JP2011075593A - Optical scanning apparatus and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanning apparatus in which occurrence of a shift in a scanning starting position is suppressed and to provide an image forming apparatus. <P>SOLUTION: The image forming apparatus 1 includes a laser scanner 2 and reciprocally scans the latent image forming region 50 of a photoreceptor drum 5 by deflecting a laser beam LB emitted from a laser diode 21 with a deflection mirror 25. To both end parts of the scanning region of the laser beam LB, beam detection sensors 23L1, 23L2 and a beam reflection mirror 24 which reflects the laser beam LB onto the beam detection sensors, are provided. Logic circuits 51 to 52 detect timing at which the magnitude of signal output by each beam detection sensor is replaced, select a signal that the logic circuits output according to the scanning direction of the laser beam, and control the formation starting position of a latent image with the laser beams and the scanning range of the deflection mirror on the basis of the detection timing in the logic circuits. Even when the spot of the laser beam is deformed, the detection timing hardly changes, thus the shift in the formation starting position of the latent image is suppressed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical scanning device that scans an object to be scanned with a light beam, and an image forming apparatus including the optical scanning device.

  An image forming apparatus such as a laser printer includes an optical scanning device that forms a latent image on a photosensitive member. Some optical scanning devices form a latent image in a latent image forming region on a photosensitive member by reciprocally scanning a laser beam with a deflection mirror (galvanomirror). Such an optical scanning device controls the maximum scanning angle of the deflection mirror so that the scanning range of the laser beam is constant.

  However, the maximum scanning angle of the deflecting mirror may change due to a change in the driving circuit characteristics of the deflecting mirror due to a temperature change in the surrounding environment. In this case, there is a problem in that the image quality is affected by deviation or variation in the formation start position of the latent image by the laser beam.

  With respect to such a problem, the optical scanning device described in Patent Document 1 is provided with an optical sensor (photodetector) that detects a laser beam irradiated by the scanning unit at both ends of the scanning range of the scanning unit. . Based on the laser beam detection signal output from this optical sensor, the deflection mirror drive is controlled to stabilize the maximum scanning angle of the deflection mirror. Is suppressed (see Patent Document 1).

JP 2004-110030 A

  In the conventional optical scanning device, the spot shape of the laser beam may change due to the temperature dependence of the light emission characteristics of the laser diode, the change in the reflectance of the reflecting surface of the deflecting mirror, the lens characteristics, the deflection of the deflecting mirror, and the like. In the optical scanning device, when the spot shape of the laser beam changes in this way, the timing at which the optical sensor detects the laser beam changes. At this time, since the optical scanning device corrects the rotation angle of the deflection mirror on the assumption that the scanning angle of the deflection mirror has changed, the image formation is affected by a deviation in the formation start position of the latent image by the laser beam. was there.

  Therefore, the present invention provides an optical scanning apparatus and an image forming apparatus that can suppress the occurrence of a shift in the formation start position of a latent image on a scanning object due to the light beam even when the spot of the light beam such as a laser beam is deformed. An object is to provide an apparatus.

  An optical scanning device according to the present invention is an optical scanning device that scans a scanning range including a scanning region of a scanning object by reciprocating a light beam in a first scanning direction and a second scanning direction by a deflecting mirror. A group, a beam reflecting means, an intersection detecting means, a position setting means, and a drive control means are provided. The detection means group includes a first detection means and a second detection means that are arranged adjacent to each other. The detection means group is disposed at one end in the scanning range of the light beam and outside the scanning region. A signal that changes according to the amount of light is output. The beam reflecting means is disposed at the other end in the scanning range of the light beam and outside the scanning area, and reflects the light beam to a different position of the detecting means group according to the scanning angle of the light beam. The intersection detection means outputs a trigger signal when the magnitude relationship between the output signals of the first detection means and the second detection means is switched. The position setting means determines the timing for starting the emission of the light beam based on the trigger signal. The drive control unit measures the interval at which the intersection detection unit outputs the trigger signal, and compares the measured value of this interval with a reference value to control the scanning range of the deflection mirror.

  When the light beam scans the first detection means and the second detection means arranged adjacent to each other, at the timing when the light beam passes through a certain position between the first detection means and the second detection means, The magnitude relationship changes while the output signals change together. The timing at which the magnitude relationship between the two output signals interchanges hardly deviates even when the light beam spot is deformed. Therefore, in the present invention, the influence of the deformation of the light beam spot is suppressed by detecting the timing described above and determining the timing for starting the emission of the light beam based on the timing.

  Moreover, every time the timing at which the magnitudes of the signals output from the first detection means and the second detection means are switched is detected, the intersection detection means is caused to output a trigger signal. Then, the interval at which this signal is output is measured to suppress the deviation of the timing for starting the emission of the light beam due to the variation of the scanning range.

  In the above configuration, the intersection detection unit includes a first signal generation unit, a second signal generation unit, and a selection unit. The first signal generation means outputs a signal corresponding to the comparison result between the voltage obtained by converting the output of the first detection means and the voltage obtained by biasing the output of the second detection means, and the second signal generation means is configured to output the first detection A signal corresponding to the comparison result between the voltage obtained by biasing the output of the means and the voltage obtained by converting the output of the second detection means is output. By providing the bias unit, when the first detection unit or the second detection unit outputs noise, it is possible to prevent erroneous detection of the timing at which the magnitude relationship between the output signals of both detection units is switched. Further, by selecting the output signal of the first signal generation unit and the output signal of the second signal generation unit by the selection unit according to the scanning direction of the light beam, both detection units are used regardless of the scanning direction of the light beam. It is possible to reliably detect the timing at which the magnitude relationship of the output signals changes.

  In the above configuration, each time the drive control unit compares the measured value of the time interval with the reference value, a correction value for correcting the scanning range of the deflection mirror is calculated and stored in the storage unit, and the light beam moves outside the scanning region. It is preferable to read the correction value during scanning to control the scanning range of the deflection mirror. With this configuration, the scanning range of the deflection mirror is not corrected when the scanning region is scanned with the light beam, so that the scanning range of the deflection mirror can be corrected without adversely affecting the scanning of the light beam. .

  Further, a high-quality image can be formed by providing the image forming apparatus with the optical scanning device configured as described above.

  According to the present invention, even if the spot of the laser beam is deformed, it is possible to suppress the occurrence of a shift in the latent image formation start position by the laser beam.

1 is a diagram showing a schematic configuration of an image forming apparatus provided with a laser scanning device according to an embodiment of the present invention. It is the external view which shows schematic structure of scanning MEMS, and the figure which shows the relationship between the rotation angle of the deflection | deviation mirror during reciprocating rotation, and time. It is a block diagram of a laser scanning device. 4 is a flowchart for explaining a printing process of the image forming apparatus. 4 is a flowchart for explaining a printing process of the image forming apparatus. It is a circuit diagram of each logic circuit of a signal selection part. It is the figure which showed the input signal and output signal of a comparator. It is the figure which showed the output signal of each part of a laser scanning apparatus. It is a circuit diagram of a MEMS drive part. FIG. 4 is a block diagram showing a part of the configuration of the laser scanning device different from that shown in FIG. It is the figure which showed the output signal of each part of the laser scanning apparatus shown in FIG.

  Hereinafter, embodiments of the present invention will be described in detail. In the following embodiments, a light beam, an object to be scanned, a scanning region, and an optical scanning device will be described as a laser beam, a photosensitive drum, a latent image forming region, and a laser scanning device, respectively.

  First, an outline of an image forming apparatus provided with a laser scanning device will be described. As shown in FIG. 1, the image forming apparatus 1 includes a laser scanning device 2, a photosensitive drum 5, a developing device 7, a charger (not shown), a cleaning unit (not shown), and a transfer roller (not shown). A fixing unit (not shown), a control unit 9 and the like, and prints a toner image on paper.

  The laser scanning device 2 reciprocally scans the photosensitive drum 5 with a laser beam LB corresponding to image data, and performs exposure processing on the photosensitive drum 5 to form an electrostatic latent image.

  The photosensitive drum 5 rotates in the direction of the arrow 5Y, and an electrostatic latent image is formed on the surface thereof by the laser beam LB emitted from the laser scanning device 2.

  The developing device 7 supplies toner to the photosensitive drum 5 on which the electrostatic latent image is formed, and visualizes the electrostatic latent image into a toner image.

  The transfer roller is disposed on the downstream side of the developing device 7 in the rotation direction of the photosensitive drum 5. The transfer roller sandwiches the paper between the photosensitive drum 5 and transfers the toner image carried by the photosensitive drum 5 onto the paper. The sheet on which the toner image is transferred is heated and pressed by the fixing unit, and is discharged to a discharge tray (not shown).

  The charger charges the surface of the photosensitive drum 5 before the surface of the photosensitive drum 5 is exposed by the laser scanning device 2.

  The cleaning unit removes the toner remaining on the surface of the photosensitive drum 5 after performing the transfer process to the paper.

  The control unit 9 controls each unit of the image forming apparatus 1.

  Next, details of the laser scanning device 2 will be described. As shown in FIG. 1, the laser scanning device 2 includes a laser diode 21, an arc sine lens 22, a beam detection sensor 23L1, a beam detection sensor 23L2, a beam reflection mirror 24, a scanning MEMS 26 having a deflection mirror 25, and a laser scanning control unit. 3 is provided. In the following description, the beam detection sensor is referred to as BD. The BD 23L1 and the BD 23L2 are collectively referred to as a beam detection sensor group 23. Note that BD23L1 corresponds to the first detection means of the present invention, and BD23L2 corresponds to the second detection means of the present invention. The beam detection sensor group 23 corresponds to the detection means group of the present invention.

  The laser beam LB emitted from the laser diode 21 is deflected by the deflection mirror 25 and scans while reciprocating the surface of the photosensitive drum 5 by the reciprocating rotation of the deflection mirror. In the following description, the direction in which the laser beam LB scans the photosensitive drum 5 when the deflection mirror 25 rotates in the direction 25A shown in FIG. (Corresponding to the first scanning direction of the present invention: the direction from the left side surface 5L to the right side surface 5R of the photosensitive drum 5). Further, the direction in which the laser beam LB scans the photosensitive drum 5 when the deflection mirror 25 rotates in the 25B direction shown in FIG. 1 is the B direction (corresponding to the second scanning direction of the present invention: right side of the photosensitive drum 5). Direction from the surface 5R to the left surface 5L). The laser beam LB passes through an arc sine lens 22 provided between the deflection mirror 25 and the photosensitive drum 5 and scans the photosensitive drum 5 at a constant speed. In FIG. 1, the laser beam LB is represented by a dotted arrow.

In the following description, the scanning angle of the laser beam LB that scans the latent image forming region 50 on the photosensitive drum 5 is defined as an effective scanning angle (θ _IMG ). The scanning angle of the laser beam LB when the deflection mirror 25 rotates to the maximum in the A direction or the B direction is defined as the maximum scanning angle (θ _MAX ). In Figure 1, a photosensitive drum at the midpoint 5C and the deflection mirror 25 of 5 the laser beam connecting point O to the reflection line L _C, the effective scan angle (theta _IMG) right effective scanning angle the angle of the divided right side ( θ _{IMG (R)} ), and the left angle is defined as the left effective scanning angle (θ _{IMG (L)} ). In Figure 1, the maximum scan angle by a line _{L C (θ MAX)} right maximum scanning angle on the right side of the angle obtained by dividing the _{(θ MAX (R)),} left maximum scan angle the angle of the left and _{(θ MAX (L))} Define.

The BD 23L1, the BD 23L2, and the beam reflection mirror 24 are used for controlling the reciprocating rotation of the deflection mirror 25 attached to the scanning MEMS 26. BD23L1 and BD23L2 are arranged adjacent to each other at one end in the scanning range of the laser beam so as not to block the laser beam LB from scanning the latent image forming region on the photosensitive member. It is arranged outside the range (θ _IMG ) (outside the scanning region) and within the range of the maximum scanning angle (θ _MAX ), and receives the laser beam LB after passing through the arc sine lens 22.

Beam reflecting mirror 24 corresponds to the beam reflecting means of the present invention are arranged substantially symmetrically to the beam detecting sensor group 23 across the line L _C. That is, the beam reflecting mirror 24 is the other end in the laser beam scanning range, outside the effective scanning angle (θ _IMG ) (outside the scanning region), and within the maximum scanning angle (θ _MAX ). Has been placed. The beam reflecting mirror 24 reflects the laser beam LB after passing through the arc sine lens 22 to the beam detection sensor group 23 and causes the BD 23L1 or BD23L2 to receive the laser beam LB. Beam reflecting mirror 24 passes through the end portion of the laser beam LB is BD23L1 reflected by the far side of the end portion 24R1 line _{L C,} the laser beam LB reflected by the side of the end portion 24R2 close to the linear _{L C} is BD23L2 The size, shape, and arrangement are adjusted to pass through the end. For example, the beam reflecting mirror 24 has a reflecting surface processed into a flat surface or an aspect. The beam reflecting mirror 24 reflects the laser beam LB to different positions on the surface of the BD23L1 or BD23L2 according to the scanning angle of the laser beam LB.

The angle at which the laser beam LB scans from the end of BD23L1 to the end of BD23L2 is the scan angle θ _BDL , and the angle at which the laser beam LB scans from one end 24R1 to the other end 24R2 of the beam reflecting mirror 24. It is defined as a scan angle θ _MR .

  The rotation angle of the deflection mirror 25 is equal to the scanning angle of the laser beam LB reflected by the deflection mirror 25.

  The scanning MEMS 26 is a mechanism unit for scanning the laser beam LB with a galvanometer mirror, and includes a deflection mirror 25 and a mirror driving unit 27 as shown in FIG. The mirror driving unit 27 includes a substantially U-shaped iron core 271 and an inductor 272 wound around the iron core 271. The inductor 272 is connected to the drive output terminal 33T3 and the drive output terminal 33T4, and rotates the deflection mirror 25 back and forth by the drive current input to both terminals. The deflection mirror 25 has a reflecting surface 252 and is rotatable about a rotation shaft 251. The deflection mirror 25 has magnetic poles on the front and back sides, and reciprocates within a predetermined angle range according to the direction of the magnetic field formed around the opening of the U-shaped iron core 271 of the mirror driving unit 27. Rotate. Thereby, the deflection mirror 25 scans the predetermined scanning range with the laser beam LB emitted from the laser diode 21.

  Note that MEMS refers to micro electro mechanical systems.

As shown in FIG. 2B, the deflection mirror 25 is controlled by the laser scanning control unit 3 to periodically reciprocate like a single vibration. In FIG. 2B, the upper side of the time axis is the side on which BD23L1 and BD23L2 are arranged, and the lower side of the time axis is the side on which the beam reflecting mirror 24 is arranged. Further, scanning in the A direction (referred to as scanning phase T1) and scanning in the B direction (referred to as scanning phase T2) are switched at the apex and valley points of the simple vibration-like curve in the figure. Right effective scanning angle θ _{IMG (R)} , left effective scanning angle θ _{IMG (L)} , right maximum scanning angle θ _{MAX (R)} , left maximum scanning angle θ _{MAX (L)} , scanning angle θ _BDL , and scanning angle θ _MR Are as shown in FIG.

Period _{T DT,} after folding the laser beam LB is detected by two detection sensors are scanned in the A direction or the B direction (BD23L1 and BD23L2), laser beam LB is scanned in the opposite direction of the two detection sensor Is the time until it is detected again.

The period _TIMG is a period (latent image forming period) in which the laser beam LB corresponding to the image scans the latent image forming area 50 to form a latent image.

  Next, control of the laser scanning device 2 will be described. As shown in FIG. 3, the laser scanning device 2 includes a beam detection sensor group 23, a beam reflection mirror 24, a scanning MEMS 26, and a laser scanning control unit 3. In FIG. 3, the laser diode 21 and its driving unit are not shown.

  The laser scanning control unit 3 includes a signal processing unit 31 and a MEMS drive unit 33 (corresponding to drive control means).

  The signal processing unit 31 generates a clock signal based on the signal received from the beam detection sensor group 23 and outputs the clock signal to the MEMS driving unit 33.

The MEMS drive unit 33 controls the rotation angle of the deflection mirror 25 of the scanning MEMS 26 based on this clock signal. Further, the MEMS drive unit 33 controls the maximum scanning angle (maximum rotation angle) θ _{MAX to} be constant.

  The signal processing unit 31 includes a signal selection unit 41 (corresponding to the intersection detection unit), a time measuring unit 43 (corresponding to the drive control unit), a comparison unit 45 (corresponding to the drive control unit), and a PWM control unit 47 (corresponding to the drive control unit). ), And a storage unit 49. The signal selection unit 41 includes a logic circuit 51, a logic circuit 52, a selection unit 55, and a selection control unit 56. The PWM control unit 47 includes a memory 47M.

  When the laser beam LB passes, each of the BD 23L1 and the BD 23L2 outputs a signal (current) that changes according to the light amount of the laser beam LB to the signal selection unit 41.

  When the laser beam LB is scanned in the A direction or the B direction shown in FIG. 1, the signal selection unit 41 receives an output signal from the beam detection sensor group 23 and uses it according to the scanning direction of the laser beam LB. A signal is selected and sent to the timer 43.

  The output signals of BD23L1 and BD23L2 are input to logic circuit 51 and logic circuit 52.

  When a signal is input, the logic circuits 51 to 52 output a signal corresponding to the signal to the selection unit 55.

  The selection unit 55 selects any of the signals output from the logic circuits 51 to 52 in accordance with the signals SEL1 and SEL2 input from the selection control unit 56 and outputs the selected signals to the timer unit 43. The selection unit 55 is configured by a multiplexer (not shown), but is not limited thereto, and may be configured by another gate circuit.

When receiving the signal from the selection unit 55, the time measuring unit 43 measures the period T _DT (trigger signal output interval) and outputs the measurement result to the comparison unit 45.

The comparison unit 45 compares the measurement result (measurement value) of the period _TDT received from the time measurement unit 43 with a preset reference time T _TG (reference value), and compares the maximum right scanning angle θ _{MAX (R). Alternatively} , the deviation between the maximum left scanning angle θ _{MAX (L)} and the reference angle θ _MAXK is calculated. Then, the comparison unit 45 outputs a control value RV corresponding to the calculation result with reference to the lookup table stored in the storage unit 49 so that the scanning angle of the deflection mirror 25 becomes the reference angle.

  When the PWM control unit 47 receives the control value RV from the comparison unit 45, the PWM control unit 47 refers to the look-up table stored in the storage unit 49 and adjusts the duty ratio of the clock 1 or clock 2 according to the control value RV. A PWM control value that is a correction value to be calculated is calculated. The PWM control unit 47 temporarily stores the PWM control value in the memory 47M. Further, when receiving the control signal from the control unit 9, the PWM control unit 47 reads the PWM control value from the memory 47M, adjusts the duty ratio, and outputs the clock 1 or the clock 2. Further, the PWM control unit 47 outputs the signal VC1 and the signal VC2 to the selection control unit 56.

  The selection control unit 56 creates the signal SEL1 and the signal SEL2 according to the levels of the signals VC1 and VC2 input from the PWM control unit 47, and outputs them to the selection unit 55.

  Next, control processing of the laser scanning device 2 in the image forming apparatus 1 during printing will be described. Note that this flowchart shows processing that is repeatedly performed after the deflection mirror 25 of the scanning MEMS 26 starts reciprocating rotation, and processing in the initial state is omitted. Further, it is assumed that the laser beam LB always passes through the BD 23L1, BD23L2, and the beam reflection mirror 24 during scanning.

  As shown in FIG. 4, in the image forming apparatus 1, when the control unit 9 detects a print instruction received by an operation unit (not shown), it outputs a control signal to the laser scanning control unit 3 to perform the next scanning. It is confirmed whether the phase is the scanning phase T1 (S1). When the next scanning phase is the scanning phase T1 (S1: Y), the control unit 9 performs the process of step S2. If the next scanning phase is the scanning phase T2 (S1: N), the process of step S15 is performed.

  In the case of the scanning phase T1, the control unit 9 outputs a control signal to the PWM control unit 47. Upon receiving the control signal, the PWM control unit 47 reads the PWM control value for the scanning phase T1 stored in the memory 47M, Start PWM control. That is, the PWM control unit 47 outputs the clock 1 having a duty ratio corresponding to the PWM control value to the MEMS drive unit 33 (S2).

Timing unit 43, when the scanning phase T1 (A direction of the scanning), continued measurement of the period _{T DT} until the falling signal selecting unit 55 detects the laser beam LB is output BD23L1 and BD23L2 (S3: N). Measurement of the period _{T DT,} in step S25 to be described later, during the scanning phase T2 (B direction of the scan), when a signal selecting unit 55 detects the laser beam LB is outputted falls in BD23L1 and BD23L2 The time counting unit 43 is started.

Timing unit 43, once fallen a signal BD23L1 and BD23L2 the selection unit 55 detects the laser beam LB is outputted (S3: Y), completes the measurement of the period _{T DT} (S4).

The comparison unit 45 of the signal processing unit 31 compares the period _TDT measured by the time measuring unit 43 with the length of the reference time _TTG read from the storage unit 49, and calculates the control value RV of the scanning phase T1. Output. Further, when receiving the control value RV from the comparison unit 45, the PWM control unit 47 refers to the lookup table stored in the storage unit 49 and calculates the PWM control value of the clock 1 according to the control value RV. To do. Then, the PWM control unit 47 temporarily stores the PWM control value in the memory 47M (S5).

  The control unit 9 (corresponding to the position setting means) sets the image writing timing on the basis of the timing when the signal output from the selection unit 55 falls in step S3 (S6).

  The controller 9 waits until the writing timing at the scanning phase T1 is reached (S7: N). When the writing timing is reached (S7: Y), the laser beam LB is emitted from the laser diode 21 in correspondence with the image data. Then, writing of an image for one line is started on the photosensitive drum 5 (S8).

  The control unit 9 continues the process until the writing of the one-line image is finished (S9: N), and when the writing of the one-line image is finished (S9: Y), the writing of the image is finished (S10).

The controller 9 waits until the laser beam LB reflected by the beam reflecting mirror 24 is detected by the BD 23L2 and BD23L1 at the scanning phase T1 (scanning in the A direction) (S11: N), and when the laser beam LB is detected (S11: N). S11: Y), the time measuring unit 43 starts measuring the period _TDT (S12). Further, the control unit 9 waits until the scanning phase T1 ends (S13: N).

  When the scanning phase T1 ends (S13: Y), the controller 9 determines whether printing for one page and the print job have ended (S14). If the printing and the print job are not completed (S14: N), the control unit 9 proceeds to step S15. On the other hand, if the printing and the print job are finished (S14: Y), the control unit 9 finishes the printing process.

  As shown in FIG. 5, the control unit 9 outputs a control signal to the PWM control unit 47 when the next scanning phase is not the scanning phase T1 in step S1 or when printing is not finished in step S14. Then, the PWM control unit 47 reads the PWM control value for the scanning phase T2 stored in the memory 47M, and starts PWM control. That is, the PWM control unit 47 outputs the clock 2 having a duty ratio corresponding to the PWM control value to the MEMS drive unit 33 (S15).

The time measuring unit 43 detects the laser beam LB reflected by the beam reflecting mirror 24 at the scanning phase T2 (scanning in the B direction) by the BD23L1 and BD23L2, and until the signal output from the selection unit 55 falls. Continue to measure _DT (S16: N). Measurement of the period _{T DT,} at step S12, during the scanning phase T1 (A direction of the scanning), the signal selecting unit 55 detects the laser beam LB reflected by the beam reflecting mirror 24 in BD23L2 and BD23L1 has output Is started by the time measuring unit 43.

Timing unit 43, once fall of the signal selecting unit 55 detects the laser beam LB reflected by the beam reflecting mirror 24 in BD23L1 and BD23L2 has outputted (S16: Y), completes the measurement of the period _{T DT} ( S17).

The comparison unit 45 of the signal processing unit 31 compares the period _TDT measured by the time measuring unit 43 with the reference time _TTG read from the storage unit 49, and calculates and outputs the control value RV of the scanning phase T2. In addition, when receiving the control value RV from the comparison unit 45, the PWM control unit 47 refers to the lookup table stored in the storage unit 49 and calculates the PWM control value of the clock 2 according to the control value RV. To do. Then, the PWM control unit 47 temporarily stores the PWM control value in the memory 47M (S18).

  The controller 9 sets the image writing timing based on the timing detected in step S17 (S19).

  The control unit 9 waits until the writing timing at the scanning phase T2 is reached (S20: N). When the writing timing is reached (S20: Y), the control unit 9 sends image data, and the image for one line is transferred onto the photosensitive drum 5. Writing is started (S21).

  The control unit 9 continues the process until the writing of the one-line image is finished (S22: N), and when the writing of the one-line image is finished (S22: Y), the writing of the image is finished (S23).

The control unit 9 waits until the laser beam LB is detected by the BD 23L2 and the BD 23L1 at the scanning phase T2 (scan in the B direction) (S24: N), and when the laser beam LB is detected (S24: Y), the timing unit 43 Then, measurement of the period _TDT is started (S25). Further, the control unit 9 waits until the scanning phase T2 ends (S26: N).

  When the scanning phase T2 is completed (S26: Y), the controller 9 determines whether printing for one page and the print job are completed (S27). If the printing and the print job are not completed (S27: N), the control unit 9 proceeds to step S2. On the other hand, if the printing and the print job are finished (S27: Y), the control unit 9 finishes the printing process.

  Next, in the laser scanning device 2, in order to perform processing as described above, the logic circuit 51 to the logic circuit 52 include two amplifiers, one bias power source, one comparator, as shown in FIG. It is set as the structure provided with.

  As shown in FIG. 6, the output currents (output signals) of BD23L1 and BD23L2 are input to logic circuit 51 and logic circuit 52. In the logic circuit 51 (corresponding to the first signal generating means of the present invention), the amplifier A1 (corresponding to the first current-voltage converting means of the present invention) performs amplification and current-voltage conversion of the output current of the BD23L1. The voltage V1 output from the amplifier A1 is input to the comparator CP1 (corresponding to the first comparison means of the present invention). Also, the amplifier A2 (corresponding to the second current / voltage converting means of the present invention) performs amplification and current-voltage conversion of the output current of the BD23L2. The reference bias voltage E1 (corresponding to the first bias means of the present invention) is added to the voltage V2 output from the amplifier A2, and the voltage V3 (= V2 + E) is input to the comparator CP1. The comparator CP1 compares the voltage V1 and the voltage V3, and outputs a signal corresponding to the comparison result. That is, when the voltage V1 is larger than the voltage V3, the output voltage (hereinafter referred to as an output signal) TL1 is set to Low, and when the voltage V1 is smaller than the voltage V3, the output signal TL1 is set to High. .

  In the logic circuit 52 (corresponding to the second signal generating means of the present invention), the amplifier A4 (corresponding to the fourth current-voltage converting means of the present invention) performs amplification and current-voltage conversion of the output current of the BD23L2. The voltage V5 output from the amplifier A4 is input to the comparator CP2 (corresponding to the second comparison means of the present invention). Also, the amplifier A3 (corresponding to the third current / voltage converting means of the present invention) performs amplification and current-voltage conversion of the output current of the BD23L1. The reference bias voltage E2 (corresponding to the second bias means of the present invention) is added to the voltage V4 output from the amplifier A3, and the voltage V6 (= V4 + E) is input to the comparator CP2. The comparator CP2 compares the voltage V5 and the voltage V6, and outputs a signal corresponding to the comparison result. That is, when the voltage V5 is larger than the voltage V6, the output voltage (hereinafter referred to as an output signal) TL2 is set to Low, and when the voltage V5 is smaller than the voltage V6, the output signal TL2 is set to High. To do.

  The output signal TL1 generated by the logic circuit 51 and the output signal TL2 generated by the logic circuit 52 are sent to the selection unit 55 (corresponding to the selection means of the present invention).

  The operation of each of the above logic circuits will be schematically described with reference to FIG.

  As shown in FIG. 7A, the voltage waveform input to the comparator CP1 is the voltage V3 obtained by amplifying, converting, and biasing the output current of the BD23L2, and then amplifying and converting the output current of the BD23L1. The voltage V1 is input. The output signal TL1 from the comparator CP1 is Low during a period in which the voltage V1 is greater than the voltage V3.

  As shown in FIG. 7B, when the laser beam LB is scanned in the B direction, the voltage V5 obtained by amplifying and converting the output current of the BD23L2 is first input to the comparator CP2, and then the output current of the BD23L1 is amplified and converted. The converted and biased voltage V6 is input. At this time, the output signal TL2 of the comparator CP2 becomes Low during a period in which the voltage V5 is larger than the voltage V6.

  As shown in FIG. 7C, the voltage waveform input to the comparator CP1 is the voltage obtained by first amplifying and converting the output current of the BD23L1 and then amplifying, converting and biasing the output current of the BD23L2. V3 is input. At this time, the output signal TL1 from the comparator CP1 becomes Low during a period in which the voltage V1 is larger than the voltage V3.

  As shown in FIG. 7D, when the laser beam is scanned in the A direction, a voltage V6 obtained by amplifying, converting, and biasing the output current of the BD23L1 is first input as the voltage waveform input to the comparator CP2, and then the BD23L2 A voltage V5 obtained by amplifying and converting the output current is input. At this time, the output signal TL2 from the comparator CP2 becomes Low during a period in which the voltage V5 is larger than the voltage V6.

  The timing to be detected by the logic circuit 51 and the logic circuit 52 is when the magnitude relationship is switched (becomes the same value) while the two input voltages of the comparators CP1 and CP2 change together. This is when the laser beam passes through a certain position between BD23L1 and BD23L2, and is an intersection C1 and an intersection C4 of the input voltage curve in FIGS. 7A and 7B.

  FIGS. 7A to 7D show the case where the spot of the laser beam is changed and the spot diameter is large and the spot diameter is small. In the present invention, as shown in FIG. 1, BD23L1 and BD23L2 are installed adjacent to each other. Therefore, as shown in FIG. 7, even when the light quantity of the laser beam LB that scans each beam detection sensor changes, the timing at which the comparator detects that the magnitudes of the two input voltages are interchanged (hereinafter referred to as intersection detection). The time deviation of the timing is so small that it hardly causes a problem. Therefore, by determining the formation start position of the latent image with reference to the intersection detection timing, it is possible to suppress the occurrence of the shift of the scan start position due to the change in the light amount. That is, the accuracy of the detection timing of the laser beam LB can be improved by using the outputs of two adjacent beam detection sensors.

  Although BD23L1 and BD23L2 are installed adjacent to each other, even if the spot size of the laser beam changes, the two input voltages of the comparator CP1 and the comparator CP2 change together and the magnitude relationship changes (the same value). In this case, a slight gap may be provided without adjacent the beam detection sensors.

  Comparators CP1 and CP2 switch output signal TL1 and output signal TL2 from Low to High or from High to Low when the magnitudes of the two input voltages are switched. Therefore, the output signal falls or rises at the intersections C1 to C8 of the input voltage curve shown in FIG. In the circuit configuration shown in FIG. 6, the jitter is large when the output signal rises due to the characteristics of the comparators CP1 to CP2 included in the logic circuits 51 to 52. That is, since it is more accurate to use the time when the output signal falls, here, a case where the falling edge of the output signal of the comparator is used as a trigger signal will be described. If it is desired to make the rise of the output signal of the comparator as accurate as the fall, a circuit for improving the rise characteristic of the comparator may be added to the circuit in FIG.

  In addition, in the logic circuit 51 to the logic circuit 52 as described above, when any of the beam detection sensor groups 23 outputs noise by adding a reference bias to the output of one amplifier, the comparator erroneously detects. Can be prevented.

  Further, as described above, by configuring the output currents of the BD 23L1 and the BD 23L2 to be input to the logic circuit 51 and the logic circuit 52, it is possible to improve the accuracy of the detection timing of the laser beam LB.

  For example, in the case of the logic circuit 51, as shown in FIG. 7A, the output signal of the comparator CP1 falls during the scanning in the B direction because the output signals of the BD23L1 and BD23L2 change together. It is time to change (become the same value). However, at the time of scanning in the A direction, the output signal of the comparator CP1 falls when the output signal of the BD23L2 is constant and the magnitude relationship is switched while the output signal of the BD23L1 changes (becomes the same value). That is, it is not when the laser beam LB passes through a certain position between BD23L1 and BD23L2. For this reason, in order to detect the falling edge of the output signal of the comparator both during the A-direction scanning and during the B-direction scanning, it is necessary to configure the two logic circuits symmetrically.

  Next, output signals of the PWM control unit 47 and the selection control unit 56 will be described. As shown in FIG. 8, the signal SEL1 and the signal SEL2 output from the selection control unit 56 to the selection unit 55 are both high-low binary signals. The signal SEL1 switches to High at the start time of the scanning phase T2 (point P4 in FIG. 8), and switches to Low at the start time of the scanning phase T1 (point P2 in FIG. 8). Further, the signal SEL2 switches to High at the zero cross point (point P1 in FIG. 8) during the scanning phase T2, and switches to Low at the zero cross point (point P3 in FIG. 8) during the scanning phase T1. The signal SEL1 and the signal SEL2 are generated from the signal VC1 and the signal VC2 by a zero cross circuit.

  As shown in the logic table of FIG. 8, the selection unit 55 selects the output signal TL1 of the logic circuit 51 when both the signal SEL1 and the signal SEL2 are High (indicated as 1 in FIG. 8, the same applies hereinafter). The output signal TL2 of the logic circuit 52 is selected when the signal SEL1 is Low (indicated as 0 in FIG. 8, the same applies hereinafter) and the signal SEL2 is High. When both the signal SEL1 and the signal SEL2 are Low, the output signal TL1 of the logic circuit 51 is selected. When the signal SEL1 is High and the signal SEL2 is Low, the output signal TL2 of the logic circuit 52 is selected. Then, the selector 55 outputs the selected signal to the timer 43.

  The PWM control unit 47 outputs the clock 1 and the clock 2 for controlling the MEMS driving unit 33 to the MEMS driving unit 33. Clock 1 and clock 2 are PWM signals.

The PWM control unit 47 uses the PWM control value of the scanning phase T1 determined during a certain scanning phase T1 (value for setting the duty ratio of the clock 1) as the PWM control value at the next scanning phase T1. This is because the time when the control value for the scanning phase T1 is determined is after the clock (clock 1) of the scanning phase T1 is output. Therefore, if the determined control value is changed in the scanning phase T1, the control value for the period T _IMG On the way, the duty of the clock 1 is changed. Therefore, appropriate control cannot be performed, and the image quality is affected.

  Similarly, the PWM control unit 47 uses a PWM control value for the scanning phase T2 determined in a certain scanning phase T2 (a value for setting the duty ratio of the clock 2) as a control value in the next scanning phase T2. . In order to perform the processing as described above, the PWM control unit 47 temporarily stores a PWM control value generated based on the control value RV received from the comparison unit 45 (in the storage unit of the present invention). Equivalent).

  When the PWM control unit 47 receives the control value RV from the comparison unit 45, the PWM control unit 47 refers to the lookup table stored in the storage unit 49 and determines the clock 1 or clock 2 (PWM signal) according to the control value RV. A PWM control value that is a value for setting (adjusting) the duty ratio is calculated. The PWM control unit 47 temporarily stores the PWM control value in the memory 47M. Further, when receiving the control signal from the control unit 9, the PWM control unit 47 reads the PWM control value from the memory 47M and outputs the clock 1 or the clock 2 with the adjusted duty ratio.

  The PWM control unit 47 outputs the clock 1 and does not output the clock 2 at the scanning phase T1, and outputs the clock 2 and does not output the clock 1 at the scanning phase T2. Clock 1 and clock 2 are generated from voltages having the same phase as VC1 in FIG. This voltage is in phase with the drive current of the scanning MEMS 26 (same as the rotation angle of the deflection mirror 25).

  Further, the PWM control unit 47 outputs the signal VC1 (the same phase as the MEMS drive voltage) and the signal VC2 (the phase is delayed by 90 degrees from the MEMS drive voltage) to the selection control unit 56.

As described above, the shift is calculated by comparing the period _TDT and the reference time _TTG , the clock is adjusted based on the calculation result, and the rotation angle of the deflecting mirror 25 is adjusted, thereby starting the formation of the latent image. The occurrence of positional deviation can be suppressed.

  Further, since the laser scanning device 2 has a simple configuration in which the laser beam is detected by the one set of beam detection sensor group 23 and the beam reflection mirror 24, the cost can be suppressed. In addition, it is easier to adjust the optical path of the laser beam than when a plurality of beam reflecting mirrors are provided.

  Next, an example of a specific configuration of the MEMS drive unit 33 will be described. As shown in FIG. 9, the MEMS drive unit 33 may be configured to include an H bridge circuit including resistors R1 to R6, transistors Q1 to Q6, diodes D1 to D4, and a capacitor CA1. The MEMS drive unit 33 receives the clock from the PWM control unit 47 at the drive input terminal 33T1 and the drive input terminal 33T2, sends the drive voltage from the drive output terminal 33T3 and the drive output terminal 33T4 to the scan MEMS 26, and is attached to the scan MEMS 26. The deflection mirror 25 is driven. The MEMS drive unit 33 alternately applies drive currents having different polar directions to the inductor 272 of the scan MEMS 26 based on the clock 1 and the clock 2 received from the PWM control unit 47. Thereby, the MEMS drive unit 33 alternately reverses the direction of the current flowing through the inductor 272 between the scanning phase T1 and the scanning phase T2, and adjusts the magnitude in each scanning phase. As a result, the deflection mirror 25 is reciprocally rotated by changing the reversal of the direction of the magnetic field formed around the opening of the iron core 271 around which the inductor 272 is wound and the strength of the magnetic field.

In the above description, the period T _DT is the time for determining the PWM control value, but the present invention is not limited to this, and the period T _IMG may be the time for determining the PWM control value.

  Next, the laser scanning device can be configured as shown in FIG. As shown in FIG. 10, the laser scanning device 2 </ b> A is configured to input output signals (TL <b> 1 to TL <b> 2) of the logic circuit 51 to the logic circuit 52 to the selection unit 55 and the selection control unit 56 </ b> A. Further, as shown in FIG. 11, the selection control unit 56 switches the selection of the output signal of the logic circuit based on the detection of the rising portion of the output signal of the logic circuit 51 to the logic circuit 52. Configure to change. That is, when the output signal TL1 of the logic circuit 51 is temporarily switched from High to Low, the selection control unit 56A switches the signal SEL1 to High (indicated as 1 in FIG. 11, the same applies hereinafter). When the output signal TL2 of the logic circuit 52 temporarily switches from High to Low, the selection control unit 56A switches the signal SEL1 to Low (indicated as 0 in FIG. 11, the same applies hereinafter).

  Therefore, as shown in the logic table of FIG. 11, the selection unit 55 selects the output signal TL2 of the logic circuit 52 when the signal SEL1 is High. The selection unit 55 selects the output signal TL1 of the logic circuit 51 when the signal SEL1 is Low.

  The operation of other parts is the same as that of the laser scanning device 2 described with reference to FIG.

  When the rising edge of the output signal of the comparator is used as a detection signal as in the intersection C4 and the intersection C6 shown in FIG. 7, the selection of the output signal of the logic circuit is switched at the time of detection of the rising edge of the output signal. There is a possibility that there is no time margin for signal processing. In this case, a timer that measures the time required for signal processing after detecting the rising edge of the output signal is provided, and the timer measures the time. When the timer completes timing, select the output signal of the logic circuit. What is necessary is just to comprise so that it may switch. Further, as in the logic table shown in FIG. 11, the selection unit 55 may be configured to select a signal output from any of the logic circuits 51 to 52.

  Even in such a configuration, as in the laser scanning device 2 shown in FIG. 3, even if the spot of the laser beam is deformed, the intersection detection timing of the selected signal hardly changes. The shift of the formation start position can be suppressed.

  In this embodiment, the optical scanning device according to the present invention is applied to a laser scanning device that forms an electrostatic latent image on the photosensitive drum 5, but the optical scanning device according to the present invention is applied to this. The present invention is not limited to this, and any optical scanning device that reciprocally scans the scanning target with light can be applied. For example, the present invention can be applied to an optical scanning device that forms a latent image on a photosensitive film.

  In the above description, the control unit 9 of the image forming apparatus 1 sets the image writing timing. However, the sub-control unit is provided in the laser scanning device 2 (2A), and the sub-control unit is configured as an image. You may make it set the writing start timing.

  Although the case where the beam detection sensor group 23 is installed on the left side 5L side of the photosensitive drum 5 has been described, the present invention is not limited to this, and the beam detection sensor group is installed on the right side 5R side of the photosensitive drum 5. A beam reflecting mirror may be installed on the left side surface 5L side of the photosensitive drum 5.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus 2, 2A ... Laser scanning device 3 ... Laser scanning control part 5 ... Photosensitive drum 7 ... Developing device 9 ... Control part 21 ... Laser diode 22 ... Arc sine lens 23 ... Beam detection sensor group 23L1, 23L2 ... Beam detection sensor 24 ... Beam reflection mirror 25 ... Deflection mirror 26 ... Scanning MEMS 27 ... Mirror drive unit 31 ... Signal processing unit 33 ... MEMS drive unit 41 ... Signal selection unit 43 ... Timing unit 45 ... Comparison unit 47 ... PWM control unit 47M ... Memory 49 ... Storage 51,52 ... Logic circuit 55 ... Selection unit 56 ... Selection control unit

Claims (4)

In an optical scanning device that scans a scanning range including a scanning region of a scanning object by reciprocating a light beam in a first scanning direction and a second scanning direction by a deflection mirror,
The first detection means and the second detection means are arranged adjacent to each other, are arranged at one end in the scanning range of the light beam and outside the scanning area, and change according to the light amount of the light beam. Detection means group for outputting a signal to be
A beam reflecting means that is disposed at the other end in the scanning range of the light beam and outside the scanning area, and reflects the light beam at a different position of the detection means group according to a scanning angle of the light beam;
An intersection detection means for outputting a trigger signal when the magnitude relationship between the output signals of the first detection means and the second detection means is switched;
Position setting means for determining the timing of starting the emission of the light beam based on the trigger signal;
Drive control means for measuring the interval at which the intersection detection means outputs a trigger signal, comparing the measured value of this interval with a reference value, and controlling the scanning range of the deflection mirror;
An optical scanning device comprising: The intersection detection means includes:
A first current-voltage conversion unit that converts an output current of the first detection unit into a voltage; a second current-voltage conversion unit that converts an output current of the second detection unit into a voltage; and a second current-voltage conversion unit. First bias means for applying a bias voltage to the output voltage, and first comparison means for outputting a signal according to a comparison result between the voltage output from the first current-voltage conversion means and the voltage output from the first bias means. First signal generating means comprising:
A third current-voltage converting means for converting the output current of the first detecting means into a voltage; a fourth current-voltage converting means for converting the output current of the second detecting means into a voltage; and a third current-voltage converting means. Second bias means for adding a bias voltage to the output voltage; second comparison means for outputting a signal corresponding to a comparison result between the voltage output from the fourth current-voltage conversion means and the voltage output from the second bias means; Second signal generating means comprising:
Selecting means for selecting an output signal of the first signal generating means and an output signal of the second signal generating means according to a scanning direction of the light beam;
The optical scanning device according to claim 1, further comprising: Storage means for storing a correction value for correcting the scanning range of the deflection mirror;
The drive control unit calculates the correction value and stores it in the storage unit each time the measured value is compared with a reference value.
3. The optical scanning device according to claim 1, wherein when the light beam is scanning outside the scanning region, the correction value is read to control a scanning range of the deflection mirror. 4.   An image forming apparatus comprising the optical scanning device according to claim 1.

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