 130, and the paper length on the read image 1003 becomes 4 [mm] longer in the sub-scanning direction due to the aforementioned paper length variation factor. It is assumed that there is no change in the main scanning direction, i.e., the width direction of the adjustment chart 601.

[0035] In step S802, the CPU 114 extracts the marks 602 to 605 included in the image 1004, and acquires the positions of the marks 602 to 605. The positions of the marks 602 to 605 are expressed as two-dimensional coordinates in the horizontal (x) and vertical (y) directions, with the upper left coordinates of the image 1004 as the origin (0,0). The positions of the marks 602 to 605 may be expressed as the coordinates of the center of gravity of each mark, or may be the results obtained by calculation with sub-pixel accuracy. The process of extracting the marks 602 to 605 is not particularly limited, and for example, a pattern matching method or the like may be used.

[0036] In step S803, the CPU 114 activates the paper size acquisition unit 121. This makes it possible to acquire the paper size of the adjustment chart 601 from the item 312 indicating the paper length in the sub-scanning direction (one direction) and the item 313 indicating the paper length in the main scanning direction on the interface screen 300 (acquisition step).

[0037] In step S804, CPU 114 extracts upper left vertical edge 607U and upper right vertical edge 608U from image 1004. Upper left vertical edge 607U is used to calculate distance B. Upper right vertical edge 608U is used to calculate distance D. Details of the process in step S804 will be described later.

[0038] In step S805, CPU 114 extracts a lower left vertical edge 607D and a lower right vertical edge 608D from image 1004. The lower left vertical edge 607D is used to calculate distance F. The lower right vertical edge 608D is used to calculate distance H. Note that the process in step S805 is similar to the process in step S804.

[0039] In step S806, the CPU 114 calculates the "tolerance" used in the horizontal paper edge extraction process described later. The tolerance is to follow the tendency of the paper length change in the sub-scanning direction in the image 1004. The tolerance may be calculated in advance for each paper size and tabulated. FIG. 8B shows the relationship between the designated value psize [mm] of the adjustment chart 601 and the measured length value [mm] of the image 1004 when the roller diameter changes. The horizontal axis of the graph is the designated value psize [mm], and the vertical axis is the calculated measured value [mm]. The measured value is calculated based on the number of pixels y [px] in the sub-scanning direction described above. When the roller diameter does not change, as shown in graph 2201, the measured value always has the same length even if the designated value psize changes. In contrast, when the roller diameter changes in the direction of increasing, graphs 2202 and 2203 are obtained. As shown in graphs 2202 and 2203, the measured value becomes shorter than the designated value psize. The reason for this is as described above. Moreover, when the roller diameter changes in a direction to decrease, graphs 2204 and 2205 are obtained. As shown in graphs 2204 and 2205, the measured value becomes longer than the designated value psize. Also, as shown in FIG. 8B, it can be seen that the variation in the measured value due to the change in roller diameter increases in proportion to the increase in the designated value psize. Also, as described above, the measured value is inversely proportional to the change in roller diameter. Therefore, the amount of change 2207 in the measured value when the roller diameter changes in a direction to decrease is larger than the amount of change 2206 in the measured value when the roller diameter changes in a direction to increase. This tendency is taken into account in the calculation of the allowable range in step S806.

[0040] Based on the trend between the specified value psize and the measured value when the roller diameter changes and on the basis of formula (3), the allowable range T R The following formulas (4-1), (4-2), and (4-3) can be used, which also increase the allowable range T R The upper limit of T R_u , the lower limit is T R_b It was decided.

[0041]

number

[0042] Here, since the roller diameter φ is changed, the rotation speed n and l [msec / line] are assumed to be constant and are summarized as a constant k. Δφ [mm] is the amount of change in the roller diameter caused by individual differences and durability, and the roller diameter is assumed to change within this numerical value. In this embodiment, φ=15 [mm], Δφ=0.1 [mm], n=215.6 [rpm], l=0.5 [msec / line], and dpi=300 are used. In the horizontal paper edge extraction process executed in steps S807 and S808, the allowable ranges calculated using formulas (4-1) to (4-3) are used. The allowable ranges for each paper are calculated based on the paper size information on the interface screen 300 in FIG. 3, and the results are shown in Table 1. The designated value psize [mm] in formula (4) is substituted with the "paper length in the sub-scanning direction." The longer the paper length in the sub-scanning direction, such as "XYZ Paper Long Size (hereinafter sometimes referred to as "Paper A")," the larger the tolerance range becomes. Also, there is an inverse relationship between the change in roller diameter and the change in measurement value, and there is a tendency for the increase in measurement value to be greater when the roller diameter is smaller than the decrease in measurement value when the roller diameter is larger. Therefore, the upper limit of the tolerance range threshold is also slightly larger.

[0043] [Table 1]

[0044] As shown in Table 1, the permissible range changes according to the length of the sheet P in the sub-scanning direction, that is, the longer the length of the sheet P in the sub-scanning direction, the larger the permissible range becomes.

[0045] In step S807, the CPU 114 extracts the upper left horizontal edge 606L and the lower left horizontal edge 609L from the image 1004. The upper left horizontal edge 606L is used to calculate the distance A. The lower left horizontal edge 609L is used to calculate the distance E. Details of the process in step S807 will be described later.

[0046] In step S808, the CPU 114 extracts the upper right horizontal edge 606R and the lower right horizontal edge 609R from the image 1004. The upper right horizontal edge 606R is used to calculate the distance C. The lower right horizontal edge 609R is used to calculate the distance G. The process in step S808 is similar to the process in step S807.

[0047] In step S809, the CPU 114 calculates the distances A to H. Specifically, the CPU 114 calculates the normal distances from the central coordinates of the marks 602 to 605 to the linear equation (ρ=xcosθ+ysinθ) of the paper side corresponding to each of the marks.

[0048] <Vertical paper edge extraction process> FIG. 11 is a flowchart showing the vertical edge extraction process (similar to step S805) executed in step S804 (subroutine) of the flowchart shown in FIG. 8A. FIG. 12 is a schematic diagram showing the positional relationship between the upper left ROI image and the upper right ROI image when extracting the upper left vertical edge and the upper right vertical edge. As shown in FIG. 11, in step S1101, the CPU 114 acquires left and right ROI (Region Of Interest) images based on the positions of the marks 602 to 605 acquired in step S802. As shown in FIG. 12, in this embodiment, a region 6 mm long horizontally and 17 mm long vertically is set as the upper left ROI image 1202, centered on a point 10 mm left and 10 mm down from the center coordinates of the mark 602. Also, a region 6 mm long horizontally and 17 mm long vertically is set as the upper right ROI image 1203, centered on a point 10 mm right and 10 mm down from the center coordinates of the mark 603.

[0049] In step S1102, the CPU 114 detects edges using an edge detection filter for the upper left ROI image 1202 and the upper right ROI image 1203 acquired in step S1101. As the edge detection filter, a kernel k shown in the following formula (5) can be used, but is not limited to this, and may be, for example, a horizontal Laplacian filter or a differential filter.

[0050]

number

[0051] In the following, the image after the edge detection filter is applied is represented as Ie(x, y), where x and y are coordinate indices.

[0052] In step S1103, the CPU 114 extracts a plurality of pairs of candidates that can be the pair of the upper left vertical edge 607U and the upper right vertical edge 608U, based on the edges in the upper left ROI image 1202 and the upper right ROI image 1203 detected in step S1102. The details of the process in step S1103 will be described later.

[0053] In step S1104, CPU 114 determines one optimal combination of upper left vertical side 607U and upper right vertical side 608U from among the multiple combinations extracted in step S1103. Details of the process in step S1104 will be described later.

[0054] The process of determining an optimal combination of the lower left vertical edge 607D and the lower right vertical edge 608D can be performed in the same manner as in steps S1101 to S1104. That is, in step S1101, the lower left ROI image 1204 and the lower right ROI image 1205 are set. Then, in step S1102, edges are detected for the lower left ROI image 1204 and the lower right ROI image 1205. In step S1103, a plurality of candidates that can be a combination of the lower left vertical edge 607D and the lower right vertical edge 608D are extracted. In step S1104, an optimal combination of the lower left vertical edge 607D and the lower right vertical edge 608D is determined. In addition, the upper left ROI image 1202 to the upper right ROI image 1203 may overlap each other, that is, may be overlapped. Also, each ROI image may include a mark.

[0055] <Paper edge candidate extraction process> Fig. 13 is a flowchart showing the paper edge candidate extraction process performed in step S1103 (subroutine) of the flowchart in Fig. 11. As shown in Fig. 13, in step S1301, CPU 114 obtains a binary image Ib(x,y) by performing a binarization process on Ie(x,y) detected in step S1102. Specifically, Ib(x,y) is calculated by the following formula (6).

[0056]

number

[0057] Here, th is a threshold value, which may be a fixed value of 128, for example, or may be dynamically determined from the image by Otsu's method.

[0058] In step S1302, the CPU 114 performs a Hough transform on the binary image Ib(x, y) acquired in step S1301. The Hough transform is a method of transforming a straight line into a vector of a line using the formula ρ=x i cosθ+y i This is a process that comprehensively detects straight lines that make a predetermined angle θ from within an image by expressing the line as sinθ. In the Hough transform, first, all pairs of x and y coordinates (xi, yi) where Ib(x, y) = 1 are obtained (0≦i≦M). Next, for each pair of (xi, yi), ρ shown in the following formula (7) is ij Calculate the value.

[0059]

number

[0060] θ j (0≦j≦N) is a predetermined value, and in this embodiment, θ is a value from 88° to 92° in increments of 0.5° (θ0=88, θ1=88.5, . . . , θ7=92.0). j ,ρ ij ) is the angle θ passing through the point (xi, yi) j Next, the above (θ j ,ρ ij ), the Hough table H(ρ, θ) is calculated using the following formula (8).

[0061]

number

[0062] Here, Em,n is a matrix with N rows (max ρ) columns that satisfies the following formula (9).

[0063]

number

[0064] FIG. 14 is a diagram showing an example of a Hough table. The value of cell (θ, ρ) of the Hough table 1400 shown in FIG. 14 represents the number of points on the straight line equation ρ=xcosθ+ysinθ in the binary image Ib(x, y). For example, there are 219 points in cell (θ=89°, ρ=2). In this case, 219 points is a larger value than the number of other points. This makes it possible to determine that the straight line defined by (θ=89°, ρ=2) exists in the image. Also, there is 0 point in cell (θ=92°, ρ=2). In this case, it can be determined that the straight line defined by (θ=92°, ρ=2) does not exist in the image.

[0065] In step S1303, the CPU 114 detects a peak position based on the Hough table calculated in step S1302. In this embodiment, the peak position is a point that satisfies all of H(θ,ρ)≧H(θ,ρ+1), H(θ,ρ)≧H(θ+1,ρ), H(θ,ρ)≧H(θ-1,ρ), H(θ,ρ)≧H(θ,ρ-1), and H(θ,ρ)>th_hough. Here, "th_hough" is a threshold value for determining whether the value of the Hough table is noise or not, and is set to 140 in this embodiment. For example, the candidates of the peak position detected based on the Hough table 1400 shown in FIG. 14 are (θ=90°,ρ=5) and (θ=89°,ρ=2). These candidates of the peak position can be used as paper edge candidates.

[0066] As described above, in the paper edge candidate extraction process, multiple paper edge candidates can be extracted from one ROI image. FIG. 15 is a schematic diagram showing an example of extraction of multiple paper edge candidates. FIG. 15(a) is a schematic diagram showing an image 1004, which is a scanned image of the adjustment chart 601, and the upper right ROI image 1203. As described above, the adjustment chart 601 is conveyed at an angle, and therefore the image 1004 is read at an angle in the same manner. FIG. 15(b) is a schematic diagram showing a binary image Ib(x,y) when the paper edge candidate extraction process is executed on the upper right ROI image 1203. A black pixel in the binary image Ib(x,y) indicates that no edge exists at the pixel position. Also, a white pixel indicates that an edge exists at the pixel position. As shown in FIG. 15(b), two paper edge candidates are extracted from the upper right ROI image 1203. An edge 1501 on the left side of FIG. 15(b) is an edge formed by the shadow of the adjustment chart 601. This edge 1501 corresponds to the paper edge candidate (θ=89°, ρ=2) in the Hough table 1400. Due to the inclination during scanning, the edge 1501 is inclined by 1 degree with respect to the transport direction. On the other hand, an edge 1502 on the right side of FIG. 15(b) is an edge that is erroneously detected due to a streak that occurs during reading by the reading unit 235 (reader). This edge 1502 corresponds to the paper edge candidate (θ=90°, ρ=5) in the Hough table 1400. The leader streak is always extracted as a streak parallel to the transport direction, regardless of the amount of inclination of the adjustment chart 601.

[0067] <Optimal paper edge pair determination process> Fig. 16 is a flowchart showing the optimum paper edge pair determination process executed in step S1104 (subroutine) of the flowchart shown in Fig. 11. As shown in Fig. 16, in step S1601, CPU 114 judges whether or not the processes in steps S1602 to S1605 have been completed for all paper edge candidates. If it is judged in step S1601 that the processes have not been completed, the process proceeds to step S1602. On the other hand, if it is judged in step S1601 that the processes have been completed, the process proceeds to step S1606. Note that, for example, if three upper left paper edge candidates and five upper right paper edge candidates have been extracted in step S1103, steps S1602 to S1605 are repeated 15 times.

[0068] In step S1602, CPU 114 acquires first paper edge candidates ρ1 and θ1. The "first paper edge candidate" refers to a candidate that can be, for example, upper left vertical paper edge 607U.

[0069] In step S1603, CPU 114 acquires second paper edge candidates ρ2 and θ2. The "second paper edge candidate" refers to a candidate that can be, for example, upper right vertical paper edge 608U.

[0070] In step S1604, CPU 114 calculates the likelihood of each candidate, taking into consideration the parallelism of the first paper edge candidates ρ1, θ1 in step S1602 and the second paper edge candidates ρ2, θ2 in step S1603, and the paper size of the adjustment chart 601. In this embodiment, the likelihood of the paper edge pair of each candidate is calculated using the following formula (10). Note that formula (10) means that the smaller the calculation result, the more likely the paper edge pair is.

[0071]

number

[0072] As described above, psize is a designated value of the adjustment chart 601, and dpi is the resolution of the image reading unit 130. Furthermore, step(x) is a step function that returns 1 when x>0 and 0 when x≦0. Furthermore, γ and ε are constants, and in this embodiment, γ=1000 and ε=0.5. The term (ρ2-ρ1)*25.4 / dpi represents the measured value of the adjustment chart 601. The term (ρ2-ρ1)*25.4 / dpi-psize represents the error between the designated value and the measured value. Furthermore, the term γstep(|θ2-θ1|-ε) is a penalty term based on the parallelism of the adjustment chart 601. For example, when the difference between θ2 and θ1 is 0.5 degrees or less, there is no penalty, and otherwise a penalty of 1000 is given. In this embodiment, the calculation of the likelihood in step S1604 is performed using formula (10), but is not limited to this, and may be performed, for example, based on a value obtained by subtracting a designated value of the adjustment chart 601 from the distance between the paper edges. In this case, the paper edge pair for which the subtracted value is a negative value can be set as a candidate paper edge pair.

[0073] In step S1605, the CPU 114 determines whether the error in the measurement value (distance) between the paper edges paired in step S1604 is within the allowable range of the specified value of the adjustment chart 601, and removes paper edge pairs that are outside the allowable range. This makes it possible to remove paper edge pair candidates that have lengths that are clearly different from the length of the adjustment chart 601 in the main scanning direction, thereby enabling accurate extraction of paper edges and reducing the amount of calculation in the next step. In this embodiment, the allowable range is ±1.5 mm.

[0074] In step S1606, CPU 114 determines the paper edge pair with the best likelihood, that is, the paper edge pair with the smallest calculation result of equation (10), as the optimal paper edge pair.

[0075] FIG. 17 is a diagram showing an example of a specific operation in the optimum paper edge pair determination process in the left-right direction. Here, the process of determining the optimum pair of the left and right paper edges will be described. FIG. 17(a) shows the result of the paper edge candidate extraction process for the upper right paper edge and the upper left paper edge for the image 1004. For the upper right paper edge, three candidates, right candidate 2-A, right candidate 2-B, and right candidate 2-C, are extracted. Right candidate 2-A is a paper stain. Right candidate 2-B is a paper edge. Right candidate 2-C is a leader streak. For the left paper edge, left candidate 1-A is extracted. Left candidate 1-A is a paper edge. Then, for all combinations of one left candidate and each right candidate, the error is calculated by the first term of formula (10). Here, the case of detecting the paper edge pair of paper A will be described as an example. As described above, paper A is "XYZ Paper Long Size" with a short side of 297 mm (see FIG. 3). In this case, psize = 297, and if the resolution in the main scanning direction is 300 dpi, then dpi = 300. If ρ1 and ρ2 in Fig. 17 are assumed to be ρ1 = 118 pixels and ρ2 = 3603 pixels, respectively, the error (paper size error) is -1.94 mm when calculated according to (ρ2-ρ1)*25.4 / dpi-psize.

[0076] FIG. 17(b) shows the error of each edge pair candidate. The parallelism penalty in FIG. 17(b) shows the value of the γstep(|θ2-θ1|-ε) term. As described above, in this embodiment, the allowable range for the error in the vertical edge extraction process is ±1.5 mm. The error of the edge pair of the left candidate 1-A and the right candidate 2-A is -1.94 mm. This error exceeds the allowable range. Therefore, in step S1605, the edge pair of the left candidate 1-A and the right candidate 2-A is removed. The error of the edge pair of the left candidate 1-A and the right candidate 2-B is -1.02 mm, and the error of the edge pair of the left candidate 1-A and the right candidate 2-C is +0.85 mm. Both of these errors are within the allowable range. In addition, the error of the edge pair of the left candidate 1-A and the right candidate 2-C is smaller than the error of the edge pair of the left candidate 1-A and the right candidate 2-B. However, the right candidate 2-C is a leader line. Also, the right candidate 2-C is not parallel to the left candidate 1-A, and cannot be the optimal paper edge candidate from the viewpoint of parallelism. On the other hand, the right candidate 2-B is parallel to the left candidate 1-A, and is determined to be the optimal paper edge candidate together with the left candidate 1-A.

[0077] <Horizontal edge extraction process> FIG. 18 is a flowchart showing the horizontal paper edge extraction process (the same applies to step S808) executed in step S807 (subroutine) of the flowchart shown in FIG. 8A. FIG. 19 is a schematic diagram showing the positional relationship between the upper left ROI image and the lower left ROI image when detecting the upper left horizontal paper edge and the lower left horizontal paper edge. As shown in FIG. 18, in step S1801, the CPU 114 acquires upper and lower ROI images based on the positions of the marks 602 to 605 acquired in step S802. At this time, as described above, the length of the image 1004 of the adjustment chart 601 may change relatively greatly, so the size of the upper and lower ROI images in the horizontal paper edge extraction process is a fixed value that is large enough to include the paper edge. In this embodiment, the CPU 114 sets the upper left ROI image (first region) 1902 at a position as close as possible to the mark 602, and sets the lower left ROI image (second region) 1904 at a position as close as possible to the mark 604. Moreover, the upper left ROI image 1902 includes at least the front end 606 (upper left horizontal paper edge 606L) with respect to the image 1004, and is set smaller than the image 1004. The lower left ROI image 1904 includes at least the rear end 609 (lower left horizontal paper edge 609L) with respect to the image 1004, and is set smaller than the image 1004. Moreover, it is preferable that the upper left ROI image 1902 and the lower left ROI image 1904 are set to the same size. And, when viewed from the conveying direction (moving direction) of the adjustment chart 601, that is, the direction of the arrow α in FIG. 19, it is preferable that the upper left ROI image 1902 and the lower left ROI image 1904 at least partially overlap as shown by the two-dot chain line in FIG. 19. 19, a region 17 mm wide and 1.5 mm long centered on a point 10 mm to the right and 10 mm up from the center coordinates of the mark 602 is set as an upper left ROI image 1902. Also, a region 17 mm wide and 1.5 mm long centered on a point 10 mm to the right and 10 mm down from the center coordinates of the mark 604 is set as a lower left ROI image 1904.

[0078] In step S1802, the CPU 114 detects edges using an edge detection filter for the left upper ROI image 1902 and the left lower ROI image 1904 acquired in step S1801. As the edge detection filter, a differential filter can be used in this embodiment, but is not limited thereto, and may be, for example, a vertical Laplacian filter or the like.

[0079] In step S1803, CPU 114 extracts multiple pairs of candidates that can be a pair of upper left horizontal edge 606L and lower left horizontal edge 609L based on the edges in upper left ROI image 1902 and lower left ROI image 1904 detected in step S1802 (extraction process). Thus, in this embodiment, CPU 114 has a function as an extraction means that extracts multiple pairs of candidates that can be a pair of upper left horizontal edge 606L and lower left horizontal edge 609L. Note that, although it is preferable that multiple pairs of candidates are extracted in the extraction process, one pair may be extracted. The process in step S1803 is similar to the process in step S1103.

[0080] In step S1804, the CPU 114 determines an optimal combination of the upper left horizontal edge 606L and the lower left horizontal edge 609L from among the multiple combinations extracted in step S1803. This combination is used later for comparison with the designated value (length in the sub-scanning direction) of the adjustment chart 601.

[0081] The process of determining an optimal combination of the upper right horizontal edge 606R and the lower right horizontal edge 609R can be performed in the same manner as in steps S1801 to S1804. That is, in step S1801, the upper right ROI image (first region) 1903 and the lower right ROI image (second region) 1905 are set. Then, in step S1802, edges are detected for the upper right ROI image 1903 and the lower right ROI image 1905. In step S1803, a plurality of candidates that can be a combination of the upper right horizontal edge 606R and the lower right horizontal edge 609R are extracted. In step S1804, an optimal combination of the upper right horizontal edge 606R and the lower right horizontal edge 609R is determined. In addition, the upper left ROI image 1902 to the lower right ROI image 1905 may overlap each other, that is, may be overlapped. Also, each ROI image may include a mark.

[0082] The optimum paper edge pair determination process executed in step S1804 is the same as the process in step S1104. The optimum paper edge pair determination process will be described with reference to FIG. 16. In formula (10), ρ1 means the number of pixels from the top edge of the scanned image 1003 to the candidate for the upper left horizontal paper edge 606L, and ρ2 means the number of pixels from the top edge of the scanned image 1003 to the candidate for the lower left horizontal paper edge 609L. As described above, when scanning is performed while conveying the adjustment chart 601, the measured value (ρ2-ρ1)*25.4 / dpi of the distance between the upper and lower paper edges of the image 1004 may vary. In particular, for long paper such as paper A, the error between the measured value and the specified value psize becomes relatively large. In the judgment process in step S1605, if the allowable range is fixed as in the vertical paper edge extraction process described above, if the error in the measured value between the paper edges paired in step S1604 becomes relatively large, the error may be judged to be outside the allowable range. Therefore, the allowable range is calculated in step S806 taking into consideration the tendency of fluctuation in the measured values. As a result, even if the measured values ​​fluctuate significantly for long paper, for example, the allowable range is determined according to the paper length, making it possible to extract the optimal paper edge pair.

[0083] FIG. 20 is a diagram showing an example of a specific operation in the optimum paper edge pair determination process in the vertical direction. Here, the process of determining the optimum pair of the upper and lower paper edges will be described. FIG. 20(a) shows the result of the paper edge candidate extraction process for the upper side paper edge and the lower left side paper edge for the image 1004. For the lower left side paper edge, two candidates, lower candidate 2-A and lower candidate 2-B, are extracted. The lower candidate 2-A is paper dirt. The lower candidate 2-B is the paper edge. For the upper left side paper edge, upper candidate 1-A is extracted. The upper candidate 1-A is the paper edge. Then, for all combinations of one upper candidate and each lower candidate, the error is calculated by the first term of formula (10). Here, the case of detecting the paper edge pair of paper A will be described as an example. As mentioned above, paper A is "XYZ Paper Long Length" with a long side of 720 mm (see FIG. 3). In this case, psize = 720, and if the resolution in the sub-scanning direction is 300 dpi, then dpi = 300. If ρ1 and ρ2 in Fig. 20 are assumed to be ρ1 = 118 pixels and ρ2 = 8578 pixels, respectively, the error (paper size error) is calculated as -3.72 mm according to (ρ2-ρ1)*25.4 / dpi-psize.

[0084] FIG. 20(b) shows the error of each edge pair candidate. The parallelism penalty in FIG. 20(b) shows the value of the γstep(|θ2-θ1|-ε) term. The likelihood is calculated using formula (10). As shown in FIG. 20(b), the error of the edge pair of the top candidate 1-A and the bottom candidate 2-A is −3.72 mm, and the error of the edge pair of the top candidate 1-A and the bottom candidate 2-B is −3.06 mm. In step S1605, it is determined whether each error is within the allowable range. However, if a fixed allowable range of ±1.5 mm is used as in the vertical edge extraction process, for example, the error in the horizontal edge extraction process is greater than +1.5 mm, so all edge candidate pairs are determined to be outside the allowable range and are removed. Therefore, in the horizontal edge extraction process, the allowable range calculated in step S806 according to formula (4) is used to perform the determination process in step S1605. As shown in Table 1, the tolerance for paper A is -4.77 to +4.83 mm. In step S1605, this tolerance is used to determine whether the error is within the tolerance. As a result of this determination, the errors are within the tolerance, so neither the paper-side pair of top candidate 1-A and bottom candidate 2-A nor the paper-side pair of top candidate 1-A and bottom candidate 2-B are removed. Then, of these pairs, the pair with the smaller error, i.e., the paper-side pair of top candidate 1-A and bottom candidate 2-B, is determined to be the optimal paper-side candidate pair.

[0085] <Usage sequence> Fig. 21 is a sequence diagram showing the processing executed between an operator, an image forming apparatus, and a host computer. In this embodiment, the main processing is executed between the operator 2100 and the image forming apparatus 100. This processing is started from a state in which the interface screen 300 is displayed on the operation panel 120 of the image forming apparatus 100. As shown in Fig. 21, in step S2101, the operator 2100 operates the print position adjustment button 323 on the interface screen 300. This operation enables the image forming apparatus 100 to determine that print position adjustment is to be started.

[0086] In step S2102, image forming apparatus 100 displays on operation panel 120 a print position adjustment screen (not shown) for designating a paper feed cassette.

[0087] In step S2103, the operator 2100 designates a paper feed cassette on the print position adjustment screen and instructs execution of the print position adjustment process.

[0088] In step S2104, the image forming apparatus 100 outputs the adjustment chart 601 (see FIG. 6).

[0089] In step S2105, the operator 2100 places the adjustment chart 601 output in step S2104 on the image reading unit .

[0090] In step S2106, the image forming apparatus 100 reads the adjustment chart 601 placed on the image reading unit .

[0091] In step S2107, the image forming apparatus 100 executes the print position adjustment process, that is, steps S802 to S809 (see FIG. 8A). The execution results are stored as the print position deviation amount in items 520 and 521 (see FIG. 5) of the paper library 500. Then, the image forming process from step S210 onwards is executed using the print position deviation amount stored in the paper library 500.

[0092] In step S210, the operator 2100 instructs the host computer 101 to execute a print job.

[0093] In step S2109, the host computer 101 transmits the print job instructed in step S210 to the image forming apparatus 100.

[0094] In step S2110, the image forming apparatus 100 executes the print job transmitted in step S2109. When executing this print job, the print position deviation amount is read from the paper library 500 and applied to the execution of the print job.

[0095] In step S2111, the image forming apparatus 100 outputs a product generated by the execution of the print job, that is, a printed matter. The print position of this printed matter has been adjusted by correcting the misalignment of the print position. If the printed matter is a double-sided print, the print position of the front side has also been adjusted, and the print position of the back side has also been adjusted.

[0096] As described above, the image forming apparatus 100 can obtain the amount of print position deviation by using the adjustment chart 601 on which the marks 602 to 605 are printed on the sheet P. At this time, the CPU 114 determines whether or not the leading end 606 and the trailing end 609 of the adjustment chart 601 (sheet P) are to be used when calculating the amount of print position deviation (determination step). This determination is made based on the length of the adjustment chart 601 in the sub-scanning direction acquired in the acquisition step and the distance between the pair of the leading end 606 and the trailing end 609 extracted in the extraction step. Specifically, first, the length of the adjustment chart 601 in the sub-scanning direction is compared with the distance between the pair of the leading end 606 and the trailing end 609. Then, if the difference between them is within an allowable range, the pair of the leading end 606 and the trailing end 609 can be determined as the leading end 606 and the trailing end 609 to be used when calculating the amount of print position deviation. On the other hand, when these differences are not within the allowable range, that is, when they are outside the allowable range, the set of the leading edge 606 and the trailing edge 609 is not determined as the leading edge 606 and the trailing edge 609 to be used when calculating the amount of print position deviation. In this case, another set of the leading edge 606 and the trailing edge 609 can be determined as the leading edge 606 and the trailing edge 609 to be used when calculating the amount of print position deviation. With this configuration, the image forming apparatus 100 can easily detect the leading edge 606 and the trailing edge 609 of the sheet P to be used when adjusting the print position, regardless of the size of the sheet P or the above-mentioned brightness (large or small). This allows the amount of print position deviation to be accurately calculated, and therefore the print position can be accurately adjusted regardless of whether double-sided printing or single-sided printing is performed.

[0097] <<Second embodiment>> Hereinafter, the second embodiment will be described with reference to FIG. 22 and FIG. 23. The differences from the above-mentioned embodiment will be mainly described, and the description of the similar matters will be omitted. In the first embodiment, when the ROI image is set in the horizontal paper edge extraction process, the ROI image is fixed at a size that sufficiently includes the paper edge. However, in this case, there is a possibility that a large amount of noise such as leader streaks and paper stains may be mixed in, and the accuracy of detecting the paper edge may decrease. Therefore, in this embodiment, the CPU 114 changes the size of the ROI image according to the length of the adjustment chart 601 (image 1004) in the sub-scanning direction to reduce the mixing of noise. This makes it possible to prevent a decrease in the accuracy of detecting the paper edge.

[0098] <Horizontal edge extraction process> FIG. 22 is a flowchart showing the horizontal paper edge extraction process (similar to step S808) executed in step S807 (subroutine) of the flowchart shown in FIG. 8A in the second embodiment. FIG. 23 is a schematic diagram showing the positional relationship of the upper left ROI image and the lower left ROI image when detecting the upper left horizontal paper edge and the lower left horizontal paper edge. As shown in FIG. 22, in step S2501, the CPU 114 calculates the vertical size of the upper and lower ROI images. As described above, in this embodiment, the vertical size (length in the sub-scanning direction) of the ROI image is changed according to the length of the adjustment chart 601 in the sub-scanning direction. The change in the vertical size of the ROI image is made to follow the tendency of the paper length change in the sub-scanning direction of the adjustment chart 601, as in the calculation of the allowable range in step S806. The paper size of the adjustment chart 601 is acquired from items 312 and 313 of the interface screen 300.

[0099] As shown in Fig. 23, the upper left ROI image 1902 is set with a point 2301 10 mm to the right and 10 mm above the center coordinate of the mark 602 as the center. The upper left ROI image 1902 is 17 mm long horizontally, which is the same as in the first embodiment. On the other hand, the vertical size of the upper left ROI image 1902 is h l [mm], h s[mm], the sum of the two is h. As mentioned above, the length of the image 1004 may change. In this case, the amount of expansion is greater than the amount of reduction in the paper length, so the vertical size of the upper left ROI image 1902 is changed to the upper side (h l [mm] and bottom (h s h is calculated using the following formulas (11-1) to (11-4).

[0100]

number

[0101] Here, Δh is the offset value. s_max h s is the maximum value of h s This is because h s This is to prevent the mark 602 from entering the upper left ROI image 190 due to the value of becoming too large. The vertical size of each sheet is calculated based on the paper size information on the interface screen 300 in FIG. 3, and the results are shown in Table 2. Examples of variables in formula (11) are Δh l = Δh s = 1.5 [mm], h s_max = 6.0 [mm], φ = 15 [mm], Δφ = 0.1 [mm]. In addition, the "paper length in the sub-scanning direction" is substituted for psize [mm] in formula (11). As shown in Table 1, the longer the paper length in the sub-scanning direction, the larger the vertical size h becomes. Also, there is a tendency that the expansion of image 1004 when the roller diameter decreases is greater than the contraction of image 1004 when the roller diameter increases. Therefore, the h outside point 2301 l The value in [mm] is inside point 2301. s In this embodiment, h s_max = 6.0 [mm], so h for "XYZ Paper Long" s [mm] was 6.00[mm].

[0102] [Table 2]

[0103] The upper right ROI image 1903, the lower left ROI image 1904, and the lower right ROI image 1905 can be set in the same manner as the upper left ROI image 1902.

[0104] In step S2502, the CPU 114 acquires upper and lower ROI images based on the positions of the marks 602 to 605 acquired in step S802 and the ROI image size calculated in step S2501.

[0105] In step S2503, similarly to step S1802, the CPU 114 detects edges in the upper and lower ROI images acquired in step S2502 using an edge detection filter.

[0106] In step S2504, similarly to step S1803, the CPU 114 extracts a plurality of sets of paper side candidates based on the edges detected in step S2503.

[0107] In step S2505, similarly to step S1804, CPU 114 determines one optimal combination from among the plurality of combinations extracted in step S2504.

[0108] By carrying out the above-described process, the edge of the paper can be detected accurately and with high precision.

[0109] <<Third embodiment>> Hereinafter, the third embodiment will be described with reference to FIG. 24, focusing on the differences from the previous embodiment, and the description of the similar matters will be omitted. In this embodiment, an ROI image acquisition process that can further suppress or prevent the inclusion of noise components compared to the second embodiment will be described. Note that the position of the paper edge on the reading start side varies less than the position of the paper edge on the reading end side. Therefore, in the ROI image acquisition process, the vertical size of the ROI image that extracts the paper edge on the reading start side of the read image 1003 can be set to a relatively short fixed value within the range including the paper edge.

[0110] <Horizontal edge extraction process> The horizontal paper edge extraction process executed in step S807 and step S808 (see FIG. 8A) in this embodiment will be described with reference to the flowchart shown in FIG. 18. Note that steps other than step S1801 are the same as those in the first embodiment, and therefore their description will be omitted. In step S1801, the CPU 114 acquires upper and lower ROI images based on the positions of the marks 602 to 605 acquired in step S802. Note that in this embodiment, the vertical size of the ROI image is changed according to the paper size. The change in the vertical size of the ROI image is in accordance with the tendency of the paper length change in the sub-scanning direction of the adjustment chart 601, as in the calculation of the allowable range in step S806. Note that the paper size of the adjustment chart 601 is acquired from items 312 and 313 of the interface screen 300.

[0111] FIG. 24 is a schematic diagram showing the positional relationship between the upper left ROI image and the lower left ROI image in the case of detecting the upper left horizontal edge and the lower left horizontal edge in the third embodiment. As shown in FIG. 24, the upper left ROI image 1902 is set at the reading start side edge 2402, and the lower left ROI image 1904 is set at the reading end side edge 2403. The reading start side edge 2402 is the front end 606, and the reading end side edge 2403 is the rear end 609. The upper left ROI image 1902 is set around a point 2401 that is 10 mm to the right and 7 mm up from the center coordinates of the mark 602. The upper left ROI image 1902 is 17 mm long horizontally, which is the same as in the first embodiment. Also, the vertical length of 6 mm is the same as in the vertical edge extraction process. The vertical size of the lower left ROI image 1904 is obtained using formula (11) as in the second embodiment. As a result, the lower left ROI image 1904 is set wider than the upper left ROI image 1902, that is, the vertical size of the lower left ROI image 1904 is set longer than the vertical size of the upper left ROI image 1902. As described above, the position of the reading start side paper edge 2402 has less variation than the position of the reading end side paper edge 2403. As a result, the vertical size of the upper left ROI image 1902 can be set shorter than the vertical size of the lower left ROI image 1904. Note that the upper right ROI image 1903 can be set in the same way as the upper left ROI image 1902, and the lower right ROI image 1905 can be set in the same way as the lower left ROI image 1904. The above-mentioned processing enables more accurate and precise detection of the paper edge.

[0112] <<Fourth embodiment>> The fourth embodiment will be described below, focusing on differences from the above-mentioned embodiments, and similar matters will not be described. In the first to third embodiments, the change (variation) of the roller diameter was taken as an example of a factor that causes the length of the image 1004 in the read image 1003 to vary. This factor is not limited to the variation of the roller diameter, and there are other factors. Therefore, the allowable range and the vertical size of the ROI image suitable for the paper size may be calculated taking other factors into consideration. In this embodiment, the calculation of the allowable range and the vertical size of the ROI image when the paper cutting tolerance also has an effect in addition to the change in the roller diameter as a factor of the paper length variation will be described. The variation at the time of cutting the paper occurs due to the cutting accuracy of the paper, and affects the variation in the length of the image 1004. Also, depending on how the change in the roller diameter and the paper cutting tolerance are combined, the variation in the length of the image 1004 becomes larger than in the above-mentioned embodiment. Then, when calculating the allowable range according to the change in the length of the image 1004, taking into account the fluctuations caused when cutting the paper, for example, the JIS standard "JIS P 0138:1998 Paper Processing Finishing Dimensions" can be used. The JIS standard defines the paper cutting accuracy (processing accuracy) as ±1.5 mm for paper dimensions of 150 mm or less, ±2 mm for dimensions between 150 mm and 600 mm or less, and ±3 mm for dimensions over 600 mm. The allowable range T due to paper cutting tolerance based on this definition is P [mm] can be calculated using the following formula (12).

[0113]

number

[0114] The roller diameter change and the paper cutting tolerance are independent variable factors. Therefore, in this embodiment, these two variable factors are added together to obtain an allowable range T R+P [mm] is obtained from the following formulas (13-1) and (13-2). Note that the allowable range T R+P The upper limit of T R+P_u、 Lower limit is T R+P_b It was decided.

[0115]

number

[0116] T R_u is the upper limit of the allowable range of the roller diameter change factor shown in formula (4). T R_b is the lower limit of the allowable range of the roller diameter change factors shown in formula (4). The formula for calculating the allowable range according to the change in the length of the image 1004, taking into account the fluctuation factors at the time of paper cutting, can be defined in the same way as formula (11) for calculating h [mm] based on formula (4) for calculating the allowable range in the second embodiment. Note that, in this embodiment, a case where the length of the image 1004 fluctuates due to two factors, the roller diameter change and the paper cutting tolerance, has been described, but the present invention is also applicable to a case where a factor other than these two fluctuations occurs.

[0117] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above-mentioned embodiments, and various modifications and changes are possible within the scope of the gist of the present invention. The present invention can also be realized by supplying a program that realizes one or more functions of the above-mentioned embodiments to a system or device via a network or storage medium, and having one or more processors of a computer in the system or device read and execute the program. The present invention can also be realized by a circuit (e.g., ASIC) that realizes one or more functions.

[0118] The disclosure of each embodiment includes the following configurations, methods, and programs. (Configuration 1) An image forming apparatus capable of forming an image on a sheet and adjusting the position of the image on the sheet prior to the image formation, comprising: an image forming means for forming an adjustment image used for the position adjustment on the sheet to obtain an adjustment chart; a reading means for obtaining a read image of the adjustment chart while relatively moving the adjustment chart in one direction; An acquisition means for acquiring the length of the sheet in one direction; a calculation unit that calculates an adjustment amount used for the position adjustment based on the adjustment image included in the read image, The calculation means is an extracting means for extracting at least one pair of a leading end located forward in a moving direction of the adjustment chart and a trailing end located backward in the moving direction from the read image; an image forming apparatus comprising: a determination means for determining, based on the length of the sheet in one direction acquired by the acquisition means and the distance between the pair of leading and trailing ends extracted by the extraction means, whether or not the pair of leading and trailing ends will be the leading and trailing ends of the sheet to be used when calculating the adjustment amount. (Configuration 2) The image forming apparatus described in Configuration 1, characterized in that the determination means compares the length of the sheet in one direction acquired by the acquisition means with the distance between the set of leading and trailing ends extracted by the extraction means, and if the difference between the length of the sheet in one direction and the distance between the set of leading and trailing ends is within an acceptable range, determines the set of leading and trailing ends as the leading and trailing ends of the sheet to be used when calculating the adjustment amount. (Configuration 3) The image forming apparatus described in configuration 1 or 2, characterized in that the determination means compares the length of the sheet in one direction acquired by the acquisition means with the distance between the pair of leading and trailing ends extracted by the extraction means, and if the difference between the length of the sheet in one direction and the distance between the pair of leading and trailing ends is not within an acceptable range, does not determine the pair of leading and trailing ends as the leading and trailing ends of the sheet to be used when calculating the adjustment amount. (Configuration 4) The image forming apparatus according to configuration 2 or 3, wherein the allowable range is changed according to the length of the sheet in the one direction. (Configuration 5) The image forming apparatus according to configuration 4, wherein the tolerance range increases as the length of the sheet in the one direction increases. (Configuration 6) An image forming apparatus described in any one of configurations 1 to 5, characterized in that the extraction means extracts multiple pairs of the leading end and the trailing end, and selects from the multiple pairs one pair of the leading end and the trailing end that is compared with the length of the sheet in one direction by the determination means. (Configuration 7) An image forming apparatus described in any one of configurations 1 to 6, characterized in that the extraction means sets a first area in the read image that includes at least the leading end and is smaller than the read image, extracts the leading end from the first area, sets a second area that includes at least the trailing end and is smaller than the read image, and extracts the trailing end from the second area. (Configuration 8) The image forming apparatus according to configuration 7, wherein the extraction means sets the first region and the second region at positions as close as possible to the adjustment image included in the read image. (Configuration 9) In the image forming apparatus according to configuration 7 or 8, the extraction means changes the sizes of the first region and the second region in accordance with the length of the sheet in the one direction. (Configuration 10) In the image forming apparatus according to any one of Configurations 7 to 9, the extraction means sets the first area and the second area to the same size. (Configuration 11) In the image forming apparatus according to any one of configurations 7 to 9, the extraction means sets the second area to be larger than the first area. (Configuration 12) In the image forming apparatus according to any one of Configurations 7 to 11, the first area and the second area at least partially overlap when viewed from the moving direction of the adjustment chart. (Configuration 13) The image forming apparatus according to any one of configurations 1 to 12, wherein the calculation means calculates the adjustment amount based on a distance from a leading edge or a trailing edge of the sheet to the adjustment image. (Configuration 14) In the image forming apparatus according to any one of Configurations 1 to 13, the reading means includes a conveying means for moving the adjustment chart in the one direction by conveying the adjustment chart. (Configuration 15) The adjustment chart has the adjustment image formed on each of its two sides, 15. The image forming apparatus according to any one of configurations 1 to 14, wherein the image forming apparatus is configured so that the position adjustment is possible for both sides of the sheet. (Method 1) A method for controlling an image forming apparatus capable of forming an image on a sheet and adjusting a position of the image on the sheet prior to the image formation, comprising the steps of: an image forming step of forming an adjustment image used for the position adjustment on the sheet to obtain an adjustment chart; a reading step of acquiring a read image of the adjustment chart while relatively moving the adjustment chart in one direction; An acquisition step of acquiring a length of the sheet in one direction; a calculation step of calculating an adjustment amount used for the position adjustment based on the adjustment image included in the read image, The calculation step includes: an extraction step of extracting at least one pair of a leading end located forward in a moving direction of the adjustment chart and a trailing end located backward in the moving direction from the read image; A control method for an image forming apparatus, comprising: a determination process for determining whether or not the set of leading and trailing ends is to be the leading and trailing ends of the sheet to be used when calculating the adjustment amount, based on the length in one direction of the sheet acquired in the acquisition process and the distance between the set of leading and trailing ends extracted in the extraction process. (Program 1) A program for causing a computer to execute each means of the image forming apparatus according to configuration 1. [Explanation of symbols]

[0119] 100 Image forming device 114 CPU 121 Paper size acquisition unit (acquisition means) 130 Image reading unit (reading means) 131 Print position measurement unit (calculation means) 150 Image forming unit (image forming means) 601 Adjustment Chart 606 Front edge (front paper edge) 609 Back edge (back paper edge)

Claims

1. An image forming apparatus capable of forming an image on a sheet and adjusting a position of the image on the sheet prior to the image formation, comprising: an image forming means for forming an adjustment image used for the position adjustment on the sheet to obtain an adjustment chart; a reading means for obtaining a read image of the adjustment chart while relatively moving the adjustment chart in one direction; An acquisition means for acquiring the length of the sheet in one direction; a calculation unit that calculates an adjustment amount used for the position adjustment based on the adjustment image included in the read image, The calculation means is an extracting means for extracting at least one pair of a leading end located forward in a moving direction of the adjustment chart and a trailing end located backward in the moving direction from the read image; an image forming apparatus comprising: a determination means for determining whether or not to use the set of leading and trailing ends as the leading and trailing ends of the sheet to be used when calculating the adjustment amount, based on the length of the sheet in one direction acquired by the acquisition means and the distance between the set of leading and trailing ends extracted by the extraction means.

2. The image forming apparatus of claim 1, characterized in that the determination means compares the length of the sheet in one direction acquired by the acquisition means with the distance between the set of leading and trailing ends extracted by the extraction means, and if the difference between the length of the sheet in one direction and the distance between the set of leading and trailing ends is within an acceptable range, determines the set of leading and trailing ends as the leading and trailing ends of the sheet to be used when calculating the adjustment amount.

3. The image forming apparatus of claim 1, characterized in that the determination means compares the length of the sheet in one direction acquired by the acquisition means with the distance between the set of leading and trailing ends extracted by the extraction means, and if the difference between the length of the sheet in one direction and the distance between the set of leading and trailing ends is not within an acceptable range, does not determine the set of leading and trailing ends as the leading and trailing ends of the sheet to be used when calculating the adjustment amount.

4. 3. The image forming apparatus according to claim 2, wherein the allowable range is changed according to the length of the sheet in the one direction.

5. 5. The image forming apparatus according to claim 4, wherein the tolerance range increases as the length of the sheet in the one direction increases.

6. 2. The image forming apparatus according to claim 1, wherein the extraction means extracts a plurality of pairs of the leading end and the trailing end, and selects from the plurality of pairs the pair of the leading end and the trailing end which is compared with the length of the sheet in one direction by the determination means.

7. The image forming apparatus according to claim 1, characterized in that the extraction means sets a first area for the read image that includes at least the leading end and is smaller than the read image, extracts the leading end from the first area, sets a second area that includes at least the trailing end and is smaller than the read image, and extracts the trailing end from the second area.

8. 8. The image forming apparatus according to claim 7, wherein the extraction unit sets the first area and the second area in a position as close as possible to the adjustment image included in the read image.

9. 8. The image forming apparatus according to claim 7, wherein the extraction unit changes the sizes of the first region and the second region in accordance with the length of the sheet in the one direction.

10. 8. The image forming apparatus according to claim 7, wherein the extraction unit sets the first area and the second area to the same size.

11. 8. The image forming apparatus according to claim 7, wherein the extraction unit sets the second area to be larger than the first area.

12. 8. The image forming apparatus according to claim 7, wherein the first area and the second area at least partially overlap each other when viewed from the moving direction of the adjustment chart.

13. 2. The image forming apparatus according to claim 1, wherein the calculation unit calculates the adjustment amount based on a distance from a leading edge or a trailing edge of the sheet to the adjustment image.

14. 2. The image forming apparatus according to claim 1, wherein the reading unit includes a conveying unit that conveys the adjustment chart to move the adjustment chart in the one direction.

15. the adjustment chart has the adjustment images formed on both sides thereof, 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is configured so that the position adjustment is possible for both sides of the sheet.

16. 1. A method for controlling an image forming apparatus capable of forming an image on a sheet and adjusting a position of the image on the sheet prior to the image forming, comprising: an image forming step of forming an adjustment image used for the position adjustment on the sheet to obtain an adjustment chart; a reading step of acquiring a read image of the adjustment chart while relatively moving the adjustment chart in one direction; An acquisition step of acquiring a length of the sheet in one direction; a calculation step of calculating an adjustment amount used for the position adjustment based on the adjustment image included in the read image, The calculation step includes: an extraction step of extracting at least one pair of a leading end positioned forward in a moving direction of the adjustment chart and a trailing end positioned backward in the moving direction from the read image; A control method for an image forming apparatus, comprising: a determination process for determining whether or not the set of leading and trailing ends is to be the leading and trailing ends of the sheet to be used when calculating the adjustment amount, based on the length in one direction of the sheet acquired in the acquisition process and the distance between the set of leading and trailing ends extracted in the extraction process.

17. 2. A program for causing a computer to execute each unit of the image forming apparatus according to claim 1.

Images