Retrieving Lost Stiffness of Planar Wire-Actuated Parallel Manipulators after Failure

In this paper, the effect of wire failure on the stiffness of planar wire-actuated parallel manipulators is investigated. Specifically, the stiffness matrix of the manipulator before and after failure is formulated and the effect of failure on the stiffness maps over the workspace of the manipulator is investigated. It is demonstrated that by changing the anchor position and mobile platform orientation, the lost stiffness due to failure of a wire or motor can be retrieved partially. Variation of the stiffness map area versus anchor position and/or mobile platform orientation of an example wire-actuated parallel manipulator are plotted. Through examination of these plots, optimum anchor position and mobile platform orientation can be identified to maximize the area of the stiffness map.