JP2018194654A - Image forming apparatus - Google Patents

Abstract

To provide an image forming apparatus capable of correcting color misregistration with high accuracy.SOLUTION: The image forming apparatus includes: first image forming means for forming an image of a first color on a first photoreceptor and transferring the image of the first color formed on the first photoreceptor onto an image carrier; second image forming means for forming an image of a second color on a second photoreceptor and transferring the image of the second color formed on the second photoreceptor onto the image carrier; first control means for controlling the first and the second image forming means to form a plurality of pattern images including images of the first color and of the second color on the image carrier; correcting means for detecting images of the first color and of the second color included in the plurality of pattern images and correcting positional deviation; and second control means for controlling scanning velocities by light on the first and the second photoreceptors. The first control means controls a distance on the image carrier between a first pattern image of the plurality of pattern images and a second pattern image formed subsequently to the first pattern image, based on the scanning velocity.SELECTED DRAWING: Figure 15

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile, and a printer.

  For example, in an image forming apparatus using an electrophotographic system, a charged photosensitive drum is irradiated with light through a polygon mirror, thereby forming a latent image on the photosensitive drum. A photosensitive drum is provided for each color used for image formation, and a toner image of each color is formed on each photosensitive drum by developing the latent image on each photosensitive drum with the corresponding color toner. The image forming apparatus sequentially transfers these toner images onto the intermediate transfer belt, and then collectively transfers the toner images from the intermediate transfer belt to the recording material. A color image is formed by superimposing and transferring the toner images formed on the respective photosensitive drums to the intermediate transfer belt. Here, a relative shift may occur in the transfer position of each toner image to the intermediate transfer belt. This phenomenon is called color shift and is one of the factors that determine image quality. As a cause of color misregistration, there is a speed fluctuation of the moving speed of the surface of the intermediate transfer belt due to the eccentricity of the driving roller that drives the intermediate transfer belt.

  Patent Document 1 discloses a configuration that reduces color misregistration caused by eccentricity of a driving roller by setting an interval between transfer positions of each photosensitive drum to an intermediate transfer belt to an integral multiple of the circumferential length of the driving roller. doing. Patent Document 2 discloses auto registration correction (color misregistration correction) in which a pattern image for color misregistration correction is formed on an intermediate transfer belt and color misregistration is corrected based on the detection result of the pattern image. Note that the detection result of color misregistration varies depending on the pattern image formation position on the intermediate transfer belt due to the speed variation of the intermediate transfer belt due to the eccentricity of the drive roller. For this reason, Patent Document 3 discloses a configuration in which a plurality of pattern images are formed and color misregistration correction is performed based on an average value of detection results of the pattern images.

JP 59-182139 A JP 2000-293084 A JP 2002-14507 A

  In the image forming apparatus, the length (magnification) in the sub-scanning direction of an image formed on the intermediate transfer belt may be adjusted. As an example, in order to increase transfer efficiency, there is a case where the peripheral speed of the intermediate transfer belt and the conveyance speed of the recording material are made different from each other at the transfer position of the toner image from the intermediate transfer belt to the recording material. . If there is a speed difference at the transfer position, the toner image on the intermediate transfer belt is expanded and contracted in the sub-scanning direction according to the speed difference and transferred to the recording material. To set the length of the toner image transferred to the recording material in the sub-scanning direction to the target value, the sub-scanning direction of the toner image formed on the photosensitive drum according to the speed difference at the transfer position of the toner image to the recording material. It is necessary to adjust the length (magnification).

  As a method for adjusting the magnification in the sub-scanning direction, for example, a method for adjusting the rotation speed of a polygon mirror is known. Specifically, when the rotation speed of the polygon mirror is decreased, the interval between the scanning lines becomes longer, and the toner image formed on the photosensitive drum expands in the sub-scanning direction. On the other hand, when the rotational speed of the polygon mirror is increased, the interval between the scanning lines is shortened, and the toner image formed on the photosensitive drum contracts in the sub-scanning direction. By the way, when the rotation speed of the polygon mirror is changed, the image writing timing changes. Therefore, the image forming apparatus needs to perform color misregistration correction when the rotation speed of the polygon mirror is changed. However, when the image writing timing is changed, the formation positions of a plurality of pattern images on the intermediate transfer belt also change. As a result, the image forming apparatus may not be able to perform color misregistration correction with high accuracy.

  Accordingly, an object of the present invention is to perform color misregistration correction with high accuracy even when the magnification in the sub-scanning direction is changed.

  According to one aspect of the present invention, an image forming apparatus forms an image of a first color on the first photoconductor by scanning the image carrier that is rotationally driven and the first photoconductor with light, and the first photoconductor. A first image forming means for forming the first color image on the image carrier by transferring the first color image formed on the one photoconductor to the image carrier; A second color image different from the first color is formed on the second photoconductor by scanning with light, and the second color image formed on the second photoconductor is transferred to the image carrier. Thus, the second image forming means for forming the second color image on the image carrier, and a plurality of pattern images, the pattern image including the first color image and the second color image First control means for controlling the first image forming means and the second image forming means so as to form the image on the image carrier Correcting means for detecting the first color image and the second color image included in each of the plurality of pattern images and correcting a positional deviation of the second color image with respect to the first color image; Second control means for controlling the scanning speed of the first photoconductor and the second photoconductor by the light, and the first control means includes a first pattern image of the plurality of pattern images, The distance on the image carrier between the second pattern image formed next to the one pattern image is controlled based on the scanning speed.

  According to the present invention, color misregistration correction can be performed with high accuracy even when the magnification in the sub-scanning direction is changed.

1 is a configuration diagram of an image forming apparatus. The block diagram and operation | movement explanatory drawing of a laser scanner. The principal part enlarged view of a secondary transfer nip part. FIG. 3 is a control block diagram of the image forming apparatus. The schematic diagram of a setting screen, and the figure which shows the fixing temperature and peripheral speed difference with respect to the basic weight of a sheet | seat. The figure which shows the pattern image of color misregistration correction. Explanatory drawing of the calculation method of the amount of color shift. Explanatory drawing of the reason for forming a some pattern image. The figure which shows the calculation result of color misregistration amount. 6 is a flowchart of an image forming operation. 10 is a flowchart of color misregistration correction control. The figure which shows a setting screen. The figure which shows the image formed by a test print. The flowchart of magnification adjustment control. Explanatory drawing of the formation method of a some pattern image. Explanatory drawing of the amount of color shift when not adjusting the space | interval of a some pattern image.

  Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings. In addition, the following embodiment is an illustration and does not limit this invention to the content of embodiment. In the following drawings, components that are not necessary for the description of the embodiments are omitted from the drawings.

(Image forming device)
FIG. 1 is a schematic sectional view of the image forming apparatus 100. The image forming apparatus 100 is a laser beam printer that forms a full-color image on a sheet 110. The image forming apparatus 100 includes a printer unit 101 and an operation panel 180. The operation panel 180 includes key buttons and a liquid crystal display 180A. The liquid crystal display 180A is a touch panel type flat panel display. The operation panel 180 is an interface through which the user inputs the number of printed images and the print mode. Using the operation panel 180, the user can select a single-sided printing mode or a double-sided printing mode, execute a face-down paper discharge mode, or select a monochrome mode or a color mode.

  The printer unit 101 includes four image forming units 120, 121, 122, and 123 that form an image for each color component. The image forming unit 120 forms a yellow image, the image forming unit 121 forms a magenta image, the image forming unit 122 forms a cyan image, and the image forming unit 123 forms a black image.

  Since the image forming units 120 to 123 have the same configuration, the configuration of the image forming unit 120 that forms a yellow image will be described below. The photosensitive drum 105 has a photosensitive layer on the surface. The photosensitive drum 105 functions as a photosensitive member. The charger 111 charges the photosensitive drum 105. The laser beam of the laser scanner 108 controlled based on the image data scans the photosensitive drum 105, whereby an electrostatic latent image is formed on the photosensitive drum 105. The developing device 112 contains a developer containing toner and a magnetic carrier. The developing device 112 develops the electrostatic latent image on the photosensitive drum 105 using a developer. As a result, a toner image is formed on the photosensitive drum 105.

  The primary transfer roller 115 forms a primary transfer nip portion by pressing the photosensitive drum 105 via the intermediate transfer belt 106. The toner image on the photosensitive drum 105 enters the primary transfer nip portion as the photosensitive drum 105 rotates. A transfer voltage is applied to the primary transfer roller 115 by a power supply unit (not shown). As a result, the toner image on the photosensitive drum 105 is transferred to the intermediate transfer belt 106 at the primary transfer nip portion. The intermediate transfer belt 106 functions as a transfer body (image carrier) to which a toner image is transferred. The toner images for each color formed by the image forming units 120 to 123 are transferred onto the intermediate transfer belt 106 so that a full-color toner image is carried on the intermediate transfer belt 106. Further, the developer that has not been transferred from the photosensitive drum 105 to the intermediate transfer belt 106 in the primary transfer nip portion remains on the photosensitive drum 105. The drum cleaner 116 removes the developer remaining on the photosensitive drum 105 by a cleaning roller that contacts the photosensitive drum 105.

  The optical sensor 9 includes a light emitting element that emits light to the intermediate transfer belt 106 and a light receiving element that receives reflected light from the intermediate transfer belt 106. The optical sensor 9 outputs a signal corresponding to the amount of reflected light from the toner image formed on the intermediate transfer belt 106.

  The secondary transfer belt 114 forms a secondary transfer nip portion by pressing the secondary transfer roller via the intermediate transfer belt 106. The toner image carried on the intermediate transfer belt 106 is conveyed to the secondary transfer nip portion as the intermediate transfer belt 106 rotates.

  Sheets 110 are accommodated in the cassettes 113A and 113B. The sheets fed one by one from the cassette 113A or the cassette 113B by the sheet feeding mechanism are conveyed along the conveyance path 109 to the secondary transfer nip portion. A conveyance roller provided in the conveyance path 109 conveys the sheet 110 toward the secondary transfer nip portion so that the timing coincides with the toner image carried on the intermediate transfer belt 106.

  A transfer voltage is applied to the secondary transfer belt 114. As a result, the secondary transfer belt 114 transfers the toner image (formed image) carried on the intermediate transfer belt 106 to the sheet 110. The secondary transfer belt 114 functions as a transfer unit that transfers the toner image carried on the intermediate transfer belt 106 to the sheet 110.

  The sheet 110 on which the toner image is transferred is conveyed to the fixing devices 150 and 160. Fixing units 150 and 160 heat and press the toner image transferred to the sheet 110 to fix it on the sheet 110. The fixing device 150 includes a fixing roller 151 having a heater 140 that heats the sheet 110, and a pressure belt 152 that presses the sheet 110 against the fixing roller 151. The fixing device 160 is disposed downstream of the fixing device 150 in the conveyance direction of the sheet 110. The fixing device 160 gives gloss to the toner image on the sheet 110 that has passed through the fixing device 150. The fixing device 160 includes a fixing roller 161 having a heater 141 for heating the sheet, and a pressure roller 162 that presses the sheet 110 against the fixing roller 161.

  When the image is fixed on the sheet 110 in the mode for imparting the gloss or when the image is fixed on the sheet 110 having a large amount of heat necessary for the fixing process, the sheet 110 that has passed through the fixing device 150 passes along the conveyance path 130A. It is conveyed to the fixing device 160. On the other hand, when fixing an image on thin paper, the sheet 110 that has passed through the fixing device 150 is conveyed along a conveyance path 130 that bypasses the fixing device 160. Note that the angle of the flapper 131 is controlled in order to control whether the sheet 110 is conveyed to the fixing device 160 or whether the sheet 110 is conveyed around the fixing device 160.

  The flapper 132 is a guide member that switches whether to guide the sheet 110 to the transport path 135 or to the transport path 139 to the outside. The sheet 110 transported along the transport path 135 is transported to the reversing unit 136. When a reverse sensor (not shown) provided in the transport path 135 detects the trailing edge of the sheet 110, the transport direction of the sheet 110 is reversed.

  The flapper 133 is a guide member that switches whether the sheet 110 is guided to the conveyance path 138 for double-sided image formation or to the conveyance path 135. When the face-down paper discharge mode is executed, the sheet 110 is conveyed again to the conveyance path 135 and is discharged from the image forming apparatus 100.

  On the other hand, when the duplex printing mode is executed, the sheet 110 is conveyed again to the secondary transfer nip portion along the conveyance path 138. When the duplex printing mode is executed, after the image is fixed on the first surface of the sheet 110, the sheet 110 is switched back in the reversing unit 136 and is moved along the conveyance path 138 to the secondary transfer nip unit. The sheet is conveyed and an image is formed on the second surface of the sheet 110.

  The flapper 134 is a guide member that guides the sheet 110 to a conveyance path for discharging the sheet 110 from the image forming apparatus 100. When the sheet 110 is discharged face-down, the flapper 134 guides the sheet switched back in the reversing unit 136 to the discharge conveyance path. The sheet 110 conveyed along the paper discharge conveyance path is discharged outside the image forming apparatus 100.

(Laser scanner)
FIG. 2A is a schematic diagram of the laser scanner 108 and the photosensitive drum 105. The laser scanner 108 includes a semiconductor laser 201 as a light source, a collimator lens 202, an aperture stop 203, a cylindrical lens 204, a polygon mirror 205, a motor 206, a toric lens 207, and a diffractive optical element 208.

  The collimator lens 202 converts the light beam emitted from the semiconductor laser 201 into a parallel light beam. The aperture stop 203 restricts the luminous flux of the laser beam that passes therethrough. The cylindrical lens 204 images the light beam that has passed through the aperture stop 203 on the reflection surface of the polygon mirror 205. A polygon mirror 205, which is a rotating polygon mirror, is rotated at an angular velocity ωs in the direction of arrow C in the figure by a motor 206, and deflects laser light imaged on a reflecting surface. The laser beam deflected by the polygon mirror 205 scans the surface of the photosensitive drum 105 in the direction of arrow A. The direction in which the laser beam scans the photosensitive drum 105 is referred to as the main scanning direction. The direction perpendicular to the main scanning direction and tangent to the surface of the photosensitive drum 105 is referred to as a sub-scanning direction.

  The toric lens 207 is an optical element having fθ characteristics and has different refractive indexes in the main scanning direction and the sub-scanning direction. The shape of both the front and back lens surfaces of the toric lens 207 in the main scanning direction is aspheric. The diffractive optical element 208 is an optical element having fθ characteristics, and has different magnifications in the main scanning direction and the sub-scanning direction. A beam detector 209 (hereinafter referred to as BD 209) is installed at a position corresponding to the outside of the image forming area of the photosensitive drum 105, and detects the laser light reflected by the reflection mirror 210. Thereby, a scanning timing signal (BD signal) is generated. Then, the semiconductor laser 201 starts light emission corresponding to the next one scanning line in the main scanning direction in synchronization with the BD signal.

  In the photosensitive drum 105, the spot of the laser beam emitted from the semiconductor laser 201 deflected to the polygon mirror 205 that is driven to rotate moves (scans) linearly in parallel to the photosensitive drum axis. The photosensitive drum 105 is rotationally driven by a drum motor 211. As the photosensitive drum 105 rotates, the laser beam scans the photosensitive drum 105, whereby an electrostatic latent image is formed on the surface of the photosensitive drum 105.

(Polygon sub-scan scaling)
Here, polygon sub-scanning scaling will be described. Polygonal sub-scanning scaling is a method in which the scanning speed (polygon mirror rotation speed) when the laser scanner 108 exposes the photosensitive drum 105 with laser light is made variable so that the expansion / contraction ratio of an image formed on the photosensitive drum 105 is increased. It is a process to change.

  FIG. 2B shows a timing chart of scanning with laser light. A vertical synchronization signal Vsync is generated in synchronization with the BD signal output from the BD 209. The semiconductor laser 201 emits laser light corresponding to the image data for each scanning line in synchronization with the vertical synchronization signal Vsync. When the angular velocity ωs of the polygon mirror 205 becomes slow at the timing X, the output period (output interval) of the BD signal becomes long. When the surface speed (circumferential speed) of the photosensitive drum 105 is constant, the interval between scanning lines increases as the output period (output interval) of the BD signal becomes longer. This increases the magnification of the image in the sub-scanning direction (sub-scanning magnification). Note that when the image is compressed in the sub-scanning direction, the angular velocity ωs of the polygon mirror 205 may be increased.

  In the polygon sub-scan scaling, the sub-scan magnification of the image is changed by changing the rotation speed (angular velocity ωs) of the polygon mirror 205. The angular speed ωs of the polygon mirror 205 is controlled based on the rotational speed of the motor 206. The motor 206 is feedback-controlled so that the rotational speed of the motor 206 becomes the target rotational speed. Therefore, polygon sub-scanning scaling is realized by the motor driver 25 (FIG. 4) changing the target value of the rotational speed of the motor 206. Note that when the angular velocity ωs of the polygon mirror 205 is changed, the geometric characteristics of the image change. Therefore, the image forming apparatus 100 generally executes the color misregistration correction control immediately after the angular velocity ωs of the polygon mirror 205 is changed. As a result, the image forming apparatus 100 suppresses the deviation in the sub-scanning direction of the image caused by the change in the angular velocity of the polygon mirror 205.

(Color misregistration correction control)
Here, a relative positional shift (color shift) that may occur between the toner images of the respective colors transferred to the intermediate transfer belt 106 by the image forming units 120 to 123 will be described. When a relative positional shift occurs in the image of each color component transferred onto the intermediate transfer belt 106, the color of the image formed on the recording material 110 changes. The inventors have called the color misregistration that the image forming positions of the respective color component images are different. The image forming apparatus 100 forms a pattern image for detecting the color misregistration amount on the intermediate transfer belt 106, and corrects the image forming position of the image of each color component based on the result of detecting the pattern image by the optical sensor 9. To do. The series of correction processes described above is color misregistration correction control. The image forming apparatus 100 performs color misregistration correction control after the power is turned on, after an image for a predetermined page is formed, or after the angular velocity of the polygon mirror 205 is changed.

(Secondary transfer part)
FIG. 3 is an enlarged view of a main part of the secondary transfer nip portion. A secondary transfer roller 1061 is inscribed in the intermediate transfer belt 106. A secondary transfer outer roller 1143a and tension rollers 1143b, 1143c, and 1143d are inscribed in the secondary transfer belt 114. The secondary transfer outer roller 1143a is electrically grounded. When the toner image on the intermediate transfer belt 106 is transferred to the sheet 110, the secondary transfer belt 114 sandwiches the sheet 110 between the intermediate transfer belt 106 and the toner image on the intermediate transfer belt 106 by electrostatic force. Transfer to the sheet 110. A brush 1141 and a cleaning blade 1142 are provided on the outer periphery of the secondary transfer belt 114. The brush 1141 and the cleaning blade 1142 are cleaning mechanisms for collecting the toner images formed on the intermediate transfer belt 106 when they are directly transferred to the secondary transfer belt 114.

  The intermediate transfer belt 106 and the secondary transfer belt 114 can be driven at mutually independent speeds. The intermediate transfer belt 106 rotates as the secondary transfer roller 1061 rotates. The motor 1062 (FIG. 4) rotationally drives the secondary transfer roller 1061 so that the surface speed (circumferential speed) of the intermediate transfer belt 106 becomes a predetermined surface speed (circumferential speed) V1. The secondary transfer belt 114 rotates as the secondary transfer outer roller 1143a rotates. The motor 1147 (FIG. 4) rotates and drives the secondary transfer outer roller 1143a so that the surface speed (circumferential speed) of the secondary transfer belt 114 becomes a predetermined surface speed (circumferential speed) V2. The secondary transfer belt 114 is a conveying member that conveys the sheet 110 to the secondary transfer unit. That is, the conveyance speed of the sheet 110 is equal to the surface speed V2 of the secondary transfer belt 114.

  The sheet 110 conveyed through the conveyance path 109 is guided to the secondary transfer nip portion by the guide 1144. The sheet 110 that has passed through the secondary transfer nip is discharged to the guide 1145. The guide 1145 guides the sheet 110 to the conveyance belt 118.

(Secondary transfer belt speed adjustment)
5A to 5C are schematic diagrams of setting screens displayed on the liquid crystal display 180A of the operation panel 180. FIG. FIG. 5D is a table showing the fixing temperature and the peripheral speed difference with respect to the basis weight of the sheet 110. This table is stored in the ROM 11, for example. The setting screen displayed on the liquid crystal display 180A by the CPU 10 includes various operation buttons (key buttons). The user sets the sheet 110 such as printing conditions by operating the operation buttons.

  The print job conditions and the sheet attributes of the sheet 110 are stored in the RAM 12. The user can set sheet attributes according to FIGS. 5A and 5C, and can set conditions for a print job according to FIG. 5B. The sheet attribute is information about the sheet such as the basis weight of the sheet 110, the type and size of the sheet 110, and the amount of expansion and contraction of the image in the conveyance direction of the sheet 110.

  The user can set the basis weight of the sheet 110 by operating the “−” key 1801 and the “+” key 1802 on the setting screen of FIG. The user operates the “OK” key 1804 to change the basis weight of the sheet attribute. When canceling the basis weight change, the user operates a “cancel” key 1803.

  With the setting screen shown in FIG. 5B, the user can set an operation mode for optimizing a print job. In this embodiment, several patterns of operation modes can be selected in accordance with the basis weight of the sheet 110 set in FIG. Here, an image quality priority mode that prioritizes image quality and a productivity priority mode that prioritizes productivity rather than image quality can be selected as the operation mode.

  In a print job in which a thin paper sheet and a thick paper sheet are mixedly loaded, in the image quality priority mode, the fixing temperature is switched so that an optimum gloss can be obtained for each sheet. Therefore, a down time occurs until the fixing temperature reaches a predetermined temperature. In the productivity priority mode, a print job is executed at a common fixing temperature, so that downtime due to switching of the fixing temperature does not occur. However, the image quality of the image formed in the productivity priority mode is not optimal gloss. The user can select the productivity priority mode using the productivity priority button 1805 on the setting screen shown in FIG. 5B, and can select the image quality priority mode using the image quality priority button 1806. When reflecting the selection result, the user operates an “OK” key 1808. When canceling the selection, the user operates a “cancel” key 1807.

  The table in FIG. 5D is the difference in fixing temperature and peripheral speed between the image quality priority mode and the productivity priority mode at a basis weight of 150 [gsm] (hereinafter referred to as a peripheral speed difference). Represents. Here, the basis weight is the weight of the sheet per square meter. The peripheral speed difference is expressed by an amount obtained by offsetting (peripheral speed V1 of the intermediate transfer belt 106) / (peripheral speed V2 of the secondary transfer belt 114) from 100 [%]. For example, a peripheral speed difference of 1.50 [%] means that the peripheral speed V1 of the intermediate transfer belt 106 is 1.50 [%] faster than the peripheral speed V2 of the secondary transfer belt 114.

  The image forming apparatus 100 according to the present exemplary embodiment is a case where the basis weight of the sheet 110 is mixed and loaded by switching the fixing temperature and changing the peripheral speed based on the basis weight 150 [gsm] of the sheet 110. However, it is possible to obtain optimum image quality while maintaining productivity. In the image quality priority mode, high-quality image formation is realized by changing the fixing temperature and the peripheral speed difference according to the basis weight. In the productivity priority mode, the fixing temperature and the peripheral speed difference are the same regardless of the basis weight. In this manner, the peripheral speed difference can be set based on the image quality setting, that is, whether or not the image quality priority mode is set, and the basis weight of the sheet.

  Further, the user can set the adjustment amount of the peripheral speed V2 of the secondary transfer belt 114 by using the setting screen shown in FIG. The user can freely change the peripheral speed V2 of the secondary transfer belt 114 by selecting the sign of the adjustment value using the “±” key 1811 and operating the “−” key 1812 and the “+” key 1813. Can do. When changing the peripheral speed V2 of the secondary transfer belt 114 having the sheet attribute, the user operates an “OK” key 1815. When canceling the change, the user operates a “cancel” key 1814.

  In the example of FIG. 5C, the speed adjustment amount of the secondary transfer belt 114 is set between “−3 to 3”, and the circumferential speed difference determined by the table of FIG. One level is offset by 0.05 [%]. For example, the peripheral speed difference of thick plain paper with a basis weight of 160 [gsm] in the image quality priority mode is 1.50 [%] with reference to the table. When “+3” is set in order to improve the “gutter” of the image in the setting screen of FIG. 5C, 1 is offset by 0.15 [%] with respect to the circumferential speed difference of 1.50 [%]. A peripheral speed difference of .65 [%] is set.

  The image forming apparatus 100 performs sub-scanning magnification (digital scaling in the conveyance direction in which the sheet 110 is conveyed) of the image so that the image transferred to the sheet 110 in the secondary transfer unit is in the sub-scanning direction (conveyance direction). ) To cancel the magnification change of the image that expands or contracts. As a result, an image having no expansion / contraction can be obtained regardless of the peripheral speed difference between the peripheral speed of the intermediate transfer belt 106 and the peripheral speed of the secondary transfer belt 114. Sub-scanning scaling includes digital sub-scanning scaling by correcting image data representing an image, and polygon sub-scanning scaling by controlling laser light when forming an image on the photosensitive drum 105. The conversion from the peripheral speed difference to the adjustment amount of the sub-scanning magnification can be performed by, for example, conversion using a predetermined arithmetic expression or a table.

(Function block diagram)
FIG. 4 is a control block diagram of the image forming apparatus 100. The image forming apparatus 100 includes a CPU 10, a ROM 11, a RAM 12, and a sensor 9. The image processing unit 20 performs image processing on the image data.

  The motor 211 rotates so that the photosensitive drum 105 has a predetermined rotation speed. The motor 206 rotates the polygon mirror 205. The motor driver 25 controls the motor 206 so that the rotational speed of the polygon mirror 205 becomes the target speed. The CPU 10 sets the target speed of the polygon mirror 205 based on the test print length information input by the user using the operation panel 180. The motor 1062 rotates the secondary transfer roller 1061 so that the rotation speed of the intermediate transfer belt 106 becomes the target speed. The motor 1147 rotates the secondary transfer outer roller 1143a. The motor driver 26 controls the motor 1147 so that the rotation speed of the secondary transfer belt 114 becomes the target speed. Note that the CPU 10 sets a target speed of the secondary transfer belt 114 based on information regarding the speed of the secondary transfer belt 114 input by the user using the operation panel 180.

  The pattern generator 24 transfers pattern image data for causing the printer unit 101 to form a pattern image used for detecting the color misregistration amount to the printer unit 101. The pattern generator 24 also transfers test image data for causing the printer unit 101 to form a test print used to adjust the target rotational speed of the polygon mirror 205 to the printer unit 101.

  The optical sensor 9 includes an intermediate transfer belt 106 or a light emitting element that emits light toward the pattern image, and a light receiving element that receives reflected light from the intermediate transfer belt 106 or the pattern image. The light receiving element receives irregularly reflected light of the light emitted from the light emitting element to the intermediate transfer belt 106. When the light receiving element receives light reflected by the intermediate transfer belt 106 or light reflected by a pattern image formed on the intermediate transfer belt 106, the light receiving element outputs a signal having a level corresponding to the amount of received light.

  The memory 21 stores the signal value output from the optical sensor 9. The calculation unit 22 calculates a color misregistration correction amount based on the detection result of the pattern image stored in the memory 21. The image processing unit 20 executes image processing on the image data in order to correct the image forming position for each color based on the color misregistration correction amount calculated by the calculation unit 22. As a result, the relative positions of the yellow, cyan, and black images and the magenta image are corrected. In this example, the position of the magenta image corresponds to the reference position. Magenta is referred to as a reference color. A method of calculating the color misregistration correction amount will be described later with reference to FIG.

(Color shift correction)
Here, a relative shift (color shift) generated between each color toner image transferred to the intermediate transfer belt 106 by each image forming unit and a correction method thereof will be described. As described above, yellow, magenta, cyan, and black toner images are formed on the photosensitive drum 105, respectively. A color image is formed on the sheet by transferring the toner image formed on each photosensitive drum to the sheet. At this time, if the toner images formed on the respective photosensitive drums are deviated from each other, the original image and the output image are different in color, so that the image quality is deteriorated.

  Therefore, the image forming apparatus 100 forms a pattern image on the intermediate transfer belt 109. Then, the relative positions of the toner images of the respective colors are corrected based on the detection result (color shift amount) of the pattern image that is the measurement image. Note that the image forming apparatus 100 executes color misregistration correction control when the power of the image forming apparatus 100 is turned on, for example. Further, for example, the image forming apparatus 100 executes color misregistration correction control when a predetermined time elapses after the power of the image forming apparatus 100 is turned on. In addition, the image forming apparatus 100 executes color misregistration correction control when, for example, the number of sheets on which an image is formed reaches a predetermined number.

  When the start of the color misregistration correction control is instructed, the driving of the intermediate transfer belt 106 is started, and the printer unit 101 starts forming a plurality of pattern images 300 shown in FIG. A plurality of pattern images 300 are continuously formed on the intermediate transfer belt 106. The pattern image 300 includes a magenta pattern image 302, a yellow pattern image 301, a cyan pattern image 303, and a black pattern image 304. The optical sensor 9 receives irregularly reflected light from the pattern image and outputs a signal value corresponding to the amount of received light. The signal value of the optical sensor 9 is input to a comparator (not shown). A comparator (not shown) compares the signal value of the optical sensor 9 with a threshold value, and outputs a binary signal based on the comparison result.

Here, a method for detecting the color misregistration amount will be described. In the present embodiment, the reference color is magenta. FIG. 7 is a schematic diagram for explaining a method of calculating the color misregistration amount (relative position difference) between the pattern image 301 and the pattern image 302. FIG. 7A shows a case where the pattern image 301 is shifted from the pattern image 302 in a direction (main scanning direction) orthogonal to the conveyance direction. At this time, the pattern image 301 is formed so as to be sandwiched between the two pattern images 302. Therefore, the distances of the respective centers of gravity are defined as A1, A2, B1, and B2, as shown in FIG. When there is no deviation in the positional relationship, A1 = A2 = B1 = B2. In the state of FIG. 7A, when the shift amount in the main scanning direction of the yellow pattern image 301 is calculated as ΔH, the following equation is obtained.
ΔH = {(B2-B1) / 2- (A2-A1) / 2} / 2 (1)
Similarly, FIG. 7B shows a state in which the yellow pattern image 301 is shifted with respect to the sub-scanning direction. Similarly, when the shift amount in the sub-scanning direction is calculated as ΔV, the following equation is obtained.
ΔV = {(B2−B1) / 2 + (A2−A1) / 2} / 2 (2)
In practice, color misregistration in the main scanning direction and the sub-scanning direction can occur simultaneously, but the above equations hold independently.

  In the present embodiment, a plurality of pattern images 300 are continuously formed, and the deviation amounts obtained by detecting each pattern image for each correction target color with respect to the reference color (magenta) are averaged. Then, based on the average value of the shift amounts obtained from each pattern image, the image forming conditions relating to the toner image forming position are corrected. Here, the reason why the color misregistration correction is performed based on the average value of the shift amounts obtained from the pattern images 300 of the plurality of pattern images 300 will be described with reference to FIG.

  As described above, the intermediate transfer belt 106 rotates depending on the rotation of the secondary transfer roller 1061. Here, consider a case where the peripheral speed of the intermediate transfer belt 106 fluctuates in the rotation period of the secondary transfer roller 1061 due to the eccentricity of the secondary transfer roller 1061. When the peripheral speed of the intermediate transfer belt 106 changes, the time interval for detecting two adjacent toner images in FIGS. 7A and 7B also changes, so that the detected values such as the distances A1, A2, B1, B2, etc. Will change accordingly. That is, the detected shift amount changes according to the peripheral speed of the intermediate transfer belt 106 when the pattern image is detected. Therefore, as shown in FIG. 8, a plurality of pattern images are formed at equal intervals at a distance corresponding to an integral multiple of the speed fluctuation period of the intermediate transfer belt 106. In FIG. 8, a total of ten sets of pattern images 300 of # 1 to # 10 are formed at equal intervals at a distance corresponding to nine cycles of speed fluctuation of the intermediate transfer belt 106. As indicated by a broken line in FIG. 8, the color misregistration amount obtained from the pattern image 300 includes an error due to the speed variation of the intermediate transfer belt 106. The error caused by the speed fluctuation of the intermediate transfer belt 106 changes periodically. Therefore, the image forming apparatus 100 according to the present embodiment obtains an average value of the color misregistration amounts detected from the pattern image groups 300 (# 1 to # 10) formed at predetermined intervals, and the peripheral speed of the intermediate transfer belt 106. The color misregistration amount in which the influence of the fluctuation of the color is suppressed is determined.

  FIG. 9A shows a certain correction target color when 10 sets of pattern images 300 are formed at equal intervals at a distance corresponding to nine cycles of speed fluctuation of the intermediate transfer belt 106 as shown in FIG. The detected value of the color misregistration amount is shown. As shown in FIG. 9A, the color shift amount detected from the pattern image 300 changes in a substantially sine wave shape. As shown in FIG. 9A, the average color misregistration amount is detected as 48 microseconds in terms of time.

(Image forming operation)
An image forming operation in which the image forming apparatus 100 forms an image based on image data will be described with reference to the flowchart of FIG. When the image data is transferred to the image forming apparatus 100, the CPU 10 reads a program stored in the ROM 11 and executes each process of the flowchart of FIG.

  The CPU 10 inputs image data to the image processing unit 20, and the image processing unit 20 executes image processing on the image data (S100). The image processing unit 20 performs image processing on the image data so that the main-scanning shift amount and the sub-scanning shift amount are corrected based on the color shift correction amount calculated by the calculation unit 22. Then, the CPU 10 controls the printer unit 101 to form an image on a sheet based on the image data output from the image processing unit 20 (S101), and completes image formation for one page. Since the image forming operation of the printer unit 101 in step S101 has already been described, description thereof is omitted here. The CPU 10 repeatedly executes the image forming operation until all the images included in the image data are formed on the sheet.

  FIG. 11 is a flowchart of color misregistration correction control using the pattern image 300. When the user instructs execution of color misregistration correction on the operation panel 180, the CPU 10 reads a program stored in the ROM 11 and executes each process of the flowchart of FIG. In addition, when the image forming apparatus 100 prints an image on a predetermined number of sheets, the CPU 10 reads a program stored in the ROM 11 and executes each process of the flowchart of FIG. At this time, the CPU 10 may be configured to interrupt the image forming operation and execute each process of color misregistration correction control illustrated in FIG. 11. In the case of this configuration, the CPU 10 restarts the image forming operation after the color misregistration correction control is executed. If the difference between the temperature when the sensor (not shown) provided in the image forming apparatus 100 previously executed the color misregistration correction control is greater than a predetermined value, the CPU 10 performs the color misregistration correction control shown in FIG. It is good also as a structure which performs each of these processes.

  First, the CPU 10 controls the printer unit 101 to form ten sets of pattern images 300 on the intermediate transfer belt 106 (S300). In step S300, the CPU 10 causes the pattern generator 24 to output pattern image data. As a result, the image forming units 120 to 123 form a plurality of pattern images 300 on the intermediate transfer belt 106. The CPU 110 adjusts the interval between the plurality of pattern images 300 to be formed according to the target rotation speed of the polygon mirror 205. Here, the interval between the plurality of pattern images 300 is sub-scanning in which a pattern image is not formed between a certain pattern image 300 and the pattern image 300 formed next on the pattern image 300 on the intermediate transfer belt 106. The length of the direction. A configuration in which the interval between the pattern images 300 is adjusted based on information about the magnification of the sub-scanning magnification of the image, that is, the expansion / contraction rate, may be employed. The reason for adjusting the interval between the pattern images 300 to be formed according to the target rotation speed of the polygon mirror 205 will be described later.

  The CPU 10 controls the optical sensor 9 to detect the pattern image 300 on the intermediate transfer belt 106 (S301). The detection result of the pattern image 300 by the optical sensor 9 is stored in the memory 21. Then, the CPU 10 calculates the color misregistration correction amount by controlling the calculation unit 22 (S302). Since the method for calculating the color misregistration correction amount has already been described, description thereof is omitted here. The CPU 10 stores the color misregistration correction amount calculated in step S302 in a nonvolatile memory (S303), and ends the color misregistration correction control process.

(Magnification adjustment control)
Magnification adjustment control in which the image forming apparatus 100 adjusts the target rotation speed of the polygon mirror 205 will be described with reference to FIGS. 12, 13, and 14. 12A to 12C are examples of setting screens displayed on the display unit 180A of the operation panel 180 in order to set the target rotation speed of the polygon mirror 205. FIG. The setting screen displayed on the display unit 180A by the CPU 10 includes various operation buttons (key buttons). The user sets the target rotation speed of the polygon mirror by operating the operation buttons.

  In the setting screen shown in FIG. 12A, the user can instruct the image forming apparatus 100 to print a test print. The user operates the key button 1820 when instructing to print a test print. If magnification adjustment control is not performed, the user operates a “cancel” key 1821. When the key button 1820 is operated in FIG. 12A, the image forming apparatus 100 prints a test print shown in FIG. The user determines the magnification of the image in the transport direction so that the length Lp of the print area of the test print becomes a predetermined length. The predetermined length is appropriately determined by the user.

  In the setting screen of FIG. 12B, the user operates a “−” key 1822 and a “+” key 1823. As a result, the sub-scanning magnification of the image is changed. That is, the length Lp of the print area can be adjusted by changing the sub-scanning magnification of the image. The user operates the “OK” key 1825 to change the sub-scanning magnification of the image. When canceling the change of the sub-scanning magnification, the user operates the “Cancel” key 1824.

  When the user presses an “OK” key 1825, the CPU 10 determines the target rotation speed of the polygon mirror 205 based on the sub-scanning magnification. Then, the screen of the display unit 180A changes to the screen of FIG. A message for notifying the user that the target rotation speed of the polygon mirror 205 has been set is displayed on the screen of FIG. Further, a message prompting the user to execute color misregistration correction control is displayed on the screen of FIG. Then, when the user operates the “OK” key 1826 on the screen of FIG. 12C, the magnification adjustment control process ends. Note that a method for determining the target rotational speed of the polygon mirror 205 based on information regarding the magnification of the image is a known technique, and thus description thereof is omitted here.

  FIG. 14 is a flowchart of magnification adjustment control. When the user operates the operation panel 180 to instruct execution of magnification adjustment control, the CPU 10 causes the display unit 180A to display the setting screen illustrated in FIG. When the key button 1820 is pressed, the CPU 10 controls the printer unit 101 to output a test print (S200). In step S200, the CPU 10 causes the pattern generator 24 to output test image data. As a result, the image forming units 120, 121, 122, and 123 form test images on the sheet. As shown in FIG. 13, the test image is a magenta image formed on the entire printing area of the sheet. A sheet on which a test image is fixed is a test print.

  When the user presses the key button 1820, the screen of the operation panel 180 is changed to the screen of FIG. After the test print is output in step S200, the CPU 10 stands by until information regarding the sub-scan magnification is input from the operation panel 180 (S201). When the “OK” key 1825 is pressed on the setting screen shown in FIG. 12B, the CPU 10 acquires information on the sub-scanning magnification input by the user, and shifts the magnification adjustment control processing to step S202.

  The CPU 10 determines the target rotational speed of the polygon mirror 205 based on the information regarding the sub-scanning magnification acquired in step S201 (S202). The conversion from the sub-scan magnification information to the target rotation speed of the polygon mirror is performed using, for example, a predetermined arithmetic expression. In the above-described conversion, for example, the change amount of the target rotational speed may be converted from the sub-scanning magnification information with reference to a table. After determining the target rotation speed in step S202, the CPU 10 displays the screen shown in FIG. 12C on the display unit 180A (S203), and ends the magnification adjustment control process. As shown in FIG. 12C, not only a message prompting the user to execute the color misregistration correction control is displayed, but also the color misregistration correction control is automatically started upon completion of the magnification adjustment control. May be.

  Next, the reason for adjusting the interval between adjacent pattern images 300 in accordance with the target rotation speed of the polygon mirror 205 in the color misregistration correction control will be described. The length of the image formed on the intermediate transfer belt 106 in the sub-scanning direction is adjusted by adjusting the rotation speed of the polygon mirror 205 by the magnification adjustment control. Specifically, when the rotation speed of the polygon mirror 205 is decreased, the length of the image formed on the intermediate transfer belt 106 in the sub-scanning direction is increased, and when the rotation speed of the polygon mirror 205 is increased, the intermediate transfer belt 106 is moved. The length of the formed image in the sub-scanning direction is shortened. The same applies to the length in the sub-scanning direction of the interval between the images to be formed where the toner image is not formed. That is, when the rotation speed of the polygon mirror 205 is changed, the length L of the pattern image 300 in the sub-scanning direction and the interval S between the continuous pattern images 300 are changed as shown in FIG. As a result, the distance A between the pattern image 302 of the pattern image 300 and the pattern image 302 of the subsequent pattern image 300 also changes. Here, in this embodiment, the peripheral speed of the intermediate transfer belt 106 is constant. Therefore, the distance that the surface of the intermediate transfer belt 106 moves in one cycle of the speed fluctuation of the intermediate transfer belt 106 is constant regardless of the rotational speed of the polygon mirror 205.

  As described above, in the color misregistration correction control, the surface of the intermediate transfer belt 106 moves during an integral multiple of the speed fluctuation period of the intermediate transfer belt 106 in order to suppress the influence of the speed fluctuation of the peripheral speed of the intermediate transfer belt 106. A plurality of pattern images 300 are formed at equal intervals at a distance to be performed. For example, in the example of FIG. 8, ten sets of pattern images 300 are formed at equal intervals at a distance corresponding to nine cycles of the speed fluctuation of the intermediate transfer belt 106. Here, since the speed fluctuation period of the intermediate transfer belt 106 is constant, the distance A in FIG. 15 must be constant regardless of the rotational speed of the polygon mirror 205.

  Here, for example, in the color misregistration correction control after increasing the rotational speed of the polygon mirror 205, it is assumed that ten sets of pattern images 300 are formed without adjusting the interval S between the pattern images 300. In this case, the distance A (FIG. 15) of the pattern image 300 is shortened. Therefore, as shown in FIG. 16, the formation position of the pattern image 300 is different from the ideal formation position for correcting the speed fluctuation of the intermediate transfer belt. As a result, the average color misregistration amount detected from the ten sets of pattern images 300 is different from the actual color misregistration amount.

  FIG. 9B shows a color formed by adjusting the rotation speed of the polygon mirror 205 to a rotation speed higher than the rotation speed of the polygon mirror 205 in FIG. The result of shift correction is shown. Although the value obtained by converting the average color misregistration amount into time is 48 microseconds, in the example shown in FIG. 9B, the average color misregistration amount is detected as 34 microseconds.

  Therefore, in this embodiment, the formation timing of the pattern image 300 is adjusted so that the distance A (FIG. 15) of the pattern image 300 becomes a predetermined distance regardless of the rotation speed of the polygon mirror 205. That is, the pattern image 300 is formed such that the distance in the sub-scanning direction between the same color toner images included in the pattern image is a predetermined distance. When the target rotational speed of the polygon mirror 205 is decreased in order to increase the magnification in the sub-scanning direction by the magnification adjustment control, the length L of the pattern image 300 becomes longer. Therefore, when the target rotation speed of the polygon mirror 205 is decreased in order to increase the magnification in the sub-scanning direction by the magnification adjustment control, the image forming apparatus 100 shortens the interval S between the pattern images 300. On the other hand, when the target rotational speed of the polygon mirror 205 is increased to reduce the magnification in the sub-scanning direction by the magnification adjustment control, the length L of the pattern image 300 is shortened. Therefore, when the target rotational speed of the polygon mirror 205 is increased to reduce the magnification in the sub-scanning direction by the magnification adjustment control, the image forming apparatus 100 increases the interval S between the pattern images 300. Accordingly, regardless of the sub-scanning magnification set in the magnification adjustment control, it is possible to suppress the influence of the speed fluctuation of the intermediate transfer belt 106 and perform color misregistration correction with high accuracy.

  Next, a method for determining the interval between the pattern images 300 based on information regarding the magnification in the sub-scanning direction will be described. In addition, the dimension shown in the following description is an example, Comprising: This invention is not limited.

  The diameter φ of the drive roller is, for example, 40 [mm]. The peripheral speed of the intermediate transfer belt 7 is, for example, 300 [mm / sec]. In this case, the time required for one rotation of the driving roller is 40 [mm] × π / 300 [mm / sec] ≈418.88 [msec]. When 10 sets of pattern images 300 are formed on the intermediate transfer belt 7, the distance A between the pattern images 300 continuous in the conveyance direction of the intermediate transfer belt 7 is 418.88 [msec] × 9/10 × 300 [mm]. /Sec]≈113.1 [mm]. When the magnification in the sub-scanning direction is 100 [%], the length L of one pattern image 300 in the conveyance direction of the intermediate transfer belt 7 is, for example, 18 [mm]. In this case, the interval S between successive pattern images 300 is 113.1 [mm] −18 [mm] = 95.1 [mm].

When the sub-scanning magnification increases to 101%, the pattern image width also increases by 1%. That is, the width of the pattern image is 18 [mm] × 1.01 = 18.18 [mm]. Therefore, the CPU 10 determines an interval S ′ when the target rotation speed of the polygon mirror 205 is changed based on the following Expression 3.
S ′ = A−L × X / 100 (3)
A: Distance between adjacent pattern images in the sub-scanning direction L: Length of one pattern image in the sub-scanning direction X: Magnification [%] in the sub-scanning direction

  When the sub-scanning magnification increases to 101%, the interval S ′ is 94.92 [mm]. When the sub-scanning magnification increases to 101%, the CPU 10 controls the formation timing of the pattern image 300 by the printer unit 101 so that the interval S becomes the interval S ′. For example, the CPU 10 controls the timing of inputting a trigger signal for forming one pattern image 300 to the printer unit 101 to adjust the formation timing of the pattern image 300.

[Other Embodiments]
The present invention supplies a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in a computer of the system or apparatus read and execute the program This process can be realized. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

  106: intermediate transfer belt, 105: photosensitive drum, 108: laser scanner, 120 to 123: image forming unit, 10: CPU, 20: image processing unit

Claims (12)

A rotationally driven image carrier;
The first photoconductor is scanned with light to form a first color image on the first photoconductor, and the first color image formed on the first photoconductor is transferred to the image carrier. A first image forming means for forming the first color image on the image carrier;
The second photoconductor is scanned with light to form a second color image different from the first color on the second photoconductor, and the second color image formed on the second photoconductor is A second image forming means for forming the second color image on the image carrier by transferring it to the image carrier;
Controlling the first image forming means and the second image forming means so as to form a plurality of pattern images including the first color image and the second color image on the image carrier. First control means for
Correction means for detecting the first color image and the second color image included in each of the plurality of pattern images and correcting a positional deviation of the second color image with respect to the first color image;
Second control means for controlling a scanning speed of the first photosensitive member and the second photosensitive member by the light;
With
The first control means determines a distance on the image carrier between a first pattern image of the plurality of pattern images and a second pattern image formed next to the first pattern image based on the scanning speed. An image forming apparatus that controls the image forming apparatus.   The image forming apparatus according to claim 1, wherein the first control unit increases the distance between the first pattern image and the second pattern image when the scanning speed increases.   The first control means sets a distance between the first color image of the first pattern image and the first color image of the second pattern image to a predetermined value regardless of the scanning speed. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   The first control means sets a distance between the second color image of the first pattern image and the second color image of the second pattern image to a predetermined value regardless of the scanning speed. The image forming apparatus according to claim 3. A driving means for rotating the image carrier;
The image forming apparatus according to claim 4, wherein the predetermined value is a value determined based on a rotation period of the driving unit. A transfer unit that transfers a formed image formed on the image carrier by at least one of the first image forming unit and the second image forming unit to a transported recording material;
6. The apparatus according to claim 1, wherein the second control unit controls the scanning speed in accordance with a speed difference between a peripheral speed of the image carrier and a conveyance speed of the recording material. The image forming apparatus described.   The image forming apparatus according to claim 6, wherein the second control unit determines the speed difference according to a quality setting of the formed image transferred to the recording material.   The image forming apparatus according to claim 6, further comprising an input unit that allows a user to input the speed difference. A transfer unit that transfers a formed image formed on the image carrier by at least one of the first image forming unit and the second image forming unit to a transported recording material;
6. The control unit according to claim 1, wherein the second control unit controls the scanning speed according to an expansion / contraction ratio of the formed image in the conveyance direction of the recording material, which is generated by transfer by the transfer unit. 2. The image forming apparatus according to item 1.   The image forming apparatus according to claim 9, further comprising an input unit that allows a user to input the expansion / contraction ratio.   The correction unit is configured to detect the first color image and the second color image included in a pattern image, and the plurality of patterns of the shift amounts of the second color image with respect to the first color image obtained by the detection. The image forming apparatus according to claim 1, wherein a position shift of the second color image with respect to the first color image is corrected by an average value over the image.   The second control means controls the scanning speed of the first photoconductor by the light by controlling the rotational speed of a polygon mirror that reflects the light emitted from the light source toward the first photoconductor. The image forming apparatus according to any one of claims 1 to 11.

Images