G-CODES FOR THE SPECIFICATION OF PYTHAGOREAN-HODOGRAPH TOOL PATHS ANDASSOCIATED FEEDRATE FUNCTIONS ON OPEN-ARCHITECTURE CNC MACHINES

A new class of machine codes for the specification of Pythagorean-hodo graph (PH) curve tool paths, and associated feedrate functions, is pro posed. The PH curves are a special family of free-form curves, compati ble with the Bezier/B-spline representations of CAD systems, that are amenable to real-time interpolation at constant or variable feedrate d irectly from their exact analytic descriptions. The proposed codes are compatible with 'ordinary' (linear/circular) G codes, and may be rega rded as extensions thereof. Compared to the customary approach of usin g piecewise-linear/circular approximations, they offer significant imp rovements in the accuracy, efficiency, data volume, and flexibility of part programs for free-form shapes. Experimental results from an impl ementation of these real-time PH curve interpolators on an 'open-archi tecture' CNC milling machine are also described. (C) 1998 Elsevier Sci ence Ltd. All rights reserved.