Improvement Of Active Lap Processing In Grinding Of 1.8m Primary Mirror

The computer controlled active lap (CCAL) is used to grind a 1.8m honeycomb primary mirror. One problem which is not totally solved by CCAL is the edge effect, also exists in many other fabricating methods. To reduce the CCAL edge effect, the pressure distribution on the contact face between lap and mirror is analyzed by finite element method (FEM). A new method is proposed to calculate the pressure curve from FEM results. A simplified model is used to approximate the pressure curve along the mirror radius when active lap covers the mirror center hole. The const-linear (C-L) model is used to describe the pressure curve when active lap overhang at the mirror out edge. The contact status between lap and mirror is also considered in this paper, and its influence is taken into the material removal rate calculation. The API's T3 laser tracker is used to measure the mirror surface shape and to check the correctness of the theoretical model. The results that we have got by now and the problems that still exist are reported in this paper.