JPH0556114B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a piezoelectric actuator that is coupled to and drives an external mechanism, and particularly relates to a piezoelectric actuator that is suitable for a minute displacement generating mechanism.

[Conventional technology]

Piezoelectric actuators are used in various fields as actuators for minute displacement. Especially μm
Piezoelectric actuators are mostly used in actuators for fine positioning mechanisms such as semiconductor integrated circuit manufacturing equipment and electron microscopes that require order adjustment. Hereinafter, an example of the use of such a piezoelectric actuator will be explained with reference to the drawings.

Figures 3a and 3b are side views of the fine positioning device. In each figure, 10, 11, and 12 are rigid body parts located on the left, right, and center of the figure, respectively. 16a,1
6a' is a flat parallel flexible beam that is formed between the rigid body parts 10, 12 and is parallel to each other, and 16b, 16b' is a parallel flexible beam that is formed between the rigid body parts 11, 12, respectively. It is a flat parallel flexible beam that is formed integrally with these and parallel to each other. 17a and 17b are parallel flexible beams 16a and 16a' and parallel flexible beam 16, respectively.
16b and 16b' and the through holes formed to integrally mold each rigid body part are shown. 18a is a protrusion that protrudes from the rigid body part 10 into the through hole 17a, and _18c1 is the rigid body part 12.
These projecting parts 18a and _18c1 overlap each other with a gap in the vertical direction of the figure. Similarly, 18
b is a protrusion that protrudes from the rigid body part 11 to the through hole 17b, _18c2 is a protrusion that protrudes from the rigid body part 12 to the through hole 17b, and these protrusions 18b, 18c ₁
are in the same relationship as the protrusions 18a and _18c1 .
19a is a piezoelectric actuator in which piezoelectric elements are laminated, which is fixed between the protruding part 18a and the protruding part _18c1 , and 19b is the same piezoelectric actuator as the piezoelectric actuator 19a fixed between the protruding part 18b and the protruding part _18c2 . be. Piezoelectric actuator 1
A piezoelectric actuator 9a generates a force in a direction perpendicular to the planes of the parallel flexible beams 16a and 16a', causing bending deformation in them, and a piezoelectric actuator 19b generates a force in a direction perpendicular to the planes of the parallel flexible beams 16b and 16b'. occurs, causing bending deformation in them. The magnitude of the force generated in these piezoelectric actuators 19a, 19b is controlled by a voltage applied to the piezoelectric actuators 19a, 19b by a device (not shown). 20 is another rigid structure that rigidly connects the rigid parts 10 and 11 to each other.

In such a fine positioning device, when a voltage of an arbitrary value is applied to the piezoelectric actuators 19a, 19b, the piezoelectric actuators 19a, 19b
expands in the direction of the arrow shown in FIG. 3b in response to the voltage, thereby generating a force f. As a result, the rigid body part 12 has parallel flexible beams 16a, 16a', 16b,
16b' is deflected and pushed up, and is displaced by a value ε from the state shown in FIG. 3a. Therefore, if an object to be processed is placed on the rigid body portion 12, it can be finely positioned as desired by applying an arbitrary voltage to the piezoelectric actuators 19a and 19b.

When applying a piezoelectric actuator not only to the above-mentioned fine positioning device but also to various other devices, it is necessary to attach and fix the piezoelectric actuator to a predetermined position of these devices. However, since the piezoelectric element is made of ceramic material, it is difficult to form screw holes for attaching it to an external mechanism. For this reason, an auxiliary member for attachment has been used in the piezoelectric actuator. This will be explained with reference to FIG.

FIG. 4 is a sectional view of a conventional piezoelectric actuator. In the figure, 21 is a laminated piezoelectric element, and 22 is a casing with an open side surface that fixes the piezoelectric element 21 at its bottom. The casing 22 has a screw hole 22a for connection with an external structure and a through hole 22b for passing a lead wire therethrough. 23 is a mounting member for mounting the piezoelectric element 21 to an external structure, and has a screw hole 23a for mounting. 24 is a piezoelectric element 21
This is an adhesive layer that fixes the mounting member 23 to the mounting member 23. Note that X and Y indicate coordinate axes.

The casing 22 is fixed to an external mechanism (for example, the protrusion 18a of the above-mentioned fine positioning device) using its screw hole 22a, and the mounting member 23 is fixed to an external mechanism (also the protrusion 18) using its screw hole 23a.
c ₁ ), the piezoelectric actuator is attached to the target device. When a voltage is applied to the piezoelectric element 21 via the lead wire, the piezoelectric element 21 expands or contracts in the X-axis direction, causing a displacement in the attached external mechanism.

The piezoelectric element 21 is mounted by the above-mentioned mounting means.
The piezoelectric element 21 is attached to a predetermined portion of the object to be driven and generates a displacement according to the voltage, but there is no proportional relationship between the voltage applied to the piezoelectric element 21 and the amount of displacement. This is shown in FIG.

FIG. 5 is a characteristic diagram of the piezoelectric element. In the figure, the horizontal axis represents voltage, and the vertical axis represents displacement. As is clear from the figure, the voltage and the amount of displacement are not in a proportional relationship and there is a hysteresis characteristic. In order to maintain displacement accuracy, it is necessary to compensate for the above hysteresis characteristic.

In conventional devices, the following means, for example, have been adopted as this compensation means. That is, the above-mentioned hysteresis characteristic is compensated by feedback control in which the amount of displacement of the displacement part of the piezoelectric actuator to be driven is detected using a known laser length measuring device, and the applied voltage is corrected based on the deviation between this detected value and the displacement target value. I was worried.

[Problems to be Solved by the Invention] However, such compensation means requires a measuring device that detects minute displacements, such as a laser length measuring device, which not only increases the size of the device, but also makes it difficult to use each device. Attaching measuring instruments to drive targets of different shapes, sizes, installation locations, etc. requires a great deal of effort and time to properly mount them, which has been a major hurdle in terms of versatility and cost reduction.

SUMMARY OF THE INVENTION An object of the present invention is to provide a piezoelectric actuator that solves the problems of the prior art described above and can easily compensate for hysteresis characteristics.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a piezoelectric actuator including a piezoelectric element that is displaced in a main displacement direction when a voltage is applied, which is attached to an external mechanism, and a casing that houses the piezoelectric element and has an opening in the main displacement direction of the piezoelectric element; a mounting member that is fixed to the opening side end of the piezoelectric element to which an external mechanism is attached; and a mounting member that is connected to the casing. The invention is characterized in that it is provided with an elastic mechanism that is attached at a symmetrical position between the piezoelectric elements and has low rigidity only in the main displacement direction of the piezoelectric element, and a detection means that detects the amount of deformation of the deformation part in this elastic mechanism. .

[Effect]

When a voltage is applied to the piezoelectric element, its expansion and contraction displacement is transmitted to the external mechanism while bending the elastic mechanism, which has low rigidity in the direction of this displacement. The detection means detects the amount of deflection caused by the deflection beam deformation, and outputs a signal proportional to the deflection amount. Since this signal is proportional to the amount of displacement, it is used as a feedback signal.

〔Example〕

Hereinafter, the present invention will be explained based on illustrated embodiments.

FIG. 1 is a sectional view of a piezoelectric actuator according to an embodiment of the present invention. In the figure, parts that are the same as those shown in FIG. 4 are given the same reference numerals, and description thereof will be omitted.
25 is an elastic member that connects the upper end of the casing 22 and the mounting member 23. This elastic member 25 is made of a flat metal material that is thin in the X-axis direction. Therefore, it has low rigidity and easily bends against forces in the X-axis direction, but exhibits high rigidity against forces and moments in other directions, making it difficult to deform. 26 is a strain gauge affixed to an appropriate position on the elastic member 25.

Next, the operation of this embodiment will be explained. Now, when a voltage is applied to the piezoelectric element 21, the piezoelectric element 21
Stretch (or contract) in the axial direction. Due to this expansion (or contraction), the elastic member 25 is easily bent and pushes up (down) the mounting member 23. That is, piezoelectric element 2
The displacement of 1 is transmitted to the external mechanism via the deflection deformation of the elastic member 25. In this case, the force generated by the piezoelectric element 21 is large, and the rigidity of the elastic member 25 in the X-axis direction is sufficiently small, so the amount of displacement transmitted does not decrease appreciably, and the amount of displacement of the piezoelectric element 21 It is transmitted almost as is. When the elastic member 25 undergoes flexural deformation, the strain gauge 26 is strained in proportion to the flexural deformation, and its resistance value changes accordingly. Therefore, if we extract this change in resistance value as an electrical signal, we can obtain the amount of displacement.
By performing feedback control using this signal, it is possible to compensate for the hysteresis characteristic of the piezoelectric element 21 and obtain highly accurate displacement. Moreover, since the elastic members are provided at symmetrical positions,
There is no deviation in displacement when the piezoelectric element is displaced, and highly accurate displacement can be performed.
Along with this, the accuracy of detecting the amount of displacement also increases. Note that the presence of the elastic member 25 sufficiently protects the piezoelectric element 21 from external forces.

FIG. 2 is a sectional view of a piezoelectric actuator according to another embodiment of the invention. In the figure, parts that are the same as those shown in FIG. 4 are given the same reference numerals, and description thereof will be omitted. 27a Upper end of casing 22 and mounting member 23
It is a parallel flexible beam structure installed between the The parallel flexible beam structure 27a includes a rigid section 28a connected to the upper end of the casing 22, and a rigid section 28a.
It is composed of parallel flat plate-shaped flexible beams 29a and 29a' that connect the mounting member 23 and the mounting member 23. The parallel flexible beam structure 27b is also the parallel flexible beam structure 27a.
The structure is similar to that of the first embodiment, and is composed of a rigid part 28b and parallel flexible beams 29b and 29b'. 3
0 is a strain gauge attached to the deflection beam 29a.

Such parallel flexible beam structures 27a and 27b have low rigidity against forces in the X-axis direction and are easily displaced, but exhibit extremely high rigidity against forces and moments in other directions and hardly deform. As in the previous embodiment, the amount of displacement of the piezoelectric element 21 is directly transmitted to the external structure.

When a voltage is applied to the piezoelectric element 21, the piezoelectric element 21 expands (or contracts) in the X-axis direction, the parallel flexible beam structures 27a and 27b are displaced accordingly, and this displacement is transmitted to the external mechanism. At this time, the flexible beam 29a is connected to the other flexible beams 29a', 29b, 29
According to this deflection, strain occurs in the strain gauge 30, and its resistance value changes. Therefore, as in the previous embodiment, by extracting this as an electrical signal and performing feedback control using this signal, the hysteresis characteristic of the piezoelectric element 21 can be compensated for and highly accurate displacement can be obtained. Moreover, as in the previous embodiment, since the elastic members are provided at symmetrical positions, there is no deviation in displacement when the piezoelectric element is displaced.
Displacement can be performed with high precision, and along with this, the detection precision of the amount of displacement also increases. Note that due to the intervention of the parallel deflection beam structures 27a and 27b, the piezoelectric element
1 is well protected from external forces.

In addition, in the description of each of the above embodiments, the casing,
Although an example has been described in which the mounting member and the elastic mechanism (elastic member, parallel flexible beam structure) are configured separately, these can be integrally formed by electric discharge machining or the like. Further, the piezoelectric element does not necessarily need to be adhesively fixed to the casing and the mounting member, and may be simply held down by the elastic force of the elastic mechanism.

[Effects of the Invention] As described above, in the present invention, an elastic mechanism having low rigidity only in the same direction as the expansion and contraction direction of the piezoelectric element is provided between the upper end of the casing and the mounting member, and the elastic mechanism is Since the deformation part is equipped with a detection means for detecting the amount of deformation, it is possible to easily compensate for the hysteresis characteristics of the piezoelectric element without using a separate measuring device, thereby realizing versatility and cost reduction. can do. Furthermore, since the elastic members are provided at symmetrical positions, there is no deviation in displacement when the piezoelectric element is displaced, and highly accurate displacement can be achieved, which also improves the detection accuracy of the displacement amount. It gets expensive.

[Brief explanation of the drawing]

FIGS. 1 and 2 are sectional views of piezoelectric actuators according to embodiments of the present invention, and FIGS.
4b is a side view of the fine positioning device, FIG. 4 is a sectional view of a conventional piezoelectric actuator, and FIG. 5 is a characteristic diagram of the piezoelectric element. 21...Piezoelectric element, 22...Casing, 23
...Mounting member, 25...Elastic member, 26, 30...
...Strain gauge, 27a, 27b...Parallel deflection beam structure.

Claims (1)

[Scope of Claims] 1. A piezoelectric actuator equipped with a piezoelectric element that is displaced in a main displacement direction when a voltage is applied, which is attached to an external mechanism, houses the piezoelectric element, and moves the piezoelectric element in the main displacement direction. a casing having an opening at the opening, a mounting member fixed to the open end of the piezoelectric element to which an external mechanism is attached, and a mounting member mounted at a symmetrical position between the mounting member and the casing, the main displacement of the piezoelectric element being A piezoelectric actuator comprising: an elastic mechanism having low rigidity only in one direction; and a detection means for detecting the amount of deformation of a deformable portion of the elastic mechanism. 2. The piezoelectric actuator according to claim 1, wherein the elastic mechanism is constituted by a flat plate having a thin thickness in the main displacement direction. 3. The piezoelectric actuator according to claim 1, wherein the elastic mechanism is a parallel flexible beam structure having a main deflection direction in the same direction as the main displacement direction.