Kinematics analysis of active reflector supporting mechanism for fast

In the application of active reflector units supporting mechanism for a large spherical radio telescope (Five-hundred meter Aperture Spherical radio Telescope: FAST), a spatial three-degree-of-freedom (DOF) parallel mechanism combining two degrees rotation and one degree translation is investigated. In this paper, the mechanism is described in detail and its inverse kinematics solutions are derived. The parasitic motion of this mechanism is analyzed, and the relationships between the parasitic motions and independent motions of the mechanism are illustrated, followed by the Jacobian matrix of the velocity equation. The distribution of conditioning index on the workspace of the mechanism is obtained. And the workspace of the mechanism is numerically generated. The analysis results prove that the parasitic motion is neglectable compared to the independent motion in this application and the mechanism can be used as the supporting mechanism of spherical radio telescope.