Excitation device, vibration device, vehicle, control method, and computer program

Abstract

An excitation device (31, 31A, 31B) comprises: output circuits (37, 37A) that output a drive signal having a frequency component for driving a piezoelectric element (15) that vibrates a target object (11) via a vibrating body (13); and a control circuit (32) that comprises a plurality of vibration modes that control the output circuits (37, 37A) so as to provide, to the piezoelectric element (15), a drive signal that has a frequency based on the resonance frequency of a vibrator (17) that includes the target object (11), the vibrating body (13) and the piezoelectric element (15). The plurality of vibration modes include a prescribed vibration mode that sets the drive signal frequency to a frequency that is 1 / (2n+1) times or (2n+1) times the resonance frequency of the vibrator (17), where n is a positive integer.

Description

[Technical Field]

[0001] This disclosure relates to an excitation device, a vibration device, a vehicle, a control method, and a computer program. [Background technology]

[0002] Conventionally, techniques have been considered for removing foreign matter adhering to lenses or covers positioned in front of sensors such as imaging devices. For example, Patent Document 1 discloses a device in which a controller provides a piezoelectric element with drive signals having different frequencies for a heating sequence and a removal sequence, causing the piezoelectric element to vibrate the top cover. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] U.S. Patent Application Publication No. 2020 / 0282435 [Overview of the project] [Problems that the invention aims to solve]

[0004] The technology disclosed in Patent Document 1 allows for the vibration of a piezoelectric element in either a heating sequence or a removal sequence. However, the device requires not only frequency changes but also control of the applied voltage, which can complicate control. Furthermore, changing the voltage during control operation can complicate the control system within the device and reduce power conversion efficiency. Patent Document 1 also discloses setting the frequency of the heating sequence higher than the frequency of the removal sequence. At high frequencies, the vibration speed of the top cover increases, and if foreign matter such as mud adheres to the top cover, wear of the top cover coating may be accelerated, potentially leading to a reduction in the coating's lifespan.

[0005] The purpose of this disclosure is to provide an excitation device, a vibration device, a vehicle, a control method, and a computer program that can execute multiple vibration modes that impart different vibrations to an object with a simple configuration. [Means for solving the problem]

[0006] The excitation device according to this disclosure includes an output circuit that outputs a drive signal having frequency components to drive a piezoelectric element that vibrates an object via a vibrating body, and a control circuit that controls the output circuit to provide the piezoelectric element with a drive signal having a frequency based on the resonant frequency of the vibrator, which includes the object, the vibrating body, and the piezoelectric element, wherein the plurality of vibration modes include a predetermined vibration mode that sets the frequency of the drive signal to a frequency that is 1 / (2n+1) times or (2n+1) times the resonant frequency of the vibrator, where n is a positive integer.

[0007] The vibration device according to this disclosure comprises an excitation device, a piezoelectric element, a vibrating body, and an object.

[0008] The vehicle relating to this disclosure comprises an excitation device, a piezoelectric element, a vibrating body, an object, and an imaging device.

[0009] The control method according to this disclosure is a control method for an output circuit that outputs a drive signal having frequency components in order to drive a piezoelectric element that vibrates an object via a vibrating body, and controls the output circuit to provide the piezoelectric element with a drive signal having a frequency based on the resonant frequency of a vibrator including the object, vibrating body and piezoelectric element, and selects a predetermined vibration mode from a plurality of vibration modes, and in the predetermined vibration mode, sets the frequency of the drive signal to a frequency that is 1 / (2n+1) times or (2n+1) times the resonant frequency of the vibrator, where n is a positive integer.

[0010] The computer program relating to this disclosure is a computer program that causes one or more processors to execute the control method relating to this disclosure. [Effects of the Invention]

[0011] According to this disclosure, it is possible to provide an excitation device, a vibration device, a vehicle, a control method, and a computer program that can perform multiple vibration modes that impart different vibrations to an object with a simple configuration. [Brief explanation of the drawing]

[0012] [Figure 1] Perspective view of the vibration device according to this embodiment [Figure 2] Schematic cross-sectional view of the configuration of the imaging unit according to this embodiment. [Figure 3] schematic block diagram of the vibration circuit according to this embodiment [Figure 4] schematic circuit diagram of the vibration circuit according to this embodiment [Figure 5] A graph showing the relationship between the frequency of the drive signal applied to a piezoelectric element and its impedance. [Figure 6] A schematic diagram illustrating an example of the relationship between the sliding angle and adhesion energy. [Figure 7] A schematic diagram showing an example of the relationship between the sliding angle and vibration acceleration. [Figure 8] Timing chart showing input and output signals for each element of the excitation circuit. [Figure 9A] This graph shows the time variation of a drive signal having a predetermined resonant frequency applied to a piezoelectric element, and the time variation of the displacement of the protective cover when the piezoelectric element is driven at that frequency. [Figure 9B] This graph shows the time variation of a drive signal having a predetermined resonant frequency applied to a piezoelectric element, and the time variation of the displacement of the protective cover when the piezoelectric element is driven at a frequency 1 / 3 of that frequency. [Figure 10A] An example of control using the first sweep method of a control circuit for determining the resonant frequency. [Figure 10B] An example of control using a second sweep method for a control circuit to determine the resonant frequency. [Figure 10C] An example of control using a third sweep method for a control circuit to determine the resonant frequency. [Figure 11]A graph showing the impedance of a piezoelectric element with respect to the switching frequency near the resonant frequency, and the phase difference between the voltage applied to the piezoelectric element and the current flowing through the piezoelectric element. [Figure 12] A schematic circuit diagram showing a modified example of the excitation circuit according to the embodiment. [Figure 13] A graph showing an example of the displacement of the protective cover in accordance with the frequency of the drive signal. [Figure 14] A schematic block diagram of a modified example of the vibration circuit according to this embodiment. [Figure 15A] This graph shows the time variation of a drive signal having a predetermined resonant frequency applied to a piezoelectric element, and the time variation of the displacement of the protective cover when the piezoelectric element is driven at that frequency. [Figure 15B] This graph shows the time variation of a drive signal having a predetermined resonant frequency applied to a piezoelectric element, and the time variation of the displacement of the protective cover when the piezoelectric element is driven at a frequency 1 / 3 of that frequency. [Figure 16] A graph showing an example of the temperature rise characteristics of a protective cover when a piezoelectric element is vibrated. [Figure 17] A graph showing an example of a method for controlling the temperature rise of the protective cover by the excitation device in de-icing mode. [Figure 18] Flowchart illustrating the vibration processing of a vibration device by the control circuit of the excitation device according to this embodiment. [Modes for carrying out the invention]

[0013] The embodiments of this disclosure will be described below with reference to the drawings. However, the configurations described below are merely examples of this disclosure, and this disclosure is not limited to the embodiments described below. Various modifications are possible in addition to these embodiments, as long as they do not depart from the technical concept of this disclosure, depending on the design, etc.

[0014] (Embodiment) 1-1. Example Configuration An excitation device according to an embodiment of the present disclosure includes an output circuit that outputs a drive signal having frequency components to drive a piezoelectric element that vibrates an object via a vibrating body, and a control circuit that controls the output circuit to provide the piezoelectric element with a drive signal having a frequency based on the resonant frequency of a vibrator including the piezoelectric element, the vibrating body, and a protective cover, in a plurality of vibration modes. The plurality of vibration modes include a predetermined vibration mode in which the frequency of the drive signal is set to a frequency of 1 / (2n+1) times or (2n+1) times the resonant frequency of the vibrator, where n is a positive integer. With this configuration, the excitation device can vibrate an object vibrated by the piezoelectric element in a plurality of vibration modes without requiring a complex configuration.

[0015] 1-1-1. Vibration device Figure 1 is a perspective view of a vibration device 10 according to an embodiment of the present disclosure. The vibration device 10 according to this embodiment comprises a protective cover 11, a vibrating body 13, a piezoelectric element 15, and an excitation circuit 31, which will be described later. The vibrating body 13 includes a first cylindrical body 13a, a spring portion 13b, a second cylindrical body 13c, and a diaphragm 13d. The vibration device 10 and the imaging unit 100 (details of which will be described later) equipped with the vibration device 10 are examples of devices vibrated by the excitation circuit 31 according to this embodiment, which will be described later, and are not limited thereto. Hereinafter, in this specification, the excitation circuit will also be called an excitation device. Furthermore, the structure including the protective cover 11, the vibrating body 13, and the piezoelectric element 15 has a predetermined resonant frequency with respect to the vibration of the piezoelectric element 15, which will be described later. Hereinafter, this structure will be referred to as the vibrator 17.

[0016] The protective cover 11 transmits light of a predetermined wavelength. The predetermined wavelength is, for example, the wavelength detected by the imaging device 20 (see Figure 2) of the imaging unit 100. The predetermined wavelength is not limited to wavelengths in the visible light region, but may also be wavelengths in the invisible light region.

[0017] The protective cover 11 is supported by the end of the cylindrical first cylindrical body 13a. Specifically, the back surface of the protective cover 11 is supported by the first cylindrical body 13a.

[0018] The protective cover 11 is hemispherical and dome-shaped. When viewed from the height direction of the vibrator 10, the protective cover 11 is circular. However, the shape of the protective cover 11 is not limited to circular. When viewed from the height direction of the vibrator 10, the shape of the protective cover 11 may be polygonal or elliptical, etc. The protective cover 11 is not limited to hemispherical and dome-shaped. For example, the protective cover 11 may have a shape in which cylinders are connected to a hemisphere, or a curved shape smaller than a hemisphere. The protective cover 11 may also be a flat plate. The protective cover 11 may also function as an optical element such as a lens.

[0019] The first cylindrical body 13a is formed in a cylindrical shape having one end and the other end. The first cylindrical body 13a supports the protective cover 11 at one end. For example, the protective cover 11 and the first cylindrical body 13a are joined together. The method of joining the protective cover 11 and the first cylindrical body 13a is not particularly limited. Examples of joining methods include, for example, bonding with adhesive, welding, fitting, and press-fitting.

[0020] In this embodiment, the first cylindrical body 13a has a flange 13aa at one end. The flange 13aa is a plate-shaped member extending outward from one end of the first cylindrical body 13a. The flange 13aa is formed in an annular plate shape. The flange 13aa increases the contact area with the protective cover 11, thereby stably supporting the protective cover 11.

[0021] The other end of the first cylindrical body 13a is supported by an elastically deformable spring portion 13b. In other words, the first cylindrical body 13a is supported by the spring portion 13b on the side opposite to the protective cover 11.

[0022] The first cylindrical body 13a is made of a hollow member with a through hole inside. The through hole is provided in the height direction of the vibrating device 10, and openings for the through hole are provided at one end and the other end of the first cylindrical body 13a. The first cylindrical body 13a has, for example, a cylindrical shape. When viewed from the height direction of the vibrating device 10, the outer shape of the first cylindrical body 13a and the openings of the through hole are formed in a circular shape.

[0023] The shape of the first cylindrical body 13a is not limited to a cylindrical shape. For example, the shape of the first cylindrical body 13a may be a polygonal cylinder or an elliptical cylinder.

[0024] The material of the first cylindrical body 13a may be, for example, metal or synthetic resin. Alternatively, the material of the first cylindrical body 13a may be moldable and / or machineable ceramic or glass. The same applies to the spring portion 13b, the second cylindrical body 13c, and the diaphragm 13d.

[0025] The spring portion 13b supports the first cylindrical body 13a so that it can be displaced relative to the second cylindrical body 13c. The spring portion 13b is an annular leaf spring. The inner circumference of the spring portion 13b supports the other end of the first cylindrical body 13a. The outer circumference of the spring portion 13b is supported by the second cylindrical body 13c. When viewed from the height direction of the vibrating device 10, the outer and inner circumference shapes of the spring portion 13b are circular.

[0026] Furthermore, the outer and inner circumferential shapes of the spring portion 13b are not limited to circular shapes. When viewed from the height direction of the vibrating device 10, the outer and inner circumferential shapes of the spring portion 13b may be polygonal or elliptical.

[0027] The second cylindrical body 13c has a cylindrical shape with one end and the other end. One end of the second cylindrical body 13c supports the outer circumference of the spring portion 13b.

[0028] A diaphragm 13d is positioned at the other end of the second cylindrical body 13c.

[0029] The second cylindrical body 13c is not limited to a cylindrical shape. For example, the second cylindrical body 13c may be a polygonal cylinder or an elliptical cylinder.

[0030] The diaphragm 13d is positioned at the other end of the second cylindrical body 13c and vibrates in the height direction of the vibrating device 10. Specifically, the diaphragm 13d is positioned at the other end of the second cylindrical body 13c, i.e., at the bottom surface.

[0031] The piezoelectric element 15 is located on the bottom surface (lower surface) of the diaphragm 13d. The vibration of the piezoelectric element 15 causes the diaphragm 13d to vibrate, which in turn causes the second cylindrical body 13c to vibrate in the height direction of the vibration device 10. For example, the piezoelectric element 15 vibrates when a voltage is applied to it.

[0032] The piezoelectric element 15 is an annular plate shape. When viewed from the height direction of the vibrating device 10, the outer and inner shapes of the piezoelectric element 15 are circular. However, the outer and inner shapes of the piezoelectric element 15 are not limited to circular. When viewed from the height direction of the vibrating device 10, the outer and inner shapes of the piezoelectric element 15 may be, for example, polygonal or elliptical.

[0033] The piezoelectric element 15 comprises a piezoelectric material and an electrode. Examples of materials for the piezoelectric material include barium titanate (BaTiO3), lead zirconate titanate (PZT:PbTiO3·PbZrO3), lead titanate (PbTiO3), lead metaniobate (PbNb2O6), and bismuth titanate (Bi4Ti3O3). 12 Examples include suitable piezoelectric ceramics such as (K,Na)NbO3, or suitable piezoelectric single crystals such as LiTaO3 or LiNbO3. The electrode may be, for example, a Ni electrode. The electrode may also be an electrode made of a thin metal film such as Ag or Au formed by sputtering. In addition to sputtering, the electrode can also be formed by plating or vapor deposition.

[0034] The diaphragm 13d is an annular plate. The diaphragm 13d supports the bottom surface of the second cylindrical body 13c.

[0035] The protective cover 11, the first cylindrical body 13a, the spring portion 13b, and the second cylindrical body 13c are configured such that the resonant frequency of the protective cover 11 is greater than the resonant frequency of the spring portion 13b. Specifically, the resonant frequency of the protective cover 11 is made greater than the resonant frequency of the spring portion 13b by determining the materials and dimensions of the protective cover 11, the first cylindrical body 13a, the spring portion 13b, and the second cylindrical body 13c as described above.

[0036] The first cylindrical body 13a, the spring portion 13b, the second cylindrical body 13c, and the diaphragm 13d are integrally formed. However, the first cylindrical body 13a, the spring portion 13b, the second cylindrical body 13c, and the diaphragm 13d may be formed separately or as separate components.

[0037] As described above, the vibration device 10 includes an excitation circuit 31 that applies a drive signal to the piezoelectric element 15 to generate vibration. The excitation circuit 31 is connected to the piezoelectric element 15, for example, via a power supply conductor. The piezoelectric element 15 vibrates in the height direction of the vibration device 10 based on the drive signal from the excitation circuit 31. The vibration of the piezoelectric element 15 causes the diaphragm 13d to vibrate in the height direction of the vibration device 10, and the diaphragm 13d causes the second cylindrical body 13c to vibrate in the height direction of the vibration device 10. The vibration of the second cylindrical body 13c allows the vibration of the piezoelectric element 15 to be transmitted to the first cylindrical body 13a via the spring portion 13b. In the vibration device 10, the protective cover 11 vibrates when the first cylindrical body 13a is vibrated, and foreign matter such as raindrops attached to the protective cover 11 is removed.

[0038] The excitation circuit 31 applies a drive signal to the piezoelectric element 15 so that the first cylindrical body 13a and the second cylindrical body 13c vibrate in opposite phases in the height direction of the vibration device 10. The excitation circuit 31 can vibrate the vibration device 10 in vibration modes other than the first cylindrical body 13a and the second cylindrical body 13c vibrating in opposite phases in the height direction of the vibration device 10 by applying the drive signal to the piezoelectric element 15.

[0039] Figure 2 is a schematic cross-sectional view of the configuration of the imaging unit 100 according to this embodiment. Figure 2 is a cross-sectional view of the vibrator 10 of Figure 1, cut by a plane passing through the center of the vibrator 10 as viewed from the height direction of the vibrator 10. The imaging unit 100 is a unit that is mounted, for example, on the front or rear of a vehicle to image an object to be imaged. Note that the imaging unit 100 is not limited to a vehicle, but may be mounted on other devices such as ships or aircraft.

[0040] The imaging unit 100 includes a vibrator 10 and an imaging device 20. The imaging device 20 is housed within the vibrator 10. The imaging device 20 includes, for example, an image sensor such as a CMOS and a CCD. The imaging device 20 can form an image based on light transmitted through the protective cover 11. The imaging unit 100 further includes a base member 21, a main body member 22, and a support member 23. The main body member 22 is a circular plate. The base member 21 is located in the center of the upper surface of the main body member 22. The imaging device 20 is fixed on the base member 21. The support member 23 extends upward from the outer periphery of the main body member 22. The vibrator 10 is supported by the support member 23. The imaging unit 100 may include one or more optical members, such as lenses, between the protective cover 11 and the imaging device 20.

[0041] When the imaging unit 100 is mounted on a vehicle or the like and used outdoors, foreign matter such as raindrops, mud, and dust may adhere to the protective cover 11 that covers the imaging device 20, and the protective cover 11 may also freeze. The vibration device 10 can generate vibrations to remove foreign matter such as raindrops that have adhered to the protective cover 11, or vibrations to eliminate freezing.

[0042] 1-1-2. Vibration Circuits Figure 3 is a schematic block diagram of a vibration circuit 30 including an excitation circuit 31 and a piezoelectric element 15 according to this embodiment. As shown in Figure 3, the excitation circuit 31 comprises a control circuit 32, a DC power supply 33, and an output circuit 37. The excitation circuit 31 may further include a current detection circuit 38. In this embodiment, as will be described in detail later, the excitation circuit 31 controls the voltage supplied from the DC power supply 33 using the control circuit 32 and applies it to the piezoelectric element 15 via the output circuit 37 as a drive signal having frequency components. Furthermore, the control circuit 32 of the excitation circuit 31 can determine the resonant frequency of the vibrator 17 and appropriately control the frequency of the drive signal by detecting the magnitude of the current output from the output circuit 37 to the piezoelectric element 15 using the current detection circuit 38.

[0043] Figure 4 is a schematic circuit diagram of an example of the vibration circuit 30A shown in Figure 3. The excitation circuit 31A comprises a control circuit 32, a DC power supply 33, an output circuit 37A including a series circuit of a first switch 35 and a second switch 36, a current detection circuit 38A, a capacitor 39, and a resistor 40.

[0044] The control circuit 32 controls the switching frequencies of the first switch 35 and the second switch 36. The control circuit 32 includes a general-purpose processor such as a CPU or MPU that performs predetermined functions by executing a program. The control circuit 32 is configured to communicate with a storage device and performs various processes in the control circuit 32, such as switching the first switch 35 and the second switch 36, by calling and executing arithmetic programs etc. stored in the storage device. The control circuit 32 is not limited to a configuration in which hardware resources and software cooperate to perform predetermined functions, but may also be a hardware circuit specifically designed to perform predetermined functions. In other words, the control circuit 32 can be implemented with various processors other than CPUs and MPUs, such as GPUs, FPGAs, DSPs, and ASICs. Such a control circuit 32 may be composed of, for example, a signal processing circuit which is a semiconductor integrated circuit.

[0045] The DC power supply 33 has an output terminal that generates a predetermined voltage between itself and the reference potential 34. The DC power supply 33 may be, for example, a battery, and its output terminal may be the positive terminal of the battery. The DC power supply 33 may also be a known device that can apply a predetermined voltage to the piezoelectric element 15 in combination with the reference potential 34.

[0046] The reference potential 34 may be, for example, ground, or body ground connected to the negative terminal of the battery.

[0047] The output circuit 37A is connected to the DC power supply 33. As shown in Figure 4, in this embodiment, the output circuit 37A is connected to the reference potential 34 via the current-voltage conversion circuit 42A, which will be described later. As described above, the output circuit 37A includes a series circuit of a first switch 35 and a second switch 36 connected to the DC power supply 33. The series circuit of the first switch 35 and the second switch 36 is also referred to as the "first leg 41A" in this specification. In the first leg 41A of the output circuit 37A, the connection point C1 between the first switch 35 and the second switch 36 is connected to the piezoelectric element 15 via a capacitor 39.

[0048] The first switch 35 is, for example, a metal-oxide-semiconductor electrolytic effect transistor (MOSFET), but is not limited thereto. The first switch 35 has one end (e.g., source) and the other end (e.g., drain). One end of the first switch 35 is connected to the DC power supply 33. The other end of the first switch 35 is connected to the second switch 36. The other end of the first switch 35 is also connected to the piezoelectric element 15 via a capacitor 39. The control circuit 32 is connected to the control terminal (e.g., gate) of the first switch 35 and can switch the first switch 35 on and off as described above. That is, by switching the first switch 35 on and off, the control circuit 32 can control the first switch 35 to electrically conduct / open the circuit between the DC power supply 33 and the piezoelectric element 15 connected to the first switch 35.

[0049] The second switch 36, like the first switch 35, is, for example, a MOSFET, but is not limited to that. The second switch 36 has one end (e.g., source) and the other end (e.g., drain). One end of the second switch 36 is connected to the other end of the first switch 35. That is, one end of the second switch 36 is connected to the piezoelectric element 15 via a capacitor 39, similar to the other end of the first switch 35. The other end of the second switch 36 is connected to the reference potential 34 via the current-voltage conversion element 45 of the current-voltage conversion circuit 42A. The control circuit 32 is connected to the control terminal (e.g., gate) of the second switch 36 and can switch the second switch 36 on / off as described above. That is, by switching the second switch 36 on / off, the control circuit 32 can control the second switch 36 to electrically conduct / open the circuit between the piezoelectric element 15 connected to the second switch 36 and the reference potential 34.

[0050] The current detection circuit 38A can detect at least one of the current flowing through the first switch 35 and the current flowing through the second switch 36, and can output a detection signal indicating the magnitude of the detected current to the control circuit 32. The current detection circuit 38A according to this embodiment includes a current-voltage conversion circuit 42A, a low-pass filter 43, and an analog-to-digital conversion circuit (AD conversion circuit) 44.

[0051] The current-voltage conversion circuit 42A has a current-voltage conversion element 45. The current-voltage conversion element 45 can convert the current flowing through it into a voltage corresponding to the magnitude of the current flowing through it. The current-voltage conversion element 45 may be configured to detect, for example, the current flowing through the first switch 35 or the current flowing through the second switch 36 as a voltage. In this embodiment, the current-voltage conversion element 45 is connected between the second switch 36 and the reference potential 34. The current-voltage conversion element 45 can detect the current flowing from the piezoelectric element 15 through the second switch 36 to the reference potential 34. The current-voltage conversion circuit 42A may have two current-voltage conversion elements, with one of the two current-voltage conversion elements configured to detect the current flowing through the first switch 35 and the other current-voltage conversion element configured to detect the current flowing through the second switch 36. In this embodiment, the current-voltage conversion element 45 is a resistor (shunt resistor) having a predetermined resistance value. The current-voltage conversion element 45 is not limited to a shunt resistor and may be a Hall element. In this case, the current-voltage conversion element 45 may be placed near the second switch 36 so as to detect the magnetic field caused by the current flowing through the second switch 36. Thus, the current-voltage conversion element 45 may be any known element that can convert current into voltage.

[0052] The low-pass filter 43 is a filter circuit that removes signals having frequency components higher than the cutoff frequency. In this embodiment, the low-pass filter 43 is connected to the connection point between the current-voltage conversion element 45 and the second switch 36. The low-pass filter 43 smooths the voltage input from the current-voltage conversion circuit 42A and then outputs it to the AD conversion circuit. 44 Output to [this location].

[0053] The AD conversion circuit 44 is a circuit that converts the voltage (analog signal) smoothed by the low-pass filter 43 into a digital signal that can be input to the control circuit 32. The AD conversion circuit 44 outputs the digital signal to the control circuit 32 as a detection signal. The current detection circuit 38A may not include the AD conversion circuit 44 and may be configured to output the voltage smoothed by the low-pass filter 43 as a detection signal to the control circuit 32.

[0054] The current detection circuit 38A in this embodiment outputs a detection signal, which is a digital signal generated based on the magnitude of the current flowing through the second switch 36, to the control circuit 32, but is not limited to this. For example, the current detection circuit 38A may be configured to include only a current-voltage conversion circuit 42A and a low-pass filter 43, and output a detection signal, which is an analog signal rather than a digital signal, to the control circuit 32.

[0055] As described above, the piezoelectric element 15 has a piezoelectric body and electrodes. The piezoelectric element 15 has one end and the other end, one end connected to the capacitor 39 and the other end connected to the reference potential 34. Specifically, the electrode on one end of the piezoelectric element 15 is connected to the capacitor 39, and the electrode on the other end of the piezoelectric element 15 is connected to the reference potential 34.

[0056] In the first state, as described later, capacitor 39 can store charge based on the voltage applied by the DC power supply 33. In the second state, as described later, capacitor 39 can release the stored charge to the reference potential 34 via the second switch 36. As a result, the excitation circuit 31A can supply currents I1 and I2 to the vibration circuit 30A, as described later, by the control circuit 32 controlling the switching process of the first switch 35 and the second switch 36.

[0057] The resistor 40 is connected between the connection point between the piezoelectric element 15 and the capacitor 39 and the reference potential 34. When the switching process by the control circuit 32 is completed, one end of the piezoelectric element 15 is connected to the reference potential 34 via the resistor 40, so the one end and the other end become equal in potential.

[0058] The excitation device 31 according to this disclosure is not limited to the circuit configuration described above. For example, the output circuit 37A is a half-bridge configuration using two switches, but it may also be a full-bridge configuration using four switches. Also, the current detection circuit 38A detects the current flowing through the second switch as a voltage using a shunt resistor, but a Hall element may also be used. Thus, the excitation device 31 is not limited to the circuit configuration described above, and existing configurations can be used.

[0059] 1-2. Example of Operation Referring to Figure 4, an example of the operation of the excitation circuit 31A according to this embodiment will be described. As mentioned above, Figure 4 shows the vibration circuit 30A including the excitation circuit 31A and the piezoelectric element 15.

[0060] The control circuit 32 of the excitation circuit 31A according to this embodiment performs a switching process that complementaryly switches the first switch 35 and the second switch 36 at the switching frequency. That is, the control circuit 32 controls the first switch 35 and the second switch 36 so that when the first switch 35 is on, the second switch 36 is off (referred to as the "first state" as appropriate). The control circuit 32 also controls the first switch 35 and the second switch 36 so that when the first switch 35 is off, the second switch 36 is on (referred to as the "second state" as appropriate). By complementaryly switching the first switch 35 and the second switch 36, the control circuit 32 applies a voltage having a frequency corresponding to the switching frequency (for example, a square wave voltage) as a drive signal to the piezoelectric element 15 based on a predetermined voltage from the DC power supply 33.

[0061] In the first state, a current I1 flows through the vibration circuit 30A via the first switch 35. The current I1 is indicated by the dashed arrow in Figure 4. As shown in Figure 4, the current I1 flows from the DC power supply 33 through the first switch 35 to the piezoelectric element 15. Therefore, a voltage is applied to the piezoelectric element 15 that makes the excitation circuit 31A side a higher potential.

[0062] In the vibration circuit 30A, when a voltage is applied to the piezoelectric element 15 in the first state, positive charge accumulates on the output circuit 37A side and negative charge accumulates on the reference potential 34 side in the capacitor 39 interposed between the output circuit 37A and the piezoelectric element 15. When the control circuit 32 changes the output circuit 37A from the first state to the second state, the capacitor 39 and the piezoelectric element 15 release the charges. In the second state, this charge release flows as a current I2 into the vibration circuit 30A via the second switch 36. The current I2 is indicated by the dashed arrow in Figure 4. As shown in Figure 4, the current I2 flows from the piezoelectric element 15 to the reference potential 34 via the second switch. Also, negative charge accumulates on the output circuit 37A side and positive charge accumulates on the piezoelectric element 15 side in the capacitor 39. Therefore, a voltage is applied to the piezoelectric element 15 that lowers the potential on the excitation circuit 31A side.

[0063] In this way, the control circuit 32 can apply a voltage with reversed polarity at a predetermined frequency to the piezoelectric element 15 by switching the first switch 35 and the second switch 36. Therefore, the vibration circuit 30A according to this embodiment can reduce the possibility of ion migration occurring in the piezoelectric element 15.

[0064] When a drive signal (for example, a square wave voltage having a predetermined frequency) is applied to the piezoelectric element 15, the impedance of the piezoelectric element 15 changes depending on the frequency of the drive signal. For example, Figure 5 is a graph showing the relationship between the frequency of the drive signal applied to the piezoelectric element 15 and its impedance. As shown in Figure 5, the piezoelectric element 15 has multiple frequencies at which its impedance decreases locally. These frequencies correspond to the resonant frequencies of the vibrator 17. In the vibration device 10 according to this embodiment, the resonant frequencies are, for example, approximately 31 kHz (arrow A), approximately 110 kHz (arrow B), and approximately 550 kHz (arrow C). When a voltage (drive signal) with a frequency corresponding to any of these resonant frequencies is applied to the piezoelectric element 15, it vibrates the protective cover 11 in a different vibration mode for each frequency. For example, when a voltage with a frequency of approximately 31 kHz is applied, the piezoelectric element 15 vibrates the protective cover 11 via the vibrator 13 in a first removal mode, which is a vibration mode that vibrates the protective cover 11 as a whole. The first removal mode is a vibration mode that can atomize and remove foreign matter such as liquid droplets adhering to the protective cover 11. Furthermore, when a voltage with a frequency of approximately 110 kHz is applied, the piezoelectric element 15 vibrates the protective cover 11 via the vibrating body 13 in a second removal mode, which vibrates the center of the protective cover 11 more strongly than the periphery. The vibration in the second removal mode corresponds to the resonant frequency of the protective cover 11. Additionally, when a voltage with a frequency of approximately 550 kHz is applied, the piezoelectric element 15 vibrates the protective cover 11 via the vibrating body 13 in a de-icing mode, which is a vibration mode that easily raises the temperature of the protective cover 11. The vibration around approximately 550 kHz is a higher-order vibration mode with more nodes than the vibration at approximately 110 kHz, causing the protective cover 11 to vibrate. In the de-icing mode, because the impedance of the piezoelectric element 15 is low, a large amount of power is applied to the piezoelectric element 15, allowing the protective cover 11 to be heated rapidly. The above resonant frequencies are examples and can be changed depending on the shape and material of the vibration device 10. The piezoelectric element 15 may be configured to impart vibrations other than those described above to the protective cover 11.

[0065] The vibration device 10 according to this embodiment further has vibration modes in which the vibration acceleration of the protective cover 11 differs, in addition to vibration modes in which the frequency of the drive signal that vibrates the piezoelectric element 15 differs. The vibration modes include, for example, a strong vibration mode in which the amplitude of vibration of the protective cover 11 is large, and a weak vibration mode in which the amplitude of vibration of the protective cover 11 is smaller than that of the strong vibration mode, when the excitation device 31 vibrates the piezoelectric element 15 in the strong vibration mode, it can atomize and remove foreign matter such as liquid droplets attached to the protective cover 11, for example. When the excitation device 31 of the vibration device 10 vibrates the piezoelectric element 15 in the weak vibration mode, it can slide off foreign matter such as liquid droplets attached to the protective cover 11, for example. The strong vibration mode is also called the first vibration mode. The weak vibration mode is also called the second vibration mode. Thus, differences in vibration modes can arise from differences in the frequency of vibrations occurring in the protective cover 11 (i.e., differences in resonant frequencies), differences in the amplitude of vibrations occurring in the protective cover 11, or a combination of these.

[0066] As described above, when the excitation device 31 drives the piezoelectric element 15 in the first removal mode, the protective cover 11 vibrates vertically as a whole. Here, the vertical direction is the direction along the height direction of the vibration device 10. Therefore, the amplitude of vibration of the central part 11a of the protective cover 11, as viewed from the height direction of the vibration device 10 in Figure 1, is approximately the same as the amplitude of vibration of the peripheral part 11b of the protective cover 11. Hereafter, the central part 11a of the protective cover 11 will also be called the top part 11a of the protective cover 11. The peripheral part 11b of the protective cover 11 will also be called the end part 11b of the protective cover 11. The first removal mode includes the strong vibration mode and the weak vibration mode described above.

[0067] When removing foreign matter such as water droplets adhering to the protective cover 11 by atomization, it is preferable that the excitation device 31 vibrates the piezoelectric element 15 so that the protective cover 11 is displaced significantly, in order to increase the area on the protective cover 11 from which foreign matter can be removed. Furthermore, it is preferable that the excitation device 31 vibrates the piezoelectric element 15 so that the distribution of displacement of the protective cover 11 is small. The distribution of displacement of the protective cover 11 is given by equation V dist =a center / a edge It means a value that can be represented by V. dist This is the displacement distribution of the protective cover 11. Hereafter, the displacement distribution will also be called the vibration distribution. center This is the amplitude of vibration at the top 11a of the protective cover 11. edge V is the amplitude of vibration at the end 11b of the protective cover 11. When the displacement distribution is large, in the region of large displacement, the coating applied to the protective cover 11 is locally worn down by friction with foreign matter such as mud adhering to the protective cover 11 due to vibration. To prevent wear of the coating of the protective cover 11 due to vibration, it is preferable that the displacement is uniform between the top 11a and the end 11b, or that the displacement on the end 11b side is greater than that on the top 11a side. That is, the above V dist A small value is preferable. By vibrating the protective cover 11 in this way, wear on the top of the protective cover 11, which is important for imaging by the imaging device 20, can be reduced, while foreign matter attached to the protective cover 11 can be removed. Therefore, the excitation device 31 can effectively remove foreign matter attached to the protective cover 11 by using the first removal mode.

[0068] When defrosting the ice adhering to the protective cover 11, in order to suppress the wear of the coating of the protective cover 11 due to vibration, it is preferable that the excitation device 31 vibrates the piezoelectric element 15 so that the displacement amount of the protective cover 11 becomes small. Also, in order to secure the visual field of the imaging device 20, which is important for imaging by the imaging device 20, it is preferable that the excitation device 31 defrosts the top 11a of the protective cover 11 prior to the end 11b of the protective cover 11. The excitation device 31 can vibrate the protective cover 11 by driving the piezoelectric element 15 in the above-described defrosting mode so that the protective cover 11 generates heat and defrosts the ice adhering to the protective cover 11. In order to defrost more efficiently, in the defrosting mode, the excitation device 31 satisfies V dist_heat >V dist_st and a center_heat <a center_st and preferably drives the piezoelectric element 15 so as to satisfy. V dist_heat is the vibration distribution of the protective cover 11 in the defrosting mode. V dist_st is the vibration distribution of the protective cover 11 in the strong vibration mode. a center_heat is the vibration amplitude of the top 11a of the protective cover 11 in the defrosting mode. a center_st is the vibration amplitude of the top 11a of the protective cover 11 in the strong vibration mode. Similarly, in the defrosting mode, the excitation device 31 satisfies V dist_heat >V dist_we and preferably drives the piezoelectric element 15 so as to satisfy. V dist_we is weak the vibration distribution of the protective cover 11 in the vibration mode. The excitation device 31 can suppress the heat propagation to the vibration device 10 by controlling so that the top 11a of the protective cover 11 generates heat earlier than the end 11b of the protective cover 11 as described above. The defrosting mode is also called the first distribution mode. The strong vibration mode is also called the second distribution mode. The weak vibration mode is also called the third distribution mode.

[0069] Next, the relationship between the sliding angle and the adhesion energy will be described.

[0070] The sliding angle is the angle between the horizontal plane and the solid surface at which a liquid droplet begins to slide downward when the solid surface is gradually tilted from the horizontal. Figure 6 is a schematic diagram illustrating an example of the relationship between the sliding angle and the adhesion energy. The relationship shown in Figure 6 can be expressed by Wolfram's proposed formula for calculating adhesion energy (1).

[0071]

number

[0072] E represents the adhesion energy, r represents the contact radius, m represents the droplet mass, g represents the acceleration due to gravity, and θ represents the sliding angle. Equation (1) above is a value experimentally determined from the fact that the sliding angle θ between water and paraffin is proportional to the radius r of the contact surface between the droplet 50 and the solid 51. It is assumed that at the sliding angle θ, the component of gravity in the direction of the tilt of the droplet 50 and the adhesion force acting on the peripheral edge of the contact circle are in equilibrium. Furthermore, this index is considered to be an evaluation index that is uniquely determined by the combination of liquid and solid, and is not affected by experimental factors such as the liquid volume or tilt angle.

[0073] From the above equation (1), it can be seen that as the sliding angle θ decreases, the adhesion energy E decreases. In other words, as the sliding angle θ decreases, the droplet 50 becomes less likely to adhere to the solid surface.

[0074] The vibrating device 10 vibrates the protective cover 11 at a predetermined vibration acceleration, thereby reducing the sliding angle θ and decreasing the adhesion energy E that causes the droplets to remain on the surface of the protective cover 11. As a result, the vibrating device 10 can efficiently remove the droplets adhering to the protective cover 11.

[0075] Figure 7 is a schematic diagram showing an example of the relationship between the sliding angle and vibration acceleration. Figure 7 shows the change in the sliding angle corresponding to the change in vibration acceleration. The vibration acceleration was calculated using the method described below.

[0076] The vibration acceleration was calculated using a vibration device similar to the vibration device 10. The excitation device 31 swept the frequency of the drive signal using the search mode described later, and the frequency at which the detected signal value detected by the current detection circuit 38 was maximized was confirmed. The frequency corresponding to the first rejection mode was found to be approximately 60 kHz. A drive signal was supplied to the piezoelectric element 15, which resonates at a frequency of around 60 kHz, using a power supply (Keysight: E26104A) and a function generator (Tektronix: AGF1022) to generate vibration. The displacement of the protective cover 11, generated by the vibration of the piezoelectric element 15, was detected using a laser displacement meter (Olympus: BX51M) and measured using a multimeter (Keysight: 2110) and an oscilloscope (Tektronix: Oscilloscope TBS1104). Let α be the vibration acceleration, f be the frequency, and A be the amplitude (displacement), then α = (2πf). 2 The vibration acceleration was calculated using the following formula.

[0077] As shown in Figure 7, the vibration acceleration α is 1.5 × 10⁻⁶ 5 m / s 2 The above 8.0 x 10 5 m / s 2 The sliding angle θ becomes 40 degrees or less when the following conditions are met (see "A1" in Figure 7). When the sliding angle θ is 40 degrees or less, the adhesion energy E of the droplet becomes smaller than the force that causes it to slide off the surface of the protective cover 11 to the outside. As a result, droplets are less likely to remain on the protective cover 11 and flow out to the outside of the protective cover 11. This improves the removal performance of foreign matter such as droplets.

[0078] Furthermore, the vibration acceleration α is 3.5 × 10⁻⁶ 5 m / s 2 The above 5.5 x 10 5 m / s 2 When the following conditions are met, the sliding angle θ becomes 22 degrees or less (see "A2" in Figure 7). When the sliding angle θ becomes 22 degrees or less, the adhesion energy E of the droplet becomes even smaller. As a result, the droplet flows more easily to the outside of the protective cover 11, further improving the performance of removing foreign matter such as droplets.

[0079] The vibration acceleration is 1.5 × 10⁻⁶ 5m / s 2 When it is smaller, or 8.0 × 10 5 m / s 2 When it is greater than this, the sliding angle θ is greater than 40 degrees. When the sliding angle θ is greater than 40 degrees, the adhesion energy E of the droplet is greater than the force that causes it to slide off the surface of the protective cover 11 to the outside. Therefore, the vibration acceleration α is 3.5 × 10⁻⁶ 5 m / s 2 The above 5.5 x 10 5 m / s 2 The droplets are less likely to slide off compared to the following conditions.

[0080] Therefore, there is a preferred range for vibration acceleration α in the weak vibration mode. In the vibration device 10 according to this embodiment, the vibration acceleration α in the weak vibration mode is 1.5 × 10⁻⁶ 5 m / s 2 The above is 8.0 x 10 5 m / s 2 Preferably, the vibration acceleration α in the weak vibration mode is 3.5 × 10⁻⁶. 5 m / s 2 The above 5.5 x 10 5 m / s 2 The following applies: The excitation device 31 can improve the sliding ability of droplets adhering to the surface of the protective cover 11 compared to cases where the vibration acceleration α is in other ranges by controlling the drive signal so that the vibration acceleration α in the weak vibration mode is within the above range.

[0081] Next, we will describe the strong vibration mode in which the vibration acceleration of the protective cover 11 is greater than that of the weak vibration mode described above.

[0082] When the excitation device 31 vibrates the piezoelectric element 15 in strong vibration mode, the protective cover 11 vibrates with a larger vibration acceleration compared to when the piezoelectric element 15 is vibrated in weak vibration mode. As a result, foreign matter such as water droplets attached to the protective cover 11 is atomized and removed. The vibration acceleration in strong vibration mode may be a larger value than the vibration acceleration in weak vibration mode, but if it is too large, the load on the vibration device 10 itself will increase. Therefore, in the vibration device 10 according to this embodiment, the vibration acceleration α in strong vibration mode is 8.1 × 10⁻⁶. 5 m / s 2 The above 1.7 × 10 6 m / s 2 The following is preferable:

[0083] Thus, the excitation device 31 according to this embodiment can vibrate the protective cover 11 with a first vibration acceleration in the strong vibration mode, and can vibrate the protective cover 11 with a second vibration acceleration smaller than the first vibration acceleration in the weak vibration mode. As described above, the first vibration acceleration is, for example, 8.1 × 10⁻⁶ 5 m / s 2 The above 1.7 × 10 6 m / s 2 The following applies: The second vibration acceleration is, for example, 1.5 × 10⁻⁶. 5 m / s 2 The above is 8.0 x 10 5 m / s 2 The following is true: The second vibration acceleration is 3.5 × 10⁻⁶ 5 m / s 2 The above 5.5 x 10 5 m / s 2 The following is also acceptable.

[0084] As shown in Figure 5, when a voltage with a frequency corresponding to the resonant frequency is applied, the impedance of the piezoelectric element 15 is locally minimized. Therefore, the control circuit 32 can determine whether the frequency of the voltage applied to the piezoelectric element 15 is the resonant frequency by detecting the current value flowing through the piezoelectric element 15.

[0085] Figure 8 is a timing chart showing the signals input to or output from each element of the excitation circuit 31A (e.g., current value, voltage value). The horizontal axis of Figure 8 represents time. Figure 8 shows signals DT1, DT2, and current I R , input voltage V AD This shows that signal DT1 is an example of a signal used by the control circuit 32 to control the on / off state of the first switch 35. Signal DT2 is an example of a signal used by the control circuit 32 to control the on / off state of the second switch 36. The first switch 35 and the second switch 36 are turned on when signals DT1 and DT2 are at a high level (i.e., the first switch 35 electrically connects the DC power supply 33 to the piezoelectric element 15, and the second switch 36 electrically connects the piezoelectric element 15 to the reference potential 34). The first switch 35 and the second switch 36 are turned off when signals DT1 and DT2 are at a low level (i.e., the first switch 35 electrically disconnects the DC power supply 33 to the piezoelectric element 15, and the second switch 36 electrically disconnects the piezoelectric element 15 to the reference potential 34). Current I R This indicates the current flowing through the current-voltage conversion element 45. Current I R This corresponds to the voltage input to the low-pass filter 43 based on the current-voltage conversion circuit 42A. Input voltage V AD This represents the smoothed voltage input from the low-pass filter 43 to the AD conversion circuit 44. As shown in Figure 8, in this embodiment, V AD This is a signal that has a DC component.

[0086] In Figure 8, current I R Multiple waveforms are shown. The current I is shown by the solid line. R This is an example of the waveform of the current flowing through the current-voltage conversion element 45 when the switching frequencies of the first switch 35 and the second switch 36 correspond to the resonant frequency of the oscillator 17 (i.e., at resonance). The dashed line shows the current I RThis is an example of the waveform of the current flowing through the current-voltage conversion element 45 when the switching frequencies of the first switch 35 and the second switch 36 do not correspond to the resonant frequency of the oscillator 17 (i.e., non-resonant). As is clear from Figure 8, the current during resonance is larger than the current during non-resonant.

[0087] Similarly, in Figure 8, the input voltage V AD Multiple waveforms are shown. The input voltage V is shown by the solid line. AD This is an example of the waveform of the voltage output from the low-pass filter 43 and input to the AD conversion circuit 44 during resonance. The input voltage V is shown by the dashed line. AD This is an example of the waveform of the voltage output from the low-pass filter 43 and input to the AD conversion circuit 44 during non-resonant conditions. As is clear from Figure 8, the input voltage during resonance is greater than the input voltage during non-resonant conditions.

[0088] Thus, the signal (voltage) input to the AD conversion circuit 44 is larger during resonance than during non-resonance. Therefore, the detection signal input from the AD conversion circuit 44 to the control circuit 32 is similarly larger during resonance than during non-resonance. As a result, the control circuit 32 can determine, based on the detection signal input from the AD conversion circuit 44, whether the switching frequency of the first switch 35 and the second switch 36, that is, the frequency of the drive signal input to the piezoelectric element 15, is the resonant frequency. For example, the control circuit 32 acquires the value of the detection signal input from the AD conversion circuit 44 at two or more switching frequencies when each switch 35 and 36 is operated at a specific switching frequency. The control circuit 32 then compares the values ​​of the detection signals at different switching frequencies and determines that the switching frequency corresponding to the detection signal with the larger value is closer to the resonant frequency. Therefore, the control circuit 32 can determine the switching frequency that is closest to the resonant frequency within the predetermined frequency range by switching each switch 35 and 36 at multiple switching frequencies within a predetermined frequency range and comparing the values ​​of multiple detection signals corresponding to multiple switching frequencies.

[0089] Note that the periods of signals DT1 and DT2 differ between resonant and non-resonant states, but for simplicity, Figure 8 shows the signal waveforms with matching widths even though the periods are different. Therefore, current I R The duration for which this current flows actually differs between resonant and non-resonant states.

[0090] In this way, the control circuit 32 can acquire the current flowing through the current-voltage conversion element 45 of the current-voltage conversion circuit 42A as a DC component based on the switching process. Therefore, unlike when detecting the current flowing through the piezoelectric element 15, the control circuit 32 does not need to set the sampling frequency for current detection to be sufficiently higher than the resonant frequency of the oscillator 17, thus reducing the cost of the current-voltage conversion circuit 42A. Furthermore, by detecting the current, the control circuit 32 can calculate the impedance of the piezoelectric element 15 and determine the resonant frequency of the oscillator 17.

[0091] As described above, the control circuit 32 can determine the resonant frequency of the oscillator 17 based on the value of the detection signal input from the current detection circuit 38A by controlling the switching frequency and changing the frequency of the voltage applied to the piezoelectric element 15. For example, the control circuit 32 can determine the resonant frequency of the oscillator 17 using multiple methods. The excitation circuit 31A according to this embodiment has three sweep methods: a first sweep method, a second sweep method, and a third sweep method (details of each will be described later). The first sweep method, the second sweep method, and the third sweep method differ in the method of changing the switching frequency for determining the resonant frequency of the oscillator 17. The control circuit 32 has multiple sequences that are executed in each of the first to third sweep methods. In this embodiment, the multiple sequences include a search mode and a drive mode.

[0092] In search mode, the control circuit 32 changes the switching frequency within a predetermined frequency range (hereinafter referred to as the "search frequency range") to determine the resonant frequency. Hereinafter, the change in the switching frequency by a predetermined increase (or decrease) within an arbitrary frequency range by the control circuit 32 to determine the resonant frequency is also referred to as "sweeping". As described above, the control circuit 32 can determine the switching frequency at which the value of the detection signal output from the AD conversion circuit 44 is the largest as the resonant frequency. Therefore, if the resonant frequency is included within the search frequency range, the control circuit 32 can determine the resonant frequency. If the value of the detection signal output from the AD conversion circuit 44 is the largest at the upper limit frequency of the search frequency range, that switching frequency may not be the resonant frequency. Therefore, in such a case, the control circuit 32 may change the search frequency range to include a higher frequency, change the switching frequency within that range, and determine the resonant frequency again. Similarly, if the value of the detection signal output from the AD conversion circuit 44 is the largest at the lower limit frequency of the search frequency range, the control circuit 32 may change the search frequency range to include a lower frequency and determine the resonant frequency again. If the control circuit 32 determines that there are multiple switching frequencies at which the value of the output detection signal is locally largest, it may perform the sweep again.

[0093] When the control circuit 32 determines the resonant frequency using the search mode, it can vibrate the protective cover 11 in a predetermined vibration mode corresponding to that frequency (for example, the first removal mode, the second removal mode, or the de-icing mode) by switching at that frequency. However, the resonant frequency can fluctuate due to various factors. For example, the resonant frequency may fluctuate depending on the temperature change of the protective cover 11. Also, the resonant frequency may fluctuate if foreign matter adheres to the protective cover 11. Therefore, the excitation circuit 31A according to this embodiment is configured in drive mode to respond to such frequency changes.

[0094] In drive mode, the control circuit 32 changes the switching frequency within a predetermined frequency range (hereinafter referred to as the "drive frequency range") that is narrower than the search frequency range, and determines the resonant frequency. When transitioning from search mode to drive mode, the control circuit 32 sets the drive frequency range so that the resonant frequency determined in search mode is at the center, and changes the switching frequency within the drive frequency range. The control circuit 32 sweeps the switching frequency within the drive frequency range, determines the switching frequency with the largest value of the detection signal output from the AD conversion circuit 44, and determines the determined switching frequency to be the current resonant frequency of the oscillator 17. Once the current resonant frequency of the oscillator 17 is determined, the control circuit 32 changes the frequency set at the center of the drive frequency range to the current resonant frequency and updates the drive frequency range. The control circuit 32 sweeps the switching frequency again within the updated drive frequency range and repeats the above update of the drive frequency range. By operating in this drive mode, the control circuit 32 can make the switching frequency follow the resonant frequency even if there is a change in the resonant frequency of the oscillator 17.

[0095] When vibrating the piezoelectric element 15, the resonant frequency of the oscillator 17 may not coincide when the frequency is changed from low frequency to high frequency and when it is changed from high frequency to low frequency. Therefore, the control circuit 32 of the excitation circuit 31A according to this embodiment is configured to sweep the switching frequency in multiple ways when determining the resonant frequency using search mode or drive mode. In this embodiment, as described above, the control circuit 32 has a first sweep method, a second sweep method and a third sweep method. In the first sweep method, the control circuit 32 changes the switching frequency from low frequency to high frequency (hereinafter also referred to as "up sweep"). In the second sweep method, the control circuit 32 changes the switching frequency from low frequency to high frequency, and further changes it from high frequency to low frequency (hereinafter also referred to as "up and down sweep"). In the third sweep method, the control circuit 32 changes the switching frequency from the high-frequency side to the low-frequency side (hereinafter also referred to as "downward sweep").

[0096] The excitation circuit 31A according to this embodiment is configured to operate the protective cover 11 in a predetermined vibration mode by matching the switching frequencies of the first switch 35 and the second switch 36 with the resonant frequency of the oscillator 17. In this regard, even when the first switch 35 and the second switch 36 are operated at a switching frequency that has a predetermined ratio with respect to the resonant frequency, the impedance is locally minimized. Here, the frequency that has a predetermined ratio is a frequency that is 1 / (2n+1) times the resonant frequency (where n is a positive integer).

[0097] Figure 9A is a graph showing the time variation of a drive signal (voltage) with a frequency of 31.5 kHz, which is near one of the resonant frequencies, applied to the piezoelectric element 15, and the time variation of the displacement of the protective cover 11 when the piezoelectric element 15 is driven at that frequency. In Figure 9A, waveform S1 shows the time variation of the drive signal, and waveform D1 shows the time variation of the displacement. The displacement of the protective cover 11 is obtained, for example, by measuring the displacement of the protective cover 11 using a laser Doppler meter, and waveform D1 in Figure 9A shows the time variation of the voltage value obtained by converting the measured displacement into a voltage. In the graph shown in Figure 9A, the horizontal axis is time, and the vertical axis is voltage.

[0098] Figure 9B is a graph showing the time variation of a drive signal with a frequency of 10.5 kHz, which is one-third the frequency of 31.5 kHz, applied to the piezoelectric element 15, and the time variation of the displacement of the protective cover 11 when the piezoelectric element 15 is driven at that frequency. In Figure 9B, waveform S2 shows the time variation of the drive signal, and waveform D2 shows the time variation of the displacement. In the graph shown in Figure 9B, the horizontal axis is time, and the vertical axis is voltage.

[0099] As can be seen from Figures 9A and 9B, even if the frequency of the drive signal is 1 / 3 of the resonant frequency, the displacement frequency of the protective cover 11 (i.e., the vibration frequency of the protective cover 11) is equivalent to the resonant frequency. Also, as can be seen from Figures 9A and 9B, the maximum displacement amount when the piezoelectric element 15 is driven at a frequency of 1 / 3 of the resonant frequency is approximately 1 / 3 of the maximum displacement amount when the piezoelectric element 15 is driven at the resonant frequency. The above relationship holds when the frequency of the drive signal is 1 / (2n+1) times the resonant frequency (where n is a positive integer). That is, when the frequency of the drive signal is 1 / (2n+1) times the resonant frequency, the maximum displacement amount of the protective cover 11 is approximately 1 / (2n+1) times the maximum displacement amount when the piezoelectric element 15 is driven at the resonant frequency. By utilizing this change in displacement amount based on the difference in the frequency of the drive signal, the vibration device 10 according to this embodiment can obtain various effects.

[0100] For example, when the excitation device 31 applies a drive signal having a voltage of 60Vp-p and a frequency of 60kHz to the piezoelectric element 15, the vibration acceleration of the protective cover 11 is 1.5 × 10⁻⁶. 6 m / s 2 Let us explain using a vibration device as an example. In the case of this vibration device, when the excitation device 31 applies a drive signal having a voltage of 60Vp-p and a frequency of 20kHz to the piezoelectric element 15, the protective cover 11 vibrates 0.5 × 10 6 m / s 2 It vibrates with a vibration acceleration of . In this way, the excitation device 31 can change the vibration acceleration of the protective cover 11 without changing the voltage by controlling the frequency of the drive signal applied to the piezoelectric element. As a result, the excitation device 31 can control the amplitude of the vibration of the protective cover 11 without requiring a complex configuration or complex control.

[0101] For example, in search mode, the control circuit 32 sweeps the switching frequency within a search frequency range that includes a frequency equivalent to 1 / 3 of the resonant frequency, and can determine the frequency corresponding to the resonant frequency. The control circuit 32 determines that the frequency three times the switching frequency determined to correspond to the resonant frequency is the resonant frequency, and executes the drive mode by setting the drive frequency range so that this three times frequency is the center. As a result, the control circuit 32 can reduce the power consumption required during this determination while suppressing the temperature rise of the piezoelectric element 15. In addition, by lowering the current value, the control circuit 32 can suppress vibrations that occur when executing the search mode, and can suppress fluctuations in the resonant frequency due to changes in the state of foreign matter etc. caused by these vibrations.

[0102] The relationship described above also holds between the resonant frequency and its 2n+1 times frequency (where n is a positive integer). For example, when the control circuit 32 applies a drive signal having a frequency three times the resonant frequency to the piezoelectric element 15, the time change in the displacement of the protective cover 11 will have a frequency corresponding to the resonant frequency, similar to the case in Figure 9A. Furthermore, the maximum value of the displacement of the protective cover 11 will be approximately 1 / 3 of the maximum value of the displacement when a drive signal having the resonant frequency is applied. Therefore, in order to suppress the temperature rise of the piezoelectric element 15, the control circuit 32 may set the switching frequency for switching the first switch 35 and the second switch 36 on and off to (2n+1) times the resonant frequency and operate accordingly.

[0103] The control circuit 32 determines whether or not foreign matter has adhered to the protective cover 11 by combining changes in the resonant frequency and changes in impedance. The resonant frequency of the vibrator 17 decreases as the temperature increases. Similarly, the minimum impedance (local minimum value of impedance) of the piezoelectric element 15 decreases as the temperature increases. In contrast, if foreign matter (e.g., water) adheres to the protective cover 11, the resonant frequency of the vibrator 17 decreases as the amount of water adhering increases. Also, the rate of change of the minimum impedance of the piezoelectric element 15 increases as the amount of water adhering increases. In this way, the control circuit 32 can determine whether or not foreign matter has adhered to the protective cover 11 by referring to changes in temperature and changes in minimum impedance. Note that changes in temperature can be obtained, for example, by a temperature sensor that may be provided on the vibration device 10. The control circuit 32 may, until foreign matter adheres to it, drive the piezoelectric element 15 in search mode at a frequency of 1 / (2n+1) times the resonant frequency (where n is a positive integer), and then switch to drive mode to drive the piezoelectric element 15 at the resonant frequency once it determines that foreign matter has adhered. By driving the piezoelectric element 15 in this way, the control circuit 32 can reduce the power consumption of the vibration device 10.

[0104] Figure 10A shows an example of control using the first sweep method of the control circuit 32 for determining the resonant frequency. Figure 10B shows an example of control using the second sweep method of the control circuit 32 for determining the resonant frequency. Figure 10C shows an example of control using the third sweep method of the control circuit 32 for determining the resonant frequency.

[0105] Figure 10A shows an example of the processing of the search mode and drive mode by the control circuit 32 using the first sweep method. In this embodiment, the control circuit 32 sets the search frequency range to include a frequency approximately 1 / 3 times the resonant frequency and executes the search mode. In Figure 10A, the search frequency range is indicated by fsearch1. The control circuit 32 sweeps the switching frequency upward until the frequency fr is reached within the search frequency range where the current is maximum. u When this is determined, the frequency fr u Multiply the value by 3, fdrive u The following is calculated. As shown in Figure 10A, the control circuit 32 performs a sweep during the period tsearch1.

[0106] The control circuit 32 calculates the fdrive u The drive frequency range is set so that it is centered at fdrive1, and the drive mode is executed. In Figure 10A, the drive frequency range is indicated by fdrive1. The control circuit 32 sweeps the switching frequency upward within the drive frequency range, determines the frequency at which the current value is maximum, and executes fdrive uThe frequency is updated to the specified frequency. As shown in Figure 10A, the control circuit 32 performs a sweep of the drive frequency range during the period tsweep1. Then, each time the control circuit 32 performs a sweep, it updates the drive frequency range and performs another sweep in the updated drive frequency range during the period tsweep1. The period tdrive1 indicates the period during which the piezoelectric element 15 is driven in drive mode. By operating in this manner, the control circuit 32 can vibrate the protective cover 11 at a more accurate frequency while following the fluctuating resonant frequency. The control circuit 32 may, after driving the piezoelectric element 15 in drive mode for a predetermined period, such as the period tdrive1, switch back to driving the piezoelectric element 15 in search mode. Alternatively, the control circuit 32 may switch from driving in drive mode to driving in search mode when it determines that the adhesion of foreign matter has been removed, for example, based on changes in temperature and impedance. The control circuit 32 may also stop driving the piezoelectric element instead of switching from drive mode to search mode. The same applies to the second and third sweep methods described later.

[0107] Figure 10B shows an example of the processing of the search mode and drive mode by the control circuit 32 using the second sweep method. In this embodiment, the control circuit 32 sets the search frequency range to include the frequency corresponding to the resonant frequency and executes the search mode. In Figure 10B, the search frequency range is indicated by fsearch2. The control circuit 32 sweeps the switching frequency upward until the frequency fr is reached within the search frequency range where the current is maximum. u When this is determined, the frequency fr u Based on fdrive u The control circuit 32 determines the fdrive. u The drive frequency range is set in the upward direction so that it is centered at this frequency. The control circuit 32 also sweeps the switching frequency downward to find the frequency fr at which the current is maximum within the search frequency range. d When this is determined, the frequency fr d Based on fdrive dis determined. The control circuit 32 sets the drive frequency range in the down direction so that the determined fdrive d is centered. As shown in FIG. 10B, the control circuit 32 executes an up sweep and a down sweep each within a period tsearch2. Note that the up sweep period tsearch2 and the down sweep period tsearch2 may be the same length or different lengths.

[0108] When the control circuit 32 sets the drive frequency ranges in the up and down directions, it executes the drive mode. The control circuit 32 sweeps the switching frequency within each drive frequency range for each of the up and down directions, determines the frequency at which the current value becomes maximum, and updates fdrive u and fdrive d to each frequency. As shown in FIG. 10B, the control circuit 32 executes an up sweep and a down sweep of the drive frequency range each within a period tsweep2. And each time the control circuit 32 executes an up sweep or a down sweep, it updates each drive frequency range and executes a sweep again within the updated drive frequency range for a period tsweep2. The period tdrive2 indicates the period during which the piezoelectric element 15 is driven in the drive mode. By operating in this way, the control circuit 32 can vibrate the protective cover 11 at a more accurate frequency while following the varying resonance frequency for each of the up sweep and the down sweep.

[0109] FIG. 10C shows an example of the processing of the search mode and the drive mode by the control circuit 32 using the third sweep method. In this embodiment, the control circuit 32 sets a search frequency range so as to include the frequency corresponding to the resonance frequency and executes the search mode. In FIG. 10C, the search frequency range is indicated by fsearch3. The control circuit 32 sweeps the switching frequency in the down direction and determines the frequency fr d at which the current is maximum within the search frequency range. When it determines the frequency fr dBased on this, determine fdrive d As shown in FIG. 10C, the control circuit 32 executes a sweep during the period tsearch3.

[0110] The control circuit 32 sets the drive frequency range centered on the determined fdrive d and executes the drive mode. In FIG. 10C, the drive frequency range is indicated by fdrive3. The control circuit 32 sweeps the switching frequency downward within the drive frequency range, determines the frequency at which the current value becomes maximum, and updates fdrive d to this frequency. As shown in FIG. 10C, the control circuit 32 executes a sweep of the drive frequency range during the period tsweep3. Then, each time the control circuit 32 executes a sweep, it updates the drive frequency range and again executes a sweep within the updated drive frequency range during the period tsweep3. The period tdrive3 indicates the period during which the piezoelectric element 15 is driven in the drive mode. By operating in this manner, the control circuit 32 can vibrate the protective cover 11 at a more accurate frequency while following the varying resonance frequency.

[0111] The control circuit 32 can, for example, use the first sweep method described above in the first removal mode. The control circuit 32 can also use the second sweep method described above in the second removal mode. Furthermore, the control circuit 32 can use the third sweep method described above in the de-icing mode. The sweep methods used in each vibration mode are not limited to those described above, and the control circuit 32 may vibrate the piezoelectric element 15 in any combination. In the first sweep method described above, the control circuit 32 drives the piezoelectric element 15 using a frequency of 1 / 3 of the resonant frequency in the search mode and the resonant frequency in the drive mode, but is not limited to this. Furthermore, in the second and third sweep methods described above, the control circuit 32 drives the piezoelectric element 15 using the resonant frequency in the search mode and the drive mode, but is not limited to this. For example, the control circuit 32 may drive the piezoelectric element 15 using the resonant frequency in the search mode and the drive mode in at least one of the first to third sweep methods. Furthermore, the control circuit 32 may drive the piezoelectric element 15 in the search mode using a frequency 1 / (2n+1) times the resonant frequency and in the drive mode using the resonant frequency in at least one of the first to third sweep methods.

[0112] As described above, the control circuit 32 can drive the piezoelectric element 15 using a search mode and a drive mode in multiple vibration modes. The control circuit 32 may change the range of at least one of the search frequency range or the drive frequency range depending on the vibration mode. For example, the control circuit 32 may control the drive frequency range in the de-icing mode to be different from the drive frequency range in the strong vibration mode. Hereinafter, the drive frequency range in the de-icing mode will also be called the first frequency range. The vibration mode in which the drive mode is performed in the first frequency range will also be called the first sweep mode. The drive frequency range in the strong vibration mode will also be called the second frequency range. The vibration mode in which the drive mode is performed in the second frequency range will also be called the second sweep mode.

[0113] Specifically, for example, if the de-icing mode is performed using the third sweep method and the strong vibration mode is performed using the first sweep method, the control circuit 32 may control the first frequency range and the second frequency range so that (HW1 / SR1) > (HW2 / SR2). Here, HW1 is the full width at half maximum of the peak at the resonant frequency in the displacement of the protective cover 11 when swept within the first frequency range. SR1 is the width of the first frequency range. HW2 is the full width at half maximum of the peak at the resonant frequency in the displacement of the protective cover 11 when swept within the second frequency range. That is, HW2 is the full width at half maximum of the peak at the resonant frequency within the second frequency range. SR2 is the width of the second frequency range.

[0114] For example, in the de-icing mode, if the resonant frequency is 500 kHz, the control circuit 32 can be controlled to sweep within a range of ±1 kHz of the resonant frequency. In this case, as an example, HW1 = 1000 and SR1 = 2000. Also, in the strong oscillation mode, if the resonant frequency is 25 kHz, the control circuit 32 can be controlled to sweep within a range of ±0.5 kHz of the resonant frequency. In this case, as an example, HW2 = 100 and SR2 = 1000. When the control circuit 32 controls the first frequency range and the second frequency range in this way, the above condition (HW1 / SR1) > (HW2 / SR2) is satisfied.

[0115] Naturally, the relationship between HW1 and SR1 and HW2 and SR2 described above is not limited to the case where the third sweep method is performed in de-icing mode and the first sweep method is performed in strong vibration mode. The control circuit 32 may also control the frequency range in the relationship between HW1 and SR1 and HW2 and SR2 when performing the de-icing mode and strong vibration mode with other sweep methods. By controlling in this way, the excitation device 31 can increase the ratio of the time spent driving the piezoelectric element at a frequency based on the resonant frequency to the time spent performing the frequency sweep in de-icing mode compared to the case of strong vibration mode, taking into account the sharpness of the resonance (so-called Q value). Therefore, the excitation device 31 can improve its contribution to the temperature rise of the protective cover 11 when the de-icing mode is performed in drive mode compared to the case of strong vibration mode. As a result, the excitation device 31 can raise the temperature of the protective cover 11 more quickly.

[0116] Figure 11 is a graph showing the impedance of the piezoelectric element 15 with respect to the switching frequency near a certain resonant frequency, and the phase difference between the voltage applied to the piezoelectric element 15 and the current flowing through the piezoelectric element 15. As shown in Figure 11, when the switching frequency changes near the resonant frequency, the impedance changes. As described above, the frequency at which the impedance is locally minimum corresponds to the resonant frequency. Also, as shown in Figure 11, when the switching frequency changes near the resonant frequency, the phase difference between the voltage applied to the piezoelectric element 15 and the current flowing through the piezoelectric element changes. When the control circuit 32 switches the first switch 35 and the second switch 36 at the resonant frequency, this phase difference becomes zero. Therefore, by configuring the excitation circuit 31A to detect this phase difference, the switching frequency corresponding to the resonant frequency can be determined more accurately.

[0117] Figure 12 shows a modified example of the excitation circuit 31A according to this embodiment. Figure 12 shows a vibration circuit 30B. The vibration circuit 30B comprises the excitation circuit 31B and a piezoelectric element 15. The excitation circuit 31B further includes a phase comparator 46 compared to the excitation circuit 31A. The excitation circuit 31B is configured so that the phase comparator 46 can compare the phase difference between the voltage applied to the piezoelectric element 15 and the current flowing through the piezoelectric element, as described above.

[0118] The phase comparator 46 is, for example, a multiplier. The phase comparator 46 can detect the voltage based on the current flowing through the current-voltage conversion element 45. The phase of the current used by the phase comparator 46 is the current flowing through the current-voltage conversion element 45 when the second switch 36 is ON. The control circuit 32 can also output control signals to the phase comparator 46 when switching the first switch 35 and the second switch 36. Therefore, the phase comparator 46 can compare the phase of the voltage applied to the piezoelectric element 15 with the phase of the current flowing through the piezoelectric element based on the phase of the control signals. The phase comparator 46 may be configured to, for example, compare the phase of the control signal for driving the second switch 36 with the phase of the voltage based on the current flowing through the current-voltage conversion element 45, and output a predetermined signal (e.g., voltage) to the control circuit 32 if there is a difference in phase. The phase comparator 46 may output a voltage with a positive value to the control circuit 32 if the phase of the control signal leads the phase of the voltage based on the current flowing through the current-voltage conversion element 45, and a voltage with a negative value if it lags behind. With this configuration, the control circuit 32 can detect whether or not there is a phase difference between the current and voltage in the piezoelectric element 15 based on the signal output from the phase comparator 46. The control circuit 32 can also detect whether the phase of the current leads or lags the phase of the voltage. As can be seen from Figure 12, when the switching frequency is near the resonant frequency, the phase lead or lag between the voltage applied to the piezoelectric element 15 and the current flowing through the piezoelectric element 15 is determined by whether the switching frequency is higher or lower than the resonant frequency. Therefore, the control circuit 32 can determine, based on the phase difference, whether the switching frequency needs to be changed to the high-frequency side or the low-frequency side in order to match the switching frequency to the resonant frequency. By controlling the switching frequency based on the phase difference detected by the phase comparator 46, the control circuit 32 can more appropriately match the switching frequency to the resonant frequency of the oscillator 17. Conversely, the phase comparator 46 may output a voltage with a negative value to the control circuit 32 if the phase of the control signal leads the phase of the voltage based on the current flowing through the current-voltage conversion element 45, and a voltage with a positive value if the phase of the control signal lags behind.

[0119] Figure 13 shows the displacement of the protective cover 11 vibrated by the piezoelectric element 15 when the piezoelectric element 15 is driven by a drive signal having a resonant frequency in the strong vibration mode and a drive signal having a frequency 1 / (2n+1) times the resonant frequency. In the graph shown in Figure 13, the horizontal axis is the frequency of the drive signal and the vertical axis is the maximum displacement (μm) of the protective cover 11 for each drive signal. In Figure 13, the drive signal having a resonant frequency is shown as the fundamental wave. Drive signals having frequencies 1 / 3 (n=1), 1 / 5 (n=2), and 1 / 7 (n=3) times the resonant frequency are shown as the 1 / 3 harmonic, 1 / 5 harmonic, and 1 / 7 harmonic, respectively. Hereafter, the drive signal having a resonant frequency will also be called the fundamental wave. Also, the drive signal having a frequency 1 / (2n+1) times the resonant frequency will also be called the 1 / (2n+1) harmonic. Furthermore, a drive signal having a frequency that is (2n+1) times the resonant frequency is also called a (2n+1)th harmonic. As is clear from Figure 13, when the excitation device 31 drives the piezoelectric element 15 with a drive signal having the 1 / 3 harmonic, the maximum displacement of the protective cover 11 vibrated by the piezoelectric element 15 is approximately 1 / 3 of the maximum displacement when driven with a drive signal having the resonant frequency. Specifically, in the example shown in Figure 13, when the excitation device 31 drives the piezoelectric element 15 with a drive signal having the fundamental frequency, the maximum displacement of the protective cover 11 was approximately 26 μm. Also, when the excitation device 31 drives the piezoelectric element 15 with a drive signal having the 1 / 3 harmonic, the maximum displacement of the protective cover 11 was approximately 8 μm. Similarly, when the excitation device 31 drives the piezoelectric element 15 with a drive signal having the 1 / 5 harmonic or 1 / 7 harmonic, the maximum displacement of the protective cover 11 is approximately 1 / 5 or 1 / 7 of the maximum displacement when driven with a drive signal having the resonant frequency. Specifically, when the excitation device 31 drove the piezoelectric element 15 with drive signals having 1 / 5th and 1 / 7th harmonics, the maximum displacement of the protective cover 11 was approximately 5 μm and approximately 4 μm, respectively.

[0120] In this way, the displacement of the protective cover 11 can be changed by controlling the frequency of the drive signal used by the excitation device 31 to drive the piezoelectric element 15. When the excitation device 31 determines the resonant frequency by sweeping the frequency of the drive signal as in the search mode described above, if it is performed in strong vibration mode, it is not necessary to perform it in weak vibration mode, thus simplifying the control. The excitation device 31 can determine the resonant frequency in strong vibration mode and the resonant frequency in weak vibration mode without changing the voltage.

[0121] Furthermore, when the excitation device 31 determines the resonant frequency by sweeping the frequency of the drive signal, it may perform the sweep using a drive signal having a frequency 1 / (2n+1) times that of the drive signal, where n is a positive integer. The excitation device 31 may also drive the piezoelectric element 15 with a drive signal having a frequency obtained by multiplying the frequency at which the detection signal output by the current detection circuit 38 reaches its maximum by (2n+1). By controlling in this way, the amount of vibration of the protective cover 11 can be reduced in search mode, and the impact of vibration of the protective cover 11 on the optical characteristics or reliability can be reduced.

[0122] In the above example, the excitation device 31 drives the piezoelectric element 15 at a frequency 1 / (2n+1) times the resonant frequency to determine the resonant frequency, and then drives the piezoelectric element 15 at the resonant frequency, but is not limited to this. For example, the excitation device 31 may drive the piezoelectric element 15 at a frequency 1 / (2n+1) times the resonant frequency. search The piezoelectric element 15 is driven at a frequency of +1) times the resonant frequency to determine the resonant frequency, and then 1 / (2n a The piezoelectric element 15 may be driven at a frequency of +1) times the frequency. Here, n a n is a non-negative integer, and search is, n a It is a larger integer.

[0123] In the above example, the excitation device 31 drives the piezoelectric element 15 using a drive signal having the resonant frequency and a frequency of 1 / (2n+1) times the resonant frequency, but is not limited to this. For example, if the excitation device 31 drives the piezoelectric element 15 with a drive signal having a frequency of (2n+1) times the resonant frequency, the maximum displacement of the protective cover 11 is approximately 1 / (2n+1) times the maximum displacement when driven with a drive signal having the resonant frequency, as in the above example. Therefore, the excitation device 31 may drive the piezoelectric element 15 using a drive signal having the resonant frequency and a frequency of (2n+1) times the resonant frequency.

[0124] As in the example above, the waveform of the drive signal used by the excitation device 31 to drive the piezoelectric element 15 is preferably a square wave, but is not limited to a square wave. For example, the excitation device 31 may use a sine wave, triangular wave, or sawtooth wave as the drive signal, having a frequency of the resonant frequency and a frequency of 1 / (2n+1) times or (2n+1) times the resonant frequency.

[0125] Figure 14 is a schematic diagram of a modified example of the vibration circuit 30 according to this embodiment. As shown in Figure 14, the vibration circuit 30C has, in addition to the excitation device 31 and the piezoelectric element 15, a switch 60 and a resistor 61 arranged in parallel between the piezoelectric element 15 and the reference potential 34.

[0126] Switch 60 can be controlled on / off by the control circuit 32. As is clear from Figure 14, when switch 60 is on, the piezoelectric element 15 is connected to the reference potential 34. When switch 60 is off, the piezoelectric element 15 is connected to the reference potential 34 via the resistor 61. Therefore, when switch 60 is off, the impedance when the excitation device 31 drives the piezoelectric element 15 increases, and the amount of displacement of the protective cover 11 decreases compared to when switch 60 is on. Thus, the excitation device 31 can further control the amplitude of the protective cover 11 in detail by combining the configuration of this modified example with a method of driving the piezoelectric element 15 with a drive signal having a frequency of 1 / (2n+1) times the resonant frequency described above.

[0127] Figure 15A is a graph showing the time variation of a drive signal (voltage) applied to the piezoelectric element 15, having a frequency of approximately 557 kHz, which is near one of the resonant frequencies, and the time variation of the displacement of the protective cover 11 when the piezoelectric element 15 is driven at that frequency. In Figure 15A, waveform S3 shows the time variation of the drive signal, and waveform D4 shows the time variation of the displacement of the protective cover 11. In the graph shown in Figure 15A, the horizontal axis is time, and the vertical axis is voltage.

[0128] Figure 15B is a graph showing the time variation of a drive signal with a frequency of approximately 190 kHz, which is about 1 / 3 the frequency of 557 kHz, applied to the piezoelectric element 15, and the time variation of the displacement of the protective cover 11 when the piezoelectric element 15 is driven at that frequency. In Figure 15B, waveform S4 shows the time variation of the drive signal, and waveform D4 shows the time variation of the displacement of the protective cover 11. In the graph shown in Figure 15B, the horizontal axis is time, and the vertical axis is voltage.

[0129] As described above, in a drive signal having a resonant frequency of approximately 557 kHz, the excitation device 31 vibrates the piezoelectric element 15 in defrosting mode. As can be seen from Figures 15A and 15B, the period T of waveform D4 D4 The period T of waveform D3 is D3 It is equivalent to the above. Also, the amplitude A of waveform D4 D4 This is the amplitude A of waveform D3. D3This is approximately 1 / 3 of the original value. Thus, in the de-icing mode, when the excitation device 31 drives the piezoelectric element 15 with a drive signal having a frequency of approximately 1 / 3 of the resonant frequency, it can vibrate the protective cover 11 with a displacement amount approximately 1 / 3 of the displacement amount when driven with a drive signal having the resonant frequency. An example of the power consumption when the excitation device 31 drives the piezoelectric element 15 with a drive signal of approximately 557 kHz was approximately 15 W. Another example of the power consumption when the excitation device 31 drives the piezoelectric element 15 with a drive signal of approximately 190 kHz was approximately 5 W. Therefore, in the de-icing mode as well, similar to the case where the piezoelectric element 15 is vibrated with the 31.5 kHz drive signal described above, the displacement amount of the protective cover 11 can be reduced, and power consumption can be reduced. In this way, in the de-icing mode, the excitation device 31 can reduce power consumption by driving the piezoelectric element 15 with a drive signal having a frequency of 1 / (2n+1) times the resonant frequency, thus eliminating the need for the excitation device 31 to use materials that can withstand high power. Therefore, the user of the excitation device 31 can reduce the cost of the excitation device 31.

[0130] Figure 16 is a graph showing an example of the temperature rise characteristics of the protective cover 11 when the excitation device 31 vibrates the piezoelectric element 15. In the graph shown in Figure 16, the horizontal axis is time t (s), and the vertical axis is the temperature rise ΔT (°C). In Figure 16, the circles indicate the temperature of the protective cover 11 when the piezoelectric element 15 is driven with a drive signal at a resonant frequency of approximately 550 kHz (i.e., the fundamental wave). The triangles indicate the temperature of the protective cover 11 when the piezoelectric element 15 is driven with a drive signal at 1 / 3 the frequency of the fundamental wave (i.e., the 1 / 3 harmonic). As can be seen from Figure 16, the temperature rise of the protective cover 11 when the piezoelectric element 15 is driven with the 1 / 3 harmonic is clearly lower than the temperature rise when the piezoelectric element 15 is driven with the fundamental wave. For example, when the piezoelectric element 15 is driven with the fundamental wave for 20 seconds, the temperature rise of the protective cover 11 is approximately 75°C. When the piezoelectric element 15 is driven at 1 / 3 harmonic for 20 seconds, the temperature of the protective cover 11 rises to approximately 40°C. In this way, the excitation device 31 can control the temperature rise of the protective cover 11 without changing the voltage of the drive signal by controlling the frequency of the drive signal that drives the piezoelectric element 15.

[0131] Figure 17 is a graph showing an example of how to control the temperature rise of the protective cover 11 by the excitation device 31 in de-icing mode. In the graph shown in Figure 17, the horizontal axis is time t, and the vertical axis is the temperature rise ΔT. When the excitation device 31 performs vibration processing in de-icing mode, the temperature of the protective cover 11 is basically low (for example, below ambient temperature). Therefore, it is desirable for the excitation device 31 to drive the piezoelectric element 15 to rapidly raise the temperature of the protective cover 11. Furthermore, after the temperature of the protective cover 11 has risen, it is desirable for the excitation device 31 to drive the piezoelectric element 15 to maintain that temperature. The excitation device 31 can control such a temperature rise by controlling the frequency of the drive signal that drives the piezoelectric element 15. Specifically, for example, the excitation device 31 first drives the piezoelectric element 15 with a drive signal at a frequency of 1 / 3 times the resonant frequency corresponding to the de-icing mode, and rapidly raises the temperature of the protective cover 11. Then, when the temperature of the protective cover 11 reaches a predetermined temperature (indicated as T1 in Figure 17), the excitation device 31 switches the frequency of the drive signal to a frequency 1 / 5 of the resonant frequency. Furthermore, when the temperature of the protective cover 11 reaches a temperature higher than T1 (indicated as T2 in Figure 17), the excitation device 31 switches the frequency of the drive signal to a frequency 1 / 7 of the resonant frequency. By controlling in this way, the excitation device 31 can raise the temperature of the protective cover 11 more quickly in the de-icing mode and prevent overheating of the protective cover 11. To control as described above, for example, the vibration device 10 may be provided with a temperature sensor configured to communicate with the excitation device 31. Alternatively, the excitation device 31 may switch the frequency of the drive signal based on the driving time for vibrating the piezoelectric element 15, rather than the temperature of the protective cover 11. For example, the excitation device 31 first drives the piezoelectric element 15 with a drive signal having a frequency 1 / 3 times the resonant frequency corresponding to the de-icing mode, thereby rapidly raising the temperature of the protective cover 11. Then, after driving the piezoelectric element 15 with a drive signal having a frequency 1 / 3 times the resonant frequency for a certain period of time (shown as t1 in Figure 17), the excitation device 31 may switch the frequency of the drive signal to a frequency 1 / 5 times the resonant frequency.Similarly, the excitation device 31 may, after driving the piezoelectric element 15 for a certain period of time (indicated by t2 in Figure 17), switch the frequency of the drive signal to a frequency 1 / 7 times the resonant frequency. Of course, the excitation device 31 may combine the control that switches the frequency of the drive signal based on the temperature of the protective cover 11 and the control that switches the frequency of the drive signal based on the driving time.

[0132] The excitation device 31 can remove foreign matter adhering to the protective cover 11 by combining the vibration modes described above. For example, if muddy water adheres to the protective cover 11, the excitation device 31 may be controlled to drive the piezoelectric element 15 in de-icing mode to dry the moisture from the muddy water, and then drive the piezoelectric element 15 in strong vibration mode to remove the mud. Alternatively, the excitation device 31 may continuously drive the piezoelectric element 15 in weak vibration mode, which consumes less power and has less impact on the vibration device 10, to slide off foreign matter adhering to the protective cover 11. The excitation device 31 may also be controlled to further remove dirt that cannot be removed in weak vibration mode using de-icing mode or strong vibration mode.

[0133] Next, the vibration processing of the vibration device 10 by the control circuit 32 will be explained based on a flowchart. Figure 18 is a flowchart for explaining the vibration processing of the vibration device 10 by the control circuit 32 of the excitation device 31 according to this embodiment.

[0134] First, the control circuit 32 selects a predetermined vibration mode from a plurality of vibration modes in order to supply a drive signal to the piezoelectric element having a frequency based on the resonant frequency of the vibrator 17 (S10). This allows the control circuit 32 to select which vibration mode to vibrate the protective cover 11 in. Next, the control circuit 32 sets the frequency of the drive signal supplied to the piezoelectric element (S11). Specifically, the control circuit 32 sets a frequency that corresponds to the resonant frequency of the selected predetermined vibration mode, 1 / (2n+1) times the resonant frequency, or (2n+1) times the resonant frequency, where n is a positive integer. Once the frequency of the drive signal is set, the control circuit 32 controls the drive signal to have that frequency (S12). In this way, the excitation device 31 can supply a drive signal to the piezoelectric element having a frequency based on the resonant frequency of the vibrator 17, and can vibrate the protective cover 11 in the predetermined vibration mode.

[0135] Thus, the excitation device 31 according to this embodiment can realize a vibration device 10 that has the function of removing foreign matter such as liquid droplets adhering to the protective cover 11 and the function of generating heat for the protective cover 11, without changing the voltage value of the voltage applied to the piezoelectric element 15. Furthermore, since the excitation device 31 can vibrate the protective cover 11 in a vibration mode having a vibration distribution and amplitude magnitude corresponding to the above functions, it is possible to reduce the acceleration of the deterioration of the lifespan of the coating on the protective cover 11.

[0136] In the embodiment described above, the excitation device 31 vibrates the light-transmitting protective cover 11 detected by the imaging device 20 via the vibrating body 13 by driving the piezoelectric element 15, but is not limited to this. For example, the vibrating device 10 may include an object that is vibrated via the vibrating body 13 by the piezoelectric element 15, and the excitation device 31 may vibrate the object by driving the piezoelectric element 15. The object may be a light-transmitting protective cover 11, for example, a translucent or opaque cover. The object is not particularly limited and may be a part that needs to be cleaned (for example, an optical component).

[0137] (Summary of the embodiments) The excitation device, vibration device, vehicle, control method, and computer program according to this embodiment, as described above, may be configured as follows.

[0138] (Aspect 1) The excitation device includes an output circuit that outputs a drive signal having frequency components to drive a piezoelectric element that vibrates an object via a vibrating body, and a control circuit that controls the output circuit to provide the piezoelectric element with a drive signal having a frequency based on the resonant frequency of the vibrator, which includes the object, the vibrating body, and the piezoelectric element, wherein the plurality of vibration modes include a predetermined vibration mode in which the frequency of the drive signal is set to a frequency of 1 / (2n+1) times or (2n+1) times the resonant frequency of the vibrator, where n is a positive integer.

[0139] (Aspect 2) The excitation device of aspect 1 may be set such that the frequency of the drive signal in a predetermined vibration mode causes the object to generate heat due to the piezoelectric element.

[0140] (Aspect 3) The excitation device of Aspect 2 may monotonically increase or decrease the frequency of the drive signal over time, under the condition that in a predetermined vibration mode, the frequency of the drive signal becomes 1 / (2n+1) times or (2n+1) times the resonant frequency corresponding to the predetermined vibration mode.

[0141] (Aspect 4) An excitation device in either Aspect 1 or Aspect 3 includes a plurality of vibration modes, the first vibration mode which causes the object to vibrate with a first vibration acceleration, and the second vibration mode which causes the object to vibrate with a second vibration acceleration which is smaller than the first vibration acceleration, wherein the frequency of the drive signal in the second vibration mode may be 1 / (2n+1) times or (2n+1) times the frequency of the drive signal in the first vibration mode.

[0142] (Aspect 5) The excitation device of aspect 4 has a first vibration acceleration of 8.1 × 10 5 m / s 2 The above 1.7 × 10 6 m / s 2 The following is true, and the second vibration acceleration is 1.5 × 10⁻⁶5 m / s 2 The above 8.0 x 10 5 m / s 2 The following is also acceptable.

[0143] (Aspect 6) The excitation device of aspect 4 or aspect 5 has a control circuit that has a search mode for determining the resonant frequency of the oscillator, and the resonant frequency corresponding to the first vibration mode is 1 / (2n a (+1) times the frequency or (2n a When outputting a drive signal with a frequency of +1), in search mode, the resonant frequency corresponding to the first vibration mode is 1 / (2n search (+1) times the frequency or (2n search A drive signal having +1) may be output. Here, n a n is a non-negative integer, and n search is n a It is a larger positive integer.

[0144] (Aspect 7) The excitation device of Aspect 1 includes a first distribution mode in which the frequency of the drive signal in a predetermined vibration mode is set so that the object generates heat, and a second distribution mode in which the object vibrates with a predetermined vibration acceleration, dist =a center / a edge If defined as such, v dist_heat >v dist_st and a center_heat center_st It may also be the case that v dist This is the distribution of vibrations in the object, and v dist_heat This is the distribution of vibrations in the object in the first distribution mode, and v dist_st This is the distribution of vibrations in the object in the second distribution mode, and a center This is the amplitude of the top of the object, and a center_heat This is the amplitude of the top of the object in the first distribution mode, and a center_st This is the amplitude of the top of the object in the second distribution mode, and a edge This is the amplitude at the end of the object.

[0145] ​(Aspect 8) The excitation device of aspect 7 further includes a third distributed mode in which the multiple vibration modes vibrate the object with a vibration acceleration smaller than a predetermined vibration acceleration, dist_heat >v dist_we It may also be the case that v dist_we This represents the vibration distribution in the object in the third distribution mode.

[0146] (Aspect 9) The excitation device of Aspect 1 has a control circuit that repeatedly performs an operation of changing the frequency of a drive signal within a predetermined frequency range determined based on the resonant frequency of the oscillator for each of a plurality of vibration modes, the plurality of vibration modes include a first sweep mode in which the control circuit changes the frequency of a drive signal within a first frequency range which includes the frequency of a drive signal that drives a piezoelectric element so that the object generates heat, and a second sweep mode in which the control circuit changes the frequency of a drive signal within a second frequency range which is wider than the first frequency range, and which corresponds to a resonant frequency lower than the resonant frequency corresponding to the first sweep mode, the full width at half maximum of the peak at the resonant frequency in the displacement of the object within the first frequency range is HW1, the width of the first frequency range is SR1, the full width at half maximum of the peak at the resonant frequency in the displacement of the object within the second frequency range is HW2, and the width of the second frequency range is SR2, the case may be (HW1 / SR1) > (HW2 / SR2).

[0147] (Aspect 10) The excitation device of aspect 9 further comprises a current detection circuit that detects a current based on the current flowing through a piezoelectric element and outputs a detection signal indicating a value based on the detected current to a control circuit, the control circuit changes the frequency of the drive signal within a predetermined frequency range in each of the first sweep mode and the second sweep mode, and acquires the change in the value of the detection signal in response to the change in the frequency of the drive signal within the predetermined frequency range, and based on the frequency at which the value of the detection signal is maximum within the predetermined frequency range vibrator The operation to update the resonant frequency may be performed repeatedly.

[0148] (Aspect 11) Any one of the excitation devices from Aspects 1 to 10 may include a protective cover that is positioned in front of the imaging device and transmits light detected by the imaging device.

[0149] (Aspect 12) The vibration device comprises one excitation device from Aspects 1 to 11, a piezoelectric element, a vibrating body, and an object.

[0150] (Aspect 13) The vehicle comprises the excitation device of Aspect 11, a piezoelectric element, a vibrating body, an object, and an imaging device.

[0151] (Aspect 14) A control method for an output circuit that outputs a drive signal having frequency components to drive a piezoelectric element that vibrates an object via a vibrating body, selects a predetermined vibration mode from a plurality of vibration modes to provide the piezoelectric element with a drive signal having a frequency based on the resonant frequency of the vibrator, which includes the object, the vibrating body, and the piezoelectric element, and in the predetermined vibration mode, sets the frequency of the drive signal to a frequency that is 1 / (2n+1) times or (2n+1) times the resonant frequency of the vibrator. Here, n is a positive integer.

[0152] (Aspect 15) The computer program can cause one or more processors to execute the control method of Aspect 14.

[0153] The excitation circuits, vibration devices, and vehicles described in this disclosure are realized through the cooperation of hardware resources, such as a processor and memory, and software resources (computer programs). [Industrial applicability]

[0154] According to this disclosure, it is possible to provide an excitation device, a vibration device, a vehicle, a control method, and a computer program that can perform multiple vibration modes that impart different vibrations to an object with a simple configuration, and therefore can be suitably used in this type of industrial field. [Explanation of Symbols]

[0155] 10 Vibration device 11. Protective cover (for the object) 11a Top (center) 11b End (periphery) 15 Piezoelectric element 20 Imaging device 30, 30A, 30B, 30C vibration circuit 31, 31A, 31B, Excitation device 32 Control circuits 33 DC power supply 34 Reference Potential 37, 37A output circuit 38, 38A current detection circuit α Vibration acceleration

Claims

1. An output circuit that outputs a drive signal having frequency components in order to drive a piezoelectric element that vibrates an object via a vibrating body, A control circuit comprising multiple vibration modes that controls the output circuit to supply a drive signal having a frequency based on the resonant frequency of the vibrator, which includes the object, the vibrating body, and the piezoelectric element, to the piezoelectric element, Equipped with, The plurality of vibration modes include a predetermined vibration mode in which the frequency of the drive signal is set to a frequency of 1 / (2n+1) times or (2n+1) times the resonant frequency of the vibrator, n is a positive integer, The aforementioned control circuit is The operation of repeatedly changing the frequency of the drive signal within a predetermined frequency range determined based on the resonant frequency of the vibrator is performed for each of the plurality of vibration modes. The aforementioned multiple vibration modes are, The control circuit has a first sweep mode in which it changes the frequency of the drive signal within a first frequency range that includes the frequency of the drive signal for driving the piezoelectric element so that the object generates heat, as the predetermined frequency range. The control circuit changes the frequency of the drive signal within a second frequency range, which is defined as the predetermined frequency range, and includes a second sweep mode corresponding to a resonant frequency lower than the resonant frequency corresponding to the first sweep mode, Includes, HW1 is the full width at half maximum of the peak at the resonant frequency in the displacement of the object within the first frequency range. The width of the first frequency range is SR1, HW2 is the full width at half maximum of the peak at the resonant frequency in the displacement of the object within the second frequency range. If the width of the second frequency range is denoted as SR2, (HW1 / SR1) > (HW2 / SR2) Excitation device.

2. An output circuit that outputs a drive signal having frequency components in order to drive a piezoelectric element that vibrates an object via a vibrating body, A control circuit comprising multiple vibration modes that controls the output circuit to supply a drive signal having a frequency based on the resonant frequency of the vibrator, which includes the object, the vibrating body, and the piezoelectric element, to the piezoelectric element, Equipped with, The plurality of vibration modes include a predetermined vibration mode in which the frequency of the drive signal is set to a frequency of 1 / (2n+1) times or (2n+1) times the resonant frequency of the vibrator, n is a positive integer, The aforementioned multiple vibration modes are, A first distribution mode that sets the frequency of the drive signal in the predetermined vibration mode so that the object generates heat, A second distribution mode that vibrates the object at a predetermined vibrational acceleration, Includes, If v dist = a center / a edge is defined, then v dist_heat > v dist_st and a center_heat < a center_st, v dist is the vibration distribution in the object, v dist_heat is the vibration distribution in the object in the first distribution mode, v dist_st is the vibration distribution in the object in the second distribution mode, a center is the amplitude of the top of the object, a center_heat is the amplitude of the top of the object in the first distribution mode, a center_st is the amplitude of the top of the object in the second distribution mode, a edge is the amplitude of the edge of the object. Excitation device.

3. The frequency of the drive signal in the predetermined vibration mode is set such that the object generates heat due to the piezoelectric element. The excitation device according to claim 1 or claim 2.

4. The excitation device, under the condition that in the predetermined vibration mode the frequency of the drive signal becomes 1 / (2n+1) times or (2n+1) times the resonant frequency corresponding to the predetermined vibration mode, monotonically increases or decreases the frequency of the drive signal over time. The excitation device according to claim 3.

5. The aforementioned multiple vibration modes are, A first vibration mode that vibrates the object with a first vibration acceleration, A second vibration mode in which the object is vibrated with a second vibration acceleration smaller than the first vibration acceleration, Includes, The frequency of the drive signal in the second vibration mode is 1 / (2n+1) times or (2n+1) times the frequency of the drive signal in the first vibration mode. The excitation device according to claim 1 or claim 2.

6. The first vibration acceleration is 8.1 × 10⁻⁶ ５ m / s ２ The above 1.7 x 10 ６ m / s ２ The following: The second vibration acceleration is 1.5 × 10⁻⁶ ５ m / s ２ The above 8.0 x 10 ５ m / s ２ The following is: The excitation device according to claim 5.

7. The aforementioned control circuit is The system has a search mode for determining the resonant frequency of the oscillator, 1 / (2n ａ +1) times the resonance frequency corresponding to the first vibration mode or (2n ａ +1) times the frequency of the drive signal having the frequency, in the search mode, 1 / (2n ｓｅａｒｃｈ +1) times the resonance frequency corresponding to the first vibration mode or (2n ｓｅａｒｃｈ +1) times the drive signal having the frequency, output n ａ n is a non-negative integer, and ｓｅａｒｃｈ is, n ａ A larger positive integer, The excitation device according to claim 5.

8. The aforementioned multiple vibration modes are, A third distribution mode that causes the object to vibrate with a vibration acceleration smaller than the predetermined vibration acceleration, It further includes, v ｄｉｓｔ＿ｈｅａｔ >v ｄｉｓｔ＿ｗｅ And, v ｄｉｓｔ＿ｗｅ This is the vibration distribution in the object in the third distribution mode. The excitation device according to claim 2.

9. A current detection circuit that detects a current based on the current flowing through the piezoelectric element and outputs a detection signal indicating a value based on the detected current to the control circuit. Furthermore, The aforementioned control circuit is In each of the first sweep mode and the second sweep mode, the frequency of the drive signal is changed within a predetermined frequency range, and the change in the value of the detection signal in response to the change in the frequency of the drive signal is acquired within the predetermined frequency range. The operation of updating the resonant frequency of the oscillator is repeatedly performed based on the frequency at which the value of the detection signal is maximized within the predetermined frequency range. The excitation device according to claim 1.

10. The object is positioned in front of the imaging device and includes a protective cover that transmits light detected by the imaging device. The excitation device according to claim 1 or claim 2.

11. An excitation device according to claim 1 or claim 2, The piezoelectric chip, The vibrating body and, The aforementioned object and, Equipped with, Vibration device.

12. The excitation device according to claim 10, The piezoelectric chip, The vibrating body and, The aforementioned object and, The imaging device and, Equipped with, vehicle.

13. A control method for an output circuit that outputs a drive signal having frequency components in order to drive a piezoelectric element that vibrates an object via a vibrating body, Select a predetermined vibration mode from a plurality of vibration modes to control the output circuit so as to supply a drive signal having a frequency based on the resonant frequency of the vibrator, which includes the object, the vibrating body, and the piezoelectric element, to the piezoelectric element, and apply this drive signal to the piezoelectric element. In the predetermined vibration mode, the frequency of the drive signal is set to a frequency that is 1 / (2n+1) times or (2n+1) times the resonant frequency of the vibrator. n is a positive integer, The control method further includes: The operation of repeatedly changing the frequency of the drive signal within a predetermined frequency range determined based on the resonant frequency of the vibrator is performed for each of the plurality of vibration modes. The aforementioned multiple vibration modes are, The predetermined frequency range includes a first sweep mode in which the frequency of the drive signal is varied within a first frequency range that includes the frequency of the drive signal used to drive the piezoelectric element so that the object generates heat, The predetermined frequency range includes a second sweep mode that changes the frequency of the drive signal in the second frequency range and corresponds to a resonant frequency lower than the resonant frequency corresponding to the first sweep mode, Includes, HW1 is the full width at half maximum of the peak at the resonant frequency in the displacement of the object within the first frequency range. The width of the first frequency range is SR1, HW2 is the full width at half maximum of the peak at the resonant frequency in the displacement of the object within the second frequency range. If the width of the second frequency range is denoted as SR2, (HW1 / SR1) > (HW2 / SR2) Control method.

14. A computer program for causing one or more processors to execute the control method described in claim 13.

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