JP2007163883A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrophotographic image forming apparatus capable of performing a density control in all printing modes with a single density control action. <P>SOLUTION: The electrophotographic image forming apparatus includes: a measuring means for measuring the density of an output image outputted based on reference input image data; an image simulating means for predicting the density of the output image of the image forming apparatus by changing a simulation condition, a density comparison means for comparing the density of the output image with the density of the simulation image predicted by the image simulating means; and a density correction control means for correcting an input image signal in accordance with the result of the density comparison means. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a printer or a copying machine to which an electrophotographic technique is applied, and an image forming method.

  2. Description of the Related Art In recent years, an image forming apparatus that employs an electrophotographic system such as a printer or a copying machine, an ink jet system, or the like has been required to improve the output image quality. In particular, the gradation of density and the stability of density have a great influence on the judgment of the quality of an image given by a human.

  However, in the image forming apparatus, when there is a change in environment such as temperature and humidity, or a change in each part of the apparatus due to long-term use, the density of the obtained image fluctuates. In particular, in the case of an electrophotographic image forming apparatus, since the density of an output image varies even with slight environmental fluctuations, a method of always maintaining a constant density is necessary.

  Conventionally, as a method of correcting the density fluctuation of an image, the latent image characteristics of the surface of the image carrier are measured by measuring one or more densities of the latent image visible image (patch image) formed on the image carrier. There has been proposed density correction control for detecting development characteristics and adjusting a condition related to the characteristics to a target density value.

For example, Patent Document 1 and Patent Document 2 can be cited as conventional examples.
Japanese Patent Laid-Open No. 11-041459 JP 2000-010380 A

  However, the conventional density control only supports a specific printing mode (screen pattern), and it is necessary to perform density control for each printing mode in order to accurately control the density of all printing modes.

  Accordingly, an object of the present invention is to provide an image forming apparatus capable of performing density control for all print modes by one density control.

  In order to achieve the above object, the image density control of the present invention is an electrophotographic image forming apparatus in which a measuring means for measuring the density of an output image output based on reference input image data, and an output of the image forming apparatus. An image simulation means for predicting image density by changing simulation conditions, a density comparison means for comparing the density of the output image, and a density of the simulation image predicted by the image simulation means, and a density comparison means According to the result, it is composed of density correction control means for correcting the input image signal.

  In the above configuration, the measured value of the density of the visible image formed by the image forming apparatus is compared with the density value of the simulation image predicted by the image simulation unit, and the simulation conditions are changed so that the density values match, The engine state of the current image forming apparatus is predicted. Using the image simulation means from the predicted engine state of the image forming apparatus, the density of the image output in each gradation in all the printing modes is obtained, and the density of each gradation in all the obtained printing modes is targeted. Image density control is performed to stabilize the density of the output image by matching the density.

  As described above, according to the present invention, by adjusting the density of the image output from the image forming apparatus to the target density from the low density side to the high density side, the density change due to environmental fluctuations such as temperature and humidity. It is possible to adjust the density change due to deterioration of each part of the apparatus. Further, it is possible to correct all the printing modes by one density control, and it is possible to form an image having a good image quality in all the printing modes without performing the density control for each printing mode.

  Hereinafter, the present embodiment will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus according to the present embodiment. FIG. 1 also shows a photosensitive drum 1 on a drum which is a latent image carrier, a charging means 2 for forming an electrostatic latent image, an exposure means 3, and a developing means 4 for making the electrostatic latent image a visible image. The image forming apparatus includes a transfer unit 5 for transferring to a transfer material that is a recording medium, and a fixing unit 7 for fixing the transfer material after the transfer process by heating and pressing.

  The photosensitive drum 1 is composed of a photosensitive layer made of OPC (organic semiconductor) or the like on the outer peripheral surface of a metal drum base, and is rotated by driving means (not shown). Around the photosensitive drum 1, charging means 2, An exposure unit 3, a developing unit 4, a transfer unit 5, a cleaning unit 6 and the like are provided.

  The charging unit 2 includes a charging roller (not shown) disposed on the surface of the photosensitive drum 1 and a charging bias electric wire for applying a charging bias to the charging roller, and uniformly charges the surface of the photosensitive drum 1.

  The exposure unit 3 includes a laser oscillator 31, a polygon mirror 32, and the like, and irradiates the surface of the photosensitive drum 1 with light based on input image information to form an electrostatic latent image on the surface of the photosensitive drum 1.

  The developing unit 4 includes a developing unit that stores developers (toners) of four colors such as yellow (Y) 4Y, magenta (M) 4M, cyan (C) 4C, and black (K) 4K. Each toner is attached to the upper electrostatic latent image and developed as a toner image.

  The transfer unit 5 includes an intermediate transfer drum 51 that is an image carrier formed in a cylindrical shape, and primarily transfers the toner image on the photosensitive drum 1 onto the intermediate transfer drum 51.

  The cleaning unit 6 has a cleaning blade disposed in contact with the surface of the photosensitive drum 1, and removes the primary transfer residual toner remaining on the photosensitive drum 1 without being primarily transferred to the intermediate transfer drum.

  A secondary transfer belt 52 is provided below the intermediate transfer drum 51, and the four-color toner images primarily transferred onto the intermediate transfer drum 51 are secondarily transferred collectively onto a transfer material S such as paper. .

  The transfer material S after the secondary transfer of the toner image is heated and pressed by the fixing device 71 to fix the toner image on the transfer material S.

  A density sensor 81 is disposed on the intermediate transfer drum 51 so as to face the surface of the intermediate transfer drum 51, and a patch image formed on the intermediate transfer drum 51 when the image forming apparatus performs image density control. Concentration can be measured.

  FIG. 2 is an explanatory diagram of the density sensor 81. In the figure, a density sensor 81 has a light emitting part 82 and a light receiving part 83, irradiates light from the light emitting part 82 to the patch image T formed on the intermediate transfer drum 51, and receives reflected light as a light receiving part. The light is received at 83 and the density is measured. Image density control can be performed by feeding back the measurement result to the image processing unit and process forming unit of the image forming apparatus so as to match the reference density target value.

  FIG. 3 is a block diagram illustrating a processing procedure of image density control. Hereinafter, description will be given along the block diagram of FIG.

  First, in the image input unit 91, reference image data (patch image) is sent to the image forming apparatus, and the reference image data becomes an image (halftone image) binarized by the image processing unit 92 of the image forming apparatus. . The reference image data may be a solid image with a dot area ratio of 100% or a halftone image with a dot area ratio of 50%. Further, the image processing of the reference image data in the image processing unit 92 is performed in one printing mode from among a plurality of printing modes.

  Next, based on the input reference image data, the process forming unit 93 uniformly charges the photosensitive drum 1 by the charging unit 2, and an electrostatic latent image is formed on the photosensitive drum 1 by the exposure unit 3. The toner is attached to the electrostatic latent image formed on the photosensitive drum 1 by means 4 and developed as a toner image.

  Next, the toner image on the photosensitive drum 1 is primarily transferred to the intermediate transfer drum 51, and the patch image, which is the toner image that has been primarily transferred, is measured by the density sensor 81.

  Next, the image simulation unit 95 predicts the patch image formed on the intermediate transfer drum, and the density evaluation unit 97 predicts the patch image density value measured by the density sensor 81 and the image simulation unit 95. Compare the density values of the patch images.

  As a means for predicting a patch image formed on the intermediate transfer drum, in this embodiment, for example, an image simulation unit 95 that predicts an image formed by an electrophotographic method described in JP-A-11-41459 is used.

  Next, according to the comparison result of the density evaluation unit 97, the image simulation unit 95 changes the value of the developing bias so as to match the density value of the patch image measured by the density sensor 81, and the current image forming apparatus. Predict engine conditions. In the present embodiment, the development bias value is changed as a simulation condition. In addition, as a method for matching the density of the patch image measured by the density sensor 81 with the density of the patch image predicted by the image simulation unit 95, for example, a bisection method is used to obtain an optimal developing bias value.

  Next, the density of each gradation in all print modes is obtained from the predicted engine state of the image forming apparatus using the image simulation unit 95.

  Next, a γ correction table for correcting the density of each gradation in all print modes to a target density characteristic is obtained, and the γ correction table for obtaining the input image signal is applied and corrected.

  FIG. 4 is a diagram showing an example in which the input image signal is corrected to a target density characteristic in each gradation of a certain printing mode by image density control. The input image signal has 256 gradations, the density of each gradation indicating the target density characteristic is the wavy line L in the figure, and the image forming apparatus matches the result of measuring the patch image formed on the intermediate transfer drum. The solid line C in the figure shows the density of each gradation obtained by the image simulation unit 95 in the engine state.

  A method of correcting the density curve C of each gradation obtained by the image simulation unit 95 to the target density characteristic L is as follows. For example, in the value of the input image signal X, the output density on the target density characteristic L is the density value OD1. Further, in the density curve C of each gradation obtained by the image simulation unit 95, the input image signal that outputs the density value OD1 is X ′. Therefore, the input image signal X is replaced with the input image signal X ′, thereby correcting the input image signal X so that the target density value OD1 is output. By performing the same correction on all input image signals, the density curve C can be corrected to the target density characteristic L. In the example of FIG. 4, linear density characteristics are handled as the target density characteristics, but it goes without saying that the target density characteristics are not limited to linear.

  By performing the above operation for each color, it is possible to control the input image signal of all the colors and the output image density of all the printing modes to match the target density and to stabilize the image density.

1 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus according to an embodiment. FIG. 3 is a diagram illustrating details of a density sensor in the image forming apparatus according to the present embodiment. It is a block diagram which shows the process sequence of the image density control in this embodiment. It is a figure which shows an example of the image density control in this embodiment.

Claims (4)

  In an electrophotographic image forming apparatus, measurement means for measuring the density of an output image output based on reference input image data, and image simulation for predicting the density of the output image of the image forming apparatus by changing simulation conditions Means, density comparison means for comparing the density of the output image with the density of the simulation image predicted by the image simulation means, and density correction control means for correcting the input image signal according to the result of the density comparison means An image forming apparatus comprising:   2. The image forming apparatus according to claim 1, wherein the measuring unit measures the density of a visible image formed on the image carrier based on the reference input image data.   2. The image simulation device according to claim 1, wherein the image simulation means is an image simulation device that predicts a visible image formed on an image carrier, and various engine states of the image formation device are changed by changing simulation conditions related to image formation. An image forming apparatus capable of predicting an output image at the above.   2. The density correction control unit according to claim 1, wherein the density correction control unit converts and corrects the input image signal so that the density characteristic obtained by the image simulation unit matching the density of the output image matches a target density characteristic. An image forming apparatus.

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