Rotary actuator

A rotary actuator in which there is a freely rotatable permanent magnetic armature between two stators. At least one of the stators produces an asymmetrical magnetic flux field that acts upon the magnetic field of the armature to cause the same to rotate.

BACKGROUND OF THE INVENTION 
The present invention relates to the construction of a rotary actuator also 
known as a sector motor, in which a rotary element is swingable between a 
pair of spaced positions, and in particular, to such devices in which the 
rotary element is latched or held in a selected position after power has 
been removed therefrom. 
Generally, the rotary actuator includes a magnetic armature element 
surrounded by one or more electromagnetic stator elements each having one 
or more windings which when driven provide a force field to drive the 
armature. Reference can be made to such devices as shown in the U.S. Pat. 
Nos. 3,694,782; 4,227,164; as well as 3,761,851; and 4,500,861. In order 
to overcome inherent slow speed, the prior art devices have resorted to 
the use of a large power input to operate the electromagnets and rather 
large masses of magnetic material to increase magnetic force. Multi-armed 
armatures with each arm having a winding are used to increase magnetic 
permeance, as are multi-electromagnets, each operated simultaneously to 
produce an increased flux pattern. As a result, the prior art devices have 
been expensive, complex, and generally quite large for the purposes 
intended. 
A manifest need, therefore, exists for small, lightweight, and extremely 
fast-acting, low-voltage and long-lived motor devices for use in such 
installations as waveguides and other electro-mechanical systems. It is 
the object of the present invention to provide such device. 
It is another object of the present invention to provide a rotary actuator 
which is maintained or latched in a given fixed position with or without 
power being supplied to the electromagnets. 
It is an object of the present invention to provide a springless rotary 
actuator having a fail safe or return latching position, to which the 
armature automatically returns when electrical drive power is removed. 
It is a further object of the present invention to provide an actuator 
wherein the range of angular movement is sufficiently large to provide for 
a mechanical advantage and a mechanical movement capable of operating 
mechanical switches or the like. 
It is another object of the present invention to provide an actuator in 
which chattering, bouncing, and vibration are completely avoided. 
These other objects and attendant advantages of the present invention, as 
well as numerous others, are set forth in the following disclosure. 
SUMMARY OF THE INVENTION 
According to the present invention a rotary actuator is provided having a 
permanent magnetic armature with diametrically opposed poles of opposite 
polarity mounted between a pair of stator elements at least one of which 
is an electromagnet so as to be rotatable between a first and second 
position on creation of a selected flux pattern in at least the one 
electromagnetic stator element. The electromagnetic stator element is 
constructed so that it produces an asymmetrical flux field which is 
greater in the vicinity of one of the opposed poles of the armature than 
in the other. 
The electromagnetic stator comprises a core of soft iron material having an 
inner face opposed to the rotor. A coil is wound on the core so as to 
provide the core with magnetic field poles on each of the core faces. The 
asymmetrical flux field is produced by providing the inner face of the 
core with an enlarged segment which increases the flux field and density 
in a given area and a smaller field corresponding to the remaining core. 
Preferably, the enlarged segment of the core face extends about and 
closely spaced from the surface of the armature for a given arcuate 
distance. 
More particularly the actuator comprises a pair of electromagnetic stators, 
each having a non-magnetic permeable core and a winding cooperating to 
provide a first and a second pole. The stators are fixedly mounted in 
spaced opposition to each other with their poles lying along a common axis 
of magnetization and are asymmetrically shaped to provide a greater force 
field to one side of the axis of magnetization than to the other. An 
armature comprising a cylindrical permanent magnet having opposed first 
and second poles lying along a diametric polar axis is rotatably mounted 
between the opposed stators so that the diametric polar axis is initially 
generally transverse to the axis of magnetization of the stators. An 
electric circuit is provided to selectively energize the electromagnetic 
stators so as to induce on the first and second poles of the driven 
stators, positive and inverse polarity respectively thus causing the force 
field to attract or to repel the pole of said cylindrical magnet lying on 
the same side of the axis of magnetization causing the armature to rotate. 
The armature is provided with a drive arm, adapted to swing conjointly with 
the armature rotation. Stop means are provided which limit the swing of 
the drive arm and switch means are provided actuably by the drive arm 
reaching its given positions. 
In a particular form of the invention, only one electromagnetic stator is 
employed, the other stator comprising an elongated permanent magnet having 
on its face adjacent the armature a given polarity causing the armature to 
be rotatively repelled. Thus, in the absence of any energization of the 
electromagnet, the armature is automatically repelled into its failsafe 
latching position. 
Full details of the present invention are set forth in the following 
description and are shown in the accompanying drawings.

DESCRIPTION OF THE INVENTION 
The two-pole, two-position latching actuator, embodying the present 
invention is structurally described with reference to FIGS. 1-5 which is 
immediately followed by a description of its operation as illustrated in 
FIGS. 6-10. 
As seen in FIGS. 1-5 the two-pole, two position latching rotary actuator, 
generally depicted by the numeral 10, is formed of a mounting base 12 of a 
non-magnetic or non-magnetizable material such as plastic, brass or the 
like. The base 12 is provided with one or more mounting apertures 14 
permitting it to be attached by suitable screws or bolts to other working 
apparatus such as a waveguide, an electronic circuit board, or the like, 
none of which is illustrated herein. 
A freely rotatable cylindrical armature 16 is mounted perpendicularly to 
the base 12 on a central shaft 18 having stub axles 20 and 22 extending 
outwardly at each end. The stub axle 20 is journalled in a radial bearing 
24 mounted within the base 12 permitting the stub axle 20 to pass 
completely through the base 12 so as to exit on the opposite side of the 
base. The stub axle 22 is journalled in a bearing 26 fixed on the frontal 
closure wall 28 of a barrel-shaped housing 30 formed of a ferrous metal or 
similar magnetizable material. As will be explained in more detail later, 
the armature 16 comprises a permanent magnet having diametrically opposed 
poles of opposite polarity along the axial length of the armature, in a 
diametric polar axis O. 
The barrel-shaped housing 30 is a hollow cylinder open at its end opposite 
to the closure wall 28 so that it can lie flat against the base 12 
concentrically about the armature 16, and is fixed to the base 12 by 
elongated set screws 32 (FIG. 1) passing through the frontal end wall 28 
into threaded engagement with the base 12. This maintains the shaft 18 and 
the axles 20 and 22 of the armature 16 between the bearings 24, 26 and 
thereby holds the assembly between the closure wall 28 and the base 12. 
The closure wall 28 is provided with windows 34, facilitating assembly and 
observation of the operation of the parts within the housing. Otherwise, 
the windows 34 are not critical. 
A pair of similar electromagnetic stators, generally depicted by the 
numeral 36 are mounted within the barrel housing 30, along the length of 
the armature 16 in diametric opposition to the armature 16. Each 
electromagnetic stator 36 comprises a rectangular core 38 having an inner 
face 40 spaced closely to the armature 16 and an outer face 42 which is 
secured to inner wall of the housing 30 by means of one or more screws 44. 
The core 38 is formed of non-permanent, but magnetizable material such as 
soft iron extending co-extensively with the length of the armature 16. 
Each core 38 is surrounded by a coil 46 wound along the length of the core 
38 in the longitudinal direction to provide opposing magnetic poles on the 
respective faces 40 and 42 lying in a common axis of magnetization T which 
intersects the polar axis O of the armature 16. 
As shown in FIG. 10, each coil 46 is connected at each of its ends to a 
source of current such as a battery 47 via contacts 48 mounted on the base 
12 (FIG. 2), and switch means 49 so that they might be separately driven, 
providing the faces 40 of each of the electromagnet stators with a 
selectively induced polarity. By selecting the polarity of one or both 
electromagnet stators which are set at 180 degrees apart, to either repell 
or attract the armature 16, the armature 16 can be made to rotate. 
As seen more clearly in FIGS. 3-5, a drive arm 50 is fixedly secured to the 
exposed end of the stub axle 20 on the rear of the base 12, so that the 
drive arm 50 moves conjointly with the rotation of the armature 16 between 
the right and left stator positions. Spaced to either side of the drive 
arm in alignment with the stub axle 20 are a pair of stop pins 52 and 54 
so that they limit the swing of the drive arm 50 to an arcuate or angular 
displacement (arrow A), the range of which is less than 180 degrees so as 
to prevent registration with the stator axis of magnetization and within a 
range preferably not exceeding 90 degrees. 
Mounted to the base 12, adjacent each of the end positions of the drive arm 
50, are a pair of micro-switches 56 and 58 being a part of an external 
circuit (not shown) as for example, a microwave circuit or machine or tool 
system. The micro switches 56 and 58 are arranged so that their actuating 
spring contacts 60 and 62 respectively are depressed to actuate their 
respective switch when the drive arm 50 reaches the limits of its 
respective stop positions. The micro-switches 56 and 58 are conventional 
and commercially available and do not require further explanation here. In 
lieu of micro-switches, other contact means or the like can be provided. 
Mounted also on the base 12 are a plurality of electrical terminals and/or 
contacts 64 enabling suitable wiring of the coils 46 of the 
electromagnetic stators 36 and of the micro-switches 56 and 58 to a source 
of current and to the circuits in which they might be located. 
While two micro-switches are shown it will be obvious that only one may be 
employed or one or both replaced with some other electrical or mechanical 
circuit element which may be activated or operated by contact with the 
drive arm 50. The switch means may also be used to interrupt flow of 
electric current to the selected electromagnetic stator, once the armature 
is fully rotated, thereby terminating application of electrical energy to 
the stator when such current is no longer required. This results in a 
reduction of generated heat and an increase in the life span of the 
actuator. 
As noted earlier, the essentially round elongated armature 16 comprises a 
permanent cylindrical magnet having its opposing poles lengthwise along 
its diametrically opposed sides and magnetically fixed with positive and 
inverse polarity, illustrated in FIGS. 6-9 conventionally by the letters N 
and S. The North (N) and South (S) poles are opposed to each other on a 
diametric polar axis O and are initially installed between the 
electromagnetic stators 36 to extend along the length of the armature 16 
perpendicularly to the common axis of magnetization T of the electromagnet 
stators 36 so that the armature 16 can swing 45 degrees to either side of 
a mid-position between the right and left pole faces 40. As shown in FIG. 
6, the permanently magnetized armature 16 produces two diametrically 
spaced rotor fields RF.sub.1, RF.sub.2, each in the shape of a 
longitudinally elongated ellipsoid, having a force vector V which extends 
in a straight line coincident with the polar axis O. 
The inner face 40 of each core 38 is asymmetrically shaped with respect to 
the axis of magnetization T having an enlarged upper pole segment 40a, 
which curves and extends, and circumferentially encompasses about an 
arcuate portion of the armature 16 for a distance preferably between 15 
and 30 degrees. The smaller lower segment 40b of the inner face 40 is 
narrower being shared to be relatively flat and trailing away and spaced 
from the armature. The cores are arranged so that the larger arcuately 
extending segments 40a are on the same side of the common axis of 
magnetization. This arrangemet enables the encompassing inner face 40 to 
be mounted unusually close to the armature to reduce the air gap 
therebetween and as small as 0.001. This is important as it reduces the 
degree of reluctance caused by the air gap on the magnetic field between 
the faces of the core 38 and the surface of armature 16. This results in a 
reduction of the power requirements for production of the stator field. In 
practice, although the air gap between the face 40 and the armature may be 
between 0.001" and 0.025" the preferred space is between 0.005" and 
0.010". By reducing and narrowing the face 40 at its pole 40b, remote from 
the enlarged pole 40a, the magnetic flux is concentrated in the area of 
the enlarged pole 40a as will be described. 
In the rest or inoperative position of the actuator as seen in FIG. 6, 
wherein neither electromagnetic stator is driven, the armature 16 is 
automatically latched or in normal biased attraction to the nearest 
electromagnetic stator 36. This latching is due to the fact that a 
considerable segment of the ellipsoidal pole field RF.sub.1 intercepts the 
larger segment 40a of the nearest core face 40. In the absence of any 
external field force or other biasing factors such as springs (none of 
which are required or desirable in the present invention) to influence the 
movement of the armature 16, latching occurs normally and automatically 
between the magnetic pole of the armature 16 and the closest face 40a of a 
electromagnetic stator 36. The position shown in FIG. 6, therefore, is 
illustrative only of the latching effect. It will be understood, that 
latching can equally take place on the other or opposing electromagnetic 
stator had the pole of the armature 16 on the same side of the large 
segment 40b been initially located closer to it. 
As seen in FIG. 7, the electromagnet coil 46 is arranged on each core 38 so 
that it produces in each face 40 and 42 first and second poles, 
respectively, of opposite polarity to the other. Depending upon the 
direction of the current impressed in the winding, a positive or North 
polarity will be induced on the inner face 40 and a negative or South 
polarity on the outer face 42. Thus, each electromagnetic stator 36 can be 
provided selectively with either a north or south polarity adjacent to the 
armature 16. Since the axis of magnetization T of the electromagnetic 
stator 36 extends in the transverse direction to the intersecting polar 
axis O of the armature 16, passing through the center of the armature 
(FIGS. 6 and 7), a pair of stator flux fields (SF) are produced. Each 
electromagnetic stator 36 provides a larger and stronger stator field SF1 
above on the sides of the axis of the magnetization T in the area of the 
large pole 40a and a smaller, weaker stator field SF2 on the side of the 
axis of the magnetization T in the area of the narrowed end 40b, remote 
from the larger core segment 40a. 
Referring to FIG. 7, it will be seen that because of the larger stator flux 
field SF1 concentrated about the larger core segment 40a, above the axis 
of magnetization T of the stators 36, the magnetic force exerted upon the 
pole of the armature 16 in the area of the pole 40a is significantly 
greater than the force exerted on the armature pole in the area of the 
shaved or narrowed pole 40b. The reduction of that segment 40b of the 
inner face 40 below the axis of magnetization T, significantly reduces the 
amount of magnetic flux insecting the armature field RF.sub.2 produced by 
the lower armature pole in its area so that the resultant difference in 
exerted force on the opposed armature poles N and S produces a larger 
torque on the armature than would be normally expected. Consequently, the 
speed of rotation is greatly increased. 
In operation, as seen in FIGS. 8 and 9, the combination of the permanent 
armature flux fields RF.sub.1 and RF.sub.2 (having the north and south 
polarities shown in the figures and a positive (N) polarity stator flux 
field SF from the selectively driven electromagnetic stators 36 produces a 
turning moment in the armature 16, by producing mutually repelling force 
having force vectors V1 and V2 (FIGS. 8 and 9) depending on which stator 
is driven. As a result the freely rotatable armature can be made to rotate 
counter-clockwise or clockwise. Once set in motion, the freely rotatable 
armature 16 would tend to continue its rotation until its polar axis O is 
coincident with the axis of magnetization T. Thus, if left uninhibited the 
armature would have a swing of 180 degrees between the opposed 
electromagnetic stators. However, the extent of the swing of the armature 
16 is limited, by the engagement of the drive arm 50 with one of the 
mechanical stop means 52, 54, to the preferred arc of approximately 90 
degrees. This reduces the time of traverse between the terminal stop 
positions 52 and 54. Once the armature 16 passes the center Point of the 
arc A (FIG. 4 and 5), i.e., when the armature polar axis O is beyond the 
perpendicular to the axis of magnetization T, attraction between the 
armature 16 and the then nearest stator 36 becomes automatic even if the 
repulsion force on the driving electromagnetic stator is withdrawn. 
Consequently, the period during which the selected stator 36 must be 
energized to effect movement of the armature may be extremely small, 
giving rise to an overall quick-acting actuator. The electric circuit 
shown in FIG. 10 for energizing the stators 36, illustrates another 
advantageous feature which can be incorporated into the present device as 
a result of the use of the asymmetrical core 40, and the production of 
asymmetrical stator fields which provides for the automatic latching 
feature even in the absence of driving power. A simple timer 68 (either 
mechanical or solid state device) can be inserted in the drive circuit so 
that power is applied to the respective coil 46 only for that small 
milli-second period needed to create the N polarity necessary to repel the 
armature 16 over the dead center position. By limiting the drive power to 
this small time period, hard contact between drive arm 50 and stop 52, 54 
can be avoided, and chattering or vibration obviated. In addition, the 
heat generated in the coil 46 is reduced since the coils are driven for 
only a short time. 
It has been found that driving the selected electromagnetic stators to 
produce in its inner core face 40a a repelling polarity, i.e., a polarity 
the same as that of the armature pole on the corresponding side of the 
common axis of magnetization T, provides the best results, as the torque 
created in the armature 16 by such repulsion acts quickly and with 
certainty to rotate the armature 16. In addition, the power needed to 
repel is significantly less than the power needed to attract. 
Consequently, a construction without any spring biasing means is possible 
to effect precise and rapid latching. 
The force and the speed at which the armature 16 may be made to rotate may 
be increased by simultaneously activating both of the opposed 
electromagnetic stators with relatively opposite polarity on their inner 
core faces 40 so that one stator 36 attracts the armature 16 while the 
other repels the armature 16 in the same direction, thus increasing the 
torque of the armature. Since in this mode of operation, the attracting 
electromagnetic stator has only an auxiliary function, the power required 
to drive it may be significantly less. On the other hand, there should be 
very few instances where the small increase in speed is practically 
necessary. Furthermore, it would also serve very little purpose to attempt 
to create balanced field forces on the armature 16 by driving both 
electromagnetic stators 36 so as to produce in each of the inner core 
faces 40 the same polarity since it is virtually impossible to create 
fields in both stators of identical value. 
It is preferred to form the housing 30 of ferrous metal or magnetizable 
material as it would help in assuring latching, i.e., the fixed attraction 
between the armature 16 and the stators 36, with or without electrical 
driving of the electromagnetic stators 36. A magnetizable housing 30 would 
complement the soft iron core 38 and provide a magnetic loop for the 
armature flux field RF so as to conduct and concentrate the flux pattern 
in close proximity to the armature. For this reason, as well as to provide 
a strong housing, it is preferred that the housing also is formed with a 
relatively thick wall. 
In FIG. 11-14, a two-pole single position latching actuator is shown, i.e., 
an actuator having a "fail-safe" return to a single fixed position when 
power is withdrawn. The overall function of this embodiment is to provide 
for rotation of the armature 16 in response to the driving of a single 
electromagnetic stator 36, from an initial fixed position to a second 
operational position and in holding the armature in the second operational 
position only so long as the driven electromagnetic stator is energized 
and immediately upon the withdrawal of the current to this electromagnetic 
stator, the armature 16 will automatically return into its initial fixed 
position. In this respect, this embodiment provides a "fail-safe" 
operation in that the armature 16 and its conjointly mounted drive arm 50 
always returns to the initial predetermined position, i.e., the rest 
condition, in the absence of an electromotive driving force. 
As seen in FIGS. 11-14, an actuator is provided having a construction 
almost identical to the earlier described embodiment and the same numerals 
identify the same parts, as shown in the earlier described embodiment, 
both structurally as well as functionally. The "fail-safe" embodiment 
shown in these figures differs, however, from the earlier embodiment, in 
that only one of the electromagnetic stators, here denoted 36 is retained 
while the other stator is replaced with a permanent magnet, generally 
designated by the numeral 70. The permanent magnet 70 comprises a magnet 
bar 72 set in a magnetizable supporting shoe 74, preferably by a non 
magnetic adhesive, and the shoe 74 is held to the housing 30 by a screw 
76. The permanent magnetic bar 72, extends along the length of the 
armature 16 in diametric opposition to the remaining electromagnetic 
stator 36', and has opposed poles N and S of fixed, opposite polarity, 
along its longitudinal edges, which lie in the transverse axis of 
magnetization T, and produce a permanent flux field PF, as seen in FIG. 
13, which is enhanced by the shoe 74. 
As in the first embodiment, the armature 16 is provided with fixed poles 
diametrically opposed to each other and nominally designated in the same 
manner N and S. The permanently magnetized bar 72 is arranged with an N 
pole adjacent the armature 16 so that a repulsion force is constantly 
applied to the armature pole N lying on the side of the axis of 
magnetization T on which the larger pole portion 40a is located. This 
constant repelling force biases the armature 16 into the latching position 
against the single electromagnetic stator 36. As seen in FIG. 13, the flux 
field PF of the permanently magnetized bar 72 is symmetrical both above 
and below the axis of magnetization T. As a result the force Vector V3 
produced on the freely rotatable armature 16, the armature 16 is normally 
biased away from the permanent magnet 70 not only by the repulsion acting 
on the armature N pole but by the simultaneous attraction between its S 
pole and the permanent magnet 70. 
As seen in FIG. 14, the driving of the single electromagnetic stator 36', 
so as to provide its inner core face 40 with an N pole causes a force 
Vector V4 which produces clockwise rotation of the armature 16 toward the 
permanent magnet 70 by repelling the N pole of the armature lying on the 
side of the enlarged stator pole portion 40a. It will be appreciated that 
the force field created by the electromagnetic stator 36 in this 
embodiment (not specifically shown in FIGS. 13 or 14) is identical to the 
asymmetrical force field SF shown in FIG. 7 wherein the field induced by 
the larger pole portion 40a is substantially greater than that produced by 
the lower pole portion 40b. These forces are nevertheless sufficient to 
overcome the constant counter repelling force created by the N pole of the 
permanently magnet 70 and there is no inhibition to the immediate rotation 
of the armature 16 toward the permanent magnet 70 upon activation of the 
electromagnetic stator 36. On the other hand, upon the withdrawal of 
current to the electromagnetic stator 36', the stator force field is 
removed, and the repulsion between the N pole of the armature 16 and the N 
pole of the permanent magnet 70 is immediately effective to swing the 
armature 16 counter-clockwise back into the stator 36' as shown in FIG. 
13, thus creating the fail-safe aspect and single position latching of 
this embodiment. 
From the foregoing it will be seen that in both embodiments, a simple, 
springless, small and lightweight rotary actuator or sector motor is 
constructed, having instantaneous response to the impression and removal 
of the driving power. With the present invention actuators operating in 50 
milli-seconds or less, delivering over one million cycles can be built, 
using 12 to 40 Volt AC or DC current. 
Various changes, modifications, as well as embodiments have been shown and 
described. Since these, as well as others, are apparent to hose skilled in 
the art all fall within the purview of the invention, it is intended that 
the disclosure be taken as illustrative only and not as limiting of the 
invention.