Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2002-02-05
2002-11-05
Sircus, Brian (Department: 2839)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
Reexamination Certificate
active
06476538
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 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. 41
, 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 the 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
206
is small, because the displacement in the direction of expansion 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.
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
202
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.
Further, the actuator described in Japanese Laid-Open Patent Publication No. 63-64640 has such a structure that the bimorph itself is composed of two piezoelectric elements which are laminated with each other, in addition to the fact that the bimorph is stuck to a fixation member or a mediating member. Therefore, the stress tends to remain, resulting from, for example, the curing and the shrinkage of an adhesive and the heating treatment required for the sticking and the lamination. It is feared that the displacement action is disturbed by the internal residual stress, and it is impossible to realize the displacement and the resonance frequency as designed. Especially, when the actuator is small in size, the influence of the adhesive is increased by itself.
Accordingly, a method is conceived in order to exclude the influence of the adhesive required to effect the sticking, in which the actuator is composed of, for example, an integrated sintered product made of ceramics to give a structure in which no adhesive is used. However, also in this case, it is inevitably feared that the internal residual stress arises due to the difference in behavior of thermal shrinkage between respective members during the sintering.
Further, when the actuator is small in size, a problem is involved such that the fixation property of the actuator and the attachment property of the actuator to another part are deficient.
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 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 realize a light weight of the device, especially a light weight of a movable section or a fixation section, and improve the handling performance of the device and the attachment performance for parts to be attached to the movable section or the fixation performance of the device, so that the movable section may be greatly displaced at a relatively low voltage, and it is possible to achieve a high speed of the displacement action of the device, especially of the movable section (realization of a high resonance frequency), as well as a sensor element which 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 and a fixation section for supporting the thin plate sections; movable sections provided at forward end portions of the pair of thin plate sections; and one or more piezoelectric/electrostrictive elements arranged on at least one thin plate section of the pair of thin plate sections; wherein any one of the movable sections and the fixation section has mutually opposing end surfaces; and a distance between the end surfaces is not less than a length of the movable section.
The movable section, the fixation section, and the thin plate section may be made of ceramics or metal. Alternatively, each of the components may be made of a ceramic material, or each of them may be made of a metal material. Further, each of the components may be constructed to have a hybrid structure obtained by combining those produced from materials of ceramics and metal.
It is also preferable that any one of the movable section and the fixation section is provided with a cutoff section; and a part of the cutoff section constitutes the mutually opposing end surfaces. It is also preferable that the thin plate section, the movable section, and the fixation section are composed of a ceramic substrate integrated into one unit by co-firing a ceramic green laminate and cutting off unnecessary portions. It is
Ikeda Koji
Kimura Koji
Nanataki Tsutomu
Shibata Kazuyoshi
Takeuchi Yukihisa
Burr & Brown
NGK Insulators Ltd.
Sircus Brian
Zarroli Michael C.
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