JP3146447B1 - Driving method and driving device for piezoelectric actuator - Google Patents

Abstract

Provided is a driving method and a driving device for a piezoelectric actuator, in which a power supply unit is reduced in size, whereby the entire device can be reduced in size. SOLUTION: In a piezoelectric actuator 1 using piezoelectric elements 100A, 100B, 100C in which a change in polarity of an applied voltage is not allowed, an AC voltage of a predetermined frequency is generated from a DC power supply, and is then superimposed on the AC voltage. In this case, a bias DC voltage having a magnitude that eliminates a change in the polarity of the voltage is generated, and the AC voltage and the bias DC voltage are superimposed on each other so that the piezoelectric elements 100A,
100B and 100C are driven.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a driving method and a driving device for a piezoelectric actuator. For more information,
The present invention relates to a driving method and a driving device suitable for a piezoelectric actuator using a piezoelectric element that does not allow a change in polarity of an applied voltage.

[0002]

2. Description of the Related Art Conventionally, piezoelectric elements have been used to adjust the angle of a ball joint, the positioning of an XY stage, the precise angle adjustment and positioning of a lens and a mirror, and the precise positioning of various analytical instruments and small precision machines. A piezoelectric actuator as a driving element is used.

FIG. 20 shows a schematic structure of such a conventional piezoelectric actuator. This piezoelectric actuator 10 '
Is a piezoelectric element 11 'that expands and contracts according to the applied voltage.
And an operation unit 12 ′ that outputs a signal corresponding to an operation to the piezoelectric actuator 10 ′, and a sine waveform voltage generated in accordance with a signal from the operation unit 12 ′ is applied to the piezoelectric element 11 ′, and Drive circuit 1 for driving actuator 10 '
3 '.

[0004] An operation unit 12 'is a piezoelectric actuator 10'.
A command to generate a sine wave signal having a frequency, an amplitude, and a phase corresponding to the operation to the drive circuit 13 'is issued. The drive circuit 13 ′
Sine wave generation circuit 1 in response to a creation command from operation unit 12 '
4 ', a sine wave signal is generated, and the sine wave signal is amplified by the linear amplifier 15' and applied to the piezoelectric element 11 '.

However, the conventional method of driving the piezoelectric actuator 10 'has a configuration in which a minute sine wave signal generated by the sine wave generation circuit 14' is amplified by the linear amplifier 15 'and applied to the piezoelectric element 11'. Therefore, there is a problem that it is not easy to apply a sine waveform voltage without distortion to the piezoelectric element 11 '.

That is, when the piezoelectric element 11 'is to be expanded and contracted at a high response speed, the current flowing through the piezoelectric element when switching the pulse becomes excessive when driving by applying a pulsed voltage, and as a result, excessive stress is applied to the piezoelectric element. Occurs,
In some cases, the piezoelectric element may be destroyed. For this reason, the voltage waveform applied to the piezoelectric element 11 'is required to be a sine wave with accurate frequency, amplitude, and phase with little distortion.

Further, since the piezoelectric element 11 'is a capacitive element, the phase of the current flowing therethrough is advanced by about 90 ° with respect to the phase of the applied voltage. The active power is smaller than the size,
This also reduces the degree of expansion and contraction. Therefore, in order to deform the piezoelectric element 11 ′ stably and largely,
A sine wave generator for generating a sine wave signal having an accurate waveform, and a linear amplifier 15 'having high output and low distortion amplification characteristics
Is required.

In general, however, the linear amplifier 15 '
When the output current is increased, the collector loss is increased and the heat generation is increased. Therefore, in order to obtain a high output and low distortion amplification characteristic, the linear amplifier 15 'needs to be increased in size. Becomes larger. Further, this configuration has a disadvantage that a sine wave generation circuit for generating a sine wave signal is separately required.

Thus, in the conventional actuator,
Since the linear amplifier is used in the drive circuit, there is a problem that the power supply unit becomes large in comparison with the size of the piezoelectric element and its mechanical output.

Furthermore, in recent years, research and development of a piezoelectric actuator using a plurality of piezoelectric elements instead of a single element have been actively conducted. In such a piezoelectric actuator, a number of drive circuits corresponding to the number of piezoelectric elements are prepared. Need
There is a problem that the power supply unit becomes larger and larger.

Although a PWM driving method is conceivable as a driving method of the piezoelectric actuator, there is a problem that the waveform is easily distorted, and in order to eliminate the distortion, a driving transistor having a high performance is required. This causes another problem that the cost of the device is increased.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and a method of driving a piezoelectric actuator which can reduce the size of the entire apparatus by reducing the size of a power supply unit. It is an object to provide a driving device.

[0013]

A method of driving a piezoelectric actuator according to the present invention is a method of driving a piezoelectric actuator using a piezoelectric element in which the polarity of an applied voltage is not allowed to change. AC voltage PW
Generated by the M driving method and by the PWM driving method.
Waveform distortion caused by output element switching
Adding a choke coil in the drive circuit
Improved by, then the generated bias DC voltage having a polarity change is eliminated such magnitude of the voltage when it is superimposed on the AC voltage, wherein by superimposing said AC and DC voltages for the bias It is characterized by driving a piezoelectric element.

[0014]

Further, in the driving method of the piezoelectric actuator of the present invention, the switching distortion is sufficiently removed, and the output for performing the PWM driving by making the impedance of the piezoelectric actuator including the choke coil inductive is provided. It is desirable to reduce the load on the element. In that case, for example, the inductance of the choke coil is set so as to substantially satisfy the following expression.

[0016] ^{_{L h = 2 / (ω 2}} (C0 + C1)) Here, L _h: a choke coil inductance omega: power supply angular frequency C0: the equivalent capacitance of the electrical characteristics of the piezoelectric element C1: the piezoelectric element mechanically Capacitance of the characteristic part

On the other hand, a driving device for a piezoelectric actuator according to the present invention is a driving device for a piezoelectric actuator using a piezoelectric element in which the polarity of an applied voltage is not allowed to change, and an AC voltage having a predetermined frequency is supplied from a DC power supply. PWM drive
Raw by generating and the PWM driving method by method
Piezoelectric element eliminates waveform distortion due to switching of output element
By providing a choke coil in the drive circuit,
Improving Te, then the generated bias DC voltage having a polarity change is eliminated such magnitude of the voltage when it is superimposed on the AC voltage, wherein by superimposing said AC and DC voltages for the bias The circuit is configured to drive the piezoelectric element.

[0018]

In the driving apparatus for a piezoelectric actuator according to the present invention, the switching distortion is sufficiently removed, and the PWM driving is performed by making the impedance of the piezoelectric actuator including the choke coil inductive. It is desirable to reduce the load on the output element. In that case, for example, the inductance of the choke coil is set so as to substantially satisfy the following expression.

[0020] ^{_{L h = 2 / (ω 2}} (C0 + C1)) Here, L _h: a choke coil inductance omega: power supply angular frequency C0: the equivalent capacitance of the electrical characteristics of the piezoelectric element C1: the piezoelectric element mechanically Therefore, the driving device is mounted on a piezoelectric actuator.

[0021]

According to the present invention, a DC voltage having a predetermined frequency can be applied to the piezoelectric element without using a large linear amplifier. Therefore, the power supply unit of the piezoelectric actuator can be downsized. Accordingly, the size of the entire piezoelectric actuator can be reduced.

[0022]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
The present invention will be described based on embodiments, but the present invention is not limited to only such embodiments.

FIG. 1 shows the impedance characteristics of the piezoelectric element P used in the vibrator of the present invention. The piezoelectric element P, as shown in FIG. 1, to the resonance angular frequency omega _r impedance is lowered, and the impedance conversely increases past the resonance angular frequency omega _r, then reaches the antiresonance angular frequency omega _ar Then, on the contrary, there is a characteristic that the impedance is reduced. Note that the resonance angular frequency ω _r and the anti-resonance angular frequency ω _ar are determined mainly by the mechanical resonance characteristics of the piezoelectric element P.

FIG. 2 is an equivalent circuit diagram of the piezoelectric element P having the impedance characteristic according to the present invention. The equivalent circuit shown in FIG. 2 is configured by connecting an electrical characteristic unit representing electrical characteristics and a mechanical characteristic unit representing mechanical characteristics in parallel. Electrical Characteristics section is specifically are those formed by parallel connection of the capacitor C ₀ and resistor R _d, also the mechanical properties section, resistance in particular the inductance L and the capacitor C ₁ 'R _M
Are connected in series.

However, in the present invention, the movement of an object is controlled by a vibrator formed by coupling the piezoelectric elements P. Therefore, in order to ensure controllability, the frequency band where mechanical resonance or anti-resonance occurs is required. Not used. Therefore, the equivalent circuit shown in FIG. 2 can be simplified to the equivalent circuit shown in FIG. That is, the mechanical characteristic portion is changed to the capacitor C
₁ and can be connected in parallel and simplification of the resistor R _M.

Next, the driving principle of the piezoelectric element P having such impedance characteristics will be described with reference to FIG.

In the circuit shown in FIG. 4, the power supply voltage is such that the DC voltage is superimposed on the high-frequency AC voltage so that the polarity does not change. The inductance is a so-called choke coil Lc. Therefore, the magnitude of this inductance needs to be set so that the current without the choke coil Lc shown in FIG. 5 is supplied to the piezoelectric element P. This is because when such a current flows, a predetermined driving force is obtained in the piezoelectric element. Here, the calculation process is omitted,
If the inductance L _h of the choke coil Lc is set to substantially satisfy the following equation, practically no problem.

[0028] ^{_{L h = 2 / (ω 2}} (C0 + C1)) Here, omega is power supply angular frequency, C0 is equivalent capacitance of the electrical characteristic part, C1 is the equivalent capacitance of the mechanical properties section.

When a high-frequency current is supplied to the RC portion forming the mechanical characteristic portion of the piezoelectric element P,
The portion is vibrated by the high-frequency current to generate a driving force.

Hereinafter, the present invention will be described specifically.

Embodiment 1 FIGS. 6 to 6 show a piezoelectric actuator according to Embodiment 1 of the present invention.
As shown in FIG. FIG. 6 is a schematic diagram of a ball joint having a built-in piezoelectric actuator according to the first embodiment of the present invention. FIG. 7 is an explanatory diagram illustrating the operation principle of the ball joint. FIG. 8 is an overall block diagram.

In the ball joint 50, the tip portions 101 of three vibrators 10 arranged in a predetermined arrangement in a sphere housing member 520 housing the sphere 510 of the ball joint are brought into contact with the sphere 510, In order to maintain this contact state, the sphere 510 is similarly placed in the sphere storage member 520.
A plurality of spring members 530 arranged in a predetermined arrangement therein
Thus, the vibrator 10 is urged in the direction of the vibrator 10 and the vibrator 10 rotates the sphere 510 in an arbitrary direction.

The size of the sphere 510 is the ball joint 5
0 is appropriately selected according to the purpose of use. The material of the ball joint 50 is also appropriately selected in accordance with the purpose of use of the ball joint 50. In consideration of prevention, it is preferable to use ceramics or hard-plated metal.

The three vibrators 10 have their tip portions 10
As long as the 1s are not arranged on the same circumference, the arrangement relationship is not particularly limited. However, in order to make the performance in the driving direction uniform, they are arranged at a position where the intervals are equal. Is preferred. In the present invention, the number of vibrators 10 is not limited to three, and may be four or more when there is no restriction on the control system.

The vibrator 10 includes three piezoelectric elements 100
The tips of A, 100B, and 100C are joined and integrated, and the joined portion forms the tip 101 of the vibrator 10. This piezoelectric element 100A, 1
00B and 100C are, for example, PT, PZT, PLZ
It is composed of laminated piezoelectric ceramics such as a ternary piezoelectric material based on T and PZT. The shape and size are appropriately selected according to the purpose of use of the ball joint 50. However, when the ball joint 50 is integrated with the vibrator 10, an effective rotational force is generated at the distal end portion 101 (see FIG. 2). It is preferable to dispose the piezoelectric elements at the positions of the three twills centered on the apex of the regular triangular pyramid in consideration of the point that movement can be uniformly generated in each direction. As described above, the tip of the piezoelectric element is
Vibrations generated from 00B and 100C are integrally connected at the distal end so as to be an effective driving force to the sphere 510, and the distal end 10 is a contact portion with the ball joint 50.
The tip of 1 is connected in the form of, for example, a metal coating on the surface to increase the contact area as a flat or spherical shape to prevent abrasion and breakage, and to effectively transmit the driving force (FIG. 7). reference).

As described above, the piezoelectric actuator 1 according to the first embodiment of the present invention includes the piezoelectric elements 100A,
By supplying power of voltage waveforms whose amplitude, frequency, and phase are adjusted to 0B and 100C, they are made to cooperate with each other,
A frictional or striking force can be applied to the sphere 510 to rotate it in a desired direction, thereby changing the angle of the ball joint 50 to a desired direction.

As shown in FIG. 8, the piezoelectric actuator 1 has three vibrators 10, a drive unit 110 for driving each vibrator 10, an operation input for each vibrator 10, and an operation input to the operation input. And a control unit 120 that controls the drive unit 110 to drive each of the transducers 10 accordingly. The drive unit 110 and the control unit 120 constitute a power supply unit 130 of the piezoelectric actuator 1, and the power supply unit 130 is configured to be supplied with power of a predetermined voltage from a DC power supply 140.

The drive section 110 includes nine piezoelectric element drive circuits 410 corresponding to the respective piezoelectric elements 100A, 100B, and 100C of the three transducers 10.

The control unit 120 includes three sets of setting devices 200 and a control circuit 300 provided for each transducer 10. The setting device 200 performs an operation input of the vibrator 10 and inputs a signal corresponding to the operation input to the control circuit 300. The control circuit 300 controls each piezoelectric element drive circuit 410 according to a signal from the setting device 200.

FIG. 9 shows a setting device 200 and a control circuit 30.
FIG. 3 is a block diagram showing an internal configuration of the ０0 ’.

The setting unit 200 includes six incremental encoders 210 as an operation unit. Each of the incremental encoders 210 rotates a shaft thereof, and a set of digital signals A and B indicating a rotation angle and a rotation direction of the shaft. Is output. The signal A and the signal B are used as a command to indicate the phase or amplitude of the voltage waveform applied to the piezoelectric elements 100A, 100B, and 100C.
Sent to

The control circuit 300 transmits the signals A and B to Up
Up / D for converting into pulse X1 and Down pulse X2
own pulse generator 310 and the Up pulses X1 and D
U that generates a sawtooth signal D from the own pulse X2
p / Down counter section 320 and the Up pulse X1
An Up / Down counter unit 330 for generating an amplitude set value signal E from the pulse signal and the Down pulse X2; a gate signal generating unit 340 for generating gate signals G and H from the sawtooth signal D and the amplitude set value signal E; An oscillator 350 for transmitting a reference clock pulse is used as a main component.

FIG. 10 is a circuit diagram of the Up / Down pulse generation circuit 310a, and its time chart is shown in FIG.
Shown in

Up / Down pulse generating circuit 310a
Are four D-type flip-flop circuits 311, 312,
313 and 314 and two AND circuits 315 and 316 are configured as main components.

Hereinafter, the configuration will be described in detail along the signal flow with reference to FIG.

The signal A input to the Up / Down pulse generation circuit 310a is input to an AND circuit 315, while being input to a D-type flip-flop circuit 311 and output from the circuit 311 as a signal A1 synchronized with a clock pulse. Is done. This signal A1 is divided into two, one of which is input to an AND circuit 316, the other is input to a D-type flip-flop circuit 312, and the signal A1 is output from the circuit 312.
The signal is input to the AND circuit 316 as the negation signal A2 delayed by one cycle of the clock pulse.

Similarly, while the signal B is input to the AND circuit 316, the signal B is input to the D-type flip-flop circuit 313 and is output from the circuit 313 to the signal B1 synchronized with the clock pulse.
Is output as This signal B1 is divided into two, one of which is input to an AND circuit 315, and the other is input to a D-type flip-flop circuit 314, and is ANDed as a NOT signal B2 bar delayed by one clock pulse from the signal B1.
The signal is input to the circuit 315.

As described above, the Up / Down pulse generation circuit 310a outputs the AND circuit 315 (A, B1, B2
Bar = X1) and the AND circuit 316 (B, A1, A2 bar = X2), the Up pulse X1 and the Down pulse X
2 with Up / Down counter 320a and Up / Down counter 320a.
This is sent to the Down counter 330a.

The incremental encoder 210 provided in the setting unit 200 is set such that turning the axis clockwise turns on the Up pulse X1 and turning the axis counterclockwise turns on the Down pulse X2. Therefore, the Up pulse X1 and the Down pulse X2 are not simultaneously turned on.

Next, the operation of the Up / Down counter 320a of the Up / Down counter section 320 will be described with reference to FIG.

(1) Clock pulse and Up pulse X1
And Down pulse X2 are input.

(2) Up pulse X1 and Down pulse X
2 is off and the counter value is Up / Down
The maximum value that the counter 320a can take, for example, (2 ⁿ −
If not 1), the counter value is incremented by 1 at every rising of the clock pulse.

(3) Up pulse X1 and Down pulse X
2 is off and the counter value is Up / Down
When the value is the maximum value (2 ⁿ -1) that the counter 320a can take, the counter value is set to zero at the rising edge of the clock pulse.

(4) When the Up pulse X1 is on and the counter value is a value (2 ⁿ -2) obtained by subtracting 1 from the maximum value (2 ⁿ -1) that the Up / Down counter 320a can take, The counter value is set to zero at the rise of the clock pulse.

(5) When the Up pulse X1 is on and the counter value is the maximum value (2 ⁿ -1) that the Up / Down counter 320a can take, the counter value is set to 1 at the rise of the clock pulse.

(6) When the Up pulse X1 is on, the counter value is not the maximum value (2 ⁿ -1) that the Up / Down counter 320a can take, but a value obtained by subtracting 1 from the maximum value (2 ^n- If it is not 2), the counter value is increased by 2 at the rise of the clock pulse.

(7) When the Down pulse X2 is ON, the value of the counter is held regardless of the counter value.

As described above, the Up pulse X1 and the Down pulse X2 sent to the Up / Down counter 320a are converted into the sawtooth signal D and sent to the gate signal creation circuit 340a.

On the other hand, the Up pulse X1 and the Down pulse X2 sent to the Up / Down counter 330a are
It is converted into an amplitude set value signal E having the number of count bits of the Up / Down counter 330a as the number of digits, and sent to the gate signal generation circuit 340a. Here, when the counter value is zero, the counter circuit is configured so that the counter value does not change even if the Down pulse X2 is turned on, and a sudden change in the amplitude set value signal E is prevented. Similarly, when the counter value is the maximum value, the Up pulse X
The counter circuit is configured so that the counter value does not change even when 1 is turned on, and prevents a sudden change in the amplitude set value signal E.

FIG. 13 shows a gate signal generation circuit 340.
FIG. 14 shows a circuit diagram of FIG.

The gate signal generation circuit 340a is provided with the comparator 3
41, a flip-flop circuit 342, and a NOR circuit 3
43 and 344 are main components.

The magnitude of the sawtooth wave signal D and the amplitude set value signal E sent to the gate signal creation circuit 340a are compared by a comparator 341 to obtain a signal F. This signal F is input to a circuit 342 and NOR
The signals are input to the circuits 343 and 344, respectively. The signal F input to the flip-flop 342 is output as a signal Q and a signal knot Q. This signal Q is output to the NOR circuit 343
, And the other signal knot Q is input to the NOR circuit 344.

Thus, the gate signal generation circuit 340a
Sends a gate signal G (G = (knot (F + Q))) and a gate signal H (H = (knot (F + knot (Q)))) from the NOR circuit 343 and the NOR circuit 344 to the driving unit 110. Send out.

The phases of the gate signal G and the gate signal H processed in this manner change according to the change in the phase of the sawtooth signal D as shown in FIG. Further, the pulse width of the gate signal G and the gate signal H increases as the amplitude set value signal E increases, and conversely, the pulse interval between the gate signal G and the gate signal H decreases as the amplitude set value signal E increases. .

As described above, the control circuit 300 controls the three sets of gate signals based on the three sets of phase commands and the amplitude commands consisting of the signals A and B for adjusting the angle of the ball joint 50 sent from the setting device 200. G and H are created and sent to each piezoelectric element drive circuit 410 one by one.

FIG. 15 is a circuit diagram of the piezoelectric element driving circuit 410. FIG. 16 is the time chart.

The piezoelectric element drive circuit 410 includes a DC power supply 14
0 and the piezoelectric elements 100A, 10A
Output terminals 410a, 410 connected to 0B, 100C
b and a transformer 411 having an iron core 411a for electromagnetically coupling the primary circuit and the secondary circuit as main components, and the DC voltage does not overlap with the DC component and the polarity does not change. Such a high-frequency voltage is converted.

The primary circuit includes switching elements 412 a and 412 b having the gate signals G and H sent from the control circuit 300 as input signals, a primary coil 413 forming a part of the transformer 411, and a capacitance. Capacitors 414a and 414b having the same value. That is, the primary circuit converts a DC power supply into an AC power supply by a so-called PWM drive method.

Two switching elements 412a, 412
b is connected in series to the DC power supply 140, and the two capacitors 414a and 414b are connected in series to the DC power supply 140. Then, the switching element 412a
The coil 4 is connected to the connection line between the
13, one end of the coil 413 is connected to a connection line between the capacitors 414a and 414b.

The secondary circuit includes an AC voltage output circuit having an output terminal 410a, a DC bias voltage output circuit having an output terminal 410b, and piezoelectric elements 100A and 100B.
The output terminals 410a, 410a are connected in parallel with 100C.
b, and a diode 410c connected to B.

The AC voltage output circuit includes the transformer 411
And a choke coil 4 having one end 430 connected in series to the coil 415.
20 and an output terminal 410 at the other end of the choke coil 420
a.

The DC bias voltage output circuit includes a transformer 4
11 and a diode 417 connected to both ends of this coil 416.
a, 417b, an output terminal 410b connected to the middle point of the coil 416, and a smoothing capacitor 418 connected to the output terminal 410b.

Each of the diodes 417a and 417b has one end connected to a corresponding end of the coil 416 and the other end connected to a connection line between the coil 415 and the capacitor 418, with the direction coming out of the coil 416 as a forward direction. Have been. The other terminal of the capacitor 418 is connected to a midpoint that bisects the coil 416 into the coils 416a and 416b and the output terminal 410b. Further, the number of turns of the coils 415, 416a, 416b of the secondary side circuit are all equal.

Next, the operation of the piezoelectric element driving circuit 410 will be described with reference to FIG.

The gate signals G and H sent from the control circuit 300 are input to the switching elements 412a and 412b of the primary circuit, respectively, to turn them on and off.

Here, the capacitors 414a and 414b are selected to have the same capacitance. Therefore, the voltage of DC power supply 140 is divided into two equal parts by capacitors 414a and 414b,
It is connected to one end of one primary coil 413. At the other end of the coil 413 on the primary side of the transformer 411, the switching element 412a is ON and the switching element 412
When b is off, the positive voltage of the DC power supply 140 is applied, so the potential difference between both ends of the primary coil 413 becomes half of the voltage of the DC power supply 140, and the current flows in the direction of the solid arrow. On the other hand, when the switching element 412a is off and the switching element 412b is on, the potential difference between both ends of the primary coil 413 is such that half of the voltage of the DC power supply 140 is applied in a direction opposite to the direction of the voltage, A current flows in the direction of the dashed arrow.

As described above, the switching elements 412a,
By alternately turning on / off 412b, half the voltage of the DC power supply 140 is applied to the coil 413 alternately while changing the polarity.

The voltage applied to both ends of the coil 413 and the voltage of the coil 415 are applied to the coil 415 of the AC voltage output circuit.
A voltage determined by the turns ratio between the coil and the coil 413 is induced.
That is, when a current flows in the primary winding in the direction of the solid line arrow, a voltage is induced in the coil 415 constituting the AC voltage output circuit such that the current of the solid line arrow flows. This voltage is supplied to one output terminal 4 via the choke coil 420.
Output from 10a. Similarly, when a current flows in the primary winding in the direction indicated by the dashed arrow, a voltage such that the current indicated by the dashed arrow flows is induced in the coil 415 constituting the AC voltage output circuit. Is output from one output terminal 410a.

On the other hand, in the DC bias voltage output circuit, a voltage is induced in the coil 416 in the same manner.
417a, 417 connected in series at both ends of
Since the forward direction of b is reversed, only one of the diodes 417a and 417b becomes forward and current flows. That is, when the current indicated by the solid arrow flows through the primary circuit, the current induced in the coil 416 passes through only the forward diode 417a to charge the smoothing capacitor 418, and as a voltage across the capacitor 418, the output terminal 4
Output from 10b. When a current in the direction indicated by a broken line flows through the primary side circuit, a current flowing in the direction indicated by a broken line flows through the diode 417b to charge the smoothing capacitor 418, and is output from the output terminal 410b as a voltage across the capacitor 418. You.

Therefore, the voltage output from the output terminal 410b of the DC bias voltage output circuit always passes through the smoothing capacitor 418 in one direction regardless of the change in the current flowing through the primary side coil and is smoothed. It is output as a DC voltage.

Next, the output waveform of the piezoelectric element driving circuit 410 having such a configuration will be described with reference to FIG. In FIG. 16, the piezoelectric elements 100A, 100B,
Along with the output voltage waveform CC4 applied to 100C and the waveforms of the gate signals G and H, the coil 4 in the circuit
13, 415, 416a, 416b, capacitor 418
, Voltage waveforms LL1, LL2, LL3, LL4,
CC3, and an output terminal 410b of a connection point 430.
Are shown together with the voltage waveform LL5 of the voltage with reference to.

Here, in order to describe the peak value of the voltage waveform, the number of turns of the coil 413 of the primary side circuit is expressed as N1,
Since the number of turns of the coils 415, 416a, and 416b of the secondary circuit are all equal as described above, N
2 and the output voltage of the DC power supply 140 is denoted as V.

Therefore, in the piezoelectric element drive circuit 410, the switching elements 412a and 412b are turned on and off by the two gate signals G and H,
An AC square wave voltage waveform LL1 having a peak voltage V / 2 is generated at both ends of the coil 413 of the primary circuit. This allows
At both ends of each of the coils 415 and 416a of the secondary side circuit, AC square wave voltage waveforms LL2 and LL3 having a peak voltage N2 / N1 × V / 2 and having the same phase as LL1 are induced. The two ends of the coil 416b are provided with a peak voltage N2 / N which is in phase opposite to LL3 with the middle point of the coil 416 as a reference point.
A voltage waveform LL4 of an AC square wave of N1 × V / 2 is induced. However, since the current in the same direction is always supplied to the capacitor 418 by the action of the diodes 417a and 417b as described above, the voltage waveforms at both ends thereof are the same as the waveform CC3 having a constant DC value N2 / N1 × V / 2. Become.

The voltage waveform LL5 of the voltage with reference to the output terminal 410b of the connection point 430 is represented by a voltage waveform CC3 at both ends of the capacitor 418 and a voltage waveform LL at both ends of the coil 415.
2 is added.

The choke coil 420 and the piezoelectric element 100
Capacities of A, 100B and 100C (C0 + C1)
Are connected in series, forming a series resonance circuit,
If the resonance angular frequency is ω _L , ω _L = 1 / (L _h (C0 + C1)) ^1/2 . As described above, when the inductance L _{h of the} choke coil 420 is selected as L _h = 2 / (ω ² (C0 + C1)), ω _L = ω / 2 ^1/2 and the power supply angular frequency ω is the series resonance. The angular frequency is ^21/2 times the resonance angular frequency ω _L of the circuit. The series voltage waveform LL5 of the voltage applied to the resonant circuit many odd harmonics a square wave, i.e. 3, fifth, containing like seventh harmonic, but the resonance angular frequency omega _L and power Angular frequency ω
Is sufficiently close to practical use, and furthermore, the angular frequency of the resonance angular frequency ω _L and the odd-order harmonic of the voltage waveform LL5, that is, 3ω,
ω and 7ω are sufficiently separated from each other, so that harmonic components are attenuated. As a result, the piezoelectric elements 100A, 100B, 100C
Is a sinusoidal waveform with little distortion as shown in FIG.

The voltage waveform LL5 of the voltage applied to the series resonance circuit and the piezoelectric elements 100A, 100B,
The reason why the voltage waveform applied to 00C is just the opposite phase is the nature of the series resonance circuit and the
This is because the inductance L _h of the coil 420 is selected to be L _h = 2 / (ω ² (C0 + C1)).

This will be described in detail below.

That is, if the choke coil 420
Of Selecting 'a L _h' inductance L _h = 1 / a ^{(ω 2 (C0 + C1)} ), the resonance angular frequency of the series resonant circuit is consistent with the power source angular frequency omega, in this case, Inpi of the series resonant circuit -The dance becomes zero and an excessive current flows through the series resonance circuit.

If the inductance L _{h of the} choke coil 420 is selected as L _h = 2 / (ω ² (C0 + C1)) = 2L _h ′ in order to prevent an excessive current from flowing through the series resonance circuit, the series resonance circuit also Inpi - dance, L _h
′ And the piezoelectric elements 100A, 1
It can be handled as a circuit in which an inductance having a value of L _h ′ is further inserted in series into a series resonance circuit constituted by the capacitance (C0 + C1) of 00B and 100C. At this time, since the impedance X of the series resonance circuit takes a non-zero value of X = jωL _h ′, no excessive current flows. Here, j indicates an imaginary unit.

Further, in this case, the phase of the current flowing through the series resonance circuit has a phase delay of 90 ° when viewed from the voltage waveform LL5 because the impedance of the series resonance circuit is inductive. The voltage applied to the capacitance (C0 + C1) of the piezoelectric elements 100A, 100B, and 100C is obtained by time-integrating the current flowing through the series resonance circuit. The phase of the voltage applied to (C0 + C1) has a 180 ° phase delay when viewed from the voltage waveform LL5, that is, the voltage waveform LL5 of the voltage applied to the series resonance circuit,
The voltage waveforms applied to the piezoelectric elements 100A, 100B, 100C have exactly opposite phases.

The impedance X of the series resonance circuit is given by X = jωL _h ′ = jωL _h / 2, where the inductance L _{h of the} choke coil 420
Is selected as L _h = 2 / (ω ² (C 0 + C 1)), so that X = j / (ω (C 0 + C 1)). On the other hand, the impedance X _{C of the} capacitance (C0 + C1) of the piezoelectric elements 100A, 100B, 100C
Is X _C = 1 / (jω (C0 + C1)) = − j / (ω (C0
+ C1)) = − X, and the impedance X of the series resonance circuit and the capacitance (C0) of the piezoelectric elements 100A, 100B, 100C
+ C1) of having Inpi - Dance X _C is the absolute value is equal opposite sign.

That is, when the choke coil 420 is short-circuited, the piezoelectric elements 100A, 100B, 100
C, the component of the angular frequency ω of the current, and the piezoelectric elements 100A, 100A when the choke coil 420 is present.
B, the magnitude of the component of the angular frequency ω of the current flowing through 100C becomes equal. This allows the piezoelectric elements 100A, 1
A predetermined driving force is obtained in 00B and 100C.

Note that the angular frequency ω of the voltage waveform CC4 is a low frequency different from the resonance angular frequency and the anti-resonance angular frequency of the piezoelectric elements 100A, 100B, and 100C, for example, the resonance angular frequency ω of the piezoelectric elements 100A, 100B, and 100C.
_It is preferably about 1/2 or less of _r .

Further, the piezoelectric elements 100A, 100B, 10
0C series with the inserted Cho - inductance L _h of choke coil 420 is also, as described above, there is a value or a value close to be obtained by the following. For example, it is 10% before and after the value obtained by the following equation.

[0095] In the ^{_{L h = 2 / (ω 2}} (C0 + C1)) above, the output terminal 410a of the piezoelectric element driving circuit 410, from 410b, the gate signal G of the square wave control circuit 300 outputs, by H A controlled output of a DC sine wave voltage waveform CC4 is obtained.

The output terminals 410a and 410b are connected by a diode 410c in parallel with the piezoelectric elements 100A, 100B and 100C.
A, 100B, and 100C are always applied with a voltage in only one direction. Therefore, it is suitable for a piezoelectric element having a restriction in the direction of voltage application.

That is, each of the piezoelectric element driving circuits 410 responds to the instruction of the control circuit 200 by the respective piezoelectric elements 100A,
It is possible to efficiently supply low-distortion DC sine waveform power to 0B and 100C and displace the power, thereby driving each vibrator 10.

As described above, according to the piezoelectric actuator 1 of Embodiment 1, the vibrator 10 can be formed by the small power supply unit 130 without using a sine wave generating circuit or a linear amplifier having poor power efficiency and large dimensions. Can be driven. That is, the piezoelectric elements 100A, 100B, 100
A step-like voltage waveform LL2 having a desired amplitude is generated in the same cycle as the sine waveform voltage CC4 to be applied to C, and this voltage waveform is shaped into a sine wave shape. Accurate sinusoidal voltages can be applied to the piezoelectric elements 100A, 100B, 100C.

Embodiment 2 FIG. 17 is a circuit diagram of a piezoelectric element driving circuit of a piezoelectric actuator 1 according to Embodiment 2 of the present invention, and FIG. 18 is a time chart thereof.

The second embodiment is a modification of the piezoelectric element drive circuit of the piezoelectric actuator 1 of the first embodiment. This piezoelectric element drive circuit 710 includes a primary circuit similar to that of the first embodiment and a piezoelectric element drive circuit. 100A, 100B, 100
C, and a secondary circuit having output terminals 710a and 710b connected to C, and the primary circuit and the secondary circuit
11a, and a transformer 711 which is electromagnetically coupled by 11a.

The remaining configuration of the second embodiment is the same as that of the first embodiment, and thus the same reference numerals are given and the detailed description is omitted.

The secondary circuit of the piezoelectric element drive circuit 710 is as follows:
Secondary coil 715 constituting the transformer 711
A choke coil 720 having one end connected in series to the coil 715; an output terminal 710a connected to the other end of the choke coil 720; and the other output terminal 710b. A diode 716 connected between the output terminal 710b and the coil 715, with the direction being a forward direction;
6 and a capacitor 717 connected in parallel.

The operation of the piezoelectric element driving circuit 710 is similar to that of the first embodiment, and the magnetic flux in the iron core 711 a of the transformer 711 is inverted by the gate signals G and H output from the control circuit 300, thereby forming the transformer 711. The following voltages are induced in the coil 715 of the secondary side circuit.

That is, when a current indicated by a solid arrow flows through the primary circuit, a voltage is induced so that a current indicated by a solid arrow flows through the coil 715 constituting the secondary circuit, and this voltage is applied via the choke coil 720. It is output from one output terminal 710a. At this time, since the current flows in the forward direction of the diode 716 and does not flow through the capacitor 717, the voltage is mainly applied to the piezoelectric elements 100A, 100B, and 100C.

When a dashed current flows through the primary circuit, a voltage is induced so that a current indicated by a broken line flows through the coil 715 of the AC voltage output circuit.
Since 16 is in the opposite direction, it is output from the output terminal 710b through the capacitor 717. At this time, the current flows through the diode 4 in parallel with the piezoelectric elements 100A, 100B, and 100C.
10c, the piezoelectric elements 100A, 100A
No voltage is applied to B and 100C, the voltage is mainly applied to the capacitor 717, and the capacitor 717 is charged. Then, the electric charge charged in the capacitor 717 is gradually released, but since the release current is in the direction opposite to the dashed arrow, the diode 716 and the diode 410c
And the piezoelectric elements 100A, 100B,
A current flows through 100C in the direction of the solid arrow.

Next, a second embodiment will be described with reference to FIG.
The output waveform of the piezoelectric element drive circuit 710 according to the first embodiment will be described. In FIG. 18, the piezoelectric elements 100A, 10A,
With the voltage waveform CC4 applied to 0B and 100C,
The voltage waveforms LL1, LL2, and CC3 at both ends of the coils 413 and 715 and the capacitor 717 in the circuit are shown in correspondence with the waveforms of the gate signals G and H.

Since the piezoelectric element drive circuit 710 operates as described above, the switching elements 412a and 412b are turned on and off by the two gate signals G and H, and the coil of the primary circuit is turned on and off. 413
Waveform LL of an AC square wave having a peak voltage V / 2
1 is generated, and a voltage waveform LL2 of an AC square wave having the same phase as LL1 of the peak voltage N2 / N1 × V / 2 is induced at both ends of the coil 715 of the secondary circuit. The capacitor 717 is
As described above, a current in the same direction is always supplied by the action of the diode 716, and the capacitance value is sufficiently larger than the equivalent capacitance value of the capacitors of the piezoelectric elements 100A, 100B, 100C. Is a waveform CC3 having a constant DC value N2 / N1 × V / 2. The voltage waveform CC3 across the capacitor 717 is the same as that of the first embodiment.
Is equal to the voltage waveform at both ends of the capacitor 418.

Therefore, as in the first embodiment, the square wave gate signal G output from the control circuit 300 is output from the output terminals 710a and 710b of the piezoelectric element drive circuit 710.
An output of a DC sine wave voltage waveform CC4 controlled by H is obtained. The output terminals 710a and 710b are
As in the first embodiment, the piezoelectric elements 100A, 100B, 1
Since they are connected by a diode 410c in parallel with 00C, only a voltage in one direction is always applied to the piezoelectric elements 100A, 100B, and 100C.

The capacitance of the capacitor 717 is about 10 times the equivalent capacitance of the capacitors of the piezoelectric elements 100A, 100B and 100C. this is,
In a state where the voltage is charged in the capacitor 717 and the waveform CC3 is obtained, the piezoelectric elements 100A, 100B,
This is because the voltage waveform CC3 across the capacitor 717 is sufficiently stable even when the AC current flows through the capacitor 717 when the AC current flows at 0C.

As described above, according to the second embodiment, the piezoelectric actuator 1 having the power supply unit 130 having a more simplified circuit configuration than the first embodiment can be obtained. Embodiment 3 FIG. 16 shows a circuit diagram of a piezoelectric element drive circuit 810 of the piezoelectric actuator 1 according to Embodiment 3 of the present invention. The third embodiment is a modification of the second embodiment. The piezoelectric element driving circuit 810 according to the third embodiment is different from the second embodiment.
Is replaced with a coil 815 having a larger inductive component, and the choke coil 720 is omitted. That is, in the piezoelectric element drive circuit 810, the induction component of the secondary coil 815 forming the transformer 711 is made larger than that of the second embodiment, thereby replacing the choke coil 720 of the second embodiment. It becomes something.

The remaining structure of the third embodiment is the same as that of the second embodiment, so that the same reference numerals are given and the description of the structure is omitted. The operation of the piezoelectric element driving circuit 810 is the same as that of the second embodiment, and therefore the description is omitted. However, the voltage waveform CC4 applied to the piezoelectric elements 100A, 100B, and 100C is equivalent to that of the second embodiment. .

As described above, according to the third embodiment, it is possible to obtain the piezoelectric actuator 1 having the power supply unit 130 having a more simplified circuit configuration than the second embodiment.

Although the present invention has been described based on the embodiments, the present invention is not limited to only such embodiments, and various modifications are possible.

For example, some types of piezoelectric elements can be driven by alternating current.
A circuit for superimposing a DC bias voltage may be omitted, or a diode connected in parallel with the piezoelectric element may be omitted.

In each embodiment, the piezoelectric actuator 1 for adjusting the angle of the ball joint 50 has been described. However, a piezoelectric actuator used for other purposes may be used. Vibrator 10 and piezoelectric elements 100A, 100B,
The number of 100C may be a required number corresponding to a desired operation within a range of dimensional restrictions of the power supply unit 130. Furthermore, the spring constant and the number of the spring 530 are appropriately selected according to the purpose of use, and the spring 530 may be omitted depending on the number and arrangement of the vibrators 10.

[0116]

As described in detail above, according to the present invention,
Since a DC voltage having a desired frequency and a desired frequency can be generated without using a large-sized linear amplifier, there is an excellent effect that the power supply unit of the piezoelectric actuator can be reduced in size. Therefore, it is possible to easily achieve complicated operations by incorporating a plurality of piezoelectric actuators in a device.

[Brief description of the drawings]

FIG. 1 is a graph schematically showing impedance characteristics of a piezoelectric element used in the present invention.

FIG. 2 is an equivalent circuit diagram of the piezoelectric element.

FIG. 3 is an equivalent circuit obtained by simplifying the equivalent circuit shown in FIG. 2;

FIG. 4 is a drive circuit diagram of the piezoelectric element.

FIG. 5 is a drive circuit diagram of the same piezoelectric element excluding a choke coil.

FIG. 6 is a diagram showing a schematic configuration of a ball joint incorporating a piezoelectric actuator of the present invention.

FIG. 7 is a diagram illustrating the operation principle of the ball joint.

FIG. 8 is a block diagram illustrating a schematic configuration of a piezoelectric actuator according to Embodiment 1 of the present invention.

FIG. 9 is a block diagram illustrating a configuration of an Up / Down pulse generation circuit control unit of the control unit of the embodiment.

FIG. 10 is a logic circuit diagram of the Up / Down pulse generation circuit of the embodiment.

FIG. 11 is a time chart of the Up / Down pulse generation circuit of the embodiment.

FIG. 12 is a time chart illustrating a process in which a saw-tooth wave is generated according to a signal from an Up / Down pulse generation circuit in the same embodiment.

FIG. 13 is a logic circuit diagram of a gate signal generation circuit of the control unit according to the embodiment.

FIG. 14 is a time chart of the gate signal creation circuit of the embodiment.

FIG. 15 is a circuit diagram of a piezoelectric element drive circuit of the drive unit of the embodiment.

FIG. 16 is a time chart of the piezoelectric element drive circuit of the embodiment.

FIG. 17 is a circuit diagram of a piezoelectric element driving circuit of the piezoelectric actuator according to the second embodiment of the present invention.

FIG. 18 is a time chart of the piezoelectric element driving power supply of the embodiment.

FIG. 19 is a circuit diagram of a piezoelectric element drive circuit of the piezoelectric actuator device according to Embodiment 3 of the present invention.

FIG. 20 is a block diagram showing a configuration of a conventional piezoelectric actuator device.

[Explanation of symbols]

 Reference Signs List 1 piezoelectric actuator 10 vibrator 110 drive unit 120 control unit 130 power supply unit 100A piezoelectric element 100B piezoelectric element 100C piezoelectric element 410 piezoelectric element drive circuit 710 piezoelectric element drive circuit 810 piezoelectric element drive circuit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-10818 (JP, A) JP-A-1-151982 (JP, A) JP-A-6-123373 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H02N 2/00 H01L 41/09

Claims (5)

(57) [Claims] 1. A method of driving a piezoelectric actuator using a piezoelectric element that does not allow a change in polarity of an applied voltage, wherein an AC voltage having a predetermined frequency is supplied from a DC power supply to a PWM driving method.
Therefore, the output generated by the PWM driving method is generated.
Waveform distortion due to switching of force element
Improved by adding a choke coil in the circuit
And, then the case where it is superimposed on the AC voltage to generate a bias DC voltage having a polarity change is eliminated such magnitude of voltage to the piezoelectric element by superimposing the said bias DC voltage and the AC voltage A method for driving a piezoelectric actuator. Wherein said Cho - inductance of choke coil is substantially drive method for a piezoelectric actuator according to claim 1, characterized in that it is set so as to satisfy the following equation. ^{_{L h = 2 / (ω 2}} (C0 + C1)) Here, L _h: a choke coil inductance omega: power supply angular frequency C0: the equivalent capacitance of the electrical characteristics of the piezoelectric element C1: mechanical properties of the piezoelectric element Equivalent capacitance of 3. A driving apparatus for a piezoelectric actuator using a piezoelectric element that does not allow a change in polarity of an applied voltage, wherein a DC driving method is used to supply an AC voltage having a predetermined frequency from a DC power supply.
Caused by generating and the PWM drive system by
Drives piezoelectric element for waveform distortion due to switching of output element
By installing a choke coil in the device circuit,
Good, then it generates a bias DC voltage having a polarity change is eliminated such magnitude of the voltage when it is superimposed on the AC voltage, wherein by superimposing said AC and DC voltages for the bias piezoelectric A driving device for a piezoelectric actuator, wherein a circuit is configured to drive an element. 4. The driving device for a piezoelectric actuator according to claim 3, wherein the inductance of the choke coil is set so as to substantially satisfy the following expression. ^{_{L h = 2 / (ω 2}} (C0 + C1)) Here, L _h: a choke coil inductance omega: power supply angular frequency C0: the equivalent capacitance of the electrical characteristics of the piezoelectric element C1: mechanical properties of the piezoelectric element Equivalent capacitance of 5. A piezoelectric actuator comprising the driving device according to claim 3 or 4 .