Ultrasonic sensor and obstacle detection system

Abstract

To provide an ultrasonic sensor and an obstacle detection system capable of changing directivity after being fixed.SOLUTION: The ultrasonic sensor 100 includes the piezoelectric elements 3, the first electrodes 2 provided on the first surfaces of the piezoelectric elements 3, the second electrodes 1a provided on the second surfaces of the piezoelectric elements 3 and sandwiching a portion of the piezoelectric elements 3 with the first electrodes 2, and the third electrodes 1b provided on the second surfaces of the piezoelectric elements 3 and sandwiching another portion of the piezoelectric elements 3 with the first electrodes 2.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to ultrasonic sensors and obstacle detection systems. [Background technology]

[0002] Conventionally, ultrasonic systems have been known that measure the distance to an obstacle by generating ultrasonic waves and measuring the time it takes for the reflected waves from the obstacle to return, thereby detecting the obstacle. Such ultrasonic systems are often installed in vehicles, and an example of such an ultrasonic system is known as an in-vehicle clearance sonar. JP 2023-31336 A (Patent Document 1) discloses an example of such an ultrasonic system. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2023-31336

[0004] [overview] Ultrasonic sensors used in ultrasonic systems for detecting obstacles are attached to the front and rear lower parts of a vehicle, and the mounting angle (vertical direction) is important. If the mounting angle is downward, the signal will be reflected by the ground, and if it is upward, the signal will be reflected less from distant obstacles, so it is important to set the angle to an optimum value.

[0005] However, vehicles can tilt due to the number of passengers and luggage on board, and it is difficult to design an installation position that will not cause problems even if such tilting occurs.

[0006] An object of the present disclosure is to provide an ultrasonic sensor that can adjust the direction of ultrasonic waves emitted after the ultrasonic sensor is attached to a vehicle or the like.

[0007] The present disclosure relates to an ultrasonic sensor including a piezoelectric element, a first electrode provided on a first surface of the piezoelectric element, a second electrode provided on a second surface of the piezoelectric element and sandwiching a part of the piezoelectric element between the first electrode and the second surface, and a third electrode provided on the second surface of the piezoelectric element and sandwiching another part of the piezoelectric element between the first electrode and the third electrode. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view showing the configuration of an ultrasonic sensor according to a first embodiment. [Figure 2] 1 is a front view showing the configuration of an ultrasonic sensor according to a first embodiment. [Figure 3] 1 is a block diagram showing a configuration of an ultrasonic sensor according to a first embodiment. [Figure 4] FIG. 1 is a diagram illustrating an example in which an ultrasonic sensor is mounted on a vehicle. [Figure 5] FIG. 1 is a block diagram showing the configuration of an ultrasonic sensor of a study example. [Figure 6] FIG. 1 is a cross-sectional view showing the structure of an ultrasonic sensor of a study example. [Figure 7] FIG. 1 is a diagram showing the correct direction of ultrasound emission. [Figure 8] FIG. 10 illustrates a downwardly shifted firing direction. [Figure 9] FIG. 10 shows an upwardly shifted firing direction. [Figure 10] 10A and 10B are diagrams for explaining a case where the directivity of the ultrasonic sensor is upward. [Figure 11] 10A and 10B are diagrams illustrating a drive signal when the directivity of the ultrasonic sensor is upward. [Figure 12] 10A and 10B are diagrams for explaining a case where the directivity of the ultrasonic sensor is downward. [Figure 13] 10A and 10B are diagrams illustrating a drive signal when the directivity of the ultrasonic sensor is downward. [Figure 14] FIG. 4 is a cross-sectional view showing the configuration of an ultrasonic sensor according to a modified example of the first embodiment. [Figure 15] FIG. 10 is a front view showing the configuration of an ultrasonic sensor according to a modified example of the first embodiment. [Figure 16] FIG. 10 is a block diagram showing the configuration of an obstacle detection system according to a second embodiment. [Figure 17] FIG. 10 is a diagram showing a state in which the firing angle is changed upward in response to the inclination of the vehicle. [Figure 18] FIG. 10 is a diagram showing a state in which the firing angle is changed downward in response to the inclination of the vehicle. [Figure 19] FIG. 10 is a block diagram showing the configuration of an obstacle detection system according to a third embodiment. [Figure 20] FIG. 10 is a diagram showing a state in which ultrasonic waves are emitted upward when the obstacle is high. [Figure 21] FIG. 10 is a diagram showing a state in which ultrasonic waves are emitted downward when the obstacle is high. [Figure 22] FIG. 10 is a diagram showing a state in which ultrasonic waves are emitted upward when the height of the obstacle is low. [Figure 23] FIG. 10 is a diagram showing a state in which ultrasonic waves are emitted downward when the height of an obstacle is low. [Figure 24] 10A and 10B are diagrams illustrating an example of control to alternately change the launch direction. [Figure 25] FIG. 10 is a block diagram showing the configuration of an obstacle detection system according to a fourth embodiment. [Figure 26] 10 is a graph illustrating the relationship between phase difference and temperature. [Figure 27] FIG. 1 is a cross-sectional view of a study example. [Figure 28] FIG. 10 is a cross-sectional view showing the configuration of an ultrasonic sensor according to a fifth embodiment. [Figure 29] FIG. 10 is a front view showing the configuration of the ultrasonic sensor according to the fifth embodiment.

[0009] [Detailed explanation] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and description thereof will not be repeated.

[0010] <First Embodiment> Fig. 1 is a cross-sectional view showing the configuration of the ultrasonic sensor according to the first embodiment, and Fig. 2 is a front view showing the configuration of the ultrasonic sensor according to the first embodiment.

[0011] The ultrasonic sensor 100 of the first embodiment includes a transmitting / receiving element 110, a transmitting / receiving circuit 4, a housing 5, and wirings 6, 7, and 8. The transmitting / receiving element 110 includes a piezoelectric element 3 and electrodes 1a, 1b, and 2.

[0012] Electrode 2 is provided on a first surface of piezoelectric element 3. Electrodes 1a and 1b are provided on a second surface of piezoelectric element 3. The second surface of piezoelectric element 3 is the surface that emits ultrasonic waves and faces the outside of housing 5. The first surface of piezoelectric element 3 is the surface opposite to the second surface and faces the inside of housing 5.

[0013] As shown in Fig. 2, the first and second surfaces of the piezoelectric element 3 are circular, the electrode 2 is circular, and the second electrode 1a and the third electrode 1b are semicircular. The arc portions of the electrodes 1a and 1b are supported by a housing 5. The housing 5 is provided with an opening A1 that exposes a central portion 1ac on the surface of the second electrode 1a opposite the piezoelectric element 3 and a central portion 1bc on the surface of the third electrode 1b opposite the piezoelectric element 3. Two ultrasonic waves with a phase difference are emitted from these central portions.

[0014] Electrode 1a is disposed so as to sandwich a part of piezoelectric element 3 between electrode 1a and electrode 2. Electrode 1b is disposed so as to sandwich another part of piezoelectric element 3 between electrode 1b and electrode 2.

[0015] Wiring 6 connects electrode 1a and the transmitting / receiving circuit 4. Wiring 7 connects electrode 2 and the transmitting / receiving circuit 4. Wiring 8 connects electrode 1b and the transmitting / receiving circuit 4. Housing 5 houses transmitting / receiving element 110, the transmitting / receiving circuit 4, and wirings 6, 7, and 8.

[0016] Electrodes 1a, 1b and electrode 2 are formed using a thin film of a conductive metal such as platinum, molybdenum, iridium, or titanium. As described above, electrodes 1a, 1b are located on the front side of piezoelectric element 3 and are electrically connected via wiring 6 and 8 to electrode pads (not shown), which are circuit patterns for applying a drive voltage to electrodes 1a, 1b, respectively. Similarly, electrode 2 is located on the back side of piezoelectric element 3 and is electrically connected via wiring 7 to electrode pads (not shown), which are circuit patterns for applying a drive voltage to electrode 2.

[0017] The piezoelectric element 3 is made of, for example, lead zirconate titanate (PZT). In addition to lead zirconate titanate, the piezoelectric element 3 can also be made of aluminum nitride (AlN), zinc oxide (ZnO), lead titanate (PbTiO3), or the like.

[0018] FIG. 3 is a block diagram showing the configuration of the ultrasonic sensor according to the first embodiment.

[0019] The configuration of the ultrasonic sensor 100 according to the first embodiment will be described with reference to Fig. 3. The ultrasonic sensor 100 includes a transmission / reception circuit 4 and an ultrasonic transmission / reception element 110. The ultrasonic sensor 100 is a sensor that can transmit ultrasonic waves via the ultrasonic transmission / reception element 110 and also receive ultrasonic waves via the ultrasonic transmission / reception element 110.

[0020] The transmission / reception circuit 4 includes a carrier wave generating unit 201, an ultrasonic wave driving unit 202, a feedback adding unit 203, an ultrasonic wave receiving unit 204, and a reflected wave detecting unit 205. The ultrasonic wave driving unit 202 includes a driver 211 that drives the electrode 1a and a driver 212 that drives the electrode 1b.

[0021] When transmitting ultrasonic waves, ultrasonic driving unit 202 applies drive wave drive voltages to electrodes 1a and 1b via separate paths, vibrating piezoelectric element 3. This generates transmitted ultrasonic waves. When receiving ultrasonic waves, the electrical signals generated by the vibration of piezoelectric element 3 when ultrasonic waves are received are added by adding unit 203, and ultrasonic receiving unit 204 performs sensing to detect the reception of ultrasonic waves with a frequency corresponding to the received waves.

[0022] When ultrasonic waves are received, an electric signal is generated between electrode 2 and electrodes 1a and 1b due to the piezoelectric effect, and this signal is extracted by transmission / reception circuit 4. In other words, the electrodes are used as vibration sensors for sensing this electric signal.

[0023] The ultrasonic sensor 100 is used, for example, in a distance measurement system that can measure the distance to an object by transmitting ultrasonic waves and measuring the time it takes for the reflected waves to return from the object, called the TOF (Time Of Flight).

[0024] 4 is a diagram illustrating an example in which an ultrasonic sensor is mounted on a vehicle. As shown in FIG. 4, four ultrasonic sensors 100 are disposed on the front and rear of a vehicle 250.

[0025] The vehicle system is configured so that when each ultrasonic sensor 100 detects the approach of an obstacle, an alarm sounds and a warning display is displayed.

[0026] Here, the problem with ultrasonic sensors will be explained. Fig. 5 is a block diagram showing the configuration of an ultrasonic sensor of the studied example. Fig. 6 is a cross-sectional view showing the structure of the ultrasonic sensor of the studied example.

[0027] In Figure 5, the carrier wave generating unit 701, the ultrasonic driving unit 702, the ultrasonic receiving unit 704, the reflected wave detecting unit 705, and the ultrasonic transmitting / receiving element 600 are blocks corresponding to the carrier wave generating unit 201, the ultrasonic driving unit 202, the ultrasonic receiving unit 204, the reflected wave detecting unit 205, and the ultrasonic transmitting / receiving element 110 in Figure 3, respectively.

[0028] 6, an electrode 502, a piezoelectric element 503, a transmitting / receiving circuit 504, and a housing 505 are elements corresponding to the electrode 2, the piezoelectric element 3, the transmitting / receiving circuit 4, and the housing 5 in FIG. 1, respectively.

[0029] Here, in the configuration shown in Figure 5, the ultrasonic transmitting / receiving element has two electrodes on the emission side, such as electrodes 1a and 1b, but in the ultrasonic sensor of the considered example, it is not separated, such as electrode 501, as shown in Figure 6.

[0030] In the ultrasonic sensor of this study example, the direction of ultrasonic waves emitted is fixed when the ultrasonic sensor is attached to a vehicle, so it is difficult to adjust if the emission direction is not optimal due to tilt caused by the vehicle model, center of gravity position, etc.

[0031] Figure 7 shows the correct emission direction of ultrasound, Figure 8 shows an emission direction that is shifted downward, and Figure 9 shows an emission direction that is shifted upward.

[0032] Ultrasonic sensors are installed at the bottom of the front and rear of the vehicle, and the installation angle (vertical direction) is important. If the installation angle is downward as shown in Figure 8, the signal will be reflected by the ground, and if it is upward as shown in Figure 9, the signal will be reflected less from distant obstacles, making it difficult to detect the obstacles.

[0033] It is possible to change the emission angle by installing two piezoelectric elements and shifting the phase of the ultrasonic waves, but installing two elements in an ultrasonic sensor such as the one shown in Figure 6 would increase the size of the ultrasonic sensor. Also, if the element size is reduced and two are installed in an ultrasonic sensor, the output level will decrease.

[0034] In contrast, the ultrasonic sensor 100 of the first embodiment has two separate electrodes on one side of the piezoelectric element, so that the emission direction, i.e., directivity, of the ultrasonic waves can be changed when the ultrasonic sensor is installed in a vehicle without increasing the size of the ultrasonic sensor significantly.

[0035] Fig. 10 is a diagram for explaining a case where the directivity of the ultrasonic sensor is upward, and Fig. 11 is a diagram showing a drive signal when the directivity of the ultrasonic sensor is upward.

[0036] As shown in Fig. 11, when the drive signal V1a applied to electrode 1a is delayed in phase by Td1 from the drive signal V1b applied to electrode 1b, the directivity of the ultrasonic waves emitted from the ultrasonic sensor points upward as shown in direction F1 in Fig. 10. Td1 is, for example, within approximately 25% of one cycle of the drive waveform.

[0037] FIG. 12 is a diagram for explaining a case where the directivity of the ultrasonic sensor is downward.

[0038] FIG. 13 is a diagram showing a drive signal when the directivity of the ultrasonic sensor is downward.

[0039] As shown in Fig. 13, when the drive signal V1b applied to electrode 1b is delayed in phase by Td2 from the drive signal V1a applied to electrode 1a, the directivity of the ultrasonic waves emitted from the ultrasonic sensor points downward as shown in direction F2 in Fig. 12. Td2 is, for example, within approximately 25% of one cycle of the drive waveform.

[0040] In the ultrasonic driving unit 202 of the transmission / reception circuit 4 in Fig. 3, if the ultrasonic driving unit 202 is configured to generate two driving waves with a phase difference based on a common carrier wave generated by the carrier wave generating unit 201 and to be able to change the phase difference later, it becomes possible to change and adjust the ultrasonic wave emission angle even after installation in the vehicle. This increases the degree of freedom in designing the installation position and angle.

[0041] According to the ultrasonic sensor of the first embodiment, the emission direction of ultrasonic waves can be adjusted after the ultrasonic sensor is attached to a vehicle, etc. This makes it possible to easily adjust the emission direction of the ultrasonic sensor even after the vehicle body design is completed.

[0042] <Modification of the First Embodiment> Fig. 14 is a cross-sectional view showing the configuration of an ultrasonic sensor according to a modification of Embodiment 1. Fig. 15 is a front view showing the configuration of an ultrasonic sensor according to a modification of Embodiment 1.

[0043] The ultrasonic sensor 100A, a variation of the first embodiment, has the same configuration as the ultrasonic sensor 100 shown in Figures 1 and 2, except that the electrode on the emitting surface (front surface) is a single circular electrode, and the electrode on the surface opposite the emitting surface (back surface) is two semicircular electrodes.

[0044] That is, the ultrasonic sensor 100A includes a transmitting / receiving element 110A, a transmitting / receiving circuit 4, and a housing 5. The transmitting / receiving element 110A includes a piezoelectric element 3 and electrodes 1, 2a, and 2b.

[0045] Electrode 1 is provided on a first surface of piezoelectric element 3. Electrodes 2a and 2b are provided on a second surface of piezoelectric element 3. In the case of a modified example, the first surface of piezoelectric element 3 is the surface that emits ultrasonic waves and faces the outside of housing 5. The second surface of piezoelectric element 3 is the surface opposite to the first surface and faces the inside of housing 5.

[0046] 15, the first and second surfaces of the piezoelectric element 3 are circular, the electrode 1 is circular, and the electrodes 2a and 2b are semicircular. An opening A2 is provided in the housing 5, which exposes a central portion 2ac on the surface of the second electrode 2a opposite to the piezoelectric element 3 and a central portion 2bc on the surface of the third electrode 2b opposite to the piezoelectric element 3. Two ultrasonic waves with a phase difference are emitted from these central portions.

[0047] Electrode 2a is disposed so as to sandwich a part of piezoelectric element 3 between electrode 2a and electrode 1. Electrode 2b is disposed so as to sandwich another part of piezoelectric element 3 between electrode 2b and electrode 1.

[0048] The other configuration is the same as that shown in FIGS. 1 and 2, and therefore description thereof will not be repeated.

[0049] Even if the electrodes are arranged as in the modified example, the deformation of the piezoelectric element can be made different between the upper and lower halves by shifting the phase of the drive signal, so it is possible to change the emission direction in a similar manner. Note that this modified example can also be applied to the second and subsequent embodiments.

[0050] <Embodiment 2> In the first embodiment, an ultrasonic sensor that can change the emission direction even after the ultrasonic sensor is fixed to a vehicle, etc. is described. In the second embodiment, an example of an obstacle detection system that uses the ultrasonic sensor of the first embodiment and changes the emission angle when the vehicle, etc., tilts will be described.

[0051] 16 is a block diagram showing the configuration of an obstacle detection system according to Embodiment 2. The obstacle detection system 400A includes an ultrasonic sensor 100A, tilt sensors 401 and 402, and a tilt correction unit 410.

[0052] The ultrasonic sensor 100A includes a transmission / reception circuit 4A and an ultrasonic transmission / reception element 110. The ultrasonic sensor 100A is a sensor that can transmit ultrasonic waves via the ultrasonic transmission / reception element 110 and also receive ultrasonic waves via the ultrasonic transmission / reception element 110.

[0053] The transmission / reception circuit 4A includes a carrier wave generation unit 201, an ultrasonic wave driving unit 202A, a feedback addition unit 203, an ultrasonic wave receiving unit 204, and a reflected wave detection unit 205. The ultrasonic wave driving unit 202A includes a driver 211 that drives the electrode 1a and a driver 212 that drives the electrode 1b, as well as phase adjustment units 213 and 214.

[0054] The tilt correction unit 410 is configured to detect the tilt of the vehicle using the tilt sensors 401 and 402. Note that the object to which the ultrasonic sensor is attached is not necessarily limited to a vehicle. For example, it may be a robot, a drone, a ship, or the like. In that case, the tilt sensors 401 and 402 detect the tilt of the housing of the object to which the ultrasonic sensor 100 is attached. The tilt correction unit 410 may be configured as hardware, or may be a computer equipped with a CPU, memory, etc.

[0055] 17 is a diagram showing a state in which the emission angle is changed to an upward direction in response to the inclination of the vehicle. As shown in FIG. 17, when the vehicle body is facing downward, the inclination correction unit 410 instructs the ultrasonic sensor 100A to emit ultrasonic waves upward (F1).

[0056] More specifically, when the tilt correction unit 410 detects that the vehicle body has tilted so that the front part of the vehicle is lower than the rear part, it sends a control signal to the ultrasonic sensor 100 to switch the emission direction of the ultrasonic waves from the normal emission direction F0 to the upward emission direction F1.

[0057] In response to this, the phase adjustment units 213 and 214 of the ultrasonic sensor 100A delay the phase of the drive signal V1a relative to the phase of the drive signal V1b, as shown in FIG.

[0058] 18 is a diagram showing a state in which the emission angle is changed to a downward direction in response to the inclination of the vehicle. As shown in FIG. 18, when the vehicle body is facing upward, the inclination correction unit 410 instructs the ultrasonic sensor 100A to emit ultrasonic waves downward (F2).

[0059] More specifically, when the tilt correction unit 410 detects that the vehicle body has tilted so that the front of the vehicle is higher than the rear, it sends a control signal to the ultrasonic sensor 100A to switch the direction of ultrasonic wave emission from the normal emission direction F0 to a downward emission direction F2.

[0060] In response to this, the phase adjustment units 213 and 214 of the ultrasonic sensor 100A delay the phase of the drive signal V1b relative to the phase of the drive signal V1a, as shown in FIG.

[0061] According to the obstacle detection system of the second embodiment, the tilt of the vehicle body is detected and the direction of emission of ultrasonic waves is adjusted according to the degree of tilt, thereby preventing malfunctions and deterioration of accuracy in the obstacle detection process due to the tilt of the vehicle body.

[0062] <Third Embodiment> In the third embodiment, an ultrasonic sensor capable of detecting the height of an obstacle will be described.

[0063] 19 is a block diagram showing the configuration of an obstacle detection system according to Embodiment 3. The obstacle detection system 400B includes an ultrasonic sensor 100B and a height determination unit 420.

[0064] The ultrasonic sensor 100B includes a transmission / reception circuit 4B and an ultrasonic transmission / reception element 110. The ultrasonic sensor 100B is a sensor that can transmit ultrasonic waves via the ultrasonic transmission / reception element 110 and also receive ultrasonic waves via the ultrasonic transmission / reception element 110. The ultrasonic sensor 100B emits ultrasonic waves alternately upward and downward to detect obstacles.

[0065] The transmission / reception circuit 4B includes a carrier wave generation unit 201, an ultrasonic wave driving unit 202B, a feedback addition unit 203, an ultrasonic wave receiving unit 204, and a reflected wave detection unit 205. The ultrasonic wave driving unit 202B includes a driver 211 that drives the electrode 1a, a driver 212 that drives the electrode 1b, phase adjustment units 213 and 214, and further includes a signal switching unit 215.

[0066] The height determination unit 420 is configured to alternately receive information on the reflected waves of upward ultrasonic waves and information on the reflected waves of downward ultrasonic waves from the ultrasonic sensor 100B, and detect the height of the target object 300. The height determination unit 420 may be configured as hardware, or may be a computer equipped with a CPU, memory, etc.

[0067] Fig. 20 is a diagram showing a state in which ultrasonic waves are emitted upward when the obstacle is high, and Fig. 21 is a diagram showing a state in which ultrasonic waves are emitted downward when the obstacle is high.

[0068] The height determination unit 420 is configured to determine that the height of the obstacle 300H is higher than the reference value when the intensity of the reflected waves is strong both in the upward and downward directions.

[0069] Fig. 22 is a diagram showing a state in which ultrasonic waves are emitted upward when the obstacle is low in height, and Fig. 23 is a diagram showing a state in which ultrasonic waves are emitted downward when the obstacle is low in height.

[0070] The height determination unit 420 is configured to determine that the height of the obstacle 300L is lower than the reference value when the intensity of the reflected wave of the upward emission is weaker than the reflected wave of the downward emission.

[0071] 24 is a diagram illustrating an example of control to alternately change the emission direction. The ultrasonic sensor 100B alternately emits upward and downward ultrasonic waves by the signal switching unit 215 periodically switching the signals.

[0072] At times t1 to t2 and t5 to t6, drive signals V1a and V1b whose phases are adjusted as shown in FIG. 11 so that they are emitted upward are emitted from ultrasonic sensor 100B, and the reflected waves are received by ultrasonic sensor 100B, and the intensity of the reflected waves is output to height determination unit 420.

[0073] At times t3 to t4 and t7 to t8, drive signals V1a and V1b whose phases are adjusted as shown in FIG. 11 so that they are emitted upward are emitted from ultrasonic sensor 100B, and the reflected waves are received by ultrasonic sensor 100B, and the intensity of the reflected waves is output to height determination unit 420.

[0074] If the intensities of the reflected waves detected twice consecutively are both greater than the reference value, the height determination unit 420 determines that the height of the obstacle 300H is greater than the reference height, as shown in Figures 20 and 21.

[0075] On the other hand, if one of the intensities of the reflected waves detected twice in succession is stronger than the reference value and the other is weaker than the reference value, the height determination unit 420 determines that the height of the obstacle 300H is lower than the reference height, as shown in Figures 22 and 23.

[0076] In the above example, the ultrasonic sensor 100B alternately changes the emission direction by itself without any particular external alternating command, but this is not necessarily limited to this.

[0077] For each detection, whether the ultrasonic sensor 100B emits ultrasonic waves upward or downward may be determined based on a control signal from the outside (for example, the height determination unit 420).

[0078] Furthermore, the ultrasonic driving unit 202B may have a configuration other than that shown in FIG. 19 as long as it can output driving signals with a phase difference corresponding to an upward direction and a phase difference corresponding to a downward direction, and it does not need to switch signals as in the signal switching unit 215 shown in FIG. 19.

[0079] As described above, the ultrasonic sensor 100B and obstacle detection system 400B of the third embodiment can determine the height of an obstacle by emitting ultrasonic waves in different emission directions and checking the difference in the reflected waves.

[0080] <Fourth Embodiment> In the fourth embodiment, an ultrasonic sensor and an obstacle detection system that respond to temperature changes will be described. Fig. 25 is a block diagram showing the configuration of the obstacle detection system of the fourth embodiment.

[0081] The obstacle detection system 400C includes the ultrasonic sensor 100C, a temperature sensor 260, and a temperature correction unit 261.

[0082] The ultrasonic sensor 100C includes a transmission / reception circuit 4C and an ultrasonic transmission / reception element 110. The ultrasonic sensor 100C is a sensor that can transmit ultrasonic waves via the ultrasonic transmission / reception element 110 and also receive ultrasonic waves via the ultrasonic transmission / reception element 110. The ultrasonic sensor 100C is configured to adjust the emission direction of the ultrasonic waves in response to a control signal from a temperature correction unit 261.

[0083] The transmission / reception circuit 4C includes a carrier wave generation unit 201, an ultrasonic wave driving unit 202C, a feedback addition unit 203, an ultrasonic wave receiving unit 204, and a reflected wave detection unit 205. The ultrasonic wave driving unit 202C includes a driver 211 that drives the electrode 1a, a driver 212 that drives the electrode 1b, and phase adjustment units 213 and 214.

[0084] Temperature sensor 260 detects the ambient temperature. Temperature correction unit 261 is configured to adjust the phase of the drive signal based on the temperature detected by temperature sensor 260. Temperature correction unit 261 may be configured as hardware, or may be a computer equipped with a CPU, memory, etc.

[0085] Since the speed of ultrasonic waves is affected by temperature (air temperature), the magnitude of the phase difference is adjusted depending on the temperature. If the temperature sensor 260 is attached to the ultrasonic sensor 100C itself, the local temperature of the vehicle body will differ from the actual air temperature. Therefore, it is better to position the temperature sensor 260 in a location appropriate for measuring the air temperature.

[0086] FIG. 26 is a graph for explaining the relationship between the phase difference and the temperature.

[0087] The propagation speed of ultrasound in air at temperature T (℃) is Vt [m / s]. Vt=331+0.6*T Here, if the propagation speed in air at 0°C is V0 = 331 [m / s], the correction coefficient for the phase difference is Vt / V0. If the phase difference at 0°C is Pd0, the phase difference at temperature T [°C] must be corrected to Pdt = Vt / V0 * Pd0.

[0088] To achieve this phase difference, the phase adjustment units 213 and 214 are configured to adjust the delay times of the drive signals.

[0089] According to the ultrasonic sensor and obstacle detection system of the fourth embodiment, obstacles can be detected with high accuracy even when the ambient temperature changes.

[0090] <Fifth Embodiment> In the fifth embodiment, a modified example of the shape of the housing of the ultrasonic sensor of the first embodiment will be described.

[0091] Figure 27 is a cross-sectional view of the study example. Figure 27 illustrates the overlap of ultrasonic waves immediately after emission in comparison with Figure 1. Ultrasonic wave Sa having a certain phase is emitted from electrode 1a, and ultrasonic wave Sb with the same frequency but a different phase is emitted from electrode 1b.

[0092] However, as shown in Figure 27, in the area close to electrode 1a and electrode 1b, it is difficult to emit ultrasonic waves with a clean phase shift due to the distortion of piezoelectric element 3 and the overlap of ultrasonic waves. This point leaves room for improvement. Therefore, in embodiment 5, a partition is inserted in the emission port to separate the outputs of the upper and lower piezoelectric elements. Also, to improve the directionality of the ultrasonic sensor, the wall surface of the emission port is angled.

[0093] Fig. 28 is a cross-sectional view showing the configuration of the ultrasonic sensor according to the fifth embodiment. Fig. 29 is a front view showing the configuration of the ultrasonic sensor according to the fifth embodiment.

[0094] Ultrasonic sensor 100D of embodiment 5 includes a housing 5D instead of housing 5 in the configuration of ultrasonic sensor 100 of embodiment 1. The other configuration is the same as the configuration described with reference to Figures 1 and 2, so description thereof will not be repeated here.

[0095] Housing 5D supports piezoelectric element 3, electrode 2, electrode 1a, and electrode 1b. Housing 5D is provided with opening 411. As shown in FIGS. 28 and 29, housing 5D has partition 412 that divides opening 411 into opening 411a and opening 411b corresponding to the boundary between second electrode 1a and third electrode 1b. Opening 411 of housing 5D exposes central portion 1ac on the surface of second electrode 1a opposite piezoelectric element 3 and central portion 1bc on the surface of third electrode 1b opposite piezoelectric element 3. Two ultrasonic waves with different phases are emitted from these central portions. This configuration makes it easy to separate ultrasonic waves with different phases into two at the time of emission.

[0096] Furthermore, as shown in Figures 26 and 27, the outer periphery of opening 411 is a horn-shaped wall surface 413. Horn-shaped wall surface 413 refers to a wall surface of the emission port that is angled so that it opens outward in order to improve directivity. This angle is preferably set to θ = 10 to 20 degrees, for example, as shown in Figure 28. With this configuration, the emission range of the ultrasonic waves can be narrowed.

[0097] It should be noted that only one of partition portion 412 and horn-shaped wall surface 413 may be applied to housing 5D.

[0098] [Note] The present embodiment will be summarized below with reference to the drawings again.

[0099] (Item 1) The present disclosure relates to an ultrasonic sensor 100. The ultrasonic sensor 100 shown in Fig. 1 includes a piezoelectric element 3, a first electrode 2 provided on a first surface of the piezoelectric element 3, a second electrode 1a provided on a second surface of the piezoelectric element 3 and sandwiching a part of the piezoelectric element 3 between the second electrode 1a and the first electrode 2, and a third electrode 1b provided on the second surface of the piezoelectric element 3 and sandwiching another part of the piezoelectric element 3 between the first electrode 2 and the third electrode 1b.

[0100] With this configuration, it is possible to emit two ultrasonic waves with a phase difference between them without increasing the size of the ultrasonic sensor too much.

[0101] (Item 2) In the ultrasonic sensor 100 described in item 1, as shown in FIG. 2, the first and second surfaces of the piezoelectric element 3 are circular, the first electrode 2 is circular, and the second electrode 1a and the third electrode 1b are semicircular.

[0102] With this configuration, the size of the piezoelectric element 3 can be reduced, and two ultrasonic waves with a phase difference between them can be emitted.

[0103] (Item 3) The ultrasonic sensor 100 described in item 1 or 2 further includes a housing 5 that supports the piezoelectric element 3, the first electrode 2, the second electrode 1a, and the third electrode 1b. As shown in FIGS. 1 and 2, the second electrode 1a and the third electrode 1b are ultrasonic wave emission surfaces. The housing 5 is provided with an opening A1 that exposes a central portion 1ac on the surface of the second electrode 1a opposite the piezoelectric element 3 and a central portion 1bc on the surface of the third electrode 1b opposite the piezoelectric element 3.

[0104] (Item 4) The ultrasonic sensor 100A described in item 1 or 2 further includes a housing 5 that supports the piezoelectric element 3, the first electrode 1, the second electrode 2a, and the third electrode 2b. As shown in FIGS. 14 and 15, the first electrode 1 is an emitting surface for ultrasonic waves. The housing 5 is provided with an opening A2 that exposes a central portion 2ac on the surface of the second electrode 2a opposite to the piezoelectric element 3 and a central portion 2bc on the surface of the third electrode 2b opposite to the piezoelectric element 3.

[0105] (Item 5) The ultrasonic sensor described in item 1 or 2 further includes a transmission circuit (transmission / reception circuit 4) configured to apply a first drive signal V1a between the first electrode 2 and the second electrode 1a, and to apply a second drive signal V1b, which is out of phase with the first drive signal V1a, between the first electrode 2 and the third electrode 1b, as shown in FIGS. 10 to 13.

[0106] With this configuration, it is possible to change the emission angle of the ultrasonic waves even after the ultrasonic sensor is fixed.

[0107] (Item 6) In the ultrasonic sensor described in item 5, the transmission circuit (transmission / reception circuit 4) is configured to be able to change the phase difference Td between the first drive signal V1a and the second drive signal V1b, as shown in FIGS.

[0108] 16, the ultrasonic sensor 100 further includes an ultrasonic driver 202A that receives a correction signal corresponding to the tilt detected by the tilt sensors 401, 402. The ultrasonic driver 202A is configured to be able to change the phase difference Td between the first drive signal V1a and the second drive signal V1b based on the correction signal.

[0109] With this configuration, the tilt sensors 401 and 402 can detect the tilt of the vehicle, and ultrasonic waves can be emitted in the emission directions F1 and F2 according to the tilt.

[0110] (Item 8) In the ultrasonic sensor described in item 6, as shown in Figures 19 to 24, the transmission circuit (transmission / reception circuit 4B) is configured to alternately transmit a first wave (upward) having a first phase difference and a second wave (downward) having a second phase difference different from the first phase difference.

[0111] By using a sensor with such a configuration, an obstacle detection system that can determine the height of the detection object 300 to some extent can be realized.

[0112] 25, the ultrasonic sensor 250C described in paragraph 6 further includes an ultrasonic driving unit 202C that receives a correction signal corresponding to the detected temperature of the temperature sensor 260. The ultrasonic driving unit 202C is configured to be able to change the difference between the delay amount of the first driving signal V1a and the delay amount of the second driving signal V1b based on the output of the temperature sensor 260.

[0113] With this configuration, it is possible to adjust the emission angle of the ultrasonic waves so that it does not change even when the temperature of the environment in which it is used changes.

[0114] (Item 10) The ultrasonic sensor according to item 1 or 2 further includes a housing 5D that supports the piezoelectric element 3, the first electrode 2, the second electrode 1a, and the third electrode 1b, as shown in Figures 28 and 29. The housing 5D has an opening 411. The housing 5D includes a partition 412 that separates the opening 411 so as to correspond to the boundary between the second electrode 1a and the third electrode 1b.

[0115] This configuration makes it easier to split ultrasonic waves with different phases into two at the point of emission.

[0116] (Item 11) In the ultrasonic sensor 100D described in item 10, the outer periphery of the opening 411 is a horn-shaped wall surface 413, as shown in FIGS.

[0117] This configuration allows the ultrasonic wave emission range to be widened.

[0118] (Item 12) In another aspect, the present disclosure relates to an obstacle detection system 400A. As shown in Fig. 16, the obstacle detection system 400A includes the ultrasonic sensor 4A described in item 7, tilt sensors 401 and 402, and a tilt correction unit 410 that controls the ultrasonic drive unit to change the phase difference between the delay amount of the first drive signal and the second drive signal based on a correction signal.

[0119] (Item 13) In another aspect, the present disclosure relates to an obstacle detection system 400B. As shown in Fig. 19, the obstacle detection system 400B includes the ultrasonic sensor 100B described in item 8 and a height determination unit 420 that receives an output from the ultrasonic sensor 100B and determines the height of an obstacle.

[0120] (Item 14) In another aspect, the present disclosure relates to an obstacle detection system 400C. As shown in Fig. 25, the obstacle detection system 400C includes the ultrasonic sensor 100C described in item 9, a temperature sensor 260, and a temperature correction unit 261 that controls the ultrasonic drive unit 202B to change the difference between the delay amount of the first drive signal and the delay amount of the second drive signal based on the output of the temperature sensor 260.

[0121] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the description of the above embodiments, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0122] 1, 1a, 1b, 2, 2a, 2b Electrodes, 3 Piezoelectric element, 4, 4A, 4B, 4C Transmitting / receiving circuit, 5, 5C Housing, 6, 7, 8 Wiring, 100, 100A, 100B, 100C Ultrasonic sensor, 110, 110A Transmitting / receiving element, 201 Carrier wave generating unit, 202, 202A, 202B, 202C Ultrasonic driving unit, 203 Adding unit, 204 Ultrasonic receiving unit, 205 Reflected wave detecting unit, 211, 212 Driver, 213, 214 Phase adjusting unit, 215 Signal switching unit, 250 Vehicle, 250B Ultrasonic sensor, 260 Temperature sensor, 261 Temperature correction unit, 300 Detection object, 400A, 400B, 400C Obstacle detection system, 401, 402 Tilt sensor, 410 Tilt correction unit, 411 opening, 412 partition unit, 413 wall surface, 420 height determination unit.

Claims

1. a piezoelectric element; a first electrode provided on a first surface of the piezoelectric element; a second electrode provided on a second surface of the piezoelectric element, the second electrode sandwiching a part of the piezoelectric element between the first electrode and the second electrode; a third electrode provided on the second surface of the piezoelectric element, sandwiching another part of the piezoelectric element between the third electrode and the first electrode.

2. the first surface and the second surface of the piezoelectric element are circular; the first electrode is circular; The ultrasonic sensor of claim 1 , wherein the second electrode and the third electrode are semicircular.

3. a housing supporting the piezoelectric element, the first electrode, the second electrode, and the third electrode, the second electrode and the third electrode are ultrasonic wave emission surfaces; 3. The ultrasonic sensor according to claim 1, wherein the housing has openings that expose a central portion of a surface of the second electrode opposite to the piezoelectric element and a central portion of a surface of the third electrode opposite to the piezoelectric element.

4. a housing supporting the piezoelectric element, the first electrode, the second electrode, and the third electrode, the first electrode is an ultrasonic wave emitting surface; 3. The ultrasonic sensor according to claim 1, wherein the housing has an opening that exposes a central portion of a surface of the second electrode opposite to the piezoelectric element and a central portion of a surface of the third electrode opposite to the piezoelectric element, and an opening that exposes a central portion of a surface of the first electrode opposite to the piezoelectric element.

5. 3. The ultrasonic sensor of claim 1, further comprising a transmitter circuit configured to apply a first drive signal between the first electrode and the second electrode, and to apply a second drive signal between the first electrode and the third electrode, the second drive signal being out of phase with the first drive signal.

6. The ultrasonic sensor according to claim 5 , wherein the transmission circuit is configured to be able to change a phase difference between the first drive signal and the second drive signal.

7. the ultrasonic sensor further includes an ultrasonic driver that receives a correction signal corresponding to the tilt detected by the tilt sensor; The ultrasonic sensor according to claim 6 , wherein the ultrasonic driving section is configured to be able to change a phase difference between an amount of delay of the first driving signal and the second driving signal based on the correction signal.

8. 7. The ultrasonic sensor according to claim 6, wherein the transmission circuit is configured to alternately transmit a first wave having the phase difference set to a first phase difference and a second wave having the phase difference set to a second phase difference different from the first phase difference.

9. the ultrasonic sensor further includes an ultrasonic driver that receives a correction signal corresponding to the temperature detected by the temperature sensor; The ultrasonic sensor according to claim 6 , wherein the ultrasonic driving section is configured to be able to change a difference between an amount of delay of the first driving signal and an amount of delay of the second driving signal based on an output of the temperature sensor.

10. a housing supporting the piezoelectric element, the first electrode, the second electrode, and the third electrode, The housing has an opening, The ultrasonic sensor according to claim 1 , wherein the housing includes a partition that partitions the opening so as to correspond to a boundary between the second electrode and the third electrode.

11. The ultrasonic sensor according to claim 10 , wherein the outer periphery of the opening is a horn-shaped wall surface.

12. The ultrasonic sensor according to claim 7; the tilt sensor; an inclination correction unit that controls the ultrasonic driving unit so as to change a phase difference between the delay amount of the first driving signal and the second driving signal based on the correction signal.

13. The ultrasonic sensor according to claim 8; an obstacle detection system comprising: a height determination unit that receives an output from the ultrasonic sensor and determines the height of an obstacle.

14. The ultrasonic sensor according to claim 9 ; the temperature sensor; an obstacle detection system comprising: a temperature correction unit that controls the ultrasonic driving unit so as to change a difference between an amount of delay of the first driving signal and an amount of delay of the second driving signal based on an output of the temperature sensor;

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