JP2006171606A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce image defects caused by spherical projections or the like formed in a manufacturing process of an a-si photosensitive drum. <P>SOLUTION: In a tandem type image forming apparatus, portions on which white dots are generated due to spherical protrusions or the like formed on the photosensitive drum in an image forming station of a certain color are complemented so that the white dots are made inconspicuous by other colors. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as an electrophotographic type or electrostatic recording type copying machine or a laser beam printer using a photoconductor, and more particularly to an image forming apparatus using an a-Si inorganic photoconductor as a photoconductor.

  Currently, electrophotographic image forming apparatuses are required to have high durability, high stability, and high resolution as output devices in the digital age. In this situation, the A-Si photosensitive drum has high durability capable of printing several million sheets because of its high hardness. In addition, it is highly stable with almost no change in electrical characteristics due to durability and temperature. Furthermore, the latent image can be formed sharply, and both positive and negative charging can be performed, so that high resolution can be achieved. Therefore, A-Si inorganic photoreceptors are often used as electrophotographic photoreceptors.

  However, the A-Si photosensitive member has not only advantages but also disadvantages. A high level of technology is required to uniformly form a large area by CVD, and the production of an A-Si photosensitive drum has a disadvantage that it takes a long time to form a film and is expensive.

  If dust adheres to the film formation surface during the manufacturing process of A-Si, abnormal growth occurs starting from the dust. In this electrophotographic image forming apparatus using a drum, when a photosensitive drum is charged with a high voltage, a high voltage leaks at an abnormal growth point and the image is not charged on the output image, and white spots occur in the image. Lead to defects.

  Furthermore, even in a situation where white spots are not apparent on the image in the initial stage, the abnormally grown portion may spread due to durability and worsen the image defect.

Conventionally, proposals have been made to find this white spot in the manufacturing process (Patent Documents 1 and 2).
JP-A-11-166905 JP 11-185040 A

  However, if a detailed inspection method is introduced in the manufacturing process, the manufacturing cost increases. Furthermore, since defective products will be discarded, cost increase is a problem.

  In the present invention, an image defect in an abnormally grown portion of the photosensitive drum is corrected as much as possible on the printer side, so that the level is practically not problematic for texts and business images.

  The present invention relates to an image forming apparatus using one or a plurality of photosensitive drums, a photosensitive drum, an exposure unit for exposing the surface of the photosensitive drum, and a defect for detecting a defective portion of the photosensitive drum. A means for outputting a detection image; and reading the defect detection image to identify a photosensitive drum having a defect and a defect portion detection means for detecting the position of the defect portion. The color image data of a portion where a defective portion on the photosensitive drum is exposed by a laser beam is changed.

  As described above, according to the present invention, it is possible to grasp a defective portion of a photosensitive drum such as electrophotography, particularly an A-Si photosensitive drum, and develop other colors when image data can be corrected and complemented. Defects can be made as inconspicuous as possible. This makes it possible to use a photosensitive drum that has been discarded or replaced in the past, and can significantly reduce the cost of the image forming apparatus and the running cost.

  Examples according to the present invention will be described below.

Example 1
FIG. 2 is a diagram illustrating a configuration of a mechanism unit of the image forming apparatus in the embodiment.

  Reference numeral 201 denotes an original table glass on which an original 202 to be read is placed. The original 202 is irradiated by the illumination 203, passes through mirrors 204, 205, and 206, and an image is projected onto the CCD 208 by the optical system 207. Here, the CCD 208 is constituted by a three-line CCD line sensor of R (red), B (blue), and G (green). Further, the first mirror unit 210 including the mirror 204 and the illumination 203 is driven at a speed V by the motor 209, and the second mirror unit 211 including the mirrors 205 and 206 is driven at a speed ½ V. Are scanned.

  An image processing unit 212 processes image information read by the CCD 208 as an electrical signal and outputs it as a print signal. Reference numerals 213, 214, 215, and 216 denote semiconductor lasers that are driven by output signals from the image processing unit 212. Laser light emitted by each semiconductor laser is scanned on the photosensitive drums 225, 226, 227, and 228 for each print color by the polygon mirrors 217, 218, 219, and 220 for each print to form a latent image. Reference numerals 221, 222, 223, and 224 denote developing devices for developing latent images with black (Bk), yellow (Y), cyan (C), and magenta (M) toners, respectively.

  One of the paper cassettes 229, 230, and 231 and the manual feed tray 232 is selected, and the fed paper is sucked onto the transfer belt 234 through the registration rollers 233 and conveyed. A photo interrupter 250 is an ITOP sensor for generating a page synchronization signal. The aforementioned paper feed timing and the start of exposure scanning of the photosensitive drum of the laser are performed in accordance with a page synchronization signal (ITOP signal) generated by this ITOP sensor. Therefore, the paper feed timing and the image formation timing are synchronized, and each color image developed on the photosensitive drums 228, 227, 226, and 225 is transferred onto the paper. The sheet on which the toner of each color is transferred is separated / conveyed, fixed, and discharged onto the discharge tray 236.

  Next, FIG. 1 which is a block diagram from image reading to writing will be described. The CCD 101 is composed of RGB three-line CCDs, which color-separate one line of light information from the original and output RGB electrical signals with a resolution of 400 dpi. In this embodiment, since a maximum of 297 mm (A4 length) is read as one line, the CCD 101 outputs an image of 4677 pixels per line for R, G, and B, respectively.

  In FIG. 1, reference numeral 110 denotes a magenta synchronization signal generation unit, which includes a main scanning address counter, a sub scanning address counter, and the like. The main scanning address counter is cleared for each line by a BD signal which is a synchronization signal for laser recording for each line on the photosensitive drum 118, counts the VCLK signal from the pixel clock generator 112, and is read out from the CCD 101. A count output H-ADR corresponding to each pixel of the image information is generated (not shown). This H-ADR counts up from 0 to 5000, and the image signal for one line can be sufficiently read from the CCD 101. Further, the synchronization signal generator 110 outputs various timing signals such as a line synchronization signal LSYNC, an image signal main scanning effective section signal VE, and a sub-scanning effective section signal PE. The sub-scanning effective interval signal is generated by the sub-scan address counter 110 operating after the ITOP signal is input to the delay unit M 140 and delayed by a predetermined amount corresponding to the predetermined set value written by the CPU 109. The delay unit C is 141, the delay unit Y is 142, the delay unit K is 143, and the delay amount for each color is set by the CPU 109.

  A CCD drive signal generator 130 decodes the H-ADR and generates a CCD-DRIVE signal as a reset pulse or a transfer clock from the shift pulse of the CCD 101. As a result, R, G, and B color separation image signals for the same pixel are sequentially output from the CCD 101 in synchronization with VCLK. Reference numeral 102 denotes an A / D converter that converts RGB image signals into 8-bit digital signals.

Reference numeral 103 denotes a light quantity-density conversion section (LOG conversion section) which converts RGB 8-bit light quantity signals into CMY 8-bit density signals by logarithmic conversion. An output masking processing unit 104 extracts a black density signal from C, M, and Y3 density product numbers by a known UCR (under color removal process). The black value is calculated as follows.
K = Min (C, M, Y)
At the same time, an existing masking operation for removing color turbidity of the developer corresponding to each density signal is performed. In this way, M, C, Y, and K density signals are generated.

  Next, the image signal (VIDEO) generated by the image processing unit, for example, a black image signal, is sent to the laser unit K (130). Reference numeral 107 denotes a laser controller that controls the amount of light emitted from the laser in accordance with a VIDEO signal that is an 8-bit density signal. Reference numeral 117 denotes a photodiode which detects the passage of laser light immediately before scanning the photosensitive drum 118 and generates a one-line synchronization signal BD. The polygon mirror 116 rotates at a rotation speed for performing laser scanning corresponding to the printing speed of the color copying machine. Therefore, the BD signal, which is the main scanning synchronization signal, is output at regular intervals for each line. 121 is a photo sensor that detects a reference flag attached to the transfer body 119 and generates a page synchronization signal ITOP as a reference position. In this embodiment, the photosensitive drum 118 and the transfer body 119 are synchronously rotated, and the circumferential lengths of the photosensitive drum 118 and the transfer body 119 are an integer ratio and are synchronously rotated by the same drive source. The other magenta, cyan and yellow photosensitive drums are also rotated in the same manner.

  Although black laser exposure has been described here, the same control is performed for the laser unit M (131), the laser unit C (132), and the laser unit Y (133). When outputting a color image, four laser units (130 to 133) of M, C, Y, and K are driven to obtain a color image by superimposing four color toner images on a sheet on a transfer belt. be able to.

  Here, the white spot determination image output will be described. The CPU 109 controls the printer and outputs an image. The CPU 109 sets, in the laser controller unit 107, settings for outputting a black halftone image having such a density that white spots are conspicuous. Then, after the photosensitive drum 118 and the transfer body 119 are rotated at an image forming speed to reach a constant speed, a halftone image is output according to the output signal of the ITOP sensor. The page synchronization signal ITOP is a signal that serves as a reference for printer control during printing, and normal printing is also performed at the same timing.

  FIG. 2 shows a timing chart for outputting the white spot determination image. 301 is a drum HP signal and 302 is an ITOP signal. Since the transfer body is synchronously driven by one rotation by two rotations of the photosensitive drum and the speed is constant at the image forming speed, the pulse outputs 301 and 302 are output at equal intervals. After the rotation of the photosensitive drum and the transfer body becomes constant, the photosensitive drum is driven by the laser by the VIDEO (M) signal created by the laser controller after the black exposure start time 303 Ts (K) msec from the rising edge of the page reference signal ITOP 302 of the printer. To form a latent image. Further, the photosensitive drums of black and magenta, magenta and cyan, and cyan and yellow are separated from each other along the circumference of the photosensitive drum. Therefore, Ts (C) -Ts (M), TS (Y) -Ts (C), and Ts (K) -Ts (Y) are set to the time for one round of the drum. However, because of the black monochrome halftone printing, the image data 307 to 309 other than black is 0, and magenta, cyan, and yellow are not developed.

  Thereafter, the latent image on the photosensitive member is developed with black toner, and the visualized toner image is transferred onto a sheet. Thereafter, the toner image on the paper is overheated and pressure-fixed by a fixing device to become a permanent image.

  FIG. 4-A shows a white-out determination image. It is an example of the image of the above-mentioned white spot judging black. By reading the output image to the reader, it is possible to specify the white spot position due to the malfunction of the photosensitive drum. Reference numeral 405 denotes paper, and reference numeral 411 denotes a halftone image portion. Reference numeral 406 denotes a defective portion of the photosensitive drum where a latent image is not formed and toner is not developed. 401 is a BD or a line synchronization signal LSYNC. Reference numeral 402 denotes a VIDEO clock, and one clock corresponds to one pixel of a CCD reading pixel. Reference numeral 404 denotes a BD signal. One clock of the BD signal corresponds to one line of the image 411. Reference numeral 403 denotes an image enable signal for sub-scanning. The output of the 8-bit CCD read by the reader is, for example, 80 (h) in the halftone part, but 230 to 255 (h) in the white part. Therefore, when this image is read by the reader, there is a white spot with a size of 1 pixel in both the main and sub positions at the position of 5 pixels from the BD and LSYNC in the main scanning direction and 4 pixels from the sub scanning effective section signal in the sub scanning direction. Can be judged. This determination is performed by the white spot determination unit 122. The white spot position is read from the white spot judging unit by the CPU 109 and stored in a nonvolatile memory (not shown).

  Next, a method for complementing white areas will be described. First, an image to be color copied is pre-scanned by a reader. The CPU 109 writes the blank position in the black character determination portion 131 before the pre-scan. Further, the CPU 109 similarly writes the blank position in the complementary data creation unit. Then, a pre-scan operation is performed. During this pre-scan, the black character determination unit 131 determines the black character portion and the black portion of the image. At this time, it is simultaneously determined whether or not the image at the above-described white spot position is black. At the same time, the supplementary data creation unit creates supplementary data for the blank areas from the R, G, and B data for when it is not black. When the complementary data creation unit determines that the density data of R, G, B at the white spot position is D = 1.8 or higher and is not yellow, the R.G. G. Data is created so as to print B black. If it is yellow, the image data is used as it is. If the black character is determined to be black by the black character determination unit, R.D. G. Data is created so as to print B black.

  FIG. 4-B will be used to describe a copy operation for whiteout complement after completion of prescanning. Reference numeral 425 denotes paper, 431 denotes an image printable area, and 426 denotes an actual print area. For example, when a black image as shown by 426 is copied to the original image, the position of 5 pixels (427) from the rising edge of the BD 421 at the main scanning position, and the rising edge of the sub scanning enable signal PE (423) in the sub scanning direction. Since it is determined that there is a defect on the photosensitive drum at the position of four pixels from the first to fourth, and the image areas 426 are printed in black. In the image area 426, since there is a defect in the black photoconductor, development is performed with magenta, cyan, and yellow drums at the same density to form black with three color toners. Therefore, it is possible to make the white spots inconspicuous by supplementing with the other development colors also the portions that have been white spots mainly due to defects of the photosensitive drum or deterioration due to durability. .

  Here, black white spots have been described as an example, but other magenta and cyan high density areas where the density D = 1.8 or higher are more noticeable by developing with black rather than white areas. In order to eliminate it, it can correct | amend similarly. In the case of yellow, since it may be easier to understand the difference from the original image when complemented with other colors, it is also possible to perform control so as not to complement with other colors.

Block diagram from image reading to writing The figure which shows the structure of the mechanism part of an image forming apparatus. White chart image output timing chart A is a diagram of a white spot determination image, and B is a diagram showing a copy operation for white spot complementation.

Explanation of symbols

116 Polygon mirror 109 CPU
112 Image clock 122 White spot judging unit 123 Complementary data creating unit

Claims (5)

An image forming apparatus using a plurality of photosensitive drums.
A photosensitive drum and exposure means for exposing the surface of the photosensitive drum;
Means for outputting a defect detection image for detecting a defective portion of the photosensitive drum;
The defect detection image is read, and a defective part on the photosensitive drum, which has a defect part detection unit for detecting a defective photosensitive drum and detecting the position of the defective part, is determined as a defect by the defect part detection unit. The color image data of a portion exposed by laser light is changed.   In the image forming apparatus described in the above item 1, if the image defect portion of the photosensitive drum is cyan and the density is at least D = 1.8 or more, the portion corresponding to the defect portion on the paper is black and magenta. It is developed and transferred to a sheet.   In the image forming apparatus described in 1 above, when the image defect portion of the photosensitive drum is magenta and the density is at least D = 1.8 or more, the portion corresponding to the defect portion on the paper is black and cyan. It is developed and transferred to a sheet.   In the image forming apparatus described in the above item 1, when the image defect portion of the photosensitive drum is yellow, the color image data is not corrected.   In the image forming apparatus described in the above item 1, when the image defective portion of the photosensitive drum is black, a portion corresponding to the defective portion on the paper is developed with magenta, cyan, and yellow and transferred to the paper. To do.

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