Driving apparatus and method using electromechanical...

Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices

Reexamination Certificate

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Reexamination Certificate

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06433461

ABSTRACT:

This application is based on application No. JP2000-298430 filed in Japan, the contents of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an improved driving apparatus and method for driving of a driven member, such as a disk-like rotor that rotates or a slider that moves in a linear fashion. Specifically, it relates to an improved driving apparatus and method using electromechanical conversion elements, and more specifically to a truss-type improved driving apparatus and method using electromechanical conversion elements. More particularly, it relates to a driving apparatus and a driving method for electromechanical conversion elements belonging to an ultrasonic motor or similar mechanism that uses drive signals that have been subjected to frequency modulation using as the central frequency a frequency near the mechanical resonance frequency of the electromechanical conversion element.
2. Description of the Related Art
As a type of ultrasonic motor mentioned above, the motor having the construction shown in
FIG. 7
is known. This ultrasonic motor is a truss-type actuator comprising a driving unit
1
and a pressure unit
6
. The driving unit
1
comprises two displacement members
2
and
3
that cross each other at a prescribed angle (for example, 90°), a synthesizing member
5
that is made to adhere at the crossing point thereof and a fixing member
4
that is made to adhere to the ends thereof. The pressure unit
6
comprises a coil spring or similar mechanism and presses the fixing member
4
toward the center of the rotor (i.e., in the direction of the arrow A), which comprises a driven member
7
.
This ultrasonic motor may be driven based on non-resonance driving, but if resonance driving is used, efficient low-voltage driving is enabled. Therefore, in general, an ultrasonic motor is driven in a resonance mode.
As a driving apparatus that performs resonance driving of an ultrasonic motor, the apparatus shown in
FIG. 8
is proposed (Japanese Laid-Open Patent Application 2001-16879, etc.).
This driving apparatus includes two power amplifiers
102
and
103
that amplify the drive signals from the oscillator
101
and drive the displacement members
2
and
3
, respectively, a phase converter
104
that is placed between the oscillator
101
and the power amplifier
103
, current detectors
105
and
106
that detect the current values drawn to the displacement members
2
and
3
using resistors R, respectively, and a phase difference detector
107
that detects the phase difference based on the output signals from the current detectors
105
and
106
. It further includes a resonance frequency detector
108
, two switches
109
and
110
, and an MPU
111
. The switch
109
has two ON/OFF switch members
109
a
and
109
b
. The switch
110
has two ON/OFF switch members
110
a
and
110
b
. When the ON/OFF switch members
109
a
and
110
a
are both ON, the resonance frequency detector
108
detects the phase difference between the output signal (voltage component) of the oscillator
101
and the output signal (current component) of the current detector
105
, and where the driving frequency of the oscillator
101
is higher than the resonance frequency that enables resonance driving (at which there should be no phase difference), the resonance frequency detector
108
outputs to the MPU
111
a signal that reduces the driving frequency of the oscillator
101
, while where the driving frequency of the oscillator
101
is lower than the resonance frequency, it outputs to the MPU
111
a signal that increases the driving frequency of the oscillator
101
. On the other hand, where the ON/OFF switch members
109
b
and
110
b
are ON, the resonance frequency detector
108
detects the phase difference based on the output signal (voltage component) of the phase converter
104
and the output signal (current component) of the current detector
106
, and where the driving frequency of the oscillator
101
is higher than the resonance frequency of the displacement member, the resonance frequency detector
108
outputs to the MPU
111
a signal that reduces the driving frequency of the oscillator
101
, while where the driving frequency of the oscillator
101
is lower than the resonance frequency, it outputs to the MPU
111
a signal that increases the driving frequency of the oscillator
101
.
The MPU
111
reduces or increases the driving frequency of the oscillator
101
based on the signal from the resonance frequency detector
108
in order to adjust the driving frequency of the oscillator
101
to a frequency that enables resonance driving. The elliptical locus of the synthesizing member of this driving apparatus depends on the phase difference of the displacement of each displacement member.
In the driving apparatus described above, drive signals are supplied to the two displacement members and both members are driven, but in addition to this scenario, it is also possible to supply a drive signal only to one of the displacement members such that only one displacement member is driven. A method for this type of one displacement member driving has also been proposed.
FIG. 9
is a block diagram showing the proposed one displacement member driving apparatus.
This driving apparatus amplifies the output signal of the oscillator
201
using the power amplifier
202
, and the amplified signal therefrom is supplied to the displacement member
2
or
3
via the switch
203
. At the same time, the currents drawn to the displacement members
2
and
3
are detected by separate current detectors
205
and
206
, respectively, and based on the current phase difference between these two currents, the MPU
211
adjusts the oscillation frequency of the oscillator
201
. The locus of the synthesizing member changes depending on the driving frequency.
Incidentally, using the above driving apparatus that drives both displacement members, the resonance frequency of the displacement member changes as the load and/or environment fluctuate, and if the driving frequency is offset from the resonance frequency, the driving characteristics change substantially. Depending on the degree of such offset, the driving apparatus may not be operated or may stop. Therefore, where an ultrasonic motor is driven based on resonance driving, the oscillation status must be fed back to ensure that the driving frequency matches the resonance frequency of each element.
In addition, in the case of the driving apparatus that drives only one displacement member, because locus control is performed by changing the driving frequency based on the phase difference of the currents that are drawn to the elements, the oscillation status of the displacement member must be fed back.
Where the oscillation status of the displacement member is fed back, a feedback circuit is needed.
OBJECTS AND SUMMARY
The present invention was created in view of this situation, and an object thereof is to provide an improved driving apparatus and method for an actuator. Specifically, an object of the present invention is to improve a truss-type driving apparatus and method using electromechanical conversion elements, and more particularly, to provide a driving apparatus that drives electromechanical conversion elements without feedback.
In order to attain this and other objects, according to one aspect of the present invention, the driving apparatus has (i) a base, (ii) multiple displacement members, the base ends of which are fixed to the base and the tip ends of which are combined at one location, said displacement members each generating a prescribed displacement, (iii) a pressure unit that keeps the synthesizing member, at which the tip ends of the displacement members are combined, in pressure contact with the driven member, which comprises the object of driving, (iv) a drive circuit that impresses drive signals to the displacement members, and (v) a controller that controls the drive circuit so that the synthesizing member moves in an elliptical path and the

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