Rigid conformal polishing tool using
non-linear visco-elastic effect

Abstract

Computer controlled optical surfacing (CCOS) relies on a stable and predictable tool influence function (TIF), which is the shape of the wear function created by the machine. For a polishing lap, which is stroked on the surface, both the TIF stability and surface finish rely on the polishing interface maintaining intimate contact with the workpiece. Pitch tools serve this function for surfaces that are near spherical, where the curvature has small variation across the part. The rigidity of such tools provides natural smoothing of the surface, but limits the application for aspheric surfaces. Highly flexible tools, such as those created with an air bonnet or magnetorheological fluid, conform to the surface, but lack intrinsic stiffness, so they provide little natural smoothing. We present a rigid conformal polishing tool that uses a non-linear visco-elastic medium (i.e. non-Newtonian fluid) that conforms to the aspheric shape, yet maintains stability to provide natural smoothing. The analysis, design, and performance of such a polishing tool is presented, showing TIF stability of <10% and providing surface finish with <10A roughness.

Misfit of rigid tools and interferometer subapertures on off-axis aspheric mirror segments

“…This gives a powerful technique for smoothing mid-spatial frequency residuals originating from grinding and subaperture polishing techniques, providing the misfit is properly managed. The method is also relevant to assessing the limits of rotating a non-Newtonian polishing tool 9 to increase removal rate, as such tools adapt to the slow change in asphericity along a tool-path, but behave like hard tools at higher response-frequencies.…”

Improving smoothing efficiency of rigid conformal polishing tool using time-dependent smoothing evaluation model

“…The use of a lowered drive pin hole allows the original RC lap to overcome the gradient pressure effect, which is induced by the moment from the shear force on the workpiece surface [4]. When polishing hard ceramic materials such as RB-SiC, the polishing pressure is higher (>1 psi) than the conventional range (0.2 psi−0.6 psi).…”

“…In 2010, Kim and Burge developed a rigid conformal (RC) lap using a visco-elastic non-Newtonian fluid to overcome the conflict between the desired rigidity and flexibility for large polishing laps [4]. Compared with active stress laps [5] and semi-flexible tools [6], an RC lap provides numerous advantages, such as ease of large-scale manufacture, superior surface roughness, and a highly stable theory-like tool influence function (TIF).…”

Manufacture and final tests of the LSST monolithic primary/tertiary mirror

“…Figure 3 shows three bending modes of the combined M1-M3. [9], [10] containing a layer of non-Newtonian fluid between a stiff metal disk and (on the polishing side) a thin rubber diaphragm covered with synthetic polishing pads. We used RC laps with diameters of 35 cm, 25 cm and 12 cm.…”