JP2012018261A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively suppress the effect of stray light caused by optical beam scanning.SOLUTION: An image forming apparatus forms electrostatic latent images of a uniform-density gray test-pattern stored in EEPROM 83 on photoreceptor drums using an optical scanning device; develops the electrostatic latent images to form toner images of a test pattern on a photoreceptor drum surface; transfers the toner images of the test pattern onto a first recording sheet on top of each other; reads the test pattern on the first recording sheet using an image reading device to store the resultant image data in an internal memory 85a of a main control section 85; and reads a white second recording sheet using the image reading device and stores the resultant image data in the internal memory 85a of the main control section 85. The main control section 85 compares the image data of the test pattern and that of a scan pattern, detects a trace of stray light caused on the first recording sheet, and lowers the intensity of a light beam when a spot on the photoreceptor drum surface corresponding to the trace of stray light is scanned by the light beam of the optical scanning device.

Description

  The present invention relates to an image forming apparatus such as an electrophotographic printer, a copying machine, and a facsimile.

  In this type of image forming apparatus, the surface of the photosensitive member is scanned with a light beam to form an electrostatic latent image on the surface of the photosensitive member, and the electrostatic latent image on the surface of the photosensitive member is developed with toner, and the surface of the photosensitive member is developed. A toner image is formed, the toner image is transferred from the photoreceptor to the recording paper, and the recording paper is heated and pressurized to fix the toner image on the recording paper.

  The photoconductor surface is scanned by the light beam by an optical scanning device. In this optical scanning device, while modulating the intensity of the light beam output from the semiconductor laser according to the image data, the light beam of the semiconductor laser is emitted to the polygon mirror, and this light beam is reflected by the polygon mirror. By rotating the polygon mirror, the light beam is repeatedly deflected in the main scanning direction, and further, the fθ lens is used to deflect the light beam at a constant speed on the photosensitive member. An electrostatic latent image is formed on the body surface.

  However, since the optical path of the light beam in the optical scanning device is complicated, stray light may be generated. This stray light is incident on the surface of the photoconductor and affects the electrostatic latent image on the surface of the photoconductor. In some cases, stray light traces were generated on the toner image on the paper, resulting in a reduction in image quality.

  For this reason, in Patent Document 1, a light shielding plate that blocks stray light is provided to prevent stray light from entering the surface of the photoreceptor.

  In Patent Document 2, although there is no technical description regarding stray light, a color pattern is stored in advance, the color pattern is printed on a recording sheet by an electrophotographic method, and the color pattern on the recording sheet is read by a scanner. Since the color pattern stored in advance is compared with the color pattern on the recording paper, there is a possibility of detecting stray light traces on the recording paper by this comparison.

JP 2003-320703 A JP 2007-71918 A

  However, in the optical scanning device, there is not only stray light that can be blocked by the light shielding plate as in Patent Document 1, but also stray light that cannot be blocked depending on the optical path.

  Further, in Patent Document 2, there is no description regarding detection of stray light traces on a recording sheet even if a color pattern stored in advance and a color pattern on the recording sheet are compared. In addition, not only stray light traces but also traces caused by dust or the like of the scanner remain in the color pattern on the recording paper, so that such a comparison alone cannot distinguish stray light traces from traces of dust and the like.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of effectively suppressing the influence of stray light caused by scanning of a light beam.

  In order to solve the above problems, the present invention includes an image reading unit, and an optical scanning unit that scans the latent image carrier with a light beam to form a latent image on the latent image carrier, In an image forming apparatus for developing a latent image on a latent image carrier into a visible image and transferring the visible image from the latent image carrier to a recording medium, a test pattern preset by the optical scanning unit is provided. A latent image is formed on the latent image carrier, the latent image of the test pattern on the latent image carrier is developed into a visible image, and the visible image of the test pattern is first recorded from the latent image carrier. A print control unit to be transferred and formed on a medium; a test pattern read image on the first recording medium read by the image reading unit; and a preset on a second recording medium read by the image reading unit A comparison unit for comparing the read image of the scanned pattern And a light quantity control unit for controlling the intensity of the light beam of the optical scanning unit based on the comparison result of the comparison unit.

  In the present invention, a latent image of a test pattern is formed on a latent image carrier by an optical scanning unit, the latent image of the test pattern on the latent image carrier is developed into a visible image, and a test pattern is allowed. The visual image is formed by transferring from the latent image carrier to the first recording medium. For this reason, if stray light is generated by the scanning of the light beam of the light scanning unit and the stray light affects the latent image on the latent image carrier, the stray light trace caused by the stray light is a test on the first recording medium. Appears in the read image of the pattern. Further, since the scan pattern on the second recording medium is merely read by the image reading unit and is not related to the optical scanning unit or the latent image carrier, the stray light trace is scanned on the second recording medium. It does not appear in the read image of the pattern. Therefore, if the read image of the test pattern on the first recording medium is compared with the read image of the scan pattern on the second recording medium, it appears in the read image on the first recording medium and The stray light trace that does not appear in the read image can be identified. If the stray light trace can be specified in this way, control for suppressing the stray light trace or the like becomes possible.

  In the image forming apparatus of the present invention, the comparison unit detects a streak of the read image of the test pattern on the first recording medium and detects a streak of the read image of the scan pattern on the second recording medium. The streaks on the first and second recording media are compared.

  Since stray light traces appear as streaks, stray light traces can be reliably detected by comparing the streaks on the first and second recording media.

  Further, in the image forming apparatus of the present invention, the comparison unit determines that the cause of the stripe is in the image reading unit when the position of the stripe on the first and second recording media matches, If only streaks on the first recording medium are detected and the density of the streaks on the first recording medium is equal to or higher than a certain density, it is determined that the cause of the streaks is in the optical scanning unit.

  Alternatively, when the positions of the streaks on the first and second recording media match, the comparison unit determines that the streaks are caused by dust in the image reading unit, and the streaks on the first recording medium are determined. If the density of streaks on the first recording medium is equal to or higher than a certain density, it is determined that streaks are caused by stray light from the optical scanning unit.

  Since both the test pattern on the first recording medium and the scan pattern on the second recording medium are read by the image reading unit, the test pattern on the first recording medium and the scan pattern on the second recording medium are common. If such a streak exists, it can be determined that the cause of this streak is in the image reading unit or its dust. The scan pattern on the second recording medium is merely read by the image reading unit and is not related to the optical scanning unit or the latent image carrier. It can be determined that the cause of streaks (stray light traces) appearing in the test pattern on the first recording medium is the optical scanning unit or stray light.

  In the image forming apparatus according to the aspect of the invention, the light amount control unit may detect the streak image carrier with the light beam of the optical scanning unit when only the streaks on the first recording medium are detected by the comparison unit. When the portion corresponding to the streak is scanned, the intensity of the light beam is changed.

  Furthermore, in the image forming apparatus of the present invention, the light amount control unit reduces the intensity of the light beam when a portion corresponding to the streaks in the latent image carrier is scanned by the light beam of the light scanning unit. I am letting.

  Alternatively, the light amount control unit reduces the density of the streaks in the latent image carrier by reducing the intensity of the light beam of the optical scanning unit.

  Further, in the image forming apparatus of the present invention, the light amount control unit inputs image data, controls the intensity of the light beam of the optical scanning unit based on the image data, and corrects the image data. Thus, the intensity of the light beam is changed when the portion corresponding to the streaks in the latent image carrier is scanned by the light beam of the light scanning unit.

  By controlling the intensity of the light beam as described above, streaks can be made inconspicuous.

  In the image forming apparatus of the present invention, the test pattern on the first recording medium is a gray-colored printing pattern having a uniform density.

  Since the intensity of the stray light incident on the latent image carrier is low, stray light traces hardly appear on the recording medium when the background is white. However, when the background is gray, stray light traces are likely to appear on the gray. For this reason, when a gray-color print pattern having a uniform density is applied as the test pattern on the first recording medium, it becomes easy to specify the stray light trace on the first recording medium.

  Furthermore, in the image forming apparatus of the present invention, the scan pattern on the second recording medium is a cloth having a uniform density on the second recording medium.

  If the scan pattern on the second recording medium is set to a uniform density of the cloth of the second recording medium, it becomes easy to specify a streak or the like caused by the image reading unit.

  In the present invention, a latent image of a test pattern is formed on a latent image carrier by an optical scanning unit, the latent image of the test pattern on the latent image carrier is developed into a visible image, and a test pattern is allowed. The visual image is formed by transferring from the latent image carrier to the first recording medium. For this reason, if stray light is generated by the scanning of the light beam of the light scanning unit and the stray light affects the latent image on the latent image carrier, the stray light trace caused by the stray light is a test on the first recording medium. Appears in the read image of the pattern. Further, since the scan pattern on the second recording medium is merely read by the image reading unit and is not related to the optical scanning unit or the latent image carrier, the stray light trace is scanned on the second recording medium. It does not appear in the read image of the pattern. Therefore, if the read image of the test pattern on the first recording medium is compared with the read image of the scan pattern on the second recording medium, it appears in the read image on the first recording medium and The stray light trace that does not appear in the read image can be identified. If the stray light trace can be specified in this way, control for suppressing the stray light trace or the like becomes possible.

1 is a cross-sectional view showing an embodiment of an image forming apparatus of the present invention. FIG. 2 is a perspective view showing an optical scanning device in the image forming apparatus of FIG. 1. (A), (b) is the top view and sectional drawing which show an optical scanning device. FIG. 2 is a block diagram showing each laser diode, each integrated circuit, EEPROM, and the like mounted on a substrate in the optical scanning device, and a main control unit and an operation panel in the image forming apparatus. It is a block diagram which shows the whole circuit structure in the board | substrate of an optical scanning device. FIG. 3 is a block diagram showing an excerpt of a pair of laser diodes and photodiodes, an integrated circuit, and an EEPROM on a substrate of an optical scanning device, and a main control unit in an image forming apparatus. (A)-(d) is a timing chart which illustrates operation | movement of the circuit of FIG. (A) shows a test pattern made of gray having a preset uniform density, (b) shows a first recording paper on which the test pattern is printed, and (c) shows a read image of the test pattern on the first recording paper. (D) shows the second recording paper of white paper (scan pattern with uniform density), and (e) shows the read image of the scan pattern on the second recording paper. (A)-(d) is a timing chart which shows operation | movement of the circuit of FIG. 6, Comprising: It is a timing chart at the time of rewriting the change pattern of the intensity | strength of the light beam in a main scanning period. (A), (b) is a figure which shows the timing in the stripe in the read image of the test pattern on the 1st recording paper, and the intensity | strength of a light beam. (A)-(d) is a timing chart which shows operation | movement of the circuit of FIG. 6, Comprising: It is a timing chart at the time of rewriting the image data in a main scanning period. (A), (b) is a figure which shows the density | concentration of each pixel which overlaps with the streak in the read image of the test pattern on the 1st recording paper, and a streak.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a cross-sectional view showing an embodiment of the image forming apparatus of the present invention. The image forming apparatus 1 is a so-called multi-function machine having a scanner function, a copying function, a printer function, a facsimile function, and the like, and transmits an image of a document read by the image reading device 41 to the outside (corresponding to a scanner function). The image of the read original or the image received from the outside is recorded and formed in color or single color on a recording sheet (corresponding to a copying function, a printer function, and a facsimile function).

  In order to print an image on a recording paper, the image forming apparatus 1 includes an optical scanning device 11, a developing device 12, a photosensitive drum 13, a drum cleaning device 14, a charger 15, an intermediate transfer belt device 16, a fixing device 17, and a paper transport. A path S, a paper feed tray 18, a paper discharge tray 19, and the like are provided.

  The image data handled in the image forming apparatus 1 uses data corresponding to a color image using each color of black (K), cyan (C), magenta (M), yellow (Y), or a single color (for example, black). This is in accordance with the monochrome image. For this reason, four each of the developing device 12, the photosensitive drum 13, the drum cleaning device 14, and the charger 15 are provided so as to form four types of toner images corresponding to the respective colors, and black, cyan, Four image stations Pa, Pb, Pc, and Pd are configured in association with magenta and yellow.

  Each photosensitive drum 13 has a photosensitive layer on the surface thereof. Each charger 15 is a charging means for uniformly charging the surface of each photosensitive drum 13 to a predetermined potential. In addition to a contact-type roller-type or brush-type charger, a charger-type charger. Is used.

  The optical scanning device 11 is a laser scanning unit (LSU) provided with a laser diode and a reflection mirror, and exposes the surface of each charged photosensitive drum 13 according to image data and corresponds to the image data on those surfaces. An electrostatic latent image is formed.

  Each developing device 12 develops the electrostatic latent image formed on the surface of each photosensitive drum 13 with toner of each color, and forms a toner image on the surface of these photosensitive drums 13. Each drum cleaning device 14 removes and collects toner remaining on the surface of each photosensitive drum 13 after development and image transfer.

  The intermediate transfer belt device 16 is disposed above each photosensitive drum 13 and includes an intermediate transfer belt 21, an intermediate transfer belt driving roller 22, a driven roller 23, four intermediate transfer rollers 24, and a belt cleaning device 25. ing.

  The intermediate transfer belt 21 is a film formed in an endless belt shape. The intermediate transfer belt drive roller 22, the driven roller 23, each intermediate transfer roller 24, and the like stretch and support the intermediate transfer belt 21, and rotate the intermediate transfer belt 21 in the direction of arrow C.

  Each intermediate transfer roller 24 is rotatably supported in the vicinity of the intermediate transfer belt 21 and is pressed against the respective photosensitive drums 13 via the intermediate transfer belt 21. The toner images on the surfaces of the photosensitive drums 13 are sequentially transferred to the intermediate transfer belt 21 so as to form color toner images (each color toner image) on the intermediate transfer belt 21. Transfer of the toner image from each photosensitive drum 13 to the intermediate transfer belt 21 is performed by each intermediate transfer roller 24 that is in pressure contact with the back surface of the intermediate transfer belt 21. Each intermediate transfer roller 24 is a roller having a metal (for example, stainless steel) shaft as a base and a surface covered with a conductive elastic material (for example, EPDM, urethane foam, or the like). Each intermediate transfer roller 24 is applied with a high-voltage transfer bias (a high voltage having a polarity (+) opposite to the toner charging polarity (−)) in order to transfer the toner image. A high voltage is uniformly applied to the recording paper by the material.

  Thus, the toner image on the surface of each photosensitive drum 13 is transferred and laminated by the intermediate transfer belt 21 to be a color toner image indicated by the image data. This color toner image is conveyed together with the intermediate transfer belt 21 and transferred onto a recording sheet in a nip region between the intermediate transfer belt 21 and the transfer roller 26a of the secondary transfer device 26.

  The transfer roller 26a of the secondary transfer device 26 has a voltage (a high voltage having a polarity (+) opposite to the toner charging polarity (-)) for transferring the toner image of each color on the intermediate transfer belt 21 onto a recording sheet. Is applied.

  In addition, the toner image on the intermediate transfer belt 21 may not be completely transferred onto the recording paper by the secondary transfer device 26, and the toner may remain on the surface of the intermediate transfer belt 21. Causes color mixing. For this reason, the residual toner on the surface of the intermediate transfer belt 21 is removed and collected by the belt cleaning device 25. The belt cleaning device 25 is provided with, for example, a cleaning blade that contacts the surface of the intermediate transfer belt 21 and removes residual toner as a cleaning member, and the intermediate transfer belt 21 is driven by the driven roller 23 at a portion where the cleaning blade comes into contact. The back side is supported.

  The recording sheet is conveyed to the fixing device 17 after the color toner image is transferred in the nip region between the intermediate transfer belt 21 and the transfer roller 26 a of the secondary transfer device 26. The fixing device 17 includes a heating roller 31, a pressure roller 32, and the like, and sandwiches and conveys a recording sheet between the heating roller 31 and the pressure roller 32.

  The heating roller 31 is controlled so as to have a predetermined fixing temperature based on a detection output of a temperature detector (not shown), and the color transferred to the recording paper by thermocompression bonding the recording paper together with the pressure roller 32. The toner image is melted, mixed, and pressed, and thermally fixed to the recording paper.

  In addition, a paper feed tray 18 for supplying recording paper is provided below the image forming apparatus 1. The image forming apparatus 1 is provided with a paper transport path S for sending the recording paper supplied from the paper feed tray 18 to the paper discharge tray 19 via the secondary transfer device 26 and the fixing device 17.

  A paper pickup roller 33 is provided at the end of the paper feed tray 18, and the recording paper is pulled out from the paper feed tray 18 one by one by the paper pickup roller 33 and conveyed to the paper conveyance path S.

  A paper registration roller 34, a fixing device 17, a transport roller 35, a paper discharge roller 36, and the like are arranged along the paper transport path S. The conveyance roller 35 is a small roller for promoting and assisting conveyance of the recording paper, and a plurality of sets are provided.

  The paper registration roller 34 temporarily stops the recording paper that has been conveyed, aligns the leading edge of the recording paper, and is placed on the intermediate transfer belt 21 in the nip region between the intermediate transfer belt 21 and the transfer roller 26a of the secondary transfer device 26. In order to transfer the color toner image onto the recording sheet, the recording sheet is conveyed in a timely manner in accordance with the rotation of each photosensitive drum 13 and the intermediate transfer belt 21.

  Further, the recording paper is fixed with a color toner image by the fixing device 17, passes through the fixing device 17, and is then discharged face down on the paper discharge tray 19 by the paper discharge roller 36.

  When printing not only on the front side of the recording paper but also on the back side, the recording paper is transported by the paper discharge roller 36, and then the paper discharge roller 36 is stopped and then reversely rotated, so that the recording paper is reversed. , Reverse the front and back of the recording paper, guide the recording paper to the paper registration roller 34, record and fix the image on the back of the recording paper, as well as the front of the recording paper, and eject the recording paper to the paper It is discharged to the tray 19.

  Next, the image reading device 41 and the document conveying device 42 mounted on the upper part of the main body of the image forming apparatus 1 will be described. The document conveying device 42 is pivotally supported by the back side of the image reading device 41 by a hinge (not shown) and opened and closed by moving the front portion up and down. When the document conveying device 42 is opened, the platen glass 44 of the image reading device 41 is opened, and the document is placed on the platen glass 44.

  The image reading device 41 includes a platen glass 44, a first scanning unit 45, a second scanning unit 46, an imaging lens 47, a CCD (Charge Coupled Device) 48, and the like. The first scanning unit 45 includes an illuminating device 51 and a first reflecting mirror 52, and illuminates the original on the platen glass 44 while moving at a constant speed V by a distance corresponding to the original size in the sub-scanning direction. The reflected light is reflected by the first reflecting mirror 52 and guided to the second scanning unit 46, whereby the image on the document surface is scanned in the sub-scanning direction. The second scanning unit 46 includes second and third reflecting mirrors 53 and 54, and follows the first scanning unit 45 while moving at a speed V / 2, while reflecting the reflected light from the document to the second and second. The light is reflected by the three reflecting mirrors 53 and 54 and guided to the imaging lens 47. The imaging lens 47 condenses the reflected light from the document on the CCD 48 and forms an image on the surface of the document on the CCD 48. The CCD 48 repeatedly scans the document image in the main scanning direction, and outputs an analog image signal of one main scanning line each time.

  Further, the image reading device 41 can read not only a stationary document but also an image on the surface of the document conveyed by the document conveying device 42. In this case, the first scanning unit 45 is moved to a reading range below the original reading glass 55, and the second scanning unit 46 is positioned according to the position of the first scanning unit 45. In this state, the original conveying device 42 Start transporting the document.

  In the document transport device 42, the pickup roller 56 is pressed against the document on the document tray 57 and rotated to pull out the document, transport the document through the document transport path 58, and transport the document between the document reading glass 55 and the reading guide plate 59. Further, the original is further conveyed from the paper discharge roller 61 to the paper discharge tray 62. Along the document conveyance path 58, a registration roller 63 that conveys the document after aligning the front end thereof and a conveyance roller 64 that conveys the document are arranged.

  When the document is conveyed, the illumination device 51 of the first scanning unit 45 illuminates the document surface via the document reading glass 55, and the reflected light from the document surface is reflected on the reflection mirrors of the first and second traveling units 45 and 46. Then, the light is guided to the imaging lens 47, and the reflected light from the document surface is condensed on the CCD 48 by the imaging lens 47, and an image on the document surface is formed on the CCD 48, thereby reading the image on the document surface.

  When reading the back side of the document, the intermediate tray 67 is rotated as indicated by the dotted line around its axis, and the discharge roller 61 is in the process of discharging the document from the discharge roller 61 to the discharge tray 62. Is stopped, the document is received on the intermediate tray 67, the paper discharge roller 61 is rotated in the reverse direction, the document is guided to the registration roller 63 through the reverse conveyance path 68, and the document surface is reversed. In the same manner as the image of FIG. 5, the image on the back side of the document is read, the intermediate tray 67 is returned to the original position indicated by the solid line, and the document is discharged from the discharge roller 61 to the discharge tray 62.

  The original image read by the CCD 48 is output from the CCD 48 as an analog image signal, and the analog image signal is A / D converted into a digital image signal (image data). The image data is subjected to various image processing and then sent to and received by the optical scanning device 11 of the image forming apparatus 1. The image forming apparatus 1 records an image on a recording sheet, and the recording sheet is used as a copy original. Is output.

  Next, the optical scanning device 11 will be described in detail. 2, 3A, and 3B are a perspective view, a plan view, and a cross-sectional view showing the optical scanning device 11, respectively.

  In the optical scanning device 11, the laser diodes 71a, 71b, 71c, 71d corresponding to the respective colors of black (K), cyan (C), magenta (M), and yellow (Y), and the laser diodes 71a to 71d. Mirrors 72a, 72b, 72c, 72d for reflecting the light beams of the mirrors, mirrors 73 for reflecting the light beams from the half mirrors or mirrors 72a to 72d, and polygon mirrors for reflecting the light beams from the mirrors 73 (Rotating polygon mirror) 74, a first fθ lens 75 that refracts each light beam from the polygon mirror 74, and a plurality of mirrors 76a, 76b, 76c, and 76d that individually reflect each light beam that has passed through the first fθ lens 75. And four second light beams that individually refract the light beams from the mirrors 76a to 76d. fθ lenses 77a, 77b, 77c, and 77d.

  The polygon mirror 74 has a regular polygonal column shape, is driven to rotate at high speed, and repeatedly scans in the main scanning direction X while reflecting each light beam by a mirror on each peripheral surface. The first fθ lens 75, each mirror 76, and each second fθ lens 77 are elongated in the main scanning direction X and reflected in the main scanning direction X in order to reflect and refract each light beam that is repeatedly scanned in the main scanning direction X. It is formed in the shape of a bar shortened in a direction orthogonal to the two, and both ends thereof are supported.

  The light beam emitted from the laser diode 71a corresponding to black is transmitted through the half mirror 72a, reflected by the mirror 73, reflected by the polygon mirror 74, scanned in the main scanning direction X, and further transmitted through the first fθ lens 75. Then, it is reflected by the mirror 76a, passes through the second fθ lens 77a, and enters the photosensitive drum 3 corresponding to black. The light beam emitted from the laser diode 71 b corresponding to cyan is sequentially reflected by the half mirrors 72 b and 72 a and the mirror 73, reflected by the polygon mirror 74, scanned in the main scanning direction X, and further transmitted through the first fθ lens 75. Then, the light is reflected by the two mirrors 76b, passes through the second fθ lens 77b, and enters the photosensitive drum 3 corresponding to cyan. The light beam emitted from the laser diode 71c corresponding to magenta is reflected by the half mirror 72c, passes through the half mirror 72b, is sequentially reflected by the half mirror 72a and the mirror 73, is reflected by the polygon mirror 74, and is subjected to main scanning. Scanned in the direction X, further transmitted through the first fθ lens 75, reflected by the two mirrors 76c, transmitted through the second fθ lens 77c, and incident on the photosensitive drum 3 corresponding to magenta. The light beam emitted from the laser diode 71d corresponding to yellow is reflected by the mirror 72d, sequentially passes through the half mirrors 72c and 72b, is sequentially reflected by the half mirror 72a and the mirror 73, and is reflected by the polygon mirror 74 and is mainly reflected. Scanned in the scanning direction X, further transmitted through the first fθ lens 75, reflected by the two mirrors 76d, transmitted through the second fθ lens 77d, and incident on the photosensitive drum 3 corresponding to magenta.

  As described above, each photoconductive drum 3 is rotationally driven in the direction of an arrow, and each light beam that is repeatedly scanned in the main scanning direction X is irradiated to each surface of each photoconductive drum 3. An electrostatic latent image is formed. The electrostatic latent image on the surface of each photoconductive drum 3 is developed to become a toner image, and these toner images are transferred onto the recording paper via the intermediate transfer belt 7 and are transferred to the color toner image on the recording paper. Become.

  Further, on the upper side of the main body casing 11a of the optical scanning device 11, only the portions of the second fθ lenses 77a to 77d are opened and the other portions are closed and shielded from light (not shown), so that disturbance light can enter. Is prevented.

  4 is a block diagram illustrating the laser diodes 71a to 71d, the integrated circuits, the EEPROM, and the like mounted on the substrate in the optical scanning device 11, and the main control unit, the operation panel, and the like in the image forming apparatus 1. . Hereinafter, reference numerals 71a to 71d of the respective laser diodes are unified with reference numeral 71.

  In FIG. 4, the substrate 81 of the optical scanning device 11 is fixed to the back side of the main body housing 11 a (shown in FIG. 2) of the optical scanning device 11, and four laser diodes 71, each on the substrate 81. Each integrated circuit 82 for controlling the laser diode 71 and the EEPROM 83 are mounted.

  Each integrated circuit 82 on the substrate 81 receives a control signal from the main control unit 85 of the image forming apparatus 1 and image data of each color of black (K), cyan (C), magenta (M), and yellow (Y). Then, based on the control signal, each main scanning period by the light beam of each laser diode 71 is set, and each laser diode 71 is turned on / off according to the image data of each color.

  The EEPROM 83 on the substrate 81 inputs control information set by the main control unit 85 or control information input from the external terminal (not shown) such as a personal computer through the LAN terminal 87 of the image forming apparatus 1. This control information is stored. Thereby, the control information in the EEPROM 83 is rewritten. Specifically, the control information in the EEPROM 83 can be rewritten from the main control unit 85 or an external terminal of the image forming apparatus 1 by applying a well-known transfer method to the memory, such as I2C or microwire.

  FIG. 5 is a block diagram showing the entire circuit configuration of the substrate 81 of the optical scanning device 11. In FIG. 5, each laser diode 71 is provided with a photodiode 91 for detecting the light output level of each laser diode 71. In any combination of each laser diode 71 and each photodiode 91, the anode of the laser diode 71 and the cathode of the photodiode 91 are commonly connected to the power supply terminal 82a of the integrated circuit 82, and the forward voltage 5V is applied to the laser diode 71. The reverse voltage 5 V is applied to the photodiode 91. The anode of the photodiode 91 is connected to the AD converter 82-1 of the integrated circuit 82, and the cathode of the laser diode 71 is connected to the DA converter 82-2 of the integrated circuit 82.

  In each integrated circuit 82, a switching element 82-3 is inserted between the analog output side of the DA converter 82-2 and the ground. Image data is applied to the gate of the switching element 82-3 via the receiver 82-4, and the switching element 82-3 is switched on and off in accordance with the binary signal of the image data.

  The EEPROM 83 inputs and stores control information. A part of the control information stored in the EEPROM 83 is loaded and stored in the register 82-5 of each integrated circuit 82.

  The control unit 82-6 of each integrated circuit 82 drives and controls each laser diode 71 based on the control information in each register 82-5.

  This control information includes a change pattern (light quantity correction data) of the intensity of the light beam during one main scanning period on the surface of the photoreceptor by the light beam of the laser diode 71. Specifically, this change pattern is a ratio of the intensity of each light beam for setting the density of each pixel of one main scanning line, and is repeated every main scanning period.

  FIG. 6 is a block diagram showing an extracted set of laser diode 71 and photodiode 91, integrated circuit 82, EEPROM 83, and main control unit 85 of image forming apparatus 1. The control of the laser diode 71 will be described in detail with reference to FIG.

  The photodiode 91 detects the light output level when the laser diode 71 emits light, and outputs a detection output corresponding to the light output level to the AD converter 82-1. The AD converter 82-1 performs analog-digital conversion on the detection output of the photodiode 91, and outputs the converted detection output value (corresponding to the light output level of the laser diode 71) to the control unit 82-6.

  When the converted detection output value is input, the control unit 82-6 obtains a value indicating the drive current IF of the laser diode 71 such that this value becomes a target specified value, and a value indicating the drive current IF. Is output to the DA converter 82-2.

  The DA converter 82-2 performs digital-to-analog conversion on the value indicating the drive current IF, and sets the drive current IF flowing through the DA converter 82-2.

  The switching element 82-3 receives the binary signal of the image data via the receiver 82-4, and is switched on / off according to the binary signal of the image data. As a result, the path of the drive current IF, which is laser diode 71 → DA converter 82-2 → switching element 82-3, is turned on / off. When this path is on, the drive current IF flows through the DA converter 82-2, and the light output level of the laser diode 201 corresponds to the target specified value. Further, the laser diode 71 is turned on and off according to the binary signal of the image data.

  7A to 7D are timing charts showing the operation of the circuit of FIG. In FIG. 7, the period from T2 to T3 is one main scanning period. Prior to this main scanning period, a period T0 to T1 is set, and as shown in FIG. 7A, a light amount correction lighting signal is transmitted through the receiver 82-4 during the period T0 to T1. 3, the switching element 82-3 is turned on, the drive current IF flows to the laser diode 71, the laser diode 71 emits light, and the detection output of the photodiode 91 is converted from analog to digital by the AD converter 82-1. Then, the converted detection output value (corresponding to the light output level of the laser diode 71) is added to the control unit 82-6. When the converted detection output value is input, the control unit 82-6 obtains a value indicating the drive current IF of the laser diode 71 such that this value converges to a reference value (a reference value as a reference). A value indicating the drive current IF is output to the DA converter 82-2. The DA converter 82-2 performs digital-to-analog conversion on the value indicating the drive current IF, and sets the drive current IF flowing through the DA converter 82-2. Thereby, the output level of the laser diode 71 is feedback-controlled.

  The sample hold value obtained by analog-digital conversion of the detection output of the photodiode 91 in the period T0 to T1 as shown in FIG. 7D is stored in the register 82-5.

  Subsequently, in the main scanning period from T2 to T3, the control unit 82-6 refers to the change pattern of the intensity of the light beam (shown in FIG. 7C) in the main scanning period in the register 82-5. For each pixel of the scanning line, the ratio of the intensity of the light beam is obtained from the change pattern, this ratio is multiplied by the sample hold value in the register 82-5, and this product is set as a target specified value, A value indicating the drive current IF of the laser diode 71 is determined such that the value indicating the detection output of the photodiode 91 becomes the specified value. As a result, as the pixels of the main scanning line are scanned with the light beam of the laser diode 71, the value of the drive current IF is sequentially determined so that the output level of the laser diode 71 changes with the change pattern. The DA converter 82-2 inputs the value of the drive current IF for each pixel in the main scanning period, converts this value into digital to analog, and sets the drive current IF of this value. Then, the switching element 82-3 is switched on and off in accordance with the binary signal of the image data as shown in FIG. 7B, and the laser diode 71 is turned on and off. As a result, as shown in FIG. 7D, in the main scanning period from T2 to T3, the output level of the laser diode 71 changes in accordance with the change pattern in the main scanning period in the register 82-5.

  The change pattern of the output level of the laser diode 71 in the main scanning period shown in FIG. 7C is for shading correction. Thereby, the peripheral light reduction of the optical system is corrected.

  Such operations of T0 to T3 are repeated for each main scan, and writing by the light beam of the laser diode 71 is performed.

  By the way, in the optical scanning device 11, since the optical path of the light beam is complicated, stray light may be generated. This stray light is incident on the surface of the photoconductive drum 13 and the electrostatic latent image on the surface of the photoconductive drum 13. May cause stray light traces on the toner image on the photosensitive drum 13 and the recording paper, resulting in a reduction in image quality.

  Therefore, in the present embodiment, the stray light trace generated on the recording paper is detected, and the intensity of the light beam when the portion corresponding to the stray light trace on the surface of the photosensitive drum 13 is scanned by the light beam of the optical scanning device 11. To reduce the latent image density of the stray light trace, thereby reducing the toner image density of the stray light trace, thereby suppressing the stray light trace on the recording paper sheet from being noticeable.

  Specifically, gray (test pattern) having a uniform density is stored in the EEPROM 83 of the optical scanning device 11, and a latent image of the test pattern is formed on the photosensitive drum 13 by the optical scanning device 11. The electrostatic latent image on the surface is developed to form a test pattern toner image on the surface of the photosensitive drum 13, and the test pattern toner image is superimposed on the first recording paper (for example, plain paper) via the intermediate transfer belt 7. Then, the test pattern on the first recording sheet is read by the image reading device 41, and this image data is stored in the memory 85a built in the main control unit 85. Also, the second recording paper (for example, plain paper) of white paper (uniform density scan pattern) is read by the image reading device 41 and this image data is stored in the memory 85 a built in the main control unit 85. The main control unit 85 compares the image data of the test pattern and the image data of the scan pattern, detects stray light traces generated on the first recording paper, and uses the light beam of the optical scanning device 11 to detect the surface of the photosensitive drum 13. When the portion corresponding to the stray light trace is scanned, the intensity of the light beam is reduced, and the latent image density of the stray light trace is reduced.

  Here, if the stray light affects the latent image on the surface of the photosensitive drum 13, stray light traces caused by the stray light appear in the read image of the test pattern (gray of uniform density) on the first recording paper. In addition, the scan pattern (blank paper) read image on the second recording paper is merely read by the image reading device 41 and is not related to the optical scanning device 11 or the photosensitive drum 13, so that stray light traces are obtained. Does not appear in the read image of the scan pattern (blank paper) on the second recording paper. Therefore, if the read image of the test pattern on the first recording paper is compared with the read image of the scan pattern on the second recording paper, it appears in the read image of the test pattern on the first recording paper and the second It is possible to identify stray light traces that do not appear in the scan pattern reading image on the recording paper. And if a stray light trace can be specified, the control for suppressing a stray light trace will be attained.

  For each color, the test pattern on the first recording paper is recorded and read, and the test pattern read image on the first recording paper is compared with the scan pattern (blank paper) read image on the second recording paper. The stray light trace of each color may be specified. Further, only black is selected, and the test pattern on the first recording paper is recorded and read, and the black test pattern read image on the first recording paper and the scan pattern on the second recording paper (blank paper). A black stray light trace may be specified by comparing the read images.

  Further, the first and second recording sheets may be of the same type, for example, the recording sheets stored in the sheet feeding tray 18 are used. As a result, it is not necessary for a service person or the like to prepare and carry special paper, and the stray light trace can be examined at any time.

  Next, the identification of the stray light trace on the first recording sheet caused by the stray light of the optical scanning device 11 and the control for suppressing the stray light trace will be described in detail.

  First, FIG. 8A illustrates a test pattern TP made of gray having a uniform density stored in advance in the EEPROM 83 of the optical scanning device 11. Since the intensity of the stray light incident on the photosensitive drum 13 is low, when the test pattern TP (background) is white, stray light traces hardly appear on the recording paper. However, when the test pattern TP (background) is gray, stray light traces are likely to appear on the gray. For this reason, a uniform gray density is applied as the test pattern TP.

  FIG. 8B shows a first recording paper (for example, plain paper) 101 on which a test pattern TP is printed. When stray light is incident on the surface of the photosensitive drum 13 when the latent image of the test pattern is formed on the photosensitive drum 13 by the optical scanning device 11, the stray light affects the electrostatic latent image on the surface of the photosensitive drum 13. In this case, the electrostatic latent image on the surface of the photosensitive drum 13 is developed to form a test pattern toner image, and the test pattern toner image is transferred onto the first recording paper 101 via the intermediate transfer belt 7. The stray light trace G1 appears in the test pattern TP on the first recording paper 101.

  The light beam of the optical scanning device 11 is repeatedly scanned in the main scanning direction. When stray light is generated at a specific portion of the main scanning line every time scanning is performed, a streak G1 extending in the sub scanning direction appears. Further, since the test pattern TP (background) is gray, the stripe G1 is likely to appear on the gray.

  FIG. 8C shows a read image of the test pattern TP on the first recording paper 101 read by the image reading device 41. In the read image of the test pattern TP on the first recording paper 101, not only the streak light streak G1 but also the streak G2 caused by the image reading device 41 appears.

  In the image reading device 41, the image on the recording paper is repeatedly read in the main scanning direction by the line sensor. However, if dust or the like is present in a specific portion of the incident light path to the line sensor, the dust is repeatedly read and the sub scanning is performed. A streak G2 extending in the direction appears.

  The read image of the test pattern TP on the first recording paper 101 on which the streaks G1 and G2 in FIG. 8C appear is stored in the memory 85a of the main control unit 85.

  As described above, the streak G1 caused by stray light from the optical scanning device 11 and the streak G2 caused by dust or the like from the image reading device 41 may appear on the first recording paper 101. For this reason, it is necessary to distinguish the streak G1 caused by stray light from the streak G2 caused by dust or the like.

  FIG. 8D shows a second recording paper (for example, plain paper) 102 of white paper (scan pattern SP with uniform density). FIG. 8E shows a read image of the scan pattern SP on the second recording paper 102 read by the image reading device 41. In the read image of the scan pattern SP on the second recording sheet 102, the streak G2 caused by the image reading device 41 appears, but the stray light trace streak G1 caused by the optical scanning device 11 does not appear. .

  The read image of the scan pattern SP on the second recording paper 102 on which the streak G <b> 2 in FIG. 8E appears is stored in the memory 85 a of the main control unit 85.

  As is apparent from a comparison between the read image of the test pattern TP on the first recording paper 101 in FIG. 8C and the read image of the scan pattern SP on the second recording paper 102 in FIG. The streak G2 caused by the device 41 appears in both read images of the patterns TP and SP. Further, the streak G1 caused by stray light from the optical scanning device 11 appears only in the read image of the test pattern TP.

  The main control unit 85 compares the read images of the patterns TP and SP stored in the memory 85a to identify the streak G2 appearing in each of the read images of the patterns TP and SP, and to test the test pattern. The streak G1 appearing only in the read image of TP is specified. For example, since the read image of the scan pattern SP is white, the streak G2 can be specified by extracting each pixel having a certain density or higher. In addition, since the fabric of the read image of the test pattern TP is gray having a uniform density, the streaks G1 and G2 can be specified by extracting each pixel having a certain density or higher.

  The main control unit 85 obtains the position of the streak G2 in the read image of the scan pattern SP, obtains the position of each streak G1, G2 in the read image of the test pattern TP, compares these positions, and compares each pattern SP. When the position of each streak G2 in the read image of TP matches, it is determined that each streak G2 is a common streak caused by the image reading device 41 or its dust. Further, since the streak G1 of the read image of the test pattern TP does not exist in the read image of the scan pattern SP, it is determined that the streak G1 is a streak caused by the optical scanning device 11 or its stray light.

  When the optical scanning device 11 or the streak G1 caused by the stray light is specified in this way, the main control unit 85 obtains a density difference between the density of the streak G1 and the gray uniform density of the test pattern TP, and this density difference is a constant value. If it is as described above, it is determined that the streak G1 is a clear stray light trace that degrades the image quality, and each pixel on the main scanning line overlapping the streak G1 is obtained.

  Then, the main controller 85 determines the intensity of the light beam in the main scanning period in the register 82-5 of the integrated circuit 82 of the optical scanning device 11 based on the density difference and each pixel on the main scanning line overlapping the streak G1. Rewrite the change pattern. That is, as shown in FIG. 9C, the change pattern of the intensity of the light beam in the main scanning period from T2 to T3 is represented by the timing t1 to t2 at which each pixel on the main scanning line overlapping the streak G1 is scanned. Rewriting is performed so that the intensity (output level) of the light beam is reduced by a level corresponding to the density difference.

  As a result, as shown in FIGS. 9D, 10A, and 10B, the output level of the laser diode 71 changes during the main scanning period in the register 82-5 during the main scanning period from T2 to T3. At timings t1 to t2 when each pixel on the main scanning line overlapping the streak G1 is scanned, the intensity of the light beam is reduced by a level corresponding to the density difference. As a result, when the portion corresponding to the streak G1 on the surface of the photosensitive drum 13 is scanned by the light beam of the light scanning device 11, the intensity of the light beam is lowered, the latent image density of the streak G1 is lowered, and the streak is reduced. The toner image density of G1 also decreases, and the streak G1 on the recording paper becomes inconspicuous.

  Alternatively, instead of rewriting the change pattern of the intensity of the light beam in the main scanning period in the register 82-5 of the integrated circuit 82 of the optical scanning device 11, for each pixel on the main scanning line overlapping the density difference and the streak G1, Image data (the density of each pixel) may be rewritten. In this case, as shown in FIG. 11B, the main control unit 85 converts the image data corresponding to the main scanning line (the main scanning period of T2 to T3) to the density of each pixel (px1 to px2) overlapping the streak G1. Is rewritten so as to decrease by a level corresponding to the density difference. As a result, as shown in FIGS. 11D, 12A, and 12B, the pixels (px1 to px2) on the main scanning line overlapping the streak G1 are scanned in the main scanning period from T2 to T3. At the timing, the intensity of the light beam is reduced by a level corresponding to the density difference. As a result, when the portion corresponding to the streak G1 on the surface of the photosensitive drum 13 is scanned by the light beam of the light scanning device 11, the intensity of the light beam is lowered, the latent image density of the streak G1 is lowered, and the streak is reduced. The toner image density of G1 also decreases, and the streak G1 on the recording paper becomes inconspicuous.

  As mentioned above, although preferred embodiment and modification of this invention were described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to the example which concerns. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. It is understood.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 11 Optical scanning device (optical scanning part)
12 Developing Device 13 Photosensitive Drum (Latent Image Carrier)
14 Drum cleaning device 15 Charger 16 Intermediate transfer belt device 17 Fixing device 18 Paper feed tray 19 Paper discharge tray 41 Image reading device 42 Document conveying devices 71, 71a to 71d Laser diode 81 Substrate 82 Integrated circuit 82-6 Control unit (light quantity) Control part)
83 EEPROM
85 Main control unit (printing control unit, comparison unit)
85a Memory 101 First recording sheet 102 Second recording sheet

Claims (10)

An image reading unit and an optical scanning unit that scans the latent image carrier with a light beam to form a latent image on the latent image carrier, and displays the latent image on the latent image carrier as a visible image. In the image forming apparatus that develops the visible image and transfers the visible image from the latent image carrier to a recording medium,
A latent image of a test pattern set in advance by the optical scanning unit is formed on the latent image carrier, the latent image of the test pattern on the latent image carrier is developed into a visible image, and a test pattern is allowed. A print control unit for transferring and forming a visual image from the latent image carrier to the first recording medium;
Comparison comparing the read image of the test pattern on the first recording medium read by the image reading unit with the read image of the preset scan pattern on the second recording medium read by the image reading unit And
An image forming apparatus comprising: a light amount control unit that controls the intensity of the light beam of the optical scanning unit based on a comparison result of the comparison unit. The image forming apparatus according to claim 1,
The comparison unit detects a streak of the read image of the test pattern on the first recording medium, detects a streak of the read image of the scan pattern on the second recording medium, and detects the streak on the first and second recording media. An image forming apparatus characterized by comparing the streaks of each other. The image forming apparatus according to claim 2,
The comparison unit determines that the cause of the streak is in the image reading unit when the streak positions on the first and second recording media match, and only the streak on the first recording medium is detected. An image forming apparatus, wherein when the density of streaks on the first recording medium is equal to or higher than a certain density, it is determined that the streaks are caused by the optical scanning unit. The image forming apparatus according to claim 2,
The comparison unit determines that the cause of the streak is dust in the image reading unit when the streak positions on the first and second recording media match, and only the streak on the first recording medium is detected. An image forming apparatus, wherein when the density of streaks on the first recording medium is detected and the density is higher than a certain density, it is determined that streaks are caused by stray light of the optical scanning unit. The image forming apparatus according to any one of claims 2 to 4,
The light amount control unit scans a portion corresponding to the streaks in the latent image carrier by the light beam of the optical scanning unit when only the streaks on the first recording medium are detected by the comparison unit. An image forming apparatus characterized in that the intensity of the light beam is sometimes changed. The image forming apparatus according to claim 5, wherein
The light quantity control unit reduces the intensity of the light beam when a portion corresponding to the streaks in the latent image carrier is scanned by the light beam of the light scanning unit. The image forming apparatus according to claim 6,
The image forming apparatus, wherein the light quantity control unit reduces the density of the streaks in the latent image carrier by reducing the intensity of the light beam of the optical scanning unit. An image forming apparatus according to any one of claims 5 to 7,
The light quantity control unit inputs image data, controls the intensity of the light beam of the optical scanning unit based on the image data, corrects the image data, and uses the light beam of the optical scanning unit to An image forming apparatus, wherein the intensity of the light beam is changed when a portion corresponding to the streak is scanned on a latent image carrier. An image forming apparatus according to any one of claims 1 to 8,
2. The image forming apparatus according to claim 1, wherein the test pattern on the first recording medium is a gray print pattern having a uniform density. An image forming apparatus according to any one of claims 1 to 9,
The scan pattern on the second recording medium is a uniform density fabric of the second recording medium.

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