Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2001-02-15
2001-12-18
Budd, Mark O. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S323020, C310S328000
Reexamination Certificate
active
06331747
ABSTRACT:
This application is based on Pat. Application No. 2000-45475 filed in Japan, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a surface acoustic wave motor using the traveling wave of surface acoustic waves excited on a piezoelectric substrate.
2. Prior Art
An actuator using an electric motor has been used heretofore for driving a photographing lens of a camera, but the disadvantages such as an increase in size of an apparatus, the generation of a magnetic field, the generation of noise and the like have been pointed out. As a means for overcoming the disadvantages, recently an ultrasonic motor has been proposed, which is adapted to take out the mechanical vibration generated by an ultrasonic vibrator mainly through the frictional force and convert the same into the rectilinear motion or the rotary motion. Further as a motor for enabling the precise drive control, it has been proposed that the motor use a traveling wave of surface acoustic waves (See Japanese Patent Laid-Open No. 07-231685, Japanese Patent Laid-Open No. 09-
233865).
The constitution and driving principle of a surface acoustic wave motor will now be described with reference to
FIGS. 6 and 7
.
FIG. 6
is a plan view showing the basic configuration of the surface acoustic wave motor, and
FIG. 7
is a side view thereof.
In
FIGS. 6 and 7
, a surface acoustic wave motor
100
is so constructed that a comb-shaped electrode having interdigital structure
102
is disposed on a piezoelectric substrate
101
which is a substrate formed of piezoelectric material such as piezoelectric ceramic material mainly composed of PZT (PbZrO
3
.PbTiO
3
), and connected to a high frequency power supply
103
.
Vibration absorbers
107
,
108
are arranged at the ends of the piezoelectric substrate
101
. These are intended to absorb surface acoustic wave vibration reaching the ends of the piezoelectric substrate
101
so that a standing wave is not generated in the piezoelectric substrate.
When the comb-shaped electrode having interdigital structure
102
is excited by the high frequency power supply
103
, surface acoustic waves (Rayleigh waves) L
1
, L
2
vibrating backwardly elliptically are generated on the right and on the left of the comb-shaped electrode having interdigital structure
102
in the piezoelectric substrate
101
, and respectively travel in the direction of going away from the comb-shaped electrode having interdigital structure
102
. That is, the surface acoustic wave L
1
travels in the direction of an arrow (a), and the surface acoustic wave L
2
travels in the direction of an arrow (b) (the opposite direction to the arrow (a)).
A solid state slider
109
placed on the piezoelectric substrate
101
gets on the crest of the surface acoustic wave L
1
or L
2
vibrating backwardly elliptically, so that it is moved in the direction of approaching the comb-shaped electrode having interdigital structure
102
which is the opposite direction to the traveling directions of the surface acoustic waves L
1
and L
2
. That is, as shown in
FIG. 7
, when the slider
109
gets on the crest of the surface acoustic wave L
1
, it is moved in the direction of an arrow (C).
When the slider
109
reaches a position striding over the comb-shaped electrode having interdigital structure
102
, the slider
109
gets on the crests of the surface acoustic waves L
1
and L
2
traveling in the opposite directions to each other so that the slider cannot be moved in either direction. Accordingly, in the configurations shown in
FIGS. 6 and 7
, the slider
109
is capable of moving in only one direction.
For application to a general driving mechanism such as the movement of a lens of a camera, it is necessary to be able move on one axis in both directions. Therefore, it has been proposed to construct a surface acoustic wave motor adapted to move a slider in a designated direction by arranging two comb-shaped electrodes having interdigital structure on a piezoelectric substrate and driving one of the comb-shaped electrodes having interdigital structure.
FIG. 8
is a perspective view showing the basic construction of a surface acoustic wave motor in which two comb-shaped electrodes having interdigital structure are arranged on a piezoelectric substrate, and
FIG. 9
is its plan view.
In
FIGS. 8 and 9
, a surface acoustic wave motor
120
is so constructed that a first comb-shaped electrode having interdigital structure
102
and a second comb-shaped electrode having interdigital structure
104
are arranged on a piezoelectric substrate
101
and respectively connected to a first high frequency power supply
103
and a second high frequency power supply source
105
. A slider
109
is arranged between the first comb-shaped electrode having interdigital structure
102
and the second comb-shaped electrode having interdigital structure
104
. Vibration absorbers
107
,
108
are arranged at the ends of the piezoelectric substrate
101
.
In this arrangement, in the case of moving the slider
109
in the direction of an arrow (d) (See FIGS.
8
and
9
), the first comb-shaped electrode having interdigital structure
102
is excited by the high frequency power supply
103
to generate a surface acoustic wave propagated to the left (in the opposite direction to the arrow (d)). Thus, the slider
109
can be moved toward the first comb-shaped electrode having interdigital structure
102
(in the direction of an arrow (d)).
In the case of moving the slider
109
in the opposite direction of the arrow (d), the second comb-shaped electrode having interdigital structure
104
is excited by the high frequency power supply
105
to generate a surface acoustic wave propagated to the right in
FIGS. 8 and 9
, thereby achieving the movement.
Though the thus constructed surface acoustic wave motor has high driving speed and is excellent in responsiveness, the energy efficiency is very low. This is because most of the surface acoustic wave energy is not used for moving the slider, but is absorbed in the ends of the piezoelectric substrate.
That is, since in the thus constructed surface acoustic wave motor, vibration absorbers are disposed at the ends of the piezoelectric substrate so as not to generate a standing wave in the piezoelectric substrate, most of surface acoustic wave energy generated on the piezoelectric substrate is absorbed in the vibration absorbers, resulting in the disadvantages that the generation of heat is large so that continuous driving is difficult and very large driving power is needed.
As a countermeasure, an energy recovery type surface acoustic wave motor has been proposed, which is so constructed that the surface acoustic wave energy generated in the piezoelectric substrate to reach the ends thereof is not absorbed in the vibration absorbers at the ends of the piezoelectric substrate, but the energy is recovered to be circulated (See Japanese Patent Laid-Open No. 11-146665).
FIG. 10
is a plan view for explaining an example of construction of an energy recovery type surface acoustic wave motor
200
, in which a first comb-shaped electrode having interdigital structure
202
and a second comb-shaped electrode having interdigital structure
203
for generating surface acoustic waves are disposed at a spacing of 1/4 &lgr; of the wavelength &lgr; of the generated surface acoustic wave on a piezoelectric substrate
201
, and respectively connected to a first high frequency power supply
204
and a second high frequency power supply
205
.
In addition to the above, a third comb-shaped electrode having interdigital structure
206
and a fourth comb-shaped electrode having interdigital structure
207
which are provided with an inductance for recovering surface acoustic wave energy and re-exciting the surface acoustic wave are disposed on the piezoelectric substrate
201
.
The piezoelectric substrate and the third comb-shaped electrode having interdigital structure
206
and the fourth comb-shaped electrode having interdigital structure
207
dispos
Okamoto Yasuhiro
Yoshida Ryuichi
Budd Mark O.
Minolta Co. , Ltd.
Sidley Austin Brown & Wood
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