Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1999-09-17
2004-04-13
Budd, Mark (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S323040
Reexamination Certificate
active
06720711
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to piezoelectric actuators represented by ultrasonic motors and bimorph type actuators used in clocks, cameras, printers, storage devices and the like and, more particularly, to a piezoelectric actuator whose output is improved from that available in the prior art.
2. Description of the Related Art
Piezoelectric actuators that utilize a vibration of a piezoelectric element in response to the application of a driving signal such as an AC voltage as a motive force to move a movable body are attracting attention especially in the field of micromechanics because of their high electromechanical energy conversion efficiency.
A description will now be made which references to
FIGS. 13A
,
13
B and
13
C on a piezoelectric actuator
100
which is an example of conventional piezoelectric actuators.
The configuration of the piezoelectric actuator
100
will now be described.
As shown in
FIG. 13A
, the piezoelectric actuator
100
is substantially comprised of a rectangular elastic plate
101
made of metal, a piezoelectric element
102
integrally stacked on one of the surfaces of the elastic plate
101
and a piezoelectric element
103
formed on the other surface of the elastic plate
101
.
The piezoelectric elements
102
and
103
are polarized in the direction of the thickness thereof. Referring to the polarizing direction, for example, surfaces
102
a
and
103
a
in contact with the elastic plate
101
are polarized to be negative and positive respectively, whereas surfaces
102
b
and
103
b
opposite thereto are polarized to be positive and negative respectively. That is, the piezoelectric elements
102
and
103
are polarized in opposite directions.
An electrode is provided on each of the surfaces
102
b
and
103
b
to substantially cover the entire surface. The elastic plate
101
serves as an electrode for the surfaces
102
a
and
103
a.
An operation of the piezoelectric actuator
100
will now be described.
As shown in
FIG. 13A
, a voltage is first applied with the electrodes on the surfaces
102
b
and
103
b
serving as the negative pole and the elastic plate
101
serving as the positive pole.
The piezoelectric element
102
expands in the longitudinal direction because the voltage is applied in the direction opposite to the polarizing direction of the surfaces
102
b
and
102
a.
The piezoelectric element
103
contracts in the longitudinal direction because the voltage is applied in the same direction as the polarizing direction of the surfaces
103
a
and
102
b.
As a result, the piezoelectric actuator
100
is bent in the direction indicated by the arrow X in
FIG. 13B
, which generates a driving force to move the movable body (not shown) in the bending direction.
When a voltage is applied with the surfaces
102
b
and
103
b
as the positive pole and the surfaces
102
a
and
103
a
as the negative pole, the piezoelectric actuator
100
is bent in the direction opposite to the arrow X, which generates a driving force to move the movable body in the direction opposite to the direction shown in FIG.
13
B.
However, upper limits have existed for the output and displacement of the piezoelectric actuator
100
because it is formed by simply forming one each piezoelectric element
102
,
103
on both sides of the elastic plate
101
integrally.
As a technique to improve the piezoelectric actuator
100
, a piezoelectric actuator
110
as shown in
FIG. 13C
has been provided in which piezoelectric elements
104
and
105
identical in configuration to the piezoelectric elements
102
and
103
are formed on the piezoelectric elements
102
and
103
, respectively. However, increases in output or displacement was smaller than expected from the magnitude of the voltage, i.e., electric power input thereto. The output or displacement of the piezoelectric actuator
110
could be smaller than the output of the piezoelectric actuator
100
depending on the conditions.
The inventors identified a cause for the above-mentioned problem with the piezoelectric actuator
110
as follows. The same piezoelectric element as the piezoelectric element
102
is used as the piezoelectric element
104
, which results in the same amount of expansion in spite of the fact that the expansion of the piezoelectric element
104
must be greater than the expansion of the piezoelectric element
102
because it is located further than the elastic plate
101
having a distortion-neutral plane. The same piezoelectric element as the piezoelectric element
103
is used as the piezoelectric element
105
, which results in the same amount of contraction in spite of the fact that the contraction of the piezoelectric element
105
must be greater than the contraction of the piezoelectric element
103
because it is located further than the elastic plate
101
.
That is, the piezoelectric element
104
has hindered the expansion of the piezoelectric element
102
, and the piezoelectric element
105
has hindered the contraction of the piezoelectric element
103
.
The invention has been conceived based on the above-described idea, and it is an object of the invention to provide a piezoelectric actuator which transmits a driving force of a plurality piezoelectric elements to the outside without loss.
SUMMARY OF THE INVENTION
In order to solve the above problem, according to one aspect of the invention, there is provided a piezoelectric actuator which is distorted according to an input driving signal to generate a driving force, characterized in that it is formed by integrally stacking a plurality of piezoelectric elements such that they do not hinder the operation of each other.
In the above-described aspect of the invention, for example, the piezoelectric actuator is a bimorph type actuator or an ultrasonic motor.
There is no limitation on the material of the piezoelectric elements.
Further, the thickness of each of the plurality of piezoelectric elements is appropriately adjusted in accordance with the operation and position of the piezoelectric element. Basically, a piezoelectric element is made thinner, the greater the distortion it must undergo. All of the plurality of piezoelectric elements may be different in thickness and, alternatively, some of them may have the same thickness.
In this aspect of the invention, by adjusting the thickness of the piezoelectric elements depending on the operations and positions of the piezoelectric elements, all of the piezoelectric elements contribute to the operation of the piezoelectric actuator without interfering with each other. It is therefore possible to fabricate a piezoelectric actuator which provides output greater than that available in the prior art with the same power consumption, which can be made smaller in size than that in the prior art having the same output and which consumes less power.
According to the invention, there is provided a piezoelectric actuator as described above, characterized in that the thickness of piezoelectric elements located on the side of the actuator with smaller distortion is larger than the thickness of piezoelectric elements located on the side thereof with greater distortion.
In this aspect of the invention, the thickness of each piezoelectric element is smaller, the further the piezoelectric element from a distortion-neutral plane of the actuator. Therefore, all of the piezoelectric elements contribute to the operation of the piezoelectric actuator without interfering with each other. It is therefore possible to fabricate a piezoelectric actuator which provides output greater than that available in the prior art with the same power consumption, which can be made smaller in size than that in the prior art having the same output and which consumes less power.
According to the invention, there is provided a piezoelectric actuator as described above, characterized in that at least two of the plurality of piezoelectric elements undergo identical vibrations.
All of the plurality of piezoelectric elements may undergo identical vibrations.
When t
Iino Akihiro
Kasuga Masao
Adams & Wilks
Budd Mark
Seiko Instruments Inc.
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