Study on Robot Sequencing Model in Flexible Manufacturing System Using Timed Petri Net

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基于Petri网的工作流过程模型及资源分布分析

针对工作流系统的特点对时延Petri网模型进行扩展,提出了一种新的工作流建模方法,即扩展时延Petri网。给出了扩展时延Petri网的定义,并用该方法分析了工作流四种基本模型;给出了利用排队论和随机Petri网理论计算工作流模型时间性能指标的新方法,用这种方法可求得与实例到达率相关的工作流模型平均完成时间。最后应用上述方法讨论了工作流资源分布的几种模式,并与模拟结果加以对比,计算结果的最大误差在3%左右,说明基于扩展时延Petri网的方法是分析工作流系统时间性能的有效方法。     

加权的时间Petri网工作流模型研究

时间性能分析是工作流模型分析和评价的重要方面。介绍了Petri网和工作流网的基本概念,提出了加权时间扩展工作流网,对加权时间扩展工作流网的基本组件进行了时间分析,给出了平均时间的计算方法。通过网上订购商品和生产车间工作流模型,利用基本组件的时间性能分析方法,对这两个工作流模型进行了时间性能分析。     

Petri net based process scheduling: A model of the control system of flexible manufacturing systems

In this paper, we propose a class of algorithms for the sub-optimal solution of a particular class of problems of process scheduling, particularly focusing on a case study in the area of flexible manufacturing systems (FMSs). The general class of problems we face in our approach is characterized as follows: there is a set of concurrent processes, each formed by a number of temporally related tasks (segments). Tasks are executable by alternate resource sets, different both in performance and costs. Processes and tasks are characterized by release times, due dates, and deadlines. Time constraints are also present in the availability of each resource in resource sets. It has been proven that such a problem does not admit an algorithm for an optimal solution in polynomial time. Our proposed algorithm finds a sub-optimal schedule according to a set of optimization criteria, based on task and process times (earliness, tardiness), and/or time independent costs of resources. Our approach to process scheduling is based on Timed Coloured Petri Nets. We describe the structure of the coordination and scheduling algorithms, concentrating on (i) the general-purpose component, and (ii) the application-dependent component. In particular, the paper focuses on the following issues: (i) theautomatic synthesis of Petri net models of the coordination subsystem, starting from the problem knowledge base; (ii) the dynamic behavior of the coordination subsystem, whose kernel is a High Level Petri net executor, a coordination process based on an original, general purpose algorithm; (iii) the structure of the real-time scheduling subsystem, based on particular heuristic sub-optimal multi-criteria algorithms. Furthermore, the paper defines the interaction mechanisms between the coordination and scheduling subsystems. Our approach clearly distinguishes the mechanism of the net execution from the decision support system. Two conceptually distinct levels, which correspond to two different, interacting implementation modules in the prototype CASE tool, have been defined: theexecutor and thescheduler levels. One of the outstanding differences between these levels is that the executor is conceived as a fast, efficient coordination process, without special-purpose problem-solving capabilities in case of conflicts. The scheduler, on the other hand, is the adaptive, distributed component, whose behavior may heavily depend on the problem class. If the scheduler fails, the executor is, in any case, able to proceed with a general-purpose conflict resolution strategy. Experimental results on the real-time performance of the kernel of the implemented system are finally shown in the paper. The approach described in this paper is at the basis of a joint project with industrial partners for the development of a CASE tool for the simulation of blast furnaces.     

基于着色赋时Petri网的堆垛机建模与调度研究

为了直观、简洁地研究AS/RS中的堆垛机运送系统,应用着色赋时Petri网（CTPN）建立了其动态模型。同时针对原有系统的不足,提出了基于双队列缓冲的堆垛机控制策略及双循环作业方式的路径优化策略,从而缓解了该系统中可能产生的阻塞现象,提高了堆垛机运送系统和出入库站台的效率,这对保证出入库的高效、正常、有序的进行有着重要的意义。     

Dynamic scheduling in flexible assembly system based on timed Petri nets model

This paper investigates a scheduling model for optimal production sequencing in a flexible assembly system. The system features a set of machines working together in the same workspace, with each machine performing a subset of operations. Three constraints are considered: (1) the precedence relation among the operations specified by the assembly tree; (2) working space that limits concurrent operations; and (3) the variation of process time. The objective is to find both a feasible assignment of operations to machines and schedule tasks in order to minimize the completion time for a single product or a batch of products. The assembly process is modeled using timed Petri nets and task scheduling is solved with a dynamic programming algorithm. The method calculates the time required precisely. A detailed case study is discussed to show the effectiveness of the model and algorithm.     

时间Petri网与GA-PSO算法相结合的并行测试

摘 要：并行测试任务调度方案在自动测试系统中一直是尚未解决的难题。本文基于Petri网理论的基础,建立了并行测试的时间Petri网模型,并且首次将GA-PSO算法引入到时间Petri网的变迁序列的寻找过程中,快速地求得了最优调度方案。仿真结果表明,本算法能够以较大的收敛概率快速地收敛,最终得到最优变迁序列。     

基于Petri net建模的资源调度的蚁群算法

利用了受控赋时Petri net建立了分布式系统中的资源调度的模型,并应用仿真器进行了仿真。由于在进行大规模的模型分析时,不适合采用仿真器来模拟,因而引进了蚁群算法来优化模型,可以得到较好的结果。     

基于Petri网的电子政务工作流模型研究

设计了一种基于Petri网扩展的、用于复杂工作流模型设计的建模方法及其相关规则。并且通过电子政务系统的网上审批子系统为例,详细阐述了用此方法及其相关规则构建Petri网工作流模型的过程。最后通过Petri网理论对模型进行了正确合理性分析,并对网上审批子系统的资源分配情况进行了定量分析。此建模方法简化了Petri网的建模过程,并保证了正确性和合理性资源分配的分析结果对合理的进行资源分配有指导作用。     

基于带抑制弧的Petri网的min-min算法模型研究*

为了解决已有的min-min算法Petri网模型不能模拟min-min算法运行过程的问题,根据min-min算法的调度特点,利用带抑制弧的Petri网提出了一种算法模型,该模型运行过程可以严格模拟min-min算法对独立任务集的调度顺序,能够正确地描述独立任务调度系统使用min-min算法的情况。最后对该模型的空间复杂度以及每调度一个任务模型的变化情况进行了分析,随着独立任务的调度执行,该基于带抑制弧的Petri网的变迁数和弧数会随之减少,模型的空间复杂度会不断降低。