Patent Publication Number: US-2023162635-A1

Title: Optical scanning device, method of driving optical scanning device, and image drawing system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation application of International Application No. PCT/JP2021/024390, filed Jun. 28, 2021, the disclosure of which is incorporated herein by reference in its entirety. Further, this application claims priority from Japanese Patent Application No. 2020-130628 filed on Jul. 31, 2020, the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     1. Technical Field 
     The technique of the present disclosure relates to an optical scanning device, a method of driving the optical scanning device, and an image drawing system. 
     2. Description of the Related Art 
     A micromirror device (also referred to as a microscanner) is known as one of micro electro mechanical systems (MEMS) devices manufactured using the silicon (Si) nanofabrication technique. Since an optical scanning device comprising the micromirror device is small and has low power consumption, it is expected to have a range of applications in an image drawing system such as a laser display or a laser projector. 
     In the micromirror device, a mirror portion is formed to be swingable around a first axis and a second axis that are orthogonal to each other, and two-dimensional scan with light reflected by the mirror portion is made by allowing the mirror portion to swing around each axis. In addition, there is known a micromirror device capable of performing Lissajous scanning with light by allowing the mirror portion to resonate around each axis. 
     In such a micromirror device, in order to accurately control a deflection angle of the mirror portion, it is known to provide an angle detection sensor that outputs a signal corresponding to an angle of the mirror portion (for example, see JP2019-082634A and JP2018-063228A). 
     JP2019-082634A discloses “obtaining an amplitude of rotation of a mirror portion based on an output signal of a detection signal acquisition unit”. Specifically, JP2019-082634A discloses “obtaining a peak to peak (P-P) value of a change of a signal voltage corresponding to rotation of the mirror portion, and obtaining an amplitude of rotation of the mirror portion based on data indicating a relationship between the signal voltage and the amplitude of rotation of the mirror portion”. The amplitude of rotation of the mirror portion corresponds to the maximum value of the deflection angle (hereinafter, the maximum deflection angle). 
     JP2018-063228A discloses “acquiring a swing angle of a MEMS mirror based on an amount of change in an angle of the MEMS mirror with respect to a resonance direction in a case where the MEMS mirror is driven at a resonance frequency”. 
     SUMMARY 
     JP2019-082634A and JP2018-063228A disclose that a first angle detection sensor that detects an angle of the mirror portion around a first axis and a second angle detection sensor that detects an angle of the mirror portion around a second axis are provided. However, in a case where the mirror portion swings around the first axis and the second axis simultaneously, a vibration component caused by the swing of the mirror portion around the second axis is superimposed on an output signal of the first angle detection sensor. A vibration component caused by the swing of the mirror portion around the first axis is superimposed on the output signal of the second angle detection sensor. As described above, in a biaxial drive type micromirror device, there is a problem that vibration of an axis different from an axis to be detected is superimposed as noise on an output signal of an angle detection sensor. Hereinafter, this noise is referred to as a vibration noise. 
     As described above, in a case where a vibration noise is superimposed on the output signal of the angle detection sensor, an amplitude of the output signal cannot be accurately obtained, and it is difficult to accurately control a deflection angle of the mirror portion. 
     According to the technique of the present disclosure, it is possible to provide an optical scanning device, a method of driving the optical scanning device, and an image drawing system which can accurately control a deflection angle of a mirror portion. 
     In order to achieve the above object, according to the present disclosure, there is provided an optical scanning device comprising: a mirror portion having a reflecting surface for reflecting incident light; a first actuator that allows the mirror portion to swing around a first axis located in a plane including the reflecting surface of the mirror portion in a stationary state; a second actuator that allows the mirror portion to swing around a second axis which is located in the plane including the reflecting surface of the mirror portion in the stationary state and is orthogonal to the first axis; a first angle detection sensor that outputs a signal corresponding to an angle of the mirror portion around the first axis; a second angle detection sensors that outputs a signal corresponding to an angle of the mirror portion around the second axis; and at least one processor, in which the processor applies a first driving signal having a first driving frequency to the first actuator, applies a second driving signal having a second driving frequency to the second actuator, generates a first angle detection signal by performing first frequency filter processing based on the first driving frequency on an output signal of the first angle detection sensor, generates a second angle detection signal by performing second frequency filter processing based on the second driving frequency on an output signal of the second angle detection sensor, derives a first angle, which is the angle of the mirror portion around the first axis, based on the first angle detection signal, derives a second angle, which is the angle of the mirror portion around the second axis, based on the second angle detection signal, adjusts the first driving signal based on the first angle, and adjusts the second driving signal based on the second angle. 
     It is preferable that the processor adjusts the first driving signal in a case where the first angle does not satisfy a first condition, and adjusts the second driving signal in a case where the second angle does not satisfy a second condition. 
     It is preferable that the processor adjusts voltage values of the first driving signal and the second driving signal. 
     It is preferable that the first frequency filter processing is band pass filter processing of extracting a signal component of a first frequency band including the first driving frequency, and that the second frequency filter processing is band pass filter processing of extracting a signal component of a second frequency band including the second driving frequency. 
     It is preferable that each of the first angle detection sensor and the second angle detection sensor is a piezoelectric element. 
     It is preferable that each of the first driving signal and the second driving signal is a sinusoidal wave. 
     It is preferable that each of the first angle and the second angle is an angle representing a maximum deflection angle of the mirror portion, and that the processor adjusts amplitudes of the first driving signal and the second driving signal based on the first angle and the second angle. 
     According to the present disclosure, there is provided an image drawing system comprising: the optical scanning device according to any one of the aspects; and a light source that irradiates the mirror portion with light, in which the processor drives the light source based on the first angle and the second angle. 
     It is preferable that the processor controls a light irradiation timing of the light source based on the first angle and the second angle. 
     According to the present disclosure, there is provided a method of driving an optical scanning device including a mirror portion having a reflecting surface for reflecting incident light, a first actuator that allows the mirror portion to swing around a first axis located in a plane including the reflecting surface of the mirror portion in a stationary state, a second actuator that allows the mirror portion to swing around a second axis which is located in the plane including the reflecting surface of the mirror portion in the stationary state and is orthogonal to the first axis, a first angle detection sensor that outputs a signal corresponding to an angle of the mirror portion around the first axis, and a second angle detection sensors that outputs a signal corresponding to an angle of the mirror portion around the second axis, the method comprising: applying a first driving signal having a first driving frequency to the first actuator; applying a second driving signal having a second driving frequency to the second actuator; generating a first angle detection signal by performing first frequency filter processing based on the first driving frequency on an output signal of the first angle detection sensor; generating a second angle detection signal by performing second frequency filter processing based on the second driving frequency on an output signal of the second angle detection sensor; deriving a first angle, which is the angle of the mirror portion around the first axis, based on the first angle detection signal; deriving a second angle, which is the angle of the mirror portion around the second axis, based on the second angle detection signal; adjusting the first driving signal based on the first angle; and adjusting the second driving signal based on the second angle. 
     According to the technique of the present disclosure, it is possible to provide an optical scanning device, a method of driving the optical scanning device, and an image drawing system which can accurately control a deflection angle of a mirror portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments according to the technique of the present disclosure will be described in detail based on the following figures, wherein: 
         FIG.  1    is a schematic view of an optical scanning device, 
         FIG.  2    is an external perspective view of a micromirror device, 
         FIG.  3    is a plan view of the micromirror device as viewed from a light incident side, 
         FIG.  4    is a cross-sectional view taken along the line A-A of  FIG.  3   , 
         FIG.  5    is a cross-sectional view taken along the line B-B of  FIG.  3   , 
         FIG.  6    is a cross-sectional view taken along the line C-C of  FIG.  3   , 
         FIG.  7    is a diagram showing an example in which a first actuator is driven, 
         FIG.  8    is a diagram showing an example in which a second actuator is driven, 
         FIGS.  9 A and  9 B  are diagrams showing examples of a first driving signal and a second driving signal, 
         FIG.  10    is a block diagram showing an example of a configuration of a driving controller, 
         FIG.  11    is a diagram showing an example of a signal output from a first angle detection sensor, 
         FIG.  12    is a diagram showing an example of a signal output from a second angle detection sensor, 
         FIG.  13    is a diagram showing characteristics of a first frequency filter, 
         FIG.  14    is a diagram showing first frequency filter processing, 
         FIG.  15    is a diagram showing characteristics of a second frequency filter, 
         FIG.  16    is a diagram showing second frequency filter processing, 
         FIG.  17    is a graph showing an example of data showing a relationship between a first maximum deflection angle and a P-P value, 
         FIG.  18    is a graph showing an example of data showing a relationship between a second maximum deflection angle and a P-P value, 
         FIG.  19    is a flowchart showing an example of voltage adjustment processing by a first voltage adjustment unit, 
         FIG.  20    is a flowchart showing an example of voltage adjustment processing by a second voltage adjustment unit, 
         FIG.  21    is a diagram showing a modification example of a micromirror device related to an angle detection sensor, 
         FIG.  22    is a block diagram showing an example of a configuration of a driving controller according to a modification example, 
         FIG.  23    is a diagram showing an example of signals output from a pair of first angle detection sensors, 
         FIG.  24    is a diagram showing an example of signals output from a pair of second angle detection sensors, 
         FIG.  25    is a circuit diagram showing a configuration of a first signal processing unit according to the modification example, 
         FIG.  26    is a circuit diagram showing a configuration of a second signal processing unit according to the modification example, 
         FIG.  27    is a circuit diagram showing an example in which a gain adjustment circuit is configured by a digital arithmetic circuit, and 
         FIG.  28    is a graph showing an example of a frequency component of an output signal of the first angle detection sensor. 
     
    
    
     DETAILED DESCRIPTION 
     An example of an embodiment relating to the technique of the present disclosure will be described with reference to the accompanying drawings. 
     First Embodiment 
       FIG.  1    schematically shows an image drawing system  10  according to an embodiment. The image drawing system  10  includes an optical scanning device  2  and a light source  3 . The optical scanning device  2  includes a micromirror device (hereinafter, referred to as micromirror device (MMD))  4  and a driving controller  5 . The driving controller  5  is an example of a “processor” according to the technique of the present disclosure. 
     The image drawing system  10  draws an image by reflecting a light beam L emitted from the light source  3  by the MMD  4  and optically scanning a surface to be scanned  6  with the reflected light beam under the control of the driving controller  5 . The surface to be scanned  6  is, for example, a screen. 
     The image drawing system  10  is applied to, for example, a Lissajous scanning type laser display. Specifically, the image drawing system  10  can be applied to a laser scanning display such as augmented reality (AR) glass or virtual reality (VR) glass. 
     The MMD  4  is a piezoelectric biaxial drive type micromirror device capable of allowing a mirror portion  20  (see  FIG.  2   ) to swing around a first axis a 1  and a second axis a 2  orthogonal to the first axis a 1 . Hereinafter, the direction parallel to the second axis a 2  is referred to as an X direction, the direction parallel to the first axis a 1  is a Y direction, and the direction orthogonal to the first axis a 1  and the second axis a 2  is referred to as a Z direction. 
     The light source  3  is a laser device that emits, for example, laser light as the light beam L. It is preferable that the light source  3  emits the light beam L perpendicularly to a reflecting surface  20 A (see  FIG.  2   ) included in the mirror portion  20  in a state where the mirror portion  20  of the MMD  4  is stationary. In a case where the light beam L is emitted from the light source  3  perpendicularly to the reflecting surface  20 A, the light source  3  may become an obstacle in scanning the surface to be scanned  6  the light beam L for drawing. Therefore, it is preferable that the light beam L emitted from the light source  3  is controlled by an optical system to be emitted perpendicularly to the reflecting surface  20 A. The optical system may include a lens or may not include a lens. An angle at which the light beam L emitted from the light source  3  is applied to the reflecting surface  20 A is not limited to the perpendicular direction, and the light beam L may be emitted obliquely to the reflecting surface  20 A. 
     The driving controller  5  outputs a driving signal to the light source  3  and the MMD  4  based on optical scanning information. The light source  3  generates the light beam L based on the input driving signal and emits the light beam L to the MMD  4 . The MMD  4  allows the mirror portion  20  to swing around the first axis a 1  and the second axis a 2  based on the input driving signal. 
     As will be described in detail below, the driving controller  5  allows the mirror portion  20  to resonate around the first axis a 1  and the second axis a 2 , so that the surface to be scanned  6  is scanned with the light beam L reflected by the mirror portion  20  such that a Lissajous waveform is drawn. This optical scanning method is called a Lissajous scanning method. 
     Next, an example of the MMD  4  will be described with reference to  FIGS.  2  to  6   .  FIG.  2    is an external perspective view of the MMD  4 .  FIG.  3    is a plan view of the MMD  4  as viewed from the light incident side.  FIG.  4    is a cross-sectional view taken along the line A-A in  FIG.  3   .  FIG.  5    is a cross-sectional view taken along the line B-B of  FIG.  3   .  FIG.  6    is a cross-sectional view taken along the line C-C of  FIG.  3   . 
     As shown in  FIGS.  2  and  3   , the MMD  4  includes a mirror portion  20 , a first support portion  21 , a first movable frame  22 , a second support portion  23 , a second movable frame  24 , a connecting portion  25 , and a fixed frame  26 . The MMD  4  is a so-called MEMS scanner. 
     The mirror portion  20  has a reflecting surface  20 A for reflecting incident light. The reflecting surface  20 A is provided on one surface of the mirror portion  20 , and is formed of a metal thin film such as gold (Au), aluminum (Al), silver (Ag), or an alloy of silver. The shape of the reflecting surface  20 A is, for example, circular with the intersection of the first axis a 1  and the second axis a 2  as the center. 
     The first axis a 1  and the second axis a 2  exist in a plane including the reflecting surface  20 A in a case where the mirror portion  20  is stationary. The planar shape of the MMD  4  is rectangular, line-symmetrical with respect to the first axis a 1 , and line-symmetrical with respect to the second axis a 2 . 
     The first support portions  21  are disposed on an outside of the mirror portion  20  at positions facing each other across the second axis a 2 . The first support portions  21  are connected to the mirror portion  20  on the first axis a 1 , and swingably support the mirror portion  20  around the first axis a 1 . In the present embodiment, the first support portion  21  is a torsion bar stretched along the first axis a 1 . 
     The first movable frame  22  is a rectangular frame that surrounds the mirror portion  20  and is connected to the mirror portion  20  on the first axis a 1  via the first support portion  21 . Piezoelectric elements  30  are formed on the first movable frame  22  at positions facing each other across the first axis a 1 . In this way, a pair of first actuators  31  are configured by forming two piezoelectric elements  30  on the first movable frame  22 . 
     The pair of first actuators  31  are disposed at positions facing each other across the first axis a 1 . The first actuators  31  allow the mirror portion  20  to swing around the first axis a 1  by applying rotational torque around the first axis a 1  to the mirror portion  20 . 
     The second support portions  23  are disposed on an outside of the first movable frame  22  at positions facing each other across the first axis a 1 . The second support portions  23  are connected to the first movable frame  22  on the second axis a 2 , and swingably support the first movable frame  22  and the mirror portion  20  around the second axis a 2 . In the present embodiment, the second support portion  23  is a torsion bar stretched along the second axis a 2 . 
     The second movable frame  24  is a rectangular frame that surrounds the first movable frame  22  and is connected to the first movable frame  22  on the second axis a 2  via the second support portion  23 . The piezoelectric elements  30  are formed on the second movable frame  24  at positions facing each other across the second axis a 2 . In this way, a pair of second actuators  32  are configured by forming two piezoelectric elements  30  on the second movable frame  24 . 
     The pair of second actuators  32  are disposed at positions facing each other across the second axis a 2 . The second actuators  32  allow the mirror portion  20  to swing around the second axis a 2  by applying rotational torque around the second axis a 2  to the mirror portion  20  and the first movable frame  22 . 
     The connecting portions  25  are disposed on an outside of the second movable frame  24  at positions facing each other across the first axis a 1 . The connecting portions  25  are connected to the second movable frame  24  on the second axis a 2 . 
     The fixed frame  26  is a rectangular frame that surrounds the second movable frame  24  and is connected to the second movable frame  24  on the second axis a 2  via the connecting portion  25 . 
     The first movable frame  22  is provided with a first angle detection sensor  11  in the vicinity of the first support portion  21 . The first angle detection sensor  11  is composed of a piezoelectric element. The first angle detection sensor  11  converts a force applied by deformation of the first support portion  21  accompanying the rotation of the mirror portion  20  around the first axis a 1  into a voltage and outputs a signal. That is, the first angle detection sensor  11  outputs a signal corresponding to an angle of the mirror portion  20  around the first axis a 1 . 
     The second movable frame  24  is provided with a second angle detection sensor  12  in the vicinity of the second support portion  23 . The second angle detection sensor  12  is composed of a piezoelectric element. The second angle detection sensor  12  converts a force applied by deformation of the second support portion  23  accompanying the rotation of the mirror portion  20  around the second axis a 2  into a voltage and outputs a signal. That is, the second angle detection sensor  12  outputs a signal corresponding to an angle of the mirror portion  20  around the second axis a 2 . 
     In  FIGS.  2  and  3   , the wiring line and the electrode pad for giving the driving signal to the first actuator  31  and the second actuator  32  are not shown. In  FIGS.  2  and  3   , a wiring line and an electrode pad for outputting signals from the first angle detection sensor  11  and the second angle detection sensor  12  are not shown. A plurality of the electrode pads are provided on the fixed frame  26 . 
     As shown in  FIGS.  4  and  5   , the MMD  4  is formed, for example, by performing an etching treatment on a silicon on insulator (SOI) substrate  40 . The SOI substrate  40  is a substrate in which a silicon oxide layer  42  is provided on a first silicon active layer  41  made of single crystal silicon, and a second silicon active layer  43  made of single crystal silicon is provided on the silicon oxide layer  42 . 
     The mirror portion  20 , the first support portion  21 , the first movable frame  22 , the second support portion  23 , the second movable frame  24 , and the connecting portion  25  are formed of the second silicon active layer  43  remaining by removing the first silicon active layer  41  and the silicon oxide layer  42  from the SOI substrate  40  by an etching treatment. The second silicon active layer  43  functions as an elastic portion having elasticity. The fixed frame  26  is formed of three layers of the first silicon active layer  41 , the silicon oxide layer  42 , and the second silicon active layer  43 . 
     The first actuator  31  and the second actuator  32  have the piezoelectric element  30  on the second silicon active layer  43 . The piezoelectric element  30  has a laminated structure in which a lower electrode  51 , a piezoelectric film  52 , and an upper electrode  53  are sequentially laminated on the second silicon active layer  43 . An insulating film is provided on the upper electrode  53 , but is not shown. 
     The upper electrode  53  and the lower electrode  51  are formed of, for example, gold (Au) or platinum (Pt). The piezoelectric film  52  is formed of, for example, lead zirconate titanate (PZT), which is a piezoelectric material. The upper electrode  53  and the lower electrode  51  are electrically connected to the driving controller  5  described above via the wiring line and the electrode pad. 
     A driving voltage is applied to the upper electrode  53  from the driving controller  5 . The lower electrode  51  is connected to the driving controller  5  via the wiring line and the electrode pad, and a reference potential (for example, a ground potential) is applied thereto. 
     In a case where a positive or negative voltage is applied to the piezoelectric film  52  in the polarization direction, deformation (for example, expansion and contraction) proportional to the applied voltage occurs. That is, the piezoelectric film  52  exerts a so-called inverse piezoelectric effect. The piezoelectric film  52  exerts an inverse piezoelectric effect by applying a driving voltage from the driving controller  5  to the upper electrode  53 , and displaces the first actuator  31  and the second actuator  32 . 
     As shown in  FIG.  6   , the first angle detection sensor  11  is also similarly composed of the piezoelectric element  30  consisting of the lower electrode  51 , the piezoelectric film  52 , and the upper electrode  53  laminated on the second silicon active layer  43 . In a case where force (pressure) is applied to the piezoelectric film  52 , polarization proportional to the pressure is generated. That is, the piezoelectric film  52  exerts a piezoelectric effect. The piezoelectric film  52  exerts a piezoelectric effect and generates a voltage in a case where force is applied by deformation of the first support portion  21  accompanying the rotation of the mirror portion  20  around the first axis a 1 . 
     Since the second angle detection sensor  12  has the same configuration as the first angle detection sensor  11 , the second angle detection sensor  12  is not shown. 
       FIG.  7    shows an example in which one piezoelectric film  52  of the pair of first actuators  31  is extended and the other piezoelectric film  52  is contracted, thereby generating rotational torque around the first axis a 1  in the first actuator  31 . In this way, one of the pair of first actuators  31  and the other are displaced in opposite directions to each other, whereby the mirror portion  20  rotates around the first axis a 1 . 
     In addition,  FIG.  7    shows an example in which the first actuator  31  is driven in an anti-phase resonance mode in which the displacement direction of the pair of first actuators  31  and the rotation direction of the mirror portion  20  are opposite to each other. The first actuator  31  may be driven in an in-phase resonance mode in which the displacement direction of the pair of first actuators  31  and the rotation direction of the mirror portion  20  are the same direction. 
     A deflection angle (hereinafter, referred to as a first deflection angle) θ 1  of the mirror portion  20  around the first axis a 1  is controlled by the driving signal (hereinafter, referred to as a first driving signal) given to the first actuator  31  by the driving controller  5 . The first driving signal is, for example, a sinusoidal AC voltage. The first driving signal includes a driving voltage waveform V 1A  (t) applied to one of the pair of first actuators  31  and a driving voltage waveform V 1B  (t) applied to the other. The driving voltage waveform Via (t) and the driving voltage waveform V 1B  (t) are in an anti-phase with each other (that is, the phase difference is) 180°. 
     The first deflection angle θ 1  is an angle at which the normal line of the reflecting surface  20 A is inclined with respect to the Z direction in an XZ plane. 
       FIG.  8    shows an example in which one piezoelectric film  52  of the pair of second actuators  32  is extended and the other piezoelectric film  52  is contracted, thereby generating rotational torque around the second axis a 2  in the second actuator  32 . In this way, one of the pair of second actuators  32  and the other are displaced in opposite directions to each other, whereby the mirror portion  20  rotates around the second axis a 2 . 
     In addition,  FIG.  8    shows an example in which the second actuator  32  is driven in an anti-phase resonance mode in which the displacement direction of the pair of second actuators  32  and the rotation direction of the mirror portion  20  are opposite to each other. The second actuator  32  may be driven in an in-phase resonance mode in which the displacement direction of the pair of second actuators  32  and the rotation direction of the mirror portion  20  are the same direction. 
     A deflection angle (hereinafter, referred to as a second deflection angle) θ 2  of the mirror portion  20  around the second axis a 2  is controlled by the driving signal (hereinafter, referred to as a second driving signal) given to the second actuator  32  by the driving controller  5 . The second driving signal is, for example, a sinusoidal AC voltage. The second driving signal includes a driving voltage waveform V 2A  (t) applied to one of the pair of second actuators  32  and a driving voltage waveform V 2B  (t) applied to the other. The driving voltage waveform V 2A  (t) and the driving voltage waveform V 2B  (t) are in an anti-phase with each other (that is, the phase difference is 180°). 
     The second deflection angle θ 2  is an angle at which the normal line of the reflecting surface  20 A is inclined with respect to the Z direction in a YZ plane. 
       FIGS.  9 A and  9 B  show examples of the first driving signal and the second driving signal.  FIG.  9 A  shows the driving voltage waveforms V 1A  (t) and V 1B  (t) included in the first driving signal.  FIG.  9 B  shows the driving voltage waveforms V 2A  (t) and V 2B  (t) included in the second driving signal. 
     The driving voltage waveforms V 1A  (t) and V 1B  (t) are represented as follows, respectively. 
         V   1A   =V   off1   +V   1  sin(2π f   d1   t )
 
         V   1B   =V   off1   +V   1  sin(2π f   d1   t +α)
 
     Here, V 1  is the amplitude voltage. V off1  is the bias voltage. f d1  is the driving frequency (hereinafter, referred to as the first driving frequency). t is time. α is the phase difference between the driving voltage waveforms V 1A  (t) and V 1B  (t). In the present embodiment, for example, α=180°. 
     By applying the driving voltage waveforms V 1A  (t) and V 1B  (t) to the pair of first actuators  31 , the mirror portion  20  swings around the first axis a 1  at the first driving frequency f d1  (see  FIG.  7   ). 
     The driving voltage waveforms V 2A  (t) and V 2B  (t) are represented as follows, respectively. 
         V   2A   =V   off2   +V   2  sin(2π f   d2   t φ)
 
         V   2B   =V   off2   +V   2  sin(2π f   d2   t +β+φ)
 
     Here, V 2  is the amplitude voltage. V off2  is the bias voltage. f d2  is the driving frequency (hereinafter, referred to as the second driving frequency). t is time. β is the phase difference between the driving voltage waveforms V 2A  (t) and V 2B  (t). In the present embodiment, for example, β=180°. In addition, φ is the phase difference between the driving voltage waveforms V 1A  (t) and V 1B  (t) and the driving voltage waveforms V 2A  (t) and V 2B  (t). In the present embodiment, for example, V off1 =V off2 =0 V. 
     By applying the driving voltage waveforms V 2A  (t) and V 2B  (t) to the pair of second actuators  32 , the mirror portion  20  swings around the second axis a 2  at the second driving frequency f d2  (see  FIG.  8   ). 
     The first driving frequency f d1  is set so as to match the resonance frequency around the first axis a 1  of the mirror portion  20 . The second driving frequency f d2  is set so as to match the resonance frequency around the second axis a 2  of the mirror portion  20 . In the present embodiment, f d1 &gt;f d2 . That is, in the mirror portion  20 , a swing frequency around the first axis a 1  is higher than a swing frequency around the second axis a 2 . The first driving frequency f d1  and the second driving frequency f d2  do not necessarily have to match the resonance frequency. For example, the first driving frequency f d1  and the second driving frequency f d2  may be frequencies within a frequency range in the vicinity of the resonance frequency, respectively. This frequency range may be, for example, a range of a half-width of frequency distribution having a resonance frequency as a peak value, or may be, for example, within a range of a so-called Q value. 
       FIG.  10    shows an example of a configuration of the driving controller  5 . The driving controller  5  includes a mirror driving unit  4 A and a light source driving unit  3 A. The mirror driving unit  4 A includes a first driving signal generation unit  60 A, a first signal processing unit  61 A, a first angle derivation unit  62 A, a first voltage adjustment unit  63 A, a second driving signal generation unit  60 B, a second signal processing unit  61 B, a second angle derivation unit  62 B, and a second voltage adjustment unit  63 B. 
     The first driving signal generation unit  60 A, the first signal processing unit  61 A, the first angle derivation unit  62 A, and the first voltage adjustment unit  63 A control a first deflection angle θ 1  of the mirror portion  20 . The second driving signal generation unit  60 B, the second signal processing unit  61 B, the second angle derivation unit  62 B, and the second voltage adjustment unit  63 B control a second deflection angle θ 2  of the mirror portion  20 . 
     The first driving signal generation unit  60 A generates the first driving signal including the above-described driving voltage waveforms V 1A  (t) and V 1B  (t) based on a reference waveform, and applies the generated first driving signal to the pair of first actuators  31 . Thereby, the mirror portion  20  swings around the first axis a 1 . The first angle detection sensor  11  outputs a signal S 1  corresponding to an angle of the mirror portion  20  around the first axis a 1 . 
     The second driving signal generation unit  60 B generates the second driving signal including the above-described driving voltage waveforms V 2A  (t) and V 2B  (t) based on a reference waveform, and applies the generated second driving signal to the pair of second actuators  32 . Thereby, the mirror portion  20  swings around the second axis a 2 . The second angle detection sensor  12  outputs a signal S 2  corresponding to an angle of the mirror portion  20  around the second axis a 2 . 
     The first driving signal generated by the first driving signal generation unit  60 A and the second driving signal generated by the second driving signal generation unit  60 B are phase-synchronized. 
       FIG.  11    shows an example of a signal output from the first angle detection sensor  11 . In  FIG.  11   , S 1   a  represents a signal output from the first angle detection sensor  11  in a case where the mirror portion  20  swings only around the first axis a 1  without swinging around the second axis a 2 . The signal S 1   a  is a waveform signal similar to a sinusoidal wave having the first driving frequency f d1 . 
     In a case where the mirror portion  20  swings around the first axis a 1  and the second axis a 2  simultaneously, a vibration noise RN 1  caused by the swing of the mirror portion  20  around the second axis a 2  is superimposed on the output signal of the first angle detection sensor  11 . The vibration noise RN 1  has the second driving frequency f d2 . S 1   b  represents a signal in which the vibration noise RN 1  is superimposed on the signal S 1   a . For the purpose of the description of this embodiment, the vibration noise RN 1  is emphasized. 
     As described above, in a case of the biaxial drive, the signal S 1   b  on which the vibration noise RN 1  is superimposed is output from the first angle detection sensor  11 , and an amplitude of the signal S 1   b  fluctuates every cycle. Therefore, it is difficult to directly obtain the deflection angle based on the signal S 1   b  output from the first angle detection sensor  11 . 
       FIG.  12    shows an example of a signal output from the second angle detection sensor  12 . In  FIG.  12   , S 2   a  represents a signal output from the second angle detection sensor  12  in a case where the mirror portion  20  swings only around the second axis a 2  without swinging around the first axis a 1 . The signal S 2   a  is a waveform signal similar to a sinusoidal wave having the second driving frequency f d2 . 
     In a case where the mirror portion  20  swings around the first axis a 1  and the second axis a 2  simultaneously, a vibration noise RN 2  caused by the swing of the mirror portion  20  around the first axis a 1  is superimposed on the output signal of the second angle detection sensor  12 . The vibration noise RN 2  has the first driving frequency f d1 . S 2   b  represents a signal in which the vibration noise RN 2  is superimposed on the signal S 2   a . For the purpose of the description of this embodiment, the vibration noise RN 2  is emphasized. 
     As described above, in a case of the biaxial drive, the signal S 2   b  on which the vibration noise RN 2  is superimposed is output from the second angle detection sensor  12 , and an amplitude of the signal S 2   b  fluctuates every cycle. Therefore, it is difficult to directly obtain the deflection angle based on the signal S 2   b  output from the second angle detection sensor  12 . 
     The first signal processing unit  61 A performs the first frequency filter processing based on the first driving frequency f d1  on the signal S 1   b  output from the first angle detection sensor  11 . For example, the first signal processing unit  61 A is a band pass filter circuit having the frequency characteristics shown in  FIG.  13   . As shown in  FIG.  13   , the first signal processing unit  61 A has a pass band B 1  having the first driving frequency f d1  as a center frequency. The pass band B 1  is, for example, a frequency band of f d1 ±5 kHz. Since the vibration noise RN 1  has a frequency outside the pass band B 1  (second driving frequency f d2 ), the vibration noise RN 1  is removed by the first frequency filter processing. The pass band B 1  is an example of a first frequency band according to the technique of the present disclosure. 
     The first signal processing unit  61 A extracts only the signal component included in the pass band B 1  from the signal S 1   b , and outputs the extracted frequency component as a first angle detection signal S 1   c .  FIG.  14    shows a state in which the first angle detection signal S 1   c  is generated from the signal S 1   b  by the first frequency filter processing. The first angle detection signal Sic is a signal obtained by removing the vibration noise RN 1  from the signal S 1   b , and corresponds to the signal S 1   a  shown in  FIG.  11   . 
     The second signal processing unit  61 B performs the second frequency filter processing based on the second driving frequency f d2  on the signal S 2   b  output from the second angle detection sensor  12 . For example, the second signal processing unit  61 B is a band pass filter circuit having the frequency characteristics shown in  FIG.  15   . As shown in  FIG.  15   , the second signal processing unit  61 B has a pass band B 2  having the second driving frequency f d2  as a center frequency. The pass band B 2  is, for example, a frequency band of f d2 ±5 kHz. Since the vibration noise RN 2  has a frequency outside the pass band B 2  (first driving frequency f d1 ), the vibration noise RN 2  is removed by the second frequency filter processing. The pass band B 2  is an example of a second frequency band according to the technique of the present disclosure. 
     The second signal processing unit  61 B extracts only the signal component included in the pass band B 2  from the signal S 2   b , and outputs the extracted frequency component as a second angle detection signal S 2   c .  FIG.  16    shows a state in which the second angle detection signal S 2   c  is generated from the signal S 2   b  by the second frequency filter processing. The second angle detection signal S 2   c  is a signal obtained by removing the vibration noise RN 2  from the signal S 2   b , and corresponds to the signal S 2   a  shown in  FIG.  12   . 
     The first angle derivation unit  62 A obtains a first angle, which is an angle of the mirror portion  20  around the first axis a 1 , based on the first angle detection signal S 1   c . Specifically, the first angle derivation unit  62 A obtains a peak to peak (P-P) value V p-p1  corresponding to an amplitude of the first angle detection signal S 1   c  (see  FIG.  14   ). The first angle derivation unit  62 A holds data showing a relationship between the maximum value (hereinafter, referred to as the first maximum deflection angle) θ m1  of the first deflection angle θ 1  and the P-P value V p-p1  shown in  FIG.  17   . Based on this data, the first angle derivation unit  62 A obtains the first maximum deflection angle θ m1  corresponding to the P-P value V p-p1  obtained from the first angle detection signal Sic. In the present embodiment, the first maximum deflection angle θ m1  corresponds to the first angle. 
     The second angle derivation unit  62 B obtains a second angle, which is an angle of the mirror portion  20  around the second axis a 2 , based on the second angle detection signal S 2   c . Specifically, the second angle derivation unit  62 B obtains a P-P value V p-p2  corresponding to an amplitude of the second angle detection signal S 2   c  (see  FIG.  16   ). The second angle derivation unit  62 B holds data showing a relationship between the maximum value (hereinafter, referred to as the second maximum deflection angle) θ m2  of the second deflection angle θ 2  and the P-P value V p-p2  shown in  FIG.  18   . Based on this data, the second angle derivation unit  62 B obtains the second maximum deflection angle θ m2  corresponding to the P-P value V p-p2  obtained from the second angle detection signal S 2   c . In the present embodiment, the second maximum deflection angle θ m2  corresponds to the second angle. 
     The first voltage adjustment unit  63 A adjusts a voltage value of the first driving signal generated by the first driving signal generation unit  60 A based on the first angle derived by the first angle derivation unit  62 A. Specifically, the first voltage adjustment unit  63 A adjusts amplitude voltages V 1  of the driving voltage waveforms V 1A  (t) and V 1B  (t) included in the first driving signal, based on the first maximum deflection angle θ m1  derived by the first angle derivation unit  62 A. 
       FIG.  19    shows an example of voltage adjustment processing by the first voltage adjustment unit  63 A. As shown in  FIG.  19   , first, the first voltage adjustment unit  63 A determines whether or not the driving of the first actuator  31  has started by outputting the first driving signal from the first driving signal generation unit  60 A (Step S 10 ). 
     In a case where it is determined that the driving of the first actuator  31  has started (Step S 10 : YES), the first voltage adjustment unit  63 A starts the operation. In a case where the first voltage adjustment unit  63 A acquires the first maximum deflection angle θ m1  as the first angle from the first angle derivation unit  62 A (Step S 11 ), the first voltage adjustment unit  63 A determines whether or not the first maximum deflection angle θ m1  is within a predetermined set range (Step S 12 ). The set range of Step S 12  is an example of a first condition according to the technique of the present disclosure. That is, in Step S 12 , it is determined whether or not the first angle satisfies the first condition. 
     In a case where the first maximum deflection angle θ m1  is out of the set range (Step S 12 : NO), the first voltage adjustment unit  63 A adjusts the amplitude voltage V 1  of the first driving signal (Step S 13 ). For example, the first voltage adjustment unit  63 A lowers the amplitude voltage V 1  in a case where the first maximum deflection angle θ m1  exceeds an upper limit value of the set range, and raises the amplitude voltage V 1  in a case where the first maximum deflection angle θ m1  falls below a lower limit value of the set range. 
     In a case where the first maximum deflection angle θ m1  is within the set range (Step S 12 : YES), the first voltage adjustment unit  63 A skips Step S 13  and shifts the process to Step S 14 . 
     In Step S 14 , the first voltage adjustment unit  63 A determines whether or not the driving of the first actuator  31  has been completed (Step S 14 ). In a case where it is determined that the driving of the first actuator  31  has not been completed (Step S 14 : NO), the first voltage adjustment unit  63 A returns the process to Step S 11 . In Step S 11 , the first voltage adjustment unit  63 A acquires the first maximum deflection angle θ m1  again from the first angle derivation unit  62 A. 
     As described above, the first voltage adjustment unit  63 A repeatedly executes Steps S 11  to S 13  until it is determined in Step S 14  that the driving of the first actuator  31  has been completed. In a case where it is determined that the driving of the first actuator  31  has been completed (Step S 14 : YES), the first voltage adjustment unit  63 A ends the voltage adjustment processing. 
     The first angle derivation unit  62 A executes a process of deriving the first maximum deflection angle θ m1  as the first angle for each predetermined cycle. 
     The second voltage adjustment unit  63 B adjusts a voltage value of the second driving signal generated by the second driving signal generation unit  60 B based on the second angle derived by the second angle derivation unit  62 B. Specifically, the second voltage adjustment unit  63 B adjusts amplitude voltages V 2  of the driving voltage waveforms V 2A  (t) and V 2B  (t) included in the second driving signal, based on the second maximum deflection angle θ m2  derived by the second angle derivation unit  62 B. 
       FIG.  20    shows an example of voltage adjustment processing by the second voltage adjustment unit  63 B. Each process of Steps S 20  to S 24  shown in  FIG.  20    is the same as each process of Steps S 10  to S 14  shown in  FIG.  19   . Since the voltage adjustment processing by the second voltage adjustment unit  63 B is the same as the voltage adjustment processing by the first voltage adjustment unit  63 A, detailed description thereof is not shown. The set range of Step S 22  is an example of a second condition according to the technique of the present disclosure. That is, in Step S 22 , it is determined whether or not the second angle satisfies the second condition. 
     The second angle derivation unit  62 B executes a process of deriving the second maximum deflection angle θ m2  as the second angle for each predetermined cycle. 
     Returning to  FIG.  10   , the light source driving unit  3 A drives the light source  3  based on drawing data supplied from the outside of the image drawing system  10 , for example. The light source driving unit  3 A controls the irradiation timing of the laser light of the light source  3  based on the drawing data. The light source driving unit  3 A may adjust the irradiation timing based on the first angle and the second angle derived by the first angle derivation unit  62 A and the second angle derivation unit  62 B. 
     As described above, according to the technique of the present disclosure, the first angle detection signal is generated by performing the first frequency filter processing on the output signal of the first angle detection sensor, and the second angle detection signal is generated by performing the second frequency filter processing on the output signal of the second angle detection sensor. The vibration noise is removed by the first frequency filter processing and the second frequency filter processing, and the first angle and the second angle are obtained accurately. Therefore, the deflection angle of the mirror portion can be accurately controlled. 
     Modification Example 
     Next, a modification example of the first embodiment will be described. In the first embodiment, although the first frequency filter processing and the second frequency filter processing are band pass filter processing, the first frequency filter processing and the second frequency filter processing are not limited to the band pass filter processing. For example, the first frequency filter processing may be high-pass filter processing having a cutoff frequency between the first driving frequency f d1  and the second driving frequency f d2 . In addition, the second frequency filter processing may be low-pass filter processing having a cutoff frequency between the first driving frequency f d1  and the second driving frequency f d2 . 
     In the first embodiment, as shown in  FIG.  3   , one first angle detection sensor  11  is provided for the first axis a 1 , and one second angle detection sensor  12  is provided for the second axis a 2 . On the other hand, as shown in  FIG.  21   , the pair of first angle detection sensors  11 A and  11 B may be provided at positions facing each other across the first axis a 1 , and the pair of second angle detection sensors  12 A and  12 B may be provided at positions facing each other across the second axis a 2 . 
     In this case, as shown in  FIG.  22   , the output signals of the pair of first angle detection sensors  11 A and  11 B are input to the first signal processing unit  61 A, respectively. The output signals of the pair of second angle detection sensors  12 A and  12 B are input to the second signal processing unit  61 B, respectively. 
       FIG.  23    shows an example of signals output from the pair of first angle detection sensors  11 A and  11 B. In  FIG.  23   , S 1   a   1  and S 1   a   2  represent signals output from the pair of first angle detection sensors  11 A and  11 B in a case where the mirror portion  20  swings only around the first axis a 1  without swinging around the second axis a 2 . The signals S 1   a   1  and S 1   a   2  are waveform signals similar to a sinusoidal wave having the first driving frequency f d1  and are in an anti-phase with each other. 
     In a case where the mirror portion  20  swings around the first axis a 1  and the second axis a 2  simultaneously, a vibration noise RN 1  caused by the swing of the mirror portion  20  around the second axis a 2  is superimposed on the output signals of the pair of first angle detection sensors  11 A and  11 B. S 1   b   1  represents a signal in which the vibration noise RN 1  is superimposed on the signal S 1   a   1 . S 1   b   2  represents a signal in which the vibration noise RN 1  is superimposed on the signal S 1   a   2 . 
       FIG.  24    shows an example of signals output from the pair of second angle detection sensors  12 A and  12 B. In  FIG.  24   , S 2   a   1  and S 2   a   2  represent signals output from the pair of second angle detection sensors  12 A and  12 B in a case where the mirror portion  20  swings only around the second axis a 2  without swinging around the first axis a 1 . The signals S 2   a   1  and S 2   a   2  are waveform signals similar to a sinusoidal wave having the second driving frequency f d2  and are in an anti-phase with each other. 
     In a case where the mirror portion  20  swings around the first axis a 1  and the second axis a 2  simultaneously, a vibration noise RN 2  caused by the swing of the mirror portion  20  around the first axis a 1  is superimposed on the output signals of the pair of second angle detection sensors  12 A and  12 B. S 2   b   1  represents a signal in which the vibration noise RN 2  is superimposed on the signal S 2   a   1 . S 2   b   2  represents a signal in which the vibration noise RN 2  is superimposed on the signal S 2   a   2 . 
     In the present modification example, the first signal processing unit  61 A performs the above-described first frequency filter processing on each of the signals S 1   b   1  and S 1   b   2  output from the pair of first angle detection sensors  11 A and  11 B. The first angle derivation unit  62 A need only derive the above-described first angle based on both or one of the first angle detection signals S 1   c   1  and S 1   c   2  generated by performing the first frequency filter processing on the signals S 1   b   1  and S 1   b   2 . 
     Similarly, the second signal processing unit  61 B performs the above-described second frequency filter processing on each of the signals s 2   b   1  and S 2   b   2  output from the pair of second angle detection sensors  12 A and  12 B. The second angle derivation unit  62 B need only derive the above-described second angle based on both or one of the second angle detection signals S 2   c   1  and S 2   c   2  generated by performing the second frequency filter processing on the signals S 2   b   1  and S 2   b   2 . 
     Next, a modification example of the first signal processing unit  61 A and the second signal processing unit  61 B will be described.  FIG.  25    shows an example in which the first signal processing unit  61 A includes an analog arithmetic circuit.  FIG.  26    shows an example in which the second signal processing unit  61 B includes an analog arithmetic circuit. 
     As shown in  FIG.  25   , the first signal processing unit  61 A is composed of a buffer amplifier  71 , a variable gain amplifier  72 , a subtraction circuit  73 , and a gain adjustment circuit  74 . The gain adjustment circuit  74  is composed of a first band pass filter (BPF) circuit  75 A, a second BPF circuit  75 B, a first detection circuit  76 A, a second detection circuit  76 B, and a subtraction circuit  77 . The subtraction circuit  73  and the subtraction circuit  77  are differential amplification circuits including an operational amplifier. 
     The signal S 1   b   1  output from the first angle detection sensor  11 A is input to a positive input terminal (non-inverting input terminal) of the subtraction circuit  73  via the buffer amplifier  71 . In addition, the signal output from the buffer amplifier  71  is branched in the middle of the process before being input to the subtraction circuit  73 , and is input to the first BPF circuit  75 A in the gain adjustment circuit  74 . 
     The signal S 1   b   2  output from the first angle detection sensor  11 B is input to a negative input terminal (inverting input terminal) of the subtraction circuit  73  via the variable gain amplifier  72 . In addition, the signal output from the variable gain amplifier  72  is branched in the middle of the process before being input to the subtraction circuit  73 , and is input to the second BPF circuit  75 B in the gain adjustment circuit  74 . 
     Each of the first BPF circuit  75 A and the second BPF circuit  75 B has a pass band having the second driving frequency f d2  as a center frequency. The first BPF circuit  75 A and the second BPF circuit  75 B are, for example, band pass filter circuits having the frequency characteristics shown in  FIG.  15   . The first BPF circuit  75 A extracts and outputs the vibration noise RN 1  (see  FIG.  13   ) from the signal input from the buffer amplifier  71 . The second BPF circuit  75 B extracts and outputs the vibration noise RN 1  (see  FIG.  13   ) from the signal input from the variable gain amplifier  72 . 
     Each of the first detection circuit  76 A and the second detection circuit  76 B is composed of, for example, a root mean squared value to direct current converter (RMS-DC converter). The first detection circuit  76 A converts the amplitude of the vibration noise RN 1  input from the first BPF circuit  75 A into a DC voltage signal and inputs the signal to the positive input terminal of the subtraction circuit  77 . The second detection circuit  76 B converts the amplitude of the vibration noise RN 1  input from the second BPF circuit  75 B into a DC voltage signal and inputs the signal to the negative input terminal of the subtraction circuit  77 . 
     The subtraction circuit  77  outputs a value d 1  obtained by subtracting the DC voltage signal input from the second detection circuit  76 B from the DC voltage signal input from the first detection circuit  76 A. The value d 1  corresponds to a difference between the amplitude of the vibration noise RN 1  included in the signal S 1   b   1  output from the first angle detection sensor  11 A and the amplitude of the vibration noise RN 1  included in the signal S 2   b   2  output from the first angle detection sensor  11 B. The subtraction circuit  77  inputs the value d 1  as a gain adjustment value to a gain adjustment terminal of the variable gain amplifier  72 . 
     The variable gain amplifier  72  adjusts an amplitude of the signal S 2   b   2  by multiplying the signal S 2   b   2  input from the first angle detection sensor  11 B by the value d 1  input as the gain adjustment value. In this way, a feedback control is performed by the gain adjustment circuit  74 , so that the amplitude of the vibration noise RN 1  included in the signal S 2   b   2  after passing through the variable gain amplifier  72  is adjusted so as to be equal to the amplitude of the vibration noise RN 1  included in the signal S 1   b   1  after passing through the buffer amplifier  71 . 
     The subtraction circuit  73  outputs a value obtained by subtracting the signal S 2   b   2  input to the negative input terminal from the signal S 1   b   1  input to the positive input terminal. Since the amplitudes of the vibration noise RN 1  included in both signals are adjusted to be equal to each other by the feedback control, the vibration noise RN 1  included in both signals is offset by the subtraction processing by the subtraction circuit  73 . Therefore, the subtraction circuit  73  outputs a signal corresponding to the first angle detection signal S 1   c  (see  FIG.  14   ), which is a signal from which the vibration noise RN 1  has been removed. The amplitude of the signal output from the subtraction circuit  73  is twice that of the first angle detection signal S 1   c  shown in  FIG.  14   . 
     As shown in  FIG.  26   , the second signal processing unit  61 B is composed of a buffer amplifier  81 , a variable gain amplifier  82 , a subtraction circuit  83 , and a gain adjustment circuit  84 . The gain adjustment circuit  84  is composed of a first BPF circuit  85 A, a second BPF circuit  85 B, a first detection circuit  86 A, a second detection circuit  86 B, and a subtraction circuit  87 . The subtraction circuit  83  and the subtraction circuit  87  are differential amplification circuits including an operational amplifier. 
     The signal S 2   b   1  output from the second angle detection sensor  12 A is input to a positive input terminal of the subtraction circuit  83  via the buffer amplifier  81 . In addition, the signal output from the buffer amplifier  81  is branched in the middle of the process before being input to the subtraction circuit  83 , and is input to the first BPF circuit  85 A in the gain adjustment circuit  84 . 
     The signal S 2   b   2  output from the second angle detection sensor  12 B is input to a negative input terminal of the subtraction circuit  83  via the variable gain amplifier  82 . In addition, the signal output from the variable gain amplifier  82  is branched in the middle of the process before being input to the subtraction circuit  83 , and is input to the second BPF circuit  85 B in the gain adjustment circuit  84 . 
     The configuration of each circuit in the gain adjustment circuit  84  is the same except that the first BPF circuit  85 A and the second BPF circuit  85 B each have a pass band having the first driving frequency f d1  as a center frequency. That is, the gain adjustment circuit  84  generates a value d 2  representing a difference between the amplitude of the vibration noise RN 2  included in the signal S 2   b   1  output from the second angle detection sensor  12 A and the amplitude of the vibration noise RN 2  included in the signal S 2   b   2  output from the second angle detection sensor  12 B. 
     The variable gain amplifier  82  adjusts an amplitude of the signal S 2   b   2  input from the second angle detection sensor  12 B based on the value d 2  input as the gain adjustment value from the gain adjustment circuit  84 . As a result, the subtraction circuit  83  outputs a signal corresponding to the second angle detection signal S 2   c  (see  FIG.  16   ), which is a signal from which the vibration noise RN 2  has been removed. The amplitude of the signal output from the subtraction circuit  83  is twice that of the second angle detection signal S 2   c  shown in  FIG.  16   . 
     The configuration of the MMD  4  shown in the above embodiment is an example. The configuration of the MMD  4  can be modified in various ways. For example, the first actuator  31  that allows the mirror portion  20  to swing around the first axis a 1  may be disposed on the second movable frame  24 , and the second actuator  32  that allows the mirror portion  20  to swing around the second axis a 2  may be disposed on the first movable frame  22 . 
     The hardware configuration of the driving controller  5  can be variously modified. The processing unit of the driving controller  5  may be composed of one processor or may be composed of a combination of two or more processors of the same type or different types. The processor includes, for example, a central processing unit (CPU), a programmable logic device (PLD), or a dedicated electric circuit. As is well known, the CPU is a general-purpose processor that executes software (program) to function as various processing units. The PLD is a processor such as a field programmable gate array (FPGA) whose circuit configuration can be changed after manufacture. The dedicated electric circuit is a processor that has a dedicated circuit configuration designed to perform a specific process, such as an application specific integrated circuit (ASIC). The processor may be an analog arithmetic circuit or a digital arithmetic circuit. 
     For example, the gain adjustment circuit  74  (see  FIG.  25   ) in the first signal processing unit  61 A and the gain adjustment circuit  84  (see  FIG.  26   ) in the second signal processing unit  61 B can include a digital arithmetic circuit such as a microcomputer, a CPU, or an FPGA. 
       FIG.  27    shows an example in which the gain adjustment circuit  74  in the first signal processing unit  61 A includes a digital arithmetic circuit. In  FIG.  27   , the gain adjustment circuit  74  includes a first analog to digital (A/D) converter  90 A, a second A/D converter  90 B, a first fast Fourier transform (FFT) circuit  91 A, a second FFT circuit  91 B, and an adjustment value calculation unit  92 . 
     The signal S 1   b   1  is input to the first A/D converter  90 A from the first angle detection sensor  11 A via the buffer amplifier  71 . The signal S 2   b   2  is input to the second A/D converter  90 B from the first angle detection sensor  11 B via the variable gain amplifier  72 . The first A/D converter  90 A converts the input signal S 1   b   1  into a digital signal and inputs the signal to the first FFT circuit  91 A. The second A/D converter  90 B converts the input signal S 2   b   2  into a digital signal and inputs the signal to the second FFT circuit  91 B. 
     The first FFT circuit  91 A decomposes the signal S 1   b   1  into frequency components by performing a Fourier transform on the input signal S 1   b   1 . The second FFT circuit  91 B decomposes the signal S 2   b   2  into frequency components by performing a Fourier transform on the input signal S 1   b   2 . As shown in  FIG.  28   , in the signal S 1   b   1  and the signal S 2   b   2 , frequency components appear in the vicinity of the first driving frequency fd 1  and the second driving frequency fd 2 . The frequency component in the vicinity of the second driving frequency fd 2  (hereinafter, referred to as a low-frequency component) is caused by the vibration noise RN 1 . 
     The adjustment value calculation unit  92  determines the value d 1  as the gain adjustment value such that an intensity P 1  of the low-frequency component of the signal S 1   b   1  matches an intensity P 2  of the low-frequency component of the signal S 2   b   2 . Specifically, the adjustment value calculation unit  92  calculates a value d 1  that satisfies “P 1 −d 1 ×P 2 =0”, and inputs the calculated value d 1  to a gain adjustment terminal of the variable gain amplifier  72 . 
     Similarly, the gain adjustment circuit  84  in the second signal processing unit  61 B can also include a digital arithmetic circuit. In this case, the gain adjustment circuit  84  has the same configuration as the gain adjustment circuit  74  shown in  FIG.  27    except that the value d 2  as the gain adjustment value is determined such that an intensity of the high-frequency component (frequency component in the vicinity of the first driving frequency f d1 ) of the signal S 2   b   1  matches an intensity of the high-frequency component of the signal S 2   b   2 . 
     The gain adjustment circuit  74  can also be configured to calculate the value d 1  as the gain adjustment value such that the low-frequency component obtained by performing a Fourier transform on a subtraction signal D1 represented by the following equation is 0. 
         D 1= S 1 b   1   −d   1   ×S 1 b   2    
     Similarly, the gain adjustment circuit  84  can also be configured to calculate the value d 2  as the gain adjustment value such that the high-frequency component obtained by performing a Fourier transform on a subtraction signal D2 represented by the following equation is 0. 
         D 2= S 2 b   1   −d   2   ×S 2 b   2    
     All documents, patent applications, and technical standards mentioned in this specification are incorporated herein by reference to the same extent as in a case where each document, each patent application, and each technical standard are specifically and individually described by being incorporated by reference.