The two-axis steering mechanism installed in the FAST focus cabin can be seen as a universal joint consisting of two
ring beams and makes role in the process of real-time adjustment of the receiver orientation. The outer ring of the
mechanism is a large-span curve beam with strict mass and rigidity requirements. The aim of this paper is to develop a
simple and effective method for constructing a truss-shape structure for the outer ring under the upper-limit constraints
of certain structural weight and mid-span deflection. Two truss configurations for weight minimization problems are
presented. One assumes consistent beam height. The second design proposes varying heights along the ring. Analytical
deflections are given based on the theory of thin-walled beam in combination of bending and torsion. In numerical
optimization of the structure, some key geometrical parameters are selected to be optimized. The optimization is
subsequently achieved by the steepest descent method, which is based on the sensitivity analysis of the variables
(reduced to be dimensionless) in each iteration. Several sets of initial conditions for optimization have been generated
randomly. Corresponding optimum results have small mutual deviations. Finally a comparison of the two designs
considering stiffness-to-mass ratios is given in the numerical examples.
The focus cabin suspension of the FAST telescope has structurally weak-stiffness dynamics with low damping
performance, which makes it quite sensitive to wind-induced vibrations. A reasonable estimation about the damping is
very important for the control performance evaluation of the prototype. It is a quite difficult task as the telescope is no at
available yet. In the paper, a preliminary analysis is first made on the aerodynamic damping. Then a series of
experimental models are tested for measuring the total damping. The scales of these models range from 10m to 50m in
diameter while 6 test parameters are specially designed to check the damping sensitivity. The Ibrahim time domain (ITD)
method is employed to identify the damping from the measured cabin response. The identification results indicate that
the lowest damping ratio of the models is about 0.2%~0.4%. Friction-type cabin-cable joint seems to have main
influence on the system damping.
The present paper presents the concept and integrated modeling analysis of a novel mechanism for supporting segmented dishes for radio telescopes and eventually segmented mirrors of optical telescopes. The concept comprises a novel type of hexapod with an original organization of actuators hence degrees of freedom, with a swaying arm based design concept for the connecting joints between panels/segments, thus achieving an iso-static master-slave active surface concept for any triangular and/or hexagonal panel/segment pattern. The integrated modeling comprises all the multifold sizing and performance aspects which must be evaluated concurrently in order to optimize and validate the design and the configuration: in particular kinematic behavior, dynamic analysis, wavefront error and sensitivity analysis. Some experimental verifications already performed validating single aspects of the integrated concept are also presented with the results obtained.
Operation of the Five-Hundred-Meter Aperture Spherical Telescope (FAST) requires accurate positioning and movement
of the receiver platform on a spherical workspace with a radius of 160 m. Supported above the 500 m diameter main
reflector it has to be positioned with an accuracy of several millimeters. To achieve this, the receiver is located in the
receiver cabin that is suspended on six cables. The cables are attached to six towers located on the circumference of the
main reflector and can be actuated via six capstans. In this paper a control concept for the cable-system is presented.
Using a detailed mathematical model of the system the performance of the control and the sensitivity to wind and other
disturbances is evaluated via simulation. The mechanics are modeled via FEM, the capstan-drives as lumped-mass
elements including nonlinear effects like friction and backlash. The control scheme presented consists of position control
loops for the capstans and numerically optimized PID-controllers for the positioning of the cabin platform.
The National Astronomical Observatories of China (NAOC) plan to build a 500m radio telescope in southern China .
The telescope has a fixed but active main reflector, and large sky coverage is achieved by moving the receivers on a
focus surface 160m above the main reflector. The paper describes recommended design concepts for the cable system,
the drives and the cabin mechanisms, which position and point the receiver platform. The simulation study, which is
basis of the presented results, was executed by engineers of the Technical University Darmstadt under a contract of
NAOC in cooperation with two visiting engineers of NAOC and lead by the author . The analysis results and end-toend
simulations itself are described in more detail in two other contributions to this conference , .
This paper devotes to the working space analysis of the main positioning system of FAST cabin suspension, a
flexible-cable-driven parallel manipulator. The problem formulation is deduced through equilibrium analysis of the cabin
platform and suspension cables, which changes subsequently into a nonlinear constrained optimization intending a
uniform allocation of the six cable tension force. The analysis verifies the accessibility of focus cabin to the whole focus
surface. The optimization investigates the orientation of the focus cabin under equilibrium and the optimal cable forces,
as well as elaborates their importance in the finite element modeling of the cable-cabin system and the respective layout
designs of the rotator, Stewart stabilizer and capstan motors. In the end, the influences of the tower height and the
position of mass center of the focus cabin on the optimization results are discussed.
FAST (Five-hundred-meter Aperture Spherical radio Telescope) focus cabin is driven by 6 cables, moving on a
spherical cap of ~ 206 meters in diameter. In order to achieve the required pointing accuracy of the telescope by
positioning and orienting the receiver properly, X/Y positioner and Stewart manipulator are employed. In addition,
reaction mass dampers (RMD) are investigated to depress the cabin's vibrations at high frequencies.
In this paper, a simulation model of FAST focus cabin is created. Control simulation is carried out to evaluate
control performance of the focus cabin. As a result of this simulation work, X/Y positioner, Stewart manipulator and
reaction mass dampers show satisfied performance in compensating the residual position and orientation errors and
depressing vibrations. The simulation work approves the feasibility of this engineering concept, and also paves an
efficient approach for optimization in the future design work.