Image forming apparatus

Abstract

To provide an image forming apparatus that updates a correction amount in front and back position correction corresponding to a toner placement amount, while reducing waste paper.SOLUTION: An image forming apparatus 100 comprises a CPU 114 that, every time the number of printed sheets reaches a predetermined number in a print job to which execution of correction of a printing position is set, causes a printer 150 to prepare a sheet for adjustment that is a sheet on which images for adjustment are printed, causes a reading device 160 to read the images for adjustment on the sheet for adjustment, and calculates a correction amount for correcting the printing position on the basis of a result of reading the images for adjustment. The CPU 114 determines an image for adjustment to be used from the plurality of images for adjustment different in image density on the basis of the toner placement amount of a page to which correction of the printing position is instructed before performing printing on the page, and corrects the printing position of the image on the page by using a correction amount calculated from a result of reading, which is performed by the reading device 160, of the sheet for adjustment on which the determined image for adjustment is printed.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] When printing on a printed matter using a commercial image forming device, the positions (printing positions) of the images printed on the front and back sides of the paper must be aligned with high precision during double-sided printing. For this reason, the image forming device has a function for aligning the printing positions of the image on the front and back sides of the paper by adjusting the printing position during double-sided printing (hereinafter referred to as a "front and back position correction function"). By having the front and back position correction function, the image forming device can adjust the printing position when printing an image on preprinted paper on which ruled lines and the like are printed in advance, and print the image so that it does not overlap with the ruled lines.

[0003] Front and back position correction using the front and back position correction function must be performed for each type of paper on which the image is printed. This is because the amount of expansion and contraction of paper differs depending on the paper's characteristics, such as the size, basis weight, and material. The optimal amount of correction using front and back position correction varies depending on the amount of expansion and contraction of the paper. Front and back position correction is performed by using a reading device to read an adjustment sheet on which marks for position detection (adjustment images) are printed on the paper to be corrected, and detecting the deviation in the print position based on the results of reading the adjustment images.

[0004] The image forming apparatus detects the misalignment of the print position based on the length from the reference position to the mark obtained from the reading result of the adjustment sheet, for example. A correction amount for correcting the print position is determined based on the detection result of the misalignment of the print position. When performing printing processing using the same type of paper as the paper to be corrected, the image forming apparatus corrects the print position based on the correction amount.

[0005] In addition to the type of paper, the cause of misalignment between the front and back sides of a print is also the amount of toner carried in the toner image printed on the paper. Differences in the amount of toner carried affect the paper transport force when the toner image is transferred to the paper. When there is a large amount of toner carried, the toner causes slippage, reducing the paper transport force, and misalignment of the print position occurs in the direction that the paper shrinks relative to the transport direction.

[0006] In order to suppress the influence of the amount of applied toner, the image forming apparatus disclosed in Patent Document 1 uses adjustment images printed on multiple sheets of paper with different amounts of applied toner to determine the amount of correction for front-back position correction corresponding to the amount of applied toner. As a result, even for printed materials with different amounts of applied toner, correction accuracy is improved by performing front-back position correction corresponding to the amount of applied toner. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2021-135466 A Summary of the Invention [Problem to be solved by the invention]

[0008] Image forming devices with a front-back position correction function generally have a front-back position correction function (hereinafter referred to as "initial front-back position correction") that determines the amount of correction according to the type of paper by correcting the front-back position of the paper to be used before printing. However, even if the print position is corrected using the correction amount determined by the front-back position correction function, the accuracy of the print position correction may decrease due to changes in the image formation environment, such as an increase in temperature inside the image forming device due to mass printing or changes in the moisture absorption state of the paper. For this reason, some image forming devices have a front-back position correction function (hereinafter referred to as "print front-back position correction") that maintains the amount of correction at an appropriate state by performing front-back position correction again at a predetermined page interval during printing.

[0009] In the print front / back position correction performed during printing, if a correction amount corresponding to the amount of applied toner is to be determined, it becomes necessary to output an adjustment sheet corresponding to the amount of applied toner. FIG. 21 is an explanatory diagram of the timing of outputting an adjustment sheet during printing. For example, when performing print front / back position correction every 100 sheets in continuous printing of 300 sheets, print front / back position correction is performed after printing the 100th sheet and the 200th sheet. In this case, if five types of adjustment sheets are required, the number of sheets to be discarded will be 5 sheets x 2 times = 10 sheets. In other words, the more sheets to be printed, the more sheets to be discarded due to print front / back position correction.

[0010] SUMMARY OF THE PRESENTLY PREFERRED EMBODIMENTS In view of the above-mentioned problems, a primary object of the present invention is to provide an image forming apparatus that updates the correction amount of the front / back position correction corresponding to the amount of applied toner while reducing the amount of wasted paper. [Means for solving the problem]

[0011] The image forming apparatus of the present invention includes a printing means for printing an image on a sheet of paper, a reading means for reading an adjustment image for correcting a print position printed on the sheet of paper, a calculation means for calculating a correction amount for correcting the print position based on a result of reading the adjustment image by the reading means, an input means for inputting an instruction as to whether or not to correct the print position for each page of a print job that instructs printing of a plurality of pages of images, a storage means for storing a plurality of adjustment images with different image densities, and a calculation means for calculating a correction amount for correcting the print position each time a predetermined number of pages have been printed by a print job in which the execution of print position correction is set. and a control means for causing the printing means to create an adjustment sheet on which the adjustment image is printed on paper, causing the reading means to read the adjustment image on the adjustment sheet, and causing the calculation means to calculate the correction amount, wherein before printing a page for which correction of the print position is instructed, the control means determines an adjustment image to be used from the plurality of adjustment images based on the amount of toner applied to the page, and corrects the print position of the image of the page using the correction amount calculated from the reading result by the reading means of the adjustment sheet on which the determined adjustment image is printed. Effect of the Invention

[0012] According to the present invention, it is possible to update the correction amount of the front / back position correction corresponding to the amount of applied toner while reducing the amount of wasted paper. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is an overall configuration diagram of a printing system. [Diagram 2] FIG. 1 is a diagram illustrating the configuration of an image forming apparatus. [Diagram 3] FIG. [Figure 4] FIG. 11 is an explanatory diagram of an adjustment image that reproduces shrinkage of paper. [Diagram 5] FIG. [Figure 6] 13 is a diagram showing an example of a paper attribute editing screen. [Figure 7] An explanatory diagram of a paper library. [Figure 8] FIG. 6 is an explanatory diagram of a method for calculating a print position deviation amount. [Figure 9] 13 is a diagram showing an example of a paper type setting screen. [Figure 10] 13A to 13C are diagrams illustrating examples of print position adjustment screens. [Figure 11] 11 is a flowchart showing an initial front and back position correction process. [Figure 12] 4 is a flowchart showing an image forming process. [Figure 13] 11 is a flowchart showing a process for setting an execution interval for print front / back position correction. [Figure 14] 13A and 13B are diagrams illustrating a paper selection screen. [Figure 15] 4A to 4C are diagrams for explaining a method for storing print adjustment page settings. [Figure 16] 11 is a flowchart showing a process of setting a page for performing print front / back position correction. [Figure 17] 6 is a flowchart showing a print front / back position correction process. [Figure 18] 13 is a view showing an example of a print adjustment page setting screen. [Figure 19] 13A and 13B are diagrams illustrating an example of a chart selection screen. [Figure 20] 5A and 5B are diagrams illustrating a method for generating an adjustment image. [Figure 21] 6 is an explanatory diagram of the timing of outputting an adjustment sheet during printing. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0015] 1 is a diagram showing the overall configuration of a printing system having an image forming apparatus according to this 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 communicatively connected via a network 105. The network 105 is a communication line such as a LAN (Local Area Network) or a WAN (Wide Area Network). Note that a plurality of image forming apparatuses 100 and a plurality of host computers 101 may be connected to the network 105.

[0016] The host computer 101 is, for example, a server, and transmits a print job to the image forming apparatus 100 via a network 105. The print job includes various information required 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 copies to be printed, and an instruction for double-sided or single-sided printing.

[0017] Image forming apparatus 100 includes controller 110, operation panel 120, paper feeder 140, printer 150, and reading device 160. Image forming apparatus 100 prints an image on paper using printer 150 based on a print job acquired from host computer 101. Controller 110, operation panel 120, paper feeder 140, printer 150, and reading device 160 are connected to each other via system bus 116 so as to be able to communicate with each other.

[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, a numeric keypad, etc. The output interface includes a display such as an LCD (Liquid Crystal Display), a speaker, etc. An operator can input print jobs, commands, print settings, etc. to the image forming apparatus 100 using the operation panel 120. The controller 110 acquires the print jobs, commands, print settings, etc. input from the operation panel 120. The operation panel 120 can display various setting screens and the status of the image forming apparatus 100 on a display under the control of the controller 110.

[0019] The paper feeder 140 includes a plurality of paper feed stages for storing paper. The paper feeder 140 feeds paper one by one, starting from the topmost paper of a stack of paper, which is a bundle of multiple sheets of paper stacked in the paper feed stages. The paper feeder 140 transports the paper fed from the paper feed stages to the printer 150. The printer 150 generates a printed matter by printing an image (output image) on the paper supplied from the paper feeder 140 based on image data. A specific configuration of the printer 150 will be described later with reference to FIG. 2. The reader 160 reads the printed matter generated by the printer 150 and transmits the reading result to the controller 110. A specific configuration of the reader 160 will be described later with reference to FIG. 2.

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

[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 the control programs and various data such as image data used in the image forming process (printing process). The RAM 113 functions as a system work memory in which the control programs stored in the ROM 112 and the storage 115 are loaded. The CPU 114 executes the control programs loaded in the RAM 113 to comprehensively control the image forming apparatus 100. The modules in the controller 110 are connected to each other via a system bus 116 so as to be able to communicate with each other.

[0022] Fig. 2 is a configuration diagram of the image forming apparatus 100. In addition to the paper feeder 140 and printer 150 described in Fig. 1, the image forming apparatus 100 of this embodiment also includes a reader 160 and a finisher 190. The finisher 190 is a post-processing device that performs predetermined post-processing on printed materials generated by the printer 150. As post-processing, the finisher 190 performs, for example, stapling processing on multiple printed materials and sorting processing on the printed materials.

[0023] Printer 150 includes multiple image forming units. In this embodiment, four image forming units are provided 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 each image forming unit are almost 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 photosensitive body having a photosensitive layer on its surface, and is rotated in the direction of an arrow R1 by a motor (not shown). The charger 220 charges the surface of the photosensitive drum 153. The exposure device 223 irradiates (exposes) the charged surface of the 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 a toner image formed by each image forming unit is transferred. The intermediate transfer belt 154 rotates in the direction of the arrow R2. The yellow, magenta, cyan, and black toner images formed by each image forming unit are transferred onto the intermediate transfer belt 154 so as to be superimposed on each other at timings 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 onto the intermediate transfer belt 154 is transported in the direction of the arrow R2 and transferred onto a sheet fed from the paper feeder 140 at a nip portion formed by the intermediate transfer belt 154 and a transfer roller 221.

[0026] The paper feeder 140 includes a plurality of paper feed stages 140a, 140b, 140c, 140d, and 140e that store paper. Paper of a type specified by a print job is fed from one of the paper feed stages 140a, 140b, 140c, 140d, and 140e according to the timing at which each image forming unit starts forming an image. The fed paper is transported to a nip portion between the intermediate transfer belt 154 and the transfer roller 221 with the timing adjusted so that the toner image on the intermediate transfer belt 154 is transferred to a predetermined position.

[0027] The printer 150 has a first fixing device 155 and a second fixing device 156 that fix the toner image transferred to the paper by applying heat and pressure to the paper. The first fixing device 155 has a fixing roller with a heater inside and a pressure belt for pressing the paper against the fixing roller. The fixing roller and the pressure belt are driven by a motor (not shown) to sandwich and transport the paper. The second fixing device 156 is disposed downstream of the first fixing device in the paper transport direction. The second fixing device 156 is used to increase the gloss of the image on the paper that has passed through the first fixing device 155 and to ensure fixability. The second fixing device 156 has a fixing roller with a heater inside and a pressure roller with a heater inside. The fixing roller and the pressure roller are driven by a motor (not shown) to sandwich and transport the paper.

[0028] Depending on the type of image to be printed (type of photo, text, etc.) and the type of paper, the second fixing device 156 is not used. In this case, the paper that has passed through the first fixing device 155 is not transported to the second fixing device 156, but is transported to the transport path 130. For this reason, a flapper 131 that guides the paper to either the transport path 130 or the second fixing device 156 is provided between the first fixing device 155 and the second fixing device 156.

[0029] The paper that has passed through either the second fixing device 156 or the transport path 130 is transported to either the transport path 135 or the discharge path 139. For this purpose, a flapper 132 is provided at a point where the transport path 135 and the discharge path 139 branch off. For example, in a double-sided printing mode, the flapper 132 guides a paper sheet with an image printed on its first side (front side) to the transport path 135, and guides a paper sheet with images printed on both sides to the discharge path 139. For example, in a face-up discharge mode, the flapper 132 guides a paper sheet with an image printed on its front side to the discharge path 139. For example, in a face-down discharge mode, the flapper 132 guides a paper sheet with an image printed on its front side to the transport path 135. Also, the flapper 132 guides a paper sheet with an adjustment image for adjusting the print position printed on its first side (front side) to the transport path 135 in order to print an adjustment image for adjusting the print position on its second side (back side).

[0030] The paper guided to the transport path 135 is transported to the reversing unit 136. The transport operation of the paper transported to the reversing unit 136 is temporarily stopped, and then the transport direction of the paper is reversed. The paper whose transport direction has been reversed is transported to either the transport path 138 or the transport path 135. A flapper 133 is provided at the branch point between the transport path 138 and the transport path 135. The flapper 133 guides the paper to either the transport path 138 or the transport path 135. For example, in the double-sided printing mode, the flapper 133 guides the paper whose transport direction has been reversed to the transport path 138, and in the face-down discharge mode, the flapper 133 guides the paper whose transport direction has been reversed to the transport path 135. The paper transported to the transport path 135 by the flapper 133 is guided to the discharge path 139 by the flapper 134. Furthermore, the flapper 133 guides the paper, whose conveying direction has been reversed, to a conveying path 138 in order to print an adjustment image on the second surface (reverse surface) of the paper.

[0031] The paper conveyed to the conveying 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 paper is turned over by the reversing portion 136, the toner image is transferred to the second surface (reverse surface) of the paper as it passes through the nip portion.

[0032] A reading device 160 that reads an adjustment image printed on a sheet of paper is connected downstream of the printer 150 in the paper transport direction. The sheet of paper on which the image is printed is sent as a printed matter to the reading device 160 via an ejection path 139. The sheet of paper (printed matter) supplied from the printer 150 to the reading device 160 is transported along a transport path 313. The reading device 160 includes a sheet detection sensor 311 and line sensors 312a, 312b along the transport path 313. The reading device 160 reads the sheet of paper on which the adjustment image is printed by the printer 150 with the line sensors 312a, 312b while transporting the sheet of paper along the transport path 313.

[0033] Details of the adjustment image will be described later. In the following description, the paper on which the adjustment image is printed is referred to as an "adjustment sheet." Paper on which an image other than the adjustment image (an output image instructed by a print job) is printed is also transported to the finisher 190 along the transport 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 in the conveying direction of the adjustment sheet conveyed on the conveying path 313. The controller 110 can obtain the amount of skew of the sheet based on the timing of detection of the leading edge of the sheet by the sheet detection sensor 311.

[0035] The line sensors 312a and 312b are disposed at positions facing each other across the conveyance path 313. The line sensors 312a and 312b each read an adjustment image on an adjustment sheet. The adjustment image is printed, for example, on both the front and back sides of the paper. While the paper is conveyed between the line sensors 312a and 312b, the adjustment images printed on both sides are read at once.

[0036] When performing print position adjustment, image forming apparatus 100 detects the amount of deviation of the print position (image forming position) of the adjustment image from the ideal position based on the results of reading the adjustment image by line sensors 312a and 312b. Controller 110 controls image formation processing based on the detected amount of deviation of the print position (image forming position) so that the print position (image forming position) on the paper becomes the ideal position. Front-back position adjustment is also performed to adjust the print positions on the front and back sides of the paper based on the results of print position adjustment.

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

[0038] (Image for adjustment) FIG. 3 is an explanatory diagram of an adjustment image. The printer 150 prints an adjustment image 700 on the front side of the paper, and prints an adjustment image 701 on the back side of the paper. The adjustment images 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 a predetermined distance from the edge of the paper. The plurality of correction marks 720 are formed with the same image density using black toner. By printing in black, the difference between the reflected light intensity from the correction marks 720 and the reflected light intensity from the paper increases, so that the contours of the correction marks 720 can be detected with high accuracy from the reading result of the reading device 160.

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

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

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

[0042] The amount of print position deviation is calculated based on length (A) to length (V). However, according to an experiment by the inventor, it was found that the amount of deformation of the paper caused by the adjustment image illustrated in FIG. 3 is different from the amount of deformation of the paper on which an output image corresponding to a print job is actually printed. This is because the amount of deformation of the paper varies depending on the amount of applied toner. The amount of applied toner of the paper on which an output image is printed varies depending on the type of image. For example, when a photo image is printed on the entire surface of the paper, the amount of applied toner of the paper is greater than the amount of applied toner of the adjustment sheet. Therefore, the amount of correction calculated from the amount of print position deviation measured using an adjustment sheet on which only the correction mark 720 is printed may not be able to correct the print position of the output image to an ideal position.

[0043] In this embodiment, a mark other than the correction mark 720 is formed at a position that does not overlap the correction mark 720, and the print position adjustment is performed using an adjustment image that is suitable for the amount of toner applied to the paper on which the output image is actually printed. In this embodiment, the amount of toner applied to the paper is divided into five sections, and an adjustment image corresponding to each of the toner amount sections is printed on the adjustment sheet. Note that even if another mark is printed at a position that does not overlap the correction mark 720, it is possible to calculate the amount of print position deviation.

[0044] FIG. 4 is an explanatory diagram of an adjustment image that reproduces the shrinkage of paper caused by differences in the amount of applied toner. The image forming apparatus 100 adjusts the print position using an adjustment image suitable for the amount of applied toner of the output image from among five types of adjustment images 70a, 70b, 70c, 70d, and 70e with different image densities shown in FIG. The toner amounts (image densities) of the adjustment images 70a to 70e correspond to the toner amount classifications 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. The adjustment images for each amount of applied toner do not need to be limited to five types as long as they have different image densities.

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

[0046] The marks 730, 731, 732, and 733 are images of the same area. The marks 730, 731, 732, and 733 are formed based on different image signal values, and therefore have different image densities. The image densities of the marks 730, 731, 732, and 733 are lowest for the mark 730, followed by the marks 731, 732, and 733. Therefore, the adjustment image 70e has the largest amount of applied toner among the adjustment images 70a, 70b, 70c, 70d, and 70e. The adjustment image 70a has the smallest amount of applied toner among the adjustment images 70a, 70b, 70c, 70d, and 70e.

[0047] (Paper Library) Paper sheets that can be used by the image forming apparatus 100 are managed by a database. This database is called 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. Paper information stored in the paper library is read and written as necessary.

[0048] 5 is a view showing an example of an edit screen for an operator to edit information about paper sheets stored in the paper library. This edit screen 400 is displayed on the operation panel 120 of the image forming apparatus 100. The edit screen 400 includes a paper list 410, an add new button 420, an edit button 421, a delete button 422, and a select button 423.

[0049] The paper list 410 displays a list of papers managed by the paper library 600. Columns 411 to 417 display attribute information that indicates the characteristics of the paper. Column 411 displays the paper name. The paper name is information set by the operator so that the operator can identify the type of paper. Columns 412 and 413 display the paper size. Column 412 displays the paper length in the short direction, and column 413 displays the paper length in the long direction. Column 414 displays the basis weight of the paper.

[0050] Column 415 displays information that allows the operator to identify the surface property of the paper. The information that allows the operator to identify the surface property of the paper is information related to the physical characteristics of the paper surface. For example, paper displayed as "coated" in column 415 indicates paper that has been subjected to a surface treatment to increase gloss. Furthermore, paper displayed as "embossed" in column 415 indicates paper that has been subjected to a textured finish. Furthermore, paper displayed as "plain paper" in column 415 indicates paper that has not been subjected to any special processing. Column 416 displays the color of the paper.

[0051] When editing paper information, 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 unselected papers. For example, the selected paper is displayed brighter than unselected papers. When "XYZ Paper Color 81" is selected, as illustrated in FIG. 5, the row for "XYZ Paper Color 81" is displayed in a different way from the rows of other unselected papers. Note that if the number of papers managed in the paper library is greater than the number that can be displayed at one time in the paper list 410, the operator can operate the scroll bar 417 to select other papers.

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

[0053] By pressing the new addition button 420 or the edit button 421 on the edit screen 400, a paper attribute edit screen for inputting paper information is displayed on the operation panel 120. Fig. 6 is a view showing an example 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 end edit button 520, and a cancel button 521.

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

[0055] Combo box 505 is an area for specifying the surface properties of the paper. The operator specifies the surface properties of the paper from among multiple types of surface properties. Information on the multiple types of surface properties is registered in advance, and is specified from a list displayed in a pull-down menu. 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 the multiple colors is registered in advance, and is specified from a list displayed in a pull-down menu. Check box 507 is a specification area for specifying whether the paper is preprinted paper. If the paper is preprinted paper, the operator checks check box 507.

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

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

[0058] Rows 601 to 605 represent paper information 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 properties of the paper. Column 612 represents the paper length in the short direction of the paper, column 613 represents the paper length in the long direction of the paper, column 614 represents the paper basis weight, and column 615 represents the surface property of the paper. Column 616 represents the paper color. Column 617 represents whether the paper is preprinted paper or not.

[0059] Columns 618 to 627 represent the amount of print misalignment on the front and back sides of the paper, respectively. The amount of print misalignment is a value that quantitatively represents the misalignment between a predicted print area predicted from the results of reading the adjustment image and an ideal print area. In this embodiment, the amount of applied toner of an image to be printed on paper is divided into five toner amount categories, and the amount of print misalignment when an image belonging to each toner amount category is printed is stored.

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

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

[0062] The amount of print position deviation is expressed by parameters such as a right-angle correction amount, a trapezoid correction amount, a lead position, a side position, a magnification in the long direction, and a magnification in the short direction, for example. The right-angle correction amount represents the amount of deviation of any corner of the print area from a right angle. For example, the right-angle correction amount is calculated by calculating an ideal perpendicular line to a straight line printed in the long direction of the print area, and the amount of deviation between the ideal perpendicular line and a straight line printed in the short direction. The trapezoid correction amount represents the amount of deviation due to expansion and contraction of the paper. For example, the trapezoid correction amount is the amount of deviation between a straight line printed in the short direction from the print start position on the paper to the short-side rear end, and a straight line printed in the short direction from the position of the long-side rear end of the paper to the short-side rear end.

[0063] The lead position represents the amount of misalignment of the print position in the short direction relative to the paper. The side position represents the amount of misalignment of the print position in the long direction relative to the paper. The lead position is adjusted by changing the print start position of the image, starting from the leading edge of the paper in the transport direction. The side position is adjusted by changing the print start position of the image, starting from the edge of the paper parallel to the transport direction. Specifically, the exposure unit 223 adjusts the start timing of irradiating the photosensitive drum 153 with laser light, thereby adjusting the lead position and side position. For example, the CPU 114 controls the exposure unit 223 to adjust the start timing of irradiating the laser light.

[0064] The magnification in the short side direction represents the deviation (magnification) of the length of the actual print area in the short side direction from the ideal length in the short side 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.

[0065] The longitudinal magnification represents the deviation (magnification) of the length of the actual print area in the longitudinal direction from the ideal length in the longitudinal direction. Specifically, the longitudinal magnification is adjusted by controlling the clock frequency of the laser light when the exposure unit 223 modulates the laser light based on the image data. For example, the CPU 114 controls the exposure unit 223 to control the clock frequency. Alternatively, the CPU 114 may perform image processing on the image data so that the print position of the output image becomes the ideal print position. The image processing for making the print position of the output image the ideal print position is, for example, image processing such as Affie conversion.

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

[0067] The initial value of each item of the print position deviation amount is “0.” When a new paper is registered in the paper library 600, or when a paper is registered but the print position has not been adjusted, the initial value is used as the print position deviation amount.

[0068] 8 is an explanatory diagram of a method for calculating the amount of print positional deviation. The amount of print positional deviation is obtained based on the actual measurement values ​​(A) to (V) measured from the results of reading the adjustment image (see FIG. 3).

[0069] Items 801 to 812 are items that indicate the amount of print misalignment. Parameters of the amount of print misalignment obtained from the adjustment image 700 include a lead position 801, a side position 802, a magnification in the longitudinal direction 803, a magnification in the lateral direction 804, a right-angle correction amount 805, and a trapezoid correction amount 806. Parameters of the amount of print misalignment obtained from the adjustment image 701 include a lead position 807, a side position 808, a magnification in the longitudinal direction 809, a magnification in the lateral direction 810, a right-angle correction amount 811, and a trapezoid correction amount 812.

[0070] The measurement values ​​820 and print position deviation amounts 822 of the adjustment images 700 and 701 are calculated based on the same formula. The same ideal values ​​are set for the same types of parameters of the adjustment images 700 and 701. The measurement values ​​820 are calculated based on formulas set for each item from the actual measured values ​​of lengths (A) to (V) shown in FIG.

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

[0072] The measured value 820 of the magnification 803 (809) in the longitudinal direction corresponds to the average value of the distance between the correction marks 720 aligned on the same line in the longitudinal direction. The measured value 820 of the magnification 804 (810) in the lateral direction corresponds to the average value of the distance between the correction marks 720 aligned on the same line in the lateral direction.

[0073] The measurement value 820 of the right angle correction amount 805 (811) corresponds to the amount of deviation S, T (U, V) in the short direction of the correction mark at the rear end of the paper in the transport direction from the reference line when the perpendicular line of the straight line connecting the correction marks 720 at the leading end of the paper in the transport direction is used as the reference line. The measurement value 820 of the trapezoid correction amount 806 (812) corresponds to the difference between the distance between the correction marks 720 lined up at the leading end of the paper in the transport direction and the distance between the correction marks 720 lined up at the trailing end of the paper in the transport direction.

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

[0075] Column 822 shows a formula for calculating the final print position deviation amount for each item based on the measured value 820 and ideal value 821. The print position deviation amount for the lead position and side position is calculated by subtracting the ideal value from the measured value (unit: mm). The print position deviation amount for the longitudinal magnification and lateral magnification is calculated by subtracting the ideal value from the measured value and dividing the result by the ideal value (unit: %). For the right angle correction amount and trapezoidal correction amount, the measured value is used as the correction amount as is. Each calculated print position deviation amount is saved in the paper library 600 (see FIG. 7).

[0076] (Paper type settings) Fig. 9 is a view showing an example of a paper type setting screen 900 displayed on operation panel 120. Paper type setting screen 900 includes a paper feed stage paper setting status 901, a print position adjustment button 902, and a paper registration button 903. Paper feed stage paper setting status 901 displays the paper type 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, Recycle 1" is registered in paper feed stage 140a. "ABC Paper, Recycle 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 print position adjustment button 902 is a button for transitioning to a print position adjustment screen described below. The paper registration button 903 is a button for registering a paper type to a selected paper feed tray. When the paper registration button 903 is pressed, the paper library editing screen 400 of FIG. 5 is displayed. When the selection button 423 on the paper library editing screen 400 is pressed, the paper selected on the paper library editing screen 400 is registered to the paper feed tray selected by the operator. Note that the print position adjustment button 902 and the paper registration button 903 cannot be pressed if a paper feed tray is not selected in the paper feed tray paper setting status 901.

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

[0080] An initial adjustment screen 1010 in FIG. 10(b) that is displayed when the initial adjustment button 1001 is pressed includes a paper feed tray selection box 1011, an execute button 1012, and a cancel button 1013. The paper feed tray selection box 1011 is a combo box for specifying a paper feed tray. In this embodiment, the paper feed tray selection box 1011 allows selection of five paper feed trays, paper feed tray 1 to paper feed tray 5 shown in FIG. The paper feed tray selection box 1011 also displays the paper type registered for the paper feed tray.

[0081] The execute button 1012 is a button for performing initial front and back position correction, described below, using the adjustment images 70a to 70e in FIG. 4 for the paper in the paper feed tray selected in the paper feed tray selection box 1011. When the execute button 1012 is pressed, the controller 110 starts the initial front and back position correction process. The cancel button 1013 is a button for canceling the initial front and back position correction. When the cancel button 1013 is pressed, the initial front and back position correction process is canceled and the screen returns to the print position adjustment screen 1000.

[0082] 10C, which is displayed when the print adjustment button 1002 is pressed, includes a print adjustment enable check box 1021, a number setting box 1022, an OK button 1023, and a cancel button 1024. The print adjustment enable check box 1021 is a check box for switching between enabling and disabling print front / back position correction, which will be described later. The number setting box 1022 is a text box for inputting the number of prints at which the print front / back position correction is performed.

[0083] When the print adjustment enable check box 1021 is checked, print front / back position correction is performed every time the number of sheets set in the number setting box 1022 is printed. The print front / back position correction is a function for maintaining the correction amount at an appropriate state by performing the front / back position correction again at a predetermined page interval during printing. The print front / back position correction adjusts the correction amount for correcting the print position every time the printer 150 generates a predetermined number of printed sheets. When the print adjustment enable check box 1021 is not checked, 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 screen returns to the print position adjustment screen 1000. When the cancel button 1024 is pressed, the print adjustment settings are not saved and the screen returns to the print position adjustment screen 1000.

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

[0085] 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 print position adjustment button 902 (S1202: N). When the print position adjustment button 902 is pressed (S1202: Y), the CPU 114 displays the print position adjustment screen 1000 of FIG. 10(a) on the operation panel 120 (S1203). The CPU 114 waits until any of the initial adjustment button 1001, the print adjustment button 1002, and the back button 1003 is pressed (S1204: N).

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

[0087] When the initial adjustment button 1001 is pressed (S1205: Y), the CPU 114 displays the initial adjustment screen 1010 of FIG. 10B on the operation panel 120 (S1206). The operator uses the initial adjustment screen 1010 to select the paper feed tray that contains the paper for which initial front / back position correction is to be performed. The CPU 114 waits until the execute button 1012 or the cancel button 1013 on the initial adjustment screen 1010 is pressed (S1208: N).

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

[0089] For example, when the operator selects "DEF Paper Embossed Paper A-1" of the paper feed stage 3, the CPU 114 reads image data of the adjustment image 70a from the storage 115 (S1211). The CPU 114 prints the adjustment image 70a on the paper fed from the paper feed stage 140c by the printer 150 based on the read image data (S1212). The printer 150 prints the adjustment image 70a on the front side of the paper, and then conveys the paper toward the inverting unit 136. The printer 150 inverts the paper in the inverting unit 136, conveys the paper to the conveying path 138, and prints the adjustment image 70a again on the back side. The adjustment image 70a is printed on both sides to create an adjustment sheet. The printer 150 then 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). The CPU 114 reads the adjustment images 70a on both sides by the line sensors 312a and 312b while transporting the adjustment sheet to the transport path 313 of the reading device 160. The adjustment sheet discharged from the reading device 160 is discharged to the discharge tray of the finisher 190.

[0091] CPU 114 obtains the reading result of the adjustment sheet from reading device 160, and calculates the amount of print position deviation from the reading result based on the calculation method of Fig. 8 (S1214). CPU 114 stores the calculated amount of print position deviation in paper library 600 in association with the paper of the paper feed tray selected by the operator (S1215). The processes of S1211 to S1215 end the initial front and back position correction using one adjustment image.

[0092] The CPU 114 determines whether the initial front and back position correction is completed for all the adjustment images 70a to 70e (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 and back position correction.

[0093] If the initial front-back position correction is completed for all adjustment images (S1216: Y), the CPU 114 ends the process of the initial front-back position correction. By the initial front-back position correction, the print position deviation amount of each toner amount classification of "DEF paper embossed paper A-1" 603 is stored in the paper library 600 of FIG. 7. 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 (reverse 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 (reverse 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 (reverse side) 623. The amount of print misalignment calculated by reading the adjustment image 70d is stored in a print misalignment amount (front side) 624 and a print misalignment amount (reverse side) 625. The amount of print misalignment calculated by reading the adjustment image 70e is stored in a print misalignment amount (front side) 626 and a print misalignment amount (reverse side) 627.

[0094] (Image formation processing) 12 is a flowchart showing an image forming process by the image forming apparatus 100. Each step of this flowchart is realized by the CPU 114 reading out 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 about the type of paper included in the print job (S100). The CPU 114 acquires toner application amount information calculated from the image data of each page of the print job (S101). Specifically, the CPU 114 acquires an image signal value T from the image data of each page of the print job as the toner application amount information. The image signal value T is a value that indicates 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 of the paper specified by the print job is stored (S102). For example, the CPU 114 refers to the paper library 600 and determines whether the amount of print position deviation of the paper specified by the print job is a value other than the initial value 0.

[0097] If the amount of print position deviation is stored (the amount of print position deviation of the paper is a value other than the initial value 0) (S102: Y), CPU 114 acquires the amount of print position deviation of 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 develops 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 prints an image on the paper based on the image data with the print position corrected (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 forming process. By performing the image forming process on a print page basis, it is possible to correct the print position based on the print position deviation amount corresponding to the toner amount for each page to be printed. This makes it possible to correct the print position with high accuracy for each page.

[0100] (Setting the interval for executing print front / back position correction) 13 is a flowchart showing the process of setting the execution interval for print front / back position correction. The 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 is performed as the print adjustment setting process of S1209 in FIG.

[0101] When the print adjustment button 1002 is pressed in the process of S1207 in FIG. 11, 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 in FIG. 11.

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

[0103] 14 is an explanatory diagram of a selection screen for paper on which the operator performs print front / back position correction.

[0104] A print job list 1410 and a job action 1420 are displayed on a job print application screen 1400 illustrated in FIG. 14(a). The print job list 1410 displays print jobs input from the host computer 101 in a list format. The print job list 1410 displays, for each print job, the job name, the number of prints (number of pages), the number of copies, and whether the print is single-sided or double-sided. The job action 1420 displays an action to be executed for the print job displayed on the print job list 1410. The job action 1420 includes a print button 1421, a RIP button 1422, a print adjustment button 1423, and a job property button 1424.

[0105] The print button 1421 is a button for causing the image forming apparatus 100 to print a print job selected by an operator from the print job list 1410. The RIP button 1422 is a button for causing the image forming apparatus 100 to render a print job selected by an operator from the print job list 1410. The print adjustment button 1423 is a button for setting correction of the print front / back position of a sheet specified by a print job selected by an operator from the print job list 1410. When the print adjustment button 1423 is pressed, the operation panel 120 displays a print adjustment page setting screen 1450 exemplified in FIG. 14B. The job property button 1424 is a button for displaying the print settings of a print job selected by an operator from the print job list 1410. When the job property button 1424 is pressed, the operation panel 120 displays a job setting list (not shown). The job setting list includes information indicating the number of copies to be printed, whether single-sided printing or double-sided printing, and the like.

[0106] When no print job is selected from the print job list 1410, the display on the operation panel 120 does not change even when the print button 1421, the RIP button 1422, the print adjustment button 1423, and the job properties button 1424 are pressed.

[0107] A print adjustment page setting screen 1450 shown in FIG. 14(b) includes a job display section 1460 which is a screen that displays the settings of the selected print job (number of pages, number of copies, single-sided or double-sided printing, etc.). The print adjustment page setting screen 1450 also includes a print front / back position correction page list 1461 which is a page list of the selected print job and is displayed for each pair of front and back pages. If the page list displayed in the print front / back position correction page list 1461 cannot be displayed all at once, a scroll bar 1462 is displayed. The operator can operate the scroll bar 1462 to check the entire page list.

[0108] In addition, print adjustment page setting screen 1450 includes print front / back position correction selection buttons 1463 (1463a to 1463e), a set all pages button 1464, a cancel all pages setting button 1465, an enter button 1470, and a cancel button 1471.

[0109] The print front / back position correction selection buttons 1463 (1463a to 1463e) are buttons for setting whether or not to perform print front / back position correction for each page displayed in the print front / back position correction page list 1461. The print front / back position correction selection button 1463 is configured to be displayed as a so-called toggle. For this reason, when the print front / back position correction selection button 1463 is pressed while displaying "OFF", it switches to display "ON", and when pressed while displaying "ON", it switches to display "OFF". Although only five print front / back position correction selection buttons 1463 are displayed in the figure, there are the same number of buttons as the number of pages (sheets) of the selected print job. By scrolling the scroll bar 1462, the print front / back position correction selection button 1463f and subsequent buttons (not shown) are displayed together with the page list.

[0110] The select all pages button 1464 is a button for setting all pages of the selected print job to perform front / back position correction all at once. Pressing the select all pages button 1464 switches the print front / back position correction selection button 1463 for all pages to display "ON". The deselect all pages button 1465 is a button for setting all pages of the selected print job not to perform front / back position correction all at once. Pressing the deselect all pages button 1465 switches the print front / back position correction selection button 1463 for all pages to display "OFF".

[0111] Note that the print front / back position correction selection button 1463, the set all pages button 1464, and the cancel all page setting button 1465 can only be pressed for a double-sided print job. Therefore, for a single-sided print job, the display on the operation panel 120 does not change even if the print front / back position correction selection button 1463, the set all pages button 1464, and the cancel all page setting button 1465 are pressed.

[0112] When the decision button 1470 is pressed, the print adjustment page settings are saved in the RAM 113, and the display of the operation panel 120 returns to the job print application screen 1400. When the cancel button 1471 is pressed, the print adjustment page settings are not saved, and the display of the operation panel 120 returns to the job print application screen 1400.

[0113] Fig. 15 is an explanatory diagram of a method for storing print adjustment page settings set for each print job on print adjustment page setting screen 1450. Here, the settings for print job 1 in Fig. 14(b) are used as an example for explanation. Fig. 15(a) shows the output image of print job 1. Fig. 15(b) is a classification table for determining the toner amount classification from the image signal value T of the output image. Fig. 15(c) shows a table of execution information for print front / back position correction for each print job.

[0114] As shown in Fig. 15(a), print job 1 is double-sided printing, with odd-numbered pages being images on the front side and even-numbered pages being images on the back side. Print job 1 is a 50-page job, but for convenience of explanation, only pages 1 to 10 will be explained. However, it goes without saying that the same applies to the subsequent pages.

[0115] Output image 1500a is the output image of the first page of print job 1. There is blank space at the top, bottom, left and right edges. Output image 1500b is the output image of the second page of print job 1. Output image 1501a is the output image of the third page, and output image 1501b is the output image of the fourth page. Output image 1502a is the output image of the fifth page, and output image 1502b is the output image of the sixth page. Output images 1501a, 1501b, 1502a, and 1502b each display text. Output image 1503a is the output image of the seventh page, and output image 1503b is the output image of the eighth page. Output image 1504a is the output image of the ninth page, and output image 1504b is the output image of the tenth page. Output images 1503a, 1503b, 1504a, and 1504b each display an image such as a photograph.

[0116] A method of determining a toner amount category from the toner amount of each output image using the toner amount category table 1520 in FIG. 15(b) will be described. The toner amount category table 1520 is stored in advance in the ROM 112. The CPU 114 determines the toner amount category of the page by comparing the image signal value T of each page of the print job acquired in the process of S101 in FIG. 12 with a threshold value previously set in the toner amount category table 1520. For example, when the image signal value of each page of the print job 1 is 50%, the toner amount category of each page is determined to be "3". Note that the toner amount category table 1520 is stored in the ROM 112, but may be stored in other non-volatile memory such as the storage 115 or an EEPROM.

[0117] The table of execution information for print front / back position correction in Fig. 15(c) is stored in the RAM 113, and is a setting table that stores execution information for print front / back position correction for each print job. The print front / back position correction setting table 1550 is a table that is configured with page numbers 1560, print front / back position correction execution page flags Fp, and image data for adjustment images 1562 (front side 1562a, back side 1562b). The print front / back position correction setting table 1550 is stored in the RAM 113 for each print job. The print front / back position correction setting table 1550 may be stored independently in the RAM 113, or may be stored as one of the job properties (not shown).

[0118] In print job 1 in FIG. 14(b), for "pages 1-2," "pages 3-4," and "pages 5-6," the print front / back position correction selection button 1463 is displayed as "OFF," meaning that no print front / back position correction is performed. Therefore, the print front / back position correction execution page flag Fp is set to "0." For "pages 7-8" and "pages 9-10," the print front / back position correction selection button 1463 is displayed as "ON," meaning that print front / back position correction is performed. Therefore, the print front / back position correction execution page flag Fp is set to "1."

[0119] Focus on a page where the print front / back position correction implementation page flag Fp is "1". When the image signal value T of the output image 1503a of the 7th page in FIG. 15A is 30%, the toner amount category is "toner amount category 2" according to the toner amount category table 1520. Therefore, the adjustment image (front side) 1562a stores an adjustment image of "toner amount category 2". At this time, the adjustment image may be stored as image data or reference information (so-called address information, pointer) of the image data of the adjustment image in FIG. 4. Similarly, when the image signal value T of the output image 1503b of the 8th page in FIG. 15A is 90%, the adjustment image of "toner amount category 5" is stored in the adjustment image (rear side) 1562b. When the image signal value T of the output image 1504a of the 9th page is 85%, the adjustment image of "toner amount category 4" is stored in the adjustment image (front side) 1562a. When the image signal value T of the output image 1504b of the 10th page is 55%, an adjustment image of "toner amount category 3" is stored in the adjustment image (reverse side) 1562b.

[0120] The table of execution information for print front / back position correction may be stored in storage 115. The table of execution information for print front / back position correction may be stored in both RAM 113 and storage 115, or in other memory such as an EEPROM. The thresholds of toner application amount classification table 1520 are not limited to the example shown here, and may be changed as appropriate.

[0121] 16 is a flowchart showing an execution page setting process for print front / back position correction executed by CPU 114 of image forming apparatus 100. Control in each step of this flowchart is realized by CPU 114 reading and executing a program stored in ROM 112. This process is performed before a print job is started.

[0122] When the operator uses the operation panel 120 to request the display of the job print application screen 1400 of Fig. 14(a), the CPU 114 displays the job print application screen 1400 on the operation panel 120 (S1601). The CPU 114 waits until the operator selects a print job and presses the print adjustment button 1423 (S1602: N). Here, a description of the case where other buttons included in the job action 1420 (print button 1421, RIP button 1422, job property button 1424) are pressed will be omitted. Note that the print job selected by the operator is a job instructing the printing of a multi-page image.

[0123] When the print adjustment button 1423 is pressed (S1602: Y), the CPU 114 displays the print adjustment page setting screen 1450 of FIG. 14B on the operation panel 120 (S1603). The CPU 114 waits until the print front / back position correction selection button 1463 is appropriately set and the decision button 1470 or the cancel button 1471 of the print adjustment page setting screen 1450 is pressed (S1604: N, S1605: N). When the cancel button 1471 is pressed (S1604: N, S1605: Y), the CPU 114 does not update the value of the print front / back position correction execution page flag Fp of FIG. 15C, returns to the process of S1601, and displays the job print application screen 1400.

[0124] When the enter button 1470 is pressed (S1604: Y), the CPU 114 updates the value of the print front / back position correction implementation page flag Fp of each page according to the setting of the print front / back position correction selection button 1463, and stores the value in the RAM 113 (S1606). That is, for a page for which the print front / back position correction selection button 1463 displays "OFF", the print front / back position correction implementation page flag Fp is set to "0". For a page for which the print front / back position correction selection button 1463 displays "ON", the print front / back position correction implementation page flag Fp is set to "1".

[0125] CPU 114 determines whether the value of the print front / back position correction execution page flag Fp of each updated page is "1" (S1607). If the value of the print front / back position correction execution page flag Fp is "1" (S1607: Y), CPU 114 refers to toner amount classification table 1520 in ROM 112 and determines the adjustment image for that page (S1608).

[0126] When the value of the print front / back position correction execution page flag Fp is "0" (S1607: N), or when an adjustment image is determined, CPU 114 judges whether or not an adjustment image has been determined for all pages of the selected print job (S1609). When there is a page for which an adjustment image has not been determined (S1606: N), CPU 114 refers to the print front / back position correction execution page flag Fp of the next page in print front / back position correction setting table 1550 in FIG. 15C, and returns to the process of S1607. When adjustment images have been determined for all pages (S1609: Y), CPU 114 ends the print front / back position correction execution page setting process.

[0127] (Print front and back position correction) 17 is a flowchart showing a print front / back position correction process executed by CPU 114 of image forming apparatus 100. Control in each step of this flowchart is realized by CPU 114 reading and executing a program stored in ROM 112.

[0128] When the operator presses the print button 1421 of the job action 1420 on the job print application screen 1400 in Fig. 14(a), the CPU 114 starts a print job (S1701). The CPU 114 determines whether the print job to be executed is double-sided printing (S1702). If it is double-sided printing (S1702: Y), the CPU 114 determines whether the print front / back position correction implementation flag F in the RAM 113 is "1" (S1703).

[0129] As described above, the print front / back position correction execution flag F is set by the print adjustment enable checkbox 1021 on the print adjustment screen 1020 of FIG. 10C. When the print front / back position correction execution flag F is "1" (S1703: Y), the print front / back position correction is performed. In this case, the CPU 114 determines whether the print front / back position correction execution number counter n stored in the RAM 113 is equal to or greater than the print front / back position correction execution interval number N (S1704). As described above, the print front / back position correction execution interval number N is set by the number setting box 1022 on the print adjustment screen 1020 of FIG. 10C.

[0130] When the print front / back position correction implementation counter n is less than the print front / back position correction implementation interval number N (S1704: N), the CPU 114 increments the print front / back position correction implementation counter n by 1 and stores it in the RAM 113 (S1714). When the print front / back position correction implementation counter n is equal to or greater than the print front / back position correction implementation interval number N (S1704: Y), the CPU 114 references the page numbers 1560 in the print front / back position correction setting table 1550 in Fig. 15C in ascending order (S1705). The CPU 114 determines whether an adjustment image 1562 is registered for the referenced page number (S1706).

[0131] If an adjustment image 1562 is registered (S1706: Y), CPU 114 reads out image data of adjustment image 1562 of the page (S1707). The image data of adjustment image 1562 read out here is determined by the processing of FIG. 16. CPU 114 prints the image of the front side (adjustment image 1562a) and the image of the back side (adjustment image 1562b) of the read adjustment image 1562 of the page by double-sided printing (S1708). That is, CPU 114 controls printer 150 to feed paper of the same type as the page from paper feed stage 140 and generate an adjustment sheet.

[0132] For example, if the type of paper for the page is "DEF Paper Embossed Paper A-1," printer 150 prints the read adjustment image 1562a on the first side (front side) of the paper fed from paper feed stage 140c. Next, printer 150 inverts the paper in inversion unit 136, and then prints adjustment image 1562b on the second side (back side) of the paper. Printer 150 conveys the adjustment sheet thus generated to reading device 160.

[0133] The CPU 114 controls the reading device 160 to read the adjustment images 1562a and 1562b of the adjustment sheet (S1709). The CPU 114 reads the adjustment images with the line sensors 312a and 312b while conveying the adjustment sheet by the reading device 160. The adjustment sheet discharged from the reading device 160 is discharged to the discharge tray of the finisher 190.

[0134] The CPU 114 obtains the reading result of the adjustment sheet from the reading device 160, and calculates the amount of print position deviation from the reading result based on the calculation method shown in Fig. 8 (S1710). The CPU 114 stores the calculated amount of print position deviation in the paper library 600 in association with the paper of the paper feed tray of the page (S1711).

[0135] For example, if "DEF Paper Embossed Paper A-1" is used for the paper of the page, the calculated amount of print misalignment is saved as the amount of print misalignment of "DEF Paper Embossed Paper A-1" 603 in the paper library 600. Specifically, if the adjustment image 1562a of the page is "toner amount category 2", the CPU 114 saves the calculated amount of print misalignment in print misalignment amount (front side) 620. If the adjustment image 1562b of the page is "toner amount category 5", the CPU 114 saves the calculated amount of print misalignment in print misalignment amount (back side) 627.

[0136] The CPU 114 determines (S1712) whether or not the print front / back position correction is completed for all adjustment images stored in the print front / back position correction setting table 1550. If not completed (S1712: N), the CPU 114 returns to the process of S1705, reads the next adjustment image from the print front / back position correction setting table 1550, and performs the print front / back position correction.

[0137] When the print front / back position correction is completed for all adjustment images (S1712: Y), the CPU 114 ends the print front / back position correction and stores "0" in the value of the print front / back position correction execution number counter n (S1713). After that, the CPU 114 prints the output image according to the print job by the printer 150 (S1715). In this case, the print position is corrected based on the print position deviation amount acquired by the print front / back position correction. When the printing of one page of images is completed, the CPU 114 judges the end of the print job (S1715). If the print job is not completed (S1716: N), the CPU 114 returns to the process of S1702 and repeats the process from S1702 onwards. If the print job is completed (S1716: Y), the CPU 114 ends the process.

[0138] In the case of single-sided printing (S1702: N), CPU 114 causes printer 150 to print an output image according to the print job (S1715). In this case, no correction of the print position is made based on the print position deviation amount obtained by the print front / back position correction. When printing of one page of image is completed, CPU 114 determines whether the print job is completed (S1715). If the print job is not completed (S1716: N), CPU 114 returns to the process of S1702 and repeats the processes from S1702 onwards. If the print job is completed (S1716: Y), CPU 114 ends the process.

[0139] Similarly, when the print front / back position correction implementation flag F is "0" (S1703: N), CPU 114 causes printer 150 to print an output image according to the print job (S1715). In this case, the print position is not corrected based on the print position deviation amount obtained by the print front / back position correction. When printing of one page of image is completed, CPU 114 determines whether the print job is completed (S1715). If the print job is not completed (S1716: N), CPU 114 returns to the process of S1702 and repeats the processes from S1702 onwards. If the print job is completed (S1716: Y), CPU 114 ends the process.

[0140] After adding 1 to the print front / back position correction implementation counter n in the process of S1714, the CPU 114 causes the printer 150 to print an output image according to the print job (S1715). In this case, the print position is corrected based on the print position deviation amount acquired by the initial front / back position correction or the print front / back position correction. When printing of one page of images is completed, the CPU 114 determines whether the print job is completed (S1715). If the print job is not completed (S1716: N), the CPU 114 returns to the process of S1702 and repeats the processes from S1702 onwards. If the print job is completed (S1716: Y), the CPU 114 ends the process.

[0141] (Modification) It is also possible to correct the front and back positions of the print by using an output image specified in a print job as an adjustment image. Fig. 18 is a view showing an example of a print adjustment page setting screen 1450. This print adjustment page setting screen 1450 has a chart selection button 1801 enclosed in a dotted line added to the screen of Fig. 14(b). The same screen configurations as those of the screen of Fig. 14(b) are given the same reference numerals. A job display section 1460 displays the print job selected by the operator from the print job list 1410 of Fig. 14(a) among the print jobs input from the host computer 101.

[0142] 19 is a view showing an example of a chart selection screen displayed on the operation panel 120. The chart selection screen 1900 is displayed on the operation panel 120 when the chart selection button 1801 is pressed with a page selected in the print front / back position correction page list 1461 on the print adjustment page setting screen 1450. The chart selection screen 1900 includes a selected chart display section 1910, a correction chart selection button 1920, an output image chart selection button 1921, a decision button 1930, and a cancel button 1931.

[0143] The selection chart display section 1910 includes a correction chart display section 1910a and an output image chart display section 1910b. The correction chart display section 1910a displays an adjustment image determined by the process of Fig. 16. The output image chart display section 1910b displays an image in which the correction mark 720 of Fig. 3 has been added to the output image of the page selected in the print front / back position correction page list 1461.

[0144] The correction chart selection button 1920 and the output image chart selection button 1921 are configured to have a so-called toggle display. Therefore, when the correction chart selection button 1920 and the output image chart selection button 1921 are pressed while displaying "OFF", they switch to display "ON", and when pressed while displaying "ON", they switch to display "OFF".

[0145] Furthermore, the correction chart display section 1910a and the output image chart display section 1910b, and the correction chart selection button 1920 and the output image chart selection button 1921 are displayed exclusively. Specifically, as shown in Fig. 19(a), when the correction chart selection button 1920 is displayed "ON", the output image chart selection button 1921 is displayed "OFF". The correction chart display section 1910a is displayed normally, and the output image chart display section 1910b is displayed grayed out. Conversely, as shown in Fig. 19(b), when the correction chart selection button 1920 is displayed "OFF", the output image chart selection button 1921 is displayed "ON". The correction chart display section 1910a is displayed grayed out, and the output image chart display section 1910b is displayed normally.

[0146] When the correction chart selection button 1920 displays "ON", the image forming apparatus 100 performs the above-mentioned process of correcting the front and back positions of the print. When the output image chart selection button 1921 displays "ON", the image forming apparatus 100 uses an image obtained by adding the correction mark 720 in Fig. 3 to the output image as an adjustment image, and registers it as the adjustment image 1562 in Fig. 15(C). Therefore, it becomes possible to perform the correction of the front and back positions of the print using the image obtained by adding the correction mark 720 to the output image.

[0147] Fig. 20 is an explanatory diagram of a method for generating an adjustment image by adding a correction mark 720 to an output image. Fig. 20(a) shows a blank area when adding a correction mark 720 to an output image. Fig. 20(b) shows an adjustment image in which a correction mark 720 has been added to an output image.

[0148] 20(a) are provided at the four corners of the paper as in FIG. 3, but for simplicity, only the upper left correction mark 720 and lengths (C) and (D) are shown here. In the modified example, lengths (A) to (V) are measured from the correction marks 720 provided at the four corners.

[0149] The correction mark margin line 2001 is a boundary line for generating a margin when the correction mark 720 is read by the reading device 160. If the output image overlaps with the area to which the correction mark 720 is added, it becomes difficult for the reading device 160 to accurately read the correction mark 720. The output image area 2002 in which the output image is formed is an area that masks the original output image with the correction mark margin line 2001 as the boundary. In this embodiment, the correction mark margin line 2001 is included in the adjustment image, but it is not necessary to include the correction mark margin line 2001 in the adjustment image.

[0150] 20(b) shows an adjustment image in which the original output image is masked using a correction mark margin line 2001 and correction marks 720 are added. An adjustment image 2012 is generated by adding the correction marks 720 to an output image 2011. In the output image 2011, the original image does not overlap the area of ​​the correction marks 720. Therefore, the adjustment image 2012 is an image in which the correction marks 720 are added to the four corners of the output image 2011.

[0151] An adjustment image 2022 is generated by adding the correction mark 720 to the output image 2021. In the output image 2021, the original image overlaps the area of ​​the correction mark 720. Therefore, the adjustment image 2022 is an image in which the correction mark 720 has been added to a margin area masked with the correction mark margin line 2001 as a boundary.

[0152] 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 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 be a total of 25 combinations of the five toner application amount categories on the front side and the five toner application amount categories on the back side.

[0153] As described above, the image forming apparatus 100 of the present embodiment corrects the print front-back position by using an adjustment image corresponding to the page selected by the operator. This makes it possible to update the correction amount corresponding to the toner amount to an appropriate value and reduce the number of adjustment sheets to be discarded.

Claims

1. An image forming means for forming an image on a sheet of paper using toner; a reading means for reading a sheet on which a correction mark is formed; The display and a control means; The control means displaying a plurality of images included in a print job on the display in a selectable manner; obtaining user selection information indicating a selection result of an image selected from the plurality of images; determining an adjustment image to be formed by the image forming means, the adjustment image including a pattern image corresponding to the amount of toner adhesion of the selected image and the correction mark, based on the user selection information; causing the image forming means to form the adjustment image on a sheet; causing the reading means to read the sheet on which the adjustment image is formed; an image forming position of the selected image formed on the sheet by the image forming means is controlled based on a reading result of the sheet on which the adjustment image is formed, the reading result being read by the reading means; Image forming device.

2. the image forming means forms a plurality of the adjustment images each having a different amount of toner adhesion of the pattern image, the control means determines an adjustment image having a pattern image corresponding to the density of the selected image from the plurality of adjustment images based on the user selection information.

2. The image forming apparatus according to claim 1.

3. The correction mark is one or more marks formed in a corner region of the paper.

2. The image forming apparatus according to claim 1.

4. the control means generates a right-angle correction amount based on a reading result of the paper on which the adjustment image is formed, the reading result being read by the reading means; The control means controls the image forming position of the selected image formed on the paper by the image forming means based on the right-angle correction amount.

2. The image forming apparatus according to claim 1.

5. The control means generates a trapezoid correction amount based on a reading result of the paper on which the adjustment image is formed, read by the reading means; The control means controls the image forming position of the selected image formed on the paper by the image forming means based on the trapezoid correction amount.

2. The image forming apparatus according to claim 1.

6. The control means generates the parameters of the lead position, the side position, the longitudinal magnification, and the transverse magnification based on the reading result of the paper on which the adjustment image is formed, read by the reading means; The control means controls the image forming position of the selected image formed on the paper by the image forming means based on each of the parameters.

2. The image forming apparatus according to claim 1.

7. The control means is characterized in that it causes the image forming means to form the adjustment image each time images are formed on a predetermined number of sheets of paper.

2. The image forming apparatus according to claim 1.

8. The control means displays a screen for setting the predetermined number of sheets on the display.

8. The image forming apparatus according to claim 7.

9. the image forming unit has a conveying roller for conveying the paper to a paper discharge tray for discharging the paper, The reading unit reads the paper being transported by the transport roller.

2. The image forming apparatus according to claim 1.

10. The reading means includes a first sensor that reads a first surface of the paper, and a second sensor that reads a second surface of the paper opposite to the first surface.

10. The image forming apparatus according to claim 9.

11. The selected image includes an image formed on the first surface and an image formed on the second surface, the control means controls an image forming position of the image for the first side based on a reading result of the first side of the paper on which the adjustment image is formed, read by the first sensor; the control means controls the image forming position of the image for the second side based on a reading result of the second side of the paper on which the adjustment image is formed, read by the second sensor. The image forming apparatus according to claim 10.

Images