JP4447975B2 - Color image forming apparatus - Google Patents

Description

  The present invention relates to a configuration of an electrophotographic image forming apparatus that develops a latent image formed on a photoreceptor with a developer, transfers the image to a recording medium, fixes the image, and performs recording. In particular, it is used in an image recording apparatus having functions such as a copying machine and a printer, a color image forming apparatus used as an output device such as a multifunction machine having such functions and a workstation.

  An image that forms a color image by sequentially transferring a developer image formed by a plurality of electrophotographic process units in which a charging device and a developing device are arranged around the photosensitive member to an intermediate transfer belt and then fixing the image to a recording medium in a lump. The forming apparatus has been put into practical use in recent years. 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, the color of the obtained image may fluctuate if there are fluctuations in each part of the apparatus due to environmental changes or long-term use. In particular, in the case of an electrophotographic color image forming apparatus, even a slight environmental change may cause a color change, which may cause a loss of color balance.

  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. A color image forming apparatus configured to detect the density or chromaticity of a patch with a color sensor has been devised.

  In these color image forming apparatuses, the final output formed on the recording medium is fed back to the calibration result for correcting the exposure amount of the image forming unit, the process conditions, and the density-gradation characteristics. Image 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.

  Further, as these color image forming apparatuses, there have been proposed apparatuses in which suppression means for suppressing fluttering based on the conveyance of the recording medium on which the calibration image is formed is provided so as to stably convey the recording medium. The suppression means is provided with a transport roller before and after the position where the density of the calibration image on the transport path is detected (see Patent Document 1).

JP-A-11-316476

  However, in the above-described conventional color image forming apparatus, the recording paper surface at the measurement position may flutter or bend at the measurement position due to the influence of the eccentricity of the conveyance roller and the behavior may become unstable. There is a concern that the accuracy of chromaticity measurement will deteriorate. If the chromaticity is not correctly measured, there may be a case where the color correction is not correctly performed.

  SUMMARY An advantage of some aspects of the invention is that it provides a color image forming apparatus that can perform stable chromaticity detection and measurement, and that can correctly perform color correction.

In order to solve the above problems, a typical configuration of a color image forming apparatus according to the present invention includes an image forming unit that forms developer images of a plurality of colors on a recording medium, and a developer that is heated and pressurized to the recording medium. A color image forming apparatus comprising: a fixing unit that fixes an image; and a detecting unit that detects density or chromaticity of a test pattern developer image formed on a recording medium by the image forming unit and fixed by the fixing unit . A biasing plate that is provided opposite to the detection unit , biases the recording medium toward the detection unit at a detection position by the detection unit, and sandwiches the recording medium with the detection unit; It said two sensing means side rollers provided on both sides of the sensing means in a direction orthogonal to a roller which is opposed to the detection means side roller, the recording medium is urged by the urging plate It has a counter roller which conveys the known means side rollers and clamping, and upon detection of the recording medium by the detecting means, in the recording medium conveyance direction, a region sandwiched the urging plate and the detection means of the recording medium An imaginary line segment connecting the detection means side roller and the axial center of the counter roller is located between the front end and the rear end of the roller .

  As described above, according to the present invention, it is possible to stably and accurately detect and measure a test pattern developer image formed on a recording medium after fixing, and to correct color correction correctly. Can do.

  An embodiment of a color image forming apparatus according to the present invention will be described with reference to the drawings. FIG. 7 is a cross-sectional view showing the configuration of the color image forming apparatus. The color image forming apparatus shown in FIG. 7 has two modes, a normal print mode and a test mode, as printer operations.

(Normal print mode operation)
First, the operation in the normal print mode will be described. The color image forming apparatus employs a four-drum full-color system having photosensitive drums 50Y, 50M, 50C, and 50K. The photosensitive drums 50Y, 50M, 50C, and 50K are provided in each image forming station that is an image forming unit provided with developers (toners) of colors of yellow, magenta, cyan, and black, respectively.

  The surface of each of the photosensitive drums 50Y, 50M, 50C, and 50K is exposed by laser light emitted from the corresponding laser scanner device 51Y, 51M, 51C, and 51K, and a latent image is formed on the surface. The laser beam is emitted based on image data from an image data input unit (not shown). Each latent image is developed with yellow, magenta, cyan, and black developers to form a developer image (toner image). The developer image for each color is primarily transferred to the intermediate transfer belt 52.

  On the other hand, a recording sheet P as a recording medium is stacked on the feeding cassette 53 and is fed by a feeding roller 54. Then, it is transported by the feed / retard roller pair 55 and the transport roller pairs 56 and 57 and transported to the resist roller pair 59 that has stopped driving.

  When feeding from the multi-feed unit 40 is designated, the recording sheets P stacked on the multi-feed tray 41 are fed by the multi-feed roller 42. Then, it is transported by the transport roller pair 57 and transported to the resist roller pair 59 that has stopped driving.

  After the skew is corrected by the registration roller pair 59, the recording sheet P is conveyed to the secondary transfer unit 60 at a predetermined timing, and the developer image on the intermediate transfer belt 52 is transferred. Next, the toner is conveyed to a fixing device 61 which is a fixing unit by a secondary transfer roller 60 a of the secondary transfer unit 60 and an intermediate transfer belt 52. The recording sheet P conveyed to the fixing device 61 is heated and pressed to fix the developer image.

  When FD discharge for discharging with the image forming surface down is designated, the flapper 67 is moved by the control means and the drive means (not shown). As a result, the recording sheet P that has passed through the fixing device 61 passes above the flapper 67 and is transported to the transport path 69 by the discharge roller pair 62. The recording sheet P conveyed to the conveyance path 69 is conveyed by the discharge roller pairs 68 and 63 and discharged and stacked on the discharge tray 64 with the image forming surface facing down.

  In addition, when the FU discharge for discharging with the image forming surface facing upward is designated, the flapper 67 is moved by the control means and the drive means (not shown). As a result, the recording sheet P that has passed through the fixing device 61 passes under the flapper 67, is conveyed by the discharge roller pair 65, and is discharged and stacked on the discharge tray 66 with the image forming surface facing up.

(Test mode operation)
Next, the operation in the test mode will be described. The test mode is performed when designated by an operation panel (not shown) on the color image forming apparatus or a personal computer connected to the color image forming apparatus. In addition, the test mode can be automatically performed by a control unit (not shown) based on a detection result such as a change in environment and a change in each part of the apparatus.

  When the test mode is performed, a test pattern (patch) signal is generated from a signal generation circuit (not shown). Then, a laser beam is emitted based on the test pattern (patch) signal data to expose the surfaces of the photosensitive drums 50Y, 50M, 50C, and 50K to form latent images.

  Thereafter, a test pattern developer image (patch) is formed on the intermediate transfer belt 52 by the same process as the operation in the normal print mode, and the test pattern developer image is transferred onto the recording sheet P separately conveyed. Further, the recording sheet P is conveyed to the fixing device 61 to fix the test pattern developer image.

  FIG. 8 is a diagram showing an installation state of test pattern developer images (patches) 81a, 81b, 81c... Formed on the recording sheet P and a color sensor. The color sensor S1, which is a detecting means, sequentially detects the test pattern developer image (patch 81) formed on the front surface side of the recording sheet P from the patch 81a. The detected result is fed back to an image forming unit (not shown), and chromaticity control of the toner image formed on the recording sheet P is performed.

(Recording sheet transport unit)
FIG. 1 is a configuration diagram of a recording sheet conveying unit 100 including a color sensor S1. In FIG. 1, a recording sheet conveyance unit 100 which is a recording sheet conveyance unit is provided in the recording sheet conveyance path 69 after fixing in FIG. In the recording sheet conveying unit 100, a space is formed in the arrow direction in FIG. 1 by a plurality of guide ribs and a plurality of opposing guide ribs (not shown). In the space, the recording sheet P is nipped and conveyed by the discharge roller pairs 62 and 68.

  FIG. 2 is a perspective view around the color sensor S1. In FIG. 2, the folder 101 supports the color sensor S <b> 1 and swings and swings on a part of the recording sheet conveyance unit 100. A counter roller 102 as a conveying unit is provided to face the color sensor S1. The cam shaft 104 operates the color sensor S1 together with the folder 101. The urging plate 103 as urging means is provided to face the color sensor S1, and urges the recording sheet P toward the color sensor S1. The swing shaft 106 swings the urging plate 103.

  FIG. 3 is a side view of the periphery of the color sensor S1. As shown in FIG. 3, a cam 107 is attached to the cam shaft 104. These are two rotating bodies that are disposed substantially symmetrically with respect to the optical measurement center line Y (see FIG. 4) next to the folder 101 including the color sensor S1 and the color sensor S1 (on both sides in the sheet width direction). The rollers 110 (110R, 110L, see FIG. 4) are pushed out to the recording material conveyance path, and the patch rows 81a, 81b,.

  Here, the roller 110 is provided on a member on which the color sensor S1 is installed. Further, the optical measurement center line Y refers to a center line in the sheet width direction of the range Ld (see FIG. 5) detected by the color sensor S1.

  The roller 110 is driven and rotated by a counter roller 102 which is given a rotational driving force from a driving train of the color image forming apparatus main body and is always driven and rotated during image formation. The opposing roller 102 is a rotating member in which a shaft member 102a is covered with a viscoelastic member except for an end portion and a central portion facing the color sensor S1 (see FIG. 2). As the rotating member covered with the viscoelastic member, in addition to the urethane roller, a known material used as a rubber roller or other conveying member can be used. The state where the end portion is not covered with rubber is a state where the end portion is not covered with rubber in a normal range in order to support the opposed roller 102. The state in which the rubber coating is not provided in the central portion is a state in which the rubber coating is not applied to the corresponding portion as the urging plate 103 is installed.

  Further, the swing shaft 106 provided with the biasing plate 103 swings, and the biasing plate 103 swings around the central urethane uncovered portion of the opposing roller 102. As a result, the urging plate 103 contacts and separates from the surface of the color sensor S1. Then, the recording sheet P is conveyed between the surface of the color sensor S1 and the urging plate 103 in the direction of the arrow (from the bottom to the top in FIG. 3).

  FIG. 4 is a front view of the periphery of the color sensor S1. FIG. 4 shows the state where the opposing roller 102 is removed. Rollers 110R and 110L are installed at positions Ly apart from the optical measurement center line Y of the color sensor S1 parallel to the sheet conveyance direction (recording medium conveyance direction). Each of the rollers 110R and 110L has a two-wheel configuration, has a so-called dumbbell shape, and a distance from the center of the two wheels is Ly.

  FIG. 5 shows the positional relationship between the color sensor S1 and the urging plate 103. As shown in FIG. As in FIG. 4, the lengths from the optical measurement center line Y parallel to the sheet conveyance direction of the color sensor S <b> 1 to both ends in the width direction of the urging plate 103 are L, respectively.

  As shown in FIGS. 4 and 5, the shape of the urging plate 103 is made substantially line symmetrical with respect to the optical measurement center line Y of the color sensor S1. Further, rollers 110R and 110L, which are auxiliary means for conveying the recording sheet P, are arranged substantially symmetrical with respect to the measurement center line Y on both sides of the color sensor S1. Thereby, flapping of the recording sheet P and conveyance of the recording sheet P obliquely can be suppressed. Therefore, highly accurate detection and measurement of the color patch 81 formed on the recording sheet P after fixing can be performed.

  When the shape of the biasing plate 103 is asymmetric with respect to the measurement center line Y of the color sensor S1, it is confirmed that the measurement stability of the color patch 81 formed on the recording sheet P after fixing is low. Has been. Further, even when the rollers 110R and 110L serving as auxiliary means during conveyance of the recording sheet P are arranged asymmetrically with respect to the measurement center line Y of the color sensor S1, they are formed on the recording sheet P after fixing. It has been confirmed that the measurement stability of the color patch 81 is low.

  FIG. 6 is a diagram showing an optical arrangement relationship of the color sensor S1. FIG. 6 shows a part of the optical device installed in the color sensor S1 in addition to FIG. 3, and an LED 108 which is an optical detection means is added. An optical path emitted from the LED 108 is indicated by a one-dot chain line. As indicated by the one-dot chain line, the light from the LED 108 is projected to the optical detection position Lp on the recording sheet P being conveyed. Further, a contact state between the roller 110 installed on the folder 101 holding the color sensor S1 and the opposing roller 102 is shown, and an axis center line Lc connecting the axis centers of the two is shown by a one-dot chain line.

  As shown in FIG. 6, when the recording sheet P is conveyed by the opposing roller 102 and the roller 110 while being sandwiched between the urging plate 103 and the surface of the color sensor S1, the optical detection position Lp is set to the axis center line Lc. Rather than the downstream side in the sheet conveying direction. The reason why the optical detection position Lp is offset from the axial center line Lc on the downstream side in the sheet conveying direction will be described below.

  The optical detection position Lp was offset by 0, 1, 2, 3 mm downstream of the axial center line Lc in the sheet conveying direction, and the stability of the color patch measurement accuracy against the eccentricity of the roller 110 was measured. As a result, when the measurement point (optical detection position Lp) of the color sensor S1 is close to (= 0) on the center line (axis center line Lc) of the opposing roller 102, the color patch measurement accuracy due to the eccentricity of the roller 110 is reduced. Deterioration was observed.

  Then, the optical detection position Lp of the color sensor S1 was moved from the center line (axis center line Lc) of the opposing roller 102 to the downstream side in the sheet conveying direction until it was offset by 2 mm and measured. As a result, it was confirmed that the stability of the color patch measurement accuracy by the color sensor S1 is improved as it moves. Further, it has been confirmed that no further improvement in measurement accuracy stability was observed even when the optical detection position was offset by 2 mm or more.

  Therefore, as shown in FIG. 6, the color patch measurement is performed in the most stable state with respect to the eccentricity of the roller 110 by offsetting the optical detection position Lp by 2 mm downstream of the axial center line Lc in the sheet conveyance direction. It is possible to implement highly accurate color patch measurement and to perform highly accurate color control.

  In the present embodiment, the intermediate transfer belt is used. However, a system using a so-called transfer conveyance belt may be used. In the present embodiment, the intermediate transfer belt is used. However, this may be a system using a so-called photosensitive belt. In the present embodiment, the transport path after fixing is described as a vertical path that is parallel to the so-called gravity direction. However, if it is within the paper transport path after fixing, the transport path is perpendicular or oblique to the gravity direction. There may be.

  As described above, the patch 81 formed by each image forming station is provided to face the color sensor S1 that detects the density or chromaticity of the patch 81 and the color sensor S1, and the recording sheet P is disposed on the color sensor S1 side. An urging plate 103 for urging and an opposing roller 102 for nipping and conveying the recording sheet P urged by the urging plate 103 are provided.

  Thereby, flapping and bending of the surface of the recording sheet P at the measurement position (the optical detection position Lp of the color sensor S1) can be suppressed. For this reason, the stable and highly accurate measurement of the patch 81 formed on the recording sheet P after fixing can be performed, and the color correction can be correctly performed.

  Further, a fixing device 61 is provided, and the color sensor S1 detects the density or chromaticity of the patch 81 after fixing the patch 81 formed by each image forming station by the fixing device 61, and changes the shape of the urging plate 103. The shape of the color sensor S1 is substantially line symmetric with respect to the optical measurement center line Y. As a result, flapping and bending of the recording sheet P can be suppressed evenly, and stable optical detection of the patch 81 is possible.

  Also, two rollers 110R and 110L are provided at positions that are substantially line symmetric with respect to the optical measurement center line Y of the color sensor S1, and the rollers 110R and 110L can be rotated together with the opposing roller 102 when detected by the color sensor S1. It was. Thereby, it can suppress that the recording sheet P is conveyed diagonally. Further, the frictional force between the opposing roller 102 and the recording sheet P can be suppressed, and the deterioration of the conveying ability of the opposing roller 102 can be suppressed. Therefore, the patch 81 can be detected stably with high accuracy for a long period of time.

  Further, the opposing roller 102 is provided to face the color sensor S1, and its end portion and the central portion opposite to the color sensor S1 are covered with a viscoelastic member. In the case of a conveyance roller consisting of a pair of rubber rollers, which are usually used frequently, image defects are likely to occur due to temperature unevenness, so that the entire shaft is covered as uniformly as possible. It is desirable to use a straight rubber roller. By the way, in the present embodiment, the center portion is cut away in accordance with the provision of the urging plate 103 for the straight rubber-coated one. Here, the influence of the temperature gradient increases toward the end of the roller, and the influence of the temperature gradient is not so large in the central portion. Therefore, the influence on the image defect due to notching the central roller is small. For this reason, in the configuration adopted in this embodiment, image defects due to temperature unevenness are not confirmed, deterioration of the conveyance capability of the opposed roller 102 is suppressed with a simple configuration, and the patch 81 is stably detected with high accuracy over a long period of time. It became possible.

  At the time of detection by the color sensor S1, the optical detection position Lp of the color sensor S1 is set on the downstream side in the sheet conveying direction from the axial center line Lc between the rollers 110R and 110L and the color sensor S1. Thereby, fluttering of the recording sheet P can be suppressed before detection by the color sensor S1, and stable conveyance can be performed, and the patch 81 can be detected stably with high accuracy.

FIG. 3 is a configuration diagram of a recording sheet conveyance unit according to the present embodiment. It is a perspective view around a color sensor. It is a side view around a color sensor. It is a front view of a color sensor periphery. It is a figure which shows the positional relationship of a color sensor and an urging | biasing board. It is a figure which shows the optical arrangement | positioning relationship of a color sensor. 1 is a configuration diagram of a color image forming apparatus. It is a figure which shows the installation state of the test pattern developer image, color sensor, etc. which were formed on the recording sheet.

Explanation of symbols

Lc ... Axis center line, Ld ... Range, Lp ... Position, Ly ... Distance, P ... Recording sheet, S1 ... Color sensor, Y ... Measurement center line, 40 ... Multi feed section, 41 ... Multi feed tray, 42 ... Multi feed roller, 50 ... photosensitive drum, 51 ... laser scanner device, 52 ... intermediate transfer belt, 53 ... feed cassette, 54 ... feed roller, 55 ... feed / retard roller pair, 56, 57 ... conveying roller pair, 59 ... Registration roller pair, 60 ... Secondary transfer portion, 60a ... Secondary transfer roller, 61 ... Fixer, 62, 63 ... Discharge roller pair, 64 ... Discharge tray, 65 ... Discharge roller pair, 67 ... Flapper, 68 ... Discharge roller pair, 69 ... conveying path, 81 ... patch pattern, 100 ... recording sheet conveying unit, 101 ... folder, 102 ... opposite roller, 103 ... biasing plate, 104 ... cam shaft, 106 ... oscillating shaft, 107 ... cam 108 ... LED, 110L, 110R ... roller

Claims (7)

Image forming means for forming a developer image of a plurality of colors on a recording medium;
Fixing means for fixing the developer image to the recording medium by heating and pressing;
A color image forming apparatus comprising: a detecting unit configured to detect a density or chromaticity of a test pattern developer image formed on a recording medium by the image forming unit and fixed by the fixing unit;
An urging plate provided opposite to the detection means, for urging the recording medium toward the detection means at a detection position by the detection means, and holding the recording medium with the detection means;
Two detection means side rollers provided on both sides of the detection means in a direction perpendicular to the recording medium conveyance direction;
A roller opposed to the detection means side roller, the opposed roller for holding and conveying the recording medium urged by the urging plate with the detection means side roller ,
When the recording medium is detected by the detection means, the detection means side roller and the counter roller are arranged between the front end and the rear end of the region sandwiched between the detection means and the urging plate of the recording medium in the recording medium conveyance direction. A color image forming apparatus, characterized in that a virtual line segment connecting the axis centers is located . The urging plate swings and is movable between a sandwiching position where the recording medium is sandwiched with the detection means and a non-pinch position where the recording medium is not sandwiched, and is in the sandwiching position when the recording medium is detected by the detection means. The color image forming apparatus according to claim 1. 3. The color image forming apparatus according to claim 1, wherein the urging unit has a shape substantially symmetrical with respect to an optical measurement center line of the detection unit. The said two detection means side roller is provided in the position which becomes substantially line symmetrical with respect to the optical measurement centerline of the said detection means, The Claim 1 thru | or 3 characterized by the above-mentioned. Color image forming apparatus. The counter roller is covered with a viscoelastic member except for an end portion and a central portion facing the detection means, and is provided with a rotational driving force from within a color image forming apparatus to convey the recording medium. The color image forming apparatus according to any one of claims 1 to 4. When the detection of the recording medium by the detecting means, in the recording medium conveying direction, one optical detection position of the detecting means of claim 1 to 5, characterized in that located in the recording medium conveyance direction downstream from the virtual line the color image forming apparatus according to an item or. The optical detection position of the detection means is located 2 mm or more downstream of the virtual line segment in the recording medium conveyance direction when the recording medium is detected by the detection means. The color image forming apparatus according to claim 6.

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