Design And Research On Adjustment Mechanism For Secondary Mirror Of Large Aperture Telescope

Telescopes are the key tools used by human to explore the universe and distant stars.Domestic and foreign research efforts on large aperture and large resolution telescopes are constantly deepening.The core components of the telescope are main mirror and secondary mirror,and the third mirrors individually.In the imaging process of the telescope,influenced by factors such as gravity,vibration,and environment,the relative positional change between the primary and secondary mirrors has a great influence on the imaging performance of the whole system,so the adjustment link must be set.Considering the factors such as power consumption and portability,it is generally used to adjust the secondary mirror.The article is based on the study background of a 4 meter diameter secondary mirror,research on the design of the secondary mirror adjustment mechanism is carried out.The structure of the secondary mirror adjustment mechanism designed in this paper adopts the 6-RRRPRR configuration.First,the inverse kinematics model of the secondary mirror adjustment mechanism is derived using Newton-Raphson method and vector analysis method.Then the least squares method and Newton-Raphson method are used to describe the positive kinematics of the adjustment mechanism.Considering the precision range of the pose error between the primary and secondary mirror of the telescope,the design of the secondary mirror adjustment mechanism must meet relatively precision requirements.By establishing an equivalent pose error model,the accuracy of the secondary mirror adjustment mechanism based on Monte Carlo method is analyzed.It is proved theoretically that the secondary mirror adjustment mechanism designed in this paper can meet the precision requirements,the configuration of the mechanism is proved reasonable.And the result of the standard deviation of the pose error is obtained.After the theoretical configuration was designed,the three dimensional modeling of secondary mirror adjustment mechanism is completed through component selection,design of single foot displacement actuator,design and optimization of offset hinge,design and lightweight treatment of upper and lower platform.There are two main design highlights in the overall structure design process: One is the first use of a small-lead planetary roller screw,which has a compact structure,high rigidity,and a large load.The second is the use of self-designed and improved offset Hooke hinges,effectively improving the stiffness of the hinge.And the electrical system is also designed in detail.The secondary mirror adjustment mechanism has strict stiffness requirement.First the simulation analysis of the mechanism is carried out,including stiffness analysis and static analysis under extreme conditions,the results meet the design requirements..Moreover,through analysis and comparison,it is proved that the selection of planetary roller screws can enhance the stiffness greatly compared with ordinary ball screws.Finally,a simple kinematic performance test is carried out on the adjustment mechanism of secondary mirror.The result shows that the error between the test value and the input value in the program is very small,which shows the correctness of the control algorithm of the secondary mirror adjustment mechanism,and also proves the rationality of the configuration and structural design.