The Space Shuttle's Remote Manipulator System (RMS) arm has proved itself to be critical in the success of several space missions, notably the Solar Max satellite repair and Hubble telescope refurbishment. The RMS Force Torque Sensor (RMS-FTS) was a flight instrument that served as an enhancement to the RMS arm by providing the detection of forces and torques acting upon the arm when in contact with other objects. The RMS-FTS was flown successfully as part of the Dextrous End Effector system, developed at NASA-JSC for onboard the STS-62 shuttle mission of March 4, 1994.
Two major elements comprised the RMS-FTS, a sensor element containing strain gauges and a data acquisition electronics unit that attached to the RMS arm near the wrist joint. The sensor element was designed and fabricated at JPL, and the on-board computer and display unit manufactured by the Southwest Research Institute. Force/torque data transmitted from the sensor element was received by an on-board computer element which provided the information to operators.
Graphical and numerical displays were used to give the operator visual force feedback during manipulator operations involving constrained motion. This allowed the performance of operations requiring very small amounts of force (5 - 50 lbs). At times when comprehensive views of the worksite were not available, the force torque sensing provided a sense of 'touch' to augment visual data in operations such as mating and de-mating connectors. Balancing end-effector forces and torques also aided in positioning and alignment of the RMS arm in preparation for insertion and detachment tasks. The magnitude and direction of excessive forces imposed by, or on the RMS arm, could be detected in real time, enabling immediate corrective action to be taken.
To control the system, keyboard commands were input to the on-board computer element in flight to enable functions such as display formatting, strain gauge offset compensation, and reference frame manipulations of translation and rotation. In-flight engineering performance data was recorded for subsequent analysis by ground personnel.