Ultrasonic sensor

• US 20090168603A1
• Filed: 12/23/2008
• Published: 07/02/2009
• Est. Priority Date: 12/26/2007
• Status: Active Grant

• Current Assignee: DENSO Corporation, Nippon Soken, Inc.
• Original Assignee: DENSO Corporation, Nippon Soken, Inc.
• Inventors: Yamanaka, Akitoshi, Kojima, Kiyonari, Ishikawa, Takayuki, Oda, Teruo, Okuda, Yasuyuki, Sugiura, Makiko, Kawai, Takaaki
• Granted Patent: US 8,009,518 B2
• Time in Patent Office: Days
• US Class Current: 367/87
• CPC Class Codes: B06B 1/0629 Square array
• CPC Class Codes: G01S 15/42 Simultaneous measurement of distance and other co-ordinates indirect measurement G01S15/46
• CPC Class Codes: G01S 15/931 of land vehicles
• CPC Class Codes: G01S 3/808 using transducers spaced apart and measuring phase or time difference between signals therefrom, i.e. path-difference systems
• CPC Class Codes: G01S 7/52004 Means for monitoring or calibrating short-range imaging G01S7/5205
• CPC Class Codes: G01S 7/521 Constructional features

Abstract

An ultrasonic sensor includes a transmitting device, receiving devices arranged in an array, and a circuit device. One receiving device is configured as a reference receiving device. The circuit device includes a reference signal generator and first and second synchronous detectors. The reference signal generator generates a reference signal by using a received signal of the reference receiving device. The first synchronous detector performs synchronous detection of a received signal of one of the receiving devices based on the reference signal to detect a distance to an object. The second synchronous detector performs synchronous detection of received signals of the receiving devices except the reference receiving device based on the reference signal to detect a direction of the object.

Claims

1. An ultrasonic sensor for detecting an object, comprising:

a transmitting device for transmitting ultrasonic wave to the object;

a plurality of receiving devices, each of which receives the ultrasonic wave reflected from the object and outputs a received signal corresponding to the received ultrasonic wave, the plurality of receiving devices including a reference receiving device and at least one non-reference receiving device; and

a circuit device electrically coupled to the plurality of receiving devices and processing the received signals outputted from the plurality of receiving devices, the circuit device including a reference signal generator, a first synchronous detector, and a second synchronous detector, wherein

the reference signal generator generates a reference signal by using the received signal of the reference receiving device,

the first synchronous detector performs synchronous detection of the received signal of one of the reference receiving device and the non-reference receiving device based on the reference signal to detect a time interval between transmitting and receiving the ultrasonic wave, the first synchronous detector calculating a distance to the object based on the detected time interval, and

the second synchronous detector performs synchronous detection of the received signal of the non-reference receiving device based on the reference signal to detect a phase difference between the received signals of the reference receiving device and the non-reference receiving device, the second synchronous detector calculating a direction of the object based on the phase difference.

2. The ultrasonic sensor according to claim 1, wherein

the reference signal generator includes a phase-looked loop.

3. The ultrasonic sensor according to claim 1, wherein

the transmitting device transmits the ultrasonic wave upon reception of a transmission signal outputted from the circuit device, and

the first synchronous detector detects the time interval based on the transmission signal.

4. The ultrasonic sensor according to claim 1, wherein

the non-reference receiving device comprises at least two non-reference receiving devices that are arranged in an array with the reference receiving device,

a first one of the non-reference receiving devices is located in a first direction with respect to the reference receiving device, and

a second one of the non-reference receiving devices is located in a second direction with respect to the reference receiving device, the second direction being perpendicular to the first direction.

5. The ultrasonic sensor according to claim 1, wherein

the non-reference receiving device comprises at least two non-reference receiving devices that are arranged in an array with the reference receiving device, and

the non-reference receiving devices are arranged circularly around the reference receiving device.

6. The ultrasonic sensor according to claim 1, wherein

the transmitting device, the reference receiving device, and the non-reference receiving device are arranged in an array.

7. The ultrasonic sensor according to claim 1, wherein

the circuit device further includes a majority circuit,

the non-reference receiving device comprises at least three non-reference receiving devices arranged in a line, and

the received signals of the non-reference receiving devices are inputted to the majority circuit.

8. The ultrasonic sensor according to claim 1, wherein

the transmitting device comprises a plurality of transmitting devices.

9. The ultrasonic sensor according to claim 1, wherein

the ultrasonic sensor is mountable on a vehicle with a speed sensor that detects a vehicle speed, and

the circuit device further includes a speed correction circuit that corrects the reference signal based on the detected vehicle speed.

10. The ultrasonic sensor according to claim 1, wherein

the ultrasonic sensor is mountable on a vehicle with a temperature sensor that detects a temperature outside the vehicle, and

the circuit device further includes a temperature correction circuit that corrects the reference signal based on the detected temperature.

11. The ultrasonic sensor according to claim 1, wherein

the transmitting device transmits the ultrasonic wave upon reception of a transmission signal outputted from the circuit device,

the circuit device includes a drive signal generator that outputs a drive signal to the plurality of receiving devices based on the transmission signal, and

the drive signal causes the plurality of receiving devices to produce a first vibration that cancels a second vibration propagating from the transmitting device to the plurality of receiving devices.

12. An ultrasonic sensor for detecting an object, comprising:

a plurality of sensing devices arranged in an array, each of which includes a piezoelectric element and an acoustic matching member having a first surface exposed to space where the object exists and a second surface joined to the piezoelectric element; and

a circuit device electrically coupled to the piezoelectric element, wherein

one of the plurality of sensing devices is configured as a transmitting device that transmits ultrasonic wave upon reception of a transmission signal outputted from the circuit device, and at least another one the plurality of sensing devices is configured as a receiving device that receives the ultrasonic wave reflected from the object and outputs a received signal corresponding to the received ultrasonic wave to the circuit device,

the circuit device includes a drive signal generator that outputs a drive signal to the receiving device based on the transmission signal, and

the drive signal causes the piezoelectric element of the receiving device to vibrate such that a vibration signal propagated from the transmitting device to the receiving device is cancelled.

13. The ultrasonic sensor according to claim 12, wherein

a phase difference between the drive signal and the vibration signal ranges from 110 degrees to 250 degrees.

14. The ultrasonic sensor according to claim 12, wherein

the drive signal comprises a plurality of continuous waves,

the vibration signal comprises a plurality of continuous waves, and

at most initial two of the plurality of continuous waves of the drive signal are inputted to the receiving device before an initial one of the plurality of continuous waves of the vibration signal propagates to the receiving device.

15. The ultrasonic sensor according to claim 12, wherein

the drive signal comprises a plurality of continuous waves,

the vibration signal comprises a plurality of continuous waves, and

at most last two of the plurality of continuous waves of the drive signal are inputted to the receiving device after a last one of the plurality of continuous waves of the vibration signal propagates to the receiving device.

16. The ultrasonic sensor according to claim 12, wherein

the drive signal comprises a plurality of continuous waves,

the vibration signal comprises a plurality of continuous waves, and

a last one of the plurality of continuous waves of the drive signal is inputted to the receiving device when a second last one of the plurality of continuous waves of the vibration signal propagates to the receiving device.

17. The ultrasonic sensor according to claim 12, wherein

a ratio of a magnitude of the drive signal to a magnitude of the vibration signal ranges from 50 percent to 100 percent.

18. The ultrasonic sensor according to claim 12, wherein

the drive signal causes the piezoelectric element of the receiving device to vibrate such that a reverberation vibration of the acoustic matching member propagating to the piezoelectric element of the receiving device is cancelled, and

the propagation of the reverberation vibration to the piezoelectric element of the receiving device follows a propagation of the received ultrasonic wave to the piezoelectric element of the receiving device.

19. An ultrasonic sensor for detecting an object, comprising:

a plurality of sensing devices arranged in an array, each of which includes a piezoelectric element and an acoustic matching member having a first surface exposed to space where the object exists and a second surface joined to the piezoelectric element; and

a circuit device electrically coupled to the piezoelectric element, wherein

a first one of the plurality of sensing devices is configured as a transmitting device that transmits ultrasonic wave upon reception of a transmission signal outputted from the circuit device, and a second one of the plurality of sensing devices is configured as a dummy device that detects only a vibration signal corresponding to a vibration propagating from the transmitting device to the dummy device,

at least another one of the plurality of sensing devices is configured as a receiving device that receives the ultrasonic wave reflected from the object and outputs a received signal corresponding to the received ultrasonic wave to the circuit device, and

the circuit device subtracts the vibration signal from the received signal of the receiving device to cancel a vibration propagated from the transmitting device to the receiving device.

20. An ultrasonic sensor for detecting a first object, comprising:

a transmitting device for transmitting ultrasonic wave to the first object, the transmitting device including a first piezoelectric element for emitting the ultrasonic wave and a first acoustic matching member having a transmitting surface, the emitted ultrasonic wave propagated through the first acoustic matching member and being transmitted through the transmitting surface to the first object, the first piezoelectric element being configured as a multilayer piezoelectric element including a plurality of piezoelectric layers and a plurality of electrode layers interleaved with the plurality of piezoelectric layers;

a receiving device, arranged in an array with the transmitting device, for receiving the ultrasonic wave reflected from the first object, the receiving device including a second piezoelectric element for detecting the reflected ultrasonic wave and a second acoustic matching member having a receiving surface, the reflected ultrasonic wave being received through the receiving surface and propagated through the second acoustic matching member to the second piezoelectric element;

a housing having an inner space for accommodating the transmitting device and the receiving device, the housing having a bottom and an opening portion, the housing being mountable to a second object at the opening portion;

a vibration damper interposed between the opening portion of the housing and each of the first and second acoustic matching members to fix the first and second acoustic matching members to the housing, the vibration damper being interposed between the first and second acoustic matching members to reduce a propagation of the ultrasonic wave between the first and second acoustic matching members; and

a vibration isolator for partitioning the inner space of the housing and located between the transmitting device and the receiving device to reduce the propagation of the ultrasonic wave between the transmitting device and the receiving device.

21. The ultrasonic sensor according to claim 20, further comprising:

a first absorber interposed between the bottom of the housing and each of the first and second piezoelectric elements and between an inner side wall of the housing and each of the first and second piezoelectric elements to protect the transmitting device and the receiving device from external force, wherein

the vibration isolator has a higher acoustic matching impedance than the first absorber.

22. The ultrasonic sensor according to claim 20, wherein

the vibration isolator is integrally formed with the housing.

23. The ultrasonic sensor according to claim 20, wherein

the vibration isolator has a first thickness on the first and second acoustic matching members side and a second thickness on the first and second piezoelectric elements side, and

the first thickness is less than the second thickness.

24. The ultrasonic sensor according to claim 20, wherein

the vibration isolator includes first and second members and a core member that are layered together such that the core member is sandwiched between the first and second members, and

each of the first and second members has a higher elastic modulus than the core member.

25. The ultrasonic sensor according to claim 20, wherein

the vibration isolator includes first and second members and a core member that are layered together such that the core member is sandwiched between the first and second members, and

each of the first and second members has a higher acoustic impedance than the core member.

26. The ultrasonic sensor according to claim 20, wherein

the vibration isolator includes first and second members that are joined together to provide a sealed space therebetween, and

the sealed space is filled with a material having a lower acoustic impedance than those of each of the first and second members.

27. The ultrasonic sensor according to claim 26, wherein

the vibration isolator includes a honeycomb structural body placed in the sealed space to partition the sealed space into a plurality of spaces.

28. The ultrasonic sensor according to claim 20, wherein

the vibration isolator has a plurality of gas bubbles trapped therein.

29. The ultrasonic sensor according to claim 20, further comprising:

a second absorber located on the first absorber to surround the first and second piezoelectric elements, wherein

the second absorber has a lower elastic modulus than the first absorber.

30. The ultrasonic sensor according to claim 29, wherein

the first absorber includes a first portion located on the first piezoelectric element side and a second portion located on the second piezoelectric element side, and

the first portion of the first absorber has a higher elastic modulus than the second portion of the first absorber.

31. The ultrasonic sensor according to claim 30, wherein

the first portion of the first absorber has a greater height, measured from the bottom of the housing, than the second portion of the first absorber.

32. The ultrasonic sensor according to claim 20, wherein

the transmitting surface of the transmitting device and the receiving surface of the receiving device are covered with the vibration damper.

33. The ultrasonic sensor according to claim 20, wherein

the transmitting device or the receiving device comprises a plurality of devices having different directivities.

34. The ultrasonic sensor according to claim 20, wherein

the bottom of the housing has a through hole, and

the vibration isolator has a portion exposed outside the housing through the through hole.

35. The ultrasonic sensor according to claim 34, wherein

the vibration isolator has a vibration inhibitor attached to the exposed potion of the vibration isolator to inhibit the exposed portion from vibrating.

36. The ultrasonic sensor according to claim 20, further comprising:

a vibration damping circuit configured to apply to the vibration isolator a vibration having an opposite phase to a vibration of the vibration isolator to damp the vibration of the vibration isolator.

37. The ultrasonic sensor according to claim 20, wherein

the vibration isolator has an uneven side surface.

38. The ultrasonic sensor according to claim 20, wherein

the vibration isolator is supported by the housing at an edge portion, and

the vibration isolator is thinner at the edge portion than at a center portion.

39. The ultrasonic sensor according to claim 20, wherein

the vibration isolator is reinforced with a reinforcing member placed on a side surface.

40. The ultrasonic sensor according to claim 39, wherein

the reinforcing member has a honeycomb structure.

41. The ultrasonic sensor according to claim 20, wherein

the vibration damper has a slit located between the first and second acoustic matching members.

42. The ultrasonic sensor according to claim 20, wherein

the receiving device comprises a plurality of receiving devices, and

a distance from each receiving device to the transmitting device is the same, and

a distance from each receiving device to the vibration isolator is the same.

43. The ultrasonic sensor according to claim 20, wherein

the receiving device comprises a plurality of receiving devices, and

the vibration isolator has a honeycomb structure to partition the inner space of the housing into a plurality of spaces,

the transmitting device is placed in a central one of the plurality of spaces,

each receiving device is placed in a corresponding space other than the central one, and

a distance from each receiving device to the transmitting device is the same.