数控机床进给系统的摩擦力特性

On the Friction Characteristics of CNC Machine Tool's Feed Drive System

基于FANUC数控系统FOCAS函数集提出了实现进给系统伺服电机的力矩电流和工作台位置实时采集的方法.利用三次样条函数,给出了力矩电流和工作台位置离散数据连续化的处理方法,进而提出了进给系统摩擦力辨识算法.利用试验结果,分析了进给系统摩擦力的均值特性和频谱特性,结果表明:由于丝杠螺母副与两端轴承不同轴,其摩擦力局部均值呈现悬链形式,其总体均值在低速进给时较大,随进给速度增加迅速下降;当进给速度达到一定值后,随进给速度增大,摩擦力略有增加.在进给系统工作过程中,滚动体在丝杠滚道内的周期运动、丝杠波纹度、滚动体进出丝杠螺母副及导轨滑块内循环轨道将激励起摩擦力对应的基频和倍频波动.

Based on the FOCAS function set for the FANUC numerical control system, a real-time acquisition method of worktable position and servo motor torque current for a feed drive system is proposed. The continuous functions of the worktable position and the servo motor torque current for time are determined by virtue of inserting their discrete data with the cubic spline function, respectively. Then, an algorithm is proposed to identify the friction of the feed system.The characteristics of average value and spectrum for the friction are analyzed by using the experimental data. The results demonstrate that the local average frictions take on a catenary form because the lead screw-nut pair and the bearings at both ends are not concentric. The average friction over the experimental feed length is larger when the feed speed is low,and it decreases rapidly with the increase of the feed speed. However,when the feed speed reaches a certain value, the friction force increases slightly with the increase of the feed speed. In the operating process of the feed drive system, the periodic motion of rolling elements inside the screw groove, screw waviness, balls going in and out of the screw-nut pair and circular rails in the guides can motivate the corresponding fundamental and harmonic frequencies of the friction.