JP2010139767A - Image forming apparatus and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate a difference between a reference signal for image writing and a reference signal for image writing after correction each rotation of a photosensitive drum. <P>SOLUTION: The number of pulses for one rotation of a reference index signal is compared with the number of pulses for one rotation of a reference index signal after correction to obtain a rotating position variation value Δt13 indicating a difference value, and the rotating position variation value Δt13 is added to or subtracted from the reference index signal after correction to reset. The difference between the reference index signal and the reference index signal after correction is thereby eliminated each rotation of the photosensitive drum. Consequently, the images of respective photosensitive drums are accurately superimposed on an intermediate transfer belt. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus and an image forming method suitable for being applied to a color printer, a color copying machine, a composite machine of these, and the like.

  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. An LPH (LED print head) unit that performs batch exposure is provided for each image forming color. Yellow (Y), magenta (M), cyan (C), and black (BK) toner images are formed on the photoconductive drums for the respective image forming colors, and the respective color formed on the photoconductive drums for the respective colors. The toner images are superimposed 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.

  By the way, according to the tandem color image forming apparatus, if the rotational speed of the photosensitive drum varies (unevenness), the printed image is disturbed, and the color image is formed by superimposing the single color images by the color image forming units. This may cause misalignment or line misalignment.

  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 detecting means) are arranged on the shafts of the respective photosensitive drums, and the variation of the rotational movement amount predicted from the rotational speed information obtained from each shaft is stored in advance. The recording timing is controlled from this rotational movement amount. If the image forming apparatus is configured in this manner, color misregistration can be eliminated when colors are superimposed on the intermediate transfer member.

JP-A-7-225544

  In a tandem color image forming apparatus, when correcting the rotational unevenness of the photosensitive drum, the rotational position variation of the photosensitive drum is detected, and a correction amount that cancels the rotational position variation of the photosensitive drum is referred to. A corrected index signal is generated by correcting the image writing reference signal (reference index signal).

  When a signal indicating one rotation of the photosensitive drum is a TRIG signal, the difference between the count value of the correction index and the reference index when the TRIG signal is input is essentially the same because the amount of addition / subtraction in one rotation is equal. It becomes zero.

  However, it is difficult to completely match the TRIG signal with the end of the photosensitive drum line due to the difficulty of making the peripheral length of the photosensitive drum an integral multiple of the line width and the amount of toner to be developed. . For example, when the amount of toner is large, the rotational speed of the photosensitive drum tends to decrease. For this reason, when the TRIG signal is input, a difference occurs between the correction index and the reference index.

  For example, FIGS. 8A and 8B are diagrams illustrating an example of fluctuations in one rotation of the photosensitive drum 1Y and the rotation position thereof. In this example, the circumference of the drum is divided into n for each of Y, M, C, and BK image forming photoconductor drums 1Y, 1M, 1C, and 1K, and the reference index signal is applied to each of the divided n blocks. , M, C, BK color images are assumed to be formed. The circumference of the photosensitive drum shown in FIG. 8A is divided into N parts. For example, the outer circumference 360 ° of the photosensitive drum 1Y shown in FIG. Set points to L, and sections A → B, B → C, C → D, D → E, E → F, F → G, G → H, H → I, I → J, J → K, K Twelve blocks indicating L, L and A are set.

  According to the rotational position variation example of the photosensitive drum 1Y shown in FIG. 8B, the section of the first six blocks of A → B → C → D → E → F → G is caused by eccentricity or other causes. In this state, the rotational position of the photosensitive drum 1Y or the like is retracted from the ideal. On the other hand, in the latter half 6 blocks of G.fwdarw.I.fwdarw.I.fwdarw.J.fwdarw.L.fwdarw.A, the rotation position is in a state of being advanced more than ideal.

  FIGS. 9A and 9B are operation time charts showing a period correction example of the reference index signal. The horizontal axis of FIG. 9A is the drum position for one turn of the photosensitive drum 1Y. In this example, two blocks in the first half of the section A → B → C and three blocks in the second half of K → L → A → B are shown. T is an ideal elapsed time (period of the reference index signal) in which the rotational speed passing through one block when there is no rotational position fluctuation is converted into time.

  The horizontal axis of the corrected index signal shown in FIG. 9B is time t, and the rotational position advances by two blocks of the A → B → C section in the state where the rotational position shown in FIG. In this state, three blocks of K → L → A → B section are shown. In this example, the point B in the block A → B section is retreated to the point B ′ with respect to the point A. Further, the point C in the block B → C section is set back to the point C ′ with respect to the point B.

  The point L in the block K → L section advances to the point L ′ with respect to the point K. Further, the point A in the block L → A section is retreated to the point A ′ with respect to the point L. The point B in the block A → B section retreats to the point Ba ′ with reference to the point A ′.

  In this example, the point of the section of the block when the rotational position variation of the photosensitive drum 1Y or the like is “no” and the same section of the block section when the rotational position variation is “present”. A time difference (phase difference) from the block point is defined as a rotational position fluctuation value Δtn. At this time, the time difference between the points B-B ′ is Δt1, and the time difference between the points C-C ′ is Δt2. Further, the time difference between the points L-L ′ is Δt12, and the time difference between the points A-A ′ is Δt13.

  As shown in FIG. 9B, when the TRIG signal is input at a point A indicating one rotation of the photosensitive drum 1Y, for example, a rotational position fluctuation value Δt13 indicating a time difference between the corrected index signal and the reference index signal is generated. It has been confirmed. Because of this rotational position variation value Δt13, when a TRIG signal is input during writing, the rotational position variation value Δt13 varies to a point Ba ′ having a period t1 with reference to the point A ′ as shown in FIG. 9B. In this case, the same time difference Δt13 ′ as the point A-A ′ is generated between the point B ′ when the rotational position variation value Δt13 is assumed not to occur and the point Ba ′ where the rotational position variation value Δt13 occurs. This time difference Δt13 ′ causes a phase shift between the photosensitive drums.

  Note that the cause of the rotational position fluctuation value Δt13 is due to the difficulty of making the circumferential length of the photosensitive drum 1Y an integral multiple of the line width as described above, the amount of toner to be developed, and the like.

  Incidentally, according to the image forming apparatus described in Patent Document 1, the rotational movement amount of the photosensitive drum is obtained by the rotary encoder, and the recording timing at which the image recording is started is controlled based on the rotational movement amount obtained by the rotary encoder. . Even in this case, when the TRIG signal is input while the image is being written, it is difficult to completely match the end ends of the lines of the correction index signal.

  Therefore, the present invention solves such a problem, and can eliminate the difference between the reference signal for image writing and the corrected reference signal for image writing every time the photosensitive drum rotates. An object is to provide an image forming apparatus and an image forming method.

  In order to solve the above-described problem, an image forming apparatus according to a first aspect includes an image forming unit that includes a plurality of photosensitive drums and forms a color image based on image data of each image forming color. A period detecting means for detecting a drum rotation signal generated by one rotation of the photosensitive drum, the drum rotation signal detected by the period detection means, and correction of rotational position fluctuation unevenness in the photosensitive drum. Correcting a reference signal for image writing based on correction data to be generated, and generating a corrected reference signal for image writing for each image forming color, and a corrected image generated by the signal generating unit Control means for comparing the number of pulses of one rotation of the reference signal for writing with the number of pulses of one rotation of the reference signal for writing the image for each image forming color, and obtaining a difference value. For example, the signal generating means is characterized in that to create a reference signal for image writing after said eliminating the difference value correction determined by said control means.

  According to the image forming apparatus of the first aspect, the difference between the reference signal for image writing and the corrected reference signal for image writing can be reset every rotation of the photosensitive drum. As a result, the images on the photosensitive drums can be accurately superimposed on the intermediate transfer belt.

  An image forming apparatus according to a second aspect is the image forming apparatus according to the first aspect, wherein the control unit sets the number of pulses of the corrected reference signal for image writing created by the signal creating unit for each rotation of the image forming color. A first count unit that counts only, a second count unit that counts the number of pulses of the reference signal for image writing by one rotation, a count value of the first count unit, and the second count unit A calculation unit that calculates a difference value with respect to the count value for each image forming color, and the signal generation unit uses the difference value obtained by the calculation unit as the corrected image writing reference signal. Add or subtract.

  According to a third aspect of the present invention, in the image forming method for forming a color image based on image data of each image forming color corresponding to a plurality of photosensitive drums, any one of the photosensitive drums rotates once. A reference signal for image writing is corrected on the basis of a first step of detecting a drum rotation signal generated by the detection, the detected drum rotation signal, and correction data for correcting rotational position variation unevenness in the photosensitive drum. Then, a second step of creating a corrected image writing reference signal for each image forming color, the number of pulses of one rotation of the generated corrected image writing reference signal, and the image writing reference signal A third step of obtaining a difference value by comparing the number of pulses of one rotation of the reference signal for each image forming color, and the difference value obtained in the third step is used as a basis for the next image writing after correction. It is characterized in that a fourth step to eliminate the signal.

  According to the image forming apparatus of claim 1 and the image forming method of claim 3, the number of pulses for one rotation of the corrected reference signal for image writing and the number of pulses for one rotation of the reference signal for image writing Are compared for each image forming color to obtain a difference value, and the difference value is eliminated by the next reference signal for image writing after correction.

  Thereby, the difference between the reference signal for image writing and the corrected reference signal for image writing can be reset every rotation of the photosensitive drum. Therefore, it is possible to accurately superimpose the images on the photosensitive drums on the intermediate transfer belt.

  According to the image forming apparatus of the second aspect, the calculation unit calculates a difference value between the count value of the first count unit and the count value of the second count unit for each image forming color. By adding or subtracting the difference value obtained by the calculation unit to the corrected image writing reference signal and correcting it to zero, the image writing reference signal and the corrected image are rotated every rotation of the photosensitive drum. The difference from the reference signal for writing can be reset.

  Hereinafter, an image forming apparatus and an image creating method according to embodiments 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 superimposes color images formed on a plurality of photosensitive drums on an intermediate transfer belt based on digital color image information. The color image is transferred to a predetermined sheet and fixed. The color image information is supplied to the printer 100 from an external device such as a personal computer.

  The color printer 100 includes an image processing unit 70, write control units 15Y, 15M, 15C, and 15K, large-capacity storage units 33Y, 33M, 33C, and 33K, and an image forming unit 80.

  The image processing unit 70 receives color image information for R, G, and B color reproduction from an external device, for example, and performs color conversion processing on the color image information to generate image data for Y, M, C, and BK colors. Dy, Dm, Dc, Dk are output.

  The image processing unit 70 is connected to write control units 15Y to 15K for Y, M, C, and BK colors. These write control units 15Y to 15K send image data to the mass storage units 33Y to 33K based on a reference (pseudo) index signal (hereinafter referred to as a reference index signal) that constitutes an example of a reference signal for image writing. Write. The write control units 15Y to 15K execute read control of the image data Dy, Dm, Dc, and Dk from the large capacity storage units 33Y to 33K to the image forming unit 80. The image forming unit 80 is an example of an image forming unit, and divides the circumference of the drum into n for each of the Y, M, C, and BK photoconductor drums 1Y, 1M, 1C, and 1K, and corrects each of the divided blocks. A later reference index signal is applied to form Y, M, C, and BK color images.

  For example, the large-capacity storage unit 33Y is connected to the Y-color write control unit 15Y, and the large-capacity storage unit 33Y receives the Y-color image data Dy output from the image processing unit 70 based on the reference index signal. Stored. The writing control unit 15Y corrects the Y rotation writing reference (synchronous) signal (hereinafter referred to as Y-IDX signal) and the reading side vertical effective area signal (hereinafter referred to as R-VVy signal) after correcting the drum rotation signal and the reference index signal. The image data Dy is read from the large-capacity storage unit 33Y and output to the image forming unit 80. Here, the drum rotation signal (hereinafter referred to as a TRIG signal) refers to a signal obtained every time the rotation of any one photosensitive drum is measured for one rotation.

  A large-capacity storage unit 33M is connected to the M color write control unit 15M, and the M color image data Dm output from the image processing unit 70 is stored based on the reference index signal. The writing control unit 15M corrects the MIG writing reference (synchronous) signal (hereinafter referred to as M-IDX signal) after correcting the TRIG signal and the reference index signal, and the reading-side vertical effective area signal (hereinafter referred to as R-VVm signal). The image data Dm is read from the large-capacity storage unit 33M and output to the image forming unit 80.

  A large-capacity storage unit 33C is connected to the C color writing control unit 15C, and stores the C color image data Dc output from the image processing unit 70 based on the reference index signal. The writing control unit 15C corrects the writing reference (synchronous) signal for C color (hereinafter referred to as C-IDX signal) after correcting the TRIG signal and the reference index signal, and the vertical effective area signal (hereinafter referred to as R-VVc signal) on the reading side. The image data Dc is read from the large-capacity storage unit 33C and output to the image forming unit 80.

  The BK color write control unit 15K is connected to a large-capacity storage unit 33K and stores the BK color image data Dk output from the image processing unit 70 based on the reference index signal. The write control unit 15K corrects the TRIG signal and the reference index signal, the write reference (synchronous) signal for BK color (hereinafter referred to as K-IDX signal), and the vertical effective area signal on the read side (hereinafter referred to as R-VVk signal). The image data Dk is read from the large-capacity storage unit 33K and output 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. An image forming unit 10C having a photosensitive drum 1C, an image forming unit 10K having a black (K) photosensitive drum 1K, and an endless intermediate transfer belt 6 are provided.

  In the image forming unit 80, each of the photosensitive drums 1Y, 1M, 1C, and 1K forms an image, and the toner images of the respective colors that are image-formed by the photosensitive drums 1Y to 1K for the respective image forming colors are transferred to the intermediate transfer belt 6. Overlapping on top forms a color image.

  In this example, the image forming unit 10Y includes, in addition to the photosensitive drum 1Y, a charger 2Y, a line-shaped LED print head (hereinafter referred to as LPH unit 5Y), a developing device 4Y, and an image forming body cleaning unit 8Y. Thus, a yellow (Y) image is formed. For example, the photosensitive drum 1Y is rotatably provided near the upper right side of the intermediate transfer belt 6 and forms 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, and charges 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 Dy for Y color with respect to the previously charged photosensitive drum 1Y. The irradiated 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 device 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 device 4Y has a developing roller for Y color (not shown). The developing device 4Y contains a Y color toner agent and a carrier.

  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 device 4Y to the opposite portion of the photosensitive drum 1Y. The electrostatic latent image is developed with a color toner. 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, and removes (cleans) the toner agent remaining on the photosensitive drum 1Y in the previous writing.

  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 device 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 device 4K, and a cleaning unit 8K for an image forming body, 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 the description thereof will be 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 superimposes the toner images transferred by the primary transfer rollers 7Y, 7M, 7C and 7K to form a color toner image (color image). Here, the primary transfer point in the primary transfer roller 7Y is P1, the primary transfer point in the primary transfer roller 7M is P2, and the primary transfer point in the primary transfer roller 7C is P3, and the primary transfer roller 7K. In the tandem method, each image on the photosensitive drums 1Y, 1M, 1C, and 1K is transferred to the intermediate transfer belt 6 in the order of Y color → M color → C color → BK color. Next transfer.

  In the case of this method, the photosensitive drum is as shown by the distances (P2-P1), (P3-P2), (P4-P3) from the primary transfer point of each image forming color to the primary transfer point of the adjacent color. The timing for writing (exposing) image data Dy, Dm, Dc, Dk on 1Y, 1M, 1C, 1K is shifted.

  The color image superimposed on the intermediate transfer belt 6 via the photosensitive drums 1Y, 1M, 1C, and 1K at such a timing causes the secondary transfer roller 7A to rotate as the intermediate transfer belt 6 rotates clockwise. It is conveyed toward. The secondary transfer roller 7A is located below the intermediate transfer belt 6, and a secondary transfer unit 7B is provided below the secondary transfer roller 7A. The secondary transfer roller 7A transfers the color toner image formed on the intermediate transfer belt 6 onto the paper P together with the secondary transfer unit 7B (secondary transfer).

  A cleaning unit 8A is provided on the upper left side of the intermediate transfer belt 6 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 supply 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 7 </ b> A transfers the color image carried on the intermediate transfer belt 6 to a predetermined paper P that is controlled for paper conveyance by the registration roller 23.

  A fixing device 17 is provided on the downstream side of the above-described secondary transfer roller 7A to fix the paper P on which the color image has been transferred. The fixing device 17 includes a fixing roller, a pressure roller, a heating (IH) heater, a fixing cleaning part 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 the toner agent remaining on the fixing roller or the like by the previous fixing.

  FIG. 2 is a perspective view illustrating a configuration example of the image forming unit 80. An image forming unit 80 shown in FIG. 2 includes photosensitive drums 1Y, 1M, 1C, and 1K, an intermediate transfer belt 6, LPH units 5Y, 5M, 5C, and 5K for image forming colors, and a rotation transmission mechanism 40. Yes. The LPH unit 5Y for Y color has a length equal to the entire width of the photosensitive drum 1Y. The LPH unit 5Y operates to collectively write Y color image data Dy for one line or several lines in the main scanning direction based on the Y-IDX signal created from the reference index signal.

  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 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 have the same length, and the M-IDX signal, the C-IDX signal, and the K- Based on the IDX signal, the M color image data Dm, the C color image data Dc, and the BK color image data Dk are collectively written in a lump. The Y-IDX signal, M-IDX signal, C-IDX signal, and K-IDX signal for each image forming color are supplied from the write control units 15Y, 15M, 15C, and 15K. The LPH units 5Y, 5M, 5C, and 5K have LED heads having several thousand to several tens of thousands of pixel dots per line, depending on the maximum width of paper handled by the printer 100.

  In this example, the image forming unit 80 includes a rotation transmission mechanism 40, and three photosensitive drums 1Y, 1M, and 1C for Y color, M color, and C color have a common motor with the rotation transmission mechanism 40 interposed therebetween. It is driven at a predetermined rotational speed by 30a. 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 image forming colors, for example, and these photosensitive drums 1Y, 1M. , 1C, and 1K. 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 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 have a predetermined gear ratio.

  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 motor gear 13c and the idle gear 12a have a predetermined gear ratio.

  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 to increase the gear ratio at a predetermined gear ratio. The 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.

  Note that one photosensitive drum 1K for BK color directly drives the large-diameter gear 11K by the motor 30b without interposing an idle gear, corresponding to the monochrome high-speed mode. The rotation transmission mechanism 40 is provided with a motor 30b in addition to the motor 30a. The motor 30b has a motor shaft 13b, and a motor gear 13d is attached to the motor shaft 13b. The motor gear 13d and the large diameter gear 11K have a predetermined gear ratio.

  In this example, an encoder 41 constituting a period detecting means is attached to the shaft portion of the M-color large-diameter gear 11M. For example, the rotational speed of the M-color photosensitive drum 1M is detected and a TRIG signal is generated. 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.

  FIGS. 3A and 3B are operation time charts showing examples of period correction of the reference index signal. The horizontal axis of FIG. 3A is the drum position for one turn of the photosensitive drum 1Y. In this example, two blocks in the first half of the section A → B → C and three blocks in the second half of K → L → A → B are shown. T is an ideal elapsed time (period of the reference index signal) in which the rotational speed passing through one block when there is no rotational position fluctuation is converted into time.

  The horizontal axis of the Index signal shown in FIG. 3B is time t, and the rotational position has advanced by two blocks from the A → B → C section in the state where the rotational position shown in FIG. The three blocks of the state K-> L-> A-> B section are shown. In this example, the point B in the block A → B section is retreated to the point B ′ with respect to the point A. Further, the point C in the block B → C section is set back to the point C ′ with respect to the point B.

  The point L in the block K → L section advances to the point L ′ with respect to the point K. Further, the point A in the block L → A section is retreated to the point A ′ with respect to the point L. The point B in the block A → B section retreats to the point B ′ with respect to the point A ′.

  The period T with respect to the points A, B, C, K, and L in the ideal section shown in FIG. 3A varies, for example, from the A → B ′ section to the period t1, and from the B → C ′ section to the period t2. Fluctuates. In addition, the K → L ′ section changes in a cycle t11, the L → A ′ section changes in a cycle t12, and the A ′ → B ′ section changes in a cycle t1 ′.

  In this example, the point of the block section when the rotation fluctuation of the photosensitive drum 1Y or the like is “no” and the block point of the same section of the block section when the rotation fluctuation is “present” A time difference (tn−T; phase difference) between the rotation positions is a rotational position fluctuation value Δtn. At this time, the time difference between the points B-B ′ is Δt1, and the time difference between the points C-C ′ is Δt2. Further, the time difference between the points L-L ′ is Δt12, and the time difference between the points A-A ′ is Δt13.

  In this example, in the corrected index generation unit 51 as shown in FIG. 6, the sections A → B, B → C, C → D, D → E, E → F, F → G, G → H, H → I, I Regarding 12 blocks of → J, J → K, K → L, and L → A, the difference from the passing time (expected value) of the points in each section, that is, FIG. 3 (B) is shown. A rotational position fluctuation value Δtn is obtained. The rotational position fluctuation value Δtn is stored in a memory (not shown) in the correction index generation unit 51 by the number of blocks. The rotational position variation value Δtn is stored as rotational position variation data D1.

  The corrected index generator 51 reads the rotational position variation data D1 (rotational position variation value Δtn) from the memory, divides the rotational position variation value ΔTn indicated by the rotational position variation data D1 by the number of lines L in the block, and 1 The rotational position line fluctuation value H (D1 / L = H) per number of lines is calculated and distributed to each block.

  The rotational position line fluctuation value H is, for example, a complement of “2”. Then, the complement H1 is added to or subtracted from the period T of the reference index signal to generate a Y-IDX signal having a period T ± H1. The Y-IDX signal reflects the correction time Δtn−Δtn−1 for each block.

  As shown in FIG. 3B, when the TRIG signal is input at a point A indicating one rotation of the photosensitive drum 1Y, for example, a rotational position fluctuation value Δt13 indicating a time difference between the Y-IDX signal and the reference index signal is generated. Due to this rotational position fluctuation value Δt13, the leading end and the terminal end in one rotation of the photosensitive drum 1Y do not coincide with each other, and a deviation occurs. In order to reset (dissolve) this shift, the cycle of the Y-IDX signal in the A → B section of the next rotation is shortened. For example, the period t1 ′ of the section A ′ → B ′ shown in FIG. 3B is set shorter than the period t1 of the section A → B ′ by the rotational position variation value Δt13. Thereby, the time difference Δt13 ′ between the points B ′ and Ba ′ shown in FIG. 9B can be reset. Therefore, the difference between the Y-IDX signal generated when the TRIG signal is input and the reference index signal can be made zero. Thereby, the images of the photosensitive drums 1Y to 1K can be accurately superimposed on the intermediate transfer belt 6.

  FIGS. 4A and 4B are diagrams illustrating an example of period correction of the reference index signal for canceling the rotational speed unevenness of the photosensitive drum 1Y and the like. FIG. 4A is a waveform diagram showing an example of fluctuations in the rotational position of the photosensitive drum 1Y before correction. The rotational position variation example shown in FIG. 4A is the same as the rotational position variation example shown in FIG.

  In this example, in the example of the rotational position fluctuation of the photosensitive drum 1Y shown in FIG. 4A, the photosensitive drum 1Y etc. is in the first six blocks of A → B → C → D → E → F → G. The image data Dy, for example, rotates more slowly than usual because the exposure amount is high and the load increases. Therefore, the Y-IDX signal is corrected by the correction time Δtn−Δtn−1 so that the period T of the reference index signal is set to be long.

  On the other hand, in the last six blocks of G → H → I → J → K → L → A, the photosensitive drum 1Y and the like have a lower exposure amount due to the image data Dy and the load is reduced, which is lower than usual. Rotates fast. Therefore, the Y-IDX signal is corrected by the correction time Δtn−Δtn−1 so that the cycle T of the reference index signal is set to be short.

  FIG. 4B is a waveform diagram showing an example of the periodic distribution of the corrected reference index signal. According to the periodic distribution example of the corrected reference index signal shown in FIG. 4 (B), the sinusoidal rotational speed unevenness shown in FIG. 4 (A) is corrected after the sinusoidal correction shown in FIG. 4 (B). Cancel by the periodic distribution of the reference index signal. According to the periodic distribution waveform of the reference index signal after correction shown in this example, when 100 lines are allocated in one block, the correction time Δtn−Δtn−1 is divided into 100 to obtain 100 lines. The Y-IDX signal is obtained by correcting the period of the reference index signal by one correction time Δtn−Δtn−1 / 100.

  FIG. 5 is a conceptual diagram showing an example of resetting the deviation between the leading end and the trailing end in one rotation of the photosensitive drum 1Y and the like. The index period addition amount U1 shown in FIG. 5 is a correction amount in the correction data table, and is a value obtained by doubling the rotational position line fluctuation value H (D1 / L = H) per one line described above. In this example, the Index period addition interval U2 is set every two lines.

  The accumulated amount U3 is a value obtained by accumulating the Index period addition amount U1 for each line. As shown in FIG. 5, the cumulative amount U3 indicates a phenomenon in which the reference index period exceeds the first (Line-00) and thereafter becomes less than the reference index period (for example, Line-19). This phenomenon is similar to the rotational speed unevenness of the photosensitive drum 1Y shown in FIG. The Index period addition amount update line number U4 indicates the number of Lines for updating the Index period addition amount U1.

  As shown in FIG. 5, for example, the rotational position fluctuation value Δt13, which is the time difference between the Y-IDX signal and the reference index signal, indicates a deviation between the leading end and the trailing end in one rotation of the photosensitive drum 1Y.

  This rotational position fluctuation value Δt13 is reset, for example, in one block in the second AB section shown in FIG. 3A. For example, consider a case where the rotational position fluctuation value Δt13, which is the difference between the count value of the Y-IDX signal and the count value of the reference index signal, is “+100”. In this case, the Y-IDX signal in the AB section (for example, 50 lines) shown in FIG. For example, “−4” is added for each Index period addition interval U2 in FIG. That is, the Y-IDX signal for every two lines in the AB section is obtained by “reference index signal” + “index period addition amount U1” − “4”. Thereby, the rotational position fluctuation value Δt13 can be reset in one block. FIG. 5 shows that the rotational position fluctuation value Δt13 generated in Line-00 is collectively reset for easy understanding of the description. As described above, the rotational position fluctuation value Δt13 is reset, for example, in units of one block (50 lines).

  FIG. 6 is a block diagram showing a configuration example of the Y color write control unit 15Y and its peripheral part. In this example, based on the TRIG signal of the M photosensitive drum 1M (see FIG. 2) among the four photosensitive drums 1Y, 1M, 1C, and 1K for Y, M, C, and BK colors. A case will be described in which the reference index signal is corrected for each image forming color and the vertical effective area signal for adjusting the writing position at the time of reading the image data is adjusted. Of course, the configuration is such that any one of the other photosensitive drums 1Y, 1C, and 1K is detected, the reference index signal is corrected for each image forming color, and the vertical effective area signal for adjusting the writing position is adjusted. May be taken.

  An encoder 41 that constitutes an example of a period detecting unit is attached to the rotating shaft of the photosensitive drum 1M, and detects the rotational speed of the photosensitive drum 1M and outputs a TRIG signal. The TRIG signal is a pulse generated once per one rotation (rotation) of the drum, and is a signal generated asynchronously with respect to the reference index signal. The TRIG signal is a signal that reflects rotational position fluctuation unevenness such as eccentricity of the photosensitive drum 1M.

  The encoder 41 is connected to the M color, C color, and BK color write control units 15M, 15C, and 15K in addition to the Y color write control unit 15Y. In addition to the Y color write control unit 15Y, The TRIG signal is output to the write control units 15M, 15C, and 15K for M, C, and BK colors. In this example, one TRIG signal is output to the Y, C, and BK color write control units 15Y, 15M, 15C, and 15K by outputting the TRIG signal detected from the rotational speed of the M photosensitive drum 1M. The image writing start position (writing position) can be adjusted from the photosensitive drums 1Y, 1M, 1C, and 1K only by the signal.

  In this example, the signals output from the image processing unit 70 to the Y color writing control unit 15Y are image data Dy, a writing horizontal effective area signal (hereinafter referred to as a W-HV signal), a reference index signal, and writing. Control signal such as a vertical effective area signal (hereinafter referred to as W-VV signal). The signals output from the image processing unit 70 to the M color write control unit 15M are the image data Dm and the control signal described above. The signals output from the image processing unit 70 to the C color writing control unit 15C are the image data Dc and the control signal described above. The signals output from the image processing unit 70 to the writing control unit 15K for BK color are the image data Dk and the control signal described above. The image data Dy, Dm, Dc, and Dk are configured by a bus for each image forming color, and the above-described control signal is supplied to each image forming color in common.

  The Y color write control unit 15 </ b> Y includes a correction index generation unit 51, a timing control unit 52, a memory control unit 53, and a write control unit 54. In this example, on the write control side (W) of the memory control unit 53, the image data Dy output from the image processing unit 70, the W-HV signal for writing, the reference index signal, and the W-VV signal for writing. A control signal such as is input.

  The correction index generation unit 51 constitutes an example of a signal generation unit, inputs the TRIG signal detected by the encoder 41, and uses the TRIG signal as a reference to convert the reference index signal from the correction amount of the correction data table and the difference detection unit 503. Correction is performed using the difference signal Sε2. For example, the correction index generator 51 shortens the cycle of the Y-IDX signal in the A → B section of the next rotation in order to reset the rotational position fluctuation value Δt13 shown in FIG. 3B. In this example, the period t1 ′ of the A ′ → B ′ section shown in FIG. 3B is set shorter than the period t1 of the A → B ′ section by the rotational position variation value Δt13. Thereby, the delayed rotational position fluctuation value Δt13 can be reset. Therefore, the difference between the Y-IDX signal generated when the TRIG signal is input and the reference index signal can be made zero.

  The corrected index generation unit 51 generates a reference signal (Y-IDX signal) for writing a corrected Y color image. The correction index generation unit 51 is provided for each image forming color. The above-described correction amount is data for correcting the rotational position variation unevenness of the photosensitive drum 1M and the like, and is prepared in advance as a correction data table, and this correction data is referred to.

  A timing control unit 52, a memory control unit 53, and a write control unit 54 are connected to the correction index generation unit 51. The timing control unit 52 includes a correction index counting unit 501, a reference index counting unit 502, a difference detection unit 503, and an inter-drum delay amount counting unit 504. The timing control unit 52 compares the number of pulses of the Y-IDX signal created by the correction index generation unit 51 with the number of pulses of the reference index signal for each image forming color, and based on the comparison result, an image for Y color The output timing of the data Dy is adjusted.

  The TRIG signal from the encoder 41 is output to two types of counting units 501 and 502. The correction index counting unit 501 constitutes an example of a first counting unit, which counts the number of pulses of the corrected Y-IDX signal created by the correction index generation unit 51 and is common to all colors as a count value Py. Output when the W-VV signal (vertical effective area signal) rises. Further, the counting unit 501 counts the number of pulses of the corrected Y-IDX signal created by the correction index generation unit 51 by one rotation, and outputs the counted value P2y. When the counting unit 501 counts the number of pulses of the corrected Y-IDX signal by one rotation, the correction amount for resetting the rotational position fluctuation value Δt13 of the Y-IDX signal shown in FIG. except. A count unit 501 is provided for each image forming color.

  The reference index counting unit 502 constitutes an example of a second counting unit, counts the number of pulses of the reference index signal, and outputs a count value Qy. Further, the count unit 502 counts the number of pulses of the reference index signal by one rotation and outputs it as a count value Q2y. A count unit 502 is provided for each image forming color. Both the count units 501 and 502 are cleared to 0 when the TRIG signal is input. The two types of count units 501 and 502 are always cleared to 0 by the TRIG signal for each image forming color. In this example, each of the counting units 501 and 502 counts the number of pulses of the reference index signal, the number of pulses of the corrected Y-IDX signal, and the like with reference to the rising time of the TRIG signal.

  The count unit 501 and the count unit 502 are connected to a Y-color difference detection unit 503 that constitutes an example of a calculation unit. The count values Py and Qy of the count unit 501 and the count unit 502 are used as pulses of the Y-IDX signal. The difference value ε (2's complement) between the number and the pulse number of the reference index signal is calculated. The difference value ε is stored and held in a memory (not shown) in the difference detection unit 503. The difference value ε is output from the difference detection unit 503 to the inter-drum delay amount counting unit 504 as a difference signal Sε. The difference detection unit 503 is provided for each image forming color, the difference calculation operation is performed for each image forming color, and the timing of outputting the difference signal Sε is simultaneous. Thereby, the read timing of the image data Dy, Dm, Dc, Dk of each image forming color can be adjusted based on the difference value ε.

  Further, the difference detection unit 503 is a rotational position indicating a difference value for one rotation between the number of pulses of the Y-IDX signal and the number of pulses of the reference index signal from the count values P2y and Q2y of the count unit 501 and the count unit 502. The fluctuation value Δt13 is calculated. The rotational position fluctuation value Δt13 is output from the difference detection unit 503 to the correction index generation unit 51 as a difference signal Sε2.

  The difference detection unit 503 is connected to an inter-drum delay amount counting unit 504, and starts counting the inter-drum delay amount [Y] from the rising time of the W-VV signal for writing common to each image forming color. Then, the inter-drum delay amount counting unit 504 adds the difference value ε from the difference detecting unit 503 to the set value Xy of the inter-drum delay amount [Y]. The inter-drum delay amount counting unit 504, when the set value Xy = count value of the inter-drum delay amount [Y] with the difference value ε added, is the write start position on the photosensitive drum 1Y when reading the Y color image data. A vertical effective area signal for adjustment (hereinafter referred to as R-VVy signal) is raised.

  In this example, the inter-drum delay amount counting unit 504 raises the R-VVy signal from a low level (hereinafter referred to as “L” level) to a high level (hereinafter referred to as “H” level). The image data Dy is allowed to be read only during a period when the R-VVy signal is at “H” level. The same applies to other image forming colors.

  In this example, assuming that image data Dy, Dm, Dc, and Dk are read out from the large capacity storage units 33Y, 33M, 33C, and 33K to the image forming unit 80 in the order of Y, M, C, and BK colors, Y The set value Xy = “4” is set in the inter-drum delay amount count unit 504, and the set value Xm = “6” is set in the inter-Drum delay amount count unit 504 for C color. The set value Xy = “8” is set in the inter-drum delay amount count unit 504, and the set value Xm = “10” is set in the inter-drum delay amount count unit 504 for BK color.

  As described above, when the Y color image data Dy is read from the large-capacity storage unit 33Y to the image forming unit 80, the setting value Xy = “4” is set so that the reading time has a margin. This is for the purpose of ensuring that the set value Xy of the inter-drum delay amount [Y] taking into account the differential signal Sε is plus 1 or more.

  The setting values Xy, Xm, Xc, and Xk of the inter-drum delay amount are for adjusting the read timing of the image data Dy, Dm, Dc, and Dk of each image forming color. When the output timing is adjusted in this way, the Y and C color images produced by the photosensitive drums 1Y and 1C for other image forming colors are placed at the start writing position (timing) of the Y color image with respect to the Y color photosensitive drum 1Y. The start writing position (timing) can be aligned.

  A Y color memory control unit 53 is connected to the write control unit 54, the image processing unit 70, and the inter-drum delay amount counting unit 504 described above. A large capacity storage unit 33Y is connected to the memory control unit 53. The memory control unit 53 performs image processing on the image data Dy for Y color based on the reference index signal, the W-HV signal for writing (horizontal effective area signal), and the W-VV signal for writing (vertical effective area signal). The data is written (written) from the unit 70 to the mass storage unit 33Y. The image data Dy is data for forming a Y color image by the image forming unit 80. The other M color, C color, and BK color image data Dm, Dc, and Dk are written with the same configuration.

  The memory control unit 53 uses the Y-IDX signal after correction, the R-HV signal for reading (horizontal effective area signal), and the R-VVy signal for reading (vertical effective area signal) for Y color image data. Dy is read (read) from the large-capacity storage unit 33Y to the write control unit 54. The other M color, C color, and BK color image data Dm, Dc, and Dk are read with the same configuration.

  The Y-color inter-drum delay amount counting unit 504 described above operates based on the reference index signal until the memory control unit 53 writes the image data Dy to the large-capacity storage unit 33Y. During the read operation, the operation is performed based on the corrected Y-IDX signal, and the inter-drum delay amount counting unit 504 outputs an R-VVy signal for reading Y-color image data.

  Similarly, the inter-drum delay amount counting unit 504 for M color operates based on the reference index signal until the memory control unit 53 writes the image data Dm in the large-capacity storage unit 33M. During the read operation, the operation is performed based on the corrected M-IDX signal, and the inter-drum delay amount counting unit 504 outputs an R-VVm signal for reading M color image data to the M color memory control unit 53. Will come to do.

  The inter-drum delay amount counting unit 504 for C color operates based on the reference index signal until the memory control unit 53 writes the image data Dc into the large capacity storage unit 33C. During the read operation, the operation is performed based on the corrected C-IDX signal, and the inter-drum delay amount counting unit 504 outputs an R-VVc signal for reading C color image data to the C color memory control unit 53. Will come to do.

  The inter-drum delay amount counting unit 504 for BK color operates based on the reference index signal until the memory control unit 53 writes the image data Dk into the large capacity storage unit 33K. During the read operation, the operation is based on the corrected K-IDX signal, and the inter-drum delay amount counting unit 504 outputs the R-VVk signal for reading the BK color image data to the BK color memory control unit 53. Will come to do.

  As described above, the reference index signal / Y-IDX signal is switched in the writing / reading processing of the image data Dy or the like because the set values Xy, Xm, Xc and Xk of the inter-drum delay amount of each image forming color are used. This is for adjusting the read timing of the data Dy, Dm, Dc, Dk.

  FIG. 7 is a flowchart illustrating an example in which the write control unit 15Y or the like illustrated in FIG. 6 generates a corrected index signal. In step ST1 shown in FIG. 7, the reference index counting unit 502 shown in FIG. 6 counts the number of pulses of the reference index signal. For example, the count unit 502 inputs a TRIG signal generated for each rotation of the drum obtained from the encoder 41 attached to the shaft portion of the photosensitive drum 1M for M color. The counting unit 502 counts the number of pulses of the reference index signal from the image processing unit 70 by one rotation with reference to the TRIG signal, outputs the counted number as a count value Q2y, and proceeds to step ST2.

  In step ST2, the correction index counting unit 501 counts the number of pulses of the correction index signal. For example, the count unit 501 inputs a TRIG signal generated from the encoder 41 every drum rotation. The counting unit 501 counts the number of pulses of the Y-IDX signal from the correction index generation unit 51 by one rotation based on the TRIG signal, outputs the counted number P2y, and proceeds to step ST3.

  In step ST3, the difference detection unit 503 detects the difference between the count value of the reference index signal and the count value of the corrected index signal. For example, the difference detection unit 503 is a rotational position indicating a difference value for one rotation between the number of pulses of the Y-IDX signal and the number of pulses of the reference index signal from the count values P2y and Q2y of the count unit 501 and the count unit 502. The fluctuation value Δt13 is detected. The difference detection unit 503 outputs the rotational position fluctuation value Δt13 as the difference signal Sε2 to the correction index generation unit 51, and proceeds to step ST4.

  In step ST4, the correction index generation unit 51 inputs the difference signal Sε2, the TRIG signal, and the reference index signal, and proceeds to step ST5.

  In step ST5, the correction index generation unit 51 generates a correction index signal that is reset by the difference signal Sε2. For example, the correction index generation unit 51 shortens the cycle of the Y-IDX signal in the A → B section of the next rotation in order to reset the rotational position fluctuation value Δt13 indicating the difference signal Sε2 shown in FIG. 3B. In this example, the period t1 ′ of the A ′ → B ′ section shown in FIG. 3B is set shorter than the period t1 of the A → B ′ section by the rotational position variation value Δt13. As a result, the rotational position fluctuation value Δt13 can be reset, so that the difference between the Y-IDX signal and the reference index signal generated when the TRIG signal is input can be made zero.

  Thus, according to the writing control unit 15Y of the color printer 100 according to the present invention, for example, the number of pulses of one rotation of the Y-IDX signal is compared with the number of pulses of one rotation of the reference index signal. A value is obtained, and this difference value is eliminated by the next Y-IDX signal.

  Thereby, the difference between the reference index signal and the Y-IDX signal or the like can be reset every rotation of the photosensitive drum 1Y or the like. Therefore, it is possible to accurately superimpose images on the photosensitive drums 1Y and the like on the intermediate transfer belt 6.

  The present invention is extremely suitable when applied to a tandem type color printer, a color copying machine, a color complex machine, or the like that has a photosensitive drum driven at a predetermined rotation speed and forms a color image.

1 is a conceptual diagram illustrating a configuration example of a color printer 100 as an embodiment according to the present invention. 3 is a perspective view illustrating a configuration example of an image forming unit 80. FIG. (A) And (B) is an operation | movement time chart which shows the period correction example of a reference | standard Index signal. (A) And (B) is a figure which shows the period correction example of the reference Index signal for canceling the rotational speed nonuniformity of the photoreceptor drum 1Y or the like. FIG. 5 is a conceptual diagram illustrating a period correction example of a reference index signal for resetting a deviation between a leading end and a trailing end in one rotation of the photosensitive drum 1Y and the like. It is a block diagram showing a configuration example of a Y color write control unit 15Y and its peripheral part. It is a flowchart which shows the example which writing control unit 15Y etc. produce | generate a correction Index signal. (A) And (B) is a figure which shows the example of a fluctuation | variation of one rotation and its rotation position, such as the photoreceptor drum 1Y. (A) And (B) is an operation | movement time chart which shows the period correction example of the reference Index signal which concerns on a prior art example.

Explanation of symbols

1Y, 1M, 1C, 1K Photosensitive drum 2Y, 2M, 2C, 2K Charger 4Y, 4M, 4C, 4K Developer 5Y, 5M, 5C, 5K LPH unit 6 Intermediate transfer belt 10Y, 10M, 10C, 10K Image formation Unit 15Y, 15M, 15C, 15K Write control unit 33Y, 33M, 33C, 33K Large capacity storage unit 40 Rotation transmission mechanism 41 Encoder (period detection means)
51 Correction Index generator (signal generator)
52 Timing control unit (control means)
53 Memory Control Unit 54 Write Control Unit 70 Image Processing Unit 80 Image Forming Unit (Image Forming Unit)
100 color printer 501 correction index count section (first count section)
502 Count section for second index (second count section)
503 Difference detection unit (calculation unit)
504 Inter-drum delay count unit

Claims (3)

An image forming unit that has a plurality of photosensitive drums and forms a color image based on image data of each image forming color;
Period detecting means for detecting a drum rotation signal generated by one rotation of any one of the photosensitive drums;
An image writing reference signal is corrected based on the drum rotation signal detected by the cycle detection means and correction data for correcting the rotational position variation unevenness in the photosensitive drum, and the corrected image writing reference signal is corrected. Creating signal for each image color;
The number of pulses for one rotation of the reference signal for image writing after correction created by the signal creation means and the number of pulses for one rotation of the reference signal for image writing are compared for each image forming color. And a control means for obtaining a difference value.
The image forming apparatus, wherein the signal creating unit creates the corrected image writing reference signal in which the difference value obtained by the control unit is eliminated. The control means includes
A first count unit that counts the number of pulses of the reference signal for image writing after correction created by the signal creation means for one rotation for each image forming color;
A second counting unit for counting the number of pulses of the reference signal for image writing by one rotation;
A calculation unit that calculates a difference value between the count value of the first count unit and the count value of the second count unit for each image forming color;
The image forming apparatus according to claim 1, wherein the signal generation unit adds or subtracts the difference value obtained by the calculation unit to the corrected reference signal for image writing. In an image forming method for forming a color image based on image data of each image forming color corresponding to a plurality of photosensitive drums,
A first step of detecting a drum rotation signal generated by one rotation of any one of the photosensitive drums;
The reference signal for image writing is corrected based on the detected drum rotation signal and correction data for correcting the rotational position variation unevenness in the photosensitive drum, and the corrected reference signal for image writing is used for each image forming color. A second step to create
A difference value is obtained by comparing the number of pulses of one rotation of the generated reference signal for image writing after correction and the number of pulses of one rotation of the reference signal for image writing for each image forming color. 3 steps,
An image forming method comprising: a fourth step of eliminating the difference value obtained in the third step by a next corrected reference signal for image writing.

Images