Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1998-03-30
2001-03-13
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
Reexamination Certificate
active
06201339
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a piezoelectric actuator, and more particularly to a piezoelectric actuator which can insure high efficiency in movement conversion even when miniaturized and has improved construction of a vibrating body as well as of a movable body to insure stable rotational movement.
Generally the principle of operation of an ultrasonic motor based on the conventional technology can largely be classified as the standing wave system and the traveling wave system. At first, description is made for an ultrasonic motor based on the standing wave system.
FIG. 9
is a perspective explanatory view showing an ultrasonic motor based on the conventional type standing wave system. This ultrasonic motor
900
comprises a vibrating body
910
with a piezoelectric element
912
for generating vibration in the longitudinal direction held between metallic bodies
911
, and a movable body
920
, and a vibrating piece
913
to be struck against the movable body
920
is provided on and projects from an edge of said vibrating body
910
. The vibrating piece
913
is inclined at a specified angle against a direction of the normal line to the movable body
920
. When a voltage having a frequency close to a resonance frequency of the vibrating body
910
is loaded, the vibrating body
910
vibrates, and the vibrating piece
913
provided at a tip thereof hits and contacts the movable body
920
. As the vibrating piece
913
is inclined at a specified angle against the movable body
920
, when the vibrating piece
913
hits the movable body
920
, displacement of the vibrating piece
913
in the longitudinal direction is partially converted to that in the lateral direction. Namely, movement of a tip of the vibrating piece follows an elliptical orbit. With this operation, the movable body
920
moves in one direction.
FIG. 10
is an explanatory view showing a principle of operation of another type of ultrasonic motor based on the standing wave system. This ultrasonic motor
1000
makes use of distorted vibration, and has a plurality of projecting sections
1011
provided at a position having a displacement component of movement in the same direction on a vibrating body
1010
(Refer to (c) in the figure). Also, a vertex section of this projecting section
1011
is inclined at a specified angle. The vibrating body
1010
has a piezoelectric element (not shown) having a plurality of electric poles. With this ultrasonic motor
1000
, a moving direction of the movable body is decided according to a position where the projection
1010
is provided. When a standing wave is generated by loading a voltage to the piezoelectric element ((a) and (b) in the figure), the projecting section
1011
having a displacement component in one direction as described above contacts a movable body
1020
((c) in the figure). For this reason, the movable body
1020
moves in one direction described above. The movable body
1020
can be moved in the opposite direction by changing a position of the projecting section
1011
((c) in the figure).
Next, description is made for an ultrasonic motor based on the traveling wave system.
FIG. 11
is a perspective view showing an ultrasonic motor
1100
based on the conventional type of traveling wave system. The ultrasonic motor
1100
comprises a vibrating body
1110
comprised of a ring-shaped metallic body
1102
with a plurality of projecting sections
1101
formed in the peripheral direction and a piezoelectric ceramic element
1103
adhered to a bottom surface of the metallic body
1102
, and a ring-shaped movable body
1120
pressure-fitted to a surface of this vibrating body
1110
. A frictional member with excellent wearing-resistance is spanned over a contact section
1121
of the movable body
1120
. Also, as shown in
FIG. 12
, a plurality of driving electrodes
1104
corresponding to the projecting sections
1101
are provided in the piezoelectric ceramics
1103
. This ring-shaped ultrasonic motor
1100
is used as a lens actuator for automatically focusing, for instance, a single-lens reflex camera.
In this ultrasonic motor
1100
, distorted vibration is loaded to the vibrating body
1110
by controlling an amplitude of the polarized piezoelectric ceramic element
1103
, and exciting a traveling wave of the distorted vibration according to a phase difference of the loaded voltage. The distorted vibration of the traveling wave converts the movement in the vertical direction to movement in the lateral direction according to a thickness of the vibrating body
1110
, and gives an elliptical movement as shown in
FIG. 13
to the projecting section
1101
of the vibrating body
1110
. The movable body
1120
is driven by the frictional force with the projecting section
1101
and moves. As height of the projecting section
1101
gives influence to displacement in the lateral direction, it is required to set a moving speed of the movable body
1120
.
Further as shown in
FIG. 14
, the ultrasonic motor based on the traveling wave may have a disk-shaped configuration. This ultrasonic motor
1200
has a vibrating body
1210
comprising a disk-shaped metallic body
1203
with a plurality of projecting sections
1201
formed in the peripheral direction, and a shaft holder
1202
located in the center, a piezoelectric element
1204
adhered to a bottom surface of the metallic body
1203
, and a disk-shaped movable body
1220
press-fitted to a surface of this vibrating body
1210
. The remaining configuration and the operation are the same as those of the ring-shaped ultrasonic motor
1100
shown in
FIG. 14
, so that description thereof is omitted herein.
In the ultrasonic motors
900
,
1000
,
1100
, and
1200
based on the conventional technology as described above, the rotationally moving capability is dependent on the bending rigidity of the vibrating body, the mass of the projecting section, and the mechanical machining precision and homogeneity of a tip of the projecting section contacting the movable body as well as on friction with a contacting surface of the movable body, so that it is difficult to improve and stabilize the movement conversion efficiency. For instance, in the disk-shaped ultrasonic motor
1100
based on the traveling wave system, there have been problems that the metallic body
1102
is hardly distorted because the metallic body
1102
is disk-shaped, the movement conversion efficiency is low and the rotation is sometimes unstable because the mass of the projecting section
1101
is large and, as a result, the projecting section can hardly be vibrated.
Also, if a diameter of the ultrasonic motor is made smaller, an oscillatory wave generated by the vibrating body
1110
has no vibration node, so that the oscillatory wave is easily attenuated as the diameter is made smaller. For this reason, the efficiency in conversion of movement from the piezoelectric element
1103
to the movable body
1120
becomes remarkably low, which makes it extremely difficult to reduce size of the ultrasonic motor. Also as the ultrasonic motor becomes smaller, influence of bending rigidity of the vibrating body
1110
becomes larger, so that miniaturization of ultrasonic motor is limited.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a piezoelectric actuator which can insure high movement conversion efficiency and stable rotational movement even when miniaturized as described above.
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patent: 5917271 (1999-06-01), Yamamura
Maeda Hidetaka
Suzuki Mizuaki
Suzuki Youko
Tani Kazuo
Adams & Wilks
Medley Peter
Ramirez Nestor
Seiko Instruments Inc.
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