Multi-channel proportional control system for operation of dc motors for use with externally-powered orthotic arm braces is described. Components of circuitry and principles of operation are described. Schematic diagram of control circuit is provided

Allen, J. R.

Blaise, H. T.

English

NASA Technical Reports Server

Motor 
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October 1972	 B72-10617 
NASA TECH BRIEF 
Marshall Space Flight Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
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be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
DC Motor Proportional Control System for Orthotic Devices 
A multi-channel proportional control system used 
for operation of dc motors has been applied to the 
operation of externally-powered orthotic arm braces. 
The original system was produced to operate remote 
manipulators located at two NASA facilities, the first 
two prototypes having the desirable feature of very 
accurately controlling the shaft positions of the motors 
that drive the remote manipulators. The units have been 
reduced in size from 0.23 to 0.004m 3 (8 ft3 to 220 in 3) 
for application to the orthotic braces and also include 
velocity proportionality capability.
The most convenient and best method of controlling 
the velocity of permanent-magnet dc motors is by pulse 
frequency modulation. These motors have linear speed/ 
torque/voltage characteristics which seem to suggest 
that a simple analog control signal would be adequate. 
However, they do not respond favorably toan amplitude-
modulated signal during the first instant of acceleration. 
Because of the static friction of the motor and other 
conditions, a substantial amount of current is required 
just to start the motor, and it tends to "leap" forward 
before settling into its governable pattern of operation. 
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Since the first increment of motion is most important 
in the powered orthotic devices, this velocity pattern 
is unacceptable. The pulsed control signal circumvents 
this feature. When pulses of high current but short 
duration are fed to the motor, it will have sufficient 
current to start but will still "leap" forward. The "leaps", 
however, will be of curtailed duration (time length of 
the pulse). If a train of pulses is fed to the motor, it 
responds with incremental bursts of rotation of reason-
able fidelity. Because of the short time duration of the 
pulses, the motor rotation appears to be one smooth 
continuous motion rather than discrete steps. Motor 
braking is applied between pulses, to prevent undesirable 
overshooting or coasting. 
The final circuit design (see figure) responds to an 
analog input signal by delivering frequency modulated 
output pulses. Increasing the magnitude of the input 
voltage increases the frequency of the output pulses. 
When large currents are required, power transistors are 
added to the circuit.
Note: 
Requests for further information may be directed to 
Technology Utilization Officer 
Marshall Space Flight Center 
Code A&PS-TU 
Marshall Space Flight Center, Alabama 35812 
Reference: B72-10617 
Patent status: 
Inquiries concerning rights for the commercial use 
of this invention should be addressed to: 
Patent Counsel 
Marshall Space Flight Center 
Code A&PS-PAT 
Marshall Space Flight Center, Alabama 35812 
Source: Herman T. Blaise of
Marshall Space Flight Center and

James R. Allen of
Rancho Los Amigos Hospital
under contract to
Marshall Space Flight Center
(MFS .2 1573) 
B72-10617	 Category 01, 05


DC motor proportional control system for orthotic devices

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