基于压缩索引的二阶四面体网格等值面抽取方法

基于二阶10节点四面体网格单元可视化过程中存在的等值面拓扑、三角等值面片结果的计算、存储及传输代价问题,提出了基于压缩索引的等值面抽取方法。为真实表现网格单元内部等值面片拓扑结构并克服其二义性,分析并简化了二阶10节点四面体单元等参插值函数,提出顶点、棱边、表面间的关系矩阵,分别在网格单元棱边、表面及体内计算提取可以表现等值面几何拓扑特征的等值点,设计了关键点匹配规则;结合三类插值点间的逻辑关系制定了令拓扑准确唯一的等值面片三角化及优化策略,设计了辅助三角化、图像优化及绘制过程的可分裂式三角面片压缩索引结构,提出了针对初始面片及优化后面片存储结构的分裂策略。试验结果证明,该方法可准确描述及确定二阶四面体网格单元内部等值面片的唯一拓扑结构,基于压缩索引结构的计算及优化分裂方法简捷有效,可适应不同的精度要求,大幅降低了计算与绘制传输中产生的代价。     

基于powermill的stl义齿模型数控编程的研究

提出了直接利用powermill对stl多面体义齿模型进行刀轨计算的方法,完成了stl多面体义齿模型在powermill数控编程软件中刀具轨迹计算和仿真的尝试,并成功的利用三轴数控加工机床加工出了义齿模型.     

复杂型腔无退刀环切刀具轨迹连接方法

为克服传统环切轨迹连接方法的不足,提出了一种简单有效的环切刀具轨迹连接方法.在该轨迹连接方法中,轨迹环被组织成区域树的形式,区域树的每个节点对应一次偏置操作的结果;为了编组轨迹环,利用轨迹环间的嵌套关系将区域树剖分为轨迹簇,进而利用过渡点和虚过渡点完成了轨迹簇的连接,形成了子轨迹;合并了多条子轨迹,以使生成的轨迹完全没有退刀.利用无需额外计算的区域树,改善了传统无退刀轨迹连接算法在处理大规模问题上的效率.     

面向复杂曲面的喷涂机器人喷枪路径的规划

根据试验数据给出了涂层生长速率模型,将自由曲面通过拓扑关系生成若干个平面片,在每一片上进行喷枪速率及轨迹间距的优化,基于面片交界处喷枪轨迹为PA-PA时涂层厚度均匀性较好的原则,根据面片的边界几何特征对喷枪路径进行了规划,提出了用变偏距的方法优化Z型路径模式,该方法通过选择两轨迹间的偏距极值及始末轨迹的长度来确定每相邻轨迹间的偏角来达到变偏距的目的,给出了其中参数的计算方法和优化算法。最后通过实例验证了该算法对Z型路径模式的优化具有一定的可行性。     

基于改进型Butterfly细分的三角网格自由曲面环形刀具轨迹规划

针对刀具轨迹连续性差、切削刀具负荷波动大的问题,提出一种基于改进型Butterfly细分的三角网格曲面环形刀具轨迹规划方法。以三角网格曲面的几何特征为基础构建曲面定点数据表达结构,结合环形刀的几何特征对刀触点(CC点)的刀具曲面及工件曲面进行几何分析,构建三角网格曲面环形刀切削模型。根据切削刀具干涉原理计算刀具的最小前倾角以获得切削路径的最大宽度,并据此采用改进型Butterfly细分方法对三角网格曲面进行细分,使刀具轨迹的行距达到切削路径宽度的要求。以曲面轮廓曲线为初始刀具轨迹,沿着三角网格边界进行螺旋型刀具轨迹刀触点(CC点)的逐行规划,最终根据环形刀几何模型求解刀心(CL点)位置。根据选择的刀具参数和给定的残余高度要求,仿真生成的三角网格曲面螺旋刀具轨迹的连续性好,从而降低了切削刀具负载的波动,最后通过机加工实验验证了刀具轨迹的可行性。     

变螺距不等深异形螺杆的几何建模及数控加工

基于变螺距不等深异形螺杆几何成形原理,分析几何建模难点,建立数学计算模型.生成轨迹曲线,巧妙控制扫掠方法构建精准几何模型;在此基础上,根据变螺距不等深异形螺杆螺旋槽型面要求,设计工艺方案,提出刀具轨迹计算方法.完成了复杂异形螺杆的几何建模及数控加工,实现了CAD与CAM无缝连接.     

面向增材制造的机器人轨迹自动生成技术

针对同轴送粉激光熔覆成形复杂曲面的工艺过程中,机器人轨迹规划困难的问题,提出一种从CAD模型自动生成机器人加工轨迹的新方法,以提高机器人熔覆的效率。首先对复杂曲面零件模型进行分析,采用拉普拉斯算子的方法对网格模型进行了优化。根据立体光刻模型提取零件的几何信息,基于三角面片边的拓扑关系重建三角面片的拓扑关系,通过包围盒的方法生成沿逆时针方向的机器人轨迹,利用仿真实验动态地演示了熔覆过程。最后,通过熔覆实验验证了该方法生成机器人轨迹的可行性。     

基于约束矩阵的数控车刀几何参数决策方法

针对数控车削刀具几何参数决策问题,结合数控车削刀具的特点和数控车削刀具几何参数选择的规则,提出基于约束矩阵的数控车削刀具几何参数决策方法。该方法从数控车削刀具几何参数的结构化表达机制、数控车削刀具与影响刀具几何参数选择的因素之间的映射关系等方面出发,构建数控车削刀具综合信息模型框架。基于该模型,采用参数选择约束矩阵表达数控车削刀具几何参数选择规则,计算数控车削刀具几何参数的权重优先级矩阵,构建数控车削刀具几何参数选择决策算法,最终实现对数控车削刀具几何参数的选择。以某企业零件的数控车削刀具选择为例,验证了该决策算法的可行性和有效性。     

散热翅片刀具斜坡加工线切割轨迹求解

建立线切割轨迹的几何模型,并推导渐开线齿轮形刀具斜坡加工线切割轨迹的求解过程,为线切割轨迹的产生提供理论依据。根据轨迹的求解过程,运用VB编制通用计算程序。利用Pro/E建立轨迹的三维模型,以三维模型为基础,提取其中的数据求出轨迹上若干点的坐标值,其结果与求解结果相吻合。计算结果表明,求解方法适合于产生线切割轨迹。试验验证了求解方法的有效性。     

基于CGAL的点云三角面片重构

点云的三角面片重构是曲面重构的基础,通过三角面片重构可得到离散点的邻接关系,这些邻接关系为曲面拟合提供必要的信息.介绍了一个功能强大的计算几何库CGAL,并利用它完成对面模型的点云三角面片重构和体模型的点云三角面片重构.     

R树上溢结点增量式k均值聚类优化分裂方法

R树能较好地满足逆向工程、CAD/CAM、机器视觉等领域的动态数据维护及空间查询需求,而CR树是其优秀的变体之一。针对CR树的上溢结点分裂算法存在的聚类结果不理想以及计算代价过高等问题,提出一种主元分析导向的增量式k均值算法,可在既有分类中心附近的第一主元方向上搜索新的初始分类中心。将该算法与Silhouette指标相结合应用于求解由上溢结点分裂问题所转化的点集聚类问题,能以较小的计算代价自适应获取近似全局最优的点集聚类结果。试验结果表明,基于增量式聚类的R树上溢结点分裂算法在R树构建效率、存储利用率及空间查询等方面的综合性能优于CR树与RR*树。     

Extracting cutter/workpiece engagements in five-axis milling using solid modeler

Predicting cutting forces in milling process simulation requires finding cutter/workpiece engagements (CWEs). The calculation of these engagements is challenging due to the complicated and changing intersection geometry between the cutter and the in-process workpiece. In this paper, a solid modeling based methodology for finding CWEs generated in five-axis milling of free form surfaces is presented. The proposed methodology is an extension of the solid modeler based three-axis CWE extraction method given in [21]. At any given instant of the five-axis tool motion, the velocity vectors along the cutter axis may move in directions that do not lie in the same plane, and therefore the cutter envelopes need to be approximated by spline surfaces. Considering the spline surface approximations, the CWE methodology described in [21] does not work properly for the five-axis milling. Therefore in the proposed method, the in-process workpiece is used instead of the removal volume for extracting the CWEs. A terminology the feasible contact surfaces (FCS), defined by the envelope boundaries, is introduced. To extract the CWEs at a given cutter location, first the BODY entity, obtained by offsetting the FCS with an infinitesimal amount, is intersected with the in-process workpiece. Then, the resultant removal volume is decomposed into faces. Finally, the surface/surface intersections are performed between those faces and the FCS to obtain the CWE boundaries. To be used in the force model, the CWE boundaries are mapped from Euclidean 3D space to a parametric space defined by the engagement angle and the depth-of-cut for a given tool geometry.     

Efficient registration for precision inspection of free-form surfaces

Precision inspection of free-form surface is difficult with current industry practices that rely on accurate fixtures. Alternatively, the measurements can be aligned to the part model using a geometry-based registration method, such as the iterative closest point (ICP) method, to achieve a fast and automatic inspection process. This paper discusses various techniques that accelerate the registration process and improve the efficiency of the ICP method. First, the data structures of approximated nearest nodes and topological neighbor facets are combined to speed up the closest point calculation. The closest point calculation is further improved with the cached facets across iteration steps. The registration efficiency can also be enhanced by incorporating signal-to-noise ratio into the transformation of correspondence sets to reduce or remove the noise of outliers. Last, an acceleration method based on linear or quadratic extrapolation is fine-tuned to provide the fast yet robust iteration process. These techniques have been implemented on a four-axis blade inspection machine where no accurate fixture is required. The tests of measurement simulations and inspection case studies indicated that the presented registration method is accurate and efficient. This work was supported primarily by the NSF Engineering Research Center for Reconfigurable Manufacturing Systems as part of the Engineering Research Centers Program of the National Science Foundation under NSF Award Number EEC 95-29125.     

基于R树的物联网医院信息管理系统仿真与研究

为提高医院医疗数据管理效率,在研究了物联网、数据检索模型基础上,本文设计了一种基于物联网的医院信息管理系统。针对所选簇数与实际空间数据分布不匹配、易受离群数据影响的问题,提出了DCC算法构建了智能医院信息管理系统中的R树。通过仿真分析,结果表明所提方法基于R树索引的数据高效检索提高了系统的工作速度。     

Pre-compensation for continuous-path running trajectory error in high-speed machining of parts with varied curvature features

Parts with varied curvature features play increasingly critical roles in engineering, and are often machined under high-speed continuous-path running mode to ensure the machining efficiency. However, the continuous-path running trajectory error is significant during high-feed-speed machining, which seriously restricts the machining precision for such parts with varied curvature features. In order to reduce the continuous-path running trajectory error without sacrificing the machining efficiency, a pre-compensation method for the trajectory error is proposed. Based on the formation mechanism of the continuous-path running trajectory error analyzed, this error is estimated in advance by approximating the desired toolpath with spline curves. Then, an iterative error pre-compensation method is presented. By machining with the regenerated toolpath after pre-compensation instead of the uncompensated toolpath, the continuous-path running trajectory error can be effectively decreased without the reduction of the feed speed. To demonstrate the feasibility of the proposed pre-compensation method, a heart curve toolpath that possesses varied curvature features is employed. Experimental results indicate that compared with the uncompensated processing trajectory, the maximum and average machining errors for the pre-compensated processing trajectory are reduced by 67.19% and 82.30%, respectively. An easy to implement solution for high efficiency and high precision machining of the parts with varied curvature features is provided.     

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.     

Two-directional toolpath correction in single-point incremental forming using model predictive control

Incremental sheet forming (ISF) is an emerging forming technology that promises high flexibility and formability. These properties make it suited for small-scale and customised production. However, the poor geometric accuracy of ISF limits the wide application of this flexible forming technology. This paper presents a two-directional toolpath correction approach to enhance ISF forming accuracy using a model predictive control (MPC) algorithm. A toolpath optimisation method for vertical toolpath correction has been validated in our previous work (Lu et al., Int J Adv Manuf Technol 72:1–14, 2015), and it helps to reduce errors in the base of the test shapes to a suitable level while its major limitation is that horizontal geometric errors are relatively large. This paper extends our previous work (Lu et al., Int J Adv Manuf Technol 72:1–14, 2015) by augmenting the vertical control module with a new control module for horizontal toolpath correction. The proposed control algorithm was experimentally validated in single-point incremental sheet forming (SPIF) using two forming case studies. In the first case study (a truncated pyramid), two control approaches with different assumptions for the horizontal springback distribution along the horizontal cross-sectional profile were tested and compared. Then, the developed MPC control algorithm was applied to form a more complex asymmetric shape. The results show that the developed strategy can reduce the forming errors in the wall and base of the formed shape compared to the existing works. The ISF process with MPC control leads to significant accuracy improvement in comparison with the typical ISF process that is without toolpath control.     

Tool-path planning for rough machining of a cavity by layer-shape analysis

In the manufacture of parts with sculptured cavities from prismatic stock, rough machining usually constitutes most of the machining time owing to the significant difference between the stock and the part shape. When using 2 1/2-D milling or a contour-map approach to do the rough machining, the appropriate selection of tool-path pattern for each cutting layer can significantly reduce rough machining time and hence increase productivity. In this paper, the commonly used toolpath patterns are summarised. A knowledge-based parametric approach for optimising the toolpath pattern of a given cutting layer is proposed. Then, a novel methodology is developed to calculate an arbitrary polygon area and locate the concave cavities in the polygon. Procedures for cutting-layer-shape analysis and the optimal comprehensive tool-path pattern generation are also built and proposed in this paper. These procedures can not only be applied to sculptured cavity parts with simple islands, but also to parts with arbitrarily-shaped islands. Finally, an example is given to illustrate the reasoning process.     

Tool path generation method for multi-axis machining of helical milling cutter with specific cross-section profile

The geometry of helical milling cutter with specific cross-section profile is normally generated with form cutter by the toolpath generating method. The general purpose CAD/CAM software can generate the cutter location file of this class of product only by the sculpturing method. To obtain the flexibility of machining process, this paper presents an interference-free toolpath generating method for semi-finish and finish machining of the helical milling cutter. The method for design and machining of the helical milling cutter is established based on the differential geometry and the enveloping theory. In the finish machining of helical milling cutter, the form grinding wheel profile is firstly derived. To reduce the cost and lead time of the generating method with the form-mill cutter for semi-finish machining, a toolpath generating method which combines the advantages of the generating method and sculpturing method was presented. The cutter location uses ball-nose conical end mill is derived according to the geometric characteristics of the enveloping element. The cutting simulations with solid model were performed to verify the proposed toolpath generation method.