Workspace Optimization of a Very Large Cable-Driven Parallel Mechanism for a Radiotelescope Application

The 6-DOF cable-driven mechanism under study in this paper is a feed positioning device for the Large Adaptive Reflector (LAR). The LAR is a concept of a very large orientable radio antenna. The study aims at optimizing the geometry of the cable mechanism to maximize the portion of the desired workspace in which the mechanism can remain in static equilibrium under the predicted external forces and torques. A general test to rapidly compute if the set of external forces and torques can be balanced is developed. This test is applicable to mechanisms with an arbitrary number (minimum six) of cables. Architectures with six to nine cables are optimized and compared. The conclusion of this study is that the prescribed task is unlikely to be achievable by this type of mechanism. Some design guidelines to improve the performance of a large cable-driven mechanism kept under tension by an aerostat are also provided.