Pierre Ladet

Consideration of machine breakdown in the control of flexible production systems

Control of operational production systems requires a reaction to disturbances. In this paper, the authors present a Petri net model describing a decision-making mechanism induced by the breakdown of a machine. The aim of such a proposal is to reassign the operations to the workshops resources. A decision-making aid methodology is essential to consider the disturbances according to several criteria. Therefore, the authors propose a Petri net model composed of Deterministic and Stochastic Petri nets (DSPN) and Object Petri nets (OPN). The decision-making process is based on the introduced concept of ‘potential’ associated with each machine. This potential is evaluated by means of several criteria to take the ‘right’ decision. In this study, the three following criteria are retained: Time, Cost, and machine reliability. A state of the art survey about the multicriteria decision aid methods has led to the choice of a method called AHP (Analytic Hierarchy Process). The authors thus present a multicriteria algorithm, based on the AHP method, developed for the reassignment of the operations that are blocked following a machine breakdown. The reassignment of the blocked operation is carried out on the machine providing ‘the best’ compromise between the three criteria.

Petri net based node structures for distributed problem solving in FMS control

Abstract A Distributed Problem Solving (DPS) architecture (SCOPE) for the control of Flexible Manufacturing Systems is presented. The controller kernel is intended to be easily adapted for different manufacturing systems, and we propose this as a basis for the standardization of control architectures from the point of view of control system designers. Our concern is the dynamic (rapid) generation of flexible solutions to a control problem with several discrete decision variables. Each node consists of the object class (or classes) that it deals with, its local model (which describes the dynamics of the node), and a set of problem solving agents (knowledge sources), that could be invoked by this node. An object class is represented by a Petri net with an object orientated interpretation (PNO), and acts as a structured local database or a local hypothesis register. The local model indicates the conditions under which this problem solving node could invoke any of its agents, and also when a node demands the services of another node, this demand is formulated through the local model. A node calling for the treatment of its local hypothesis modification does not know the node which will respond. Inside a node its KSs are also disconnected (uncoupled), and react in an opportunistic manner. This control structure permits parallel activation of KSs. The protocols for activation, running, termination (normal and abnormal) and resumption of the different KS types are specified with generic Petri net structures. A detailed description of the problem solving mechanism in SCOPE is given for the activities involving the Batching node.

Distributed Intelligence Systems for FMS Control Using Objects Modelled with Petri Nets (Scope Blackboard)

Abstract A flexible framework for the resolution of FMS control problems is developed based on the definition of problem solving nodes cooperating according to the opportunistic paradigm. This approach is unique in its node structure constructed using Petri nets interpreted as objects in Prolog and the generic representation of Knowledge Sources. Further, our strategy facilitates the use of the token player in real-time situations by effectively reducing the compilation difficulties arising from its non-incrementality.

Une programmation opératoire robuste

Le bloc opératoire est un lieu hautement stratégique pour les établissements hospitaliers car il est un coeur des compétences médicales et emploie une part importante du budget de l’établissement pour son exploitation. Ce papier présente une étude sur la programmation opératoire que l’on pratique dans les établissements privés. Une approche pour la construction de plages flexibles est présentée afin de permettre aux gestionnaires du bloc de proposer aux groupes de chirurgiens des plannings adéquats à leurs exigences et demandes, et qui permettent de faire face aux aléas tout en maintenant la performance du bloc opératoire en termes du taux d’exploitation de cette ressource coûteuse et du taux des interventions reportées. L’approche proposée se décline sur les deux niveaux de planification : tactique, opérationnel et recourt à la programmation linéaire à variables entières.

Petri Nets Interpreted As Objects for Distributed Intelligent Control: Implementation Issues

Abstract: In this paper implementation problems resulting from the use of Petri nets as a modelling formalism in the distributed real-time control of manufacturing systems are treated at two levels, at the level of model construction and at the level of the implementation. The problem reduces to one of real-time pattern matching, The special structure of the problem domain is exploited for obtaining a distribution of the nodes susceptible of being communication bottlenecks. Then we demonstrate how the structure of coloured Petri nets allows an extremely efficient parallel interpretation using associative memories. This has the potential of radically increasing the real-time response of the distributed controller.

SUPPLYING THE OPERATING THEATRE: CYCLIC AND SUPPLY CHAIN APPROACHES

Abstract The operating theatre is the resource neck of the hospitals. It would be interesting to optimize its functions. The principal activity of the block is the surgical act related to the art of medicine, which we cannot optimize. However, we can improve the performances of the operating theatre by developing the logistics activities. We are particularly interested in the procurement or supply activities. We propose and compare two approaches to supply the operating theatre: (1) a cyclic approach and (2), a supply chain approach.

Supplier selection under purchasing and transportation conditions

Abstract Little attention is given in the literature to the transportation impact on the supplier selection decision. In this paper, we propose a mixed nonlinear programming model to simultaneously determine the optimal number of suppliers to employ and the order quantities to allocate to them, taking into account the transportation. The objective of the model is to minimize the total cost, which includes purchasing, transportation, ordering and inventory costs subject to suppliers, buyer and transportation constraints. The model is solved several times, evaluating various scenarios. Each scenario depends on the shipment type used between the suppliers and the buyer.

Overcoming Communication Bottlenecks in Distributed Intelligent Control of FMS

Abstract An approach to reduce the effect of problems related to inter-node communication in Distributed Problem Solvers (DPS) is presented for the special case of real-time control of Computer Integrated Manufacturing Systems (CIMS). Some techniques based on the distribution of control and VLSI implementations of control Petri nets were presented in (DEVAPRIYA, 91c; 92a). The present paper discusses the necessity for furnishing the system with a panoplie of diverse communication techniques and letting the system learn to use the best technique for a given situation. This permits a high degree of flexibility of the system without sacrificing unduely on communication efficiency while avoiding bottleneck situations in the DPS network.

Evaluation Methods for a Distributed Intelligent Control Architecture : Case of Integrated Manufacturing Systems

Abstract Evaluation is a difficult, but essential phase in the development of a distributed intelligence architecture. This process of evaluation has to be a continuing task during the development phases of the system. In this paper, we limit ourselves to the evaluation of a distributed problem solving architecture, SCOPE (System for Control in an Object oriented framework using PEtri nets), being developed for the control of integrated manufacturing systems (refered to as FMS in the suite). An introduction is given to SCOPE through an illustration of an instance of a problem solving mode of SCOPE. We propose a synthesis of the available techniques for evaluation and some new criteria for the particular case of a distributed intelligent FMS controller.

OVERCOMING COMMUNICATION BOTTLENECKS IN DISTRIBUTED INTELLIGENT CONTROL OF FMS

An approach to reduce the effect of problems related to inter-node communication in Distributed Problem Solvers (DPS) is presented for the special case of real-time control of Computer Integrated Manufacturing Systems (CIMS). Some techniques based on the distribution of control and VLSI implementations of control Petri nets were presented in (DEVAPRIYA, 91c; 92a). The present paper discusses the necessity for furnishing the system with a panoplie of diverse communication techniques and letting the system learn to use the best technique for a given situation. This permits a high degree of flexibility of the system without sacrificing unduely on communication efficiency while avoiding bottleneck situations in the DPS network.