Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2002-11-19
2004-10-12
Nguyen, Tran (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S316010, C310S316020, C310S323020
Reexamination Certificate
active
06803699
ABSTRACT:
This application is based upon application No. 2002-240864 filed in Japan, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a drive mechanism employing an electromechanical transducer and a drive method therefor. More specifically, the present invention relates to the drive mechanism employing the electromechanical transducer such as a piezoelectric element and the like, suitable for driving a lens of a camera, a precision stage and the like, and the method for controlling the drive mechanism.
2. Description of the Related Arts
Conventionally, there has been proposed a drive mechanism employing an electromechanical transducer.
For example,
FIGS. 1A through 1C
show such a drive mechanism of an element-fixed type schematically. One end of a piezoelectric element in an extending and contracting direction is connected to a fixed member (or a stationary member) . The other end of the piezoelectric element in the same direction is connected to a drive member. The drive member moves in forward direction and backward direction, when the piezoelectric element extends or contracts. A moving body (or a driven member) is engaged with the drive member by a frictional force.
The moving body is driven when a voltage is applied to the piezoelectric element so as to cause the piezoelectric element to extend at a first velocity, and to contract at a second velocity, different from the first velocity.
FIGS. 1A
,
1
B and
1
C show respective states at points of time indicated by the reference characters A, B and C in FIG.
1
D.
When the voltage gradually increases during a section A-B as shown in
FIG. 1D
, the piezoelectric element relatively slowly extends so that the state as shown in
FIG. 1A
changes into the state as shown in FIG.
1
B. At the time, the moving body slides little, or it does not slide with respect to the drive member, and therefore the moving body moves together with the drive member substantially.
Secondly, when the voltage abruptly decreases during a section B-C as shown in
FIG. 1D
, the piezoelectric element contracts relatively fast so that the drive member returns to an initial position. At the time, the moving body stays at the present position substantially, and the moving body slides with respect to the drive member. Therefore, only the drive member returns to the initial position. As the result, the moving body moves from the initial position as shown in
FIG. 1A
to a forward position as shown in FIG.
1
C.
Repeating such a cycle, the moving body moves along the drive member in a forward direction.
In the mean time, the moving body moves in a backward direction, when a voltage applied to the piezoelectric element has a waveform including rapidly increasing parts and gradually decreasing parts.
In order to run the drive mechanism, there are two manners of applying a voltage having a saw-tooth waveform to the piezoelectric element.
FIGS. 2
shows a first manner thereof. As shown in
FIG. 2A
, a waveform generator W, specifically a digital-analog transducer therein, for example, of 8 bits and 1-5 volts type, generates a voltage having a saw-tooth waveform. The voltage having the saw-tooth waveform is amplified, for example, up to 1-10 volts, by an amplifier M, and then is applied to a piezoelectric element X in order to run the drive mechanism. By adjusting the waveform generator W, a waveform of forward direction as shown in
FIG. 2B and a
waveform of backward direction as shown in
FIG. 2C
can be generated.
FIGS. 3 and 4
show a second manner thereof.
FIG. 3
shows a circuit for applying a power-supply voltage V to a piezoelectric element X. The circuit includes constant current circuits A, D and switching circuits B, C. The waveform of forward direction or the waveform of backward direction are generated by actuating the constant current circuit A and the switching circuit B alternately, or by actuating the constant current circuit D and the switching circuit C alternately.
For example, the circuit is constituted as shown in FIG.
4
A. When control signals are input to terminals “a”, “b”, “c” and “d” of the circuit, the waveform of forward direction or the waveform of backward direction is generated, as shown in FIG.
4
B.
Specifically, when the terminal “a” is supplied with Hi input, the voltage applied to a piezoelectric element X gradually increases through the constant current circuit A as shown by the reference numeral
10
in FIG.
3
B. Next, when the terminal “b” is supplied with Hi input, the piezoelectric element X is grounded through the switch circuit B, so that the voltage applied to the piezoelectric element X rapidly decreases as shown by the reference numeral
12
in FIG.
4
B. Thus, the waveform of forward direction is generated.
In the mean time, when the terminal “c” is supplied with Hi input, the piezoelectric element X is connected to the power-supply voltage V through the switch circuit C, so that the voltage applied to the piezoelectric element X rapidly increases as shown by the reference numeral
14
in FIG.
4
B. Then, when the terminal “d” is supplied with Hi input, the voltage applied to the piezoelectric element X gradually decreases through the constant current circuit D as shown by the reference numeral
16
in FIG.
4
B. Thus, the waveform of backward direction is generated.
In the first manner, the waveform generator W and the power amplifier M are needed. In the second manner, the constant current circuits A, D and the switch circuits B, C are needed. Thus, the construction of the circuit is complex and leads to high cost. Moreover, it is difficult to achieve stable low-speed running of the drive mechanism.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a drive mechanism which comprises a drive circuit employing a simple construction and achieving stable low-speed driving.
It is another object of the present invention to provide a drive method for carrying out the stable low-speed driving.
In order to achieve one of the above objects, according to one aspect of the present invention, there is provided a drive mechanism, comprising: an electromechanical transducer having a pair of ends in expanding and contracting direction; a drive member fixed to one of the ends of the electromechanical transducer; a driven member which contacts frictionally with the drive member under a predetermined frictional force exerted therebetween; and a drive circuit for applying a drive voltage to the electromechanical transducer, wherein the drive voltage repeats a cycle of a first voltage having a value which is one of a maximum value and a minimum value, a second voltage having a value which is a value intermediate between the maximum value and the minimum value, and a third voltage having a value which is the other of the maximum value and the minimum value, and wherein applying the drive voltage to the electromechanical transducer causes the electromechanical transducer to expand and to contract so as to move the driven member along the drive member relatively.
Generally, the electromechanical transducer (for example, piezoelectric transducer, electrostriction transducer, magnetostriction transducer, electrostatic actuator and the like) changes the electrical energy (for example, electric voltage, electric current, electric field, magnetic field, static electricity and the like) supplied thereto into the mechanical energy (for example, transformation or strain such as prolonging, compressing, expanding, contracting, bending, twisting and the like).
In the configuration, while the drive voltage changes from the first voltage to the third voltage through the second voltage, the change of the drive voltage is relatively gradual. Therefore, the electromechanical transducer expands or contracts gradually so that the driven member moves together with the drive member without sliding with respect to the drive member substantially. In the meantime, while the drive voltage changes from the third voltage to the f
Yoshida Ryuichi
Yuasa Tomoyuki
Aguirrechea J.
McDermott Will & Emery LLP
Minolta Co. , Ltd.
Nguyen Tran
LandOfFree
Drive mechanism employing electromechanical transducer and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Drive mechanism employing electromechanical transducer and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Drive mechanism employing electromechanical transducer and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3312005