An automatic system for the avoidance of wrist singularities in anthropomorphic manipulators

The automatic management of kinematic singularities for trajectories planned in the operational space is a topic which is attracting a renewed interest in the scientific community. In fact, the numerical efficiency of the strategies recently proposed makes them suitable to be exploited in industrial contexts. The approach proposed in this paper can be collocated within this framework, since it allows executing trajectories in the operational space which pass through wrist singularities. It introduces several novelties w.r.t. known alternative strategies. First of all, trajectories in the operational space are planned on-the-fly, so that singularities are handled in real-time. This result is obtained by changing slightly the tool-frame orientation, while strictly preserving the assigned Cartesian paths and the time-laws. Furthermore, the approach is effective also for manipulators moving at standard operative speeds and it explicitly handles given limits on joint velocities and accelerations. Results are experimentally validated through an anthropomorphic industrial manipulator.