Simulation study for a proposed segmented automated material handling system design for 300-mm semiconductor fabs

With the increase in the size and weight of 300-mm wafers, the factory area must be enlarged accordingly. Due to the flow of material over long distances, the elimination of manual wafer handling has become necessary. Consequently, an automated material handling system (AMHS) is required for 300-mm semiconductor manufacturing facilities. The design of an AMHS must not only be capable of meeting numerous complex material handling requirements, but it must also simplify control and reduce capacity loss. In this study, a segmented dual-track bidirectional loop (SDTBL) design for an AMHS is proposed. The configuration is based on a double-loop flow path structure that is divided into non-overlapping segments, each containing a certain number of vehicles operating in bidirectional mode. A transfer buffer is set to enable conversion between segments and connect each independent zone. This structure eliminates congestion and blocking without requiring additional investment by operating vehicles on mutually exclusive tracks. The segmentation strategies and steps for two scenarios are developed in this research, and a simulation is performed to evaluate the performance of each segmented strategy. The simulation results show that the proposed strategies can reduce the cycle time and increase stocker utilization by up to 55.55% and 39.39%, respectively, while the throughput remains the same. The proposed design has great potential for practical application.     

Avoidance versus detection and recovery problem in buffer-spaceallocation of flexibly automated production systems

Motivated by recent developments in the semiconductor manufacturing industry, this paper undertakes an analytical investigation of the problem of selecting optimally the deadlock resolution strategy for buffer space allocation in flexibly automated production systems. In the process, it extends the behavioral models for the aforementioned systems currently considered in the literature, to account for probabilistic uncontrollable effects like the requirement for extra finishing steps and/or rework, and it introduces a new deadlock resolution scheme, characterized as randomized deadlock avoidance. The combination of these two extensions brings the considered system behavior(s) to the realm of probabilistic automata, an area of increasing academic interest. For the resulting model, and under the assumption of Markovian timings, it develops an analytical methodology for selecting the optimal deadlock resolution strategy that maximizes the steady-state system throughput, and it demonstrates its effectiveness through application to a "prototype" system configuration. The obtained results provide an interesting analytical expression of the need to assess the gains obtained by the increased concurrency supported by the deadlock detection and recovery strategy versus the productivity losses experienced under this approach due to increased system blocking, and/or additional material handling overheads. It turns out that, for the considered system configuration, the optimal selection scheme switches between detection and recovery and pure deadlock avoidance, every time that the time cost of deadlock recovery, tau(d), crosses a threshold Theta, which is a function of the remaining system behavioral and timing parameters. Beyond its own theoretical merit, this last result raises also the question of whether the policy randomization introduced in this work will ever enhance the performance of any configuration in the considered class of Resource Allocation Systems (RAS); this issue will be investigated in a sequel paper.     

Advanced material handling system for computer integrated manufacturing

A cordless linear synchronous motor (LSM) material handling system for CIM has been developed. The system incorporates a courier that moves without tether restrictions. This provides for an automated material handling system with improved travel and flexibility. The material handling system runs on an integrated reverse air bearing system which eliminates friction and backlash. The proposed system forms part of a manufacturing assembly, interacting with overhead manipulators and part feeders to form a comprehensive production system. The design and implementation of the cordless linear motor material handling system (MHS) is outlined and described in the paper.     

An ant colony optimization routing algorithm for two order pickers with congestion consideration

This paper develops a routing method to control the picker congestion that challenges the traditional assumption regarding the narrow-aisle order picking system. We proposes a new routing algorithm based on Ant Colony Optimization (ACO) for two order pickers (A-TOP) with congestion consideration. Using two extended dedicated heuristics with congestion consideration as reference group, a comprehensive simulation study is conducted to evaluate the effectiveness of A-TOP. The simulation proves that A-TOP achieves the shortest total picking time in most instances and performs well in dealing with the congestion. The impacts of warehouse layout, order size, and pick:walk-time ratio on A-TOP and system performance are analyzed as well. A-TOP can adapt to different warehouse configurations, meanwhile, it can be easily extended to the situation with more than two order pickers.     

Design and implementation of a hybrid manufacturing facility

A method for the design of hybrid, cellular/functional, facilities is presented in this paper. This method targets the minimization of inter-cell material handling and the maximization of intra-cell directional material flow. Furthermore it develops a shop redesign plan that maximizes the net benefit obtained from the facility rearrangement.     

Localized congestion control in advanced switching interconnects

The PCI Express advanced switching interconnect architecture includes status-based flow control (SBFC), a localized congestion-control mechanism that aims to alleviate the effects of transient congestion. The SBFC scheme suffices for handling persistent congestion in single-stage switch fabrics and complements traditional congestion management schemes in larger switch.     

基于OpenGL与3DS MAX的虚拟场景漫游系统的设计与实现

讨论了基于OpenGL与3DS MAX的虚拟环境的建模与漫游,并以此开发出一个虚拟的环境.系统以Visual C 6.0为开发平台,结合OpenGL以及3DS MAX建模,进行了南平师范高等专科学校部分场景的建模,以及漫游的实现,并具有光照、材质等真实感增强处理方法,建立的虚拟场景立体视觉效果明显,且实现了场景的可交互性.     

Software congestion, mobile servers, and the hyperbolic model

The phenomenon of software congestion is examined. The term refers to situations in which the performance bottleneck of a system is an element of software, rather than a hardware device. Software congestion can occur in any system which contains one or more elements of software whose services may be simultaneously desired by multiple clients, but which can service only one client at a time. It is shown that the use of models which ignore software congestion can produce results that are completely irrelevant to actual system behavior. Furthermore, software congestion is frequently invisible to conventional performance measurement tools. A notational scheme, called mobile servers representation, is introduced for describing those systems in which software congestion may be important. An approximate analytical model, called the hyperbolic model, is developed for analyzing systems with software congestion     

Scheduling automated transport vehicles for material distribution systems

The rise of advanced manufacturing technology has led to enhanced, efficient material handling equipment in manufacturing and container terminal environments. In order to exploit the full potential of advanced material handling equipment in real-world industrial environments, novel scheduling approaches capable of ensuring integrated operations for multiple automated transport vehicles need to be developed. This research develops a methodology for scheduling automated transport vehicles to ensure the smooth flow of materials in production and container terminal environments. The procedure consists of a mixed-integer programming model and two meta-heuristic-based algorithms that are proposed to achieve quality schedules within a reasonable amount of time. The obtained results show a significant reduction in the earliness or lateness of material delivery tasks and an improvement in operational performance, demonstrating that the proposed approaches are capable of ensuring smooth material distribution by scheduling automated transport vehicles in an integrated manner.     

On the role of a queueing network model in the design of a complex assembly system

This paper describes the modeling, analysis and re-design of a complex assembly system consisting of many processes (assembly, testing and inspection) and resources (machines and operators) and an advanced material handling system with intricate routing logics. It presents a systematic approach using both analytical and simulation models for the evaluation and modification of the complex assembly system. It demonstrates the application of a queueing network model to quickly generate rough-cut solutions and provide qualitative information for the evaluation of design alternatives. Iteratively, processes and resources that affect the system performance are identified, one at a time, and the system modified accordingly, until a satisfactory performance is obtained. The preliminary analyses using the queueing network model help to identify bottleneck processes, estimate optimal pallets, and determine a more efficient system layout. The use of the analytical model significantly reduces the number of the lengthy simulation runs. A detailed simulation model is subsequently employed for fine-tuning and further improvement. Compared with the original design, significant improvements have been made: a higher throughput, a reduced cycle time with less operators, and lower WIP inventories.     

基于RTT的TCPW拥塞控制算法的改进

无线网络受传输介质的限制,传输过程中会受到较大干扰,产生抖动,这种抖动会产生零星丢失而被拥塞控制机制误认为拥塞发生.TCP Westwood 协议(简称TCPW)就是这样不能区分拥塞丢失和无线抖动丢失,导致拥塞机制过于敏感,降低了带宽利用率.基于此,根据RTT值的估计对TCPW协议进行修改--称之为TCPW BR.该算法以测得的平滑RTT值并依据加权平均思想划分拥塞等级,判断拥塞丢失和无线抖动丢失.仿真结果表明,TCPW BR算法增强了无线网络对拥塞和随机差错的判断处理能力,提高了带宽利用率和吞吐量,并保持良好的公平性与友好性.     

Deadlock Resolution in Automated Manufacturing Systems With Robots

An automated manufacturing system (AMS) contains a number of versatile machines (or workstations), buffers, and an automated material handling system (MHS). The MHS can be an automated guide vehicle (AGV) system, and/or a system that consists of multiple robots. Deadlock resolution in AMS is an important issue. For the AMS with an AGV system as MHS, the problems of deadlock resolution for part processing process and AGV system as an integrated system has been studied. It is shown that AGVs can serve as both material handling devices and central buffers at the same time to help resolve deadlocks. For AMS with robots as MHS, the existing work treated the robots just as material handling devices and showed that the robots had contribution to deadlock. In this paper, such AMS is modeled by resource-oriented Petri nets. Contrary to the existing work, it is shown that the robots have no contribution to deadlock by adopting such nets to control AMS. More interestingly, they can be used to resolve deadlock by serving as temporary part storage devices. A new deadlock control policy is proposed by treating robots as both material handling devices and buffers. The new policy outperforms the existing ones.     

仓库物料运输系统多目标调度方法

为了提高仓库物料运输系统的效率,建立了考虑任务完成和AGV小车运行时间的多目标的调度模型,并提出了云模型影响下的出入库任务优先级分配策略。在此基础上,利用文化算法对问题进行了求解,讨论了算法的规则设计。最后,仿真结果表明,该算法是可行的,可以获得较好的效果,为AGV小车在仓库物料运输系统的应用提供了一种研究途径。     

Expected Response Times for Closed-Loop Multivehicle AMHS

We present an analytical approach for estimating the expected time for an automated material handling system (AMHS) to respond to move requests at loading stations in a vehicle-based, unidirectional, closed-loop AMHS. The expected response times are important for estimating the expected work-in-process (WIP) levels at the loading stations for design purposes, and for evaluating the performance of the AMHS as delayed response can impact the production cycle times. The expected response time approximation is validated by comparing the analytical model to the simulation results using a SEMATECH 300 mm hypothetical fab data set. Note to Practitioners - This paper describes an analytic method for estimating the average time for the AMHS to respond to lots ready for movement in a 300 mm wafer fab. The analysis is based on a large-scale model, requires standard solvers, and provides a very fast and reasonably accurate alternative to high-fidelity simulation. It is intended to support the early stage of fab design/redesign, allowing engineers to examine many different options before committing to the time and expense of simulation.     

A deadlock recovery strategy for unified automated material handling systems in 300 mm wafer fabrications

A key issue emerging from the unified automated material handling systems (UAMHSs) in 300 mm wafer fabrications is the system deadlock. This paper addresses the deadlock recovery strategy of unified automated material handling systems (UAMHSs) with limited buffers. A formal model for UAMHSs deadlock detection is proposed. Sufficient conditions for system deadlocks based on actual UAMHS characteristics are defined along with a novel deadlock recovery strategy. Moreover, an effective heuristic algorithm is proposed for parallel resolving UAMHS deadlocks. The performances are evaluated in simulation by monitoring indexes reflecting efficiency of the material handling system. Results of the simulation experiments show that the novel deadlock recovery strategy is superior to the benchmark strategy in reducing deadlock time and improving tools’ utilization. Furthermore, the proposed algorithm features real-time operation and large scale cases, and is suitable for practical applications.     

Modeling, analysis, and performance evaluation of a robotic grippersystem for limp material handling

This paper presents an analytical model of a flat surfaced robotic gripper designed to automate the process of reliable, rapid and distortion-free limp material handling. The designed gripper prototype is integrated with an industrial robot manipulator. The gripper geometry and its grasp stability are justified. Performance of the overall system is experimentally tested, based on a set of industry dictated operational constraints. It is found that the gripper system has high reliability, grasp stability, and that it is capable of rapid rates of manipulation.     

大型船舶物资补给可视化仿真

大型船舶物资补给可视化仿真可以形象地模拟物资补给搬运流程, 计算搬运时间, 发现搬运中的瓶颈问题, 进而实现搬运流程优化. 在定性分析大型船舶物资补给类型和搬运流程的基础上, 提出了基于Flexsim的大型船舶物资补给可视化仿真体系结构, 设计了仿真模型, 探讨了仿真平台实现的关键技术. 结合具体的案例, 开展了仿真实验, 结果表明, 可视化仿真对于大型船舶物资补给物料搬运系统的设计和运行管理具有重要作用.     

Implementing a hybrid simulation model for a Kanban-based material handling system

Plant floor material handling is a loose loop in most assembly plants. Simulation offers a quick, controllable and tunable approach for prototyping complex material handling processes in manufacturing environments. This paper proposes a hybrid simulation approach, using both discrete event and agent-based technologies, to model complex material handling processes in an assembly line. A prototype system is implemented using a commercial multi-paradigm modeling tool. In this prototype, JIT principles are applied to both the production and the material handling processes. The system performance is evaluated and system optimization directions are suggested. The proposed hybrid modeling approach facilitates the implementation of a responsive and adaptive environment in that various “what-if” scenarios can be simulated under different simulation configurations and real-time situations.     

Adaptive feedback control algorithms for large data transfers inhigh-speed networks

Two linear feedback control algorithms for handling and preventing congestion in broadband asynchronous transfer mode networks are proposed and analyzed. The fluid approximation model is described with a continuous-time system of delay-differential equations. The algorithms are asymptotically stable, and the transient processes are nonoscillatory. The control parameters are locally optimal (optimality is based on the asymptotic rate of convergence). The results of numerical experiments suggest that these parameters are globally optimal as well