New indices for performance evaluation of cable-driven parallel robots: Motion/force transmissibility

Cable-driven parallel robots (CDPRs) have attracted considerable attention due to their enlarged workspaces and high acceleration values. However, no very intuitive and universally applicable indices have been developed to evaluate CDPR performance. By modifying a general motion/force performance index proposed by Sutherland and Roth, this paper proposes a unified transmission index to quantitatively evaluate the motion/force transmissibility of CDPRs. This index is frame-free and relative to singularities. Furthermore, the power coefficients of the positive and negative output motion directions are calculated. Thus, the fundamental issue of CDPR implementation, namely, that the cable can transmit only positive force, is considered in this performance evaluation method. To introduce the performance evaluation method and transmission index, motion/force transmissibility analyses of a completely-restrained CDPR and redundantly-restrained CDPR are presented. Finally, the local transmission index (LTI) distributions of different cable geometry connections and cable attachment point positions are compared to determine appropriate geometric connections and geometric parameters.