面向伺服动态特性匹配的轮廓误差补偿控制研究

Research on Contour Error Compensation Method with Matched Servo Dynamic Characteristics

在多轴数控加工中,轮廓误差直接决定零件最终加工精度。交差耦合控制和任务坐标系法通过估计轮廓误差,并设计轮廓跟踪控制器来提高轮廓精度。这两种方法存在大曲率位置轮廓误差估计精度差,轮廓控制增益整定依赖于工程经验等问题。为此,从伺服轴动态特性匹配出发,提出了一种基于轮廓误差精确计算的轮廓误差补偿控制方法。根据足点定义,采用解析方法快速准确计算轮廓误差。将轮廓误差分量分别补偿到各伺服轴的速度环和转矩环,提高各伺服轴动态特性的匹配程度。采用两维和三维NURBS曲线开展轮廓跟踪试验。试验结果表明:所提出的轮廓误差计算方法可以精确求解轮廓误差;所提出的轮廓误差补偿控制方法不需要建立轮廓误差与伺服跟踪误差间的映射关系,且可通过调整控制器增益定量显著减小轮廓误差。

In multi-axis CNC machining, the final machining precision of the parts is determined directly by the contour error. Cross-coupling controller and task coordinate frame approach can improve the contour accuracy by estimating the contour error and designing the contouring controller. There exist some problems such as the poor contour error estimation accuracy in the large curvature position and contour control gain setting depending on engineering experience with the two methods. To solve this issue, proceeding from the dynamic characteristics matching of the servo axes, a contour error compensation method based on the precise calculation of the contour error is proposed. According to the definition of the foot point, the contour error is calculated quickly and accurately using the analytical method. Then, the contour error component is compensated to every servo axis＇s speed loop and torque loop to improve the matching degree of the dynamic characteristics. Finally, the experiments are conducted using the two-dimensional and three-dimensional NURBS curves. The experiment results show that the contour error can be estimated exactly by the proposed contour error calculation method. The proposed contour error compensation method does not need to establish the relationship between the contour error and the tracking errors, and reduce the contour error quantitatively and significantly by adjusting the controller gains.