A real-time surface interpolator methodology for precision CNC machining of swept surfaces

A real–time surface interpolator is developed, to machine a family of swept surfaces directly from their high–level procedural definitions. All the computations required for machining are performed in real time based on the exact surface geometry, including tool path planning, tool path interpolation, tool offsetting, and tool path step–over to achieve a prescribed scallop height. A G–code command (G05) is introduced, to concisely communicate the precise surface geometry and all necessary process parameters to the controller. The swept surface interpolator offers profound accuracy and efficiency advantages over the traditional approach of generating voluminous piecewise–linear/circular tool path approximations as a preprocessing step. For example, in one instance a 36,000–line piecewise–linear (G01) approximate part program file is replaced by a 3–line exact swept surface (G05) part program file. The methodology is verified by machining a variety of swept surface forms in aluminum and wax, using a 3–axis milling machine with the surface interpolator incorporated into an open–architecture CNC controller.