JP2019028244A - Image formation device - Google Patents

Abstract

To suppress a time needed for cleaning of patch images.SOLUTION: An image formation device comprises: a color deviation sensor 31 that has a cartridge 12 having a plurality of photoreceptor drums 13 and an intermediate transfer belt 17, and transferring patch images formed on the plurality of photoreceptor drums 13 to the intermediate transfer belt 17, an LED 61 irradiating the intermediate transfer belt 17 having the patch image formed with light, and a phototransistor 62 receiving reflection light of the light from the LED 61; and main control unit 72 that controls an image formation condition for correcting color deviations of the image. A first patch image formed by black toner, and a second patch image formed by cyan toner adjacent to the first patch image in a sub-scan direction are formed so that a segment TT where the image is formed and a segment TS where the image is not formed are alternately in respective main scan directions. The segment TT in the first patch image and the segment TT in the second patch image are located at a different position in the main scan direction.SELECTED DRAWING: Figure 6

Description

  The present invention relates to an image forming apparatus using an electrophotographic method, and more particularly to an image forming apparatus that forms a color misregistration detection patch.

  In an electrophotographic color image forming apparatus, a so-called tandem configuration is known in which an image forming unit for each color is independently provided in order to perform printing at high speed. In a tandem color image forming apparatus, a toner image formed on the photosensitive drum of each color image forming unit is sequentially superimposed and transferred onto an intermediate transfer belt to form a color image, and further on the intermediate transfer belt. A configuration is adopted in which color images are collectively transferred to a recording medium. In the color image forming apparatus having such a configuration, when a toner image (image) formed in each image forming unit is superimposed on the intermediate transfer belt due to a mechanical factor in each color image forming unit, a color shift ( Misalignment) may occur. In particular, in a configuration in which a laser scanner (optical scanning device) and a photosensitive drum unit are provided independently for each color image forming unit, the positional relationship between these units differs for each color, resulting in color misregistration. Sometimes. For this reason, in color image forming apparatuses, color misregistration detection patch images are transferred from a photosensitive drum onto an intermediate transfer belt, and color misregistration is detected based on the result of detecting the transferred solid image using an optical sensor. However, control for correcting color misregistration is performed. In addition, in the image forming apparatus, the toner image formed on the photosensitive drum of the image forming unit for each color is sequentially transferred to the recording medium on the conveying belt while the recording medium is conveyed by the conveying belt, and a color image is obtained. There is an image forming apparatus of the type that forms the image. In such an image forming apparatus, the color misregistration detection patch image for each color is formed on the transport belt, and controls to detect the color misregistration using an optical sensor and correct the color misregistration.

  In addition, as a method of cleaning the patch image formed on the intermediate transfer belt, there are a blade cleaning method and an electrostatic cleaning method. For example, Patent Document 1 proposes a blade cleaning method in which a cleaning blade is brought into contact with the intermediate transfer belt and the toner on the intermediate transfer belt is physically peeled off by the cleaning blade. The toner is also stripped off by the blade cleaning method for the patch image formed on the above-described conveyance belt. For example, Patent Document 2 proposes the following electrostatic cleaning method. The charging unit charges the toner on the intermediate transfer belt to a polarity opposite to the charged state at the time of development, and applies a voltage to the primary transfer roller to perform reverse transfer from the intermediate transfer belt to the photosensitive drum. The toner transferred to the photosensitive drum is collected by a cleaning device that cleans the photosensitive drum.

JP 2009-288481 A JP 2009-205112 A

  In the above-described blade cleaning method and electrostatic cleaning method, when a solid image is formed and color misregistration correction control is executed, the intermediate transfer belt is rotated once when the solid image formed on the intermediate transfer belt is cleaned. It may not be possible to remove all of them. The same applies to the solid image formed on the conveyance belt. For this reason, in cleaning after color misregistration correction control, it is necessary to rotate the intermediate transfer belt and the conveyor belt a plurality of times in order to ensure stable cleaning performance, and the time required for cleaning (also referred to as down time) is required. There is a problem of becoming longer.

  The present invention has been made under such circumstances, and an object thereof is to suppress the time required for cleaning the patch image.

  In order to solve the above-described problems, the present invention has the following configuration.

  (1) An image forming unit that includes a plurality of photoconductors and a rotator that carries a toner image or a recording material, and that transfers a patch image formed on the plurality of photoconductors to the rotator, and the patch A detecting unit having a light emitting unit that emits light toward the rotating body on which an image is formed; a light receiving unit that receives reflected light of the light emitted from the light emitting unit; and the rotation by the image forming unit Control means for detecting a patch image formed on the body by the detecting means and controlling image forming conditions to correct color misregistration of the image based on the detected result, and a first color toner The first patch image formed in step 1 is formed so that the first section in which the image is formed in the main scanning direction and the second section in which the image is not formed are alternately repeated. In the first patch image and the sub-scanning direction, Adjacent first color The second patch image formed with different second color toners is formed so that the third section in which the image is formed and the fourth section in which no image is formed are alternately repeated in the main scanning direction. The image forming apparatus, wherein the first section in one patch image and the third section in the second patch image are at different positions in the main scanning direction.

  According to the present invention, the time required for cleaning the patch image can be suppressed.

Sectional drawing which shows the structure of the image forming apparatus of Examples 1-3. FIG. 5 is a diagram illustrating a cleaning method for an intermediate transfer belt according to first to third embodiments. The figure which shows the structure of the color shift sensor of Examples 1-3. 1 is a block diagram illustrating a configuration of an image forming apparatus according to first to third embodiments. FIG. 6 is a diagram illustrating color misregistration correction control according to first to third embodiments. FIG. 6 is a diagram illustrating a color misregistration detection pattern according to the first embodiment. FIG. 6 is a diagram illustrating a color misregistration detection pattern according to the second embodiment.

  Embodiments of the present invention will be described below in detail with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in the following embodiments should be appropriately changed according to the configuration of the apparatus to which the present invention is applied and various conditions. Therefore, unless specifically stated otherwise, the scope of the present invention is not intended to be limited thereto.

[Configuration of Image Forming Apparatus]
FIG. 1 is a cross-sectional view illustrating the configuration of the image forming apparatus according to the first embodiment. The image forming apparatus shown in FIG. 1 is an in-line color image forming apparatus 2 (hereinafter referred to as an image forming apparatus 2) in which a cartridge 12 as an image forming unit is provided for each toner color. The image forming apparatus 2 can output a full color image by superimposing four color toner images of yellow (Y), magenta (M), cyan (C), and black (K) formed in each cartridge 12. It is configured. The image forming apparatus 2 includes cartridges 12Y, 12M, 12C, and 12K that are image forming units, and laser scanner units 11YM and 11CK. The laser scanner units 11YM and 11CK are exposure apparatuses that form electrostatic latent images on the photosensitive drums 13Y, 13M, 13C, and 13K of the cartridges 12Y, 12M, 12C, and 12K. The configuration of the laser scanner units 11YM and 11CK will be described later. Further, the subscripts Y, M, C, and K in FIG. 1 indicate configurations corresponding to yellow (Y), magenta (M), cyan (C), and black (K), respectively. In the following, reference numerals are omitted except when referring to a specific photosensitive drum or the like.

  The cartridge 12 includes a photosensitive drum 13, a cleaning blade 14, a charging roller 15, and a developing roller 16 that rotate in an arrow direction (clockwise direction) in the drawing. The surface of the photosensitive drum 13 as a photosensitive member is charged to a constant potential by the charging roller 15, and then an electrostatic latent image is formed by scanning the laser beam from the laser scanner unit 11. Development is performed to form a toner image. The cleaning blade 14 is flexible (rubber elastic), contacts the photosensitive drum 13 in a predetermined pressure contact state, and wipes the surface of the photosensitive drum 13 to remove the surface of the photosensitive drum 13 (on the photosensitive member). Scraping off the toner. Further, the cleaning blade 14 is disposed in contact with the photosensitive drum 13 in a direction reverse to the rotation direction of the photosensitive drum 13 in order to improve the cleaning efficiency. The cartridge 12 is provided with a non-volatile memory 7 and stores information about each cartridge 12.

  The intermediate transfer belt 17 which is a rotating body to which the toner image formed on the photosensitive drum 13 (on the photosensitive drum) is transferred while moving in the direction of the arrow (counterclockwise direction) in the drawing while being in contact with each photosensitive drum 13. Is provided. The toner image on the photosensitive drum 13 is transferred to the intermediate transfer belt 17 by applying a voltage to the primary transfer roller 18 provided at a position facing the photosensitive drum 13 via the intermediate transfer belt 17. Further, the intermediate transfer belt 17 is provided with a conductive brush 19 and a conductive roller 20 for cleaning the toner on the intermediate transfer belt 17 (on the rotating body).

  In addition, the cassette 22 that stores the paper 21 that is a recording material includes a size guide 23 that regulates the position of the paper 21 placed in the cassette 22, and a paper presence sensor that detects the presence or absence of the paper 21 in the cassette 22. 24 is provided. In the conveyance path through which the sheet 21 is conveyed, the sheet feeding roller 25 that feeds the sheet 21, the double feeding of the sheet 21, the separation rollers 26 a and 26 b that convey one sheet, and the skew of the sheet 21 are prevented. A registration roller 27 is provided. A registration sensor 28 for detecting the conveyed paper 21 is provided near the downstream side of the registration roller 27 in the paper conveyance direction. The sheet 21 fed from the cassette 22 by the sheet feeding roller 25 is conveyed to a secondary transfer unit that nips the sheet 21 by the intermediate transfer belt 17 and the secondary transfer roller 29. When the sheet 21 is conveyed to the secondary transfer unit, the toner image on the intermediate transfer belt 17 is secondarily transferred to the sheet 21 by the secondary transfer roller 29 to which a secondary transfer bias is applied. Thereafter, the sheet 21 on which the toner image is secondarily transferred is conveyed to the fixing device 30. The toner image is fixed on the paper 21 by being heated and pressurized by the fixing device 30 and discharged outside the apparatus. The color misregistration sensor 31 serving as a color misregistration detection unit reads a color misregistration detection pattern that is a toner image formed on the intermediate transfer belt 17 and detects color misregistration by a method described later.

[Causes of color misregistration]
Next, factors that cause color misregistration of the toner image formed on the intermediate transfer belt 17 will be described. Here, the color shift with time in which the laser irradiation position varies due to the temperature rise of the laser scanner units 11YM and 11CK will be described. First, the configuration of the laser scanner units 11YM and 11CK shown in FIG. 1 will be described. The laser scanner unit 11YM is an exposure device that scans the surfaces of the photosensitive drums 13Y and 13M of the cartridges 12Y and 12M to form an electrostatic latent image. The laser scanner unit 11YM drives the rotary polygon mirror 32YM and the rotary polygon mirror 32YM to rotate. A motor 33YM is provided. On the other hand, the laser scanner unit 11CK is an exposure device that scans the surfaces of the photosensitive drums 13C and 13K of the cartridges 12C and 12K to form an electrostatic latent image, and rotates the rotary polygon mirror 32CK and the rotary polygon mirror 32CK. A drive motor 33CK is provided.

  Laser light emitted from a laser light emitting element (not shown) in the laser scanner unit 11YM is deflected by a rotary polygon mirror 32YM and a plurality of reflecting mirrors (not shown), and is irradiated onto the surfaces of the photosensitive drums 13Y and 13M. The position where the laser light on the photosensitive drums 13Y and 13M is irradiated may deviate from the original position to be irradiated due to the following factors. That is, an irradiation position shift occurs due to the axis of the drive motor 33YM due to the heat generated from the drive motor 33YM, the heat generated from the outside of the laser scanner unit 11YM, the tilt of the reflection mirror (not shown), and the distortion of the laser scanner unit 11. Note that the laser scanner unit 11CK has the same configuration as the laser scanner unit YM, and in the laser scanner unit 11CK, as in the laser scanner unit 11YM, the irradiation position deviation may occur in the photosensitive drums 13C and 13K.

  The laser beam irradiation position deviation described above is different for each photosensitive drum 13 because the inclination of the plurality of reflecting mirrors and the tendency of distortion of the laser scanner unit 11 are different. For this reason, when the toner image formed on the photosensitive drum 13 is superimposed and transferred onto the intermediate transfer belt 17 in a state where the irradiation position deviation occurs on the photosensitive drum 13, the positions of the toner images of the respective colors are aligned. Instead, color misregistration occurs. Further, the color misregistration includes a sudden color misregistration caused by a variation due to a tolerance of mechanical parts when the cartridge 12 is replaced. In the present embodiment, the color misregistration correction control applicable to both the color misregistration that occurs over time and the color misregistration that occurs suddenly will be described later.

[Cleaning of intermediate transfer belt]
(Electrostatic cleaning method)
Next, a cleaning method of the toner on the intermediate transfer belt 17 in this embodiment by an electrostatic cleaning method will be described with reference to FIG. FIG. 2 is an enlarged schematic view of the periphery of the conductive brush 19, the conductive roller 20, and the yellow (Y) cartridge 12Y with the intermediate transfer belt 17 as the center. FIG. 2A is a diagram for explaining cleaning of the toner on the intermediate transfer belt 17 during the printing operation, and FIG. 2B is a diagram illustrating cleaning of the toner on the intermediate transfer belt 17 during color misregistration correction control. It is a figure explaining.

  First, a method for cleaning the toner of the intermediate transfer belt 17 during the printing operation will be described with reference to FIG. During the printing operation, the electrostatic latent image formed on the photosensitive drum 13 is developed by adhering negatively charged toner by the developing roller 16 to form a toner image on the photosensitive drum 13. Thereafter, a toner image on the photosensitive drum 13 is transferred to the intermediate transfer belt 17 by applying a positive voltage to the primary transfer roller 18. The toner image formed on the intermediate transfer belt 17 is transferred to the paper 21 by applying a positive voltage to the secondary transfer roller 29, and the toner image transferred to the paper 21 is transferred to the paper by the fixing device 30. Then, the printing operation is completed. As shown in FIG. 2A, the toner that is not transferred to the paper 21 by the secondary transfer roller 29 and remains on the intermediate transfer belt 17 is affected by the positive voltage applied by the secondary transfer roller 29. , Positive and negative polarity toners are mixed. Further, the toner remaining on the intermediate transfer belt 17 under the influence of the unevenness on the surface of the paper 21 is in a state of locally overlapping a plurality of layers (FIG. 2A).

  The conductive brush 19 installed facing the conveyance path in the toner conveyance direction indicated by the arrow direction of the intermediate transfer belt 17 in the drawing has a predetermined intrusion amount (contact amount) with respect to the rotating intermediate transfer belt 17. Are arranged as follows. For this reason, the toner deposited on the intermediate transfer belt 17 in a plurality of layers is scattered (equalized) to a substantially higher height according to the amount of penetration of the conductive brush 19 when passing through the conductive brush 19 (see FIG. 2 (a) B). Further, a positive voltage is applied to the conductive brush 19 from the voltage output circuit 42 for the conductive brush 19, and constant current control is performed. As a result, the toner on the intermediate transfer belt 17 is charged to a positive polarity that is opposite in polarity to the toner at the time of development when passing through the conductive brush 19. The negative polarity toner that has not been fully charged to the positive polarity is collected by the conductive brush 19.

  Thereafter, when the toner on the intermediate transfer belt 17 passes through the conductive brush 19, the toner moves in the rotation direction of the intermediate transfer belt 17 and reaches the conductive roller 20. A positive voltage is applied to the conductive roller 20 by the voltage output circuit 43 for the conductive roller 20. Therefore, the toner charged to the positive polarity passing through the conductive brush 19 is further charged to the positive polarity when passing through the conductive roller 20, and an optimum positive charge is given to realize simultaneous transfer cleaning in the photosensitive drum 13Y. (FIG. 2 (a) C). Note that the negative charge toner that has not been collected by the conductive brush 19 is also given an optimal positive charge by the conductive roller 20 when it passes through the conductive roller 20.

  The toner to which the optimum positive charge is applied moves in the rotation direction of the intermediate transfer belt 17 and is reversely transferred to the photosensitive drum 13Y by the positive polarity voltage applied to the primary transfer roller 18Y in the yellow cartridge 12Y. The toner reversely transferred to the photosensitive drum 13Y is scraped and removed from the photosensitive drum 13 by the cleaning blade 14Y disposed on the photosensitive drum 13Y (FIG. 2 (a) D). On the other hand, the negative toner image formed on the photosensitive drum 13Y is transferred onto the intermediate transfer belt 17 by the positive voltage applied to the primary transfer roller 18Y and conveyed to the secondary transfer roller 29 (FIG. 2 (a) D). Note that the toner collected by the conductive brush 19 and the toner attached to the conductive roller 20 are periodically collected by a post-processing operation at the end of the printing operation. That is, the toner attached to the conductive brush 19 and the conductive roller 20 by applying a voltage while switching the polarity of the voltage applied to the conductive brush 19 and the conductive roller 20 while the intermediate transfer belt 17 is rotationally driven. Is transferred to the intermediate transfer belt 17. Thereafter, the toner transferred to the intermediate transfer belt 17 is reversely transferred to the photosensitive drum 13Y, whereby the toner is collected.

  Next, a method for cleaning a patch image formed on the intermediate transfer belt 17 when color misregistration correction control is performed will be described with reference to FIG. In general, a solid pattern having a toner density of 100% is used for a patch image forming a detection pattern used in color misregistration correction control. Further, unlike the printing operation, the patch image is not transferred to the paper 21. Therefore, the toner of the patch image formed on the intermediate transfer belt when the color misregistration correction control is performed, the negative polarity toner transferred from the photosensitive drum 13 is divided into a plurality of layers as shown in FIG. Is formed on the intermediate transfer belt 17 (FIG. 2B).

  The toner deposited in a plurality of layers on the intermediate transfer belt 17 is uniform as in the printing operation of FIG. 2A because a large amount of toner accumulates when passing through the positively charged conductive brush 19. It cannot be leveled to the height of one layer. As a result, since toner is accumulated in a plurality of layers, a large amount of toner is not charged positively when passing through the conductive brush 19 but is collected by the conductive brush 19. In addition, a large amount of negative toner that passes through the conductive brush 19 and is conveyed in the direction of the conductive roller 20 without being collected by the conductive brush 19 is also produced (FIG. 2B). Further, among the toners that have passed through the conductive brush 19 without being charged by the conductive brush 19, even when the positively charged conductive roller 20 has passed, negative toner is not charged positively. Toner that passes through will also come out (FIG. 2 (b) C).

  In the yellow cartridge 12Y, the positively charged toner on the intermediate transfer belt 17 is reversely transferred to the photosensitive drum 13Y. Therefore, a positive voltage is applied to the primary transfer roller 18Y. However, as described above, the toner that has not been charged positively by the conductive roller 20 and has passed through the negative polarity is applied with a positive voltage by the primary transfer roller 18Y, and thus is not reversely transferred to the photosensitive drum 13Y. Then, it remains on the intermediate transfer belt 17 (FIG. 2 (b) D). Since toner that is not positively charged remains on the intermediate transfer belt 17 as described above, the intermediate transfer belt 17 needs to be rotated a plurality of times in cleaning the intermediate transfer belt 17 after color misregistration correction control. The time required for cleaning becomes longer. Further, since it is necessary to discharge (collect) the toner collected on the conductive brush 19, further cleaning time is required.

(Blade cleaning method)
Next, a cleaning method using a blade cleaning method for toner on the intermediate transfer belt 17 in this embodiment will be described. First, a method for cleaning the toner of the intermediate transfer belt 17 during the printing operation will be described. In the case of the blade cleaning method, a blade for stripping off the toner on the intermediate transfer belt 17 is provided at the position of the conductive brush 19 in FIG. Then, the toner that is not transferred onto the paper 21 by the secondary transfer roller 29 shown in FIG. 2A and remains on the intermediate transfer belt 17 is peeled off by the blade, and the intermediate transfer belt 17 is cleaned. Further, the cleaning of the patch image formed on the intermediate transfer belt 17 when the color misregistration correction control is performed is performed in the same manner as in the printing operation. However, the toner of the patch image formed on the intermediate transfer belt when the color misregistration correction control is performed, the toner transferred from the photosensitive drum 13 becomes a plurality of layers as shown in FIG. It is formed on the transfer belt 17. For this reason, it is impossible to remove all the toner at one time, and it is necessary to rotate the intermediate transfer belt 17 a plurality of times, which increases the time required for cleaning.

  Conventionally, the solid image formed when the color misregistration correction control is executed is formed at the same position in the direction (main scanning direction) orthogonal to the conveyance direction of the intermediate transfer belt 17. When a solid image is formed in this way, the conventional cleaning technique performs cleaning using the same portion of a cleaning member such as a blade. For this reason, a specific portion of the cleaning member is locally deteriorated. As a result, a cleaning defect in which toner remains on the intermediate transfer belt 17 may occur, and image quality may be deteriorated.

  In this embodiment, it is possible to reduce the time required for cleaning after the color misregistration correction control by executing the color misregistration correction control using the color misregistration detection pattern capable of efficiently cleaning the intermediate transfer belt 17. To. The color misregistration detection pattern that is a feature of the present invention will be described later.

[Configuration and operation of color misregistration sensor]
Next, the configuration of the color misregistration sensor 31 that detects color misregistration using the color misregistration detection pattern will be described with reference to FIG. FIG. 3A is a schematic diagram for explaining the position where the color misregistration sensor 31 is arranged, and FIG. 3B is a schematic diagram for explaining the configuration of the color misregistration sensor 31.

  First, the arrangement of the color misregistration sensor 31 will be described with reference to FIG. FIG. 3A is a schematic diagram when the intermediate transfer belt 17 is viewed from above the intermediate transfer belt 17. As shown in FIG. 3A, two color misregistration sensors 31 are installed facing the intermediate transfer belt 17, and the color misregistration sensor 31L is installed on the left side in the figure, and on the right side. The color misregistration sensor 31R is installed. In the figure, the sub-scanning direction is the direction in which the intermediate transfer belt 17 rotates (moving direction), the main scanning direction is the direction orthogonal to the sub-scanning direction, and the surface of the photosensitive drum 13 from the laser scanner unit 11 is It is also the direction in which the laser beam scans. That is, it can be said that the color misregistration sensor 31L is arranged on the image writing start side in the main scanning direction, and the color misregistration sensor 31R is arranged on the image writing end side in the main scanning direction.

  Next, the configuration of the color misregistration sensor 31 will be described. The color misregistration sensors 31L and 31R have the same configuration, and will be described as the color misregistration sensor 31 here. FIG. 3B is a schematic diagram illustrating the configuration of the color misregistration sensor 31 when the color misregistration sensor 31 is viewed from the side surface of the intermediate transfer belt 17. As shown in FIG. 3B, the color misregistration sensor 31 includes an LED 61 that is a light emitting portion mounted obliquely with respect to the surface of the intermediate transfer belt 17, and a phototransistor 62 (a light receiving portion that detects the amount of light). Hereinafter referred to as PTR62). The LED 61 is mounted obliquely with respect to the surface of the intermediate transfer belt 17 that is a detection surface. The LED 61 is a light that efficiently guides light incident from one side to the other using internal reflection of a transparent resin such as an acrylic resin. A configuration may be used in which the detection surface is irradiated obliquely using a guide or the like. The LED 61 and the PTR 62 are respectively inclined by an angle A from the detection surface so as to be optically symmetric. The PTR 62 receives the light emitted from the LED 61 and regularly reflected on the surface of the intermediate transfer belt 17. The regularly reflected surface on the intermediate transfer belt at this time is defined as a regular reflection spot 41. The shape of the regular reflection spot in the present embodiment is a circular shape having a diameter of 2.1 mm. In this embodiment, the color misregistration sensor 31 that detects only regular reflection light is used. However, even if the color misregistration sensor to which a phototransistor that detects irregular reflection light is added is used, the reflected light is detected. Good.

[Configuration of Control Unit of Image Forming Apparatus]
FIG. 4 is a control block diagram illustrating a configuration of a control unit related to color misregistration correction control of the image forming apparatus 2 of the present embodiment. The image forming apparatus 2 includes a controller 71 that converts image data into an image signal and outputs it, and a main control unit 72 that is a control unit that controls the entire image forming apparatus. The main control unit 72 includes a scanner driving unit 73, a color misregistration pattern forming unit 74, a color misregistration sensor control unit 75, and a cleaning control unit 79. The scanner drive unit 73 controls the rotation of the drive motor 33YM of the laser scanner unit 11YM and the drive motor 33CK of the laser scanner unit 11CK. The drive motor 33YM is a drive unit that rotates the rotary polygon mirror 32YM for the yellow photosensitive drum 13Y and the magenta photosensitive drum 13M. On the other hand, the drive motor 33CK is a drive unit that rotates the rotating polygon mirror 32CK for the cyan photosensitive drum 13C and the black photosensitive drum 13K. Based on the image signal received from the controller 71, the color misregistration pattern forming unit 74 transfers the toner image formed on the photosensitive drum 13 of each cartridge 12 to the intermediate transfer belt 17 and detects the color misregistration on the intermediate transfer belt 17. Form a pattern. The color misregistration detection pattern received from the controller 71 is a feature of the present invention, and details will be described later.

  The color misregistration sensor control unit 75 includes a sensor driving unit 76, a color misregistration pattern measurement unit 77, and a color misregistration calculation unit 78, and controls the color misregistration sensors 31L and 31R. The color misregistration sensor 31L includes an LED 61, a transistor 63 that controls the on / off state of the LED 61, and a resistor 64 that limits a current flowing through the LED 61. The color misregistration sensor 31L compares the threshold voltage 67 with the voltage 65 converted by the resistor 65, the threshold voltage 67 of the comparator 66, and the threshold voltage 67, and outputs the detection signal a. Comparator 66 is provided. Since the configuration of the color misregistration sensor 31R is the same as that of the color misregistration sensor 31L, the description thereof is omitted and the following description of the color misregistration sensor 31 is performed using the color misregistration sensor 31L.

  Further, the sensor driving unit 76 outputs a driving signal (a, b) for turning on or off the LED 61 of the color misregistration sensor 31. When the sensor driving unit 76 outputs a high-level drive signal a to turn on the LED 61 of the color misregistration sensor 31L, the transistor 63 is turned on, whereby the LED 61 is turned on and emits light. . When the PTR 62 receives light emitted from the LED 61 and regularly reflected by the intermediate transfer belt 17, the PTR 62 generates a photocurrent corresponding to the amount of light received. The comparator 66 compares the optical voltage converted by the resistor 65 (generated at both ends of the resistor 65) with the photocurrent flowing in the PTR 62, which is input to the + terminal, and the threshold voltage 67 input to the − terminal. The comparator 66 outputs a LOW (low) level detection signal a when the optical voltage is lower than the threshold voltage 67, and HIGH (high) level detection signal a when the optical voltage is higher than the threshold voltage 67. Is output. As will be described later, the threshold voltage 67 indicates sensitivity according to the amount of light received by the PTR 62, and is configured to be changeable according to the color shift detection pattern to be used.

  The color misregistration pattern measuring unit 77 measures the output time of the detection signals (a, b) output from the color misregistration sensors 31 (31L, 31R). Specifically, the measurement unit 77a of the color misregistration pattern measurement unit 77 measures the output time of the detection signal a, and the measurement unit 77b measures the output time of the detection signal b. The color misregistration calculation unit 78 calculates the color misregistration amount detected by each of the color misregistration sensors 31L and 31R based on the measurement result of the color misregistration pattern measurement unit 77, and calculates a correction value such as the image writing position based on the calculated result. calculate. Specifically, the color misregistration calculation unit 78a calculates the color misregistration amount detected by the color misregistration sensor 31L based on the measurement result of the color misregistration pattern measurement unit 77a, and the image writing position and the like based on the calculated result. A correction value is calculated. Similarly, the color misregistration calculation unit 78b calculates the color misregistration amount detected by the color misregistration sensor 31R based on the measurement result of the color misregistration pattern measurement unit 77b, and the correction value such as the image writing position based on the calculated result. Is calculated.

  The cleaning control unit 79 includes a high voltage control unit 80 and a drive control unit 83. The high voltage control unit 80 controls the voltage output circuit 42 that applies a positive voltage to the conductive brush 19 and the voltage output circuit 43 that applies a positive voltage to the conductive roller 20. The drive control unit 83 drives the motor 82 that rotates the intermediate transfer belt 17 to rotate the intermediate transfer belt 17 and clean the toner on the intermediate transfer belt 17. Note that the cleaning method of the intermediate transfer belt 17 after the color misregistration correction control of the present embodiment is the electrostatic cleaning method described with reference to FIG.

[Color misregistration correction control]
Next, color misregistration correction control in this embodiment will be described. As is well known, the image forming apparatus 2 executes color misregistration correction control using the color misregistration sensor 31 in order to correct the color misregistration between the colors. In the image forming apparatus 2, when the controller 71 instructs the main control unit 72 to start color misregistration correction control, the main control unit 72 performs the following operation. The color misregistration pattern forming unit 74 of the main control unit 72 forms a toner image corresponding to the color misregistration detection pattern stored in the memory in the controller 71 on the photosensitive drum 13 of each cartridge 12 and transfers it to the intermediate transfer belt 17. . In the color misregistration sensor control unit 75, the sensor driving unit 76 drives the color misregistration sensor 31, and the color misregistration sensor 31 detects a color misregistration detection pattern formed on the intermediate transfer belt 17 and detects the color misregistration signal. Output to the pattern measurement unit 77. The color misregistration pattern measurement unit 77 measures the output time of the detection signal output from the color misregistration sensor 31. The color misregistration calculation unit 78 determines the color misregistration amount in the sub-scanning direction between the colors (the rotation direction of the intermediate transfer belt 17) and the main scanning direction between the colors (the width of the intermediate transfer belt 17) based on the output time of the detection signal. Direction) color misregistration amount is calculated.

Here, a method of calculating the amount of color misregistration in the sub-scanning direction and the main scanning direction will be described with reference to FIG. FIG. 5A is a diagram illustrating a signal output from the color misregistration sensor 31 to the color misregistration pattern measurement unit 77 when the color misregistration sensor 31 detects a color misregistration detection pattern. 5A and 5A show a toner image 81 of a color misregistration detection pattern formed on the intermediate transfer belt 17 that moves in the direction of the arrow in the drawing. FIG. 5A-2 shows the photovoltage input to the + terminal of the comparator 66 of the color misregistration sensor 31. When the toner image 81 is detected by the PTR 62 of the color misregistration sensor 31, the value of the flowing current changes (decreases), and the photovoltage generated by the resistor 65 changes. From FIG. 5A-2, it can be seen that when the toner image 81 is detected, the photovoltage is lower than the threshold voltage 67.
The comparator 66 compares the photovoltage input to the + terminal with the threshold voltage 67 input to the − terminal. The comparator 66 outputs a LOW level signal when the optical voltage is equal to or lower than the threshold voltage 67, and outputs a HIGH level signal when the optical voltage is higher than the threshold voltage 67 (FIGS. 5A and 5A). -3)). Based on the detection signal output from the comparator 66, the color misregistration pattern measurement unit 77 detects the timing T1 (leading edge timing) when the leading edge of the toner image formed on the intermediate transfer belt 17 is detected and the timing when the trailing edge is detected. T2 (rear end timing) is detected. Then, the color misregistration pattern measurement unit 77 calculates a centroid point T3 that is the center timing of the toner image 81 based on the timing T1 (front end timing) and the timing T2 (rear end timing). The color misregistration calculation unit 78 calculates the color misregistration amount of each color based on the barycentric point T3 for each toner image 81.

  FIG. 5B is a schematic diagram illustrating an example of a color misregistration detection pattern formed on the intermediate transfer belt 17 in the color misregistration correction control. The intermediate transfer belt 17 is viewed from above the intermediate transfer belt 17. It is a schematic diagram at the time. The color misregistration sensor 31L detects a color misregistration detection pattern formed on the left side in the main scanning direction, and the color misregistration sensor 31R detects a color misregistration detection pattern formed on the right side in the main scanning direction. The color misregistration detection pattern is formed in the sub-scanning direction, which is the direction in which the intermediate transfer belt 17 rotates from top to bottom in the drawing.

  The color misregistration detection patterns 90 (Y, M, C, K) and 91 (Y, M, C, K) are color misregistration detection patterns for detecting the amount of color misregistration in the sub-scanning direction. The color misregistration detection patterns 92 (Y, M, C, K) and 93 (Y, M, C, K) have an inclination of 45 degrees with respect to the sub-scanning direction for detecting the color misregistration amount in the main scanning direction. This is a color misregistration detection pattern provided with. Note that the subscripts Y, M, C, and K denoted by reference numerals 90 to 93 indicate toner colors. In addition, Tsl1 to Tsl4 and Tsr1 to Tsr4 indicated by dotted lines in the drawing are the barycentric points (detection timings) of the color misregistration detection patterns 90 (Y, M, C, K) and 91 (Y, M, C, K), respectively. Indicates. Similarly, Tml1 to Tml4 and Tmr1 to Tmr4 indicated by dotted lines in the figure are the barycentric points (detection timings) of the color misregistration detection patterns 92 (Y, M, C, K) and 93 (Y, M, C, K), respectively. ). In the present embodiment, the color misregistration amount of each color in the sub-scanning direction and main scanning direction is calculated based on the theoretical distance between the center of gravity of each color and black (K), which is a reference color for color misregistration detection, and each color pattern. .

  Here, a method of calculating the color misregistration amount will be described with reference to FIG. The moving speed of the intermediate transfer belt 17 is v (mm / s), and the theoretical distance between each color misregistration detection pattern 90 and 91 for detecting the color misregistration amount in the sub-scanning direction and the black (Bk) pattern is dsC (mm ), DsM (mm), and dsY (mm). Further, the color misregistration detection patterns 90 and 91 for detecting the color misregistration amount of each color in the sub scanning direction and the inclination of 45 degrees with respect to the sub scanning direction for detecting the color misregistration amount in the main scanning direction are provided. The measured distance between the displayed color misregistration detection patterns 92 and 93 is defined as follows for each of the left and right sides. That is, the measured distances between the left color misregistration detection patterns 92 and 93 are dmlK (mm), dmlC (mm), dmlM (mm), and dmlY (mm). Similarly, the measured distances between the right color misregistration detection patterns 92 and 93 are dmrK (mm), dmrC (mm), dmrM (mm), and dmrY (mm). These theoretical distances are all equal.

The color misregistration amount δes of each color in the sub-scanning direction with black (Bk) as a reference color is
δesY = v × {(Tsl4-Tsl1) + (Tsr4-Tsr1)} / 2-dsY (Expression 1)
δesM = v × {(Tsl3−Tsl1) + (Tsr3−Tsr1)} / 2−dsM (Expression 2)
δesC = v × {(Tsl2-Tsl1) + (Tsr2-Tsr1)} / 2-dsC (Equation 3)
It becomes.

The color misregistration amounts δeml and δemr for each of the left and right colors in the main scanning direction are
dmlK = v × (Tml1-Tsl1) (Formula 4)
dmlC = v × (Tml2-Tsl2) (Formula 5)
dmlM = v × (Tml3-Tsl3) (Formula 6)
dmlY = v × (Tml4-Tsl4) (Expression 7)
When,
dmrK = v × (Tmr1−Tsr1) (Equation 8)
dmrC = v × (Tmr2−Tsr2) (Equation 9)
dmrM = v × (Tmr3−Tsr3) (Equation 10)
dmrY = v × (Tmr4−Tsr4) (Equation 11)
Than,
δemlY = dmlY−dmlK (Equation 12)
δemlM = dmlM−dmlK (Equation 13)
δemlC = dmlC−dmlK (Equation 14)
When,
δemrY = dmrY−dmrK (Equation 15)
δemrM = dmrM−dmrK (Expression 16)
δemrC = dmrC−dmrK (Expression 17)
It becomes. Then, the color misregistration direction can be determined from the sign of the calculation result, the writing position in the main scanning direction is corrected from the color misregistration amount δeml of each color in the left direction, and the width in the main scanning direction is corrected from the color misregistration amount (δemr−δeml). If there is an error in the width in the main scanning direction, the main scanning writing position is calculated in consideration of not only the color misregistration amount δeml but also the amount of change in the image clock frequency that has been changed along with the main scanning width correction. When a plurality of sets of color misregistration toner patterns are formed, the color misregistration amount of each color in the main scanning direction and the sub scanning direction may be calculated by averaging the color misregistration amounts.

  The color misregistration calculation unit 78 notifies the controller 71 of color misregistration information based on the calculated color misregistration amount. The controller 71 creates image data based on the notified color misregistration information, and controls image forming conditions so as to suppress color misregistration on the paper 21. The color misregistration information notified to the controller 71 by the color misregistration calculation unit 78 includes the following information as information regarding the sub-scanning direction. That is, in the information about the sub-scanning direction, the laser beam emission timing of other colors is delayed by the number of scanning lines based on the yellow (Y) laser beam emission timing (TOP signal output timing) that is the reference color for image formation. There is such information. The controller 71 delays the timing for transmitting the image data to the main control unit 72 according to the notified information. In this embodiment, since the color misregistration amount in the sub-scanning direction with black (K) as a reference is calculated, the color misregistration information is notified to the controller 71 after conversion with yellow (Y) as the reference. The information on the amount of color misregistration in the main scanning direction includes the emission timings of laser beams of other colors with respect to the laser beam emission timing of black (K), which is a reference color for color misregistration detection, in the main scanning direction. There is information on whether to advance or delay only. The controller 71 adjusts the timing for transmitting the image data to the main control unit 72 according to the notified information. In the present exemplary embodiment, the configuration for calculating the color misregistration amount based on the color misregistration detection pattern illustrated in FIG. 5B has been described. However, the color misregistration detection pattern and the calculation method are not limited to those described in the present exemplary embodiment. .

[Color shift detection pattern]
Next, the color misregistration detection pattern which is the first patch image pattern that makes it possible to reduce the time required for cleaning the toner of the color misregistration detection pattern on the intermediate transfer belt 17 after the color misregistration correction control of this embodiment. Will be described with reference to FIG. FIG. 6 is a schematic diagram showing a color misregistration detection pattern formed on the intermediate transfer belt 17 of this embodiment, as in FIG. 5B, and shows the intermediate transfer belt 17 from above the intermediate transfer belt 17. It is a schematic diagram when seen. In FIG. 6, color misregistration detection patterns 100 (Y, M, C, K) and 101 (Y, M, C, K) are color misregistration detection patterns (first patterns) in the sub-scanning direction, and dotted lines are The barycentric points Tsl1 to Tsl4 and Tsr1 to Tsr4 of each color misregistration detection pattern are shown. On the other hand, the color misregistration detection patterns 102 (Y, M, C, K) and 103 (Y, M, C, K) are color misregistration detection patterns (second patterns) in the main scanning direction. The barycentric points Tml1 to Tml4 and Tmr1 to Tmr4 of the detection pattern are shown. These color misregistration detection patterns 100, 101, 102, and 103 are hereinafter referred to as patch images.

  First, the size of the patch image of the color misregistration detection pattern in this embodiment will be described. The image length TP in the sub-scanning direction of the patch image is about 2 mm (≈48 dots × 25...) Of 48 dots (600 DPI) which is the same as the size of the regular reflection spot 41 of the color misregistration sensor 31 (indicated by 41L and 41R in the figure). 4 mm / 600 dots). This is to minimize the patch size in the sub-scanning direction while ensuring the maximum output of the photovoltage input to the comparator 66 when the color misregistration sensor 31 detects the patch image. Further, the image length TD in the main scanning direction of the patch image is set according to the maximum range of color misregistration. The case where the color misregistration is the maximum is an abrupt color misregistration caused by variation due to the tolerance of the mechanical parts when the cartridge 12 is replaced. The maximum color misregistration range in this case is 48. It is a dot. Therefore, in consideration of the fact that the patch image fits within the spot size (48 dots) of the regular reflection spot 41 even if the maximum color shift occurs on both sides of the regular reflection spot 41 in the main scanning direction, the patch image in the main scanning direction. The image length TD is as follows. That is, the image length TD in the main scanning direction of the patch image is obtained by adding the length of the regular reflection spot 41 in the main scanning direction to twice the maximum color misregistration amount of the image formed on the photosensitive drum 13. It becomes length. Therefore, the image length TD in the main scanning direction of the patch image is set to about 6.1 mm (≈144 dots × 25.4 mm / 600 dots) of 144 dots (= 48 dots + 2 × 48 dots) (600 DPI). The color shift in the main scanning direction assumed in this embodiment is about 2 mm (48 dots).

  Next, the pattern of the patch image formed on the intermediate transfer belt 17 in this embodiment will be described. In FIG. 6, the figure which expanded the patch image of the circular broken line part of the color misregistration detection patterns 100K and 100C is shown. Similarly, the figure which expanded the patch image of the circular broken line part of the color misregistration detection patterns 102K and 102C is shown. The patch images of the color misregistration detection patterns 100M and 100Y are the same as the patch images of the color misregistration detection patterns 100K and 100C, and the patch images of the color misregistration detection patterns 102M and 102Y are patches of the color misregistration detection patterns 102K and 102C. It is the same as the image. The color misregistration detection patterns 101 and 103 are the same as the color misregistration detection patterns 100 and 102.

  The patch image shown in FIG. 6 has a configuration in which patch formation sections TT and non-patch formation sections TS are alternately and repeatedly arranged in the main scanning direction in order to reduce the amount of toner used and improve the cleaning efficiency. In this embodiment, the patch forming section TT is a 4-dot patch image in the main scanning direction (image length), and the patch non-forming section TS is 4 dots in the main scanning direction. In this embodiment, the sum (8 dots) of the length (4 dots) of the patch forming section TT and the length (4 dots) of the patch non-forming section TS, and the main reflection spot 41 of the color shift sensor 31 are used. The length in the scanning direction (48 dots) has an integer multiple relationship. As a result, even when color misregistration occurs in the main scanning direction and the spot where the color misregistration sensor 31 detects the color misregistration detection pattern is misaligned, the patch forming section TT and the patch non-forming section TS included in the spot are detected. The number can always be constant. As a result, the toner amount detected by the color misregistration sensor 31 can be kept constant. In this embodiment, since one color misregistration sensor 31 detects a color misregistration detection pattern of a plurality of colors, Y, M, C, and K, this relationship is common to each color.

  Next, the relationship between the colors of the patch image in the present embodiment will be described. As shown in FIG. 6, in the color misregistration detection patterns 100K and 100C, the positional relationship between the patch forming section TT and the patch non-forming section TS is opposite. That is, the position of the patch formation section TT in the color misregistration detection pattern 100K is the position of the patch non-formation section TS in the color misregistration detection pattern 100C. Further, the position of the patch non-formation section TS in the color misregistration detection pattern 100K is the position of the patch formation section TT in the color misregistration detection pattern 100C. Similarly, in the color misregistration detection patterns 102K and 102C, the positional relationship between the patch formation section TT and the patch non-formation section TS is opposite. In addition, patch images are formed so that the color misregistration detection patterns 101 and 103 have the same relationship. As described above, in this embodiment, the patch images are formed so that the positional relationship between the patch forming section TT and the patch non-forming section TS in the black (K) and magenta (M) patch images is the same. Further, the patch images are formed so that the positional relationship between the patch forming section TT and the patch non-forming section TS in the cyan (C) and yellow (Y) patch images is the same. As described above, in the color misregistration detection patterns 100, 101, 102, and 103 adjacent in the sub-scanning direction, patch images are formed so that the positions of the patch forming section TT and the patch non-forming section TS do not overlap. As a result, in the black (K), cyan (C), magenta (M), and yellow (Y) patch images that are sequentially formed on the intermediate transfer belt 17 from the upstream side in the rotation direction, the position of the pattern formation section TT is It is set to be alternately arranged in the main scanning direction. As a result, the toner formed (deposited) on the intermediate transfer belt 17 can be dispersed, and the uniformity of uniformizing the toner when the patch image passes through the conductive brush 19 can be improved.

  Next, the threshold voltage 67 input to the negative terminal of the comparator 66 in this embodiment will be described. The threshold voltage 67 of the comparator 66 is determined according to the toner amount detected in the regular reflection spot 41 of the color misregistration sensor 31. As described above, in this embodiment, since the patch forming section TT in which toner is used is 4 dots and the patch non-forming section TS in which toner is not used is 4 dots, the patch image is a solid image in FIG. Compared to the case, the amount of toner used is halved. In the color misregistration sensor 31, the photovoltage generated in the resistor 65 is adjusted to 2.5 V by the amount of reflected light detected from the intermediate transfer belt 17 in a state where no patch image is formed. Further, the threshold voltage 67 of the comparator 66 when a solid image is formed on the intermediate transfer belt 17 as a conventional patch image is set to 1.3V. Therefore, in this embodiment, since the amount of toner used is halved, the threshold voltage 67 of the comparator is 1.9 V (= 2.5 V− (2.5−1.3 V) / 2). The threshold voltage 67 indicates the sensitivity for detecting the patch image of the PTR 62 of the color misregistration sensor 31. The threshold voltage 67 in this example is 1.9V, and the conventional threshold voltage 67 is 1.3V. Therefore, when color misregistration detection is performed using the color misregistration detection pattern of the present embodiment, the sensitivity of the PTR 62 is set higher than in the case of the color misregistration detection pattern using the conventional solid image. .

As described above, in this embodiment, the patch image of the color misregistration detection pattern used at the time of executing the color misregistration correction control is alternately arranged in the main scanning direction between the patch forming section and the patch non-forming section. By using such a color misregistration detection pattern, the amount of toner can be suppressed as compared with the case of using a solid patch image. Further, the negative polarity toner can be prevented from passing through the conductive brush 19 and the conductive roller 20 without being charged, and the amount of negative polarity toner adhering to the conductive brush 19 can be suppressed. As a result, it is possible to suppress downtime, which is the time required for cleaning the patch image. In addition, patch images are not formed only at specific locations in the main scanning direction of the intermediate transfer belt or the conveyance belt, but are formed in a dispersed manner. Therefore, the amount of toner used can be reduced, and the progress of deterioration of the cleaning member can be suppressed. In this embodiment, the configuration in which the exposure of the photosensitive drums of the two cartridges is performed by one scanner unit is described, but the present invention is not limited to this configuration. For example, this embodiment can also be applied to a configuration in which one or four cartridges of photosensitive drums are exposed by one scanner unit.
As described above, according to the present embodiment, the time required for cleaning the patch image can be suppressed.

  In the second embodiment, a color misregistration detection pattern that is more advantageous for improving the cleaning efficiency than the color misregistration detection pattern in the first embodiment will be described. Note that the configurations of the image forming apparatus and the control unit used in the present embodiment are the same as those in the first embodiment, and the same reference numerals are used for the same apparatuses, and the description thereof is omitted here.

[Color shift detection pattern]
The color misregistration detection pattern, which is the second patch image pattern of this embodiment, will be described with reference to FIG. FIG. 7 is a schematic diagram showing a color misregistration detection pattern formed on the intermediate transfer belt 17 of this embodiment, and is a schematic diagram when the intermediate transfer belt 17 is viewed from above the intermediate transfer belt 17. In FIG. 7, color misregistration detection patterns 200 (Y, M, C, K) and 201 (Y, M, C, K) are color misregistration detection patterns in the sub-scanning direction, and a dotted line indicates the center of gravity of each color misregistration detection pattern. Points Tsl1 to Tsl4, Tsr1 to Tsr4 are shown. On the other hand, the color misregistration detection patterns 202 (Y, M, C, K) and 203 (Y, M, C, K) are the color misregistration detection patterns in the main scanning direction, and the dotted line indicates the center of gravity Tml1 of each color misregistration detection pattern. -Tml4 and Tmr1-Tmr4 are shown. Further, an enlarged view of the broken line frame part of the color misregistration detection pattern 200 is a broken line enlarging part shown in the lower part of FIG. 7, and the color misregistration detection pattern 200 (Y, M) for detecting the color misregistration amount in the sub-scanning direction. , C, K) shows the relationship between the patch forming section TT and the patch non-forming section TS for each color. Although only the color misregistration detection pattern 200 is shown in the broken line enlarged portion, the patch formation section TT and the patch non-formation section TS of each color misregistration detection pattern 201, 202, 203 have the same relationship as the color misregistration detection pattern 200. . Note that the image length TP in the sub-scanning direction and the image length TD in the main scanning direction of the patch image in this embodiment shown in FIG. 7 are about 2 mm and 144 dots (48 dots (600 DPI)), respectively, as in the first embodiment. 600 DPI) of about 6.1 mm.

  First, the patch image in the present embodiment will be described. In the patch image formed in this embodiment, in order to suppress the amount of toner to be used and improve the cleaning efficiency, the patch forming section TT and the patch non-forming section TS are alternately arranged in the main scanning direction. In this embodiment, the patch forming section TT is 1 dot in length, and the patch non-forming section TS is 3 dots in length. The length (number of dots) between the patch forming section TT and the patch non-forming section TS in this embodiment is 4 dots in the patch forming section TT in Embodiment 1 and 4 dots in the patch non-forming section TS. Compared to the case, the toner consumption is halved. As a result, the time required for cleaning the patch image formed on the intermediate transfer belt 17 can be further reduced as compared with the first embodiment.

  Next, the relationship between the colors of the patch image in the present embodiment will be described. The patch image of each color misregistration detection pattern is set so that the position of the pattern formation section TT is arranged at a different position in the main scanning direction between all colors. As a result, the toner supplied (contacted) to the cleaning member (conductive brush 19 and conductive roller 20) can be dispersed more than in the first embodiment. As a result, the progress of the local deterioration of the cleaning member can be suppressed, and the occurrence of defective cleaning can be reduced. In addition, a part of the non-patch section TS between all colors overlaps in the main scanning direction (positions in the main scanning direction overlap).

  Next, the threshold voltage 67 of the comparator 66 in this embodiment will be described. The threshold voltage 67 of the comparator 66 is determined according to the toner amount detected in the regular reflection spot 41 of the color misregistration sensor 31. As described above, in this embodiment, since the patch forming section TT in which the toner is used is 1 dot and the patch non-forming section TS in which the toner is not used is 3 dots, the patch image is a solid image in FIG. Compared to the case, the amount of toner used is ¼. In the color misregistration sensor 31, the photovoltage generated in the resistor 65 is adjusted to 2.5 V by the amount of reflected light detected from the intermediate transfer belt 17 in a state where no patch image is formed. Further, the threshold voltage 67 of the comparator 66 when a solid image is formed on the intermediate transfer belt 17 as a conventional patch image is set to 1.3V. Therefore, in this embodiment, the amount of toner to be used is 1/4, so that the threshold voltage 67 of the comparator is 2.2 V (= 2.5 V− (2.5 V−1.3 V) / 4). . The threshold voltage 67 indicates the sensitivity for detecting the patch image of the PTR 62 of the color misregistration sensor 31. The threshold voltage 67 in this example was 2.2V, and the threshold voltage 67 in Example 1 described above was 1.9V. Therefore, when color misregistration detection is performed using the color misregistration detection pattern of this embodiment, the sensitivity of the PTR 62 is set higher than that of the color misregistration detection pattern of the first embodiment.

  In this embodiment, the difference between the photovoltage value (2.5 V) when there is no patch image and the threshold voltage 67 (2.2 V) of the comparator 66 is small. This is because if the irregularity on the surface of the intermediate transfer belt 17 becomes large after a predetermined time has passed through the intermediate transfer belt 17, noise due to the irregularity on the belt surface is erroneously detected as a patch image during color misregistration correction control. there's a possibility that. Therefore, when the usage time is less than a predetermined time (for example, less than half of the guaranteed use time) after the start of use of the intermediate transfer belt 17, the color misregistration correction control is performed using the color misregistration detection pattern of this embodiment. I do. When the usage time of the intermediate transfer belt 17 is equal to or longer than a predetermined time, color misregistration correction control using the color misregistration detection pattern described in the first embodiment may be performed.

  In the first embodiment and the present embodiment, the patch image formed in the patch forming section TT uses a linear color misregistration detection pattern parallel to the sub-scanning direction. However, the patch image is inclined with respect to the sub-scanning direction. Alternatively, a diagonal color misregistration detection pattern may be used. In this way, by using diagonal lines in the color misregistration detection pattern, the blade is supplied (contacted) to a blade in the blade cleaning method, or to a cleaning member such as a dielectric brush or a dielectric roller in the electrostatic cleaning method. The toner can be further dispersed. Therefore, the progress of local deterioration of the cleaning member can be suppressed, and the occurrence of defective cleaning can be reduced.

  As described above, in this embodiment, the patch image of the color misregistration detection pattern used when executing the color misregistration correction control is arranged by alternately repeating the patch forming section and the patch non-forming section in the main scanning direction. Furthermore, the position of the pattern formation section TT is arranged at a different position with respect to the main scanning direction for each color. By using such a color misregistration detection pattern, the amount of toner to be used can be suppressed, and the toner of the color misregistration detection pattern can be prevented from concentrating on the same location of the cleaning member. As a result, it is possible to further reduce the occurrence of defective cleaning while suppressing downtime, which is the time required for cleaning.

  As described above, according to the present embodiment, the time required for cleaning the patch image can be suppressed.

  Color misregistration includes sudden color misregistration and temporal color misregistration. Sudden color misregistration is, for example, color misregistration that occurs when the cartridge 12 is replaced, and color misregistration with time is color misregistration caused by, for example, the inclination of the rotary polygon mirror caused by self-temperature rise. In the third exemplary embodiment, the color misregistration correction control is performed by suppressing the consumption of toner to be used by properly using the color misregistration detection pattern for the color misregistration with time and the color misregistration detection pattern for the sudden color misregistration. explain. Note that the configurations of the image forming apparatus and the control unit used in the present embodiment are the same as those in the first and second embodiments, and the same reference numerals are used for the same apparatuses, and description thereof is omitted here.

[Color misregistration correction control]
In the present embodiment, color misregistration correction control is executed by switching between a color misregistration detection pattern for a color misregistration with time and an abrupt color misregistration detection pattern. Specifically, when performing color misregistration correction control for sudden color misregistration, the color in which the patch image length TD in the main scanning direction described in the first and second embodiments is set to about 6.1 mm (144 dots). A shift detection pattern is used. This is because the maximum color shift in the main scanning direction that occurs when the cartridge 12 is replaced is about 2 mm (48 dots). For example, the maximum value of the color shift in the main scanning direction due to the temperature rise of the scanner, which is the color shift over time, is about 0.4 mm (≈10 dots × 25.4 mm / 600 dots) of 10 dots. Therefore, in the case of color misregistration correction control for color misregistration over time, the patch image length TD in the main scanning direction is about 2.9 mm (≈68 dots × 25.4 mm / 68) (68 dots (= 48 dots + 2 × 10 dots)). The color misregistration detection pattern set to (600 dots) is used. As described above, the color misregistration correction control performed when the cartridge 12 is replaced uses the color misregistration detection pattern described in the first and second embodiments. In the color misregistration correction control performed in other cases, the color misregistration correction control is performed. A shift detection pattern is used.

  As described above, in this embodiment, the color misregistration correction control is executed by properly using the color misregistration detection pattern for the color misregistration with time and the sudden color misregistration detection pattern depending on the case. Thus, the color misregistration detection pattern can be optimized according to the maximum value of color misregistration occurring in the main scanning direction, and the amount of toner used during color misregistration correction control can be suppressed. As a result, the time (downtime) required for cleaning can be reduced. In addition, patch images are not formed only at specific locations in the main scanning direction of the intermediate transfer belt or the conveyance belt, but are formed in a dispersed manner. Therefore, the amount of toner used can be reduced, and the progress of deterioration of the cleaning member can be suppressed.

  As described above, according to the present embodiment, the time required for cleaning the patch image can be suppressed.

[Other embodiments]
In the first to third embodiments, the image forming apparatus 2 having the intermediate transfer belt 17 has been described. However, an image forming apparatus that employs a system that directly transfers a toner image formed on a photosensitive drum, which is a photosensitive member, to a recording material. The present invention can also be applied to. In other words, the intermediate transfer belt can be replaced with a transfer material conveyance belt which is a rotating member carrying a recording material, and the color misregistration correction control process of the present invention can be applied to this transfer material conveyance belt. In an image forming apparatus using a transfer material conveyance belt, the color component of each color formed on the photosensitive drum corresponding to each color is transferred to the transfer material conveyance belt on the recording material by the transfer unit. The corresponding color misregistration detection pattern is transferred. In the same manner as in the first to third embodiments, a color misregistration sensor detects a patch image of a color misregistration detection pattern on the transfer material conveyance belt, and executes color misregistration detection control.
As described above, also in other embodiments, the time required for the patch image cleaning time can be suppressed.

12 Cartridge 13 Photosensitive drum 17 Intermediate transfer belt 31 Color misregistration sensor 61 LED
62 Phototransistor 72 Main controller

Claims (18)

An image forming unit that has a plurality of photosensitive members and a rotating member that carries a toner image or a recording material, and that transfers a patch image formed on the plurality of photosensitive members to the rotating member;
A detecting unit having a light emitting unit that emits light toward the rotating body on which the patch image is formed, and a light receiving unit that receives reflected light of the light emitted from the light emitting unit;
Control means for detecting a patch image formed on the rotating body by the image forming means by the detecting means, and controlling image forming conditions to correct color misregistration of the image based on the detected result;
With
The first patch image formed with the first color toner is formed such that a first section in which an image is formed and a second section in which no image is formed are alternately repeated in the main scanning direction, and the first patch image is formed. The second patch image formed with the second color toner different from the first color adjacent to each other in the sub-scanning direction includes the third section where the image is formed in the main scanning direction and the fourth section where the image is not formed. In which the first section in the first patch image and the third section in the second patch image are at different positions in the main scanning direction. Forming equipment. A third patch image that is adjacent to the second patch image in the sub-scanning direction and is formed of a third color toner different from the first color and the second color is formed in the main scanning direction. The fifth section and the sixth section where no image is formed are alternately repeated,
A fourth patch image formed of toner of a fourth color that is adjacent to the third patch image and the first patch image in the sub-scanning direction and is different from the first color, the second color, and the third color. Is formed such that the seventh section in which the image is formed and the eighth section in which the image is not formed are alternately repeated in the main scanning direction,
The image forming apparatus according to claim 1, wherein the fifth section in the third patch image and the seventh section in the fourth patch image are at different positions in the main scanning direction.   The control means is configured to cause the first patch image, the second section, the third section, and the seventh section to be in the same position in the main scanning direction by the image forming means, and the second patch image, the second section, and the second section. The patch image, the first patch image pattern on which the third patch image and the fourth patch image are formed, or the first section, the third section, the fifth section and the seventh section are the main scans, respectively. The second patch image pattern in which the first patch image, the second patch image, the third patch image, and the fourth patch image which are different positions in the direction are formed is formed. The image forming apparatus described in 1.   The said 1st patch image pattern WHEREIN: The said 2nd area, the said 6th area, the said 4th area, and the said 8th area are the same positions in the said main scanning direction, respectively. Image forming apparatus.   In the first patch image pattern, the first section and the second section, the third section and the fourth section, the fifth section and the sixth section, and the seventh section and the eighth section. The image forming apparatus according to claim 4, wherein the lengths of the sections in the main scanning direction are equal.   In the second patch image pattern, partial sections of the second section, the fourth section, the sixth section, and the eighth section are provided at the same position in the main scanning direction. The image forming apparatus according to claim 3.   In the second patch image pattern, the lengths in the main scanning direction of the first section, the third section, the fifth section, and the seventh section are the second section, the fourth section, The image forming apparatus according to claim 6, wherein the length of the sixth section and the eighth section is shorter than the length in the main scanning direction.   The sum of the lengths of the first section and the second section in the main scanning direction, the sum of the lengths of the third section and the fourth section in the main scanning direction, the fifth section and the sixth section The sum of the lengths in the main scanning direction and the sum of the lengths in the main scanning direction of the seventh section and the eighth section are equal to each other. The image forming apparatus described in 1.   A sum of lengths of the first section and the second section in the main scanning direction in the first patch image pattern; a sum of lengths of the third section and the fourth section in the main scanning direction; The sum of the lengths in the main scanning direction of the fifth section and the sixth section, and the sum of the lengths in the main scanning direction of the seventh section and the eighth section are respectively in the second patch image pattern. The sum of the lengths of the first section and the second section in the main scanning direction, the sum of the lengths of the third section and the fourth section in the main scanning direction, the fifth section and the sixth section The image forming apparatus according to claim 8, wherein the image forming apparatus is equal to a sum of lengths in the main scanning direction and a sum of lengths of the seventh section and the eighth section in the main scanning direction. The image lengths in the sub-scanning direction of the first patch image, the second patch image, the third patch image, and the fourth patch image are reflected by the rotating body that reflects the light emitted from the light emitting unit. Equal to the length of the spot in the sub-scanning direction,
The image length in the main scanning direction of the first patch image, the second patch image, the third patch image, and the fourth patch image is twice the maximum color shift amount of the image formed on the photoconductor. The image forming apparatus according to claim 9, wherein the length is a length obtained by adding a length of the reflection spot in the main scanning direction.   The image formation according to claim 10, wherein a length of the reflection spot in the main scanning direction is an integral multiple of a sum of the lengths of the first section and the second section in the main scanning direction. apparatus. The first patch image pattern and the second patch image pattern respectively include the first patch image, the second patch image, the third patch image, and the like for detecting color misregistration of the image in the sub-scanning direction. A first pattern composed of the fourth patch image, and the first patch image, the second patch image, the third patch image, and the fourth patch image for detecting a color shift of the image in the main scanning direction. A second pattern comprising:
The first patch image, the second patch image, the third patch image, and the fourth patch image of the first pattern are formed in parallel to the main scanning direction;
The first patch image, the second patch image, the third patch image, and the fourth patch image of the second pattern are formed so as to have an inclination with respect to the main scanning direction. The image forming apparatus according to claim 11.   The first patch image, the second patch image, the third patch image, and the fourth patch image of the first pattern and the second pattern have a linear shape parallel to the sub-scanning direction. The image forming apparatus according to claim 12.   The first patch image, the second patch image, the third patch image, and the fourth patch image of the first pattern and the second pattern have a diagonal shape that is inclined with respect to the sub-scanning direction. The image forming apparatus according to claim 12, wherein the image forming apparatus is provided.   The control means forms a patch image of the second patch image pattern when the time from the start of use of the rotating body is less than a predetermined time, and the time from the start of using the rotating body 15. The image forming apparatus according to claim 10, wherein a patch image of the first patch image pattern is formed when a predetermined time is equal to or longer than a predetermined time.   The detection means switches the sensitivity with which the light receiving unit detects the patch image according to the patch image of the first patch image pattern or the patch image of the second patch image pattern to be formed. The image forming apparatus according to claim 15. The image forming means has a cleaning means for removing toner on the photoconductor,
The image forming apparatus according to any one of claims 1 to 16, wherein the patch image formed on the rotating body is transferred to the photoconductor and removed by the cleaning unit. The image forming means has a cleaning means for removing toner on the rotating body,
The image forming apparatus according to claim 1, wherein the patch image formed on the rotating body is removed by the cleaning unit.

Images