Pose Planning for the Feed Support System of FAST

A six-cable driven parallel manipulator and an A-B rotator in the feed support system of the Five-hundred-meter Aperture Spherical radio Telescope (FAST) are adopted for realizing the position and pose of nine feeds. The six-cable driven parallel manipulator is a flexible mechanism, which may not be stably controlled due to a small cable tension. The A-B rotator is a rigid mechanism, and its stability and accuracy can be improved by small pose angle. Based on the different characteristics, a pose planning function is presented. The optimization target of the pose planning function is to get the smallest pose angle of the A-B rotator, and the constraint condition can reflect the controllability of the six-cable driven parallel manipulator. Then, the pose planning realization process of the feed support system is proposed. Based on the pose planning method, optimized pose angles of the feed support system for the nine feeds are obtained, which suggests that the pose angle of the six-cable driven parallel manipulator changes from 0° to 14° and the pose angle of the A-B rotator changes from 0° to 26.4°. 1. Introduction China is now building the largest single dish radio telescope in the world in Guizhou province, which is called Five-hundred-meter Aperture Spherical radio Telescope (FAST) [1–3]. Figure 1(a) shows the conceptual design of the FAST. The feed support system of FAST includes two parts: one is a six-cable driven parallel manipulator with a large span that drives the feed adjustable mechanism equipped with a coarse positioning; the other one is a feed adjustable mechanism. Figure 1: FAST. (a) Conceptual design of the FAST. (b) Focus cabin. Figure 1(b) shows the feed adjustable mechanism. The feed adjustable mechanism looks like a cabin, and it moves on a focus surface. So it is also called the focus cabin. The diameter of the focus cabin is about 13？m. There are two main mechanisms in the focus cabin: an A-B rotator and a Stewart manipulator. As shown in Figure 2, nine feeds are fitted on moving platform of the Stewart manipulator. The feeds move on a focus surface to track the celestial sources, and the theoretical position and pose of the nine feeds are controlled by a six-cable driven parallel manipulator and an A-B rotator. A Stewart manipulator, fixed on the A-B rotator, is used to improve the position and pose accuracy of the nine feeds in real time. Figure 2: Nine feeds on moving platform of the Stewart manipulator. Poses of the nine feeds are redundantly controlled by both the six-cable driven parallel manipulator and A-B rotator.