截面线等误差步长法计算点云刀具路径规划

提出了一种利用截面线等误差步长法计算点云刀具路径的算法。首先定义一组截平面,运用点云切片算法求出截平面与点云的交线,作为刀触点(CC)轨迹。刀触点轨迹是由大量离散点组成的点集,本文中提出了一种等误差步长法对刀触点轨迹计算刀触点,然后利用最小二乘法拟合刀触点附近点获得平面,平面法矢作为刀触点的法矢,沿法矢偏置刀具半径得到对应的刀位点,并对生成的刀位点进行干涉处理。该算法计算出的刀具路径包含的刀位点数量更少,误差均匀且都满足最大误差要求,最后通过实例验证了算法的可行性。     

复杂参数曲面高精度刀具轨迹规划算法

在对等残余高度刀具轨迹规划算法加工参数曲面研究的基础上,提出带有误差补偿值的复杂参数曲面高精度刀具轨迹规划算法——高精度刀轨误差补偿算法。通过分析刀触点及与之相应的相邻路径上的粗、精刀位对应点间的关系,引入误差补偿值以提高精对应刀位点的求解精度,得到经过合理简化的误差补偿值表达式,并得出粗、精对应刀位点与理论刀位点的距离误差表达式。高精度刀轨误差补偿算法可以在满足插补运算实时性要求的前提下,使相邻轨迹上与刀触点相对应的刀位点的参数值计算精度得到极大提高,进而提高复杂参数曲面的加工刀具轨迹精度。以使用平底铣刀为例进行仿真加工,结果表明高精度刀轨误差补偿算法适合进行对复杂参数曲面的高精度加工。     

三角Bézier曲面数控精加工刀轨快速生成算法

为了解决三角Bézier曲面精加工刀轨生成效率低以及存在的刀轨干涉等问题,提出一种基于三角Bézier曲面的数控精加工刀轨快速生成算法,该算法引入动态索引组织三角Bézier面片的拓扑近邻关系,基于该索引快速获取与刀轨截平面相交的三角Bézier面片集,对其中任一相交面片进行初始交点迭代计算,从初始交点开始跟踪迭代获取跨越三角Bézier面片的完整交线,将获得的有序交线各端点作为刀触点获取相应刀位点,依据刀触点处曲面法矢与刀杆矢量的关系快速确定可能存在干涉的区域,进而对干涉区域刀位点进行调整获取无干涉刀位点,顺次连接各刀位点生成数控加工刀轨,实例证明该算法可对任意复杂三角Bézier曲面精确、快速生成数控加工刀轨,并通过三角Bézier曲面模型的数控刀轨生成验证了该算法的实用性。     

基于定向距离理论的五轴加工刀具轨迹规划算法

针对环形刀五轴加工自由曲面的残留误差问题,在传统等残留高度算法的基础上,提出了一种基于定向距离理论的等最大残留高度刀具轨迹规划算法。首先根据微分几何理论计算已知刀触点的初始侧向行距,并在侧向行距方向进行偏置得到相邻刀触点;然后以基于定向距离理论的残高误差计算模型对相邻刀触点间的实际残高值进行计算;最后通过迭代计算规划出等最大残留高度的相邻刀具轨迹。如此循环,从而获得整个曲面的刀具轨迹。实验结果表明,相对于商用软件MasterCAM9.0,该算法在充分保证曲面加工质量的同时最大限度地减小了刀具轨迹的总长度,从而提高了加工效率。     

等误差步长法计算点云数控加工刀轨方法研究

为了最小化冗余刀位点数量,提出了运用等误差步长法对点云计算加工刀轨的方法。根据行距和预设步长计算出每一行刀位点,运用筛选法计算出接近满足误差条件的刀位点;为提高刀位点精度,新增此刀位点的小步长邻域刀位点,通过构造误差圆求切线以搜索误差最大允许值的刀位点,再以与点云相切为约束条件计算出刀位点偏移量,最终获得等误差刀位点。所提出的算法求出的刀位点数量最少,误差均匀均为误差最大允许值,最后通过算例验证了算法的可行性。     

基于MMR的三角网格曲面五轴加工刀轨生成算法

为了提高三角网格曲面五轴加工的加工效率,提出了基于最大材料去除率(maximal materialremoval rate,MMR)的平底刀五轴加工刀轨生成算法。首先计算无曲率干涉且具有最大材料去除率的网格曲面五轴加工的刀具方位角;然后在确定网格曲面可能干涉区域的基础上,提出刀触点处干涉性假设,并以最大材料去除率、刀具无曲率干涉和全局干涉为约束条件,采用二分法确定具有最大材料去除率的无干涉刀具方位角;最后采用截面线法生成三角网格曲面MMR平底刀五轴加工刀轨。通过实验验证了采用文中算法生成的刀轨进行加工能够获得较高的加工效率和表面质量。     

点云模型的五轴无干涉数控加工刀轨生成方法

提出了一种对点云模型直接计算五轴数控加工刀轨的方法。所求出的刀轨无局部、全局干涉且具有较高的切削效率。首先将点云划分到立方体栅格中,对刀触点获取附近可能发生干涉的栅格,根据栅格中的点计算出无局部干涉的最小前倾角,基于此前倾角,再以迭代判断的方式计算出无全局干涉的最小旋转角,最后获得无干涉刀轴矢量。提出的方法避免了传统方法中曲面拟合这一复杂、耗时的过程,效率较高,对算例生成的无干涉刀轨验证了方法的可行性。     

基于散乱点云的层切法粗加工刀轨规划方法研究

提出了一种对散乱点云运用层切法规划三轴粗加工行切刀轨的方法。采用点云切片法计算出切削平面上的轮廓点集,提出直接对每一行刀轨切削范围内的轮廓点集计算无干涉刀位点、规划刀轨的方法;为了避免相邻行刀轨连接时在凸区域产生过切、凹区域切削余量过大的问题,提出一种新增过渡刀位点、再通过过渡刀位点连接的方法。所提出的方法直接对点和刀轨计算,无需组织切削区域或构造中间数据结构,实现了刀轨高效生成和误差控制,最后对算例生成刀轨并进行加工仿真,验证了算法的可行性。     

点云模型行距自适应数控加工刀轨生成方法研究

行切法规划刀轨时,为了使残留高度满足要求同时行距最大化,对点云提出了一种行距自适应的刀轨生成方法。首先采用刀位点截面线法计算出首行刀位点,然后对点云局部轮廓和刀位点计算残留高度点,再根据残留高度点计算出下一行刀位点。为了提高计算效率、保证精度,提出运用预设初值、迭代逼近策略直接计算出残留高度点、刀位点的方法,最后根据相邻刀位点之间的距离获取满足残留高度的最大行距。对算例生成刀轨验证了算法的可行性。     

基于CQEM的海量测量点集刀位轨迹生成算法研究

提出基于约束二次误差度量(CQEM)的海量测量点集刀位轨迹生成算法。算法以大规模测量点集为待加工曲面,依据刀具大小动态生成刀具邻域的插值网格,以平面截交网格交点作为初始刀触点,对其进行CQEM优化并细分该截交网格,在此基础上生成无干涉刀位轨迹。算法不仅利用网格的动态局部构造节约了大量的空间消耗而且通过刀触点集的COEM优化减小了加工曲面逼近测量点所在曲面的误差。     

An improved calculation method for cutting contact point and tool orientation analysis according to the CC points

Tool path generation is an important step of five-axis NC milling which plays an important role in parametric surfaces and free-form surfaces manufacturing. Cutter contacting (CC) point calculation is considered as a basic procedure of tool path generation. The step lengths formed by cutter contacting points have an effect on the chord error along feed direction. In traditional calculation method for CC point discretization, the segments connected by adjacent CC points distribute on both sides of the theoretical tool path curve. This situation magnifies the cutting error to some extent and enlarges the expected margin if the surface demands polishing or grinding. Aiming at this issue, this paper proposes an improved constant chord error method for CC point calculation. In the proposed method, the CC points lay on the theoretical tool path curve when the tool path curve is concave and lay on the chord error offset curve when is convex, which ensures the segments connected by the adjacent CC points distribute on one side of design surface, the side of the scallop height between tool paths. Therefore, the actual margin of polishing or grinding can be reduced. The influence of inflection points is also considered in this method to avoid accuracy deterioration caused by the long steps occurring near the inflection points. In part processing, local gouging and global collision must be avoided in tool orientation determination. This paper analyzes tool orientations with no rear gouging and no collision based on the calculated CC points. The novel discretization method for CC points is calculated on a single blade model, and the tool orientations are generated on an open integral impeller. A DMG DMU50 machine tool and a Hexagon three coordinates measuring machine are applied for experiments and measurements. The results show that, the CC point discretization method proposed in this paper offers many advantages over the traditional constant chord error method and commercial software, such as quantity of points, curve fitting, no overcut, and residual margin distributing. At last, blade and tunnel of the open integral impeller with safety tool orientation is machined and verified on the DMG DMU50 machine tool.     

类回转体曲面数控加工刀位轨迹规划

针对类回转体曲面高速进给数控加工,提出螺旋线驱动方式下圆环刀具加工轨迹的规划方法。构造螺旋线作为类回转体曲面的导动线,根据曲面上已知接触点轨迹的切线方向估算后续导动点对应的初始接触点。计算初始接触点处圆环刀具的刀心位置,再计算初始刀心位置与后续导动点对应的目标刀位点分别在圆周方向以及轴向的距离差值,利用相邻刀位点与相邻接触点存在的准相似关系,得到接近目标接触点的搜索方向和步长,经过迭代得到目标接触点和刀位点。在分析接触点处曲面曲率和圆环刀曲率的基础上,给出圆环刀加工误差计算方法。将所提出的算法用于鞋楦的五轴数控轨迹规划中,计算结果表明,该算法搜索效率较高,具有理论和实际应用价值,并通过鞋楦的五轴数控加工试验验证了算法的有效性。     

Five-axis tool path generation for 3D curves created by projection on B-spline surfaces

This paper presents a new tool-path-generating methodology for five-axis machining of 3D curves that are projected from 2D planes onto free-form part surfaces. In our approach, the scanning for mapping is planned directly on parameter domain. The DXF pattern was scaled to parametric dimension and transferred to parametric domain, and thus, all entity coordinates were transferred from X,Y to (u,v). By using a B-spline surface equation algorithm, the projected curves were obtained on a free-form surface for tool path generation. 2D pattern models were delineated with the DXF format; 3D free-form surfaces were delineated with the STEP-AP214 format and the “B_Spline_surface_with_knots” entity was used to define the free-form B-spline surface geometry. Windows® based software written in Borland® Delphi has been developed according to the presented algorithm. Cutter contact (CC) data and surface normals for CC points were obtained with this software. The obtained CC data and surface normal data were transferred to cutter location (CL) data and the tool path verification is obtained by simulation successfully.     

基于Hermite插值的复杂光学曲面车削加工路径规划

为解决复杂光学曲面加工难题,探讨其车削加工路径规划。基于慢刀伺服加工技术对复杂光学曲面的刀位点规划进行设计,分析刀触点等角度离散方案及刀具圆弧半径补偿方案。轨迹插补采用可编程多轴控制器(Programmable multi-axiscontroller,PMAC)提供的位置、速度、时间(Position velocity time,PVT)插补运动模式,分析PVT的数学实质Hermite分段插值模型,并根据此模型提出恒速法、面积法和三点法三种PVT入口参数生成算法。以离轴抛物面、环曲面、正弦面为例进行仿真,加工路径的仿真表明刀位点的设计可以应用于复杂光学曲面加工。同时z轴运动特性的分析表明z轴往复频率和C轴回转频率相仿时,面积法(c=2/3)和三点法均能满足z轴速度光顺要求;z轴往复频率明显大于主轴频率时,采用三点法的加速度变化明显优于面积法。提出的加工路径方法可为复杂光学曲面的实际加工提供指导意义。     

Near net-shape five-axis face milling of marine propellers

We present an optimal cutter location (CL) data computation for face-milling of large marine propellers composed of CL point optimization and CL path optimization on a given tool path. The CL point optimization at a single cutter contact (CC) point is conducted by maximizing the effective radius of the face milling cutter, while the CL path optimization on a series of CC points is performed by conforming deviation of the tool-swept surface from the design surface between consecutive CL data to a given machining tolerance. The proposed algorithm was implemented and applied to the machining of a large marine propeller which proved effective from a quantitative point of view, and is used on the shop floor in a Korean ship building company.     

An accurate surface error optimization for five-axis machining of freeform surfaces

This paper presents an accurate surface error interpolation algorithm for five-axis machining of freeform surfaces. One of the most important steps in the interpolation process is to calculate the next cutter contact (CC) point according to the present one. In this paper, the next CC point is calculated by an accurate chord evaluation method. This method is developed based on the cutting simulation process, which can be vividly described as firstly planting dense grasses on the tool path curve and then cutting them when the tool moves by. The left lengths of the grasses either positive or negative are considered to be the machining error. The method is accurate also because the tool geometry and the tool orientation changes during five-axis machining are taken into consideration. With this method, the chord errors between CC points are controlled uniform along the tool path. The proposed interpolation algorithm is compared with the commercial CAM systems like PowerMILL and UG. The results show that the proposed algorithm can significantly reduce the number of cutter locations meanwhile confine the chord error. A real cutting experiment is implemented, and the result indicates its promising value in industrial applications.     

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。     

基于网格化局部差值拟合的自由曲面加工路径规划方法

基于网格化局部插值拟合的曲面加工路径规划方法是在传统的等参数离散法基础上,对离散的密集的刀心点云进行网格化重新规划。提出了一种对刀心点云投影并进行网格化的新方法。在网格点局部根据临近的刀心点进行局部插值拟合的方法得到新的刀心点,在保证刀心点集能够满足重建要求的前提下,使加工路径规则化。可以根据误差计算公式对网格密度和离散密度进行判断和调整以实现优化。