In context
By mid-2023, the Five-hundred-meter Aperture Spherical Radio Telescope (FAST) had been in formal operation for over three years, relying on a novel cable-driven parallel mechanism to position its feed cabin. While earlier studies often simplified cables as straight or parabolic, the need for precise pointing demanded a more accurate dynamic model that includes cable flexibility and vibration.
What was reported
Researchers from the National Astronomical Observatories of the Chinese Academy of Sciences presented a mechanical analysis of the six-cable-driven parallel mechanism used in FAST's feed support system. They first established a catenary model for a single cable under static equilibrium, considering both the cable's dead weight and elastic deformation.
For dynamic analysis, they employed the absolute nodal coordinate formulation (ANCF) to describe length-varying cable elements, deriving the dynamic equations for the entire cable. By incorporating constraints between the cables and the feed cabin, as well as at the cable outlet points, they obtained the full dynamic model of the six-cable mechanism.
Simulations using actual cable speeds from FAST operations showed that cable dynamic characteristics influence the feed cabin's pose. The simulated pose trends matched real observation data, with a maximum relative error not exceeding 20%.
Why it mattered
This work provided a more realistic model for large-span cable-driven parallel mechanisms, capturing the effects of cable vibration on positioning accuracy. It highlighted the limitations of current linear-model-based controllers under high acceleration or speed, pointing toward the need for advanced control strategies in large-scale precision automation.
"The simulation results show the influence of the dynamic characteristics of the cable on the pose of the feed-cabin, and the consistency of the simulation data of the feed cabin pose and the trend of the actual observation data."
Source: 《机器人》期刊 (robot.sia.cn) · Published 2023-07-08 · “基于FAST馈源支撑系统的索牵引并联机构的力学分析”