An Investigation of Stochastic Analysis of Flexible Manufacturing Systems Simulation

This paper describes the use of an ARIMA (autoregressive-integrated- moving-average) model and its equivalent state space models to produce rule-based knowledge for flexible manufacturing systems (FMS) that can be used to investigate a wide variety of problems including machine breakdown, material shortage, and changes of scheduling rules. One great advantage of using the proposed models is the ease with which the simulation results can be summarised, analysed and captured, as well as the availability of the mathematical representation of the knowledge that can be kept in a knowledge database for evaluation and selection of alternative FMS strategies in a real-time environment. Various case studies are used to illustrate the methodology and the development of ARIMA and state space models, the analysis includes the system cost and stability of changes or interventions, the relationships among the simulation inputs and outputs, and the formulation of the production rule-base for the FMS scheduler. Management can use this integrated approach to describe and predict the dynamic behaviour of a complex FMS.     

Evaluation of the impact of information delays on flexible manufacturing systems performance in dynamic scheduling environments

The significance of the adverse effects of information delays (IDs) on flexible manufacturing system (FMS) performance is getting increasing attention from manufacturing systems managers, planners, schedulers, Enterprise Resource Planning software developers, and researchers because of their potential to disrupt production schedules. In this paper, we examine the extent of the adverse impact that IDs have on FMS performance. The FMSs are assumed to operate in a “review period” mode; i.e., the control decisions (e.g., sequencing and dispatching) are taken based on information monitored at predetermined intervals of time called “review periods”. The performance deterioration occurs due to the obsolescence of system status information. Key empirical findings based on extensive simulation experiments are: (1) IDs significantly degrade FMS performance for due date-based measures (mean tardiness and percent of jobs tardy); (2) IDs also degrade FMS performance for non-due date-based measures (mean flowtime and average machine utilization), albeit to a less severe degree; (3) routing flexibility, often regarded as a significant factor to influence FMS performance, is superseded by status review information delay.     

Development and evaluation of feature-focused dynamic routing policy

This paper reports on a development of feature-focused dynamic routing policy and its evaluation in a flexible manufacturing systems (FMS) simulation framework. The dynamic policy is based on an integrative methodology in which process planning system IMPlanner is integrated with FMS simulation module. IMPlanner’s rule-based system process selection system performs knowledge-intensive task of generating alternative processing options for each feature for parts in production plan. Generated alternative routings (process plan network) for each part are utilized in the FMS simulation module such that routing decision in FMS are made on periodic intervals by considering alternative processes for each feature and making decision based on the current system status and performance. The proposed framework has been evaluated in an experimental FMS simulation module, implemented in Arena, in which two performance criteria, machine utilization and WIP, were used to make routing decisions. The feature-focused approach is compared with traditional static decision-making, and its improved performance is demonstrated.     

An FMS scheduling and control decision support system based on generalised stochastic Petri nets

This paper presents an FMS scheduling and control DSS (decision support system) using generalised stochastic Petri nets (GSPNs) for model representation and analysis. The function of the DSS is to assist the FMS operator to search for suitable control strategies that will achieve efficient performance. It can also be called upon in the event of unforeseen changes in production requirements, component failures, or other related contingencies. The GSPN modelling approach is employed because GSPNs can characterise random processing times, machine breakdown and repair rates. The GSPN employed in the proposed DSS also incorporates dispatching control at conflicting immediate transitions and can be used to determine various performance measures pertaining to scheduling and control. An application example of the DSS for the processing of two part types in a three-machine FMS is also described.     

柔性制造系统的生产物流调度仿真与分析

采用假定的工件工艺文件和机床作业调度文件作为仿真程序运行的原始数据,通过运行仿真程序得到仿真结果,对运行过程中的生产物流数据进行分析、结果进行记录。从单台设备的运行状态和多设备运行时动作的协调性方面对仿真运行结果进行了分析,验证了柔性制造系统中的生产物流系统模型和仿真程序设计的正确性,以及FMS物流系统规划与组织的有效性。     

Simultaneous scheduling of parts and automated guided vehicles in an FMS environment using adaptive genetic algorithm

Automated Guided Vehicles (AGVs) are among various advanced material handling techniques that are finding increasing applications today. They can be interfaced to various other production and storage equipment and controlled through an intelligent computer control system. Both the scheduling of operations on machine centers as well as the scheduling of AGVs are essential factors contributing to the efficiency of the overall flexible manufacturing system (FMS). An increase in the performance of the FMS under consideration would be expected as a result of making the scheduling of AGVs an integral part of the overall scheduling activity. In this paper, simultaneous scheduling of parts and AGVs is done for a particular type of FMS environment by using a non-traditional optimization technique called the adaptive genetic algorithm (AGA). The problem considered here is a large variety problem (16 machines and 43 parts) and combined objective function (minimizing penalty cost and minimizing machine idle time). If the parts and AGVs are properly scheduled, then the idle time of the machining center can be minimized; as such, their utilization can be maximized. Minimizing the penalty cost for not meeting the delivery date is also considered in this work. Two contradictory objectives are to be achieved simultaneously by scheduling parts and AGVs using the adaptive genetic algorithm. The results are compared to those obtained by conventional genetic algorithm.     

Simultaneous scheduling of parts and automated guided vehicles in an FMS environment using adaptive genetic algorithm

Automated Guided Vehicles (AGVs) are among various advanced material handling techniques that are finding increasing applications today. They can be interfaced to various other production and storage equipment and controlled through an intelligent computer control system. Both the scheduling of operations on machine centers as well as the scheduling of AGVs are essential factors contributing to the efficiency of the overall flexible manufacturing system (FMS). An increase in the performance of the FMS under consideration would be expected as a result of making the scheduling of AGVs an integral part of the overall scheduling activity. In this paper, simultaneous scheduling of parts and AGVs is done for a particular type of FMS environment by using a non-traditional optimization technique called the adaptive genetic algorithm (AGA). The problem considered here is a large variety problem (16 machines and 43 parts) and combined objective function (minimizing penalty cost and minimizing machine idle time). If the parts and AGVs are properly scheduled, then the idle time of the machining center can be minimized; as such, their utilization can be maximized. Minimizing the penalty cost for not meeting the delivery date is also considered in this work. Two contradictory objectives are to be achieved simultaneously by scheduling parts and AGVs using the adaptive genetic algorithm. The results are compared to those obtained by conventional genetic algorithm.     

Integrated definition modeling and Taguchi analysis of flexible manufacturing systems: aircraft industry application

In this paper, flexible manufacturing systems (FMS) are studied. Firstly, an FMS design approach is proposed using integrated definition for function methodology. A systematic layout design and performance evaluation scheme is presented and detailed using this modeling framework. Then, the proposed approach is carried out with a case study from an aircraft industry to convert an existing traditional production system to FMS. To improve the system performance, a simulation-based method with Taguchi approach consisting of multiproducts is utilized. The objective is to find the machine and the product mix that achieves the maximum utilization while minimizing the cycle time. FMS system performance has been greatly improved by determining the most advantageous level of system components. It has also shown that FMS is a practicable production system in aircraft industry.     

Information system architecture for heterarchial control of large FMSs

In this paper we investigate the design of a distributed information management system for heterarchical (decentralized) shopfloor control in large Flexible Manufacturing Systems (FMS). We characterize the complexity of information management in automated manufacturing, and study the interaction between the shopfloor control system and the information management system. We describe protocols for a heterarchical control scheme, and identify the information content of messages that are transmitted between autonomous manufacturing system entities under this control paradigm. On the basis of the proposed shopfloor control protocols and the information requirements at each type of manufacturing system entity, we develop an information system architecture that is capable of supporting heterarchical shopfloor control in large FMSs.     

Multiactivity paradigm for the design and coordination of FMSs

This paper introduces a methodology and a set of tools that allow a manufacturing engineer to integrate programable work cells such as flexible machining cells (FMCs) and flexible assembly cells (FACs), linked by an automated transport system, into an FMS that can be reprogrammed easily for the inclusion of additional products, thus making small- and medium-size production runs economical. The proposed method is based on the multiactivity paradigm that separates activity executions from their coordination by viewing systems as a set of assignable executors controlled by a coordinator. In this view, an FMS has at least three layers: a top layer in which the work cells are considered as assignable resources that can be programmed to execute the activities required to produce a given product; a middle layer in which the elements of the work cells (robot arms, NC machines, vision systems, etc.) are the assignable resources that execute in the required order the various machining, assembly and/or transfer operations; and a bottom layer that controls directly the various actuators and sensors. Because of the wide variety of work cell elements, only the top two layers are considered here. At the top level a control computer is used to coordinate the activities of the work cells and the transport system, and at the middle level each work cell includes a coordinator that oversees the operation of its elements. This paper introduces the process activity language, PAL, a high level specification language that matches the multiactivity view and allows the specification of the production steps and the operation of the work cells in a highly structured way. A number of PAL-based tools that aid the manufacturing engineer, to check for specification errors, to configure the FMS to meet the various production constraints, and that simplify the design and programming of the coordinators, have been developed and are outlined here.     

FMS的实时生产过程监视和智能化故障诊断系统研究

以上海第四机床厂箱体零件ＦＭＳ为例．从分析现代ＦＭＳ的过程监视和故障诊断的需求入手，确定所需采集的各个生产状态信号和故障信号，并在微机ＷＩＮＤＯＷＳ环境中用Ｃ￣（＋＋）语言开发实用的软件，建立ＦＭＳ的实时生产过程监视和智能化故障诊断系统。     

The analysis of flexible manufacturing systems for reliability

Flexible manufacturing systems (FMS) constitute a considerable capital investment which must be fully utilised by uninterrupted production. The analysis of reliability at planning and development stages in the implementation of FMS is essential, since it can change both the system design and the operating philosophy to give improvements in the overall system performance. The main objective of this paper is to propose a technique for assessing the reliability of flexible manufacturing systems and further to discuss the unsuitability of the traditional reliability techniques in the study of such systems. It is shown that simulation studies in thereliability of flexible manufacturing can be applied in the analysis of alternative approaches to system design. The key terms, ‘Manufacturing Capability’, ‘Production Efficiency’ and ‘Demanded Production Lead Time Success Ratio’ are introduced as measures which can assess a system's performance. A typical flexible manufacturing cell is then analysed for reliability using predicted reliability data. The effect of equipment redundancy, buffer stock size and production priority rules on the cells performance are finally discussed.     

Performance Analysis of an FMS Operating Under Different Failure Rates and Maintenance Policies

Flexible manufacturing Systems (FMSs) typically operate at 70–80% utilization, which is much higher than the utilization of traditional machines that can operate with as low as 20% utilization. A result is that an FMS may incur four times more wear and tear than a traditional system. This requests the execution of effective maintenance plans on FMSs. While maintenance actions can reduce the effects of breakdowns due to wear-outs, random failures are still unavoidable. It is important to understand the implications of a given maintenance plan on an FMS before its implementation. This paper discusses a procedure that combines simulation and analytical models to analyze the effects of corrective, preventive, and opportunistic maintenance policies on the performance of an FMS. The FMS performance is measured by its operational availability index, which is determined using the production output rate of the FMS under a variety of time between failure distributions and different operational conditions. The effects of various maintenance policies on FMS performance are simulated and the results are compared to determine the best policy for a given system.     

Scheduling algorithms for a two-machine flexible manufacturing system

The flexible manufacturing system (FMS) considered in this paper is composed of two CNC machines working in series—a punching machine and a bending machine connected through rollers acting as a buffer system of finite capacity. The main difference between the present problem and the standard two-machine flow shop problem with finite intermediate capacity is precisely the buffer system, which in our problem consists of two stacks of parts supported by rollers: the first stack contains the output of the punching machine, while the second stack contains the input for the bending machine. When the second stack is empty, the first stack may be moved over. Furthermore, the capacity of each stack depends on the particular part type being processed.The FMS can manufacture a wide range of parts of different types. Processing times on the two machines are usually different so that an unbalance results in their total workload. Furthermore, whenever there is a change of the part type in production, the machines must be properly reset—that is, some tools need to be changed or repositioned.A second important difference between the present problem and the usual two-machine flow shop problem is the objective. Given a list ofp part types to be produced in known quantities, the problem considered here is how to sequence or alternate the production of the required part types so as to achieve various hierarchical targets: minimize the makespan (the total time needed to complete production) and, for instance, compress the idle periods of the machine with less workload into a few long enough intervals that could be utilized for maintenance or other reasons.Although Johnson's rule is optimal in some particular cases, the problem addressed in the paper isNP-hard in general: heuristic procedures are therefore provided.     

A heuristic algorithm to batching and loading problems in a flexible manufacturing system

Part type selection and machine loading are two major problems in the production planning of flexible manufacturing systems (FMS). The two problems are viewed as selecting subsets from the jobs of part types in a planning horizon and allocating jobs of the subsets among machines. In this paper, in order to develop a practical and efficient approach to solving FMS production planning problems, a heuristic algorithm is suggested that develops heuristic rules with the objective of minimisation of the number of tool changes and minimisation of the imbalance in per machine. To compare the proposed algorithm, a series of computational experiments is done on randomly generated test problems and the results show that the developed algorithm is very simple and efficient.     

Pilot plants to assist FMS/CIM evaluation,design and industrial applications

A CAD-oriented and a CAM-oriented CIM pilot plant are implemented ind Budapest, Hungary to assist research, development and education, and to help industrial engineers and managers to get a better understanding of CAD/CAM/CIM technologies. In the first part of the paper a short account is given on Hungarian R&D and implementation activities in the field of FMS and industrial networks. Then details of the main goals and the structures of the pilot plants are given. As design is one of the most important issues, at a given design and simulation aspects of flexible manufacturing cells/systems are touched upon. Finally, experiments are discussed, the evaluation of which should give information on manufacturing strategies of planned, future FMS/CIM investments.     

FM车间环境下自动化立体仓库系统

本文介绍的“ＦＭ车间环境下自动化立体仓库系统”具有多功能的特点。其一是车间设备集成的核心；其二集成车间物流和信息流；其三控制生产；其四可进行生产调度；其五可暂存缓冲托盘。文章给出了郑州纺织机械厂机械加工二分厂初级ＦＭ车间自动化立体仓库系统的设计思想     

Modeling FMS with decision Petri nets

Decision point extended timed Petri nets or decision Petri nets (DPN) are introduced as an extended modeling framework for FMS performance evaluation. The decision point extension allows the explicit modeling of the control of the flow of tokens in timed Petri nets and hence represents the control of the flow of material, resources, and information in FMS. Further, the concept of a bounded transition is proposed to conveniently model the blocking logic in an FMS with limited buffer capacities. The motivation to present these conventions is to develop a user-friendly graphic model to represent FMS designs for analysis by discrete event simulation. DPN affords concise models that can be conveniently developed and easily transformed into discrete event simulation models. With the help of a simple FMS example, which includes a number of part types, loading rules, dispatching rules, and probabilistic branching (at an inspection station), we illustrate the DPN model development. As an illustration of the ease with which it can be tranformed into a simulation model, we have developed a generalized simulator called ROBSIM and outline here its methodological basis. The proposed concepts should be of interest to users of discrete event simulation in FMS design or elsewhere to tap the potential of basic Petri net concepts for graphic representation and specification purposes. In particular, our work should encourage other researchers to develop extensions relevant to their own areas of interest.     

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.     

柔性制造系统中的实物期权识别和定价

在对柔性制造系统的不确定性来源分析的基础上，指出产品需求是影响柔性生产的主要不确定性来源；通过与金融期权的对比，辨识和描述柔性制造系统中所蕴含的实物期权，即单品种生产期权．多品种生产期权和多周期、多品种、有生产准备的生产期权；建立生产期权多维格型定价模型，并以多品种生产期权为例进行了案例研究，表明该模型可以有效地处理柔性制造系统中的环境不确定性。