面向微线段高速加工的Ferguson样条过渡算法

针对微小线段高速加工控制需求，在分析常用直接过渡法不足的基础上提出了一种基于Ferguson样条的微线段过渡算法。首先探讨了Ferguson样条曲线的性质，然后从精度优化分配、控制三角形获取和插补前瞻控制三方面阐述了算法原理，最后与传统算法进行了效率对比分析。仿真与实例验证表明，此算法具有过渡平稳、误差易控、效率高的特点，适合于微小线段的高速加工控制。     

Lateral control of autonomous vehicles based on fuzzy logic

Autonomous vehicles have attracted considerable attention in the research community and industry. This paper addresses a problem in designing lateral control law and develops a strategy to determine the given speed of autonomous vehicles. An improved method for calculating the lateral offset and heading angle error is proposed to reduce the impact of reference path data noise. Multiple fuzzy inference engines are used to design the steering controller and determine the given driving speed, including the forward and backward directions. The stability condition is given to guide the design of fuzzy inference engines. Satisfactory simulation and experimental results have been obtained from different reference paths.     

Scheduling Video Streams in Video-on-Demand Systems: A Survey

Developments in multimedia technology over the past decade has caused video-on-demand services to emerge as a new paradigm in home entertainment. Because of the large volume of data involved in the process and stringent continuity and real-time constraints, these services pose challenges that are different from the standard file transfer operations in the network. The necessity of efficient usage of scarce resources like network bandwidth and server capacity (in terms of I/O bandwidth) demands novel and easy-to-use schemes for scheduling continuous video streams. This paper presents an overview of the major scheduling policies that have emerged in the recent past. In particular, the paper provides detailed discussion on policies based on principles of broadcasting, batching, caching, and piggybacking or merging. Policies like look-ahead scheduling schemes that are designed exclusively to provide certain interactive VCR-like control operations are also covered. A conceptual comparison between the various classes of scheduling policies is carried out to identify common threads and key concepts. Performance of these policies in terms of bandwidth demand reduction, customer waiting time reduction, provision of interactive control by the user, and fairness of service are given special emphasis. The paper concludes with a discussion on the possible avenues of further reasearch and development in this potentially interesting and challenging field.     

超前进位加法器的优化设计

在对超前加法器逻辑算法分析的基础上,介绍了一种优化设计方法。宽位加法器采用多层CLA（ Carry Look-ahead Adder）块技术,按四位为一组进行组间超前进位,减小硬件延时,达到并行、高速的目的。并在晶体管级重点对全加器进行优化设计,从而降低整个电路的延时、面积和功耗。仿真结果表明,在SMIC65 nm工艺下,设计出的16位超前进位加法器,其延时,面积,功耗相比传统结构都有了明显的改善,达到了优化的效果。     

基于过控制顶点曲线的微线段过渡插补方法

针对微线段数控加工过程中的插补问题,为减小微线段数控加工中的速度波动,实现转接点的平滑过渡,提出过控制顶点曲线的过渡插补算法。首先构建微线段曲线的过渡矢量模型,根据基于特征多边形顶点的曲线模型的几何特性,构建过控制顶点曲线的过渡矢量模型,然后采用过控制顶点曲线过渡模型对微线段进行插补计算,根据加工误差计算控制顶点,确定约束速度并实时进行前瞻处理,最后通过实例进行了验证。实验结果表明,所提出的方法有效地提高了微线段转接速度,缩短了加工时间,实现了曲线的平滑过渡。     

基于前瞻算法的高效非均匀有理B样条曲线插补器

根据计算机数字控制系统的实际性能和非均匀有理B样条曲线的几何特性,设计了一种能够实现加速度平滑过渡的高效非均匀有理B样条曲线插补器。首先,该插补器利用快速插补计算模拟实际加工过程,找到加速度不连续的点;然后,采用S曲线加减速方法向后逆求减速点,并通过约束速度和加速度的方法,预估S曲线加减速第三阶段起点,不仅提高了所求减速点位置的精度,还实现了减速点处加速度的连续性。仿真结果表明,该插补器能在保证加工精度的前提下,以较高效率实现加速度的平滑过渡。     

五轴NURBS插补中的速度前瞻控制方法

为提高五轴非均匀有理B样条的插补精度,减轻段间转接时对机床的机械冲击,提出了一种速度前瞻控制处理方法.采用曲率圆逼近的方法建立了插补误差计算模型,并推导出满足插补误差要求的最小曲率半径与进给速度间的关系.采用数值分析方法预先计算出减速点的参数值,对样条插补进行了加减速前瞻规划处理.实时插补时对样条曲线上曲率半径较小的地方进行减速处理,以提高插补曲线的逼近精度.实例证明,该方法能有效降低插补误差和段间转接时的加速度,具有良好的实时性,可以应用到实际的数控系统中.     

基于自适应前瞻和预测校正的实时柔性加减速控制算法

为了提高离散小线段的加工效率和质量,提出一种实时柔性加减速控制算法。该算法由三部分组成：前瞻处理部分利用加减速可行性判断条件,保证加减速可达和实时前瞻;速度规划部分在保证速度和加速度连续变化的条件下,实时计算下一插补周期的进给速度;动态修调部分对当前速度规划结果进行调整,及时响应加工中机床参数的改变。实验结果表明,该算法能够实现数控系统的实时柔性加减速控制,支持动态修调,满足实际加工的要求。     

The use of partial observations,partial models and partial residuals to improve the least-squares refinement of crystal structures

Some common misconceptions in least-squares crystal structure refinement can be resolved by recasting the usual equations in terms of partial observations, partial models and partial residuals. An observation has components that are determined by an initial calculated model and each component, including the background, is considered to be a partial observation of the total observation. The use of partial observations, partial models and partial residuals allows various misconceptions to be identified and suggests ways to improve the least-squares methodology. A fixed component of a model of peak-plus-background does not fix its contribution to the observation for each refinement step. A covariance matrix obtained from the least-squares equations enables a standard uncertainty to be estimated for any function of the structural parameters. An oversight in current refinement methods is the failure to estimate the variances of components of the calculated model of an observation and the fraction of each residual associated with the various features of a refinement. A distinction should be made between least-squares equations for model development and least-squares equations for the estimation of a variance–covariance matrix. Methods for detecting systematic errors are discussed. A proposed look-ahead option for model development includes the assessment of the ability to refine parameters. For pseudo-symmetric structures, the use of symmetrized combinations of pseudo-equivalent intensities allows the reliability of minor components of the intensities to be better evaluated. It is also shown how homometric structure solutions can result from the use of powder diffraction data or equally twinned crystals.     

SMDP基于性能势的M步向前策略迭代

运用基于性能势的M步向前(look-ahead)异步策略迭代算法研究了半Markov决策过程(SMDP)优化问题。首先给出了基于性能势理论求解的一种M步向前策略迭代算法。该算法不仅对标准策略迭代算法和一般的异步策略迭代算法都适用,而且对SMDP在折扣和平均准则下的优化也是统一的;另外给出了两种性能准则下基于即时差分学习的M步向前仿真策略迭代。最后通过一个数值算例比较了各种算法的特点。