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Hui Li 1,2 and Rui Yao 1,2
Academic Editor:Yuanying Qiu
1, The National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing 100012, China
2, Key Laboratory of Radio Astronomy, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing 100012, China
Received 1 November 2013; Accepted 5 February 2014; 20 March 2014
This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
1. Introduction
Cable-driven parallel robots have many important applications over the past decade. One is verified in the Five-hundred-meter Aperture Spherical radio Telescope (FAST) which is being built in southwest China [1]. The giant telescope has a relatively light airborne focus cabin carrying the precise expensive feed receivers to observe stars in the sky. Because of its large size, it is very difficult to build a solid support structure between the cabin and the ground. Flexible cables, however, provide the possibility and further conveniences beyond other means: light weight, very large ranges of motion, and little inertia. The cable-driven parallel robot used in the FAST telescope might be the largest robot over the world, as shown in Figure 1. As the end effector, the 30-ton focus cabin is supported and driven by 6 parallel steel cables so that it can move in a large calotte, so-called focal surface, which is about 206 meters in aperture. The 6 steel cables are, respectively, suspended by 6 steel towers more than 100 meters high and equally spaced on a circle of 600 meters in diameter. Each is driven by a capstan motor with the common tension force reaching tens of tons.
Figure 1: An overlook of FAST telescope.
[figure omitted; refer to PDF]
The FAST cable-driven parallel robot is a typical incompletely restrained parallel mechanism (IRPM) similar to the Skycam [2]. The gravity plays as the seventh cable to fully constrain the 6-degree-of-freedom (6-DOF) cabin. Obviously in this case the sagging effect should not be neglected for the 6 steel cables. Although the FAST robot has huge size, this fact makes it mainly different from many other fully or redundant restrained cable-driven parallel mechanisms, such as...