Contact Modeling and Identification of Planar Somersaults on the Trampoline

This paper presents an extensive study on the trampoline-performed planar somersaults. First, a multibody biomechanical model of the trampolinist and the recurrently interacting trampoline bed are developed, including both the motion equations and the determination of joint reactions. The mathematical model is then identified –the mass and inertia characteristics of the human body are estimated, and the stiffness and damping characteristics of the trampoline bed are measured. By recording the actual somersault performances the motion characteristics of the stunts, i.e. the time variations of positions, velocities and accelerations of the body parts are also obtained. Finally, an inverse dynamics formulation for the system designated as an under-controlled system, is developed. The followed inverse dynamics simulation results in the torques of muscle forces in the joints that assure the realization of the actual motion. The reaction forces in the joints during the analyzed evolutions are also determined. Using the kinematic and dynamics characteristics, the nature of the stunts, the way the human body is maneuvered and controlled, can be studied.     

Efficient Tools for the Calculation of Drag Forces on Planar Microelectromechanical Systems

In air-packaged surface micromachined devices, drag forces introduce coupling between moving mechanical parts and are an important energy loss mechanism, thus playing an important role in device performance. In these devices, the amount of drag is greatly influenced by the presence of the nearby substrate. In this paper, we present a precorrected fast Fourier transform (pFFT) accelerated boundary element method specialized for calculating the drag force on structures above a substrate. Our method uses the Green's function for Stokes flow bounded by an infinite plane to implicitly represent the device substrate, requiring a number of modifications to the pFFT algorithm. Computational results demonstrate that the use of the implicit representation of the substrate reduces computation time and memory while increasing the solution accuracy. The results demonstrate that surprisingly, and unfortunately, even though representing the substrate implicitly has many benefits, it does not completely decouple discretization fineness from distance to the substrate.     

一种基于抓取簇和碰撞体素的工业零件抓取姿态检测算法

针对工业上常见的散乱堆叠零件的抓取问题,提出一种基于抓取簇和碰撞体素的抓取姿态检测算法。所提出的抓取簇是定义在零件上的连续抓取姿态集合,解决了传统方法中因采用离散固定抓取点而导致可抓取点丢失、筛选效率低的问题。先对料箱和场景点云进行体素化;然后把包含料箱或点云的体素标记为碰撞体素,并把与碰撞体素相邻的体素标记为风险体素,从而建立体素化的碰撞模型;接下来,根据抓取簇的几何性质计算出候选的抓取姿态及其对应的抓取路径;最后,通过检测抓取路径所经过的体素类型来完成快速的碰撞检测,从而筛选出最优抓取姿态。基于所提算法搭建了完整的Bin-Picking系统,并对多种实际工业场景中常见的零件进行仿真实验和实际抓取实验,结果表明：该算法能够快速、准确地检测出安全的抓取姿态,实际抓取的平均成功率达92.2%,料箱平均清空率达87.2%,较传统方法有明显提升,且抓取过程均未发生碰撞,可满足实际工业应用的要求。     

A Panoramic Survey on Grasping Research Trends and Topics

Abstract

Grasping and object manipulation is a key element of intelligent behavior. Many innovative cyberphysical systems involve some kind of object grasp and manipulation, to the extent that grasping has been recognized as a critical technology for the next generation industrial systems. In this survey, we aim to draw a broad landscape of applications and current research trends and topics relating to grasping techniques and tools. Applications range from biomedical and surgical to industrial warehouse pick and place tasks, covering a wide range of spatial scales, from micro to macro scales. The resources involved and research lines under development include the latest computational intelligence tools as well as the research on new materials and devices for sensing and actuation.     

A Tight Upper Bound on Kolmogorov Complexity and Uniformly Optimal Prediction

This paper links the concepts of Kolmogorov complexity (in complexity theory) and Hausdorff dimension (in fractal geometry) for a class of recursive (computable) ω -languages. It is shown that the complexity of an infinite string contained in a Σ ₂ -definable set of strings is upper bounded by the Hausdorff dimension of this set and that this upper bound is tight. Moreover, we show that there are computable gambling strategies guaranteeing a uniform prediction quality arbitrarily close to the optimal one estimated by Hausdorff dimension and Kolmogorov complexity provided the gambler's adversary plays according to a sequence chosen from a Σ ₂ -definable set of strings. We provide also examples which give evidence that our results do not extend further in the arithmetical hierarchy. Received February 1995, and in revised form February 1997, and in final form October 1997.     

基于AFM的机器人化纳米操作中纳观力的初步研究

针对基于原子力显微镜(AFM)的机器人化纳米操作，对探针作用下探针—基片—微粒之间纳观力的作用规律进行了初步分析．指出起主要作用的纳观力为范德华力、接触斥力、纳米摩擦力、毛细作用力以及纳米静电力等五种，并初步推导了各种纳观力的表达形式．通过力—距离曲线仿真与实验验证了所进行分析的合理性；该分析有助于进行纳米操作的精确控制．     

A New Lower Bound on the Maximum Number of Satisfied Clauses in Max-SAT and Its Algorithmic Applications

A pair of unit clauses is called conflicting if it is of the form (x), $(\bar{x})$ . A CNF formula is unit-conflict free (UCF) if it contains no pair of conflicting unit clauses. Lieberherr and Specker (J. ACM 28:411?C421, 1981) showed that for each UCF CNF formula with m clauses we can simultaneously satisfy at least $\hat{ \varphi } m$ clauses, where $\hat{ \varphi }=(\sqrt{5}-1)/2$ . We improve the Lieberherr-Specker bound by showing that for each UCF CNF formula F with m clauses we can find, in polynomial time, a?subformula F?? with m?? clauses such that we can simultaneously satisfy at least $\hat{ \varphi } m+(1-\hat{ \varphi })m'+(2-3\hat {\varphi })n''/2$ clauses (in F), where n?? is the number of variables in F which are not in F??. We consider two parameterized versions of MAX-SAT, where the parameter is the number of satisfied clauses above the bounds m/2 and $m(\sqrt{5}-1)/2$ . The former bound is tight for general formulas, and the later is tight for UCF formulas. Mahajan and Raman (J. Algorithms 31:335?C354, 1999) showed that every instance of the first parameterized problem can be transformed, in polynomial time, into an equivalent one with at most 6k+3 variables and 10k clauses. We improve this to 4k variables and $(2\sqrt{5}+4)k$ clauses. Mahajan and Raman conjectured that the second parameterized problem is fixed-parameter tractable (FPT). We show that the problem is indeed FPT by describing a polynomial-time algorithm that transforms any problem instance into an equivalent one with at most $(7+3\sqrt{5})k$ variables. Our results are obtained using our improvement of the Lieberherr-Specker bound above.     

一种基于双目视觉传感器的遮挡目标期望抓取点识别与定位方法

在不确定性较高的室内复杂场景中,机器人常需识别遮挡物体并对其抓取.遮挡问题会导致抓取点预估位置脱离目标,产生位置漂移.针对该问题,本文提出一种基于双目视觉的遮挡目标抓取点识别与定位策略.采用基于期望位置模型的方法估计,以特征检测进行遮挡目标识别,并进行轮廓还原;根据期望抓取点模型,采集目标的期望抓取位置,构建位置模型库.将待检测目标与模型库匹配,提取双目视野中未遮挡区域的期望抓取点.实验表明本方法在复杂环境下具有较高的鲁棒性,抗干扰能力强,对遮挡目标具有较高的定位精度.     

基于搜索树的平面图支配集算法

许多来自工业应用的优化问题都是NP难问题。确定参数可解FPT作为处理这类问题的另外一种思路,在最近的10多年中受到了广泛的关注。支配集问题是图论中最重要的NP完全的组合优化问题之一,即使对于FPT体系而言,一般图中的支配集问题属于W[2]完全的,意味着不可能设计出复杂度为f(k)no(1)的算法。在本文中,我们考虑在给定的平面图G=(V,E)中参数化支配集问题,给定参数k,看是否存在大小为k的顶点集合支配图中的其他顶点,当把问题限定在平面图上,这个问题属于确定参数可解。本文给出了基于两组归约规则的搜索树算法,通过使用规约技术化简实例,构造搜索树,得到了复杂度为O(8kn)的算法,同时通过相关实验结果显示了归约规则对算法的作用。     

接触网电气闪络与故障检测数据库案例的研究

接触网电气闪络现象发生在供电输出端,电力机车与受电弓脱离或剐蹭,造成铁道沿线设备跳闸和线路运营中断。通过接触网暂态电流过程分析,采集故障瞬态点通道数据,仿真模型针对接触网运行中如雷击、风雨、电压闪变和噪声干扰滤波具有预防作用。在综合分析接触网供电故障特点的基础上,建立数据库实时检测查询系统和案例分析库,通过参数对比与归类,能够迅速准确地分辨故障前后发生的问题,最大程度减小电气故障对接触网的影响,保证供电系统安全可靠地运行。     

A Simple Parallel Algorithm for the Single-Source Shortest Path Problem on Planar Digraphs

We present a simple parallel algorithm for the single-source shortest path problem in planar digraphs with nonnegative real edge weights. The algorithm runs on the EREW PRAM model of parallel computation in O((n^2ε+n^1−ε) log n) time, performing O(n^1+ε log n) work for any 0<ε<1/2. The strength of the algorithm is its simplicity, making it easy to implement and presumable quite efficient in practice. The algorithm improves upon the work of all previous parallel algorithms. Our algorithm is based on a region decomposition of the input graph and uses a well-known parallel implementation of Dijkstra's algorithm. The logarithmic factor in both the work and the time can be eliminated by plugging in a less practical, sequential planar shortest path algorithm together with an improved parallel implementation of Dijkstra's algorithm.     

产品人机接触曲面形状的CAD研究

对产品形态设计中人机接触曲面的人机工程学性能的评价与设计方法进行了分析,研究了合理人机接触曲面设计的解决方案,应用遗传算法工具实现了对人机接触曲面形态解方案的随机搜索,以及通过程序进行自动评价与选择的机制,建立了基于Unigraphics造型平台的曲面人机设计过程机制与原型系统。     

A Nonreducible System of Constraints of a Combinatorial Polyhedron in a Linear-Fractional Optimization Problem on Arrangements

A system of linear constraints is investigated. The system describes the domain of feasible solutions of a linear optimization problem to which a linear-fractional optimization problem on arrangements is reduced. A system of nonreducible constraints of a polyhedrom is established for the linear-fractional optimization problem on arrangements.__________Translated from Kibernetika i Sistemnyi Analiz, No. 2, pp. 107–116, March–April 2005.     

基于正交完备U-系统的图形分类与识别方法

为了探索有效的图形分类与识别的新方法,引进一类正交完备的分段k次多项式系统(简称U-系统).U-系统是一类属于L²[0,1]的正交完备分段k次多项式系统.该系统下的U级数展开式具有良好的平方逼近及一致逼近性质.基于U-系统理论,提出了U描述子的概念,给出了U描述子的性质并在理论上予以证明.为了更好地对图形分类与识别,对U描述子进行了归一化,同时在理论上证明了归一化U描述子具有旋转、平移、尺度大小等不变的性质.实验表明,归一化的U描述子能够高效、准确地对图形进行分类与识别,与Fourier描述子相比,具有更好的识 别率.     

基于弹塑性变形的快速展平算法与网格参数化

针对复杂CAD模型的展平问题,提出在三角网格上数值模拟汽车覆盖件一步逆成形的优化算法,实现了对车身零件毛坯料的快速估计.首先对初始网格进行补洞与局部重新网格化等预处理,得到辅助网格;为了减少变形,采用基于能量释放的初始解预示算法,并用基于金属板材弹塑性变形的一步逆算法进行迭代优化,得到修正的展平网格,经后处理得到最终参数化结果.将文中算法应用到自由边界网格参数化上,通过大量数值实验和比较结果表明,该算法不仅适用于工业上的坯料预估,而且在网格参数化的面积、扭曲变形方面有明显改善,同时具有较好的保角效果.     

A Linear Time Lower Bound on McCreight and General Updating Algorithms for Suffix Trees

Suffix trees are the fundamental data structure of combinatorial pattern matching on words. Suffix trees have been used in order to give optimal solutions to a great variety of problems on static words, but for practical situations, such as in a text editor, where the incremental changes of the text make dynamic updating of the corresponding suffix trees necessary, this data structure alone has not been used with success. We prove that, for dynamic modifications of order O(1) of words of length n, any suffix tree updating algorithm, such as the ones proposed by McCreight, requires O(n) worst-case running time, as for the full reconstruction of the suffix tree. Consequently, we argue that this data structure alone is not appropriate for the solution of combinatorial problems on words that change dynamically.     

A Linear Time Algorithm for the Arc Disjoint Menger Problem in Planar Directed Graphs

Given a graph G=(V,E) and two vertices s,t ∈ V , s\neq t , the Menger problem is to find a maximum number of disjoint paths connecting s and t . Depending on whether the input graph is directed or not, and what kind of disjointness criterion is demanded, this general formulation is specialized to the directed or undirected vertex, and the edge or arc disjoint Menger problem, respectively. For planar graphs the edge disjoint Menger problem has been solved to optimality [W2], while the fastest algorithm for the arc disjoint version is Weihe's general maximum flow algorithm for planar networks [W1], which has running time \bf O (|V| log |V|) . Here we present a linear time, i.e., asymptotically optimal, algorithm for the arc disjoint version in planar directed graphs. Received August 1997; revised January 1999.     

一种具有相依关系的二维云推理方法及其在预测中的应用

基于云模型的定性知识推理通过构造规则发生器实现不确定性推理。然而传统的二维云推理方法并未考虑条件云之间的相互影响,故此对传统方法进行改进,通过条件云云滴的乘积作用,构造相应的规则发生器,提出一种基于相依条件云的二维云推理方法。将该方法应用于美国GDP预测,预测结果表明该方法的效果明显优于传统方法,进而表明该方法可行且有效,并在一定程度上弥补了传统方法的不足。     

多跳无线网络中基于分支限界法的广播算法

现有的广播算法一般采用分层的方法构建近似的最多叶子最短生成树作为广播树。分析此类算法存在的不足,提出利用分支限界的思想建立最多叶子最短生成树引导广播操作的方法。分析和仿真结果表明,与基于分层的广播算法相比,基于分支限界法的广播算法具有更低的转发比且不增加广播树的深度,能更有效地节省带宽和能量资源。