Control of an Overactuated Cable-Driven Parallel Mechanism for a Radio Telescope Application

The large adaptive reflector is a Canadian design concept for a new type of large-scale radio telescope. This new telescope would be composed of a reflector made of individually actuated panels and a multitethered feed platform held aloft by an aerostat. This paper focuses on the position and orientation control of the feed platform. Models of both the cables and the feed platform are first derived. Then, a control strategy adapted to the particular system's dynamics is designed. This control strategy is based on a cascade-control architecture, in which the inner control loop adjusts the tension in each cable. This inner loop controller is synthesized using the H-infinity optimal-control technique. In addition, gain scheduling is used to adapt the H-infinity optimal controller to the cable lengths. The outer control loop adjusts the pose of the feed platform, using inverse-dynamics control and PID control. The model derived is coupled to the multiloop controller, and simulations are run to evaluate the performance level of the control strategy.