Tool-path generation for sidewall machining

Presented in this paper is a tool-path generation procedure for sidewall machining, a process that is essential in the fabrication of many mechanical parts. While sculptured surface machining has received a significant amount of attention, there has been relatively less study of the technological requirements of sidewall machining. In this paper, three technological requirements are identified: (1) machining clean-up regions after rough machining, (2) avoiding unbalanced tool wear, and (3) retaining down-milling. For the generation of a roughing tool-path, the PWID offset algorithm is utilized. After roughing, it is necessary to identify the clean-up regions. Identifying these regions requires two major computations: a 2D-curve offsetting and a 2D-booleaning operation. To avoid these heavy operations, this paper proposes a method that identifies clean-up regions by making use of the byproducts (interfering ranges) of the PWID offset algorithm. As a result, it is possible to identify clean-up regions efficiently with minimum effort.     

Polygonal extrusion

A sweeping operation called polygonal extrusion is defined to improve the modeling power of CSG-based modeling. It is assumed that a 2D cross-sectional polygon (sweeping polygon) moves in space while its containing plane is kept orthogonal to the tangent direction of the trajectory curve, a planar polygonal chain having no self-intersections. The objective of the paper is to compute the boundary of the swept volume of the sweeping polygon as a set of polygons (or triangles). The most significant challenge to accomplishing this objective is the problem of trimming the swept volume. To solve the trimming problem, 2D-curve offsetting methods are employed. Two algorithms are presented for polygonal extrusion that are based on different offsetting methods, the Voronoi diagram and PWID offset. The proposed algorithms have been implemented and tested with various examples. Published online: 28 January 2003     

GPU-based offset surface computation using point samples

We present an efficient algorithm to perform approximate offsetting operations on geometric models using GPUs. Our approach approximates the boundary of an object with point samples and computes the offset by merging the balls centered at these points. The underlying approach uses Layered Depth Images (LDI) to organize the samples into structured points and performs parallel computations using multiple cores. We use spatial hashing to accelerate intersection queries and balance the workload among various cores. Furthermore, the problem of offsetting with a large distance is decomposed into successive offsetting using smaller distances. We derive bounds on the accuracy of offset computation as a function of the sampling rate of LDI and offset distance. In practice, our GPU-based algorithm can accurately compute offsets of models represented using hundreds of thousands of points in a few seconds on a GeForce GTX 580 GPU. We observe more than 100 times speedup over prior serial CPU-based approximate offset computation algorithms.     

A new approach to z-level contour machining of triangulated surface models using fillet endmills

Precision z-level contour machining is important for various computer-aided manufacturing (CAM) applications such as pocket machining and high-speed machining (HSM). This paper presents a new z-level contour tool-path generation algorithm for NC machining of triangulated surface models. Traditional approaches of z-level machining rely on the creation of accurate CL (cutter location) surfaces by surface offsetting or high-density z-map generation, which is computationally expensive and memory demanding. In contrast, this paper presents a novel approach to the generation of CL data directly from the section polygon of a triangulated surface model. For each polygon vertex of the contour, the offset direction is determined by the normal to the edge, while the offset distance is not fixed but is determined from the cutter shape and the part surface. An interference-free tool-path computation algorithm using fillet endmills is developed. Since there is no need to create a complete CL surface or high-density z-map grids, this proposed method is highly efficient and more flexible, and can be directly applied to triangulated surfaces either tessellated from CAD models, or reconstructed from 3D scanned data for reverse engineering (RE) applications.     

Polygon offsetting using a Voronoi diagram and two stacks

The generation of the trimmed offset of a simple polygon is a conceptually simple but important and computationally non-trivial geometric problem for many applications. This article presents a linear time algorithm to compute a trimmed offset of a simple polygon consisting of arcs as well as line segments in a plane. Assuming that a Voronoi diagram of the polygon is available, the algorithm uses two stacks: T-stack and C-stack. The T-stack contains intersections between an offset and Voronoi edges, and the C-stack contains an offset chain which is a part of the trimmed offset. The contents of both stacks are pushed into and popped from the stacks in a synchronized fashion depending on the events that occur during the offsetting process.     

用遗传算法生成NURBS曲线的等距线

提出一种生成NURBS曲线等距线的新方法,即从原始NURBS曲线求得一组精确NURBS等距点后,采用遗传算法对参数进行优化,提高等距线的逼近精度,优化目标函数为各精确等距点至逼近曲线的距离平方和取极小值,结果表明,遗传算法具有一定的优越性。     

Offset of curves on tessellated surfaces

Geodesic offset of curves on surfaces is an important and useful tool of computer aided design for applications such as generation of tool paths for NC machining and simulation of fibre path on tool surfaces in composites manufacturing. For many industrial and graphic applications, tessellation representation is used for curves and surfaces because of its simplicity in representation and for simpler and faster geometric operations. The paper presents an algorithm for computing offset of curves on tessellated surfaces. A curve on tessellation (COT) is represented as a sequence of 3D points, with each line segment of every two consecutive points lying exactly on the tessellation. With an incremental approach of the algorithm to compute offset COT, the final offset curve position is obtained through several intermediate offset curve positions. Each offset curve position is obtained by offsetting all the points of COT along the tessellation in such a way that all the line segments gets offset exactly along the faces of tessellation in which the line segments are contained. The algorithm, based entirely on tessellation representation, completely eliminates the formation of local self-intersections. Global self-intersections if any, are detected and corrected explicitly. Offset of both open and closed tessellated curves, either in a plane or on a tessellated surface, can be generated using the proposed approach. The computation of offset COT is very accurate within the tessellation tolerance.     

A dynamically scheduled parallel DSP architecture for stream flow programming

This paper presents a dynamically scheduled parallel DSP architecture for general purpose DSP computations. The architecture consists of multiple DSP processors and of one or more scheduling units. DSP applications are first captured by stream flow graphs, and then stream flow graphs are statically mapped onto a parallel architecture. The ordering and starting time of DSP tasks are determined by the scheduling unit(s) using a dynamic scheduling algorithm.The main contributions of this paper are summarized as follows:• A scalable parallel DSP architecture: The parallel DSP architecture proposed in this paper is scalable to meet signal processing requirements. For parallel DSP architectures with large configurations, the scheduling unit may become a performance bottleneck. A distributed scheduling mechanism is proposed to address this problem.• A mapping algorithm: An algorithm is proposed to systematically map a stream flow graph onto a parallel DSP architecture.• A dynamic scheduling algorithm: We propose a dynamic scheduling algorithm that will only schedule a node for execution when both input data and output storage space are available. Such scheduling algorithm will allow buffer sizes to be determined at compile time.• A simulation study: Our simulation study reveals the relationships among the grain-size, the processor utilization, and the scheduling capability. We believe these relationships have significant impact on parallel computer architecture design involving dynamic scheduling.     

Error analysis of reparametrization based approaches for curve offsetting

This paper proposes an error analysis of reparametrization based approaches for planar curve offsetting. The approximation error in Hausdorff distance is computed. The error is bounded by O(rsin²β), where r is the offset radius and β is the angle deviation of a difference vector from the normal vector. From the error bound an interesting geometric property of the approach is observed: when the original curve is offset in its convex side, the approximate offset curve always lies in the concave side of the exact offset, that is, the approximate offset is contained within the region bounded by the exact offset curve and the original curve. Our results improve the error estimation of the circle approximation approaches, as well as the computation efficiency when the methods are applied iteratively for high precision approximation.     

A strongly competitive randomized paging algorithm

Thepaging problem is that of deciding which pages to keep in a memory ofk pages in order to minimize the number of page faults. We develop thepartitioning algorithm, a randomized on-line algorithm for the paging problem. We prove that its expected cost on any sequence of requests is within a factor ofH _k of optimum. (H _k is thekth harmonic number, which is about ln(k).) No on-line algorithm can perform better by this measure. Our result improves by a factor of two the best previous algorithm.     

Die-cavity pocketing via cutting simulation

For die-cavity pocketing, the cavity volume is sliced into a number of cutting-layers by horizontal cutting-planes, and each layer is pocket-machined using the contour-parallel offset method in which the tool-paths are obtained by repeatedly offsetting the boundary-pocketing curve. The major challenges in die-cavity pocketing include: 1) finding a method for obtaining the boundary-pocketing curve, 2) generating evenly spaced contour-parallel offset toolpaths, 3) detecting and removing uncut-regions, and 4) estimating chip-loads for an adaptive feed control. No systematic solution for these problems has been offered in the literature, except the curve offsetting methods for computing contour-parallel offset curves. Presented in the article is a straightforward approach to die-cavity pocketing, in which all the four challenges are handled successfully by using the existing cutting-simulation methods.     

A low offset chopper amplifier with three-stage nested Miller configuration

A low offset,low noise chopper amplifier for sensor system application is presented.Low 1/f noise is achieved by employing chopper technique,and low offset is achieved by employing residual offset suppression circuit.The open-loop gain is extended using three-stage nested Miller configuration.The chip was implemented in 0.5μm 2P3M CMOS process.The amplifier is featured by an open-loop gain of 135 dB and a GBW of3 MHz.The measured offset voltage is 3μV,and the equivalent input noise power spectrum density at 1 Hz is96 nV/√Hz.     

平面轮廓的螺旋填充轨迹生成算法

在快速成型和数控领域中对平面轮廓区域的填充是比较繁琐复杂的步骤。为充分扬弃顶点偏置和线段偏置的优缺点,提出了顶点线段混合偏置算法,即在凹点处采用线段偏置,而在凸点处则采用顶点偏置或插入线段方式;为优化起落刀次数,提出用对角曲线连接偏置曲线形成螺旋轨迹的算法,即在归类相同的相邻两条偏置曲线中,以顶点较多的作为主偏置曲线,利用K-D树在相邻多边形查找主偏置曲线每个顶点的最近点,依次求出对角曲线的离散点并且连接获得螺旋轨迹。     

Offsetting operations on non-manifold topological models

This paper describes non-manifold offsetting operations that add or remove a uniform thickness from a given non-manifold topological model. The mathematical definitions and properties of the non-manifold offsetting operations are investigated first, and then an offset algorithm based on the definitions is proposed and implemented using the non-manifold Euler operators proposed in this paper. In this algorithm, the offset elements of minimal size for the vertices, edges and faces of a given non-manifold model are generated first. Then, they are united into a single body using the non-manifold Boolean operations. In order to reduce computation time and numerical errors, the intersections between the offset elements are calculated considering the origins of the topological entities during union. Finally, all topological entities that are within the offset distance are detected and removed in turn. In addition to the original offset algorithm based on mathematical definitions, some variant offset algorithms, called sheet thickening and solid shelling, are proposed and implemented for more practical and efficient solid modeling of thin-walled plastic or sheet metal parts. In virtue of the proposed non-manifold offset operation and its variations, different offsetting operations for wireframes, sheets and solids can be integrated into one and applied to a wide range of applications with a great potential usefulness.     

基于像素的多边形等距区域子分算法

目的 多边形等距是计算机图形学、计算几何、计算机辅助几何设计领域的一个基础性问题,并且有着广泛的应用。为了有效地处理各种类型的多边形等距问题,提出一种基于像素的多边形等距区域子分算法。方法 利用四叉树数据结构对给定区域进行子分,再利用区间算术计算出符合等距要求的全体像素集。针对只是由线段组成的多边形采用点到线段的最短距离算子加快计算速度。结果 利用区域子分算法处理了不同类型的多边形等距问题,并与传统的基于像素的多边形等距膨胀算法进行了比较。本文算法能有效处理各种多边形的等距问题,相对于传统的基于像素的膨胀算法,在顶点处的处理效果上更好,并且耗时也更短。所提区域子分算法比传统边等距方法适用范围更广,能够有效地处理一些边等距算法不能处理的多边形等距问题。结论 本文算法其优点是不需要考虑自交和连接问题,并且可以处理其他许多常规方法处理不了的各种类型的多边形等距问题,包括带有弧段和孤岛的情况。     

Comments on “single-link characteristics of a mode-seeking clustering algorithm”

The paper refutes the assertion of Shaffer et al.⁽¹⁾ that, in general, the minimum spanning tree algorithm and the mode-seeking clustering algorithm⁽²⁾ yield identical results. An example is given to exhibit the differences of these two algorithms.     

On the impacts of human interactions in MMORPG traffic

Game traffic depends on two main factors, the game protocol and the gamers’ behavior. Based on a few popular real-time multiplayer games this paper investigates the latter factor showing how a set of typical game phases—e.g., player movement, changes in the environment—impacts traffic on different observation levels. The nature of human behavior has such a high impact on traffic characteristics that it influences the traffic both at a macroscopic—e.g., traffic rate—and at a microscopic—payload content—level. First, by understanding the nature of this impact a user behavior detection algorithm is introduced to grab specific events and states from passive traffic measurements. The algorithms focus on the characteristics of the traffic rate, showing what information can be gathered by observing only packet header information. Second, as an application of our method some results, including a detailed analysis of measurements taken from an operational broadband network, are presented. Third, a novel model and an algorithm are introduced to extend the Deep Packet Inspection traffic classification method with the analysis of non-fix byte signatures, which are not considered in current methods. The model captures the variation of the dynamic byte segments and provides parameters for the algorithm. The introduced algorithm exploits the spatial and temporal correlation by examining and extracting the correlation structure of the traffic and constructing signatures based on the observed correlation. The algorithm is evaluated by examining proprietary gaming traffic and also other known non-gaming protocols.     

多UAV协同突防规划与仿真

针对在复杂大范围环境下低窄突防的多无人飞行器,通过分析威胁环境和协同突防的相关要素,提出了协同规划框架.设计了基于空间冲突预处理的打击时序协同算法;提供突防效能计算的基于变步长时间同步日标分配算法:通过协同突防航迹选掸优化算法的不断迭代计算,实现协同突防规划.仿真分析验证了规划算法的有效性.     

A study of context inference for Web-based information systems

Recently, context-awareness has been a hot topic in the ubiquitous computing field. Numerous methods for capturing, representing and inferring context have been developed and relevant projects have been performed. Existing research has tried to determine user’s contextual information physically by using stereo type cameras, RFID, smart devices, etc. These are heavily focusing on external context such as location, temperature, light, etc. However, cognitive elements of the context are important and need more study. This paper confines its research domain to the Web-based information system (IS) and, first, proposes two algorithms, the context inference algorithm and the service recommendation algorithm, for inferring cognitive context in the IS domain. Second, this paper demonstrates cognitive context-awareness on the Web-based information systems through implementing prototype deploying the proposed algorithms. The proposed system deploying the context inference and service recommendation algorithm can help the IS user to work with an IS conveniently and enable an existing IS to deliver ubiquitous service. In this fashion, we show the direction of existing IS and, ultimately, shows the typical services of a ubiquitous computing-based IS.     

离散曲面的等距面生成算法

离散曲面的等距面生成问题是一个不同于传统的等距面计算的新问题。拟对该问题展开研究并提出一个有效的离散曲面的等距面生成算法。该算法通过计算离散曲面的包络面上的离散体元而生成等距面。所提算法可以有效地解决等距计算过程中发生的拓扑、自相交等现象。实验结果表明了该算法的有效性。