JP2005181673A - Color image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color image forming device of an electrophotographic system, capable of executing feedback control of color image density in an arbitrary printing image, without requiring printing a color patch. <P>SOLUTION: The device can be constituted of images to be measured in a minute image by calculating an amount of reduction of paper from before and after fixation, based on the relation of the image position after fixation and the write-in position prior to fixation, calculating the position of the image to be measured after fixing, reading the concentration, and executing a process control to it. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electrophotographic color image forming apparatus.

  In recent electrophotographic color image forming apparatuses, for the purpose of improving the color reproducibility of the output image and the color stability at the time of continuous printing, the color of the test image after fixing as the final output is detected, Based on this, a configuration for adjusting and controlling various conditions of the image forming process has been put into practical use (for example, see Patent Document 1). FIG. 5 is a block diagram showing a configuration example of the image forming apparatus in this case.

  In the figure, reference numeral 1 denotes a photoconductor that changes the conductive characteristics of its surface by light irradiation, 2 denotes a primary charger for uniformly charging the surface of the photoconductor 1, and 3 denotes image information to be formed. A laser irradiating means for irradiating the photosensitive member 1 with laser light; 4 a developing device for developing the electrostatic latent image formed on the surface of the photosensitive member 1 by the laser irradiating means 3 with toner of a predetermined color; A transfer charger that acts to transfer the toner image developed by the developing unit 4 to transfer paper, 6 is a cleaning unit that cleans foreign matter such as residual toner from the surface of the photoreceptor 1 after transfer, and 7 is on the transfer paper. Fixing means for fixing the toner image transferred onto the transfer paper by the action of heat and pressure, 8 a color sensor for detecting color information of the toner image after fixing formed on the transfer paper, and 9 for the color An image control means for adjusting the image forming conditions based on the measurement result by the capacitors 8.

  In the above configuration, the photoconductor 1 receives corona irradiation from the primary charger 2 while rotating, and the surface thereof is uniformly charged. The uniformly charged photoconductor 1 is irradiated with laser light from the laser irradiation means 3 based on the image information, whereby the surface of the photoconductor 1 is changed from the uniformly charged state to the image information. An electrostatic latent image due to the unevenness of the charged potential is formed. The electrostatic latent image is developed by attracting the floating toner charged by the action of the developing device 4 to the latent image.

  The developed toner image is transferred onto the transfer paper conveyed so as to pass through the transfer charger 5 by the action of the transfer charger 5 at the same time. The toner image transferred onto the transfer paper is melted and fixed by heat and pressure from the fixing device 7. On the other hand, the photoconductor 1 after the transfer of the toner image continues to rotate, and dirt such as residual toner is scraped off by the cleaner 6 and reaches the primary charger 2 again.

  By the way, the color sensor 8 detects the color density of the patch based on the control to print a color image (patch) of a predetermined color / predetermined shape as a measurement object, and transmits it to the image control means 9. The image control unit 9 adjusts the image forming unit so as to reduce the difference between the color density information at the time of patch formation and the detection result, or adjusts correction characteristics of image data used for laser irradiation. .

  In the above description, only the single-color image forming process has been described. However, the above image forming process is performed for each color of yellow, magenta, cyan, and black, and is configured to be superimposed on a single transfer sheet. A full-color image can be formed.

  FIG. 6 shows an example of a color sensor. As the color sensor, various forms such as those using a CCD and those using a photodiode have been put into practical use. In the figure, a case where a CCD is used is shown as an example. In the figure, 201 is an irradiation lamp that irradiates the transfer paper, 202 is a cylindrical lens array that forms an image of a reflection component, 203 is a CCD array that is a light receiving unit sequentially covered with R, G, and B filters, and 204 is A circuit board 205 on which the CCD array is formed is a recording surface glass for making the optical path length with the recording paper constant.

  In the above configuration, the illumination lamp 201 irradiates the reference patch on the transfer paper, and the reflected light is imaged on each cell of the CCD via the lens array 202. Each cell is sequentially covered with R, G and B filters. On the other hand, when the fixed image is a yellow Y patch, the B component is cyan, and when the fixed image is a magenta M patch, the G component is cyan. In the case of the C patch, since the R component is absorbed by the patch on the transfer paper, the signal of the CCD cell covered with the B filter in the Y patch is the same as that of the CCD cell covered with the G filter in the M patch. In the case of the C patch, the signal of the CCD cell covered with the R filter becomes a low level.

FIG. 7 shows the relationship between the output of the CCD cell and the transferred image density. In the figure, the solid line indicates the actual output level, and the broken line indicates the signal level when the sensor characteristics and environmental fluctuations are corrected. The signal level in this correction is determined by reading a density signal of a reference white plate in which each color density is measured in advance and determining a correction coefficient so that the level of the CCD output at that time represents the known density level measured. It is corrected by. As a result, the absolute density of the transferred image can be detected without including environmental fluctuations and deterioration of the light source. On the other hand, it is necessary to place a reference white plate having a known density at the measurement position of the sensor.
JP-A-10-19389

  The conventional color image forming apparatus as described above has the following problems.

  A color patch needs to be printed along with the color adjustment sequence, but when this color patch is printed exclusively for the color patch at a predetermined timing, the transfer paper is consumed each time the color patch is generated. However, there is a problem that the user-friendliness is lowered, such as disposal of the transfer paper or the like, or the printing time is increased by the amount of patch formation.

  In addition, when forming a color patch outside the print image area of the transfer paper, it is necessary to enlarge the transfer paper, or to narrow the image area, or it is necessary for the user to cut off the print portion of the color patch after printing. There was a problem that occurred.

  According to the present invention, the following means are used to solve the above problems.

  First, it has a color density sensor arranged to detect the image density after fixing, and performs feedback control so as to reduce the difference between the measurement result of the color density sensor and the writing data of the measurement target image. In an electrophotographic color image forming apparatus that forms a full-color image by superimposing a plurality of color toner images on transfer paper, the image at the time of fixing is determined from the relationship between the image position information after fixing and the position information of the written image before fixing. And calculating a post-fixing position of the measurement target image for detecting the image density after fixing based on the calculation result, and detecting the image density of the measurement target image based on the calculation result Configured to do.

  Second, the color image forming apparatus controls the formed image and the formed image to have a predetermined positional relationship, and forms a plurality of reference position display images serving as position indexes with respect to the formed image on the same transfer sheet, and The image shrinkage amount at the time of fixing is calculated based on the relative positional relationship by the image writing data of the plurality of reference position display images and the position information of each reference position display image after identification, and based on the calculation result, The image forming position of a predetermined density measurement target image is calculated from the image of the above.

  Third, the color image forming apparatus extracts a plurality of position index images serving as position indices from the image data to be formed, and compares the relative positional relationship and the identification position of the extracted plurality of position index images with image writing data. An image shrinkage amount at the time of fixing is calculated based on position information of each subsequent reference position display image, and an image forming position of a predetermined density measurement target image is calculated from the image after fixing based on the calculation result.

  Fourth, the color image forming apparatus extracts a plurality of position index images serving as position indices from the image data to be formed, selects an image density measurement target image in the vicinity of the extracted image, and extracts the extracted image data. The image forming position of the measurement target image is calculated from the positional information of the position index image after fixing based on the relative positional relationship between the position index image and the selected measurement target image based on the image writing data.

  Fifth, the color image forming apparatus performs image density measurement around the measurement target image in parallel with the position calculation control of the measurement target image from the fixed image, and temporarily stores the measurement data. Then, after the position calculation control is completed, the image density data of the measurement target image is selected from the stored data.

  According to the present invention, since the amount of shrinkage of the image after fixing is calculated from the image positional relationship before fixing and the image positional relationship after fixing, the position of the image to be measured for color image density is grasped. The image can be composed of minute images, which enables feedback control of the color image density in any print image, eliminates the need for color patch printing, and eliminates the consumption of excess toner and transfer paper while reproducing color. It is possible to realize a color image forming apparatus excellent in performance, color stability, and user operability.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is an explanatory diagram for explaining the present embodiment in the case where a registration mark indicating a position reference for a print image is printed on a transfer sheet. In the figure, 8 is a color sensor composed of a line sensor such as a CCD for measuring the image density on the transfer paper after fixing, 101 is a transfer paper on which a print image is formed, 102 is a print image formation area on the transfer paper, Ta to Td each have a predetermined positional relationship, and a registration mark with a positional relationship defined with the printed image, Y, M, and C are images on which image densities of yellow, magenta, and cyan are measured, respectively. The measurement target image extracted by a predetermined process.

  In the configuration shown in the figure, the transfer paper 101 passes through the fixing device, is conveyed in the direction of the arrow in the figure, and passes through the color sensor 8. The color sensor 8 reads the image density on the transfer paper according to the passage of the transfer paper 101, and first detects the cross centers of the register marks Ta and Tb from the density of the image, and grasps the positional relationship between them.

  Subsequently, according to the conveyance of the transfer paper 101, the surrounding image density including the measurement target images Y, M, and C is measured, and the measurement result is temporarily stored together with the position information. Further, the transfer paper 101 is conveyed, the center of the registration marks Tc and Td is detected from the image information of the transfer paper passing through the color sensor unit, and when the respective position information is grasped, the transfer paper is discharged.

  The shrinkage amount of the image after fixing is calculated from the relationship between the position information of the registration marks Ta to Td read by the above operation and the writing position information of Ta to Td at the time of image formation. Based on the calculation result, The fixing position of the measurement target image after fixing is calculated. Further, based on the calculation result, the amount of shrinkage of the transfer paper is converted from the stored image density measurement results, and the measured density of the measurement target image is selected, and the image is written according to this data. The laser light quantity adjustment and the image forming process adjustment amount are changed, and control is performed so as to obtain a desired color density during subsequent image formation.

  Next, an example of a method for calculating the shrinkage amount of the transferred image by fixing will be described. As shown in FIG. 1, the straight line connecting the registration marks Ta and Tb is parallel to one side of the print image area 102, and the distance between this Ta and Tb is α in the writing state before fixing. Be controlled. Further, the relationship between the registration marks Ta and Tc is arranged so as to be parallel to the sub-scanning direction of the print image area 102, and the distance between the two is controlled to be β. Similarly, the distance between the registration marks Tc and Td is α, the distance between Tb and Td is β, and the rectangle composed of Ta, Tb, Tc, and Td is controlled to be a rectangle surrounding the print image range.

  By the way, when the print image including the registration mark on the transfer paper passes through the fixing device, the transfer paper is heated to evaporate water, and the transfer paper 101 is slightly shrunk. As a result, the distance between the registration marks Ta and Tb (= Tc and Td) and the distance between Ta and Tc (= Tb and Td) detected by the color sensor 8 after fixing is reduced to a and b, respectively. Based on this measurement result, the amount of shrinkage of the fixed image is a / α in the main scanning direction and b / β in the sub-scanning direction.

  From the above, the movement position due to the shrinkage of the image to be measured after fixing to be measured can be calculated as follows, for example, as the distance from the registration mark Ta.

Main scanning direction: Fms = Pms × a / α (1-1)
Fms is a distance in the main scanning direction after fixing Pms is a distance in the main scanning direction before fixing Sub-scanning direction: Fss = Pss × b / β (1-2)
Fss is the distance in the sub-scanning direction after fixing Pss is the distance in the sub-scanning direction before fixing

  FIG. 2 is a control block diagram of the image control circuit in this embodiment. The figure shows an image control circuit that operates in response to, for example, any one of Y, M, and C image signals.

  In the figure, 201 is a measurement target image extracting means for extracting an appropriate measurement target image for density detection from transmitted image signals, and 202 is a memory for storing a reference image such as a registration mark as a position reference on transfer paper. , 203 is a memory for storing measured density data of a peripheral image including a measurement target image detected by the color sensor 8, 204 is a laser control means for writing an image, 205 is a process control means for adjusting an image forming process, and 206 is as described above. It is an image control means for controlling the operation between the blocks.

  In the configuration shown in FIG. 6, the measurement object extraction unit 201 receives the transmitted image signal, selects an image suitable for image density measurement, and sends the image density information and position information to the image control unit 206. Based on the extraction result, the image control means 206 calculates the positional relationship between the measurement target image and each register mark to be written, that is, the above-described calculation of Pms and Pss.

  Incidentally, the image control means 206 controls the position control of the measurement target image, controls the operation of the laser control means 204 by the image signal, and further controls the image forming operation on the transfer paper by the process control means. As described above, an image is formed on the transfer paper in accordance with the image signal, and the formed image is fixed on the transfer paper by applying heat and pressure with a fixing device. Next, the fixed image passes through the color sensor 8 to detect the center position of each registration mark and the peripheral image density including the measurement target image, and the image density detection result is stored in the memory 203. The

  When the detection of the center position of each registration mark is completed in accordance with the above operation, the image control unit 206 calculates the amount of shrinkage of the fixed image according to the above-described calculation method, and based on the calculation result, Then, the density data of the measurement target image is extracted. Further, the image control unit 206 adjusts the laser control unit 204 or the process control unit 205 so that the measured density data matches the written data based on the relationship between the extracted density data and the written data of the measurement target image. Execute control.

  As described above, according to the present embodiment, the shrinkage amount of the image after fixing is calculated from the distance relationship between the register marks before fixing and the distance relationship between the register marks measured after fixing, and at the same time, the image to be measured is measured. Since the density of the measurement target image in the stored data is selected based on the calculation result, the density of the surrounding image including the image is also saved. In consideration of the above, density measurement at an accurate position is possible, and it is configured to perform print color density adjustment control based on this density information, so there is no need to generate a special color patch for density adjustment, Adjustment and stabilization of the color density of the printed image can be realized by avoiding wasteful consumption of transfer paper and toner.

  In the first embodiment, a shrinkage amount of an image after fixing is calculated based on a registration mark described on a transfer paper, an accurate position of an image to be measured is determined, a density measurement is performed to correct and stabilize an output image density. As described above, here, a plurality of appropriate images serving as position references are extracted from the printed image, the amount of shrinkage of the fixed image is calculated from the positional relationship after fixing the image, and the accurate position determination of the measurement target image is performed. The case of performing will be described.

  FIG. 3 is a principle explanatory diagram for explaining the calculation principle of the shrinkage amount and the post-fixing position of the measurement target image in this case. In the figure, (a) shows a written image, and points A and B are characteristic minute images extracted from the image information for calculating the amount of shrinkage and having relatively clear image edges. . A point C is a measurement target image extracted as a color image density measurement target. Next, (b) shows the state of the transfer paper and image when the above image information is formed on the transfer paper and fixed by applying heat and pressure. A point and a Z point respectively indicate positions after fixing of the points A, B, and C in the image information before fixing.

  In the above, first, the A-B distance α, the A-C distance β, and the B-C distance γ are calculated from the image information shown in FIG. Subsequently, the point X and the point Y are extracted from the image after fixing, and the XY distance a is calculated from the extraction result. Further, based on the above information, the shrinkage rate a / α of the post-fixing image is calculated, and the X-Z distance b and Y-Z distance c are calculated using this. This calculation can be performed as follows.

b = β × a / α (2-1)
c = γ × a / α (2-2)
Using the above result, the position of the point Z can be calculated by calculating the intersection of the distance b from the point X and the distance c from the point Y.

  According to the calculation method described above, the position after fixing of the measurement target image can be accurately grasped even when the relationship between the transfer paper and the image is skewed as shown in FIG. it can.

  Here, a case will be described in which a reference image is set in the vicinity of the measurement target image as means for grasping the measurement target image.

  FIG. 4 is an explanatory view of the principle of the method for grasping the position of the measurement target image in this case. (A) in the figure shows the positional relationship between the point A extracted as the reference position image and the minute image C extracted as the measurement target image in the vicinity of the point A, and an enlarged view of the upper part of (c). It is. Also, (b) in the figure shows the positional relationship between the reference position image point X after fixing and the measurement target image Z, and the lower part of (c) is an enlarged view of this. As shown in (c), since the reference position image point A and the measurement target image C are extracted in the very vicinity, the positional relationship between the reference position image point X and the measurement target image Z after fixing is the same as that of the transfer paper and fixing. The position of the measurement target image Z from the reference position image point X can be grasped from the positional relationship before fixing without being affected by the skew relationship of the image and the amount of shrinkage of the image after fixing.

  As described above in Embodiments 1 to 3, according to the present invention, the amount of shrinkage of the image after fixing is calculated from the image positional relationship before fixing and the image positional relationship after fixing, and the color image density measurement target image is calculated. Since the position is grasped, the image to be measured can be composed of a minute image, which enables feedback control of the color image density in any print image, eliminates the need for color patch printing, extra toner and A color image forming apparatus excellent in color reproducibility, color stability, and user operability can be realized while eliminating the consumption of transfer paper.

  In the above description, the case where a line sensor is used as a color sensor has been described as an example. However, the present invention is not limited to this, and for example, an area sensor is used to implement a part of a print image. It is also possible to do. Further, by using the same area sensor so that the area sensor can be moved in the main scanning direction, it is also possible to carry out in the same manner as described in the first to third embodiments.

FIG. 6 is an explanatory diagram illustrating Example 1 in the case where a registration mark indicating a position reference with respect to a print image is printed on a transfer sheet. 2 is a control block diagram of an image control circuit in Embodiment 1. FIG. FIG. 10 is a principle explanatory diagram illustrating a calculation principle of a shrinkage amount and a post-fixing position of a measurement target image according to the second exemplary embodiment. It is a principle explanatory view of a position grasping method of a measuring object picture in Example 3. It is a block diagram which shows the structural example of the image forming apparatus in a prior art example. It is a figure which shows an example of the color sensor in a prior art example. It is a figure which shows the example of a relationship between the output of a CCD cell and the transfer image density in a prior art example.

Explanation of symbols

1Y to 1K Photoconductor 7 Fixing device 8 Color sensor 9 Image control means 101 Transfer paper 102 Print image area Ta to Td Registration mark Y, M, C Measurement target image 201 Measurement target image extraction means 202, 203 Memory 204 Laser control means 205 Process control means 206 Image control means

Claims (5)

  A color density sensor arranged to detect the image density after fixing, and performing feedback control so as to reduce the difference between the measurement result of the color density sensor and the writing data of the measurement target image. In an electrophotographic color image forming apparatus that forms a full-color image by superimposing toner images on transfer paper, the amount of image shrinkage at the time of fixing is determined from the relationship between the image position information after fixing and the position information of the written image before fixing. And calculating a position after fixing of the measurement target image for detecting the image density after fixing based on the calculation result, and detecting the image density of the measurement target image based on the calculation result. A color image forming apparatus.   The color image forming apparatus controls a formed image and a plurality of reference position display images, which are controlled to have a predetermined positional relationship with the formed image, and serve as a position index for the formed image on the same transfer sheet, and An image shrinkage amount at the time of fixing is calculated based on the relative positional relationship of the display image based on the image writing data and the position information of each reference position display image after identification, and based on the calculation result, a predetermined amount is calculated from the image after fixing The color image forming apparatus according to claim 1, wherein an image forming position of the density measurement target image is calculated.   The color image forming apparatus extracts a plurality of position index images serving as position indices from image data to be formed, relative positional relationships of the extracted plurality of position index images according to image writing data, and each reference after identification An image shrinkage amount at the time of fixing is calculated based on position information of a position display image, and an image forming position of a predetermined density measurement target image is calculated from the image after fixing based on the calculation result. The color image forming apparatus according to claim 1.   The color image forming apparatus extracts a plurality of position index images serving as position indices from image data to be formed, selects an image density measurement target image in the vicinity of the extracted images, and extracts the extracted position index images. 2. The image forming position of the measurement target image is calculated from position information of the position index image after fixing based on a relative positional relationship based on image writing data between the measurement target image and the selected measurement target image. Color image forming apparatus.   The color image forming apparatus executes a peripheral image density measurement including the measurement target image in parallel with the position calculation control of the measurement target image from the post-fixing image, temporarily stores the measurement data, and performs the position calculation. 5. The color image forming apparatus according to claim 1, wherein after the control is completed, image density data of a measurement target image is selected from the stored data.

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