AN APPROACH FOR ENSURING MANIPULATOR TIP ACCURACY NEAR SINGULARITIES

An approach for ensuring both manipulator tip accuracy and feasible joint rates near singularities is presented for serial-chain manipulators. The approach is based upon joint rate truncation and on-line planning of a suitable alternative end effector velocity. Screw quantities reciprocal to the nontruncated joint axes are used to define feasible alternative motions. Optimization, subject to these reciprocity-based motion feasibility constraints, is used to find an alternative velocity satisfying priority objectives of the original desired motion. In this work, alternative velocity components satisfying end tip translational accuracy at the sacrifice of minimal angular error are derived. Furthermore, a method for resolving the reciprocal screw quantities required to enforce alternative motion feasibility is presented, The method is suitable for manipulators having at least one pair of intersecting revolute axes. Analytical and numerical results are presented to illustrate the alternative velocity planning approach.