A two phase procedure for the study of computer network reliability in automated manufacturing systems

This paper presents a simple procedure for the study of unreliable networks in production systems. An automated manufacturing system requires a network support for its stations in specific topological forms. However, the analysis presented in this study is topology independent. It reveals that, in most cases, the incremental cost due to failure of any component in the network will justify addition of standby units. The manufacturing facilities are assumed to be failure free and therefore, excluded from the analysis. A case study is presented to illustrate the importance of reliability analysis during the design phase.     

谈工业计算机系统工程化应用的抗干扰问题

系统抗干扰能力是关系到工业计算机系统的运行可靠性的关键，如果不综合考虑和处理好现场电磁环境和兼容问题，不能保证工业企业特别是火力发电厂的安全生产和经济运行。要提高工业计算机系统的可靠性在要求生产制造单位提高系统的抗干扰能力的同时还要要求工程设计、安装施工和使用维护单位引起高度重视，多方面配合比较完善地解决问题，有效地增强系统的抗干扰性能。     

System reliability maximization for a computer network by finding the optimal two-class allocation subject to budget

In the real world, a computer/communication system is usually modeled as a capacitated-flow network since each transmission line (resp. facility) denoted by an edge (resp. node) has multiple capacities. System reliability is thus defined to be a probability that d units of data are transmitted successfully from a source node to a sink node. From the perspective of quality management, system reliability is a critical performance indicator of the computer network. This paper focuses on maximizing system reliability for the computer network by finding the optimal two-class allocation subject to a budget, in which the two-class allocation is to allocate exactly one transmission line (resp. facility) to each edge (resp. node). In addition, allocating transmission lines and facilities to the computer network involves an allocation cost where the cost for allocating a transmission line depends on its length. For solving the addressed problem, a genetic algorithm based method is proposed, in which system reliability is evaluated in terms of minimal paths and state-space decomposition. Several experimental results demonstrate that the proposed algorithm can be executed in a reasonable time and has better computational efficiency than several popular soft computing algorithms.     

Fault tolerance in partitioned manufacturing networks

Fault tolerance is especially important for computer systems that require a high degree of confidence. Computer Integrated Manufacturing (CIM) is an area where computer systems must not be disturbed by uncontrolled failures. This article deals with two problems that are related to fault tolerance and network partitions in automated manufacturing systems.The first problem relates to the distribution of information in partitioned data networks in CIM systems. We indicate how to overcome this problem by using the material network as a redundant data network:The second problem relates to fault detection and diagnosis in manufacturing systems. The problem is whether the indication of a fault means that a production unit itself has actually broken down, or that the indication is instead due to disturbances in the transmission of material. That is, the production unit continues to operate propcrly despite indications to the contrary. We describe how the material network can be used for detection and diagnosis.     

A simulation analysis of the impact of finite buffer storage on manufacturing system reliability

This paper develops a Monte Carlo Simulation (MCS) approach to estimate the system reliability for a multistate manufacturing network with parallel production lines (MMN-PPL) considering finite buffer storage. System reliability indicates the probability that all workstations provide sufficient capacity to satisfy a specified demand and buffers possess adequate storage. The buffers are modeled as a network-structured MMN-PPL. Storage usage of buffers is analyzed based on the MMN-PPL. MCS algorithms are developed to generate the capacity state and to check the storage usage of buffers to determine whether the demand can be satisfied or not. System reliability of the MMN-PPL is estimated through simulation. The MCS approach is an efficient method to estimate system reliability for an MMN-PPL with a reasonable accuracy and time. A pair of practical examples including a tile and a touch panel manufacturing systems shows that system reliability is overestimated when buffer storage is assumed to be infinite. Demand satisfaction probability is further addressed to provide guidance for a proper production policy.     

Use of local area networks within manufacturing systems

Proposals have recently been made within the computer industry to standardize local area computer networking hardware and, although such standards are primarily aimed at the office automation market, they will undoubtedly find many applications in distributed industrial control where a requirement for high speed reliable standardized digital communications also exists. A simple manufacturing cell will be described which demonstrates the advantage of distributed control by using an integrated communications network employing low cost twin axial cable. The individual cell element control systems are supervised by a single computer station providing both control and management information. It will also be shown how such techniques can be applied within industrial manufacturing systems by considering the use of computer networks within a process plant and for the integration of industrial robot systems.     

Routing policy of stochastic-flow networks under time threshold and budget constraint

The quickest path problem is to find a path which sends a given amount of data from the source to the sink such that the transmission time is minimized. More specifically, the capacity of each arc in the network is assumed to be deterministic. However, in many real-life networks such as computer systems, telecommunication systems, etc., the capacity of each arc is stochastic due to failure, maintenance, etc. Such a network is named as stochastic-flow network. Hence, the minimum transmission time is not a fixed number. The purpose of this paper is to provide a decision procedure for a stochastic-flow network under the time and budget constraints. We try to evaluate the probability that d units of data can be sent through the network under both time threshold and budget according to the routing policy. Such a probability is named the system reliability, which is a performance index to measure the system quality. An efficient algorithm is proposed to derive the optimal routing policy with highest system reliability. The sensitive analysis can be conducted to improve the most important component which increases the system reliability most significantly.     

Assessment of spare reliability for multi-state computer networks within tolerable packet unreliability

From a quality of service viewpoint, the transmission packet unreliability and transmission time are both critical performance indicators in a computer system when assessing the Internet quality for supervisors and customers. A computer system is usually modelled as a network topology where each branch denotes a transmission medium and each vertex represents a station of servers. Almost every branch has multiple capacities/states due to failure, partial failure, maintenance, etc. This type of network is known as a multi-state computer network (MSCN). This paper proposes an efficient algorithm that computes the system reliability, i.e., the probability that a specified amount of data can be sent through k (k ≥ 2) disjoint minimal paths within both the tolerable packet unreliability and time threshold. Furthermore, two routing schemes are established in advance to indicate the main and spare minimal paths to increase the system reliability (referred to as spare reliability). Thus, the spare reliability can be readily computed according to the routing scheme.     

The utilization of stand-alone microprocessor units to control energy intensive systems

Most energy intensive process control systems utilize an oversize dedicated computer system. The utilization of stand-alone microprocessor units to control energy intensive systems, reduces costs, facilitates rapid troubleshooting and provides a means to initially inexpensively monitor the operations of these systems to provide control design data. A manufacturing company inquired as to the possibility of reducing their operational costs utilizing computers. This resulted in the design of a multiple, stand-alone and modular Z8 microcomputer configuration to control their steam and compressed air production.     

网络可靠度最优配置

本文研究拓扑结构给定情况下网络可靠的理论问题.当单元的可靠度给定后,研究一 种最优配置方法,使网络具有最高的可靠度.提出了求得可靠度最优配置问题最优解的几个 原理,给出了三个定理,并用一些例子说明了所提原理的应用.     

System reliability for a multi-state manufacturing network with joint buffer stations

This paper studies system reliability for a multi-state manufacturing network with multiple production lines (MSMN-MPL) considering joint buffer station. Joint buffer stations with finite volumes are set into the MSMN-MPL to temporally store blocked outputs from upstream workstations. The usage volume of each joint buffer station is therefore affected by the capacity states of workstations. An adjustment term, defined as the probability that all buffer stations are not blocked, is proposed to analyze volume usage and corresponding probability for joint buffer stations. The system reliability with finite buffer volume is evaluated accurately in terms of the adjustment term. In particular, the relationship between system reliabilities with infinite and finite buffer volumes can be formulated by multiplying the adjustment term. A practical case of footwear manufacturing system is utilized to demonstrate system reliability evaluation with both infinite and finite buffer volumes. The suggested production policy for the case is to produce 144 and 96 products by two production lines because this policy can result a higher reliability. Moreover, experimental results show that the system reliabilities with infinite and finite buffer volume are 87.190% and 83.099%, respectively. This indicates that the assumption of infinite buffer volume overestimates the system reliability in the footwear manufacturing system.     

Asynchronous transmission protocols for WDM LANs using multichannel control architecture

In this paper we study a single-hop WDM network for passive star topology, based on a new network architecture which uses several wavelengths as control channels with an appropriate Network Interface Unit at each station for coordination of packet transmissions on the data channels referred to as Multichannel Control Architecture (MCA). With MCA, control informations are distributed over the total control channels and in conjunction with the suitable NIU reduces the headers electronic processing bottleneck at each end station. We propose a multiple access protocol which operates asynchronously, i.e data channels are not slotted. The proposed scheme adopts the ALOHA protocol for the access to MCA and data channels. Analytic model is developed and analysed for performance measures evaluation based on Poisson approximations statistics of both the infinite and finite population. Numerical results are discussed for various number of control and data channels. The effect of receiver collisions is analysed and estimated by the average rejection probabilities at destination.     

Extend the quickest path problem to the system reliability evaluation for a stochastic-flow network

From the point of view of quality management, it is an important issue to reduce the transmission time in the network. The quickest path problem is to find the path in the network to send a given amount of data from the source to the sink such that the transmission time is minimized. Traditionally, this problem assumed that the capacity of each arc in the network is deterministic. However, the capacity of each arc is stochastic due to failure, maintenance, etc. in many real-life networks. This paper proposes a simple algorithm to evaluate the probability that d units of data can be sent from the source to the sink through the stochastic-flow network within T units of time. Such a probability is called the system reliability. The proposed algorithm firstly generates all lower boundary points for (d,T) and the system reliability can then be computed in terms of such points.Scope and purposeThe shortest path problem is a well-known problem in operations research, computer science, etc. Chen and Chin have proposed a variant of the shortest path problem, termed the quickest path problem. It is to find a path in the network to send a given amount of data from the source to the sink with minimum transmission time. More specifically, the capacity of each arc in the network is assumed to be deterministic. However, in many real-life networks such as computer systems, telecommunication systems, etc., the capacity of each arc is stochastic due to failure, maintenance, etc. Such a network is named a stochastic-flow network. Hence, the minimum transmission time is not a fixed number. This paper proposes a simple algorithm to evaluate the probability that the specified amount of data can be sent from the source to the sink through the network within a given time. Such a probability is called the system reliability.     

A multi-tier linking approach to analyze performance of autonomous vehicle-based storage and retrieval systems

To improve operational flexibility, throughput capacity, and responsiveness in order fulfillment operations, several distribution centers are implementing autonomous vehicle-based storage and retrieval system (AVS/RS) in their high-density storage areas. In such systems, vehicles are self-powered to travel in horizontal directions (x- and y- axes), and use lifts or conveyors for vertical motion (z-axis). In this research, we propose a multi-tier queuing modeling framework for the performance analysis of such vehicle-based warehouse systems. We develop an embedded Markov chain based analysis approach to estimate the first and second moment of inter-departure times from the load-dependent station within a semi-open queuing network. The linking solution approach uses traffic process approximations to analyze the performance of sub-models corresponding to individual tiers (semi-open queues) and the vertical transfer units (open queues). These sub-models are linked to form an integrated queuing network model, which is solved using an iterative algorithm. Performance estimates such as expected transaction cycle times and resource (vehicle and vertical transfer unit) utilization are determined using this algorithm, and can be used to evaluate a variety of design configurations during the conceptualization phase.     

一种基于完整性保护的终端计算机安全防护方法

终端计算机是网络空间活动的基本单元,其安全性直接关系着网络环境和信息系统的安全.提出了一种基于完整性保护的终端计算机安全防护方法,它将完整性度量和实时监控技术相结合,保证终端计算机运行过程的安全可信.建立了以TPM为硬件可信基、虚拟监控器为核心的防护框架,采用完整性度量方法建立从硬件平台到操作系统的基础可信链;在系统运行过程中监控内核代码、数据结构、关键寄存器和系统状态数据等完整性相关对象,发现并阻止恶意篡改行为,以保证系统的完整、安全和可靠.利用Intel VT硬件辅助虚拟化技术,采用半穿透结构设计实现了轻量级虚拟监控器,构建了原型系统.测试表明,该方法能够对终端计算机实施有效的保护,且对其性能的影响较小.     

基于COTS的宇航计算单元冗余架构可靠性研究

随着商业航天的发展,为了能以更低成本使宇航计算单元得到应用,需要结合设计成本、预期寿命、实时性和系统复杂度等因素,对不同计算单元冗余架构的可靠性进行评估;目前在基于高性能商用货架(COTS,commercial off-the-shelf)器件的宇航计算单元研究多满足于工程应用,缺乏关于对不同架构可靠性的对比;首先,针对几种不同冗余计算单元冗余架构,简单介绍具体的拓扑结构和工作方式;其次,根据工作方式给出了他们的故障状态转移图;最后,根据上述几种架构,运用马尔可夫模型理论,对这些计算单元结构进行可靠性建模,在考虑失效率和维修率两个参数对系统可靠性影响的情况下,并以一个虚拟的长时期任务为背景对各结构的可靠性指标进行了评价;仿真结果为更低成本基于COTS器件制造宇航计算单元提供了设计支撑。     

Lead time control in multi-class multi-stage assembly systems with finite capacity

In this paper, we model multi-class multi-stage assembly systems with finite capacity as queueing networks. It is assumed that different classes (types) of products are produced by the production system and products’ orders for different classes are received according to independent Poisson processes. Each service station of the queueing network specifies a manufacturing or assembly operation, in that processing times for different types of products are independent and exponentially distributed random variables with service rates, which are controllable, and the queueing discipline is First Come First Served (FCFS). Different types of products may be different in their routing sequences of manufacturing and assembly operations. For modeling multi-class multi-stage assembly systems, we first consider every class separately and convert the queueing network of each class into an appropriate stochastic network. Then, by using the concept of continuous-time Markov processes, a system of differential equations is created to obtain the distribution function of manufacturing lead time for any type of product, which is actually the time between receiving the order and the delivery of finished product. Furthermore, we develop a multi-objective model with three conflicting objectives to optimally control the service rates, and use goal attainment method to solve a discrete-time approximation of the original multi-objective continuous-time problem.     

基于ZigBee与数传电台的矿井环境检测系统节点设计及其组网方案

针对因煤矿井下环境复杂造成无线传感器网络无法有效地远距离传输信息的问题,提出了一种基于ZigBee无线传感器网络与数传电台的矿井环境检测系统的设计方案,给出了系统总体结构,介绍了以CC2430为核心的传感器节点和网关节点的设计,阐述了适合于矿井环境的ZigBee无线传感器树形网络组网方案的实现。实际测试结果表明,该系统采用ZigBee无线传感器网络与数传电台相结合的通信方案是切实可行的,有效解决了低功耗、远距离传输、高可靠性方面的问题;对节点进行编号的组网规则使网络拓扑结构更具有针对性,提高了节点的精确定位功能,降低了井下作业的危险性。     

Analysis of a linear walking worker line using a combination of computer simulation and mathematical modeling approaches

It has become increasingly important in the last few years to develop rapid, dynamic, responsive and reconfigurable manufacturing processes and systems. This is because manufacturing enterprises are now being forced to develop and constantly improve their production systems so that they can quickly and economically react to unpredictable conditions such as varying production volumes and product variants with small lot size, high quality and low costs. One effective method to achieve this is to create a more flexible, highly skilled and agile workforce capable to perform multiple or all the required tasks in a production area where the system can be reconfigured easily as needed to accommodate changes of production requirement on a daily or weekly basis.This paper presents a study of a so-called linear walking worker assembly line based on a combination of computer simulation and mathematical analysis. The linear walking worker assembly line is a flexible assembly system where each worker travels down the line carrying out each assembly task at each station; and each worker accomplishes the assembly of a unit from start to finish. This design attempts to combine the flexibility of the U-shaped moving worker assembly cell with the efficiency of the conventional fixed worker assembly line. The paper aims to evaluate one critical factor of in-progress waiting time that affects the overall system performance providing a dynamic simulation outlook as well as an insight into the mechanism of such a flexible and reconfigurable manufacturing system.     

考虑多维修台异步多重休假的温贮备冗余系统可靠性模型

考虑多维修台保障多个系统时维修力量存在调度与分配的情况,引入多维修台异步多重休假策略;以温贮备冗余系统为研究对象,针对以往研究利用指数分布等典型分布导致模型约束条件过于严格的问题,采用连续phase-type(PH)分布描述系统中工作部件寿命、温贮备部件寿命以及维修台休假时间和维修时间,建立通用性更好的系统可靠性解析模型,给出系统可靠度、系统稳态可用度等冗余系统可靠性指标和稳态忙期维修台数量等维修台稳态指标;利用算例验证模型适用性,演示了维修台数量、系统温贮备部件数量变化以及修理工休假速率、维修速率变化对系统各可靠性指标和维修台稳态指标的影响.算例计算结果表明,所提出的可靠性模型能够有效复现多维修台调度对冗余系统可靠性的影响,从而为维修台数量的合理安排及系统部件数量的优化配置提供理论基础和实践参考.