WO2021192161A1 - Optical scanning device, control method for optical scanning device, and distance measuring device - Google Patents

Abstract

An optical scanning device (100) is provided with a mirror (10), a mirror actuator (2a, 2b, 53), an adjustment mechanism (51, 52, 61, 62), and a controller (3). The mirror is configured to be rotatable about a rotation axis (X1) and reflect light. The mirror actuator is configured to rotate the mirror about the rotation axis (X1). The adjustment mechanism is configured to change resonant frequency about the rotation axis (X1) of the mirror by applying force to the mirror. The controller is configured to control the mirror actuator and the adjustment mechanism. The controller is configured to control the mirror actuator by a waveform signal. The controller is configured to control the adjustment mechanism to thereby control the resonant frequency about the rotation axis (X1) of the mirror such that the resonant frequency about the rotation axis (X1) of the mirror is separated from a frequency component included in the waveform signal.

Description

Optical scanning device, control method of optical scanning device, and distance measuring device

The present disclosure relates to an optical scanning device, a control method for the optical scanning device, and a distance measuring device.

There is known an optical scanning device that adjusts the light emission direction with a mirror when scanning light. For example, the direction of the light reflected by the mirror can be changed by changing the posture of the mirror on which the light is incident. Japanese Unexamined Patent Publication No. 2019-191226 (Patent Document 1) discloses an optical scanning device that changes the posture of a mirror by a piezoelectric actuator.

In the optical scanning device described in Patent Document 1, the mirror swings in the vertical direction by applying a drive voltage having a serrated waveform to the vertical drive source (more specifically, the piezoelectric actuator), and the horizontal drive source. (More specifically, the piezoelectric actuator) is subjected to a sinusoidal driving voltage, so that the mirror swings in the horizontal direction.

JP-A-2019-191226

The optical scanning apparatus described in Patent Document 1 performs vertical mirror control using a driving voltage having a serrated waveform. In such an optical scanning device, the period during which the scanning speed becomes constant can be lengthened by utilizing the ascending period or descending period of the serrated waveform. However, when the high frequency component contained in the serrated waveform is amplified by the resonance characteristic of the mirror, ringing (that is, distortion of the waveform due to signal vibration) may occur. In Patent Document 1, since an optical scanning device is used for displaying an image, the above ringing causes deterioration in image quality (for example, horizontal stripes).

In the technique described in Patent Document 1, analysis by high-speed Fourier transform (FFT) is performed to obtain the resonance frequency of the mirror (more specifically, the mechanical resonance frequency), and the resonance frequency component of the mirror is the drive signal. The occurrence of ringing is suppressed by adjusting the frequency of the drive signal of the serrated waveform so that it is not included in the waveform (specifically, the voltage waveform).

However, such a technique requires that the drive signal be generated so that the resonance frequency component of the mirror is not included in the waveform of the drive signal, which limits the drive signals that can be used and determines the drive signal. The degree of freedom is reduced.

The present disclosure has been made to solve the above-mentioned problems, and the purpose of the present disclosure is to ensure the degree of freedom in determining the drive signal of the mirror, and to perform unstable operation of the mirror due to a resonance phenomenon (for example,). , Ringing), a control method for the optical scanning device, and a distance measuring device.

The optical scanning device of the present disclosure includes a mirror, a mirror actuator, an adjusting mechanism, and a control device. The mirror is configured to be rotatable around an axis of rotation and is configured to reflect light. The mirror actuator is configured to rotate the mirror around the axis of rotation. The adjusting mechanism is configured to apply a force to the mirror to change the resonance frequency around the rotation axis of the mirror. The control device is configured to control the mirror actuator and the adjusting mechanism. The control device is configured to control the mirror actuator by a waveform signal. The control device is configured to control the resonance frequency around the rotation axis of the mirror so that the resonance frequency around the rotation axis of the mirror is separated from the frequency component included in the waveform signal by controlling the adjustment mechanism. ..

In the above-mentioned optical scanning device and the distance measuring device provided with the above-mentioned optical scanning device, it is possible to suppress unstable operation (for example, ringing) of the mirror due to a resonance phenomenon while ensuring a degree of freedom in determining the drive signal of the mirror. It will be possible.

It is a figure which shows the schematic structure of the optical scanning apparatus which concerns on Embodiment 1 of this disclosure. It is a perspective view which shows the structure of the MEMS mirror shown in FIG. It is a figure which shows the upper surface structure of the MEMS mirror shown in FIG. It is a figure which shows the cross-sectional structure along the IV-IV line in FIG. It is a figure which shows the cross-sectional structure along the VV line in FIG. It is a figure which shows the cross-sectional structure along the VI-VI line in FIG. It is a figure which shows the control method of the optical scanning apparatus which concerns on Embodiment 1 of this disclosure. It is a figure which shows an example of the direction of the electric current and the magnetic field when a mirror is driven in the optical scanning apparatus which concerns on Embodiment 1 of this disclosure. It is a figure which shows the Lorentz force generated by the electric current and the magnetic field shown in FIG. It is a figure which shows the torque generated by the Lorentz force shown in FIG. 2 is a diagram showing the reflection direction of the light beam incident on the MEMS mirror shown in FIGS. 2 to 6. It is a figure which shows the posture detection circuit which comprises the piezoresistive element shown in FIG. It is a figure which shows an example of the drive signal of the mirror in the control method of the optical scanning apparatus which concerns on Embodiment 1 of this disclosure. It is a figure which shows the frequency component included in the drive signal of the mirror shown in FIG. It is a figure which shows an example of the resonance frequency of a mirror which is prone to ringing. It is a figure which shows the transition of the X rotation angle of a mirror when ringing occurs. It is a flowchart which shows the detail of the process which concerns on the determination of the adjustment signal shown in FIG. It is a figure which shows the 1st example of the X rotation mirror characteristic acquired in the process of FIG. It is a figure which shows the 2nd example of the X rotation mirror characteristic acquired in the process of FIG. In the control method of the optical scanning apparatus according to the first embodiment of the present disclosure, an example of the resonance frequency of the mirror when no voltage is applied between the comb tooth electrodes is shown. In the control method of the optical scanning apparatus according to the first embodiment of the present disclosure, an example of the resonance frequency of the mirror when the adjustment signal is applied between the comb tooth electrodes is shown. It is a flowchart which shows the modification of the process shown in FIG. It is a figure which shows the modification of the voltage signal applied between a movable electrode and a fixed electrode in the control method of an optical scanning apparatus. It is a figure which shows the 1st modification of the movable electrode and the fixed electrode shown in FIG. 3 and FIG. It is a figure which shows the 2nd modification of the movable electrode and the fixed electrode shown in FIG. 3 and FIG. It is a figure which shows the modification of the adjustment mechanism shown in FIG. It is a figure which shows the cross-sectional structure along the line XXVII-XXVII in FIG. It is a figure which shows the detailed structure of the piezoelectric structure shown in FIG. 26 and FIG. 27. It is a figure which shows the upper surface structure of the MEMS mirror provided in the optical scanning apparatus which concerns on Embodiment 2 of this disclosure. It is a figure which shows the cross-sectional structure along the XXXX-XXX line in FIG. It is a figure for demonstrating the arrangement of the magnet in the optical scanning apparatus which concerns on Embodiment 2 of this disclosure. It is a figure which shows the modification of the structure of the MEMS mirror shown in FIG. It is a figure which shows the cross-sectional structure along the line XXXXIII-XXXIII in FIG. 32. It is a figure which shows the distance measuring apparatus which concerns on Embodiment 3 of this disclosure. It is a figure which shows the modification of the distance measuring apparatus shown in FIG. 34.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The X-axis, Y-axis, and Z-axis in each figure indicate three axes that are orthogonal to each other. With respect to each of the X-axis, Y-axis, and Z-axis, "+" may be added to the direction indicated by the arrow, and "-" may be added to the opposite direction to indicate each direction. For example, the direction indicated by the arrow on the X-axis may be written as "+ X", and the opposite direction may be written as "-X". Further, the + Z direction may be referred to as “up” and the −Z direction may be referred to as “down”. In the following, the same or corresponding parts in the drawings will be designated by the same reference numerals, and the explanations will not be repeated in principle. Further, it is planned from the beginning of the application that the configurations described in the following embodiments are appropriately combined within a technically consistent range.

Embodiment 1.
FIG. 1 is a diagram showing a schematic configuration of an optical scanning device 100 according to a first embodiment of the present disclosure. With reference to FIG. 1, the optical scanning device 100 includes a MEMS mirror 1, magnets 2a and 2b, and a control device 3. Permanent magnets can be used as the magnets 2a and 2b. Although the details will be described later, the magnets 2a and 2b are arranged so as to sandwich the MEMS mirror 1 and are configured to apply a magnetic field in the Y-axis direction to the MEMS mirror 1. MEMS is an abbreviation for "Micro Electro Mechanical Systems", which incorporates minute electrical elements and minute mechanical elements on a single substrate using various microfabrication technologies such as semiconductor manufacturing technology and laser processing technology. It means a system (or device).

As the control device 3, a microcomputer equipped with a processor, RAM (Random Access Memory), and a storage device can be adopted. As the processor, for example, a CPU (Central Processing Unit) can be adopted. The number of processors included in the control device 3 is arbitrary, and may be one or a plurality. The RAM functions as a working memory that temporarily stores the data processed by the processor. The storage device is configured to be able to store the stored information. In addition to the program, the storage device stores information used in the program (for example, maps, mathematical formulas, and various parameters). In the first embodiment, the processor executes the program stored in the storage device to execute the processes shown in FIGS. 7 and 17, which will be described later. However, various processes in the control device 3 are not limited to execution by software, and can also be executed by dedicated hardware (electronic circuit). FPGA (Field-Programmable Gate Array) may be adopted instead of the microcomputer. It is also possible to realize the same control function by dividing the functions of software and hardware.

FIG. 2 is a perspective view showing the configuration of the MEMS mirror 1. With reference to FIG. 1 and FIG. 2, the MEMS mirror 1 includes a mirror portion 5 for scanning light, hinges (for example, beams 11 and 12) for supporting the mirror portion 5, and a mirror actuator for rotating the mirror portion 5. (Details will be described later). The light incident on the mirror unit 5 is reflected by the mirror unit 5 (more specifically, the mirror 10 described later). The MEMS mirror 1 is configured so that the reflection angle of light can be adjusted by rotating the mirror unit 5, and the light is scanned in a predetermined scanning range. The operation of the MEMS mirror 1 is controlled by the control device 3 (FIG. 1). The control device 3 is configured to control the direction of the light reflected by the mirror unit 5 by causing the hinge to be twisted by the mirror actuator.

The MEMS mirror 1 includes beams 11 and 12, support members 4a and 4b, fixing members 6a and 6b, base materials 7a and 7b, movable electrodes 51 and 52, and fixed electrodes 61 and 62. The base material 7a is a rectangular frame arranged so as to surround the mirror portion 5. The base material 7b is a rectangular plate located below the mirror portion 5. A gap is provided between the base material 7a and the base material 7b. Each of the support members 4a and 4b and the fixing members 6a and 6b is arranged on the base material 7a. However, an insulating layer 55 is arranged between the base material 7a and the support members 4a and 4b, between the base material 7a and the fixing members 6a and 6b, and between the mirror portion 5 and the base material 7b. ing.

FIG. 3 is a diagram showing the upper surface structure of the MEMS mirror 1. FIG. 4 is a diagram showing a cross-sectional structure along the IV-IV line in FIG. FIG. 5 is a diagram showing a cross-sectional structure along the VV line in FIG. FIG. 6 is a diagram showing a cross-sectional structure along the VI-VI line in FIG.

With reference to FIGS. 3 to 6, the mirror portion 5 includes a base material 50 and a mirror 10 provided on the base material 50. The mirror portion 5 has a mirror 10 on its surface. The mirror 10 is configured to be rotatable around the X-axis and to reflect light. The mirror 10 is, for example, a rectangular reflective film. Since the mirror 10 constitutes a part of the mirror portion 5, when the mirror portion 5 rotates, the mirror 10 also rotates. As the mirror 10 rotates around the X axis, the reflection angle of the light incident on the mirror 10 changes.

Beams 11 and 12 are connected to the first end (end on the −X side) and the second end (end on the + X side) corresponding to both ends of the mirror portion 5 in the X-axis direction, respectively. In the first embodiment, each of the beam 11 and the beam 12 has a long shape in the X-axis direction and functions as a rotation axis of the mirror 10. More specifically, each of the beam 11 and the beam 12 functions as a torsion type elastic hinge. The axis X1 in FIG. 3 is an axis parallel to the X axis and indicates the position of the rotation axis of the mirror 10. Each of the beam 11 and the beam 12 is formed along the axis X1. By twisting each of the beam 11 and the beam 12 around the axis X1, the mirror 10 can rotate around the axis X1 (hereinafter, also referred to as “X1 rotation”). In the first embodiment, the base material 7a is fixed to a housing (not shown), and the mirror portion 5 (including the mirror 10) rotates relative to the base material 7a.

The MEMS mirror 1 has a structure that is line-symmetrical with respect to the axis X1. The support member 4a is arranged on the side of the base material 7a on the −X side, and is connected to the first end of the mirror portion 5 via the beam 11. The beam 11 may be formed integrally with the support member 4a and the base material 50, or may be formed separately from the support member 4a and the base material 50 and joined to each of the support member 4a and the base material 50. .. The support member 4b is arranged on the + X side of the base material 7a and is connected to the second end of the mirror portion 5 via the beam 12. The beam 12 may be formed integrally with the support member 4b and the base material 50, or may be formed separately from the support member 4b and the base material 50 and joined to each of the support member 4b and the base material 50. ..

Piezoresistive elements 91 and 92 are provided at the boundary between the support member 4a and the beam 11. The piezoresistive element 91 is located on the + Y side of the shaft X1, and the piezoresistive element 92 is located on the −Y side of the shaft X1. Piezoresistive elements 93 and 94 are provided at the boundary between the support member 4b and the beam 12. The piezoresistive element 93 is located on the + Y side of the shaft X1, and the piezoresistive element 94 is located on the −Y side of the shaft X1. The piezoresistive elements 91, 92, 93, 94 are electrically insulated from each of the mirror 10, the movable electrodes 51, 52, the fixed electrodes 61, 62, and the beams 11, 12. Although details will be described later, in the first embodiment, the piezoresistive elements 91, 92, 93, 94 are connected so as to form a bridge circuit (see FIG. 12). The control device 3 (FIG. 1) is configured to acquire a rotation position (hereinafter, also referred to as “X rotation angle”) around the axis X1 of the mirror 10 based on the midpoint voltage of the bridge circuit. In the non-rotated state, the X rotation angle of the mirror 10 is "0".

Movable electrodes 51 and 52 are provided at the third end (+ Y side end) and the fourth end (-Y side end) corresponding to both ends of the mirror portion 5 in the Y-axis direction, respectively. The movable electrodes 51 and 52 (including the comb tooth electrodes described later) are electrically connected to each of the mirror 10, the beams 11, 12 and the support members 4a, 4b, and are electrically equipotentially connected to these. be. On the other hand, the movable electrodes 51 and 52 are electrically insulated from the fixed electrodes 61 and 62, the drive wiring 53, and the piezoresistive elements 91, 92, 93, and 94, respectively. Each of the movable electrodes 51 and 52 is provided on the side surface of the base material 50. Each of the movable electrodes 51 and 52 may be formed integrally with the base material 50, or may be formed separately from the base material 50 and bonded to the base material 50. Since the movable electrodes 51 and 52 and the mirror portion 5 (including the mirror 10 and the base material 50) change their postures integrally, the movable electrodes 51 and 52 also rotate in conjunction with the X1 rotation of the mirror 10.

The fixing members 6a and 6b are arranged on the + Y side and the −Y side of the base material 7a, respectively. The fixing members 6a and 6b are not directly connected to the mirror portion 5. Since the rotational force of the mirror portion 5 is absorbed by the elastic deformation of each of the beams 11 and 12, it is not transmitted to the base material 7a. Therefore, the fixing members 6a and 6b are not interlocked with the X1 rotation of the mirror 10. The fixed electrode 61 is provided on the side surface of the fixing member 6a on the −Y side. The fixed electrode 61 may be formed integrally with the fixing member 6a, or may be formed separately from the fixing member 6a and joined to the fixing member 6a. The fixed electrode 62 is provided on the + Y side side surface of the fixing member 6b. The fixed electrode 62 may be formed integrally with the fixing member 6b, or may be formed separately from the fixing member 6b and joined to the fixing member 6b. Since the fixed electrodes 61 and 62 are supported by the fixing members 6a and 6b, they are not interlocked with the X1 rotation of the mirror 10. Although the wiring in the MEMS mirror 1 is omitted in FIGS. 3 to 6, the fixed electrode 61 (including each comb tooth electrode described later) and the fixed electrode 62 (including each comb tooth electrode described later) are They are electrically connected to each other and are electrically equipotential. On the other hand, the fixed electrodes 61 and 62 are electrically insulated from the mirror 10, the movable electrodes 51 and 52, the drive wiring 53, and the piezoresistive elements 91, 92, 93, 94, respectively.

In the first embodiment, each of the movable electrodes 51 and 52 and the fixed electrodes 61 and 62 is formed in a comb-teeth shape. The side surface of the mirror portion 5 on which the movable electrode 51 is formed (the side surface on the + Y side) and the side surface of the fixing member 6a on which the fixed electrode 61 is formed (the side surface on the −Y side) face each other. Further, since the comb teeth of both the movable electrode 51 and the fixed electrode 61 are arranged alternately, each comb tooth electrode of the movable electrode 51 and each comb tooth electrode of the fixed electrode 61 face each other. The side surface of the mirror portion 5 (the side surface on the −Y side) on which the movable electrode 52 is formed and the side surface (the side surface on the + Y side) of the fixing member 6b on which the fixed electrode 62 is formed face each other. Further, since the comb teeth of both the movable electrode 52 and the fixed electrode 62 are arranged alternately, each comb tooth electrode of the movable electrode 52 and each comb tooth electrode of the fixed electrode 62 face each other. By adopting the comb tooth electrode structure as described above, the capacitance between the movable electrodes 51 and 52 and the fixed electrodes 61 and 62 can be increased. Therefore, a large electrostatic force can be generated between the electrodes with a small applied voltage. Details will be described later, but in the first embodiment, the fixed electrodes 61 and 62 are grounded, and a positive potential is applied to the movable electrodes 51 and 52.

The drive wiring 53 is provided on the support member 4a, the beam 11, and the base material 50. However, an insulating film 54 is arranged between each of the support member 4a, the beam 11, and the base material 50 and the drive wiring 53. The drive wiring 53 is electrically insulated from the mirror 10, the movable electrodes 51, 52, the fixed electrodes 61, 62, the beams 11, 12, and the piezoresistive elements 91, 92, 93, 94 by the insulating film 54. There is. The electrode pads 56 and 57 are provided at the + Y side and −Y side ends of the support member 4a, respectively, and are located at both ends of the drive wiring 53. The drive wiring 53 is a wiring that connects the electrode pad 56 and the electrode pad 57. The drive wiring 53 crosses the beam 11 from the support member 4a to reach the mirror portion 5, goes around the outer edge portion of the mirror portion 5 (around the mirror 10) once, and returns to the support member 4a across the beam 11 again. By applying a voltage between the electrode pad 56 and the electrode pad 57, a current flows through the drive wiring 53.

As shown in FIGS. 2 to 6, the MEMS mirror 1 includes a base material 7a, a support member 4a (first support member) provided on the base material 7a via an insulating layer 55, and a support member 4b (first support member). 2 support member), a fixing member 6a (first fixing member) and a fixing member 6b (second fixing member) provided on the base material 7a via an insulating layer 55, a mirror portion 5, and a beam 11 (first fixing member). 1 beam) and 12 (second beam) are provided. The first end (-X side end) and the second end (+ X side end) located at both ends of the mirror portion 5 in the X-axis direction (direction of the rotation axis) are supported members 4a via beams 11 and 12, respectively. And 4b. The movable electrode 51 (first movable electrode) and the movable electrode 52 (second movable electrode) are the third ends (+ Y side ends) located at both ends of the mirror portion 5 in the Y-axis direction (direction orthogonal to the rotation axis), respectively. ) And the fourth end (the end on the −Y side). Further, the fixed electrode 61 (first fixed electrode) supported by the fixed member 6a and the fixed electrode 62 (second fixed electrode) supported by the fixed member 6b face the movable electrode 51 and the movable electrode 52, respectively. It is arranged to do. Each of the beams 11 and 12 functions as a rotation axis of the mirror portion 5 (including the mirror 10). The mirror portion 5 has a structure that is line-symmetrical with respect to the axis X1 (rotational axis). Further, the movable electrode 51 and the fixed electrode 61, and the movable electrode 52 and the fixed electrode 62 are formed line-symmetrically with respect to the axis X1 (rotational axis).

The structure of the MEMS mirror 1 shown in FIGS. 2 to 6 can be manufactured by using, for example, an SOI (Silicon On Insulator) substrate. The SOI substrate is a substrate having a silicon substrate, a surface silicon layer (for example, a single crystal silicon layer), and an insulating layer (for example, a silicon oxide layer or a silicon nitride layer) formed between them. In the MEMS mirror 1 using the SOI substrate, the insulating layer 55 corresponds to the insulating layer of the SOI substrate. Semiconductor microfabrication technology and MEMS device technology can be applied to the manufacture of the MEMS mirror 1. The base materials 7a and 7b can be formed by processing the silicon substrate of the SOI substrate. By repeating processes such as film formation, doping (for example, ion implantation or thermal diffusion), patterning (for example, patterning by lithography), and etching, the mirror 10, the beams 11, 12, the support members 4a, 4b, and the fixing member 6a are repeated. , 6b, movable electrodes 51, 52, fixed electrodes 61, 62, drive wiring 53, electrode pads 56, 57, and piezo resistance elements 91, 92, 93, 94 can be formed. By a known MEMS device technology, the base material 50 of the mirror portion 5, the beams 11 and 12, the movable electrodes 51 and 52, and the support members 4a and 4b can be easily integrally molded. The mirror 10 is formed of a metal film such as an Au film. Each of the movable electrodes 51 and 52 and the fixed electrodes 61 and 62 can be formed by, for example, imparting conductivity to the surface silicon layer by impurities. Each of the movable electrodes 51 and 52 and the fixed electrodes 61 and 62 may be formed of conductive silicon to which B (boron) is added as an impurity. However, the type of impurities can be changed as appropriate, and P (phosphorus) may be used instead of B (boron). The drive wiring 53 and the electrode pads 56 and 57 are formed of, for example, Al (aluminum). However, the present invention is not limited to this, and at least one of the drive wiring 53 and the electrode pads 56 and 57 may be formed of Au (gold). The piezoresistive elements 91, 92, 93, 94 can be formed, for example, by diffusing B (boron) as an impurity in the surface silicon layer so that the resistance value changes according to the applied stress. can. However, the type of impurities can be changed as appropriate, and P (phosphorus) may be used instead of B (boron). It is also possible to fabricate the structure of the MEMS mirror 1 shown in FIGS. 2 to 6 by using a known substrate bonding technique and film forming technique without using an SOI substrate. Further, the material of each part in the MEMS mirror 1 is not limited to the above-mentioned material, and can be changed as appropriate. However, as the material of the mirror 10, a material that easily reflects the scanned light is suitable. The material of the mirror 10 may be determined according to the wavelength of the light being scanned. As the electrode material, a material that can withstand the application of voltage is suitable. As the wiring material, a material having low electrical resistance is suitable. Since the piezoresistive elements 91, 92, 93, and 94 are used for detecting the attitude of the mirror 10, a material whose electrical resistance changes according to a stress change accompanying the rotation of the mirror 10 is suitable as a material for each piezoresistive element. ing.

Although the drawing of the wiring from the MEMS mirror 1 is not shown in FIGS. 2 to 6, the movable electrodes 51 and 52, the fixed electrodes 61 and 62, the electrode pads 56 and 57, and the piezo resistance elements 91, 92, 93, Each of the 94s may be electrically connected to an external circuit (eg, power supply circuit or detection circuit) by wiring. The electrical connection may be made by wire bonding. In the first embodiment, the control device 3 (FIG. 1) is electrically connected to each of the movable electrodes 51 and 52, the fixed electrodes 61 and 62, and the electrode pads 56 and 57. The control device 3 is configured so that a voltage signal can be applied between the electrode pad 56 and the electrode pad 57. Further, the control device 3 is configured so that a voltage signal can be applied between the movable electrodes 51 and 52 and the fixed electrodes 61 and 62. The piezoresistive elements 91, 92, 93, 94 are connected by wiring provided outside the MEMS mirror 1 to form a bridge circuit (see FIG. 12 described later).

FIG. 7 is a diagram for explaining the process executed by the control device 3 shown in FIG. With reference to FIG. 7, scanning conditions such as a scanning range and a driving frequency are input to the control device 3. The scanning range is the range in which light is scanned by the MEMS mirror 1. The drive frequency corresponds to the frequency of the drive signal of the mirror 10. The frame rate (ie, the number of frames processed per unit time) tends to change depending on the drive frequency. The drive frequency is determined, for example, to obtain the desired frame rate. The drive frequency can be arbitrarily set, and may be, for example, about several tens of Hz.

In step S1, the control device 3 determines a current signal (hereinafter, also referred to as “drive current signal”) to be passed through the drive wiring 53 in order to scan light in the scanning range. The drive current signal is a waveform signal and corresponds to an example of a “waveform signal for controlling a mirror actuator”. The frequency of the fundamental wave included in the drive current signal corresponds to an example of "drive frequency". When a current flows through the drive wiring 53, the mirror 10 is driven and the X rotation angle of the mirror 10 changes. The drive current signal is determined so that, for example, the light reflected by the mirror 10 is scanned in a desired direction. In step S2, the control device 3 generates a voltage signal (hereinafter, also referred to as “drive voltage signal”) for flowing the drive current signal determined in step S1 to the drive wiring 53. The current flowing through the drive wiring 53 is controlled by the drive voltage signal.

FIG. 8 is a diagram showing an example of the directions of the current and the magnetic field (magnetic flux density) when the mirror 10 is driven. With reference to FIG. 8, in this example, a magnetic field in the Y-axis direction is applied by the magnets 2a and 2b. The direction of the magnetic flux density B of the magnetic field is the direction from the magnet 2a to the magnet 2b (direction of −Y). A current flows from the electrode pad 57 to the electrode pad 56 in the drive wiring 53. At the edge R1 on the + Y side (the movable electrode 51 side shown in FIG. 3) of the mirror portion 5, the portion parallel to the X axis of the drive wiring 53 (hereinafter referred to as “R1 wiring”) has a direction in which the current J1 is −X. Flow to. At the edge R2 of the mirror portion 5 on the −Y side (the movable electrode 52 side shown in FIG. 3), the portion parallel to the X axis of the drive wiring 53 (hereinafter referred to as “R2 wiring”) has a direction in which the current J2 is + X. Flow to. The vectors of the currents J1 and J2 and the vector of the magnetic flux density B are orthogonal to each other.

FIG. 9 is a diagram showing the Lorentz force generated by the current and the magnetic field (magnetic flux density) shown in FIG. With reference to FIG. 9, at the edge R1 of the mirror portion 5, a Lorentz force Fmag1 in the + Z direction is generated by the current J1 flowing through the R1 wiring and the magnetic flux density B. At the edge R2 of the mirror portion 5, a Lorentz force Fmag2 in the direction of −Z is generated by the current J2 flowing through the R2 wiring and the magnetic flux density B.

FIG. 10 is a diagram showing the torque generated by the Lorentz force shown in FIG. With reference to FIG. 9 and FIG. 10, the Lorentz forces Fmag1 and Fmag2 shown in FIG. 9 generate a torque Tmag around the axis X1. The torque Tmag twists the beams 11 and 12 that support the mirror portion 5, and the mirror portion 5 (including the mirror 10 shown in FIGS. 3 to 6) rotates around the axis X1.

With reference to FIGS. 8 to 10, the magnitude of the Lorentz force Fmag generated when a current J is passed from the electrode pad 57 to the electrode pad 56 through the drive wiring 53 is determined by the magnetic flux density as shown in the following equation (1). It corresponds to the product of B, the length L of the portion of the drive wiring 53 parallel to the X axis (see FIG. 8), and the current J. Since the current J1 and the current J2 have the same magnitude (J) and the R1 wiring and the R2 wiring have the same length (L), the Lorentz forces Fmag1 and Fmag2 have the same magnitude (Fmag).

Fmag = B × J × L… (1)
As shown in the following equation (2), the magnitude of the torque Tmag around the shaft X1 is the point where the Lorentz force Fmag generated at the two locations of the R1 wiring and the R2 wiring and the force applied from the shaft X1 (rotating shaft) are applied (that is,). , Corresponds to the product of the distance Rmag to the above two places). Since the MEMS mirror 1 has a structure that is line-symmetrical with respect to the axis X1, the distance between the R1 wiring and the axis X1 and the distance between the R2 wiring and the axis X1 have the same dimensions (Rmag).

Tmag = 2 x Fmag x Rmag ... (2)
When the mirror portion 5 is rotated around the X axis by the torque Tmag, the beams 11 and 12 supporting the mirror portion 5 are twisted. At this time, due to the restoring force of the beams 11 and 12 (that is, the force of the beams 11 and 12 to return to the original state), a torque Tmec opposite to the torque Tmag is applied to the mirror portion 5. As shown in the following equation (3), the torque Tmec corresponds to the product of the spring constant Kmec in the twisting direction of the beams 11 and 12 and the X rotation angle θx of the mirror portion 5 (or the mirror 10).

Tmec = -Kmec x θx ... (3)
When the above-mentioned drive current signal flows through the drive wiring 53, the mirror unit 5 changes its posture so that the torque Tmag due to the Lorentz force and the torque Tmec due to the restoring force of the beams 11 and 12 are balanced. The control device 3 (FIG. 1) can control the posture (more specifically, the X rotation angle) of the mirror unit 5 by the drive current signal. As the mirror portion 5 rotates, the mirror 10 (FIGS. 3 to 6) included in the mirror portion 5 also rotates.

FIG. 11 is a diagram showing the reflection direction of the light beam incident on the MEMS mirror 1 of the optical scanning device 100. With reference to FIGS. 1 and 2, the light beam incident on the MEMS mirror 1 of the optical scanning apparatus 100 is reflected by the mirror 10 and then emitted from the optical scanning apparatus 100. When the mirror 10 rotates X1, the reflecting surface of the mirror 10 is tilted by an X rotation angle θx from the reference surface (that is, the reflecting surface when the mirror 10 is not rotated). As a result, the optical axis of the light beam reflected by the mirror 10 is only 2θx (that is, an angle twice the X rotation angle θx) from the reference direction (that is, the reflection direction when the mirror 10 is not rotated). It will tilt.

As described above, the direction of the light emitted from the optical scanning device 100 (FIG. 1) changes according to the X rotation angle θx of the mirror 10. The control device 3 (FIG. 1) can control the X rotation angle θx of the mirror 10 by the drive current signal. The control device 3 controls the mirror actuator (including the magnets 2a and 2b and the drive wiring 53) with a drive current signal (that is, a periodic signal), whereby the mirror unit 5 (including the mirror 10) is determined. The posture is repeated periodically. More specifically, the mirror 10 swings around the axis X1 by repeating forward rotation and reverse rotation. As a result, the optical axis of the light emitted from the optical scanning device 100 periodically repeats a fixed direction. The optical scanning device 100 can scan light by such mirror control.

The posture of the mirror unit 5 (including the mirror 10) is detected by the piezoresistive elements 91, 92, 93, 94 shown in FIGS. 3 and 6. FIG. 12 is a diagram showing a posture detection circuit composed of the piezoresistive elements 91, 92, 93, 94. With reference to FIG. 12 together with FIGS. 3 and 6, the piezoresistive elements 91, 92, 93, 94 are connected by wiring to form a bridge circuit (posture detection circuit) as shown in FIG. As shown in FIGS. 3 and 6, the piezoresistive elements 91, 92, 93, 94 are arranged at the roots of the beams 11 and 12 ( support members 4a, 4b side), and the X rotation angle θx of the mirror 10 is set. When changed, stress is generated in the piezoresistive elements 91, 92, 93, 94. Due to such a stress change, the resistance value of each piezoresistive element changes. When the beams 11 and 12 are twisted by the X1 rotation of the mirror 10, the stress applied to the piezoresistive elements 91 and 94 and the piezoresistive elements 92 and 93 is opposite, and the direction of resistance change (+/-) is also The opposite is true. When a constant voltage is applied to the bridge circuit shown in FIG. 12, a voltage Vc corresponding to the resistance value of each piezoresistive element is output to the midpoint of the bridge circuit. Since the resistance value of each piezoresistive element changes according to the twist angle of the beams 11 and 12 (that is, the X rotation angle of the mirror 10), the control device 3 (FIG. 1) is output to the midpoint of the bridge circuit. The X rotation angle of the mirror 10 can be acquired based on the voltage Vc.

By the way, when the mirror 10 is driven by the drive current signal, the resonance frequency around the axis X1 of the mirror 10 (hereinafter, also referred to as "X1 resonance frequency") is close to the frequency of the harmonics included in the drive current signal. , Ringing is likely to occur. Therefore, in the optical scanning apparatus 100 according to the first embodiment, ringing is suppressed by controlling the X1 resonance frequency of the mirror 10 by the adjustment signal described below.

With reference to FIG. 7 again, in step S3, the control device 3 applies a voltage signal (hereinafter, “adjustment signal”) applied between the movable electrodes 51 and 52 and the fixed electrodes 61 and 62 (that is, between the comb tooth electrodes). Also called). The X1 resonance frequency of the mirror 10 can be controlled by this adjustment signal. Details will be described later, but in step S3, the target value of the X1 resonance frequency is first determined, and the adjustment signal is determined so that the X1 resonance frequency of the mirror 10 approaches the target value. The control device 3 generates the adjustment signal determined in step S3 in step S4.

As shown in FIGS. 3 to 5, the comb teeth of both the movable electrode 51 and the fixed electrode 61 are arranged alternately, so that each comb tooth electrode of the movable electrode 51 and each comb tooth electrode of the fixed electrode 61 are arranged alternately. Is opposed to. Further, by arranging the comb teeth of both the movable electrode 52 and the fixed electrode 62 in a staggered manner, each comb tooth electrode of the movable electrode 52 and each comb tooth electrode of the fixed electrode 62 face each other. Considering the capacitance C between one set of facing comb-tooth electrodes in a parallel flat plate model, the capacitance C is proportional to the facing area of the comb-tooth electrodes and inversely proportional to the gap between the comb-tooth electrodes. Of these, the facing area of the comb tooth electrodes changes according to the X rotation angle θx of the mirror 10. When a voltage Vele is applied between the comb-tooth electrodes, the amount of change in capacitance with respect to the X rotation angle θx of the mirror 10 (∂C / ∂θx: differential value of capacitance rotation angle) and between the comb-tooth electrodes The generated electrostatic force Feel has a relationship as shown in the following formula (4). The positive / negative voltage between the comb tooth electrodes can be set arbitrarily, but in the first embodiment, the fixed electrodes 61 and 62 are negative (grounded) and the movable electrodes 51 and 52 are positive.

Feel = (-1 / 2) × (∂C / ∂θx) × (Vele) ² … (4)
As described above, an electrostatic force Feel proportional to the square of the voltage Vele is generated between the comb tooth electrodes. The electrostatic force Feel acts in the direction of reducing the absolute value of the X rotation angle θx of the mirror 10. A portion where the comb-tooth electrodes of the movable electrode 51 and the fixed electrode 61 face each other (hereinafter, also referred to as a “first comb-tooth facing portion”) and a portion where the comb-tooth electrodes of the movable electrode 52 and the fixed electrode 62 face each other (hereinafter, also referred to as a “first comb-tooth facing portion”). , Also referred to as "second comb tooth facing portion"), electrostatic force Feel is generated at two locations. Due to these electrostatic force Feels, a torque tele is generated around the axis X1. The direction of the torque TV is opposite to that of the torque Tmag (FIG. 10) described above, and is the same as the direction of the torque Tmec due to the mechanical restoring force of the beams 11 and 12. The torque Tele acts to increase the restoring force of the beams 11 and 12 with respect to the X1 rotation of the mirror 10. As shown in the following formula (5), the magnitude of the torque tele is determined by the electrostatic force Feel generated at the two locations and the point where the force is applied from the axis X1 (rotating axis) (that is, the first and second comb tooth facing portions). ) Corresponds to the product of the distance Rele. Since the MEMS mirror 1 has a structure that is axisymmetric with respect to the axis X1, the distance between the first comb tooth facing portion and the axis X1 and the distance between the second comb tooth facing portion and the axis X1 are the same dimensions ( Rele).

Tele = 2 x Feel x Relay ... (5)
The magnitude of the electrostatic force Feel is basically proportional to the X rotation angle θx of the mirror 10. The torque Tele is also proportional to the X rotation angle θx of the mirror 10. Therefore, the electrostatic force Feel and the torque Tele can be expressed by the following equations (6) and (7), respectively. It should be noted that each of "α" in the equation (6) and "Kele" in the equation (7) is a proportionality constant.

Feel = −α × θx × (Vele) ² … (6)
Tele = -Kele x θx ... (7)
As can be seen from the formulas (5) to (7), Kele can be expressed by the following formula (8).

Kele = 2α × Relay × (Vele) ² … (8)
Kele can be equivalently treated as a spring constant for the X1 rotation of the mirror 10. Since the Kele is proportional to the square of the voltage Vele between the comb tooth electrodes, the Kele (spring constant) can be controlled by the above-mentioned adjustment signal. When a voltage (adjustment signal) is applied between the comb tooth electrodes while the mirror 10 is rotated X1, torque is applied in the direction of restoring the posture of the mirror 10 (that is, the direction of reducing the absolute value of the X rotation angle θx). Tele occurs. Applying a voltage between the comb-tooth electrodes can be treated as equivalent to increasing the rigidity of the beams 11 and 12 and increasing the spring constant with respect to the X1 rotation of the mirror 10.

When no voltage (adjustment signal) is applied between the comb tooth electrodes, the X1 resonance frequency of the mirror 10 is determined by the mechanical properties of the structure that supports the mirror 10. The X1 resonance frequency fmec of the mirror 10 when no voltage is applied between the comb tooth electrodes is the moment of inertia M around the X axis of the mirror 10 and the spring around the X axis of the mirror 10 as shown in the following equation (9). It can be represented by the constant Kmec.

fmec = (1/2) × π × √ (Kmec / M)… (9)
On the other hand, when a voltage (adjustment signal) is applied between the comb-tooth electrodes, a torque tele is generated by the electrostatic force between the comb-tooth electrodes, and the torque tele increases the spring constant around the X-axis of the mirror 10. At this time, the spring constant around the X-axis of the mirror 10 is increased by the Kele represented by the above equation (8). The X1 resonance frequency feel of the mirror 10 when a voltage is applied between the comb tooth electrodes can be expressed by the following equation (10).

feel = (1/2) × π × √ ((Kmec + Kele) / M)… (10)
As can be seen from the equations (9) and (10), the X1 resonance frequency of the mirror 10 is increased by applying a voltage (adjustment signal) between the comb tooth electrodes.

With reference to FIG. 7 again, in step S5, the control device 3 applies the drive voltage signal generated in step S2 to both ends (electrode pads 56, 57) of the drive wiring 53, and is generated in step S4. The adjustment signal is applied between the movable electrodes 51 and 52 and the fixed electrodes 61 and 62 (that is, between the comb tooth electrodes). When a drive voltage signal is applied to both ends of the drive wiring 53, a drive current signal flows through the drive wiring 53.

FIG. 13 is a diagram showing an example of a drive signal of the mirror 10 (that is, a drive current signal flowing through the drive wiring 53). In FIG. 13, the horizontal axis represents time and the vertical axis represents current value. With reference to FIG. 13, this drive signal is a serrated waveform signal. The rising period of the serrated waveform (for example, the period during which the mirror 10 rotates forward) can be used to lengthen the period during which the scanning speed becomes constant. The drive frequency (frequency of the drive signal) is fd, and the drive cycle (cycle of the drive signal) is 1 / fd.

FIG. 14 is a diagram showing an example of a frequency component included in the drive signal of the mirror 10 (that is, the drive current signal flowing through the drive wiring 53). In FIG. 14, the horizontal axis represents frequency and the vertical axis represents amplitude. With reference to FIG. 14, this drive signal includes a fundamental wave frequency fd and a plurality of harmonic frequencies nfd. The frequency of the harmonic is n times the frequency (fd) of the fundamental wave (nfd), and n is an integer of 2 or more. For example, the frequency of the second harmonic is twice the frequency of fd (2fd). The frequency of the third harmonic is three times the frequency of fd (3fd).

FIG. 15 is a diagram showing an example of the X1 resonance frequency of the mirror 10 in which ringing is likely to occur. In FIG. 15, the horizontal axis represents frequency and the vertical axis represents amplitude. With reference to FIG. 15, in this example, the X1 resonance frequency fo of the mirror 10 coincides with the frequency (3fd) of the third harmonic. When the X1 resonance frequency fo of the mirror 10 matches the frequency (nfd) of the harmonics included in the drive signal of the mirror 10, the rotational displacement of the mirror 10 is amplified by the resonance phenomenon, and ringing is likely to occur. FIG. 16 is a diagram showing a transition of the X rotation angle θx of the mirror 10 when ringing occurs. With reference to FIG. 16, when ringing occurs, the waveform generated by the resonance phenomenon (for example, the waveform having a period of 1/3 fd) is superimposed on the waveform of the desired X rotational displacement (θx), and the mirror 10 The X rotation angle θx deviates from a desired angle. Therefore, when ringing occurs, the scanning accuracy of light is impaired.

In the optical scanning device 100 (FIG. 1) according to the first embodiment, the control device 3 has a frequency component included in the drive signal (drive current signal) of the mirror 10 by the processing of steps S3 to S5 of FIG. 7 described above. The X1 resonance frequency of the mirror 10 is controlled so that the X1 resonance frequency of the mirror 10 is separated from the mirror 10. FIG. 17 is a flowchart showing details of the process related to the determination of the adjustment signal executed in S3 of FIG. 7.

With reference to FIGS. 1 to 6, the control device 3 has a frequency response characteristic (in step S10) with respect to the X1 rotational displacement of the mirror 10 when no voltage (adjustment signal) is applied between the comb tooth electrodes. Hereinafter, it is also referred to as "X rotation mirror characteristic").

In the first embodiment, the control device 3 acquires the X-rotation mirror characteristic obtained in advance and stored in the storage device (not shown) by reading it from the storage device in step S10. A plurality of X-rotating mirror characteristics measured in different environments (for example, temperature) are prepared in the storage device, and in step S10, the control device 3 reads the X-rotating mirror characteristics corresponding to the current environment from the storage device. You may. The control device 3 may periodically measure the X-rotation mirror characteristic and update the data in the storage device with the measured data. For example, the control device 3 may measure the X rotation mirror characteristic each time the optical scanning device 100 (including the control device 3) is activated. The X-rotating mirror characteristic can be obtained by frequency sweeping the drive current signal flowing through the drive wiring 53 as a sine wave in a state where no voltage (adjustment signal) is applied between the comb-tooth electrodes. The amplitude of the drive current signal used when obtaining the X-rotation mirror characteristic may be a value close to the amplitude of the drive current signal used during optical scanning in order to reduce the influence of the hard spring effect and the soft spring effect. However, the amplitude is not limited to this, and the amplitude of the drive current signal used when obtaining the X rotation mirror characteristic is basically arbitrary.

When the mirror 10 is rotated X1 while changing the drive frequency, the X1 rotation displacement (waveform) of the mirror 10 changes according to the drive frequency. By measuring the X1 rotational displacement (waveform) of the mirror 10 for each drive frequency, the X rotational mirror characteristics described below can be acquired. FIG. 18 is a diagram showing a first example of the X rotation mirror characteristic. With reference to FIG. 18, the X-rotation mirror characteristic according to the first example shows the relationship between the frequency and the amplitude of the X1 rotation displacement (waveform) of the mirror 10. FIG. 19 is a diagram showing a second example of the X rotation mirror characteristic. With reference to FIG. 19, the X-rotation mirror characteristic according to the second example shows the relationship between the frequency and the phase of the X1 rotation displacement (waveform) of the mirror 10.

With reference to FIGS. 1 to 6 again, in step S11, the control device 3 acquires the mechanical X1 resonance frequency fmec of the mirror 10 based on the X rotation mirror characteristic acquired in step S10. .. For example, in the X rotation mirror characteristic shown in FIG. 18, the amplitude of the X1 rotation displacement (waveform) of the mirror 10 shows a peak when the drive frequency becomes fmec. Further, in the X rotation mirror characteristic shown in FIG. 19, when the drive frequency becomes fmec, the phase of the X1 rotation displacement (waveform) of the mirror 10 changes abruptly. The control device 3 can acquire the mechanical X1 resonance frequency fmec of the mirror 10 by using at least one of the X rotation mirror characteristic shown in FIG. 18 and the X rotation mirror characteristic shown in FIG. 19, for example. .. The mechanical X1 resonance frequency fmec of the mirror 10 may be obtained in advance and stored in the storage device of the control device 3.

In step S12, the control device 3 acquires the drive current signal determined in step S1 of FIG. Then, in step S13, the control device 3 sets a target value of the X1 resonance frequency (hereinafter, also referred to as “target X frequency”) so that the X1 resonance frequency of the mirror 10 is separated from the frequency component included in the drive current signal. decide. More specifically, the control device 3 uses the following equation (11) based on the drive frequency fd corresponding to the frequency of the fundamental wave included in the drive current signal and the mechanical X1 resonance frequency fmec of the mirror 10. Find the N that meets.

(N-0.5) × fd <fmec ≦ (N + 0.5) × fd… (11)
“N” in the equation (11) indicates the order (integer of 1 or more) of the frequency component included in the drive current signal. The control device 3 uses the equation (11) to specify the order (N) of the frequency component closest to fmec in the drive current signal. Then, the control device 3 calculates the target X frequency according to the following equation (12) using N specified by the equation (11).

Target X frequency = (N + 0.5) x fd ... (12)
Subsequently, in step S14, the control device 3 increases the Kele (spring constant due to the electrostatic force Fele) and the Vele (between the comb tooth electrodes) so that the feel represented by the above equation (10) matches the target X frequency. Calculate the applied voltage). The control device 3 can obtain the Kele from the file (target X frequency) by using the above equation (10). The control device 3 can obtain a Vele (for example, a DC voltage) from the Kele by using the above equation (8). The constants (α, Relay, M, and Kmec) in each equation are obtained in advance and stored in the storage device of the control device 3.

The Vele (DC voltage signal) determined as described above corresponds to the adjustment signal. In step S5 of FIG. 7, the X1 resonance frequency of the mirror 10 is controlled by the adjustment signal determined as described above. As a result, the X1 resonance frequency of the mirror 10 is controlled to the target X frequency.

As described above, the control device 3 of the optical scanning device 100 according to the first embodiment executes the control method of the optical scanning device shown in FIGS. 7 and 17. The control method of this optical scanning device is to determine the drive current signal (waveform signal for controlling the mirror actuator) (step S1 in FIG. 7), the X1 resonance frequency of the mirror 10, and the X1 resonance frequency. The target X frequency (target value of the resonance frequency around the axis X1 of the mirror 10) is determined so that the difference from the frequency component of the close drive current signal becomes a predetermined target value (for example, 0.5 fd) (FIG. 17). Step S13), the drive current signal is passed through the drive wiring 53 to rotate the mirror 10 by X1, and a force is applied to the mirror 10 by the above adjustment signal to change the X1 resonance frequency of the mirror 10. This includes controlling the X1 resonance frequency to the target X frequency (step S5 in FIG. 7).

Hereinafter, an operation example of the resonance frequency control will be described with reference to FIGS. 20 and 21. FIG. 20 shows an example of the X1 resonance frequency of the mirror 10 when no voltage is applied between the comb tooth electrodes. With reference to FIG. 20, since the X1 resonance frequency fo of the mirror 10 substantially matches the frequency (3fd) of the third harmonic, ringing is likely to occur in this state. FIG. 21 shows an example of the X1 resonance frequency of the mirror 10 when the adjustment signal (Vele) determined by the series of processes shown in FIG. 17 is applied between the comb tooth electrodes. With reference to FIG. 21, when the X1 resonance frequency fo of the mirror 10 is close to the frequency (3 fd) of the third harmonic, N specified by the equation (11) is “3” in step S13 of FIG. The target X frequency is "3.5 fd". Therefore, as shown in FIG. 21, the X1 resonance frequency fo of the mirror 10 is controlled to be intermediate between 3fd and 4fd (position corresponding to 3.5fd). As a result, the difference between the X1 resonance frequency fo of the mirror 10 and the frequency (3fd) of the third harmonic becomes "0.5fd". The control device 3 applies an electrostatic force between the movable electrodes 51 and 52 and the fixed electrodes 61 and 62 (that is, between the comb tooth electrodes) to strengthen the restoring force around the X axis of the mirror 10. Feel can be generated. Due to such electrostatic force Feel, the X1 resonance frequency of the mirror 10 becomes high. By adjusting the magnitude of the electrostatic force Feel, the control device 3 can keep the X1 resonance frequency of the mirror 10 away from the frequency component included in the drive current signal. Ringing is suppressed by separating the X1 resonance frequency of the mirror 10 from the frequency component of the drive current signal.

As a method of suppressing ringing, a method of determining the drive signal of the mirror so that the frequency component contained in the drive signal of the mirror (for example, the drive current signal) does not match the resonance frequency of the mirror can be considered. However, such a method impairs the degree of freedom in determining the drive signal of the mirror. For example, when the drive frequency of the mirror (frequency of the drive signal) changes, the frame rate tends to change accordingly. When light is scanned over a wide range using a plurality of optical scanning devices to create an image, if the frame rate shifts between the optical scanning devices, an appropriate image cannot be obtained. It is conceivable to interpolate the difference in frame rate by information processing, but adding such information processing causes an increase in processing load.

It is also conceivable to suppress ringing by removing a specific frequency component included in the drive signal of the mirror using a filter having steep characteristics (for example, a notch filter). However, the addition of filters leads to increased costs. Further, in such a method, a step for preparing a filter suitable for the characteristics of the mirror is required, which increases the work load.

In the optical scanning device 100 according to the first embodiment, the control device 3 executes the processes shown in FIGS. 7 and 17, so that ringing can be suppressed without using the above filter. The optical scanning device 100 applies a force to the mirror 10 in addition to a mirror actuator (for example, magnets 2a and 2b and a drive wiring 53) that rotates the mirror 10 around the axis X1 to obtain a resonance frequency around the axis X1 of the mirror 10. It is equipped with a changing adjustment mechanism. Specifically, the movable electrodes 51 and 52 and the fixed electrodes 61 and 62 function as "adjustment mechanisms". The movable electrodes 51 and 52 and the fixed electrodes 61 and 62 are placed between the movable electrodes 51 and 52 and the fixed electrodes 61 and 62 by applying a voltage between the movable electrodes 51 and 52 and the fixed electrodes 61 and 62. It is configured to generate an electrostatic force and change the X1 resonance frequency of the mirror 10 by the electrostatic force. The control device 3 controls the mirror actuator by a waveform signal (more specifically, a drive current signal flowing through the drive wiring 53), and a voltage signal (that is, that is, between the movable electrodes 51 and 52 and the fixed electrodes 61 and 62). By applying an adjustment signal for controlling the adjustment mechanism), the X1 resonance frequency of the mirror 10 is controlled so that the X1 resonance frequency of the mirror 10 is separated from the frequency component included in the waveform signal. The control device 3 changes the X1 resonance frequency of the mirror 10 according to the waveform signal (drive signal of the mirror 10). Therefore, the control device 3 can suppress ringing without changing the drive signal of the mirror 10. According to the optical scanning device 100, ringing can be suppressed while ensuring a degree of freedom in determining the drive signal of the mirror.

In the first embodiment, the control device is set so that the difference between the X1 resonance frequency of the mirror 10 and the frequency component of the drive current signal closest to the X1 resonance frequency becomes a predetermined target value (for example, 0.5 fd). 3 controls the X1 resonance frequency of the mirror 10. The X1 resonance frequency of the mirror 10 is separated from each frequency of the fundamental wave and the harmonic contained in the drive current signal. As a result, the operation of the mirror 10 is less affected by the resonance phenomenon, and the unstable operation of the mirror 10 due to the resonance phenomenon is suppressed. The target value is not limited to 0.5 fd and can be changed as appropriate. The target value may be less than 0.5 fd, for example, about 0.3 fd. The target value may be a fixed value or may be variable depending on the situation.

In the first embodiment, after the target X frequency is determined, the Vele (adjustment signal) is determined so that the X1 resonance frequency of the mirror 10 approaches the target X frequency (see FIG. 17). However, the present invention is not limited to this, and the control device 3 detects the X1 rotational displacement (θx) of the mirror 10 driven by the drive current signal while changing the voltage (Vele) applied between the comb tooth electrodes, and the mirror 10 causes the mirror 10. You may search for a Vele that operates stably. Through such a search, it is possible to find a Vele in which ringing is sufficiently suppressed.

The control device 3 may be configured to execute the process shown in FIG. 22 instead of the process shown in FIG. FIG. 22 is a flowchart showing a modified example of the process shown in FIG. The process shown in FIG. 22 is the same as the process shown in FIG. 17, except that step S12A is added between steps S12 and S13. With reference to FIG. 22, in step S12A, the difference between the mechanical X1 resonance frequency fmec of the mirror 10 acquired in step S11 and each frequency component included in the drive current signal acquired in step S12 is predetermined. The control device 3 determines whether or not the value is equal to or higher than the reference value. If the difference between the mechanical X1 resonance frequency fmec of the mirror 10 and the frequency component of the drive current signal closest to fmec is equal to or greater than the reference value (YES in step S12A), the processes of steps S13 and S14 are not executed, and they are not executed. When the difference between the above values is less than the reference value (NO in step S12A), the processes of steps S13 and S14 are executed. The reference value used in step S12A corresponds to the minimum permissible interval and is set at an interval sufficient to suppress ringing. This reference value may be determined based on the required scanning accuracy, scanning range, and Q value (Quality factor). The reference value may be about 0.3 fd.

If YES is determined in step S12A, it means that the X1 resonance frequency of the mirror 10 is sufficiently separated from each frequency component of the drive current signal. Therefore, if YES is determined in step S12A, no voltage is applied between the comb tooth electrodes. On the other hand, if NO is determined in step S12A, the processes of steps S13 and S14 are executed, so that a vel (voltage signal) is applied between the comb tooth electrodes. As a result, the X1 resonance frequency of the mirror 10 is controlled so that the difference between the X1 resonance frequency of the mirror 10 and the frequency component of the drive current signal closest to the X1 resonance frequency becomes the target value (for example, 0.5 fd). Will be done.

According to the process shown in FIG. 22, the difference between the X1 resonance frequency of the mirror 10 and the frequency component of the drive current signal closest to the X1 resonance frequency is equal to or greater than the reference value (for example, 0.3 fd). The X1 resonance frequency of the mirror 10 is controlled. According to such processing, the difference between the X1 resonance frequency of the mirror 10 and each frequency component of the drive current signal does not fall below the reference value. Further, when the X1 resonance frequency of the mirror 10 is sufficiently separated from each frequency component of the drive current signal, the voltage is not applied between the comb-tooth electrodes, so that the frequency of applying the voltage between the comb-tooth electrodes should be reduced. Can be done.

In the first embodiment, a DC voltage is applied between the movable electrodes 51 and 52 and the fixed electrodes 61 and 62. The control device 3 is configured to control the X1 resonance frequency of the mirror 10 based on the magnitude of the DC voltage. However, the present invention is not limited to this, and the voltage signal applied between the movable electrodes 51 and 52 and the fixed electrodes 61 and 62 may be a rectangular wave voltage signal. The movable electrodes 51 and 52 and the fixed electrodes 61 and 62 may be connected to a power source via a switch, and when the switch is turned on, a power source voltage may be applied between the electrodes. By controlling the on / off of such a switch by the control device 3, the rectangular wave voltage signal described below may be applied between the electrodes.

FIG. 23 is a diagram showing a modified example of the voltage signal applied between the movable electrodes 51 and 52 and the fixed electrodes 61 and 62. With reference to FIG. 23, the rectangular wave voltage signal is a signal that periodically repeats an on-period Ta in which a power supply voltage Von is applied between the electrodes and an off-period Tb in which a voltage is not applied between the electrodes. The cycle T is composed of the on period Ta and the off period Tb. If the on / off switching cycle is sufficiently faster than the X1 resonance frequency of the mirror 10, an electric charge can be supplied to the capacitance between the comb tooth electrodes, and the restoring force of the mirror 10 with respect to the X1 rotation can be strengthened. In this case, the value (Von × Ta / T) obtained by multiplying the duty ratio (Ta / T) of the rectangular wave voltage signal by the power supply voltage Von is the “Von × Ta / T) in the above equations (4), (6), and (8). It corresponds to the size of "Vele". The control device 3 may be configured to control the X1 resonance frequency of the mirror 10 based on the duty ratio of the rectangular wave voltage signal. According to the square wave voltage signal, the X1 resonance frequency of the mirror 10 can be adjusted by changing the duty ratio even if the power supply voltage Von remains constant. Since the optical scanning apparatus using such a rectangular wave voltage signal does not need to be equipped with a variable voltage power supply, the apparatus can be miniaturized and simplified.

In the first embodiment, each of the movable electrodes 51 and 52 is provided on both side surfaces of the mirror portion 5 in the direction orthogonal to the axis X1 (rotation axis) (see FIGS. 3 and 4). In such a structure, the distance (Rele) between the shaft X1 (rotating shaft) and the movable electrodes 51 and 52 becomes large, and a large torque tele is easily generated by the electrostatic force Feel (see the above equation (5)). However, the positions, shapes, and numbers of the movable electrodes 51 and 52 and the fixed electrodes 61 and 62 are not limited to the examples shown in FIGS. 2 to 6, and can be changed as appropriate.

FIG. 24 is a diagram showing a first modification of the movable electrode and the fixed electrode. With reference to FIG. 24, in this example, each of the movable electrode and the fixed electrode is not a comb-shaped electrode as shown in FIGS. 3 and 4. A movable electrode is formed using the side surface of the base material of the mirror portion. The four corner side surfaces (more specifically, the YY plane) of the mirror portion 5A function as movable electrodes R11 to R14. The movable electrodes R11, R12, R13, and R14 are arranged on the + Y / -X side, + Y / + X side, -Y / -X side, and -Y / + X side of the mirror portion 5A, respectively. Fixed electrodes 611, 612, 621, and 622 are provided so as to face the movable electrodes R11, R12, R13, and R14 in the X-axis direction, respectively. Each of the fixed electrodes 611, 612, 621, 622 is not formed in a comb-teeth shape, and has a flat plate shape having a YY surface as a main surface. Each of the fixed electrodes 611 and 612 is supported by the fixing member 6a, and each of the fixed electrodes 621 and 622 is supported by the fixing member 6b. When the movable electrodes R11 to R14 and the fixed electrodes 611, 612, 621, 622 face each other, an electrostatic force corresponding to the voltage applied between the electrodes is generated between the electrodes.

FIG. 25 is a diagram showing a second modification of the movable electrode and the fixed electrode. With reference to FIG. 25, in this example, the fixed electrode is formed by utilizing the side surface of the fixing member. Both side surfaces (more specifically, ZX surfaces) of the mirror portion 5B in the Y-axis direction function as movable electrodes R21 and R22. Further, the side surface on the −Y side (more specifically, the ZX surface) of the fixing member 6c functions as the fixing electrode R31, and the side surface on the + Y side (more specifically, the ZX surface) of the fixing member 6d. ) Functions as the fixed electrode R32. The movable electrode R21 and the fixed electrode R31 face each other in the Y-axis direction, and an electrostatic force corresponding to the applied voltage is generated between these electrodes. The movable electrode R22 and the fixed electrode R32 face each other in the Y-axis direction, and an electrostatic force corresponding to the applied voltage is generated between these electrodes.

In both the modified examples shown in FIGS. 24 and 25, by reducing the distance between the movable electrode and the fixed electrode, it becomes easy to generate a large electrostatic force between the electrodes. Further, by increasing the facing area between the movable electrode and the fixed electrode, it becomes easy to generate a large electrostatic force between the electrodes. In order to make the semiconductor substrate (for example, a silicon substrate) function as an electrode, the conductivity of the semiconductor substrate may be adjusted by the amount of impurities added to the semiconductor substrate (for example, the dose amount).

In the first embodiment described above, the fixed electrodes 61 and 62 are grounded and a positive potential is applied to the movable electrodes 51 and 52, but conversely, a positive potential is applied to the fixed electrodes 61 and 62. The movable electrodes 51 and 52 may be grounded.

In the optical scanning apparatus 100 according to the first embodiment, the mirror portion 5, the movable electrodes 51 and 52, and the fixed electrodes 61 and 62 have a structure that is axisymmetric with respect to the rotation axis of the mirror portion 5. With such a symmetrical structure, the disturbing force is canceled out, and the operation of the optical scanning apparatus 100 can be stabilized. However, it is not essential that the structures of the mirror portion, the movable electrode, and the fixed electrode have symmetry in the optical scanning device. Further, the shape of the mirror is not limited to a rectangular shape, and may be, for example, a circular shape.

The optical scanning apparatus 100 according to the first embodiment employs two beams 11 and 12 (see FIGS. 2 to 6). However, the position, shape, and number of beams are not limited to the examples shown in FIGS. 2 to 6, and can be changed as appropriate.

In the optical scanning device 100 according to the first embodiment, the magnets 2a and 2b and the drive wiring 53 are used as mirror actuators. The magnets 2a and 2b are arranged so that a magnetic field is applied in a direction orthogonal to the rotation axis of the mirror portion 5 (see FIG. 8). Further, the drive wiring 53 is arranged so as to go around the outer edge portion of the mirror portion 5 once (see FIG. 8). However, the form in which the rotational force of the mirror is generated by the magnet and the drive wiring is not limited to the form shown in FIG. 8, and may be another form. For example, the direction of the magnetic field due to the magnet, the arrangement of the magnet, and the type of the magnet may be changed. The magnet is not limited to a permanent magnet, and may be an electromagnet. Further, the position, shape, and number of laps of the drive wiring can be changed as appropriate. The number of laps of the drive wiring may be two or more.

Mirror actuators are not limited to those that use electromagnetic force. For example, a mirror actuator that uses electrostatic force to generate a rotational force in the mirror can also be adopted. Further, a mirror actuator that generates a rotational force in the mirror by utilizing the deformation of the piezoelectric film can also be adopted.

In the optical scanning apparatus 100 according to the first embodiment, the piezoresistive elements 91, 92, 93, 94 are arranged at the roots ( support members 4a, 4b side) of the beams 11 and 12 (see FIG. 3). However, the position of each piezoresistive element is not limited to the position shown in FIG. 3, and may be arranged at another position where a stress change according to the posture of the mirror portion 5 (including the mirror 10) can be detected. Further, the number of piezoresistive elements can be changed as appropriate.

The method of detecting the posture (rotation angle) of the mirror 10 is not limited to the method using the piezoresistive element, and is arbitrary. For example, a photodetector that detects the direction of the optical axis of the light beam reflected by the mirror 10 may be provided outside the MEMS mirror 1. The control device 3 may estimate the posture (rotation angle) of the mirror 10 based on the direction of the optical axis detected by the photodetector.

In the optical scanning apparatus 100 according to the first embodiment, a force is applied to the mirror 10 by utilizing the electrostatic force generated when a voltage is applied between the movable electrodes 51 and 52 and the fixed electrodes 61 and 62. As a result, an adjustment mechanism that changes the resonance frequency around the axis X1 of the mirror 10 is adopted. However, the present invention is not limited to this, and the adjusting mechanism may apply a force to the mirror 10 by a method other than the electrostatic force.

FIG. 26 is a diagram showing a modified example of the adjustment mechanism shown in FIG. FIG. 27 is a diagram showing a cross-sectional structure along the line XXVII-XXVII in FIG. With reference to FIGS. 26 and 27, in this example, the beams 80a to 80d and the piezoelectric structures 8a to 8d are adopted instead of the fixing members 6a and 6b shown in FIG. The beams 80a and 80b are arranged on both sides of the beam 11 and are connected to each of the mirror portion 5 and the support member 4a like the beam 11. The beams 80c and 80d are arranged on both sides of the beam 12 and are connected to each of the mirror portion 5 and the support member 4b like the beam 12. The piezoelectric structures 8a to 8d are arranged on the beams 80a to 80d, respectively. The piezoelectric structures 8a to 8d basically have the same structure. Further, the beams 80a to 80d basically have the same structure. Therefore, in the following, each of the piezoelectric structures 8a to 8d will be referred to as a “piezoelectric structure 8”, and each of the beams 80a to 80d will be referred to as a “beam 80”, except for cases where they will be described separately.

FIG. 28 is a diagram showing a detailed structure of the piezoelectric structure 8. With reference to FIG. 28, the piezoelectric structure 8 is formed on the beam 80. The beam 80 is made of, for example, silicon. The piezoelectric structure 8 has a laminated structure in which the insulating layer 81, the electrode layer 82, the piezoelectric layer 83, and the electrode layer 84 are laminated in this order from the beam 80 side. The insulating layer 81 is formed of, for example, a silicon oxide layer or a silicon nitride layer. Each of the electrode layers 82 and 84 is formed of, for example, a metal film. The piezoelectric layer 83 is formed of, for example, lead zirconate titanate (PZT). The electrode layer 82 and the electrode layer 84 are electrically insulated from each other, and a voltage can be applied between the electrode layers. By applying a voltage between the electrode layer 82 and the electrode layer 84, an electric field in the Z-axis direction is applied to the piezoelectric layer 83. Due to this electric field, the piezoelectric layer 83 generates a force that expands and contracts in the X-axis direction. For example, when a voltage with the electrode layer 82 negative and the electrode layer 84 positive is applied between the electrode layers, the piezoelectric layer 83 generates a force that contracts in the X-axis direction. Such a force acts to increase the restoring force of the mirror 10 with respect to the X1 rotation. The magnitude of the restoring force changes according to the voltage between the electrodes. Therefore, the control device 3 (FIG. 1) can adjust the resonance frequency around the axis X1 of the mirror 10 based on the voltage between the electrodes. In the example shown in FIG. 26, the piezoelectric structures 8a to 8d are arranged on the beams 80a to 80d, respectively, but the position and number of the piezoelectric structures 8 can be changed. For example, the piezoelectric structure 8 may be arranged on the beams 11 and 12.

The adjustment mechanism adopted in the optical scanning apparatus 100 according to the first embodiment is configured to apply a force in the same direction as the mechanical restoring force generated by the rotational displacement of the mirror 10 to the mirror 10. However, the present invention is not limited to this, and an adjustment mechanism that applies a force opposite to the restoring force to the mirror 10 may be adopted. According to such an adjustment mechanism, by applying a force to the mirror 10, the beams 11 and 12 can be softened and the spring constant with respect to the X1 rotation of the mirror 10 can be reduced.

The waveform of the mirror drive signal is not limited to the serrated waveform and can be changed as appropriate. The waveform of the drive signal of the mirror may be a triangular wave instead of a serrated waveform.

In the first embodiment described above, one control device 3 (single unit) is configured to control both the mirror actuator and the adjustment mechanism, but controls the control device and the adjustment mechanism that control the mirror actuator. The control device may be a separate unit.

Embodiment 2.
In the first embodiment, the rotation axis of the mirror 10 is one axis (X-axis), and the optical scanning device 100 is configured to perform optical scanning in the one-axis direction. In the second embodiment, the rotation axes of the mirror 10 are set to two axes (X-axis and Y-axis) to enable optical scanning in two-axis directions. Hereinafter, the optical scanning apparatus according to the second embodiment will be described with a focus on the differences from the optical scanning apparatus according to the first embodiment.

The optical scanning apparatus according to the second embodiment includes the MEMS mirror 1A described below instead of the MEMS mirror 1 shown in FIG. FIG. 29 is a diagram showing a top surface structure of the MEMS mirror 1A included in the optical scanning apparatus according to the second embodiment. FIG. 30 is a diagram showing a cross-sectional structure along the XXX-XXX lines in FIG. 29.

With reference to FIGS. 29 and 30, the MEMS mirror 1A includes an intermediate frame 20 between the mirror portion 5 and the base material 7a. The base material 7c is a rectangular frame located below the intermediate frame 20, and is arranged so as to surround the base material 7b located below the mirror portion 5. A gap is provided between the base material 7b and the base material 7c. Further, a gap is also provided between the base material 7a and the base material 7c.

The intermediate frame 20 is a rectangular frame provided on the base material 7c via an insulating layer 55. The −X side end of the intermediate frame 20 is connected to the support member 4a via the beam 11B, and the + X side end of the intermediate frame 20 is connected to the support member 4b via the beam 12B. The axis X2 in FIG. 29 is an axis parallel to the X axis and indicates the position of the rotation axis of the intermediate frame 20. Each of the beam 11B and the beam 12B is formed along the axis X2. The intermediate frame 20 is configured to be rotatable around the axis X2. By twisting each of the beam 11B and the beam 12B around the axis X2, the intermediate frame 20 can rotate around the axis X2 (hereinafter, also referred to as “X2 rotation”).

A comb-shaped movable electrode 51B is provided on the + Y side side surface of the intermediate frame 20, and a comb-shaped movable electrode 52B is provided on the −Y side side surface of the intermediate frame 20. Each comb tooth electrode of the movable electrode 51B faces each comb tooth electrode of the fixed electrode 61 supported by the fixing member 6a. Each comb tooth electrode of the movable electrode 52B faces each comb tooth electrode of the fixed electrode 62 supported by the fixing member 6b.

The mirror portion 5 is arranged inside the intermediate frame 20. The + Y side end of the mirror portion 5 is connected to the intermediate frame 20 via the beam 11A, and the −Y side end of the mirror portion 5 is connected to the intermediate frame 20 via the beam 12A. The axis Y2 in FIG. 29 is an axis parallel to the Y axis and indicates the position of the rotation axis of the mirror portion 5. Each of the beam 11A and the beam 12A is formed along the axis Y2. The mirror portion 5 is configured to be rotatable around the axis Y2. By twisting each of the beam 11A and the beam 12A around the axis Y2, the mirror portion 5 can rotate around the axis Y2 (hereinafter, also referred to as “Y2 rotation”).

Piezoresistive elements 91B and 92B are provided at the boundary between the support member 4a and the beam 11B. Piezoresistive elements 93B and 94B are provided at the boundary between the support member 4b and the beam 12B. The piezoresistive elements 91B, 92B, 93B, 94B are used to detect the rotation position (hereinafter, also referred to as “frame X rotation angle”) of the intermediate frame 20 around the axis X2. The detection method is the same as that of the first embodiment. The control device 3 (FIG. 1) is configured to acquire the frame X rotation angle based on the outputs of the piezoresistive elements 91B, 92B, 93B, and 94B.

Piezoresistive elements 91A and 92A are provided at the boundary between the intermediate frame 20 and the beam 11A. Piezoresistive elements 93A and 94A are provided at the boundary between the intermediate frame 20 and the beam 12A. The piezoresistive elements 91A, 92A, 93A, 94A are used to detect the rotation position of the mirror unit 5 around the axis Y2 (hereinafter, also referred to as “mirror Y rotation angle”). The detection method is the same as that of the first embodiment. The control device 3 (FIG. 1) is configured to acquire the mirror Y rotation angle based on the outputs of the piezoresistive elements 91A, 92A, 93A, and 94A.

As shown in FIG. 29, the MEMS mirror 1A has a line-symmetrical structure with respect to each of the axis X2 and the axis Y2. The intermediate frame 20 and the mirror portion 5 (including the mirror 10) integrally change their postures with respect to the rotation around the axis X2. Therefore, the mirror portion 5 also rotates around the axis X2 in conjunction with the X2 rotation of the intermediate frame 20 described above. The X2 rotation of the intermediate frame 20 and the Y2 rotation of the mirror portion 5 make the mirror 10 rotatable both around the axis X2 and around the axis Y2. The mirror 10 rotates relative to the base material 7a. The frame X rotation angle corresponds to the rotation angle around the axis X2 of the mirror 10, and the mirror Y rotation angle corresponds to the rotation angle around the axis Y2 of the mirror 10.

The drive wiring 53B is provided on the support member 4a, the beam 11B, and the intermediate frame 20. However, an insulating film 54 is arranged between each of the support member 4a, the beam 11B, and the intermediate frame 20 and the drive wiring 53B. The electrode pads 56B and 57B are provided at the + Y side and −Y side ends of the support member 4a, respectively, and are located at both ends of the drive wiring 53B. The drive wiring 53B crosses the beam 11B from the support member 4a to reach the intermediate frame 20, goes around the outer edge of the intermediate frame 20 once, crosses the beam 11B again, and returns to the support member 4a. By applying a voltage between the electrode pad 56B and the electrode pad 57B, a current flows through the drive wiring 53B.

The drive wiring 53A is provided on the support member 4a, the beam 11B, the intermediate frame 20, and the base material 50. However, an insulating film 54 is arranged between each of the support member 4a, the beam 11B, the intermediate frame 20, and the base material 50 and the drive wiring 53A. The electrode pads 56A and 57A are provided at the + Y side and −Y side ends of the support member 4a, respectively, and are located at both ends of the drive wiring 53A. The drive wiring 53A reaches the intermediate frame 20 from the support member 4a across the beam 11B, and reaches the mirror portion 5 from the intermediate frame 20 across the beam 12A. Then, the drive wiring 53A goes around the outer edge portion (around the mirror 10) of the mirror portion 5 once, crosses the beams 12A and 11B again, and returns to the support member 4a. By applying a voltage between the electrode pad 56A and the electrode pad 57A, a current flows through the drive wiring 53A.

In the second embodiment, the arrangement of the magnets 2a and 2b (FIG. 1) is changed to a different arrangement from that of the first embodiment. FIG. 31 is a diagram for explaining the arrangement of the magnets 2a and 2b in the optical scanning apparatus according to the second embodiment. With reference to FIG. 31, the magnets 2a and 2b are arranged so as to apply a magnetic field including both a component in the X-axis direction and a component in the Y-axis direction to the MEMS mirror 1A. The direction of the magnetic flux density B of the magnetic field is the direction from the magnet 2a to the magnet 2b (direction of −Y / + X).

With reference to FIGS. 29 to 31, in the second embodiment, the drive wiring 53A and the drive wiring 53B are not electrically connected to each other, and the drive wiring 53A and the drive wiring 53B are connected by individual drive signals. Can be passed separately. Since a magnetic field as shown in FIG. 31 is applied to the MEMS mirror 1A, the control device 3 (FIG. 1) also refers to a drive current signal (hereinafter, also referred to as “first drive current signal”) to be passed through the drive wiring 53B. ) And the drive current signal (hereinafter, also referred to as “second drive current signal”) flowing through the drive wiring 53A, the X2 rotation and the Y2 rotation of the mirror 10 can be controlled. In the second embodiment, the drive wiring 53B and the magnets 2a and 2b function as a first mirror actuator that rotates the mirror 10 around an axis X2 (first rotation axis). The first drive current signal corresponds to an example of "a first waveform signal for controlling the first mirror actuator". Further, the drive wiring 53A and the magnets 2a and 2b function as a second mirror actuator that rotates the mirror 10 around the axis Y2 (second rotation axis). The second drive current signal corresponds to an example of "a second waveform signal for controlling the second mirror actuator". The driving principle of each mirror actuator is basically the same as that of the mirror actuator according to the first embodiment.

The light beam incident on the MEMS mirror 1A is reflected by the mirror 10 and then emitted from the optical scanning device. The control device 3 (FIG. 1) can control the emission direction of the light beam by controlling the X2 rotation and the Y2 rotation of the mirror 10 by the first drive current signal and the second drive current signal. Such control enables light scanning in a two-dimensional direction. Hereinafter, the optical scanning by X2 rotation is referred to as "X-axis scanning", and the optical scanning by Y2 rotation is referred to as "Y-axis scanning".

The first drive current signal is a serrated current signal similar to the drive current signal according to the first embodiment. The control device 3 (FIG. 1) provides a voltage signal (hereinafter, also referred to as “first adjustment signal”) for controlling the resonance frequency (hereinafter, also referred to as “X2 resonance frequency”) around the axis X2 of the mirror 10. It is applied between the movable electrodes 51B and 52B and the fixed electrodes 61 and 62. The control device 3 (FIG. 1) controls the X2 resonance frequency of the mirror 10 by the first adjustment signal so that the X2 resonance frequency of the mirror 10 is separated from the frequency component included in the first drive current signal. In the control device 3 (FIG. 1), for example, the difference between the X2 resonance frequency of the mirror 10 and the frequency component of the first drive current signal closest to the X2 resonance frequency becomes the target value (or the reference value or more). The X2 resonance frequency of the mirror 10 is controlled. Since the control of the resonance frequency using the adjustment signal has already been described in the first embodiment, the details will be omitted.

On the other hand, the second drive current signal is a sinusoidal current signal having a frequency close to the resonance frequency around the axis Y2 of the mirror 10 (hereinafter, also referred to as “Y2 resonance frequency”). When such a second drive current signal is adopted, the operation of the mirror 10 is easily affected by the resonance phenomenon, and the amplitude of the Y2 rotational displacement can be increased.

As described above, regarding the X2 rotation of the mirror 10, the control device 3 (FIG. 1) suppresses the unstable operation (for example, ringing) of the mirror 10 due to the resonance phenomenon by using the first adjustment signal. This enables stable X-axis scanning. On the other hand, in Y-axis scanning, a wide range of scanning becomes possible by high-speed scanning by positively utilizing the resonance phenomenon.

The control device 3 (FIG. 1) is based on the drive frequency fdy of the Y-axis scan (that is, the frequency of the fundamental wave included in the second drive current signal) in order to synchronize the scans in the two-axis directions with each other. The scan drive frequency fdx (ie, the frequency of the fundamental wave included in the first drive current signal) may be determined. The control device 3 may determine the drive frequency (fdx) of the X-axis scan according to the following equation (13), for example.

fdx = (p / q) x fdy ... (13)
Each of "p" and "q" in the formula (13) can be arbitrarily set. For example, appropriate natural numbers obtained in advance by experiments or simulations are set in p and q.

The optical scanning apparatus according to the second embodiment includes a first adjusting mechanism that applies a force to the mirror 10 to change the resonance frequency around the axis X2 of the mirror 10. Specifically, the movable electrodes 51B and 52B and the fixed electrodes 61 and 62 function as the "first adjustment mechanism". The control device 3 (FIG. 1) controls the X2 resonance frequency of the mirror 10 so that the X2 resonance frequency of the mirror 10 is separated from the frequency component included in the first drive current signal by controlling the first adjustment mechanism. By such control, the effect according to the above-described first embodiment is achieved.

The optical scanning apparatus according to the second embodiment includes only an adjustment mechanism related to X-axis scanning (first adjustment mechanism), and does not include an adjusting mechanism related to Y-axis scanning. However, the present invention is not limited to this, and an adjustment mechanism related to Y-axis scanning may be added to the structures shown in FIGS. 29 and 30.

FIG. 32 is a diagram showing a modified example of the structure of the MEMS mirror shown in FIG. 29. FIG. 33 is a diagram showing a cross-sectional structure along the line XXXIII-XXXIII in FIG. 32. With reference to FIGS. 32 and 33, in the MEMS mirror 1B, a comb-shaped movable electrode 51A is provided on the side surface of the mirror portion 5 on the −X side, and a comb tooth is provided on the side surface of the mirror portion 5 on the + X side. A movable electrode 52A in the shape of a shape is provided. The movable electrodes 51A and 52A are electrically connected to each of the mirror 10, the beams 11A and 12A, the intermediate frame 20, the beams 11B and 12B, and the support members 4a and 4b, and are electrically equipotential with these. .. Further, a comb-shaped fixed electrode 61A is provided so as to face each comb-tooth electrode of the movable electrode 51A, and a comb-tooth-shaped fixed electrode 62A is provided so as to face each comb-tooth electrode of the movable electrode 52A. Has been done. The fixed electrodes 61A and 62A are provided on the base material 7c via the insulating layer 55 together with the intermediate frame 20. A gap is provided between the fixed electrodes 61A and 62A and the intermediate frame 20, and the fixed electrodes 61A and 62A and the intermediate frame 20 are electrically insulated by the insulating layer 55. However, the fixed electrode 61A and the fixed electrode 62A are electrically connected to each other by wiring (not shown), and are electrically equipotential. Since the force due to the Y2 rotation of the mirror portion 5 is absorbed by the elastic deformation of the beams 11A and 12A, each of the intermediate frame 20 and the fixed electrodes 61A and 62A is not interlocked with the Y2 rotation of the mirror 10.

In this modification, each of the first drive current signal and the second drive current signal is a serrated current signal. The MEMS mirror 1B includes, in addition to the first adjustment mechanism described above, a second adjustment mechanism that applies a force to the mirror 10 to change the resonance frequency around the axis Y2 of the mirror 10. Specifically, the movable electrodes 51A and 52A and the fixed electrodes 61A and 62A function as a "second adjusting mechanism". The control device 3 (FIG. 1) controls the first adjusting mechanism and the second adjusting mechanism as described below.

By applying the above-mentioned first adjustment signal between the movable electrodes 51B and 52B and the fixed electrodes 61 and 62, the control device 3 obtains the X2 resonance frequency of the mirror 10 from the frequency component included in the first drive current signal. The X2 resonance frequency of the mirror 10 is controlled so as to be separated. Further, the control device 3 applies a voltage signal for controlling the Y2 resonance frequency of the mirror 10 (hereinafter, also referred to as “second adjustment signal”) between the movable electrodes 51A and 52A and the fixed electrodes 61A and 62A. By doing so, the Y2 resonance frequency of the mirror 10 is controlled so that the Y2 resonance frequency of the mirror 10 is separated from the frequency component included in the second drive current signal. Since the control of the resonance frequency using the adjustment signal has already been described in the first embodiment, the details will be omitted.

With the above control, it is possible to suppress unstable operation (for example, ringing) of the mirror 10 due to the resonance phenomenon in both X-axis scanning and Y-axis scanning. This enables stable X-axis scanning and Y-axis scanning.

Embodiment 3.
The distance measuring device may be configured by the above-mentioned optical scanning device. The optical scanning device (optical scanning device 200 described later) included in the ranging device according to the third embodiment is the optical scanning device (see FIGS. 29 to 31) according to the second embodiment.

FIG. 34 is a diagram showing a distance measuring device according to the third embodiment. With reference to FIG. 34, the ranging device 300 has a housing 305, a light source 301 that emits a light beam, an optical scanning device 200 that deflects the light beam, and a photodetector 303 in the housing 305. And. Then, the distance measuring device 300 is configured to irradiate the object with a light beam deflected by the light scanning device 200, and detect at least a part of the light reflected by the object by the photodetector 303. The distance measuring device 300 further includes an information processing device 3A. The information processing device 3A is configured to form a distance image by using the information about the light beam emitted from the light source 301 and the detection result by the photodetector 303. The distance image is an image showing the distance to an object for each pixel. The information processing device 3A may display a distance image on a display device (not shown). The distance measuring method may be a TOF (Time Of Flight) method. The distance measuring device 300 can acquire a distance image around the device.

The information processing device 3A may be configured to control the optical scanning device 200. The information processing device 3A may have the same function as the control device 3 (FIG. 1) according to the second embodiment. As the information processing device 3A, a microcomputer including a processor, RAM, and a storage device can be adopted. The above storage device may store the program and information used in the program (for example, maps, mathematical formulas, and various parameters). The image processing circuit may be mounted on the information processing apparatus 3A.

The light source 301 is configured to irradiate the MEMS mirror of the optical scanning device 200 with a light beam. As the light source 301, for example, a laser light source can be adopted. The wavelength of the light beam emitted by the light source 301 is arbitrary and may be in the visible region or in the infrared region. In the third embodiment, a laser light source that emits a laser beam having a wavelength of 870 nm to 1500 nm is used as the light source 301. Although FIG. 34 shows only one light source 301, the number of light sources included in the distance measuring device 300 is arbitrary, and the distance measuring device 300 may include a plurality of light sources.

The housing 305 is provided with a window 306 through which the light beam emitted from the light source 301 and the light beam reflected by the object are transmitted. A beam splitter 302 is provided between the light source 301 and the MEMS mirror of the optical scanning device 200 in the housing 305.

The light beam emitted from the light source 301 passes through the beam splitter 302 and is deflected by the light scanning device 200 as shown by the line L1. In the optical scanning device 200, the light beam is reflected by a mirror (reflection film) driven by a drive signal. Then, the reflected light beam passes through the window 306 and irradiates an object outside the housing 305 (more specifically, an object within the scanning range of the optical scanning device 200).

The light beam reflected by the object outside the housing 305 enters the housing 305 through the window 306. The photodetector 303 is arranged at a position where such a light beam can be detected. As the photodetector 303, for example, an avalanche photodiode (APD) can be adopted. The light reflected by the object is taken in from the window 306 and reflected toward the beam splitter 302 by the MEMS mirror of the optical scanning device 200 as shown by the line L2, and further, the light detector 303 is reflected by the reflecting surface of the beam splitter 302. It is reflected toward. In this way, the light reflected by the object enters the photodetector 303 through the window 306, the optical scanning device 200, and the beam splitter 302.

The information processing device 3A acquires information on the emitted light from the light source 301 and information on the incident light from the photodetector 303. The information processing device 3A can measure the distance to the object by comparing the emitted light and the incident light. For example, when an object is irradiated with a pulsed light beam, pulsed reflected light can also be obtained from the object. The information processing device 3A can calculate the distance to the object from the time difference between the pulse of the emitted light and the pulse of the reflected light. Since the optical scanning device 200 scans the light beam in two dimensions, the information processing device 3A obtains a two-dimensional distance image around the device based on the above distance information and information on the scanning direction of the light beam. Can be obtained.

The distance measuring device 300 may function as LiDAR (Light Detection and Ringing). The ranging device 300 may be mounted on the vehicle. The distance measuring device 300 may be mounted on a connected car and used for obstacle detection in driving support control or automatic driving control.

In the distance measuring device 300 according to the third embodiment described above, the optical scanning device according to the second embodiment described above is adopted as the optical scanning device 200. Therefore, even in the third embodiment, the same effect as that of the second embodiment described above can be obtained. In the distance measuring device 300 according to the third embodiment, since the ringing of the light emitted from the optical scanning device 200 is suppressed, it becomes easy to accurately detect the position and shape of the object, and a distance image with less distortion can be obtained.

In the ranging device 300 according to the third embodiment, the reflected light (line L2) from the object is guided to the photodetector 303 via the same optical system as the emitted light (line L1), but the housing 305 The optical system and the path of light inside can be changed as appropriate. FIG. 35 is a diagram showing a modified example of the distance measuring device shown in FIG. 34. With reference to FIG. 35, the window 306A through which the light beam (line L1) emitted from the light source 301 is transmitted and the light beam (line L2) reflected by the object are transmitted through the housing 305 of the distance measuring device 300A. The window 306B to be used is provided separately. Further, in the distance measuring device 300A, the beam splitter is omitted. As shown by the line L1, the light beam emitted from the light source 301 is deflected by the optical scanning device 200, passes through the window 306A, and irradiates an object outside the housing 305. The light reflected by the object is taken in through the window 306B and incident on the photodetector 303, as shown by line L2. Even in such a distance measuring device 300A, the information processing device 3A can calculate the distance to the object by comparing the emitted light and the reflected light. The information processing device 3A can acquire a distance image around the device.

In the distance measuring device 300 according to the third embodiment, the optical scanning device according to the second embodiment is adopted as the optical scanning device 200, but instead of the optical scanning device according to the second embodiment, the first embodiment The optical scanning apparatus according to the above may be adopted. An optical scanning device arbitrarily selected from the above-described optical scanning device according to the first embodiment and its modification and the optical scanning device according to the second embodiment and its modification is used as the optical scanning device of the distance measuring device. It may be applied.

The embodiments disclosed this time should be considered to be exemplary in all respects and not restrictive. The scope of the present disclosure is indicated by the scope of claims rather than the above description, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

1,1A, 1B MEMS mirror, 2a, 2b magnet, 3 control device, 3A information processing device, 4a, 4b support member, 5,5A, 5B mirror part, 6a, 6b, 6c, 6d fixing member, 7a, 7b, 7c, 50 base material, 8,8a to 8d piezoelectric structure, 10 mirror, 11,11A, 11B, 12,12A, 12B, 80,80a to 80d beam, 20 intermediate frame, 51,51A, 51B, 52,52A , 52B, R11 to R14, R21, R22 Movable electrodes, 53, 53A, 53B Drive wiring, 54 Insulation film, 55 Insulation layer, 56, 56A, 56B, 57, 57A, 57B Electrode pads, 61, 61A, 62, 62A , 64A, R31, R32 fixed electrode, 81 insulating layer, 82,84 electrode layer, 83 piezoelectric layer, 91 to 94, 91A to 94A, 91B to 94B piezo resistance element, 100, 200 optical scanning device, 300, 300A ranging Equipment, 301 light source, 302 beam splitter, 303 light detector, 305 housing, 306, 306A, 306B window.

Claims (10)

1. A mirror that is configured to rotate around the axis of rotation and reflects light,
   A mirror actuator that rotates the mirror around the rotation axis,
   An adjustment mechanism that applies force to the mirror to change the resonance frequency around the rotation axis of the mirror.
   The mirror actuator and the control device for controlling the adjustment mechanism are provided.
   The control device is configured to control the mirror actuator by a waveform signal.
   By controlling the adjustment mechanism, the control device controls the resonance frequency around the rotation axis of the mirror so that the resonance frequency around the rotation axis of the mirror is separated from the frequency component included in the waveform signal. , Optical scanning device.
2. The adjustment mechanism
   A movable electrode configured to be interlocked with the rotation of the mirror around the rotation axis,
   Includes a fixed electrode configured not to interlock with the rotation of the mirror around the axis of rotation.
   The adjusting mechanism generates an electrostatic force between the movable electrode and the fixed electrode by applying a voltage between the movable electrode and the fixed electrode, and the electrostatic force causes the rotation of the mirror. It is configured to change the resonance frequency around the axis,
   The optical scanning device according to claim 1, wherein the control device is configured to apply a voltage signal between the movable electrode and the fixed electrode.
3. The adjusting mechanism is configured to apply a force to the mirror so as to increase the restoring force of the mirror with respect to rotation about the rotation axis.
   Each of the movable electrode and the fixed electrode is formed in a comb-teeth shape.
   The optical scanning apparatus according to claim 2, wherein the movable electrode and the fixed electrode are arranged so that both comb teeth are staggered.
4. The control device rotates the mirror so that the difference between the resonance frequency around the rotation axis of the mirror and the frequency component of the waveform signal closest to the resonance frequency becomes a target value or a reference value or more. The optical scanning device according to claim 2, wherein the resonance frequency around the axis is controlled.
5. The voltage signal is a DC voltage signal and
   The optical scanning device according to any one of claims 2 to 4, wherein the control device controls a resonance frequency around the rotation axis of the mirror based on the magnitude of the DC voltage of the voltage signal.
6. The voltage signal is a square wave voltage signal.
   The optical scanning device according to any one of claims 2 to 4, wherein the control device controls a resonance frequency around the rotation axis of the mirror based on the duty ratio of the voltage signal.
7. With the base material
   A first support member and a second support member provided directly or indirectly on the base material,
   The first fixing member and the second fixing member provided directly or indirectly on the base material,
   A mirror portion having the mirror on the surface and
   Further equipped with a first beam and a second beam,
   The first end and the second end of the mirror portion located at both ends in the direction of the rotation axis are connected to the first support member and the second support member via the first beam and the second beam, respectively. Ori,
   The movable electrode includes a first movable electrode and a second movable electrode.
   The first movable electrode and the second movable electrode are provided at the third and fourth ends of the mirror portion located at both ends in a direction orthogonal to the rotation axis, respectively.
   The fixed electrode includes a first fixed electrode supported by the first fixed member and a second fixed electrode supported by the second fixed member.
   The first fixed electrode and the second fixed electrode are arranged so as to face the first movable electrode and the second movable electrode, respectively.
   Each of the first beam and the second beam functions as the rotation axis and functions as the rotation axis.
   The first movable electrode and the first fixed electrode, and the second movable electrode and the second fixed electrode are formed line-symmetrically with respect to the rotation axis, according to any one of claims 2 to 4. The optical scanning device according to the description.
8. The rotation axis is the first rotation axis, and is
   The mirror actuator is a first mirror actuator.
   The waveform signal is a first waveform signal and
   The adjustment mechanism is a first adjustment mechanism.
   The mirror is configured to be rotatable around a second rotation axis orthogonal to the first rotation axis.
   The optical scanning device is
   A second mirror actuator that rotates the mirror around the second rotation axis,
   Further provided with a second adjusting mechanism that applies a force to the mirror to change the resonance frequency around the second rotation axis of the mirror.
   The control device is configured to control the second mirror actuator by a second waveform signal.
   By controlling the second adjustment mechanism, the control device performs the second rotation of the mirror so that the resonance frequency around the second rotation axis of the mirror is separated from the frequency component included in the second waveform signal. The optical scanning device according to any one of claims 1 to 4, which controls the resonance frequency around the axis.
9. A light source that emits a light beam, an optical scanning device that deflects the light beam, and a photodetector are provided, and an object is irradiated with a light beam deflected by the optical scanning device, and the light reflected by the object A ranging device configured to detect at least a part by the photodetector.
   An information processing device that forms a distance image using the information about the light beam emitted from the light source and the detection result by the photodetector is further provided.
   The optical scanning device is a distance measuring device according to any one of claims 1 to 8.
10. A control method for an optical scanning device including a mirror that is rotatably configured around a rotation axis and reflects light, and a mirror actuator that rotates the mirror around the rotation axis.
    Determining the waveform signal for controlling the mirror actuator and
    The resonance frequency of the mirror around the rotation axis so that the difference between the resonance frequency around the rotation axis of the mirror and the frequency component of the waveform signal closest to the resonance frequency becomes equal to or more than a target value or a reference value. Determining the target frequency, which is the target value,
    The mirror actuator is controlled by the waveform signal to rotate the mirror around the rotation axis, and a force is applied to the mirror to change the resonance frequency around the rotation axis of the mirror to rotate the mirror. A method for controlling an optical scanning device, which comprises controlling a resonance frequency around an axis to the target frequency.

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