Failure Tolerance through Active Braking: A Kinematic Approach

For a manipulator operating in a hazardous or remote environment, an important concern is its capability after a component failure, since retrieval or repair is not always possible. Methods have been presented in the literature for optimizing capabilities after specific types of failures. However, techniques for achieving failure tolerance when conversion between failure types is possible has not been fully explored. This paper presents an approach to improving postfailure performance by converting between locked-joint failures and freeswinging failures through active braking. When a manipulator is moved slowly, gravitational forces can be used to control the failed joint in free-swinging mode, allowing the problem to be cast as a kinematic one. The validity of the kinematic formulation and its implementation and global consequences are explored. KEY WORDS—failure tolerance, free-swinging failure, passive joint, active braking, underactuated manipulator