Stiffness enhancement and motion control of a 6-DOF wire-driven parallel manipulator with redundant actuations for wind tunnels

Abstract

This article addresses the high dynamic positioning errors and poor force measurement precision of an aircraft model under the action of a wind load by means of a six degree-of-freedom wire-driven parallel manipulator with redundant actuations for low speed wind tunnels. First, an analytic expression of the stiffness of the manipulator is derived from the differential transformation principle. Then dynamic models of the end-effector and actuators are established, respectively. In view of the characteristics of redundant actuations, strong coupling, and nonlinearity, a modified proportional differential (PD) control strategy with feedforward compensation in the wire length coordinates is developed based on stiffness enhancement, and an optimal tension distribution is implemented for the enhancement of stiffness in lift, along-wind and pitching directions. Simulation results demonstrate that the dynamic positioning accuracy of the aircraft model is effectively improved by the control strategy based on stiffness enhancement as compared with the minimum wire tension control strategy.