Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1997-03-28
2001-06-26
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S328000, C310S317000
Reexamination Certificate
active
06252332
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an ultrasonic motor utilizing ultrasonic vibration and an ultrasonic actuator.
As an ultrasonic motor of this kind, there is known a “heteromorphic degeneration longitude L
1
−bend B
4
mode planar motor” described, for example, in “the Lecture Papers in the 5th Dynamics Symposium Related to Electromagnetic Force”.
FIGS. 4A
to
4
C of the accompanying drawings show the structure of the ultrasonic motor described in the above-mentioned publication.
FIG. 4A
is a view of the ultrasonic motor as it is seen from just above it,
FIG. 4B
is a cross-sectional view of the ultrasonic motor taken in the direction of arrow P, and
FIG. 4C
is a cross-sectional view of the ultrasonic motor taken in the direction of arrow Q.
In
FIGS. 4A
to
4
C, the reference numeral
1
designates a resilient member having piezoelectric elements
11
and
12
adhesively secured to the upper surface thereof, and electrodes, not shown, are adhesively secured to the upper surfaces of the piezoelectric elements
11
and
12
. Also, projected portions
13
and
14
are formed on the lower surface of the resilient member
1
, and vibration created in the resilient member
1
is taken out by these projected portions
13
and
14
. These projected portions
13
and
14
will hereinafter be called the drive force taking-out portions. The piezoelectric elements
11
and
12
are polarized in the same direction, and high frequency voltages differing in phase by 90 degrees (&pgr;/2) from each other are applied to the respective piezoelectric elements
11
and
12
through the electrodes.
2. Related Background Art
FIG. 7
of the accompanying drawings shows the relation between the frequency of the high frequency voltages applied to the piezoelectric elements
11
and
12
of the ultrasonic motor of
FIGS. 4A
to
4
C and the amplitude of the vibration created in the resilient member
1
.
As shown in
FIG. 7
, as the frequency of the high frequency voltages is gradually dropped from a maximum frequency f
max
, the amplitude of the vibration becomes gradually greater. When the frequency of the high frequency voltages becomes lower than a frequency f
b
for which the amplitude of the vibration becomes maximum, the amplitude of the vibration suddenly decreases and the ultrasonic motor becomes stopped. The frequency for which the shown amplitude of the vibration becomes greatest is generally called the resonance frequency, and when the ultrasonic motor is driven at this frequency, the ultrasonic motor can be driven most efficiently.
On the other hand, as the frequency of the high frequency voltages is gradually increased from a minimum frequency f
min
, the amplitude of the vibration suddenly increases at a point of time whereat the frequency exceeds a frequency fa which is a frequency higher than the frequency fb, and the ultrasonic motor begins to be driven and thereafter, the amplitude of the vibration decreases gradually.
In the ultrasonic motor shown in
FIGS. 4A
to
4
C, the frequency of the high frequency voltages applied to the piezoelectric elements
11
and
12
can be varied to thereby control the speed of the ultrasonic motor. However, when an attempt is made to drive the ultrasonic motor, for example, at a frequency between the shown frequencies fb and fa, if the frequency is gradually dropped from the maximum frequency f
max
side, the ultrasonic motor can be driven within the above-mentioned frequency range without any problem, whereas if the frequency is gradually increased from the minimum frequency f
min
side, the ultrasonic motor remains stopped within the above-mentioned frequency range as shown in FIG.
7
. Accordingly, when for example, in an attempt to drive the ultrasonic motor at the resonance frequency, the frequency of the high frequency voltages are variously varied to effect the retrieval of the resonance frequency, there is the possibility that in some cases, the frequency may be dropped too much and the ultrasonic motor may become unable to be started.
Further,
FIG. 18
of the accompanying drawings is a perspective view showing an example of an ultrasonic actuator of the longitudinal and torsional vibration type according to the prior art.
In an ultrasonic actuator of this kind, a stator
201
(see
FIG. 19
) is such that a piezoelectric element
204
for torsional vibration is interposed between two vibrators
202
and
203
of the cylinder type and a piezoelectric element
205
(see
FIG. 19
) for longitudinal vibration is disposed on the upper side of the vibrator
203
. The piezoelectric element
204
for torsional vibration is polarized circumferentially thereof, and the piezoelectric element
205
for longitudinal vibration is polarized in the direction of the thickness thereof. Further, a rotor
206
is disposed on the upper side of the piezoelectric element
205
for longitudinal vibration.
The vibrators
202
,
203
and piezoelectric elements
204
,
205
constituting the stator
201
are fixed to a shaft
207
(threadably engaged with the threaded portion of the shaft
207
), and the rotor
206
is rotatably provided on the shaft
207
through a ball bearing
208
. The tip end of the shaft
207
is threadably engaged by a nut
210
through a spring
209
to thereby bring the rotor
206
into pressure contact with the stator
201
.
The piezoelectric element
204
for torsional vibration and the piezoelectric element
205
for longitudinal vibration are driven by a voltage of the same frequency oscillated by an oscillator
211
which is phase-controlled by a phase device
212
.
The piezoelectric element
204
for torsional vibration gives mechanical displacement for the rotor
206
to rotate, and the piezoelectric element
205
for longitudinal vibration performs the function of synchronizing a frictional force working between the stator
201
and the rotor
206
with the period of the torsional vibration by the piezoelectric element
204
and periodically fluctuating it, thereby converting vibration into motion in one direction.
FIG. 19
of the accompanying drawings is a developed perspective view showing the stator of the ultrasonic actuator according to the prior art.
The piezoelectric element
204
for torsional vibration need be polarized circumferentially thereof and therefore. As shown in
FIG. 18
, a piezoelectric material has once been divided into six to eight sector-shaped small pieces, and each small piece has been polarized, whereafter the small pieces have been again combined into an annular shape. The reference character
204
a
designates an electrode.
However, in the aforedescribed prior-art ultrasonic actuator, it has been difficult to yield shape accuracy when the piezoelectric elements for torsional vibration are combined into an annular shape.
On the other hand, the areas of the piezoelectric elements for longitudinal vibration and for torsional vibration have been substantially equal to or smaller than the cross-sectional area of the stator. Also, in order to pass a shaft through the piezoelectric elements, it has been necessary to form a hole in the central portions of the piezoelectric elements. Therefore, the areas of the piezoelectric elements have become smaller and it has been difficult to obtain high torque and high-speed rotation of the motor.
In order to solve such problems, applicant has already proposed an ultrasonic actuator of the longitudinal and torsional vibration type which can be driven by high torque and high-speed rotation and moreover is simple in structure and simple to manufacture (Japanese Patent Application No. 6-180279).
The stator of this ultrasonic actuator of the longitudinal and torsional vibration type is of a construction which comprises a thick resilient member divided into semicircular tubular shapes, and electro-mechanical conversion elements for torsional vibration and longitudinal vibration joined to the divided surfaces of the resilient member (see
FIGS. 12A and 12B
of the accompanying drawings). The rotor of the ultrasonic actuat
Ashizawa Takatoshi
Takagi Tadao
Dougherty Thomas M.
Nikon Corporation
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