由测量数据点直接生成刀位轨迹的方法研究

随着激光测量、三坐标测量技术的发展,对测得的数据点直接进行刀位规划和加工,在计算速度、加工可靠性以及加工效率方面比传统加工方式有了较大的提高.本文对基于测量数据的刀位轨迹生成技术的研究状况进行了概括和总结,阐述了直接由点云数据生成刀位轨迹的关键技术,并指出了各种方法的优缺点.     

基于散乱测量数据点的三轴数控粗加工刀位轨迹生成算法

提出了一种直接利用三维散乱测量数据点的三轴数控粗加工刀位轨迹生成算法。首先根据切层深度作一组垂直于Z轴的平面,去截取测量点云,得到一系列切层截面点集,再在每个切层面上组环并判断加工区域,规划出刀位轨迹,将每一分层平面上的刀位轨迹按适当的方式连接起来,就可构成零件的整体加工轨迹。该算法避免了由测量点构造曲面且由曲面来进行刀位轨迹生成的这一复杂过程。     

从测量的散乱数据点云直接生成数控刀具路径的研究

提出了一种直接从测量的散乱数据点云用球头刀对自由曲面进行三轴数控加工时生成刀具路径的方法。不同于现有散乱点云基于逆向工程的刀具路径生成方法,本法考虑并估计了曲面加工误差和粗糙度。将散乱数据点云向XY平面投影,以获得的投影边界为刀具路径的主方向,然后根据曲面所需的加工误差和残留高度要求划分该投影数据点云,得到一系列刀位网格单元。通过最小化每个刀位网格单元的加工误差以确定每个刀位网格的节点位置,加权平均相关联刀位网格节点来对齐相邻刀位网格单元的边缘。为了缩短加工时间,裁去刀位路径上多余的线段,最终生成高效合理的数控加工刀具路径。已用实测的数据点云验证了本法直接生成刀具路径的有效性。     

基于散乱数据点的数控加工刀位直接生成

研究了测量得到的散乱数据点在平面上投影点的边界轮廓提取算法；以抬刀次数最少为优化目标，通过引入计算几何中单调链的概念，确定了最佳的行切加工方向和最少单调链数；给出了在平面区域内行切法加工的刀位计算与Z字形刀位连接方法，该方法适用于模具型腔的刀位规划；针对圆环刀、球头刀和平头刀，提出了不发生干涉的曲面三轴加工刀位计算方法，可基于散乱点测量数据直接生成数控加工刀位，此刀位计算方法也可用于模具型腔的修复。最后，通过数值仿真验证了算法的可行性。     

基于Z-buffer的组合曲面圆环面刀具加工方法

为解决组合曲面五轴加工问题提出一种基于计算机图形学Z-buffer技术的圆环面刀具刀位生成算法。首先借助Z-buffer技术确定刀位计算的检测区域,然后在保证圆环面刀具和检测区域不干涉的前提下调整刀位,使刀具端面和模型曲面充分贴合,从而得到更宽的加工行宽。算法充分利用计算机硬件的快速高效性,直接对加工检测区域内的点进行读取和存贮,避免复杂的搜索和迭代过程。算法过程中集成对刀位干涉的检测和避让,可直接生成无干涉的刀位数据。刀位算法计算过程使用曲面的多面体信息,适用于以裁剪曲面为元素的组合曲面模型的无干涉刀位的计算。针对某组合曲面模型进行刀位计算和仿真,仿真结果相比传统的球头刀加工算法效率提高了10倍。最后对生成的刀轨进行了实际加工试验验证。     

面向并联机床的叶片加工程序后置处理及仿真软件研究

采用专用汽轮机叶片编程软件所生成的叶片刀具轨迹具有良好的工艺性,但其针对的是专用机床,不能直接被其他机床使用.通过对专用机床、并联机床的结构进行分析和对加工程序代码的后置处理,开发了面向并联机床的叶片加工程序后置处理软件,实现了专用机床叶片加工程序代码转换为并联机床加工程序代码.同时为了对转换后的叶片刀位轨迹进行仿真,采用OpenGL和多线程技术开发了叶片加工刀位轨迹仿真软件,实现了叶片加工刀位轨迹的仿真.     

带倒角平底刀曲面加工无干涉刀具轨迹生成

对自由曲面ＮＣ加工中刀具轨迹生成技术和干涉处理方法进行了分析,以曲面模型→刀具接触点数据→无干涉刀位数据为基本求解策略,研究开发出适用于带倒角平底刀无干涉刀具轨迹生成的新算法。该算法具有干涉检测彻底、处理效率高、稳定性好等优点。     

基于MLS拟合带容差的测量数据加工刀位面生成算法

传统的刀位面生成算法无法直接生成存在缺陷的离散数据的刀位面,因此,针对球头铣刀提出了一种基于MLS拟合带容差的离散数据加工刀位面生成算法。该方法首先依据球头铣刀构造离散数据的点膨胀球模型,然后根据凸包原理获取该模型的最外层包络面,最终通过MLS投影拟合方法剔除奇异点、修补裂缝,生成刀位面网格模型。实例表明,该算法具有较高的稳定性,能够有效解决存在缺陷的离散数据刀位面生成问题,适用于实际工程应用加工。     

带倒角平底刀曲面加工干涉刀具轨迹生成

对自由曲面ＮＣ加工中刀具轨迹生成技术和干涉处理方法进行了分析,以同面模型→刀具接触点数据→无干涉刀位数据为基本求解策略,研究开发出适用于带倒角平底刀无干涉刀具轨迹生成的新算法。该算法具有干涉检测彻底、处理效率高、稳定性好等优点。     

自由曲面三轴联动数控加工刀位轨迹生成的研究

自由曲面数控加工刀位轨迹的自动生成，是相关ＣＡＭ技术的关键问题。本文利用点涉法原理推导出刀位点的计算公式，在此基础上，考虑存在干涉的刀具与被加工曲面接触点具有区间连续的特性，以非均匀走刀方式，介绍空间自由曲面三轴联动数控加工刀位轨迹的生成方法。     

离散点云等残留高度数控加工刀轨生成方法

为了最大化刀轨行间距,从而减少刀轨总长度,针对离散点云提出了一种等残留高度刀轨生成方法。提出以点云局部轮廓点集直接生成残留高度点的迭代计算方法,再根据残留高度点和点云局部点集迭代计算出下一行等残留高度刀位点,从而获得等残留高度刀轨。算法无需点云等距或曲面重构,为了提高算法效率,提出了算法所需数据初值的优化计算方法。最后对典型的点云模型生成刀轨,与等行距刀轨相比,提出的算法生成的等残留高度刀轨总长度大幅减少,验证了算法的可行性和有效性。     

自由曲面五轴变步长数控加工刀轨生成方法

为了在满足逼近误差要求的同时最大程度减少冗余刀轨,对自由曲面提出了一种五轴变步长数控加工刀轨生成方法。首先对刀触点轨迹基于线性误差计算出初始刀触点点集,再以局部干涉调整前倾角的方式计算出无干涉刀位点和刀轴矢量;以最大非线性误差刀位处到刀触点轨迹的最小值作为相邻刀位点之间的逼近误差,并基于数据点自适应离散法计算逼近误差;在满足逼近误差要求的前提下,通过刀触点参数迭代增减步长的方式计算出最大步长;最后对曲面生成刀轨,验证了算法的可行性和有效性。     

基于点搜索组合曲面清根加工轨迹优化算法

清根加工质量严重地影响着组合曲面体零件的工作性能。为提高清根加工刀心轨迹的精度和自动化处理程度,在点搜索的基础上提出了初始点自适应调整和多搜索中心分区域搜索优化算法。以航空发动机叶片缘板与叶型过渡区域清根加工为研究对象,在参数域内分析了点搜索算法。在此基础上,以寻找临界不确定点为引导方向对初始搜索点进行自动调整并优化搜索区域。又针对搜索到的控制点分布不均问题,提出多搜索中心分区域搜索方法,得到可控且分布均匀的刀心轨迹控制点。将控制点拟合得到的样条曲线向缘板偏置面投影作为刀心轨迹线,并对其进行了误差分析。以叶片叶型与安装缘板和阻尼台两处过渡区域的清根加工为例,对算法的有效性进行了仿真验证,证实所提方法的正确性和有效性。     

基于遗传算法的笔式加工刀具路径优化

为缩短笔式加工时间和提高加工效率,提出了一种新的基于遗传算法的刀具路径优化方法。笔式加工的特点决定了生成的刀具路径为一系列离散的切削路径段,为了精简搜索数目,将每段刀具路径看作两个遗传基因。使用十进制码构造分段染色体模型,采用改进的遗传算法对笔式加工分段路径进行优化排序,得到刀具路径排布的近似最优解。实验结果表明:改进的自适应遗传算法比一般遗传算法搜索速度提高若干倍,可以明显缩短加工路径的总长度。     

鼓形砂轮周磨自由曲面刀位算法

对采用鼓形砂轮周磨自由曲面的刀位计算进行了研究。为了提高加工效率，提出了一种基于避免加工中砂轮和工件曲面局部干涉的鼓形砂轮几何参数的优化方法。在刀位计算中，砂轮被限定在摆刀平面中旋转；离散鼓形砂轮表面，计算采样点到工件曲面的有向距离，获得当前刀位的加工误差分布和加工带宽；以砂轮轴和工件曲面最小法曲率方向的夹角为优化变量，以当前刀位的加工带宽的最大化为优化目标，用格点法进行了鼓形砂轮周磨自由曲面的刀位优化。利用UG二次开发技术编程，生成了Bezier曲面的加工轨迹的计算实例，验证了所提出的砂轮几何参数和刀位的优化算法。     

A Cutter Orientation Modification Method for the Reduction of Non-linearity Errors in Five-Axis CNC Machining

In the machining of sculptured surfaces, five-axis CNC machine tools provide more flexibility to realize the cutter position as its axis orientation spatially changes. Conventional five-axis machining uses straight line segments to connect consecutive machining data points, and uses linear interpolation to generate command signals for positions between end points. Due to five-axis simultaneous and coupled rotary and linear movements, the actual machining motion trajectory is a non-linear path. The non-linear curve segments deviate from the linearly interpolated straight line segments, resulting in a non-linearity machining error in each machining step. These non-linearity errors, in addition to the linearity error, commonly create obstacles to the assurance of high machining precision. In this paper, a novel methodology for solving the non-linearity errors problem in five-axis CNC machining is presented. The proposed method is based on the machine type-specific kinematics and the machining motion trajectory. Non-linearity errors are reduced by modifying the cutter orientations without inserting additional machining data points. An off-line processing of a set of tool path data for machining a sculptured surface illustrates that the proposed method increases machining precision.     

Multi-nozzle spraying path generation directly from scanned data for rapid prototyping

This study aims to build a triangular-mesh model directly from scanned 3D data points, which then generate the stereolithography (STL) file, thus avoiding the troublesome task of producing a CAD model. Accuracy of the triangular-mesh model is achieved because the pitch between data points is generally very small. In addition, the paper proposes a multi-nozzle path algorithm to increase both spraying efficiency and part accuracy. The processing procedure includes: (1) Establishing the triangular-mesh model from scanned data points, which are retrieved by means of contact- or non-contact type measuring machines as well as developing the algorithm to add the radius of the probe automatically. (2) Equally slicing the triangular-mesh solid model and plan spraying paths. (3) Determining the amount and diameter of nozzles appropriate for each slice to generate multi-nozzle spraying paths.     

NC machining of free-form Kriging surfaces

An algorithm for three-axis NC tool path generation on sculptured surfaces is introduced when the free-form surface is modeled parametrically by free-form surface Kriging. The flexibility of dual Kriging that easily defines the intersection of the surfaces with a set of parallel planes and Cartesian method are combined to generate the tool-paths automatically. The presented algorithm can simultaneously generate the tool path with a predefined machining accuracy and remove gougings along the tool path. The algorithms are validated by three experiments in rough and finish machining and the results prove its reliability. Since Kriging is based on the interpolation of data points, the proposed algorithm can be used for reverse engineering applications. The system was executed on a standard micro-computer and the software was structured to offer a library of machining functions for endusers.     

Direct tool path regeneration for physical object modification from digitized points in reverse engineering

To reuse the tool paths in tool path regeneration for physical object modification in reverse engineering, this paper presented a novel CL tool path regeneration algorithm based on the CL tool path generated from the measured data points. When a physical part captured is modified, the new tool paths for the modified part can be regenerated efficiently by only calculating the affected CL tool paths on the modified region. With this strategy, if a measured physical part has been modified and the CL tool paths were generated directly from its corresponding digitized points, the affected CL tool paths are identified first; then, new CL tool paths are regenerated and used to replace the affected CL tool paths for a given machining accuracy δ. The tool paths not affected are maintained in the new NC-codes. For the method, only the tool paths for the modified regions need to be regenerated; thus, the tool path, which combines the original and modified tool paths, can be regenerated efficiently.     

Optimal five-axis tool path generation algorithm based on double scalar fields for freeform surfaces

In order to generate efficient tool path with given precision requirements, scallop height should be kept under a given limit, while the tool path should be as short as possible to reduce machining time. Traditional methods generate CC curves one by one, which makes the final tool path far from being globally optimal. This paper presents an optimal tool path generation model for a ball-end tool which strives to globally optimize a tool path with various objectives and constraints. Two scalar functions are constructed over the part surface to represent the path intervals and the feedrate (with directions). Using the finite element method (FEM), the tool path length minimization model and the machining time minimization model are solved numerically. The proposed method is also suitable for tool path generation on mesh surfaces. Simulation results show that the generated tool path can be direction parallel or contour parallel with different boundary conditions. Compared to most of the conventional tool path generation methods, the proposed method is able to generate more effective tool paths due to the global optimization strategy.