Posture optimization of a 3-6R parallel mechanism for secondary mirror truss applied on large telescopes

Abstract

The traditional truss structure adopts a fixed form, which is the main reason for the over-height of the vehicle telescope. In order to achieve larger vehicle-mobile telescopes and solve the over-height problem, the new truss mechanism based on robotics is proposed in this paper. Based on the new structure, the posture and dimension parameters need to be determined. Stiffness has great effects on accuracy and resonance of the telescope system, which is influenced by the posture and dimension parameters. So the stiffness performance index is used to optimize the posture. Meanwhile, in order to simulate the force of the telescope in different states, translation evaluation index (TEI) and rotation evaluation index (REI) are represented in this paper. Wavefront aberrations can be obtained by establishing the relationship between TEI, REI and Zernike polynomials. The optimized posture is verified to meet the error requirement through this method and the accuracy is obviously improved through comparison.