JP2010217562A - Image forming apparatus, positional deviation correction method, and positional deviation correction program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform accurate positional deviation correction, by excluding detection errors of a positional deviation amount for accurate positional deviation correction and stably detecting a color pattern by even a low-cost optical detection means, in a color image forming apparatus of such a type that a black BK image forming means is located in the most-upstream position in the rotation direction of a conveyance belt or an intermediate transfer belt. <P>SOLUTION: A positional deviation correction pattern 26 has two edges forming a tilt angle θ, with respect to a subscanning direction and includes patterns of black BK and cyan C on the most upstream side which are formed apart from each other in the subscanning direction, and patterns of yellow Y and magenta M, having a narrow width, which are formed over patterns of black BK and cyan C, respectively. A light beam is emitted from a red LED, having a peak in spectral sensitivity characteristics of the reflected light of cyan C, and a CPU detects the edges of yellow Y and magenta M on black BK and cyan C and performs positional deviation correction. <P>COPYRIGHT: (C)2010,JPO&INPIT

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., which has a function of correcting misalignment of image positions of a plurality of colors performed when a plurality of colors are superimposed to obtain a visible image. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a misregistration correction method implemented by an apparatus and a computer program for executing misregistration correction control of the image forming apparatus by a computer.

  In an electrophotographic image forming apparatus, generally, an image is formed for each color, and finally, a four-color image is superimposed to form a full-color visible image. As an image forming apparatus for forming an image in this way, for example, a tandem type color image forming apparatus is known. There are two types of tandem type image forming apparatuses: an indirect transfer type and a direct transfer type. The former is an intermediate transfer belt for primary transfer of an image carried on an image carrier, and the latter is carried on an image carrier. A pattern for correcting misregistration is formed for each color on a conveyance belt that conveys transfer paper that directly transfers the transferred image, and this correction pattern is read by an optical sensor, a so-called TM (Toner Marking) sensor. The timing is corrected so that the positions where the four colors are superimposed coincide. As such a tandem image forming apparatus, for example, the inventions described in Patent Document 1 (Patent No. 2858735) and 2 (Patent No. 2642351) are known.

  By executing the misregistration correction, the YMCK four-color images overlap at substantially the same position, and the color misregistration amount approaches zero. However, the amount of color misregistration increases due to various factors as time elapses after execution of misregistration correction. In particular, the positional deviation of the reflecting mirror accompanying a rise in temperature in the exposure apparatus tends to be a main factor in increasing the amount of color deviation. Although the reflection mirror is fixed in the exposure apparatus using screws or an adhesive, the shape of the reflection mirror itself or the shape of the support member changes as the temperature rises. Since these occur independently or in combination, the inclination of the irradiation light with respect to the optical path is likely to change. This change in inclination causes an increase in the amount of color misregistration.

  In order to correct the enlarged color misregistration amount, it is necessary to execute misregistration correction. However, if there are scratches or deposits on the transport belt or intermediate transfer belt, the detection means using the TM sensor may detect the scratches or deposits as part of the misalignment correction pattern. It becomes a factor which makes misalignment correction fail. If misregistration correction failures occur frequently, the amount of color misregistration increases and the quality of the color image cannot be maintained. Therefore, in order to maintain the quality of the color image, scratches and deposits on the conveying belt or intermediate transfer are detected and the influence thereof is reduced.

  As a technique for performing such processing, for example, the invention described in Patent Document 3 (Japanese Patent Application Laid-Open No. 2007-148080) is known. The present invention provides an intermediate transfer belt to which toner images formed by a plurality of image forming units are transferred so as to overlap each other, a light source for irradiating measurement light to the intermediate transfer belt, and reflected light from the intermediate transfer belt A color image forming apparatus comprising: a toner sensor including a photoelectric sensor that detects color misregistration; and a color misregistration correction unit that corrects color misregistration based on a color misregistration pattern transferred on the intermediate transfer belt read by the toner sensor. And a threshold setting means for variably setting the detection threshold of the color misregistration pattern by the toner sensor so as to be lower than the minimum value of the surface detection level of the intermediate transfer belt. This makes it possible to perform color misregistration correction quickly and reliably regardless of the presence or absence of color.

  In the invention described in Patent Document 3, in order to eliminate the influence of scratches on the intermediate transfer belt, color deviation correction is performed promptly and reliably regardless of the presence or absence of scratches on the intermediate transfer belt that cause disturbance by changing the threshold value. However, depending on the state of scratches and deposits, it may not be possible to cope with the change of the threshold value.

  Therefore, as another method, the diffuse reflection component of the TM sensor can be obtained by overlaying the black BK misregistration correction reference pattern on one color misregistration correction target pattern so that both ends in the main scanning direction are exposed. In this case, the image position of each color is detected. However, in this method, when the black BK image forming means is positioned upstream of the overlapping position deviation correction target pattern image forming means with respect to the rotation direction of the transport belt or the intermediate transfer belt, this means. Cannot be used.

  Therefore, the problem to be solved by the present invention is that accurate color misregistration correction is performed in a color image forming apparatus in which the black BK image forming means is located most upstream with respect to the rotation direction of the conveying belt or the intermediate transfer belt. Is to be able to do.

  In order to solve the above-mentioned problem, the first means is that a plurality of image carriers are arranged side by side along the moving direction of the endless carrier, and images of different colors are applied to each image carrier by an electrophotographic process. A plurality of image forming means for forming and transferring to the endless conveyance body; and a pattern forming means for forming a misregistration correction pattern comprising a plurality of patterns formed for each color by the image forming means on the endless conveyance body. And a pattern detection means for irradiating the misregistration correction pattern formed on the endless carrier with a light beam to detect regular reflection light and diffuse reflection light from the pattern, and the pattern detection means by the pattern detection means. An image forming apparatus comprising: a misregistration amount detecting unit configured to detect a misregistration amount of an image on the endless carrier based on a detection result of a misregistration correction pattern, wherein the misregistration correction pattern Has two edges that form an inclination angle θ in the sub-scanning direction, and is formed on the most upstream side, which is formed at an interval in the sub-scanning direction, with the black reference color and first color patterns, and the reference A second color pattern and a third color pattern which are formed on the color and first color patterns and are narrower than the reference color and the first pattern, and the light beam includes the first color. The irradiation light has a peak in the spectral sensitivity characteristic of the reflected light.

  According to a second means, in the first means, a pattern width in a sub-scanning direction of the misregistration correction pattern composed of a plurality of colors including the reference color, the first color, the second color, and the third color is set. The spot diameter of the regular reflection light receiving element of the pattern detection means is equal to or larger than the spot diameter.

  A third means is characterized in that, in the first or second means, an interval between the reference color and the misregistration correction pattern of the first color is equal to or larger than a spot diameter of a regular reflection light receiving element of the detection means. And

  The fourth means is any one of the first to third means, wherein the misregistration correction patterns of the second color and the third color are main scans of the misregistration correction patterns of the reference color and the first color. It is characterized by being formed to overlap each other so that both ends in the direction are exposed.

  A fifth means is any one of the first to fourth means, wherein the reference color and the first color misregistration correction pattern have a width in a direction of ± 90 ° with respect to the inclination angle θ. It is characterized by being set to about three times the spot diameter of the regular reflection light receiving element of the means.

  A sixth means is any one of the first to fifth means, wherein the second color and third color misregistration correction patterns have a width in the direction of ± 90 ° with respect to the inclination angle θ. It is equal to the spot diameter of the regular reflection light receiving element of the detecting means.

  A seventh means is characterized in that, in any one of the first to sixth means, the inclination angle θ is any one of 90 °, 45 °, and 135 ° with respect to the sub-scanning direction. .

  The eighth means is characterized in that, in any one of the first to seventh means, the light emitting element of the pattern detection means is a red LED, and the first color is cyan.

  A ninth means is characterized in that, in any one of the first to seventh means, the light emitting element of the pattern detecting means is a blue LED, and the first color is yellow.

  According to a tenth means, a plurality of image carriers are juxtaposed along the moving direction of the endless carrier, and images of different colors are formed on each image carrier by an electrophotographic process. A plurality of image forming means for transferring to the body side, a pattern forming means for forming a misregistration correction pattern composed of a plurality of patterns formed for each color by the image forming means on the endless transport body, and the endless transport body A pattern detecting means for irradiating the misregistration correction pattern formed above with a light beam and detecting regular reflection light and diffuse reflection light from the pattern, and detection of the misregistration correction pattern by the pattern detection means And a misregistration amount detecting means for detecting a misregistration amount of an image on the endless conveyance body based on a result, the misregistration correction method in the image forming apparatus, wherein an inclination angle θ in the sub-scanning direction is provided. Forming a black reference color and a first color pattern having two edges formed on the uppermost stream side with an interval in the sub-scanning direction; and on the reference color and the first color pattern By overlapping and forming the second color and third color patterns narrower than the reference color and the first pattern, respectively, and the irradiation light having a peak in the spectral sensitivity characteristics of the reflected light of the first color, The method includes irradiating the misregistration correction pattern and detecting a misregistration amount based on the output of the reflected light irradiated in the irradiating step.

  According to an eleventh means, a plurality of image carriers are juxtaposed along the moving direction of the endless carrier, and images of different colors are formed on each image carrier by an electrophotographic process. A plurality of image forming means for transferring to the body side, a pattern forming means for forming a misregistration correction pattern composed of a plurality of patterns formed for each color by the image forming means on the endless transport body, and the endless transport body A pattern detecting means for irradiating the misregistration correction pattern formed above with a light beam and detecting regular reflection light and diffuse reflection light from the pattern, and detection of the misregistration correction pattern by the pattern detection means A misregistration correction control in an image forming apparatus provided with misregistration amount detection means for detecting the misregistration amount of an image on the endless carrier based on the result is executed by a computer A misregistration correction program for a black reference color and a first color having two edges having an inclination angle θ in the sub-scanning direction and spaced apart from each other in the sub-scanning direction. A step of forming a pattern, a step of forming a pattern of the second color and the third color narrower than the reference color and the first pattern on the reference color and the first color pattern, respectively, The amount of misalignment is detected based on the procedure of irradiating the misalignment correction pattern with the irradiation light having a peak in the spectral sensitivity characteristic of the reflected light of the first color and the output of the reflected light irradiated in the irradiating step. And a procedure to perform.

  In the embodiment described later, the image carrier is on the photosensitive drum 9, the endless carrier is on the conveyor belt 5 or the intermediate transfer belt 5a, and the image forming means is the charger 10, the developing device 12, the transfer device 15, and the photosensitive member. The body cleaner 13 and the image forming unit 6 are provided with a pattern 26 for misregistration correction, the pattern forming unit is provided with the image forming unit 6 and the CPU 49, the light beam is provided with the symbol 23a, and the pattern detecting unit is provided with the TM sensors 17, 18, 19, the regular reflection light receiving unit 24, and the positional deviation amount detection means correspond to the CPU 49.

  According to the present invention, the black reference color and the first color pattern located on the most upstream side in the moving direction of the endless transport body, and the reference color formed on the reference color and the first color pattern, A positional deviation correction pattern is formed from the second and third color patterns that are narrower than the first pattern, and the positional deviation is irradiated by irradiation light having a peak in the spectral sensitivity characteristic of reflected light of the first color. In the color image forming apparatus of the type in which the black image forming means is located most upstream with respect to the rotation direction of the conveyance belt or the intermediate transfer belt, since the amount of positional deviation is detected based on the output of the reflected light from the correction pattern. , Can perform accurate misalignment correction

1 is a schematic configuration diagram illustrating a configuration of an image forming unit of an image forming apparatus according to Embodiment 1 of the present invention. It is a figure which shows the outline of the internal structure of an exposure device. It is a figure which shows the detection structure which detects the pattern formed on the conveyance belt by TM sensor. FIG. 3 is a schematic perspective view of an image forming unit showing a relationship among a TM sensor, a positional deviation correction pattern, and a photosensitive drum. It is a figure which shows an example of the pattern for a position shift correction implemented conventionally. It is a figure for demonstrating the detection principle of the pattern for position shift correction of FIG. FIG. 6 is a diagram illustrating a linear pattern among the misregistration correction patterns according to the first embodiment. It is a characteristic view which shows the spectral sensitivity characteristic with respect to the color pattern of LED irradiation light. FIG. 6 is a diagram illustrating a hatched pattern among the misregistration correction patterns according to the first embodiment. FIG. 8 is an explanatory diagram illustrating a detection principle of the misregistration correction pattern of FIG. 7. It is a block diagram which shows the circuit structure of the position shift correction circuit which processes the detected data for calculating the correction amount required for position shift correction. 10 is a flowchart showing a control procedure for performing misregistration correction control by forming the misregistration correction pattern shown in FIGS. 5, 7, and 9. It is a figure which shows a linear pattern among the patterns for position shift correction in Example 2. It is a figure which shows a diagonal line pattern among the patterns for position shift correction in Example 2. FIG. It is explanatory drawing which shows the detection principle of the pattern for position shift correction of FIG. FIG. 15 is a flowchart showing a control procedure for performing misregistration correction control by forming the misregistration correction pattern shown in FIGS. 5, 13, and 14. FIG. FIG. 10 is a diagram illustrating a schematic configuration of an image forming unit of an image forming apparatus according to Embodiment 3.

  In this embodiment, the black BK image forming unit is positioned upstream of the image forming unit of the misregistration correction target pattern to superimpose a plurality of colors with respect to the rotation direction of the conveyance belt or the intermediate transfer belt. Corresponding to the image forming apparatus, the emission color of the TM sensor is a complementary color of one color other than the black BK, and the position deviation correction reference pattern of the pattern black BK and the position complementary to the emission color of the TM sensor Other misalignment correction target patterns are superimposed on the misalignment correction target pattern so that both ends in the main scanning direction (width direction) are exposed. As a result, it is possible to reduce false detection by forming a pattern on the flaws or deposits on the conveyance belt or the intermediate transfer belt and reducing the exposed area.

  Since the black BK misregistration correction reference pattern and the emission color complementary color misregistration correction target pattern do not reflect regular reflection light, a difference is caused in the regular reflection voltage between the exposed portion of the conveyance belt or the intermediate transfer belt, and the edge is changed. Can be detected. In addition, the misregistration correction target pattern superimposed on the misregistration correction reference pattern of the black BK and the misregistration color of the TM sensor emits diffuse reflection light. A difference is generated in the voltage (output signal intensity) of the combined wave, and the edge can be detected.

  Since the light receiving portion of the TM sensor has a sensitivity peak near 700 nm, position detection is facilitated by using a red emission color having a peak near 700 nm. Therefore, in the present embodiment, red is used as the emission color, and cyan is used as the pattern color that is complementary to the emission color. As described above, when the black BK image forming means is located on the most upstream side with respect to the rotation direction of the transport belt or the intermediate transfer belt, in order to avoid detection of scratches or adhering matter on the transport belt or the intermediate transfer belt. In addition, the emission color of the TM sensor is set to be a complementary color of any one of the misregistration correction target patterns, and the overlay of the misregistration correction patterns and the combined wave of the regular reflection light and diffuse reflection light of the TM sensor are used to accurately Misalignment correction was performed.

  Hereinafter, each example in the embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic configuration diagram illustrating a configuration of an image forming unit of the color image forming apparatus according to the first embodiment. In FIG. 1, the image forming apparatus according to the first exemplary embodiment is a direct transfer type tandem image forming apparatus in which image forming units of respective colors are arranged along a conveying belt which is an endless moving unit. The image forming apparatus includes a paper feed tray 1, an exposure device 11, an image forming unit 6, a conveyance belt 5, a transfer device 15, and a fixing device 16.

  The conveyor belt 5 electrostatically attracts and conveys paper (recording paper) 4 separated and fed by the paper feed roller 2 and the separation roller 3 from the paper feed tray 1, and the image forming unit 6 is black (BK). The image forming section (electrophotographic process section) 6BK, 6M, 6C, 6Y of four colors of magenta (M), cyan (C), and yellow (Y) is provided from the upstream side along the rotation direction of the conveyor belt 5. Arranged in order. The plurality of image forming units 6BK, 6M, 6C, and 6Y have the same internal configuration except that the colors of the toner images to be formed are different. The image forming unit 6BK forms a black image, the image forming unit 6M forms a magenta image, the image forming unit 6C forms a cyan image, and the image forming unit 6Y forms a yellow image.

  In the following description, the subscripts BK, M, C, and Y indicating colors are omitted for the configuration common to the respective colors, and a general description is given instead of the description for each color.

  The conveyor belt 5 is an endless belt, and is stretched between the driving roller 7 and the driven roller 8. The drive roller 7 is rotationally driven by a drive motor (not shown) and moves in the direction of the arrow shown (counterclockwise in the figure). At the time of image formation, the sheets 4 stored in the sheet feeding tray 1 are sent out in order from the uppermost one, and are attracted to the conveying belt 5 by electrostatic attraction, and the first image forming unit 6BK is rotated by the rotating conveying belt 5. The black toner image is transferred here.

  The image forming unit 6 includes a photoconductor drum 9 as a photoconductor, a charger 10 disposed along the outer periphery of the photoconductor drum 9, a developing device 12, a transfer device 15, a photoconductor cleaner 13, and a static eliminator (not shown). And the like, and an exposure unit 14w that is irradiated with the laser beam 14 emitted from the exposure unit 11 is provided between the charger 10 and the developing unit 12. The exposure unit 11 irradiates the exposure unit 14 w of the photosensitive drum 9 of each image forming unit 6 with a laser beam 14 that is an exposure beam corresponding to the image color formed by the image forming unit 6. Further, the transfer unit 15 is provided so as to face the photosensitive drum 9 with the conveying belt 5 interposed therebetween.

  FIG. 2 is a view showing an outline of the internal structure of the exposure unit 11. Laser beams 14BK, 14Y, 14C, and 14M that are exposure beams of the respective image colors are emitted from laser diodes 21BK, 21Y, 21C, and 21M that are light sources, respectively. The irradiated laser light passes through the optical systems 22BK, 22Y, 22C, and 22M by the reflecting mirror 20, the optical path is adjusted, and then scanned onto the surfaces of the photosensitive drums 9BK, 9Y, 9C, and 9M. The reflecting mirror 20 is a hexahedral polygon mirror, and scans an exposure beam for one line in the main scanning direction per rotation of the polygon mirror. In the example of FIG. 2, four of the laser diodes 21 of the light source are scanned with one polygon mirror that is the reflecting mirror 20. The laser beam 14 is divided into exposure beams of two colors, laser beams 14BK and 14Y, and 14C and 14M, and scanning is performed using the opposing reflecting surface of the polygon mirror (reflecting mirror) 20, whereby four different photosensitivities are simultaneously obtained. The body drum 9 can be exposed. The optical system 22 includes an f-θ lens that aligns reflected light at equal intervals and a deflection mirror that deflects laser light.

  At the time of image formation, the outer peripheral surface of the photosensitive drum 9BK is uniformly charged by the charger 10BK in the dark, and then exposed by the laser beam 14BK corresponding to the black image from the exposure device 11, and the surface of the photosensitive drum 9BK is exposed. An electrostatic latent image is formed. The developing device 12BK visualizes the electrostatic latent image by attaching black toner thereto. As a result, a black toner image is formed on the photosensitive drum 9BK.

This toner image is transferred onto the sheet 4 by the action of the transfer unit 15BK at a position (transfer position) where the photosensitive drum 9BK and the sheet 4 on the conveying belt 5 are in contact with each other. By this transfer, an image of black toner is formed on the paper 4. After the transfer of the toner image is completed, unnecessary toner remaining on the outer peripheral surface of the photoconductor drum 9BK is cleaned by the photoconductor cleaner 13BK, and is then discharged by a charge eliminator (not shown) to be used for the next image formation. stand by.

  As described above, the sheet 4 on which the black toner image is transferred by the image forming unit 6BK is conveyed to the next image forming unit 6Y by the conveying belt 5. Meanwhile, in the image forming units 6Y, 6C, and 6M, toner images of yellow, cyan, and magenta are transferred to the photoconductor drums 9Y, 9C, and 9M in the transfer unit 15 by the same process as the image forming process in the image forming unit 6BK. The toner images are formed shifted by the transfer timing, and the toner images are sequentially superimposed and transferred onto the black image formed on the paper 4. Thus, a full-color image is formed on the paper 4. The sheet 4 on which the full-color superimposed image is formed is peeled off from the conveying belt 5 and the image is fixed by the fixing device 16 and then discharged to the outside of the image forming apparatus.

  In the color image forming apparatus configured as described above, an error in the inter-axis distance between the photosensitive drums 9BK, 9Y, 9C, and 9M, a parallelism error in the photosensitive drums 9BK, 9Y, 9C, and 9M, and deflection in the exposure unit 11 Due to the mirror installation error and the writing timing error of the electrostatic latent images on the photosensitive drums 9BK, 9Y, 9C, and 9M, the toner images of the respective colors do not overlap each other at the positions where they should overlap, and the positions of each color are shifted. May occur. As components of such color misregistration, there are mainly known skew, sub-registration misregistration, magnification error in the main scanning direction, and misregistration in the main scanning direction.

  In order to eliminate such a shift, it is necessary to correct a position shift of each color toner image. The positional deviation correction is performed by aligning the image positions of the three colors of yellow Y, cyan C, and magenta M with the image position of BK. As shown in FIG. 1, on the downstream side of the image forming unit 6M, first to third toner mark sensors (hereinafter referred to as TM sensors) 17, 18, 19 for detecting a toner pattern facing the conveying belt 5 are provided. Is provided. The TM sensors 17, 18, and 19 are reflection-type optical sensors, and are supported on the same substrate so as to follow a main scanning direction orthogonal to the conveyance direction of the paper 4. In order to calculate the information on the amount of misalignment necessary for the misalignment correction, a misalignment correction pattern 26 as shown in FIG. 5 (described later) is formed on the transport belt 5, and the TM sensors 17, 18, 19 each color. The correction pattern 26 is read, and the amount of positional deviation between the colors is detected. The positional deviation correction pattern 26 is detected by the TM sensors 17, 18, 19 and then removed from the transport belt 5 by the cleaning unit 20.

  3 is an enlarged view of the image detecting means including the TM sensors 17, 18, and 19. FIG. 4 is a diagram showing a detection configuration when pattern detection is performed by the TM sensors 17, 18, and 19. The photoconductor 9 and the conveyor belt 5 are illustrated. The positional relationship between the correction pattern 26 and the TM sensors 17, 18, and 19 is shown. In FIG. 3, the TM sensors 17, 18, and 19 each include a light emitting unit 23, a regular reflection light receiving unit 24, and a diffuse reflection light receiving unit 25. The light emitting unit 23 irradiates the light beam 23a to the misregistration correction pattern 26 formed on the conveyor belt 5, and the regular reflection light receiving unit 24 receives the reflected light including the regular reflection light component and the diffuse reflection light component. The TM sensor 17, 18, 19 detects the misalignment correction pattern 26. In the detection of the adhesion amount correction pattern, the regular reflection light receiving unit 24 receives the reflected light including the regular reflection light component and the diffuse reflection light component, and the diffuse reflection light reception unit 25 receives the diffuse reflection light. As shown in FIG. 4, the first and third TM sensors 17 and 19 are arranged at both ends in the main scanning direction, and the second TM sensor 18 is arranged at the center. 27a, 27b, and 27c are formed. FIG. 4 shows a minimum set of pattern rows necessary for obtaining various color misregistration amounts for each color.

  FIG. 5 is a diagram showing an example of a misregistration correction pattern row 27 conventionally employed. The correction pattern row is formed by an aggregate of misregistration correction patterns 26. The conventional misregistration correction pattern 26 includes a total of 8 linear patterns 26Y_Y, 26BK_Y, 26C_Y, 26M_Y (26BKYCM_Y) and diagonal patterns 26Y_S, 26BK_S, 26C_S, 26M_S (26BKYCM_S) each having four colors BK, M, C, and Y. A pattern string of books is used as a set of pattern strings. The oblique line patterns 26Y_S, 26BK_S, 26C_S, and 26M_S are all diagonal lines on the upper right (in the drawing, the right end in plan view is the upper position and the left end is the lower position in the sub-scanning direction). This pattern row is created for each of the first to third TM sensors 17, 18, and 19, and a plurality of sets are created in the sub-scanning direction. The straight line pattern is a straight line parallel to the so-called main scanning direction, and the oblique line pattern is a straight line inclined at a predetermined angle θ with respect to the main scanning direction.

  FIG. 6 is a diagram for explaining the detection principle of the misalignment correction pattern of FIG. FIG. 6A shows the relationship between the correction pattern, the spot diameter of the irradiated light, and the spot diameter of the regular reflection light receiving unit, and FIG. 6B shows the diffused light component and the regular reflection component of the light reception signal of the correction pattern. FIG. 6C shows how to obtain the output signal of the regular reflection light receiving unit and the midpoint of the correction pattern.

  As shown in FIG. 5, correction patterns 26 for BK, M, C, and Y colors are formed on the conveyor belt 5. In FIG. 6A, the pattern width in the sub-scanning direction of the linear patterns 26BK_Y, 26M_Y, 29C_Y, 29Y_Y is denoted by reference numeral 30, and the interval between the adjacent linear patterns 26BK_Y, 26Y, C, M_Y is denoted by reference numeral 31. The spot diameter at the pattern position of the light emitting section 26 is denoted by reference numeral 28, and the spot diameter detected by the regular reflection section is denoted by reference numeral 29. Since the principle is explained in FIG. 6, the order and combination of patterns in FIG. 6A are arbitrary.

  A light beam 23 a is emitted from the light emitting unit 23 onto the pattern of the conveyor belt 5. The output signal of the regular reflection light receiving unit 24 is reflected light from the conveyor belt 5 and includes a regular reflected light component and a diffuse reflected light component. Therefore, when the conveyor belt 5 moves under such a relationship, the diffuse reflection component of the light reception signal of the TM sensors 17, 18, and 19 has a characteristic indicated by reference numeral 33 in FIG. The component exhibits characteristics as indicated by reference numeral 34. In FIG. 6C, reference numeral 32 indicates an output signal of the regular reflection light receiving unit 24. In FIG. 6C, the vertical axis of the graph indicates the output signal intensity of the regular reflection light receiving unit 22, and the horizontal axis indicates time. The CPU 49 to be described later has a pattern edge 38BK_1, 38BK_2, 38Y, C, M_1, 38Y, at a position where the detection waveform of the output signal 32 of the regular reflection light receiving unit 24 of the TM sensors 17, 18, 19 intersects the threshold line 37. It is determined that C and M_2 are detected. Furthermore, the average value of these two edges is taken to determine the image position. The output signal intensity of the regular reflection light receiving unit 24, that is, the reflected light intensity is a preset intensity, for example, the median value of the reflected light intensity from the surface of the conveyor belt 5 and the reflected light intensity of the pattern having the highest density, that is, The intensity of the reflected light is set as the threshold line 40.

  In FIG. 6B, reference numeral 33 denotes a diffuse reflected light component of the received light signal. The diffuse reflected light component is not reflected from the surface of the transport belt 5 and the BK misregistration correction pattern 26BK_Y pattern, but is reflected from the M, C, Y misregistration correction pattern 26M, C, Y_Y pattern. Yes. Reference numeral 34 denotes a regular reflection light component of the received light signal. The specularly reflected light component is strongly reflected on the surface of the conveyor belt 5 and is not reflected from the pattern of the misregistration correction pattern 26 regardless of the color.

  The image detection unit shown in FIG. 4 can accurately detect the misalignment correction pattern 26 by adjusting the alignment of the light emitting unit 23 and the regular reflection light receiving unit 24. When this alignment deviates due to mechanical tolerances, attachment errors, etc., as can be seen from FIG. 6B, the regular reflected light component 34 waveform and the diffuse reflected light component 33 from the linear patterns 26BK, Y, C, M_Y of the respective colors. The peak position of the waveform is shifted. That is, in the output signal from the regular reflection light receiving unit 24 (regular reflection component 34 waveform), the midpoint of the actual pattern of the 26BK pattern coincides with the peak position of the output signal, but the 26Y, C, and M patterns are actually actual. And the peak position of the output signal (regular reflection component 34 waveform) is different. As a result, an error occurs in the detection position of the color pattern, and an accurate position cannot be detected. When the color pattern is detected, the S / N ratio decrease and the detection error become larger when the oblique line patterns 26BK, Y, C, and M_S are detected than the straight line patterns 26BK, Y, C, and M_Y.

  For the purpose of improving the S / N ratio at the time of color pattern detection and reducing the detection error, the line width 30 in the sub-scanning direction of the linear patterns 26BK, Y, C, M_Y is 0.6 mm which is substantially the same as the spot diameter 28 of the irradiation light. It has become. The shortest portion of the line width of the oblique line pattern 26BK, Y, C, M_S is also 0.6 mm. Further, the spot diameter 29 of the diffuse reflected light is about 2 mm. On the other hand, if diffusely reflected light is simultaneously reflected from two patterns, the pattern cannot be normally detected. In order to prevent this, the interval 31 between the patterns of the linear patterns 26BK, Y, C, M_Y is 2 mm or more. In the hatched patterns 26BK, Y, C, and M_S, the shortest portion between the patterns is 2 mm or more.

  In the detection method of the conventional misregistration correction pattern 26 shown in FIG. 5 and the conventional misregistration correction pattern 26 described with reference to FIG. 6, since the exposed area of the conveyor belt 5 between the patterns is large, scratches and deposits are generated. If there is, the signal intensity of the output signal 32 of the regular reflection light receiving unit 24 decreases, crosses the threshold line 37, and may be erroneously detected as the misalignment correction pattern 26. In order to cope with this problem, there is a method of superimposing patterns and reading the pattern with diffuse reflected light. However, when the image forming unit 6BK of black BK is located at the most upstream with respect to the rotation direction of the transport belt 5. Could not be used.

  Therefore, in the present embodiment, when the black BK image forming unit 6BK is located at the most upstream with respect to the rotation direction of the transport belt 5, a red LED is used for the light emitting unit 23, and a pattern as shown in FIG. By superimposing and reducing the exposed area of the conveyor belt between patterns, false detection of scratches and deposits is reduced.

  FIG. 7 is a diagram illustrating the misalignment correction pattern 26 according to the first embodiment. The misregistration correction pattern 26BKYCM_Y_SP is obtained by forming black and cyan patterns 26BK_Y_SP and 26C_Y_SP using BK and C, and superposing the yellow and magenta patterns 26Y_Y_SP and 26M_Y_SP so that both ends of each pattern are exposed. It is. When the red LED is used, there is no diffuse reflection light from black or cyan which is a complementary color, so that it is possible to distinguish yellow Y and magenta M by a composite wave of regular reflection light and diffuse reflection light.

  FIG. 8 is a characteristic diagram showing spectral sensitivity characteristics with respect to the color pattern of the LED irradiation light. In the figure, the vertical axis of the characteristic diagram is the spectral sensitivity of the LED irradiation light, and the horizontal axis is the wavelength of the LED irradiation light. This characteristic diagram shows the spectral sensitivity characteristic in the visible light region (wavelength 400 nm to 800 nm). 55_Yellow is a spectral sensitivity characteristic when the yellow toner pattern is irradiated with light. 55_Yellow has a peak at 56_Blue (wavelength 435 nm to 480 nm), which indicates that blue light is absorbed by the yellow pattern (blue light and yellow are complementary colors). Similarly, 55_Magenta has a peak at 56_Green (wavelength: 500 nm to 560 nm). 55_Cyan has a peak at 56_Red (wavelength 610 nm to 750 nm).

  As described above, when the LED irradiation light and the color pattern have a complementary color relationship, the irradiation light is absorbed on the pattern and is not reflected. That is, the diffuse reflected light component contained in the regular reflected light is very small. The black pattern has no diffuse reflection component regardless of the wavelength of the irradiation light. Therefore, when the LED irradiation light is set to a wavelength in the visible light region, the color misalignment correction of the color complementary to the irradiation light and black is corrected. The detection error of the pattern for use is reduced, and the positional deviation between the two colors can be corrected with high accuracy.

  In FIG. 7, in this embodiment, the pattern width in the main scanning direction of the linear pattern 26BKYCM_Y_SP for correcting misalignment is in a range in which the spot diameter 28 of the regular reflection light receiving unit 24 may be shifted in the main scanning direction. The value obtained by adding 1 mm is 1.6 mm. The pattern width in the sub-scanning direction of the oblique line pattern 26BKYCM_Y_SP is 0.6 mm, which is the spot diameter 28 of the regular reflection light receiving unit 24 in yellow Y and magenta M, and yellow Y and magenta M in black BK and cyan C. 2.8 mm (approximately 3 spot diameter) because it is necessary to consider 1 mm of a range that may be shifted in the sub-scanning direction and to secure an exposure width of both ends of 0.6 mm or more of the regular reflection light receiving unit 24. Double). In this case, the yellow Y and magenta M patterns 26Y_Y_SP and 26M_Y_Y are arranged at the centers of the black BK and cyan C patterns 26BK_Y_SP and 26C_Y_SP, respectively. The interval between the black BK and cyan C of the misregistration correction pattern 26BKYCM_Y_SP needs to be wide enough for the regular reflection light receiving unit 24 so that both reflected lights are not detected at the same time. This means that a value of 1.6 mm, which is obtained by adding a spot diameter of 0.6 mm of the regular reflection light receiving unit 24 and a range of 1 mm that may be shifted in the sub-scanning direction, is sufficient.

  FIG. 9 is a diagram showing a hatched pattern 26BKYCM_S_SP of the misregistration correction pattern 26. The oblique line pattern 26BKYCM_S_SP has an inclination of θ in the sub-scanning direction with respect to the straight line pattern 26BKYCM_Y_SP. Similar to 26BKYCM_Y_SP, the pattern arrangement is such that the yellow Y and magenta M patterns 26C_S_SP and 26M_S_SP are overlapped so that both ends of the black BK and cyan C patterns are exposed. At this time, the diagonal pattern 26BKYCM_S_SP of the misregistration correction pattern 26 has a width in the main scanning direction of 1.6 mm, a width in the θ ± 90 ° direction with respect to the black BK and cyan C sub-scanning directions, 2.8 mm, and yellow Y The width in the θ ± 90 ° direction with respect to the sub-scanning direction of magenta M is 0.6 mm. The interval between black BK and cyan C is 1.6 mm apart in the θ ± 90 ° direction with respect to the sub-scanning direction. The inclination (inclination angle) θ is any one of 90 °, 45 °, and 135 ° with respect to the sub-scanning direction. In this embodiment, θ is set to 45 °.

  FIG. 10 is a diagram illustrating a detection method of the linear pattern 26BKYCM_Y_SP of the positional deviation correction pattern 26 of FIG. Since the regular reflection light receiving unit 24 can detect regular reflection light and diffuse reflection light, if the pattern of black BK and cyan C that does not reflect regular reflection light and diffuse reflection light enters the spot diameter 28 of the regular reflection light reception unit 24, regular reflection is performed. The signal intensity of the output signal 32 of the light receiving unit 24 decreases. Therefore, the intersections 38BK_1 and 38BK_2 and 38C_1 and 38C_2 of the falling and rising edges of the output signal 32 with the threshold line 37 are obtained, and the positions of black BK and cyan C are determined based on the respective average values. On the other hand, since yellow Y and magenta M return diffusely reflected light, the signal intensity of the output signal 32 increases with respect to black BK and cyan C when entering the spot diameter 28 of the regular reflection light receiving unit 24. Therefore, the intersections 38Y_1 and 38Y_2 and 38M_1 and 38M_2 with the threshold line 37 are obtained, and the positions of Y and M are determined by their average values.

  Then, based on the detection result of the misregistration correction pattern 26 shown in FIGS. 7 and 9, the execution timing of misregistration correction using the misregistration correction pattern 26 of FIG. 6 is determined and executed. The image positions of the linear patterns 26BK, Y, C, and M_Y of the correction pattern 26 are obtained from the detection result of the positional deviation correction, and the CPU 46 (to be described later) obtains the deviation amount and skew of the sub-scanning resist by performing predetermined arithmetic processing. Can do. Further, when the CPU 46 obtains the image positions of the hatched patterns 26BK, Y, C, and M_S in addition to the image positions of the linear patterns 26BK, Y, C, and M_Y of the correction pattern 26 and performs a predetermined calculation process, the main scanning direction is obtained. Magnification error and registration deviation amount in the main scanning direction are respectively obtained. Based on this result, misalignment correction is performed.

  The skew can be corrected, for example, by adding a tilt to the deflecting mirror in the exposure unit 11 or the exposure unit 11 itself by an actuator. The registration deviation in the sub-scanning direction is performed by, for example, line writing timing and surface phase control of the polygon mirror 20. The magnification error in the main scanning direction is corrected by changing the writing image frequency, for example. The registration deviation in the main scanning direction can be corrected by changing the writing timing of the main scanning line.

  FIG. 11 is a block diagram showing a circuit configuration of a misalignment correction circuit that processes detected data for calculating a correction amount necessary for misalignment correction. In the figure, the misregistration correction circuit includes a control circuit CONT and a detection circuit SCT, and the detection circuit SCT is connected to the control circuit CONT via the I / O port 44 of the control circuit CONT.

  The detection circuit SCT includes TM sensors 17, 18 and 19, an amplifier 39, a filter 40, an A / D conversion unit 41, a sampling control unit 42, a FIFO memory 43, and a light emission amount control unit 49. In the control circuit CONT, a RAM 47 and a ROM 48 are connected to the CPU 46 via a path 45, and an I / O port 44 is connected to the bus 45.

  In such a control configuration, the output signal obtained by the regular reflection light receiving unit 24 of the TM sensors 17, 18, 19 is amplified by the amplifier 39, and only the signal component of the line detection is passed by the filter 40. The converter 41 converts analog data into digital data. Sampling of data is controlled by the sampling control unit 42, and the sampled data is stored in the FIFO memory 43. After the detection of one set of the misregistration correction patterns 26 is completed, the stored data is loaded to the CPU 46 and the RAM 47 via the I / O port 44 through the data bus 45, and the CPU 46 performs predetermined arithmetic processing. The above-described various shift amounts are obtained.

  The ROM 48 stores various programs for controlling the misregistration correction apparatus and the image forming apparatus according to the present embodiment, in addition to the above-described programs for calculating the misregistration amounts. In addition, the CPU 46 monitors the detection signal from the regular reflection light receiving unit 24 at an appropriate timing, and the light emission amount control unit 49 ensures that even if the conveyance belt 5 and the light emitting unit 23 deteriorate or the like is detected. The amount of light emission is controlled so that the level of the light reception signal from the regular reflection light receiving unit 24 is always constant. The RAM 47 functions as a work area and a data buffer when the CPU 46 executes the program. Thus, the CPU 46 and the ROM 48 function as a control unit that controls the operation of the entire image forming apparatus.

  In this way, the misregistration correction pattern 26 is formed, and by detecting the pattern 26 by the TM sensors 17, 18, 19, the misregistration correction between the respective colors is performed, and a high-quality image can be output. . In order to further reduce color misregistration and obtain a high-quality image, it is essential to reduce color pattern detection errors. For this reason, the misregistration correction apparatus according to the present embodiment pays attention to the monochromaticity of the LED light source, and irradiates light having a complementary color relationship with a certain color among the plurality of color patterns 26 from the light emitting unit 23. The color pattern can be corrected with high accuracy.

FIG. 12 is a flowchart showing the processing procedure of the arithmetic processing in the positional deviation correction control in the first embodiment executed by the CPU 46.
In the figure, when the misregistration correction control is started, first, the conventional misregistration correction patterns 26BKYCM_Y and 26BKYCM_S shown in FIG. 5 or the misregistration correction patterns 26BKCM_Y_SP and 26BKYCM_S_SP shown in FIGS. Which pattern is to be created as a correction pattern is selected (step S101). If there is no previous failure in the misalignment correction, the image formation of the misalignment correction patterns 26BKYCM_Y and 26BKYCM_S in FIG. 5 is selected, and exposure for image formation of the misalignment correction patterns 26BKYCM_Y and 26BKYCM_S is started (step S102). . The image forming patterns are all M sets (M is an integer of 1 or more).

  When the misregistration correction patterns 26BKYCM_Y and 26BKYCM_S are formed on the transport belt 5, reading of positional information of the misregistration correction patterns 26BKYCM_Y and 26BKYCM_S of the Nth set (N ≦ M) of the M sets is started. (Step S103). In step S103, when the position information reading of the N-th set of misregistration correction patterns 26BKYCM_Y and 26BKYCM_S in FIG. 5 is completed (step S104), the position information of the patterns in the Nth set is stored in the RAM 47 (step S105). . This storing process is executed until all M sets are completed (step S106—NO).

  When the storage of the position information in the RAM 47 of all M sets of the positional deviation correction patterns 26BKYCM_Y and 26BKYCM_S is completed (step S106-YES, step S107), and the number of failed detection sets of the positional deviation correction patterns is equal to or less than the specified value. In (step S108-YES), the CPU 46 calculates various displacement amounts based on the position information stored in the RAM 47 (step S109). Further, a correction amount corresponding to the calculated deviation amount is calculated, and this correction amount is stored in the RAM (step S110).

  On the other hand, when the number of misregistration correction pattern detection failure sets exceeds the specified value (step S108-NO), it is estimated that scratches and the like are present on the transport belt 5, and the misregistration correction pattern 26 from the next time is changed to the conventional one. Instead of the positional deviation correction patterns 26BKYCM_Y and 26BKYCM_S, the positional deviation correction patterns 26BKCM_Y_SP and 26BKYCM_S_SP of the present embodiment shown in FIGS. 7 and 9 are changed (step S111), and the pattern of the next positional deviation correction pattern 26 is changed. The patterns shown in FIGS. 7 and 9 are drawn. Therefore, from the next time, NO is selected in step S101, and the processing after step S112 is executed.

  On the other hand, if the number of misregistration correction pattern detection failure sets is less than or equal to that defined in step S108 (step S108-NO), various misalignment amounts are calculated from the position information of the misalignment correction patterns 26BKYCM_Y and 26BKYCM_S (step S109). ), The correction amount corresponding to the positional deviation amount is stored in the RAM 47, and the process is completed.

  Further, when the correction patterns 26BKYCM_Y and 26BKYCM_S in FIG. 5 are not formed in step S101 (step S101-NO), the image formation of the misalignment correction patterns 26BKYCM_Y_SP and 26BKYCM_S_SP shown in FIGS. 7 and 9 is selected. Then, exposure of all M sets of the misregistration correction patterns 26BKYCM_Y_SP and 26BKYCM_S_SP is started (step S112).

  When the misregistration correction patterns 26BKYCM_Y_SP and 26BKYCM_S_SP are formed on the conveyor belt 5, reading of positional information of the misregistration correction patterns 26BKYCM_Y_SP and 26BKYCM_S_SP of the Nth set (N ≦ M) of the M sets is started. (Step S113). In step S113, when the position information reading of the N-th set of misregistration correction patterns 26BKYCM_Y_SP and 26BKYCM_S_SP in FIGS. 7 and 9 is completed (step S114), the position information of the patterns in the N-th set is stored in the RAM 47 (step S114). Step S115). This saving process is executed until all M sets are completed (step S116—NO).

  When the storage of the positional information in the RAM 47 of all the M sets of positional deviation correction patterns 26BKYCM_Y_SP and 26BKYCM_S_SP is completed (step S116-YES, step S117), various deviation amounts are calculated from the positional information of the positional deviation correction patterns 26BKYCM_Y_SP and 26BKYCM_S_SP. Calculation is performed (step S109), the correction amount corresponding to the positional deviation detected based on the patterns of FIGS. 7 and 9 is stored in the RAM 47, and the process ends.

  By processing in this way, when the normal misregistration correction is insufficient, the pattern width is expanded, and the conveyance belt exposure area between the patterns is reduced by using the red LED for the light emitting unit 23, thereby conveying the pattern. It is possible to reduce false detection of scratches and deposits formed on the belt 5. As a result, a high quality image can be formed.

  In the second embodiment, the light emission color of the light beam 23a output from the light emitting unit 23 of the TM sensor is blue, and yellow Y, which is a complementary color of blue, is used as a position shift correction target pattern. Since the configuration of the color image forming apparatus is the same as that of the first embodiment, the same reference numerals are given to the same parts, and duplicate descriptions are omitted.

  FIG. 13 is a diagram illustrating a linear pattern 26BKYCM_Y_SP of the misregistration correction pattern 26 according to the second embodiment. The misregistration correction pattern 26BKYCM_Y_SP uses BK and Y to form black and yellow patterns 26BK_Y_SP and 26Y_Y_SP, and both ends of the patterns 26BK_Y_SP and 26Y_Y_SP are exposed in the main scanning direction of the C and M patterns 26C_Y_SP and 26M_Y_SP. It is a superposition. By using a blue LED as shown in FIG. 8, there is no diffuse reflection light from black BK or yellow Y as a complementary color, so cyan C and magenta M are a combined wave of regular reflection light and diffuse reflection light. 32 can be identified.

  The pattern width in the main scanning direction of the misregistration correction pattern 26BKYCM_Y_SP is a value obtained by adding 1 mm, which is likely to be shifted in the main scanning direction, to 0.6 mm of the spot diameter 28 of the regular reflection light receiving unit 24 as in the first embodiment. At 1.6 mm. The pattern width in the sub-scanning direction of the misregistration correction pattern 26BKYCM_Y_SP is 0.6 mm of the spot diameter 28 of the regular reflection light receiving unit 24 for cyan C and magenta M, and cyan C, for black BK and yellow Y. In consideration of 1 mm in a range in which the magenta M may be shifted in the sub-scanning direction, and it is necessary to secure an exposure width of both ends of 0.6 mm or more of the regular reflection light receiving unit 24, it is set to 2.8 mm. In this case, the cyan C and magenta M patterns 26C_Y_SP and 26M_Y_CP are arranged at the centers of the black BK26BK_Y_SP and the yellow Y pattern 26Y_Y_SP, respectively. The gap between the black BK and the yellow Y of the positional deviation correction pattern 26BKYCM_Y_SP needs to be wide enough for the regular reflection light receiving unit 24 so that both reflected lights are not detected at the same time. This means that the value of 1.6 mm is sufficient if a spot diameter of 0.6 mm of the regular reflection light receiving unit 24 and a range of 1 mm that may be shifted in the sub-scanning direction are added.

  FIG. 14 is a diagram illustrating a hatched pattern 26BKYCM_S_SP of the misregistration correction pattern 26 in the second embodiment. The oblique line pattern 26BKYCM_S_SP has an inclination of θ in the sub-scanning direction with respect to the straight line pattern 26BKYCM_Y_SP. Similar to 26BKYCM_Y_SP, the pattern arrangement is such that cyan C and magenta M patterns 26C_S_SP and 26M_S_SP are overlapped so that both ends of the black BK and yellow Y patterns in the main scanning direction are exposed. At this time, the diagonal pattern 26BKYCM_S_SP of the misregistration correction pattern 26 has a width in the main scanning direction of 1.6 mm, a width in the θ ± 90 ° direction with respect to the black BK and yellow Y sub-scanning directions, 2.8 mm, and cyan C. The width in the θ ± 90 ° direction with respect to the sub-scanning direction of magenta M is 0.6 mm. Further, the distance between black BK and yellow Y is 1.6 mm apart in the θ ± 90 ° direction with respect to the sub-scanning direction.

  FIG. 15 shows a method for detecting the positional deviation correction pattern 26BKYCM_Y_SP in FIG. Although the principle itself is the same as that of the first embodiment, since the color relationship is different, the main part will be described again. Since the regular reflection light receiving unit 24 can detect regular reflection light and diffuse reflection light, when a pattern of black BK and yellow Y that does not return regular reflection light and diffuse reflection light enters the spot diameter 28 of the regular reflection light reception unit 24. The signal intensity of the output signal 32 of the regular reflection light receiving unit 24 decreases. Therefore, the intersections 38BK_1 and 38BK_2 and 38Y_1 and 38Y_2 of the falling and rising edges of the output signal 32 with the threshold line 37 are obtained, and the positions of black BK and yellow Y are determined based on the respective average values. On the other hand, since cyan C and magenta M return diffusely reflected light, the signal intensity of the output signal 32 increases with respect to black BK and yellow Y when entering the spot diameter 28 of the regular reflection light receiving unit 24. Therefore, intersections 38C_1 and 38C_2 and 38M_1 and 38M_2 with the threshold line 37 are obtained, and the positions of cyan C and magenta M are determined based on the average values of the intersections.

  Based on the detection result of the misalignment correction pattern 26 shown in FIGS. 13 and 14, the execution timing of misalignment correction using the misalignment correction pattern 26 shown in FIG. 5 is determined and executed. The CPU 46 obtains the image positions of the misregistration correction patterns 26BK, Y, C, and M_Y from the detection result of the misregistration correction, and the CPU 46 performs predetermined calculation processing, whereby the deviation amount and skew of the sub-scanning resist can be obtained. These processes are as described in the first embodiment.

  FIG. 16 is a flowchart showing the processing procedure of the arithmetic processing in the misregistration correction control in the second embodiment executed by the CPU 46. Steps S101 to S111 are the same as those in the first embodiment, and steps S201 to S206 are the same as those in FIG. 7 and FIG. The only difference is the pattern for correcting misalignment shown in FIG.

  As described above, red is used as the emission color in the first embodiment, whereas blue is used as the emission color in the second embodiment, and yellow Y, which is a complementary color of blue, is used as the misalignment correction target pattern. Other configurations and controls are the same except for the differences. By processing in this way, when the normal misalignment correction is insufficient, the pattern width is increased, and the blue belt is used for the light emitting unit 23 to reduce the exposed area of the conveyor belt between the patterns. It is possible to reduce false detection of scratches and deposits formed on the belt 5. As a result, a high quality image can be formed.

  FIG. 17 is a diagram illustrating a schematic configuration of the image forming unit of the color image forming apparatus according to the third embodiment. The color image forming apparatus according to the third embodiment is an indirect transfer type tandem image forming apparatus, which is an intermediate transfer belt instead of the direct transfer type conveyance belt in the first embodiment, and is primarily transferred to the intermediate transfer belt. A full-color image is formed on the paper by collectively transferring the four color superimposed images onto the paper.

  In the third embodiment, the image forming unit 6 arranges a plurality of image forming units (electrophotographic process units) 6BK, 6Y, 6C, and 6M in order from the upstream side in the transport direction along the intermediate transfer belt 5a. This is a transfer type tandem type color image forming apparatus.

  With this configuration, the formation and detection of the misregistration correction pattern and the misregistration correction processing are executed in the same manner as in the first or second embodiment. Therefore, also in the third embodiment, a red LED or a blue LED is used for the light emitting portion 23 of the TM sensors 17, 18, and 19, and a color complementary to the colored light is used for the misregistration correction target pattern. It is possible to reduce false detection of scratches and deposits formed on the transfer belt 5a. As a result, a high quality image can be formed.

  Other parts not specifically described are configured in the same manner as in the first and second embodiments and function in the same manner.

  The program executed by the CPU 46 can be traded in the distribution process by using a recording medium. Examples of the recording medium include FD, CD-ROM (R, RW), DVD-ROM (R, RW), MO, MD, magnetic tape, server hard disk, and the like.

  Further, the present invention is not limited to the present embodiment, but covers all technical matters included in the technical idea of the invention described in the claims.

  The present invention can be applied to an apparatus that obtains a visible image by superimposing a plurality of colors, and a general apparatus that has a function of correcting a positional deviation of an image position that is performed when a visible image is obtained by superimposing a plurality of colors.

4 Paper 5 Conveying Belt 5a Intermediate Transfer Belt 6 Image Forming Section 9 Photosensitive Drum 10 Charger 12 Developer 13 Photoconductor Cleaner 15 Transfer Device 17, 18, 19 TM Sensor 23 Light Emitting Section 26a Light Beam 24 Regular Reflection Light Receiving Section 26 Position Deviation correction pattern 32 Output signal of regular reflection light receiving unit 33 Diffuse reflection component of received light signal 34 Regular reflection component of received light signal 46 CPU

Japanese Patent No. 2858735 Japanese Patent No. 2642351 JP 2007-148080 A

Claims (11)

A plurality of image carriers are juxtaposed along the direction of movement of the endless carrier, and images of different colors are formed on each image carrier by an electrophotographic process and transferred to the endless carrier side. Imaging means,
Pattern forming means for forming a positional deviation correction pattern consisting of a plurality of patterns formed for each color by the image forming means on the endless carrier;
Pattern detection means for irradiating the misregistration correction pattern formed on the endless carrier with a light beam and detecting regular reflection light and diffuse reflection light from the pattern;
A misregistration amount detecting means for detecting the misregistration amount of the image on the endless carrier based on the detection result of the misregistration correction pattern by the pattern detecting means;
An image forming apparatus comprising:
The misregistration correction pattern has two edges that form an inclination angle θ in the sub-scanning direction and is formed with a black reference color and a first color pattern on the most upstream side formed at intervals in the sub-scanning direction. A second color and a third color pattern which are formed on the reference color and the first color pattern and are narrower than the reference color and the first pattern,
The image forming apparatus, wherein the light beam is irradiation light having a peak in spectral sensitivity characteristics of the reflected light of the first color. The image forming apparatus according to claim 1,
A pattern width in the sub-scanning direction of the misregistration correction pattern composed of a plurality of colors including the reference color, the first color, the second color, and the third color is a spot of the regular reflection light receiving element of the pattern detection unit. An image forming apparatus having a diameter equal to or larger than a diameter. The image forming apparatus according to claim 1, wherein:
An image forming apparatus, wherein an interval between the reference color and the first color misregistration correction pattern is equal to or greater than a spot diameter of a regular reflection light receiving element of the detection unit. The image forming apparatus according to any one of claims 1 to 3,
The misregistration correction patterns of the second color and the third color are formed so as to overlap each other in the main scanning direction of the misregistration correction pattern of the reference color and the first color. An image forming apparatus. The image forming apparatus according to any one of claims 1 to 4, wherein
The misregistration correction pattern of the reference color and the first color has a width in the ± 90 ° direction with respect to the inclination angle θ set to about three times the spot diameter of the regular reflection light receiving element of the pattern detection means. An image forming apparatus. An image forming apparatus according to any one of claims 1 to 5,
The misregistration correction patterns of the second color and the third color have a width in the ± 90 ° direction with respect to the inclination angle θ equal to the spot diameter of the regular reflection light receiving element of the pattern detection unit. Forming equipment. The image forming apparatus according to any one of claims 1 to 6,
The image forming apparatus, wherein the inclination angle θ is any one of 90 °, 45 °, and 135 ° with respect to the sub-scanning direction. The image forming apparatus according to any one of claims 1 to 7,
An image forming apparatus, wherein the light emitting element of the pattern detecting means is a red LED, and the first color is cyan. The image forming apparatus according to any one of claims 1 to 7,
An image forming apparatus, wherein the light emitting element of the pattern detecting means is a blue LED, and the first color is yellow. A plurality of image carriers are juxtaposed along the direction of movement of the endless carrier, and images of different colors are formed on each image carrier by an electrophotographic process and transferred to the endless carrier side. Imaging means,
Pattern forming means for forming a positional deviation correction pattern consisting of a plurality of patterns formed for each color by the image forming means on the endless carrier;
Pattern detection means for irradiating the misregistration correction pattern formed on the endless carrier with a light beam and detecting regular reflection light and diffuse reflection light from the pattern;
A misregistration amount detecting means for detecting the misregistration amount of the image on the endless carrier based on the detection result of the misregistration correction pattern by the pattern detecting means;
A misregistration correction method in an image forming apparatus comprising:
Forming a black reference color and a first color pattern having two edges having an inclination angle θ in the sub-scanning direction and spaced apart in the sub-scanning direction and positioned on the most upstream side;
Forming a pattern of the second color and the third color, which are narrower than the reference color and the first pattern, on the reference color and the first color pattern, respectively,
Irradiating the misregistration correction pattern with irradiation light having a peak in spectral sensitivity characteristics of the reflected light of the first color;
Detecting a displacement amount based on the output of the reflected light irradiated in the irradiating step;
A misregistration correction method comprising: A plurality of image carriers are juxtaposed along the direction of movement of the endless carrier, and images of different colors are formed on each image carrier by an electrophotographic process and transferred to the endless carrier side. Imaging means,
Pattern forming means for forming a positional deviation correction pattern consisting of a plurality of patterns formed for each color by the image forming means on the endless carrier;
Pattern detection means for irradiating the misregistration correction pattern formed on the endless carrier with a light beam and detecting regular reflection light and diffuse reflection light from the pattern;
A misregistration amount detecting means for detecting the misregistration amount of the image on the endless carrier based on the detection result of the misregistration correction pattern by the pattern detecting means;
A misregistration correction program for executing misregistration correction control in an image forming apparatus provided with a computer,
A procedure for forming a black reference color and a first color pattern that have two edges that form an inclination angle θ in the sub-scanning direction and that are spaced apart in the sub-scanning direction and located on the most upstream side;
A step of superimposing a pattern of the second color and the third color narrower than the reference color and the first pattern on the reference color and the first color pattern, respectively,
Irradiating the misregistration correction pattern with irradiation light having a peak in spectral sensitivity characteristics of reflected light of the first color;
A procedure for detecting a displacement amount based on the output of the reflected light irradiated in the irradiating step;
A misregistration correction program characterized by comprising: