Fast and High Precision Control Approach: Polyline Analysis and Optimal NURBS Interpolation for CNC Machine Tools

Abstract In CNC operations, smooth motions generated using a parametric curve such as NURBS, Bezier curve, and B-spline are crucial for surface quality and machine control. A parametric curve is formed by microlines in CAD/CAM software; however, instead of microlines, polylines are used to define a parametric curve to prevent an increase in NC-file size. It is also possible to see situations where smooth motion is not required due to production requirements. In these cases, point-to-point motion is necessary instead of smooth motion. In this study, a polyline analysis algorithm is proposed to classify the normal line and polyline within the NC-file. A global tool path smoothing method is also applied, where the data points in a polyline group are converted into NURBS because CAD/CAM software commonly uses NURBS as a parametric curve for precision control of CNC machines. In addition, this study presents an optimal feedrate scheduling algorithm for the NURBS curve that generates an optimal feedrate profile for each segment by considering critical parameters such as segment length, initial and final velocity of each segment, maximum jerk, acceleration, and velocity. As the proposed algorithm is compatible with existing feedrate scheduling methods in which different feedrate values at the transition point of the NURBS segments are determined, this study provides an important contribution to the literature. The proposed methods in this study are verified by operating a spherical surface using industrial NC-files on a 3-axis CNC-Milling machine. The proposed methods demonstrate effective performance in experiments that require precision production operations.