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基于三角网格模型的铣削加工路径规划关键技术研究
Alternative TitleResearch on Key Techniques of Triangular Mesh Model Based Milling Tool Path Planning
王华兵1,2
Department先进制造技术研究室
Thesis Advisor王天然 ; 刘伟军
ClassificationTH122
Keyword三角网格 铣削加工刀具路径规划 平面多边形偏置 多边形布尔运算 顶点法矢量估计
Call NumberTH122/W31/2008
Pages124页
Degree Discipline机械电子工程
Degree Name博士
2008-05-30
Degree Grantor中国科学院沈阳自动化研究所
Place of Conferral沈阳
Abstract随着经济的发展,企业的生产呈现出多品种、小批量和定制化的趋势,产品的快速开发能力成为决定企业生存和发展的重要因素之一和迫切的需求。而产品的三维几何量反求工程以及快速成形技术正是在这种形势下发展起来的,为企业的快速产品开发提供了技术上的支持。三角网格模型是反求工程几何建模主要的产品数字模型输出格式之一,也是快速成形制造系统与反求工程以及其它产品建模系统的标准接口。快速成形系统按照输入的三角网格模型制作出实体工件,用于产品的快速开发,但通过快速成形技术制造的零件通常精度比较低,为提高精度,需要对成形工件进行精加工。对于组合曲面所描述的工件的加工路径规划,也通常先将其转化为三角网格的表达形式,再进行处理。在模具加工、自由曲面加工以及其他包含复杂形状工件加工的领域中,数控铣削加工是应用最广的。故对基于三角网格模型的铣削加工刀具路径规划的进行深入的研究是必要和很有意义的。 本文阐述了三角网格的定义、标准数据格式、数据结构、拓扑重建以及绘制方法,分析了基于三角网格模型的加工路径规划的研究现状和存在的问题,选择了一套利用平底铣刀进行粗加工和半精加工、利用球头铣刀进行精加工的三轴铣削加工路径规划的方案。进而着重研究了基于三角网格模型的铣削加工路径规划的若干关键技术,如三角网格模型的适应性分层方法、基于多边形布尔运算的可加工轮廓的计算方法、平面多边形偏置轮廓计算方法和加工路径生成方法等,并利用我们搭建的减式快速成形系统平台对相关的方法的可行性和有效性进行了验证。本文的主要工作包括: (1) 分析了现有的三角网格模型分层算法,针对水平分层粗加工以及半精加工的工序安排下大水平面附近可能存在的加工余量过大的问题,提出了一种基于面片法矢分组以及分组面积阈值准则的适应性分层算法,保证了精加工余量均匀分布。 (2) 针对工件在直角坐标三轴铣床上的可加工性分析问题,提出并实现了一种基于多边形布尔运算的加工轮廓提取算法,为三轴数控铣床实现多面加工的路径规划提供技术基础支持。 (3) 分析了现有的平面多边形偏置算法,针对基于边偏移的算法中凹顶点处的反射现象所引起的复杂自交问题,提出了一种顶点局部调整算法,保证基于边的偏置处理过程的实现。阐述了平面多边形顶点凸凹性的判别方法,并按照凸凹性分类分别给出了顶点的偏置矢量的计算方法。针对用途广泛的点在平面多边形中的包含测试方法,分析了现有的方法的优缺点,并基于射线法提出了一种改进的平面多边形的点包含测试算法。在偏置轮廓多边形局部自交环的处理过程中,我们提出了一种改进的自交环递归分解算法,解决了局部自交环的高效分解问题,同时提出一种综合运用内点射线穿越次数的奇偶性、多边形距离以及一致性规则的局部自交环的有效性判别算法,解决了局部无效环的去除问题。在全局自交环的处理过程中,提出了一种基于顶点搜索的全局自交环分解算法,并运用内点射线穿越次数的奇偶性与环的内外性的关系以及多边形的距离规则解决了全局自交环的有效性判别问题,进而实现了无自交的平面多边形偏置轮廓的计算。 (4) 按照工件加工阶段的划分,分别阐述和实现了基于层面轮廓获取方法以及平面轮廓偏置计算方法的粗加工和半精加工路径生成算法。分析了现有的三角网格曲面顶点法矢量估计方法,提出了两种新的方法,即基于顶点一邻域面片的顶角与相应面片面积的比值加权三角形面片法矢量的计算方法以及基于顶点一邻域的顶角正弦加权三角形面片法矢量的计算方法,并利用球体以及椭球体的三角网格模型比较了各估计方法的计算精度。针对球头刀精加工路径的生成,结合坐标变换、平面等距分层及平面多边形偏置方法实现了行共面初始刀位的计算,同时结合坐标变换、三角网格顶点法矢量估计以及平面分层方法实现了行初始刀触点共面的初始刀位的计算。针对初始刀位的干涉检验和调整问题,提出一种基于二分搜索的刀位点调整方法,实现了无干涉精加工刀位轨迹的生成。
Other AbstractWith the developments of economy, there is a trend of multi-type, small-batch and customization in the production of enterprises. The ability of rapidly developing new products plays a critical role in the survival and development of enterprises and becomes one of their urgent demands. Under such circumstances, the 3D geometrical reverse engineering (RE) and rapid prototyping (RP) technologies are important in rapidly products developing process. Triangular mesh model is one of the main output data formats of the digitalized products in RE and is also the standard data interface between RP and RE and other product modeling systems. According to the triangular mesh model input, the solid part can be manufactured for rapidly product developing by the RP system. However, the accuracy of the part is relatively low for its nature of being laminated. To improve its accuracy, it is necessary to add a finishing process of machining. It is usually an approach to planning the tool path for a compound surface that it is firstly transferred to a triangular mesh and then the tool path is planned on the mesh. Numerical milling is most widely used in machining molds, free form surfaces and other parts with complex surfaces. So it is necessary and significant to make deep researches on triangular mesh based milling tool path planning. In this thesis, some base knowledge about triangular mesh such as its definition, standard data format, data structure, topologically reconstruction method and drawing is introduced. After the precedent works on the path planning based on triangular mesh are reviewed and the existing problems are analyzed, a new approach to the path planning based on triangular mesh for 3-axis milling machine that commits the roughing and semi-finishing processes with flat end milling cutter and commits the finishing process with ball end milling cutter is chosen. And some key techniques on triangular mesh model based milling tool path planning are studied, including adaptive slicing method of triangular mesh, planar polygon Boolean operation based machinable contour computing, planar polygon offsetting and tool path generation. Some parts are machined on the subtractive rapid prototyping platform with the tool paths generated by the new approach to verify its feasibility and validity. The main parts of this thesis are described as follows. 1. On the basis of analysis of the existing slicing methods, a new kind of adaptive slicing method based on facets grouping by their normal vectors and group area threshold value criteria is proposed to solve the problem of uneven finish. 2. A new algorithm based on polygon Boolean operation for machining contour calculation is put forward as an approach to the machinablity analysis of the part on 3-axis milling machine, which is the basis of the tool path planning for multi-face machining of 3-axis numerical controlled milling machine. 3. The existing planar polygon offsetting methods are reviewed and the complex self-intersection cases in the edge offsetting based methods are analyzed, in which the contour polygon can hardly be decomposed to simple ones and it is almost impossible to judge the validity of the contour rings. A recursive locally adjusting vertex method is applied to the concave vertices of the crossing contour polygons to simplify the self-intersection cases of their offsetting rings. The method to classify each vertex in the contour rings into the convex, the plain and the concave is given. According to the classification, the offset vector calculating method is outlined. Point inclusion test for planar polygon is very useful in many kinds of fields and acts a fairly important role in the self-intersection ring arrangement. So the previous methods for point inclusion test is reviewed and the shortcoming of the traditional ray crossing method is analyzed and an improved one based on ray crossing method is proposed. An improved recursive decomposition method is put forward as an effective and efficient approach to the decomposition of the local self-intersection ring. A new method using three rules is proposed to judge the validity of the decomposed rings. The rules are the relation between the parity of internal point ray crossing times and the rotating direction of vertex in the simple ring, distance criterion between rings and conformity of the unique ring. For the global self-intersection ring, a vertex searching based method is applied to decompose the ring into simple ones and a new method using two rules which are the relation between the parity of internal point ray crossing times and the rotating direction of vertex in the simple ring and distance criterion between rings is proposed to judge the validity of the decomposed rings. 4. The path generating method based on crossing contour and planar polygon offsetting for roughing and semi-finishing is given. For vertex normal vector estimation is one of the basis problems in many fields including finishing tool path generation, the existing methods are reviewed and two new methods is presented, one of which uses the ratio of the angle at the vertex and the area of the triangle as the weight of each triangular facet normal in the first order neighbor field of the vertex and the other of which uses the sine value of the angle at the vertex as the weight of each triangular facet normal in the first order neighbor field of the vertex. To determine which of these vertex normal vector estimating methods are better, the deviation angle between the theoretic normal vector and the estimated one is made the error evaluation standard factor. The ball and elliptical ball manifold triangular mesh models are used to analyze the performance of all these estimating methods. For finishing tool path generation, the initial cutter location point locus with row in a common plane is calculated through coordination transformation, slicing with constant step and planar polygon offsetting. Another initial cutter location locus with cutter contact point row in a common plane is calculated through coordination transformation, vertex normal vector estimation for triangular mesh and slicing with constant step. To verify the initial path and adjust the invalid point, a half-partition based searching method is adopted and the gouge free finishing path is generated.
Language中文
Contribution Rank1
Document Type学位论文
Identifierhttp://ir.sia.cn/handle/173321/274
Collection工业信息学研究室_先进制造技术研究室
Affiliation1.中国科学院沈阳自动化研究所
2.中国科学院研究生院
Recommended Citation
GB/T 7714
王华兵. 基于三角网格模型的铣削加工路径规划关键技术研究[D]. 沈阳. 中国科学院沈阳自动化研究所,2008.
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