Image forming apparatus

Abstract

To solve the problem in which: many sheets of paper are wasted in control of adjusting a printing position of an image to be printed on the sheet.SOLUTION: An image forming apparatus 100 comprises a CPU 114 that, every time the number of sheets printed by a print job reaches a predetermined number, causes a printer 150 to create a sheet for adjustment on which an image for adjustment is printed, causes a reading device 160 to read the image for adjustment on the sheet for adjustment, and calculates a correction amount for correcting a printing position on the basis of a result of reading of the image for adjustment. The CPU 114 divides the amount of toner placed on the image printed on the sheet into a plurality of toner placement amount sections, and on the basis of the amount of toner placed on an image of each page of a predetermined number of pages in the print job, determines the toner placement amount section of each page. The plurality of images for adjustment correspond to the plurality of toner placement amount sections. The CPU 114 determines the image for adjustment used for calculating the correction amount on the basis of the determined toner placement amount section of each page.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an image forming apparatus capable of performing double-sided printing.

Background Art

[0002] When printing a printed matter using a commercial image forming apparatus, it is necessary to accurately align the positions (printing positions) of the images printed on the first side (front surface) and the second side (back surface) of the paper during double-sided printing. Therefore, the image forming apparatus has a function (hereinafter referred to as the "front-back position correction function") of aligning the printing positions of the image on the front surface and the image on the back surface of the paper by adjusting the printing position during double-sided printing. By having the front-back position correction function, the image forming apparatus can, for example, adjust the printing position when printing an image on pre-printed paper with grid lines or the like pre-printed thereon so that the image does not overlap the grid lines.

[0003] The front-back position correction by the front-back position correction function needs to be executed for each type of paper on which the image is printed. This is because the amount of expansion and contraction of the paper varies depending on the characteristics of the paper such as the size, basis weight, and material of the paper. Due to the difference in the amount of expansion and contraction, the optimal correction amount by the front-back position correction varies. The front-back position correction is performed by reading an adjustment sheet on which a mark (adjustment image) for position detection is printed on the paper to be corrected with a reading device and detecting the deviation of the printing position based on the reading result of the adjustment image.

[0004] The image forming apparatus detects the deviation of the printing position based on, for example, the distance from the reference position obtained from the reading result of the adjustment sheet to the mark. Based on the detection result of the deviation of the printing position, a correction amount for correcting the printing position is determined. When the image forming apparatus performs a printing process using the same type of paper as the paper to be corrected, the printing position is corrected based on the correction amount.

[0005] In addition to the type of paper, the amount of toner loaded on the toner image printed on the paper is also related to the cause of the displacement between the front and back printing positions during printing. The difference in the amount of toner loaded affects the paper conveyance force when transferring the toner image onto the paper. When the amount of toner loaded is large, slipping due to the toner occurs, resulting in a decrease in the paper conveyance force and a displacement in the printing position in the direction of contraction with respect to the paper conveyance direction.

[0006] In order to suppress the influence of the amount of toner loaded, the image forming apparatus disclosed in Patent Document 1 determines the correction amount for the front-back position correction corresponding to the amount of toner loaded by using adjustment images with different amounts of toner loaded printed on a plurality of sheets of paper. As a result, even for printed matter with different amounts of toner loaded, by performing front-back position correction corresponding to the amount of toner loaded, the correction accuracy is improved.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] An image forming apparatus equipped with a front-back position correction function generally has a front-back position correction function (hereinafter referred to as "initial front-back position correction") that determines the correction amount according to the type of paper by performing front-back position correction of the paper used before executing printing. However, even if the printing position is corrected using the correction amount determined by the front-back position correction function, due to changes in the image forming environment such as the temperature rise inside the image forming apparatus due to mass printing or the change in the moisture absorption state of the paper, the correction accuracy of the printing position may decrease. Therefore, there is an image forming apparatus equipped with a front-back position correction function (hereinafter referred to as "print front-back position correction") that maintains the correction amount in an appropriate state by performing front-back position correction again at predetermined print sheet intervals during printing.

[0009] In the print front and back position correction performed during printing, when trying to determine the correction amount corresponding to the toner loading amount, it becomes necessary to output an adjustment sheet corresponding to the toner loading amount. FIG. 21 is an explanatory diagram of the timing for outputting the adjustment sheet during printing. For example, when performing print front and back position correction every 100 sheets in continuous printing of 300 sheets, the print front and back position correction is performed after printing the 100th and 200th sheets. At this time, if 5 types of adjustment sheets (adjustment images) are required, the number of sheets to be discarded is 5 sheets × 2 times = 10 sheets. That is, the more the number of sheets to be printed increases, the more the number of discarded sheets due to print front and back position correction increases.

[0010] In view of the above problems, the main object of the present invention is to reduce waste paper in the control for adjusting the printing position of the image printed on the paper.

Means for Solving the Problems

[0011] The image forming apparatus of the present invention includes printing means for printing an image on a sheet, reading means for reading an adjustment image for correcting the printing position of the image printed on the sheet, calculating means for calculating a correction amount for correcting the printing position based on the reading result of the adjustment image by the reading means, storage means for storing a plurality of adjustment images with different toner loading amounts, and control means for creating an adjustment sheet on which the adjustment image is printed on the sheet by the printing means every time the number of sheets printed by a printing job reaches a predetermined number, causing the reading means to read the adjustment image from the adjustment sheet, and causing the calculating means to calculate the correction amount. The printing job includes information for printing a plurality of images in a plurality of parts with a plurality of pages as one part. The control means divides the toner loading amount of the image printed on the sheet into a plurality of toner loading amount categories. When there is no first page among the predetermined number of pages to be printed after the execution of the correction process for the printing position and the toner loading amount of all the pages of the first part is acquired, based on the toner loading amount of each page of the image of all the pages of the first part, the toner loading amount category of each page is determined. The plurality of adjustment images stored in the storage means correspond to the plurality of toner loading amount categories. The control means determines an adjustment image to be used for calculating the correction amount based on the determined toner loading amount category of each page. Another image forming apparatus of the present invention includes a printing unit that prints an image on a sheet, a reading unit that reads an adjustment image for correcting a printing position of the image printed on the sheet, a calculation unit that calculates a correction amount for correcting the printing position based on a reading result of the adjustment image by the reading unit, a storage unit that stores a plurality of adjustment images with different toner loading amounts, and a control unit that creates an adjustment sheet on which an adjustment image is printed on the sheet by the printing unit each time the number of sheets printed by a printing job reaches a predetermined number, causes the reading unit to read the adjustment image from the adjustment sheet, and causes the calculation unit to calculate the correction amount. The control unit divides the toner loading amount of the image printed on the sheet into a plurality of toner loading amount categories, acquires image data that can be acquired prior to printing by the printing job, determines the toner loading amount category of each page for which image data has been acquired prior to printing based on the toner loading amount obtained from the acquired image data if the number of pieces of image data acquired prior to printing is equal to or greater than the predetermined number, the plurality of adjustment images stored in the storage unit correspond to the plurality of toner loading amount categories, and the control unit determines an adjustment image to be used for calculating the correction amount based on the determined toner loading amount category of each page.

Effect of the Invention

[0012] According to the present invention, waste paper can be reduced in the control for adjusting the printing position of the image printed on the sheet.

Brief Description of the Drawings

[0013]

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Embodiments for Carrying Out the Invention

[0014] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

[0015] FIG. 1 is an overall configuration diagram of a printing system having an image forming apparatus according to the present embodiment. The printing system includes an image forming apparatus 100 and a host computer 101. The image forming apparatus 100 and the host computer 101 are communicably connected via a network 105. The network 105 is a communication line such as, for example, a LAN (Local Area Network) or a WAN (Wide Area Network). Note that the image forming apparatus 100 and the host computer 101 may each be connected to the network 105 in plurality.

[0016] The host computer 101 is, for example, a server, and transmits a print job to the image forming apparatus 100 via the network 105. The print job includes various types of information necessary for printing, such as image data representing an image to be printed (output image), the type of paper to be used for printing, the number of printed sheets, an instruction for double-sided or single-sided printing, and the like.

[0017] The image forming apparatus 100 includes a controller 110, an operation panel 120, a paper feeding device 140, a printer 150, and a reading device 160. The image forming apparatus 100 prints an image on paper by the printer 150 based on the print job acquired from the host computer 101. The controller 110, the operation panel 120, the paper feeding device 140, the printer 150, and the reading device 160 are communicably connected to each other via a system bus 116.

[0018] The controller 110 controls each unit of the image forming apparatus 100. The operation panel 120 is a user interface having an input interface and an output interface. The input interface includes operation buttons, numeric keys, etc. The output interface includes a display such as an LCD (Liquid Crystal Display), a speaker, etc. An operator can input a print job, a command, print settings, etc. to the image forming apparatus 100 through the operation panel 120. The controller 110 acquires the print job, command, print settings, etc. input from the operation panel 120. The operation panel 120 can display various setting screens and the state of the image forming apparatus 100 on the display under the control of the controller 110.

[0019] The paper feeding device 140 includes a plurality of paper feeding stages for accommodating papers. The paper feeding device 140 feeds the papers one by one in order from the topmost paper of a stack of papers (paper stack) loaded on the paper feeding stage. The paper feeding device 140 conveys the papers fed from the paper feeding stage to the printer 150. The printer 150 generates a printed matter by printing an image (output image) on the papers supplied from the paper feeding device 140 based on the image data. The specific configuration of the printer 150 will be described later with reference to FIG. 2. The reading device 160 reads the printed matter generated by the printer 150 and transmits the reading result to the controller 110. The specific configuration of the reading device 160 will be described later with reference to FIG. 2.

[0020] The controller 110 is an information processing device including a ROM (Read Only Memory) 112, a RAM (Random Access Memory) 113, and a CPU (Central Processing Unit) 114. Further, the controller 110 includes an I / O control unit 111 and a storage 115. The storage 115 is a large-capacity storage device such as an HDD (Hard Disk drive) or an SSD (Solid State Drive).

[0021] The I / O control unit 111 is a communication interface that controls communication between the host computer 101 and other devices via the network 105. The ROM 112 is a storage device that stores various control programs. The storage 115 stores various data such as control programs and image data used for image formation processing (printing processing). The RAM 113 functions as a system work memory in which the control programs stored in the ROM 112 and the storage 115 are expanded. The CPU 114 executes the control programs expanded in the RAM 113 to comprehensively control the image forming apparatus 100. Each module in the controller 110 is communicably connected to each other via the system bus 116.

[0022] FIG. 2 is a configuration diagram of the image forming apparatus 100. The image forming apparatus 100 of the present embodiment includes a reading device 160 and a finisher 190 in addition to the paper feeding device 140 and the printer 150 described in FIG. 1. The finisher 190 is a post-processing device that performs predetermined post-processing on the printed matter generated by the printer 150. As post-processing, the finisher 190 performs, for example, staple processing on a plurality of printed matters and sorting processing of the printed matters.

[0023] The printer 150 includes a plurality of image forming units. In the present embodiment, the number of image forming units is provided as 4 according to the number of colors of the image to be formed. The four image forming units are an image forming unit that forms a yellow image, an image forming unit that forms a magenta image, an image forming unit that forms a cyan image, and an image forming unit that forms a black image. The configurations of the respective image forming units are substantially the same.

[0024] One image forming unit includes a photosensitive drum 153, a charger 220, an exposure device 223, and a developing device 152. The photosensitive drum 153 is a drum-shaped photoreceptor having a photosensitive layer on its surface, and rotates in the direction of arrow R1 by a motor (not shown). The charger 220 uniformly charges the surface of the photosensitive drum 153. The exposure device 223 irradiates (exposes) the surface of the uniformly charged photosensitive drum 153 with laser light modulated based on image data. As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 153. The developing device 152 develops the electrostatic latent image using a developer (toner). As a result, the electrostatic latent image on the surface of the photosensitive drum 153 is visualized, and an image (toner image) is formed on the photosensitive drum 153.

[0025] The printer 150 includes an intermediate transfer belt 154 onto which the toner images formed by each image forming unit are transferred. The intermediate transfer belt 154 rotates in the direction of arrow R2. The yellow, magenta, cyan, and black toner images formed by each image forming unit are transferred so as to overlap the intermediate transfer belt 154 at a timing corresponding to the rotation speed of the intermediate transfer belt 154. As a result, a full-color toner image is formed on the intermediate transfer belt 154. The toner image transferred to the intermediate transfer belt 154 is conveyed in the direction of arrow R2, and is transferred to the paper fed from the paper feeding device 140 at the nip portion formed by the intermediate transfer belt 154 and the transfer roller 221.

[0026] The paper feeding device 140 includes a plurality of paper feeding trays 140a, 140b, 140c, 140d, 140e for accommodating paper. The paper is fed from one of the paper feeding trays 140a, 140b, 140c, 140d, 140e, which contains the type of paper indicated by the print job, at a timing corresponding to the timing when each image forming unit starts forming an image. The fed paper is conveyed to the nip portion formed by the intermediate transfer belt 154 and the transfer roller 221 while adjusting the timing so that the toner image on the intermediate transfer belt 154 is transferred to a predetermined position.

[0027] The printer 150 has a first fuser 155 and a second fuser 156 that fix an image on a sheet by heating and pressing the toner image transferred onto the sheet. The first fuser 155 includes a fixing roller having a heater inside, and a pressure belt for pressing the sheet against the fixing roller. The fixing roller and the pressure belt are driven by a motor (not shown) to sandwich and convey the sheet. The second fuser 156 is disposed downstream of the first fuser in the sheet conveyance direction. The second fuser 156 is used to increase the gloss of the image on the sheet that has passed through the first fuser 155 and to ensure fixability. The second fuser 156 includes a fixing roller having a heater inside, and a pressure roller having a heater inside. The fixing roller and the pressure roller are driven by a motor (not shown) to sandwich and convey the sheet.

[0028] Depending on the type of image to be printed (type such as photo, text, etc.) and the type of sheet, the second fuser 156 is not used. In this case, the sheet that has passed through the first fuser 155 is not conveyed to the second fuser 156, but is conveyed to the conveyance path 130. Therefore, a flapper 131 for guiding the sheet to either the conveyance path 130 or the second fuser 156 is provided between the first fuser 155 and the second fuser 156.

[0029] The sheet that has passed through either the second fuser 156 or the conveyance path 130 is conveyed to either the conveyance path 135 or the discharge path 139. Therefore, a flapper 132 is provided at the point where the conveyance path 135 and the discharge path 139 branch. The flapper 132 guides, for example, a sheet with an image printed on the first side (front surface) to the conveyance path 135 and a sheet with images printed on both sides to the discharge path 139 in the double-sided printing mode. The flapper 132 guides, for example, a sheet with an image printed on the front surface to the discharge path 139 in the face-up paper discharge mode. The flapper 132 guides, for example, a sheet with an image printed on the front surface to the conveyance path 135 in the face-down paper discharge mode. Also, the flapper 132 guides a sheet with an adjustment image for printing position adjustment printed on the first side (front surface) to the conveyance path 135 for printing an adjustment image for printing position adjustment on the second side (back surface).

[0030] The paper guided to the conveyance path 135 is conveyed to the inversion unit 136. The paper conveyed to the inversion unit 136 has its conveyance direction inverted after the conveyance operation is once stopped. The paper with the inverted conveyance direction is conveyed to either the conveyance path 138 or the conveyance path 135. A flapper 133 is provided at the branch between the conveyance path 138 and the conveyance path 135. The flapper 133 guides the paper to either the conveyance path 138 or the conveyance path 135. For example, in the duplex printing mode, the flapper 133 guides the paper with the inverted conveyance direction to the conveyance path 138, and in the face-down paper discharge mode, the flapper 133 guides the paper with the inverted conveyance direction to the conveyance path 135. The paper conveyed to the conveyance path 135 by the flapper 133 is guided to the discharge path 139 by the flapper 134. Also, the flapper 133 guides the paper with the inverted conveyance direction to the conveyance path 138 in order to print an adjustment image on the second side (back side) of the paper.

[0031] The paper conveyed to the conveyance path 138 by the flapper 133 is conveyed toward the nip portion between the intermediate transfer belt 154 and the transfer roller 221. Since the front and back of the paper are inverted by the inversion unit 136, the toner image is transferred to the second side (back side) when the paper passes through the nip portion.

[0032] On the downstream side of the printer 150 in the paper conveyance direction, a reading device 160 for reading the adjustment image printed on the paper is connected. The paper on which the image is printed is sent to the reading device 160 as a printed matter via the discharge path 139. The paper (printed matter) supplied from the printer 150 to the reading device 160 is conveyed along the conveyance path 313. The reading device 160 includes a sheet detection sensor 311 and line sensors 312a, 312b along the conveyance path 313. The reading device 160 reads the paper on which the adjustment image is printed by the printer 150 while conveying it along the conveyance path 313 with the line sensors 312a, 312b.

[0033] Details of the adjustment image will be described later. In the following description, the sheet on which the adjustment image is printed is referred to as an "adjustment sheet". Also, the sheet on which an image other than the adjustment image (output image instructed by the print job) is printed is also conveyed to the finisher 190 along the conveyance path 313.

[0034] The sheet detection sensor 311 is, for example, an optical sensor having a light emitting element and a light receiving element. The sheet detection sensor 311 detects the leading edge of the adjustment sheet conveyed along the conveyance path 313 in the conveyance direction. Note that the controller 110 can obtain the skew amount of the sheet based on the detection timing of the sheet leading edge by the sheet detection sensor 311.

[0035] The line sensor 312a and the line sensor 312b are arranged at positions facing each other with the conveyance path 313 therebetween. The line sensors 312a and 312b respectively read the adjustment image from the adjustment sheet. The adjustment image is printed, for example, on both the front and back surfaces of the sheet. While the sheet is being conveyed between the line sensor 312a and the line sensor 312b, the adjustment image printed on both sides is read at once.

[0036] When performing print position adjustment, the image forming apparatus 100 detects the deviation amount of the print position (image forming position) of the adjustment image with respect to the ideal position based on the reading result of the adjustment image by the line sensors 312a and 312b. The controller 110 controls the image forming process based on the detected deviation amount of the print position (image forming position) so that the print position (image forming position) with respect to the sheet becomes the ideal position. Based on the result of the print position adjustment, front-back position adjustment for adjusting the print positions of the front and back surfaces of the sheet is also performed.

[0037] The finisher 190 performs predetermined post-processing on the printed matter that has passed through the reading device 160 and discharges it. At this time, the printed matter on which the output image instructed by the print job is printed is discharged after post-processing, but the adjustment sheet on which the adjustment image is printed is discharged without being post-processed. The adjustment sheet is discharged, for example, to a discharge tray different from the printed matter on which the output image is printed.

[0038] (Image for adjustment) FIG. 3 is an explanatory diagram of the image for adjustment. The printer 150 prints the image for adjustment 700 on the front surface of the paper and the image for adjustment 701 on the back surface of the paper. The images for adjustment 700 and 701 each include a plurality of correction marks 720. The correction marks 720 are located at the four corners of the paper and are printed at positions at a predetermined distance from the paper edge. The plurality of correction marks 720 are formed using black toner and at the same image density. By printing in black, the difference in the reflected light intensity between the correction mark 720 and the paper can be increased, so that the contour of the correction mark 720 can be detected with high precision from the reading result of the reading device 160.

[0039] If the printing position is the ideal position, the distance from the paper edge to the correction mark 720 is the predetermined distance. The controller 110 measures the position of the correction mark 720 on the paper in order to detect the deviation amount of the printing position. The controller 110 measures the lengths (A) to (V) in FIG. 3 based on the reading result of the image for adjustment by the reading device 160.

[0040] The measurement of the lengths (A) to (V) is performed as follows. The controller 110 causes the line sensors 312a and 312b to read the image for adjustment. The controller 110 detects the paper edge and the edge of the correction mark 720 (the boundary between the paper and the correction mark 720) based on the difference between the read image of the image for adjustment by the line sensors 312a and 312b and the read values such as the luminance value of the paper. The controller 110 counts the number of read pixels from the detected paper edge to the edge of the correction mark 720 and measures the lengths (A) to (V) based on the count value.

[0041] Note that the length (A) is the length in the short side direction of the adjustment sheet, and the length (B) is the length in the long side direction of the adjustment sheet. The ideal lengths of the length (A) and the length (B) are defined by the size of the paper. The lengths (C) to (V) correspond to the distances (lengths) from the paper edge to the nearby correction marks 720.

[0042] The amount of printing position deviation is calculated based on lengths (A) to (V). However, according to the inventor's experiments, it was found that the amount of paper deformation caused by the adjustment image illustrated in FIG. 3 is different from the amount of paper deformation of the paper on which the output image corresponding to the actual printing job is printed. This is because the amount of paper deformation varies depending on the toner loading amount. The toner loading amount of the paper on which the output image is printed differs depending on the type of image. For example, when a photographic image is printed on the entire surface of the paper, the toner loading amount of the paper is larger than that of the adjustment sheet. Therefore, there is a possibility that the printing position cannot be corrected to an ideal position with the correction amount obtained from the amount of printing position deviation measured using the adjustment sheet on which only the correction mark 720 is printed.

[0043] In the present embodiment, another mark different from the correction mark 720 is formed at a position that does not overlap with the correction mark 720, and printing position adjustment is performed using an adjustment image suitable for the toner loading amount of the paper on which the output image is actually printed. In the present embodiment, the toner loading amount of the paper is divided into five categories, and adjustment images corresponding to each toner loading amount category are printed on the adjustment sheet. Note that even if another mark is printed at a position that does not overlap with the correction mark 720, it is possible to calculate the amount of printing position deviation.

[0044] FIG. 4 is an explanatory diagram of an adjustment image that reproduces the shrinkage of the paper caused by the difference in the toner loading amount. The image forming apparatus 100 performs printing position adjustment using an adjustment image suitable for the toner loading amount of the output image from among five types of adjustment images 70a, 70b, 70c, 70d, and 70e having different image densities (toner loading amounts) shown in FIG. 4. The toner loading amounts (image densities) of the adjustment images 70a to 70e are the toner loading amounts corresponding to the toner loading amount categories 1 to 5, respectively. The adjustment image data for causing the printer 150 to print the adjustment images 70a, 70b, 70c, 70d, and 70e is stored in advance in the storage 115. Note that the adjustment images for each toner loading amount are not necessarily limited to five types as long as the image densities are different.

[0045] The adjustment image 70a has only the correction mark 720 formed thereon. The adjustment image 70b includes the correction mark 720 and the rectangular mark 730. The mark 730 is formed at a position different from that of the correction mark 720 so as not to overlap the correction mark 720. The mark 730 is a toner image formed based on 25% of the image signal value. The adjustment image 70c includes the correction mark 720 and the rectangular mark 731. The mark 731 is formed at a position different from that of the correction mark 720 so as not to overlap the correction mark 720. The mark 731 is a toner image formed based on 50% of the image signal value. The adjustment image 70d includes the correction mark 720 and the rectangular mark 732. The mark 732 is formed at a position different from that of the correction mark 720 so as not to overlap the correction mark 720. The mark 732 is a toner image formed based on 75% of the image signal value. The adjustment image 70e includes the correction mark 720 and the rectangular mark 733. The mark 733 is formed at a position different from that of the correction mark 720 so as not to overlap the correction mark 720. The mark 733 is a toner image formed based on 100% of the image signal value.

[0046] The marks 730, 731, 732, and 733 are images of the same area. Since the marks 730, 731, 732, and 733 are formed based on different image signal values respectively, they have different image densities. The image density of each of the marks 730, 731, 732, and 733 increases in the order of the mark 730 being the smallest, followed by the marks 731, 732, and 733. Therefore, the adjustment image 70e has the largest toner loading amount among the adjustment images 70a, 70b, 70c, 70d, and 70e. The adjustment image 70a has the smallest toner loading amount among the adjustment images 70a, 70b, 70c, 70d, and 70e.

[0047] (Paper Library) The papers that can be used by the image forming apparatus 100 are managed by a database. This database is referred to as a "paper library". The paper library is stored, for example, in a host computer 101 (server) connected to the image forming apparatus 100 or in a storage 115. The information of the papers stored in the paper library is read and written as necessary.

[0048] FIG. 5 is an exemplary diagram of an editing screen for an operator to edit the information of the papers stored in the paper library. This editing screen 400 is displayed on the operation panel 120 of the image forming apparatus 100. The editing screen 400 includes a paper list 410, a new addition button 420, an edit button 421, a delete button 422, and a selection button 423.

[0049] In the paper list 410, a list of the papers managed by the paper library 600 is displayed. Attribute information representing the characteristics of the papers is displayed in columns 411 to 417. The paper name is displayed in column 411. The paper name is information set by the operator so that the operator can identify the type of the paper. The paper size is displayed in columns 412 and 413. Column 412 represents the paper length in the short side direction, and column 413 represents the paper length in the long side direction. The basis weight of the paper is displayed in column 414.

[0050] In column 415, information for the operator to identify the surface property of the paper is displayed. The information for the operator to identify the surface property of the paper is information regarding the physical properties of the paper surface. For example, a paper displayed as "coated" in column 415 refers to a paper with a surface treatment for increasing glossiness. Also, a paper displayed as "embossed" in column 415 refers to a paper with embossing. Also, a paper displayed as "plain paper" in column 415 refers to a paper without special processing. The color of the paper is displayed in column 416.

[0051] When the operator edits the information of the paper, the operator selects the paper (paper name) to be edited from the paper list 410 displayed on the operation panel 120. The display method of the selected paper changes so that it can be distinguished from the unselected papers. For example, the selected paper is displayed brighter than the unselected papers. When "XYZ Paper Color 81" is selected, as illustrated in FIG. 5, the row of "XYZ Paper Color 81" has a different display method from the rows of other unselected papers. When the number of papers managed in the paper library is larger than the number that can be displayed in the paper list 410 at one time, the operator can operate the scroll bar 417 to select other papers.

[0052] The new addition button 420 is a button for newly adding paper information to the paper library 600. The edit button 421 is a button for editing the information of the paper selected by the operator from the paper list 410. The delete button 422 is a button for deleting the paper selected by the operator from the paper list 410 from the paper library 600. The selection button 423 is a button for associating the paper selected by the operator from the paper list 410 with the paper feed stage.

[0053] When the new addition button 420 or the edit button 421 on the edit screen 400 is pressed, a paper attribute edit screen for inputting paper information is displayed on the operation panel 120. FIG. 6 is an exemplary diagram of the paper attribute edit screen. The paper attribute edit screen 500 includes text boxes 501 to 504, combo boxes 505 and 506, a check box 507, an edit end button 520, and a cancel button 521.

[0054] The text box 501 is an input area for the paper name. The text box 502 is an input area for the paper length in the short side direction. The text box 503 is an input area for the paper length in the long side direction. The text box 504 is an input area for the basis weight of the paper. Inputs to each of the text boxes 501 to 504 are performed using a software keyboard or the operation panel 120.

[0055] The combo box 505 is an area for specifying the surface property of the paper. The operator specifies the surface property of the paper from among multiple types of surface properties. Information on multiple types of surface properties is registered in advance and is specified from the list displayed in a pull-down manner. The combo box 506 is an area for specifying the color of the paper. The operator specifies the color of the paper from among multiple colors. Information on multiple colors is registered in advance and is specified from the list displayed in a pull-down manner. The check box 507 is a specified area for specifying whether the paper is pre-printed paper. When the paper is pre-printed paper, the operator checks the check box 507.

[0056] The editing completion button 520 is a button for saving the paper information input on the paper attribute editing screen 500 to the paper library 600. When the editing completion button 520 is pressed, the information on the paper input at that time is saved to the paper library 600. After the paper information is saved to the paper library 600, the paper attribute editing screen 500 switches to the editing screen 400 in FIG. 5. The cancel button 521 is a button for transitioning to the editing screen 400 in FIG. 5 without saving the paper information input on the paper attribute editing screen 500 to the paper library 600. When the cancel button 521 is pressed, the editing of the paper information is aborted.

[0057] FIG. 7 is an explanatory diagram of the paper library. The paper library 600 is stored as digital information. Here, the digital information is, for example, information described using XML (Extensible Markup Language) or CSV (Comma-Separated Values).

[0058] Rows 601 to 605 represent the information of the papers registered in the paper library 600. Columns 611 to 627 represent paper attributes. Column 611 represents the name of the paper. Columns 612 to 615 represent the physical characteristics of the paper. Column 612 represents the paper length in the short side direction of the paper, column 613 represents the paper length in the long side direction of the paper, column 614 represents the basis weight of the paper, and column 615 represents the surface property of the paper. Column 616 represents the color of the paper. Column 617 represents whether the paper is pre-printed paper or not.

[0059] Columns 618 to 627 represent the printing position deviation amounts on the front and back surfaces of the paper respectively. The printing position deviation amount is a value that quantitatively represents the deviation between the predicted printing area predicted from the reading result of the adjustment image and the ideal printing area. In this embodiment, the toner loading amount of the image printed on the paper is divided into five toner loading amount categories, and the printing position deviation amounts when printing the images belonging to each toner loading amount category are stored.

[0060] Columns 618 and 619 represent the printing position deviation amounts on the front and back surfaces when the toner loading amount of the image printed on the paper belongs to toner loading amount category 1. Columns 620 and 621 represent the printing position deviation amounts on the front and back surfaces when the toner loading amount of the image printed on the paper belongs to toner loading amount category 2. Columns 622 and 623 represent the printing position deviation amounts on the front and back surfaces when the toner loading amount of the image printed on the paper belongs to toner loading amount category 3. Columns 624 and 625 represent the printing position deviation amounts on the front and back surfaces when the toner loading amount of the image printed on the paper belongs to toner loading amount category 4. Columns 626 and 627 represent the printing position deviation amounts on the front and back surfaces when the toner loading amount of the image printed on the paper belongs to toner loading amount category 5.

[0061] Note that the ideal printing area is a rectangle with the lengths of the four sides being predetermined lengths, one side of the printing area is parallel to a predetermined side of the paper, and the distance between the predetermined side of the paper and the side of the printing area parallel to the predetermined side is a predetermined distance.

[0062] The printing position deviation amount is represented by parameters such as the right-angle correction amount, trapezoid correction amount, lead position, side position, main scanning magnification (magnification in the longitudinal direction), and sub-scanning magnification (magnification in the lateral direction). The right-angle correction amount represents the amount by which any corner of the printing area is deviated from a right angle. For example, the right-angle correction amount is calculated by finding an ideal perpendicular line to a straight line printed in the longitudinal direction of the printing area, and is the deviation amount between the ideal perpendicular line and the straight line printed in the lateral direction. The trapezoid correction amount represents the deviation amount due to the stretching and shrinking of the paper. For example, the trapezoid correction amount is the deviation amount between a straight line printed from the printing start position in the lateral direction to the lateral rear end on the paper and a straight line printed from the position of the longitudinal rear end of the paper to the lateral rear end in the lateral direction.

[0063] The lead position represents the printing position deviation amount in the lateral direction with respect to the paper. The side position represents the printing position deviation amount in the longitudinal direction with respect to the paper. The lead position is adjusted by changing the printing start position of the image starting from the leading edge of the paper in the conveyance direction. The side position is adjusted by changing the printing start position of the image starting from the edge of the paper parallel to the conveyance direction. Specifically, the lead position and the side position are adjusted by adjusting the laser light irradiation start timing of the exposure device 223 to the photosensitive drum 153. For example, the CPU 114 controls the exposure device 223 to adjust the laser light irradiation start timing.

[0064] The main scanning magnification (magnification in the longitudinal direction) represents the deviation (magnification) of the actual printing area length in the longitudinal direction from the ideal length in the longitudinal direction (main scanning direction). Specifically, the magnification in the longitudinal direction is adjusted by controlling the clock frequency of the laser light when the exposure device 223 modulates the laser light based on the image data. For example, the CPU 114 controls the exposure device 223 to control the clock frequency. Alternatively, the CPU 114 may perform image processing on the image data so that the printing position of the output image becomes the ideal printing position. The image processing for making the printing position of the output image the ideal printing position is, for example, image processing such as affine transformation.

[0065] The sub-scanning magnification (magnification in the short-side direction) represents the deviation (magnification) of the length of the actual printing area in the short-side direction from the ideal length in the short-side direction (sub-scanning direction). Specifically, the magnification in the short-side direction is adjusted by controlling the rotation speed of the photosensitive drum 153 or the rotation speed of the intermediate transfer belt 154. For example, the CPU 114 adjusts the magnification in the short-side direction by adjusting the rotation speed of a motor (not shown) that rotates the photosensitive drum 153 or a motor (not shown) that rotates the intermediate transfer belt 154.

[0066] When printing an output image on a sheet based on a print job, the controller 110 adjusts the printing position so that the image is printed at an ideal position on the sheet based on the printing position deviation amount. The controller 110 refers to the printing position deviation amount in the sheet library 600 and performs image processing on the image data so that the printing position becomes the ideal printing position. The controller 110 controls the printer 150 to print an image on the sheet based on the image-processed image data.

[0067] The initial value of each item of the printing position deviation amount is "0". When a new sheet is registered in the sheet library 600 or when the printing position adjustment has not been performed even though the sheet is registered, the initial value is used as the printing position deviation amount.

[0068] FIG. 8 is an explanatory diagram of a method for calculating the printing position deviation amount. The printing position deviation amount is obtained based on the measured values of lengths (A) to (V) measured from the reading result of the adjustment image (see FIG. 3).

[0069] Items 801 to 812 are the items representing the printing position deviation amount. The parameters of the printing position deviation amount on the front surface obtained from the adjustment image 700 include the lead position 801, the side position 802, the magnification in the longitudinal direction 803, the magnification in the short-side direction 804, the right-angle correction amount 805, and the trapezoidal correction amount 806. The parameters of the printing position deviation amount on the back surface obtained from the adjustment image 701 include the lead position 807, the side position 808, the magnification in the longitudinal direction 809, the magnification in the short-side direction 810, the right-angle correction amount 811, and the trapezoidal correction amount 812.

[0070] The measured values 820 of the same type of parameters and the printing position deviation amounts 822 of the adjustment image 700 and the adjustment image 701 are calculated based on the same calculation formula. The same ideal value is set for the same type of parameters of the adjustment image 700 and the adjustment image 701. The measured value 820 is calculated based on the calculation formula set for each item from the actually measured values of the lengths (A) to (V) shown in FIG. 3.

[0071] The measured value 820 of the lead position 801 (807) corresponds to the average value of the distances C and E (K, M) from the end at the leading edge in the paper conveyance direction to the nearby correction mark 720. The measured value 820 of the side position 802 (808) corresponds to the average value of the distances F and J (N, R) from the end on the left side in FIG. 3 with respect to the paper conveyance direction to the nearby correction mark 720.

[0072] The measured value 820 of the magnification in the longitudinal direction 803 (809) corresponds to the average value of the distances between the correction marks 720 arranged on the same line in the longitudinal direction. The measured value 820 of the magnification in the short-side direction 804 (810) corresponds to the average value of the distances between the correction marks 720 arranged on the same line in the short-side direction.

[0073] The measured value 820 of the right-angle correction amount 805 (811) corresponds to the average value of the deviations S and T (U, V) in the short-side direction with respect to the reference line of the correction mark on the trailing edge side in the paper conveyance direction when the perpendicular line connecting the correction marks 720 on the leading edge side in the paper conveyance direction is used as the reference line. The measured value 820 of the trapezoid correction amount 806 (812) corresponds to the difference between the distance between the correction marks 720 arranged on the leading edge side in the paper conveyance direction and the distance between the correction marks 720 arranged on the trailing edge side in the paper conveyance direction.

[0074] Column 821 represents the ideal value for each corresponding item. The correction marks 720 are ideally printed at positions each separated from the corresponding paper edge by the ideal value. The ideal values for the lead position and the side position are, for example, 1 [cm]. The ideal value for the magnification in the longitudinal direction is a length that is, for example, 2 [cm] shorter than the longitudinal paper length of the paper registered in the paper library 600. The ideal value for the magnification in the lateral direction is a length that is, for example, 2 [cm] shorter than the lateral paper length of the paper registered in the paper library 600.

[0075] Column 822 represents a calculation formula for calculating the final print position deviation amount for each item based on the measured value 820 and the ideal value 821. The print position deviation amounts for the lead position and the side position are calculated by subtracting the ideal value from the measured value (unit: mm). The print position deviation amounts for the magnification in the longitudinal direction and the magnification in the lateral direction are calculated by dividing the result of subtracting the ideal value from the measured value by the ideal value (unit: %). The right angle correction amount and the trapezoid correction amount are such that the measured value is used as the correction amount as it is. The calculated print position deviation amounts for each are saved in the paper library 600 (see Fig. 7).

[0076] (Paper type setting) Fig. 9 is an illustrative diagram of a paper type setting screen 900 displayed on the operation panel 120. The paper type setting screen 900 includes the paper setting status 901 of the paper feed stage, the print position adjustment button 902, and the paper registration button 903. The paper setting status 901 of the paper feed stage displays the paper types registered in each paper feed stage (paper feed stages 140a to 140e). In Fig. 9, paper feed stage 1 corresponds to paper feed stage 140a, paper feed stage 2 corresponds to paper feed stage 140b, paper feed stage 3 corresponds to paper feed stage 140c, paper feed stage 4 corresponds to paper feed stage 140d, and paper feed stage 5 corresponds to paper feed stage 140e.

[0077] In Fig. 9, "ABC Paper Recycling 1" is registered in paper feed stage 140a. "ABC Paper Recycling 2" is registered in paper feed stage 140b. "DEF Paper Embossed Paper A-1" is registered in paper feed stage 140c. "DEF Paper Coated Paper P-1" is registered in paper feed stage 140d. "XYZ Paper Color 81" is registered in paper feed stage 140e.

[0078] The printing position adjustment button 902 is a button for transitioning to the printing position adjustment screen described later. The paper registration button 903 is a button for registering the paper type in the selected paper feed stage. When the paper registration button 903 is pressed, the editing screen 400 of the paper library in FIG. 5 is displayed. When the selection button 423 on the editing screen 400 of the paper library is pressed, the paper selected on the editing screen 400 of the paper library is registered in the paper feed stage selected by the operator. Note that the printing position adjustment button 902 and the paper registration button 903 cannot be pressed when the paper feed stage is not selected in the paper setting status 901 of the paper feed stage.

[0079] FIG. 10 is an exemplary view of the printing position adjustment screen displayed on the operation panel 120. FIG. 10(a) is the printing position adjustment screen displayed by pressing the printing position adjustment button 902 on the paper type setting screen 900. The printing position adjustment screen 1000 includes an initial adjustment button 1001, a print adjustment button 1002, and a return button 1003. The initial adjustment button 1001 is a button for transitioning to the initial adjustment screen 1010 in FIG. 10(b). The print adjustment button 1002 is a button for transitioning to the print adjustment screen 1020 in FIG. 10(c). The return button 1003 is a button for transitioning to the paper type setting screen 900 in FIG. 9.

[0080] The initial adjustment screen 1010 in FIG. 10(b) displayed by pressing the initial adjustment button 1001 includes a paper feed stage selection box 1011, an execution button 1012, and a cancel button 1013. The paper feed stage selection box 1011 is a combo box for specifying the paper feed stage. In the present embodiment, in the paper feed stage selection box 1011, five paper feed stages from paper feed stage 1 to paper feed stage 5 shown in FIG. 9 can be selected. The paper type registered in the paper feed stage is also displayed in the paper feed stage selection box 1011.

[0081] The execution button 1012 is a button for performing the initial front-back position correction described below on the paper of the paper feed stage selected by the paper feed stage selection box 1011. When the execution button 1012 is pressed, the controller 110 starts the process of initial front-back position correction. The cancel button 1013 is a button for canceling the initial front-back position correction. When the cancel button 1013 is pressed, the process of initial front-back position correction is canceled and the printing position adjustment screen 1000 is returned to.

[0082] The printing adjustment screen 1020 in Fig. 10(c) displayed when the print adjustment button 1002 is pressed includes a print adjustment enable checkbox 1021, a sheet count setting box 1022, an OK button 1023, and a cancel button 1024. The print adjustment enable checkbox 1021 is a checkbox for switching the enable / disable of the print front-back position correction described below. The sheet count setting box 1022 is a text box for inputting the number of printed sheets at intervals for performing the print front-back position correction.

[0083] When the print adjustment enable checkbox 1021 is checked, the print front-back position correction is performed every time the number of prints set in the sheet count setting box 1022 is printed. The print front-back position correction is a function of maintaining the correction amount in an appropriate state by performing the front-back position correction again at a predetermined number of printed sheet intervals during printing. By the print front-back position correction, every time the printer 150 generates a predetermined number of printed materials, the correction amount for performing the correction of the printing position is adjusted. When the print adjustment enable checkbox 1021 is not checked, the print front-back position correction is not performed. When the OK button 1023 is pressed, the print adjustment settings are saved in the RAM 113 and the printing position adjustment screen 1000 is returned to. When the cancel button 1024 is pressed, the print adjustment settings are not saved and the printing position adjustment screen 1000 is returned to.

[0084] (Initial front-back position correction) FIG. 11 is a flowchart showing the initial front-back position correction process. The control in each step of this flowchart is realized by the CPU 114 reading and executing the program stored in the ROM 112. The initial front-back position correction calculates the correction amount of the printing position shift amount for each toner loading amount using a plurality of adjustment sheets generated by printing the five types of adjustment images 70a to 70e shown in FIG. 4 on the paper of the paper feed stage selected by the operator. As a result, the printing position shift amount that occurs in the actual printed matter can be obtained with high precision, and the correction amount of the printing position suitable for the output image actually printed by the printing job can be obtained. This process is performed before the printing job is started.

[0085] When the operator requests the display of the paper type setting screen 900 in FIG. 9 from the operation panel 120, the CPU 114 displays the paper type setting screen 900 on the operation panel 120 (S1201). The CPU 114 waits until the operator presses the printing position adjustment button 902 (S1202: N). When the printing position adjustment button 902 is pressed (S1202: Y), the CPU 114 displays the printing position adjustment screen 1000 in FIG. 10(a) on the operation panel 120 (S1203). The CPU 114 waits until any one of the initial adjustment button 1001, the print adjustment button 1002, and the return button 1003 is pressed (S1204: N).

[0086] When a button other than the initial adjustment button 1001 is pressed (S1204: Y, S1205: N), the CPU 114 determines whether the pressed button is the print adjustment button 1002 (S1207). When the return button 1003 is pressed (S1207: N), the CPU 114 returns to the process of S1203 and displays the printing position adjustment screen 1000 on the operation panel 120. When the print adjustment button 1002 is pressed (S1207: Y), the CPU 114 performs the print adjustment setting process described later (S1209). When the print adjustment setting process is completed, the CPU 114 returns to the process of S1203 or ends the process.

[0087] When the initial adjustment button 1001 is pressed (S1204: Y, S1205: Y), the CPU 114 displays the initial adjustment screen 1010 in Fig. 10(b) on the operation panel 120 (S1206). The operator selects the paper feed tray in which the paper for performing the initial front-back position correction is stored using the initial adjustment screen 1010. The CPU 114 waits until the execution button 1012 or the cancel button 1013 on the initial adjustment screen 1010 is pressed (S1208: N).

[0088] When the cancel button 1013 is pressed (S1208: Y, S1210: N), the CPU 114 returns to the process of S1203 and displays the print position adjustment screen 1000 on the operation panel 120. When the execution button 1012 is pressed (S1208: Y, S1210: Y), the CPU 114 controls the printer 150 to print an adjustment image on the paper stored in the paper feed tray selected by the operator. For this purpose, the CPU 114 reads the image data of the adjustment image from the storage 115 (S1211), and the printer 150 prints the adjustment image based on the image data (S1212).

[0089] For example, when the operator selects "DEF Paper Embossed Paper A-1" in paper feed tray 3, the CPU 114 reads the image data of the adjustment image 70a from the storage 115 (S1211). The CPU 114 controls the printer 150 to print the adjustment image 70a on the paper fed from the paper feed tray 140c based on the read image data (S1212). After the printer 150 prints the adjustment image 70a on the front surface of the paper, it conveys the paper toward the inversion unit 136. The printer 150 inverts the paper in the inversion unit 136 and then conveys the paper to the conveyance path 138 to print the adjustment image 70a on the back surface again. The adjustment sheet is created by printing the adjustment image 70a on both sides. After that, the printer 150 conveys the created adjustment sheet to the reading device 160.

[0090] The CPU 114 controls the reading device 160 to read the adjustment images 70a printed on both sides of the adjustment sheet (S1213). While the CPU 114 conveys the adjustment sheet through the conveyance path 313 of the reading device 160, the adjustment images 70a on both sides are read by the line sensors 312a and 312b. The adjustment sheet discharged from the reading device 160 is discharged to the discharge tray of the finisher 190.

[0091] The CPU 114 acquires the reading result of the adjustment sheet from the reading device 160, and calculates the printing position deviation amount based on the calculation method shown in FIG. 8 from the reading result (S1214). The CPU 114 stores the calculated printing position deviation amount in the paper library 600 corresponding to the paper of the paper feeding stage selected by the operator (S1215). Through the processes of S1211 to S1215, the initial front-back position correction using one adjustment image is completed.

[0092] The CPU 114 determines whether the initial front-back position correction for all the adjustment images 70a to 70e has been completed (S1216). If not completed (S1216: N), the CPU 114 returns to the process of S1211, reads the image data of the next adjustment image (here, the adjustment image 70b) from the storage 115, and performs the initial front-back position correction.

[0093] When the initial front-back position correction has been completed for all adjustment images 70a to 70e (S1216: Y), the CPU 114 ends the initial front-back position correction process. By the initial front-back position correction, in the paper library 600 of FIG. 7, the print position deviation amounts for each toner loading amount category of "DEF Paper Embossed Paper A-1" 603 are stored. Specifically, the print position deviation amount calculated by reading the adjustment image 70a is stored in the print position deviation amount (front side) 618 and the print position deviation amount (back side) 619. The print position deviation amount calculated by reading the adjustment image 70b is stored in the print position deviation amount (front side) 620 and the print position deviation amount (back side) 621. The print position deviation amount calculated by reading the adjustment image 70c is stored in the print position deviation amount (front side) 622 and the print position deviation amount (back side) 623. The print position deviation amount calculated by reading the adjustment image 70d is stored in the print position deviation amount (front side) 624 and the print position deviation amount (back side) 625. The print position deviation amount calculated by reading the adjustment image 70e is stored in the print position deviation amount (front side) 626 and the print position deviation amount (back side) 627.

[0094] (Image forming process) FIG. 12 is a flowchart showing the image forming process by the image forming apparatus 100. Each step of this flowchart is realized by the CPU 114 reading and executing a program stored in the ROM 112.

[0095] When a print job is input from the host computer 101 or the operation panel 120, the CPU 114 acquires information regarding the type of paper included in the print job (S100). The CPU 114 acquires toner loading amount information based on the page unit image data of the print job (S101). Specifically, the CPU 114 acquires the image signal value T from the page unit image data of the print job as the toner loading amount information. The image signal value T is a value indicating the image density.

[0096] Based on the information acquired in the processes of S100 and S101, the CPU 114 determines whether the amount of print position deviation for the paper specified by the print job is saved (S102). For example, the CPU 114 refers to the paper library 600 and determines whether the amount of print position deviation for the paper specified by the print job is a value other than the initial value 0.

[0097] If the amount of print position deviation has been saved (the amount of print position deviation for the paper is a value other than the initial value 0) (S102: Y), CPU 114 acquires the amount of print position deviation for the specified paper (S103). CPU 114 corrects the print position by processing the image data included in the print job using the acquired amount of print position deviation (S104). For example, CPU 114 converts the image data included in the print job into a bitmap image and corrects the print position by affine converting the bitmap image based on the acquired amount of print position deviation. CPU 114 controls printer 150 to feed the specified paper from paper feeder 140 and print an image on the paper based on the image data with the corrected print position (S105).

[0098] If the print position deviation amount is not saved (the print position deviation amount of the paper is the initial value 0) (S102: N), CPU 114 does not correct the print position. In this case, CPU 114 controls printer 150 to feed the specified paper from paper feeder 140 and print an image on the paper based on the image data included in the print job (S105).

[0099] This completes the image formation process. By performing the image formation process on a print page basis, it is possible to correct the print position based on the print position deviation amount corresponding to the amount of toner applied for each printed page. This makes it possible to correct the print position with high precision for each page.

[0100] (Setting the interval for correcting the print front and back position) 13 is a flowchart showing the process of setting the execution interval for print front / back position correction. The control of each step in this flowchart is realized by the CPU 114 reading and executing a program stored in the ROM 112. This process is performed as the print adjustment setting process in S1209 in FIG.

[0101] 11, when the print adjustment button 1002 is pressed, the CPU 114 displays the print adjustment screen 1020 of FIG. 10C on the operation panel 120 (S1301). The CPU 114 waits until the OK button 1023 or the cancel button 1024 on the print adjustment screen 1020 is pressed (S1302: N). When a button is pressed (S1302: Y), the CPU 114 determines whether the pressed button is the OK button 1023 or the cancel button 1024 (S1303). When the cancel button 1024 is pressed (S1303: N), the CPU 114 ends the process of setting the execution interval for print front / back position correction, and returns to the process of S1203 of FIG. 11.

[0102] If the OK button is pressed (S1303: Y), the CPU 114 saves the input results of the print adjustment screen 1020 (input values in the print adjustment enable checkbox 1021 and the number setting box 1022) (S1304). For example, if the print adjustment enable checkbox 1021 is checked, the CPU 114 sets the print front / back position correction execution flag F saved in the RAM 113 to "1." If the print adjustment enable checkbox 1021 is not checked, the CPU 114 sets the print front / back position correction execution flag F to "0." The CPU 114 also saves the number of sheets input in the number setting box 1022 in the execution interval number N of print front / back position correction in the RAM 113. The print front / back position correction is performed every time printing is performed for the saved execution interval number N of print front / back position correction. After saving the input results, the CPU 114 ends the execution interval setting process for print front / back position correction.

[0103] (Print front and back position correction) 14 is a flowchart showing the print front / back position correction performed during execution of a print job. The control of each step in this flowchart is realized by the CPU 114 reading and executing a program stored in the ROM 112. This process begins when a print job is input from the host computer 101 or the operation panel 120.

[0104] When CPU 114 acquires a print job, it acquires the execution interval number N of sheets for print front / back position correction stored in RAM 113 (S1501). CPU 114 sets the execution determination number n of sheets for print front / back position correction to "0" (S1502). The execution determination number n indicates the number of sheets printed by the print job, and is reset to "0" when print front / back position correction is performed. CPU 114 determines whether execution determination number n is equal to or less than execution interval number N of sheets (S1503).

[0105] If the execution determination number n is equal to or less than the execution interval number N (S1503: Y), the CPU 114 prints one image on a sheet of paper as instructed by the acquired print job (S1504). After printing, the CPU 114 adds "1" to the execution determination number n (S1505).

[0106] The CPU 114 acquires applied toner amount information for the printed page (S1506). As described above, the applied toner amount information is acquired by acquiring the image signal value T from the image data for each page of the print job. It is also possible to acquire applied toner amount information based on the brightness obtained by reading the image printed on the paper using a sensor (not shown). The CPU 114 associates the acquired applied toner amount information with page information that can be acquired from the print job and stores it in the RAM 113 (S1507). The page information includes, for example, an identifier for identifying a page of the print job (hereinafter referred to as a "page ID") and information indicating which copy of the print job the page of the page ID corresponds to.

[0107] FIG. 15 is an example diagram of a table linking page information with applied toner information. The print job in FIG. 15 is information for printing multiple copies of an image, with each copy consisting of multiple pages. Here, the print job is information for printing five copies, with each copy consisting of 50 pages. In FIG. 15, page information and applied toner amount information for a print job that prints five copies of 50 pages are linked. In this embodiment, pages with page IDs 1 to 50 correspond to the first copy. Similarly, pages with page IDs 51 to 100 correspond to the second copy, pages with page IDs 101 to 150 correspond to the third copy, pages with page IDs 151 to 200 correspond to the fourth copy, and pages with page IDs 201 to 250 correspond to the fifth copy.

[0108] The CPU 114 determines whether printing of all pages of images specified in the print job has been completed (S1508). If not completed (S1508: N), the CPU 114 repeats the processing from S1503 onwards. If completed (S1508: Y), the CPU 114 ends the correction of the print front and back positions.

[0109] If the execution determination sheet count n is greater than the execution interval sheet count N (S1503: N), the CPU 114 acquires the print front / back position correction execution flag F stored in the RAM 113 (S1510). The CPU 114 determines whether the acquired print front / back position correction execution flag F is "1" (S1511).

[0110] If the print front / back position correction execution flag F is "1" (S1511: Y), the CPU 114 executes print front / back position correction. To do so, the CPU 114 executes a front / back position correction execution section determination process (described later) (S1512). After the front / back position correction execution section determination process is completed, the CPU 114 executes a print front / back position correction process (described later) (S1513). The front / back position correction execution section determination process determines the adjustment image to be used in the print front / back position correction process from among the adjustment images 70a to 70d illustrated in FIG. 4. After executing the print front / back position correction process, the CPU 114 sets the execution determination number n of print front / back position correction to "0" (S1514).

[0111] Note that the CPU 114 does not perform the print front / back position correction when the print front / back position correction execution flag F is not "1," i.e., when the print front / back position correction execution flag F is "0" (S1511: N), the CPU 114 sets the print front / back position correction execution determination number n to "0" (S1514) without performing the processes of S1512 and S1513.

[0112] The CPU 114 determines whether printing of all pages of images specified in the print job has been completed (S1508). If not completed (S1508: N), the CPU 114 repeats the processing from S1503 onwards. If completed (S1508: Y), the CPU 114 ends the correction of the print front and back positions.

[0113] 16 is a flowchart showing the process of determining the front / back position correction execution section in S1512. The front / back position correction execution section is a section for determining the adjustment image to be used when correcting the front / back position of the print. In this embodiment, the adjustment images 70a to 70e in FIG. 4 correspond to the toner amount sections set in the front / back position correction execution section, and the adjustment image to be used for correcting the front / back position of the print is determined by the toner amount section.

[0114] CPU 114 determines whether or not there is a page corresponding to the first copy of the print job among the N pages to be printed after the print front / back position correction is performed (S1601). In the example of FIG. 15, the execution interval number N of print front / back position correction is "100". When making a determination about page ID 101, the IDs of the pages to be printed after the print front / back position correction is performed are page IDs 101 to 200. In this case, since the pages with page IDs 101 to 200 are the third and fourth copies, it is determined that there is no page corresponding to the first copy of the print job.

[0115] If there is no page corresponding to the first part of the print job (S1601: Y), the CPU 114 determines whether the toner loading amount information of the pages corresponding to the first part of the print job including N pages to be printed after the execution of the front-back position correction has been acquired (S1602). In the example of FIG. 15, when making a determination for page ID 101, the pages corresponding to the first part of the job of the pages to be printed after the execution of the front-back position correction are page IDs 1 to 50. In this case, at the timing of making a determination for page ID 101, it is determined that the toner loading amount information for page IDs 1 to 50 has been acquired in the process of S1506.

[0116] If the toner loading amount information of the pages of the first part of the print job has been acquired (S1602: Y), the CPU 114 determines the toner loading amount category for each page of the first part of the print job based on the toner loading amount information (S1603). The toner loading amount category is determined, for example, by acquiring an image signal value (toner loading amount) from the page unit image data of the print job and based on the acquired image signal value and a predetermined threshold value. FIG. 17 is a classification table for determining the toner loading amount category based on the image signal value. For example, when each page of the first part of print job 1 has an image signal value of 50%, the toner loading amount category of each page is determined to be "3".

[0117] The CPU 114 determines the toner loading amount category of each page of the first part of the print job determined in the process of S1603 as the front-back position correction execution category and ends the front-back position correction execution category determination process (S1604). For example, when the page of the first part of the print job has a toner loading amount category of "3", the CPU 114 determines the toner loading amount category of "3" as the front-back position correction execution category. Also, when different toner loading amount categories are determined for a plurality of pages of the first part of the print job, the CPU 114 determines the plurality of toner loading amount categories as the front-back position correction execution category.

[0118] When there is a page corresponding to the first part of the print job (S1601: N), the CPU 114 determines all toner loading amount categories as the front-back position correction execution categories and ends the front-back position correction execution category determination process (S1605). That is, the CPU 114 determines the toner loading amount categories "1" to "5" as the front-back position correction execution categories. Similarly, when the toner loading amount information of the page of the first part of the job has not been acquired (S1602: N), the CPU 114 determines all toner loading amount categories as the front-back position correction execution categories and ends the front-back position correction execution category determination process (1605).

[0119] FIG. 18 is a flowchart showing the print front-back position correction process of S1513.

[0120] The CPU 114 generates an adjustment sheet on which an adjustment image corresponding to the front-back position correction execution category determined in the front-back position correction execution category determination process is printed (S1701). For example, when the front-back position correction execution category is determined to be the toner loading amount category "3" in the front-back position correction execution category determination process, the adjustment image 70c in FIG. 4 is printed.

[0121] The CPU 114 controls the reading device 160 to read the adjustment image printed on the adjustment sheet (S1702). The CPU 114 acquires the reading result of the adjustment sheet (adjustment image) by the reading device 160, and based on the reading result and the calculation method shown in FIG. 8, acquires the print position deviation amount (S1703).

[0122] The CPU 114 stores the acquired print position deviation amount in the paper library 600 corresponding to the paper used for the print job (S1704). For example, when the paper is "DEF Paper Embossed Paper A-1", the CPU 114 stores the acquired print position deviation amount as the print position deviation amount of "DEF Paper Embossed Paper A-1" 603 in the paper library 600 in FIG. 7. Specifically, when the toner loading amount category "3" is determined as the front-back position correction execution category and the adjustment image 70c is printed, the CPU 114 stores the acquired print position deviation amount in the print position deviation amount (front surface) 622 and the print position deviation amount (back surface) 623.

[0123] The CPU 114 determines whether acquisition of print position deviation amounts using adjustment images for all front and back position correction execution sections has been completed (S1705). If not completed (S1705: N), the CPU 114 repeats the processes from S1701 onwards. For example, if multiple (e.g., all) toner application amount sections have been determined as front and back position correction execution sections, the processes of S1701 to S1704 are sequentially performed using the adjustment images 70a to 70e in Fig. 4. If completed (S1705: Y), the CPU 114 ends the print front and back position correction process.

[0124] (Another example of print front and back position correction) 19 is another flowchart showing print front / back position correction performed during execution of a print job. Control in each step of this flowchart is realized by the CPU 114 reading and executing a program stored in the ROM 112. This process begins when a print job is input from the host computer 101 or the operation panel 120.

[0125] As in the processes of S1501 and S1502, CPU 114 acquires the execution interval sheet count N and sets the execution determination sheet count n to "0" (S2101, S2102). CPU 114 acquires toner application information for pages of the acquired print job for which image data can be acquired on a page-by-page basis in advance of printing (S2103). As described above, toner application amount information is acquired by acquiring image signal value T from image data on a page-by-page basis of the print job. In this embodiment, image data (toner application information) for TN pages can be acquired in advance of printing.

[0126] CPU 114 determines whether execution determination sheet count n is equal to or less than execution interval sheet count N (S2104). If execution determination sheet count n is equal to or less than execution interval sheet count N (S2104: Y), CPU 114 performs the same processes as S1504 and S1505 (S2105, S2106). CPU 114 determines whether printing of images on all pages specified in the print job has been completed (S2107). If not completed (S2107: N), CPU 114 repeats the processes from S2103 onwards. If completed (S2107: Y), CPU 114 ends print front / back position correction.

[0127] If the execution determination sheet count n is greater than the execution interval sheet count N (S2104: N), the CPU 114 acquires the print front / back position correction execution flag F (S2110), similar to the process of S1510. The CPU 114 determines whether the acquired print front / back position correction execution flag F is "1" (S2111), similar to the process of S1511. If the print front / back position correction execution flag F is "1" (S2111: Y), the CPU 114 executes the front / back position correction execution division determination process (S2112), which will be described later.

[0128] After completing the front / back position correction execution section determination process, the CPU 114 executes the print front / back position correction process similar to the process of S1513 (S2113). After executing the print front / back position correction process, the CPU 114 sets the execution determination number n of print front / back position correction to "0" (S2114). Note that the CPU 114 also sets the execution determination number n of print front / back position correction to "0" (S2114) when the print front / back position correction execution flag F is not "1", i.e., when the print front / back position correction execution flag F is "0" (S2111:N).

[0129] The CPU 114 determines whether printing of all pages of images specified in the print job has been completed (S2107). If not completed (S2107: N), the CPU 114 repeats the processing from S2103 onwards. If completed (S2107: Y), the CPU 114 ends the correction of the print front and back positions.

[0130] 20 is a flowchart showing the process of determining the execution section of the front and back position correction in S2112. First, the CPU 114 determines whether the number of pages TN of image data that can be acquired in advance before printing is equal to or greater than the execution interval number N of pages for the print front and back position correction (S1801).

[0131] If the number of pages TN is equal to or greater than the execution interval number of sheets N (S1801: Y), CPU 114 determines the toner amount category for each page based on the image data (toner information) for TN pages acquired in the process of S2103 (FIG. 19) (S1802). CPU 114 determines the toner amount category for each page based on the toner amount information for N pages to be printed after executing the print front / back position correction, out of the toner information for TN pages. The process of determining the toner amount category from the toner amount is the same as the process of S1603 in FIG. 16. CPU 114 determines the determined toner amount category as the front / back position correction execution category and ends the front / back position correction execution category determination process (S1803). If the number of pages TN is less than the execution interval number of sheets N (S1801: N), the CPU 114 determines all applied toner amount sections as front and back position correction execution sections and ends the front and back position correction execution section determination process (S1805).

[0132] For the sake of simplicity, the image on the front side is not mentioned when determining the amount of misregistration of the print on the back side of the paper, but it is known that the amount of misregistration of the print on the back side actually differs depending on the amount of toner applied to the front side image. Therefore, for example, when there are five toner application amount categories, the amount of misregistration of the print on the back side may have a total of 25 combinations, combining the five toner application amount categories on the front side and the five toner application amount categories on the back side.

[0133] As described above, when performing front-back print position correction, the image forming apparatus 100 according to the present embodiment performs front-back print position correction using an adjustment image for adjusting the toner loading amount according to the content of the print job. In the present embodiment, the toner loading amount category for each page is determined based on the toner loading amount for a predetermined number of pages, and front-back print position correction is performed using an adjustment image corresponding to the determined toner loading amount category. The predetermined number of pages is, for example, the number of pages in one copy when the print job performs printing in multiple copies. Alternatively, the predetermined number of pages is the number of pages of image data that can be acquired in advance before the execution of printing.

[0134] If the predetermined number of pages is equal to or more than a predetermined number (equal to or more than the execution interval number of sheets N), the adjustment image used for front-back print position correction is determined to be the adjustment image corresponding to the toner loading amount category. If the predetermined number of pages is less than the predetermined number (less than the execution interval number of sheets), the adjustment image used for front-back print position correction is determined to be all the adjustment images. As a result, it is possible to reduce the number of adjustment sheets that become waste paper while updating the correction amount corresponding to the toner loading amount to an appropriate value.

Claims

1. Printing means for printing an image on a sheet, Reading means for reading an adjustment image for correcting the printing position of the image printed on the sheet, Calculating means for calculating a correction amount for correcting the printing position based on the reading result of the adjustment image by the reading means, Storage means for storing a plurality of adjustment images with different toner loads, Control means for creating an adjustment sheet on which an adjustment image is printed on a sheet by the printing means every time the number of sheets printed by a printing job reaches a predetermined number, causing the reading means to read the adjustment image from the adjustment sheet, and causing the calculating means to calculate the correction amount, The printing job includes information for printing a plurality of images with a plurality of pages as one part, The control means divides the toner load of the image printed on the sheet into a plurality of toner load categories. When there is no first page among the predetermined number of pages to be printed after the execution of the printing position correction process and the toner loads of all the pages of the first part have been acquired, based on the toner loads of the images of each page of all the pages of the first part, the toner load category of each page is determined, The plurality of adjustment images stored in the storage means correspond to the plurality of toner load categories, The control means determines an adjustment image to be used for calculating the correction amount based on the determined toner load category of each page, An image forming apparatus.

2. The control means is characterized in that when there is the first page among the predetermined number of pages to be printed after the execution of the correction of the printing position, it determines all the pages of the printing job in all toner load categories, The image forming apparatus according to Claim 1.

3. The control means is characterized in that when there is no first page among the predetermined number of pages to be printed after the execution of the printing position correction process and the toner loads of all the pages of the first part have not been acquired, it determines all the pages of the printing job in all toner load categories, The image forming apparatus according to Claim 2.

4. Printing means for printing an image on a sheet, Reading means for reading an adjustment image for correcting the printing position of the image printed on the sheet, Calculating means for calculating a correction amount for correcting the printing position based on the reading result of the adjustment image by the reading means, Storage means for storing a plurality of adjustment images with different toner loads, Each time the number of sheets printed by a printing job reaches a predetermined number, a control means creates an adjustment sheet on which an adjustment image is printed on a sheet by the printing means, causes the reading means to read the adjustment image from the adjustment sheet, and causes the calculating means to calculate the correction amount. The control means divides the toner loading amount of the image printed on the sheet into a plurality of toner loading amount categories, acquires image data that can be acquired prior to printing by the printing job, and if the number of image data acquired prior to printing is equal to or greater than the predetermined number, determines the toner loading amount category of each page for which image data was acquired prior to printing based on the toner loading amount obtained from the acquired image data. The plurality of adjustment images stored in the storage means correspond to the plurality of toner loading amount categories. The control means determines an adjustment image to be used for calculating the correction amount based on the determined toner loading amount category of each page. An image forming apparatus.

5. If the control means acquires image data that can be acquired prior to printing in the printing job and the number of image data acquired prior to printing is less than the predetermined number, the control means determines all pages of the printing job in all toner loading amount categories. The image forming apparatus according to claim 4.

6. The printing means is capable of double-sided printing for printing images on both sides of the sheet. The reading means is capable of reading the adjustment image printed on both sides of the sheet. The calculating means calculates a correction amount for each printing position on the first side and the second side of the sheet based on each reading result of the adjustment image printed on both sides of the sheet by the reading means. The control means aligns the printing positions of the image on the first side and the image on the second side based on the correction amount of each printing position on the first side and the second side. The image forming apparatus according to claim 1 or 4.

7. The adjustment image includes a first mark formed at a position a predetermined distance from the sheet edge and a second mark formed at a position different from the first mark so as not to overlap the first mark. In the plurality of adjustment images, the image density of the first mark is the same and the image density of the second mark is different. The image forming apparatus according to claim 1 or 4.

8. The calculation means calculates the correction amount based on the reading result of the first mark. The image forming apparatus according to claim 7.

Images