Reconfigurable Multiagent Embedded Control Systems: From Modeling to Implementation

The article deals with Distributed Multiagent Reconfigurable Embedded Control Systems following the International Industrial Standard IEC61499 in which a Function Block (Abbreviated by FB) is an event-triggered software component owning data and a control system is a network of distributed blocks. We define a multiagent embedded architecture in which a Reconfiguration Agent is affected to each device of the execution environment to apply local reconfigurations, and a Coordination Agent is proposed for coordination between devices in order to guarantee safe and coherent distributed reconfigurations. A Communication Protocol is proposed to handle such coordination by using well-defined Coordination Matrices . A prototype is developed to simulate the whole architecture when faults occur or system’s optimizations are applied. We specify Reconfiguration Agents to be modeled by nested state machines, and the Coordination Agent according to the formalism Net Condition/Event Systems (Abbreviated by NCES) which is an extension of Petri nets. To allow correct and coherent distributed reconfigurations, we check all possible interactions between controllers by verifying that whenever a reconfiguration is applied in a device, the Coordination Agent and other concerned devices react as described in user requirements. We propose finally XML-based implementations of both Coordination and Reconfiguration Agents according the the technology IEC61499. The article’s contributions are applied to two Benchmark Production Systems available in our research laboratory.

Reconfiguration Protocol for Multi-Agent Embedded Control Systems

This work proposes a supervisory control method for reconfigurable manufacturing systems (RMSs) based on net condition/event systems (NCESs) under the firing rule `maximal single spontaneous transition steps'. It is assumed that the occurrence of a reconfiguration event changes the system configuration immediately and a reconfiguration requirement is triggered randomly in the current work. For the safety of an RMS, the implementation of system reconfigurations is only permitted at some specific plant states. However, it is unreasonable to execute a system reconfiguration immediately at a reconfigurable state, when current on-going manufacturing tasks are not finished. In order to keep the continuity of production process and to avoid confusion of an RMS, a novel reconfiguration control structure based on NCESs is proposed, where a reconfiguration controller (RC) performs the implementation of reconfigurations and a task supervisor (TS) monitors the execution status of tasks. The applicability of the method is illustrated by using a simple RMS.

This paper addresses formal validation of distributed logic controllers represented in Visual Flowchart Language (VFL) that is a high-level programming language used in industrial automation. Traditional validation approaches based on simulation become obsolete in reconfigurable manufacturing systems where complex machines have decentralized control and are built by reuse of components. The source code based validation is also important for OEMs to unify their development procedures from embedded systems to machine controllers. For modeling the VFL design we used net condition/event systems (NCES) - a modular formalism developed for modeling systems with distributed states such as closed-loop control systems in distributed mechatronic devices. The methodology was implemented in software tools automatically generating the model's modules given the controller's source code. Then the hierarchical NCES model is assembled into a place/transition net that is subjected to model checking. The proposed approach facilitates integration of formal validation into software/hardware development in control systems' engineering.

Reconfigurable systems have received much attention from academia and industry because they are efficient, agile, and reasonably priced, and they are the trend of all future systems. The chapter focuses on dynamic automatic reconfigurations of Control Systems to be classically modeled by Petri nets. Several modeling and verification methods for such systems are shown and compared before the introduction of the research work on feasible dynamic reconfigurations and the implementation of manufacturing systems based on Petri nets. Three different reconfiguration scenarios can be applied at run-time to such systems: Addition/Removal of places, Addition/Removal/Update of transitions, or finally, the simple modification of the initial marking. Three formal modules are defined accordingly, which allow the reconfigurations of the system’s Petri nets model: the first module to dynamically change places of the model, the second to dynamically reconfigure transitions within a given subset of places, and the third to modify the initial markings of places. To check the correct behavior of this architecture according to user requirements, the model checker SESA is applied for the verification of CTL-based properties of the proposed modules and also of the system. The contribution is applied to a real-world Benchmark Production System.

The article focuses on a type of client/server multiagent system. Such system consists of several server environments, each populated by a single server agent and multiple client agents. We propose that a server agent should monitor clients activity in order to perform better. We employ the term agent tracking, introduced by Tambe and Rosenbloom. We introduce the idea of distributed tracking. Our multiagent system includes client tracking agents, which are responsible for agent tracking of clients and are devoted to a server. Each tracking agent executes a single model, which can apply to a single client agent or a group of client agents. All tracking agents work cooperatively and make collective decisions about formation of client groups. Tracking agents derive facts about client behavior and supply the server with conclusions. Generalized nets (GNs - an extension of Petri nets) are used as a tool for modeling multiagent system. A GN model of a single server environment with tracking agents is described.

FPGA chips in reconfigurable computer systems are used as malleable coprocessors where components of a hardware library of functions can be configured as needed. As the number of hardware functions to be configured typically exceeds the underlying chip area during the execution of an application, previous efforts have introduced configuration caching. Those efforts, however, have focused on two run-time-reconfiguration scenarios, which consider a single application running on the reconfigurable system. In the full reconfiguration scenario, functions of an application are arranged into blocks each of which has enough functions to fill the entire chip. The blocks are configured in a deterministic sequence needed by the application based on the a priori knowledge about the application. In the partial reconfiguration scenario, each function is configured or replaced on a function-by-function basis, based on the application needs. In the former technique, spatial processing locality is well exploited. In the latter, only temporal processing locality is exploited. In this work, we propose a technique suitable for multitasking and for cases of single applications that can change the course of processing in a non-deterministic fashion based on data. In order to exploit processing locality, both spatial and temporal simultaneously, the proposed model groups hardware functions into hardware configuration blocks (pages) of fixed size, where multiple pages can be configured on a chip simultaneously. By grouping only related functions that are typically requested together, processing spatial locality can be exploited. Temporal locality is exploited through page replacement techniques. Data mining techniques were used to group related functions into pages. Standard, replacement algorithms as those found in caching were considered. Simulations, as well as emulation using the Cray XD1 reconfigurable high-performance computer were used in the experimental study. The results show a significant improvement in performance using the proposed paging technique.

This research paper deals with combining semi-formal and formal methods to develop distributed reconfigurable control systems. The reconfiguration consists in modifying the system behavior to adapt it to the changes in its related environment caused by user needs and operating constraints. A DRCS which consists of networked reconfigurable control systems (RCSs), is a set of functional operations such that only a subset is executed by adding or removing operations after a well-defined reconfiguration scenario. To dynamically handle reconfiguration scenarios at run-time, a defined multi-agent architecture is proposed and affects a reconfiguration agent (RA) for the local reconfiguration of each RCS and a global coordination agent to harmonize the different RCSs for a required coherence. To provide a documented and safe reconfigurable system, we propose a new methodology called DRec-UML-B that covers all software development phases from modeling and verification to code generation using UML and B. The DRec-UML-B development process consists of two complementary phases: UML specification and B specification. In the first phase, we model the different agents with UML to specify the static and dynamic aspects of the DRCS. The second phase translates the UML specification to obtain the B abstract model using defined DRec-rules and reduces the number of operations to be transformed from a UML class diagram to B ones. Then, we apply successive refinements to obtain the C code and we check the system using Atelier B and Check R-B tools for the consistency and accuracy of the specification, refinement, and code generation levels to avoid the redundant control of B machines that share similar sequences of operations. We apply all the proposed contributions to two benchmark production systems FESTO and EnAS to discuss the benefits of DRec-UML-B methodology in terms of the number of generated B operations.

This paper is interested in the run-time adaptation of reconfigurable Multiprocessor System on Chip MPSoC architectures to their environment. A reconfiguration consists in the addition, removal or update of OS tasks to be executed in the different processors under real-time constraints. These tasks are with precedence constraints and exchange messages on the Network on Chip NoC that links different processors. Nevertheless, the intensive application of reconfigurations increases the frequency of the exchanged messages which become more and more important. The saturation problem of routers is then possible. We aim to prove by this research that all reconfigurable messages reach their target destinations and also respect their time constraints. Thus, the need to explore several paths instead of a faulty one is recommended. We propose a routing algorithm that allows a feasible real-time NoC after any reconfiguration scenario. This algorithm is split into two steps where the former deals with the look for minimal possible paths and the latter deals with a selected path that the messages will follow. This contribution is applied to a case study that we model by the formalism Reconfigurable Timed Net Condition Event System R-TNCES to verify temporal logic properties with the model Checker SESA.

SPN as a tool for risk modeling of fires in process industries

The unfolding technique is an efficient tool to explore the runs of a Petri net in a true concurrency semantics, i.e. without constructing all the interleavings of concurrent actions. But even small real systems are never modeled directly as ordinary Petri nets: they use many high-level features that were designed as extensions of Petri nets. We focus here on two such features: colors and compositionality. We show that the symbolic unfolding of a product of colored Petri nets can be expressed as the product of the symbolic unfoldings of these nets. This is a necessary result in view of distributed computations based on symbolic unfoldings, as they have been developed already for standard unfoldings, to design modular verification techniques, or modular diagnosis procedures, for example. The factorization property of symbolic unfoldings is valid for several classes of colored or high-level nets. We derive it here for a class of (high-level) open nets, for which the composition is performed by connecting places rather than transitions.

Modeling computer software, hardware, and other systems using Petri nets is discussed. The various analysis techniques and extension of Petri nets are considered. Problems in Petri net analysis techniques are examined, and analysis techniques that solve them are given.

In this paper, we propose the new method for the parallel system design based on expanded the logical coloured Petri net (LCPN). An LCPN is an extended Petri net that solves the problem of system description in previously proposed place/transition nets and coloured Petri nets. This extension of Petri nets is suitable for designing complex control systems and for discussing methods of evaluating such systems realistically. In order to study the behaviour of the server system modelled with this net we simulated a Java program. This program confirmed that this extended Petri net is an effective tool for modelling the parallel system.

With the growing use of UML diagrams for software architecture description and the importance of non-functional requirements evaluation at software architecture level, filling the scientific gap between architect and requirement analyst is considered to be significant. Software architects are not usually familiar with non-functional requirement analysis and are not able to analyze such requirements easily. On the other hand, non-functional requirements cannot be evaluated directly by UML diagrams. Therefore, the architect should annotate additional information of the nonfunctional requirements to software architecture description and then an executable model can be produced. These executable models can be petri nets, queuing networks, stochastic process algebra and etc. One kind of the UML diagrams that can be used to describe software architecture is component diagram. In this paper, we propose a new algorithm that enables an architect to transform a component diagram into an executable model based on different extensions of petri nets. Moreover, we show how to use this petri net model for performance evaluation and simulation and the implications of this transformation are described completely. Finally, to represent the usage of our proposed algorithm, we consider a case study as an example.

An algorithm is introduced for solving multiprocess scheduling problems, based on an extension of Petri nets (PNs) able to cope both with multiple processes and with time constraints. These nets are called timed colored PNs (TCPNs). The class of problems faced by the approach can be 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 proved that the problem does not admit an algorithm for an optimal solution in polynomial time. The proposed algorithm finds a suboptimal schedule according to a set of optimization criteria, based on the tasks' and processes' times (earliness, tardiness) and/or on the time-independent resources' costs. >