模拟实时系统的点区间优先级时间Petri网与TCTL验证

时间Petri网为实时系统提供了一种形式化的建模方法, 时间计算树逻辑(TCTL)为描述实时系统与时间相关的设计需求提供了一种逻辑化的表达方式, 因此基于时间Petri网的TCTL模型检测广泛应用于实时系统的正确性验证.然而对于一些涉及优先级的实时系统, 例如多核多任务实时系统, 这里不仅需要考虑任务之间的时间约束还要考虑任务执行的优先级以及引入优先级带来的抢占式调度问题, 致使相应的建模和分析变得更加困难.为此, 本文提出了点区间优先级时间Petri网, 通过在时间Petri网上定义变迁发生的优先级以及变迁的可挂起性, 从而可以模拟实时系统的抢占式调度机制, 即首先高优先级的任务抢占低优先级的任务所占用的资源, 导致后者被中断, 然后前者执行完毕后释放资源, 最后后者再次获得资源从中断的地方恢复.本文通过点区间优先级时间Petri网来模拟多核多任务实时系统, 使用TCTL来描述它们的设计需求, 设计了相应的模型检测算法, 开发了相应的模型检测器以验证它们的正确性.我们通过一个实例来说明我们的模型和方法的有效性.     

变计时过程ö变迁网模型及其应用研究

基于过程运行的离散标识(逻辑变量)和剩余时间连续标识(时间变量)，提出一种新的混合标识过程／变迁网——变计时过程／变迁网模型．基于该模型，混杂动力学系统离散事件的实时监控、连续子过程的实时调度等问题可得到有效解决．     

基于正态Petri网的模型参数识别研究

时间因素在对实时系统的分析中占据着重要的位置。随着时间因素在Petri网应用分析中的地位越发重要,各种与时间相关的Petri网模型相继被提出。文中结合动态实时系统的运行特征,设计了一种变迁点火时间服从正态分布的随机Petri网模型,并基于对系统行为的统计分析,提出了一种用于对变迁时间参数进行识别的数值算法。以一种随机制造单元为例,建立正态随机Petri网模型,并运用参数识别算法确定变迁时间参数。仿真结果符合系统的实际运行结果,证明了该方法的有效性。     

基于平行Petri网的制造系统调度与控制一体化方法

为了消除制造系统调度层与控制层之间的隔阂,实现对生产事件快速灵活响应,本文提出了一种调度与控制一体化的方法.首先,定义了一种新型Petri网模型,即平行Petri网,从而集成地描述了传感器、执行器、任务和资源信息,构建制造系统的信息物理系统模型;其次,提出了一种从平行Petri网到赋时Petri网的抽象简化方法,大规模压缩优化调度所需搜索的状态空间;再次,定义了策略Petri网以描述最优调度策略.最后,给出了平行Petri网与策略Petri网同步执行算法,使得平行Petri网与物理系统同步执行.     

一类区段赋时弧有色Petri网的可达性和可阻断性分析

为了描述和分析实际复杂产时系统,提出了一种新的时间限制Ｐｅｒｔｉ网模型,区段赋时弧有色Ｒｅｔｒｉ网模型。这种Ｐｅｔｒｉ网在有色Ｐｅｔｒｉ网的库所输出弧上标注以输入库所的颜色为自变量的时间区间函数,基于一种充分考虑了系统时间不确定性的激发规划,给我段赋时弧有色Ｐｅｔｒｉ网的发生元序列的时间界估计,并以此为依据,提出了基于状态类的可达性分析方法和可阻断性分析方法。     

时间Petri网的随机模拟

模拟是Peri网进行系统分析的常用方法之一。由于时间Petri网采用时间区间来描述变迁实施的时间范围,因此变迁的实施时间点在区间内是不确定的。提出了时间Petri网的随机模拟方法。该方法在变迁开始使能时,根据某种随机分布确定实施区间内的实施时间点;然后基于模拟仿真的实验数据,运用统计分析方法及算法,构造时间Petri网状态类树,计算变迁实施区间及实施概率,为时间Petri网的系统模拟提供了一种新的探索途径。     

Hard real-time tasks' scheduling considering voltage scaling, precedence and exclusion relations

Several scheduling approaches have been developed to address DVS in time-critical systems, however, overheads, precedence and exclusion relations have been neglected. This paper presents a pre-runtime scheduling method for hard real-time systems considering DVS, overheads as well as inter-task relations. The proposed method adopts a formal model based on time Petri nets in order to find a feasible schedule that satisfies timing and energy constraints.     

Modeling and analysis of scheduling for distributed real-time embedded systems

Aimed at the deficiencies of resources based time Petri nets (RBTPN) in doing scheduling analysis for distributed real-time embedded systems, the assemblage condition of complex scheduling sequences is presented to easily compute scheduling length and simplify scheduling analysis. Based on this, a new hierarchical RBTPN model is proposed. The model introduces the definition of transition border set, and represents it as an abstract transition. The abstract transition possesses all resources of the set, and has the highest priority of each resource; the execution time of abstract transition is the longest time of all possible scheduling sequences. According to the characteristics and assemblage condition of RBTPN, the refinement conditions of transition border set are given, and the conditions ensure the correction of scheduling analysis. As a result, it is easy for us to understand the scheduling model and perform scheduling analysis.     

Timed high-level nets

Petri nets have been widely used for modeling and analyzing concurrent systems. Several reasons contribute to their success: the simplicity of the model, the immediate graphical representation, the easy modeling of asynchronous aspects, the possibility of reasoning about important properties such as reachability, liveness, boundedness. However, the original model fails in representing two important features: complex functional aspects, such as conditions which rule the flow of control, and time. Due to that, two different classes of extensions of Petri nets have been proposed: high-level nets and timed Petri nets. High-level nets allow the representation of functional aspects in full details, but do not provide a means for representing time; on the other hand, timed Petri nets have been thought for time representation, but they do not provide a means for representing detailed functinal aspects. Thus, these two important aspects cannot be mastered together. In particular, it is difficult to express relationships between time and functional aspects.This paper investigates the relationships between high-level nets and timed Petri nets, thus extending a first set of results published in a previous paper, where a unifying Petri net based model for time representation has been proposed. It first recalls how time can be represented in a Petri net extension called ER nets, and assesses its generality. It then investigates the relationships of ER nets with the best known high-level nets. In particular it shows the overall equivalence of ER nets, Colored Petri nets and Predicate/Transition nets, and extends the mechanism for time representation introduced in ER nets to both Colored Petri nets and Predicate/Transition nets. It also shows that these models cannot be simplified without significantly constraining the timing aspects that can be modeled.     

基于多环面向对象着色Petri网的装配调度研究

采用多环面向对象着色Ｐｅｔｒｉ网（ＴＯＯＣＰＮＭ）同启发式算法相结合的方法，研究装配系统的调度问题。先用ＴＯＯＣＰＮＭ来表述系统的调度问题，然后生成并搜索网的部分可达图，以变迁发生顺序的方式给出一个最优或次优的可行调度。由于给出的是一个可行的调度，系统潜在的死锁可以自然得到避免，因此对模型或系统的活性分析可以省略。     

面向能耗优化的容错实时系统任务调度模型研究

为了支持面向能耗优化的容错实时任务调度算法研究,提出一种频率相关的时间Petri网—FRTPN.FRTPN引入用于动态电压调整的变迁频率设置空间以及和频率相关的静态引发时域,以支持调度算法的能耗评估及优化;同时它增加一类抑制弧刻画容错故障恢复过程.通过对基于检查点的容错实时能耗优化任务调度进行建模证明了FRTPN的有效性.     

柔性制造系统的时间Petri网建模与分析

时间Petri网是描述和验证实时系统最常用的形式模型之一。建立基于时间 Petri网的典型柔性制造系统模型,利用状态类分析方法,定量计算所有可行调度及其执行时间,进而获得最优调度,为复杂柔性制造系统的建模与调度提供有效的模型支持。     

复杂工业过程集成建模及其实时监控与调度

采用一种新的混合标识过程／变迁网模型一变计时过程／变迁网来描述复杂工业过程。该模型通过引入过程运行标志离散标识(逻辑变量)和过程运行剩余时间连续标识(时间变量)，有效解决了多工位多工况复杂工业过程底层子过程的集成建模问题、离散事件与连续状态和过程控制与生产控制之间的耦合衔接问题，以及离散事件实时监控、连续子过程实时调度与控制等问题。给出了其实时监控、实时调度与过程控制的最佳策略求解方法。     

Modeling and online scheduling of flexible manufacturing systemsusing stochastic Petri nets

The authors discuss the modeling of flexible manufacturing systems (FMSs) under uncertainty and evaluate a rule base for online scheduling. To represent uncertain events in an FMS, such as failure of machine tools, repair time, and processing time, they develop continuous-time and discrete-time stochastic Petri nets with hierarchical structures for constructing the FMS model. For obtaining an efficient schedule for the FMS with an online real-time basis, they construct a rule base and evaluate its performance using the FMS simulation system proposed     

Suboptimal time management of discrete event systems with uncontrollable events modeled by Petri nets

Preventing systems from entering to forbidden states is a crucial issue in discrete event systems control. Adding supervisors to the system is a common method to avoid entering to forbidden states. In discrete event systems modeled by Petri net adding a supervisor could be done by means of control places. Since, the time is not considered in designing this supervisor, in presence of uncontrollable transitions adding control places can lead to increase the operation time of the system modeled by timed Petri net. Because, the firing of some transitions is prevented when it is not necessary. So, to design a more efficient controller, we will be required to use time information of the system component. Therefore, in this paper, a method for optimizing the time behavior of a supervised timed Petri net will be proposed. To obtain an efficient operation, some timed places as timer will be added to the net. The time of this timer places is calculated to permit firing of some controllable transitions in order to enter into some weakly forbidden states while entering to forbidden states is prevented. This concept leads to increase the speed of system as well as obtain an acceptable operation. This method can be applied for all systems modeled by Petri nets. The efficiency of proposed approach will be discussed and validated with a case study.     

Multiple-objective scheduling and real-time dispatching for the semiconductor manufacturing system

Implementing efficient scheduling and dispatching policies is a critical means to gain competitiveness for modern semiconductor manufacturing systems. In contemporary global market, a successful semiconductor manufacturer has to excel in multiple performance indices, consequently qualified scheduling approaches should provide efficient and holistic management of wafer products, information and manufacturing resources and make adaptive decisions based on real-time processing status to reach an overall optimized system performance. To cope with this challenge, a timed extended object-oriented Petri nets (EOPNs) based multiple-objective scheduling and real-time dispatching approach is proposed in this paper. Four performance objectives pursued by semiconductor manufacturers are integrated into a priority-ranking algorithm that serves as the initial scheduling guidance, and then all wafer lots will be dynamically dispatched by the hybrid real-time dispatching control system. A set of simulation experiments validate the proposed multiple-objective scheduling and real-time dispatching algorithm may achieve satisfactory performances.     

时间Petri网的可调度分析及在FMS中的应用

在实时系统中,检查任务执行的计划是否满足要求的时间约束称为可调度分析.通过把时间特性与其他行为特性分离,提出了一种以时间Petri网建模的实时系统调度分析方法.如果特定任务的执行是可调度的,则可以计算任务执行的时间跨度,否则确定出不可调度的变迁以便于调整时间约束和纠正设计错误.提出了一种通过把复杂的任务序列分解成一些子序列来进行可调度性分析的综合时序分析技术,它不仅提高了效率,也有助于关于调度的可达性问题的讨论.讨论了柔性制造系统FMS中的车间装配子系统的可调度性.     

Polynomial-time algorithm for the legal firing sequences problem of a type of synchronous composition Petri nets

As far as we know, the testing problem of legal firing sequence is NP-complete for gener-al Petri net, the related results of this problem on the polynomial-time solvability are limited only to some special net classes, such as persistent Petri nets, conflict-free Petri nets and state machine Petri nets. In this paper, the language properties of synchronous composition net are discussed. Based on these results, the testing algorithm polynomial-time complexity for legal firing sequence is proposed. Therefore, net classification of polynomial-time solvability for testing legal firing sequence is extended.     

点发序列问题的控制策略

在离散事件系统的Petri网模型下,讨论是否存在控制策略使得仅有希望的序列使 能,而又保持事件的并发性的问题.证明了存在这种策略的必要充分条件是给定的目标序 列集是可控的.在目标序列集不可控而所考虑的序列集都是Petri网点发序列集时,提出了 综合给定序列集的极大可控子序列集生成器的方法.