复杂曲面切削纹理约束下的五轴奇异问题前摄避免方法研究

The five-axis singular problem happens when the machine tool approaches the singular point. At this time, even very slight changes of the cutter orientation will be substantially amplified, stimulating violent revolves of the rotary axes. This phenomena has negative effects on the machining accuracy and efficiency. Existing technologies tend to solve the problem after the toolpath has been generated, leaving the geometrical errors uncontrolled. What’s worse, so far, the irregular machined surface texture problem caused by tool axis modifications in existing technologies has not yet been extensively noticed. In fact, the texture quality has a direct effect on the surface properties and even fatigue life of the workpiece. ..The current project intends to solve the singular problem, and meanwhile improve the machined surface textures in five-axis machining before the toolpath is fully generated. At first, the mechanism of the five-axis singularity will be studied by considering the interpolation principles of the numerical systems. And the cutter behavior near the singular point will be quantitatively analyzed. Then the influences of the cutter contact micro morphology under different tool postures on the surface textures will be investigated, using the basic theory of differential geometry. By doing these, the precise predicting model of the singular problem can be established; and the theoretical mapping model of the tool posture, surface texture and cutting error can also be established. On the basis of these models, the mapping space of the tool axis orientations can be constructed. Then at the initial stage of toolpath planning, the orientation curve proactive adjusting strategy in the mapping space will be worked out, with the purpose of avoiding the five-axis singular problem and reducing geometrical errors. Finally, based on the Acceptable-Texture Orientation Region (ATOR) concept, the orientation curve will be optimized, so that the machined surface texture can be improved while the singular problem is avoided. The implementation of the project will further enhance the accuracy and surface texture quality for five-axis complex surface machining.

五轴奇异问题是指当机床靠近奇异点时，刀姿的细微变化都将被大幅放大，激发旋转轴剧烈转动，严重影响五轴加工精度和效率。现有技术大都在刀路生成之后处理奇异问题，缺乏有效的误差控制机制；且对因姿角调整造成的曲面切削纹理变化关注不多，而纹理质量直接影响到工件的表面性能甚至疲劳寿命。..本项目拟从五轴奇异问题的产生机理入手，结合数控系统插补原理，定量研究刀具在奇异附近的切削行为；结合微分几何原理，探究不同姿角下刀具微观切触形态对切削纹理变化的影响，从而建立奇异问题的精准预测准则以及姿角/纹理/误差三者映射模型。在此基础上，构建刀矢映射空间，在刀路生成的初始阶段，以规避奇异问题及降低加工误差为目标，制定姿角曲线前摄调整策略；构建刀位点可接受纹理刀姿区域（ATOR），在该区域内规划刀轴矢量，优化姿角曲线，在规避奇异问题的前提下改善切削纹理。本项目顺利实施将进一步提升复杂曲面五轴加工精度和表面纹理性能。

五轴奇异问题是指当机床靠近奇异点时，刀姿的细微变化都将被大幅放大，激发旋转轴剧烈转动，严重影响五轴加工精度和效率。现有技术大都在刀路生成之后处理奇异问题，缺乏有效的误差控制机制；且对因姿角调整造成的曲面切削纹理变化关注不多，而纹理质量直接影响到工件的表面性能甚至疲劳寿命。. 本项目（1）首先对工件表面切削纹理改变的内在机理进行分析，得出纹理变化主要和刀具角度调整相关。在此基础上，从约束刀具角度改变的角度出发，提出一种基于粒子群算法的方向曲线优化平移方法，控制平移方向及位移，从而达到优化切削纹理的目的。（2）提出可接受纹理姿角区域（ATOR）的概念，并在ATOR内对方向曲线进行局部调整，采用B样条曲线拟合的方法获得新的方向曲线。采用方向曲线局部调整的方法可在规避奇异问题的同时，进一步提升工件表面纹理质量，避免因整体平移对整条路径对应的纹理造成影响。（3）在五轴奇异规避及纹理改善研究的基础上，针对非规则复合曲面路径规划中存在的路径不连续等问题，提出了一种基于旅行商问题（TSP）求解器LKH的无提刀空间填充曲线（SFC）刀路生成方法。（4）针对SFC刀路上的拐角，提出了一系列刀路拐角的识别、分类及合并方法，减少刀路上的拐角数量，最终实现光顺复合曲面SFC无提刀刀路的目的。