JP2013195485A - Optical scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a drive starting method for reducing the start-up time when starting driving an optical scanner showing nonlinear characteristics.SOLUTION: A determination method for determining a drive starting method which controls an AC voltage to be supplied to a driving part when starting driving an optical scanner showing nonlinear characteristics includes: determining a resonance frequency and a resonance amplitude for an AC voltage having a first voltage value, where the first voltage value is such a voltage value that a resonance amplitude of the optical scanner is smaller than a desired amplitude; determining a resonance frequency and a resonance amplitude for a second voltage value higher than the first voltage value; and determining, if the resonance amplitude for the second voltage value is equal to or larger than the desired amplitude, that a frequency should be changed from the resonance frequency for the first voltage value toward the resonance frequency for the second voltage value when driving the optical scanner is started.

Description

  The present invention relates to a determination method for determining a drive start method for controlling an AC voltage supplied to a drive unit for driving an optical scanner, and a light when starting driving of an optical scanner that scans light such as a laser. The present invention relates to a scanner driving method and an optical scanner.

  Currently, an optical scanner that scans light such as laser light with a swinging mirror is known. In the optical scanner, the mirror swings when a voltage is applied to the drive unit. In order to periodically swing the mirror, an AC voltage is applied to the drive unit.

  An optical scanner that uses resonance of a torsion beam that holds a mirror and is driven to resonate at a resonance frequency is also known. When an AC voltage having a frequency corresponding to the resonance frequency is applied to the drive unit, the optical scanner is driven to resonate. Some optical scanners that are resonantly driven exhibit nonlinear characteristics. For example, in the optical scanner described in Patent Document 1, as an example of nonlinear characteristics, the resonance frequency changes when the drive voltage changes.

JP 2011-133728 A

  When driving an optical scanner, a certain amount of rise time is required from the start of driving to the stabilization of the mirror amplitude. The definition of the rise time will be described later. In order to shorten the waiting time until the apparatus using the optical scanner is turned on and becomes usable, it is desirable that the rise time is short.

  At present, little research is known from the viewpoint of shortening the rise time. Therefore, for example, little is known about how to start driving the optical scanner in order to shorten the rise time.

  In the case of an optical scanner capable of resonance driving, in order to drive at a resonance frequency, a method of applying an AC voltage having a frequency equal to the resonance frequency from the start of driving can be considered. However, for example, in the case of an optical scanner that exhibits nonlinear characteristics, the resonance frequency varies with the magnitude of the amplitude, in other words, with the voltage value of the AC voltage. Therefore, it is unclear how to start driving the optical scanner in order to shorten the rise time in the optical scanner exhibiting nonlinear characteristics.

  An object of the present invention is to provide a determination method for determining a drive start method for shortening the rise time at the start of drive of an optical scanner exhibiting non-linear characteristics, an optical scanner drive method, and an optical scanner. .

  In order to solve the above-described problem, one aspect of the present invention is to drive the optical scanner when starting to drive an optical scanner that exhibits a non-linear characteristic in which resonance driving is possible and resonance frequency changes according to amplitude. A determination method for determining a driving start method for controlling an AC voltage supplied to a driving unit, wherein a resonance amplitude that is an amplitude in a state where the optical scanner is resonantly driven is desired for the driving unit. A supply start step for starting supply of the AC voltage having a first voltage value smaller than the amplitude of the light; and a light detection step for detecting light scanned by the optical scanner driven after the supply start step; Based on the detection result of the light detection step, at least an amplitude determination step for determining the amplitude of the optical scanner, and a state in which the frequency of the AC voltage is changed, A first determination step for determining a resonance frequency and a resonance amplitude of the optical scanner at the first voltage value by executing a light detection step and the amplitude determination step; and a voltage value of the AC voltage as the first voltage value. The resonance frequency and the resonance amplitude of the optical scanner at the second voltage value are determined by executing the light detection step and the amplitude determination step with the second voltage value being larger than the voltage value. A second determining step; a determining step for determining whether or not the resonance amplitude determined in the second determining step is equal to or greater than the desired amplitude; and the resonance amplitude is equal to or greater than the desired amplitude in the determining step. When it is determined, when the driving of the optical scanner is started, the resonance frequency at the second voltage value is changed from the resonance frequency at the first voltage value. , A drive start determination step of determining to change the frequency in the direction toward the a determination method, characterized in that it comprises a.

  As described above, among optical scanners exhibiting non-linear characteristics, there are optical scanners whose resonance frequency changes according to amplitude. Now, the voltage of the AC voltage necessary for obtaining a desired amplitude during resonance driving is set as the second voltage value. Driving of the optical scanner exhibiting non-linear characteristics is started at a driving frequency equal to the resonance frequency at the second voltage value. When the optical scanner mirror is driven from a stationary state, the amplitude increases from zero. In other words, in the case of an optical scanner that exhibits nonlinear characteristics, the resonance frequency changes as the amplitude increases after driving is started. This means that the resonance frequency of the optical scanner when the amplitude of the mirror starts immediately after the start of driving is different from the resonance frequency at the second voltage value. When the optical scanner is driven at a drive frequency equal to the resonance frequency at the second voltage value from the start of driving, the driving frequency and the resonance frequency are shifted immediately after the start of driving. As a result, the rise time becomes longer. Therefore, in order to shorten the rise time, the optical scanner is driven by a drive frequency that is distant from the resonance frequency at the second voltage value, in other words, by a drive frequency close to the resonance frequency at the first voltage value that is smaller than the second voltage value. It is desirable to start the drive and sweep the drive frequency towards the resonant frequency.

  According to one aspect of the present invention, the resonance frequency and resonance amplitude of the optical scanner at the first voltage value are determined. Further, the resonance frequency and resonance amplitude of the optical scanner at the second voltage value larger than the first voltage value are determined. When it is determined that the resonance amplitude of the optical scanner at the second voltage value is greater than or equal to a desired amplitude, the resonance frequency at the second voltage value is shifted from the resonance frequency at the first voltage value when driving of the optical scanner is started. It is decided to change the frequency in the direction. As a result, it is possible to obtain an optical scanner driving start method capable of obtaining a desired amplitude while shortening the rise time.

  Further, when the resonance amplitude is determined to be less than the desired amplitude in the determination step, the voltage value is larger than the second voltage value in the second determination step that has been performed previously. The second determination step may be executed again, and the determination step may be executed again after the second determination step is executed again. By executing the second determination step and the determination step again, it is possible to determine a second voltage value that can obtain a desired amplitude.

  The drive start determination step may further include a step of changing the frequency from the resonance frequency at the first voltage value toward the resonance frequency at the second voltage value when driving the optical scanner. Further, it may be determined that the AC voltage having the frequency equal to the resonance frequency at the first voltage value is supplied. According to this, at the start of driving, an AC voltage having the frequency equal to the resonance frequency at the first voltage value is supplied. Therefore, the rise time can be minimized.

  The drive start determination step may further determine that the frequency is changed from the resonance frequency at the first voltage value until the resonance frequency at the second voltage value is reached. According to this, after driving the optical scanner, the drive frequency is swept from the resonance frequency at the first voltage value to the resonance frequency at the second voltage value. Therefore, the shortest rise time can be obtained and a desired amplitude can be obtained accurately.

  The driving start determination step may further determine that the AC voltage having the second voltage value is supplied when driving of the optical scanner is started. According to this, it is determined that an AC voltage having the resonance frequency at the first voltage value and the second voltage is applied at the start of driving. When the drive start method determined by this method is applied to the optical scanner, it is only necessary to change the frequency after the drive start, and the voltage change routine can be omitted. Therefore, the rise time is further shortened.

  According to another aspect of the present invention, a resonance amplitude, which is an amplitude in a state where the optical scanner is resonantly driven, is equal to a resonance frequency at a first voltage value that is smaller than a desired amplitude with respect to a driving unit that drives the optical scanner. An initial supply step of supplying the AC voltage having a frequency and a second voltage value at which the desired amplitude is obtained in a state where the optical scanner is resonantly driven; and after the initial supply step, the second voltage value In a state where the frequency of the AC voltage is changed from the resonance frequency at the first voltage value until the resonance frequency at the second voltage value is reached, and the change of the AC voltage by the supply change step. In a state where the frequency becomes the resonance frequency at the second voltage value, the steady drive drive that continues the supply of the AC voltage to the optical scanner is performed. Tsu and up, a driving method comprising. According to this, the driving of the optical scanner is started by an AC voltage having a driving frequency equal to the resonance frequency in the second voltage value and the first voltage value. After driving the optical scanner, the drive frequency is swept until the resonance frequency at the second voltage value is reached while maintaining the second voltage value. Therefore, the rise time of the optical scanner is the shortest.

  Still another aspect of the present invention has a reflecting surface that reflects incident light and is configured to be swingable about a first axis, and a pair of torsion beams that support both of the mirrors, A plate-like structure having a main body connected to the ends of the pair of torsion beams; a pedestal to which a part of the structure is fixed; and a voltage applied to the main body. A driving unit capable of applying a force to the structure and swinging the mirror unit about the first axis; and a control unit for controlling an AC voltage applied to the driving unit; The optical scanner is capable of resonance driving and exhibits a nonlinear characteristic in which a resonance frequency changes according to amplitude, and the control unit applies to the driving unit when starting the driving of the optical scanner. And the amplitude of the optical scanner in a state of being driven by resonance. Of the AC voltage having a frequency equal to a resonance frequency at a first voltage value at which the resonance amplitude is smaller than a desired amplitude and a second voltage value at which the desired amplitude is obtained in a state where the optical scanner is driven to resonate. The supply is started, and after the supply is started, the frequency of the AC voltage is changed from the resonance frequency at the first voltage value to the resonance frequency at the second voltage value while maintaining the second voltage value. It is an optical scanner to change. According to this, an optical scanner with the shortest rise time can be obtained.

  According to the present invention, it is possible to obtain a determination method, a driving method, and an optical scanner for determining a driving start method for shortening a rise time at the start of driving an optical scanner exhibiting nonlinear characteristics.

(A) The figure which shows the relationship between the drive frequency and amplitude in the optical scanner which shows a linear characteristic, (B) The figure which shows the drive frequency and rise time at the time of the drive start in the optical scanner which shows a linear characteristic. The figure explaining the definition of rise time. (A) The figure which shows the relationship between the frequency and amplitude in the optical scanning part 100 which shows a nonlinear characteristic, (B) The figure which shows the drive frequency at the time of the drive start in the optical scanning part 100 which shows a nonlinear characteristic, and rise time. (A) Perspective view of optical scanning unit 100, (B) Plan view and cross-sectional view of optical scanning unit 100 1 is a diagram showing a configuration of an optical scanner 1. FIG. 6 is a flowchart for explaining drive start determination processing for determining a drive start method of the optical scanner. The figure explaining the resonant frequency determination process which determines the resonant frequency of the optical scanner. FIG. 6 is a diagram for explaining a driving process for driving the optical scanner.

  The inventor first studied to shorten the rise time for an optical scanner that does not exhibit nonlinear characteristics, that is, an optical scanner that exhibits linear characteristics.

  FIG. 1A shows the result of measuring the amplitude of the mirror with respect to the frequency (drive frequency) of the AC voltage applied to the drive unit in the optical scanner having the linear characteristics. In FIG. 1A, the solid line shows the relationship between the drive frequency and the amplitude when the optical scanner is driven with a voltage value that can obtain a desired amplitude during resonance driving. The desired amplitude is determined in advance by, for example, required specifications of an apparatus in which the optical scanner is incorporated. That is, the desired amplitude is first determined and the optical scanner is driven at the voltage value necessary to obtain the desired amplitude. The broken line in FIG. 1A shows an example of the relationship between the drive frequency and the amplitude when the optical scanner is driven with a voltage value smaller than that indicated by the solid line. A dashed line in FIG. 1A indicates a ridge line connecting values of a resonance frequency and an amplitude when resonance driving is performed at the resonance frequency when the voltage value is changed. Hereinafter, this ridge line is referred to as a spine curve.

  As shown by the spine curve in FIG. 1A, in the case of an optical scanner that exhibits linear characteristics, the resonance frequency is substantially constant even if the drive voltage changes. In this optical scanner, when the optical scanner is driven at a voltage value corresponding to the solid line in FIG. 1A, the rise time required from the start of driving at a certain driving frequency to the stabilization of the amplitude was examined. . The rise time is defined as the time interval from the start of driving to when the difference from the stable amplitude becomes less than ± 1%. Hereinafter, the rise time will be described with reference to FIG.

  The horizontal axis in FIG. 2 indicates time. The driving frequency is constant. The vertical axis in FIG. 2 indicates the swing speed of the mirror in the swing state. Since the mirror swings in both forward and return paths, one speed is positive and the other speed is negative. Therefore, the swinging speed of the mirror is distributed in both positive and negative directions centering on “0”. The mirror swing speed is measured using a Doppler interferometer. The swing speed of the mirror can be converted into an amplitude that is a swing angle by performing time integration. Therefore, it can be considered that the vertical axis in FIG. 2 corresponds to the amplitude.

  At point A in FIG. 2, an AC voltage is applied to the drive unit. The mirror swing speed rapidly increases and then decreases. The mirror swing speed converges to a constant value after a sufficient amount of time while repeating increasing and decreasing. The constant value of the positive speed is defined as the upper stable amplitude, and the constant value of the negative speed is defined as the lower stable amplitude. At point B in FIG. 2, the mirror swing speed falls within a range of less than ± 1% of the upper and lower stable amplitudes. After point B, the mirror swing speed always has a value less than ± 1% of the upper and lower stable amplitudes. This point B is defined as the time when the amplitude of the mirror is stabilized. The time interval between the time when the application of AC voltage starts (point A) and the time when the mirror swing speed becomes less than ± 1% of the upper and lower stable amplitudes (point B) rises. Defined as time.

  Returning to FIG. 1B again, the relationship between the drive frequency and the rise time in the optical scanner exhibiting linear characteristics will be described. The vertical axis in FIG. 1B represents the rise time. The horizontal axis in FIG. 1B shows the difference between the resonance frequency and the drive frequency. That is, “0” on the horizontal axis means that the drive frequency is equal to the resonance frequency.

  As a result of an experiment by the present inventor, as shown in FIG. 1B, in the case of an optical scanner exhibiting linear characteristics, it was found that the start-up time is the shortest when driving is started at the resonance frequency. . The rise time tended to increase as the difference between the resonance frequency and the drive frequency increased. That is, in an optical scanner that exhibits linear characteristics, the start-up time is minimized by applying a drive frequency equal to the resonance frequency from the start of driving.

  The deformation stress applied to the structure of the optical scanner changes depending on the amplitude when the optical scanner is driven. It is considered that the resonance frequency fluctuates in an optical scanner that exhibits nonlinear characteristics due to a change in deformation stress. As shown in FIG. 2, the mirror swing speed changes at the start of driving of the optical scanner. Since the oscillation speed of the mirror corresponds to the amplitude of the mirror, the resonance frequency of the nonlinear scanner is considered to change at the start of driving. Therefore, the present inventor has studied to shorten the rise time even for an optical scanner exhibiting nonlinear characteristics.

  FIG. 3A shows the result of measuring the amplitude of the mirror with respect to the drive frequency in an optical scanner exhibiting nonlinear characteristics. In FIG. 3A, the solid line shows the relationship between the drive frequency and the amplitude when the optical scanner is driven with a voltage value that can obtain a desired amplitude during resonance driving. The broken line in FIG. 3A shows an example of the relationship between the drive frequency and the amplitude when the optical scanner is driven with a voltage value smaller than that indicated by the solid line. Also in FIG. 3A, the spine curve is shown by a one-dot chain line.

  In the case of an optical scanner exhibiting non-linear characteristics, the resonance frequency varies as the amplitude changes. In the example of FIG. 3A, the resonance frequency increases as the amplitude increases. Accordingly, the spine curve shows a right-curved gradually stiffened spring characteristic in which the frequency value increases as the amplitude increases. Specifically, as shown in FIG. 3A, there is an opening of the frequency width A between the distal end portion of the spine curve and the root portion of the spine curve. The tip portion of the spine curve corresponds to the resonance frequency and amplitude when the optical scanner is driven at the second voltage value, which is a voltage value that can obtain a desired amplitude during resonance driving. The root portion of the spine curve corresponds to the resonance frequency and amplitude when the optical scanner is driven at a voltage value at which a small amplitude of the optical scanner is obtained. The voltage value at which a minute amplitude is obtained is an example of a first voltage value that is smaller than the second voltage value. The minute amplitude is the minimum amplitude that can detect the mirror swing using an amplitude detection mechanism such as a Doppler interferometer or a BD sensor.

  In this optical scanner, when the optical scanner is driven at a voltage value corresponding to the solid line in FIG. 3A, the required rise time from the start of driving at a certain frequency to the stabilization of the amplitude was examined. . With reference to FIG. 3B, the relationship between the drive frequency and the rise time in an optical scanner exhibiting nonlinear characteristics will be described. The vertical axis in FIG. 3B represents the rise time. The horizontal axis in FIG. 3B represents the difference between the resonance frequency and the drive frequency when the optical scanner is driven at the voltage value indicated by the solid line in FIG.

  As a result of experiments by the present inventor, it was found that in the case of an optical scanner exhibiting non-linear characteristics, the rise time is not shortened even when driving is started at the resonance frequency at the second voltage value. When a mirror of an optical scanner exhibiting non-linear characteristics is driven from a stationary state, the amplitude increases from zero. In other words, in the case of an optical scanner that exhibits nonlinear characteristics, the resonance frequency changes as the amplitude increases after driving is started. This means that the resonance frequency of the optical scanner when the mirror starts to swing immediately after the start of driving is different from the resonance frequency at the second voltage value. In other words, the start of driving of the optical scanner that exhibits nonlinear characteristics at the resonance frequency at the second voltage value means that the drive is started at a driving frequency different from the resonance frequency at the start of driving. As shown in FIG. 1B, when the optical scanner is driven at a driving frequency different from the resonance frequency, the rise time becomes long. This understanding is consistent with the results of FIG.

  In an optical scanner that exhibits non-linear characteristics, the rise time decreases as the drive frequency moves away from the resonance frequency. The rise time is minimized when the drive frequency is separated from the resonance frequency by the frequency width A. The rise time starts to increase again when the drive frequency is separated from the resonance frequency by the frequency width A or more. Accordingly, in order to shorten the rise time, it is preferable to start driving the optical scanner at a drive frequency that is far from the resonance frequency, and to sweep the drive frequency toward the resonance frequency. The rise time is the shortest when the optical scanner starts to be driven at a frequency corresponding to the root of the spine curve, that is, a drive frequency equal to the resonance frequency at the first voltage value at which a minute amplitude is obtained. is there.

  From the viewpoint of shortening the rise time when starting the driving of the optical scanner exhibiting nonlinear characteristics, the driving frequency at the start of driving should be set at a position shifted from the resonance frequency in the second voltage value. . More preferably, in order to minimize the rise time, the driving frequency at the start of driving should be set equal to the resonance frequency at the first voltage value at which a minute amplitude is obtained.

However, when the optical scanner is continuously driven at a drive frequency that is shifted from the resonance frequency at the second voltage value, the desired amplitude cannot be obtained even if the second voltage value is applied to the drive unit (see FIG. 3A). ). In order to obtain a desired amplitude, it is necessary to finally drive the optical scanner at the resonance frequency at the second voltage value and at the second voltage value. Therefore, the present inventor
1. At the start of driving, an AC voltage having a second voltage value and a driving frequency shifted from the resonance frequency in the second voltage value is applied to the driving unit.
2. After driving, with the second voltage value maintained, the drive frequency is swept to the resonance frequency at the second voltage value.
Accordingly, a method for starting driving of an optical scanner capable of obtaining a desired amplitude while shortening the rise time is proposed. In the above “1”, a drive frequency equal to the resonance frequency at the first voltage value may be used in order to minimize the rise time. In order to realize this driving start method, it is necessary to know the direction in which the driving frequency is swept. For example, when an optical scanner that exhibits nonlinear characteristics exhibits a gradually hardening type spring characteristic as shown in FIG. 3A, the drive frequency needs to be swept up. On the other hand, when the optical scanner showing the nonlinear characteristic shows a gradually soft spring characteristic with the spine curve turning to the left, the drive frequency needs to be swept down.

<First Embodiment>
Based on the above knowledge, in this embodiment, the direction in which the drive frequency is swept when the drive of the optical scanner exhibiting nonlinear characteristics is started is determined. First, the optical scanning unit 100 that scans light in the optical scanner 1 used in the present embodiment will be described with reference to FIG.

[Configuration of Optical Scanning Unit 100]
The optical scanning unit 100 includes a structure 110 and a pedestal 120. The mirror 111 of the structure 110 is swung around the first axis a by the driving unit 114. By this oscillation, the light incident on the mirror 111 is scanned. In FIG. 4, the first axis a is parallel to the front-rear direction.

  The structure 110 is a plate-like structure having a rectangular shape in a plan view, which includes a pair of short sides extending in the front-rear direction and a pair of long sides extending in the left-right direction. The structure 110 includes a mirror 111, a pair of torsion beams 112, and a main body 113. A drive unit 114 is provided on one surface (for example, the upper surface) of the main body unit 113. The structure 110 is made of a metal material such as titanium or stainless steel, for example. However, the structure 110 may be formed of a nonmetallic material such as silicon. Hereinafter, the structure 110 will be described.

  The mirror 111 includes a reflection surface that reflects light such as a laser. In the present embodiment, the shape of the mirror 111 is rectangular in plan view. However, the shape of the mirror 111 may be an arbitrary shape such as a circle, an ellipse, or a polygon in plan view. The reflection surface is provided on the upper surface of the mirror 111. The reflection surface is formed, for example, by mirror polishing the upper surface of the mirror 111. However, a reflective surface may be formed by attaching a transparent dielectric having a metal thin film to the upper surface of the mirror 111. Specifically, a transparent dielectric having a metal thin film can be obtained by depositing silver, aluminum, or the like on a base material such as sapphire or diamond by vapor deposition or the like.

  One end of the pair of torsion beams 112 is connected to both sides of the mirror 111. The pair of torsion beams 112 respectively extend in a direction away from the mirror 111. In the present embodiment, the extending direction of the pair of torsion beams 112 is parallel to the first axis a. Specifically, the first axis a passes through the centers of the pair of torsion beams 112. By the pair of torsion beams 112, both sides of the mirror 111 are elastically supported so as to be swingable about the first axis a. That is, the pair of torsion beams 112 serves as a torsion bar that supports the mirror 111 so as to be swingable about the first axis a.

  The main body 113 is connected to the other ends of the pair of torsion beams 112. The main body 113 is separated from the mirror 111 and extends in a direction intersecting the first axis a. In the present embodiment, the main body 113 extends from the connecting portion with the pair of torsion beams 112 to both sides in the left-right direction. The main body 113 has a fixed portion 113a and a bridging portion 113b. A pair of fixed portions 113a are provided in the front-rear direction with the pair of torsion beams 112 and the mirror 111 interposed therebetween. In the present embodiment, a pair of through holes along the left-right direction are provided at both ends of the main body 113 in the front-rear direction. The fixed portion 113a is a partial region of the main body 113 that is located farther from the mirror 111 than the pair of through holes in the front-rear direction. In the fixed portion 113a, the structure 110 and the pedestal 120 are fixed by adhesion, welding, or the like. The bridging portion 113b is provided at a central portion in the left-right direction of the pair of through holes. The bridging portion 113b extends in the front-rear direction, and bridges the main body 113 closer to the mirror 113 than the pair of through holes and the fixed portion 113a. More specifically, the bridging portion 113b is aligned with the pair of torsion beams 112 in the front-rear direction.

  A driving unit 114 is provided on the upper surface of the main body unit 113. The drive unit 114 is provided at an intermediate position in the front-rear direction of the main body unit 113. A pair of drive units 114 are provided at both ends in the left-right direction of the main body unit 113. For example, the drive unit 114 is a laminate of 0.2 μm to 0.6 μm of gold, platinum, or the like as an electrode layer on both surfaces of a piezoelectric material such as lead zirconate titanate formed into a flat plate having a thickness of 30 μm to 100 μm. It is formed by doing. The drive unit 114 and the main body unit 113 are bonded with a conductive adhesive. A thin metal wire (not shown) such as gold is connected to the upper surface of the drive unit 114 by wire bonding or the like.

  The pedestal 120 has a rectangular shape in plan view. The pedestal 120 has a rectangular through-hole penetrating in the vertical direction at the center. The longitudinal direction of the through hole is parallel to the left-right direction. Along the longitudinal direction of the through hole, the fixed portion 113 a of the structure 110 is fixed to an adjacent portion of the through hole of the pedestal 120. The thickness of the pedestal 120 is sufficiently larger than the thickness of the structure 110 (for example, about 10 times). Therefore, even if the structure 110 swings, the pedestal 120 hardly deforms. The pedestal 120 is made of, for example, a metal material such as stainless steel or titanium, similarly to the structure 110.

  Since the structure body 110 is formed of metal, the driving section 114 can be deformed by applying a voltage between the structure body 110 and the electrode layer on the upper surface of the driving section 114. An AC voltage is applied to the drive unit 114 provided at the right end of the main body 113 and the drive unit 114 provided at the left end so as to be in opposite phases. When the drive frequency corresponds to the resonance frequency of the optical scanning unit 100, a plate wave is excited in the main body 114 with the deformation of the drive unit 114. The plate wave is transmitted to the mirror 111 through the main body 113 and the pair of torsion beams 112, so that the mirror 111 swings around the first axis a at a predetermined resonance frequency. Here, the structure body 110 is fixed to the pedestal 120 at the fixed portion 113 a, and the main body 113 sandwiched between the fixed portions 113 a is in a state of being suspended in the air by the pedestal 120. Therefore, when the optical scanning unit 100 is driven, the main body unit 113 is displaced in the vertical direction. However, since the torsion beam 112 is provided at a position that becomes a vibration node of the main body 113, even if the main body 113 is displaced up and down, the torsion beam 112 is not displaced up and down. Further, a bridging portion 113 b provided on the same straight line as the torsion beam 112 connects the fixed portion 113 a and the torsion beam 112. Therefore, the torsion beam 112 is further suppressed from being displaced in the vertical direction. Therefore, when the mirror 111 is swung around the first axis a, the vertical displacement is suppressed. Therefore, the light incident on the mirror 111 is always incident on the same position on the mirror 111, so that stable light scanning is possible.

[Configuration of Optical Scanner 1]
As shown in FIG. 5, the optical scanner 1 includes an optical scanning unit 100 and a control unit 200. Using this optical scanner 1, the BD sensor 300, and the light source LD, a driving start method at the start of driving of the optical scanner 1 is determined. The determination of the drive start method is, for example, determining the drive frequency at the start of driving of the optical scanning unit 100 and the direction in which the drive frequency is swept after the drive starts. The light source LD is composed of, for example, a semiconductor laser. The light emitted from the light source LD is scanned by the mirror 111.

  The BD sensor 300 detects scanning light scanned by the optical scanning unit 100. The BD sensor 300 is disposed at a predetermined position in a scanning range through which scanning light passes. In other words, the BD sensor 300 is disposed at a predetermined relative position with respect to the optical scanning unit 100 so that the scanning light can be received when the amplitude of the mirror 111 reaches a predetermined angle. The BD sensor 300 is a position slightly offset (for example, several degrees) from the center of the scanning range of the optical scanning unit 100 so that the minute amplitude in a state where the first voltage value is applied to the driving unit 114 can be detected. Placed in. The BD sensor 300 is configured by, for example, a single element avalanche photodiode. However, an array sensor in which light receiving elements are arranged in a matrix may be used as the BD sensor 300. The BD sensor 300 receives the scanning light and generates a detection signal. This detection signal is transmitted from the BD sensor 300 to the control unit 200.

  The control unit 200 includes a scanning state determination unit 210, a determination control unit 220, a storage unit 230, and an AC voltage generation unit 240. The configuration included in the control unit 200 is defined by its function. Therefore, the configuration included in the control unit 200 may be achieved by the same electronic circuit or may be divided into individual electronic circuits. The control unit 200 includes, for example, a microcomputer, a field-programmable gate array (FPGA), and an application specific integrated circuit (ASIC).

  The scanning state determination unit 210 determines the scanning state of the optical scanning unit 100 based on the detection signal from the BD sensor 300. The scanning state of the optical scanning unit 100 includes, for example, the amplitude of the mirror 111. When the optical scanning unit 100 is driven to resonate, the amplitude of the mirror 111 changes sinusoidally with respect to time. In other words, the time variation of the amplitude of the mirror 111 can be represented by a sine function having time as a variable and having two coefficients of amplitude and frequency. Since the BD sensor 300 is slightly offset from the center of the scanning range, the BD sensor 300 generates a detection signal twice in one cycle of scanning. The scanning state determination unit 210 determines the amplitude of the mirror 111 based on the timing of two detection signals in one cycle of scanning and the position of the BD sensor 300 determined in advance. This determination may be performed by calculation, for example, or a table in which the timing of the detection signal and the amplitude of the mirror 111 are associated with each other may be used. The scanning state determination unit 210 can also determine the driving frequency of the mirror 111 as another example of the scanning state. The amplitude determined by the scanning state determination unit 210 is transmitted to the determination control unit 220 as a scanning state signal.

The determination control unit 220 performs various processes based on the scanning state signal from the scanning state determination unit 210. Specifically, the judgment control unit 220
1. 1. Determination of resonance frequency and amplitude at resonance frequency (hereinafter referred to as resonance amplitude) 2. Comparison of resonance amplitude with desired amplitude The drive frequency and voltage value at the start of driving, and the sweep direction and sweep amount of the drive frequency after starting driving are determined. The determination control unit 220 acquires and stores necessary information in the storage unit 230 when performing various processes. The determination control unit 220 reads and writes information from and to the storage unit 230. The storage unit 230 is a writable nonvolatile storage medium such as a flash memory, for example. The determination control unit 220 adjusts the frequency and voltage value of the AC voltage generated by the AC voltage generation unit 240 by transmitting a control signal to the AC voltage generation unit 240.

  The AC voltage generator 240 generates an AC voltage applied to the drive unit 114. The frequency of the AC voltage, that is, the driving frequency and the voltage value are adjusted according to a control signal from the determination control unit 220.

[Driving process of driving start method]
The drive start method determination process will be described with reference to FIG. 6 is executed by the configuration included in the control unit 200. In step S <b> 1, determination control unit 220 transmits to AC voltage generation unit 240 a control signal for generating an AC voltage having first voltage value V <b> 1 and a predetermined drive frequency. The first voltage value V1 and the predetermined drive frequency are stored in advance in the storage unit 230, for example. Further, the first voltage value V1 is a voltage value at which a minute amplitude is obtained. The AC voltage generator 240 applies an AC voltage having the first voltage value V1 and a predetermined drive frequency to the drive unit 114. By step S1, supply of AC voltage to the drive unit 114 is started. Thereafter, the process proceeds to step S2.

  In step S2, the resonance frequency f1 at the first voltage value V1 and the amplitude at the resonance frequency f1 are determined based on the detection signal from the BD sensor 300. This process will be described later in detail with reference to FIG. Thereafter, the process proceeds to step S3.

  In step S3, the determination processing unit 220 stores the resonance frequency f1 determined in step S2 and the resonance amplitude at the resonance frequency f1 in the storage unit 230. Specifically, after the process of step S2 is completed, the current drive frequency and amplitude stored in the storage unit 230 are stored in the storage unit 230 as the resonance frequency f1 and the resonance amplitude at the resonance frequency f1. . Thereafter, the process proceeds to step S4.

  In step S <b> 4, determination control unit 220 transmits to AC voltage generation unit 240 a control signal for generating an AC voltage having second voltage value V <b> 2 and a predetermined drive frequency. The predetermined drive frequency is the same as that in step S1. The second voltage value V2 is larger than the first voltage value V1. The second voltage value V2 is obtained, for example, by adding a predetermined voltage width ΔV to the first voltage value V1. The voltage width ΔV is stored in advance in the storage unit 230, for example. The determination control unit 220 stores the second voltage value V2 in the storage unit 230. The AC voltage generator 240 applies an AC voltage having the second voltage value V2 and a predetermined drive frequency to the drive unit 114. Thereafter, the process proceeds to step S5.

  In step S5, based on the detection signal from the BD sensor 300, the resonance frequency f2 at the second voltage value V2 and the amplitude at the resonance frequency f2 are determined (see FIG. 7). Thereafter, the process proceeds to step S6.

  In step S6, the determination processing unit 220 stores the resonance frequency f2 determined in step S5 and the amplitude at the resonance frequency f2 in the storage unit 230. Specifically, after the process of step S5 is completed, the current drive frequency and amplitude stored in the storage unit 230 are stored in the storage unit 230 as the resonance frequency f2 and the resonance amplitude at the resonance frequency f2. . Thereafter, the process proceeds to step S7.

  In step S7, the determination control unit 220 determines whether the amplitude determined in step S6 is equal to or greater than a desired amplitude. The desired amplitude value is stored in advance in the storage unit 230. If the amplitude determined in step S6 is less than the desired amplitude, that is, if the determination in step S7 is negative, the process proceeds to step S8.

  Step S8 is executed when the amplitude of the mirror 111 has not reached the desired amplitude. The determination control unit 220 increases the value of the second voltage value V2 stored in the storage unit 230. For example, the voltage width ΔV used in step S4 is added to the second voltage value V2. The determination control unit 220 overwrites the storage unit 230 with the second voltage value V2 added with the voltage width ΔV. Determination control unit 220 transmits a control signal based on second voltage value V <b> 2 to which voltage width ΔV is added to AC voltage generation unit 240. The AC voltage generation unit 240 applies an AC voltage having the second voltage value V2 to which the voltage width ΔV is added and a predetermined driving frequency to the driving unit 114. Thereafter, the process returns to step S5. Therefore, the second voltage value is increased by repeating steps S5 to S8 until the determination in step S7 becomes affirmative, in other words, until a desired amplitude is obtained. By this processing, it is possible to obtain the second voltage value that provides a desired amplitude.

  If the amplitude determined in step S6 is greater than or equal to the desired amplitude, that is, if the determination in step S7 is affirmative, the process proceeds to step S9. In step S9, the determination control unit 220 determines a drive start method from the resonance frequency f1, the resonance frequency f2, and the second voltage value V2 stored in the storage unit 230. Specifically, the drive frequency at the start of driving is determined to be equal to the resonance frequency f1. Further, by subtracting the resonance frequency f2 from the resonance frequency f1, the sweep direction and the sweep width of the drive frequency at the start of driving are determined. If the subtraction result is a positive value, the sweep direction is determined in a direction (negative direction) in which the drive frequency decreases from the resonance frequency f1. On the other hand, if the subtraction result is a negative value, the sweep direction is determined in the direction (positive direction) in which the drive frequency increases from the resonance frequency f1. The sweep width is defined as the absolute value of the difference between the resonance frequency f1 and the resonance frequency f2. The second voltage value V2 is determined as the voltage value of the AC voltage at the start of driving. These parameters necessary for starting driving are stored in the storage unit 230. This completes the drive start method determination process.

  The parameters necessary for starting the driving of the optical scanner 1 are determined by the driving start determining process shown in FIG. Examples of parameters include a drive frequency and voltage value at the start of driving, and a sweep direction and a sweep width of the drive frequency after starting driving. By using these parameters, the startup time of the optical scanner 1 can be shortened as shown in FIG.

[Resonance frequency determination process]
The resonance frequency determination process executed in steps S2 and S6 in FIG. 6 will be described with reference to FIG. 7 is also executed by the configuration included in the control unit 200.

  In step S501, scanning light is detected. Specifically, the scanning state determination unit 210 receives a detection signal transmitted from the BD sensor 300 that has received the scanning light. Thereafter, the process proceeds to step S502.

  In step S502, the amplitude is determined. Specifically, the scanning state determination unit 210 determines the amplitude of the mirror 111 based on the received detection signal. The amplitude determined by the scanning state determination unit 210 is transmitted to the determination control unit 220 as a scanning state signal. The determination control unit 220 stores the current amplitude and drive frequency in the storage unit 230. Thereafter, the process proceeds to step S503.

  In step S503, the drive frequency is changed. Specifically, the determination control unit 220 adds a predetermined frequency width Δf to the current drive frequency. The predetermined frequency width Δf is stored in the storage unit 230 in advance. Determination control unit 220 transmits a control signal based on the changed drive frequency to AC voltage generation unit 240. Thereafter, the process proceeds to step S504.

  In step S504, scanning light is detected. This process is the same as step S501. Thereafter, the process proceeds to step S505.

  In step S505, the amplitude corresponding to the drive frequency changed in step S503 is determined. This process is the same as step S502. The storage unit 230 includes the amplitude and the driving frequency stored in step S502. The determination control unit 220 stores the amplitude and drive frequency stored in step S502 in the storage unit 230 as the previous amplitude and drive frequency. Then, the determination control unit 220 stores the newly determined amplitude and drive frequency in the storage unit 230 as the current amplitude and drive frequency. Therefore, both the current amplitude and drive frequency and the previous amplitude and drive frequency exist in the storage unit 230. Thereafter, the process proceeds to step S506.

  When the optical scanning unit 100 is driven with a constant voltage, the amplitude increases as the drive frequency approaches the resonance frequency. On the other hand, the amplitude decreases as the drive frequency moves away from the resonance frequency. In step S506, the determination control unit 220 compares the previous amplitude stored in step S502 with the current amplitude stored in step S505. As a result of the comparison, when it is determined that the amplitude is increased (Yes in step S506), the drive frequency approaches the resonance frequency by increasing the drive frequency. In this case, the process proceeds to step S508. On the other hand, if it is determined that the amplitude has not increased as a result of the comparison (No in step S506), the process proceeds to step S507.

  The case where step S506 is negative is a case where the amplitude is reduced by the addition of the frequency width Δf in step S503. At this time, in order to bring the drive frequency close to the resonance frequency, it is necessary to reduce the drive frequency. Accordingly, in step S507, the determination control unit 220 switches the frequency change direction. Specifically, in step S507, the frequency width Δf is subtracted in the process of changing the frequency to be executed in the future. Thereafter, the process proceeds to step S508.

  In step S508, the drive frequency is changed. Specifically, if step S506 is positive, determination control unit 220 adds frequency width Δf to the current drive frequency. On the other hand, if step S506 is negative, the determination control unit 220 subtracts the frequency width Δf from the current drive frequency. Determination control unit 220 transmits a control signal based on the changed drive frequency to AC voltage generation unit 240. Thereafter, the process proceeds to step S509.

  In step S509, scanning light is detected. This process is the same as step S501. Thereafter, the process proceeds to step S510.

  In step S510, the amplitude corresponding to the drive frequency changed in step S508 is determined. This process is the same as step S502. The determination control unit 220 stores the current amplitude and drive frequency already stored in the storage unit 230 in the storage unit 230 as the previous amplitude and drive frequency. Then, the determination control unit 220 stores the new amplitude and driving frequency obtained in step S508 in the storage unit 230 as the current amplitude and driving frequency. Thereafter, the process proceeds to step S511.

  In step S511, it is determined whether the amplitude is maximized. Specifically, the determination control unit 220 compares the current amplitude stored in the storage unit with the previous amplitude. When the current amplitude is greater than or equal to the previous amplitude, the drive frequency is approaching the resonance frequency. Therefore, if the current amplitude is greater than or equal to the previous amplitude, the determination control unit 220 determines that the amplitude is not maximized (No in step S511). If the determination in step S511 is negative, the process returns to step S508. Accordingly, the drive frequency is changed by repeating steps S508 to S511 until the determination in step S511 becomes affirmative, in other words, until the amplitude becomes maximum. On the other hand, when the current amplitude is smaller than the previous amplitude, the drive frequency is away from the resonance frequency. Therefore, it is considered that the drive frequency at the previous amplitude is closest to the resonance frequency. If the current amplitude is smaller than the previous amplitude, the determination control unit 220 determines that the amplitude is maximized (Yes in step S511). If the determination in step S511 is affirmative, the resonance frequency determination process ends. The current amplitude and drive frequency stored in the storage unit 230 are referred to in the drive start determination process shown in FIG. 6 as the resonance amplitude and the resonance frequency.

[Drive processing]
The drive process of the optical scanner 1 using the drive start method determined by the drive start method determination process of FIG. 6 will be described with reference to FIG. The process shown in FIG. 8 is executed by the control unit 200.

  In step S101, the determination processing unit 220 transmits a control signal for generating an AC voltage having a drive frequency equal to the second voltage value V2 and the resonance frequency f1 to the AC voltage generation unit 240. The second voltage value V2 and the resonance frequency f1 are stored in advance in the storage unit 230 by the drive start determination process shown in FIG. The AC voltage generator 240 applies an AC voltage having a drive frequency equal to the second voltage value V2 and the resonance frequency f1 to the drive unit 114. Note that the determination control unit 220 stores the second voltage value V2 and the resonance frequency f1 in the storage unit 230 as the current voltage value and the drive frequency. Thereafter, the process proceeds to step S102.

  In step S102, the determination control unit 220 determines whether the drive frequency has been swept until the resonance frequency f2 is reached. If the drive frequency has not reached the resonance frequency f2 (No at Step S102), the process proceeds to Step S103.

  If the determination in step S102 is negative, the determination control unit 220 changes the current drive frequency by the frequency width Δf. The change direction of the frequency width Δf, that is, whether to add or subtract the frequency width Δf, is stored in advance in the storage unit 230 by the drive start determination process shown in FIG. At this time, the voltage value of the AC voltage is maintained at the second voltage value V2. Determination control unit 220 transmits a control signal based on the changed drive frequency to AC voltage generation unit 240. Thereafter, the process proceeds to step S102. That is, the drive frequency is swept until the drive frequency reaches the resonance frequency f2.

  The case where the determination in step S102 is affirmative is a case where the drive frequency has reached the resonance frequency f2. If there is no instruction for termination of driving from the outside to the optical scanner 1, the determination control unit 220 denies the determination in step S103. When the determination in step S103 is negative, the AC voltage generation unit 240 continuously supplies an AC voltage having a drive frequency equal to the second voltage value V2 and the resonance frequency f2 to the drive unit 114. As a result, the driving of the optical scanner 1 is continued.

  On the other hand, when an instruction to finish driving is given to the optical scanner 1 from the outside, the determination control unit 220 affirms the determination in step S103. If the determination in step S103 is affirmative, the process proceeds to step S104. In step S <b> 104, determination control unit 220 transmits a control signal for stopping application of AC voltage to drive unit 114 to AC voltage generation unit 240. Thereby, the drive of the optical scanner 1 is stopped.

  The driving of the optical scanner 1 is started by an AC voltage having a driving frequency equal to the second voltage value V2 and the resonance frequency f1 by the driving process shown in FIG. After starting the driving of the optical scanner 1, the drive frequency is swept to the resonance frequency f2 while maintaining the second voltage value V2. Therefore, the rise time of the optical scanner 1 is the shortest as shown in FIG.

  In the present invention, the AC voltage applied to the drive unit is not limited to a sine wave, and includes, for example, a non-sine wave AC such as a rectangular wave AC or a triangular wave AC. Further, it is understood that a pulse width-modulated voltage is applied to the drive unit as being included in the AC voltage.

  In the present invention, the optical scanner 1 is not limited to the embodiment described above. For example, the optical scanner may have an arbitrary shape as long as resonance driving is possible. The optical scanner may be driven by a driving method other than the piezoelectric element (for example, electromagnetic or electrostatic).

DESCRIPTION OF SYMBOLS 1 Optical scanner 100 Optical scanning part 110 Structure 111 Mirror 112,212 Torsion beam 113,213 Main body part 113a Fixed part 113b Bridging part 114 Drive part 120 Base 200 Control part 300 BD sensor

Claims (7)

Drive that controls the AC voltage supplied to the drive unit that drives the optical scanner when starting to drive the optical scanner that exhibits resonance characteristics that can be resonantly driven and whose resonance frequency changes according to the amplitude A decision method for determining a starting method,
A supply start step for starting the supply of the AC voltage having a first voltage value in which a resonance amplitude that is an amplitude in a state in which the optical scanner is resonance-driven to the drive unit is smaller than a desired amplitude;
A light detection step of detecting light scanned by the optical scanner after the supply start step;
An amplitude determining step for determining an amplitude of the optical scanner based on a detection result of the light detecting step;
A first determination step of determining a resonance frequency and a resonance amplitude of the optical scanner at the first voltage value by executing the light detection step and the amplitude determination step in a state where the frequency of the AC voltage is changed; ,
By executing the light detection step and the amplitude determination step in a state where the voltage value of the AC voltage is changed to a second voltage value larger than the first voltage value, the optical scanner at the second voltage value is executed. A second determining step for determining a resonance frequency and a resonance amplitude;
A determination step of determining whether the resonance amplitude determined in the second determination step is greater than or equal to the desired amplitude;
When the resonance amplitude is determined to be greater than or equal to the desired amplitude in the determination step, the resonance at the second voltage value from the resonance frequency at the first voltage value is started when driving the optical scanner. A drive start determination step for determining to change the frequency in a direction toward the frequency;
A determination method comprising: When it is determined in the determination step that the resonance amplitude is less than the desired amplitude, the second voltage value is larger than the second voltage value in the second determination step that has been performed previously. Run the decision step again,
After the second determination step is performed again, the determination step is performed again.
The determination method according to claim 1. The drive start determination step further includes, when starting the driving of the optical scanner, before changing the frequency from the resonance frequency in the first voltage value toward the resonance frequency in the second voltage value. Determining to supply the alternating voltage having the frequency equal to the resonant frequency at the first voltage value;
The determination method according to claim 1 or 2. The drive start determination step further determines to change the frequency from the resonance frequency at the first voltage value until the resonance frequency at the second voltage value is reached.
The determination method according to claim 3. The driving start determination step further determines that the AC voltage having the second voltage value is supplied when driving the optical scanner is started.
The determination method according to claim 3 or 4. The optical scanner resonates with a frequency equal to a resonance frequency at a first voltage value at which a resonance amplitude that is an amplitude in a state where the optical scanner is resonantly driven is smaller than a desired amplitude with respect to a driving unit that drives the optical scanner. An initial supply step of supplying the alternating voltage having a second voltage value at which the desired amplitude is obtained in a driven state;
After the initial supply step, a supply change that changes the frequency of the AC voltage from the resonance frequency at the first voltage value to the resonance frequency at the second voltage value while maintaining the second voltage value. Steps,
A steady driving step of continuing the supply of the AC voltage to the optical scanner in a state where the frequency of the AC voltage becomes the resonance frequency at the second voltage value by the supply changing step;
A driving method comprising: A mirror having a reflecting surface for reflecting incident light and configured to be swingable about a first axis;
A pair of torsion beams for supporting the mirror on both sides;
A main body connected to the ends of the pair of torsion beams;
A planar structure having
A pedestal to which a part of the structure is fixed;
A driving unit that is provided in the main body unit, applies a voltage to the structure to apply a force, and can swing the mirror unit around the first axis;
A control unit for controlling an AC voltage applied to the drive unit,
The optical scanner is capable of resonance driving and exhibits nonlinear characteristics in which the resonance frequency changes according to the amplitude,
When the controller starts driving the optical scanner,
A state in which the optical scanner is resonantly driven with a frequency equal to a resonant frequency at a first voltage value at which a resonance amplitude that is an amplitude in a state where the optical scanner is resonantly driven with respect to the driving unit is smaller than a desired amplitude. And starting the supply of the AC voltage having the second voltage value at which the desired amplitude is obtained,
After the start of the supply, with the second voltage value maintained, the frequency of the AC voltage is changed from the resonance frequency at the first voltage value until the resonance frequency at the second voltage value is reached.
An optical scanner characterized by that.