JP5169889B2 - Image forming apparatus, color misregistration correction method, and color misregistration correction control program - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, a digital multi-function peripheral, etc. that forms a plurality of color images independently and superimposes each color to obtain a color image, and a color for correcting the color misregistration. The present invention relates to a misregistration correction method and a color misregistration correction control program for executing the color misregistration correction method by a computer.

  Conventionally, a tandem type color image forming apparatus is known as an image forming apparatus for forming a color image by an electrophotographic method. A tandem type color image forming apparatus includes an indirect transfer type or a direct transfer type. For example, an indirect transfer tandem color image forming apparatus includes an image forming station having an electrophotographic image forming element for each of yellow (Y), magenta (M), cyan (C), and black (K). A latent image is formed for each color on the photosensitive drum of each color image forming station by the light beam emitted from the laser diode, and the latent image is developed for each color at each station. Thereafter, the image is sequentially transferred to the intermediate transfer belt for each color to form a full-color image in which four colors of toner are superimposed, and the image is transferred to a transfer sheet as a transfer medium and fixed. Is formed.

  In this tandem color image forming apparatus, when an image generated by a writing unit different for each color is transferred to the intermediate transfer belt, the color is slightly shifted in the sub-scanning direction, for example, the paper transport direction, that is, each color. A so-called color shift occurs in which the sensed pixel position is shifted. For this reason, a technique is known in which a specific correction pattern image is formed on an intermediate transfer belt before image formation, and correction processing is performed using this correction pattern image to suppress the occurrence of color misregistration for each color.

  On the other hand, one of the color misregistration elements is skew misalignment (scan line tilt misalignment). This is a color shift caused by a shift in the inclination of the scanning line of each color due to a mechanical attachment error of the writing unit. In general, the skew deviation is corrected by measuring a skew deviation amount from a correction pattern on the intermediate transfer belt and rotating an optical mirror or the like with a stepping motor or the like according to the deviation amount.

  However, when this skew deviation is corrected, there is a problem that a shift deviation (registration deviation) of the pixel position in the main scanning and sub-scanning directions occurs. This is because the rotation center of the scanning line at the time of correcting the skew deviation does not coincide with the image center, and the main and sub resists are displaced at the same time as the skew is moved. Therefore, if skew correction and registration correction are performed by one color matching correction, registration deviation due to skew correction remains.

  The registration misalignment state will be described below together with the configuration of the tandem color image forming apparatus.

  FIG. 1 is a diagram illustrating a schematic configuration of an image forming unit of a tandem color image forming apparatus (hereinafter simply referred to as an image forming apparatus) 100 of an indirect transfer method that has been conventionally performed. In FIG. 1, an image forming apparatus 100 includes an optical device 102 including optical elements such as a semiconductor laser and a polygon mirror, and an image forming unit 112 including image forming elements such as a photosensitive drum, a charging device, a developing device, and a cleaning device. The transfer unit 122 includes a primary transfer unit, an intermediate transfer belt, a secondary transfer unit, and the like.

  In the optical device 102, a light beam emitted from a light source such as a semiconductor laser (not shown) is deflected by a polygon mirror 102c and is incident on an fθ lens 102b. In the illustrated embodiment, the light beam is emitted from the light source in a number corresponding to each color of cyan (C), magenta (M), yellow (Y), and black (K), and after passing through the fθ lens 102b, the reflection mirror 102a is reflected.

  The WTL lens 102d disposed at the rear stage of the reflecting mirror 102a shapes the light beam, guides the light beam to the reflecting mirror 102e, deflects the light beam with the reflecting mirror 102e, and outputs M as a light beam L used for exposure. , C, Y, and K, the surfaces of the photosensitive drums 104a, 106a, 108a, and 110a are irradiated. Irradiation of the light beam L to the M, C, Y, and K photoconductive drums 104a, 106a, 108a, and 110a is performed using a plurality of optical elements as described above. Timing synchronization is performed with respect to the direction. Hereinafter, the main scanning direction is defined as the scanning direction of the light beam, and the sub-scanning direction is a direction orthogonal to the main scanning direction. In the image forming apparatus 100 according to the present embodiment, the photosensitive drums 104a, 106a, It is defined as the rotating direction of 108a and 110a.

  The M-color photosensitive drum 104a includes a photoconductive layer including at least a charge generation layer and a charge transport layer on a conductive drum such as aluminum. The photoconductive layer is disposed corresponding to each of the photoconductive drums 104a, 106a, 108a, and 110a, and includes a M, C, Y, and K charger 104b that includes a corotron, a scorotron, a charging roller, or the like. , 106b, 108b, 110b, surface charges are applied.

  The electrostatic charges applied to the surfaces of the photosensitive drums 104a, 106a, 108a, and 110a of the respective colors by the chargers 104b, 106b, 108b, and 110b of the respective colors are exposed by the light beam L, and the static charge based on the modulated image signal is obtained. An electrostatic latent image is formed. The electrostatic latent images formed on the respective color photoconductive drums 104a, 106a, 108a, 110a are developed along the outer circumferences of the respective color photoconductive drums 104a, 106a, 108a, 110a, developer supply rollers, Development is performed by the developing devices 104c, 106c, 108c, and 110c including a regulating blade, and toner images of M, C, Y, and K colors are formed.

  The toner carried on the photosensitive drums 104a, 106a, 108a, and 110a is stretched between the transport rollers 114a, 114b, and 114c, and obtained on the intermediate transfer belt 114 that moves in the direction of the arrow T2 with driving force. The primary transfer rollers 104d, 106d, 108d, and 110d sequentially transfer each color, and finally a full color image in which four colors are superimposed is formed on the intermediate transfer belt 114. The full-color toner image superimposed with four colors is conveyed to the secondary transfer unit while being carried on the intermediate transfer belt 114. The secondary transfer unit includes a secondary transfer belt 118 and conveying rollers 118a and 118b, and is conveyed in the direction of arrow T3 by the conveying rollers 118a and 118b. A recording medium 124 such as transfer paper (high quality paper, thick paper), a plastic sheet, or the like is supplied to the secondary transfer unit from a recording medium storage unit 128 such as a paper feed cassette by a conveyance roller 126.

  The secondary transfer unit applies a secondary transfer bias to transfer the multi-color toner image carried on the intermediate transfer belt 114 to the recording medium 124 held by suction on the secondary transfer belt 118. The recording medium 124 is supplied to the fixing device 120 along with the conveyance of the secondary transfer belt 118. The fixing device 120 includes a fixing member 130 such as a fixing roller containing silicone rubber, fluorine rubber, or the like, pressurizes and heats the recording medium 124 and the toner image, and an image is formed as a printed matter 132 in which the toner image is fixed on the recording medium 124. Output to the outside of the forming apparatus 100. After the toner image is transferred, the intermediate transfer belt 114 is supplied to the next image forming process after the transfer residual developer is removed by a cleaning unit 116 including a cleaning blade.

  It should be noted that the photosensitive drums 104a, 106a, 108a, and 110a are arranged downstream of the intermediate transfer belt 114 in the rotation direction, in FIG. 1, at positions facing the intermediate transfer belt 114 winding portion of the transport roller 114a. Detection sensors 115a, 115b, and 115c are provided to detect the formed alignment marks. Then, based on the mark detection results of the detection sensors 115a, 115b, and 115c, various deviation amounts of each color with respect to the reference color, that is, skew deviation amounts, main / sub-registration deviation amounts, and magnification deviation amounts are calculated and corrected.

  FIG. 2 is a view showing a part of an alignment toner mark row (hereinafter also referred to as a correction pattern) 117 formed on the intermediate transfer belt 114. As can be seen from the figure, a set of four horizontal lines and four diagonal lines for each color of K, C, M, and Y is set as one set. In this embodiment, eight sets of these sets are formed. Then, the average of these detection results is calculated, and the correction amount is determined from the average value. As a result, it is possible to form a high-quality image with little misalignment of each color.

  The alignment toner mark rows 117 are formed on the back side, the center, and the near side in the main scanning direction of the intermediate transfer belt 114, and are respectively formed by the back side detection sensor 115a, the center detection sensor 115b, and the near side detection sensor 115c. To detect. In this detection, each sensor is constituted by a light reflection type sensor, and the intensity of reflected light from the surface of the intermediate transfer belt 114 and the mark of each color is detected, and a reference color (in this case, black K) is detected based on the detection result. Skew, sub-scanning registration error, main-scanning registration error, and main-scanning magnification error are calculated. Various deviation amounts, correction amount calculation, and correction execution commands are executed by a correction amount calculation unit described later. The detected pattern is cleaned by the cleaning unit 116.

  FIG. 3 is a view of the optical device viewed from the direction of arrow T1 in FIG. The optical device 102 includes an LD (laser diode) unit 102f, a cylinder lens 102g, a reflection mirror 102h, and cylinder mirrors 102i and 102j in addition to the reflection mirror 102a, the fθ lens 102bYH, the polygon mirror 102c, and the WTL lens 102d shown in FIG. , Sensors 102k and 102l are further provided. As can be seen from FIG. 3, the laser emission system including the LD unit 102f is provided at a position where the optical path of the emitted laser beam does not interfere with the fθ lens 102b, and the cylinder mirrors 102i and 102j are the laser emitted from the LD unit 102f. The beam is provided at a position where it passes through the end of the fθ lens 102b but does not interfere with the reflection mirror 102a.

  In the optical device 120 configured as described above, the light beams emitted from the LD units 102fK and 102fY pass through the cylinder lenses 102gK and 102gY, respectively, and enter the lower surface of the polygon mirror 102c by the reflecting mirrors 102hK and 102hY. The polygon mirror 102c is deflected by rotating, passes through the fθ lenses 102bKC and 102bYM, and is folded back by the first mirrors 102aK and 102aY.

  On the other hand, light beams from the LD units 102fC and 102fM pass through the cylinder lenses 102gC and 102gM, enter the upper surface of the polygon mirror 102c, are deflected by the rotation of the polygon mirror 102c, and pass through the fθ lenses 102bKC and 102bYM. The first mirrors 102aC and 102aM are folded back.

Cylinder mirrors 102iKC and 102iYM and sensors 102kKC and 102kYM are arranged upstream from the writing position in the main scanning direction, and the light beams that pass through the fθ lenses 102bKC and 102bYM are reflected and condensed by the cylinder mirrors 102iKC and 102iYM, and the sensor Incident at 102 kKC and 102 kYM. These sensors 102kKC and 102kYM are synchronization detection sensors for synchronizing in the main scanning direction. Further, similarly to the upstream side described above, cylinder mirrors 102jKC and 102jYM and sensors 102lKC and 102lYM are arranged downstream of the image area in the main scanning direction, and the light beam passing through the fθ lenses 102bKC and 102bYM is cylinder mirrors. The light is reflected and collected by 102jKC and 102jYM, and is incident on the sensor 102lKC and the sensor 102lYM.
Further, in the light beams from the LD units 102fK and 102fC, synchronous detection is performed by using the cylinder mirror 102iKC and the sensor 102kKC in common on the writing side and the cylinder mirror 102jKC and the sensor 102lKC in common on the end side. In the light beams from the LD unit 102fY and the LD unit 102fM, synchronous detection is performed using the cylinder mirror 102jYM and the sensor 102lYM in common on the writing side and the cylinder mirror 102iYM and the sensor 102kYM in common on the end side. In this method, since two color light beams are incident on the same sensor, the timing at which each light beam is incident on each sensor by making the incident angle of the polygon mirror 102c of the light beam of each color different. And is output as a pulse train in time series.

  As can be seen from FIG. 3, the light beams of black (K) and cyan (C), and yellow (Y) and magenta (M) are scanned in opposite directions. Each color beam passes through two beam detection sensors 102kKC, 102lKC, and 102lYM, 102kYM, respectively. Therefore, the passage time interval of each of the two sensors is measured by counting with a pixel clock or the like, the writing image frequency is changed so that the count value and the preset reference count value coincide, and the magnification is set. Correction (magnification correction of two-point synchronization method).

  However, if the mark for alignment shown in FIG. 2 is formed on the intermediate transfer belt 114, and it takes time to detect the mark and correct misalignment, it cannot be performed frequently. Especially during continuous printing, the temperature inside the optical device 120 rises, which causes the temperature of the fθ lens 102b to rise. Since the magnification of the fθ lens 102b changes abruptly as the temperature rises, a two-point synchronous magnification correction technique that can be executed in a short time is essential. In particular, when the material of the fθ lens is made of a synthetic resin such as plastic, the temperature rise of the fθ lens is abrupt because the heat capacity is small, and the influence of the temperature rise is very large. Therefore, a two-point synchronous magnification correction that can be performed in a short time is performed in this type of apparatus.

In the tandem type color image forming apparatus according to the present embodiment, an image is formed for each color separately, and then the respective colors are superimposed, so that an alignment technique between the colors becomes an important issue. As the color misregistration component of each color,
(1) Skew deviation, which is a color deviation caused by an angular deviation (scanning line inclination) in the beam scanning direction (main scanning direction),
(2) Registration shift in the sub-scanning direction, which is a color shift caused by a shift in writing timing on the photosensitive member in the moving direction (sub-scanning direction) of the transfer belt 114,
(3) Registration shift in the main scanning direction, which is a color shift caused by a shift in writing timing to the photoconductor in the main scanning direction,
(4) Magnification error in the main scanning direction due to expansion / contraction of the image in the main scanning direction,
There are four components.
FIG. 4 is a diagram showing the concept of skew deviation, and FIG. 5 is a diagram showing a state when the deviation is corrected. FIG. 4 shows the skew of the M color with respect to the K color on the transfer paper P. When a line is drawn in the main scanning direction, the scanning line of the M color is inclined with respect to the K color. When such a skew deviation is corrected, the M-color scanning line is corrected as M ′ as shown in FIG. 5, and as shown in FIG. 5, the registration deviation Hm, Hs is generated. This is because the skew rotation center O on the image does not coincide with the image center, and the resist moves at the same time as the skew is moved.

  FIG. 6 is a block diagram illustrating a configuration of a color misregistration correction circuit that performs color misregistration correction. The color misregistration correction circuit 200 includes a pattern detection unit 201, a correction amount calculation unit 202, a memory 203, and write control units 204M, 204C, 204Y, and 204K for each color, and is controlled by a CPU (not shown). The CPU reads a program stored in a ROM (not shown) and executes control defined by the program while using a RAM (not shown) as a work area and a data buffer.

  Signals (reflection intensity detection signals) from the detection sensors 115a, 115b, and 115c for detecting the alignment marks 117 formed on the intermediate transfer belt 114 are input to the pattern detection unit 201, and this pattern detection unit In 201, the position of the pattern is detected. The position information of the pattern detected by the pattern detection unit 201 is sent to the correction amount calculation unit 202, and the correction amount calculation unit 202 calculates the color misregistration amount and the color matching correction amount. The calculated color misregistration amount and color matching correction amount are stored in the memory 203, and then sent to the write control units 204M, 204C, 204Y, and 204K for each color. Note that the position detection and the color misregistration amount and color matching correction amount calculation processing executed by the pattern detection unit 201 and the correction amount calculation unit 202 are known techniques, and a detailed description thereof will be omitted here. .

  FIG. 7 is a flowchart showing a control procedure of the color misregistration correction control, which is executed by the CPU. In this control procedure, first, an alignment mark (correction pattern) 117 is formed on the intermediate transfer belt 114 (step S101), and the correction pattern 117 is output from the outputs of the detection sensors 115a, 115b, and 115c in the pattern detection unit 201. The position is detected (step S102). Next, in the correction amount calculation unit 202, based on the pattern detection value (position information) input from the pattern detection unit 201, the skew deviation amount D1, the main registration deviation amount D2, the sub-registration deviation amount D3, and the main scanning magnification deviation amount. D4 is calculated (step S103), and a skew correction amount C1, a main registration correction amount C2, a sub registration correction amount C3, and a sub scanning magnification correction amount C4 are calculated based on the calculated deviation amounts (step S104). Thereafter, skew correction, main / sub resist correction, and main scanning magnification correction are executed according to the calculated various correction amounts (step S105).

  On the other hand, in the invention described in, for example, Patent Document 1 (Japanese Patent No. 3351435), correction for skew registration deviation and correction for other registration deviation are performed in different sampling cycles. Registration deviation is corrected.

  In the invention described in Patent Document 2 (Japanese Patent Application Laid-Open No. 2007-155664), a plurality of color images are formed on the transfer belt so as to be superimposed, and a correction pattern for correcting misregistration of each color is formed on the transfer belt. The writing unit to be formed, the detection sensor and pattern detection unit for detecting the correction pattern, and the skew deviation amount and other color misregistration amounts of the writing unit are obtained based on the detected correction pattern, and each obtained color misregistration amount is corrected. A correction amount calculation unit for calculating a correction amount for the control unit, a writing control unit that controls the writing unit based on the correction amount, and a skew correction motor control unit, and the number of color misregistration correction processes is determined based on a predetermined condition. And a determination processing unit that performs control so that the color misregistration correction process is executed the determined number of times so as to perform highly accurate color misregistration correction in a short time. To have.

  As described above, in the invention described in Patent Document 1, the correction for the skew registration deviation and the correction for the other registration deviation are performed in different sampling cycles. Color misregistration correction is performed continuously. That is, in the invention described in Patent Document 1, control for correcting only skew deviation is performed in the correction control by the first correction pattern formation, and then correction control by the second correction pattern formation is performed. Control is performed to correct only the misalignment. As a result, the registration error is corrected after the skew error is eliminated, so that the registration error caused by the skew error can be corrected with high accuracy.

  However, in the invention described in Patent Document 1, since the correction pattern is formed twice on the transfer belt, the correction amount is calculated and the correction control is performed, the time required for the correction process must be increased. On the other hand, the invention described in Patent Document 2 has a control means for determining the number of times of color misregistration execution, that is, whether to execute color misregistration correction once or twice based on a predetermined condition in order to reduce processing time. However, the process of correcting the skew deviation and the registration deviation simultaneously by forming the correction pattern once has not been realized, and an increase in the color misregistration correction time cannot be denied.

  Therefore, a problem to be solved by the present invention is to enable highly accurate color misregistration correction in a short time.

  In order to solve the above problems, the first means forms an image forming unit that forms a plurality of color images on the image carrier, and forms a correction pattern for correcting misregistration of each color on the image carrier. Determining the color misregistration amount of the image forming unit based on the correction pattern detected by the pattern forming means, the detection means for detecting the correction pattern formed on the image carrier, and the detection means; Further, a correction amount calculating unit that calculates a correction amount for correcting the obtained color misregistration amount, and a writing control that controls a writing position in the image forming unit based on the correction amount calculated by the correction amount calculating unit. And an image forming apparatus for forming an image by transferring an image formed on the image carrier to a recording medium, wherein the correction amount calculating means is based on the detected correction pattern. And calculating a coefficient for correcting the registration correction amount calculated based on the detected correction pattern, based on the skew correction amount calculated in the above, and the configuration of the optical element involved in the skew correction amount and the skew correction. Features.

  According to a second means, in the first means, the correction amount calculating means calculates the correction amount according to the skew correction amount for each of the main scanning registration correction amount and the sub-scanning registration correction amount. The correction amount is added or subtracted.

  According to a third means, in the first means, the correction amount calculating means calculates a deviation corresponding to the skew correction amount with respect to each of the main scanning registration deviation amount and the sub-scanning registration deviation amount when calculating the correction amount. The registration correction amount for main scanning and sub-scanning is calculated from the amount of deviation after addition or subtraction.

  The fourth means includes storage means for storing, in any of the first to third means, a shift amount or a correction amount of each of the main scanning resist and the sub-scanning resist per unit movement amount of the skew correction. It is characterized by that.

  The fifth means includes an image forming unit that forms a plurality of color images on the image carrier, a pattern forming means that forms a correction pattern for correcting misregistration of each color on the image carrier, and Based on a detection unit that detects the correction pattern formed on the image carrier, and the correction pattern detected by the detection unit, the color misregistration amount of the image forming unit is obtained, and each of the obtained color misregistration amounts is obtained. Correction amount calculating means for calculating a correction amount for correcting image correction, and control means for controlling an image forming position in the image forming unit based on the correction amount calculated by the correction amount calculating means, A misregistration correction method in an image forming apparatus that performs image formation by transferring an image formed on an image carrier to a recording medium, and a skew correction amount calculated based on a detected correction pattern; Based on the configuration of the optical elements involved in the skew correction amount and the skew correction, and calculates a coefficient for correcting the registration correction amount calculated based on the detected correction pattern.

  Sixth means includes an image forming unit that forms a plurality of color images on an image carrier, a pattern forming unit that forms a correction pattern for correcting misregistration of each color on the image carrier, and Based on the detection unit that detects the correction pattern formed on the image carrier, and the correction pattern detected by the detection unit, the color misregistration amount of the image forming unit is obtained, and the obtained color misregistration amounts are obtained. A correction amount calculation unit that calculates a correction amount for correction; and a control unit that controls an image forming position in the image forming unit based on the correction amount calculated by the correction amount calculation unit. A misregistration correction control program for executing misregistration correction control in an image forming apparatus that performs image formation by transferring an image formed on a carrier onto a recording medium. Coefficient for correcting the resist correction amount calculated based on the detected correction pattern based on the skew correction amount calculated based on the corrected correction pattern and the configuration of the optical element involved in the skew correction amount. It is characterized by having a procedure for calculating.

  In the embodiment described later, the image carrier is applied to the intermediate transfer belt 114, the image forming unit and the pattern forming unit to 112, and the detecting unit to the pattern detecting unit 201 including the detecting sensors 115a, 115b, and 115c. The calculation unit corresponds to the correction amount calculation unit 202, the write control unit corresponds to the write control units 204M, 204C, 204Y, and 204K, the correction pattern corresponds to the code 117, the image forming apparatus corresponds to the code 100, and the storage means corresponds to the memory 208. .

  According to the present invention, the correction amount is corrected using a coefficient for correcting the registration correction amount calculated based on the detected correction pattern. Therefore, the main scanning and sub-scanning by skew correction can be performed by one color misregistration correction. Registration shift can be corrected, and highly accurate color shift correction can be realized in a short time.

It is a figure which shows schematic structure of the color image forming apparatus in this embodiment currently implemented conventionally. FIG. 4 is a diagram illustrating a part of an alignment toner mark row formed on an intermediate transfer belt. It is the figure which looked at the optical apparatus from the arrow T1 direction in FIG. It is a figure which shows the concept of skew deviation. It is a figure which shows a state when correct | amending deviation | shift. It is a block diagram which shows the structure of the color misregistration correction circuit which performs color misregistration correction. It is a flowchart which shows the control procedure of color misregistration correction control. It is a flowchart which shows the control procedure of the correction process which concerns on this embodiment. It is a flowchart which shows the process sequence of the correction process which concerns on other embodiment. FIG. 10 is a block diagram illustrating an example of a color misregistration correction circuit suitable for performing the processes of FIGS. 8 and 9. It is a top view which shows the structure of the optical element at the time of skew correction. It is the side view seen from the transversal direction of the mirror which shows the relationship between the movement amount of a mirror, and a photosensitive drum. It is a figure which shows the calculation method of the skew correction amount B on a real image. It is a figure which shows the calculation method of the shift | offset | difference Bs of the subscanning direction by the skew correction | amendment on a real image. It is a figure which shows the calculation method of the shift | offset | difference Bm of the main scanning direction by the skew correction | amendment on a real image.

  According to the present invention, correction for skew registration deviation and correction for other registration deviation can be efficiently performed, and highly accurate color misregistration correction can be performed in a short time. Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1 to 7, the color image forming apparatus 100 shown in FIG. 1, the positioning correction mark (correction pattern) 117 shown in FIG. 2, the optical device 102 shown in FIG. 3, and the color misregistration correction shown in FIG. Since the circuit 200 is the same as in the present embodiment, the same reference numerals are given to the same components in the following description, and redundant descriptions are omitted. In the example of FIG. 1, an indirect transfer type tandem color image forming apparatus is taken as an example, but a direct transfer type tandem color image forming apparatus is also the same. However, the correction pattern 117 is formed not on the intermediate transfer belt but on a conveyance belt that adsorbs and conveys transfer paper as a recording medium.

  When the skew deviation shown in FIG. 4 is corrected as described above, the M-color scanning line is corrected as M ′ as shown in FIG. 5, and main scanning and sub-scanning as shown in FIG. In this case, resist misalignments Hm and Hs occur. This is because the skew rotation center O on the image does not coincide with the image center, and the resist moves at the same time as the skew is moved. Since the rotation center O of the skew is determined by the configuration of the optical system, the influence of the skew correction on the resist varies depending on the configuration of the optical elements of the optical device 120. Therefore, in this embodiment, the main and sub registration deviations due to skew correction are corrected as follows.

  In other words, in the present embodiment, the color matching accuracy is improved by calculating the registration correction amount in consideration of main and sub registration deviations due to skew correction when calculating each correction value. FIG. 8 is a flowchart showing a control procedure of correction processing according to the present embodiment.

  The flowchart shown in FIG. 8 is obtained by replacing step S104 in the flowchart of FIG. 7 with step S201, and other steps are the same as those in FIG. In step S201, the correction amount Am corresponding to the main scanning registration deviation amount per skew step and the correction amount As corresponding to the sub-scanning registration deviation amount per skew step are set in advance in the image forming apparatus 100 by the configuration of the optical system. It is obtained by estimating the theoretical value from the configuration of the optical element of the optical device 102. In this case, instead of estimating the theoretical value, the skew is actually moved by a specific number of steps, the pattern 117 is formed on the intermediate transfer belt 114 before and after the movement, and the movement amount of the main / sub resist is measured. May be. An estimation method for estimating the theoretical value from the optical configuration will be described later with reference to FIG.

  When the color misregistration correction is executed, the skew correction amount C1 is first calculated. Next, main and sub registration correction amounts C2 and C3 are calculated. At this time, registration correction amounts Am * C1 in the main scanning direction and registration correction adjustment amounts As * in the sub scanning direction are added to the registration correction amounts C2 and C3, respectively. C1 is further added. At the same time, the main operation magnification correction amount C4 is calculated. By doing so, it is possible to correct the main and sub resist misalignment due to skew correction.

  FIG. 9 is a flowchart showing a processing procedure according to another embodiment. The flowchart shown in FIG. 9 is obtained by replacing step S103 in the flowchart of FIG. 7 with step S301 and step S104 with step S302, and other steps are the same as those in FIG. Therefore, in step S301, the main scanning registration deviation amount Bm per skew step and the sub-scanning registration deviation amount Bs per skew step are determined in advance from the configuration of the optical system of the optical device 120 of the image forming apparatus 100. Estimate. The estimation will be described later with reference to FIGS.

  In step S301, a skew deviation amount D1 and a skew correction amount C1 are calculated. In step S302, the main and sub resist correction amounts C2 and C3 are calculated. At this time, the main resist shift amount Bm * C1 per one skew step and the sub resist shift are added to the main and sub resist shift amounts D2 and D3 in advance. The quantity Bm * C2 is added. Main and sub registration correction amount correction amounts C2 and C3 are calculated from the added deviation amount. In step S302, a main scanning magnification deviation amount D4 and a main scanning magnification correction amount C4 are calculated. By doing so, it is possible to correct the main and sub resist misalignment due to the skew correction.

  FIG. 10 is a block diagram showing an example of a color misregistration correction circuit 210 suitable for performing the processes of FIGS. 8 and 9. The color misregistration correction circuit 210 is provided with a memory 208 for storing the correction amounts and misregistration amounts of the main and sub resists at the time of skew correction in addition to the color misregistration correction circuit 200 shown in FIG. As described above, when the memory 208 for storing the correction amounts and the shift amounts of the main and sub resists at the time of skew correction is installed in the color misregistration correction circuit 210, the correction amount and the shift can be previously determined by referring to the memory 208. It is not necessary to incorporate the amount into the control, and each value is measured after the image forming apparatus 100 is assembled and stored in the memory 208, so that highly accurate correction can be performed.

  In step S201 in FIG. 8 and step S301 in FIG. 9, the resist correction amounts Am, As, Bm, and Bs are estimated from the configuration of the optical system. This estimation method will be described with reference to FIGS. In the following description, when components are generally described, subscripts of M, C, Y, and K indicating colors are omitted.

FIG. 11 is a plan view showing the configuration of the optical element at the time of skew correction, and FIG. 12 is a side view showing the relationship between the amount of movement of the mirror and the photosensitive drum as seen from the short side of the mirror. In FIG. 11, the skew is corrected by finely adjusting the angle of the first stage mirror 102a of the optical system by the stepping motor 102m. Since the stepping motor moves by the number of input pulses by giving a pulsed electric signal, the number of steps corresponds to the moving range on a one-to-one basis. Therefore, assuming that the operating range of the mirror 102a by the stepping motor 120m per pulse with respect to the rotation center (fulcrum) O1 of the mirror 102a is A, the movement amount A of the mirror by the stepping motor 102m per step as shown in FIG. And the amount of movement B ′ of the latent image position in the sub-scanning direction of the beam on the photosensitive drum 104a is defined as follows.
B ′ = A / cos θ
It becomes.
In this way, the skew correction amount B ′ on the image plane can be calculated per step of the stepping motor.

When this skew correction amount B ′ is replaced with an image area, the skew correction amount B on the actual image is calculated as shown in FIG. 13 according to the similarity rule of a triangle having the skew rotation center O as a vertex. That means
B = B ′ × a1 / a2
It becomes. Here, a1 is the distance from the skew rotation center O to the image end on the image, and a2 is the distance from the skew rotation center O to the beam irradiation position at the mirror end.

As shown in FIG. 14, the deviation Bs in the sub-scanning direction due to skew correction is a stepping motor where m1 is the distance from the skew rotation center O to the image end and m2 is the distance from the skew rotation center O to the image center. From the skew correction amount B on the actual image per step of 102 m,
Bs = (m2 / m1) * B
Is calculated as

As shown in FIG. 15, the deviation Bm in the main scanning direction due to the skew correction is set to θ2 as a deviation amount with respect to the rotation center O of the skew, and passes through the skew rotation center O from the edge of the skewed image M. Assuming that the distance between the end of the perpendicular line drawn on the image M ′ in which only the skew is corrected as a line extending in the direction and the skew rotation center O is s1, the skew correction amount B on the actual image per step of the stepping motor 102m. From
Bm = m1-s1
And
s1 = m1 * cos θ2
Because
Bm = m1 (1-cos θ2)
Is calculated. Here, θ2 is θ2 = sin ⁻¹ (B / m1)
So that
Bm = m1 (1-sin ⁻¹ (B / m1))
It becomes.

Am and As are values obtained by dividing Bm and Bs by the resist correction resolution in the main scanning direction and the sub-scanning direction, respectively. That is, Am = Bm / (main scanning correction minimum unit)
As = Bs / (sub scanning correction minimum unit)
Can be obtained as These registration correction amounts Am, As, Bm, and Bs correspond to coefficients for correcting the registration correction amounts.

  Note that the registration correction amounts Am, As, Bm, and Bs obtained in this way are determined to be fixed values depending on the configuration of the optical element (optical system). Therefore, if the estimation is performed once (calculation of the estimation is performed once), There is no need to estimate each time the skew is corrected.

  By estimating the resist correction amounts Am, As, Bm, and Bs in this way, the correction amounts in step S201 and step S302 can be calculated.

  Other parts not specifically described are configured in the same manner as the above-described conventional example and function in the same manner.

  In addition, this invention is not limited to this embodiment, All the technical matters contained in the technical thought described in the claim are object.

  The present invention relates to a color image forming apparatus having a color misregistration correction function when forming images of a plurality of colors independently and superimposing the colors to obtain a color image, such as a color copier, printer, facsimile, The present invention can be applied to a digital image forming apparatus such as a digital multi-function peripheral, particularly an image forming apparatus that forms an image by electrophotography.

DESCRIPTION OF SYMBOLS 100 Image forming apparatus 112 Image forming part 114 Intermediate transfer belt 115a, 115b, 115c Detection sensor 117 Correction pattern (Toner mark for alignment)
201 pattern detection unit 202 correction amount calculation unit 204M, 204C, 204Y, 204K write control unit 208 memory

Japanese Patent No. 3351435 JP 2007-155664 A

Claims (6)

An image forming unit that forms and superimposes images of a plurality of colors on an image carrier;
Pattern forming means for forming a correction pattern for correcting misregistration of each color on the image carrier;
Detecting means for detecting the correction pattern formed on the image carrier;
Based on the correction pattern detected by the detection unit, a correction amount calculation unit that calculates a color shift amount of the image forming unit and calculates a correction amount for correcting the calculated color shift amount;
Writing control means for controlling a writing position in the image forming unit based on the correction amount calculated by the correction amount calculating means;
An image forming apparatus that performs image formation by transferring an image formed on the image carrier to a recording medium,
The correction amount calculation means includes a resist correction calculated based on the detected correction pattern based on the skew correction amount calculated based on the detected correction pattern and the configuration of the optical element involved in the skew correction amount and the skew correction. An image forming apparatus that calculates a coefficient for correcting a correction amount. The image forming apparatus according to claim 1,
When calculating the correction amount, the correction amount calculating means adds or subtracts a correction amount corresponding to the skew correction amount with respect to each of the main scanning registration correction amount and the sub-scanning registration correction amount. Image forming apparatus. The image forming apparatus according to claim 1,
When calculating the correction amount, the correction amount calculation means adds or subtracts a deviation amount corresponding to the skew correction amount to each of the main scanning registration deviation amount and the sub-scanning registration deviation amount, and a deviation amount after addition / subtraction A registration correction amount for main scanning and sub-scanning is calculated from the image forming apparatus. The image forming apparatus according to any one of claims 1 to 3,
An image forming apparatus comprising storage means for storing a shift amount or a correction amount of each of the main scanning registration and the sub-scanning registration per unit movement amount of the skew correction. An image forming unit that forms and superimposes images of a plurality of colors on an image carrier;
Pattern forming means for forming a correction pattern for correcting misregistration of each color on the image carrier;
Detecting means for detecting the correction pattern formed on the image carrier;
Correction amount calculation means for calculating a color misregistration amount of the image forming unit based on the correction pattern detected by the detection means, and calculating a correction amount for correcting the obtained color misregistration amounts;
Control means for controlling an image forming position in the image forming section based on the correction amount calculated by the correction amount calculating means;
A positional deviation correction method in an image forming apparatus for forming an image by transferring an image formed on the image carrier to a recording medium,
Based on the skew correction amount calculated based on the detected correction pattern and the configuration of the optical element involved in the skew correction amount and the skew correction amount, the resist correction amount calculated based on the detected correction pattern is corrected. A misregistration correction method characterized by calculating a coefficient. An image forming unit that forms and superimposes images of a plurality of colors on an image carrier;
Pattern forming means for forming a correction pattern for correcting misregistration of each color on the image carrier;
Detecting means for detecting the correction pattern formed on the image carrier;
Correction amount calculation means for calculating a color misregistration amount of the image forming unit based on the correction pattern detected by the detection means, and calculating a correction amount for correcting the obtained color misregistration amounts;
Control means for controlling an image forming position in the image forming section based on the correction amount calculated by the correction amount calculating means;
A misregistration correction control program for executing misregistration correction control in an image forming apparatus that performs image formation by transferring an image formed on the image carrier to a recording medium,
Based on the skew correction amount calculated based on the detected correction pattern and the configuration of the optical element involved in the skew correction amount and the skew correction amount, the resist correction amount calculated based on the detected correction pattern is corrected. A misregistration correction control program comprising a procedure for calculating a coefficient.

Images