JP5145189B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus using electrophotography, and more particularly to a method for correcting the density of an output image in a tandem color image forming apparatus.

  In a color image forming apparatus using an electrophotographic process, when a mode for appropriately setting image density and registration (hereinafter referred to as a calibration mode) is set, it is directly applied on a toner carrier (print medium). The toner is transferred to form a patch image (reference image), and the toner amount and the deviation amount from the reference position are detected to correct the density and color deviation. For example, in the case of a tandem type full-color image forming apparatus, a magenta, cyan, yellow, and black image forming unit forms a reference image for correcting each color on a conveyance belt or an intermediate transfer belt, and the density and position of the reference image are detected by a detection unit. Is detected and density and color misregistration correction is performed.

  In recent years, the demand for higher image quality has increased, and improvements in technology that corrects changes in image density (density correction) and correction of misregistration between colors (color misregistration correction), which cause color changes, have been improved. Therefore, it is essential to perform these corrections with high accuracy. Therefore, a method for performing such correction with higher accuracy has been proposed.

  For example, Patent Document 1 discloses a first light receiving device that receives a P wave component of light emitted from a light emitting unit and reflected by a toner pattern (reference image) and an image carrier through a first polarizing filter; A second light-receiving device that transmits the S-wave component perpendicular to the P-wave component through the second polarizing filter and receives light, and the detection output of the light-receiving device that has entered first among the first and second light-receiving devices. By providing a delay unit that delays the time and a calculation unit that calculates the difference between detection outputs caused by the delay as toner reflected light information, the time difference in detection by the two light receiving devices due to the installation interval is eliminated, and the color shift A method for more accurately detecting the amount is disclosed.

In Patent Document 2, a resiston pattern is formed on the intermediate transfer member for each color in a predetermined color order with black as the last, and the positional deviation of the resister pattern and the density of the toner image are detected by the same detection means. By performing density correction based on the density detection result in a state in which the position shift of the resister pattern is corrected based on the detection result of the position shift, it is possible to efficiently detect the position shift and density while avoiding an increase in size and cost of the apparatus. A well-implemented method is disclosed. In Patent Document 2, in order to improve detection accuracy, black toner is printed using color toner as a base.
JP 2005-134778 A JP 2007-140570 A

  However, in the method of Patent Document 1, the installation interval of the light receiving devices is corrected using only the same reference image. Therefore, in the first light receiving device that receives the same polarization component (P wave component) as that of the light emitting unit, when the surface roughness of the print medium such as the intermediate transfer belt becomes equal to the surface roughness of the color reference image, the print medium Since the detection amount of the light receiving element is equal to that of the reference image and the peak of the light receiving device with respect to the reference image disappears, the detection becomes difficult. Further, the surface roughness of the print medium deteriorates and increases each time printing is performed due to contact with other members such as paper.

  Further, in the second light receiving device that receives the polarization component (S wave component) in the vertical direction with respect to the light emitting unit, the output of the black reference image is weak, and the center of gravity of the detection signal of the light receiving device can be accurately grasped. It becomes difficult. Further, although a correction method according to the installation interval between the two light receiving elements is disclosed, a method for detecting the installation interval and its installation error is not disclosed. In addition, although there are a component parallel to the scanning direction of the light beam and a component perpendicular to the scanning direction of the light beam, the detailed correction method for each component is not disclosed.

  Further, in the method of Patent Document 2, color toner is used as a background only for detecting black toner, but there is no disclosure regarding a decrease in accuracy of color misregistration correction due to an installation error of the light receiving device. In the first place, accuracy is not considered.

  In view of the above problems, an object of the present invention is to provide a tandem color image forming apparatus that can detect an installation error of a light receiving unit of a detection unit and can correct the installation error.

In order to achieve the above object, the present invention comprises an image carrier, an exposure device, and a developing device, and a plurality of image forming units for forming images of a plurality of colors including black, and developed on the image carrier. An intermediate transfer belt on which the toner images are sequentially laminated, a transfer means for laminating the toner image developed on the image carrier on the intermediate transfer belt, and a toner image laminated on the intermediate transfer belt. Secondary transfer means for transferring onto a medium at a time, and detection means for detecting a reference image for color misregistration detection formed on at least one of the image carrier, the intermediate transfer belt, and the recording medium, In the image forming apparatus that performs color misregistration correction based on the detection result of the detection unit, the detection unit includes a light emitting unit that irradiates the print medium and a scanning direction of the image carrier among reflected light from the print medium. parallel A first light receiving portion capable of receiving a first reflected light of polarization, and a second light receiving unit that can receive a second reflected light of the scanning direction perpendicular polarization, which has a first and An installation error detection reference image for detecting an installation error of the second light receiving unit can be detected, and the installation error detection reference image includes two color images selected from the plurality of color images, The two color images are alternately arranged adjacent to each other.

The present invention also includes an image carrier, an exposure device, and a developing device, a plurality of image forming units for forming images of a plurality of colors including black, a transport belt that transports a recording medium to the image forming unit, Color transfer detection formed on at least one of the image carrier, the conveyance belt, and the recording medium, and a transfer unit that transfers the toner image developed on the image carrier onto the recording medium or the conveyance belt. An image forming apparatus that performs color misregistration correction based on a detection result of the detection unit. The detection unit includes: a light emitting unit that irradiates the print medium; and the print medium. A first light receiving unit capable of receiving a first reflected light polarized parallel to the scanning direction of the image carrier, and a second reflected light polarized perpendicular to the scanning direction. A second light receiving portion; In addition, it is possible to detect an installation error detection reference image for detecting an installation error of the first and second light receiving units, and the installation error detection reference image is selected from the images of the plurality of colors. Including two-color images, the two-color images are alternately arranged adjacent to each other.

  Further, according to the present invention, the reference image for detecting the installation error is based on a first color image of the two color images, and a second color image is superimposed on the first color image. It is characterized by being formed.

  According to the present invention, the first or second color image is a black image.

  In the invention, it is preferable that the installation error detection reference image includes at least a first installation error reference image in which a boundary between the first and second color images is arranged in a direction perpendicular to the scanning direction. It is said.

  In the present invention, the installation error detection reference image is arranged such that a boundary between the first installation error detection reference image and the first and second color images is inclined at a predetermined angle with respect to the scanning direction. And a second reference image for installation error detection.

  In the invention, it is preferable that the predetermined angle is approximately 45 °.

  Further, the present invention is characterized in that the installation error is corrected based on a detection result for the installation error detection reference image by the first and second light receiving units.

  Further, the present invention is characterized in that the installation error in the scanning direction is corrected based on a detection result of the first installation error detection reference image by the first and second light receiving units.

  Further, the present invention corrects the installation error in the scanning direction based on a detection result of the first installation error detection reference image by the first and second light receiving units, and detects the first and second installation error. The installation error in a direction perpendicular to the scanning direction is corrected based on the detection result of the reference image for use.

  Further, the present invention is characterized in that the installation error is corrected based on a difference in detection time of the installation error detection reference image by the first and second light receiving units.

  Further, the present invention is characterized in that the color misregistration correction is performed after the installation error is corrected.

  According to the first configuration of the present invention, the detection means includes a light emitting unit, a first light receiving unit capable of receiving the first reflected light, and a second light receiving unit capable of receiving the second reflected light. In addition, the installation error detection reference image for detecting the installation error of the first and second light receiving units includes two color images selected from a plurality of color images including black, By assuming that the images are alternately arranged adjacent to each other, it is possible to calculate the installation error based on the difference between the detection results of the two color images by the first and second light receiving units, and to correct the installation error. Therefore, highly accurate color misregistration correction can be performed without being affected by installation errors.

  According to the second configuration of the present invention, the detecting means includes a light emitting unit, a first light receiving unit capable of receiving the first reflected light, and a second light receiving unit capable of receiving the second reflected light. A reference image for installation error detection for detecting installation errors of the first and second light receiving units, including two-color images selected from a plurality of color images including black. By assuming that the color images are alternately arranged adjacent to each other, it is possible to grasp the installation error based on the difference between the detection results of the two color images by the first and second light receiving units and to correct the installation error. Become. Therefore, highly accurate color misregistration correction can be performed without being affected by installation errors.

  Further, according to the third configuration of the present invention, in the image forming apparatuses having the first and second configurations, the installation error detection reference image is the base color image of the first color of the two color images. By forming the second color image on the first color image, the installation error detection reference image can be easily created without complicated settings.

  According to the fourth configuration of the present invention, in the image forming apparatus having any one of the first to third configurations, the first or second color image is changed to a black image. Since the reflectance of light is greatly different from that of the other color, it is possible to more easily and accurately detect the installation error in the first and second light receiving units. In addition, even if the surface roughness of the print medium deteriorates due to printing, installation errors can be detected with high accuracy.

  According to the fifth configuration of the invention, in the image forming apparatus having any one of the first to fourth configurations, the installation error detection reference image has a boundary between the first and second color images. By having at least the first installation error reference image arranged in the direction perpendicular to the scanning direction, it is possible to detect the installation error in the scanning direction with a simple configuration. This makes it possible to more effectively correct the installation error in the scanning direction.

  According to the sixth configuration of the present invention, in the image forming apparatus having the fifth configuration, the installation error detection reference image includes the first installation error detection reference image and the first and second colors. And a second installation error detection reference image that is arranged at a predetermined angle with respect to the scanning direction, so that the second installation error detection reference image in the scanning direction is provided by the first installation error group detection reference image. The error detection reference image can detect an installation error in a direction perpendicular to the scanning direction. This makes it possible to correct the installation error in more detail.

  According to the seventh configuration of the invention, in the image forming apparatus having the sixth configuration, the predetermined angle is set to approximately 45 °, so that the scanning direction in the detection result of the second installation error detection reference image is obtained. Since the vertical installation error and the scanning direction can be made equal to each other, the vertical installation error can be detected more easily.

  According to the eighth configuration of the present invention, in the image forming apparatus having any one of the first to fourth configurations, based on the detection result for the reference image for installation error detection by the first and second light receiving units. Since the installation error can be eliminated by correcting the installation error, it is possible to perform highly accurate color misregistration correction without being affected by the installation error.

  According to the ninth configuration of the present invention, in the image forming apparatus having the fifth configuration, based on the detection result of the first setting error detection reference image by the first and second light receiving units, By correcting the installation error, the installation error can be detected with higher accuracy, and the installation error can be resolved more reliably.

  According to the tenth configuration of the present invention, in the image forming apparatus having the sixth or seventh configuration, based on the detection result of the first installation error detection reference image by the first and second light receiving units, By correcting the installation error in the scanning direction and correcting the installation error in the direction perpendicular to the scanning direction based on the detection results of the first and second installation error detection reference images, the installation error can be detected with higher accuracy. Installation errors can be reliably eliminated.

  According to the eleventh configuration of the present invention, in the image forming apparatus having any one of the eighth to tenth configurations, a difference in detection time of the reference image for installation error detection by the first and second light receiving units. Based on the above, by correcting the installation error, the installation error can be detected more easily and the installation error can be eliminated more easily.

  According to the twelfth configuration of the present invention, in the image forming apparatus having any one of the eighth to eleventh configurations, after the installation error is corrected, the color misregistration correction is performed, whereby the installation error is reduced. Since color misregistration correction can be performed without being affected, color misregistration correction can be performed with high accuracy.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram showing the configuration of a tandem color image forming apparatus according to the first embodiment of the present invention. In the main body of the image forming apparatus 100, four image forming portions Pa, Pb, Pc, and Pd are sequentially arranged from the upstream side in the transport direction (the right side in FIG. 1). These image forming portions Pa to Pd are provided corresponding to images of four different colors (black, magenta, cyan, and yellow), and black, magenta, and cyan are respectively obtained by charging, exposure, development, and transfer processes. And yellow images are sequentially formed.

  Photosensitive drums 1a, 1b, 1c, and 1d that carry visible images (toner images) of the respective colors are disposed in the image forming portions Pa to Pd, and are formed on the photosensitive drums 1a to 1d. The toner images thus transferred are sequentially transferred (primary transfer) onto an intermediate transfer belt (print medium) 8 that moves adjacent to each image forming portion while rotating clockwise in FIG. 1 by a driving means (not shown). After that, the image is transferred (secondary transfer) onto the paper (recording medium, print medium) P at a time by the secondary transfer roller 9, and further fixed on the paper P by the fixing unit 7, and then discharged from the apparatus main body. It is the composition which becomes. An image forming process for each of the photosensitive drums 1a to 1d is executed while rotating the photosensitive drums 1a to 1d counterclockwise in FIG.

  The paper P onto which the toner image is transferred is housed in a paper cassette 16 at the lower part of the apparatus, and is conveyed to the secondary transfer roller 9 via the paper feed roller 12a and the registration roller pair 12b. A sheet made of a dielectric resin is used for the intermediate transfer belt 8, and a belt in which both ends thereof are overlapped and joined to form an endless shape, or a belt without a seam (seamless) is used. Further, a cleaning blade 19 for removing toner remaining on the surface of the intermediate transfer belt 8 is disposed on the downstream side of the secondary transfer roller 9.

  Next, the image forming units Pa to Pd will be described. There are chargers 2a, 2b, 2c, and 2d for charging the photosensitive drums 1a to 1d and image information on the photosensitive drums 1a to 1d around and below the photosensitive drums 1a to 1d that are rotatably arranged. An exposure unit 4 for exposing the photosensitive drums 1a to 1d, developing units (developing devices) 3a, 3b, 3c and 3d for forming toner images on the photosensitive drums 1a to 1d, and a developer (toner) remaining on the photosensitive drums 1a to 1d. Cleaning portions 5a, 5b, 5c and 5d are provided. Details of the developing devices 3a to 3d will be described later.

  When the image formation start is input by the user, first, the surfaces of the photosensitive drums 1a to 1d are uniformly charged by the chargers 2a to 2d, and then light is irradiated by the exposure unit 4 to each of the photosensitive drums 1a to 1d. An electrostatic latent image corresponding to the image signal is formed on the top. Each of the developing units 3a to 3d includes a developing roller (developer carrying member) disposed opposite to the photosensitive drums 1a to 1d, and toners of black, magenta, cyan, and yellow are respectively supplied by a replenishing device (not shown). A predetermined amount is filled. This toner is supplied onto the photosensitive drums 1a to 1d by the developing rollers of the developing units 3a to 3d, and electrostatically adheres to the electrostatic latent image formed by exposure from the exposure unit 4. A toner image is formed.

  After an electric field is applied to the intermediate transfer belt 8 at a predetermined transfer voltage, black, magenta, cyan and yellow toner images on the photosensitive drums 1a to 1d are transferred onto the intermediate transfer belt 8 by the transfer rollers 6a to 6d. Primary transcription. These four color images are formed with a predetermined positional relationship predetermined for forming a predetermined full-color image. Thereafter, the toner remaining on the surfaces of the photosensitive drums 1a to 1d is removed by the cleaning units 5a to 5d in preparation for the subsequent formation of a new electrostatic latent image.

  The intermediate transfer belt 8 is stretched over a driven roller 10, a drive roller 11, and a tension roller 20, and the intermediate transfer belt 8 starts to rotate clockwise as the drive roller 11 is rotated by a drive motor (not shown). Then, the sheet P is conveyed from the registration roller 12b to the secondary transfer roller 9 provided adjacent to the intermediate transfer belt 8 at a predetermined timing, and the sheet P is conveyed at a nip portion (secondary transfer nip portion) with the intermediate transfer belt 8. A full color image is secondarily transferred onto P. The paper P on which the toner image is transferred is conveyed to the fixing unit 7.

  The sheet P conveyed to the fixing unit 7 is heated and pressurized when passing through the nip portion (fixing nip portion) of the pair of fixing rollers 13 to fix the toner image on the surface of the sheet P, and a predetermined full-color image is formed. It is formed. The paper P on which the full-color image is formed is distributed in the transport direction by the branching section 14 that branches in a plurality of directions. When an image is formed on only one side of the paper P, it is discharged as it is onto the discharge tray 17 by the discharge roller 15.

  On the other hand, when forming images on both sides of the paper P, a part of the paper P that has passed through the fixing unit 7 is once projected from the discharge roller 15 to the outside of the apparatus. Thereafter, the paper P is distributed to the paper transport path 18 by the branching section 14 by rotating the discharge roller 15 in the reverse direction, and is transported again to the secondary transfer roller 9 with the image surface reversed. Then, after the next image formed on the intermediate transfer belt 8 is transferred to the surface of the paper P on which the image is not formed by the secondary transfer roller 9 and conveyed to the fixing unit 7 to fix the toner image, It is discharged to the discharge tray 17.

  2A is a side cross-sectional view showing the arrangement of detection sensors around the intermediate transfer belt of the image forming apparatus of the present embodiment, and FIG. 2B is a cross-sectional view around the detection sensors shown in FIG. It is the elements on larger scale seen in the direction. Portions common to FIG. 1 are denoted by the same reference numerals and description thereof is omitted. In FIG. 2A, the chargers 2a to 2d and the cleaning units 5a to 5d are not shown.

  In the width direction of the intermediate transfer belt 8 on the downstream side of the photosensitive drum 1d disposed on the most downstream side in the traveling direction of the intermediate transfer belt 8 and on the upstream side of the secondary transfer roller 9 (left and right in FIG. 2B). A detection sensor (detection means) 21 for detecting the toner density and color misregistration of the patch image (reference image) is disposed at a predetermined interval in the direction). FIG. 3 is a schematic diagram illustrating a configuration of a detection sensor used in the image forming apparatus of the present embodiment.

  As shown in FIG. 3, the detection sensor 21 includes an optical sensor, and a light emitting unit 22 that irradiates the intermediate transfer belt 8, and a first light receiving unit (first light receiving unit) 23 that receives reflected light from the intermediate transfer belt 8. , A second light receiving unit (second light receiving unit) 24, and a beam splitter 25. The light emitting unit 22 includes a light emitting element 22a made of an LED or the like disposed at an angle inclined by a predetermined amount with respect to the surface of the intermediate transfer belt 8, and P of the light emitted from the light emitting element 22 parallel to the scanning direction. A first polarizing filter 22b that transmits only the wave component, and only P-polarized measurement light is incident on the intermediate transfer belt 8 from the light emitting element 22.

  A beam splitter 25 is disposed between the intermediate transfer belt 8 and the first and second light receiving portions 23 and 24. The beam splitter 25 is for separating the reflected light reflected from the intermediate transfer belt 8 into reflected light toward the first light receiving unit 23 and reflected light toward the second light receiving unit 24.

  The first light receiving unit 23 includes a first light receiving element 23 a made of a photodiode that receives reflected light from the intermediate transfer belt 8, and a second polarized light disposed between the first light receiving element 23 a and the beam splitter 25. And a filter 23b. The second polarizing filter 23b is for transmitting the P wave component parallel to the scanning direction out of the reflected light separated by the beam splitter 25. Thus, the first light receiving element 23a receives only the P wave component of the reflected light.

  The second light receiving unit 24 includes a second light receiving element 24 a made of a photodiode or the like that receives reflected light from the intermediate transfer belt 8, and a third polarized light disposed between the second light receiving element 24 a and the beam splitter 25. And a filter 24b. The third polarizing filter 24b is for transmitting the S wave component perpendicular to the scanning direction out of the reflected light separated by the beam splitter 25. Thus, the second light receiving element 23a receives only the S wave component of the reflected light.

  With this configuration, the measurement light composed of the P wave component emitted from the light emitting unit 22 is reflected by the intermediate transfer belt 8, the reflected light is separated by the beam splitter 25, and the first light receiving unit 23 performs the P wave component of the reflected light. , And the second light receiving unit 24 can receive the S wave component.

  Further, the first light receiving element 23a can detect the P wave component of the reflected light from the intermediate transfer belt 8 and the P wave component of the reflected light from the black image. Here, since the black image absorbs light more than the intermediate transfer belt 8, the reflectance of the black image with respect to the measurement light is smaller than the reflectance of the intermediate transfer belt 8. Therefore, the sensor output of the first light receiving element 23 a can be expressed as a decrease in the P wave component of the black image with respect to the P wave component of the intermediate transfer belt 8. Thereby, a black image can be detected using the first light receiving element 23a.

  The second light receiving element 24a can detect the S wave component of the reflected light from the intermediate transfer belt 8 and the S wave component of the reflected light from the cyan, magenta, or yellow color image. Here, since the color image reflects light more than the intermediate transfer belt 8, the reflectance of the color image with respect to the measurement light is larger than the reflectance of the intermediate transfer belt 8. Therefore, the sensor output of the second light receiving element 24 a can be expressed as an increase in the S wave component of the color image with respect to the S wave component of the intermediate transfer belt 8. Thereby, a color image can be detected using the second light receiving element 24.

  When the toner density on the intermediate transfer belt 8 is measured, the measurement light is irradiated from the light emitting unit 22 to, for example, a square density correction patch image (not shown) formed on the intermediate transfer belt 8. The measurement light is reflected by the intermediate transfer belt 8 and the toner, and the P wave component of the reflected light from the intermediate transfer belt 8 and the toner is received by the first light receiving unit 23 and the S wave component is received by the second light receiving unit 24.

  When the toner adhesion amount is large, the reflected light from the belt surface is blocked by the toner, so that the light reception amounts of the first and second light receiving portions 23 and 24 are reduced. On the other hand, when the amount of toner attached is small, the amount of reflected light from the belt surface increases, resulting in an increase in the amount of light received by the first and second light receiving portions 23 and 24. Therefore, by detecting the density of the density correction patch image for each color based on the output value of the received light signal based on the amount of reflected light received, and adjusting the development bias characteristic value and the like in comparison with a predetermined reference density, each color Density correction can be performed.

  Further, when measuring the amount of color misregistration on the intermediate transfer belt 8, measurement light is applied to a color misregistration patch image (not shown) formed on the intermediate transfer belt 8 and composed of, for example, diagonal lines and straight lines. , The first light receiving unit 23 detects the positional relationship between the P wave component of the reflected light from the belt surface and the P wave component of the reflected light from the black toner. Further, the second light receiving unit 24 detects the positional relationship between the S wave component of the reflected light from the belt surface and the S wave components of cyan, magenta, and yellow toner.

  The positional relationship detected for each color is compared with a predetermined reference position, and when the color shift in the main scanning direction is corrected, the exposure start position of the exposure unit 4 is adjusted, and the sub-scanning direction (the direction perpendicular to the scanning direction) is adjusted. In the case of correcting the color misregistration, the color misregistration correction can be performed for each color by adjusting the exposure start timing of the exposure unit 4.

  The detection sensor 21 may be disposed at another position where the patch image for density correction, the color misregistration correction and the patch image for installation error detection described later can be detected on the intermediate transfer belt 8, for example, secondary When arranged on the downstream side of the transfer roller 9, the time from when the reference image is transferred onto the intermediate transfer belt 8 until detection is increased, and further, these patch images come into contact with the secondary transfer roller 9. As a result, the surface state of these patch images may change. For this reason, it is preferable to dispose the image forming unit Pd in the vicinity of the most downstream side as shown in FIG. The detection sensor 21 transmits an output signal corresponding to the detection result to the control unit 32 described later.

  FIG. 4 is a block diagram illustrating a control path of the tandem color image forming apparatus according to the first embodiment. Portions common to FIGS. 1 to 3 are denoted by the same reference numerals and description thereof is omitted. The image forming apparatus 100 includes image forming units Pa to Pd, an image input unit 30, an AD conversion unit 31, a control unit 32, a storage unit 33, an operation panel 34, a fixing unit 7, an intermediate transfer belt 8, a detection sensor 21, and the like. It is a configuration.

  When the image forming apparatus 100 is a color copying machine, the image input unit 30 includes a scanning lamp mounted with a scanner lamp that illuminates the original during copying and a mirror that changes the optical path of reflected light from the original, and reflection from the original. 1 is an image reading unit that includes a condenser lens that collects light to form an image and a CCD that converts the formed image light into an electrical signal. In the case of a printer, the receiving unit receives image data transmitted from a personal computer or the like. The image signal input from the image input unit 30 is converted into a digital signal by the AD conversion unit 31 and then sent to the image memory 40 in the storage unit 33.

  The storage unit 33 includes an image memory 40, a RAM 41, and a ROM 42. The image memory 40 stores an image signal input from the image input unit 30 and digitally converted by the AD conversion unit 31, and is stored in the control unit 32. Send it out. The RAM 41 and the ROM 42 store a processing program, processing content, and the like of the control unit 32.

  The RAM 41 (or ROM 42) stores the relationship between the output value of the detection sensor 21 and the toner adhesion amount as toner adhesion amount data. The toner density, the charge amount, and the development bias determined from the toner adhesion amount are stored. A density correction table in which each parameter value used for density correction, such as a characteristic value or exposure amount, is stored in association with each other, a color shift amount of each color image, and an exposure start timing or exposure start position of the exposure unit 4. A color misregistration correction table stored in association with each other is stored.

  In addition, the RAM 41 (or ROM 42) associates the installation position error of the first and second light receiving units 23 and 24 with each parameter used for correction of the installation error such as the exposure timing of the exposure unit 4 or the exposure start position. The stored installation error correction table is stored.

  The parameter values used for density correction, color misregistration correction, and installation error correction may be calculated each time using the output value of the detection sensor 21 in the control unit 32, but in order to reduce the processing load on the control unit 32. In addition, it is preferable to store the data in the RAM 41 (or ROM 42) in advance as a table.

  The operation panel 34 includes an operation unit composed of a plurality of operation keys, and a display unit (none of which is shown) that displays setting conditions, the state of the apparatus, and the like, and the user sets printing conditions and the like. In addition, for example, when the image forming apparatus 100 has a facsimile function, it is also used for various settings such as registering a facsimile transmission destination in the storage unit 33 and reading or rewriting the registered transmission destination.

  The control unit 32 is, for example, a central processing unit (CPU), and according to a set program, the image input unit 30, the image forming units Pa to Pd, the fixing unit 7, and the sheet P from the sheet cassette 16 (see FIG. 1). In addition to overall control of conveyance and the like, the image signal input from the image input unit 30 is converted into image data by scaling processing or gradation processing as necessary. The exposure unit 4 irradiates a laser beam based on the processed image data, and forms latent images on the photosensitive drums 1a to 1d.

  Further, when the calibration mode or the like is set by a key operation or the like on the operation panel 34, the control unit 32 receives an output signal from the detection sensor 21 and stores toner adhesion amount data and color misregistration data stored in the storage unit 33. A function of calculating the toner adhesion amount and the color misregistration amount based on the toner image, determining the density of the reference image based on the calculated toner adhesion amount, and comparing the density of the image forming units Pa to Pd with a predetermined standard density. A function for performing density correction for each color by adjusting at least one of the image forming conditions, and color misregistration correction by adjusting the image forming timing of the image forming units Pa to Pd based on the calculated color misregistration amount. Has the function to perform. The calibration mode may be automatically set when the apparatus is turned on or when a predetermined number of image forming processes are completed.

  In addition, the control unit 32 receives an output signal from the detection sensor 21 when the installation error correction mode or the like is set by a key operation or the like on the operation panel 34, and is based on the installation error data stored in the storage unit 33. A function for calculating the installation error, and a function for correcting the installation error by adjusting the image formation timing of the image forming units Pa to Pd based on the calculated installation error amount.

  Next, installation error correction of this embodiment will be described. FIG. 5 is a diagram showing the output of the detection sensor with respect to the first installation error correction reference image, showing the sensor output when no installation error occurs, and FIG. 6 shows the installation error occurring. It is a figure which shows the sensor output in a case. Portions common to FIGS. 1 to 3 are denoted by common reference numerals and description thereof is omitted.

  As shown in FIG. 5, a substantially square first patch image (first installation error detection reference image) 45 is formed at a position of the intermediate transfer belt 8 facing the detection sensor 21 (see FIG. 2). . Note that the first patch images 45 are formed at positions facing the two detection sensors 21, respectively, but the two first patch images 45 have exactly the same configuration, and therefore, here, the first patch image 45 is one of the first patch images 45. Will be described.

The first patch image 45, two sides one opposing the other two opposite sides while being placed along an intermediate transfer belt 8 is disposed along the belt width Direction. In addition, the first patch image 45 is formed by forming a substantially square black image by the black image forming unit Pa (see FIG. 1), and then using the black image as a base, the yellow image forming unit Pd performs the horizontal center of the black image. It is formed by superimposing a yellow image on the part along the vertical direction.

  As a result, the first patch image 45 is arranged adjacently alternately in the order of the black image B1, the yellow image Y1, and the black image B2 from the left side with substantially the same width in the left-right direction in the figure. Further, the boundaries between the black images B1 and B2 and the yellow image Y1 are arranged along the vertical direction in the figure.

  When the first patch image 45 is detected by the detection sensor 21, the sensor output shown in FIG. 5 is obtained when the first and second light receiving portions 23 and 24 are arranged at predetermined reference positions. That is, as described above, the first light receiving unit 23 receives the P wave component of the reflected light from the intermediate transfer belt 8 and the black images B1 and B2, and the black image B1, In order to detect B2, the black images B1 and B2 can be detected as negative peaks (detection results) protruding downward with the intermediate transfer belt 8 as the base line.

  Further, as described above, the second light receiving unit 24 receives the S wave component of the reflected light from the intermediate transfer belt 8 and the yellow image Y1, and detects the yellow image Y1 by the increase of the S wave component with respect to the intermediate transfer belt 8. Therefore, the yellow image Y1 can be detected as a positive peak (detection result) protruding upward with the intermediate transfer belt 8 as a base line.

  Then, for example, the deviation of the black images B1 and B2 can be detected based on the start point of the black images B1 and B2 (rise of the left end), end point (fall of the right end), or the center of gravity position. . Further, for example, the shift of the yellow image Y1 can be detected based on the start point (rise of the left end) and the end point (rise of the right end) of the yellow image Y1 or the position of the center of gravity. Here, the shift of the yellow image Y1 is detected at the end of the peak.

  At this time, if the first and second light receiving units 23 and 24 are installed at predetermined reference positions, the black images B1 and B2 and the yellow image Y1 do not overlap with each other as shown in FIG. The peak end point of B1 coincides with the peak start point of yellow image Y1, and the peak end point of yellow image Y1 coincides with the peak start point of black image B2. In this case, an installation error of the first and second light receiving units 23 and 24 does not occur.

  However, there is a case where installation of at least one of the first light receiving unit 23 or the second light receiving unit 24 is deviated from the reference position due to assembly during manufacture, vibration during transportation, and the like, resulting in an installation error from the reference position. In such a case, it is difficult to sufficiently correct the color misregistration even if the color misregistration correction is performed with an installation error. Therefore, the installation error of the first and second light receiving units 23 and 24 is detected, and the installation error is corrected based on the detection result.

  If the relative installation error of the first and second light receiving units 23 and 24 can be corrected, the influence on the color misregistration correction can be eliminated. Therefore, here, the reference position is set to a predetermined position of the second light receiving unit 24 with respect to the first light receiving unit 23. Hereinafter, an installation error of the second light receiving unit 24 with respect to the first light receiving unit 23 is detected and the installation error is corrected. A method will be described.

It is assumed that the installation position of the second light receiving unit 24 with respect to the first light receiving unit 23 is shifted, and for example, detection results of the first and second light receiving units 23 and 24 as shown in FIG. 6 are obtained. In Figure 6, the peak of the sensor output of the second light receiving section 24, shifted to the right side of the reference position against the right and left side direction in the figure, a delay occurs in the appearance of the peak. That is, a detection time difference (time difference) T1 occurs between the peaks of the black images B1 and B2 and the peak of the yellow image Y1.

  Since the time difference T1 is caused by an installation error of the second light receiving unit 24 in the scanning direction, a second parameter is set based on the time difference T1 by setting a parameter relating the time difference T1 and the installation error of the second light receiving unit 24 in advance. The installation error of the light receiving unit 24 can be calculated. The installation error of the second light receiving unit 24 in the scanning direction can be corrected by adjusting the image formation timing according to the installation error.

  Then, by changing the image formation timing by the installation error correction, and further performing color misregistration correction in the changed state, the installation error correction result can be reflected in the image formation timing of the color misregistration correction. As a result, color misregistration correction can be performed with high accuracy without being affected by installation errors. Furthermore, it is possible to perform more appropriate density correction by performing density correction in a state where color misregistration correction is normally performed.

  Next, installation error correction control using the first installation error correction reference image in the image forming apparatus of the present embodiment will be described. FIG. 7 is a flowchart showing the installation error correction procedure of the image forming apparatus of this embodiment. A calibration execution procedure will be described with reference to FIGS.

  When the installation error correction mode is executed and installation error correction is started (start), a first patch image 45 (see FIGS. 5 and 6) is formed (step 1), and the detection sensor 21 (FIGS. 2 and 3). The positional relationship of the first patch image 45 is detected by the first light receiving unit 23 and the second light receiving unit 24 (see step 2). The detected positional relationship is compared with a reference position in the control unit 32 (see FIG. 4), and an installation error amount of the second light receiving unit 24 with respect to the first light receiving unit 23 is calculated.

  Then, parameter values used for installation error correction are read from the installation error correction table in the storage unit 33 (see FIG. 4) according to the installation error amount obtained in step S2, and the control unit 32 sets the installation error correction parameter value. A control signal for changing the transmission error is transmitted to perform installation error correction (step S3). Thereafter, the first patch image 45 on the intermediate transfer belt 8 is removed by the cleaning blade 19 (see FIG. 1) (step S4), and the installation error correction is completed.

  By performing the installation error correction according to the above procedure, the installation error of the first and second light receiving units 23 and 24 can be eliminated, and highly accurate color misregistration correction can be performed without being affected by the installation error. Further, since the first patch image 45 is used here, the installation error in the scanning direction can be detected with a simple configuration, and the installation error in the scanning direction can be effectively corrected.

  However, the reference image for installation error correction is not particularly limited as long as the installation error of the first and second light receiving elements 45 can be detected. Further, the present invention is not particularly limited to the detection and correction of the installation error in the scanning direction, and the installation error in the direction perpendicular to the scanning direction can be detected and corrected.

  FIG. 8 is a diagram illustrating the output of the detection sensor with respect to the second installation error correction reference image, and is a diagram illustrating the sensor output when an installation error occurs. FIG. 9 is a diagram illustrating the reference of the second light receiving unit. It is a figure which shows the installation error with respect to a position. Portions common to those in FIG. 6 are denoted by common reference numerals and description thereof is omitted. As shown in FIG. 8, a substantially square first patch image 45 and second patch image (second setting error detection reference image) are located at positions facing the detection sensor 21 (see FIG. 2) of the intermediate transfer belt 8. 46 is formed.

  The second patch image 46 has a square shape that is substantially the same size as the first patch image 45, and is arranged so that the sides facing the first patch image are substantially parallel. Further, the second patch image 46 is formed by forming a substantially square black image by the black image forming portion Pa (see FIG. 1), and then using the black image as a base, by the yellow image forming portion Pd, the lower left end portion of the black image. Is formed by superimposing a yellow image from the top toward the upper right end.

Thereby, in the second patch image 46, the black image B3, the yellow image Y2, and the black image B4 are alternately and adjacently arranged in this order from the left side in the horizontal direction of the drawing. Also, the yellow image Y2 has a predetermined width, the inclination angle against the left and right side direction of FIG. Are arranged so as to be approximately 45 °. Further, the boundaries between the first and second black images B3 and B4 and the yellow image Y2 are both arranged in parallel so as to be approximately 45 ° with respect to the horizontal direction in the drawing .

For example, it is assumed that the detection results of the first and second light receiving units 23 and 24 as shown in FIG. 8 are obtained. In FIG. 8, the reference position of the second light receiving unit 24 with respect to the first light receiving unit 23 is S0, and it is assumed that the second light receiving unit 24 is disposed at the installation position S. The broken line and the solid line are the reference position S0 and the installation position S. The scan lines are shown. In Figure 8, the peak of the sensor output of the second light receiving portion 24 with respect to the first patch image 45 is displaced rightward from the reference position against the right and left side direction in the figure, a delay occurs in the appearance of the peak.

  Accordingly, as described above, a time difference T1 is generated between the peaks of the black images B1 and B2 and the peak of the yellow image Y1. Therefore, as described above, the second light receiving unit 24 has an installation error in the scanning direction, and can detect the installation error in the scanning direction based on the time difference T1.

  In addition, the peak of the sensor output of the second light receiving unit 24 with respect to the second patch image 46 is also shifted to the right with respect to the horizontal direction in the figure, and there is a delay in the appearance of the peak. That is, there is a time difference T2 between the peaks of the black images B3 and B4 and the peak of the yellow image Y2. Since the time difference T2 is an installation error of the installation position S with respect to the reference position S0, as shown in FIG. 9, the time difference of the second light receiving unit 24 at the installation position S with respect to the second light receiving unit 24 ′ at the reference position S0. T2 is composed of a time difference T21 in the scanning direction and a time difference T22 in the direction perpendicular to the scanning direction.

  Here, since the time difference T1 of the first patch image 45 represents the time difference in the scanning direction of the second light receiving unit 24, the time difference T21 in the scanning direction is changed from the time difference T21 in the scanning direction to the time difference T1 in the scanning direction. By subtracting the corresponding time difference, the time difference T22 between the scanning direction and the vertical direction can be calculated. For example, the time difference T21 is calculated by subtracting the time difference corresponding to the time difference T1 from the time difference T2 in the second patch image 46, and the angle of the yellow image Y2 with respect to the scanning direction is approximately 45 ° and T21 and T22 are equal to each other. Can be calculated.

  A parameter that associates the time difference T1 with the installation error in the scanning direction and a parameter that associates the time difference T22 and the installation error in the vertical direction with respect to the scanning direction are set in advance, so that the second difference is set based on the time difference T1. The installation error amount in the scanning direction of the light receiving unit 24 and the installation error amount perpendicular to the scanning direction of the second light receiving unit 24 can be calculated based on the time difference T22.

  Then, by adjusting the image forming timing in accordance with the installation error amount in the vertical direction with respect to the scanning direction and the scanning direction, not only the scanning direction but also the installation error in the vertical direction with respect to the scanning direction can be corrected. Thereby, the installation error of the second light receiving unit 24 with respect to the first light receiving unit can be corrected with higher accuracy.

  Next, installation error correction control using the second installation error correction reference image in the image forming apparatus of the present embodiment will be described. FIG. 10 is a flowchart showing the installation error correction procedure of the image forming apparatus of this embodiment. The calibration execution procedure will be described in accordance with the steps of FIG. 10 with reference to FIGS.

  When the installation error correction mode is executed and installation error correction is started (start), a first patch image 45 is formed (step 1), and the first light receiving unit 23 of the detection sensor 21 (see FIGS. 2 and 3). And the positional relationship of the 1st and 2nd patch images 45 and 46 is detected by the 2nd light-receiving part 24 (step 2). The detected positional relationship is compared with the reference position in the control unit 32 (see FIG. 4), and the time difference T1 of the peak of the yellow image Y1 by the first patch image 45 and the time difference T2 of the yellow image Y2 by the second patch image 46 are obtained. Calculated (step 3).

  Next, a time difference T22 perpendicular to the scanning direction in the second patch image 46 is calculated from the calculated time difference T1 and time difference T2, and the scanning direction in the second light receiving unit 24 relative to the first light receiving unit 23 is calculated from the time difference T1. The installation error amount in the direction perpendicular to the scanning direction is calculated from the time difference T22 (step 4).

  Then, parameter values used for installation error correction are read from the installation error correction table in the storage unit 33 (see FIG. 4) according to the installation error amount in the direction perpendicular to the scanning direction and the scanning direction obtained in step S4. The control unit 32 transmits a control signal for changing the installation error correction parameter value and executes installation error correction (step S5). Thereafter, the first and second patch images 45 and 46 on the intermediate transfer belt 8 are removed by the cleaning blade 19 (see FIG. 1) (step S6), and the installation error correction is completed.

  By performing the installation error correction according to the above procedure, the installation error in the direction perpendicular to the scanning direction as well as the scanning direction of the first and second light receiving units 23 and 24 can be eliminated. Can be done with precision.

  In the present embodiment, the installation error of the second light receiving unit 24 with respect to the first light receiving unit 23 is detected. However, the installation error of the first light receiving unit 23 with respect to the second light receiving unit 24 is detected, and the installation error of the first light receiving unit 23 is detected. It is also possible to correct the installation error of the first and second light receiving elements 23 and 24. It is also possible to detect installation errors from the respective reference positions of the first and second light receiving units 23 and 24 and correct the installation errors of the respective light receiving units 23 and 24.

  Here, in the first and second patch images 45 and 46, the black images B1 and B2 are arranged with the yellow image Y1 sandwiched therebetween, and the black images B3 and B4 are arranged with the yellow image Y2 sandwiched therebetween. A configuration may be adopted in which two yellow images Y are formed with B interposed therebetween.

  In addition, since the boundary between the black image B and the yellow image Y can be clarified by using the black image B, the installation error can be detected easily and reliably. Further, by using the black image B and the yellow image, even when the surface roughness of the intermediate transfer belt 8 is deteriorated due to printing, the boundary between these can be detected, so that the installation error can be detected with higher accuracy. .

  Although the yellow image Y is formed here as a color image, a cyan image or a magenta image can also be formed. Further, if an installation error can be detected by the first and second light receiving elements 23 and 24, a two-color image can be used, and the black image B is not necessarily formed.

  Further, here, by setting the inclination angle of the boundary between the black image B and the yellow image Y in the second patch image 46 to about 45 °, the time difference T21 in the scanning direction and the time difference in the vertical direction from the scanning direction are set. Since T22 can be made equal, the installation error in the direction perpendicular to the scanning direction can be easily calculated. However, the inclination angle is not particularly limited as long as an installation error in a direction perpendicular to the scanning direction can be calculated.

  In the above embodiment, the black photosensitive drum 1a is disposed on the most upstream side (see FIG. 1), the first and second patch images 45 and 46 are used as the background, and the yellow image Y is formed thereon. Therefore, the black image B and the yellow image Y can be easily formed without complicated settings. However, the method of forming the first and second patch images 45 and 46 is not particularly limited as long as the boundary between the black image B and the yellow image Y can be formed. In addition, the black photosensitive drum 1a is disposed on the most downstream side, The yellow image Y can be formed first, and the black images B1 and B2 can be formed at predetermined positions with the yellow image Y in between.

  In the present embodiment, a tandem color image of an intermediate transfer system in which a full color image formed by sequentially laminating toner images of respective colors on an intermediate transfer belt 8 which is an example of a toner carrier is transferred onto a sheet P at a time. Although the forming apparatus has been described, the present invention can be applied in exactly the same manner to a direct transfer tandem color image forming apparatus that sequentially transfers toner images of each color onto a sheet P carried and conveyed on a conveying belt. is there.

  FIG. 11 is a schematic diagram showing the configuration of the image forming apparatus according to the second embodiment of the present invention, and FIG. 12 is a side view showing the configuration around the conveyance belt of the tandem color image forming apparatus according to the second embodiment. It is sectional drawing. In this embodiment, instead of the intermediate transfer belt 8, a conveyance belt (print medium) 50 that sequentially conveys the paper P to the image forming portions Pa to Pb is disposed so as to contact the lower portions of the photosensitive drums 1 a to 1 d. Instead of the exposure unit 4, LED heads 4a to 4d for individually exposing the photosensitive drums 1a to 1d are provided. Since the configuration of other parts is exactly the same as that of the first embodiment, description thereof is omitted.

  In the present embodiment, the same first patch image 45 or first and second patch images 45 and 46 as described above are formed on the conveyor belt 50, and the patch images 45 and 46 are detected to perform installation error correction. be able to. Since the installation error correction method and its control procedure are exactly the same as in the first embodiment, description thereof is omitted.

  In addition, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, the size, pattern, and quantity of the first and second patch images 45 and 46 shown in the above embodiment are merely examples, and other patterns may be used as necessary, such as the device configuration. Also, images other than the first and second patch images 45 and 46 can be formed simultaneously.

  In each of the above embodiments, the first and second patch images 45 and 46 are formed on the intermediate transfer belt 8 and the conveyance belt 50. In addition, the first and second patch images 45 and 46 are formed on the paper P. You can also.

The present invention includes an image carrier, an exposure device, and a developing device, and a plurality of image forming units for forming images of a plurality of colors including black and a toner image developed on the image carrier are sequentially laminated. An intermediate transfer belt or a conveyance belt for conveying a recording medium, means for transferring a toner image developed on the image carrier onto the intermediate transfer belt or the conveyance belt, the image carrier, the intermediate transfer belt, and a conveyance A detection unit configured to detect a reference image for color misregistration detection formed on at least one of a belt and a recording medium, and performing the color misregistration correction based on a detection result of the detection unit. means includes a light emitting portion that irradiates the print medium, a first light receiving portion of the reflected light that can receive the first light reflected polarized light parallel to the scanning direction of the image bearing member from said print medium And having a second light receiving unit that can receive a second reflected light of the scanning direction perpendicular polarization, installation error detection criteria for detecting the installation error of the first and second light receiving portions An image can be detected, and the installation error detection reference image includes two color images selected from the plurality of color images, and the two color images are alternately arranged adjacent to each other.

  As a result, the installation error is calculated based on the difference between the detection results of the two colors by the first and second light receiving units, and the installation error can be corrected. Therefore, the highly accurate color is not affected by the installation error. Deviation correction is possible. Further, by forming a reference image for detecting an installation error using a first color image of two color images as a base, and superimposing a second color image on the first color image, It is possible to easily create a reference image for installation error detection without performing complicated settings. In addition, by setting the first or second color image as a black image, it is possible to more easily and accurately detect installation errors in the first and second light receiving units.

  Further, the installation error detection reference image has at least a first installation error reference image in which the boundary between the first and second color images is arranged in a direction perpendicular to the scanning direction. It is possible to detect the installation error and correct the installation error in the scanning direction more effectively. In addition, the second installation error in which the installation error detection reference image is arranged such that the boundary between the first installation error detection reference image and the first and second color images is inclined at a predetermined angle with respect to the scanning direction. By having the reference image for detection, it becomes possible to correct the installation error in more detail.

  Further, by setting the predetermined angle to about 45 °, it becomes possible to more easily detect an installation error in a direction perpendicular to the scanning direction. Further, by correcting the installation error based on the detection result for the installation error detection reference image by the first and second light receiving units, it is possible to perform highly accurate color misregistration correction. Further, by correcting the installation error in the scanning direction based on the detection result of the first installation error detection reference image by the first and second light receiving units, the installation error can be detected with higher accuracy, and the installation error can be more reliably performed. Can be eliminated.

  Further, based on the detection result of the first installation error detection reference image by the first and second light receiving units, the installation error in the scanning direction is corrected, and based on the detection result of the first and second installation error detection reference image. By correcting the installation error in the direction perpendicular to the scanning direction, the installation error can be detected with higher accuracy, and the installation error can be eliminated more reliably. Further, by correcting the installation error based on the difference in detection time of the reference image for installation error detection by the first and second light receiving units, the installation error can be detected more easily and the installation error can be eliminated more easily. . Further, the color misregistration correction can be performed with high accuracy by performing the color misregistration correction after correcting the installation error.

FIG. 1 is a schematic diagram illustrating an overall configuration of a tandem color image forming apparatus according to a first embodiment of the present invention. FIG. 2 is a view showing the arrangement of detection sensors around an intermediate transfer belt used in the image forming apparatus of the present embodiment, FIG. 2A is a side sectional view, and FIG. 2B is a view in FIG. It is the elements on larger scale which looked at the detection sensor periphery of a) to the U direction. These are the schematic diagrams which show the structure of the detection sensor used for the image forming apparatus of this embodiment. FIG. 3 is a block diagram showing a control path of the image forming apparatus of the present embodiment. These are figures which show the output of the detection sensor with respect to the reference image for 1st installation error correction, Comprising: It is a figure which shows the sensor output in case the installation error has not arisen. These are figures which show the output of the detection sensor with respect to the reference image for 1st installation error correction, Comprising: It is a figure which shows the sensor output in case the installation error has arisen. These are the flowcharts which show the installation error correction procedure using the 1st installation error detection reference image in the image forming apparatus of this embodiment. These are figures which show the output of the detection sensor with respect to the 2nd installation error correction reference | standard image, Comprising: It is a figure which shows the sensor output in case the installation error has arisen. These are figures which show the installation error with respect to the reference position of a 2nd light-receiving part. These are the flowcharts which show the installation error correction procedure using the 1st installation error detection reference image in the image forming apparatus of this embodiment. These are the schematic diagrams which show the whole structure of the tandem type color image forming apparatus which concerns on 2nd Embodiment of this invention. FIG. 3 is a side cross-sectional view illustrating a configuration around a conveyance belt of the image forming apparatus according to the exemplary embodiment.

Explanation of symbols

Pa to Pd Image forming section 1a to 1d Photosensitive drum 2a to 2d Charger 3a to 3d Developing unit (developing device)
4 Exposure unit 4a-4d LED head 6a-6d Transfer roller (transfer means)
7 Fixing part 8 Intermediate transfer belt (printing medium)
9 Secondary transfer roller (secondary transfer means)
21 Detection sensor (detection means)
22 light emitting part 22a light emitting element 22b first polarizing filter 23 first light receiving part (first light receiving part)
23a 1st light receiving element 23b 2nd polarizing filter 24 2nd light-receiving part (2nd light-receiving part)
24a Second light receiving element 24b Third polarizing filter 25 Beam splitter 32 Control unit 33 Storage unit 45 First patch image (first installation error correction reference image)
46 Second patch image (second setting error correction reference image)
50 Conveyor belt (printing medium)
100 Image forming apparatus B Black image Y Yellow image P Paper (recording medium, printing medium)

Claims (7)

A plurality of image forming units for forming images of a plurality of colors including black having an image carrier, an exposure device, and a developing device;
An intermediate transfer belt on which the developed toner images are sequentially laminated on the image carrier;
Transfer means for laminating the toner image developed on the image carrier on the intermediate transfer belt;
Secondary transfer means for transferring the toner images laminated on the intermediate transfer belt onto a recording medium at a time;
Detecting means for detecting a reference image for color misregistration detection formed on at least one of the image carrier, the intermediate transfer belt, and the recording medium;
A control unit that performs color misregistration correction based on a detection result of the detection unit;
In an image forming apparatus comprising:
The detection means includes
A light emitting unit for irradiating the print medium with P- polarized light;
A first light receiving unit capable of receiving, as first reflected light, P-polarized light of specularly reflected light among reflected light from the print medium;
A second light receiving unit capable of receiving S-polarized light of the specularly reflected light as second reflected light;
I have a,
Wherein the control unit, a two-color installation error detection reference image images are located adjacent to the alternating selected plurality of colors or al, a boundary of the two colors of the image is parallel to the main scanning direction And obtaining the installation error of both from the output signals of the first and second light receiving sections when the installation error detection reference image passes through the detection area of the detection means. An image forming apparatus. A plurality of image forming units for forming images of a plurality of colors including black having an image carrier, an exposure device, and a developing device;
A conveying belt for conveying a recording medium to the image forming unit;
Transfer means for transferring a toner image developed on the image carrier onto a recording medium or the transport belt;
Detecting means for detecting a reference image for color misregistration detection formed on at least one of the image carrier, the conveyor belt, and the recording medium;
A control unit that performs color misregistration correction based on a detection result of the detection unit;
In an image forming apparatus comprising:
The detection means includes
A light emitting unit for irradiating the print medium with P- polarized light;
A first light receiving unit capable of receiving, as first reflected light, P-polarized light of specularly reflected light among reflected light from the print medium;
A second light receiving unit capable of receiving S-polarized light of the specularly reflected light as second reflected light;
I have a,
Wherein the control unit, a two-color installation error detection reference image images are located adjacent to the alternating selected plurality of colors or al, a boundary of the two colors of the image is parallel to the main scanning direction And obtaining the installation error of both from the output signals of the first and second light receiving sections when the installation error detection reference image passes through the detection area of the detection means. An image forming apparatus.   The installation error detection reference image is formed by using a first color image of the two color images as a base, and superimposing a second color image on the first color image. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   The image forming apparatus according to claim 1, wherein the first or second color image is a black image. Based on the detection result of the previous Ki設置誤difference detection reference image by the first and second light receiving portions, in any one of claims 1 to 4, characterized in that to correct the installation error of the main scanning direction The image forming apparatus described. Based on the difference between the detection time of the first and second of said installation error detection reference image by the light receiving unit, an image forming apparatus according to claim 1, characterized in that to correct the installation error . The image forming apparatus according to claim 5 , wherein the color misregistration correction is performed after the installation error correction is performed.