JP2005274919A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus, capable of being substituted for a printer, which forms images of high quality by correcting positions in a main scanning direction and a subscanning direction and misregistration correction amounts of skews of lead, side skews, etc. even if there are errors in the attaching position of a detection means for detecting a pattern for misregistration detection. <P>SOLUTION: A misregistration correction means not only corrects the image positions for a recording medium in the main scanning direction and the subscanning direction, but is also capable of changing one or more of image position correction amounts for the recording medium of a magnification in the main scanning direction, a partial magnification in the main scanning direction, a magnification in the subscanning direction, a partial magnification in the subscanning direction, lead skew, side skew, lead linearity, side linearity, etc. when the pattern for misregistration detection and forming an image is formed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a full color printer or a full color copying machine that employs an electrophotographic method, and more particularly to an image forming apparatus for forming a high-quality image that can be substituted for a printing machine. .

Japanese Patent No. 2765626

  In recent years, in image forming apparatuses such as full-color printers and full-color copiers that employ this type of electrophotographic method, a plurality of image forming units are arranged in series to achieve high productivity, and full color is achieved in one pass. The tandem method for forming the image is becoming mainstream. In this tandem image forming apparatus, for example, an image formed by a plurality of image forming units corresponding to each color such as yellow, magenta, cyan, and black is directly multiplexed on a recording sheet conveyed by a sheet conveying belt. After transfer or primary transfer multiple times on the intermediate transfer belt, images of each color such as yellow, magenta, cyan, black, etc. transferred multiple times on the intermediate transfer belt are batch-recorded on the recording paper. A full color image is formed by performing the next transfer and fixing the unfixed image on the recording paper.

  In the tandem image forming apparatus, there is a misalignment of the photosensitive drum and the exposure device in the yellow, magenta, cyan, and black image forming units, and a mechanical error that drives components such as the photosensitive drum. Since the color shift appears on the recording sheet as it is, a color shift control (registration control, hereinafter referred to as “registon” for short) technique is indispensable.

  As a specific method of the above-described registration control, in general, a registration error detection pattern for each color of yellow, magenta, cyan, and black is formed on a paper conveyance belt or an intermediate transfer belt, and a registration error detection pattern for each color is formed. The amount of registration deviation is calculated from the result of reading with a sensor and fed back to the writing timing of an image writing unit (ROS, LED array, laser array, etc.) to correct the registration deviation.

  For example, the one disclosed in Japanese Patent No. 2765626 has been proposed as an application of such a regicon technology.

  The image forming apparatus according to Japanese Patent No. 2765626 includes a plurality of recording apparatuses that form images of respective colors, and an image forming apparatus that sequentially transfers the transfer paper to each recording apparatus by a transfer belt and transfers the images in an overlapping manner. The pattern image signal generating means for forming the measurement pattern image for each color on the transfer belt, the detection means for detecting the measurement pattern image for each color, and the measurement for each color by detection by the detection means Measuring means for measuring a distance between a measurement pattern image of a specific color as a reference in the pattern image for measurement and a pattern image for measurement of another color, and measurement of the specific color as a reference based on the measurement of the measurement means Calculating means for calculating the amount of deviation between the pattern image for measurement and the pattern image for measurement of another color, and adjusting the image writing timing of the recording device for the other color based on the amount of deviation Is obtained by configured to have a that adjusting means.

  In the regicon technology disclosed in the above-mentioned Japanese Patent No. 2765626 and the like, the measurement position of a regicon sensor as a measurement means is used as a reference position, and the image positions of all colors yellow, magenta, cyan, and black (sensors) In general, the image width (= magnification in the main scanning direction), skew, and other misalignment components are generally adjusted.

  In the above-described regicon technology, the image positions of all colors of yellow, magenta cyan, and black are aligned with the position of the regicon sensor, and the position of the entire image with respect to the paper position for each paper feed tray (only in the X and Y directions) ).

  However, the above prior art has the following problems. That is, in an image forming apparatus such as a full-color printer that forms a full-color document used in a normal office or the like, sufficient image position accuracy can be obtained by applying the above-described regicon technology. The following problems may occur in the case of high-performance machines intended to form high-quality images.

  1) If there is an error in the mounting position of the registration control sensor, the error in the mounting position of the registration control sensor causes a shift in the image width in the main scanning direction, a partial magnification difference in the main scanning direction, skew with respect to the recording paper, linearity, etc. There has been a problem that it is impossible to form a high-quality image that can be substituted for a printing press.

  2) Depending on the moisture content and material of the recording paper at the time of fixing, the recording paper may be stretched or shrunk, the image size, shape, position, etc. may change, or in the case of double-sided printing, an image will be formed with a single fixing There is a problem that it is impossible to cope with a difference between the image on the front surface side and the image on the back surface side formed through two fixings as the recording paper.

  3) The above problems 1) and 2) vary depending on various factors such as the paper quality of the recording paper and environmental conditions such as humidity and temperature, but there are various factors such as the paper quality of the recording paper and environmental conditions such as humidity and temperature. When the size, shape, position, or the like of the image changes due to various factors, there is a problem that it cannot be handled.

  4) When an image of a document is read by an image reading device at the time of copying, if there is a reading error in the image reading device, there is a problem that an image size shift due to the reading error of the image reading device cannot be corrected. there were.

  Accordingly, the present invention has been made to solve the above-described problems of the prior art, and a first object of the present invention is that there is an error in the attachment position of the detection means for detecting the registration deviation detection pattern. Even in this case, the position in the main scanning direction and the sub-scanning direction, the magnification in the main scanning direction, the partial magnification in the main scanning direction, the magnification in the sub-scanning direction, the partial magnification in the sub-scanning direction, the lead skew, the side skew, An object of the present invention is to provide an image forming apparatus capable of correcting a registration error correction amount such as a linearity of a lead and a linearity of a side to form a high-quality image that can be substituted for a printing press.

  Further, a second aspect of the present invention is that, even when a double-sided image is formed, the registration deviation correction amount generated between the front side image and the back side image is corrected to replace the printing press. An object of the present invention is to provide an image forming apparatus capable of forming a high-quality image possible.

  Furthermore, a third object of the present invention is to provide a high-quality image that can be substituted for a printing press by correcting the registration error correction amount even when there is an image reading error when the image is read by the image reading apparatus. An object of the present invention is to provide an image forming apparatus capable of forming an image.

  A fourth object of the present invention is to provide a high-quality image that can be substituted for a printing press by correcting the registration misalignment correction amount even when the material of the recording medium, environmental conditions, or the like changes. Is to provide an image forming apparatus capable of forming the image.

  In order to achieve the above object, the invention described in claim 1 includes a plurality of image forming units that form images having different colors, and a plurality of images having different colors formed by the plurality of image forming units. An image forming apparatus for forming a registration error detection pattern on a recording medium, wherein a registration error detection pattern is formed on the detected medium by the plurality of image forming units, and the registration error detection pattern is detected by a detection unit. In the image forming apparatus having the registration error correction unit for correcting the registration error of the image, the registration error correction unit records in the main scanning direction and the sub-scanning direction when the registration error detection pattern is formed and when the image is formed. In addition to image position correction on the medium, the magnification in the main scanning direction, the partial magnification in the main scanning direction, the magnification in the sub scanning direction, the partial magnification in the sub scanning direction, the lead skew, the side skew, and the leakage Linearity, of the image position correction amount for a recording medium of linearity such side is an image forming apparatus which is characterized in that the changeable at least one or more.

  According to a second aspect of the present invention, in an image forming apparatus capable of forming an image on both sides of a recording medium, when forming an image on both sides of the recording medium, the front side image is formed and the back side image is formed. In addition to the position in the main scanning direction and the sub-scanning direction, the magnification in the main scanning direction, the partial magnification in the main scanning direction, the magnification in the sub-scanning direction, the partial magnification in the sub-scanning direction, the lead skew, the side skew, and the lead The image forming apparatus is characterized in that at least one of the image position correction amounts for the recording medium such as the linearity and the side linearity can be changed.

  Furthermore, the invention described in claim 3 is an image forming apparatus including an image reading unit that reads an image of a document, and the main scanning direction and the sub-scanning are performed so as to cancel a reading error of the image reading unit that is obtained in advance. In addition to the position in the direction, magnification in the main scanning direction, partial magnification in the main scanning direction, magnification in the sub scanning direction, partial magnification in the sub scanning direction, lead skew, side skew, lead linearity, side linearity, etc. An image forming apparatus characterized in that at least one of image position correction amounts with respect to a recording medium can be changed.

  According to a fourth aspect of the present invention, marks for specifying an image position are formed on both the front and back surfaces of a recording medium, the image position specifying mark is read by a reading unit, and a registration error is corrected by a registration error correcting unit. In the image forming apparatus configured to correct, the registration error correction unit includes a back surface of the recording medium based on a result of reading at least two or more image position specifying marks formed on the surface of the recording medium by the reading unit. When forming an image on the main scanning direction, the position in the main scanning direction and the sub scanning direction, the magnification in the main scanning direction, the partial magnification in the main scanning direction, the magnification in the sub scanning direction, the partial magnification in the sub scanning direction, the lead skew, It is possible to change at least one of image position correction amounts for a recording medium such as skew, lead linearity, and side linearity. The image forming apparatus according to symptoms.

  Further, in the invention described in claim 5, the registration error correction unit is configured such that at least two or more image position specifying marks respectively formed on the front and back surfaces of the recording medium overlap each other. Recording medium such as scanning direction position, main scanning direction magnification, main scanning direction partial magnification, sub-scanning direction magnification, sub-scanning direction partial magnification, lead skew, side skew, lead linearity, side linearity, etc. 5. The image forming apparatus according to claim 4, wherein at least one of the image position correction amounts for the image can be changed.

  According to a sixth aspect of the present invention, the registration error correcting means includes a recording medium storage tray, a recording medium conveyance state, a recording medium shape, a detected medium, a recording medium material information, an in-machine environment, and a surrounding environment. Based on at least one of the information for image formation such as the number of image formations after power-on, the number of continuous image formations, the total number of image formations, the position in the main scanning direction and the sub-scanning direction, and the magnification in the main scanning direction At least one of image position correction amounts for the recording medium, such as a partial magnification in the main scanning direction, a magnification in the sub-scanning direction, a partial magnification in the sub-scanning direction, a lead skew, a side skew, a lead linearity, and a side linearity The image forming apparatus according to claim 1, wherein one or more of the image forming apparatuses can be changed.

  Furthermore, the invention described in claim 7 is characterized in that the registration error correction means corrects registration error by moving a pixel position of image data to be formed. An image forming apparatus as described above.

  According to the present invention, even when there is an error in the attachment position of the detection means for detecting the registration error detection pattern, the position in the main scanning direction and the sub-scanning direction, the magnification in the main scanning direction, and the portion in the main scanning direction High image quality that can be substituted for a printing press by correcting the registration error correction amount such as magnification, sub-scanning direction magnification, sub-scanning direction partial magnification, lead skew, side skew, lead linearity, side linearity, etc. An image forming apparatus capable of forming an image can be provided.

  Further, according to the present invention, even when a double-sided image is formed, a registration image correction amount generated between the front-side image and the back-side image is corrected so that a high-quality image that can be substituted for a printing press is obtained. An image forming apparatus capable of being formed can be provided.

  Further, according to the present invention, when both images are read by the image reading apparatus, even if there is an image reading error, the registration deviation correction amount is corrected to form a high-quality image that can be substituted for a printing press. It is possible to provide an image forming apparatus capable of performing the above.

  Further, according to the present invention, even when the material of the recording medium, the environmental conditions, etc. change, it is possible to correct the registration misalignment correction amount and form a high-quality image that can be substituted for a printing press. Image forming apparatus can be provided.

  Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1
FIG. 2 shows a tandem full-color printer as an image forming apparatus according to Embodiment 1 of the present invention. Note that this tandem full-color printer includes an image reading device and functions as a full-color copying machine. Of course, the full-color printer does not have to include an image reading device.

  In FIG. 2, reference numeral 1 denotes a main body of a tandem type full-color printer, and an image reading device (IIT: Image Input Terminal) 4 for reading an image of a document 2 is provided at an upper portion on one end side of the full-color printer main body 1. It is arranged. The image reading device 4 illuminates a document 2 placed on a platen glass 5 with a light source 6, and reflects a reflected light image from the document 2 from a full-rate mirror 7, half-rate mirrors 8 and 9, and an imaging lens 10. The image reading element 11 made of a CCD or the like is scanned and exposed through the reduction optical system, and the image reading element 11 reads both images of the document 2 at a predetermined dot density (for example, 1200 dpi or 2400 dpi). ing.

  Both images of the document 2 read by the image reading device 4 are, for example, image processing device 12 (Image Processing System) as image data of three colors of red (R) green (G) and blue (B) (each 8 bits). In this image processing apparatus 12, predetermined image processing such as shading correction, position shift correction, brightness / color space conversion, gamma correction, frame deletion, color / moving editing, etc. is performed on the image data of the document 2. Is given.

  The image data that has been subjected to the predetermined image processing by the image processing device 12 as described above is an image of four colors of yellow (Y), magenta (M), cyan (C), and black (K) (each 8 bits). As described below, yellow (Y), magenta (M), cyan (C), and black (K) image forming units 13Y, 13M, 13C, and 13K ROSs 14Y, 14M, 14C, 14K (Raster Output Scanner), and in these ROSs 14Y, 14M, 14C, and 14K, image exposure by the laser beam LB is performed according to the image data of each color.

  Incidentally, four image forming units 13Y, 13M, 13C, and 13K of yellow (Y), magenta (M), cyan (C), and black (K) are horizontally arranged in the tandem full color printer main body 1. They are arranged in series with a certain distance in the direction.

  These four image forming units 13Y, 13M, 13C, and 13K are all configured in the same manner, and are roughly divided into a photosensitive drum 15 that rotates at a predetermined rotational speed in the direction of the arrow, and the photosensitive drum 15. A primary charging scorotron 16 that uniformly charges the surface of the photosensitive drum 15, an ROS 14 that forms an electrostatic latent image by exposing an image corresponding to each color on the surface of the photosensitive drum 15, and a photosensitive drum 15. The developing unit 17 and the cleaning device 18 develop the developed electrostatic latent image with the corresponding color toner.

  As shown in FIGS. 2 and 3, the ROS 14 modulates the semiconductor laser 19 according to the image data and emits a laser beam LB from the semiconductor laser 19 according to the gradation data. The laser beam LB emitted from the semiconductor laser 19 is collimated by the collimator lens 19a, then deflected and scanned by the rotary polygon mirror 22 via the reflecting mirror 2021, and the f-θ lens 22a according to the scanning angle. In a state where the focal length is adjusted, scanning exposure is performed on a photosensitive drum 15 as an image carrier through a plurality of reflection mirrors 23 and 24. In FIG. 3, the reflection mirror 23 and the like are partially omitted. In FIG. 3, a scanning start end (SOS: Start Of Scan) sensor 24a that detects that the laser beam LB has passed the scanning start end is disposed at the end of the photosensitive drum 15 in the main scanning direction. ing.

  From the image processing apparatus 12, each color of the image forming units 13Y, 13M, 13C, and 13K of ROS14Y, 14M, 14C, and 14K of each color of yellow (Y), magenta (M), cyan (C), and black (K). Are sequentially output, and laser beams LB emitted according to the image data from these ROSs 14Y, 14M, 14C, and 14K are scanned and exposed on the surfaces of the respective photosensitive drums 15Y, 15M, 15C, and 15K. An electrostatic latent image is formed. The electrostatic latent images formed on the photosensitive drums 15Y15M, 15C, and 15K are respectively yellow (Y), magenta (M), cyan (C), and black (by the developing units 17Y, 17M, 17C, and 17K. K) is developed as a toner image of each color.

  Yellow (Y), magenta (M), cyan (C), and black (K) sequentially formed on the photosensitive drums 15Y, 15M, 15C, and 15K of the image forming units 13Y, 13M, 13C, and 13K. The toner images of the respective colors are respectively transferred to primary transfer rolls 26Y, 26M, 26C, and 26K on an intermediate transfer belt 25 as an intermediate transfer body (detected medium) disposed below the image forming units 13Y, 13M, 13C, and 13K. Are transcribed in multiples. The intermediate transfer belt 25 is wound around the drive roll 27, the idle roll 28, the steering roll 29, the idle roll 30, the backup roll 31, and the idle roll 32 with a constant tension. The drive roll 27 is rotationally driven by a dedicated drive motor with excellent constant speed, and is circulated at a predetermined speed in the direction of the mark. As the intermediate transfer belt 25, for example, a flexible synthetic resin film such as PET is formed in a band shape, and both ends of the synthetic resin film formed in a band shape are connected by means such as welding, thereby endless A belt-shaped one is used.

  The yellow (Y), magenta (M), cyan (C), and black (K) toner images transferred onto the intermediate transfer belt 25 in a multiple manner are transferred to the backup roll 31 by a secondary transfer roll 33. The recording paper 34 that has been secondarily transferred onto the recording paper 34 as a recording medium by the pressure contact force and the electrostatic force is transferred to the fixing device 37 by the two transport belts 35 and 36. Is done. The recording paper 34 onto which the toner images of the respective colors have been transferred is subjected to fixing processing by heat and pressure by a fixing device 37. In the case of single-sided printing, the recording paper 34 is directly on a discharge tray 38 provided outside the printer main body 1. To be discharged.

  As shown in FIG. 2, the recording paper 34 has a predetermined size or material from any of a plurality of paper trays 39, 40, 41, and a paper feed roller 42 and a pair of paper transport rollers 43, The paper is once transported to the registration roll 47 via a paper transport path 46 composed of 44 and 45 and then stopped. The recording paper 34 supplied from any one of the paper trays 39, 40, and 41 is sent onto the intermediate transfer belt 25 by a registration roll 47 that is rotationally driven at a predetermined timing.

  Further, when images are formed on both sides of the recording paper 34 by the full-color printer, the recording paper 34 on which the image is fixed on one side by the fixing device 37 is not discharged out of the apparatus as it is, but by a switching gate (not shown). Then, the conveyance path of the recording paper 34 is switched downward, and the recording paper 34 is once conveyed to the reversal paper conveyance path 48. Then, the recording paper 34 conveyed to the reversing paper conveyance path 48 is reversed, with the conveyance direction reversed, through the double-sided paper conveyance path 49 and the normal paper conveyance path 46. In this state, the sheet is conveyed again to the secondary transfer position of the intermediate transfer belt 25 and an image is formed on the back surface thereof. Then, the image is subjected to a fixing process with heat and pressure by a fixing unit 37 and provided outside the printer main body 1. It is discharged onto the discharge tray 38.

  By the way, in the tandem type full-color printer configured as described above, each of the image forming units 13Y, 13M, and the like is caused by various factors such as vibration during transportation and installation, opening and closing of a paper tray, temperature change and secular change. Positional fluctuations may occur in the positions of 13C and 13K themselves, and the photosensitive drums 15Y, 15M, 15C, and 15K constituting the image forming units 13Y, 13M, 13C, and 13K, and image misregistration may occur. There is.

  First, in each of the image forming units 13Y, 13M, 13C, and 13K, if there is a positional shift in the photosensitive drums 15Y, 15M, 15C, and 15K and the ROSs 14Y, 14M, 14C, and 14K, as shown in FIG. , 14C, 14K and the photosensitive drums 15Y, 15M, 15C, 15K vary in distance (optical path length) and inclination, magnification shift in the main scanning direction (laser beam scanning direction), and partial magnification in the main scanning direction Deviation occurs. Further, in each of the image forming units 13Y, 13M, 13C, and 13K, when the writing positions of the ROS 14Y, 14M, 14C, and 14K are misaligned along the main scanning direction, or when the skew state of the belt changes, FIG. As shown in FIG. 5, a margin (position) shift in the main scanning direction occurs.

  Further, in each of the image forming units 13Y, 13M, 13C, and 13K, as shown in FIG. 6, it is caused by the inclination of the rotation axis of the photosensitive drums 15Y, 15M, 15C, and 15K, the paper skew at the time of secondary transfer, and the like. As a result, skew of the lead and side occurs. Also, as shown in FIG. 7, if each photoconductor drum 15Y, 15M, 15C, 15K has a positional shift along the sub-scanning direction, a margin (position) shift in the sub-scanning direction occurs.

  Further, in addition to the above-described registration misregistration, in each of the image forming units 13Y, 13M, 13C, and 13K, as shown in FIG. 8, if the photosensitive drums 15Y, 15M, 15C, and 15K have speed fluctuations, the sub-scanning direction This causes periodic fluctuations (AC fluctuations), and this causes registration misregistration between different colors. Furthermore, due to the meandering of the belt and the like, as shown in FIG. 9, periodic fluctuations (AC fluctuations) in the main scanning direction occur, and this causes misregistration between different colors.

  Further, when scanning exposure is performed with the image curved on the photosensitive drums 15Y, 15M, 15C, and 15K, a registration error of linearity (linearity) such as a lead or a curved side is generated.

  Thus, depending on various factors, the position in the main scanning direction and the sub-scanning direction, the magnification in the main scanning direction, the partial magnification in the main scanning direction, the magnification in the sub-scanning direction, the partial magnification in the sub-scanning direction, the skew of the lead, Registration deviations such as skew, lead linearity, side linearity, periodic deviation in the sub-scanning direction, and periodic deviation in the main scanning direction occur. These registration deviations of these images are superimposed, as shown in FIG. In some cases, a DC shift (uniform shift) or an AC shift (periodic shift) occurs and appears as a color registration shift.

  Therefore, in the tandem full-color printer, as shown in FIG. 11, in the yellow (Y), magenta (M), cyan (C), and black (K) image forming units 13Y, 13M, 13C, and 13K, For example, even when exactly the same grid-like images 55M and 55C are formed in magenta (M) and cyan (C) colors, as described above, the positions in the main scanning direction and the sub-scanning direction, Main scanning direction magnification, main scanning direction partial magnification, sub scanning direction magnification, sub scanning direction partial magnification, lead skew, side skew, lead linearity, side linearity, periodic deviation in sub scanning direction, Since there is a registration shift such as a periodic shift in the main scanning direction, a distorted grid-like image 56M, 57M is formed on the recording paper as it is.

  Therefore, in this embodiment, as shown in FIG. 12, a registration error detection pattern 50 called a chevron pattern is formed on the intermediate transfer belt 25 at a predetermined timing, and this registration error detection pattern 50 is formed as an image position. It is configured to form a desired color image after being detected and detected by the detector (detecting means) 60 and correcting the registration deviation amount of the image formed by each of the image forming units 13Y, 13M, 13C, and 13K. ing. The image position detectors 60A, 60B, and 60C are arranged in the main scanning direction as shown in FIG. 12 at the detection position provided on the downstream side of the black image forming unit 13K as shown in FIG. Along the OUT side (front side in the figure), the CENTER part (center part), and the IN side (back side in the figure) of the full-color printer main body 1. A plurality (four or more) may be provided at equal intervals along the width direction of the transfer belt 25, and are appropriately arranged according to the type of registration deviation to be detected.

  As the registration misalignment detection pattern 50, patterns having various shapes can be used. For example, as shown in FIG. 13, the center portion is the head and the left and right sides are equally angled along the sub-scanning direction (for example, A mountain-shaped mark 51 made of a linear image inclined by 45 degrees is formed in correspondence with the positions of the image position detectors 60A, 60B, 60C. A plurality of registration deviation detection patterns 50 are formed at predetermined intervals along the sub-scanning direction (the moving direction of the intermediate transfer belt 25).

  More specifically, as shown in FIG. 13, the registration deviation detection pattern 50 includes a first chevron mark 51CC composed of a first reference color (cyan in the illustrated example), and a second object. The second chevron mark 51YY composed of the measurement color (yellow color in the illustrated example) and the third chevron mark 51CY mark composed of the first color and the second color are measured as one unit. A pattern combining all colors is used. The combination of the registration error detection patterns 50 shown in FIG. 13 is one block for the reference color and the measured color. When this registration deviation detection pattern 50 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. Note that the image data for outputting the registration deviation detection pattern 50 is stored in advance in, for example, a non-volatile memory 90 (see FIG. 16) of the control unit of the color printer, as described later.

  FIG. 14 is a block diagram showing an image position detector 60 for detecting the registration deviation detection pattern 50.

  In FIG. 14, reference numeral 61 denotes a housing of the image position detector 60, and 62 and 63 denote light emitting elements composed of two LEDs or the like that respectively illuminate the registration deviation detection pattern 50 formed on the intermediate transfer belt 25. 64, 65 show a pair of light receiving elements called “bi-cell”, each of which is a set of two light receiving elements. 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. The two detection positions on the belt 25 are arranged to illuminate in a state where they are inclined at 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. Is set to

  When the image position detector 60 detects the registration error detection pattern 50 formed on the intermediate transfer belt 25, the linear detection mark 51 of the registration error detection pattern 50 causes the one light receiving element 64b to A mountain-shaped waveform corresponding to the amount of reflected light is output, and the other light-receiving element 64a outputs a mountain-shaped waveform with some delay, and the waveforms output from these two light-receiving elements 64b and 64a are amplified. Then, by taking the difference or amplifying after taking the difference, as shown in FIG. 13, an output waveform that once falls into a mountain shape and then rises into a mountain shape is 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 registration deviation detection pattern 50 can be determined without using a high-precision sensor such as a CCD. It becomes possible to detect with high resolution and high accuracy.

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

  As described above, when focusing only on “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 above patterns is measured. From the result, the amount of deviation of each color with respect to the image of the reference color is calculated, and a plurality of deviations are calculated from the amount of deviation. It is possible to always obtain a stable / good image by determining the amount of registration misregistration and correcting it at each image forming unit.

  FIG. 15 is a block diagram showing a signal processing circuit of the image position detector 60.

  As shown in FIG. 15, 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 66 a, the output end of the photodiode 64 a serving as a light receiving element is connected to a microcomputer (a control unit 93) via a current-voltage converter 80, an amplifier (AMP) 81, and an A / D converter 82. CPU) 83, and a current having a magnitude corresponding to the amount of light received from photodiode 64a is converted into digital data representing the output voltage of photodiode 64a and input to microcomputer 83. 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 94a. 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. 13, an approximate change in the output voltage of the differential input amplifier 86 when the image position detector 60 detects the registration error detection pattern 50 is shown in correspondence 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 (referred to as “ON” for convenience), When the level of the signal is less than the threshold value, 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 repeatedly counted.

  The microcomputer 83 detects the position of the registration error detection pattern 50 based on the count result input from the counter 89 when the image position detector 60 detects the registration error detection pattern 50 during the registration error correction operation. The image forming units 13Y, 13M, 13C, and 13K are configured to correct the registration error when forming an image.

  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. 15, it is the same as each part of the connected circuit. The description is omitted.

  The microcomputer 83 adjusts yellow (Y), magenta (M), and magenta (M) so that a registration error detection pattern 50 as shown in FIG. 13 is formed on the outer peripheral surface of the intermediate transfer belt 25 during the registration error correction operation. The image forming units 13Y, 13M, 13C, and 13K for cyan (C) and black (K) are controlled.

  When the registration displacement detection pattern 50 is formed on the intermediate transfer belt 25, the registration displacement detection pattern 50 is detected by the image position detector 60. Here, since the detection positions by the photodiodes 64a and 64b on the outer peripheral surface of the intermediate transfer belt 25 are shifted in the sub-scanning direction, the current from the differential input amplifier 86 is detected when the registration shift 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 25 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 amplifier 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 greater than or equal to 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. 17).

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

  By the way, in this embodiment, a registration error detection pattern is formed on a detected medium by a plurality of image forming units, and the registration error detection pattern is detected by a detection unit to correct an image registration error. In the image forming apparatus having the misalignment correcting unit, the misregistration correcting unit is configured to perform magnification in the main scanning direction in addition to the positions in the main scanning direction and the sub-scanning direction when the pattern for detecting misregistration is detected and when the image is formed. , At least one of the registration deviation correction amounts such as the partial magnification in the main scanning direction, the magnification in the sub scanning direction, the partial magnification in the sub scanning direction, the lead skew, the side skew, the lead linearity, and the side linearity. Configured to be modifiable

  Further, in this embodiment, the registration error correcting unit performs image processing to position in the main scanning direction and sub-scanning direction, magnification in the main scanning direction, partial magnification in the main scanning direction, magnification in the sub-scanning direction, and sub-scanning. At least one or more of registration misalignment correction amounts such as direction partial magnification, lead skew, side skew lead linearity, side linearity, and the like are changed.

  FIG. 16 is a block diagram showing a control unit of the full-color printer according to this embodiment.

  In FIG. 16, reference numeral 83 denotes a microcomputer for controlling the image forming operation of the full-color printer. This microcomputer 83 stores image information and parameters of the registration error detection pattern 50 used as appropriate in the registration error correction operation. A non-volatile memory (NVM) 90 is connected as storage means. 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 14Y, 14M, 14C, and 14K.

  The image data development circuit (Video Asic) 92 uses, for example, a logic circuit as hardware, as will be described later, the position in the main scanning direction and the sub scanning direction, the magnification in the main scanning direction, and the portion in the main scanning direction. Some or all of the registration error correction amounts such as magnification, sub-scanning direction magnification, sub-scanning direction partial magnification, lead skew, side skew, lead linearity, side linearity, etc., can be changed to yellow (Y), magenta ( M), cyan (C), and black (K) that are corrected for some or all colors are used.

  FIG. 17 shows a function relating to correction of misregistration (hereinafter, this function is realized) among various functions realized by the microcomputer 83 or a logic circuit as a part of hardware in the full-color printer according to this embodiment. Software and hardware for doing so are collectively referred to as a registration error correction unit 100 as registration error correction means), and are divided into blocks for each detailed function.

  As shown in FIG. 17, the registration correction unit 100 mainly detects a registration deviation amount 101 for detecting (calculating) registration deviation amounts of a plurality of types of images based on an input pattern detection signal, and the registration deviation. Based on the calculation result of the amount calculation unit 101, the registration error correction amount calculation unit 102 that calculates a correction amount for correcting the registration error of the plurality of types of images, and the registration error correction amount calculation unit 102 are used. A registration error correction unit 103 that corrects the registration error of the image based on the registration error correction amount is provided.

  The registration deviation amount detection unit 101 determines the time interval for forming the chevron 51 in each part in the registration deviation detection pattern 50 based on the count value input from each counter 89 (time interval shown in FIG. 18A). a, b, c, d) are detected. Time inquiry intervals a, b, and cd obtained from two count values inputted from a single image position detector 60 are a main scanning direction (hereinafter referred to as FS (Fast Scan) direction) and a sub-scanning direction ( If there is no shift in the 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. 18B, 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 registration misregistration amount detection unit 101 performs color misregistration amounts in the FS direction of other three colors (for example, Y, M, and K) based on a specific color (for example, C) according to the following calculation formula (Equation 1). FSerr and SS misregistration amount SSerr are calculated for image position detectors 60A, 60B, and 60C, respectively.

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 registration deviation amount along the sub-scanning direction in the central image position detector 60B, becomes the registration deviation amount along the SS direction as it is.

  As a result, registration displacement amounts at respective positions along the FS direction (near SOS (Start Of Scan), near COS (Center Of Scan), and EOS (End Of Scan)) are detected in the FS direction and SS direction, respectively. The Then, based on the color shift amounts FSerr and SSerr in the vicinity of SOS, COS, and EOS for a certain color, the relationship between the position (coordinate value Y) along the FS direction and the color shift amounts FSerr and SSerr (example) 19 as a relationship (shown by a solid line in FIG. 19), and a calculation formula for calculating a registration deviation correction amount for correcting registration deviation from the coordinate value y (the coordinate value y and the color registration correction amount represented by this calculation formula). Are obtained for FSerr and SSerr respectively for three colors other than the reference color.

  By substituting the coordinate value y at each position along the FS direction on the image into the calculation formula obtained above, the registration deviation correction amount at each position along the FS direction on the image can be obtained. The registration error can be corrected by independently correcting the position of each pixel for each color based on the error correction amount. FIG. 19 shows a case where the deviation between the color shift amount near the SOS and the color shift amount near the COS, and the deviation between the color shift amount near the COS and the color shift amount near the EOS are equal. Are not necessarily the same. When the two are not equal, the relationship between the position along the FS direction and the registration deviation amount, and the calculation formula for obtaining the registration deviation correction amount from the position along the FS direction may be obtained by applying, for example, the least square method. .

  Further, the registration error correction amount calculation unit 91 detects the registration error with respect to the timing at which the registration error detection pattern 50 is detected by the image position detectors 60A, 60B, and 60C and the detection positions of the image position detectors 60A, 60B, and 60C. Based on the shift amount of the formation position of the pattern for scanning 50, the positional deviation (Y margin) along the sub-scanning direction of the scanning line, the inclination (skew) of the scanning line, the curvature (bow) of the scanning line, the overall magnification change and the left and right Each change in magnification is detected, and a correction amount for correcting each change is obtained.

  As for the scanning line inclination, as shown in FIG. 20A, the xy coordinates (x1, y1) (x, y) of the formation position of the registration deviation detection pattern 50 at the detection positions of the image position detectors 60A, 60B, 60C. ) (X2, y2) are detected, and based on the positional relationship (see FIG. 20B), the scanning line inclination amount is calculated according to the following calculation formula, and the position (coordinate value y) along the FS direction is calculated. A calculation formula for calculating a correction amount for the scanning line inclination is obtained.

  By substituting the coordinate value y at each position along the FS direction on the image into the calculation formula obtained above, the scanning line inclination correction amount at each position along the FS direction on the image can be obtained. The scanning line inclination can be corrected by correcting the position of each pixel based on the scanning line inclination correction amount.

  As for the scanning line curve, the angle θ, as the scanning line curve is calculated according to the following calculation formula based on the xy coordinates (x1, y1) (x, y) (x2, y2) of the formation position of the registration error detection pattern 50. Each of x and y (see also FIG. 21) is calculated, and a calculation formula for calculating a correction amount for the scanning line curvature is obtained from a position (coordinate value y) along the FS direction.

  By substituting the coordinate value y at each position along the FS direction on the image into the calculation formula obtained above, the scanning line curvature correction amount at each position along the FS direction on the image can be obtained. The scanning line curvature can be corrected by correcting the position of each pixel based on the scanning line curvature correction amount.

  As for the overall magnification change and the horizontal magnification change, first, the deviation ΔXL along the FS direction between the registration position detection pattern 50 forming position and the detection position at the detection position of the image position detector 60A, the image position detector 60C. Deviations ΔX R (see FIG. 22) along the FS direction between the registration position detection pattern 50 formation position and the detection position at the detection positions are obtained, and the correction amount for the overall magnification is obtained according to the following calculation formula.

  As for the change in the horizontal magnification (see FIG. 23B for the cause of occurrence), in addition to the above-mentioned deviations ΔXL and ΔXR, the registration position detection pattern 50 is formed at the detection position of the image position detector 60B. A deviation ΔXc (see FIG. 23A) along the FS direction between the left magnification and the detected position is also obtained, and correction amounts for the left magnification and right magnification are obtained according to the following calculation formulas.

  In accordance with the magnification correction amount obtained above, for the region on the left side (EOS side in FIG. 23) centered on the pixel corresponding to COS, the pixel interval along the FS direction is corrected according to the left side magnification correction amount and corresponds to COS. For the region on the right side (SOS side in FIG. 23) with the pixel at the center, the overall magnification change and the left / right magnification change can be corrected by correcting the pixel interval along the FS direction according to the right magnification correction amount. Note that the registration deviation in the sub-scanning direction, the scanning line inclination, the scanning line curvature, the overall magnification change, and the left / right magnification change all correspond to the DC component of the registration deviation.

Next, detection of an AC component for registration error will be described. The AC component of misregistration in the FS direction is mainly caused by the wobbles of the photosensitive drums 15Y, 15M, 15C, and 15K and the end face profile of the intermediate transfer belt 25. As an example, FIG.
As shown in (A), when the wobble of the photosensitive drum has occurred due to the actual rotation axis being inclined with respect to the axis of the photosensitive drum, the photosensitive drum is in the scanning exposure position by the scanning exposure unit. By periodically changing the position of the peripheral surface in the FS direction, as shown in FIG. 24B, the image formation position on the peripheral surface of the photosensitive drum periodically changes along the FS direction.

  For this reason, the registration error correction amount calculation unit 102 follows the FS direction in one cycle of rotation of the photosensitive drum based on some reference signal (for example, a Z-phase signal of a rotary encoder attached to the photosensitive drum). The registration displacement detection pattern 50 is formed at a predetermined sampling frequency (according to Shannon's theorem, the sampling frequency may be twice the reproduction frequency, but considering the influence of noise, the reproduction frequency is at least 6 to 10 times the reproduction frequency. And the period, amplitude, and phase of the variation along the FS direction of the image forming position (relation with the position on the circumferential surface of the photoreceptor) are detected based on the sampling result.

  Based on the detection result of the FS direction AC registration deviation detected above (period, amplitude and phase of fluctuation along the FS direction of the image forming position), the FS of the image forming position where the position along the FS direction of each pixel is detected. FS direction of the image forming position is set by setting a correction amount that is periodically changed so as to cancel the fluctuation along the direction (the cycle and amplitude are the same and the phase is the opposite phase), and correction is performed according to the correction amount. Can be corrected.

  Further, the AC component of the registration misalignment in the SS direction mainly includes eccentricity of the photosensitive drums 15Y, 15M, 15C, and 15K and the rollers 27 to 32 that drive the intermediate transfer belt 25, unevenness of the thickness of the intermediate transfer belt 25, and the like. Caused by As an example, as shown in FIG. 24C, when the actual rotation axis is eccentric with respect to the axis of the photosensitive drum, the peripheral speed of the photosensitive member is periodically changed at the scanning exposure position by the scanning exposure unit. By varying, the pixel interval along the SS direction periodically varies. For example, in a region where the density is constant, the periodic fluctuation of the pixel interval is visually recognized as a periodic density fluctuation along the SS direction as shown in FIG.

  For this reason, the registration error correction amount calculation unit 102 follows the SS direction in one cycle of rotation of the photosensitive drum based on some reference signal (for example, a Z-phase signal of a rotary encoder attached to the photosensitive drum). The formation position of the registration error detection pattern 50 is sampled at a predetermined sampling frequency, and the period, amplitude, and phase of the fluctuation of the pixel interval along the SS direction based on the sampling result (relation with the position on the circumferential surface of the photoreceptor) ) Is detected.

  Based on the detection result of the AC registration deviation in the SS direction detected above (period, amplitude and phase of fluctuation of the pixel interval along the SS direction), the pixel interval along the SS direction is changed to the pixel along the detected SS direction. The pixel interval along the SS direction is set by setting a correction amount that periodically changes so as to cancel the variation in the interval (the cycle and amplitude are the same and the phase is the opposite phase), and correction is performed according to the set correction amount. Fluctuations can be corrected.

  In the case where wobble has occurred due to the tilt of the rotation axis of the photosensitive drum, the amplitude and phase of the circumferential speed fluctuation of the photosensitive drum are different at each position along the FS direction, and accordingly, the pixel The amplitude and phase of the interval variation are different at each position along the FS direction. For this reason, in consideration of the above, the period, amplitude, and phase of the fluctuation of the pixel interval along the SS direction are detected at each position of SOS, COS, and EOS, and based on the detection result, at each position along the FS direction. It is desirable to obtain the period, amplitude, and phase of the variation in the pixel interval along the SS direction by interpolation calculation, and correct the variation in the pixel interval along the SS direction based on the calculation result.

  In addition, the geometrical distortion of the image (specifically, the fluctuation along the FS direction of the image forming position and the fluctuation of the pixel interval along the SS direction) is not conspicuous like a photographic image, but the density cycle. For an image in which a significant fluctuation is visually recognized, only density correction may be performed instead of the above-described correction of the pixel position along the FS direction and the pixel interval along the SS direction. In this case, instead of the registration error detection pattern 50, a solid image having a constant density is formed, and the density fluctuation cycle, amplitude (density fluctuation width) and phase along the FS direction and SS direction of the formed solid image are set. It is desirable to detect, and based on the detected period, amplitude, and phase of density fluctuation, correction may be performed to periodically change the density of each pixel so that the detected density fluctuation is canceled.

  On the other hand, as shown in FIG. 17, image data representing an image to be formed by the image forming units 13Y, 13M, 13C, and 13K is also input to the registration correcting unit 100. The image data may be image data obtained by the image reading device 4 reading the document 2 or image data received from another facsimile device via a telephone line. Alternatively, image data obtained by expanding data received from an information processing apparatus such as a personal computer (PC) via a communication line as bitmap data may be used.

  Further, in this embodiment, as the image data, the image to be formed is decomposed into a large number of pixels at a resolution of 2400 dpi in the FS direction and the SS direction, and for each Y, M, C, and K color of each pixel. Although image data each representing the density with 8 bits (256 gradations from 0 to 255) is used, the resolution and the number of gradations of the image data are not limited to the above values.

  As shown in FIG. 17, the registration correction unit 100 includes a registration deviation correction unit 103. The registration deviation correction unit 103 includes the main scanning direction calculated by the registration deviation correction amount calculation (calculation) unit 102, and In addition to the position in the sub scanning direction, the magnification in the main scanning direction, the partial magnification in the main scanning direction, the magnification in the sub scanning direction, the partial magnification in the sub scanning direction, the skew of the lead skew side, the linearity of the lead, the linearity of the side, etc. When correcting at least one of the registration error correction amounts, the correction amount can be changed between the registration error detection pattern formation and the image formation.

  That is, when the image data is developed by the image data development circuit (Video Asic) 92, the registration error correction unit 103, in addition to the position in the main scanning direction and the sub scanning direction, The registration deviation correction amount such as the read linearity and the side linearity is corrected by moving the pixel position of the image data. For example, when a skew as shown by a solid line in FIG. 19 exists in the image to be formed, the pixel position of the image data as shown by a broken line in FIG. 19 so as to cancel the skew of the pixel position of the image data. Correction is made by moving the.

  Specifically, the registration error correction unit 103, when forming the registration error detection pattern 50, differs from that at the time of image formation in that the registration error detection pattern 50 is used by the image position detectors 60A, 60B, and 60C as registration detection sensors. The position of the entire registration deviation detection pattern 50 is manipulated so that it is directly below or near the top. At this time, the registration error correction amount is not changed, and the position of the entire registration error detection pattern 50 is moved. Specifically, in addition to the positions of the registration deviation detection pattern 50 in the main scanning direction and the sub main scanning direction, the magnification in the main scanning direction, the partial magnification in the main scanning direction, the magnification in the sub scanning direction, and the portion in the sub scanning direction For some or all of magnification, lead skew, side skew, lead linearity, side linearity, etc., the image position is manipulated to form a registration deviation detection pattern 50.

  Further, when the image is output, image distortion due to expansion / contraction of the sheet, skew of the sheet, and the like occurs. Therefore, in addition to the correction of the color registration deviation read above, the image on the sheet is scanned in the main scanning direction and the sub-scanning direction. In addition to the position in the main scanning direction, magnification in the main scanning direction, partial magnification in the main scanning direction, magnification in the sub scanning direction, partial magnification in the sub scanning direction, lead skew, side skew, lead linearity, side linearity Such a configuration is possible.

  In the above configuration, in the tandem full-color printer according to the first embodiment, even when there is an error in the attachment position of the detection means for detecting the registration error detection pattern, the main scanning is performed as follows. Position in the direction and sub-scanning direction, magnification in the main scanning direction, partial magnification in the main scanning direction, magnification in the sub-scanning direction, partial magnification in the sub-scanning direction, lead skew, side skew, lead linearity, side linearity It is possible to form both high-quality images that can be replaced by a printing press by correcting the registration error correction amount.

  That is, in the tandem full-color printer according to the first 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 tray is opened or closed, etc. At a predetermined timing, as shown in FIG. 12, the registration error detection pattern 50 is formed on the intermediate transfer belt 25 by the image forming units 13Y, 13M, 13C, and 13K for yellow, magenta, cyan, and black, The registration deviation detection pattern 50 is detected by three image position detectors 60A, 60B, and 60C.

  At this time, in order to form the registration error detection pattern 50 on the intermediate transfer belt 25, the image data for forming the registration error detection pattern 50 stored in the nonvolatile memory 92 is used as it is. Thus, the correction process in the registration error correction unit as shown in FIG.

  The registration deviation detection pattern 50 signal detected by the image position detectors 60A, 60B, and 60C is processed by the signal processing circuit shown in FIG. 15, and then input to the microcomputer 83 as a pattern detection signal.

  In the microcomputer 83, as shown in FIG. 17, based on various functions realized by the software and hardware of the microcomputer 83, the calculation of the image registration deviation amount and the correction amount as shown below are performed. Calculation, image forming position correction processing, and the like are executed.

  First, in the registration deviation amount calculation unit 101 realized by the microcomputer 83, as shown in FIG. 25, based on the pattern detection signals from the image position detectors 60A, 60B, 60C, the main scanning direction and the sub scanning direction. The registration deviation amount such as the position, the magnification in the main scanning direction, the partial magnification in the main scanning direction, the lead skew, and the linearity of the lead is calculated.

  Next, as shown in FIG. 25, the registration deviation correction amount calculation unit 102 calculates the position in the main scanning direction and the sub-scanning direction calculated by the registration deviation amount calculation unit 101, the magnification in the main scanning direction, and the main scanning direction. A registration error correction amount (correction coordinates) for correcting registration error such as partial magnification, lead skew, and lead linearity is calculated based on the above-described mathematical formula.

  Then, the registration deviation such as the position in the main scanning direction and the sub-scanning direction, the magnification in the main scanning direction, the partial magnification in the main scanning direction, the lead skew, and the linearity of the lead calculated by the registration deviation correction amount calculation unit 102 is corrected. As shown in FIG. 16, the registration error correction amount (correction coordinates) to be stored is stored in the nonvolatile memory 92 and used during image formation.

  Next, when the image is formed, the image of the color original 2 to be printed is read by the image reading device 4 or full color image data is transmitted from a personal computer (not shown) or the like to print the full color image. Done.

  By the way, the registration error detection pattern 50 is formed as described above, the registration error detection pattern 50 is detected by the image position detectors 60A, 60B, and 60C, and the microcomputer 83 detects the position in the main scanning direction and the sub scanning direction. The registration deviation amount such as the magnification in the main scanning direction, the partial magnification in the main scanning direction, the lead skew, and the linearity of the lead is calculated, the registration deviation correction amount for correcting the registration deviation amount is obtained, and the registration deviation is corrected. Even when processing is performed, as shown in FIG. 26, if there is an error in the attachment position of the image position detectors 60A, 60B, and 60C, a high-quality image equivalent to that of a printing press may not be obtained. is there.

  Therefore, in this embodiment, even when a process for correcting registration misalignment is performed, if a desired high-quality full-color image cannot be obtained, the outer periphery of the desired full-color image as shown in FIG. In addition, a cross-shaped print position reference mark 130, which is a so-called registration mark in the printing field, has four colors, yellow (Y), magenta (M), and cyan (C) black (K), at predetermined corners of the recording paper 34. The manual mode to be formed at the position is selected, and the cross-shaped print position reference mark 130 is formed. This manual mode is executed by the microcomputer 83 when, for example, a serviceman or a user operates the user interface of the printer.

  Next, the service person or the user manually sets the length and position between the cross-shaped print position reference marks 130 on the recording paper 34 on which the cross-shaped print position reference marks 130 are formed at predetermined positions at the four corners. Measurement is performed, or the recording paper 34 is set in the high-precision image reading device 4 and is read by the image reading device 4.

  When the length and position between the cross-shaped print position reference marks 130 formed on the recording paper 34 are deviated from predetermined values, the service person or the user can use the image position detector 60A, When it is determined that any one or more of 60B and 60C has an attachment position error and the printer 83 calculates the registration deviation correction amount by operating the user interface of the printer, the image position detection is performed. Settings are made to reflect the error in the attachment positions of the devices 60A, 60B, and 60C in the registration error correction amount.

  Thereafter, the service person or the user prints the recording paper 34 on which the cross-shaped print position reference marks 130 are formed at the predetermined positions at the four corners again, and the cross-shaped print position reference marks 130 are at the predetermined positions at the four corners. After confirming that it is formed, a desired printing operation is executed.

  As described above, in the above embodiment, when the registration error detection pattern 50 is formed, unlike the image formation, the registration error detection pattern 50 is used by the image position detectors 60A, 60B, and 60C as the registration detection sensors. The position of the entire registration deviation detection pattern 50 is manipulated so that it is directly below or near the top. At this time, the registration error correction amount is not changed, and the position of the entire registration error detection pattern 50 is moved. Specifically, in addition to the positions of the registration deviation detection pattern 50 in the main scanning direction and the sub main scanning direction, the magnification in the main scanning direction, the partial magnification in the main scanning direction, the magnification in the sub scanning direction, and the portion in the sub scanning direction For some or all of the magnification, lead skew, side skew, lead linearity, side linearity, etc., the image position is manipulated to form a registration deviation detection pattern 50 to obtain the registration deviation correction amount.

  At the time of actual image formation, the registration misalignment correction unit performs positions in the main scanning direction and the sub scanning direction, magnification in the main scanning direction, partial magnification in the main scanning direction, magnification in the sub scanning direction, partial magnification in the sub scanning direction, An image is formed by correcting the amount of misregistration such as lead skew, side skew, lead linearity, and side linearity.

  Next, as described above, the position in the main scanning direction and the sub scanning direction, the magnification in the main running spine direction, the partial magnification in the main scanning direction, the magnification in the sub scanning direction, the partial magnification in the sub scanning direction, the lead skew, A desired high-quality image can be obtained by forming an image by correcting the amount of misregistration such as skew, lead linearity, and side linearity.

  If there is an error in the attachment position of the image position detectors 60A, 60B, 60C for detecting the registration error detection pattern 50, the registration error detection pattern 50 is formed and the registration error correction process is performed. However, a desired high-quality image cannot be obtained.

  Therefore, in this case, a cross-shaped print position reference mark 130 as a mark for specifying both image positions is printed on the recording paper 34, and the position of the cross-shaped print position reference mark 130 is determined by a serviceman or user. Alternatively, an error in the attachment position of the image position detectors 60A, 60B, and 60C is obtained by detection with a high-accuracy image reading apparatus, and the error in the attachment position of the image position detectors 60A, 60B, and 60C is calculated as a registration error correction amount. Feedback is to come.

Therefore, in this embodiment, even in the case where there is an error in the attachment position of the detection means for detecting the registration error detection pattern, the magnification in the main scanning direction and the magnification in the main scanning direction and the main scanning direction Can be replaced with a printing press by correcting the registration error correction amount such as partial magnification, sub-scanning direction magnification, sub-scanning direction partial magnification, lead skew, side skew, lead linearity, side linearity, etc. Both images with high image quality can be formed.
In this embodiment, the number of sensors is three, but it is also possible to adopt a configuration in which bending of higher-order scanning lines and partial magnification can be detected by more than five sensors.

Embodiment 2
FIG. 28 shows a second embodiment of the present invention. The same parts as those of the first embodiment are denoted by the same reference numerals. In the second embodiment, images are printed on both sides of a recording medium. In the image forming apparatus configured to be capable of forming the image, the registration error correcting unit is configured to form an image on both sides of the recording medium in the main scanning direction and the sub-scanning direction during the front surface image formation and the back surface image formation. In addition to the position, the main scanning direction magnification, the main scanning direction partial magnification, the sub-scanning direction magnification, the sub-scanning direction partial magnification, the lead skew, the side skew, the lead linearity, the side linearity, etc. At least one of the deviation correction amounts is changed.

  In the second embodiment, the plurality of image forming units form marks for specifying the image position on both the front and back surfaces of the recording medium, the image position specifying mark is read by the reading unit, and the registration error correcting unit In the image forming apparatus configured to correct the registration error, the registration error correction unit is configured to read at least two or more image position specifying marks formed on the surface of the recording medium by the reading unit. When forming an image on the back side of the recording medium, the position in the main scanning direction and the sub scanning direction, the magnification in the main scanning direction, the partial magnification in the main scanning direction, the magnification in the sub scanning direction, the partial magnification in the sub scanning direction, and the read At least one of the registration deviation correction amounts such as skew, side skew, lead linearity, and side linearity is changed. It is configured.

  Further, in the second embodiment, the registration error correcting means is arranged in the main running direction and the sub-scanning direction so that at least two or more image position specifying marks respectively formed on the front and back surfaces of the recording medium overlap each other. Position deviation, main scanning direction partial magnification, sub-scanning direction magnification, sub-scanning direction partial magnification, lead skew, side skew, lead linearity, side linearity, etc. Of these, at least one of them is changed.

  That is, in the second embodiment, as shown in FIG. 28, a cross-shaped print position reference as an image position specifying mark formed (fixed) on the surface of the recording paper 34 in the double-sided paper transport path 49. A reading sensor 150 including a CCD or the like as reading means for reading the mark 130 is provided. The reading sensor 150 is provided at two positions along the main scanning direction corresponding to the position of the cross-shaped print position reference mark 130.

  In this embodiment, the cross-shaped print position reference mark 130 formed (fixed) on the surface of the recording paper 34 is read by the reading sensor 150 during double-sided printing.

  Then, the microcomputer 83 reads each color of yellow (Y), magenta (M), cyan (C), and black (K) based on the position of the cross-shaped print position reference mark 130 that is read by the reading sensor 150. It is calculated how much the image is shifted along the main scanning direction and the sub-scanning direction.

  At that time, since the recording paper 34 passes through the fixing device 37, the image may be stretched or shrunk depending on the moisture content or material of the recording paper 34. Therefore, the microcomputer 83 obtains the amount of deviation along the main scanning direction and the sub-scanning direction of the image formed on the recording paper 34, and forms the image on the back surface of the recording paper 34. Thus, the shift amount along the main scanning direction and the sub-scanning direction is corrected in accordance with the correction of the registration shift described above.

  Also, with other registration misalignment correction amounts, the position in the main scanning direction and the sub-scanning direction, the magnification in the main scanning direction, the partial magnification in the main scanning direction, the magnification in the sub-scanning direction, and the portion in the sub-scanning direction, depending on the case. It is configured to change at least one of registration deviation correction amounts such as magnification, lead skew, side skew, lead linearity, and side linearity.

  By doing so, an image can be formed such that at least two or more print position reference marks 130 formed on the front and back surfaces of the recording paper 34 overlap each other.

  Since other configurations and operations are the same as those of the first embodiment, description thereof is omitted.

Embodiment 3
The third embodiment of the present invention will be described by attaching the same reference numerals to the same parts as those in the first embodiment. In the third embodiment, the registration error correcting means includes a recording medium storage tray, a recording medium, and the like. Information for image formation, such as transport status, recording medium shape, detected medium, recording medium material, etc., in-machine environment, peripheral environment, number of images formed after power-on, number of images continuously formed, number of images formed in total Based on at least one of the following, positions in the main scanning direction and sub-scanning direction, magnification in the sheep scanning direction, partial magnification in the main scanning direction, magnification in the sub-scanning direction, partial magnification in the sub-scanning direction, lead skew, side At least one or more of registration deviation correction amounts such as skew, lead linearity, side linearity, and the like are changed.

  That is, in the third embodiment, the microcomputer 83 as the registration error correcting unit is configured to control the image forming operation of the full-color printer. At the same time, the microcomputer 83 is controlled by a sensor or the like (not shown). Information on the state of the paper trays 39 to 41, the conveyance state of the recording paper 34, the shape of the recording paper 34, the intermediate transfer belt 25 or the paper conveyance belt (not shown) as a detected medium, the material of the recording paper, the in-machine environment, and the surrounding environment Detecting at least one of information for image formation, such as the number of image formations after power-on, the number of continuous image formations, the total number of image formations, and the like, and based on the information for image formation, the main scanning direction Position in the sub-scanning direction, magnification in the main scanning direction, partial magnification in the main scanning direction, magnification in the sub-scanning direction, partial magnification in the sub-scanning direction, Skew, side skew, of the color registration adjusting amount of linearity, such as linearity side leads, and is configured to change at least one or more.

  The microcomputer 83 stores a table of relationships between various environmental conditions and registration deviation correction amounts in advance in the non-volatile memory 92. Based on the correction table, the recording paper material, etc. The registration error correction amount is adjusted according to at least one of the information for image formation, such as the image information, the in-machine environment, the surrounding environment, the number of image formations after power-on, the number of continuous image formations, the total number of both image formations In addition, a registration error correction operation is executed.

  Further, the microcomputer 83 may be configured to be able to sequentially learn a reading result by an image reading device built in the printer body 1 or an external image reading device and a table calibration result based on an adjustment amount setting by a user or the like.

  At that time, in the calibration of the “correction table” based on the information from the image reading device 4, the internal temperature / humidity and the ambient temperature / humidity (1) when the image is output to a part of the original to be read. Measured values at multiple locations), number of output sheets after power-on (after returning from sleep), number of continuous output sheets until the above document is output, material of output media, fiber orientation characteristics, thickness, moisture content, size -Some or all of one or more pieces of information such as surface properties may be coded and entered like a barcode.

  In addition, the fixing device 37, the paper transport unit, the belt module, the image reading device, the registration control sensor, and the like are detected by the shock sensor, etc., based on the detection information. The contents of the correction amount table may be cleared and the reference table may be returned.

  The present invention is not limited to forming a registration error detection pattern, but can be applied to multiple color machines and monochrome machines.

FIG. 1 is a schematic perspective view showing a tandem type color image forming apparatus as an image forming apparatus according to Embodiment 1 of the present invention. FIG. 2 is a block diagram showing a tandem color image forming apparatus 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 an explanatory diagram showing a magnification shift in the main scanning direction. FIG. 5 is an explanatory diagram showing a margin shift in the main scanning direction. FIG. 6 is an explanatory diagram showing skew deviation. FIG. 7 is an explanatory diagram showing a margin shift in the sub-scanning direction. FIG. 8 is an explanatory diagram showing periodic fluctuations in the sub-scanning direction. FIG. 9 is an explanatory diagram showing periodic fluctuations in the main scanning direction. FIG. 10 is an explanatory diagram showing a color registration error in which various registration errors are combined. FIG. 11 is an explanatory diagram showing a state of occurrence of color registration misalignment. FIG. 12 is a perspective view showing a color registration misalignment detection pattern. FIG. 13 is a plan view showing a color registration misalignment detection pattern. FIG. 14 is a block diagram showing color registration misalignment detection means. FIG. 15 is a block diagram showing a color registration misalignment detection circuit. FIG. 16 is a block diagram showing a color registration misalignment detection pattern forming circuit. FIG. 17 is a block diagram showing a color registration misalignment correction circuit. FIG. 18 is an explanatory diagram showing a detection state of color registration misalignment. FIG. 19 is an explanatory diagram showing a detection state of color registration misalignment. FIG. 20 is an explanatory diagram showing a color registration misalignment detection state. FIG. 21 is an explanatory diagram showing a detection state of color registration misalignment. FIG. 22 is an explanatory diagram showing a method for correcting the overall magnification. FIG. 23 is an explanatory diagram showing a method for correcting the horizontal magnification. FIG. 24 is an explanatory diagram showing a wobble occurrence state. FIG. 25 is an explanatory diagram showing a registration error correction method of the image forming apparatus according to the first embodiment of the present invention. FIG. 26 is an explanatory diagram showing a registration error correction method of the image forming apparatus according to the first embodiment of the present invention. FIG. 27 is an explanatory diagram showing a registration error correction method for the image forming apparatus according to the first embodiment of the present invention. FIG. 28 is a block diagram showing an image forming apparatus according to Embodiment 2 of the present invention.

Explanation of symbols

  50: Registration deviation detection pattern, 60: Image position detector, 92: Image data development circuit, 100: Registration correction unit (registration deviation correction means), 101: Registration deviation amount calculation unit, 102: Registration deviation correction amount calculation unit 103: Registration displacement correction unit.

Claims (7)

An image forming apparatus that includes a plurality of image forming units that form images of different colors, and that forms a plurality of images of different colors formed by the plurality of image forming units in a state of being superimposed on a recording medium. An image forming apparatus having a registration error correction unit that forms a registration error detection pattern on a detected medium by the plurality of image forming units, detects the registration error detection pattern by a detection unit, and corrects an image registration error. The registration error correction means includes a magnification in the main scanning direction and main scanning in addition to image position correction on the recording medium in the main scanning direction and the sub-scanning direction during registration error detection pattern formation and image formation. For recording media such as direction partial magnification, sub-scanning direction magnification, sub-scanning direction partial magnification, lead skew, side skew, lead linearity, side linearity Of the image position correction amount, an image forming apparatus which is characterized in that the changeable at least one or more. In an image forming apparatus capable of forming an image on both sides of a recording medium, when forming an image on both sides of the recording medium, it is positioned at the position in the main scanning direction and the sub-scanning direction during the front surface image formation and the back surface image formation. In addition, images on the recording medium such as main scanning direction magnification, main scanning direction partial magnification, sub-scanning direction magnification, sub-scanning direction partial magnification, lead skew, side skew, lead linearity, side linearity, etc. An image forming apparatus characterized in that at least one of position correction amounts can be changed. In an image forming apparatus including an image reading unit that reads an image of a document, a magnification in the main scanning direction is added to the position in the main scanning direction and the sub-scanning direction so as to cancel the reading error of the image reading unit that is obtained in advance. At least one of image position correction amounts for the recording medium, such as a partial magnification in the main scanning direction, a magnification in the sub-scanning direction, a partial magnification in the sub-scanning direction, a lead skew, a side skew, a lead linearity, and a side linearity An image forming apparatus characterized in that one or more can be changed. In the image forming apparatus configured to form a mark for specifying the image position on both the front and back surfaces of the recording medium, read the image position specifying mark by the reading unit, and correct the registration error by the registration error correction unit. The registration error correction unit is configured to form an image on the back surface of the recording medium based on a result of reading at least two or more image position specifying marks formed on the surface of the recording medium by the reading unit, Recording of sub-scanning direction position, main scanning direction magnification, main scanning direction partial magnification, sub-scanning direction magnification, sub-scanning direction partial magnification, lead skew, side skew, lead linearity, side linearity, etc. An image forming apparatus capable of changing at least one of image position correction amounts with respect to a medium. The registration misalignment correcting unit is configured to position at least two or more image position specifying marks respectively formed on the front and back surfaces of the recording medium in the main scanning direction and the sub-scanning direction, the magnification in the main scanning direction, and the main scanning direction. At least one or more of image position correction amounts for the recording medium, such as partial magnification in the scanning direction, magnification in the sub-scanning direction, partial magnification in the sub-scanning direction, lead skew, side skew, lead linearity, side linearity, etc. The image forming apparatus according to claim 4, wherein the image forming apparatus is changeable. The registration misalignment correction unit includes information such as a recording medium storage tray, a recording medium conveyance state, a recording medium shape, a detected medium, a recording medium material, an in-machine environment, a peripheral environment, the number of images formed after power-on, and continuous image formation. Based on at least one or more pieces of information for image formation such as the number of sheets and the total number of image formations, the position in the main scanning direction and the sub scanning direction, the magnification in the main scanning direction, the partial magnification in the main scanning direction, and the sub scanning direction It is possible to change at least one or more of image position correction amounts with respect to the recording medium such as magnification, partial magnification in the sub-scanning direction, lead skew, side skew, lead linearity, and side linearity. The image forming apparatus according to claim 1. 7. The image forming apparatus according to claim 1, wherein the registration error correction unit corrects registration error by moving a pixel position of image data to be formed.

Images