总线式数控机床动态误差测量及辨识

Measurement and Identification of Dynamic Errors for Bus CNC Machine Tools

多轴联动高速加工中,运动参数引起的机床动态误差是产生零件加工误差的重要因素。针对EtherCAT总线型数控机床,以球杆仪QC20-W和工业以太网探头工具ET2000为测量工具,建立了机床动态误差和静态误差模型。首先基于齐次坐标变换理论建立球杆仪杆长变化量与机床动、静态误差的数学关系;然后根据这两类误差的不同特性,构建了以坐标位置表达的静态误差多项式及以速度、加速度的角频率及相位表达的动态误差低阶正弦多项式。并采用小波变换针对位置信息中的噪声进行降噪处理。最后采用最小二乘理论求解误差表达式中的未知系数。结果表明,指令速度为动态误差的主要因素,加速度为次要因素。在加速度不变,指令速度由20 mm/s依次上升至40、80 mm/s时,动态误差占总误差的比例由2.13%增加到11.74%、49.15%;指令速度不变,加速度由200 mm/s^(2)上升至800 mm/s^(2)时,动态误差占比由22.72%上升至26.83%。

In high speed machining with multi-axis linkage,the dynamic error of machine tool caused by motion parameters is an important factor to produce machining errors.In this paper,the dynamic error and static error models of EtherCAT bus CNC machine tools are established by using the rod instrument QC20-W and the industrial Ethernet probe tool ET2000 as measuring tools.Firstly,based on the homogeneous coordinate transformation theory,the mathematical relationship among the rod length variation and the dynamic and static errors of the machine tool is established.Then,according to the different characteristics of the two kinds of errors,we construct the static error polynomial expressed by coordinate positions and the dynamic error low order sine polynomial expressed by velocity,acceleration angular frequency,and phase.In order to obtain the angular frequency and phase information of velocity and acceleration in sinusoidal polynomial,Wireshark and ET2000 are used to capture the position information of axis,and the velocity and acceleration are obtained by differentiating.Wavelet transform is used to reduce the noise in position information.Finally,the least square theory is used to solve the unknown coefficients in the error expression.The results show that instruction speed is the main factor of dynamic error,and acceleration is the secondary factor.When the acceleration is constant and the instruction speed increases from 20 mm/s to 40 mm/s and 80 mm/s,the proportion of dynamic error in the total error increases from 2.13%to 11.74%and 49.15%.When the command speed is unchanged and the acceleration increases from 200 mm/s^(2) to 800 mm/s^(2),the proportion of dynamic error increases from 22.72%to 26.83%,respectively.