Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2002-10-09
2004-11-09
Budd, Mark (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S316020, C318S116000
Reexamination Certificate
active
06815871
ABSTRACT:
This application is based upon application No. 2002-202750 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, a drive method and a circuit employed therein. More specifically, the present invention relates to the circuit suitable for applying a saw-tooth waveform of a voltage to a capacitive load, the drive mechanism provided with the circuit, and the drive method employing the circuit.
2. Description of the Related Arts
Conventionally, there have been two manners of running a drive mechanism in which a saw-tooth waveform of voltage is applied to a piezoelectric element.
Referring to
FIGS. 1A through 1C
, the first manner of running the drive mechanism will be explained. As shown in
FIG. 1A
, 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 running the drive mechanism. By adjusting the waveform generator W, a waveform of forward direction as shown in
FIG. 1B and a
waveform of backward direction as shown in
FIG. 2C
can be generated.
FIGS. 2
,
3
A and
3
B show a second manner of running the drive mechanism.
FIG. 2
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.
3
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.
3
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.
3
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.
3
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.
3
B. Therefore, 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 introduces high cost. Additionally, the waveform includes high-order harmonic waves, which are not needed, and causes undesirable influence upon the drive mechanism.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a drive mechanism, a drive method and a circuit employing a simple construction, in which a voltage having a saw-tooth waveform to be applied can be generated.
In order to achieve the above object, according to one aspect of the present invention, there is provided a drive mechanism, comprising: an electromechanical transducer operating as a capacitor and having a pair of terminals; an inductive element operating as an inductor and having a pair of terminals; and a resistive element operating as a resistor and having a pair of terminals, wherein the electromechanical transducer, the inductive element and the resistive element are connected by terminals thereof in series so as to constitute a series resonance circuit, and wherein a voltage having a saw-tooth waveform applied to the electromechanical transducer causes the electromechanical transducer to expand at a first velocity and to contract at a second velocity, different from the first velocity.
In the configuration, the electromechanical transducer (for example, electrostatic actuator, piezoelectric transducer, electrostriction transducer, magnetostriction transducer, and so on) changes the electrical energy (for example, electric voltage, electric current, electric field, electric charge, static electricity, magnetic field) supplied thereto into the mechanical energy (for example, transformation or strain such as prolonging, compressing, expanding, contracting, bending, twisting).
In the configuration, the transfer function of the series resonance circuit, which is a serial RLC circuit, includes a second-order lag element, and therefore a suitable waveform of the voltage applied to the series resonance circuit causes the saw-tooth or slant waveform of the voltage applied to the electromechanical transducer.
According to the configuration, it is possible to make parts of the circuit for generating a voltage applied to the electromechanical transducer less than that of conventional drive mechanisms. Thus, the voltage having the saw-tooth waveform applied to the electromechanical transducer can be generated, employing a simple construction.
As an embodiment, a voltage having a square waveform applied to the series resonance circuit generates the voltage having the saw-tooth waveform applied to the electromechanical transducer.
In the configuration, it is easy to apply the voltage having the square waveform so as to generate the voltage having the saw-tooth waveform applied to the electromechanical transducer.
As an embodiment, one of the terminals of the electromechanical transducer is connected to ground. The other of the terminals of the electromechanical transducer is connected to one of the terminals of the resistive element. The other of the terminals of the resistive element is connected to one of the terminals of the inductive element. The voltage having the square waveform applied to the other of the terminals of the inductive element generates the voltage having the saw-tooth waveform applied to the other of the terminals of the electromechanical transducer.
As an embodiment, an inequality of
0.4
×fr<fd
<1.0
×fr
(1)
is satisfied, where fd is a frequency of the voltage having the square waveform applied to the series resonance circuit, and where fr is a resonance frequency of the series resonance circuit.
Preferably, an inequality of
0.6
×fr<fd
<0.8
×fr
(2)
is satisfied.
As an embodiment, one of inequalities of
0.05<Du<0.48 and 0.52<Du<0.95 (3)
is satisfied, where Du is a duty ratio of the voltage having the square waveform applied to the series resonance circuit.
Preferably, one of inequalities of
0.15<Du<0.40 and 0.60<Du<0.85 (4)
is satisfied.
More preferably, one of inequalities of
0.25<Du<0.35 and 0.65<Du<0.75 (5)
is satisfied.
As an embodiment, an inequality of
(1/15)×(
L/C
)
1/2
<R
<(
L/C
)
1/2
(6)
is satisfied, where C is a capacitance of the electromechanical transducer, where L is an inductance of the inductive element, and where R is a resistance of the resistive element.
Preferably, an inequality of
(1/10)×(
L/C
)
1/2
<R
<(1/1.5)×(
L/C
)
1/2
(7)
is satisfied.
As an embodiment, the electromechanical transducer has a pair of ends in an expanding and contracting directi
Yoshida Ryuichi
Yuasa Tomoyuki
Budd Mark
McDermott Will & Emery LLP
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