JP2002218772A - Piezoelectric actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively drive an impact type piezoelectric actuator using a drive pulse of low-voltage rectangular waveform. SOLUTION: The impact type piezoelectric actuator 1 is formed of a drive member 5 consisting of a base 2, a piezoelectric element 3 and a rod 4, a moving member 6 and a drive controller 7. For the drive member 5, a physical condition such as the length of rod or the like is set to satisfy fatr1/3<frr1<fatr1, when the first-order antiresonance frequency of the drive member is defined as fatr1 and the primary resonance frequency of the rod 4, under the condition that one end is fixed as frr1. The piezoelectric actuator 1 is driven, when a drive voltage of the rectangular waveform having a first-order sinusoidal waveform component at the frequency near the flow frequency side of the first-order resonance frequency ftr1, and also has a prescribed duty is applied to the piezoelectric element 3 from a drive circuit 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an impact type piezoelectric actuator.

[0002]

2. Description of the Related Art Conventionally, there is known an impact type piezoelectric actuator in which a moving member is attached to a rod so as to be movable in an axial direction, and a piezoelectric element is fixed to one end of the rod so that a polarization direction coincides with the axial direction. ing.

FIG. 17 is a diagram showing a basic configuration of an impact type piezoelectric actuator. The impact type piezoelectric actuator 100 includes a laminated piezoelectric element 101, a support member 102 for fixing one end of the laminated piezoelectric element 101 in the laminating direction, and a rod 103 coaxially fixed to the other end of the laminated piezoelectric element 101. And this rod 103
And a drive circuit 105 for applying a drive voltage to the laminated piezoelectric element 101. An object to be driven such as a photographing lens is fixed to the moving member 104.

The impact type piezoelectric actuator 100 utilizes the difference in the operation time of the frictional force generated between the rod 103 and the moving member 104 when the rod 103 is vibrated at different speeds, to move the moving member 104 to the rod 103. Relative to the camera. That is,
The action time of the frictional force between the moving member 104 and the rod 103 is short when the rod 103 moves at a high speed and long when the rod 103 moves at a low speed. The movement in the direction is referred to as “forward movement” or “forward movement”. The movement is performed at a low speed, and the movement toward the proximal end is performed (hereinafter, the movement in this direction is referred to as “backward movement” or “reverse movement”). Is performed at a high speed so that the moving member 104
Is moved toward the distal end side relative to the rod 103 (driving in the forward direction), and the moving member 104 is moved at a high speed during the forward movement of the rod 103 and at a low speed during the backward movement.
3 is moved relatively to the proximal end side (reverse drive).

Japanese Unexamined Patent Publication No. Hei 11-98865 discloses that a resonance inducing section comprising a spring and a weight is provided at the tip of a rod of an impact type piezoelectric actuator so that a displacement member as a rod and a weight as a whole has two different natural frequencies. f
By applying a drive pulse including the same frequency components as the natural frequencies f1 and f2 to the piezoelectric element, the amplitude and the moving speed of the rod tip can be increased without increasing the voltage of the drive pulse. Shown is an impact-type piezoelectric actuator that is made larger.

In the impact type actuator described in the above publication, when a piezoelectric element is driven by a driving pulse obtained by synthesizing sine waves of two different frequencies, a displacement waveform of a rod connected to the piezoelectric element has a saw blade. Therefore, by setting two frequency components included in the drive pulse as the natural frequency of the displacement member, a saw blade-like displacement having a large displacement amount is generated at the tip of the rod.

[0007]

By the way, the impact type piezoelectric actuator described in Japanese Patent Application Laid-Open No. H11-98865 has a spring and a weight attached to the tip of the rod so that the rod has two different natural frequencies. It is necessary to provide a resonance inducing section consisting of: and the structure of the actuator becomes complicated. In addition, the natural frequency of the rod varies for each impact-type piezoelectric actuator due to the variation of the resonance inducing portion, and there is a problem that it is necessary to adjust the frequency component of the drive pulse for each impact-type piezoelectric actuator.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has a configuration in which a driving member including a piezoelectric element and a rod has predetermined resonance characteristics without providing a resonance inducing section, and supplies the driving element to the piezoelectric element. By setting the frequency component of the driving pulse to a predetermined frequency based on the resonance frequency of the driving member, an impact type piezoelectric actuator that can be efficiently driven by a low-voltage driving pulse is realized.

[0009]

According to the present invention, there is provided a driving means comprising an electromechanical conversion element which expands and contracts when a driving voltage is applied, and a rod member fixed to one end of the electromechanical conversion element in the expansion and contraction direction. Support means for supporting the other end of the electromechanical transducer of the drive member, moving means engaged with a rod member of the drive means with a predetermined frictional force, and drive voltage generation means for generating the drive voltage In the piezoelectric actuator having the above, the driving means may be represented as fatr1 / fat1 if the primary antiresonance frequency of the driving means is fatr1 and the primary resonance frequency of the rod member alone under the condition that one end is fixed is frr1. The driving voltage generating means has a primary sine wave component near a low-frequency side of a primary resonance frequency ftr1 of the driving means and has a predetermined duty. It is intended to generate a driving voltage of the square wave (claim 1).

It is to be noted that the driving means is one of the driving means.
Assuming that the secondary resonance frequency is ftr1 and the secondary resonance frequency is ftr2, it is preferable to configure so as to satisfy 2.multidot.ftr1> ftr2.

According to the present invention, when a driving voltage of a rectangular wave is applied to the electromechanical transducer, the driving voltage changes (ON).
/ OFF change), the tip of the electromechanical transducer vibrates, and this vibration is directly transmitted to the rod member, and the rod member vibrates.

The driving means supported by the supporting means has an anti-resonance frequency at the same frequency as the anti-resonance frequency of the electro-mechanical transducer when one end of the electro-mechanical transducer is fixed, and the electro-mechanical transducer is Has a primary resonance frequency ftr1 on the lower frequency side than the primary resonance frequency fatr1. Further, the driving means fixes the primary anti-resonance frequency fatr1 of the driving means and one end of the rod member by appropriately setting physical conditions such as the length, thickness, and density of the electromechanical transducer and the driving member. The rod member has a secondary resonance frequency ftr2 (> frr1) between the rod member and the primary resonance frequency frr1 (<fatr1) when the other end is a free end.

The driving means has a first resonance frequency frr1 of the rod member alone when one end is fixed and the other end is a free end. Fatr1 /
Since 3 <frr1 <fatr1 is satisfied, the primary resonance frequency ftr1 of the driving means is generated on the lower frequency side than fatr1 / 2, and the secondary resonance frequency ftr2 is 2
It occurs in a region close to ftr1 and the displacement of the tip of the driving means (free end of the bar member) does not drop sharply even in the frequency region between the primary resonance frequency ftr1 and the secondary resonance frequency ftr2.

On the other hand, since a driving voltage of a rectangular wave having a primary sine wave component and a predetermined duty is supplied to the electromechanical transducer near the low frequency side of the primary resonance frequency ftr1, the driving means is provided. The displacement waveform at the tip is a vector composite wave mainly composed of a displacement waveform based on a primary sine wave component of a rectangular wave and a displacement waveform based on a secondary sine wave component. , The vector composite wave has a sawtooth waveform having a relatively large amplitude.

Therefore, the moving member can be moved efficiently by the driving voltage of the rectangular wave having a relatively low voltage.

Further, according to the present invention, the piezoelectric actuator further comprises a moving direction control means for controlling a moving direction of the moving member by controlling a duty of the driving voltage (claim 3).

According to this configuration, the moving member moves to the one end side of the rod member by setting the duty of the drive voltage to a predetermined duty greater than 50%, for example, and reduces the duty of the drive voltage to a predetermined duty smaller than 50%. With this duty, the rod moves to the other end.

[0018]

FIG. 1 is a diagram showing the configuration of an embodiment of an impact type piezoelectric actuator according to the present invention.

In FIG. 1, an impact type piezoelectric actuator 1 (hereinafter abbreviated as a piezoelectric actuator 1).
Is composed of a driving member 5 including a base (supporting member) 2, an electromechanical transducer 3, and a rod (rod member) 4, a moving member 6, and a drive control unit 7.

The base 2 fixes one end of the electromechanical transducer 3 of the driving member 5 (hereinafter, this one end is referred to as a base end). The electromechanical transducer 3 is composed of, for example, a laminated piezoelectric body formed by bonding a plurality of plate-shaped piezoelectric members having a required thickness and sandwiching a thin-film electrode (not shown) between the piezoelectric members. Have been. The plurality of piezoelectric members are stacked such that the polarization directions of adjacent piezoelectric members are opposite to each other. This is because the driving voltage is applied to each electrode in parallel so that the positive and negative polarities between the adjacent electrodes are opposite to each other, so that each piezoelectric member expands and contracts in the same direction and the entire electromechanical transducer 3 is large. This is for obtaining the amount of expansion and contraction.

The rod 4 is, for example, a columnar or prismatic rod member that performs an expansion and contraction movement by an expansion and contraction movement of the piezoelectric element 3 integrally with the electromechanical transducer 3 (hereinafter, referred to as a piezoelectric element 3). The cross-sectional shape of the rod 4 is not limited to a columnar shape or a prismatic shape, but may be an elliptical shape or a polygonal shape. One end (base end) of the rod 4 is fixed to the other end of the piezoelectric element 3 (hereinafter, the other end is referred to as a tip), and the other end (tip) is a free end.

The driving member 5 vibrates the rod 4 by the vibration of the piezoelectric element 3 to move the moving member 6 onto the rod 4. The moving member 6 is a member that relatively moves with respect to the rod 4 by the expansion and contraction movement of the rod 4. The moving member 6 is attached to the rod 4 with a predetermined frictional force, and can slide on the rod 4 when a force greater than this frictional force acts.

Therefore, when the moving member 6 is caused to reciprocate in the axial direction by the reciprocating movement of the moving member 6 based on the expansion and contraction of the piezoelectric element 3, the time required for accelerating the moving member 6 to the distal end (that is, The time for applying the frictional force may be longer than the time for accelerating toward the base end. That is, when the rod 4 is vibrated at a low speed toward the distal end and at a sufficiently high speed toward the proximal end, the moving member 6 is accelerated toward the distal end longer than the time accelerated toward the proximal end. , Move to the tip side. On the other hand, if the rod 4 is moved forward at a high speed toward the distal end and moved backward at a low speed toward the proximal end, the moving member 6 relatively slides on the rod 4 toward the proximal end.

FIG. 2 is a perspective view showing one embodiment of a specific structure of the impact type piezoelectric actuator.

The piezoelectric actuator shown in FIG. 1 includes a cylindrical rod-shaped base 20, a prismatic piezoelectric element 22, a cylindrical rod 24 having a smaller diameter than the base 20, and a rectangular parallelepiped moving member 26.

The base 20 has a first housing space 204 and a second housing space 205 formed by hollowing out the inside thereof, leaving both ends in the axial direction and a partition wall 203 substantially at the center. The piezoelectric element 22 is accommodated in the first accommodation space 204 having a short length in the axial direction, with the lamination direction coinciding with the axial direction of the base 20. Further, the rod 24 is accommodated in the second accommodation space 205 having a long axial length.

One end face of the piezoelectric element 22 in the longitudinal direction (hereinafter, this end face is referred to as a base end face) has a first accommodation space 204.
Is fixed to the end face opposite to the partition wall 203. A round hole is formed at the axial center position at the end (the end of the base 20) of the base 20 on the side where the partition wall 203 and the second storage space 205 are adjacent, and the rod 24 passes through both round holes. It is accommodated in the two accommodation space 205 so as to be movable in the axial direction.

The first accommodation space 204 of the rod 24
Is fixed to the other end surface of the piezoelectric element 22 (hereinafter, this surface is referred to as a front end surface), and the end of the rod 24 protruding from the front end of the base 20 is fixed by a leaf spring 28 at a required spring pressure. It is urged toward the piezoelectric element 22 side. The urging of the rod 24 by the leaf spring 28 stabilizes the axial displacement of the rod 24 due to the expansion and contraction of the piezoelectric element 22.

The moving member 26 includes a base 262 having mounting portions 261 on both sides in the axial direction of the rod 24, and a holding member 263 mounted between the mounting portions 261. The base 262 is attached to the rod 24. The moving member 26 is loosely fitted, and is contacted with the rod 24 by being pressed by the leaf spring 264, whereby the moving member 26 is coupled to the rod 24 with a predetermined frictional force. When a driving force larger than the frictional force acts, the rod 24 can move along the axial direction. When the piezoelectric actuator 1 is used for driving a lens of a camera, for example, a lens to be driven is attached to the moving member 26.

Returning to FIG. 1, the drive control section 7 controls the drive of the piezoelectric actuator 1. The drive control unit 7 includes a position detection sensor 8 for detecting the position of the moving member 6,
A waveform shaping circuit 9 for shaping the waveform of a detection signal output from the position detection sensor 8; a position detection circuit 10 for detecting the movement position of the moving member 6 using the position detection signal output from the waveform shaping circuit 9; 3 and a power supply battery 11 for supplying power to each circuit in the drive control unit 7, and a DC voltage (or DC current) output from the power supply battery 11 is converted into a predetermined rectangular wave DC voltage (or DC current) or an AC voltage (or DC voltage). Or an AC current), and a drive circuit 12 that outputs the drive signal to the piezoelectric element 3, a voltage detection circuit 13 that detects the battery voltage of the power supply battery 11, and information on the moving direction of the moving member 6 is input to the control unit 15. , And a control unit 15 for controlling the driving of the drive circuit 12.

The position detecting sensor 8 comprises a magnet scale 81 attached to the moving member 6 and a magnetic sensor 82 arranged opposite to the magnet scale 81. The magnet scale 81 is formed by alternately magnetizing N-poles and S-poles on a long substrate at a predetermined pitch in the longitudinal direction. The magnetic sensor 82 is a magnet scale 8
1 detects the magnetic field near the magnetized surface. Since the N pole and the S pole are alternately magnetized at a predetermined pitch on the magnetized surface of the magnet scale 81, a sine wave magnetic field is distributed near the magnetized surface. Therefore, when the magnet scale 81 moves relative to the magnetic sensor 82 based on the reciprocating motion of the moving member 6, a sine wave signal is detected from the magnetic sensor 81.

This detection signal is shaped into a rectangular wave signal (pulse train signal) by the waveform shaping circuit 8 and then input to the position detecting circuit 10. Then, the position detection circuit 10 sets the initial position (for example, when the moving member 6 is located at the base end position).
The position of the moving member 6 is detected by counting the number of pulses of the pulse train signal shaped into a rectangular wave from the controller 6, and the position information of the moving member 6 is output to the control unit 15 based on the detection signal. For example, the moving range of the moving member 6 from the base end to the distal end of the rod 4 is divided into five zones, and it is determined which zone of the moving range is located from the detection signal,
The determination result is used as the position information of the moving member 6 by the control unit 15.
Output to

The drive circuit 12 is provided, for example, from the power battery 11.
Input voltage V_BTo be intermittent with a predetermined modulation signal
A drive voltage of a more square wave is generated. Voltage detection circuit 13
Is composed of, for example, two divided resistors, and the battery voltage V_BA minute
The voltage is divided by the split resistance and input to the control unit 15. The control unit 15
Voltage V of power supply battery 11 input from voltage detection circuit 13
_BMonitor the life of the power supply battery 11 or replace the battery.
Manage time.

The switches 14a and 14b detect an operation of an operation member (not shown) for instructing a moving direction of the moving member 6, and input a detection signal to the control unit 15. The switch 14a is turned on when the operating member is operated in a direction (retracting direction) for moving the moving member 6 toward the base end of the rod 4, and the switch 14b is turned on when the operating member moves the moving member 6 toward the distal end of the rod 4. It is turned on when operated in the direction (moving-out direction) for moving the camera to

The control unit 15 outputs a control signal for generating a drive voltage for moving the moving member 6 in the direction instructed based on the ON signals of the switches 14a and 14b.
Output to The drive circuit 12 generates a drive voltage (drive pulse) having a predetermined duty based on the control signal. As will be described later, the moving direction of the moving member 6 is switched by changing the duty of the drive voltage. For example, if the duty is larger than 50%, the moving member 6 moves in one direction, and the duty is increased from 50%. If you make it smaller,
The moving member 6 moves in the opposite direction.

Next, the driving circuit 1 of the piezoelectric actuator 1
2 will be described.

As described in the background art, even when a rectangular drive pulse is supplied to the piezoelectric element 3, the displacement of the rod 4 can be made to have a saw-tooth shape under a certain condition, and the moving member 6 moves forward and backward. It is known to be moved or moved back.
Therefore, first, conditions for optimizing the driving efficiency when driving with a driving pulse of a rectangular wave will be described.

As is well known, a square wave is a primary, secondary, tertiary,
... Since the n-th sine wave is superimposed, the displacement (expansion and contraction) of the piezoelectric element 3 when a rectangular wave driving voltage is applied to the piezoelectric element 3 causes the driving of each sine wave included in the rectangular wave. It can be considered that the displacement of the piezoelectric element 3 due to the voltage is obtained by vector synthesis. Therefore, it can be considered that the displacement of the rod 4 connected to the piezoelectric element 3 is obtained by superimposing the displacement of the rod 4 due to the driving voltage of each next sine wave included in the rectangular wave.

In order to increase the driving efficiency as much as possible, the following frequency components f1, f2,.
.., And the displacement at the frequencies f1, f2,.
.., Θ3,... In the phase characteristics of the driving member 5 with respect to the phase at the frequency f1 at the second and subsequent frequencies f2, f3,. Therefore, the magnitude Ai (i = 1, i) of each next-order frequency component included in the rectangular wave so that the above equation (1) is maximized.
,... N), the displacement amount Li (i = 1, 2,... N) of the driving member 5 in each frequency component and the phase difference θi + 1 (i =
1, 2,... N).

On the other hand, the amplitude ratio of each of the following frequency components included in the rectangular wave changes depending on the duty (the ratio of the ON period in one cycle), and the driving member 5 has a length, thickness, density (weight), It is known that there is a unique resonance frequency based on physical conditions such as a shape. Therefore, when the applicant examined by simulation in consideration of these,
The displacement B1 (= A1 · L1) and the secondary frequency component fd2 (= 2 · fd) of the driving member 5 due to the primary frequency component fd1 of the rectangular wave.
The displacement B2 (= A2 · L2) due to 1) is B1: B2.
= 1: 0.26, and when the phase difference θ2 between the displacement amount B1 and the displacement amount B2 is 90 °, the driving efficiency becomes maximum (output is maximum).

Therefore, the above equation (1) is substantially equal to L = A1
· L1 + A2 · L2 · sin (θ2), and A1 · L1 =
1, A2 · L2 = 0.26, θ2 = 90 ° (hereinafter, this condition is referred to as an optimum condition). It is only necessary to set the physical condition of the driving member 5 and to set the duty of the driving pulse. be able to.

However, when actually manufacturing the piezoelectric actuator 1, it is not easy to realize a piezoelectric actuator that satisfies the optimum conditions. Therefore, the physical conditions of the driving member 5 are appropriately set, and the voltage, frequency, and duty of the driving pulse are set. It is necessary to actually measure the output while changing the conditions, and to set the physical condition of the driving member 5 and the driving pulse frequency and duty conditions which are closest to the optimum conditions.

FIG. 3 shows the frequency characteristics of the amount of displacement and the phase difference of the driving member 5 according to the present embodiment, which is configured to satisfy a condition relatively close to the optimum condition. The driving member 5 is driven at a driving frequency fd (a frequency appropriately selected on the low frequency side of the primary resonance frequency ftr1) with a driving pulse of a rectangular wave having a duty of 30% or 70%.

As shown in the drawing, the driving member 5 has a displacement at the tip of the rod whose primary resonance frequency ftr1 unique to the driving member 5 is changed.
, The displacement L is maximized, and the secondary resonance frequency ftr2, the tertiary resonance frequency ftr3,. Then, the driving member 5 has a frequency at which the secondary resonance frequency ftr2 is substantially twice or slightly lower than the primary resonance frequency ftr1.
It is configured to have a resonance characteristic in which no anti-resonance point exists between the secondary resonance frequency ftr2 and the secondary resonance frequency ftr2.

Therefore, the displacement L at the rod tip portion sharply decreases in the vicinity of the peak of the primary resonance point after passing the peak, but decreases gradually in the frequency region of the foot, and then decreases in the second order. The displacement L increases again due to the presence of the resonance point. Note that, in FIG. 3, the displacement L is not shown since the displacement L is negligible at the third resonance frequency ftr3 or higher.

In the driving member 5, the phase difference θ gradually decreases monotonically before the peak of the primary resonance frequency ftr1, but decreases sharply before and after the peak, and thereafter gradually decreases again monotonically. It has the property to settle at about -210 °. In addition, it exhibits an unstable characteristic of increase / decrease before and after the secondary resonance frequency ftr2, but thereafter has a characteristic in which the phase difference θ monotonously decreases.

From the frequency characteristics of the displacement amount L and the phase difference θ shown in FIG. 3, the frequency components of the displacement of the driving member 5 are mainly the primary resonance frequency ftr1 and the secondary resonance frequency ftr2, and the resonance frequency components of the third or higher order are: Hardly contributes. Accordingly, when the piezoelectric element 3 is driven by the driving pulse of the rectangular wave, the primary frequency component of the rectangular wave becomes the displacement L on the low frequency side of the primary resonance frequency ftr1.
If the frequency of the drive pulse is set so that 1 becomes an appropriate frequency fd that changes relatively steeply, the displacement of the rod tip will equivalently be the sine of the primary frequency component fd and the secondary frequency component 2fd of the drive pulse. Displacement L1 due to wave component
L2 is obtained by vector synthesis.

The ratio of the amplitude A1 of the primary frequency component to the amplitude A2 of the secondary frequency component of the rectangular wave signal having a duty of 30% is A1: A2 ≒ 1: 0.6. The piezoelectric actuator 1 having the frequency characteristics of the displacement amount and the displacement phase shown in FIG. 3 is driven by a drive pulse (with a duty of 30% and a drive frequency fd (appropriate on the low frequency side of the primary resonance frequency ftr1) shown in FIG. In FIG. 3, the displacement L2 at the driving frequency 2fd is approximately 1/2 of the displacement L1 at the driving frequency fd when the driving pulse is driven by a rectangular wave driving pulse having a different frequency). Displacement B1 of next frequency component
(= A1 · L1) and the displacement amount B2 of the secondary frequency wave component (= A
2 · L2) is B1: B2 ≒ 1: 0.3 (= 0.6
× 1/2), and B1: B2 = 1: 0.2 of the optimum condition
A value close to 6 is obtained.

The displacement B1 and the displacement B of the driving member 5
2, the phase at the driving frequency fd is approximately −50 °, and the phase at the driving frequency 2fd is approximately −21.
Since it is 0 °, the phase at the drive frequency fd is converted to the phase at the drive frequency 2fd, and the phase difference θ2 between the two phases is obtained.
Is calculated, θ2 ≒ −50 × 2-(− 210) = 11
0 °, which is a value close to the optimum condition θ2 = 90 °.

Therefore, the driving frequency fd and the duty 30
% When the piezoelectric actuator 1 is driven by a square-wave driving pulse, the displacement waveforms of the primary frequency wave component and the secondary frequency wave component at the rod tip end are as shown in FIG. When the waveforms are vector-combined, the result is as shown in FIG. As is clear from the displacement waveform of FIG. 4B, the displacement waveform of the rod tip becomes a sawtooth-like waveform composed of a gradual extension displacement and a steep contraction displacement, and the moving member 6 is moved in the feeding direction (hereinafter, referred to as “movement member”). This direction is also referred to as the forward direction.).

On the other hand, a rectangular wave signal having a duty of 70% corresponds to a signal obtained by inverting the phase of the secondary frequency wave component of a rectangular wave signal having a duty of 30%. When the piezoelectric actuator 1 is driven by the drive pulse (a rectangular wave drive pulse having a duty of 70% and a drive frequency fd) shown in FIG. 5A, the displacement amount L1 of the primary frequency wave component at the rod tip portion is obtained. And 2
The duty ratio of the next frequency wave component to the displacement L2 is 30%.
And the same as the case of driving with a square-wave drive pulse having the drive frequency fd, and only the phase difference θ2 changes. That is, since the phase of the secondary frequency wave component of the rectangular wave signal with the duty of 70% is advanced by 180 ° with respect to the phase of the secondary frequency wave component of the rectangular wave with the duty of 30%, 180 ° −2
10 ° = −30 °. Since the phase of the primary frequency component of the rectangular wave signal having a duty of 70% is the same as the phase of the primary sine wave component of the rectangular wave having a duty of 30%, the phase is −50 °.
It is.

Therefore, the phase difference θ2 is θ2 ≒ −50 × 2−
(−30) = − 70 °, and the phase difference θ2 when driven by a rectangular wave drive pulse with a duty of 70% and a drive frequency fd is a duty of 30% and a square wave drive with a drive frequency fd Phase difference θ when driven by pulse
This is 180 ° ahead of 2. For this reason, when the piezoelectric actuator 1 is driven with a rectangular wave signal having a drive frequency fd and a duty of 70%, the displacement waveforms of the primary frequency wave component and the secondary frequency wave component at the rod tip are respectively shown in FIG.
When these displacement waveforms are further vector-synthesized, the result is as shown in FIG. FIG. 5 (b)
As is apparent from the displacement waveform of FIG. 3, since the displacement waveform of the rod 4 is a sawtooth-shaped waveform composed of a steep extension displacement and a gradual contraction displacement, the moving member 6 is moved in the retreating direction (hereinafter, referred to as the moving direction).
This direction is also called a reverse direction. ).

In consideration of the driving efficiency, the driving frequency fd is the primary resonance frequency ftr1 where the displacement amount L of the rod 4 is large.
However, if the drive frequency fd is set near the peak of the primary resonance frequency ftr1, the change amount of the displacement L and the displacement phase θ near the frequencies ftr1 and ftr2 is large, and the temperature / humidity etc. Since the behavior of the rod 4 becomes unstable due to the frequency shift with respect to the environmental change, the circuit for the stable control becomes complicated, and it is necessary to design the circuit for the stable control according to the individual difference of the piezoelectric actuator. In addition, since the conditions for mass production of the piezoelectric actuator become severe, it is difficult to realize it technically and cost-wise. For this reason, in the present embodiment, the drive frequency fd is not set near the peak of the primary resonance frequency ftr1 in FIG. 3 and an appropriate frequency having a relatively large displacement L on the low frequency side of the primary resonance frequency ftr1 is set to the drive frequency fd. And

Next, the relationship between the physical conditions of the driving member 5 and the resonance characteristics will be described. In the following description, a case where only the rod length Lr of the driving member 5 is changed will be described as an example for convenience.

FIGS. 6A and 6B show the relationship between the frequency f of the driving voltage and the displacement speed v of the driving member 5. FIG. 6A shows the case where the rod length Lr of the driving member 5 is 0 mm (that is, the piezoelectric element 3). (B) when the rod length Lr of the driving member 5 is 4 mm, and (c) when the driving member 5 is driven.
(D) when the rod length Lr of the driving member 5 is 12 mm, (e) when the rod length Lr of the driving member 5 is 16 mm, and (f) when the rod length Lr of the driving member 5 is 16 mm. This is a case where the rod length Lr of No. 5 is 32 mm.

In FIG. 6, the vertical axis represents the displacement speed v on a logarithmic scale, and the displacement amount L is not taken. However, as the displacement speed v increases, the displacement amount also increases. The change tendency of v indicates the change tendency of the displacement L.

In FIG. 9A, P1, P2, P3,
P4 is the resonance point of the piezoelectric element 3 alone (the point where the displacement L is the largest). If the frequencies at the respective resonance points are fp1, fp2,..., Then fp2ｆ3fp1, fp3 ≒ 5fp1,. Are the anti-resonance points of the piezoelectric element 3 alone (points where the amount of displacement is the smallest). The frequency at each anti-resonance point is fq
1, fq2,..., Fq1 ≒ 2fp1, fp2 ≒ 4fp1,
...

In FIGS. 6B to 6E, the waveform indicated by the dashed line indicates the displacement speed of the rod tip (point A in FIG. 1), and the waveform indicated by the dotted line indicates the piezoelectric element tip (piezoelectric element 3 and rod 4). (Point B in FIG. 1).

When the rod length Lr of the driving member 5 is not "0", the rod 4 also has a unique resonance characteristic corresponding to the length, so that the resonance characteristic of the piezoelectric element 3 alone and the resonance characteristic of the rod 4 (one side) It is easily imagined that the end of the rod is fixed and the other end is set as a free end, and the resulting characteristic becomes a displacement characteristic of the rod end portion. When the rod length Lr is short, even if the rod 4 resonates, the displacement amount and the phase shift with respect to the piezoelectric element 3 are small, so that the displacement characteristic of the rod tip portion is similar to the displacement characteristic of the piezoelectric element 3 alone. Conceivable. On the other hand, when the rod length Lr is long, the displacement amount of the rod 4 and the phase shift from the piezoelectric element 3 become large at the resonance point, so that the displacement characteristic of the rod tip portion is greatly different from the resonance characteristic of the piezoelectric element 3 alone. Conceivable.

In FIG. 6B, since the rod length Lr is short, the resonance characteristic of the rod 4 has little effect on the resonance characteristic of the piezoelectric element 3 alone, and the primary resonance point P1 of the resonance characteristic at the tip B of the piezoelectric element is a piezoelectric element. The element 3 is slightly shifted from the primary resonance point P1 of the element 3 to the low frequency side. FIG. 6 (c)-
(F) is a graph in which the rod length Lr is gradually increased, and the resonance characteristics at the tip B of the piezoelectric element are greatly affected by the resonance characteristics of the rod 4 as the rod length Lr is increased. That is, the primary resonance point P1 of the resonance characteristic at the tip B of the piezoelectric element shifts more and more toward the low frequency side from the resonance point P1 of the piezoelectric element 3 alone. For example, in FIG.
A new resonance point P between the secondary resonance point P1 and the secondary resonance point P2
A new resonance point is generated between the resonance points so that 1 ′ occurs.

The anti-resonance points Q1, Q2,.
In this case, the piezoelectric element 3 is hardly displaced.
Is hardly displaced. This tendency is the same even if the rod length Lr is changed.
.. Can be said to be also the anti-resonance points of the driving member 5 (see the anti-resonance points in FIGS. 3B to 3F).

When the driving member 5 is attached to the piezoelectric element 3,
In the displacement characteristics of the piezoelectric element tip B, the anti-resonance points Q1, Q
Anti-resonance points Ql1, Ql2,... Other than 2,. The anti-resonance points Ql1, Ql2,... Are influenced by the vibration of the rod 4, and are found to be equal to the resonance frequency of the rod 4 alone with one end fixed and the other end free. When the rod length Lr is short, these anti-resonance points Ql1, Ql2,... Have a higher frequency than the resonance point P1 and the anti-resonance point Q1, but shift to a lower frequency side as the rod length Lr increases. It moves (see FIGS. 6D and 6E) and comes close to the resonance point P1.

When the rod 4 is connected to the piezoelectric element 3, the displacement characteristics of the tip B of the piezoelectric element indicate that the anti-resonance points Q1, Q
In addition to the resonance points Pl1, Pl2,... Appearing in addition to the appearance of the anti-resonance points Ql1, Ql2, ..., the displacement characteristics of the rod tip A correspond to these resonance points Pl1, Pl2,. Also appear at the resonance points P1 ', P2'.
(See (c) to (e)).

When the length Lr of the rod 4 of the driving member 5 is changed as described above, the resonance point in the displacement characteristic of the rod tip A changes as shown in FIGS. By appropriately selecting Lr, one of the driving members 5 can be selected.
The displacement velocity v is not sharply reduced between the secondary resonance frequency ftr1 and the secondary resonance frequency ftr2, that is, an anti-resonance frequency is not generated between the primary resonance frequency ftr1 and the secondary resonance frequency ftr2. The resonance characteristics can be set.

By setting the resonance characteristics of the driving member 5 to such characteristics, the primary resonance frequency ft of the driving member 5 is obtained.
r1 occurs on the relatively low frequency side, and the primary resonance frequency ft
Since the displacement L of the driving member 5 at the frequency 2ftr1 twice as large as r1 can be kept relatively large, it is possible to realize a condition close to the above-mentioned optimum condition. Therefore,
When a rectangular driving pulse is used, the piezoelectric actuator 1 can be driven by a low-voltage driving pulse in a state where the driving efficiency is as close to the optimum as possible.

In the example of FIG. 6, the frequency fp1 'of the secondary resonance point P1' is equal to the frequency f1 'of the primary resonance point P1 in FIGS.
Since the displacement speed v is about twice as large as p1 and the displacement velocity v does not drop sharply between the primary resonance point P1 and the secondary resonance point P1 ', an appropriate value is obtained near the low frequency side of the primary resonance frequency fp1. By selecting the frequency, 30% and 70% duty
It can be seen that the driving can be performed in a state close to the optimum driving efficiency by using the rectangular driving pulse.

FIG. 7 shows that the rod length Lr is 4 mm and 16 mm.
This is a result of examining the displacement characteristics of the rod tip in the case of, and corresponds to the displacement characteristic shown in FIG. FIG. 7A shows the case where the rod length Lr is 4 mm (FIG. 6C).
FIG. 7B shows the displacement characteristics of the rod length Lr of 16 m.
This is the displacement characteristic when m is used (the one shown in FIG. 6E).
In the figure, the horizontal axis is the frequency f of the sinusoidal drive voltage supplied to the piezoelectric element 3, and the vertical axis is the displacement L of the rod tip A.
It is.

The waveform diagram of FIG. 7 corresponds to the waveform diagram of FIG. 4, and shows the primary frequency component and the secondary frequency component of the displacement waveform of the rod tip A, respectively. FIG.

When the rod length Lr is 4 mm, FIG.
As shown in FIG.
The frequency fp2 of the secondary resonance point P2 is equal to the frequency f of the primary resonance point P1.
Since the primary anti-resonance point Q1 exists between the primary resonance point P1 and the secondary resonance point P2, which is much larger than twice p1, the displacement amount of the rod tip A as shown in FIG. L reaches a peak at one resonance frequency fp1, and continues to decrease gradually even after sharply decreasing.

When the driving frequency fd is set near the low frequency side of one resonance frequency fp1 in consideration of the driving stability as described above, the optimal condition is that the displacement at the frequency 2fd is the displacement L1 at the frequency fd. 2 is reduced to about 1/2, and the frequency fd satisfying this condition is shown in FIG.
As shown in (a), the displacement amount L is located at the foot of a change curve that changes gradually, and cannot be set near the peak of the displacement amount L.

For this reason, with the displacement characteristic shown in FIG. 6C, sufficient driving efficiency cannot be obtained. This is shown in FIG.
It can also be understood from the fact that the amplitude of the displacement waveform of the rod tip A has not sufficiently increased.

On the other hand, when the rod length Lr is 16 mm, as shown in FIG. 6E, the frequency fp1 'of the secondary resonance point P1' in the displacement characteristic of the rod tip A is changed to the primary resonance point Pr.
Since the frequency becomes approximately twice the frequency fp1 of 1 and there is no occurrence of an anti-resonance point between the primary resonance point P1 and the secondary resonance point P1 ', the displacement amount of the rod tip as shown in FIG. L1
Peaks at one resonance frequency fp1, and increases again toward the second resonance frequency fp1 'without decreasing even after sharply decreasing. Therefore, the frequency fd that satisfies the optimal condition
Can be set at a position near the peak where the displacement L sharply increases as shown in FIG. 7B, and a state as close to the optimum driving efficiency as possible can be obtained. This means that the amplitude of the displacement waveform at the rod end A in FIG.
It can be understood from the fact that the displacement is doubled as compared with the displacement characteristic shown in FIG.

Note that even when the rod length Lr is set to 32 mm (FIG. 6F), the frequency fp1 'of the secondary resonance point P1' in the displacement characteristic of the rod tip A is changed to the primary resonance point Pr.
1 which is about twice the frequency fp1 of the first resonance point, and satisfies the condition that no anti-resonance point occurs between the primary resonance point P1 and the secondary resonance point P1 '.
Since p1 became too low and the frequency fp1 of the secondary resonance point P1 'was close to the frequency fp1', high-power driving could not be performed.

Therefore, the frequency fp1 'of the secondary resonance point P1' on the lower frequency side than the primary anti-resonance point Q1 in the displacement characteristic of the rod tip A is about twice the frequency fp1 'of the primary resonance point P1. If the rod length Lr is adjusted (in the example of FIG. 6, the rod length Lr is adjusted to around 16 mm), it can be said that the piezoelectric actuator 1 can be driven in a state as close to the optimum drive efficiency as possible.

Accordingly, from the relationship between the above-described optimum conditions, the physical conditions of the driving member 5 and the resonance characteristics, the physical characteristics of the driving member 5 that can efficiently drive the impact type piezoelectric actuator with a low-voltage rectangular-wave driving pulse. The condition is that the primary anti-resonance frequency of the piezoelectric element 3 alone, that is, the primary anti-resonance frequency of the driving member 5 is fatr1, and the primary resonance of the rod 4 alone when one end is fixed and the other end is a free end. Assuming that the frequency is frr1, it can be said that it suffices to satisfy the following expression: fatr1 / 3 <frr1 <fatr1 (2).

If the primary resonance frequency of the piezoelectric element 3 alone is fpzt1, the primary anti-resonance frequency f
Since apzt1 is 2fpzt1, the above equation (2) becomes 2fpzt1 / 3 <frr1 <2fpzt1 (3).

In the resonance characteristic of the driving member 5, 1
In order to reliably suppress a decrease in the amount of displacement between the secondary resonance frequency ftr1 and the secondary resonance frequency ftr2 and to realize a state close to the above-described optimum condition, the driving member 5 is set so that 2ftr1> ftr2. May be set.

In the above description, only the case where the lot Lr of the driving member 5 is changed has been described. However, as shown in FIG.
Since it easily changes depending on the density, the thickness of the lot 4, the density, and the like, when actually designing the piezoelectric actuator 1, the resonance characteristics of the driving member 5 are determined by combining the above conditions (2) or (3). ) To satisfy the condition of (3).
And the physical conditions of the rod 4 may be adjusted.

FIG. 8 is a diagram showing a change tendency of the resonance characteristics of the driving member 5 when the physical conditions such as the length, thickness, and density of the piezoelectric element 3 and the rod 4 are changed. 6
Is drawn in the same way as shown in

As shown in the figure, when the lengths of the piezoelectric element 3 and the rod 4 are increased, the primary and secondary resonance points P1, P1 'are obtained.
Move to the low frequency side, and when the lengths of the piezoelectric element 3 and the rod 4 are shortened, the primary and secondary resonance points P1 and P1 'move to the high frequency side.

When the piezoelectric element 3 is made thinner, the primary resonance point P1 moves to the lower frequency side and the secondary resonance point P1 '
Moves to the high frequency side (the primary resonance point P1 and the secondary resonance point P1).
1 '), and when the piezoelectric element 3 is made thicker,
Conversely, the primary resonance point P1 moves to the high frequency side and the secondary resonance point P1 'moves to the low frequency side (the interval between the primary resonance point P1 and the secondary resonance point P1' becomes narrower).

When the rod 4 is made thinner, the primary resonance point P1 moves to the high frequency side and the secondary resonance point P1 'moves to the low frequency side (the primary resonance point P1 and the secondary resonance point P1').
When the distance between the rods 4 becomes narrower, and the rod 4 is made wider,
The secondary resonance point P1 moves to the low frequency side and the secondary resonance point P1 'moves to the high frequency side (the interval between the primary resonance point P1 and the secondary resonance point P1' increases).

The primary resonance point Ql1 of the rod 4 does not depend on the thickness or the density of the rod 4, and when the rod length is increased,
When the rod moves to the low frequency side and the rod length is shortened, it moves to the high frequency side.

As described above, in the present embodiment, the driving member 5 is configured to satisfy the above expression (2) or (3) (configured to have the displacement amount and phase difference characteristics shown in FIG. 3). In addition, the drive circuit 12 generates a rectangular wave drive pulse having a predetermined drive frequency fd on the low frequency side of the primary resonance frequency ftr1 of the drive member 3 and supplies the drive pulse to the piezoelectric element 3.

When the piezoelectric actuator 1 is actually manufactured, there are large variations due to individual differences and manufacturing accuracy of the piezoelectric actuator 1, and it is not easy to realize the optimum conditions obtained by simulation. In particular,
The moving speed v of the moving member 5 is the displacement amount due to the combination of the displacement of the rod 4 due to the primary frequency component and the displacement of the rod 4, the phase difference between the two displacements, and the primary resonance frequency f of the driving member 5.
It depends on the ratio of the displacement amount L1 at tr1 to the displacement amount L2 at the secondary resonance frequency frt2 and the like, and the optimum state is easily changed by these conditions. Therefore, the physical condition of the driving member 5 shown in FIG. It is better to actually manufacture the piezoelectric actuator 1 based on the relationship with the characteristics and determine the optimum conditions by actual measurement.

In the present embodiment, the drive pulse is driven at a duty of 30% or 70%. However, the duty of the drive pulse is not limited to this. An appropriate value can be set accordingly. In this case, if a rectangular wave drive signal having a duty smaller than 50% is used, the piezoelectric actuator 1 can be driven in the forward direction, and the duty is 5%.
If a rectangular wave drive signal larger than 0% is used, the piezoelectric actuator 1 can be driven in the reverse direction.

Therefore, when the duty of the drive pulse for forward drive is set to D1 (<50%), the duty D2 of the drive pulse for reverse drive is preferably set to (100-D1). Although a square-wave drive signal having a duty of 50% can be used, the duty waveform is preferably not 50% because the displacement waveform of the rod 4 is unstable and it is difficult to control the moving direction of the moving member 5. It is desirable to use a square wave.

FIG. 9 is a diagram showing an example of the frequency characteristics of the displacement of the tip of the piezoelectric element and the tip of the rod of the piezoelectric actuator 1 according to the present embodiment and the displacement of the rod alone.

In the figure, the characteristic shown by the solid line is the displacement characteristic of the tip of the rod 4 (point A in FIG. 1), and the characteristic shown by the dotted line is the displacement characteristic of the tip of the piezoelectric element 3 (point B in FIG. 1). , Two-dot chain lines show the displacement characteristics of the rod 4 alone. The characteristic is the displacement characteristic of the piezoelectric element 3 alone, and the characteristic is the displacement characteristic of the rod 4 alone.

As shown in FIG. 9, the primary resonance frequency ftr1 and the secondary resonance frequency ftr2 of the driving member 5 are set to ftr1 / ftr2 ≒.
Since the relationship is set to 1/2, and the drive is performed by a square wave drive pulse having an appropriate frequency fd near the low frequency side of ftr1, the tip of the rod 4 is largely displaced even at a relatively low drive frequency fd. Piezoelectric actuator 1 with high drive efficiency
Can be driven.

As apparent from the characteristics shown in FIG. 9, the displacement L on the base end side of the rod 4 (the portion near the point B of the rod 4 in FIG. 1) is smaller than that on the distal end side of the rod 4. In order to ensure a sufficient moving speed of the moving member 6 on the base end side of the rod 4 and prevent the moving speed from largely changing depending on the position of the moving member 6 on the rod 4, an engagement area of the moving member 6 with the rod 4 is set. Is made as large as possible (that is, the engagement portion in the axial direction of the rod 4 is lengthened).
It is desirable.

Alternatively, the moving speed of the moving member 6 is stabilized over the entire range of the rod 4 by changing the driving frequency fd and the duty D of the driving pulse according to the position of the moving member 6 on the rod 4. Is also good.

In the piezoelectric actuator 1 according to the present invention, the driving member 5 determined by the resonance characteristics of the piezoelectric element 3 and the resonance characteristics of the rod 4 connected to the piezoelectric element 3 is used.
In order to make the whole resonance characteristic a characteristic that provides optimum driving efficiency, the physical condition of the piezoelectric element 3 or the rod 4 needs to satisfy certain conditions.

However, of the physical conditions, the length Lr of the rod 4 is a limiting condition in terms of miniaturization of the piezoelectric actuator 1. That is, in the example of FIG.
mm, the driving member 5 as shown in FIG.
Are appropriate resonance characteristics, but when the rod length Lr is reduced to 8 mm, the resonance characteristics of the driving member 5 change as shown in FIG. 7C, and the proper resonance characteristics cannot be obtained.

For example, when the moving range of the moving member 6 is 4 mm,
The length of frictional engagement between the moving member 6 and the rod 4 is 4 m.
In the case of m, the rod length Lr is sufficient to be 8 mm, but in consideration of the driving efficiency, the rod length Lr for obtaining the resonance characteristics of FIG. 6E is required to be 16 mm, and the rod length Lr is unnecessarily long. Become. On the other hand, if the rod length Lr is reduced to about 8 mm for miniaturization, the driving efficiency is significantly reduced, and the performance is reduced.

Therefore, in order to shorten the rod length Lr while ensuring proper driving efficiency, it is preferable to attach a weight 16 to the tip of the rod 4 as shown in FIG.

FIG. 11 shows that the rod length of the rod 4 is 16 mm.
FIG. 10 is a diagram showing a change in resonance characteristics of the displacement member when a weight is fixed to the tip when the length is reduced to 8 mm from FIG.

The displacement characteristics shown in FIGS. 6A and 6B are the same as the displacement characteristics shown in FIGS. 6E and 6C, respectively. FIG. 11C is a diagram showing resonance characteristics when the weight 16 is fixed to the tip of the rod length Lr = 4 mm.

As shown in FIGS. 11A and 11B, the rod 4
When the length Lr is reduced from 16 mm to 8 mm, the secondary resonance frequency ftr2 is greatly different from 2ftr1, and the above-described condition for optimizing the driving efficiency cannot be obtained.
By fixing a weight 16 having an appropriate weight to the tip of the rod 4 having a rod length Lr = 4 mm as shown in FIG. 7, the secondary resonance frequency ftr2 can be lowered to the vicinity of 2ftr1, and the rod length Lr = 16 mm is substantially obtained. It is possible to obtain a resonance characteristic equivalent to the resonance characteristic in the case of (1). Therefore, the length L of the rod 4
When r is shorter than the appropriate length, the resonance displacement characteristic of the driving member 5 (piezoelectric element 3 + rod 4 + weight 16) is fixed by attaching an appropriate weight 16 corresponding to the length to the tip of the rod 4 to improve the driving efficiency. Optimum conditions can be set, and the drive frequency fd is changed to the primary resonance frequency ft based on the resonance characteristics.
It is good to set to an appropriate frequency near r1.

Next, the relationship between the driving voltage and the driving frequency will be described.

FIG. 12 shows the result of examining the change in the drive frequency at which the drive efficiency becomes maximum when the voltage of the drive pulse is changed. As shown in the figure, the driving frequency fopt at which the driving efficiency becomes the highest (hereinafter referred to as the optimum driving frequency fopt) differs depending on the voltage level of the driving pulse, and the optimum driving frequency fopt increases as the voltage level increases. It has the characteristic of monotonically decreasing.

This means that, for example, the voltage V =
When the driving pulse voltage V drops below 5 [V] due to the consumption of the power supply battery 11 while supplying a rectangular wave driving pulse of 5 [V] and a driving frequency fd = 83.5 [kHz],
The driving frequency fd = 83.5 [kHz] corresponds to the driving voltage V
Does not become the optimal driving frequency fopt, and this means that the driving efficiency is reduced. That is, the driving voltage V
Becomes, for example, 5 [V] to 3 [V], the driving voltage V
= 3 [V], the optimum driving frequency fopt is 86 [kHz], so that the driving frequency fd = 83.5 [kHz] is greatly shifted from the optimum driving frequency fopt = 86 [kHz] to the lower frequency side.

FIG. 13 shows the change of the moving speed v of the moving member 6 when the driving pulse period when the driving voltage V = 3 [V] and the discharge timing of the piezoelectric element 3 within the period are changed. It is a thing which investigated. That is, the driving voltage V =
The driving frequency fd [kHz] of the driving pulse at 3 [V]
z] and a change in the moving speed v of the moving member 6 when the duty D [%] is changed. In FIG. 14, the cycle of the drive pulse is a period T from the time when the pulse changes to “H” to the time when the pulse next changes to “H”, and the discharge timing is set after the pulse changes to “H”. "
This is the period T _ON until the voltage changes to L ”.

In the figure, the horizontal axis represents the discharge timing T _ON
[Μsec], the vertical axis indicates the period T of drive pulse [μsec]
And the moving speed v of the moving member 6 is shown by a contour line graph. Therefore, a closed area filled with white or oblique lines indicates that the moving member 6 has moved at the same moving speed v.

The maximum output area is a white area, and the moving speed v of the moving member 6 is characterized by increasing from the peripheral part of the graph area toward the central part slightly below (ie, high output). Also, for example, the discharge timing T _ON = 3.8
When the change in the moving speed v of the moving member 6 with respect to the period T at 75 [μsec] is extracted, the result is as shown in FIG.
There is a characteristic that the output decreases gradually on the low frequency side centering on the region of the maximum output, but sharply decreases on the high frequency side.

Therefore, when the piezoelectric actuator 1 according to the present embodiment is used in a device in which the drive voltage changes easily, the drive frequency fd is adjusted to the optimum drive frequency according to the change in the drive voltage while monitoring the drive voltage. It is desirable to perform feedback control so that fopt is obtained.

If the drive frequency fd is not changed in accordance with the change in the drive voltage V, the drive frequency fd is relatively shifted from the optimum drive frequency fopt in accordance with the change in the drive voltage V. Care must be taken so that the direction does not shift to the high frequency side. This is because, as shown in FIG. 15, when the drive frequency fd changes to the high frequency side, if the drive frequency fd after the change exceeds the maximum output range, the output may drop sharply and drive may be stopped.

Therefore, for example, the change range of the drive voltage V is 3
In the case of ５5 [V], the driving frequency fd is equal to the driving voltage 5
Optimal driving frequency fopt at [V] = 83.5 [kHz
z]. With this setting, for example, even if the drive voltage V drops from 5 [V] to 4 [V],
As shown in FIG. 12, the optimum driving frequency fopt for the driving voltage 4 [V] is about 85.25 [kHz], and the driving frequency fd = 83.5 for this optimum driving frequency fopt.
This is because [kHz] changes relatively to the lower frequency side, so that the output does not drop sharply and the driving is not stopped.

FIG. 15 is a flowchart showing the drive control of the piezoelectric actuator 1 according to this embodiment.

The flowchart shown in FIG.
Can be changed according to the load conditions within a predetermined range, and the appropriate drive pulse period T and discharge timing T _ON are set according to the change in the drive voltage V (ie, the drive frequency fd of the drive pulse). And duty D).

According to this drive control, when operation information of the switch 14a or the switch 14b is input to the control unit 15 (# 1), it is determined whether or not the content of the operation information is "OFF"(# 1). 3) If the switch operation is “OFF” (YES in # 3), the process proceeds to step # 13, and the output of the drive pulse from the drive circuit 12 to the piezoelectric element 3 is stopped.

On the other hand, if the switch operation is not “OFF” (NO in # 3), the battery voltage V _B
Is input, and a determination process is performed as to whether or not driving is possible based on the information (# 5). Subsequently, the position detection circuit 1
The position information of the moving member 6 is input from 0, and the position of the moving member 6 on the rod 4 is determined based on the position information (# 7). Subsequently, the parameters of the drive frequency fd and the duty D of the drive pulse are set with reference to a table (not shown) (stored in the ROM in the control unit 15) based on the position determination result (# 9, #). 11). The driving member 5 including the piezoelectric element 3 and the rod 4 is, for example, as shown in FIG.
2 and FIG. 13, for example, a table shown in Table 1 is prepared, and this table is prepared from information on the battery voltage V _B , the designated driving direction, and the position of the moving member 6. The cycle T of the drive pulse and the discharge timing T _ON are set by using this. For example, when the battery voltage V _B is 5
In [V], if the designated driving direction is the feeding direction and the position of the moving member 6 is “zone 3”, the driving pulse cycle T is “12 μsec” and the discharge timing T _ON is “3.4”.
μsec ”.

[0113]

[Table 1]

The information on the set driving frequency fd and the duty D is input to the driving circuit 12, and the driving circuit 12 generates a driving pulse of a rectangular wave having the driving frequency fd and the duty D and supplies it to the piezoelectric element 3. . As a result, the piezoelectric element 3 vibrates, the driving member 5 is displaced like a saw blade, and the moving member 6 relatively moves on the rod 4 in the direction specified by the switch 14a or the switch 14b.

[0115]

As described above, according to the present invention,
In the impact type piezoelectric actuator, when the driving means including the piezoelectric element and the rod member has a primary anti-resonance frequency of the driving means as fatr1, and the primary resonance frequency of the rod member alone under the condition that one end is fixed is frr1, fatr1 /
3 <frr1 <fatr1, and a driving voltage of a rectangular wave having a primary sine wave component near the low frequency side of the primary resonance frequency ftr1 of the driving means and having a predetermined duty is applied to the piezoelectric element. Since the actuator is supplied and driven, it is possible to drive the actuator in a state in which the driving efficiency is as close as possible to the optimum with a relatively low voltage rectangular wave driving voltage.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a schematic configuration of an embodiment of an impact type piezoelectric actuator according to the present invention.

FIG. 2 is a perspective view showing one embodiment of a specific configuration of an impact type piezoelectric actuator.

FIG. 3 is a diagram illustrating a frequency characteristic of a displacement amount and a phase difference of a driving member of a piezoelectric actuator according to the present invention configured to satisfy a condition relatively close to an optimum condition.

4A shows a drive signal of a rectangular wave with a duty of 30%, and FIG. 4B shows a displacement waveform of the rod when driven by the drive signal, and a primary frequency component and a secondary frequency component of the displacement waveform. FIG.

FIG. 5A shows a drive signal of a rectangular wave with a duty of 70%, and FIG. 5B shows a displacement waveform of a rod driven by the drive signal and a primary frequency component and a secondary frequency component of the displacement waveform. FIG.

FIGS. 6A to 6F are diagrams showing the relationship between the frequency of the driving voltage and the displacement speed of the driving member, wherein FIGS. 6A to 6F show rod lengths of the driving member of 0 mm, 4 mm, 8 mm, 12 mm, and 16 m, respectively.
m, 32 mm.

7A is a diagram illustrating displacement characteristics of a rod tip when the rod length of the driving member is 4 mm, and FIG. 7B is a diagram illustrating displacement characteristics of the rod tip when the rod length of the driving member is 16 mm. FIG.

FIG. 8 is a diagram showing a tendency of a resonance characteristic of a driving member to change when physical conditions such as the length, thickness, and density of a piezoelectric element and a rod are changed.

FIG. 9 is a diagram illustrating an example of a frequency characteristic of a displacement amount of a tip of a piezoelectric element and a tip of a rod of the piezoelectric actuator according to the present embodiment and a displacement amount of a rod alone.

FIG. 10 is a view in which a rod length is shortened by attaching a weight to the tip of the rod.

FIG. 11 is a diagram showing a change in resonance characteristics of a displacement member when a weight is fixed to the tip when the rod length of the rod is reduced from 16 mm to 8 mm.

FIG. 12 is a diagram illustrating a change in a drive frequency at which the drive efficiency is maximized when the drive voltage of the drive pulse is changed.

FIG. 13 is a diagram illustrating a cycle of a drive pulse when a drive voltage V = 3 [V] and a change in a moving speed of a moving member when a discharge timing of a piezoelectric element is changed within the cycle.

FIG. 14 is a diagram for explaining a cycle of a drive pulse and a discharge timing of the piezoelectric element within the cycle.

15 is a discharge timing T _ON = 3.875 in FIG. 12;
It is a figure which shows the change of the moving speed of the moving member with respect to period T in [microsecond].

FIG. 16 is a flowchart showing drive control of the piezoelectric actuator according to the embodiment.

FIG. 17 is a diagram showing a basic configuration of a conventional impact type piezoelectric actuator.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piezoelectric actuator 2 Base (support member) 3 Piezoelectric element (electromechanical conversion element) 4 Rod (bar member) 5 Driving member (driving means) 6 Moving member (moving means) 7 Drive control part (moving direction control means) 8 Position Detection sensor 9 Waveform shaping circuit 10 Position detection circuit 11 Power supply battery 12 Drive circuit (drive voltage generation means) 13 Voltage detection circuit 14a, 14b Switch 15 Control unit 16 Weight

Claims (3)

[Claims] 1. A driving unit comprising: an electromechanical conversion element that expands and contracts when a driving voltage is applied; and a rod member fixed to one end of the electromechanical conversion element in the expansion and contraction direction. In a piezoelectric actuator comprising: a supporting unit that supports the other end of the conversion element; a moving unit that is engaged with a rod member of the driving unit with a predetermined frictional force; and a driving voltage generating unit that generates the driving voltage. The driving means sets the primary anti-resonance frequency of the driving means to f
atr1, one of the rod members alone with one end fixed
If the next resonance frequency is frr1, fatr1 / 3 <frr1 <f
The driving voltage generation means is configured to satisfy atr1, and the driving voltage generation means has a square-wave driving voltage having a primary sine wave component near a low frequency side of a primary resonance frequency ftr1 of the driving means and having a predetermined duty. A piezoelectric actuator characterized by generating the following. 2. The driving means according to claim 1, wherein the primary resonance frequency of the driving means is ftr1 and the secondary resonance frequency is ftr2.
2. The piezoelectric actuator according to claim 1, wherein the piezoelectric actuator is configured to satisfy ftr1> ftr2. 3. The piezoelectric actuator according to claim 1, further comprising moving direction control means for controlling a moving direction of the moving means by controlling a duty of the driving voltage. .