JP2005233983A - Image forming apparatus and the method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of accurately correcting out-of color registration even when several kinds of out-of color registration are simultaneously corrected by performing a cycle of correcting out-of color registration once, realizing the shortening of processing time required for correcting the out-of color registration and preventing toner consumption from increasing and the durability of parts for forming an image and of parts such as a sensor from being lowered, and to provide an image forming method. <P>SOLUTION: The image forming apparatus is equipped with a displacement correction amount calculation means which is a calculation means for calculating correction amount for correcting several kinds of displacement of images based on the result of calculation by a displacement calculation means and which calculates the correction amount of displacement in a subscanning direction with the displacement in the subscanning direction of a scanning line newly caused with the correction of the tilt of the scanning line and the curve of the scanning line in calculating the correction amount of the several kinds of displacement of images by the said calculation means. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a color printer or a color copying machine employing an electrophotographic method, and a method thereof, and more particularly, to an image forming apparatus having a function of correcting a shift amount between a plurality of different colors. It is about.

JP-A-4-264417 JP-A-8-146317 JP 2001-301939 A

  In recent years, image forming apparatuses such as color printers and color copiers that employ this type of electrophotographic system have increasingly adopted a so-called tandem system that is advantageous for high speed and high productivity. An image forming apparatus that employs this tandem method includes, for example, a plurality of image forming stations corresponding to each color such as yellow, magenta, cyan, black, and the like. Images of each color such as magenta, cyan, black, etc. are primary-transferred on the intermediate transfer belt while being superimposed on each other, and images of each color such as yellow, magenta, cyan, black, etc. are transferred onto the intermediate transfer belt in multiple layers. The image is secondarily transferred onto a recording sheet in a batch and then fixed, thereby forming a color image.

  In such a tandem image forming apparatus, it is important how to accurately superimpose images of each color such as yellow, magenta, cyan, and black formed at each image forming station to obtain a single color image. It becomes.

  Therefore, in the conventional image forming apparatus, the shift amount of each color image such as yellow, magenta, cyan, black, etc. is determined in the main scanning direction (intermediate transfer belt width direction), the sub-scanning direction (intermediate transfer belt movement direction), Various techniques for providing a mechanism for correcting color misregistration for each deviation amount separated into each component have been studied and adopted in actual machines.

  At that time, when the sub-scanning direction component of the sub-scanning direction component is the Y-direction, the correction of the Y margin shift, which is the shift of the image forming position in the Y-direction, is corrected by controlling the read write timing. The correction of (image inclination) and bow (image curvature) are configured to be performed independently using a mechanism mechanism in the image forming apparatus.

  As a technique for performing the above correction, for example, those disclosed in Japanese Patent Laid-Open Nos. 8-146317 and 4-264417 have already been proposed.

  An image forming apparatus according to the above-mentioned Japanese Patent Application Laid-Open No. 8-146317 includes a photosensitive member that forms an image, and a rotatable member by a predetermined angle with one end serving as a fulcrum. An optical component capable of changing the inclination of a scanning line of an optical image to be scanned is provided, and each scanning line of the optical image is sequentially formed on the photoconductor using a light beam transmitted or reflected by the optical component. An optical system that rotates, a motor that rotates the optical component in conjunction with rotation of the rotating shaft, reference position detection means that detects a reference position that is a reference for rotation of the motor, and a scanning line for the optical image The correction data input means for inputting the rotation direction and the rotation amount of the motor for correcting the inclination based on the reference position according to the inclination of the reference position, and the correction data input means. Correction execution means for detecting a reference position first by reference position detection means when the optical component is rotated based on the corrected data, and correcting the inclination of the scanning line based on the reference position. It is comprised so that it may comprise.

  Further, the optical device of the image forming apparatus according to the above-mentioned Japanese Patent Application Laid-Open No. 4-264417 is an optical device of an image forming apparatus configured to irradiate a photosensitive member with a laser beam via a mirror to form an electrostatic latent image. The apparatus is configured to include curved surface forming means for bending the reflecting surface of the mirror.

  However, the above prior art has the following problems. That is, in the case of the technique disclosed in the above Japanese Patent Laid-Open Nos. 8-146357 and 4-264417, an optical image is scanned on the photosensitive member by rotating an optical component such as a mirror. The mechanism is such that the tilt of the scanning line to be changed or the reflection surface of the mirror is curved by the curved surface forming means, but the optical component such as the mirror is rotated or the reflection surface of the mirror is curved. The mechanism is required to have high accuracy and high cost, and it is difficult to correct the target color misregistration with a single registration control operation. Therefore, the registration control operation must be performed several times. In this case, there is a problem that the color misregistration cannot be corrected.

  Therefore, as a technique that can solve such a problem, the present applicant, as disclosed in Japanese Patent Laid-Open No. 2001-309139, does not use a mechanism mechanism, and performs image processing due to skew or bow by image processing. An image forming apparatus configured to be corrected has already been proposed.

  An image forming apparatus according to Japanese Patent Laid-Open No. 2001-309139 forms a plurality of images represented by a plurality of image data in units of pixels, and combines the formed images as a single image. Calculating a registration correction amount for correcting a registration error of the plurality of images for each part of the plurality of images; and a registration correction amount calculated by the calculation unit on the image data A correcting unit that corrects image data in accordance with the correction amount, and a correction amount that is divided into a correction amount for a value for each pixel and a fine adjustment amount that is less than a pixel interval with respect to a recording position of each pixel; The plurality of images are formed by using the image data corrected by the correcting unit, and the recording positions of the individual pixels are finely adjusted according to the fine adjustment amount. And control means for controlling the stage, which is constituted to include.

  However, in the case of the image forming apparatus according to Japanese Patent Application Laid-Open No. 2001-309139, a mechanism mechanism for rotating an optical component such as a mirror or curving the reflecting surface of the mirror is unnecessary, but shown in FIG. Thus, for example, when a registration control cycle for skew is required, it is necessary to repeat the correction operation for each registration error a plurality of times depending on the type of registration error to be corrected, so that the processing time is also long. Or the consumption of toner increases due to the formation of the pattern of the resister, and the durability of the part for image formation and the parts such as the resister sensor is reduced.

  Therefore, the present inventors have invented and attempted to simultaneously correct registration errors of a plurality of products in one registration error correction cycle in order to shorten the processing time required for each registration error correction operation. However, if a skew (image inclination) or bow (image curvature) registration error is corrected, a margin error in the Y direction is newly generated, and a target color error correction can be realized. I found it impossible. Therefore, in order to realize the target high-accuracy color misregistration correction, it is necessary to accurately obtain the margin amount in the Y direction accompanying correction of skew (image inclination) and bow (image curvature) registration misalignment. .

  More specifically, in the conventional image forming apparatus, for the sake of convenience, the detection result of the registration sensor on the front side of the apparatus is OUT and the detection result of the registration control sensor on the back side of the apparatus is calculated from the amount of deviation in the Y direction obtained from the detection results of the plurality of registration control sensors. Assuming that the detection result is IN and the detection result of the regicon sensor in the center of the apparatus is Center, the skew correction amount, bow correction amount, or Y margin correction amount is calculated as follows.

Skew correction amount = OUT-IN
Bow correction amount = Center- (IN + OUT) / 2
Y margin = (IN + Center × 2 + OUT) ÷ 4

  However, in order to reduce the processing time required for the correction operation for each registration error, if it is attempted to correct a plurality of types of registration error simultaneously in one registration error correction cycle by image processing, the same image memory is used. Since it is necessary to perform image conversion for all correction factors with the image processing origin as a reference point, a new Y-direction margin can be obtained by skew or bow correction processing that could not occur with conventional mechanical correction. It has been found by the present inventors that a shift occurs on the image data in the image memory.

  When the skew is corrected using image processing, as shown in FIG. 29, a new margin shift in the Y direction occurs due to the correction of the skew. Similarly, when the bow is corrected using image processing, a margin shift in the Y direction newly occurs as a result of correcting the bow as shown in FIG.

  That is, when the registration control operation is performed using the image processing method, there is a problem that the correction amount obtained from the detection of the registration control sensor cannot be used as it is by the conventional method.

  Accordingly, the present invention has been made to solve the above-described problems of the prior art, and the object of the present invention is to simultaneously correct a plurality of types of registration misalignment in one registration misalignment correction cycle. However, it is possible to correct the color misregistration with high accuracy, reduce the processing time required for the color misregistration correction, increase the amount of toner consumption, An object of the present invention is to provide an image forming apparatus capable of preventing the durability of components such as a sensor from being lowered and a method thereof.

  In order to achieve the above object, according to the first aspect of the present invention, a plurality of images having different colors are formed along the main scanning direction and the sub-scanning direction based on image data of each color, and the plurality of images are formed. In an image forming apparatus that forms a single image by superimposing each other, a plurality of image position detecting means for detecting image forming positions of the plurality of images at a plurality of positions along a main scanning direction; Based on the detection result of the image position detecting means, a positional deviation amount calculating means for calculating the positional deviation amounts of a plurality of types of images, and based on the calculation result of the positional deviation amount calculating means, the positional deviations of the plurality of types of images. Computation means for computing a correction amount for correcting image correction, and when the computation means computes the misregistration correction amounts of the plurality of types of images, along with correction of scan line inclination and scan line curvature. New The positional deviation correction amount calculation means for calculating the positional deviation correction amount along the sub-scanning direction by combining the positional deviation amounts along the sub-scanning direction of the scanning line to be calculated, and the positional deviation correction amount calculation means. An image forming apparatus comprising: a misregistration correction unit that corrects misregistration of the image based on a misregistration correction amount.

  According to a second aspect of the present invention, the amount of positional deviation along the sub-scanning direction of the scanning line newly generated along with the correction of the inclination of the scanning line and the curvature of the scanning line is measured along the main scanning direction. The image forming apparatus according to claim 1, wherein the image forming apparatus is obtained with reference to a central portion.

  Furthermore, the invention described in claim 3 includes storage means for storing the amount of positional deviation along the sub-scanning direction of the scanning line newly generated along with the correction of the inclination of the scanning line and the curvature of the scanning line. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.

  According to a fourth aspect of the present invention, the misregistration amount calculation is performed on the misalignment amount along the sub-scanning direction of the scanning line newly generated along with the correction of the inclination of the scanning line and the curvature of the scanning line. 4. The image forming apparatus according to claim 1, further comprising storage means for storing a value obtained by adding a positional deviation amount along the sub-scanning direction of the scanning line calculated by the means. .

  Furthermore, the invention described in claim 5 is characterized in that the misregistration correction unit corrects misregistration of a plurality of types of images at a time by image processing. An image forming apparatus.

  Further, in the invention described in claim 6, the positional deviation correction amount calculating means is configured such that, out of the plurality of image position detecting means, the image position detecting means located at the center is shifted from the true center position in the main scanning direction. 2. The correction amount of the positional deviation along the sub-scanning direction is calculated by correcting the deviation amount along the main scanning direction of the image position detecting means located at the center. 6. The image forming apparatus according to any one of items 1 to 5.

  Furthermore, in the invention described in claim 7, a plurality of images having different colors are formed along the main scanning direction and the sub-scanning direction based on the image data of each color, and the plurality of images are overlapped with each other. In the image forming method for forming a single image, an image position detecting step for detecting image forming positions of the plurality of images at a plurality of positions along a main scanning direction, and a detection result of the image position detecting step. And calculating a correction amount for correcting the misregistration of the plurality of types of images based on the calculation result of the misregistration amount calculating step and the misregistration amount calculation step. A calculation step for calculating a positional deviation correction amount of the plurality of types of images in the calculation step, which is newly generated along with the correction of the inclination of the scanning line and the curvature of the scanning line. A positional deviation correction amount calculating step for calculating a positional deviation correction amount along the sub-scanning direction by combining the positional deviation amounts along the sub-scanning direction of the scanning line, and a position calculated by the positional deviation correction amount calculating step. An image forming method comprising: a misregistration correction step for correcting misregistration of the image based on a misalignment correction amount.

  As described above, according to the present invention, even when a plurality of types of registration misalignment are corrected simultaneously in one registration misalignment correction cycle, color misregistration can be corrected with high accuracy. It is possible to reduce the processing time required for misalignment correction, and to prevent the consumption of toner from increasing and the durability of parts such as image forming parts and sensors. An image forming apparatus and a method thereof can be provided.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 2 is a block diagram showing a tandem digital color copying machine as an image forming apparatus according to an embodiment of the present invention. Further, this tandem type digital color copying machine has an image reading device, but does not include the image reading device, and a printer that forms an image based on image data output from a personal computer (not shown) or the like. Of course, an image forming apparatus such as a facsimile may be used.

  In FIG. 2, reference numeral 1 denotes a main body of a tandem type digital color copying machine. The digital color copying machine main body 1 has an image reading device (IIT: Image) for reading an image of a document 2 at an upper portion on one end side thereof. Input Terminal 3). In the digital color copying machine main body 1, image data output from the image reading device 3, a personal computer (not shown) or the like, or image data sent via a communication line such as a telephone line or a LAN is stored. Processing in a color copier, which includes an image processing system (IPS) 4 that temporarily accumulates as necessary and applies predetermined image processing to the image data, and a CPU, ROM, RAM, etc. A control unit 5 that controls the whole, and an image output device (IOT) that outputs an image based on image data that has been subjected to predetermined image processing by the image processing device 4 by controlling an image forming operation by the control unit 5 : Image Output Terminal 6).

  In the digital color copying machine main body 1, as a plurality of image forming means constituting the image output device 6, it corresponds to each color of yellow (Y), magenta (M), cyan (C), and black (Bk). The image forming units 7Y, 7M, 7C, and 7Bk are arranged at regular intervals along the horizontal direction. Further, below the four image forming units 7Y, 7M, 7C, and 7Bk, intermediate toners as intermediate transfer members that transfer toner images of respective colors sequentially formed by these image forming units in a state of being superimposed on each other. The transfer belt 8 is disposed so as to be able to circulate along the arrow B direction. The toner images of each color transferred onto the intermediate transfer belt 8 in a multiple manner are collectively transferred onto a recording paper 10 as a recording medium fed from a paper feed tray 9 or the like, and then the fixing device 11. Thus, the image recording paper 10 fixed on the recording paper 10 and having a color image formed thereon is discharged to the outside.

  Further, the configuration of the tandem digital color copying machine will be described in detail with reference to FIG.

  In FIG. 2, reference numeral 1 denotes the main body of the tandem digital color copying machine as described above. A platen glass 12 on which the document 2 is placed is placed on the upper end of the digital color copying machine main body 1. An image reading device 3 that reads an image of the document 2 placed on the platen glass 12 is provided. The image reading apparatus 3 illuminates a document 2 placed on a platen glass 12 with two light sources 13, and reflects a reflected light image from the document 2 with a full-rate mirror 14, half-rate mirrors 15 and 16, and an image. Scanning exposure is performed on an image reading element 18 formed of a CCD sensor or the like via a scanning optical system including a lens 17, and the reflected light image of the document 2 is read with a predetermined resolution by the image reading element 18. .

  The reflected light image of the document 2 read by the image reading device 3 is, for example, the image processing device 4 as document reflectance data of three colors of red (R), green (G), and blue (B) (each 8 bits). The image processing apparatus 4 sends shading correction, position shift correction, brightness / color space conversion, gamma correction, frame erasing to the reflectance data of the document 2 as necessary. Predetermined image processing such as color / movement editing is performed.

  The image data subjected to the predetermined image processing by the image processing apparatus 4 as described above is four colors of yellow (Y), magenta (M), cyan (C), and black (Bk) (for example, 8 bits each). As described below, yellow (Y), magenta (M), cyan (C), and black (Bk) image forming units 7Y, 7M, 7C, and 7Bk are converted into gradation data (raster data). Are sent to ROS (Raster Output Scanner) 19Y, 19M, 19C, and 19Bk. In these ROS 19Y, 19M, 19C, and 19Bk, image exposure by the laser beam LB is performed according to the gradation data of the corresponding color. Done.

  By the way, inside the tandem type digital color copying machine main body 1, as described above, four image forming portions 7Y, 7M of yellow (Y), magenta (M), cyan (C), and black (Bk) are provided. , 7C, 7Bk are arranged in parallel at a certain interval in the horizontal direction.

  These four image forming portions 7Y, 7M, 7C, and 7Bk are all configured in the same manner except that the colors of the images to be formed are different. In general, the photosensitive members rotate at a predetermined speed along the arrow A direction. The photosensitive drum 20, the primary charging scorotron 21 that uniformly charges the surface of the photosensitive drum 20, and the surface of the photosensitive drum 20 are exposed to an image corresponding to each color to form an electrostatic latent image. ROS 19 as an exposure device, developing device 22 that develops the electrostatic latent image formed on the photosensitive drum 20, toner supply device 23 that supplies toner of a predetermined color to the developing device 22, and cleaning device 24 It consists of and.

  From the image processing apparatus 4, each color of the image forming units 7Y, 7M, 7C, and 7Bk of yellow (Y), magenta (M), cyan (C), and black (Bk) is assigned to each of the ROSs 19Y, 19M, 19C, and 19Bk. Image data is sequentially output, and laser beams LB emitted according to the image data from these ROSs 19Y, 19M, 19C, and 19Bk are scanned and exposed on the surfaces of the respective photosensitive drums 20Y, 20M, 20C, and 20Bk. An electrostatic latent image is formed.

  The ROSs 19Y, 19M, 19C, and 19Bk include a semiconductor laser 70 that emits a laser beam LB modulated in accordance with image data, as shown in FIG. The laser beam LB emitted from the semiconductor laser 70 is collimated by the collimator lens 71, reflected by the two plane mirrors 72 and 73, and then irradiated on the surface of the polygon mirror 74. The polygon mirror 74 is rotationally driven at a predetermined speed along the arrow direction, and the laser beam LB applied to the surface (mirror surface) of the polygon mirror 74 is along the main scanning direction (axial direction of the photosensitive drum). Are deflected and scanned. The laser beam LB deflected and scanned by the polygon mirror 74 is dot-dotted onto the photosensitive drum 20 via the folding mirror 77 with the focal length adjusted by the f-θ lenses 75 and 76 according to the deflection angle. Irradiated after being squeezed into a shape. Further, at one end of the photosensitive drum 20 in the axial direction, a scanning start position detection sensor 78 is located at a position corresponding to an end on the scanning start side (SOS: Start Of Scan) in the scanning direction of the laser beam LB. Is arranged.

  The electrostatic latent images formed along the main scanning direction and the sub-scanning direction on the photosensitive drums 20Y, 20M, 20C, and 20Bk by the ROSs 19Y, 19M, 19C, and 19Bk configured as described above are shown in FIG. As shown, the developing devices 22Y, 22M, 22C, and 22Bk are developed as yellow (Y), magenta (M), cyan (C), and black (Bk) toner images, respectively.

  Yellow (Y), magenta (M), cyan (C), and black (Bk) sequentially formed on the photosensitive drums 20Y, 20M, 20C, and 20Bk of the image forming units 7Y, 7M, 7C, and 7Bk. The toner images of the respective colors are transferred to primary transfer corotrons 25Y, 25M, 25C, and 25Bk as primary transfer means on an intermediate transfer belt 8 as an intermediate transfer member disposed below the image forming units 7Y, 7M, 7C, and 7Bk. Are sequentially transferred in a state of being superimposed on each other. The intermediate transfer belt 8 is wound around the drive roll 26, the tension roll 27, the steering roll 28, and the backup roll 29 with a constant tension, and is a dedicated drive excellent in constant speed (not shown). A drive roll 26 that is rotationally driven by a motor is driven to circulate at a predetermined speed in the direction of arrow B. As the intermediate transfer belt 8, for example, a flexible synthetic resin film such as polyimide is formed in a strip shape, and both ends of the synthetic resin film formed in a strip shape are connected by means such as welding, thereby being endless. A belt-shaped one is used.

  The yellow (Y), magenta (M), cyan (C), and black (Bk) toner images transferred onto the intermediate transfer belt 8 in a multiple manner are used as secondary transfer means that press-contact the backup roll 29. The recording paper 10 that has been secondarily transferred onto the recording paper 10 by the pressure and electrostatic force by the secondary transfer roll 30 and onto which the toner image of each color has been transferred is transported to the fixing device 11 by the transport roller pair 31. . The recording paper 10 onto which the toner images of the respective colors have been transferred undergoes a fixing process with heat and pressure by the fixing device 11 and is discharged onto a discharge tray 32 provided outside the copying machine main body 1.

  As shown in FIG. 2, the recording paper 10 having a desired size from the paper feed tray 9 passes through a paper conveyance path 36 including a paper feed roller 33 and a pair of paper conveyance rollers 34 and 35. In a state of being separated one by one, it is once transported to the resist roll 37 and stopped. The recording paper 10 supplied from the paper feed tray 9 is sent onto the intermediate transfer belt 8 by a registration roll 37 that is driven to rotate at a predetermined timing in synchronization with the toner image on the intermediate transfer belt 8.

  Prior to that, in the four image forming units 7Y, 7M, 7C, and 7Bk of yellow, magenta, cyan, and black, as described above, the yellow, magenta, cyan, and black toner images respectively have predetermined timings. Are sequentially formed.

  Further, the upper surface of the tandem digital color copying machine main body 1 configured as described above includes a display 39 for displaying messages and a keyboard 40 for an operator to input various commands. An operation unit 41 is provided.

  In FIG. 2, reference numeral 42 denotes an adsorbing roll disposed on the upstream side of the yellow image forming unit 7Y. The adsorbing roll 42 increases the toner adsorbing property of the intermediate transfer belt 8 as required. In order to improve the surface potential, the surface potential of the intermediate transfer belt 8 is maintained at a predetermined potential. Reference numeral 43 denotes a reference position detection sensor for detecting a reference position on the intermediate transfer belt 8. As the reference position detection sensor 43, for example, a sensor that detects the reference position of the intermediate transfer belt 8 by optically detecting a reflector or an opening provided on the surface of the intermediate transfer belt 8 is used. .

  The photosensitive drums 20Y, 20M, 20C, and 20Bk are subjected to the next image formation after the toner image transfer process is completed and the residual toner and paper dust are removed by the cleaning devices 24Y, 24M, 24C, and 24Bk. Prepare for the process. Further, residual toner and the like are removed from the intermediate transfer belt 8 by the belt cleaner 38.

  By the way, in the tandem digital color copying machine configured as described above, each image forming unit itself is caused by various factors such as vibration during transportation and installation, opening and closing of a paper feed tray, temperature change and secular change. Position and the photosensitive drums of the respective image forming units may cause positional fluctuations, which may cause misalignment of the field image.

  Therefore, in this embodiment, as shown in FIG. 4, an image position detection pattern 50 called a chevron pattern is formed on the intermediate transfer belt 8 at a predetermined timing. After detecting by the detector (image position detecting means) 60 and obtaining and correcting the positional deviation amount of the image formed by each of the image forming units 7Y, 7M, 7C, and 7Bk, a desired color image is formed. It is configured. The image position detectors 60A, 60B, and 60C are arranged in the main scanning direction as shown in FIG. 4 at the detection position 44 provided on the downstream side of the black image forming unit 7Bk as shown in FIG. Are arranged on the OUT side (front side in the figure), the CENTER part (center part), and the IN side (rear side in the figure) of the color copying machine main body 1, respectively. A plurality of (four or more) may be provided at equal intervals along the width direction of the intermediate transfer belt 8 and are appropriately arranged according to the type of image position deviation to be detected.

  As the image position detection pattern 50, patterns having various shapes can be used. For example, as shown in FIG. 5, the image is detected at an equal angle along the sub-scanning direction from the center to the left and right sides as shown in FIG. The one formed by forming the mountain-shaped mark 51 made of a linear image so as to correspond to the positions of the image position detectors 60A, 60B, 60C is used. A plurality of the image position detection patterns 50 are formed at predetermined intervals along the sub-scanning direction (movement direction of the intermediate transfer belt 8).

  More specifically, as the image position detection pattern 50, as shown in FIG. 5, the first chevron mark 51CC made of the first reference color (cyan in the illustrated example), The second chevron mark 51YY composed of the measured color (yellow color in the illustrated example) and the third chevron mark 51CY mark composed of the first color and the second color are covered as one unit. A pattern combining all of the measurement colors is used. The combination of the patterns 50 shown in FIG. 5 is one block for the reference color and the measured color. When this pattern is actually used, processing such as forming and sampling repeatedly for several blocks and averaging the sampling values is performed. In order to improve detection accuracy, the black chevron mark 51 has a yellow background with a high reflectance, and a black toner is applied to the black chevron mark 51 so that a predetermined chevron mark 51 is opened. It is desirable to form a black chevron mark 51. The image data for outputting the image position detection pattern 50 is stored in advance in, for example, the ROM of the control unit 5 of the image forming apparatus.

  FIG. 6 is a block diagram showing an image position detector 60 that detects the image position detection pattern 50.

  In FIG. 6, reference numeral 61 denotes a housing of the pattern detector 60, and 62 and 63 denote light-emitting elements including two LEDs that respectively illuminate the image position detection pattern 50 formed on the intermediate transfer belt 8. Reference numerals 64 and 65 denote a pair of light receiving elements called “bi-cell” in which two light receiving elements are each set. As the light receiving element pair 64 and 65 called “bi-cell”, for example, as disclosed in JP-A-6-118735, the light receiving elements 64a and 64b and 65a and 65b made of two photodiodes are combined. The detectors arranged symmetrically are used. The inclination angle of the light receiving element pairs 64 and 65 is set equal to the inclination angle (for example, 45 degrees) of the mountain pattern 51. As the two light-emitting elements 62 and 63, for example, LEDs that emit light having a specific wavelength (infrared region) or light having a predetermined wavelength distribution are used. It arrange | positions so that two detection positions on the intermediate transfer belt 8 may be illuminated in a state inclined by a predetermined angle. The two pairs of light receiving element pairs 64 and 65 are elongated parallelograms arranged adjacent to each other with their center portions in contact with each other and both end portions inclined downward by a predetermined angle with respect to the horizontal direction. The light receiving elements 64a, 64b and 65a, 65b are provided, and the light receiving elements 64a, 64b and 65a, 65b have different detection timings and detection angles of reflected light as shown in FIG. 6B. Is set to

  When the image position detector 60 detects the image position detection pattern 50 formed on the intermediate transfer belt 8, the amount of reflected light is reflected from one light receiving element 64 b by a linear mark 51 of the image position detection pattern 50. A mountain-shaped waveform corresponding to is output, and the other light-receiving element 64a also outputs a mountain-shaped waveform with some delay. Then, by amplifying the waveforms output from these two light receiving elements 64b and 64a, or by taking the difference and then amplifying it, as shown in FIG. From this, an output waveform that rises in a large mountain shape can be obtained. Therefore, by taking the difference between the waveforms output from the two light receiving elements 64a and 64b, the position of the linear mark 51 of the image position detection pattern 50 can be increased without using a highly accurate sensor such as a CCD. It becomes possible to detect with high accuracy by resolution.

  When the image position detection pattern 50 is detected by the image position detector 60, the waveform as shown at the right end of FIG. 5 is detected from the image position detector 60 only when the image position detection pattern 50 is detected. Is output. Therefore, when the image position detection pattern 50 is detected by comparing the output from the image position detector 60 with a certain threshold value, the image position detection pattern 50 changes from “OFF” to “ON”. When the signal passes, a pulse signal that changes from “ON” to “OFF” is obtained.

  In this way, focusing on only “ON” in this result, as described above, the “ON” period is a period during which a pattern is detected, and the “OFF” period is a period during which no pattern is detected. is there. Therefore, if the time interval from “ON” to “ON” is measured, the distance between the patterns is measured, and the deviation amount of each color with respect to the reference color image is calculated from the result, and a plurality of deviation amounts are calculated from the deviation amount. It is possible to always obtain a stable / good image by obtaining the amount of misregistration and correcting it by each image forming unit.

  FIG. 7 is a block diagram showing a signal processing circuit of the image position detector 60.

  As shown in FIG. 7, the image position detector 60 includes a reflected light amount detector 66a corresponding to the LED 62 as one light emitting element, and a reflected light amount detector 66b corresponding to the LED 63 as the other light emitting element. ing. In one reflected light amount detection unit 66a, the output terminal of the photodiode 64a as the light receiving element is connected to the microcomputer 83 of the control unit 5 via the current-voltage converter 80, the amplifier (AMP) 81, and the A / D converter 82. The current having a magnitude corresponding to the amount of light received from the photodiode 64a is converted into digital data representing the output voltage of the photodiode 64a and input to the microcomputer 83. The microcomputer 83 is connected to a light emitting element (LED) 62 via an LED driver 84. The microcomputer 83 controls the drive current supplied to the LED 62 via the LED driver 84 so that the output voltage from the photodiode 64a is within a predetermined range.

  The output terminal of the other photodiode 64b is connected to one of the two input terminals of the differential input amplifier 86 via the current-voltage converter 85, and is connected to the other of the two input terminals. Is connected to the output terminal of a current-voltage converter 80 which is an output from the photodiode 64a. The differential input amplifier 86 amplifies and outputs a difference between signals input from the current-voltage converters 85 and 80 (corresponding to a difference in received light amount between the photodiodes 64a and 64b). In FIG. 5, an approximate change in the output voltage of the differential input amplifier 86 when the image position detector 60 detects the image position detection pattern 50 is shown in association with the pattern 51.

  The output terminal of the differential input amplifier 86 is connected to the microcomputer 83 via a comparator 87, a buffer 88, and a counter 89. The comparator 87 compares the level of the signal input from the differential input amplifier 86 with a preset threshold, and when the level of the signal is equal to or higher than the threshold, the output signal is at a high level (for convenience, referred to as “ON”). When the level is less than the threshold, the output signal is switched to a low level (referred to as “OFF” for convenience). An output signal from the comparator 87 is input to the counter 89 via the buffer 88.

  The counter 89 starts counting when the level of the input signal is switched from “OFF” to “ON”, and after the level of the signal is switched from “ON” to “OFF”, the counter 89 changes from “OFF” to “ When switched to “ON”, the count value up to that time is output to the microcomputer 83 and the count value is reset, and then the time until the signal level is switched from “OFF” to “ON” is counted repeatedly.

  The microcomputer 83 detects the position of the image position detection pattern 50 based on the count result input from the counter 89 at the time of image position correction described later (when the image position detector 60 detects the image position detection pattern 50). The image forming units 7Y, 7M, 7C, and 7Bk are configured to correct image forming position shifts (registration shifts).

  Since the circuit having the same configuration as that of the reflected light amount detection unit 66a is also connected to the photodiodes 65a and 65b of the other reflected light amount detection unit 66b, as shown in FIG. 7, it is the same as each part of the connected circuit. The description is omitted.

  The microcomputer 83 controls the image forming units 7Y, 7M, 7C, and 7Bk so that an image position detection pattern 50 as shown in FIG. 5 is formed on the outer peripheral surface of the intermediate transfer belt 8 when the registration error is corrected. To do.

  When the image position detection pattern 50 is formed on the intermediate transfer belt 8, the image position detection pattern 50 is detected by the image position detector 60. Here, since the detection positions of the photodiodes 64a and 64b on the outer peripheral surface of the intermediate transfer belt 8 are shifted in the sub-scanning direction, the current from the differential input amplifier 86 is detected when the image position detection pattern 50 is detected. -Waveform corresponding to the difference between the signals input from the voltage converters 85 and 80 (difference in received light amount of the photodiodes 64a and 64b), that is, the outer peripheral surface of the intermediate transfer belt 8 as shown as "detection waveform" in FIG. Each time a single peak mark crosses the detection position by the photodiodes 64a and 64b above, a signal having a waveform in which the level of the output signal changes in a pulse shape in the negative direction and the positive direction is output.

  The output signal of the differential input multiplier 86 is input to the comparator 87, and the comparator 87 compares the level of the output signal with a preset threshold value. The comparator 87 sets the level of the output signal to “ON” when the level of the input signal is equal to or higher than the threshold, and sets the level of the output signal to “OFF” when the level of the input signal is less than the threshold. . The signal output from the comparator 87 is input to the counter 89 via the buffer 88, and the time intervals when the signal level is switched from “OFF” to “ON” are sequentially counted. The count value obtained by the counter 89 is input to the microcomputer 83 as a pattern detection signal (see FIG. 1).

  The microcomputer 83 receives count values from two (total six) counters 89 per single image position detector 60 as pattern detection signals. In the signal output from the comparator 87, the period in which the level is “ON” corresponds to the period in which the detector detects the mountain pattern, and the period in which the level is “OFF” is detected. This corresponds to a period during which the vessel does not detect the chevron pattern (a period during which a gap between chevron patterns is detected). Therefore, the count value input from the counter 89 represents the formation interval of the chevron pattern 51 in the image position detection pattern 50.

  By the way, in this embodiment, based on the detection results of the plurality of image position detection means and the plurality of image position detection means for detecting the image forming positions of the plurality of images at the plurality of positions along the main scanning direction, A misregistration amount calculating means for calculating misregistration amounts of a plurality of types of images, and a calculation for calculating a correction amount for correcting misregistration of the plurality of types of images based on the calculation results of the misregistration amount calculating means. A misregistration correction amount calculating means for calculating a misregistration correction amount of the plurality of types of images by the calculation means, and based on the misregistration correction amount calculated by the misregistration correction amount calculation stage, A misalignment correcting unit that corrects misalignment of the image is provided.

  Further, in this embodiment, the amount of misalignment along the sub-scanning direction of the scanning line newly generated in accordance with the correction of the inclination of the scanning line and the curvature of the scanning line is represented in the central portion along the main scanning direction. It is comprised so that it may obtain | require with reference | standard.

  Further, this embodiment is configured to include storage means for storing a positional deviation amount along the sub-scanning direction of the scanning line newly generated in accordance with the correction of the inclination of the scanning line and the curvature of the scanning line. ing.

  In this embodiment, the positional deviation amount calculation means calculates the positional deviation amount along the sub-scanning direction of the scanning line newly generated in accordance with the correction of the inclination of the scanning line and the curvature of the scanning line. Storage means for storing a value obtained by adding the amount of positional deviation along the sub-scanning direction of the scanning line.

  Furthermore, in this embodiment, the positional deviation correction means is configured to correct positional deviations of a plurality of types of images at a time by image processing.

  FIG. 8 is a block diagram showing a control circuit of the digital color copying machine according to this embodiment.

  In FIG. 8, reference numeral 83 denotes a microcomputer (CPU) for controlling the image forming operation of the digital color copying machine, and this microcomputer 83 serves as a storage means for storing parameters appropriately used in the image forming position correcting operation. Nonvolatile memory (NVM) 90 is connected. The microcomputer 83 is connected to an image data development circuit (Video Asic) 92 having a drawing memory 91 for developing image data. From the image data development circuit (Video Asic) 92, Image data of each color is sent to the ROSs 19Y, 19M, 19C, and 19Bk.

  FIG. 1 shows a digital color copier according to the present embodiment. Among various functions realized by the microcomputer 83 and hardware connected thereto, a function related to correction of image formation misalignment (hereinafter referred to as this function). Software and hardware for realizing the above are collectively referred to as a registration correction unit 100), and are divided into blocks for each detailed function.

  As shown in FIG. 1, the registration correction unit 100 mainly calculates a positional deviation amount based on the pattern detection signals input from the image position detectors 60 </ b> A, 60 </ b> B, and 60 </ b> C. As a positional deviation amount calculation unit 101 as a means, and a positional deviation correction amount calculation unit that calculates a correction amount for correcting the positional deviation of the plurality of types of images based on the calculation result of the positional deviation amount calculation unit 101. And a positional deviation correction unit 103 as positional deviation correction means for correcting the positional deviation of the image based on the positional deviation correction amount calculated by the positional deviation correction amount calculation unit 102. Have.

  In the present embodiment, among the DC component and the AC component of the registration error, the registration error related to the positional error in the sub-scanning direction is targeted. Therefore, only the DC error of the registration error is considered. Of course, the AC component of the misregistration may be corrected together.

  Based on the count value input from each counter 89 shown in FIG. 7, the positional deviation amount calculation unit 101 sets the mountain-shaped mark 51 formation time interval (in FIG. 9A) in each part in the image position detection pattern 50. The indicated time intervals a, b, c, d) are detected. The time intervals a, b, c, and d obtained from the two count values input from the single image position detector 60 are the main scanning direction (hereinafter referred to as FS (Fast Scan) direction) and the sub scanning direction ( If there is no shift in pattern formation position (hereinafter referred to as SS (Slow Scan) direction), the values are equal to each other (a = b = c = d) as shown in FIG. 9B, but FIG. Or, when the pattern formation position is shifted in the FS direction as shown in (D), or when the pattern formation position is shifted in the SS direction as shown in FIG. At least one of the intervals a, b, c, d is different from the other values.

  Therefore, the misregistration amount calculation unit 101 performs color misregistration amounts FSerr and SS directions of the other three colors (for example, Y, M, and Bk) in the FS direction based on a specific color (for example, C) according to the following arithmetic expression. The color misregistration amount SSerr is calculated based on the count values input from the image position detectors 60A, 60B, and 60C.

FSerr [sec] = (ba) / 2
FSerr [mm] = FSerr [sec] (distance per unit time) [mm / sec]
SSerr [sec] = (dc) + (ba) / 2
SSerr [mm] = SSerr [sec] (distance per unit time) [mm / sec]
Here, for example, the value of SSerr [mm], which is the amount of positional deviation along the sub-scanning direction in the image position detector 60B in the center, becomes the amount of positional deviation along the SS direction as it is.

  As a result, the color misregistration amounts in the vicinity of each position (SOS (Start Of Scan), COS (Center Of Scan), and EOS (End Of Scan) along the FS direction are detected in the FS direction and the SS direction, respectively. Here, the relationship between the position (coordinate value Y) along the FS direction and the color misregistration amounts FSerr, SSerr based on the color misregistration amounts FSerr, SSerr near SOS, COS, and EOS for a certain color. Is shown as a solid line in FIG.

  The misregistration correction amount calculation unit 102 calculates a color misregistration correction amount for correcting the color misregistration from the coordinate value Y using the reference axis as a coordinate axis (the coordinate value Y representing the reference color and the color misregistration correction amount are calculated). The relationship is shown as a broken line in FIG. 10). Then, for each of the three colors other than the reference color, a calculation is performed to obtain a color misregistration correction amount based on the color misregistration amounts FSerr and SSerr.

  Color misregistration can be corrected by independently correcting the position of each pixel for each color based on the color misregistration correction amount Y obtained above. FIG. 10 shows a case where the deviation between the color misregistration amount near SOS and the color misregistration amount near COS, and the deviation between the color misregistration amount near COS and the color misregistration amount near EOS are the same. Are not necessarily the same.

  That is, the misregistration correction amount calculation unit 102 determines the timing at which the image position detection pattern 50 is detected by the image position detectors 60A, 60B, and 60C and the image position detection pattern with respect to the detection positions of the image position detectors 60A, 60B, and 60C. Based on the amount of deviation of the formation position of 50, the positional deviation (Y margin), the inclination (skew) of the scanning line, and the curvature (bow) of the scanning line are detected and corrected respectively. The amount of misalignment correction is calculated. There are various other image displacement amounts, such as a change in overall magnification and a change in lateral magnification. In the present invention, when correcting image displacement, the displacement in the sub-scanning direction is corrected. The new scan line tilt (skew) and scan line bow (bow) are particularly problematic.

  As for the inclination (skew) of the scanning line, as shown in FIG. 11, the XY coordinates (L_Err (2, n), P_Err) of the formation position of the image position detection pattern 50 at the detection positions of the image position detectors 60A, 60B, 60C. (2, n)), (L_Err (1, n), P_Err (1, n)), (L_Err (0, n), P_Err (0, n)) (n represents color) Based on the positional relationship, the scanning line inclination amount is calculated according to the following arithmetic expression, and the correction amount SK (n) for the scanning line inclination is calculated from the reference color position (coordinate value X) along the FS direction.

Scan line inclination (skew) deviation amount calculation formula ΔSK (n) = P_Err (2, n) −P_Err (0, n)
Scan line inclination (skew) correction amount calculation formula SK (n) = − ΔSK (n) × Wall ÷ Wsnr
Here, Wall is a correction reference interval, and Wsnr is a sensor interval. In general, Wall ≧ Wsnr.

  The scanning line inclination correction amount SK (n) along the FS direction on the image can be obtained from the deviation amount obtained above, and based on this scanning line inclination correction amount SK (n), the position deviation correction unit 103 is obtained. Thus, it is possible to correct the inclination of the scanning line by correcting the position of each pixel.

  That is, when correcting the scanning line inclination (skew) in the misalignment correction unit 103, when the image data is stored in the drawing memory 92, the scanning line inclination (skew) is canceled in advance so as to cancel the scanning line inclination (skew). If image data is stored with an inclination opposite to (skew) and image formation is performed as usual based on the image data stored in the drawing memory 92, the scanning line inclination (skew) is corrected. Can do.

  As for the curve (bow) of the scanning line, as shown in FIG. 12, the XY coordinates (L_Err (2, n), P_Err (2, n)), (L_Err (1) of the formation position of the image position detection pattern 50 are provided. , N), P_Err (1, n)), (L_Err (0, n), P_Err (0, n)), and the XY coordinates (L_Err (2, n), When P_Err (2, n)), (L_Err (0, n), P_Err (0, n)) are made to coincide with the X axis, the bending amount BW of the center image is calculated as shown in FIG. Then, an arithmetic expression for calculating the correction amount BW (n) for the scanning line curvature is obtained from the position (coordinate value X) along the FS direction.

Scan line curve (bow) deviation amount calculation formula ΔBW (n) = P_Err (1, n) −P_Err (2, n) + P_Err (0, n) / 2
Scan line curve (bow) correction amount calculation formula BW (n) = − ΔBW (n) × (Wall ÷ Wsnr) ²
Here, BW (n) is the scanning line curve, and the XY coordinates (L_Err (2, n), P_Err (2, n)), (L_Err (0, n), P_Err (0, n)) coincide with the X axis. This is the value at the center when

  In the present embodiment, a case has been described in which the scanning line curve (bow) is approximated by a quadratic function and is corrected and corrected, but other functions such as cosh may be used as a matter of course. It is.

Also, the positional deviation along the sub-scanning direction is
ΔYMn = P_Err (1, n)
And the amount of correction is
YMn = −ΔYMn
Can be obtained as

  Basically, as described above, the positional deviation correction amount calculation unit 102 causes the positional deviation (Y margin) of the scanning line in the sub-scanning direction, the inclination (skew) of the scanning line, and the curvature (bow) of the scanning line. Each is detected, and a process for obtaining a correction amount for correcting each is performed.

  By the way, in this embodiment, as described above, when the misregistration correction amount calculation unit 102 calculates a plurality of types of misregistration correction amounts based on the calculation result of the misregistration amount calculation unit 101, The correction amount of the positional deviation along the sub-scanning direction is calculated by adding the positional deviation amount along the sub-scanning direction of the scanning line newly generated along with the correction of the inclination of the scanning line and the curvature of the scanning line. It is configured.

  That is, in this embodiment, the misregistration correction amount calculation unit 102 calculates the misalignment correction amount for correcting the inclination (skew) of the scanning line and the curvature (bow) of the scanning line, and the inclination of the scanning line. In accordance with the correction amount of the (skew) and the curve (bow) of the scanning line, a position shift amount of the position (Y margin) along the sub-scanning direction of the newly generated scanning line is calculated, and the calculated amount is calculated based on the scanning line. By feeding back to the correction of the position (Y margin) displacement amount along the sub-scanning direction, all the image misalignment elements along the sub-scanning direction are corrected by reading the image position detection pattern 50 once. Is possible.

  As will be described later, among the image position detectors 60A, 60B, and 60C, when the image position detector 60B arranged at the center is not arranged at the ideal center, that is, deviated from the ideal center. Even when the image position detection patterns 50 are arranged, it is possible to correct all the positional deviation elements of the image along the sub-scanning direction by reading the image position detection pattern 50 once.

  First, as shown in FIG. 14, the image positional deviation calculated by the positional deviation amount calculation unit 101 based on the pattern signals from the image position detectors 60A, 60B, and 60C is along the sub-scanning direction of the scanning line. Misalignment (Y margin), scanning line inclination (skew), and scanning line curvature (bow), of which the amount of correction of the scanning line inclination (skew) is SK (n), scanning As an example, when the amount of correction of the curvature of the line (bow) is BW (n), the amount of positional deviation of the image along the sub-scanning direction at the ideal center is P_Err (1, n). The calculation operation of the misregistration correction amount calculation unit 102 will be described. Note that n is a value representing a color. When cyan is used as a reference color, for example, n = 1 corresponds to a yellow color, n = 2 corresponds to a magenta color, and n = 3 corresponds to a black color.

  Here, when calculating the correction amount of the positional deviation of the image along the sub-scanning direction, the scanning line newly generated along with the correction of the inclination (skew) of the scanning line and the curvature (bow) of the scanning line is calculated. Arithmetic processing for obtaining a positional deviation amount along the sub-scanning direction is performed. Now, when correction of the inclination (skew) of the scanning line and the curvature (bow) of the scanning line is performed, the image indicated by the solid line E in FIG. 14 moves to the image indicated by the solid line F in FIG. It is formed on the transfer belt 8. A line indicated by a solid line I is a virtual ideal of cyan as a reference color. The distance between the line indicated by the solid line I in FIG. 14 and the image indicated by the solid line F is the position of the image along the sub-scanning direction newly generated as a result of the skew and bow correction processing. It is a gap.

  In this embodiment, among the image position detectors 60A, 60B, and 60C arranged at three locations, in order to correct misalignment components such as the inclination (skew) of the scanning line and the curvature (bow) of the scanning line, The position of the image position detector 60B arranged at the center is used as a reference.

  Hereinafter, when the position of the image position detector 60B arranged at the center is arranged at the ideal center in the main scanning direction, and the position of the image position detector 60B arranged at the center is the main scanning direction. Correction of the scan line inclination (skew) and the scan line curvature (bow) in two ways: when the center is not located at the ideal center, that is, when the center is shifted from the ideal center. A method for calculating the amount of image misregistration along the sub-scanning direction that is newly generated in accordance with the processing will be described.

  (1) When the image position detector 60B arranged at the center is arranged at the ideal center in the main scanning direction

  First, as shown in FIG. 15, the misregistration correction amount calculation unit 102 constituted by the microcomputer 83 has a misalignment amount (Y margin) in the sub-scanning direction at the position of the image position detector 60B located at the ideal center. Is calculated (step 101).

  In this embodiment, the position of the image position detector 60B arranged at the center is used as a reference, and the image position detector 60B is arranged at the ideal center in the main scanning direction.

  Therefore, if the image formed on the intermediate transfer belt 8 is not misaligned along the sub-scanning direction, the position of the image forming position pattern 50 formed at the center coincides with the position of the image position detector 60B. It should be.

However, in the case of FIG. 14, the image position in the sub-scanning direction at the ideal center is shifted by P_Err (1, n). Therefore, the deviation amount ΔYM (n) in the sub-scanning direction at the ideal center is ΔYM (n) = P_Err (1, n). As a result, the corrected value YM (n) _{NEW due to} the position shift in the sub-scanning direction at the ideal center is
YM (n) _NEW = YM (n) −ΔYM (n)
(Step 101). Here, the subscript NEW means a value newly obtained by the current calculation of the correction amount.

Therefore, the positional deviation correction amount calculation unit 102 stores YM (n) _NEW , which is a value after correcting the deviation in the sub-scanning direction at the ideal center, as shown in FIG. Store in (NVM) 92.

  Next, the misregistration correction amount calculation unit 102 performs the correction processing of the scan line inclination (skew) and the scan line curvature (bow), and the newly generated image along the sub-scanning direction. A position (Y margin) shift amount, that is, a shift amount along the sub-scanning direction between the solid line I and the solid line F in FIG.

  Here, the inclination (skew) of the scanning lines and the curvature (bow) of the scanning lines are corrected by the values of the inclination (skew) of the scanning lines and the curvature (bow) of the scanning lines detected by the image position detection pattern 50. Therefore, the center position (Y2), which is the center position in the main scanning direction of the image when arranged on the image memory 91, differs from the value of the vertex (YMIN) of the image, and the center position (Y2) of the image and the vertex of the image Depending on the value of (YMIN), an image position (Y margin) shift amount along the sub-scanning direction newly generated at the center of the image in the main scanning direction varies.

  Therefore, if the cases are classified according to the values of the inclination (skew) of the scanning line and the curvature (bow) of the scanning line detected by the image position detection pattern 50, as shown in FIGS. It is divided into. Here, a case has been described in which correction is performed in the sub-scanning direction divided into four regions along the main scanning direction, but the number of regions to be divided is not limited to four. is there.

  That is, FIG. 16 shows that an image E transferred onto the intermediate transfer belt 8 has a scanning line inclination (skew) SK in which the right end E ′ is shifted downstream in the sub-scanning direction. This shows a state in which a scanning line curve (bow) BW that is convex downward is generated. In this case, the center position (Y2) of the image when it is arranged on the image memory 91 as shown in FIG. 16A, depending on the values of the scan line inclination (skew) SK and the scan line curve (bow) BW. And the value of the vertex (YMIN) of the image and the center position (Y2) of the image when arranged on the image memory 91 as shown in FIGS. The value of the vertex (YMIN) is divided into a case where the values are shifted to the right side and the right end in the figure. In FIG. 16, a rectangular image indicated by H represents an image transferred onto the intermediate transfer belt 8 in a state where the inclination (skew) of the scanning line and the curvature (bow) of the scanning line are corrected. .

  In contrast to FIG. 16, FIG. 17 shows an image E transferred onto the intermediate transfer belt 8, and a scanning line inclination (skew) SK in which the left end E ″ is shifted downstream in the sub-scanning direction. 16, and a scanning line curve (bow) BW that is convex downward is generated as in Fig. 16. Also in this case, Figs. C), when the center position (Y2) of the image when placed on the image memory 91 matches the value of the vertex (YMIN) of the image, and when the image is placed on the image memory 91, The value of the vertex (YMIN) of the image with respect to the center position (Y2) is divided into a case where the values are shifted to the left side and the left end in the drawing.

  Further, FIG. 18 shows that an image E transferred onto the intermediate transfer belt 8 has a scanning line inclination (skew) SK in which the left end E ″ is shifted downstream in the sub-scanning direction. This shows a state in which a scanning line curve (bow) BW that is convex upward is generated.

  Further, FIG. 19 shows that an image E transferred onto the intermediate transfer belt 8 has a scanning line inclination (skew) SK in which the right end E ′ is shifted downstream in the sub-scanning direction. Similarly to FIG. 18, the scanning line curve (bow) BW that is convex upward is shown.

  First, in FIG. 16, the misregistration amount calculation unit 102 corrects the scan line inclination (skew) SK and the scan line curve (bow) BW by image processing, and therefore the image memory 91 stores image data. In order to correct the generated scanning line inclination (skew) SK and the scanning line curvature (bow) BW, as shown by SK 'in FIG. 16, the right end is the upstream side in the sub-scanning direction. The image data is stored in a state in which it is inclined by the opposite amount and curved so as to be convex upward as indicated by BW ′ in FIG.

  The movement of the image data on the image memory 91 is performed by comparing the Y value at the X coordinate along the main scanning direction with the Y value at the center where the sensor is located.

That is, the image data stored in the image memory 91 on the basis of the point G as the coordinate origin when the image data is stored in the image memory 91 is the main scanning direction of the image in the case of FIG. The center position (Y2) along the image and the vertex (head position) (YMIN) along the main scanning direction of the image are equal, and the scan line inclination (skew) and the scan line curve (bow) are processed by image processing. In the image corrected by the above, the image position (Y margin) deviation amount along the sub-scanning direction newly generated at the center position along the main scanning direction of the image is zero.
YM = Y2-YMIN = 0

On the other hand, in the case of FIG. 16B, the image data stored in the image memory 91 is based on the point G as the coordinate origin when the image data is stored in the image memory 91. The value of the center position (Y2) along the main scanning direction and the value of the vertex (head position) (YMIN) along the main scanning direction of the image are different, and the inclination (skew) of the scanning line and the curve (bow) of the scanning line are different. In the image after being corrected by the image processing, an image position (Y margin) deviation amount along the sub-scanning direction newly generated at the center position along the main scanning direction of the image is
YM = Y2-YMIN
It becomes.

Similarly, in FIG. 16C, the image data stored in the image memory 91 is aligned along the main scanning direction of the image with reference to the point G as the coordinate origin when the image data is stored in the image memory 91. After the center position (Y2) and the value of the vertex (head position) (YMIN) along the main scanning direction of the image are different, the inclination (skew) of the scanning line and the curvature (bow) of the scanning line are corrected by image processing In the image of, an image position (Y margin) deviation amount along the sub-scanning direction newly generated at the center position along the main scanning direction of the image is
YM = Y2-YMIN
It becomes.

17 to 19, as in FIG. 16, in the image after correcting the scan line inclination (skew) SK and the scan line curve (bow) BW by image processing, the main scan direction of the image The amount of deviation of the image position (Y margin) along the sub-scanning direction at the center position along
YM = Y2-YMIN
It turns out that it becomes.

Thus, the positional deviation correction amount calculation unit 102
CNT_YM _NEW = Y2-YMIN
By correcting the scan line inclination (skew) and scan line curvature (bow) by image processing, the image position (Y margin) shift amount along the sub-scanning direction newly generated is calculated. CNT_YM _NEW is obtained (step 103 in FIG. 15).

  Further, since the value of (Y2−YMIN) varies depending on the value of the scanning line inclination (skew) and the scanning line curvature (bow), it is necessary to perform correction based on the previous correction amount.

As a result, the positional deviation correction amount calculation unit 102 corrects the scanning line inclination (skew) SK and the scanning line curvature (bow) BW to the positional deviation amount YM of the image along the normal sub-scanning direction. The image position (Y margin) deviation amount CNT_YM _NEW newly generated in the sub-scanning direction is combined with the image position (Y margin) deviation amount YM_ALL along the true sub-scanning direction.
YM_ALL = YM- (CNT_YM _NEW- CNT_YM)
Is calculated (step 104 in FIG. 15).

Then, the misregistration correction amount calculation unit 102 corrects the calculated scan line inclination (skew) SK and scan line curvature (bow) BW to newly generate an image position along the sub-scanning direction ( The Y margin) shift amount CNT_YM _NEW is stored in the nonvolatile memory 92 (step 105 in FIG. 15).

  Further, the misregistration correction amount calculation unit 102 stores the calculated image position (Y margin) misalignment amount YM_ALL along the true sub-scanning direction in the nonvolatile memory 92, and performs the misregistration correction amount calculation process. The process ends (step 106 in FIG. 15).

  (2) When the image position detector 60B arranged at the center is arranged deviated from the ideal center in the upper scanning direction.

  In this case, as shown in FIG. 20, the amount of deviation (YM_CNT) in the sub-scanning direction between the actual position of the image position detector 60B and the ideal center in the main scanning direction is represented by the inclination (skew) of the scanning line. ) It is necessary to obtain from the correction amount of SK and curve (bow) BW of the scanning line.

  First, the correction amount of the inclination (skew) of the scanning line and the curvature (bow) of the scanning line at the actual position of the image position detector 60B is obtained.

Now, as shown in FIG. 21, if the leftmost image is skewed by SK (n) upstream in the sub-scanning direction, the Y-axis is set along the sub-scanning direction at the ideal center in the main scanning direction. When placed, the linear expression indicating the skew component is
Yval = (SK (n) ÷ Wall) × Xva1 + (SK (n) ÷ 2)
It can be expressed as.

Further, when the Y coordinate at the center position (Xval, Yval) = (W_cc, T_SK (n)) that is the actual position of the image position detector 60B is obtained,
TSK (n)
= (SK (n) ÷ Wall) × Wcc + (SK (n) ÷ 2)
= SK (n) × (Wcc ÷ Wall + 0.5)
= SK (n) x AA
Thus, the skew component T_SK (n) at the center position, which is the actual position of the image position detector 60B, can be calculated. Here, AA = (Wcc ÷ Wall + 0.5) = constant.

Further, as shown in FIG. 22, if the image is curved upward and convex with the Y axis as the center, the Y axis along the sub scanning direction is centered on the ideal center in the main scanning direction. The quadratic equation indicating the bow component is
Yval = A × (Xval) ² + BW (n)
It can be expressed as. A is a constant indicating the curvature of the scanning line curve (bow).

Further, when the Y coordinate at the center position (Xval, Yval) = (W_cc, T_BW (n)) that is the actual position of the image position detector 60B is obtained,
T_BW (n) = A × (W_cc) ² + BW (n)
It becomes. Furthermore, if the value (Xval, Yval) = (Wall ÷ 2, 0) at the right end is substituted into the quadratic expression indicating the bow component,
0 = A × (Wall ÷ 2) ² + BW (n)
Thus, T_BW (n) can be obtained from the above two equations.
T_BW (n) = BW (n) × BB
Here, BB = (1− (2W_cc / Wall) ² ) = constant.

As a result, the deviation T_YM in the sub-scanning direction between the actual position of the image position detector 60B and the ideal center in the main scanning direction is
T_YM =
(T_SK (n) + (T_BW (n)) − (SK (n) ÷ 2 + BWn)
It can be asked.

Therefore, the deviation amount ΔYM (n) in the sub-scanning direction at the ideal center is
ΔYM = P_Err (1, n) + T_YM
It becomes.

  Since the calculation after this is the same as that after step 101 in (1) as shown in FIG. 14, the description thereof is omitted.

  As described above, the true misregistration amount YM_ALL along the sub-scanning direction of the scan image obtained by the misregistration correction amount calculation unit 102, the scan line inclination (skew) SK, and the scan line curve (bow). Based on the BW correction amount, as shown in FIG. 1, the image misalignment is corrected by the image processing by the misalignment correcting unit 103.

  Next, the positional deviation correction unit 103 executes image positional deviation correction by image processing as described below.

  The positional deviation correction unit 103 receives, as input information, the values of the scanning line inclination (skew) SK and the scanning line curvature (bow) BW calculated by the positional deviation correction amount calculation unit 102 as correction amounts. The Then, in the positional deviation correction unit 103, parameters “SACOUNTn”, “SINTAIn”, “SINTBIn”, “SINTBIn”, based on the values of the scanning line inclination (skew) SK and the scanning line curvature (bow) BW, which are input information, “SINTCIn”, “SINTDIn”, “SUDCOUNTn”, and “LSFCOUNTn” are output.

  In the present embodiment, as shown in FIG. 1, as image data to be input to the registration correction unit 100, an image to be formed has a resolution of 2400 dpi in the main scanning direction and the sub-scanning direction. Here, it is assumed that 32768 pixels having a size of 2400 dpi are provided in the main scanning direction in order to perform correction. The correction of the scan line inclination (skew) and the scan line curve (bow) may be performed one dot at a time along the main scanning direction. However, when the correction process is performed one dot at a time, a video as shown in FIG. Since the configuration of the Asic 92 is complicated, for example, it is considered that correction is performed for each 16-dot pixel with a 16-dot pixel as one unit. Further, in the correction, as shown in FIG. 23, only 32768 pixels arranged in the main scanning direction are divided into four areas (area A, area B, area C, and area D) as shown in FIG. Think. In the area divided for each of 8192 pixels, as shown in FIG. 25, misalignment correction is performed in units of 16 pixels. Therefore, the number of blocks in units of 16 pixels in the area is 8192 ÷ 16. = 512.

  Of the various parameters used in the misregistration correction unit 103, the parameter “SACOUNTn” is a value of 512 indicating the number of blocks in units of 16 pixels in the one area, and is a fixed value.

  The Video Asic 92 functioning as the misregistration correction unit 103 shifts the pixel block in units of 16 pixels along the main scanning direction in units of one line along the sub-scanning (SS) direction, so that the inclination of the scanning line ( (Skew) and scanning line curvature (bow) are corrected. At this time, as described later, the start line to be corrected by the Video Asic 92 is designated by a parameter “LSFCOUNTn”. ) And the curvature of the scanning line (bow) are corrected. In addition, the number of times of correction of the scan line inclination (skew) and the scan line curvature (bow) by the Video Asic 92 is specified by a parameter “SUDCOUNT”, as will be described later. During the correction of the curve (bow) of the line, the value of the parameter “SUDCOUNT” is sequentially reduced. When the value of the parameter “SUDCOUNT” becomes “0”, the inclination of the scanning line (skew) and the curvature of the scanning line (bow) are corrected in the opposite direction. .

  The Y margin, which is a shift in the sub-scanning direction, is corrected by adjusting the image writing timing.

First, the misregistration correction unit 103 obtains interval values (= number of pixel blocks in units of 16 pixels) for image manipulation in four areas (area A, area B, area C, and area D) in the main scanning direction. . As the interval value, first, five values are obtained as shown below by dividing each area into four.
<Y0n> = 0
<Y1n> = SKn ÷ 4 + (BWn × 3 ÷ 4)
<Y2n> = SKn ÷ 3 + BWn
<Y3n> = (SKn × 3 ÷ 4) + (BWn × 3 ÷ 4)
<Y4n> = SKn

Next, the increase amounts of the four areas are calculated as follows.
<YAreaAn> = <Y1n>-<Y0n>
<YAreaBn> = <Y2n>-<Y1n>
<YAAreaCn> = <Y3n>-<Y2n>
<YAAreaDn> = <Y4n>-<Y3n>

  Then, a skew interval value (= number of pixel blocks in units of 16 pixels) of each area is obtained from the values obtained here.

Further, the following values are used as the parameters “SINTAIn”, “SINTBIn”, “SINTCIn”, and “SINTDIn” output from the positional deviation correction unit 103.
SINTAn = 512 ÷ (| <YAreaAn> |)
SINTBn = 512 ÷ (| <YAAreaBn> |)
SINTCn = 512 ÷ (| <YAAreaCn> |)
SINTDn = 512 ÷ (| <YAAreaDn> |)
However, when the value of <YAreaXn> is zero, it is not necessary to correct the inclination (skew) of the scanning line and the curvature (bow) of the scanning line, so the calculation of the parameter “SINTXn” is performed. For example, when the parameter value that is not corrected is set to 0xFFFF, the value is set in the Video Aic 92.

  Further, the parameter “SUDCOUNTn” output from the misregistration correction unit 103 is a parameter for obtaining the number of consecutive increases / decreases from the head block when performing a line shift operation.

  The value of the above-mentioned parameter “SUDCOUNTn” is determined by checking the sign of each register whose value is not zero among <YAreaAn>, <YAAreaBn>, <YAreaCn>, <YAAreaDn> It is required by going.

The count value of the first COUNTn is “0”. First, the count value of <YAreaAn> becomes the value of COUNT. That means
COUNT = <YAAreaAn>
It becomes. Next, if the signs of <YAreaAn> and <YAreaBn> are the same, COUNT = COUNT + <YAreaBn>. Further, if the signs of <YAreaBn> and <YAreaCn> are the same, COUNT = COUNT + <YAreaCn>, and if the signs of <YAreaCn> and <YAreaDn> are the same, COUNT = COUNT + <YAreaDn>.

  However, when <YAAreaAn> is zero, the result of the sign comparison with <YAAreaBn>. When <YAAreaAn> and <YAreaBn> is zero, the result of the sign comparison with <YAAreaCn>, <YAreaAn> and <YAreaBn > And <YAreaCn> are zero, <YAAreaDn> is calculated as a count value.

  When COUNT> 0, the value of the parameter “SUDCOUNTn” is SUDSEL = 0 and SUDCOUNT = COUNT. When COUNT <0, SUDSEL = 1 and SUDCOUNT = | COUNT | (absolute value).

  Here, the value of SUDSEL represents the direction at the start of correction of the inclination (skew) of the scanning line and the curvature (bow) of the scanning line. When the SUDSEL value is “0”, correction in the positive direction is performed, and when the SUDSEL value is “1”, correction in the negative direction is performed.

  Furthermore, the parameter “LSFCOUNTn” output from the positional deviation correction unit 103 is a parameter for obtaining the line shift amount of the first pixel. That is, the head (start) line is a parameter indicating the position, and is “0” or a positive value.

This parameter “LSFCOUNTn” is obtained by calculating the difference between the maximum value and the minimum value of the skew maximum line shift amount in the sub-scanning direction as an internal variable for calculating the Y margin as follows.
<YLSCn> = <YMAXn>-<YMINn>
Here, <YMAXn> means the largest value among <Y0n>, <Y1n>, <Y2n>, <Y3n>, <Y4n>, and <YMINn> means <Y0n>, <Y1n> , <Y2n>, <Y3n>, <Y4n> means the smallest value.

  Specifically, when SUDSEL of SUDCOUNT = 1, LSFCOUNTn = SUDCOUNT, and when SUDSEL of SUDCOUNT = 0, LSFCOUNTn = <YLSCn> −SUDCOUNT.

  As described above, in the microcomputer 83 and the video ASIC 92 constituting the misregistration correction unit 103, as shown in FIGS. ”,“ SUDCOUNTn ”, and“ LSFCOUNTn ”are used to correct the inclination (skew) SK of the scanning line and the curvature (bow) BW of the scanning line by image processing using a video ASIC 92 or the like.

  With the above configuration, the color image forming apparatus according to this embodiment has high accuracy even when a plurality of types of registration misalignment are corrected simultaneously in one registration misalignment correction cycle as follows. Can correct color misregistration, shorten the processing time required for color misregistration correction, increase toner consumption, and durability of components such as image forming components and sensors. Can be prevented from decreasing.

  That is, in the color image forming apparatus according to this embodiment, when the apparatus is turned on, when the environmental temperature changes by a predetermined value or more, when a predetermined number of sheets are printed, or when the paper feed tray is opened or closed, etc. At predetermined timing, as shown in FIG. 4, an image position detection pattern 50 is formed on the intermediate transfer belt 8 by the image forming units 7Y, 7M, 7C, and 7Bk of yellow, magenta, cyan, and black, and the image The position detection pattern 50 is detected by three image position detectors 60A, 60B, and 60C.

  The signal of the image position detection pattern 50 detected by the image position detectors 60A, 60B, and 60C is processed by the signal processing circuit shown in FIG. 7, and then input to the microcomputer 83 as a pattern detection signal.

  In the microcomputer 83, as shown in FIG. 1 and FIG. 8, the software and hardware of the microcomputer 83 and the various functions realized by the hardware connected to the microcomputer 83 are as follows. The calculation of the positional deviation amount of the image forming position, the calculation of the correction amount, the correction processing of the image forming position, and the like as shown in FIG.

  First, in the misregistration amount calculation unit 101 realized by the microcomputer 83, as shown in FIG. 14, the position along the sub-scanning direction is based on the pattern detection signals from the image position detectors 60A, 60B, 60C. (Y margin), scan line inclination (skew), and scan line curve (bow) shift amount are calculated.

  Next, in the misregistration correction amount calculation unit 102, the position along the sub-scanning direction (Y margin), the scan line inclination (skew), and the scan line curve (bow) calculated by the misregistration amount calculation unit 101 are calculated. ), The correction amount for correcting the shift in the position along the sub-scanning direction (Y margin), the inclination of the scanning line (skew), and the curvature of the scanning line (bow) is calculated. The

The correction amount for correcting the deviation of the scan line inclination (skew) and the scan line curve (bow) is the following scan line tilt (skew) correction amount calculation formula and scan line curve (bow) correction amount calculation formula. Is calculated based on
Scan line inclination (skew) correction amount calculation formula SK (n) = − ΔSK (n) × Wall ÷ Wsnr
(ΔSK (n) is the detected deviation amount)
Scan line curve (bow) Correction amount calculation formula BW (n) = − ΔBW (n) × (Wall ÷ Wsnr) ²
(ΔBW (n) is the detected deviation amount)

Further, as described above, the positional deviation correction amount calculation unit 102 corrects the inclination (skew) of the scanning line and the curvature (bow) of the scanning line, thereby correcting the position (Y Margin) shift amount CNT_YM is obtained. The newly generated displacement amount CNT_YM of the position (Y margin) along the sub-scanning direction depends on the values of the inclination (skew) of the scanning line and the curvature (bow) of the scanning line, as shown in FIGS. Divided into 12 patterns. Therefore, the misregistration correction amount calculation unit 102 newly calculates from the 12 patterns as shown in FIGS. 16 to 19 based on the values of the scan line inclination (skew) and the scan line curve (bow). A shift amount CNT_YM _NEW of a position (Y margin) along the sub-scanning direction that occurs is calculated.

Next, the misregistration correction amount calculation unit 102 reads out the misalignment amount CNT_YM of the position (Y margin) along the previous sub-scanning direction stored in the non-volatile memory 92 as a storage unit, and in the sub-scanning direction. Based on the amount of displacement YM of the along position (Y margin), the displacement fold YM_ALL of the position (Y margin) along the true sub-scanning direction is calculated by the following equation.
YMALL = YM- (CNT_YM _NEW- CNT_YM)

  Then, the correction amount calculated based on the correction amount calculation formula is output to the misalignment correction unit 103. The displacement amount YM_ALL of the position (Y margin) along the true sub-scanning direction is recorded in the nonvolatile memory 92 as the displacement amount YM of the position (Y margin) along the sub-scanning direction. In the correction, since it is used as the value of YM, the positional deviation is always corrected in consideration of the previous correction.

  The misregistration correction unit 103 receives a misalignment correction amount (Y margin) along the sub-scanning direction, a scan line inclination (skew), and a scan line curve (bow) input from the misregistration correction amount calculation unit 102. As shown in FIGS. 23 to 27, the image processing is performed on the basis of the correction amount, and the position (Y margin) shift along the sub-scanning direction, the inclination (skew) of the scanning line, and the scanning line are changed. Correct the bow at once.

  At this time, the image data input to the positional deviation correction unit 103 is shifted in position (Y margin) along the sub-scanning direction by scanning each pixel position of the image data based on the correction amount. Line tilt (skew) and scan line bow (bow) are corrected at once.

  As described above, in the above-described embodiment, the position (Y margin) shift, the scan line inclination (skew), and the scan line curvature (bow) along the sub-scanning direction are once corrected in one registration shift correction cycle. The processing time required for color misregistration correction can be shortened, toner consumption associated with the formation of the pattern 50 is increased, and parts for image formation, sensors, etc. It is possible to prevent the durability of the steel from being lowered.

  Further, in the above-described embodiment, the position misalignment along the sub-scanning direction (Y margin), the inclination of the scanning line (skew), and the curvature of the scanning line (bow) are corrected at a time in one registration misalignment correction cycle. In this case, the position (Y margin) shift along the sub-scanning direction newly generated in accordance with the correction of the scan line inclination (skew) and the scan line curvature (bow) is also taken into consideration in the sub-scanning direction. Since it is configured to correct the positional deviation (Y margin) along the line, it is possible to correct the color misregistration with high accuracy even when a plurality of types of registration misregistration are corrected simultaneously.

  In the above description, the image position detectors 60A, 60B, and 60C are provided at three positions corresponding to SOS, COS, and EOS, and a pattern is formed at a position corresponding to the image position detector to detect a registration error. However, the present invention is not limited to this, and a larger number of image position detectors may be provided to detect registration misalignment. In this case, the scanning line curve approximated by a straight line in the above embodiment is approximated by a function (for example, a bending strain function) closer to the actual scanning line curve based on the detection results by a large number of image position detectors. It becomes possible to do.

  Furthermore, the present invention is not limited to the embodiments described above, and various modifications can be made within the scope of the technical matters described in the claims.

1 is a block diagram showing a control circuit of an image forming apparatus according to Embodiment 1 of the present invention. FIG. 2 is a block diagram showing a digital color copying machine as an image forming apparatus according to Embodiment 1 of the present invention. FIG. 3 is a block diagram showing the ROS. FIG. 4 is a perspective configuration diagram showing the arrangement of the image position detectors. FIG. 5 is a configuration diagram showing an image position detection pattern and its detection waveform. FIG. 6 is a block diagram showing the image position detector. FIG. 7 is a block diagram showing a signal processing circuit of the image position detector. FIG. 8 is a block diagram showing a control circuit of the image forming apparatus according to Embodiment 1 of the present invention. FIG. 9 is an explanatory diagram showing the detection state of the image position detection pattern. FIG. 10 is a graph showing a detection result and a correction amount when a skew deviation occurs in the image. FIG. 11 is a graph showing the detection result of the skew deviation amount and the correction amount. FIG. 12 is a graph showing a detection result and a correction amount when a bow shift occurs in the image. FIG. 13 is a graph showing the detection result of the bow shift amount and the correction amount. FIG. 14 is a graph showing the detection result and the correction amount when both skew and bow shift occur in the image. FIG. 15 is a flowchart showing a registration error correction process. FIG. 16 is a schematic diagram showing a method of calculating a correction amount for skew and bow registration error. FIG. 17 is a schematic diagram illustrating a method of calculating a correction amount for skew and bow registration error. FIG. 18 is a schematic diagram illustrating a method of calculating a correction amount of skew and bow registration error. FIG. 19 is a schematic diagram showing a method of calculating a correction amount for skew and bow registration error. FIG. 20 is a graph showing a detection result and a correction amount when both skew and bow shift occur in an image. FIG. 21 is a graph showing the detection result of the skew deviation amount. FIG. 22 is a graph showing the detection result of the bow shift amount. FIG. 23 is a schematic diagram showing a correction method for skew and bow registration error. FIG. 24 is a schematic diagram showing a method for correcting skew and bow registration error. FIG. 25 is an enlarged schematic view showing a correction method for skew and bow registration error. FIG. 26 is a schematic diagram showing a method for correcting skew and bow registration error. FIG. 27 is a schematic diagram showing a method for correcting skew and bow registration error. FIG. 28 is a flowchart showing a conventional registration error correction method. FIG. 29 is an explanatory diagram showing a registration error newly generated by a conventional skew registration correction. FIG. 30 is an explanatory view showing a registration error newly generated by a conventional bow registration error correction.

Explanation of symbols

  50: Image position detection pattern, 60A, 60B, 60C: Image position detector, 101: Position shift amount calculation unit, 102: Position shift correction amount calculation unit, 103: Position shift correction unit.

Claims (7)

In an image forming apparatus that forms a plurality of images of different colors along the main scanning direction and the sub-scanning direction based on image data of each color, and forms the single image by superimposing the plurality of images on each other ,
A plurality of image position detecting means for detecting image forming positions of the plurality of images at a plurality of positions along a main scanning direction;
Based on the detection results of the plurality of image position detection means, a position shift amount calculation means for calculating the position shift amounts of a plurality of types of images;
Computation means for computing a correction amount for correcting misregistration of the plurality of types of images based on a computation result of the misregistration amount computation means, wherein the computation means corrects misregistration of the plurality of types of images. When calculating the amount, correction of misalignment along the sub-scanning direction is performed by adding the amount of misalignment along the sub-scanning direction of the scanning line newly generated along with the correction of the inclination of the scanning line and the curvature of the scanning line. Misregistration correction amount calculating means for calculating the amount;
An image forming apparatus comprising: a positional deviation correction unit that corrects the positional deviation of the image based on the positional deviation correction amount calculated by the positional deviation correction amount calculation unit. A positional deviation amount along the sub-scanning direction of a scanning line newly generated along with the correction of the inclination of the scanning line and the curvature of the scanning line is obtained with reference to a central portion along the main scanning direction. The image forming apparatus according to claim 1. 3. The storage device according to claim 1, further comprising a storage unit configured to store a displacement amount of the scanning line newly generated along the sub-scanning direction in accordance with the correction of the inclination of the scanning line and the curvature of the scanning line. The image forming apparatus described. In the sub-scanning direction of the scanning line calculated by the positional deviation amount calculation means, the amount of positional deviation along the sub-scanning direction of the scanning line newly generated in accordance with the correction of the inclination of the scanning line and the curvature of the scanning line. The image forming apparatus according to claim 1, further comprising a storage unit that stores a value obtained by adding the amount of positional deviation along the line. The image forming apparatus according to claim 1, wherein the misregistration correction unit corrects misregistration of a plurality of types of images at a time by image processing. The misregistration correction amount calculating means detects an image position located at the center when the image position detecting means located at the center of the plurality of image position detecting means is deviated from the true center position in the main scanning direction. 6. The image forming apparatus according to claim 1, wherein a correction amount of a positional shift along the sub-scanning direction is calculated by correcting a shift amount along a main scanning direction of the unit. In an image forming method of forming a plurality of images having different colors along a main scanning direction and a sub-scanning direction based on image data of each color and superimposing the plurality of images on each other to form a single image ,
An image position detecting step for detecting image forming positions of the plurality of images at a plurality of positions along a main scanning direction;
Based on the detection result of the image position detection step, a displacement amount calculation step for calculating displacements of a plurality of types of images;
A calculation step for calculating a correction amount for correcting a positional shift of a plurality of types of foresight images based on a calculation result of the positional shift amount calculation step, wherein the positional shifts of the plurality of types of images are performed in the calculation step. When calculating the correction amount, the position along the sub-scanning direction is calculated by adding the amount of misalignment along the sub-scanning direction of the scanning line newly generated along with the correction of the scanning line curve and the curve of the scanning line. A positional deviation correction amount calculating step for calculating a correction amount of deviation;
An image forming method comprising: a position shift correction step for correcting a position shift of the image based on the position shift correction amount calculated by the position shift correction amount calculation step.

Images