JP2003259666A - Piezoelectric element control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric element control device with reduced deviation between 'the output signal of a charge detecting circuit for detecting the amount of charge accumulated in the piezoelectric element' and 'the amount of the displacement of the piezoelectric element', particularly in low frequency regions. <P>SOLUTION: The piezoelectric control device is provided with a drive circuit 40 that applies a voltage to the piezoelectric element 10, a charge detecting circuit 20 that detects the amount of charge accumulated in the piezoelectric element 10, and a correction circuit 30 that performs signal processing on an output signal from the charge detecting circuit 20. The charge detecting circuit 20 comprises an operational amplifier 21, a feedback capacitor 22, and an inverting circuit 23. The electrostatic capacity Cs of the capacitor 22 is set to be 10-20 times the electrostatic capacity Cp of the piezoelectric element 10. The inverting circuit 23 regulates phases of the drive circuit 40 output and the charge detecting circuit 20 output. The correction circuit 30 has an input/ output characteristic that is roughly equivalent to the frequency characteristic of the 'amount of displacement of the piezoelectric element 10' to the 'output signal of the charge detecting circuit'. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for a piezoelectric element used for minute positioning.

[0002]

2. Description of the Related Art Generally, since a piezoelectric element has a driving characteristic having hysteresis as shown in FIG. 9, it is difficult to control and drive it with high accuracy. In order to drive the piezoelectric element with high accuracy, a method is generally used in which a displacement sensor such as a capacitance sensor is additionally provided and the piezoelectric element is controlled based on the displacement information of the displacement sensor. However, as a recent trend, there is a demand for size reduction and price reduction in the market, and a driving method and a control method for a piezoelectric element that do not rely on an external displacement sensor such as a capacitance sensor are desired.

As a conventional driving method and control method for a piezoelectric element that does not rely on an external displacement sensor, control based on the amount of charge accumulated in the piezoelectric element is well known. The amount of charge accumulated in the piezoelectric element has a substantially linear relationship with the amount of displacement of the piezoelectric element, and the hysteresis is significantly reduced as shown in FIG.

Japanese Unexamined Patent Publication No. 63-204673 discloses an example of such control. This detects the amount of charge accumulated in the piezoelectric element and uses it as a displacement sensor. Hereinafter, the operation principle will be briefly described with reference to FIG.

In FIG. 11, the piezoelectric element 10 is displaced in response to the application of voltage. The charge detection circuit 20 includes an operational amplifier 21, a capacitor 22, and an inverting circuit 23.

The piezoelectric element 10 is displaced in response to the application of the voltage V0, and the piezoelectric element 10 has a charge q corresponding to the amount of displacement.
Is accumulated. The same amount of charge is stored in the capacitor 22. If the capacitance of the capacitor 22 is Cs,
The operational amplifier 21 outputs a voltage signal of q / Cs.

Since the electric charge q has a substantially linear relationship with the displacement amount of the piezoelectric element 10 and Cs is a constant, the operational amplifier 21
The voltage signal output from the device substantially indicates the amount of displacement of the piezoelectric element 10.

The inverting circuit 23 is provided to make the applied voltage V0 and the output voltage of the operational amplifier 21 out of phase with each other by 180 degrees, in other words, because the phase is inverted, so that they match.

As described above, the output of the charge detection circuit 20 can be used as a displacement signal indicating the displacement of the piezoelectric element 10.
Furthermore, by controlling the piezoelectric element 10 based on the output of the charge detection circuit 20, the displacement of the piezoelectric element 10 can be controlled with high accuracy.

[0010]

However, the above-mentioned conventional control method based on the charge amount has the following drawbacks.

In the charge detection system shown in FIG. 11, the "actual displacement amount of the piezoelectric element 10" and the "charge signal (piezoelectric element 10 when a rectangular wave having a constant amplitude and a frequency of 1 Hz" is applied to the piezoelectric element 10. FIG. 12 shows a signal based on the amount of electric charge accumulated in “)”. In this case, it can be seen that the "charge signal" substantially matches the "actual displacement amount of the piezoelectric element 10."

In the charge detection system shown in FIG. 11, the "actual displacement amount of the piezoelectric element 10" when a "rectangular wave having a constant amplitude and a frequency of 0.01 Hz" is applied to the piezoelectric element 10.
And "charge signal" are shown in FIG. In this case, there is a large difference between the "charge signal" and the "actual displacement amount of the piezoelectric element 10."

This is because the relationship between the amount of electric charge accumulated in the piezoelectric element and the amount of displacement of the piezoelectric element differs between the frequency range of 1 Hz or higher and the frequency range of 1 Hz or lower. Another cause is the difference in the electrical characteristics of the piezoelectric element and the capacitors used in the charge detection circuit. Therefore, it is difficult for the method of controlling the amount of charge accumulated in the piezoelectric element to control the piezoelectric element with high accuracy in a wide band including a low frequency region.

The characteristics shown in FIGS. 12 and 13 are merely examples, and "the boundary frequency at which the characteristics differ"
Depends on the material and shape of the piezoelectric element. Furthermore, it also depends on the type of capacitor used in the charge detection circuit. The "boundary frequency at which the characteristics differ" is considered to be in the range of approximately 0.1 Hz to 100 Hz in a general piezoelectric element.

The present invention has been made in consideration of such an actual situation, and its object is to make a difference between the "charge detection circuit output signal" and the "piezoelectric element displacement amount" particularly in a low frequency region. (EN) Provided is a piezoelectric element control device which can drive a piezoelectric element with high accuracy in a wide band including a low frequency region.

[0016]

A piezoelectric element control device according to the present invention comprises a driving means for applying a voltage to the piezoelectric element and a charge detection circuit for detecting the amount of electric charge stored in the piezoelectric element. A charge detection circuit that outputs a signal according to the detected charge amount, and a signal processing unit that performs signal processing on the output signal of the charge detection circuit, the "piezoelectric element for at least the output signal of the charge detection circuit" Displacement of
In the frequency region below the boundary where the frequency characteristics of the change significantly, the signal processing means having an input / output characteristic almost equal to the frequency characteristic of the “displacement amount of the piezoelectric element” with respect to the “output signal of the charge detection circuit” is provided. I have it.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

First Embodiment The first embodiment of the present invention is one embodiment of the piezoelectric element control device. FIG. 1 shows a schematic configuration of the piezoelectric element control device.

As shown in FIG. 1, the piezoelectric element control apparatus of this embodiment includes a drive circuit 40 for applying a voltage to the piezoelectric element 10, in other words, an electric field, and a piezoelectric element 1.
Charge detection circuit 2 for detecting the amount of charge stored in 0
0, and a correction circuit 30 that is a signal processing circuit that performs signal processing on the output signal of the charge detection circuit 20.

The piezoelectric element 10 expands and generates displacement in response to the application of voltage. The capacitance Cp of the piezoelectric element 10 changes depending on the amount of displacement, but since it is a level that does not matter, the change of the capacitance of the piezoelectric element 10 will not be discussed here.

The charge detection circuit 20 comprises an operational amplifier 21, a feedback capacitor 22 and an inverting circuit 23. The capacitance Cs of the capacitor 22 is the operational amplifier 2
The output of 1 is 1 / 20th of the voltage applied to the piezoelectric element
(The maximum voltage applied to the piezoelectric element is 200V.
Is set to V or less), the capacitance Cp of the piezoelectric element 10 is set to 10 to 20 times.

The phase of the output voltage signal of the operational amplifier 21 is
The output of the drive circuit 40, that is, the phase of the applied voltage signal is shifted by 180 degrees, that is, inverted. The inverting circuit 23
It is provided in order to make the phase of the applied voltage signal from the drive circuit 40 and the phase of the output voltage signal of the charge detection circuit 20 uniform, that is, to match them. The effect is not affected even if this inverting circuit 23 is not provided. That is, the inverting circuit 23 may be omitted.

The correction circuit 30 has a frequency characteristic of "displacement amount of the piezoelectric element 10" with respect to "output signal of the charge detection circuit",
In other words, the piezoelectric element 10 has an input / output characteristic almost equivalent to the displacement / charge signal frequency characteristic. Here, “substantially equivalent input / output characteristics” are a general term for “matching input / output characteristics” and “similar input / output characteristics”.

Since the correction circuit 30 has an input / output characteristic almost equal to the frequency characteristic of the "displacement amount of the piezoelectric element 10" with respect to the "output signal of the charge detection circuit", the correction circuit 30.
The output of indicates the displacement of the piezoelectric element 10 with high accuracy.

In other words, the correction circuit 30 has a "displacement amount of the piezoelectric element 10" with respect to the "output signal of the charge detection circuit" so that its output indicates the displacement of the piezoelectric element 10 with high accuracy.
So that it has an input / output characteristic almost equal to the frequency characteristic of
More preferably, it is designed to have matching input / output characteristics. In designing the correction circuit 30, first, the “displacement amount of the piezoelectric element 10” with respect to the “output signal of the charge detection circuit”
The frequency characteristics of are measured or calculated. The correction circuit 30 is designed based on the obtained frequency characteristic.

FIG. 5 shows an example of the frequency characteristic of the "displacement amount of the piezoelectric element 10" with respect to the "charge detection circuit output signal". In FIG. 5, the displacement amount / charge signal at the frequency of 100 Hz is normalized to be 1. Further, the phase characteristic is almost constant regardless of the frequency.

Hereinafter, assuming that the frequency characteristic of the "displacement amount of the piezoelectric element 10" with respect to the "output signal of the charge detection circuit" is as shown in FIG. 5, a configuration example of the correction circuit 30 will be described.

The correction circuit 30, as shown in FIG.
It is composed of a first filter 31, a second filter 32, and an adder 33. The input / output characteristic of the correction circuit 30 is represented by “1 + input / output characteristic of the filter 31 + input / output characteristic of the filter 32”. The filters 31 and 32 may be either analog filters or digital filters.

As shown in FIG. 3, the filter 31 is for amplifying the output signal of the filter 31a and the filter 31a for selectively passing a component of a specific frequency band in the input signal to itself. And a gain circuit 31b. More specifically, the filter 31 is a 0.08 Hz first-order low-pass filter (L
PF) 31a and a gain circuit 31b with a gain of 1/2. The input / output characteristic of the filter 31 is shown by a broken line with a long gap between the cuts in FIG.

As shown in FIG. 4, the filter 32 has two filters 32a for selectively passing a component of a specific frequency band in the input signal to itself.
And 32b, and a gain circuit 32c for amplifying the output signal of the filter 32b. More specifically, the filter 32 includes a 0.006 Hz first-order high-pass filter (HPF) 32a, a 0.02 Hz first-order low-pass filter (LPF) 32b, and a gain of 1/5.
And a gain circuit 32c. The input / output characteristics of the filter 32 are shown by broken lines with short gaps in FIG.

Therefore, "the input / output characteristic of the filter 31+
The "input / output characteristic of the filter 32" is shown by the solid line in FIG.

Therefore, the input / output characteristic of the correction circuit 30 is as shown in FIG.
It is almost the same as the characteristics shown in. As a result, the output of the correction circuit 30 indicates the displacement of the piezoelectric element 10 with high accuracy in a frequency range of at least 0.01 Hz or higher.

In the phase characteristic of the correction circuit 30, the displacement amount of the piezoelectric element 10 and the phase characteristic of the charge signal, that is, the actual phase characteristic is constant regardless of the frequency, but a slight deviation occurs. Further, the output of the correction circuit 30 is slightly distorted. However, the effect is almost negligible.

As described above, in the piezoelectric element control device according to the present embodiment, the correction circuit having the input / output characteristic substantially equal to the frequency characteristic of the “displacement amount of the piezoelectric element” with respect to the “output signal of the electric charge detection circuit” is provided. The difference between the “charge detection circuit output signal” and the “piezoelectric element displacement amount” in the frequency domain is reduced. Thereby, the displacement of the piezoelectric element can be obtained with high accuracy in a wide band including a low frequency region.

In the present embodiment, the correction is made in the frequency region of 0.01 Hz or higher.
In the case of correcting the frequency range including z or less as well, the frequency characteristic including the range of 0.01 Hz or less of the “displacement amount of the piezoelectric element 10” with respect to the “output signal of the charge detection circuit” is first obtained as in the first embodiment. The same effect can be obtained if the correction circuit is designed and the filter is added so as to be found by actual measurement or calculation, and to match it.

Second Embodiment The second embodiment of the present invention is one embodiment of the piezoelectric element control device. FIG. 7 shows a schematic configuration of this piezoelectric element control device.

As shown in FIG. 7, the piezoelectric element control apparatus according to the present embodiment has a drive circuit 40 for applying a voltage to the piezoelectric element 10 and a charge amount stored in the piezoelectric element 10. A charge detection circuit 20, a correction circuit 30 that performs signal processing on the output signal of the charge detection circuit 20, and a control circuit 50 that feedback-controls the drive circuit 40 based on the output signal of the correction circuit 30 are provided. There is.

The drive circuit 40, the charge detection circuit 20, and the correction circuit 30 are the same as those described above in the first embodiment.

The control circuit 50 is, for example, a PID control circuit, and controls so that the output signal of the correction circuit 30 matches the reference signal (operation command signal).

In the piezoelectric element control device of this embodiment, the displacement of the piezoelectric element 10 is feedback-controlled based on the output of the correction circuit 30. Therefore, the piezoelectric element control device of the present embodiment can drive the piezoelectric element 10 with high accuracy in a wide band including a low frequency region.

Third Embodiment The third embodiment of the present invention is one embodiment of the piezoelectric element control device. FIG. 7 shows a schematic configuration of this piezoelectric element control device.

As shown in FIG. 8, the piezoelectric element control device of this embodiment includes a current amplifier 60 for injecting charges into the piezoelectric element 10, a voltage follower 70, a capacitor 22, and a correction circuit 30. I have it. This piezoelectric element control device is substantially the same as that disclosed in JP-A-63-204672.
The configuration is such that the correction circuit 30 described in the first embodiment is added to the charge control circuit disclosed in the publication.

When the drive voltage V0 is input to the current amplifier 60, the charge Q is injected into the piezoelectric element 10. Here, when the displacement of the piezoelectric element 10 is X and the input / output characteristic shown in FIG. 5 is an input / output function G, a relationship of X / Q = G is obtained.

When the electric charge Q is injected into the piezoelectric element 10, the electric charge Q (= X / G) is also charged in the capacitor 22, and the voltage of the input terminal of the voltage follower 70, that is, the output voltage of the voltage follower 70 becomes Q. / Cs (= X / (CsG)). Since the input / output characteristic of the correction circuit 30 can be G,
The output voltage V of the correction circuit 30 is V = G × X / (CsG) = X / Cs. Since the current amplifier 60 operates so that the two inputs (V0 and V) are the same, V0 = V = X / Cs is obtained. From this, it can be seen that the drive voltage V0 and the displacement X of the piezoelectric element 10 operate in a linear manner.

In the piezoelectric element control device of this embodiment, the displacement of the piezoelectric element 10 is feedback-controlled based on the output of the correction circuit 30. Therefore, the piezoelectric element control device of the present embodiment can drive the piezoelectric element 10 with high accuracy in a wide band including a low frequency region.

Although the embodiments of the present invention have been described with reference to the drawings, the present invention is not limited to these embodiments, and various modifications and alterations can be made without departing from the scope of the invention. Changes may be made.

[0047]

According to the present invention, the "output signal of the charge detection circuit" and the "displacement amount of the piezoelectric element" particularly in the low frequency region.
Provided is a piezoelectric element control device with reduced deviation. As a result, the piezoelectric element is controlled with higher accuracy in a wide band including the low frequency region.

[Brief description of drawings]

FIG. 1 shows a schematic configuration of a piezoelectric element control device according to a first embodiment of the present invention.

2 shows a schematic configuration of the correction circuit shown in FIG.

3 shows a schematic configuration of the first filter shown in FIG.

4 shows a schematic configuration of the second filter shown in FIG.

FIG. 5 shows an example of frequency characteristics of “displacement amount of piezoelectric element 10” with respect to “output signal of charge detection circuit”.

FIG. 6 shows the input / output characteristics of the first filter, the input / output characteristics of the second filter, and the input / output characteristics of the first filter + the input / output characteristics of the second filter.

FIG. 7 shows a schematic configuration of a piezoelectric element control device according to a second embodiment of the present invention.

FIG. 8 shows a schematic configuration of a piezoelectric element control device according to a third embodiment of the present invention.

FIG. 9 shows a relationship between an applied voltage and a displacement amount in a general piezoelectric element, that is, a driving characteristic of the piezoelectric element.

FIG. 10 shows a relationship between a charge amount and a displacement amount in a general piezoelectric element.

FIG. 11 shows a conventional example of a charge detection system used to drive a piezoelectric element without using an external displacement sensor and for detecting the amount of charge accumulated in the piezoelectric element.

FIG. 12 shows “actual displacement amount of piezoelectric element” and “charge signal” when “rectangular wave of constant amplitude and frequency of 1 Hz” is applied to the piezoelectric element in the charge detection system shown in FIG. 11. .

13 shows "actual displacement amount of piezoelectric element" and "charge signal" when "rectangular wave of constant amplitude and frequency of 0.01 Hz" is applied to the piezoelectric element in the charge detection system shown in FIG. ing.

[Explanation of symbols]

10 Piezoelectric element 20 Charge detection circuit 21 operational amplifier 22 condenser 23 Inversion circuit 30 Correction circuit 31 Filter 31a Primary low-pass filter 31b Gain circuit 32 filters 32a primary high-pass filter 32b secondary low-pass filter 32c gain circuit 33 adder 40 drive circuit

Claims (5)

[Claims] 1. A drive unit for applying a voltage to a piezoelectric element, and a charge detection circuit for detecting the amount of electric charge stored in the piezoelectric element, the electric charge outputting a signal according to the detected amount of electric charge. A detection circuit and signal processing means for performing signal processing on the output signal of the charge detection circuit, which is at least below the boundary where the frequency characteristic of the "displacement amount of the piezoelectric element" with respect to the "output signal of the charge detection circuit" greatly changes. And a signal processing unit having an input / output characteristic that is substantially equal to the frequency characteristic of the “displacement amount of the piezoelectric element” with respect to the “output signal of the charge detection circuit” in the frequency region of. 2. The piezoelectric element control device according to claim 1, further comprising control means for controlling the drive means based on the signal processed by the signal processing means. 3. The signal processing means according to claim 1 or 2, in the frequency region above the boundary,
A piezoelectric element control device having substantially the same input / output characteristics as the frequency characteristics of the "displacement amount of the piezoelectric element" with respect to the "output signal of the charge detection circuit". 4. The signal processing means according to claim 1, wherein each of the plurality of filter means for independently performing signal processing on an input signal to itself and each of the input signal to itself and the plurality of filter means. A piezoelectric element control device, comprising: an addition / subtraction means for performing an addition / subtraction process on the output signal of and the output signal. 5. The filter means according to claim 4, wherein each filter means amplifies an output signal of the filter circuit and at least one filter circuit for selectively passing a component of a specific frequency band in an input signal to itself. And a gain circuit having an amplification factor of 1 or less for controlling the piezoelectric element.