U.S. patent application number 09/964861 was filed with the patent office on 2002-05-16 for driving apparatus and method using electromechanical conversion elements.
Invention is credited to Shibatani, Kazuhiro.
Application Number | 20020057038 09/964861 |
Document ID | / |
Family ID | 18780396 |
Filed Date | 2002-05-16 |
United States Patent
Application |
20020057038 |
Kind Code |
A1 |
Shibatani, Kazuhiro |
May 16, 2002 |
Driving apparatus and method using electromechanical conversion
elements
Abstract
In a truss-type actuator, drive signals that have been subjected
to frequency modulation are impressed to the electromechanical
conversion elements in order to improve the driving of the
actuator. By doing so, stable driving that is not affected by
fluctuations in the resonance frequency is enabled without
feedback.
Inventors: |
Shibatani, Kazuhiro; (Osaka,
JP) |
Correspondence
Address: |
MCDERMOTT WILL & EMERY
600 13TH STREET, N.W.
WASHINGTON
DC
20005-3096
US
|
Family ID: |
18780396 |
Appl. No.: |
09/964861 |
Filed: |
September 28, 2001 |
Current U.S.
Class: |
310/317 ;
310/323.16 |
Current CPC
Class: |
H02N 2/103 20130101;
H01L 41/0906 20130101; H02N 2/008 20130101; H02N 2/0025
20130101 |
Class at
Publication: |
310/317 ;
310/323.16 |
International
Class: |
H01L 041/04 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 29, 2000 |
JP |
2000-298430 |
Claims
What is claimed is:
1, A driving apparatus comprising: a base; 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; 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; a drive
circuit that impresses drive signals to the displacement members,
and a controller that controls the drive circuit so that the
synthesizing member moves in an elliptical path and the drive force
is transmitted to the driven member, wherein the controller drives
at least one of the multiple displacement members using a drive
signal that has been subjected to frequency modulation.
2, A driving apparatus according to claim 1, wherein the central
frequency of the drive signal that has been subjected to frequency
modulation essentially matches the resonance frequency of the
displacement member.
3, A driving apparatus according to claim 2, wherein the modulation
difference of the drive signal is larger than the range of change
in the resonance frequency of the displacement member that occurs
due to fluctuations in the ambient environment of the displacement
member.
4, A driving apparatus according to claim 3, wherein the modulation
difference of the drive signal is larger than the range of change
in the resonance frequency of the displacement member that occurs
due to fluctuations in the load placed on the displacement
member.
5, A driving apparatus according to claim 1, wherein the controller
controls the speed of the motion of the driven member by changing
the central frequency of the frequency-modulated signal, which is
the drive signal.
6, A driving apparatus according to claim 1, wherein the controller
controls the speed of the motion of the driven member by changing
the modulation difference of the frequency-modulated signal, which
is the drive signal.
7, A driving apparatus according to claim 1, wherein the controller
controls the speed of the motion of the driven member by changing
the modulated frequency of the frequency-modulated signal, which is
the drive signal.
8, A driving apparatus according to claim 1, wherein the controller
drives the multiple displacement members.
9, A driving apparatus comprising: a base; 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, 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; a drive
circuit that impresses drive signals to the displacement members,
and a controller that controls the drive circuit such that one of
the multiple displacement members is driven using a drive signal
that has been subjected to frequency modulation, said controller
causes the synthesizing member to perform an elliptical motion such
that the driving force is transmitted to the driven member.
10, A driving apparatus according to claim 9, wherein the
controller impresses to the displacement member to be driven a
drive signal that has been subjected to frequency modulation and
uses as its central frequency a drive frequency at which the
current phase difference between the driven displacement member and
the following displacement member, which is not directly driven,
becomes approximately 90 degrees.
11, A driving apparatus according to claim 10, wherein the
modulation difference of the drive signal is larger than the range
of change in the resonance frequency of the displacement member
that occurs due to fluctuations in the ambient environment of the
displacement member.
12, A driving apparatus according to claim 11, wherein the
modulation difference of the drive signal is larger than the range
of change in the resonance frequency of the displacement member
that occurs due to fluctuations in the load placed on the
displacement member.
13, A driving apparatus according to claim 10, wherein the
controller controls the speed of the motion of the driven member by
changing the modulation difference of the frequency-modulated
signal, which is the drive signal.
14, A driving apparatus according to claim 10, wherein the
controller controls the speed of the motion of the driven member by
changing the modulated frequency of the frequency-modulated signal,
which is the drive signal.
Description
[0001] 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
[0002] 1. Field of the Invention
[0003] 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.
[0004] 2. Description of the Related Art
[0005] 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.degree.), 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.
[0006] 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.
[0007] 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.).
[0008] 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 109a and 109b. The
switch 110 has two ON/OFF switch members 110a and 110b. When the
ON/OFF switch members 109a and 110a 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 109b and 110b 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.
[0009] 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.
[0010] 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.
[0011] FIG. 9 is a block diagram showing the proposed one
displacement member driving apparatus.
[0012] 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.
[0013] 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.
[0014] 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.
[0015] Where the oscillation status of the displacement member is
fed back, a feedback circuit is needed.
OBJECTS AND SUMMARY
[0016] 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.
[0017] 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 drive force is
transmitted to the driven member, wherein the controller drives at
least one of the multiple displacement members using a drive signal
that has been subjected to frequency modulation.
[0018] According to this aspect of the invention, because the
displacement member or elements are driven using a drive signal or
signals that have been subjected to frequency modulation, it is no
longer necessary to match the driving frequency to the resonance
frequency regardless whether resonance or non-resonance driving is
performed, and the oscillation status of the displacement members
need not be fed back. As a result, the circuitry may be simplified
and the number of components may be reduced.
[0019] In the driving apparatus according to another aspect of the
invention, the central frequency of the drive signal that has been
subjected to frequency modulation essentially matches the resonance
frequency of the displacement member. In addition, the modulation
difference of the drive signal is larger than the range of change
in the resonance frequency of the displacement member that occurs
due to fluctuations in the ambient environment of the displacement
member. Moreover, the modulation difference of the drive signal is
larger than the range of change in the resonance frequency of the
displacement member that occurs due to fluctuations in the load
placed on the displacement member.
[0020] According to this aspect of the invention, because the drive
signal uses as its central frequency a frequency near the resonance
frequency, the actuator may be driven based on resonance driving.
In addition, because the modulation difference of the drive signal
is set to be larger than the range of change in the resonance
frequency that occurs due to fluctuations in the load or the
environment, even when the resonance frequency changes due to
fluctuations in the load or the environment, driving may be
performed regardless of such fluctuations.
[0021] In the driving apparatus according to another aspect of the
invention, the controller controls the speed of the motion of the
driven member by changing at least one of (i) the central
frequency, (ii) the modulation difference, or (iii) the modulated
frequency of the frequency-modulated signal, which is the drive
signal.
[0022] According to this aspect of the invention, if at least one
of the central frequency, the modulation difference or the
modulated frequency of the frequency-modulated signal is changed,
the proportion of the higher-than-resonance frequency range in the
frequency-modulated signal changes, through which the speed of the
driven member is controlled. Consequently, low-speed driving, at
which an actuator is not particularly effective, is enabled.
[0023] According to another 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 a drive signal to one of the displacement
members, and (v) a controller that causes the synthesizing member
to perform an elliptical motion such that the driving force is
transmitted to the driven member. Such motion is made to occur
through control of the drive circuit such that one of the multiple
displacement members is driven using a drive signal that has been
subjected to frequency modulation, wherein the controller impresses
to the displacement member to be driven a drive signal that has
been subjected to frequency modulation and uses as its central
frequency a drive frequency at which the current phase difference
between the driven displacement member and the following
displacement member, which is not directly driven, becomes
approximately 90 degrees.
[0024] Using this driving apparatus as an actuator, an area exists
in which the driven member moves at an essentially constant speed,
as shown by the black dots in FIG. 6 (i.e., the area between
approximately 79 kHz and 95 kHz), and the drive-enabled area is
large. As a result, driving at an essentially constant speed is
possible without feedback of the oscillation status of the
displacement members.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] These and other objects and features of the present
invention will become apparent from the following description of
preferred embodiments thereof taken in conjunction with the
accompanying drawings, in which:
[0026] FIG. 1 is a block diagram of a driving apparatus comprising
the present invention that is applied in the truss-type actuator
shown in FIG. 7, for example, and that drives the actuator based on
resonance driving;
[0027] FIG. 2 is a drawing showing an example of the modulation
signal used in the present invention;
[0028] FIG. 3 is a drawing that was obtained when the central
frequency of the modulated waves was set close to the resonance
frequency and the modulation cycle was adjusted appropriately in
accordance with the present invention;
[0029] FIG. 4 is a block diagram showing another example of the
construction of the driving apparatus pertaining to a first
embodiment of the present invention;
[0030] FIG. 5 is a block diagram showing the driving apparatus
pertaining to a second embodiment of the present invention;
[0031] FIG. 6 is a drawing showing the results of experimentation
in which the frequency-modulated driving and non-modulated driving
using the second embodiment were compared;
[0032] FIG. 7 is a drawing showing one example of the actuator
driven by the driving apparatus of the present invention;
[0033] FIG. 8 is a block diagram showing an example of the
conventional driving apparatus; and
[0034] FIG. 9 is a block diagram showing another example of the
conventional driving apparatus.
[0035] In the following description, like parts are designated by
like reference numbers throughout the several drawings.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0036] An embodiment according to one aspect of the present
invention is explained below with reference to the drawings.
[0037] (First Embodiment)
[0038] FIG. 1 is a block diagram of a driving apparatus that is
applied in the truss-type actuator shown in FIG. 7, for example,
and that drives such actuator based on resonance driving.
[0039] This driving apparatus supplies drive signals to the
displacement members 2 and 3 of the truss-type actuator shown in
FIG. 7, and comprises an MPU (microprocessing unit) 11, which
functions as a signal generator, an oscillator 12 that performs
oscillation based on the output signal from the MPU 11, a power
amplifier 13 that inputs the output signal from the oscillator 12
and amplifies it, a phase converter 14 that inputs the output
signal from the oscillator 12 and converts it, and a power
amplifier 15 that inputs the output signal from the phase converter
14 and amplifies it. The output signal from the power amplifier 13
is supplied to the displacement member 2 of the truss-type
actuator. The output signal from the power amplifier 15 is supplied
to the displacement member 3 of the truss-type actuator.
[0040] For the oscillator 12, a voltage-controlled oscillator (Vco)
is used in this embodiment. The MPU 11 generates a voltage signal
(digital signal) with the triangular-wave frequency modulation
function shown in FIG. 2, for example, as a modulation signal, and
outputs the signal to the oscillator 12 after D/A conversion. When
this is done, if the central voltage A is high, the oscillator 12
outputs modulated waves in which the central frequency of the
oscillation frequency is high, and if the central voltage A is low,
it outputs modulated waves in which the central frequency of the
oscillation frequency is low.
[0041] In addition, if the difference between the maximum voltage B
and the minimum voltage C is small, the oscillator 12 outputs
modulated waves in which the modulation difference of the
oscillation frequency is small, and if the difference between the
maximum voltage B and the minimum voltage C is large, it outputs
modulated waves in which the modulation difference of the
oscillation frequency is large.
[0042] In addition, if the distance between the adjacent maximum
voltage points B or the adjacent minimum voltage points C is
narrow, i.e., if the output pitch of the voltage signal to the
oscillator 12 is short, the angle .theta. representing the gradient
of voltage change becomes small, and the oscillator 12 outputs
modulated waves in which the modulation cycle of the oscillation
frequency is short, and if the output pitch of the voltage signal
to the oscillator 12 is long, the oscillator 12 outputs modulated
waves in which the modulation cycle of the oscillation frequency is
long.
[0043] In addition, the MPU 11 generates a signal that adjusts the
shift amount for the phase converter 14, and outputs the signal to
the phase converter 14.
[0044] The phase converter 14 adjusts the phase shift of the drive
signal received from the oscillator 12 based on the signal from the
MPU 11. The power amplifiers 13 and 15 amplify the input signals to
prescribed voltages and drive the displacement members 2 and 3 via
oscillation. Consequently, the driven member 7 shown in FIG. 7
performs rotational movement, for example. The direction of
rotation of the driven member 7 is controlled through the phase
adjustment performed by the phase converter 14.
[0045] In the driving apparatus having the above construction, the
speed of the driven member 7 may be adjusted using the modulated
waves described above.
[0046] In other words, the rotation speed of the driven member 7
decreases gradually when the driving frequency comprises a
frequency higher than the resonance frequency of each displacement
member, and rapidly when a frequency lower than the resonance
frequency is used, and because the Q value of the mechanical
resonation of the actuator is large, the range in which driving is
performed using a frequency near the resonance frequency is small.
Consequently, if the central frequency of the modulated waves is
shifted from the vicinity of the resonance frequency, the average
speed of the driven member 7 may be reduced. In addition, depending
on the direction in which the central frequency of the modulated
waves is shifted, the speed of the driven member 7 may be
controlled.
[0047] Furthermore, by adjusting the size of the modulation
difference, the proportions of the range in which it is easy to
drive the actuator (the frequency range in which the driving
frequency is higher than the central resonance frequency) and the
range in which it is difficult to drive the actuator or in which
the actuator is not driven (the frequency range in which the
driving frequency is lower than the central resonance frequency)
may be changed. Through this characteristic, if the modulation
difference is increased, control may be performed such that the
speed of the driven member 7 is low.
[0048] In addition, by adjusting the size of the modulation cycle
(or the modulated frequency), the proportion of the range per unit
time in which it is easy to drive the actuator, i.e., more
specifically, the proportion of the time in which the resonance
frequency exists per unit time, may be changed. Through this
characteristic, if the modulation cycle is made short, the speed
decreases, so that the speed of the driven member 7 may be
controlled.
[0049] Therefore, using the driving apparatus of the first
embodiment, by using a drive signal that has been subjected to
frequency modulation through the changing of at least one of the
central frequency, the modulation difference or the modulation
cycle, the speed of the driven member may be controlled. In
particular, if the modulation difference is set to be larger than
the range of change in the resonance frequency that occurs due to
fluctuations in the load or the environment, even if the resonance
frequency changes, it is ensured that the drive signal will pass
through the resonance frequency. Consequently, such problems that
the actuator is not operated or stops due to the causes described
above no longer occur, and therefore it is no longer necessary to
match the drive frequency to the resonance frequency. Therefore, it
is no longer necessary to feed back the oscillation status of the
displacement members 2 and 3 as in the conventional art, and as a
result, the circuit construction may be simplified, and at the same
time, the number of components may be reduced.
[0050] FIG. 3 is a drawing that was obtained when the central
frequency of the modulated waves was set near the resonance
frequency and the modulation cycle was appropriately adjusted. FIG.
3(a) shows the voltage input by the oscillator, FIG. 3(b) shows the
voltage output by the oscillator, FIG. 3(c) shows the speed of the
driven member, and FIG. 3(d) shows the average speed of the driven
member. D in the drawing indicates a point at which driving was
performed using the resonance frequency.
[0051] As can be understood from this drawing, the drive signal
shown in FIG. 3(b), which was subjected to frequency modulation, is
output from the oscillator in response to the input voltage shown
in FIG. 3(a), and over a short period of time, the speed of the
driven member increases near the resonance frequency and decreases
otherwise (see FIG. 3(c)). By adjusting the modulation cycle
appropriately, as described above, over a long period of time, the
average speed of the driven member 7 may be made essentially
constant (see FIG. 3(d)). Therefore, when driving is performed
based on such frequency modulation, while the speed drops relative
to resonance driving, low-speed driving, at which an actuator is
not particularly effective, is enabled.
[0052] It is also acceptable if a speed sensor 16 that detects the
rotation speed of the driven member 7 is included, as shown in FIG.
4, such that the output value from the sensor is fed back to the
MPU 11. In this case, if the modulation signal for each speed is
stored in the memory of the MPU 11 in advance, driving may be
performed by the MPU 11 such that the degree of frequency
modulation is changed in response to the detected speed, enabling
automatic speed adjustment. In this case, it is also acceptable if
driving is performed such that a high torque is used during
low-speed driving, and a low torque is used during high
speed-driving.
[0053] (Second Embodiment)
[0054] FIG. 5 is a block diagram of a driving apparatus of the
present invention that is applied in a truss-type actuator and that
drives one of the displacement members. The same numbers are used
for members that perform the same functions described with
reference to FIG. 1.
[0055] This driving apparatus comprises an MPU 11, an oscillator 12
that performs oscillation based on the output signal from the MPU
11, a power amplifier 13 that inputs the output signal from the
oscillator 12 and amplifies it, and a switch 24. The switch 24
comprises a switch member 24a that supplies the drive signal to the
displacement member 2 and a switch member 24b that supplies the
drive signal to the displacement member 3, and is used to control
the method of rotation of the driven member.
[0056] The MPU 11 generates a voltage signal (digital signal) with
a triangular-wave frequency modulation function as a modulation
signal, and outputs the signal to the oscillator 12 after D/A
conversion. The oscillator 12 changes at least one of the central
frequency, the modulation difference or the modulated frequency of
the frequency-modulated signal, based on the input signal. In this
embodiment, frequency modulation is carried out using the resonance
frequency as the central frequency. `Resonance frequency` as
referred to herein is the frequency with which the phase difference
between the current drawn to the driving displacement member 2 (or
3) and the current drawn to the following displacement member 3 (or
2) becomes approximately 90 degrees (see Japanese Laid-Open Patent
Application 2000-72245).
[0057] Therefore, the actuator is driven using a drive signal that
has been subjected to frequency modulation in the second embodiment
as well, and therefore the same effect obtained in the first
embodiment is obtained in the second embodiment.
[0058] FIG. 6 shows the results of experimentation in which
frequency-modulated driving (black circles) and non-modulated
driving (white circles) using the second embodiment were compared.
The horizontal axis shows the value of the central frequency, and
the vertical axis shows the speed of rotation of the rotor
circumference. The experiment conditions are shown below. For the
driven member, a round column-like rotor that had a 30 mm diameter
and was Tufftride-treated on the outer surface was used. The
pressing force from the pressure unit was 150 gf, the drive voltage
was 10Vp-p (sine waves), the modulation difference was .+-.10 kHz,
the modulated frequency was 30 Hz, the modulation function was a
triangular-wave function, and the speed as measured by a velocity
sensor was the average speed of the circumference of the rotor.
[0059] As can be understood from FIG. 6, when driving was performed
without modulation, because the Q value of the mechanical resonance
is large, the frequency-speed characteristic comprises a waveform
that has sharp peaks. Namely, the point at which the speed becomes
the largest is the resonance frequency point, and when the driving
frequency moves away from the resonance frequency, the speed
suddenly drops, and the driving frequency enters the range in which
driving is not enabled. Regarding the speed before and after the
resonance frequency is reached, the speed gradually drops in the
range in which the frequency is larger than the resonance
frequency.
[0060] By contrast, with regard to frequency-modulated driving, a
range exists in which the rotor rotates at an essentially constant
speed (approximately 79 kHz to 95kHz), although the speed is low,
and the range in which driving is possible is larger. In addition,
because there is a large range over which the rotor rotates at an
essentially constant speed, an essentially constant speed may be
maintained with a driving apparatus that does not feed back signals
from the displacement members, as in the present invention. From
these experimental results, it can be seen that the driving method
pertaining to the present invention is effective.
[0061] A voltage-controlled oscillator is used for the oscillator
in the embodiments described above, but the present invention is
not limited to this type of oscillator, and other types of
oscillators, such as a direct digital synthesizer (DDS) or a
numerically controlled oscillator (NCO), for example, may be used
instead.
[0062] In addition, in the above embodiments, a truss-type actuator
based on phase-difference driving is driven using resonance
driving, but the present invention is not limited to this
implementation, and may be used in non-resonance driving of a
phase-difference drive truss-type actuator. This is because in
non-resonance driving, when the synthesizing member is to draw a
locus having the same diameters, the speed of the driven member
increases as the driving frequency increases, and the present
invention may be used to control the speed.
[0063] Furthermore, in the above embodiments, the actuator shown in
FIG. 7 is driven, but the present invention is not limited to this
implementation. The driving apparatus of the present invention may
be generally used to drive any actuator that comprises a driving
unit comprising (i) a fixing member, (ii) multiple (i.e., three or
more) displacement members, which are fixed to the fixing member at
the base ends thereof such that they cross each other at the tip
ends thereof, and a synthesizing member that is located such that
it is in contact with the tip ends of all of the displacement
members, and (iii) a pressure unit that keeps the synthesizing unit
in pressure contact with the driven member, which is the object of
driving.
[0064] As explained in detail above, using the present invention,
the displacement member or members are driven based on a drive
signal or signals that have been subjected to frequency modulation,
and therefore regardless whether resonance driving or non-resonance
driving is performed, it is no longer necessary to match the
driving frequency to the resonance frequency. Consequently, it is
not necessary to feed back the oscillation status of the
displacement members, and as a result, the circuitry may be
simplified and the number of components may be reduced.
[0065] Although the present invention has been fully described by
way of examples with reference to the accompanying drawings, it is
to be noted that various changes and modifications will be apparent
to those skilled in the art. Therefore, unless such changes and
modification depart from the scope of the present invention, they
should be construed as being included therein.
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