Kinematics analysis of 3-RCU 3-DOF parallel robot for a secondary mirror based on screw theory

With the development of astronomy, the resolution of the telescope is required to be higher and higher, and higher requirements are put forward for the support of the secondary mirror. The traditional four wing beam support structure can realize automatic focusing, but it cannot actively correct the pose of the secondary mirror. Therefore, it is of great practical significance to analyze two rotating and one moving 3-DOF secondary mirror support mechanisms to adjust the focal length and pose of the secondary mirror relative to the primary mirror real-timely, stably and accurately. To meet the requirements of a 3-DOF parallel platform for a telescope secondary mirror, the 3-DOF configuration and kinematics analysis based on screw theory were carried out. The constrained screw theory is used to analyze the 3-RCU three struts telescope secondary mirror parallel platform. According to the driving and constraint characteristics of the two turn one shift 3-DOF parallel robot, the kinematics model is established and the kinematics simulation is carried out. The simulation results show that the parallel platform has the required two rotational degrees of freedom and one translational degree of freedom, the rotation range is ±1°, and the translational range is ±2mm, the resolution of θ degree of freedom is 1'', ɸ degree of freedom is 1'', and the resolution of Z degree of freedom is 100nm, which satisfies the requirements of adjustment range and resolution of secondary mirror adjustment.