Driving device equipped with a piezoelectric element deterioration detection circuit and deterioration detection method

Abstract

[Problem] To provide a driving device provided with a piezoelectric element deterioration detection circuit and a deterioration detection method which enable detection of deterioration of a piezoelectric element for use in the driving device without stopping a normal operation of the driving device. [Solution] A driving device 1 is provided with a piezoelectric element 2, a power source 3, a first resistor 11, a second resistor 12, a measurement unit, and a control unit, wherein: the resistance values of the first and second resistors are smaller than the insulating resistance value of the piezoelectric element; the measurement unit measures a voltage across the both ends of the first resistor (voltage between a first terminal 13 and a second terminal 14) in a state where a prescribed voltage is supplied from the power source; and the control unit 3 calculates the resistance value of the piezoelectric element from a voltage value acquired through the measurement carried out by the measurement unit, and determines whether deterioration has occurred in the piezoelectric element on the basis of the calculated resistance value.

Description

[Technical Field]

[0001] The present invention relates to a driving device equipped with a deterioration detection circuit for a piezoelectric element used as a driving source for a driving device such as an actuator, and a method for detecting deterioration of a piezoelectric element, and more particularly to a pressure-type flow rate control device that is a control device used to supply fluids such as gas in semiconductor manufacturing facilities or chemical plants, and that is equipped with a deterioration detection circuit for a piezoelectric element, and a method for detecting deterioration of a piezoelectric element in a pressure-type flow rate control device. [Background technology]

[0002] Pressure-type flow rate control devices are known for use in supplying fluids such as gases in semiconductor manufacturing facilities, chemical plants, and the like (see, for example, Patent Documents 1 and 2). These pressure-type flow rate control devices may employ control valves using piezoelectric elements. For example, Patent Document 1 below discloses a pressure-type flow rate control device equipped with a piezoelectric-element-driven metal diaphragm control valve (hereinafter simply referred to as a control valve) 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 voltage to the piezoelectric element 101, and a diaphragm valve element 104 provided in a valve body 103. The piezoelectric element 101 is housed in a cylindrical support tube 105, and is deformed in the longitudinal direction by controlling the on / off of a predetermined voltage supply via the connector 102. Deformation of the piezoelectric element 101 deforms the diaphragm valve element 104, thereby opening and closing the valve.

[0003] The pressure-type flow rate control device includes a throttle unit 106, such as an orifice, in a flow path 107 for fluid G. Under critical expansion conditions where the upstream pressure P1 of the throttle unit 106 is maintained at approximately twice the downstream pressure P2 of the throttle unit 106, the upstream pressure P1 detected by a first pressure sensor 108 provided upstream of the throttle unit 106 is adjusted by a control valve 100 provided upstream of the throttle unit 106. The basic principle of this system is to calculate the flow rate Qc downstream of the throttle unit 106 using the equation Qc = KP1 (where K is a constant dependent on the type of fluid and its temperature) and control the flow rate Qc to a predetermined set value. Even if the difference between the upstream pressure P1 and the downstream pressure P2 is small and does not satisfy the critical expansion condition, the downstream pressure P2 can be detected by a second pressure sensor (not shown) provided downstream of the throttle unit 106, and the flow rate can be calculated. That is, based on the upstream pressure P1 and downstream pressure P2 measured by the first pressure sensor 108 and the second pressure sensor, the flow rate Q can be calculated from Q=K2·P2m(P1-P2)n (where K2 is a constant that depends on the type of fluid and the fluid temperature, and m and n are exponents derived based on the actual flow rate).In addition, in Figure 8, reference numeral 109 denotes a control circuit board (control unit).

[0004] The above-described control valves are used continuously for long periods of time in semiconductor manufacturing facilities, chemical plants, etc. The piezoelectric elements used in the control valves deteriorate over time and break down, but it is impossible to predict when the control valve will break down due to deterioration of the piezoelectric element.

[0005] Control valves are also used to supply gases containing moisture, and the lifespan of the piezoelectric element varies greatly depending on whether or not moisture is present in the operating environment. Some control valves have a case containing the piezoelectric element filled with a material (moisture absorbent) to absorb moisture. Therefore, even if control valves are used for the same period of time and with the same number of opening and closing cycles, the degree of deterioration of the piezoelectric element will vary depending on the operating environment (i.e., the operating environment of the piezoelectric element) and whether or not a moisture absorbent is included. For this reason, it is difficult to predict the deterioration of the piezoelectric element and the replacement time for the pressure-type flow control device.

[0006] Due to the deterioration of the piezoelectric element, the control valve will not be able to control the flow rate as planned, and if it breaks down, it will no longer be able to supply fluid. If the control valve is replaced after it has broken down, the equipment will be shut down at an unplanned time. To prevent this, it is possible to replace the control valve at regular intervals. However, this means that control valves with piezoelectric elements that have not yet broken down will also have to be replaced.

[0007] Patent Document 3 listed below discloses a piezoelectric actuator that detects abnormalities in a piezoelectric element in advance. This piezoelectric actuator includes an abnormality detection circuit that is separate from a drive circuit for normal operation, and a switch that switches between the drive circuit and the abnormality detection circuit. Before operating the piezoelectric actuator, the switch is flipped to check whether an abnormality has occurred in the piezoelectric element using the abnormality detection circuit. If no abnormality is found, the switch is flipped to operate the piezoelectric actuator using the drive circuit. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 4119109 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-116904 [Patent Document 3] Japanese Patent Application Laid-Open No. 2017-60356 Summary of the Invention [Problem to be solved by the invention]

[0009] As described above, it would be desirable to detect the deterioration of the piezoelectric element in advance so that the control valve can be replaced before it deteriorates or breaks down. To achieve this, the deterioration of the piezoelectric element itself must be detected.

[0010] Although Patent Document 3 can detect the deterioration of the piezoelectric element, it is necessary to provide an abnormality detection circuit separate from the drive circuit for normal operation, which complicates the configuration and increases costs.In addition, it is necessary to determine whether or not there is an abnormality in the piezoelectric element using the abnormality detection circuit before normal operation begins, which is an issue that makes it inapplicable to equipment that is used continuously for long periods of time, such as in semiconductor manufacturing facilities or chemical plants.

[0011] The present invention aims to solve the above problem and provide a driving device equipped with a piezoelectric element deterioration detection circuit and a deterioration detection method that can detect deterioration of a piezoelectric element used in the driving device without stopping the normal operation of the driving device. [Means for solving the problem]

[0012] In order to achieve the above-mentioned object, a driving device according to a first aspect of the present invention comprises 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 the series-connected circuit formed by the piezoelectric element and the first resistor, a measurement unit that measures the 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 while a predetermined voltage is supplied from the voltage supply unit, and the control unit calculates the resistance value of the piezoelectric element from the voltage value obtained by measurement by the measurement unit, and determines whether or not the piezoelectric element has deteriorated based on the calculated resistance value.

[0013] The measurement unit measures the voltage of the first resistor multiple times while a predetermined voltage is supplied from the voltage supply unit, and the control unit calculates the resistance value of the piezoelectric element from each of the multiple voltage values ​​obtained from the multiple measurements, calculates a representative value of the multiple calculated resistance values ​​of the piezoelectric element, and compares the representative value with a predetermined threshold value to determine whether or not the piezoelectric element has deteriorated.

[0014] The measurement unit may measure the voltage of the first resistor multiple times while a predetermined voltage is supplied from the voltage supply unit, and the control unit may repeat the process of calculating the resistance value of the piezoelectric element from each of the multiple voltage values ​​obtained by the multiple measurements and the process of calculating a representative value of the multiple calculated resistance values ​​of the piezoelectric element, calculate the slope of the calculated representative values, and compare the slope with a predetermined threshold value to determine whether or not the piezoelectric element has deteriorated.

[0015] The measuring section can determine whether or not the piezoelectric element has deteriorated when a predetermined period of time has elapsed since the voltage was first applied to the piezoelectric element.

[0016] The above-mentioned drive device may have a mechanism for opening and closing the valve using a piezoelectric element, and the measurement unit may determine whether or not the piezoelectric element has deteriorated when the number of times the valve has been opened and closed exceeds a predetermined number of times.

[0017] The above-mentioned driving device further includes a second resistor, which is connected in series with the piezoelectric element and the first resistor, and which is connected between the positive terminal of the voltage supply unit and the first resistor, and it is preferable that 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.

[0018] A deterioration detection method according to a second aspect of the present invention is a method for detecting deterioration of a piezoelectric element in a driving device comprising a piezoelectric element, a first resistor connected in series to the piezoelectric element, a voltage supply unit that supplies a DC voltage, and a measurement unit that measures the voltage, and includes a step of supplying a predetermined DC voltage to both ends of a series-connected circuit formed by the piezoelectric element and the first resistor by the voltage supply unit, a measurement step of measuring the voltage of the first resistor by the measurement unit while the predetermined DC voltage is being supplied, a calculation step of calculating the resistance value of the piezoelectric element from the voltage value obtained by the measurement step, and a step of determining whether or not deterioration has occurred in the piezoelectric element based on the resistance value calculated by the calculation step. [Effects of the Invention]

[0019] According to the present invention, it is possible to determine whether or not a piezoelectric element has deteriorated without affecting the normal operation of the drive device. That is, a detection circuit is provided in the wiring for normal control of the piezoelectric element so as not to affect normal control, so that it is possible to determine whether or not a piezoelectric element has deteriorated during normal control without providing any additional equipment or circuitry. Therefore, it is possible to determine whether or not the drive device itself needs to be replaced during normal control of the drive device.

[0020] Furthermore, it is possible to determine whether the piezoelectric element has deteriorated and whether the drive unit needs to be replaced, regardless of the operating environment of the drive unit (piezoelectric element) and whether the drive unit is equipped with a moisture absorbent.

[0021] It is also possible to determine whether the piezoelectric element has deteriorated when the driving device is stopped or when the gas supply is terminated.

[0022] When the resistance value of a piezoelectric element calculated from a single measurement is compared with a predetermined threshold value to determine whether the piezoelectric element has deteriorated, there is a possibility that an erroneous determination that the piezoelectric element has deteriorated may occur even if the resistance value accidentally exceeds the threshold value. In contrast, by comparing a representative value (e.g., average value) of the multiple calculated resistance values ​​or the tendency (e.g., slope) of the representative value with a predetermined standard (threshold value), erroneous determination can be prevented. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a block diagram showing a schematic configuration of a driving device including a piezoelectric element deterioration detection circuit according to an embodiment of the present invention; [Figure 2] 2 is a circuit diagram showing an equivalent circuit of a circuit that supplies a voltage to the piezoelectric element of FIG. 1. FIG. [Figure 3] FIG. 2 is a block diagram showing a control portion related to deterioration detection of a piezoelectric element. [Figure 4] 10 is a flowchart showing a method for detecting deterioration of a piezoelectric element. [Figure 5] 10 is a graph showing the measurement results obtained by a data logger. [Figure 6] 2 is a block diagram showing a schematic configuration of a drive device including a deterioration detection circuit different from that in FIG. 1. FIG. [Figure 7] 10 is a graph showing the resistance value of the piezoelectric element calculated from the measurement results. [Figure 8] FIG. 1 is a longitudinal sectional view showing the configuration of a conventional piezoelectric element-driven metal diaphragm type control valve. DETAILED DESCRIPTION OF THE INVENTION

[0024] A driving device including a piezoelectric element deterioration detection circuit and a deterioration detection method according to an embodiment of the present invention will be described below with reference to the drawings. Note that the same or similar components are designated by the same reference numerals throughout the drawings and embodiments.

[0025] 1 shows a driving device (hereinafter referred to as driving device) equipped with a piezoelectric element deterioration detection circuit according to an embodiment of the present invention. Driving device 1 is, for example, a pressure-type flow control device. Driving device 1 includes a piezoelectric element 2, a control unit 3, a power supply unit 4, a first connector 5, a second connector 6, a first positive terminal 7, a first negative terminal 8, a second positive terminal 9, a second negative terminal 10, a first resistor 11, a second resistor 12, a first terminal 13, and a second terminal 14.

[0026] 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 electrical wiring. Unless otherwise specified, "connected" below means "electrically connected." 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 composed of a single piezoelectric body, or may be composed of multiple piezoelectric bodies stacked together.

[0027] The power supply unit 4 outputs a DC voltage (hereinafter simply referred to as voltage) of a predetermined magnitude. This applies a predetermined voltage between the second positive terminal 9 and the second negative terminal 10 via the first positive terminal 7 and the first negative terminal 8, deforming the piezoelectric element 2. This deforms or displaces the displacement unit (such as a diaphragm valve body), controlling the operation of the drive unit (such as opening and closing the valve), and can control the supply of a fluid such as gas, for example.

[0028] Both ends of the first resistor 11 are connected to a first terminal 13 and a second terminal 14, respectively. As a result, the first resistor 11, the second resistor 12, the first terminal 13, and the second terminal 14 constitute a deterioration 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, which will be described later.

[0029] 2 shows an equivalent circuit of the circuit including the power supply unit 4, piezoelectric element 2, first resistor 11, and second resistor 12 of FIG. 1. The resistance values ​​of the first resistor 11, second resistor 12, and piezoelectric element 2 are indicated by R1, R2, and R3, respectively. The first resistor 11, second resistor 12, and 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.

[0030] The insulation resistance of the undegraded piezoelectric element 2 is very large, and the resistance value R3 is, for example, R3>1×109 (Ω)=1×103 (MΩ). The first resistor 11 and the second resistor 12 have resistance values ​​that are sufficiently smaller than the resistance value R3 of the undegraded piezoelectric element 2 (R1< <R3、R2<<R3)。ここでは、R1=10kΩ、R2=39kΩである。

[0031] If the voltage between the first terminal 13 and the second terminal 14 is represented by V1, the current I flowing through the circuit in FIG. 2 is I = V1 / R1. Therefore, if R1 << R3 and R2 << R3, and the output voltage value of the power supply unit 4 is V0, the resistance value R3 of the piezoelectric element 2 can be obtained as R3 ≒ V0 / I = V0 / (V1 / R1). That is, in a state where a predetermined voltage (V0) is supplied from the power supply unit 4, by measuring the voltage (V1) between the first terminal 13 and the second terminal 14, the resistance value of the piezoelectric element 2 can be calculated from the measured voltage.

[0032] When a voltage is applied to the piezoelectric element 2 for a long time and repeatedly, the piezoelectric element 2 deteriorates and its insulation resistance value decreases. Therefore, by operating the drive device 1 normally 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, calculating the resistance value R3 of the piezoelectric element 2, and comparing the calculated value (R3) with a predetermined threshold value Rth, it is possible to determine whether the piezoelectric element 2 has deteriorated. For example, if R3 ≥ Rth, the piezoelectric element 2 has not deteriorated, and if R3 < Rth, it can be determined that the piezoelectric element 2 has deteriorated.

[0033] Regarding the method for detecting the deterioration of the piezoelectric element 2 described above, it will be described more specifically. Among the components of the drive device 1, the components related to the detection of the deterioration of the piezoelectric element 2 are shown in FIG. 3. Referring to FIG. 3, the control unit 3 controls the entire drive device 1 to operate normally. 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.

[0034] An external measurement unit 25 and an information presentation unit 26 are connected to the I / O unit 23. Here, regarding the deterioration detection circuit 15, only the first terminal 13 and the second terminal 14 are shown, and other components are not illustrated.

[0035] The CPU 20 realizes the functions of the drive device 1 by executing a program recorded in the ROM 21. The ROM 21 is, for example, an electrically writable non-volatile memory, and stores a predetermined program and data necessary for executing the program. The necessary data includes, for example, a determination threshold value Rth, a voltage value V0 supplied from the power supply unit 4 to the piezoelectric element 2, and a resistance value R1 of the first resistor 11. The RAM 22 is a volatile memory, and is used as a work area when the CPU 20 executes the program and for temporarily storing values ​​of calculation results.

[0036] 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 CPU 20 outputs a signal (such as a control code; hereinafter, also referred to as a measurement start signal) to the measurement unit 25 via the I / O unit 23, causing the measurement unit 25 to start measurement. The I / O unit 23 acquires data (measurement data) output from the measurement unit 25 and stores it in the RAM 22. The I / O unit 23 also outputs predetermined data output from the CPU 20 to the information presentation unit 26.

[0037] 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 allows programs and data to be written to the ROM 21 via the interface with the external device. If no interface with the external device is provided, the ROM 21 may be configured as detachable, and the programs and parameters can be updated by replacing the ROM 21 with a new one. Furthermore, data in the detached ROM 21 can also be updated using an external device.

[0038] The bus 24 is a parallel electrical wiring for exchanging data among the CPU 20, ROM 21, RAM 22, I / O unit 23, and power supply unit 4. Although not shown in Figures 1 and 3, the drive device 1 also includes components necessary for its operation, such as a clock signal generator for synchronously operating each unit.

[0039] The measurement terminals of the measurement unit 25 are connected to the first terminal 13 and the second terminal 14 of the deterioration detection circuit 15. When the measurement unit 25 receives a measurement start signal from the CPU 20, it measures the voltage between the first terminal 13 and the second terminal 14. The measurement unit 25 is, for example, a known tester or data logger capable of measuring voltage.

[0040] The information presenting unit 26 is capable of presenting information, and is, for example, a display device (liquid crystal panel, LED panel, etc.) or a lighting device (LED lamp, etc.) capable of displaying information such as text.

[0041] Because the drive device 1 is configured in this manner, it is possible to supply voltage from the power supply unit 4 to the piezoelectric element 2 at a predetermined timing by the CPU 20, thereby driving the drive unit. Furthermore, while voltage is being supplied from the power supply unit 4 to the piezoelectric element 2, the CPU 20 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 calculate the resistance value R3 of the piezoelectric element 2 as described above, thereby making it possible to determine whether the piezoelectric element 2 has deteriorated.

[0042] A method for detecting deterioration of the piezoelectric element 2 in the drive device 1 will be described with reference to the flowchart in Fig. 4. Each step in the flowchart in Fig. 4 is realized when the drive device 1 is powered on and the CPU 20 executes a predetermined program read from the ROM 21. Here, the CPU 20 reads a control program for operating the drive device 1 normally (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 parallel. Fig. 4 shows the detection program and does not include the normal drive program.

[0043] In step 40 of the detection program, the CPU 20 performs initial setting. For example, the CPU 20 reads a predetermined threshold value (Rth) from the ROM 21 into the RAM 22, allocates an area in the RAM 22 to be used as a counter, reads a value stored in the ROM 21 indicating the number of times the drive unit of the drive device 1 has been driven (hereinafter referred to as the number of times the valve has been opened and closed, in the case of a control valve, for example), and sets this value as the initial value of the counter. When the CPU 20 executes the normal drive program, the counter is incremented by "1" each time the drive unit of the drive device 1 is driven. Note that when the power supply to the drive device 1 is turned off, the current value of the counter in the RAM 22 is stored in the ROM 21 in advance as the number of times the valve has been driven.

[0044] In step 41, the CPU 20 determines whether or not to perform voltage measurement of the first resistor 11 by the measurement unit 25. If it is determined that voltage measurement is to be performed, control proceeds to step 42; otherwise, control proceeds to step 47. The execution of voltage measurement is performed by determining whether or not the counter value has exceeded a predetermined value. For example, if the counter value exceeds a value that is an integer multiple of a predetermined number of times (500,000 times, 1,000,000 times, etc.), it is determined that voltage measurement is to be performed. Otherwise, it is determined that voltage measurement is not to be performed.

[0045] In step 42, the CPU 20 performs voltage measurement using the measurement unit 25. Specifically, while the power supply unit 4 is supplying a predetermined voltage (V0) to the piezoelectric element 2, the CPU 20 outputs a measurement start signal to the measurement unit 25 via the I / O unit 23. Upon receiving the measurement start signal, the measurement unit 25 repeatedly performs voltage measurement at predetermined time intervals. The measurement unit 25 outputs measurement data (V1) to the I / O unit 23, and the I / O unit 23 stores the received data in the RAM 22.

[0046] When stopping the operation of the drive unit, the CPU 20 outputs a control signal (hereinafter referred to as a measurement stop signal) instructing the measurement unit 25 to stop measurement via the I / O unit 23 before stopping the supply of voltage from the power supply unit 4 to the piezoelectric element 2. Upon receiving the measurement stop signal, the measurement unit 25 stops voltage measurement. The method by which the measurement unit 25 outputs the measurement data to the I / O unit 23 is arbitrary. For example, the measurement unit 25 may output the measurement data to the I / O unit 23 every time measurement data is obtained, or may temporarily store the measurement data in a memory unit (such as a buffer) within the measurement unit 25 and output the measurement data collectively to the I / O unit 23 when a measurement stop signal is received or when the amount of temporarily stored measurement data reaches a predetermined amount.

[0047] As described above, since the normal drive program is executed simultaneously with the main detection program, the start and stop of voltage supply from the power supply unit 4 can be communicated to the main detection program from the normal drive program by an interrupt or the like.

[0048] In step 43, the CPU 20 reads out the measurement data (V1) from the RAM 22 and calculates the resistance value of the piezoelectric element 2 from each measurement data V1i (i is a data number, i = 1 to n). Specifically, the calculated resistance value is defined as Ri and is calculated as Ri = V0 / (V1i / R1). V0 and R1 are values ​​read out from the ROM 21 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 = 1 to n) is stored in the RAM 22.

[0049] In step 44, the CPU 20 reads out the resistance values ​​Ri (i = 1 to n) calculated in step 43 from the RAM 22, and calculates an evaluation value A for determining the presence or absence of deterioration of the piezoelectric element 2. The evaluation value A is a value that represents the set of calculated resistance values ​​Ri (i = 1 to n), and is, for example, the average value or median of Ri (i = 1 to n).

[0050] An example of the measured result of the resistance value of the first resistor 11 is shown in FIG. 5. As will be described later, for each of the three types of piezoelectric elements 2 (indicated by ID1 to ID3), the voltage was measured by a data logger at intervals of 2 seconds. The vertical axis and the horizontal axis represent voltage (in mV) and time (in seconds), respectively. The data shown in FIG. 5 is for 100 seconds. As can be seen from FIG. 5, since the resistance value of the first resistor 11 fluctuates within a certain range, rather than comparing a single measured value with a threshold value, it is preferable to calculate a representative value (for example, an average value) from a plurality of measured values at a predetermined time and compare that value with the threshold value.

[0051] In step 45, the CPU 20 reads the threshold value Rth from the RAM 22 and determines whether the evaluation value A calculated in step 44 is smaller than the threshold value Rth. If A < Rth, the control proceeds to step 46; otherwise (A ≥ Rth), the control proceeds to step 47.

[0052] In step 46, the CPU 20 reads predetermined information from the ROM 21 and outputs it 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. If the information presentation unit 26 is a liquid crystal display device, it is text data ("The piezoelectric element of the drive device is deteriorated", "Please replace the drive device", etc.); if the information presentation unit 26 is a lighting device, it is a signal instructing lighting. By lighting the lighting device, it is possible to indicate that the piezoelectric element of the drive device is deteriorated and that the drive device needs to be replaced.

[0053] [[ID=Eleven]] [[ID=Twelve]]In step 47, the CPU 20 determines whether an end instruction has been given. If an end instruction is received, the present detection program is terminated; otherwise, the control returns to step 41. The end instruction is made, for example, by turning off the power switch of the drive device 1.

[0054] As described above, during normal operation of the drive device 1, with a voltage applied to the piezoelectric element 2, the voltage across the first resistor 11 is measured to calculate the resistance value of the piezoelectric element 2, thereby making it possible to determine whether the piezoelectric element 2 has deteriorated. If the threshold value Rth is set appropriately, by repeating voltage measurement and deterioration determination as the number of times the drive unit of the drive device 1 is driven increases, it is possible to detect deterioration of the piezoelectric element 2 before the drive device 1 ceases to operate normally, and recommend replacing the piezoelectric element 2 or the drive device 1 including the piezoelectric element 2.

[0055] As shown in Figure 5, the measured voltage value fluctuates (vibrates), and the calculated resistance value of the piezoelectric element also fluctuates. Therefore, when a resistance value calculated from a single measurement is compared with a predetermined threshold value to determine deterioration, there is a possibility that an erroneous determination that deterioration has occurred may occur even if the resistance value accidentally exceeds the threshold value. To address this issue, as described above, a representative value (for example, an average value) of the calculated resistance values ​​of the piezoelectric element can be compared with a predetermined standard (threshold value) to prevent erroneous determination.

[0056] In the above, a case has been described in which whether or not to perform voltage measurement in step 41 is specified based on the number of times of driving, but this is not limiting. Whether or not to perform voltage measurement may also be specified based on time. In this case, when the elapsed time since the driving device 1 first started operating (supplying voltage to the piezoelectric element 2) exceeds the specified time, it is determined that measurement should be performed, and steps 42 to 45 are executed.

[0057] Although the above describes a case where a representative value (e.g., average value) of multiple measured values ​​is used as the evaluation value, this is not limiting. The tendency of change in the representative value may be compared with a predetermined standard (threshold value). For example, the rate of change (slope) of the representative value may be calculated as the evaluation value. In this case, the representative value calculated each time step 44 is executed as described above may be stored in RAM 22 (or stored in ROM 21 in advance if the power is turned off). After measuring the voltage and calculating the representative value, the previously calculated representative value may be read from RAM 22, the slope may be calculated, and the calculated slope may be compared with a predetermined threshold value as the evaluation value. As shown in the experimental results described below, when the piezoelectric element 2 deteriorates, the resistance value R3 continues to decrease at a certain slope from a non-deteriorated state (R3 > 1 × 10 (MΩ)). Therefore, the change (slope) of the representative value can be used to determine whether the piezoelectric element 2 has deteriorated.

[0058] The trend of change in the representative value can be calculated using any known method. For example, the slope can be calculated from two consecutive calculated representative values. Alternatively, the regression line (slope) can be calculated by applying the least squares method to three or more calculated representative values.

[0059] Furthermore, the representative value or the tendency of the representative value may be used as one of the conditions for judgment, thereby enabling more accurate detection of the deterioration of the piezoelectric element.

[0060] 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 are R1=10 kΩ and R2=39 kΩ, but are not limited to this. R1 and R2 can be selected according to the input range (the range of resistance values ​​to be measured) of the measuring device that measures the voltage across the first resistor 11, and they only need to be sufficiently small compared to the resistance value R3 of the piezoelectric element 2 so that R1 and R2 can be ignored when calculating the resistance value of the piezoelectric element 2.

[0061] In the above description, the case where the resistance value (Ri) of the piezoelectric element 2 is calculated from each measurement data V1i by Ri = V0 / (V1i / R1) (V0 is the output voltage of the power supply unit 4) has been described, but it is not limited thereto. Referring to FIG. 2, since V0 = (R1 + R2 + R3)×I = (R1 + R2 + R3)×(V1 / R1) using the measured value V1 of the voltage across both ends of the first resistor 11, R3 = V0 / (V1 / R1) - R1 - R2. Therefore, the resistance value (Ri) of the piezoelectric element 2 may be calculated from each measurement data V1i by Ri = V0 / (V1i / R1) - R1 - R2. In this case, the values of R1 and R2 do not have to satisfy R1 << R3 and R2 << R3.

[0062] In the above description, the case where the deterioration detection circuit 15 is provided on the electrical wiring between the negative output terminal of the power supply unit 4 and the piezoelectric element 2 has been described, but it is not limited thereto. The deterioration detection circuit may be provided on the electrical wiring between the positive output terminal of the power supply unit 4 and the piezoelectric element 2. Also in that case, the first resistor 11, the second resistor 12, and the piezoelectric element 2 are connected in series. In order to achieve the same voltage division as the circuit shown in FIG. 1, it is preferable that the second resistor 12 is arranged closer to the positive electrode side of the power supply unit 4 than the first resistor 11.

[0063] Also, as shown in FIG. 6, the first resistor 11 and the second resistor 12 may be arranged on both sides of the piezoelectric element 2. Note that the second resistor 12 may not be provided depending on the measuring device used to measure the voltage across both ends of the first resistor 11.

Embodiment

[0064] The experimental results are shown below to demonstrate the effectiveness of the present invention.

[0065] In the pressure-type flow rate control device configured as shown in Figure 1, the voltage across the first resistor 11 (the voltage between the first terminal 13 and the second terminal 14) was measured with a DC voltage of 140 V supplied to the piezoelectric element 2, and the average value was calculated. The resistance values ​​of the first resistor 11 and the second resistor 12 were set to 10 kΩ and 39 kΩ, respectively. A tester (FLUKE Digital Multimeter 289) and a data logger (Yokogawa Electric Corporation Mobile Recorder MV200) were used to measure the voltage.

[0066] In each of three pressure-type flow control devices (ID1 to ID3) using the same type of piezoelectric element, the control valve was opened and closed 3 million times, and then the voltage was measured using the two types of measuring devices described above. The measured voltage of the first resistor 11 and the resistance value of the piezoelectric element 2 calculated from it are shown in Table 1.

[0067] [Table 1] The measurement conditions for the data logger were a measurement range of ±20 mV and a sampling period of 2 seconds. The average measured voltage (mV) is the average value of the measurement data over 100 seconds. Figure 5 shows the voltage values ​​measured over 100 seconds using the data logger. As can be seen from Figure 5, the amplitude of the voltage measured by the data logger was approximately 5 mV. [Example]

[0068] For pressure-type flow rate control devices using different types of piezoelectric elements, the voltage across first resistor 11 was measured and the resistance value of the piezoelectric element used in each pressure-type flow rate control device was calculated, as in Example 1. The results are shown in Figure 7.

[0069] Figure 7 shows a schematic diagram of the change in resistance calculated from the measured values ​​for each piezoelectric element. In Figure 7, the vertical axis represents the calculated resistance of the piezoelectric element, and the horizontal axis represents the drive time of the control valve. As the drive time increases, the number of times the control valve opens and closes (the number of times voltage is applied to the piezoelectric element) increases. The solid line represents the measurement results for a control valve equipped with a moisture adsorbent, and the dashed line represents the measurement results for a control valve without a moisture adsorbent. As can be seen from the graph in Figure 7, the insulation resistance value of each piezoelectric element differs depending on the type. However, for all piezoelectric elements, the resistance value decreases from the initial insulation resistance (approximately 1 x 1010 Ω) as the drive time increases and degradation occurs. The timing at which the insulation resistance value of the piezoelectric element begins to decrease differs depending on whether or not a moisture adsorbent is used. It can be seen that the inclusion of a moisture adsorbent delays the onset of the decrease in insulation resistance value, i.e., slows the degradation of the piezoelectric element.

[0070] The present invention has been described above by explaining the embodiments, but the above-described embodiments are merely examples, and the present invention is not limited to the above-described embodiments, and can be implemented with various modifications. [Explanation of symbols]

[0071] 1. Drive unit 2 Piezoelectric element 3. Control Unit 4 Power supply section 5 First Connector 6 Second Connector 7 First positive terminal 8 First negative terminal 9 Second positive terminal 10 Second negative terminal 11 1st resistor 12 2nd resistor 13 1st terminal 14 2nd terminal 15 Deterioration detection circuit 20 CPU 21 ROM 22 RAM 23 I / O section 24 Bus 25 Measuring part 26 Information Presentation Department 100 Valve body 110 Piezoelectric element 102 Diaphragm valve body 115 Connector 123 Support tube

Claims

1. a piezoelectric element; a first resistor connected in series with the piezoelectric element; a voltage supply unit that supplies a DC voltage to both ends of a series connection circuit formed by the piezoelectric element and the first resistor; a measurement unit that measures a voltage across the first resistor; A drive device including a control unit that controls the voltage supply unit and the measurement unit, a resistance value of the first resistor is smaller than an insulation resistance value of the piezoelectric element; the measurement unit measures the voltage across the first resistor multiple times while a predetermined voltage is being supplied from the voltage supply unit; The control unit Repeating 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 a slope, which is a rate of change of the calculated representative values; determining whether the piezoelectric element has deteriorated by comparing the slope with a predetermined threshold value; the drive device has a mechanism for opening and closing a valve using the piezoelectric element, The drive device is characterized in that the control unit determines whether or not the piezoelectric element has deteriorated each time the number of times the valve is opened and closed exceeds an integral multiple of a predetermined number of times.

2. Further comprising a second resistor; the second resistor is connected in series with the piezoelectric element and the first resistor; the second resistor is connected between a positive terminal of the voltage supply unit and the first resistor, 2. The driving device according to claim 1, wherein 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.

3. A method for detecting deterioration of a piezoelectric element in a driving device including a piezoelectric element, a first resistor connected in series to the piezoelectric element, a voltage supply unit that supplies a DC voltage, and a measurement unit that measures the voltage, comprising: supplying a predetermined DC voltage to both ends of a series connection circuit formed by the piezoelectric element and the first resistor by the voltage supply unit; a measuring step of measuring the voltage of the first resistor a plurality of times while a predetermined voltage is supplied from the voltage supply unit; a step of repeating 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 in the measuring step, and a process of calculating a representative value of the plurality of calculated resistance values ​​of the piezoelectric element; calculating a slope that is a rate of change of the calculated representative values; and determining whether or not the piezoelectric element has deteriorated by comparing the slope with a predetermined threshold value; the drive device has a mechanism for opening and closing a valve using the piezoelectric element, A deterioration detection method characterized in that the supplying step, the measuring step, the repeating step, the calculating step, and the judging step are performed every time the number of times the valve is opened and closed exceeds an integer multiple of a predetermined number of times.

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