Analysis and resolution of singularities for a 5-DOF gryphon manipulator

Many industrial robots have only five axes. When a manipulator is approaching a singular configuration, a certain degree of freedom will be lost such that there are no feasible solutions of the manipulator to move into this singular direction. In this paper, the singularities of a 5-DOF GRYPHON manipulator are analyzed in detail and all the corresponding singular directions in task space are clearly identified. In order to resolve this singularity problem, an approach denoted Singularity Isolation plus Compact QP (SICQP) method is proposed. The SICQP method isolates the singular directions, maintains the exactness of the achievable directions and minimizes the tracking errors in the singular directions under the condition that feasible joint solutions must be obtained. The simulation results reveal that when a manipulator is near or at the singular points, the SICQP method may minimize the tracking errors to the extent possible.