Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2000-07-10
2003-03-25
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S328000
Reexamination Certificate
active
06538362
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, it is desirable to realize a displacement element that makes it possible to adjust an optical path length and position in an order of submicron, for example, in the fields of optics, magnetic recording, and precision machining. The development for such a displacement element is advanced and is based on the use of the displacement brought about by an inverse piezoelectric effect or an electrostrictive effect caused when a voltage is applied to a piezoelectric/electrostrictive material (for example, a ferroelectric material).
As shown in
FIG. 44
, 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 the fixation and movable sections. The displacement element is 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 (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 a circular arc-shaped displacement or a 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, a highly accurate positioning is performed at a high speed. This patent document (especially in
FIG. 4
) discloses a structure 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 expansion and contraction of the piezoelectric/electrostrictive material (i.e., in the inplane 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 a 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 a filler material having flexibility is supplied to a hole included in the device. However, it is clear that a decreased amount of displacement resulting from the inverse piezoelectric effect or the electrostrictive effect remains in effect, even when the filler material is supplied to the above-mentioned hole.
On the other hand, FIG. 4 in Japanese Laid-Open Patent Publication No. 63-64640 resides in the junction of a mediating member and a bimorph in which the mediating member is joined with the portion at which no divided electrode exists. The effect of the divided electrode cannot be utilized at the joined portion. That is, the junction is merely made at the bimorph portion which is not the displacement-generating section. A similar form is adopted for the junction of the head and the bimorph.
As a result, the following structure is brought about. That is, a bending displacement of the bimorph is expressed toward an internal space between the mediating member and the head. Therefore, it is impossible to effectively displace the head itself with respect to the external space.
In many cases, the conventional devices of this type have such a structure rendering it difficult to realize a high resonance frequency required for a high speed operation, or such devices have such a structure rendering it impossible to increase the displacement of the movable section. Consequently, the following contradicting structure is obtained. That is, whenever a high resonance frequency is desired, the displacement amount of the movable section is sacrificed. On the other hand, whenever the displacement amount of the movable section is increased, it is impossible 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. An object of the present invention 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 vibrations during its operation. Another object is to provide a device capable of achieving a high speed response with a high mechanical strength while being excellent in handling performance, shock resistance, and moisture resistance. A further object is to provide a device wherein a movable section can be greatly displaced with a high speed of the displacement action and thus, realizing a high resonance frequency. Yet another object is to provide a sensor element which makes it possible to accurately detect a 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 is arranged on at least one of the thin plate sections. A hole is formed by the inner walls of the pair of thin plate sections, an inner wall of the movable section, and an inner wall of the fixation section. The movable section has a cutout portion. It is also preferable that the cutout portion includes a hollow section and/or a through-hole provided for the movable section.
Accordingly, the movable section is allowed to have a light weight owing to the presence of the cutout. Therefore, it is possible to increase the resonance frequency without decreasing the displacement amount of the movable section. Further, it is possible to appropriately decrease the rigidity of the movable section. Therefore, an advantage is obtained such that the displacement amount of the movable section can be increased. When the thin plate section, the movable section, and the fixation section are integrated into one unit, it is unnecessary to construct all parts with the piezoelectric/electrostrictive material which is a fragile material having a relatively heavy weight. Therefore, an advantage is obtained such that the mechanical strength is high while being excellent in handling performance, shock resistance, and moisture resistance, and the operation is scarcely affected by harmful vibration (
Kimura Koji
Nanataki Tsutomu
Takeuchi Yukihisa
Burr & Brown
Dougherty Thomas M.
NGK Insulators Ltd.
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