Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2000-09-27
2002-09-24
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
Reexamination Certificate
active
06455984
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a piezoelectric/electrostrictive device that 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 that 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 invention relates to a piezoelectric/electrostrictive device that is excellent in strength, shock resistance, and moisture resistance and that makes it possible to efficiently operate a movable section to a great extent, and a method for producing the same.
2. Background of the Invention
Recently, a displacement element, which makes it possible to adjust the optical path length and the position in an order of submicron, is demanded, for example, in the fields of optics, magnetic recording, and precision machining. Development is advanced for the displacement element based on the use of the 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. 26
, for example, those hitherto disclosed as such a displacement element include a piezoelectric actuator comprising a fixing section
204
, a movable section
206
, and a beam section
208
for supporting the fixing and movable sections, which are formed integrally 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 fixing 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, the electrodes of the bimorph actuator are provided in a divided manner. The actuator is driven by selecting the divided electrodes, and thus highly accurate positioning is performed at a high speed. JP '640 discloses a structure (especially in
FIG. 4
) in which, for example, two opposed bimorphs are used.
However, the piezoelectric actuator described above involves a problem that the amount of operation of the movable section
206
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
200
) is transmitted to the movable section
206
as it is.
Since all the parts of the piezoelectric actuator are made of piezoelectric/electrostrictive materials, which are fragile materials having a relatively heavy weight, the mechanical strength is low, and the piezoelectric actuator is inferior in handling performance, shock resistance, and moisture resistance. Furthermore, 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).
Then, a method may be proposed which increases the strength and the resonant frequency by thickening a beam portion, for example, in order to improve stiffness. However, displacement and a response speed are significantly deteriorated due to the improvement of stiffness.
Further, the following structure is disclosed in FIG. 4 in Japanese Laid-Open Patent Publication No. 63-64640, a joined form exists between a mediating member and a bimorph and between a head and the bimorph (i.e., so-called piezoelectric operating sections, both of which cause the strain). In other words, the bimorph is formed contiuously 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 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 external forces in many situations. A problem arises in that it is difficult to handle the device and to achieve the realization of a high resonance frequency.
SUMMARY OF THE INVENTION
The present invention has been made taking the foregoing problems into consideration, and an object thereof is to provide a piezoelectric/electrostrictive device and a method for manufacturing the same. According to the piezoelectric/electrostrictive device of the present invention, it is possible to obtain a displacement element that is easy in handling, high in shock resistance against external forces without deteriorating the device characteristics such as the displacement characteristic and the response characteristic, and scarcely affected by harmful vibration, and that is capable of large displacement and high speed response with high mechanical strength while being excellent in moisture resistance, as well as a sensor element that makes it possible to accurately detect vibration of the movable section.
Further, an object of the present invention is to provide a piezoelectric/electrostrictive device and a method for manufacturing the same which can suppress occurrence of problems caused by unnecessary vibrations during its manufacture and improve the productivity of manufacturing the piezoelectric/electrostrictive device.
According to the present invention, a piezoelectric/electrostrictive device has a pair of mutually opposing thin plate sections, a movable section, and a fixing section for supporting the thin plate sections and the movable section, the piezoelectric/electrostrictive device includes:one or more piezoelectric/electrostrictive elements arranged on at least one thin plate section of the pair of thin plate sections, and
a hole is 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 fixing section.
A mechanism is provided for restricting amplitude of the thin plate sections. Thus, when the external force is applied to the thin plate section and the movable section, which causes their large vibration (amplitude), the mechanism can restrict the vibration (amplitude) of the thin plate section. As a result, it can prevent the thin plate section from being damaged. In this case, the thin plate section does not need to be thickened. Therefore, material characteristics of the piezoelectric/electrostrictive element provided on the thin plate section are not deteriorated, which does not correspondingly deteriorate device characteristics such as the displacement characteristic and the response characteristic.
In other words, the present invention can provide a displacement element that is easy in handling, high in shock resistance against the external force without deteriorating the device characteristics such as the displacement characteristic and the response characteristic, and is scarcely affected by harmful vibration, and that is capable of a large displacement and high speed response with high mechanical strength while being excellent in moisture resistance, as well as a sensor element that makes it possible to accurately detect vibration of the mova
Kimura Koji
Namerikawa Masahiko
Nanataki Tsutomu
Shibata Kazuyoshi
Takeuchi Yukihisa
Burr & Brown
Dougherty Thomas M.
NGK Insulators Ltd.
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