U.S. patent application number 09/732963 was filed with the patent office on 2001-06-21 for ultrasonic motor and electronic apparatus having an ultrasonic motor.
Invention is credited to Iino, Akihiro, Kasuga, Masao.
Application Number | 20010004179 09/732963 |
Document ID | / |
Family ID | 18428052 |
Filed Date | 2001-06-21 |
United States Patent
Application |
20010004179 |
Kind Code |
A1 |
Iino, Akihiro ; et
al. |
June 21, 2001 |
Ultrasonic motor and electronic apparatus having an ultrasonic
motor
Abstract
To carry out speed control of an ultrasonic motor driven by a
self-excited oscillation circuit utilizing the ultrasonic motor per
se as a vibrating body and promote reliability of the self-excited
oscillation circuit, an instruction signal for controlling a state
of the self-excited oscillation circuit constituting a drive
circuit, is set in a range capable of stably driving the ultrasonic
motor in an aimed state. The self-excited oscillation circuit can
be controlled to be brought into a drive state or a stop state in
accordance with a drive command signal or a stop command signal
from a control signal generating circuit and the control signal
generating circuit is set such that a length (TD) of the drive
command signal becomes longer than a time period (t1) from when the
drive command signal is applied to the self-excited oscillation
circuit until oscillation is started. By setting the control signal
generating circuit such that a length (TS) of the stop command
signal to be shorter than a time period (t9) from when the stop
command signal is inputted to the self-excited oscillation circuit
until oscillation is stopped, a state of a moving body can be
controlled without stopping the oscillation.
Inventors: |
Iino, Akihiro; (Chiba-shi,
JP) ; Kasuga, Masao; (Chiba-shi, JP) |
Correspondence
Address: |
Adams & Wilks
31st Floor
50 Broadway
New York
NY
10004
US
|
Family ID: |
18428052 |
Appl. No.: |
09/732963 |
Filed: |
December 8, 2000 |
Current U.S.
Class: |
310/314 ;
310/318 |
Current CPC
Class: |
H02N 2/147 20130101;
H02N 2/166 20130101; H02N 2/14 20130101 |
Class at
Publication: |
310/314 ;
310/318 |
International
Class: |
H02N 002/00; H01L
041/04 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 13, 1999 |
JP |
11-353023 |
Claims
What is claimed is:
1. An ultrasonic motor apparatus comprising: a self-excited
oscillation circuit by a vibrating body having a piezoelectric
element and an amplifier circuit for amplifying an output signal of
the piezoelectric element for oscillating the vibrating body in a
predetermined natural mode and operating a moving body in contact
with the vibrating body, and; a control signal generating circuit
for outputting to the self-excited oscillation circuit, a drive
command signal or a stop command signal for instructing the
self-excited oscillation circuit to be brought into a drive state
or a stop state; wherein the control signal generating circuit is
set such that a length (TD) of the drive command signal is made to
be longer than a time period (t1) from when the drive command
signal is applied to the self-excited oscillation circuit until the
self-excited circuit starts oscillating.
2. The ultrasonic motor apparatus according to claim 1: wherein the
length (TD) of the drive command signal is a time period (t2) by
elapse of which the self-excited oscillation circuit starts
oscillating by a frequency component used in driving the moving
body.
3. The ultrasonic motor apparatus according to claim 1: wherein the
length (TD) of the drive command signal is longer than a time
period (t3) until an amplitude of the oscillation of the
self-excited oscillation circuit is increased over time and reaches
a value of the amplitude capable of operating the moving body.
4. The ultrasonic motor apparatus according to claim 1: wherein the
length (TD) of the drive command signal is longer than a time
period (t4) until an amplitude of the oscillation of the
self-excited oscillation circuit is increased over time and
saturated to a constant value of the amplitude.
5. The ultrasonic motor apparatus according to claim 1: wherein
length (TD) of the drive command signal falls in a range between
the time period (t3) and the time period (t4).
6. An ultrasonic motor apparatus comprising: a self-excited
oscillation circuit by a vibrating body having a piezoelectric
element and an amplifier circuit for amplifying an output signal of
the piezoelectric element for oscillating the vibrating body in a
predetermined natural mode and operating a moving member in contact
with the vibrating body, and; a control signal generating circuit
for outputting to the self-excited oscillation circuit, a drive
command signal or a stop command signal for instructing the
self-excited oscillation circuit to be brought into a drive state
or a stop state; wherein a length (TS) of the stop command signal
is made to be shorter than a time period (t9) from when the stop
command signal is inputted to the self-excited oscillation circuit
until the oscillation is stopped.
7. An ultrasonic motor apparatus comprising: a self-excited
oscillation circuit by a vibrating body having a piezoelectric
element and an amplifier circuit or amplifying an output signal of
the piezoelectric element for oscillating the vibrating body in a
predetermined natural mode and operating a moving body in contact
with the vibrating body, and; a control signal generating circuit
for outputting to the self-excited oscillation circuit, a drive
command signal or a stop command signal for instructing the
self-excited oscillation circuit to be brought into a drive state
or a stop state; wherein when the ultrasonic motor apparatus is
driven by alternately inputting the drive command signal and the
stop command signal to the self-excited oscillation circuit, a time
period (TD) and a time period (TS) are set such that an amount of
changing a voltage value of an input unit for inputting the output
signal of the piezoelectric element during a time period of
applying the drive command signal in the time period (TD), is
larger than an amount of changing the voltage value of the input
unit of the amplifier circuit during a time period of applying the
stop command signal in the time period (TS).
8. An ultrasonic motor apparatus comprising: a self-excited
oscillation circuit by a vibrating body having a piezoelectric
element and an amplifier circuit for amplifying an output signal of
the piezoelectric element for oscillating the vibrating body in a
predetermined natural mode and operating a moving body in contact
with the vibrating body, and; a control signal generating circuit
for outputting to the self-excited oscillation circuit, a drive
command signal or a stop command signal for instructing the
self-excited oscillation circuit to be brought into a drive state
or a stop state; wherein when the ultrasonic motor apparatus is
driven by alternately inputting the drive command signal and the
stop command signal to the self-excited oscillation circuit, a
frequency (1/(TD+TS)) determined by a time period (TD) of the drive
command signal and a time period (TS) of the stop command signal,
is higher than a frequency in the predetermined natural mode.
9. An ultrasonic motor apparatus comprising: a self-excited
oscillation circuit by a vibrating body having a piezoelectric
element and a plurality of amplifier circuits for amplifying an
output signal of the piezoelectric element for oscillating the
vibrating body in a predetermined natural mode and operating a
moving body in contact with the vibrating body: wherein among the
plurality of amplifier circuits, a number of the amplifier circuit
which are brought into an active state is made variable and a first
oscillating state for operating the moving body and a second
oscillating state for not operating the moving body are
switched.
10. An electronic apparatus having an ultrasonic motor, comprising
the ultrasonic motor according to any one of claim 1 through claim
9.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an ultrasonic motor and an
electronic apparatus using an ultrasonic motor, particularly to a
method of controlling an ultrasonic motor in which a self-excited
oscillation circuit constituted by using the ultrasonic motor per
se is operated as a drive circuit and an electronic apparatus using
an ultrasonic motor.
[0003] 2. Description of the Related Art
[0004] An ultrasonic motor begins to be used in various electronic
apparatus since the ultrasonic motor is provided with excellent
features of being small-sized, having high torque and high
positioning resolution, and having hold force when electricity is
not conducted. The drive circuit of an ultrasonic motor generally
needs a frequency tracking circuit for tracking resonance frequency
of the ultrasonic motor which is varied by temperature or external
load to thereby pose a problem of bringing about complicated
formation of the drive circuit or large-sized formation or high
cost formation of a circuit mounting unit thereof. Hence, in recent
years, there has been an example in which simplification of a drive
circuit is achieved by using a self-excited oscillation circuit
constituted by using an ultrasonic motor per se and an amplifying
circuit.
[0005] However, when a drive circuit is constituted by using a
self-excited oscillation circuit, there is a drawback that a time
period is taken from when the drive circuit is brought into a
drivable (ON) state until oscillation is started and an amplitude
of oscillation increases and grows to a signal necessary for
driving the ultrasonic motor.
[0006] Although when an ultrasonic motor is used for controlling
position or speed, it is necessary to operate the ultrasonic motor
intermittently by a very small amount by providing an intermittent
signal to the ultrasonic motor or to make speed variable, when such
a control is carried out by using the self-excited oscillation
circuit in the drive circuit, there poses a problem in which a
drive signal actually produced by the self-excited oscillation
circuit cannot follow intermittent commands of driving/stopping the
drive circuit, the ultrasonic motor cannot be started or operation
thereof becomes unstable by causing abnormal oscillation.
SUMMARY OF THE INVENTION
[0007] Hence, according to the invention, a command signal for
controlling a state of a self-excited oscillation circuit
constituting a drive circuit is set in a range capable of stably
driving an ultrasonic motor in an aimed state.
[0008] That is, according to an aspect of the invention, in an
ultrasonic motor apparatus constituting a self-excited oscillation
circuit by a vibrating body having a piezoelectric element and an
amplifier circuit for oscillating the vibrating body in a
predetermined natural mode and operating a moving body in contact
with the vibrating body, the self-excited oscillation circuit can
be controlled to be brought into a drive state or a stop state in
accordance with a drive command signal or a stop command signal
from a control signal generating circuit, and the control signal
generating circuit is set such that a length TD of the drive
command signal is made to be longer than a time period t1 from when
the drive command signal is applied to the self-excited oscillation
circuit until the self-excited circuit starts oscillating.
[0009] In this case, particularly, the length of the time period t1
is made to be a time period t2 until the self-excited oscillation
circuit starts oscillating by a frequency component used for
driving the moving body.
[0010] Further, in accordance with a situation or a purpose, the
length TD of the drive command signal is made longer than a time
period t3 until an amplitude of oscillation of the self-excited
oscillation circuit grows and reaches an amplitude value capable of
operating the moving body, or longer than a time period t4 until
the amplitude of the oscillation of the self-excited oscillation
circuit grows and is saturated to a specific amplitude value. Or,
the length TD is set to fall in a range between the time period t3
and time period t4.
[0011] Further, by setting the control signal generating circuit
such that a length TS of the stop command signal becomes shorter
than a time period t9 from when the stop command signal is inputted
to the self-excited oscillation circuit until the oscillation is
stopped, a state of the moving body is controlled without stopping
the oscillation.
[0012] When the ultrasonic motor apparatus is driven by alternately
inputting the drive command signal and the stop command signal to
the self-excited oscillation circuit, the time period TD and the
time period TS are set such that an amount of changing a voltage
value of an input unit of the amplifier circuit during a time
period for applying the drive command signal in the time period TD,
becomes larger than an amount of changing the voltage value of the
input unit of the amplifier circuit during a time period for
applying the stop command signal in the time period TS.
[0013] Further, in making variable the speed of the ultrasonic
motor, a frequency 1/(TD+TS) of a control command signal
constituted by the time period TD of the drive command signal and
the time period TS of the stop command signal, is set to be higher
than a frequency of the predetermined natural mode.
[0014] Further, by switching an oscillation state of operating the
moving body and an oscillation state for making the moving body
unable to operate by making a number of amplifier circuits brought
into an active state among a plurality of the amplifier circuits,
periodically variable, the moving body is driven or stopped or a
speed thereof is changed without stopping the self-excited
oscillation circuit to thereby produce stable oscillation.
[0015] Further, by mounting the above-described ultrasonic motor to
an electronic apparatus, controllability of the electronic
apparatus is promoted and small-sized and low power consumption can
be achieved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a diagram showing a behavior of a drive command
signal and rise of an oscillation amplitude;
[0017] FIG. 2 is a diagram showing a behavior of a stop command
signal and stop of an oscillation amplitude;
[0018] FIG. 3 is a diagram showing the other example of a behavior
of a drive command signal and rise of an oscillation amplitude;
[0019] FIG. 4 is a diagram showing the other example of a behavior
of a stop command signal and an oscillation amplitude;
[0020] FIG. 5 shows a structure of an ultrasonic motor according to
the invention;
[0021] FIG. 6 shows operation principle of the ultrasonic motor
according to the invention;
[0022] FIG. 7 shows a drive circuit of the ultrasonic motor
according to the invention;
[0023] FIG. 8 is a diagram showing a behavior of an oscillation
amplitude in correspondence with a drive command signal;
[0024] FIG. 9 is a diagram showing the other example of a behavior
of an oscillation amplitude in correspondence with a drive command
signal;
[0025] FIG. 10 is a diagram showing a behavior of an oscillation
amplitude in correspondence with a drive command signal time period
and a stop command signal time period;
[0026] FIG. 11 shows a behavior of an oscillation amplitude when a
frequency of a control signal is made higher than a drive frequency
of an ultrasonic motor;
[0027] FIG. 12 is a diagram showing a state of an oscillation
amplitude when a number of buffers constituting an active state is
made variable; and
[0028] FIG. 13 shows an example of application in which an
ultrasonic motor according to the invention is applied to an
electronic apparatus.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] A detailed explanation will be given of embodiments to which
the invention is applied in reference to FIG. 1 through FIG. 13 as
follows.
[0030] (Embodiment 1)
[0031] According to a drive circuit (separate excitation system) of
a general ultrasonic motor, a drive signal having a constant
amplitude is applied to the ultrasonic motor approximately
simultaneously with application of a drive command signal.
Meanwhile, according to a self-excited oscillation circuit dealt
with by the invention, a time period is needed until start of
oscillation and a time period is further needed to grow the
oscillation to a constant value and accordingly, the conventional
control method is not applicable and caution is required in a
method of controlling the circuit. In this invention, a description
will be given of a method of stably controlling and a method of
driving an ultrasonic motor using a self-excited oscillation
circuit constituting such a new drive circuit.
[0032] FIG. 5 shows a structure of an ultrasonic motor 1 according
to an embodiment applicable to the invention and FIG. 6 shows
operation principle of the ultrasonic motor 1. In FIG. 5, a
vibrating body 6 in a circular plate shape is supported by a center
shaft 5 the center of which is fixed to a support plate 4. A first
face of the vibrating body 6 is bonded with a piezoelectric element
7 and a second face thereof is provided with projections 6a for
enlarging vibration displacement of the vibrating body 6 and
providing rotational force to a moving body 8. A bearing 3 is
provided at center of the moving body 8 and the center is guided by
the center shaft 5. Further, contact pressure is provided between
the projections 6a of the vibrating body 6 and a friction member 8a
of the moving body 8 by pressing an inner ring of the bearing 3 by
a pressure mechanism 2. A vibration wave excited at the vibrating
body 6 is converted into the rotational force of the moving body 8
by the piezoelectric effect of the piezoelectric element 7.
[0033] FIG. 6 shows detailed operation principle. The piezoelectric
element 7 bonded to the vibrating body 6 is polarized in a
thickness direction such that a polarized area is divided in the
circumferential direction at every quarter wavelength and a
polarizing direction is reversed at every other division of the
polarizing area. Electrode patterns disposed on one face of the
piezoelectric element 7 and provided at the respective divisions of
the polarizing area, are electrically short-circuited at every
other division to thereby constitute two electrode pattern groups
of hatched portions 12a and non-hatched portions 12b. Further, the
vibrating body 6 and the piezoelectric element 7 are bonded such
that the projections 6a of the vibrating body 6 are disposed right
at boundaries of the electrode patterns. An electrode 12c is
provided over a total of a bonded face thereof.
[0034] When a signal having a predetermined frequency is applied to
the piezoelectric element of the pattern group 12a at the hatched
portions, a standing wave as shown by FIG. 6C is generated at the
vibrating body 6. The projections 6a which are elevated at that
time, are inclined to the right side and accordingly, the moving
body 8 in contact therewith is moved to the right. When the signal
is applied to the pattern group 12b at the non-hatched portions, a
standing wave as shown by FIG. 6(d) is generated at the vibrating
body 6 and the moving body 8 is moved in the left direction at this
occasion.
[0035] FIG. 7 shows a drive circuit 18 of the ultrasonic motor
using the self-excited oscillation circuit.
[0036] Two buffers 22 and 23 are connected to the two electrode
pattern groups of the piezoelectric element 7 (the hatched portions
12a and the non-hatched portions 12b in FIG. 6) of the
piezoelectric element 7 independently from each other. A resonating
circuit is constituted by the vibrating body 6 bonded with the
piezoelectric element 7 and two condensers 24 and 26 and an
inverted amplifier constituted by an inverter 21 and a resistor 20
continues oscillation by invertedly amplifying a signal from the
resonating circuit and returning the signal to the resonating
circuit. A resistor 25 constitutes a low pass filter along with the
condenser 24 to thereby restrain sprius oscillation at a higher
order.
[0037] In this case, the inverter 21 and the two buffers 22 and 23
are of a tri-state constitution and depending on signals inputted
to control terminals 21L and 22L and 23L (for example, Low level
signal), an output terminal can be brought into a high impedance
state, that is, an output signal can be made OFF.
[0038] For example, by making an output signal of either of the
buffers 22 and 23 OFF, switching of regular rotation or reverse
rotation can be carried out. Further, by making the output signal
of the inverter 21 or the two buffers 22 and 23 (bringing the
output terminal into the high impedance state) OFF, the motor is
stopped.
[0039] FIG. 1 shows a state of an oscillation amplitude at a point
18a of the self-excited oscillation circuit 18 when the inverter 21
and the buffer 22 are brought into an active state and a drive
command signal for bringing the self-excited oscillation circuit 18
into a drive state, that is, a high level signal is outputted from
a control signal generating circuit 27 and is inputted to a control
terminal. (A similar state is constituted even when the inverter 21
is brought into the active state after the inverter 21 is brought
into the active state).
[0040] In FIG. 1, when a time period t1 has elapsed since the drive
command signal was applied to the self-excited oscillation circuit,
oscillation of the self-excited oscillation circuit is started,
after elapse of a time period t4, the oscillation amplitude is
saturated to a constant value. At this occasion, a drive signal
applied to the ultrasonic motor 1 also becomes a constant
value.
[0041] Although the oscillation includes factors of the circuit
constitution, the state of the ultrasonic motor 1, depending on
cases, a component of a high sprius oscillation initially at the
start of the oscillation, after elapse of a time period t2, there
is constituted the oscillation of an aimed frequency component.
Further, when there is constituted the oscillation amplitude after
elapse of a time period t3, the amplitude of the vibrating body 6
grows to an amplitude value sufficient for moving the moving body 8
and the moving body 8 starts operating.
[0042] Actually, when the self-excited oscillation circuit 18 is
constituted as shown by FIG. 7, the inverted amplifier circuit is
constituted by the resistor 20 and the inverter 21 and the time
period t1 until start of the oscillation is substantially equal to
a time period until voltage at the point 18a becomes an operating
point (VDD/2) of the inverted amplifier circuit. Although the
voltage at the point 18a is initially 0V (Low level), when the
active state is constituted by inputting the drive command signal
to the control terminal of the inverter 21, the voltage at the
point 18b becomes power source voltage VDD (High level). The
voltage at a point 18b is charged to the condenser (C) 26 via the
resistor (R) 20 and reaches the operating point after elapse of the
time period t1. That is, t1.congruent.-CRln0.5=0.693 CR.
[0043] Further, when a stop command signal is applied to the
control terminal 21L of the inverter 21 the self oscillation
circuit which is in the state of oscillation, as shown by FIG. 2,
after elapse of a time period t9, the oscillation amplitude becomes
0. Further, after elapse of a time period t10, the voltage becomes
0V (Low level).
[0044] Depending on the circuit constitution or a method of
inputting the control signal, according to states of starting and
stopping the oscillation with respect to the drive command signal
and the stop command signal, as shown by FIGS. 3 and 4, only the
oscillation is started and stopped while maintaining the voltage
level at operating point, however, with respect to other point, the
states are similar to those in FIGS. 1 and 2 and a control method
shown below may be regarded as similar thereto. For example,
according to the circuit constitution of FIG. 7, when the buffer 22
is brought into the active state after bringing the inverter 21
into the active state by the drive command signal from the control
signal generating circuit 27, the states become similar to the
states of starting and stopping the oscillation as shown by FIGS. 3
and 4.
[0045] Therefore, as shown by FIG. 8, the oscillation can firmly be
carried out by previously setting the control signal generating
circuit 27 such that a length TD of the drive command signal (High
level signal) from the control signal generating circuit 27 is made
always longer than the time period t1 from when the drive command
signal is applied until the oscillation is started. Particularly,
when there are included signal components other than the aimed
frequency at an initial stage of the oscillation, the control
signal generating circuit 27 is set such that the length TD becomes
always longer than the time period t2 at which these components
have been attenuated and the oscillation of the aimed frequency
component is constituted. The control signal generating circuit 27
comprises, other than the signal generating circuit for generating,
for example, the control signal, CPU providing command thereto and
ROM storing conditions and parameters of the length TD of the drive
command signal and a length TS of the stop command signal and the
like.
[0046] By determining a lower limit value of the length TD of the
drive command signal from the control signal generating circuit 27
as described above, there can be carried out a stable step
operation of the ultrasonic motor 1 without oscillation failure or
abnormal oscillation. Further, when the length TD of the drive
command signal is made variable in a range larger than the lower
limit value, an amount of step or speed can be controlled
stably.
[0047] Further, when there is a considerable difference between the
time period t1 or t2 until start of the oscillation and the time
period t3 until the moving body 8 actually starts moving, the lower
limit value of the length TD of the drive command signal is set to
be larger than the time period t3. Further, when the length TD of
the drive command signal is made larger than the time period t4
until the oscillation has grown and saturated into a constant
amplitude value, the drive signal applied to the ultrasonic motor
is provided with a magnitude the same as that in a steady state and
also in step drive, torque equivalent to that in continuous
rotation can be provided.
[0048] As shown by FIG. 9, by setting the length TD of the drive
command signal between the time periods t3 and t4, an amount of
moving the moving body 8 during the time period TD applied with the
drive command signal becomes a very small amount and accordingly,
fine positioning can be carried out.
[0049] Meanwhile, when the control signal generating circuit 27 is
set such that the length TD of the drive command signal is driven
between the time periods t3 and t4, the moving body can be moved
finely.
[0050] (Embodiment 2)
[0051] According to the embodiment, there is shown a control method
for providing stable oscillation and operation when the drive
command signal and the stop command signal are alternately inputted
to the self-excited oscillation circuit 18 to thereby drive the
circuit.
[0052] When the self-excited oscillation circuit having the
constitution as shown by FIG. 7 is used, as shown by FIG. 1 and
FIG. 2, the voltage at the point 18a in the circuit gradually
approaches the operating point (VDD/2) of the amplifier circuit
comprising the resistor 20 and the inverter 21 with application of
the drive command signal and starts oscillating from a time point
substantially reaching the operating point. Further, thereafter,
when the stop command signal is applied, the oscillation finally
stops and finally settles to 0V (GND level).
[0053] Therefore, when the drive command signal and the stop
command signal are alternately inputted to the self-excited
oscillation circuit 18 to thereby drive the circuit, the time
period TD of applying the drive command signal and the time period
TS for applying the stop command signal are set such that an
increase amount .DELTA.IV of the voltage at the point 18a by the
drive command signal (an amount of being proximate to the operating
point: state after elapse of time period t1), becomes larger than a
decrease amount .DELTA.DV of the voltage at the point 18a by the
stop command signal (an amount of being remote from the operating:
state after elapse of time period t10), that is,
.DELTA.IV(TD)>.DELTA.- DV(TS).
[0054] For example, when a rate of increase and a rate of decrease
of the voltage at the point 18a with respect to the time periods TD
and TS of applying the drive command signal and the stop command
signal are the same, in a period (TD+TS) constituted by the time
period TD of applying the drive command signal and the time period
TS of applying the stop command signal, by increasing a rate of the
time period TD of applying the drive command signal by more than
50%, it is possible that the voltage at the point 18a gradually
reaches the operating point to thereby provide the oscillation.
[0055] Further, by determining the period (TD+TS) such that the
time period TS of applying the stop command signal becomes shorter
than the time period t9 from when the stop command signal is
inputted to the self-excited oscillation circuit 18 until the
oscillation is stopped, waveform and amplitude of the oscillation
can be changed without stopping the oscillation and the speed of
the ultrasonic motor 1 can be adjusted. FIG. 10 shows a behavior of
the control signal and the oscillation amplitude at this occasion.
In this case, a maximum value of the oscillation amplitude reaches
a saturated values of the oscillation amplitude and accordingly,
only the rotational number can be made variable while hardly
reducing starting torque in comparison with that in steady state
rotation.
[0056] By carrying out chopping control or PWM control by changing
respective lengths and a ratio of the lengths of the control
signals, that is, the drive command signal and the stop command
signal from the control signal generating circuit 27 under the
above-described condition, while restraining a reduction in torque,
only the rotational number can be made variable.
[0057] (Embodiment 3)
[0058] According to the embodiment, there is shown the other
embodiment of making variable the speed. In this case, when the
ultrasonic motor 1 is driven by alternately inputting the drive
command signal and the stop command signal to the self-excited
oscillation circuit 18, the control signal generating circuit 27 is
set such that a frequency 1/(TD+TS) of the control signal
constituted by the time period TD of applying the drive command
signal and the time period TS of applying the stop command signal,
becomes higher than the drive frequency of the ultrasonic motor 1,
that is, the frequency of the oscillation.
[0059] Thereby, energy flowing to the self-excited oscillation
circuit 18 during one period of the oscillation can be controlled,
in accordance with the ratio of the time period TD of applying the
drive command signal to the time period TS of applying the stop
command signal and the frequency 1/(TD+TS) , the oscillation, that
is, the amplitude value of the drive signal of the ultrasonic motor
1 can be made variable and speed control of the moving body 8 can
be carried out.
[0060] FIG. 11 shows a change in the amplitude of the oscillation
when the ratio of the time period TD of applying the drive command
signal to the time period TS of applying the stop command signal is
changed. FIG. 10(a) shows a state of the amplitude of the
oscillation when the drive command signal is constantly applied and
FIG. 10(b) shows the amplitude of the oscillation when the stop
command signals are applied at intervals shorter than the period of
the oscillation.
[0061] Different from the case of FIG. 10, the amplitude of the
oscillation becomes always a constant value and accordingly, a
variation in the rotational number is extremely small and the motor
can be driven at a lower speed.
[0062] (Embodiment 4)
[0063] A description will be given here of a method of improving a
rise time period which is the drawback of the ultrasonic motor 1
using the self-excited oscillation circuit 18.
[0064] In the self-excited oscillation circuit 18 of FIG. 7,
pluralities of the buffers 22 and 23 constituting the amplifier
circuit are provided in parallel with each other. Among pluralities
of buffers 22a, 22b, 22c, 23a, 23b and 23c, firstly, only a
specific number of the buffers are brought into the active state to
thereby oscillate and thereafter, the number of the buffers which
are brought into the active state is increased to thereby operate
the moving body 8.
[0065] The behavior is shown by FIG. 12. Before the moving body 8
is operated, only the buffer 22a is brought into the active state
to thereby previously produce oscillation having an amplitude which
cannot move the moving body 8, thereby, there can be realized the
ultrasonic motor 1 capable of reducing the time period t1 until the
oscillation is started, provided with a short time period for
growing to an amplitude value capable of operating the moving body
8 since there is provided previously a constant amplitude value and
having extremely fast rise. Further, there can be avoided non-start
of the ultrasonic motor 1 by abnormal oscillation caused in
starting the self-excited oscillation circuit 18. For example, in
positioning by using a sensor such as an encoder, when the
oscillation is not stopped at a vicinity of an aimed position for
the time being, only operation of the moving body 8 is stopped and
thereafter a deviation amount between the aimed position and a
current position is corrected, fast positioning can be carried out.
Further, when the oscillation is not similarly stopped even when
the aimed position is exceeded, only the operation of the moving
body 8 is stopped and thereafter, the deviation amount between the
aimed position and the current position is corrected, fast
positioning can be carried out.
[0066] (Embodiment 5)
[0067] FIG. 13 shows a block diagram of Embodiment 5 in which the
ultrasonic motor according to the invention is applied to an
electronic apparatus.
[0068] The electronic apparatus is featured in having the
above-described vibrating body 6 and the moving body 8 driven by
the vibrating body 6, a pressure means 2 for providing contact
pressure to the moving body 8 and the vibrating body 6, a
transmission mechanism 13 capable of moving in cooperation with the
moving body 8 and an output mechanism 14 moving based on operation
of the transmission mechanism 13. Further, in this case, a
description has been given of driving and controlling the
ultrasonic motor 1 in Embodiments 1 through 4 and therefore, an
explanation will be omitted here.
[0069] In this case, in the transmission mechanism 13, there is
used a transmission wheel such as gear or friction wheel. The
transmission mechanism 13 may be omitted and the output mechanism
may be provided directly. At the output mechanism 14, for example,
there is used an indicator or an indicator drive mechanism, a
display board such as calendar, or a display board drive mechanism
in the case of an indicating apparatus or an electronic time piece,
a mirror for changing a direction of laser in the case of a copy
machine or a printer, a shutter drive mechanism, a diaphragm drive
mechanism, a lens drive mechanism, or a film windup mechanism in
the case of a camera or a video camera, a slit plate or a filter
for blocking or transmitting light or transmitting only light
having a specific wavelength in the case of a measuring instrument
or a fabricating apparatus utilizing laser or light, a contact
mechanism or a gap plate for making variable a resistance value or
a capacitance value for a volume of an acoustic apparatus, or a
pickup drive mechanism in the case of a hard disk or an optical
disk.
[0070] Further, when there is constructed a constitution having a
power transmission mechanism attaching an output shaft to the
moving body 8 and transmitting torque from the output shaft, there
can be realized a dive mechanism by the ultrasonic motor per
se.
[0071] As described above, according to the invention, a command
signal for controlling a state of a self-excited oscillation
circuit constituting a drive circuit, is set in a range capable of
stably driving an ultrasonic motor in an aimed state.
[0072] That is, firm self-excited oscillation is provided by an
ultrasonic motor apparatus constituting a self-excited oscillation
circuit by a vibrating body having a piezoelectric element and an
amplifier circuit for oscillating the vibrating body in a
predetermined natural mode and operating a moving body in contact
with the vibrating body, the self-excited oscillation circuit can
be controlled to be brought into a drive state or a stop state in
accordance with a drive command signal or a stop command signal
from a control signal generating circuit, and the control signal
generating circuit is set such that a length TD of the drive
command signal is made to be longer than a time period t1 from when
the drive command signal is applied to the self-excited oscillation
circuit until the self-excited circuit starts oscillating.
[0073] In this case, particularly, when there is generated
oscillation of sprius oscillation or the like at rise of the
oscillation, the aimed oscillation can firmly be provided by
constituting the length of the time period t1 by the time period t2
at which a signal at a frequency used for driving the moving body
starts oscillating.
[0074] Further, the ultrasonic motor is firmly operated by making
the length TD of the drive command signal longer than the time
period t3 until the oscillation grows and reaches an amplitude
value capable of operating the moving body.
[0075] Further, by setting the length TD of the drive command
signal longer than the time period t4 until the oscillation grows
and is saturated to a specific amplitude value, voltage applied to
the ultrasonic motor is provided with a value in a steady state and
the torque is not lowered even when the ultrasonic motor is driven
intermittently.
[0076] Further, by setting the length TD of the drive command
signal between the time period t3 and the time period t4, ultra
fine movement of the ultrasonic motor can be realized and high
precision positioning control can be carried out.
[0077] Further, by setting the control signal generating circuit
such that the length TS of the stop command signal become shorter
than the time period t9 from when the stop command signal is
inputted to the self-excited oscillation circuit until the
oscillation is stopped, stable oscillation continues and control of
rotational number can be carried out without lowering the torque of
the ultrasonic motor.
[0078] When the ultrasonic motor is driven by alternately inputting
the drive command signal and the stop command signal to the
self-excited oscillation circuit, the time period TD and the time
period TS are set such that an amount of changing a voltage value
of an input unit of the amplifier circuit during a time period of
applying the drive command signal in the time period TD, becomes
larger than an amount of changing the voltage value of the input
unit of the amplifier circuit during a time period of applying the
stop command signal in the time period TS.
[0079] Further, by setting the frequency 1/ (TD+TS) of a control
command signal constituted by the time period TD of the drive
command signal and the time period TS of the stop command signal to
be higher than the frequency in the predetermined natural mode, an
amplitude value of the drive signal can be controlled constant in
accordance with a ratio of the time periods TD and TS and the
frequency 1/(TD+TS) and the rotational number can be controlled
while restraining a variation in rotational number or a variation
in torque.
[0080] Further, by making variable a number of the amplifier
circuits which are brought into the active state among the
plurality of amplifier circuits, the state of driving/stopping the
ultrasonic motor can be controlled without stopping the oscillation
and the ultrasonic motor can be driven stably and in excellent
response.
[0081] Further, by using the ultrasonic motor to which the
invention is applied, there is realized an electronic apparatus
which is small-sized and is driven with low power consumption.
* * * * *