Position analysis of a two DOF parallel mechanism - the Canterbury tracker

The forward and inverse kinematics of a two degrees of freedom (DOF) parallel mechanism for beam aiming applications is derived in closed form. The mechanism has three arms attached to a base via revolute joints. Another three arms are also attached to an upper platform via passive revolute joints. Each of the three base arms is connected to its respective opposing passive arm via a spherical joint. A central strut between the platform and the base is connected with spherical joints so that the platform retains the two rotational degrees of freedom with respect to the base. Any two of the three arms on the base are driven to set the required azimuthal and elevation pointing directions.