Edge control in CNC polishing, paper 2: simulation and validation of tool influence functions on edges

Abstract

Edge mis-figure is regarded as one of the most difficult technical issues for manufacturing the segments of extremely large telescopes, which can dominate key aspects of performance. A novel edge-control technique has been developed, based on 'Precessions' polishing technique and for which accurate and stable edge tool influence functions (TIFs) are crucial. In the first paper in this series [D. Walker Opt. Express 20, 19787-19798 (2012)], multiple parameters were experimentally optimized using an extended set of experiments. The first purpose of this new work is to 'short circuit' this procedure through modeling. This also gives the prospect of optimizing local (as distinct from global) polishing for edge mis-figure, now under separate development. This paper presents a model that can predict edge TIFs based on surface-speed profiles and pressure distributions over the polishing spot at the edge of the part, the latter calculated by finite element analysis and verified by direct force measurement. This paper also presents a hybrid-measurement method for edge TIFs to verify the simulation results. Experimental and simulation results show good agreement.

Process mechanism in shape adaptive grinding (SAG)

“…the force increases more slowly than the grinding area when the tool offset increases). This is likely due to the effect of stresses at the boundary of the contact zone: as the area increases, boundary stresses do not reach any longer the center of the grinding area [6].…”

Effect of the inflated-pressure to the tool influence function for polishing using SR bonnet

“…Half of the polishing model is used to simplify the procedure and improve the solution efficiency. To simplify the simulation model, just the spherical part of the bonnet tool is used, and the polishing pad is ignored here [12]. Different with the normal bonnet, the SR bonnet has two layers, which are synthetic rubber layer and stainless steel layer, respectively.…”

Research on edge-control methods in CNC polishing

“…This concept has found applications in other areas [3]. One important requirement of mirror segments is achieving adequate control of edge mis-figure, as this can deflect stray light or infrared emissivity into the science beam, reducing contrast and signal-to-noise ratio [4]. For polishing in the semiconductor sector it can be important because of depth-of-focus limitations of photolithography, and the need to maximize silicon useful real-estate.…”