JP2020189419A - Image formation apparatus - Google Patents

Abstract

To provide an image formation apparatus which prevents reduction in the correction accuracy of a printing position even when a test sheet is conveyed with turning with respect to a line sensor.SOLUTION: An image formation apparatus 100 generates a test chart by forming adjustment charts for detecting the printing positions of images on both surfaces of a sheet by a printer 150. A controller 110 detects whether or not the test chart is turned at the reading on the basis of the reading result of the test chart by a reading device 160. When the test chart is not turned, the controller 110 generates a correction value of the printing position on the basis of the reading result of the adjustment charts on both surfaces of the test chart. The controller 110 does not generate the correction value when the test chart is turned.SELECTED DRAWING: Figure 1

Description

The present invention relates to an image forming apparatus having a function of adjusting a print position.

The image forming apparatus has a printing position adjusting function for adjusting a printing position (also referred to as an image forming position) of an image on the paper so that the image is printed at an intended position on the paper. By adjusting the print position, for example, it is possible to align the print positions of the respective images on the front side and the back side of one sheet of paper during double-sided printing. In order to adjust the print position, for example, a test sheet in which a mark for detecting the print position is printed on both sides of the paper is created. The test sheet is read by a reader. The deviation of the print position is detected based on the reading result of the test sheet. The print position is adjusted based on the detected deviation.

Patent Documents 1 and 2 disclose a reading device in which line sensors such as CIS (Contact Image Sensor) are arranged in a staggered pattern. This reading device can read, for example, images of a test sheet line by line by means of line sensors arranged in a staggered pattern.

The image forming apparatus detects the length from the reference position of the test sheet to the mark based on the reading result of the test sheet. The amount of deviation of the print position is detected based on the length from the reference position to the mark. The image forming apparatus determines the correction amount for correcting the print position based on the detected deviation amount of the print position. The image forming apparatus adjusts the printing position by correcting the image forming conditions based on the correction amount when forming an image on the same paper type as the test sheet.

JP-A-2017-28604 Japanese Unexamined Patent Publication No. 2016-134870

The reading device reads while transporting the test sheet. The test sheet is conveyed to the reading position of the reading device (line sensor) by the conveying roller. Due to manufacturing variations of the transport rollers, the force applied by the transport rollers to the test sheet becomes uneven, and the test sheet may be transported while turning with respect to the line sensor. In addition, paper that exceeds the transport force of the transport roller or a test sheet that uses paper with an irregular thickness or shape may also be transported while turning with respect to the line sensor.

When the test sheet is read while rotating, the reading result of the test sheet by the reading device becomes a fan-shaped image. When the print position is detected from the reading result of the front surface and the back surface, the correction accuracy of the print position is lowered because the turning amount at the time of reading is different between the front surface and the back surface. Therefore, when the test sheet is read while turning, it is desirable that the print position is not corrected based on the reading result of the test sheet. In addition, it is important to accurately detect the turning of the test sheet. In the reading device of Patent Document 1, it is difficult to separate the shape of the test sheet and the swivel of the test sheet to read the test sheet. The reading device of Patent Document 2 does not consider that the test sheet rotates.

In view of the above problems, the main object of the present invention is to provide an image forming apparatus that prevents a decrease in correction accuracy of the print position even when the test sheet is swiveled and conveyed with respect to the line sensor. And.

The image reading device of the present invention includes an image forming means for forming an image on paper, a first line sensor unit that reads the image on the first surface from the conveyed paper, and a second line sensor unit that reads the image on the second surface. An adjustment chart for detecting a print position of an image formed on the paper is formed on the first surface and the second surface of the paper by a reading means having a line sensor unit and the image forming means. Based on the reading results of the first surface and the second surface of the paper by the reading means, the print position of the adjustment chart on the first surface and the print position of the adjustment chart on the second surface are detected. The control means includes a control means for generating a correction value of the print position, and the control means receives a reading result of the paper by the first line sensor unit and a reading result of the paper by the second line sensor unit, respectively. It is determined whether or not the paper is being conveyed while being swirled based on the above, and the correction value is generated when the swirl of the paper is not detected, and the correction value is generated when at least one of the swirls of the paper is detected. It is characterized in that it does not generate.

According to the present invention, it is possible to prevent a decrease in the correction accuracy of the print position even when the test sheet is conveyed while rotating with respect to the line sensor.

Explanatory drawing of the printing system. The block diagram of the image forming apparatus. Explanatory drawing of a reading device. Configuration explanatory view of the line sensor unit. A flowchart showing the print position adjustment process. A flowchart showing the surface detection process. An example diagram of a test sheet. (A) and (b) are explanatory views of turning judgment of a test sheet. A flowchart showing the calculation process of the passing distance. A flowchart showing an edge position detection process. (A) and (b) are explanatory views of a print position detection process. A flowchart showing a print position detection process.

An embodiment of the present invention will be described with reference to the drawings.

(Print system configuration)
FIG. 1 is an explanatory diagram of a printing system having the image forming apparatus of 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 communicably connected to each other via the network 105. The network 105 is, for example, a communication line such as a LAN (Local Area Network) or a WAN (Wide Area Network). A plurality of the image forming apparatus 100 and the host computer 101 may be connected to the network 105, respectively.

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

The image forming apparatus 100 forms an image on paper based on a printing job. Therefore, the image forming apparatus 100 includes a controller 110, an operation panel 120, a paper feeding device 140, a printer 150, and a reading device 160. The controller 110, the operation panel 120, the paper feeding device 140, the printer 150, and the reading device 160 are communicably connected to each other via the system bus 116.

The operation panel 120 is a user interface and includes operation buttons, a numeric keypad, and an LCD (Liquid Crystal Display). The operator can input print jobs, commands, print settings, and the like to the image forming apparatus 100 by using the operation panel 120. The image forming apparatus 100 will perform an image forming process based on a print job acquired from either the host computer 101 or the operation panel 120. The operation panel 120 displays the setting screen and the state of the image forming apparatus 100 on the LCD.

The paper feed device 140 includes a plurality of paper feed stages for accommodating paper. The paper feeding device 140 feeds paper one by one in order from the top of the plurality of sheets (paper bundle) loaded on each paper feeding stage. The paper feed device 140 conveys the paper fed from each paper feed stage to the printer 150. The printer 150 forms an image on the paper fed from the paper feeding device 140 based on the image data included in the print job, and generates a printed matter. The reading device 160 reads the printed matter generated by the printer 150 and transfers the reading result to the controller 110.

The controller 110 controls the operation of each part of the image forming apparatus 100. The controller 110 includes a ROM (Read Only Memory) 112, a RAM (Random Access Memory) 113, and a CPU (Central Processing Unit) 114. In addition, the controller 110 includes an I / O control unit 111 and a storage 115. Each part in the controller 110 is connected to the system bus 116.

The I / O control unit 111 is a communication interface that communicates with an external device such as a host computer 101 via a network 105. The CPU 114 comprehensively controls the operation of the image forming apparatus 100 by executing the control program stored in the ROM 112 or the storage 115 by using the RAM 113 as the work area. The storage 115 stores various data such as a control program and image data used for image forming processing (printing processing). The storage 115 is a large-capacity storage device such as an HDD (Hard Disk Drive) or an SSD (Solid State Drive).

(Configuration of image forming apparatus)
FIG. 2 is a configuration diagram of the image forming apparatus 100. The image forming apparatus 100 includes a finisher 190 in addition to the paper feeding device 140, the printer 150, and the reading device 160. The finisher 190 is a post-processing device that performs a predetermined post-processing on the printed matter produced by the printer 150. The finisher 190 performs, for example, stapling processing on a plurality of printed matter and sorting processing of printed matter.

The printer 150 includes a plurality of image forming units 200 (4 in this embodiment) that form images of different colors. The four image forming units 200 form a yellow image, a magenta image, a cyan image, and a black image. The configuration of each image forming unit 200 is almost the same.

The image forming unit 200 includes a photosensitive drum 153, a charger 220, an exposure device 223, and a developer 152. The photosensitive drum 153 is rotationally driven in the direction of arrow R1 by a motor (not shown). The charger 220 uniformly charges the rotating photosensitive drum 153. The exposure device 223 exposes the uniformly charged photosensitive drum 153 based on the image data. As a result, an electrostatic latent image corresponding to the image data is formed on the photosensitive drum 153. The developer 152 develops an electrostatic latent image using a developer (toner) of the corresponding color. The electrostatic latent image on the photosensitive drum 153 is visualized by the development, and an image of the color corresponding to the photosensitive drum 153 is formed.

The printer 150 includes an intermediate transfer belt 154 on which each image formed by the plurality of image forming units 200 is transferred. The intermediate transfer belt 154 is rotationally driven in the direction of arrow R2. The yellow, magenta, cyan, and black images formed by the plurality of image forming units 200 are transferred so as to overlap the intermediate transfer belt 154 at a timing corresponding to the rotation speed of the intermediate transfer belt 154. As a result, a full-color image is formed on the intermediate transfer belt 154. The image on the intermediate transfer belt 154 is conveyed by the rotation of the intermediate transfer belt 154 to the transfer portion formed by the intermediate transfer belt 154 with the transfer roller 221.

The paper on which the image is formed by the printer 150 is supplied from the paper feeding device 140. The paper feed device 140 includes a plurality of paper feed stages 140a, 140b, 140c, 140d, 140e, each of which accommodates paper. The paper feed device 140 supplies paper to the printer 150 from a paper feed stage that accommodates paper of the paper type (size, paper quality, etc.) specified in the print job. The paper supplied to the printer 150 is conveyed to the transfer unit.

The image formed on the intermediate transfer belt 154 is transferred to the paper conveyed from the paper feeding device 140 at the nip portion between the intermediate transfer belt 154 and the transfer roller 221. The printer 150 fixes the image on the paper by heating and pressurizing the image transferred to the paper. The printer 150 includes a first fixing device 155 and a second fixing device 156.

The first fixing device 155 includes a fixing roller having a heater inside and a pressure belt for pressing the paper against the fixing roller. The fixing roller is driven by a motor (not shown) to convey the paper.
The second fixing device 156 is arranged on the downstream side of the first fixing device 155 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 the fixing property. The second fuser 156 includes a fixing roller having a heater inside and a pressurizing roller having a heater inside. The second fuser 156 may not be used depending on the type of paper. In this case, the paper is conveyed from the first fixing device 155 to the transfer path 130 without passing through the second fixing device 156. Therefore, on the downstream side of the first fixing device 155, a flapper 131 for guiding the paper to either the transport path 130 or the second fixing device 156 is provided.

On the downstream side of the second fixing device 156 and the transport path 130, a flapper 132 that guides the paper to either the transport path 135 or the discharge path 139 is provided. The flapper 132, for example, guides the paper on which the image is formed on the first surface in the double-sided printing mode to the transport path 135. The flapper 132, for example, guides the paper on which the image is formed on the first surface in the face-up paper ejection mode to the ejection path 139. The flapper 132, for example, guides the paper on which the image is formed on the first surface to the transport path 135 in the face-down paper ejection mode. For example, when creating a test sheet to be described later, the flapper 132 is used to print a paper on which an adjustment chart including a mark for detecting a print position is printed on the first surface and an adjustment chart on the second surface. Guide to the transport path 135.

The paper conveyed to the transfer path 135 is conveyed to the reversing section 136. The paper conveyed to the reversing section 136 is inverted in the conveying direction after the conveying operation is temporarily stopped. A flapper 133 and a flapper 134 are provided in the transport path 135. The paper whose transport direction is reversed is guided to either the transport path 138 or the transport path 135 by the flapper 133. The flapper 133, for example, guides the paper switched back in the double-sided printing mode to the transport path 138. The flapper 133, for example, guides the paper switched back in the face-down paper ejection mode to the transport path 135. The paper guided to the transport path 135 by the flapper 133 is guided to the discharge path 139 by the flapper 134. The flapper 133 guides the paper switched back for printing the adjustment chart on the second side of the paper to the transport path 138.

The paper conveyed to the transfer path 138 by the flapper 133 is conveyed toward the nip portion (transfer portion) between the intermediate transfer belt 154 and the transfer roller 221. As a result, the front and back sides of the paper as it passes through the transfer section are reversed. That is, the surface on which the image of the paper is transferred is inverted.

A reading device 160 that reads an adjustment chart printed on the paper is connected to the downstream side of the printer 150 in the paper transport direction. The printed paper passes through the discharge path 139 and is conveyed from the printer 150 to the reader 160.

The reading device 160 includes a document detection sensor 311 and two line sensor units 312a and 312b in this order from the upstream side in the paper transport direction along the transport path 313. The paper conveyed from the printer 150 to the reader 160 is conveyed along the transfer path 313. The reading device 160 reads the adjustment chart of the test sheet by the line sensor units 312a and 312b while transporting it along the transport path 313. The test sheet is transported to the finisher 190 along the transport path 313. Paper on which an image other than the adjustment chart is formed is transported to the finisher 190 along the transport path 313 without being read by the line sensor units 312a and 312b.

The document detection sensor 311 is, for example, an optical sensor having a light emitting element and a light receiving element. The document detection sensor 311 detects the tip (paper tip) in the transport direction of the test sheet transported along the transport path 313. The controller 110 starts the operation of reading the adjustment chart by the reading device 160 (line sensor units 312a and 312b) based on the detection timing of the paper tip by the document detection sensor 311.

The line sensor units 312a and 312b read the adjustment chart formed on the test sheet. The adjustment chart is printed on both the front and back sides of the paper. The line sensor units 312a and 312b are provided at positions that sandwich the transport path 313 in order to read the adjustment chart from both sides of the test sheet. The line sensor unit 312a reads an adjustment chart formed on the surface (first surface) of the test sheet. The line sensor unit 312b reads the adjustment chart formed on the back surface (second surface) of the test sheet. In the present embodiment, the line sensor unit 312b is provided on the downstream side of the line sensor unit 312a in the paper transport direction.

When the print position adjustment is executed, the image forming apparatus 100 detects the deviation amount of the printing position (image forming position) of the adjustment chart based on the reading result of the test sheet by the line sensor units 312a and 312b. The controller 110 performs a normal image forming process according to a printing job by the printer 150 based on the amount of deviation of the printing position (image forming position) so that the printing position (image forming position) with respect to the paper becomes an ideal position. Control.

(Configuration of reader)
FIG. 3 is an explanatory diagram of the reading device 160. The reading device 160 includes AD converters 302a, 302b, 302c, 302d, and an image memory 303 in addition to the document detection sensor 311, the line sensor unit 312a, and the line sensor unit 312b. The operation of each part of the reading device 160 is controlled by the CPU 114. The line sensor unit 312a includes a memory 300a and two line sensors 301a and 301b. The line sensor unit 312b includes a memory 300b and two line sensors 301c and 301d. The plurality of AD converters 302a, 302b, 302c, 302d are provided corresponding to the plurality of line sensors 301a, 301b, 301c, 301d.

The AD converters 302a, 302b, 302c, 302d convert the analog signals output from the corresponding line sensors 301a, 301b, 301c, 301d into digital signals and transmit them to the CPU 114. The AD converters 302a and 302b transmit a digital signal representing the reading result of the surface of the test sheet by the line sensor unit 312a to the CPU 114. The AD converters 302c and 302d transmit a digital signal representing the reading result of the back surface of the test sheet by the line sensor unit 312b to the CPU 114. The image memory 303 stores image data necessary for image processing by the CPU 114.

(Structure of line sensor unit)
FIG. 4 is a configuration explanatory view of the line sensor unit 312a. The line sensor unit 312a and the line sensor unit 312b have the same configuration. Here, the configuration of the line sensor unit 312a will be described, and the description of the configuration of the line sensor unit 312b will be omitted.

The line sensor 301a and the line sensor 301b have a substantially rectangular parallelepiped shape and have the same configuration, and the longitudinal direction is the main scanning direction. The line sensor 301a and the line sensor 301b are arranged in a staggered pattern (positions different in the sub-scanning direction) including overlapping portions (overlapping portions) in the sub-scanning direction. The sub-scanning direction is the paper transport direction on the transport path 313. Therefore, the main scanning direction is orthogonal to the paper transport direction. The line sensor 301a and the line sensor 301b are arranged at different positions in the main scanning direction. The paper is read by both the line sensor 301a and the line sensor 301b at the position of the overlapping portion in the main scanning direction, and is read by either the line sensor 301a or the line sensor 301b at a position other than the overlapping portion in the main scanning direction. Be done. For each line sensor 301a, 301b, for example, CIS can be used. The memory 300a stores information (sub-scanning distance information) representing the distance in the sub-scanning direction between the two line sensors 301a and 301b.

The line sensors 301a and 301b each include an LED (Light Emitting Diode) 400, a light guide body 402, a lens array 403, and a sensor chip group 401. The LED 400 is a light source that emits white light, and is provided at both ends of the light guide body 402. The sensor chip group 401 is composed of a three-line sensor coated with R (red), G (green), and B (blue) color filters.

The light emitted from the LED 400 is diffused inside the light guide body 402, emitted from a portion having a curvature of the light guide body 402, and illuminates the entire area of the paper transported along the transport path 313 in the main scanning direction. The line sensors 301a and 301b have a “both-sided illumination configuration” capable of irradiating light from the position of the lens array 403, that is, two directions of the front end side and the rear end side in the sub-scanning direction with respect to the document reading line. The light emitted from the light guide body 402 and irradiating the paper is reflected on the surface of the paper and is imaged on the light receiving surface of the sensor chip group 401 by the lens array 403.

(Print position adjustment)
FIG. 5 is a flowchart showing the print position adjustment process of the present embodiment. This process is a process of calculating a correction value for adjusting the print position.

When the CPU 114 receives an instruction (print job) such as a document size and a print mode from the operation panel 120, the CPU 114 sets information necessary for printing in each part of the printer 150 (S500). The CPU 114 receives the print start instruction from the operation panel 120 and starts the print process (S501: Y). The CPU 114 initializes the page count value P in response to the print start instruction and sets it to 0 (S502).

The CPU 114 controls the printer 150 to print an image corresponding to the image data included in the print job on the paper, and print the adjustment chart on both sides of the paper to generate a test sheet (S503). The generated test sheet is supplied from the printer 150 to the reader 160. The CPU 114 uses the printer 150 to perform image forming processing for the number of images specified in the print job. The printer 150 continuously supplies the generated test sheet to the reader 160. When the document detection sensor 311 of the reading device 160 detects the tip of the test sheet supplied from the printer 150, the state of the signal representing the detection result changes. The detection result changes from 0 to 1, for example, by detecting the tip of the test sheet. When the document detection sensor 311 detects the tip of the test sheet, the CPU 114 increments the page count value P by 1 (S504).

The CPU 114 performs a surface detection process for detecting the turning of the surface of the test sheet based on the reading result of the test sheet by the line sensor unit 312a (S505). By this process, it is detected whether or not the test sheet is conveyed while rotating and the surface is read. Details of the surface detection process will be described later. As a result of the surface detection process, the CPU 114 determines whether or not the test sheet is swiveling (S506). When not swiveling (S506: Y), the CPU 114 performs a back surface detection process for detecting the swirling of the back surface of the test sheet based on the reading result of the test sheet by the line sensor unit 312b (S507). By this process, it is detected whether or not the test sheet is conveyed while rotating and the back surface is read. The details of the back surface detection process will be described later. After the back surface detection process, the CPU 114 determines whether or not the page count value P is equal to or greater than the print position detection end number P1 (S508). The print position detection end number P1 is a predetermined number set in advance. The CPU 114 repeats the processes S504 to S508 until the page count value P becomes equal to or greater than the print position detection end number P1 (S508: N). If the test sheet is not swiveled as a result of the front surface detection process (S506: N), the CPU 114 does not perform the back surface detection process, and whether or not the page count value P is equal to or greater than the print position detection end number P1. To judge.

When the page count value P becomes equal to or greater than the print position detection end number P1 (S508: Y), the CPU 114 calculates a correction value for correcting the deviation amount of the print position based on the results of the front surface detection process and the back surface detection process (S508: Y). S509). For example, the CPU 114 has a position of the adjustment chart that should have been printed at the same position on the front surface and the back surface of the test sheet, and a position of the adjustment chart on the front surface and the back surface detected by the front surface detection process and the back surface detection process. From, the amount of deviation of the printing position is calculated. At this time, the CPU 114 calculates the difference value from the detected position of the adjustment chart of the other surface with reference to the position of the detected adjustment chart of the other surface. The CPU 114 calculates the difference value for P1 of the number of print position detection ends, and sets the average value as the amount of deviation of the print position. The average value is calculated from the difference value excluding the pages where the test sheet is judged to be turning.

The CPU 114 determines whether or not the turning of the test sheet is detected at least on one side by the front surface detection process and the back surface detection process (S510). When the rotation of the test sheet is detected at least once by the front surface detection process and the back surface detection process (S510: Y), the CPU 114 displays an alarm on the operation panel 120 to notify that the test sheet has been rotated. (S511), the print position adjustment process is completed. When the rotation of the test sheet is not detected by the front surface detection process and the back surface detection process (S510: N), the CPU 114 ends the print position adjustment process without displaying an alarm.

(Front surface detection process and back surface detection process)
FIG. 6 is a flowchart showing the front surface detection process and the back surface detection process of S505 and S507. The front surface detection process and the back surface detection process are the same processes. Here, the front surface detection process will be described, and the description of the back surface detection process will be omitted. The turning of the test sheet is detected by the front surface detection process and the back surface detection process.

The CPU 114 calculates the number of lines in the main scanning direction of the overlapping portion in the sub-scanning direction between the line sensor 301a and the line sensor 301b of the line sensor unit 312a according to the reading resolution determined by the transport speed of the test sheet (S600). The calculated number of lines is hereinafter referred to as "the number of lines between sub-scannings". The reading resolution is included in the print job instructed in the process of S500. The calculation of the number of lines between sub-scans is performed by converting the distance between the overlapping portions of the line sensor 301a and the line sensor 301b in the sub-scan direction (sub-scan interval Base0) according to the reading resolution. The sub-scanning interval Base0 is measured in advance at the time of shipment from the factory of the line sensor unit 312a and stored in the memory 300a.

For example, if the resolution in the sub-scanning direction is 1200 [dpi (dot per inch)] and the sub-scanning interval Base0 is 1370 lines, and the reading resolution is 600 [dpi], the number of sub-scanning lines (Base1) is as follows. It is calculated as.
Base1 = 1370 x 600/1200 = 685 lines

The CPU 114 instructs the line sensor unit 312a to read the test sheet supplied from the printer 150, and starts the image reading process (S601). The reflected light from the test sheet is photoelectrically converted by the sensor chip groups 401 of the line sensors 301a and 301b, and converted into digital signals by the AD converters 302a and 302b. This digital signal is stored in the image memory 303 as image data of the test sheet. Two storage areas (image memory A and image memory B) are formed in the image memory 303. The image data of the line sensor 301a is stored in the image memory A. The image data of the line sensor 301b is stored in the image memory B.

The CPU 114 reads the image data stored in the image memory A, detects the edge of the test sheet, and acquires the passing distance γ (n) of the tip of the test sheet in the transport direction (S602). The CPU 114 detects the edge position in the sub-scanning direction corresponding to the same position in the main scanning direction (main scanning position) in the overlapping portion from the reading results (image data) of the line sensors 301a and 301b. The difference between the edge positions detected from the reading results of the line sensors 301a and 301b is the passing distance γ (n). n is the number of points in the image data used for processing. n is preset within the range of the number of pixels of the overlapping portions of the 1-line sensors 301a and 301b. The passing distance γ (n) may be calculated at a plurality of points. The details of the calculation process of the passing distance γ (n) will be described later.

The CPU 114 determines whether or not the passing distance γ (n) of each main scanning position is within a predetermined range (S603). The CPU 114 determines whether or not the passing distance γ (n) is within a predetermined range (± ξ) centered on the number of lines between sub-scannings (Base 1). ξ is a numerical value that is set in advance and is determined, for example, according to the variation in the transport speed of the test sheet.

When all the passing distances γ (n) of the main scanning position of the overlapping portion are within a predetermined range (S603: Y), the CPU 114 detects the position of the adjustment chart from the image data in which the edge is detected in the process of S602. .. The CPU 114 performs a detection process for detecting the inclination and the print position of the test sheet based on the detected position of the adjustment chart (S604). FIG. 7 is an example diagram of a test sheet. The test sheet 700 is formed by printing marks, which are adjustment charts, on the four corners of the paper. The CPU 114 extracts these marks from the image data and performs a printing position detection process. The CPU 114 stores the detected information (detection information) in the internal register and ends the surface detection procedure. The details of the detection process will be described later.

When even one passing distance γ (n) is out of the predetermined range (S603: N), the CPU 114 instructs the line sensor unit 312a to stop the reading process and stops the image reading process (S605). The CPU 114 stores the page (page count value P) determined that the passing distance γ (n) is out of the predetermined range in the internal register, and ends the surface detection treatment.

(Swirl of test sheet)
FIG. 8 is an explanatory diagram of turning determination of the test sheet. Although the case of the line sensor unit 312a will be described here, the turning determination is similarly performed in the case of the line sensor unit 312b. FIG. 8 shows the reading results (image data) of the line sensors 301a and 301b when the test sheet is swiveled while being conveyed from the reading position of the line sensor 301a to the reading position of the line sensor 301b. FIG. 8A shows a scanned image when the test sheet is swiveled and scanned. When the test sheet turns, the test sheet is read in a fan shape. FIG. 8B is an explanatory diagram of the processing of S602 to S606.

The edge position is detected within the range Dup0 to Dup1 in the main scanning direction x and the range 0 to high in the sub-scanning direction y of the overlapping portion of the line sensor 301a and the line sensor 301b. The edge position is detected, for example, in the range of the main scanning positions xdet (0) to xdet (2). The edge position is detected based on the brightness value for each line in the sub-scanning direction y. The line whose brightness value is equal to or greater than the threshold value (position in the sub-scanning direction) is determined to be the edge position. In FIG. 8B, the sub-scanning positions y0 (0), y0 (1), y0 (2), y1 (0), y1 (with respect to the main scanning positions xdet (0), xdet (1), xdet (2)) 1) and y1 (2) are edge positions. Details of the passing distances γ (0) to γ (2) will be described later.

(Passing distance γ (n))
FIG. 9 is a flowchart showing the calculation process of the passing distance γ (n) of S602. The passing distance γ (n) is calculated in order to detect the turning of the test sheet in each of the two line sensor units 312a and 312b.

The CPU 114 detects the edge position from the image data stored in the image memory A (S900). The CPU 114 detects the edge position within the range of the overlapping portion between the line sensor 301a and the line sensor 301b. The CPU 114 detects the main scanning position xdet (n) and the sub-scanning position y0 (n) as edge positions.

The CPU 114 detects the edge position from the image data stored in the image memory B (S901). The CPU 114 detects the edge position within the range of the overlapping portion between the line sensor 301c and the line sensor 301d. The CPU 114 detects the main scanning position xdet (n) and the sub-scanning position y1 (n) as edge positions.

The CPU 114 compares the sub-scanning positions of the same main scanning position with respect to the edge positions detected in the processing of S900 and the processing of S901, and calculates the passing distance γ (n) (S902). The passing distance γ (n) will be described with reference to FIG. The CPU 114 has sub-scanning positions y0 (0), y0 (1), y0 (2) and sub-scanning positions y1 (0) with respect to the three main scanning positions xdet (0), xdet (1), and xdet (2). The amount of change from y1 (1) and y1 (2) is calculated. The amount of change is the passing distances γ (0), γ (1), and γ (2).
γ (0) = | y0 (0) -y1 (0) | = | 17-8 | = 9 lines γ (1) = | y0 (1) -y1 (1) | = | 14-7 | = 7 lines γ (2) = | y0 (2) -y1 (2) | = | 11-6 | = 5 lines

When the range for determining the turning of the test sheet (Base 1 ± ξ%) is 4 to 6 lines, the passing distance γ (0) and the passing distance γ (1) are out of the predetermined range. In this case, the CPU 114 determines that the test sheet is turning.

FIG. 10 is a flowchart showing the edge position detection processing of S900 and S901. By this process, the coordinates (edge position) of the tip in the transport direction in the reading result of the test sheet are detected. This process is the same for the line sensor 301a and the line sensor 301b. Here, the processing in the case of the line sensor 301a will be described, and the description of the processing in the case of the line sensor 301b will be omitted.

The CPU 114 initializes the number (sub-scanning position y) of the image data of one line read from the image memory A to 0 (S1000). The CPU 114 reads out one line of image data corresponding to the number of the sub-scanning position y from the image memory A (S1001). The CPU 114 sets Dup0, which is the start position of the detection range of the edge position, at the main scanning position x (S1002). The CPU 114 starts searching for a plurality of predetermined main scanning positions xdet (n) from the 0th pixel of Dup with respect to one line of image data read from the image memory A. The CPU 114 performs edge detection at the main scanning position xdet (n).

The CPU 114 determines that the main scanning position x of the acquired image data matches the main scanning position xdet (n) for edge detection (S1003). If they do not match (S1003: N), the CPU 114 increments the main scanning position x by 1 (S1010), and again determines that the main scanning position x and the main scanning position xdet (n) match. If they match (S1003: Y), the CPU 114 acquires the luminance value xdet_lum (n) at the main scanning position xdet (n) and the sub-scanning position y0 (n) of the image data (S1004).

The CPU 114 compares the acquired luminance value xdet_lum (n) with a predetermined threshold value (S1005). The threshold value is an 8-bit digital value within 0 (black) to 255 (white) and is set in advance. In the present embodiment, the intermediate value 127 is set as the threshold value.

When the luminance value xdet_lum (n) is equal to or greater than the threshold value (S1005: Y), the CPU 114 sets the main scanning position xdet (n) and the sub-scanning position y0 (n) above the threshold value as coordinates of the edge position in the internal register. Store (S1007). The CPU 114 determines whether or not n + 1 coordinates of the edge position have been acquired (S1008). When n + 1 coordinates of the edge position are acquired (S1008: Y), the CPU 114 ends the edge position detection process.

When the luminance value xdet_lum (n) is smaller than the threshold value (S1005: N), the CPU 114 determines whether or not the luminance value has been detected until the main scanning position x reaches Dup1, which is the end position of the detection range of the edge position. (S1006). Even when n + 1 coordinates of the edge position have not been acquired (S1008: N), the CPU 114 detects the luminance value until the main scanning position x becomes Dup1 which is the end position of the detection range of the edge position. It is determined whether or not it is (S1006). When the luminance value is not detected until the main scanning position x becomes Dup1 (S1006: N), the CPU 114 increments the main scanning position x by 1 (S1010) and performs the processing after S1003.

When the luminance value is detected until the main scanning position x becomes Dup1 (S1006: Y), the CPU 114 compares the sub-scanning position y with the height which is the end position of the detection range of the edge position in the sub-scanning direction (S1009). .. When the sub-scanning position y is light or less (S1009: N), the CPU 114 increments the sub-scanning position y by 1 (S1011) and performs the processing after S1001. When the sub-scanning position y is larger than high (S1009: Y), the CPU 114 ends the edge position detection process.

(Print position detection)
FIG. 11 is an explanatory diagram of the print position detection process. As shown in FIG. 11A, the print position is detected by the position of the corner of the adjustment chart closest to the corner of the paper of the test sheet 700 illustrated in FIG. 7.

From the image data stored in the image memory A or the image memory B, edge detection is performed in the edge detection range for the adjustment charts 1101, 1102, 1103, and 1104 (marks) at the four corners. The edge detection range is the range of the main scanning positions xdet_st_m to xdet_ed_m and the sub-scanning positions ydet_st_m to ydet_ed_m. m is 0 and 1.

FIG. 11B is an explanatory diagram of the printing position of the corner of the adjustment chart 1101. When detecting the print position of the corner of the adjustment chart 1101, first, the edge of the tip and the side surface of the adjustment chart 1101 near the edge of the test sheet is detected in the edge detection range. Approximate straight lines 1105 and 1106 are calculated from the edge of the tip and the edge of the side surface of the adjustment chart 1101, respectively. The intersection of the approximate straight lines 1105 and 1106 is stored in the internal register of the CPU 114 as the print position 1107 which is the corner of the adjustment chart 1101. Similarly, for the other adjustment charts 1102, 1103, and 1104, the intersection of the approximate straight lines is detected as the print position.

FIG. 12 is a flowchart showing the print position detection process. The CPU 114 detects the print position of the adjustment chart by the following processing based on the image data which is the reading result of the test sheet.

The CPU 114 detects the edges of the adjustment chart at the four corners based on the edge detection range (S1200). The CPU 114 calculates two approximate straight lines for each of the four corners of the adjustment chart based on the edge of the tip side and the side surface of the adjustment chart closest to the edge of the test sheet (S1201). The CPU 114 stores the intersections of the two approximate straight lines for each adjustment chart at the four corners in the internal register as the print position of each adjustment chart (S1202).

The image forming apparatus 100 of the present embodiment as described above can accurately detect the rotation of the test sheet when the reading apparatus 160 reads the test sheet for detecting the printing position. Therefore, the image forming apparatus 100 can prevent erroneous detection of the printing position. The image forming apparatus 100 can detect the correction value for the print position correction excluding the print position detected from the page where the test sheet is swiveled, and improves the accuracy of the print position correction on the front surface and the back surface of the test sheet. It becomes possible.

Claims (12)

An image forming means for forming an image on paper,
A reading means having a first line sensor unit for reading the image on the first surface and a second line sensor unit for reading the image on the second surface from the conveyed paper.
An adjustment chart for detecting a print position of an image formed on the paper is formed on the first surface and the second surface of the paper by the image forming means, and the first surface of the paper is formed by the reading means. Based on the reading results of the first surface and the second surface, the print position of the adjustment chart on the first surface and the print position of the adjustment chart on the second surface are detected to generate a correction value of the print position. With control means to
The control means determines whether or not the paper is being swirled and conveyed based on the reading result of the paper by the first line sensor unit and the reading result of the paper by the second line sensor unit. However, the correction value is generated when the swirl of the paper is not detected, and the correction value is not generated when the swirl of the paper is detected at least on the other hand.
Image forming device. The control means is characterized in that, when it detects that the paper has swirled, it notifies that the paper has swirled by a predetermined notification means.
The image forming apparatus according to claim 1. The control means is characterized in that the notification is given by displaying on a predetermined display means that the paper has turned.
The image forming apparatus according to claim 2. The first line sensor has two line sensors arranged at different positions in the main scanning direction orthogonal to the transport direction, including overlapping portions overlapping in the transport direction of the paper.
The second line sensor has two line sensors arranged at different positions in the main scanning direction including overlapping portions overlapping in the transport direction.
The control means determines the turning of the paper based on the reading results of the two line sensors of the first line sensor, and is based on the reading results of the two line sensors of the second line sensor. It is characterized in that the turning of the paper is determined.
The image forming apparatus according to any one of claims 1 to 3. The control means detects and detects the edge position in the transport direction at the same position in the main scanning direction in the overlapping portion from the reading results of the two line sensors of the first line sensor, respectively. It is characterized in that the turning of the paper is determined based on the amount of change in the edge position of the paper.
The image forming apparatus according to claim 4. The control means is characterized in that when the amount of change is out of a predetermined range, it is determined that the paper is swirling.
The image forming apparatus according to claim 5. The control means is characterized in that the edge position is detected by comparing the reading result of each of the two line sensors of the first line sensor with a threshold value for each line in the transport direction. To do
The image forming apparatus according to claim 5 or 6. The control means is characterized in that if the luminance value included in the reading result is equal to or greater than the threshold value, the position of the luminance value is set as the edge position.
The image forming apparatus according to claim 7. The control means detects the edge position in the transport direction at the same position in the main scanning direction in the overlapping portion from the reading results of the two line sensors of the second line sensor, and detects the edge. It is characterized in that the turning of the paper is determined based on the amount of change in the position.
The image forming apparatus according to any one of claims 4 to 8. The control means is characterized in that when the amount of change is out of a predetermined range, it is determined that the paper is swirling.
The image forming apparatus according to claim 9. The control means is characterized in that the edge position is detected by comparing the reading result of each of the two line sensors of the second line sensor with a threshold value for each line in the transport direction. To do
The image forming apparatus according to claim 9 or 10. The control means is characterized in that if the luminance value included in the reading result is equal to or greater than the threshold value, the position of the luminance value is set as the edge position.
The image forming apparatus according to claim 11.