Integrated Sensor End Effector for Remote Inspection

NASA's Jet Propulsion Laboratory, Pasadena, Califomia

A proposed two-arm robotic manipulator would be capable of changing its mechanical structure to fit a given task. Heretofore, the structures of reconfigurable robots have been changed by replacement and/or reassembly of modular links. In the proposed manipulator, there would be no reassembly or replacement in the conventional sense: instead, the arms would be commanded during operation to assume any of a number of alternative configurations., The configurations (see figure) are generally classified as follows: (1) serial structure, in which the base of arm 1 is stationary, the tip of arm 1 holds the base of arm 2, and the tip of arm 2 holds the manipulated object; (2) parallel structure, in which the bases of both arms are stationary and the tips of both arms make contact with the manipulated object at two different points; and (3) the bracing structure, in which the bases of both arms are stationary and the tip of arm 2 grasps some intermediate point along the length of arm 1. The serial and parallel structures can be regarded as special cases of the bracing structure. Optionally, each configuration could involve locking of one or more joints of either or both arms, and the bracing contact between the two arms could be at a fixed position of arm 1 or else allowed to slide along a link of arm 1. The performances of the various configurations can be quantified in terms of quantities called "dual-arm manipulabilities," and "dual-arm resistivities." Dual-arm manipulabilities are defined on the basis of kinematic and dynamic constraints; dual-arm resistivities are defined on the basis of static-force constraints. These quantities serve as measures of how well such dextrous-bracing actions as relocation of the bracing point, sliding contact, and locking of joints affect the ability of the dual-arm manipulator to generate motions and to apply static forces.

Theoretical study and computer simulation have shown that dextrous bracing yields performance characteristics that vary continuously and widely as the bracing point is moved along the braced arm. In general, performance characteristics lie between those of the serial and parallel structures. Thus, one can select configurations dynamically, according to their performance characteristics, to suit the changing requirements of changing tasks.

More details can be found in:

RA Self-Reconfigurable Dual-Arm System,S Proceedings of the 1991 IEEE International Conference on Robotics and Automation, April 1991, Sacramento, CA and in RA Self-Reconfigurable Manipulator System with Dextrous Bracing Structure,S Proceedings of the 30th IEEE Conference on Decision and Control, Dec. 1991, Brighton, England, pp. 1033-1038.

Point of Contact:
Sukhan Lee
Mail Stop 198-219
Jet Propulsion Laboratory
4800 Oak Grove Drive
Pasadena, CA 91109
818-354-2013
Sukhan.Lee@jpl.nasa.gov

Telerobotics Program page

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Last updated: May 10, 1996