Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2000-09-08
2003-08-26
Feild, Lynn D. (Department: 2839)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S323010
Reexamination Certificate
active
06611081
ABSTRACT:
INCORPORATION BY REFERENCE
The disclosures of the following priority applications are incorporated herein by reference:
Japanese Patent Application No. 11-257872 filed Sep. 10, 1999.
Japanese Patent Application No. 11-259708 filed Sep. 14, 1999.
Japanese Patent Application No. 11-339514 filed Nov. 30, 1999.
Japanese Patent Application No. 2000-106960 filed Apr. 7, 2000.
Japanese Patent Application No. 2000-120296 filed Apr. 21, 2000.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a vibration actuator which employs both a symmetric expansion vibration mode in the radial direction and also a vibration mode in a non-axisymmetric plane.
2. Description of the Related Art
Vibration actuators which employ both a radial symmetric expansion vibration mode and also a non-axisymmetric planar vibration mode are known. Such a vibration actuator utilizes a vibration element which simultaneously generates a radial symmetric expansion vibration mode in which it expands and contracts from the center in the direction towards the circumference (expanding and contracting in the radial direction), and also a non-axisymmetric planar vibration mode in which it is deformed in a non-axisymmetric manner within its plane. This vibration element is shaped as a circular plate having a central hole. Such vibration actuators are disclosed in Japanese Patent Publication No. 6-26994 etc., and they are well adapted to thin construction and are distinguished by high speed and high propulsive force and the like.
FIGS. 21A through 21D
are figures for explanation of a prior art vibration element of a vibration actuator which employs both a radial symmetric expansion vibration mode and also a non-axisymmetric planar vibration mode.
A vibration element
10
comprises a piezoelectric element
11
and an electrode
12
, etc. The piezoelectric element
11
may, for example, be formed from a piezoelectric material such as PZT or the like in the shape of a plate doughnut, and its entire surface is polarized in the thickness direction. This plate doughnut shape is formed so that its resonant frequencies in the radial symmetric expansion vibration mode (R,
1
) and also in the non axially symmetric planar vibration mode ((
1
,
1
)) are almost equal.
As shown in
FIG. 21A
, first and second fan shaped electrodes
12
a
and
12
b
are formed upon the front surface of the piezoelectric element
11
. As shown in
FIG. 21B
, a third electrode
12
c
is formed over almost the entire rear surface of the piezoelectric element
11
.
A first AC voltage is applied to the first electrode
12
a
by a drive voltage generation apparatus (not shown in the figures) which comprises an oscillator, a phase shifter, an amplifier and the like. Further, a second AC voltage which differs in electrical phase from the first AC voltage by 90° is applied by the drive voltage generation apparatus to the second electrode
12
b
. The third electrode
12
c
upon the rear surface is connected to earth so as to be at electric ground potential.
The vibration element
10
resonates so as to vibrate in both the two above described modes by the frequency of the AC voltage which is applied being brought close to the resonant frequencies of these two modes, and thereby a radial symmetric expansion vibration and also a non-axisymmetric vibration are simultaneously generated.
As shown in
FIG. 21C
, the radial symmetric expansion vibration mode (R,
1
) is a vibration mode in which the vibration element
10
extends and withdraws in the radial direction with respect to the vibration center point A, which is at nearly the same position as the central position of the outer circumferential shape of the vibration element
10
. The displacement component Ur in the radial direction is generated at the points C
1
and C
2
which are positioned on the circumference of the vibration element
10
.
Further, as shown in
FIG. 21D
, the non axially symmetric planar vibration mode ((
1
,
1
)) is a vibration mode in which the vibration element
10
is repeatedly deformed leftwards and rightwards in a single plane, as shown by the dashed lines, with the points B
1
and B
2
being nodes, so that displacement components U&thgr; in the directions of the arrows are generated at the points C
1
and C
2
.
And an elliptic motion like that shown in
FIG. 21A
is generated as the combined displacement due to both these two vibrations in the vibration element
10
at the positions of the points C
1
and C
2
, which are the drive force take-out portions of the vibration element
10
. When the vibration element
10
is pressed into contact with a relative movement member
30
at the positions of these points C
1
and C
2
, a frictional force is generated in the direction of displacement of the relative movement member
30
, and thereby it is possible to supply direct drive force to the relative movement member
30
.
Since a prior art vibration actuator takes advantage of vibration modes like those described above, it is thereby possible to realize a thin drive apparatus of small size, because according to theory the vibrational displacement only takes place in one plane.
However, when it is contemplated to apply this vibration actuator to a small sized portable electronic device which is powered by a battery, or the like, the requirement arises for the drive voltage to be reduced as much as possible. In particular, with current portable electronic devices, along with reduction of battery size, there is a tendency to reduce the voltage of the power source for the incorporated circuitry, and these requirements become more and more demanding.
SUMMARY OF THE INVENTION
A primary objective of the present invention is to provide a vibration actuator of sufficient rigidity which can drive with good efficiency relative to the drive voltage, and which moreover can drive at high torque with low drive voltage; and with which at the same time, further, the reduction of size can be anticipated with a simple and also cheap structure.
Another objective of the present invention is to provide a vibration actuator which can support its vibration element so as not to damp the vibration energy which this vibration element imparts to its relative movement member.
The vibration actuator according to the present invention includes a vibration actuator including a vibration element, which simultaneously generates a radial symmetric expansion vibration mode in which the vibration element expands and contracts in the radial direction and a non-axisymmetric planar vibration mode in which the vibration element bends to and fro in a non-axisymmetric manner within the same plane on which the radial symmetric expansion vibration is generated, and thereby drives a relative movement member. And this vibration element comprises at least one superimposed layer structure comprising an elastic member sandwiched between a pair of electrical energy to mechanical energy conversion elements.
The electrical energy to mechanical energy conversion elements and the elastic member included in this vibration actuator may be shaped as circular plates with central holes, and the elastic member is provided with a support member which supports the vibration element at at least one portion of the outer or inner circumference of the elastic member.
The electrical energy to mechanical energy conversion elements and the elastic member included in this vibration actuator may be shaped as circular plates, and the vibration actuator may further comprises a drive force take out portion, formed so as to project outwards from the outer circumference of the elastic member, and which transmits drive force obtained from vibration which is generated in the vibration element to the relative movement member.
It is desirable for the thickness of the elastic member to be equal to or greater than the thickness of the electrical energy to mechanical energy conversion elements.
Each of the pair of electrical energy to mechanical energy conversion elements may include a plurality of electrodes which are symmetrically arrange
Gonda Tunemi
Matsumoto Tsuyoshi
Nasu Nobuyoshi
Okazaki Mitsuhiro
Sugaya Isao
Feild Lynn D.
Nikon Corporation
Zarroli Michael C.
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