Accuracy prediction of workpieces considering machine errors of multi-axis machine tools and its identification

针对五轴加工中心这一典型的多轴机床，通过计算机仿真和实验研究了蜗轮节距误差和数控控制器伺服误差等机床误差对加工精度的影响。首先，研究了ISO 10791-6中K6条款规定的双枢轴头五轴加工中心检测方法的有效性。从我们的结果中指出，ISO标准中规定的测试方法不能给出任何有用的数据。提出了一种替代测试方法，该方法提供了一些与几何精度有关的有用信息。在此基础上，研制了一种可替代的倾斜转台五轴加工中心运动轨迹测量仪。研制的仪器非常简单。提出了一种检测直线轴与旋转轴同步精度的新方法。在该方法中，一个直线轴与一个旋转轴同时被控制，并由两个轴来描述一个圆路径。结果表明，该方法可以有效地检测各轴的伺服延迟。最后，考虑工作齿轮的俯仰误差和伺服延迟以及几何偏差，研究了同步五轴运动的行为。指出三维圆轨迹的倾角和中心偏移量决定了五个被控轴的动态特性。此外，还发现蜗轮的齿隙和节距误差对锥体形状工件的精加工精度有很大影响。

In this research work, the influence of machine errors such as the pitch error of worm-gears and the servo-error of NC controller for five-axis machining centers, which are a typical multi-axis machine tool, is investigated by the computer simulation and experiment. Firstly, the effectiveness of the testing method defined by the clause K6 of ISO 10791-6, which is specified for the five-axis machining centers with a double pivot spindle head, is investigated. It is pointed out from our results that the specified testing method in the ISO standard does not give any useful data. An alternative testing method is proposed, and its method gives us some useful information relating to the geometric accuracy. Then, an alternative measuring instrument of the motion trajectory of five-axis machining centers with a tilting rotary table is also developed. The developed instrument is very simple.A new testing method for checking the synchronous accuracy of a linear axis and a rotary axis is proposed. In the proposed method, a linear axis is simultaneously controlled with a rotary axis, and a circular path is described by the two axes. It is found that the proposed method is useful to check the servo-delay of each axis. Finally, the behavior of the simultaneous five-axis motion is investigated, considering the pitch error of the work gear and servo-delay as well as the geometric deviations. It is pointed out that the inclination angle and the center offset of the three dimensional circular path governs the dynamic behavior of the five controlled axes. In addition, it is found that the backlash and pitch error of the worm gear largely affect to the finishing accuracy of the workpiece of which shape is cone frustum.