Abstract: One of the essential roles, a parallel manipulator plays, is to transmit the motions and forces between the inputs and outputs. When evaluating the performance of a parallel manipulator, the motion and force transmissibility based on the essential property should be considered. In screw theory, the reciprocal product of a twist and wrench screw is indeed the instantaneous power of the force acted on the rigid body in the direction of movement. Via the ratio coefficient method, the ratio between the actual instantaneous power and the potential maximum power is commonly defined as the evaluation index. One of the vital issues for the functional index is how to calculate the maximum transmission power effectively. According to the different combinations of the wrenches and twists, the calculation of maximum power is divided into five aspects, and the detailed derivation and proof to every aspect is given. In particularly, the improved characteristic point method is introduced to build the effective calculation model for the case that the wrench and twist of the rigid body are both floating. Three typical parallel manipulators are taken

Key words: parallel manipulator;motion/force transmission;maximum transmission power;characteristic point method