ＮＣ加工命令の高速な生成手法 逆オフセット法の高精度化

Abstract

Molds and dies are usually fabricated using 3-axis NC milling machines with a spherical cutter. In order to avoid gouging problems in the milling process, a tool reference surface representing the offset shape of the designed surface is computed prior to the cutter path generation. Inverse offset method is used in practice which approximates the tool reference surface as a set of dense points. These points are usually derived as an elevation map of uniform grid points on the xy-plane, therefore distance between the points on the near vertical surface often becomes larger than the acceptable value. Such grid based computation causes stair-case errors on the wall shape, which also deteriorate the surface quality. In this paper, the authors propose an improvement of the inverse offset method. Our method computes the points on the tool reference surface by using additional two grids on the yz-plane and zx-plane. Different from the conventional method, proposed method can control the distance between the points on the tool reference surface being smaller than a certain constant value. Most part of the computation in our method can be accelerated by using the hardware power of the polygon rendering LSI, which is already equipped in most PCs. An experimental program is implemented and some computations of the tool reference surfaces are demonstrated.