Multiple-Objective Scheduling for the Hierarchical Control of Flexible Manufacturing Systems

This paper presents a hierarchical approach to scheduling flexible manufacturing systems (FMSs) that pursues multiple performance objectives and considers the process flexibility of incorporating alternative process plans and resources for the required operations. The scheduling problem is solved at two levels: the shop level and the manufacturing system level. The shop level controller employs a combined priority index developed in this research to rank shop production orders in meeting multiple scheduling objectives. To overcome dimensional complexity and keep a low level of work-in-process inventory, the shop controller first selects up to three production orders with the highest ranking as candidates and generates all possible release sequences for them, with or without multitasking. These sequences are conveyed to the manufacturing system controller, who then performs detailed scheduling of the machines in the FMS using a fixed priority heuristic for routing parts of multiple types while considering alternative process plans and resources for the operations. The FMS controller provides feedback to the shop controller with a set of suggested detailed schedules and projected order completion times. On receiving these results, the shop controller further evaluates each candidate schedule using a multiple-objective function and selects the best schedule for execution. This allows multiple performance objectives of an FMS to be achieved by the integrated hierarchical scheduling approach.     

虚拟仿真柔性制造系统的开发

采用计算机仿真技术开发了一套虚拟仿真柔性制造系统．给出了系统设计的总体方案、作业排序的优化算法以及动画仿真的实现过程,为在仿真环境中进行FMS研究,提供了经济灵活的途径,也为制造出配置合理、运行高效的FMS提供了参考和依据。     

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。     

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.     

Dissimilarity Maximization Method for Real-time Routing of Parts in Random Flexible Manufacturing Systems

This paper presents a dissimilarity maximization method (DMM) for real-time routing selection and compares it via simulation with typical priority rules commonly used in scheduling and control of flexible manufacturing systems (FMSs). DMM aims to reduce the congestion in the system by selecting a routing for each part among its alternative routings such that the overall dissimilarity among the selected routings is maximized. In order to evaluate the performance of DMM, a random FMS, where the product mix is not known prior to production and off-line scheduling is not possible, is selected for the simulation study. A software environment that consists of a computer simulation model, which mimics a physical system, a C++ module, and a linear program solver is used to implement the DMM concept. In addition to DMM, the simulation study uses two priority rules for routing (i.e., machine) selection and seven priority rules for selecting parts awaiting service at machine buffers. The results show (1) DMM outperforms the other two routing selection rules on production rate regardless of the part selection rule used, and (2) its performance is highly dependent on the part selection rules it is combined with.     

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.     

Manufacturing Flexibility: Assessing Managerial Perception and Utilization

This paper presents an empirical study of how consumer electronics companies in Brazil deal with the issue of manufacturing flexibility. The main purpose is to provide an understanding into how flexibility is being perceived and utilized in a newly industrialized country. It begins by explaining the relevance of this study. The participation of Brazil in the world economy is important. Here, companies can be very flexible, based on low cost and an abundant skilled work force, yet flexibility has not been addressed. The paper explains how indicators were established to obtain an analytical structure with which to assess the managerial perception and the actual industrial use of flexibility. Finally, we show the most relevant results of our investigation of 16 leading firms in Brazil, including multinational ones. The findings are divided according to managerial perception of flexibility and effective utilization of flexibility in the organization. The paper concludes that firms in the consumer electronics industry in Brazil do not use flexibility practices in the same proportion that they perceive its importance.     

Effects of Dispatching and Routeing Decisions on the Performance of a Flexible Manufacturing System

This paper is concerned with the effects of dispatching and routeing decisions on the performance of a flexible manufacturing system (FMS). Three routeing policies, no alternative routeings, alternative routeings dynamic, and alternativerouteings planned are first considered with four dispatching rules with infinite buffer capacity. However, in real-life, the size of the local buffers in FMSs may be limited by the size of the part types. Therefore, further experiments to investigate the above three routeing policies with the four dispatching rules with finite buffer capacity are also conducted in order to study the impact of limited buffer capacity on system performance. In addition, the effect of changing part mix ratios is discussed with both infinite and finite buffer capacity. The performance measures considered are makespan, average machine utilisation, average flow-time, and average delay at local input buffers. The simulation results indicate that for infinite buffer capacity, the alternative routeings planned policy, combined with the shortest total processing time dispatching rule, gives the best results for all the above performance measures. For finite buffer capacity, the alternative routeings dynamic policy gives the best results in three performance measures, except for average delay at local input buffers. Further, the effect of changing part mix ratios is not significant. ID="A1"Correspondance and offprint requests to: Dr F. T. S. Chan, Department of Industrial and Manufacturing Systems Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong. E-mail: ftschan@hkucc.hku.hk     

柔性制造系统的发展

随着生产力的发展与科技的进步,市场竞争日趋激烈,人们对产品功能与质量的要求不断提高。传统的生产方式越来越无法满足当今市场对短周期、多品种和小批量产品制造的需求,即生产柔性的需求[1]。柔性制造系统将计算机、自动化控制、微电子技术和系统工程等复杂技术进行了有机结合,既具有机械加工的高自动化与高效率,又具有良好的生产柔性。本文根据柔性制造系统的特点,对其基本组成、类型、工作优势以及未来的发展方向进行了阐述。     

Performance Analysis of Flexible Manufacturing Systems with a Single Discrete Material-Handling Device

We present an analytical model for performance prediction of flexible manufacturing systems (FMSs) with a single discrete material-handling device (MHD). This configuration of FMS is significant for many reasons: it is commonly found in industry, it simplifies material-handling control, it is amenable to analytical modeling, and it forms a building block for more complex systems.Standard queueing models are inadequate to analyze this configuration because of the need to take into consideration many nontrivial issues such as state-dependent routing, interference from the MHD, and the analysis of the MHD. To account for state-dependent routing, we develop an iterative method that is built around mean value analysis. To analyze the MHD interference, we use two queueing network models. In the first, we ignore queueing at the MHD but model the interference from the MHD by inflating the station service times. The second network models the queueing for the MHD and estimates the blocking (inflation) times needed for the first model. By iterating between the two networks, we are able to predict the performance of this configuration of FMS. Our analytical estimates are validated against discrete event simulation and shown to be quite accurate for initial system design.     

网络化制造执行系统作业计划的研究

作业计划的制定是一项非常重要的工作,在网络化制造环境下作业计划的影响因素很多,本文应用层次分析法,结合众多影响因素,给出了其调度模型.     

柔性工艺路线蚁群优化单元作业调度

在柔性工艺路线的作业调度问题中,根据设备的约束以及加工过程中的费用、加工时间等因素,建立初始有向图,采用新颖的基于动态信息素更新策略的蚁群优化算法,迅速收敛并得到最优解,从而提高调度系统的可行性,增强系统稳定性和健壮性。该方法以减少外协,均衡生产,确保设备连续生产为目标,有效地支持了分布式制造单元的管理过程,增强了单元系统信息分布处理和规模可扩展能力。最后给出了算例,并对计算结果进行了分析和讨论。     

P-FMS小型柔性制造系统的研制与开发

本文简要介绍了一种用于教学的小型柔性制造系统 ,简述了控制系统的组成、硬件设备以及软件环境。     

基于节拍平衡的高柔性数控单元调度研究

为提高柔性数控单元生产效率,提出一种基于工序平衡的高柔性数控单元调度方法。第一阶段,根据产品生产工艺和设备生产能力进行工艺路线规划,在考虑生产约束、生产准备时间、工艺柔性和设备产能的基础上,构建产品节拍平衡优化目标,获得其最优加工视图组合;第二阶段,基于工序平衡的结果,在考虑产品换线时间的基础上构建整单调度模型,并采用遗产算法求解。最后,将所提调度方法在某壳体产品高柔性数控生产单元进行应用研究,并与分批量调度模型进行了比较分析。研究表明,所提出的工序平衡的柔性数控单元整批量调度方法可以有效缩短单元的制造周期,提高单元控设备利用率。     

云制造环境下资源动态调度系统研究

云制造环境下资源动态调度是云制造中的关键技术之一。针对云制造环境下制造资源调度的特点和存在的问题,提出了基于资源负载均衡的动态调度策略,建立了以完成任务的总服务成本最小为优化目标的模型,并通过建立应用实例说明了该系统的实际应用过程。     

基于自适应遗传算法的柔性动态调度研究

提出了柔性生产环境下动态调度系统的框架结构。系统主要由评估模块，动态数据库管理模块以及遗传算法模块组成，它能够在扰动发生后快速提供新的调度计划；而自适应策略保证遗传算法有很好的收敛速度与精度。该方案减少了人为的干预，完全可以在实时生产条件下运行。     

基于MAZAK柔性制造线的粒子群与免疫算法研究

将免疫遗传算法运用到柔性生产中能够极大地改进遗传算法的缺点,提高收敛效果。在此基础上提出了粒子群算法,并与免疫遗传算法进行对比,分析最优结果;将其应用到车间调度中能极大地提高调度路径的优化。运用仿真将克隆免疫算法的调度结果与粒子群算法的调度结果对比,以获得较优的结果。     

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     

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。     

智能制造 调度为先——《制造系统智能调度方法与云服务》导读

随着越来越多小微型企业对制造车间“万物感知、万物互联、万物智能”的需求,结合大数据和云计算技术,针对制造资源和生产任务,构建多种制造类型下的调度算法库,提供智能调度方案,是实现制造系统高效运行的关键。为了探讨智能调度的原理、方法和云端化实现路径,笔者撰写了《制造系统智能调度方法与云服务》一书,全面介绍了制造系统中多种复杂调度问题,重点介绍了各类调度问题对应的调度方法,结合云服务框架介绍了不同调度方法的云端化技术与实现方式,搭建了基于云计算的制造车间智能调度算法库及服务系统。本书为推动我国制造业的智能化发展和企业应用提供参考,对提升我国制造业的核心竞争力具有重要意义。