Virtual CNC system. Part II. High speed contouring application

This paper presents a trajectory planning strategy for maintaining the tool positioning accuracy in high speed cornering applications. A 3D contour error estimation algorithm is presented for determining the geometric deviation from arbitrarily shaped toolpaths. Two spline fitting strategies are developed for smoothening sharp corners. The under-corner approach reduces the toolpath length, and therefore the cornering time. This technique yields successful results when used with a high bandwidth servo controller (such as sliding mode control), capable of accurately tracking the commanded toolpath. The over-corner approach is based on stretching out the sharp corner with a smooth curve, which counteracts the ‘undercut’ caused by the large phase lag in low bandwidth servo controllers (such as P-PI control). The cornering feedrate is adjusted in the Virtual CNC platform, developed in the first part of this article, to ensure that contour error violation does not occur. The achieved cornering accuracy is verified in experiments, which are in close agreement with predictions obtained with the Virtual CNC.