A parametric interpolator with confined chord errors, acceleration and deceleration for NC machining

Parametric interpolation has many advantages over linear interpolation in machining curves. Real time parametric interpolation research so far has addressed achieving a uniform feed rate, confined chord errors and jerk limited trajectory planning. However, simultaneous consideration of confined chord errors that respect the acceleration and deceleration capabilities of the machine has not been attempted. In this paper, the offline detection of feed rate sensitive corners is proposed. The velocity profile in these zones is planned so that chord errors are satisfied while simultaneously accommodating the machine's acceleration and deceleration limits. Outside the zone of the feed rate sensitive corners, the feed rate is planned using the Taylor approximation. Simulation results indicate that the offline detection of feed rate sensitive corners improves parametric interpolation. For real time interpolation, the parametric curve information can be augmented with the detected feed rate sensitive corners that are stored in 2×2 matrices.     

Determination of non-spherical particle size distribution from chord length measurements. Part 2: Experimental validation

In this paper, the theory on the translation of a measured chord length distribution (CLD) into its particle size distribution (PSD), which was developed in the first part of this study [Li and Wilkinson, 2005. Determination of non-spherical particle size distribution from chord length measurements. Part 1: theoretical analysis. Chemical Engineering Science 60, 3251-3265], has been validated using experimental results. CLDs were measured using the Lasentec focused beam reflectance measurement (FBRM) with three different materials, spherical ceramic beads and non-spherical plasma aluminium and zinc dust particles. Meanwhile, the particle shape and PSD of each material were also investigated by image analysis (IA). Comparison of the retrieved PSDs with the measured PSDs by IA shows that the PSD can be retrieved from a measured CLD successfully using the proposed iterative nonnegative least squares (NNLS) method based on the PSD-CLD model.     

Adaptive interpolation scheme for NURBS curves with the integration of machining dynamics

This paper develops a comprehensive interpolation scheme for non-uniform rational B-spline (NURBS) curves, which does not only simultaneously meet the requirements of both constant feedrate and chord accuracy, but also real-time integrates machining dynamics in the interpolation stage. Although the existing work in this regard has realized the importance to simultaneously consider chord error and machining dynamics, none has really incorporated these in one complete interpolation scheme. In this paper, machining dynamics is considered for three aspects: sharp corners or feedrate sensitive corners on the curves, components with high frequencies or frequencies matching machine natural ones and high jerks. A look-ahead module was developed for detecting and adaptively adjusting the feedrate at the sharp corners. By Fast Fourier Transform (FFT) analysis with a moving window in the interpolation stage identified were some special frequency components such as those containing high frequencies or with frequencies matching machine natural ones. Then, the notch filtering or time spacing method was used to eliminate these components. To more completely reduce feedrate and acceleration fluctuations, the jerk-limited algorithm was also developed. Finally, the interpolated feedrate was further smoothened with B-spline fitting method and the NURBS curves were re-interpolated with the smoothened feedrate. During the interpolation, the chord error was repeatedly checked and confined in the prescribed tolerance. Two NURBS curves were used as examples to test the feasibility of the developed interpolation scheme.     

Chord协议的改进双向路由表结构

在结构化P2P网络中有效快速地定位节点非常重要。Chord是结构化网络中一种比较成功的路由算法。但是Chord的路由表存在着一定的信息冗余,且只能从环的一个方向查询,对于后半环节点信息的查询支持不足,由此导致查询定位的效率不高。基于这种不足,本文提出了一种改进后的Chord路由表结构,将路由表中的冗余信息替换为反向环中部分节点信息,同时在路由表中增加剩余反向环的节点信息,由于利用了原表的冗余项,因此在不至于增加过多路由表项数的情况下实现了路由表的双向查找。仿真实验表明,改进后的路由表结构提高了查询效率。     

S-Chord环模拟器的仿真测试分析

用S-Chord环模拟器仿真软件测试分析了S-Chord的效率,以及节点在Chord环中分布与搜索效率之间的规律.仿真测试分两种情况进行,分别为节点在Chord环中平均分布和随机分布.实验结果表明,在节点数目固定的情况下,finger表记录项数目随文件数量增减的变化规律,以及在文件数目固定的情况下,finger表记录项数目随节点数量增减的变化规律,从而显示出S-Chord优势.     

支持多属性网络数据检索的P2P覆盖网研究

互联网上的Web数据集往往通过标准的服务描述语言WSDL和消息交换协议SOAP封装为Web服务,以实现共享和应用。然而对于海量的Web数据资源,通过传统搜索引擎的单一注册中心往往会造成单点失效和可扩展性差等问题。P2P覆盖网技术由于具备可扩展性、负载均衡性和自组织性,为数据生产者提供了一套分布式Web数据发现解决方案：通过引入P2P和Web服务技术,对Web数据描述元数据的结构特性进行了分析,提供了一套支持多属性查询等复杂查询机制的混合P2P覆盖网.实验结果证明,这种机制具备可扩展性和高效查询功能.     

基于Chord的多集群网格系统资源查找算法改进

分析了P2P-Grid模式下的多集群网格系统资源查找问题,提出了一种基于Chord的优化资源查找算法P-RN-Tree算法来提高资源定位的效率。通过P-RN-Tree算法,设计并实现了基于Chord的分布式计算资源查找策略。理论分析表明,RN-Tree和P-RN-Tree的高度总是接近lbN,但由于优势集群选择算法的加入,P-RN-Tree平均查找长度要低于RN-Tree。仿真实验结果表明,该算法将进一步减少了资源调度所需的代价,提高了多集群网格系统的性能。     

基于Chord的Web服务模型研究

Web服务是目前互联网的发展热点。虽然Web服务已经提供了分布式的操作,可是服务发布和发现都是以一个服务注册中心为基础的。针对Web服务的瓶颈性缺陷,提出了P2P模式下基于Chord协议的Web服务模型,介绍了在此模型中服务发布、服务发现、加入节点、删除节点的方法。     

基于多环的Chord改进算法

通过分析Chord协议,提出基于多环的Chord改进算法MR-Chord。MR-Chord采用多环和组相结合的结构,在组内每个节点记录全组的路由,组与组之间以递归算法相连成多个环。通过理论分析和仿真实验对Chord和MR-Chord进行比较,结果表明,MR-Chord使系统的性能和适应性更好,路由表中的冗余很少。     

P2P环境下基于语义的Web服务组合研究

利用OWL-S语言描述Web服务,在组合操作中加入语义信息,实现了Web服务组合的自动化。为了提高Web服务的搜索速度,采用Chord路由算法。构建了一个P2P环境下基于Chord网络的Web服务组合模型,在其上实现了基于语义的Web服务组合,最后通过实例给出了语义Web服务自动组合过程。