Control apparatus for controlling vibration device and method for controlling vibration device

Abstract

To provide a control apparatus for controlling a vibration device capable of improving a search performance of a resonant frequency, and a method for controlling the vibration device.SOLUTION: A method for controlling a vibration device comprising a piezoelectric element using a control apparatus includes the steps of: changing a voltage waveform applied to the piezoelectric element; measuring a value relating to impedance of the piezoelectric element; and determining a resonant frequency of the piezoelectric element based on the measured value relating to the impedance of the piezoelectric element.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present disclosure relates to a control device for controlling a vibration device and a method for controlling a vibration device.

Background Art

[0002] The resonance frequency of a piezoelectric element provided in a vibration device or the like changes due to various factors. Patent Document 1 discloses a piezoelectric motor drive circuit that controls and drives so that the alternating current flowing through the piezoelectric element becomes substantially constant even when the resonance frequency characteristics of the piezoelectric element fluctuate due to fluctuations in the ambient temperature or the like.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In recent years, in a vibration device including a piezoelectric element, it has been demanded to improve the search performance of the resonance frequency.

[0005] Therefore, an object of the present disclosure is to provide a control device for controlling a vibration device and a method for controlling a vibration device that can improve the search performance of the resonance frequency.

Means for Solving the Problems

[0006] The method according to the present disclosure is a method for controlling a vibration device including a piezoelectric element by a control device, the step of changing a voltage waveform applied to the piezoelectric element, the step of measuring a value related to the impedance of the piezoelectric element, the step of determining the resonance frequency of the piezoelectric element based on the measured value related to the impedance of the piezoelectric element including

[0007] The control device according to the present disclosure is a control device for controlling a vibration device including a piezoelectric element, a processor that transmits a drive signal for driving the piezoelectric element, a memory that stores instructions executed by the processor, and includes The instructions include changing a voltage waveform applied to the piezoelectric element, measuring a value related to the impedance of the piezoelectric element after changing the voltage waveform, and determining a resonance frequency of the piezoelectric element based on the measured value related to the impedance of the piezoelectric element.

Advantages of the Invention

[0008] According to the control device of the vibration device and the control method of the vibration device according to the present disclosure, the search performance of the resonance frequency can be improved.

Brief Description of the Drawings

[0009]

Figure 1

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Figure 8

Figure 9A

Figure 9B

Figure 10

Figure 11

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Figure 14

Figure 15

Figure 16

Embodiments for Carrying Out the Invention

[0010] (Background Leading to the Present Disclosure) An imaging unit is provided at the front or rear of a vehicle, and the image captured by the imaging unit is used to control a safety device or perform automatic driving control. Since such an imaging unit is often provided outside the vehicle, foreign matters such as raindrops, mud, and dust may adhere to the light-transmitting body (lens or protective glass) covering the outside. When foreign matters adhere to the light-transmitting body, the foreign matters adhering to the image captured by the imaging unit are reflected, and a clear image cannot be obtained.

[0011] Therefore, a vibration device that vibrates the light-transmitting body to remove foreign matters has been developed. Such a vibration device vibrates the light-transmitting body using, for example, a piezoelectric element. However, the resonance frequency of the piezoelectric element changes due to various factors such as the heat generated by the piezoelectric element and foreign matters adhering to the light-transmitting body.

[0012] As one method of improving the resonance frequency search performance, a method of increasing the performance of the processor of the control device can be considered. However, increasing the performance of the processor of the control device has problems such as increasing the manufacturing cost and increasing the mounting area of the processor.

[0013] Therefore, the present inventor has intensively studied to solve these problems and has reached the present disclosure.

[0014] The method according to the first aspect of the present disclosure is a method of controlling a vibration device including a piezoelectric element by a control device, the step of changing the voltage waveform applied to the piezoelectric element, the step of measuring a value related to the impedance of the piezoelectric element, and the step of determining the resonance frequency of the piezoelectric element based on the measured value related to the impedance of the piezoelectric element. and includes.

[0015] With such a configuration, the search performance for the resonance frequency can be improved. Furthermore, with such a configuration, the search performance for the resonance frequency can be improved without changing the performance of the processor that constitutes the control device and without increasing the mounting area of the processor, so that the manufacturing cost can be suppressed.

[0016] The step of changing the voltage waveform may include changing the effective voltage of the voltage waveform.

[0017] With such a configuration, the search performance for the resonance frequency can be improved.

[0018] The step of changing the voltage waveform may include changing the amplitude of the voltage waveform.

[0019] With such a configuration, the search performance for the resonance frequency can be improved.

[0020] The step of changing the voltage waveform may include increasing the amplitude of the voltage waveform.

[0021] With such a configuration, the search performance for the resonance frequency can be improved.

[0022] The step of changing the voltage waveform may include decreasing the amplitude of the voltage waveform.

[0023] With such a configuration, the search performance for the resonance frequency can be improved.

[0024] The method further includes the step of changing the frequency of the drive signal for driving the piezoelectric element. The step of measuring the value related to the impedance may include measuring the value related to the impedance while the frequency is changing.

[0025] With such a configuration, the search performance for the resonance frequency can be further improved.

[0026] In the step of determining the resonance frequency, if the resonance frequency cannot be determined based on the value related to the impedance measured while the frequency is changing, the step of changing the voltage waveform may be executed.

[0027] With such a configuration, the search performance for the resonance frequency can be further improved.

[0028] The value related to the impedance is an impedance value, The step of determining the resonance frequency includes: determining whether the value related to the impedance is equal to or less than a predetermined threshold value; when it is determined that the value related to the impedance is equal to or less than the predetermined threshold value, determining the frequency of the drive signal for driving the piezoelectric element as the resonance frequency; and may have.

[0029] With such a configuration, the search performance for the resonance frequency can be improved.

[0030] The control device according to the first aspect of the present disclosure is a control device for controlling a vibration device including a piezoelectric element, a processor that transmits a drive signal for driving the piezoelectric element, a memory that stores instructions executed by the processor, and includes the instructions include a step of changing a voltage waveform applied to the piezoelectric element; a step of measuring a value related to the impedance of the piezoelectric element after changing the voltage waveform; and a step of determining the resonance frequency of the piezoelectric element based on the measured value related to the impedance of the piezoelectric element.

[0031] With such a configuration, the search performance for the resonance frequency can be improved. Furthermore, with such a configuration, the search performance for the resonance frequency can be improved without changing the performance of the processor constituting the control device and without increasing the mounting area of the processor, so that the manufacturing cost can be suppressed.

[0032] The step of changing the voltage waveform may include changing the effective voltage of the voltage waveform.

[0033] With such a configuration, the search performance for the resonance frequency can be improved.

[0034] The step of changing the voltage waveform may include changing the amplitude of the voltage waveform.

[0035] With such a configuration, the search performance for the resonance frequency can be improved.

[0036] The step of changing the voltage waveform may include increasing the amplitude of the voltage waveform.

[0037] With such a configuration, the search performance for the resonance frequency can be improved.

[0038] The step of changing the voltage waveform may include decreasing the amplitude of the voltage waveform.

[0039] With such a configuration, the search performance for the resonance frequency can be improved.

[0040] The method further includes the step of changing the frequency of the drive signal, The step of measuring the value related to the impedance may include measuring the value related to the impedance while the frequency is changing.

[0041] With such a configuration, the search performance for the resonance frequency can be further improved.

[0042] In the step of determining the resonance frequency, if the resonance frequency cannot be determined based on the value related to the impedance measured while the frequency is changing, the step of changing the voltage waveform may be executed.

[0043] With such a configuration, the search performance of the resonance frequency can be further improved.

[0044] The value related to the impedance is an impedance value, The step of determining the resonance frequency includes determining whether the value related to the impedance is less than or equal to a predetermined threshold value, and if it is determined that the value related to the impedance is less than or equal to the predetermined threshold value, determining the frequency of the drive signal as the resonance frequency. may have.

[0045] With such a configuration, the search performance of the resonance frequency can be improved.

[0046] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. Also, in each figure, for the sake of easy explanation, each element is shown exaggerated.

[0047] In this specification, terms such as "first" and "second" are used only for the purpose of explanation and should not be understood as explicitly or implicitly indicating relative importance or the order of technical features. The features limited to "first" and "second" explicitly or implicitly include one or more of the said features.

[0048] (Embodiment 1) <Overall Structure of the Vibration Device> Hereinafter, an imaging unit including the vibration device according to Embodiment 1 will be described with reference to the drawings. FIG. 1 is a perspective view for explaining the configuration of the imaging unit according to Embodiment 1. FIG. 2 is a schematic cross-sectional view showing the cross-sectional configuration of the imaging unit in which the imaging unit according to Embodiment 1 is arranged in the imaging device. FIG. 3 is a schematic cross-sectional view showing the cross-sectional configuration of the vibration device according to Embodiment 1. FIG. 4 is an exploded perspective view showing each component of the vibration device according to Embodiment 1.

[0049] As shown in FIGS. 1 and 2, the imaging unit 100 includes a housing 1, a vibration device 10, and an imaging device 5.

[0050] As shown in FIGS. 1 and 2, the housing 1 houses the imaging device 5. The housing 1 exposes a part of the vibration device 10. The material of the housing 1 is, for example, resin.

[0051] As shown in FIGS. 3 and 4, the vibration device 10 includes a light-transmitting body 2, a vibrating body 12 that vibrates the light-transmitting body 2, and a retainer 13 that supports the light-transmitting body 2 at its outer peripheral edge. As shown in FIG. 1, the vibration device 10 exposes the light-transmitting body 2, the retainer 13, and a part of the vibrating body 12 from the housing 1. The vibration device 10 vibrates the light-transmitting body 2 to remove attached foreign matter.

[0052] The light-transmitting body 2 is disposed in front of the imaging device 5. The vibration device 10 removes foreign matter attached to the light-transmitting body 2. The light-transmitting body 2 has light-transmitting properties that allow energy rays or light of the wavelength detected by the imaging device 5 to pass through. Further, the light-transmitting body 2 may be a lens having a light-collecting property.

[0053] The vibrating body 12 vibrates the light-transmitting body 2 to remove the adhered foreign matter. As shown in FIG. 4, the vibrating body 12 is provided with a hollow circular piezoelectric element 14 on, for example, the surface opposite to the surface in contact with the light-transmitting body 2. Further, the piezoelectric element 14 is provided with a wiring 15 having a hollow circular electrode on the surface opposite to the surface in contact with the vibrating body 12. By applying a voltage to the wiring 15 to vibrate the piezoelectric element 14 in the penetrating direction of the cylindrical vibrating body 12, the light-transmitting body 2 can be vibrated in the penetrating direction of the vibrating body 12 through the vibrating body 12.

[0054] Note that the position of the piezoelectric element 14 provided on the vibrating body 12 is not limited to the position shown in FIG. 3.

[0055] The retainer 13 is connected to the vibrating body 12. The retainer 13 and the vibrating body 12 are each subjected to a threading process, and the threaded portions of the retainer 13 and the vibrating body 12 are fitted and connected. The material of the retainer 13 may be, for example, not only metals such as stainless steel, aluminum, iron, titanium, and duralumin, but also plastic.

[0056] The vibration device 10 may further have a configuration for discharging a cleaning liquid (cleaning body) to the light-transmitting body 2 to remove the adhered foreign matter. For example, the cleaning nozzle 3 that discharges the cleaning liquid to the light-transmitting body 2 shown in FIG. 1 has a configuration for discharging the cleaning liquid to the light-transmitting body 2 to remove the adhered foreign matter.

[0057] The imaging device 5 images an imaging object outside the vibration device 10 through the light-transmitting body 2 of the vibration device 10. The imaging device 5 incorporates, for example, an optical element, an imaging element, sensor components, and the like.

[0058] Next, the configuration of the control device 50 that controls the vibration device 10 will be described with reference to the drawings. FIG. 5 is a block diagram for explaining the configuration of the control device that controls the vibration device according to the first embodiment.

[0059] The control device 50 includes a processor 20, a piezoelectric drive unit 30, an impedance detection unit 70, and a power supply circuit 80. The processor 20 is a control unit that processes the imaging signal from the imaging device 5 and supplies a control signal to the piezoelectric drive unit 30.

[0060] The processor 20 is provided with a CPU (Central Processing Unit) as a control center, a ROM (Read Only Memory) that stores programs, control data, etc. for the operation of the CPU, a RAM (Random Access Memory) that functions as a work area for the CPU, an input / output interface for maintaining signal consistency with peripheral devices, etc. The processor 20 may also be a microcontroller, an MPU (Micro-Processing Unit), a GPU (Graphics Processong Unit), a DSP (Digital Signal Processor), an FPGA (Field Programmable Gate Array), or an ASIC (Application Specific Integrated Circuit).

[0061] The piezoelectric drive unit 30 generates a drive signal according to the drive voltage and frequency in the piezoelectric drive unit 30 based on the control signal from the processor 20.

[0062] The piezoelectric element 14 vibrates when the drive signal generated by the piezoelectric drive unit 30 is applied. Due to the vibration of the piezoelectric element 14, the vibrating body 12 and the light-transmitting body 2 vibrate and foreign matter is removed. As the material for forming the piezoelectric element 14, for example, appropriate piezoelectric ceramics such as barium titanate (BaTiO3), lead titanate-zirconate (PZT:PbTiO3·PbZrO3), lead titanate (PbTiO3), lead metaniobate (PbNb2O6), bismuth titanate (Bi4Ti3O 12 )、(K,Na)NbO3, etc., or appropriate piezoelectric single crystals such as LiTaO3, LiNbO3, etc. can be used.

[0063] When the piezoelectric element 14 is vibrating, the impedance detection unit 70 monitors a value related to the impedance of the piezoelectric drive unit 30. The value related to the impedance is, for example, current, impedance, or the like.

[0064] The power supply circuit 80 outputs an alternating current signal. The effective voltage of the power supply circuit 80 is, for example, 0V or more and 70V or less.

[0065] The piezoelectric drive unit 30 and the impedance detection unit 70 can be realized by, for example, an electronic circuit. The functions of the piezoelectric drive unit 30 and the impedance detection unit 70 may be configured by hardware only, or may be realized by combining hardware and software. The piezoelectric drive unit 30 and the impedance detection unit 70 may realize a predetermined function by reading data and programs stored in a storage unit such as a memory and performing various arithmetic processes.

[0066] Next, the operation of the control device 50 will be described based on the transition diagram and the flowchart. FIG. 6 is a transition diagram of operation modes for explaining the operation of the control device that controls the vibration device according to the first embodiment. FIG. 7 is a flowchart for explaining the operation of the control device that controls the vibration device according to the first embodiment.

[0067] As shown in FIG. 6, the control device 50 drives the piezoelectric element 14 in the search mode and the drive mode. The search mode vibrates the piezoelectric element 14 to determine the resonance frequency fc of the piezoelectric element 14. The drive mode vibrates the piezoelectric element 14 to remove foreign matter attached to the surface of the light-transmitting body 2 by vibrating the vibrating body 12 at the resonance frequency fc determined in the search mode. The search mode and the drive mode are alternately implemented. The detailed steps of the search mode will be described below.

[0068] The search mode in Embodiment 1 includes a first search step and a second search step. The first search step sweeps the frequency fr of the drive signal between fmin and fmax to search for the resonance frequency fc of the piezoelectric element 14. Sweeping means changing the frequency fr step by step as time elapses. For example, increasing the frequency fr by Δf every time a time Δt elapses. Also, fmin is the minimum value of the frequency fr of the drive signal, and fmax is the maximum value of the frequency fr of the drive signal. The second search step is performed when the resonance frequency fc cannot be searched in the first search step. The second search step searches for the resonance frequency fc by changing the drive voltage Vpp applied to the piezoelectric element 14.

[0069] First, the control device 50 sets the drive voltage Vpp of the drive signal for driving the piezoelectric element 14 to the voltage V1 (step S1), and sets the update count Nv of the drive voltage Vpp to 1 (step S2). The drive voltage Vpp is, for example, an alternating voltage. The effective voltage of the voltage V1 is, for example, 0 V or more and 70 V or less.

[0070] Next, the control device 50 sets the frequency fr of the drive signal to the frequency fmin (step S3). The frequency fmin is, for example, 20 kHz or more and 1 MHz or less.

[0071] Next, the control device 50 applies the drive signal with the drive voltage Vpp set in step S1 and the frequency fr set in step S3 to the piezoelectric element 14 (step S4).

[0072] Next, the control device 50 measures the impedance value Z of the piezoelectric element 14 at the frequency fr of the drive signal (step S5).

[0073] Next, the control device 50 determines whether the measured impedance value Z is less than or equal to a predetermined threshold value Zth (step S6). The threshold value Zth is, for example, greater than 0 Ω and 1 kΩ or less.

[0074] Here, with reference to FIG. 8, the relationship between the impedance and the resonance frequency of the piezoelectric element 14 will be described. FIG. 8 shows the relationship between the resonance frequency fc and the impedance Z of the piezoelectric element 14 when the drive voltage Vpp is constant. In FIG. 8, the horizontal axis represents the frequency [kHz], and the vertical axis represents the impedance [Ω]. In the graph shown in FIG. 8, the frequency at the location where the impedance changes abruptly is the resonance frequency fc of the piezoelectric element 14. Therefore, when the frequency fr of the drive signal coincides with the resonance frequency fc of the piezoelectric element 14 or is close to the resonance frequency fc of the piezoelectric element 14, the measured impedance value Z of the piezoelectric element 14 is equal to or less than the threshold value Zth.

[0075] Therefore, when it is determined that the impedance value Z measured in step S5 is equal to or less than the threshold value Zth, the control device 50 determines the frequency fr of the drive signal as the resonance frequency fc of the piezoelectric element 14 (step S7).

[0076] Next to step S5, the control device 50 operates in a drive mode to vibrate the piezoelectric element 14 at the resonance frequency fc to remove foreign matter attached to the light-transmitting body 2 (step S8). In the drive mode, in conjunction with the vibration of the piezoelectric element 14, the cleaning liquid may be discharged from the cleaning nozzle 3 shown in FIG. 1 to remove foreign matter attached to the light-transmitting body 2.

[0077] In step S6, when it is determined that the measured impedance value Z is not equal to or less than the threshold value Zth, the control device 50 updates the frequency fr of the drive signal to fr + Δf (step S9). Δf is, for example, 1 Hz or more and 1 kHz or less.

[0078] Next, the control device 50 determines whether the frequency fr of the drive signal exceeds the frequency fmax (step S10). The frequency fmax is, for example, 1 MHz or less.

[0079] If it is determined in step S10 that the frequency fr of the drive signal does not exceed the frequency fmax, the process returns to step S4.

[0080] The above steps S1 to S10 are the first search step. If it is determined in step S10 that the frequency fr of the drive signal exceeds the frequency fmax, the following second search step is performed.

[0081] If it is determined in step S10 that the frequency fr of the drive signal exceeds the frequency fmax, the control device 50 changes the voltage waveform of the drive voltage Vpp. As a result, the voltage waveform of the drive signal applied to the piezoelectric element 14 changes. For example, the effective voltage of the voltage waveform changes. For example, the amplitude of the voltage waveform changes. Also, for example, the amplitude of the voltage waveform increases. Also, for example, the amplitude of the voltage waveform decreases. Specifically, the drive voltage Vpp is updated to Vpp + ΔV (step S11). ΔV may be a positive value or a negative value. That is, the amplitude of the voltage waveform applied to the piezoelectric element 14 increases or decreases. The absolute value of ΔV is, for example, greater than 0V and 70V or less.

[0082] Next, the control device 50 updates the update count Nv of the drive voltage Vpp to Nv + 1 (step S12).

[0083] Next, the control device 50 determines whether the update count Nv updated in step S12 exceeds the maximum update count Nvmax (step S13). The maximum update count Nvmax may be a predetermined number. Nvmax, for example, is 1 or more and 10 or less.

[0084] If it is determined in step S13 that the update count Nv exceeds Nvmax, the control device 50 detects an error (ERROR) (step S14) and ends the operation in the search mode (step S15).

[0085] If it is determined in step S13 that the update count Nv does not exceed Nvmax, the process returns to step S3.

[0086] Here, referring to FIGS. 9A and 9B, the relationship between the resonance frequency and impedance of the piezoelectric element 14 when the effective voltage of the driving voltage Vpp changes will be described. In FIG. 9A, the horizontal axis represents the effective voltage [V], and the vertical axis represents the resonance frequency [Hz]. FIG. 9A is an example of the change in the resonance frequency fc of the piezoelectric element 14 when the effective voltage is changed step by step from 10V to 50V. As can be seen from the graph shown in FIG. 9A, as the effective voltage increases, the resonance frequency fc of the piezoelectric element 14 decreases. In FIG. 9B, the horizontal axis represents the frequency [kHz], and the vertical axis represents the impedance [Ω]. In the graph shown in FIG. 9B, the state of the change in the resonance frequency when the effective voltage is changed from Vpp1 to Vpp3 is illustrated. In the effective voltages shown in FIG. 9B, Vpp1 > Vpp2 > Vpp3. The frequency f1 in FIG. 9B is an example of the frequency fr of the driving signal where fmin ≦ f1 ≦ fmax. From the graph of FIG. 9B, when the effective voltages are Vpp1 and Vpp2, for the driving signals with frequencies f1 and f1 + Δf, the impedance value Z is greater than the threshold value Zth, and the resonance frequency fc cannot be searched. However, when the effective voltage is Vpp3, by using the driving signal with the frequency f1, a frequency at which the impedance value Z becomes equal to or less than the threshold value Zth can be searched. That is, by changing the driving voltage Vpp by Vpp + ΔV in step S11 and further implementing the steps after step S3, the resonance frequency fc of the piezoelectric element 14 can be made to coincide with the frequency fr of the driving signal or be made closer to the frequency fr of the driving signal.

[0087] Therefore, by implementing the second search step of the above control method, the search performance for the resonance frequency fc of the piezoelectric element 14 can be improved. Further, the above control method can improve the search performance for the resonance frequency without changing the performance of the processor 20, and can suppress the manufacturing cost.

[0088] Modification Example 1 of Embodiment 1 In Embodiment 1, the second search step is performed after the first search step, but the first search step can be omitted. Referring to FIG. 10, the operation of the vibration device 10 of the imaging unit 100 in this modification will be described. FIG. 10 is a flowchart for explaining the operation of the control device that controls the vibration device according to this modification.

[0089] First, the control device 50 sets the frequency fr of the drive signal to f0 (step S101). f0 is, for example, an arbitrary resonance frequency searched in the preceding search mode.

[0090] Next, the control device 50 sets the drive voltage Vpp to V1 (step S102), and sets the update count Nv of the drive voltage Vpp to 1 (step S103).

[0091] Next, the control device 50 applies a drive signal with the frequency fr set in step S101 and the drive voltage Vpp set in step S102 to the piezoelectric element 14 (step S104).

[0092] Next, the control device 50 measures the impedance value Z of the piezoelectric element 14 at the frequency fr of the drive signal (step S105).

[0093] Next, the control device 50 determines whether the measured impedance value is equal to or less than a predetermined threshold value Zth (step S106).

[0094] If it is determined in step S106 that the measured impedance value Z is equal to or less than the predetermined threshold value Zth, the control device 50 determines the frequency fr of the drive signal as the resonance frequency fc of the piezoelectric element 14 (step S107).

[0095] After step S107, the control device 50 operates in a drive mode in which the piezoelectric element 14 is vibrated at the resonance frequency fc to remove foreign matter attached to the light-transmitting body 2 (step S108). In the drive mode, in conjunction with the vibration of the piezoelectric element 14, cleaning liquid may be discharged from the cleaning nozzle 3 shown in FIG. 1 to remove foreign matter attached to the light-transmitting body 2.

[0096] In step S106, when it is determined that the impedance value Z exceeds a predetermined threshold value Zth, the control device 50 updates the drive voltage Vpp to Vpp + ΔV (step S109).

[0097] Next, the control device 50 updates the update count Nv of the drive voltage Vpp to Nv + 1 (step S110).

[0098] Next, the control device 50 determines whether the update count Nv updated in step S110 exceeds the maximum update count Nvmax (step S111).

[0099] If it is determined in step S111 that the update count Nv exceeds Nvmax, the control device 50 detects an error (ERROR) (step S112) and ends the operation in the search mode (step S113).

[0100] If it is determined in step S111 that the update count Nv does not exceed Nvmax, the process returns to step S104.

[0101] [Effect] The above control method can improve the search performance of the resonance frequency fc of the piezoelectric element 14. Further, the above control method can simplify the control steps and shorten the frequency search time.

[0102] Modification Example 2 of Embodiment 1 In the above control method, the control device 50 detects the impedance value Z of the piezoelectric element 14, but the control device 50 may detect the current value I of the piezoelectric element 14.

[0103] Since the current value is the reciprocal of the impedance, when the control device 50 detects the current value I of the piezoelectric element 14, the current value I is measured in step S5 of the above control method, and it is determined in step S6 whether the current value I is greater than a predetermined threshold value Ith.

[0104] Fig. 11 shows a flowchart for explaining the operation of a control device that controls the vibration device according to this modified example.

[0105] First, steps S1 to S4 of Embodiment 1 shown in Fig. 7 are performed.

[0106] Next, the control device 50 measures the current value I of the piezoelectric element 14 (step S5A).

[0107] Next, the control device 50 determines whether the current value I measured in step S5A is greater than a predetermined threshold value Ith (step S6A).

[0108] In step S6A, if it is determined that the current value I is greater than the predetermined threshold value Ith, steps S7 and S8 of Embodiment 1 shown in Fig. 7 are performed.

[0109] In step S6A, if it is determined that the current value I is not greater than the predetermined threshold value Ith, steps S9 and S15 of Embodiment 1 shown in Fig. 7 are performed.

[0110] [Effect] The above control method can improve the search performance for the resonance frequency. Also, in the above control method, since the measured value for determining the resonance frequency fc of the piezoelectric element 14 is the current value I of the piezoelectric element 14, the measurement is easy.

[0111] Embodiment 2 Embodiment 2 differs from Embodiment 1 in the method of searching for the resonance frequency in the search mode. The search mode in Embodiment 2 includes a first A search step and a third search step. In the first A search step, the frequency fr of the drive signal is swept between fmin and fmax to search for the resonance frequency fc of the piezoelectric element 14. The third search step is performed when the resonance frequency fc of the piezoelectric element 14 cannot be found in the first A search step. In the third search step, the resonance frequency fc of the piezoelectric element 14 is searched by changing the clock widths of some of the plurality of clocks included in the drive signal. Here, changing the clock width may be performed by changing the duty ratio.

[0112] FIG. 12 is a flowchart for explaining the operation of the control device that controls the vibration device according to Embodiment 2. Referring to FIG. 12, the control method of the vibration device in Embodiment 2 will be described.

[0113] First, the control device 50 sets the drive voltage Vpp to Vdr (step S201). The effective voltage of the voltage Vdr is, for example, 0 V or more and 70 V or less.

[0114] Next, the control device 50 sets the clock width a of the plurality of clocks included in the drive signal to amin (step S202), and sets the update count Nc of the clock width a to 1 (step S203). Amin is the minimum value of the clock width a and is, for example, a preset value. Amin is, for example, 1 usec (1 MHz) or more and 50 usec (20 kHz) or less. Here, since the frequency fr of the drive signal depends on the clock width, when the clock width a is set, the frequency fr of the drive signal is set to fr(a). Also, when the clock widths of the plurality of clocks are a single width a, fr = fr(a) = a. Therefore, when the clock width a is set to amin, the frequency fr is set to fr(a) = amin = fmin.

[0115] Next, the control device 50 applies a drive signal with the drive voltage Vpp set in step S201 and the frequency fr set in step S202 to the piezoelectric element 14 (step S204).

[0116] Next, the control device 50 measures the impedance value Z of the piezoelectric element 14 at the frequency fr of the drive signal (step S205).

[0117] The control device 50 determines whether the measured impedance value Z is less than or equal to a predetermined threshold value Zth (step S206).

[0118] If it is determined in step S206 that the measured impedance value Z is less than or equal to the threshold value Zth, the control device 50 determines the frequency fr of the drive signal as the resonance frequency fc of the piezoelectric element 14 (step S207).

[0119] Next to step S207, the control device 50 operates in a drive mode in which the piezoelectric element 14 is vibrated at the resonance frequency fc determined in step S207 to remove foreign matter attached to the light-transmitting body 2. In the drive mode, together with the vibration of the piezoelectric element 14, cleaning liquid may be discharged from the cleaning nozzle 3 shown in FIG. 1 to remove foreign matter attached to the light-transmitting body 2.

[0120] If it is determined in step S206 that the measured impedance value Z is not less than or equal to the threshold value Zth, the control device 50 updates the clock width a of a plurality of clocks included in the drive signal to a + Δa (step S209). As a result, the frequency fr of the drive signal is updated to fr(a + Δa) = a + Δa. Δa is, for example, 1 Hz or more and 1 kHz or less.

[0121] Next, the control device 50 updates the update count Nc of the clock width a to Nc + 1 (step S210).

[0122] Next, the control device 50 determines whether the update count Nc updated in step S210 exceeds a predetermined threshold value Ncth1 (step S211). Ncth1 is, for example, 1 time or more and 10 times or less.

[0123] When it is determined in step S211 that the update count Nc does not exceed Ncth1, the process returns to step S203.

[0124] Steps S201 to S211 described above are the first A search steps. When it is determined in step S211 that the update count Nc exceeds Ncth1, the frequency fr of the drive signal has reached fmax. Therefore, in the first A search steps, the frequency fr of the drive signal is swept from fmin to fmax. That is, in the first A search steps, the clock width changes from amin to amax. When it is determined in step S211 that the update count Nc exceeds Ncth1, the following third search steps are performed.

[0125] When it is determined in step S211 that the update count Nc exceeds Ncth1, the control device 50 changes the clock widths such that the clock widths of some of the plurality of clocks are different from those of the other clocks (step S212). In other words, some of the plurality of clocks are referred to as a plurality of first clocks, and the remaining clocks are referred to as a plurality of second clocks. The clock widths of the plurality of first clocks are maintained at amax, and the clock widths of the plurality of second clocks are changed to a1. The clock width a1 is, for example, a value less than 1 times the clock width amax, preferably a value of 0.5 times or more and less than 1 times, and more preferably a value of 0.99 times or more and less than 1 times. That is, the control signal 50 changes the clock widths of some of the plurality of clocks to a value less than 1 times the clock widths of the other clocks, preferably a value of 0.5 times or more and less than 1 times, and more preferably a value of 0.99 times or more and less than 1 times. Also, the width a1 is, for example, amax - Δa, and Δa is, for example, the same as Δa in step S209. As the clock width a is changed, the frequency fr of the drive signal is changed to fr(a(amax, a1)). In this embodiment, the clock widths of the plurality of second clocks among the plurality of clocks are less than 1 times the clock widths of the plurality of first clocks, but the present invention is not limited to this, and the clock widths of the plurality of second clocks among the plurality of clocks may be made larger than 1 times the clock widths of the plurality of first clocks. In this case, for example, the clock widths of the plurality of second clocks are larger than 1 times and 1.5 times or less the clock widths of the plurality of first clocks, preferably larger than 1 times and 1.01 times or less.

[0126] Also, in step S212, the control device 50 changes the clock widths of 0.1% or more and 99.9% or less of the plurality of clocks included in the drive signal. A specific example will be described with reference to FIG. 13. FIG. 13 shows an example of a plurality of clocks included in the drive signal whose clock widths have been changed. As shown in FIG. 13, the control device 50 changes the clock widths of 1 / 2 (50%) of the plurality of clocks included in the drive signal to the width amax, and changes the clock widths of the remaining 1 / 2 (50%) of the clocks to the width a1.

[0127] Also, in step S212, the control device 50 periodically changes the clock widths of, for example, a plurality of clocks. As a result, some clocks are periodically positioned among the plurality of clocks. For example, some clocks are positioned at equal intervals among the plurality of clocks. Specifically, the control device 50 periodically changes the clock widths of the plurality of clocks such that clocks with a width of amax and clocks with a width of a1 are alternately included among the plurality of clocks included in the drive signal.

[0128] Next, the control device 50 updates the update count Nc of the clock width a to Nc + 1 (step S213).

[0129] Next, the control device 50 measures the impedance value Z of the piezoelectric element 14 at the frequency fr (a(amax, a1)) of the drive signal (step S214).

[0130] Next, the control device 50 determines whether or not the impedance value Z measured in step S214 is equal to or less than a predetermined threshold value Zth (step S215).

[0131] If it is determined in step S215 that the impedance value Z measured is equal to or less than the predetermined threshold value Zth, the control device 50 determines the frequency fr of the drive signal as the resonance frequency fc of the piezoelectric element 14 (step S216).

[0132] Next to step S216, the control device 50 operates in a drive mode in which the piezoelectric element 14 is vibrated at the resonance frequency fc determined in step S216 to remove foreign matter attached to the light transmissive body 2. In the drive mode, in conjunction with the vibration of the piezoelectric element 14, cleaning liquid may be discharged from the cleaning nozzle 3 shown in FIG. 1 to remove foreign matter attached to the light transmissive body 2.

[0133] In step S215, when it is determined that the measured impedance value Z is not less than the threshold value Zth, the control device 50 updates the clock widths a - Δa of the plurality of clocks included in the drive signal (step S218). As a result, the frequency fr of the drive signal is updated to fr(a - Δa). Updating the clock widths to a - Δa means, for example, decreasing both the clock width amax and the clock width a1 by Δa. Δa is, for example, the same as Δa in step S209.

[0134] Next, the control device 50 updates the update count Nc of the clock width a to Nc + 1 (step S219).

[0135] Next, the control device 50 determines whether the update count Nc updated in step S219 exceeds the threshold value Ncth2 (step S220). Ncth2 is, for example, 1 or more and 10 or less.

[0136] If it is determined in step S220 that the update count Nc does not exceed Ncth2, the process returns to step S214.

[0137] If it is determined in step S220 that the update count Nc exceeds Ncth2, the control device 50 detects an error (ERROR) and ends the operation in the search mode (step S221).

[0138] When the plurality of clocks included in the drive signal include two or more clock widths, the frequency fr of the drive signal becomes the frequency fr depending on the two or more clock widths. For example, when the plurality of clocks included in the drive signal include a clock with a clock width A1 at a ratio of N1% and a clock with a clock width A2 at a ratio of N2% (N2 = 100 - N1), the frequency fr of the drive signal is represented by the following formula 1.

[0139] (Formula 1) fr = fr(a(A1, A2)) = N1 / 100 × A1 + N2 / 100 × A2 = N1 / 100 × fr(A1) + N2 / 100 × fr(A2)

[0140] Specifically, for example, when a plurality of clocks included in a drive signal include a clock with a clock width of amax at a ratio of 50% and a clock with a clock width of a1 = amax - Δa at a ratio of 50%, the frequency fr of the drive signal is represented by the following Equation 2.

[0141] (Equation 2) fr = fr(a(amax, a1)) = fr(a(amax, amax - Δa)) = 50 / 100 × amax + 50 / 100 × (amax - Δa) = 1 / 2 × amax + 1 / 2 × (amax - Δa) = 1 / 2 × fr(amax) + 1 / 2 × fr(amax - Δa)

[0142] Therefore, by performing the third search step, a drive signal having a frequency fr between fr(amax) and fr(amax - Δa) can be emitted.

[0143] Here, refer to FIG. 14. FIG. 14 shows the relationship between the frequency of the drive signal and the resonance frequency in a graph showing the relationship between the resonance frequency and the impedance of the piezoelectric element. In the graph shown in FIG. 14, the horizontal axis represents the frequency [kHz] and the vertical axis represents the impedance [Ω]. In the example shown in FIG. 14, the resonance frequency fc of the piezoelectric element 14 exists between f(amax) and f(amax - Δa). Also, when the frequency fr of the drive signal is f(amax) or f(amax - Δa), the measured impedance Z is greater than the threshold value Zth. Therefore, it cannot be searched in the first search step 1A. However, as shown in Equation 2, by performing the third search step, a drive signal having a frequency fr(a(amax, amax - Δa)) between fr(amax) and fr(amax - Δa) can be emitted. Thereby, it is possible to search for the resonance frequency fc existing between fr(amax) and fr(amax - Δa) that could not be searched in the first search step 1A.

[0144] [Effect] Therefore, according to the third search step of the above control method, the frequency resolution can be improved regardless of the performance of the processor 20. Thereby, the search performance of the resonance frequency fc of the piezoelectric element 14 can be improved. Also, since an expensive processor 20 does not need to be used, an increase in manufacturing cost can be suppressed.

[0145] Modification Example 1 of Embodiment 2 In the control method of Embodiment 2, the third search step is performed after the first A search step, but the first A search step can be omitted. Referring to FIG. 15, the operation of the vibration device 10 of the imaging unit 100 in this modification example will be described. FIG. 15 is a flowchart for explaining the operation of the control device that controls the vibration device according to this modification example.

[0146] First, the control device 50 sets the drive voltage Vpp to Vdr (step S301).

[0147] Next, the control device 50 sets the clock widths such that the clock widths of some of the plurality of clocks are different from the clock widths of the other clocks (step S302). For example, the clock widths of 50% of the plurality of clocks included in the drive signal are set to the width amax, and the clock widths of the remaining 50% of the clocks are set to the width a1. The width a1 is, for example, amax - Δa, and Δa is, for example, the same as Δa in step S209 of Embodiment 2. Along with the change in the clock width, the frequency fr of the drive signal is set to fr(a(amax, a1)).

[0148] Also, in step S302, the method by which the control device 50 makes the clock widths of some of the plurality of clocks different from the clock widths of the other clocks can adopt the same method as the method of changing the clock width in step S212 of Embodiment 2.

[0149] Next, the control device 50 sets the update count Nc of the clock width a to 1 (step S303).

[0150] Next, the control device 50 applies a drive signal with a drive voltage Vpp set in step S301 and a frequency fr(a(amax, a1)) set in step S302 to the piezoelectric element 14 (step S304).

[0151] Next, the control device 50 measures the impedance value Z of the piezoelectric element 14 at the frequency fr(a(amax, a1)) of the drive signal (step S305).

[0152] Next, the control device 50 determines whether or not the impedance value Z measured in step S305 is less than or equal to a predetermined threshold value Zth (step S306).

[0153] If it is determined that the impedance value Z measured in step S305 is less than or equal to the threshold value Zth, the control device 50 determines the frequency fr of the drive signal as the resonance frequency fc of the piezoelectric element 14 (step S307).

[0154] Next to step S307, the control device 50 operates in a drive mode in which the piezoelectric element 14 is vibrated at the resonance frequency fc determined in step S407 to remove foreign matter attached to the light-transmitting body 2 (step S308). In the drive mode, together with the vibration of the piezoelectric element 14, cleaning liquid may be discharged from the cleaning nozzle 3 to remove foreign matter attached to the light-transmitting body 2.

[0155] In step S306, if it is determined that the measured impedance value Z is not less than or equal to the threshold value Zth, the control device 50 updates the clock widths a - Δa of a plurality of clocks included in the drive signal (step S309). As a result, the frequency fr of the drive signal is updated to fr(a - Δa). Updating to the clock widths a - Δa means, for example, decreasing both the clock width amax and the clock width a1 by Δa. Δa is, for example, the same as Δa in step S209 of Embodiment 2.

[0156] Next, the control device 50 updates the update count Nc of the clock width a to Nc + 1 (step S310).

[0157] Next, the control device 50 determines whether the update count Nc updated in step S410 exceeds zNcmax (step S311). The maximum update count Ncmax may be a preset update count. Ncmax is, for example, 1 or more and 10 or less.

[0158] If it is determined in step S311 that the update count Nc does not exceed Ncmax, the process returns to step S305.

[0159] If it is determined in step S311 that the update count Nc exceeds Ncmax, the control device 50 detects an error (ERROR) (step S312) and ends the operation in the search mode (step S313).

[0160] [Effect] In the above control method, the search performance of the resonance frequency fc of the piezoelectric element 14 can be improved. Further, the above control method can simplify the control and shorten the frequency search time.

[0161] Modification Example 2 of Embodiment 2 In the control method of Embodiment 2, in step S212, the control device 50 maintains the clock width of 1 / 2 (50%) of the plurality of clocks included in the drive signal at the width amax, and changes the clock width of the remaining 1 / 2 (50%) of the clocks to the width a1. However, the method of changing the clock width so that the clock widths of some of the plurality of clocks are different from the clock widths of other clocks is not limited to this.

[0162] For example, as shown in FIG. 16, the control device 50 may maintain the clock width of 2 / 3 of the plurality of clocks included in the drive signal at the width amax and change the clock width of the remaining 1 / 3 of the clocks to the width a1. In this case, the clocks with the clock width a1 are emitted, for example, at a period of once every three times. Also, in this case, the frequency fr of the drive signal is represented by the following Equation 3.

[0163] (Formula 3) fr = fr(a(amax, a1)) = fr(a(amax, amax - Δa)) = 2 / 3 × amax + 1 / 3 × (amax - Δa) = 2 / 3 × fr(amax) + 1 / 3 × fr(amax - Δa)

[0164] That is, it is possible to generate a drive signal having a different frequency fr from a drive signal that includes a clock with a width of amax at a ratio of 2 / 3 and a clock with a clock width of a1 at a ratio of 1 / 3, and a drive signal that includes a clock with a width of amax and a clock with a width of a1 at the same ratio.

[0165] [Effect] From the above, it becomes possible to generate drive signals having various frequencies fr according to the method of changing the clock widths of a plurality of clocks included in the drive signal. Thereby, it is possible to generate a drive signal having a desired frequency and improve the search performance for the resonance frequency fc.

Industrial Applicability

[0166] The control method for controlling the vibration device and the control device of the vibration device according to the present disclosure can be applied to vibration devices used in in-vehicle cameras, surveillance cameras, or optical sensors such as LiDAR used outdoors.

Explanation of Signs

[0167] 1 Housing 2 Translucent body 3 Cleaning nozzle 5 Imaging device 10 Vibration device 12 Vibration body 13 Retainer 14 Piezoelectric element 15 Wiring 20 Processor 30 Piezoelectric drive unit 50 Control device 70 Impedance detection unit 80 Power supply circuit 100 Imaging unit

Claims

1. A method for controlling a vibration device including a piezoelectric element by a control device, comprising: changing a voltage waveform applied to the piezoelectric element; measuring a value related to the impedance of the piezoelectric element; determining a resonance frequency of the piezoelectric element based on the measured value related to the impedance of the piezoelectric element; and the method.

2. The method according to claim 1, wherein the step of changing the voltage waveform includes changing the effective voltage of the voltage waveform.

3. The method according to claim 1 or 2, wherein the step of changing the voltage waveform includes changing the amplitude of the voltage waveform.

4. The method according to claim 3, wherein the step of changing the voltage waveform includes increasing the amplitude of the voltage waveform.

5. The method according to claim 3, wherein the step of changing the voltage waveform includes decreasing the amplitude of the voltage waveform.

6. The method according to any one of claims 1 to 5, further comprising changing a frequency of a drive signal for driving the piezoelectric element, wherein the step of measuring the value related to the impedance includes measuring the value related to the impedance while the frequency is changing.

7. The method according to claim 6, wherein in the step of determining the resonance frequency, if the resonance frequency cannot be determined based on the value related to the impedance measured while the frequency is changing, the step of changing the voltage waveform is executed.

8. The method according to any one of claims 1 to 7, wherein the value related to the impedance is an impedance value, and the step of determining the resonance frequency includes determining whether the value related to the impedance is less than or equal to a predetermined threshold, and if it is determined that the value related to the impedance is less than or equal to the predetermined threshold, determining the frequency of the drive signal for driving the piezoelectric element as the resonance frequency.

9. A control device for controlling a vibration device including a piezoelectric element, comprising: a processor for transmitting a drive signal for driving the piezoelectric element; a memory storing instructions executed by the processor; wherein the instructions include changing a voltage waveform applied to the piezoelectric element; measuring a value related to the impedance of the piezoelectric element after changing the voltage waveform; ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Determining the resonance frequency of the piezoelectric element based on the value related to the impedance of the measured piezoelectric element, Control device. **Claim 10** The step of changing the voltage waveform includes changing the effective voltage of the voltage waveform. The control device according to claim 9. **Claim 11** The step of changing the voltage waveform includes changing the amplitude of the voltage waveform. The control device according to claim 9 or 10. **Claim 12** The step of changing the voltage waveform includes increasing the amplitude of the voltage waveform. The control device according to claim 11. **Claim 13** The step of changing the voltage waveform includes decreasing the amplitude of the voltage waveform. The control device according to claim 11. **Claim 14** Further including the step of changing the frequency of the drive signal, The step of measuring the value related to the impedance includes measuring the value related to the impedance while the frequency is changing. The control device according to any one of claims 9 to 13. **Claim 15** In the step of determining the resonance frequency, if the resonance frequency cannot be determined based on the value related to the impedance measured while the frequency is changing, the step of changing the voltage waveform is executed. The control device according to claim 14. **Claim 16** The value related to the impedance is an impedance value, The step of determining the resonance frequency includes: Determining whether the value related to the impedance is less than or equal to a predetermined threshold; When it is determined that the value related to the impedance is less than or equal to a predetermined threshold, determining the frequency of the drive signal as the resonance frequency. having The control device according to any one of claims 9 to 15.

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