U.S. patent application number 09/784515 was filed with the patent office on 2001-08-23 for surface acoustic wave motor and apparatus having the same.
This patent application is currently assigned to MINOLTA CO., LTD.. Invention is credited to Okamoto, Yasuhiro, Yoshida, Ryuichi.
Application Number | 20010015591 09/784515 |
Document ID | / |
Family ID | 18568051 |
Filed Date | 2001-08-23 |
United States Patent
Application |
20010015591 |
Kind Code |
A1 |
Yoshida, Ryuichi ; et
al. |
August 23, 2001 |
Surface acoustic wave motor and apparatus having the same
Abstract
A surface acoustic wave motor with high energy efficiency, which
may efficiently execute recovery of energy of surface acoustic
waves propagated to the ends of piezoelectric substrate and
re-excitation by the recovered energy. A comb-shaped electrode
having interdigital structure for generating surface acoustic waves
and two unidirectional comb-shaped electrodes having interdigital
structure for recovering and re-exciting surface acoustic wave
energy are arranged on a piezoelectric substrate, and a slider is
disposed between the comb-shaped electrode for generating surface
acoustic waves and the unidirectional comb-shaped electrodes for
recovering and re-exciting surface acoustic wave energy. The
surface acoustic wave generated by the comb-shaped electrode is
recovered as an electric power by the unidirectional comb-shaped
electrode arranged at one end of the piezoelectric substrate, and
applied to the unidirectional comb-shaped electrode arranged at the
other end thereof to re-excite the piezoelectric substrate.
Inventors: |
Yoshida, Ryuichi;
(Sakai-Shi, JP) ; Okamoto, Yasuhiro;
(Tondabayashi-Shi, JP) |
Correspondence
Address: |
SIDLEY AUSTIN BROWN & WOOD
717 NORTH HARWOOD
SUITE 3400
DALLAS
TX
75201
US
|
Assignee: |
MINOLTA CO., LTD.
|
Family ID: |
18568051 |
Appl. No.: |
09/784515 |
Filed: |
February 15, 2001 |
Current U.S.
Class: |
310/313B ;
310/313D |
Current CPC
Class: |
H02N 2/08 20130101 |
Class at
Publication: |
310/313.00B ;
310/313.00D |
International
Class: |
H01L 041/04 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 23, 2000 |
JP |
2000-045475 |
Claims
What is claimed is:
1. A surface acoustic wave motor, comprising: a substrate which is
formed of piezoelectric material capable of propagating a surface
acoustic wave with a wavelength .lambda.; a first comb-shaped
electrode having interdigital structure for recovery and
re-excitation, which is a unidirectional comb-shaped electrode
having interdigital structure arranged at one end of the substrate,
and not connected to an external power supply, said first
comb-shaped electrode having interdigital structure including a
first electrode and a second electrode arranged outside the first
electrode on the substrate, said first electrode and the second
electrode being arranged at a space of .lambda./4; a second
comb-shaped electrode having interdigital structure for recovery
and re-excitation, which is a unidirectional comb-shaped electrode
having interdigital structure arranged at the other end of the
substrate and not connected to an external power supply, said
second comb-shaped electrode having interdigital structure
including a third electrode and a fourth electrode arranged outside
the third electrode on the substrate, said third electrode and the
fourth electrode being arranged at a space of .lambda./4; a
comb-shaped electrode having interdigital structure for generating
surface acoustic waves, which is arranged between the first and
second comb-shaped electrodes having interdigital structure for
recovery and re-excitation, connected to an external high frequency
power supply, and capable of generating surface acoustic waves with
a wavelength .lambda. toward both ends of the substrate in the
substrate; and connecting parts for electrically connecting the
first electrode and the fourth electrode to each other, and the
second electrode and the third electrode to each other.
2. A surface acoustic wave motor according to claim 1, wherein the
first electrode to the fourth electrode are respectively formed by
plural pairs of comb-shaped electrodes having interdigital
structure, and the number of pairs of the first electrode and the
third electrode is larger than the number of pairs of the second
electrode and the fourth electrode.
3. A surface acoustic wave motor according to claim 1, wherein the
surface acoustic waves which have reached the first and second
comb-shaped electrodes having interdigital structure for recovery
and re-excitation from the comb-shaped electrode having
interdigital structure for generating a surface acoustic wave are
recovered in the respective comb-shaped electrodes having
interdigital structure for recovery and re-excitation applied as
electric power to the other comb-shaped electrode having
interdigital structure for recovery and re-excitation, and again
radiated as the surface acoustic waves traveling in the same
direction.
4. A surface acoustic wave motor according to claim 1, wherein the
piezoelectric material for forming the substrate is piezoelectric
ceramics.
5. A surface acoustic wave motor according to claim 1, wherein the
comb-shaped electrode having interdigital structure for generating
the surface acoustic waves includes a fifth electrode and a sixth
electrode.
6. A surface acoustic wave motor according to claim 5, wherein the
fifth electrode and the sixth electrode are arranged at a space of
.lambda./4.
7. A surface acoustic wave motor according to claim 5, wherein
voltages of waveforms having a phase difference of .pi./2 are
respectively applied to the fifth electrode and the sixth electrode
from the high frequency power supply.
8. An apparatus, comprising: a substrate which is formed of
piezoelectric material capable of propagating a surface acoustic
wave with a wavelength .lambda.; a slider arranged on the
substrate; a first comb-shaped electrode having interdigital
structure for recovery and re-excitation which is a unidirectional
comb-shaped electrode having interdigital structure arranged at one
end of the substrate, and not connected to an external power
supply, said first comb-shaped electrode having interdigital
structure including a first electrode and a second electrode
arranged outside the first electrode on the substrate, said first
electrode and the second electrode being arranged at a space of
.lambda./4; a second comb-shaped electrode having interdigital
structure for recovery and re-excitation, which is a unidirectional
comb-shaped electrode having interdigital structure arranged at the
other end of the substrate and not connected to an external power
supply, said second comb-shaped electrode having interdigital
structure including a third electrode and a fourth electrode
arranged outside the third electrode on the substrate, said third
electrode and the fourth electrode being arranged at a space of
.lambda./4; a comb-shaped electrode having interdigital structure
for generating surface acoustic waves, which is arranged between
the first and second comb-shaped electrodes having interdigital
structure for recovery and re-excitation, and capable of generating
a surface acoustic wave with a wavelength .lambda. toward both ends
of the substrate on the substrate; a high frequency power supply
device which is connected to the comb-shaped electrode having
interdigital structure for generating surface acoustic waves and
adapted to apply voltage to the comb-shaped electrode having
interdigital structure for generating surface acoustic waves; and
connecting parts for electrically connecting the first electrode
and the fourth electrode to each other, and the second electrode
and the third electrode to each other.
9. An apparatus according to claim 8, wherein the first electrode
to the fourth electrode are respectively formed by plural pairs of
comb-shaped electrodes having interdigital structure, and the
number of pairs of the first electrode and the third electrode is
larger than the number of pairs of the second electrode and the
fourth electrode.
10. An apparatus according to claim 8, wherein the surface acoustic
waves which have reached the first and second comb-shaped
electrodes having interdigital structure for recovery and
re-excitation from the comb-shaped electrode having interdigital
structure for generating surface acoustic waves are recovered by
the respective comb-shaped electrodes having interdigital structure
for recovery and re-excitation, applied as electric power to the
other comb-shaped electrode having interdigital structure for
recovery and re-excitation and again radiated as the surface
acoustic waves traveling in the same direction.
11. An apparatus according to claim 8, wherein the piezoelectric
material for forming the substrate is piezoelectric ceramics.
12. An apparatus according to claim 8, wherein the comb-shaped
electrode having interdigital structure for generating surface
acoustic waves includes a fifth electrode and a sixth
electrode.
13. An apparatus according to claim 12, wherein the fifth electrode
and the sixth electrode are arranged at a space of .lambda./4.
14. An apparatus according to claim 12, wherein voltages of
waveforms having a phase difference of .pi./2 are respectively
applied to the fifth electrode and the sixth electrode from the
high frequency power supply devices corresponding to the fifth
electrode and the sixth electrode.
Description
[0001] This application is based on the patent application No.
2000-45475 filed in Japan, the contents of which are hereby
incorporated reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to a surface acoustic wave motor
using the traveling wave of surface acoustic waves excited on a
piezoelectric substrate.
[0004] 2. Prior Art
[0005] 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 means for overcoming the disadvantages, recently an
ultrasonic motor has been proposed, which is adapted to takeout 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, and further as a motor for
enabling the precise drive control, it has been proposed that the
motor uses a traveling wave of surface acoustic waves (See Japanese
Patent Laid-Open No. 07-231685, Japanese Patent Laid-Open No.
09-233865).
[0006] 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.
[0007] 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.sub.3.PbTiO.sub.3),
and connected to a high frequency power supply 103.
[0008] 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.
[0009] When the comb-shaped electrode having interdigital structure
102 is excited by the high frequency power supply 103, surface
acoustic waves (Rayleigh waves) L1, L2 vibrating backward
elliptically are generated on the right and 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 L1 travels in the direction
of an arrow (a), and the surface acoustic wave L2 travels in the
direction of an arrow (b) (the opposite direction to the arrow
(a)).
[0010] A solid state slider 109 placed on the piezoelectric
substrate 101 gets on the crest of the surface acoustic wave L1 or
L2 vibrating backward 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 L1 and L2. That
is, as shown in FIG. 7, when the slider 109 gets on the crest of
the surface acoustic wave L1, it is moved in the direction of an
arrow (c).
[0011] 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 L1 and L2
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.
[0012] For application to a general driving mechanism such as the
movement of a lens of a camera, it is requested to 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.
[0013] 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.
[0014] 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.
[0015] 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)).
[0016] 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.
[0017] 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 surface acoustic
wave energy is not used for moving the slider, but absorbed in the
ends of the piezoelectric substrate.
[0018] That is, since in the thus constructed surface acoustic wave
motor, vibration absorbers are disposed at the ends of the
piezoelectric substrate not to generate a standing wave on 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 generation
of heat is large so that the continuous driving is difficult, and
very large driving power is needed.
[0019] 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).
[0020] 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 space of 1/4.lambda. to the wavelength .lambda.
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.
[0021] 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.
[0022] The piezoelectric substrate and the third comb-shaped
electrode having interdigital structure 206 and the fourth
comb-shaped electrode having interdigital structure 207 disposed
thereon constitute an electromechanical transducer element, which
functions as a mechanical-electric transducer element for
converting the mechanical vibration into the high frequency
electric power when the surface acoustic wave propagated on the
piezoelectric substrate is received, and also functions as an
electromechanical transducer element for converting the high
frequency electric power into the surface acoustic wave power which
is mechanical vibration when the high frequency electric power is
input.
[0023] An inductance 208 is connected in parallel to the third
comb-shaped electrode having interdigital structure 206, and an
inductance 209 is connected in parallel to the fourth comb-shaped
electrode having interdigital structure 207. These inductances are
provided for restraining reflection of the surface acoustic waves
propagated on the piezoelectric substrate and re-exciting the
same.
[0024] A slider 210 is disposed between the first comb-shaped
electrode having interdigital structure 202 and the fourth
comb-shaped electrode having interdigital structure 207.
[0025] In this arrangement, the phase of high frequency voltage
applied to the first comb-shaped electrode having interdigital
structure 202 and the second comb-shaped electrode having
interdigital structure 203 is shifted to control the traveling
direction of generated surface elastic waves.
[0026] In this arrangement, at the time of moving the slider 210 to
the right (in the direction of an arrow (e) in FIG. 10, it will be
sufficient to generate the surface elastic wave toward the left (in
the opposite direction to the arrow (e))
[0027] First, voltage
V1=V01.multidot.sin(.omega.t)
[0028] is applied from the high frequency power supply 204 to the
first comb-shaped electrode having interdigital structure 202, and
voltage
V2=V02.multidot.sin(.omega.t-.pi./2)
[0029] is applied from the high frequency power supply 205 to the
second comb-shaped electrode having interdigital structure 203 to
drive the second comb-shaped electrode having interdigital
structure 203 with a phase difference of .pi./2 to the first
comb-shaped electrode having interdigital structure 202.
[0030] On the piezoelectric substrate 201, surface acoustic waves
heading toward the left (in the opposite direction to the arrow
(e)) in FIG. 10 are generated, and the surface acoustic waves
propagated on the piezoelectric substrate 201 are converted into
the high frequency electric power by the fourth comb-shaped
electrode having interdigital structure 207. The converted high
frequency electric power is circulated and applied to the third
comb-shaped electrode having interdigital structure 206, and again
converted to the surface acoustic waves heading toward the left (in
the opposite direction to the arrow (e)) to excite the
piezoelectric substrate 201. Thus, the slider 210 can be moved
toward the right (in the direction of the arrow (e)) in FIG.
10.
[0031] At the time of moving the slider 210 to the left (in the
opposite direction to the arrow (e)) in FIG. 10, it will be
sufficient to generate the surface acoustic waves toward the right
(in the direction of the arrow (e)) in FIG. 10.
[0032] First, voltage
V1=V01.multidot.sin(.omega.t-.pi./2)
[0033] is applied from the high frequency power supply 204 to the
first comb-shaped electrode having interdigital structure 202, and
voltage
V2=V02.multidot.sin(.omega.t)
[0034] is applied from the high frequency power supply 205 to the
second comb-shaped electrode having interdigital structure 203 to
drive the electrode.
[0035] On the piezoelectric substrate 201, surface acoustic waves
heading toward the right (in the direction of the arrow (e)) in
FIG. 10 are generated, and the surface acoustic waves propagated on
the piezoelectric substrate 201 are converted into the high
frequency electric vibration by the third comb-shaped electrode
having interdigital structure 206. The converted high frequency
electric vibration is circulated and applied to the fourth
comb-shaped electrode having interdigital structure 207, and again
converted into the surface acoustic waves heading toward the right
(in the direction of the arrow (e)) to excite the piezoelectric
substrate 201. Thus, the slider 210 can be moved toward the left
(in the opposite direction to the arrow (e)) in FIG. 10.
[0036] Thus, the surface acoustic waves propagated on the
piezoelectric substrate to one end thereof are recovered by the
comb-shaped electrode having interdigital structure disposed at one
end of the piezoelectric substrate, and circulated to the
comb-shaped electrode having interdigital structure disposed at the
other end of the piezoelectric substrate to re-excite the
piezoelectric substrate, so that the energy efficiency can be
heightened.
[0037] In the energy recovery-type surface acoustic wave motor, in
addition to the ordinary surface acoustic wave generating
comb-shaped electrode having interdigital structure, there are
provided two comb-shaped electrodes having interdigital structure
to which an inductance is connected in parallel, whereby the
surface acoustic waves propagated on the piezoelectric substrate to
the end are recovered by one comb-shaped electrode having
interdigital structure, and circulated to the other comb-shaped
electrode having interdigital structure. This arrangement, however,
has the disadvantages that even if the optimum value of inductance
is selected, actually it is difficult to hold down the reflection
of surface acoustic waves at the ends of the piezoelectric
substrate, and further when the recovered surface acoustic wave
energy is again emitted from the other comb-shaped electrode having
interdigital structure, the energy is emitted from both ends of the
comb-shaped electrode having interdigital structure so that an
energy loss is caused, and the improvement in energy efficiency has
its limit.
SUMMARY OF THE INVENTION
[0038] The present invention has been made in view of the above
circumstances and it is a major object of the present invention to
provide a new surface acoustic wave motor having a high energy
efficiency.
[0039] It is another object of the present invention to provide a
surface acoustic wave motor having a high energy efficiency, which
may efficiently recover the energy of surface acoustic waves
propagated to the end of a surface acoustic wave element and
re-excite the surface acoustic wave element by the recovered
energy.
[0040] It is still another object of the present invention to
provide a device including the surface acoustic wave motor having a
high energy efficiency.
[0041] Other objects of the present invention will be made clear by
the detailed description of the invention referring to the
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0042] FIG. 1 is a plan view showing the basic construction of a
surface acoustic wave motor according to an embodiment of the
invention (in the case of moving a slider toward the right);
[0043] FIG. 2 is a plan view showing the basic construction of the
surface acoustic wave motor shown in FIG. 1 (in the case of moving
the slider toward the left) FIGS. 3(a), 3(b), 3(c) and 3(d) are
diagrams for explaining the condition of reflection of surface
acoustic waves at unidirectional comb-shaped electrodes having
interdigital structure;
[0044] FIGS. 4(a) and 4(b) are diagrams for explaining the
condition of re-excitation of surface acoustic waves at
unidirectional comb-shaped electrodes having interdigital
structure;
[0045] FIG. 5 is a diagram for explaining the operation of the
whole including re-excitation of the surface acoustic wave
motor;
[0046] FIG. 6 is a plan view showing the basic construction of the
conventional surface acoustic wave motor;
[0047] FIG. 7 is a side view of the conventional surface acoustic
wave motor shown in FIG. 6;
[0048] FIG. 8 is a perspective view showing the basic construction
of the conventional surface acoustic wave motor where two
comb-shaped electrodes having interdigital structure are arranged
on a piezoelectric substrate;
[0049] FIG. 9 is a plan view of the conventional surface acoustic
wave motor where two comb-shaped electrodes having interdigital
structure are arranged on a piezoelectric substrate shown in FIG.
8; and
[0050] FIG. 10 is a plan view showing the construction of the
conventional energy recovery type surface acoustic wave motor.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0051] The embodiments of the invention will now be described. FIG.
1 is a plan view showing the basic construction of a surface
acoustic wave motor 10 according to an embodiment of the
invention.
[0052] In FIG. 1, the reference numeral 11 is a piezoelectric
substrate constituting a surface acoustic wave element, in which
LiNbO.sub.3 is used as piezoelectric ceramic material.
[0053] A comb-shaped electrode having interdigital structure 12 for
generating surface acoustic waves and unidirectional comb-shaped
electrodes having interdigital structure 13 and 14 for recovering
the surface acoustic wave energy and re-excitation are arranged on
the piezoelectric substrate 11, and a slider 16 is arranged between
the surface acoustic wave generating comb-shaped electrode having
interdigital structure 12 and the unidirectional comb-shaped
electrode having interdigital structure 14.
[0054] The comb-shaped electrode having interdigital structure 12
is formed by electrodes 12a and 12b arranged at a space of
1/4.lambda. to the wavelength .lambda. of the surface acoustic
wave. The electrodes 12a and 12b are respectively formed by plural
pairs, ten pairs in the embodiment, the electrode 12a is connected
to a high frequency power supply 15a, and the electrode 12b is
connected to a high frequency power supply 15b. In FIG. 1, the
electrode 12a and the electrode 12b are respectively shown in only
two pairs to avoid complicatedness of the drawing.
[0055] On the other hand, the unidirectional comb-shaped electrode
having interdigital structure 13 is formed by a first electrode 13a
and a second electrode 13b arranged at a space of 1/4.lambda. to
the wavelength .lambda. of the surface acoustic wave, and the
unidirectional comb-shaped electrode having interdigital structure
14 is formed by a third electrode 14a and a fourth electrode 14b
arranged at a space of 1/4.lambda. to the wavelength .lambda. of
the surface acoustic wave.
[0056] The second electrode 13b and the fourth electrode 14b closer
to the comb-shaped electrode having interdigital structure 12 are
respectively formed by plural pairs, five pairs in the embodiment,
and the unidirectional first electrode 13a and the third electrode
14a farther away from the comb-shaped electrode having interdigital
structure 12 are respectively formed by plural pairs, fifteen pairs
in the embodiment. In FIG. 1, the second electrode 13b and the
fourth electrode 14b are respectively shown in only two pairs, and
the first electrode 13a and the third electrode 14a are
respectively shown in only three pairs to avoid complicatedness of
the drawing.
[0057] The first electrode 13a and the fourth electrode 14b are
electrically connected to each other, and the second electrode 13b
and the third electrode 14a are electrically connected to each
other.
[0058] Further, the second electrode 13b is disposed
(n+1/4).lambda. (wavelength) apart to the electrode 12b, and the
fourth electrode 14b is disposed (m+1/4).lambda. (wavelength) apart
to the electrode 12a.
[0059] In this arrangement, in the case of moving the slider 16
toward the right (in the direction of an arrow (f)) in FIG. 1, it
will be sufficient to generate the surface acoustic wave toward the
left (in the opposite direction to the arrow (f))
[0060] First, voltage
V1=V01.multidot.sin(.omega.t)
[0061] is applied from a high frequency power supply 15a to the
electrode 12a of the comb-shaped electrode having interdigital
structure 12, and voltage
V2=V02 sin(.omega.t-.pi./2)
[0062] is applied from a high frequency power supply 15b to the
electrode 12b of the comb-shaped electrode having interdigital
structure 12 (See FIG. 1).
[0063] Provided that V01, V02 are high frequency voltage.
[0064] On the piezoelectric substrate 11, surface acoustic waves
heading toward the left (in the opposite direction to the arrow
(f)) in FIG. 1 are generated, and the surface acoustic waves
propagated on the piezoelectric substrate 11 are converted into the
high frequency electric power by the fourth electrode 14b and the
third electrode 14a. The high frequency electric power converted by
the fourth electrode 14b is circulated to the first electrode 13a,
and the high frequency electric power converted by the third
electrode 14a is circulated to the second electrode 13b and again
converted into the surface acoustic wave heading toward the left
(in the opposite direction to the arrow (f)) to excite the
piezoelectric substrate 11. Thus, the slider 16 can be moved toward
the right (in the direction of an arrow (f)) in FIG. 1.
[0065] At this time, as described above, on the side where the
slider 16 is arranged, the electrodes 12a and 12b of the
comb-shaped electrode having interdigital structure 12 are arranged
at a space of 1/41.lambda. to the wavelength .lambda. of the
surface acoustic wave, so that the phase difference between the
phase of the surface acoustic wave propagated from the electrode
12a toward the left and the phase of the surface acoustic wave
propagated from the electrode 12b toward the left becomes 0 (zero),
so the surface acoustic wave is strengthened.
[0066] On the other hand, on the side where the slider 16 is not
arranged, the phase difference between the phase of the surface
acoustic wave propagated from the electrode 12a toward the right
and the phase of the surface acoustic wave propagated from the
electrode 12b toward the right is .pi., so that both waves cancel
each other, so the surface acoustic wave is weakened.
[0067] The high frequency voltage V01, V02 generated from the high
frequency power supplies 15a, 15b are adjusted to equalize the
amplitude of the surface acoustic wave on the side where the slider
16 is not arranged, whereby they are made completely cancel each
other to restrain a loss of energy.
[0068] FIG. 2 shows the case of moving the slider 16 toward the
left (in the direction of an arrow (g), that is, in the opposite
direction to the arrow (f) in FIG. 1), and voltage
V2=V02.multidot.sin(.omega.t-.pi./2)
[0069] is applied from a high frequency power supply 15a to the
electrode 12a of the comb-shaped electrode having interdigital
structure 12, and voltage
V1=V01.multidot.sin(.omega.t)
[0070] is applied from a high frequency power supply 15b to the
electrode 12b of the comb-shaped electrode having interdigital
structure 12.
[0071] On the piezoelectric substrate 11, surface acoustic waves
heading toward the right (in the opposite direction to the arrow
(g)) in FIG. 2 are generated, and the surface acoustic waves
propagated on the piezoelectric substrate 11 are converted into the
high frequency electric power by the second electrode 13b and the
first electrode 13a. The high frequency electric power converted by
the second electrode 13b is circulated to the third electrode 14a,
and the high frequency electric power converted by the third
electrode 14a is circulated to the second electrode 13b and again
converted into the surface acoustic wave heading toward the right
(in the opposite direction to the arrow (g)) to excite the
piezoelectric substrate 11. Thus, the slider 16 can be moved toward
the left (in the direction of an arrow (g) in FIG. 2.
[0072] At this time, as described above, on the side where the
slider 16 is arranged, the electrodes 12a and 12b of the
comb-shaped electrode having interdigital structure 12 are arranged
at a space of 1/4.lambda. to the wavelength .lambda. of the surface
acoustic wave, so that the phase difference between the phase of
the surface acoustic wave propagated from the electrode 12a toward
the right and the phase of the surface acoustic wave propagated
from the electrode 12b toward the right becomes 0 (zero), so the
surface acoustic wave is strengthened.
[0073] On the other hand, on the side where the slider 16 is not
arranged, the phase difference between the phase of the surface
acoustic wave propagated from the electrode 12a toward the right
and the phase of the surface acoustic wave propagated from the
electrode 12b toward the right is .pi., so that both waves cancel
each other, so the surface acoustic wave is weakened.
[0074] The high frequency voltage V01, V02 generated from the high
frequency power supplies 15a, 15b are adjusted to equalize the
amplitude of the surface acoustic wave on the side where the slider
16 is not arranged, whereby they are made completely cancel each
other to restrain a loss of energy.
[0075] FIGS. 3(a) to 3(d) are diagrams for explaining the condition
of reflection of surface acoustic waves at the third electrode 14a
and the fourth electrode 14b of the unidirectional comb-shaped
electrode having interdigital structure 14.
[0076] As shown in FIG. 3(a), the surface acoustic wave P
propagated on the piezoelectric substrate 11 from the right to the
left in FIG. 3 is, first, as shown in FIG. 3(b), reflected from the
fourth electrode 14b to travel as the reflected wave R1 toward the
right. Further, the surface acoustic wave P passed through the
fourth electrode 14b is, a<s shown in FIG. 3(c), reflected from
the third electrode 14a to travel as the reflected wave R2 toward
the right. The space between the third electrode 14a and the fourth
electrode 14b is wavelength 1/4.lambda., so that the phase
difference between two reflected waves is .pi.. Thus, the reflected
waves R1 and R2 of the surface acoustic waves are composed to
cancel each other, and as shown in FIG. 3(d), the composed
reflected wave R3 disappears.
[0077] As the reflected wave R2 from the third electrode 14a is the
reflected wave of the surface acoustic wave passed through the
fourth electrode 14b, in order to make the surface acoustic wave P
easily pass through the fourth electrode 14b, the number of pairs
of the fourth electrodes 14b is made smaller than the number of
pairs of the third electrodes 14a. Though there are provided five
pairs of the fourth electrodes 14b and fifteen pairs of the third
electrodes 14a in this embodiment, the proper number of pairs for
mutually canceling the reflected waves is determined depending on
the electromechanical coupling factor of the piezoelectric
substrate.
[0078] FIGS. 4(a) and 4(b) are diagrams for explaining the
condition of re-excitation of the surface acoustic waves by the
first electrode 13a and the second electrode 13b of the
unidirectional comb-shaped electrode having interdigital structure
13, and FIG. 5 is a diagram for explaining the whole operation
including re-excitation of the surface acoustic wave motor.
[0079] The condition of re-excitation of the surface acoustic wave
by the unidirectional comb-shaped electrode having interdigital
structure and the whole operation including re-excitation of the
surface acoustic wave motor will now be described with reference to
FIGS. 4(a) and 4(b) and FIG. 5.
[0080] As described before, the first electrode 13a is connected to
the fourth electrode 14b, and the second electrode 13b is connected
to the third electrode 14a.
[0081] Among the surface acoustic waves M propagated on the
piezoelectric substrate 11 from the right toward the left in FIGS.
4 and 5, the surface acoustic wave received by the fourth electrode
14b is converted into high frequency electric power E1 (See FIG.
5), input to the first electrode 13a, and again converted into the
surface acoustic wave T1 propagated from the right toward the left
to excite the piezoelectric substrate 11.
[0082] Among the surface acoustic waves M propagated on the
piezoelectric substrate 11 from the right toward the left in FIGS.
4 and 5, the surface acoustic wave received by the fourth electrode
14a is converted into high frequency electric power E2 (See FIG.
5), input to the second electrode 13b, and again converted into the
surface acoustic wave T2 to excite the piezoelectric substrate
11.
[0083] At this time, the space between the third electrode 14a and
the fourth electrode 14b is wavelength 1/4.lambda., and also the
space between the first electrode 13a and the second electrode 13b
is wavelength 1/4.lambda., so that there is no phase difference
between the surface acoustic waves T1 and T2, the surface acoustic
waves T1 and T2 are composed to be strengthened to excite the
piezoelectric substrate 11 as the surface acoustic wave T with a
large amplitude (see FIGS. 4(a) and 4(b)). This excitation and the
excitation of the piezoelectric substrate 11 by the surface
acoustic wave M generated by the comb-shaped electrode having
interdigital structure 12 (the electrode 12a and the electrode 12b)
are composed to move the slider 16 in the direction of the arrow
(f).
[0084] According to the invention, as described above in detail,
the surface acoustic wave motor may efficiently execute recovery of
the surface acoustic wave energy propagated to the end of the
surface acoustic wave element and re-excitation of the surface
acoustic wave element by the recovered energy, and reflection of
the surface acoustic wave at the ends of the surface acoustic wave
element is held down so that the energy is efficiently recovered
and re-excited without an element member such as inductance or the
like by the construction and configuration of the comb-shaped
electrodes having interdigital structure for recovering and
re-exciting the energy to provide the surface acoustic wave motor
with high energy efficiency.
[0085] Although the present invention has been fully described by
way of examples with reference to the accompanying drawings, it is
to be noted that various changes and modifications will be apparent
to those skilled in the art. Therefore, unless otherwise such
changes and modifications depart from the scope of the present
invention, they should be construed as being included therein.
* * * * *