Research On Tool Radius Compensation Algorithm Of Cnc System Supported By NURBS Interpolation

The module of tool radius compensation plays an important role in the CNC system.In the process of contour machining,realizing tool radius compensation algorithm affects the machining accuracy of the machine tool and the machining quality of the machined parts.With the continuous research of NURBS interpolation,some foreign companies have successfully NURBS CNC system interpolation used in high-grade machine tool,so the NURBS interpolation algorithm will become the mainstream method of free form curve and surface processing.Because there has not yet appeared on the NURBS algorithm of tool radius compensation,with curved surface parts in cutter radius compensation,the CAM software can only use a huge amount of micro-line data to approximate this contour of free surface,which must lead to decreased efficiency and accuracy.Therefore,in order to solve this problem,this paper will establish a complete set of NURBS tool radius compensation algorithm.Compared with the traditional trajectory(line segments and arc),NURBS is more complex,not to consider the problem with the tool radius compensation of original thinking,such as in the calculation of single NURBS cutter radius compensation algorithm,we need to consider the self-intersection of NURBS equidistant curve,this is never encountered in the traditional tool radius compensation algorithm.After processing the NURBS interpolation G code generated from the CAM,it needs to detect whether the NURBS curve is smooth,the non-smooth of curve need to be segmented pretreatment.For a single smoothing NURBS cutter radius compensation algorithm,this paper solved the problem of self-intersection of equidistant curve by dispersing NURBS method.In the calculation of tool radius compensation algorithm for shortened type with two adjacent tracks including NURBS,the intersection of cutter center track are sometimes more,So this paper can accurately judge and calculate the intersection by reversing search algorithm.In the algorithm of tool radius compensation for extended type,according to the actual processing parameters of the machine: the maximum acceleration,turning time and radius of the cutter calculates the critical deflection angle about the three parameters,compared with the deflection angle of two adjacent sections of track for extended type,so as to choose a way to transition to improve the machining efficiency.At present,the global interference detection method of the tool center path can only consider three sections of trajectory,the look forward overcutting process in this paper can detect and deal with the interference problem of more tool center tracks.In order to output the tool center path by G code which contains the NURBS form,the NURBS discrete offset points are used to approximate by the method of extracting feature points.