Method for removing foreign matter from a sensor foreign matter removal device and sensor foreign matter removal device

Abstract

The present invention provides a method for removing foreign matter that is firmly attached to the cover member of a sensor, and that can suppress damage to the piezoelectric vibrator or adhesive layer. [Solution] A method for removing foreign matter is provided in which at least one piezoelectric vibrator 12 is provided so as to surround a predetermined area 3a of the cover glass 3 of an optical sensor, the piezoelectric vibrator 12 is equipped with a piezoelectric body polarized in the thickness direction, and a drive signal 11a, which is an AC drive voltage, is applied to the piezoelectric body to generate vibration in a predetermined area 13, wherein a first drive voltage having a frequency corresponding to the combined resonant frequency of the piezoelectric vibrator 12 and the cover glass 3 and a second drive voltage having a frequency corresponding to the resonant frequency unique to the piezoelectric vibrator 12 are applied to the piezoelectric body of the piezoelectric vibrator 12 in combination.

Description

[Technical Field]

[0001] The present invention relates to a foreign matter removing method for removing foreign matter adhering to a cover member that protects an optical sensor such as a camera or an electromagnetic wave sensor such as a millimeter wave radar, and a foreign matter removing device for a sensor to which the foreign matter removing method is applied. [Background Art]

[0002] In recent years, for the purpose of driving assistance and automatic driving, optical sensors such as cameras and LiDAR (Light Detection And Ranging) have been installed not only on the front part of vehicles but also on the rear and side parts of vehicles. In addition, optical sensors such as surveillance cameras are installed outdoors for the purpose of crime prevention and fixed-point surveillance. These optical sensors are provided with a glass or resin cover member on the front surface so as not to be directly exposed to rain, wind and snow. However, when foreign matter (water droplets, snow accreted and frozen ice, dust, insects, etc.) adheres to the cover member, light is blocked by the adhering foreign matter, and optical information such as images may not be obtained accurately. Accordingly, foreign matter removing devices for removing foreign matter adhering to the cover member have been provided. Further, electromagnetic wave sensors such as millimeter wave radars are sometimes used in automatic driving sensors and surveillance cameras. Electromagnetic waves have good transmittance in fog and snowfall and are resistant to disturbances, and the cover member does not necessarily need to be transparent. However, when foreign matter such as dust, ice and snow adheres to the cover member, electromagnetic waves may be blocked or absorbed, so sensor information may not be obtained accurately.

[0003] Among recent foreign matter removing devices, there are some that use vibration generated by a piezoelectric vibrator. In general, a piezoelectric vibrator includes a polarized piezoelectric body, and when an alternating voltage is applied to the piezoelectric body, the piezoelectric body expands and contracts to generate vibration. By vibrating the cover glass using this piezoelectric vibrator, foreign matter (water droplets, snow accreted and frozen ice, dust, insects, etc.) adhering to the cover member is removed from the surface of the cover member.

[0004] Patent Document 1 describes a water droplet removal device for removing water droplets adhering to a hood glass attached to the front of a camera. A disc-shaped piezoelectric vibrator with a hole larger than the viewing area of ​​the camera lens is fixed to the hood glass. By vibrating the resonant system including this piezoelectric vibrator and the hood glass at the resonant frequency, a standing wave is generated inside the central hole of the piezoelectric vibrator, which atomizes and removes the water droplets adhering to the hood glass. In addition, an electrical resistance heating element is provided separately to heat the hood glass, causing fine water droplets that cannot be atomized by the piezoelectric vibrator to sublimate and be removed.

[0005] Patent Document 2 describes a water droplet removal device comprising a camera case housing the camera body, an external lens attached to the part of the camera case that corresponds to the shooting range of the camera body, and a piezoelectric element that vibrates the external lens. By applying an AC signal to the piezoelectric element, the piezoelectric element is driven and the water droplets adhering to the external lens are atomized.

[0006] Patent Document 3 describes a dome-type surveillance camera system comprising a dome-type surveillance camera equipped with a dome-type cover, a piezoelectric ceramic vibrator attached to the dome-type cover, and a control device for controlling the piezoelectric ceramic vibrator. When it detects that water droplets or a water film have adhered to the dome-type cover, the control device vibrates the piezoelectric ceramic vibrator to remove the water droplets or water film adhering to the dome-type cover. The control device adjusts the vibration frequency so that the positions of the nodes and antinodes of the vibration amplitude change depending on whether the dome-type surveillance camera is facing downwards or sideways, and excites the dome-type cover to generate an appropriate vibration mode. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Utility Model Publication No. 5-32191 [Patent Document 2] Japanese Patent Publication No. 2007-82062 [Patent Document 3] Japanese Patent Publication No. 2012-138768 [Overview of the project] [Problems that the invention aims to solve]

[0008] However, the foreign matter removal device that uses the piezoelectric vibrator described above to vibrate the cover member and remove foreign matter has the following problems. As vibrations generated by a piezoelectric vibrator propagate through the cover material, the vibrations gradually attenuate as the distance from the piezoelectric vibrator increases. Due to this vibration attenuation, it is difficult to completely remove water droplets in areas far from the piezoelectric vibrator.

[0009] Furthermore, if foreign matter that is difficult to flow (such as ice, snow, dust, or insects) adheres firmly to the cover material, simply vibrating the piezoelectric vibrator will not be sufficient to remove such foreign matter. In addition, foreign matter that remains on the glass surface and cannot be removed may obstruct the dripping of water droplets, etc. While increasing the amplitude of the piezoelectric vibrator's vibration can broaden the region over which vibrations can propagate, prolonged high-amplitude driving of the piezoelectric vibrator may cause overheating due to internal heat generation, potentially damaging the piezoelectric vibrator itself or the adhesive layer securing it to the cover member.

[0010] In the water droplet removal device described in Patent Document 1, a resonant system including a piezoelectric vibrator and a hood glass is driven at a resonant frequency to atomize water droplets. However, the effective range for atomization within the region where vibrations generated by the piezoelectric vibrator propagate through the hood glass is limited to the area directly above the piezoelectric vibrator and its adjacent areas. Therefore, it is difficult to adequately remove water droplets in areas outside this effective range. In addition, if the piezoelectric vibrator is driven at a high-frequency resonant frequency that is high enough to atomize water droplets for a long period of time, self-heating due to internal friction occurs, which may result in the piezoelectric vibrator being damaged due to overheating, or the adhesive layer fixing the piezoelectric vibrator to the hood glass being damaged.

[0011] In the water droplet removal device described in Patent Document 2, the effective range in which water droplets can be atomized is limited to the area directly above the piezoelectric element and its adjacent areas, making it difficult to adequately remove water droplets outside the effective range. Furthermore, if the piezoelectric element is driven at a high frequency of 1.6 to 2.4 MHz for a long period of time, overheating may cause damage to the piezoelectric element or adhesive layer.

[0012] In the dome-type surveillance camera system described in Patent Document 3, it is necessary to position the piezoelectric vibrator at a location where the vibration antinode of the vibration occurs, corresponding to the position of the water droplet to be removed from the dome-type cover, and to drive it with appropriate resonant vibration, which has the problem of lacking versatility.

[0013] In view of the above problems, the object of the present invention is to provide a foreign matter removal method and a foreign matter removal apparatus that can efficiently remove foreign matter firmly adhering to the cover member of a sensor and suppress damage to the piezoelectric vibrator or adhesive layer. [Means for solving the problem]

[0014] This invention encompasses the following: [1] A method for removing foreign matter from a sensor, comprising: providing at least one piezoelectric vibrator so as to surround a predetermined area of ​​a cover member of an optical sensor or an electromagnetic wave sensor; the piezoelectric vibrator comprises a piezoelectric body polarized in the thickness direction with electrodes provided on both sides; and generating vibration in the predetermined area by applying an alternating current driving voltage to the piezoelectric body via the electrodes, A method for removing foreign matter from a sensor, characterized by applying a combination of a first drive voltage having a frequency corresponding to the combined resonant frequency of the piezoelectric vibrator and the cover member, and a second drive voltage having a frequency corresponding to the resonant frequency unique to the piezoelectric vibrator, to the piezoelectric body of the piezoelectric vibrator. [2] The method for removing foreign matter from a sensor according to [1], further comprising: the piezoelectric vibrator, at least one feedback electrode for detecting voltage changes that occur in accordance with the expansion and contraction of the piezoelectric body. [3] The method for removing foreign matter from a sensor according to [2], wherein the piezoelectric vibrator changes the frequency and / or voltage of the first driving voltage applied to the piezoelectric body within a predetermined range based on information of voltage change obtained from the feedback electrode, and adjusts the piezoelectric vibrator so that the amplitude of expansion and contraction in the thickness direction of the piezoelectric vibrator is maximized. [4] The method for removing foreign matter from a sensor according to [2], wherein the piezoelectric vibrator changes the frequency and / or voltage of the second driving voltage applied to the piezoelectric body within a predetermined range based on information of voltage change obtained from the feedback electrode, and adjusts the piezoelectric vibrator so that the amplitude of expansion and contraction in the thickness direction of the piezoelectric vibrator is maximized. A sensor foreign matter removal device using the sensor foreign matter removal method described in [5][1] or [2]. [6] A method for removing foreign matter from a sensor according to [1] or [2], wherein the combination of a first drive voltage having a frequency corresponding to the combined resonant frequency of the piezoelectric vibrator and the cover member and a second drive voltage having a frequency corresponding to the resonant frequency inherent to the piezoelectric vibrator is applied to the piezoelectric body of the piezoelectric vibrator, and the first drive voltage and the second drive voltage are repeatedly applied alternately. A sensor foreign matter removal device using the sensor foreign matter removal method described in [7][6]. [8] A method for removing foreign matter from a sensor according to [1] or [2], wherein the combination of a first drive voltage having a frequency corresponding to the combined resonant frequency of the piezoelectric vibrator and the cover member and a second drive voltage having a frequency corresponding to the resonant frequency unique to the piezoelectric vibrator applied to the piezoelectric body of the piezoelectric vibrator is such that the second drive voltage is intermittently applied in superimposed on the first drive voltage. A sensor foreign matter removal device using the sensor foreign matter removal method described in [9][8]. [Effects of the Invention]

[0015] According to the present invention, by combining the vibration based on the combined resonant frequency of the piezoelectric vibrator and the cover member and the vibration based on the resonant frequency inherent to the piezoelectric vibrator, foreign matter adhering to a predetermined region of the cover member is lifted from the cover member and caused to flow, thereby enabling efficient removal of the foreign matter from the predetermined region. Furthermore, by intermittently performing vibration at the resonant frequency inherent to the piezoelectric vibrator to control overheating caused by self-heating of the piezoelectric vibrator, damage to the piezoelectric vibrator itself or to the adhesive layer between the piezoelectric vibrator and the cover member can be suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] [Figure 1] It is a schematic diagram for explaining a piezoelectric body polarized in the thickness direction. [Figure 2] It is a schematic diagram showing the configuration of a foreign matter removing apparatus according to a first embodiment of the present invention. [Figure 3] It is a cross-sectional view schematically showing the cross-sectional structure of a piezoelectric vibrator constituting the foreign matter removing apparatus shown in Fig. 2. [Figure 4] It is a schematic diagram showing an application example of the foreign matter removing apparatus shown in Fig. 2. [Figure 5] It is a diagram for explaining an example of drive control of the piezoelectric vibrator shown in Fig. 2. [Figure 6] It is a block diagram showing an adjustment circuit that adjusts the frequency of a drive voltage. [Figure 7] It is a diagram for explaining another example of drive control of the piezoelectric vibrator shown in Fig. 2. [Figure 8] It is a schematic diagram showing the configuration of a foreign matter removing apparatus according to a second embodiment of the present invention. [Figure 9] It is a schematic diagram showing the configuration of a foreign matter removing apparatus according to a third embodiment of the present invention. [Figure 10] It is a cross-sectional view schematically showing the cross-sectional structure of a piezoelectric vibrator constituting the foreign matter removing apparatus shown in Fig. 9. [Figure 11] It is a schematic diagram showing the configuration of a foreign matter removing apparatus according to a fourth embodiment of the present invention. [Figure 12] It is a schematic diagram showing a first modified example of a piezoelectric vibrator. [Figure 13]This is a schematic diagram showing a second modified example of a piezoelectric vibrator. [Figure 14] This is a schematic diagram showing a third modified example of a piezoelectric vibrator. [Figure 15] This is a schematic diagram showing a third modified example of a piezoelectric vibrator. [Modes for carrying out the invention]

[0017] Embodiments of the present invention will be described in detail below with reference to the drawings. However, the components described in the embodiments are merely examples and are not intended to limit the scope of the present invention to them.

[0018] First, let's briefly explain the basic structure of a piezoelectric vibrator. Generally, a piezoelectric vibrator is equipped with a polarized piezoelectric body, and when an alternating voltage is applied to this piezoelectric body, it expands and contracts, generating vibrations.

[0019] Figure 1 is a schematic diagram illustrating a piezoelectric material polarized in the thickness direction. In Figure 1, (a) shows the state of the piezoelectric material before polarization, and (b) shows the state of the piezoelectric material after polarization. As shown in Figure 1(a), the direction of spontaneous polarization in a fired piezoelectric material (ceramics) is random. As shown in Figure 1(b), by applying a high voltage to the piezoelectric material (ceramics), the direction of spontaneous polarization can be aligned in the thickness direction (direction of arrow A in the figure). This polarized piezoelectric material (ceramics) maintains its state of having the direction of spontaneous polarization aligned in the thickness direction even after the voltage application is stopped.

[0020] When an AC voltage is applied to a polarized piezoelectric material, the piezoelectric material expands and contracts in the thickness direction. Conversely, when external pressure is applied to a polarized piezoelectric material, a positive charge is generated on one side of the piezoelectric material and a negative charge is generated on the other side. Conversely, when a polarized piezoelectric material is stretched, a negative charge is generated on one side of the piezoelectric material and a positive charge is generated on the other side. In this invention, vibration is generated using a piezoelectric vibrator made of a piezoelectric material polarized in the thickness direction as shown in Figure 1.

[0021] (First Embodiment) Figure 2 is a schematic diagram showing the configuration of a foreign matter removal device according to the first embodiment of the present invention. Figure 3 is a schematic cross-sectional view showing the cross-sectional structure of a piezoelectric vibrator constituting the foreign matter removal device shown in Figure 2. In Figure 3, (a) is a cross-sectional view along line AA, (b) is a cross-sectional view along line BB, (c) is a cross-sectional view along line CC, and (d) is a cross-sectional view along line DD. Figure 4 is a schematic diagram showing an application example of the foreign matter removal device shown in Figure 2. In Figures 2 to 4, the illustrated components are depicted schematically and do not differ from their actual size (thickness, width, etc.).

[0022] Referring to Figures 2 and 3, the foreign object removal device 10 of this embodiment includes a piezoelectric vibrator 12 and a control device 11 that controls the driving of the piezoelectric vibrator 12. As shown in Figure 4, the optical sensor 1 is housed in a housing 2. The optical sensor 1 is, for example, an in-vehicle camera, LiDAR, or surveillance camera. The housing 2 has an opening in the imaging direction of the camera of the optical sensor 1, and a cover glass 3 is attached to this opening as a cover member to protect the optical sensor 1. The piezoelectric vibrator 12 is attached to the surface of the cover glass 3 on the optical sensor 1 side. The cover glass 3 is made of a material (transparent material) that allows the optical sensor 1 to detect objects.

[0023] The piezoelectric vibrator 12 comprises a piezoelectric body 4 polarized in the thickness direction, electrodes 13a and 13b for applying an AC voltage to the piezoelectric body 4, a feedback electrode 14 that outputs a detection signal indicating a voltage change corresponding to the expansion and contraction of the piezoelectric body 4 to which the AC voltage is applied, and a ground (GND) electrode 15. The piezoelectric body 4 extends so as to surround a predetermined region 3a of the cover glass 3. Here, the predetermined region 3a means the light transmission region, that is, the region necessary for camera imaging by the optical sensor 1 (camera field of view).

[0024] In the example shown in Figure 2, the predetermined region 3a is rectangular in shape, and the piezoelectric element 4 is provided to surround the predetermined region 3a. Electrode 13a is provided to surround the upper half of the predetermined region 3a, and electrode 13b is provided to surround the lower half of the predetermined region 3a. Electrodes 13a and 13b are, for example, U-shaped. A feedback electrode 14 is provided between one end of electrode 13a and one end of electrode 13b. A ground electrode 15 is provided between the other end of electrode 13a and the other end of electrode 13b. Electrodes 13a, 13b, the feedback electrode 14, and the ground electrode 15 are electrically insulated from each other.

[0025] As shown in Figure 3(a), near the feedback electrode 14, the piezoelectric element 4 has driving regions 16a, 16b and a non-driving region 17a. The driving regions 16a, 16b and the non-driving region 17a are all polarized in the thickness direction (Z direction) (the direction of spontaneous polarization is aligned in the thickness direction). In Figure 3, the direction of polarization is represented by "-" and "+" for convenience. The piezoelectric element 4 has a first surface 4a located on the cover glass 3 side and a second surface 4b located on the opposite side of the piezoelectric element 4 from the first surface 4a, with the side of the first surface 4a being "+" and the side of the second surface 4b being "-". Here, the direction of polarization of the driving region 16a and the direction of polarization of the driving region 16b are the same, and the direction of polarization of the non-driving region 17a is the same as the direction of polarization of the driving regions 16a and 16b.

[0026] In the extending direction (X direction) of the piezoelectric element 4, the non-driving region 17a is located between the driving region 16a and the driving region 16b. In the driving regions 16a and 16b, the electrode 13a is provided on the second surface 4b, and the ground electrode 15 is provided on the first surface 4a. In the non-driving region 17a, the feedback electrode 14 is provided on the second surface 4b, and the ground electrode 15 is provided on the first surface 4a. The ground electrode 15 is located on the opposite side of the piezoelectric element 4 from the electrodes 13a, 13b and the feedback electrode 14. The ground electrode 15 of the piezoelectric resonator 12 is fixed to the cover glass 3 via an adhesive layer 18.

[0027] As shown in Figures 3(b) and 3(c), the piezoelectric element 4 has a non-driven region 17b that is not polarized. In the direction of extension of the piezoelectric element 4 (X direction), the non-driven region 17b is located between the driven region 16a and the driven region 16b. In the non-driven region 17b, a portion of the ground electrode 15 extends from the side of the first surface 4a to the side of the second surface 4b, wrapping around the end of the piezoelectric element 4. The cross-sectional shape of the ground electrode 15 in the non-driven region 17b is, for example, U-shaped. The extension of the ground electrode 15 to the side of the second surface 4b allows connection to the control device 11 on the side of the second surface 4b.

[0028] In the portion surrounding the upper half of a predetermined area 3a of the cover glass 3, the piezoelectric element 4 extends in the X direction, and in this portion, as shown in Figure 3(d), the piezoelectric element 4 has a drive region 16a. The drive region 16a is the same as that shown in Figure 3(a). In the drive region 16a, the ground electrode 15 is formed on the first surface 4a, and the electrode 13a is formed on the second surface 4b. Although not shown, in the portion surrounding the lower half of the predetermined area 3a of the cover glass 3, the piezoelectric element 4 has the same structure as that shown in Figure 3(d).

[0029] Next, the operation of the foreign object removal device 10 will be described. As shown in Figure 2, the control device 11 is connected to electrodes 13a and 13b of the piezoelectric vibrator 12 via a drive signal line, and to the feedback electrode 14 of the piezoelectric vibrator 12 via a detection signal line. The control device 11 is also connected to the ground electrode 15 of the piezoelectric vibrator 12 via a ground line. The ground line is branched and connected to the ground. The control device 11 controls the drive of the piezoelectric vibrator 12.

[0030] Figure 5 illustrates an example of drive control for the piezoelectric vibrator 12. Figure 5 shows the waveform of the drive signal 11a, which is the drive voltage (AC voltage) used to drive the piezoelectric vibrator 12. The vertical axis represents amplitude, and the horizontal axis represents time. Note that the waveform shown is a schematic representation and does not represent the actual waveform.

[0031] As shown in Figure 5, the control device 11 drives the piezoelectric vibrator 12 in a first vibration mode during period T1 and drives the piezoelectric vibrator 12 in a second vibration mode during period T2. In the first vibration mode, i.e., during period T1, the control device 11 supplies a drive signal 11a, which is a first drive voltage (AC voltage) having a frequency corresponding to the combined resonant frequency of the piezoelectric vibrator 12 and the cover glass 3, to the electrodes 13a and 13b of the piezoelectric body 4. In the second vibration mode, i.e., during period T2, the control device 11 supplies a drive signal 11a, which is a second drive voltage (AC voltage) having a frequency corresponding to the resonant frequency unique to the piezoelectric vibrator 12, to the electrodes 13a and 13b of the piezoelectric body 4. The combined resonant frequency depends on the structure of the piezoelectric vibrator 12, the rigidity of the cover glass 3, the bonding structure between the piezoelectric vibrator 12 and the cover glass 3, etc., but in this embodiment, it is set to 950 kHz, for example. The inherent resonant frequency of the piezoelectric vibrator 12 depends on the structure of the piezoelectric vibrator 12 (thickness, size, shape, material, etc.), but in this embodiment, it is set to 1.6 MHz, for example.

[0032] The control device 11 alternately repeats driving by a first vibration mode (period T1) and driving by a second vibration mode (period T2). In the first vibration mode, rainwater, snow, dust, insects, and other foreign matter adhering to the cover glass 3 can be removed from a predetermined area 3a by causing them to drip and flow due to the vibration generated on the surface of the cover glass 3. The effective range of the first vibration mode (the area in which the vibration generated by the resonance between the piezoelectric vibrator 12 and the cover glass 3 is effective) is relatively wide because it is a vibration caused by the resonance of the cover glass 3 itself. By using multiple piezoelectric vibrators 12 to coordinately generate resonance between the piezoelectric vibrators 12 and the cover glass 3, a wider and larger vibration can be achieved. On the other hand, in the second vibration mode, ice, snow, dust, insects, and other foreign matter firmly adhering to the cover glass 3 can be lifted from the surface of the cover glass 3 by the vibration generated by the piezoelectric vibrator 12, making them flowable. Furthermore, water droplets directly above can be atomized and removed by the vibration of the piezoelectric vibrator 12. The effective range of the second vibration mode (the region in which the vibrations generated by the piezoelectric vibrator 12 have an effective effect) is effectively limited to the region directly above the piezoelectric body 4 and its adjacent regions. Applying a larger voltage can broaden the effective range of the second vibration mode, but in that case, the load on the piezoelectric body 4 will increase, and there is a high risk of overheating and fracture. Furthermore, by adjusting the first and second vibration modes, and periods T1 and T2, it is possible to control the self-heating of the piezoelectric vibrator 12 and liquefy the ice and snow adhering to the surface of the cover glass 3 to increase its fluidity.

[0033] According to the drive control of the piezoelectric vibrator 12 shown in Figure 5, by alternately repeating the first vibration mode and the second vibration mode, foreign matter (water droplets, ice and snow, dust, insects, etc.) adhering to a predetermined area 3a of the cover glass 3 can be efficiently removed by applying different types of vibrations, causing it to float and flow.

[0034] Furthermore, the second vibration mode is more prone to self-heating due to internal friction in the piezoelectric vibrator 12 than the first vibration mode. Therefore, if the second vibration mode is performed for a long period of time, there is a risk that the piezoelectric vibrator 12 may be damaged due to overheating. According to the drive control described above, the second vibration mode is performed only during period T2, and not during period T1. By performing the second vibration mode intermittently in this way, damage to the piezoelectric vibrator 12 due to overheating can be suppressed. In the drive control of the piezoelectric vibrator described in Figure 5, the first vibration mode and the second vibration mode are performed alternately without interruption, but a pause period in which neither drive signal 11a is applied may be provided.

[0035] Furthermore, the inherent resonant frequency of the piezoelectric vibrator 12 varies depending on its structure (thickness, size, shape, material, etc.), and the combined resonant frequency varies depending on the structure of the piezoelectric vibrator 12, the rigidity of the cover glass 3, and the bonding structure between the piezoelectric vibrator 12 and the cover glass 3. In addition, these resonant frequencies and combined resonant frequencies may change due to the self-heating effect of the piezoelectric vibrator 12. In the foreign matter removal device 10 of this embodiment, if the resonant frequency or combined resonant frequency differs from the set value (1.6 MHz or 950 kHz), the control device 11 adjusts the frequency of the driving voltage of the piezoelectric vibrator 12 using the feedback electrode 14. The adjustment of the driving voltage using the feedback electrode 14 will be described in detail below.

[0036] In the piezoelectric vibrator 12, the feedback electrode 14 outputs a detection signal 11b that indicates a voltage change corresponding to the expansion and contraction (vibration) of the piezoelectric body 4, i.e., a change in the magnitude of the voltage, and / or the period (frequency) of the voltage displacement. For example, in the structure shown in Figure 3(a), the drive regions 16a and 16b adjacent to both sides of the non-drive region 17a expand and contract in the thickness direction (Z direction) in response to the drive signal 11a. The drive regions 16a and 16b alternately repeat a contracted state and an extended state, and the cover glass 3 vibrates accordingly. Pressure is applied to the non-drive region 17a in response to the expansion and contraction of these drive regions 16a and 16b and the vibration of the cover glass 3. As a result, the non-drive region 17a also alternately repeats a contracted state and an extended state. In the non-drive region 17a, when it is contracted, a positive charge is generated on one side of the non-drive region 17a and a negative charge is generated on the other side, and when it is extended, charges with the opposite positive and negative charges are generated on both sides of the non-drive region 17a compared to the contracted state. These positive and negative charge generation correspond to the expansion and contraction of the drive regions 16a and 16b and the vibration of the cover glass 3. Therefore, the feedback electrode 14 provided in the non-drive region 17a outputs a detection signal 11b that indicates a voltage change corresponding to the expansion and contraction of the drive regions 16a and 16b. When the temperature of the piezoelectric vibrator 12 has not risen excessively, the frequency of the vibration waveform of the piezoelectric vibrator 12 (drive regions 16a and 16b) is approximately the same as the frequency of the drive signal 11a, and the frequency of the detection signal 11b is approximately the same as the frequency of the drive signal 11a.

[0037] In the first vibration mode (period T1), the control device 11 applies a first drive voltage (drive signal 11a in period T1), which is either pre-set or determined by learning, to the electrodes 13a and 13b of the piezoelectric element 4, while adjusting the frequency of the first drive voltage so that the amplitude of the detection signal 11b output from the feedback electrode 14 is maximized. This makes it possible to vibrate the piezoelectric vibrator 12 and the cover glass 3 at the actual combined resonant frequency of the piezoelectric vibrator 12 and the cover glass 3 at that time, even if the resonant frequency of the piezoelectric vibrator 12 and the cover glass 3 at that time deviates from the set value (in this case, 950 kHz).

[0038] Furthermore, in the second vibration mode (period T2), the control device 11 applies a second drive voltage (drive signal 11a in period T2), which is either pre-set or determined by learning, to the electrodes 13a and 13b of the piezoelectric element 4, while adjusting the frequency of the second drive voltage so that the amplitude of the detection signal 11b output from the feedback electrode 14 is maximized. This makes it possible to vibrate the piezoelectric vibrator 12 at the actual resonant frequency of that moment, even if the actual resonant frequency of the piezoelectric vibrator 12 at that moment deviates from the set value (in this case, 1.6 MHz). In the above explanation, the frequencies of the first drive voltage and the second drive voltage were adjusted to vibrate at the actual combined resonant frequency of the piezoelectric vibrator 12 and the cover glass 3, and the actual resonant frequency of the piezoelectric vibrator 12 at that moment, respectively. However, the magnitudes of the first drive voltage and the second drive voltage can also be adjusted as needed.

[0039] Figure 6 is a block diagram showing an adjustment circuit for adjusting the frequency of the drive voltage. As shown in Figure 6, the adjustment circuit 20 includes a control unit 21, an amplitude detection unit 22, and a drive signal generation unit 23. The drive signal generation unit 23 generates a drive signal 11a and adjusts the frequency of the drive signal 11a based on a control signal from the control unit 21. The amplitude detection unit 22 detects the amplitude of the detection signal 11b output from the feedback electrode 14 and outputs a detection signal indicating the detected value to the control unit 21. The control unit 21 controls the adjustment operation of the frequency of the drive signal 11a in the drive signal generation unit 23 so that the amplitude value of the detection signal 11b detected by the amplitude detection unit 22 is maximized.

[0040] For example, in the first vibration mode, the control unit 21 changes the frequency of the drive signal 11a within a predetermined frequency range, with upper and lower limits set based on a preset value (950 kHz) that is either pre-set or learned and set by a learning unit (not shown). The control unit 21 determines the frequency at which the amplitude value of the detection signal 11b detected by the amplitude detection unit 22 is maximum as the combined resonance frequency of the piezoelectric vibrator 12 and the cover glass 3. The control unit 21 then changes the frequency of the drive signal 11a to achieve the determined combined resonance frequency. This process of determining the combined resonance frequency is performed at predetermined time intervals.

[0041] Furthermore, in the second vibration mode, the control unit 21 changes the frequency of the drive signal 11a within a predetermined frequency range, with upper and lower limits set based on a preset value (1.6 MHz) that is either pre-set or learned and set by a learning unit (not shown). The control unit 21 determines the frequency at which the amplitude value of the detection signal 11b detected by the amplitude detection unit 22 is maximum as the intrinsic resonant frequency of the piezoelectric vibrator 12. The control unit 21 then changes the frequency of the drive signal 11a to match the determined resonant frequency. This resonant frequency determination process is performed at predetermined time intervals.

[0042] In the adjustment circuit 20 shown in Figure 6, the amplitude detection unit 22 can be replaced with an amplitude and frequency detection unit that detects the frequency in addition to the amplitude of the detection signal 11b output from the feedback electrode 14. In this case, the control unit 21 controls the frequency adjustment operation of the drive signal generation unit 23 so that the detected amplitude value of the amplitude and frequency detection unit is maximized.

[0043] For example, in the first vibration mode, the control unit 21 changes the frequency of the drive signal 11a within a predetermined frequency range, determines the frequency at which the detected amplitude of the detection signal 11b is maximum as the combined resonance frequency of the piezoelectric vibrator 12 and the cover glass 3, and changes the frequency of the drive signal 11a to match the determined combined resonance frequency. In the second vibration mode, the control unit 21 changes the frequency of the drive signal 11a within a predetermined frequency range, determines the frequency at which the detected amplitude of the detection signal 11b is maximum as the intrinsic resonance frequency of the piezoelectric vibrator 12, and changes the frequency of the drive signal 11a to match the determined resonance frequency.

[0044] As described above, frequency adjustment using the feedback electrode 14 makes it possible to vibrate the piezoelectric vibrator 12 at the actual combined resonant frequency or resonant frequency even if the set value of the frequency of the drive signal 11a differs from the actual combined resonant frequency or resonant frequency. This allows for the generation of vibrations suitable for the surface of the cover member, without being affected by the shape of the cover glass 3, i.e., the cover member, and enables efficient removal of foreign matter. Furthermore, if the frequency adjustment range based on the feedback electrode 14 increases rapidly, this can be judged as the piezoelectric vibrator 12 being in an overheating state, and the period T2 of the second vibration mode can be shortened, or, in some cases, the application of the drive signal 11a can be stopped to allow for a cooling time and suppress fracture due to self-heating of the piezoelectric vibrator 12.

[0045] In the drive control of the piezoelectric vibrator 12 of the foreign matter removal device 10 of this embodiment, the following modifications are possible. The control device 11 alternately repeats driving by a first vibration mode (period T1) and driving by a second vibration mode (period T2). The period of this alternating repetition is preferably determined in consideration of the effectiveness of foreign matter removal, but it is preferable that it matches or is close to the intrinsic resonant frequency (period) of the cover glass 3. By setting this alternating repetition period near the intrinsic resonant frequency of the cover glass 3, it becomes possible to excite the resonance of the cover member, and the combination of multiple vibrations on the cover glass 3 provides a more efficient effect in lifting and flowing away even firmly attached foreign matter from the surface of the cover glass 3 for removal. The intrinsic resonant frequency of the cover glass 3 is greatly influenced by the structure of the cover glass 3 (thickness, size, shape, material, etc.) and the state of fixation, but here, for example, it is within the frequency range of 200 to 800 Hz.

[0046] Figure 7 illustrates another example of drive control for the piezoelectric vibrator 12. In Figure 7, (a) shows the waveform of the drive signal 11a-1, which is the first drive voltage (AC voltage) for driving the piezoelectric vibrator 12, and (b) shows the waveform of the drive signal 11a-2, which is the second drive voltage (AC voltage) for driving the piezoelectric vibrator 12. The vertical axis represents amplitude, and the horizontal axis represents time. Note that the waveforms shown are schematic representations and do not represent actual waveforms.

[0047] As shown in Figure 7(a), the control device 11 drives the piezoelectric vibrator 12 in a first vibration mode. In the first vibration mode, the control device 11 supplies a drive signal 11a-1, which is a first drive voltage (AC voltage) having a frequency corresponding to the combined resonant frequency of the piezoelectric vibrator 12 and the cover glass 3, to the electrodes 13a and 13b of the piezoelectric body 4. In this embodiment as well, the combined resonant frequency of the piezoelectric vibrator 12 and the cover glass 3 is, for example, 950 kHz. The drive signal 11a-1 is supplied during periods T1 and T2. That is, the drive signal 11a-1 is supplied continuously.

[0048] Furthermore, as shown in Figure 7(b), the control device 11 drives the piezoelectric vibrator 12 in a second vibration mode. In the second vibration mode, the control device 11 supplies a drive signal 11a-2, which is a second drive voltage (AC voltage) having a frequency corresponding to the intrinsic resonant frequency of the piezoelectric vibrator 12, to the electrodes 13a and 13b of the piezoelectric body 4. In this embodiment as well, the intrinsic resonant frequency of the piezoelectric vibrator 12 is, for example, 1.6 MHz. The drive signal 11a-2 is supplied during period T1 and not during period T2. That is, the drive signal 11a-2 is supplied intermittently.

[0049] In period T1 of this embodiment, the first vibration mode (drive signal 11a-1) and the second vibration mode (drive signal 11a-2) are superimposed and applied to the piezoelectric vibrator 12 within the drive signal generation unit 23. In other words, a combined drive signal of drive signal 11a-1 (950 kHz in this case) and drive signal 11a-2 (1.6 MHz in this case) is applied, resulting in a complex and strong combined waveform of vibrations generated in the piezoelectric vibrator 12. Therefore, foreign matter such as rainwater, ice and snow, dust and insects firmly attached to the cover glass 3 can be lifted more efficiently from the glass surface. Then, in period T2, drive signal 11a-2 is stopped and only drive signal 11a-1 vibrates, so the foreign matter that has been lifted from the cover glass 3 and made easily flowable in period T1 is flowed out of the predetermined area 3a and removed.

[0050] According to the drive control shown in Figure 7, the second vibration mode is intermittently superimposed on the first vibration mode. This generates complex and strong vibrations on the surface of the cover glass 3, i.e., the cover member, making it possible to remove foreign matter (water droplets, ice and snow, dust, insects, etc.) that is firmly attached to a predetermined area 3a. By superimposing the second vibration mode on the first vibration mode, effective vibrations can be achieved, and the application time of the second vibration mode, which is prone to generating heat due to internal friction in the piezoelectric vibrator 12, can be shortened. Therefore, damage to the piezoelectric vibrator 12 and damage to the adhesive layer 18 that fixes the piezoelectric vibrator 12 to the cover glass 3 can be suppressed.

[0051] In this embodiment as well, during periods T1 and T2, the control device 11 applies drive signal 11a-1 and a combined drive signal of drive signal 11a-1 and drive signal 11a-2 to electrodes 13a and 13b, while monitoring the detection signal 11b output from the feedback electrode 14. The control device 11 adjusts the frequency and / or voltage magnitude of drive signal 11a-1 and / or drive signal 11a-2 so that the amplitude of each detection signal 11b is maximized. The adjustment of drive signal 11a-1 and drive signal 11a-2 can be achieved with the adjustment circuit described in the first embodiment. Of course, while adjusting to maximize the amplitude of the detection signal 11b, the frequency, voltage amplitude, and application time are also adjusted to prevent the piezoelectric vibrator 12 from overheating and being damaged.

[0052] In the drive control of this embodiment, the following modifications are possible. The control device 11 intermittently superimposes a drive using a second vibration mode (period T1) on the drive using a first vibration mode (periods T1 and T2...). The period of this superposition is preferably determined in consideration of the effectiveness of removing foreign matter, but it is preferable that it matches or is close to the intrinsic resonant frequency (period) of the cover glass 3. By setting this superposition period near the intrinsic resonant frequency of the cover glass 3, it becomes possible to excite the resonance of the cover member, and the combination of multiple vibrations on the cover glass 3 provides a more efficient effect in lifting and flowing away the attached foreign matter from the surface of the cover glass 3 for removal. The intrinsic resonant frequency of the cover glass 3 is greatly influenced by the structure of the cover glass 3 (thickness, size, shape, material, etc.) and its fixing state, but here, for example, it is within the frequency range of 200 to 800 Hz.

[0053] (Second embodiment) Figure 8 is a schematic diagram showing the configuration of a foreign matter removal device according to a second embodiment of the present invention. The foreign matter removal device 10A of this embodiment is equipped with two piezoelectric vibrators 12A and 12B instead of the piezoelectric vibrator 12, and in this respect it differs from the foreign matter removal device 10 of the first embodiment. Components that are the same as those in the foreign matter removal device 10 are denoted by the same reference numerals, and detailed descriptions are omitted.

[0054] The piezoelectric vibrator 12A has basically the same configuration as the lower portion of the piezoelectric vibrator 12 shown in Figure 2 (the region surrounding the lower half of the predetermined region 3a), but has a feedback electrode 14a in the middle portion of the part extending in the Y direction. The piezoelectric vibrator 12A can be called the first piezoelectric vibrator. The piezoelectric vibrator 12B has basically the same configuration as the upper portion of the piezoelectric vibrator 12 shown in Figure 2 (the region surrounding the upper half of the predetermined region 3a), but has a feedback electrode 14b in the middle portion of the part extending in the Y direction. The piezoelectric vibrator 12B can be called the second piezoelectric vibrator. The piezoelectric vibrators 12A and 12B can be driven independently of each other. The feedback electrodes 14a and 14b have basically the same structure as the feedback electrode 14 shown in Figure 2.

[0055] In the foreign matter removal device 10A, the control device 11 is connected to the electrode 13b of the piezoelectric vibrator 12A via a first drive signal line and to the electrode 13a of the piezoelectric vibrator 12B via a second drive signal line. In the figure, the two electrodes 13a are connected with a single first drive signal line, but the first drive signal line may be split into two and connected to each electrode 13a. The same applies to the second drive signal line. The control device 11 is also connected to the feedback electrode 14a of the piezoelectric vibrator 12A via a first detection signal line and to the feedback electrode 14b of the piezoelectric vibrator 12B via a second detection signal line. Furthermore, the control device 11 is connected to the ground electrode 15 via a ground line. The ground line is branched and connected to the ground. The control device 11 controls the driving of the piezoelectric vibrators 12A and 12B.

[0056] In the foreign matter removal device 10A, the piezoelectric vibrators 12A and 12B may be subjected to the same drive control, or they may be subjected to different drive control. They can also be controlled cooperatively after being subjected to different drive control. As an example of cooperative control, the frequencies of the drive signals applied to piezoelectric vibrators 12A and 12B may be set to be out of phase with respect to one of them, or a second vibration mode may be applied to piezoelectric vibrator 12B when a first vibration mode is applied to piezoelectric vibrator 12A. However, for cooperative control, it is necessary to select an appropriate cooperative control according to the shape of the piezoelectric vibrators and the structure of the cover glass 3 (thickness, size, shape, material, etc.).

[0057] (Third embodiment) Figure 9 is a schematic diagram showing the configuration of a foreign matter removal device according to a third embodiment of the present invention. Figure 10 is a schematic cross-sectional view showing the cross-sectional structure of a piezoelectric vibrator constituting the foreign matter removal device shown in Figure 9. In Figure 10, (a) is a cross-sectional view along line AA, and (b) is a cross-sectional view along line BB. In Figures 9 and 10, the illustrated components are depicted schematically and do not differ from their actual size (thickness, width, etc.).

[0058] Referring to Figures 9 and 10, the foreign object removal device 10B includes a piezoelectric vibrator 12C and a control device 11 that controls the driving of the piezoelectric vibrator 12C. The piezoelectric vibrator 12C is mounted on a cover glass 3 that protects the optical sensor 1 shown in Figure 4.

[0059] The piezoelectric vibrator 12C has the same structure as the piezoelectric vibrator 12 described in the first embodiment, except that the polarity directions of the drive region 16a and the drive region 16b are different from each other, and the drive region 16a and the drive region 16b are alternately arranged along the outer circumference of a predetermined region 3a. Below, the structure that differs from the first embodiment will be described, and the description of the same structure will be omitted.

[0060] As shown in Figure 10(a), near the feedback electrode 14, the driving regions 16a, 16b, and non-driving region 17a are all polarized in the thickness direction (Z direction). The polarization direction of the driving region 16a is "+" on the side of the first surface 4a and "-" on the side of the second surface 4b. The polarization direction of the driving region 16b is "-" on the side of the first surface 4a and "+" on the side of the second surface 4b. The polarization direction of the non-driving region 17a is "-" on the side of the first surface 4a and "+" on the side of the second surface 4b. In the direction of extension of the piezoelectric element 4 (X direction), the non-driving region 17a is located between the driving region 16a and the driving region 16b.

[0061] As shown in Figure 10(b), a non-driven region 17b that is not polarized is provided between the driven regions 16a and 16b in the vicinity of the ground electrode 15. The polarization direction of the driven region 16a is "+" on the side of the first surface 4a and "-" on the side of the second surface 4b. The polarization direction of the driven region 16b is "-" on the side of the first surface 4a and "+" on the side of the second surface 4b.

[0062] In the portion surrounding the upper half of a predetermined area 3a of the cover glass 3, the piezoelectric element 4 extends in the Y direction, and in this portion, drive regions 16a and drive regions 16b are arranged alternately. Similarly, in the portion surrounding the lower half of a predetermined area 3a of the cover glass 3, the piezoelectric element 4 extends in the Y direction, and in this portion, drive regions 16a and drive regions 16b are arranged alternately. Electrodes 13a are provided for each drive region 16a, and electrodes 13b are provided for each drive region 16b.

[0063] The control device 11 is connected to the electrodes 13a of each drive region 16a and the electrodes 13b of each drive region 16b via drive signal lines, and is connected to the feedback electrode 14 via detection signal lines. The control device 11 is connected to the ground electrode 15 via a ground line. The ground line is branched and connected to ground.

[0064] The control device 11 supplies the drive signal 11a shown in Figure 5 to the electrodes 13a and 13b of the piezoelectric vibrator 12C. The control device 11 drives the piezoelectric vibrator 12C in the first vibration mode during period T1, and drives the piezoelectric vibrator 12C in the second vibration mode during period T2. The control device 11 alternately repeats driving in the first vibration mode (period T1) and driving in the second vibration mode (period T2). At this time, adjacent piezoelectric bodies 4 with different polarization directions will each undergo different expansion and contraction movements, thus exciting more complex vibrations depending on the direction in which the piezoelectric vibrator 12C of the cover glass 3 extends.

[0065] According to the foreign matter removal device 10B of this embodiment, in addition to the same effects as in the first embodiment, by exciting complex vibrations in the direction in which the piezoelectric vibrator 12C of the cover glass 3 extends, foreign matter such as rainwater, ice and snow, dust and insects that are firmly attached to the cover glass 3 can be lifted more efficiently from the glass surface. Furthermore, in this embodiment as well, the modifications described in the first or second embodiment can be applied.

[0066] (Fourth embodiment) Figure 11 is a schematic diagram showing the configuration of a foreign matter removal device according to a fourth embodiment of the present invention. In Figure 11, the illustrated components are depicted schematically and do not differ from their actual size (thickness, width, etc.).

[0067] The foreign matter removal device 10C of this embodiment has the same structure as the foreign matter removal device 10B of the third embodiment, except that it uses drive signals 11a-1 and 11a-2 instead of drive signal 11a. The following describes the structure that differs from the third embodiment, and the description of the same structure is omitted.

[0068] The control device 11 is connected to each electrode 13a of the piezoelectric vibrator 12C via a first drive signal line, and to each electrode 13b of the piezoelectric vibrator 12C via a second drive signal line. In the diagram, for convenience, the electrode labeled (-) is electrode 13a, and the electrode labeled (+) is electrode 13b. These (-) and (+) indicate the polarization direction of the piezoelectric body 4. The control device 11 is also connected to the feedback electrode 14 of the piezoelectric vibrator 12C via a detection signal line. Furthermore, the control device 11 is connected to the ground electrode 15 via a ground line. The ground line is branched and connected to the ground. The control device 11 performs drive control of the piezoelectric vibrator 12C.

[0069] The control device 11 drives each drive region 16a of the piezoelectric vibrator 12C in the first vibration mode shown in Figure 7(a). Specifically, it supplies a drive signal 11a-1 to each electrode 13a of the piezoelectric vibrator 12C. The drive signal 11a-1 is supplied during periods T1 and T2. In other words, the drive signal 11a-1 is supplied continuously.

[0070] Furthermore, the control device 11 drives each drive region 16b of the piezoelectric vibrator 12C in the second vibration mode shown in Figure 7(b). Specifically, it supplies drive signals 11a-2 to each electrode 13b of the piezoelectric vibrator 12C. The drive signals 11a-2 are supplied during period T1, and not during period T2. In other words, the drive signals 11a-2 are supplied intermittently.

[0071] In the foreign matter removal device 10C of this embodiment, each drive region 16a of the piezoelectric vibrator 12C is continuously driven in the first vibration mode, and each drive region 16b of the piezoelectric vibrator 12C is intermittently driven in the second vibration mode. As a result, during period T1, the first vibration mode and the second vibration mode are combined on the surface of the cover glass 3, forming a complex and strong combined waveform in a predetermined region 3a. This makes it possible to efficiently remove foreign matter (water droplets, ice and snow, dust, insects, etc.) that is firmly attached to the predetermined region 3a, and during period T2, the drive region 16b is stopped, so damage due to overheating of the piezoelectric vibrator 12C or damage to the adhesive layer 18 that fixes the piezoelectric vibrator 12C to the cover glass 3 can be suppressed.

[0072] Furthermore, in the drive control of this embodiment, the first vibration mode and the second vibration mode may be periodically switched. In that case, the load on the drive regions 16a and 16b can be leveled, which can be expected to extend the lifespan of the piezoelectric vibrator 12C. Furthermore, in this embodiment as well, the modifications described in the first or second embodiment can be applied.

[0073] In each of the embodiments described above, the shape of the piezoelectric vibrators 12, 12A to 12C attached to the cover glass 3 is not limited to the illustrated shape. Furthermore, although the embodiments described above were explained using cover glass used for optical sensors such as cameras, they can of course also be applied to electromagnetic wave sensors and the like using cover members that do not transmit light. Below, variations of the piezoelectric vibrators 12, 12A to 12C will be described.

[0074] (Variation 1) Figure 12 is a schematic diagram showing a first modified example of a piezoelectric vibrator. As shown in Figure 12, when a predetermined region 3a of the cover glass 3 is circular in shape, the piezoelectric vibrator 12A is formed in a circular shape along the circumferential direction. The electrodes 13a of the driving region 16a and the electrodes 13b of the driving region 16b are arranged alternately in the circumferential direction. Similar to piezoelectric vibrator 12A, the other piezoelectric vibrators 12, 12B, and 12C can also be formed in a circular shape so as to surround a predetermined region 3a.

[0075] (Modification 2) Figure 13 is a schematic diagram showing a second modified example of a piezoelectric vibrator with feedback. As shown in Figure 13, a predetermined region 3a of the cover glass 3 is rectangular in shape, and two piezoelectric vibrators 12 are arranged above and below the predetermined region 3a. Each piezoelectric vibrator 12 is formed in a straight line. Note that the piezoelectric vibrators 12 may be provided on only one side, either the upper or lower side. This second modified example can also be applied to the other piezoelectric vibrators 12A to 12C.

[0076] (Variation 3) Figure 14 is a schematic diagram showing a third modified example of the piezoelectric vibrator. As shown in Figure 13, a predetermined region 3a of the cover glass 3 is rectangular in shape, and two piezoelectric vibrators 12 are arranged on the left and right sides of the predetermined region 3a. Each piezoelectric vibrator 12 is formed in a straight line. Note that the piezoelectric vibrators 12 may be provided on only one side, either the left or the right. This third modified example can also be applied to the other piezoelectric vibrators 12A to 12C.

[0077] (Modification 4) Figure 15 is a schematic diagram showing a fourth modified example of the piezoelectric vibrator. As shown in Figure 14, a predetermined region 3a of the cover glass 3 is circular in shape, and the piezoelectric vibrator 12 is arranged so as to sandwich the predetermined region 3a. The piezoelectric vibrator 12 has an upper piezoelectric vibrator section 12-1 and a lower piezoelectric vibrator section 12-2. In the piezoelectric vibrator section 12-1, the electrode 13a of the drive region 16a and the electrode 13b of the drive region 16b are provided along the circumferential direction, and the feedback electrode 14 of the non-drive region 17a is positioned between the electrode 13a and the electrode 13b. In the piezoelectric vibrator section 12-2, the electrode 13a of the drive region 16a and the electrode 13b of the drive region 16b are provided along the circumferential direction, and the ground electrode 15 of the non-drive region 17b is positioned between the electrode 13a and the electrode 13b. Although not shown in the diagram, ground electrodes 15 are formed on the first surface 4a of both the piezoelectric resonator section 12-1 and the piezoelectric resonator section 12-2, and each ground electrode 15 is electrically connected. This fourth modification can also be applied to the other piezoelectric vibrators 12A to 12C.

[0078] The above-described modifications 1 to 4 are examples, and the present invention is not limited to these modifications. For example, three or more piezoelectric vibrators may be arranged to surround a predetermined area 3a of the cover glass 3. In this case, the first vibration mode and the second vibration mode may be performed alternately for each piezoelectric vibrator. Alternatively, at least one piezoelectric vibrator may be driven in the first vibration mode, and the remaining piezoelectric vibrators may be driven in the second vibration mode. [Explanation of Symbols]

[0079] 1 Optical sensor 2 cabinets 3. Cover glass 4 Piezoelectric element 10 Foreign matter removal device 11 Control device 11a Drive signal 11b Detection signal 12 Piezoelectric vibrator 13a, 13b electrode 14 Feedback electrodes 15 Ground electrode 16a, 16b drive area 17a, 17b Non-driven region

Claims

1. A method for removing foreign matter from a sensor, comprising: providing at least one piezoelectric vibrator so as to surround a predetermined area of ​​a cover member of an optical sensor or an electromagnetic wave sensor; the piezoelectric vibrator comprises a piezoelectric body polarized in the thickness direction with electrodes provided on both sides; and generating vibration in the predetermined area by applying an AC driving voltage to the piezoelectric body via the electrodes; A method for removing foreign matter from a sensor, characterized by applying a combination of a first drive voltage having a frequency corresponding to the combined resonant frequency of the piezoelectric vibrator and the cover member, and a second drive voltage having a frequency corresponding to the resonant frequency unique to the piezoelectric vibrator, to the piezoelectric body of the piezoelectric vibrator.

2. The method for removing foreign matter from a sensor according to claim 1, wherein the piezoelectric vibrator further comprises at least one feedback electrode for detecting a voltage change that occurs in accordance with the expansion and contraction of the piezoelectric body.

3. The method for removing foreign matter from a sensor according to claim 2, wherein the piezoelectric vibrator adjusts the piezoelectric vibrator to change the frequency and / or voltage of the first driving voltage applied to the piezoelectric body within a predetermined range based on information of voltage change obtained from the feedback electrode, so that the amplitude of expansion and contraction of the piezoelectric vibrator in the thickness direction is maximized.

4. The method for removing foreign matter from a sensor according to claim 2, wherein the piezoelectric vibrator adjusts the piezoelectric vibrator to maximize the amplitude of expansion and contraction in the thickness direction by changing the frequency and / or voltage of the second driving voltage applied to the piezoelectric body within a predetermined range based on information of voltage change obtained from the feedback electrode.

5. A sensor foreign matter removal device using the sensor foreign matter removal method described in claim 1 or 2.

6. A method for removing foreign matter from a sensor according to claim 1 or 2, wherein the combination of a first drive voltage having a frequency corresponding to the combined resonant frequency of the piezoelectric vibrator and the cover member and a second drive voltage having a frequency corresponding to the resonant frequency inherent to the piezoelectric vibrator, applied to the piezoelectric body of the piezoelectric vibrator, includes repeatedly applying the first drive voltage and the second drive voltage alternately.

7. A sensor foreign matter removal device using the sensor foreign matter removal method described in claim 6.

8. A method for removing foreign matter from a sensor according to claim 1 or 2, wherein the combination of a first drive voltage having a frequency corresponding to the combined resonant frequency of the piezoelectric vibrator and the cover member and a second drive voltage having a frequency corresponding to the resonant frequency inherent to the piezoelectric vibrator, applied to the piezoelectric body of the piezoelectric vibrator, includes intermittently applying the second drive voltage in superimposed on the first drive voltage.

9. A sensor foreign matter removal device using the sensor foreign matter removal method described in claim 8.

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