Sensor and sensor processing device

Abstract

A sensor and a sensor processing device are provided. The sensor (1) includes a piezoelectric body (40), a resistor body (30) disposed on a first main surface (401) of the piezoelectric body (40), a vibration detection electrode (50) disposed on a second main surface (402) of the piezoelectric body (40), a resistor voltage dividing circuit (90) having a first input terminal (P1) and a voltage dividing point (P2), and a feedback processing circuit (91) having a second input terminal (P3). The resistor body (30) is connected to the voltage dividing point and the first input terminal (P1), and the vibration detection electrode (50) is connected to the second input terminal (P3).

Description

Technical Field

[0001] One embodiment of the present invention relates to a sensor for detecting static strain and minute vibrations. Background Technology

[0002] The sensor in Patent Document 1 has a resistive element formed on the surface of a polymer piezoelectric material. The sensor in Patent Document 1 uses the polymer piezoelectric material to measure elastic waves (micro-vibrations). Furthermore, the sensor in Patent Document 1 measures static strain by measuring the resistance change of the resistive element.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2007-170942

[0004] The sensor in Patent Document 1 measures static strain based on the change in the time constant caused by the resistance of a resistive element and the capacitance of a piezoelectric element. Therefore, the sensor in Patent Document 1 requires a charging pulse waveform and a timer, and thus requires complex circuitry. Summary of the Invention

[0005] Therefore, one embodiment of the present invention aims to provide a sensor for detecting both static strain and minute vibrations with a simpler structure.

[0006] A sensor according to one embodiment of the present invention includes: a piezoelectric element; a resistive element disposed on a first main surface of the piezoelectric element; a vibration detection electrode disposed on a second main surface of the piezoelectric element; a resistive voltage divider circuit having a first input terminal and a voltage divider point; and a feedback processing circuit having a second input terminal. Furthermore, the resistive element is connected to the voltage divider point and the first input terminal, and the vibration detection electrode is connected to the second input terminal.

[0007] If a piezoelectric element experiences strain, the resistance of the resistive element changes. This change in resistance leads to a change in the output voltage of the resistive voltage divider circuit. Therefore, the sensor can detect static strain. Furthermore, by utilizing a feedback processing circuit with a high input impedance, the sensor converts the charge generated by the vibration of the piezoelectric element into voltage, enabling high-level detection even of minute vibrations.

[0008] According to one embodiment of the invention, static strain and minute vibrations can be detected with a simple structure. Attached Figure Description

[0009] Figure 1 This is a side cross-sectional view of sensor 1.

[0010] Figure 2 This is a circuit diagram showing the structure of a resistor voltage divider circuit 90.

[0011] Figure 3This is a circuit diagram showing the structure of the feedback processing circuit 91.

[0012] Figure 4 (A) is a diagram showing the output voltage Vout of the feedback processing circuit 91. Figure 4 (B) is a diagram representing the output voltage e of the resistor voltage divider circuit 90.

[0013] Figure 5 This is a circuit diagram showing the structure of the modified feedback processing circuit 91B.

[0014] Figure 6 This is a circuit diagram showing the structure of a modified resistor voltage divider circuit of 90A.

[0015] Figure 7 This is a block diagram showing the structure of a sensor processing device consisting of sensor 1 and microcomputer 95. Detailed Implementation

[0016] The sensor of the present invention will now be described with reference to the accompanying drawings. Figure 1 This is a side cross-sectional view of sensor 1. The sensor, for example, is adhered to human skin to detect pulsations as minute vibrations and static strain. Sensor 1 is adhered to the object 2, such as human skin, using adhesive 5.

[0017] The sensor 1 includes a piezoelectric element 40, a resistive element 30 disposed on a first main surface 401 of the piezoelectric element 40, and a vibration detection electrode 50 disposed on a second main surface 402 of the piezoelectric element 40. Furthermore, the sensor 1 has an insulator 60 and a shielding electrode 70 disposed opposite to the second main surface 402 of the piezoelectric element 40. The insulator 60 has a third main surface 601 and a fourth main surface 602, with the third main surface 601 disposed opposite to the second main surface 402 of the piezoelectric element 40. Additionally, the shielding electrode 70 is disposed on the fourth main surface 602 of the insulator 60. However, the insulator 60 and the shielding electrode 70 are not essential structures in this invention.

[0018] The piezoelectric element 40 is made of, for example, a ceramic or polymer-based piezoelectric material. Examples of polymeric piezoelectric materials include polyvinylidene fluoride (PVDF) or uniaxially stretched polylactic acid (PLA). Uniaxially stretched PLA has a very high piezoelectric constant among polymers. This means it can detect minute vibrations and static strain with high sensitivity. Furthermore, since PLA is not pyroelectric, the amount of charge generated does not change even when heat is transferred to human skin. Therefore, PLA is suitable as a sensor that can be adhered to human skin. Moreover, the piezoelectric constant of PLA is very stable and does not change over time.

[0019] The insulator 60 is made of, for example, polyethylene terephthalate (PET) or polymethyl methacrylate resin (PMMA).

[0020] The resistive element 30, the vibration detection electrode 50, and the shielding electrode 70 are made of a thin metal film of copper-nickel alloy or nickel-chromium alloy.

[0021] The vibration detection electrode 50 is a full-surface electrode covering approximately the entire surface of the second main surface 402 of the piezoelectric body 40. The shielding electrode 70 is a full-surface electrode with an area approximately the same as that of the vibration detection electrode 50 when viewed from above, and covers approximately the entire surface of the vibration detection electrode 50 via an insulator 60. When viewed from above, the resistive body 30 is, for example, patterned in a zigzag shape.

[0022] Resistor 30 is connected to resistor voltage divider circuit 90 via wiring. One end of the wiring is connected to resistor voltage divider circuit 90 via connection point P1, and the other end is connected to resistor voltage divider circuit 90 via connection point P2. Additionally, shielding electrode 70 is connected to connection point P2. Furthermore, vibration detection electrode 50 is connected to feedback processing circuit 91 via wiring and connection point P3. Feedback processing circuit 91 is connected to shielding electrode 70 and resistor 30 via connection point P2.

[0023] Figure 2 This is a circuit diagram showing the structure of a resistor voltage divider circuit 90. Figure 3 This is a circuit diagram showing the structure of the feedback processing circuit 91.

[0024] Figure 2 The resistor voltage divider circuit 90 shown has resistors R1, R2, and R3. Connection point P1 corresponds to the input point (first input terminal) of the resistor voltage divider circuit 90. Connection point P2 corresponds to the voltage division point of the resistor voltage divider circuit 90 (the voltage division point of resistor R3 and resistor body 30). Resistors R1, R2, R3, and resistor body 30 form a bridge circuit.

[0025] A power supply voltage (bridge voltage) E is applied to the first input terminal, i.e., connection point P1. The potential difference between the output voltage divider point (connection point P2) of the resistor voltage divider circuit 90 and the voltage divider point (connection point) P4 of resistors R1 and R2 is the output voltage e.

[0026] Here, if the object being tested 2 deforms and the piezoelectric element 40 deforms, the shape of the resistive element 30, which is patterned into a tortuous shape, changes, and therefore the resistance value of the resistive element 30 changes. If the resistance value of the resistive element 30 changes, the output voltage e also changes. For example, if the resistance values ​​of resistors R1, R2, R3, and the resistive element 30 are all R, and the change in the resistance value of the resistive element 30 is ΔR, the output voltage e is represented by e = (1 / 4)·(ΔR / R)·E.

[0027] Therefore, by measuring the output voltage e, sensor 1 can determine the change in resistance of resistive element 30. Moreover, sensor 1 can calculate the strain by dividing the change in resistance by the strain rate (a value determined by the material of resistive element 30).

[0028] In addition, sensor 1 can also amplify the potential difference by connecting connection points P2 and P4 to a differential amplifier circuit (not shown), thereby measuring the minute output voltage e with higher precision.

[0029] Next, Figure 3 The feedback processing circuit 91 shown includes an operational amplifier OP. A circuit consisting of a piezoelectric element 40, a resistor R4, and a capacitor C connected in parallel is connected to the operational amplifier OP. The operational amplifier OP forms a voltage follower whose output is connected to the inverting input terminal. The resistance value of resistor R4 and the capacitance of capacitor C are, for example, adjusted to a time constant for detecting the output voltage of the piezoelectric element 40 generated by minute vibrations of approximately 100 ms.

[0030] Connection point P2 is connected to the shielding electrode 70 and the resistive element 30 as described above, becoming a reference potential. If the resistive element 30 is made a reference potential, it also functions as a shielding electrode through its electrical connection to the shielding electrode 70. That is, since the two main surfaces of the vibration detection electrode 50 are covered by the shielding electrode 70 and the resistive element 30 at the reference potential, noise can be reduced. In particular, if the resistive element 30, which is close to the object being detected 2, is made a reference potential, noise from the object being detected 2 can be prevented, and minute signals can be detected with higher precision.

[0031] The connection point P3 corresponding to the second input terminal of this invention is connected to the vibration detection electrode 50. If vibration is generated in the piezoelectric element 40, a small signal is input to the non-inverting input of the operational amplifier. Since the voltage follower composed of the operational amplifier OP has a very high input impedance, it is possible to output the output voltage Vout without attenuating such a small input signal. Therefore, the sensor 1 can detect the small vibration generated in the piezoelectric element 40.

[0032] Furthermore, assuming that AC hum noise or other noises are superimposed on the output voltage Vout, an analog filter circuit can be connected to reduce the noise, or digital signal processing can be used for noise reduction.

[0033] Figure 4 (A) is a diagram showing the output voltage Vout of the feedback processing circuit 91. Figure 4 (B) is a diagram representing the output voltage e of the resistor divider circuit 90. For example... Figure 4As shown in (A), the output voltage Vout of the feedback processing circuit 91 represents a stable voltage value of approximately 1V when no minor vibrations occur, while in the case of minor vibrations, it represents a voltage fluctuation of 1 ± 0.1V or more. Furthermore, as... Figure 4 As shown in (B), the output voltage e of the resistor voltage divider circuit 90 represents a voltage value of about 0.5V when no strain occurs, and a voltage value of about 0.7V when strain occurs.

[0034] Therefore, sensor 1 does not use complex circuits such as charging pulse waveforms and timers. It can detect both minute vibrations and static strains using only a simple circuit structure consisting of a piezoelectric element, a resistive element, a vibration detection electrode, a resistive voltage divider circuit (resistive circuit), and a feedback processing circuit (operational amplifier).

[0035] Next, Figure 5 This is a circuit diagram showing the structure of the modified feedback processing circuit 91B. For... Figure 3 Shared structures are labeled with the same reference numerals, and descriptions are omitted. The feedback processing circuit 91B is a non-inverting amplifier circuit.

[0036] Connection point P2 is connected to the inverting input terminal (reference input terminal) of operational amplifier OP via resistor R5. In other words, shielding electrode 70 and resistor 30 are connected to the reference input terminal of the non-inverting amplifier circuit. Additionally, the output of operational amplifier OP is connected to the reference input terminal via resistor R6.

[0037] The output voltage Vout, relative to the voltage at connection point P3, is amplified by a factor determined by the ratio of the resistance values ​​of resistors R5 and R6. That is, the output voltage Vout becomes (1 + R6 / R5) times the voltage at connection point P3.

[0038] In a feedback processing circuit 91B that functions as a non-inverting amplifier, the output voltage Vout can be output without attenuating a small input signal. Furthermore, since the feedback processing circuit 91B amplifies the input voltage, even input signals with minute vibrations can be properly detected by appropriately setting the resistance values ​​of resistors R5 and R6.

[0039] Figure 6 This is a circuit diagram showing the structure of a modified 90A resistor voltage divider circuit. (And...) Figure 2 Shared structures are labeled with the same reference numerals, and descriptions are omitted. The resistor divider circuit 90A has a resistor R7. Connection point P1 corresponds to the input point (first input terminal) of the resistor divider circuit 90A. Connection point P2 corresponds to the voltage division point of the resistor divider circuit 90A (the voltage division point of resistor R7 and resistor element 30).

[0040] A power supply voltage E is applied to the first input terminal, i.e., connection point P1. The voltage at the output voltage divider point, i.e., connection point P2, of the resistor divider circuit 90A is then used as the output voltage e. Here, if the object 2 deforms and the piezoelectric element 40 and the resistive element 30 experience strain, the resistance value of the resistive element 30 changes. If the resistance value of the resistive element 30 changes, the output voltage e also changes. For example, if the resistance value of resistor R7 is R and the change in resistance value of the resistive element 30 is ΔR, the output voltage e is represented by e = E / {2 + (ΔR / R)}.

[0041] Therefore, in Figure 6 In the resistive voltage divider circuit 90A shown, sensor 1 can measure the change in resistance of resistive element 30 simply by measuring the output voltage e. Furthermore, sensor 1 can calculate the strain by dividing the change in resistance by the strain rate (a value determined by the material of resistive element 30).

[0042] In this way, sensor 1 can detect static strain even with a simpler structure. However, when the strain is small and the change in resistance of resistive element 30 is minimal, a more sensitive resistive voltage divider circuit is preferred. Figure 2 The bridge circuit shown.

[0043] Next, Figure 7 This is a block diagram showing the structure of a sensor processing device consisting of sensor 1 and microcomputer 95. On microcomputer 95, the output 900 of the resistor divider circuit 90 of sensor 1 and the output 911 of the feedback processing circuit 91 are connected.

[0044] The microcomputer 95 corresponds to the processing unit that performs arithmetic processing, and performs arithmetic processing on the output of the feedback processing circuit 91 based on the output of the resistor voltage divider circuit 90. Furthermore, the microcomputer 95 performs arithmetic processing on the output of the resistor voltage divider circuit 90 based on the output of the feedback processing circuit 91. For example, in the case where the sensor 1 is attached to a person's skin to detect a pulse, as described above, the resistor voltage divider circuit 90 detects large strains in the skin, and the feedback processing circuit 91 detects pulsations. Moreover, if the strain detected by the resistor voltage divider circuit 90 exceeds a certain value, the microcomputer 95 determines that an accurate pulsation cannot be obtained, and invalidates the pulsation detected by the feedback processing circuit 91. Thus, the sensor processing circuit can accurately detect the pulse. Additionally, for example, when the sensor 1 is attached to a soft robotic arm for adjusting the gripping force, the resistor voltage divider circuit 90 can detect the deformation and amount of deformation of the robotic arm. The microcomputer 95 can, for example, adjust the gripping force based on the amount of deformation. Furthermore, the feedback processing circuit 91 can detect slippage caused by the weight of the object being gripped. If the slippage detected by the feedback processing circuit 91 exceeds a certain value, the microcomputer 95 determines that there is a risk of the held object falling and shifts the output of the resistor voltage divider circuit 90. By compensating for the deformation caused by the shift, the gripping force of the robot arm is increased. Thus, a robot arm that suppresses the risk of falling can be realized.

[0045] The description of this embodiment is illustrative in all respects and is not restrictive. The scope of the invention is not limited to the embodiments described above, but is defined by the claims. Furthermore, the scope of the invention is intended to include all modifications within the scope of the claims.

[0046] For example, in the above embodiment, skin is shown as the detection object 2, and the person's pulsation and strain are detected. However, the detection object 2 could also be a robotic arm. In this case, sensor 1 can detect minute mechanical vibrations and larger strains.

[0047] Explanation of reference numerals in the attached figures

[0048] 1…Sensor; 2…Object to be detected; 5…Adhesive; 30…Resistor; 40…Piezoelectric element; 50…Vibration detection electrode; 60…Insulator; 70…Shielding electrode; 90…Resistor voltage divider circuit; 90A…Resistor voltage divider circuit; 91…Feedback processing circuit; 91B…Feedback processing circuit; 95…Microcomputer.

Claims

1. A sensor, comprising: piezoelectric elements; A resistive element is disposed on the first main surface of the piezoelectric element described above; A vibration detection electrode is disposed on the second main surface of the piezoelectric material. A resistor divider circuit has a first input terminal and a voltage divider point; and The feedback processing circuit has a second input terminal. The aforementioned resistor is connected to the aforementioned voltage divider point and the aforementioned first input terminal. The vibration detection electrode is connected to the second input terminal. The feedback processing circuit described above includes a non-inverting amplifier circuit. The aforementioned resistor is connected to the reference input terminal of the aforementioned non-inverting amplifier circuit.

2. The sensor according to claim 1, wherein, The resistor divider circuit described above is a bridge circuit.

3. The sensor according to claim 2, wherein, It also has a differential amplifier circuit, which is connected to the bridge circuit.

4. The sensor according to any one of claims 1 to 3, wherein, have: An insulator having a third main surface and a fourth main surface, wherein the third main surface and the second main surface are disposed opposite each other; and A shielding electrode is disposed on the fourth main surface of the aforementioned insulator.

5. A sensor processing device, comprising: The sensor according to any one of claims 1 to 4; and The processing unit adjusts the output of the resistor divider circuit based on the output of the feedback processing circuit.

6. A sensor processing device, comprising: The sensor according to any one of claims 1 to 4; and The processing unit adjusts the output of the feedback processing circuit based on the output of the resistor voltage divider circuit.

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