JP2005202028A - Color image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To allow a color sensor of an image forming apparatus to automatically detect patches on a first and second sides of a recording medium by conducting one-time test printing. <P>SOLUTION: The color sensor S1 is disposed in a conveyance path that is shared between a both-sided conveyance path H and a paper ejection conveyance path 77. Accordingly, in the course of test printing for both-sided recording, the density or chromaticity of a toner image on the first side is detected by the color sensor S1 right after fixing on the first side of the recording medium, and the density or chromaticity of a toner image on the second side is detected by the color sensor S1 right after fixing on the second side of the recording medium inverted via the both-sided conveyance path H. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a color image forming apparatus such as a color printer and a color copying machine, and more particularly to improvement of image quality and color reproducibility in the color image forming apparatus.

  A plurality of electrophotographic process units having a charging device and a developing device arranged around the photosensitive member are juxtaposed in the device, and an optical image is formed on the surface of the photosensitive member in each process unit by an exposure device using laser, LED light, or the like. A latent image is formed on the surface of the photosensitive member by image formation, and the latent image is visualized using toner by a developing device, and then sequentially transferred to the intermediate transfer belt, and then collectively onto a recording medium (also referred to as a transfer material). In recent years, an image forming apparatus for fixing and forming a color image has been put to practical use.

  In addition, color image forming apparatuses employing an electrophotographic system such as a color printer and a color copying machine are required to have higher output image quality.

  However, in the color image forming apparatus, when there is a change in each part of the apparatus due to a change in environment or long-term use, the color of the obtained image changes. In particular, in the case of an electrophotographic color image forming apparatus, even slight environmental fluctuations may cause color fluctuations, which may cause the color balance to be lost. Therefore, there is a means for stably reproducing colors and color gradations. doing.

  For example, for each color toner, the absolute humidity measured by the temperature / humidity sensor has gradation correction means such as several kinds of exposure amount and development bias according to the absolute humidity, process conditions such as a developing bias, and a lookup table (LUT). Based on the above, the process condition at that time and the optimum value for gradation correction are selected. In addition, a density detection toner patch is formed on the intermediate transfer member, the photosensitive member, etc. with a single color toner so that a constant color and gradation of the color can be obtained even if variations in each part of the apparatus occur. The density of an unfixed single color toner patch is detected by a density detection sensor for unfixed toner (hereinafter referred to as a density sensor), and feedback is provided to process conditions such as exposure amount and development bias and tone correction means such as LUT based on the detection result By performing the density control over time, a stable color and color gradation are obtained.

  However, density control using the density sensor detects patches by forming patches on an intermediate transfer member or drum, and controls the change in image color balance due to subsequent transfer and fixing to a recording medium. Not done. The color balance also changes depending on the transfer efficiency in transferring the toner image to the recording medium, and heating and pressurization by fixing. This change cannot be dealt with by density control using the density sensor.

  Therefore, cyan (C), magenta (M), yellow (Y), and black (K) single-color gradation patches or C, M, and Y mixed-color patches are formed on the recording medium, and after fixing, on the recording medium. There is also a color image forming apparatus provided with a sensor (hereinafter referred to as a color sensor) that detects the density or chromaticity of a patch (see, for example, Patent Document 1 below).

  In this color image forming apparatus, the final output image formed on the recording medium is fed back to the calibration table for correcting the exposure amount of the image forming unit, the process conditions, and the density-gradation characteristics. Density or chromaticity can be controlled. Although it is possible to detect the output image of the color image forming apparatus with an external image reading device or a densitometer / chromaticity meter and perform the same control, this method completes the control within the color image forming apparatus. Is excellent. This color sensor uses, for example, three or more light sources having different emission spectra such as red (R), green (G), and blue (B) as light emitting elements, or the light emitting elements emit light of white (W). Are used, and three or more types of filters having different spectral transmittances such as red (R), green (G), and blue (B) are formed on the light receiving element. As a result, three or more different outputs such as RGB output can be obtained.

  Here, FIG. 2 is a cross-sectional view showing a configuration of a conventional color LBP, and a specific operation function will be described using the same.

These printers have a normal print mode and a test mode.
First, the operation in the normal print mode will be described.

  The illustrated LBP is a four-drum full-color LBP, and 50Y, 50M, 50C, and 50K are photosensitive drums, which are provided in each image forming station equipped with developing materials (toners) of yellow, magenta, cyan, and black, respectively. It has been.

  On the surface of each photosensitive drum 50Y, 50M, 50C, 50K, laser beams emitted from the corresponding laser scanner devices 51Y, 51M, 51C, 51K based on image data from an image data input unit (not shown) are used. A latent image is formed by exposure, and a toner image is formed by developing with each developer of yellow, magenta, cyan, and black. An intermediate transfer belt 52 primarily transfers the toner images of the respective colors formed by the photosensitive drums 50Y, 50M, 50C, and 50K. A sheet P as a recording medium is stacked on the paper feed cassette 53, fed by a paper feed roller 54, transported by a feed / retard roller pair 55, and transport roller pairs 56, 57, and stopped driving. It is conveyed to the roller pair 59.

  When feeding from a multi-feed unit (not shown) is designated, sheets P as recording media are stacked on the multi-feed tray, fed by a multi-feed roller, and fed by a transport roller pair 57. It is conveyed to the registration roller pair 59 that has been conveyed and stopped.

  After the skew is corrected by the registration roller pair 59, the sheet P is conveyed to the secondary transfer unit 60 at a predetermined timing, and the toner image on the intermediate transfer belt 52 is transferred. The toner image is fixed by being conveyed to the fixing device 61 by the secondary transfer roller 60a and the intermediate transfer belt 52.

  When FD paper discharge with the image forming surface down is designated, the sheet P that has passed through the fixing device 61 is moved by moving the flapper 67 to a position indicated by a solid line by a control means and a drive means (not shown). The paper passes through the upper side of the flapper 67, is transported to the paper discharge roller pair 62, and is transported to the transport path 77. The sheet P conveyed to the conveyance path 77 is conveyed by a pair of paper discharge rollers 68 and 63 and discharged and stacked on a paper discharge port (also referred to as a paper discharge tray) 64 with the image forming surface facing down.

  Further, when FU paper discharge is specified with the image forming surface facing upward, the sheet P that has passed through the fixing device 61 is moved by moving the flapper 67 to a position indicated by a broken line by a control means and a drive means (not shown). Passes through the lower side of the flapper 67, is conveyed by the pair of paper discharge rollers 65, and is discharged and stacked on the paper discharge port 66 with the image forming surface facing up.

  Further, when an image is subsequently formed on the back surface of the sheet P, the flapper 69 is operated by a control unit and a driving unit (not shown), and the conveyance direction of the sheet material P is changed using the reverse roller pair 71 via the conveyance roller pair 70. The front and rear are reversed, and the flapper 72 is operated to be guided to the duplex conveyance path 73. The sheet material P is conveyed again to the registration roller pair 59 via the conveyance roller pair 57 using the double-sided conveyance roller pairs 74, 75, and 76, and after the skew feeding is corrected, the secondary transfer unit at a predetermined timing. The toner image on the intermediate transfer belt 52 is transferred to the back surface of the sheet P. Next, the toner image is fixed to the back surface of the sheet P by the secondary transfer roller 60a and the intermediate transfer belt 52 of the secondary transfer device 60, and is transported to the paper discharge port 64 or 66. Paper.

  Next, the operation in the test mode will be described.

  When the test mode is specified on the operation panel (not shown) on the printer or a personal computer connected to the printer, or when the control unit (not shown) automatically detects the change in the environment, the changes in each part of the device, etc. , A test pattern (patch) signal is generated from a signal generation circuit (not shown), and the surfaces of the photosensitive drums 50Y, 50M, 50C, and 50K are exposed by laser light emitted based on the test pattern (patch) signal data. A latent image is formed. Thereafter, a test pattern toner image is formed on the sheet P by the same process as the operation in the normal print mode, and is transported to the fixing device 61 to fix the toner image.

  An example of the patch pattern formed on the sheet P is shown in FIG. The density or chromaticity control patch pattern is the center of the color gamut and is a gray tone patch pattern that is a very important color for achieving color balance. 80 and a process gray gradation patch 81 in which yellow (Y), magenta (M), and cyan (C) are mixed, and standard images such as 80a and 81a, 80b and 81b, and 80c and 81c. In the forming apparatus, a gray gradation patch 80 of only black (K) having the same or the closest chromaticity and a process gray gradation patch 81 are arranged in a pair.

  The sheet P that has passed through the fixing device 61 and has a patch pattern formed on the surface P1 passes through the upper side of the flapper 67 by moving the flapper 67 to a position 67b indicated by a solid line by a control means and a driving means (not shown). A pair of paper rollers 62 is conveyed to a conveyance path 77.

At that time, the color sensor S1 is disposed in the conveyance path 77, and the color sensor S1 emits light from the light emitting portion SH made of a light emitting element and is formed on the P1 side which is the surface on the sheet P shown in FIG. Are sequentially detected by the light receiving unit SJ from the patch 80a, and the detected result is fed back to an image forming unit (not shown) to control the density or chromaticity of the toner image formed on the recording medium. The sheet P transported by the paper discharge roller pair 68 is transported by the paper discharge roller pair 63 and discharged and stacked on the paper discharge port 64 with the patch forming surface down.
Japanese Patent Laid-Open No. 2003-98771

  However, the conventional example described above has the following problems.

  When forming color images on both sides of the recording medium, after forming an image on the recording medium 1 (surface) through a so-called electrophotographic image forming process, heat and pressure are applied to the toner image by a fixing device, After fixing the toner image on the surface of the recording medium 1, the desired color image is fixed on the second surface of the recording medium through the same image forming process on the second surface (back surface) of the recording medium. As a result, color images are formed on both sides of the recording medium.

  However, when the image on the second side is formed on the recording medium, the moisture content of the recording medium once passed through the fixing device is different from that on the first side, and as a result, the process conditions of the recording medium at the time of forming the first side image In particular, since the volume resistance changes, it is necessary to change the voltage applied to the recording medium.

  Here, in consideration of surrounding environmental fluctuations and the like, the image forming process conditions for the second side are matched as much as possible to the first side, but as a result, the toner images on the recording medium are the first and second side. It is known that the transfer state (eg, roughness) differs depending on the surface. Therefore, even if toner images with the same data are formed on the front and back sides of the recording medium, the toner images visually recognized on the first side and the second side are different.

  At this time, when the color sensor is arranged at the position as in the conventional example, when acquiring the patch data on the second surface, the recording medium once passed through the fixing device is manually fed or a special paper path is provided again. It was necessary to make it happen.

  In the case of a double-sided original formed on both sides of the recording medium, the image on the second side passes through the fixing once and is calibrated with the same toner image as that on the first side even though the transfer process conditions are changed. If the color correction is performed based on the color calibration value, a deviation from the original appropriate color balance value occurs.

  In other words, when color correction is applied to a double-sided toner image with the same configuration as the color correction effective for a single-sided toner image, the color correction value on each side may not be appropriate, and at the same time, color correction is performed. There is a problem that the color balance is different between the first and second images. In the conventional image forming apparatus, when a patch is formed on both sides of a recording medium and the second patch is detected by a color sensor, a test print is manually performed a plurality of times or a special paper pass mode is not provided. There was a need to not.

  The present invention has been made under such circumstances, and in a color image forming apparatus equipped with a color sensor, when a patch on a recording medium is detected by the color sensor of the image forming apparatus, the first side and the second side are provided. It is an object of the present invention to provide a color image forming apparatus that can automatically detect the image with a single test print, increase the accuracy, and obtain a high-quality output image with good color reproducibility. It is.

  In order to solve the above problems, in the present invention, a color image forming apparatus is configured as described in the following (1) to (5).

(1) A fixing device that fixes a toner image on a recording medium, a paper discharge port that discharges the recording medium fixed by the fixing device, and a paper that does not discharge the fixed recording medium from the paper discharge port. In a color image forming apparatus comprising a double-sided conveyance path for conveying to enable printing on two sides of the recording medium, and a color sensor,
A color image forming apparatus, wherein the color sensor is disposed on a common conveyance path of the duplex conveyance path and the discharge conveyance path.

(2) In the color image forming apparatus according to (1),
A color image forming apparatus using an intermediate transfer belt.

(3) In the color image forming apparatus according to (1),
A color image forming apparatus using a transfer conveyance belt.

(4) In the color image forming apparatus according to (1),
A color image forming apparatus using a photoreceptor belt.

(5) In the color image forming apparatus according to any one of (1) to (4),
A color image forming apparatus using the color sensor also as a jam detecting means.

  In the present invention, color patches provided on both sides of the recording medium are detected by a single color sensor sequentially at the time of test printing without providing a special paper path, and color balance correction data corresponding to the fixing history of the recording medium is obtained. By generating the toner image, the color balance of the toner images formed on both sides of the recording medium can be optimized. Since it is possible to give an optimum color balance to each of the images formed on both sides of the recording medium, it is possible to form a high-quality image on both sides of the recording medium.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to examples.

  FIG. 1 is a cross-sectional view illustrating a configuration of a “color image forming apparatus (color LBP)” according to a first embodiment.

  Since the apparatus configuration of the present embodiment is substantially the same as that of the conventional example, the description of the conventional example is cited and detailed description thereof is omitted here. The difference from the conventional example is that the color sensor S1 provided in the conveyance path 77 after fixing is provided on a common conveyance path H upstream of the paper discharge port and the double-side conveyance path.

  Here, a paper conveyance path for double-sided printing in the image forming apparatus in which the conveyance path for performing double-sided printing is partially different from the conventional example and the color sensor S1 is arranged in the conveyance path common to the double-sided conveyance path and the paper discharge conveyance path will be described. To do.

  After forming the image on the front surface using the same image formation path as in the conventional example, first, the recording medium provided with the color patch on the surface is rotated to the position 67b by the flapper 67 by the control means and drive means (not shown). The paper is transported to the paper transport path H. At this time, the color patch provided on the surface side P1 of the recording medium is detected by using the color sensor S1. Subsequently, the recording medium is stopped in a state of being nipped with the conveyance roller 62, and the conveyance roller 62 starts to rotate reversely to the conveyance toward the paper discharge side, and at the same time, the double-side conveyance path is switched by a control unit and a driving unit (not shown). The flapper 67 to be rotated is rotated to the position 67c, and the recording medium is guided to the double-sided conveyance path, and again conveyed to the registration roller pair 59 via the conveyance roller pair 57 using the double-sided conveyance roller pair 74, 75, 76. After the skew is corrected, the toner image on the intermediate transfer belt 52 is transferred to the back surface of the sheet P by being conveyed to the secondary transfer unit 60 at a predetermined timing. Next, the secondary transfer roller 60 a of the secondary transfer device 60 and the intermediate transfer belt 52 are conveyed to the fixing device 61 to fix the toner image on the back surface of the sheet P, pass through the fixing device 61, and pass through the patch pattern 82. The sheet P formed on the back surface P2 passes through the upper side of the flapper 67 by moving the flapper 67 to a position 67b by a control means and a driving means (not shown), and is conveyed to the common conveyance path H, to the P2 side. The formed color patch is detected by the color sensor S1.

  Through the paper path, the color sensor S1 sequentially detects the patches 82 formed on the P1 side and the P2 side on the sheet P from the patch 80a, and the detection result of each of the first side and the second side is sent to an image forming unit (not shown). Feedback is performed to control the density or chromaticity of the toner image formed on the recording medium. The color patches provided on the respective surfaces P1 and P2 are detected with different fixing histories. That is, the P1 side is detected in a state where a color patch is formed and fixed on the surface of the virgin recording medium, and the P2 side is detected in a state where the color patch is formed on the surface of the recording medium once passed through the fixing device and fixed again. Is done. These color patches provided on the P1 and P2 sides of the recording medium are sequentially detected without providing a special paper path, and color balance correction data corresponding to the fixing history of the recording medium is generated, whereby both sides of the recording medium are generated. It is possible to optimize the color balance of the toner image formed on the side, and a color original having a high-quality double-sided image can be created.

  When performing normal printing, when the user sets the paper discharge port to 64 and performs double-sided printing, the flapper 67 controls the recording medium P that is first fed, transferred, and fixed on the P1 side, not shown. First, it is rotated to the position 67b by the means and the driving means and passes through the double-sided conveyance path 73. After being transferred and fixed to the P2 side by the above-described process, the flapper 67 rotates to the position 67b, passes through the paper discharge conveyance path 77, and is discharged to the paper discharge port 64. Similarly, when the paper discharge port 66 is set, the path to double-sided printing is the same as described above, and after the transfer and fixing to the P2 side of the recording medium P, the flapper 67 is controlled by a control means and a drive means (not shown). It rotates to the position 67a and is discharged to the discharge port 64 by the discharge roller pair 65.

  As described above, according to the present embodiment, the color patches provided on both sides of the recording medium are sequentially detected by a single color sensor at the time of test printing without providing a special paper path, and the recording medium is fixed. By generating color balance correction data corresponding to the history, the color balance of the toner images formed on both sides of the recording medium can be optimized.

  The image recording apparatus according to the first exemplary embodiment is a color image forming apparatus using a so-called intermediate transfer belt. However, in the color image forming apparatus using a so-called transfer conveying belt that performs direct transfer onto a recording medium while conveying the recording medium. Can be similarly implemented.

  The image recording apparatus of Example 1 is a color image forming apparatus using a so-called intermediate transfer belt, but the same applies to a color image forming apparatus using a so-called photosensitive belt that directly forms an image on an image carrier on the belt. Can be implemented.

  In the first to third embodiments, the color sensor S1 can detect the timing at which the recording medium is guided to the conveyance path H except during the test printing, and at the same time, can detect whether the recording medium remains or remains. It can also be implemented in the form used as a jam (JAM) detection means.

  Each embodiment is an example using a color LBP as a color image forming apparatus, but is not limited to this, and can be applied to other apparatuses such as a copying machine and a facsimile apparatus.

Sectional drawing which shows the structure of Example 1 Sectional drawing which shows the structure of a prior art example Diagram showing the configuration of the color patch Sectional drawing which shows schematic structure of color sensor

Explanation of symbols

P Recording media 50Y, 50M, 50C, 50K Photosensitive drum 52 Intermediate transfer belt 61 Fixing device 73 Double-sided conveyance path H Common conveyance path upstream of the paper discharge port and the double-sided conveyance path

Claims (5)

A fixing device for fixing a toner image on a recording medium, a paper discharge port for discharging the recording medium fixed by the fixing device, and the recording medium without discharging the fixed recording medium from the paper discharge port In a color image forming apparatus provided with a double-sided conveyance path that conveys in order to enable printing on the two sides, and a color sensor,
A color image forming apparatus, wherein the color sensor is disposed on a common conveyance path of the duplex conveyance path and the discharge conveyance path. The color image forming apparatus according to claim 1.
A color image forming apparatus using an intermediate transfer belt. The color image forming apparatus according to claim 1.
A color image forming apparatus using a transfer conveyance belt. The color image forming apparatus according to claim 1.
A color image forming apparatus using a photosensitive belt. The color image forming apparatus according to any one of claims 1 to 4,
A color image forming apparatus, wherein the color sensor is also used as a jam detecting means.

Images