五轴加工奇异问题机理分析及其避免策略

Mechanism Analysis and Avoiding Strategy of Singular Problem in Five-axis Machining

五轴加工后置处理在奇异区域内反解旋转角时,产生的旋转轴运动突变,不仅会引起较大的加工非线性误差,而且会损害工件与机床部件。针对以上问题,以五轴AB双转台卧式数控机床为研究对象,根据机床结构与运动链,运用齐次坐标变换原理,推导出其后置处理算法,将刀轴矢量的可行值域简化为球体,并通过将AB轴的运动类似为球体上的AB阶跃,分析了奇异问题的产生机理,提出了加工奇异区域的检测方法。对刀轴矢量投影局部放大后,通过刀位点和刀轴矢量插值分解B阶跃后重新生成刀具路径的方法,得到了奇异问题的避免策略。仿真加工验证表明,该方法可以在原有刀位轨迹不变的基础上较好地消除奇异问题,提高加工质量,同时也可推广到同类结构相似的机床上用于消除奇异问题。

In five-axis machining, the drastic motion of rotation generated in post processing for inverse solving rotating angle in the singular area will cause large non-linear machining errors and induce damages to the workpiece and machine tool as well. To solve this problem, the paper taking five-axis table-tiliting horizontal type machine tool with two rotational axes AB as studying object, the post processing algorithm was deduced based on the structure and kinematic chain of the machine tool and homogeneous coordinate transformation theory. The feasible value range of cutter axis vector is simplified as a sphere. The corresponding detection method was obtained after analyzing the generation mechanism of the singular problem with an analogy of AB axis motion to the AB step on the sphere. The avoiding strategy for the singular problem is obtained with the method of CL point and tool axis vector interpolation for disintegrating B step and tool path regeneration after projecting by local zooming the tool axis vector. The experiment results show that the present method can effectively eliminate the singularity problem without any changing of the original cutter locus and improve the processing quality. At the same time, it can be extended to the similar structure of machine tool for eliminating singular problem.