JPS6273787A - Displacement generator - Google Patents

Abstract

PURPOSE:To obtain a displacement generator which can improve the reproducibility of a displacing position without an effect of the hysteresis of a piezoelectric actuator by composing the actuator of a plurality of actuator units having different displacing amounts, and selectively driving the units ON, OFF. CONSTITUTION:The first to sixth units 61-66 are selectively driven ON, OFF in response to a displacement set signal to be controlled for displacement without hysteresis by resolution of 6 bits to the set signal. That is, when the signal is '1', only the first unit 21 is driven, when the signal is '2', only the second unit 22 is driven, when the signal is '3', the units 21, 22 are driven, and the units can be controlled to be displaced in relation of integer number times of the displacement of the first unit 21 of the minimum displacement. Thus, the effect of the hysteresis of a piezoelectric actuator can be eliminated to improve the reproducibility of th displacing position.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to improvements in displacement generating devices using piezoelectric actuators, and particularly to a displacement generating device that solves the problem of hysteresis in piezoelectric actuators.

[Technical background of the invention and its problems]

Piezoelectric actuators are small and lightweight devices for applying minute displacements, and have numerous advantages such as fast response speed, no heat generation, low power consumption, and no magnetic influence on other parts. . For this reason, mask positioning in semiconductor manufacturing equipment, laser beam deflection equipment, V
TR auto tracking or JP-A-58-292
The present invention can be expected to be applied to various fields, such as high-resolution Fi-image type actuators as seen in No. 75 and Japanese Patent Application Laid-Open No. 58-130677.

However, piezoelectric actuators have a drawback called hysteresis, which is a major obstacle in performing minute position control. As shown in Figure 4, hysteresis is a phenomenon in which the amount of displacement differs when the voltage increases and when the voltage decreases. However, they do not show the same amount of displacement. For this reason, the reproducibility of the displacement position is reduced. Note that hysteresis depends on the shape of the piezoelectric actuator, the type of piezoelectric material, the applied drive voltage, etc., but in general, the hysteresis is approximately 10% relative to the applied displacement amount.
It is known that there is a hysteresis of about 30%. The hysteresis IH described here is based on the applied voltage V
The amount of displacement (final displacement point) when , and the amount of displacement when the applied voltage is V/2 when the voltage increases is Dr, i! If the amount of displacement when the applied voltage is V/2 during the voltage drop is [)f, it is expressed as H=((Dr − Or )/D)xl 00.

On the other hand, in order to eliminate the above-mentioned hysteresis, a method has been proposed in which the displacement of a piezoelectric actuator is controlled by a closed loop equipped with a sensor for detecting displacement, as seen in, for example, Japanese Patent Publication No. 54-29359. However, the control method using sensors generally has a number of drawbacks, such as not only requiring a large-scale device, but also increasing cost and making it difficult to downsize the device. Therefore, it is desired to eliminate the hysteresis of the piezoelectric actuator using a simple control method that does not use sensors or the like.

[Purpose of the invention]

The present invention has been made in consideration of the above circumstances, and its purpose is to be able to eliminate the effects of hysteresis of piezoelectric actuators using a simple control method without using sensors, etc., and to improve the reproducibility of displacement positions. The object of the present invention is to provide a displacement generating device that can be improved.

[Summary of the invention]

The mother and child of the present invention uses a piezoelectric actuator at an initial displacement point and a final displacement point that are not affected by hysteresis, and
The piezoelectric actuator is composed of a plurality of units, and displacement is generated by selectively driving these units.

That is, the present invention provides a displacement generating device including a piezoelectric actuator and a drive circuit for driving the piezoelectric actuator, in which the piezoelectric actuator is configured with a plurality of actuator units each having a different amount of displacement, and these units are selectively driven on and off. It was designed to do so.

〔Effect of the invention〕

According to the present invention, only the initial displacement point position in the voltage OFF state and the final displacement point position in the voltage ON state of each unit constituting the piezoelectric actuator are used, and the piezoelectric actuator Since the displacement is controlled, it is possible to obtain the same displacement waveform as the input signal waveform without hysteresis. In other words, it is possible to improve the reproducibility of displacement positions. Since the displacement amounts of the plurality of units are made different, by combining these units, it is possible to obtain far more displacement point positions than the number of units.

In addition, an actuator unit that generates the minimum displacement amount of the piezoelectric actuator, and 21.22 of this unit, ~
．． By configuring the actuator unit to generate a displacement amount of 2n times, it is possible to control the displacement amount according to an integral multiple of the minimum displacement amount, and effective displacement control can be performed.

[Embodiments of the invention]

Hereinafter, details of the present invention will be explained with reference to illustrated embodiments.

FIG. 1 is a schematic configuration diagram showing a displacement generating device according to an embodiment of the present invention. This device basically consists of a piezoelectric actuator IQ- and a drive circuit 40 that drives it. The piezoelectric actuator 10 is a piezoelectric plate subjected to polarization treatment (for example, T-96, 10 manufactured by Toshiba Ceramic).
The first to sixth actuator units 21, 26, each having 1°2.4.8.16.32 sheets of φ) laminated
It consists of That is, the first to sixth units 2
1, ~. 26 are stacked in series along the displacement direction, and spacers 31, 35 made of an insulator are inserted between each unit 21, 26, respectively. In addition,
In the figure, the unit and the spacer are shown separated for clarity.

Each of the units 21 to 26 is similar to a known longitudinal effect W4-layer actuator, and generates a displacement proportional to the number of layers stacked in accordance with the applied voltage.

On the other hand, the drive circuit U includes a displacement setter 51° A/D converter 5
2 and the first to sixth drivers 61, -. It consists of 66. The displacement setter 51 generates an analog signal according to a desired amount of displacement, and its output is supplied to the A/D converter 52. The A/D converter 52 converts the input analog signal into a 6-bit digital signal. This 6-bit digital signal becomes the drive signal. That is, among each output bit of the A/D converter 52,
The output of the first bit (LSB) is supplied to a first driver 61 made of one layer, and this driver 61 drives the first unit 21. The output of the second bit is supplied to a second driver 62, which is a two-layer stack, and this driver 62 drives the second unit 22. Similarly, the output of the 3rd bit is sent to the third driver 63 of 4 layers, the output of the 4th bit is sent to the 4th driver 64 of 8 layers, and the output of the 5th bit is sent to the 5th driver 64 of 16 layers. The output of the 6th bit of the driver 65 is supplied to a sixth driver 66 of 32 laminated layers, and these drivers 63, . unit 2 by 66
3, . . . , 26 are driven, respectively. As a result, the first to sixth units are selectively turned on and off according to the setting value of the displacement setting device 51, and the amount of displacement of the piezoelectric actuator is controlled.

・In addition, switching circuits are used as the drivers 61 to 66, and when the input signal is 0'°, the output is O[V],
The output was set to 500 [V] when the input signal was 1''.

With such a configuration, the first to sixth units 61 to 66 can be selectively turned on and off according to the displacement setting signal.
F-driven, displacement control can be performed with a 6-bit resolution and without hysteresis with respect to the displacement setting signal as shown in FIG. That is, when the displacement setting signal is "1", only the first unit 21 is driven, when the displacement setting signal is "2", only the second unit 22 is driven, and when the displacement setting signal is "3", only the second unit 22 is driven. In this case, the first and second units 21 and 22 are driven, and it becomes possible to perform displacement control based on an integral multiple of the minimum displacement amount of the first unit 21.

As described above, according to this embodiment, the influence of hysteresis of the piezoelectric actuator can be eliminated, and the reproducibility of displacement positions can be improved. Moreover, six units 21,
Even though only ~, 26 and the driver 61°~, 66 are used, 63 displacements, which are integral multiples of the displacement m (minimum displacement) of the first unit 21, are possible, making it extremely suitable for minute displacement control. It is valid. Further, a sensor for measuring the amount of displacement of the piezoelectric actuator is not necessary, and there is an advantage that the displacement control described above can be performed with simple control.

FIG. 3 is a schematic configuration diagram showing another embodiment.

Note that the same parts as in FIG. 1 are given the same reference numerals, and detailed explanation thereof will be omitted.

This embodiment differs from the previously described embodiments in that a bimorph actuator is used as the piezoelectric actuator. That is, the piezoelectric actuator U is a known bimorph type actuator, and includes two piezoelectric plates 91.9.
A common electrode 80 sandwiched between the two electrodes is used as a ground, and divided electrodes 81a, 81b, . . . , 86a, 86b are attached to both outer ends. The divided electrode has a displacement of 2°4.8, with the smallest displacement, that is, the shortest part of the electrode, being 1.
．． 16.32 times, that is, the length of the division type t is J
Six units were constructed as T, 2.2 and 4.4f'i times. The output of the driver was O[V] when the input was O'', and 15[V] when the input was ``1''.

Even with such a configuration, the six actuator units are selectively driven ON and OFF according to the displacement setting signal, and the displacement M'm without hysteresis can be performed. Therefore, the same roofing effect as in the previous embodiment can be obtained.

Note that the present invention is not limited to the embodiments described above. For example, as the piezoelectric actuator, it is also possible to use a sliding laminated actuator. Further, the number of units is not limited to 6al in any way, and can be changed as appropriate according to specifications. Furthermore, the number of piezoelectric elements that make up the unit that generates the minimum displacement is 11.
The number is not limited to Il, and may be a plurality of numbers. In addition, various modifications can be made without departing from the gist of the present invention.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram showing a displacement generating device according to an embodiment of the present invention, Fig. 2 is a characteristic diagram showing displacement amount changes in response to a displacement setting signal in the above device, and Fig. 3 shows another embodiment. FIG. 4 is a characteristic diagram for explaining the conventional problems. LCL, LQ-...piezoelectric actuator, 21. ~
. 26... Actuator unit, 40... Drive circuit, 51... Displacement setter, 52... A/D conversion MI
! device, 61°~, 66... driver, 8o... common electrode, 81a. 8 l b, ~, 86a, 86b... divided electrode, 9
1°92...Piezoelectric plate. To Applicant's Representative Patent Attorney Takehiko Suzue 21 Figure 1 OV12 V 1t'#I Electric Box Figure 2

Claims (3)

[Claims] (1) A piezoelectric actuator consisting of a piezoelectric element that expands and contracts according to an applied voltage, and in which a plurality of actuator units with different displacement amounts are connected in series with their displacement directions aligned, and the actuator units are selectively operated.
1. A displacement generating device comprising: a drive circuit for N-OFF driving. (2) The piezoelectric actuator has an actuator unit that generates the minimum displacement and a displacement that is 2^1, 2^2, ~, 2^n (n is a positive integer) times the displacement of this unit. 2. The displacement generating device according to claim 1, further comprising an actuator unit. (3) The drive circuit includes an A/D converter and a driver that selectively drives the actuator unit according to each bit output of the A/D converter, and each actuator unit has a displacement amount of Above A/ in descending order
3. The displacement generating device according to claim 2, wherein the displacement generating device is driven by each bit output in the direction from the lower bit to the upper bit of the D converter.