Displacement detection device and displacement detection method

• US 9,772,236 B2
• Filed: 04/25/2014
• Issued: 09/26/2017
• Est. Priority Date: 10/28/2011
• Status: Active Grant

• Current Assignee: Murata Manufacturing Co Limited
• Original Assignee: Murata Manufacturing Co Limited
• Inventors: Ando, Masamichi, Kawamura, Hideki
• Primary Examiner(s): Dunlap, Jonathan
• Application Number:
  US14/261,862
• Publication Number:
  US 20140230573A1
• Time in Patent Office: 1,250 Days
• Field of Search: 73777, 7386268, 324123 C, 324123 R, 324678
• CPC Class Codes: G01B 7/16 for measuring the deformation in a solid, e.g. by resistance strain gauge
• CPC Class Codes: G01B 7/22 using change in capacitance
• CPC Class Codes: G01L 1/16 using properties of piezoelectric devices
• CPC Class Codes: G01L 1/25 using wave or particle radiation, e.g. X-rays , microwaves, neutrons G01L1/24 takes precedence
• CPC Class Codes: G01L 9/008 using piezoelectric devices piezoelectric resonators G01L9/0022; surface acoustic waves G01L9/0025
• CPC Class Codes: G01L 9/08 by making use of piezoelectric devices , i.e. electric circuits therefor

Abstract

A displacement detection device includes a piezoelectric sensor. The piezoelectric sensor is provided with a piezoelectric sheet on both principal surfaces of which detection electrodes are formed. When stress is applied to the piezoelectric sensor, charge is generated, and an output voltage in accordance with this generated charge is detected in a DC voltage detector. A controller measures this output voltage at a predetermined time interval. Every time the controller measures the output voltage, the controller makes a short-circuit control of a switch, and causes the charge generated in the piezoelectric sensor to be released. The controller can thereby detect an amount of change in output voltage generated at the predetermined time interval in accordance with an amount of displacement of the piezoelectric sensor. By sequentially integrating this, the controller can accurately detect the amount of displacement of the piezoelectric sensor which changes across measurement timings.

Claims

1. A displacement detection device comprising:

a piezoelectric sensor including a piezoelectric substance and a pair of detection electrodes disposed on opposing surfaces of the piezoelectric substance;

a voltage detector configured to measure a voltage generated by the piezoelectric sensor in response to displacement of the piezoelectric substance;

a switch coupled between the pair of detection electrodes; and

a controller configured to open the switch for the voltage detector to measure the voltage generated by the piezoelectric sensor,

wherein the controller is coupled to the voltage detector to detect an output voltage from the voltage detector and further configured to short-circuit the switch for a predetermined period of time after detecting the output voltage, and

wherein the controller includes memory and is configured to;

calculate a displacement voltage as a difference from the output voltage and an initial value of a storage voltage in the memory, the initial value being a value of a reference voltage,

update the storage voltage by adding the displacement voltage to the storage voltage, and

calculate an amount of displacement of the piezoelectric sensor based on the updated storage voltage stored in the memory of the controller.

2. The displacement detection device according to claim 1, wherein the controller calculates the amount of displacement based on an integrated value of an amount of change in the calculated displacement voltage that is calculated immediately before the controller short-circuits the switch.

3. The displacement detection device according to claim 2, wherein the controller is further configured to integrate the amount of change sequentially from the initial value of the storage voltage in the memory.

4. The displacement detection device according to claim 3, wherein the controller is further configured to transition to a standby state upon detection that the storage voltage in the memory is not updated for predetermined time.

5. The displacement detection device according to claim 4, wherein the controller is further configured to:

set a temporary storage voltage as the initial value of the storage voltage,

compare the output voltage detected by the controller and the temporary storage voltage while the output voltage is output by the voltage detector during a temporary storage time that is based on a charge release time constant of the piezoelectric sensor,

update the temporary storage voltage with the output voltage output during the temporary storage time when the output voltage output during the temporary storage time and the temporary storage voltage are different from each other, and

set the output voltage output during the temporary storage time as the storage voltage in the memory when the output voltage output during the temporary storage time and the temporary storage voltage are substantially equal to each other.

6. The displacement detection device according to claim 1, further comprising a capacitor connected in parallel to the piezoelectric sensor.

7. The displacement detection device according to claim 1, wherein the piezoelectric substance is a flat membrane comprising polylactic acid subjected to stretching treatment at least in a uniaxial direction.

8. The displacement detection device according to claim 7, wherein the uniaxial direction is substantially ±

45°

with respect to a direction in which the piezoelectric substance is displaced.

9. The displacement detection device according to claim 8, wherein

a length of a first direction in the piezoelectric substance is larger than a length of a second direction orthogonal to the length of the first direction, and

an angle formed by the first direction and the uniaxial direction is substantially ±

45°

.

10. The displacement detection device according to claim 8, wherein

a length of a first direction in the piezoelectric substance is larger than a length of a second direction orthogonal to the length of the first direction, and

an angle formed by the first direction and the uniaxial direction is either approximately 0°

or approximately 90°

.

11. The displacement detection device according to claim 8, wherein

the piezoelectric sensor further includes an additional piezoelectric substance and an additional pair of detection electrodes disposed on opposing surfaces of the additional piezoelectric substance, and also includes a tabular elastic body, each of the piezoelectric substance and the additional piezoelectric substance being disposed on opposing surfaces of the tabular elastic body,

a length of a first direction in the piezoelectric substances is larger than a length of a second direction orthogonal to the length of the first direction,

an angle formed by the first direction and the uniaxial direction in the piezoelectric substance is approximately ±

45°

, and

an angle formed by the first direction and the uniaxial direction in the additional piezoelectric substance is either approximately 0°

or approximately 90°

.

12. The displacement detection device according to claim 11, wherein the tabular elastic body includes a conductor on a surface thereof, and the conductor serves as one electrode of the pair of detection electrodes disposed on one of the opposing surfaces of the piezoelectric substance or the additional piezoelectric substance.

13. The displacement detection device according to claim 11, wherein the tabular elastic body and at least one of the pair of additional detection electrodes comprise transparent materials.

14. The displacement detection device according claim 1, wherein the piezoelectric substance is laminated with the detection electrode interposed therebetween.

15. The displacement detection device according claim 1, wherein the controller is configured to short-circuit the switch for a predetermined period of time immediately after the controller detects the output voltage output from the voltage detector.

16. The displacement detection device according claim 1, further comprising an operational amplifier coupled between the piezoelectric sensor and the voltage detector,

wherein the piezoelectric sensor is coupled to a non-inverting input terminal of the operational amplifier and the voltage detector is coupled to an output terminal of the operational amplifier, and

wherein the output terminal of the operational amplifier is further coupled to an inverting input terminal of the operational amplifier.

17. A displacement detection method for detecting an amount of displacement of a piezoelectric sensor from an output voltage of the piezoelectric sensor, the method comprising:

setting a storage voltage for displacement calculation as a reference voltage;

measuring an output voltage of the piezoelectric sensor at a predetermined interval of time to obtain a measured voltage;

calculating a displacement voltage as a difference between the measured voltage and the reference voltage;

resetting the measured voltage to the reference voltage after calculating the displacement voltage;

sequentially integrating the displacement voltages to the reference voltage while updating and storing the obtained voltage as the storage voltage; and

calculating the amount of displacement from the storage voltage.

18. The displacement detection method according to claim 17, further comprising transitioning to a standby state upon detection that the storage voltage remains to be the reference voltage for predetermined time.

19. The displacement detection method according to claim 18, further comprising:

setting a temporary storage voltage as an initial value upon detection of a different voltage from the reference voltage;

comparing the output voltage and the temporary storage voltage while detecting the output voltage for temporary storage time based on a charge release time constant of the piezoelectric sensor;

updating the temporary storage voltage with the output voltage when the output voltage and the temporary storage voltage are different from each other; and

setting the output voltage as the storage voltage when the output voltage and the temporary storage voltage are substantially equal to each other.