Two or more arms holding an object can apply both forces that cause the object to move and forces that build up within the object but do not cause it to move: the former are called "external" or "move" forces, while the latter are called "internal" or "squeeze" forces. The DAGCM primitive decomposes the forces sensed at the wrists of the two manipulators into move and squeeze forces, which it then controls separately. The desired contact interaction between the held object and its environment is specified via contact-force-control parameters in the move subspace; the desired internal forces in the held object are specified via force-control parameters in the squeeze subspace.
The DAGCM primitive uses the generalized-compliant-motion concept to control the motion of the held object on the basis of a specified trajectory of the object in Cartesian coordinates, the control of the move forces from the move/squeeze decomposition, and the outputs of several sensors in addition to the force sensors on the wrists. The sensors can be either real (e.g., force and torque sensors) or virtual (e.g., a computed distance to collision). Each sensor is provided an individual task space for control, and the resulting motion commanded by each sensor is merged in the common coordinate frame in which the actual position of the held object is measured.
Various tasks have been performed in the laboratory using the primitive such as orbital replacement unit manipulation, fluid coupler mating and capture of a spinning satellite.
Reference:
Paul G. Backes. "Dual-Arm Supervisory and Shared Control Task Description and Execution." Journal Robotics and Autonomous Systems, 12:29-54, 1994.
Point of Contact:
Paul G. Backes,
Mail Stop 198-219
Jet Propulsion Laboratory
4800 Oak Grove Drive
Pasadena, CA 91109
818-354-3850
Paul.G.Backes@jpl.nasa.gov
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Last updated: May 10, 1996