Failure recoverability by exploiting kinematic redundancy

Various physical limitations which exist in the manipulator inverse kinematic system, for example joint travel and velocity limits, induce inevitable motion errors. This paper deals with the problem on how to reconstruct such an inverse kinematic solution using redundancy, in order not to entail any task motion error. By analyzing the error due to hardware limitations with respect to the kinematically decoupled coordinates, we show that the recoverability limitation reduces to the solvability of a reconstruction equation under the feasibility condition. Next it is shown that the reconstruction equation is solvable if the configuration is not a joint-limit singularity. The reconstruction method is proposed based on the geometrical analysis of the recoverability of hardware limitations. The method has the feature that no task motion error is induced by the hardware limitations while minimizing a possible null motion error, under the recoverability assumed.