Actuator device, optical scanning device, and method for driving actuator device

Abstract

This actuator device comprises: a piezoelectric element that has a piezoelectric film, a first electrode which is disposed on one surface of the piezoelectric film, and a second electrode which is disposed on the other surface of the piezoelectric film; and a voltage application unit that applies a voltage to the piezoelectric element. The voltage application unit applies, to the first electrode, an offset voltage, which is a positive voltage, and applies, to the second electrode, a fluctuation voltage for operating the piezoelectric film.

Description

Actuator device, optical scanning device, and method for driving actuator device

[0001] The technology of the present disclosure relates to an actuator device, an optical scanning device, and a method for driving an actuator device.

[0002] Micromirror devices (also called microscanners) are known as one type of microelectromechanical systems (MEMS) device fabricated using silicon (Si) microfabrication technology. Because these micromirror devices are small and consume little power, they are expected to be widely used in laser displays, laser projectors, optical coherence tomography, and other applications.

[0003] There are various drive methods for micromirror devices, but the piezoelectric drive method, which uses a piezoelectric actuator with a piezoelectric element, is considered promising because it generates a higher torque per input energy and can achieve a wide scan angle compared to other methods. In particular, when a wide scan angle is required, such as in laser displays, a wider scan angle can be achieved by resonantly driving a piezoelectric drive micromirror device.

[0004] The piezoelectric element has a laminated structure in which a lower electrode, a piezoelectric film, and an upper electrode are stacked in this order. The piezoelectric film is, for example, a Nb-doped PZT (lead zirconate titanate) thin film. For example, a fluctuating voltage for operating the piezoelectric film is applied to the upper electrode, and a ground potential is applied to the lower electrode (see, for example, WO 2022 / 025012).

[0005] The direction of spontaneous polarization of a piezoelectric film is determined by the thin-film formation process, and the direction of spontaneous polarization is from the bottom electrode to the top electrode. To effectively displace the piezoelectric film under this spontaneous polarization through the inverse piezoelectric effect, a voltage is applied in the opposite direction to the spontaneous polarization, i.e., the bottom electrode is set to ground potential and the fluctuating voltage is set to a negative voltage (see, for example, Takamitsu Fujii and six others, "Formation of High-Piezoelectric Constant Nb-Doped PZT Thin Films and Their MEMS Applications," [online], accessed May 24, 2023, Internet <URL: https: / / asset.fujifilm.com / www / jp / files / 2019-10 / e582ff969a0ab0bee223d390961ac66f / rd_report_ff_rd059_008.pdf>).

[0006] To apply a voltage in the opposite direction to the spontaneous polarization as described above, the voltage application unit must be configured to generate a fluctuating negative voltage. However, there are few options for circuit elements for generating negative voltages, and this has disadvantages such as increased power consumption.

[0007] Although it is conceivable to solve the above problem by making the fluctuating voltage a positive voltage, this requires reversing the polarization direction of the piezoelectric film, which is difficult to do because the direction of spontaneous polarization of the piezoelectric film is forcibly determined by the thin film formation process as described above.

[0008] As described above, actuator devices using piezoelectric elements have the problem of high power consumption due to the spontaneous polarization of the piezoelectric film. A similar problem also exists in actuator devices used in devices other than optical scanning devices with micromirror devices.

[0009] The technology of the present disclosure aims to provide an actuator device, an optical scanning device, and a method for driving an actuator device that can reduce power consumption.

[0010] In order to achieve the above object, the actuator device of the present disclosure comprises a piezoelectric element having a piezoelectric film, a first electrode arranged on one side of the piezoelectric film, and a second electrode arranged on the other side of the piezoelectric film, and a voltage application unit that applies a voltage to the piezoelectric element, wherein the voltage application unit applies an offset voltage that is a positive voltage to the first electrode and applies a fluctuating voltage to the second electrode to operate the piezoelectric film.

[0011] The piezoelectric film has spontaneous polarization, and the direction of the spontaneous polarization is preferably from the first electrode to the second electrode.

[0012] The piezoelectric film is preferably a Nb-doped PZT thin film.

[0013] The maximum value of the fluctuating voltage is preferably equal to the offset voltage.

[0014] The minimum value of the fluctuating voltage is preferably a positive voltage.

[0015] The minimum value of the fluctuating voltage may be a negative voltage.

[0016] The optical scanning device disclosed herein comprises a mirror section having a reflective surface that reflects incident light, a first actuator that oscillates the mirror section around a first axis, a second actuator that oscillates the mirror section around a second axis that intersects the first axis, and a voltage application section that oscillates the mirror section by applying a voltage to each of the first actuator and the second actuator, wherein each of the first actuator and the second actuator has a piezoelectric element composed of a piezoelectric film, a first electrode arranged on one side of the piezoelectric film, and a second electrode arranged on the other side of the piezoelectric film, and the voltage application section applies an offset voltage that is a positive voltage to the first electrode and applies a fluctuating voltage to the second electrode to operate the piezoelectric film.

[0017] The method for driving an actuator device disclosed herein is a method for driving an actuator device including a piezoelectric element having a piezoelectric film, a first electrode arranged on one side of the piezoelectric film, and a second electrode arranged on the other side of the piezoelectric film, and a voltage application unit that applies a voltage to the piezoelectric element, and includes the voltage application unit applying an offset voltage that is a positive voltage to the first electrode, and applying a fluctuating voltage to the second electrode to operate the piezoelectric film.

[0018] According to the technique of the present disclosure, it is possible to provide an actuator device, an optical scanning device, and a method for driving an actuator device that can reduce power consumption.

[0019] 4 is a schematic diagram of an optical scanning device. FIG. 4 is a perspective view of the appearance of a micromirror device. FIG. 5 is a plan view of the micromirror device as viewed from the light incident side. FIG. 5 is a cross-sectional view taken along line A-A in FIG. 3. FIG. 6 is a cross-sectional view taken along line B-B in FIG. 3. FIG. 6 is a cross-sectional view taken along line CC in FIG. 3. FIG. 7 is a diagram showing an example of driving a first actuator. FIG. 8 is a diagram showing an example of driving a second actuator. FIG. 9 is a graph showing an example of a first drive signal and a second drive signal. FIG. 10 is a block diagram showing an example of the configuration of a drive control unit. FIG. 11 is a diagram showing the direction of spontaneous polarization of a piezoelectric film. FIG. 12 is a graph showing an example of a first drive signal and a second drive signal according to a second embodiment.

[0020] An example of an embodiment of the technology of the present disclosure will be described with reference to the accompanying drawings.

[0021] 1 is a schematic diagram of an image drawing system 10 according to one embodiment. The image drawing system 10 includes an optical scanning device 2 and a light source 3. The optical scanning device 2 includes a micro mirror device (MMD) 4 and a drive control unit 5.

[0022] The image drawing system 10 draws an image by optically scanning a surface 6 to be scanned with a light beam L emitted from a light source 3, which is reflected by an MMD 4, under the control of a drive control unit 5. The surface 6 to be scanned is, for example, a screen.

[0023] The image rendering system 10 is applicable to, for example, a Lissajous scanning laser display. Specifically, the image rendering system 10 is applicable to a laser scan display such as an augmented reality (AR) glass or a virtual reality (VR) glass.

[0024] MMD4 is the first axis a １ and the first axis a １ The second axis a intersects with ２The micromirror device is a piezoelectric two-axis drive type that can oscillate the mirror portion 20 (see FIG. 2) around the second axis a. ２ The direction parallel to the axis a is the X direction. １ The direction parallel to the axis a is the Y direction. １ and the second axis a ２ The direction perpendicular to the X direction is called the Z direction. In this embodiment, the X direction and the Y direction are perpendicular to each other.

[0025] The light source 3 is a laser device that emits, for example, laser light as the light beam L. The light source 3 may irradiate the light beam L perpendicularly to a reflecting surface 20A (see FIG. 2 ) of the mirror unit 20 when the mirror unit 20 of the MMD 4 is stationary. Note that if the light beam L is irradiated perpendicularly to the reflecting surface 20A from the light source 3, the light source 3 may become an obstacle when the light beam L is scanned and drawn on the scanned surface 6. For this reason, it is preferable to control the light beam L emitted from the light source 3 by an optical system so that the light beam L is irradiated perpendicularly to the reflecting surface 20A. The optical system may or may not include a lens. Furthermore, the angle at which the light beam L emitted from the light source 3 is irradiated onto the reflecting surface 20A is not limited to being perpendicular, and the light beam L may be irradiated obliquely with respect to the reflecting surface 20A.

[0026] The drive control unit 5 outputs drive signals to the light source 3 and the MMD 4 based on the optical scanning information. The light source 3 generates a light beam L based on the input drive signal and irradiates the MMD 4 with the light beam L. The MMD 4 rotates the mirror unit 20 along the first axis a based on the input drive signal. １ and the second axis a ２ Rock it around.

[0027] As will be described in detail later, the drive control unit 5 rotates the mirror unit 20 along the first axis a １ and the second axis a ２ , and the light beam L reflected by the mirror portion 20 is scanned so as to trace a Lissajous waveform on the surface to be scanned 6. This optical scanning method is called a Lissajous scanning method.

[0028] 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 seen from the light incident side. Fig. 4 is a cross-sectional view taken along line A-A in Fig. 3. Fig. 5 is a cross-sectional view taken along line B-B in Fig. 3. Fig. 6 is a cross-sectional view taken along line CC in Fig. 3.

[0029] 2 and 3, the MMD 4 has a mirror section 20, a first support section 21, a first movable frame 22, a second support section 23, a second movable frame 24, a connection section 25, and a fixed frame 26. The MMD 4 is a so-called MEMS scanner.

[0030] The mirror section 20 has a reflecting surface 20A that reflects incident light. The reflecting surface 20A is formed of a metal thin film, such as gold (Au), aluminum (Al), silver (Ag), or a silver alloy, provided on one surface of the mirror section 20. The shape of the reflecting surface 20A is, for example, a first axis a １ and the second axis a ２ It is a circle with the intersection point of

[0031] 1st axis a １ and the second axis a ２ The plane shape of the MMD 4 is rectangular, and the first axis a １ and is symmetrical about the second axis a ２ It is symmetric with respect to .

[0032] The first support portion 21 is provided on the outer side of the mirror portion 20 with a second axis a ２ The first support portion 21 is disposed at a position facing each other with the first axis a １ The mirror section 20 is connected to the first axis a １ In this embodiment, the first support portion 21 supports the first axis a １ It is a torsion bar extending along the

[0033] The first movable frame 22 is a rectangular frame that surrounds the mirror unit 20 and is １ The first movable frame 22 is connected to the mirror unit 20 via the first support unit 21. １The piezoelectric elements 30 are formed at positions facing each other with the first movable frame 22 therebetween. In this way, the two piezoelectric elements 30 formed on the first movable frame 22 constitute a first actuator 31.

[0034] The two piezoelectric elements 30 constituting the first actuator 31 are arranged along the first axis a １ The first actuator 31 is arranged at a position facing the mirror unit 20 with the first axis a １ By applying a rotational torque around the first axis a １ Swing it around.

[0035] The second support portion 23 is provided on the outside of the first movable frame 22 along the first axis a １ The second support portion 23 is disposed at a position facing each other with the second axis a ２ The first movable frame 22 and the mirror unit 20 are connected to the second axis a ２ In this embodiment, the second support portion 23 supports the second axis a ２ It is a torsion bar extending along the

[0036] The second movable frame 24 is a rectangular frame that surrounds the first movable frame 22 and is oriented along the second axis a ２ The second movable frame 24 is connected to the first movable frame 22 via the second support portion 23. The second movable frame 24 is connected to the second axis a ２ The piezoelectric elements 30 are formed at positions facing each other with the second movable frame 24 therebetween. In this way, the two piezoelectric elements 30 formed on the second movable frame 24 constitute a second actuator 32.

[0037] The two piezoelectric elements 30 constituting the second actuator 32 are arranged along the second axis a ２ The second actuator 32 is arranged at a position facing the mirror unit 20 and the first movable frame 22 with the second axis a ２ By applying a rotational torque around the second axis a ２ The mirror portion 20 is swung around the

[0038] The connecting portion 25 is provided on the outside of the second movable frame 24 with the first axis a １The connecting portions 25 are arranged at positions facing each other with the second axis a ２ It is connected to the second movable frame 24 at the top.

[0039] The fixed frame 26 is a rectangular frame body that surrounds the second movable frame 24 and is oriented along the second axis a ２ The upper surface of the movable frame 22 is connected to the second movable frame 24 via a connecting portion 25 .

[0040] The first movable frame 22 has a first axis a １ The first angle detection sensors 11A and 11B are provided at positions facing each other with the first axis a of the mirror unit 20 in between. The first angle detection sensors 11A and 11B are each composed of a piezoelectric element. １ The force applied by the deformation of the first support part 21 due to the rotation around the mirror part 20 is converted into a voltage and output as a signal. １ It outputs a signal according to the surrounding angle.

[0041] The second movable frame 24 has a second axis a ２ The second angle detection sensors 12A and 12B are provided at positions facing each other with the second axis a of the mirror unit 20 in between. The second angle detection sensors 12A and 12B are each configured with a piezoelectric element. ２ The second angle detection sensors 12A and 12B convert the force applied by the deformation of the second support part 23 due to the rotation around the second axis a of the mirror part 20 into a voltage and output a signal. ２ It outputs a signal according to the surrounding angle.

[0042] 2 and 3 , wiring and electrode pads for supplying drive signals to the first actuator 31 and the second actuator 32 are not shown. Also, wiring and electrode pads for outputting signals from the first angle detection sensors 11A, 11B and the second angle detection sensors 12A, 12B are not shown in FIGS. 2 and 3 . A plurality of electrode pads are provided on the fixed frame 26.

[0043] 4 and 5, the MMD 4 is formed, for example, by etching an SOI (Silicon On Insulator) 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.

[0044] The mirror section 20, first support section 21, first movable frame 22, second support section 23, second movable frame 24, and connection section 25 are formed from a second silicon active layer 43 that remains after removing the first silicon active layer 41 and silicon oxide layer 42 from the SOI substrate 40 by etching. The second silicon active layer 43 functions as an elastic section having elasticity. The fixed frame 26 is formed from three layers: the first silicon active layer 41, the silicon oxide layer 42, and the second silicon active layer 43.

[0045] The first actuator 31 and the second actuator 32 have a piezoelectric element 30 on a second silicon active layer 43. The piezoelectric element 30 has a layered structure in which a lower electrode 51, a piezoelectric film 52, and an upper electrode 53 are layered in this order on the second silicon active layer 43. The lower electrode 51 is disposed on one side of the piezoelectric element 30. The upper electrode 53 is disposed on one side of the piezoelectric element 30. The lower electrode 51 is an example of a "first electrode" according to the technology of the present disclosure. The upper electrode 53 is an example of a "second electrode" according to the technology of the present disclosure. Note that an insulating film is provided on the upper electrode 53, but is not shown in the figure.

[0046] The upper electrode 53 and the lower electrode 51 are made of, for example, gold (Au) or platinum (Pt). The piezoelectric film 52 is, for example, an Nb-doped PZT thin film. The upper electrode 53 and the lower electrode 51 are electrically connected to the drive control unit 5 via wiring and electrode pads.

[0047] As will be described in detail later, a periodically fluctuating voltage is applied to the upper electrode 53 from the drive control unit 5. A positive offset voltage is applied to the lower electrode 51 from the drive control unit 5.

[0048] Spontaneous polarization occurs in the piezoelectric film 52 in the direction from the lower electrode 51 to the upper electrode 53. That is, the piezoelectric film 52 is spontaneously polarized so that the lower electrode 51 side has negative polarity and the upper electrode 53 side has positive polarity. The direction of this spontaneous polarization is determined by sputtering, which is the thin film formation process used to form the piezoelectric film 52. The lower electrode 51 is disposed in the opposite direction of the spontaneous polarization from the piezoelectric film 52. The upper electrode 53 is disposed in the positive direction of the spontaneous polarization from the piezoelectric film 52.

[0049] The piezoelectric film 52 undergoes deformation (e.g., expansion and contraction) proportional to the applied voltage due to the inverse piezoelectric effect. When a fluctuating voltage is applied to the upper electrode 53 from the drive control unit 5, the piezoelectric film 52 periodically displaces the first actuator 31 and the second actuator 32.

[0050] 6, the first angle detection sensor 11A is similarly configured with a piezoelectric element 30 consisting of a lower electrode 51, a piezoelectric film 52, and an upper electrode 53 stacked on the second silicon active layer 43. When a force (i.e., pressure) is applied to the piezoelectric film 52, polarization proportional to the pressure occurs. In other words, the piezoelectric film 52 exhibits a piezoelectric effect. The piezoelectric film 52 is configured to rotate along the first axis a of the mirror section 20. １ When a force is applied due to deformation of the first support portion 21 accompanying rotation of the periphery, a piezoelectric effect is exerted and a voltage is generated.

[0051] The first angle detection sensor 11B has the same configuration as the first angle detection sensor 11A, and therefore is not shown in the drawings. The second angle detection sensors 12A and 12B have the same configuration as the first angle detection sensor 11A, and therefore are not shown in the drawings.

[0052] FIG. 7 shows the first actuator 31 expanding one piezoelectric film 52 and contracting the other piezoelectric film 52, thereby moving the piezoelectric element along the first axis a １ In this way, one of the pair of piezoelectric films 52 is displaced in the opposite directions, and the mirror section 20 rotates around the first axis a １ rotates around the

[0053] 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 first actuator 31 and the rotation direction of the mirror section 20 are opposite to each other. Note that the first actuator 31 may also be driven in an in-phase resonance mode in which the displacement direction of the first actuator 31 and the rotation direction of the mirror section 20 are the same.

[0054] The first axis a of the mirror section 20 １ The swing angle around the center (hereinafter referred to as the first swing angle) θ １ is controlled by a drive signal (hereinafter referred to as the first drive signal) that the drive control unit 5 gives to the first actuator 31. The first drive signal includes the above-mentioned variable voltage and offset voltage. The first drive signal is a variable voltage V applied to one of the two piezoelectric elements 30 that constitute the first actuator 31. １Ａ (t) and the fluctuating voltage V applied to the other １Ｂ (t) and the fluctuating voltage V １Ａ (t) and fluctuating voltage V １Ｂ (t) are in opposite phase to each other (i.e., the phase difference is 180°). １Ａ (t) and the fluctuating voltage V １Ｂ (t) is applied to the upper electrode 53. An offset voltage is applied to the lower electrode 51.

[0055] The first deflection angle θ １ is the angle at which the normal to the reflecting surface 20A is inclined with respect to the Z direction in the XZ plane.

[0056] FIG. 8 shows the second actuator 32 expanding one piezoelectric film 52 and contracting the other piezoelectric film 52, thereby moving the piezoelectric element along the second axis a ２ In this way, one of the pair of piezoelectric films 52 is displaced in the opposite directions, and the mirror section 20 rotates around the second axis a ２ rotates around the

[0057] 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 second actuator 32 and the rotation direction of the mirror section 20 are opposite to each other. Note that the second actuator 32 may also be driven in an in-phase resonance mode in which the displacement direction of the second actuator 32 and the rotation direction of the mirror section 20 are the same.

[0058] The second axis a of the mirror portion 20 ２ The surrounding deflection angle (hereinafter referred to as the second deflection angle) θ ２ is controlled by a drive signal (hereinafter referred to as the second drive signal) that the drive control unit 5 provides to the second actuator 32. The second drive signal includes the above-mentioned variable voltage and offset voltage. The second drive signal is a variable voltage V applied to one of the two piezoelectric elements 30 that constitute the second actuator 32. ２Ａ (t) and the fluctuating voltage V applied to the other ２Ｂ (t) and the fluctuating voltage V ２Ａ (t) and fluctuating voltage V ２Ｂ (t) are in opposite phase to each other (i.e., the phase difference is 180°). ２Ａ (t) and the fluctuating voltage V ２Ｂ (t) is applied to the upper electrode 53. An offset voltage is applied to the lower electrode 51.

[0059] The second deflection angle θ ２ is the angle at which the normal to the reflecting surface 20A is inclined with respect to the Z direction in the YZ plane.

[0060] 9A and 9B show examples of the first and second drive signals. FIG. 9A shows the fluctuating voltage V １Ａ (t) and V １Ｂ (t) and offset voltage V ＯＳ FIG. 9B shows the fluctuating voltage V ２Ａ (t) and V ２Ｂ (t) and offset voltage V ＯＳ Indicates that.

[0061] Fluctuating voltage V １Ａ (t) and V １Ｂ (t) are expressed as follows: V １Ａ (t) = V １sin(2πf ｄ１ t) + V ＯＳ -V １ V １Ｂ (t) = V １ sin(2πf ｄ１ t + α) + V ＯＳ -V １

[0062] Here, V １ is the amplitude voltage. ｄ１ is the drive frequency (hereinafter referred to as the first drive frequency), t is time, and α is the variable voltage V １Ａ (t) and V １Ｂ In this embodiment, for example, α=180°.

[0063] As expressed by the above formula, in this embodiment, the variable voltage V １Ａ (t) and V １Ｂ The maximum value of (t) is the offset voltage V ＯＳ In this embodiment, the variable voltage V １Ａ (t) and V １Ｂ The minimum value of (t) is a positive voltage greater than 0 V. That is, in this embodiment, the offset voltage V ＯＳ is the fluctuating voltage V １Ａ (t) and V １Ｂ PP, which is the difference between the maximum and minimum values ​​of (t) １ It is set to a constant positive voltage greater than the value.

[0064] A fluctuating voltage V is applied to the upper electrodes 53 of the two piezoelectric elements 30 that constitute the first actuator 31. １Ａ (t) and V １Ｂ (t) is applied, and an offset voltage V ＯＳ When the mirror section 20 is driven at the first drive frequency f ｄ１ The first axis a １ (See Figure 7).

[0065] Fluctuating voltage V ２Ａ (t) and V ２Ｂ (t) are expressed as follows: V ２Ａ (t) = V ２ sin(2πf ｄ２ t + φ) + V ＯＳ-V ２ V ２Ｂ (t) = V ２ sin(2πf ｄ２ t + β + φ) + V ＯＳ -V ２

[0066] Here, V ２ is the amplitude voltage. ｄ２ is the drive frequency (hereinafter referred to as the second drive frequency). t is time. β is the variable voltage V ２Ａ (t) and V ２Ｂ In this embodiment, for example, β is set to 180°. φ is the phase difference of the variable voltage V １Ａ (t) and fluctuating voltage V ２Ａ (t) is the phase difference between the amplitude voltage V １ and amplitude voltage V ２ may be different from

[0067] As expressed by the above formula, in this embodiment, the variable voltage V ２Ａ (t) and V ２Ｂ The maximum value of (t) is the offset voltage V ＯＳ In this embodiment, the variable voltage V ２Ａ (t) and V ２Ｂ The minimum value of (t) is a positive voltage greater than 0 V. That is, in this embodiment, the offset voltage V ＯＳ is the fluctuating voltage V ２Ａ (t) and V ２Ｂ PP, which is the difference between the maximum and minimum values ​​of (t) ２ It is set to a constant positive voltage greater than the value.

[0068] A fluctuating voltage V is applied to the upper electrodes 53 of the two piezoelectric elements 30 that constitute the second actuator 32. ２Ａ (t) and V ２Ｂ (t) is applied, and an offset voltage V ＯＳ When the mirror section 20 is driven at the second drive frequency f ｄ２ and the second axis a ２ It swings around (see Figure 8).

[0069] First drive frequency f ｄ１ is the first axis a of the mirror part 20 １The second drive frequency f is set to match the surrounding resonant frequency. ｄ２ is the second axis a of the mirror part 20 ２ It is set to match the surrounding resonant frequency. ｄ１ >f ｄ２ That is, the mirror unit 20 is １ The oscillation frequency around the second axis a ２ The first driving frequency f ｄ１ and the second driving frequency f ｄ２ does not necessarily have to coincide with the resonant frequency.

[0070] 10 shows an example of the configuration of the drive control unit 5. The drive control unit 5 has a mirror drive unit 4A and a light source drive unit 3A. The mirror drive unit 4A has a first variable voltage 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 variable voltage generation unit 60B, a second signal processing unit 61B, a second phase shift unit 62B, a second zero-cross pulse output unit 63B, and an offset voltage generation unit 64. The mirror drive unit 4A is an example of a "voltage application unit" according to the technology of the present disclosure.

[0071] The first variable voltage generating unit 60A, the first signal processing unit 61A, and the first phase shift unit 62A are １ The second variable voltage generating unit 60B, the second signal processing unit 61B, and the second phase shifting unit 62B perform feedback control so that the oscillations around the mirror unit 20 maintain a resonant state. ２ Feedback control is performed to maintain the surrounding oscillations in a resonant state.

[0072] The first variable voltage generating unit 60A generates the variable voltage V １Ａ (t) and V １Ｂ (t) is generated, and the generated fluctuating voltage V １Ａ (t) and V １Ｂ (t) is applied to the upper electrodes 53 of the two piezoelectric elements 30 that constitute the first actuator 31 via the first phase shift section 62A. As a result, the mirror section 20 is rotated along the first axis a １The first angle detection sensors 11A and 11B are arranged to rotate about the first axis a of the mirror unit 20. １ It outputs a signal according to the surrounding angle.

[0073] The second variable voltage generating unit 60B generates the variable voltage V ２Ａ (t) and V ２Ｂ (t) is generated, and the generated fluctuating voltage V ２Ａ (t) and V ２Ｂ (t) is applied to the upper electrodes 53 of the two piezoelectric elements 30 that constitute the second actuator 32 via the second phase shift section 62B. As a result, the mirror section 20 is ２ The second angle detection sensors 12A and 12B are arranged to detect the second axis a of the mirror unit 20. ２ It outputs a signal according to the surrounding angle.

[0074] The offset voltage generating unit 64 generates an offset voltage V ＯＳ The generated offset voltage V ＯＳ is applied to the lower electrodes 51 of the plurality of piezoelectric elements 30 that constitute the first actuator 31 and the second actuator 32 .

[0075] The first signal processing unit 61A detects the second axis a based on the signals output from the first angle detection sensors 11A and 11B. ２ The second signal processing unit 61B generates a first angle detection signal from which vibration noise caused by surrounding vibrations has been removed. １ A second angle detection signal is generated from which vibration noise caused by surrounding fluctuations has been removed.

[0076] The first zero-cross pulse output unit 63A generates a first zero-cross pulse ZC1 based on the first angle detection signal input from the first signal processing unit 61A. The second zero-cross pulse output unit 63B generates a second zero-cross pulse ZC2 based on the second angle detection signal input from the second signal processing unit 61B. The first zero-cross pulse ZC1 and the second zero-cross pulse ZC2 are input to the light source driving unit 3A.

[0077] The light source driver 3A drives the light source 3 based on, for example, drawing data supplied from outside the image drawing system 10. The light source driver 3A also controls the irradiation timing of the laser light so that the irradiation timing is synchronized with the first zero-cross pulse ZC1 and the second zero-cross pulse ZC2 input from the mirror driver 4A.

[0078] 11 shows the direction Ps of spontaneous polarization of the piezoelectric film 52. FIG. 11 shows the piezoelectric element 30 constituting the first actuator 31. As described above, the direction Ps of spontaneous polarization is determined by the thin film formation process for forming the piezoelectric film 52, and is the direction from the lower electrode 51 to the upper electrode 53. In the example shown in FIG. 11, an offset voltage V ＯＳ is applied to the upper electrode 53, and a variable voltage V １Ａ (t) is applied. ＯＳ is a constant positive voltage, and the fluctuating voltage V １Ａ (t) is the offset voltage V ＯＳ Since the voltage Ps is smaller than the direction Ps of the spontaneous polarization, a voltage is applied to the piezoelectric film 52 in the direction opposite to the direction Ps of the spontaneous polarization. This allows the piezoelectric film 52 to be effectively displaced. The same applies to the piezoelectric element 30 that constitutes the second actuator 32.

[0079] As described above, according to the technology of the present disclosure, it is not necessary to reverse the polarization direction of the piezoelectric film and to configure the voltage application unit to generate a fluctuating negative voltage. Therefore, according to the technology of the present disclosure, it is not necessary to configure the voltage application unit using a circuit element for generating a negative voltage, and therefore power consumption can be reduced.

[0080] [Second Embodiment] Next, a second embodiment will be described. In the above embodiment, the minimum value of the variable voltage is set to a positive voltage, but in this embodiment, the minimum value of the variable voltage is allowed to be set to a negative voltage. For example, as shown in FIG. 12, the drive control unit 5 １Ａ (t), V １Ｂ (t), V ２Ａ (t), and V ２Ｂ The minimum value of (t) is allowed to be a negative voltage. ＯＳThe maximum value of the fluctuating voltage is a positive voltage, as in the above embodiment. The other configurations and operations of the image drawing system according to this embodiment are the same as those of the above embodiment.

[0081] If the minimum value of the fluctuating voltage is allowed to be a negative voltage as in this embodiment, the offset voltage V ＯＳ The offset voltage V ＯＳ By adjusting the offset voltage V, it is possible to adjust the bias of the variable voltage applied to the piezoelectric element 30. For example, the offset voltage V is adjusted so that the lower limit of the variable voltage becomes the lower limit of the voltage required by the entire drive control unit 5. ＯＳ This allows the upper limit of the positive voltage required by the entire drive control unit 5 to be lowered, thereby further reducing power consumption.

[0082] [Modifications] Various modifications of the first and second embodiments will be described below.

[0083] In the first and second embodiments, the offset voltage V ＯＳ is set to the maximum value of the fluctuating voltage, but the offset voltage V ＯＳ is sufficient as long as it is equal to or greater than the maximum value of the fluctuating voltage, and does not have to be equal to the maximum value of the fluctuating voltage.

[0084] In the first and second embodiments, the variable voltage V １Ａ (t) and V １Ｂ (t) offset voltage V ＯＳ and the fluctuating voltage V ２Ａ (t) and V ２Ｂ (t) offset voltage V ＯＳ Although the values ​​of the two are the same, they may be individually set to different values.

[0085] The configuration of the MMD 4 shown in the first embodiment is an example. The configuration of the MMD 4 can be modified in various ways. For example, １ The first actuator 31 that swings the mirror unit 20 around the second axis a is disposed on the second movable frame 24. ２ A second actuator 32 for swinging the periphery may be disposed on the first movable frame 22 .

[0086] The hardware configuration of the drive control unit 5 can be modified in various ways. The drive control unit 5 may be configured with either an analog circuit or a digital circuit, or both. The drive control unit 5 may be configured with a single processor, or may be configured with a combination of two or more processors of the same or different types. Processors include a central processing unit (CPU), a programmable logic device (PLD), a dedicated electrical circuit, etc. As is well known, a CPU is a general-purpose processor that executes software (programs) and functions as various processing units. A PLD is a processor, such as a field programmable gate array (FPGA), whose circuit configuration can be changed after manufacturing. A dedicated electrical circuit is a processor, such as an application specific integrated circuit (ASIC), having a circuit configuration designed specifically to execute specific processing.

[0087] The piezoelectric element 30 and the mirror driver 4A as a voltage application unit described in the first and second embodiments constitute an "actuator device" according to the technology of the present disclosure. The actuator device according to the technology of the present disclosure is not limited to optical scanning devices, and can also be applied to devices other than optical scanning devices.

[0088] All publications, patent applications, and technical standards mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent application, or technical standard was specifically and individually indicated to be incorporated by reference.

[0089] The above description allows the understanding of the following technologies. [Supplementary Item 1] An actuator device comprising: a piezoelectric element having a piezoelectric film, a first electrode arranged on one surface of the piezoelectric film, and a second electrode arranged on the other surface of the piezoelectric film; and a voltage application unit that applies a voltage to the piezoelectric element, wherein the voltage application unit applies a positive offset voltage to the first electrode and applies a fluctuating voltage to the second electrode for operating the piezoelectric film. [Supplementary Item 2] The actuator device according to Supplementary Item 1, wherein the piezoelectric film has spontaneous polarization, and the direction of the spontaneous polarization is from the first electrode to the second electrode. [Supplementary Item 3] The actuator device according to Supplementary Item 2, wherein the piezoelectric film is an Nb-doped PZT thin film. [Supplementary Item 4] The actuator device according to any one of Supplementary Items 1 to 3, wherein the maximum value of the fluctuating voltage is equal to the offset voltage. [Supplementary Item 5] The actuator device according to any one of Supplementary Items 1 to 4, wherein the minimum value of the fluctuating voltage is a positive voltage. [Supplementary Item 6] The actuator device according to any one of Supplementary Items 1 to 4, wherein the minimum value of the fluctuating voltage is a negative voltage.

Claims

1. An actuator device comprising: a piezoelectric element having a piezoelectric film, a first electrode arranged on one side of the piezoelectric film, and a second electrode arranged on the other side of the piezoelectric film; and a voltage application unit that applies a voltage to the piezoelectric element, wherein the voltage application unit applies a positive offset voltage to the first electrode, and applies a fluctuating voltage to the second electrode for operating the piezoelectric film.

2. The actuator device according to claim 1, wherein the piezoelectric film has spontaneous polarization, and the direction of the spontaneous polarization is from the first electrode to the second electrode.

3. The actuator device according to claim 2, wherein the piezoelectric film is a Nb-doped PZT thin film.

4. The actuator device according to claim 1, wherein a maximum value of the fluctuating voltage is equal to the offset voltage.

5. The actuator device according to claim 4, wherein the minimum value of the fluctuating voltage is a positive voltage.

6. The actuator device according to claim 4, wherein the minimum value of the fluctuating voltage is a negative voltage.

7. An optical scanning device comprising: a mirror section having a reflective surface that reflects incident light; a first actuator that oscillates the mirror section about a first axis; a second actuator that oscillates the mirror section about a second axis intersecting the first axis; and a voltage application section that oscillates the mirror section by applying a voltage to each of the first actuator and the second actuator, wherein each of the first actuator and the second actuator has a piezoelectric element composed of a piezoelectric film, a first electrode arranged on one surface of the piezoelectric film, and a second electrode arranged on the other surface of the piezoelectric film, and the voltage application section applies a positive offset voltage to the first electrode, and applies a fluctuating voltage to the second electrode for operating the piezoelectric film.

8. A method for driving an actuator device comprising: a piezoelectric element having a piezoelectric film, a first electrode arranged on one side of the piezoelectric film, and a second electrode arranged on the other side of the piezoelectric film; and a voltage application unit that applies a voltage to the piezoelectric element, the method including the voltage application unit applying an offset voltage which is a positive voltage to the first electrode, and applying a fluctuating voltage to the second electrode for operating the piezoelectric film.

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