Task space stiffness analysis of wire driven parallel manipulator

A wire driven parallel manipulator is pulled by several wires on motors or passive devices over pulleys at the other ends. The motors or passive ends are mounted on a framed structure and the platform moves within the volume. Wires can apply only unilateral force and so these manipulators need redundancy in actuation and characterized by Force closure of the wire tensions. This article presents an analysis of and method for determining the force-closure workspace. Due to elastic behaviour of wires and proportional gain of motor controller, the moving platform exhibits directional stiffness in any position within workspace. The stiffness again also varies on all over the workspace. This article presents a detailed analysis of the task space stiffness behaviour of the moving platform. Illustrations are given with numerical results of analyses on example cases of 4-wire driven planar and 8-wire driven spatial manipulators.