Measurement of two-dimensional distribution of pure axial force in active polishing

We present a new technique of real-time measurement for the pure axial forc e distribution exerted by a full size active polishing tool on large. asphe ric surfaces. The technique uses art array of custom developed flat line lo ad cells incorporating semiconductor strain gauges that can withstand the l arge shear forces in polishing. Design, manufacture and characterization of the force sensor array and its instrumentation to the active polisher are described. In particular, thermal characterization of the sensors proved th at the temperature change by a few degrees required for a polishing tool ha s negligible effects on sensitivity and zero-point offset. Effects of non a xial force components were compensated with four independent half-bridge si gnals inside a sensor unit. This was further removed with a gap condition b etween the sensor array and the structural membrane, of which the latter fu nctions as a point of pushing and pulling the polishing lap. The sensor arr ay shows a potential usage in detecting and controlling the non-axial force components in operation. The real-time graphical map of axial polishing fo rce generated by the sensor array improved the polishing efficiency by at l east 30% compared to the traditional polishing technique.