Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2000-04-06
2002-06-11
Sircus, Brian (Department: 2839)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S330000, C310S324000, C310S367000
Reexamination Certificate
active
06404109
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a piezoelectric/electrostrictive device which is provided with a movable section to be operated on the basis of a displacement action of a piezoelectric/electrostrictive element, or a piezoelectric/electrostrictive device which is capable of detecting displacement of a movable section by the aid of a piezoelectric/electrostrictive element, and a method for producing the same. In particular, the present invention relates to a piezoelectric/electrostrictive device which is excellent in strength, shock resistance, and moisture resistance and which makes it possible to efficiently operate a movable section to a great extent, and a method for producing the same.
2. Description of the Related Art
Recently, a displacement element, which makes it possible to adjust optical path length and position on the order of submicrons, is required, for example, in the fields of optics, magnetic recording, and precision machining. Development has advanced for displacement elements based on the use of displacement brought about by the inverse piezoelectric effect or the electrostrictive effect caused when a voltage is applied to a piezoelectric/electrostrictive material (for example, a ferroelectric material).
As shown in
FIG. 32
, for example, those hitherto disclosed as such a displacement element include a piezoelectric actuator comprising a fixation section
204
, a movable section
206
, and a beam section
208
for supporting them which are formed in an integrated manner with a hole
202
provided through a plate-shaped member
200
composed of a piezoelectric/electrostrictive material and with an electrode layer
210
provided on the beam section
208
(see, for example, Japanese Laid-Open Patent Publication No. 10-136665).
The piezoelectric actuator is operated such that when a voltage is applied to the electrode layer
210
, the beam section
208
makes expansion and contraction in a direction along a line obtained by connecting the fixation section
204
and the movable section
206
in accordance with the inverse piezoelectric effect or the electrostrictive effect. Therefore, the movable section
206
can perform circular arc-shaped displacement or rotational displacement in the plane of the plate-shaped member
200
.
On the other hand, Japanese Laid-Open Patent Publication No. 63-64640 discloses a technique in relation to an actuator based on the use of a bimorph. In this technique, electrodes for the bimorph are provided in a divided manner. The actuator is driven due to the selection of the divided electrodes, and thus highly accurate positioning is performed at a high speed. This patent document discloses a structure especially in
FIG. 4
in which, for example, two bimorphs are used in an opposed manner.
However, the piezoelectric actuator described above involves such a problem that the amount of operation of the movable section is small, because the displacement in the direction of extension and contraction of the piezoelectric/electrostrictive material (i.e., in the in-plane direction of the plate-shaped member) is transmitted to the movable section as it is.
All of the parts of the piezoelectric actuator are made of the piezoelectric/electrostrictive material which is a fragile material having a relatively heavy weight. Therefore, the following problems arise. That is, the mechanical strength is low, and the piezoelectric actuator is inferior in handling performance, shock resistance, and moisture resistance. Further, the piezoelectric actuator itself is heavy, and its operation tends to be affected by harmful vibrations (for example, residual vibration and noise vibration during high speed operation).
In order to solve the problems described above, it has been suggested that the hole is filled with a filler material having flexibility. However, it is clear that the amount of displacement, which is brought about by the inverse piezoelectric effect or the electrostrictive effect, is decreased even when the filler material is used.
On the other hand, the following structure is disclosed in
FIG. 4
in Japanese Laid-Open Patent Publication No. 63-64640. That is, in a joined form between a mediating member and a bimorph and between a head and the bimorph, so-called piezoelectric operating sections, both of which cause the strain, extend over respective joined portions. In other words, the bimorph is formed continuously ranging from the mediating member to the head.
As a result, when the bimorph is operated, the displacement action, which is effected with the supporting point of the joined portion between the mediating member and the bimorph, mutually interferes with the displacement action which is effected with the supporting point of the joined point between the head and the bimorph. The expression of the displacement is inhibited. In this structure, it is impossible to obtain such a function that the head is greatly displaced with respect to the external space.
The conventional device of this type has a structure which is weak against the external force in many cases. A problem arises in that it is difficult to contemplate the realization of a high resonance frequency.
SUMMARY OF THE INVENTION
The present invention has been made taking the foregoing problems into consideration, an object of which is to provide a piezoelectric/electrostrictive device and a method for producing the same which make it possible to obtain a displacement element that is scarcely affected by harmful vibration during operation and capable of high speed response with high mechanical strength while being excellent in handling performance, shock resistance, and moisture resistance, making it possible to enhance the strength against the external force, easily achieve the realization of a high resonance frequency, and increase the displacement amount of a movable section, as well as a sensor element that makes it possible to accurately detect vibration of the movable section.
According to the present invention, there is provided a piezoelectric/electrostrictive device comprising a pair of mutually opposing thin plate sections, a movable section, and a fixation section for supporting the thin plate sections and the movable section; one or more piezoelectric/electrostrictive elements arranged on at least one thin plate section of the pair of thin plate sections; and a hole formed by both inner walls of the pair of thin plate sections, an inner wall of the movable section, and an inner wall of the fixation section; wherein at least a part of at least one thin plate section of the pair of thin plate sections is previously bent in a direction to make mutual separation.
According to another aspect of the present invention, there is provided a piezoelectric/electrostrictive device as described above, wherein at least parts of the pair of thin plate sections are previously bent in directions to make mutual separation. In this arrangement, it is also preferable that at least the part of at least one thin plate section of the pair of thin plate sections, or at least the parts of the pair of thin plate sections are previously bent outwardly in convex configurations.
Usually, the movable section cannot be operated exceeding the resonance frequency of the vibration of the thin plate section (bending displacement action of the thin plate section brought about by the application of the voltage to the piezoelectric/electrostrictive element). In order to realize the high speed displacement action of the movable section, it is effective that the rigidity of the thin plate section is increased, and the resonance frequency of the vibration itself of the thin plate section is increased.
In the present invention, at least the part of at least one thin plate section of the pair of thin plate sections, or at least the parts of the pair of thin plate sections are previously bent in the directions to make separation from each other to give the outwardly convex configuration. Therefore, high rigidity is exhibited for the vibration (bending displac
Kimura Koji
Nanataki Tsutomu
Takeuchi Yukihisa
Burr & Brown
NGK Insulators Ltd.
Sircus Brian
Zarroli Michael C.
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