JP2006211462A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of measuring slanting slippage for a manuscript prior to image formation onto a form, and conducting correction processing for the slanting slippage based on the result of the measurement to form an image in a form position same as the manuscript. <P>SOLUTION: In the copying machine, a manuscript is conveyed by a manuscript conveying part 11 to a slanting correction detection position S4 on a reflection plate 117 for slanting correction detection. Prior to formation of an electrostatic latent image onto a surface of a photoconductor drum by an LED head, image data for correction is generated from the manuscript by a manuscript reading part 17. While slanting slippage for the manuscript is measured from the image data for correction by a CPU, correction processing is applied to image data generated at a normal reading position S3 based on the result of the measurement. Then the image data are sent to the LED head, and image formation onto a form is carried out by a image forming part. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, or a multifunction machine, and more particularly to a technique for correcting the image data in an image forming apparatus having an automatic document feeding function.

  In an image forming apparatus having a conventional automatic document feeding function (that is, ADF [Auto Document Feeder] or DP [Document provision]; hereinafter referred to as ADF), the ADF technology is mechanically transferred to the document reading unit. By only reducing the oblique feeding as much as possible, it was only possible to faithfully reproduce the document placed on the ADF document table.

Recently, as a device for correcting the oblique feeding of the document to the document reading unit, the sensor at the positions at both ends of the document based on the detection result of the sensor provided at the both-end conveying position between the document placing table and the document reading position. Image information that detects the amount of misalignment at the timing of passing the image, and controls the acceleration / deceleration of the skew correction roller in the direction to correct the misalignment so that the skew amount can be corrected before the leading edge of the document reaches the reading position A processing apparatus has been disclosed and proposed (see, for example, Patent Document 1).
JP 2000-98672 A

  Certainly, with the image forming apparatus having the above-described configuration, the oblique sheet feeding from the document table to the document reading unit can be reduced as much as possible.

  In the image information processing apparatus disclosed in Patent Document 1, the amount of misalignment of a document being conveyed is detected by a sensor, and the amount of misalignment is corrected by a skew correction roller. Paper feeding can be reduced.

  However, in the conventional image forming apparatus, in order to mechanically reduce the oblique feeding, strict management is required from the viewpoint of variation in mass production, and the oblique feeding that has not occurred at the time of purchase due to deterioration due to use is over time. There is a problem that a copy image of a document skewed on a sheet is formed due to a change.

  In addition, the image information processing apparatus of Patent Document 1 requires a new sensor for detecting the amount of misalignment of the document being conveyed and a roller for correcting the same, which increases the cost of the apparatus. was there.

  In view of the above problems, the present invention makes it possible to measure the amount of skew of a document prior to image formation on a sheet without adding a new sensor, and based on the measurement result, the skew displacement of the document. An object of the present invention is to provide an image forming apparatus capable of performing an amount correction process and forming an image on a paper position similar to that of a document.

  In order to achieve the above object, an image forming apparatus according to the present invention includes a document reading unit that reads an image of a document placed at a predetermined reading position and generates image data, and a document that is stored in a predetermined portion of the document reading unit. A document conveying unit that conveys the image to a reading position; and an image forming unit that forms an image on a sheet based on the image data. The document conveying unit has a predetermined area in a region facing the reading position. A memory unit having a color reflecting plate and a white reflecting plate, and storing an oblique correction value corresponding to an oblique displacement amount of the document conveyed by the document conveying unit for each document size; and After the original is conveyed to an oblique correction detection reading position facing a reflector of a predetermined color and the original reading unit generates correction image data from the leading edge of the original to a predetermined area, the original conveyance is further performed. Part of the white reflection A control unit that transports the document to a normal reading position opposite to the image forming unit, and causes the document reading unit to generate image data of the document, and calculates a skew amount from the correction image data, and corresponds to the skew amount. And a correction processing unit that performs correction processing on the image data based on the oblique correction value. By adopting such a configuration, it is possible to suppress the variation in printing caused by the oblique deviation due to the oblique feeding of the original without adding a new sensor, and further, the oblique feeding caused by the change of the apparatus with time. Therefore, it is possible to provide a copy image in which the image forming position on the paper is always stable.

  Further, the memory unit of the image forming apparatus having the above-described configuration stores the coordinates of the edge of the document when the document is conveyed without oblique displacement for each document size, and the correction processing unit is configured to store the correction image. The coordinates of the edge of the document are discriminated from the data, and the coordinates of the edge and the coordinates of the edge of the document stored in the memory unit are compared to calculate the amount of skew. By adopting such a configuration, it is possible to accurately obtain the amount of oblique deviation from the coordinates of the edge of the document, so that it is possible to always provide a copy image with a stable image forming position on the paper.

  Further, the image forming unit of the image forming apparatus having the above-described configuration includes a light emitting diode head in which a predetermined number of light emitting diodes that form an electrostatic latent image are arranged on the surface of the photosensitive drum, and the memory unit includes: An attachment correction value corresponding to the attachment position of the light emitting diode head is stored, and the correction processing unit is configured to perform correction processing on the image data based on the attachment correction value and the oblique correction value. By adopting such a configuration, even when a light emitting diode head is used, the amount of oblique deviation can be accurately obtained from the coordinates of the edge of the document, so that a copy image in which the image forming position on the paper is always stable Can be provided.

  In the image forming apparatus having the above-described configuration, the oblique correction mode in which an image is formed on a sheet based on the image data subjected to the correction processing by the correction processing unit, and the correction processing by the correction processing unit are converted into image data. It is configured to include means for selecting one of print modes in which image formation is performed on a sheet without being applied. By adopting such a configuration, it is possible to select a print mode having a high copying speed when image data correction processing is not necessary.

  As described above, with the image forming apparatus according to the present invention, it is possible to suppress variations in printing caused by oblique misalignment due to oblique feeding of an original without adding a new sensor, and further, over time of the apparatus. It is possible to suppress variations in printing due to oblique paper feeding caused by changes, and it is possible to provide a copy image in which the image forming position on the paper is always stable.

  Hereinafter, a case where the present invention is applied to a copying machine will be described as an example. FIG. 1 is a block diagram showing the configuration of the main part of a copying machine according to the present invention, and FIG. 2 is a longitudinal sectional view schematically showing the structure of the main part of the copying machine according to the present invention. As shown in both figures, the copier 1 of this embodiment includes a central processing unit 10 (hereinafter referred to as a CPU [Central Processing Unit] 10) that controls the operation of the entire apparatus, and a document transport that automatically transports a document. Unit 11, a document reading unit 17 that reads the document transported from document transport unit 11 to generate normal image data and generates image data related to detection of the amount of oblique deviation from the normal reading position of the document, and a predetermined document data An image processing unit 16 that performs image processing, an operation display unit 12 including an operation unit (such as a numeric keypad or a touch panel) and a display unit (such as a liquid crystal display), and image formation that forms a toner image on a sheet based on the image data Unit 15, fixing unit 18 that fixes an image formed of the toner image formed on the sheet by image forming unit 15 to the sheet, sheet discharge unit 19 that is a sheet discharge destination, and image forming unit A paper feed unit 13 that feeds paper 5 and an oblique correction value corresponding to the number of lines of a preset line width of image data for correcting an oblique displacement amount of the document for each paper size, as will be described later. An attachment correction value for correcting an oblique displacement of a copy image (that is, an electrostatic latent image on a photosensitive drum) at the time of image formation due to an inherent attachment position displacement of an LED head (that is, a light emitting diode head) described later, ROM (Read Only Memory) storing the coordinates of the edge of the document and various control programs when the document is conveyed without skew, RAM [Random Access Memory] used as a work area, and various data and programs are stored. And a memory unit 14 composed of a hard disk. The document transport unit 11 corresponds to an ADF.

  In addition to controlling the operation of the entire apparatus, the CPU 10 controls the measurement of the amount of oblique displacement of the document in order to prevent oblique displacement during formation of an electrostatic latent image on the surface of the photosensitive drum by the LED head, which will be described in detail later. It also serves as a correction processing unit that performs correction processing on the image data based on the attachment correction value and the skew correction value, and performs control related to the correction processing of the image data of the document that is generated obliquely.

  As shown in FIG. 2, the paper feed unit 13 includes a plurality of (three in this embodiment) paper storage units 131 a to 131 c serving as a paper supply source to the image forming unit 15, and each of the paper storage units 131 a to 131 c. A sheet conveyance unit 132 serving as a common sheet conveyance path from the image forming unit 15 to the image forming unit 15.

  The image forming unit 15 includes a yellow image forming unit 15a that forms a yellow toner image on a paper, a magenta image forming unit 15b that forms a magenta toner image on the paper, and a cyan toner image on the paper. The image forming apparatus includes a cyan image forming unit 15c that forms an image and a black image forming unit 15d that forms a black toner image on a sheet.

  Further, as shown in FIG. 2, the yellow image forming unit 50a, the magenta image forming unit 50b, the cyan image forming unit 50c, and the black image forming unit 50d are arranged in yellow, magenta, cyan, and black colors based on the image data. Image end support photosensitive drums 21a to 21d on which toner images are formed on the surfaces of the drums, chargers 24a to 24d for uniformly charging the surfaces of the photosensitive drums 21a to 21d to predetermined potentials, and LED [ An LED array in which Light Emitting Diodes are arranged in a line corresponding to the width of the photosensitive drums 21a to 21d (that is, the printing width) is used as a light source, and the electrostatic latent image is irradiated to each photosensitive drum by irradiating LED light based on image data. LED heads 23a to 23d formed on the surfaces of 21a to 21d and electrostatic latent images on the surfaces of the photosensitive drums 21a to 21d, respectively. Developing units 22a to 22d that form toner images of yellow, magenta, cyan, and black on the surfaces of the respective photosensitive drums 21a to 21d, and a sheet on which the toner images formed on the surfaces of the respective photosensitive drums 21a to 21d are conveyed. Transfer rollers 26a to 26d for electrostatic transfer, and cleaning units 25a to 25d for collecting toner remaining on the surfaces of the photosensitive drums 21a to 21d and discharging the surfaces of the photosensitive drums 21a to 21d. It consists of A solid line arrow in FIG. 2 indicates a sheet conveyance path.

  Next, the document conveying unit 11 and the document reading unit 17 in the copying machine 1 of the present embodiment will be described below with reference to the drawings. FIG. 3 is a longitudinal sectional view schematically showing the document conveying unit 11 and the document reading unit 17.

  As shown in FIGS. 1 to 3, the document transport unit 11 detects a document table 114 for placing a document and the presence or absence of a document on the document table 114, and is turned on when the document is detected. A document presence / absence detection switch 111 that transmits a signal to the CPU 10, a pair of rollers 115 that convey the document set on the document table 114 from the lower document one by one toward the document reading unit 17, and the rollers 115. A pair of rollers 116 for transporting a document to be described later to a document glass contact glass 173 and the presence / absence of a document that passes through the installation position are detected. When a document is detected, it is turned on and a detection signal is transmitted to the CPU 10. It is arranged in a region facing the document detection switch 112 and a document conveying portion contact glass 173 described later, and is capable of clearly distinguishing the color difference from the document. Of the color (for example, black, silver, or yellow), and is inclined in a region facing the oblique correction detecting reflective plate 117 used for obtaining the oblique correction value and a document conveying portion contact glass 173 described later. A document holding plate 118 that is disposed on the downstream side of the document conveyance path 123 with respect to the correction detection reflection plate 117 and is formed of a white reflection plate and is used when reading a document image using the normal document conveyance unit 11. Then, the document discharge table 121 that is the discharge destination of the document that has been read by the document reading unit 17 at the position of the document pressing plate 118 and the document at the position of the document pressing plate 118 are directed toward the document discharge table 121. A pair of rollers 119 for conveying, a pair of rollers 120 for discharging the document conveyed by the rollers 119 to the document discharge table 121, a roller 115, The document conveying stepping motor 113, which is a driving source for rotationally driving 16, 119, and 120, and a white reflector, the document conveying unit 11 is not used, and the document is manually placed on a contact glass 174 described later. A document holding plate 122 for manual placement used for printing. Note that the oblique correction detection reflector 117, the document pressing plate 118, and the manual placement document pressing plate 122 are pressed from above by a spring or the like in the direction of the white arrow so that the document does not bend when the sheet is passed. ing.

  As shown in FIGS. 1 to 3, the document reading unit 17 has a document conveying unit contact glass 173 serving as a dedicated document image reading window when the document conveying unit 11 is used, and a document is manually placed. A contact glass 174 serving as a reading window for the original image, a light source (not shown), and a reflection glass 175a. The light source (not shown) is driven by a driving force of a moving frame driving stepping motor 172 described later. Irradiates the original light, the oblique correction detection reflecting plate 117, the document pressing plate 118, or the hand-held document pressing plate 122 with the reflected light toward the second moving frame 176 described later by the reflecting glass 175a. While having a first moving frame 175 to be reflected and reflecting glasses 176a and 176b, while being driven by a driving force of a moving frame driving stepping motor 172 described later, The second moving frame 176 that reflects the light incident from the first moving frame 175 by the reflection glasses 176a and 176b and collects the light on the CCD 171 described later, and the light collected from the second moving frame 176 is blue, green, and A CCD (Charge Coupled Devices) 171 that inputs image data color-separated into three red components to the CPU 10 or the image processing unit 16, and a drive source for driving the first moving frame 175 and the second moving frame 176 And a moving frame driving stepping motor 172. As shown in FIG. 3, the first moving frame 175 and the second moving frame 176 are positioned at the standby position S1 in the standby state, and are moved to the diagonal correction detection position S2 when the diagonal correction value is detected. Further, when the original image is read when the original conveying unit 11 is used, the first moving frame 175 moves to the normal reading position S3.

  The document conveying unit contact glass 173 includes an oblique correction detection region 173a that serves as a reading region when obtaining an oblique correction value from the amount of oblique displacement, and an original reading that serves as an original image reading region using the ordinary document conveying unit 11. A use area 173b.

  Next, the operation display unit 12 will be described below. FIG. 4 is a schematic cross-sectional view of the operation display unit 12 and the document reading unit 17 for explaining the detection of the oblique shift amount in the copying machine 1 of the present embodiment as viewed from above. As shown in FIG. 4, the operation display unit 12 is used to input a start key 12a that is pressed when the copying process is started, a stop key 12b that is pressed when the copying process is stopped, and numerical values. It includes a numeric keypad 12c and a liquid crystal display 12d that includes a touch sensor and accepts various guidance displays and input operations.

  Next, an example of a normal document copying operation in the copying machine 1 having the above-described configuration (that is, when the skew amount and the skew correction value are not detected) will be described. In the document copying operation in the copying machine 1, first, a document is transported from the document transport unit 11 to the document reading unit 17, and the document is read by the document reading unit 17, and color separation into three components of blue, green, and red is performed. Image data is generated. The generated image data is converted into image data expressed in four colors of yellow, magenta, cyan, and black by the CPU 10, temporarily stored in the memory unit 14, and then read out again to the image forming unit 15. Sent out. Then, the CPU 10 corrects the image data based on the attachment correction value at the time of attachment specific to each of the LED heads 23a to 23d.

  Subsequently, electrostatic latent images are created by the LED heads 23a to 23d on the surfaces of the photosensitive drums 21a to 21d, which are uniformly charged to a predetermined potential by the chargers 24a to 24d, based on the image data. The toner images of one color are respectively formed on the surfaces of the photosensitive drums 21a to 21d by the electrostatic latent images 22a to 22d. The toner images formed on the surfaces of the photosensitive drums 21a to 21d are sequentially transferred onto the paper conveyed from the paper supply unit 13 by the transfer rollers 26a to 26d.

  Thereafter, the paper carrying the unfixed toner image is sent to the fixing unit 18 and heated and pressed by the fixing unit 18 to fix the toner image on the paper. It is discharged to the part 19.

  Note that the copying machine 1 according to the present embodiment is configured to detect and control the skew amount of the original document and perform the skew control prior to the formation of the electrostatic latent images on the surfaces of the photosensitive drums 21a to 21d formed by the LED heads 23a to 23d. A feature of the control is that the correction processing is performed on the image data generated by the document reading unit 17 using the oblique correction value obtained from the deviation amount.

  Therefore, in the following, with reference to the drawings, an original document that is formed prior to the formation of electrostatic latent images on the surfaces of the photosensitive drums 21a to 21d formed by the LED heads 23a to 23d in the copying machine 1 of the present embodiment. A detailed description will be given of the detection control of the skew displacement amount and the control in which the correction processing is performed on the image data generated by the document reading unit 17 using the skew correction value obtained from the skew displacement amount. FIG. 5 is a flowchart illustrating an example of control related to correction processing performed on image data in the copying machine 1 according to the present embodiment.

  In the copying machine 1 of the present embodiment, when a document P is set on the document table 114 in step S5-1 as shown in FIGS. 1 to 5, the document presence / absence detection switch 111 is turned on and the input of the document P is detected. Along with the ON signal, the display on the liquid crystal display 12d is changed by the CPU 10 to the ADF mode, which is a mode in which the original conveying unit 11 is used to copy the original.

  Subsequently, in step S5-2, the liquid crystal display 12d is subjected to an oblique correction mode in which image data is corrected based on an oblique correction value, and a print in which normal copying is performed without performing oblique correction on the image data. A message to select one of the modes is displayed. If the print mode is selected (S5-2 NO), the process proceeds to step S5-6 described later. If the diagonal correction mode is selected (YES in S5-2), the first moving frame 175 and the second moving frame 176 are moved to the standby position 1 by the driving force of the moving frame driving stepping motor 172 in Step S5-3. To the oblique correction detection position S2. When the print mode is selected, the image data correction process is not performed, so that the copying speed is increased and the copying completion time is increased.

  Subsequently, in step S5-4, when a predetermined input such as the number of copies is made and the start key 12a is pressed, the document P set on the document table 114 is moved to the oblique correction detection area 173 by the roller 115. The conveyance is started. Then, the document P is conveyed from the roller 115 to the roller 116, and when the leading edge of the document P is detected by the document detection switch 112, the document detection switch 112 is turned on, and a detection signal thereby is input to the CPU 10 to input the document P. Is recognized by the CPU 10. Further, when the document P is conveyed by the roller 116 and the document P is no longer detected by the document detection switch 112, the CPU 10 recognizes that the document P has passed the installation position of the document detection switch 112. In the following, the position of the document P on the transport path is calculated by the CPU 10 using the number of pulses for driving the document transport stepping motor 113, starting from when the document detection switch 112 is turned on. The

  Subsequently, in step S5-5, the amount of oblique displacement of the document P conveyed to the oblique correction detection position S4 on the oblique correction detection region 173 is detected as follows.

  Here, the detection operation of the amount of oblique displacement of the document P conveyed to the oblique correction detection area 173 in step S5-5 will be described below. The case where the document P conveyed to the oblique correction detection position S4 on the oblique correction detection region 173 is obliquely shifted downward in the drawing as shown in FIG. 4 will be described as an example. As shown in FIG. 4, when the original P is conveyed to the oblique correction detection position S4 on the oblique correction detection area 173, the reading of the image of the original P from the leading edge P1 of the original P to a predetermined area is performed in the first manner. The correction image data of the document P read by the moving frame 175, the second moving frame 176, and the CCD 171 is sent to the CPU 10.

  Then, the CPU 10 estimates the size of the original P from the correction image data, and information on the coordinates of the normal left end P4 and the normal right end P5 of the original when the original of the same size as the original P is correctly conveyed is obtained. Read from the memory unit 14. Note that the CPU 10 may estimate the coordinates of the normal left end P4 and the normal right end P5 of the document.

  Then, as shown in FIG. 4, the CPU 10 discriminates the left end P2 and the right end P3 in the image data of the document P which is obliquely shifted from the image data, and further obtains their coordinates. Subsequently, the coordinates of the left end P2 and the right end P3 in the correction image data of the document P which is obliquely shifted are compared with the coordinates of the normal left end P4 and the normal right end P5, respectively, and for what number of lines of a predetermined line width It is calculated whether the amount of diagonal displacement is 31 or 32. The origin of these coordinates is the origin 177 on the document conveying portion contact glass 173 as shown in FIG. 4, but is not particularly limited. Returning to the flowchart of FIG.

  In step S5-6, the CPU 10 determines the original P described above from the oblique correction value according to the number of lines having a preset line width for each paper size of the original stored in advance from the memory unit 14 by the CPU 10. The oblique correction values corresponding to the oblique displacement amounts 31 and 32 are extracted and temporarily stored in the memory unit 14.

  Subsequently, in step S5-7, the document is temporarily stopped by the control of the CPU 10, and the first moving frame 175 is moved to the normal reading position S3 as shown in FIG.

  Subsequently, in step S5-8, the conveyance of the document P is resumed by the roller 116, and when the CPU 10 recognizes that the leading edge P1 of the document P has reached the reading start position S5 on the normal reading position S3, Similarly, the image of the original P is read and temporarily stored in the memory unit 14.

  Subsequently, in step S5-9, the CPU 10 performs oblique correction values corresponding to the oblique displacement amounts 31, 32 stored in the memory unit 14 in step S5-6, the attachment correction values of the LED heads 23a to 23d, and the document P. Image data is read. Then, the CPU 10 performs correction processing on the image data of the document P using the correction value obtained by adding the diagonal correction value corresponding to the diagonal shift amounts 31 and 32 and the mounting correction values of the LED heads 23a to 23d. Corrected image data corresponding to each of the LED heads 23a to 23d is sent.

  Here, the original P to be applied using the correction value obtained by adding the oblique correction value corresponding to the oblique displacement amounts 31 and 32 performed by the CPU 10 in step S5-9 and the attachment correction values of the LED heads 23a to 23d. Image data correction processing will be described below. FIG. 6 is a diagram illustrating an example of a document P copied by the copying machine 1 according to the present embodiment. FIG. 7 is a diagram showing a predetermined portion of the memory area of the memory unit 14 in which the image data of the original P shown in FIG. FIG. 8 is a diagram illustrating an example of a case where the image data of the document P shown in FIG. 6 read with an oblique shift is printed on a sheet without being subjected to correction processing. FIG. 9 is a diagram showing a predetermined portion of the memory area of the memory unit 14 for explaining the correction processing to the image data shown in FIG.

  For example, as shown in FIG. 6, for the sake of easy understanding, an original P on which one straight line P6 is described is read in an obliquely shifted state by the original reading unit 17 as described above. Data is generated. Then, the image data of the obliquely displaced document P is stored in the memory area of the memory unit 14 by the CPU 10.

  For example, as shown in FIG. 7, the CPU 10 stores image data of the straight line P6 portion of the obliquely shifted document P in M7, M13, and M19 in the memory areas M1 to M25 of the memory unit 14. Note that only a part of the memory area in which the image data of the document P is stored is described in the memory areas M1 to M25 of the memory unit 14 in FIG.

  When the image data of the original P shown in FIG. 7 is formed on the paper by the image forming unit 15 and the fixing unit 18 without being subjected to correction processing, as shown in FIG. 8, one straight line is formed on the paper P7. P6 forms an image at an angle.

  Therefore, in the copying machine 1 according to the present invention, the CPU 10 adds the oblique correction values corresponding to the oblique displacement amounts 31 and 32 and the attachment correction values of the LED heads 23a to 23d to the image data of the obliquely displaced document P. The generated correction values are used, and are not sequentially read out from the memory area M1, but are generated by the oblique displacement amounts 31 and 32 of the obliquely fed document P and the inherent attachment displacements of the LED heads 23a to 23d. The image data portions of the original P, which are obliquely shifted, are sequentially read from the memory areas of the memory unit 14 so that the electrostatic latent image writing shifts by the LED heads 23a to 23d to the photosensitive drums 21a to 21d are canceled. Correction processing is performed, and corrected image data is sent to the LED heads 23a to 23d.

  For example, when the description is limited to the image data of the straight line P6 portion of the original P shown in FIG. 7, the image data of the straight line P6 portion of the original P is stored when the above correction processing is performed. As shown in FIG. 9, the memory areas M7, M13, and M19 are not read in order from the memory area M1, but are read in the order of the memory areas M7, M13, and M19 in the straight line P6 portion. . Note that the image data of the image data of the document P that has been obliquely shifted using the correction values as described above is temporarily stored in the memory unit 14, and then the LED head 23a as described later. May be sent to ~ 23d. Further, the memory area of the memory unit 14 shown in FIG. 9 describes only a part of the memory area in which the image data of the document P is stored.

  Subsequently, in step 5-10, correction processing is performed using the correction value obtained by adding the oblique correction value based on the oblique displacement amounts 31, 32 and the attachment correction values of the LED heads 23a to 23d by the CPU 10 in step S5-9. The image data of the original P subjected to the above is transmitted from the CPU 10 according to the LED heads 23a to 23d, and electrostatic latent images are written on the surfaces of the photosensitive drums 21a to 21d by the LED heads 23a to 23d.

  Subsequently, in Step 5-11, toner images of one color are respectively formed on the surfaces of the photosensitive drums 21a to 21d from the electrostatic latent images by the developing units 22a to 22d. The toner images formed on the surfaces of the photosensitive drums 21a to 21d are sequentially transferred onto the paper conveyed from the paper supply unit 13 by the transfer rollers 26a to 26d. Thereafter, the paper carrying the unfixed toner image is sent to the fixing unit 18 and heated and pressed by the fixing unit 18 to fix the toner image on the paper. It is discharged to the section 19 and this operation is completed.

  If the left end P2 and / or the right end P3 of the document P cannot be determined from the correction image data due to a color close to the oblique correction detection reflector 117, the document reading area 173b is used. The left end P2 and the right end P3 of the document P may be determined from the image data generated by reading the document P, and the coordinates thereof may be obtained.

  In this embodiment, the case where the copying machine 1 includes the LED heads 23a to 23d has been described as an example. However, the present invention is not limited to the LED head, and the exposure head uses laser light. May be provided in the copying machine 1.

  As described above, the copying machine 1 according to the present embodiment can form the electrostatic latent images on the surfaces of the photosensitive drums 21a to 21d by the LED heads 23a to 23d without adding a new sensor. In this configuration, the amount of oblique deviation of the original is measured, and the amount of oblique deviation is corrected based on the measurement result. Therefore, it is possible to suppress variations in printing due to the oblique feeding of the document, and it is possible to further suppress variations in printing due to the oblique feeding caused by changes in the apparatus over time, and the position of image formation on the paper is always stable. A copy image can be provided.

  The present invention can be widely applied to image forming apparatuses such as facsimiles and multifunction peripherals in addition to copying machines, and is a technique useful for providing a stable copy image having no oblique displacement.

FIG. 2 is a block diagram showing a main configuration of a copier according to the present invention. These are the longitudinal cross-sectional views which show typically the principal part structure of the copying machine which concerns on this invention. FIG. 3 is a longitudinal sectional view schematically showing the document conveying unit 11 and the document reading unit 17. FIG. 3 is a schematic cross-sectional view of the operation display unit 12 and the document reading unit 17 for explaining the detection of the amount of oblique displacement in the copying machine 1 of the present embodiment as viewed from above. These are the flowcharts which show an example of the control regarding the correction process performed to the image data in the copying machine 1 of this embodiment. These are views showing an example of a document P copied by the copying machine 1 of the present embodiment. FIG. 7 is a diagram showing a predetermined portion of the memory area of the memory unit 14 in which image data of the original P shown in FIG. 6 fed obliquely is stored. FIG. 7 is a diagram illustrating an example of a case where image data of the original P shown in FIG. 6 read with an oblique shift is printed on a sheet without being subjected to correction processing. These are figures which show the predetermined part of the memory area of the memory part 14 for demonstrating the correction process to the image data shown in FIG.

Explanation of symbols

1 Copier 10 Central processing unit (CPU)
DESCRIPTION OF SYMBOLS 11 Document conveyance part 111 Document presence detection switch 112 Document detection switch 113 Document conveyance stepping motor 114 Document table 115, 116, 119, 120 Roller 117 Diagonal correction detection reflector 118 Document holding plate 121 Document discharge table 122 Document for manual placement Presser plate 12 Operation display unit 12a Start key 12b Stop key 12c Numeric keypad 12d Liquid crystal display 13 Paper feed unit 131a to 131c Paper storage unit 132 Paper transport unit 14 Memory unit 15 Image forming unit 15a Yellow image forming unit 15b Magenta image forming unit 15c Cyan Image forming unit 15d Black image forming unit 16 Image processing unit 17 Document reading unit 171 CCD
172 Moving frame driving stepping motor 173 Document conveying part contact glass 173a Oblique correction detection area 173b Document reading area 174 Contact glass 175 First moving frame 175a, 176a, 176b Reflecting glass 176 Second moving frame 18 Fixing part 19 Discharge Paper portion 21a to 21d Photosensitive drum 22a to 22d Developer 23a to 23d LED head (light emitting diode head)
24a-24d Charger 25a-25d Cleaning unit 26a-26d Transfer roller S1 Standby position S2, S4 Oblique correction detection position S3 Normal reading position S5 Reading start position P Original

Claims (4)

A document reading unit that reads an image of a document placed at a predetermined reading position and generates image data, a document transport unit that transports the document to a predetermined reading position of the document reading unit, and a sheet based on the image data In an image forming apparatus comprising: an image forming unit that forms an image on
The document conveying section has a predetermined color reflector and a white reflector in a region facing the reading position,
A memory unit that stores, for each document size, a skew correction value corresponding to the skew amount of the document transported by the document transport unit, and a skew correction detection reading that faces the reflector of the predetermined color in the document transport unit. A normal reading position facing the white reflecting plate to the original conveying unit after the original is conveyed to a position and the original reading unit generates correction image data from the leading end of the original to a predetermined area. A control unit that transports the document and causes the document reading unit to generate image data of the document, and calculates a skew amount from the correction image data, and based on a skew correction value corresponding to the skew amount. An image forming apparatus comprising: a correction processing unit that performs correction processing on the image data. The memory unit stores, for each document size, the coordinates of the edge of the document when the document is transported without skew.
The correction processing unit discriminates the coordinates of the edge of the document from the correction image data, compares the coordinates of the edge with the coordinates of the edge of the document stored in the memory unit, and the amount of the oblique displacement The image forming apparatus according to claim 1, wherein: The image forming unit includes a light emitting diode head in which a predetermined number of light emitting diodes for forming an electrostatic latent image are arranged on the surface of the photosensitive drum.
The memory unit stores an attachment correction value according to an attachment position of the light emitting diode head,
The image forming apparatus according to claim 1, wherein the correction processing unit performs correction processing on the image data based on the attachment correction value and the oblique correction value.   An oblique correction mode in which an image is formed on a sheet based on the image data that has been corrected by the correction processing unit, and an image is formed on a sheet without the correction processing by the correction processing unit being performed on the image data. 4. The image forming apparatus according to claim 1, further comprising means for selecting one of the print modes.

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