U.S. patent application number 09/764143 was filed with the patent office on 2001-09-13 for actuator and driving method thereof.
Invention is credited to Kosaka, Akira, Matsuda, Shinya, Matsuo, Takashi, Okada, Hiroyuki, Shibatani, Kazuhiro, Ueyama, Masayuki.
Application Number | 20010020809 09/764143 |
Document ID | / |
Family ID | 26583905 |
Filed Date | 2001-09-13 |
United States Patent
Application |
20010020809 |
Kind Code |
A1 |
Matsuo, Takashi ; et
al. |
September 13, 2001 |
Actuator and driving method thereof
Abstract
An actuator includes at least two piezoelectric devices arranged
for crossing displacing directions thereof at a predetermined
angle, a chip member provided at a coupling point of the
piezoelectric devices, and a spring for contacting the chip member
to a rotor driven by the actuator. The piezoelectric device is
driven for moving the chip member trailing an elliptical trail. The
rotation velocity or the driving torque of the rotor is controlled
by varying at least one of a length of a major axis or a minor axis
of the elliptical trail and an inclination angle of the major axis
or the minor axis with respect to a normal at a contacting point of
the chip member and the rotor.
Inventors: |
Matsuo, Takashi; (Itami-Shi,
JP) ; Ueyama, Masayuki; (Takarazuka-Shi, JP) ;
Okada, Hiroyuki; (Osaka, JP) ; Shibatani,
Kazuhiro; (Osaka, JP) ; Matsuda, Shinya;
(Takarazuka-Shi, JP) ; Kosaka, Akira; (Osaka,
JP) |
Correspondence
Address: |
Kenneth L. Cage, Esquire
McDERMOTT, WILL & EMERY
600 13th Street, N.W.
Washington
DC
20005-3096
US
|
Family ID: |
26583905 |
Appl. No.: |
09/764143 |
Filed: |
January 19, 2001 |
Current U.S.
Class: |
310/328 ;
310/317 |
Current CPC
Class: |
H02N 2/142 20130101;
H02N 2/103 20130101; H02N 2/0025 20130101 |
Class at
Publication: |
310/328 ;
310/317 |
International
Class: |
H01L 041/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 21, 2000 |
JP |
2000-12568 |
Mar 31, 2000 |
JP |
2000-97091 |
Claims
What is claimed is:
1. An actuator comprising: a base member; a plurality of displacing
elements for generating a predetermined displacement, in which top
ends of them are coupled at one point and base ends of them are
respectively fixed on the base member; a pressing member for
contacting the coupled top ends of the displacing elements to a
driven object with a predetermined pressure; a driving circuit for
applying at least one driving signal to at least one displacing
elements; and a controller for controlling the driving signal so
that the coupled top ends of the displacing elements moves for
trailing an elliptical trail; wherein the controller controls the
driving signal in a manner so that shape of the elliptical trail of
the coupled top ends of the displacing elements is varied.
2. The actuator in accordance with claim 1, wherein the controller
controls a driving characteristic of the driven object by varying
diameters of the elliptical trail of the driving member in a normal
direction and a tangential direction at a contacting point of the
driving member with the driven object.
3. The actuator in accordance with claim 2, wherein the controller
controls a phase difference between at least two driving signals
respectively applied to the displacing elements for varying the
diameters of the elliptical trail of the driving member in a normal
direction and a tangential direction at a contacting point of the
driving member with the driven object.
4. The actuator in accordance with claim 2, wherein the controller
controls amplitudes of at least two driving signals respectively
applied to the displacing elements for varying the diameters of the
elliptical trail of the driving member in a normal direction and a
tangential direction at a contacting point of the driving member
with the driven object.
5. The actuator in accordance with claim 2, wherein the controller
can drive the displacing elements in a manner so that the coupled
top ends of the displacing elements moves for trailing at least two
elliptical trails respectively having different shapes, and
switches driving conditions of the displacing elements for
selecting one of the elliptical trails corresponding to a desired
velocity of the driven object.
6. The actuator in accordance with claim 5, wherein the controller
selects an elliptical trail of the coupled top ends of the
displacing elements by which a larger torque can be outputted when
the actuator is start-up, and select another elliptical trail by
which a faster moving velocity of the driven object can be obtained
after a load of the actuator is reduced.
7. The actuator in accordance with claim 1, wherein the controller
varies an inclination angle of a minor axis or a major axis of the
elliptical trail of the coupled top ends of the displacing elements
with respect to a normal direction at a contacting point of the
driving member with the driven object.
8. The actuator in accordance with claim 7, wherein the controller
varies an amplitude of at least one driving signal so as to vary
the inclination angle.
9. The actuator in accordance with claim 7, wherein the controller
varies an amplitude of at least one driving signal so as to vary
the inclination angle corresponding to moving velocity of the
driven object.
10. The actuator in accordance with claim 1, wherein the controller
controls the driving characteristic of the driven object by varying
a length of a minor axis of the elliptical trail of the coupled top
ends of the displacing elements under a condition that the minor
axis of a major axis of the elliptical trail is inclined with
respect to a normal direction at a contacting point of the driving
member with the driven object.
11. The actuator in accordance with claim 10, wherein the
controller controls the length of the minor axis of the elliptical
trail by varying an amplitude of at least one driving signal.
12. The actuator in accordance with claim 7, wherein the controller
divides the plurality of the displacing elements into a first group
and a second group, and drives the first and second groups by
different driving signals.
13. A driving method of an actuator having: a base member; a
plurality of displacing elements for generating a predetermined
displacement, in which top ends of them are coupled at one point
and base ends of them are respectively fixed on the base member;
and a pressing member for contacting the coupled top ends of the
displacing elements to a driven object with a predetermined
pressure for transmitting a driving force to the driven object;
wherein the displacing elements are driven in a manner so that the
coupled top ends thereof moves for trailing an elliptical trail,
and an inclination angle of a minor axis or a major axis of the
elliptical trail with respect to a normal direction at a contacting
point of the driving member with the driven object are varied.
14. The driving method in accordance with claim 13, wherein at
least an amplitude of at least one driving signal applied to the
displacing elements is controlled so as to vary the inclination
angle of the minor axis or the major axis of the elliptical
trail.
15. The driving method in accordance with claim 13, wherein an
amplitude of at least one driving signal is controlled so as to
vary the inclination angle corresponding to moving velocity of the
driven object.
16. A driving method of an actuator having: a base member; a
plurality of displacing elements for generating a predetermined
displacement, in which top ends of them are coupled at one point
and base ends of them are respectively fixed on the base member;
and a pressing member for contacting the coupled top ends of the
displacing elements to a driven object with a predetermined
pressure for transmitting a driving force to the driven object;
wherein driving characteristic of the driven object is controlled
by varying a length of a minor axis of the elliptical trail of the
coupled top ends of the displacing elements under a condition that
the minor axis of a major axis of the elliptical trail is inclined
with respect to a normal direction at a contacting point of the
driving member with the driven object.
17. The driving method in accordance with claim 16, wherein the
length of the minor axis of the elliptical trail is controlled by
varying an amplitude of at least one driving signal.
18. The driving method in accordance with claim 13, wherein the
plurality of the displacing elements are divided into a first group
and a second group, and the first and second groups are
respectively driven by different driving signals.
19. The driving method in accordance with claim 16, wherein the
plurality of the displacing elements are divided into a first group
and a second group, and one of the first and second groups is
driven.
20. A driving method of an actuator having: a base member; a
plurality of displacing elements for generating a predetermined
displacement, in which top ends of them are coupled at one point
and base ends of them are respectively fixed on the base member;
and a pressing member for contacting the coupled top ends of the
displacing elements to a driven object with a predetermined
pressure for transmitting a driving force to the driven object;
wherein the plurality of the displacing elements are divided into a
first group and a second group; and one of the first and second
groups is driven in a manner to satisfy the following equations
(A1) and
(A2);1<fn.sub.1/fn.sub.2<{.alpha..+-.(.alpha..sup.2-1).sup-
.1/2} (A1).alpha.=(1-2.zeta..sup.2)/(1-4.zeta..sup.4) (A2)hereupon,
the symbol "fn.sub.1" designates a resonance frequency in the same
phase mode where the displacing elements contained in the first and
second groups are expanded and contracted at the same phase; the
symbol "fn.sub.2" designates a resonance frequency in the opposite
phase mode where the displacing elements contained in the first
groups are expanded and contracted when the displacing elements
contained in the second groups are contracted and expanded; and the
symbol ".zeta." designates a damping ratio.
21. An actuator comprising: a base member; a plurality of
displacing elements for generating a predetermined displacement, in
which top ends of them are coupled at one point and base ends of
them are respectively fixed on the base member, and divided into a
first group and a second group; a pressing member for contacting
the coupled top ends of the displacing elements to a driven object
with a predetermined pressure for transmitting a driving force to
the driven object; and a driving controller for driving the
displacing elements included in the first and second groups in a
manner so that the coupled top ends thereof moves for trailing an
elliptical trail, and an inclination angle of a minor axis or a
major axis of the elliptical trail with respect to a normal
direction at a contacting point of the driving member with the
driven object are varied; wherein the driving controller further
comprises: a driving signal generator for generating two kinds of
driving signals having a predetermined phase difference; two
amplifiers respectively for amplifying the driving signals and for
applying the driving signals to the displacing elements included in
the first and second groups; a velocity sensor for sensing a moving
velocity of the driven object; an amplitude controller for
controlling an amplification factor of at least one amplifiers
corresponding to a sensed result of the velocity sensor; and a
phase difference controller for controlling the phase difference
between the driving signals corresponding to the sensed result of
the velocity sensor.
22. An actuator comprising: a base member; a plurality of
displacing elements for generating a predetermined displacement, in
which top ends of them are coupled at one point and base ends of
them are respectively fixed on the base member, and divided into a
first group and a second group; a pressing member for contacting
the coupled top ends of the displacing elements to a driven object
with a predetermined pressure for transmitting a driving force to
the driven object; and a driving controller for driving the
displacing elements included in the first and second groups in a
manner so that the coupled top ends thereof moves for trailing an
elliptical trail, and an inclination angle of a minor axis or a
major axis of the elliptical trail with respect to a normal
direction at a contacting point of the driving member with the
driven object are varied by controlling an amplitude of at least
one driving signal; wherein the driving controller further
comprises: a driving signal generator for generating two kinds of
driving signals having a predetermined phase difference; two
amplifiers respectively for amplifying the driving signals and for
applying the driving signals to the displacing elements included in
the first and second groups; an amplitude controller for
controlling an amplification factor of at least one amplifiers; a
phase difference controller for controlling the phase difference
between the driving signals; a memory for storing a plurality of
driving patterns corresponding to elapsed time from the start-up of
driving of the actuator; and a velocity controller for controlling
at least one of the amplitude controller and the phase difference
controller corresponding to the driving pattern when the elapsed
time reaches to a predetermined time period.
23. An actuator comprising: a base member; a plurality of
displacing elements for generating a predetermined displacement, in
which top ends of them are coupled at one point and base ends of
them are respectively fixed on the base member, and divided into a
first group and a second group; a pressing member for contacting
the coupled top ends of the displacing elements to a driven object
with a predetermined pressure for transmitting a driving force to
the driven object; and a driving controller for driving the
displacing elements included in the first and second groups in a
manner so that the coupled top ends thereof moves for trailing an
elliptical trail, and an inclination angle of a minor axis or a
major axis of the elliptical trail with respect to a normal
direction at a contacting point of the driving member with the
driven object are varied by controlling an amplitude of at least
one driving signal; wherein the driving controller further
comprises: a driving signal generator for generating two kinds of
driving signals having a predetermined phase difference; two
amplifiers respectively for amplifying the driving signals and for
applying the driving signals to the displacing elements included in
the first and second groups; an amplitude controller for
controlling an amplification factor of at least one amplifiers; a
phase difference controller for controlling the phase difference
between the driving signals; a velocity sensor for sensing a moving
velocity of the driven object; a memory for storing a plurality of
driving patterns corresponding to the moving velocity of the driven
object; and a velocity controller for controlling at least one of
the amplitude controller and the phase difference controller
corresponding to the driving pattern when the moving velocity of
the driven object reaches to a predetermined velocity.
Description
[0001] This application is based on patent applications 2000-012568
and 2000-097091 filed in Japan, the contents of which are hereby
incorporated by references.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an actuator and a driving
method thereof for moving a driven object such as a rotor or a rod
by intermittently contacting a driving member to the driven object,
in which the driving member is moved for trailing a circular or an
elliptical trail by utilizing vibrations of at least one of a
plurality of displacing elements such as piezoelectric devices.
[0004] 2. Description of the Related Art
[0005] In recent years, a truss-type actuator is proposed for
rotating or moving a driven object in a predetermined direction. In
the truss-type actuator, two displacing elements such as
piezoelectric devices are arranged to cross the displacing
directions thereof at a predetermined angle such as 90 degrees. The
displacing elements are respectively driven by alternating voltage
signals having a predetermined phase difference so that a driving
member provided at a crossing point of the displacing elements is
moved for trailing a circular or an elliptical trail. When the
driving member is intermittently contacted with the driven object,
the driven object is rotated or moved in the predetermined
direction by a friction force acting between the driving member and
the driven object.
[0006] When sinusoidal voltage signals respectively having
different phases are applied two piezoelectric devices, the
piezoelectric devices respectively repeat expansion and
contraction, so that they sinusoidally displace corresponding to
the phase of the driving voltages. Thus, a chip member serving as a
driving member coupled to the piezoelectric devices is moved for
trailing an elliptical trail. When the phase difference of the
sinusoidal displacements of the piezoelectric devices is 90
degrees, the chip member is moved for trailing a circular
trail.
[0007] When the chip member is moved circularly or elliptically,
the chip member is intermittently contacted with a rotor serving as
a driven object. The rotor follows the movement of the chip member
by a friction force acting between the chip member and the rotor
while the chip member is contacted with the rotor, so that the
rotor is intermittently rotated in a predetermine direction. By
repeating these motions, a power of the actuator can be outputted
via the rotation of the rotor.
[0008] For controlling the rotation velocity of the rotor, it is
proposed to vary at least one of a frequency, a voltage and a phase
difference of driving signals (sinusoidal voltage signals) applied
to the piezoelectric devices. In a first conventional actuator
shown in Publication Gazette of Examined Japanese Patent
application Hei 7-114550, a velocity of a driven object is
controlled by switching between a first velocity control for
varying a voltage of driving signals applied to piezoelectric
devices and a second velocity control for varying a frequency of
the driving signals corresponding to a desired velocity of the
driven object. The first conventional actuator, however, has a
disadvantage that a variation of an electric power consumption is
larger and a burden of an electric power supply becomes larger,
since the moving velocity of the driven object is controlled by
varying the voltage or the frequency of the driving signals.
[0009] In a second conventional truss-type actuator shown in
Publication Gazette of Examined Japanese Patent application Hei
6-36673, a phase difference between two driving signals applied to
two piezoelectric devices is fixed to be 120 degrees, and the
piezoelectric devices are driven in a manner so that a chip member
is moved to trail a compressed elliptical trail for increasing a
moving velocity and a torque of a driven object. The second
conventional actuator, however, has a disadvantage that the moving
velocity varies corresponding to variation of a load of the
actuator, since the phase difference of the driving signals is
fixed.
SUMMERY OF THE INVENTION
[0010] A purpose of the present invention is to provide an actuator
and a driving method thereof in which the moving velocity and the
torque of the driven object can be controlled to be desired values
even though the electric power consumption of the actuator is
substantially constant.
[0011] An actuator in accordance with the present invention
comprises: a base member; a plurality of displacing elements for
generating a predetermined displacement, in which top ends of them
are coupled at one point and base ends of them are respectively
fixed on the base member; a pressing member for contacting the
coupled top ends of the displacing elements to a driven object with
a predetermined pressure; a driving circuit for applying at least
one driving signal to at least one displacing elements; and a
controller for controlling the driving signal so that the coupled
top ends of the displacing elements moves for trailing an
elliptical trail; wherein the controller controls the driving
signal in a manner so that shape of the elliptical trail of the
coupled top ends of the displacing elements is varied.
[0012] By such a configuration, a velocity or a torque of the
driven object can be varied corresponding to the shape of the
elliptical trail of the coupled top ends of the displacing
elements. More concretely, a diameter of the elliptical trail in
the tangential direction at the contacting point of the coupled top
ends of the displacing elements and the driven object influences to
the velocity of the driven object, and a diameter of the elliptical
trail in the normal direction influences to the torque or driving
force of the driven object. Thus, it is possible to make the
velocity of the driven object faster by enlarging the diameter of
the elliptical trail in the tangential direction, and to make the
torque of the driven object stronger by enlarging the diameter of
the elliptical train in the normal direction, and vice versa.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a front view showing a configuration of a
lamination type piezoelectric device used as a displacing device in
embodiments of the present invention;
[0014] FIG. 2 is a graph for showing a relation between
displacement of a piezoelectric device and electric field applied
to the piezoelectric device;
[0015] FIG. 3 is front view for showing a configuration of an
actuator in the first embodiment;
[0016] FIG. 4 is a block diagram for showing a configuration of a
driving circuit of the actuator in the first embodiment;
[0017] FIG. 5A is a graph for showing an example of a trail of
movement of a chip member serving as a driving member in the first
embodiment;
[0018] FIG. 5B is a graph for showing another example of the trail
of movement of the chip member in the first embodiment;
[0019] FIG. 6 is a graph for showing characteristic curves of
relations between contact ratios of the chip member and a rotor
serving as a driven object and pressures of a spring for pressing
the chip member to the rotor with respect to voltages of the
driving signals applied to piezoelectric devices in the first
embodiment;
[0020] FIG. 7 is a graph for showing characteristic curves of
relations between rotation velocities of the rotor and loads of the
actuator with respect to the pressure of the spring in the first
embodiment;
[0021] FIG. 8 is a graph for showing characteristic curves of
relations between rotation velocities of the rotor and loads of the
actuator with respect to a phase difference of driving signals in
the first embodiment;
[0022] FIG. 9 is a graph for showing characteristic curves of
relations between rotation velocities of the rotor and loads of the
actuator in the first embodiment;
[0023] FIG. 10 is front view for showing a configuration of an
actuator in a second embodiment of the present invention;
[0024] FIG. 11 is a block diagram for showing a configuration of a
driving circuit of the actuator in the second embodiment;
[0025] FIG. 12 is a front view for showing a configuration of an
actuator in a third embodiment;
[0026] FIGS. 13A to 13C are front views respectively for showing
trails of a chip member when a phase difference of driving signals
applied to piezoelectric devices is varied in a fourth embodiment
of the present invention;
[0027] FIGS. 14A to 14D are front views respectively for showing
the trails of the chip member when not only the phase difference
but also amplitudes of the driving signals applied to the
piezoelectric devices are varied in the fourth embodiment;
[0028] FIG. 15 is a partial front view for showing the details of
inclination of a major axis of an elliptical trail of the chip
member in the fourth embodiment;
[0029] FIG. 16 is a block diagram for showing a configuration of a
driving circuit of the actuator in the fourth embodiment;
[0030] FIG. 17A is a block diagram for showing a configuration of a
modified driving circuit of the actuator in the fourth
embodiment;
[0031] FIG. 17B is a block diagram for showing a configuration of
another modified driving circuit of the actuator in the fourth
embodiment;
[0032] FIG. 18A is a front view for showing a vibration of two
piezoelectric devices in the same phase mode in which the
piezoelectric devices are expanded and contracted at the same
timing;
[0033] FIG. 18B is a front view for showing a vibration of two
piezoelectric devices in the opposite phase mode in which one
piezoelectric device is expanded or contracted when the other
piezoelectric device is contracted or expanded;
[0034] FIG. 19 is a front view for showing an equivalent
single-degree-of-freedom of viscous damping vibration system of the
actuator in a fifth embodiment;
[0035] FIG. 20A is a graph for showing relations between an
amplitude of a vibration and a frequency of a driving signal with
respect to both of the same phase mode and the opposite phase mode
when the actuator is driven under a condition that the trail of the
chip member becomes circular;
[0036] FIG. 20B is a graph for showing a relation between a phase
difference of vibrations in the same phase mode and in the opposite
phase mode and the frequency of the driving signal simultaneous
with the above-mentioned case of FIG. 20A;
[0037] FIGS. 20C to 20G are graphs respectively for showing trails
of the chip member with respect to the frequency of the driving
signal;
[0038] FIG. 21A is a graph for showing relations between the
amplitude of the vibration and the frequency of the driving signal
with respect to both of the same phase mode and the opposite phase
mode when resonance frequencies of vibration systems corresponding
to the same phase mode and the opposite phase mode are largely
different from each other;
[0039] FIG. 21B is a graph for showing a relation between the phase
difference of vibrations in the same phase mode and in the opposite
phase mode and the frequency of the driving signal simultaneous
with the above-mentioned case of FIG. 21A;
[0040] FIGS. 21C to 21G are graphs respectively for showing trails
of the chip member with respect to the frequency of the driving
signal;
[0041] FIG. 22A is a graph for showing relations between the
amplitude of the vibration and the frequency of the driving signal
with respect to both of the same phase mode and the opposite phase
mode when resonance frequencies of vibration systems corresponding
to the same phase mode and in the opposite phase mode are close to
each other;
[0042] FIG. 22B is a graph for showing a relation between the phase
difference of vibrations in the same phase mode and in the opposite
phase mode and the frequency of the driving signal simultaneous
with the above-mentioned case of FIG. 22A;
[0043] FIGS. 22C to 22G are graphs respectively for showing trails
of the chip member with respect to the frequency of the driving
signal;
[0044] FIG. 23 is a front view for showing a driving mode of the
chip member along the ellipse having the major axis inclined
against the normal direction at the contacting point of the chip
member with the rotor in the fifth embodiment;
[0045] FIG. 24 is a front view for showing another driving mode of
the chip member along the ellipse having the major axis parallel to
the tangential direction in the fifth embodiment;
[0046] FIG. 25A is a graph for showing shapes of trails of the chip
member when the actuator was driven by different driving conditions
"A" to "E" under a predetermined driving force in the
above-mentioned fourth embodiment;
[0047] FIG. 25B is a graph for showing shapes of trails of the chip
member when the actuator was driven by different driving conditions
"A" to "E" under another predetermined driving force in the
above-mentioned fourth embodiment;
[0048] FIG. 25C is a graph for showing characteristic curves
between the rotation velocity of the rotor and the driving force of
the actuator with respect to the conditions "A" to "E" under the
driving mode corresponding to FIG. 25A;
[0049] FIG. 25D is a graph for showing characteristic curves
between the rotation velocity of the rotor and the driving force of
the actuator with respect to the conditions "A" to "E" under the
driving mode corresponding to FIG. 25B;
[0050] FIG. 26A is a graph for showing relations between the
rotation velocity of the rotor and the driving force of the
actuator in the fifth embodiment when the actuator was driven in a
manner that the length of the minor axis of the ellipse is varied
while the minor axis is inclined with respect to the normal
direction at the contacting point of the chip member with the
rotor, as shown in FIG. 23;
[0051] FIG. 26B is a graph for show relations between the rotation
velocity of the rotor and the driving force of the actuator in the
fifth embodiment when the actuator was driven in a manner that the
trail of the chip member becomes elliptical and the minor axis of
the ellipse is in the normal direction at the contacting point of
the chip member with the rotor, as shown in FIG. 24; and
[0052] FIG. 27 is a perspective view for showing a configuration of
a modified actuator in the first to fifth embodiment.
DETAILED DESCRIPTION OF THE EMBODIMENT
First Embodiment
[0053] A first embodiment of an actuator in accordance with the
present invention is described. A configuration of a lamination
type piezoelectric device used as a displacing device in the
following embodiments is shown in FIG. 1. The lamination type
piezoelectric device 10 is formed by piling up of a plurality of
ceramic thin plates 11 and electrodes 12 and 13 alternately
disposed. The ceramic thin plates 11 is made of such as PZT showing
piezoelectric characteristic. The ceramic thin plates 11 and the
electrodes 12 and 13 are fixed by an adhesive. Two groups of
electrodes 12 and 13 which are alternately disposed are
respectively connected to a driving power source 16 via cables 14
and 15. When a predetermined voltage is applied between the cables
14 and 15, an electric field is generated in each ceramic thin
plate 11 disposed between the electrodes 12 and 13. The direction
of the electric field in the ceramic thin plates alternately
disposed is the same. Thus, the ceramic thin plates 11 are piled in
a manner so that polarization direction of the ceramic thin plates
11 alternately disposed becomes the same. In other words, the
polarization directions of adjoining two ceramic thin plates are
opposite to each other. Furthermore, protection layers 17 are
provided on both ends of the piezoelectric device 10.
[0054] When a DC driving voltage is applied between the electrodes
12 and 13, each ceramic thin plate 11 expands or contracts in the
same direction. Thus, whole the piezoelectric device 10 can expand
and contract. When the electric field in the ceramic thin plate 11
is sufficiently small and hysteresis of the displacement of the
ceramic thin plate 11 can be ignored, it is possible to consider
that a relation between the displacement of the piezoelectric
device 10 and the electric field generated between the electrodes
12 and 13 is linear. The relation between the displacement of the
piezoelectric device and the electric field is shown in FIG. 2. In
FIG. 2, the abscissa shows the intensity of electric field and the
ordinate shows the ratio of strain of the piezoelectric device.
[0055] When an AC driving voltage (signal) is applied between the
electrodes 12 and 13 by the driving power source 16, all the
ceramic thin plates 11 repeat the expansion and the contraction in
the same direction corresponding to the intensity of the electric
fields. As a result, the piezoelectric device 10 can repeat the
expansion and the contraction. The piezoelectric device 10 has an
inherent resonance frequency defined by the configuration and the
electric characteristics thereof. When the frequency of the AC
driving voltage coincides with the resonance frequency of the
piezoelectric device 10, the impedance of the piezoelectric device
10 is reduced and the displacement thereof increases. Since the
displacement of the piezoelectric device 10 is small with respect
to the size thereof, it is preferable to utilize the resonance
phenomenon for driving the piezoelectric device by a low driving
voltage.
[0056] A configuration of a truss type actuator in the first
embodiment is shown in FIG. 3. A first piezoelectric device 10 and
a second piezoelectric device 10' serving as displacing devices are
disposed to cross substantially at right angle. A chip member 20
serving as a compound member for compounding the displacements of
the first piezoelectric device 10 and the second piezoelectric
device 10' is disposed at crossing point and connected on
respective top ends of the first piezoelectric device 10 and the
second piezoelectric device 10' by an adhesive. Base ends of the
first piezoelectric device 10 and the second piezoelectric device
10' are respectively fixed on a base member 30 by an adhesive. As a
material of the chip member 20, it is preferable to use a material
such as tungsten having high friction factor and high wear
resistance. As a material of the base member 30, it is preferable
to use a material such as stainless steel having high workability
and strength. As a material of the adhesive, it is preferable to
use a material such as epoxy resin having high adhesive strength.
The first piezoelectric device 10 and the second piezoelectric
device 10' are substantially the same as the piezoelectric device
10 shown in FIG. 1. Elements for constituting the second
piezoelectric device 10' are distinguished from those of the first
piezoelectric device 10 by adding (') to the numerals.
[0057] In this actuator, the first piezoelectric device 10 and the
second piezoelectric device 10' are respectively driven by AC
driving signals having a predetermined phase difference, so that
the chip member 20 can be moved elliptically or circularly. When
the chip member 20 is pushed on, for example, a cylindrical surface
of a rotor 40 which can rotate around a predetermined axis, the
elliptic or circular movement of the chip member 20 can be
converted to the rotation of the rotor 40. Alternatively, when the
chip member 20 is pushed on a plane surface of a rod shaped member
(not shown), the elliptic or circular movement of the chip member
20 can be converted to a rectilinear motion of the rod shaped
member. As a material of the rotor 40, it is preferable to use a
material such as aluminum having a light weight. Furthermore, it is
preferable to form an anodic oxide coating on the surface of the
rotor 40 for preventing the wear due to the friction between the
chip member 20 and the rotor 40.
[0058] When two independent movements crossing at right angle are
compounded, the crossing point moves along an elliptic trail
including the circular trail defined by the Lissajous' equation. In
the actuator of the first embodiment, it is possible to control the
rotation direction, the rotation velocity and the torque of the
rotor 40 by controlling the trail of the chip member 20. More
concretely, when the diameter of the trail of the chip member 20 in
the tangential direction of the rotor 40 is enlarged, the rotation
velocity of the rotor 40 can be increased. Alternatively, when the
diameter of the trail of the chip member 20 in the normal direction
of the rotor 40 is enlarged, the torque of the rotor 40 can be
increased. When the phase difference between the driving signals
for the first piezoelectric device 10 and the second piezoelectric
device 10' are reversed, the rotation direction of the rotor 40 can
be reversed.
[0059] A block diagram of a driving circuit is shown in FIG. 4. An
oscillator 50 generates a sinusoidal signal having a predetermined
frequency coinciding with resonance frequencies of the first
piezoelectric device 10 and the second piezoelectric device 10'. A
velocity sensor 56 such as a pulse encoder or a magneto-resistive
device senses a rotation velocity of the rotor 40 and outputs the
sensed result to a phase difference controller 51. The phase
difference controller 51 compares the actual rotation velocity of
the rotor 40 inputted from the velocity sensor 56 with a desires
rotation velocity inputted from a velocity controller 57 such as a
computer for controlling the actuator, calculates the most suitable
phase difference between two driving signals respectively applied
to the first and second piezoelectric devices 10 and 10', and
controls a delay circuit 52 corresponding to the calculated result.
The delay circuit 52 generates a sinusoidal signal having a
predetermined phase difference with the sinusoidal driving signal
from the oscillator 50. A first amplifier 54 amplifies the
sinusoidal driving signal from the oscillator 50. A second
amplifier 55 amplifies the sinusoidal driving signal from the delay
circuit 52. The amplified sinusoidal signals amplified by the first
amplifier 54 and the second amplifier 55 are respectively applied
to the first piezoelectric device 10 and the second piezoelectric
device 10'.
[0060] When the frequency of the sinusoidal voltage signals applied
to the first piezoelectric device 10 and the second piezoelectric
device 10' is larger than a predetermined value, and the rotation
velocity of the chip member 20 becomes faster than a predetermined
velocity, the actuator cannot follow the movement of the chip
member 20 by a pressing force of a spring 41 for pressing the
actuator to the rotor 40, so that the chip member 20
instantaneously is detached from the rotor 40. In other words, the
chip member 20 is intermittently contacted with the rotor 40. The
chip member 20 is moved in a predetermined direction while the chip
member 20 is detached from the rotor 40, and the chip member 20 is
moved in the opposite direction while the chip member 20 is
contacted with the rotor 40, so that the rotor 40 can be
rotated.
[0061] On the other hand, when the displacement of the first and
second piezoelectric actuators 10 and 10' are sufficiently small,
and the displacement of the chip member 20 becomes smaller than
several .mu.m, it is found that the chip member 20 and the rotor 40
always contact each other by elasticity of the materials of them.
In the latter case, the rotor 40 is elastically deformed by the
pressure of the spring, 41 and the chip member 20 is put into the
deformed portion of the rotor 40, so that the chip member 20 is
moved for trailing an elliptical trail under a condition that the
chip member 20 is always contacted with the rotor 40. Thus, the
movement of the rotor 40 is decelerated by the friction force
acting between the rotor 40 and the chip member 20, so that the
output power of the actuator is reduced. This phenomenon is notable
when the pressure of the spring 41 is increased. When the
elliptical trail of the chip member 20 is completely included in
the deformed portion of the rotor 40, a start-up force
corresponding to a start-up torque of the actuator becomes constant
with no relation to the pressing force of the spring 41.
[0062] The actuator shown in FIG. 3 was actually manufactured, and
contacting condition of the chip member 20 with the rotor 40 and
output characteristics of the actuator with respect to the pressure
of the spring 41 were measured.
[0063] FIG. 6 shows a relation between the contact ratio of the
chip member 20 with the rotor 40 and the pressure of the spring 41.
When the voltage or amplitude of the driving signal was 70V, the
contact ration of the chip member 20 with the rotor 40 was
substantially in proportion to the pressure of the spring 41. It
was considered that the displacements of the piezoelectric devices
10 and 10' were larger when the voltage is 70V, and the elastic
deformations of the chip member 20 and the rotor 40 due to the
reaction force of the pressure of the spring 41 was smaller than a
diameter of the trail of the chip member 20 in the normal
direction, so that the chip member 20 could completely be detached
from the rotor 40. By the way, the larger the pressure of the
spring 41 became, the larger the elastic deformations of the chip
member 20 and the rotor 40 became. However, the diameter of the
trail of the chip member 20 was constant, so that the time period
while the chip member 20 was detached from the rotor 40 became
shorter.
[0064] When the voltage was 50V or 30V, the displacements of the
piezoelectric devices 10 and 10' were smaller, and the diameter of
the trail of the chip member 20 was smaller. The elastic
deformations of the chip member 20 and the rotor 40 due to the
pressure of the spring 41, however, were constant, so that it was
considered that the chip member 20 could always be contacted with
the rotor 40 even when the pressure of the spring 41 was smaller.
In comparison with both cases, the displacements of the
piezoelectric devices 10 and 10' under 30V of the voltage of the
driving signal was smaller than those under 50V, so that a region
of the pressure of the spring 41 under 30V, where the rotor 20 was
always contacted with the rotor 40, was wider than that under 50V.
In case that the voltage was 50V, it was found that a transition
point between the first condition where the chip member 20 was
intermittently contacted with and the rotor 40 and the second
condition where the chip member 20 was always contacted with and
the rotor 40 was existed in the vicinity of the point of the
pressure of 2.5N.
[0065] Furthermore, a characteristic between load and velocity of
the rotor 40 was measured under a condition that the voltage, the
frequency and the phase difference of the driving signals of the
piezoelectric devices 10 and 10' were respectively fixed to be 50V,
25 kHz and 90 degrees, and pressure of the spring 41 was varied
from 0.5N to 5N. FIG. 7 shows the measurement results of the
load-velocity characteristics.
[0066] When the ordinate of FIG. 7 was noticed, it was found that
the velocity V of the rotor with no-load was gradually reduced
corresponding to the increase of the pressure of the spring 41.
When the characteristic curves of 0.5N, 1N, 1.5N and 2N
corresponding to the above-mentioned first condition, where the
chip member 20 was intermittently contacted with the rotor 40, were
noticed, it was found that the friction force acting between the
chip member 20 and the rotor 40 was increased corresponding to the
increase of the pressure of the spring 41, so that the start-up
force corresponding to the start-up torque of the actuator was
increased.
[0067] On the other hand, when the characteristic curves of 3N, 4N
and 5N corresponding to the above-mentioned second condition, where
the chip member 20 was always contacted with the rotor 40, were
noticed, it was found that the friction force acting between the
chip member 20 and the rotor 40 was increased corresponding to the
increase of the pressure of the spring 41, so that not only the
start-up force (torque) of the actuator but also the deceleration
force were increased. Since the voltage of the driving signal was
fixed to be 50V, the amplitude of the displacements of the
piezoelectric devices 10 and 10' was constant. Thus, a difference
between the acceleration force and the deceleration force which
corresponds to the torque became substantially constant. The
rotation velocity of the rotor 40, however, was decreased
corresponding to the increase of the pressure of the spring 41, so
that the output power of the actuator was decreased,
consequently.
[0068] FIG. 8 shows the load-velocity characteristics of the rotor
40 when the phase difference between the driving signals was set to
be 60 degrees and 120 degrees and the other conditions were the
same as those in the above-mentioned case. The trails of the chip
member 20 are shown in FIGS. 5A and 5B.
[0069] As can be seen from FIGS. 5A and 5B, when the phase
difference between the driving signals was made smaller, the trail
of the chip member 20 became elliptical where the diameter in the
normal direction at the contacting point of the chip member 20 with
the rotor 40 was longer than that in the tangential direction.
Alternatively, when the phase difference between the driving
signals was made larger, the trail of the chip member 20 became
elliptical where the diameter in the tangential direction was
longer than that in the normal direction. When the phase difference
between the driving signals was made 90 degrees, the trail of the
chip member 20 became substantially circular. The pressure of the
spring 41 was selected in a manner so that the chip member 20 was
always contacted with the rotor 40.
[0070] When a region from 0N to 0.2N on the abscissa of FIG. 8
corresponding to no-load condition and light-load condition was
noticed, the characteristic curve in the case of the phase
difference 120 degrees was positioned above that in the case of the
phase difference 60 degrees. As mentioned above, when the phase
difference between the driving signals was larger, the diameter of
the trail of the chip member 20 in the tangential direction at the
contact point of the chip member 20 and the rotor 40 became larger
and that in the normal direction became smaller. In other words,
the moving velocity or the displacement of the chip member 20 in
the tangential direction was larger and that in the normal
direction was smaller. Alternatively, when the phase difference
between the driving signals was smaller, the diameter of the trail
of the chip member 20 in the tangential direction became smaller
and that in the normal direction became larger. The moving velocity
or the displacement of the chip member 20 in the tangential
direction became smaller and that in the normal direction became
larger.
[0071] With respect to the trail of the chip member 20, the
velocity of the chip member 20 in the tangential direction directly
influences the rotation velocity of the rotor 40 under no-load
condition, and the displacement of the chip member 20 in the normal
direction influences the torque of the actuator. That is, when the
phase difference of the driving signals is made larger, the
rotation velocity of the rotor 40 under no-load condition becomes
faster, but the torque of the actuator becomes smaller. FIG. 8
reflects these consideration.
[0072] Subsequently, a method for varying the driving
characteristics of the actuator by controlling the phase difference
between the driving signals will be described.
[0073] In order to control the velocity of the rotor 40 serving as
the driven object in the truss-type actuator, the diameter of the
trail of the chip member 20 has generally been varied by
controlling the amplitudes of the displacements of the
piezoelectric devices 10 and 10'. Furthermore, in the actuator
utilizing the resonance phenomenon, the diameter of the trail of
the chip member 20 has generally been varied by controlling the
frequency of the driving signals applied to the piezoelectric
devices 10 and 10' in the vicinity of the natural frequencies of
the piezoelectric devices 10 and 10'. These conventional methods,
however, have disadvantages that the energy supplied to the
actuator is varied and the burden of the electric power supply
becomes larger. On the contrary, the method for varying the phase
difference between the driving signals applied to the piezoelectric
devices in the first embodiment has an advantage that the energy
supplied to the actuator is rarely varied and the burden of the
electric power supply becomes much smaller.
[0074] FIG. 9 shows characteristic curves between the load and the
rotation velocity the rotor 40 when the phase difference between
the driving signals was set to be 60 degrees and 120 degrees. In
FIG. 9, the symbol "A" designates the load when the rotor 40 is
continuously rotated (normal rotation load), the symbol "C"
designates the load when the rotor 40 is started up to be rotated
(start-up load), and the symbol "B" designates the middle load
between the loads "A" and When the characteristic curve of the
phase difference of 120 degrees was noticed, it was found that the
velocity of the rotor 40 became 0 between the loads "B" and "C".
When the phase difference of the driving signals applied to the
piezoelectric devices 10 and 10' was set to be 120 degrees, the
start-up force of the actuator was smaller than the static friction
force of the rotor 40, so that it was impossible to rotate the
rotor 40. When the characteristic curve of the phase difference of
60 degrees was noticed, it was found that the velocity of the rotor
40 became zero, when the load is larger than the load "C". When the
phase difference of the driving signals was set to be 60 degrees,
the start-up force of the actuator was larger than the static
friction force of the rotor 40, so that it was possible to rotate
the rotor 40. Thus, the actuator in accordance with the first
embodiment is controlled to be driven by the driving signals having
the phase difference of 60 degrees at the start-up time, and to be
driven by the driving signals having the phase difference of 120
degrees after when the load becomes smaller. By such the control
system, it is possible to provide the actuator having a large
start-up force and a high rotation velocity of the rotor 40.
[0075] Subsequently, it was considered that the load was varied
from "A" to "B" while the actuator was driven. When the load "B"
was noticed, it was found that the velocity of the rotor 40 driven
by the driving signals having the phase difference of 60 degrees
was faster than that driven by the driving signals having the phase
difference of 120 degrees. Thus, it is possible to rotate the rotor
40 faster by switching the driving signals of the piezoelectric
devices 10 and 10' from having the phase difference of 120 degrees
to having the phase difference of 60 degrees. In this example, when
the velocity of the rotor 40 is faster than the velocity v1 where
two characteristic curves cross, the phase difference of the
driving signals applied to the piezoelectric devices 10 and 10' is
set to be 60 degrees, and when the velocity of the rotor 40 is
slower than the velocity v1, the phase difference of the driving
signals applied to the piezoelectric devices 10 and 10' is set to
be 120 degrees. Thus, the rotor 40 is rotated as fast as
possible.
[0076] In the above-mentioned first embodiment, the phase
difference between the driving signals applied to the piezoelectric
devices 10 and 10' is controlled for varying the diameter of the
trail of the chip member 20 in a manner to make the rotation
velocity of the rotor 40 faster and to make the start-up force of
the actuator larger. As a result, the electric power consumption of
the actuator becomes substantially constant with no relation to the
rotation velocity of the rotor 40 or the load of the actuator, so
that it is possible to make the burden of the electric power supply
much smaller, substantially to zero. Furthermore, the phase
difference between the driving signals applied to the piezoelectric
devices 10 and 10' is switched corresponding to the rotation
velocity of the rotor 40 or the load of the actuator after the
starting-up of the driving of the actuator, the rotor 40 can be
rotated at the fastest velocity or be driven by the largest torque
as possible.
Second Embodiment
[0077] A second embodiment of an actuator in accordance with the
present invention is described. FIG. 10 shows a configuration of a
truss-type actuator in the second embodiment. As can be seen from
FIG. 10, the first piezoelectric device 10 is arranged in parallel
with the normal direction at the contacting point of the chip
member 20 with the rotor 40, and the second piezoelectric device
10' is arranged in parallel with the tangential direction. The
other elements except the shape of the chip member 20 and the
position of the spring 41 are substantially the same as those in
the above-mentioned first embodiment.
[0078] A block diagram of a driving circuit is shown in FIG. 11. An
oscillator 50 generates a sinusoidal signal having a predetermined
frequency coinciding with resonance frequencies of the first
piezoelectric device 10 and the second piezoelectric device 10'. A
velocity sensor 56 such as a pulse encoder or a magneto-resistive
device senses a rotation velocity of the rotor 40 and outputs the
sensed result to an amplitude controller 53. The amplitude
controller 53 compares the actual rotation velocity of the rotor 40
inputted from the velocity sensor 56 with a desires rotation
velocity inputted from a velocity controller 57 such as a computer
for controlling the actuator, calculates the most suitable
amplitude of two driving signals respectively applied to the first
and second piezoelectric devices 10 and 10', and controls
amplification factors of a first amplifier 54 and a second
amplifier 55 corresponding to the calculation results. The first
amplifier 54 amplifies the sinusoidal driving signal from the
oscillator 50 corresponding to the control signal from the
amplitude controller 53. The second amplifier 55 amplifies the
sinusoidal driving signal from the delay circuit 52 corresponding
to the control signal from the amplitude controller 53. The
amplified sinusoidal driving signals amplified by the first
amplifier 54 and the second amplifier 55 are respectively applied
to the first piezoelectric device 10 and the second piezoelectric
device 10'. In the second embodiment, the phase difference between
the driving signals applied to the piezoelectric devices 10 and 10'
is fixed.
[0079] In the second embodiment shown in FIG. 10, the shape of the
trail of the chip member 20 is varied by the variations of the
amplitudes of the displacements of the piezoelectric devices 10 and
10'. For varying the diameter of the trail of the chip member 20 in
the tangential direction, the voltage of the driving signal applied
to the second piezoelectric device 10' is controlled. For varying
the diameter of the trail of the chip member 20 in the normal
direction, the voltage of the driving signal applied to the first
piezoelectric device 10 is controlled. Furthermore, it is
preferable to reverse the direction of the voltage of one driving
signal applied to one piezoelectric device when the voltage of the
other driving signal applied to the other piezoelectric device is
controlled so as to make the electric power consumption of the
actuator be constant. In the latter case, the electric power
consumption becomes constant, so that the burden of the electric
power supply be much smaller, substantially to zero.
Third Embodiment
[0080] In the above-mentioned first and second embodiment, the
piezoelectric device is used as the displacing device. The ceramics
which is a material of the ceramic thin plate has larger damping
ratio of the vibrations and the smaller magnification factor of the
resonant vibration than those of the metal materials. Furthermore,
the ceramics is stronger with respect to the pressure but weaker
with respect to the tension, so that it will be separated from the
adhered faces in the lamination type piezoelectric device. In a
third embodiment, a series connection of a single layered
piezoelectric device and an elastic member made of a metal is used
as a displacing device.
[0081] A configuration of the actuator in accordance with the third
embodiment is shown in FIG. 12. A first displacing device 60 and a
second displacing device 60' are respectively configured by single
layered piezoelectric devices (ceramic thin plates) 61 and 61', and
elastic members 62 and 62'. No electrode is provided on both
surface of the piezoelectric devices 61 and 61'. Base ends of the
first displacing device 60 and the second displacing device 60' are
respectively fixed on the base member by screws 63 and 63' without
using any adhesive. On the other hand, the chip member 20 is
connected on top ends of the first displacing device 60 and the
second displacing device 60' by an adhesive or screws. The elastic
members 62 and 62' and the base member 30 are respectively formed
by conductive materials. Two driving power sources 16 and 16' are
connected between the elastic members 62 and the base member 30 and
the elastic member 62' and the base member 30 so as to drive the
first displacing device 60 and the second displacing device 60' at
the above-mentioned resonance frequencies.
[0082] When the elastic member 62 or 62' is vibrated at the
resonance frequency by the piezoelectric device 61 or 61' using as
an oscillator, the displacement of the first displacing device 60
or the second displacing device 60' can be enlarged. Furthermore,
the tension acting on the piezoelectric devices 61 and 61' becomes
smaller, so that the destruction of the piezoelectric devices 61
and 61' can be prevented. As a material of the elastic members 62
and 62', aluminum, titanium, iron, copper, and an alloy including
at least one of them can be used. Since the ratio of the
piezoelectric devices 61 and 61' in the length of the displacing
devices 60 and 60' is very small, the affect due to the
piezoelectric devices 61 and 61' can be ignored when the
above-mentioned normal vibration is calculated.
[0083] Furthermore, in the above-mentioned first to third
embodiments, the frequencies of the driving signals applied to the
piezoelectric devices 10 and 10' or 61 and 61' are not described
concretely. It, however, is possible to drive the piezoelectric
devices 10 and 10' by the driving signals having a frequency equal
to the natural frequency of the piezoelectric devices 10 and 10'
for utilizing the resonance phenomenon, or to drive the
piezoelectric devices 61 and 61' by the driving signals having a
frequency so as to vibrate the elastic members 62 and 62' at the
resonance frequency. In these cases, impedance of the piezoelectric
devices 10 and 107 is reduced, so that the electric power
consumption of the actuator can be reduced. In other words, a high
power can be obtained by a small electric power consumption.
[0084] Furthermore, in the above-mentioned description of the first
to third embodiment, the trail of the movement of the chip member
20 is explained as elliptical shape. It, however, is needless to
say that the circular trail of the chip member 20 can be included
in the scope of the present invention by controlling the phase
difference or the voltages of the driving signals applied to the
piezoelectric devices 10 and 10' or 61 and 61'.
Fourth Embodiment
[0085] A fourth embodiment of a driving method for an actuator in
accordance with the present invention is described. In the fourth
embodiment, the amplitudes and the phase difference of the driving
signals applied to the piezoelectric devices 10 and 10' are varied
so as to control the direction of the major axis or the minor axis
of the elliptical trail of the chip member 20. The actuator driven
by the method in the fourth embodiment is substantially the same as
that shown in FIG. 3.
[0086] FIGS. 13A to 13C respectively show the trails of the chip
member 20 when the phase difference of the driving signals applied
to the piezoelectric devices 10 and 10' is varied. FIG. 13A shows
the trail when the phase difference between the driving signals
applied to the piezoelectric actuators 10 and 10' is 60 degrees.
FIG. 13B shows the trail when the phase difference between the
driving signals is 90 degrees. FIG. 13C shows the trail when the
phase difference between the driving signals is 120 degrees.
[0087] As can be seen from FIGS. 13A to 13C, when the phase
difference between the driving signals is set to be 90 degrees, the
trail of the chip member 20 becomes circular. When the phase
difference between the driving signals is smaller than 90 degrees,
the trail of the chip member 20 becomes elliptical where the major
axis of the ellipse is oriented in the normal direction at the
contacting point of the chip member 20 with the rotor 40 (not
shown). Alternatively, when the phase difference between the
driving signals is larger than 90 degrees, the trail of the chip
member 20 becomes elliptical where the major axis of the ellipse is
oriented in the tangential direction at the contacting point of the
chip member 20 with the rotor 40.
[0088] FIGS. 14A to 14D respectively show the trails of the chip
member 20 when not only the phase difference but also the
amplitudes of the driving signals applied to the piezoelectric
devices 10 and 10' are varied. FIG. 14A shows the trail when the
phase difference between the driving signals is 60 degrees and the
amplitude of the driving signal applied to the first piezoelectric
device 10 is smaller than that applied to the second piezoelectric
device 10'. FIG. 14B shows the trail when the phase difference is
60 degrees and the amplitude of the driving signal applied to the
first piezoelectric device 10 is larger than that applied to the
second piezoelectric device 10'. FIG. 14C shows the trail when the
phase difference is 120 degrees and the amplitude of the driving
signal applied to the first piezoelectric device 10 is smaller than
that applied to the second piezoelectric device 10'. FIG. 14D shows
the trail when the phase difference is 120 degrees and the
amplitude of the driving signal applied to the first piezoelectric
device 10 is larger than that applied to the second piezoelectric
device 10'.
[0089] As can be seen from FIGS. 14A to 14D, in case that the phase
difference between the driving signals is 60 degrees, when the
amplitude of the driving signal applied to the first piezoelectric
device 10 is made smaller than that applied to the second
piezoelectric device 10', the major axis of the elliptical trail of
the chip member 20 inclines toward the first piezoelectric device
10 from the normal direction. Alternatively, when the amplitude of
the driving signal applied to the second piezoelectric device 10'
is made smaller than that applied to the first piezoelectric device
10, the major axis of the elliptical trail of the chip member 20
inclines toward the second piezoelectric device 10 from the normal
direction.
[0090] On the other hand, in case that the phase difference of the
driving signals is 120 degrees, when the amplitude of the driving
signal applied to the first piezoelectric device 10 is made smaller
than that applied to the second piezoelectric device 10', the minor
axis of the elliptical trail of the chip member 20 inclines toward
the second piezoelectric device 10' from the normal direction.
Alternatively, when the amplitude of the driving signal applied to
the second piezoelectric device 10' is made smaller than that
applied to the first piezoelectric device 10, the minor axis of the
elliptical trail of the chip member 20 inclines toward the first
piezoelectric device 10 from the normal direction.
[0091] FIG. 15 shows the details of the inclination of the major
axis of the elliptical trail of the chip member 20 in case that the
phase difference between the driving signals is 60 degrees and the
amplitude of the driving signal applied to the first piezoelectric
device 10 is smaller than that applied to the second piezoelectric
device 10', which corresponds to FIG. 14A.
[0092] In FIG. 15, a symbol ".theta." designates an inclination
angle between the normal direction designated by a symbol "A" and
the major axis of the ellipse. When the actuator is driven, the
chip member 20 is contacted with the rotor 40 (not shown in FIG.
15) by the pressure of the spring 41 (not shown), so that the rotor
40 serving as the driven object is elastically deformed. The
deformation quantity of the rotor 40 is designated by a symbol
".delta.". At this time, a force "Fr" which is applied to the rotor
(driven object) 40 by the chip member 20 is shown by the following
equation (1).
Fr=kr.times..delta. (1)
[0093] Hereupon, the symbol "kr" is a spring constant obtained from
an elastic modulus of a material of the driven object (rotor 40). A
driving force "Ft" following to an outer surface of the driven
object for moving the driven object is shown by the following
equation (2).
Ft=Fr.times.sin.theta. (2)
[0094] Since the driving force "Ft" is a function of the
inclination angle ".theta.", it is possible to control the driving
force of the actuator by varying the inclination angle ".theta."
which is varied by controlling the phase difference and the
amplitude of the driving signals applied to the piezoelectric
devices 10 and 10'.
[0095] FIG. 16 shows a block diagram of a driving circuit in the
fourth embodiment. An oscillator 50 generates a sinusoidal signal
having a predetermined frequency coinciding with resonance
frequencies of the first piezoelectric device 10 and the second
piezoelectric device 10'. A velocity sensor 56 such as a pulse
encoder or a magneto-resistive device senses a rotation velocity of
the rotor 40 and outputs the sensed result to a phase difference
controller 51 and an amplitude controller 53. The phase difference
controller 51 compares the actual rotation velocity of the rotor 40
inputted from the velocity sensor 56 with a desires rotation
velocity inputted from a velocity controller 57 such as a computer
for controlling the actuator, calculates the most suitable phase
difference between two driving signals respectively applied to the
first and second piezoelectric devices 10 and 10', and controls a
delay circuit 52 corresponding to the calculated result. The delay
circuit 52 generates a sinusoidal signal having a predetermined
phase difference with the sinusoidal driving signal from the
oscillator 50.
[0096] The amplitude controller 53 compares the actual rotation
velocity of the rotor 40 inputted from the velocity sensor 56 with
a desires rotation velocity inputted from the velocity controller
57, calculates the most suitable amplitude of two driving signals
respectively applied to the first and second piezoelectric devices
10 and 10', and controls amplification factors of a first amplifier
54 and a second amplifier 55 corresponding to the calculation
results. The first amplifier 54 amplifies the sinusoidal driving
signal from the oscillator 50 corresponding to the control signal
from the amplitude controller 53. The second amplifier 55 amplifies
the sinusoidal driving signal from the delay circuit 52
corresponding to the control signal from the amplitude controller
53. The amplified sinusoidal signals amplified by the first
amplifier 54 and the second amplifier 55 are respectively applied
to the first piezoelectric device 10 and the second piezoelectric
device 10'.
[0097] Alternatively, it is possible to use another driving circuit
shown in FIG. 17A or 17B. In the driving circuit shown in FIG. 17A,
it uses a memory 58 and a timer 59 connected to the velocity
controller 57 instead of the velocity sensor 56. The memory 58
stores several kinds of driving patterns from a low velocity and
high torque driving to a high velocity and low torque driving
respectively including the phase difference information and the
amplitude information of the driving signals. The timer 59 counts a
time from the start-up of the actuator. When the timer 59 counts a
predetermined time period, the velocity controller 57 reads out a
driving pattern corresponding to the time period from the start-up
from the memory 58, and controls the phase difference controller 51
or the amplitude controller 53 corresponding to the phase
difference information or the amplitude information included in the
driving pattern.
[0098] In the driving circuit shown in FIG. 17B, output signal from
the velocity sensor 56 is input to the velocity controller 57, and
a memory 58 is connected to the velocity controller 57. The memory
58 stores several kinds of driving patterns from a low velocity and
high torque driving to a high velocity and low torque driving
respectively including the phase difference information and the
amplitude information of the driving signals. The velocity sensor
56 senses the rotation velocity of the rotor 40. When the rotation
velocity of the rotor 40 reaches to a predetermined velocity, the
velocity controller 57 reads out a driving pattern corresponding to
the rotation velocity of the rotor 40 from the velocity sensor 56,
and controls the phase difference controller 51 or the amplitude
controller 53 corresponding to the phase difference information or
the amplitude information included in the driving pattern.
[0099] In the above-mentioned description of the fourth embodiment,
the phase difference and the amplitudes of the driving signals are
varied for controlling the inclination angle of the elliptical
trail of the chip member 20. It, however, is possible to vary the
amplitudes of the driving signals for controlling the inclination
angle of the elliptical trail of the chip member 20. When not only
the rotation speed of the rotor 40 but also the start-up torque of
the actuator are controlled, it is possible to vary the phase
difference of the driving signals, too.
[0100] With respect to the driving mode of the piezoelectric
devices 10 and 10', it is possible to drive the piezoelectric
devices 10 and 10' in alternative of the resonance vibration mode
in which the frequency of the driving signals is substantially the
same as the natural frequency of the piezoelectric devices 10 and
10' and the non-resonance vibration mode in which the frequency of
the driving signals is different from the natural frequency of the
piezoelectric devices 10 and 10'. The resonance vibration mode has
an advantage that the driving efficiency of the actuator is higher,
so that the voltage of the driving signals of the actuator can be
made lower. In the resonance vibration mode, the voltage of the
driving signals and the phase of the displacement of the
piezoelectric devices are largely varied in the vicinity of the
resonance frequency. When the resonance frequency of the first
piezoelectric device 10 is different from that of the second
piezoelectric device 10', it is preferable to detect the current
values of the driving signals flowing in the piezoelectric devices
10 and 10', and to control the phase difference of the voltage of
the driving signals so as to coincide the phase difference of the
currents with a predetermined value, since the phases of the
currents are in proportion to the phases of the displacements of
the piezoelectric devices 10 and 10'.
[0101] Furthermore, the driving method in accordance with the
fourth embodiment can be applied to the actuator in accordance with
the third embodiment shown in FIG. 12.
Fifth Embodiment
[0102] A fifth embodiment of a driving method for an actuator in
accordance with the present invention is described. In the
above-mentioned first to fourth embodiments, the first
piezoelectric device 10 and the second piezoelectric device 10' are
simultaneously driven. In the fifth embodiment, only one of the
piezoelectric devices 10 and 10' is driven so as to move the chip
member 20 for trailing a desired trail. The driving method in the
fifth embodiment cannot be realized by utilizing the resonance
phenomenon. It, however, is possible to simplify the driving
circuit, since only one piezoelectric device is driven. Numerical
treatment and the experiment results of the driving method in the
fifth embodiment will be described.
[0103] FIG. 18A shows the vibration of the piezoelectric devices 10
and 10' in the same phase mode in which the piezoelectric devices
10 and 10' are expanded and contracted at the same timing. FIG. 18B
shows the vibration of the piezoelectric devices 10 and 10' in the
opposite phase mode in which the first piezoelectric device 10 is
expanded or contracted when the second piezoelectric device 10' is
contracted or expanded.
[0104] FIG. 19 shows an equivalent single-degree-of-freedom of
viscous damping vibration system of the actuator including springs,
weights and dash pots (not shown in the figure). In FIG. 19, the
same phase mode is shown as a first vibration system vibrating in
the normal direction A at the contacting point of the chip member
20 with the rotor 40 (not shown in the figure), and the opposite
phase mode is shown as a second vibration system vibrating in the
tangential direction B. The direction of the displacement in the
same phase mode crosses the direction of the displacement in the
opposite phase mode at right angle, so that the vibration forces of
the first piezoelectric device 10 in the axial direction thereof is
symmetrically separated in the normal direction A and the
tangential direction B.
[0105] When a sinusoidal vibration force
f(t)=F.sub.0.multidot.cos.omega.t is applied to the
single-degree-of-freedom vibration system (k: spring constant; m:
mass of the weight; and .eta.: viscosity), the displacement
.chi.(t) of the vibration system is shown by the following equation
(3).
.chi.(t)=X.multidot.cos(.omega.t-.phi.) (3)
[0106] Hereupon, the symbol "X" designates the amplitude of the
vibration of the vibration system and the symbol ".phi." designates
the phase delay of the actual displacement of the piezoelectric
device with respect to the phase of the driving signal. The same
rule applies correspondingly to the following. The amplitude X and
the phase delay .phi. are shown by the following equations.
X=X.sub.0[{1-(.omega./.omega.n).sup.2}.sup.2+(2.zeta..omega./.omega.n).sup-
.2].sup.1/2
.phi.=tan.sup.-1(2.zeta..omega..omega.n)/{1-(.omega./.omega.n).sup.2}
[0107] In the above-mentioned equations, the symbol ".omega.n"
designates the natural frequency of the vibration system and
.omega. n=(k/m).sup.1/2; the symbol ".zeta." designates the damping
ratio of the vibration system and .zeta.=.eta./2(mk).sup.1/2; the
symbol "X.sub.0" designates the static displacement of the
vibration system and X.sub.0=F.sub.0/k; and the symbol "fn"
designates the resonance frequency of the vibration system and
fn=.omega.n/2.pi..
[0108] When the driving force F.sub.0=cos.omega.t generated by the
piezoelectric device 10 is separated to a first component
f.sub.1(t) of the first vibration system in the normal direction A
and a second component f.sub.2(t) in the second vibration system in
the tangential direction B, the first and second components
f.sub.1(t) and f.sub.2(t) are respectively shown by the following
equation (4).
f.sub.1(t)=f.sub.2(t)=(F.sub.0/2.sup.1/2).multidot.cos.omega.t
(4)
[0109] When the equation (4) is substituted into the
above-mentioned equation (3), the .chi..sub.1(t) of the first
vibration system and the displacement .chi..sub.2(t) of the second
vibration system are respectively shown by the following equations
(5) and (6).
.chi..sub.1(t)=X.sub.1.multidot.cos(.omega.t-.phi..sub.1) (5)
.chi..sub.2(t)=X.sub.2.multidot.cos(.omega.t-.phi..sub.2) (6)
[0110] Hereupon, the symbol "X.sub.1" designates the amplitude of
the first vibration system, the symbol "X.sub.2" designates the
amplitude of the second vibration system, the symbol ".phi..sub.1"
designates the phase delay of the displacement in the same phase
mode with respect to phase of the driving signal, and the symbol
".phi..sub.2" designates the phase delay of the displacement in the
opposite phase mode with respect to the phase of the driving
signal. The amplitudes X.sub.1, X.sub.2 and the phase delays
.phi..sub.1, .phi..sub.2 are shown by the following equations.
X.sub.1=X.sub.01[{1-(.omega./.omega.n.sub.1).sup.2}.sup.2+(2.zeta..sub.1.o-
mega./.omega.n.sub.1).sup.2].sup.1/2
.phi..sub.1=tan.sup.-1(2.zeta..sub.1.omega./.omega.n.sub.1)/{1-(.omega./.o-
mega.n.sub.1).sup.2}
X.sub.2=X.sub.02[{1-(.omega./.omega.n.sub.2).sup.2}.sup.2+(2.zeta..sub.2.o-
mega./.omega.n.sub.2).sup.2].sup.1/2
.phi..sub.2=tan.sup.-1(2.zeta..sub.2.omega./.omega.n.sub.2)/{1-(.omega./.o-
mega.n.sub.2).sup.2}
[0111] In the above-mentioned equations, the symbol
".omega.n.sub.2" designates the natural frequency of the first
vibration system and (t) n.sub.1=(k.sub.1/m.sub.1).sup.1/2; the
symbol ".omega.n.sub.2" designates the natural frequency of the
second vibration system and
.omega.n.sub.2=(k.sub.2/m.sub.2).sup.1/2; the symbol ".zeta..sub.1"
designates the damping ratio of the first vibration system and
.zeta..sub.1=.eta..sub.1/2(m.sub.1k.sub.1).sup.1/2; the symbol
".zeta..sub.2" designates the damping ratio of the second vibration
system and .zeta..sub.2=.eta..sub.2/2(m.sub.2k.sub.2).sup.1/2; the
symbol "X.sub.01" designates the static displacement of the first
vibration system and X.sub.01=F.sub.01/2.sup.1/2k.sub.1; the symbol
"X.sub.02" designates the static displacement of the second
vibration system and X.sub.02=F.sub.02/2.sup.1/2k.sub.2; the symbol
"fn.sub.1" designates the resonance frequency of the first
vibration system and fn.sub.1=.omega.n.sub.1/2.pi.; and the symbol
"fn.sub.2" designates the resonance frequency of the second
vibration system and fn.sub.2=.omega.n.sub.2/2.pi..
[0112] When the natural frequencies .omega.n.sub.1 and
.omega.n.sub.2, damping ratios .zeta..sub.1 and .zeta..sub.2, and
static displacements X.sub.01 and X.sub.02 of the first and second
vibration systems are obtained, it is possible to find the relation
between the frequency f=.omega./2.pi. of the driving signal and the
displacements .chi..sub.1(t) and .chi..sub.2(t) of the first and
second vibration systems.
[0113] Conditions that the trail of the chip member 20 is to be
circular are considered. Since the first vibration system and the
second vibration system are cross at right angle, it is known from
the Lissajous' equation that the trail of the chip member 20
becomes circular when amplitudes of the vibration of the first
vibration system and the second vibration system are the same but
the phase difference between them becomes 90 degrees. Thus, the
condition can be shown by the following equations (7) and (8). The
equation (8) shows the condition that the amplitudes of the
vibrations of the first vibration system and the second vibration
system become the same. The equation (9) shows the condition that
the phase difference between the vibrations of the first vibration
system and the second vibration system becomes 90 degrees. 1 X 01 /
[ { 1 - ( / n 1 ) 2 } 2 + ( 2 1 / n 1 ) 2 ] 1 / 2 = X 02 / [ { 1 -
( / n 2 ) 2 } 2 + ( 2 2 / n 2 ) 2 ] 1 / 2 ( 7 ) ( 2 1 / n ) 1 - ( /
n 1 ) 2 .times. ( 2 2 / n 2 ) 1 - ( / n 2 ) 2 = - 1 ( 8 )
[0114] For simplifying the above-mentioned equations (7) and (8),
it is assumed that .zeta..sub.1=.zeta..sub.2 and X.sub.01=X.sub.02.
The .omega. is deleted from the equations (7) and (8), the relation
between the .zeta. and the fn.sub.1, fn.sub.2 can be shown the
following equation (9). The equation (9) shows a ratio of the
resonance frequencies of the first and second vibration
systems.
fn.sub.1/fn.sub.2={.alpha..+-.(.alpha..sup.2-1).sup.1/2} (9)
(1-2.zeta..sup.2)/(1-4.zeta..sup.4)=.alpha.
[0115] When the damping ratio of the vibration system is obtained,
the ratio of the resonance frequencies of the first and second
vibration systems by which the trail of the chip member becomes
circular can be known. At this time, the frequency of the driving
signal f.sub.3 is shown by the following equation (10).
f.sub.3=.omega..sub.3/2.pi. (10)
.omega..sub.3.sup.2=[(2.omega.n.sub.1.sup.2.multidot..omega.n.sub.2.sup.2)-
/(.omega.n.sub.1.sup.2+.omega.n.sub.2.sup.2)].multidot.(1-2.zeta..sup.2)
[0116] Subsequently, a relation between the ratio of the resonance
frequencies and the trail of the chip member 20 in FIG. 19 is
considered.
[0117] FIGS. 20A to 20G relate to a condition that the trail of the
chip member 20 becomes circular when the ratio of the resonance
frequencies of the vibration systems satisfies the above-mentioned
equation (9). FIGS. 21A to 21G relate to an example when the
resonance frequencies of the vibration systems are largely
different. FIGS. 22A to 22G relates to another example that the
resonance frequencies of the vibration systems are close to each
other. In these cases, the first piezoelectric device 10 is driven
and the damping ratio of the first and second vibration systems
.zeta..sub.1 and .zeta..sub.2 are set to be 0.025. The values of
the resonance frequencies are suitably selected.
[0118] FIG. 20A shows relations between the amplitude of the
vibration and the frequency of the driving signal with respect to
both of the same phase mode and the opposite phase mode. FIG. 20B
shows a relation between the phase difference between the
vibrations in the same phase mode and in the opposite phase mode
and the frequency of the driving signal. FIG. 20C shows the trails
of the chip member 20 when the frequency of the driving signal is
at a low frequency. FIG. 20D shows the trails of the chip member 20
when the frequency of the driving signal is at the resonance
frequency in the same phase mode. FIG. 20E shows the trails of the
chip member 20 when the frequency of the driving signal is the
middle between the resonance frequencies in the same phase mode and
in the opposite phase mode. FIG. 20F shows the trails of the chip
member 20 when the frequency of the driving signal is at the
resonance frequency in the opposite phase mode. FIG. 20G shows the
trails of the chip member 20 when the frequency of the driving
signal is at a high frequency. The same rules applies
correspondingly to the FIGS. 21A to 21g and 22! to 22G.
[0119] In FIG. 20A, when the resonance frequency fn.sub.1 in the
same phase mode (first vibration system) is defined to be
f.sub.1=64 kHz, the resonance frequency in the opposite phase mode
(second vibration system) fn.sub.2 becomes f.sub.2=67 kHz from the
equations (9) and (10), so that the frequency of the driving signal
f.sub.3 becomes f.sub.3=65.4 kHz.
[0120] When the frequency of the driving signal f.sub.3 is equal to
65.4 kHz, the amplitude of the vibrations in both of the same phase
mode and the opposite phase mode coincide with each other, so that
the phase difference between the vibrations in the same phase mode
and in the opposite phase mode becomes 90 degrees. Thus, the trail
of the chip member 20 becomes circular as shown in FIG. 20E. With
respect to the first vibration system corresponding to the same
phase mode, the frequency of the driving signal is larger than the
resonance frequency of the first vibration system, and the
amplitude of the vibration is a little smaller than the largest
value at the peak on the characteristic curve with respect to the
same phase mode, as shown in FIG. 20A. The phase delay of the
vibration in the same phase mode with respect to the driving signal
becomes larger than 90 degrees, as shown in FIG. 20B. On the other
hand, with respect to the vibration in the second vibration system
corresponding to the opposite phase mode, the frequency of the
driving signal is smaller than the resonance frequency in the
opposite phase mode, and the amplitude of the vibration is a little
smaller than the largest value at the peak on the characteristic
curve with respect to the opposite phase mode, as shown in FIG.
20A. The phase delay of the vibration in the opposite phase mode
with respect to the phase of the driving signal becomes smaller
than 90 degrees, as shown in FIG. 20B. Furthermore, the phase delay
of the vibration in the same phase mode is larger than that in the
opposite phase mode, so that the chip member 20 rotates in
counterclockwise direction.
[0121] When the frequency of the driving signal is much smaller
than the resonance frequencies of the first and second vibration
systems, the amplitudes of the first and second vibration systems
are substantially the same, as shown in FIG. 20A, and the phase
difference between vibrations of the first and second vibration
systems becomes near to zero, as shown in FIG. 20B. Thus, the trail
of the chip member 20 becomes a small ellipse having a major axis
along the displacing direction of the piezoelectric device 10, as
shown in FIG. 20C. When the frequency of the driving signal is much
larger than the resonance frequencies of the first and second
vibration systems, the same rules are applied correspondingly (see
FIG. 20G). When the frequency of the driving signal coincides with
one of the resonance frequencies of the first and second driving
systems, both of the ratio of the amplitudes of the vibrations of
the first and second vibration systems and the phase difference
between the vibrations of the first and second vibration systems
become larger. Thus, the trail of the chip member 20 becomes a
large ellipse having a major axis along the vibration direction of
the first or second vibration system, as shown in FIG. 20D or FIG.
20F.
[0122] When the resonance frequencies in the same phase mode and in
the opposite phase mode are largely different, as shown in FIG.
21A, the steep sloped portions of both characteristic curves are
rarely overlapped. The phase difference between the vibrations in
the first and second driving systems is continuously varied between
0 to 180 degrees, as shown in FIG. 21B. When the frequency of the
driving signal is much larger or much smaller than the resonance
frequencies in the same phase mode and in the opposite phase mode,
the trail of the chip member 20 becomes a small ellipse having a
major axis along the displacing direction of the piezoelectric
actuator 10, as shown in FIG. 21C or 21G. When the frequency of the
driving signal coincides with one of the resonance frequencies in
the same phase mode and in the opposite phase mode, the difference
between the amplitudes of the vibrations of the first and second
vibration systems is much larger, the trail of the chip member 20
becomes a large ellipse having a major axis along the displacing
direction of the piezoelectric device 10, as shown in FIG. 21D or
21F. When the frequency of the driving signal is at the middle
between the resonance frequencies, the amplitudes of the vibrations
of the first and second vibration systems become equal to each
other but small. The phase difference between the vibrations of the
first and second vibration systems becomes close to 180 degrees.
Thus, the trail of the chip member 20 becomes a small ellipse
having a major axis vertical to the driving direction, as shown in
FIG. 21E.
[0123] When the resonance frequencies in the same phase mode and in
the opposite phase mode are close to each other, as shown in FIG.
22A, the steep sloped portions of both characteristic curves are
substantially overlapped. The peak of the characteristic curve with
respect to the phase difference between the vibrations of the first
and second vibration systems becomes lower, as shown in FIG. 22B.
When the frequency of the driving signal is much larger or smaller
than the resonance frequencies in the same phase mode and in the
opposite phase mode, the trail of the chip member 20 becomes a
small ellipse having a major axis along the displacing direction of
the piezoelectric device 10, as shown in FIG. 22C or 22G. When the
frequency of the driving signal coincides with one of the resonance
frequencies in the same phase mode and in the opposite phase mode,
the amplitudes of the vibrations of the first and second vibration
system become substantially the same, and the phase difference
between the vibrations of the first and second vibration systems
becomes a little smaller, so that the trail of the chip member 20
becomes a large ellipse having a major axis along the displacing
direction of the piezoelectric device 10, as shown in FIG. 22D or
22F. When the frequency of the driving signal is at the middle
between the resonance frequencies, the amplitudes of the vibrations
of the first and second vibration systems becomes equal to each
other and large. The phase difference between the vibrations in the
first and second vibration systems becomes smaller. Thus, the trail
of the chip member becomes a large ellipse having a major axis
vertical to the displacing direction of the piezoelectric device
10, as shown in FIG. 22E.
[0124] In the above-mentioned description, the first piezoelectric
device 10 arranged in the horizontal direction in FIG. 19 is
driven. Alternatively, when the second piezoelectric device 10'
arranged in the vertical direction is driven, the vibration model
becomes symmetrical to that in the above-mentioned case, so that
the chip member 20 rotates in the clockwise direction. Furthermore,
when the resonance frequency in the same phase mode is larger than
that in the opposite phase mode, the phase delay in the opposite
phase mode becomes larger than that in the same phase mode, so that
the chip member 20 rotates in the clockwise direction.
[0125] Driving method in the fifth embodiment is described. As
mentioned above, several kinds of elliptical trails of the chip
member 20 can be obtained by driving only one piezoelectric device,
corresponding to the values of the resonance frequencies in the
same phase mode and in the opposite phase mode.
[0126] In the fifth embodiment, the resonance frequency fn.sub.1 in
the same phase mode is set to be larger than the resonance
frequency fn.sub.2 in the opposite phase mode, so that the trail of
the chip member 20 shown in FIGS. 23 and 24 are obtained. In the
examples shown in FIGS. 23 and 24, only the second piezoelectric
device 10' is driven.
[0127] For obtaining an elliptical trail of the chip member 20, it
is necessary to satisfy the following formula (11) in view of the
above-mentioned equation (9) which shows the condition for
obtaining the circular trail.
fn.sub.1/fn.sub.2<{.alpha..+-.(.alpha..sup.2-1).sup.1/2}
(11)
[0128] For preventing the phenomenon that the moving direction of
the rotor 40 serving as the driven object is reverse to the moving
direction of the chip member 20 serving as a driving member when
the chip member 20 is elliptically moved, it is necessary to
satisfy the following formula (12).
1<fn.sub.1/fn.sub.2 (12)
[0129] Thus, it is necessary to satisfy the following formula (13)
for moving the chip member 20 along an elliptical trail by driving
only one piezoelectric device in the fifth embodiment.
1<fn.sub.1/fn.sub.2<{.alpha..+-.(.alpha..sup.2-1).sup.1/2}
(13)
[0130] When the formula (13) is satisfied, it is possible to
coincide the displacing direction of the piezoelectric device 10'
with the moving direction of the rotor 40 when the chip member 20
is moved along the elliptical trail. When the formula (12) is not
satisfied, that is fn.sub.1/fn.sub.2<1, the displacing direction
of the piezoelectric device 10' becomes opposite to the moving
direction of the rotor 40 when the chip member 20 is moved along
the elliptical trail, so that it is difficult to rotate the rotor
40.
[0131] Furthermore, it is possible to move the chip member 20 along
the elliptical trail having the major axis inclined against the
normal direction at the contacting point of the chip member 20 with
the rotor 40 as shown in FIG. 23 or along the elliptical trail
having the major axis parallel to the tangential direction as shown
in FIG. 24 by suitably selecting the resonance frequencies in the
same phase mode and in the opposite phase mode and the frequency of
the driving signal. In FIGS. 23 and 24, the chip member 20 is moved
in the clockwise direction. It, however, is possible to move the
chip member 20 in the counterclockwise direction by switching the
driven piezoelectric device from the second piezoelectric device
10' to the first piezoelectric device 10.
OTHER MODIFICATIONS
[0132] In the above-mentioned embodiments, the actuator has two
piezoelectric devices serving as the displacing elements. The
present invention is not restricted to the configuration having two
displacing elements, and can be applied to the actuator having the
displacing elements more than three.
[0133] FIG. 27 shows a modification having four displacing elements
10A to 10D. For generating a vibration in a direction designated by
arrow x, it is considered that the displacing elements 10A and 10B
are considered to be a first group corresponding to one of the
piezoelectric device 10 or 10' and the displacing elements 10C and
10D are considered to be a second group corresponding to the other.
Similarly, for generating a vibration in a direction designated by
arrow y, it is considered that the displacing elements 10A and 10D
are considered to be a first group corresponding to one of the
piezoelectric device 10 or 10' and the displacing elements 10B and
10C are considered to be a second group corresponding to the
other.
[0134] Furthermore, in the above-mentioned embodiments, the rotor
40 is used as the driven object. The present invention, however, is
not restricted to the above-mentioned embodiment. It is possible to
apply an actuator having a rotor having an elliptical section or a
sliding member as the driven object. In the former case, the
actuator is driven in a manner so that the major axis or the minor
axis of the elliptical trail of the chip member is inclined with
respect to the normal direction at the contacting point of the chip
member with the elliptical rotor. When the sliding member is a
plate, the actuator is driven in a manner so that the major axis or
the minor axis of the elliptical trail of the chip member is
inclined with respect to a line perpendicular to the contacting
plane of the sliding member.
[0135] In the above-mentioned embodiments, two displacing devices
are disposed for crossing at right angle. It, however, is not
restricted by this disposition. It is possible to cross at another
angle such as 45 degrees or 135 degrees. Furthermore, the number of
the displacing devices are not restricted by two. It is possible to
use more than three displacing devices for realizing a movement
having three- or four-degrees-of-freedom. Still furthermore, it is
possible to use another mechanical or electric displacing device
such as a magnetostrictive device as a driving source.
EXPERIMENTAL RESULT
[0136] The trails of the chip member 20 and the driving
characteristics of the actuator in accordance with the fourth
embodiment are described with reference to FIGS. 25A to 25D. FIGS.
25A and 25B respectively show the shapes of the trails of the chip
member 20 when the actuator was driven by different driving
conditions "A" to "E". The difference between FIG. 25A and 25B was
the condition of the driving force of the actuator. For example,
FIG. 25A corresponds to the driving force "M" in FIG. 25C or 25D,
and FIG. 25B corresponds to the driving force "N". In the figures,
numerals designate the actual sizes of the elliptical trails and
the unit thereof was ".mu.m".
[0137] FIG. 25C shows the characteristic curves between the
rotation velocity of the rotor 40 and the driving force of the
actuator with respect to the conditions "A" to "E". In FIG. 25C,
the abscissa designates the driving force of the actuator, and the
ordinate designates the rotation velocity of the rotor 40. The
direction of the pressure of the spring 41 was applied in parallel
with the abscissa in FIGS. 25A and 25B. FIG. 25D shows the
characteristic curves between the efficiency and the driving force
of the actuator with respect to the conditions "A" to "E". In FIG.
25C, the abscissa designates the driving force of the actuator, and
the ordinate designates the efficiency of the actuator. In FIGS.
25C and 25D, the dotted line "M" designates the condition
corresponding to FIG. 25A, and the dotted line "N" designates the
condition corresponding to FIG. 25B.
[0138] As can be seen from FIGS. 25A and 25B, under the driving
condition "A", the major axis of the elliptical trail of the chip
member 20 was parallel to the tangential direction at the
contacting point of the chip member 20 with the rotor 40. Under the
driving conditions "B" to "E", the inclination angle of the minor
axis or the major axis of the elliptical trail of the chip member
20 with respect to the tangential direction was gradually
increased.
[0139] As can be seen from FIGS. 25C and 25D, it was found that the
output power and the efficiency of the actuator driven by the
driving conditions "B" to "D" became larger than those driven by
the driving condition "A". However, when the actuator was driven by
the driving condition "E", the minor axis of the elliptical trail
became too short so that the chip member 20 moved rather linear
than elliptical. Thus, the output power and the efficiency of the
actuator driven by the driving condition "E" became smaller than
those driven by the driving condition "A".
[0140] Accordingly, it is preferable to drive the actuator by
controlling at least one of the phase difference and the amplitudes
of the driving signals so that the trail of the chip member 20
becomes an ellipse having a minor axis inclined with respect to the
normal direction at the contacting point of the chip member 20 with
the rotor 40 in a region where the minor axis of the ellipse is not
too small. The same rules are applied correspondingly to the fifth
embodiment.
[0141] FIG. 26A shows the relations between the rotation velocity
of the rotor 40 and the driving force of the actuator in accordance
with the fifth embodiment when the actuator was driven in a manner
that the length of the minor axis of the ellipse is varied while
the minor axis is inclined with respect to the normal direction at
the contacting point of the chip member 20 with the rotor 40, as
shown in FIG. 23. FIG. 26B shows the relations between the rotation
velocity of the rotor 40 and the driving force of the actuator in
accordance with the fifth embodiment when the actuator was driven
in a manner that the trail of the chip member 20 becomes elliptical
and the minor axis of the ellipse is in the normal direction at the
contacting point of the chip member 20 with the rotor 40, that is
the ellipse was not inclined, as shown in FIG. 24. In the FIGS. 26A
and 26B, the symbols "TS48" and so on designate the driving
conditions; the symbol "v" designates the rotation velocity of the
rotor 40; and the symbol ".eta." designates the efficiency of the
actuator.
[0142] In comparison with FIG. 26A and FIG. 26B, it was found that
the output power and the efficiency of the actuator were increased
by driving one piezoelectric device 10 or 10' in a manner so that
the minor axis of the elliptical trail of the chip member 20 is
inclined with respect to the normal direction at the contacting
point of the chip member 20 with the rotor 40. Thus, it is
preferable to control the phase difference and the amplitude of the
driving signals of the actuator in there manner.
[0143] Although the present invention has been fully described by
way of example with reference to the accompanying drawings, it is
to be understood 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.
* * * * *