JP2009063660A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus allowing comprehensive color matching control against AC variation and DC variation and achieving more precise color shift correction. <P>SOLUTION: A color printer creates a lookup table based on angular velocity variation (AC variation) of a photoreceptor drum by index active control (step S110). After the creation of the lookup table, a registration mark is formed on the photoreceptor drum by using the lookup table, the formed registration mark is detected to calculate a color shift amount (DC variation), and the color registration correction is thereby performed (step S120). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention is applied to a color printer or a color copying machine having a tandem configuration in which an image carrier is provided for each image forming color and a color image is formed by superimposing colors on an intermediate transfer belt, and these multifunction devices. The present invention relates to a suitable image forming apparatus.

  In recent years, tandem color printers, color copiers, and these color multifunction devices have been increasingly used. According to this type of image forming apparatus, when reproducing R (red) color, G (green) color, and B (blue) color of a color image, for example, laser light sources are arranged in a line shape, and line units are provided. A LPH (Line Photo diode Head) unit for batch exposure is provided for each image forming color, and toner images of yellow (Y), magenta (M), cyan (C), and black (BK) are used for each image forming color. Each color toner image formed by the photosensitive drum and the photosensitive drum for each color is superposed on the intermediate transfer belt. The color toner images superimposed on the intermediate transfer belt are transferred to a desired sheet, and then fixed and discharged.

  In connection with this type of tandem color printer, Patent Document 1 discloses an image forming apparatus. According to this image forming apparatus, a photosensitive drum is provided for each image forming color, and a plurality of photosensitive drums are rotated by a belt with one driving source. Encoders (speed detection means) are arranged on the shafts of the respective photosensitive drums, and fluctuations in the rotational movement amount predicted from the rotational speed information obtained from each shaft are stored in advance, and the recording timing is controlled from the rotational movement amount. To be made. If the image forming apparatus is configured in this manner, color misregistration can be eliminated when colors are superimposed on the intermediate transfer member.

  In addition, according to the image forming apparatus disclosed in Patent Document 2, the rotation operation detection unit, the signal filter, and the write timing control unit are provided, and the rotation operation detection unit rotates the photoconductor drum when correcting the rotation unevenness of the photoconductor drum. Unevenness is detected and a rotation unevenness detection signal is output to the signal filter. In the signal filter, the low frequency component signal after removing the repetitive component from the rotation unevenness detection signal is extracted and output to the write timing control means. The above-mentioned low frequency component signal is caused by drum eccentricity. The writing timing control means calculates the rotation fluctuation amount from the low frequency component signal, and determines the image writing timing in the writing unit based on the rotation fluctuation amount. By configuring the image forming apparatus in this way, it is possible to correct the rotation unevenness of the photosensitive drum accurately and quickly.

JP-A-7-225544 JP 2000-089640 A

  By the way, as color matching correction by color misregistration or the like, color registration correction using a color registration mark is used in addition to the above-described method. In this color registration correction, color registration marks of each color are written on the photosensitive drum, an average value of the shift amounts of the respective colors is calculated with reference to normal black, and the writing timing of each color image is determined.

  For this reason, the correction by so-called index active control for correcting the deviation of the writing timing of the color image based on the angular velocity fluctuation of the photosensitive drum disclosed in the above-mentioned Patent Documents 1 and 2 and the above-described color registration correction are the photosensitive They are common to each other in that they are affected by fluctuations in the rotation of the body drum. For example, in color registration correction, the DC fluctuation of the color registration mark is mainly corrected. However, the fluctuation of the color registration mark also reflects the angular velocity fluctuation (AC fluctuation) component of the photosensitive drum.

  Conventionally, in these color registration correction and index active correction, correction values are independently calculated and each correction control is executed, and the interrelation between them is unclear. For this reason, no consideration is given to the overall color matching control for AC fluctuation and DC fluctuation, and there is a problem that the correction accuracy cannot be improved with higher accuracy. Furthermore, since correction is performed independently, there is a problem that the correction execution time increases.

  Therefore, the present invention solves the above-described problems, and an object of the present invention is to enable comprehensive color matching control with respect to AC fluctuation and DC fluctuation, and to realize more accurate color misregistration correction. It is to provide a forming apparatus.

  In order to solve the above-described problem, an image forming apparatus according to claim 1 is an image forming apparatus that transfers a color image formed on an image carrier to a transfer target, and performs color misregistration correction on the image carrier. An image forming means for forming a mark image for use, a speed detecting means for detecting an angular velocity fluctuation of the image carrier, and the color image on the image carrier based on the angular velocity fluctuation detected by the speed detector. And a control means for creating a correction table for correcting the image forming timing for forming the image, and the control means creates the correction table before forming the mark image for color misregistration correction. The image forming means corrects the image forming timing based on the correction table created before forming the mark image and forms the mark image on the image carrier.

  According to the image forming apparatus of the first aspect, the printed image for color misregistration correction is obtained by a correction table (index active control) created based on the angular velocity fluctuation (AC fluctuation) of the image carrier. Therefore, a printed image from which AC fluctuations have been removed can be formed on the image carrier. Furthermore, by performing color misregistration correction (DC fluctuation correction) using this printed image from which AC fluctuations have been removed, color matching control can be comprehensively performed with respect to AC fluctuations and DC fluctuations, realizing highly accurate color matching. it can.

  In the present invention, the index active control is based on the index cycle error for one rotation of the photosensitive drum by calculating the angular error between exposure and transfer from the angular velocity fluctuation of the photosensitive drum and using the reference signal for one rotation of the photosensitive drum as a trigger. In this control, a lookup table is created and the index period is corrected based on the correction value (time information) of the lookup table.

  According to a second aspect of the present invention, the image forming apparatus according to the first aspect further includes an image detecting unit that detects the mark image formed by the image forming unit, and the control unit is detected by the image detecting unit. After calculating the shift amount of the mark image based on the mark image, the correction table is updated based on the calculated color shift amount.

  According to a third aspect of the present invention, there is provided an image forming apparatus according to the first aspect, wherein the color image formed on the image carrier is transferred to the transfer body, and the image carrier is used for color misregistration correction. Image forming means for forming a printed image, image detecting means for detecting the printed image formed by the image forming means, speed detecting means for detecting angular velocity fluctuations of the image carrier, and detection by the image detecting means Based on the printed image, the amount of deviation of the printed image is calculated to correct the image forming position, and the color image is displayed on the image carrier based on the angular velocity fluctuation detected by the velocity detecting means. Control means for creating a correction table for correcting the image forming timing for image formation, and the control means performs the creation of the correction table and the correction of the image forming position by the print image by parallel processing. It said image forming means after the creation of the correction table and the correction of the image forming position by the indicia image has been completed, and performs updating of the correction table based on the shift amount of the mark image.

  According to the image forming apparatus of the third aspect, the correction table is used to update the correction value stored in the correction table based on the color shift amount (DC fluctuation) of the printed image from which the DC fluctuation is removed. In correction control of angular velocity fluctuation (AC fluctuation) of the image carrier, not only AC fluctuation but also DC fluctuation can be removed at the same time. Furthermore, according to the present invention, since correction table creation and image formation position correction using a printed image are performed in parallel processing, color matching is comprehensively performed for AC fluctuation and DC fluctuation while realizing high-speed printing. Control becomes possible.

  According to the image forming apparatus of claim 1, since the mark image for color misregistration correction is formed by the correction table created based on the angular velocity fluctuation (AC fluctuation) of the image carrier, AC fluctuation and DC fluctuation are formed. Therefore, it is possible to control color matching comprehensively and realize high-precision color matching.

  According to the image forming apparatus of the second aspect, the color misregistration amount calculated from the print image formed using the correction table is fed back to the correction table again, and the correction table is updated. A high correction table can be created.

  According to the image forming apparatus of the third aspect, since the creation of the correction table and the correction of the image forming position by the print image are performed by parallel processing, high-speed printing can be realized and AC fluctuation and DC fluctuation can be prevented. Color matching control is possible comprehensively.

Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a conceptual diagram showing a configuration example of a color printer 100 as an embodiment according to the present invention. A tandem color printer 100 shown in FIG. 1 constitutes an example of an image forming apparatus, and performs color registration correction based on a look-up table created by index active control, thereby comprehensively dealing with AC fluctuation and DC fluctuation. Color matching control is possible. Further, the color printer 100 drives a plurality of photosensitive drums 1Y, 1M, and 1C via the rotation transmission mechanism 40 and a common motor 30a (drive source) based on digital color image information (see FIG. 2). The color images formed by the photosensitive drums 1Y, 1M, and 1C are superimposed on the intermediate transfer belt 6. The color image is transferred and fixed on a predetermined paper (transfer object) P. The color image information is supplied from an external device such as a personal computer to the color printer 100 and transferred to the image forming unit 80.

  The image forming unit 80 includes an image forming unit 10Y having a photosensitive drum 1Y for yellow (Y), an image forming unit 10M having a photosensitive drum 1M for magenta (M), and a cyan (C) color. The image forming unit 10 </ b> C having the photosensitive drum 1 </ b> C, the image forming unit 10 </ b> K having the black (K) photosensitive drum 1 </ b> K, and the endless intermediate transfer belt 6 are configured. In the image forming unit 80, image formation processing is performed for each of the photosensitive drums 1Y, 1M, 1C, and 1K, and the toner images of the respective colors that are image-processed by the photosensitive drums 1Y, 1M, 1C, and 1K of the respective colors. They are superimposed on the intermediate transfer belt 6 to form a color image.

  In this example, the image forming unit 10Y includes a charger 2Y, a line-shaped optical head (hereinafter referred to as LPH unit 5Y), a developing unit 4Y, and a cleaning for an image forming body in addition to the photosensitive drum 1Y. Means 8Y is provided to form a yellow (Y) color image. The photosensitive drum 1Y constitutes an example of an image carrier, and is provided, for example, so as to be rotatable in the vicinity of the upper right side of the intermediate transfer belt 6 so as to form a Y-color toner image. In this example, the photosensitive drum 1Y is rotated counterclockwise by a rotation transmission mechanism 40 as shown in FIG. A charger 2Y is provided on the lower right side of the photosensitive drum 1Y so as to charge the surface of the photosensitive drum 1Y to a predetermined potential.

  An LPH unit 5Y is provided almost directly beside the photosensitive drum 1Y, and has a predetermined strength based on the image data for Y color with respect to the previously charged photosensitive drum 1Y. A laser beam is irradiated at once. As the LPH unit 5Y, an LED head (not shown) arranged in a line is used. As the image writing system, a scanning exposure system using a polygon mirror (not shown) may be used instead of the LPH unit. An electrostatic latent image for Y color is formed on the photosensitive drum 1Y.

  A developing unit 4Y is provided above the LPH unit 5Y, and operates to develop a Y-color electrostatic latent image formed on the photosensitive drum 1Y. The developing unit 4Y has a Y-color developing roller (not shown). In the developing unit 4Y, a Y color toner agent and a carrier are stored.

  The Y-color developing roller has a magnet disposed therein, and rotates and conveys the two-component developer obtained by stirring the carrier and the Y-color toner agent in the developing unit 4Y to the opposite part of the photosensitive drum 1Y. The electrostatic latent image is developed by the color toner agent. The Y color toner image formed on the photosensitive drum 1Y is transferred to the intermediate transfer belt 6 by operating the primary transfer roller 7Y (primary transfer). A cleaning unit 8Y is provided below the left side of the photosensitive drum 1Y so as to remove (clean) the toner remaining on the photosensitive drum 1Y in the previous writing.

  A registration sensor 26 as an example of an image detection unit is provided in an area where the upper surface of the intermediate transfer belt 6 can be seen on the upstream side of the cleaning unit 8A of the color printer 100. The image forming units 10Y and 10M described above are provided. An image detection signal is generated by detecting a color misregistration correction mark image (hereinafter referred to as a registration mark CR) formed on the intermediate transfer belt 6 by 10C and 10K.

  In this example, an image forming unit 10M is provided below the image forming unit 10Y. The image forming unit 10M includes a photosensitive drum 1M, a charger 2M, an LPH unit 5M, a developing unit 4M, and an image forming member cleaning unit 8M, and forms a magenta (M) color image. . An image forming unit 10C is provided below the image forming unit 10M. The image forming unit 10C includes a photosensitive drum 1C, a charger 2C, an LPH unit 5C, a developing unit 4C, and a cleaning unit 8C for an image forming body, and forms a cyan (C) color image. .

  An image forming unit 10K is provided below the image forming unit 10C. The image forming unit 10K includes a photosensitive drum 1K, a charger 2K, an LPH unit 5K, a developing unit 4K, and an image forming member cleaning unit 8K, and forms a black (BK) image. . An organic photoconductor (OPC) drum is used as the photoconductor drums 1Y, 1M, 1C, and 1K.

  Note that the functions of the members of the image forming units 10M to 10K can be applied by replacing Y with M, C, and K for the same reference numerals of the image forming unit 10Y, and thus description thereof is omitted. A primary transfer bias voltage having a polarity opposite to that of the toner agent to be used (positive polarity in this embodiment) is applied to the primary transfer rollers 7Y, 7M, 7C, and 7K.

  The intermediate transfer belt 6 constitutes an example of an image carrier, and forms a color toner image (color image) by polymerizing the toner images transferred by the primary transfer rollers 7Y, 7M, 7C, and 7K. The color image formed on the intermediate transfer belt 6 is conveyed toward the secondary transfer roller 7A as the intermediate transfer belt 6 rotates clockwise. The secondary transfer roller 7A is located below the intermediate transfer belt 6 and transfers the color toner image formed on the intermediate transfer belt 6 onto the paper P in a lump (secondary transfer). The secondary transfer roller 7A is provided with a cleaning unit 7B for removing the toner agent remaining on the secondary transfer roller 7A in the previous transfer.

  In this example, a cleaning unit 8A is provided on the upper left side of the intermediate transfer belt 6 and operates to clean the toner agent remaining on the intermediate transfer belt 6 after transfer. The cleaning unit 8 </ b> A has a neutralization unit (not shown) that neutralizes the charge of the intermediate transfer belt 6 and a pad that removes toner remaining on the intermediate transfer belt 6. The intermediate transfer belt 6 after the belt surface is cleaned by the cleaning unit 8A and discharged by the discharging unit enters the next image forming cycle. As a result, a color image can be formed on the paper P.

  In addition to the image forming unit 80, the color printer 100 includes a paper feeding unit 20 and a fixing device 17. A sheet supply unit 20 is provided below the image forming unit 10K, and includes a plurality of paper supply trays (not shown). A paper P of a predetermined size is accommodated in each paper feed tray. Conveying rollers 22A and 22C, a loop roller 22B, a registration roller 23, and the like are provided on a sheet conveying path from the sheet supply unit 20 to the lower side of the image forming unit 10K. For example, the registration roller 23 holds a predetermined sheet P fed from the sheet supply unit 20 in front of the secondary transfer roller 7A and sends it to the secondary transfer roller 7A in accordance with the image timing. The secondary transfer roller 7A is configured to transfer the color image carried on the intermediate transfer belt 6 onto a predetermined paper P whose paper conveyance is controlled by the registration roller 23.

  A fixing device 17 is provided on the downstream side of the secondary transfer roller 7A described above, and the paper P on which the color image is transferred is fixed. The fixing device 17 includes a fixing roller, a pressure roller, a heating (IH) heater, a fixing cleaning unit 17A, and the like (not shown). In the fixing process, the paper P is heated and pressed by passing the paper P between a fixing roller heated by a heater and a pressure roller. The fixed sheet P is nipped by the sheet discharge roller 24 and discharged onto a sheet discharge tray (not shown) outside the apparatus. The fixing cleaning unit 17A removes (cleans) the toner agent remaining on the fixing roller or the like by the previous fixing.

  Next, the configuration of the image forming unit 80 will be described. FIG. 2 is a perspective view illustrating a configuration example of the image forming unit 80.

  The image forming unit 80 includes photoreceptor drums 1Y, 1M, 1C, and 1K, an intermediate transfer belt 6, LPH units 5Y, 5C, 5C, and 5K for each color, and a rotation transmission mechanism 40.

  The Y color LPH unit 5Y has a length equal to the entire width of the photosensitive drum 1Y, and based on a Y color write permission (index) signal (hereinafter referred to as a Y-IDX signal), a Y color image. The data Dy operates so as to be collectively written in the main scanning direction for one line or several lines.

  Here, the main scanning direction is a direction parallel to the rotation axis of the photosensitive drum 1Y. The photosensitive drum 1Y rotates in the sub-scanning direction. The above-described intermediate transfer belt 6 is moved in the sub-scanning direction at a constant linear velocity. The sub-scanning direction is a direction orthogonal to the rotation axis of the photosensitive drum 1Y. The photosensitive drum 1Y rotates in the sub-scanning direction, and an electrostatic latent image for Y color is formed on the photosensitive drum 1Y by line-by-line batch exposure in the main scanning direction by the LPH unit 5Y.

  The LPH units 5M, 5C, and 5K for other colors also have the same length, and M color image data based on the M-IDX signal, C-IDX signal, and K-IDX signal for each color. The Dm, C color image data Dc, and BK color image data Dk are operated to be collectively written in a similar manner. The Y-IDX signal, M-IDX signal, C-IDX signal, and K-IDX signal for each color are supplied from the timing generator 54 (see FIG. 4). The LPH units 5Y, 5C, 5C, and 5K have LED heads having several thousand to several tens of thousands of pixels per line, depending on the maximum width of paper handled by the color printer 100.

  The rotation transmission mechanism 40 includes large-diameter gears 11Y, 11M, and 11C, idle gears 12a and 12b, a motor 30a, and an encoder 41. In this example, the three photosensitive drums 1Y, 1M, and 1C for Y color, M color, and C color are driven by a common motor 30a with a rotation transmission mechanism 40 interposed therebetween.

  The large diameter gears 11Y, 11M, 11C, and 11K have diameters larger than the diameters of the photosensitive drums 1Y, 1M, 1C, and 1K for the respective colors, and correspond to the photosensitive drums 1Y, 1M, 1C, and 1K. It is attached. For example, the large diameter gear 11Y is attached to the photosensitive drum 1Y. Other large-diameter gears 11M, 11C, and 11K are attached in the same manner.

  The idle gear 12a is meshed with the large diameter gears 11Y and 11M, and the idle gear 12b is meshed with the large diameter gears 11M and 11C. The gear ratio of the idle gear 12a and the large diameter gears 11Y and 11M, the idle gear 12b and the large diameter gears 11M and 11C, and the like is 1: α.

  In this example, the motor 30a is meshed with the idle gear 12b via the motor gear 13c. The motor 30a has a motor shaft 13a, and a motor gear 13c is attached to the motor shaft 13a. The gear ratio between the motor gear 13c and the idle gear 12a is 1: β.

  In the rotation transmission mechanism 40, when the motor 30a rotates counterclockwise, the idle gear 12b rotates clockwise based on the gear ratio 1: β, and the idle gear 12b rotates, so that the gear ratio 1: α. The large diameter gear 11M and the large diameter gear 11C rotate counterclockwise. As the large-diameter gear 11M rotates, the photosensitive drum 1M rotates counterclockwise. Similarly, when the large-diameter gear 11C rotates, the photosensitive drum 1C rotates counterclockwise.

  Further, when the large-diameter gear 11M rotates counterclockwise, the idle gear 12a rotates clockwise. As the idle gear 12a rotates clockwise, the large-diameter gear 11Y rotates counterclockwise. As the large-diameter gear 11Y rotates, the photosensitive drum 1Y rotates counterclockwise. Accordingly, the three photosensitive drums 1Y, 1M, and 1C for Y color, M color, and C color can be driven by a single common motor 30a with the rotation transmission mechanism 40 interposed therebetween.

  Incidentally, one photosensitive drum 1K for BK color is adapted to directly drive the large-diameter gear 11K by the motor 30b without interposing an idle gear, corresponding to the monochrome high-speed mode. The motor 30b has a motor shaft 13b, and a motor gear 13d is attached to the motor shaft 13b. The gear ratio between the motor gear 13d and the large diameter gear 11K is 1: γ.

  In this example, an encoder 41 constituting a function of speed detecting means is attached to the shaft portion of the M-color large-diameter gear 11M to detect the angular (rotational) speed of the M-color photosensitive drum 1M. An angular velocity signal S41 is output. In this way, the three photoreceptor drums 1Y, 1M, and 1C for Y color, M color, and C color are driven by one motor 30a, and the photoreceptor drum for BK color is driven by a single motor 30b. An image forming unit 80 that can be directly driven is configured.

  Next, an example of setting the exposure position Qy of the photosensitive drum 1Y and the transfer position Py on the intermediate transfer belt 6 will be described. FIG. 3 is a conceptual diagram illustrating a setting example of the exposure position Qy of the photosensitive drum 1Y with respect to the transfer position Py on the intermediate transfer belt 6.

  In this example, the exposure position Qy with respect to the transfer position Py of the photosensitive drum 1Y on the intermediate transfer belt 6 shown in FIG. 3 is set to an angle θy. Here, θy is set to, for example, θy = 22.2 °, where θy is an angle formed by a vertical line of the transfer position Py and a line segment connecting the exposure position Qy and the rotation center axis of the photosensitive drum 1Y. The Similarly for the photoconductor drums 1M, 1C, and 1K for other colors, θm, θc, and θk are defined, and θy = θm = θc = θk is set.

  The diameter D1 of the Y-color photosensitive drum 1Y shown in FIG. 3 is, for example, 60 mm. The other M, C, and BK color photosensitive drums 1M, 1C, and 1K have the same diameter D1. The diameter D2 of the large-diameter gear 11Y of the Y color photosensitive drum 1Y is, for example, 114.93 mm. The other large diameter gears 11M, 11C, and 11K of the M, C, and BK photosensitive drums 1M, 1C, and 1K have the same diameter D2.

  The influence of the rotation delay or the like of the idle gears 12a and 12b is set to an integral multiple of the distance Lm between the transfer position Qm and the exposure position Pm. For this reason, the distance Ly set to an integral multiple at the transfer position Qy on the belt surface of the intermediate transfer belt 6 with respect to the Y transfer position Qy and the transfer position Qc on the belt surface with respect to the C transfer position Qc. , Lm, Lc to Y, M, C color overlay reproducibility can be ensured.

  From such a relationship, the rotation angle error of the M color photosensitive drum 1M having the same drive system is sampled, and based on this sampling, the other Y, C, BK color photosensitive drums 1Y, 1C, 1K are sampled. By creating an image formation timing correction table (hereinafter referred to as a rotation angle error table), the fluctuation component can be ignored.

  FIG. 4 is a block diagram illustrating a configuration example of a control system in the color printer 100. The color printer 100 shown in FIG. 4 is based on a tandem configuration, detects angular velocity fluctuations of the photosensitive drums 1Y, 1M, 1C, and 1K, calculates a rotation angle error, and calculates the LPH units 5Y, 5M, 5C, and 5K. It has a function of modulating the index period to adjust the image interval on the drum surface and suppressing pitch unevenness and resist position shift (low frequency) due to eccentricity.

  A color printer 100 shown in FIG. 4 includes a control unit 50, an operation unit 14, a display unit 34, an IDC (image density controller) sensor 28, a registration sensor 26, an image memory 46, and LPH units 5Y, 5M, 5C, and 5K. Prepare. The control unit 50 includes an I / O interface 51, a ROM (Read Only Memory) 52, a RAM (Random Access Memory) 53, a look-up table memory (hereinafter referred to as LUT memory) 70, a motor drive unit 56, a belt control unit 57, A speed detector 58 and a timing generator 54 are included.

  A ROM 52 is connected to the CPU 55, and system startup program data D52 for controlling the entire color printer 100 is stored. In the RAM 53, program data D52, control commands for executing various calculations, and the like are temporarily stored. When the power is turned on, the CPU 55 reads the program data D52 from the ROM 52 to the RAM 53, starts the system, and controls the entire color printer 100.

  The LUT memory 70 includes a Y color lookup table 71 corresponding to the photosensitive drum 1Y, an M color lookup table 72 corresponding to the photosensitive drum 1M, and a C color corresponding to the photosensitive drum 1C. A lookup table 73 and a lookup table 74 for K color corresponding to the photosensitive drum 1K are provided. The LUT memory 70 is composed of a nonvolatile memory, for example, and is connected to the CPU 55.

  A look-up table 71 for Y color (hereinafter referred to as Y-LUT 71) refers to information for correcting the color image formation timing (write permission signal) at the exposure position Qy for forming a color image on the photosensitive drum 1Y. It is a table. The Y-LUT 71 stores time information D71 as a correction value.

  A lookup table 72 for M color (hereinafter referred to as M-LUT 72) refers to information for correcting the color image formation timing (write permission signal) at the exposure position Qm for forming a color image on the photosensitive drum 1M. It is a table. The M-LUT 72 stores time information D72.

  The C color lookup table 73 is an information reference table for correcting the color image formation timing (write permission signal) at the exposure position Qc for forming a color image on the photosensitive drum 1C. The C-LUT 73 stores time information D73.

  The K color lookup table 74 is an information reference table for correcting the color image formation timing (write permission signal) at the exposure position Qk for forming a color image on the photosensitive drum 1K. The K-LUT 74 stores time information D74.

  Of course, the configuration of the LUT memory 70 is not limited to the above-described configuration, and four Y-LUTs 71, M-LUTs 72, C-LUTs 73, and K-LUTs 74 are divided by dividing the memory area of one nonvolatile memory. You may make it store.

  The CPU 55 constitutes an example of a control unit, and creates the M-LUT 72 of the photosensitive drum 1M set as a reference based on the angular velocity data D41 supplied from the velocity detector 58, and other color photosensitive members. The Y-LUT 71 and C-LUT 73 of the drums 1Y, 1C, and 1K are created based on the fluctuation value of the photosensitive drum 1M. For example, when the Y color look-up table 71 is created, the CPU 55 performs the Y color photosensitive drive driven by the motor 30a from the large diameter gear 11M of the M color photosensitive drum 1M via the rotation transmission mechanism 40. A transfer function to the body drum 1Y is calculated as angular velocity data D41, and a rotation angle error table of the Y-color photosensitive drum 1Y is created.

  In the color registration correction, the CPU 55 forms a registration mark CR for color misregistration correction on the intermediate transfer belt 6 via the photosensitive drums 1Y, 1M, 1C, and 1K, and reads the passage timing of the registration mark CR. Then, the positional deviation amount of the registration marks CR of other colors with respect to the registration mark CR of the reference color is calculated, and the image forming position is corrected based on the positional deviation amount. In this example, the registration mark CR is created based on the lookup tables 71 to 74 created before the color registration correction.

  The operation unit 14 is connected to the CPU 55 via the I / O interface 51 and includes, for example, operation buttons for operating a copy function and a fax function, operation buttons for setting various correction modes, and the like. When the operation button of the operation unit 14 is operated by the user, operation data D14 corresponding to the operation button is input to the CPU 55 via the I / O interface 51.

  The display unit 34 is connected to the CPU 55 via the I / O interface 51, and is configured by, for example, a liquid crystal display. The display unit 34 displays a menu screen for performing operations. In addition, by adopting a touch panel as the display unit 34, the function of the operation unit 14 can be given to the display unit 34.

  The IDC sensor 28 forms a pattern composed of a plurality of gradations on the photosensitive drums 1Y, 1M, 1C, 1K, etc., and acquires the gradation (density) of the pattern based on the reflectance of the reflected light from the pattern. It is. The gradation data obtained by the IDC sensor 28 is used for Dmax correction described later.

  In addition to the operation unit 14, a motor drive unit 56, a belt control unit 57, and a speed detection unit 58 are connected to the I / O interface 51. The motor drive unit 56 is connected to the motors 30a and 30b, and drives the motors 30a and 30b based on the motor drive information D56. The motor 30a applies a rotational force to the rotation transmission mechanism 40, and the motor 30b applies a rotational force to the large-diameter gear 11K. The motor drive unit 56 is connected to the CPU 55 via the I / O interface 51, and the motor drive information D56 is output from the CPU 55 to the motor drive unit 56.

  The belt control unit 57 is connected to a solenoid or a motor (not shown) that drives the primary transfer rollers 7Y, 7M, 7C, and 7K. The belt control unit 57 receives the transfer control information D57 and inputs roller control signals S7Y, S7M, S7C, and S7K. Create etc. For example, the belt controller 57 drives the primary transfer roller 7Y based on the roller control signal S7Y, contacts the intermediate transfer belt 6 with the photosensitive drum 1Y, or separates the intermediate transfer belt 6 from the photosensitive drum 1Y. To do. The other primary transfer rollers 7M, 7C, 7K and the like are similarly controlled. As a result, the intermediate transfer belt 6 is brought into contact with the photosensitive drums 1Y, 1M, 1C, and 1K all at once, or the intermediate transfer belt 6 is separated from the photosensitive drums 1Y, 1M, 1C, and 1K all at once, or individually. Be able to contact / separate. The belt control unit 57 is connected to the CPU 55 via the I / O interface 51, and the transfer control data D57 is output from the CPU 55 to the belt control unit 57.

  The speed detection unit 58 has an input end connected to the encoder 41 and an output end connected to the CPU 55 via the I / O interface 51. The encoder 41 detects the angular velocity of the reference M-color photosensitive drum 1 </ b> M and outputs an angular velocity signal S <b> 41 to the velocity detector 58. The speed detector 58 receives the speed detection signal S41 from the encoder 41 and outputs the binarized angular speed data D41 to the CPU 55. Further, the speed detector 58 generates a drum rotation reference trigger signal DS for each rotation of the photosensitive drum 1M based on the speed detection signal S41 output from the encoder 41, and the generated drum rotation reference trigger signal DS is generated. It supplies to CPU55.

  The registration sensor 26 includes a light emitting element and a light receiving element. The light emitting element irradiates the registration mark CR with emitted light, and the light receiving element detects the reflected light. The registration sensor 26 is connected to the CPU 55 and outputs an image detection signal SR based on the registration mark CR detected by the light receiving element to the CPU 55 when the color misregistration correction mode is executed. As will be described later, the image detection signal SR includes a front edge detection signal component and a rear edge detection signal component of the registration mark CR. The image detection signal SR is converted into image detection data Dp by an A / D converter (not shown) and supplied to the CPU 55. As the resist sensor 26, for example, a reflective optical sensor, an image sensor, or the like is used.

  The timing generator 54 is connected to the CPU 55, and generates an index reference signal by dividing or multiplying a clock signal (hereinafter referred to as a CLK signal) supplied from a clock generator (not shown). The timing generator 54 is supplied with a timing control signal D54 corresponding to each of the time information D71, D72, D73 and D74 read from the lookup tables 71 to 74 by the CPU 55. The timing generator 54 generates a Y-IDX signal, an M-IDX signal, a C-IDX signal, and a K-IDX signal based on the index reference signal and the timing control information D54.

  Here, the Y-IDX signal is a signal for permitting batch exposure in units of lines based on the Y color image data Dy. The M-IDX signal is a signal for permitting batch exposure in units of lines based on the M color image data Dm. The C-IDX signal is a signal for permitting collective exposure in units of lines based on the C color image data Dc. The K-IDX signal is a signal for permitting batch exposure in units of lines based on the BK color image data Dk.

  The timing generator 54 is supplied with a timing control signal D54 'corresponding to the image detection data Dp from the CPU 55. The timing generator 54 generates a Y-IDX signal ', an M-IDX signal', a C-IDX signal ', and a K-IDX signal' based on the index reference signal and the timing control information D54 '.

  Here, the Y-IDX signal 'is a signal for permitting collective exposure in units of lines based on the Y color image data Dy'. The M-IDX ′ signal is a signal for permitting batch exposure in units of lines based on the M color image data Dm ′. The C-IDX 'signal is a signal for permitting batch exposure in units of lines based on the C color image data Dc'. The K-IDX 'signal is a signal for permitting batch exposure in units of lines based on the BK color image data Dk'.

  The image memory 46 is composed of a non-volatile memory such as a hard disk (HDD) or EEPROM, and the image data Dy, Dm, Dc, Dk in the normal image forming mode and the image data Dy for forming the registration mark in the color misregistration correction mode. ', Dm', Dc ', Dk' are stored. The image memory 46 is connected to each of the timing generator 54 and the LPH units 5Y, 5M, 5C, and 5K. Based on the timing control signals D54 and D54 ′ supplied from the timing generator 54, the image memory Dy, Any one of Dm, Dc, Dk and image data Dy ′, Dm ′, Dc ′, Dk ′ is selected and outputted to LPH units 5Y, 5M, 5C, 5K.

  Each of the LPH units 5Y, 5M, 5C, and 5K is connected to the timing generator 54 and the image memory 46, respectively. When the Y-IDX signal is supplied, the LPH unit 5Y operates to collectively write Y color image data Dy for one line or several lines in the main scanning direction of the photosensitive drum 1M. Further, when the Y-IDX ′ signal is supplied, Y color image data Dy ′ (registration mark CR) for color misregistration correction is collectively collected for one line or several lines in the main scanning direction of the photosensitive drum 1M. Operates to write. The other LPH units 5M, 5C, and 5K operate in the same manner as the LPH unit 5Y.

  Next, an example of fluctuations in angular velocity when the photosensitive drums 1Y, 1M, and 1C for each color of the color printer 100 described above are rotationally driven will be described. FIG. 5 is a graph showing an example of speed fluctuations in the photosensitive drums 1Y, 1M, and 1C for Y color, M color, and C color. In this example, an example of speed variation when driving the three photosensitive drums 1Y, 1M, and 1C for Y color, M color, and C color by the common motor 30a with the rotation transmission mechanism 40 interposed therebetween is given. . In FIG. 5, the horizontal axis is the drum position, and shows sampling points in the drum circumference. The vertical axis represents the fluctuation range of each drum, and shows the low-frequency amplitude obtained by removing high-frequency noise and DC components from the drum fluctuation component.

  Since the Y-color photosensitive drum 1Y is driven via the large-diameter gear 11M and the idle gear 12a, the fluctuation range of the photosensitive drum 1Y with respect to the drum position indicated by the wavy line in the drawing is in a wavy state. This state is the angle (180) between the reference position (exposure position Qy) of the exposure system caused by the delay of the rotation transmission mechanism 40 and the transfer position Py where the colors are superimposed on the intermediate transfer belt 6 during normal operation. This is because (° −θy) = 157.8 ° shifts (see FIG. 3). The same applies to the photosensitive drums 1M and 1C for other colors.

  After this wavy state is matched (converted) with a large period of low-frequency fluctuation like the M-color photosensitive drum 1M, correction is performed so as to eliminate the rotation angle error between the exposure position Qy and the transfer position Py. The In this example, 81 sampling points are set with respect to the drum circumferential length of one rotation cycle of the photosensitive drums 1Y, 1M, and 1C, and the lookup table 71 for each color is set with reference to the 81 sampling points. , 72, 73 are created. The grounds for setting the sampling point = 81 are based on the output performance (45 [c / v]) of the encoder 41 and the gear ratio between the idle gear 12a and the large-diameter gear 11Y, in this example, 18: 1. . Then, as will be described later, the writing timing of the image data to the photosensitive drum 1Y or the like is corrected using the look-up tables 71, 72, 73 for eliminating the above-described deviation.

  By this correction, the angle (180 ° −θy) formed by the exposure (reference) position on each of the photosensitive drums 1Y, 1M, 1C, and 1K and the transfer position where colors are superimposed on the intermediate transfer belt 6 can be kept constant. become. In the sentence, please read θy with θm, θc, and θk. In addition, it is not necessary to attach photosensitive drums 1Y, 1C, and 1K for Y, C, and BK other than the photosensitive drum 1M for the reference color, thereby reducing the cost of the color printer 100 and a color copying machine. Leads to a more compact design.

  FIG. 6 is a diagram illustrating a storage example of the time information D72 in the M-LUT 72. As illustrated in FIG. In this example, the configuration of the M color M-LUT 72 will be described.

  The M-LUT 72 has 81 (A to ZZ) sampling numbers corresponding to 81 sampling points of the photosensitive drum 1M. There are areas, and time information D72 (correction value) for M color corresponding to each sampling point is stored in each of these areas. That is, the M-LUT 72 includes 81 sampling numbers at the peripheral surface of the photosensitive drum 1M. And this sampling number. Is stored in association with time information D72 (correction value) corresponding to. For example, sampling No. No. 1 stores a correction value A. In the area 2, the correction value B. In the area 81, a correction value ZZ is stored.

  Note that the same configuration of the M color M-LUT 72 described above is employed for the Y color Y-LUT 71, the C color C-LUT 73, and the K color K-LUT 74.

  Next, an example of correcting the angle error in the photosensitive drums 1Y, 1M, and 1C for each color will be described. FIGS. 7A to 7D are diagrams illustrating examples of correcting an angular error in the photosensitive drum for each color. In this example, the correction value in the rotation angle error table is expressed as a time difference between a certain rotation angle of each of the photosensitive drums 1Y, 1M, 1C, and 1K and another normal rotation angle.

  Sample No. 1 shown in FIG. No. 1, no. 2, no. 3, no. 4 ... No. 81 (not shown). In FIG. 7B, the horizontal axis is time t. The broken line in the figure indicates time information obtained by dividing 661 ms obtained by converting the drum 1 circumference (60π = 188.5 mm) into time at 81 sampling points. Sample No. 1 shown in FIG. The reference time for 1 is 8.16 ms, and the correction value is + A. Therefore, in the rotation angle error table, the sample No. 1 is set to the reference time (8.16 ms) + the correction value A. Similarly, sample no. For 2, the reference time is 16.32 ms, and the correction value is + B. Therefore, sample no. 2, the exposure timing is set to the reference time (16.32 ms) + correction value B.

  Sample No. The reference time for 3 is 24.48 ms and its correction value is -C. Therefore, sample no. 3 is set to the reference time (24.48 ms) -correction value C. Similarly, sample no. For 4, the reference time is 32.64 ms and its correction value is -D. Therefore, sample no. 4 is set to the reference time (32.64 ms) -correction value D.

  In this example, the rise of the Y-IDX signal shown in FIG. 1-No. The correction is made based on the time information corresponding to 81. That is, the image data Dy shown in FIG. 7D is photosensitized from the LPH unit 5Y for Y color shown in FIG. 2 in synchronization with the rising edge of the Y-IDX signal after correction shown in FIG. 7C. It is written to the body drum 1Y. The same applies to the photosensitive drums 1M, 1C, 1K for other colors and the LPH units 5M, 5C, 5K.

Next, color registration correction and registration marks CR used for this correction will be described.
FIG. 8 is a perspective view showing an example of registration mark CR detection by two registration sensors 26A and 26B. The registration sensors 26A and 26B shown in FIG. 8 are areas where the intermediate transfer belt surface can be seen, and are provided on both ends of the intermediate transfer belt 6, and when the color misregistration correction mode is executed, the image forming units 10Y, 10M, 10C, and 10K. Thus, registration marks CR formed on both sides of the intermediate transfer belt 6 are detected.

  FIG. 9 is a diagram showing an example of forming a registration mark CR for color misregistration correction. The registration mark CR shown in FIG. 9 is formed when the color misregistration correction mode is executed. In this example, when the width direction of the intermediate transfer belt 6 is the main scanning direction, the registration mark CR has a line segment parallel to the main scanning direction and a predetermined angle (for example, 45 °) with respect to the main scanning direction. It is comprised by the line segment. For example, the registration mark CR forms a “F” character. The image forming units 10Y, 10M, 10C, and 10K are controlled so that the registration mark CR is formed on the intermediate transfer belt 6 by the CPU 55 shown in FIG.

  In this example, in the sub-scanning direction, which is the moving direction of the intermediate transfer belt 6, four BK-shaped registration marks CR for correcting color misregistration are formed in succession on the left and right ends. Subsequently, four C-color registration marks CR are formed continuously on the left and right ends, and four M-color registration marks CR are formed on the left and right ends. Subsequently, a Y-color registration mark CR is formed. Four marks CR are continuously formed on the left and right ends, respectively. The reason why the four registration marks CR of each color are formed at the left and right ends is to detect the image forming position of the registration mark CR of each color and correct it accurately.

  The registration marks CR for correcting the color misregistration are detected by the registration sensors 26A and 26B, the color misregistration amounts with respect to the image forming positions of the registration marks CR of the respective colors are calculated, and the image forming positions of Y, M, and C colors are corrected. . This correction is for accurately superimposing color images based on arbitrary image data Dy, Dm, Dc, Dk in the image forming system after execution of the color misregistration correction mode.

10A to 10H are diagrams illustrating binarization examples of the image detection signal SR by the registration sensor 26A and the like.
The registration sensor 26A shown in FIG. 10A detects the edges of the straight line portion (i) and the inclined portion (ii) of the registration mark CR on the intermediate transfer belt 6 and outputs an image detection signal SR. In this example, the angle θ formed by the “F” -shaped registration mark CR is 45 °. The intermediate transfer belt 6 moves in the sub scanning direction at a constant linear velocity. In the registration sensor 26A, light is emitted from a light emitting element (not shown) to the registration mark CR, and the reflected light is detected by the light receiving element.

  The image detection signal SR shown in FIG. 10B is obtained from the registration sensor 26A. In this image detection signal SR, L1 is a belt (surface) detection level. Lth is a threshold value for binarizing the image detection signal SR, and L2 is a mark detection level related to the registration mark CR. Point a is a point where the image detection signal SR based on the front end edge of the registration mark straight line portion (i) crosses the threshold value Lth, and gives a front end edge detection time ta. At the front edge detection time ta, the first passage timing pulse signal Sp shown in FIG. 10D rises.

  Similarly, point b is the trailing edge passing time tb of the registration mark straight line portion (i), and based on this, the passing timing pulse signal Sp shown in FIG. 10D falls. Point c is the front edge passing time tc of the registration mark inclined portion (ii), and based on this, the second passing timing pulse signal Sp shown in FIG. 10D rises. Point d is the trailing edge passing time td of the registration mark inclined portion (ii), and based on this, the passing timing pulse signal Sp shown in FIG. 10D falls.

  The binarized passage timing pulse signal Sp becomes image detection data Dp. The image detection data Dp is used to calculate the shift amount of the Y, M, and C color writing positions with respect to the writing position of the BK registration mark CR.

  The VTOP signal shown in FIG. 10C is a signal (image leading edge signal) that permits writing of the registration mark CR on the photosensitive drums 1Y, 1M, 1C, and 1K.

  In the elapsed time T1 shown in FIG. 10E, the write start signal (VTOP signal) rises at time t0 shown in FIG. 10C, a counter (not shown) is started, and then the number of pulses of the reference clock signal is counted, and the leading edge detection time When ta is reached, it is obtained from the output value (elapsed time information D [T1]) output from the counter.

  Similarly, the elapsed time information D [T2]) is obtained when the trailing edge detection time tb is reached (FIG. 10F), and the elapsed time information D [T3]) is obtained when the leading edge detection time tc is reached. (FIG. 10G), the elapsed time information D [T4]) is obtained when the trailing edge detection time td is reached (FIG. 10H). The elapsed time information D [T1], D [T2], D [T3], and D [T4] are stored in the RAM 53.

  FIG. 11 is a diagram illustrating a calculation example of the color misregistration correction amount in the color misregistration correction mode. In this example, the color misregistration correction amount is calculated on the basis of the BK color registration mark CR in order to adjust the writing position of the Y, M, and C color registration marks CR to match the BK color registration mark CR. The

For example, the time when the registration sensor 26A shown in FIG. 11 detects the straight line portion (i) in the main scanning direction of the BK registration mark CR at the left end is T11, and the straight line in the main scanning direction of the left C registration mark CR. When the time at which the portion (i) is detected is T12 and the separation distance (reference value) B1 between the left BK registration mark CR and the left C registration mark CR in the sub-scanning direction is sub-scanning. The fine adjustment value T is calculated by the following equation (1).
T = A (design value) −B = A− (T12−T11) (1)
However, A is a design value of the separation distance of BK color and C color. The actual distance varies depending on how to shift.

  Similarly, regarding the other M and Y color writing position adjustments, the amount of deviation between the writing position of the BK color registration mark CR and the writing position of the M or Y color registration mark CR is detected. Each correction amount is calculated from the amount. Thereafter, the C, M, and Y color image forming positions other than the BK color image forming unit 10K are adjusted.

  Next, an example of the operation of the CPU 55 of the color printer 100 according to the present invention will be described. In this example, an operation when index active control and color registration correction are performed immediately after the color printer 100 returns from the sleep mode will be described. Here, the sleep mode is an operation mode for reducing power consumption. For example, when a certain time elapses after the copy function or the print function is completed, the normal operation mode is shifted to the sleep mode. On the other hand, when a user input from the display unit 34 or reception of image data from a network (not shown) is received, the mode returns from the sleep mode to the normal operation mode.

  FIG. 12 is a flowchart showing the operation of the CPU 55 when the color printer 100 is corrected. Hereinafter, correction of a color image formed on the photosensitive drum 1M will be described. First, in step S10, the CPU 55 determines whether or not the off time until the color printer 100 shifts from the normal mode to the sleep mode and returns to the normal mode is 8 hours or more. The CPU 55 proceeds to step S20 when determining that the off-time has elapsed for 8 hours or longer, and proceeds to step S50 when determining that the off-time has not elapsed for 8 hours or longer.

  If it is determined that the color printer 100 has been stopped for 8 hours or more, IDC sensor offset control is performed in step S20. Next, IDC sensor base control is performed in step S30, and IDC sensor detection control is performed in step S40.

  Next, in step S50, the CPU 55 performs Dmax correction. This is because at the time of returning to the sleep mode (in the morning), the developer charge amount is decreased and the developability changes, so that it is necessary to adjust the density of the toner image. The IDC sensor 28 detects a pattern formed on the photosensitive drum 1M or the intermediate transfer belt 6 based on a control signal supplied from the CPU 55, and supplies the detected reflectance or the like to the CPU 55 as an output value. The CPU 55 determines a development potential (development bias) such that the maximum density of the toner image is constant based on the output value (Dmax correction).

  In step S60, the CPU 55 performs dot diameter correction. This is because, in the LPH unit or the like, the light amount of the LPH unit or the like that performs image writing decreases due to contamination, and the diameter of one dot may be reduced. In the dot diameter correction, the power of the laser light for each color output from the LPH unit 5Y is controlled so that the dot diameter developed on the photosensitive drum 1M has an appropriate value (a constant size).

  In step S70, the CPU 55 performs γ correction. This is because, for example, the gradation (density) of the input image to be reproduced and the gradation (density) of the output image to be reproduced are not exactly proportional to each other due to factors such as the photosensitive characteristics of the photosensitive drum 1M and the installation environment. Because. Therefore, the gradation of the input image is faithfully reproduced in the output image by γ correction.

  In step S80, the CPU 55 calls a subroutine shown in FIG. 13 in parallel with the above-described dot diameter correction (step S60) to perform index active control and color registration correction.

  In step S100 shown in FIG. 13, the CPU 55 determines whether it is time to perform color registration correction in parallel with the dot diameter correction (step S60) described above. For example, it is determined whether it is time to perform color registration correction based on the stop time of the color printer 100 and the cumulative number of printed pages. When the CPU 55 determines that it is time to perform color registration correction, the CPU 55 proceeds to step S110. When it is determined that it is not time to perform color registration correction, the CPU 55 returns to step S80 shown in FIG. End the operation.

  In step S110, the CPU 55 creates an M-LUT 72 for correcting a shift in the transfer position due to a change in angular velocity during rotation of the photosensitive drum 1M by index active control. Specifically, sampling is performed at 81 locations of the index period in one rotation period (n period) of the photosensitive drum 1M. Then, when the drum rotation reference trigger signal DS at the time of (n + 1) rotation of the photosensitive drum 1M is detected, a correction value at each sampling point of the index period acquired at the n rotation period of the photosensitive drum 1M is calculated.

  In the calculation of the correction value of the M-LUT 72, the subroutine shown in FIG. 14 is called, and the CPU 55 receives the angular velocity data D41 (Data = enc) from the velocity detector 58 in step S200. At this time, the encoder 41 attached to the shaft of the M photosensitive drum 1M outputs an angular velocity signal S41 to the velocity detector 58. In the speed detector 58, the angular speed signal S41 is converted into binary (digital) angular speed data D41.

  Next, in step S210, the CPU 55 acquires angular velocity data D41 for each of the 81 sampling points, and calculates an average value thereof (10 sum average value). Thereafter, in step S220, the CPU 55 calculates the difference between the reference value (count value) and the 10-average value of angular velocities (reference value-data).

  Next, in step S230, the CPU 55 performs LPF (low pass filter) processing on the angular velocity data D41. This is because harmonic vibration is removed from the angular velocity data D41 and low frequency components are extracted.

  Further, in step S240, the CPU 55 calculates the difference between the angular velocity data D41 at each sampling point of the drum circumference and the angular velocity average data D41 ″ obtained by averaging the angular velocity data D41 for the drum circumference to remove the DC component. (Data-data average value) The angular velocity data D41 is temporarily stored in the RAM 53.

  Next, in step S250, the encoder pulse period measurement values are integrated (integrated) to determine the rotation angle of the M-color photosensitive drum 1M. In step S260, a rotation angle error between the exposure position Qm and the transfer position Pm is calculated. Such a rotation angle error based on the drum outer peripheral distance Lm represents a change in angular velocity at the transfer position Pm. As a result, the M-LUT 72 of the M color photosensitive drum 1M can be created.

  In this example, an M-LUT 72 indicating the amount of time deviation between the exposure position Qm and the transfer position Pm is created from the angular velocity variation. At this time, the CPU 55 calculates time information D72 (lookup value; time shift amount) obtained by dividing the rotation angle by the angular velocity, and the time information D72 obtained by the calculation is set to the sampling number. Are stored in the M-LUT 72 in association with each other to create a lookup table. As a result, the amount of time deviation versus sampling No. The M-LUT 72 (/ ω = M-axis time table) of the photoconductor drum for M color 1M can be created. After a series of subroutine processing is completed and the process returns to step S110, the process proceeds to step S120.

  In step S120, the CPU 55 performs color registration correction. In color registration correction, a subroutine shown in FIG. 15 is called.

  In step S300 shown in FIG. 15, the CPU 55 creates a registration mark CR using (reflecting) the time information D72 stored in the M-LUT 72. First, the time information D72 is read from the M-LUT 72, and the timing control signal D54 'corresponding to the read time information D72 is supplied to the timing generator 54. The timing generator 54 generates a Y-IDX 'signal for writing a registration mark based on the index reference signal and the timing control information D54'. This Y-IDX 'signal is a signal in which the write timing of the index reference signal is corrected based on the timing control signal D54' corresponding to the time information D72 of the M-LUT 72.

  The CPU 55 supplies the image processing control signal S54 to the image memory 46 via the timing generator 54 in parallel with the generation of the Y-IDX ′ signal. In the image memory 46, based on the image processing control signal S54, image data Dy 'for color misregistration correction is read and supplied to the LPH unit 5Y. In the LPH unit 5Y, based on the Y-IDX ′ signal output from the CPU 55 and the image data Dy ′ (Y color write data) output from the image memory 46, the image data Dy ′ is stored in the photosensitive drum 1M. The laser beam for Y color having a predetermined intensity is collectively irradiated for one line or several lines. Then, the photosensitive drum 1M rotates in the sub-scanning direction, and an electrostatic latent image for color misregistration correction is formed on the photosensitive drum 1M. By developing this electrostatic latent image, a registration mark is formed on the intermediate transfer belt 6. CR is formed.

  In step S <b> 310, the CPU 55 detects the Y, M, and C color registration marks CR formed on the intermediate transfer belt 6. Specifically, the registration sensor 26A shown in FIG. 10 irradiates light from a light emitting element (not shown) onto the intermediate transfer belt 6 that moves in the sub-scanning direction at a constant linear velocity, and is reflected from the registration mark CR or the like. The reflected light is detected by the light receiving element. The registration sensor 26A detects an edge of the registration mark CR on the intermediate transfer belt 6 such as a straight line portion (i) and outputs an image detection signal SR. The image detection signal SR is binarized by an A / D converter (not shown) and becomes image detection data Dp. The image detection data Dp is stored in the RAM 53. The CPU 55 acquires elapsed time information D [T1], D [T2], D [T3], and D [T4] based on the image detection data Dp (see FIG. 10), and uses these elapsed time information as D [T1 ], D [T2], D [T3], D [T4] are stored in the RAM 53.

  In step S320, the CPU 55 calculates a color misregistration correction amount. The color misregistration correction amount is calculated on the basis of the BK color registration mark CR in order to adjust the writing position of the Y, M, and C color registration marks CR to match the BK color registration mark CR. For example, for the M color writing position adjustment, the writing position of the BK registration mark CR and the writing position of the M registration mark CR are detected, and the deviation amount of the M color writing position from the BK color is calculated. The correction amount is obtained. Specifically, the sub-scanning fine adjustment value T is calculated from the above equation (1), and the calculated correction value is stored in the RAM 53 as the color misregistration correction data Dε.

  In step S330, the CPU 55 determines whether the color misregistration amount is within an allowable range. At this time, the CPU 55 reads out and compares the color misregistration correction data Dε and the color misregistration amount threshold data Dth (color misregistration amount design allowable value) from the RAM 53. If it is determined that the color misregistration amount is within the allowable range, the process returns to step S80 in FIG. 12 to end the color registration correction. If it is determined that the color misregistration amount is out of the allowable range, the color misregistration correction needs to be reprocessed. Therefore, the process returns to step S300, and the above-described color misregistration correction processing is repeated again.

  The correction of the registration mark CR formed on the other photosensitive drums 1Y, 1C, and 1K can be corrected by the same operation as the correction of the photosensitive drum 1M described above.

  As described above, according to the present embodiment, the color misregistration correction resist is created by the lookup tables 71 to 74 created based on the angular velocity fluctuations (AC fluctuations) of the photosensitive drums 1Y, 1M, 1C, and 1K. In order to form the mark CR, the registration mark CR from which the AC variation is removed can be formed on the photosensitive drums 1Y, 1M, 1C, and 1K. Furthermore, by performing color registration correction (DC fluctuation correction) using the registration mark CR from which the AC fluctuation has been removed, color matching control can be comprehensively performed with respect to AC fluctuation and DC fluctuation, and high-precision color matching can be achieved. realizable.

[Second Embodiment]
Embodiments of the present invention will be described below with reference to the drawings. This embodiment is different from the above-described first embodiment in that the look-up tables 71 to 74 are created (updated) based on color misregistration image data obtained by color registration correction after color registration correction. ing. Since the configuration and operation of the other color printer 100 are the same as those in the first embodiment described above, common components are denoted by the same reference numerals, and detailed description thereof is omitted.

  FIGS. 16A and 16B are diagrams showing an example of the relationship between the drum rotation reference trigger signal DS and the write timing of the registration mark CR. FIG. 16C is a diagram showing correction values of the photosensitive drums 1Y, 1M, 1C, and 1K obtained by the index active control. The vertical axis shows the correction value and the horizontal axis shows time.

  The registration mark CR is applied to each of the photosensitive drums 1Y, 1M, 1C, and 1K in synchronization with the falling edge of the drum rotation reference trigger signal DS generated every rotation of the photosensitive drum (see FIG. 16A). It is written (see FIG. 16B). At this time, the registration mark CR is formed based on the correction values of the lookup tables 71 to 74 obtained by the index active control (see FIG. 16C). That is, in synchronization with the falling edge of the drum rotation reference trigger signal DS, the time information D71 to D74 is read sequentially from the 81 storage areas of the lookup table, and the registration mark CR is read based on the read time information D71 to D74. By correcting the writing timing, a registration mark CR from which AC fluctuation is removed is formed.

  Next, the operation of the CPU 55 at the time of correction of the color printer 100 according to the present embodiment will be described. FIG. 17 is a flowchart showing the operation of the CPU 55 during color registration correction. In this example, an operation when index active control and color registration correction are performed immediately after the color printer 100 returns from the sleep mode will be described. Therefore, the processing from the sleep mode recovery to γ correction shown in FIG. 12 (step S10 to step S70) is the same operation as that of the first embodiment described above, and thus the description thereof is omitted.

  In step S80 shown in FIG. 12, the CPU 55 calls a subroutine shown in FIG. 17, and proceeds to step S400.

  In step S400, the CPU 55 determines whether it is time to perform color registration correction. If it is determined that it is time to perform color registration correction, the process proceeds to step S410. If it is determined that it is not time to perform color registration correction, a series of correction operations at the time of returning to the sleep mode is terminated.

  In step S410, the CPU 55 creates an M-LUT 72 for correcting a shift in the transfer position due to a change in angular velocity during rotation of the photosensitive drum 1M by index active control. For calculation of the correction value of the M-LUT 72, the subroutine shown in FIG. Store in association with.

  In step S420, the CPU 55 performs color registration correction. In the color registration correction, a subroutine shown in FIG. 15 is called to form a registration mark CR using (reflecting) the time information D72 stored in the M-LUT 72. Then, the formed registration mark CR is detected, and a color misregistration correction amount (color misregistration correction data Dε) is calculated.

  In step S430, the CPU 55 updates (creates) the M-LUT 72 based on the color misregistration correction data Dε obtained by the color registration correction described above. Specifically, each sampling number of the M-LUT 72 corresponding to the color misregistration correction data Dε. The M-LUT 72 is updated by rewriting the time information D72 in the above to color misregistration correction data Dε (sub-scanning fine adjustment value T).

  In the present embodiment, the registration mark CR from which the AC variation is removed is formed with reference to the lookup tables 71 to 74, and the color misregistration correction data Dε is calculated based on the formed registration mark CR. The color misregistration correction data Dε is fed back to the lookup tables 71 to 74 again to update the correction information D72. Therefore, according to the present embodiment, it is possible to create the lookup tables 71 to 74 with higher accuracy, and it is possible to perform comprehensive color matching control with respect to AC fluctuation and DC fluctuation and to achieve higher precision. Color misregistration correction can be realized.

[Third Embodiment]
Embodiments of the present invention will be described below with reference to the drawings. This embodiment is different from the above-described first embodiment in that color registration correction and index active control are processed in parallel. Since the configuration and operation of the other color printer 100 are the same as those in the first embodiment described above, common components are denoted by the same reference numerals, and detailed description thereof is omitted.

  FIG. 18 is a flowchart showing the operation of the CPU 55 during color registration correction. In this example, an operation when index active control and color registration correction are performed immediately after the color printer 100 returns from the sleep mode will be described. Therefore, the processing from the sleep mode recovery to γ correction shown in FIG. 12 (step S10 to step S70) is the same operation as that of the first embodiment described above, and thus the description thereof is omitted.

  In step S600, the CPU 55 determines whether it is time to perform color registration correction. If it is determined that it is time to perform color registration correction, the process proceeds to step S610. If it is determined that it is not time to perform color registration correction, a series of correction operations at the time of returning to the sleep mode is terminated.

  In step S610, the CPU 55 creates an M-LUT 72 for correcting a shift in the transfer position due to a change in angular velocity during rotation of the photosensitive drum 1M by index active control. For calculation of the correction value of the M-LUT 72, the subroutine shown in FIG. Store in association with.

  In step S620, the CPU 55 performs color registration correction in parallel with the index active control (step S610). In the color registration correction, a subroutine shown in FIG. 15 is called to form a registration mark CR using (reflecting) the time information D72 stored in the M-LUT 72. Then, the formed registration mark CR is detected, and a color misregistration correction amount (color misregistration correction data Dε) is calculated.

  In step S700, after the index active control and the color registration correction are completed, the CPU 55 updates (creates) a lookup table based on the color misregistration correction data Dε obtained by the color registration correction described above.

  According to the present embodiment, since index active control and color registration correction are processed in parallel, the correction time can be shortened compared to the case where each processing is performed independently, and while realizing highly accurate color misregistration correction, High-speed print processing (high-speed mode) can be realized.

  It should be noted that the technical scope of the present invention is not limited to the above-described embodiments, and includes those in which various modifications are made to the above-described embodiments without departing from the spirit of the present invention. For example, in the above-described embodiment, the color misregistration correction at the time of returning to the sleep mode in the morning has been described. However, the present invention is not limited to this. In addition to returning from the sleep mode, the present invention can also be applied at the start of printing, during printing, at the end of printing, at the time of unit replacement, after adjustment by a service person, at the time of environmental movement, and at the low power mode. As a result, high-quality printing can be performed in consideration of AC fluctuation and DC fluctuation.

  The present invention includes a photosensitive drum that collectively exposes an electrostatic latent image in line units from an LPH unit in which light sources are arranged in a line for each image forming color, and colors are superimposed on an intermediate transfer belt. The present invention is extremely suitable when applied to a color printer, a color copying machine, a multi-function machine or the like having a tandem configuration for forming an image.

1 is a diagram illustrating a configuration example of a color printer according to an embodiment of the present invention. It is a perspective view which shows the structural example of an image formation part. It is a figure which shows the example of a setting of an exposure position. 3 is a block diagram illustrating a configuration example of a control system of a color printer. FIG. It is a graph which shows the example of a speed fluctuation of the photoconductive drum for each image forming color. It is a figure which shows the structural example of a look-up table. It is a figure which shows the example of a correction | amendment of the angle error in the photoconductive drum for each color. It is a perspective view which shows the example of a detection of the registration mark by two registration sensors. It is a figure which shows the example of formation of the registration mark for color misregistration correction. It is a figure which shows the binarization example of the image detection signal by a registration sensor. It is a figure which shows the example of calculation of color misregistration correction amount. 6 is a flowchart illustrating an operation example when the color printer returns to sleep mode. 5 is a flowchart illustrating an operation example during correction of the color printer according to the embodiment of the present invention. It is a figure which shows the example of calculation of the color shift correction amount in the color shift correction mode. It is a flowchart which shows the operation example of a color registration correction | amendment. 5 is a timing chart showing an example of registration mark writing timing. It is a flowchart which shows the operation example at the time of correction | amendment of the color printer which concerns on other embodiment of this invention. It is a flowchart which shows the operation example at the time of correction | amendment of the color printer which concerns on other embodiment of this invention.

Explanation of symbols

1Y, 1M, 1C, 1K Photosensitive drum 5Y, 5M, 5C, 5K LPH unit
6 Intermediate transfer belts 7Y, 7M, 7C, 7K Primary transfer rollers 10Y, 10M, 10C, 10K Image forming unit 26 Registration sensor 26A Registration sensor 26B Registration sensor 50 Controller 53 RAM
55 CPU
70 LUT Memory 71 Y Color Lookup Table 72 M Color Lookup Table 73 C Color Lookup Table 74 K Color Lookup Table 80 Image Forming Unit 100 Color Printer CR Registration Mark Dε Color Shift Correction Data

Claims (3)

An image forming apparatus for transferring a color image formed on an image carrier to a transfer target,
Image forming means for forming a color misregistration correction printed image on the image carrier;
Speed detection means for detecting angular velocity fluctuations of the image carrier;
Control means for creating a correction table for correcting the image forming timing for forming the color image on the image carrier based on the angular velocity fluctuation detected by the speed detecting means;
The control means includes
Creating the correction table before forming the printed image for color misregistration correction;
The image forming unit includes:
An image forming apparatus comprising: correcting the image forming timing based on the correction table created before forming the mark image, and forming the mark image on the image carrier. An image detecting means for detecting the mark image formed by the image forming means;
The control means includes
The correction table is updated based on the calculated color shift amount after calculating the shift amount of the print image based on the mark image detected by the image detection unit. The image forming apparatus described. An image forming apparatus for transferring a color image formed on an image carrier to a transfer target,
Image forming means for forming a color misregistration correction printed image on the image carrier;
Image detecting means for detecting the mark image formed by the image forming means;
Speed detection means for detecting angular velocity fluctuations of the image carrier;
Based on the mark image detected by the image detection means, the deviation amount of the mark image is calculated to correct the image forming position, and the image carrier is based on the angular velocity fluctuation detected by the speed detection means. Control means for creating a correction table for correcting the image forming timing for forming the color image above,
The control means includes
Creation of the correction table and correction of the image forming position by the mark image are performed by parallel processing,
The image forming unit includes:
An image forming apparatus according to claim 1, wherein after the creation of the correction table and the correction of the image forming position by the mark image are completed, the correction table is updated based on the shift amount of the mark image.