This paper studies the degree to which the kinematic redundancy of a manipulator may be utilized for failure tolerance. A redundant manipulator is considered to be fault tolerant with respect to a given task if it is guaranteed to be capable of performing the task after any one of its joints has failed and is locked in place. A method is developed for determining the necessary constraints which insure the failure tolerance of a kinematically redundant manipulator with respect to a given critical task. This method is based on estimating the bounding boxes enclosing the self-motion manifolds for a given set of critical task points. The intersection of these bounding boxes provides a set of artificial joint limits that may guarantee the reachability of the task points after a joint failure. An algorithm for dealing with the special case of 2-D self-motion surfaces is presented, These techniques are illustrated on a PUMA 560 that is used for a 3-D Cartesian positioning task.

This paper formulates an algorithm for trajectory generation for two robots cooperating to perform an assembly task. Treating the two robots as a single redundant system, this paper derives two Jacobian matrices which relate the joint rates of the entire system to the relative motion of the grippers with respect to one another. The main advantage of this method over previous methods is that operations may be described in the coordinates of the assembly rather than in world coordinates. To join parts using this algorithm, the desired relative position is specified and the algorithm automatically determines where the robots perform the assembly. In the process of generating the trajectory, the dexterity of the highly redundant dual-robot system is taken advantage of to satisfy a variety of secondary constraints. Secondary constraints may include obstacle and joint limit avoidance and constraints to satisfy certain absolute position and orientation goals. The algorithm typically involves two phases. First the parts to be assembled are brought from an arbitrary initial configuration to an approach configuration. This phase uses a newly derived relative distance Jacobian formulation which inherently avoids collisions. Then, a more traditional Jacobian formulation is used to join the parts.

The high cost involved in the retrieval and repair of robotic manipulators used for remediating nuclear waste, processing hazardous chemicals, or for exploring space or the deep sea, places a premium on the reliability of the system as a whole. For such applications, kinematically redundant manipulators are inherently more reliable since the additional degrees of freedom (DOF) may compensate for a failed joint. In this work, a redundant manipulator is considered to be fault tolerant with respect to a given task if it is guaranteed to be capable of performing the task after any one of its joints has failed and is locked in place. A method is developed for insuring the failure tolerance of kinematically redundant manipulators with respect to a given critical task. Techniques are developed for analyzing the manipulator's workspace to find regions which are inherently suitable for critical tasks due to their relatively high level of failure tolerance. Then, constraints are imposed on the range of motion of the manipulator to guarantee that a given task is completable regardless of which joint fails. These concepts are illustrated for a PUMA 560 that is used for a three-dimensional positioning task.>