阅读说明：本技术 具备压电元件的劣化检测电路的驱动装置以及劣化检测方法 (Drive device provided with piezoelectric element degradation detection circuit and degradation detection method ) 是由 日高敦志 杉田胜幸 中谷贵纪 西野功二 池田信一 于 2020-04-20 设计创作，主要内容包括：本发明提供一种具备不停止驱动装置的通常动作,就能够检测在驱动装置中使用的压电元件的劣化的压电元件的劣化检测电路的驱动装置以及劣化检测方法。驱动装置(1)具备：压电元件(2)、电源部(3)、第一电阻(11)、第二电阻(12)、测定部以及控制部,第一电阻以及第二电阻的电阻值比压电元件的绝缘电阻值小,测定部在从电源部供给规定电压的状态下,测定第一电阻的两端的电压(第一端子(13)以及第二端子(14)之间的电压),控制部(3)根据通过测定部的测定而得到的电压值计算压电元件的电阻值,基于所计算出的电阻值,判定压电元件是否发生了劣化。(The invention provides a drive device and a deterioration detection method, which are provided with a deterioration detection circuit of a piezoelectric element and can detect the deterioration of the piezoelectric element used in the drive device without stopping the normal operation of the drive device. A drive device (1) is provided with: the piezoelectric element comprises a piezoelectric element (2), a power supply unit (3), a first resistor (11), a second resistor (12), a measurement unit, and a control unit, wherein the resistance values of the first resistor and the second resistor are smaller than the insulation resistance value of the piezoelectric element, the measurement unit measures the voltage at both ends of the first resistor (the voltage between a first terminal (13) and a second terminal (14)) in a state where a predetermined voltage is supplied from the power supply unit, the control unit (3) calculates the resistance value of the piezoelectric element from the voltage value obtained by the measurement of the measurement unit, and determines whether or not the piezoelectric element is deteriorated based on the calculated resistance value.)

1. A drive device is characterized by comprising:

a piezoelectric element;

a first resistor connected in series to the piezoelectric element;

a voltage supply unit configured to supply a dc voltage to both ends of a series circuit formed by the piezoelectric element and the first resistor;

a measuring unit that measures a voltage of the first resistor; and

a control unit that controls the voltage supply unit and the measurement unit,

the resistance value of the first resistor is smaller than the insulation resistance value of the piezoelectric element,

the measuring unit measures the voltage of the first resistor in a state where a predetermined voltage is supplied from the voltage supply unit,

the control unit calculates a resistance value of the piezoelectric element based on the voltage value measured by the measurement unit,

determining whether or not the piezoelectric element is deteriorated based on the calculated resistance value.

2. The drive device according to claim 1,

the measuring unit measures the voltage of the first resistor a plurality of times in a state where the predetermined voltage is supplied from the voltage supplying unit,

the control unit calculates a resistance value of the piezoelectric element from each of a plurality of voltage values obtained by a plurality of measurements,

calculating a representative value of the plurality of the calculated resistance values of the piezoelectric element,

whether or not the piezoelectric element is deteriorated is determined by comparing the representative value with a predetermined threshold value.

3. The drive device according to claim 1,

the measuring unit measures the voltage of the first resistor a plurality of times in a state where the predetermined voltage is supplied from the voltage supplying unit,

the control unit repeatedly performs: a process of calculating a resistance value of the piezoelectric element from each of a plurality of voltage values obtained by a plurality of measurements, and a process of calculating a representative value of the plurality of calculated resistance values of the piezoelectric element,

calculating slopes of the calculated plurality of representative values,

whether or not the piezoelectric element is deteriorated is determined by comparing the slope with a predetermined threshold value.

4. The drive device according to any one of claims 1 to 3,

the measurement unit determines whether or not the piezoelectric element is deteriorated, based on a predetermined time after the piezoelectric element is initially applied with a voltage.

5. The drive device according to any one of claims 1 to 3,

the drive device has a mechanism for opening and closing the valve by the piezoelectric element,

the measuring unit determines whether or not the piezoelectric element is deteriorated, based on a case where the number of times the valve is opened and closed exceeds a predetermined number of times.

6. The drive device according to any one of claims 1 to 5,

further comprises a second resistor, and the second resistor is provided,

the second resistor is connected in series to the piezoelectric element and the first resistor,

the second resistor is connected between the positive-side terminal of the voltage supply unit and the first resistor,

the resistance value of the second resistor is smaller than the insulation resistance value of the piezoelectric element and larger than the resistance value of the first resistor.

7. A method for detecting deterioration of a piezoelectric element, the method including a driving device having the piezoelectric element, a first resistor connected in series to the piezoelectric element, a voltage supply unit for supplying a DC voltage, and a measurement unit for measuring a voltage, the method comprising:

supplying a predetermined direct-current voltage to both ends of a series circuit formed by the piezoelectric element and the first resistor by the voltage supply unit;

a measuring step of measuring a voltage of the first resistor by the measuring unit in a state where the predetermined dc voltage is supplied;

a calculation step of calculating a resistance value of the piezoelectric element from the voltage value obtained in the measurement step; and

and determining whether or not the piezoelectric element is deteriorated based on the resistance value calculated in the calculating step.

Technical Field

The present invention relates to a drive device including a piezoelectric element degradation detection circuit used as a drive source of a drive device such as an actuator, and a method of detecting degradation of a piezoelectric element, and more particularly, to a pressure type flow rate control device including a piezoelectric element degradation detection circuit and a method of detecting degradation of a piezoelectric element for use as a control device for supplying a fluid such as a gas in a semiconductor manufacturing facility, a chemical plant, or the like.

Background

There is known a pressure type flow rate control device used for supplying a fluid such as a gas in a semiconductor manufacturing facility, a chemical plant, or the like (patent documents 1, 2, and the like). In this pressure type flow rate control device, a control valve (valve) using a piezoelectric element (Piezo element) can be used. For example, patent document 1 listed below discloses a pressure type flow rate control device including a piezoelectric element driven metal diaphragm type control valve (hereinafter, simply referred to as a control valve) as shown in fig. 8. The control valve 100 includes: a piezoelectric element 101, a connector 102 connected to a power source (not shown) for supplying a voltage to the piezoelectric element 101, and a diaphragm valve body 104 provided in a valve main body 103. The piezoelectric element 101 is accommodated in a cylindrical support tube 105, and is deformed in the longitudinal direction by on/off control of supply of a predetermined voltage via a connector 102. The diaphragm valve body 104 is deformed by the deformation of the piezoelectric element 101, and the valve is opened and closed.

The pressure type flow rate control device includes a throttle portion 106 such as an orifice in a flow path 107 of a fluid G, and adjusts an upstream side pressure P1 detected by a first pressure sensor 108 provided on an upstream side of the throttle portion 106 by a control valve 100 on the upstream side of the throttle portion 106 under a critical expansion condition in which an upstream side pressure P1 of the throttle portion 106 is maintained at about twice or more of a downstream side pressure P2 of the throttle portion 106. Thus, the basic principle is that the flow rate Qc on the downstream side of the throttle unit 106 is calculated from Qc-KP 1 (where K is a constant depending on the type of fluid and the fluid temperature), and the flow rate Qc is controlled to be a predetermined set value. Even in a situation where the difference between the upstream pressure P1 and the downstream pressure P2 is small and the above-described critical expansion condition is not satisfied, the downstream pressure P2 can be detected by a second pressure sensor (not shown) provided on the downstream side of the throttle portion 106, and the flow rate can be calculated. That is, the flow rate Q can be determined from the upstream pressure P1 and the downstream pressure P2 measured by the first pressure sensor 108 and the second pressure sensor, based on Q2 · P2m (P1-P2) n (here, K2 is a constant depending on the type of fluid and the fluid temperature, and m and n are indices derived based on the actual flow rate). In fig. 8, reference numeral 109 denotes a control circuit board (control unit).

The control valve described above is used for a long time and continuously in a semiconductor manufacturing facility, a chemical plant, or the like. The piezoelectric element used for the control valve may fail due to deterioration with age, but it is impossible to predict when the control valve fails due to deterioration of the piezoelectric element.

The control valve is also used for supplying gas containing moisture, and the service life of the piezoelectric element greatly varies depending on whether or not there is moisture in the use environment. Some control valves include a case in which a piezoelectric element is accommodated and a member (moisture adsorbent) for absorbing moisture is filled in the case. Therefore, even in a situation where the control valve is used for the same time and the same number of times of opening and closing, the degree of deterioration of the piezoelectric element varies depending on the usage environment (i.e., the usage environment of the piezoelectric element) and whether or not the moisture adsorbent is provided. Therefore, it is difficult to predict the deterioration of the piezoelectric element and to predict the replacement timing of the pressure type flow rate control device.

The control valve cannot control the flow rate as intended due to deterioration of the piezoelectric element, and cannot supply the fluid if a failure occurs. In the case of replacement of the control valve after a failure, the apparatus is stopped at a timing other than the predetermined timing. To prevent this situation, the control valve may be replaced at regular intervals. However, the control valve having a piezoelectric element without a failure may be replaced together.

Patent document 3, which will be described later, discloses a piezoelectric actuator in which an abnormality of a piezoelectric element is detected in advance. The piezoelectric actuator includes: an abnormality detection circuit different from a drive circuit used for a normal operation, and a switch for switching the drive circuit and the abnormality detection circuit. Before the piezoelectric actuator is operated, the switch is switched, and whether or not the piezoelectric element is abnormal is determined by an abnormality detection circuit. If there is no abnormality, the switch is switched to operate the piezoelectric actuator via the drive circuit.

Prior art documents

Patent document

Patent document 1: japanese patent No. 4119109

Patent document 2: japanese patent laid-open No. 2009-116904

Patent document 3: japanese patent laid-open publication No. 2017-60356

As described above, it is preferable that deterioration of the piezoelectric element be detected in advance and replaced before deterioration or failure of the control valve. Therefore, deterioration of the piezoelectric element itself must be detected.

In patent document 3, although deterioration of the piezoelectric element can be detected, it is necessary to provide an abnormality detection circuit other than the drive circuit in the normal operation, which causes a problem that the structure becomes complicated and the cost increases. Further, before the normal operation is performed, it is necessary to determine whether or not the piezoelectric element is abnormal by an abnormality detection circuit, and there is a problem that it is difficult to apply the method to a device used continuously for a long time in a semiconductor manufacturing facility, a chemical plant, or the like.

Disclosure of Invention

An object of the present invention is to solve the above-described problems and to provide a driving device and a deterioration detection method including a deterioration detection circuit for a piezoelectric element, which can detect deterioration of the piezoelectric element used in the driving device without stopping a normal operation of the driving device.

In order to achieve the above object, a drive device according to a first aspect of the present invention includes: a piezoelectric element; a first resistor connected in series to the piezoelectric element; a voltage supply unit that supplies a dc voltage to both ends of a series circuit formed by the piezoelectric element and the first resistor; a measuring unit that measures a voltage of the first resistor; and a control unit that controls the voltage supply unit and the measurement unit, wherein the resistance value of the first resistor is smaller than the insulation resistance value of the piezoelectric element, the measurement unit measures the voltage of the first resistor in a state where a predetermined voltage is supplied from the voltage supply unit, the control unit calculates the resistance value of the piezoelectric element from the voltage value obtained by the measurement of the measurement unit, and determines whether or not the piezoelectric element is deteriorated based on the calculated resistance value.

The measuring unit measures the voltage of the first resistor a plurality of times in a state where the predetermined voltage is supplied from the voltage supply unit, and the control unit can calculate the resistance value of the piezoelectric element from each of a plurality of voltage values obtained by the plurality of measurements, calculate a representative value of the plurality of calculated resistance values of the piezoelectric element, and determine whether or not the piezoelectric element is deteriorated by comparing the representative value with a predetermined threshold value.

The measuring unit may measure the voltage of the first resistor a plurality of times in a state where the predetermined voltage is supplied from the voltage supplying unit, and the control unit may repeat: the processing of calculating the resistance value of the piezoelectric element from each of the plurality of voltage values obtained by the plurality of measurements and the processing of calculating the representative value of the plurality of calculated resistance values of the piezoelectric element calculate the slope of the plurality of calculated representative values, and compare the slope with a predetermined threshold value to determine whether or not the piezoelectric element is deteriorated.

The measuring section can determine whether or not the piezoelectric element is deteriorated, based on a predetermined time period after the piezoelectric element is initially applied with a voltage.

The above-described driving device may have a mechanism for opening and closing the valve by the piezoelectric element, and the measuring unit may determine whether or not the piezoelectric element is deteriorated, based on a case where the number of times the valve is opened and closed exceeds a predetermined number of times.

Preferably, the driving device further includes a second resistor connected in series to the piezoelectric element and the first resistor, the second resistor being connected between the positive-side terminal of the voltage supply unit and the first resistor, and a resistance value of the second resistor is smaller than an insulation resistance value of the piezoelectric element and larger than a resistance value of the first resistor.

A deterioration detection method according to a second aspect of the present invention is a deterioration detection method for a piezoelectric element of a drive device including the piezoelectric element, a first resistor connected in series to the piezoelectric element, a voltage supply unit for supplying a dc voltage, and a measurement unit for measuring a voltage, the deterioration detection method including: supplying a predetermined direct-current voltage to both ends of a series circuit formed by a piezoelectric element and a first resistor by the voltage supply unit; a measuring step of measuring a voltage of the first resistor by the measuring unit in a state where a predetermined direct current voltage is supplied; a calculation step of calculating a resistance value of the piezoelectric element from the voltage value obtained in the measurement step; and determining whether or not the piezoelectric element is deteriorated based on the resistance value calculated in the calculating step.

Effects of the invention

According to the present invention, it is possible to determine whether or not the piezoelectric element is deteriorated without affecting the normal operation of the driving device. That is, since the detection circuit is provided in the middle of the wiring for normally controlling the piezoelectric element so as not to affect the normal control, it is possible to determine whether the piezoelectric element is deteriorated or not at the time of the normal control without providing an extra device or circuit. Therefore, it is possible to determine whether or not the drive device itself should be replaced at the time of normal control of the drive device.

In addition, it is possible to determine whether or not the deterioration of the piezoelectric element has occurred and whether or not the drive device should be replaced, independently of the use environment of the drive device (piezoelectric element) and whether or not the drive device is provided with the moisture adsorbent.

Further, the presence or absence of deterioration of the piezoelectric element can be determined even when the driving device is stopped or when the gas supply is completed.

When the resistance value of the piezoelectric element calculated by one measurement is compared with a predetermined threshold value to determine whether or not the piezoelectric element is deteriorated, there is a possibility that an erroneous determination that the piezoelectric element is deteriorated may occur even in a situation where the resistance value accidentally exceeds the threshold value. In contrast, it is possible to prevent erroneous determination by comparing a representative value (for example, an average value) or a tendency (for example, a slope) of the representative value of the plurality of calculated resistance values with a predetermined reference (threshold value).

Drawings

Fig. 1 is a block diagram (block diagram) showing a schematic configuration of a drive device including a deterioration detection circuit for a piezoelectric element according to an embodiment of the present invention.

Fig. 2 is a circuit diagram showing an equivalent circuit of a circuit for supplying a voltage to the piezoelectric element of fig. 1.

Fig. 3 is a block diagram showing a control section regarding degradation detection of the piezoelectric element.

Fig. 4 is a flowchart showing a method of detecting deterioration of a piezoelectric element.

Fig. 5 is a graph showing the measurement results by the data logger.

Fig. 6 is a block diagram showing a schematic configuration of a driving device including a degradation detection circuit different from that of fig. 1.

Fig. 7 is a graph showing the resistance value of the piezoelectric element calculated from the measurement result.

Fig. 8 is a longitudinal sectional view showing the structure of a conventional piezoelectric element driven metal diaphragm control valve.

Description of the symbols

1 drive device

2 piezoelectric element

3 control part

4 power supply unit

5 first connector

6 second connector

7 first positive terminal

8 first negative terminal

9 second positive terminal

10 second negative terminal

11 first resistance

12 second resistance

13 first terminal

14 second terminal

15 degradation detection circuit

20 CPU

21 ROM

22 RAM

23I/O section

24 bus

25 measuring part

26 information presentation unit

100 valve body

110 piezoelectric element

102 diaphragm valve body

115 connector

123 supporting cylinder

Detailed Description

Embodiments of a driving device including a deterioration detection circuit for a piezoelectric element and a deterioration detection method according to the present invention will be described with reference to the drawings. In addition, the same or similar components are denoted by the same reference numerals throughout the drawings and the entire embodiment.

Fig. 1 shows a driving device (hereinafter, referred to as a driving device) including a deterioration detection circuit for a piezoelectric element according to an embodiment of the present invention. The drive device 1 is, for example, a pressure type flow rate control device. The drive device 1 includes: the piezoelectric element 2, the control section 3, the power supply section 4, the first connector 5, the second connector 6, the first positive terminal 7, the first negative terminal 8, the second positive terminal 9, the second negative terminal 10, the first resistor 11, the second resistor 12, the first terminal 13, and the second terminal 14.

The power supply unit 4 is included in the control unit 3. The first positive terminal 7 and the second positive terminal 9 are electrically connected by an electric wiring. Hereinafter, unless otherwise noted, connection represents electrical connection. The first negative terminal 8 is connected to the second negative terminal 10 via a first resistor 11 and a second resistor 12 connected in series. The piezoelectric element 2 may be formed of one piezoelectric body, or may be formed by laminating a plurality of piezoelectric bodies.

The power supply unit 4 outputs a dc voltage (hereinafter, simply referred to as a voltage) of a predetermined magnitude. As a result, a predetermined voltage is applied between the second positive terminal 9 and the second negative terminal 10 via the first positive terminal 7 and the first negative terminal 8, and the piezoelectric element 2 is deformed. This deforms or displaces the displacement portion (diaphragm valve body or the like) to control the operation of the drive portion (opening and closing of the valve or the like), and thus, for example, the supply of a fluid such as a gas can be controlled.

Both ends of the first resistor 11 are connected to the first terminal 13 and the second terminal 14, respectively. Thus, the first resistor 11, the second resistor 12, the first terminal 13, and the second terminal 14 constitute the degradation detection circuit 15. The first resistor 11 and the second resistor 12 are voltage dividing resistors for reducing the voltage at the second terminal 14 to a voltage value that can be input to a measuring device to be described later.

Fig. 2 shows an equivalent circuit of a circuit including the power supply unit 4, the piezoelectric element 2, the first resistor 11, and the second resistor 12 of fig. 1. The resistance values of the first resistor 11, the second resistor 12, and the piezoelectric element 2 are represented by R1, R2, and R3, respectively. The first resistor 11, the second resistor 12, and the piezoelectric element 2 are connected in series, and a predetermined voltage is supplied from the power supply unit 4 to both ends of the formed series circuit.

The insulation resistance of the piezoelectric element 2 that has not been degraded is very large, and the resistance value R3 is, for example, R3 > 1 × 109(Ω) ═ 1 × 103(M Ω). The first resistor 11 and the second resistor 12 use resistors having a resistance value sufficiently smaller than the resistance value R3 of the piezoelectric element 2 in an undegraded state (R1 < R3, R2 < R3). Here, R1 ═ 10k Ω, and R2 ═ 39k Ω.

When the voltage between the first terminal 13 and the second terminal 14 is represented by V1, the current I flowing through the circuit of fig. 2 becomes I ═ V1/R1. Therefore, if R1 < R3 and R2 < R3 are used, the resistance value R3 of the piezoelectric element 2 can be determined by R3 ≈ V0/I ═ V0/(V1/R1) when the output voltage value of the power supply unit 4 is V0. That is, when the voltage between the first terminal 13 and the second terminal 14 is measured (V1) in a state where a predetermined voltage (V0) is supplied from the power supply unit 4, the resistance value of the piezoelectric element 2 can be calculated from the measured voltage.

When a voltage is applied to the piezoelectric element 2 for a long time or repeatedly, the piezoelectric element 2 deteriorates and the insulation resistance value thereof decreases. Therefore, by normally operating the drive device 1, and measuring the voltage between the first terminal 13 and the second terminal 14 in a state where a predetermined voltage is supplied from the power supply unit 4, the resistance value R3 of the piezoelectric element 2 is calculated, and the calculated value (R3) is compared with a predetermined threshold value Rth, whereby the presence or absence of deterioration of the piezoelectric element 2 can be determined. For example, if R3 ≧ Rth, it can be determined that the piezoelectric element 2 is not deteriorated, and if R3 < Rth, it can be determined that the piezoelectric element 2 is deteriorated.

The method of detecting deterioration of the piezoelectric element 2 will be described more specifically. Fig. 3 shows a configuration related to detection of deterioration of the piezoelectric element 2 in the configuration of the driving device 1. Referring to fig. 3, the control unit 3 controls the entire drive device 1 to normally operate. The control unit 3 includes a CPU (central processing unit) 20, a ROM (read only memory) 21, a RAM (random access memory) 22, an I/O unit 23, a bus 24, and a power supply unit 4.

The I/O unit 23 is connected to an external measurement unit 25 and an information presentation unit 26. Here, only the first terminal 13 and the second terminal 14 are shown in the degradation detection circuit 15, and other components are not shown.

The CPU20 realizes the functions of the drive apparatus 1 by executing the programs recorded in the ROM 21. The ROM21 is, for example, an electrically writable nonvolatile memory, and stores predetermined programs and data necessary for executing the programs. The necessary data are, for example, the determined threshold Rth, the voltage value V0 supplied from the power supply section 4 to the piezoelectric element 2, the resistance value R1 of the first resistor 11, and the like. The RAM22 is a volatile memory, and is used as a work area for the CPU20 to execute programs and for storing values of operation results at once.

The I/O unit 23 is an interface for exchanging data with the outside of the control unit 3 (the measurement unit 25 and the information presentation unit 26). The CPU20 outputs a signal (control code or the like, hereinafter also referred to as a measurement start signal) for starting measurement by the measurement unit 25 to the measurement unit 25 via the I/O unit 23. The I/O unit 23 acquires data (measurement data) output from the measurement unit 25, and stores the data in the RAM 22. The I/O unit 23 outputs predetermined data output from the CPU20 to the information presentation unit 26.

Although not shown, the I/O unit 23 may be provided with an interface for exchanging information with an external device such as a computer. This enables input of programs and data to the ROM21 via an interface with an external device. When the ROM21 is configured to be detachable when an interface with an external device is not provided, the program and the parameters can be updated by replacing the ROM21 with a new one. In addition, the data of the detached ROM21 can be updated using an external device.

The bus 24 is a parallel electric wiring for exchanging data among the CPU20, the ROM21, the RAM22, the I/O unit 23, and the power supply unit 4. Although not shown in fig. 1 and 3, the driving device 1 also includes components necessary for its operation, such as a frequency signal generator for synchronizing the respective units.

The measurement terminal of the measurement unit 25 is connected to the first terminal 13 and the second terminal 14 of the degradation detection circuit 15. When the measurement unit 25 receives the measurement start signal from the CPU20, the voltage between the first terminal 13 and the second terminal 14 is measured. The measurement unit 25 is, for example, a known tester or data recorder capable of measuring a voltage.

The information presentation unit 26 is a display device (a liquid crystal panel, an LED panel, or the like) capable of presenting information, for example, text or the like, or a lighting device (an LED lamp or the like).

By configuring the driving device 1 in this manner, the CPU20 can supply a voltage from the power supply unit 4 to the piezoelectric element 2 at a predetermined timing to drive the driving unit. In a state where the voltage is supplied from the power supply unit 4 to the piezoelectric element 2, the CPU20 controls the measurement unit 25 to measure the voltage between the first terminal 13 and the second terminal 14 (the voltage across the first resistor 11), and as described above, the resistance value R3 of the piezoelectric element 2 can be calculated to determine whether or not the piezoelectric element 2 is deteriorated.

A method of detecting deterioration of the piezoelectric element 2 of the driving device 1 will be described with reference to the flowchart of fig. 4. The steps of the flowchart of fig. 4 are realized by the CPU20 executing a predetermined program read from the ROM21 after the drive apparatus 1 is powered ON (turned ON). Here, the CPU20 reads out a control program for normally operating the drive device 1 (hereinafter also referred to as a normal drive program) and a control program for detecting deterioration of the piezoelectric element 2 (hereinafter also referred to as a detection program), and executes these control programs in synchronization with each other. Fig. 4 shows the detection routine, and does not include a normal driver.

In step 40 of the detection routine, the CPU20 performs initial setting. For example, the CPU20 reads out a predetermined threshold (Rth) from the ROM21 to the RAM22, secures a region used as a counter in the RAM22, reads out a value of the number of times the drive unit of the drive device 1 stored in the ROM21 is driven (hereinafter, referred to as the number of times of driving, for example, the number of times the valve is opened and closed in the case of controlling the valve), and sets the value as an initial value of the counter. The counter is incremented by "1" every time the driving section of the driving apparatus 1 is driven by executing a normal driver using the CPU 20. When the drive apparatus 1 is powered OFF, the current value of the counter of the RAM22 is stored in the ROM21 as the number of driving times.

At step 41, the CPU20 determines whether or not the voltage measurement of the first resistor 11 by the measuring unit 25 is performed. If it is determined that voltage measurement is to be performed, the control proceeds to step 42, and if not, the control proceeds to step 47. The voltage measurement is performed by determining whether or not the value of the counter exceeds a predetermined value. For example, if the number exceeds an integral multiple of a predetermined number of times (50 ten thousand times, 100 ten thousand times, etc.), it is determined that voltage measurement is to be performed. If not, the voltage measurement is determined not to be executed.

At step 42, the CPU20 measures the voltage by the measuring unit 25. Specifically, when a predetermined voltage (V0) is supplied from the power supply unit 4 to the piezoelectric element 2, the CPU20 outputs a measurement start signal to the measurement unit 25 via the I/O unit 23. When the measurement unit 25 receives the measurement start signal, the voltage measurement is repeated at predetermined time intervals. The measurement unit 25 outputs the measurement data (V1) to the I/O unit 23, and the I/O unit 23 stores the received data in the RAM 22.

When the operation of the driving unit is stopped, the CPU20 outputs a control signal (hereinafter referred to as a measurement stop signal) instructing the measurement unit 25 to stop the measurement via the I/O unit 23 before the voltage supply from the power supply unit 4 to the piezoelectric element 2 is stopped. When the measurement unit 25 receives the measurement stop signal, the voltage measurement is stopped. The method of outputting the measurement data to the I/O unit 23 by the measurement unit 25 is arbitrary. For example, even if the measurement unit 25 outputs measurement data to the I/O unit 23 every time the measurement unit acquires the measurement data, the measurement data is temporarily stored in a storage unit (such as a buffer) inside the measurement unit 25, and when a measurement stop signal is received or the amount of the temporarily stored measurement data reaches a predetermined amount, the measurement data is collected and output to the I/O unit 23.

As described above, since the normal driver is executed simultaneously with the present detection program, the supply and stop of the voltage from the power supply unit 4 can be transmitted from the normal driver to the present detection program by insertion or the like.

In step 43, the CPU20 reads the measurement data (V1) from the RAM22, and calculates the resistance value of the piezoelectric element 2 from each measurement data V1i (i is a data number (serial number), and i is 1 to n). Specifically, the calculated value of the resistance is Ri, and is calculated from Ri as V0/(V1 i/R1). V0 and R1 are values read from the ROM21, and are the voltage supplied to the piezoelectric element 2 and the resistance value of the first resistor 11, respectively. The calculated resistance value Ri (i is 1 to n) is stored in the RAM 22.

In step 44, the CPU20 reads out the resistance value Ri (i is 1 to n) calculated in step 43 from the RAM22, and calculates an evaluation value (evaluation value) a for determining the presence or absence of deterioration of the piezoelectric element 2. The evaluation value a represents a value of a set Ri (i ═ 1 to n) of the calculated resistance values, for example, an average value, a median (median) or the like of Ri (i ═ 1 to n).

Fig. 5 shows an example of the measurement result of the resistance value of the first resistor 11. As described later, the voltage was measured by the data recorder at two-second intervals for each of the three types (ID1 to ID3) of piezoelectric elements 2. The vertical axis and the horizontal axis represent voltage (mV unit) and time (second unit), respectively. Fig. 5 shows data for 100 seconds. As is apparent from fig. 5, since the resistance value of the first resistor 11 fluctuates to some extent, it is preferable to calculate a representative value (for example, an average value) of a plurality of times of measurement values over a predetermined time period and compare the value with a threshold value, rather than comparing the one time measurement value with the threshold value.

In step 45, the CPU20 reads out the threshold Rth from the RAM22, and determines whether the evaluation value a calculated in step 44 is smaller than the threshold Rth. If a < Rth, control proceeds to step 46, and if not (a ≧ Rth), control proceeds to step 47.

At step 46, the CPU20 reads predetermined information from the ROM21 and outputs the information to the information presentation unit 26 via the I/O unit 23. The predetermined information is information indicating the possibility of deterioration of the piezoelectric element 2. The information presentation unit 26 is text data ("deterioration of piezoelectric element of driving device", "replacement of driving device", and the like) if it is a liquid crystal display device, and is a signal for instructing lighting if the information presentation unit 26 is a lighting device. By lighting the lighting device, deterioration of the piezoelectric element of the drive device can be indicated, and the drive device needs to be replaced.

In step S47, the CPU20 determines whether or not an instruction to end has been given, and if an instruction to end has been received, the present detection routine is ended, and if not, the control returns to step S41. The instruction to end is performed by, for example, turning OFF (turning OFF) a power switch of the drive device 1.

As described above, in the normal operation of the driving device 1, the resistance value of the piezoelectric element 2 is calculated by measuring the voltage across the first resistor 11 in a state where the voltage is applied to the piezoelectric element 2, and the presence or absence of deterioration of the piezoelectric element 2 can be determined. By setting the threshold value Rth appropriately, voltage measurement and deterioration determination are repeated in accordance with an increase in the number of times of driving of the driving unit of the driving device 1, and deterioration of the piezoelectric element 2 is detected before the driving device 1 malfunctions, and replacement of the piezoelectric element 2 or the driving device 1 including the piezoelectric element 2 can be recommended.

As shown in fig. 5, the measured voltage value fluctuates (vibrates), and thus the calculated resistance value of the piezoelectric element also fluctuates. Therefore, when the resistance value calculated by one measurement is compared with a predetermined threshold value to determine deterioration, there is a possibility that an erroneous determination that deterioration is determined may occur even when the threshold value is accidentally exceeded. In contrast, as described above, by comparing the representative value (for example, the average value) of the plurality of calculated resistance values of the piezoelectric element with a predetermined reference (threshold value), it is possible to suppress erroneous determination.

In the above, the case where whether or not to perform the voltage measurement is specified by the number of times of driving in step 41 has been described, but the present invention is not limited thereto. Whether or not to perform voltage measurement may be specified in terms of time. In this case, if the elapsed time from the initial start of operation (voltage supply to the piezoelectric element 2) exceeds a predetermined time, the driving device 1 determines that measurement is to be performed, and steps 42 to 45 may be executed.

In the above description, the case where a representative value (for example, an average value) of a plurality of measured values measured is used as an evaluation value has been described, but the present invention is not limited thereto. The tendency of the change in the representative value may be compared with a predetermined reference (threshold). For example, a ratio (slope) of change in the representative value may be calculated as the evaluation value. In this case, as described above, the representative value calculated in step 44 may be stored in the RAM22 (in the ROM21 when the power is OFF). After the voltage is measured to calculate the representative value, the previously calculated representative value is read from the RAM22, the slope is calculated, and the calculated slope is compared with a predetermined threshold value as an evaluation value. As shown in the experimental results described later, when the piezoelectric element 2 deteriorates, the resistance value R3 never deteriorates (R3 > 1 × 103(M Ω)), and decreases continuously with a certain degree of inclination. Therefore, the presence or absence of deterioration of the piezoelectric element 2 can be determined using the change (slope) in the representative value.

The method of calculating the tendency of change in the representative value may be a known method. For example, the slope may be obtained from two consecutive representative values calculated. Further, linear regression (slope) can be obtained by applying a least squares method or the like to the calculated three or more representative values.

Further, the representative value or the tendency of the representative value may be used as one of the determination conditions, whereby the deterioration of the piezoelectric element can be detected more accurately.

In the above description, the resistance values R1 and R2 of the first resistor 11 and the second resistor 12 connected in series to the piezoelectric element 2 were set to R1 ═ 10k Ω and R2 ═ 39k Ω, but the present invention is not limited to this. R1 and R2 may be selected in accordance with the input range (the region of the resistance value to be measured) of the measuring device for measuring the voltage across the first resistor 11, and when the resistance value of the piezoelectric element 2 is calculated, it is sufficient that the resistance value is sufficiently smaller than the resistance value R3 of the piezoelectric element 2 to the extent that R1 and R2 can be ignored.

In the above description, the resistance value (Ri) of the piezoelectric element 2 is calculated from Ri ═ V0(V1i/R1) (V0 is the output voltage of the power supply unit 4) from each measurement data V1i, but the present invention is not limited to this. Referring to fig. 2, since the measured value V1 of the voltage across the first resistor 11 is used and V0 is (R1+ R2+ R3) × I is (R1+ R2+ R3) × (V1/R1), R3 is V0/(V1/R1) -R1-R2. Therefore, the resistance value (Ri) of the piezoelectric element 2 may be calculated from the measurement data V1i based on Ri ═ V0/(V1i/R1) -R1-R2. In this case, the values of R1 and R2 may not satisfy R1 < R3 and R2 < R3.

In the above description, the case where the deterioration detecting circuit 15 is provided on the electric wiring between the output terminal on the negative side of the power supply unit 4 and the piezoelectric element 2 has been described, but the present invention is not limited to this. A deterioration detection circuit may be provided in the electric wiring between the output terminal on the positive electrode side of the power supply unit 4 and the piezoelectric element 2. In this case, the first resistor 11, the second resistor 12, and the piezoelectric element 2 are also connected in series. In order to realize the same voltage division as the circuit shown in fig. 1, the second resistor 12 is preferably disposed closer to the positive electrode side of the power supply unit 4 than the first resistor 11.

As shown in fig. 6, the first resistor 11 and the second resistor 12 may be disposed on both sides of the piezoelectric element 2. Further, the second resistor 12 may not be provided, depending on the measuring device used for measuring the voltage across the first resistor 11.

Example 1

The following shows experimental results, showing the effectiveness of the present invention.

In the pressure type flow rate control device having the configuration shown in fig. 1, the voltage across both ends of the first resistor 11 (the voltage between the first terminal 13 and the second terminal 14) is measured in a state where the dc voltage 140V is supplied to the piezoelectric element 2, and the average value thereof is calculated. The resistance values of the first resistor 11 and the second resistor 12 are set to 10k Ω and 39k Ω, respectively. For the voltage measurement, a tester (Digital Multimeter289 manufactured by Fuluke (FLUKE)) and a data recorder (Mobile recorder MV200 manufactured by Yokogawa electric Co.) were used.

In each of the same pressure type flow rate control devices (ID1 to ID3) using three same type piezoelectric elements, after the control valve was opened and closed 300 ten thousand times, the voltage was measured using the above-mentioned two types of measuring devices. Table 1 shows the measured voltage of the first resistor 11 and the resistance value of the piezoelectric element 2 calculated from the measured voltage.

[ TABLE 1 ]

The measurement range was. + -. 20mV and the sampling time was two seconds, depending on the measurement conditions of the data logger. The measurement voltage average (mV) is the average of the measurement data over 100 seconds. Fig. 5 shows the voltage values measured using the data logger for 100 seconds. As can be seen from FIG. 5, the amplitude of the voltage measured by the data logger was about 5 mV.

Example 2

In the pressure type flow rate control devices using different types of piezoelectric elements, the voltage across the first resistor 11 was measured and the resistance value of the piezoelectric element used in each pressure type flow rate control device was calculated in the same manner as in example 1. The results are shown in FIG. 7.

Fig. 7 schematically shows changes in resistance values calculated from the measured values of the respective piezoelectric elements. In fig. 7, the vertical axis represents the resistance value (calculated value) of the piezoelectric element, and the horizontal axis represents the drive time of the control valve. As the driving time increases, the number of times of opening and closing the control valve (the number of times of applying the voltage to the piezoelectric element) also increases. The solid line shows the measurement results of the control valve provided with the moisture adsorbent, and the broken line shows the measurement results of the control valve not provided with the moisture adsorbent. As is apparent from the graph of fig. 7, the insulation resistance values of the piezoelectric elements differ depending on the type, but when the drive time becomes long and deterioration occurs from the initial insulation resistance (about 1 × 1010 Ω) in any of the piezoelectric elements, the resistance value decreases. The timing at which the decrease in the insulation resistance value of the piezoelectric element starts differs depending on the presence or absence of the moisture adsorbent. It is found that the presence of the moisture adsorbent slows the start of the decrease in the insulation resistance value, i.e., slows the deterioration of the piezoelectric element.

The present invention has been described above by way of the embodiments, but the above embodiments are merely examples, and the present invention is not limited to the above embodiments, and various modifications can be made.