Patent Description:
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 <CIT> and <CIT>).

<CIT> discloses "obtaining an amplitude of rotation of a mirror portion based on an output signal of a detection signal acquisition unit". Specifically, <CIT> 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).

<CIT> 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". <CIT> is another relevant document.

<CIT> and <CIT> 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.

In order to keep the maximum deflection angle of the mirror portion constant, it is necessary to accurately detect the amplitude of the output signal of the angle detection sensor. In addition, in a case where the mirror portion is resonantly driven, it is necessary to accurately detect a phase of the output signal of the angle detection sensor in order to maintain the resonance state of the swing of the mirror portion.

However, in a case where a vibration noise is superimposed on the output signal of the angle detection sensor, the amplitude and phase of the output signal of the angle detection sensor cannot be accurately detected, and it is difficult to accurately control the swing of the mirror portion.

An object of the technique of the present disclosure is to provide an optical scanning device, a method of driving the optical scanning device, and an image drawing system which can accurately control swing of a 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 pair of first angle detection sensors that output a signal corresponding to an angle of the mirror portion around the first axis, the pair of first angle detection sensors being disposed at positions facing each other across the first axis or the second axis; and at least one processor, in which the processor generates a first angle detection signal representing the angle of the mirror portion around the first axis by adding or subtracting a pair of first output signals output from the pair of first angle detection sensors.

It is preferable that the processor adjusts an amplitude level of at least one of the pair of first output signals to match amplitudes of vibration noises respectively included in the pair of first output signals with each other, and then adds or subtracts the pair of first output signals.

It is preferable that the pair of first angle detection sensors are disposed at the positions facing each other across the first axis, and that the processor generates the first angle detection signal by subtracting one of the pair of first output signals whose amplitude level has been adjusted from the other.

It is preferable that the pair of first angle detection sensors are disposed at the positions facing each other across the second axis, and that the processor generates the first angle detection signal by adding the pair of first output signals whose amplitude level has been adjusted.

It is preferable that the processor includes a first driving signal generation unit that generates a first driving signal applied to the first actuator, and feeds back the first angle detection signal to the first driving signal generation unit.

It is preferable that the first driving signal generation unit is a drive circuit having a phase synchronization circuit.

It is preferable that the first driving signal is a sinusoidal wave.

It is preferable that the first angle detection sensor is a piezoelectric element.

It is preferable that the optical scanning device further comprises: a pair of second angle detection sensors that output a signal corresponding to an angle of the mirror portion around the second axis, the pair of second angle detection sensors being disposed at positions facing each other across the first axis or the second axis, and that the processor generates a second angle detection signal representing the angle of the mirror portion around the second axis by adjusting an amplitude level of at least one of a pair of second output signals output from the pair of second angle detection sensors and adding or subtracting the pair of second output signals whose amplitude level has been adjusted.

It is preferable that the processor adjusts the amplitude level of at least one of the pair of second output signals to match amplitudes of vibration noises respectively included in the pair of second output signals with each other, and then adds or subtracts the pair of second output signals.

It is preferable that the pair of second angle detection sensors are disposed at the positions facing each other across the second axis, and that the processor generates the second angle detection signal by subtracting one of the pair of second output signals whose amplitude level has been adjusted from the other.

It is preferable that the pair of second angle detection sensors are disposed at the positions facing each other across the first axis, and that the processor generates the second angle detection signal by adding the pair of second output signals whose amplitude level has been adjusted.

It is preferable that the processor includes a second driving signal generation unit that generates a second driving signal applied to the second actuator, and feeds back the second angle detection signal to the second driving signal generation unit.

It is preferable that the second driving signal generation unit is a drive circuit having a phase synchronization circuit.

It is preferable that the second driving signal is a sinusoidal wave.

It is preferable that the second angle detection sensor is a piezoelectric element.

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 controls a light irradiation timing of the light source based on the first angle detection signal and the second angle detection signal.

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, and a pair of first angle detection sensors that output a signal corresponding to an angle of the mirror portion around the first axis, the pair of first angle detection sensors being disposed at positions facing each other across the first axis or the second axis, the method comprising: generating a first angle detection signal representing the angle of the mirror portion around the first axis by adding or subtracting a pair of first output signals output from the pair of first angle detection sensors.

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 swing of a mirror portion.

An example of an embodiment relating to the technique of the present disclosure will be described with reference to the accompanying drawings.

<FIG> schematically shows an image drawing system <NUM> according to an embodiment. The image drawing system <NUM> includes an optical scanning device <NUM> and a light source <NUM>. The optical scanning device <NUM> includes a micromirror device (hereinafter, referred to as micromirror device (MMD)) <NUM> and a driving controller <NUM>. The driving controller <NUM> is an example of a "processor" according to the technique of the present disclosure.

The image drawing system <NUM> draws an image by reflecting a light beam L emitted from the light source <NUM> by the MMD <NUM> and optically scanning a surface to be scanned <NUM> with the reflected light beam under the control of the driving controller <NUM>. The surface to be scanned <NUM> is, for example, a screen.

The image drawing system <NUM> is applied to, for example, a Lissajous scanning type laser display. Specifically, the image drawing system <NUM> can be applied to a laser scanning display such as augmented reality (AR) glass or virtual reality (VR) glass.

The MMD <NUM> is a piezoelectric biaxial drive type micromirror device capable of allowing a mirror portion <NUM> (see <FIG>) to swing around a first axis a<NUM> and a second axis a<NUM> orthogonal to the first axis a<NUM>. Hereinafter, the direction parallel to the second axis a<NUM> is referred to as an X direction, the direction parallel to the first axis a<NUM> is a Y direction, and the direction orthogonal to the first axis a<NUM> and the second axis a<NUM> is referred to as a Z direction.

The light source <NUM> is a laser device that emits, for example, laser light as the light beam L. It is preferable that the light source <NUM> emits the light beam L perpendicularly to a reflecting surface 20A (see <FIG>) included in the mirror portion <NUM> in a state where the mirror portion <NUM> of the MMD <NUM> is stationary. In a case where the light beam L is emitted from the light source <NUM> perpendicularly to the reflecting surface 20A, the light source <NUM> may become an obstacle in scanning the surface to be scanned <NUM> the light beam L for drawing. Therefore, it is preferable that the light beam L emitted from the light source <NUM> is controlled by an optical system to be emitted perpendicularly to the reflecting surface 20A. 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 <NUM> is applied to the reflecting surface 20A is not limited to the perpendicular direction, and the light beam L may be emitted obliquely to the reflecting surface 20A.

The driving controller <NUM> outputs a driving signal to the light source <NUM> and the MMD <NUM> based on optical scanning information. The light source <NUM> generates the light beam L based on the input driving signal and emits the light beam L to the MMD <NUM>. The MMD <NUM> allows the mirror portion <NUM> to swing around the first axis a<NUM> and the second axis a<NUM> based on the input driving signal.

As will be described in detail below, the driving controller <NUM> allows the mirror portion <NUM> to resonate around the first axis a<NUM> and the second axis a<NUM>, so that the surface to be scanned <NUM> is scanned with the light beam L reflected by the mirror portion <NUM> such that a Lissajous waveform is drawn. This optical scanning method is called a Lissajous scanning method.

Next, an example of the MMD <NUM> will be described with reference to <FIG>. <FIG> is an external perspective view of the MMD <NUM>. <FIG> is a plan view of the MMD <NUM> as viewed from the light incident side. <FIG> is a cross-sectional view taken along the line A-A in <FIG>. <FIG> is a cross-sectional view taken along the line B-B of <FIG>. <FIG> is a cross-sectional view taken along the line C-C of <FIG>.

As shown in <FIG> and <FIG>, the MMD <NUM> includes a mirror portion <NUM>, a first support portion <NUM>, a first movable frame <NUM>, a second support portion <NUM>, a second movable frame <NUM>, a connecting portion <NUM>, and a fixed frame <NUM>. The MMD <NUM> is a so-called MEMS scanner.

The mirror portion <NUM> has a reflecting surface 20A for reflecting incident light. The reflecting surface 20A is provided on one surface of the mirror portion <NUM>, 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 20A is, for example, circular with the intersection of the first axis a<NUM> and the second axis a<NUM> as the center.

The first axis a<NUM> and the second axis a<NUM> exist in a plane including the reflecting surface 20A in a case where the mirror portion <NUM> is stationary. The planar shape of the MMD <NUM> is rectangular, line-symmetrical with respect to the first axis a<NUM>, and line-symmetrical with respect to the second axis a<NUM>.

The first support portions <NUM> are disposed on an outside of the mirror portion <NUM> at positions facing each other across the second axis a<NUM>. The first support portions <NUM> are connected to the mirror portion <NUM> on the first axis a<NUM>, and swingably support the mirror portion <NUM> around the first axis a<NUM>. In the present embodiment, the first support portion <NUM> is a torsion bar stretched along the first axis a<NUM>.

The first movable frame <NUM> is a rectangular frame that surrounds the mirror portion <NUM> and is connected to the mirror portion <NUM> on the first axis a<NUM> via the first support portion <NUM>. Piezoelectric elements <NUM> are formed on the first movable frame <NUM> at positions facing each other across the first axis a<NUM>. In this way, a pair of first actuators <NUM> are configured by forming two piezoelectric elements <NUM> on the first movable frame <NUM>.

The pair of first actuators <NUM> are disposed at positions facing each other across the first axis a<NUM>. The first actuators <NUM> allow the mirror portion <NUM> to swing around the first axis a<NUM> by applying rotational torque around the first axis a<NUM> to the mirror portion <NUM>.

The second support portions <NUM> are disposed on an outside of the first movable frame <NUM> at positions facing each other across the first axis a<NUM>. The second support portions <NUM> are connected to the first movable frame <NUM> on the second axis a<NUM>, and swingably support the first movable frame <NUM> and the mirror portion <NUM> around the second axis a<NUM>. In the present embodiment, the second support portion <NUM> is a torsion bar stretched along the second axis a<NUM>.

The second movable frame <NUM> is a rectangular frame that surrounds the first movable frame <NUM> and is connected to the first movable frame <NUM> on the second axis a<NUM> via the second support portion <NUM>. The piezoelectric elements <NUM> are formed on the second movable frame <NUM> at positions facing each other across the second axis a<NUM>. In this way, a pair of second actuators <NUM> are configured by forming two piezoelectric elements <NUM> on the second movable frame <NUM>.

The pair of second actuators <NUM> are disposed at positions facing each other across the second axis a<NUM>. The second actuators <NUM> allow the mirror portion <NUM> to swing around the second axis a<NUM> by applying rotational torque around the second axis a<NUM> to the mirror portion <NUM> and the first movable frame <NUM>.

The connecting portions <NUM> are disposed on an outside of the second movable frame <NUM> at positions facing each other across the first axis a<NUM>. The connecting portions <NUM> are connected to the second movable frame <NUM> on the second axis a<NUM>.

The fixed frame <NUM> is a rectangular frame that surrounds the second movable frame <NUM> and is connected to the second movable frame <NUM> on the second axis a<NUM> via the connecting portion <NUM>.

The first movable frame <NUM> is provided with a pair of first angle detection sensors 11A and 11B at positions facing each other across the first axis a<NUM> in the vicinity of the first support portion <NUM>. Each of the pair of first angle detection sensors 11A and 11B is composed of a piezoelectric element. Each of the first angle detection sensors 11A and 11B converts a force applied by deformation of the first support portion <NUM> accompanying the rotation of the mirror portion <NUM> around the first axis a<NUM> into a voltage and outputs a signal. That is, the first angle detection sensors 11A and 11B output signals corresponding to angles of the mirror portion <NUM> around the first axis a<NUM>.

The second movable frame <NUM> is provided with a pair of second angle detection sensors 12A and 12B at positions facing each other across the second axis a<NUM> in the vicinity of the second support portion <NUM>. Each of the pair of second angle detection sensors 12A and 12B is composed of a piezoelectric element. Each of the second angle detection sensors 12A and 12B converts a force applied by deformation of the second support portion <NUM> accompanying the rotation of the mirror portion <NUM> around the second axis a<NUM> into a voltage and outputs a signal. That is, the second angle detection sensors 12A and 12B output signals corresponding to angles of the mirror portion <NUM> around the second axis a<NUM>.

In <FIG> and <FIG>, the wiring line and the electrode pad for giving the driving signal to the first actuator <NUM> and the second actuator <NUM> are not shown. In <FIG> and <FIG>, a wiring line and an electrode pad for outputting signals from the first angle detection sensors 11A and 11B and the second angle detection sensors 12A and 12B are not shown. A plurality of the electrode pads are provided on the fixed frame <NUM>.

As shown in <FIG> and <FIG>, the MMD <NUM> is formed, for example, by performing an etching treatment on a silicon on insulator (SOI) substrate <NUM>. The SOI substrate <NUM> is a substrate in which a silicon oxide layer <NUM> is provided on a first silicon active layer <NUM> made of single crystal silicon, and a second silicon active layer <NUM> made of single crystal silicon is provided on the silicon oxide layer <NUM>.

The mirror portion <NUM>, the first support portion <NUM>, the first movable frame <NUM>, the second support portion <NUM>, the second movable frame <NUM>, and the connecting portion <NUM> are formed of the second silicon active layer <NUM> remaining by removing the first silicon active layer <NUM> and the silicon oxide layer <NUM> from the SOI substrate <NUM> by an etching treatment. The second silicon active layer <NUM> functions as an elastic portion having elasticity. The fixed frame <NUM> is formed of three layers of the first silicon active layer <NUM>, the silicon oxide layer <NUM>, and the second silicon active layer <NUM>.

The first actuator <NUM> and the second actuator <NUM> have the piezoelectric element <NUM> on the second silicon active layer <NUM>. The piezoelectric element <NUM> has a laminated structure in which a lower electrode <NUM>, a piezoelectric film <NUM>, and an upper electrode <NUM> are sequentially laminated on the second silicon active layer <NUM>. An insulating film is provided on the upper electrode <NUM>, but is not shown.

The upper electrode <NUM> and the lower electrode <NUM> are formed of, for example, gold (Au) or platinum (Pt). The piezoelectric film <NUM> is formed of, for example, lead zirconate titanate (PZT), which is a piezoelectric material. The upper electrode <NUM> and the lower electrode <NUM> are electrically connected to the driving controller <NUM> described above via the wiring line and the electrode pad.

A driving voltage is applied to the upper electrode <NUM> from the driving controller <NUM>. The lower electrode <NUM> is connected to the driving controller <NUM> 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 <NUM> in the polarization direction, deformation (for example, expansion and contraction) proportional to the applied voltage occurs. That is, the piezoelectric film <NUM> exerts a so-called inverse piezoelectric effect. The piezoelectric film <NUM> exerts an inverse piezoelectric effect by applying a driving voltage from the driving controller <NUM> to the upper electrode <NUM>, and displaces the first actuator <NUM> and the second actuator <NUM>.

As shown in <FIG>, the first angle detection sensor 11A is also similarly composed of the piezoelectric element <NUM> consisting of the lower electrode <NUM>, the piezoelectric film <NUM>, and the upper electrode <NUM> laminated on the second silicon active layer <NUM>. In a case where force (pressure) is applied to the piezoelectric film <NUM>, polarization proportional to the pressure is generated. That is, the piezoelectric film <NUM> exerts a piezoelectric effect. The piezoelectric film <NUM> exerts a piezoelectric effect and generates a voltage in a case where force is applied by deformation of the first support portion <NUM> accompanying the rotation of the mirror portion <NUM> around the first axis a<NUM>.

Since the first angle detection sensor 11B has the same configuration as the first angle detection sensor 11A, the first angle detection sensor 11B is not shown. In addition, since the second angle detection sensors 12A and 12B have the same configuration as the first angle detection sensor 11A, the second angle detection sensors 12A and 12B are not shown.

<FIG> shows an example in which one piezoelectric film <NUM> of the pair of first actuators <NUM> is extended and the other piezoelectric film <NUM> is contracted, thereby generating rotational torque around the first axis a<NUM> in the first actuator <NUM>. In this way, one of the pair of first actuators <NUM> and the other are displaced in opposite directions to each other, whereby the mirror portion <NUM> rotates around the first axis a<NUM>.

In addition, <FIG> shows an example in which the first actuator <NUM> is driven in an anti-phase resonance mode in which the displacement direction of the pair of first actuators <NUM> and the rotation direction of the mirror portion <NUM> are opposite to each other. The first actuator <NUM> may be driven in an in-phase resonance mode in which the displacement direction of the pair of first actuators <NUM> and the rotation direction of the mirror portion <NUM> are the same direction.

A deflection angle (hereinafter, referred to as a first deflection angle) θ<NUM> of the mirror portion <NUM> around the first axis a<NUM> is controlled by the driving signal (hereinafter, referred to as a first driving signal) given to the first actuator <NUM> by the driving controller <NUM>. The first driving signal is, for example, a sinusoidal AC voltage. The first driving signal includes a driving voltage waveform V1A (t) applied to one of the pair of first actuators <NUM> and a driving voltage waveform V1B (t) applied to the other. The driving voltage waveform V1A (t) and the driving voltage waveform V1B (t) are in an anti-phase with each other (that is, the phase difference is <NUM>°).

The first deflection angle θ<NUM> is an angle at which the normal line of the reflecting surface 20A is inclined with respect to the Z direction in an XZ plane.

<FIG> shows an example in which one piezoelectric film <NUM> of the pair of second actuators <NUM> is extended and the other piezoelectric film <NUM> is contracted, thereby generating rotational torque around the second axis a<NUM> in the second actuator <NUM>. In this way, one of the pair of second actuators <NUM> and the other are displaced in opposite directions to each other, whereby the mirror portion <NUM> rotates around the second axis a<NUM>.

In addition, <FIG> shows an example in which the second actuator <NUM> is driven in an anti-phase resonance mode in which the displacement direction of the pair of second actuators <NUM> and the rotation direction of the mirror portion <NUM> are opposite to each other. The second actuator <NUM> may be driven in an in-phase resonance mode in which the displacement direction of the pair of second actuators <NUM> and the rotation direction of the mirror portion <NUM> are the same direction.

A deflection angle (hereinafter, referred to as a second deflection angle) θ<NUM> of the mirror portion <NUM> around the second axis a<NUM> is controlled by the driving signal (hereinafter, referred to as a second driving signal) given to the second actuator <NUM> by the driving controller <NUM>. The second driving signal is, for example, a sinusoidal AC voltage. The second driving signal includes a driving voltage waveform V2A (t) applied to one of the pair of second actuators <NUM> and a driving voltage waveform V2B (t) applied to the other. The driving voltage waveform V2A (t) and the driving voltage waveform V2B (t) are in an anti-phase with each other (that is, the phase difference is <NUM>°).

The second deflection angle θ<NUM> is an angle at which the normal line of the reflecting surface 20A is inclined with respect to the Z direction in a YZ plane.

<FIG> show examples of the first driving signal and the second driving signal. <FIG> shows the driving voltage waveforms V1A (t) and V1B (t) included in the first driving signal. <FIG> shows the driving voltage waveforms V2A (t) and V2B (t) included in the second driving signal.

The driving voltage waveforms V1A (t) and V1B (t) are represented as follows, respectively. <MAT> <MAT>.

Here, V<NUM> is the amplitude voltage. Voff1 is the bias voltage. fd1 is the driving frequency (hereinafter, referred to as the first driving frequency). α is the phase difference between the driving voltage waveforms V1A (t) and V1B (t). In the present embodiment, for example, α = <NUM>°.

By applying the driving voltage waveforms V1A (t) and V1B (t) to the pair of first actuators <NUM>, the mirror portion <NUM> swings around the first axis a<NUM> at the first driving frequency fd1 (see <FIG>).

The driving voltage waveforms V2A (t) and V2B (t) are represented as follows, respectively. <MAT> <MAT>.

Here, V<NUM> is the amplitude voltage. Voff2 is the bias voltage. fd2 is the driving frequency (hereinafter, referred to as the second driving frequency). β is the phase difference between the driving voltage waveforms V2A (t) and V2B (t). In the present embodiment, for example, β = <NUM>°. In addition, ϕ is the phase difference between the driving voltage waveforms V1A (t) and V1B (t) and the driving voltage waveforms V2A (t) and V2B (t). In the present embodiment, for example, Voff1 = Voff2 = <NUM> V.

By applying the driving voltage waveforms V2A (t) and V2B (t) to the pair of second actuators <NUM>, the mirror portion <NUM> swings around the second axis a<NUM> at the second driving frequency fd2 (see <FIG>).

The first driving frequency fd1 is set so as to match the resonance frequency around the first axis a<NUM> of the mirror portion <NUM>. The second driving frequency fd2 is set so as to match the resonance frequency around the second axis a<NUM> of the mirror portion <NUM>. In the present embodiment, fd1 > fa2. That is, in the mirror portion <NUM>, a swing frequency around the first axis a<NUM> is higher than a swing frequency around the second axis a<NUM>. The first driving frequency fd1 and the second driving frequency fd2 do not necessarily have to match the resonance frequency. For example, the first driving frequency fd1 and the second driving frequency fd2 may be frequencies within a frequency range in the vicinity of the resonance frequency (for example, a range of half-width of frequency distribution having the resonance frequency as a peak value). This frequency range is, for example, within a range of a so-called Q value.

<FIG> shows an example of a configuration of the driving controller <NUM>. The driving controller <NUM> includes a mirror driving unit 4A and a light source driving unit 3A. The mirror driving unit 4A includes a first driving signal generation unit 60A, a first signal processing unit 61A, a first phase shift unit 62A, a first zero cross pulse output unit 63A, a second driving signal generation unit 60B, a second signal processing unit 61B, a second phase shift unit 62B, and a second zero cross pulse output unit 63B.

The first driving signal generation unit 60A, the first signal processing unit 61A, and the first phase shift unit 62A perform feedback control such that the swing of the mirror portion <NUM> around the first axis a<NUM> maintains a resonance state. The second driving signal generation unit 60B, the second signal processing unit 61B, and the second phase shift unit 62B perform feedback control such that the swing of the mirror portion <NUM> around the second axis a<NUM> maintains a resonance state.

The first driving signal generation unit 60A generates the first driving signal including the above-described driving voltage waveforms V1A (t) and V1B (t) based on a reference waveform, and applies the generated first driving signal to the pair of first actuators <NUM> via the first phase shift unit 62A. Thereby, the mirror portion <NUM> swings around the first axis a<NUM>. The first angle detection sensors 11A and 11B output signals corresponding to angles of the mirror portion <NUM> around the first axis a<NUM>.

The second driving signal generation unit 60B generates the second driving signal including the above-described driving voltage waveforms V2A (t) and V2B (t) based on a reference waveform, and applies the generated second driving signal to the pair of second actuators <NUM> via the second phase shift unit 62B. Thereby, the mirror portion <NUM> swings around the second axis a<NUM>. The second angle detection sensors 12A and 12B output signals corresponding to angles of the mirror portion <NUM> around the second axis a<NUM>.

The first driving signal generated by the first driving signal generation unit 60A and the second driving signal generated by the second driving signal generation unit 60B are phase-synchronized.

<FIG> shows an example of signals output from the pair of first angle detection sensors 11A and 11B. In <FIG>, S1a<NUM> and S1a<NUM> represent signals output from the pair of first angle detection sensors 11A and 11B in a case where the mirror portion <NUM> swings only around the first axis a<NUM> without swinging around the second axis a<NUM>. The signals S1a<NUM> and S1a<NUM> are waveform signals similar to a sinusoidal wave having the first driving frequency fd1 and are in an anti-phase with each other.

In a case where the mirror portion <NUM> swings around the first axis a<NUM> and the second axis a<NUM> simultaneously, a vibration noise RN1 caused by the swing of the mirror portion <NUM> around the second axis a<NUM> is superimposed on the output signals of the pair of first angle detection sensors 11A and 11B. S1b<NUM> represents a signal in which the vibration noise RN1 is superimposed on the signal S1a<NUM>. S1b<NUM> represents a signal in which the vibration noise RN1 is superimposed on the signal S1a<NUM>. For the purpose of the description of this embodiment, the vibration noise RN1 is emphasized.

As described above, in a case of the biaxial drive, the signals S1b; and S1b<NUM> on which the vibration noise RN1 is superimposed are output from the first angle detection sensors 11A and 11B, and amplitudes of the signals S1b; and S1b<NUM> fluctuate every cycle. Therefore, it is difficult to directly obtain the amplitude and the phase based on the signals S1b<NUM> and S1b<NUM> output from the first angle detection sensors 11A and 11B.

<FIG> shows an example of signals output from the pair of second angle detection sensors 12A and 12B. In <FIG>, S2a<NUM> and S2a<NUM> represent signals output from the pair of second angle detection sensors 12A and 12B in a case where the mirror portion <NUM> swings only around the second axis a<NUM> without swinging around the first axis a<NUM>. The signals S2a<NUM> and S2a<NUM> are waveform signals similar to a sinusoidal wave having the second driving frequency fd2 and are in an anti-phase with each other.

In a case where the mirror portion <NUM> swings around the first axis a<NUM> and the second axis a<NUM> simultaneously, a vibration noise RN2 caused by the swing of the mirror portion <NUM> around the first axis a<NUM> is superimposed on the output signals of the pair of second angle detection sensors 12A and 12B. S2b<NUM> represents a signal in which the vibration noise RN2 is superimposed on the signal S2a<NUM>. S2b<NUM> represents a signal in which the vibration noise RN2 is superimposed on the signal S2a<NUM>. For the purpose of the description of this embodiment, the vibration noise RN2 is emphasized.

As described above, in a case of the biaxial drive, the signals S12b<NUM> and S2b<NUM> on which the vibration noise RN2 is superimposed are output from the second angle detection sensors 12A and 12B, and amplitudes of the signals S2b<NUM> and S2b<NUM> fluctuate every cycle. Therefore, it is difficult to directly obtain the amplitude and the phase based on the signals S2b<NUM> and S2b<NUM> output from the second angle detection sensors 12A and 12B.

The first signal processing unit 61A generates a signal (hereinafter, a first angle detection signal) S1c from which the vibration noise RN1 has been removed based on S1a<NUM> and S1a<NUM> output from the pair of first angle detection sensors 11A and 11B. The second signal processing unit 61B generates a signal (hereinafter, a second angle detection signal) S2c from which the vibration noise RN2 has been removed based on S2a<NUM> and S2a<NUM> output from the pair of second angle detection sensors 12A and 12B.

<FIG> shows a configuration of the first signal processing unit 61A. The first signal processing unit 61A includes an analog arithmetic circuit. As shown in <FIG>, the first signal processing unit 61A is composed of a buffer amplifier <NUM>, a variable gain amplifier <NUM>, a subtraction circuit <NUM>, and a gain adjustment circuit <NUM>. The gain adjustment circuit <NUM> is composed of a first band pass filter (BPF) circuit 75A, a second BPF circuit 75B, a first detection circuit 76A, a second detection circuit 76B, and a subtraction circuit <NUM>. The subtraction circuit <NUM> and the subtraction circuit <NUM> are differential amplification circuits including an operational amplifier.

The signal S1b; output from the first angle detection sensor 11A is input to a positive input terminal (non-inverting input terminal) of the subtraction circuit <NUM> via the buffer amplifier <NUM>. In addition, the signal output from the buffer amplifier <NUM> is branched in the middle of the process before being input to the subtraction circuit <NUM>, and is input to the first BPF circuit 75A in the gain adjustment circuit <NUM>.

The signal S1b<NUM> output from the first angle detection sensor 11B is input to a negative input terminal (inverting input terminal) of the subtraction circuit <NUM> via the variable gain amplifier <NUM>. In addition, the signal output from the variable gain amplifier <NUM> is branched in the middle of the process before being input to the subtraction circuit <NUM>, and is input to the second BPF circuit 75B in the gain adjustment circuit <NUM>.

Each of the first BPF circuit 75A and the second BPF circuit 75B has a pass band B1 having the second driving frequency fd2 as a center frequency, as shown in <FIG>. The pass band B1 is, for example, a frequency band of fd2 ± <NUM>. Since the vibration noise RN1 has the second driving frequency fd2, the vibration noise RN1 passes through the pass band B1. Therefore, the first BPF circuit 75A extracts and outputs the vibration noise RN1 (see <FIG>) from the signal input from the buffer amplifier <NUM>. The second BPF circuit 75B extracts and outputs the vibration noise RN1 (see <FIG>) from the signal input from the variable gain amplifier <NUM>.

Each of the first detection circuit 76A and the second detection circuit 76B is composed of, for example, a root mean squared value to direct current converter (RMS-DC converter). The first detection circuit 76A converts the amplitude of the vibration noise RN1 input from the first BPF circuit 75A into a DC voltage signal and inputs the signal to the positive input terminal of the subtraction circuit <NUM>. The second detection circuit 76B converts the amplitude of the vibration noise RN1 input from the second BPF circuit 75B into a DC voltage signal and inputs the signal to the negative input terminal of the subtraction circuit <NUM>.

The subtraction circuit <NUM> outputs a value d<NUM> obtained by subtracting the DC voltage signal input from the second detection circuit 76B from the DC voltage signal input from the first detection circuit 76A. The value d<NUM> corresponds to a difference between the amplitude of the vibration noise RN1 included in the signal S1b<NUM> output from the first angle detection sensor 11A and the amplitude of the vibration noise RN1 included in the signal S1b<NUM> output from the first angle detection sensor 11B. The subtraction circuit <NUM> inputs the value d<NUM> as a gain adjustment value to a gain adjustment terminal of the variable gain amplifier <NUM>.

The variable gain amplifier <NUM> adjusts an amplitude level of the signal S1b<NUM> by multiplying the signal S1b<NUM> input from the first angle detection sensor 11B by the value d<NUM> input as the gain adjustment value. In this way, a feedback control is performed by the gain adjustment circuit <NUM>, so that the amplitude of the vibration noise RN1 included in the signal S1b; after passing through the variable gain amplifier <NUM> is adjusted so as to match the amplitude of the vibration noise RN1 included in the signal S1b; after passing through the buffer amplifier <NUM>.

The subtraction circuit <NUM> outputs a value obtained by subtracting the signal S1b<NUM> input to the negative input terminal from the signal S1b; input to the positive input terminal. Since the amplitudes of the vibration noise RN1 included in both signals match with each other by the feedback control, the vibration noise RN1 included in both signals is offset by the subtraction processing by the subtraction circuit <NUM>. Therefore, the subtraction circuit <NUM> outputs the first angle detection signal S1c (see <FIG>), which is a signal from which the vibration noise RN1 has been removed.

<FIG> shows a state in which the first angle detection signal S1c is generated based on S1b; and S1b<NUM> output from the pair of first angle detection sensors 11A and 11B. The first angle detection signal S1c corresponds to a signal obtained by doubling an amplitude of a signal obtained by removing the vibration noise RN1 from the signal S1b<NUM>.

The first angle detection signal S1c generated by the first signal processing unit 61A is input to the first driving signal generation unit 60A and the first zero cross pulse output unit 63A. In a case where the swing of the mirror portion <NUM> around the first axis a<NUM> maintains a resonance state, as shown in <FIG>, the first angle detection signal S1c output from the first signal processing unit 61A has a phase delay of <NUM>° with respect to the driving voltage waveform V1A (t) included in the first driving signal.

As shown in <FIG>, the second signal processing unit 61B is composed of a buffer amplifier <NUM>, a variable gain amplifier <NUM>, a subtraction circuit <NUM>, and a gain adjustment circuit <NUM>. The gain adjustment circuit <NUM> is composed of a first BPF circuit 85A, a second BPF circuit 85B, a first detection circuit 86A, a second detection circuit 86B, and a subtraction circuit <NUM>. The subtraction circuit <NUM> and the subtraction circuit <NUM> are differential amplification circuits including an operational amplifier.

The signal S2b<NUM> output from the second angle detection sensor 12A is input to a positive input terminal of the subtraction circuit <NUM> via the buffer amplifier <NUM>. In addition, the signal output from the buffer amplifier <NUM> is branched in the middle of the process before being input to the subtraction circuit <NUM>, and is input to the first BPF circuit 85A in the gain adjustment circuit <NUM>.

The signal S2b<NUM> output from the second angle detection sensor 12B is input to a negative input terminal of the subtraction circuit <NUM> via the variable gain amplifier <NUM>. In addition, the signal output from the variable gain amplifier <NUM> is branched in the middle of the process before being input to the subtraction circuit <NUM>, and is input to the second BPF circuit 85B in the gain adjustment circuit <NUM>.

Each of the first BPF circuit 85A and the second BPF circuit 85B has a pass band B2 having the first driving frequency fd1 as a center frequency, as shown in <FIG>. The pass band B2 is, for example, a frequency band of fd1 ± <NUM>. Since the vibration noise RN2 has the first driving frequency fd1, the vibration noise RN2 passes through the pass band B2. Therefore, the first BPF circuit 85A extracts and outputs the vibration noise RN2 (see <FIG>) from the signal input from the buffer amplifier <NUM>. The second BPF circuit 85B extracts and outputs the vibration noise RN2 (see <FIG>) from the signal input from the variable gain amplifier <NUM>.

Each of the first detection circuit 86A and the second detection circuit 86B is composed of, for example, an RMS-DC converter. The first detection circuit 86A converts the amplitude of the vibration noise RN2 input from the first BPF circuit 85A into a DC voltage signal and inputs the signal to the positive input terminal of the subtraction circuit <NUM>. The second detection circuit 86B converts the amplitude of the vibration noise RN2 input from the second BPF circuit 85B into a DC voltage signal and inputs the signal to the negative input terminal of the subtraction circuit <NUM>.

The subtraction circuit <NUM> outputs a value d<NUM> obtained by subtracting the DC voltage signal input from the second detection circuit 86B from the DC voltage signal input from the first detection circuit 86A. The value d<NUM> corresponds to a difference between the amplitude of the vibration noise RN2 included in the signal S2b<NUM> output from the second angle detection sensor 12A and the amplitude of the vibration noise RN2 included in the signal S2b<NUM> output from the second angle detection sensor 12B. The subtraction circuit <NUM> inputs the value d<NUM> as a gain adjustment value to a gain adjustment terminal of the variable gain amplifier <NUM>.

The variable gain amplifier <NUM> adjusts an amplitude level of the signal S2b<NUM> by multiplying the signal S2b<NUM> input from the second angle detection sensor 12B by the value d<NUM> input as the gain adjustment value. In this way, a feedback control is performed by the gain adjustment circuit <NUM>, so that the amplitude of the vibration noise RN2 included in the signal S2b<NUM> after passing through the variable gain amplifier <NUM> is adjusted so as to match the amplitude of the vibration noise RN2 included in the signal S2b<NUM> after passing through the buffer amplifier <NUM>.

The subtraction circuit <NUM> outputs a value obtained by subtracting the signal S2b<NUM> input to the negative input terminal from the signal S2b<NUM> input to the positive input terminal. Since the amplitudes of the vibration noise RN2 included in both signals match with each other by the feedback control, the vibration noise RN2 included in both signals is offset by the subtraction processing by the subtraction circuit <NUM>. Therefore, the subtraction circuit <NUM> outputs the second angle detection signal S2c (see <FIG>), which is a signal from which the vibration noise RN2 has been removed.

<FIG> shows a state in which the second angle detection signal S2c is generated based on S2b<NUM> and S2b<NUM> output from the pair of second angle detection sensors 12A and 12B. The second angle detection signal S2c corresponds to a signal obtained by doubling an amplitude of a signal obtained by removing the vibration noise RN2 from the signal S2b<NUM>.

The second angle detection signal S2c generated by the second signal processing unit 61B is input to the second driving signal generation unit 60B and the second zero cross pulse output unit 63B. In a case where the swing of the mirror portion <NUM> around the second axis a<NUM> maintains a resonance state, as shown in <FIG>, the second angle detection signal S2c output from the second signal processing unit 61B has a phase delay of <NUM>° with respect to the driving voltage waveform V2A (t) included in the second driving signal.

Returning to <FIG>, the first angle detection signal S1c input from the first signal processing unit 61A is fed back to the first driving signal generation unit 60A. The first phase shift unit 62A shifts the phase of the driving voltage waveform output from the first driving signal generation unit 60A. The first phase shift unit 62A shifts the phase by <NUM>°, for example.

<FIG> shows an example of a configuration of the first driving signal generation unit 60A. As shown in <FIG>, the first driving signal generation unit 60A includes a signal generation circuit 91A and a phase synchronization circuit 92A. The first driving signal generation unit 60A is a so-called phase locked loop (PLL) type drive circuit.

A sampling reset signal having the first driving frequency fd1 is input to the phase synchronization circuit 92A from the signal generation circuit 91A, and the first angle detection signal S1c is input from the first signal processing unit 61A (see <FIG>). The phase synchronization circuit 92A adjusts a phase of a sampling clock signal generated by itself based on the sampling reset signal and the first angle detection signal S1c.

The signal generation circuit 91A generates the driving voltage waveforms V1A (t) and V1B (t) constituting the first driving signal based on the sampling clock signal input from the phase synchronization circuit 92A.

In this way, the feedback control is performed such that a phase difference between the first driving signal and the first angle detection signal S1c is maintained at <NUM>° by the first phase shift unit 62A and the first driving signal generation unit 60A of the PLL type. By maintaining the phase difference between the first driving signal and the first angle detection signal S1c at <NUM>°, the swing of the mirror portion <NUM> around the first axis a<NUM> is maintained in a resonance state.

The second angle detection signal S2c input from the second signal processing unit 61B is fed back to the second driving signal generation unit 60B. The second phase shift unit 62B shifts the phase of the driving voltage waveform output from the second driving signal generation unit 60B. The second phase shift unit 62B shifts the phase by <NUM>°, for example.

<FIG> shows an example of a configuration of the second driving signal generation unit 60B. As shown in <FIG>, the second driving signal generation unit 60B includes a signal generation circuit 91B and a phase synchronization circuit 92B. The second driving signal generation unit 60B is a so-called PLL type drive circuit.

A sampling reset signal having the second driving frequency fd2 is input to the phase synchronization circuit 92B from the signal generation circuit 91B, and the second angle detection signal S2c is input from the second signal processing unit 61B (see <FIG>). The phase synchronization circuit 92B adjusts a phase of a sampling clock signal generated by itself based on the sampling reset signal and the second angle detection signal S2c.

The signal generation circuit 91B generates the driving voltage waveforms V2A (t) and V2B (t) constituting the second driving signal based on the sampling clock signal input from the phase synchronization circuit 92B.

In this way, the feedback control is performed such that a phase difference between the second driving signal and the second angle detection signal S2c is maintained at <NUM>° by the second phase shift unit 62B and the second driving signal generation unit 60B of the PLL type. By maintaining the phase difference between the second driving signal and the second angle detection signal S2c at <NUM>°, the swing of the mirror portion <NUM> around the second axis a<NUM> is maintained in a resonance state.

Returning to <FIG>, the first zero cross pulse output unit 63A generates a zero cross pulse (hereinafter, referred to as a first zero cross pulse) ZC1 based on the first angle detection signal S1c input from the first signal processing unit 61A. The first zero cross pulse output unit 63A is composed of a zero cross detection circuit.

As shown in <FIG>, the first zero cross pulse output unit 63A generates the first zero cross pulse ZC1 at a timing at which the first angle detection signal S1c, which is an AC signal, crosses zero volt. The first zero cross pulse output unit 63A inputs the generated first zero cross pulse ZC1 to the light source driving unit 3A.

The second zero cross pulse output unit 63B generates a zero cross pulse (hereinafter, referred to as a second zero cross pulse) ZC2 based on the second angle detection signal S2c input from the second signal processing unit 61B. The second zero cross pulse output unit 63B is composed of a zero cross detection circuit.

As shown in <FIG>, the second zero cross pulse output unit 63B generates the second zero cross pulse ZC2 at a timing at which the second angle detection signal S2c, which is an AC signal, crosses zero volt. The second zero cross pulse output unit 63B inputs the generated second zero cross pulse ZC2 to the light source driving unit 3A.

The light source driving unit 3A drives the light source <NUM> based on drawing data supplied from the outside of the image drawing system <NUM>, for example. In addition, the light source driving unit 3A controls the irradiation timing such that the irradiation timing of the laser light is synchronized with the first zero cross pulse ZC1 and the second zero cross pulse ZC2 input from the mirror driving unit 4A.

As described above, according to the technique of the present disclosure, by subtracting one of the pair of first output signals output from the pair of first angle detection sensors from the other, the vibration noise caused by the swing of the mirror portion around the second axis is removed. As a result, since the first angle detection signal representing the angle of the mirror portion around the first axis, from which the vibration noise is removed, is generated, the swing of the mirror portion can be accurately controlled. In addition, by maintaining the swing of the mirror portion in a resonance state, the amplitude (maximum deflection angle) of the swing of the mirror portion is maintained constant.

Next, an image drawing system according to a second embodiment will be described. In the image drawing system of the present embodiment, the disposition of the pair of first angle detection sensors 11A and 11B and the pair of second angle detection sensors 12A and 12B in the MMD <NUM> is different from that of the first embodiment. In the first embodiment, the pair of first angle detection sensors 11A and 11B are disposed at positions facing each other across the first axis a<NUM>, whereas, in the second embodiment, the pair of first angle detection sensors 11A and 11B are disposed at positions facing each other across the second axis a<NUM>. In the first embodiment, the pair of second angle detection sensors 12A and 12B are disposed at positions facing each other across the second axis a<NUM>, whereas, in the second embodiment, the pair of second angle detection sensors 12A and 12B are disposed at positions facing each other across the first axis a<NUM>.

<FIG> is a plan view showing the configuration of the MMD <NUM> according to the present embodiment. As shown in <FIG>, the pair of first angle detection sensors 11A and 11B are disposed in the vicinity of the first support portion <NUM> on the first movable frame <NUM>. The first angle detection sensor 11A is disposed in the vicinity of the first support portion <NUM> connected to one side of the mirror portion <NUM>. The first angle detection sensor 11B is disposed in the vicinity of the first support portion <NUM> connected to the other side of the mirror portion <NUM>. Therefore, the pair of first angle detection sensors 11A and 11B are disposed at positions facing each other across the second axis a<NUM> and facing each other across the mirror portion <NUM>. In addition, the pair of first angle detection sensors 11A and 11B are disposed at positions deviated from the first axis a<NUM> in the same direction (in the present embodiment, -X direction).

The pair of second angle detection sensors 12A and 12B are disposed in the vicinity of the second support portion <NUM> on the second movable frame <NUM>. The second angle detection sensor 12A is disposed in the vicinity of the second support portion <NUM> connected to one side of the first movable frame <NUM>. The second angle detection sensor 12B is disposed in the vicinity of the second support portion <NUM> connected to the other side of the first movable frame <NUM>. Therefore, the pair of second angle detection sensors 12A and 12B are disposed at positions facing each other across the first axis a<NUM> and facing each other across the mirror portion <NUM> and the first movable frame <NUM>. In addition, the pair of second angle detection sensors 12A and 12B are disposed at positions deviated from the second axis a<NUM> in the same direction (in the present embodiment, +Y direction).

<FIG> shows an example of signals output from the pair of first angle detection sensors 11A and 11B in the present embodiment. In <FIG>, S1a represents a signal output from the pair of first angle detection sensors 11A and 11B in a case where the mirror portion <NUM> swings only around the first axis a<NUM> without swinging around the second axis a<NUM>. In the present embodiment, since the first angle detection sensors 11A and 11B are disposed at positions deviated in the same direction with respect to the first axis a<NUM>, waveform signals having the same phase and having the first driving frequency fd1 are output from the first angle detection sensors 11A and 11B.

In a case where the mirror portion <NUM> swings around the first axis a<NUM> and the second axis a<NUM> simultaneously, a vibration noise RN1a caused by the swing of the mirror portion <NUM> around the second axis a<NUM> is superimposed on the output signal of the first angle detection sensor 11A. Similarly, in a case where the mirror portion <NUM> swings around the first axis a<NUM> and the second axis a<NUM> simultaneously, a vibration noise RN1b caused by the swing of the mirror portion <NUM> around the second axis a<NUM> is superimposed on the output signal of the first angle detection sensor 11B. Since the first angle detection sensors 11A and 11B are disposed at positions facing each other across the second axis a<NUM>, the vibration noises RN1a and RN1b superimposed on the first angle detection sensors 11A and 11B are in an anti-phase with each other.

As described above, in a case of the biaxial drive, the signal S1b; on which the vibration noise RN1a is superimposed is output from the first angle detection sensor 11A, and the signal S1b<NUM> on which the vibration noise RN1b is superimposed is output from the first angle detection sensor 11B.

<FIG> shows an example of signals output from the pair of second angle detection sensors 12A and 12B in the present embodiment. In <FIG>, S2a represents a signal output from the pair of second angle detection sensors 12A and 12B in a case where the mirror portion <NUM> swings only around the second axis a<NUM> without swinging around the first axis a<NUM>. In the present embodiment, since the second angle detection sensors 12A and 12B are disposed at positions deviated in the same direction with respect to the second axis a<NUM>, waveform signals having the same phase and having the second driving frequency fd2 are output from the second angle detection sensors 12A and 12B.

In a case where the mirror portion <NUM> swings around the first axis a<NUM> and the second axis a<NUM> simultaneously, a vibration noise RN2a caused by the swing of the mirror portion <NUM> around the first axis a<NUM> is superimposed on the output signal of the second angle detection sensor 12A. Similarly, in a case where the mirror portion <NUM> swings around the first axis a<NUM> and the second axis a<NUM> simultaneously, a vibration noise RN2b caused by the swing of the mirror portion <NUM> around the first axis a<NUM> is superimposed on the output signal of the second angle detection sensor 12B. Since the second angle detection sensors 12A and 12B are disposed at positions facing each other across the first axis a<NUM>, the vibration noises RN2a and RN2b superimposed on the second angle detection sensors 12A and 12B are in an anti-phase with each other.

As described above, in a case of the biaxial drive, the signal S2b<NUM> on which the vibration noise RN2a is superimposed is output from the second angle detection sensor 12A, and the signal S2b<NUM> on which the vibration noise RN2b is superimposed is output from the second angle detection sensor 12B.

In the present embodiment, the driving controller <NUM> is different from the configuration of the driving controller <NUM> of the first embodiment only in the configuration of the first signal processing unit 61A and the second signal processing unit 61B. As shown in <FIG>, in the present embodiment, the first signal processing unit 61A includes an addition circuit 73A instead of the subtraction circuit <NUM>. The addition circuit 73A outputs a value obtained by adding the signal S1b; input from the first angle detection sensor 11A via the buffer amplifier <NUM> and the signal S1b<NUM> input from the first angle detection sensor 11B via the variable gain amplifier <NUM>.

In the present embodiment, the gain adjustment circuit <NUM> adjusts an amplitude level of the vibration noise RN1b included in the signal S1b<NUM> so as to match an amplitude level of the vibration noise RN1a included in the signal S1b<NUM>. Therefore, the vibration noises RN1a and RN1b are offset by addition processing by the addition circuit 73A. Therefore, the addition circuit 73A outputs the first angle detection signal S1c which is a signal from which the vibration noises RN1a and RN1b have been removed.

<FIG> shows a state in which the first angle detection signal S1c is generated based on S1b; and S1b<NUM> output from the pair of first angle detection sensors 11A and 11B in the present embodiment. Also in the present embodiment, the same first angle detection signal S1c as in the first embodiment is obtained (see <FIG>).

As shown in <FIG>, in the present embodiment, the second signal processing unit 61B includes an addition circuit 83A instead of the subtraction circuit <NUM>. The addition circuit 83A outputs a value obtained by adding the signal S2b<NUM> input from the second angle detection sensor 12A via the buffer amplifier <NUM> and the signal S2b<NUM> input from the second angle detection sensor 12B via the variable gain amplifier <NUM>.

In the present embodiment, the gain adjustment circuit <NUM> adjusts an amplitude level of the vibration noise RN2b included in the signal S2b<NUM> so as to match an amplitude level of the vibration noise RN2a included in the signal S2b<NUM>. Therefore, the vibration noises RN2a and RN2b are offset by addition processing by the addition circuit 83A. Therefore, the addition circuit 83A outputs the second angle detection signal S2c which is a signal from which the vibration noises RN2a and RN2b have been removed.

<FIG> shows a state in which the second angle detection signal S2c is generated based on S2b<NUM> and S2b<NUM> output from the pair of second angle detection sensors 12A and 12B in the present embodiment. Also in the present embodiment, the same second angle detection signal S2c as in the first embodiment is obtained (see <FIG>).

As described above, the pair of first angle detection sensors 11A and 11B need only be disposed at positions facing each other across the first axis a<NUM> or the second axis a<NUM>. In a case where the pair of first angle detection sensors 11A and 11B are disposed at positions facing each other across the first axis a<NUM>, the vibration noise can be removed by subtracting one of the output signals of the first angle detection sensors 11A and 11B from the other. In a case where the pair of first angle detection sensors 11A and 11B are disposed at positions facing each other across the second axis a<NUM>, the vibration noise can be removed by adding the output signals of the first angle detection sensors 11A and 11B.

Similarly, the pair of second angle detection sensors 12A and 12B need only be disposed at positions facing each other across the first axis a<NUM> or the second axis a<NUM>. In a case where the pair of second angle detection sensors 12A and 12B are disposed at positions facing each other across the second axis a<NUM>, the vibration noise can be removed by subtracting one of the output signals of the second angle detection sensors 12A and 12B from the other. In a case where the pair of second angle detection sensors 12A and 12B are disposed at positions facing each other across the first axis a<NUM>, the vibration noise can be removed by adding the output signals of the second angle detection sensors 12A and 12B.

Next, a modification example of each of the above-described embodiments will be described. In each of the above-described embodiments, the gain adjustment circuit <NUM> extracts a vibration noise having the second driving frequency fd2 by the first BPF circuit 75A and the second BPF circuit 75B. Alternatively, the vibration noise having the second driving frequency fd2 may be extracted by a low-pass filter circuit having a cutoff frequency between the first driving frequency fd1 and the second driving frequency fd2. In addition, in each of the above-described embodiments, the gain adjustment circuit <NUM> extracts a vibration noise having the first driving frequency fd1 by the first BPF circuit 85A and the second BPF circuit 85B. Alternatively, the vibration noise having the first driving frequency fd1 may be extracted by a high-pass filter circuit having a cutoff frequency between the first driving frequency fd1 and the second driving frequency fd2.

The configuration of the MMD <NUM> shown in the above embodiment is an example. The configuration of the MMD <NUM> can be modified in various ways. For example, the first actuator <NUM> that allows the mirror portion <NUM> to swing around the first axis a<NUM> may be disposed on the second movable frame <NUM>, and the second actuator <NUM> that allows the mirror portion <NUM> to swing around the second axis a<NUM> may be disposed on the first movable frame <NUM>.

The hardware configuration of the driving controller <NUM> can be variously modified. In each of the above-described embodiments, the driving controller <NUM> includes an analog arithmetic circuit, and can also include a digital arithmetic circuit. The driving controller <NUM> 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).

Next, a comparative example with the technology of the present disclosure will be described. In the technique of the present disclosure, a vibration noise is removed by adding or subtracting a pair of output signals output from a pair of angle detection sensors as described above. With respect to this, it is considered to remove a vibration noise by performing frequency filter processing on the output signal output from the angle detection sensor. Hereinafter, as a comparative example, an example of removing a vibration noise by frequency filter processing will be described.

In the present comparative example, at least any one of the pair of first angle detection sensors 11A and 11B need only be provided. In addition, at least any one of the pair of second angle detection sensors 12A and 12B need only be provided.

In the present comparative example, the first signal processing unit 61A is a band pass filter circuit that has a pass band having the first driving frequency fd1 as a center frequency. Similarly, the second signal processing unit 61B is a band pass filter circuit that has a pass band having the second driving frequency fd2 as a center frequency. As a result, a signal from which the vibration noise having the second driving frequency fd2 has been removed is output from the first signal processing unit 61A. A signal from which the vibration noise having the first driving frequency fd1 has been removed is output from the second signal processing unit 61B.

In this way, a vibration noise can be removed by using the first signal processing unit 61A and the second signal processing unit 61B as a band pass filter circuit, but accurate phase information may not be obtained from a signal from which the vibration noise has been removed. This is due to a phase response of the band pass filter circuit.

<FIG> shows an example of gain and phase characteristics of the band pass filter circuit. A center frequency of the band pass filter circuit shown in <FIG> is <NUM>. A phase changes abruptly in the vicinity of the center frequency. Therefore, in a case where a frequency of a signal input to the band pass filter circuit deviates from the center frequency, a phase of an output signal from the band pass filter circuit changes significantly. In this way, since the phase of the output signal from the angle detection sensor may change significantly due to passing through the band pass filter circuit, it is difficult to use the output signal from the band pass filter circuit as timing information for maintaining a resonance state.

In a case where a zero cross pulse is generated based on the output signal from the band pass filter circuit and input to the light source driving unit 3A, an image out of synchronization with the scanning of light by the MMD <NUM> is drawn on the surface to be scanned <NUM>. In this case, it is necessary to provide a phase shifter capable of manually adjusting the phase of the output signal from the band pass filter circuit and to manually adjust the phase shifter so that there is no deviation while a user observes the image drawn on the surface to be scanned <NUM>.

Claim 1:
An optical scanning device (<NUM>) comprising:
a mirror portion (<NUM>) having a reflecting surface for reflecting incident light;
a first actuator (<NUM>) 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 (<NUM>) 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 pair of first angle detection sensors (11A, 11B) that output a signal corresponding to an angle of the mirror portion around the first axis, the pair of first angle detection sensors being disposed at positions facing each other across the first axis; and
at least one processor,
wherein the processor generates a first angle detection signal representing the angle of the mirror portion around the first axis by adjusting an amplitude level of at least one of the pair of first output signals to match amplitudes of vibration noises respectively included in the pair of first output signals output from the pair of first angle detection sensors with each other, and subtracting one of the adjusted pair of first output signals from the other.