Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2000-01-04
2001-11-27
Budd, Mark O. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
Reexamination Certificate
active
06323578
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a piezoelectric actuator capable of efficiently moving a moving member, a method of driving a piezoelectric actuator and a computer readable storage medium stored with a program for making a computer execute a method of driving a piezoelectric actuator.
Currently, downsizing of OA apparatus and information processing apparatus has been progressed. In accordance therewith, attention is attracted to a piezoelectric actuator as a power supply used for driving and transferring. As an example of such a piezoelectric actuator, there is known an ultrasonic motor of a progressive wave type applying elongation and contraction operation on a piezoelectric element.
A progressive wave type ultrasonic motor is constituted by a stator and a rotor in a ring-like shape as shown by “Introduction to Ultrasonic Motor” by Kenjo, Shidacho, p.7, edited by Sogo Densi Shuppan. A piezoelectric oscillator comprising PZT ceramic is bonded onto a rear face of the stator by an adhering agent to thereby oscillate integrally therewith.
The piezoelectric member in the ring-like shape is divided into a plurality of small regions which are respectively polarized in directions alternately opposed to each other to produce a flexural wave of a progressive wave (refer to drawings at pp. 11 and 197 of the cited literature). Further, in order to apply sine wave voltages accompanied by phase differences on piezoelectric members at the respective divided regions, similarly divided metal electrode films must by formed. Further, in many case, the stator has a number of grooves or projections in a diameter direction in order to enlarge displacement. Such a complicated structure can easily be fabricated in the case of an ultrasonic motor having a diameter of several cm and therefore, there poses no problem. However, when a motor having a diameter equal to or smaller than 10 mm is desired, fine dimensional accuracy is required and the fabrication becomes considerably difficult with fabrication technologies currently used in the industry.
In order to resolve the above-described problem and realize a small-sized piezoelectric actuator having the diameter equal to or smaller than 10 mm, structures of an oscillator and a piezoelectric member may be constructed by a simple flat plate structure referred to as a unimorpl structure and there may be used a fabrication technology excellent in mass production performance of photolithography or etching.
However, as described on page 77 of the cited literature, according to the unimorph structure which is a simple structure of pasting together the oscillator and the piezoelectric member in the flat plate shape, there also poses a problem in which a flexural wave necessary for functioning the ultrasonic motor cannot be produced.
In order to resolve the above-described problem in the conventional technology, according to the invention, there is provided a method capable of producing a flexural wave even with the simple unimorph structure.
However, according to the above-described conventional micro piezoelectric motor
500
shown in
FIG. 7
, a flexural displacement mechanism unit
22
is oscillated at a primary mode and accordingly, there poses a problem in which produced torque is insufficient and a rotational number thereof is also small. Further description of the motor
500
is omitted here, reference being made to the detailed description of the motor
100
given hereinbelow.
SUMMARY OF THE INVENTION
Hence, the invention has been carried out in view of the above-described and it is an object of the invention to provide a piezoelectric actuator capable of providing sufficient torque and a large rotational number, a method of driving a piezoelectric actuator and a computer readable storage medium stored with a program for making a computer execute a method of driving a piezoelectric actuator.
In order to achieve the above-described object, according to a first aspect of the invention, there is provided a piezoelectric actuator comprising a moving member, a supporting member which is arranged opposedly to the moving member, one end of which is fixed to constitute a cantilever and other end of which is brought into contact with the moving member when the supporting member is oscillated, a piezoelectric member spread onto the supporting member and a power supply for supplying a voltage to the piezoelectric member to thereby oscillate the supporting member at a secondary mode or a higher mode.
When the supporting member is oscillated at the second mode or the higher mode, although an amplitude of oscillation is reduced, a component in the horizontal direction of the moving member is increased. Further, in order to produce the oscillation at the higher mode, a high resonance frequency in accordance therewith is requested and therefore, a number of bringing the supporting member into contact with the moving member is increased. Therefore, an amount of moving the moving member is increased and the torque is increased.
Further, according to a second aspect of the invention, there is provided a piezoelectric actuator comprising a moving member, a supporting member which is arranged opposedly to the moving member, one end of which is fixed to constitute a cantilever and other end of which is brought into contact with the moving member when the supporting member is oscillated, a piezoelectric member spread onto the supporting member and a power supply for supplying a power to the piezoelectric member to thereby make the supporting member execute an oscillation including a tertiary mode.
In this way, it is preferable to supply the piezoelectric member with the voltage for oscillating the supporting member at the tertiary mode. As described above, both the torque and the amount of moving are promoted in the case of the higher mode, it is difficult in view of the power supply and other constitution to oscillate the piezoelectric member at an excessively high mode. Further, both the torque and the amount of moving are larger in the case of the tertiary mode than in the case of the secondary mode. Therefore, the supporting member is made to be able to oscillate at a mode including at least the tertiary mode.
Further, according to a third aspect of the invention, there is provided the piezoelectric actuator wherein a frequency of the voltage supplied to the piezoelectric member falls in a range of 100 kHz through 1 MHz.
According to a size of a beam portion of a general micromotor, when voltage having a frequency of 100 kHz through 1 MHz is applied, oscillation at a higher mode can easily be provided.
Further, according to a fourth aspect of the invention, there is provided a piezoelectric actuator comprising a rotational moving member, an oscillator comprising supporting members each extended in a tangential line direction of an inner circle of the rotational moving member and having one fixed end and other free end and piezoelectric members pasted on the respective supporting members and a power supply for specifying a frequency of oscillating the supporting members at a higher mode based on a size and Young's modulus of each of the supporting members and supplying a voltage at the specified frequency to the piezoelectric members.
In an example of a rotational type, the frequency of the voltage supplied to the piezoelectric member is determined based on the size and Young's modulus of the supporting member. By oscillating the supporting member at the higher mode, large torque and rotational number can be provided to the rotational type piezoelectric actuator.
Further, according to a fifth aspect of the invention, there is provided a method of driving a piezoelectric actuator of constituting the piezoelectric actuator comprising a moving member, a supporting member which is arranged opposedly to the moving member, one end of which is fixed to constitute a cantilever and other end of which is brought into contact with the moving member in oscillating the supporting member and a piezoelectric member spread onto the supporting memb
Maeda Hidetaka
Suzuki Mizuaki
Suzuki Yoko
Tani Kazuo
Adams & Wilks
Budd Mark O.
Seiko Instruments Inc.
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