Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2000-04-21
2002-04-02
Budd, Mark O. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S323080
Reexamination Certificate
active
06366004
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a progressive wave type ultrasonic motor.
A typical ultrasonic motor has a stator and a rotor. The stator includes a piezoelectric element. The rotor is pressed against and rotatable relative to the stator. When an axial vibration having a resonant frequency is applied to the stator, the piezoelectric element vibrates axially, which generates axial vibration on the upper surface of the stator. The axial vibration on the stator is transmitted to the rotor, which generates a torsional vibration in the entire rotor. The torsional vibration rotates the rotor in a predetermined direction.
The amplitude of the torsional vibration in the rotor is preferably large. That is, the greater the amplitude, the greater the driving force of the rotor and thus the more efficiently the rotor rotates. To increase the amplitude of the torsional vibration, an ultrasonic motor having a rotor
91
shown in
FIG. 14
has been proposed.
Rotor slits
92
are formed in the outer surface of the rotor
91
. The rotor slits
92
promote the torsional vibration generated in the entire rotor
91
. That is, the slits
92
increase the amplitude of the torsional vibration, which efficiently rotates the rotor
91
.
The rotor
91
is rotated by generating torsional vibration in the entire rotor
91
. In this case, the smaller the axial dimension of the rotor
91
, the less the driving force of the rotor
91
. That is, if the axial dimension of the rotor
91
is decreased, it is difficult to generate axial vibration in the entire rotor
91
. Specifically, if the rotor
91
is excessively flattened, a bending vibration as in a plate is generated in the rotor
91
, which hinders torsion of the rotor
91
. Therefore, the axial dimension of the rotor
91
cannot be decreased beyond a certain limit. This limitation of reduction in the rotor axial direction limits the reduction of the rotor size, which prevents the size of the ultrasonic motor having the rotor
91
from being decreased.
SUMMARY OF THE INVENTION
Accordingly, it is an objective of the present invention to provide a compact ultrasonic motor.
To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, an ultrasonic motor is provided. The motor includes a stator vibrated by a piezoelectric element and a rotor. The rotor includes a plurality of contact portions arranged about an axis of the rotor. The contact portions contact the stator. Each contact portion independently vibrates in response to the vibration of the stator, thereby causing the rotor to rotate.
The present invention may also be embodied as a method for designing an ultrasonic motor. The motor includes a stator, which is vibrated by a piezoelectric element, and a rotor, which rotates in response to the vibration of the stator. The method comprising: computing a resonant frequency of the stator, wherein an alternating current having the computed frequency or a frequency close to the computed frequency is applied to the piezoelectric element; forming a plurality of contact portions on the rotor that are arranged about the axis of the rotor and contact the stator; and designing each contact portion such that each contact portion has a resonant frequency that is equal to or close to the frequency of a vibration generated in the stator.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.
REFERENCES:
patent: 4752711 (1988-06-01), Tuskimoto et al.
patent: 5233257 (1993-08-01), Luthier et al.
patent: 5237237 (1993-08-01), Ueda et al.
patent: 5473215 (1995-12-01), Luthier
patent: 6018213 (2000-01-01), Yano
patent: 6166477 (2000-12-01), Komoda et al.
Ishikawa Masashi
Yano Motoyasu
Asmo Co. Ltd.
Budd Mark O.
TraskBritt
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