基于扩展随机高级判断Petri网的FMS调度和仿真

本文提出一种新的更适合FMS调度仿真的扩展随机高级E-net,简称ESHLEP-N(Extended stochastic High Level Evluation Petri Net)。以ESHLEP-N模型为基础,设计并建立了FMS调度仿真专家系统。借助于该系统提出并研究了新的旨在减少空闲(no-inputs)和阻塞的实时动态再调度规则。经过仿真,证明新规则的产率(throughput)比传统规则平均提高6.48％。本文的部分成果已经用于航空航天部159厂的高级DNC系统的设计之中。     

Modeling, scheduling and simulation of product development process by extended stochastic high-level evaluation Petri nets

This paper presents a methodology for modeling and simulating product development process-based on the extended stochastic high-level evaluation Petri nets (ESHLEP-N). A product development process is composed of many design activities and the ESHLEP-N model can describe some special features of design activity in detail, such as randomness of its duration, uncertainty of its interruption and complexity of design iteration. Therefore, the ESHLEP-N model is employed to simulate a product development process. The initial product development plan obtained by a mathematical method beforehand is taken as the input of the simulation. Then the simulation procedure is proposed, along with four types of rules, i.e. activity-sequencing rules, resource-assigning rules, state-changing rules and the simulation-terminating rule, for scheduling the design activities. An example of the development process of an automobile drive system in concurrent engineering environment is presented to illustrate the method of the ESHLEP-N-based modeling, simulation procedure and scheduling rules. The simulation results show that the simulation procedure and the scheduling rules are effective.     

Search strategy for scheduling flexible manufacturing systems simultaneously using admissible heuristic functions and nonadmissible heuristic functions

To scheduling flexible manufacturing system (FMS) efficiently, we propose and evaluate an improved search strategy and its application to FMS scheduling in the P-timed Petri net framework. On the execution of Petri net, the proposed method can simultaneously use admissible heuristic functions and nonadmissible heuristic functions for A^* algorithm. We also prove that the resulting combinational heuristic function is still admissible and more informed than any of its constituents. The experimental results of an example FMS and several sets of random generated problems show that the proposed search method performs better as we expected.     

Agent-based FMS control

Future manufacturing systems will be integrated into the networks of distributed resources, and at the same time, such systems will be capable of processing both knowledge and material. It will probably be required that manufacturing systems be agile, flexible, and fault-tolerant. Petri nets (PN) and object-oriented design (OOD) are used together in order to develop the integrated agent-based FMS control system. The flexible manufacturing system (FMS) consists of machines, workstations, and automated material handling system, distributed buffer storage sites and computer-based supervisory control, all which can be modeled as an agent in OOD with PN. This paper introduces the design of an agent-based FMS control system through PNs and evaluates the performance using timed placed Petri nets (TPPN). In order to do so, the agent control design, FMS structure has been evaluated in detail and the agent definitions have been submitted. The system includes the sharing and distribution of tasks among agents and the mentioned structure has been simulated by TPPN. The simulation procedure has been realized through Petri Net 2.0—MATLAB Demo Program [Mahulea CF, Motcovschi MH, Pastravanu O. Department of Automatic Control Industrial Informatics, Technical University “Gh. Asachi” of Iasi, Blvd., Mangeron 53A, 6600 Iasi, Romania, 〈http://www.ac.tuiasi.ro/pntool,pntool@ac.tuiasi.ro〉, 2004.]. Each case is modeled, and then the agent's machine processing time is considered in this program. As for the evaluation of the study, the system performance is assessed through the waiting time of the parts in queue and the task distributions.     

基于EHLEP-N模型的FMS实时调度和控制

本文提出一种新的更适合柔性制造系统(FMS)建模的扩展高级E-Net,简称EHLEP-N (Extended High Level Evaluation Petri Net).将EHLEP-N与专家系统技术相结合,使 EHLEP-N对FMS更具有描述性,推理和决策能力.以EHLEP-N为FMS的建模工具,设 计并建立FMS实时调度控制专家系统.借助于该系统,提出并研究新的旨在减少空闲(noinputs) 和消除阻塞的实时动态再调度规则.加工实验结果表明:1)该系统满足实时性和调 度控制功能的要求;2)新规则的产率(throughputs)比传统规则平均提高7％.     

Robust design of flexible manufacturing systems using, colored Petri net and genetic algorithm

A method is presented for the robust design of flexible manufacturing systems (FMS) that undergo the forecasted product plan variations. The resource allocation and the operation schedule of a FMS are modeled as a colored Petri net and an associated transition firing sequence. The robust design of the colored Petri net model is formulated as a multi-objective optimization problem that simultaneously minimizes the production costs under multiple production plans (batch sizes for all jobs), and the reconfiguration cost due to production plan changes. A genetic algorithm, coupled with the shortest imminent operation time (SIO) dispatching rule, is used to simultaneously find the near-optimal resource allocation and the event-driven schedule of a colored Petri net. The resulting Petri net is then compared with the Petri nets optimized for a particular production plan in order to address the effectiveness of the robustness optimization. The simulation results suggest that the proposed robustness optimization scheme should be considered when the products are moderately different in their job specifications so that optimizing for a particular production plan creates inevitably bottlenecks in product flow and/or deadlock under other production plans.     

Identifying FMS repetitive patterns for efficient search-based scheduling algorithm: A colored Petri net approach

The multiple lot size scheduling problem plays a crucial role in minimizing production and setup costs in order to respond to constant fluctuations in customer demands. However, the computational cost to optimize a scheduling problem increases as the lot size of jobs increases, leading to a scalability problem for most scheduling algorithms. This paper presents an efficient search approach based on colored Petri net (CPN) formalism that addresses the state explosion problem of reachability graphs used for finding the optimal solutions to scheduling problems. To reduce the memory requirements, the proposed approach exploits the structural equivalence found in the reachability graphs of flexible manufacturing systems’ (FMS) CPNs to discard states once they are no longer needed to explore the state space. The hypothetical structural equivalence is attributed to the repetitive patterns identified in the execution of manufacturing processes when the lot sizes of jobs are scaled for FMS whose underlying layout configuration is fixed. We present the concept of structural equivalence based on duplicate state detection for FMS of different lot sizes and give sufficient conditions under which the structural equivalence obtained from a few lot size (smaller) instances holds for the same FMS of a larger size. The approach is validated experimentally on different FMS examples which confirm that the behavior of an FMS of any large lot size can be inferred from the FMS of a smaller size. Experimental results indicate that this work performs better than prior search methods and obtains optimal schedules of FMS with large lot sizes. Also, we show that the approach is applicable to FMS problems of similar configurations where the problem size differ by the number of jobs, resources and operations.     

基于Petri网的FMS物流系统建模与仿真

在建立FMS物流系统Petri网模型的基础上,采用“映射”思想,将Petri网模型转化为物流系统的仿真程序,提出了库所映射为程序数据、变迁映射为程序函数、系统子网映射为FMS系统基本类的映射方法,通过实例仿真验证了软件程序与模型的一致性。     

基于混合法的叶片FMS控制系统研究

本文基于Ｐｅｔｒｉ网建模的混合法，建立了叶片ＦＭＳ控制系统活的、安全和可逆的Ｐｅｔｒｉ网模型，应用该模型开发了叶片ＦＭＳ控制系统仿真器，可成功地避免叶片ＦＭＳ的死锁产生。     

Improved methods for scheduling flexible manufacturing systems based on Petri nets and heuristic search

This paper proposes and evaluates two improved Petri net （PN）-based hybrid search strategies and their applications to flexible manufacturing system （FMS） scheduling. The algorithms proposed in some previous papers, which combine PN simulation capabilities with A＊ heuristic search within the PN reachability graph,may not find an optimum solution even with an admissible heuristic function. To remedy the defects an improved heuristic search strategy is proposed, which adopts a different method for selecting the promising markings and reserves the admissibility of the algorithm. To speed up the search process, another algorithm is also proposed which invokes faster termination conditions and still guarantees that the solution found is optimum. The scheduling results are compared through a simple FMS between our algorithms and the previous methods. They are also applied and evaluated in a set of randomly-generated FMSs with such characteristics as multiple resources and alternative routes.     

Improved methods f or scheduling flexible manufacturing systems based on Pet ri nets and heuristic search

This paper proposes and evaluates two improved Petri net (PN) - based hybrid search strategies and their applications to flexible manufacturing system (FMS) scheduling. The algorithms proposed in some previous papers ,which combine PN simulation capabilities with A 3 heuristic search within the PN reachability graph ,may not find an optimum solution even with an admissible heuristic function. To remedy the defects an improved heuristic search strategy is proposed ,which adopts a different method for selecting the promising markings and reserves the admissibility of the algorithm. To speed up the search process ,another algorithm is also proposed which invokes faster termination conditions and still guarantees that the solution found is optimum. The scheduling results are compared through a simple FMS between our algorithms and the previous methods. They are also applied and evaluated in a set of randomly- generated FMSs with such characteristics as multiple resources and alternative routes.     

Evaluations of operational control rules in scheduling a flexible manufacturing system

In this paper, computer simulation is used to evaluate the effects of various control rules on the performance of a flexible manufacturing system (FMS) operating under different manufacturing environment. Alternative routings are available, if the operation of a part can be performed by more than one machine. Three control rules, namely, dynamic alternative routings, planned alternative routings, and no alternative routings, are proposed to control the selection of alternative routings for each part. The effects of the universal loading station and also those of the dedicated loading station are investigated. In addition, the impact of buffer existence on the system’s performance is also examined by considering machines with and without local buffers. The effects of changing production ratios of different part types on the performance of various operational control rules are also investigated. Moreover, the effects of system having machine breakdown are also discussed. The simulation results indicate that the FMS with dedicated loading stations outperforms the FMS with universal loading stations in all aspects. The dynamic alternative routings generally produces the best results in system performance if the universal loading station is provided. The planned alternative routings generally gives the best system performance when both the dedicated loading stations and local buffers are available. The no alternative routings usually remains at the bottom of the rank, occasionally with some exceptions. Problems in actual implementation are also highlighted.     

A knowledge-based decision support system for the management of parts and tools in FMS

Flexible manufacturing systems (FMS) are very complex systems with large part, tool, and information flows. The aim of this work is to develop a knowledge-based decision support system (KBDSS) for short-term scheduling in FMS strongly influenced by the tool management concept to provide a significant operational control tool for a wide range of machining cells, where a high level of flexibility is demanded, with benefits of more efficient cell utilization, greater tool flow control, and a dependable way of rapidly adjusting short-term production requirements. Development of a knowledge-based system to support the decision making process is justified by the inability of decision makers to diagnose efficiently many of the malfunctions that arise at machine, cell, and entire system levels during manufacturing. In this context, this paper proposes three knowledge-based models to ease the decision making process: an expert production scheduling system, a knowledge-based tool management decision support systems, and a tool management fault diagnosis system. The entire system has been created in a hierarchical manner and comprises more than 400 rules. The expert system (ES) was implemented in a commercial expert system shell, Knowledge Engineering System (KES) Production System (PS).     

基于一阶混杂Petri网的柔性制造系统粗糙控制

研究基于一阶混杂Petri网模型的柔性制造系统粗糙控制.为构造正确的一阶混杂Petri网模型行为演变图,提出了确定改变Macro状态事件的新方法;进而给出了柔性制造系统优化与控制算法,并基于粗糙集合理论和所给出的算法,提出了柔性制造系统的粗糙控制方法.最后通过一个实例验证了该方法的有效性.     

A knowledge-based system for reactive scheduling decision-making in FMS

This paper describes research into the development of an intelligent simulation environment. The environment was used to analyze reactive scheduling scenarios in a specific flexible manufacturing systems (FMS) configuration. Using data from a real FMS, simulation models were created to study the reactive scheduling problem and this work led to the concept of capturing instantaneous FMS status data as snapshot data for analysis. Various intelligent systems were developed and tested to asses their decision-making capabilities. The concepts of History Logging and expert system learning is proposed and these ideas are implemented into the environment to provide decision-making and control across a FMS schedule lifetime. This research proposes an approach for the analysis of reactive scheduling in an FMS. The approach and system that was subsequently developed was based on the principle of automated intelligent decision-making via knowledge elicitation from FMS status data, together with knowledge base augmentation to facilitate a learning ability based on past experiences.     

The simulation design and analysis of a Flexible Manufacturing System with Automated Guided Vehicle System

This paper presents the simulation design and analysis of a Flexible Manufacturing System (FMS) with an Automated Guided Vehicle system (AGVs). To maximize the operating performance of FMS with AGVs, many parameters must be considered, including the number, velocity, and dispatching rule of AGV, part-types, scheduling, and buffer sizes. Of the various critical factors, we consider the following three: (1) minimizing the congestion; (2) minimizing the vehicle utilization; and (3) maximizing the throughput. In this paper, we consider the systematic analysis methods that combine a simulation-based analytic and optimization technique that is Multi-Objective Non-Linear Programming (MONLP) and Evolution Strategy (ES). MONLP determines the design parameters of the system through multi-factorial and regression analyses. ES is used to verify each parameter for simulation-based optimization. A validation test for the two methods is conducted. This method-based approach towards design yields the correct experimental results, ensures confidence in the specification of design parameters and supports a robust framework for analysis.     

一种嵌入式实时数据库系统查询优化算法

针对嵌入式实时数据库系统的特点，提出了一种新的连接顺序优化算法 (Greedy Iterative Improvement, GII)。该算法结合了贪婪算法和迭代改进算法的优点，能满足系统的实时要求，可以控制查询优化时间，比传统查询优化策略更好地适应不同类型事务的需要。模拟实验结果表明，该算法在穷举式搜索适用时，能以比它小得多的时间和内存开销找到最优解；在穷举式搜索无法实现优化时，GII算法生成解的质量也明显优于贪婪算法和迭代改进。     

基于多Agent的FMS可靠性复合建模方法研究

提出了一种基于多Agent的面向对象的FMS可靠性建模方法，该方法将面向对象方法与高级Petri网技术相结合，并通过多Agent机制加以表述，使模型具有较好的通用性和可重用性，能够反映FMS的动态柔性特点。最后提出了便于用户使用的仿真建模软件的基本框架。