JP2000070851A - Driver of capacitive load - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a driver of capacitive load which is suitable as the driver of an ultrasonic actuator by getting rid of higher harmonic wave contained in a generated driving signal. SOLUTION: The driver 11 is equipped with an oscillating circuit 12 and a phase-shifting circuit 13. A transmission four-terminal network is equipped with an original generator for digital driving which generates two original signals having a prescribed phase difference for digital driving, with both three capacities arranged in parallel and three resistances arranged in series. The transmission four-terminal network is equipped with a low-pass filter which respectively converts two original signals for digital driving into sine wave signals and with linear amplifiers 15a, 15b or the like which are constituted by using a semiconductor and amplify the sine wave signals and supply these signals to the piezo-electric body 13 of an ultrasonic actuator 10. Then, higher harmonic wave is removed by the low-pass filter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a driving device for a capacitive load, for example, a driving device for driving a capacitive load such as a piezoelectric element in an ultrasonic actuator.

[0002]

2. Description of the Related Art For example, a piezoelectric element is joined to the surface of an elastic body, and a drive voltage is applied to the piezoelectric element to generate a plurality of vibration modes in the elastic body in harmony. 2. Description of the Related Art There is known a vibration actuator which generates an elliptical motion and generates a relative motion between a relative motion member which is in pressure contact with the elastic body. Among these types of vibration actuators, those utilizing the vibration range of ultrasonic waves are called ultrasonic actuators.

A driving ultrasonic power source for driving such an ultrasonic actuator generally has a driving voltage of, for example, 12V.
By operating a DC power source having a low potential at a driving frequency by a semiconductor at a driving frequency, for example, a phase difference π /
2. A two-phase rectangular wave with a duty ratio of 50% is supplied by being boosted to a high potential by a boosting transformer.

FIG. 6 is a block diagram showing a configuration example of a conventional driving device 1 using a step-up transformer. As shown in FIG. 1, in the driving device 1, the driving source signal output from the oscillation circuit 2 is sent to the phase shift circuit 3.

The driving source signal sent to the phase shift circuit 3 is A
It is divided into a phase drive signal and a B phase drive signal. The A-phase drive signal is output from the phase shift circuit 3 as a rectangular wave.
The B-phase drive signal is output from the phase shift circuit 3 as a rectangular wave with a phase shift of (π / 2) from the A-phase. In addition,
The input P of the exclusive OR gate 7 is controlled by a control system (not shown) and functions as a buffer or an inverter. Thereby, the normal rotation and the reversal of the ultrasonic actuator 6 are controlled.

These drive signals output in a rectangular shape are respectively switched by switching elements 4a and 4b using semiconductors. Then, the two-phase drive signals are further increased by, for example, 1
The voltage is boosted to a high voltage of about 00 Vpp. Thus, the two-phase drive signal has been input to the piezoelectric element of the ultrasonic actuator 6.

[0007]

In this drive device 1,
As described above, the two-phase drive signal supplied to the ultrasonic actuator 6 is obtained by performing a switching operation of the two-phase rectangular wave by the switching elements 4a and 4b using semiconductors. Therefore, the two-phase drive signal includes a number of harmonics having a frequency that is an integral multiple of the drive frequency.

For this reason, in the conventional driving device 1, extra energy called harmonics is inevitably supplied with the input of the driving signal to the piezoelectric element. As a result, unnecessary vibration other than the fundamental wave is generated in the ultrasonic actuator 6, and there is a problem that the electromechanical conversion characteristics of the ultrasonic actuator 6 are complicated. For this reason, in particular, in the case of a deformed mode degenerate type ultrasonic actuator that simultaneously generates primary longitudinal vibration and quaternary bending vibration in a rectangular plate-shaped vibrator, the electromechanical conversion characteristics deviate from the design target. As a result, the driving performance had to be reduced.

Further, in the conventional driving device 1, since the harmonics are also supplied to the piezoelectric element, the ultrasonic actuator 6 easily generates heat correspondingly. For this reason, the conventional driving device 1 has a problem that the driving performance is liable to be lowered from this point as well.

[0010] It is an object of the present invention to provide a driving device for a capacitive load which can eliminate harmonics contained in a generated driving signal and is suitable as a driving device for an ultrasonic actuator.

[0011]

According to the present invention, a digital drive source signal is converted into a sine wave signal of only a fundamental wave by suppressing harmonics by a filter, and this sine wave signal is formed using a semiconductor. The present invention is based on a novel finding that the above-mentioned problem can be solved by amplifying by a linear amplifier and supplying it to an ultrasonic motor.

In order to solve the above problem, according to the first aspect of the present invention, a driving source signal for outputting a first rectangular wave and a second rectangular wave having a predetermined phase difference from the first rectangular wave. A generator and a filter for converting a first rectangular wave into a first sine wave and a second rectangular wave into a second sine wave by passing a current in a preset frequency range. Means, and an amplifier for amplifying the first sine wave and the second sine wave and supplying the amplified sine wave to the capacitive load.

According to a second aspect of the present invention, in the capacitive load driving device according to the first aspect, the filter means is a low-pass filter. According to a third aspect of the present invention, in the capacitive load driving device according to the second aspect, the low-pass filter includes a capacitor and a resistor.

According to a fourth aspect of the present invention, in the driving device for a capacitive load according to the third aspect, the low-pass filter comprises:
It is a transmission four-terminal network having three capacitors arranged in parallel and three resistors arranged in series.

Further, according to a fifth aspect of the present invention, in the driving apparatus for a capacitive load according to any one of the second to fourth aspects, the reciprocal of the time constant of the low-pass filter is the same as that of the capacitive load. The driving frequency is set to be 1.5 times or more and 5 times or less.

[0016]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a driving apparatus for a capacitive load according to the present invention. In the following description of the embodiment, a drive device for a capacitive load according to the present invention is applied to a deformed mode degenerate type in which a rectangular plate-shaped vibrator simultaneously generates primary longitudinal vibration and quaternary bending vibration. An example in which the present invention is applied to an ultrasonic actuator will be described.

FIG. 1 is a perspective view showing a schematic configuration of an ultrasonic actuator 10 used in this embodiment. FIG. 2 is an explanatory diagram showing the vibrator 11 constituting the ultrasonic actuator 10 together with an example of a generated vibration waveform.

As shown in FIGS. 1 and 2, the vibration actuator 10 of the present embodiment has a primary longitudinal vibration L1,
A vibrator 11 that generates the next bending vibration B4 is provided. The vibrator 11 includes an elastic body 12 and a piezoelectric body 13 mounted on one plane of the elastic body 12.

The elastic body 12 is preferably made of a metal material having a large resonance sharpness Q, such as steel, stainless steel, phosphor bronze, or Elinvar material.
It is formed in a rectangular flat plate shape. The dimensions of each part of the elastic body 12 are set such that the natural frequencies of the generated primary longitudinal vibration L1 and the generated quaternary bending vibration B4 substantially match each other.

A piezoelectric body 13, which is a capacitive load, is adhered to one plane of the elastic body 12, for example. Also, the elastic body 1
In the other plane of the two, two grooves are provided in the width direction of the elastic body 12 at a predetermined distance from each other in the relative movement direction (the direction of the double arrow in FIG. 1). A rectangular rod-shaped sliding member having a rectangular cross-sectional shape and composed mainly of a polymer material or the like is fitted and adhered to these grooves, and is mounted in a protruding manner. Examples of the polymer material include PTFE, polyimide resin, PEN, PPS, PEEK, and the like.

The sliding member serves as the driving force take-out portion 12.
Functions as a and 12b. Therefore, the elastic body 12
Are driving force take-out portions 12a, 12
It contacts the relative motion member 21 via b.

The driving force take-out sections 12a and 12b are
As shown in the figure, the fourth-order bending vibration B generated in the elastic body 12
It is provided at a position that matches antinode positions l _1, l ₄ located outside of the four loop position l ₁ to l ₄ of 4. In addition, the driving force extraction parts 12a and 12b are provided at the antinode position l of the bending vibration B4.
_1, l need not be provided in a position that exactly matches the _4, it may be provided in the vicinity of the antinode position.

In the present embodiment, the piezoelectric body 13 is formed of a thin plate-shaped piezoelectric element made of PZT (lead zirconate titanate). In the piezoelectric body 13, the input regions 13a and 13c to which the drive signal of the A phase is input and the phase of the A phase are (π
/ 2) input areas 13b, 1 where the B phase shifted by
3d is formed. Each input region 13a~13d, as shown in FIG. 2, is formed continuously in four regions partitioned by five nodal position n ₁ ~n ₅ bending vibration B4 generated in the elastic member 12. That is, each input region 13a~13d be deformed by input of the driving signal are both, does not cross five nodal position n ₁ ~n ₅ is fixed point. Therefore, nodal position n ₁ variant of input area 13a~13d is ~n ₅
It is not suppressed by. Thereby, the electric energy input to each of the input areas 13a to 13d can be transformed into the elastic body 12 with maximum efficiency, that is, converted into mechanical energy.

At the nodal positions n ₂ and n ₄ of the bending vibration B4, detection areas 13p and 13p 'for outputting electric energy by the longitudinal vibration L1 generated by the vibrator 11 are provided.
Thus, the vibration state of the longitudinal vibration L1 generated by the vibrator 11 is monitored.

Each input area 13a to 13d and each detection area 1
3p and 13p 'are silver electrodes 15a on their respective surfaces.
１５15d, 15p, 15p ′ are adhered. As a result, it is possible to input a drive signal to each of the input areas 13a to 13d independently, and to output a detection signal independently from each of the detection areas 13p and 13p '.

Although not shown, each of the silver electrodes 15a to 15d,
Lead wires for transmitting and receiving electric energy are connected to the wires 15p and 15p 'by soldering, respectively. In the present embodiment, as shown in FIG.
Are formed so as to be point-symmetric about the center of the plane. As a result, the driving force extracting portions 12a, 1
The elliptical motion generated in 2b can be made to have substantially the same shape, and the driving difference due to the reversal of the relative motion direction is almost eliminated.

A drive device 31 for generating drive signals to be applied to the two groups of input areas 13a, 13c and 13b, 13d of the ultrasonic actuator 10 will be described.
FIG. 3 shows an ultrasonic actuator 10 according to the present embodiment.
FIG. 3 is a block diagram showing a configuration of a driving device 31 of FIG.

As shown in the figure, in the driving device 31, the driving source signal output from the oscillation circuit 32 is sent to the phase shift circuit 33. As the drive source signal sent to the phase shift circuit 33, an A-phase drive signal and a B-phase drive signal are generated. The A-phase drive signal is output from the phase shift circuit 33 as a rectangular wave. The B-phase drive signal is output from the phase shift circuit 33 as a rectangular wave with a phase shift of (π / 2) from the A-phase. Reference numeral 37 denotes an exclusive OR gate, as in FIG.

In this embodiment, in order to generate a two-phase rectangular wave drive signal, the oscillation circuit 32 and the phase shift circuit 3 are used.
Although three is used, such a two-phase drive signal may be generated by providing a drive program in a personal computer, for example.

In the present embodiment, among these drive signals output in a rectangular shape, the A-phase drive signal is the low-pass filter 3.
4a, and the B-phase drive signal is supplied to the low-pass filter 34.
b.

FIG. 4 is an equivalent circuit diagram of the low-pass filters 34a and 34b in the present embodiment. Hereinafter, the operation of the low-pass filters 34a and 34b will be described with reference to FIG. Since the low-pass filters 34a and 34b have the same configuration, the following description uses the low-pass filter 34a as an example.

As shown in FIG. 4, the low-pass filter 34a in the present embodiment comprises three capacitors C, C / K and C / K ² arranged in parallel, and three resistors R and KR arranged in series. , K ² R and a transmission four-terminal network.

The symbol K is a constant larger than 1. Also, K ₁ instead of K and K ² instead of K ²
₂ (however, K ₁ <K ₂ ) may be set as constants. Here, the voltage transfer function TF of the low-pass filter 34a is

[0034]

TF = e ₀ (S) / e _i (S) = K ² / {1 + 2 (K + 2) ST + (2K + 3) (ST) ² + (ST) ³ } However, in the equation, T = RC,
S is a complex frequency.

In this embodiment, the low-pass filter 34a
Transfer function K ² / ｛1 + 2 (K + 2) ST + (2K
It is desirable to set the reciprocal 1 / T of the time constant T = RC of (+3) (ST) ² + (ST) ³ } to be 1.5 times or more and 5 times or less the driving frequency of the ultrasonic actuator 10. 1.
If it is less than five times, the fundamental wave component becomes too small.
This is because if the frequency exceeds twice, the deviation of the fundamental wave from the sine wave (waveform distortion) becomes large.

In FIG. 4, by setting the reciprocal 1 / T of the time constant T = RC of the voltage transfer function expressed by the equation to be approximately three times as large as the drive frequency of the ultrasonic actuator 10, a low-pass filter can be obtained. When a rectangular wave having a TTL level of about 5 V and a voltage e _i of about 5 V is input to the power supply side terminal A of the low-pass filter 34 a, a sine wave of a fundamental wave having a voltage e ₀ of about 1 Vpp is applied to the load side terminal B of the low-pass filter 34 a. can get.

In this embodiment, the low-pass filter 34a
Is constituted by the capacitor C and the resistor R, the voltage change of the sine wave taken out from the load side terminal can be reduced even if the frequency changes to some extent (for example, about 10%). Therefore, there is almost no effect on frequency sweeping such as speed control, which is convenient.

Further, in this embodiment, three combinations of the capacitance and the resistance, that is, the capacitance C and the resistance R, and the capacitance C / K
And the resistor KR, and the capacitance C / K ² and the resistor K ² R, constitute a low-pass filter 34a. Therefore, the amplitude of the sine wave of the fundamental wave can be taken out with great reliability, and the cutoff characteristics of the three-stage frequency can be obtained. A low-pass filter 34a having a steepness is obtained.

The number of combinations of the capacitance and the resistance may be set as appropriate according to the purity of the sine wave extracted by the low-pass filter 34a. In this way, the low-pass filter 34a shown in FIG. 4, the harmonics are removed from the rectangular wave, the load side terminal B, can be taken out sine wave of the fundamental wave voltage is e _0.

As described above, the low-pass filter 34a
Removes the included harmonics in order to extract the fundamental wave of the A-phase drive signal. Thereby, the low-pass filter 34
The A-phase drive signal that has passed through “a” becomes a sine wave of the fundamental wave. Similarly, the low-pass filter 34b removes harmonics contained in the B-phase drive signal in order to extract the fundamental wave. As a result, B passing through the low-pass filter 34b
The phase drive signal is a sine wave of the fundamental wave.

The sine wave of the fundamental wave A
The phase drive signal and the B-phase drive signal are sent to a linear amplifier including preamplifiers 35a and 35b and drive amplifiers 36a and 36b, respectively.

FIG. 5A is an equivalent circuit diagram of the preamplifiers 35a and 35b in the present embodiment. FIG.
(B) shows the drive amplifiers 36a and 36 in the present embodiment.
It is an equivalent circuit diagram of b. FIG. 5A and FIG.
The operation of the preamplifiers 35a and 35b and the drive amplifiers 36a and 36b will be briefly described with reference to FIG. In the following description, the preamplifiers 35a and 35b have the same configuration, so the preamplifier 35a is used as an example, and the drive amplifiers 36a and 36b have the same configuration, so the drive amplifier 36a is used as an example.

The preamplifier 35a, as shown in FIG. 5 (a), and four capacitor C ₁ -C _4, 9 single resistor R ₁ to R
₉ and three NPN transistors Tr _{1 to} Tr ₃ . On the other hand, the driving amplifier 36a, as shown in FIG. 5 (b), and three capacitors C ₅ -C _7, 7 single resistor R ₁₀ to R
₁₆ , two NPN transistors Tr _{4 to} Tr ₅ ,
And a diode D _1. And the preamplifier 35a
A transformer 41 is provided on the load side of the
A transformer 42 is also provided on the load side of “a”.

In FIG. 5A, the low-pass filter 3
When an A-phase drive signal having a sine wave output voltage e ₀ (about 1 Vpp) is input to the input terminal C of the preamplifier 36a, the load terminal of the transformer 41 of the preamplifier 36a. D outputs a sine wave amplified to about 6 Vpp.

In FIG. 5B, the sine wave amplified by about 6 Vpp by the preamplifier 36a is
When supplied to the input terminal D of the drive amplifier 36b, a sine wave amplified to about 150 Vpp is output from the load terminal E of the transformer 42 of the drive amplifier 36b.

Thus, the preamplifiers 35a and 35a
The sine wave whose voltage is e ₀ (about 1 Vpp) is amplified to about 150 Vpp by the linear amplifier composed of b and the drive amplifiers 36 a and 36 b.

The preamplifier 3 used in this embodiment is
Instead of the linear amplifier including the amplifiers 5a and 35b and the drive amplifiers 36a and 36b, the sine wave may be amplified using an operational amplifier. Alternatively, an audio low-frequency power amplification IC may be used.

The two-phase sine wave drive signal generated in this manner is applied to the piezoelectric element 13 of the ultrasonic actuator 10.
Is input to That is, the drive signal of the A-phase is input region 1
3a and 13c, and the B-phase drive signal is
3b and 13d.

As a result, as shown in FIG. 2, the primary longitudinal vibration L1 is applied to the vibrator 11 of the ultrasonic actuator 10.
And the fourth-order bending vibration B4 are generated at the same time, and these vibrations are combined to generate a physical elliptical motion in the driving force extracting portions 12a and 12b. The vibrator 11 generates a relative motion between the vibrator 11 and the relative motion member 21 that is brought into pressure contact.

As described above, according to the driving device 31 of the present embodiment, the two-phase driving signal input to the ultrasonic actuator 10 has a sine wave, and harmonics are suppressed. For this reason, it is possible to avoid supplying extra energy called harmonics to the ultrasonic actuator 10, and to obtain electromechanical conversion characteristics as designed. Thereby, it is possible to prevent the driving performance of the ultrasonic actuator 10 from being lowered.

The harmonics are transmitted to the ultrasonic actuator 10.
, The temperature rise of the ultrasonic actuator 10 is also suppressed. As a result, it is possible to suppress a decrease in drive performance of the ultrasonic actuator 10 due to a rise in temperature.

Further, since the drive signal handled by a computer or digitally is converted into a sine wave by the low-pass filters 34a and 34b, advantages such as digital processing and control are not lost. Therefore, the possibility of applying the ultrasonic actuator 10 to other devices is expanded.

Further, in the driving device 31 of the present embodiment,
The output of the transformer 42 of the drive amplifier 36b is fed back to the preamplifier 36a. Therefore, by driving the ultrasonic actuator 10 using the driving device 31, the output impedance is reduced, and as a result, the load fluctuation resistance characteristics of the ultrasonic actuator 10 are also improved.

(Modification) In the description of the embodiment, the case where the driving device for a capacitive load according to the present invention is applied to an ultrasonic actuator is taken as an example. However, the present invention is similarly applied to a vibration actuator using a vibration region other than the ultrasonic wave.

In the description of the embodiment, the driving device for a capacitive load according to the present invention is provided with a deformed mode degenerate type in which a rectangular plate-shaped vibrator simultaneously generates primary longitudinal vibration and quaternary bending vibration. The case where the present invention is applied to the ultrasonic actuator 10 described above is taken as an example. However, the present invention relates to a vibrator that generates longitudinal vibration and torsional vibration in a columnar vibrator as disclosed in Japanese Patent Application Laid-Open No. 9-84367, which was previously proposed by the present applicant. Like an ultrasonic actuator,
The same applies to other types of ultrasonic actuators.

Further, in the description of the embodiment, a piezoelectric body is used as an element for performing mutual conversion between electric energy and mechanical energy. However, the present invention is not limited to this. For example, other elements such as an electrostrictive element and a magnetostrictive element may be used. The same applies to the case where the electromechanical conversion element of (1) is used.

[0057]

As described in detail above, claims 1 to 5
According to the fifth aspect of the present invention, it is possible to provide a capacitive load driving device capable of eliminating harmonics included in a generated driving signal. Thereby, various performance degradations of the vibration actuator caused by harmonics included in the drive signal can be suppressed.

[Brief description of the drawings]

FIG. 1 is a perspective view illustrating a schematic configuration of an ultrasonic actuator used in an embodiment.

FIG. 2 is an explanatory diagram showing a vibrator constituting an ultrasonic actuator used in the embodiment together with an example of a generated vibration waveform.

FIG. 3 is a block diagram illustrating a configuration of a driving device of the ultrasonic actuator according to the embodiment.

FIG. 4 is an equivalent circuit diagram of a low-pass filter according to the embodiment.

FIG. 5A is an equivalent circuit diagram of a preamplifier according to the embodiment, and FIG. 5B is an equivalent circuit diagram of a drive amplifier according to the embodiment.

FIG. 6 is a block diagram showing a configuration of a conventional driving device using a step-up transformer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Ultrasonic actuator 11 Vibrator 12a, 12b Driving force extraction part 13 Piezoelectric body (capacitive load) 13a-13d Input area 31 Driver 32 Oscillation circuit 33 Phase shift circuit 34a, 34b Low-pass filter 35a, 35b Preamplifier 36a, 36b drive amplifier

Claims (5)

[Claims] 1. A driving source signal generator for outputting a first rectangular wave and a second rectangular wave having a predetermined phase difference from the first rectangular wave, and a current in a predetermined frequency domain And a filter means for converting the first rectangular wave into a first sine wave, and the second rectangular wave into a second sine wave, respectively; An amplifier for amplifying the second sine wave and supplying the amplified sine wave to the capacitive load. 2. The apparatus according to claim 1, wherein the filter is a low-pass filter. 3. The driving apparatus according to claim 2, wherein the low-pass filter includes a capacitor and a resistor. 4. The low-pass filter according to claim 3, wherein the low-pass filter is a transmission four-terminal network having three capacitors arranged in parallel and three resistors arranged in series.
A driving device for a capacitive load according to claim 1. 5. The reciprocal of the time constant of the low-pass filter is at least 1.5 times the drive frequency of the capacitive load and 5
The driving device for a capacitive load according to any one of claims 2 to 4, wherein the driving speed is set to twice or less.