JP4920369B2 - Image forming apparatus - Google Patents

Description

  The present invention provides a laser beam for each of a predetermined number of colors of two or more (for example, four colors of magenta (M), cyan (C), yellow (Y), and black (K)) via a polygon mirror. Is applied to the photosensitive drum to form a latent image, a toner image corresponding to the formed latent image is formed, and the formed toner images of a predetermined number of colors are superimposed and transferred onto a recording sheet to obtain a color. The present invention relates to an image forming apparatus for forming an image. In particular, the present invention relates to a color copying machine, a color printer, and a multifunction machine having any one of these functions.

  In recent years, each of a predetermined number of colors of two or more (for example, four colors of magenta (M), cyan (C), yellow (Y), and black (K)) is exposed to a laser beam via a polygon mirror. A latent image is formed by irradiating the drum, a toner image corresponding to the formed latent image is formed, and the toner image of the predetermined number of colors formed is superimposed and transferred onto a recording paper, thereby forming a color image. In an image forming apparatus such as a copier or printer (so-called electrophotographic system) to be formed, an external operation or the like is input for a predetermined time (for example, 1 minute) or longer in order to reduce power consumption. If not, it will be in the standby state.

  In a state other than the printing operation such as the standby state, the polygon motor that drives the polygon mirror is not driven. Therefore, when returning from the standby state to the operating state, the “rotation phase” of the polygon mirror corresponding to each color In some cases, color misregistration may occur due to misalignment (= phase difference occurs). Therefore, in order to prevent the occurrence of color misregistration, it is necessary to control the driving of the polygon motor so that the rotational phases of two or more predetermined numbers (here, four colors) of polygon mirrors coincide.

  Here, the rotation angle of the mirror surface of one polygon mirror relative to the reference direction (for example, the direction of a perpendicular line from the center of the rotation axis of the polygon mirror to the axis of the photosensitive drum) is expressed as “ This is called “rotational phase”. For example, in the case of a polygon mirror having six mirror surfaces, the difference in rotational phase between the polygon mirrors is a value in the range of −30 ° to + 30 °.

For example, a laser beam that detects a laser beam to be scanned at a preset position on the scanning path by a polygon mirror corresponding to each color of magenta (M), cyan (C), yellow (Y), and black (K). All other polygon mirrors (here, magenta (M), cyan, etc.) having a detector and using one polygon mirror (for example, a polygon mirror corresponding to black (K)) as a reference based on the output signal. (C) and yellow (Y) three polygon mirrors) are calculated by calculating the difference in rotational phase (= phase difference) and changing the rotational frequency of the polygon motor corresponding to the three polygon mirrors for a predetermined time. A printer that matches the rotational phases of (four) polygon mirrors is disclosed. (See Patent Document 1).
JP-A-9-233281

  However, in the printer, the difference in rotational phase (for example, a polygon mirror corresponding to magenta (M)) based on one polygon mirror (for example, a polygon mirror corresponding to black (K)) ( = The phase difference), the rotational frequency of the polygon motor that drives the other polygon mirror (here, the magenta (M) corresponding polygon mirror) is changed, so that the rotational phase difference (= phase difference) is If it is larger, the time required for matching the rotational phases (herein referred to as phase control time) becomes longer. Also, if the amount of change in the rotation frequency of the polygon motor is increased in order to shorten the phase control time, an overshoot or undershoot of the rotation frequency of the polygon motor occurs, and as a result, it is difficult to match the rotation phases. There is a case.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of efficiently matching the rotational phases of polygon mirrors.

In order to achieve the above object, the image forming apparatus of the present invention is formed by irradiating a photosensitive drum with a laser beam through a polygon mirror for each of a predetermined number of two or more colors to form a latent image. An image forming apparatus for forming a color image by forming a toner image corresponding to the latent image and transferring the formed toner images of the predetermined number of colors to a recording paper in a superimposed manner. A beam for detecting a laser beam to be scanned at a preset position on the scanning path by a polygon driving means for rotating the polygon mirror at a preset steady rotation frequency and the predetermined number of polygon mirrors, respectively. Based on the detection results of the detection means and the predetermined number of beam detection means, a reference phase that is a reference phase for the rotational phase of the predetermined number of polygon mirrors is set. And the reference phase setting means, the rotational phase of the polygon mirror of the predetermined number so as to match the reference phase, the phase control means for controlling the polygon drive means, Ru comprising a.

Previous SL reference phase setting means, based on a detection result of said predetermined number of beam detecting means, among the rotational phase of the polygon mirror of the predetermined number, the most advanced phase and, in middle of the most delayed phase phase Is set as the reference phase, or the center phase between the most advanced phase and the most delayed phase among the rotation phases of a predetermined number of polygon mirrors is obtained, and the polygon mirror closest to the obtained center phase is obtained. Is set as the reference phase .

Further , the phase control means controls the predetermined number of polygon driving means so as to coincide with the reference phase by sequentially increasing / decreasing the respective rotation frequencies by a predetermined frequency in a stepwise manner. It may be .

Further, the polygon drive means, controls the rotation frequency through the PLL (Phase Locked Loop), the predetermined frequency may be as has been set below a preset threshold.

Further , when the rotational phase of the predetermined number of polygon mirrors is delayed with respect to the reference phase, the phase control unit presets the rotational frequency of the corresponding polygon driving unit stepwise from the steady rotational frequency. When the predetermined number of polygon mirrors are sequentially increased and then gradually decreased to the steady rotational frequency by a predetermined frequency set in advance, and the rotational phase of the predetermined number of polygon mirrors is advanced with respect to the reference phase In this case, the rotational frequency of the corresponding polygon driving means is sequentially decreased from the steady rotational frequency by a predetermined frequency stepwise in advance, and then gradually increased to the steady rotational frequency by a predetermined frequency stepwise. You may make it make it .

And a pattern storage means for storing a change pattern of a rotational frequency of the polygon driving means in association with a phase difference of the rotational phase of the polygon mirror with respect to the reference phase, wherein the phase control means comprises the predetermined number of polygons. A phase difference of the rotational phase of the mirror with respect to the reference phase is calculated, a change pattern corresponding to the calculated phase difference is read out from the pattern storage means, and the predetermined number of polygon drives are driven based on the read out change pattern The rotational frequency of the means may be controlled.

According to the image forming apparatus of the present invention, the laser beam respectively scanned by the predetermined number of polygon mirrors is detected by the beam detecting unit at a preset position on the scanning path, and based on the detection result, the predetermined laser beam is detected. A reference phase that is a reference phase for the rotational phase of several polygon mirrors is set. Since the polygon mirror is driven and controlled so that the rotational phase of a predetermined number of polygon mirrors matches the reference phase, it is possible to efficiently match the rotational phase of the polygon mirror by appropriately setting the reference phase. it can.

Further, since the reference phase is set based on the detection result of the beam detecting means, it is possible to easily set an appropriate reference phase . Among the rotational phase of the polygon mirror of Tokoro constants, the most advanced phase, the phase of the center of the most delayed phase, either set as a reference phase, of the rotational phase of the predetermined number of the polygon mirror, the most advanced The center phase between the phase and the most delayed phase is obtained, and the polygon mirror rotation phase closest to the determined center phase is set as the reference phase, thereby efficiently matching the polygon mirror rotation phase. Can be made.

That is, conventionally, it was necessary to control the polygon drive means to vary the rotational phase of the polygon mirror by the phase difference between the most advanced phase as most delayed phase, for example, the most advanced phase, the most delayed phase center of the a phase, to be set as the reference phase, change 1/2 retardation by a rotation phase of the polygon mirror of the phase difference between the most advanced phase as most delayed phase Since the polygon driving means need only be controlled to achieve this, the rotational phase of the polygon mirror can be matched more efficiently.

In addition , since each rotation frequency is sequentially increased or decreased by a predetermined frequency step by step by a predetermined number of polygon driving means, occurrence of rotation frequency overshoot (or undershoot) is suppressed. The rotational phase of the mirror can be matched more efficiently.

In addition , the rotation frequency is controlled via a PLL (Phase Locked Loop), and a predetermined frequency that is a change amount of the rotation frequency that is increased or decreased by the polygon driving unit is set to be equal to or less than a preset threshold value. It is possible to prevent the polygon mirror from rotating out of the locked state, and to more efficiently match the rotational phase of the polygon mirror.

Further , when the rotational phase of a predetermined number of polygon mirrors is delayed with respect to the reference phase, the rotational frequency of the corresponding polygon driving means is sequentially increased from the steady rotational frequency by a predetermined frequency that is set in advance step by step. After that, since the rotational frequency is gradually reduced to the steady rotational frequency by a predetermined frequency in advance, the occurrence of rotational frequency overshoot (or undershoot) is suppressed, so that the rotational phase of the polygon mirror can be made more efficient. Can be matched.

  Further, when the rotational phase of a predetermined number of polygon mirrors is advanced with respect to the reference phase, the rotational frequency of the corresponding polygon driving means is sequentially decreased from the steady rotational frequency by a predetermined frequency set in advance step by step. Thereafter, since the rotational frequency is gradually increased up to the steady rotational frequency by a predetermined frequency in advance, the occurrence of rotational frequency overshoot (or undershoot) is suppressed, so that the rotational phase of the polygon mirror can be made more efficient. Can be matched.

Further , a phase difference with respect to the reference phase of the rotational phase of a predetermined number of polygon mirrors is calculated, a change pattern corresponding to the calculated phase difference is read from the pattern storage means, and based on the read change pattern, Since the rotational frequency of the corresponding polygon driving means is controlled, the rotational phase of the polygon mirror can be matched efficiently with a simple configuration.

  Hereinafter, an example of an image forming apparatus according to the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram showing an example of a schematic configuration of an image forming apparatus according to the present invention. Although the case where the image forming apparatus is a printer will be described here, a latent image is formed by irradiating a photosensitive drum with a laser beam via a polygon mirror for each of a predetermined number of colors of two or more. Then, another image forming apparatus that forms a color image by forming a toner image corresponding to the formed latent image and transferring the formed toner images of the predetermined number of colors to a recording paper (for example, A copying machine, a multifunction machine, etc.).

  As shown in FIG. 1, the printer 100 includes a paper feeding unit 1, a first transport path 2, an image forming unit 3, an intermediate transfer unit 4, a density sensor 5, a fixing unit 6, a second transport path 7, and a discharge tray. 8 is provided. In addition, the printer 100 is provided with a control unit 9 (see FIG. 4) (not shown) that controls the operation of the printer 100 at an appropriate place. The printer 100 is communicably connected to an unillustrated personal computer (PC) or the like, and forms an image corresponding to a document image received from the PC on a recording sheet.

  The sheet feeding unit 1 is configured such that recording sheets are stacked and loaded, and the uppermost recording sheet can be sent in response to an instruction from a control unit 9 described later. The first conveyance path 2 conveys the recording paper supplied from the paper feeding unit 1 to the image forming unit 3. The image forming unit 3 has a predetermined number of colors (four colors of magenta (M), cyan (C), yellow (Y), and black (K)) on the recording paper conveyed from the first conveyance path 2. The toner images are formed in an overlapping manner, and are provided with image forming units 3M, 3C, 3Y, and 3K for magenta (M), cyan (C), yellow (Y), and black (K).

  The intermediate transfer unit 4 transports the recording paper supplied from the first transport path 2 to the fixing unit 6 via the image forming unit 3 and receives it from a PC (not shown) via the image forming unit 3. A toner image (or color misregistration correction pattern) corresponding to the document image is formed. The density sensor 5 detects the density of the color misregistration correction pattern formed on the intermediate transfer unit 4 by the image forming unit 3. The fixing unit 6 heats and fixes the toner image formed on the recording paper by the intermediate transfer unit 4. The second conveyance path 7 is disposed on the downstream side of the fixing unit 6 and conveys the recording paper on which the toner image is heated and fixed by the fixing unit 6 to the discharge tray 8. The discharge tray 8 is disposed on the downstream side of the second transport path 7 and is stacked and placed with heat-fixed recording paper.

  FIG. 2 is a configuration diagram showing an example of the image forming unit 3 and the intermediate transfer unit 4 shown in FIG. The image forming units 3M, 3C, 3Y, and 3K for magenta (M), cyan (C), yellow (Y), and black (K) of the image forming unit 3 have substantially the same configuration. Around the photosensitive drum 31, a charger 32, a laser irradiation unit 33, a developing unit 34, a cleaner 35, and a static eliminator 36 are sequentially arranged from above the photosensitive drum 31 along the rotation direction (arrow direction).

  The photosensitive drum 31 rotates clockwise (in the direction of the arrow). First, the surface of the photosensitive drum 31 is uniformly charged by the charger 32. Next, the laser irradiation unit 33 irradiates a laser beam corresponding to a document image (or a color misregistration correction pattern) received from a PC (not shown) to form an electrostatic latent image on the surface of the photosensitive drum 31. Is done.

  Then, toner is supplied to the electrostatic latent image on the photosensitive drum 31 by the developing device 34 and visualized as a toner image. Next, the photosensitive drum 31 further rotates, and the toner image is transferred from the photosensitive drum 31 to the recording paper conveyed by the intermediate transfer unit 4. Residual toner that has not been transferred is removed from the photosensitive drum 31 by a cleaner 35 having a blade or the like in contact with the photosensitive drum 31, and then the surface charge of the photosensitive drum 31 is removed by the static eliminator 36 to complete a series of image forming processes. To do.

  The intermediate transfer unit 4 includes a primary transfer roller 41, an endless belt 42, and drive rollers 43 and 44. The endless belt 42 is disposed on the upper outer peripheral surface so as to be in sliding contact with the photosensitive drums 31 of the image forming units 3M, 3C, 3Y, and 3K, and a color misregistration correction pattern is formed via the image forming unit 3. In this case, the drive rollers 43 and 44 are stretched. The drive rollers 43 and 44 are configured so that the endless belt 42 is stretched and rotationally driven in the counterclockwise direction (arrow direction) in FIG.

  FIG. 3 is a block diagram showing an example of the configuration of the laser irradiation unit 33 shown in FIG. The laser irradiation unit 33 includes a polygon motor 330, a laser diode 331, a polygon mirror 332, an fθ lens 333, a sensor mirror 334, and a beam sensor 335.

  The laser beam emitted from the laser diode 331 is incident on a polygon mirror 332 that is rotationally driven by a polygon motor 330. Here, the polygon mirror 332 has a regular hexagon shape, and is driven by a polygon motor 330 (not shown) to rotate clockwise at a constant speed.

  Further, the polygon motor 330 (corresponding to a part of the polygon driving means) is driven according to an instruction from the CPU 91 of the control unit 9 via a motor driving device 37 described later with reference to FIG. The polygon mirror 332 is not limited to a regular hexagon, and other shapes can be used as long as they are regular polygons. Further, the rotation direction and rotation speed of the polygon mirror 332 can be appropriately set according to the specifications of the apparatus.

  The laser beam reflected by the polygon mirror 332 enters the fθ lens 333 and is converted to a constant velocity, and forms an image on the photosensitive drum 31 through a mirror (not shown) as a beam spot. In this way, the laser beam is scanned in the main scanning direction of the photosensitive drum 31 (left direction in FIG. 3). The sensor mirror 334 reflects the laser beam emitted from the laser diode 331 to the beam sensor 335 and is disposed on the left side of the fθ lens 333.

  The beam sensor 335 (corresponding to a part of the beam detecting means) is composed of a photosensor such as a photodiode or a phototransistor, and is disposed on the right side of the fθ lens 333 and emits a laser beam scanned by the polygon mirror 332. The detection is performed at the position where the sensor mirror 334 is disposed on the scanning path (here, the left side of the fθ lens 333). A detection signal from the beam sensor 335 (hereinafter referred to as a BD (Beam Detect) signal) is input to the CPU 91 of the control unit 9 described with reference to FIG.

  FIG. 4 is a block diagram showing an example of the configuration of the main part according to the present invention. The control unit 9 that controls the operation of the printer 100 includes a CPU (Central Processing Unit) 91, a RAM (Random Access Memory) 92, and an unillustrated ROM (Read Only Memory). Further, the motor driving device 37 (corresponding to a part of the polygon driving means) controls the polygon motor 330 that rotationally drives the polygon mirror 332 shown in FIG. 3 in accordance with an instruction from the CPU 91 (drive control unit 914 described later). A basic clock generation circuit 371, a frequency divider 372, a setting register 373, and a motor driver 374 are provided.

  The basic clock generation circuit 371 includes a crystal oscillator or the like, generates a clock signal (hereinafter referred to as “basic clock signal”) having a frequency (here, 2 kHz) corresponding to the steady rotation frequency of the polygon motor 330, and a frequency divider. Is output to 372.

  The frequency divider 372 generates a clock signal having a frequency set in the setting register 373 by dividing the basic clock signal from the basic clock generation circuit 371 and outputs the clock signal to the motor driver 374.

  The setting register 373 stores a frequency (hereinafter referred to as a setting frequency) set by the CPU 91 (drive control unit 914 described later), and outputs the setting frequency to the frequency divider 372.

  The motor driver 374 controls the number of rotations of the polygon motor 330 by PLL (Phase Locked Loop) control based on the clock signal from the frequency divider 372. Specifically, the motor driver 374 controls the polygon motor 330 so as to match the rotation speed (for example, 2000 rps (= 2000 rotations per second)) corresponding to the frequency (for example, 2 kHz) set in the setting register 373. To do.

  The CPU 91 functionally includes a beam detection unit 911, a reference phase setting unit 912, a phase control unit 913, and a drive control unit 914, and the RAM 92 functionally includes a pattern storage unit 921. Here, the CPU 91 functions as functional units such as a beam detection unit 911, a reference phase setting unit 912, a phase control unit 913, and a drive control unit 914 by reading and executing a program stored in advance in a ROM or the like. The RAM 92 functions as a functional unit such as the pattern storage unit 921.

  Of the various data stored in the RAM 92 and ROM, data that can be stored in a removable recording medium is, for example, a driver such as a hard disk drive, an optical disk drive, a flexible disk drive, a silicon disk drive, or a cassette medium reader. In this case, the recording medium is, for example, a hard disk, an optical disk, a flexible disk, a CD, a DVD, a semiconductor memory, or the like.

  The beam detection unit 911 (corresponding to a part of the beam detection means) receives a detection signal from the beam sensor 335, and sets a laser beam scanned by the polygon mirror 332 to a preset position on the scanning path (FIG. 3). , And a BD signal is generated.

  A reference phase setting unit 912 (corresponding to a reference phase setting unit) sets a reference phase, which is a reference phase of the rotational phase of the polygon mirror 332, based on the detection result (= BD signal) of the beam detection unit 911. Is. Here, based on the detection results of a predetermined number (here, four) of beam sensors 335, the reference phase setting unit 912 is the most out of the rotational phases of a predetermined number (here, four) of polygon mirrors 332. The center phase between the advanced phase and the most delayed phase is set as the reference phase.

  FIG. 5 is a timing chart showing an example of a reference phase setting method by the reference phase setting unit 912. The BD signals SM, SC, SY, SK and the reference phase signal S0 corresponding to the respective colors of magenta (M), cyan (C), yellow (Y), and black (K) are shown in order from the upper side of the figure. Here, for the BD signal SC corresponding to cyan (C), the BD signals SM, SY, and SK corresponding to the respective colors of magenta (M), yellow (Y), and black (K) are time TA, time TB, The phase is advanced by time TC.

  Therefore, the reference phase setting unit 912 generates a reference signal S0 having a central phase (= reference phase) between the BD signal SK that is the most advanced signal and the BD signal SC that is the most delayed signal. Generated.

  Returning to FIG. 4 again, the functional configuration of the CPU 91 will be described. The phase control unit 913 (corresponding to the phase control means) controls the polygon motor 330 so that the rotational phase of a predetermined number (here, four) of polygon mirrors 332 matches the reference phase corresponding to the reference signal S0. Is. Further, the phase control unit 913 sequentially increases or decreases each rotation frequency by a predetermined frequency ΔF that is set in advance step by step with respect to a predetermined number (four in this case) of polygon motors 330, thereby generating a reference signal S0. Is controlled so as to match the reference phase corresponding to.

  Further, when the rotation phase of a predetermined number (four in this case) of polygon mirrors 332 is delayed with respect to the reference phase corresponding to the reference signal S0, the phase control unit 913 After sequentially increasing the rotation frequency by a predetermined frequency ΔFA (here, 10 Hz) preset in a stepwise manner from the steady rotation frequency (here, 2 kHz), the predetermined frequency ΔFB (here, which is preset in a stepwise manner) 10 Hz) is sequentially reduced to a steady rotational frequency (here, 2 kHz).

  The predetermined frequencies ΔFA and ΔFB (here, 10 Hz) are set to be equal to or lower than a preset threshold value. Specifically, the predetermined frequencies ΔFA and ΔFB are threshold values (for example, lower than a limit change frequency (for example, 300 Hz) that is out of the locked state when the rotational speed of the polygon motor 330 is PLL controlled by the motor driver 374. 50 Hz = a preset threshold value) or less.

  For example, in the case shown in FIG. 5, the BD signals SC and SY corresponding to cyan (C) and yellow (Y) colors are delayed with respect to the reference phase corresponding to the reference phase signal S0 (see FIG. 5). Therefore, the phase control unit 913 corresponds to advance the BD signals SC and SY corresponding to cyan (C) and yellow (Y), respectively, by time (TC / 2) and time (TC / 2−TB). The rotational frequency of the polygon motor 330 is sequentially increased from a steady rotational frequency (here, 2 kHz) by a predetermined frequency (in this case, 10 Hz) in a stepwise manner, and then is set in a stepwise predetermined frequency (in this case) In this case, the frequency is reduced to 10 Hz in order to a steady rotational frequency (here, 2 kHz).

  Further, when the rotational phase of a predetermined number (four in this case) of the polygon mirrors 332 is advanced with respect to the reference phase corresponding to the reference signal S0, the phase control unit 913 causes the corresponding polygon motor 330 to The rotational frequency is sequentially decreased from the steady rotational frequency (here 2 kHz) by a predetermined frequency ΔFB (here, 10 Hz) that is preset in a stepwise manner, and then the predetermined frequency ΔFA (here, that is preset in a stepwise manner) 10 Hz) is sequentially increased to a steady rotational frequency (here, 2 kHz).

  For example, in the case shown in FIG. 5, the BD signals SC and SY corresponding to the respective colors of magenta (M) and black (K) are advanced with respect to the reference phase corresponding to the reference phase signal S0. Reference numeral 913 denotes a rotational frequency of the corresponding polygon motor 330 so as to delay the BD signals SM and SK corresponding to magenta (M) and black (K), respectively, by time (TA-TC / 2) and time (TC / 2). Is sequentially increased from the steady rotation frequency (here, 2 kHz) by a predetermined frequency (here, 10 Hz) in a stepwise manner, and then sequentially increased by a predetermined frequency (here, 10 Hz) in a stepwise manner. The frequency is reduced to a steady rotational frequency (here, 2 kHz).

  Further, the phase control unit 913 calculates and calculates the phase difference of the rotation phase of the predetermined number (here, four) of polygon mirrors 332 with respect to the reference phase corresponding to the reference phase signal S0 (see FIG. 5). The change pattern corresponding to the phase difference is read from the pattern storage unit 921 and the rotation frequency of a predetermined number (here, four) of polygon motors 330 is controlled based on the read change pattern.

  The drive control unit 914 has a setting register 373 and a frequency divider 372 so that the rotational phase of a predetermined number (here, four) of polygon mirrors 332 matches the reference phase corresponding to the reference phase signal S0 (see FIG. 5). The polygon motor 330 is controlled via the motor driver 374.

  The pattern storage unit 921 (corresponding to the pattern storage means) correlates the rotational frequency of the polygon motor 330 with the phase difference of the rotational phase of the polygon mirror 332 relative to the reference phase corresponding to the reference phase signal S0 (see FIG. 5). A change pattern which is a pattern to be changed is stored.

  FIG. 6 is a graph showing an example of the change pattern stored in the pattern storage unit 921. (A) is a graph which shows an example of the change pattern stored in the pattern memory | storage part 921, (b) is a graph which shows the change of the rotation phase of the polygon mirror 332. FIG. Here, the rotation phase of the polygon mirror 332 is 30 μsec (= 21.6 ° (= 30 / 1,000, converted to rotation angle) with respect to the reference phase corresponding to the reference phase signal S0 (see FIG. 5). 000 / ((1 / 2,000) ×) × 360) The case of advance is described.

  As shown in (a), at the timing of time T11, the phase controller 913 reduces the rotational frequency of the polygon motor 330 by 10 Hz from the steady rotational frequency (here, 2 kHz) and sets it to 1.99 kHz. Then, at the timing of time T12 when 0.5 msec (= time corresponding to one cycle of the steady rotational frequency (here, 2 kHz)) has elapsed from time T11, the phase controller 913 further reduces the frequency by 10 Hz to 1.98 kHz. Set to Further, at the timing of time T13 when 0.5 msec (= time corresponding to one cycle of the steady rotational frequency (here, 2 kHz)) has elapsed from time T12, the phase control unit 913 further reduces the frequency by 10 Hz, and 1.97 kHz Set to

  Then, at the timing of time T14 when 1.0 msec (= time corresponding to two cycles of steady rotational frequency (here 2 kHz)) has elapsed from time T13, the phase control unit 913 increases the frequency by 10 Hz to 1.98 kHz. Is set. Next, at the timing of time T15 when 0.5 msec (= time corresponding to one cycle of the steady rotational frequency (here, 2 kHz)) has elapsed from time T14, the phase control unit 913 further increases the frequency by 10 Hz. It is set to 99 kHz. Furthermore, at the timing of time T16 when 0.5 msec (= time corresponding to one period of the steady rotational frequency (here, 2 kHz)) has elapsed from time T15, the phase control unit 913 further increases the frequency by 10 Hz to 2.0 kHz. (= Steady rotation frequency).

  As described above, after the phase control unit 913 sequentially decreases the rotation frequency of the polygon motor 330 from the steady rotation frequency (here, 2 kHz) by a predetermined frequency (here, 10 Hz) in a stepwise manner, (In this case, 10 Hz) is sequentially increased to a steady rotational frequency (here, 2 kHz), so that the rotational phase of the polygon mirror 332 changes as shown in (b), and the reference phase signal S0 (see FIG. 5). ) Substantially matches the reference phase corresponding to.

  FIG. 7 is a graph showing another example of the change pattern stored in the pattern storage unit 921 from FIG. (A) is a graph which shows an example of the change pattern stored in the pattern memory | storage part 921, (b) is a graph which shows the change of the rotation phase of the polygon mirror 332. FIG. Here, the rotation phase of the polygon mirror 332 is 30 μsec (= 21.6 ° (= 30 / 1,000, converted to rotation angle) with respect to the reference phase corresponding to the reference phase signal S0 (see FIG. 5). A case where there is a delay of 000 / ((1 / 2,000) ×) × 360) will be described.

  As shown in (a), at the timing of time T21, the rotation frequency of the polygon motor 330 is increased by 10 Hz from the steady rotation frequency (here, 2 kHz) by the phase control unit 913 and set to 2.01 kHz. Then, at the timing of time T22 when 0.5 msec (= time corresponding to one cycle of the steady rotational frequency (here, 2 kHz)) has elapsed from time T21, the phase control unit 913 further increases the frequency by 10 Hz, to 2.02 kHz Set to Furthermore, at the timing of time T23 when 0.5 msec (= time corresponding to one cycle of the steady rotational frequency (here, 2 kHz)) has elapsed from time T22, the phase control unit 913 further increases the frequency by 10 Hz, to 2.03 kHz Set to

  Then, at the timing of time T24 when 1.0 msec (= time corresponding to two cycles of the steady rotational frequency (here, 2 kHz)) has elapsed from time T23, the phase control unit 913 reduces the frequency by 10 Hz to 2.02 kHz. Is set. Next, at the timing of time T25 when 0.5 msec (= time corresponding to one cycle of the steady rotational frequency (here, 2 kHz)) has elapsed from time T24, the phase control unit 913 further reduces the frequency by 10 Hz. Set to 01 kHz. Furthermore, at the timing of time T26 when 0.5 msec (= time corresponding to one cycle of the steady rotational frequency (here 2 kHz)) has elapsed from time T25, the phase control unit 913 further reduces the frequency by 10 Hz to 2.0 kHz. (= Steady rotation frequency).

  Thus, the phase control unit 913 sequentially increases the rotational frequency of the polygon motor 330 from the steady rotational frequency (here, 2 kHz) stepwise by a predetermined frequency (here, 10 Hz), and then stepwise to the predetermined frequency. Since the rotation speed is successively reduced to a steady rotation frequency (here, 2 kHz) by (here 10 Hz), the rotation phase of the polygon mirror 332 changes as shown in (b), and the reference phase signal S0 (see FIG. 5). ) Substantially matches the reference phase corresponding to.

  FIG. 8 is a flowchart showing an example of the operation of the printer 100 (mainly the CPU 91). Here, a case where the printer 100 is in a standby state as an initial state (= a state where the polygon motor 330 that drives the polygon mirror 332 is not driven) will be described. First, the reference phase setting unit 912 determines whether or not instruction information for starting printing is input from a personal computer (PC) or the like (S101). If it is determined that the instruction information for starting printing has not been input (NO in S101), the process is set to a standby state.

  When it is determined that the instruction information to start printing is input (YES in S101), the reference phase setting unit 912 starts driving the polygon motor 330 (S103). Then, the reference phase setting unit 912 determines whether or not the polygon motor 330 has rotated at a constant speed at a steady rotation frequency (here, 2 kHz) (S105). If it is determined that the rotation speed is not constant (NO in S105), the process is set to a standby state. If it is determined that the rotation speed is constant (YES in S105), the beam detector 911 generates a BD signal via the beam sensor 335 (S107).

  Then, the reference phase setting unit 912 sets a reference phase that is a reference phase of the rotational phase of the polygon mirror 332 based on the detection result (= BD signal) of the beam detection unit 911 (S109). Next, the phase control unit 913 calculates the phase difference of the rotation phase of a predetermined number (here, four) of polygon mirrors 332 with respect to the reference phase corresponding to the reference phase signal S0 (see FIG. 5) (S111). ).

  Then, the phase control unit 913 reads the change pattern corresponding to the phase difference calculated in step S111 from the pattern storage unit 921 and changes the rotation frequency of the polygon motor 330 according to the change pattern (S113). Next, the phase control unit 913 determines whether or not the change of the rotation frequency of the polygon motor 330 corresponding to the change pattern is completed (S115). If it is determined that the change has not been completed (NO in S115), the process returns to step S113, and the processes after step S113 are repeatedly executed. If it is determined that the change has been completed (YES in S115), the process ends.

  In this way, the laser beams respectively scanned by the predetermined number (four in this case) of the polygon mirrors 332 by the beam detector 911 are set on the scanning path in advance (the beam sensor 335 shown in FIG. 3). Based on the detection result, a reference phase that is a reference phase for the rotational phase of a predetermined number (here, four) of polygon mirrors 332 is set. Since the polygon motor 330 is driven and controlled so that the rotational phase of a predetermined number (here, four) of polygon mirrors 332 matches the reference phase, the polygon mirror 332 can be controlled by appropriately setting the reference phase. The rotational phase can be matched efficiently.

  Further, since the reference phase is set based on the detection result of the beam detection unit 911, an appropriate reference phase can be easily set. For example, as shown in FIG. 5, among the rotational phases of a predetermined number (here, four) of polygon mirrors 332, the phase at the approximate center between the most advanced phase and the most delayed phase is set as the reference phase. By doing so, the rotational phase of the polygon mirror 332 can be matched efficiently (see FIG. 5).

  That is, in the past, it was necessary to control the polygon motor 330 to change the rotational phase of the polygon mirror 332 by the phase difference between the most advanced phase and the most delayed phase. Since the phase in the approximate center of the delayed phase is set as the reference phase, the rotational phase of the polygon mirror 332 is set by the phase difference of approximately 1/2 of the phase difference between the most advanced phase and the most delayed phase. Since the polygon motor 330 may be controlled so as to be changed, the rotational phase of the polygon mirror 332 can be matched more efficiently.

  Furthermore, since each rotation frequency is sequentially increased or decreased by a predetermined frequency (here, 10 Hz) in a stepwise manner by a predetermined number (here, four) of polygon motors 330, the rotation frequency overshoot ( (Or undershoot) is suppressed, so that the rotational phase of the polygon mirror 332 can be matched more efficiently.

  Further, the rotational frequency of the polygon motor 330 is controlled via a PLL (Phase Locked Loop) of the motor driver 374, and a predetermined frequency (here, 10 Hz) that is a change amount of the rotational frequency increased or decreased by the polygon motor 330 is set in advance. Since the threshold value is set to be equal to or lower than a set threshold value (for example, 100 Hz), the PLL is prevented from being out of the locked state, and the rotational phase of the polygon mirror 332 can be matched more efficiently.

  Further, when the rotation phase of a predetermined number (here, four) of polygon mirrors 332 is delayed with respect to the reference phase, the rotation frequency of the corresponding polygon motor 330 is changed from the steady rotation frequency (here, 2 kHz). After sequentially increasing by a predetermined frequency ΔFA (here, 10 Hz) that is preset in steps, the steady rotational frequency (here, 2 kHz) is sequentially increased by a predetermined frequency ΔFB (here, 10 Hz) preset in steps. Therefore, the occurrence of rotational frequency overshoot (or undershoot) is suppressed, so that the rotational phase of the polygon mirror 332 can be matched more efficiently.

  Similarly, when the rotational phase of a predetermined number (here, four) of polygon mirrors 332 is advanced with respect to the reference phase, the rotational frequency of the corresponding polygon motor 330 is the steady rotational frequency (here, 2 kHz). Are sequentially decreased by a predetermined frequency ΔFB (here, 10 Hz) that is preset in a stepwise manner, and then are sequentially increased to a steady rotational frequency (here, 2 kHz) by a predetermined frequency ΔFA that is preset in a stepwise manner. Since the occurrence of overshoot (or undershoot) of the rotational frequency is suppressed, the rotational phase of the polygon mirror can be matched more efficiently.

  Further, a phase difference with respect to the reference phase of the rotation phase of a predetermined number (four in this case) of polygon mirrors 332 is calculated, and a change pattern corresponding to the calculated phase difference is read from the pattern storage unit 921 and read. Since the rotation frequency of the corresponding polygon motor 330 is controlled based on the change pattern that has been issued, the rotation phase of the polygon mirror 332 can be efficiently matched with a simple configuration.

The present invention can also be applied to the following forms.
(A) In the present embodiment, the reference phase setting unit 912 rotates the predetermined number (here, four) polygon mirrors 332 based on the detection results of the predetermined number (here, four) beam sensors 335. The case where the center phase between the most advanced phase and the most delayed phase is set as the reference phase has been described. However, the reference phase setting unit 912 may also set the reference phase by other methods. Good.

  For example, the reference phase setting unit 912 obtains the center phase between the most advanced phase and the most delayed phase among the rotation phases of a predetermined number (here, four) of polygon mirrors 332, and the obtained center The reference phase may be set to the rotational phase of the polygon mirror 332 closest to the phase (in the example shown in FIG. 5, the BD signal SY corresponding to yellow (Y) is set as the reference phase signal S0).

  (B) In the present embodiment, a case has been described in which the predetermined frequencies ΔFA and ΔFB, which are changes in frequency that the phase control unit 913 increases or decreases, are constant (here, 10 Hz), but the frequency that the phase control unit 913 increases or decreases. The predetermined frequency ΔFA, ΔFB, which is the amount of change in the above, may be variable. For example, the predetermined frequencies ΔFA and ΔFB may be decreased as the rotational phase of the polygon mirror 332 approaches the reference phase. In this case, the rotational phase of the polygon mirror 332 can be matched more accurately.

  (C) In the present embodiment, when the rotation phase of the polygon mirror 332 is delayed with respect to the reference phase, the phase control unit 913 sets the rotation frequency of the corresponding polygon motor 330 to the steady rotation frequency (here, 2 kHz). ) From a predetermined frequency ΔFA (here, 10 Hz) that is preset in a stepwise manner, and then a steady rotational frequency (here, 2 kHz) that is sequentially increased by a predetermined frequency ΔFB (here, 10 Hz) that is preset in a stepwise manner. However, when the rotational phase of the polygon mirror 332 is delayed with respect to the reference phase, at least the frequency may be decreased stepwise when the frequency is decreased.

  That is, when the rotational phase of the polygon mirror 332 is delayed with respect to the reference phase, the phase control unit 913 increases the frequency by a predetermined frequency ΔFA (for example, 30 Hz) set in advance, and then stepwise. A configuration may be adopted in which the frequency is sequentially reduced to a steady rotational frequency (here 2 kHz) by a predetermined frequency ΔFB (here 10 Hz). On the other hand, when the rotational phase of the polygon mirror 332 is advanced with respect to the reference phase, the phase control unit 913 reduces the frequency by a predetermined frequency ΔFB (for example, 30 Hz) set in advance once, and then stepwise Alternatively, a predetermined frequency ΔFA (here, 10 Hz) set in advance may be sequentially increased to a steady rotational frequency (here, 2 kHz). In this case, the process is simplified.

  Further, the phase controller 913 may increase and decrease the frequency only once. That is, when the rotation phase of the polygon mirror 332 is delayed with respect to the reference phase, the phase control unit 913 increases the frequency by a predetermined frequency ΔFA (for example, 30 Hz) that is set only once and then only once. It may be configured to decrease by a predetermined frequency ΔFB (for example, 30 Hz) set in advance. Further, when the rotation phase of the polygon mirror 332 is advanced with respect to the reference phase, the phase control unit 913 decreases the frequency by a predetermined frequency ΔFB (for example, 30 Hz) only once and then only once. A mode in which the frequency is increased by a predetermined frequency ΔFA (for example, 30 Hz) set in advance may be used. In this case, the process is further simplified.

FIG. 1 is a configuration diagram illustrating an example of a schematic configuration of a printer according to the present invention. FIG. 2 is a configuration diagram illustrating an example of an image forming unit and an intermediate transfer unit illustrated in FIG. 1. These are block diagrams which show an example of a structure of the laser irradiation unit shown in FIG. These are block diagrams which show an example of a structure of the principal part which concerns on this invention. These are timing charts which show an example of the setting method of the reference phase by a reference phase setting part. These are graphs which show an example of the change pattern stored in the pattern memory | storage part. These are the graphs which show an example different from FIG. 6 of the change pattern stored in the pattern memory | storage part. These are the flowcharts which show an example of operation | movement of a printer (mainly CPU).

Explanation of symbols

100 Copier 3 Image forming unit 33 Laser irradiation unit 330 Polygon motor (part of polygon driving means)
331 Laser diode 332 Polygon mirror 335 Beam sensor (part of beam detection means)
37 Motor drive device (part of polygon drive means)
371 Basic clock generation circuit 372 Frequency divider 373 Setting register 374 Motor driver 9 Control unit 91 CPU
911 Beam detector (part of beam detector)
912 Reference phase setting unit (reference phase setting means)
913 Phase control unit (phase control means)
914 Drive control unit (part of polygon drive means)
92 RAM
921 Pattern storage unit (pattern storage means)

Claims (5)

A latent image is formed by irradiating a photosensitive drum with a laser beam through a polygon mirror for each of a predetermined number of colors of 2 or more, and a toner image corresponding to the formed latent image is formed. An image forming apparatus that forms a color image by superimposing and transferring the toner images of the predetermined number of colors onto a recording sheet,
Polygon driving means for rotationally driving each of the predetermined number of polygon mirrors at a preset steady rotational frequency;
Beam detecting means for detecting a laser beam scanned by the predetermined number of polygon mirrors at a preset position on the scanning path;
A reference phase setting means for setting a reference phase that is a reference phase of a rotational phase of the predetermined number of polygon mirrors based on detection results of the predetermined number of beam detection means;
Phase control means for controlling the polygon drive means to match the rotational phase of the predetermined number of polygon mirrors with the reference phase;
Equipped with a,
The reference phase setting means, based on the detection results of the predetermined number of beam detection means, the center phase of the most advanced phase and the most delayed phase among the rotation phases of the predetermined number of polygon mirrors, Set the reference phase or calculate the center phase of the most advanced phase and the most delayed phase among the rotation phases of a predetermined number of polygon mirrors, and rotate the polygon mirror closest to the determined center phase An image forming apparatus , wherein a phase is set as the reference phase . The phase control means controls the predetermined number of polygon driving means so as to coincide with the reference phase by sequentially increasing or decreasing each rotation frequency by a predetermined frequency set in advance step by step. The image forming apparatus according to claim 1 . The polygon driving means controls the rotation frequency via a PLL (Phase Locked Loop),
The image forming apparatus according to claim 2 , wherein the predetermined frequency is set to be equal to or less than a preset threshold value. The phase control means includes
When the rotation phases of the predetermined number of polygon mirrors are delayed with respect to the reference phase, the rotation frequency of the corresponding polygon driving means is sequentially increased from the steady rotation frequency by a predetermined frequency step by step. After that, the predetermined rotational frequency is decreased step by step to the steady rotational frequency sequentially,
When the rotation phase of the predetermined number of polygon mirrors is advanced with respect to the reference phase, the rotation frequency of the corresponding polygon driving means is sequentially decreased from the steady rotation frequency by a predetermined frequency step by step. after the image forming apparatus according to claim 2 or claim 3, characterized in that increased to successively the steady rotational frequency by a predetermined frequency set stepwise advance. In association with a phase difference of the rotational phase of the polygon mirror with respect to the reference phase, pattern storage means for storing a change pattern of the rotational frequency of the polygon driving means,
The phase control unit calculates a phase difference of the rotation phase of the predetermined number of polygon mirrors with respect to the reference phase, reads a change pattern corresponding to the calculated phase difference from the pattern storage unit, and reads the read change 5. The image forming apparatus according to claim 4 , wherein a rotation frequency of the predetermined number of polygon driving units is controlled based on a pattern.

Images