Design of a parallel kinematic manipulator (PKM) with actuation redundancy is one of the main issues in the field. In this paper, the
local minimized transmission index
(LMTI) is proposed as the motion/force transmissibility evaluation criterion for such a manipulator. The optimum kinematic design of the 4-
SS-PU PKM with actuation redundancy is then carried out based on this index and the optimized parameters are given. For the purpose of comparison, the transmission performance of the 3-
SS-PU PKM without redundant actuation is analyzed. Performance comparison shows that the motion/force transmissibility and orientation capability have been improved greatly by the introduction of actuation redundancy. The LMTI proposed here can be applied into the optimum kinematic design of other parallel manipulators with actuation redundancy.