Research On A New 6-DOF Parallel Mechanism For The Secondary Mirror In Telescopes

As a high-precision instrument,an astronomical telescope is very strictly required maintain the relative positions of its primary mirror and secondary mirror.If the optical axis of the primary and the secondary deviates the telescope's tracking accuracy and optical system's imaging quality will be degraded.At present,astronomical telescopes often use six-DOF parallel mechanism to support and adjust the secondary mirror,so as to control the deviation of two optical axes within an allowable range.In this paper,a novel six-DOF parallel mechanism for the secondary mirror support system of astronomical telescopes had been researched including mechanism design,theory analysis,prototyping,and experiment.A novel six-DOF parallel mechanism of 3SPS+3(SP-U)type has been conceived,which manifests advantage in decoupling of DOFs between three-translation and three-rotation.The detailed kinematic processes of the mechanism have been carried out,including the configuration,singular position and kinematic problems.The solutions of kinematic problems are performed with numerical simulations for the models of inverse position,velocity and acceleration,positive position based on the numerical iteration method and the closed-form method.According to the structural features of the novel mechanism,this paper designed two kinds of flexible hinges and established a full prototype of the mechanism.The static stiffness of the flexible hinges was accessed by means of the flexibility matrix method.Considering the constraints of hinge angles,bar length and the component interference in the mechanism,we explored the mechanism's workspace by the analytic geometry method.Further,the prototype of the mechanism together with its motion control system was built.And the accuracy of the prototype and its location workspace as well as attitude workspace at the initial position were test by a laser tracker,the results show that the translational movement of the moving platform can reach ±3mm,the rotational space can reach ±1°.Finally,the fine test of the accuracy and repeatability of the prototype were fulfilled by the laser displacement sensors,get the repositioning precision in translation is less than 0.2?m and the repositioning precision in rotation is less than 0.2?.