JP2013144273A - Drive circuit of piezoelectric actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a drive circuit of a piezoelectric actuator, capable of reducing the load on the piezoelectric actuator to prevent occurrence of failure when driving the actuator with a drive voltage involving a rising edge or falling edge.SOLUTION: There is provided a drive circuit 10 of a piezoelectric actuator applying a drive voltage involving a rising edge or falling edge. The voltage having only the frequency component below the mechanical resonance frequency of the piezoelectric actuator 15 is applied to the actuator 15, with the wave pattern starting from the angle of inclination 0 in a rising edge or falling edge. Thus, the change of the voltage in the rising or falling edge becomes slow. As a result, a load on the actuator 15 is reduced, and the durability is improved. Thus, the above drive circuit can be effectively applied, for example, to that of the piezoelectric actuator used for opening/closing of a valve.

Description

  The present invention relates to a drive circuit for a piezoelectric actuator that applies a drive voltage with rising or falling.

  In recent years, piezoelectric actuators have been used in camera lens driving mechanisms, precision positioning devices, and the like, and circuits that protect piezoelectric actuators from abnormal voltages and currents generated in such mechanisms and devices have been proposed.

  For example, in the piezoelectric actuator device described in Patent Document 1, when a failure is determined by a failure determination device, the voltage supply from the drive signal amplification circuit to the piezoelectric actuator is cut off, and the piezoelectric actuator is protected from an abnormal applied voltage at the time of failure. doing.

  Further, the actuator drive mechanism described in Patent Document 2 is controlled so that even when the piezoelectric element is short-circuited, the overcurrent protection circuit connected to both ends of the overcurrent detection resistor stops energization and no overcurrent flows to the piezoelectric element. doing.

  Further, in Patent Document 3, when an overvoltage drive signal is input to a piezoelectric actuator, the resistance of the overvoltage limiting element is suddenly lowered to flow a current, thereby blocking an inappropriate signal from the piezoelectric actuator element. The actuator element is protected from unexpected damage.

Japanese Patent No. 4190904 Japanese Patent No. 3798832 Japanese Patent No. 4700466

  On the other hand, the piezoelectric actuator is required to have durability against the OnOff operation represented by opening and closing of the valve. For example, in the valve opening / closing mechanism, there is a case where it is required to perform expansion and contraction within 0.5 seconds 10 million times or more for gas switching. When the piezoelectric actuator is driven with a drive waveform with a steep voltage change such as a rectangular wave, a failure corresponding to the number of voltage changes occurs earlier than when DC is applied.

  The techniques described in Patent Documents 1 to 3 described above merely protect the piezoelectric actuator from overcurrent and overvoltage, and do not correspond to the magnitude of voltage change. Therefore, even if such a circuit is used, the durability of the piezoelectric actuator is not improved with respect to a drive waveform accompanied by a steep voltage change.

  The present invention has been made in view of such circumstances, and when a piezoelectric actuator is driven with a driving voltage that involves rising or falling, the driving of the piezoelectric actuator can reduce the burden on the piezoelectric actuator and prevent failure. An object is to provide a circuit.

  (1) In order to achieve the above object, the piezoelectric actuator drive circuit of the present invention is a piezoelectric actuator drive circuit that applies a drive voltage with rising or falling, and at the rising or falling of voltage application, The piezoelectric actuator is formed with a frequency component equal to or lower than the mechanical resonance frequency of the piezoelectric actuator, and is applied to the piezoelectric actuator with a waveform starting from an inclination of zero.

  As described above, the piezoelectric actuator drive circuit according to the present invention applies only a frequency component equal to or lower than the mechanical resonance frequency of the piezoelectric actuator to the piezoelectric actuator with a waveform starting from the gradient 0 at the rising or falling edge. When driven by a voltage having a waveform with a rise or fall, the change in the rise or fall voltage becomes gradual. As a result, the burden on the piezoelectric actuator is reduced and its durability is improved. For example, it can be effectively applied to a drive circuit for a piezoelectric actuator used for opening and closing a valve.

  (2) In addition, the piezoelectric actuator drive circuit of the present invention has a frequency that is 1/3 of the mechanical resonance frequency of the piezoelectric actuator at the rising or falling of the voltage application, from a phase of −90 ° or + 90 °. A voltage is applied to the piezoelectric actuator with a waveform having a smaller first-order differential value than a starting sine wave. Thereby, the waveform especially in the vicinity of rising or falling becomes gentle. As a result, the burden on the piezoelectric actuator is reduced and the durability is improved.

  (3) Further, the piezoelectric actuator drive circuit of the present invention is characterized by including a secondary or higher-order RC low-pass filter that applies a power supply voltage to the piezoelectric actuator with a voltage having the applied voltage waveform. Accordingly, it is possible to easily realize a configuration in which the power supply voltage that is too steep is changed to a gentle waveform and applied to the piezoelectric actuator.

  (4) In addition, the piezoelectric actuator drive circuit of the present invention includes an RLC low-pass filter that applies a power supply voltage to the piezoelectric actuator with a voltage of the applied voltage waveform. Accordingly, it is possible to easily realize a configuration in which the power supply voltage that is too steep is changed to a gentle waveform and applied to the piezoelectric actuator.

  (5) Further, the drive circuit for the piezoelectric actuator of the present invention has a frequency equal to or lower than 1/3 of the mechanical resonance frequency of the piezoelectric actuator at the rising or falling of the voltage application, and a phase of −90 ° or + 90 °. A voltage is applied to the piezoelectric actuator with a half-cycle waveform of a sine wave starting from. Thereby, the waveform especially in the vicinity of rising or falling becomes gentle. As a result, the burden on the piezoelectric actuator is reduced and the durability is improved.

  ADVANTAGE OF THE INVENTION According to this invention, when driving a piezoelectric actuator with the drive voltage accompanying a rise or fall, the burden to a piezoelectric actuator can be eased and a failure can be prevented.

It is a circuit diagram which shows the drive circuit of the piezoelectric actuator which concerns on 1st Embodiment. It is a circuit diagram which shows the drive circuit of the piezoelectric actuator which concerns on 2nd Embodiment. It is a circuit diagram which shows the drive circuit of the piezoelectric actuator which concerns on 3rd Embodiment. It is a circuit diagram which shows the drive circuit of the piezoelectric actuator of a comparative example. It is a circuit diagram which shows the drive circuit of the piezoelectric actuator of a comparative example. It is a circuit diagram which shows the drive circuit of the piezoelectric actuator of a comparative example. 6 is a diagram illustrating an applied voltage waveform of Comparative Example 1. FIG. 6 is a diagram illustrating an applied voltage waveform of Comparative Example 1. FIG. 6 is a diagram illustrating an applied voltage waveform of Comparative Example 1. FIG. It is a figure which shows the applied voltage waveform of the comparative example 2. FIG. It is a figure which shows the applied voltage waveform of the comparative example 2. FIG. It is a figure which shows the applied voltage waveform of the comparative example 2. FIG. It is a figure which shows the applied voltage waveform of the comparative example 3. It is a figure which shows the applied voltage waveform of the comparative example 3. It is a figure which shows the applied voltage waveform of the comparative example 3. It is a figure which shows the applied voltage waveform of the comparative example 4. It is a figure which shows the applied voltage waveform of the comparative example 4. It is a figure which shows the applied voltage waveform of the comparative example 4. It is a figure which shows the applied voltage waveform of the comparative example 5. It is a figure which shows the applied voltage waveform of the comparative example 5. It is a figure which shows the applied voltage waveform of the comparative example 5. FIG. 3 is a diagram showing an applied voltage waveform of Example 1. FIG. 3 is a diagram showing an applied voltage waveform of Example 1. FIG. 3 is a diagram showing an applied voltage waveform of Example 1. FIG. 6 is a diagram illustrating an applied voltage waveform of Example 2. FIG. 6 is a diagram illustrating an applied voltage waveform of Example 2. FIG. 6 is a diagram illustrating an applied voltage waveform of Example 2. FIG. 6 is a diagram showing an applied voltage waveform of Example 3. FIG. 6 is a diagram showing an applied voltage waveform of Example 3. FIG. 6 is a diagram showing an applied voltage waveform of Example 3. It is a figure which shows the applied voltage waveform of Example 4. FIG. It is a figure which shows the applied voltage waveform of Example 4. FIG. It is a figure which shows the applied voltage waveform of Example 4. FIG. It is a figure which shows the applied voltage waveform immediately after the rise of each example.

  Next, embodiments of the present invention will be described with reference to the drawings. In order to facilitate understanding of the description, the same reference numerals are given to the same components in the respective drawings, and duplicate descriptions are omitted.

[First Embodiment]
FIG. 1 is a diagram showing a drive circuit 10 for a piezoelectric actuator having a secondary RC low-pass filter. The drive circuit 10 is used for an application in which a drive voltage with a rising edge or a falling edge is applied, and is frequently turned off. Examples of such circuit applications include valve opening and closing mechanisms. The drive circuit 10 includes a power supply 11, a piezoelectric actuator 15, and a secondary RC low-pass filter.

  The power supply 11 generates a power supply voltage with rising or falling like a rectangular wave, for example, according to an OnOff instruction. The piezoelectric actuator 15 has a piezoelectric layer formed of PZT or the like between electrodes, and expands and contracts according to an applied voltage. The rising edge of voltage application refers to the state when the constant voltage starts to increase, and the falling edge of voltage application refers to the state when the constant voltage starts to decrease.

  The secondary RC low-pass filter is configured by installing the resistors 12 and 13 and the capacitor 14 having characteristics corresponding to the capacitance value of the piezoelectric actuator 15. That is, a secondary RC low-pass filter including the piezoelectric actuator 15 is configured. The resistor 12 and the capacitor 14 constitute a first-stage RC low-pass filter, and the resistor 13 and the piezoelectric actuator 15 constitute a second-stage RC low-pass filter.

  The second-order RC low-pass filter passes only the frequency component equal to or lower than the mechanical resonance frequency of the piezoelectric actuator 15 in the OnOff power supply voltage waveform, and applies to the piezoelectric actuator 15 in a waveform starting from a slope 0 at the rising or falling of voltage application. To do. In this way, not only the change in applied voltage is moderated, but also the change in voltage per time when the applied voltage changes from a constant voltage is reduced. The characteristic values (resistance value, capacitance value) of the resistors 12 and 13 and the capacitor 14 are designed so that a voltage can be applied to the piezoelectric actuator 15 with the waveform as described above.

  When a primary RC low-pass filter is configured instead of the secondary RC low-pass filter, the slope of rising of the applied voltage is not sufficiently reduced. However, the RC low-pass filter may be higher order.

  At the rise of voltage application, the piezoelectric actuator 15 has a waveform that has a frequency that is 1/3 of the mechanical resonance frequency of the piezoelectric actuator 15 and whose absolute value of the first-order differential value is smaller than a sine wave that starts at a phase of −90 °. It is preferable that a voltage is applied to. At the fall of voltage application, the piezoelectric actuator 15 has a frequency which is 1/3 of the mechanical resonance frequency of the piezoelectric actuator 15 and has a smaller first-order differential value than the sine wave starting from the phase + 90 °. 15 is preferably configured to apply a voltage.

[Second Embodiment]
The drive circuit of the piezoelectric actuator may include an RLC low-pass filter instead of the secondary or higher-order RC low-pass filter. FIG. 2 is a diagram illustrating a drive circuit 20 for a piezoelectric actuator including an RLC low-pass filter. The drive circuit 20 includes a power supply 11, a piezoelectric actuator 15, and an RLC low-pass filter.

  The RLC low-pass filter includes a resistor 22, a coil 23, and a capacitor 24 having predetermined characteristics. The RLC low-pass filter passes only a frequency component equal to or lower than the mechanical resonance frequency of the piezoelectric actuator 15 in the OnOff power supply voltage waveform, and applies the waveform starting from 0 to the piezoelectric actuator 15. The characteristic values (resistance value, inductance, capacitance value) of the resistor 22, the coil 23, and the capacitor 24 are designed so that a voltage can be applied to the piezoelectric actuator 15 with such a waveform.

  At the rise of voltage application, an applied voltage waveform having a frequency that is 1/3 of the mechanical resonance frequency of the piezoelectric actuator 15 and having an absolute value of a first-order differential value smaller than a sine wave starting from a phase of −90 °, It is preferable that a voltage is applied to the piezoelectric actuator 15. Further, at the fall of voltage application, the applied voltage waveform has a frequency that is 1/3 of the mechanical resonance frequency of the piezoelectric actuator 15 and the absolute value of the first-order differential value is smaller than the sine wave starting from the phase + 90 °. It is preferable that a voltage is applied to the piezoelectric actuator 15.

[Third Embodiment]
The drive circuit for the piezoelectric actuator may be one in which the power supply itself operates in the same manner as a secondary or higher-order RC low-pass filter or RLC low-pass filter. FIG. 3 is a diagram showing a drive circuit 30 of a piezoelectric actuator in which the power supply itself performs a predetermined operation. The drive circuit 30 includes a power supply 31 and a piezoelectric actuator 15. The power source 31 is formed with only a frequency component equal to or lower than the mechanical resonance frequency of the piezoelectric actuator 15, and applies a driving voltage to the piezoelectric actuator 15 with a waveform starting from the slope 0. Further, the power supply 31 has an applied voltage waveform whose absolute value of the first-order differential value is smaller than a sine wave having a frequency of 1/3 of the mechanical resonance frequency of the piezoelectric actuator 15 at the rising or falling of voltage application. It is preferable to apply a voltage to 15.

  Further, instead of the applied voltage waveform as described above, at the rise of voltage application, it has a frequency equal to or less than 1/3 of the mechanical resonance frequency of the piezoelectric actuator 15 and has a half cycle of a sine wave starting from a phase of −90 °. A voltage may be applied to the piezoelectric actuator 15 with an applied voltage waveform. Further, at the fall of voltage application, a voltage is applied to the piezoelectric actuator 15 with a half-cycle applied voltage waveform of a sine wave having a frequency equal to or less than 1/3 of the mechanical resonance frequency of the piezoelectric actuator 15 and starting from the phase + 90 °. It is good also as a structure to apply.

[Durability test]
The circuit of the Example corresponding to said embodiment and the comparative example for comparing with this was comprised, and the test which confirms durability of a piezoelectric actuator was done. Specifically, a drive voltage was generated at the rated voltage OnOff for each circuit in each circuit, the waveform was measured, and the insulation resistance was measured periodically to determine that a failure occurred when the value was below 1 MΩ.

  As piezoelectric actuators, 10 PRB-4040s manufactured by Nippon Ceratech Co., Ltd. were prepared for each level, and a preload of about 300 N was applied via a spring. The capacitance of this piezoelectric actuator was about 6.5 μF. When the resonance frequency was measured in this state, it was about 300 Hz. In each circuit, the power supply voltage was generated by a function generator capable of creating an arbitrary waveform and a 2 amp 4-quadrant amplifier. The voltages of the rectangular waves were all 0-150V, the frequency was 1 Hz, and the duty ratio was 50%.

(Comparative Example 1)
FIG. 4 is a circuit diagram showing a drive circuit 40 of the piezoelectric actuator of Comparative Example 1. A drive circuit 40 was configured by connecting a 2.2 kΩ resistor 42 in series with the piezoelectric actuator 15. A power source 11 was configured using a function generator and a 2-ampere 4-quadrant amplifier, and a rectangular wave voltage was applied.

(Comparative Example 2)
A drive circuit 40 for the piezoelectric actuator shown in FIG. 4 was configured using a resistor 42 of 10 kΩ. A power source 11 was configured using a function generator and a 2-ampere 4-quadrant amplifier, and a rectangular wave voltage was applied.

(Comparative Example 3)
FIG. 5 is a circuit diagram showing a drive circuit 50 of the piezoelectric actuator of Comparative Example 3. The drive circuit 50 of the piezoelectric actuator includes a first-order RC first-order low-pass filter having a resistance 52 of 2.2 kΩ and a capacitor 53 having a capacitance value of 1 μF. Similarly to Comparative Examples 1 and 2 described above, the power source 11 was configured using a function generator and a 2-ampere 4-quadrant amplifier, and a rectangular wave voltage was applied.

(Comparative Example 4)
The piezoelectric actuator drive circuit of Comparative Example 4 was configured using the piezoelectric actuator drive circuit 60 shown in FIG. An RLC low-pass filter as shown in FIG. 2 composed of a resistance of 1 kΩ, a coil of inductance 1 mH, and a capacitor of 6.5 μF was constituted by a power supply 61 using a function generator and a 2-ampere 4-quadrant amplifier. Then, the power supply voltage was applied to the piezoelectric actuator 15 via the RLC low-pass filter.

(Comparative Example 5)
FIG. 6 is a circuit diagram showing a drive circuit 60 of the piezoelectric actuator of Comparative Example 5. The piezoelectric actuator drive circuit 60 includes a power supply 61 and a piezoelectric actuator 15. A power supply 61 was configured using a function generator and a 2-ampere 4-quadrant amplifier, and a voltage of a rectangular wave having a rising and falling edge formed by a half cycle of a 1 kHz sine wave was applied to the piezoelectric actuator 15.

Example 1
As Example 1, the drive circuit 10 of the piezoelectric actuator shown in FIG. A secondary RC low-pass filter was constituted by a resistor having a resistance value of 1 kΩ and a capacitor having a capacitance value of 1 μF, and a voltage was applied to the piezoelectric actuator 15.

(Example 2)
As Example 2, the piezoelectric actuator drive circuit 20 shown in FIG. A secondary RLC low-pass filter was constituted by a resistor having a resistance value of 1 kΩ and a capacitor having a capacitance value of 2.5 μF, and a voltage was applied to the piezoelectric actuator 15.

(Example 3)
A voltage of the same drive waveform as that when a rectangular wave was input by connecting a 1 kΩ resistor and a 1 H coil in series to the piezoelectric actuator was applied.

  The piezoelectric actuator drive circuit of Example 3 was configured using the piezoelectric actuator drive circuit 30 shown in FIG. An RLC low-pass filter including a 1 kΩ resistor, an inductance 1H coil, and a 6.5 μF capacitor was pseudo-configured by a power supply 31 using a function generator and a 2 amp 4-quadrant amplifier. Then, the power supply voltage was applied to the piezoelectric actuator 15 via the RLC low-pass filter.

Example 4
As Example 4, the drive circuit 30 of the piezoelectric actuator shown in FIG. A power source 11 was configured using a function generator and a 2-ampere four-quadrant amplifier, and applied to the piezoelectric actuator 15 with an applied voltage waveform in which the rising and falling portions of the rectangular wave were in the shape of a half cycle of a 100 Hz sine wave.

(Waveform in each example)
7A to 14C are diagrams showing applied voltage waveforms in Comparative Examples 1 to 5 and Examples 1 to 4. FIG. In the figure, applied voltage waveforms are shown on a three-stage time scale for each example.

  In Comparative Example 1, when the resistor 42 of 2.2 kΩ was provided between the power supply 11 and the piezoelectric actuator 15, the voltage change became gentle as shown in FIGS. 7A to 7B, but as shown in FIG. 7C. The slope of the applied voltage waveform at the rising edge remained steep. In Comparative Example 2, when the resistor 42 of 10 kΩ was provided between the power supply 11 and the piezoelectric actuator 15, the voltage change became more gradual as shown in FIGS. 8A to 8B. The inclination of was not significantly different from that of Comparative Example 1. In Comparative Example 3, a primary low-pass filter was provided between the power supply 11 and the piezoelectric actuator 15, but the applied voltage waveform was not much different from that of Comparative Example 1 as shown in FIGS. 9A to 9C.

  On the other hand, in the first and second embodiments, when a second-order RC low-pass filter is configured in the circuit, as shown in FIGS. 12A to 12C and FIGS. 13A to 13C, as shown in FIGS. 12A to 12B and FIGS. As shown, the change in voltage became gradual. Further, as shown in FIGS. 12C and 13C, the slope of the rising applied voltage waveform also became gentle.

  In Comparative Example 4, an RLC low-pass filter was configured, but the inductance of the coil was 1 mH, and the slope of the applied voltage at the rising edge remained large. On the other hand, in Example 3, a pseudo RLC low-pass filter was configured with the coil inductance set to 1H, so that an applied voltage waveform with a gradual rising slope was obtained as shown in FIG.

  In Comparative Example 5, the voltage generated by the function generator with the rising and falling edges corresponding to a half cycle of a 1 kHz sine wave was applied, but the slope of the applied voltage waveform did not decrease as shown in FIGS. . On the other hand, in Example 4, when the voltage generated by the function generator with a half cycle of a sine wave of 100 Hz is applied by the function generator, the gradient of the applied voltage becomes gentle as shown in FIGS. became.

(MTTF)
For the circuits of Comparative Examples 1 to 5 and Examples 1 to 4, Weibull plotting was performed with the number of times of failure, and MTTF (Mean Failure Life) was estimated. Table 1 shows the cutoff frequency (Hz) and MTTF for each circuit. As shown in Table 1, there was a clear difference in durability between Comparative Examples 1-5 and Examples 1-4. The durability did not always match the magnitude of the cutoff frequency of the drive circuit.

  FIG. 16 is a diagram showing rising applied voltage waveforms in Comparative Examples 1 to 5 and Examples 1 to 4. It can be seen that Comparative Examples 1 to 5 have a large voltage change rate from the beginning of the voltage change, and that in the example, the voltage change rate starts from 0. In the voltage waveform of the comparative example, since the acceleration of the piezoelectric actuator increases at the beginning of the voltage change, the movement becomes faster than the resonance frequency of the system, and a time during which the operation of the piezoelectric actuator cannot keep up with the drive voltage occurs. For this reason, it is considered that failure of the piezoelectric actuator is likely to occur. On the other hand, in the waveform of the example, since the acceleration is sufficiently small and does not exceed the resonance frequency of the system, it is considered that the operation of the piezoelectric actuator was not forced.

  As shown in FIG. 16, the voltages in Examples 1 to 3 are smaller than the voltage in Example 4. Moreover, if it is in 0.00015 s, the voltage of Example 4 is smaller than the voltage of Comparative Examples 1-5. From such a result, the rising or falling time can be specified as 0.00015 s, for example. Further, for example, as shown in FIG. 16, the slope 0 is a voltage waveform with respect to time rising substantially horizontally (or falling) on a graph having a scale of about 0.01 s to 0.001 s. That means.

10, 20, 30 Drive circuit 11, 31 Power source 12, 13, 22 Resistor 14, 24 Capacitor 15 Piezoelectric actuator 23 Coil

Claims (5)

A drive circuit for a piezoelectric actuator that applies a drive voltage with rising or falling,
A drive circuit for a piezoelectric actuator, which is formed with a frequency component equal to or lower than a mechanical resonance frequency of the piezoelectric actuator and applied to the piezoelectric actuator with a waveform starting from a slope of 0 at the rise or fall of voltage application.   A waveform having a frequency that is 1/3 of the mechanical resonance frequency of the piezoelectric actuator and having an absolute value of a first-order differential value smaller than a sine wave starting from a phase of −90 ° or + 90 ° at the rising or falling of the voltage application. The piezoelectric actuator drive circuit according to claim 1, wherein a voltage is applied to the piezoelectric actuator.   The piezoelectric actuator drive circuit according to claim 2, further comprising a secondary or higher-order RC low-pass filter that applies a power supply voltage to the piezoelectric actuator with a voltage of the applied voltage waveform.   The piezoelectric actuator drive circuit according to claim 2, further comprising an RLC low-pass filter that applies a power supply voltage to the piezoelectric actuator with a voltage of the applied voltage waveform.   At the rise or fall of the voltage application, the piezoelectric actuator has a half-cycle waveform of a sine wave having a frequency equal to or less than 1/3 of the mechanical resonance frequency of the piezoelectric actuator and starting from a phase of −90 ° or + 90 °. 2. The piezoelectric actuator drive circuit according to claim 1, wherein a voltage is applied.

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