五轴数控系统旋转轴快速平滑插补控制策略

Fast Smooth Interpolation Control Strategy of Rotary Axes for Five-axis CNC Systems

在五轴联动加工中,刀轴矢量与旋转轴运动坐标之间存在非线性关系,刀轴矢量的平滑过渡不能保证旋转轴的平滑运动,尤其是当刀轴矢量接近机构奇异点时会引起旋转轴的剧烈震动,导致伺服报警,甚至损伤机床部件。通过分析旋转轴线性插补和矢量插补过程中刀具姿态的变化情况,抽象出刀具姿态误差模型。根据加工允许的刀具姿态误差,在矢量插值段中插入线性插值段,防止靠近奇异点处产生的旋转轴急速转动。结合指令行程和旋转轴性能进行旋转轴插补速度钳制,使用三次样条曲线对矢量插值段和线性插值段进行平滑连接,保证整个插补过程中速度的连续平滑。试验结果表明,本策略可以在满足刀姿误差要求的同时,实现旋转轴的快速平滑插补,并且已经应用于某航空结构件的批量加工生产中。

In the five-axis machining,due to the non-linear relationship between the tool orientation vector and the rotary axis coordinates,smooth interpolation movement of rotary axes cannot be ensured by smooth transition of the tool axis vector.Especially when the vectors pass through the singular point or its neighborhood,the strenuous mechanical vibration of the rotary axis causes the servo alarm,even damages the machine parts.The tool posture error model is constructed by analyzing the changing situation of the tool posture in the process of the rotary axis linear interpolation and vector interpolation.According to the allowable tool posture error in five-axis machining process,the linear interpolation segment is inserted into the vector interpolation segment to avoid the rapid rotation movement of the rotary axes close to the singular point.Then the limiting velocity is determined according to the linear interpolation segment and the performance of rotary axes.Finally,a cubic spline curve is used to eliminate the discontinuity of speed produced on the boundary of the range which performs linear interpolation and the range which interpolates by the vector interpolation,and smooth operation is realized.Experimental results show that the fast smooth interpolation of rotary axes is feasible,while maintaining accuracy required with respect to the tool posture error,and is applied to the batch process of a certain structural part.