Positioning And Orientating Control Study On The Feed Support System Of A Large Radio Telescope

As part of the Five-hundred-meter Aperture Spherical Telescope (FAST) project from the National Astronomical Observatory, this work carries out dynamics and control all-in-one simulation research and feedback control scheme study on the moving-car platformless feed support system, which is one of the key technologies of FAST.In order to simulate dynamics of the large-scale time varying cable network combined with a Stewart parallel mechanism, which arises from the moving-car platformless feed support system, this paper implements a large-displacement first order continuous long cable element, uses it as the base to simulate dynamics of winding cable and sliding cable through fixed pulley, and numerically solves the time varying cable network and rigid bodies combined system under the framework of flexible multibody dynamics.To achieve high precision positioning and orientating control in large-range tracing of the radio telescope feed, this paper proposes a terminal feedback control scheme by directly measuring the position and orientation of the platform to be controlled. Nonlinear control for distributing tension among cable network is applied simultaneously with positioning control of the cable drive architecture and effectively avoids runtime cable over-sagging. Feedback control scheme for the feed support mechanism consisting of a large scale cable drive architecture, an orientating platform and a Stewart platform is verified through field and virtual control tests. For the measurement noise problem, this paper proposes a real time filter based on frequency analysis. Derived from traditional least square polynomial fit filter, the new filter employs dynamic frequency analysis and prediction technique, making the filter-introduced-delay only one third of the sampling period and particularly suits applications where real time is heavily demanded. Application of the proposed filter improves control effect remarkably in the flexible-supported Stewart platform vibration control experiments. This paper constructs a set of feedback control simulation system based on flexible multibody dynamics. Dynamics and control all-in-one simulation is made on tracing control experiments of the 50-meter-scale cable driven trolley and vibration control experiments of the flexibly supported Stewart platform, results of which generally agree with the corresponding physical experiments. This paper then conducts simulation research on the 500-meter-scale moving-car platformless feed support system employing the feedback control simulation system based on multibody dynamics. Simulation experiments on the virtual digital model coupling large-displacement time varying mechanism and feedback control components are carried out on PC to optimize the mechanical structure,control algorithms and parameters and to investigate positioning and orientating precision of the feed in long term tracing under wind load. Quite a lot of result data from systematic virtual feedback control experiments are processed and provide design advices and reference for construction of the feed support system for FAST.