JP2007065162A - Image forming apparatus and image adjusting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of stably reproducing an electrostatic latent image and a toner image on a photoreceptor and always forming a distinct image by forming dots on a real scanning line with the resolution of the real scanning line, and to provide an image adjusting method. <P>SOLUTION: In the image forming apparatus having a paper conveying part for conveying recording paper S, and an image forming means for forming the image on the recording paper S conveyed by the paper conveying part, the position of the image in the conveying direction of the recording paper S is adjusted by locally increasing/decreasing the number of image data lines in the conveying direction of the recording paper S on the image formed by the image forming means. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus and an image adjustment method, and more particularly to an image forming apparatus and an image adjustment method for correcting color misregistration when forming a color image.

  A full color image in a full color image forming apparatus using an electrophotographic method or an ink jet method that is currently popular is usually formed by superimposing three to four color component images. Therefore, the position of each color component image needs to be matched with high accuracy on the recording medium or the intermediate transfer member. As a cause of deteriorating the image quality of the formed full color image, there is a color shift due to a position shift of each color image.

  Causes of misalignment in the recording medium conveyance direction (hereinafter referred to as “sub-scanning direction”) include the following.

  In the electrophotographic image forming apparatus, the distance between the image forming stations is corrected by controlling the exposure timing of the LED or laser beam as the exposure means, but each image forming station is independent of each other. In an image forming apparatus that forms an image, the image expansion and contraction occurs due to uneven rotation of the photosensitive drum at each image forming station and uneven speed of the transfer belt or recording medium when transferring the toner image on the photosensitive drum. Therefore, a positional deviation in the sub-scanning direction occurs.

  In an image forming apparatus having an intermediate transfer body that sequentially forms toner images of each color on one photosensitive drum and transfers and holds the single color toner on the photosensitive drum so as to overlap each color, In addition to the rotation unevenness, in particular, the rotation unevenness of the intermediate transfer member greatly affects the positional deviation in the sub-scanning direction. Causes of uneven rotation of the intermediate transfer member include shocks due to attachment / detachment of a cleaning device for cleaning the toner on the intermediate transfer member, and shocks due to attachment / detachment of the transfer roller when the toner image on the intermediate transfer member is transferred to the recording medium. Misalignment occurs.

  Even in an inkjet image forming apparatus, unevenness in the speed of a motor that drives a roller that conveys a recording medium, variation in gear that transmits driving from the motor, and unevenness in the conveyance speed of a recording medium caused by eccentricity of the conveying roller. As a result, a positional shift in the sub-scanning direction occurs.

  Means for eliminating drive unevenness have been proposed in order to correct image misalignment that occurs locally in the sub-scanning direction due to the above causes, and misalignment due to image expansion / contraction. For this purpose, drive unevenness is detected. A detection means and a correction means for correcting it by feeding it back are necessary, and the mechanism is complicated and expensive, so that it is difficult to realize. In addition, misalignment in the sub-scanning direction due to a shock that is not related to the rotation cycle of the rotating body, such as transfer to the intermediate transfer body and attachment / detachment of the cleaning device, is very difficult to correct only by controlling the rotating body. It was.

Therefore, as a means for correcting such a positional deviation in the sub-scanning direction, a method of forming dots by processing image data having a resolution equal to or higher than the actual scan in an intermediate line between actual scan lines (eg, sub-scan). An electrophotographic apparatus that scans at 600 dpi, inputs 1200 dpi image data, and reproduces dots drawn at 1200 dpi between 600 dpi scan lines (see, for example, Patent Document 1) and the same sub-scanning direction as in actual scanning That corrects the position of dots by reproducing dots between lines (eg, an electrophotographic apparatus that scans at 600 dpi sub-scanning, inputs 600 dpi image data, As a position correction, a technique for shifting a dot position drawn between 600 dpi scan lines) (for example, Patent Document 2) Irradiation) there is.
US Pat. No. 5,134,495 US Pat. No. 6,229,555

  However, the above prior art is a technique for correcting only the position of the dot on the photoconductor in the electrophotographic apparatus, and also controls to form dots on an intermediate line that is not on the actual scanning line to be subjected to laser exposure. The electrostatic latent image and toner image of the dots formed on the surface become very unstable due to environmental fluctuations, and it has been difficult to always obtain a clear image.

  Therefore, an object of the present invention is to solve at least one of such problems and other problems. Other issues can be understood throughout the specification.

  The image forming apparatus of the present invention can achieve the above object by the following technical configuration.

  In an image forming apparatus having a conveying unit that conveys a recording medium and an image forming unit that forms an image on the recording medium conveyed by the conveying unit, conveying the recording medium of an image formed by the image forming unit An image forming apparatus, wherein the number of image data lines in the direction is locally increased or decreased to adjust the image position of the image in the recording medium conveyance direction.

  According to the present invention, an image that can form dots on the actual scan line at a resolution of the actual scan line, stably reproduce the electrostatic latent image and the toner image on the photoreceptor, and can always form a clear image. A forming apparatus and an image adjustment method can be provided.

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

(First embodiment)
FIG. 1 is a configuration diagram of a main part of a full-color printer which is an example of an image forming apparatus according to the present embodiment.

  A photosensitive drum (hereinafter simply referred to as “photosensitive member”) 1 is provided so as to be rotated in the direction of arrow A by a motor (not shown). Around the photosensitive member 1, a primary charger 7, an exposure device 8, a developing unit 13, a transfer charger 10, and a cleaner device 12 are arranged. These constitute image forming means.

  The developing unit 13 includes three color developing devices 13Y (yellow), 13M (magenta), 13C (cyan) for full color development, and a rotating developer including a black developing device 13K (black). The developing devices 13Y, 13M, 13C, and 13K develop the electrostatic latent images on the photoreceptor 1 with Y, M, C, and K toners, respectively. When developing each color, the developing unit 13 is rotated in the direction of arrow R by a motor (not shown), and the developing device for the corresponding color is aligned so as to face the photoreceptor 1.

  The toner images of each color (Y, M, C, K) developed on the photosensitive member 1 are sequentially transferred to an intermediate transfer belt 2 as an intermediate transfer member by a transfer device 10, and four color toner images are intermediately transferred. Overlaid on the belt 2. The intermediate transfer belt 2 is stretched around rollers 17, 18, 19, and 20. The roller 17 is coupled to a driving source (not shown) and functions as a driving roller that drives the intermediate transfer belt 2. The roller 18 and the roller 20 function as tension rollers that adjust the tension of the intermediate transfer belt 2. The roller 19 is a secondary roller. It functions as a backup roller for the transfer roller 21 as a transfer device.

  A belt cleaner 22 is provided at a position facing the roller 17 across the intermediate transfer belt 2, and residual toner on the intermediate transfer belt 2 is scraped off by a blade provided on the belt cleaner 22.

  The recording paper as the recording medium drawn from the recording paper cassette 23 to the conveyance path by the pickup roller 24 is brought into a nip portion, that is, a contact portion between the transfer roller 21 and the intermediate transfer belt 2 by a pair of rollers 25 and 26 as conveyance means. Be fed. The toner image formed on the intermediate transfer belt 2 is transferred onto the recording paper at this nip portion, thermally fixed by the fixing device 5 and discharged outside the device.

  In the full color printer configured as described above, an image is formed as follows. First, a voltage is applied to the charging device 7 so that the surface of the photoreceptor 1 is negatively charged uniformly at a predetermined charged portion potential. Subsequently, exposure is performed by an exposure device 8 formed of a laser scanner so that the charged image portion on the photosensitive member 1 has a predetermined exposure portion potential, and an electrostatic latent image is formed. The exposure device 8 forms an electrostatic latent image corresponding to the image by turning on and off based on the image signal.

  A developing bias set in advance for each color is applied to the developing rollers of the developing devices 13Y, 13M, 13C, and 13K, and the electrostatic latent image is developed with toner when passing through the position of the developing roller. Visualized as an image. The toner image is transferred to the intermediate transfer belt 2 by the transfer device 10, and further transferred to the recording paper by the transfer roller 21, and then fed to the fixing device 5. (Includes desorption operation).

  In full-color printing, toner images of four colors are superimposed on the intermediate transfer belt 2 and then transferred onto a recording sheet. The toner remaining on the photoconductor 1 is easily cleaned by a preliminary cleaning device, and is removed and collected by the cleaner device 12. Finally, the photoconductor 1 is uniformly removed by a static eliminator (not shown). The charge is removed to near 0 volts to prepare for the next image forming cycle.

  The image forming timing of the full-color printer is controlled based on the detection signal detected by detecting a reference mark provided on the intermediate transfer belt 2. FIG. 25 is a diagram showing an example of the configuration of the intermediate transfer belt 2 of the present embodiment shown in FIG. The intermediate transfer belt 2 is stretched over rollers including a driving roller 17, tension rollers 18 and 20, and a backup roller 19, and a predetermined tension is applied by the tension rollers 18 and 20.

  Between the backup roller 19 and the tension roller 20, a reflective sensor 36 for detecting the reference position is disposed. The reflective sensor 36 detects a reference mark 41 such as a reflective tape provided at the end of the outer peripheral surface of the intermediate transfer belt 2 and outputs a reference mark signal. The intermediate transfer belt 2 is long enough to form two images, and the photoreceptor 1 makes two turns while the intermediate transfer belt 2 makes one turn, that is, the circumference is an integer ratio of 1: 2. It is configured as follows. When the reference mark 41 serving as the reference position of the image formation timing provided on the intermediate transfer belt 2 is read by the reflection sensor 36, image formation of each color is started with the signal as the exposure timing of the exposure means 8. By doing so, the writing start timing of each color becomes the same every time at the image forming position of the photosensitive member 1 and the position of the intermediate transfer belt 2, and image forming with little color misregistration in the sub-scanning direction is realized in image writing.

  The image forming apparatus shown in FIG. 1 is provided with an image reading apparatus 31 as an image reading means constituting an image forming means. Image data read by the image reading apparatus 31 is transmitted to a printer unit 32, and an image is read. It has a structure that can be used as a copying machine by forming.

  Note that, unlike the image forming apparatus shown in the fifth embodiment, the image forming unit may not include an image reading unit as the image reading unit.

  A system related to correction of positional deviation in the sub-scanning direction in the image forming apparatus according to the present embodiment described above will be described with reference to FIGS. 2, 3, and 5.

  FIG. 2 shows an example of a chart output for measuring the positional deviation. FIG. 3 shows an example of a system configuration of image correction for correcting image positional deviation. FIG. 5 shows an example of a sequence for measuring the image displacement.

  FIG. 2 is a chart (pattern image) for measuring the positional deviation output in the present embodiment. This chart is formed on the recording medium so that each color is a stripe in the sub-scanning direction with a predetermined interval with reference to the detection signal of the reference mark 41 provided on the intermediate transfer belt 2. This is a band image. As for the predetermined sub-scanning interval here, for example, if the image formation in the sub-scanning direction is 2400 dpi, images are formed at intervals of 256 pixels (distance is about 2.71 mm). A line for one pixel is formed in the main scanning direction, and then a pattern having a margin of 255 pixels in the sub scanning direction is repeated in the sub scanning direction.

  The misregistration measurement chart formed here is set in an image reading device 31 as misregistration detection means by a user or an operator, the image data of the chart is read by the image reading device 31, and the read image data From this, the amount of displacement is measured. The amount of misregistration is measured by measuring how much a toner image of another color deviates from a certain reference color (here, cyan) with respect to the sub-scanning direction. The measured positional deviation amount data is input to the sub-scanning position adjustment memory 305 as the storage means shown in FIG.

  The table shown in FIG. 4 is an example of data for adjusting the positional deviation of a certain color stored in the sub-scanning position adjustment memory 305. Here, the sub-scanning line is the number of sub-scanning lines from which an image of a certain color is written and the position-adjustment dummy dummy image is inserted and the image data for one line is deleted from the image data of which line. Data indicating the count value of the number and whether to insert or delete at that time is input.

  The above contents will be described with reference to the sequence of FIG. The operator corrects misalignment according to the sequence shown in FIG. First, the operator selects a misalignment adjustment mode from the operation unit of the image forming apparatus, and starts a misalignment adjustment sequence (S1). Next, the misalignment measurement chart shown in FIG. 2 is formed and output as described above (S2). The output misregistration measurement chart is set in the image reading device 31 by the operator, the image data of the misregistration measurement chart is read, and the misregistration amount is measured from the read image data (S3). The measured misregistration amount data is input to the sub-scan position adjustment memory 305 of the image misregistration correction block shown in FIG. 3 (S4), and the misregistration adjustment sequence is completed when the misregistration adjustment data is stored (S4). S5).

  Next, an image correction system configuration for correcting the image misalignment shown in FIG. 3 will be described. First, image data is input to the FIFO 301. Here, in order to simplify the description, the input data is gradation data of 4 bits per pixel, and the input data for one line of sub-scanning (input data of sub-scanning resolution 2400 dpi with an engine having an actual scanning resolution of 2400 dpi) is obtained. It is assumed that it is input at any time according to the scanning time of laser exposure.

  The image data input to the FIFO 301 is then input to a sub-scanning image position adjustment block 302 serving as a positional deviation adjustment unit. The sub-scanning image position adjustment block 302 has a line buffer for three lines, the value of the sub-scanning line counter 304 counting the sub-scanning lines from the time of image writing, and the image stored in the sub-scanning position adjustment memory 305. The image is transmitted to the image processing block 303 while comparing with the position adjustment line counter value.

  When an image in which the value of the sub-scanning line counter 304 matches the image position adjustment line counter value stored in the sub-scanning position adjustment memory 305 is input, the sub-scanning image position adjustment block 302 Depending on the image adjustment value for the sub-scanning line counter value stored in the scanning position adjustment memory 305, for example, if the value is +1, one line of an image (dummy image) that is not in the actual image is inserted, and − If 1, the image data for one line is deleted from the actual image data.

  Image insertion and image deletion in units of lines in the sub-scanning line will be described with reference to FIGS.

  FIG. 6 shows an example of original image data before being input to the sub-scanning image position adjustment block 302 of FIG. 3 and processed. Columns indicate pixels in the main scanning direction, and rows indicate pixels in the sub-scanning direction. Here, it is assumed that one square has a resolution of 2400 dpi for both main and sub.

  FIG. 7 shows an example in which a dummy image (image data line) for one line is inserted into the 8th sub-scanning line of the image data in FIG. 6, and the dummy image to be inserted here is image data of one line before and after. Determined by. The sub-scanning image position adjustment block 302 has a line buffer for three lines. When a dummy image is inserted in the eighth line, the seventh line image and the eighth line image data before processing are input. Then, these data are compared and calculated in units of one pixel to generate dummy line image data.

  This will be described in more detail with reference to FIGS. 11 and 12.

  FIG. 11 shows the gradation data of the image data on the 6th to 8th lines of the subscanning image data before being input to the subscanning image position adjustment block 302 and processed.

  FIG. 12 is an example showing the method for generating a dummy image to be inserted in an easy-to-understand manner. When a dummy image is inserted into the eighth line, a dummy image is generated from the image data of the seventh and eighth lines of the image data before processing. FIG. 12 shows a method in which the average value of the gradation data of the seventh line and the eighth line is used as dummy image data for easier understanding.

  That is, when the image data at the main scanning position of the 7th line is 0 and the image data of the 8th line is 0, the image data of the dummy line is obtained by taking the average of the image data of the 7th line and the 8th line. The key data is 0. When the seventh line is F and the eighth line is F, the dummy image data is also F. Further, when the seventh line is F and the eighth line is 0, or when the seventh line is 0 and the eighth line is F, the dummy image data is averaged to be 8. The dummy image data created in this way is inserted between the 7th line and the 8th line before being processed, and the image is extended in the sub-scanning direction by one line of 2400 dpi (about 10.5 um), and the positional deviation is corrected. Adjust it.

  In this embodiment, the dummy image data to be inserted is generated from the average value of the preceding and subsequent image data. However, when the image data is slightly increased or decreased depending on the situation of the image forming apparatus, the influence of the dummy image is more visible. Needless to say, in this case, the average value is not always used.

  FIG. 8 shows another example in which a dummy image for one line is inserted into the eighth sub-scanning line of the image data in FIG. In FIG. 8, for the dummy image to be inserted, the image data of the line to be inserted (here, the eighth line) is directly inserted as a dummy image. That is, the inserted dummy image and the image of the 8th line scanned next are the same image, and the same image of 2 lines is exposed. By simplifying the data generation of the dummy image to be inserted in this manner, the image data processing circuit can be simplified and the circuit can be further reduced.

  FIG. 9 shows still another example in which a dummy image for one line is inserted into the eighth sub-scanning line of the image data in FIG. In FIG. 9, for the dummy image to be inserted, the image data one line before the line to be inserted (here, the eighth line) is directly inserted as a dummy image. That is, the image data on the seventh line and the inserted dummy image are the same image, and the same image on the two lines is exposed.

  Next, FIG. 10 will be described. FIG. 10 shows an example of this embodiment in which one line of the seventh sub-scanning line of the image data in FIG. 6 is deleted. The sub-scanning image position adjustment block 302 in FIG. 3 has a line buffer for three lines. When the image data for the seventh line is deleted, the image data for the sixth line, the seventh line, and the eighth line are stored. Input and delete the density data of the 7th line to be deleted in units of one pixel and add them to the 6th and 8th lines, respectively, to generate new 6th and 8th line image data The sixth line data and the eighth line data are transmitted to the image processing block 303 as continuous image data.

  This will be described in more detail with reference to FIGS.

  FIG. 13 shows an example in which the image data deletion method for one line shown in FIG. 10 is more easily understood. When deleting the seventh line in FIG. 10, the image data of the sixth line and the eighth line of the image data before processing is corrected according to the image data of the seventh line to be deleted. In FIG. 13, for easier understanding, half the gradation data of the seventh line to be deleted is added to the sixth and eighth lines, respectively, and the sixth and eighth lines are continuously added. A method of deleting the seventh line is shown.

  That is, when the image data at the main scanning position of the seventh line in FIG. 13 is 0, the data is 0 even if it is 1/2, and 0 is added to the images of the sixth and eighth lines. The gradation data of the line and the 8th line are not corrected. Also, if the 7th line is F and both the 6th and 8th lines are F, 8 is added to the bits of the 6th and 8th lines, respectively. The 6th line and the 8th line are F, that is, the maximum value is taken as 4-bit gradation data, and cannot be added any more. However, if the 7th line is F and the 6th and 8th lines are 0, the data of 1/2 of the 7th line F is taken as 8 and added to the 6th and 8th lines. Therefore, the gradation data of the corresponding bits in the 6th and 8th lines is 8 respectively. Thus, the image data of the 6th and 8th lines are corrected, and then the 6th and 8th lines are transmitted as a continuous image, so that the image data of the 7th line is deleted and the image is 1400 of 2400 dpi. The image is shrunk in the sub-scanning direction for the line (about 10.5 μm) to adjust the positional deviation.

(Second Embodiment)
FIG. 18 is a cross-sectional view showing the overall configuration of the image forming apparatus according to the second embodiment, and shows a schematic configuration of an electrophotographic full-color printer having an image forming unit for each color.

  In the figure, 201 is a printer body, 202Y, 202M, 202C, and 202BK are photoconductors for four colors (yellow (Y), magenta (M), cyan (C), and black (BK)), 203Y, 203M, and 203C. , 203BK is a charger for each of the four color photoreceptors, 204Y, 204M, 204C and 204BK are respective cleaners, 205Y, 205M, 205C and 205BK are respective laser scanning units, and 206Y, 206M, 206C and 206BK are respective transfer units. Blades 207Y, 207M, 207C, and 207BK are developing units, 208 is an intermediate transfer belt, 210 and 211 are rollers that support the intermediate transfer belt 208, and 212 is a cleaner for the intermediate transfer belt 208.

  213 is a manual feed tray storing recording paper S, 214 and 215 are pickup rollers thereof, 216 is a registration roller, 217 is a paper feed cassette storing recording paper S, 218 and 219 are pickup rollers thereof, 220 is a vertical pass roller, and 221 is A rotation roller, 222 is a secondary transfer roller, 223 is a fixing unit, 224 is a discharge roller, and 225 is a discharge tray.

  In the full-color printer having the above-described configuration, electrostatic latent images are formed by the respective laser scanning units 205Y, 205M, 205C, and 205BK using a semiconductor laser as a light source on the photosensitive members 202Y, 202M, 202C, and 202BK of the respective colors. The electrostatic latent images are developed by the developing devices 207Y, 207M, 207C, and 207BK. The four color toner images developed on the surfaces of the photoreceptors 202Y, 202M, 202C, and 202BK are collectively transferred onto the recording sheet S by the secondary transfer roller 222 via the intermediate transfer belt 208 and the like. Then, the toner is welded to the recording paper S through a heat fixing device including a fixing unit 223, a paper discharge roller 224, and the like, and a permanent image is obtained.

  On the other hand, the recording paper S is fed from the paper feed cassette 217 or the manual feed tray 213 and conveyed to the secondary transfer roller 222 while taking registration timing by the registration roller 216. At that time, a sheet conveying unit as a conveying unit such as pickup rollers 218 and 219, a vertical path roller 220, a registration roller 216 for feeding paper from the paper feeding cassette 217, and pickup rollers 214 and 215 for feeding paper from the manual feed tray 213. Are driven by independent stepping motors in order to realize a high-speed and stable conveying operation. Reference numeral 31 denotes an image reading apparatus similar to that shown in FIG. The scanning resolution in the sub-scanning direction of the image forming apparatus of this embodiment is 2400 dpi.

  A procedure for correcting misalignment in the sub-scanning direction in the present embodiment will be described. Also in the present embodiment, the misalignment correction procedure is the same as that in the first embodiment. That is, the sequence described with reference to FIG. 5 is executed, the misregistration measurement chart of FIG. 2 is output, this chart is read by the image reading device 31, and the misregistration amount is measured. Are input to the sub-scanning position adjustment memory 305. The positional deviation amount here may be an absolute deviation amount of each color with respect to the ideal position on the recording paper S, or may be a relative deviation amount of other colors with respect to one reference color.

  Next, according to the positional deviation amount data of each color input to the sub-scanning position adjustment memory 305, the circuit of FIG. 3 provided for each color uses FIGS. 7, 8, and 9 described in the first embodiment. As shown in FIG. 10, one line of dummy image data is formed in the sub-scanning direction, and the image is locally stretched, or the image data for one line in the sub-scanning direction is deleted as shown in FIG. Or

  14 to 17 are diagrams for more easily explaining the effect of the positional deviation correction of the present invention in the image forming apparatus according to the present embodiment.

  FIG. 14 shows an example of misregistration in this embodiment, and shows misregistration amounts for two colors read by the image reading device 31 from the misregistration measurement chart of FIG. Since the four photoconductors rotate in phase with each other as a feature of this embodiment, as shown in FIG. 14, the amplitude of misregistration varies depending on the rotational eccentricity of the photoconductors of the respective colors. . Here, in order to simplify the description, it is assumed that the writing positions of the respective colors coincide. In addition, the photoconductor is rotated by two revolutions to form the misregistration measurement chart of FIG. 2, and the misregistration for two revolutions of the photoconductor can be measured. At this time, the maximum positional shift amount between the first color and the second color is indicated by L1, and there is a positional shift of about 50 μm.

  FIG. 15 shows a method of correcting misalignment in the first color of FIG. In the waveform of the transition of the measured displacement amount indicated by the solid line, the displacement amount from the ideal position is generated at an amount corresponding to one line (about 10.5 um) of the resolution in the sub-scanning direction. The image is adjusted by inserting or deleting one line. Points shown as +1 and -1 in the figure are a 1-line insertion point and a 1-line deletion point of the image, respectively.

  FIG. 16 shows a method of correcting misalignment in the second color, as in FIG.

  FIG. 17 is a result of correcting the positional deviation of the first color and the positional deviation of the second color by the method described with reference to FIGS. 15 and 16, and is a waveform of the transition of each positional deviation amount. This makes it possible to correct the positional deviation to twice the exposure resolution in the sub-scanning direction, that is, 2400 dpi × 2 = 10.5 μm × 2 = 21 μm or less.

(Third embodiment)
In the second embodiment described above, an example in which the present invention is applied to an image forming apparatus that forms an image on a photoconductor of each color by a laser scanning optical system provided for each color has been described. An example in which the present invention is applied to an image forming apparatus having a laser scanning optical system that scans four laser beams shown in FIG. 19 with one polygon mirror and exposes four photosensitive members will be described. In FIG. 19, reference numeral 233 denotes a polygon mirror, and 230, 231 and 232 denote mirrors for guiding a laser beam to the photosensitive member 202 of each color.

  Adjustment of the image position in the sub-scanning direction in the laser scanning type image forming apparatus can be realized by electrically controlling the emission timing of the laser beam. However, since the formation of the electrostatic latent image can be started only when the polygon mirror 233 is at a predetermined angle, the recording position can be changed only in units corresponding to the resolution in the sub-scanning direction. . That is, in such a laser scanning optical system, unlike the image forming apparatus according to the second embodiment having a polygon mirror for each color independently, the writing start position accuracy does not exceed the resolution in the sub-scanning direction. For this reason, the drive unevenness of the photosensitive member 202 and the transfer belt 208 immediately leads to the positional deviation of the image. Therefore, this has been dealt with by using a circuit or a motor that does not generate drive unevenness or increasing the accuracy of the components. According to the present invention, even if there is such unevenness, the sub-scanning position of the image can be corrected. Therefore, even in the image forming apparatus according to the present embodiment, it is possible to increase the accuracy of the positional deviation. In addition, this technique is also effective in terms of cost.

(Fourth embodiment)
In the above embodiment, the example in which the present invention is applied to the electrophotographic full-color image forming apparatus has been described. However, the recording heads of 3 to 4 colors are reciprocally scanned in the main scanning direction of the recording paper, line by line, Alternatively, the present invention can be applied to a serial scan type full-color image forming apparatus that forms an image with a predetermined bandwidth, for example, an ink jet printer.

  FIG. 20 is a diagram illustrating a configuration example of the periphery of the recording head of the ink jet printer. In this method, during pixel recording, a recording head 52 that discharges Y (yellow), M (magenta), C (cyan), and K (black) inks arranged at a predetermined interval d in the main scanning direction performs main scanning. When the pixels are not recorded, the recording head 52 is returned and the recording paper 54 is conveyed by the recording width in the sub-scanning direction, thereby forming a color image by a predetermined bandwidth.

  The interval in the main scanning direction of the nozzle row of each color ink of the recording head 52 depends on the dimensional accuracy of the recording head 52, but by electrically adjusting the ejection timing of each nozzle row with respect to the reference color, a pixel unit, It is possible to adjust the image position in minute units. On the other hand, a deviation in the sub-scanning direction may occur depending on the dimensional accuracy of the recording head 52. When the recording head positions of the respective colors are shifted in the sub-scanning direction, the sub-scanning is caused by speed unevenness when the recording paper 54 is conveyed in the sub-scanning direction even if the accuracy of the recording head is adjusted. Misalignment occurs in the direction.

  In the present invention, it is possible to cope with the positional deviation of the image in the sub-scanning direction that occurs when the recording paper is conveyed. First, the misalignment measurement chart as shown in FIG. 2 is output as in the above-described embodiment. The chart is read by an image reading device (not shown) and the amount of positional deviation is measured. By inputting the data to the circuit shown in FIG. 3 in the ink head, the positional deviation generated in the sub-scanning direction of the image is corrected. Note that reference numeral 53 in FIG. 20 denotes a drive pulley for scanning the recording head 52 in the main scanning direction.

(Fifth embodiment)
FIG. 21 shows an image forming apparatus that does not have the image reading device 31 as compared with the image forming apparatus according to the first embodiment, and the rotating developer of the developing unit 13 has three colors Y, M, and C. The BK developing device is a fixed developing unit 14 that is fixed in contact with the photosensitive member 1 at all times. The black fixed developing unit 14 is configured such that the developing roller is always in contact with the photosensitive member 1, and the high-voltage bias of the black fixed developing unit 14 is prevented so that the black toner is not developed when developing each color other than black. To control. During black development, the black toner is developed by switching to a high-voltage bias that develops the toner. Further, the developing device according to the present embodiment is provided with a misregistration detection sensor 65 as misregistration detection means for reading a misregistration patch image for measuring the misregistration formed on the intermediate transfer belt 2. Yes.

  FIG. 25 is a diagram showing an example of the configuration of the intermediate transfer belt 2 of the present embodiment. 2 is an intermediate transfer belt, 36 is a reflection type sensor for detecting the position of the intermediate transfer belt 2, 66 is a position shift patch image for measuring the position shift formed on the intermediate transfer belt 2, and 65 is a position shift patch image. Reference numeral 66 denotes a positional deviation detection sensor for measuring the positional deviation amount. As the misregistration detection sensor 65, a light reflection type sensor is used in this embodiment.

  The image writing position of each color is performed at the timing when the mark 41 on the intermediate transfer belt 2 is detected by the reflective sensor 36. In the present embodiment, the misregistration patch image 66 is formed outside the image area of the intermediate transfer belt 2 during normal image formation and the misregistration detection sensor 65 is not subject to the misregistration correction sequence of FIG. 66 is read and misalignment data is input to the sub-scanning position adjustment memory 305 of FIG. The positional deviation patch image 66 is cleaned each time an image of each color is formed by the cleaner 22 of the intermediate transfer belt after the positional deviation amount is read by the positional deviation detection sensor 65.

  If the cleaner 22 is always in contact outside the image area and cleans the toner image outside the image area, the misregistration patch image 66 reduces the amount of misregistration of one color while one full-color image is formed. It is possible to measure. Further, if the cleaner 22 is configured to contact and clean the toner on the intermediate transfer belt 2 after being transferred to the recording medium, and to clean the toner image outside the image area at that time, the misregistration patch image is one full color. While the image is formed, it is possible to measure the amount of misregistration of each color.

  FIG. 26 shows an image forming method for the misregistration patch image 66 and a method for measuring the misalignment between the image formation timing (= ideal image position) and the detected misregistration patch image 66.

  First, with respect to the image formation timing of the misregistration patch image 66, the mark 41 provided on the intermediate transfer belt in FIG. 25 is detected by the reflective sensor 36 as in the case of normal full-color image formation, and the detection signal It starts at the time of rising or with reference to the rising. FIG. 26 shows an example when the rising edge of the detection signal is used as a reference for writing. Image formation of the misaligned patch image 66 is started after a predetermined number of lines of sub-scanning determined in advance from the detection signal.

  As in FIG. 2, the misaligned patch image 66 is scanned with a laser beam on the photoconductor 1 so as to have stripes in the sub-scanning direction with a predetermined interval, and electrostatic latent images of a plurality of lines. Formed as. The drawn electrostatic latent image is developed by a developing device of a color to be measured and transferred to the intermediate transfer belt 2. The misregistration patch image 66 reproduces, as an image, an image misregistration generated due to the rotation unevenness of the exposed photoreceptor 1 and the rotation unevenness of the intermediate transfer belt 2 on the intermediate transfer belt 2. The ideal position of the misregistration patch image 66 measured by the misregistration detection sensor 65 is detected after elapse of a predetermined time from the detection signal (= image writing reference signal) of the mark 41, as shown in FIG. (Ra, Rb, Rc, Rd, Re, Rf, Rg, Rh).

  One example of a signal actually measured by the displacement detection sensor 65 is represented by the displacement detection sensor signal of FIG. The positional deviations Ta, Tb, Tc, Td, Te, Tf, Tg, Th of the positional deviation detection sensor signal with respect to the ideal position are positional deviations. For example, if the rotation speed of the intermediate transfer belt 2 is 300 mm / sec and Ta is 50 μsec, it means that a deviation of 15 μm occurs. 3 is input to the sub-scanning position adjustment memory 305, and the position of the image is adjusted by inserting and deleting one line in the sub-scanning direction of the image described in the first embodiment.

  FIG. 22 is an example of misalignment data found in an image forming apparatus that forms an image with a single photoconductor of the first and fifth embodiments, and a reference for correcting relative misalignment. Color misregistration data and second color misregistration data to be corrected with respect to the reference color. Here, the maximum positional shift amount with respect to the reference color is expressed as L2, and a shift of about 21 μm occurs.

  FIG. 23 shows the amount of positional deviation between the reference color and the second color when the writing start timing of the reference color is corrected. The method of adjusting the image writing timing and correcting the writing positions of the respective colors in this way is one of the conventional misalignment correction methods. However, in this case, the amount of misregistration with respect to the reference color in the vicinity of 200 mm is larger than before adjustment of the reference color writing timing.

  FIG. 24 is a graph showing the amount of misregistration as a result of applying the image misregistration correction method for inserting or deleting image data in the sub-scanning direction of the image according to the present invention for the second color. . Here, when the amount of displacement of the second color with respect to the reference color exceeds 2400 dpi (= 10.5 um), which is the scanning resolution of exposure in the sub-scanning direction, the sub-scan image of the second color image data. Is locally increased by 1 line or decreased by 1 line so that the positional deviation is ± 10.5 μm or less with respect to the reference color. In FIG. 24, the portions indicated by −1 and +1 are correction points for the second color.

  According to the present invention, not only a color image but also a single-color image forming apparatus, image position correction in the sub-scanning direction and image expansion / contraction correction can be easily performed by inserting and deleting image data in the sub-scanning direction. Needless to say, it can be performed with high accuracy.

  In the present invention, since an image is actually formed to obtain a pattern, the rotation irregularity of the photosensitive drum, the rotation irregularity of the intermediate transfer member, the shock caused by the attachment / detachment of the cleaning device for cleaning the toner on the intermediate transfer member, and the intermediate transfer member A pattern affected by the displacement caused by the impact of the transfer roller attachment / detachment shock when the upper toner image is transferred to the recording medium is obtained, and the displacement is corrected based on the pattern. Corrections can be made even for those that cannot be corrected by control alone. Accordingly, it is possible to provide an image forming apparatus and an image adjustment method capable of always forming a clear image.

Sectional drawing which shows the principal part structure of the image forming apparatus which concerns on the 1st Embodiment of this invention. Chart for measuring misalignment Block diagram of image correction circuit system configuration for correcting image misalignment Diagram showing misalignment adjustment data for a certain color The figure which shows the sequence for measuring the position gap of the image The figure which shows the image data before a position shift correction process is performed The figure which shows one example which inserts the dummy image for 1 line The figure which shows one example which inserts the dummy image for 1 line The figure which shows one example which inserts the dummy image for 1 line The figure which shows one example which deletes 1 line of the 7th sub-scanning line The figure which shows the one part gradation data of the image data before a positional offset correction process is performed. Diagram showing how to create a dummy image The figure which shows the deletion method of the image data for 1 line The figure which shows the example of the position shift in 2nd Embodiment. The figure which shows the method of the positional offset correction in a 1st color. The figure which shows the method of the positional offset correction in a 2nd color. The figure which shows the transition waveform of the positional offset amount as a result of correct | amending the positional offset of the 1st and 2nd color. Sectional drawing which shows the whole structure of the image forming apparatus which concerns on 2nd Embodiment. FIG. 9 is a perspective view illustrating a main part configuration of an image forming apparatus according to a third embodiment. The perspective view which shows the structure of the recording head periphery part of the inkjet printer which concerns on 4th Embodiment. Sectional drawing which shows the main structures of the image forming apparatus which concerns on 5th Embodiment FIG. 10 is a diagram showing misregistration data found in the image forming apparatuses according to the first and fifth embodiments. The figure which shows the amount of position shifts of the reference color and the second color when the writing start timing of the reference color is corrected The figure which shows the position shift amount of the result of having corrected position shift with respect to the 2nd color. FIG. 9 is a perspective view illustrating a configuration of an intermediate transfer belt of an image forming apparatus according to a fifth embodiment. The figure which shows the amount of position shifts between the image formation timing and the position shift patch image measured by the position shift detection sensor using the rising edge of the detection signal of the reflection type sensor as a reference.

Explanation of symbols

301 FIFO
302 Sub-scanning image position adjustment block (corresponding to misalignment adjusting means)
303 Image processing block 304 Sub-scanning line counter 305 Sub-scanning position adjustment memory (corresponding to storage means)

Claims (14)

Conveying means for conveying the recording medium;
In an image forming apparatus having image forming means for forming an image on the recording medium transported by the transporting means,
An image formation characterized in that the image position of the image in the recording medium conveyance direction is adjusted by locally increasing or decreasing the number of image data lines in the recording medium conveyance direction of the image formed by the image forming means. apparatus. The image forming means is
A misregistration detection means for detecting misregistration of the image in the recording medium conveyance direction;
Storage means for storing a positional deviation amount detected by the positional deviation detection means;
A displacement adjustment means for adjusting the displacement;
The positional deviation adjusting means detects the number of image data lines in the recording medium conveyance direction of the image formed by the image forming means based on the positional deviation information detected by the positional deviation detection means and stored in the storage means. The image forming apparatus according to claim 1, wherein the image forming apparatus is locally increased or decreased.   The misregistration detecting means detects misregistration of the image in the recording medium conveyance direction by measuring an image expansion / contraction amount in a local portion of an image repeatedly and continuously formed in the recording medium conveyance direction formed on the recording medium. The image forming apparatus according to claim 2. The image forming means is
An intermediate transfer body for transferring and holding the image formed by the image forming means;
The misregistration detection means detects the misregistration of the image in the recording medium conveyance direction by measuring the amount of image expansion and contraction in a local portion of the image continuously repeated in the recording medium conveyance direction formed on the intermediate transfer member. The image forming apparatus according to claim 2. The image forming means is
Having image reading means for reading image data of a document;
The image forming apparatus according to claim 2, wherein the displacement detection unit is the image reading unit.   A predetermined pattern image for detecting a positional deviation of the image in the recording medium conveyance direction is formed, and the positional deviation detection unit measures the pattern image to thereby determine the positional deviation of the image in the recording medium conveyance direction. The image forming apparatus according to claim 2, wherein the image forming apparatus is detected.   The image forming apparatus according to claim 2, wherein the misregistration detection unit uses a light reflection type sensor.   The position deviation adjusting unit locally increases or decreases the number of image data lines in the recording medium conveyance direction of an image formed by the image forming unit by inserting or deleting image data lines. The image forming apparatus according to any one of 2 to 7.   9. The image forming apparatus according to claim 2, wherein the image data line to be inserted is image data one line before the insertion position.   9. The image forming apparatus according to claim 2, wherein the image data line to be inserted is image data one line after the insertion position.   9. The image forming apparatus according to claim 2, wherein the image data line to be inserted is determined by image data one line before the insertion position and image data after one line. .   When deleting the image data lines in order that the misregistration adjusting means locally reduces the number of image data lines in the recording medium conveyance direction of the image, the image data lines to be deleted are one line before and one line after The image forming apparatus according to claim 2, wherein density addition data determined based on image data of the image data line to be deleted is added to the image data. The image forming means forms a plurality of color images respectively, and transfers the plurality of color images so as to overlap to form a color image on a recording medium,
13. The image forming apparatus according to claim 2, wherein the misregistration detection unit detects a relative misregistration of an image of another color with respect to an image of a reference color. . An image adjustment method for an image formed by an image forming apparatus, comprising: a conveying unit that conveys a recording medium; and an image forming unit that forms an image on the recording medium conveyed by the conveying unit,
Adjusting the image position of the image in the recording medium conveyance direction by locally increasing or decreasing the number of image data lines in the conveyance direction of the recording medium of the image formed by the image forming means. Image adjustment method.