JP4561385B2 - Color image forming apparatus - Google Patents

Description

  The present invention relates to a color image forming apparatus such as a color copying machine, a color laser printer, or a color facsimile that employs an electrophotographic method, and in particular, can maintain a stable color balance by a single color image forming condition control operation. The present invention relates to a possible color image forming apparatus.

JP 2004-258281 A

  Conventionally, as a color image forming apparatus such as a color copying machine, a color laser printer, or a color facsimile employing this type of electrophotographic method, for example, a single photosensitive drum is provided, and yellow ( A toner image corresponding to each color such as Y), magenta (M), cyan (C), and black (K) is formed, and yellow (Y), magenta (M), and cyan are sequentially formed on the photosensitive drum. (C) The toner images of each color such as black (K) are collectively transferred onto a recording medium via an intermediate transfer belt, or sequentially transferred directly onto the recording medium, whereby a full color image is obtained. Various so-called four-cycle color image forming apparatuses configured to form have been proposed and have already been commercialized.

  Further, as the color image forming apparatus, four image forming units corresponding to respective colors such as yellow (Y), magenta (M), cyan (C), black (K), and the like are arranged in series, and images of the respective colors are arranged. Whether the toner images of each color such as yellow (Y), magenta (M), cyan (C), black (K), etc., formed by the forming unit are collectively transferred onto a recording medium via an intermediate transfer belt. Various so-called tandem color image forming apparatuses configured to form full-color images by sequentially transferring directly onto a recording medium have been proposed and have already been commercialized.

  In the color image forming apparatus, intermediate transfer is performed so that the image density and color balance of each color such as yellow (Y), magenta (M), cyan (C), and black (K) satisfy a predetermined condition. A toner image (test patch) of each color of yellow (Y), magenta (M), cyan (C), and black (K) is formed on the belt and the like, and the density of the test patch of each color is detected, and the developing device The toner density in the developer (Toner Concentration), the developing bias, or the image forming process conditions such as the charging condition and exposure amount of the photosensitive drum are fed back and controlled.

  However, in the case of the above-described conventional image forming apparatus, the image forming process conditions are mostly corrected essentially due to density variations when generating test patches and detection errors when detecting the density of test patches. However, there is a problem in that the color balance may be lost before and after executing the process control due to correction.

  In the case of the above-described conventional image forming apparatus, the apparent color balance is in spite of the expected variation in process control and the correction amount is very small depending on the process conditions to be controlled. It had the problem that it collapsed.

  Therefore, as a technique that can solve such a problem, for example, a technique disclosed in Japanese Patent Application Laid-Open No. 2004-258281 has already been proposed.

  The image forming apparatus according to Japanese Patent Application Laid-Open No. 2004-258281 is a technique for adjusting so as to satisfy color balance, and forms density detection patterns having different densities, and the density of the density detection patterns is changed to a density. The density is adjusted by detecting the detection means and adjusting the development bias, the charging potential, or the exposure amount, and the second density detection pattern is drawn using the first adjustment result. The second density adjustment is performed.

  However, the conventional technique has the following problems. That is, in the case of the image forming apparatus according to Japanese Patent Application Laid-Open No. 2004-258281, it is necessary to form the density detection pattern twice in total, the first time and the second time, in order to adjust so as to satisfy the color balance. When the density detection pattern is formed multiple times, not only the amount of toner consumed other than printing increases, but it also takes a long time to control the process conditions, resulting in a decrease in print productivity. Had a point.

  Accordingly, the present invention has been made to solve the above-described problems of the prior art, and the object of the present invention is to enable stable color balance to be maintained by a single density adjustment and to be consumed in addition to printing. An object of the present invention is to provide a color image forming apparatus capable of reducing the amount of toner to be processed, reducing the time required for controlling process conditions, and improving productivity.

In order to solve the above-described problem, the invention described in claim 1 detects the density of the density detection pattern formed on the detected medium by the density detection means, and based on the detection result of the density detection means. In a color image forming apparatus for controlling a toner density control amount of a developing unit corresponding to a plurality of colors and an exposure amount of an image exposure unit by a control unit to form an image,
The control unit calculates a control amount candidate value of the toner density of the developing unit and an exposure amount candidate value of the image exposure unit corresponding to a plurality of colors based on the detection result of the density detection unit, and changes the exposure amount candidate value. It is determined whether or not the absolute value of the difference between a plurality of colors is equal to or smaller than a threshold value. If the absolute value of the difference exceeds the threshold value, the exposure amount correction value is within a predetermined range. The color image forming apparatus is characterized in that the correction value of the limited exposure amount is compensated by correcting the control amount of the toner density.

  According to a second aspect of the present invention, when the control means corrects the control value of the toner density in order to compensate the correction value of the limited exposure amount, the correction value of the limited exposure amount is used. 2. The color image forming apparatus according to claim 1, wherein a value obtained by multiplying a correction value of the toner density control amount to be compensated by a predetermined coefficient is used as a correction value of the toner density control amount.

  Furthermore, the invention described in claim 3 is the color image forming apparatus according to claim 2, wherein the predetermined coefficient is set to a value of 1 or less.

  According to a fourth aspect of the present invention, the threshold value provided for the absolute value of the difference between the colors of the change amount of the exposure amount candidate value is variable according to the change over time of the environment and the apparatus. The color image forming apparatus according to claim 1, wherein the color image forming apparatus is a color image forming apparatus.

  Furthermore, the invention described in claim 5 is characterized in that the predetermined coefficient is variable in accordance with a change with time of environment or apparatus. Forming device.

  According to a sixth aspect of the present invention, when the absolute value of the difference exceeds a threshold value, the priority order is set between the plurality of colors when the exposure correction value is limited within a predetermined range. 5. The color image forming apparatus according to claim 1, wherein the color image forming apparatus is limited in the attached state.

  At this time, the plurality of colors are yellow, magenta, and cyan, and the difference between the plurality of colors is the difference between yellow and magenta, the difference between magenta and cyan, and the difference between cyan and yellow. For example, the highest priority is given to the difference between the magenta color and the cyan color, and then the priority is given in the order of yellow and magenta, and then cyan and yellow. .

  The reason is that in the color balance, the weight occupied by the difference between the magenta color and the cyan color is large, and then the weight is large in the order of yellow and magenta, and then cyan and yellow.

  According to the present invention, it is possible to maintain a stable color balance by one density adjustment, reduce the amount of toner consumed in addition to printing, reduce the time required for controlling process conditions, and reduce production. It is possible to provide a color image forming apparatus capable of improving the properties.

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

Embodiment 1
FIG. 2 shows a four-cycle full-color printer as a color image forming apparatus according to Embodiment 1 of the present invention.

  In FIG. 2, reference numeral 1 denotes a main body of a full-color printer. Inside the main body of the full-color printer 1, a photosensitive drum 2 as an image carrier is rotatably disposed at a slightly upper right portion from the center. Has been. As this photosensitive drum 2, for example, a drum made of a conductive cylinder having a diameter of about 47 mm whose surface is coated with a photosensitive layer made of OPC or the like is used. It is rotationally driven at a process speed of about 150 mm / sec. This full-color printer has a process speed of about 150 mm / sec, which is set to be relatively high in similar models, and has high productivity. Of course, the process speed of the full color printer may be set faster than 150 mm / sec in the monochrome mode, for example.

  The surface of the photosensitive drum 2 is charged to a predetermined potential by a charging roll 3 serving as a charging unit disposed almost directly below the photosensitive drum 2, and then at a position just below the photosensitive drum 2. Image exposure with a laser beam (LB) is performed by ROS4 (Raster Output Scanner) as the arranged image exposure means, and an electrostatic latent image corresponding to image information is formed. As will be described later, the ROS 4 as the image exposure means is configured such that the exposure amount can be controlled and the exposure portion potential of the electrostatic latent image formed on the photosensitive drum 2 can be changed. Has been. The electrostatic latent image formed on the photosensitive drum 2 passes through the developing devices 5Y, 5M, 5C, and 5K of yellow (Y), magenta (M), cyan (C), and black (K) in the circumferential direction. The toner is developed by a rotary developing device 5 arranged along the toner image to form a toner image of a predetermined color.

  As shown in FIG. 2, the rotary developing device 5 includes four developing devices 5Y, 5M, 5C, and 5K for yellow (Y), magenta (M), cyan (C), and black (K). The rotating frames 52 that rotate about the shaft 51 are mounted so as to form an angle of 90 degrees along the circumferential direction. Further, the four developing devices 5Y, 5M, 5C, and 5K of yellow (Y), magenta (M), cyan (C), and black (K) have the rotational position of the rotating frame 52 set to the rotating frame 52. By detecting and controlling according to the position of the provided slit 53, the developing roll 55 provided in the opening 54 of each developing device 5Y, 5M, 5C, 5K is stopped at the developing position facing the photosensitive drum 2. The electrostatic latent image formed on the photosensitive drum 2 is developed with toner of a desired color.

  Further, the developing devices 5Y, 5M, 5C, and 5K adopting the two-component developing system of yellow (Y), magenta (M), cyan (C), and black (K) include the developing devices 5Y, 5M. A toner cartridge (not shown) is mounted so as to be adjacent to 5C and 5K, and each development is performed by appropriately supplying toner from the toner cartridge to the corresponding developing devices 5Y, 5M, 5C, and 5K at a predetermined timing. The toner density in the containers 5Y, 5M, 5C, 5K can be adjusted.

  On the surface of the photosensitive drum 2, charging, exposure, and development processes are repeated a predetermined number of times according to the color of the image to be formed. In the rotary developing device 5, the developing rollers 55 of the corresponding color developing devices 5 </ b> Y, 5 </ b> M, 5 </ b> C, and 5 </ b> K move to a developing position facing the photosensitive drum 2. For example, when a full-color image is formed, the charging, exposure, and development processes are performed on the surface of the photosensitive drum 2 in yellow (Y), magenta (M), cyan (C), and black (K) colors. The toner image corresponding to each color of yellow (Y), magenta (M), cyan (C), and black (K) is sequentially formed on the surface of the photosensitive drum 2. . The number of rotations of the photosensitive drum 2 when the toner image is formed varies depending on the size of the image. For example, in the case of A4 size, one image can be obtained by rotating the photosensitive drum 2 three times. It is formed. In other words, each time the photosensitive drum 2 rotates three times, toner images corresponding to yellow (Y), magenta (M), cyan (C), and black (K) colors are sequentially formed on the surface of the photosensitive drum 2. It is formed.

  The yellow (Y), magenta (M), cyan (C), and black (K) toner images sequentially formed on the photosensitive drum 2 are arranged on the outer periphery of the photosensitive drum 2 as intermediate transfer bodies. At the primary transfer position around which the transfer belt 6 is wound, the primary transfer is performed by the primary transfer roll 7 while being superimposed on the intermediate transfer belt 6. The yellow (Y), magenta (M), cyan (C), and black (K) toner images transferred in multiple onto the intermediate transfer belt 6 are fed by the secondary transfer roll 8 at a predetermined timing. The recording sheet 9 is secondarily transferred at a secondary transfer position A at a time. The recording paper 9 is fed by a feed roll 11 from a paper feed cassette 10 disposed at the lower part of the full-color printer main body 1 and is fed in a state where the recording paper 9 is rolled one by one by the feed roll 11 and the retard roll 12. The sheet is conveyed to the secondary transfer position A of the intermediate transfer belt 6 through the sheet conveyance path 13 in a state of being synchronized with the toner image transferred onto the intermediate transfer belt 6 by the registration roll 14.

  The intermediate transfer belt 6 is stretched by a plurality of rolls and is driven along with the rotation of the photosensitive drum 2 so as to circulate and move at a predetermined process speed (about 150 mm / sec). The intermediate transfer belt 6 is configured to be stretchable by an elastic body made of a rubber material or the like. The intermediate transfer belt 6 intermediately transfers a wrap-in roll 15 that specifies the wrap position of the intermediate transfer belt 6 on the upstream side in the rotational direction of the photosensitive drum 2 and a toner image formed on the photosensitive drum 2. The primary transfer roll 7 to be transferred onto the belt 6, the wrap-out roll 16 for specifying the wrap position of the intermediate transfer belt 6 on the downstream side of the wrap position, and the secondary transfer roll 8 are in contact with each other via the intermediate transfer belt 6. The backup roll 17, the first cleaning backup roll 19 facing the cleaning device 18 of the intermediate transfer belt 6, and the second cleaning backup roll 20 are stretched with a predetermined tension.

  Further, as described above, the intermediate transfer belt 6 is stretched by a plurality of rolls 7, 8, 15 to 17, 19, and 20. In this embodiment, the full-color printer main body 1 is reduced in size. Therefore, the cross-sectional shape on which the intermediate transfer belt 6 is stretched is configured to be a flat and elongated substantially trapezoidal shape.

  Furthermore, in this embodiment, as shown in FIG. 2, the entire full-color printer is miniaturized as much as possible, but the rotary developing device 5 occupies a large space of the full-color printer main body 1. Therefore, the full-color printer main body 1 is designed to improve the maintainability of the intermediate transfer belt 6 and the rotary developing device 5 while achieving downsizing of the device. Specifically, the intermediate transfer belt 6 includes the photosensitive drum 2, the charging roll 3, and the like, and integrally constitutes a process cartridge 21, and the upper cover 22 of the full-color printer main body 1 is opened to open the intermediate transfer belt 6. As shown in FIG. 3, the entire process cartridge 21 is configured to be detachable from the full-color printer body 1. A reflection type photosensor that detects the density of a test patch of toner as a density detection pattern formed on the intermediate transfer belt 6 as a medium to be detected is upstream of the secondary transfer roll 8 of the intermediate transfer belt 6. An automatic density detection (ADC) sensor 23 is provided as a density detection means comprising

  Further, as shown in FIG. 2, the cleaning device 18 for the intermediate transfer belt 6 includes a scraper 24 disposed so as to abut on the surface of the intermediate transfer belt 6 stretched by a first cleaning backup roll 19; A cleaning brush 25 disposed so as to be in pressure contact with the surface of the intermediate transfer belt 6 stretched by the second cleaning backup roll 20, and residual toner and paper dust removed by the scraper 24 and the cleaning brush 25 Is collected in the cleaning device 18. The cleaning device 18 is disposed so as to be able to swing counterclockwise around the swing shaft 26. Until the secondary transfer of the final color toner image is completed, the intermediate transfer is performed. The belt 6 is retracted to a position separated from the surface of the belt 6 and is configured to come into contact with the surface of the intermediate transfer belt 6 when the secondary transfer of the final color toner image is completed.

  Further, the recording paper 9 onto which the toner image is transferred from the intermediate transfer belt 6 is conveyed to the fixing device 27 as shown in FIG. 2, and the heating roller 27a and the pressure belt (or the pressure belt) of the fixing device 27 are conveyed. The toner image is fixed on the recording paper 9 by heat and pressure by the roller 27b, and is discharged as it is from the discharge port 29 onto the discharge tray 30 provided on the upper portion of the printer body 1 by the discharge roll 28.

  It should be noted that the surface of the photosensitive drum 2 after the toner image transfer process has been completed, the cleaning blade 32 of the cleaning device 31 disposed obliquely below the photosensitive drum 2 every time the photosensitive drum 2 rotates once. As a result, residual toner and the like are removed to prepare for the next image forming process.

  By the way, in this embodiment, the density of the density detection pattern formed on the medium to be detected is detected by the density detection means, and the toner density of the developing means corresponding to a plurality of colors based on the detection result of the density detection means. In the color image forming apparatus for forming an image by controlling the control amount and the exposure amount of the image exposure means by the control means, the control means is a developing means corresponding to a plurality of colors based on the detection result of the density detection means. The toner density control amount candidate value and the exposure amount candidate value of the image exposure unit are calculated, and it is determined whether or not the absolute value of the difference between the plurality of colors of the change amount of the exposure amount candidate value is equal to or less than a threshold value. When the absolute value of the difference exceeds a threshold value, the exposure amount correction value is limited within a predetermined range, and the correction value of the limited exposure amount is corrected for the control amount of the toner density. Possibly It is configured to compensate.

  In this embodiment, the control means compensates for the limited exposure amount correction value, so that when the toner density control amount is corrected, the control unit compensates for the limited exposure amount correction value. A value obtained by multiplying the correction value for the control amount by a predetermined coefficient is used as the correction value for the toner density control amount.

  Furthermore, in this embodiment, the predetermined coefficient is set to a value of 1 or less.

  Further, in this embodiment, the threshold value provided for the absolute value of the difference between the colors of the change amount of the exposure amount candidate value is variable according to the change over time of the environment and the apparatus.

  Furthermore, in this embodiment, the predetermined coefficient is variable in accordance with changes over time of the environment and the apparatus.

  Further, in this embodiment, when the absolute value of the difference exceeds a threshold, when the exposure correction value is limited within a predetermined range, a priority order is set between the plurality of colors. Configured to restrict.

  That is, in the full-color printer according to the first embodiment, as shown in FIG. 4, yellow (Y), magenta (M), cyan (C), black (K) are placed on the intermediate transfer belt 6 as a detected medium. ), The first test patches 60Y, 60M, 60C, and 60K formed of halftone dot images with a density of 50% are used as the first density detection patterns for controlling the exposure amounts of the images of the respective colors by the ROS4. As a second density detection pattern for controlling the toner density in each of the developing devices 5Y, 5M, 5C, and 5K, second test patches 61Y, 61M, and 61C made of a 100% density (solid) image are used. , 61K are formed at a predetermined timing, and the first test patches 60Y, 60M, 60C, 60K and the second test patches 61Y, 61M, 61C, 61K It is configured to detect the degree of ADC sensor 23.

  Note that the first density detection pattern does not necessarily have to be formed with toners of four colors of yellow (Y), magenta (M), cyan (C), and black (K), but yellow (Y), You may form only with the color toner of magenta (M) and cyan (C).

  The detection result of the ADC sensor 23 is sent to the patch density calculation unit 101 as shown in FIG. 1, and the patch density calculation unit 101 uses the first test patches 60Y, 60M, 60C, 60K and the second test. The densities of the patches 61Y, 61M, 61C, 61K are calculated. The patch density calculated by the patch density calculation unit 101 is sent to the exposure amount calculation unit 102 and the toner density correction calculation unit 103, respectively. In the exposure amount calculation unit 102, the first test patches 60Y, 60M, Correction values for image exposure amounts of yellow (Y), magenta (M), cyan (C), and black (K) in ROS4 are calculated according to the densities of 60C and 60K. Then, based on the exposure amount calculated by the exposure amount calculation unit 102, each color of yellow (Y), magenta (M), cyan (C), and black (K) by ROS4 by the ROS control unit 104 as the control means. The image exposure amount is controlled.

  Note that when the first density detection pattern is formed of only three color toners of yellow (Y), magenta (M), and cyan (C), the exposure calculated by the exposure calculation unit 102 is used. Based on the amount, the ROS control unit 104 as the control means controls the image exposure amounts of three colors of yellow (Y), magenta (M), and cyan (C) by ROS4. The reason for this is that the image exposure amounts of the three colors of yellow (Y), magenta (M), and cyan (C) directly affect the color balance and must be controlled within a predetermined range. This is because black (K) affects only a black-and-white image, so even if the exposure amount varies slightly, the color balance is not greatly affected.

  The toner density correction calculation unit 103 also functions as a control unit. The toner density correction calculation unit 103 supplies the toner cartridges 5Y, 5M, 5C, and 5K from the toner cartridge according to the patch density. The toner supply motor 105 provided in each of the developing devices 5Y, 5M, 5C, and 5K of the developing device 5 is calculated based on the toner density correction value calculated by the toner density correction calculating unit 103. The toner is driven at a predetermined timing for a predetermined time, and the toner of the color corresponding to each developing device 5Y, 5M, 5C, 5K is supplied from the toner cartridge 106 provided corresponding to each developing device 5Y, 5M, 5C, 5K. It has become so. As a result, the toner density in each developer 5Y, 5M, 5C, 5K is controlled to be a predetermined value.

  Further, in this embodiment, yellow (Y), magenta (M), cyan (calculated by the exposure amount calculation unit 102 in accordance with the density detection results of the first test patches 60Y, 60M, 60C, and 60K. C) In order to control the color balance and the like based on the correction value of the image exposure amount of each color of black (K), each color color of yellow (Y), magenta (M), and cyan (C) by ROS4 is controlled. The following control is performed when controlling the image exposure amount.

  That is, the ROS control unit 104 calculates the toner density control amount candidate value and the ROS4 exposure amount candidate value of each of the developing devices 5Y, 5M, and 5C corresponding to a plurality of colors based on the detection result of the ADC sensor 23. It is determined whether or not the absolute value of the difference between the colors of the change amount of the exposure amount candidate value is equal to or less than a threshold value. If the absolute value of the difference exceeds the threshold value, the exposure amount correction is performed in advance. Further, the correction value of the limited exposure amount is compensated by correcting the control amount of the toner density.

  Further, when the absolute value of the difference between the colors of the exposure amount candidate value change amount is within the threshold range, the exposure of the ROS 4 corresponding to each of a plurality of colors is performed based on the detection result of the ADC sensor 23. An amount correction value is calculated, and the exposure amount by the ROS 4 is directly controlled based on the exposure amount correction value.

  The ROS control unit 104 is configured to transfer the intermediate transfer belt at a predetermined timing, for example, when the image forming apparatus is turned on, when the temperature in the apparatus changes by a predetermined value or more, and when a predetermined number of print jobs are completed. 6, first test patches 60Y, 60M, 60C, 60K of yellow (Y), magenta (M), cyan (C), and black (K) colors, and second test patches 61Y, 61M, 61C, 61K is formed, and the ADC sensor 23 detects the densities of the first test patches 60Y, 60M, 60C, and 60K and the second test patches 61Y, 61M, 61C, and 61K. As shown in FIG. 1, the density of the first test patches 60Y, 60M, 60C, 60K and the second test patches 61Y, 61M, 61C, 61K detected by the ADC sensor 23 is determined by the patch density calculation unit 101. The calculated value is sent to the exposure amount calculation unit 102 and the toner density correction unit, and the control described below is performed.

  In the above configuration, the full-color printer as the color image forming apparatus according to this embodiment can maintain a stable color balance by one-time density adjustment as described below, and the amount of toner consumed other than printing can be maintained. In addition to being able to reduce the amount, it is possible to shorten the time required to control the process conditions and improve productivity.

  That is, in the full-color printer, when the printer is turned on, when the temperature in the printer main body 1 changes by a certain value or more, or when a certain number of print jobs are completed, as shown below, An operation for controlling various image forming conditions is performed. As shown in FIG. 1, the full-color printer includes a temperature sensor 107 that detects the temperature inside the machine. The temperature inside the machine detected by the temperature sensor 107 is the ROS control unit 104 and the toner density calculation unit 103. To be sent to.

  In this full-color printer, as shown in FIG. 5, a predetermined number of times such as when the printer is turned on, when the temperature in the printer body 1 changes by a certain value or more, or when a certain number of print jobs are completed, etc. At the timing, the image density detection of the first test patches 60Y, 60M, 60C, 60K for controlling the latent image exposure output by the ROS 4 and the toner density in the developing devices 5Y, 5M, 5C, 5K are controlled. Image density detection of the second test patches 61Y, 61M, 61C, 61K is performed (step 101). In the image density detection for controlling the latent image exposure output and the toner density, as shown in FIG. 4, yellow (Y), magenta (M), cyan (C) are formed on the intermediate transfer belt 6 as a detected medium. ) And black (K) toners, the first test patches 60Y, 60M, 60C, and 60K including a halftone dot image having a density of 50% as a density detection pattern, and the second test patch 61Y having a density of 100%. , 61M, 61C, 61K are formed, and the density of the first test patches 60Y, 60M, 60C, 60K and the second test patches 61Y, 61M, 61C, 61K is detected by the ADC sensor 23.

  Then, the density data of the first test patches 60Y, 60M, 60C, 60K and the second test patches 61Y, 61M, 61C, 61K detected by the ADC sensor 23 are calculated as shown in FIG. The patch density calculation unit 101 calculates the densities of the first test patches 60Y, 60M, and 60C and the second test patches 61Y, 61M, 61C, and 61K.

  Next, the density calculation values of the first test patches 60Y, 60M, 60C, and 60K and the second test patches 61Y, 61M, 61C, and 61K calculated by the patch density calculation unit 101 are the exposure amount calculation unit 102 and The exposure amount calculation unit 102 sends the toner density correction calculation unit 103 to yellow (Y), magenta (M), and cyan by ROS4 according to the density calculation values of the first test patches 60Y, 60M, 60C, and 60K. (C) An exposure correction value (candidate value) for each color image of black (K) is calculated (step 101). In addition, the toner density correction calculation unit 103 supplies toner (candidates) to be supplied to the developing devices 5Y, 5M, 5C, and 5K of the respective colors according to the density calculation values of the second test patches 61Y, 61M, 61C, and 61K. Value) is calculated (step 101).

  The exposure value correction value obtained by the ROS 4 calculated by the exposure value calculation unit 102 is sent to the ROS control unit 104, and the ROS control unit 104 uses the exposure value correction value calculated by the exposure value calculation unit 102. Then, control is performed so as to correct the exposure amount of each color image of yellow (Y), magenta (M), cyan (C), and black (K) by ROS4.

  At this time, the ROS control unit 104 calculates an exposure amount correction value ΔY obtained by subtracting the current yellow (Y) latent image exposure output from the previous yellow (Y) latent image exposure output (Step S1). 102). Similarly, for the magenta (M) color and cyan (C) color, the ROS control unit 104 determines the current magenta (M) color from the previous latent image exposure output of magenta (M) color and cyan (C) color. Then, exposure correction values ΔM and ΔC obtained by subtracting the cyan (C) latent image exposure planned output are calculated (step 102).

  Then, the ROS controller 104 determines the absolute values ΔYM = | ΔY−ΔM |, ΔMC = | ΔM−ΔC |, ΔCY = | ΔC−ΔY | of the differences between the exposure amount correction values ΔY, ΔM, and ΔC. Are not more than threshold values ΔYM1, ΔMC1, ΔCY1 (in the example shown, ΔYM1 = ΔMC1 = ΔCY1 = 0.1) (step 102). The ROS control unit 104 may be configured to simultaneously determine whether or not the exposure correction values ΔY, ΔM, and ΔC themselves are equal to or less than a threshold value (0.1 in the illustrated example).

  The ROS control unit 104 has the absolute values ΔYM = | ΔY−ΔM |, ΔMC = | ΔM−ΔC |, ΔCY = | ΔC−ΔY | of the differences between the exposure amount correction values ΔY, ΔM, and ΔC. When the threshold values ΔYM1, ΔMC1, and ΔCY1 (ΔYM1 = ΔMC1 = ΔCY1 = 0.1 in the illustrated example) are all equal to or less than the threshold values, the exposure amounts of the yellow (Y), magenta (M), and cyan (C) are set to the candidate values. In addition to controlling the exposure amount of the ROS 4 for each color, the candidate value is also applied to the toner density control (step 105).

For example, as shown in FIG. 6, the correction value ΔY for the yellow (Y) exposure amount and the correction value ΔK for the black (K) exposure amount are “0”, and the magenta (M) color is corrected. Assume that the exposure amount correction value ΔM is “+0.1” and the cyan (C) exposure amount correction value ΔC is “−0.1”.
Then, the absolute value of the difference between the exposure amount correction values ΔY, ΔM, and ΔC is
ΔYM = | ΔY−ΔM | = | 0 − (+ 0.1) | = 0.1
ΔMC = | ΔM−ΔC | = | (+0.1) − (− 0.1) | = 0.2
ΔCY = | ΔC−ΔY | = | (−0.1) − (0) | = 0.1
It becomes.

  Therefore, the absolute value ΔMC = | ΔM−ΔC | of the difference between the magenta color and the cyan color among the exposure amount correction values ΔY, ΔM, and ΔC exceeds the threshold value ΔMC1 = 0.1. Therefore, if any one of the absolute values ΔYM, ΔMC, and ΔCY of the difference exceeds the thresholds ΔYM1, ΔMC1, ΔCY1 (in the illustrated example, ΔYM1 = ΔMC1 = ΔCY1 = 0.1), the ROS control unit By 104, the exposure amount of each color is corrected so as to be equal to or less than the threshold values ΔYM1, ΔMC1, and ΔCY1.

  In order to correct the exposure amount of each color so that the threshold values ΔYM1, ΔMC1, and ΔCY1 are less than or equal to each other, various methods such as uniformly compressing the exposure amount of each color can be considered. For example, the following correction operation is performed. Is done.

  That is, when the ROS control unit 104 determines that any one of the above conditions is not satisfied, that is, the absolute value ΔYM of the difference between the exposure amount correction values ΔY, ΔM, and ΔC. = | ΔY−ΔM |, ΔMC = | ΔM−ΔC |, ΔCY = | ΔC−ΔY |, any one of the threshold values ΔYM1, ΔMC1, ΔCY1 (in the illustrated example, ΔYM1 = ΔMC1 = ΔCY1 = 0.1) ) Exceeding the threshold value, the absolute values ΔYM = | ΔY−ΔM |, ΔMC = | ΔM−ΔC |, ΔCY = | The exposure amount correction value for each color is limited so that ΔC−ΔY | is less than or equal to threshold values ΔYM1, ΔMC1, and ΔCY1 (ΔYM1 = ΔMC1 = ΔCY1 = 0.1 in the illustrated example).

  Specifically, it is individually determined whether or not the yellow exposure amount correction value ΔY is within a predetermined range −0.05 ≦ ΔY ≦ 0.05, and the yellow exposure amount correction value ΔY is determined. If the predetermined range is −0.05 ≦ ΔY ≦ 0.05, the expected yellow (Y) latent image exposure output is set as ROS4 as the latent image exposure output, and the image exposure is executed. .

  If the yellow exposure correction value ΔY is not within the predetermined range −0.05 ≦ ΔY ≦ 0.05, is the yellow exposure correction value ΔY greater than 0 (positive or negative)? ) If the yellow exposure amount correction value ΔY is greater than or equal to 0, a value obtained by adding 0.05 to the previous yellow latent image exposure planned output is the current latent image exposure output. Is set to ROS4, and image exposure is executed. If the yellow exposure correction value ΔY is 0 or less (negative), a value obtained by subtracting 0.05 from the previous yellow latent image exposure scheduled output is used as the current latent image exposure output. Set to ROS4 and execute image exposure.

  Next, the ROS control unit 104 determines whether or not the magenta exposure amount correction value ΔM is within a predetermined range −0.05 ≦ ΔM ≦ 0.05, and the magenta exposure amount correction value. When ΔM is within a predetermined range −0.05 ≦ ΔM ≦ 0.05, the magenta (M) latent image exposure scheduled output is set in ROS 4 as the latent image exposure output, and image exposure is performed. Execute.

  If the magenta exposure amount correction value ΔM is not within the predetermined range −0.05 ≦ ΔM ≦ 0.05, is the magenta exposure amount correction value ΔM greater than 0 (whether positive or negative)? ) If the magenta exposure amount correction value ΔM is equal to or greater than 0, a value obtained by adding 0.05 to the previous magenta latent image exposure planned output is the current latent image exposure output. Is set to ROS4, and image exposure is executed. If the magenta exposure amount correction value ΔY is 0 or less (negative), a value obtained by subtracting 0.05 from the previous magenta latent image exposure output is used as the current latent image exposure output. Set to ROS4 and execute image exposure.

  Further, the ROS control unit 104 determines whether or not the cyan exposure correction value ΔC is within a predetermined range −0.05 ≦ ΔC ≦ 0.05, and the cyan exposure correction value ΔC. Is within the predetermined range −0.05 ≦ ΔC ≦ 0.05, the cyan (C) latent image exposure scheduled output is set to ROS4 as the latent image exposure output, and image exposure is performed. Execute.

  If the cyan exposure correction value ΔC is not within a predetermined range of −0.05 ≦ ΔC ≦ 0.05, is the cyan exposure correction value ΔC greater than 0 (positive or negative)? ) If the cyan exposure amount correction value ΔC is equal to or greater than 0, a value obtained by adding 0.05 to the previous cyan latent image exposure scheduled output is set to the current latent image exposure output. Is set to ROS4, and image exposure is executed. When the cyan exposure correction value ΔC is 0 or less (negative), a value obtained by subtracting 0.05 from the previous cyan latent image exposure planned output is used as the current latent image exposure output. It is set to ROS4 and image exposure is executed.

  Next, in order to compensate for the exposure amount corrected by the ROS 4, the color that has been down-corrected with respect to the exposure amount candidate value increases the toner density according to the down amount, and the color that has been up-corrected The toner density is reduced according to the amount.

  At this time, the toner density change amount is calculated by the toner density correction calculation unit 103 using coefficients Y2, M2, and C2 of 1 or less (for example, around 0.5) so that the toner density is not over-controlled. (Step 104).

  In the above example, the correction value ΔM for the magenta (M) color exposure amount should be “+0.1”, but is limited to “+0.05”, and the cyan (C) color exposure amount correction is performed. The value ΔC is limited to “−0.05” where it should be “−0.1”. Therefore, the magenta (M) exposure value correction value ΔM is down-corrected from “+0.1” to “+0.05”, and the cyan (C) exposure value correction value ΔC is “−0”. .1 "" to "-0.05".

  Accordingly, the magenta (M) color whose exposure amount correction value ΔM is down-corrected is corrected by the toner concentration correction calculation unit 103 so as to increase the toner concentration, and the exposure amount correction value ΔC is up-corrected cyan. (C) The color is corrected so as to lower the toner density. At this time, the toner density is calculated by using predetermined coefficients Y2, M2, and C2 (for example, around 0.5) that are equal to or less than 1 in accordance with the exposure value correction value.

  The threshold values ΔYM1, ΔMC1, ΔCY1, and / or the predetermined coefficient may be appropriately changed according to environmental conditions such as temperature and humidity in the apparatus and conditions of the apparatus such as the number of prints.

  As described above, in the full-color printer according to the above-described embodiment, the image by the ROS 4 is based on the density detection results of the first test patches 60Y, 60M, 60C, and 60K and the second test patches 61Y, 61M, 61C, and 61K. When controlling the exposure amount and toner density, if a threshold value is set for the correction value of the image exposure amount of each color by the ROS 4 and all the conditions below the threshold value are satisfied, the latent image exposure scheduled output for each color is output as it is. When the image exposure is performed by setting as the latent image exposure output of each color and any one of the conditions equal to or less than the threshold is not satisfied, the correction value of the image exposure amount of each color by the ROS 4 is limited to a certain value. In this state, image exposure is performed by setting the latent image exposure output for each color.

  Therefore, the full color printer can maintain a stable color balance. Further, when limiting the image exposure amount control by the ROS 4 and the image exposure amount control by the ROS 4, the toner density is controlled in accordance with the exposure amount limit. By adjusting the density, it is possible to maintain a stable color balance, reduce the amount of toner consumed in addition to printing, reduce the time required to control process conditions, and improve productivity. It has become.

FIG. 1 is a block diagram showing a main part of a full-color printer as a color image forming apparatus according to Embodiment 1 of the present invention. FIG. 2 is a block diagram showing a full-color printer as a color image forming apparatus according to Embodiment 1 of the present invention. FIG. 3 is a block diagram showing a full-color printer as a color image forming apparatus according to Embodiment 1 of the present invention. FIG. 4 is an explanatory diagram showing a test patch. FIG. 5 is a flowchart showing the control operation of the full-color printer as the color image forming apparatus according to Embodiment 1 of the present invention. FIG. 6 is an explanatory diagram showing the control operation of the full-color printer as the color image forming apparatus according to Embodiment 1 of the present invention.

Explanation of symbols

  4: ROS, 23: ADC sensor, 60, 61: test patch, 103: toner density correction calculation unit, 104: ROS control unit.

Claims (6)

The density detection unit detects the density of the density detection pattern formed on the detection medium, and controls the toner density control amount of the developing unit corresponding to a plurality of colors and the image exposure unit based on the detection result of the density detection unit. In a color image forming apparatus in which an exposure amount is controlled by a control means to form an image,
The control unit calculates a control amount candidate value of the toner density of the developing unit and an exposure amount candidate value of the image exposure unit corresponding to a plurality of colors based on the detection result of the density detection unit, and changes the exposure amount candidate value. It is determined whether or not the absolute value of the difference between a plurality of colors is equal to or smaller than a threshold value. If the absolute value of the difference exceeds the threshold value, the exposure amount correction value is within a predetermined range. A color image forming apparatus that limits and compensates the limited exposure amount correction value by correcting a control amount of toner density. The control means compensates for the correction value of the toner density control amount that compensates for the correction value of the limited exposure amount when the control amount of the toner density is corrected in order to compensate the correction value of the limited exposure amount. 2. The color image forming apparatus according to claim 1, wherein a value obtained by multiplying a predetermined coefficient is used as a correction value for the toner density control amount. The color image forming apparatus according to claim 2, wherein the predetermined coefficient is set to a value of 1 or less. 4. The threshold value provided for the absolute value of the difference between the colors of the change amount of the exposure amount candidate value is variable according to changes in the environment and the apparatus over time. 5. The color image forming apparatus described. 5. The color image forming apparatus according to claim 2, wherein the predetermined coefficient is variable according to a change with time of an environment or the apparatus. When the absolute value of the difference exceeds a threshold value, the exposure amount correction value is limited within a predetermined range, and is limited in a state where priority is given between the plurality of colors. The color image forming apparatus according to claim 1.

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