复杂曲面上机器人自动喷涂路径规划方法

针对目前含有岛屿或空洞的复杂曲面上机器人喷涂路径规划中存在的问题,提出一种能够保持轮廓平行的机器人喷涂路径设计方法。利用最小二乘坐标映射原理,将被喷涂曲面映射到二维平面域,建立目标曲面与二维平面域之间的一一映射关系,然后对平面映射域的内外边界进行连续偏置,构造能够保持轮廓平行的二维偏置曲线;进而以被喷涂曲面到二维平面域的坐标映射为向导,将无干涉二维偏置曲线逆映射到被喷涂曲面上,生成能够保持轮廓平行的喷涂路径,实现多岛屿或空洞复杂曲面上三维喷绘路径设计到二维平面的降维处理。实例仿真实验结果表明,所提方法简单实用,可在含有岛屿或空洞的复杂曲面上快速地生成能够保持轮廓平行的机器人喷涂路径。     

Adaptive tool-path generation on point-sampled surfaces

In this paper, we present a new approach to generate tool paths for machining point sampled surfaces using a direct projection algorithm, which is based on generating tool paths along planar intersection curves. In our implementation, a guide surface, with simple geometry like planes or cylinder surfaces, is first created according to the bound volume of the point cloud and initial tool paths are planned on it in terms of the motion pattern of the cutters. For each point of the initial tool paths, then, the corresponding cutter contact point (CC) of the point set surface is located by projecting the point onto the point cloud using the direct projection algorithm. In order to obtain adaptive cutter location points (CL), a least squares-based curve fitting method is applied to approximate the CC points using piecewise cubic Bezier, and a numerical method derived to estimate the length of the curve is used to adjust the position of the points along the curve, and make them evenly spaced on the curve with equal arc lengths. In addition, considering that offset curves or surfaces are necessary for locating CL points in many applications, such as machining using ball end milling cutter, torus ended milling cutters, an offset strategy for cubic Bezier curves is also studied. By testing the proposed method on several point clouds, it has been demonstrated to be promising.     

螺旋刀具轨迹规划的水平集方法

提出了一种新的螺旋线刀具轨迹生成方法。运用水平集边界推进技术，以型腔边界作为初始零水平集，通过求解水平集方程得到一系列等距线；同时运用曲率流技术平滑等距线的高曲率交点，避免高速加工过程中的刀具损伤。最后，使用相邻等距线的对角线来生成螺旋线刀具轨迹。该方法能够生成连续平滑的加工轨迹，适用于平面型腔的高速切削加工。     

基于B样条曲面裁剪计算的局部协调设计

在反求工程曲面重构中,为了对跨多张曲面的局部矩形拓扑裁剪区域进行重新设计,提出了两种基于矩形拓扑区域的曲面局部协调设计方法:自动截面线蒙皮和最小二乘逼近。两种方法均插值于边界曲线和跨界切矢,保证了模型的整体G1连续性,并逼近或插值裁剪区域数据,具有较好的保形性,实际应用效果良好。     

基于边等距偏移的环切加工刀具路径生成方法

针对由直线和圆弧组成的封闭轮廓生成环切加工刀具路径的问题,提出了一种基于边等距偏移的环切加工刀具路径生成方法。该方法分别从封闭轮廓的凸点和干涉凹点出发,结合边干涉检测程序和圆弧边分段处理方法对包含直线和圆弧的轮廓分别进行局部和全局无效区域检测,删除轮廓的无效区域后进行等距偏移,生成无干涉环切加工路径。利用自主开发的CAD/CAM软件实现了该方法,仿真实验结果表明,该方法能够准确、有效地生成无干涉区域的刀具加工路径,同时适用于带有孤岛的封闭轮廓偏移。     

面向高速加工的复合曲线螺旋轨迹生成方法

针对现有螺旋切削方式仅仅适合圆形或类圆形边界曲面的问题,提出了一种复合曲线螺旋切削法,利用直线圆弧构建规则形状的辅助边界以包容不规则的曲面原始边界,以辅助边界构建光顺网格曲面作为螺旋线的投影曲面,然后桥接投影曲线与平面螺旋线作为驱动曲线从而生成复合螺旋刀路,在避免边界尖角影响的同时保留了刀轨连续的优点,适用于各种具有不规则边界的平坦曲面。软件模拟和实际加工结果表明,复合曲线螺旋切削法有效解决了刀轨的连续性和矢量突变问题,特别适合复合曲面的高速加工。     

A topological-free method for three-axis tool path planning for generalized radiused end milled cutting of a triangular mesh surface

A tool path generation method for a sculptured surface defined by a triangular mesh is presented. Existing tool methods require extensive computer processing power mainly because surface topology for triangular meshes is not provided. The three-axis tool path planning method presented in this paper for generalized radius end mills avoids this problem (and does not need topological information) by offsetting each triangular facet individually. Offsetting a single triangle results in many more triangles, many of which are redundant, increasing the time required for data handling in subsequent steps. To avoid the large number of triangles, the proposed method creates a bounding space to which the offset surface is limited. Applying the boundary space limits the size of the offset surface resulting in a reduction in the number of triangular surfaces generated. The offset surface generation may still result in unwanted intersecting triangles. The tool path planning strategy addresses this issue by applying hidden-surface removal algorithms. Simulation and machining tests are used to validate the tool paths generated using this method.     

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。     

Combined reparameterization-based spiral toolpath generation for five-axis sculptured surface machining

Reparameterization-based toolpath generation methods are usually adopted for machining triangular meshes, trimmed surfaces and compound surfaces. The quality of the reparameterization has an important effect on that of the surface. In this paper, a combined reparameterization procedure is introduced to generate an optimal mapping between the designed surface and a specified planar circular region with relatively less distortion both in length and in angle. Then, for five-axis sculptured surface machining the mathematical model of spiral guide path with maximum path interval is constructed in the circular region. Cutter contact paths are obtained by inversely mapping the guide path onto the designed surface. Under constraints of gouging and collision, continuous and optimal cutter orientations are subsequently calculated. Finally, the results of simulation and experiment of the machining process are given to illustrate the feasibility and applicability of the proposed method.     

2D curve offset algorithm for pockets with islands using a vertex offset

An offset edge algorithm is a common method of creating contour-parallel paths that has been widely studied. The method includes approaches such as pair-wise intersection and Voronoi diagrams. The method proposed in this paper is unlike these approaches in that it determines an offset algorithm via the offset vertex. In addition, the proposed method differs from common approaches because: (1) the offset vertices are computed based on bisectors, (2) the validity of combining the direction and position checking for each offset edge is the main point of the proposed method; (3) an efficient algorithm is constructed to connect all offset edges simultaneously to generate raw offset lines without local invalid loops, and (4) an offset-distance check is performed to remove the global invalid loops from the raw offset lines as well as the interference loops in joining boundaries and multiple islands. The proposed method was verified with various slice contour shapes, with or without islands, and good results were obtained with significant reductions in the calculation time.     

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.     

Adaptive Gregory Patch Approximation to Z-Map Data

A method is proposed for Gregory surface approximation to 3D array data points. Surface approximation is the process of constructing a compact representation to model an object surface based on a fairly large number of measured 3D data points. Based on an adaptive subdivision technique, the proposed method begins with a rough initialisation of the surface and progressively refines it in successive steps in the regions where the data is poorly approximated. The method has been implemented using piecewise bicubic Gregory patches with G 1 continuity. An advantage of this approach is that the refinement is essentially local, reducing the computational requirements that permit the processing of a large number of data points This method, combined with the inverse offsetting method, can be used to obtain an offset surface without self-interference. The offset surface can be used to generate gouging-free CL tool paths for machining compound surfaces on milling machines.     

开式整体叶盘通道侧铣粗加工技术的研究

整体叶盘从锻造毛坯到最终零件加工成型,需要切除大量的多余材料。本文提出了一种开式整体叶盘通道区域五坐标粗加工刀具轨迹规划方法。该方法通过生成整体叶盘薄壁叶片的直纹包络面,以确定叶盘通道粗加工区域的边界轮廓;基于直纹面五轴侧铣加工刀具轨迹双点偏置生成方式,利用投影法规划开式整体叶盘通道区域粗铣加工的刀心点轨迹与刀轴矢量方向。加工实践表明,开式整体叶盘的粗加工效率提高30%以上,同时,显著优化了后续半精加工和精加工工序的环境。     

Generation of Tool Paths for Machining Free-Form Pockets with Islands Using Distance Maps

In this paper, we present a new procedure for generating tool paths using discrete distance maps, especially for dealing with free-form shaped pockets with multiple islands. In this procedure, a discrete distance map is computed by shading a right circular cone having the height of a given offset distance, while moving its apex along the boundary curve segments. Using the discrete distance maps, the proposed algorithm effectively extracts the characteristic points or the valid self-intersection points of offset curve segments. For an offset distance, one or more offset profiles are constructed without the topological problems by offsetting the boundary curve segments within the parameter values specified by these chararteristic points, and connecting them into closed profiles using the topological information contained in the distance map. The gouging-free tool path is constructed by connecting these offset profiles, starting from the innermost offset profile. In the proposed method, we do not need any artificial bridges for a pocket with multiple islands to merge the pocket profile and the island profiles into a single boundary profile.     

Incomplete two-manifold mesh-based tool path generation

This paper presents a new paradigm for three-axis tool path generation based on an incomplete two-manifold mesh model; namely, an inexact polyhedron. When geometric data is transferred from one system to another system and tessellated for tool path generation, the model does not have any topological data between meshes and facets. In contrast to the existing polyhedral machining approach, the proposed method generates tool paths from an incomplete two-manifold mesh model. In order to generate gouge-free tool paths, cutter-location meshes (CL-meshes) are generated by offsetting boundary edges, boundary vertices, and facets. The CL-meshes are sliced by machining planes and the calculated intersections are sorted, trimmed, and linked. The grid method is used to reduce the computing time when range searching problems arise. The method is fully implemented and verified by machining an incomplete two-manifold mesh model.     

带任意多岛屿的型腔环切加工刀轨生成

对带任意多岛屿的型腔环切加工刀轨生成进行了研究 ,提出了一种等距环互交处理的快速简便算法 ,设计了多个岛屿之间、岛屿与型腔之间的干涉处理方法 ,算法在超人CAD/CAM软件中实现 ,实践表明 ,该功能模块运行速度快 ,稳定性好 ,具有工程应用价值。     

裁剪B样条曲面重建算法研究

提出了具有不规则边界的裁剪B样条曲面重建方法。采用基准平面对数据点进行参数化，并建立以B样条曲面控制顶点为未知量的超定方程组；提出了基于有效点判别条件的孔洞识别算法，通过对孔洞区域的控制顶点施加顶点形状保持约束,确保方程组最小二乘解的存在；基于误差控制重构B样条曲面整体覆盖数据区域，通过边界线提取或曲面求交剪裁来重构裁剪曲面的边界。该方法具有符合设计意图、曲面在孔洞区域具有良好的形状一致性、曲面重构精度高等特点。     

Double-spiral tool path in configuration space

Using a spiral tool path is a common strategy in many NC machining applications. It can be used for high-speed machining of pockets or as a space-filling curve for finish applications. When using spirals for finishing application, a double spiral is desired to avoid having a starting or end-point at the center of the workpiece. In this paper, we present an algorithm to create a double spiral from offset curves in a precomputed configuration space (c-space). CAD/CAM systems that operate on NURBS surfaces or on triangular meshes have to deal with the issues of patch-boundary oscillations or long, stretched triangles, respectively. This can be avoided when operating in c-space. The c-space is given in the form of a regular quadrilateral heightfield mesh, which may be adaptively subdivided, where the slope is large. This simple data structure is memory efficient and has proven to be beneficial in CAD/CAM frameworks. Our algorithm creates a double spiral by blending adjacent offset curves. The center of the spiral is filled by a b-spline curve. When given offset curves split into multiple components, the algorithm creates multiple smaller spirals and connects them appropriately. The resulting tool path is one large intersection-free curve with starting and end-point on the boundary of the workpiece.     

Tool-path generation for pockets with freeform curves using Bezier convex hulls

The objective of this paper is to generate tool paths for pockets with freeform curves, i.e. Bezier curves or B-spline curves. Time efficiency and overcut avoidance are two of the most important factors in NC machining. A method, based on the convex hull property of Bezier curves, is thus developed so that the portion of the boundary defined by a Bezier curve is replaced by parts of its convex hull on the cavity side. Therefore, the new pocket boundary, redefined by only segments of straight lines, can be solved efficiently based on current algorithms without overcuts. Cutting tool paths can be generated for pockets with islands avoiding computation of higher degree curve/curve intersections. Furthermore, recursive subdivisions on Bezier curves are used to improve the accuracy of the cut with an allowance criterion based on sizes of convex hulls.The portion of the boundary defined by a B-Spline curve is transformed into piecewise Bezier curves. The tool-path generation for pockets with B-spline curves can thus be solved by reducing the problem to one of pockets with Bezier curves.     

基于FANUC系统的等距型面粗铣宏程序开发

铣削加工中,在精加工轮廓程序的基础上,采用改变刀具偏置量大小的方法,可进行工件轮廓的粗铣加工.通过应用FANUC系统宏程序给系统变量赋值的功能,设置刀具半径补偿,探讨了用环切的方法进行直线包络等距型面外轮廓的粗铣加工,达到简化粗铣程序,提高粗加工效率的目的.