基于数字制造环境的可重构装配线仿真分析平台

以某汽车变速箱装配生产线制造系统为背景,应用多Agent制造及Holon制造模式改造传统装配生产线以提升其柔性与重构能力·针对基于agent与holon混合思想的可重构装配生产线的基础框架与实现等理论提供分析验证环境,提出应用数字制造技术构建面向可重构装配线的数字仿真验证平台·在分析面向重构装配线的仿真平台功能特征的基础上,构建了数字仿真验证平台的框架·研究了仿真平台开发中的系统集成、可视化仿真、可重构装配线性能分析等关键技术,最后给出了仿真平台的实例系统·

基于Agent的分布式多机器人系统建模及分析

进行一个多装配机器人系统 DAMAS的模型研究 ,介绍离散事件动态系统的重要建模工具 Petri网 ,提出解决模型复杂性的有效方法 ,建立了系统中各个 Agent及整个系统的 Petri网模型 ,对这些模型及相互间的交互模型进行了重要的活性和有界性分析 ,对多机器人系统的协作机制进行了验证分析。

Petri网理论在柔性制造系统(FMS)性能分析中的应用

本文用 Petri 网的一个子类——时间事件图对流水车间型和作业车间型的柔性制造系统(FMS)建模并进行理论分析,给出了可行排序的判定条件及系统中托盘数量配置与系统生产率的关系,对系统的主要性能指标,如生产周期、工件驻留时间、在制品库存等给出了定量描述.这些结果为系统的设计和运行提供了理论依据.

自动生产线和柔性制造系统的建模、分析与控制

自动生产线和柔性制造系统是典型的离散事件动态系统,近几年在控制理论界受到极大重视。本文首先对自动生产线的建模与分析的研究概况做了综述,重点放在排队网络模型。然后介绍了柔性制造系统的管理与控制问题。

复杂离散制造过程建模与性能评价方法研究

离散制造系统是制造业中最为复杂的制造系统之一，其生产特点表现在：生产方式的异步、并行；生产柔性强；调度复杂性高等方面。要实现对复杂离散制造系统的控制，首先必须对其建模。随着制造系统自动化程度提高，规模的增大，组成因素的复杂化，性能评价问题变得日益复杂并越来越受到人们的重视。提供直观的模型描述方法、有效的数学理论工具和模型分析方法及分析软件，是制造系统性能评价迫切需要解决的问题。为此本文进行了以下工作： 首先，提出了一种支持性能评价的制造过程模型框架。该框架体现了车间生产闭环控制机制，全面描述了车间制造过程相关组成要素之间的关系，可用于指导制造过程的建模和基于性能评价的优化控制。模型框架核心部分是生产过程模型、过程控制模型和过程性能模型，这三部分构成了制造过程模型。该过程模型在工厂模型的支持下，由事件模型驱动，受策略模型约束，通过一些过程准则和方法进行测量和监视，对性能相关数据进行统计、分析和评估，反映在性能指标上。 第二，确定了离散车间性能评价指标体系。该指标体系建立了不同性能指标与不同层次、不同类型的制造过程以及不同性能评价主体之间的关联，为选择评价方法奠定了基础。该指标体系按照车间目标将性能指标分为三大类，即时间、质量、成本；每一类细化为三个层次，分别是基本性能指标、扩展性能指标和综合性能指标。 第三，基于随机Petri网建立了具有随机机器故障的制造过程性能模型。该模型包含两个基本的状态转换环，将正常状态和异常情况分别描述；基于故障的随机特征，设置了服从泊松分布的故障发生模块；根据不同的故障发现模式，衍生出若干状态转换环，清晰地将故障发生、发现分离；还考虑了中断作业的处理，使模型更接近实际系统动态行为特征。另外，本文设计了考虑成本信息的作业优先级调度规则，并基于随机高级Petri网（SHLPN）应用到混流装配线动态调度问题中；针对流水线上存在的一类共享资源—维修工人，建立了考虑系统状态的维修排序规则SHLPN模型。通过数学分析和仿真方法结合实现了对以上制造过程模型的性能评价，验证了模型的有效性。 第四，针对性能评价的需求和Petri网在制造过程成本分析方面存在的不足，提出了一种适合制造过程成本分析的价格时间Petri网，并给出了相应的状态空间化简方法。通过对装配生产线多目标工人指派问题的求解，验证了模型和方法的有效性。 最后，根据管理控制过程和生产过程的特点以及它们之间的关系，提出了基于进程代数与Petri网的分层生产控制方法。采用Petri网和进程代数相结合的方法将物流和信息流集成在一个模型中，Petri网描述基于状态的与生产过程有关的过程流，进程代数描述计划、调度等与控制有关的推理过程，构成了两层分布式的车间生产控制结构。 综上可见，本文提出的制造过程建模、性能评价和控制方法，可以支持复杂离散制造系统的分析和综合；基于过程模型实现了复杂离散制造系统的生产过程模拟和性能分析；能够发现影响系统性能的瓶颈环节；为制造过程的改进和制造系统性能的提高提供了依据；进而实现了制造系统自主闭环自适应的优化控制。本文的研究工作具有重要的理论意义和实际应用价值。

Characterization of a Laser-Discrete Quenched Steel Substrate/Chromium System by Dissolving Coatings

A laser-discrete quenched steel (LDQS) substrate/as-deposited chromium (top high-contraction (HC) and underlying low-contraction (LC) chromium) system was investigated by dissolving coatings in order to reveal the mechanism that the service life of the coated parts is largely improved using the hybrid technique of laser pre-quenching plus chromium post-depositing. It was found that the surface characteristics of the substrate, LC and HC chromium layer can be simultaneously revealed owing to the dissolution edge effect of chromium coatings. Moreover, the periodical gradient morphologies of the LDQS substrate are clearly shown: the surfaces of laser transformation-hardened regions are rather smooth; a lot of fine micro-holes exist in the transition zones; there are many micro-dimples in the original substrate. Furthermore, the novel method of dissolving coatings with sharp interfaces may be used to reveal the structural features of a substrate/coating system, explore the effect of the substrate on the initial microstructure and morphologies of coatings, and check the quality of the coated-parts.

A discrete square global grid system based on the parallels plane projection

Knowledge Innovation Project of Chinese Academy of Sciences [KZCX3-SW-347]; National Science Fund for Distinguished Young Scholar [40225004]

A discrete square global grid system based on the parallels plane projection

We developed a direct partitioning method to construct a seamless discrete global grid system (DGGS) with any resolution based on a two-dimensional projected plane and the earth ellipsoid. This DGGS is composed of congruent square grids over the projected plane and irregular ellipsoidal quadrilaterals on the ellipsoidal surface. A new equal area projection named the parallels plane (PP) projection derived from the expansion of the central meridian and parallels has been employed to perform the transformation between the planar squares and the corresponding ellipsoidal grids. The horizontal sides of the grids are parts of the parallel circles and the vertical sides are complex ellipsoidal curves, which can be obtained by the inverse expression of the PP projection. The partition strategies, transformation equations, geometric characteristics and distortions for this DGGS have been discussed. Our analysis proves that the DGGS is area-preserving while length distortions only occur on the vertical sides off the central meridian. Angular and length distortions positively correlate to the increase in latitudes and the spanning of longitudes away from a chosen central meridian. This direct partition only generates a small number of broken grids that can be treated individually.

Size Effect and Geometrical Effect of Polycrystals and Thin Film/Substrate System in Micro-indentation Test

Micro-indentation test at scales on the order of sub-micron has shown that the measured hardness increases strongly with decreasing indent depth or indent size, which is frequently referred to as the size effect. Simultaneously, at micron or sub-micron scale, the material microstructure size also has an important influence on the measured hardness. This kind of effect, such as the crystal grain size effect, thin film thickness effect, etc., is called the geometrical effect by here. In the present research, in order to investigate the size effect and the geometrical effect, the micro-indentation experiments are carried out respectively for single crystal copper and aluminum, for polycrystal aluminum, as well as for a thin film/substrate system, Ti/Si3N4. The size effect and geometrical effect are displayed experimentally. Moreover, using strain gradient plasticity theory, the size effect and the geometrical effect are simulated. Through comparing experimental results with simulation results, length-scale parameter appearing in the strain gradient theory for different cases is predicted. Furthermore, the size effect and the geometrical effect are interpreted using the geometrically necessary dislocation concept and the discrete dislocation theory. Member Price: $0; Non-Member Price: $25.00

Degradation failure features of chromium-plated gun barrels with a laser-discrete-quenched substrate

The effect of substrate laser-discrete quenching on the degradation failure of chromium-plated gun barrels was metallurgically investigated. The results show that substrate laser-discrete quenching changes the failure patterns of chromium coatings during firing, and some periodic through-thickness cracks in the fired chromium coatings are justly located at original substrate zones between two adjacent laser-quenched tracks. Moreover, chromium coatings and the laser-quenched zones on the substrate are simultaneously degraded in microstructure and property during firing. Furthermore, the periodic structure of the laser-discrete-quenched steel (LDQS) substrate near the breech remains after firing, and the hardness of the fired laser-quenched zones is still higher than that of original substrates. The specific failure features were utilized to illustrate the mechanism of the extended service life of chromium-plated gun barrels with the LDQS substrate. (c) 2007 Elsevier B.V All rights reserved.

Methane hydrate growth velocity in seepage system of Qiongdongnan Basin, South China Sea

The occurrences of diapirs, gas-filled zones and gas plumes in seawater in Qiongdongnan Basin of South China Sea indicate that there may exist seepage system gas-hydrate reservoirs. Assuming there has a methane venting zone of 1500 m in diameter, and the methane flux is 1000 kmol/a, and the temperature of methane hydrate-bearing sediments ranges from 3 degrees C to 20 degrees C, then according to the hydrate film growth theory, by numerical simulation, this paper computes the temperatures and velocities in 0 mbsf, 100 mbsf, 200 mbsf, 425 mbsf over discrete length, and gives the change charts. The results show that the cementation velocity in sediments matrix of methane hydrate is about 0.2 nm/s, and the seepage system will evolve into diffusion system over probably 35000 years. Meanwhile, the methane hydrate growth velocity in leakage system is 20 similar to 40 times faster than in diffusion system.

Timing system of HIRFL-CSR

The national science project HIRFL-CSR has recently been officially accepted. As a cyclotron and synchotron complex, it puts some particularly high demands on the control system. There are hundreds of pieces of equipment that need to be synchronized. An integrated timing control system is built to meet these demands. The output rate and the accuracy of the controller are 16 bit/mu s. The accuracy of the time delay reaches 40 ns. The timing control system is based on a typical event distribution system, which adopts the new event generation and the distribution scheme. The scheme of the tuning control system with innovation points, the architecture and the implemented method are presented in the paper.

Development of multi-channel gated integrator and PXI-DAQ system for nuclear detector arrays

A multi-channel gated integrator and PXI based data acquisition system have been developed for nuclear detector arrays with hundreds of detector units. The multi-channel gated integrator can be controlled by a programmable Cl controller. The PXI-DAQ system consists of NI PXI-1033 chassis with several PXI-DAQ cards. The system software has a user-friendly GUI which is written in C language using LabWindows/CVI under Windows XP operating system. The performance of the PXI-DAQ system is very reliable and capable of handling event rate up to 40 kHz. (C) 2010 Elsevier B.V. All rights reserved.

The electrochemical behavior of a system with a limited number of molecules

In this paper, based on Einstein relationship between diffusion and random walk, the electrochemical behavior of a system with a limited number of molecules was simulated and explored theoretically. The transition of the current vs time responses from discrete to continuous was clearly obtained as the number of redox molecules increased from 10 to 10(6).

Formation and evolution of the modern warm current system in the East China Sea and the Yellow Sea since the last deglaciation

To reconstruct the formation and evolution process of the warm current system within the East China Sea (ECS) and the Yellow Sea (YS) since the last deglaciation, the paleoceangraphic records in core DGKS9603, core CSH1 and core YSDP102, which were retrieved from the mainstream of the Kuroshio Current (KC), the edge of the modern Tsushima Warm Current (TWC) and muddy region under cold waters accreted with the Yellow Sea Warm Current (YSWC) respectively, were synthetically analyzed. The results indicate that the formation and evolution of the modern warm current system in the ECS and the YS has been accompanied by the development of the KC and impulse rising of the sea level since the last deglaciation. The influence of the KC on the Okinawa Trough had enhanced since 16 cal kyr BP, and synchronously the modern TWC began to develop with the rising of sea level and finally formed at about 8.5 cal kyr BP. The KC had experienced two weakening process during the Heinrich event 1 and the Younger Drays event from 16 to 8.5 cal kyr BP. The period of 7-6 cal kyr BP was the strongest stage of the KC and the TWC since the last deglaciation. The YSWC has appeared at about 6.4 cal kyr BP. Thus, the warm current system of the ECS and the YS has ultimately formed. The weakness of the KC, indicated by the occurrence of Pulleniatina minimum event (PME) during the period from 5.3 to 2.8 cal kyr BP, caused the main stream of the TWC to shift eastward to the Pacific Ocean around about 3 cal kyr BP. The process resulted in the intruding of continent shelf cold water mass with rich nutrients. Synchronously, the strength of the YSWC was relatively weak and the related cold water body was active at the early-mid stage of its appearance against the PME background, which resulted in the quick formation of muddy deposit system in the southeastern YS. The strength of the warm current system in the ECS and the YS has enhanced evidently, and approached to the modern condition gradually since 3 cal kyr BP.