运动学特性约束下曲面高速进给数控加工轨迹规划

发布时间：2018-11-03 09:41

【摘要】：曲面数控高速、高效加工是机械制造不懈的追求。随着进给速度的提高,由于加工曲面轮廓的复杂性,机床运动轴的运动剧烈,会使得机床产生振动与冲击,直接影响着曲面加工质量,严重甚至破坏机床的内部结构。本文针对曲面高速进给数控加工中机床运动轴的运动学特性超出机床限制的问题,提出一种运动学特性约束下的曲面加工轨迹规划方法。主要思路是在考虑各轴运动学特性约束的基础上,通过分析加工轨迹与机床运动轴的运动特性之间的关系,结合曲面加工方式,对高速进给加工下曲面的刀位轨迹规划展开研究,从而最终在保证加工效率的同时,使加工过程中机床运动轴的运动更加平稳,不发生振动与冲击,提高曲面加工质量。主要工作如下:(1)机床的运动学特性分析。在对五轴数控机床进行运动学变换的基础上,推导出刀位数据与机床各轴运动坐标的数学关系。深入分析五轴数控加工过程中机床的运动学特性,给出运动学特性参量的计算方法以及加工轨迹规划的运动学特性约束条件,并估算机床各轴允许的运动学特性约束值。(2)运动学特性约束下的刀位点确定。针对类回转体曲面,以螺旋线导动法生成的刀位点和切触点为基础,利用B样条曲线对生成的初始切触点轨迹进行拟合,考虑机床各轴的运动学特性及其曲面加工误差,计算最终切触点轨迹。分析B样条曲线上切触点与节点的对应性,提出利用初始切触点处的初始法矢量插值获得最终法矢量的方法,进而完成刀位点的重新确定。(3)运动学特性约束下的刀轴矢量规划。基于已知的刀位点轨迹,首先考虑速度特性约束,对刀轴矢量与机床运动轴速度的关系展开分析,提出一种满足速度特性约束条件的刀轴矢量规划方法,并对机床进给速度进行一定调整;其次,分析运动轴的加速度特性,以考虑速度特性的刀轴矢量规划为基础,建立数学优化模型,优化确定最终的刀轴矢量,调整机床进给速度;然后,对个别加加速度超限刀位点处的机床进给速度进行调整,保证加加速度也满足运动学特性约束条件。最后给出算例理论验证刀轴矢量规划方法的有效性。(4)鞋楦五轴加工与加速度测量实验。以鞋楦曲面的高速五轴数控加工为例,经过后置处理编写数控加工程序,在五轴数控机床上展开精加工实验,并同时进行加速度测量实验。分析实验结果,验证本文所提出的运动学特性参量理论计算方法的正确性以及加工轨迹规划方法的有效性。
[Abstract]:Surface NC high-speed and high-efficiency machining is the unremitting pursuit of mechanical manufacturing. With the increase of feed speed, because of the complexity of machining curved surface contour and the violent movement of machine tool axis, the machine tool will produce vibration and impact, which will directly affect the quality of curved surface machining and even destroy the internal structure of the machine tool seriously. In order to solve the problem that the kinematic characteristics of the moving axis of the machine tool exceed the limit of the machine tool in the high-speed feed NC machining of curved surface, this paper presents a trajectory planning method for the curved surface machining under the constraint of the kinematic characteristics. On the basis of considering the constraints of the kinematics characteristics of each axis, the main idea is to analyze the relationship between the machining track and the kinematic characteristics of the moving axis of the machine tool, and to combine the machining method of the curved surface. In this paper, the tool path planning of the curved surface under high-speed feed machining is studied, so as to ensure the machining efficiency, make the movement of the moving shaft of the machine tool more stable, avoid vibration and impact, and improve the machining quality of the curved surface at the same time. The main work is as follows: (1) Kinematic characteristics of machine tools are analyzed. On the basis of kinematic transformation of five-axis NC machine tool, the mathematical relation between the tool position data and the coordinate of each axis of the machine tool is deduced. The kinematics characteristics of the machine tool in the process of five-axis NC machining are deeply analyzed. The calculation method of kinematics characteristic parameter and the constraint condition of kinematics characteristic of machining path planning are given. The allowable constraint values of kinematic characteristics of each axis of the machine tool are estimated. (2) the tool location is determined under the constraint of kinematic characteristics. Based on the cutter position and tangent contact generated by helical lead method, the initial tangent contact trajectory is fitted by B-spline curve, and the kinematics characteristics of each axis of the machine tool and the machining error of the curved surface are considered. The final tangent contact trajectory is calculated. The correspondence between the tangent contact and the node on the B-spline curve is analyzed, and the method of obtaining the final normal vector by using the initial normal vector interpolation at the initial tangent contact is proposed. Then the tool location is redetermined. (3) the tool axis vector programming under the constraint of kinematics characteristics. Based on the known tool locus trajectory, the relationship between the cutter axis vector and the velocity of the moving axis of the machine tool is analyzed, and a tool axis vector programming method satisfying the constraint condition of the speed characteristic is proposed. The feed speed of the machine tool is adjusted to a certain extent. Secondly, the acceleration characteristic of the moving shaft is analyzed. Based on the vector programming of the tool shaft considering the velocity characteristic, the mathematical optimization model is established, the final tool axis vector is optimized and the feed speed of the machine tool is adjusted. Then, the feeding speed of individual machine tools with acceleration exceeding the limit is adjusted to ensure that the addition speed also meets the constraint condition of kinematics characteristics. Finally, an example is given to verify the effectiveness of the tool shaft vector programming method. (4) the experiment of shoe last five-axis machining and acceleration measurement. Taking the high speed five-axis NC machining of shoe last surface as an example, the NC machining program is compiled after post-processing, and the finishing experiment is carried out on the five-axis NC machine tool, and the acceleration measurement experiment is carried out at the same time. The experimental results verify the correctness of the theoretical calculation method of kinematic characteristic parameters and the validity of the machining trajectory planning method.
【学位授予单位】：北京交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG659

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