基于遗传算法的可重入半导体生产线的调度

半导体生产线的可重入性使得半导体生产车间的调度成为NP难题.基于遗传算法的调度是将遗传算法应用到半导体生产线的投料策略和调度策略上,通过合理的编码来寻找一组投料策略和调度策略的组合,来解决可重入半导体生产线的调度问题.和以往的方法不同,这种方法可以从全局上来调度半导体生产线,充分发挥出各种策略的优势.仿真结果表明这种方法对于产出量、制造周期偏差、瓶颈设备利用率等关键生产指标都有明显改善.     

Modeling and control of workstation level information flow in FMS using modified Petri nets

A flexible manufacturing system (FMS) has a traditional structure of three levels: cell, workstation, and equipment. The workstation level plays an important role in the overall performance of the FMS. This paper focuses on modeling and control of the FMS workstation level information flow. In order to have a unified workstation level system structure, front-end interfaces are introduced as a standard communication medium between the workstation level and the equipment level. A detailed information flow analysis is then carried out on the workstation level. For modeling purposes, a modified Petri net is proposed with its increased modeling capability over an ordinary Petri net. It associates data structures with places and programs with transitions. Finally, the modified Petri net is used to model and control the FMS workstation level information flow. The designed control system has been implemented in a real manufacturing factory with satisfactory performance.     

Genetic algorithm using sequence rule chain for multi-objective optimization in re-entrant micro-electronic production line

Re-entrant production lines, such as those which occur in micro-electronic wafer fabrication, are characterized by a product routing that consists of multiple visits to a facility during the manufacturing process. With the development of micro-electronic technology, the research on the scheduling and control problem of re-entrant micro-electronic production line has attracted more and more people from both academia and industry to study and has become a challenging research subject. Some results of the scheduling of re-entrant micro-electronic production line based on heuristic sequence rules have been obtained. However, performances of these sequence rules are not good enough in re-entrant micro-electronic production line because of their sensitivity to the variation of types of production line. A genetic algorithm using sequence rule chain for multi-objective optimization in re-entrant micro-electronic production line is proposed in this paper. Comparisons between the proposed algorithm and some other typical sequence rules have been made through the simulations of a practical micro-electronic production line. The static and dynamic simulation results show that the algorithm has considerable improvements on performances of the micro-electronic production such as mean cycle time, mean number of work-in-process, production rate.     

On defect propagation in multi-machine stochastically deteriorating systems with incomplete information

In many manufacturing environments, costly job inspection provides information about the random deterioration of the machines. The resulting maintenance and inspection problem is extensively studied for a single machine system by using the framework of Partially Observable Markov Decision Processes (POMDPs). In this work, this concept is extended to multiple operations and multiple job types by considering two process flow topologies: (i) re-entrant flow, (ii) hybrid flow. The resulting (significantly large sized) POMDPs are solved using a point based method called PERSEUS, and the results are compared with those obtained by conventionally used periodic policies.     

Combining flow control techniques with Petri nets methodologies for real-time control of FMS

This paper focuses on the combination of the flow control techniques with Petri net methodologies. The flow control techniques are improved in order to handle multiple routing. A general and unified Petri net formalism is introduced. The integration of the flow control techniques with an interpreter based on this new Petri net formalism is discussed. Results for simulation of a very flexible manufacturing system are provided.     

基于流随机Petri网模型的可重入生产线稳定性分析

可重入生产线是作为芯片制造生产线模型被研究的，其特点是具有“可重入性”。该文基于流随机Petri网(Fluid Stochastic Petri Net,FSPN)对可重入生产线进行建模，并得到了一些相关的稳定性结论。     

Matrix approach to deadlock-free dispatching in multi-class finite buffer flowlines

For finite-buffer manufacturing systems, the major stability issue is "deadlock," rather than "bounded-buffer-length stability." The paper introduces the concept of "system deadlock," defined rigorously in Petri net terms, and system operation with uninterrupted part-flow is characterized in terms of the absence of this condition. For a large class of finite-buffer multiclass re-entrant flowline systems, an analysis of "circular waits" yields necessary and sufficient conditions for the occurrence of "system deadlock." This allows the formulation of a maximally permissive one-step-look-ahead deadlock-avoidance control policy for dispatching jobs, while maximizing the percent utilization of resources. The result is a generalized kanban dispatching strategy, which is more general than the standard multiclass last buffer first serve (LBFS) dispatching strategies for finite buffer flowlines that typically under-utilize the resources. The problem of computational complexity associated with Petri net (PN) applications is overcome by using certain sub-matrices of the PN incidence matrix. Computationally efficient matrix techniques are given for implementing the deadlock-free dispatching policy.     

信标基底的可选择性在制造系统死锁控制中的应用

本文基于Petri网模型,讨论柔性制造系统的死锁控制问题.为了建立结构简单的Petri网控制器,本文在以前的工作中提出了信标基底的概念.信标基底是一组满足特定条件的严格极小信标集合.本文证明基于不同的信标基底,建立的受控系统其容许性能也不同.而容许性是评价死锁控制策略优劣的重要标准之一.故如何选择信标基底,提高受控系统的容许性能是值得研究的问题.本文讨论了使受控系统容许性能大大提高的信标基底的选择条件.基于该条件,为柔性制造系统建立有效的死锁控制策略.最后,通过两个例子解释该条件和策略.     

Mean value analysis of re-entrant line with batch machines and multi-class jobs

We propose an approximate approach for estimating the performance measures of the re-entrant line with single-job machines and batch machines based on the mean value analysis (MVA) technique. Multi-class jobs are assumed to be processed in predetermined routings, in which some processes may utilize the same machines in the re-entrant fashion. The performance measures of interest are the steady-state averages of the cycle time of each job class, the queue length of each buffer, and the throughput of the system. The system may not be modeled by a product form queueing network due to the inclusion of the batch machines and the multi-class jobs with different processing times. Thus, we present a methodology for approximately analyzing such a re-entrant line using the iterative procedures based upon the MVA and some heuristic adjustments. Numerical experiments show that the relative errors of the proposed method are within 5% as compared against the simulation results.Scope and purposeWe consider a re-entrant shop with multi-class jobs, in which jobs may visit some machines more than once at different stages of processing, as observed in the wafer fabrication process of semiconductor manufacturing. The re-entrant line also consists of both the single-job machine and the batch machine. The former refers to the ordinary machine processing one job at a time, and the latter means the machine processing several jobs together as a batch at a time. In this paper, we propose an approximation method based on the mean value analysis for estimating the mean cycle time of each class of jobs, the mean queue length of each buffer, and the throughput of the system.     

Modeling of reconfigurable manufacturing systems based on colored timed object-oriented Petri nets

To cope with the rapid change in manufacturing market requirements, reconfigurable manufacturing systems (RMSs) with the feature of reconfigurability, have to be developed. A model that describes the reconfiguring process of a manufacturing system is developed by applying colored timed object-oriented Petri nets. Based on the main difference between configurations of RMSs and flexible manufacturing systems (FMSs), a modular hierarchical structure of RMS is developed. By the object-oriented method, all the object classes in the RMS model are identified. A macro-place is used to model the aggregation of many processes and a macro-transition is used to link all the related macro-places. Macro-places and macro-transitions are connected with arcs to form a Petri net named a macro-level Petri net so that the control logic of RMS is represented. The macro-level Petri net is refined by hierarchical steps, each step describing these macro-places by more detailed sub macro-places until all the macro-places cannot be divided. Then the characteristics of material flow and time constraints in RMS are modeled by applying colored tokens and associated time-delay attributes. This model integrates object-oriented methods, stepwise refinement ideas and Petri nets together. The RMS activities can be encapsulated and modularized by the proposed method, so that RMS can be easily constructed and investigated by the system developers.     

On systematic methods to remove redundant monitors from liveness-enforcing net supervisors

Petri nets based deadlock prevention for flexible manufacturing systems has received much attention over the past decade, primarily due to the seminal work of Ezpeleta et al. in 1995. A Petri net based deadlock prevention mechanism is usually implemented by adding monitors or control places to a plant Petri net model such that liveness can be enforced. The significance of this methodology lies in that both a plant model and its supervisor are in a same formalism-Petri nets. Due to the inherent complexity of Petri nets, in theory, the number of additional monitors that have to been added to achieve liveness-enforcement purpose for an uncontrolled plant model is exponential with respect to the size of the model. This paper first proposes a systematic method to minimize the number of additional monitors in a liveness-enforcing Petri net supervisor such that the resultant net system has the same permissive behavior while liveness can still be preserved. Furthermore, for the liveness-enforcing Petri net supervisors of flexible manufacturing systems, which have some particular property, an algorithm is developed such that more permissive liveness-enforcing Petri net supervisors can be obtained after liveness-restrictive monitor removal. Compared with the existing techniques of eliminating redundant monitors in the literature, the complete state enumeration of a supervisor is avoided, which implies the high computational efficiency of the methods in this paper. Flexible manufacturing examples are used to demonstrate the proposed approaches.     

Petri net modelling of buffers in automated manufacturing systems

This paper presents Petri net models of buffers and a methodology by which buffers can be included in a system without introducing deadlocks or overflows. The context is automated manufacturing. The buffers and models are classified as random order or order preserved (first-in-first-out or last-in-first-out), single-input-single-output or multiple-input-multiple-output, part type and/or space distinguishable or indistinguishable, and bounded or safe. Theoretical results for the development of Petri net models which include buffer modules are developed. This theory provides the conditions under which the system properties of boundedness, liveness, and reversibility are preserved. The results are illustrated through two manufacturing system examples: a multiple machine and multiple buffer production line and an automatic storage and retrieval system in the context of flexible manufacturing.     

可重构制造系统的Petri网建模和分析方法

提出一种针对可重构制造系统的Petri网建模和分析方法．根据生产流程图可以得出制造系统的基本网模型,扩展基本网模型即可得到系统的Petri网模型．当生产任务发生改变并建立新的生产流程图时,可直接从原来的基本网模型构造出新构形的基本网模型．此外给出了系统重构代价的评价方法．仿真研究验证了该方法的有效性。     

一种制造系统模型及其简化

本文采用随机Petri网的方法,建立制造系统基本单元模型。在保持系统可靠性等特性的前提下,对单一加工制造单元、串行加工系统这两种基本系统模型进行有效变换,从而最大程度地简化模型,降低模型的复杂度。     

基于Petri网的组合设备建模与调度综述

组合设备是半导体晶圆制造的核心装备, 其调度与控制优化是半导体制造领域极具挑战性的课题. Petri网因其强大的建模能力和简约的图形化表达优势, 被广泛地应用于组合设备的建模与调度. 对基于Petri网的组合设备建模与调度方法进行综述, 归纳总结了组合设备的结构类型、晶圆流模式、调度策略及Petri网建模方法, 并系统阐述组合设备的7类典型调度问题, 包括驻留时间约束、作业时间波动、晶圆重入加工、多品种晶圆加工、加工模块(Process module, PM)故障、PM清洗和组合设备群. 最后, 讨论了当前组合设备调度存在的挑战及后续可能的研究方向.     

A sufficient condition for instability of buffer priority policies in re-entrant lines

We use a buffer-boundedness approach to study the stability of re-entrant lines with a buffer priority scheduling policy. Using Petri net models we establish a sufficient condition for instability of such systems having a positive feedback loop. An example of unstable systems is also given.     

The numerical solution of laminar flow in a re-entrant tube geometry by a Chebyshev spectral element collocation method

A Chebyshev spectral element collocation method is used for the numerical solution of laminar flow in a re-entrant tube geometry. The high accuracy of the method allows the study of the merging process of the vortices in the re-entrant region. Results are presented for values of the Reynolds number up to 400 and for different lengths of the re-entrant tube lip. For low Reynolds number, the observed behaviour of the flow in the re-entrant region may be interpreted by analytical results on Stokes flow from the literature. As the Reynolds number is increased, a vortex that grows in size with the Reynolds number, is detected below the tip of the re-entrant lip.     

Implementation of rule-based information systems for integratedmanufacturing

Focuses on the development of a methodology within a software environment for automating the rule-based implementation of specifications of integrated manufacturing information systems. The specifications are initially formulated in a natural language and subsequently represented in terms of a graphical representation by the system designer. A new graphical representation tool is based on updated Petri nets (UPN) that we have developed as a specialized version of colored Petri nets. The rule-based implementation approach utilizes the similarity of features between UPN and the general rule specification language used for the implementation. The automation of the translation of UPN to the rule specification language is expected to considerably reduce the life-cycle for design and implementation of the system. The application presented deals with the control and management of information flow between the computer-aided design, process planning, manufacturing resource planning and shop floor control databases. This provides an integrated information framework for computer integrated manufacturing systems     

共享竞争择一资源Petri网的形式化设计方法

自动制造系统中有许多共享资源，例如，机器人、数控加工中心、无人导引自动小车等，竞争择一是其共享方式之一。以往，自动制造系统的Ｐｅｔｒｉ网控制系统器设计几乎都是试凑，而且一些性质不能得到满足，如无死锁。这主要是对共享资源的不适当设计造成的。对于多个子系统，为了使之能很好地工作，必须研究一种设计有界、无死锁的Ｐｅｔｒｉ网控制器的方法。本文在以往工作的基础上，提出了有界、无死锁、安全Ｐｅｔｒｉ网控制器…     

离散制造装配系统的活性控制

首次研究离散制造装配系统的活性控制问题.建立了系统的工件加工过程Petri网模型.通过对系统Petri网模型的结构分析,提出了导致系统死锁的两类元素结构及活性特征.对一类离散制造装配系统提出了避免死锁的Petri网控制器,这类控制器容易实现,对系统的限制小,而且使得受控系统仍具Petri网模型.对一般离散制造装配系统提出了保证系统活性的控制策略.