JP2008188790A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of optimizing the rotating action of a rotary polygon mirror while preventing the magnification of a formed toner image from being varied in a main scanning direction and a sub-scanning direction. <P>SOLUTION: While a control section 43 is not in a state of writing out an image (NO at #4), the control section 43 detects rotational phase differences of polygon mirrors 34C, 34M and 34Y with respect to a rotational phase of a polygon mirror 34B (#5) to determine whether or not the rotational phase differences are adequate (#6). When they are not (NO at #6), the control section 43 changes a drive frequency of each of polygon motors 36C, 36M and 36Y (#7) in order to change rotational phases of polygon mirrors 34C, 34M, 34Y on the basis of the rotational phase of the polygon mirror 34B. While the control section 43 is in a state of writing out an image, (YES at #4) and the rotational phase differences are adequate (YES at #6), the control section 43 carries out no changing operation of the drive frequencies of the polygon motors 36C, 36M and 36Y (#8). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention belongs to the technical field of image forming apparatuses, and particularly relates to a laser irradiation technique for performing exposure by irradiating a surface of a photosensitive drum with a laser.

  2. Description of the Related Art Conventionally, an image forming unit for forming a toner image is provided for each of a plurality of colors, and these image forming units are disposed on a transport belt for transporting a recording paper along the transport direction of the recording paper. A so-called tandem type image forming apparatus is known in which toner images of respective colors are multiplex-transferred onto a recording sheet conveyed in the conveying direction. In this type of image forming apparatus, each image forming unit exposes the surface of the photosensitive drum by reflecting the laser beam emitted from the laser irradiating unit on each reflecting surface of the rotary polygon mirror, thereby exposing the photosensitive drum. An electrostatic latent image is formed on the surface.

Japanese Patent Application Laid-Open No. 2004-228688 discloses that in this type of image forming apparatus, the rotary polygon mirror and other elements in a predetermined image forming unit are used for the purpose of optimizing the writing timing of each color image in the sub-scanning direction by each image forming unit. A technique for controlling the operation of the rotary polygon mirror so that the rotary polygon mirror in the image forming unit rotates with a predetermined phase difference is disclosed.
JP 2001-162857 A

  However, if rotation control of the rotary polygon mirror is performed at the time of toner image generation (image writing operation), the magnification of the generated toner image changes in the main scanning direction and the sub-scanning direction, respectively. The printed image may be uncomfortable or difficult to see.

  The present invention has been made to solve the above-described problems, and prevents the magnification of the generated toner image from changing in the main scanning direction and the sub-scanning direction, while rotating the rotary polygon mirror. An object of the present invention is to provide an image forming apparatus that can be optimized.

  The invention according to claim 1 is provided with a plurality of reflecting surfaces for reflecting the light beam output from the light source toward the photoconductor, and rotating the light beam on the surface of the photoconductor using the reflecting surface. A rotating polygon mirror that repeatedly scans in the main scanning direction, a drive unit that rotationally drives the rotating polygon mirror, and a light beam scanned by the rotating polygon mirror is received at a predetermined position, and a photoelectric conversion operation is performed to generate a BD signal. An image forming apparatus including a plurality of image forming units arranged in a predetermined direction in the apparatus main body, and a plurality of image forming units that transfer toner images to a transfer body that moves in the arrangement direction. The rotational phase difference of another rotary polygon mirror with respect to the rotation phase of the rotary polygon mirror set as a reference among the rotary polygon mirrors provided in each image forming unit is detected using the BD signal. When the rotational phase difference detected by the phase difference detection unit and the phase difference detection unit coincides with a predetermined reference phase difference, the drive frequency of each drive unit in each image forming unit is maintained, A drive control unit that changes a drive frequency of each of the drive units so that the rotation phase difference matches the reference phase difference when the rotation phase difference does not match the reference phase difference; The unit is characterized in that the drive frequency of each drive unit in each image forming unit is not changed during the image writing operation for generating the toner image.

  According to the present invention, when the rotation phase difference detected by the phase difference detection unit matches a predetermined reference phase difference, the drive frequency of each drive unit in each image forming unit is maintained, and the rotation When the phase difference does not match the reference phase difference, the drive frequency of each drive unit is changed so that the rotation phase difference matches the reference phase difference, so that the rotation operation of the rotary polygon mirror is optimized. be able to.

  Further, during an image writing operation for generating a toner image (a period from the start point to the end point of light beam scanning for generating a toner image), regardless of whether the rotational phase difference and the reference phase difference match or not. Since the drive frequency of each drive unit in each image forming unit is not changed, the magnification of the generated toner image can be prevented from changing in the main scanning direction and the sub-scanning direction.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the drive control unit performs an image writing operation using only an image forming unit having a rotary polygon mirror set as the reference. If the rotational phase difference does not match the reference phase difference, the drive frequency of the drive unit in another image forming unit is set to match the reference phase difference during the image writing operation. It is to be changed as follows.

  When the image writing operation is performed using only the image forming unit having the rotary polygon mirror set as the reference, the generated toner image even if the driving frequency of the driving unit in the other image forming unit is changed. The magnification of will not change.

  Therefore, as in the present invention, when the image writing operation is performed using only the image forming unit having the rotary polygon mirror set as the reference, the rotational phase difference does not match the reference phase difference. In this case, during the image writing operation, the drive frequency of the drive unit in the other image forming unit is changed so that the rotational phase difference matches the reference phase difference. The rotational phase can be set as appropriate as possible.

  According to the present invention, it is possible to set the rotation phase of the rotary polygon mirror in each image forming unit to an appropriate state while preventing the magnification of the generated toner image from changing in the main scanning direction and the sub-scanning direction. it can.

  An embodiment of an image forming apparatus according to the present invention will be described. FIG. 1 is an overall cross-sectional view showing an example of a tandem type color printer 1 that is suitable for use as an image forming apparatus according to the present invention. FIG. 2 is an enlarged cross-sectional view of a main part near the image forming portion of the color printer. FIG.

  The color printer 1 includes four image forming units 7M corresponding to toners of magenta M, cyan C, yellow Y, and black B from the downstream side in the paper conveyance path (from left to right in FIG. 1). 7C, 7Y, and 7B are arranged in tandem on the paper transport belt 8. As shown in FIG. 2, each of the image forming units 7M, 7C, 7Y, and 7B includes a photosensitive drum 4 made of amorphous silicon or the like as an image carrier, and a charger disposed around the photosensitive drum 4. 5, an optical scanning device 6, a developing device 3 having a developing sleeve 3 a, a transfer roller 9, and a cleaning mechanism 20. A continuous sheet conveying belt 8 is held between the photosensitive drums 4 and transfer rollers 9 of the image forming units 7M, 7C, 7Y, and 7B. The recording paper supplied via the conveyance path 13 is conveyed. After the toner images are sequentially transferred onto the recording paper by the image forming units 7M, 7C, 7Y, and 7B, a color image is formed by the fixing process of the toner image by the fixing unit 14 and passes through the paper transport path 15. Then, it is discharged to the discharge unit 16.

  A cleaning mechanism 20 provided in each of the image forming units 7M, 7C, 7Y, and 7B is for removing residual toner and the like on the photosensitive drum 4, and for cleaning the surface of the photosensitive drum 4. The cleaning roller 21 and the cleaning blade 22, and the cleaning spiral 23 and the casing 25 for discharging the toner removed from the surface of the photosensitive drum 4 to the outside of the image forming units 7M, 7C, 7Y, and 7B are provided.

  The cleaning roller 21 is made of an elastic material such as urethane foam, and is disposed at a position facing the photosensitive drum 4. The cleaning roller 21 is disposed so as to slide on the surface of the photosensitive drum 4 on the downstream side of the toner image transfer position (a position facing the transfer roller 9) by the photosensitive drum 4, and the rotation direction of the photosensitive drum 4. It is rotatably provided in the forward direction (arrow direction in FIG. 2). The cleaning blade 22 is a plate-like member made of a material such as a urethane rubber member, and is disposed so that one end thereof slides on the photosensitive drum 4 further downstream from the cleaning roller 21. It is provided for scraping off the toner remaining on the surface of the photosensitive drum 4 after cleaning. A spiral blade is formed around the rotation shaft of the spiral 23, and the spiral 23 is provided with cleaning toner (waste toner) removed from the surface of the photosensitive drum 4 on the front plate of the cleaning mechanism 20. The rotation is controlled in the direction of discharging through the toner discharge port.

  FIG. 3 is a configuration diagram of the optical scanning device 6. As shown in FIG. 3, each of the image forming units 7M, 7C, 7Y, and 7B includes an optical scanning device 6 as shown in FIG. 3, for example. The optical scanning device 6 includes a laser irradiation unit 31, a collimator lens 32, a prism 33, a polygon mirror (rotating polygon mirror) 34, an f-θ lens 35, a polygon motor 36, and a beam detector sensor (hereinafter referred to as a BD (Beam Detect) sensor. 37).

  The laser irradiation unit 31 includes a laser light source (LD). Laser light output from the laser light source is converted into parallel light by the collimator lens 32, the prism 33, and the like. This parallel light is reflected toward the polygon mirror 34 by a reflection mirror (not shown), and is incident on the rotating polygon mirror 34 by driving the polygon motor 36.

  The polygon mirror 34 has a plurality of reflection surfaces that reflect the laser light output from the laser irradiation unit 31 toward the photosensitive drum 4, and the laser beams emitted from the laser irradiation unit 31 are different reflection surfaces of the polygon mirror 34. Is reflected toward the photosensitive drum 4. The laser beam reflected toward the photosensitive drum 4 by the polygon mirror 34 is imaged in a spot shape having a predetermined diameter on the surface of the photosensitive drum 4 by the f-θ lens 35. The polygon mirror 34 is driven to rotate at a constant speed by a polygon motor 36 in the direction of an arrow in FIG. 3, for example, so that the laser beam is reflected by each reflecting surface and in the rotation axis direction (main scanning direction) of the photosensitive drum 4. The electric charges on the surface of the photosensitive drum 4 are removed by scanning.

  The BD sensor 37 is configured using a photodiode, and is used to adjust the timing of performing light beam scanning (hereinafter referred to as image writing operation) for forming a toner image on the photosensitive drum 4. Is. When the laser reflected by the polygon mirror 34 rotating in the direction of the arrow shown in FIG. 3 passes through the f-θ lens 35 and enters the BD sensor 37, a detection signal is output from the BD sensor 37. The detection signal of the BD sensor 37 is input to an image writing timing adjustment unit 433, which will be described later, and is used to adjust the image writing timing of laser light scanned on the surface of the photosensitive drum 4.

  Further, a common control unit 43 is electrically connected to each optical scanning device 6. The control unit 43 takes an operation timing based on the reference clock signal output from the reference oscillator 41, adjusts the image writing timing at the operation timing, and performs laser adjustment based on the image signal of the image to be written output from the image memory 42. The irradiation unit 31 is driven and controlled.

  The control unit 43 has a CPU (Central Processing Unit) (not shown) storing a RAM (Random Access Memory) and a ROM (Read Only Memory) that store a program that defines the operation of the CPU, and temporarily. A peripheral device such as a storage unit such as a RAM for storing data is provided, and the color is determined according to instruction information received by an operation unit (not shown) and detection signals from sensors provided in various parts of the color printer 1. The overall control of the printer 1 is performed.

  The control unit 43 functionally includes an LD drive control unit 431, a drawing unit 432, and an image writing timing adjustment unit 433. The drawing unit 432 starts driving of the LD drive control unit 431 based on the image signal of the writing target image output from the image memory 42. The LD drive control unit 431 controls the drive of the laser irradiation unit 31 based on an instruction from the drawing unit 432. The image writing timing adjustment unit 433 adjusts the image writing timing for scanning the surface of the photosensitive drum 4 based on the BD signal output from the BD sensor 37 and outputs the adjusted image writing timing to the drawing unit 432.

  FIG. 4 is a diagram showing the configuration of the rotation control system of the polygon mirror 34. In the following description, the polygon mirror 34 and the polygon motor 36 of each optical scanning device 6 are referred to as “34B”, “34R”, “34G”, “34B”, “36B”, “36R”, “36G”. , “36B”.

  As shown in FIG. 4, the operations of the polygon motors 36 </ b> B, 36 </ b> R, 36 </ b> G, 36 </ b> B are performed based on the reference clock signal output from the reference oscillator 41 and the output signal output from the BD sensor 37. PLL control is performed by the control unit 43, and the rotation speed of the polygon mirrors 34B, 34R, 34G, 34B is changed by changing the cycle of the drive clock signal generated based on the reference clock signal by the control unit 43. Can be changed.

  In addition, the control unit 43 is functionally configured as a configuration related to operation control of the polygon motors 36B, 36R, 36G, and 36B, and functionally includes a first determination unit 434, a phase difference detection unit 435, a second determination unit 436, and a motor. And a drive control unit 437.

  The first determination unit 434 determines whether an image is currently being written (drawing).

  When the first determination unit 434 determines that the image is not currently being written (drawn), the phase difference detection unit 435 uses, for example, the rotation phase of the polygon mirror 34B as a reference to determine the rotation phase of the polygon mirror 34B. The rotational phase difference between the polygon mirrors 34C, 34M, and 34Y is detected.

  If the arrival position of the laser beam output from each laser irradiation unit 36 on the surface of the photosensitive drum 4 is the positions A, B, C, and D shown in FIG. The output timing of the output signal of the BD sensor 37 by light is shifted by a time difference corresponding to the positional shift amount in the main scanning direction of each position A, B, C, D. Since this time difference corresponds to the rotational phase difference of each polygon mirror 34, the phase difference detection unit 435 uses the output timing of the signal output from the BD sensor 37 to each image forming unit 7M, 7C, 7Y, 7B. The rotational phase difference between the polygon mirrors 34C, 34M, and 34Y is detected.

  The second determination unit 436 determines whether or not the phase difference detected by the phase difference detection unit 435 matches a predetermined phase difference, that is, the phase difference detected by the phase difference detection unit 435 is appropriate. Whether or not.

  For example, it is appropriate that the arrival position (spot light position) of the laser beam on the surface of the photosensitive drum 4 at a certain timing has a positional relationship of positions A, B, C, and D shown in FIG. It is appropriate when the rotational phase difference detected by the phase difference detector 435 is the reference rotational phase difference, assuming that the rotational phase difference (reference rotational phase difference) is in the rotating state. On the other hand, the rotational phase difference detected by the phase difference detection unit 435 is not the reference rotational phase difference, for example, positions A, B ′, C ′, and D ′ shown in FIG. If the rotational phase difference corresponds to the relationship, it is determined to be inappropriate. Possible causes for the rotational phase difference detected by the phase difference detection unit 435 to be in an inappropriate state include, for example, fluctuations in the voltage supplied to the polygon motors 36C, 36M, 36Y, and 36B, electrical noise, or vibration.

  The motor drive control unit 437 controls the operation of the polygon motors 36C, 36M, 36Y, and 36B. Particularly in this embodiment, the rotational phase difference detected by the phase difference detection unit 435 when the image is not being written out. Is in an inappropriate state, the polygon motor 36C that drives the polygon mirrors 34C, 34M, 34Y to change the rotation phases of the other polygon mirrors 34C, 34M, 34Y with reference to the rotation phase of the polygon mirror 34B. , 36M, and 36Y are changed (the period of the drive clock signal output to the polygon motors 36C, 36M, and 36Y is changed). The change of the driving frequency is such that the rotational phase difference of the other polygon mirrors 34C, 34M, 34Y with respect to the rotational phase of the polygon mirror 34B becomes the reference rotational phase difference.

  On the other hand, the motor drive control unit 437 determines the rotational phase difference detected by the phase difference detection unit 435 when the image is being written out (a period from the start point to the end point of the light beam scanning for generating the toner image). Regardless of suitability, the drive frequency of each polygon motor 36B, 36R, 36G, 36B is not changed. This is because when the drive frequency of each polygon motor 36B, 36R, 36G, 36B is changed during image writing, the magnification of the toner image to be generated differs in each of the main scanning direction and the sub-scanning direction, and the appropriate size. This is because the toner image cannot be obtained.

  FIG. 6 is a flowchart showing the rotation control of the polygon mirror 34.

  As shown in FIG. 6, when the power of the color printer 1 is turned on (YES in Step # 1), the control unit 43 starts the operation of the polygon motors 36B, 36R, 36G, and 36B (Step # 2). The laser light source of each laser irradiation unit 31 is turned on (step # 3).

  Next, the control unit 43 determines whether or not the image is being written (whether or not drawing is being performed) (step # 4). If the image is not being written (NO in step # 4), The rotational phase difference of the other polygon mirrors 34C, 34M, 34Y with respect to the rotational phase of the polygon mirror 34B is detected (step # 5). Control unit 43 determines whether or not the rotational phase difference detected in step # 5 is appropriate (step # 6). If not (NO in step # 6), control unit 43 determines the rotational phase of polygon mirror 34B. As a reference, the drive frequencies of the polygon motors 36C, 36M, and 36Y that drive the polygon mirrors 34C, 34M, and 34Y are changed to change the phases of the other polygon mirrors 34C, 34M, and 34Y (step # 7).

  On the other hand, when the image is being written out at step # 4 (YES at step # 4) and when the rotational phase difference is appropriate at step # 6 (YES at step # 6), control unit 43 causes other polygons to be The drive frequency changing process for the motors 36C, 36M, 36Y is not executed (step # 8).

  Then, control unit 43 determines whether or not the power is turned off (step # 9). If the power is not turned off (NO in step # 9), the control unit 43 returns to step # 3 and the power is turned off. If YES (YES in step # 9), the series of processes is terminated.

  As described above, when the phase difference detected by the phase difference detection unit 435 is inappropriate when the image is not being written out, the rotational phase difference of the other polygon mirrors 34C, 34M, and 34Y with respect to the rotational phase of the polygon mirror 34B. Since the polygon mirrors 34C, 34M, and 34Y are driven so as to achieve the reference rotational phase difference, the polygon mirrors are caused by fluctuations in voltage supplied to the polygon motors 36C, 36M, 36Y, and 36B, electrical noise, vibration, or the like. Even if an error occurs in the rotation phases of 34B, 34C, 34M, and 34Y, the error can be corrected and the polygon mirrors 34B, 34C, 34M, and 34Y can be set to appropriate rotation states.

  In particular, in the present embodiment, when the image is being written out, the driving frequency of each of the polygon motors 36B, 36R, 36G, and 36B is not changed regardless of whether the rotational phase difference detected by the phase difference detection unit 435 is appropriate. Thus, by changing the drive frequency of each polygon motor 36B, 36R, 36G, 36B during image writing, the magnification of the generated toner image differs in each of the main scanning direction and the sub-scanning direction. It is possible to prevent a toner image having an appropriate size from being obtained.

  Note that this case includes the following modes in place of or in addition to the above embodiments.

  (1) The tandem type color printer 1 as in the first embodiment has a mode for performing normal monochrome printing. When this monochrome printing is executed, the image forming unit 7B (rotation) corresponding to black is performed. Only the image forming unit 7B) having the rotating polygon mirror set as a reference when performing the rotation control of the polygon mirror is used, and the other image forming units 7C, 7M, and 7Y are not used. Therefore, in the first embodiment, when the image is being written, the driving frequencies of the polygon motors 36B, 36R, 36G, and 36B are set regardless of whether the rotational phase difference detected by the phase difference detection unit 435 is appropriate or not. Although not changed, it is considered that when monochrome printing as described above is executed, even if the drive frequency is changed, the magnification of the generated toner image is hardly adversely affected.

  Therefore, at the time of executing monochrome printing, if the rotational phase difference detected by the phase difference detection unit 435 is in an inappropriate state, the drive frequency may be changed.

1 is an overall cross-sectional view illustrating an example of a tandem type color printer that is a preferred embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view near an image forming unit of the color printer shown in FIG. 1. It is a block diagram of an optical scanning device. It is a figure which shows the structure of the rotation control system of a polygon mirror. It is a figure which shows an example of the positional relationship of the spot light on the photoconductive drum corresponding to a state with an appropriate rotation phase difference, respectively. It is a flowchart which shows rotation control of a polygon mirror.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Color printer 4 Photosensitive drum 6 Optical scanning device 7B, 7C, 7M, 7Y Image formation unit 8 Paper conveyance belt 31 Laser irradiation part 34B, 34C, 34M, 34Y Polygon mirror 36B, 36C, 36M, 36Y Polygon motor 37 BD sensor 41 Reference oscillator 43 Control unit 431 Drive control unit 432 Drawing unit 433 Timing adjustment unit 434 First determination unit 435 Phase difference detection unit 436 Second determination unit 437 Motor drive control unit

Claims (2)

Rotating multiple surfaces that include a plurality of reflecting surfaces that reflect the light beam output from the light source toward the photoconductor, and repeatedly scan the light beam on the surface of the photoconductor in the main scanning direction using the reflecting surface by rotating. An image comprising: a mirror; a drive unit that rotationally drives the rotary polygon mirror; and a BD sensor that receives a light beam scanned by the rotary polygon mirror at a predetermined position, performs a photoelectric conversion operation, and outputs a BD signal. An image forming apparatus in which a plurality of forming units are arranged in a predetermined direction in the apparatus main body, and the toner images are multiplex-transferred by the image forming units to a transfer body that moves in the arrangement direction.
A phase difference detection unit that detects a rotational phase difference of another rotary polygon mirror with respect to a rotation phase of the rotary polygon mirror set as a reference among the rotary polygon mirrors provided in each of the image forming units, using the BD signal;
When the rotational phase difference detected by the phase difference detection unit matches a predetermined reference phase difference, the driving frequency of each driving unit in each image forming unit is maintained, and the rotational phase difference is the reference phase difference. A drive control unit that changes the drive frequency of each of the drive units so that the rotational phase difference matches the reference phase difference when the phase difference does not match,
The image forming apparatus, wherein the drive control unit does not change a drive frequency of each drive unit in each image forming unit during an image writing operation for generating the toner image.   The drive control unit is a case where an image writing operation is performed using only an image forming unit having a rotary polygon mirror set as the reference, and when the rotational phase difference does not match the reference phase difference, The image forming apparatus according to claim 1, wherein during an image writing operation, a driving frequency of a driving unit in another image forming unit is changed so that the rotational phase difference coincides with the reference phase difference.

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