JP2010217520A - Optical scanner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase vibration amplitude of a mirror face part in an optical scanner constructing a three-freedom-degree coupled vibration system. <P>SOLUTION: In the optical scanner 1, the three-freedom-degree coupled vibration system, which performs torsional vibration with a large rotation angle when a specific periodic external force is applied, is composed of a mirror 13, an inner gimbal 12, an outer gimbal 11, a support part 3, elastic coupling parts 16a and 16b, elastic coupling parts 15a and 15b, and elastic coupling parts 14a and 14b. When a voltage is applied between comb electrode parts 17 and 19 and comb electrode parts 4a and 4b so that the specific periodic external force works on the outer gimbal 11, a three-freedom-degree torsional vibrator is set to a resonance condition. Then, when a rotation angle of the outer gimbal 11 is within a previously set voltage application angle range (a range giving torque of 90% or more of maximum torque) including the rotation angle of the outer gimbal 11 maximizing torque working on the outer gimbal 11, a voltage is applied. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical scanning device that scans a light beam.

In recent years, various optical scanning devices using MEMS (Micro Electro Mechanical System) technology have been proposed for the purpose of downsizing the optical scanning device.
In contrast, the applicant of the present application provides a third frame having a mirror surface portion formed on the surface, a second frame provided with a predetermined gap with respect to the third frame, and a predetermined gap with respect to the second frame. And a 0th frame provided with a predetermined gap with respect to the first frame, and the third frame, the second frame, and the first frame are respectively connected to the respective rotation shafts. An optical scanning device having a three-degree-of-freedom coupled vibration system has been proposed (see, for example, Patent Document 1).

  In the optical scanning device configured as described above, the three-degree-of-freedom torsional vibrator can be brought into a resonance state by applying an inherent periodic excitation force to the first frame. Then, by superimposing periodic excitation forces corresponding to the vibrations of the second frame and the third frame, the second frame and the third frame are vibrated at different frequencies and amplitudes, respectively. The light can be scanned two-dimensionally by reflecting the light at the mirror surface.

JP 2008-129068 A

  However, in the optical scanning device described in Patent Document 1, since the two frames of the second frame and the third frame are vibrated only by the vibration of the first frame, the vibration of the third frame in which the mirror surface portion is formed. There was a problem that the amplitude was small.

  The present invention has been made in view of these problems, and an object of the present invention is to increase the vibration amplitude of a mirror surface portion in an optical scanning device having a three-degree-of-freedom coupled vibration system.

  In order to achieve the above object, an optical scanning device according to claim 1, further comprising: a reflecting portion having a reflecting surface for reflecting the light beam; and an elastically deformable first elastic connecting portion connected to the reflecting portion. A first support portion that supports the reflection portion in a swingable manner with the first elastic connection portion as a rotation axis, and a second elastic connection portion that is elastically deformable connected to the first support portion, and has a second elasticity. A second support part that pivotably supports the first support part about the connection part as a rotation axis; and a third elastic connection part that is elastically deformable connected to the second support part. A third support portion that pivotally supports the second support portion as a rotation shaft, and includes a reflection portion, a first support portion, a second support portion, a third support portion, a first elastic coupling portion, and a second elasticity. The coupling part and the third elastic coupling part are coupled with three degrees of freedom torsionally vibrate at a large rotation angle when an inherent periodic external force is applied. Constitute the dynamic system.

  For this reason, the optical scanning device according to claim 1 has a torsional freedom degree with respect to the first elastic connecting portion, the second elastic connecting portion, and the third elastic connecting portion with the third support portion as a fixed end. It is a torsional vibrator with a degree of freedom.

  A three-degree-of-freedom torsional vibrator theoretically has three vibration modes. That is, the three vibration modes have different resonance frequencies, and the ratios of the angular amplitudes of the torsional vibrations of the reflection part, the first support part, and the second support part with respect to each resonance frequency are different (this is called a vibration mode). . Therefore, when the angular amplitude of the second support portion increases in a certain vibration mode, the angular amplitude of the reflection portion and the first support portion increases according to the ratio of the angular amplitude in the vibration mode.

  And the 1st comb-tooth-shaped electrode part formed in the comb-tooth shape is provided in the 2nd support part, and the 2nd comb-tooth-shaped electrode formed in the comb-tooth shape which can mesh | engage with a 1st comb-tooth-shaped electrode part And the voltage applying means applies a voltage between the first comb-shaped electrode portion and the second comb-shaped electrode portion. An electrostatic attractive force is generated between the electrode portions.

  For this reason, the voltage applying means applies a voltage between the first comb-shaped electrode portion and the second comb-shaped electrode portion to cause a specific periodic external force to act on the second support portion. The torsional vibrator can be brought into a resonance state.

  Further, if a periodic excitation force having a frequency corresponding to each of the three vibration modes is given, each vibration mode can be excited. In addition, if a plurality of periodic excitation forces with a plurality of frequencies are superimposed and applied, a plurality of vibration modes can be excited simultaneously.

  Accordingly, the periodic excitation force corresponding to the vibration mode having a large angular amplitude of the reflecting portion and the periodic excitation force corresponding to the vibration mode having a large angular amplitude of the first support portion are superimposed and given. The laser beam reflected by the part can be scanned two-dimensionally.

  Then, the voltage application control means sets the rotation angle of the second support part with the third elastic coupling part as the rotation axis as the second support part rotation angle, and applies the electrostatic force generated by the voltage application by the voltage application means to the second support part. The torque that acts is the second support portion torque, the second support portion rotation angle when the second support portion torque is maximum is the torque maximum rotation angle, and the second support portion rotation angle includes the torque maximum rotation angle in advance. A voltage is applied to the voltage applying means when the voltage is within a voltage application angle range that is a range of the set second support portion rotation angle.

  Therefore, when the torque that acts on the second support portion is maximized, the maximum torque can be applied to the second support portion. Thereby, a larger torque can be applied to the second support part than when the maximum torque does not act on the second support part, and the angular amplitude of the second support part can be increased. As described above, when the angular amplitude of the second support portion is increased, the angular amplitude of the reflective portion is increased according to the ratio of the angular amplitude in the vibration mode, so that the angular amplitude of the reflective portion can be increased.

  Further, in the optical scanning device according to claim 1, as described in claim 2, the voltage application angle range generates the second support portion torque in which the difference from the maximum value of the second support portion torque is 10%. The second support portion rotation angle and the torque maximum rotation angle larger than the maximum torque rotation angle is the upper limit angle of the voltage application angle range, and the difference between the second support portion torque and the maximum value is 10%. A rotation angle that is the second support portion rotation angle when the portion torque is generated and is smaller than the maximum torque rotation angle may be set as the lower limit angle of the voltage application angle range.

  In the optical scanning device configured as described above, the voltage application angle range can be set only when the magnitude of the torque acting on the second support portion is in the vicinity of the maximum value. In other words, when the torque acting on the second support portion is small, it is possible to prevent the voltage applying means from applying a voltage. For this reason, when the torque which acts on the 2nd support part is small and it is difficult to contribute to the increase in the angle amplitude of a reflection part, it is suppressed that a voltage is applied vainly and power consumption of the optical scanning device concerned is reduced. Can do.

  Further, in the optical scanning device according to claim 2, as described in claim 3, the rotation angle of the reflection portion with the first elastic coupling portion as the rotation axis is set as the rotation angle of the reflection portion, and the reflection portion swings. The maximum value of the reflection part rotation angle at the time of the reflection is the reflection part target angle, the reflection part target angle is θm, the second support part rotation angle when the reflection part rotation angle is the reflection part target angle is θj, and the upper limit angle is θ1 Assuming that the lower limit angle is θ2, the reflecting portion target angle is preferably set within the range represented by the following expression (1).

{Θ2 × (θm / θj)} <θm <{θ1 × (θm / θj)} (1)
According to the optical scanning device configured as described above, the torque acting on the second support portion is maximized in the vicinity of the reflection portion target angle of the reflection portion, and therefore the first comb-like electrode portion and the second comb-tooth shape. Torque generated between the electrode portions can be utilized to the maximum, and the reflecting portion can be scanned with low power consumption and wide angular amplitude.

  Further, in the optical scanning device according to any one of claims 1 to 3, as described in claim 4, the second support portion torque with respect to a change in a predetermined change angle of the second support portion rotation angle set in advance. The second support portion torque change rate within the voltage application angle range is outside the voltage application angle range, and is in the vicinity of the upper limit angle and the lower limit angle of the voltage application angle range. The voltage application control means is configured to apply a voltage to the voltage application means only when the second support rotation angle is within the voltage application angle range. Is preferably applied.

  In the optical scanning device configured as described above, the torque change rate within the voltage application angle range is substantially flat because the rate of change in torque of the second support portion within the voltage application angle range is sufficiently small. Then, since the voltage is applied to the voltage application means only when the torque curve is within the flat voltage application angle range, electrostatic torque having a shape approximating a rectangular wave acts on the second support portion.

  As a result, the amplitude of the resonance frequency component for bringing the three-degree-of-freedom torsional vibrator into a resonance state among the electrostatic torque having a shape approximating a rectangular wave is greater than the amplitude of the electrostatic torque of the sine wave that vibrates at the resonance frequency. Also grows. Therefore, it is possible to increase the angular amplitude of the reflecting portion that oscillates at the resonance frequency, compared to the case where a sinusoidal electrostatic torque is applied.

  Specifically, when the rectangular wave is Fourier-expanded, it is expressed by Expression (2), and the component of the resonance frequency f in the rectangular wave is expressed by Expression (3). On the other hand, a sine wave having a resonance frequency f is expressed by Expression (4).

Therefore, the amplitude of the component of the resonance frequency f in the rectangular wave is (4 / π) times larger than the amplitude of the sine wave of the resonance frequency f.

1 is a plan view showing a configuration of an optical scanning device 1. FIG. 2 is a block diagram showing an electrical configuration of the optical scanning device 1. FIG. It is a figure which shows the angle amplitude ratio of the outer gimbal 11, the inner gimbal 12, and the mirror 13. FIG. It is a graph which shows the relationship between the electrostatic torque between comb teeth, and an external gimbal rotation angle. It is a graph which shows the time change of outer gimbal rotation angle (theta), an applied voltage, and the electrostatic torque between comb teeth.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a plan view showing a configuration of an optical scanning device 1 according to an embodiment to which the present invention is applied.
The optical scanning device 1 is manufactured, for example, by processing an SOI (Silicon On Insulator) wafer by a semiconductor process, and as shown in FIG. 1, a light beam scanning unit 2 that scans a light beam, and a light beam scanning. A support unit 3 that supports the unit 2, a drive unit 4 that applies a rotational driving force to the light beam scanning unit 2, and an angle detection unit 5 that detects a rotation angle of the light beam scanning unit 2.

  The light beam scanning unit 2 includes an outer gimbal 11, an inner gimbal 12, a mirror 13, elastic connecting portions 14a and 14b, elastic connecting portions 15a and 15b, elastic connecting portions 16a and 16b, comb electrode portions 17, 18, 19, 20.

  Among these, the mirror 13 has a circular shape, and a mirror surface portion of an aluminum thin film is formed on the surface. The inner gimbal 12 has a rectangular frame shape, and a mirror 13 is disposed in the frame. The outer gimbal 11 has a rectangular frame shape, and the inner gimbal 12 is arranged in the frame.

  The elastic connecting portion 16 a is made of an elastically deformable material, and is disposed within the frame of the inner gimbal 12 to connect the mirror 13 and the inner gimbal 12. The elastic connecting portion 16b is made of an elastically deformable material, and is disposed in the frame of the inner gimbal 12. The mirror 13 and the inner gimbal 12 are connected to the opposite side of the elastic connecting portion 16a with the mirror 13 in between. Link. The elastic connecting portion 16 a and the elastic connecting portion 16 b are arranged on the same straight line passing through the center of gravity JS of the mirror 13 and serve as the rotation axis k of the mirror 13. As a result, the mirror 13 is configured to be capable of torsional vibration about the rotation axis k.

  The elastic connecting portion 15 a is made of an elastically deformable material, and is disposed in the frame of the outer gimbal 11 to connect the inner gimbal 12 and the outer gimbal 11. The elastic connecting portion 15b is made of an elastically deformable material, and is disposed in the frame of the outer gimbal 11. The inner gimbal 12 and the outer gimbal 11 are disposed on the opposite side of the elastic connecting portion 15a with the inner gimbal 12 in between. And The elastic connecting portion 15 a and the elastic connecting portion 15 b are arranged on the same straight line passing through the center of gravity JS of the mirror 13 and the inner gimbal 12 and serve as the rotation axis j of the mirror 13. As a result, the inner gimbal 12 is configured to be capable of torsional vibration about the rotation axis j.

  The elastic connecting portion 14 a is made of an elastically deformable material, and connects the upper side 11 a of the outer gimbal 11 and the support portion 3. The elastic connecting portion 14b is made of an elastically deformable material, and connects the lower side 11b of the outer gimbal 11 and the support portion 3 on the opposite side of the elastic connecting portion 14a across the outer gimbal 11. The elastic coupling portion 14 a and the elastic coupling portion 14 b are arranged on the same straight line passing through the center of gravity JS of the mirror 13, the inner gimbal 12, and the outer gimbal 11, and serve as the rotation axis i of the outer gimbal 11. As a result, the outer gimbal 11 is configured to be torsionally vibrated around the rotation axis i.

  The comb electrode portion 17 is formed in a comb shape along the left side 11 c of the outer gimbal 11. Further, the comb electrode portion 18 is formed in a comb shape along the left side 11 c above the comb electrode portion 17.

  Further, the comb electrode portion 19 is formed in a comb shape along the right side 11 d of the outer gimbal 11. Further, the comb electrode portion 20 is formed in a comb shape along the right side 11 d above the comb electrode portion 17.

  Next, the support portion 3 includes an upper support portion 3a connected to an end portion of the elastic connection portion 14a on the side not connected to the upper side 11a, and an end portion of the elastic connection portion 14b on the side not connected to the lower side 11b. It is comprised from the lower side support part 3b connected.

  Further, the driving unit 4 is formed in a comb-teeth electrode portion 4a formed in a comb-teeth shape that meshes with the comb-teeth electrode unit 17 with a predetermined interval, and in a comb-teeth shape that meshes with the comb-teeth electrode unit 19 with a predetermined interval. And the comb electrode portion 4b.

  Further, the angle detection unit 5 is formed in a comb-teeth shape that is meshed with the comb-teeth electrode unit 18 with a predetermined interval and a comb-teeth shape that is meshed with the comb-teeth electrode unit 20 with a predetermined interval. It is comprised from the comb-tooth electrode part 5b made.

Next, the electrical configuration of the optical scanning device 1 will be described. FIG. 2 is a block diagram showing an electrical configuration of the optical scanning device 1.
As shown in FIG. 2, the optical scanning device 1 includes a drive signal generation circuit 31 that outputs a pulse voltage as a drive signal for rotationally driving the light beam scanning unit 2, and the drive output by the drive signal generation circuit 31. Amplifying circuit 32 that amplifies the signal and applies it to comb-tooth electrode portions 4a and 4b, and C− that converts the capacitance between comb-tooth electrode portions 5a and 5b and comb-tooth electrode portions 19 and 20 into a voltage value. From the V conversion circuits 33a and 33b (hereinafter, the CV conversion circuits 33a and 33b are collectively referred to as the CV conversion circuit 33), the semiconductor laser 34 serving as a light source of the light beam, and the CV conversion circuit 33. A control circuit 35 that monitors the output voltage, controls the semiconductor laser 34 based on the voltage value, and controls the drive signal generation circuit 31 is provided.

Next, the operation principle of the optical scanning device 1 will be described.
The optical scanning device 1 is a three-degree-of-freedom torsional vibrator having a degree of freedom of twisting with respect to the rotation axes i, j, and k with the support portion 3 as a fixed end.

  A three-degree-of-freedom torsional vibrator theoretically has three vibration modes. That is, the three vibration modes have different resonance frequencies, and the ratio of the angular amplitude of the torsional vibration of each frame to each resonance frequency is different (this is called a vibration mode). Hereinafter, these three vibration modes are referred to as vibration mode 1, vibration mode 2, and vibration mode 3, respectively.

  When a voltage is applied to the comb electrode portions 4a and 4b, an electrostatic force is generated between the comb electrode portions 17 and 19. Further, while the outer gimbal 11 vibrates for one cycle, the comb electrode portions 17 and 19 come closest to the comb electrode portions 4a and 4b twice. For this reason, if a periodic electrostatic force close to twice the resonance frequency is applied, the three-degree-of-freedom torsional vibrator can be brought into a resonance state (hereinafter, an excitation force for making the resonance state is referred to as a periodic excitation force). Further, every time the comb electrode portions 17 and 19 approach the comb electrode portions 4a and 4b, a periodic excitation force can be applied.

  If a periodic excitation force having a frequency corresponding to each of vibration mode 1, vibration mode 2, and vibration mode 3 is applied, the respective vibration modes can be excited. In addition, if a plurality of periodic excitation forces with a plurality of frequencies are superimposed and applied, a plurality of vibration modes can be excited simultaneously.

Here, for example,
The resonance frequency f1 of vibration mode 1 is 1000 Hz,
The resonance frequency f2 of vibration mode 2 is 5000 Hz,
The resonance frequency f3 of vibration mode 3 is 40000 Hz,
The amplitude ratio r1 of the outer gimbal 11, the inner gimbal 12, and the mirror 13 in the vibration mode 1 is “1: −20: 0.5”,
The amplitude ratio r2 of the outer gimbal 11, the inner gimbal 12, and the mirror 13 in the vibration mode 2 is “1: 0.01: −50”,
The amplitude ratio r3 of the outer gimbal 11, the inner gimbal 12, and the mirror 13 in the vibration mode 3 is “1: 0.02: −0.03”,
The operation of the three-degree-of-freedom torsional vibrator will be described.

  The amplitude ratio in each vibration mode is described in the order of the outer gimbal 11, the inner gimbal 12, and the mirror 13 from the left. For example, when the amplitude of the outer gimbal 11 is “1”, the amplitude ratio r1 indicates that the amplitude of the inner gimbal 12 is “−20” and the amplitude of the mirror 13 is “0.5”.

  In the resonance state of the three-degree-of-freedom torsional vibrator, the phase angle between the frames is theoretically 0 degree or 180 degrees. Therefore, when describing the amplitude ratio, the sign is “+” when the phase angle difference is 0 degree, and the sign is “−” when the difference is 180 degrees. For example, the amplitude ratio r1 indicates that the phase angle difference between the outer gimbal 11 and the mirror 13 is 0 degree, and the phase angle difference between the outer gimbal 11 and the inner gimbal 12 is 180 degrees.

  When the resonance frequency and amplitude ratio of each vibration mode are designed as described above, in the vibration mode 1, mainly the inner gimbal 12 and the mirror 13 connected to the inner gimbal 12 are largely torsionally vibrated at 1000 Hz. Further, in the vibration mode 2, the mirror 13 is largely twisted and vibrated at 5000 Hz.

  For this reason, the laser beam is reflected by the mirror surface portion of the mirror 13 and the vibration mode 1 and the vibration mode 2 are simultaneously excited, so that the vibration mode 2 is in the main scanning direction (5000 Hz) and the vibration mode 1 is in the sub-scanning direction ( 1000 Hz), the laser beam can be scanned two-dimensionally.

Next, the operation of the optical scanning device 1 will be described.
When the drive signal generating circuit 31 outputs a drive signal based on the control by the control circuit 35, the voltage value of the drive signal is amplified by the amplifier circuit 32 and applied to the comb electrode portions 4a and 4b. Thereby, a pulse voltage is applied between the comb-tooth electrode portions 4a and 4b and the comb-tooth electrode portions 17 and 19 to generate an electrostatic attractive force that periodically changes, and the elastic coupling portions 14a and 14b are elastically deformed. By twisting, the light beam scanning unit 2 reciprocally vibrates about the elastic coupling portions 14a and 14b as the rotation axis i.

  Here, as shown in FIG. 3, the drive signal generation circuit 31 outputs a drive signal having a frequency twice the resonance frequency of the vibration mode in which the angular amplitude of the mirror 13 is larger than that of the outer gimbal 11 and the inner gimbal 12. As a result, the vibration system composed of the light beam scanning unit 2 and the elastic coupling portions 14a and 14b resonates, and the light beam scanning unit 2 reciprocally vibrates at the resonance frequency.

  In this state, when the mirror 13 is irradiated with a light beam from the semiconductor laser 34, the light beam is emitted by being reflected by the mirror surface of the mirror 13. Scanning is performed in a direction corresponding to the rotation angle.

  On the other hand, with the reciprocal vibration of the outer gimbal 11, the distance between the comb electrode portions 5a and 5b and the comb electrode portions 18 and 20 also periodically changes. As a result, the capacitance between the comb electrode portions 5 a and 5 b and the comb electrode portions 18 and 20 changes according to the rotation angle of the outer gimbal 11. The control circuit 35 detects the rotation angle of the outer gimbal 11 based on these capacitances. As described above, in the resonance state of the three-degree-of-freedom torsional vibrator, since the phase angle between the frames is theoretically 0 degree or 180 degrees, the mirror is detected by detecting the rotation angle of the outer gimbal 11. Thirteen rotation angles can be detected.

  FIG. 4A shows an electrostatic torque generated between the comb-tooth electrode portions 4a and 4b and the comb-tooth electrode portions 17 and 19 (hereinafter also referred to as inter-comb electrostatic capacitance), and rotation of the outer gimbal 11. It is a graph which shows the relationship with an angle (henceforth an outer gimbal rotation angle). In FIG. 4A, the sign of the inter-combine electrostatic torque indicates the direction in which the inter-combine electrostatic torque acts. Further, the absolute value of the inter-combine electrostatic torque shown in FIG. 4A is referred to as the inter-combine electrostatic torque absolute value.

  As shown in FIG. 4 (a), the inter-combine electrostatic torque exhibits a point-symmetric characteristic around a point where the outer gimbal rotation angle is 0 ° and the inter-combine electrostatic torque is zero. The region R1 in which the outer gimbal rotation angle θ is negative is divided into four regions R11, R12, R13, and R14 according to the change rate of the intercombine electrostatic torque absolute value. The first negative region R11 is a region where the outer gimbal rotation angle θ is 0 to less than θ11, the second negative region R12 is a region where the outer gimbal rotation angle θ is greater than θ11 and less than θ12, and the third negative region R13 is an outer gimbal rotation angle. The region where θ is not less than θ12 and less than θ13, and the fourth negative region R14 is a region where the outer gimbal rotation angle θ is not less than θ13 (provided that θ11> θ12> θ13).

  First, in the first negative region R11, as the outer gimbal rotation angle θ changes from 0 ° in the negative direction, the inter-combine electrostatic torque absolute value increases rapidly from 0. In the second negative region R12, the change in the inter-combine electrostatic torque absolute value is small with respect to the change in the negative direction of the outer gimbal rotation angle θ. That is, in the second negative region R12, the inter-combine electrostatic torque curve is substantially flat. Note that the inter-combine electrostatic torque absolute value is maximized in the second negative region R12. Further, in the third negative region R13, the inter-combine electrostatic torque absolute value rapidly decreases as the outer gimbal rotation angle θ changes in the negative direction. In the fourth negative region R14, the change in the inter-combine electrostatic torque absolute value is small with respect to the change in the negative direction of the outer gimbal rotation angle θ. That is, in the fourth negative region R14, the inter-combine electrostatic torque absolute value maintains a value close to zero.

  Further, the region R2 in which the outer gimbal rotation angle θ is positive is divided into four regions R21, R22, R23, and R24 according to the change rate of the inter-combine electrostatic torque absolute value. The first positive region R21 is a region where the outer gimbal rotation angle θ is 0 or more and less than θ21, the second positive region R22 is a region where the outer gimbal rotation angle θ is θ21 or more and less than θ22, and the third positive region R23 is an outer gimbal rotation angle. The region where θ is not less than θ22 and less than θ23, the fourth positive region R24 is a region where the outer gimbal rotation angle θ is not less than θ23 (provided that θ21 <θ22 <θ23).

  First, in the first positive region R21, as the outer gimbal rotation angle θ changes from 0 ° to the positive direction, the inter-combine electrostatic torque absolute value increases rapidly from zero. In the second positive region R22, the change in the inter-combine electrostatic torque absolute value is small with respect to the change in the positive direction of the outer gimbal rotation angle θ. That is, in the second positive region R22, the inter-comb electrostatic electrostatic torque curve becomes substantially flat. Note that the inter-combine electrostatic torque absolute value is maximized in the second negative region R22. Further, in the third positive region R23, the inter-combine electrostatic torque absolute value rapidly decreases as the outer gimbal rotation angle θ changes in the positive direction. In the fourth positive region R24, the change in the inter-combine electrostatic torque absolute value is small with respect to the change in the positive direction of the outer gimbal rotation angle θ. That is, in the fourth positive region R24, the inter-combine electrostatic torque absolute value maintains a value close to zero.

  FIG. 4B is an enlarged view of the region R1 in FIG. FIG. 5 is a graph showing temporal changes in the outer gimbal rotation angle θ, the applied voltage, and the inter-combination electrostatic torque for indicating the voltage application timing. In FIG. 5, the waveform Wθ represents the time change of the outer gimbal rotation angle θ, the waveform WV represents the time change of the voltage applied by the drive unit 4, and the waveform WT represents the time change of the electrostatic torque acting on the outer gimbal 11.

  Then, as shown in FIG. 4B and FIG. 5, the control circuit 35 sets the angle range (− | θ2 |) of the outer gimbal rotation angle θ in which the inter-combine electrostatic torque absolute value is 90% or more of the maximum value Tmax. ~ − | Θ1 |) and (+ | θ1 | ˜ + | θ2 |) as the maximum torque range RT, based on the detection result by the angle detection unit 5, as shown in FIG. 5 within the preset voltage application angle ranges RV (− | θu | ˜− | θd |) and (+ | θd | ˜ + | θu |) included in the maximum torque range RT (the rotation in FIG. 5). The drive signal generation circuit 31 is caused to output a drive signal (see the drive voltage waveform WV in FIG. 5). The voltage application angle range RV includes the outer gimbal rotation angle θ when the inter-combine electrostatic torque is maximized.

  Specifically, first, when the outer gimbal rotation angle θ is 0 or more and less than (+ | θu |), the drive signal is not output. Thereafter, when the outer gimbal rotation angle θ becomes (+ | θu |) or more, a drive signal is output. Further, the outer gimbal rotation angle θ is increased, and the maximum value (+ | θm |) of the rotation angle of the mirror 13 when the mirror 13 is oscillating (hereinafter also referred to as the maximum mirror angle (+ | θm |)) is obtained. Until the outer gimbal rotation angle θ becomes less than (+ | θd |).

  The drive signal is not output until the outer gimbal rotation angle θ is less than (+ | θd |) and is equal to or less than (− | θu |). Thereafter, when the outer gimbal rotation angle θ becomes (− | θu |) or less, a drive signal is output. Further, the outer gimbal rotation angle θ is increased to a minimum value (− | θm |) of the rotation angle of the mirror 13 when the mirror 13 is oscillating (hereinafter also referred to as a mirror minimum angle (− | θm |)). Until the outer gimbal rotation angle θ reaches (− | θd |) or more.

Hereinafter, the mirror maximum angle (+ | θm |) and the mirror minimum angle (− | θm |) are collectively referred to as a mirror target angle θm.
Further, in the optical scanning device 1, when the outer gimbal rotation angle θ when the rotation angle of the mirror 13 is θm is θj, the mirror target angle θm is within the range represented by the following expressions (5) and (6). Designed to be

{− | Θ2 | × (θm / θj)} <(− | θm |) <{− | θ1 | × (θm / θj)} (5)
{+ | Θ1 | × (θm / θj)} <(+ | θm |) <{+ | θ2 | × (θm / θj)} (6)
Note that “(θm / θj)” in the equations (5) and (6) represents the amplitude ratio between the mirror 13 and the outer gimbal 11.

  The optical scanning device 1 configured as described above includes a mirror 13 having a mirror surface portion that reflects a light beam, and elastically deformable elastic connecting portions 16 a and 16 b connected to the mirror 13. An inner gimbal 12 that supports the mirror 13 so as to be swingable about a rotation axis k, and elastically deformable elastic connection portions 15a and 15b connected to the inner gimbal 12, and the elastic connection portions 15a and 15b as rotation axes An outer gimbal 11 that swingably supports the inner gimbal 12 as j, and a support that swingably supports the outer gimbal 11 with the elastically deformable elastic connecting portions 14a and 14b connected to the outer gimbal 11 as the rotation axis i. Part 3, mirror 13, inner gimbal 12, outer gimbal 11, support part 3, elastic coupling parts 16 a and 16 b, elastic coupling parts 15 a and 15 b, and elastic coupling part 14 a, 4b constitute three degrees of freedom coupled vibration system of torsional vibration with a large rotation angle when the specific periodic external force acts.

  For this reason, the optical scanning device 1 has a three-degree-of-freedom torsion having a degree of freedom of twisting the elastic connecting portions 16a and 16b, the elastic connecting portions 15a and 15b, and the elastic connecting portions 14a and 14b with the support portion 3 as a fixed end. It is a vibrator.

  A three-degree-of-freedom torsional vibrator theoretically has three vibration modes. That is, the three vibration modes have different resonance frequencies, and the ratios of the angular amplitudes of the torsional vibrations of the mirror 13, the inner gimbal 12, and the outer gimbal 11 with respect to the respective resonance frequencies are different (this is called a vibration mode). Therefore, when the angular amplitude of the outer gimbal 11 increases in a certain vibration mode, the angular amplitude of the mirror 13 and the inner gimbal 12 increases according to the ratio of the angular amplitude in this vibration mode.

  Comb electrode portions 17 and 19 formed in a comb shape are provided on the outer gimbal 11, and comb electrode portions 4a and 4b formed in a comb shape that can mesh with the comb electrode portions 17 and 19 are provided. Is fixedly installed at a position where it can mesh with the comb electrode portions 17 and 19, and the drive signal generating circuit 31 applies a voltage between the comb electrode portions 17 and 19 and the comb electrode portions 4a and 4b. Thus, an electrostatic attractive force is generated between both electrode portions.

  For this reason, the drive signal generation circuit 31 applies a voltage between the comb electrode portions 17 and 19 and the comb electrode portions 4a and 4b to cause a specific periodic external force to act on the outer gimbal 11. The three-degree-of-freedom torsional vibrator can be brought into a resonance state.

  Further, if a periodic excitation force having a frequency corresponding to each of the three vibration modes is given, each vibration mode can be excited. In addition, if a plurality of periodic excitation forces with a plurality of frequencies are superimposed and applied, a plurality of vibration modes can be excited simultaneously.

  Therefore, by applying the periodic excitation force corresponding to the vibration mode with a large angular amplitude of the mirror 13 and the periodic excitation force corresponding to the vibration mode with a large angular amplitude of the inner gimbal 12 in a superimposed manner, the mirror 13 The laser beam reflected by can be scanned two-dimensionally.

  When the control circuit 35 is within a preset voltage application angle range RV including the outer gimbal rotation angle θ (hereinafter also referred to as the torque maximum rotation angle) when the inter-combine electrostatic torque is maximum, A voltage is applied to the drive signal generation circuit 31.

  Therefore, when the torque acting on the outer gimbal 11 is maximized, this maximum torque can be applied to the outer gimbal 11. As a result, a larger torque can be applied to the outer gimbal 11 than when no maximum torque is applied to the outer gimbal 11, and the angular amplitude of the outer gimbal 11 can be increased. As described above, when the angular amplitude of the outer gimbal 11 is increased, the angular amplitude of the mirror 13 is increased in accordance with the ratio of the angular amplitude in the vibration mode, so that the angular amplitude of the mirror 13 can be increased.

  Further, the voltage application angle range RV is included in the torque maximum range RT, and the outer gimbal rotation when the inter-combine electrostatic torque is 10% different from the maximum value of the inter-combine electrostatic torque. The angle θ that is larger than the maximum torque rotation angle is defined as the upper limit angle (− | θ1 | or + | θ2 |) of the voltage application angle range RV, and the difference from the maximum value of inter-combine electrostatic torque is 10%. The outer gimbal rotation angle θ when the inter-combine electrostatic torque is generated and smaller than the maximum torque rotation angle is the lower limit angle (− | θ2 | or + | θ1 |) of the voltage application angle range RV. To do.

  Therefore, the voltage application angle range RV can be set only when the magnitude of the torque acting on the outer gimbal 11 is near the maximum value. In other words, it is possible to prevent the drive signal generation circuit 31 from applying a voltage when the torque acting on the outer gimbal 11 is small. For this reason, when the torque acting on the outer gimbal 11 is small and it is difficult to contribute to the increase in the angular amplitude of the mirror 13, it is possible to suppress the useless application of voltage, and to reduce the power consumption of the optical scanning device 1. it can.

  The optical scanning device 1 is designed so that the mirror target angle θm is within the range represented by the above equations (5) and (6). As a result, the torque acting on the outer gimbal 11 is maximized in the vicinity of the mirror target angle θm, so that the torque generated between the comb electrode portions 17 and 19 and the comb electrode portions 4a and 4b is utilized to the maximum. The mirror 13 can be scanned with low power consumption and wide angular amplitude.

  Further, the inter-combine electrostatic torque change rate with respect to the change of the predetermined change angle of the outer gimbal rotation angle θ set in advance as the inter-combine electrostatic torque change rate is defined as the inter-comb electrostatic capacitance within the voltage application angle range RV. The torque change rate is configured to be sufficiently smaller than the inter-combine electrostatic torque change rate in a region outside the voltage application angle range RV and in the vicinity of the upper limit angle and the lower limit angle of the voltage application angle range RV. The control circuit 35 causes the drive signal generation circuit 31 to apply a voltage only when the outer gimbal rotation angle θ is within the voltage application angle range RV.

  Since the rate of change in inter-combine electrostatic torque within the voltage application angle range RV is sufficiently small, the torque curve within the voltage application angle range RV is substantially flat. Then, since the voltage is applied to the drive signal generation circuit 31 only when the torque curve is within the substantially flat voltage application angle range RV, electrostatic torque having a shape approximating a rectangular wave acts on the outer gimbal 11. To do.

  As a result, the amplitude of the resonance frequency component for bringing the three-degree-of-freedom torsional vibrator into a resonance state among the electrostatic torque having a shape approximating a rectangular wave is greater than the amplitude of the electrostatic torque of the sine wave that vibrates at the resonance frequency. Also grows. For this reason, the angular amplitude of the mirror 13 that oscillates at the resonance frequency can be made larger than when a sinusoidal electrostatic torque is applied.

  Specifically, when the rectangular wave is Fourier-expanded, it is expressed by Expression (2), and the component of the resonance frequency f in the rectangular wave is expressed by Expression (3). On the other hand, a sine wave having a resonance frequency f is expressed by Expression (4).

Therefore, the amplitude of the component of the resonance frequency f in the rectangular wave is (4 / π) times larger than the amplitude of the sine wave of the resonance frequency f.

  In the embodiment described above, the mirror 13 is the reflection part in the present invention, the elastic connection parts 16a and 16b are the first elastic connection part in the present invention, and the inner gimbal 12 is the first support part and the elastic connection parts 15a and 15b in the present invention. Is the second elastic connecting portion in the present invention, the outer gimbal 11 is the second supporting portion in the present invention, the elastic connecting portions 14a and 14b are the third elastic connecting portions in the present invention, the supporting portion 3 is the third supporting portion in the present invention, The comb electrode portions 17 and 19 are the first comb electrode portions in the present invention, the comb electrode portions 4a and 4b are the second comb electrode portions in the present invention, and the drive signal generating circuit 31 is the voltage applying means in the present invention. The control circuit 35 is voltage application control means in the present invention.

As mentioned above, although one Embodiment of this invention was described, this invention is not limited to the said embodiment, As long as it belongs to the technical scope of this invention, a various form can be taken.
For example, in the above embodiment, the torque curve within the voltage application angle range RV is substantially flat. However, when it is not necessary to apply an electrostatic torque having a shape approximate to a rectangular wave, the torque curve in the voltage application angle range RV may not be flat.

  DESCRIPTION OF SYMBOLS 1 ... Optical scanning device, 2 ... Light beam scanning part, 3 ... Support part, 4 ... Drive part, 4a, 4b ... Comb electrode part, 5 ... Angle detection part, 5a, 5b ... Comb electrode part, 11 ... Out Gimbal, 12 ... Inner gimbal, 13 ... Mirror, 14a, 14b, 15a, 15b, 16a, 16b ... Elastic connection part, 17, 18, 19, 20 ... Combine electrode part, 31 ... Drive signal generating circuit, 32 ... Amplification Circuit 33 ... CV conversion circuit 34 ... Semiconductor laser 35 ... Control circuit

Claims (4)

A reflecting portion having a reflecting surface for reflecting the light beam;
A first support part that has an elastically deformable first elastic connection part that is connected to the reflection part, and that supports the reflection part in a swingable manner with the first elastic connection part as a rotation axis;
A second support portion that has an elastically deformable second elastic connection portion that is connected to the first support portion, and that supports the first support portion in a swingable manner using the second elastic connection portion as a rotation axis;
A third support portion that has an elastically deformable third elastic connection portion that is connected to the second support portion, and that supports the second support portion in a swingable manner with the third elastic connection portion as a rotation axis. The reflection unit, the first support unit, the second support unit, the third support unit, the first elastic connection unit, the second elastic connection unit, and the third elastic connection unit are unique. A three-degree-of-freedom coupled vibration system that torsionally vibrates at a large rotation angle when a periodic external force is applied,
Furthermore, the first comb-shaped electrode portion provided in the second support portion and formed in a comb-tooth shape,
A second comb-shaped electrode portion that is formed in a comb-tooth shape that can mesh with the first comb-shaped electrode portion, and is fixedly installed at a position that can mesh with the first comb-shaped electrode portion;
Voltage applying means for applying a voltage between the first comb-shaped electrode portion and the second comb-shaped electrode portion to generate an electrostatic attractive force between the two electrode portions;
The rotation angle of the second support part with the third elastic coupling part as the rotation axis is the second support part rotation angle, and the torque acting on the second support part by the electrostatic force generated by the voltage application by the voltage application means Is the second support portion torque, the second support portion rotation angle when the second support portion torque is maximum is the torque maximum rotation angle, and the second support portion rotation angle includes the torque maximum rotation angle. An optical scanning device comprising: a voltage application control unit that applies a voltage to the voltage application unit when the voltage application angle is within a preset voltage application angle range that is a range of the second support unit rotation angle. The voltage application angle range is:
A voltage that is the second support portion rotation angle when the second support portion torque is generated with a difference from the maximum value of the second support portion torque being 10% and is larger than the maximum torque rotation angle. The upper limit angle of the applied angle range,
The second support portion rotation angle when the second support portion torque is generated such that the difference from the maximum value of the second support portion torque is 10% and smaller than the torque maximum rotation angle The optical scanning device according to claim 1, wherein the lower limit angle of the application angle range is set. The rotation angle of the reflection part with the first elastic coupling part as a rotation axis is a reflection part rotation angle, and the maximum value of the reflection part rotation angle when the reflection part is swinging is a reflection part target angle. When the reflection part target angle is θm, the second support part rotation angle when the reflection part rotation angle is the reflection part target angle is θj, the upper limit angle is θ1, and the lower limit angle is θ2, the reflection part The optical scanning device according to claim 2, wherein the target angle is set within a range represented by the following expression (1).
{Θ2 × (θm / θj)} <θm <{θ1 × (θm / θj)} (1) As a second support portion torque change rate, a change amount of the second support portion torque with respect to a change of a predetermined change angle set in advance of the second support portion rotation angle.
The second support portion torque change rate within the voltage application angle range is outside the voltage application angle range, and the second support portion torque in a region near the upper limit angle and the lower limit angle of the voltage application angle range. It is configured to be sufficiently smaller than the rate of change,
The voltage application control means causes the voltage application means to apply a voltage only when the rotation angle of the second support portion is within the voltage application angle range. Any one of the optical scanning devices.