Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2001-06-28
2002-10-22
Budd, Mark O. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S323120, C310S316010, C310S325000
Reexamination Certificate
active
06469419
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ultrasonic motor and a method for operating the ultrasonic motor.
2. Description of Related Art
One example of a previously proposed ultrasonic motor is a standing-wave type ultrasonic motor, such as shown in
FIGS. 16 and 17
. This type of ultrasonic motor includes a rotor
101
and a stator
102
. The stator
102
includes metal blocks
104
,
105
, piezoelectric elements
106
,
107
, drive electrode plate
108
, longitudinal-vibration sensing electrode plate
109
and common electrode plates
110
,
111
, which are all connected and fastened together by a single bolt
112
. With reference to
FIG. 16
, the drive electrode plate
108
and the longitudinal-vibration sensing electrode plate
109
are integrated in a single disk and are electrically insulated from each other.
With reference to
FIG. 17
, a portion of the bolt
112
that protrudes from a top surface of the stator
102
(metal block
104
) is received within the rotor
101
, and a nut
113
is tightened onto the bolt
112
to tightly connect the rotor
101
and the stator
102
together.
The ultrasonic motor is rotated both forward and backward by a drive control circuit
119
. With reference to
FIG. 17
, the drive control circuit
119
includes a rotational direction selection circuit
120
, a frequency variable oscillation circuit
121
and a power amplifier
122
. The rotational direction selection circuit
120
outputs a forward rotational signal s
1
and a backward rotational signal s
2
to the frequency variable oscillation circuit
121
when the ultrasonic motor is rotated forward and backward, respectively. The frequency variable oscillation circuit
121
generates a signal SGf
1
having a resonance frequency f
1
(or a signal SGf
2
having a resonance frequency f
2
) for rotating the ultrasonic motor forward (or backward) based on the forward rotational signal s
1
(or backward rotational signal s
2
) outputted from the rotational direction selection circuit
120
and then outputs it to the power amplifier
122
. The power amplifier
122
amplifies the signal SGf
1
having the frequency f
1
(or the signal SGf
2
having the frequency f
2
) and applies it between the drive electrode plate
108
and each one of the common electrode plates
110
,
111
.
Then, the ultrasonic motor is rotated forward with the high frequency voltage that has the resonance frequency f
1
and that has been amplified through the power amplifier
122
. Vibrations of the stator
102
generated during the forward rotation of the ultrasonic motor are complex vibrations that include torsional vibrations (mainly secondary torsional vibrations) as a major component and additionally include longitudinal vibrations as a minor component. Also, the ultrasonic motor is rotated backward with the high frequency voltage that has the resonance frequency f
2
and that has been amplified through the power amplifier
122
. Vibrations of the stator
102
generated during the backward rotation of the ultrasonic motor are complex vibrations that include longitudinal vibrations (mainly primary longitudinal vibrations) as a major component and additionally include torsional vibrations as a minor component.
A change in an ambient temperature or a load applied to the ultrasonic motor may cause the ultrasonic motor (stator
102
) to vibrate at a frequency other than the resonance frequency f
1
although the high frequency voltage having the resonance frequency f
1
for the forward rotation is applied to the ultrasonic motor from the power amplifier
122
. This results in reduced rotational efficiency of the ultrasonic motor. The same thing happens when the ultrasonic motor is rotated backward upon application of the high frequency voltage having the resonance frequency f
2
for the backward rotation to the ultrasonic motor.
In order to vibrate the ultrasonic motor at the resonance frequency f
1
(or resonance frequency f
2
) regardless of the change in the ambient temperature or the load, the frequency of the high frequency voltage to be applied between the drive electrode plate
108
and each one of the common electrode plates
110
,
111
is controlled. More specifically, the drive control circuit
119
includes a vibration comparator circuit
130
and a frequency control circuit
131
.
The vibration comparator circuit
130
receives a signal indicative of a current vibrational state of the stator
102
from a longitudinal-vibration sensing electrode plate
109
and thereby obtains a vibrational frequency (actual vibrational frequency) of the stator
102
. The vibration comparator circuit
130
compares the actual vibrational frequency with the resonance frequency f
1
(or the resonance frequency f
2
in the case of the backward rotation) and outputs this comparison result to the frequency control circuit
131
.
The frequency control circuit
131
computes a required control amount to shift the actual vibrational frequency of the stator
102
to the resonance frequency f
1
(or the resonance frequency f
2
in the case of the backward rotation) based on the comparison result and outputs the computed control amount to the frequency variable oscillation circuit
121
. The frequency variable oscillation circuit
121
shifts the frequency of the signal SGf
1
(or the signal SGf
2
) in such a manner that the actual vibrational frequency of the stator
102
substantially coincides with the resonance frequency f
1
(or the resonance frequency f
2
in the case of the backward rotation) based on the control amount outputted from the frequency control circuit
131
and outputs it to the power amplifier
122
.
Thus, even though the ambient temperature or the load changes, the ultrasonic motor can vibrate at the resonance frequency f
1
(or the resonance frequency f
2
in the case of the backward rotation), so that the ultrasonic motor can be rotated effectively.
However, the vibrations of the stator
102
are complex vibrations comprising the longitudinal vibrations and the torsional vibrations. A vibrational pattern of the longitudinal vibrations is different from a vibrational pattern of the torsional vibrations. Thus, it is difficult to accurately sense the vibrational pattern of each one of the longitudinal and torsional vibrations with the single longitudinal-vibration sensing electrode plate
109
. Furthermore, the previously proposed ultrasonic motor uses the vibration comparator circuit
130
and the frequency control circuit
131
which are rather complex and expensive, resulting in an increase in a manufacturing cost of the ultrasonic motor.
SUMMARY OF THE INVENTION
Thus, it is an objective of the present invention to provide an ultrasonic motor that can optimize its operating conditions and that allows a reduction in a manufacturing cost of the ultrasonic motor. It is another objective of the present invention to provide a method for operating such an ultrasonic motor.
To achieve the objectives of the present invention, there is provided an ultrasonic motor including a rotor and a stator. The stator generates complex vibrations for rotating the rotor. The complex vibrations include longitudinal vibrations and torsional vibrations. The rotor is rotatably urged against the stator. The stator includes a plurality of piezoelectric drive elements, a plurality of power supply electrode plates for supplying power to the piezoelectric drive elements, a longitudinal-vibration sensing means for sensing the longitudinal vibrations, a first metal block, a second metal block and a torsional-vibration sensing means for sensing the torsional vibrations. The piezoelectric drive elements, the power supply electrode plates and the longitudinal-vibration sensing means are securely clamped between the first metal block and the second metal block. The torsional-vibration sensing means is provided separately from the piezoelectric drive elements and the power supply electrode plates.
There is also provided a method for operating an ultrasonic motor including a stator and a rotor. The s
Kato Yukiyasu
Komoda Masahiko
Yano Motoyasu
Asmo Co. Ltd.
Budd Mark O.
Law Offices of David G. Posz
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