基于刀具空间包围体算法的数控切削仿真

采用计算刀具空间包围体和刀具旋转体的方法来对仿真过程中的有效切削计算进行判断,刀具在一般运动情况下所占空间包围体的计算公式可由刀具的长度、半径以及刀具在任意时刻的刀位点、刀轴矢量来共同推导;刀具的旋转体范围可以通过刀具在当前时刻的刀轴矢量、母线方程以及刀具的半径、长度进行计算.该方法已经成功应用到基于OpenGL的VC6.0环境下所开发的五轴数控仿真系统中,实验结果表明,该方法能够提高有效切削率和减少切削计算耗时.     

Hybrid cutting simulation via discrete vector model

Geometric cutting simulation and verification play an important role in detecting NC machining errors in mold and die manufacturing, thereby reducing the correcting time and cost on the shop floor. According to workpiece model, current researches may be categorized into view-based, solid-based, and discrete vector-based methods. Each methodology has its own strengths and weaknesses in terms of computing speed, representation accuracy, and its ability to perform numerical inspection. This paper proposes a cutting simulation methodology via a hybrid workpiece model which consists of the general discrete vector model and its simplified model. Workpiece modeling scheme, cutting simulation via tool swept surface modeling and vector intersection, and some case studies of mold and die machining are presented in this paper.     

End mill design and machining via cutting simulation

This paper describes a design process for an end mill. A solid model of the designed cutter is constructed together with the computation of the cutter’s geometry, wheel geometry, and wheel positioning data for fabricating end mills with the required cutter geometry. The main idea of the process is to use the cutting simulation method to obtain the machined shape of an end mill by using Boolean operations between a given grinding wheel and a cylindrical workpiece (raw stock). The major design parameters of a cutter, such as rake angle and inner radius, can be verified by interrogating the section profile of its solid model. This study investigates the relationship between various dimensional parameters and proposes an iterative approach to obtain the required geometry of a grinding wheel and cutter location (CL) data for machining an end mill that satisfies the design parameters. This research was implemented using a commercial computer aided design (CAD) system with API function programming and is currently used by a commercial tool maker in Korea. It can eliminate the need to produce a physical prototype during the design stage and can be used in virtual cutting tests and analyses.     

煤岩刨削中的刨刀受力有限元模拟研究

建立刨煤机刨刀刨削煤层的三维模型,利用有限元分析软件LS-DYNA,模拟刨刀刨削煤层的过程。通过研究,得到了刨削速度、刨刀刨削阻力等的时间历程曲线,分析了不同刨削深度、刨刀间距和刨刀宽度对刨削阻力的影响。     

Mesh cutting during real-time physical simulation

The ability to cut through meshes in real-time is an essential ingredient in a number of practical interactive simulations. Surgical simulation, cloth design, clay sculpting and many other related VR applications require the ability to introduce arbitrary discontinuities through models to separate, reposition, and reshape various pieces of the model as needed for the target application. In addition, in order to provide the necessary realism for these applications, model deformations must be computed from an underlying physically-based model—most commonly a continuum-based finite element model.In this work, we present a method for representing and computing, at interactive rates, the deformations of a mesh whose topology is being dynamically modified with multiple virtual tools. The method relies on introducing controlled discontinuities in the basis functions used to represent the geometry of deformation, and on fast incremental methods for updating global model deformations. The method can also generate the forces needed for force rendering in a haptic environment. The method is shown to scale well with problem size (linearly in the number of nonzeros of the Cholesky factor) allowing realistic interaction with fairly large models.     

基于LS-DYNA刨刀刨削煤岩的模拟研究

利用有限元分析软件LS-DYNA,建立刨煤机刨刀刨削煤层的三维模型,模拟刨刀刨削煤层的动态过程。研究中,获取了刨刀刨削阻力、应力分布等时间历程曲线,分析了刨刀不同刨削深度、刨刀间距和刨刀宽度对刨削能耗的影响。     

Parallel simulation of DEDS via event synchronization

In this paper we use the event synchronization scheme to develop a new method for parallel simulation of many discrete event dynamic systems simultaneously. Though a few parallel simulation methods have been developed during the last several years, such as the well-known Standard Clock method, most of them are largely limited to Markovian systems. The main advantage of our method is its applicability to non-Markovian systems. For Markovian systems a comparison study on efficiency between our method and the Standard Clock method is done on Connection Machine CM-5. CM-5 is a parallel machine with both SIMD (Single Instruction, Multiple Data) and MIMD (Multiple Instruction Multiple Data) architectures. The simulation results show that if event rates of Markovian systems do not differ by much then both methods are compatible but the Standard Clock method performs better in most cases. For Markovian systems with very different event rates, our method often yields better results. Most importantly, our simulation results also show that our method works as efficiently for non-Markovian systems as for Markovian systems.     

Algorithms for 3D guillotine cutting problems: Unbounded knapsack, cutting stock and strip packing

We present algorithms for the following three-dimensional (3D) guillotine cutting problems: unbounded knapsack, cutting stock and strip packing. We consider the case where the items have fixed orientation and the case where orthogonal rotations around all axes are allowed. For the unbounded 3D knapsack problem, we extend the recurrence formula proposed by [1] for the rectangular knapsack problem and present a dynamic programming algorithm that uses reduced raster points. We also consider a variant of the unbounded knapsack problem in which the cuts must be staged. For the 3D cutting stock problem and its variants in which the bins have different sizes (and the cuts must be staged), we present column generation-based algorithms. Modified versions of the algorithms for the 3D cutting stock problems with stages are then used to build algorithms for the 3D strip packing problem and its variants. The computational tests performed with the algorithms described in this paper indicate that they are useful to solve instances of moderate size.     

Hybrid heuristic algorithm for two-dimensional steel coil cutting problem

This paper is concerned with the problem of two-dimensional cutting of small rectangular items, each of which has its own deadline and size, from a large rectangular plate, whose length are more than one thousand times its width, so as to minimize the trim loss and the reduction of the times of clamping and changing speed are also concerned. This problem is different with the classical two-dimensional cutting problem. In view of the distinguishing features of the problem proposed, we put forward the definition of non-classical cutting, that is to say, put a series of items on the rectangular plates in their best layout, so as to enhance utility and efficiency at the same time. These objectives may be conflicting and a balance should be necessary, so we present a Hybrid Heuristic Algorithm (HHA), consisting of clustering, ordering, striping and integer programming etc. We demonstrate the efficiency of the proposed algorithm through the comparison with the algorithm we studied before.     

CO_2激光器加工晶圆切缝控制工艺研究

晶体硅是当前最重要的半导体材料,主要用于微电子技术。随着微电子技术的发展,对晶圆的切割技术要求越来越高,而在实际切割中,对晶圆的切割十分注重于晶圆的切割宽度,以降低晶圆损耗。研究CO2激光切割机的脉宽、频率以及切割速度对晶圆切割宽度的影响,从而达到高效率、小宽度、高标准的激光切割加工。     

原位脱碳流化床煤气化反应器的数值模拟

为了减少温室效应,对于煤气化过程中CO_2的减排与零排放技术的研究成为必要。本文建立了全面的煤气化反应器的数值模型,对以CaO作为吸收剂的原位脱碳的流化床煤气化反应器进行了数值模拟。模拟以简化结构的二维反应器为求解域,应用标准k-ε模型描述气相湍动,EDC模型描述反应器中湍流与反应的偶合,EDC模型将详细的化学动力学融入到湍流混合中。讨论了反应器中温度、气速、压力及气体产物的分布。     

玻璃切割系统的设计与实现

玻璃切割系统是玻璃行业用于切割各种玻璃的自动化的数控系统,介绍了玻璃切割系统JXGC的设计与实现,特别分析了其中采用的专门针对玻璃切割的CAD技术。     

基于CASE推理的排样算法

优化排料的目的是根据给定待排样品对板材进行最优切割使得板材的利用率尽可能的高。提出了一种基于case推理的优化排样算法,基本思想是对每块板材的布局都进行case推理,选取CASE中的最佳布局,若没有相应的Case,则调用启发式算法搜索。算法不但避免了组合爆炸,加快了排料速度,而且具有满意的材料利用率。目前算法已集成了作者研制的《布局之星》切割系统,实际应用表明算法是成功的。     

基于贪心算法与多边形剖分的印鉴匹配算法

将计算几何中平面点集的三角剖分方法之一贪心算法与多边形三角剖分方法引入印鉴匹配,研究了一种基于三角网格(用贪心算法进行平面点集的三角剖分)的印鉴匹配方法.用贪心算法对基于线条的细节点集进行三角剖分,而对于基于多边形的细节点直接进行多边形的三角剖分.通过对两种细节点(基于线条的细节点和基于多边形的细节点)的拓扑结构进行三角划分,把空间上位置相近的细节点按照一定的规则相连,得到三角形网格.然后基于该网格寻找若干参考点对,并根据获得的参考点对将两幅印鉴图像进行姿势调整.最后使用获得的参考点时实现基于点模式的印鉴匹配,经分析该方法是一种行之有效的印鉴识别方法.     

Heuristic for constrained T-shape cutting patterns of rectangular pieces

T-shape patterns are often used in dividing stock plates into rectangular pieces, because they make good balance between plate cost and cutting complexity. A dividing cut separates the plate into two segments, each of which contains parallel strips, and the strip orientations of the two segments are perpendicular to each other. This paper presents a heuristic algorithm for constrained T-shape patterns, where the optimization objective is to maximize the pattern value, and the frequency of each piece type does not exceed the demand. The algorithm considers many dividing-cut positions, determines the pattern value associated to each position using a layout-generation procedure, and selects the one with the maximum pattern value as the solution. Pseudo upper bounds are used to skip some non-promising positions. The computational results show that the algorithm is fast and able to get solutions better than those of the optimal two-staged patterns in terms of material utilization.     

A note on envy-free cake cutting with polynomial valuations

The cake cutting problem models the fair allocation of a heterogeneous divisible resource among multiple players. The central fairness criterion is envy-freeness and a major open question in this domain is the design of a bounded protocol that can compute an envy-free allocation of the cake for any number of players. The only existing finite envy-free cake cutting protocol for any number of players, designed by Brams and Taylor [4], has the property that its runtime can be made arbitrarily large by setting up the valuation functions of the players appropriately. Moreover, there is no closed formula that relates the valuation functions to the number of queries required by the protocol.     

基于运动控制卡的机器人智能切割系统

本文介绍了基于运动控制卡的机器人智能切割系统的软硬件设计。该机器人具有四个自由度,采用三轴联动的工作方式,第三轴可与选定的两轴的运动轨迹保持正切。实验表明该机器人切割系统工作稳定,满足玻璃切割等行业的加工要求。     

Hardware-in-the-loop simulator for stability study in orthogonal cutting

The self-excited vibrations due to the regenerative effect, commonly known as chatter, are one of the major problems in machining processes. They cause a reduction in the surface quality and in the lifetime of mechanical elements including cutting tools. Furthermore, the experimental investigations of chatter suppression techniques are difficult in a real machining environment, due to repeatability problems of hard to control parameters like tool wear or position dependent dynamic flexibility. In this work, a mechatronic hardware-in-the-loop (HIL) simulator based on a flexible structure is proposed for dimensionless study of chatter in orthogonal cutting. Such system reproduces experimentally, on a simple linear mechanical structure in the laboratory, any stability situation which can be used to test and optimise active control devices. For this purpose, a dimensionless formulation is adopted and the delay related to the phase lag of the actuator and the controller employed on the HIL is compensated.     

An exact algorithm for generating homogenous T-shape cutting patterns

Both the material usage and the complexity of the cutting process should be considered in generating cutting patterns. This paper presents an exact algorithm for constrained two-dimensional guillotine-cutting problems of rectangles. It uses homogenous T-shape patterns to simplify the cutting process. Only homogenous strips are allowed, each of which contains rectangular blanks of the same size and direction. The sheet is divided into two segments. Each segment consists of strips of the same length and direction. The strip directions of the two segments are perpendicular to each other. The algorithm is based on branch and bound procedure combined with dynamic programming techniques. It is a bottom-up tree-search approach that searches the solution tree from the branches to the root. Tighter bounds are established to shorten the searching space. The computational results indicate that the algorithm is efficient both in computation time and in material usage.