Note: Descriptions are shown in the official language in which they were submitted.
_ - 1 - 2048400
Vibration Driven Motor
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to an ultrasonic motor
in which electrical energy is supplied to an electro-
mechanical energy conversion element provided on a bar-
like resilient member to thereby vibrate the resilient
member as a bar-like vibration member and cause circular
or elliptical motion at the surface particle of the
vibration member, thus frictionally driving a movable
member pressed against the vibration member, and
particularly to an ultrasonic motor suitable for use in
optical instruments such as camera and business machines
such as printers.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 shows a first embodiment of an
ultrasonic motor according to the present invention.
Figure 2 is a pictorical perspective view of an
ultrasonic motor according to the prior art.
Figure 3 is a cross-sectional view of the
ultrasonic motor according to the prior art.
Figure 4 shows the state of the flexural
vibration of the ultrasonic motor according to the prior
- 2 - 2 0 ~8 4 0
art.
Figure 5 shows the vibration displacement locus
of a vibration member according to the prior art.
Figure 6 diagrammatically shows the equivalent
circuit of the vibration member according to the prior
art.
Figure 7 shows the positional relation between
the strain distribution of the vibration member according
to the prior art and piezo-electric elements.
Figure 8 is a graph showing the vibration
characteristic of the prior art.
Figure 9 shows a modification of the first
embodiment.
Figure 10 shows a modification of the first
embodiment.
Figure 11 is a schematic view of a driving
apparatus using an ultrasonic motor as a drive source.
Figure 12 is a schematic view of a vibration
member according to the prior art.
Figure 13 is a schematic view of a vibration
member according to the prior art.
Figure 14 shows the positional relation between
the strain distribution of the vibration member of Figure
13 and piezo-electric elements.
Figure 15 shows the positional relation between
the strain distribution of a vibration member according
to a second embodiment and piezo-electric elements.
_ _ 3 - 2~8400
Figure 16 is a graph showing the vibration
characteristic of the vibration member of Figure 15.
Figure 17 shows the positional relation between
the strain distribution of a vibration member according
to a third embodiment and piezo-electric elements.
Figures 18A - 18F show an embodiment of an
ultrasonic motor according to the present invention,
Figure 18A being a side view of the motor, Figure 18B
showing the amplitude distribution in the radial (r)
direction, Figure 18C showing the strain distribution in
the axis (z) direction of the side of the vibration
member, Figures 18D and 18E being plan views of piezo-
electric element plates, and Figure 18F showing the
expanded and contracted state of the piezo-electric
element plate when a voltage is applied thereto.
Figure 19 is a diagram of the electric
equivalent circuit of the vibration member.
Figures 20A - 20C show a modification of the
embodiment shown in Figures 18A - 18F, Figure 2OA being a
side view of a motor, Figure 20B showing the amplitude
distribution in the radial (r) direction, and Figure 20C
showing the strain distribution in the axial (z)
direction of the side of a vibration member.
Figures 2lA - 2lD show another embodiment,
Figure 21A being a side view of a motor, Figure 21B
showing the amplitude distribution in the radial (r)
direction, Figure 21C showing the strain distribution in
20~18~00
_ -- 4
the axial (z) direction of the side of a vibration
member, and Figure 2lD showing the vibrated state of the
vibration member.
Figures 22A - 22C show another embodiment,
Figure 22A being a side view of a motor, Figure 22B
showing the amplitude distribution in the radial (r)
direction, and Figure 22C showing the strain distribution
in the axial (z) direction of the side of a vibration
member.
Figure 23 is a partly cut-away side cross-
sectional view showing another embodiment.
Figure 24 is a cross-sectional view of an
apparatus using an ultrasonic motor.
Figures 25A - 25F show an embodiment of the
ultrasonic motor according to the present invention,
Figure 25A being a schematic side view of a vibration
member, Figure 25B showing the amplitude distribution in
the radial (r) direction, Figure 25C showing the strain
distribution in the axial (z) direction of the side of a
vibration member, Figures 25D and 25E being plan views of
piezo-electric element plates, and Figure 25F showing the
deformed state of the piezo-electric element plate.
Figures 26A - 26C show another embodiment,
Figure 26A being a schematic cross-sectional view of a
vibration member, Figure 26B showing the amplitude
distribution in the radial (r) direction, and Figure 26C
showing the strain distribution in the axial (z)
,
~ ~ 5 ~ 2 0 ~8~00
direction of the side of the vibration member.
Figures 27A and 27B and Figures 28A and 28B
show the shapes and the amplitude distributions in the
radial (r) direction, respectively, of further vibration
members.
Figure 29 shows an apparatus using the
ultrasonic motor of the present invention as a drive
source.
Related Background Art
Ultrasonic motors of the type in which flexural
vibration is caused in a circular ring-like resilient
member and a lens driving movable member is driven by a
frictional force have heretofore been put into practical
use in AF mechanisms of cameras. However, the ultrasonic
motor of this conventional type is of a ring-like shape
and therefore is relatively high in cost as a unit
including a pressing mechanism and disadvantageous in
cost as a motor which is required to be hollow. So, a
motor of the type as shown in Figures 2 to 4 of the
6 2C~48400
1 accompanying drawings which is solid and easy to
construct a pressing system has been proposed in
recent years.
This proposed motor will hereinafter be
described briefly with reference to Figures 2 to 4.
Figure 2 is a perspective view of the
vibration member of a bar-like ultrasonic motor, and
Figure 3 is a vertical cross-sectional view showing
the construction of the motor.
A vibration member creates primary flexural
vibration as shown in Figure 4 by electro-mechanical
energy conversion elements (hereinafter referred to
as PZTs) al and a2. PZT al and PZT a2 have a phase
difference of 90 in position therebetween, and PZT
al and PZT a2 each are comprised of two piezo-
electric element plates (polarization-processed into
different polarities with the diametrical portion
thereof as a boundary). The letter C designates a
bolt having a thin pillar-like shape in the upper
portion thereof. PZT al and PZT a2 are sandwiched
and fixed between a fore metal block b1 and a rear
metal block b2 which are vibration member
constituting members made of a metal relatively small
in attenuation such as brass or stainless steel.
The shape of a pillar portion C-l is
determined such dimensions that the displacement
during the vibration of the vibration member becomes
21~48400
~ }
1 small near the upper part of the pillar portion which
is coupled to a vibration member fixing member g. A
movable member d is given the spring force of a coil
spring k in a spring case f through a bearing e and
S is in pressure contact with the upper surface of the
vibration member.
Now, the primary flexural mode created by
PZTs al and a2 is excited in two kinds in a direction
having a positional phase difference of 90 relative
to a direction 0 (an angle in a plane orthogonal to
the axis) and with a deviation of 90 in terms of
time and therefore, the point A of the portion of
contact with the movable member (shown in Figure 4)
effects elliptical motion. The direction of this
lS motion is determined by the shape of the vibration
member, and the point A effects elliptical motion in
a plane inclined by an angle a with respect to the Z-
axis. At this time, the movable member which is in
pressure contact is frictionally driven.
In such an ultrasonic motor, AC voltages of
the kinds corresponding to the number of flexural
vibrations excited become necessary.
Also, these AC voltages should desirably be
of the same voltage amplitude from the convenience of
a driving circuit, and this also holds true of the
circular ring type ultrasonic motor of the prior art.
In the bar-like ultrasonic motor, however, it has
X- 21~48400
1 been found that when two sets of flexural vibrations
by the A phase and B phase piezo-electric elements a1
and a2 are driven by the same voltage, the amplitudes
of the vibraitons differ from each other and
elliptical motions differing in shape are created on
the circumference of the vibration member. This
state is shown in Figure 5 of the accompanying
drawings. Two sets of flexural vibrations are
excited by PZTs al and a2 in Figure 3. If at this
time, the amplitudes of the vibrations differ from
each other, uniform circular motion will not take
place on the circumference, as shown in Figure 5.
Here, each ellipse is a displacement locus, and
becomes such as shown when the amplitude excited by
PZT al is smaller than the amplitude excited by PZT
a2. At this time, the circumferential speed at a
point B is greater than the value at a point C, and
the movable member is driven at a different feed
speed while the vibration of the vibration member
makes one round.
On the other hand, the movable member rotates
at a certain constant speed by the inertial mass of
itself and therefore, does not follow this speed
difference but slips, and this provides a sliding
loss which reduces the efficiency of the motor.
Generally, the equivalent circuit of one
phase (e.g. A phase) of the driving circuit of the
204~00
,~
..
1 ultrasonic motor is shown as in Figure 6 of the
accompanying drawings when for example, the vibration
speed of the portion of contact with the movable
member is the standard. In Figure 6, cd is the
S electrostatic capacity of PZT used, A is -the force
coefficient, Cm is the equivalent attenuation
constant (including the load output), k is the
equivalent spring constant, and m is the equivalent
mass.
That is, in order that speeds VeiWt created
in two phases (two flexural modes) when a voltage
Ve cost is applied to the input terminal of the
piezo-electric element of one phase of the driving
circuit for the vibration member may be equal to each
other, these constants can become equal to each
other.
cd is determined by the dielectric constant,
shape, etc. of PZTs. Accordingly, the make cd equal,
the materials and shapes of PZTs can be made
coincident with each other. This condition is
generally satisfied and in the prior àrt as well,
as shown in Figure 4, two PZTs having a thickness of
0.5 mm are used for PZT al and two PZTs of the same
thickness and shape are used for PZT a2, and this
condition is satisfied and irregularity is small.
Also, Cm, k, m, etc. are coincident between
PZT al and PZT a2 because flexural vibrations of the
Z048~0C)
~ /
l same shape are utilized in the vibration member
having an axis-symmetrical shape.
Accordingly, the reason why the speeds, i.e.,
displacements, between the two phases are made
incoincident (because frequencies are equal) is that
the force coefficient A differs. Also, the force
coefficient A is given by the ratio between the
vibration speed and the electric current and
therefore, the reason is considered to be that this
coefficient differs.
On the other hand, the electric current is
determined by the materials, shapes and strains of
PZTs, but since the materials, shapes, etc. of PZTs
are made the same in order to make the electrostatic
capacities cd of PZTs equal, the difference between
the electric currents flowing through the two PZTs is
considered to be due to the difference in strain,
that is, considered to be because the strains created
in PZT al and PZT a2 when equal vibration
displacements are obtained in directions 0a1 and ~a2
shown in Figure 5 differ from each other.
Now, a bar-like ultrasonic motor of the both
end surface (surface tl and surface t2) driving type
shown in Figure 12 of the accompanying drawings is
generally made in a symmetrical shape with the
central surface in the lengthwise direction (the
axial direction) in order to equalize the vibration
204~0
A -11
1 speeds on the both end surfaces.
However, in a bar-like ultrasonic motor of
the type which is driven only on one end surface
(e.g. surface tl), it is desirable to make only the
amplitude on the driving surface side great.
The reason for this is that by making the
vibration amplitudes on the other portions than the
driving portion small and thus, making the strain
created in the vibration member small, it is possible
to make the energy loss in the vibration member
small. Paying attention to such a fact, the
applicant has proposed an invention in which a
constriction is provided near the driving surface.
A vibration member embodying this invention is shown
lS in Figure 13 of the accompanying drawings.
With regard to this vibration member, the
admittance when the A phase piezo-electric element
al is driven and the admittance when the B phase
piezo-electric element a2 is driven superposed one
upon the other are shown in Figure 8 of the
accompanying drawings. As will be seen from this
figure, in the case of this vibration member, the
admittance Y at a resonance point F is considerably
greater when the A phase piezo-electric element al is
driven.
Now, when the angular frequency is ~, the
admittance Y can be expressed as follows by the use
~ ~, 26)~ 00
l of the aforementioned symbols:
y =
A2k ~ + C
A 2 ~`) A 2
During the resonation of the vibration
member, the imaginary number portion in the
parentheses is zero and therefore, Y = A2/Cm, that
is, Y is proportional to the square of the force
coefficient.
Accordingly, in the vibration member shown
in Figure 13, it is foreseen that the strains when
driving flexural vibrations are created in the A
phase pizeo-electric element a1 and the B phase
piezo-electric element a2 differ greatly from each
other. The result of the actual calculation of the
strains created in the vibration member effected by
the use of FEM is shown in Figure 14 of the
accompanying drawings.
From this result, it is seen that the strain
created in the B phase piezo-electric element al is
considerably smaller than the strain created in the A
phase piezo-electric element al.
That is, in Figure 14, the strain in the A
phase piezo-electric element al is greater than the
strain in the B phase piezo-electric element a2 and
therefore, even if voltages of the same level are
~, "~ , 2~ o~
1 applied to the A and B phases, a greater electric
current will flow through the A phase piezo-electric
element a with a result that a difference will occur
between the amplitudes of flexural vibrations.
SUMMARY OF THE INVENTION
It is an object of the present invention to
solve the above-noted problem and to provide an
ultrasonic motor (hereinafter also referred to as a
vibration driven motor or actuator) in which driving
signals of voltages of the same magnitude are
supplied to piezo-electric elements of two phases,
whereby flexural vibrations of the same amplitude can
be formed.
Other objects of the present invention will
become apparent from the following detailed
description of the invention.
The feature of the present invention is that
in an ultrasonic motor wherein a driving signal is
applied to an electro-mechanical energy conversion
element provided in a vibration member to thereby
excite flexural vibrations of the same shape in the
two different planes of said vibration member with a
phase difference in time and thereby create
rotational motion on the surface of said vibration
member, thus frictionally driving a movable member
which is in pressure contact with the vibration
- 14 - 2 04 84 00
forming surface, electro-mechanical energy conversion
elements for exciting the flexural vibrations are each
disposed at a position whereat the sum totals of strains
created in the electro-mechanical energy conversion
elements are substantially equal to each other.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Figure l shows a first embodiment of an
ultrasonic motor according to the present invention, and
more particularly shows the relation between a vibration
member and the vibration mode thereof. Elements
functionally similar to those of the motor according to
the prior art are given similar reference characters and
need not be described.
This embodiment is one applied to a vibration
member in the front portion of which there is formed a
circumferential groove b1-l and in which the vibration
amplitude in this circumferential groove b1-l is made
great so that the portion forward thereof may be greatly
displaced. Accordingly, the strain (~z) of the vibration
member during driving formed rearwardly of the
circumferential groove b1-1 of the vibration member is
smaller than the strain formed in the circumferential
groove portion.
If the sum totals of the flexural vibrations of
A phase piezo-electric element a1 (comprised of
- ls - 2~4~400
1 two piezo-electric element plates) and B phase piezo-
electric element a2 (comprised of two piezo-electric
element plates) constituting the vibration member
are equal, flexural vibrations of equal amplitudes
are obtained when voltages of the same magnitude
are applied and therefore, in the present embodiment,
the A phase piezo-electric element al and the B phase
pizeo-electric element a2 are disposed on the
opposite sides of the peak of a strain curve (the
region in which maximum strain is created).
The groups of PZTs for providing flexural
vibration need not be disposed in spaced apart
relationship with each other as shown in Figures 12 -
14. Rather, it is more advantageous in manufacturing
that the groups are closely adjacent to each other.
The reason is that a metal block b3 shown in Figures12 - 14 becomes unnecessary, that the electrode on
the boundary surface between the groups can be made
common to the groups because the groups are closely
adjacent to each other and that the groups can be
assembled with the electrode phases of the PZTs of
the groups brought into a desired positional relation
in advance, and in this case, if necessary, metal
blocks bl and b2 can be joined together for formation
before they are coupled together by a bolt.
Examining the conditions hitherto described
with respect to the vibration member of this type,
Z~ 34~
l the strain distribution of the vibration member shown
in Figure 4 is as shown in Figure 7. In this case,
the B phase piezo-electric element a2 is disposed at
a position whereat strain is great as compared with
that of the A phase piezo-electric element a1, and
the admittance during the driving of the B phase
piezo-electric element a2 is always great as compared
with the admittance during the driving of the A phase
piezo-electric element a1. In the present embodiment
(Figure 1), in order to correct this, E (see Figure
7) which is the boundary surface between the A phase
and B phase piezo-electric elements al and a2 is
moved to the maximum point D of the strain
distribution (i.e., the maximum point D of the
vibration amplitude), and the rear metal block b2 is
made short and the fore metal block b1 is made long.
An embodiment shown in Figure 9, like the
embodiment shown in Figure 1, achieves the
coincidence between the maximum value position of the
vibration member utilizing a secondary flexural
moment and the boundary surface between the A phase
piezo-electric element a1 and the B phase piezo-
electric element a2, and in this embodiment, as
compared with the embodiment shown in Figure 1, the
maximum value position of strain is formed on the
rear end side of the vibration member.
In an embodiment shown in Figure 10,
- 17 - ~ ~4~
l conversely from the embodiment shown in Figures 1 and
9, the minimum value position of the vibration member
and the boundary surface between the A phase piezo-
electric element a1 and the B phase piezo-electric
element a2 are made coincident with each other. In
the case of the present embodiment, the strain
created in the boundary surfaces between fore end
rear metal blocks b2 and b11 for obtaining a
predetermined amplitude in the vibration member and
the piezo-electric elements a1 and a2 and in the
boundary surface between the piezo-electric elements
is small and the mechanical loss therein decreases
and thus, the motor efficiency is improved.
Figure 15 shows a second embodiment of the
present invention.
In the present embodiment, like the vibration
members shown in Figures 13 and 14, the A phase
piezo-electric element a1 is disposed between the
fore metal block b1 and the middle metal block b3
and the B phase piezo-electric element a2 is disposed
between the middle metal block b3 and the rear metal
block b2, and the A phase piezo-electric element a
and the B phase piezo-electric element a2 are
disposed at positions equal in the longitudinal
direction from the maximum position of the strain
formed in the vibration member. The strains at these
two positions are equal and thus, the amplitudes of
o
- 18 -
1 flexural vibrations excited by the A phase and B
phase piezo-electric elements a1 and a2 become equal
to each other.
Figure 16 shows the admittances during the
driving of the A phase piezo-electric element al and
the B phase piezo-electric element a2. In this case,
the two admittances substantially coincide with each
other, and the vibration displacement locus at each
point on the vibration member when the A phase piezo-
electric element al and the B phase piezo-electric
element a2 are driven by the same voltage becomes
circular, and the sliding loss between the movable
member and the vibration member decreases and the
motor efficiency is improved.
Figure 17 shows a third embodiment of the
present invention.
In each of the above-described embodiments,
electro-mechanical energy conversion elements for
exciting a flexural vibration have been considered
to be unit comprising one set of two elements, but
a similar effect will be obtained even if they are
separately disposed. That is, assuming that a
flexural vibration is excited by piezo-electric
element plates al-l and al-2 and a flexural vibration
is excited by piezo-electric element plates a2-1 and
a2-2, if these four piezo-electric element plates
are disposed at a position of the construction shown
zo~
-- 19 --
1 in Figure 17 wherein the strain distribution varies
substantially linearly, the strain in the piezo-
electric element plate al-l is great and the strain
in the piezo-electric element plate al-2 is small and
thus, the strain per one phase, i.e., the sum of the
strains in the two piezo-electric element plates
becomes substantially equal to the strain per the
other phase, i.e., the sum of the strains in the
piezo-electric element plates a2-1 and a2-2.
Figure 11 shows a driving apparatus for the
photo-taking lens of a camera utilizing the bar-
like ultrasonic motor of the present invention as
a drive source. In Figure 11, the letter i
designates an output take-out gear which is coupled
to a movable member d through anti-vibration butyl
rubber o. A connection gear j has mounted thereon
an encoder slit plate k and a photocoupler m for
detecting the position of said lens, and these detect
the rotated position of the gear.
Figures 18A - 18F show an embodiment of the
ultrasonic motor according to the present invention,
Figure 18A being a schematic view of the vibration
member thereof.
In the present embodiment, a vibration member
lOOA is formed in a construction similar to the
example of the prior art, and piezo-electric element
plates 103 and 104 shown in Figures 18D and 18E are
- 20 - 2 ~ 4~0
1 sandwiched and fixed between vibratory resilient
members 100 and 102 made of a metal (SUS, Bs, Al,
INVAR or the like).
The piezo-electric element plates 103 and
104, as shown in Figures 18D and 18E, each have
positive and negative polarized patterns formed on
the opposite sides of the diametrical portion
thereof, and are disposed with a phase difference of
90 therebetween. When magnetic fields of the same
direction are applied to these piezo-electric element
plates 103 and 104 in the direction of the thickness
thereof, the piezo-electric element plates 103 and
104 are deformed as indicated by broken line in
Figure 18F.
Accordingly, if the electric fields are
alternating ones and the frequencies thereof are
adjusted to the natural frequency of the flexure
of the vibration member, the vibration member will
make flexural resonation (the amplitude distribution
in the radial (r) direction shown in Figures 18A and
18B).
Also, since the piezo-electric element plate
104 is disposed with a phase difference of 90 with
respect to the piezo-electric element plate 103, the
flexural vibration created thereby is flexural
vibraiton having a phase difference of 90 in a
direction 0 with respect to the flexural vibration
- 21 - ~
l created by the piezo-electric element plate 103.
Further, by a time phase difference of 90
being provided between the flexural vibration created
by the piezo-electric element plate 104 and the
flexural vibration created by the piezo-electric
element plate 103, the particles on the surface of
the vibration member make circular or elliptical
motion.
Figure 18C shows the strain distribution in
the z direction of the side of the vibration member
corresponding to the amplitude distribution in the
r direction, the position at which the piezo-electric
element plates 103 and 104 are sandwiched and fixed
is selected to the antinode position of the inherent
lS vibration mode for driving shown in Figure 18B at
which the strain becomes greatest.
Now, considering the equivalent circuit of
the vibration member, there is only a resistance
component on the mechanical arm side during
resonation, as shown in Figure 19.
Accordingly, supplied electric power is
P = Vil, but i1 is determined by the total amount
of strain of the piezo-electric element plates (the
piezo-electric elements create charges by strain).
That is, by the piezo-electric element plates
103 and 104 being disposed at a position whereat
strain is great, as shown in Figure 18C, i.e., the
- 22 - ~ ~4~
l antinode position of the strain, the electric current
becomes great and the voltage becomes small and thus,
there is provided a construction of low voltage.
Even where as shown in Figures 20A - 20C, a
piezo-electric element plate 110 for vibration
detection is provided, it is necessary in the
construction of the low voltage type to provide the
piezo-electric element plates 103 and 104 for driving
at the maximum strain position as in the case shown
in Figures 18A - 18F.
Figures 2lA-2lD show another embodiment.
This embodiment is one in which the vibration
member has a constricted portion, and in the
vibration mode shown in Figure 21D, the maximum
lS strain position and the vibration antinode position
are not coincident with each other as shown in
Figures 21B and 21C, but the piezo-electric element
plates 103 and 104 are disposed in the constricted
portion which is the maximum strain position.
Again in this case, as in the embodiment
shown in Figures 18A - 18F, there is the effect as
the low voltage type.
When in actual mounting or manufacturing,
it is difficult to dispose the piezo-electric element
plates 103 and 104 in the constricted portion, the
piezo-electric element plates 103 and 104 may be
provided on the opposite sides of the antinode in
2~ 00
- 23 -
1 which strain is next greatest, as shown in Figures
22A - 22C.
Figure 23 shows still another embodiment.
This embodiment is similar in outward
appearance to the embodiment of Figures 22A - 22C,
but the inner diameters of the piezo-electric element
plates 103 and 104 are made large and these piezo-
electric element plates are disposed on the outer
peripheral portion of the vibration member in which
strain is great.
In the present embodiment, the total amount
of strain somewhat decreases, but since the piezo-
electric element plates 103 and 104 are disposed only
on the opposite sides of the maximum strain position
in the axial and radial directions of the vibration
member, the strain per unit volume of the piezo-
electric element plates 103 and 104 becomes greatest,
and such location of disposition can be effectively
utilized and the number of piezo-electric elements
required may be small.
Also, the area of contact between the piezo-
electric element plate 103 and the fore vibratory
resilient member 100 and the area of contact between
the piezo-electric element plate 104 and the rear
vibratory resilient member 102 decrease and
therefore, the friction loss resulting from sliding
therebetween can be made small.
2~ Q~
- 24 -
1Figure 24 shows an embodiment in which the
barrel of an optical lens is driven by the use of the
motor according to the present invention.
The reference numeral 112 designate a gear
joined coaxially with a movable member 108 to
transmit the rotational output of the motor to a gear
113 and rotate the lens barrel 114 of a camera which
has a gear meshing with the gear 113.
An optical type encoder slit plate llS is
disposed coaxially with the gear 113 to detect the
rotated positions and rotational speeds of the
movable member 108 and the lens barrel 114, and
detects the positions and speed by a photocoupler
116.
15Figures 25A - 25F show an embodiment of the
ultrasonic motor according to the present invention.
The vibration member A of the present
embodiment, as shown in Figure 25A, is similar in
basic construction to the example of the prior art,
20and piezo-electric element plates 203 and 204 shown
in Figures 25D and 25E are sandwiched and fixed
between resilient members made of a metal (SUS, Bs,
Al, ZNUAR or the like).
The piezo-electric element plates 203 and
204 each are polarized in opposite directions with
the non-electrode portion of the diametrical part
thereof as a boundary, and when electric fields of
- 25 - 2~
1 the same direction are applied to the two polarized
areas in the direction of the thickness thereof,
the piezo-electric element plates are deformed into
a shape as indicated by dotted line in Figure 25F.
Accordingly, if the electric fields are
alternating ones and the frequencies thereof are
adjusted to the natural frequency of the flexure of
the vibration member, the entire vibration member
will make resonation of flexural mode, as shown in
Figure 25B.
on the other hand, the piezo-electric element
plates 203 and 204 are disposed with a phase
difference of 90 therebetween and therefore,
flexural vibrations created by these two piezo-
electric element plates 203 and 204 have a phase
difference of 90 therebetween in a direction 0.
Accordingly, by a time phase difference of
90 being provided between the flexural vibration
created by the piezo-electric element plate 204 and
the flexural vibration created by the piezo-electric
element plate 203, the particles on the surface of
the vibration member make circular or elliptical
motion and at that time, the strain distribution in
the z (axial) direction of the side of the vibration
member corresponding to the amplitude distribution
in the r direction shown in Figure 25B becomes such
as shown in Figure 25C.
2~ 0~)
- 26 -
1 Description will now be made of the position
at which a piezo-electric element plate for enhancing
the efficiency of the motor is disposed.
To obtain a certain constant motor output,
if energy dispersed by the other members than the
vibration member is made constant with the other
conditions such as the support of the vibration
member, the structure of the movable member (rotor)
and the sliding material being fixed, the vibration
energy being accumulated (created) by the vibration
member need be of a certain predetermined amount.
Now, the energy to be supplied in order to
obtain a certain amount of vibration energy is
determined by the attenuation constant of the entire
vibration member.
The vibration member is comprised of a
combination of a vibration structure made of a metal
(such as aluminum, brass or stainless steel) and a
piezo-electric element plate. Also, the attenuation
constant inherent to a material is small for metals,
and the attenuation constant of the piezo-electric
element plate having the piezo-electric property is
relatively great. Q of metals is of the order of
3000 - 10000, and Q of the piezo-electric element
plate is of the order of 20 - 1800.
Accordingly, to decrease the loss in the
vibration member, i.e., the internal frict`ion loss
oo
- 27 -
1 caused by the material being distorted (although
there are other losses including the radiation loss
into the air and the dielectric material loss in
the piezo-electric element plate, these losses are
small), it is desirable that the piezo-electric
element plate having a relatively great attenuation
constant be disposed in a portion of small strain.
So, in the present embodiment, the position
of the antinode of vibration at which strain is
great is avoided and piezo-electric element plates
are disposed before and behind the position of the
middle node.
In fact, Q of the vibration member when the
piezo-electric element plates 203 and 204 were
disposed at the antinode position of vibration was of
the order of 1000, but in the present embodiment,
it has been improved to the order of 1500.
Also, at the node of vibration near the
opposite ends of the vibration member A, strain is
not zero but is small as compared with that near the
antinode of vibration and therefore, even if the
piezo-electric element plates 203 and 204 are
disposed at this node position, some improvement in
the motor efficiency can be expected.
Strain is zero at the opposite ends of the
vibration member, but it is impossible in the
structure of the present motor to dispose the
- 28 -
1 piezo-electric element plates at these positions.
Figures 26A - 26C show another embodiment.
In this embodiment, as in the embodiment
described above, the piezo-electric element plates
203 and 204 are disposed before and behind the node
position of vibration, but the outer diameters of the
piezo-electric element plates 203 and 204 are made
small and the piezo-electric element plates 203 and
204 are disposed inside the vibration member of small
strain.
By adopting such structure, the internal loss
in the vibration member becomes smaller than in the
embodiment of Figures 25A - 25F.
In the present invention, the shape of the
vibration member is not limited to the pencil-like
shape, but may also be a shape having a constricted
portion in the intermediate portion, as shown in
Figures 26A and 26B, or a shape having a large
diameter in the opposite end portions, as shown in
Figures 27A and 27B.
Also, where as shown in Figures 27A and 27B,
the vibration member is supported at the node
position of vibration by a support member comprising
a resilient bar or a resilient plate, there will be
substantially no problem even if the piezo-electric
element plates 203 and 204 are disposed somewhat
off the node position of vibration.
Z04t~0~
- 29 -
1 Figure 29 shows an example of the
construction in a case where the barrel of an
optical lens is driven by the use of the motor
according to the present invention.
The reference numeral 209 denotes a gear
joined coaxially with a movable member R to transmit
the rotational output of the motor to a gear 210 and
rotate the lens barrel 211 of a camera which has a
gear meshing with the gear 210.
As described above, according to the present
invention, the motor efficiency can be improved by
simple structure in which electro-mechanical energy
conversion elements such as piezo-electric element
plates are disposed at or near the node position of
vibration for driving.
