Kinematic performance evaluation of high-speed Delta parallel robots based on motion/force transmission indices

Motion and force transmission indices are a common measure for the kinematic performance analysis and optimization of parallel manipulators. However, a separate consideration of the constraint characteristics is inevitable for the analyses of limited-dof parallel manipulators. Such separation may distort the performance evaluation as the design parameters of parallel manipulators are highly coupled. In this context, different formulations for the transmissibility and constrainability of parallel manipulators based on the notion of power coefficients and pressure angles are revisited and applied to the performance evaluation of a non-overconstraint Delta robot, a well-known lower-dof parallel robot. Following the concept of pressure angles, a physically meaningful measure is proposed, which aggregates the transmission and constraint characteristics into a single index. The simple definition does not require the tedious computation of the normalization factor as used for power coefficients. Moreover, the applicability of the different formulations for the performance evaluation and optimization is critically discussed revealing insights into the particularities of the different indices and their interactions as well as proving the validity of the new approach.