Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2000-05-11
2002-06-25
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S328000, C310S323160
Reexamination Certificate
active
06411010
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a piezoelectric actuator in which at least one-directional movement of a moving body is facilitated, and which can insure high movement conversion efficiency even when miniaturized.
2. Background Information
FIG. 7
is a perspective drawing showing an example of a piezoelectric actuator of the related art. This piezoelectric actuator
300
is used as an XY stage for movement over a microscopic distance, and movement in each axial direction is realized by stacked piezoelectric elements. A metal plate is punched by wire discharge or die processing on an anchor block and a movable table
303
is placed inside the punched out part
302
. Respective support springs
304
are formed on the four edges of the movable table
303
and guide sections
305
are attached to the four edges of the movable table
303
through the support springs
304
. Also, stacked piezoelectric elements
306
are attached to ends of the guide sections at right angles to the movable table
306
.
An enlarged plan view of a support spring
304
is shown in FIG.
8
. This support spring
304
is formed as a rectangular frame, and a long edge
304
a
is thin while a short edge
304
b
is thick. This is because by making the long edge
304
a
long and thin, stress for a given amount of displacement is lowered exponentially or linearly so that the structure of the movable table
303
connected through the support springs
304
has a degree of freedom with respect to movement in an X axis direction in the drawings, which is the width direction of the long edge
304
a
. As shown in
FIG. 9
, in the case where the width of the support spring is a and the thickness is b, an aspect ratio (b/a) is set to at least 1 and twisting displacement is suppressed when the movable table
303
is moved.
When this piezoelectric actuator
300
is moved in the X axis direction, a fixed voltage is applied to the stacked piezoelectric elements
306
a
for X direction movement to cause displacement. If the stacked piezoelectric elements
306
a
are displaced in the thickness direction, the movable table
303
connected by the guide sections
305
a
is joined and moves in the X direction. At this time, support springs
304
formed on the X direction edges move in the direction of the short edge. Also, X direction guide sections
305
a
function to guide the movable table
303
in the X direction. On the other hand, support springs
304
formed on the Y direction edges have difficulty moving in the direction of the long edge and so it is difficult to absorb displacement of the stacked piezoelectric elements
306
a
. The same also applies to movement in the Y direction.
However, with the above described piezoelectric actuator
300
of the related art, since stacked piezoelectric elements
306
are generally used it is necessary to first of all form the stacked piezoelectric elements
306
so as to satisfy relevant standards. The stacked piezoelectric elements
306
are generally manufactured using a green sheet method employing a green sheet made from a piezoelectric slurry. After conductive paste for internal electrodes has been screen printed on green sheets, a specified number of the green sheets are laminated and baked. Characteristics of a stacked piezoelectric element formed in this way are that strong generated force is obtained, but displacement is microscopic. The thus formed stacked piezoelectric element is fitted between a guide section
305
and a fixed table
301
, and joining and complicated adjustment steps are necessary. This means that the manufacture of the XY stage for movement and the piezoelectric actuator
300
are difficult and complicated, and with increased amount of movement of the movable table
303
it is necessary to provide support points between the guide sections
305
and the fixed table
301
and to provided an enlarged cantilever. As a result, a correspondingly complicated structure results from further structural miniaturization.
SUMMARY OF THE INVENTION
The present invention has been conceived in view of the above described problems in the related art, and its object is to provide a novel approach to the problems.
In order to achieve this object, a piezoelectric actuator of a first aspect of the present invention comprises a base, a flat moving body constituting a cantilever with one end free and another end fixed and provided with piezoelectric elements, and support springs for supporting the moving body so as to track a surface of the base and for regulating direction of movement of the moving body.
If a alternating voltage is applied to the piezoelectric elements provided on the flat cantilever, the cantilever bends with oscillation and a free end of the cantilever comes into contact with the base. The free end of the cantilever undergoes elliptical motion which means that a sideways direction component excites movement of the moving body. Also, the contact state between the moving body and the base is kept stable by the support springs and the moving direction of the moving body is limited by the structure of the support springs, which means that motion and positioning of the moving body can be carried out easily.
A piezoelectric actuator of a second aspect of the present invention comprises a base, a flat moving body comprising a long-edged portion on which piezoelectric elements are provided and a short-edged section, and constituting a cantilever having the long-edged section free and the short-edged section fixed, and support springs for supporting the moving body so as to track a surface of the base and for regulating direction of move; of the moving body.
If the cantilever is formed having a long-edged section and a short-edged section, twisting vibration is excited at the same time as the cantilever bends with oscillation. As a result, the amplitude of oscillation at the free end becomes large and it is easy to obtain a larger motion of the moving body compared to the first piezoelectric actuator structure described above.
A third aspect of the present invention is the piezoelectric actuator of either the first or second aspects in which pressurization means is provided for causing the base and the moving body to be pressed into contact with each other. By pressing the moving body and the base with the pressurization means, not only is following further improved, and the state of contact with the cantilever made good, but also motion and locating of the moving body are made more stable.
REFERENCES:
patent: 4742260 (1988-05-01), Shimizu et al.
patent: 5063321 (1991-11-01), Carter
patent: 5473214 (1995-12-01), Hildebrand
patent: 6201339 (2001-03-01), Tani et al.
patent: 6222302 (2001-04-01), Imada et al.
patent: 6223601 (2001-05-01), Harada et al.
patent: 6307299 (2001-10-01), Suzuki et al.
patent: 06-277624 (1994-10-01), None
Sato Tatsuru
Suzuki Yoko
Tani Kazuo
Watanabe Satoshi
Adams & Wilks
Medley Peter
Ramirez Nestor
Seiko Instruments Inc.
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