大口径非球面反射镜误差分离组合加工技术

Fabrication of large aspheric mirror using multi-mode polishing based on error separation

为了解决大口径非球面反射镜材料去除效率与面形收敛效率之间的矛盾,提出了基于高低阶面形误差分离的组合加工技术。首先,分析了不同尺寸磨头对不同周期面形误差的控制能力。然后,比较了不同磨头的收敛效率与加工时间之间的关系。最后,根据大口径非球面反射镜加工过程中面形误差的特点,将大口径非球面反射镜的面形误差分离为低阶面形误差与高阶面形误差,使用不同加工方式分别对高、低阶面形误差驻留时间进行求解。通过多种加工方式组合加工的方法建立了具有针对性的加工策略,有效提高加工效率。结合工程实例,对一块口径为2.04m的非球面SiC反射镜进行了加工试验,单个组合加工周期内面形收敛效率达到61.2%。结果表明,高阶与低阶面形误差均得到较好的去除。材料去除效率与面形收敛效率均得到提高,达到了良好的效果,满足加工需求。

In order to improve material removal efficiency and error map convergence efficiency of large aspheric mirror, a multi-mode technique was introduced based on the separation of high and low order errors. First, the effect of tool size on period of surface error was analyzed. Then the convergence ef- ficiency and dwell time between small and big polishing heads were compared. According to the error features during the fabrication process of large aspheric mirror, the surface error map was divided to low-order and high-order frequency errors. The dwell time of different tools was calculated. Accord- ingly multi-mode polishing strategy was employed in terms of the low order and high order errors, thus improving the processing efficiency. A large aspheric mirror with the aperture of 2.04 m was pol- ished by the multi-mode technique. The result shows that the convergence rate is 61.20%in a single polishing circle. The low-order and high-order frequency errors are well removed, and the material re- moval efficiency and error map convergence efficiency are improved. Good processing results are a-chieved, which meet the demand of fabrication.