Electromechanical rotary actuator, which operates over wide temperature range, contains a spring stop which has been calculated to limit internal deceleration loads to a magnitude equal to stall torque. Cryogenic capability is obtained by using dry lubricant on the gears and no lubrication on the bearings

Sullivan, S. F.

English

NASA Technical Reports Server

April 1969	 Brief 69-10100 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Electromechanical Rotary Actuator

Operates Over Wide Temperature Range 
	
Cover	 Outer 
Bearing Race
	 Belleville Spring 
Spacer Washer 
Actuator Frame 
Section
Motor Drive 
Pinion
Recess 
	
B	 U	 I Reduction Gear 
	
Train	 DETAIL A 
/	 Bearings
Cap 
B I /
I	
Frame	 Cap	 Compression Screw 
Spanner-Type 

Fitting 
Output Shaft	 Shaft Lugs	 Inner Seal _
put  
Sector 
Pinion
Outer Seal	 Gasket Potentiometer  
Fastening Screw	 Actuator Frame 
Section	 Pot 
To Atmosphere
DETAIL B 
The problem: 
To design, an electromechanical actuator that will 
operate over the temperature range from + 140° to 
- 300°F. Available actuators were not suitable for 
cryogenic applications. Also, stroke limiting was ef-
fected either by an infinitely rigid stop or a clutch. In 
the first case, the impact loading on the gear train was 
undesirable, and in the second, precise control of the 
detent with respect to positioning would increase the
complexity of the actuator, with a reduction in re-
liability. 
The solution: 
An electromechanical rotary actuator incorporating 
a spring stop which has been calculated to limit in-
ternal deceleration loads to a magnitude equal to stall 
torque. Overtravel is below 1 ½ degrees, which is less 
than one full revolution of the motor. Thus, overload-
ing of the gear train is avoided. Cryogenic capability is 
iiIC dcii I 
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Aeronautics and Space Administration. Neither the United States 	 information contained in this document, or warrants that such use 
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obtained by use of dry lubricant on the gears and no 
lubrication on the bearings, which perform properly 
at all operating temperatures. The actuator is designed 
for applications requiring accurate positioning of the 
stroke limit and for low-temperature environments in 
which petroleum based greases become unsuitable for 
lubricating purposes. 
How it's done: 
The actuator unit comprises a reduction gear train, 
motor drive pinion, output shaft, and potentiometer. 
Rotation of the shaft is limited to approximately 600 
travel. The gear segment on the shaft includes a pair 
of lugs which engage limit stops. The stop members 
are in the form of small cantilever beam elements 
secured to the actuator frame. The sector mounted on 
the output shaft drives the pinion on the shaft of the 
potentiometer to provide a position signal. 
Each of the shaft bearings in the unit is installed 
with an axial preload to prevent possible damage at 
high vibration levels. This is accomplished as shown 
in Detail A by means of Belleville springs. The outer 
peripheral edge of the conic member bears against the 
outer bearing race, while the apex engages the spacer 
washer inserted behind the bearing in the recess. The 
Belleville springs are compressed a predetermined 
amount upon assembly of the frame sections and se-
cured by screws. The spacers may be selectively fitted 
to provide the required loading. The bearings are non-
lubricated for operation in a -300°F environment. 
Oil and grease are eliminated completely, although a 
TFE spacer for the ball elements, impregnated with
dry lubricant material, may be used. 
The entire assembly is environmentally sealed by 
welding a cover to the frame. The output shaft, which 
serves to move the valve member (not shown) extends 
through the frame section on the right. To avoid 
penetration of fluids along the shaft, inner and outer 
seals (Detail B) are provided. The inner seal is re-
tained by a spanner type fitting against which the outer 
seal is seated and retained by the projecting portion 
of the cap. A gasket is located between the cap and 
outer surface of the frame and held in compres-
sion by screws. The area between the seals is ported 
to atmosphere to drain any fluid passing the outer seal 
and thereby avoid the possibility of such material 
entering the inner sealed area. 
Notes: 
No additional documentation is available. Technical 
questions concerning this innovation may be directed 
to:
Technology Utilization Officer 
Marshall Space Flight Center 
Huntsville, Alabama 35812 
Reference: B69-10100 
Patent status: 
No patent action is contemplated by NASA. 
Source: S. F. Sullivan 
of North American Rockwell Corporation 
under contract to 
Marshall Space Flight Center 
(MFS-1 8402)
. 
. 
. 
Brief 69-10100	 Category 05


Electromechanical rotary actuator operates over wide temperature range

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