3-D Guidance System With Proximity
Sensors For Shuttle RMS
A 3-D guidance system which utilizes four proximity sensors on a remotely-
controlled mechanical claw has been developed by the Jet Propulsion Laboratory.
The sensors feed pitch and range information to a manned control station
indicating how the claw is oriented relative to a mating fixture it is about
to grasp. The operator then alines the claw so that the fixture is grasped
correctly. This system developed for coupling space vehicles can be used
in other remote manipulators. The sensors are mounted on the center square
frame of the end-effector of a four-claw grapple. Each sensor consisting
of an LED source and a photodetector is aimed to sense the object parallel
to the shaft (the roll axis) supporting the grapple. Thus four sensitive
areas are established ahead of the claws. Using the claws to define four
corners of a square, the sensors are mounted at midpoints of the sides of
the square. Thus, two orthogonal lines connecting opposite pairs of sensors
define the pitch-and-yaw axis of the system. In the simplest arrangement,
each sensor is operated in a two-state binary sensing mode, where a zero
indicates a too far state while 1 indicates a too close state when the system
is in the vicinity of the target. The detection distances of sensors B
and D are somewhat shorter than of A and C. Thus a success state when the
claws are alined with the target is defined by A signaling 1, B a zero,
C a 1, and D a zero. An all-zero state shows that the entire claw is too
far from the target and an all-1 that it is too close. A total of 16 combinations
is possible (2**4) indicating various misalinements of yaw and pitch axes
with respect to the target. One of the 16 states never occurs, when A and
C are zero and B and D are 1, because of the detection pattern setup. A
more precise alternative would involve three-state sensing. A signal with
a value of 2 would indicate too close, 1 on target, and zero too far. Success
would be defined by all 1's, and a total of 75 workable logic states would
be possible, giving a more accurate feedback.
Point of Contact:
Antal Bejczy
Mail Stop 198-219
Jet Propulsion Laboratory
4800 Oak Grove Drive
Pasadena, CA 91109
818-354-4568
bejczy@telerobotics.jpl.nasa.gov
Telerobotics Program
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Maintained by: Dave Lavery
Last updated: May 10, 1996
3-D Guidance System With Proximity
Sensors For Shuttle RMS