JP2008191424A - Image forming apparatus and control method - Google Patents

Abstract

Image formation capable of forming a high-quality image (realizing high image quality) while having a configuration of forming a latent image using a single polygon mirror for a plurality of image carriers. Providing the device.
An image forming apparatus for forming an image on a recording medium, comprising: a plurality of image carriers each carrying a latent image of each color constituting the image; and image light forming a latent image of each color A rotary polygon mirror that deflects at least two image lights to an image carrier corresponding to the at least two image lights among the plurality of image carriers, and a writing position in the sub-scanning direction of the latent image of each color are detected. There is provided an image forming apparatus comprising: a detection unit configured to control a rotation speed of the plurality of image carriers based on a detection result of the detection unit.
[Selection] Figure 8

Description

  The present invention relates to an image forming apparatus using an electrophotographic system. The present invention is suitable for an image forming apparatus such as a copying machine, a printer, and a facsimile machine.

  With the widespread use of image forming apparatuses utilizing electrophotographic processes, such image forming apparatuses are increasingly required to have higher image quality and smaller size. In order to meet such demands, in recent years, a plurality of process cartridges in which an image carrier unit having an image carrier and a charge developing unit having a charging member and a developing member are integrated are detachably disposed. An image forming apparatus capable of performing the same has been attracting attention. Such an image forming apparatus has, for example, one polygon mirror for two image carriers as a laser scanner unit for forming a latent image on an image carrier of each process cartridge (see Patent Document 1). In addition, the image forming apparatus includes an intermediate transfer body for transferring multiple toner images (latent images) formed on the image carrier.

In an image forming apparatus that multi-transfers toner images, it is necessary to adjust the writing timing of each image and to match the writing position of each image. Therefore, in the image forming apparatus, the irradiation (scanning timing) of the laser beam to the image carrier is adjusted according to the correction value calculated based on the information from the writing position detecting means arranged in the apparatus, and the writing of each image is performed. Image formation is performed in accordance with the position.
JP 2005-157030 A

  However, the conventional image forming apparatus forms a latent image using one polygon mirror (for example, one polygon mirror for two image carriers) for a plurality of image carriers. Therefore, between two colors using the same polygon mirror, the polygon surface opposite to the polygon surface used when forming the latent image of one color is used when forming the latent image of the other color. For this reason, the image writing position in the sub-scanning direction can only be corrected in units of one dot for one color with respect to the other color. In other words, since the writing position of the other color with respect to one color can be adjusted only within a range of ± 1/2 dot, color misregistration occurs in the sub-scanning direction, resulting in higher image quality as required in recent years. Can no longer be satisfied.

  Therefore, the present invention is capable of forming a high-quality image (realizing high image quality) while having a configuration of forming a latent image using a single polygon mirror for a plurality of image carriers. It is an exemplary object to provide an image forming apparatus that can be used.

  In order to achieve the above object, an image forming apparatus according to an aspect of the present invention is an image forming apparatus that forms an image on a recording medium, and a plurality of images that respectively carry latent images of the respective colors constituting the image. A rotating polygon mirror that deflects at least two image lights among the image light forming the latent image of each color to the image carrier corresponding to the at least two image lights among the plurality of image carriers. A detection unit that detects a writing position of the latent image of each color in the sub-scanning direction, and a control unit that controls the rotation speed of the plurality of image carriers based on the detection result of the detection unit. Features.

  According to another aspect of the present invention, there is provided a control method comprising: a plurality of image carriers each carrying a latent image of each color constituting an image formed on a recording medium; and at least two of image lights forming the latent image of each color. A method for controlling an image forming apparatus, comprising: a rotary polygon mirror that deflects one image light to an image carrier corresponding to the at least two image lights of the plurality of image carriers, and the latent image of each color And a control step of controlling the rotational speeds of the plurality of image carriers based on the detection result of the detection step.

  Further objects and other features of the present invention will become apparent from the preferred embodiments described below with reference to the accompanying drawings.

  According to the present invention, it is possible to form a high-quality image (to achieve high image quality) while having a configuration for forming a latent image using a single polygon mirror for a plurality of image carriers. it can.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the accompanying drawings. In addition, in each figure, the same reference number is attached | subjected about the same member and the overlapping description is abbreviate | omitted.

  FIG. 1 is a schematic cross-sectional view showing a configuration of an image forming apparatus 1 in Embodiment 1 of the present invention. FIG. 2 is a schematic block diagram of the image forming apparatus 1 in Embodiment 1 of the present invention. The image forming apparatus 1 is an image forming apparatus that forms an image (color image) on a recording medium, and is embodied as a color laser printer in the present embodiment.

  As shown in FIG. 1, the image forming apparatus 1 includes an image carrier 11 that carries a latent image of an image, a charging roller 12, a developing device 14 that develops the latent image on the image carrier 11, a transfer roller 15, and the like. An image forming unit is included. In the present embodiment, the image carrier 11 includes image carriers 11a to 11d that respectively carry latent images of colors of yellow (Y), magenta (M), cyan (C), and black (Bk). The In this embodiment, the image carrier 11d carries a reference color (Bk) latent image, and the image carriers 11a to 11c carry colors (Y, M, C) other than the reference color. The charging roller 12 includes charging rollers 12a to 12d that uniformly charge the surfaces of the image carriers 11a to 11d. The developing device 14 includes developing devices 14a to 14d that develop the latent images of the respective colors formed on the image carriers 11a to 11d. The transfer roller 15 includes transfer rollers 15a to 15d that transfer toner images of respective colors on the image carriers 11a to 11d to a transfer material S as a recording medium. In this embodiment, the image carrier 11 is the image carriers 11a to 11d, the charging roller 12 is the charging rollers 12a to 12d, the developing device 14 is the developing devices 14a to 14d, and the transfer roller 15 is the transfer rollers 15a to 15d. 15d is generically named.

  In addition, the image forming apparatus 1 includes a sheet feeding unit 21 that stores the transfer material S, a sheet feeding roller 22 and the like, a sheet feeding unit including a sheet feeding roller 21, a conveyance roller 42a to 42d, a registration roller 43 and the like. And a scanner unit 50 that exposes the image carrier 11 to form a latent image. Furthermore, the image forming apparatus 1 discharges the toner image transferred onto the transfer material S to a fixing unit 60 that thermally fixes the toner image and the transfer material S that has received the heat fixing of the toner image to a discharge tray 71 on the upper surface of the apparatus. A paper discharge unit 70 including a paper discharge roller 72 and the like.

  The image carrier 11 is integrally formed with the developing device 14 and constitutes a process cartridge PC. The process cartridge PC is a process cartridge PCa in which the image carrier 11a and the developing device 14a are integrally formed. Similarly, the process cartridge PC is a process in which the image carriers 11b to 11d and the developing devices 14b to 14d are integrally formed. Cartridges PCb to PCd. The process cartridge PC is detachably supported with respect to the image forming apparatus 1 and can be easily replaced according to the life of the image carrier 11. In the present embodiment, the process cartridge PC is a generic name of the process cartridges PCa to PCd.

  In the present embodiment, the image carrier 11 is a photosensitive drum in which an organic photoconductor layer is coated on the outside of an aluminum cylinder, and is supported rotatably with respect to the developing device 14. In addition, the image carrier 11 is connected to a driving mechanism 30 described later, and rotates counterclockwise by the driving force transmitted from the driving mechanism 30.

  The conveyor belt 41 is driven in synchronization with the rotation of the image carrier 11 in order to multiplex-transfer the toner image on the image carrier 11 developed (visualized) by the developing device 14 onto the transfer material S. For example, the transport belt 41 is supported by four axes with the transport rollers 42a to 42d as fulcrums, and is rotated (driven) clockwise by the transport rollers 42a to 42d. The transport belt 41 electrostatically holds the transfer material S supplied from the paper feeding unit and sequentially transports it to the image carrier 11 (image carriers 11a to 11d).

  The toner image formed on the image carrier 11 is multiplex-transferred onto the transfer material S on the conveyor belt 41 at a transfer point that is a contact point between the image carrier 11 and the transfer roller 15. The transfer roller 15 is disposed at a position facing the image carrier 11 with the conveyance belt 41 interposed therebetween, and applies a predetermined voltage from the back surface of the transfer material S via the conveyance belt 41.

  The scanner unit 50 includes, for example, a laser diode and a polygon mirror as a rotary polygon mirror, and exposes the image carrier 11 to form a latent image on the image carrier 11. The laser diode irradiates the polygon mirror with image light IL corresponding to the image formed on the transfer material S. The image light IL includes image light ILa to ILd corresponding to each color constituting the image. The polygon mirror is rotated at a high speed by a motor and deflects (reflects) the image light IL to the image carrier 11. The image light IL exposes the surface of the image carrier IL to form a latent image (electrostatic latent image) on the image carrier 11. In this embodiment, the polygon mirror deflects at least two of the image lights forming the latent images of the respective colors to the image carriers corresponding to at least two of the plurality of image carriers. To do. In the present embodiment, the image light IL is a general term for the image lights ILa to ILd.

  In the operation of the image forming apparatus 1, first, the sheet feeding roller 22 rotates to separate the transfer material S stored in the sheet feeding cassette 21, and the transfer material S is supplied to the registration roller 43.

  On the other hand, the conveyance belt 41 is driven in synchronization with the rotation of the image carrier 11 and conveys the transfer material S supplied from the paper feeding unit to the image forming unit. The rotation of the image carrier 11 will be described in detail later.

  Next, the scanner unit 50 irradiates the image carrier 11 uniformly charged by the charging roller 12 with the image light IL to form a latent image on the image carrier 11. The developing unit 14 applies a voltage having the same polarity as the charging polarity of the image carrier 11 and substantially the same potential to adhere toner to the latent image on the image carrier 11 (that is, the latent image on the image carrier 11). Develop the image).

  The transfer material S is conveyed in accordance with the timing at which the toner image on the image carrier 11a reaches the transfer point. At the transfer point, the transfer roller 15 applies a voltage having a polarity opposite to that of the toner image to the transfer material S, and the toner image on the image carrier 11 is transferred to the transfer material S. The transfer material S is conveyed separately from the toner images on the image carriers 11a to 11d and at the timing when the leading ends of the toner images transferred to the transfer material S coincide. In this manner, the four color toner images on the image carriers 11a to 11d are multiplex-transferred onto the transfer body S.

  The transfer material S on which the toner image on the image carrier 11 is transferred is separated from the image carrier 11 and conveyed to the fixing unit 60. The toner image transferred to the transfer material S is heat-pressed by the fixing unit 60 and fixed on the transfer material S to form an image. The transfer material S on which the image is formed is discharged to a discharge tray 71 via a discharge roller 72.

  Here, the process cartridge PC will be described in detail with reference to FIGS. FIG. 3 is a schematic sectional view of the process cartridge PC. FIG. 4 is a schematic perspective view of the image carrying unit IMU and the developing unit DPU constituting the process cartridge PC. The process cartridges PCa to PCd for each color of yellow, magenta, cyan, and black have the same configuration.

  The process cartridge PC includes an image carrier 11, an image carrier unit IMU including a charging roller (primary charging device) 12, and a cleaning unit 13, and a developing unit DPU including a developing device 14.

  In the image carrier unit IMU, the image carrier 11 is rotatably attached to the cleaning frame 131 via bearing members (bearings) 111a and 111b. Around the image carrier 11, a charging roller 12 that uniformly charges the surface of the image carrier 11 and a cleaning blade 132 that removes residual toner on the image carrier 11 are disposed. The cleaning frame 131 and the cleaning blade 132 constitute a cleaning unit.

  The developing unit DPU is a developing device including a developing roller 141 that contacts the image carrier 11 and rotates clockwise (in the direction of arrow Y shown in FIG. 2), a toner container 142 that contains toner, and a developing frame 143. 14. The developing roller 141 is rotatably supported by the developing frame 143 via bearing members (bearings) 144a and 144b. The developing roller 141 rotates at a predetermined rotation speed by a driving force branched from the driving mechanism 30 that drives the image carrier 11. The image carrier 11 is connected to a drive mechanism 30 to be described later, and rotates counterclockwise at a predetermined rotation speed by a driving force transmitted from the drive mechanism 30.

  The drive mechanism 30 that drives the image carrier 11 will be described with reference to FIGS. 5 and 6. FIG. 5 is a schematic cross-sectional view showing the configuration of the drive mechanism 30. FIG. 6 is a schematic perspective view of one drive unit (drive unit 30 a) constituting the drive mechanism 30.

  In the first embodiment, the driving mechanism 30 includes driving units 30a, 30b, 30c, and 30d in order to independently drive the four image carriers 11a to 11d. A drive unit 30a including a drive motor 31a, a reduction gear 32a, a coupling 33a, a drive gear 34a, a flange 36a, and a photo interrupter 37a drives the image carrier 11a. Similarly, a drive unit 30b including a drive motor 31b, a reduction gear 32b, a coupling 33b, a drive gear 34b, a flange 36b, and a photo interrupter 37b drives the image carrier 11b. A drive unit 30c including a drive motor 31c, a reduction gear 32c, a coupling 33c, a drive gear 34c, a flange 36c, and a photo interrupter 37c drives the image carrier 11c. A drive unit 30d including a drive motor 31d, a reduction gear 32d, a coupling 33d, a drive gear 34d, a flange 36d, and a photo interrupter 37d drives the image carrier 11d.

  The drive mechanism 30 transmits a driving force from the drive motors 31a to 31d to the drive gears 34a to 34d configured integrally with the couplings 33a to 33d via the reduction gears 32a to 32d. Further, the driving mechanism 30 transmits driving force from the driving gears 34a to 34d to the image carriers 11a to 11d via the couplings 33a to 33d.

  Further, in order to suppress color misregistration due to gear accuracy of the drive gears 34a to 34d, the drive gears 34a to 34d are provided with cylindrical flanges 36a to 36d having slits 35a to 35d. Specifically, the slits 35a to 35d are detected by the photo interrupters 37a to 37d, and based on the detection result, control is performed so that the phases of the drive gears 34a to 34d with respect to the image position are matched with each color.

  Further, the drive gears 34a to 34d are all formed of a molded product of the same mold, and the fluctuation profile of one rotation cycle is unified. By matching the phases of the drive gears 34a to 34d, the profiles of the respective colors can be matched, and color misregistration can be reduced. The operation of aligning the phases of the drive gears 34a to 34d is performed at a timing other than the operation of forming the image at the end or start of the print job, and the target image carrier is accelerated or decelerated with respect to the reference color. Realize with.

  Next, the scanner unit 50 will be described in detail. The scanner unit 50 includes a first scanner unit 50ab that exposes the image carriers 11a and 11b, and a second scanner unit 50cd that exposes the image carriers 11c and 11d. The first scanner unit 50ab includes a polygon mirror 51ab that deflects the image light ILa and ILb from the laser diode, a lens 52a that condenses the image light ILa and ILb deflected by the polygon mirror 51ab on the image carriers 11a and 11b, and 52b. The second scanner unit 50cd includes a polygon mirror 51cd that deflects the image light ILc and ILd from the laser diode, a lens 52c that condenses the image light ILc and ILd deflected by the polygon mirror 51cd on the image carriers 11c and 11d, and 52d.

  In the first scanner unit 50ab, the laser diode irradiates the polygon mirror 51ab with the image light ILa and ILb. The polygon mirror 51ab deflects (reflects) the image lights ILa and ILb. The image lights ILa and ILb expose the image carriers 11a and 11b via the lenses 52a and 52b, and are latent on the image carriers 11a and 11b. Form an image. Accordingly, the cyan image light ILc is deflected by the polygon surface opposite to the polygon surface that deflects the black image light ILd with respect to the black image light ILd as the reference color. Therefore, it is necessary to shift the timing of irradiating cyan image light ILc (image writing position) in units of polygon planes (that is, in units of one line (dot)) with respect to black image light ILd as a reference color. is there.

  In the second scanner unit 50cd, the laser diode irradiates the polygon mirror 51cd with the image light ILc and ILd. The polygon mirror 51cd deflects (reflects) the image lights ILc and ILd, and the image lights ILc and ILd expose the image carriers 11c and 11d through the lenses 52c and 52d, and are latent on the image carriers 11c and 11d. Form an image. Accordingly, the yellow image light ILa is deflected by the polygon surface opposite to the polygon surface that deflects the magenta image light ILb. Therefore, it is necessary to shift the timing of irradiating yellow image light ILa (image writing position) in units of polygon planes (that is, in units of one line (dot)) with respect to magenta image light ILb.

  The magenta image light ILb is deflected by a polygon mirror 51ab different from the polygon mirror 51cd that deflects the black image light ILd. Accordingly, the timing (writing start position) for irradiating the magenta image light ILb can be adjusted to the black image light ILd by adjusting the phase of the polygon mirror 51ab.

  The writing position of the image light IL (image light ILa to ILd) of each color is detected by the detection unit 80. Specifically, the detection unit 80 reads a predetermined writing position correction pattern formed on the transport belt 41 and detects a writing position in the sub-scanning direction of the image light IL of each color.

  Further, the control unit 90 calculates the amount of deviation of the writing position of other colors (cyan, magenta, yellow) with respect to black as the reference color from the detection result of the detection unit 80. In this embodiment, the control unit 90 controls the rotation speed of the image carrier 11 based on the detection result of the detection unit 80, as will be described later. The control unit 90 also has a function of adjusting the phases of the polygon mirrors 51ab and 51cd.

  Adjustment of the writing position of each color in the image forming apparatus 1, that is, control of the writing position of the image light IL by the control unit 90 will be described. For example, consider a case where the deviation amount of the writing position in the sub-scanning direction of a certain color with respect to the reference color (black in this embodiment) is +2.75 lines (dots). In this case, the control unit 90 performs control so that the writing start position of the color is delayed by 3 lines (dots). Therefore, 2.75-3 = −0.25 (−1/4) line (dot) cannot be corrected and remains as a residual. In other words, a deviation residual that cannot be corrected by adjusting the phase of the polygon mirrors 51ab and 51cd (that is, ± 1/2 dot or less) remains. Note that “+” means that the writing position is delayed, and “−” means that the writing position is advanced.

  Therefore, the control unit 90 controls the rotation speed of the image carriers 11a to 11d in order to reduce the deviation residual of the writing position of the image light IL in the sub-scanning direction. For example, consider a case where the resolution of the image forming apparatus 1 is 600 dpi. As described above, the deviation residual is ± 1/2 dot or less, and one dot is 2.54 cm / 600 dots≈42.3 μm. Therefore, in order to correct the deviation error of ± 1/2 dot, it is only necessary to adjust the writing position by ± 21.2 μm.

  The control unit 90 can adjust the writing position within a range of ± 21.2 μm by controlling the rotation speed of the image carriers 11a to 11d. For example, as shown in FIG. 7, the diameter of the image carrier 11 is D (24 mm in this embodiment), and the rotation is made between the exposure point Pe on the circumference of the image carrier 11 and the transfer point Pt. The angle is defined as θ (180 ° in this embodiment). The peripheral length Ld of the image carrier 11 between the exposure point Pe and the transfer point Pt is expressed by πD × θ / 360, and in this embodiment, 24π / 2 = 12π≈37.7 mm. The rotational speed Vc of the image carrier 11 for correcting the deviation residual of ± 21.2 μm while the image moves along the circumference Ld is the rotational speed of the image carrier 11 of the reference color × (Ld ± 0.0212) / Ld. Therefore, the control unit 90 can accelerate or decelerate the rotational speed of the image carriers 11a to 11c to be corrected within a range of ± 0.056% with respect to the rotational speed of the black image carrier 11d as the reference color. That's fine. The controller 90 accelerates or decelerates the rotation speed of the image carriers 11a to 11c except during image formation, and maintains the rotation speed of the image carriers 11a to 11c constant during image formation. . As a result, the misalignment residual of the writing position in the sub-scanning direction remaining when the latent image is formed can be corrected, and an image with good image quality that matches the writing position can be obtained. Here, FIG. 7 is a diagram showing the positional relationship between the exposure point Pe and the transfer point Pt in the image carrier 11 of the image forming apparatus 1.

  With reference to FIG. 8, the control of the writing start position of each color image in the image forming apparatus 1 will be described. FIG. 8 is a flowchart for explaining a method of controlling the writing position of each color image in the image forming apparatus 1.

  In step S802, a writing position correction pattern is formed on the conveyor belt 41. Specifically, first, the scanner unit 50 irradiates image light corresponding to the writing position correction pattern to form a latent image of the writing position correction pattern on the image carrier 11. Subsequently, the latent image on the image carrier 11 is developed, and the toner image on the image carrier 11 is transferred to the conveyance belt 41. It should be noted that the formation of the latent image of the writing position correction pattern and the transfer of the toner image are similarly performed by shifting each color by an amount corresponding to the transfer position. As a result, a four-color writing position correction pattern is formed on the conveyor belt 41.

  In step S <b> 804, the detection unit 80 reads the writing position correction pattern formed on the conveyance belt 41. The detection unit 80 transmits the read information (detection result) to the control unit 90.

  In step S806, based on the detection result of the detection unit 80, the control unit 90 writes out the sub-scanning direction of each color (cyan, magenta, yellow in this embodiment) with respect to the reference color (black in this embodiment). The amount of deviation is calculated. Further, in step S808, the control unit 90 calculates a correction value for adjusting the phases of the polygon mirrors 51ab and 51cd based on the shift amount calculated in step S806. Here, the correction value is a value for delaying or accelerating the writing position of each color with respect to the reference color, and is a value in units of one line (dot) as described above. The controller 90 adjusts (controls) the phases of the polygon mirrors 51ab and 51cd in accordance with the correction value calculated in step S808.

  Next, in step S810, the control unit 90 determines whether a deviation residual that cannot be corrected by adjusting the phases of the polygon mirrors 51ab and 51cd remains in the deviation amount calculated in step S806.

  In the case where a deviation residual remains in the deviation amount calculated in step S806, in step S812, based on the deviation residual, the control unit 90 rotates the image carriers 11a and 11c with respect to the rotation speed of the image carrier 11d. Is calculated. The controller 90 controls the rotational speeds of the image carriers 11a and 11c according to the rotational speed calculated in step S812. In other words, the control unit 90 accelerates or decelerates the rotational speeds of the image carriers 11a and 11c with respect to the rotational speed of the image carrier 11d. Then, the control of the writing position of each color image is completed.

  On the other hand, if no deviation residual remains in the amount of deviation calculated in step S806, the rotation speed of the image carriers 11a and 11c with respect to the rotation speed of the image carrier 11d is not calculated, and the image writing position of each color is written. End control.

  In Example 1, the image carriers that need to be controlled in rotation speed are the yellow image carrier 11a and the cyan image carrier 11c. As described above, the magenta writing position can be adjusted to the black writing position by adjusting the phase of the polygon mirror 51ab. Therefore, it is not necessary to control the rotational speed of the magenta image carrier 11b.

  When the image carriers 11a and 11c are rotated at a rotational speed that is accelerated or decelerated with respect to the rotational speed of the reference color image carrier 11d, phase shifts of the drive gears 34a to 34d occur during continuous printing, and the color shift is caused. May occur. However, the phase shift generated by accelerating or decelerating the rotational speeds of the image carriers 11a and 11c can be estimated by calculation. Accordingly, an operation of accelerating or decelerating the image carriers 11a and 11c to adjust the phase between images during continuous printing (so-called paper interval) is performed every predetermined number of sheets (for example, every five sheets). Can maintain good image quality. Further, if printing is performed for each sheet, there is no problem because the phase of the image carrier is adjusted before and after the image forming operation.

  As described above, the image forming apparatus 1 has a configuration in which a latent image is formed on a plurality of image carriers using a single polygon mirror, but by controlling the rotation speed of the image carrier, A high-quality image can be formed (high image quality can be realized). In the first embodiment, the image forming apparatus 1 is configured to form an image with two polygon mirrors on four image carriers, but is not limited to this configuration. For example, even in a configuration in which an image is formed with one polygon mirror for four image carriers, the rotational speed of the three image carriers is controlled in the same manner with respect to the reference image carrier, A good image with no color shift can be obtained.

  FIG. 9 is a schematic block diagram of an image forming apparatus 1A according to the second embodiment of the present invention. The image forming apparatus 1A is different from the image forming apparatus 1 in the configuration of a drive mechanism 30A that drives the image carriers 11a to 11d. The image forming apparatus 1A has the same configuration as that of the image forming apparatus 1 of Embodiment 1 except for the configuration of the drive mechanism 30A.

  The drive mechanism 30A will be described with reference to FIG. FIG. 10 is a schematic cross-sectional view showing the configuration of the drive mechanism 30A. In the second embodiment, the driving mechanism 30A includes a driving unit 30ab that drives the two image carriers 11a and 11b and driving units 30c and 30d that independently drive the two image carriers 11c and 11d.

  The drive unit 30ab includes a drive motor 31ab, reduction gears 32a and 32b, couplings 33a and 33b, drive gears 34a and 34b, flanges 36a and 36b, a photo interrupter 37a, and a connection gear 38. The connection gear 38 connects the drive motor 31ab and the drive gears 34a and 34b. In other words, the drive gears 34 a and 34 b are driven by the common drive motor 31 ab via the connection gear 38. Therefore, the drive unit 30ab drives the image carriers 11a and 11b at the same rotational speed.

  Adjustment of the writing position of each color in the image forming apparatus 1A, that is, control of the writing position of the image light IL by the control unit 90 will be described. As for the cyan image light ILc, as in the first embodiment, the writing position can be adjusted by controlling the rotational speed of the image carrier 11c.

  On the other hand, for yellow and magenta image lights ILa and ILb, the image carriers 11a and 11b are driven by a common drive unit 30ab. Therefore, the image carrier 11a and the image carrier 11b cannot be individually set to the optimum rotation speed. However, between the two colors of yellow and magenta, as described above, the shift amount in the sub-scanning direction can be corrected within a range of ± 1/2 dot by adjusting the phase of the polygon mirror 51ab. Therefore, the entire image can be suppressed to a shift amount of ½ dot or less. Specifically, the phase of the polygon mirror 51ab is increased by an amount obtained by adding the amount of deviation of the writing position in the sub-scanning direction of the magenta and yellow image light ILa and ILb with respect to the black image light ILd as the reference color and dividing by two. Adjust it. As a result, partial color misregistration can be reduced, and image quality can be improved.

  In the control of the writing position of each color image in the image forming apparatus 1A, for the cyan image, the rotation speed of the image carrier 11c is controlled by the control method shown in FIG. Further, as described above, the magenta and yellow images are controlled by adjusting the phase of the polygon mirror 51ab in accordance with the shift amount in the sub-scanning direction. In the second embodiment, the image carrier that needs to control the rotation speed is the cyan image carrier 11c.

  The image forming apparatus 1A reduces the color deviation of the image in the sub-scanning direction by controlling the rotational speed of the image carrier 11c and adjusting the phase of the polygon mirror 51ab to shift the image writing position. / 2). As described above, the image forming apparatus 1A forms a high-quality image (provides high image quality) while having a configuration of forming a latent image using a single polygon mirror for a plurality of image carriers. can do.

  FIG. 11 is a schematic cross-sectional view showing the configuration of the image forming apparatus 1B according to the third embodiment of the present invention. FIG. 12 is a schematic block diagram of an image forming apparatus 1B according to the third embodiment of the present invention. The image forming apparatus 1B is different from the image forming apparatus 1 in the configuration of the drive mechanism 30A that drives the image carriers 11a to 11d and the configuration of the scanner unit 50B that exposes the image carriers 11a to 11d. The image forming apparatus 1A has the same configuration as that of the image forming apparatus 1 of the first embodiment except for the configuration of the drive mechanism 30A and the scanner unit 50B.

  The scanner unit 50B includes a polygon mirror 51abcd for deflecting image light ILa to ILd from the laser diode, and lenses 52a to 52d for condensing the image light ILa to ILd deflected by the polygon mirror 51abcd on the image carriers 11a to 11d. .

  In the scanner unit 50B, the laser diode irradiates the polygon mirror 51abcd with image light ILa to ILb. The polygon mirror 51abcd deflects the image lights ILa to ILd, and the image lights ILa to ILd expose the image carriers 11a to 11d via the lenses 52a to 52d, thereby forming latent images on the image carriers 11a to 11d. To do. Therefore, the cyan image light ILc is deflected by the same polygonal surface as that for deflecting the black image light ILd with respect to the black image light ILd as the reference color. The yellow and magenta image light ILa and ILb are deflected by the polygon surface opposite to the polygon surface that deflects the black image light ILd. Therefore, it is necessary to shift the writing position of the other three color image lights ILa, ILb, and ILc with respect to the black image light ILd in units of polygon planes (that is, in units of one line (dot)).

  Adjustment of the writing position of each color in the image forming apparatus 1B, that is, control of the writing position of the image light IL by the control unit 90 will be described. As for the cyan image light ILc, as in the first embodiment, the writing position can be adjusted by controlling the rotational speed of the image carrier 11c.

  On the other hand, for yellow and magenta image lights ILa and ILb, the image carriers 11a and 11b are driven by a common drive unit 30ab. Therefore, the image carrier 11a and the image carrier 11b cannot be individually set to the optimum rotation speed.

  Therefore, as described below, the control unit 90 carries the yellow and magenta image in accordance with the yellow misalignment residual Zy and the magenta misalignment residual Zm (−1/2 <Zy, Zm ≦ 1/2). The rotational speed of the bodies 11a and 11b is controlled.

  When | Zy−Zm | ≦ 1/2, the controller 90 controls the image carriers 11a and 11b at a rotation speed for correcting (Zy + Zm) / 2 dots.

  When 1/2 <| Zy−Zm | ≦ 1 and | Zy | <| Zm | and Zy <0, the control unit 90 corrects ((Zy + 1) + Zm) / 2 dots. The image carriers 11a and 11b are controlled at the rotation speed. Further, the control unit 90 adjusts the phase of the polygon mirror 51abcd with a correction value obtained by adding 1 dot to the yellow correction value.

  When 1/2 <| Zy−Zm | ≦ 1, and | Zy | <| Zm |, and Zy> 0, the control unit 90 sets ((Zy−1) + Zm) / 2 dots. The image carriers 11a and 11b are controlled at the rotational speed to be corrected. Further, the control unit 90 adjusts the phase of the polygon mirror 51abcd with a correction value obtained by subtracting one dot from the yellow correction value.

  When 1/2 <| Zy−Zm | ≦ 1 and | Zy |> | Zm | and Zm <0, the control unit 90 corrects ((Zm + 1) + Zy) / 2 dots. The image carriers 11a and 11b are controlled at the rotation speed. Further, the control unit 90 adjusts the phase of the polygon mirror 51abcd with a correction value obtained by adding one dot to the magenta correction value.

  When 1/2 <| Zy−Zm | ≦ 1, and | Zy |> | Zm |, and Zm> 0, the control unit 90 sets ((Zm−1) + Zy) / 2 dots. The image carriers 11a and 11b are controlled at the rotational speed to be corrected. Further, the control unit 90 adjusts the phase of the polygon mirror 51abcd with a correction value obtained by subtracting one dot from the magenta correction value.

  With reference to FIG. 13, the control of the writing start position of each color image in the image forming apparatus 1B will be described. FIG. 13 is a flowchart for explaining a method for controlling the writing start position of each color image in the image forming apparatus 1B.

  In step S902, a writing position correction pattern is formed on the conveyor belt 41. Specifically, first, the scanner unit 50 </ b> B irradiates image light corresponding to the writing position correction pattern to form a latent image of the writing position correction pattern on the image carrier 11. Subsequently, the latent image on the image carrier 11 is developed, and the toner image on the image carrier 11 is transferred to the conveyance belt 41. It should be noted that the formation of the latent image of the writing position correction pattern and the transfer of the toner image are similarly performed by shifting each color by an amount corresponding to the transfer position. As a result, a four-color writing position correction pattern is formed on the conveyor belt 41.

  In step S <b> 904, the detection unit 80 reads the writing position correction pattern formed on the transport belt 41. The detection unit 80 transmits the read information (detection result) to the control unit 90.

  In step S906, based on the detection result of the detection unit 80, the control unit 90 writes out the respective colors (cyan, magenta, yellow in this embodiment) in the sub-scanning direction with respect to the reference color (black in this embodiment). The amount of deviation is calculated. Further, in step S908, the control unit 90 calculates a correction value for adjusting the phase of the polygon mirror 51abcd based on the shift amount calculated in step S906.

  Next, in step S910, the control unit 90 determines whether a deviation residual that cannot be corrected by adjusting the phase of the polygon mirror 51abcd remains in the deviation amount calculated in step S906.

  If a deviation residual remains in the deviation amount calculated in step S906, the control unit 90 calculates the rotational speed of the cyan image carrier 11c based on the deviation residual in step S912. Note that the control unit 90 controls the rotation speed of the image carrier 11c according to the rotation speed calculated in step S912.

  In step S <b> 914, the control unit 90 determines that the deviation residual between yellow and magenta is | Zy−Zm | ≦ 1/2, 1/2 <| Zy−Zm | ≦ 1, and | Zy | <| Zm. |, Or 1/2 <| Zy−Zm | ≦ 1, and | Zy |> | Zm |.

  If | Zy−Zm | ≦ 1/2, the control unit 90 controls the image carriers 11a and 11b at a rotation speed for correcting (Zy + Zm) / 2 dots (step S916).

  If 1/2 <| Zy−Zm | ≦ 1 and | Zy | <| Zm |, the control unit 90 determines that the yellow shift residual is Zy <0 or Zy> in step S918. Determine if it is zero. When Zy <0, the control unit 90 controls the image carriers 11a and 11b at a rotational speed for correcting ((Zy + 1) + Zm) / 2 dots, and adds 1 dot to the yellow correction value. The phase of the polygon mirror 51abcd is adjusted with the correction value (step S920). When Zy> 0, the control unit 90 controls the image carriers 11a and 11b at a rotation speed for correcting ((Zy-1) + Zm) / 2 dots, and sets 1 dot to the yellow correction value. The phase of the polygon mirror 51abcd is adjusted with the subtracted correction value (step S922).

  If 1/2 <| Zy−Zm | ≦ 1 and | Zy |> | Zm |, the control unit 90 determines that the magenta deviation residual is Zm <0 or Zm> in step S924. Determine if it is zero. When Zm <0, the control unit 90 controls the image carriers 11a and 11b at a rotation speed for correcting ((Zm + 1) + Zy) / 2 dots, and adds 1 dot to the magenta correction value. The phase of the polygon mirror 51abcd is adjusted with the correction value (step S926). When Zm> 0, the control unit 90 controls the image carriers 11a and 11b at a rotation speed for correcting ((Zm-1) + Zy) / 2 dots, and sets 1 dot as the magenta correction value. The phase of the polygon mirror 51abcd is adjusted with the subtracted correction value (step S928).

  On the other hand, if no deviation residual remains in the deviation amount calculated in step S906, the control of the writing start position of the image of each color is finished as it is.

  When the image carriers 11a to 11c are rotated at a rotational speed that is accelerated or decelerated with respect to the rotational speed of the reference color image carrier 11d, a phase shift of the drive gears 34a to 34d occurs during continuous printing, and the color shift occurs. May occur. However, the phase shift generated by accelerating or decelerating the rotation speed of the image carriers 11a to 11c can be estimated by calculation. Accordingly, by performing the operation of accelerating or decelerating the phase of the image carriers 11a to 11c between images during continuous printing (so-called paper interval) to adjust the phase every predetermined number of sheets (for example, every five sheets). Good image quality can be maintained.

  As described above, the image forming apparatus 1B has a configuration in which a latent image is formed using a single polygon mirror for a plurality of image carriers, but by controlling the rotation speed of the image carrier, A high-quality image can be formed (high image quality can be realized).

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to these embodiments, and various modifications and changes can be made within the scope of the gist. For example, the present invention is not limited to an image forming apparatus having a conveyance belt, but can also be applied to an image forming apparatus using an intermediate transfer member.

1 is a schematic cross-sectional view illustrating a configuration of an image forming apparatus as one aspect of the present invention. It is a schematic block diagram of the image forming apparatus shown in FIG. FIG. 2 is a schematic cross-sectional view of a process cartridge of the image forming apparatus shown in FIG. FIG. 4 is a schematic perspective view of an image carrying unit and a developing unit constituting the process cartridge shown in FIG. 3. FIG. 2 is a schematic cross-sectional view illustrating a configuration of a drive mechanism included in the image forming apparatus illustrated in FIG. 1. It is a schematic perspective view of one drive part which comprises the drive mechanism shown in FIG. FIG. 2 is a diagram showing a positional relationship between an exposure point and a transfer point in the image carrier of the image forming apparatus shown in FIG. 3 is a flowchart for explaining a method of controlling the writing position of each color image in the image forming apparatus shown in FIG. 1. 1 is a schematic block diagram of an image forming apparatus as one aspect of the present invention. It is a schematic sectional drawing which shows the structure of the drive mechanism which the image forming apparatus shown in FIG. 9 has. 1 is a schematic cross-sectional view illustrating a configuration of an image forming apparatus as one aspect of the present invention. It is a schematic block diagram of the image forming apparatus shown in FIG. 12 is a flowchart for explaining a method of controlling the writing position of each color image in the image forming apparatus shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 11 (11a thru | or 11d) Image carrier 12 (12a thru | or 12d) Charging roller 14 (14a thru | or 14d) Developing device 15 (15a thru | or 15d) Transfer roller 30 Drive mechanism 30a thru | or 30d Drive part 31a thru | or 31d Drive motor 32a to 32d Reduction gears 33a to 33d Couplings 34a to 34d Drive gears 35a to 35d Slits 36a to 36d Flange 37a to 37d Photointerrupter 50 Scanner unit 50ab First scanner unit 50cd Second scanner unit 51ab and 51cd Polygon mirror 52a to 52d Lens S Transfer material PC (PCa to PCd) Process cartridge IL (ILa to ILd) Image light IMU Image carrying unit DPU Development unit 1A Image forming apparatus 30A Drive mechanism 30ab Drive unit 31 b drive motor 38 connection gear 1B image forming apparatus 50B scanner section 51abcd polygon mirror

Claims (7)

An image forming apparatus for forming an image on a recording medium,
A plurality of image carriers each carrying a latent image of each color constituting the image;
A rotating polygon mirror that deflects at least two image lights of the image light forming the latent images of the respective colors to image carriers corresponding to the at least two image lights of the plurality of image carriers;
A detection unit for detecting a writing position in the sub-scanning direction of the latent image of each color;
An image forming apparatus comprising: a control unit that controls a rotation speed of the plurality of image carriers based on a detection result of the detection unit.   The control unit calculates a deviation amount of the writing position in the sub-scanning direction of the latent image of each color based on the detection result of the detection unit, and corrects the deviation amount by adjusting the phase of the rotary polygon mirror. The image forming apparatus according to claim 1, wherein a rotation speed of the plurality of image carriers is controlled in accordance with a deviation residual that cannot be performed. The plurality of image carriers include a first image carrier that carries a latent image of a reference color, and a second image carrier that carries a latent image of a color other than the reference color,
The control unit accelerates or decelerates the rotational speed of the second image carrier relative to the rotational speed of the first image carrier except during the formation of the image, and during the formation of the image. 2. The image forming apparatus according to claim 1, wherein the rotation speed of the second image carrier is maintained constant. The plurality of image carriers include a first image carrier that carries a latent image of a reference color, a second image carrier that carries a latent image of a color other than the reference color, and a third image carrier. And a fourth image carrier,
2. The image forming apparatus according to claim 1, further comprising a drive mechanism that rotates the third image carrier and the fourth image carrier at the same rotational speed.   The control unit calculates a deviation amount of the writing position in the sub-scanning direction of the latent image of each color based on the detection result of the detection unit, and corrects the deviation amount by adjusting the phase of the rotary polygon mirror. The rotational speed of the second image carrier is controlled in accordance with a deviation residual that cannot be performed, and the image light is applied to the third image carrier and the fourth image carrier in accordance with the amount of deviation. 5. The image forming apparatus according to claim 4, wherein the phase of the deflecting rotary polygon mirror is adjusted.   The control unit calculates a deviation amount of the writing position in the sub-scanning direction of the latent image of each color based on the detection result of the detection unit, and corrects the deviation amount by adjusting the phase of the rotary polygon mirror. The rotational speeds of the second image carrier, the third image carrier, and the fourth image carrier are controlled according to a deviation residual that cannot be performed, and the third image carrier according to the deviation amount. 5. The image forming apparatus according to claim 4, wherein a phase of a rotary polygon mirror that deflects the image light to the image carrier or the fourth image carrier is adjusted. A plurality of image carriers each carrying a latent image of each color constituting an image to be formed on a recording medium, and at least two image lights among image lights forming the latent images of each color are supplied to the plurality of image carriers. A control method for an image forming apparatus having a rotary polygon mirror that deflects the image carrier corresponding to the at least two image lights.
A detection step of detecting a writing position in the sub-scanning direction of the latent image of each color;
And a control step of controlling a rotation speed of the plurality of image carriers based on a detection result of the detection step.

Images