JP2008111940A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which allows rotational phases of polygon mirrors to efficiently agree with one another. <P>SOLUTION: A CPU 91 is provided with: a beam detection part 911 for detecting laser beams respectively scanned by polygon mirrors 332 of the prescribed number (herein, four pieces) in positions preset on scanning paths (disposition positions of a beam sensor 335); a reference phase setting part 912 for setting reference phases each of which is a phase becoming the reference of rotational phase of the polygon mirrors 332, based on the detection result of the beam detection part 911; a phase difference calculation part 913 which determines a phase difference between the reference phase and the rotational phase of a polygon motor 330 every time the laser beam is detected by the beam detection part 911; a frequency presetting part 914 for presetting a rotational frequency of the polygon motor 330, based on the determined phase difference; and a frequency control part 915 for controlling the rotational frequencies of the polygon motors 330 into the preset rotational frequencies. <P>COPYRIGHT: (C)2008,JPO&INPIT

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. By irradiating the drum to form a latent image, forming a toner image corresponding to the formed latent image on the recording paper, and transferring the formed toner images of the predetermined number of colors onto the recording paper. In an image forming apparatus such as a copier or printer that forms a color image (so-called electrophotographic system), an external operation is performed for a predetermined time (for example, 1 minute) or longer in order to reduce power consumption. When no etc. is input, it will be in a 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, an image forming apparatus according to claim 1 forms a latent image by irradiating a photosensitive drum with a laser beam via a polygon mirror for each of a predetermined number of two or more colors. An image forming apparatus for forming a color image by forming a toner image corresponding to the formed latent image and transferring the formed toner images of a predetermined number of colors to a recording paper in an overlapping manner, A polygon driving means for rotating a predetermined number of polygon mirrors at a preset steady rotation frequency and a laser beam scanned by the predetermined number of polygon mirrors at a predetermined position on the scanning path, respectively. Based on the detection results of the beam detection means to be detected and the predetermined number of beam detection means, the phase serves as a reference for the rotational phase in the predetermined number of polygon driving means. A reference phase setting means for setting a quasi-phase; a reference phase set by the reference phase setting means based on a detection result each time a laser beam is detected by the predetermined number of beam detection means; A phase difference calculating means for determining a phase difference from the rotational phase of each of the polygon driving means, and a rotational frequency of the predetermined number of polygon driving means is set based on the phase difference obtained by the phase difference calculating means. And a frequency control means for controlling the rotational frequency of the predetermined number of polygon driving means to the rotational frequency set by the frequency setting means.

  An image forming apparatus according to a second aspect is the image forming apparatus according to the first aspect, wherein the reference phase setting means includes a rotational phase of one polygon driving means among the predetermined number of polygon driving means. Is set as the reference phase.

  An image forming apparatus according to a third aspect is the image forming apparatus according to the first aspect, wherein the reference phase setting means determines the predetermined number of polygons based on detection results of the predetermined number of beam detecting means. Of the rotational phases in the driving means, a phase approximately in the middle of the most advanced phase and the most delayed phase is set as the reference phase.

  An image forming apparatus according to a fourth aspect is the image forming apparatus according to any one of the first to third aspects, wherein the frequency setting means increases the steady rotation as the absolute value of the phase difference increases. It is characterized in that it is set to a rotational frequency with a large difference from the frequency.

  An image forming apparatus according to a fifth aspect is the image forming apparatus according to any one of the first to fourth aspects, further comprising a rotation speed storage unit that stores a rotation frequency in association with the phase difference. The frequency setting means sets the rotation frequency by reading the rotation frequency corresponding to the phase difference obtained by the phase difference calculation means from the rotation speed storage means.

  The image forming apparatus according to claim 6 is the image forming apparatus according to claim 5, wherein the polygon driving unit controls a rotation frequency via a PLL (Phase Locked Loop), and the rotation number storage unit. However, the rotation frequency set to make the difference between the stored rotation frequency and the steady rotation frequency a value within a predetermined range set in advance is stored.

  According to the image forming apparatus of claim 1, a laser beam is detected by a predetermined number of beam detecting means, and based on the detection result, a reference that is a phase serving as a reference for a rotational phase in the predetermined number of polygon driving means. When the phase is set and the laser beam is detected by a predetermined number of beam detecting means, the reference phase set by the reference phase setting means and the rotation of the predetermined number of polygon driving means are detected based on the detection result. A phase difference from the phase is obtained. Then, based on the phase difference obtained by the phase difference calculating means, the rotational frequency of the predetermined number of polygon driving means is set, and the rotational frequency of the predetermined number of polygon driving means is controlled to the set rotational frequency. The

  Therefore, every time the laser beam is detected by the beam detecting means, the rotational frequency of a predetermined number of polygon driving means is controlled in accordance with the phase difference obtained based on the detection result, so that the rotational phase of the polygon mirror is controlled. Can be matched efficiently. That is, for example, the rotational phase of the polygon mirror can be brought closer to the reference phase quickly by setting the rotational frequency so that the greater the phase difference is, the greater the frequency difference from the steady rotational frequency is.

  According to the image forming apparatus of the second aspect, since the rotational phase of one polygon driving unit is set as the reference phase from among a predetermined number of polygon driving units, by appropriately selecting the reference phase The rotational phase of the polygon mirror can be matched more efficiently.

  For example, among the rotation phases of a predetermined number of polygon mirrors, the center phase between the most advanced phase and the most delayed phase is obtained, and the rotation phase of the polygon mirror closest to the obtained center phase is determined as the reference phase. If set, the phase difference between the rotational phase of the predetermined number of polygon mirrors and the reference phase becomes small, and the rotational phases of the polygon mirrors can be matched more efficiently.

  According to the image forming apparatus of the third aspect, since the most advanced phase and the most delayed phase among the rotational phases in the predetermined number of polygon driving units are set as the reference phase. The rotational phase of the polygon mirror can be matched more efficiently.

  That is, conventionally, it has been necessary to control the polygon driving means to change the rotational phase of the polygon mirror by the phase difference between the most advanced phase and the most delayed phase. Since the phase approximately in the center of the phase is set as the reference phase, the rotational phase of the polygon mirror is changed by a phase difference that is approximately half of the phase difference between the most advanced phase and the most delayed phase. Since the polygon driving means need only be controlled as much as possible, the rotational phase of the polygon mirror can be matched more efficiently.

  According to the image forming apparatus of the fourth aspect, as the absolute value of the phase difference between the rotational phase of the predetermined number of polygon driving means and the reference phase is larger, the rotational frequency is set to have a larger difference from the steady rotational frequency. For this reason, since the amount of reduction in the phase difference between the rotational phase of the predetermined number of polygon driving means per unit time (for example, 1 msec) and the reference phase becomes large, the rotational phase of the polygon mirror can be matched more efficiently. It is.

  According to the image forming apparatus of the fifth aspect, the rotation frequency is set by reading the rotation frequency corresponding to the phase difference obtained by the phase difference calculation unit from the rotation number storage unit. Can set an appropriate frequency.

  According to the image forming apparatus of the sixth aspect, the rotation frequency is controlled via a PLL (Phase Locked Loop), and the difference between the stored rotation frequency and the steady rotation frequency is within a predetermined range. Since the rotation frequency set to be the value of is stored in the rotation number storage means, the PLL is prevented from being out of the locked state, and the rotation phase of the polygon mirror can be matched more efficiently.

  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 image information 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 emits laser light corresponding to image information (or color misregistration correction pattern information) received from an unillustrated PC or the like, and an electrostatic latent image is formed on the surface of the photosensitive drum 31. It is formed.

  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 (frequency control unit 915 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 (frequency control unit 915 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 difference calculation unit 913, a frequency setting unit 914, and a frequency control unit 915, and the RAM 92 functionally includes a frequency storage unit 921. I have. Here, the CPU 91 reads and executes a program stored in advance in a ROM or the like, so that the beam detection unit 911, the reference phase setting unit 912, the phase difference calculation unit 913, the frequency setting unit 914, the frequency control unit 915, etc. In addition to functioning as a function unit, the RAM 92 functions as a function unit such as the frequency 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. A phase difference calculation unit 913 (corresponding to a phase difference calculation unit) is configured to generate a reference phase based on the detection result every time a laser beam is detected by the beam detection unit 911 (= every time a BD signal is generated). The phase difference between the reference phase set by the setting unit 912 and the rotational phase of a predetermined number (here, four) of polygon motors 330 is obtained.

  For example, when the BD signal shown in FIG. 5 is generated, the phase difference calculation unit 913 calculates the phase difference corresponding to each color of magenta (M), cyan (C), yellow (Y), and black (K). , Time (TA-TC / 2), time (-TC / 2), time (TB-TC / 2), and time (TC / 2), respectively. Here, when the time indicating the phase difference is positive, it indicates that the rotational phase of the polygon motor 330 is advanced with respect to the reference phase, and when the time indicating the phase difference is negative, the reference phase This shows that the rotational phase of the polygon motor 330 is delayed.

  The frequency setting unit 914 (corresponding to the frequency setting unit) sets the rotation frequency of a predetermined number (here, four) of polygon motors 330 based on the phase difference obtained by the phase difference calculation unit 913. Is. Further, the frequency setting unit 914 sets the rotation frequency having a larger difference from the steady rotation frequency (here, 2 kHz) as the absolute value of the phase difference obtained by the phase difference calculation unit 913 is larger (see FIG. 6). Further, the frequency setting unit 914 sets the rotation frequency by reading out the rotation frequency corresponding to the phase difference obtained by the phase difference calculation unit 913 from the frequency storage unit 921.

  The frequency control unit 915 (corresponding to the frequency control means) sets the rotation frequency of the polygon motor 330 of a predetermined number (here, four) to the rotation frequency set by the frequency setting unit 914, the setting register 373, and the frequency division. It is controlled via a device 372 and a motor driver 374.

  The frequency storage unit 921 (corresponding to the frequency storage unit) stores the rotational frequency of the polygon motor 330 in association with the phase difference between the reference phase set by the reference phase setting unit 912 and the rotational phase of the polygon motor 330. To do. The frequency storage unit 921 is set so that the difference between the stored rotation frequency and the steady rotation frequency (here, 2 kHz) is a value within a predetermined range (for example, 100 Hz or less). The rotation frequency is stored.

  FIG. 6 is a chart showing an example of the phase difference Δφ and the rotation frequency stored in the frequency storage unit 921. As shown in the figure, the frequency storage unit 921 includes, for example, 2 when the phase difference Δφ between the reference phase set by the reference phase setting unit 912 and the rotation phase of the polygon motor 330 is −20 μsec or less. If .03 kHz is stored and is greater than −20 μsec (= greater than) and −8 μsec or less, 2.02 kHz is stored, and if it is greater than −8 μsec (= greater than) and −2 μsec or less, then 2 .01 kHz is stored.

  Further, for example, when the phase difference Δφ between the reference phase set by the reference phase setting unit 912 and the rotation phase of the polygon motor 330 is 20 μsec or more, the frequency storage unit 921 stores 1.97 kHz. If it is 8 μsec or more and less than 20 μsec, 1.98 kHz is stored, and if it is 2 μsec or more and less than 8 μsec, 1.99 kHz is stored.

  When the phase difference Δφ between the reference phase set by the reference phase setting unit 912 and the rotation phase of the polygon motor 330 is more than −2 μsec and less than 2 μsec, 2.0 kHz (= steady rotation frequency) is stored. ing. That is, when the phase difference between the reference phase set by the reference phase setting unit 912 and the rotation phase of the polygon motor 330 is more than −2 μsec and less than 2 μsec, the frequency of the polygon motor 330 is the steady rotation frequency (= 2). .0 kHz).

  FIG. 7 is a graph showing an example of the phase difference Δφ calculated by the phase difference calculation unit 913 and the frequency set by the frequency setting unit 914. (A) is a graph showing an example of the frequency set by the frequency setting unit 914, and (b) is a graph showing an example of the phase difference Δφ calculated by the phase difference calculating unit 913.

  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 where the phase difference Δφ is 30 μsec will be described.The phase difference calculation unit 913 receives the laser beam by the beam detection unit 911. The phase difference Δφ is calculated every time it is detected. Here, since the steady rotation frequency of the polygon motor 330 is 2.0 kHz, the phase difference Δφ is calculated every 0.5 msec (= 1/2000). Is to be calculated.

  As shown in (a), at the timing of time T11, the phase difference calculation unit 913 calculates that the phase difference Δφ is 30 μsec, and the frequency setting unit 914 rotates from the frequency storage unit 921 corresponding to the phase difference Δφ. The frequency is read (see FIG. 6), the rotation frequency is set to 1.97 kHz, and further, the frequency control unit 915 changes the rotation frequency of the polygon motor 330 from the steady rotation frequency (here, 2 kHz) to 1. It is controlled to 99 kHz. Then, at the timing of time T12 when 1.0 msec (= time corresponding to two cycles of the steady rotational frequency (here, 2 kHz)) has elapsed from time T11, the phase difference Δφ is 15 μsec by the phase difference calculation unit 913. The frequency setting unit 914 reads the rotation frequency corresponding to the phase difference Δφ from the frequency storage unit 921 (see FIG. 6), sets the rotation frequency to 1.98 kHz, and further, the frequency control unit 915 Thus, the rotational frequency of the polygon motor 330 is controlled from 1.97 kHz to 1.98 kHz.

  Next, at the timing of time T13 when 1.0 msec (= time corresponding to two cycles of steady rotational frequency (here 2 kHz)) has elapsed from time T12, the phase difference Δφ is 5 μsec by the phase difference calculation unit 913. The frequency setting unit 914 reads the rotation frequency corresponding to the phase difference Δφ from the frequency storage unit 921 (see FIG. 6), sets the rotation frequency to 1.99 kHz, and further, the frequency control unit By 915, the rotational frequency of the polygon motor 330 is controlled from 1.98 kHz to 1.99 kHz. Then, at the timing of time T14 when 1.0 msec (= time corresponding to two cycles of steady rotation frequency (here, 2 kHz)) has elapsed from time T13, the phase difference calculation unit 913 causes the phase difference Δφ to be approximately 0 μsec. The frequency setting unit 914 reads the rotation frequency corresponding to the phase difference Δφ from the frequency storage unit 921 (see FIG. 6), sets the rotation frequency to 2.0 kHz, and further, the frequency control unit By 915, the rotational frequency of the polygon motor 330 is controlled from 1.99 kHz to 2.0 kHz (= steady rotational frequency).

  As described above, the phase difference calculation unit 913 calculates the phase difference Δφ between the reference phase set by the reference phase setting unit 912 and the rotation phase of the polygon motor 330, and the frequency setting unit 914 corresponds to the phase difference Δφ. The rotation frequency is read and set (see FIG. 6), and the frequency control unit 915 controls the rotation frequency of the polygon motor 330 to the rotation frequency set by the frequency setting unit 914. Each time the laser beam is detected by the beam detector 911 (= every 0.5 msec), the above operation is repeated, so that the phase difference Δφ between the reference phase and the rotation phase of the polygon motor 330 becomes (b). As shown, the rotation phase of the polygon mirror 332 is substantially matched with the reference phase corresponding to the reference phase signal S0 (see FIG. 5).

  FIG. 8 is a graph showing another example of the phase difference Δφ calculated by the phase difference calculation unit 913 and the frequency set by the frequency setting unit 914 different from FIG. (A) is a graph showing an example of the frequency set by the frequency setting unit 914, and (b) is a graph showing an example of the phase difference Δφ calculated by the phase difference calculating unit 913.

  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) (when the phase difference Δφ is −30 μsec) The phase difference calculation unit 913 uses the beam detection unit 911 to transmit the laser beam. The phase difference Δφ is calculated every time when is detected, but here, since the steady rotation frequency of the polygon motor 330 is 2.0 kHz, the phase difference Δφ is every 0.5 msec (= 1/2000). Is calculated.

  As shown in (a), at the timing of time T21, the phase difference calculation unit 913 calculates that the phase difference Δφ is −30 μsec, and the frequency setting unit 914 corresponds to the phase difference Δφ from the frequency storage unit 921. The rotation frequency is read (see FIG. 6), the rotation frequency is set to 2.03 kHz, and the frequency control unit 915 further changes the rotation frequency of the polygon motor 330 from the steady rotation frequency (here, 2 kHz) to 2. Controlled to .03 kHz. Then, at the timing of time T22 when 1.0 msec (= time corresponding to two cycles of steady rotation frequency (here, 2 kHz)) has elapsed from time T21, the phase difference Δφ is −15 μsec by the phase difference calculation unit 913. The frequency setting unit 914 reads the rotation frequency corresponding to the phase difference Δφ from the frequency storage unit 921 (see FIG. 6), sets the rotation frequency to 2.02 kHz, and further, the frequency control unit By 915, the rotational frequency of the polygon motor 330 is controlled from 2.03 kHz to 2.02 kHz.

  Next, the phase difference Δφ is −5 μsec by the phase difference calculation unit 913 at the timing of time T23 when 1.0 msec (= time corresponding to two cycles of steady rotation frequency (here, 2 kHz)) has elapsed from time T22. The frequency setting unit 914 reads the rotation frequency corresponding to the phase difference Δφ from the frequency storage unit 921 (see FIG. 6), sets the rotation frequency to 2.01 kHz, and further controls the frequency. The rotation frequency of the polygon motor 330 is controlled by the unit 915 from 2.02 kHz to 2.01 kHz. Then, at the timing of time T24 when 1.0 msec (= time corresponding to two cycles of steady rotation frequency (here 2 kHz)) has elapsed from time T13, the phase difference calculation unit 913 causes the phase difference Δφ to be approximately 0 μsec. The frequency setting unit 914 reads the rotation frequency corresponding to the phase difference Δφ from the frequency storage unit 921 (see FIG. 6), sets the rotation frequency to 2.0 kHz, and further, the frequency control unit By 915, the rotational frequency of the polygon motor 330 is controlled from 2.01 kHz to 2.0 kHz (= steady rotational frequency).

  As described above, the phase difference calculation unit 913 calculates the phase difference Δφ between the reference phase set by the reference phase setting unit 912 and the rotation phase of the polygon motor 330, and the frequency setting unit 914 corresponds to the phase difference Δφ. The rotation frequency is read and set (see FIG. 6), and the frequency control unit 915 controls the rotation frequency of the polygon motor 330 to the rotation frequency set by the frequency setting unit 914. Each time the laser beam is detected by the beam detector 911 (= every 0.5 msec), the above operation is repeated, so that the phase difference Δφ between the reference phase and the rotation phase of the polygon motor 330 becomes (b). As shown, the rotation phase of the polygon mirror 332 is substantially matched with the reference phase corresponding to the reference phase signal S0 (see FIG. 5).

  FIG. 9 is a flowchart illustrating 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 difference calculation unit 913 calculates the phase difference Δφ with respect to the reference phase corresponding to the reference phase signal S0 (see FIG. 5) of the rotation phases of the predetermined number (here, four) of the polygon mirrors 332. (S111).

  Then, the rotation frequency corresponding to the phase difference Δφ calculated in step S111 is read from the frequency storage unit 921 by the frequency setting unit 914, and the rotation frequency of the polygon motor 330 is changed by the frequency control unit 915 (S113). ). Next, the frequency setting unit 914 determines whether or not the phase difference Δφ is equal to or smaller than a threshold value (here, whether −2 μsec <Δφ <2 μsec) (S115). If it is determined that it is not less than the threshold value (here, -Δφ ≦ 2 μsec or Δφ ≧ 2 μ) (NO in S115), the process returns to step S107, and the processes after step S107 are repeatedly executed. . If it is determined that the value is equal to or less than the threshold value (here, −Δφ ≦ 2 μsec or Δφ ≧ 2 μ) (YES in S115), the process ends.

  In this manner, every time a laser beam is detected by the beam detection unit 911 via the beam sensor 335, a predetermined number (here, four) is determined according to the phase difference Δφ obtained based on the detection result. Since the rotational frequency of the polygon motor 330 is controlled, the rotational phase of the polygon mirror 332 can be matched efficiently. That is, for example, as the phase difference Δφ is larger, the rotational phase of the polygon mirror 332 can be quickly brought closer to the reference phase by setting the rotational frequency so that the difference in frequency from the steady rotational frequency (here, 2 kHz) is larger. It can be done.

  In addition, among the rotation phases of a predetermined number (here, four) of polygon motors 330, a substantially center phase between the most advanced phase and the most delayed phase is set as the reference phase, and therefore the polygon mirror 332 is set. Can be made to coincide with each other more efficiently.

  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.

  Further, as the absolute value of the phase difference Δφ between the rotational phase of the predetermined number (here, four) of polygon motors 330 and the reference phase is larger, the rotational frequency has a larger difference from the steady rotational frequency (here, 2 kHz). Since it is set (see FIG. 6), the amount of reduction in the phase difference between the rotational phase of the predetermined number (here, 4) of polygon motor 330 per unit time (for example, 1 msec) and the reference phase becomes large. The rotational phase of the polygon mirror 332 can be matched more efficiently.

  Further, since the rotation frequency is set by reading the rotation frequency corresponding to the phase difference Δφ obtained by the phase difference calculation unit 913 from the frequency storage unit 921, an appropriate frequency can be set with a simple configuration. it can.

  Further, the rotational frequency of the polygon motor 330 is controlled via a PLL (Phase Locked Loop) of the motor driver 374, and the difference from the steady rotational frequency is stored in the frequency storage unit 921 within a predetermined range (for example, Since the rotation frequency is set to a value of 100 Hz or less, the PLL is prevented from being out of the locked state, and the rotation phase of the polygon mirror 332 can be matched more efficiently.

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, the case where the frequency setting unit 914 sets the rotation frequency by reading the rotation frequency corresponding to the phase difference Δφ obtained by the phase difference calculation unit 913 from the frequency storage unit 921 has been described. The frequency setting unit 914 may set the rotation frequency corresponding to the phase difference Δφ by other methods. For example, the frequency setting unit 914 may calculate and set the rotational frequency from the phase difference Δφ using a predetermined equation (for example, the following equation (1)). In this case, a more appropriate frequency can be set.

Rotation frequency = 2.0−Δφ (μsec) × 0.01 (1)
(C) In this embodiment, the frequency storage unit 921 associates the rotation frequency of the polygon motor 330 with the phase difference Δφ between the reference phase set by the reference phase setting unit 912 and the rotation phase of the polygon motor 330. Although the case of storing has been described, the frequency storage unit 921 has a polygon corresponding to each color (here, magenta (M), cyan (C), yellow (Y), and black (K)). The rotational frequency of the motor 330 may be stored in association with the phase difference Δφ. In this case, a more appropriate frequency can be set.

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. FIG. 4 is a chart showing an example of a phase difference Δφ and a rotation frequency stored in the frequency storage unit. These are graphs showing an example of the phase difference Δφ calculated by the phase difference calculation unit and the frequency set by the frequency setting unit. These are the graphs which show an example different from FIG. 7 of the phase difference (DELTA) (phi) calculated by a phase difference calculation part, and the frequency set by a frequency setting 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 difference calculation unit (phase difference calculation means)
914 Frequency setting unit (frequency setting means)
915 Frequency control unit (frequency control means)
92 RAM
921 Frequency storage unit (frequency storage means)

Claims (6)

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, which is a reference phase of a rotation phase in the predetermined number of polygon driving means, based on detection results of the predetermined number of beam detecting means;
Each time a laser beam is detected by the predetermined number of beam detecting means, the reference phase set by the reference phase setting means and the rotational phase of the predetermined number of polygon driving means are determined based on the detection result. A phase difference calculating means for obtaining each of the phase differences;
Frequency setting means for setting the rotational frequencies of the predetermined number of polygon driving means based on the phase difference obtained by the phase difference calculating means;
Frequency control means for controlling the rotation frequency of the predetermined number of polygon driving means to the rotation frequency set by the frequency setting means;
An image forming apparatus comprising:   The image forming apparatus according to claim 1, wherein the reference phase setting unit sets a rotation phase of one polygon driving unit as the reference phase among the predetermined number of polygon driving units.   The reference phase setting means is based on a detection result of the predetermined number of beam detecting means, and is a phase approximately in the middle of the most advanced phase and the most delayed phase among the rotational phases of the predetermined number of polygon driving means. The image forming apparatus according to claim 1, wherein the reference phase is set.   The image forming apparatus according to claim 1, wherein the frequency setting unit sets the rotational frequency having a larger difference from the steady rotational frequency as the absolute value of the phase difference is larger. apparatus. A rotation speed storage means for storing the rotation frequency in association with the phase difference;
5. The frequency setting unit according to claim 1, wherein the frequency setting unit sets the rotation frequency by reading out a rotation frequency corresponding to the phase difference obtained by the phase difference calculation unit from the rotation number storage unit. The image forming apparatus according to any one of the above. The polygon driving means controls the rotation frequency via a PLL (Phase Locked Loop),
The rotational speed storage means stores a rotational frequency set to set a difference between the stored rotational frequency and the steady rotational frequency to a value within a predetermined range set in advance. The image forming apparatus according to claim 5.

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