JP2007102090A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately and simultaneously detect the lengths of a sheet in the main and the sub scanning directions without being affected by uneven velocity at conveying the sheet, and, to realize high-accuracy correction of images. <P>SOLUTION: The image forming apparatus includes two line sensors 105 and 106 for detecting four detection points on the outline of the sheet. The apparatus also includes a main scanning direction calculation part 114 for calculating the length of the sheet in the main scanning direction: and a sub scanning direction calculation part 115 for calculating the length of the sheet in the sub scanning direction, based on the detection points detected by the two line sensors 105 and 106. The apparatus also includes an image correction and control part 116 for deciding an image correction ratio, related to the image formation on the sheet based on the calculated lengths in the main and sub scanning directions. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a printer, a copying machine, and a facsimile, and more particularly to an image forming apparatus that performs image correction processing on an image formed on a sheet.

  2. Description of the Related Art Conventionally, image forming apparatuses such as printers, copiers, and facsimiles are known that form an image on the back side of a sheet that has once passed through a fixing unit during double-sided printing.

  The sheet that has passed through the fixing unit may shrink due to application of heat and pressure when passing through the fixing unit. Therefore, in order to match the front and back magnification during double-sided printing, the sheet length is detected and image correction is performed.

In such an image forming apparatus, a method for detecting the length of a sheet on a sheet conveyance path has been proposed (for example, see Patent Document 1). Specifically, a method for detecting the length of a sheet by measuring the time from the leading edge to the trailing edge of the sheet by an output signal of a sensor arranged on the conveyance path during conveyance of the sheet is disclosed.
Japanese Patent Laid-Open No. 03-172255

  However, the actual sheet conveyance speed may be uneven due to the eccentricity of the sheet conveyance roller. However, the invention described in Patent Document 1 does not disclose a technique for eliminating the uneven speed.

  In other words, if speed unevenness occurs during sheet conveyance, there is a problem in that when measuring the time from the leading edge to the trailing edge of the sheet, it is affected by the speed unevenness and the exact sheet length cannot be detected. .

  SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and the object of the present invention is to accurately detect the lengths of the main scanning and sub-scanning directions of the sheet simultaneously without being affected by the speed unevenness during sheet conveyance. An object of the present invention is to provide an image forming apparatus capable of performing the above.

  In order to achieve the above object, an image forming apparatus according to the present invention includes a sheet conveying unit that conveys a sheet, and two line sensors that detect four detection points from the outline of the sheet conveyed by the sheet conveying unit. . Further, a main scanning length calculation unit for calculating a length in the main scanning direction of the sheet from the detection points detected by the two line sensors, and a sub scanning direction of the sheet from the detection points detected by the two line sensors. Sub-scanning length calculating means for calculating the length. Further, control for determining an image correction rate of image formation performed on the sheet based on the main scanning direction length calculated by the main scanning length calculation unit and the sub scanning direction length calculated by the sub scanning length calculation unit. And means.

  According to the present invention, it is possible to accurately detect the length of the main scanning and sub-scanning directions of the sheet simultaneously without being affected by the speed unevenness during sheet conveyance, and to realize highly accurate image correction.

  Embodiments of an image forming apparatus according to the present invention will be described with reference to the drawings. Hereinafter, a color image forming apparatus will be described as an example, but it goes without saying that the present invention may be applied to a black and white image forming apparatus.

  An electrophotographic color image forming apparatus of this embodiment will be described with reference to FIG. The color image forming apparatus of the present embodiment forms an electrostatic latent image with image light formed based on an image signal in an image forming unit, and develops the electrostatic latent image to form a visible image. . Further, this color visible image is transferred to a sheet as a recording medium, and then the color visible image is fixed.

  The image forming unit includes photosensitive drums 5Y, 5M, 5C, and 5K and injection charging units 7Y, 7M, 7C, and 7K as primary charging units arranged in parallel for the number of development colors. The image forming unit includes developing units 8Y, 8M, 8C, and 8K, toner cartridges 11Y, 11M, 11C, and 11K, an intermediate transfer body 12, a material supply unit, a transfer unit, and a fixing unit 13.

  The photosensitive drums 5Y, 5M, 5C, and 5K are configured by applying an organic optical transmission layer to the outer periphery of an aluminum cylinder, and rotate by receiving a driving force of a driving motor (not shown). The drive motor rotates the photosensitive drums 5Y, 5M, 5C, and 5K in the counterclockwise direction according to the image forming operation. Exposure light to the photosensitive drums 5Y, 5M, 5C, and 5K is sent from the scanner units 10Y, 10M, 10C, and 10K, and the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K are selectively exposed to sequentially expose the light. An electrostatic latent image is formed.

  As primary charging means, four injection chargers 7Y for charging the photosensitive drums 5Y, 5M, 5C, and 5K of yellow (Y), magenta (M), cyan (C), and black (K) for each station, 7M, 7C, 7K. Each injection charger is equipped with sleeves 7YS, 7MS, 7CS, and 7KS.

  As developing means, in order to visualize the electrostatic latent image, four developing devices 8Y, 8M for developing yellow (Y), magenta (M), cyan (C), and black (K) for each station, 8C and 8K. Each developing device is provided with sleeves 8YS, 8MS, 8CS, and 8CK. Each developing device is detachably attached to the apparatus main body.

  The intermediate transfer body 12 is an endless belt that is stretched around the driving roller 18a and the driven rollers 18b and 18c. The intermediate transfer body 12 is in contact with the photosensitive drums 5Y, 5M, 5C, and 5K, and rotates in the clockwise direction when forming a color image, and is acted upon by the primary transfer rollers 6Y, 6M, 6C, and 6K for the respective colors. Receive sequential transfer. The sheet P conveyance path includes an A route from a feed tray (not shown), a B route from a feed cassette (not shown), and a C route from a duplex unit. The sheet P is conveyed along a conveyance path constituted by the conveyance rollers 24 and the like, and reaches the registration rollers 23. This sheet P is detected by the pre-registration sensor 19.

  During image formation, the pre-registration sensor 19 stops the conveyance of the sheet P for a predetermined time in accordance with the timing at which the color visible image on the intermediate transfer body 12 reaches the transfer area. When the sheet P is fed from the registration roller 23 to the transfer area, the secondary transfer roller 9 comes into contact with the intermediate transfer body 12 and the sheet P is nipped and conveyed, the sheet P is transferred to the sheet P on the intermediate transfer body 12. These color visible images are simultaneously superimposed and transferred.

  The secondary transfer roller 9 contacts the intermediate transfer body 12 as indicated by the solid line while the color visible image is superimposed and transferred onto the intermediate transfer body 12, but at the end of the printing process, the position indicated by the dotted line Separate.

  The fixing unit 13 fixes the transferred color visible image while conveying the sheet P, and includes a fixing roller 14 that heats the sheet P and a pressure roller 15 that presses the sheet P against the fixing roller 14. ing. The fixing roller 14 and the pressure roller 15 are formed in a hollow shape, and each includes a heater (not shown). The sheet P holding the color visible image is conveyed by the fixing roller 14 and the pressure roller 15, and the toner is fixed on the surface by applying heat and pressure.

  The sheet P after the fixation of the visible image is then discharged by the discharge roller 29 to the discharged material part (D or E route) or the duplex unit (route F), and the image forming operation is completed. Switching of the transport path is performed by flappers 27 and 28. The discharged material from the fixing unit 13 of the sheet P is detected by a fixed discharged material sensor 20.

  The cleaning unit 21 stores waste toner after the four color visible images formed on the intermediate transfer body 12 are transferred to the sheet P.

  At the time of duplex printing, the sheet P is conveyed to the duplex unit (route F). The sheet P is conveyed by the sheet conveying rollers 107 to 109, and the lengths of the sheet P in the main scanning and sub-scanning directions are detected by the line sensors 105 and 106 during the conveyance. Details of the length detection of the sheet P in the main scanning and sub-scanning directions will be described later.

  FIG. 2 is a schematic diagram illustrating a configuration for detecting the sheet length of the present embodiment, and FIG. 3 is a block diagram illustrating a control configuration of the present embodiment. First, a sheet size detection method and an image correction rate determination method will be described with reference to FIGS. In this configuration, the length can be detected by extracting two points. Here, the case of extracting three points will be described.

  The sheet P in FIG. 2 is a sheet that has been transported after passing through the fixing unit 13 and reversed in the reverse path. In FIG. 2, the line sensor 105 and the line sensor 106 are arranged in the diagonal direction of the conveyed sheet P. Specifically, the line sensor 105 is provided so as to cross two sides constituting the vertex of the sheet, and the line sensor 106 is provided so as to cross two sides constituting the vertex positioned in the diagonal direction.

  The sheet P conveyed by the sheet conveying roller 109 detects four points 101 to 104 of the sheet by the line sensor 105 and the line sensor 106. By providing the line sensors 105 and 106 on the double-sided conveyance path, it is possible to detect the length of the sheet after fixing the front surface image and before transferring the back surface image, and to appropriately perform image correction of the back surface image. it can. Further, as shown in FIG. 1, the line sensors 105 and 106 are provided in a substantially straight conveyance path, so that the length of the sheet can be accurately detected without considering the bending of the sheet.

  Here, as shown in FIG. 4, the line sensor 105 and the line sensor 106 are arranged at a predetermined interval. Therefore, for example, the main scanning direction distance Lm0 and the sub-scanning direction distance Ls0 between the leftmost detection point of the line sensor 105 and the leftmost detection point of the line sensor 106 are also predetermined distances. Similarly, the main scanning direction distance Lmn and the sub-scanning direction distance Lsn between the rightmost detection point of the line sensor 105 and the rightmost detection point of the line sensor 106 are also predetermined distances. In addition, the main scanning direction and the sub-scanning direction between the arbitrary detection points of the line sensor 105 and the line sensor 106 are predetermined distances.

  Three detection points 101 to 104 detected by the line sensor 105 and the line sensor 106 are extracted by the main scanning direction extraction unit 112 in FIG. Similarly, three points 101, 102, and 103 are extracted by the sub-scanning direction extraction unit 113.

Next, in the main scanning direction calculation unit 114, the length Lm in the main scanning direction is Lm = Lm1 + Lm2 from the detection points 101, 102, 104 extracted by the main scanning direction extraction unit 112.
Is calculated.

Similarly, in the sub-scanning direction calculation unit 115, the length Ls in the sub-scanning direction is Ls = Ls1 + Ls2 from the detection points 101, 102, 103 extracted by the sub-scanning direction extraction unit 113.
Is calculated. As described above, the lengths of the main scanning and sub-scanning directions of the sheet are calculated simultaneously.

  As described above, if the detection points 101 to 104 are detected at the timing when the sheet P is applied to the line sensors 105 and 106, the sheet P is accurately detected in the main scanning and sub-scanning directions without being affected by the speed unevenness of the conveying roller. The length can be detected simultaneously.

  The calculated Lm and Ls are compared by the image correction control unit 116 with the length of the sheet before fixing in the main scanning and sub-scanning directions to determine the image correction rate. Here, the length in the main scanning and sub-scanning directions of the sheet before fixing is determined from the size data (A4, A3, etc.) of the fed sheet.

  After that, the image corrected by the image forming unit 117 is formed on the sheet that has been transported once through the fixing unit 13 and reversed in the reverse path. That is, even when the sheet is shrunk after passing through the fixing unit 13, image formation can be performed with an image correction rate that matches the shrinkage amount.

  When an image is formed on a sheet based on the calculated image correction rate, the image may be formed using magnification correction using, for example, known image clock modulation. Since this method is disclosed in Japanese Patent Application Laid-Open No. 2001-324852 and the like, description thereof is omitted.

  Note that when the line sensors 105 and 106 cannot detect the detection points 101 to 104 of the reversely conveyed sheet, image correction is performed at a predetermined correction rate determined in advance for each sheet size. Is done.

  In the present embodiment, the case of three-point extraction has been described, but the length of the sheet P in the main scanning and sub-scanning directions may be detected by two-point extraction. That is, it goes without saying that Lm may be calculated from the detection points 101 and 104 and Ls may be calculated from the detection points 102 and 103.

  Next, the movement of the line sensors 105 and 106 will be described.

  FIG. 5A shows a state in which the line sensors 105 and 106 are in the initial position while the image forming apparatus is on standby. The initial standby positions of the line sensors 105 and 106 are positions where a minimum size sheet that can be fed to the image forming apparatus can be detected.

  After the user sets double-sided printing from an operation unit (not shown) attached to the image forming apparatus and gives an instruction to start image formation, the original is read by an image reading apparatus (not shown) to determine the sheet size. . Thereafter, as shown in FIG. 5B, the line sensor 105 moves to a predetermined standby position according to the sheet size in the main scanning direction (arrow 123) and the sub-scanning direction (arrow 124).

  In the figure, the line sensor 106 is fixed in position. In the figure, reference numeral 50 denotes an HP sensor for detecting the home position of the line sensor 105. The line sensor 105 is moved by a predetermined amount by a main scanning direction moving motor and a sub scanning direction moving motor (both pulse motors) (not shown). When the line sensor 105 is moved, it waits at the same position until the sheet size is changed. When the size is changed, the line sensor 105 returns to the HP sensor 50 and waits according to the changed size. Move again to position.

  FIG. 6 is a flowchart showing the main image correction control. First, the length of the sheet P reversely conveyed by the line sensors 105 and 106 is detected (S101). Next, it is determined whether or not the detection points 101 to 104 of the sheet have been detected by the main scanning direction extraction unit 112 and the sub scanning direction extraction unit 113 (S102).

  If the detection points 101 to 104 of the sheet can be detected in step S102, the detected length is compared with the length of the fed sheet, and the correction magnification is determined (S103).

  If the detection points 101 to 104 of the sheet cannot be detected in step S102, image correction is performed at a predetermined correction magnification determined for each sheet size (S104). Then, an image according to the correction magnification is formed on the sheet P (S105).

  In this embodiment, the case where the line sensor 105 moves has been described. However, the line sensor 106 may be set to move.

  Further, the line sensors 105 and 106 may be moved simultaneously. In this case, the movement time of the line sensor can be shortened.

  In this embodiment, the length in the main scanning and sub-scanning directions of the sheet before fixing is determined from the size data of the fed sheet. However, the sheet before fixing is conveyed to the position of the line sensors 105 and 106. Actual length may be measured.

  According to the present embodiment described above, even when an image is formed on the back side of the sheet that has shrunk through the fixing unit, the main scanning of the sheet is accurately performed without being affected by the speed unevenness during sheet conveyance. The length in the sub-scanning direction can be detected, and high-accuracy image correction can be realized.

1 is a schematic view of an electrophotographic color image forming apparatus according to an embodiment of the present invention. It is the schematic explaining the structure which detects the length of the sheet | seat which concerns on the Example of this invention. It is a block diagram explaining the control structure which concerns on the Example of this invention. It is a figure explaining arrangement | positioning of the line sensor which concerns on the Example of this invention. It is a figure explaining the movement of the line sensor which concerns on the Example of this invention. It is a flowchart which shows the image correction control which concerns on the Example of this invention.

Explanation of symbols

50 HP sensors 101 to 104 Detection points 105 and 106 Line sensors 107 to 109 Sheet conveyance rollers 112 Main scanning direction extraction unit 113 Sub scanning direction extraction unit 114 Main scanning direction calculation unit 115 Sub scanning direction calculation unit 116 Image correction control unit 117 Image Forming part P sheet

Claims (10)

Sheet conveying means for conveying the sheet;
Two line sensors for detecting four detection points from the contour of the sheet conveyed by the sheet conveying means;
Main scanning length calculation means for calculating the main scanning direction length of the sheet from the detection points detected by the two line sensors;
Sub-scanning length calculating means for calculating the sub-scanning direction length of the sheet from the detection points detected by the two line sensors;
Control means for determining an image correction rate for image formation performed on the sheet based on the main scanning direction length calculated by the main scanning length calculating means and the sub-scanning direction length calculated by the sub-scanning length calculating means; ,
An image forming apparatus comprising: Transfer means for transferring a toner image to a sheet;
A fixing unit for fixing the toner image transferred by the transfer unit to the sheet;
The control unit determines the image correction rate of the back image when forming a double-sided image based on the main scanning direction length and the sub-scanning direction length of the sheet before and after fixing by the fixing unit. The image forming apparatus according to claim 1. The length in the main scanning direction and the length in the sub scanning direction of the sheet before fixing by the fixing unit is determined from the sheet size data,
3. The image forming apparatus according to claim 2, wherein the main scanning direction length and the sub scanning direction length of the sheet fixed by the fixing unit are calculated by the main scanning length calculation unit and the sub scanning length calculation unit. apparatus.   The length before and after fixing by the fixing unit is calculated by the main scanning length calculating unit and the sub-scanning length calculating unit, respectively. 2. The image forming apparatus according to 2.   The image forming apparatus according to claim 1, wherein at least one of the two line sensors is movable to a predetermined standby position corresponding to a sheet size. The two line sensors are composed of a first line sensor and a second line sensor,
The image forming apparatus according to claim 1, wherein the first line sensor and the second line sensor are provided in a diagonal direction of the sheet. The first line sensor is provided at a position crossing two sides constituting the vertex of the sheet,
The image forming apparatus according to claim 6, wherein the second line sensor is provided at a position crossing two sides constituting a vertex that is located diagonally to the vertex of the sheet.   The control unit performs image correction at a predetermined correction rate determined in advance for each sheet size when the two line sensors cannot detect four detection points. The image forming apparatus described.   The image forming apparatus according to claim 1, wherein the two line sensors are provided in a double-sided conveyance path used during double-sided printing.   The image forming apparatus according to claim 1, wherein the two line sensors are provided in a substantially straight conveyance path.

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