Real-Time Manipulation of Alternative Routeings in Flexible Manufacturing Systems: A Simulation Study

This paper presents the results of a simulation study of a typical flexible manufacturing system (FMS) that has routeing flexibility. The objective is this study is to test the effectiveness of the dissimilarity maximisation method (DMM) for real-time FMS scheduling. DMM is an alternative process plan selection method developed for routeing selection in off-line FMS sched-uling. An integrated framework that consists of a computer simulation model, which mimics a physical system, a C++ module, and a linear program solver is used to evaluate the effects of various operational control rules on the system performance. The hypothetical FMS employed in this study consists of seven machining centres, a loading and an unloading area, and six different part types. Owing to the existence of identical machining centres in the system, the part types have alternative routeings. For selecting an incoming part and later routeing it to a machining centre for its next operation, three control rules, namely, first-in first-out/first available (FIFO/FA), equal probability loading (EPL), and dissimilarity maximisation method/first-in first-out (DMM/ FIFO) are used. In this study, DMM is 1. Used as a real-time decision-making tool to select routeings for the parts that are in the system. 2. Tested and benchmarked against FIFO/FA and EPL. The results show that DMM/FIFO outperforms FIFO/FA and EPL on system throughput. Other measures such as average waiting time, average transportation time, and percentage utilisation rates are also investigated to provide insights for the effectiveness of the DMM rule for real-time FMS control applications.     

Dynamic Scheduling for a Flexible Manufacturing System - The Pre-emptive Approach

This paper presents a simulation model of a flexible manufacturing system (FMS) which minimises three performance criteria simultaneously, i.e. mean flow-time, mean tardiness, and mean earliness. The dispatching rule will be changed at a frequency that is varied by the quantity of output produced by the system. Therefore, the dynamic system is an event-trigger rather than triggered by changing the rule at regular time intervals, which is passive. Three indices are used to represent the three criteria being monitored, and the indices are ranked in descending order. The larger the index, the worse is the condition of the criterion in the system. An appropriate rule will be selected for the next operation in order to tackle that criterion with the largest index. This mechanism is called the pre-emptive method. Furthermore, the indices can be biased by the decision maker so that a particular criterion can have larger weighting. Results show that a solution (range of frequency) can always be obtained for changing the dispatching rule so that the system is better than one which just uses fixed FMS scheduling rules.     

Holonic Concept Based Methodology for Part Routeing on Flexible Manufacturing Systems

A flexible manufacturing system (FMS) is designed to achieve good productivity and low cost. The success of an FMS depends largely on effective production scheduling and control. However, it has been found that current manufacturing scheduling and control algorithms lack the flexibility to handle interruptions or resource breakdowns; hence, system performance drops dramatically and abruptly when interruptions occur. This research develops a computer-simulation-based framework of FMS scheduling and control system using the holonic concept. This framework can maintain stability and flexibility while accommodating system disturbance, increase throughput, reduce part flow-time and work-in-process inventory, and balance workload among identical workstations. The significance of this research is the investigation of an innovative approach to revolutionary advances of control technologies for advanced manufacturing systems, and to the revitalisation of control and scheduling algorithms used by existing FMSs. A case study has been provided to substantiate the effectiveness of this proposed framework.     

An Intelligent Decision Support System for Part Launching in a Flexible Manufacturing System

The effective control of flexible manufacturing systems (FMS) poses a major challenge to designers and the research community. In this paper, the framework of a unique decision support system to assist in the control of a FMS through intelligent part-launching is introduced. The proposed system makes usr of a new heuristic method based on the pull concept, and a neural network trained with data from a system simulation model, which in turn provides a desision about choosing a part to be launched into the FMS. The performance of the proposed heuristic method was tested against another popular heuristic method normally used in existing FMS via discrete event simulation models. Data sets from the simulation program of the proposed system were used to train the neural network, which can be used on the shop floor for realtime decision support. The output from the trained neural network is based on the same principle as the proposed heuristic method used in the simulation program. Therefore, the descision support provided by the neural network can be used for improved shop floor control.     

组合模型的柔性制造实验系统

介绍了组合模型的柔性制造实验系统,它以“慧鱼”创意组合模型构建包括物流、加工和仓储等底层功能模块。该系统以计算机为监控部件,可实现数据的实时显示、工序的判断、资源的分配和方案的调度;以PLC为中间环节,实现设备与监控部件之间的数据联系。该系统的研制成功为学生提供了良好的柔性制造系统设计、构建和调试的实践平台。     

Impact of operation flexibility and dispatching rules on the performance of a flexible manufacturing system

Operation flexibility is one of the eight common types of flexibility that exist in flexible manufacturing systems. Dispatching rules are commonly used in loading the machines. This paper studies the effects of different levels of operation flexibility and various dispatching rules on the performance of a flexible manufacturing system. The system performance considered is mean flow time. Simulation results indicate that the mean flow time cannot be always improved by increasing the level of operation flexibility. Altering the dispatching rules seems to have a more significant effect on the mean flow time performance than changing the level of operation flexibility.     

The Effects of Scheduling Rules and Routing Flexibility on the Performance of a Random Flexible Manufacturing System

The increased use of flexible manufacturing systems to efficiently provide customers with diversified products has created a significant set of operational challenges for managers. Many issues concerning procedures and policies for the day-to-day operation of these systems still are unresolved. Previous studies in this area have concentrated on various problems by isolating or simplifying the systems under study. The primary objective of this study is to extend previous research by examining the effects of scheduling rules and routing flexibility on the performance of a constrained, random flexible manufacturing system (FMS). Other experimental factors considered are shop load, shop configuration, and system breakdowns. Within the bounds of this experiment, the results indicate that, in the presence of total routing flexibility, the effects of shop load, system breakdowns, and scheduling rules are significantly dampened. In particular, when total routing flexibility exists, the choice of scheduling rules is not critical. We also show that the behavior of scheduling rules in a more constrained FMS environment (i.e., where system breakdowns occur and material handling capability is limited) is consistent with the findings of previous research conducted under less constrained environments. Finally, results indicate that the shop configuration factor has little or no impact on a system's flow-time performance.     

Performance Modelling and Evaluation of Dynamic Tool Allocation in Flexible Manufacturing Systems using Coloured Petri Nets: An Object-Oriented Approach

Manufacturing systems are faced with ever-increasing customisation and unstable demand. The traditional hierarchical control structures for shop floor (pre-release planning, scheduling, dispatching and activity control) are often inflexible in responding to unexpected scenario changes and are thus not robust to system disturbances. In this paper, an object-oriented approach to modelling of FMS dynamic tool allocation and control under a non-hierarchical shop floor control scheme using coloured Petri nets is presented. A client–server paradigm is used in the proposed modelling method. The complete FMS model is partitioned into individual classes (machines, magazines, tool transport system, SGVs, tool storage, etc.) thereby significantly reducing the complexity of the model to a tractable size. The system performance under different tool request selection rules is also evaluated using coloured Petri net simulation. The proposed method can provide the designer of a tool management system with a high-level and structured representation of the tool-sharing control. It also provides an effective method for prototyping and evaluating performance of object-oriented shop floor control software.     

基于柔性制造系统(FMS)的刀具编码及刀具组装技术研究

在柔性制造系统(FMS)中,刀具编码技术和刀具组装是刀具管理的重要组成部分。该文研究了刀具的编码原理、基本构成和实现方法,在此基础上探讨了刀具在组装过程中遇到的一些问题,提出了相应解决办法,并应用SQL Server 2000数据库和Visual Basic 6.0进行了刀具管理信息系统的设计与开发。     

模糊分析法在柔性制造中的建模与分析

详细介绍了模糊分析法在柔性制造系统中的建模、分析,以及这一数学建模的实际意义。     

柔性制造与市场经济

论述了在市场经济下建立柔性制造系统的必要性以及要注意的问题;经纬纺织机械股份有限公司为适应市场经济,根据国情、厂情,成立了柔性化车间。     

A Fuzzy Multi-Criteria Decision-Making Technique for Evaluation of Scheduling Rules

When examining manufacturing systems using simulation models, different combinations of scheduling rules can be applied to the models. Each combination satisfies a very limited number of performance measures. The problem now is "how to evaluate these combinations" and "how to reflect the weighting of each performance measure in the system". Evaluation of scheduling rules is an inevitable task for any scheduler. Only a few evaluation procedures of the results obtained from computer simulation were found in the literature. In this paper, a framework for the evaluation of combinations of scheduling rules has been developed using fuzzy multi-criteria decision-making techniques, which are called MAW, Max–Min, and Max–Max. A simulation model is used to illustrate the proposed techniques. The results are compared with a simple approach for multi-criteria decision-making method, which is called SAW. Results show that MAW is the best technique for obtaining a high score in the analysis.     

板材冲孔FMS生产管理系统的信息流分析及实现

结合国产板材冲孔 FMS的开发 ,分析了板材 FMS生产管理系统的信息流。将生产管理系统分为 :系统设置、数据管理、计划与调度、通信接口以及 CAD/ CAM管理等五个模块 ,研究了计划及调度模块的功能及其实现 ,基于关系型数据库 SQL Server及 Client/ Server结构开发了相应的生产管理软件     

Reliability Optimisation of Flexible Manufacturing Systems with Spare Tooling

Tool reliability plays an important role in the performance and justification of flexible manufacturing systems (FMSs). Failure of a single tool can cause downtimes over the entire system. This would cause due dates to be missed and can result in inferior products. Therefore, in order to justify the large capital investment associated with FMSs, the system must perform in a reliable manner to give an acceptable or required rate of return on the investment. In order to arrive at this objective, FMS reliability must be studied at the planning and design stages, tool failures pose a major obstacle to achieving this objective. In this paper, a mathematical model has been developed to determine the spare tooling requirement for the tooling system in an FMS, so that a desired system reliability is achieved and the cost is minimised. The influence of tool sharing on cost, reliability, spares requirement, and tool magazine capacity of the FMS are analysed. The tools and tool transporter are subject to general failure distributions.     

The State of the Art in Simulation Study on FMS Scheduling: A Comprehensive Survey

Scheduling of flexible manufacturing systems (FMSs) has been one of the most attractive areas for both researchers and practitioners. A considerable body of literature has accumulated in this area since the late 1970s when the first batch of papers was published. A number of approaches have been adopted to schedule FMSs, including simulation techniques and analytical methods. Numerous articles can be found on each of these approaches. This paper reviews scheduling studies of FMSs which employ simulation techniques as an analysis tool, since simulation is the most widely used tool for modelling FMSs. Scheduling methodologies are categorised into simulation of general scheduling studies, multi-criteria scheduling approaches, and artificial intelligence (AI) approaches in FMSs. Comments on the publications, and suggestions for further research and development are given.     

The Solution of a Multi-Objective Tool Selection Model Using the GA Approach

Tool switching problems in flexible manufacturing systems have been investigated over the last ten years. Work has also been carried out on minimising the number of tool switches and tool switching instances. Optimisation techniques are successful in locating optimum solutions. However, some solutions are slow in convergence and require time to attain the global minimum. Alternative methods which attempt to overcome this problem may risk being trapped at the local minima and fail to give the best solution. In this paper, a model was developed to minimise both the number of tool switches and tool switching instances simultaneously. Genetic algorithms (GAs) which have not been used to solve tool selection problems have been adopted to seek for the global optimum. GAs are found to be fast and efficient in locating an optimum or near optimum solution within an affordable time.     

Flexible Fixturing with Phase-Change Materials. Part 1. Experimental Study on Magnetorheological Fluids

Flexible fixturing is an important issue in manufacturing, where a single set of fixtures are used for locating and holding a variety of workpieces. Flexible fixturing with phase-change materials involves the use of functional materials which change the status from liquid to solid under certain conditions. The workpiece is located in the liquid fixture material and held firmly when the material is changed into the solid state. Therefore, the material strength in the solid state is crucial for a successful application to production. This paper presents an experimental study of magnetorheological (MR) fluid material. With the application of a compression technique, a thick column structure is formed and enhanced. Hence, a high shear strength of the MR fluid in solid status is achieved. Experimental results are reported in this paper. Further application of this technique is under development for flexible fixturing in industrial applications.     

Attribute Selection for Neural Network-Based Adaptive Scheduling Systems in Flexible Manufacturing Systems

System attribute selection is an integral part of adaptive scheduling systems. Owing to the existence of irrelevant and redundant attributes in manufacturing systems, by selecting the important attributes, better performance or accuracy in prediction can be expected in scheduling knowledge bases. In this study, we first propose an attribute selection algorithm based on the weights of neural networks to measure the importance of system attributes in a neural network-based adaptive scheduling (NNAS) system. Next, the NNAS system is combined with the attribute selection algorithm to build scheduling knowledge bases. This hybrid approach is called an attribute selection neural network-based adaptive scheduling (ASNNAS) system. The experimental results show that the proposed ASNNAS system works very well, when measured by a variety of performance criteria, as opposed to the traditional NNAS system and a single dispatching strategy. Furthermore, the scheduling knowledge bases in the ASNNAS system can provide a stronger generalisation ability compared with NNAS systems under various performance criteria. ID="A1" Correspondence and offprint requests to: Dr C.-T. Su, Department of Industrial Engineering and Management, National Chiao Tung University, 1001 Ta Hsueh Road, Hsin-Chu, Taiwan. E-mail: ctsu@cc.nctu.edu.tw     

柔性制造系统控制系统的重构技术

可重构制造系统是制造系统的新的发展方向。本文运用模块化理论和面向对象相结合的方法 ,提出了一种基于可重构的柔性制造系统控制系统的总体结构 ,说明了其功能划分、模块接口及支持环境 ;并从系统结构设计和软件开发的角度 ,对实现重构的相关技术问题提出了解决方案。     

FMS的模块化建模及动态仿真方法的研究

介绍了FMS的基本特点以及FMS建模仿真的必要性。并以一套FMS教学系统为示例，利用MSM建模仿真软件详细地描述了FMS模块化建模厦动态仿真的实现。