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DESCRIPTION JP2000134962

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DESCRIPTION JP2000134962
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the
technical field of a drive circuit of an ultrasonic motor, and in particular, of a drive circuit of an
ultrasonic motor for producing alternating current of high voltage necessary to operate a
progressive ultrasonic motor. It belongs to the technical field.
[0002]
2. Description of the Related Art Conventionally, various ultrasonic motors have been developed,
and a traveling ultrasonic motor, which is one of the ultrasonic motors, operates according to the
following principle. That is, as shown in FIG. 4, on the surface of the elastic body a which is the
stator S, a traveling wave formed by combining the longitudinal wave and the transverse wave is
formed, and this traveling wave propagates at the speed of sound in the longitudinal direction W
of the elastic body a. After a predetermined time from the state of wave 1 shown by the solid line,
the state of wave 2 shown by the two-dot chain line is reached. Now, focusing on the mass point
at the position α on the surface of the wave 1 state, this mass point moves to the position β on
the surface of the wave 2 state when the traveling wave is in the wave 2 state. The motion of this
mass point is an elliptical motion in the counterclockwise rotation direction with a lateral
amplitude w and a longitudinal amplitude u in the counterclockwise direction opposite to the
traveling direction of the wave. In other words, the surface of the elastic body a performs
elliptical vibration of the vibration velocity V (= 2πfu; f is the frequency of vibration). Then,
when the rotor R is brought into pressure contact with the surface of the elastic body a
performing such elliptical vibration, the rotor R contacts the apex due to the elliptical vibration of
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the elastic body, and between the rotor R and the stator S In the vibration velocity V, it moves in
the opposite direction to the traveling wave.
[0003]
In order to form a traveling wave on the elastic body a of the stator S in such a traveling type
ultrasonic motor, a bending elastic wave is used. A method of generating this bending elastic
wave will be described. As shown in FIG. 5 (a), affixing to the elastic body a a piezoelectric body
(piezoelectric ceramic) b in which adjacent sections are alternately polarized in the thickness
direction to form a predetermined number of electrodes. It consists of In the figure (a), the arrow
of the piezoelectric material b represents the polarization direction of each electrode.
[0004]
When a high frequency voltage is applied to the piezoelectric ceramic b, if the applied frequency
is equal to the natural frequency of the stator a, the stator S resonates to cause bending vibration
in the circumferential direction as shown in FIG. When the vibration wave of the stator S is
divided into nine wavelengths in the circumferential direction, for example, as shown in FIG. 6,
nine wave peaks m1 to m9 are formed, and this wave is a so-called standing wave. It is called.
[0005]
On the other hand, as shown in FIG. 5B and FIG. 7, the phase of the mutual position of segment A
and segment B of the piezoelectric ceramic b is shifted by 3⁄4 wavelength (λ) of the applied high
frequency voltage, and segment A and segment B When applying motor applied voltages Ф0 and
Ф90 with high frequency voltages different in temporal phase by 90 ° from each other,
standing waves are generated by the respective motor applied voltages Ф0 and Ф90 as
described above, but these standing waves are generated Interfering with each other causes the
traveling wave to be formed for the first time.
[0006]
Then, when the stator S is formed in an annular shape and the rotor R is formed in an annular
shape of the same diameter, the traveling wave based on the elliptical vibration of the stator S
causes the rotor R to rotate by friction between the stator S and the rotor R. Will come to do.
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In that case, a resin-made sliding material as a friction material is entirely bonded to the sliding
surface of the rotor R (that is, the contact surface with the stator S), so that the friction between
the stator S and the rotor R becomes large. It has been Thus, the ultrasonic motor is configured
by the annular stator S and the annular rotor R.
[0007]
By the way, as the power required for the operation of the ultrasonic motor, as described above,
alternating currents of high frequency voltages Ф 0 and Ф 90 which are 90 ° out of phase with
each other as described above are required. To increase the efficiency of the sonic motor it is
necessary to keep the alternating current at an optimal frequency. In addition, the drive circuit of
the ultrasonic motor is required to improve its reliability. In addition, the drive circuit of the
ultrasonic motor is required to make such alternating current more easily. In addition, depending
on the purpose of use of the ultrasonic motor, it is required to be able to form the drive circuit of
the ultrasonic motor as small, compact and inexpensive as possible.
[0008]
The present invention has been made in view of such circumstances, and it is an object of the
present invention to provide a drive circuit of an ultrasonic motor which is reliable and can easily
produce an alternating current of an optimum frequency. . Another object of the present
invention is to provide a drive circuit of an ultrasonic motor which can be made as small and
compact as possible and which can reduce the manufacturing cost.
[0009]
SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, a drive circuit
of an ultrasonic motor according to the invention of claim 1 generates an alternating current of
high voltage necessary to operate the ultrasonic motor. In a drive circuit of a motor, a DC power
supply, a transformer applied to an AC ultrasonic motor of two-phase high frequency voltage of a
predetermined phase difference for driving an ultrasonic motor, a DC current from the DC power
supply is specified to the transformer And a central processing unit that operates and controls
the switching means at the predetermined timing, and the transformer is formed of a
piezoelectric transformer using a piezoelectric element. And
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[0010]
Further, according to the invention of claim 2, the piezoelectric transformer comprises a
piezoelectric ceramic consisting of a rectangular flat plate having a predetermined thickness, and
a primary plate consisting of thin plates located on the left and right sides on the upper and
lower surfaces of this piezoelectric ceramic. It is characterized in that it is equipped with a side
electrode and a secondary side electrode consisting of a thin plate which is positioned and joined
at the center on the upper and lower surfaces of the piezoelectric ceramic.
[0011]
In the drive circuit of the ultrasonic motor according to the present invention configured as
described above, an alternating current for driving the ultrasonic motor can be easily generated
from direct current.
Moreover, external information is taken into consideration and the rotational state of the
ultrasonic motor is fed back, whereby the alternating current applied to the ultrasonic motor is
maintained at an optimum frequency, and the efficiency of the ultrasonic motor is increased.
[0012]
Further, since the transformer is formed of a piezoelectric transformer using a piezoelectric
element, the volume of the transformer is considerably smaller than that of a transformer using
magnetic flux.
Therefore, the drive circuit of the ultrasonic motor is formed to be very small and compact as
compared with a transformer using magnetic flux. In addition, since the number of parts is
extremely reduced, the cost of the ultrasonic motor is reduced.
[0013]
In particular, in the invention of claim 2, since a flat plate-like piezoelectric ceramic is used as the
piezoelectric element, and a thin plate-like electrode is joined to the piezoelectric ceramic, a
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transformer is formed. It will be configured as one part. Therefore, the drive circuit of the
ultrasonic motor is further miniaturized and made compact, and the management is extremely
easy. Moreover, since the number of parts is further reduced, the cost of the ultrasonic motor is
further reduced.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be
described below with reference to the drawings. FIG. 1 is an electric circuit diagram showing an
example of an embodiment of a drive circuit of an ultrasonic motor according to the present
invention, and FIG. 2 is a perspective view showing a piezoelectric transformer used in the drive
circuit of the ultrasonic motor of this embodiment. .
[0015]
In the drive circuit of the ultrasonic motor in this example, a low voltage direct current is used to
create a two-phase high frequency alternating current whose phase difference is 90 ° or -90 °.
A drive circuit for this will be described.
[0016]
As shown in FIG. 1, the drive circuit 1 of the ultrasonic motor includes a direct current power
supply (DC power supply) 2 for generating direct current of low voltage and a relay (RL) 3 for
supplying direct current from the DC power supply 2 and interrupting control. And the switching
element unit 4 that controls the supply of direct current from the DC power supply 2 with a
predetermined timing pulse, and the direct current controlled and controlled by the switching
element unit 4 in two phases with a phase difference of 90 °. A signal based on external
information such as the transformer unit 6 generating an alternating current of high frequency
voltage boosted to a voltage and supplying it to the ultrasonic motor 5, a monitoring signal
monitoring the state of the power supply voltage of the DC power supply 2 , Relay 3 and the
switching element unit so that the frequency of the alternating current generated by the
transformer unit 6 becomes optimal based on each feedback signal from the switching element
unit 4 and the ultrasonic motor 5 It consists of a central processing unit (CPU) 7 that controls 4.
[0017]
The switching element unit 4 includes two switching elements Q1 and Q2, and one switching
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element Q1 transmits low-voltage direct current of the DC power source 2 to the transformer
unit 6 based on timing pulses P1 and P2 described later from the CPU 7. The other switching
element Q2 is adapted to supply a low voltage DC current of the DC power supply 2 to the
transformer 6 based on timing pulses P3 and P4 described later from the CPU 7 as well as being
supplied.
[0018]
The transformer unit 6 includes two piezoelectric transformers T1 and T2 having exactly the
same configuration.
The piezoelectric transformers T1 and T2 are respectively joined to the upper and lower surfaces
(upper and lower in FIG. 2) of the piezoelectric ceramic 8 which is a rectangular flat plate having
a predetermined thickness as shown in FIG. A primary side electrode 9 made of a thin plate and a
secondary side electrode 10 made of a thin plate joined to the right side surface of the
piezoelectric ceramic 8 are provided.
Then, a low voltage direct current of the DC power source 2 is supplied to the primary electrode
9 from the upper side or the lower side based on the timing pulses P1, P2, P3 and P4 to make
the primary side of the piezoelectric ceramic 8 longitudinal. As mechanical vibration is excited,
this mechanical vibration causes distortion on the secondary side of the piezoelectric ceramic 8,
and this distortion is detected as an electrical signal in the secondary side electrode 10 so that a
high voltage alternating current is generated. It has become. It goes without saying that the
output voltages of the piezoelectric transformers T1 and T2 are set sufficiently to correspond to
the voltage levels required by the ultrasonic motor 5.
[0019]
Next, a method will be described in which the drive circuit 1 of the ultrasonic motor generates
two-phase high-frequency alternating current whose phase difference is 90 ° from low-voltage
direct current. First, the CPU 7 outputs a control signal to the relay 3 to close the relay 3. Then,
DC power is supplied from the DC power source 2 to the two switching elements Q1 and Q2. In
this state, the CPU 7 uses four layers of clock pulses for driving the ultrasonic motor 5 as shown
in FIG. 3 based on temperature information in the switching element unit 4, monitoring
information of the voltage of the power supply 2, and external information. The timing pulses P1,
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P2, P3 and P4 are obtained, and the timing pulses P1 and P2 are output to the switching element
Q1, and the timing pulses P3 and P4 are output to the switching element Q2, respectively. The
timing pulses P1, P2, P3 and P4 shown in FIG. 3 are outputted in the order of P1 → P3 → P2 →
P4 → P1.
[0020]
Thus, the switching elements Q1 and Q2 supply the DC current of the DC power supply to the
primary electrodes 9 of the transformers T1 and T2 in accordance with the timing pulses P1, P2,
P3 and P4. Then, the mechanical vibration on the primary side of the piezoelectric ceramic 8
generates distortion on the secondary side, and the distortion of the piezoelectric ceramic 8
generates an alternating current of high voltage in the central secondary electrode 10, that is, a
transformer An alternating current Ф 0 of the high frequency voltage boosted is generated at the
secondary side electrode 10 of T1, and an alternating current wedge 90 of the high frequency
voltage boosted is generated at the secondary side electrode 10 of the transformer T2. At this
time, the phase difference between the two alternating currents Ф0 and Ф90 generated is 90 °
due to the timing pulses P1, P2, P3 and P4 shown in FIG. In this way, an alternating current of a
two-phase high frequency voltage with a phase difference of 90 ° is produced from direct
current. Then, the two-phase alternating current is applied to the ultrasonic motor 5 to operate
the ultrasonic motor 5. At this time, information on the rotational state (rotational speed) is fed
back to the CPU 7.
[0021]
Then, the CPU 7 obtains an optimum AC waveform for driving the ultrasonic motor 5 based on
the external information and the rotation state of the ultrasonic motor 5, and the timing pulses
P1, P2,. P3 and P4 will be set.
[0022]
As described above, according to the drive circuit 1 of the ultrasonic motor 5 of this example, the
alternating current applied to the ultrasonic motor 5 can be held at the optimum frequency, so
the efficiency of the ultrasonic motor is increased. be able to.
Moreover, according to the drive circuit 1, it is possible to easily create a high voltage alternating
current by the direct current of the point voltage.
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[0023]
When each transformer T1 and T2 of the transformer unit 6 uses a transformer using magnetic
flux from a conventional primary and secondary winding, not only the volume occupied by the
transformer is relatively large but also the core and bobbin The number of parts such as primary,
winding, insulating tape, etc. will be very large. Moreover, the cost of the ultrasonic motor
becomes very high. In particular, design specifications such as the number of turns of the
winding and the method of insulating the winding make the cost even higher.
[0024]
On the other hand, according to the drive circuit 1 of the ultrasonic motor of this example, since
the piezoelectric transformer using the flat plate-like piezoelectric ceramic 8 is formed, the
volume of the transformer 6 is the transformer using the magnetic flux described above It
becomes considerably smaller than. Moreover, since the transformers T1 and T2 are formed by
joining thin plate electrodes to the flat plate-like piezoelectric ceramic 8, these transformers T1
and T2 can be configured as a single component. Therefore, the drive circuit 1 of the ultrasonic
motor can be formed to be extremely compact and compact as compared with a transformer
using magnetic flux, and the management becomes extremely simple. Moreover, since the
number of parts can be extremely reduced, the cost of the ultrasonic motor 5 can be significantly
reduced.
[0025]
As apparent from the above description, according to the drive circuit of the ultrasonic motor of
the present invention, it is possible to easily create an alternating current for driving the
ultrasonic motor from direct current. Further, by considering external information and feeding
back the rotational state of the ultrasonic motor, alternating current applied to the ultrasonic
motor can be maintained at an optimum frequency, and the efficiency of the ultrasonic motor can
be improved.
[0026]
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Furthermore, since the transformer is formed of a piezoelectric transformer using a piezoelectric
element, the volume of the transformer can be made much smaller than that of a transformer
using magnetic flux. Therefore, the drive circuit of the ultrasonic motor can be formed to be very
small and compact as compared with a transformer using magnetic flux. In addition, since the
number of parts can be extremely reduced, the cost of the ultrasonic motor can be reduced.
[0027]
In particular, according to the invention of claim 2, since the transformer is formed by using a
flat plate-like piezoelectric ceramic as the piezoelectric element and bonding a thin plate-like
electrode to the piezoelectric ceramic, the transformer is a single component. It can be
configured as. Therefore, the drive circuit of the ultrasonic motor can be formed to be smaller
and smaller, and the management can be extremely simplified. Moreover, since the number of
parts can be further reduced, the cost of the ultrasonic motor can be further reduced.
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