Véronique Carré-Ménétrier

Grafcet: Behavioural Issues and Control Synthesis

This paper discusses the difficulties encountered in identifying the correct behaviour of Grafcet specifications in view of synthesising a correct control execution model. Formal algorithms for the synthesis of supervisory controllers related to Grafcet are also proposed. These algorithms consider the constraints induced by the behaviour of the controlled plant so as to identify the required correct behaviour of Grafcet during control execution. The resulting control execution is deadlock-free, and represents the minimal possible restriction of the behaviour of a given Grafcet, subject to a number of specified constraints.

UNCONDITIONAL DECENTRALIZED STRUCTURE FOR THE FAULT DIAGNOSIS OF DISCRETE EVENT SYSTEMS

Abstract This paper proposes an unconditional decentralized structure to realize the fault diagnosis of Discrete Event Systems (DES), specially manufacturing systems with discrete sensors and actuators. This structure is composed on the use of a set of local diagnosers, each one of them is responsible of a specific part of the plant. These local diagnosers are based on a modular modelling of the plant in order to reduce the state explosion. Each local diagnoser uses event-based, state based and timed models to take a decision about faults occurrences. These models are obtained using the information provided by the plant, the controller and the actuators reactivity. All local diagnosis decisions are then merged by a Boolean operator in order to obtain one global diagnosis decision. Finally, the diagnosers are polynomial-time in the cardinality of the state space of the system. This approach is illustrated using an example of manufacturing system.

A METHODOLOGY TO DESIGN AND CHECK A PLANT MODEL

Abstract Applications on manufacturing systems (diagnosis, control, supervision…) often require a plant model. Obtaining the plant model is a difficult task because of systems complexity and deepth knowledge of physical materials. A necessary condition that must be verified by the plant model is its capability to respond to all the requests of the specification model. This paper ends by two complementary approaches a mathematical property is proposed to check formally and this capability and a methodology to design the plant model is proposed in order to guarantee the model capability according to the most permissive control model.

SYNTHESIS OF SUPERVISED CONTROLLER BASED ON BOOLEAN CONSTRAINTS AND BOOLEAN AUTOMATA

Abstract In order to establish a method to synthesis controllers, an essential step is the modelling of both plant and constraints. However, this step remains a very complex task. To mitigate this difficulty and facilitate modelling, we present a methodology for plant modelling based on rules; as well as a user friendly methodology for constraints modelling based on logical equations in the traditional Boolean algebra. Then, we present an adaptation of the Kumar algorithm synthesis adequated to these new modelling. To conclude, we show that our synthesis approach can constitute a help in controller development and to be diverted from its first function to be used in controller validation.

Centralised controller for manufacturing systems through liveness extraction approach

Following our work on the control synthesis based on the Ramadge and Wonham theory, we propose a refined centralised control approach. This approach requires modelling the plant, and some safety and liveness constraints. We propose to model the plant by a method based on occurrence and precedence rules to model the plant, and to use logical equations to model the constraints. The control synthesis approach makes it possible to use liveness extraction of controller to get functional behaviour of manufacturing discrete systems. To illustrate these new concepts, we propose to test them on an example of transfer system.

Modelling of a discrete manufacturing system by Parts of plant

Abstract The paper presents an original approach to model a discrete manufacturing system by Parts of Plant (PoP). This approach takes into account technical and technological specifications of each plant element. The aim of this works is to realize a reliable simulation of discrete manufacturing systems during the design stage before producing them. Models are established from the process functional chain. They take into account the information distribution of manufacturing system through each PoP with its sensors, pre-actuators and actuators. A PoP library is proposed with their corresponding model. An application example is used to illustrate the approach.

Decentralized implementation approach of control synthesis of manufacturing systems

This paper presents a decentralized approach for implementation of controller synthesized by supervisory Control Theory. It is based on a synthesis algorithm and a modular modeling of the plant to avoid combinatory explosion found in centralized structure. Firstly, from the local Plant Elements, local constraints are defined to build local supervisors. Local constraints restrict the system behavior within a desired specification. Secondly, global constraints are user to establish a global supervisor able to coordinate between local supervisors. These different elements for control are translated in a normalized language for implementation in a Programmable Logic Controller. The approach is illustrated using a benchmark.

Elaboration of distributed optimal controller for manufacturing systems through synthesis approach

This paper deals with a distributed approach to obtain an optimal controller for manufacturing systems. It bases on a synthesis algorithm and a modular modeling of the plant to avoid combinatory explosion found in centralized structure. Firstly, from the local Plant Elements, local constraints are defined to build local supervisors. Local constraints restrict the system behavior within a desired specification. Secondly, global constraints are user to establish distributed supervisors. The resulting automata are translated in a normalized language for implementation in a Programmable Logic Controller. The approach is illustrated using a benchmark.

Proposition of completeness property to perform the plant modelling for manufacturing applications

Research dealing with control behavior determination often needs plant modelling to use formal methods. However, plant models are difficult to obtain because a manufacturing application is composed of a huge set of components with numerous interactions each other. The goal of this paper is to propose and demonstrate a property to improve the designers confidence in his plant model. The property is used a posteriori from plant model design. The completeness property tests whether a plant model is able to respond to specification solicitations. The application on several examples shows the usefulness of the verification in the context of independence of the plant model according to control behavior. Property can be used before control synthesis application design to determine if a plant model is able to respond to all control changes.

On-line synthesis approach based on a structured plant modeling

Abstract This paper is based on an approach of synthesis and optimal control. For a given Grafcet, a plant and constraints models, this method must respect the process evolution. We developed two improvements of this approach to be used on complex real systems. The new results obtain concern the plant modelling and the on-line synthesis. Formal algorithms and an example are presented in the paper.