JP2009222784A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent an image defect in multi-color in an electrophotographic image forming apparatus. <P>SOLUTION: A control part 2 receives a signal showing the class of an image of a raster image from a multi-image discriminating part 42, and determines whether or not the signal is a line image signal. When the signal is a half-tone image signal, the control part 2 reads a parameter P1 for a half-tone image from a storage part 3, and forms a half-tone image based on a pattern generated by a pattern generating part 113. On the other hand, when the signal is a line image signal, the control part 2 determines whether or not the image is multi-color. In this case, when the image is determined to be not multi-color, the control part 2 reads a parameter P2 for a single color line image from the storage part 3 and forms an image. When the image is determined to be multi-color, the control part 2 reads a parameter P3 for a multi-color line image from the storage part 3 and forms an image. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus.

In an electrophotographic color image forming apparatus, a color image is formed by superposing a plurality of colors of toner on a recording material. However, when the amount of toner increases, a so-called blur phenomenon may occur in which the toners stacked due to electrostatic repulsion between the toners are scattered around the image.
Japanese Patent Application Laid-Open No. 2004-151561 describes a technique for suppressing image distortion by limiting the output level only to a chromatic color portion when an image is formed on a transparent recording material. Patent Document 2 describes a technique for preventing toner scattering of a multi-color toner image in which a plurality of color toners are superimposed by increasing the relative permittivity of an intermediate transfer member.
JP-A-8-98048 JP 2000-122440 A

  An object of the present invention is to prevent image defects in multiple colors in an electrophotographic image forming apparatus.

  In order to solve the above-described problem, an image forming apparatus according to the present invention analyzes description data describing the contents of an image, identifies an image type of the image, and determines a raster based on the description data. Raster image generation means for generating an image, and the raster image generated by the raster image generation means must be analyzed for each pixel, and two or more developers must be accumulated during development, and the image density is predetermined. Detection means for detecting pixels having a density higher than that of a multi-color high-density pixel, and latent image formation for forming an electrostatic latent image by exposing the surface of the image carrier charged by the charging means based on the description data And the latent image forming means is adapted to detect pixels of which the image type is identified as a line drawing or a character by the identification means and detected as multi-color high density pixels by the detection means. Te, characterized in that to reduce the amount of exposure light.

Preferably, the electrostatic latent image formed by the latent image forming unit is developed with a developer, the obtained image is transferred to a recording material, and an image transfer unit that forms an image on the surface of the recording material; Pattern forming means for forming an image with a predetermined pattern on a recording material, reading means for reading an image formed by the pattern forming means, analysis of the reading result of the reading means, and exposure light by the latent image forming means It is preferable to provide correction means for correcting the amount of light.
Preferably, the image forming apparatus includes a fixing unit that fixes the image formed by the image transfer unit to the recording material, and the reading unit is disposed downstream of the fixing unit.
In addition, it is preferable that a pulse width control unit that controls a pulse width of the exposure light with respect to a pixel whose image type is identified as a picture or a photograph by the identification unit.

  According to the present invention, image defects in multiple colors can be prevented in an electrophotographic image forming apparatus.

Embodiments of the present invention will be described below with reference to the drawings.
[A. Constitution]
FIG. 1 is a block diagram illustrating the overall configuration of the image forming apparatus 1000.
The control unit 2 is a CPU (Central Processing Unit) or the like, and controls each unit of the image forming apparatus 1000. The storage unit 3 is a storage device such as a RAM (Random Access Memory), a ROM (Read Only Memory), or an EEPROM (Electrically Erasable Programmable Read Only Memory), and stores a control program read by the control unit 2 as well as various controls. Store the parameters. The image processing unit 4 receives and receives description data (hereinafter referred to as PDL data) described in a page description language (hereinafter referred to as PDL) from the external device 9 under the control of the control unit 2. Based on the PDL data, a raster image, which is raster format image data, is generated and output to the image forming unit 1. Based on the raster image received from the image processing unit 4, the image forming unit 1 forms a toner image under the control of the control unit 2 and forms an image on the recording material.

FIG. 2 is a diagram illustrating the structure of the image forming unit 1 of the image forming apparatus 1000.
As shown in the figure, the image forming unit 1 includes a paper storage unit 12, an image forming unit 13, a transfer unit 14, a fixing unit 15, a cooling unit 16, a transport unit 17, and an inline sensor 18. I have. The paper storage unit 12 stores paper cut into a predetermined size such as A3 or A4. The sheets stored in the sheet storage unit 12 are picked up one by one by a pickup roller or the like, and are conveyed to the transfer unit 14 via a sheet conveyance path.

  The image forming units 13Y, 13M, 13C, and 13K (hereinafter simply referred to as the image forming unit 13 when not distinguished from each other) are a photosensitive drum that is an image holding member, a charging unit that charges the surface of the photosensitive drum, A latent image forming unit that exposes the surface of the photosensitive drum that has been charged by the unit to form a latent image, and supplies a toner as a developer to the surface of the photosensitive drum on which the latent image is formed to develop the latent image. A developing unit, a primary transfer roll, and a cleaning member are provided, and a toner image corresponding to the raster image is formed and transferred onto the intermediate transfer belt 141 of the transfer unit 14 in an overlapping manner. The transfer unit 14 includes an intermediate transfer belt 141, a secondary transfer roll 142, and a counter roll 143 that faces the secondary transfer roll 142 across the intermediate transfer belt 141, and is developed by the developing unit of the image forming unit 13. Transfer means for transferring the obtained toner image to a sheet. The intermediate transfer belt 141 is rotated in the direction A in the figure by a drive roll (not shown). When the toner image is transferred in an overlapping manner by the image forming unit 13, the toner image is opposed to the secondary transfer roll 142. Transport to the position of the roll 143. The secondary transfer roll 142 transfers the toner image on the intermediate transfer belt 141 to the sheet conveyed from the sheet storage unit 12 by the potential difference with the intermediate transfer belt 141. The sheet on which the toner image is transferred from the intermediate transfer belt 141 is conveyed to the fixing unit 15. Note that the symbols Y, M, C, and K indicate configurations corresponding to yellow, magenta, cyan, and black toners, respectively. The transfer unit 14, the developing unit of the image forming unit 13, and the primary transfer roll are controlled by the control unit 2 and are obtained by developing the electrostatic latent image formed by the latent image forming unit of the image forming unit 13 with a developer. The toner image is transferred to a sheet and functions as an image transfer unit that forms a toner image on the surface of the sheet.

  The fixing unit 15 includes a heating roll 151 and a pressure roll 152. The sheet conveyed from the secondary transfer roll 142 is sandwiched between the heating roll 151 and the pressure roll 152, and heat and pressure are applied to the sheet. In addition, the toner image formed by the image forming unit 13 is fixed on the paper. The heating roll 151 has a heat source such as a halogen lamp inside, and heats the surface of the paper to about 100 degrees. The pressure roll 152 is pressed against the heating roll 151 and applies pressure to the sheet passing between the heating roll 151 and the pressure roll 152. In addition, a peeling member 153 made of metal or resin is provided near the surface of the heating roll 151. The paper that has undergone the fixing process by applying heat and pressure by the heating roll 151 and the pressure roll 152 is peeled off from the heating roll 151 by the peeling member 153 and transported to the cooling section 16 by the transport section 17. It has become.

The transport unit 17 is provided between the fixing unit 15 and the cooling unit 16. The transport unit 17 includes two transport rolls and a transport belt wound around the transport rolls, and transports the paper discharged from the fixing unit 15 to the cooling unit 16.
The cooling unit 16 is a solidifying unit that is disposed on the downstream side of the fixing unit 15 in the sheet conveyance direction, and cools and solidifies the toner image that has been melted by the fixing unit 15. The cooling unit 16 has two endless belt members wound around a plurality of rolls. When the paper transported from the transport unit 17 is nipped and transported by these two endless belt members, heat is taken from the paper by the heat sink provided inside the endless belt member, and the paper is cooled.
The in-line sensor 18 has a light source such as an incandescent lamp or a white light emitting diode and a light receiving element such as a CCD (Charge Coupled Device). The in-line sensor 18 is disposed on the downstream side of the cooling unit 16 in the sheet conveyance direction, and the light source irradiates the surface of the sheet after being nipped and conveyed by the cooling unit 16 and the reflected light reflected from the sheet surface is received by the light receiving element Measures and outputs a signal corresponding to the reflected light. Thereby, the in-line sensor 18 functions as a reading unit that reads an image formed on the surface of the paper.
The above is the structure of the image forming unit 1.

FIG. 3 is a diagram illustrating an electrical configuration of the image processing unit 4 and the image forming unit 1.
As shown in the figure, the image processing unit 4 includes a raster image generation unit 41, a multiple image identification unit 42, a color conversion processing unit 43, a gradation processing unit 44, and a selector 45. In addition to the above-described configuration, the image forming unit 1 includes a modulation unit 11 that modulates a raster image into an exposure signal for exposure.

The raster image generation unit 41 generates a raster image based on the received PDL data and outputs the raster image to the color conversion processing unit 43. The raster image generation unit 41 analyzes the PDL data and identifies the type of the image described therein. The image type identification signal corresponding to the type is output to the multiple image identification unit 42. Here, the types of images include line drawings, characters, patterns, photographs, and the like. In particular, an image composed of lines such as a line drawing or a character is called a line image, and an image represented by an intermediate gradation such as a picture or a photograph is called a halftone image.
The color conversion processing unit 43 converts the raster image generated by the raster image generation unit 41 from the three primary colors of R (red), G (green), and B (blue) into four colors of Y, M, C, and K for each pixel, The converted raster image is output to the multiple image identification unit 42 and the gradation processing unit 44.

The multiple image identification unit 42 has the following two functions.
The first function of the multiple image identification unit 42 receives the image type identification signal output from the raster image generation unit 41, and the raster image generated by the raster image generation unit 41 is a line image or a halftone image. This is a function of determining whether or not to notify the control unit 2 of the determination result. Specifically, when the image type identification signal is “line drawing” or “character”, the multiple image identification unit 42 generates a signal indicating that the raster image is a line image (hereinafter referred to as a line image signal). In the case of “picture” or “photograph”, a signal indicating that the raster image is a halftone image (hereinafter referred to as a halftone image signal) is output to the control unit 2.

  The second function of the multiple image identification unit 42 is to analyze the raster image generated by the raster image generation unit 41 and converted by the color conversion processing unit 43 for each pixel, and the color of each pixel is a multiple color and its image density Is a function that detects the pixel as a multi-color high-density pixel and notifies the control unit 2 of the detection result. Here, the multiple color is a color represented by two or more developers during development. For example, yellow and cyan are colored with only one color toner, so they are not a multiple color but a single color, but green (green) is a multiple color because it is colored by overlapping yellow and cyan. The multiple image identification unit 42 stores threshold values set for each of four colors Y, M, C, and K, and compares the gradation value of each color of the analyzed pixel with each threshold value so that two or more colors are stored. Is detected as a multi-color high-density pixel.

The gradation processing unit 44 receives a raster image expressed in four colors Y, M, C, and K from the color conversion processing unit 43, and under the control of the control unit 2, the characteristics and dynamic range of the photoconductor in image formation. The gradation value of each pixel is adjusted so as to match.
The selector 45 switches the output destination for outputting the raster image whose gradation value is adjusted by the gradation processing unit 44. Specifically, when the control unit 2 receives a line image signal from the multiple image identification unit 42, the selector 45 is a raster whose gradation value is adjusted by the gradation processing unit 44 under the control of the control unit 2. The image is output to the power modulation circuit 111 of the modulation unit 11. On the other hand, when the control unit 2 receives the halftone image signal from the multiple image identification unit 42, the selector 45 outputs the raster image to the pulse modulation circuit 112 of the modulation unit 11.

  The modulation unit 11 of the image forming unit 1 includes a power modulation circuit 111 and a pulse modulation circuit 112. Each is a circuit that modulates a raster image expressed in 256 gradations for each color into binary image data of each color. The power modulation circuit 111 is a circuit that adjusts the amount of exposure light in accordance with the pixel value of the raster image. The pulse modulation circuit 112 is a circuit that controls the pulse width of the exposure light and generates a halftone image corresponding to the pixel value of the raster image.

[B. Operation]
Next, the operation of the image forming apparatus 1000 in this embodiment will be described.
[B-1. Printing operation]
FIG. 4 is a flowchart for explaining the flow of the printing operation of the image forming apparatus 1000. The control unit 2 receives a signal representing the type of image of the raster image from the multiple image identification unit 42 of the image processing unit 4 for each pixel of the raster image (step SA01). The controller 2 determines whether this signal is a line image signal (step SA02). When this signal is a halftone image signal (step SA02; NO), the control unit 2 reads the halftone image parameter P1 from the storage unit 3 to generate an exposure signal, and the exposure signal generates a halftone image. An image is formed by, for example, writing an electrostatic latent image corresponding to the pixels constituting the image on the image carrier (step SA03). In this case, the pattern generation unit 113 generates a halftone image based on the gradation value of the raster image received by the modulation unit 11.

  On the other hand, when this signal is a line image signal (step SA02; YES), the control unit 2 determines whether or not this pixel is a multi-color high-density pixel based on the detection result received from the multiple image identification unit 42. Is determined (step SA04). If the control unit 2 determines that this pixel is not a multi-color high-density pixel (step SA04; NO), the control unit 2 reads the parameter P2 for the single color line image from the storage unit 3. An exposure signal is generated, and an image is formed by writing an electrostatic latent image corresponding to the pixels constituting the single color line image on the image holding body by the exposure signal (step SA05). When the control unit 2 determines that this pixel is a multi-color high-density pixel (step SA04; YES), the control unit 2 reads the parameter P3 for the multi-color line image from the storage unit 3 and outputs an exposure signal. And an electrostatic latent image corresponding to the multi-color high-density pixels is written on the image holding body by the exposure signal to form an image (step SA06). In this case, the power modulation circuit 111 uses the control unit 2 to control the exposure light amount when forming the electrostatic latent image corresponding to the multi-color high-density pixel, and the electrostatic latent image corresponding to the other pixels. A process of lowering the exposure light amount when forming is performed.

  In this way, by changing the parameters used for modulation of the raster image depending on the type of image and whether or not it is a multi-color high-density pixel, blurring is less likely to occur when printing a multi-color line image. Also, if the exposure light amount is reduced uniformly regardless of whether it is multiple colors or not, the blur in the multiple color image area is suppressed, but in the single color image area, the line drawing is faint due to insufficient light quantity. May end up. In the present invention, since the conventional parameter P2 is used for a single color line image, blurring is suppressed in printing a multicolor line image, and whether printing is performed in printing a single color line image. Strain is suppressed. Also, since the parameters are switched for each pixel, a single color line image and a multi-color line image are mixed on the same page, or a line image and a halftone image are mixed on the same page. Even in the case of printing, suitable parameters are used for printing.

[B-2. Parameter correction operation]
Next, the parameter correction operation will be described. FIG. 5 is a flowchart for explaining the flow of the parameter correction operation of the image forming apparatus 1000.
In addition to the printing operation described above, the image forming apparatus 1000 receives a maintenance instruction from a user via an operation unit (not shown) and performs a series of maintenance operations.
First, the image forming apparatus 1000 performs registration adjustment (step SB01). As shown in FIG. 2, the Y, M, C, and K photoconductor drums are in contact with the intermediate transfer belt 141 of the transfer unit 14, and the toner image formed on the surface of the photoconductor drum is intermediate transferred. The image is transferred onto the belt 141. At this time, when the toners of the respective colors are superimposed on the intermediate transfer belt 141, multiple colors are developed, but the position where the toner is transferred may be shifted. Registration adjustment means correction of this position, and is, for example, the following processing. The image forming apparatus 1000 forms a toner image of each color in a predetermined pattern, and transfers and fixes it on a sheet. The inline sensor 18 reads this, generates corresponding image data, and outputs it to the control unit 2. The control unit 2 analyzes this image data. When the controller 2 detects a variation in the interval between the color toners transferred to the sheet from the analysis result, the controller 2 adjusts the light emission timing of an exposure LED (Light Emitting Diode) according to the variation.

  Next, the image forming apparatus 1000 forms an image of a predetermined pattern in which toner of each color is superimposed on the paper, and transfers and fixes the image on the paper (step SB02). The inline sensor 18 reads this, generates corresponding image data, and outputs it to the control unit 2 (step SB03). The control unit 2 analyzes the image data and measures the line width of each multi-color line (step SB04). The control unit 2 calculates a correction value for the amount of light emitted by the exposure LED in accordance with the thickness of the line width included in the analysis result (step SB05). Then, the control unit 2 corrects the parameter P3 for the multiple color line image according to the calculated correction value and stores it in the storage unit 3 (step SB06).

  If the driving time of the image forming apparatus 1000 is long and the photosensitive drum is repeatedly used, the film pressure of the photosensitive drum may be reduced, or the charging of the developer may be reduced. Such a secular change also affects the occurrence rate of blur in the multi-color line image, but if the parameters for the multi-color line image are fixed, it becomes impossible to cope with the secular change. Even if such parameters can be set, if they are set manually, it is necessary to visually determine a large number of test patterns and adjust the parameters, which is complicated. As described above, since the in-line sensor 18 is disposed downstream of the fixing unit 15 in the paper conveyance direction, the toner image after fixing can be measured. Therefore, the in-line sensor 18 can automatically correct the parameters of the multi-color line image in conjunction with the registration adjustment, blurring is suppressed according to the secular change of the photosensitive drum, and the user for the correction is corrected. Saves time and waiting time.

[C. Modified example]
The embodiment described above may be modified as in the following example. Moreover, you may combine these modifications suitably.
(1) In the above-described embodiment, the inline sensor 18 is provided immediately after the cooling unit 16 and the surface of the paper discharged from the cooling unit 16 is measured. However, the sensor may be provided at another position. . For example, it may be determined whether the paper is plain paper or coated paper from the reflected light of the paper before transfer stored in the paper storage unit 12. Coated paper is paper in which a resin layer is formed on the surface of plain paper made of pulp fibers. In this case, the intensity of the specularly reflected light is lower because the plain paper diffuses and reflects light than the coated paper. Therefore, this sensor measures the intensity of the specularly reflected light out of the reflected light and takes a ratio with the irradiated light. If this ratio exceeds a predetermined threshold, it is determined that the paper is coated paper. do it.
Since coated paper has a smooth surface and lower toner fixing power than plain paper, blurring is more likely to occur than plain paper even with the same amount of toner. Therefore, when the image forming apparatus 1000 determines that the paper is coated paper, the amount of exposure light may be reduced. Note that the amount of exposure light may be adjusted according to the type of paper, and the transfer voltage may be adjusted as appropriate.

(2) Further, the inline sensor 18 reads the toner image formed on the surface of the paper, but may read the toner image formed on the surface of the intermediate transfer member. In this case, a predetermined pattern may be formed by transferring toner of each color to the end of the surface of the intermediate transfer belt 141 that is not in contact with the paper, and the inline sensor 18 may measure this pattern. In this way, it is not necessary to consume paper for printing the test pattern. In addition, it is possible to measure the ease of blurring and the like even during the standby time when the transfer to the paper is not performed.

(3) In the above-described embodiment, the multiple image identification unit 42 analyzes the raster image converted by the color conversion processing unit 43 for each pixel and determines whether or not the color of each pixel is a multiple color. The multiple image identification unit 42 may analyze the raster image generated by the raster image generation unit 41 before the color conversion processing unit 43 performs conversion. In this case, it is only necessary to have a specifying means for specifying whether a single color or multiple colors from the R, G, B gradation values. Specifically, the multiple image identification unit 42 may store a table in which each of the R, G, and B gradation values is divided into an appropriate range and the combination and the number of colors are associated with each other. The multiple image identification unit 42 may acquire the gradation value of the raster image for each pixel and refer to this table to determine whether or not the pixel is a multiple color high density pixel.

(4) In the above-described embodiment, the multiple image identification unit 42 compares the gradation value of each color of the analyzed pixel with each threshold value, and when the gradation values of two or more colors are equal to or more than the threshold value, The pixel was detected as a multi-color high density pixel. However, the threshold value may not be set individually for each color. For example, when two or more color toners are used for printing and the total image density exceeds a threshold value, the pixel may be detected as a multi-color high-density pixel.

1 is a block diagram illustrating an overall configuration of an image forming apparatus. 2 is a diagram illustrating a structure of an image forming unit of the image forming apparatus. FIG. FIG. 2 is a diagram illustrating an electrical configuration of an image processing unit and an image forming unit. FIG. 6 is a flowchart for explaining a flow of a printing operation of the image forming apparatus. FIG. 6 is a flowchart for explaining the flow of a parameter correction operation of the image forming apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image formation part, 1000 ... Image formation apparatus, 11 ... Modulation part, 111 ... Power modulation circuit, 112 ... Pulse modulation circuit, 113 ... Pattern generation part, 12 ... Paper storage part, 13 ... Image formation unit, 14 ... Transfer , 141: Intermediate transfer belt, 142: Secondary transfer roll, 143: Opposing roll, 15 ... Fixing section, 151 ... Heating roll, 152 ... Pressure roll, 153 ... Peeling member, 16 ... Cooling section, 17 ... Conveying section 18 ... Inline sensor, 2 ... Control unit, 3 ... Storage unit, 4 ... Image processing unit, 41 ... Raster image generation unit, 42 ... Multiple image identification unit, 43 ... Color conversion processing unit, 44 ... Tone processing unit, 45 ... selector, 9 ... external device.

Claims (4)

Analyzing the description data describing the contents of the image, and identifying means for identifying the image type for each pixel included in the image;
Raster image generating means for generating a raster image which is image data in a raster format based on the description data;
The raster image generated by the raster image generation means is analyzed for each pixel, and pixels that are colors represented by two or more developers and whose image density is a predetermined density or more are detected as multi-color high-density pixels. Detecting means for
Latent image forming means for forming an electrostatic latent image by exposing the surface of a charged image carrier based on the raster image, wherein the identification means identifies the image type as a line drawing or a character, and the detection means When forming an electrostatic latent image corresponding to a pixel detected as a multi-color high-density pixel, the amount of light when performing the exposure is larger than when forming an electrostatic latent image corresponding to a pixel other than the pixel. An image forming apparatus comprising: a latent image forming means for lowering. Developing the electrostatic latent image formed by the latent image forming means with a developer, transferring the obtained image to a recording material, and forming an image on the surface of the recording material; and
Pattern forming means for forming an image in a predetermined pattern on the recording material;
Reading means for reading an image formed by the pattern forming means;
The image forming apparatus according to claim 1, further comprising: a correction unit that analyzes a reading result of the reading unit and corrects the amount of exposure light by the latent image forming unit according to the analysis result. A fixing unit for fixing the image formed by the image transfer unit to the recording material;
The image forming apparatus according to claim 1, wherein the reading unit is disposed downstream of the fixing unit in a conveyance direction of the recording material.   2. A pulse width control means for controlling a pulse width of exposure light when forming an electrostatic latent image corresponding to a pixel whose image type is identified as a picture or a photograph by the identification means. 4. The image forming apparatus according to any one of items 3 to 3.

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