JP2007155895A - Color image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To drastically shorten a processing time required for a correction control and frequently perform the correction control, consequently, to secure a high quality image without causing the reduction of productivity in image forming processing. <P>SOLUTION: Colors having the same scanning direction of light beam related to a photoreceptor are grouped into the same group, and only black and yellow resist patterns PK and PY as typical colors selected for every group are formed at respective detecting positions of resist sensors 32a and 32c, the state of the positional change of other colors belonging to the same group is predicted based on the obtained state of the positional change of black and yellow as the typical colors, then, information on the positional deviation of each color other than the reference color from the reference color in the main scanning direction is obtained. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention provides a color image forming apparatus which forms an image on the photosensitive member for each color individually by scanning a light beam by an exposure unit for the photosensitive member for each color and synthesizes them on an intermediate transfer member to obtain a color image. It is about.

  A so-called tandem type color image forming apparatus in which process units for respective colors of yellow, magenta, cyan, and black are arranged along an intermediate transfer belt so that toner images of the respective colors are superimposed on the intermediate transfer belt. Widely used. In this type of tandem color image forming apparatus, after images are individually formed on the photosensitive drums for the respective colors, the images for the respective colors are sequentially superimposed on the intermediate transfer belt. If the image is misaligned, color misregistration occurs in the image superimposed on the intermediate transfer belt, and the image quality is deteriorated.

  Such color misregistration occurs when the positional relationship of an optical component or the like that guides the light beam emitted from the light source to the photoreceptor changes with environmental changes such as temperature, and color misregistration detection formed on the intermediate transfer belt. The correction control based on the pattern image shift state can be suppressed by executing it at an appropriate timing. However, it takes time to perform operations such as pattern image formation necessary for this, so that If the correction control is frequently performed, the productivity of the image forming process is greatly reduced. On the contrary, if the execution interval of the correction control becomes long, the control cannot follow the environmental change and the high-quality control is performed. There arises a problem that it is difficult to secure an image.

Therefore, an area that does not affect the required image forming process so that high-quality images can be secured by frequently executing correction control without causing a significant decrease in productivity of the image forming process. There is known a configuration in which a pattern image for alignment is formed on the sensor and correction control can be performed in parallel with the image forming process (see Patent Documents 1 and 2).
JP-A-8-6347 Japanese Patent Laid-Open No. 2005-4121

  However, in the conventional technique, it is necessary to set the widths of the photosensitive drum and the intermediate transfer belt larger than usual in order to form a pattern image for alignment in an area that does not affect the required image forming process. As a result, there is a disadvantage in that the size of the apparatus is increased and the manufacturing cost is increased, and the pattern image for alignment is formed outside the normal image forming area, so that sufficiently high alignment accuracy is ensured. The problem that cannot be done. For this reason, a technique for shortening the correction control processing time by a method of forming a pattern image in a normal image forming area is desired.

  The present invention has been devised to solve such problems of the prior art, and its main purpose is to greatly reduce the processing time of correction control, thereby improving the productivity of image forming processing. An object of the present invention is to provide a color image forming apparatus configured so that a high-quality image can be secured by frequently performing correction control without causing a decrease.

  In the color image forming apparatus of the present invention, an image is individually formed on the photoconductor for each color by scanning a light beam with an exposure unit for the photoconductor for each color, and the color image is synthesized on the intermediate transfer member. A color image forming apparatus to be obtained, wherein a plurality of light sources for each color are arranged so that a scanning direction of a light beam with respect to the photoconductor is opposite in accordance with a positional relationship with respect to the rotary polygon mirror, and the intermediate An image detecting unit that detects a pattern image for alignment formed on the transfer body at a plurality of detection positions separated in the main scanning direction, and a pattern image on the intermediate transfer body is detected by the image detecting unit. Correction control means for acquiring positional deviation information for each color based on the detection result and performing correction processing. The correction control means is configured so that the scanning directions of the light beams with respect to the photosensitive member are mutually different. The same color is grouped into the same group, and only the representative color pattern image selected for each group is formed at each detection position of the image detection means, and the representative color pattern obtained thereby A position change situation of pattern images of other colors belonging to the same group is predicted from the position change situation of the image, and positional deviation information in the main scanning direction for each other color with respect to the reference color is obtained.

  According to the present invention, the number of pattern images for alignment is reduced, and the calculation load is reduced, so that the processing time can be greatly shortened, so that the productivity of image forming processing is not reduced. Further, correction control can be frequently performed to ensure a high-quality image, and a remarkable effect can be obtained in achieving both improvement in productivity of image formation processing and improvement in image quality. In particular, the shortening of the processing time of the misregistration correction reduces the productivity of the image forming process when the misregistration correction is performed by forming a pattern image so as to be inserted between sheets, that is, between images for each page. It is effective in suppressing.

  According to a first aspect of the present invention for solving the above-described problems, an image is individually formed on the photosensitive member for each color by scanning a light beam by an exposure unit for the photosensitive member for each color, and the image is formed on the intermediate transfer member. A color image forming apparatus that combines to obtain a color image, wherein a plurality of light sources for each color are arranged so that the scanning direction of the light beam with respect to the photosensitive member is reversed according to the positional relationship with respect to the rotary polygon mirror An exposure unit; an image detection unit that detects a pattern image for alignment formed on the intermediate transfer member at a plurality of detection positions spaced apart in a main scanning direction; and a pattern image on the intermediate transfer member. Correction means for detecting the detection means and acquiring positional deviation information for each color based on the detection result to perform correction processing. The correction control means includes a light beam for the photoconductor. The colors having the same scanning direction are grouped into the same group, and only the pattern image of the representative color selected for each group is formed at each detection position of the image detection unit, and thus acquired. The position change situation of pattern images of other colors belonging to the same group is predicted from the position change situation of the pattern image of the representative color, and the positional deviation information in the main scanning direction for each of the other colors with respect to the reference color is obtained. .

  According to this, since the number of pattern images for alignment is reduced and the calculation burden is reduced, the processing time can be greatly shortened, so that correction can be performed without reducing the productivity of image forming processing. Control can be performed frequently to ensure a high quality image.

  In the so-called spray type exposure apparatus, the light beam emitted from the light source is incident on the reflecting surface at different angular positions of a single rotating polygon mirror, and is distributed to the opposite sides across the rotating polygon mirror. In such an exposure apparatus, the scanning directions of the light beams with respect to the photosensitive member are the same for colors reflected by the light beams incident on the reflecting surfaces at the same angular positions of the rotary polygon mirror and reflected in substantially the same direction. In addition, since the light sources are arranged close to each other and the light beam shares an optical element, they exhibit substantially the same variation characteristics with respect to the positional deviation in the main scanning direction accompanying an environmental change such as temperature. For this reason, if the scanning direction of the light beam with respect to the photoconductor is grouped into the same group with the same color, only the pattern image of the representative color selected for each group is formed. The position change situation in the main scanning direction of other colors belonging to the same group can be predicted from the position change situation of the representative color.

  In addition, for the colors that are incident on the reflecting surfaces at different angular positions of the rotating polygon mirror and are distributed to opposite sides across the rotating polygon mirror, the scanning directions of the light beams on the photoreceptor are opposite to each other. Therefore, compared to an exposure apparatus configured to scan all color light beams in the same direction, the amount of color shift in the main scanning direction is likely to increase. It is effective to do it frequently.

  In this case, since pattern images for each color are not formed at a plurality of detection positions separated in the main scanning direction, it is not possible to obtain information on the inclination and curvature state of the scanning line for each color. Misalignment due to the change is particularly remarkable in the main scanning direction, and high image quality can be ensured by frequently performing corrections related to misalignment in the main scanning direction.

  According to a second aspect of the invention for solving the above-described problem, the correction control unit causes the pattern image of the representative color to be formed at each detection position of the image detection unit, and the pattern image is stored in the image detection unit. It is possible to execute a shortening mode for detection and a standard mode in which all pattern images for each color are formed at respective detection positions of the image detection unit and the pattern detection unit detects the pattern image. After executing the above, the validity of the correction process in the shortening mode is determined based on the position change state of the pattern image of the representative color acquired in the shortening mode. It is possible to adopt a configuration in which the standard mode is executed and correction processing is performed based on the positional deviation information acquired in the standard mode.

  According to this, since the standard mode is executed when it is determined that the correction processing based on the shortening mode is not appropriate based on the position change state of the representative color pattern image, it is possible to ensure high alignment accuracy. it can.

  In this case, the criteria for determining the validity of the correction processing based on the shortening mode are the position change status of the pattern image of the representative color, for example, the measured value of the representative color acquired in the shortening mode and the previous representative acquired in the latest standard mode. What is necessary is just to make it a variation ratio with the actual measurement value of color. At this time, if the fluctuation ratio falls below a predetermined threshold, correction processing based on the shortening mode is performed. Conversely, if the fluctuation ratio exceeds a predetermined threshold, the standard mode is performed again. The correction process may be performed based on the positional deviation amount acquired in the standard mode.

  It should be noted that the validity of the correction process in the shortening mode is not determined based only on the position change state of the representative color pattern image as described above, but is added with other determination criteria such as required image quality. Anyway. Further, it may be configured such that whether or not to perform the operation of changing to the standard mode by judging the validity of the correction processing in the shortening mode can be selected and set according to the needs of the user.

  According to a third aspect of the present invention for solving the above-described problem, the correction control unit causes the pattern image of the representative color to be formed at each detection position of the image detection unit, and the pattern image is stored in the image detection unit. It is possible to execute a shortening mode for detection and a standard mode in which all pattern images for each color are formed at respective detection positions of the image detection unit and the pattern detection unit detects the pattern image. In addition, either of the standard mode and the standard mode can be selected according to the fluctuation state of the environmental condition.

  According to this, since the standard mode is executed when the high accuracy for the misalignment correction cannot be sufficiently secured only by the misalignment information acquired by the shortening mode due to the fluctuation condition of the environmental conditions, the high alignment is performed. Accuracy can be ensured.

  In this case, the environmental condition that is a criterion for selecting the shortening mode and the standard mode may be, for example, the temperature inside the apparatus detected by the temperature detecting means, and according to this, the temperature variation is the main color shift. Therefore, the selection of the shortening mode and the standard mode can be performed appropriately. At this time, the temperature variation is obtained by comparing the temperature detected by the temperature detection means with the previous detected temperature, and when the temperature variation is below a predetermined threshold, the shortening mode is selected, and the temperature is reversed. The standard mode may be selected when the amount of fluctuation exceeds a predetermined threshold.

  In addition, it is good also as a structure which can be set selectively according to a user's necessity whether to perform shortening mode according to the fluctuation | variation state of environmental conditions.

  According to a fourth aspect of the present invention for solving the above problems, the correction control means predicts a position change situation of a pattern image of another color belonging to the same group from a position change situation of the pattern image of the representative color. The actual value of the representative color based on the pattern image is compared with the previous actual value of the representative color to obtain a variation ratio, and the variation ratio and the previous color of the other colors belonging to the same group as the representative color are obtained. The predicted value of the other color can be calculated from the actually measured value.

  According to this, it is possible to obtain a predicted value with sufficiently high accuracy and to perform simple proportional calculation, so that the circuit scale of the correction control means can be reduced.

  In this case, the last actual measurement values of the representative color and other colors are preferably acquired in the latest standard mode.

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

  FIG. 1 is a schematic diagram showing an example of a color image forming apparatus according to the present invention. The color image forming apparatus includes an image forming unit 1 that forms an image on a recording sheet through processes of charging, exposure, development, transfer, and fixing. The recording paper stored in the cassette is sequentially fed through the paper feeding path A, and the recording paper on which a required image is formed by the image forming unit 1 is discharged onto the tray of the paper discharging unit 3 through the paper discharging path B. The

  The image forming unit 1 forms a plurality of process units 11 to 14 that form toner images for respective color components of yellow, magenta, cyan, and black, and image formation of the photosensitive drums 11a to 14a of the process units 11 to 14. LSU (laser scanning unit: exposure means) 16 that scans the surface with a light beam for exposure, and toner images for each color formed on the photosensitive drums 11a to 14a of the process units 11 to 14 And an intermediate transfer belt (intermediate transfer member) 17 that is sequentially transferred and combined, and the photosensitive drums 11 a to 14 a for each color are arranged along the intermediate transfer belt 17 in a tandem configuration. ing.

  In each of the process units 11 to 14, an electrostatic latent image is formed by scanning an exposure light beam from the LSU 16 on the image forming surfaces of the photosensitive drums 11a to 14a that are uniformly charged by a charger. The electrostatic latent images on the photosensitive drums 11a to 14a are developed with toner supplied from a developing device, and single color toner images for the respective color components are formed on the image forming surfaces of the photosensitive drums 11a to 14a.

  The intermediate transfer belt 17 is supported by being wound around a pair of support rollers 21 and 22, and the toner images on the photosensitive drums 11 a to 14 a are pressed inside the intermediate transfer belt 17 by pressing the intermediate transfer belt 17. Primary transfer rollers 24 to 27 for each color to be transferred to the intermediate transfer belt 17 are provided. Further, a secondary transfer roller 28 for transferring the toner image on the intermediate transfer belt 17 to a recording sheet is provided on the side of the intermediate transfer belt 17, and the recording to which the toner image is transferred by the secondary transfer roller 28 is provided. The paper is conveyed to the fixing device 19 and a process for fixing the toner image on the recording paper by heat and pressure is performed.

  On the upstream side of the secondary transfer portion 29 by the secondary transfer roller 28 and the support roller 21, a registration roller 31 is provided for aligning the toner image on the intermediate transfer belt 17 and the recording paper. Recording paper feed timing is adjusted based on the detection result of a registration sensor for recording paper (not shown).

  In addition, in the vicinity of the secondary transfer unit 29, color misregistration due to the misregistration of the toner image for each color that has been imaged by each of the process units 11 to 14 and transferred onto the intermediate transfer belt 17 is detected. A resist sensor (image detection means) 32 for detecting the resist pattern is disposed.

  Further, this color image forming apparatus is provided with a temperature sensor (temperature detection means) 34 for detecting the temperature in the apparatus, for example, the ambient temperature in the vicinity of the LSU 16 that greatly affects the color shift.

  FIG. 2 is a block diagram showing a schematic configuration of a main part related to control in the color image forming apparatus shown in FIG. The image forming apparatus includes a host controller 41 that comprehensively controls the operation of the apparatus and an engine controller 42 that controls various operations for image formation on recording paper, and is connected to a network-connected PC 43. Necessary image processing is performed by the host controller 41 based on the print data received in response to the print request from the printer, and image formation processing is performed by the engine controller 42 based on the image data obtained thereby.

  The engine controller 42 includes an electrophotographic process control unit 44 that comprehensively controls the electrophotographic process in the image forming unit 1 shown in FIG. 1, a fixing control unit 45 that controls a fixing operation by the fixing device 19, and a paper feeding unit. A series of correction operations including image misregistration correction, and a sheet feeding / conveying control unit 46 that controls sheet feeding and conveying operations by 2 and other conveying rollers, an LSU control unit 47 that controls laser scanning by the LSU 16 and the like. It has an image correction controller (correction control means) 48 for controlling, and an engine CPU 60 for comprehensively controlling the operations of these parts.

  The registration sensors 32 are provided at a total of three locations separated in the main scanning direction (width direction), and a registration sensor 32a disposed in the vicinity of the left edge of the intermediate transfer belt 17 and the intermediate transfer belt. 17, a registration sensor 32b arranged at the center position in the width direction, and a registration sensor 32c arranged near the right edge of the intermediate transfer belt 17, and these registration sensors 32a. The output signals 32b and 32c are input to the image correction controller 48 via the AD converter 51.

  Further, the output signal of the temperature sensor 34 is input to the image correction controller 48 via the AD converter 51.

  FIG. 3 is a block diagram showing a schematic configuration of the image correction controller 48 shown in FIG. The image correction controller 48 includes a correction value acquisition unit 53 that acquires correction values from detection results of the registration sensors 32a, 32b, and 32c, and a resist pattern generation unit that generates image data of a resist pattern based on instructions from the control unit 56. 54, a correction processing unit 55 that performs color misregistration correction processing according to the correction value acquired by the correction value acquisition unit 53, and a control unit 56 that controls these units.

  The correction processing unit 55 corrects the writing position in the LSU 16 with respect to the positional deviation in the main scanning direction. Further, the writing timing correction by the LSU 16 is performed for the positional deviation in the sub-scanning direction. Further, correction by rearrangement of image data is performed for the inclination and curvature of the scanning line.

  FIG. 4 is a schematic diagram showing a schematic configuration of the LSU 16 shown in FIG. The LSU 16 includes light sources 61 to 64 for each color of yellow, magenta, cyan, and black, a polygon mirror (rotating polygon mirror) 65, and fθ lenses 66 and 67, and light emitted from the light sources 61 to 64 for each color. After the beam is deflected in the main scanning direction by the polygon mirror 65, it passes through the fθ lenses 66 and 67 and is scanned onto the photosensitive drums 11a to 14a shown in FIG. In addition, the LSU 16 is appropriately provided with an optical element such as a mirror for guiding the light beams emitted from the light sources 61 to 64 for the respective colors to the photosensitive drums 11a to 14a for the respective colors without interfering with each other.

  In particular, here, the yellow and magenta light beams are incident on the reflecting surfaces at the same angular position of the polygon mirror 65, reflected in substantially the same direction, and guided to the respective photosensitive drums 11a and 12a. The cyan and black light beams are respectively incident on the reflecting surfaces at the same angular position of the polygon mirror 65, reflected in substantially the same direction, and guided to the respective photosensitive drums 13a and 14a. The reflecting surfaces of the incident polygon mirror 65 are different between the yellow and magenta light beams and the cyan and black light beams, and the light beams are distributed to opposite sides with the polygon mirror 65 interposed therebetween.

  Therefore, when the polygon mirror 65 rotates in the direction of the arrow A, the yellow and magenta light beams are scanned in the direction of the arrow S1 on the yellow and magenta photosensitive drums 11a and 12a. The light beam is scanned in the direction of the arrow S2 opposite to the arrow S1 on the cyan and black photosensitive drums 13a and 14a.

  As described above, in the yellow and magenta colors, the scanning directions of the light beams with respect to the respective photosensitive drums 11a and 12a are the same, and the yellow and magenta light sources 61 and 62 are arranged close to each other. Since the optical elements such as the lens 66 are shared, they exhibit substantially the same variation characteristics with respect to the positional deviation in the main scanning direction accompanying the environmental change such as temperature. Similarly, the cyan and black colors also exhibit substantially the same variation characteristics with respect to the positional deviation in the main scanning direction accompanying the environmental change such as temperature.

  For this reason, the patterns of the representative colors selected for each group are grouped by a combination of colors in which the scanning directions of the light beams with respect to the photoconductors 11a to 14a are the same, that is, yellow and magenta, and cyan and black. If only the image is formed, it is possible to predict the position change situation in the main scanning direction of other colors belonging to the same group from the position change situation of the representative color thus obtained.

  In this example, the yellow and magenta light sources 61 and 62 and the cyan and black light sources 63 and 64 are arranged at point-symmetrical positions about the central axis of the polygon mirror 65 when viewed from above. The exposure apparatus according to the invention is not limited to such a configuration. For example, a configuration in which yellow and magenta light sources 61 and 62 and cyan and black light sources 63 and 64 are arranged at symmetrical positions with a straight line passing through the central axis of the polygon mirror 65 in a top view is also possible. .

  FIG. 5 is a schematic diagram showing a resist pattern image forming state in the standard mode in the color image forming apparatus shown in FIG. The positional deviation of the toner image for each color is caused by the registration of each color that is formed by the process units 11 to 14 for each color of yellow, magenta, cyan, and black and transferred onto the intermediate transfer belt 17 shown in FIG. This is performed by causing the registration sensors 32a, 32b, and 32c to read patterns (pattern images for alignment) PY, PM, PC, and PK. Each of the resist patterns PY, PM, PC, and PK has a V-shape that is a combination of front and rear belt-like portions whose inclination directions are opposite to each other.

  Here, a pattern composed of resist patterns PY, PM, PC, and PK for each color of yellow, magenta, cyan, and black at detection positions of the left registration sensor 32a, the center registration sensor 32b, and the right registration sensor 32c. Groups GYMCK are formed respectively.

  These resist patterns are created by the process units 11 to 14 so as to be inserted between the images for each page when there is an instruction for color misregistration correction even during continuous printing as well as during standby (non-printing). An image is formed and transferred onto the intermediate transfer belt 17. The same applies to the resist patterns shown below.

FIG. 6 is a schematic diagram showing a procedure for acquiring a positional deviation amount by the resist pattern in the standard mode shown in FIG. Here, the distance L _Y between the front part PYa and the rear part PYb of the yellow resist pattern PY, the distance L _M between the front part PMa and the rear part PMb of the magenta resist pattern PM, and the front part PCa and the rear part of the cyan resist pattern PC The distance L _{C from} the PCb and the distance L _K between the front part PKa and the rear part PKb of the black resist pattern PK are measured, and these distances L _Y , L _M , L _C, and L _K are respectively calculated as theoretical values. Based on the compared difference, a relative amount of positional deviation in the main scanning direction for each color of yellow, magenta, and cyan based on black is obtained.

Further, the distances L _KC and L _KM of the front part PYa of the yellow resist pattern PY, the front part PMa of the magenta resist pattern PM, and the front part PCa of the cyan resist pattern PC with respect to the front part PKa of the black resist pattern PK.・ L _KY is measured, and relative sub-scan for each color of yellow, magenta and cyan based on black by the difference between these distances L _KC , L _KM, and L _KY compared to their theoretical values A displacement amount in the direction is obtained.

  In this way, the amount of misregistration in the main scanning direction and the sub-scanning direction for each color of yellow, magenta, and cyan on the basis of black is acquired, and based on this, the writing position and the sub-scanning position in the main scanning direction in the LSU 16 Correction of the writing position in the scanning direction is performed by the correction processing unit 55 of the image correction controller 48.

  FIG. 7 is a schematic diagram showing a procedure for acquiring information related to the state of inclination and curvature of the scanning line in the color image forming apparatus shown in FIG. As described above, in the standard mode, the displacement amounts SL, SC, SR in the sub-scanning direction at the detection positions of the left registration sensor 32a, the center registration sensor 32b, and the right registration sensor 32c are acquired. As shown in FIG. 5, if the amount of displacement SL / SC / SR in the sub-scanning direction at each detection position gradually increases or decreases in the main scanning direction, the inclination of the scanning line (the parallelism of the scanning line) It can be seen that there is a deviation. Further, as shown in FIG. 5B, if there is a large difference between the positional deviation amount SL / SR in the sub-scanning direction on both sides and the positional deviation amount SC in the central sub-scanning direction, the scanning line is curved. I understand that.

  In the standard mode shown in FIG. 5, the amount of misregistration in the sub-scanning direction for each color of yellow, magenta, and cyan based on black is obtained, and the amount of misregistration in the sub-scanning direction for each of these colors. Based on the above, it is possible to acquire information regarding the state of the inclination of the scanning line for each color (shift in the parallelism of the scanning line) with respect to the black scanning line. In the same manner, it is possible to acquire information related to the curve state of the scanning line for each color with reference to the black scanning line.

  In this way, information regarding the inclination and curvature state of the scanning line is acquired, and based on this, correction by rearranging the image data is performed by the correction processing unit 55 of the image correction controller 48.

  FIG. 8 is a schematic diagram showing a resist pattern image forming state in the shortening mode in the color image forming apparatus shown in FIG. Here, as shown in FIG. 4, from the color groups having the same scanning direction of the light beam and the light beam positional deviation being substantially the same, ie, the cyan and black groups, and the yellow and magenta groups. Black and yellow are selected as the group representative colors, and the black and yellow resist patterns PK and PY are formed at the detection positions of the left and right resist sensors 32a and 32c, respectively.

  As described later, the black and yellow resist patterns PK and PY obtain black and yellow misregistration amounts, and the misregistration amounts of other colors, that is, cyan and magenta, are resist patterns of representative colors of the same group. Predict from the position change situation. That is, the cyan positional deviation amount is acquired based on the cyan positional change situation predicted from the black positional change situation, and the magenta positional deviation amount is obtained from the magenta positional change situation predicted from the yellow positional change situation. Get based on.

FIG. 9 is a schematic diagram showing a procedure for acquiring a positional deviation amount by a resist pattern in the shortening mode shown in FIG. Here, the distance L _K between the front part PKa and the rear part PKb of the black resist pattern PK is measured.

Here, the distance L _K is measured by obtaining the detection timing of the on-edge (rising edge) and off-edge (falling edge) of the signal output from the registration sensor 32a from the count value of the counter that starts at the start of reading. The

  Specifically, first, the front part PKa and the rear part PKb of the black resist pattern PK are sequentially detected by the resist sensor, and the counter values K1, K2, K3, and K4 indicating the on edge and the off edge of the resist sensor signal at this time are obtained. get.

Next, the distance L _K is calculated from the counter values K1, K2, K3, and K4 based on the center positions of the front portion PKa and the rear portion PKb of the black resist pattern PK as follows.
L _K = (K3 + K4) / 2− (K1 + K2) / 2

  The counter counts 1 / n (n is an integer) of the recording cycle of one line. n is a value set in accordance with the required accuracy of the positional deviation amount, and the accuracy increases as the value increases.

In this way, the distance L _K that defines the position in the main scanning direction of the black resist pattern PK formed at the detection position of the left registration sensor 32a is measured. Similarly, the detection by the right registration sensor 32c is performed. The distance L _Y that defines the position in the main scanning direction of the yellow resist pattern PY formed at the position is measured.

On the other hand, the cyan and magenta distances L _C and L _{M that} are not representative colors are predicted from the black and yellow distances L _K and L _Y obtained by actual measurement of the resist pattern as the representative colors as described above.

Specifically, since the cyan distance L _C varies in proportion to the black distance L _K which is the representative color of the same group, the actual measured value L _{K of} black obtained in the current shortening mode and the latest standard mode The predicted value L _{C of} cyan is calculated from the black fluctuation ratio L _K / L _K ′ obtained from the measured black value L _K ′ acquired in step 1 and the measured cyan value L _C ′ acquired in the latest standard mode. Approximately calculated by the equation.
L _C = L _C '× L _K / L _K '.

The magenta distance L _M varies in proportion to the yellow distance L _Y , which is the representative color of the same group, so the yellow actual value L _Y acquired in the current shortening mode and the yellow acquired in the latest standard mode The magenta predicted value L _M is approximated by the following equation using the yellow fluctuation ratio L _Y / L _Y 'obtained from the actual measured value L _Y ' and the measured magenta value L _M 'obtained in the latest standard mode. Is calculated.
L _M = L _M '× L _Y / L _Y '.

In this way, the distances L _Y , L _M , L _C, and L _K for each color of yellow, magenta, cyan, and black are obtained, and based on this, the colors for each color of yellow, magenta, and cyan based on black are obtained. A positional deviation amount in the main scanning direction is obtained. Based on these positional deviation amounts in the main scanning direction, the LSU 16 corrects the writing position in the main scanning direction.

  FIG. 10 is a flowchart showing a procedure for acquiring the positional deviation amount in the shortening mode shown in FIG. When reading of the resist pattern is started, first, a counter for counting the position of the resist pattern is started (step 101). When the front portion PKa of the black resist pattern PK on the intermediate transfer belt moving in the sub-scanning direction reaches the detection position of the registration sensor, the registration sensor signal is turned on (step 102), and the counter value K1 at this time is stored in the memory. (Step 103). Further, when the black resist pattern PK moves in the sub-scanning direction and the front portion PKa is out of the detection position of the registration sensor, the registration sensor signal is turned off (step 104), and the counter value K2 at this time is stored in the memory. (Step 105).

  Then, in the same manner as this, the rear portion PKb of the black resist pattern PK is detected by the resist sensor, and the counter values K3 and K4 at that time are stored in the memory (steps 106 to 109), and all the resist patterns are detected. When finished, the counter stops (step 110).

Next, the black distance L _K shown in FIG. 9 is calculated based on the counter values K1, K2, K3, and K4 stored in the memory (step 111), and then the black distance L _K calculated here is calculated. , And the yellow distance L _Y calculated in the same procedure, and the distances L _Y ', L _M ', L _C ', L _K ' for each color of yellow, magenta, cyan, and black obtained in the latest standard mode Based on the above, the distances L _C and L _M between cyan and magenta are predicted, and based on this, the amount of misregistration in the main scanning direction for each color of yellow, magenta, and cyan based on black is calculated ( Step 112).

  Based on the amount of misregistration in the main scanning direction calculated as described above, the image misregistration correction is executed in the correction processing unit 73 of the image correction controller 48. That is, the writing position is corrected by the LSU 16 with respect to the positional deviation in the main scanning direction.

  FIG. 11 is a flowchart showing an operation procedure in the color image forming apparatus shown in FIG. First, the current temperature detected by the temperature sensor is acquired (step 201), the temperature acquired at the time of the previous correction is read (step 202), and then the current temperature is compared with the previous temperature to determine the temperature. A fluctuation amount is obtained, and it is determined whether or not the fluctuation amount of the temperature exceeds a predetermined threshold value (step 203). If the temperature fluctuation amount exceeds a predetermined threshold value, the standard mode shown in FIG. 5 is executed (step 204), and then the main scanning direction and the sub-scanning direction are based on the positional deviation amount acquired in the standard mode. Corrections regarding the positional deviation in the scanning direction and the inclination and curvature of the scanning line are executed (step 205).

On the other hand, if it is determined whether or not the temperature fluctuation amount exceeds a predetermined threshold value (step 203), if the temperature fluctuation amount does not exceed the predetermined threshold value, a representative by the shortening mode shown in FIG. Formation of a color resist pattern and measurement of the distances L _K and L _Y are executed (step 206).

Next, the actual black measured value L _K ′ acquired in the previous standard mode is read (step 207), and then the actual black measured value L _K acquired in the shortening mode (step 206) is used as the previous actual measured value L _K ′. And the black fluctuation ratio L _K / L _K ′ is calculated, and it is determined whether or not the black fluctuation ratio exceeds a predetermined threshold (step 208). Here, if the black fluctuation ratio exceeds a predetermined threshold value, the standard mode is executed (step 204), and then correction based on the positional deviation amount acquired in the standard mode is executed (step 205).

  On the other hand, if it is determined whether or not the black fluctuation ratio exceeds a predetermined threshold (step 208), and if the black fluctuation ratio does not exceed the predetermined threshold, it is acquired in the shortening mode (step 206). Based on the amount of displacement, correction relating to displacement in the main scanning direction is executed (step 209).

  In this way, it is determined in advance whether the shortening mode or the standard mode is appropriate based on the temperature fluctuation state from the previous correction, and here, the temperature fluctuation amount from the previous correction is small. The shortening mode is selected when sufficiently high accuracy can be ensured only by correcting the misregistration in the main scanning direction by the shortening mode, but the amount of temperature fluctuation from the previous correction is large, and the shortening mode If it is determined that it is difficult to ensure sufficiently high accuracy, the standard mode is selected, and the positional deviation correction in the main scanning direction and the positional deviation correction in the sub-scanning direction and the correction regarding the inclination and curvature of the scanning line are performed. .

  In addition, after executing the shortening mode, the validity of the correction processing based on the positional deviation information in the main scanning direction acquired in the shortening mode based on the position change state of the resist pattern from the previous correction, that is, the main mode by the shortening mode. It is determined in advance whether or not sufficiently high accuracy can be ensured only by correcting the positional deviation in the scanning direction. Here, the positional change of the resist pattern from the previous correction is small, and the shortening mode is sufficient. When high accuracy can be ensured, correction based on the shortening mode is performed, but the resist pattern position change from the previous correction is large, and it is difficult to ensure sufficiently high accuracy in the shortening mode. Is determined, the correction based on the shortening mode is not performed, and the process of acquiring the misalignment information in the standard mode is performed again. At this time, the correction is performed in the shortening mode. Is the positional displacement information discarded, correction is performed based on the acquired positional displacement information in the standard mode.

Note that the determination of the validity of the correction processing in the shortening mode (step 208) can also be performed based on the yellow variation ratio L _Y / L _Y '. Further, the validity of the shortening mode may not be determined based only on the position change state of the resist pattern, but may be determined by adding other determination criteria such as required image quality.

  In addition, a configuration in which the shortening mode is executed from the beginning without performing the process of selecting the shortening mode and the standard mode (steps 201 to 203) based on the temperature fluctuation state from the previous correction is also possible. On the contrary, the process (steps 207 and 208) for determining the validity of the shortening mode based on the position change status of the representative color resist pattern acquired in the shortening mode is not performed, and the process from the previous correction time is not performed. A configuration in which only the shortening mode and the standard mode are selected based on the temperature fluctuation state is also possible.

  In the above example, the amount of misregistration for each color of yellow, magenta, and cyan is obtained with reference to black, but the amount of misregistration with respect to other colors is obtained to obtain the position of the image. It is also possible to execute deviation correction.

  The color image forming apparatus according to the present invention ensures a high-quality image by frequently performing correction control without significantly reducing the productivity of image formation processing by significantly reducing the processing time of correction control. An image can be individually formed on the photoconductor for each color by scanning the light beam by the exposure means for the photoconductor for each color, and these images are combined on the intermediate transfer body to form a color image. It is useful as a color image forming apparatus to be obtained, for example, a printer, a facsimile machine, a copying machine, a multifunction machine, and the like.

Schematic diagram showing an example of a color image forming apparatus according to the present invention. 1 is a block diagram showing a schematic configuration of a main part related to control in the color image forming apparatus shown in FIG. The block diagram which shows schematic structure of the image correction controller shown in FIG. Schematic diagram showing the schematic configuration of the LSU shown in FIG. FIG. 2 is a schematic diagram showing a resist pattern image formation state in a standard mode in the color image forming apparatus shown in FIG. Schematic diagram showing the procedure for obtaining the amount of misalignment by the resist pattern in the standard mode shown in FIG. FIG. 2 is a schematic diagram showing a procedure for acquiring information related to the state of inclination and curvature of a scanning line in the color image forming apparatus shown in FIG. FIG. 3 is a schematic diagram showing a resist pattern image formation state in a shortened mode in the color image forming apparatus shown in FIG. FIG. 8 is a schematic diagram showing a procedure for acquiring a positional deviation amount by a resist pattern in the shortening mode shown in FIG. FIG. 8 is a flowchart showing a procedure for acquiring a positional deviation amount in the shortening mode shown in FIG. FIG. 1 is a flowchart showing an operation procedure in the color image forming apparatus shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image formation part 11-14 Process unit 11a-14a Photosensitive drum 16 LSU (exposure means)
17 Intermediate transfer belts 32a to 32c Registration sensor (image detection means)
48 Image correction controller (correction control means)
61-64 Light source 65 Polygon mirror (rotating polygon mirror)
GYMCK pattern group PK / PC / PM / PY resist pattern (pattern image for alignment)

Claims (4)

A color image forming apparatus that individually forms an image on the photoconductor for each color by scanning a light beam by an exposure unit for the photoconductor for each color, and combines them on an intermediate transfer body to obtain a color image,
A plurality of light sources for each color are arranged so that the scanning direction of the light beam with respect to the photosensitive member is reversed according to the positional relationship with respect to the rotary polygon mirror, and the alignment formed on the intermediate transfer member Image detecting means for detecting a pattern image for use at a plurality of detection positions spaced apart in the main scanning direction, and causing the image detecting means to detect the pattern image on the intermediate transfer member, and for each color based on the detection result Correction control means for acquiring positional deviation information and performing correction processing,
The correction control means groups the colors having the same scanning direction of the light beam with respect to the photoconductor into the same group, and only the pattern image of the representative color selected for each group is the image detection means. The position change statuses of the pattern images of the other colors belonging to the same group are predicted from the position change status of the pattern images of the representative colors obtained by the respective detection positions, and for each other color with respect to the reference color A color image forming apparatus characterized by acquiring positional deviation information in a main scanning direction. The correction control unit forms a pattern image of the representative color at each detection position of the image detection unit and causes the image detection unit to detect the pattern image, and all the pattern images for each color are It is possible to execute a standard mode in which the image detection unit is formed at each detection position of the image detection unit and the image detection unit detects the pattern image.
After executing the shortening mode, the validity of the correction processing by the shortening mode is determined based on the position change situation of the pattern image of the representative color acquired in the shortening mode, and when it is determined that it is not valid here 2. The color image forming apparatus according to claim 1, wherein the standard mode is executed again, and correction processing is performed based on positional deviation information acquired in the standard mode. The correction control unit forms a pattern image of the representative color at each detection position of the image detection unit and causes the image detection unit to detect the pattern image, and all the pattern images for each color are It is possible to execute a standard mode in which the image detection unit is formed at each detection position of the image detection unit and the image detection unit detects the pattern image.
The color image forming apparatus according to claim 1, wherein one of the shortening mode and the standard mode is selected according to a change state of environmental conditions.   When the correction control unit predicts the position change situation of the pattern image of another color belonging to the same group from the position change situation of the pattern image of the representative color, the measured value of the representative color based on the pattern image A variation ratio is obtained by comparison with the previous actual measurement value of the color, and a predicted value of the other color is calculated from the variation ratio and the previous actual measurement value of another color belonging to the same group as the representative color. The color image forming apparatus according to claim 1.

Images