VARIABLE-FEEDRATE CNC INTERPOLATORS FOR CONSTANT MATERIAL REMOVAL RATES ALONG PYTHAGOREAN-HODOGRAPH CURVES

An NC system that machines a curved shape at fixed depth of cut experi ences time-varying cutting forces due to the 'curvature effect'-the ma terial removal rate is higher than nominal in concave regions, and low er in convex regions. A curvature-dependent feedrate function that aut omatically compensates for this effect is formulated, and it is shown that, for Pythagorean-hodograph (PH) curves, the periodic real time co mputation of reference points in accordance with this function can be analytically reduced to a sequence of root-finding problems for simple monotone functions. Empirical results from an implementation of this variable-feedrate interpolators on an open-architecture CNC milling ma chine are presented and compared with results from fixed-feedrate inte rpolators. The curvature-compensated feedrate scheme has important pot ential applications in ensuring part accuracy and in optimizing part p rograms consistent with a prescribed accuracy. (C) 1998 Elsevier Scien ce Ltd. All rights reserved.