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

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Last updated: May 10, 1996