An evaluation approach for motion-force interaction performance of parallel manipulators with closed-loop passive limbs

Abstract

Motion/force transmissibility and constrainability are common and widely used measures for performance evaluation and dimension optimization of parallel manipulators (PMs). However, the transmission and constraint indices in current use do not seem simple or intuitive for PMs with closed-loop passive limbs due to the difficulties in the wrench identification. To deal with this problem, this paper presents a blocking-and-actuating strategy to evaluate the motion-force interaction performance of such PMs. On this basis, the distal wrenches and proximal wrenches are identified inside the closed-loop passive limbs. Note that both of these wrenches are physically available, and they are distinct from the pure transmission and pure constraint wrenches. Examples of identifying these wrenches inside the passive limbs of some typical PMs are presented. Several performance indices are then defined based on the power coefficient via screw theory. Based on this foundation, this paper proposes a generalized approach for the coupled motion/force transmissibility and constrainability evaluation of PMs with closed-loop passive limbs. The motion-force interaction performance evaluation of a spatial 3-P(SS)S (P, actuated prismatic joint; S, spherical joint) PM with closed-loop passive limbs is finally derived to illustrate the generality and validity of this evaluation approach. Furthermore, results show that the proposed approach can reveal the effect of the structural parameters inside closed-loop passive limbs on the motion-force interaction performance.