JPH06148497A - Piezoelectric actuator - Google Patents

Abstract

PURPOSE:To provide a piezoelectric actuator which drives to make the durability of a piezoelectric element excellent. CONSTITUTION:This piezoelectric actuator 1 obtains driving force by moving by means of using inertial force associated with the quick deformation of the piezoelectric element 23 on which high frequency pulse voltage is impressed and possesses a means 5 to switch the high frequency pulse voltage impressed on the piezoelectric element 23 to that of driving waveform whose spectrum of high frequency component is small after a specified time from the start of moving.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric actuator that obtains a driving force by moving by utilizing inertial force caused by rapid deformation of a piezoelectric element to which a high frequency pulse voltage is applied.

[0002]

2. Description of the Related Art Conventionally, as shown in, for example, Japanese Patent Application No. 2-305182, there has been known a rapid deformation piezoelectric actuator which has a simple and compact structure to perform a moving operation of a lens quickly and reliably.

In this actuator, a movable body is connected to a lens frame which holds a movable lens in a lens group which constitutes an objective optical system, and an axial direction is arranged along an axial direction along which the lens frame is to be moved. An expandable and contractable piezoelectric element is provided, one end of the piezoelectric element is substantially fixed to the moving body, and an inertial body is attached to the other end of the piezoelectric element to control the drive voltage applied to the piezoelectric element. The position adjustment is performed by moving the lens frame while utilizing the inertial force of the inertial body when the piezoelectric element expands and contracts in the axial direction and the frictional force that the moving body receives from the moving road surface. is there. In this case, the voltage waveform applied to the piezoelectric element by the control means is a pulse waveform having different rising speeds and falling speeds.
The actuator can be moved by one step by applying the pulse, and the actuator can be continuously moved by continuously applying the pulse waveform.

[0004]

By the way, the frictional force received by the moving body from the moving road surface is different between the step of moving the actuator from the stationary state and the step of continuously moving the actuator thereafter. In other words, the rising speed, the falling speed, or the peak voltage value of the pulse wave applied to the piezoelectric element can be smaller when the actuator is continuously moved than when the actuator is moved from the stationary state.

However, the conventional actuator is
Since the same pulse waveform as that at the time of starting the movement is used and the subsequent continuous movement is performed, the load on the piezoelectric element is large and the piezoelectric element may be deteriorated quickly.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a piezoelectric actuator which can be driven so as to improve the durability of the piezoelectric element.

[0007]

In order to solve the above problems, the present invention obtains a driving force by moving by utilizing the inertial force associated with the rapid deformation of a piezoelectric element to which a high frequency pulse voltage is applied. The piezoelectric actuator includes means for switching the high frequency pulse voltage applied to the piezoelectric element after a predetermined time from the start of movement to a drive waveform having a small spectrum of high frequency components.

[0008]

After a predetermined time from the start of the movement, the driving force of the piezoelectric element becomes small, but the frictional force that acts as a resistance for driving the actuator also becomes small, so that the moving speed of the actuator hardly changes.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. 1 and 2 show a first embodiment of the present invention. As shown in FIG. 1A, the piezoelectric actuator 1 of this embodiment includes an actuator body 8 and a drive device 10 that drives the actuator body 8. The piezoelectric actuator 1 is provided in the tip portion 32 of the endoscope 30 as a moving mechanism for moving the objective lens 20 of the endoscope 30 as shown in FIG.

As shown in FIG. 1B, a lens frame 22 for holding the objective lens 20 is provided at a distal end portion 32 of the endoscope 30.
Are held so as to be movable in the axial direction of the endoscope 30. The lens frame 22 has a protrusion 24, which is integrated with the inertial body 35, fixed to one end of the piezoelectric element 23. The moving body 26 is fixed to the other end of the piezoelectric element 23. The moving body 26 slidably contacts with the inner peripheral surface of the outer tubular tube 25 arranged along the axial direction of the endoscope 30. A lead wire 27 is pulled out from the piezoelectric element 23 along the axial direction of the endoscope 30 to the near side, and is electrically connected to the drive device 8.

As shown in FIG. 1A, the driving device 8
Is a triangular wave oscillator 2, a device X electrically connected to the triangular wave oscillator 2, a comparator 4, an n-ary counter 7,
It is composed of a changeover switch 5 and an amplifier 6. Device X
It is a device such as a power bleeder, a voltage limiter, a high frequency filter, or a gain 1 differential amplifier.

In order to drive the piezoelectric actuator 1 having the above structure, a pulse wave having a portion showing a rapid voltage change and a portion showing a slow voltage change is applied to the piezoelectric element 23 which is a constituent element of the actuator 1. As a result, an impact force is generated on the moving body 26 by the inertial body 35, and the moving body 2
6 can be slid on the inner peripheral surface of the outer tube 25.

In the present embodiment, as shown in FIG. 2, at the time of starting the driving of the actuator 1, a high frequency component is obtained so that a large force generated by the piezoelectric element 23 is taken to obtain an impact force that overcomes a large static friction force. A pulse wave having a large spectrum is applied to the piezoelectric element 23. In the figure, (a) is a case where the device X is a power bleeder, (b) is a case where the device X is a voltage limiter, (c) is a case where the device X is a high frequency filter, and (d) is a case where the device X is a gain. Each of the cases is a differential amplifier of No. 1.

At the time of n pulses after the start of driving, the actuator 1 comes to have a momentum, so that the friction acting on the moving body 26 and the inner peripheral surface of the outer tube 25 becomes kinetic friction and becomes smaller than static friction. After n pulses, the changeover switch 5 is switched from the terminal A to the terminal B by the carry signal of the n-ary counter.
The triangular wave passing through the device X is applied to the piezoelectric element 23. For this reason, the driving force of the piezoelectric element 23 becomes small, but the frictional force that acts as a resistance for driving the actuator 1 also becomes small, so that the moving speed of the actuator 1 does not decrease. In this embodiment, the actuator 1
The lens frame 22 can be moved back and forth along the axial direction of the endoscope 30 by driving, and zooming and focusing can be performed.

As described above, the piezoelectric actuator 1 according to the present embodiment does not consistently drive with a waveform having a large spectrum of high frequency components from the start to the end of driving, so that the load on the piezoelectric element 23 is reduced and the durability of the piezoelectric element 23 is reduced. Goes up.

FIGS. 3 and 4 show a second embodiment of the present invention. As shown in FIG. 4A, the actuator body 49 of the piezoelectric actuator 40 of this embodiment.
The piezoelectric element 23 and the moving body 46 fixed to one end of the piezoelectric element 23 are tightly bound by the band 45. Further, the moving body 46 slidably contacts the inner peripheral surface of the outer tube 25 arranged along the axial direction of the endoscope 30.
A lead wire 27 is pulled out from the piezoelectric element 23 to the proximal side along the axial direction of the endoscope 30 and is electrically connected to a drive device 44.

As shown in FIG. 3, the piezoelectric actuator 4
The driving device 44 of 0 outputs the third timer IC 42 and a triangular pulse having a rising time longer than the rising time of the triangular pulse of the third timer IC 42 in synchronization with the square wave pulse of the first timer IC 41. A triangular wave pulse is output from any one of the second timer ICs 43. In this case, the second timer IC
The drive generation force of the piezoelectric element 23 by the pulse wave output through 43 is smaller than the drive generation force of the piezoelectric element 23 by the pulse wave output through the third timer IC 42.

The pulse wave of the first timer IC 41 is also input to the n-ary counter 7. n
The advance counter 7 switches the switch 5 by outputting a carry signal to the analog switch 5 when the number of input pulses reaches n. As a result, the amplifier 6
The signal input to is switched from that via the third timer IC 42 to that via the second timer IC 43.

When a triangular wave having a steep rise and a gradual fall is applied to the piezoelectric element 23 of the actuator body 49 by such a driving device 44, the piezoelectric element 2
3 grows rapidly from a contracted state. At this time, the moving body 46 is sandwiched between the band 45 and the piezoelectric element 23 and extends in the radial direction of the outer tube 25. As a result, the frictional force between the outer tube 25 and the moving body 46 is increased. At this time, an inertial force is generated due to the weight of the piezoelectric element 23, and the moving body 46 moves to the left in the figure against the frictional force with the outer tube 25.

When a triangular wave having a gentle rise and a sharp fall is applied to the piezoelectric element 23, the piezoelectric element 23 suddenly contracts from the expanded state. At this time, since the moving body 46 is loosely tightened by the band 45, the moving body 46 contracts in the radial direction of the outer cylinder tube 25, and the frictional force between the outer cylinder tube 25 and the moving body 46 decreases.
At this time, an inertial force is generated due to the weight of the piezoelectric element 23, and the moving body 46 moves to the right in the figure against the frictional force with the outer tube 25. In addition, since the frictional force between the outer tube 25 and the moving body 46 is different between the movement in the left direction and the movement in the right direction in the figure, a fast movement and a slow movement can be performed. That is, in the piezoelectric actuator 1 of the present embodiment, the frictional force between the outer tube 25 and the moving body 46 changes as the piezoelectric element 23 expands and contracts, and the moving speed and the driving force are changed depending on the moving direction. change. That is, the movement in the left direction of the drawing has a larger frictional force between the outer tube 25 and the moving body 46 than the movement in the right direction of the drawing, so that the movement amount decreases but the driving force increases (usually the frictional force). You can get the maximum generated power of about 1/2).

When the actuator main body 49 is driven by the drive device 44, first, in order to overcome the static frictional force between the outer tube 25 and the moving body 46 at the start of driving, a triangular wave having a short rise time (through the third timer IC 42 is used). Drive with output pulse wave). After n pulses at which the speed of the actuator body 49 stabilizes, the actuator body 49 is switched to a triangular wave having a long rise time (a pulse wave output through the second timer IC 43) for driving. At this time, since the frictional force generated between the outer tube 25 and the moving body 46 is a kinetic frictional force smaller than the static frictional force, the rising time of the triangular wave is lengthened to lower the drive generation force of the piezoelectric element 23. However, the moving speed of the actuator body 49 does not decrease.

The drive device 50 shown in FIG. 5 has a speed sensor 53 in addition to the circuit configuration of the drive device 44 shown in FIG.
And the output is High based on the output of this speed sensor 53.
The circuit configuration is such that a comparator 4 that switches to low or a switch 52 that switches a signal line by the output of the comparator 4 is provided.

In such a circuit structure, the speed of the actuator main body 49 is monitored by the speed sensor 53, so that the outer cylinder tube 25 and the moving body 46 are not damaged by the damage of the outer cylinder tube 25.
When the frictional force between the actuator and the actuator body suddenly decreases and the speed of the actuator body suddenly decreases, the actuator body 49 is restored by returning the triangular wave applied to the piezoelectric element 23 to the triangular wave of the third timer IC 42 at the start of driving. It is possible to perform speed feedback control in which the speed of the second timer IC 43 is returned to the triangular wave when the speed of the actuator body 49 is stabilized again.

By the way, in each piezoelectric actuator shown in FIG. 6, the moving speed and the driving force can be changed according to the moving direction of the actuator body without using electrical means.

That is, the piezoelectric actuator 60 shown in FIG. 6A comprises a piezoelectric element 62 and a leaf spring 63. The leaf spring 63 is fixed to the electrode surface 61 of the piezoelectric element 62 and is in slidable contact with the outer tube 25.

In this structure, when a triangular wave having a steep rise and a gradual fall is applied to the piezoelectric element 62, the piezoelectric element 62 suddenly extends in the radial direction of the outer cylindrical tube 25 and contracts in the major axis direction, Since the frictional force between the leaf spring 63 and the outer tube 25 increases, an inertial force is generated due to the weight of the piezoelectric element 62, and the leaf spring 63 together with the piezoelectric element 62 causes the outer tube 25 to move.
It moves to the left in the drawing against the frictional force with.

When a triangular wave having a gentle rise and a sharp fall is applied to the piezoelectric element 62, the piezoelectric element 6
2 rapidly contracts in the radial direction of the outer cylindrical tube 25 and rapidly extends in the long axis direction, and the frictional force between the leaf spring 63 and the outer cylindrical tube 25 decreases, so that the inertial force due to the own weight of the piezoelectric element 62. Occurs, the leaf spring 63 moves rightward in the drawing against the frictional force with the outer tube 25 together with the piezoelectric element 62. It should be noted that the movement in the left direction in the drawing has a larger frictional force than the movement in the right direction in the drawing, so the amount of movement is small but the driving force is large.

The piezoelectric actuator 65 shown in FIG. 6B is composed of a piezoelectric element 66 and a leaf spring 63. The leaf spring 63 is fixed to the non-electrode surface 67 of the piezoelectric element 66 and slidably contacts the outer tube 25. Therefore, the piezoelectric actuator 65 of this configuration is also shown in FIG.
An operation similar to that of the above can be performed.

Further, the piezoelectric actuator 70 shown in FIG. 6 (c) has a movable body 72 fixed to one end of a piezoelectric element 71. The moving body 72 slidably contacts the outer tube 25. In this configuration, there is no difference in the movement amount depending on the movement direction, unlike the case of the two piezoelectric actuators 60 and 65 described above. However, the application of the voltage waveform having the abrupt rising and falling causes an inertial force due to the weight of the piezoelectric element 71, and the moving body 72 can be slid with respect to the outer tube 25.

FIG. 7 shows a third embodiment of the present invention. In the actuator body 75 of the piezoelectric actuator 79 of the present embodiment, the inertial body 77 fixed to one end of the piezoelectric element 23 is formed in the projection 78 of the lens frame 22 to form the lateral hole 7.
3 and is held slidably by a screw 76 with an appropriate frictional force, and the other structure is the same as that of the first embodiment.

In this structure, when a triangular wave having a steep rise and a gentle fall is applied to the piezoelectric element, the moving body 26 moves ΔX to the right in the drawing with respect to the outer tube 25 at the rise.
The inertial member 77 moves by .DELTA.X2 with respect to the lens frame 22 to the left in the drawing.

When the lens frame 22 falls, the lens frame 22 moves ΔX1 + ΔX2 rightward in the drawing in accordance with the contraction of the piezoelectric element 23 together with the inertial body 77. When a triangular wave with a slow rise and a sharp fall is applied, the lens frame moves ΔX1 + ΔX2 to the left in the drawing. In the case of the first embodiment, since the inertial body and the lens frame are fixed, the lens frame moves only .DELTA.X1. With this configuration, the moving speed is the first
It is faster than that of the embodiment.

8 to 10 show a linear actuator using a piezoelectric element. These actuators are actuators that do not require abrupt voltage changes.

The piezoelectric actuator 80 shown in FIG. 8 is arranged in the outer tubular tube 25 with the oblique hairs 81 and 84 bonded to the outer surface of the piezoelectric element 82. 8A is a plan view of the piezoelectric actuator 80 inside the outer tube 25 as seen from above, and FIG. 8B is a view of the piezoelectric actuator 80 inside the outer tube 25 as seen from the side. is there. That is, the slant bristles 86 inclined to the left in the drawing are adhered to the non-electrode surfaces 86 that are the upper surface and the lower surface of the piezoelectric element 34, and the slanted hairs 86 that are inclined to the right in the drawing are attached to the electrode surfaces 83 that are both side surfaces of the piezoelectric element 34. The hair 81 is adhered.

In this configuration, when the voltage waveform shown in A of FIG. 8C is applied, the piezoelectric element 82 first expands in the bias portion toward the electrode surface 83 and contracts toward the non-electrode surface 86. Therefore, the bristles 31 are inscribed in the outer tube 25, and the bristles 84 separate from the outer tube 25. Next, the oblique voltage 81 is pressed against the outer tube 25 by the pulse voltage applied with the bias applied, and the operation of returning is repeated. Then, while repeating this operation, the outer tube 25 and the slant 81
The leftward impulse generated between the actuator 8 and
0 moves leftward in the figure. When the voltage waveform shown in B of FIG. 8C is applied, a rightward impulse is generated between the slanted hair 84 and the outer tube 25, and the actuator 80 is moved.
Moves to the right in the figure.

As described above, the actuator 80 can improve the durability of the piezoelectric element by dropping the high frequency component spectrum of the driving waveform during movement, as in the above-described embodiments.

In the piezoelectric actuator 90 shown in FIG. 9, a slanted hair 95 inclined to the right in the drawing is bonded to the inner surface of a cylindrical piezoelectric element 94. Further, a slanted hair 92 that is inclined to the left in the drawing is attached to the outer periphery of the piezoelectric element 94. Further, the outer cylinder tube 25 in which the piezoelectric actuator 90 is arranged has a center bar 91, and this center bar 91 is inserted into the inner hole of the cylindrical element 94.

In this structure, when the voltage waveform shown in A of FIG. 8C is applied, the piezoelectric element 94 first swells in the radial direction of the outer cylinder tube 25 at the bias voltage portion, and the oblique hairs 92 are formed. Touch the inner surface of. On the other hand, the slanted hair 95 is the center bar 91.
Get away from. Next, the oblique voltage 92 is pressed against the inner surface of the outer tube 25 by the pulse voltage applied with the bias applied, and the operation of returning is repeated. While repeating this operation, the actuator 90 moves to the right in the drawing due to the impulse generated between the outer tube 25 and the slanted hair 92. When the voltage waveform shown in B of FIG. 8C is applied, the piezoelectric element 94 first causes the outer cylinder tube 2 at the bias voltage portion.
5, the bristles 95 contact the center cover 43. On the other hand, the slanted hair 92 separates from the inner peripheral surface of the outer tube 25.
Then, the oblique voltage 95 is pressed against the central bar 91 and returned by the pulse voltage applied while biasing is repeated. Then, by repeating this operation, the actuator 90 moves to the left in the drawing due to the impulse generated between the center bar 91 and the oblique hair 95.

Next, the piezoelectric actuator 100 shown in FIG.
Will be described. As shown in (a) of FIG. 10, a bristles 102 tilted to the right in the drawing are adhered to the one surface electrode surface 101 of the bimorph element 103 near the center thereof, and diagonally tilted to the left in the drawing at both ends thereof. Hair 105 is attached. The other surface electrode surface 10 of the bimorph element 103
In FIG. 1, a slanted bristles 106 inclined to the left in the drawing are adhered near the center thereof, and slanted bristles 107 inclined to the right in the drawing are attached to both ends thereof.

In this configuration, when the voltage waveform shown in A of FIG. 8C is applied, the central portion of the piezoelectric element 103 is bent downward by the voltage of the bias portion of the piezoelectric element 103, and the oblique fibers 105, 106. Is inscribed in the outer tube 25, and the oblique hair 1
02 and 107 are separated from the inner surface of the outer tube 25. Next, with the pulse voltage applied with the bias voltage applied, the slants 105, 106 are repeatedly pressed against the inner surface of the outer tube 25 and returned. Then, while repeating this operation, the actuator 100 moves to the right in the drawing due to the impulse generated between the outer tube 25 and the oblique fibers 105, 106. Further, when the voltage waveform shown in B of FIG. 8C is applied, the central portion of the piezoelectric element 103 bends and vibrates upward in the drawing, so that the oblique fibers 102, 107 and the outer tube 2
5, an impulse is generated in the left direction between the actuator 100 and the actuator 100.
Moves to the left.

[0041]

As described above, in the piezoelectric actuator of the present invention, the driving force of the piezoelectric element is reduced after a predetermined time from the start of driving, and the spectrum of the high frequency component is consistently large from the start to the end of driving. Since it is not driven in a waveform, the load applied to the piezoelectric element can be reduced and the durability of the piezoelectric element can be improved.

[Brief description of drawings]

FIG. 1A is a configuration diagram of a piezoelectric actuator showing a first embodiment of the present invention, and FIG. 1B is a sectional view of a distal end portion of an endoscope in which the piezoelectric actuator of FIG.

FIG. 2 is a waveform diagram showing a waveform of a high frequency pulse voltage formed by the driving device of the piezoelectric actuator of FIG.

FIG. 3 is a configuration diagram of a piezoelectric actuator showing a second embodiment of the present invention.

4A is a cross-sectional view of a distal end portion of an endoscope in which the piezoelectric actuator of FIG. 3 is incorporated, and FIG. 4B is a waveform showing a waveform of a high frequency pulse voltage formed by the driving device of the piezoelectric actuator of FIG. It is a figure.

FIG. 5 is a configuration diagram of a piezoelectric actuator showing a modification of the second embodiment.

FIG. 6 is a configuration diagram of a piezoelectric actuator capable of changing a moving speed and a driving force according to a moving direction of an actuator body without using an electric means.

FIG. 7 is a cross-sectional view of a piezoelectric actuator according to a third embodiment of the present invention and a distal end portion of an endoscope having a built-in electric actuator.

FIG. 8 is an explanatory diagram showing a first example of a piezoelectric actuator that does not require a particularly rapid voltage change.

FIG. 9 is an explanatory diagram showing a second example of a piezoelectric actuator that does not require a particularly rapid voltage change.

FIG. 10 is an explanatory diagram showing a third example of a piezoelectric actuator that does not require a particularly rapid voltage change.

[Explanation of symbols]

1, 40, 50, 79 ... Piezoelectric actuator, 23 ... Piezoelectric element, 5, 51, 52 ... Changeover switch.

Claims (1)

[Claims] 1. A piezoelectric actuator that obtains a driving force by moving by utilizing inertial force associated with rapid deformation of a piezoelectric element to which a high-frequency pulse voltage is applied, and applies the piezoelectric force to the piezoelectric element after a predetermined time from the start of movement. A piezoelectric actuator comprising means for switching a high frequency pulse voltage to a drive waveform having a high frequency component having a small spectrum.