JP2003219664A - Deterioration detector of piezoelectric actuator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a deterioration detector in which the degree of elongation/ contraction of a piezoelectric actuator can be grasped without fixing a sensor element externally, and deterioration of the piezoelectric actuator can be detected surely in the early stage. <P>SOLUTION: The deterioration detector comprises a piezoelectric actuator A, a DC controlled power supply S, a high frequency power supply H, a circuit for applying a high frequency voltage to the piezoelectric actuator from the high frequency power supply through a capacitor circuit, a circuit for measuring a signal voltage indicating the variation in the high frequency terminal voltage between a pair of electrodes 20 and 21 generated by variation in the capacitance of the piezoelectric actuator, and a comparison/alarm circuit delivering an alarm based on a measured voltage level wherein deterioration of a piezoelectric actuator under driving is detected by blocking DC currents by means of a capacitor in the high frequency voltage applying circuit so that subsequent high frequency circuit is not affected by the DC control power supply S. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for detecting deterioration of a piezoelectric actuator which converts electric energy into mechanical displacement energy by utilizing a piezoelectric element such as a piezo ceramic or a piezo element.

[0002]

2. Description of the Related Art Piezoelectric actuators are widely used in many industrial fields today because they have characteristics such as a small thrust, a large thrust that can be obtained, a fast response speed and suitable for precise control. Devices such as printers, fine movement stages of machine tools, gene manipulation devices,
Although its application fields such as medical manipulators and robots are expanding, there is still room for further research on their reliability and lifespan, and it would be extremely useful if the characteristics of actuators could be diagnosed and lifespan predicted. is there.

Conventionally, strain gauges have been used as means for detecting and measuring the operation of a piezoelectric actuator and its mechanical displacement. However, such a means only measures the mechanical displacement from the outside, and it is difficult to measure a minute mechanical displacement. Therefore, it has not been possible to reliably detect / predict the deterioration and life of the piezoelectric actuator, which is considered to be a sign of deterioration due to a slight decrease in mechanical displacement.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to replace the conventional mechanical displacement, that is, strain of an actuator with an external measuring instrument, and to change the electrical characteristics of the piezoelectric element itself. It is an object of the present invention to provide a device that enables deterioration and life prediction of a piezoelectric actuator by directly detecting and monitoring. The present inventors have paid attention to the fact that the piezoelectric element is originally a capacitor, regard the capacitance of the piezoelectric element itself as a sensor element, and take it into an electric circuit configured for detecting the deterioration of the piezoelectric actuator, and (EN) A device that reliably monitors the operation of an actuator without externally attaching a new sensor element to the piezoelectric actuator by reading the change in capacitance due to repeated expansion and contraction of the piezoelectric actuator as the output of a deterioration detection circuit. It is a thing.

[0005]

The present invention relates to a piezoelectric actuator for applying a DC voltage or current to a piezoelectric element to generate mechanical displacement energy by utilizing an inverse piezoelectric effect. Means for applying a high frequency voltage to the circuit, a circuit for continuously measuring the change in capacitance of the piezoelectric element detected by the application of the high frequency voltage, and an alarm signal when the measured capacitance value is out of a predetermined reference level range. The invention provides a deterioration detecting device for a piezoelectric actuator, characterized in that it further comprises means for generating and outputting.

More specifically, the present invention constitutes an apparatus for detecting deterioration of a piezoelectric actuator by knowing a change in capacitance of an actuator composed of a piezoelectric element, which is driven and controlled by a DC control power supply. This device is composed of a piezoelectric element having an electrode pair, and a piezoelectric actuator in which a mechanical displacement is generated by applying a constant DC voltage and a DC voltage which can be arbitrarily adjusted between the electrode pair of the piezoelectric actuator. A direct current control power supply configured to be applied, a high frequency power supply, a high frequency voltage application circuit for applying a high frequency voltage between the electrode pair of the piezoelectric actuator from the high frequency power supply via a capacitor circuit, and the piezoelectric actuator A high-frequency signal voltage measuring circuit that measures a signal voltage that represents a change in a high-frequency terminal voltage between the electrode pairs caused by a change in capacitance between the electrode pair, and a value of the high-frequency signal voltage measured by the high-frequency signal voltage measuring circuit. Is provided with a comparison / warning means for issuing an alarm when the voltage exceeds a certain reference value. Blocking the DC by the capacitor in the circuit, and it has the characteristics where the subsequent high-frequency circuit was not affected by the DC control power source.

According to this structure, the mechanical displacement of the piezoelectric actuator can be measured without relying on an external means such as a strain gauge. In addition, by using the property that the capacitance of the piezoelectric actuator itself changes due to the mechanical displacement of the piezoelectric actuator, the amount of change in the capacitance of the piezoelectric actuator is measured, for example, as the amount of change in the high frequency terminal voltage. Even a slight difference in the mechanical displacement amount can be detected, and the deterioration of the piezoelectric actuator can be warned to the outside promptly and reliably. Furthermore, since the piezoelectric actuator itself to be measured can be handled as a sensor element, there is no possibility of failure of only the sensor, and a sensor failure can be treated immediately as a failure of the piezoelectric actuator itself. The reliability of the entire device to be applied can also be increased.

In the above deterioration detecting device, the high frequency signal voltage measuring circuit uses the high frequency power source as a power source branch,
A series circuit of the piezoelectric actuator in the high frequency voltage applying circuit and a capacitor directly connected to the high frequency voltage applying circuit is defined as one side, and the other three sides are composed of another capacitor in the high frequency voltage applying circuit and a capacitor outside the high frequency voltage applying circuit. It is preferable to have a configuration including a bridge circuit, and with such a configuration, it is possible to avoid complication of the deterioration detection device.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION A deterioration detecting device for a piezoelectric actuator according to the present invention will be described below. The present invention does not use a strain gauge to measure the mechanical displacement of the actuator,
The amount of capacitance change caused by mechanical displacement of the actuator is used.The capacitance change caused by repeated expansion and contraction of this actuator is applied to the piezoelectric actuator by applying a high frequency voltage, and the resulting change between the electrode pair of the piezoelectric actuator. By reading the change in the voltage value of the high frequency terminal voltage, the degree of expansion and contraction of the piezoelectric actuator can be constantly measured to detect the deterioration. The object detected by the detection device of the present invention is the mechanical displacement of the piezoelectric actuator, and whether the mechanical displacement of the piezoelectric actuator during driving always reaches a predetermined mechanical displacement. Can be monitored to warn the outside of malfunctions of the actuator including insufficient mechanical displacement. On the other hand, the high-frequency voltage supply source used to measure the amount of change in capacitance due to mechanical displacement of the piezoelectric actuator may be a function generator for experiments, but a commercially available OP amplifier IC is used. An oscillating circuit that excites a desired high-frequency voltage can also be configured.

According to the present invention, in a high frequency terminal voltage measuring circuit capable of measuring a high frequency terminal voltage generated between electrode pairs of a piezoelectric actuator being driven by passing a high frequency current between the electrode pairs, the mechanical displacement of the piezoelectric actuator The amount of change in capacitance accompanying it is output as a voltage value,
At this time, a well-known bridge circuit can be used as the deterioration detecting circuit as the measuring means. Although FIG. 1 shows a preferred circuit configuration example of the deterioration detection device of the present invention, the structure of the deterioration detection circuit used in the present invention is not limited to this.

A deterioration detecting apparatus 1 for a piezoelectric actuator A shown in FIG. 1 includes a piezoelectric valve P which is a piezoelectric actuator A and a piezoelectric valve control power source S which is a DC variable voltage source.
And a control signal generator 8 for supplying a drive signal to the piezo valve control power source S, and a deterioration determination warning circuit M. The deterioration determination warning circuit M further includes a deterioration detection circuit 2 and an amplifier 3.
Frequency signal voltage measuring circuit T as a deterioration detecting section consisting of
And a comparison / warning circuit W that compares the output from the deterioration detection unit T with a reference value prepared in advance and issues an alarm according to the comparison result. The configuration of the deterioration detection circuit 2 is not limited to the above, and for example, the comparison result in the comparison / warning circuit W may be fed back to the control signal generation unit 8 and treated as one parameter for controlling the piezo valve control power source S. . The deterioration detection circuit 2 is as shown in FIG. 1, the piezoelectric element is originally a capacitor, and its capacitance changes according to the degree of expansion and contraction due to the electrostrictive effect. Is configured as an output of the bridge circuit B.

Here, the deterioration detection circuit 2 illustrated in FIG.
Is a device in which all the elements constituting the bridge circuit B are capacitors, and the electrodes 20 and 21 of the piezoelectric actuator A are inserted in series into any one of the sides 11 to 14 of the bridge circuit B. As a result, a high frequency power source H is connected between xy and a high frequency voltage is applied between the electrodes 20 and 21 through capacitors included in these bridge sides. In such a detection circuit, points a and b
By sampling the ground potential of each of the points and measuring the voltage difference between them, it is possible to read the voltage-converted value of the amount of change in capacitance due to the displacement generated in the piezoelectric actuator A, and to externally connect the sensor element. It is possible to measure the mechanical displacement of the piezoelectric actuator A without attaching it.

In the present invention, the voltage signal obtained at a predetermined position on the deterioration detection circuit by thus supplying the high frequency voltage to the piezoelectric actuator A is sampled,
The signal voltage for deterioration determination output through the processing step is finally guided to the comparison / warning circuit W, where the mechanical voltage that would be obtained if the piezoelectric actuator A was operating normally. It is compared and collated with the value corresponding to the displacement data. In the case of the deterioration detection device of the present invention, the result of the comparison,
When it is determined that the mechanical displacement of the piezoelectric actuator A during driving has not reached a predetermined specified value or the change amount of the signal voltage is excessive, an alarm signal is output.

The deterioration detecting circuit 2 of the deterioration detecting device 1 of the present invention.
Is as described above, and the detailed configuration of the deterioration detection circuit 2 will be described below. First, the deterioration detection circuit 2 includes a bridge circuit B including capacitors C1 to C4 as constituent elements of each side 11 to 14 of the bridge circuit B, a high frequency power supply H connected between xy of the bridge circuit B, and a bridge. Rectifier diodes D1 to D4 connected for extraction of high-frequency voltage signals from the points a and b of the circuit B and subsequent signal processing, and a deterioration detection target, a point x of the bridge circuit B and a capacitor. It consists of a piezo valve P inserted in series between C1 and the point x of the bridge circuit B is connected to the ground potential GND. The capacitors C1 to C4 may all be the same element, and even in the case of this embodiment, the same element having the same capacitance C is used. Electrode 2 of piezo valve P
0 and 21 are, for example, 100 KΩ to 1 as shown in FIG.
It is connected to a piezo valve control power source S, which is a DC variable voltage source, via a current limiting resistor R of the order of 0 MΩ, and from this piezo valve control power source S to the electrodes 20, 2 of the piezo valve P.
A DC voltage of, for example, 0 to 150 V is applied between 1 and. On the other hand, the high frequency voltage applied to the piezo valve P for the purpose of deterioration detection has a frequency of, for example, 10 KHz to 100 KHz.
It has a sine waveform of kHz and a peak-to-peak voltage value of about 5-10V. Since the high frequency power source H and the piezo valve control power source S which is a direct current power source are connected via the resistor R and the capacitor C1, the direct current of the piezo valve control power source S is blocked by the capacitor C1 and the high frequency power source H is supplied. The high-frequency power supply H does not enter the high-frequency circuit including the same, and the high-frequency power supply H suppresses the high-frequency current flowing to the piezo-valve control power supply S by the resistor R and does not substantially affect the piezo-valve control power supply S. In this way, since the high frequency power supply H and the piezo valve control power supply S do not affect each other, the high frequency power supply H and the piezo valve control power supply S remain connected at the same time, that is, the piezo valve P is maintained in the driven state. Moreover, the piezo valve P is controlled by the high frequency power source H without being affected by the piezo valve control power source S.
It is possible to measure the high frequency voltage supplied between the electrodes 20 and 21 of the. Further, the high frequency voltage signals extracted from the points a and b of the bridge circuit B are input to the amplifier 3, and subsequently signal processing for deterioration determination is performed.
In the circuit illustrated in FIG. 1, the amplifier 3 is a differential amplifier, and the voltage signals sampled from the points a and b of the bridge circuit B are the non-inverting input terminal (+) and the differential amplifier 3 respectively. It is connected to the inverting input terminal (-).

Next, the circuit operation which serves as the function of the deterioration detecting circuit 2 having the above-mentioned structure will be described. In order to simplify the description of this circuit, first, only the portion of the deterioration detection circuit 2 shown in FIG. 1 is redrawn to the form in which the high frequency power supply H is placed outside the bridge circuit B as shown in FIG. Furthermore, FIGS.
As shown in FIG. 3, the circuit operation is divided into a path passing through the capacitor C1 and the piezo valve P existing on the upper half surface of the x point of the bridge circuit B and a path passing through the capacitor C2 existing on the lower half surface, and further, for each of them. The polarity of the voltage applied from the high-frequency power source H is divided into two cases, that is, the case where the right side of each drawing shown in FIG. 3 has a positive polarity and the case where the left side has a positive polarity on the contrary, a total of four equivalent circuits will be described. In each figure, the + and − signs respectively marked on the high frequency power supply H, the capacitors C1 to C4 and the piezo valve P indicate the polarity of the voltage. Here, a) FIG. 3a shows a path through which the high-frequency current passes through the capacitor C1 and the piezo valve P during a half cycle in which the polarity of the high-frequency power supply H is positive on the right side of the figure, and b) FIG. The high frequency current passes through the capacitor C1 and the piezo valve P during a half cycle in which the polarity of the high frequency power source H is positive on the left side of the figure. C) FIG. 3c shows the polarity of the high frequency power source H on the right side of the figure. Shows the path through which the high-frequency current passes through the capacitor C2 during the positive half-cycle, and d) FIG. 3d shows that the high-frequency current changes during the half-cycle in which the polarity of the high-frequency power supply H is positive on the left side of the figure. It shows a path passing through the capacitor C2.

Now, when the piezo valve P is connected to the capacitor C1 in series, the piezo valve P has the capacitance component as described above, which is equivalent to the formation of the series connection of the capacitors. Since these combined capacitances are smaller than the capacitance C of the capacitor C1, the reduced amount is referred to as “−ΔC” for convenience, and the combined capacitance when the piezo valve P is connected to the capacitor C1 in series is referred to as “C−ΔC”. Shall be called. The capacitance C of the capacitors C1 to C4 is, for example, about several hundreds nF to several μF,
Also, the range of capacitance that the piezo valve P can take is about the same, and the value of C is designed and adjusted appropriately according to the piezo valve P. By the way, the capacitor C
When a capacitance component is connected in series to 1, the combined capacitance of these is less than or equal to the original capacitance C, and the larger the capacitance component connected in series, the closer to the original capacitance C. On the other hand, the capacitance of the piezo valve P becomes smaller as the mechanical displacement to be caused in the piezo valve P becomes larger, because the electrode plate interval of the piezoelectric element has to be expanded, and the capacitance of the piezo valve P tends to be made conversely. The smaller the mechanical displacement, the larger it becomes.
Therefore, the value of ΔC, which is the absolute value of the difference between the combined capacitance when the capacitance of the piezo valve P is connected in series with the capacitor C1 and the capacitance C of the capacitor C1 itself, is It is inversely proportional to the magnitude of the mechanical displacement (referred to as “ΔX” for convenience).

The state of the deterioration detection circuit 2 of the present invention will be described for each equivalent circuit shown in FIG. 3. a) In the case of the equivalent circuit of FIG. 3a, the ground potential at the point a of the bridge circuit B is Va = V _{C1- ΔC} , which is the voltage applied to the capacitor C1 and the piezo valve P. b) In the case of the equivalent circuit of FIG. 3b, the ground potential at the point b of the bridge circuit B becomes Vb = -VC1 _-AC , and a negative voltage is generated. c) In the case of the equivalent circuit of FIG. 3c, the ground potential at the point b of the bridge circuit B becomes Vb = V _C2 , and the capacitor C2
Voltage. For the equivalent circuit of d) FIG. 3d, ground potential at a point of the bridge circuit B is Va = _{-V C2,} and the negative voltage is generated. By the way, regarding the equivalent circuits shown in FIGS. 3a and 3c, for convenience sake, a path passing through the capacitor C1 and the piezo valve P on the upper half surface of the point x of the bridge circuit B,
It is only shown by dividing the path through the capacitor C2 on the lower half of the point x of the bridge circuit B, and it is an event that occurs simultaneously on the actual deterioration detection circuit. The same applies to the equivalent circuits shown in FIGS. 3b and 3d. Now, if the amplification ratio of the amplifier 3 is set to 1 for simplicity, the output voltage Vout of the amplifier 3 can be represented by Va-Vb. Therefore, the output voltage Vout is supplied from the high frequency power supply H by using the superposition principle of electric circuits. When the polarity of the generated voltage is positive on the right side of each figure shown in FIG. 3 and conversely on the left side is positive, Vout is expressed as follows, and Vout is the same in both cases. It becomes a value.

Formula 1 Vout = Va-Vb = V _C1-ΔC- V _C2 = (ΔC
/ (2 ・ (2C-ΔC))) ・ Vin

Here, if the voltage supplied from the high frequency power source H is Vin, the capacitor C is used in this embodiment.
Since 1 to C4 are the same element having the same capacitance C, the respective values of V _C1-ΔC and V _C2 are as follows.

Equation 2 V _C1-ΔC = (C / (2C-ΔC)) · Vin

Formula 3 V _C2 = Vin / 2

If the high-frequency voltage generated by the high-frequency power supply H is a sine waveform, the waveform of the output voltage Vout of the amplifier 3 will be observed as a so-called full-wave rectified waveform.

Here, using the relationship that the value of ΔC is inversely proportional to the magnitude ΔX of mechanical displacement occurring in the piezo valve P, Vout is transformed as follows.

Equation 4 Vout ∝1 / 2 ・ (C ・ ΔX-1)

Therefore, the output of the amplifier 3 has a relation depending on the magnitude ΔX of the mechanical displacement generated in the piezo valve P, and by monitoring this value, the problem to be solved by the present invention. It is possible to detect deterioration of the piezoelectric actuator.

The signal of Vout thus obtained is always output from the amplifier 3 when the piezoelectric actuator is driven. Signal Vout output from amplifier 3
Is then guided to the capacitance-flow rate conversion unit E in connection with an embodiment to be described later, and the flow rate data 7 is a value corresponding to the range of flow rates that can be taken when the piezoelectric actuator is operating normally. The value converted from the voltage value Vout into the form of the flow rate signal is compared in the comparison / warning circuit W. As a result of the comparison processing, an alarm is transmitted to the outside when an abnormality occurs, that is, when it is determined that it is outside the planned range. The signal Vout
Directly to the comparison / alarm circuit W, the value set as the voltage value corresponding to the capacitance range of the piezoelectric actuator A and the obtained Vout value are compared in the comparison / alarm circuit W, and when an abnormality occurs, That is, the configuration may be such that an alarm is issued when a voltage outside the expected range is detected.

The deterioration detecting apparatus having the structure shown in FIG. 1 applies a high-frequency voltage to the piezoelectric actuator by applying a high-frequency voltage to the piezoelectric actuator for the change in capacitance obtained with the change in mechanical displacement occurring in the driving piezoelectric actuator. The deterioration of the piezoelectric actuator, which can be grasped by measuring the change in the voltage value of the high-frequency terminal voltage between the electrode pair of the piezoelectric actuator obtained by the above method, is mainly estimated from the mechanical displacement of the piezoelectric actuator. The device itself can be regarded as a sensor element and directly measured instantly to make a determination. In particular, the device having such a configuration is suitable for detecting deterioration of a piezoelectric actuator that does not rely on a sensor element to be externally attached. Hereinafter, as a specific example of the deterioration detecting device for a piezoelectric actuator according to the present invention, a case where the device is applied as deterioration detecting means for a flow rate control passage opening / closing valve of a gas flow rate automatic control device will be described, but the present invention is not limited thereto. Not a thing.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 4 shows an outline of a gas flow rate automatic controller 50 which is an embodiment of the present invention. The automatic gas flow rate control device 50 includes a main body 33 having a gas flow path 32 including a bypass 30 and a sensor flow path 31, a gas flow rate sensor 34, a gas flow rate sensor control circuit 6, an arithmetic circuit 5, and a comparison control circuit 4. The control signal generator 8 includes a piezo valve control power source S, a piezo valve P, and a deterioration determination warning circuit M, and the gas flow rate is automatically controlled based on a flow rate command signal 35 input to the comparison control circuit 4. is there. The gas enters the gas inlet 36 from the gas supply source, passes through the gas passage 32, the bypass 30 or the sensor passage 31, and the piezo valve P in this order in the main body 33, and is discharged from the gas outlet 37. It Gas flow sensor 3
Reference numeral 4 is attached to a sensor passage 31 provided in parallel with a bypass 30 through which gas mainly flows, and is composed of a heater and a resistance temperature detector. The flow rate ratio between the bypass 30 and the sensor channel 31 is, for example, 10: 1,
By connecting the bypasses 30 in parallel and providing them in multiple rows, the rated gas flow rate of the present device can be increased. In this embodiment, the piezoelectric actuator A is used as an opening / closing piezo valve P that controls the flow of gas, and the deterioration detecting device 1 of the present invention is incorporated in the piezoelectric actuator A for the purpose of determining the deterioration. At this time, the piezo valve P is a normally open type in which the load applied to the valve is maximum when the flow path is blocked, and when the mechanical displacement of the piezo valve P reaches the maximum position, the valve 38 is fully closed and the gas flow is reduced. The path 32 is completely blocked. For the piezoelectric actuator, not only the laminated piezoelectric actuator type but also the bimorph type can be used. Here, the flow path opening / closing piezo valve P is
The piezo valve P has a structure in which a displacement supply unit 39 including a piezoelectric actuator A that operates in the vertical direction and a valve 38 provided below the displacement supply unit 39 are joined via a diaphragm 41 having elasticity and flexibility. The diaphragm 41 responds to the mechanical displacement, which causes the valve 38 to open and close. Therefore, automatic control of the gas flow rate is realized by controlling the opening / closing of the valve 38.

In the automatic gas flow rate control device 50 having the structure shown in FIG. 4, the deterioration detecting device 1 of the present invention having the structure shown in FIG. 1 is incorporated by being directly connected to the piezo valve P. Therefore, by constantly monitoring the result of the determination process obtained by the deterioration detection device of the present invention, it is possible to always grasp the expansion and contraction status of the piezoelectric actuator, and because an alarm is issued instantly when the deterioration is detected, It is possible to grasp the deterioration status of the piezoelectric actuator at an early stage and reliably.

The case where the deterioration detecting device for a piezoelectric actuator according to the present invention is incorporated as a part of a failure alarm device for a gas flow rate automatic control device has been described above. It can be applied to any type of device, and exerts a great effect on the deterioration of the piezoelectric actuator and the detection of its life.

[Brief description of drawings]

FIG. 1 is a diagram illustrating an example of a deterioration detection circuit.

FIG. 2 is a diagram in which the deterioration detection circuit of FIG. 1 is redrawn.

FIG. 3 is a diagram showing an equivalent circuit of the deterioration detection circuit of FIG.

FIG. 4 is a diagram showing an embodiment of the present invention.

[Explanation of symbols]

1 Deterioration detection device 2 Deterioration detection circuit 3 amplifier 4 Comparison control circuit 5 arithmetic circuit 6 Flow sensor control circuit 7 Flow rate data 8 Control signal generator 11 One side of bridge circuit 12 One side of bridge circuit 13 One side of bridge circuit 14 One side of bridge circuit 20 electrodes 21 electrodes 30 bypass 31 Sensor flow path 32 gas flow paths 33 body 34 Gas flow rate sensor 35 Flow rate command signal 36 gas inlet 37 Gas outlet 38 valves 39 Displacement supply unit 41 diaphragm 50 Gas flow rate automatic control device A piezoelectric actuator B bridge circuit C1 capacitor C2 capacitor C3 capacitor C4 capacitor D1 rectifier diode D2 rectifier diode D3 rectifier diode D4 rectifier diode E Capacitance-flow rate converter GND ground potential H high frequency power supply M deterioration judgment alarm circuit P Piezo valve R Current limiting resistor S Piezo valve control power supply T deterioration detector Vout Amplifier output voltage Vin High frequency power supply voltage W comparison / alarm circuit

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yama-saki Takeshi             16 Umehata Goshonoguchi-cho, Ukyo-ku, Kyoto-shi, Kyoto Prefecture             Local Yamazaki Co., Ltd. (72) Inventor Kiyoharu Tsujimura             982 Hiruda, Nakasu Town, Yasu-gun, Shiga Prefecture             Synergy Inc. (72) Inventor Makoto Mizukoshi             1-39, Minami Tokiwadai, Itabashi-ku, Tokyo Wealth             Toh Sangyo Co., Ltd.

Claims (2)

[Claims] 1. A DC voltage or current is applied to a piezoelectric element,
In a piezoelectric actuator that generates mechanical displacement energy using the inverse piezoelectric effect, means for applying a high-frequency voltage between the biasing electrodes of the piezoelectric element,
A circuit for continuously measuring a change in capacitance of the piezoelectric element detected by applying the high-frequency voltage, and means for generating and outputting an alarm signal when the measured capacitance value is out of a predetermined reference level range. A deterioration detecting device for a piezoelectric actuator, comprising: 2. The deterioration detecting device for a piezoelectric actuator according to claim 1, wherein the capacitance change detecting circuit is constituted by a capacitive bridge circuit in which a piezoelectric actuator element is incorporated in one side thereof.