五轴微段平滑插补算法

Smooth Interpolation of Short Lines in Five-axis CNC Machining

在五轴加工编程中,计算机辅助制造系统对曲面加工通常采用以折代曲,采用大量的微小G01直线段来加工曲面,在曲率半径较大的工件表面会出现明显折痕,严重影响工件表面的加工质量。为提高五轴数控加工工件的表面质量,提出一种五轴微段平滑插补算法。该算法考虑五轴加工中刀位数据的量纲差异,根据相邻数据点间的线性轴长度、线性轴的夹角和旋转轴角度变化量识别五轴数控加工程序中非连续微段和连续微段加工区域。对非连续微段加工区域按照原始直线段和旋转轴直接插补,从而保证加工精度。对连续微段加工区域,先通过五维变量获取节点参数,采用最小二乘法对指令点在允许的精度范围内进行修正;对修正后的指令点采用4点构造法计算二阶切矢,根据连续微段的指令点修正值,节点参数值和对应的二阶切矢值获取二阶连续的三次样条曲线;在二阶连续平滑的曲线上进行实时插补计算,控制机床进行五轴加工。试验结果表明:通过提出的五轴微段平滑压缩算法拟合后的路径要更加接近原始的曲面模型,平滑处理过的实际工件加工表面也要优于未进行处理的工件加工表面,提高了五轴自由曲面的表面质量。

In the programming of five-axis machining, computer aided manufacturing system manufacture usually uses lines instead of curves while surface machining. A large number of micro G01 straight line segments are used to machine surface, sharp creases will appear on surface of workpieces with large radius of curvature, which results in bad surface machining quality of workpieces. In order to improve the surface quality of workpieces machined by five-axis CNC machining system, a micro-line smooth interpolation algorithm for five-axis CNC machining is presented. In view of the dimensional difference of cutter axis vectors, our algorithm identifies discontinuous and continuous micro-line blocks of cutter axis vectors machining regions through the length of linearity axis, the angular variation of rotation axis and the intersection angle of linearity axis between adjacent command points. For the discontinuous micro-line blocks of machining regions, direct interpolation is conducted to guarantee the processing precision based on original lines and the rotation axis. For the continuous micro-line blocks of machining regions, get node parameters using five dimensions variables, least square method is used to correct command points in an allowed error range; Second-order tangent vectors of corrected command points are calculated by using four continuous corrected command points, cubic spline curves with continuity of second order are obtained according to corrected command points, node parameters and second-order tangent vectors; Real-time interpolation calculation is conducted on the second order smooth curves, machine tool is controlled to five-axis machining. Experimental results demonstrate that fitted path by smooth interpolation of micro lines in five-axis CNC machining is more close to the original surface model, the surface quality of smoothing pieces is better than the non-smoothing, our algorithm can improve the free curved surface quality of five-axis.