An actuator for rotating an output member, having an epicyclic transmission adapted to rotate the output member in response to the motion of a rotor which contains a plurality of radial projections which interact with a stator or non-rotating portion of the actuator to produce a rotating tangential force vector directed substantially perpendicular to the radial projections.

BACKGROUND AND SUMMARY OF THE INVENTION 
This invention concerns rotary actuators and more specifically rotary 
actuators having means for generating a tangential force vector on a rotor 
housed therein. 
Eccentric or epicyclic reduction gearing has long been known and utilized 
as a compact and efficient transmission system for rotary actuators. These 
actuators have integrated the power element and the epicyclic transmission 
into an integral actuator which has the attributes of a low inertia and 
high efficiencies at rated loads. The basic components of these rotary 
actuators comprise a rotor, a ring gear attach thereto, a stationary or 
ground gear and output gear. In essence the eccentric positioning of the 
ring gear in relationship to the output gear forms the epicyclic 
transmission system. In high gear ratio applications the rotor motion 
consists of a high speed orbital motion combined with a low speed rotation 
about the ground gear. In low gear ratio applications the gear mesh 
between the ring gear and the stationary or ground gear provides a 
displacement motion without rotation since both gears have exactly the 
same number of teeth. Illustrative of these types of rotary actuator, 
using epicyclic gearing, is U.S. Pat. No. 3,770,997 to Presley. The basic 
deficiencies with this type of rotary actuator, as well as other variable 
reluctance electric actuators or similar hydraulic or pneumatic actuators 
as illustrated by Boyadjieff et al in U.S. Pat. No. 3,516,765 is that the 
force vector that is exerted on the rotor is essentially applied in a 
radial direction. It can be shown that the force is directed through the 
center of the rotor which is eccentrically located relative to the center 
of the output gear. Typically this eccentric distance is only a few tenths 
of an inch and consequently only a small component of the applied force 
goes into producing useful work that is, goes into producing a moment to 
drive the output member. Consequently the prior art requires the 
generation of extremely high forces in order to produce significant levels 
of output torques thus requiring an actuator that is large and one that 
will typically consume excessive power because of its size, weight, 
inertia and inherent internal friction. 
The present invention relates to a new rotary actuator concept for 
producing forces that are applied tangentially to the rotor as opposed to 
forces which are directed through the eccentric as illustrated in the 
prior art. Consequently virtually all of the force generated by the new 
actuator goes into producing torque or useful work. According to the 
specific embodiments detailed below the present invention relates to an 
electric rotary actuator having a rotor that is constrained to move in an 
orbiting, non-rotating fashion about an output gear. The orbiting 
non-rotating motion of the rotor is produced by the interaction of 
circular holes in the rotor with fix reaction pins or equivalent. As will 
be discussed below the rotor displaces or orbits about these reaction 
pins. The orbiting motion of the rotor is transmitted through an epicyclic 
transmission to the output gear or member which is adapted to engage a 
load to be rotated or otherwise moved. The rotor contains a number of 
radially situated rectangular projections or poles which extend into coil 
spaces between respective poles of a stator which in turn is affixed to a 
housing. By controlling the excitation sequence of the coils on the stator 
the rotor is set into the orbiting motion about the reaction pins. The 
selective interaction between the rotor projections or poles and the coils 
mounted on the stator produce a tangentially rotating force vector. 
In an alternate embodiment of the invention the reaction pins and circular 
holes within the rotor are replaced by a rotor having a ring gear with a 
peripherally situated gear teeth which interact with a stationary or 
ground gear which is affixed to the housing. The gear mesh therebetween 
permits the required orbiting motion without rotation of the rotor because 
of the number of gear teeth in the rotor and in the ground gear may be 
chosen to be exactly the same. 
A further embodiment of the invention illustrates a pneumatic or a 
hydraulic version of the electric rotary actuator. In this embodiment the 
rotor includes a low inertia non-rotating member having a plurality of 
collapsible vanes peripherally distributed thereon. The vanes cooperate to 
form clearance volumes between adjacent vanes and the housing. These 
volumes may be considered as variable volume displacement chambers which 
collapse at the same speed as the rotating force vector. Commutator means 
sequentially introduce pressurized fluid into the displacement chambers to 
produce a tangentially rotating force vector similar to the force vector 
produced by the electric actuator. 
A further embodiment of the present invention illustrates a dual mode 
actuator that combines the features of the electric and pneumatic or 
hydraulic actuators into an integrated unit to power a common shaft. The 
dual mode actuator can be operated in either electric or hydraulic (or 
pneumatic) modes or in a combined mode during which time it can be 
simultaneously electrically and hydraulically (or pneumatically) operated 
thereupon developing twice the output power. 
A principal limit to the output torque delivered is the strength of the 
output gear. It is well known that the load carrying capacity of a gear 
increases as the square of its diameter. Consequently in certain 
applications it is desirable to make the output gear as large as possible. 
A further embodiment of the invention increases the load carrying capacity 
of the actuator by situating the rotor inside the output gear. 
A feature of the present invention is the use of the eccentrically mounted 
rotor having a plurality of radial projections thereon. The interaction 
between these radial projections and a coil or displacement chamber 
produces in cooperation with a commutator means a rotating tangential 
force vector. The actuator displays a high torque to inertia ratio and a 
high efficiency at rated loads. The development of the tangentially 
situated force vector permits the development of torques that are 
substantially larger than the torque developed by prior art actuators of 
the similar size. In addition the use of the non-rotating orbiting rotor 
in low gearing applications reduces the gear contact velocities between 
the rotor and output gear or member yielding a simpler and more reliable 
design. 
Many other advantages features and objects of the invention will be clear 
from the detailed description of the drawings.

DETAILED DESCRIPTION OF THE DRAWINGS 
Reference is now made to FIGS. 1, 2 and 3 which illustrate one embodiment 
of the present invention. There is shown a four pole rotary actuator 20 
comprising a housing 22 having situated therein a rotor 24 constructed of 
a ferro-magnetic material and eccentrically located in driving engagement 
with an output gear 26. The output gear 26 is disposed in driving 
engagement with a shaft 30. The shaft 30 is maintained in radial alignment 
with the axis of rotation 32 by the bearings 34a and b. The motion of 
rotor 24 is transmitted to the output gear 26 through a ring gear 40. The 
center or axis of the ring gear 40 is denoted by numeral 42. The rotor 24 
and ring gear 40 are maintained in a floating relationship relative to the 
output gear by the interaction of the rotor 24 with the eccentric bearing 
comprising bearings 44a and b which are eccentrically located relative to 
bearings 46a and b by the eccentric spacers 48a and b. In a low gear ratio 
configuration the rotor and ring gear are integral. (In the high gearing 
ratio configuration, an example of which is shown in FIG. 12. The ring 
gear is driven by the rotor through drive bearings and the ring gear 40 
rotates slowly while the rotor 24 does not rotate.) The rotor 24, output 
gear 26 and ring gear 40 are maintained in axial alignment within the 
housing 22 by the thrust bearings 52, 54 and 56. 
The actuator 20 further includes a stator 70 that is preferably fabricated 
of magnetic laminates. The stator 70 comprises a continuous laminate 
design however other configurations including a segmented stator design 
may be substituted. As illustrated in FIG. 2 the stator 70 comprises a 
four pole configuration however additional magnetic poles may be employed 
depending upon the application of the actuator to a specific purpose. The 
stator 70 further comprises a plurality of projecting members forming 
poles 72a-d and 74a-d adapted to receive a plurality of coils 76a-d and 
78a-d. The physical placement of the opposing poles 72 and 74 and the 
placement of their respective coils 76 and 78 form the electrical poles on 
stator 70 as well as cooperate to form a plurality of radially situated 
coil spaces. 
The rotor 24 further includes a plurality of radial projections or 
rectangular poles 80a-d equal in number to the number of coil spaces 
formed by the stator poles. In addition the coils 76, 78 are so situated 
relative to the plane of the rotor 24 such that when they are excited they 
produce a tangential electromagnetic force that is perpendicular to the 
radial projections 80. In addition the rotor 24 further includes a 
plurality of circular holes 82a-d that are sized to receive reaction pins 
60a-d. The rotor 24 is constrained to move within the housing in an 
orbiting, non-rotating motion by the interaction of the circular holes 
(82a-d) of the rotor 24 with its corresponding reaction pins (60a-d). The 
stator 70 further includes a plurality of holes 86 which are adapted to 
receive a plurality of bolts (not shown) which serve to mount the stator 
70 to the housing 22. 
TABLE I 
__________________________________________________________________________ 
EXCITATION SEQUENCE FOR 4 POLE ACTUATOR 
DIRECTION 
OF STEP 
COIL EXCITATION 
ROTOR ORBIT 
NO 76a 
78a 
76b 
78b 
76c 
78c 
76d 
78d 
__________________________________________________________________________ 
CLOCKWISE 
1 ON ON 
2 ON ON 
3 ON ON 
4 ON ON 
COUNTER- 1 ON ON 
CLOCKWISE 
2 ON ON 
3 ON ON 
4 ON ON 
__________________________________________________________________________ 
The method of moving the rotor 24 is discussed below. By sequentially 
exciting coils 76a-d and/or 78a-d the rotor 24 will be forced to move in 
an orbiting manner with respect to the reaction pins 60a-d. More 
specifically, it should be recalled that stator 70 comprises a plurality 
of poles 72a-d and 74a-d. These poles contain respective coils 76a-d or 
78a-d. The coils 72a-d are situated on the right hand side of the 
respective rotor projections 80a-d while coils 78a-d are situated on the 
left hand side of each rotor projection. By appropriately exciting 
particular coils 76a-d each of the rotor rectangular poles or projections 
80 will be attracted to move to the right. By exciting the coils 78 the 
rotor projections will be moved to the left. It should be appreciated that 
upon the selective activation of any coil a tangential force of 
attraction, F.sub.i where i=1, 2, 3, 4, will be generated to draw the 
appropriate rotor projection to the corresponding activated coil. 
The forces of attraction F.sub.1 -F.sub.4 are illustrated in FIGS. 4a-4d 
which diagrammatically illustrates an excitation sequence to cause the 
rotor 24 to orbit about the reaction pins 60 in a clockwise manner. A 
clockwise orbiting motion of the rotor may be obtained by the serial 
excitation of one half of the coils 76a-d located on the right hand side 
of each rotor projection 80. As an example, first coils 76a and b are 
excited. The magnetic forces, F.sub.1 and F.sub.2 so developed tend to 
move the rotor 24 to the right towards stator pole 72a and downward 
towards stator pole 72b. Coil 76a is then deactivated and coil 76c 
activated. With both coils 76b and c excited the rotor 24 will have a 
tendency to move down and to the left. Coil 76b is then deactivated and 
coil 76d activated. Thereafter coil 76c is deactivated and coil 76d again 
excited completing a four (4) step excitation sequence which is then 
continuously repeated. 
Table 1 summarizes the coil excitation sequences to achieve both a 
clockwise and a counter-clockwise orbiting motion of the rotor. 
While the above discussed coil excitation sequences require the selective 
excitation of only the coils 76 or 78 in a paired manner, other excitation 
sequences utilizing the combined excitation of selected ones of both of 
the coils 76 and 78. As an example, one such combined sequence would 
require the following sequence of coil pair activation, 76a-78c, 76b-78d, 
76c-78a and 76d-78b. 
Reference is briefly made to FIG. 5 which illustrates a circuit for the 
distribution of power to the appropriate coils 76 and 78. As depicted 
schematically in FIG. 5 coils 76a-d and 78a-d are supplied with electrical 
power from power source 90 via the step and sequencing logic 92 and the 
switches 93 and 94. In operation the step and sequencing logic 92 will 
control switch 93 so that power is distributed to either coils 76a-d or to 
coils 78a-d. If power is to be supplied to coils 76a-d then the logic 92 
will command switch 94 such that coils 78a-d are grounded. The logic 92 
will then generate the coil excitation sequence previously described. 
Methods of commutating or selectively exciting coils once the excitation 
sequence is specified are known as discussed by Pressley in U.S. Pat. No. 
3,770,997 which is expressly incorporated herein by reference. 
Reference is now made to FIGS. 6, 7 and 8 which illustrates an alternate 
embodiment of the present invention. It is well known that a principal 
limit to the torque transmitted to a load is dependent upon the strength 
of the output gear. It can be shown that the load carrying capacity of the 
output gear increases as the square of its diameter. Consequently under 
certain circumstances it may be desirable to make the output gear as large 
as possible. One way of achieving this while still packaging an actuator 
in a small housing is by utilizing an inverted gearing arrangement. FIGS. 
6 and 7 illustrate cross-sectional views of a four pole array actuator 100 
having a stator 101 that is situated within rotor 102. The stator 
comprises a plurality of poles 103a-d and 104a-d that are adapted to 
receive cooperating coils 105a-d and 106a-d. The rotor 102 includes a 
number of inwardly directed radial projections 107a-d that are adapted to 
fit between the spaces formed by the stator poles 103a-d and 104a-d. These 
rotor projections 107 are ferromagnetic and responsive to the magnetic 
fields created upon the excitation of the coils 105 and/or 106. The rotor 
102 is positioned eccentrically relative to the central axis 108 by 
bearings 109,110 and the eccentric spacer 111. The rotor further includes 
a ring gear 112 which may be integrally formed in its outer surface. The 
rotor further includes a plurality of holes 113a-d that are adapted is 
coact with reaction pins 114a-d in a manner previously described. The 
rotor is caused to orbit relative to the stator 101 by the interaction 
with these reaction pins. 
An outer gear 116, is positioned concentric to the central axis 108 and the 
housing 117 and is adapted to engage and be driven by the ring gear 112. 
The outer surface of the outer gear contains a tab 119 that is adapted to 
engage a cooperating apparatus (not shown) to be driven. The tab 119 
extends through an opening 120 in the housing 118. The relationship 
between the tab 119, the outer surface of the output gear 116 and the 
opening 120 in the housing is more clearly illustrated in FIG. 8. 
Reference is made to FIGS. 9, 10 and 11 which illustrate a sectional view 
of an eight (8) pole electric rotary actuator, a sectional view 
illustrating the relationship of the rotor 127 to the stator 121, and a 
plan view showing, in isolation, the gear mesh which may be used to 
replace the reaction pins and rotor holes previously discussed. 
More specifically the actuator includes a laminated stator 121 having a 
first set of eight poles 122a-h and another set of opposingly situated 
poles 123a-h. The poles 122 and 123 are adapted to receive coils 125a-h 
and 126a-h respectively. The actuator further includes a rotor 127 having 
eight radially situated projections 128a-h extending into the spaces 
formed by the stator poles 122 and 123. In addition, the rotor 127 is 
fabricated with a pair of gears 129a and b disposed about periphery of the 
rotor flange 131. The gears 129a and b are eccentrically positioned 
relative to coacting stationary gears 130a and b. The ground or stationary 
gears 130 are fixed to and situated concentric with the housing 22 of the 
actuator and to axis 108. The gears 129 may be operatively fixed to the 
rotor or fabricated as an integral part of the rotor flange 131. 
The gear mesh between the gear 129b and the stationary gear 130b is 
illustrated in FIG. 11. 
The operation of the actuator discussed above and shown in FIGS. 9-11 is 
similar to the operation of the four pole actuator shown in FIGS. 1-3. In 
response to the magnetic fields generated upon the selective activation of 
coils 125a-h and/or 126a-h the rotor 127 will be displaced relative to the 
stator 101 thus causing the gears 129a and b to be displaced relative to 
the stationary gears 130a and b. The interaction between the gears 129 and 
130 causes the rotor 127 to exhibit an orbiting motion relative to the 
output gear 26. The ring gear 40 situated on the rotor coacts with the 
output gear 26 to power the shaft 30. 
One possible excitation sequence for the coils 125 or 126 can be derived 
using a similar rationale to that employed in the excitation sequence for 
the four pole rotary actuator. It should be recalled that half of the 
right hand or left hand coils were activated at any specific time. Using 
this philosophy an eight (8) step sequencing logic exciting four coils at 
any time can be utilized. As an example the excitation sequence to produce 
a clockwise orbiting motion of the rotor 127 which in turn causes a 
counter-clockwise motion of the shaft 30 is as follows: 
125abcd-125bcde-125cdef-125defg-125efgh-125fgha-125ghab-125habc. 
The coils 126 may be activated to achieve a clockwise rotation of the shaft 
32. One such sequence is as follows: 
126hgfe-126gfed-126fedc-126edcb-126dcba-126cbah-126bahg. 
Reference is now made to FIGS. 12 and 13 which show a pneumatic or 
hydraulic version of the four pole electric rotary actuator in a high 
gearing configuration. The eccentric bearing and epicyclic transmission 
used herein are similar to that previously discussed and will not be 
discussed further. The pneumatic or hydraulic version of the actuator 130 
includes a rotor 132 which orbits within a housing 134. The rotor 132 
contains a plurality of radial projections 136a-d extending in the housing 
134. While the actuator 130 illustrates a rotor 132 having four 
projections 136 other rotor configurations may be substituted. The rotor 
132 is separated from a ring gear 180 by a set of ring gear drive bearings 
182a and b. The orbiting motion of the rotor 132 is transferred to the 
ring gear 180 through these ring gear drive bearings. The rotor 132 is 
eccentrically mounted relative to the axis of shaft 30 by the interaction 
of the bearings 184 and 186 and the eccentric spacer 188 in response to 
the hydraulic or pneumatic forces generated on the projections 136a-d and 
due to the interaction between the ring gear and the stationary or ground 
gears 210a and b. The rotor will move with orbiting motion to drive the 
shaft through the output gear to the ring gear 180. In the embodiment 
illustrated in FIGS. 12 and 13 the ring gear will move with both rotating 
and orbiting motion. 
The housing 134 further includes a plurality of slots 144a-d corresponding 
to one of the rotor projections 136a-d. The slots are adapted to loosely 
receive each of the poles 136. Inspection of FIG. 13 reveals that the 
poles 136 on the rotor 132 and the slots 144 on the housing 134 create a 
plurality of interfitting lands and recesses. Each land and recess is 
separately by vanes 150a-d and 152a-d. The volumes between adjacent vanes 
150 and 152 form a plurality of displacement chamber 156a-h. Each of the 
vanes form a pneumatic or hydraulic seal between its respective land and 
recess. By way of example, vanes 150a-d is of the type which comprises a 
piston 160 that is received within a bore 162 and which is biased by the 
action of spring 164 against the recess formed within the housing 134. To 
achieve a compact motor design having a housing which is characterized by 
a relatively thin wall, vanes 152a-d are preferably of the captured vane 
type that are suitably received within notches 166a-d and 168a-h. Those 
skilled in the art will appreciate that if the land area of the housing 
was increased in thickness the captured vane 152 may be replaced by the 
reciprocating piston type vane 150 wherein a spring and piston would be 
inserted within a bore within the land area of the housing and biased 
against the recessed area of the rotor 132. It should be appreciated that 
the vanes 150 and 152 used to form the plurality of displacement chambers 
156 are used to obtain a compact motor design, however, any of the methods 
used in fluid motors may be applied, including radial pistons, bellows, 
flexible diaphragms, etc., could be used to form displacement chambers. As 
can be seen from FIGS. 12 and 13 the rotor 132 and housing 134 form a 
powering element which may be considered as a positive displacement low 
inertia non-rotating vane motor, which generates a tangential force vector 
on each rotor projection 136a-d which rotates at a relatively high speed 
in either direction. The direction of rotation is determined by 
sequentially pressurizing certain displacement chambers 156 while 
depressurizing others as described below. 
Reference is now made to FIG. 14 which schematically illustrates a 
pneumatic or hydraulic commutator which may be used to selectively 
pressurize the displacement chambers 156 to obtain the clockwise and 
counter clockwise rotation of the shaft 30. A similar technique is shown 
by Boyadjieff in U.S. Pat. No. 3,516,765 which is expressly incorporated 
by reference. Pairs of kidney shape of ports 170a-170d and 171a-171d are 
located in the rotor faces, and pairs of ports 172a-172d, 173a-173d, and 
174a-174d are located in the housing. These ports are connected to a servo 
valve 180 through passages fabricated in the housing. The intermediate 
housing ports 173a-d are always maintained at a discharge pressure 
P.sub.d. The housing ports 174a-d are connected to the P.sub.1 servovalve 
outlet port 175. The housing ports 172a-d are connected to the P.sub.2 
servo valve outlet port 176. The rotor ports 170a-d are connected to the 
pressure chambers 156a, d, e, g, which as illustrated in FIG. 13, are 
displaced in the clockwise direction from the rotor projections 178. The 
rotor ports 171a-d are connected to the pressure chambers 156b, d, f, h, 
which are displaced in the counterclockwise direction from the rotor 
projections. 
For the clockwise direction of rotation, the input signal to the servovalve 
180 causes pressure P.sub.1 to be high and pressure P.sub.2 to be at the 
discharge pressure P.sub.d. For the commutator position shown in FIG. 14, 
the pressures in rotor ports 171c and 171d are high or at pressure P.sub.s 
and the pressures in all the other ports are low. The high pressure in 
ports 171c and 171d will be communicated to two of the chambers such as 
156d and f thereby applying a tangential pressure force to the projections 
136c, d to move the rotor. As the rotor moves a small distance with 
orbiting motion, rotor port 171c will be brought into communication with 
housing port 173c, and the pressure in rotor port 171c will drop to the 
low or discharge pressure. At the same time, rotor port 171a will be 
brought into communication with P.sub.1 port 174a, and the pressure in 
rotor port 171a will increase to high valve thereby applying a pressure 
force to projection 136a. After one quarter cycle of orbiting motion, 
rotor port 171d will be brought into communication with stator port 173d, 
and the pressure in rotor port 171d will drop to low. At the same time, 
rotor port 171b will come into communication with port 174b, and the 
pressure in rotor port 171b will increase to a high value. As the rotor 
continues to orbit the P.sub.1 pressure will be directed into two of the 
displacement chambers at a time to achieve a pressurizing sequence and 
rotating force vector similar the electrical sequencing shown in Table I. 
For the opposite direction of rotation, the servovalve is switched so 
pressure P.sub.2 is high, and pressure P.sub.1 is low. 
Reference is now briefly made to FIG. 15. The embodiment of the invention 
illustrated in FIG. 14 is conceptually closer to the operation of the 
electric actuators previously discussed than with the hydraulic actuator 
illustrated in FIGS. 12 through 14. FIG. 15 schematically illustrates 
another hydraulic actuator comprising a housing 200 having situated 
therein a rotor 202 having a predetermined number of radially extending 
projections 204. In the embodiment illustrated herein, the rotor includes 
four projections 204a-d. Each of the projections 204a-d is sized to be 
received within a recess 206a-d fabricated within the housing 200. The 
rotor 202 has fabricated on its inner surface a ring gear 210. The rotor 
is maintained within the housing by appropriate bearings and the like, 
such that in response to forces input to the projections 204, the rotor 
will be caused to be moved in an orbiting manner relative to the axis 212. 
The ring gear is drivingly positioned relative to an output gear 214 which 
is coupled to a shaft 216. The actuator further includes four pairs of 
hydraulically actuated pistons 220a,b, 222a,b, 224a,b and 226a,b. Each 
piston 220-226 is mounted perpendicularly to its corresponding rotor 
projection 204. Each piston is mounted within a pressure chamber 230a-h. 
Each of the pressure chambers 230a-h is connected via internal fuel 
passages (not shown) to a hydraulic or pneumatic commutating means 240. By 
selectively pressurizing and depressurizing particular chambers 230, the 
corresponding pistons will be forced to move outward therein applying a 
tangential force to a coacting rotor projection 204. By commutating, that 
is, by sequentially pressurization and depressurization various pressure 
chambers 230, a rotating tendential force can be created to cause the 
rotor 202 to move in an orbital manner relative to the output gear therein 
driving the output gear 214 and shaft 216. Using the commutation sequence 
illustrated in Table 1 for the electric actuator, a typical commutation 
sequence for the hydraulic or pneumatic actuator illustrated in FIG. 15, 
can be achieved. One such commutation sequence, which requires the 
selective pressurization and depressurization of two adjacent pressure 
chambers 230a-h, is as follows. To achieve a clockwise orbiting motion of 
the rotor 220, pressure chamber 230h and 230b would first be pressurized 
therein inparting to the rotor the forces F.sub.1 and F.sub.2 as 
illustrated in FIG. 15. After a period of time, the pressure chamber 230h 
would be depressurized and pressure chamber 230d pressurized, thus causing 
the rotor 202 to move under the influence of force F.sub.2 and a new force 
F.sub.3. In this manner, selective pairs of pressure chambers are 
activated and then sequentially deactivated to obtain a rotating force 
vector. A complete sequence of excitation would be as follows: 230h-230b, 
230b-230d, 230d-230f, 230f-230h, 230h-230b. The above sequence may be 
reversed or altered to achieve a counterclockwise orbiting motion of the 
rotor 202 relative to the output gear 214. 
Reference is now made to FIG. 16 which illustrates a dual mode actuator 
300. A comparison of FIGS. 12 and 16 would reveal that the dual mode 
actuator 300 is substantially equivalent to the hydraulic or pneumatic 
actuator 130 illustrated in FIG. 12 with the following exception. The 
rotor 132 has been modified to include a plurality of radially situated 
projections 250a-d. These projections can be identical to projections 
80a-d of the electric actuator as illustrated in FIG. 2. The radial 
projections 250 are fabricated from ferromagnetic material and may be an 
integral part of the rotor 132 or attached thereto in a known manner. The 
housing of the actuator illustrated in FIG. 12 is modified to accomodate a 
stator 252 having a plurality of coils 254 situated thereon. The 
relationship of the stator 254, coils 254 and rotor projections 250 can be 
identical to that illustrated in FIG. 2. The housing is further modified 
to incorporate a seal 260 to isolate the hydraulic or pneumatic fluid 
within the left hand position of the actuator from entering into the 
electric or right hand portion of the actuator. The operation of the 
actuator illustrated in FIG. 16 is identical with the operation of the 
actuator illustrated in FIG. 2 or FIG. 12. The actuator may be operated in 
either a pure electric mode or in a pure hydraulic or pneumatic mode. In 
addition, by simultaneously activating the appropriate coils 254 and by 
introducing pressurized fluid to the pressure chambers within the 
hydraulic portions of the dual mode actuator, a dual mode of operation can 
be realized. 
Many changes and modifications in the abovedescribed embodiments of the 
invention can of course be carried out without departing from the scope 
thereof. Accordingly, that scope is intended to be limited only by the 
scope of the appended claims.