JP2011164619A - Image forming apparatus, and control method for the same - Google Patents

Abstract

An image forming apparatus capable of forming an appropriate image on both sides of an image forming medium and a method for controlling the image forming apparatus are provided.
Image reading means Si reads an image on a first surface of an image forming medium on which an image including a mark is formed by image forming means 2. The detecting means 51 detects the mark from the image data read by the image reading means Si. The calculating unit 51 is generated on the image forming medium by the image forming unit 2 based on the amount of variation between the mark position detected by the detecting unit Si and the mark position in the image formed on the first surface. Calculate the degree of contraction. The correcting unit 51 corrects the image formed on the second surface of the image forming medium based on the contraction degree calculated by the calculating unit 51. The control unit 51 causes the image forming unit 2 to form the image corrected by the correcting unit 51 in a print area corresponding to the contraction degree on the second surface of the image forming medium.
[Selection] Figure 3

Description

  The present embodiment relates to an image forming apparatus for forming an image on an image forming medium and an image forming method applied to the image forming apparatus.

  2. Description of the Related Art Conventionally, when performing double-sided printing, an image forming apparatus such as a digital multifunction peripheral performs a scaling process on the front side image data and the back side image data at the same magnification in an image processing unit. Also, the origin of the print area is the same coordinate position on both sides. However, in the image forming apparatus, the physical size of the image forming medium may change during the printing process. For example, in an image forming apparatus in which heat is applied to an image forming medium, the size of the image forming medium may be reduced. In double-sided printing, if the physical size of the image-forming medium changes in the printing process on the first side, the image printed on the front side and the image printed on the back side have the same size or print position. There is a problem of not doing it.

JP 2004-347842 A

  An object of the present embodiment is to provide an image forming apparatus and an image forming apparatus control method capable of forming an appropriate image on both sides of an image forming medium.

  According to the embodiment, the image forming apparatus includes an image forming unit, an image reading unit, a detection unit, a calculation unit, a correction unit, and a control unit. The image forming unit forms an image including a position detection mark on the first surface of the image forming medium. The image reading unit reads an image on the first surface of the image forming medium on which an image including the mark is formed by the image forming unit. The detecting means detects the mark from the image data read by the image reading means. The calculating means calculates the degree of contraction that has occurred in the image forming medium during image formation by the image forming means based on the amount of variation between the mark position detected by the detecting means and the mark position in the image formed on the first surface. calculate. The correcting unit corrects the image formed on the second surface of the image forming medium based on the contraction degree calculated by the calculating unit. The control unit causes the image forming unit to form the image corrected by the correcting unit in a print area corresponding to the contraction degree on the second surface of the image forming medium.

FIG. 1 is a perspective view illustrating an external configuration example of a digital multifunction peripheral. FIG. 2 is a cross-sectional view schematically showing an example of the internal configuration of the digital multifunction peripheral. FIG. 3 is a block diagram for explaining a configuration example of a control system in the digital multi-function peripheral. FIG. 4A is a diagram illustrating an example of a test pattern for detecting the degree of contraction of a sheet. FIG. 4B is a diagram illustrating an example of a sheet on which a test pattern is printed. FIG. 5 is a configuration example of a mark for position detection. FIG. 6A is a diagram illustrating a state in which an image is printed on the first surface. FIG. 6B is a diagram illustrating an example in which an image corrected according to the degree of shrinkage of the paper generated in the printing process on the first surface is printed on the second surface. FIG. 7 is a flowchart for explaining the flow of the duplex printing process.

  Hereinafter, embodiments will be described with reference to the drawings.

First, the configuration of a digital multifunction peripheral (MFP, Multi-Functional Peripheral) as an image forming apparatus will be described.
FIG. 1 is a perspective view illustrating an external configuration example of a digital multifunction peripheral. FIG. 2 is a cross-sectional view schematically showing an example of the internal configuration of the digital multifunction peripheral. As shown in FIG. 1, the digital multifunction peripheral includes a scanner 1, a printer 2, a finisher 3, a control panel 4, and a system control unit 5.

The scanner 1 is installed on the upper part of the main body of the digital multifunction peripheral. The scanner 1 is controlled by the system control unit 5. The scanner 1 is an apparatus that reads an image of a document and converts it into image data. The scanner 1 outputs image data of a document to the system control unit 5.
The scanner 1 includes an image reading unit 10 as a photoelectric conversion unit including a CCD line sensor that converts an image of one line in the main scanning direction of a document into image data. The image reading unit 10 reads an image of the entire original by scanning the original with a CCD line sensor in the sub-scanning direction of the original.

  The scanner 1 has a document table glass 11 and a document sensor 12. The document table glass 11 places a document to be scanned by the image reading unit 10. The image reading unit 10 scans a document on the platen glass 11 through the glass of the platen glass 11. The document sensor 12 detects a document on the platen glass 11. The document sensor 12 outputs a signal indicating the presence or absence of a document on the document table glass 11. The document sensor 12 detects the document size on the document table glass 11.

  The scanner 1 has an automatic document feeder (ADF) 13. The ADF 13 has a paper feed tray 14. The paper feed tray 14 holds a document to be read. The ADF 13 conveys originals held by the paper feed tray 14 one by one. The scanner 1 reads an image of a document conveyed by the ADF 13. In the scanner 1, the ADF 13 also functions as a cover for the document placed on the document table glass 11.

The printer 2 functions as an image forming unit. The printer 2 is controlled by the system control unit 5. The printer 2 prints the image data supplied from the system control unit 5 on a sheet as an image forming medium.
The printer 2 includes paper feed cassettes 21A, 21B, and 21C. These paper feed cassettes 21A, 21B, and 21C store sheets as image forming media on which images are printed. For example, each of the paper feed cassettes 21A, 21B, and 21C can be attached to and detached from the lower part of the digital multi-function peripheral body. Each of the paper feed cassettes 21A, 21B, and 21C has paper feed rollers 22A, 22B, and 22C, respectively. Each of the paper feed rollers 22A, 22B, and 22C takes out one sheet at a time from each of the paper feed cassettes 21A, 21B, and 21C.

  The transport unit 23 transports the paper within the printer 2. The conveyance unit 23 includes a plurality of conveyance rollers 23 a to 23 f and a registration roller 24. The transport unit 23 transports the paper taken out by the paper feed rollers 22 </ b> A, 22 </ b> B, and 22 </ b> C to the registration roller 24. The registration roller 24 conveys the paper to the transfer position at the timing of transferring the image.

  The plurality of image forming units 25 (25Y, 25M, 25C, 25K) each form an image of each color (yellow, magenta, cyan, black). The exposure unit 26 serves as an image to be developed in each color on a photosensitive drum D (Dy, Dm, Dc, Dk) as an image carrier in each image forming unit 25 (25Y, 25M, 25C, 25K) by laser light. An electrostatic latent image is formed. The exposure unit 26 irradiates the photosensitive drum D with a laser beam controlled according to the image data through an optical system such as a polygon mirror. An electrostatic latent image is formed on the surface of the photosensitive drum irradiated with the laser light. The exposure unit 26 controls the laser beam according to a control signal from the system control unit 5. For example, the exposure unit 26 controls the power of the laser light according to a control signal from the system control unit 5. Further, the exposure unit 26 also controls the modulation amount of the pulse width for controlling the emission of the laser light according to the control signal from the system control unit 5.

  Each image forming unit 25 (25Y, 25M, 25C, 25K) converts the electrostatic latent image formed on the photosensitive drum D (Dy, Dm, Dc, Dk) into each color (yellow, magenta, cyan, black). A toner image is formed by developing with this toner. The intermediate transfer belt 27 is an intermediate transfer member. Each image forming unit 25 (25Y, 25M, 25C, 25K) transfers the toner image of each color formed on the photosensitive drum D (Dy, Dm, Dc, Dk) onto the intermediate transfer belt 27 (primary transfer). To do.

  Each image forming unit 25 (25Y, 25M, 25C, 25K) includes sensors such as a potential sensor Sv and a density sensor Sd. The potential sensor Sv is a sensor that detects the surface potential of the photosensitive drum. In each image forming unit 25 (25Y, 25M, 25C, 25K), the surface of each photoconductive drum D is charged by the charging charger before being exposed by the exposure unit 26. The charging condition of the charging charger can be changed by a control signal from the system control unit 5. The potential sensor Sv detects the surface potential of the photosensitive drum after the surface is charged by the charging charger. The density sensor Sd detects the density of the toner image transferred onto the intermediate transfer belt 27. Further, the density sensor Sd may detect a toner image formed on the photosensitive drums Dy, Dm, Dc, and Dk.

  Each of the image forming units 25Y, 25M, 25C, and 25K superimposes and transfers (primarily transfers) a toner image developed with toner of each color (yellow, magenta, cyan, and black) onto the intermediate transfer belt 27. The intermediate transfer belt 27 holds a color image in which toner images of respective colors are overlapped. The transfer unit 28 transfers a color image of a plurality of color toners on the intermediate transfer belt 27 to a sheet at the secondary transfer position. The secondary transfer position is a position where the toner image on the intermediate transfer belt 27 is transferred to a sheet. The secondary transfer position is a position where the support roller 28a and the secondary transfer roller 28b face each other.

  An image sensor Si as an image reading unit is provided between the time when the surface of the transfer belt 27 passes through each image forming unit 25 and reaches the secondary transfer position. The image sensor Si reads a toner image formed on the transfer belt 27 by each image forming unit 25. The image sensor Si functions as a sensor that detects the density value of each pixel constituting the image formed on the transfer belt 27. That is, the image sensor Si reads an image on the transfer belt 27 as two-dimensional image data composed of predetermined pixel units. Image data acquired by the image sensor Si is output to the system control unit 5. The system control unit 5 detects the image quality of the image formed on the transfer belt 27 by analyzing the image data from the image sensor Si.

  The registration roller 24 conveys the sheet to the secondary transfer position in synchronization with the toner image on the intermediate transfer belt 27. The transfer unit 28 supplies the sheet on which the toner image is transferred at the secondary transfer position to the fixing unit 29. The fixing unit 29 fixes the toner image on the sheet. The fixing unit 29 heats the paper on which the transfer unit 28 has transferred the toner image in a pressurized state. The fixing unit 29 conveys (discharges) the fixed sheet to any of the paper discharge unit 30, the finisher 3, and the duplex printing mechanism 40.

  Further, an image sensor Si serving as an image reading unit that reads an image on the fixed paper is provided at the subsequent stage of the fixing unit 29. The image sensor Si outputs image data read from the paper after the fixing process to the system control unit 5. The system control unit 5 detects the shrinkage rate of the paper after the fixing process by analyzing the image data from the image sensor Si. The sheet subjected to the fixing process by the fixing unit 29 is read by the image sensor Si, and is conveyed (discharged) to any of the sheet discharge unit 30, the finisher 3, or the duplex printing mechanism 40. Note that the image sensor Si may read only an image on a sheet conveyed to the duplex printing mechanism 40 among the sheets fixed by the fixing unit 29.

  The double-sided printing mechanism 40 inverts and conveys the sheet fixed by the fixing unit 29 and supplies the sheet to the registration roller 24 again. Further, the duplex printing mechanism 40 stacks the reversed sheets until a desired printing timing (back surface printing timing) is reached. The double-sided printing mechanism 40 includes a reverse conveyance path 41 that guides the paper after the fixing process to the registration roller 24. The reverse conveyance path 41 conveys the paper after the fixing process in a reversed state. The reverse conveyance path 41 stacks the reversed sheets until the desired printing timing is reached. The reverse conveyance path 41 supplies the registration roller 24 with the paper reversed at a desired printing timing. As a result, the registration roller 24 can convey the paper that can be printed on the back surface at a desired timing.

The finisher 3 includes a paper discharge mechanism 32 that processes the paper on which the printer 2 has formed an image and a paper discharge tray 33 that stacks the paper. The control panel 4 is a user interface. For example, the user inputs information such as setting information on the control panel 4. The control panel 4 is controlled by the system control unit 5.
Note that the printer 2 shown in FIG. 2 is an electrophotographic printer. However, the printer of this embodiment is not limited to an electrophotographic printer. This embodiment can also be applied to printers other than electrophotographic systems such as an ink jet system or a thermal transfer system.

Next, the configuration of the control system of the digital multi-function peripheral will be described.
FIG. 3 is a block diagram for explaining a configuration example of a control system in the digital multi-function peripheral.
The digital multi-function peripheral has a system control unit 5 that controls the entire apparatus. The system control unit 5 is connected to the scanner 1, printer 2, finisher 3, and control panel 4 via a system bus or the like.

  The system control unit 5 includes a CPU (processor) 51, a main memory 52, a ROM 53, a nonvolatile memory 54, an HDD 55, a page memory 56, a printer controller 57, a FAX controller 58, an electronic data creation unit 59, and an external interface (I / F). 57a, 58b, 59a and an image processing unit 60.

  The CPU 51 controls the entire digital multi-function peripheral. The CPU 51 is a processor that realizes processing by executing a program. The CPU 51 is connected to each unit in the apparatus via the system bus. The CPU 51 connects not only each unit in the system control unit 5 but also the scanner 1, the printer 2, the finisher 3, the control panel 4, and the like via the system bus. The CPU 51 outputs an operation instruction to each unit and acquires various information from each unit through bidirectional communication with the scanner 1, the printer 2, and the control panel 4. In addition, the CPU 51 inputs information indicating detection signals and operation states of various sensors installed in each unit in the apparatus.

  The main memory 52 is constituted by a RAM or the like. The main memory 52 functions as a working memory or a buffer memory. The ROM 53 is a non-rewritable nonvolatile memory that stores programs, control data, and the like. The CPU 51 implements various processes by executing programs stored in the ROM 53 (or the non-volatile memory 54 and the HDD 55) while using the main memory 52. For example, the CPU 51 functions as a detection unit, a calculation unit, and a control unit by executing a program.

  The nonvolatile memory 54 is a rewritable nonvolatile memory. The nonvolatile memory 54 stores a control program executed by the CPU 51 and control data. The nonvolatile memory 54 stores setting information, processing conditions, and the like. The hard disk drive (HDD) 55 is a large-capacity storage device. The HDD 55 stores image data and various history information. The HDD 55 may store a control program and control data. The HDD 55 may store setting information and processing conditions.

  The page memory 56 is a memory for developing image data to be processed. For example, the image data read by the scanner 1 is stored in the page memory 56 after being subjected to image processing. The image data stored in the page memory 56 is subjected to image processing for printing and output to the printer 2, stored in the HDD 55, or transmitted to an external device via the external interface 57a.

  The printer controller 57 controls print processing in response to a print request from an external device. The printer controller 57 is connected to an external device via an external interface 57a. The printer controller 57 receives print data from an external device via the external interface 57a. The FAX controller 58 controls FAX communication (transmission / reception of facsimile data). The FAX controller is connected to a public line via a FAX interface 58a. The FAX controller 58 transmits and receives facsimile data via the FAX interface 58a and the public line. The electronic data creation unit 59 creates electronic data including image data read by the scanner 1. The external interface 59a is an interface for transmitting electronic data to an external device. For example, the external interfaces 57a and 59a may be network interfaces via a network.

The image processing unit 60 includes an input image processing unit 61, a compression unit 62, a decompression unit 63, and an output image processing unit 64.
The input image processing unit 61 functions as a scanner-type image processing unit that processes an image read by the scanner 1 as an input image. The input image processing unit 61 executes shading correction processing, gradation conversion processing, interline correction processing, and the like on the image data read by the scanner 1.

  The shading correction process is a process for correcting image data in accordance with the sensitivity variation of each photoelectric conversion element such as a CCD or the light distribution characteristic of a lamp for illuminating a document. The gradation conversion process is a process of converting the value of each pixel constituting the image data (for example, each signal value of R, G, and B) according to a lookup table. The inter-line correction process is a process for correcting a physical positional shift of each of the RGB sensors in the CCD line sensor of the scanner 1. In addition, the input image processing unit 61 may perform resolution conversion, scaling processing, brightness adjustment, contrast adjustment, saturation adjustment, sharpness adjustment, and the like on the image data acquired by the scanner 1.

  The compression unit 62 compresses the image data. For example, the compression unit 62 compresses the image data processed by the input image processing unit 61. The compression unit 62 stores the compressed image data in the page memory 56. Note that the compression unit 62 may output the compressed image data to the HDD 55 or the like. The decompression unit 63 decompresses the compressed image data. For example, the decompression unit 63 reads compressed image data from the page memory 56 and decompresses the compressed image data. The decompression unit 63 outputs the decompressed image data to the output image processing unit 64. Note that the decompressing unit 63 may output the decompressed image data to the HDD 55 or the like.

  The output image processing unit 64 functions as a correction unit. The output image processing unit 64 converts the image data into image data for printing. The output image processing unit 64 functions as a printer-type image processing unit that generates image data for printing as an output image. In the copy process, the output image processing unit 64 converts the image data read by the scanner 1 supplied through the input image processing unit 61, the page memory 56, and the like into image data for printing. In the printing process, the output image processing unit 64 converts the image data acquired by the printer controller 57 from the external device via the external interface 57a into image data for printing.

  The output image processing unit 64 includes color conversion processing, sharpening processing, image area identification processing, scaling processing, gradation correction processing, dither processing, and the like. For example, in color conversion processing, color image data composed of R (red), G (green), and B (blue) signals is converted from C (cyan), M (magenta), Y (yellow), and K (black) signals. To color image data for printing. In the sharpening process, the image data is sharpened by, for example, image data correction processing such as filter processing, inking processing, and gamma correction processing. The image area identification process identifies the type of image (character, photograph, etc.). The scaling process reduces or enlarges the image. The gradation correction process corrects the gradation in the image data. In the dithering process, the dithering process is performed on the tone-corrected image data.

Next, the deformation of the paper that occurs in the image forming process in the image forming apparatus will be described.
In an image forming apparatus such as a digital multi-function peripheral, the physical size of the image forming medium may change in the process of forming an image on the image forming medium (printing process). For example, in an electrophotographic image forming apparatus, in a fixing process, moisture contained in a sheet as an image forming medium may evaporate and the size of the sheet may be reduced. Specifically, depending on the surrounding environment and the material of the image forming medium, the A3 size may be reduced by several millimeters.

  When printing images on both sides of the paper, if the size of the paper shrinks in the printing process on the first side (front side), the image printed on the second side (back side) under the same printing conditions as the first side is The image is printed in a different size (print area deviated from the print area on the first surface) with a different size from the image printed on the first surface. In other words, when the printing process on the second side is executed under the same conditions in the printing process on the first side even though the paper size is shrunk, the image size on the front side and the back side of the paper after double-sided printing is reduced. And the print area will not fit.

  The digital multifunction peripheral according to the present embodiment has a function of reading an image printed on a sheet at a stage where a series of printing processes is completed (after fixing processing), and calculating a contraction degree of the sheet based on the read image. When detecting the contraction degree of the paper, the digital multi-function peripheral prints a test pattern for detecting the contraction degree on the paper. For example, the test pattern is added to image data to be printed on paper. In this case, the test pattern is difficult for the user to visually recognize. The test pattern is composed of a plurality of marks (position detection marks) for detecting the position. The position detection mark is formed in a very small size or a color (for example, yellow) that is difficult for humans to visually recognize so that it is difficult for the user to visually recognize the position. For example, in a normal print process, a plurality of marks may be printed in an area outside the image print area. Note that the degree of contraction of the paper may be calculated by printing an image consisting only of the test pattern on the paper.

FIG. 4A is a diagram illustrating an example of a test pattern for detecting the degree of contraction of a sheet. FIG. 4B is a diagram illustrating an example of a sheet on which the test pattern of FIG. 4A is printed.
The test pattern shown in FIG. 4A is a pattern in which position detection marks are arranged at three of the four corners of a rectangular sheet. The position detection mark can be read by the image sensor Si and is difficult for the user to visually recognize. Each position detection mark may be any mark that indicates one point on the image data.

  FIG. 5 is a configuration example of a mark for position detection. In the example shown in FIG. 5, the position detection mark has a shape in which two straight lines intersect. In each mark shown in FIG. 5, the intersection of two straight lines indicates one point in the image. A mark as shown in FIG. 5 can be composed of two straight lines having a width corresponding to a minimum of one pixel. For example, in the case of two straight lines having a minimum width of one pixel, the intersection is also one pixel. In addition, since the mark shown in FIG. 5 is composed of two straight lines, even if the entire mark cannot be read, if a plurality of points (at least two points) can be read for each line, each straight line can be predicted, and the intersection between them can be predicted. Can also be detected.

  However, the position detection mark is not limited to a cross-shaped pattern as shown in FIG. The mark for position detection should just be a thing which can pinpoint a position from the image which image sensor Si read. For example, as long as the distance between the pattern pair in the main scanning direction and the sub-scanning direction, which will be described later, is obtained, the position detection mark may have any shape. Also, the color for printing the position detection mark may be any color as long as it is difficult for the user to visually recognize the color.

  In the test pattern shown in FIG. 4A, three marks indicating three points on a sheet as an image forming medium are arranged. Each mark indicates a point for calculating a relative positional relationship in the main scanning direction and the sub-scanning direction. For this reason, in the test pattern, each mark is arranged at a position spaced apart from each other by a predetermined interval.

  The test pattern shown in FIG. 4A includes a first mark m1 disposed near the upper left of the sheet, a second mark m2 disposed near the upper right of the sheet, and a third mark disposed near the lower left of the sheet. m3. In the example shown in FIG. 4A, the first, second, and third marks m1, m2, and m3 are represented by coordinates indicating the position in the main scanning direction and the position in the sub-scanning direction with reference to the upper right end point of the sheet. Each point (intersection) shown is expressed by a coordinate value. For example, in the image shown in FIG. 4A, the first mark m1 has an intersection (X1, Y1), the second mark m2 has an intersection (X2, Y1), and the third mark m3 has an intersection ( X1, Y2).

  On the other hand, FIG. 4B shows an image after the test pattern shown in FIG. 4A is printed on paper. For example, in the image forming apparatus having the configuration example shown in FIG. 2, the image shown in FIG. 4B corresponds to an image read by the image sensor Si. In the example shown in FIG. 4B, the intersection of the first mark m1 ′ in the image printed on the paper is (Xa, Ya), the intersection of the second mark m2 ′ is (Xb, Yb), The intersection of the third mark m3 ′ is (Xc, Yc).

  Therefore, the relative positions of the first, second, and third marks in the image data before printing as shown in FIG. 4A and the first and second in the image data after printing as shown in FIG. The contraction degree of the paper generated in the printing process can be calculated from the relationship between the relative positions of the second and third marks. Here, a method for calculating the contraction degree of the sheet based on the relative distance between the marks will be described.

First, the following distance values DX and DY are calculated as the first pattern distance in the image data before printing as shown in FIG.
DX = X2-X1
DY = Y2-Y1
The distance value DX is a value indicating the relative distance between the first mark m1 and the second mark m2 in the image data before printing. In this example, the distance value DX is adopted as a reference value in the main scanning direction in the image data before printing. The distance value DY is a value indicating the relative distance between the first mark m1 and the third mark m3 in the image data before printing. In this example, the distance value DY is employed as a reference value in the sub-scanning direction in the image data before printing.

  The distance values DX and DY may be calculated each time using the above-described calculation formula. Further, when a test pattern is prepared in advance corresponding to the paper size, that is, when the positions of the first, second, and third marks can be specified corresponding to the paper size, the distance values DX and DY are set in advance. You may set it.

  After the fixing process is performed on the paper on which the test pattern shown in FIG. 4A is printed, the image sensor Si reads an image (test pattern after printing) printed on the paper. In the case of duplex printing, the sheet on which the image on the first surface is read by the image sensor Si is conveyed to the duplex printing mechanism 40 and temporarily stored. Here, it is assumed that the image sensor Si has read the image data after printing as shown in FIG.

Based on the coordinate values of the intersections of the first, second, and third marks m1 ′, m2 ′, and m3 ′ in the image data after printing as shown in FIG. 'And DY' are calculated.

  The distance value DX ′ is a value indicating the relative distance between the first mark m1 ′ and the second mark m2 ′ in the image data after printing. The distance value DY ′ is a value indicating the relative distance between the first mark m1 ′ and the third mark m3 ′ in the image data before printing.

  If the distance value DX in the image data before printing is used as a reference, the contraction degree in the main scanning direction can be calculated from the distance value DX ′ in the image data after printing. If the distance value DY in the image data before printing is used as a reference, the contraction degree in the sub-scanning direction can be calculated from the distance value DY ′ in the image data after printing.

That is, the contraction degree of the sheet generated by the printing process in the image forming apparatus is obtained from the distance values DX and DY as the first pattern distance and the distance values DX ′ and DY ′ as the second pattern distance. For example, the image forming apparatus calculates the shrinkage degree of the paper in the main scanning direction (ShrinkX) and the shrinkage degree of the paper in the sub-scanning direction (ShrinkY) by the following calculation formulas, respectively.
Shrinkage of paper in the main scanning direction (ShrinkX) = DX ′ / DX
Shrinkage of paper in the sub-scanning direction (ShrinkY) = DY ′ / DY.

  FIG. 6A is a diagram illustrating a state in which an image is printed on the first surface. In the example shown in FIG. 6A, it is assumed that the paper contracts in the process of printing an image on the first surface. Further, the shrinkage in the main scanning direction generated on the sheet shown in FIG. 6A is ShrinkX, and the shrinkage in the sub-scanning direction is ShrinkY.

  FIG. 6B is a diagram illustrating an example in which an image corrected according to the shrinkage ShrinkX and ShrinkY of the paper generated when the image of FIG. 6A is printed is printed on the second surface. The example shown in FIG. 6B shows a print area To without image correction and a print area with image correction (print area of an image scaled according to the shrinkage rate of the paper) Tc. The print region Tc with image correction is a region obtained by reducing the print region To without image correction according to the shrinkage rate of the paper, and printing corrected according to the shrinkage rate of the paper in the main scanning direction and the sub-scanning direction. This is the area to be the starting position.

  That is, an image reduced in accordance with the shrinkage rate of the paper from the print start position corrected according to the shrinkage rate of the paper in the main scanning direction and the sub-scanning direction is printed in the print region Tc. As a result, the print region Tc with image correction on the second surface of the paper as shown in FIG. 6B is printed on the first surface of the paper that has contracted in the printing process as shown in FIG. 6A. It is possible to make the region, position, size, and the like match.

Next, the flow of double-sided printing processing will be described.
FIG. 7 is a flowchart for explaining the flow of the duplex printing process.
When performing duplex printing, the CPU 51 of the system control unit 5 acquires image data to be printed on the first side (front side) and image data to be printed on the second side (back side), and a buffer memory such as the page memory 56. (ACT11). The CPU 51 generates image data to be printed on the first surface (first surface print data) by adding a test pattern to the image data to be printed on the first surface.

The CPU 51 calculates the first pattern distance in the test pattern included in the print data of the first surface (ACT12). The first pattern distance is, for example, the distance value DX in the main scanning direction and the distance value DY in the sub scanning direction as described above. The CPU 51 temporarily stores the calculated first pattern distance in a storage unit such as the main memory 52 (ACT 13).
When the test pattern is determined in advance according to the size of the paper, the first pattern distance is also determined in advance. In this case, the processing of ACTs 13 and 14 may be omitted by storing the first pattern distance in a storage unit such as the nonvolatile memory 54 according to the size of the paper.

  The CPU 51 prints the image on the first side to which the test pattern is added by the printer 2 on the first side of the paper (ACT 15). The printer 2 takes out one sheet from any of the sheet feeding cassettes and prints image data including a test pattern on the first surface of the sheet. The printer 2 forms a toner image of image data including a test pattern by an electrophotographic process and transfers it to the first surface of the paper. The fixing unit 29 fixes the toner image transferred on the paper to the paper by heating and pressurizing the paper.

  The image sensor Si reads an image on the first surface of the sheet fixed by the fixing unit 29 (ACT 16). The image sensor Si outputs image data read from the first surface of the paper fixed by the fixing unit 29 to the system control unit 5. Further, the sheet subjected to the fixing process is conveyed to the duplex printing mechanism 40. The double-sided printing mechanism 40 takes in and reverses the paper and stacks the paper until a desired print timing is reached (until a print start instruction is received from the system control unit 5) (ACT 17).

  The system control unit 5 receives the image data from the image sensor Si, calculates the contraction degree of the paper, and corrects the image printed on the second surface according to the calculated contraction degree. That is, the CPU 51 of the system control unit 5 detects a plurality of position detection marks from the image data read by the image sensor Si (ACT 18). For example, in the case of a mark indicating the position at the intersection of two straight lines as shown in FIG. 5, the CPU 51 may detect the two straight lines constituting the mark and detect the coordinates of the intersection. In the case of the mark shown in FIG. 5, for example, if two or more pixels can be detected for each line, each straight line can be predicted. Therefore, even if the mark as shown in FIG. 5 cannot be read completely, two straight lines can be detected (predicted), and the coordinates of their intersection can be detected.

  When the position detection marks are detected, the CPU 51 calculates the second pattern distance from the positions (coordinate values) indicated by these marks (ACT 19). The second pattern distance is a value corresponding to the first pattern distance. The second pattern distance is, for example, the distance value DX ′ in the main scanning direction and the distance value DY ′ in the sub-scanning direction as described above. The distance value DX ′ in the main scanning direction and the distance value DY ′ in the sub-scanning direction can be calculated from the coordinate values of each mark by the above-described calculation formula.

  When the second pattern distance is calculated, the CPU 51 calculates a contraction degree in the main scanning direction and a contraction degree in the sub-scanning direction from the stored first pattern distance and the calculated second pattern distance ( ACT20). The CPU 51 generates print data for the second surface by correcting the image to be printed on the second surface based on the calculated degree of contraction (ACT 21). For example, the CPU 51 reduces the main scanning direction of an image to be printed on the second surface at a reduction ratio according to the contraction degree in the main scanning direction, and prints on the second surface at a reduction ratio according to the contraction degree in the sub-scanning direction. The sub-scanning direction of the image to be reduced is reduced.

  When the print data for the second surface is generated, the CPU 51 calculates the print start position of the image on the second surface based on the contraction degree in the main scanning direction and the contraction degree in the sub-scanning direction (ACT22). When the print start position for the second side is calculated, the CPU 51 causes the printer 2 to execute print processing on the second side of the paper stacked in the double-sided printing mechanism 40 (ACT 23). The printing process on the second surface is performed by printing the print data of the second surface, which is corrected according to the shrinkage rate of the paper, on the second surface of the paper with the calculated print start position as a base point.

As described above, the image forming apparatus includes an image sensor that reads an image of a sheet after the fixing process in order to detect the contraction degree of the sheet in the printing process. The image sensor reads a plurality of position detection marks printed on the surface of the paper. The image forming apparatus calculates the contraction degree of the paper based on the relative distance between the marks in the image data before printing and the relative distance between the marks in the image data read from the paper after the image processing by the image sensor. The image to be printed on the back surface is reduced according to the contraction degree of the paper, and the image reduced from the print start position according to the contraction degree is printed on the back surface of the paper.
According to the image forming apparatus as described above, double-sided printing in which the printing area on the front surface and the printing area on the back surface coincide with each other can be realized even when the paper contracts in the printing process.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... Scanner, 2 ... Printer, 5 ... System control part, 24 ... Registration roller, 25 ... Image formation part, D ... Photosensitive drum, 26 ... Exposure part, 27 ... Intermediate transfer belt, Si ... Image sensor, 28 ... Transfer , 29... Fixing unit, 40... Double-sided printing mechanism, 41... Reverse conveyance path, 51.

Claims (10)

An image forming apparatus,
Image forming means for forming an image including a mark for position detection on the first surface of the image forming medium;
Reading means for reading an image on the first surface of the image forming medium on which an image including the mark is formed by the image forming means;
Detecting means for detecting the mark from image data read by the image reading means;
Calculation means for calculating the degree of contraction generated in the image forming medium in image formation by the image forming means based on the amount of variation between the mark position detected by the detection means and the mark position in the image formed on the first surface. When,
Correction means for correcting an image formed on the second surface of the image forming medium based on the contraction degree calculated by the calculation means;
Control means for causing the image forming means to form an image corrected by the correcting means in a print area corresponding to the degree of contraction on the second surface of the image forming medium;
An image forming apparatus comprising: The image forming unit forms a plurality of marks on the first surface indicating a plurality of positions for measuring a distance in the main scanning direction and a distance in the sub scanning direction on the image forming medium;
The image forming apparatus according to claim 1, wherein: The calculating means calculates a contraction degree in the main scanning direction generated in the image forming medium and a contraction degree in the sub-scanning direction generated in the image forming medium;
The image forming apparatus according to claim 2, wherein: The correcting unit reduces an image formed on the second surface in accordance with a contraction degree in the main scanning direction and a contraction degree in the sub-scanning direction;
The image forming apparatus according to claim 3, wherein: The control unit forms an image corrected by the correction unit from a printing start position on the second surface according to the contraction degree in the main scanning direction and the contraction degree in the sub-scanning direction;
The image forming apparatus according to claim 4, wherein: An image forming apparatus control method comprising:
Forming an image including a mark for position detection on the first surface of the image forming medium;
Read an image of the first surface of the image forming medium on which an image including the mark is formed,
Detecting the mark from the read image data;
Calculating a degree of contraction generated in the image forming medium in the image formation based on a variation amount between the detected mark position and the mark position in the image formed on the first surface;
Correcting the image formed on the second surface of the image forming medium based on the calculated shrinkage,
Forming the corrected image in a print area corresponding to the degree of shrinkage on the second surface of the image forming medium;
A control method for an image forming apparatus. A plurality of marks indicating a plurality of positions for measuring a distance in the main scanning direction and a distance in the sub-scanning direction on the image forming medium are formed on the first surface of the image forming medium.
The method of controlling an image forming apparatus according to claim 6, wherein: As the degree of contraction, the degree of contraction in the main scanning direction generated on the image forming medium and the degree of contraction in the sub-scanning direction generated on the image forming medium are calculated.
The method of controlling an image forming apparatus according to claim 7, wherein: The correction reduces the image formed on the second surface in accordance with the contraction degree in the main scanning direction and the contraction degree in the sub-scanning direction.
The method of controlling an image forming apparatus according to claim 8, wherein: The corrected image is formed from a print start position on the second surface according to a contraction degree in the main scanning direction and a contraction degree in the sub-scanning direction.
The method for controlling an image forming apparatus according to claim 9, wherein:

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