Designing a robot manipulator with fewer actuators than the dimension of its configuration space – to reduce bulk, weight and cost – becomes feasible by introducing mechanical elements that lead to non-holonomic constraints. Unfortunately, the mechanical advantages of these non-holonomic designs are usually darkened by the complexity of their control. This paper deals with motion planning for parallel robots with non-holonomic joints shedding new light on their control strategies. As a case study, the motion planning problem is solved for a 3-ŬPU parallel robot, where Ŭ stands for a non-holonomic joint whose instantaneous kinematics are equivalent to that of a universal joint. It is thus shown how the three prismatic actuators can maneuver to reach any six-degree-of-freedom pose of the moving platform. The motion planning has been addressed as a control problem in the control system representation of the robot’s kinematics and a motion planning algorithm has been devised based on a Jacobian inversion of the end-point map of the representation. Performance of the algorithm is illustrated with numeric computations.

Presentado al 13th International Symposium on Advances in Robot Kinematics (ARK) celebrado en Austria del 24 al 28 de junio de 2012.

The research of the first two authors was supported by a statutory grant from Wrocław University of Technology.

Peer Reviewed