Optimal random storage allocation for an AS/RS in an FMS

A flexible manufacturing system (FMS) comprises, automated machine tools, automated material handling, and an automated storage and retrieval system (AS/RS) as essential components. Optimal performance of each element of this system would improve the productivity and efficiency of the total FMS. In this context, this paper attempts to link the operation of the AS/RS with the production schedule and suggests two different classes of algorithms, namely, heuristics and genetic algorithms to improve the performance of the AS/RS operation by allocating the materials with minimum movement of the shuttle.     

AGV schedule integrated with production in flexible manufacturing systems

Flexible manufacturing systems (FMS) comprise, automated machine tools, automated material handling, and automated storage and automated retrieval systems (AS/RS) as essential components. Effective sequencing and scheduling of the material handling systems (MHS) can have a major impact on the productivity of the manufacturing system. The material handling cannot be neglected while scheduling the production tasks. It is necessary to take into account the interaction between machines, material handling systems and computer. In this context, this paper attempts to link the operation of automated guided vehicles (AGV) with the production schedule and suggests a heuristic algorithm that employs vehicle dispatching rules (vdr) for conflict resolution. The vdrs considered in this paper are: shortest operation time (SPT), longest operation time (LPT), longest travel time (LTT) and shortest travel time (STT). The performance of the vdrs in the proposed heuristic is compared with makespan criteria. The results show that the STT provides the best solutions compared to other vdrs.     

An integrated methodology for operations analysis of computer integrated manufacturing systems: Application to an FMS for manufacture of medical instruments

This paper contributes a novel methodology for operations analysis of computer integrated manufacturing systems. The methodology employs an integrated set of personal computer-based manufacturing systems modelling software, and is conducted in three stages. The methodology is illustrated in detail for analysis of materials flow and staffing for a flexible manufacturing system (FMS) installed at a medical instruments manufacturing plant. First, a rough-cut capacity and materials flow analysis was performed using a queueing model. Second, a detailed analysis of FMS system characteristics was conducted by creating and analysing a discrete-event simulation model. Finally, a graphical animation package was used to verify previous results and provide visual feedback on FMS system performance. Analysis results were obtained rapidly and conveniently, and were used to advise manufacturing managers regarding FMS operating policy. This analysis methodology can be applied to a wide range of computer integrated manufacturing systems and manufacturing cells.     

Object-oriented approach of MCTPN for modelling Flexible manufacturing systems

Manufacturing industry is facing a stricter challenge than ever before owing to the rapid change in market requirements. Flexible manufacturing systems (FMSs) have a much greater capability than traditional fixed-type production systems for coping with the rapid change. In this paper, a modified coloured-timed Petri net (MCTPN) is developed to model the dynamic activities in an FMS. The MCTPN provides an object-oriented and modular method of modelling manufacturing activities. It includes colour, time, modular and communication attributes. The features of object-oriented modelling allow the FMS to be modelled with the properties of classes, objects, and container trees. Since the system activities can be encapsulated and modularised by the proposed MCTPN, the manufacturing systems can be easily constructed and investigated by the system developers. It makes the concept of software IC possible for modelling complex FMSs. Once all of the MCTPN objects are well defined, the developers need to consider only the interfaces and operations relating to the MCTPN objects. In order to demonstrate the capability of the proposed MCTPN, the FMS in the Manufacturing Automation Technology Research Center (MATRC) of the National Taiwan University will be stimulated and justified by using the proposed MCTPN along with the G2 expert system.     

Dynamic availability-oriented control of the automated storage/retrieval system. A computer integrated manufacturing perspective

Dynamic scheduling of the storage/retrieval (S/R) requests and increasing the utilization of the storage spaces, are the two common approaches to improve the efficiency of the automated storage/retrieval systems (AS/RS) in industry practice. However, the actual improvement of the AS/RS has to be justified from the perspective of computer integrated manufacturing system (CIMS) because the ultimate objective of the AS/RS is to assist the CIMS in enhancing its material handling efficiency as well as synchronizing the production. Targeting on this crucial requirement, a dynamic availability-oriented controller (DAOC) is developed in this paper to minimize the mean request fulfilment time of the AS/RS. Firstly, while considering the three types of critical dynamic constraints from the CIMS’ shop floor: the availabilities for both machines and the AS/RS, the process plan of the product, and the production schedule, DAOC is capable of determining the optimal execution sequence of the S/R requests issued from the CIMS and activating dynamic storage space consolidation commands of the AS/RS. Secondly, simulation experiments are conducted and the results show that DAOC successfully improves the S/R request control scheme of the traditional class-based assignment method and significantly outperforms four comparable approaches under various CIMS configurations.     

Design of cellular manufacturing systems using objective functional clustering algorithms

Cellular manufacturing (CM) has emerged as an alternative to conventional batch-type manufacturing owing to the former's capability of reducing set-up times, in-process inventories and throughput times. It provides the basis for implementation of just-in-time (JIT) and flexible manufacturing systems (FMS). The machine-part group formation is an important issue in the design of CMSs. This paper presents objective functional clustering algorithms for cell formation problems in the design of cellular manufacturing systems. A deterministic objective functional algorithm (hard clustering) and a fuzzy objective functional algorithm (fuzzy clustering) are used to form the part families and machine cells simultaneously. A collection of data sets from open literature is used to test these algorithms. A software package has been developed to verify the implementation.     

A review of some issues and identification of some barriers in the implementation of FMS

Global competition, advancements in technology and ever changing customers’ demand have made the manufacturing companies to realize the importance of flexible manufacturing systems (FMS). These organizations are looking at FMS as a viable alternative to enhance their competitive edge. But, implementation of this universally accepted and challenging technology is not an easy task. A large number of articles have been reviewed and it is found that the existing literature lacks in providing a clear picture about the implementation of FMS. In this paper, work of various researchers has been studied and it is found that it is really a very difficult task for any organization to transform into FMS on the basis of existing research results. A wide gap exists between the proposed approaches/algorithms for the design of different components of FMS and the real-life complexities. Besides describing the gap in various issues related to FMS, some barriers, which inhibit the adaptation and implementation of FMS, have also been identified in this paper.     

An Analytical Queueing Network Model for Flexible Manufacturing Systems with a Discrete Handling Device and Transfer Blockings

In this paper, we study job shop-like flexible manufacturing systems (FMSs) with a discrete material handling system (MHS). In such FMSs, the MHS is a critical device, the unavailability of which may induce transfer blockings of the machines. The FMS devices therefore are hierarchically structured into primary and secondary devices to manage such blocking and avoid deadlocks in these FMSs.For evaluating the quantitative steady-state performance of such FMSs, we propose an analytical queueing network model that relies on an approximate method proposed for analyzing computer systems with simultaneous possessions of resources. Such a model is obtained using the concept of passive resources and by aggregating the FMS workload data so that models are much more tractable.The analytical results are validated against discrete event simulation and shown to be very encouraging. We also show how to increase their robustness, especially under light workload conditions, by modifying an assumption of the method concerning service time distributions.     

Object-oriented graphical modeling of FMSs

Presented in the article is a method for constructing a graphical model of an FMS by using a new modeling tool called JR-net (Job Resource relation-net). JR-net is an object-oriented graphical tool for modeling automated manufacturing systems (AMSs), such as FMSs, FASs, and AS/RSs. As with the object-oriented modeling paradigm of Rumbaugh et al. (1991), the JR-net modeling framework supports the three stages of models: static layout model (object model); job flow model (functional model); and supervisory control model (dynamic model). In this article, the existing JR-net structure (Park 1992, Han et al., 1995) is extended further to make it a graphical tool for FMS modeling. Using the extended JR-net, a step-by-step procedure for constructing a graphical model of FMSs is presented. Also addressed are issues of classifying FMSs in terms of their generic functions and of utilizing the JR-net model of FMSs.     

An innovative automated storage and retrieval system for B2C e-commerce logistics

Flexible and timely warehousing activities provide a strong foundation for logistic systems. However, increasing B2C e-commerce with a variety of small internet orders may have a tremendous impact on warehousing. Automated storage/retrieval systems (AS/RSs) are a valid alternative for warehousing. Typical AS/RSs design and control problems in a static environment and cannot effectively manage parcel, small, and irregular items. This study proposes a new AS/RS that is more efficient and flexible for handling B2C e-commerce logistics. An auto-access multilevel conveying device (IMCD) with three-dimensional movement is integrated into the AS/RS. The ant colony system algorithm locates near-optimal routes for the IMCD. Typical travel distance/time measures evaluate the performance of an S/R device running on a warehouse floor. However, the performance index in this study looks at the IMCD’s travel time with three-dimensional movement in completing a batch order. To validate the new AS/RS, two simulation experiments were conducted to examine the effects of three-dimensional velocity and rack shape. Finally, this study compares a typical S/R system with the new AS/RS and makes recommendations for practical applications and further research.     

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.     

Simulation for maintenance of an FMS: an integrated system of maintenance and decision-making

Flexible manufacturing systems (FMSs) are designed to produce a variety of different part types with high machine utilisation, so the maintenance technique is necessary and very important in an FMS. This paper discusses the maintenance problem in an FMS and its simulation, analyses the maintainability of a real FMS shop, and presents the architecture of an integrated system of maintenance and decision-making/scheduling for manufacturing shop control. The modelling and simulation of the maintenance activities in the shop are shown. The simulation program is written in SLAM II and the special subroutines are realised in Fortran. The interest is directed towards the use of the method of simulation for maintenance and decision-making in FMSs.     

基于FMS的自动化立体仓库监控系统开发与应用术

为了实现对基于柔性制造系统（FMS）的自动化立体仓库（AS／RS）的监控与管理,以浙江机电职业技术学院示范院校建设FMS项目为背景,根据具体实验教学的要求,进行了自动化立体仓库集成监控系统设计,实现了一套功能完备、规范化、工程化的集成监控软件。研究结果表明,该系统的运行效果令人满意。     

Scheduling tasks and vehicles in a flexible manufacturing system

Due to their increasing applicability in modern industry, flexible manufacturing systems (FMSs), their design, and their control have been studied extensively in the recent literature. One of the most important issues that has arisen in this context is the FMS scheduling problem. This article is concerned with a new model of an FMS system, motivated by the practical application that takes into account both machine and vehicle scheduling. For the case of a given machine schedule, a simple polynomial-time algorithm is presented that checks the feasibility of a vehicle schedule and constructs it whenever one exists. Then a dynamic programming approach to construct optimal machine and vehicle schedules is proposed. This technique results in a pseudopolynomialtime algorithm for a fixed number of machines.     

面向仓储物流的建模及控制系统设计方法

为提高现代企业仓储物流的设计质量和效率,提出了一种基于资源颜色时序信号的扩展Petri网建模及控制系统设计方法.该方法首先采用资源颜色时序信号的扩展Petri网建立了仓储系统的动态模型,清晰地描述了各种物流活动的顺序、并发,冲突等关系,并结合关联矩阵,阐述了判断死锁和陷阱的方法.该方法建立的模型可根据Petri网运算规则进行保性化简,便于仿真分析和验证,且可直接用于系统可编程逻辑控制器的控制程序设计.最后,以仓储物流控制系统为例,阐述了系统建模及控制设计过程.     

Flexible Manufacturing Systems' compliance to the safety standards

Safety improvements of Flexible Manufacturing Systems (FMSs) are improving usability of the system usability and also the competitiveness of the manufacturing. The aims of this study were 1) to analyze the deficiencies in and the risks of flexible manufacturing system (FMS) implementations 2) to clarify whether the systems meet the demands of safety standards and 3) to suggest safety system improvements. The study was made by using the Safety Analysis for Production Automation and the Safety Checklist for FMSs. The data were gathered by interviewing key managers and workers employed by 22 Finnish companies with FMS implementations. The study showed that although the companies considered the FM systems as one of their safest functions in the workshops, many of the systems do not fulfill the most common requirements of the safety standards. The requirements were met by 70% of the targets studied. Installation and maintenance functions best meet these requirements, whereas the layout of the systems and their mechanical structure were the most poorly designed areas. Especially poor were the safety and ergonomics of the loading/unloading stations. This paper presents additional information about the deficiencies found in the FM-systems and companies' involvement in them. The results shed new light on safety and ergonomic aspects to be considered in designing and using FM-systems. The data can be used to help industry meet safety demands and to improve the efficiency of new FMS implementations.     

Modeling and analysis for a kind of flexible manufacturing system involving time factors

Time control and management are important in flexible manufacturing systems (FMS). The time to finish the machining unit is uncertain because of the uncertainties of the workpieces, so the whole time to finish the FMS is also variable. In order to reduce the time to finish for the whole FMS to improve efficiency, the modeling and analysis method for this timing kind of FMS based on standard Petri net is proposed. The modeling method is a mapping from the machining units to the component of a Petri net, and the timing factors are represented by a timing function on the place set. With the Petri net model obtained and its reachability graph, the timing factors influencing the implementation of the FMS are analysed and presented. In addition, the method is obtained to find the best state line for the implementation of the FMS.     

Reliability Optimisation of FMS with Spare Tooling

Tool reliability plays an important role in the performance and justification of flexible manufacturing systems (FMS). Failure of a single tool can cause downtimes over the entire system. This results in missing due dates, and inferior products. Therefore, in order to justify the large capital investment associated with FMS, the system must perform in a reliable manner to give an acceptable or expected rate of return on capital. FMS reliability should be studied at the planning and design stages, as tool failures pose a major obstacle to achieving this objective. In this paper, a mathematical model has been developed to determine the spares requirement of the tooling system in an FMS, so that the 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.