Author Topic: A Dynamic Construction Algorithm and Verification of the Grafcet  (Read 1980 times)

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A Dynamic Construction Algorithm and Verification of the Grafcet
« on: September 20, 2011, 06:13:03 am »
Author : Marcellin Nkenlifack, Emmanuel Tanyi and Janvier Nzeutchap
International Journal of Scientific & Engineering Research Volume 2, Issue 9, September-2011
ISSN 2229-5518
Download Full Paper : PDF

Abstract— This article proposes an approach of interactive construction of Grafcets. We especially studied the problem of the research of a verification method and of holds it of the consistency, and we arrived to formulas and an algorithmic method of interactive construction and progressive checking of this characteristic that we present. This algorithm has been implemented and has been examined on convenient examples. The developed environment includes in more, a module of description and a module of simulation. The object approach and the UML language have been put to profit during the process. We illustrate functionalities of the simulator to specifics systems.
Index Terms— Hybrid Dynamic Systems, Algorithms, Verification, Simulation, Sequential Systems, Grafcet, Validation, Human-Computer Interface. 

1   INTRODUCTION                                                                      
THe present methods of production are more and more complexes in the industrial enterprises. They undergo important technological transformations and need in general on the computerization, in order to reduce to the strict minimum the physical stress as intellectual of the man. This evolution is characterized by a spectacular development of the programmed systems. Automatic control systems are often modeled either as continuous systems (equations, transfer functions) or discret systems (Grafcets, Petri Nets). In practice, however, most industrial control systems incorporate both continuous and discret elements. These so called hybrid systems have recently become the subject of intensive research [1] [2] [3] [4] [5] [6] [7]. The research on the automatic industrial checking systems tackle to solve the following questions [1] :
- The modelling
It is about having resort to a “system approach” structuring the different objects while taking into account the physical sense and the causality of their interactions.
- The analysis
It assumes the development of tools of checking and validation of the Hybrid Dynamic Systems (HDS), then the mastery of the complexity of this analysis and the physical interpretation of some qualities to analyze as the global stability of the system through his consecutive phases of performance.
- The Simulation
The present research concerning the methods and formal tools relative to the analysis of the behavior of the HDS and to the synthesis of the command laws are some again to their beginnings [8].
The simulation remains therefore an obligated passage when it is necessary to help towards the implementation of an installation, to enable the model elaborated (in a goal of forecast) for an existing installation, or to validate the command conceived for an installation.
We are interested in the implementation of an envi-ronment of verification of the Grafcets in construction. This paper is a shutter of an a lot vast project on the set-ting up of a modelling and simulation of the hybrid process automations including the discret systems (de-scribed by the Grafcets) and the continuous systems (described by the differential equations), combining the techniques of the software engineering and the control engineering, and having been the object of several expe-rimentations and subjects [2] [4] [5] [6] [7] [9] [10] [11] [12].
Our paper that describes the implementation of a check-ing environment and validation of the Grafcets in con-struction, start with a brief presentation of the automatic industrial control systems and the Grafcets, follow by the modelling of the components, the specification of the criterias of validation of the modules in construction and the algorithmic design. After the techniques of implementation used, we illustrate the setting through the simulation of the Grafcets of the command system of a mill.

The different methods and tools (specification, analy-sis, simulation) are numerous on the mathematical plan, in control engineering and software engineering. Some approaches and basic mathematical tools that can be operated are described in [1] [13]: Theory of command, classified Command, Boolean algebra, Graph theory, Petri networks (one of the forebears of the Grafcet), Statemachines or Statecharts.
One distinguishes three approaches of description of the Automatic Control Systems [1] [14] :
- The Discretes Systems (DS)
- The Continuous Systems (CS)
- The Hybrid Dynamic Systems (HDS) combining the two first approaches.
The GRAFCET (in French “Graphe Fonctionnel de Commande Etape Transition”) is a "language" of the con-trol engineering, adapted to the description of automatic systems. It is also a normalized tool [16], and functional flowchart whose goal is to describe (graphically) the different behaviors of a sequential automatic system [15].
The Grafcet formalism has some constructs - STEPs, TRANSITIONs, LINKs, ACTIONs, and TRANSITION CONDITIONs -. Steps, denoted by numbered rectangles, represent the steps in a sequence. Transitions, denoted by horizontal bars, define the logical conditions which govern the passage from one Step to another. Links are vertical lines which interconnect Steps and Transitions. The Actions, denoted by long rectangles connected to Steps, define the operations performed by the actuators of the system when the associated Steps become active.
It is necessary to note that today, a lot of researchs lean on the Grafcet and try to improve it or to add some add-on facilities there [1] [3] [6] [7] [12] [14] [17] [18].
The Grafcets are also a tool of functional specification of some types of Hybrid Automatic Systems. As particu-larity of the Hybrid Systems, one has the Interactions (mutual action between parts of the System). The sequential-continuous Interactions is materialize to the level of the Actions (Steps of the Grafcet). The conti-nuous-sequential Interactions recovered to the level of the Transition condition bound to the Transitions of the Grafcet.
An excerpt of the Rolling Mill Grafcet is shown in fig-ure 1. The details of this Hybrid System are provided in [3].

Fig. 1. An Excerpt from the Rolling Mill Grafcet (a hybrid sys-tem)
The problem studied in the article dedicates itself to the interactive construction of a coherent specification of a system. The Grafcet will be described on differents plans: lexical (construction), syntactic (description), and semantical (functional). To every time, one of the checking algorithms is started to permit to alter the Grafcet. At the end, it is simulated.

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