Research on Catenary Characteristics of FAST Tie-Down Cable and its Effect on Actuator and Joint

To study catenary characteristics of FAST (Five-hundred-meter Aperture Spherical radio Telescope) tie-down cable, this paper establishes tie-down cable equilibrium differential equation and cable length formula based on catenary theory, analyzes numerical simulation of multi-segment bar element method, and designs an experimental scheme. Taking 1×7 Ø12.7steel cable and Ø10 CFRP (Carbon Fiber Reinforced Polymer) cable for example, we can obtain three results respectively through manners mentioned above, and the agreement among them is excellent. Meanwhile, difference between results and elastic deformation of no-weight cable is not so big that catenary of two cables can be negligible. Further research shows that cable length is more sensitive to catenary than horizontal angle; cable longer deformation will benefit actuator to meet position precision effortlessly, however, stroke and velocity of actuator will increase and initial tension displacement of tie-down cable decrease correspondingly, this alteration should be compensated during reflector surface measuring and controlling; due to chord-tangent angle and tangential force is less than 1.28°and 241.4N, catenary effect on joint pose is weaker; generally speaking, CFRP cable has less catenary problem than steel cable, better mechanics characteristics, but bigger stroke and velocity for actuator and smaller initial tension displacement for tie-down cable. The research will provide references for design of tie-down cable, actuator, joint, and reflector measurement and control.