U.S. patent number 3,694,782 [Application Number 05/091,359] was granted by the patent office on 1972-09-26 for rotary actuator.
Invention is credited to Ralph D. Ray.
United States Patent |
3,694,782 |
Ray |
September 26, 1972 |
ROTARY ACTUATOR
Abstract
A rotary actuator comprising a rotor including a permanent
magnet and a stator of magnetic material substantially surrounding
the rotor. A force field is set up in the magnetic material of the
stator, and the permanent magnet of the rotor adds to this field to
apply magnetic forces to the rotor tending to rotate the latter.
The rotary actuator has various features which contribute to a
relatively long stroke and high torque output.
Inventors: |
Ray; Ralph D. (Newport Beach,
CA) |
Family
ID: |
22227378 |
Appl.
No.: |
05/091,359 |
Filed: |
November 20, 1970 |
Current U.S.
Class: |
335/230;
335/272 |
Current CPC
Class: |
H01F
7/145 (20130101) |
Current International
Class: |
H01F
7/08 (20060101); H01F 7/14 (20060101); H01f
007/08 () |
Field of
Search: |
;335/229,230,276,272,268 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Harris; George
Claims
I claim:
1. A rotary actuator comprising:
first and second stator sections, each of said stator sections
including magnetic material;
means for mounting said stator sections with said stator sections
being separated by a relatively high reluctance region;
a rotor including a permanent magnet having first and second poles
of opposite polarity;
means for mounting said rotor for rotation about an axis with the
rotor being adjacent said stator sections, said rotor being
rotatable from a first position through a predetermined number of
degrees about said axis to a second position;
said stator sections extending for a substantial distance around
the rotor in a direction circumferentially of the axis of
rotation;
first electrical means for magnetizing said stator sections to move
said rotor from said first position to said second position, at
least one zone of said first stator section attracting said
permanent magnet toward said second position and at least one zone
of said second stator section repelling said permanent magnet from
said first position toward said second position;
said rotor including a segment constructed of magnetic material
which is not permanently magnetized and located adjacent the
periphery of the rotor; and
said segment being a first peripheral surface segment, said rotor
having a second peripheral surface segment intersecting said first
peripheral surface segment at a zone of intersection, said surface
segments being of different configurations, said magnet having an
axis of magnetization extending generally toward the zone of
intersection.
2. A rotary actuator as defined in claim 18 including biasing means
for urging said rotor from said second position toward said first
position.
3. A rotary actuator as defined in claim 1 wherein said relatively
high reluctance region is a first region, said stator sections
being separated by a second relatively high reluctance region, said
first and second stator sections extending substantially completely
around said rotor, said first stator section attracting one pole of
said permanent magnet and repelling the other pole of said
permanent magnet when the first electrical means is energized and
said second stator section attracting said other pole of said
permanent magnet and repelling said one pole of said permanent
magnet when said first electrical means is energized.
4. A rotary actuator as defined in claim 1 wherein said region
extends circumferentially of said rotor as it extends between said
stator sections to thereby affect the torque of said rotor as said
rotor rotates from said first position to said second position.
5. A rotary actuator comprising:
first and second stator sections, each of said stator sections
including magnetic material;
means for mounting said stator sections with said stator sections
being separated by a relatively high reluctance region;
a rotor including a permanent magnet having first and second poles
of opposite polarity;
means for mounting said rotor for rotation about an axis with the
periphery of said rotor being closely adjacent said stator
sections;
the dimension of said region circumferentially of said axis being
relatively small when compared with the circumferential dimension
of said stator sections circumferentially of said axis;
said rotor including a segment adjacent the periphery thereof of
substantially nonmagnetized, magnetizable material; and
electrical means for magnetizing said stator sections to rotate the
rotor from a first position to a second position, at least one zone
of said first stator section attracting said permanent magnet from
said first position toward said second position and at least one
zone of said second stator section repelling said permanent magnet
from said first position toward said section position, said
electrical means setting up a force field having lines of flux
which pass from one of said stator sections through said segment of
said rotor to the other of said stator sections.
6. A rotary actuator as defined in claim 5 wherein the axial
dimension of at least a portion of said segment tapers
circumferentially of the rotor.
7. A rotary actuator as defined in claim 5 wherein said magnet has
an axis of magnetization and a central transverse axis, said axes
being nonparallel.
Description
BACKGROUND OF THE INVENTION
There have been many attempts to provide a rotary actuator having
high torque and a relatively long, for example, 40.degree., stroke.
Consequently, the prior art is replete with devices whose purpose
is allegedly to increase the torque or length of stroke. Heretofore
none of the devices has been satisfactory.
One such prior art device is a linear solenoid with a cam to change
the linear motion of the solenoid into rotary motion. This unit is
relatively expensive, complex, and large due to the need for the
cam and the associated parts. Moreover, the stroke and torque are
not as large as desired for many applications.
Another prior art device is the rotary solenoid, and this device is
capable of producing only very low torque and has a very short
stroke. The mag wheel is another prior art device. The mag wheel is
an electromagnetically powered indicator having a rotor which is
adapted to be accurately positioned at any of several different
locations. The mag wheel is not an actuator or a driver and its
torque is extremely low.
SUMMARY OF THE INVENTION
The present invention provides an electromagnetically powered
rotary actuator which has a long stroke and produces very high
torque in relation to its power consumption and size, In addition
the torque curve can be tailored to suit particular operating
requirements. As used herein and unless otherwise indicated, the
torque produced by the actuator has reference to the torque as
measured at the output of the actuator.
Generally the rotary actuator includes a rotor and stator of
magnetic material with the stator having one or more windings for
providing a force field to drive the rotor. The torque produced by
a device of this type is proportional to the flux and to the change
of permeance. To increase the flux and hence the torque, the rotor
includes a permanent magnet.
To further increase torque, the rotor is driven by forces of
attraction and repulsion. Preferably each pole of the permanent
magnet is acted upon by the electromagnetic force field to drive
the rotor from an initial position to a second position.
For maximum torque, the stator includes first and second stator
sections separated by first and second regions of relatively high
reluctance with each of the stator sections extending for
approximately 180.degree.. However, good results can be obtained if
the stator extends for only approximately the arc of stroke of the
rotor.
The regions of relatively high reluctance are small
circumferentially of the axis of rotation, and accordingly, the
stator sections are close together. With the actuator energized,
lines of flux extend from the first stator section through only a
peripheral region of the rotor and into the second stator section.
Thus, the primary flux path from the stator to the rotor does not
pass through significant portions of the permanent magnet which is
of high reluctance.
Another feature of the invention is to construct a peripheral
segment of the rotor of unmagnetized, highly permeable material.
This can be accomplished by adding elements or shoes of highly
permeable material to the permanent magnet. The increase in
permeance created by the shoes contributes to torque.
Torque can be increased by providing a relatively high change of
permeance. This is accomplished by appropriately shaping and
orienting the rotor. For example, the rotor can be provided with
first and second peripheral surface portions of different
configurations intersecting at a zone of intersection. The rotor is
oriented so that the zone of intersection will rotate past the
region of relatively high reluctance. This causes a change of
permeance due to the difference in distances between the stator
sections and the first and second peripheral surface portions.
The rotor of the rotary actuator moves from an initial to a second
position in response to energizing the windings. When the coils are
de-energized, the rotor tends to return toward the initial
position. The rotor seeks a position in the de-energized condition
in which the axis of magnetization points at the region of
relatively high reluctance. To augment the natural tendency of the
rotary actuator to return toward the initial position, biasing
means such as a spring may be employed as the actuator has more
than adequate torque to overcome the return spring force.
Energization of the windings causes some electromagnetic force to
be applied to the rotor tending to rotate the same. Thus, it is
possible to plot a curve of angular position or displacement of the
rotor versus torque applied to the rotor, and it is also possible
to plot a curve of rotor displacement versus output torque of the
actuator. With the present invention, it is possible to select the
portion of the torque curve which will define the operating range
of the particular actuator by controlling the initial and second
positions of the rotor.
According to one practice of the present invention, the return
spring is sized to pull the rotor back somewhat from the inherent
position which it seeks when the windings are de-energized. By so
doing, the starting point of the operating range of the torque
curve is selected. To minimize the strength of the return spring
required, the permanent magnet should have an axis of magnetization
which is properly oriented relative to the permanent magnet. An
advantage of using a relatively weak return spring is that useful
or output torque is increased. If the rotor is pulled back too far,
a heavy return spring is required, and if the rotor is not pulled
back at all from its natural de-energized position, it may not be
possible to obtain a long stroke such as 40.degree..
The present invention provides several ways for tailoring the
torque curve to suit particular requirements. One way to tailor the
torque curve is to change the direction of the axis of
magnetization relative to the permanent magnet. For example, by
moving the axis of magnetization toward the zone of intersection
referred to hereinabove, torque near the end of the stroke is
increased.
Shaping of the torque curve can also be accomplished by shaping of
the region of relatively high reluctance. For example, if the
region of relatively high reluctance extends somewhat
circumferentially of the axis of rotation of the rotor the torque
curve tends to flatten out.
If the highly permeable shoes are utilized, the torque curve can be
tailored by shaping of the shoes. For example, by progressively
narrowing the shoes in the direction of rotation of the rotor, the
torque curve tends to flatten out. This change is the result of the
change in permanence caused by shaping of the shoes.
The invention can best be understood by reference to the following
description taken in connection with the accompanying illustrative
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a front elevational view of a rotary actuator constructed
in accordance with the teachings of this invention.
FIG. 2 is a side elevational view taken generally along line 2--2
of FIG. 1.
FIG. 3 is an enlarged sectional view taken generally along line
3--3 of FIG. 1.
FIG. 4 is an enlarged view partially in section taken generally
along line 4--4 of FIG. 3 with the rotary actuator in the
de-energized condition.
FIG. 4a is a sectional view taken generally along line 4 a--4a of
FIG. 4.
FIG. 4b is a sectional view similar to FIG. 4a showing a
modification of the high reluctance region between stator
sections.
FIG. 4c is a fragmentary elevational view of the modification shown
in FIG. 4b taken generally along line 4c --4c of FIG. 4b.
FIG. 5 is a sectional view similar to FIG. 4 with the rotary
actuator being in the energized condition.
FIG. 6 is a sectional view similar to FIG. 4 of a second embodiment
of the present invention with the rotary actuator being
de-energized.
FIG. 7 is an elevational view of one of the shoes taken along line
7--7 of FIG. 6.
FIG. 8 is a sectional view similar to FIG. 6 with the rotary
actuator being energized.
FIG. 9 is a view similar to FIG. 4 showing another embodiment of
the invention in which the torque arm is movable in either
direction from a center position.
FIG. 10 is a fragmentary sectional view similar to FIG. 3 showing
the return spring and the adjacent structure for the embodiment of
FIG. 9.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIGS. 1 and 2 show a rotary actuator 11 constructed in accordance
with the teachings of this invention. The rotary actuator 11 has a
pair of mounting apertures 13 to facilitate mounting of the
actuator 11 on supporting structure (not shown). The rotary
actuator 11 has a torque arm 15 which is pivotable between an
initial or first position shown in FIGS. 1 and 2 in which the
rotary actuator 11 is de-energized and a second or final position
shown in dashed lines in FIG. 1 in which the rotary actuator is
energized. The torque arm 15 has a slot 17 in the outer end thereof
adapted to receive a driven member 19 of some driven device (not
shown) which the rotary actuator 11 is to actuate. The external
device can be actuated by energizing the rotary actuator 11 to
thereby move the driven member 19 from the full line position shown
in FIG. 1 to the dashed line position shown in FIG. 1.
With reference to FIGS. 2-4a, the rotary actuator 11 includes first
and second frame sections or stator sections 21 and 23 constructed
of magnetic material such as low carbon steel. The stator sections
21 and 23 are separated by two diametrically opposed, relatively
high reluctance regions which are defined in the embodiment
illustrated by brass slugs 25 and 27 brazed to the stator sections
to thereby interconnect the stator sections. The stator sections 21
and 23 have arcuate cut-out regions cooperating to define a
cylindrical rotor receiving aperture 29. As shown in FIG. 4a, the
brass slug 25 extends axially of the rotor receiving aperture 29.
The slug 27 also extends axially of the aperture 29.
The stator section 21 has an arcuate, upwardly opening slot 31
which receives the torque arm 15 and permits angular movement
thereof relative to the stator section 21. Flanges 33 and 35 are
formed integrally with the stator sections 21 and 23, respectively,
as shown in FIGS. 4 and 4a with the flanges 33 being generally
coplanar and with the flanges 35 being coplanar. The flanges 33 are
parallel to the flanges 35.
Cores 37 and 39 of ferromagnetic material are mounted on the
flanges 33 and 35 in generally parallel relationship. The cores 37
and 39 extend in a direction transverse to the axis of the rotor
receiving aperture 29. Although the cores 37 and 39 may be
connected to the flanges 33 and 35 in any desired manner, in the
embodiment illustrated, each of the cores has a flared portion 41
flared radially outwardly to cooperate with a corresponding
countersink in the adjacent flange. Each of the cores 37 and 39 has
a tapped hole 42 at the lower end thereof to facilitate mounting of
the rotary actuator. Coils 43 and 45 are wound on tubular bobbins
44 received on the cores 37 and 39, respectively. The coils 43 and
45 are preferably connected in series and are energizable through
leads 46.
A rotor 47 is mounted on a shaft 49 for rotation within the rotor
receiving aperture 29. The shaft 49 is in turn supported by a
bearing 51 mounted on the stator sections 21 and 23. The bearing 51
is constructed of nonmagnetic material such as aluminum.
Specifically, the bearing 51 includes a plate section 53 staked in
a counterbore 55 formed in both of the stator sections 21 and 23.
The bearing 51 has a tubular section 57 integral with the plate
section 53. The tubular section 57 has a passage 59 which receives
the shaft 49. The shaft 49 is supported at one end by a bearing 61
pressed on the end of the shaft and rotatable in a counterbore 63
of the bearing 51. Another portion of the shaft 49 is supported for
rotation by an integral annular flange 65 of the tubular section
57. The bearing 61 may be constructed of stainless steel.
The rotor 47 includes a permanent magnet 67, a cap 69 of
nonmagnetic material such as brass and a tube or cover 71 of
nonmagnetic material such as aluminum. The cap 69 and the tube 71
are suitably interconnected as by an epoxy adhesive to form a well
or receptacle for the permanent magnet 67 which in turn is suitably
connected to the cap and the tube as by an adhesive. The tube 71
completely encases the circumferential periphery of the permanent
magnet 67 and the cap 67 covers the righthand face (as viewed in
FIG. 3) of the magnet 67. The torque arm 15 which is preferably
constructed of a nonmagnetic material such as stainless steel has a
plate portion 72 which is mounted on the lefthand face (as viewed
in FIG. 3) of the permanent magnet 67 by an epoxy adhesive and/or
spot welding.
One end of the shaft 49 is pressed into aperture of the cap 69 to
thereby connect the shaft 49 and the cap 69 for rotation together.
A torsion coil spring 73 has one end connected to the fixed bearing
51 and the other end connected to the rotatable cap 69 to thereby
urge the rotor 47 and the torque arm 15 to the initial position
shown in FIGS. 1, 2 and 4. The initail position is established by
the limits of travel of the driven member 19 or by engagement of
the torque arm 15 against a stop 75 which forms one end of the slot
31 in the stator section 21. A counterweight 76 is mounted on the
cap 69 for rotation therewith to counterbalance the mass of the
driven element 19.
The magnet 67 has an axial cylindrical aperture 77 extending
therethrough. The magnet 67 is cylindrical except for
diammetrically opposed, flat, parallel surfaces 79 and 81 which are
perpendicular to a radially extending line and equidistant from the
axis of rotation of the rotor 47. The magnet 67 is magnetized along
a diametrically extending axis 83 which is parallel to the surfaces
79 and 81 with typical north/south polarity being indicated. The
magnet 67 is symmetrical about the axis of magnetization 83.
In the initial or de-energized position, the torque arm 15 is in
the position shown in FIG. 4 and is retained there by the return
spring 73. In this position, the axis of magnetization 83 forms an
angle a with a line drawn through the axis of rotation of the rotor
and a central region of the slugs 25 and 27. In the embodiment
illustrated, the angle a is approximately 12.degree. (however, this
angle can be varied depending upon the portion of the torque curve
which is selected and the length of stroke required of the torque
arm 15).
With the coils 43 and 45 energized, the stator sections 21 and 23
form an electromagnet. For purposes of illustration, the stator
sections 21 and 23 form south and north poles, respectively, to
thereby cause each of the stator sections 21 and 23 to attract one
pole of the permanent magnet 67 while repelling the other pole of
the permanent magnet. Stated differently, the north pole of the
permanent magnet 67 is repelled by the stator section 23 and
attracted by the stator section 21 while the south pole of the
permanent magnet is attracted by the stator section 23 and repelled
by the stator section 21. This push-pull effect on the permanent
magnet 67 produces substantial torque with the result that the
rotor 47 and the torque arm 15 rotate to a second or final position
shown in FIG. 5. The second position is defined by the limits of
travel of the driven member 19 or by a stop 85 which defines the
other end of the slot 31 in the stator section 21.
As will be appreciated from FIG. 3, the magnet 67, the cap 69, the
tube 71, the shaft 49 and the bearing 61 rotate while the bearing
51 is held stationary by virtue of its attachment to the stator
sections 21 and 23. Moreover, such movement is accomplished against
the biasing force of the torsion return spring 73. In the
embodiment illustrated, the torque arm 15 and the rotor 47 rotate
through an angle of 40.degree., and this is a stroke of substantial
length for rotary actuators of this general type.
The lines of flux extend through the cores 37 and 39 and through
the stator sections 21 and 23. Because of the high reluctance of
the slugs 25 and 27, the lines of flux extend across the small gap
87 between the rotor 47 and the stator sections 21 and 23 and
through a peripheral portion of the permanent magnet which is of
relatively high reluctance. Because the stator sections 21 and 23
substantially surround the permanent magnet 67, leakage flux is
likely to occur through the permanent magnet 67 to thereby generate
useful torque.
The spring 73 tends to return the torque arm 15 to the initail
position shown in FIG. 4. In addition, when the coils 43 and 45 are
de-energized, the rotor 47 inherently tends to return to the
position in which the angle a (FIG. 4) is 0.degree.. This is caused
by the natural tendency of the permanent magnet to center itself
between the stator sections 21 and 23. The spring 73 is
sufficiently strong to move the rotor through the position in which
angle a equals 0.degree. to a position such as that shown in FIG. 4
where angle a is greater than 0.degree.. The purpose of this pull
back of the rotor 47 is to select the most advantageous starting
point on the torque versus displacement curve for this particular
application.
FIGS. 4b and 4c show a modification of the present invention which
is identical to the embodiment shown in FIGS. 1-5 except to the
extent indicated herein. Corresponding parts are designated by
corresponding reference characters followed by the letter a. In
FIGS. 4b and 4c a rotary actuator 11a has stator sections 21a and
23 a separated by regions of relatively high reluctance material
which, in the embodiment illustrated, are brass slugs 25a and 27a.
Unlike the construction shown in FIG. 4a, the brass slugs 25a and
27a extend axially and circumferentially of the rotor receiving
aperture 29a. In all other respects, the rotary actuator 11a is
identical to the rotary actuator 11. In the initial position the
axis of magnetization 83a points at one end of the slug 27a;
however, other orientations can be used. The slugs 25a and 27a
extend circumferentially for the full arc of travel so that in the
final position, the axis 83a points at the other end of the slug
27a.
The purpose of varying the shape of the high reluctance region
between the stator sections 21a and 23a is to vary the shape of the
torque curve obtainable. By causing the slug 25a to extend
circumferentially in the direction of rotation, the so-called "gap"
is effectively spread throughout at least a portion of the arc of
travel of the rotor 47. This flattens the torque curve.
FIGS. 6-8 show a rotary actuator 11b which is identical to the
rotary actuator 11 except to the extent specifically noted herein.
In FIGS. 6-8, portions corresponding to portions in FIGS. 1-5 are
designated by corresponding reference characters followed by the
letter b. The actuator 11b is identical to the actuator 11 except
that the latter has a rotor 47b which includes a pair of shoes 89
and 91, and the axis of magnetization 83b extends in a different
direction relative to the permanent magnet 67b. The shoes 89 and 91
are identical and are constructed of highly permeable magnetic
material such as soft iron. The shoes are suitably attached to the
tube 71b and form arcuate peripheral segments of the rotor 47. The
advantage of the shoes 89 and 91 is to provide a low reluctance
path for the lines of flux between the stator sections 21b and 23b
to thereby improve the torque.
The torque curve can also be shaped by appropriately shaping the
shoes as shown, for example, in FIG. 7. The shoe 91 has a ramp or
tapered portion 93 and a maximum axial length portion 95 with the
tip 97 of the ramp being adjacent the slug 27b in the initail
position shown in FIG. 6. The shoe 89 is identical in construction
to the shoe 91 and has a ramp 98 with a tip 99 which confronts the
slug 25b in the initial position. As the rotor rotates from the
initial position shown in FIG. 6 toward the second position shown
in FIG. 8, there is a continuous increase in permeance due to the
increase in the amount of the highly permeable shoes 89 and 91
which confront the slugs 25b and 27b, respectively. As torque is
proportional to the change in permeance, the result is an increase
in torque and a flattening of the torque curve. In the embodiment
illustrated, the ramp 93 extends circumferentially for the arc of
travel of the rotor 47b, and accordingly, there is a continuing
increase in permeance throughout the full stroke of the rotor
47b.
Another feature of the present invention is the angle of the axis
83b with respect to the central transverse axis 101 of the rotor
47b. The axes 83b and 101 form an angle b which in the embodiment
illustrated is 55.degree. and which in the embodiment of FIGS. 1-5
was 0.degree.. The axis 83b extends through the axis of rotation of
the rotor 47b in a direction transverse thereto and substantially
intersects the zone of intersection between the flat and arcuate
peripheral surface portions 79b and 105, respectively, of the rotor
47. In the de-energized condition, the rotor 47b tends to orient
itself so that the axis 83b points generally toward the slug
25b.
The advantage of this construction is two-fold. First, in the
initial position there is a relatively large gap between the planar
surface 79b and the confronting arcuate surface portion of the
rotor receiving aperture 29b. Accordingly, the performance of the
gap is relatively high due to this relatively wide spacing.
However, as the rotor rotates toward the final position shown in
FIG. 8, the cylindrical surface portion 105 is progressively
brought into registry with the surfaces of the rotor receiving
aperture 29b on both sides of the slugs 27b with the result that
permeance is increased. This change in permeance increases
torque.
Secondly, the inherent tendency of the rotor to return to the
position of FIG. 6 is reduced so that if pull back of the rotor 47b
is desired to from an angle a such as in FIG. 4, it can be
accomplished with a relatively weak return spring.
FIGS. 9 and 10 illustrates a rotary actuator 11c which is identical
to the rotary actuator 11 in all respects not specifically noted
herein. The actuator 11c has a torque arm 15c which is rotatable in
either direction from the centered position shown in FIG. 9. In the
centered or initial position shown in FIG. 9, the axis of
magnetization 83c of the magnet 67c points toward the slug 27c. By
energizing the windings 43c and 45c in one direction, the force
field generated rotates the rotor 47c in the clockwise direction
and by energizing the coils in the reverse direction, the rotor
rotates in the counter clockwise direction. The forces operating on
the rotor 47c to rotate the latter are substantially identical to
those described hereinabove.
A return or centering spring 111 is utilized to bias the rotor 47c
toward the neutral position. In the embodiment illustrated, the
spring 11 includes a loop section 113 suitably affixed to the
tubular section 57c and a pair of resilient legs 115 and 117. A pin
119 is mounted on the rotor 47c for movement therewith and projects
between the two legs 115 and 117. A fixed pin 121 is suitably
mounted such as on the plate 53c and projects between the legs 115
and 117. With this construction, clockwise rotation of the rotor
(as viewed in FIG. 9) is resisted by the resilient leg 115 and
counter clockwise rotation of the rotor is resisted by the
resilient leg 117. The return spring 73 provided in the embodiment
of FIG. 1 is eliminated.
Although exemplary embodiments of the invention have been shown and
described, many changes, modifications, and substitutions may be
made by one having ordinary skill in the art without necessarily
departing from the spirit and scope of this invention.
* * * * *