JP2007155971A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus, capable of reducing consumption of image forming material used for detecting color shift amount and density, accurately detecting color shift and inappropriate density, and correcting the color shift and the density. <P>SOLUTION: The image forming apparatus has an image-carrying means, on the surface of which an image is carried based on image data, and an intermediate transfer means, to which the image carried on the image carrying means is transferred. Whether a color shift detection, suitable area suitable for detecting the color shift caused when the image is transferred to the intermediate transfer means exists in the image, is decided based on the image data. When a color shift detection suitable area deciding means decides that the color shift detection suitable area exists therein, the color-shift amount of the image in the color shift detection appropriate area is detected. When the color-shift amount is detected, image quality is corrected based on the color shift amount. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that detects a color misregistration amount or an inappropriate density and corrects the color misregistration or density.

  In recent years, image forming apparatuses such as printers capable of forming color images have become common. In order to form an image in color, since four types of toner (CMYK) are usually used, it takes more time than monochrome printing. Therefore, in order to further increase the image formation speed, a tandem engine system that sequentially forms an image using a drum corresponding to each color toner of CMYK has been rapidly widespread in recent years. Since the image forming positions of the drums are different, color misregistration is likely to occur and the density may not be appropriate. Various methods for preventing this have been proposed.

  In order to prevent problems related to color misregistration and density, it is necessary to detect and correct them. The process of reliably detecting and correcting can be performed by a dedicated cycle for image quality correction established by conventional techniques. However, the cycle dedicated to image quality correction, for example, interrupts image formation and draws a color misregistration detection pattern on the entire circumference of the belt to detect the color misregistration amount and improper density and perform image quality correction. This is a relatively large process such as consuming a large amount of toner.

  In order to prevent color misregistration and improper density only by this image quality correction cycle, it is only possible to check by executing the image quality correction cycle even when no color misregistration actually occurs. In this case, toner is completely wasted and printing is interrupted. Therefore, preventing color misregistration and the like by only the image quality correction cycle causes inconvenience to users and waste of resources.

  Therefore, it is important to determine in advance whether it is necessary to execute a cycle dedicated to image quality correction.

  Japanese Patent Application Laid-Open No. 2004-133826 detects and selects a region including a reference color and other color components from a printed image, and compares the result detected by the color misregistration detection sensor with the data in the image memory. A method for detecting and correcting a relative color shift amount is disclosed.

  Since the detection or correction cycle in Patent Document 1 can be executed without the need for a detection pattern or cycle dedicated for color misregistration adjustment during normal image formation, it is possible to prevent consumption of toner other than the customer image, and after assembly and installation. Does not cause a drop in productivity. In addition, when a large color shift is predicted such as when the apparatus is assembled or installed, a conventional dedicated color shift adjustment cycle is executed. As the detection sensor, use of a density sensor or a line sensor that covers the entire image width in the main scanning direction has been proposed.

  Patent Document 2 discloses a tandem engine system that has means for determining the execution timing of a color misregistration adjustment cycle. The process disclosed in Patent Document 2 is a process for forming a color misregistration detection pattern dedicated to a color misregistration detection sensor between print images (interimages) that are continuously formed on a belt.

The detection patterns are formed by different image forming engines, but are physically located at the same position, and the detected width is compared with a reference width to determine whether or not color misregistration has occurred. When it is determined that color misregistration correction is necessary, image formation is interrupted and a dedicated color misregistration correction cycle is executed.
JP 2003-005481 A JP 2003-098794 A

  However, the above-mentioned Patent Documents 1 and 2 have the following problems and do not exhibit sufficient effects in practice.

  In the method disclosed in Patent Document 1, when the detection sensor is replaced with a density detection sensor arranged in the vicinity of the center of the image width, a density detection sensor different from the color shift detection application is used even if the color shift amount can be detected. Since it is used, in fact, high-precision detection cannot be expected.

  Further, in the method described in Patent Document 2, although the problem of accuracy is solved by using a sensor and pattern dedicated to color misregistration, a dedicated color misregistration detection pattern is always required. Regardless, toner is always consumed.

  In view of the above problems, the present invention reduces the amount of image forming material used for color misregistration and density detection, and detects color misregistration and improper density with high accuracy, and corrects color misregistration and density. An object is to provide a forming apparatus.

  In order to achieve the above object, the invention of claim 1 is based on image data, an image carrying means for carrying an image on the surface, and an intermediate transfer means for transferring the image carried on the image carrying means. In the image data, whether or not a color misregistration detection suitable region suitable for detecting a color misregistration amount generated when the image is transferred to the intermediate transfer unit exists in the image transferred to the intermediate transfer unit. When the color misregistration detection suitable area is determined by the color misregistration detection suitable area judging means and the color misregistration detection suitable area judging means determines that the color misregistration detection suitable area exists, A color misregistration detecting unit that detects the color misregistration amount, and an image quality correcting unit that corrects the image quality based on the color misregistration amount when the color misregistration detection unit detects the color misregistration amount.

  In this case, the image forming apparatus according to the first aspect includes an image carrying unit that carries an image on the surface and an intermediate transfer unit that transfers an image carried on the image carrying unit based on image data. Whether or not there is a color misregistration detection suitable area suitable for detecting the amount of color misregistration generated when the image is transferred to the intermediate transfer means is determined based on the image data, and the color misregistration detection suitable area is determined. When it is determined by the means that the color misregistration detection suitable region exists, the color misregistration amount of the image in the color misregistration detection suitable region is detected, and when the color misregistration amount is detected, the image quality is determined based on the color misregistration amount. Therefore, since the toner dedicated to the color misregistration detection sensor described in Patent Document 2 is not consumed, the toner consumption can be reduced and the color misregistration amount can be detected accurately to correct the color misregistration. it can.

  According to a second aspect of the present invention, the color misregistration detection suitable area judging means includes a plurality of independent partial areas configured with different colors, and the color of the partial area is between the partial areas. A region where partial regions of different colors exist is determined as the color misregistration detection suitable region.

  In this case, in the image forming apparatus according to claim 2, the image forming apparatus includes a plurality of independent partial areas configured in different colors, and a partial area having a color different from the color of the partial area exists between the partial areas. Since the area to be used is the color misregistration detection matching area, an area for accurately detecting the color misregistration amount can be obtained.

  According to a third aspect of the present invention, the image data includes color misregistration detection data for carrying an image for color misregistration detection in a margin area, and the color misregistration detection suitable area judging means determines the margin area as the color area. Judged as a deviation detection compatible area.

  Here, in the image forming apparatus according to the third aspect, detection with higher accuracy can be performed by the data for detecting color misregistration.

  According to a fourth aspect of the present invention, the density detection adapted to determine whether or not a density detection suitable region suitable for detecting the density of the image exists in the image transferred to the intermediate transfer means based on the image data. An area determination unit; and a density detection unit that detects a density of an image in the density detection compatible region when the density detection compatible region is determined to exist by the density detection compatible region determination unit, and the image quality The correction unit corrects the image quality based on the density when the density detected by the density detection unit is not appropriate.

  In the image forming apparatus according to the fourth aspect of the present invention, an inappropriate density is detected without always using a toner for detecting the density. Therefore, the amount of toner used for density detection is reduced and the accuracy is improved. It is possible to detect an inappropriate density and correct the density.

  According to a fifth aspect of the present invention, the density detection suitable area judging means judges a single color area included in an area detectable by the density detecting means as the density detection suitable area.

  Here, in the image forming apparatus according to the fifth aspect, since the monochrome area is set as the density detection suitable area, it is possible to obtain an area for detecting the density with high accuracy.

  According to a sixth aspect of the present invention, the image data includes density detection data for carrying an image for density detection in a blank area, and the density detection suitable area judging means determines the blank area as the density detection suitable area. Judge.

  In the image forming apparatus according to the sixth aspect of the present invention, more accurate detection is possible by using the density detection data.

According to a seventh aspect of the present invention, there is provided an image carrying means for carrying an image on a surface based on image data, a recording medium to which the image carried on the image carrying means is transferred, and the image to the recording medium. Color misregistration detection suitable area determination for judging whether or not a color misregistration detection suitable area suitable for detecting the amount of color misregistration generated when transferred exists in the image transferred to the recording medium based on the image data. And a color misregistration detection unit for detecting a color misregistration amount of an image in the color misregistration detection suitable area when the color misregistration detection suitable area is determined to be present by the color misregistration detection suitable area determination means, The image forming apparatus according to claim 7, further comprising: an image quality correction unit configured to correct an image quality based on the color misregistration amount when the color misregistration amount is detected by the misregistration detection unit. The image Based on the image data, it is determined whether there is a color misregistration detection suitable area suitable for detecting the amount of color misregistration that occurs when it is transferred to the surface of the recording medium. When it is determined that a misregistration detection compatible area exists, the color misregistration amount of the image in the color misregistration detection suitable area is detected, and when the misregistration amount is detected, the image quality is corrected based on the color misregistration amount. Therefore, since the toner dedicated to the color misregistration detection sensor described in Patent Document 2 is not consumed, the toner consumption can be reduced, the color misregistration amount can be detected with high accuracy, and the color misregistration can be corrected.

The invention according to claim 8 is based on image data and is adapted to detect a color shift suitable for detecting a recording medium on which an image is formed on a surface and an amount of color shift generated when the image is formed on the recording medium. Color misregistration detection suitable area judging means for judging based on the image data whether the area exists in the image formed on the recording medium, and the color misregistration detection suitable area judging means A color misregistration detecting means for detecting the color misregistration amount of the image in the color misregistration detection suitable area when it is determined that the color misregistration detection area is present; And an image quality correction unit configured to correct the image quality based on the image data. The image forming apparatus according to claim 8, wherein the color misregistration amount generated when the image is formed on the surface of the recording medium based on the image data. Color suitable for detection It is determined based on the image data whether or not a misregistration detection compatible area exists in the image formed on the recording medium, and when it is determined by the color misregistration detection suitable area determination means that a color misregistration detection suitable area exists, Since the color misregistration amount of the image in the color misregistration detection compatible region is detected and the color misregistration amount is detected, the image quality is corrected based on the color misregistration amount. Therefore, it is possible to reduce the consumption of the image forming material, detect the color misregistration amount with high accuracy, and correct the color misregistration.

  According to the present invention, an image forming apparatus that reduces the amount of image forming material used for color misregistration amount and density detection, detects color misregistration and inappropriate density accurately, and corrects color misregistration and density. Can be provided.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic diagram showing the overall configuration of the image forming apparatus according to the present embodiment. As shown in FIG. 1, the image forming apparatus 1 includes an image reading unit 2, an image forming unit 3, and a sheet conveying device 4.

  The image reading unit 2 reads an image of a document set on a transparent document table (platen glass). The image reading unit 2 includes, for example, an optical scanning system including a lamp, a mirror, a carriage, and the like, a lens system that forms an optical image read and scanned by the optical scanning system, and an optical image formed by the lens system. And an image reading sensor (for example, RGB 3-line CCD sensor) that receives the light and converts it into an electrical signal.

  The image forming unit 3 forms an image by a general electrophotographic method, and corresponds to the exposure device 10 and each color of K (black), Y (yellow), M (magenta), and C (cyan). Photosensitive drums 10A, 10B, 10C, and 10D, developing devices 10a, 10b, 10c, and 10d corresponding to the respective photosensitive drums, an intermediate transfer belt 15, a secondary transfer roller 20, a vacuum conveyance unit 45, a fixing unit The tandem type configuration is provided with a device 46. The photosensitive drum corresponds to an image carrying unit, and the intermediate transfer belt corresponds to an intermediate transfer unit.

  The toner images carried on the photosensitive drums 10A, 10B, 10C, and 10D are transferred (primary transfer) to the intermediate transfer belt 15. The intermediate transfer belt 15 is looped around a plurality of support rollers. The secondary transfer roller 20 is disposed so as to face the intermediate transfer belt 15. The secondary transfer roller 20 transfers the toner image formed on the intermediate transfer belt 15 to the paper (secondary transfer) as described above, and the transfer position (secondary transfer position) of the toner image is the image formation. This is the image output position in the unit 3.

  Further, the image forming unit 3 includes a sensor 12. The illustrated sensor 12 includes two color misregistration detection sensors and one density detection sensor. Details of these sensors will be described later.

  The vacuum conveyance unit 45 conveys the sheet on which the toner image is transferred by the secondary transfer roller 20 to the fixing device 46. The fixing device 46 fixes the toner image on the paper by heating and pressing.

  On the other hand, the paper transport device 4 uses the paper in the tray selected by the user operation or the automatic selection function from among the papers stored in the first tray 50, the second tray 51, and the third tray 52. Each sheet of the selected tray is conveyed by a predetermined route. In the vicinity of each of the trays 50, 51, 52, corresponding delivery rollers 53, 54, 55 are disposed.

  Each of the delivery rollers 53, 54, and 55 is configured to pinch (nip) the paper that is separated and delivered from the corresponding trays 50, 51, and 52, and send the paper downstream in the paper conveyance direction. is there. Further, in the vicinity of the image reading unit 2, an operation panel 56 operated by the user and a control unit 40 for controlling each unit of the image forming apparatus are provided.

  Here, a series of paper transport paths R1 to R5 from the paper delivery position by the delivery rollers 53, 54, 55 to the discharge tray 57 via the image output position in the image forming unit 3 are respectively provided for the paper. Rollers for conveyance are provided as appropriate. The paper stored in the first tray 50 is sent out by the feed roller 53 and then sent to the merging / conveying section 58 via the first paper transport path R1. The paper stored in the second tray 51 is sent out by the feed roller 54 and then sent to the merging / conveying section 58 via the first paper transport path R1. On the other hand, the paper stored in the third tray 52 is sent directly to the merging and conveying unit 58 by the delivery roller 55.

  Further, the sheet sent to the merging / conveying unit 58 is sent to the image output position of the image forming unit 3 after the orientation of the sheet is adjusted via the second sheet conveying path R2. Further, the paper that has passed through the image output position is sent to the fixing device 46 by the vacuum transport unit 45 and then discharged to the discharge tray 57 via the third paper transport path R3. On the other hand, the sheet on which images are formed on both sides (the first side and the second side) passes through the fixing unit 46 and is sent to the double-side reversing unit 59 via the fourth sheet conveyance path R4. Then, after being turned upside down, the paper is again fed into the merging and conveying unit 58 via the fifth sheet conveying path R5.

  In such paper transport paths R1 to R5, a paper alignment section 60 and a registration roller 61 are disposed in the second paper transport path R2. The sheet aligning unit 60 is a part that performs skew correction of the sheet conveyed along the second sheet conveyance path R2. The sheet aligning unit 60 includes, for example, an aligning mechanism that reduces the side skew of the conveyed sheet and a side shift mechanism that performs side registration control of the conveyed sheet.

  The registration roller 61 is composed of a pair of rollers held in pressure contact with each other. The sheet is sandwiched between the pair of rollers, and the sheet is fed to the image output position by the rotation of the roller.

  When the sheet is fed by the registration roller 61, the timing of arrival of the sheet with respect to the image output position is adjusted by a timing adjusting unit (not shown). The timing adjusting unit varies the sheet conveyance speed by the registration roller 61 based on the timing at which a registration sensor (not shown) provided in front of the registration roller 61 (upstream side) detects the passage of the sheet. The servo registration mechanism adjusts the arrival timing of the paper at the image output position in accordance with the arrival timing of the toner image at the output position.

  That is, the sheet aligning unit 60 and the timing adjusting unit are controlled by the control unit 40 and operate to correct the sheet skew, the drawing timing, and the sheet transport timing.

  In addition, curl correction units 62 and 63 are provided in the paper transport paths R3 and R5, respectively. Each of the curl correction units 62 and 63 is for correcting a curl of the paper that occurs when the fixing device 46 fixes the toner image.

  The sheet aligning unit 60, the registration roller 61, the secondary transfer roller 20, the vacuum conveying unit 45, and the fixing unit 46 arranged along the second sheet conveying path R2 are arranged in the same casing, and are conveyed with the conveying module. (Not shown) is configured. The transport module is configured to be detachable from the frame of the image forming unit 3 so that paper remaining due to paper jam or the like can be removed. The transport module is configured to be pulled out to the front side of the drawing, for example.

  Next, the operation of the image forming apparatus 1 configured as described above will be described. First, when an image of a document is read by the image reading unit 2, a toner image is formed by the image forming unit 3 based on an image signal obtained thereby. In the image forming unit 3, the toner images of the respective colors carried by the four photosensitive drums 10 </ b> A, 10 </ b> B, 10 </ b> C, and 10 </ b> D are sequentially transferred onto the intermediate transfer belt 15. As a result, a multicolor (full color) toner image is formed on the intermediate transfer belt 15 by superimposing four color toners. The toner image transferred to the intermediate transfer belt 15 in this way is carried on the intermediate transfer belt 15 and sent to the image output position (secondary transfer position).

  On the other hand, the tray paper selected by the user using the operation panel 56 or the tray paper selected by the automatic selection function is fed by the registration roller 61 in accordance with the timing at which the toner image reaches the image output position. Thereby, at the image output position of the image forming unit 3, the toner image carried on the intermediate transfer belt 15 is collectively transferred (secondary transfer) onto the paper by the secondary transfer roller 20. Thereafter, the sheet is sent to the fixing unit 46 by the vacuum conveyance unit 45, where the toner image is fixed, and then discharged to the discharge tray 57 via the third sheet conveyance path R3.

  Further, the sheet on which the image is formed on both sides is sent to the double-side reversing unit 59 via the fourth sheet conveyance path R4, and is turned upside down and sent to the fifth sheet conveyance path R5. Thereafter, the sheet is conveyed along the fifth sheet conveyance path R5, and then the timing is adjusted by the rotation of the delivery roller 69, and the sheet is fed again to the merging and conveying unit 58. Thereafter, after the toner image is transferred and fixed on the paper in the same manner as described above, the paper is discharged to the discharge tray 57 via the third paper transport path R3.

  Next, the color misregistration detection sensor and the density detection sensor will be described. FIG. 2 is a diagram illustrating the color misregistration detection sensor, the density detection sensor, and the periphery thereof. FIG. 3 is a diagram showing a perspective view of FIG. 2 viewed from the sub-scanning direction. In FIG. 2, the color misregistration detection sensors 12A and 12B, the density detection sensor 12C, the exposure device 10, the photosensitive drums 10A, 10B, 10C, and 10D, the developing devices 10a, 10b, 10c, and 10d, and the intermediate transfer belt are illustrated. 15 and an image formation controller 16 are shown. Of these, the color misregistration detection sensors 12A and 12B correspond to the color misregistration detection means, and the density detection sensor 12C corresponds to the density detection means.

  The image formation control unit 16 controls the entire image formation unit 3 (see FIG. 1), and includes a CPU, a RAM, a ROM, and the like. The image formation control unit 16 according to the present exemplary embodiment determines whether the toner image has a color misregistration detection suitable region suitable for detecting the color misregistration amount generated when the toner image is transferred to the intermediate transfer belt 15. Judgment based on data. Further, the image formation control unit 16 determines whether or not a density detection suitable region suitable for detecting the density of the toner image exists in the toner image transferred to the intermediate transfer belt 15 based on the image data.

  The image quality correction process executed by the image formation control unit 16 is an image quality correction unit that corrects the image quality based on the detected color misregistration amount when the color misregistration detection sensors 12A and 12B detect the color misregistration amount. Corresponding to Further, the image quality correction process executed by the image formation control unit 16 corresponds to an image quality correction unit that corrects the image quality based on the detected density when the density detected by the density detection sensor 12C is not appropriate.

  Details of the determination of the color misregistration amount and the density detection suitable region and the correction of the image quality described above will be described later.

  As shown in FIG. 3, the color misregistration detection sensors 12A and 12B and the density detection sensor 12C can detect a region immediately below. Note that areas A, B, and C shown in FIG. 3 are areas that can be detected by the color shift and density detection sensors. Specifically, the area A indicates an area that can be detected by the color misregistration detection sensor 12A. A region B indicates a region that can be detected by the color misregistration detection sensor 12B. A region C indicates a region that can be detected by the density detection sensor 12C. The number of these regions increases or decreases depending on the number of sensors. In addition, the width of each region is usually set differently depending on the color shift and density detection sensor.

  The color misregistration detection sensors 12A and 12B detect the color misregistration amount of the toner image in the color misregistration detection suitable area when the image forming control unit 16 determines that the color misregistration detection suitable area exists. By this detection, the color misregistration detection sensors 12A and 12B are decomposed into each component of the color misregistration amount (main scanning position deviation, sub-scanning position deviation, skew deviation, magnification deviation, etc.) based on the detected information.

  The density detection sensor 12C can detect a region immediately below, as shown in FIG. Further, the density detection sensor 12C detects the density of the toner image in the density detection compatible area when the image formation control unit 16 determines that the density detection compatible area exists. Further, the density of the toner image detected by the density detection sensor 12C in the present embodiment is used for adjustment of gradation of each color and adjustment of density maintenance, particularly when a pattern dedicated to the density detection sensor 12C is detected. Is capable of highly accurate detection.

  The density detection sensor 12C may be shared with the color misregistration detection sensors 12A and 12B described above, or may be disposed individually. However, in the case of sharing, it is a dedicated sensor that can detect both the density and the amount of color misregistration with high accuracy while requiring different dedicated patterns.

  The determination of the color misregistration and density detection suitable area described above and the configuration of the image forming unit 3 that detects the color misregistration amount and density will be described with reference to FIG.

  FIG. 4 is a block diagram of the image forming unit 3. FIG. 4 shows the control unit 40 (see FIG. 1) and the image forming unit 3. The image forming unit 3 further includes a video board 32, ROS (Raster Output Scanner) 26Y, 26M, 26C, and 26K, a sensor control unit 28, color misregistration detection sensors 12A and 12B, and a density detection sensor 12C. ing. Among these, the video board 32 and the sensor control unit 28 are included in the image formation control unit 16.

  The video board 32 will be described. The video board 32 receives image data of each color sent from the control unit 40 to the image forming unit 3 and includes screen generation units 22Y, 22M, 22C, and 22K, and a detection suitable region determination unit 24. .

  Each screen generation unit is provided corresponding to each color of YMCK and generates a screen of image data of each color in a RAM (not shown), and the generated screen is output to each corresponding ROS.

  The detection suitable region determination unit 24 includes pixel counters 24Y, 24M, 24C, and 24K, a region A determination unit 24A, a region B determination unit 24B, and a region C determination unit 24C. The region A determination unit 24A and the region B determination unit 24B correspond to the color misregistration detection suitable region determination unit, and the region C determination unit 24C corresponds to the density detection detection region determination unit.

  The pixel counter is provided corresponding to each color of YMCK, and counts the number of pixels that are not white among the pixels in the regions A, B, and C from the screen-generated image.

  The region A determination unit 24A and the region B determination unit 24B determine whether the corresponding region is a color misregistration detection suitable region based on the pixel count value counted by the pixel counter and the color of the pixel. The region C determination unit 24C determines whether the region C is a density detection suitable region based on the pixel count value counted by the pixel counter and the pixel color.

  In this embodiment, the pixel count value is the number of pixels that display one of CMYK colors among the pixels on the scanning line in the main scanning direction.

  The determination results obtained by the respective determination units described above are output to the sensor control unit 28, and the sensor control unit 28 controls the color misregistration detection sensors 12A and 12B and the density detection sensor 12C based on the determination results.

  The above is the configuration of the image forming apparatus according to this embodiment. Next, color misregistration and density detection suitable area determination processing, color misregistration amount and density detection processing, and color misregistration and density correction processing executed in accordance with these configurations will be described in order.

  First, the determination process of the color misregistration and density detection suitable region will be described. This process is executed by the area A determination unit 24A, the area B determination unit 24B, and the area C determination unit 24C as described above.

  The determination of whether or not it is a color misregistration detection suitable region includes a plurality of independent partial regions that are included in a region that can be detected by the color misregistration detection sensor and are configured with different colors, and the partial regions between the partial regions An area where a partial area of a color different from the color of the color exists is determined as a color misregistration detection matching area.

  A specific example will be described with reference to FIG. The area within the rectangle shown in FIG. 4 is an area that can be detected by the color misregistration detection sensor. In addition, partial areas 34A, 34B, and 34C are included in the rectangle. For example, the partial area 34A is a partial area of one magenta color, and the partial area 34B is a partial area of one black color, for example. The partial region 34C is a region that is not printed, for example.

  As shown in the figure, the partial areas 34A and 34B are a plurality of independent partial areas each having the same color and different colors. A partial region 34C having a color different from the color of the partial region is present between the partial regions 34A and 34B. Such a region is a color misregistration detection matching region.

  Next, the determination of whether or not it is a density detection compatible region will be described. The density detection suitable area is an area including the effective detection area of the density detection sensor to be used. As an example, when the effective detection area of the density detection sensor is 5 mm square and the output resolution of the image forming apparatus is 2400 dpi, 472 pixels (= 2400 dpi ÷ 25.4 mm × 5 mm) are pixels on the main scanning and sub-scanning lines. Number.

  For accurate density detection, it is necessary to enlarge the area slightly in consideration of the color shift, but if the area is made too large, the probability of recognizing it as a detectable area is reduced. It is desirable to keep it in pixels.

  Since the density of the area thus determined as the density detection suitable area is obtained according to the number of pixels existing in the pixel count area independent for each color, the density is recognized as the density detected by the density detection sensor. .

  Note that it is not possible to determine for each color whether the density detection sensor should actually detect. This is because the density detection sensor can detect the density of a single-color image, but it is extremely difficult to separate the density states of each engine when two colors, three colors, and four colors overlap.

  Therefore, in the determination in the present embodiment, a single-color area where no density of other colors exists is determined as the density detection suitable area from the density on the image data recognized for each color.

  As an example, if the color composition of the area is Y color = 40%, M color, C color, and K color = 0% (yellow), it is determined as a Y color density detection suitable area. In addition, when Y color, M color = 30%, and C color, K color = 0% (red), this region is not determined as a density detection suitable region.

  In this embodiment, an image exists when image data of a certain color is other than 0%. However, in an actual electrophotographic method, image data of several percent or less may not be developed. Is preferably selected as appropriate.

  Based on the color shift and density detection suitable area determination described above, it is determined whether there is a color shift detection sensor or an area that can be detected by the density detection sensor.

  In the present embodiment, the video board 32 determines whether the image data drawn in each color area is a single color or two or more colors when formed on a sheet. It is not limited to this. When the original image data is separated into YMCK images by the control unit 40, it may be determined whether the image data is a single color or two or more colors, and output to the image forming unit 3 as tag data attached to the pixel data.

  Next, the color misregistration amount and density detection processing will be described. When the photosensitive drum starts to transfer the toner image to the transfer belt, the color misregistration detection sensors 12A and 12B sequentially determine whether the current color misregistration detection area is a color misregistration detection suitable area, and when the color misregistration detection suitable area appears. Detects the color misregistration amount.

  As an example, a process when there are two partial areas, that is, a determination with two colors will be described. There are six color combinations in the case of two colors: YM, YC, YK, MC, MK, and CK.

  Since these six types of detected color misregistration amounts include periodic components, the error is large as it is. Here, the periodic component depends on, for example, the sizes of the intermediate transfer belt and the photosensitive drum, and a small color shift amount in a certain region, but a large color shift amount in a different region. This is due to the occurrence of variations in the amount of color misregistration.

  Accordingly, since the true color misregistration amount is not known unless it is sampled a certain effective number of times, the average value of the color misregistration amounts is taken. Note that the effective number is, for example, ten times, and is a number depending on the size of the transfer belt and the drum. In this way, the periodic component is removed, and the color shift amount is obtained.

  In the case of the two colors described above, the six color misregistration amounts are sequentially stored in the RAM included in the image formation control unit. Then, it is determined that the average color misregistration amount at the time when the number of appearances of one color set reaches the effective number in at least one color misregistration detection sensor exceeds the color misregistration amount defined in advance by another threshold value. In this case, the image formation control unit 16 instructs execution of a dedicated image quality correction cycle.

  Next, the density detection process will be described. Similar to the color misregistration detection sensor, when the photosensitive drum starts transferring the toner image onto the transfer belt, the density detection sensor sequentially determines whether the current density detection area is a density detection compatible area, and the density detection compatible area appears. Then, the density is detected.

  The density detected by the density sensor has a density of 0% to 100% for each color. Similar to color misregistration detection, each density value is stored in the RAM each time the density is detected as data for each density of each color.

  Again, in order to ensure the accuracy of the density to be detected, the process is repeated until the number of times each density is detected reaches the effective number. When the number of effective times is reached, a density value obtained by averaging the density values is obtained, and compared with the density value obtained in the image data, if it is determined that there is a difference greater than the specified density value, the image formation control unit 16 designates execution of an image quality correction cycle.

  In addition, as an object to be compared with the averaged density, the density value obtained in the above-described image data may be an ideal value detected by the density detection sensor for each ideal density patch, It may be a value that holds the result of a gradation density detection cycle that is executed in advance when the image forming apparatus is powered on.

  The gradation density cycle may be 1%. However, for example, a single color patch of each color is formed in 10% increments, and the density value of the density detection sensor that detects the single color patch is held. For example, in the case of 10% increments, the density value may be defined as 10%, 20%,.

  Next, a dedicated image quality correction cycle will be described. This dedicated cycle for image quality correction is a dedicated cycle established by conventional techniques. This cycle dedicated to image quality correction may be either a cycle in which image formation is interrupted and a dedicated color misregistration detection pattern is drawn on the entire circumference of the belt or a dedicated color misregistration detection pattern is drawn on an inter image. This is detected by detecting the pattern.

  As described above, the color misregistration detection sensor decomposes each component of the color misregistration amount (main scanning position deviation, sub-scanning position deviation, magnification deviation, skew deviation, etc.), and correction corresponding to these components is performed. For the correction of each component of the color misregistration amount, a conventionally used one is used.

  For example, the correction for the main scanning position deviation is performed by adjusting the delay amount from the laser beam reference signal (SOS signal). Correction for the sub-scanning position shift is performed by shifting the image writing timing. Correction for magnification shift is performed by controlling the frequency of the video clock. Correction for the skew deviation is performed by a method of mechanically adjusting the angle of the optical system mirror inside the ROS. In addition to the above correction, the image data itself may be deformed.

  The series of processes described above will be described using the flowchart of FIG. This flowchart is started when image data is input from the control unit 40 to the video board 32.

  Step S101 is processing for determining whether image data has been input from the control unit 40. When the image data is input, in step S102, color misregistration and density detection suitable area determination processing is performed based on the image data. In the next step S103, it is determined whether or not there is a color misregistration and density matching area by color misregistration and density matching area judgment processing. If not, the color misregistration amount and density detection processing is not performed, and the processing proceeds to step S111.

  If there is a color misregistration and density matching region, a toner image transfer start wait is performed in step S104, and when the toner image transfer is started, color misregistration amount and density detection processing is performed in step S105. When this process ends, it is determined whether the color misregistration amount and the number of density detections are equal to or greater than the effective number. If the number of effective times is not reached, the process returns to step S101 to perform the process for the next image data.

  If the color misregistration amount and the density detection count are equal to or greater than the effective count, it is determined in step S107 whether the average value of the color misregistration amount and the average value of the density values satisfy predetermined values. If the predetermined value is satisfied, the process proceeds to step S111.

  If the predetermined value is not satisfied, the job is interrupted in step S108, and an image quality correction cycle is executed in step S109. Thereafter, the job suspended in step S110 is resumed.

  In step S111, it is determined whether all jobs have been completed. If not, the process proceeds to step S101 again.

  The above is a series of processing of this embodiment. Two processes described below are processes to which the above processes are applied. One is processing performed when printing on a sheet to be cut, and the other is processing performed when a page is printed.

  First, processing performed in the case of printing on a sheet to be cut will be described. Recent image forming apparatuses use a finisher such as staples or punches in addition to standard sheets (A4, A3, etc.) that have been generally used so far, and then form a margin area of the sheet after binding a plurality of pages. It is also used for cutting and finishing on booklets.

  Therefore, as shown in FIG. 7, the image data used for the above-mentioned application includes data indicating a so-called register mark 38 in the blank area of the sheet so as to be a guide for cutting. In addition, data indicating the color patch 36 as color misregistration detection data such as a secondary color and a tertiary color as well as a single color is included so that the density of each color in the margin area can be confirmed visually or with an off-line densitometer. It is often done.

  Therefore, a region indicating a registration mark or a color patch included in these image data is set as a color misregistration detection matching region, and as shown in FIG. 8, sensors (density detection sensors may be used) at both ends outside the A3 size region. ). In this way, the color misregistration detection process described above is performed.

  Next, processing performed when a page is printed will be described. A page can be printed on an image in an image forming apparatus as well as an application such as a word processor.

  Therefore, the control unit 40 or the above-described video board 32 or the application software to be output can be printed by adding a character string such as a page and printing date and time as shown in FIG. These allow not only numbers but also symbols such as “<”, “>”, “<”, “■” to be printed before and after the numbers. In FIG. 9, 4, <4>, (1), (1), etc. are shown as page printing examples. Other than these, = 1 =, = 2 =, and the like may be used. As shown in FIG. 10, if the areas where such pages are printed are printed in areas 42 </ b> A to 42 </ b> F that can be detected by the sensors, the areas where the pages are printed are shifted in color shift and density. It can be a detection compatible region.

  The numbers and symbols to be added are not limited to those described above as long as they can be easily read by the color misregistration detection sensor or the density detection sensor.

  According to the two application examples described above, the color patch for color misregistration detection significantly improves the appearance frequency of a desired image at the time of color misregistration detection and density detection, thereby enabling more reliable detection. Further, by using an image printed every time such as a page, the appearance frequency of a desired image at the time of color misregistration detection or density detection is remarkably improved, and more reliable detection is possible. Further, compared to a case where a dedicated pattern is provided and waste toner is used, added value can be given.

  In addition, according to the present embodiment, the color misregistration check or the density check is performed on an arbitrary image printed by the user, and an instruction for executing a dedicated cycle is issued based on the result. The density adjustment execution timing can be limited to when it is really necessary, and wasteful toner consumption can be prevented. In addition, since the detection result in a dedicated cycle is used at the time of actual correction, the color misregistration amount and density correction error can be suppressed as much as possible, and high-quality image output is always possible.

  The image forming apparatus according to the present embodiment described above is an image forming apparatus provided with color misregistration detection means such as an intermediate transfer belt system (Imari / SFIDA), a paper transport belt system, or an intermediate transfer roll system (Ginga). Any device may be used.

  Further, in the present embodiment, correction was made regarding the color misregistration amount and density of the toner image transferred to the intermediate transfer belt, but the toner image carried on the photosensitive drum is directly transferred to the recording medium. The present invention can also be applied to an image forming apparatus having a configuration. Specifically, as in the case of the intermediate transfer belt, a color misregistration amount and density may be detected and corrected using a toner image directly transferred to a recording medium such as paper.

  Furthermore, in the present embodiment, the image is described as a toner image, but the present embodiment can also be applied to an image forming apparatus that forms an image using droplets such as ink droplets. Specifically, as in the case of the toner image, the color misregistration amount and density may be detected and corrected using an image formed by droplets such as ink droplets. That is, the image forming material used by the image forming apparatus may be ink droplets as well as toner.

  In addition, as long as it is limited to density detection, the image forming apparatus is not necessarily a full-color image forming apparatus, and can be applied to an image forming apparatus such as a two-color machine such as a monochrome machine or a plus 1 color machine. The color misregistration detection need not be full color, and can be applied to a plus one color machine.

1 is a diagram illustrating an image forming apparatus according to an exemplary embodiment. It is a figure which shows a color shift detection sensor and a density | concentration detection sensor, and its periphery. It is a figure which shows a mode that the color misregistration detection sensor and the density | concentration detection sensor were seen from the subscanning direction. 2 is a block diagram of an image forming unit 3. FIG. It is a figure which shows an example of a color shift detection suitable area | region. 3 is a flowchart illustrating processing of the image forming apparatus. It is a figure which shows a register mark and a color patch. It is a figure which shows the position of the sensor at the time of detecting in a blank area | region. It is a figure which shows the example of the printed page. It is a figure which shows the position which prints a page.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 3 Image forming part 10 Exposure apparatus 10A, 10B, 10C, 10D Photosensitive drum 12A, 12B Color shift detection sensor 12C Density detection sensor 15 Intermediate transfer belt 16 Image formation control part 24 Detection suitable area judgment part 24A Area A Determination unit 24B Region B determination unit 24C Region C determination unit 28 Sensor control unit 32 Video board 34A, 34B, 34C Partial region 36 Color patch 38 Dragonfly 40 Control unit

Claims (8)

An image carrying means for carrying an image on the surface based on the image data;
Intermediate transfer means for transferring the image carried on the image carrying means;
Based on the image data, whether or not a color misregistration detection suitable region suitable for detecting a color misregistration amount generated when the image is transferred to the intermediate transfer unit exists in the image transferred to the intermediate transfer unit. Color misregistration detection suitable area judging means for judging,
Color misregistration detection means for detecting the color misregistration amount of an image in the color misregistration detection suitable area when the color misregistration detection suitable area is determined by the color misregistration detection suitable area determination means,
An image quality correction unit that corrects the image quality based on the color misregistration amount when the color misregistration detection unit detects the color misregistration amount;
An image forming apparatus. The color misregistration detection suitable area judging means is
The partial area of the color different from the color of the partial area between the partial areas, including a plurality of independent partial areas that are included in the areas that can be detected by the color misregistration detection unit and that are different from each other. 2. The image forming apparatus according to claim 1, wherein an area in which color misalignment exists is determined as the color misregistration detection matching area.   The image data includes color misregistration detection data for carrying an image for color misregistration detection in a margin area, and the color misregistration detection suitable area judging means judges the margin area as the color misregistration detection suitable area. The image forming apparatus according to claim 1. A density detection suitable area determining means for determining whether a density detection compatible area suitable for detecting the density of the image exists in the image transferred to the intermediate transfer means, based on the image data;
Density detection means for detecting the density of the image in the density detection compatible area when the density detection compatible area is determined to be present by the density detection compatible area determination means;
4. The image forming apparatus according to claim 1, wherein the image quality correction unit corrects the image quality based on the density when the density detected by the density detection unit is not appropriate. 5. The density detection suitable area determination means includes:
The image forming apparatus according to claim 4, wherein a single color area included in an area detectable by the density detection unit is determined as the density detection compatible area. 5. The image data includes density detection data for carrying a density detection image in a blank area, and the density detection suitable area determination unit determines the blank area as the density detection compatible area. The image forming apparatus described. An image carrying means for carrying an image on the surface based on the image data;
A recording medium to which the image carried on the image carrying means is transferred;
Based on the image data, it is determined whether or not a color misregistration detection suitable region suitable for detecting a color misregistration amount generated when the image is transferred to the recording medium is present in the image transferred to the recording medium. Color misregistration detection suitable area determination means to perform,
Color misregistration detection means for detecting the color misregistration amount of an image in the color misregistration detection suitable area when the color misregistration detection suitable area is determined by the color misregistration detection suitable area determination means,
An image quality correction unit that corrects the image quality based on the color misregistration amount when the color misregistration detection unit detects the color misregistration amount;
An image forming apparatus. A recording medium having an image formed on the surface based on the image data;
Based on the image data, it is determined whether a color misregistration detection suitable region suitable for detecting a color misregistration amount generated when the image is formed on the recording medium exists in the image formed on the recording medium. Color misregistration detection suitable area determination means to perform,
Color misregistration detection means for detecting the color misregistration amount of an image in the color misregistration detection suitable area when the color misregistration detection suitable area is determined by the color misregistration detection suitable area determination means,
An image quality correction unit that corrects the image quality based on the color misregistration amount when the color misregistration detection unit detects the color misregistration amount;
An image forming apparatus.

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