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BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic motor and a CRT display
device using the ultrasonic motor. More specifically, the present
invention relates to an electrostrictive revolution type ultrasonic motor
having an improved rotor structure.
The present invention further relates to a driving device for an ultrasonic
motor which is required to be driven under a predetermined frequency such
as under a resonant condition of the ultrasonic motor as a load.
An ultrasonic motor is utilized as a servo motor in a precise adjustment
mechanism because of the ability which permits a very fine operation
without necessitating interposing of such as a reduction gear and of a
large holding torque during no voltage application. In particular, a so
called electrostrictive revolution type ultrasonic motor, which makes use
of a disk shaped ceramic piezoelectric stator of which center of gravity
precessions through excitation by ultrasonic input power as disclosed in
JP-A-63-257474 and JP-A-63-181676 which partly corresponds to U.S. Pat.
No. 4,868,446, is suitable for reducing the size and cost thereof because
of its comparatively simple structure thereof.
FIGS. 9A and 9B show a structure of a conventional electrostrictive
revolution type ultrasonic motor. The ultrasonic motor as illustrated in
FIGS. 9A and 9B is constituted by a disk shaped stator 1 formed by a
piezo-electric element of ferroelectric substance subjected to a
polarization treatment in advance such as PZT, a rotor 2 formed from a
phosphor bronze plate in Petri dish shape through drawing and fitted
around the circumference of the stator 1, an insulator spacer 6 of Mylar
for preventing short circuiting between electrodes formed on the surface
of the stator 1 and the metallic rotor 2 and others. The rotor 2 is
provided with three projecting portions 3 formed by drawing and the rotor
2 contacts the outer circumference of the stator 1 via these projecting
portions 3 with a proper contacting pressure.
For divided fan shaped electrodes 11 through 14 are formed by spattering on
both faces of the stator 1 and one of the electrodes on the front face
thereof is connected to the electrode on the back face thereof facing in
180.degree. relation each other so as to constitute two sets of electrodes
corresponding to two phases. Further, the two sets of the electrodes are
constituted to receive two phase pulse like voltage of which frequency is
tuned to the resonant frequency via a coil spring (not shown) so as not to
disturbe the mechanical resonance of the stator 1. The details for driving
the stator are disclosed in the above indicated patent documents,
therefore the explanation thereof is omitted in the present specification.
In the ultrasonic motor as illustrated in FIGS. 9A and 9B having the above
explained structure, one electrode portion of the stator 1 slightly
expands, normally below 1.mu.m, in response to the polarity of the applied
pulse like voltage, and the other portion displaced by 180.degree. with
respect to the one electrode portion contracts, as a result, the center of
gravity of the stator 1 moves eccentrically thereby to cause a so called
precession. Such motion is transferred to the projecting portions 3 of the
rotor 2 via frictional contact and induces a rotating torque in the rotor
2 to rotate the same.
However, with the conventional ultrasonic motor having the above explained
structure, the generated rotating torque is small, variation of the
generated rotating torque is large by product by product and a complex and
fine adjustment of the spring pressure of the respective projecting
portions was indispensable. Further, even when a necessary rotating torque
is generated, a time depending torque variation due to such as damaging of
the stator contacting face was large, therefore the ultrasonic motor
having the above explained structure has not been reduced into practice as
a mass-producable product until now. Still further, since metal is used
for the rotor material in the conventional ultrasonic motor, such
ultrasonic motor is not suitable for an application wherein mutual action
or interference with respect to electric field and magnetic field causes
problems, for example, an application for a flyback voltage adjustment for
focusing adjustment in a CRT display device in which an intense
electro-magnetic field is generated or a medical use electronic
measurement equipment in which a slight electro-magnetic disturbance
causes problems.
According to experimental study performed by the present inventors, it is
found out that the above conventional problems are caused by the rotor
formed from a phosphor bronze plate through drawing method. The drawing is
an only method of forming a thin spring material such as a phosphor bronze
plate in mass-production scale, however it is found out that the variation
in the dimensional accuracy through such drawing reaches about
.+-.50.mu.m, and such variation is too large exceeding an allowable
variation of about .+-.15.mu.m for flexing amount when the rotor of the
electro-strictive revolution type ultrasonic motor is contacted. Further,
it is also found out that hardness change due to stress during spreading
by the drawing operation causes variation. Still further, because of a
high hardness of the contacting portion of the rotor which is formed from
a metallic spring material the stator contacting face is likely to be
damaged in time depending manner during the contacting rotation which
brings about a large variation of frictional contacting force and a time
depending change thereof.
An ultrasonic motor is one examples which can operate only by a
predetermined frequency signal called as a resonant frequency signal. Such
a machine necessitates a so called frequency tracking operation in which
the operating frequency is tuned to the resonant frequency prior to the
primary control operation thereof in order to maintain the resonant
condition in response to the state change of the machine.
An ultrasonic motor generates a maximum torque at its resonant condition
and when the operating frequency deviates from the resonant frequency, the
torque generation is either extremely reduced or totally ceased to stop
the operation of the motor such that the resonant frequency tracking
operation is an indispensable measure so as to ensure a stable operation
of the ultrasonic motor even under temperature change and load variation
thereof.
Conventional resonant frequency tracking method uses such as a synchronous
method using a phase-locked loop (PLL) as disclosed for example in
JP-A-62-85684 and a resonant frequency searching method using a digital
storage means as disclosed for example in JP-A-63-02774. However, with the
former method when noises are high a stable operation can hardly be
realized, and further with the later method using the digital technology
when a high resolution searching is required the circuit scale is enlarged
and complexed as well as the searching time thereby is prolonged.
SUMMARY OF THE INVENTION
The present invention relates to an ultrasonic motor in which the rotor is
constituted so as to limit the variation of rotating torque to thereby
achieve a stable and high rotating torque with a reduced cost.
The present invention also relates to an ultrasonic motor using a
non-metallic rotor having a desirable environmental property being hardly
affected by such as electric field and magnetic field as well as hardly
affecting others.
The present invention further relates to an ultrasonic motor driving device
which is constituted by a simple circuit with a reduced production cost as
well as operable at a high speed, a high resolution and a high effeciency.
Additionally the present invention provides a simple and small size voltage
adjusting device for a plurality of high voltage focusing potentiometers
in a CRT display device.
The benefits of the present invention are achieved by forming a rotor
having substantially a cylindrical shape of which inner face is provided
with spring means through injection molding so as to contact with a stator
which is constituted operable as an ultrasonic vibrating element for an
electrostrictive revolution type ultrasonic motor. Further, the former
objects are achieved by using as a molding material for the rotor a
material having hardness lower than that of the stator material and having
a high Young's modulus, for example, a plastic material, more
specifically, a material mainly containing such as polycarbonate or acylic
resin possibly containing a reinforcing material.
According to an advantage of the present invention, since the rotor is
formed by injection molding, the dimentional variation and the processing
distortion of the rotor are limited, as a result, the contact pressure of
the rotor with respect to the stator can be controlled almost within a
predetermined desirable range and a stable rotating torque with a limited
variation is obtained.
Further, a plastic material having a comparatively high Young's modulus is
used for the injection molded rotor, the productivity thereof is improved
as well as the production cost thereof is reduced. Further, since the
rotor thus produced is soft in comparison with a hard metallic material,
even when the contacting pressure against the contacting face of the
stator of a dielectric ceramic material is increased, a stable frictional
force is obtained without damaging the contacting face. As a result, the
rotating torque as well as the static holding torque of the ultrasonic
motor are increased and stabilized. Further, because of no use of metallic
material for the rotor, the rotor is not affected by electric field and
magnetic field and is applicable in an environment requiring a high
resistance to electricty, for example, for a focusing voltage adjusting
servo in a flyback circuit for a TV receiver.
The present invention achieves by a driving device for driving at least one
ultrasonic motor which comprises an oscillator which generates variable
frequencies in response to a variable signals from a computer for finely
dividing a predetermined frequency range and causing a successive
scanning, a driver which amplifies the oscillation signal from the
oscillator and drives the ultrasonic motor, a voltage detecting means
which samples and detects a load current for driving the ultrasonic motor
for every variable frequency, a comparing means which compares the
magnitude between the current detection value and a current value held in
a holding means which holds the larger current value determined in the
comparing means in a sample hold analogue circuit, wherein the driving
frequency for the ultrasonic motor is set where the driving current for
the ultrasonic motor maximizes.
Further, in the driving device for driving the ultrasonic motor according
to the present invention, the output stage of the driver is constituted by
an inverter including a bridge circuit outputting a rectangular pulse
voltage and the current detection circuit includes a resistor connected in
series at one DC side terminal of the above bridge circuit and detects the
load current in a DC amount by means of the above resistor regardless to
the driving phase and polarity.
Still further, in the driving device for driving the ultrasonic motor
according to the present invention, a plurality of ultrasonic motors are
provided and when driving one of the motors after changing-over the
respective ultrasonic motors, the arms constituting the above bridge
circuit are used as a changing-over means.
Further, the present invention achieves a voltage adjusting device for a
high voltage focusing potentiometer in a CRT display device wherein a
plurality of potentiometers integrated with and driven by the respective
ultrasonic motors are provided and are designed to be driven by a single
driving device.
When a set value of the driving frequency for the ultrasonic motor is
successively varied, the bridge inverter at the output stage drives the
load with the successively set frequencies, the load current corresponding
to the respective driving frequencies are detected as DC voltages at the
common ground side of the inverter circuit, the detected voltage is
compared with a comparison reference which represents the maximum value
already stored in the sample hold analogue circuit in the comparator to
discriminate the magnitude of the load current at respective frequencies,
namely, the setting from the outside and reading-out are performed by
making use of digital values, however the internal operation is performed
through an analogue operation, thereby a high speed operation as well as a
high resolution operation are realized. Further, the bridge circuit is
constituted by switching elements operable at a low voltage, because the
driving efficiency of the ultrasonic motor is determined based on the
effective voltage value applied thereto and a better driving efficiency is
achieved by the use of rectangular waveform voltage other than by a
sinusoidal waveform voltage.
Further, through the provision of a plurality of ultrasonic motors and the
use of the arms constituting the bridge circuit as the changing-over means
other than the use of such as a transfer switch when driving one of
ultrasonic motors after changing over between the respective ultrasonic
motors, a simple and low cost circuit is realized.
Still further, through the voltage adjustment of a plurality of high
voltage focusing potentiometers in a CRT display device by a single
driving device, a simple and small size adjusting mechanism for the CRT
display device is realized.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A is a cross sectioned front view of a first embodiment of the
ultrasonic motors according to the present invention;
FIG. 1B is a cross sectioned side view of the first embodiment;
FIG. 2A is a cross sectioned front view of a second embodiment of the
ultrasonic motors according to the present invention;
FIG. 2B is a cross sectioned side view of the second embodiment;
FIG. 3A is a cross sectioned front view of a third embodiment of the
ultrasonic motors according to the present invention;
FIG. 3B is a cross sectioned side view of the third embodiment;
FIG. 4A is a cross sectioned front view of a fourth embodiment of the
ultrasonic motors according to the present invention;
FIG. 4B is a cross sectioned side view of the fourth embodiment;
FIG. 5A is a cross sectioned front view of a fifth embodiment of the
ultrasonic motors according to the present invention;
FIG. 5B is a cross sectioned side view of the fifth embodiment;
FIG. 6A is a cross sectioned front view of a sixth embodiment of the
ultrasonic motors according to the present invention;
FIG. 6B is a cross sectioned side view of the sixth embodiment;
FIG. 7A is a cross sectioned front view of one embodiment of ultrasonic
motor for driving a potentiometer according to the present invention;
FIG. 7B is a cross sectioned side view of the embodiment illustrated in
FIG. 7A;
FIG. 8 is a circuit diagram for automatic focusing adjustment in a CRT
display device according to the present invention;
FIG. 9A is a cross sectioned front view of a conventional ultrasonic motor;
FIG. 9B is a cross sectioned side view of the conventional ultrasonic motor
as illustrated in FIG. 9A;
FIG. 10 is a block diagram of one embodiment of driving circuits for an
ultrasonic motor according to the present invention;
FIG. 11 is an operation characteristic diagram of the embodiment as
illustrated in FIG. 10;
FIG. 12 is a detailed IC circuit block diagram of the embodiment as
illustrated in FIG. 10;
FIG. 13 is a further detailed circuit diagram of one part of the block
diagram as illustrated in FIG. 12;
FIG. 14 is a further detailed circuit diagram of another part of the block
diagram as illustrated in FIG. 12;
FIG. 15 is a timing chart for explaining the operation of the circuits
illustrated in FIGS. 13 and 14;
FIG. 16 is a table for explaining the operation of the circuits illustrated
in FIGS. 13 and 14;
FIG. 17 is a further detailed circuit diagram of still another part of the
block diagram as illustrated in FIG. 12;
FIG. 18 is a further detailed circuit diagram of a further part of the
block diagram as illustrated in FIG. 12; and
FIG. 19 is a further detailed circuit diagram of a still further part of
the block diagram as illustrated in FIG. 12.
DETAILED DESCRIPTION
FIGS. 1A and 1B show the structure of a first embodiment of the ultrasonic
motors according to the present invention. In FIGS.1A and 1B, a
cylindrical shaped rotor 2 is assembled with a disk shaped stator 1 of
piezoelectric ceramic in such a manner that the rotor 2 contacts the outer
circumference of the stator 1. The cylindrical rotor 2 is provided with
rotor contacting portions 3 for making contact with the outer
circumference of the stator 1 which are formed by linearizing the part of
the inner face thereof around the inner face thereof with an equal
distance of every 120.degree.. Further, a disk shaped rotor side plate 4
which transmits a rotating torque to an external load (not shown) is
attached to the cylindrical shaped ring rotor 2 via side plate supporting
portions 5 arranged between the respective contacting portions 3.
Now, the ring rotor 2, the rotor contacting portions 3, the rotor side
plate 4 and the side plate supporting portions 5 are formed integrally by
making use of a resilient plastic material having a comparatively high
Young's modulus and, when required, containing a filler such as
polycarbonate or acrylic resin via injection molding.
On the front and back faces of the stator 1 four divided fan shaped
electrodes (not shown) are formed by spattering evaporation as explained
previously and two phase pulse like voltage having the resonant frequency
of the ceramic stator is applied to the respective electrodes via metallic
spring wires.
As an exemplary dimension of the first embodiment as illustrated in FIGS.
1A and 1B, the diameter of the stator 1 is 20 mm and the thickness thereof
is 1.5 mm, and the cylindrical inner diameter of the rotor 2 is 23 mm, the
cylinder portion width thereof is 3 mm and the thickness thereof is 1 mm
or slightly larger. Under the condition when the stator 1 is fitted into
the rotor 2, the contacting portions 3 of the rotor 2 is flexed by the
stator 1 to about 50 .mu.m to thereby generate a holding torque of about
150 gfcm.
For the thus structured ultrasonic motor, when the stator 1 is excited by a
two phase pulse like voltage of 5Vp-p having a resonant frequency of about
100 kHz, a portion where the voltage of the same polarity with respect to
the polarization is applied is compressed to thereby extend in radial
direction and contrary the opposing portion is contracted, as a result,
the stator 1 begins a precession of 1 .mu.m or slightly less at the
resonant frequency and the precession is transmitted to the rotor 2
located outside via frictional contact to rotate the rotor 2.
Although the rpm of the rotor 2 varies depending on loads, the rpm about
100 is obtained when no load, and a maximum starting torque of about 70
gfcm is also obtained, of which torque amounts more than two times of the
maximum torque of the conventional ultrasonic motor of the same size using
the phosphor bronze rotor formed by drawing, and with the present rotor 2,
the variation of maximum starting torque possibly due to unstable
contacting force is greatly reduced. These advantages owe to a limited
dimensional variation of less than .+-.10 .mu.m which amounts 1/5 of the
conventional ultrasonic motor as well as to a limited distortion during
processing, and further through the use of the plastic ring shaped rotor
the damaging of the contacting face of the ceramic stator is prevented
which was caused when a hard metal for a spring material was used.
Accordingly, even when the contacting pressure is increased the contact
friction is stabilized for long time and together with the structure
giving a broad contacting area a high and stable torque is obtained with
the present embodiment.
Further, the rotor is formed by a comparatively inexpensive material via
injection molding, therefore together with the adjustment free production
the production cost of the rotor is reduced.
FIGS. 2A and 2B show a second embodiment of the ultrasonic motors according
to the present invention. The same or equivalent portions in FIGS. 2A and
2B as in FIGS. 1A and 1B are designated by the same reference numerals as
in FIGS. 1A and 1B.
The ultrasonic motor of FIGS. 2A and 2B is constituted by a stator 1 of
piezoelectric ceramic, a ring rotor 2 contacting the outer circumference
of the stator 1, projecting portions 31 formed on the rotor, a rotor side
plate 4 and side plate supporting portions 5. The projecting portions 31,
the rotor side plate 4 and the side plate supporting portions 5 are made
of the same material as the rotor 2 and are formed integrally at the same
time with the rotor 2 via injection molding.
Further, such as electrode structure on the stator 1 is the same as those
already explained in connection with FIGS. 9A and 9B and FIGS. 1A and 1B.
Further, the rotor 2 is rotated in the same manner as explained above, in
that, by causing the precession on the stator 1 through application
thereto of a two phase pulse like voltage of a high frequency as the
fundamental operation thereof.
In FIGS. 2A and 2B embodiment, the contact between the rotor 2 and the
stator 1 is performed by projecting portions of easily produced simple
shape, thereby the maximum diameter of the rotor 2 is slightly reduced.
However, the torque variation due to friction change of the contacting
portions depending on time slightly increases in comparison with the rotor
structure as illustrated in FIGS. 1A and 1B.
FIGS. 3A and 3B show the third embodiment of the ultrasonic motors
according to the present invention. The rotor 2 in FIGS. 3A and 3B
embodiment is provided with rotor contacting portions at more portions of
four than the previous embodiments. For this reason, with the ultrasonic
motor of FIGS. 3A and 3B structure the rotating torque due to increase of
the contact friction force transmission is slightly increased.
In the ultrasonic motor, the rotating torque is induced by the contact
friction, therefore it is assumed on one hand that when the number of the
portions for the contact friction is increased the rotating torque is
correspondingly increased, however on the other hand when the number of
the portions for the contact friction is increased it becomes difficult to
keep the contacting pressure at respective contacting points uniform
because of their dimensional variation, in particular, increase of out of
roundness and the non-uniformity of the contact pressure cause irregular
rotation. Accordingly, the number of contacting portions on the rotor is
preferably to be three or four and at most about six.
FIGS. 4A and 4B show the fourth embodiment of the ultrasonic motors
according to the present invention. In FIGS. 4A and 4B embodiment, the
ring shaped rotor 2 arranged around the outer circumference of the stator
functioning as an ultrasonic vibrating element is provided with
cantilevers 32 contacting the stator 1. Further, the side plate 4 for the
rotor 2 is integrated with the ring shaped rotor 2 without clearances
different from the previous embodiments.
With the present embodiment, although the ring portion of the rotor 2 is
restricted by the side plate 4 to prevent flexing, through the flexing of
the cantilever portions 32 a stable frictional contact can be obtained
between the rotor 2 and the stator 1, therefore, the ring portion of the
rotor 2 can be integrated with the side plate 4 without clearances.
Accordingly, a large creeping distance between the stator side and the
load side, in that the outside of the rotor side plate, corresponding to
the eliminated clearances, is obtained, thus the present embodiment is
suitable for driving a load of a high voltage. One of the application
which can make use of the above advantage in maximum is a servo motor used
for a high focusing voltage adjustment in a CRT display device of which
application is illustrated in
FIG. 8 and will be explained later in detail. In the present embodiment,
all of the contacting pressure in the plastic rotor is provided via the
cantilever portion, the spring function due to flexing of the ring portion
can be eliminated.
FIGS. 5A and 5B show the fifth embodiment of the ultrasonic motors
according to the present invention. In FIGS. 5A and 5B, the ultrasonic
motor is constituted by a stator 1 and a rotor 2 in which a rotor side
plate 4 and contacting portions 32 are formed integrally. The contacting
portions 32 function as a cantilever to provide the contacting pressure to
the stator 1.
In FIGS. 5A and 5B embodiment the ring portion of the rotor 2 is
eliminated, the weight of the rotor 2 is reduced and corresponding thereto
the inertia of the rotor 2 is reduced, thereby the response time for
starting and stopping the motor is speeded-up to about 10.about.20 ms as
well as the production cost thereof is reduced because of the simple
structure.
However, with FIGS. 5A and 5B embodiment since the effective length of the
cantilevers is short, the relative thickness of the stator 1 can not be
neglected and the contacting pressure on the stator can not be treated
equal in its thickness direction, an optimum design for the frictional
force as well as the holding torque is somewhat difficult. For this reason
an modification for elongating the effective length of the cantilevers is
explained in the following.
FIGS. 6A and 6B show the sixth embodiment of the ultrasonic motors
according to the present invention. In FIGS. 6A and 6B embodiment, the
cantilever type contacting portions 32 of the rotor 2 contacting the
stator 1 are formed in lateral U shape, thereby the effective length of
the cantilever is set sufficiently long with respect to the thickness of
the stator 1, and with the elongated cantilevers a uniform contacting
pressure is obtained in the thickness direction of the stator 1.
In the embodiments explained hereinabove, the contacting pressure to the
stator 1 from the rotor 2 is maintained by the rigidity of the rotor
itself, however, in addition to the rigidity of the rotor another force
can be used for maintaining the contacting pressure, the following is such
an embodiment.
FIGS. 7A and 7B show the seventh embodiment of the ultrasonic motors
according to the present invention. The features of FIGS. 7A and 7B
embodiment are that as seen from the front view in FIG. 7A a ring shaped
rotor 2 contacts disk shaped stator 1 of piezoelectric element via
linearized portions 3, and as seen from the side view in FIG. 7B both the
stator 1 and the rotor 2 are provided with inclined contacting faces.
The structure of the present embodiment is explained with reference to the
side view as illustrated in FIG. 7B. The electrode face of the stator 1 is
led via metal coils 10 serving for supplying power as well as holding the
same and a terminal plate 21 and along a holding box 22 to a power supply
conductor 23 on a substrate 7. On the other hand, a side plate 4 with a
manual rotation use shaft 41 for transmitting a rotating torque to a load
is fitted to the rotor 2 and to the side plate 4 a metallic lever type
brush 9 for a potentiometer constituting the load is attached. The ends of
the brush 9 is contacted to a resistance pattern 8 for the potentiometer
and a common conductor pattern 91 for current collection formed in advance
on the substrate 7 through thick film printing.
The ultrasonic motor having the structure as explained with reference to
FIGS. 7A and 7B operates as follows. When a high frequency voltgae is
applied to the stator 1 via the power supply conductor 23, the revolving
vibration of the stator 1 is transmitted to the rotor 2 in a form of
rotating torque via the conical shaped contacting face to rotate the rotor
2 as well as the side plate 4. Accordingly, the brush 9 for the
potentiometer is rotated so that a small sized motor driven potentiometer
is realized which permits an accurate operation.
In FIGS. 7A and 7B embodiment the contacting pressure at the contacting
face between the stator 1 and the rotor 2 is adjustable not only by the
rigidity of the rotor 2 but also primarily by the thrust due to the
metallic coils 10 at the stator side and the brush 9 for the potentiometer
at the load side, accordingly materials for the rotor 2 having a variety
of rigidities can be selected, thereby the design freedom therefor is
increased. Further, another advantage of the present embodiment is that
since the thrust from the load side is held at the contacting face a
thrust bearing otherwise required is eliminated for a load requiring a
thrust.
A conventional example wherein the contacting face between the stator and
rotor is inclined and the thrust bearing is eliminated is disclosed in
JP-A-63-181677 which partly corresponds to U.S. Pat. No. 4,868,446.
However, in the conventional example the stator and the rotor are designed
to contact through all the circumference thereof, therefor both the stator
and the rotor are required to be finished with a high degree of roundness
and smoothness, for example both at about .+-. a few .mu.m allowance,
therefore the conventional ultrasonic motor had drawbacks with regard to
productivity and durability thereof. On the other hand, in FIGS. 7A and 7B
embodiment the stator and the rotor contact only at three point other than
all the circumferential faces thereof, the requirement with regard to
roundness and smoothness is greatly relaxed.
In the above embodiments of the ultrasonic motors according to the present
invention several rotors formed by injection molding are explained,
however the shapes of the rotors are not limited those explained with
reference to the embodiments and can be modified according to the general
concept of the present invention. The same can be said to plastic
materials to be used for the rotor.
Usually several types of reinforcing materials or fillers can be properly
mixed in the plastic material for the rotor depending on requirements for
the rotor. For example, in order to improve elasticity or Young's modulus
for the purpose of reducing the size of the rotor, oxide particles such as
silica and alumina, carbide particles such as calcium carbonate and
silicate particles such as glass can be used. Further, as will be
explained in the following application example when the ultrasonic motor
serving as a servo motor for a high voltage focusing adjustment is
integrated with a high voltage flyback circuit portion, the plastic rotor
is required to have a fire resistant and an improved temperature
characteristic, in other words a reduced linear expansion coefficient,
therefore for fulfilling the former property hydroxides such as magnesium
hydroxide and aluminum hydroxide, and for fulfilling the later property
oxides such as calcium carbonate and silicates such as glass are mixed.
Further, in order to increase durability it is effective to coat the
frictional contacting face at the rotor side with a paint containing
fillers having a high abrasion resistance at least upto a few .mu.m thick.
Now, one of typical application example of the ultrasonic motors according
to the present invention is explained in the following.
FIG. 8 shows an application example wherein the present invention is
applied for a focusing voltage adjustment and a screen voltage adjustment
in a CRT display device. In FIG. 8, a high voltage generating circuit 50
is constituted by a flyback transformer 51, an automatic adjusting device
54 and others, and elements thereof except for movable elements are
integrally molded with a resin so as not to expose the high voltage
portions. A primary winding 56 of the flyback transformer 51 is connected
in parallel with a horizontal deflection coil 77 via a resistor 78 and is
driven by +B power source supplied to a terminal 79 and a horizontal
deflection driving circuit 74, more specifically driven by a pulse voltage
generated during its flyback line period. Further, a horizontal
synchronous pulse is inputted to a terminal 75.
On the other hand, the output of secondary windings 57 and 58 of the
flyback transformer 51 is rectified by rectfying diodes 59 and 60,
smoothed by a capacitor 61 and supplied as the anode voltage for a CRT 73
via a high voltage output terminal 67. An example of the anode voltage is
in a range about 25 KV through 30 KV. The other terminal of the secondary
winding 58 of the flyback transformer 51 is grounded via another current
detecting circuit 80 constituted by a resistor 83 and a capacitor 82.
The anode output voltage of the flyback transformer 51 is detected via a
voltage dividing circuit constituted by a high resistance resistors 62 and
63 and the pulse voltage of the horizontal deflection driving circuit 74
is controlled via the high voltage control circuit 76 so that the anode
voltage is kept at a constant value.
The high voltage to the anode output terminal 67 is divided by a high
resistance resistor 64 and the automatic adjusting device 54 constituted
by potentio-meters 55a and 55b having a high resistance value and their
associating ultrasonic motors 52a and 52b, and the divided output is
applied from a determinal 68 to the focusing electrode of the CRT 73 (in a
high precision use CRT display device and a large scale TV two focusing
electrodes are usually provided, however in FIG. 8 embodiment only one
focusing electrode is illustrated for the sake of simplifying the
drawing). In the like manner, another divided output voltage is applied
from a terminal 69 to the screen electrode of the CRT 73. These required
divided voltages are usually in a range of 6.about.8 KV for the focusing
electrode and in a range of 500.about.800 V for the screen electrode.
The resistance value of the potentiometer 55a for adjusting the focusing
voltage is from a few M.OMEGA. to 10 M.OMEGA.. The potentiometer 55a and
the associating ultrasonic motor 52a for driving the same are mechanically
integrated and the small electrostrictive revolution type ultrasonic motor
according to the present invention, which is suitable to form integrally
together with the flyback transformer and is comparatively less affected
by electromagnetism, is used for the potentiometer driving motor.
At the tube face side of the CRT 73 industrial scale image pickup device
(ITV) 84 including an optical magnifying lens series and a light receiving
sensor is arranged of which output 85 is connected to a controller 86
incorporating a microcomputer. Driving outputs 87 and 88 from the
controller 86 are respectively connected to an input line 53a of the
ultrasonic motor 52a for focus voltage adjustment and an input line 53b of
the ultrasonic motor 52b for screen voltage adjustment.
In FIG. 8 circuit thus constituted, when a synchronous input is applied to
the synchronous input terminal 75, the horizontal deflection driving
circuit 74 drives the deflection coil 77 as well as the primary coil 56 of
the flyback transformer 51 and generates a voltage of about 30 KV at the
anode output terminal 67 at the secondary side of the flyback transformer
51. The generated voltage is detected by the voltage driving circuit
constituted by the high resistance resistors 62 and 63 and is fedback to
the high voltage control circuit 76 so as to maintain the same at a
constant voltage and to enable display at the CRT 73.
After reaching the above condition, the automatic focusing adjustment in
FIG. 8 circuit is performed in the following way. At first, at a position
on the tube face of the CRT 73 of which focus is to be adjusted a cross
hatch or cross pattern (not shown) of the most fine segment is indicated,
the cross hatch at the portion where the focusing adjustment is to be
performed is focused by the image pickup device 84 and the cross hatch
segment is converted into an electrical signal having a time width
corresponding to the line width as illustrated in FIG. 8. Namely, the
waveform illustrated in FIG. 8 is an electrical signal output when a cross
hatch segment is scanned with the image pickup device 84, wherein the line
width or boldness is defined by the scanning time width Tw at the half
magnitude A/2. In other words, a count value W, which is obtained by
counting tw with a counter operating on a predetermined clock, is used as
focusing information, and the focusing voltage is adjusted so as to
minimized the value W of which condition is assumed as the best focus.
The control and the condition judgement in the above focusing operation are
performed by the controller 86 as illustrated in FIG. 8 which makes use of
a microcomputer. Namely, a stepping drive voltage from the output 87 of
the controller 86 is applied to the ultrasonic motor 52a of the automatic
adjusting device 54, thereby the divided voltage of the focusing use
potentiometer 55a is finely adjusted so as to minimize the signal Tw
relating to the line width.
In the like manner, for the screen voltage adjustment, the brightness of
the tube face is measured with the image pickup device (ITV) 84 and the
screen use potentiometer 55b is driven so that the brightness reaches to a
predetermined level.
In the automatic adjusting system of the focusing voltage and the screen
voltage as illustrated in FIG. 8, the automatic adjusting device 54 as
illustrated as a function of a motor driven potentiometer is in particular
important in connection with the adjustment accuracy and reliability.
For the adjustment accuracy of the focusing and screen voltage, about 1% of
the output voltage is required, thereby it is appropriate to select about
1/4 (0.25%) of the required % output voltage as an adjustment interval for
one step. Further, it is desirable that the automatic adjusting device 54
is operable when molded integrally together with the flyback transformer
in view of the reliable operation thereof. Accordingly, it is desirable
for the motor for driving the automatic adjusting device to satisfy the
following conditions.
(1) The motor can operate under an intense magnetic field without any
troubles.
(2) The heat generation of the motor in a steady condition is low.
(3) The motor shows stepping property of a microscopic angle level and a
large static torque.
For fulfilling the above conditions, in the present application example one
of the ultrasonic motors according to the present invention as explained
in detail in connection with FIGS. 1A, 1B, 2A, 2B, 3A, 3B, 4A, 4B, 5A, 5B,
6A, 6B, 7A and 7B embodiments is used for the potentiometer driving use
motor.
In the application example in FIG. 8, an example wherein the potentiometer
and the ultrasonic motor are in advance integrated and then accommodated
in the flyback circuit box at the high voltage side is illustrated,
however, as an alternative only the potentiometer can be accommodated in
the high voltage side box while exposing the shaft of the potentiometer to
the outside and thereafter the ultrasonic motor can be fitted to the
outside shaft to permit the driving thereof. In such installation although
the load torque is increased due to the rotating mechanism for the shaft,
the potentiometer at the high voltage side is isolated from the ultrasonic
motor at the low voltage side by the box, thereby the structure is not
limited by the other wise required insulation distance.
According to one aspect of the present invention, through the use of a
rotor produced via injection molding as the rotor for a electrostrictive
revolution type ultrasonic motor, an ultrasonic motor of a reduced cost
with a limited contacting pressure variation and a high stable torque is
realized. Further, through the use of a plastic material having a high
Young's modulus as the rotor material the above advantages are further
enhanced. Still further, through the use of the plastic rotor, the adverse
effect by magnetic field and electric field to the ultrasonic motor is
minimized and the application thereof under an intense magnetic field as
well as an intense electric field is enabled.
FIG. 10 shows one embodiment of driving devices for an ultrasonic motor
according to the present invention. In FIG. 10 circuit, an ultrasonic
motor 110 is connected in the circuit so that the driving voltage therefor
is applied from an integrated motor drive control circuit 1200 via
terminals 1111 and 1112. The motor drive control circuit 1200 is
constituted | | |
