Rough cut tool path planning for B-spline surfaces using convex hull boxes

The objective of this paper is to present a non-uniform layered rough cut plan for B-spline surfaces using convex hull boxes. The tool path plan generated by this method will rapidly remove most redundant material from stock material without overcutting.First, a B-spline surface is decomposed into piecewise Bezier surfaces, of which the convex hull boxes form an approximate model for rough cutting. Then, according to the top planes of those convex hull boxes, the stock material is divided into layers of different thickness. The cavity contour for each layer is obtained using a simplified union Boolean operation on convex hull boxes. Finally, from the top down, each layer is processed like a 2D pocket die cavity.The algorithm is implemented on a personal computer. It is shown that the rough cut plan is very efficient since no computation for solving nonlinear equations is needed, and no overcutting occurs since B-spline surfaces are protected by the convex hull property of Bezier surfaces.     

B样条曲面在模具型腔描述及3维网格生成中的应用

采用３次Ｂ样条曲面进行模具型腔及锻件动态几何构形描述,提出基于Ｂ样条曲面描述的３维网格样条生成技术及改进的分块样条生成法,探讨了复杂锻件网格生成中的子域部分、疏密网格过渡、子域拼装等技术技巧。     

自由曲面的非等参数超声检测轨迹生成算法

针对复杂曲面工件内部缺陷的超声检测，提出了一种新的近似等弧长超声检测轨迹生成算法。该方法采用近似等弧长方法对参数重新进行参数化，使生成的扫查点间距分布更合理，与等参数的复杂曲面超声检测轨迹生成法相比，在满足扫查要求的前提下，检测点数明显减少，从而可生成更有效的检测轨迹。仿真实验表明，所提出的方法是有效、可行的，运用该方法可提高工件的检测效率和检测系统的利用率。     

利用数值图谱法进行多杆直线导向机构的轨迹综合

给出了类四杆五杆机构的几何约束条件,讨论了类四杆五杆机构连杆轨迹与连杆转角算子之间的关系,建立了包含137052组机构基本尺寸型的特征参数数值图谱库,实现了对带有预定时标多杆直线导向机构的轨迹综合,文中最后给出了算例对其进行验证。     

A Rough Set Approach to the Ordering of Basic Events in a Fault Tree for Fault Diagnosis

The performance of manufacturing systems or equipment is, to a great extent, dependent upon the condition of their components. Closely monitoring the condition of the critical components and carrying out timely system diagnosis whenever a fault symptom is detected would help to reduce system downtime and improve overall productivity. Fault tree analysis (FTA) is a powerful tool for reliability studies and risk assessment. However, most research on FTA focuses on the generation of minimum cut sets and how to calculate the probability of main events. As a result, the issue concerning the ordering of basic events in a fault tree has been largely neglected. In this paper, a novel approach based on rough set theory and a pairwise comparison table for fault diagnosis is proposed. The approach attempts to learn from the pattern of decision-making by domain experts from past experience and uses the knowledge acquired, which is in the form of a minimum decision rule set, to determine the ordering of basic events in a fault tree. The details of the approach, together with the basic concepts of rough set theory, are presented. A case study is used to illustrate the application of the proposed approach. Results show that a reasonable ordering of basic events in a fault tree can be generated easily. With the ordering of basic events determined, a maintenance engineer in a manufacturing plant can then carry out fault diagnosis in an efficient and orderly manner.     

G2 Continuity for Multiple Surfaces Fitting

Fitting 3D known data into sculptured surfaces has received extensive attention. However, most algorithms available are suitable only for an isolated surface. A part typically contains multiple surface regions that must be blended to a degree of continuity. The conventional approach based on blending, lofting, stitching, etc. cannot guarantee the quality of the surface near the jointed area. The purpose of this work is to present a surface-fitting algorithm for multiple sets of data, concentrating on G 2 continuity across the boundary of the fitted surfaces. The proposed surface-fitting algorithm essentially fits several sets of data simultaneously, and yields a B-spline surface for each set of data. The G 0 ,G 1 , and G 2 continuity conditions between B-spline surface patches were addressed. Based on these results, additional constraints were specified to achieve G 2 continuity across the surface boundary. A successful demonstration of the proposed strategy is provided also.     

A Path Interval Generation Algorithm in Sculptured Object Machining

The features of a sculptured object are represented by a set of section curves. A fast algorithm is presented to calculate cutting depths based on the scallop height using these curves. The calculated cutting depth can be used for tool-path generation. This tool-path generation approach is particularly useful for constant z level contouring and high-speed machining.     

Modeling Clutter from Bosnian and Puerto Rican Rough Ground Surfaces for GPR Subsurface Sensing Applications Using the SDFMM

The Steepest Descent Fast Multipole Method (SDFMM) is used to analyze the distorting effect of random rough ground surfaces on scattered and transmitted electromagnetic waves. Two well-measured loamy soils: Bosnian and Puerto Rican clay loam are investigated, each with a variety of surface roughness. This study is important in understanding the effects of different soil properties and is meant to be an a priori phase of investigating scattering from buried targets under the rough ground. In this work, we investigated the scattering from rough soil ground without buried objects. The SDFMM is an integral equation-based fast algorithm that is well suited for two-dimensional penetrable rough surfaces (3-D scattering) in the frequency domain. The scattered and transmitted near electric field of an incident Gaussian beam are calculated at different locations above and below the mean plane of the dielectric rough interface. The receiver locations above are chosen to simulate GPR measurement protocols. The obtained numerical results show that the scattered field undergoes more distortion than the transmitted field from both soil types. Moreover, the transmitted fields into the higher dielectric constant Puerto Rican soil experience more distortion than those transmitted into Bosnian soil.     

对称多型腔粗加工刀轨快速生成算法

对具有对称特性的多型腔零件的刀轨规划方法进行了研究，提出了一种新的算法：首先生成其中一个型腔的刀轨，然后通过阵列生成其余刀轨，并对刀轨的进退刀进行处理，从而快速生成完整的、连续的、有序的刀具轨迹。该算法尤其适用于高速加工的刀轨规划，实践表明，可大大提高编程效率．节省加工时间。     

基于混沌的平面四杆机构轨迹综合优化设计

对于解决平面四杆机构轨迹综合等复杂非线性约束优化问题,传统优化算法存在局部收敛等缺点。对混沌的特性及其优化应用进行了分析,建立了混沌结合传统Powell法的混合算法。设计实例表明,该方法全局收敛性好,搜索效率高,是解决工程设计中具有复杂非线性约束优化特性问题的理想方法。     

自由曲面NC加工无干涉刀具轨迹生成

对自由曲面ＮＣ加工中的干涉情况和现有处理方法进行分析，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。综合多种优化措施，设计一个完整与高效的无干涉刀具轨迹生成算法并在微机上成功地实现。     

Robust Spiral Tool-Path Generation for Arbitrary Pockets

When converting CC data (cutter contact point data) into CL data (cutter location data) for tool-path generation for arbitrary pockets, overcut avoidance plays an important role in CNC pocket milling. Complicated calculations of the self-intersections in the offset of spiral cutting is one of the main considerations in some algorithms. This study presents a quasi-offset method to solve complicated self-intersection calculations. Instead of using offsetting methods, the proposed method uses the location points and their track types to generate the son loop. The proposed quasi-offset method also makes it much easier to generate spiral tool paths.     

超光滑表面的加工、表征和功能

超精密加工的目标是通过表面质量控制获得预定的表面功能。一定的加工过程产生相应的表面特征 ,而表面特征在很大程度上又决定着表面的实际功能。为了通过预先设计及加工控制获得要求的功能表面 ,必须对超光滑表面的加工、表征、功能及其相互关系进行全面而深入的研究     

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。     

用广义逆矩阵及Roberts-Chebyshev定理进行再现计时轨迹平面铰链四杆机构的近似运动综合

提出了再现计时轨迹平面铰链四杆机构近似运动综合的一种新方法。首先利用 Ｒｏｂｅｒｔｓ Ｃｈｅｂｙｓｈｅｖ 定理将再现计时轨迹四杆机构运动综合转化为刚体导引四杆机构的运动综合。然后用广义逆矩阵将刚体导引四杆机构的近似运动综合方程组转化为二元二次多项式方程组,采用连续法或消元法求解该方程组,即可得到刚体导引四杆机械近似运动综合方程组的所有解。由刚体导引四杆机构近似运动综合方程组的每一组解出发,利用 Ｒｏｂｅｒｔｓ Ｃｈｅｂｙｓｈｅｖ 定理,可分别得到再现计时轨迹四杆机构近似运动综合的两组解,这样便求得再现计时轨迹四杆机构近似运动综合的所有机构方案。     

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。     

复杂型腔行切轨迹生成算法研究

复杂型胶类零件的加工是数控编程中的一个难点.本文从提高加工算法的稳定性和加工效率的角度出发.提出了一个复杂平面型腔数控加工的优化算法.即通过二维环的等距、自交、集合等基本运算.按“端点同环最短距离优先剖面线算法”规划并优化刀具轨迹.最后给出了应用实例.     

基于遗传算法和结构误差的平面四杆机构轨迹优化综合

提出了基于结构误差进行平面四杆机构轨迹优化综合的方法。基于结构误差建立了一个统一的优化综合模型 ,使连杆轨迹曲线上的点与原动件的运动可以相关也可以不相关 ,采用改进的遗传算法进行优化计算 ,保证了获得全局最优解。该优化综合模型应用与机构分析相同的解析函数方法来完成机构的轨迹综合 ,因此计算便利。给出了三个综合实例 :与原动件运动不相关的直线轨迹和直角轨迹、与原动件运动相关的 8字形轨迹 ,结果表明了本方法的有效性     

A Next Generation NC Machining System Based on NC Feature Unit and Real-Time Tool-Path Generation

In order to improve the control and information integration capability of an NC machining system, this paper provides a new concept – an NC feature unit (NCFU), which is a feature-based and a basic control unit. First, as a feature-based control unit, NCFU possesses geometric form and control parameters, which are a subclass of high-level CAD/CAM features so that it can be used as an information exchange medium between NC machining systems and other manufacturing execution systems. Secondly, as a basic machining control unit, NCFU uses a geometrically defined closed and non-gouging machined area. On the one hand, through decompo-sition, a machined object can be divided into a combination of several NCFUs. On the other hand, since NCFUs are non-gouging, the algorithm for NCFU-based tool-path generation is simple enough to be executable in real-time. This paper discusses NCFU-based applications in 2.-D profile/pocket and 3D surface mill machining, including the NCFU definition and the related algorithms for decomposition calculation and area interpolation. A next generation NC machining system based on NCFU, including an NCFU-based NCP and an NCFU-based CNC system, has been prototyped by China’s State 863/CIMS Design Automation Laboratory in Beijing University of Aeronautics and Astronautics. An NCFU is being used as the information exchange medium in an internet-integrated manufacturing system with NC machining at Hong Kong Polytechnic University.     

计入润滑油粘压效应和表面形貌的倾斜轴颈轴承润滑分析

提出了轴颈倾斜情况下的轴承油膜厚度方程。采用平均Reynolds方程，分析了倾斜轴颈轴承的润滑性能。通过不考虑和考虑润滑油粘压效应的轴承润滑性能对比，验证了分析倾斜轴颈轴承润滑性能时计入润滑油粘压效应的重要性；通过光滑轴承与粗糙轴承润滑性能的对比，验证了分析倾斜轴颈轴承润滑性能时考虑表面粗糙度影响的必要性。计算了不同偏心率、轴颈倾斜角、表面粗糙度、表面方向参数下的轴承润滑性能，结果表明，表面粗糙度在最小油膜厚度较小时对倾斜轴颈轴承润滑性能产生影响，而表面方向参数在最小油膜厚度与综合粗糙度的比值较小时会对倾斜轴颈轴承润滑性能产生显著影响。