A methodology to quantify the stochastic distribution of friction coefficient required for level walking

The required friction coefficient is defined as the minimum friction needed at the shoe and floor interface to support human locomotion. The available friction is the maximum friction coefficient that can be supported without a slip at the shoe and floor interface. A statistical model was recently introduced to estimate the probability of slip and fall incidents by comparing the available friction with the required friction, assuming that both the available and required friction coefficients have stochastic distributions. This paper presents a methodology to investigate the stochastic distributions of the required friction coefficient for level walking. In this experiment, a walkway with a layout of three force plates was specially designed in order to capture a large number of successful strikes without causing fatigue in participants. The required coefficient of friction data of one participant, who repeatedly walked on this walkway under four different walking conditions, is presented as an example of the readiness of the methodology examined in this paper. The results of the Kolmogorov-Smirnov goodness-of-fit test indicated that the required friction coefficient generated from each foot and walking condition by this participant appears to fit the normal, log-normal or Weibull distributions with few exceptions. Among these three distributions, the normal distribution appears to fit all the data generated with this participant. The average of successful strikes for each walk achieved with three force plates in this experiment was 2.49, ranging from 2.14 to 2.95 for each walking condition. The methodology and layout of the experimental apparatus presented in this paper are suitable for being applied to a full-scale study.     

On the allowance for support costs in Prager-Rozvany’s optimal layout theory

A recent study by Rozvany and Sokó? (Struct Multidisc Optim, 2012) discussed an important topic in structural design: the allowance for support costs in layout optimization. Herein a frequently used kind of support will be examined, that of simple foundation with horizontal reaction by friction. This support does not seem to be covered by Authors’ approach. To illustrate this case some solutions obtained by standard design rules are included.     

An integrated fixture planning and analysis system for machining processes

Fixture planning is an important part of computer-aided process planning (CAPP), which is the link between design and manufacturing in a CIM environment. This paper presents a rational approach to computer-assisted fixture planning (CAFP), emphasizing integration of fixture planning with process planning, an issue that has not been adequately addressed until very recently. A systematic approach to fixture selection is outlined for planning of modular fixtures. A prototype CAPP-CAFP system has been developed at UCLA and linked to a commercial CAD system, namely, CADAM. Part design information can be extracted from the CAD model and multiple-view engineering drawings of a part stored in the CADAM system. Modular fixture elements can be selected automatically by the CAPP-CAFP system and the generated fixture layout can be displayed on the screen. Included also in the system is a fixture analysis module for verification and rationalization of a fixturing scheme. The force analysis module has a built-in local optimization routine that can determine the clamping forces of more reasonable magnitudes. The friction forces between the fixture and the workpiece can also be considered for simple cases.     

一种能够提高驱动能力和ESD保护能力的亚微米CMOS输出晶体管的新设计方法

本文给出了一种新的输出驱动器的设计方法，利用这种方法可以有效地减少CMOS输出驱动器的面积、同时提高驱动能力和ESD可靠性，输出驱动器是由许多电路单元组成的，电路单元有正方形、六边形和八边形三种形状。利用这种新的设计风格制成的输出晶体管结构更加对称，在ESD过程中触发更一致。理论计算和实验证明，在非硅化物CMOS工艺中，在小的设计面积内，利用新的设计方法研制成的CMOS输出缓冲器的输出驱动能力更高，ESD保护能力更强，有许多电路单元组成的输出晶体管和传统的指状设计相比，栅电阻更低，漏电容更小。     

粮仓储粮数量在线检测模型

粮仓储粮数量在线检测是国家粮食数量安全的重要保障技术, 是粮食库存检查的重要内容. 本文根据储粮数量在线检测精度和可靠性的要求, 针对粮仓压强分布的随机性, 提出了基于粮仓底面零内摩擦压强估计的粮仓储粮数量检测的新思路, 建立了粮仓压力传感器布置模型, 给出了粮堆底面与侧面压力分布随机性消除和侧面摩擦力影响补偿的具体方法, 提出了基于底面压力传感器检测均值的粮仓储粮数量检测模型和快速建模方法. 实仓实验结果表明, 所提出的储粮数量检测模型检测误差远小于3%, 且检测系统成本低, 可有效满足国家粮库储粮数量在线实时监测的实际需要.     

求解布局模型的并行矩阵算法研究

布局设计通常要建立抽象状态空间模型。求解布局模型，实现从模型状态到坐标图的转化，是计算机辅助布局设计的重要研究内容之一。本文在简要介绍一种层次布局模型ＨＬＭ１的基础上，引入了模型的解的概念；研究了ＨＬＭ１的子模型－层次约束图解的存在条件；提出了求解层次约束图，实现从模型到坐标图转化以及检测约束矛盾的一种并行矩阵算法，并给出了一个计算实例。     

空间布局的约束图方法

空间布局的自动化是智能CAD领域的研究方向之一,旨在为设计师提供智能辅助工具，用于求解在建筑、厂房设备、大规模集成电路以及产品包装等等若干领域出现的布局问题.图论方法是空间布局研究的主要途径之一.以往的布局模型由于难以充分表达知识与约束,使得设计过程与结果难以控制.本文提出一种可应用于2D及3D布局的规范约束图及层次约束图模型,给出了约束图解的存在条件.该模型可以表示精细的布局知识与约束,在一定程度上克服了以往图模型不能充分表达布局知识与约束的不足.本文还给出了基于约束图的布局生成算法.     

一种LuGre摩擦模型自适应补偿的分析及仿真

介绍一种降低低速转台伺服系统在转动过程中由于摩擦因数影响转动精度的方法。在低速转台转动的过程中由于摩擦力等的影响,转台的速度、位置都会发生偏差,所以在转台系统上引入摩擦控制补偿。利用公式推理,通过与理论值对比,发现自适应摩擦补偿方式与传统摩擦补偿方式相比,其跟踪误差大大降低,能有效抑制摩擦干扰对伺服系统的不利影响。进行基于MATLAB环境下的仿真效果。     

Contact Friction Compensation for Robots Using Genetic Learning Algorithms

In this paper, the issues of contact friction compensation for constrained robots are presented. The proposed design consists of two loops. The inner loop is for the inverse dynamics control which linearizes the system by canceling nonlinear dynamics, while the outer loop is for friction compensation. Although various models of friction have been proposed in many engineering applications, frictional force can be modeled by the Coulomb friction plus the viscous force. Based on such a model, an on-line genetic algorithm is proposed to learn the friction coefficients for friction model. The friction compensation control input is also implemented in terms of the friction coefficients to cancel the effect of unknown friction. By the guidance of the fitness function, the genetic learning algorithm searches for the best-fit value in a way like the natural surviving laws. Simulation results demonstrate that the proposed on-line genetic algorithm can achieve good friction compensation even under the conditions of measurement noise and system uncertainty. Moreover, the proposed control scheme is also found to be feasible for friction compensation of friction model with Stribeck effect and position-dependent friction model.     

动态摩擦模型仿真

为了深入分析摩擦力动态特性在高精度的伺服系统控制中造成的影响,检验摩擦补偿方法对动态摩擦的补偿效果,需要建立一个有效的动态仿真摩擦模型。如今摩擦的仿真研究都局限于非线性静态模型的实现,而对于微分方程描述的动态模型,还没有有效的实现方法。尤其是系统启动时,静摩擦给系统造成的小误差观察不到。基于动态刚毛摩擦模型,通过定义“粘滞”和“滑动”两个状态,成功地模拟出摩擦在启动和制动时对系统的不同影响。在跟踪正弦轨迹的误差仿真结果中可以观察到:速度转向时摩擦造成了启动小误差,与实际情况一致。这种处理方法适用于微分方程描述的动态摩擦模型,同样可以用于代数方程描述的静态模型仿真。     

Multi-purpose system for plant layout design

This paper develops a computer system for the production of plant layout design. The system includes three major components. One component builds the relationships between the production departments. The criteria considered in creating these relationships include: production volume, material flow, product design, and processing operations.Another component of the system uses the departmental relationships to produce three unique design alternatives, each of which is generated by different techniques. The approaches used by the system to arrange the layout are heuristic in nature. The arrangement routines are included in the system in order to develop initial layout arrangement. The methods used in these routines can be, either allocating the most important department in the median, or the physical middle; or using the idea of the “minimal spanning tree” technique. An exchange algorithm uses the steepest-descent pairwise interchange procedure to improve the initial layout designs.A third component evaluates each of the suggested designs with respect to manufacturing the product. Each design is analyzed, and the bottlenecks in the design are indicated. The software is formulated so that it can be used to initiate a new layout design, or to analyze an existing layout.     

Analysis of undercompensation and overcompensation of friction in 1DOF mechanical systems

This paper investigates the effects of undercompensation and overcompensation of friction in PD controlled 1DOF mechanical systems. The friction force that is acting on the mechanical system and the friction compensation term in the feedback loop are described by a class of discontinuous friction models consisting of static, Coulomb and viscous friction, and including the Stribeck effect. Lyapunov's stability theorem and LaSalle's invariance principle are applied to prove that undercompensation of friction leads to steady-state errors and the properties of the ω-limit set of trajectories of a two-dimensional autonomous differential inclusion are used to show that overcompensation of friction may induce limit cycling. Furthermore, the analysis also indicates that the limit cycling effect can be eliminated by tuning the PD controller gains.     

基于自抗扰控制的伺服系统摩擦补偿研究

伺服系统中由于摩擦的非线性和不确定性,严重影响了系统的控制性能。为抑制摩擦对系统性能的影响,设计了一个线性的自抗扰控制器进行摩擦补偿控制。该控制器无需任何系统的模型信息,可将摩擦作为扰动实时估计,并加以补偿。算法简单,鲁棒性强,易于工程实现。对某炮控伺服系统的仿真结果表明,该算法是有效的。     

基于LLVM的RISC-V向量扩展栈帧布局优化

为了能够生成正确、优化的机器指令代码,需要在编译器后端代码的生成阶段,设计和使用合适的程序栈帧布局.由于RISC-V向量扩展架构具有可伸缩性、其向量寄存器的长度在编译时不可知,传统的栈帧布局无法适用.之前LLVM中针对向量扩展实现的栈帧布局虽然能够生成正确的机器指令,但存在访存指令较多,栈帧空间较大,以及预留寄存器较多等问题.我们对原有实现所存在的问题进行分析,在此基础上提出了新的布局方式以及向量对象地址计算方式,并通过巴塞罗那超算中心开发的测试集进行验证.实验表明新的栈帧布局能够有效减少访存指令数和栈空间大小.     

Techniques for Edge Stratification of Complex Graph Drawings

We propose an approach that allows a user (e.g., an analyst) to explore a layout produced by any graph drawing algorithm, in order to reduce the visual complexity and clarify its presentation. Our approach is based on stratifying the drawing into layers with desired properties; to this aim, heuristics are presented. The produced layers can be explored and combined by the user to gradually acquire details. We present a user study to test the effectiveness of our approach. Furthermore, we performed an experimental analysis on popular force-directed graph drawing algorithms, in order to evaluate what is the algorithm that produces the smallest number of layers and if there is any correlation between the number of crossings and the number of layers of a graph layout. The proposed approach is useful to explore graph layouts, as confirmed by the presented user study. Furthermore, interesting considerations arise from the experimental evaluation, in particular, our results suggest that the number of layers of a graph layout may represent a reliable measure of its visual complexity. The algorithms presented in this paper can be effectively applied to graph layouts with a few hundreds of edges and vertices. For larger drawings that contain lots of crossings, the time complexity of our algorithms grows quadratically in the number of edges and more efficient techniques need to be devised. The proposed approach takes as input a layout produced by any graph drawing algorithm, therefore it can be applied in a variety of application domains. Several research directions can be explored to extend our framework and to devise new visualization paradigms to effectively present stratified drawings.     

Atomic-scale friction control by vibration using friction force microscope

Manipulation of friction at the nanoscale has been traditionally approached by chemical means (lubrication). Recent friction force microscopy (FFM) experiments demonstrated that it can be done mechanically by applying vibration to accessible elements of the system. This paper provides analytic understanding on why vibration can reduce friction based on a 1D model imitating the FFM tip moving on a substrate. Open-loop stability is first studied, and a feedback vibration control is then designed using the accessible variable. Comparing to the open-loop system, friction force is significantly reduced in the closed-loop system. Numerical simulations show satisfactory performances.     

布局优化子问题的改进遗传神经网络算法

带性能约束的航天舱布局问题可分解为有限多个子问题,每个子问题克服了关于优化变量的时断时续性。本文针对子问题(关于同构布局等价类),首先构造了用于产生与已知布局方案同构的布局方案的优化算法,然后在给出组合变异策略的基础上,设计了连续空间上基于实数编码的改进遗传神经网络算法。将该算法应用于二维布局优化子问题,数值实验表明该遗传神经网络进行布局逼近是有效的。这种方法是对布局问题求解的有效探索。     

单线图动态规划最优布局成图技术

提出了一种基于动态规划算法得到布局最优解实现区域电网单线图生成的方法.根据电网空间数据构建拓扑模型,执行广度优先算法得到多个能构成连通图的邻接矩阵以及矩阵遍历序列,根据邻接矩阵宽度计算出能容纳全部设备的正方形范围,并建立了设备最小间距为优化目标的数学模型.提出了动态规划最优布局求解的算法,应用该算法求解布局最优解数组,最后按照最少交叉原则进行正交化处理.应用实例表明通过最优解布局的成图美观且高效.     

A linear time layout algorithm for business process models

The layout of a business process model influences how easily it can be understood. Existing layout features in process modeling tools often rely on graph representations, but do not take the specific properties of business process models into account. In this paper, we propose an algorithm that is based on a set of constraints which are specifically identified toward establishing a readable layout of a process model. Our algorithm exploits the structure of the process model and allows the computation of the final layout in linear time. We explain the algorithm, show its detailed run-time complexity, compare it to existing algorithms, and demonstrate in an empirical evaluation the acceptance of the layout generated by the algorithm. The data suggests that the proposed algorithm is well perceived by moderately experienced process modelers, both in terms of its usefulness as well as its ease of use.