JP2011242703A - Mirror amplitude controller for optical scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mirror amplitude controller for an optical scanner capable of keeping cost balance of a system and accurately controlling mirror amplitude.SOLUTION: A signal measurement section 14 includes: a timer counter 17 for measuring detection signal intervals in a measurement object period; a first time constant circuit 18 for varying a voltage value from a reference voltage by charging and discharging according to the input of a detection signal for the start of the measurement object period; a voltage measurement section 20 for measuring the voltage variation of the first time constant circuit 18; and a second time constant circuit 19 whose time constant differs from the first time constant circuit 18 and which varies a voltage value by charging and discharging when the voltage of the voltage measurement section 20 reaches a predetermined voltage. A comparison section 15 outputs the difference between the voltage value of the second time constant circuit 19 held by a detection signal for the end of the measurement object period and the reference voltage value as an error signal to an amplitude level adjustment section 12, thereby performing feed back control of the amplitude level.

Description

  The present invention relates to a mirror amplitude control device for an optical scanning device that performs scanning by reflecting a light beam emitted from a light source by a oscillating mirror.

  An optical scanning device that scans a light beam such as a laser beam emitted from a light source is used as an optical device such as a barcode reader, a laser printer, or a head-mounted display, or a light intake device of an imaging device such as an infrared camera.

  For example, as an example of an optical scanning device, a mirror unit in which both sides are connected by a beam unit is provided in an opening formed in a rectangular substrate (for example, a stainless steel substrate or a silicon substrate). The mirror part is mirror-finished, a reflective film is formed, or a mirror is attached to the substrate.

  In addition, the substrate is provided with a vibration source made of a thin film of any one of a piezoelectric body, a magnetostrictive body, and a permanent magnet. For example, in the case of a piezoelectric body, when a positive voltage is applied from a driving source (not shown), an extension occurs and a negative voltage Since the shrinkage occurs when the voltage is applied, the substrate is bent. Torsional vibration is generated in the beam portion with respect to the vertical deflection of the substrate, and the mirror portion swings. The optical scanning is performed by maintaining the driving frequency in the vicinity of the resonance frequency between the mirror part and the beam part and reflecting the laser beam by the vibrating mirror part.

  As a result, the manufacturing cost is lower than that of an optical scanning device that swings a micro mirror manufactured using MEMS (Micro Electro Mechanical System), and a large vibration is generated in the mirror portion by a small vibration source. (See Patent Document 1).

  In the drive control of the optical scanning device, two sensor signals are generated by sensors provided at two locations along the mirror portion and its vibration direction. In order to stabilize the vibration of the mirror, the generation interval of two sensor signals is measured, and compared with a reference value, feedback control is applied. The voltage signal for vibrating the mirror unit is corrected by feedback control, and the amplitude level is changed.

JP 2006-293116 A

  When the interval of the sensor output signal for detecting the scanning amplitude of the mirror unit is measured and monitored by a timer counter or the like, for example, when the scanning frequency is 2 kHz and the target jitter value is 0.01%, the resolution of the timer counter is about 0. 01 μs. Considering the detection error, it is necessary to count at 200 MHz to 300 MHz, and a timer is required at high speed. Further, when a timer counter that can operate at several hundred MHz is used, there is a problem that the timer counter itself generates heat and costs due to high-speed operation. When the timer counter generates a large amount of heat, the control circuit cannot be arranged near the optical unit.

  In feedback control, the frequency component of jitter to be suppressed is several hundred Hz, and a sampling frequency of several kHz is sufficient. Therefore, feedback control can be realized with an inexpensive system, but an expensive system is used for the interval measurement unit. There is a problem that the cost balance of the system that is required is poor.

  It is an object of the present invention to provide a mirror amplitude control device for an optical scanning device that can perform mirror amplitude control with high accuracy while maintaining the cost balance of the system.

Means for solving the above-described problems includes the following configuration.
That is, the driving voltage is supplied from the driving circuit to operate the vibration source provided on the substrate to bend the substrate, thereby reflecting the irradiation light while swinging the mirror portion having the beam portion as the swing axis. A mirror amplitude control device for an optical scanning device that scans in this manner, an amplitude detection unit that detects an amplitude of a mirror unit that is oscillated by operating the vibration source, and a signal of a detection signal that is detected by the amplitude detection unit If an error signal is generated in the comparison unit, a signal measurement unit that measures the interval, a comparison unit that compares the measurement value measured by the signal measurement unit and the reference value output from the reference value generation unit, the error occurs. An amplitude level adjusting unit that performs feedback control to output to the drive circuit for a predetermined time so as to cancel the increase / decrease value of the signal, and the signal measuring unit measures the signal interval of the detection signal within the measurement target section The first time constant circuit that changes the voltage value from the reference voltage by charging and discharging according to the input of the start detection signal of the measurement target section, and the voltage measurement that measures the voltage change of the first time constant circuit And a second time constant circuit that is different in time constant from the first time constant circuit and changes the voltage value by charging and discharging when the voltage of the voltage measuring unit reaches a predetermined voltage, and the comparing unit is a section to be measured The amplitude level feedback control is performed by outputting the difference between the voltage value of the second time constant circuit held by the end detection signal and the reference voltage value to the amplitude level adjustment unit as an error signal. .

  The first time constant circuit is provided with a first time constant required to correct the operation deviation of the timer counter, and the second time constant circuit is provided with a second time constant required to correct the range width of the amplitude error. And the second time constant is set to be larger than the first time constant.

The signal measuring unit performs a charge and discharge according to the input of the start detection signal in the measurement target section and changes the voltage value from the reference voltage by measuring the signal interval of the detection signal within the measurement target section. Constant circuit, voltage measurement unit that measures the voltage change of the first time constant circuit, and the time constant is different from the first time constant circuit, and when the voltage of the voltage measurement unit reaches a predetermined voltage, charge and discharge are performed to change the voltage value A second time constant circuit for causing the comparator to output the difference between the voltage value of the second time constant circuit held by the end detection signal of the measurement target section and the reference voltage value as an error signal to the amplitude level adjustment unit. By outputting, feedback control of the amplitude level is performed.
Therefore, even if a relatively inexpensive and low-speed timer counter is used, the amplitude is monitored while monitoring the difference between the measurement target section and the measurement timing by changing the voltage value from the reference voltage value of the first and second time constant circuits having different time constants. Level feedback control can be performed. Therefore, it is possible to reduce the cost balance of the system while maintaining the accuracy of feedback control of the amplitude level of the mirror unit. Further, it is possible to install the control device in the vicinity of the optical system while suppressing the heat generation amount by using a low-speed timer counter.

  The first time constant circuit is set with a first time constant to correct a timer counter operation deviation, and the second time constant circuit is set with a second time constant to correct an amplitude error range width. Therefore, by selecting a time constant circuit corresponding to the measurement target section that is not counted by the timer counter, it is possible to provide a control device with a good cost balance at low cost.

It is the top view and arrow AA sectional drawing of an optical scanning device. It is explanatory drawing about the sensor arrangement | positioning and sensor signal which detect the amplitude of a mirror part. It is a block block diagram of the drive control apparatus of an optical scanning device. It is a wave form diagram which shows the relationship between a mirror amplitude change and a correction voltage. It is a block diagram which shows the circuit structure of a signal measurement part. It is a graph which shows the operation | movement waveform of each part of FIG.

  Hereinafter, an embodiment of a mirror driving method of an optical scanning device according to the present invention will be described with reference to the drawings. In this embodiment, an optical scanning device (scanner) used for a laser beam printer will be described as an example.

A schematic configuration of the optical scanning device will be described with reference to FIGS.
The substrate 1 is preferably a rectangular substrate such as a metal plate (stainless steel; SUS304) or a silicon substrate (Si). The substrate 1 is sandwiched between a support member 7 and a clamp member 6 on one side in the longitudinal direction and is supported in a cantilever manner.

  A pair of substrate tongues 8 are formed on the other end side (free end side) of the substrate 1. In the opening 2 formed between the substrate tongues 8, a mirror part 4 (optical MEMS mirror) supported on both sides by the beam part 3 is provided.

  Further, a piezoelectric element (PZT; lead zirconate titanate) is provided as an oscillation source 5 at the center of one end side of the substrate 1 by adhesion or the like. By operating the vibration source 5 to vibrate the substrate 1, scanning is performed by reflecting the irradiation light while swinging the mirror portion 4 with the beam portion 3 as the swing axis.

  As the vibration source 5, in addition to the piezoelectric element, any one of a piezoelectric body, a magnetostrictive body, and a permanent magnet body may be directly formed in a film shape on the substrate. As a film formation method, for example, an aerosol deposition method (AD method), a vacuum deposition method, a sputtering method, a chemical vapor deposition method (CVD: Chemical Vapor Deposition), or a sol-gel method is used. When any one of the piezoelectric body, the magnetostrictive body, and the permanent magnet body is directly formed in a film shape on the substrate, an optical scanning device that is driven at a low voltage and consumes low power can be provided.

  When a magnetostrictive body or a permanent magnet body is used, an alternating magnetic field applied from the outside generates an alternating magnetic field by passing an alternating current through a coil provided near the substrate portion on which the magnetostrictive film and the permanent magnet film are formed. In addition, when forming on a board | substrate with a magnetostriction film | membrane or a permanent magnet film, the direction where a board | substrate material is a nonmagnetic material can generate | occur | produce bending more efficiently.

  The mirror unit 4 may be a mirror-finished substrate 1 when a metal plate is used for the substrate 1. When a substrate other than a metal plate or a metal plate is required to have higher reflection performance, a thin film is formed on the mirror portion 4 by a thin film forming technique such as vacuum deposition, sputtering, or CVD (chemical vapor deposition). Alternatively, a mirror reflection material may be separately attached to the mirror unit 4.

In addition, the material for forming the thin film is selected from gold (Au), silicon dioxide (SiO ₂ ), aluminum (Al), or magnesium fluoride (MgF ₂ ), or a combination of two or more materials. Furthermore, by controlling the same layer (= single layer) or a multilayer structure of two or more layers by the thin film forming technique to an appropriate film thickness, a thin film that improves reflection performance can be formed. Alternatively, as a material for separately attaching a reflector for mirror to the mirror part 4, a thin film is formed on the mirror-finished silicon (Si) or alumina titanium carbide (Al ₂ O ₃ -TiC) ceramic by the above-mentioned thin film forming technique. May be formed.

  Further, regarding the thickness of the substrate 1, considering the flatness of the mirror part 4 in operation and the mirror size required for application to a projector device, silicon (Si), stainless steel (SUS304, etc.), or the like Further, assuming a substrate in which carbon nanotubes are grown on the material, a thickness of at least 10 μm or more is desirable.

  As shown in FIG. 2, the scanning amplitude of the mirror unit 4 includes, for example, a first photoelectric sensor 9 and a second photoelectric sensor 10 (amplitude detection unit) provided at two locations along the scanning range of the mirror unit 4. The first sensor signal S1 and the second sensor signal S2 are generated by the reflected light sensed by the second photoelectric sensors 9 and 10.

  Next, an example of the drive control device for the optical scanning device will be described with reference to the block diagram of FIG. In the drive control device, in order to stabilize the scanning amplitude of the mirror unit 4, the generation intervals of the first sensor signal S1 and the second sensor signal S2 are measured, and feedback control is performed in comparison with the reference value. Hereinafter, the driving method will be described in detail together with the device configuration.

  In FIG. 3, the frequency generation unit 11 generates a predetermined driving frequency that has been set. The amplitude level adjusting unit 12 adjusts the amplitude level of the driving frequency generated by the frequency generating unit 11 and outputs the adjusted level to the driving circuit 13. The drive circuit 13 supplies a drive voltage corresponding to the amplitude level input from the amplitude level adjustment unit 12 to operate the vibration source 5. As a result, the mirror part 4 swings around the beam part 3. The first and second photoelectric sensors 9 and 10 serving as amplitude detection units detect the amplitude of the mirror unit 4 that is oscillated when a drive voltage is applied from the drive circuit 13. As shown in FIG. 2, the signal measuring unit 14 measures the signal interval from the waveforms of the first sensor signal S1 and the second sensor signal S2 detected by the first and second photoelectric sensors 9, 10. Then, the comparison unit 15 compares the measurement value (voltage value) of the signal measurement unit 14 with the reference value signal (reference voltage value) of the reference value generation unit 16 stored in advance. As a result, the amplitude level adjustment unit 12 calculates a correction voltage and corrects the drive voltage applied to the drive circuit 13 as shown in FIG.

Next, an example of the signal measuring unit 14 will be described with reference to the block configuration diagram of FIG. 5 and the operation waveform diagram of FIG.
When either the first sensor signal S1 or the second sensor signal S2 (measurement start signal) detected by the first and second photoelectric sensors 9 and 10 is input to the flip-flop FF, the MPU timer counter 17 detects the signal interval. (FIG. 6; measurement target section T1) starts measurement. Since the MPU timer counter 17 uses a counter that is low (several μs) and inexpensive compared to the operating frequency of the mirror unit 4, the measurement start is delayed by T2 from the rise time of the measurement target section T1. Note that T2 is a different time for each measurement. Further, the first time constant circuit 18 is charged (or discharged) for a predetermined time with the input of the measurement start signal, and the voltage value VT1 of the first time constant circuit 18 from the reference voltage is changed to the voltage value V1. The voltage value VT2 of the second time constant circuit 19 is charged (or discharged) in advance and held in the second time constant circuit 19 in advance.

  Immediately after the MPU timer counter 17 starts counting, the MPU timer counter 17 holds the voltage value VT1 of the first time constant circuit 18 at the voltage value V1. The voltage value V1 is held as a delay value at the start of counting by the MPU timer counter 17. The hold operation of the voltage value VT1 is delayed by the operation frequency of the MPU timer counter 17, but since it is a fixed value, it does not affect the count operation.

  The MPU timer counter 17 performs a counting operation for a preset fixed time T3. The fall time of T3 is before the end of the measurement target section, that is, before the input of the next sensor signal. The first time constant circuit 18 and the second time constant circuit 19 are known CR circuits.

  When the MPU timer counter 17 finishes counting the fixed time T3, charging (or discharging) of the first time constant circuit 18 is started and the voltage value VT1 is changed again. Although this operation is also delayed by the operation frequency of the MPU timer counter 17, it is a fixed value and does not affect the count operation.

  The voltage level of the voltage value VT1 is detected by the voltage meter 20, and when the measured value is preset and reaches the voltage value V2 at time T4, the second time constant circuit 19 is discharged (or charged) for a short time T5. To change the voltage value VT2. Next, the MPU timer counter 17 holds the voltage value VT2 after waiting for the end of the measurement target section (T1), that is, input of the next sensor signal (falling time T1). At this time, feedback control is performed in which the held voltage value VT2 is compared with the reference voltage in the comparison unit 15 and the voltage value difference V3 is output to the amplitude level adjustment unit 12 as an error signal.

  As described above, the MPU timer counter 17 converts the detection deviation of the sensor signal interval of the MPU timer counter 17 into voltage changes of the first and second time constant circuits 18 and 19 having different time constants and outputs them as error signals. By resetting the measurement value of 17 and performing feedback control, amplitude adjustment can be performed accurately even using an inexpensive signal measurement unit, and the cost balance of the system can be achieved by using a relatively inexpensive and low-speed timer counter. In addition, the control circuit can be installed near the mirror while suppressing the amount of heat generated.

  Further, the first and second time constant circuits 18 and 19 are set such that the second time constant is larger than the first time constant. This is because the first time constant circuit 18 is provided with a first time constant necessary for correcting the operation deviation of the MPU timer counter 17, and is set to a value from 0 to about the timer clock frequency (several hundred ns), for example. Is done. On the other hand, the second time constant circuit 19 is provided with a second time constant necessary for correcting the range width of the amplitude error, and is set to a range of several μs width.

  For example, when both the first time constant circuit 18 and the second time constant circuit 19 are operated at the first time constant, the observation width of the sensor signal (time T5 portion) is extremely short because the charge / discharge speed is fast. Since the detection interval becomes short due to shortening, two different time constant circuits are provided so as to adapt to the amplitude change of the mirror unit 4.

DESCRIPTION OF SYMBOLS 1 Board | substrate 2 Opening part 3 Beam part 4 Mirror part 5 Vibration source 6 Clamp member 7 Support member 8 Board tongue part 9 1st photoelectric sensor 10 2nd photoelectric sensor 11 Frequency generation part 12 Amplitude level adjustment part 13 Drive circuit 14 Counter 15 Comparison Unit 16 Reference value generation unit 17 MUP timer counter 18 First time constant circuit 19 Second time constant circuit 20 Voltage measuring device

Means for solving the above-described problems includes the following configuration.
That is, one end of the rectangular substrate in the longitudinal direction is sandwiched and cantilevered, and the other end is provided with substrate tongues on both sides, and is supported by a beam in the opening formed between the substrate tongues. While the mirror portion having the beam portion as a swing axis is swung by bending the substrate by operating the vibration source provided on the substrate by supplying a drive voltage from the drive circuit A mirror amplitude control device for an optical scanning device that scans by reflecting irradiated light, wherein the first and second photoelectric detectors are provided at two locations in a scanning range of the mirror portion that is swung by operating the vibration source. An amplitude detector that detects the amplitude from the interval between the first and second sensor signals detected by the sensor, and a rise time T1 of the measurement target interval within the measurement target interval corresponding to the interval between the first and second sensor signals Start counting after T2 later , A timer counter which performs a fixed time T3 by counting which is set in advance, and operating at a first time constant, said start charging or discharging in accordance with the input of the start detection signal of the measurement target section the charge or discharge The first time when the timer counter that has changed from the reference voltage at the start holds the voltage value V1 immediately after the start of counting, and the charging or discharging starts again with the end of the counting of the timer counter to change the voltage value V1. A constant circuit, a voltage measurement unit for measuring a voltage change of the first time constant circuit and detecting a voltage value V2 changed from the voltage value V1 , and a second time constant that is larger than the first time constant. The voltage value that has been charged or discharged for a predetermined time from the start of the measurement target section and held and is measured by the voltage measurement unit. It begins to charge or discharge to a value V1 reaches the voltage value V2 by changing the voltage value, the second time constant circuit for outputting a voltage value held at the end of the measurement target section, the second time constant The voltage value output from the circuit is compared with the reference voltage value, which is a voltage conversion value for the ideal amplitude of the mirror amplitude stored in advance output from the reference value generation unit, and the voltage value difference V3 is used as an error signal. A comparison unit that outputs, and an amplitude level adjustment unit that calculates a correction voltage that cancels an error signal according to a comparison result of the comparison unit and instructs the drive circuit to correct the drive voltage, and the amplitude The level adjustment unit outputs a command for adjusting the amplitude level of the signal having the drive frequency generated by the frequency generation unit according to the voltage value difference V3 to the drive circuit, and the drive circuit passes the vibration source. In this case, feedback control for adjusting the amplitude of the mirror unit is performed.

Claims (2)

By supplying a drive voltage from the drive circuit and operating a vibration source provided on the substrate to bend the substrate, reflecting the irradiation light while swinging the mirror portion having the beam portion as the swing axis A mirror amplitude control device for an optical scanning device for scanning,
An amplitude detector for detecting the amplitude of the mirror that swings by operating the vibration source;
A signal measurement unit for measuring the signal interval of the detection signal detected by the amplitude detection unit;
A comparison unit that compares the measurement value measured by the signal measurement unit with the reference value output from the reference value generation unit;
When the error signal is generated in the comparison unit, the amplitude level adjustment unit for performing feedback control to output to the drive circuit for a predetermined time so as to cancel the increase / decrease value of the error signal,
The signal measuring unit performs a charge / discharge according to the input of the start detection signal in the measurement target section and a timer counter that measures the signal interval of the detection signal in the measurement target section, and changes the voltage value from the reference voltage. The time constant circuit, the voltage measurement unit for measuring the voltage change of the first time constant circuit, and the time constant is different from the first time constant circuit, and when the voltage of the voltage measurement unit reaches a predetermined voltage, charge / discharge is performed to obtain the voltage value. A second time constant circuit for changing,
The comparison unit outputs the difference between the voltage value of the second time constant circuit held by the end detection signal of the measurement target section and the reference voltage value to the amplitude level adjustment unit as an error signal, thereby performing amplitude level feedback control. A mirror amplitude control device for an optical scanning device.   The first time constant circuit is provided for correcting an operation shift of the timer counter, and the second time constant circuit is provided for correcting a range width of the amplitude error, and the second time constant is set more than the first time constant. 2. The mirror amplitude control device for an optical scanning device according to claim 1, wherein the mirror amplitude control device is set to a large value.

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