Piezoelectric element driving circuit and piezoelectric element driving method

Abstract

To provide a driving circuit for a piezoelectric element and a driving method for a piezoelectric element, by which the driving characteristic of a piezoelectric element can be improved.SOLUTION: A driving system 100 includes a switch SW configured to switch between a first state in which a voltage / frequency variable signal source 120, a piezoelectric element 140, and a resistor R are electrically connected, and a second state in which the voltage / frequency variable signal source 120 and the piezoelectric element 140 are electrically connected, a correction unit configured to correct the input voltage so that, when the input voltage of the voltage / frequency variable signal source 120 is applied to the piezoelectric element 140 and the resistor R in the first state, the voltage of the piezoelectric element 140 is within a predetermined range with respect to the change of frequency, an acquisition unit configured to acquire the resonance frequency and the resonance impedance of the piezoelectric element 140 on the basis of the voltage of the piezoelectric element 140 relative to the input voltage after the correction, and a setting unit configured to set the driving voltage, which is applied to the piezoelectric element 140 in the second state, on the basis of the resonance frequency and the resonance impedance acquired by the acquisition unit.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a driving circuit for a piezoelectric element and a driving method for a piezoelectric element. [Background technology]

[0002] A drive circuit for a piezoelectric element includes a piezoelectric element and a power source that drives the piezoelectric element (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 10-174436 Summary of the Invention [Problem to be solved by the invention]

[0004] A piezoelectric element driven at a resonant frequency may have a change in resonant frequency and resonant impedance depending on the usage environment and individual differences of the piezoelectric element. In order to improve the driving characteristics of a piezoelectric element, it is necessary to set a driving voltage based on the resonant frequency and resonant impedance of the piezoelectric element. If the resonant frequency and resonant impedance of the piezoelectric element in the usage environment can be accurately determined, it is possible to maximize the driving characteristics of the piezoelectric element in the usage environment. The resonant frequency and resonant impedance can be obtained by measuring the current when the input voltage of the power supply is applied. One method for measuring the current is to use a current sensor. However, since the current sensor is expensive, a configuration including the current sensor may increase costs.

[0005] Therefore, there is a method of measuring the voltage of each of the piezoelectric element and the resistor when an input voltage is applied by connecting a resistor in series to the piezoelectric element. In this method, since resistors are generally inexpensive, an increase in cost can be avoided. However, in a configuration in which a resistor is connected to a piezoelectric element, a voltage drop occurs in the resistor. The voltage drop in the resistor becomes large near the resonant frequency of the piezoelectric element, and a voltage lower than the input voltage is applied to the piezoelectric element by the amount of the voltage drop in the resistor. When the voltage applied to the piezoelectric element decreases, the resonant frequency becomes higher than the true value (the value when no voltage drop occurs in the resistor) and the resonant impedance becomes lower than the true value. When the measurement accuracy of the resonant frequency and the resonant impedance decreases, the driving characteristics of the piezoelectric element cannot be maximized.

[0006] An object of one aspect of the present invention is to provide a piezoelectric element drive circuit and a piezoelectric element drive method that can improve the drive characteristics of a piezoelectric element. [Means for solving the problem]

[0007] A driving circuit for a piezoelectric element according to one aspect of the present invention includes a switching unit that switches between a first state in which a power source, a piezoelectric element, and a resistor are electrically connected, and a second state in which the power source and the piezoelectric element are electrically connected, a correction unit that corrects the input voltage when the input voltage of the power source is applied to the piezoelectric element and the resistor in the first state so that the voltage of the piezoelectric element is within a predetermined range in response to changes in frequency, an acquisition unit that acquires a resonant frequency and resonant impedance of the piezoelectric element based on the voltage of the piezoelectric element relative to the corrected input voltage, and a setting unit that sets the driving voltage to be applied to the piezoelectric element in the second state based on the resonant frequency and resonant impedance acquired by the acquisition unit.

[0008] In a driving circuit for a piezoelectric element according to one aspect of the present invention, when an input voltage from a power source is applied to a piezoelectric element and a resistor, the input voltage is corrected so that the voltage of the piezoelectric element falls within a predetermined range in response to changes in frequency. Therefore, in the driving circuit, the acquisition unit can accurately acquire the resonant frequency and resonant impedance of the piezoelectric element. This allows the driving circuit to appropriately set the driving voltage. As a result, the driving circuit can improve the driving characteristics of the piezoelectric element.

[0009] In one embodiment, the correction unit may change the frequency at a constant input voltage, measure the voltage of the piezoelectric element for each frequency, and correct the input voltage for each frequency based on the input voltage and the voltage of the piezoelectric element. In this configuration, the input voltage can be corrected so that the voltage of the piezoelectric element falls within a predetermined range with respect to the change in frequency.

[0010] In one embodiment, the correction unit may measure the voltage of the piezoelectric element relative to the input voltage at a predetermined frequency, and correct the input voltage for each frequency based on the input voltage and the voltage of the piezoelectric element. In this configuration, the input voltage can be corrected so that the voltage of the piezoelectric element falls within a predetermined range with respect to changes in frequency.

[0011] In one embodiment, in the first state, the power source, the piezoelectric element, and the resistor may be connected in series in this order. Alternatively, in the first state, the power source, the resistor, and the piezoelectric element may be connected in series in this order.

[0012] In one embodiment, the piezoelectric element may have properties such that the resonant frequency decreases and the resonant impedance increases with increasing input voltage.

[0013] A method for driving a piezoelectric element according to one aspect of the present invention includes a connection step for electrically connecting a power source, a piezoelectric element, and a resistor; a correction step for correcting the input voltage when the input voltage of the power source is applied to the piezoelectric element and the resistor so that the voltage of the piezoelectric element falls within a predetermined range in response to changes in frequency; an acquisition step for acquiring a resonant frequency and a resonant impedance of the piezoelectric element based on the voltage of the piezoelectric element relative to the corrected input voltage; and a setting step for setting a driving voltage to be applied to the piezoelectric element based on the resonant frequency and the resonant impedance acquired in the acquisition step.

[0014] In a method for driving a piezoelectric element according to one aspect of the present invention, when an input voltage from a power source is applied to a piezoelectric element and a resistor, the input voltage is corrected so that the voltage of the piezoelectric element falls within a predetermined range with respect to changes in frequency. Therefore, in the driving method, the resonant frequency and resonant impedance of the piezoelectric element can be accurately acquired in the acquisition step. This makes it possible to appropriately set the driving voltage in the driving method. As a result, the driving characteristics of the piezoelectric element can be improved in the driving method. Effect of the Invention

[0015] According to one aspect of the present invention, it is possible to improve the driving characteristics of a piezoelectric element. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a diagram showing a drive system. [Diagram 2] 2(a) and 2(b) are perspective views of a piezoelectric element. [Diagram 3] FIG. 3 is an exploded perspective view of the piezoelectric element. [Figure 4] FIG. 4(a) is a diagram showing a first state in the measurement mode, and FIG. 4(b) is a diagram showing a second state in the drive mode. [Diagram 5]FIG. 5(a) is a diagram for explaining the correction of the input voltage in the measurement mode and shows the measurement results in the first step, and FIG. 5(b) is a diagram for explaining the correction of the input voltage in the measurement mode and shows the measurement results in the second step. [Figure 6] FIG. 6 is a flow chart showing a method for determining the resonant frequency and resonant impedance of a piezoelectric element. [Figure 7] FIG. 7 is a flowchart showing a method for determining the resonant frequency and resonant impedance of a piezoelectric element according to a modified example. [Figure 8] FIG. 8(a) is a diagram showing a first state in a measurement mode in a circuit according to a modified example, and FIG. 8(b) is a diagram showing a second state in a drive mode in a circuit according to a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same or corresponding elements are designated by the same reference numerals, and duplicated explanations will be omitted.

[0018] 1, the drive system (drive circuit) 100 includes a microcontroller (correction unit, acquisition unit, setting unit) 110, a variable voltage / frequency signal source (power supply) 120, a drive circuit 130, a piezoelectric element 140, and a position sensor 150. In the drive system 100, for example, the piezoelectric element 140 drives a camera lens (object to be driven 160).

[0019] The microcontroller 110 performs overall control of the drive system 100. The microcontroller 110 may be a computer system or a processor implemented in an integrated circuit. The microcontroller 110 is composed of a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), an input / output interface, etc. Various programs and data are stored in the ROM. The microcontroller 110 outputs a control signal to the variable voltage / frequency signal source 120 based on the detection result (position information) of the position sensor 150. The microcontroller 110 constitutes a correction unit, an acquisition unit, and a setting unit.

[0020] The voltage / frequency variable signal source 120 outputs an AC voltage. The voltage / frequency variable signal source 120 is capable of varying the voltage (amplitude) and frequency. The voltage / frequency variable signal source 120 outputs an AC voltage of a predetermined voltage and a predetermined frequency based on a control signal output from the microcontroller 110.

[0021] The drive circuit 130 applies the AC voltage output from the variable voltage / frequency signal source 120 to the piezoelectric element 140 to drive the piezoelectric element 140 .

[0022] The position sensor 150 detects the position of the driven object 160 and outputs a signal (information) indicating the position of the driven object 160 to the microcontroller 110 .

[0023] The piezoelectric element 140 has a function of moving the driven object 160 by being displaced by application of an AC voltage. The piezoelectric element 140 has a characteristic that the resonant frequency decreases and the resonant impedance increases with an increase in the input voltage. As shown in Fig. 2(a) and Fig. 2(b), the piezoelectric element 140 includes a laminate 2. The laminate 2 has a rectangular parallelepiped shape. The laminate 2 has a pair of end faces 2a, 2b facing each other, a pair of main faces 2c, 2d facing each other, and a pair of side faces 2e, 2f facing each other.

[0024] The laminate 2 is made of a piezoelectric ceramic material. The piezoelectric ceramic material is PZT [Pb(Zr,Ti)O 3 ], PT(PbTiO 3 ), PLZT[(Pb,La)(Zr,Ti)O 3 ], or barium titanate (BaTiO 3 In this embodiment, the laminate 2 is formed by laminating rectangular piezoelectric layers 20a-20h, which are sintered bodies of ceramic green sheets containing a piezoelectric ceramic material. The outer surface of the piezoelectric layer 20a forms a main surface 2c of the laminate 2, and the outer surface of the piezoelectric layer 20h forms a main surface 2d of the laminate 2.

[0025] As shown in FIG. 3, the piezoelectric element 140 includes a first internal electrode 22, a second internal electrode 24, a third internal electrode 26, a fourth internal electrode 28, and a fifth internal electrode 30.

[0026] A first internal electrode 22, a second internal electrode 24, a third internal electrode 26, and a fourth internal electrode 28 are disposed on the piezoelectric layer 20b. The first internal electrode 22 and the second internal electrode 24 are electrically insulated (separated) from each other on the piezoelectric layer 20b. The third internal electrode 26 and the fourth internal electrode 28 are electrically connected to each other on the piezoelectric layer 20b.

[0027] The first internal electrode 22 has a main electrode portion 22a and a connection portion 22b. The connection portion 22b extends from the main electrode portion 22a toward the other side surface 2f of the laminate 2 and is exposed at the side surface 2f of the laminate 2. The second internal electrode 24 has a main electrode portion 24a and a connection portion 24b. The connection portion 24b extends from the main electrode portion 24a toward one side surface 2e of the laminate 2 and is exposed at the side surface 2e of the laminate 2.

[0028] The third internal electrode 26 has a main electrode portion 26a and a connection portion 26b. The connection portion 26b extends from the main electrode portion 26a toward the other side surface 2f of the laminate 2 and is exposed at the side surface 2f of the laminate 2. The fourth internal electrode 28 has a main electrode portion 28a and a connection portion 28b. The connection portion 28b extends from the main electrode portion 28a toward the one side surface 2e of the laminate 2 and is exposed at the side surface 2e of the laminate 2.

[0029] A fifth internal electrode 30 is disposed on the piezoelectric layer 20c. The fifth internal electrode 30 has a main electrode portion 30a and connection portions 30b and 30c. The main electrode portion 30a faces the first internal electrode 22 (main electrode portion 22a), the second internal electrode (main electrode portion 24a), the third internal electrode 26 (main electrode portion 26a), and the fourth internal electrode (main electrode portion 28a) via the piezoelectric layer 20b.

[0030] A first internal electrode 22, a second internal electrode 24, a third internal electrode 26, and a fourth internal electrode 28 are disposed on the piezoelectric layer 20d, the piezoelectric layer 20f, and the piezoelectric layer 20h. A fifth internal electrode 30 is disposed on the piezoelectric layer 20e and the piezoelectric layer 20g.

[0031] As shown in FIGS. 2(a) and 2(b), the piezoelectric element 140 includes a first external electrode 4, a second external electrode 5, a third external electrode 6, and a fourth external electrode .

[0032] The first external electrode 4 has a first electrode portion 4a, a second electrode portion 4b, a third electrode portion 4c, a fourth electrode portion 4d, and a fifth electrode portion 4e. The first electrode portion 4a is directly connected to a connection portion 22b exposed on the side surface 2f. This allows the first external electrode 4 to be electrically connected to the first internal electrode 22. The second electrode portion 4b is directly connected to a connection portion 24b exposed on the side surface 2e. This allows the first external electrode 4 to be electrically connected to the second internal electrode 24.

[0033] The second external electrode 5 has a first electrode portion 5a, a second electrode portion 5b, a third electrode portion 5c, a fourth electrode portion 5d, and a fifth electrode portion 5e. The first electrode portion 5a is directly connected to a connection portion 26b exposed on the side surface 2f. This allows the second external electrode 5 to be electrically connected to the third internal electrode 26. The second electrode portion 5b is directly connected to a connection portion 28b exposed on the side surface 2e. This allows the second external electrode 5 to be electrically connected to the fourth internal electrode 28.

[0034] The third external electrode 6 has a first electrode portion 6a, a second electrode portion 6b, and a third electrode portion 6c. The first electrode portion 6a is directly connected to a connection portion 30b exposed on the side surface 2f. This allows the third external electrode 6 to be electrically connected to the fifth internal electrode 30.

[0035] The second electrode portion 6b is disposed on one of the principal surfaces 2c. The second electrode portion 6b is electrically connected to an end portion of the first electrode portion 6a on the principal surface 2c side. The third electrode portion 6c is disposed on one of the principal surfaces 2d. The third electrode portion 6c is electrically connected to an end portion of the first electrode portion 6a on the principal surface 2d side.

[0036] The fourth external electrode 7 has a first electrode portion 7a, a second electrode portion 7b, and a third electrode portion 7c. The first electrode portion 7a is disposed on one side surface 2e of the laminate 2. The first electrode portion 7a is formed from one main surface 2c to the other main surface 2d. The first electrode portion 7a is directly connected to a connection portion 30c exposed on the side surface 2e. As a result, the fourth external electrode 7 is electrically connected to the fifth internal electrode 30.

[0037] The second electrode portion 7b is disposed on one of the principal surfaces 2c. The second electrode portion 7b is electrically connected to an end portion of the first electrode portion 7a on the principal surface 2c side. The third electrode portion 7c is disposed on one of the principal surfaces 2d. The third electrode portion 7c is electrically connected to an end portion of the first electrode portion 7a on the principal surface 2d side.

[0038] The piezoelectric element 140 is provided with a friction portion 10. The friction portion 10 comes into contact with the driven object 160. The friction portion 10 is disposed on one end surface 2a of the laminate 2. The friction portion 10 has, for example, a cylindrical shape. The friction portion 10 is made of zirconia, alumina, or the like. The friction portion 10 is provided, for example, by adhering a cylindrical member to the end surface 2a.

[0039] 1, the drive system 100 executes a measurement mode and a drive mode. In the measurement mode, the resonant frequency and resonant impedance (absolute value) of the piezoelectric element 140 are obtained. In the drive mode, the drive voltage of the piezoelectric element 140 is set based on the resonant frequency and resonant impedance obtained in the measurement mode, and the piezoelectric element 140 is driven.

[0040] 4(a) and 4(b), the drive circuit 130 has a resistor R and a switch (switching unit) SW. The resistor R is a shunt resistor. The resistor R may be a resistive element (pure resistor) or may have any impedance. The switch SW switches between a first state in which the piezoelectric element 140 and the resistor R are connected and a second state in which the piezoelectric element 140 and the resistor R are not connected (connection step).

[0041] In the measurement mode, the switch SW is switched to the first state. In the measurement mode, the microcontroller 110 outputs a control signal to the drive circuit 130 to set the drive circuit 130 to the first state. As shown in FIG. 4(a), in the measurement mode, the piezoelectric element 140 and the resistor R are electrically connected in series. Specifically, the voltage / frequency variable signal source 120, the piezoelectric element 140, and the resistor R are connected in this order. The microcontroller 110 executes the measurement mode at a predetermined timing. That is, the microcontroller 110 obtains the resonant frequency and the resonant impedance at a predetermined timing. The predetermined timing may be, for example, when a product in which the drive system 100 is mounted is shipped, or may be a periodically set timing.

[0042] In the measurement mode, the input voltage is corrected so that the voltage of the piezoelectric element 140 is constant relative to the frequency of the input voltage of the voltage / frequency variable signal source 120. In this embodiment, the input voltage is corrected in two steps. In the first step, the input voltage of the voltage / frequency variable signal source 120 is set to a fixed amplitude, and the frequency is changed from a start frequency to an end frequency, and the voltage of the piezoelectric element 140 for each frequency is measured. In the second step, the input voltage of the voltage / frequency variable signal source 120 is corrected, and the frequency is changed from a start frequency to an end frequency, and the voltage of the piezoelectric element 140 for each frequency is measured. The voltage is measured by a voltage sensor.

[0043] Fig. 5(a) is a diagram for explaining the correction of the input voltage in the measurement mode, and is a diagram showing the measurement results in the first step. As shown in the circuit diagram of Fig. 5(a), the input voltage of the voltage / frequency variable signal source 120 is "V", the voltage measured at the piezoelectric element 140 is "Vx", and the voltage measured at the resistor R is "Vr". In the graph shown in Fig. 5(a), the "white circle" indicates the input voltage V of the voltage / frequency variable signal source 120, and the "black circle" indicates the measurement result of the voltage Vx of the piezoelectric element 140. In Fig. 5(a), the vertical dashed line indicates the resonance frequency.

[0044] In the first step of measurement, the input voltage V is set to a fixed (constant) amplitude, and the frequency is changed from the start frequency to the end frequency to measure the voltage Vx of the piezoelectric element 140 for each frequency. The start frequency and the end frequency are set appropriately. The resonant frequency of the piezoelectric element 140 is included between the start frequency and the end frequency. As shown in FIG. 5(a), the voltage Vx of the piezoelectric element 140 decreases near the resonant frequency. This is because the voltage drop across the resistor R increases near the resonant frequency. Thus, the voltage Vx of the piezoelectric element 140 is not constant with respect to frequency.

[0045] FIG. 5(b) is a diagram for explaining the correction of the input voltage in the measurement mode, and is a diagram showing the measurement results in the second step. As shown in the circuit diagram of FIG. 5(b), the input voltage of the variable voltage / frequency signal source 120 is "V'", the voltage measured at the piezoelectric element 140 is "Vx'", and the voltage measured at the resistor R is "Vr'". In the graph shown in FIG. 5(b), the "white circle" indicates the input voltage V' of the variable voltage / frequency signal source 120, and the "black circle" indicates the measurement result of the voltage Vx' of the piezoelectric element 140. In addition, in FIG. 5(b), the vertical dashed line indicates the resonance frequency.

[0046] In the second step of measurement, the voltage / frequency variable signal source 120 outputs the input voltage V' corrected for each frequency based on the measurement result in the first step. Specifically, for example, if the input voltage V is 1Vrms in the measurement in the first step and the voltage Vx at a certain frequency is 0.9Vrms, in the measurement in the second step, the input voltage V' at that frequency is corrected to 1 / 0.9=1.11Vrms and output, and the voltage Vx' of the piezoelectric element 140 is measured. This makes it possible to make the voltage Vx' of the piezoelectric element 140 approximately constant (within a predetermined range) from the start frequency to the end frequency. That is, as shown in FIG. 5(b), the voltage Vx' of the piezoelectric element 140 does not drop even near the resonant frequency. This makes the voltage Vx' of the piezoelectric element 140 approximately constant with respect to the frequency.

[0047] Next, a method (driving method) for determining the resonant frequency and resonant impedance of the piezoelectric element 140 in the measurement mode will be described.

[0048] 6, first, in the voltage / frequency variable signal source 120, the frequency is set to a start frequency (step S01). The start frequency is set appropriately. Also, in the voltage / frequency variable signal source 120, the amplitude of the input voltage is set to a fixed input voltage V (step S02). Then, the voltage Vx(f) of the piezoelectric element 140 with respect to the input voltage V at the start frequency is measured and recorded (step S03).

[0049] Next, it is determined whether the frequency is the end frequency (step S04). If it is determined that the frequency is the end frequency (step S04: YES), proceed to step S06. If it is not determined that the frequency is the end frequency (step S04: NO), set the frequency to the next frequency (step S05).

[0050] In step S06, the frequency is set to the starting frequency. Also, the amplitude of the input voltage is set to a predetermined correction voltage (correction step). The correction voltage, input voltage V'(f), is input voltage V (input voltage V / voltage Vx(f)). Then, the voltage Vx'(f) of the piezoelectric element 140, the voltage Vr'(f) of the resistor R, and the phase φ(f) with respect to the input voltage V' at the starting frequency are measured and recorded (step S08).

[0051] Next, it is determined whether the frequency is the end frequency (step S09). If it is determined to be the end frequency (step S09: YES), the impedance Zx(f) of the piezoelectric element 140 is calculated based on the recorded voltage Vx'(f), voltage Vr'(f), and phase φ(f), and the resonant frequency and resonant impedance of the piezoelectric element 140 are obtained (step S10, acquisition step). If it is not determined to be the end frequency (step S09: NO), the frequency is set to the next frequency (step S11).

[0052] The microcontroller 110 calculates the resonant frequency and resonant impedance of the piezoelectric element 140 based on the calculated impedance Zx(f) of the piezoelectric element 140. Specifically, the microcontroller 110 sets the frequency at which the impedance Zx(f) is smallest as the resonant frequency, and sets the impedance Zx(f) as the resonant impedance.

[0053] In the drive mode, the switch SW is switched to the second state. In the drive mode, the microcontroller 110 outputs a control signal to the drive circuit 130 to set the second state. As shown in FIG. 4(b), in the drive mode, the piezoelectric element 140 and the resistor R are not electrically connected in series. In the drive mode, the microcontroller 110 sets the drive voltage of the piezoelectric element 140 based on the resonance frequency and resonance impedance (setting step). That is, the microcontroller 110 controls the AC voltage output from the voltage / frequency variable signal source 120 based on the resonance frequency and resonance impedance of the piezoelectric element 140. For example, when the resonance impedance of the piezoelectric element 140 is high, the microcontroller 110 sets the drive voltage to a high level, and when the resonance impedance is low, the microcontroller 110 sets the drive voltage to a low level.

[0054] As described above, in the drive system 100 according to this embodiment, when the input voltage of the voltage / frequency variable signal source 120 is applied to the piezoelectric element 140 and the resistor R, the input voltage is corrected so that the voltage of the piezoelectric element 140 falls within a predetermined range with respect to changes in frequency. Therefore, in the drive system 100, the resonant frequency and resonant impedance of the piezoelectric element 140 can be obtained with high accuracy. This allows the drive system 100 to appropriately set the drive voltage. As a result, in the drive system 100, the drive characteristics of the piezoelectric element 140 can be improved.

[0055] In the drive system 100 according to this embodiment, the frequency is changed at a constant input voltage, the voltage of the piezoelectric element 140 for each frequency is measured, and the input voltage is corrected for each frequency based on the input voltage and the voltage of the piezoelectric element 140. In this configuration, the input voltage can be corrected so that the voltage of the piezoelectric element 140 falls within a predetermined range in response to changes in frequency.

[0056] Although the embodiment of the present invention has been described above, the present invention is not necessarily limited to the above-described embodiment, and various modifications are possible without departing from the gist of the present invention.

[0057] In the above embodiment, an example has been described in which the voltages Vx, Vx' from the start frequency to the end frequency are measured in each of the first and second steps of the measurement mode, and the resonant frequency and resonant impedance of the piezoelectric element 140 are obtained. However, in the measurement mode, the resonant frequency and resonant impedance of the piezoelectric element 140 may be obtained by other methods.

[0058] 7, first, in the voltage / frequency variable signal source 120, the frequency is set to a starting frequency (step S21). Also, in the voltage / frequency variable signal source 120, the amplitude of the input voltage is set to a fixed input voltage V (step S22). Then, the voltage Vx(f) of the piezoelectric element 140 with respect to the input voltage V at the starting frequency is measured and recorded (step S23).

[0059] Next, the amplitude of the input voltage is set to a predetermined correction voltage (step S24). The correction voltage, input voltage V'(f), is input voltage V (input voltage V / voltage Vx(f)). Then, at the start frequency, the voltage Vx'(f) of the piezoelectric element 140, the voltage Vr'(f) of the resistor R, and the phase φ(f) with respect to the input voltage V' are measured and recorded (step S25).

[0060] Next, it is determined whether the frequency is the end frequency (step S26). If it is determined to be the end frequency (step S26: YES), the impedance Zx(f) of the piezoelectric element 140 is calculated based on the recorded voltage Vx'(f), voltage Vr'(f), and phase φ(f), and the resonant frequency and resonant impedance of the piezoelectric element 140 are obtained (step S27). If it is not determined to be the end frequency (step S26: NO), the frequency is set to the next frequency (step S28).

[0061] In the above embodiment, as shown in Fig. 4(a), in the measurement mode, the voltage / frequency variable signal source 120, the piezoelectric element 140, and the resistor R are connected in this order. However, as shown in Fig. 8(a) and Fig. 8(b), in the measurement mode, the voltage / frequency variable signal source 120, the resistor R, and the piezoelectric element 140 may be connected in this order.

[0062] In the above embodiment, the piezoelectric element 140 has been described by taking as an example the configuration shown in Figures 2(a), 2(b) and 3. However, the piezoelectric element 140 may have other configurations.

[0063] In the above embodiment, an example has been described in which the drive circuit 130 includes the resistor R and the switch SW. However, the resistor R and the switch SW may be provided in other circuits.

[0064] In the above embodiment, an example has been described in which the impedance Zx(f) of the piezoelectric element 140 is calculated based on the voltage Vx'(f), the voltage Vr'(f), and the phase φ(f), and the resonant frequency and the resonant impedance of the piezoelectric element 140 are obtained. However, the impedance Zx(f) of the piezoelectric element 140 may be calculated based on the voltage Vx'(f) and the voltage Vr'(f), and the resonant frequency and the resonant impedance of the piezoelectric element 140 may be obtained. [Explanation of symbols]

[0065] 100... drive system (drive circuit), 110... microcontroller (correction unit, acquisition unit, setting unit), 120... variable frequency signal source (power supply), 140... piezoelectric element, R... resistor, SW... switch (switching unit).

Claims

1. a switching unit that switches between a first state in which a power source, a piezoelectric element, and a resistor are electrically connected and a second state in which the power source and the piezoelectric element are electrically connected; a correction unit that corrects an input voltage of the power source when the input voltage is applied to the piezoelectric element and the resistor in the first state so that a voltage of the piezoelectric element falls within a predetermined range with respect to a change in frequency; an acquisition unit that acquires a resonance frequency and a resonance impedance of the piezoelectric element based on a voltage of the piezoelectric element with respect to the corrected input voltage; A drive circuit for a piezoelectric element comprising: a setting unit that sets a drive voltage to be applied to the piezoelectric element in the second state based on the resonance frequency and the resonance impedance acquired by the acquisition unit.

2. The correction unit is The frequency is changed at a constant input voltage, and the voltage of the piezoelectric element is measured for each frequency.

2. The piezoelectric element drive circuit according to claim 1, wherein the input voltage is corrected for each frequency based on the input voltage and the voltage of the piezoelectric element.

3. The correction unit is measuring a voltage across the piezoelectric element in response to the input voltage at a predetermined frequency; 2. The piezoelectric element drive circuit according to claim 1, wherein the input voltage is corrected for each frequency based on the input voltage and the voltage of the piezoelectric element.

4. 4. The piezoelectric element drive circuit according to claim 1, wherein in the first state, the power supply, the piezoelectric element, and the resistor are connected in series in this order.

5. 4. The piezoelectric element drive circuit according to claim 1, wherein in the first state, the power supply, the resistor, and the piezoelectric element are connected in series in this order.

6. 6. The piezoelectric element drive circuit according to claim 1, wherein the piezoelectric element has a characteristic that, as the input voltage increases, the resonant frequency decreases and the resonant impedance increases.

7. a connecting step of electrically connecting a power source, a piezoelectric element, and a resistor; a correcting step of correcting an input voltage of the power source when the input voltage is applied to the piezoelectric element and the resistor so that the voltage of the piezoelectric element falls within a predetermined range with respect to a change in frequency; an acquisition step of acquiring a resonant frequency and a resonant impedance of the piezoelectric element based on a voltage of the piezoelectric element with respect to the corrected input voltage; A method for driving a piezoelectric element, comprising: a setting step of setting a drive voltage to be applied to the piezoelectric element based on the resonance frequency and the resonance impedance acquired in the acquisition step.

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