Modelling and measurement of polishing tool influence functions for edge control

Abstract

We present progress on our development of edge control for fabrication of mirror segments potentially for the European Extremely Large Telescope (E-ELT). Zeekoś Bonnet polishing technology has been adopted to achieve the form correction target. Like other Computer Numerical Controlled (CNC) polishing, accurate and stable tool Influence Functions (IFs) are important. Particular challenges arisen when polishing up to edges where the geometry of the IFs created by a bonnet changes. We described a model based on measured IFs data that allowed us accurately to predict the edge profile. To obtain IFs at the edge, data from interferometers and profilometers have been stitched. Numerical models with empirical Ifs as input data have been used to predict edge profiles with some preliminary success.

Modelling and simulation of mid-spatial-frequency error generation in CCOS

“…These optical systems have put forward the higher requirements (i.e., MSF errors, surface roughness, and surface defects) of optical elements than those in the traditional optical systems. Consequently, in order to achieve high performance optics in advanced optical systems, various sub-aperture polishing technologies have been well developed, including Magnetorheological Finishing (MRF) [4], Ion Beam Figuring (IBF) [5], Plasma Jet Machining (PJM) [6] and Bonnet Polishing (BP) [7][8][9], etc.…”

Research on edge-control methods in CNC polishing

“…There are published theoretical reports on modelling edge-effects in polishing, one studying the parametric tool influence functions [5]. Other reports [6,7] considered a "skin model" related to the Preston equation. Further reports [8,9] have presented experimental data showing variation of tool influence functions when encroaching an edge, delivering improved edge performance.…”