Bruno Denis

Evaluation of response time in ethernet-based automation systems

This paper presents a method to assess response time of automation system architectures including industrial switched Ethernet networks using client/server protocols. The method relies upon modeling the behavior of the components of these architectures in the form of hierarchical timed colored Petri nets and upon simulation of these models. A case study exemplifies the method and shows how it can facilitate design of automation systems including this kind of industrial Ethernet networks.

LOGIC CONTROLLERS DEPENDABILITY VERIFICATION USING A PLANT MODEL

Abstract This paper focuses on usefulness of a plant model for model-checking of untimed properties of logic controllers. Verification results obtained on a case study by using the symbolic model-checker NuSMV and three methods: verification of the only controller, constraints-based verification, in which the plant is simply modeled as a set of physical constraints, and model-based verification, that relies on a detailed model of the plant, are presented. The results yielded by these approaches enable to draw up application rules for formal verification of logic controllers.

Measuring the impact of vertical integration on response times in ethernet fieldbuses

The introduction of Ethernet and Internet technologies in the fieldbuses of automation systems widely facilitates vertical integration. Control functions can coexist more easily with higher level functions such as supervision, production reporting or maintenance. But what does the response time of the control function become when architecture components -e.g. controllers, remote input-output modules or fieldbuses -are requested in parallel by other functions? In this paper, we focus on switched Ethernet-based fieldbuses using Modbus TCP/IP. The evaluation of the impact of vertical integration on the response time of control functions is obtained from a series of measurements on a real system. A great number of response times were measured with a specific automated equipment that we developed. Three types of load on the control architecture are studied: traffic on fieldbuses, requests on controllers and requests on remote input-output modules. The analysis of the measurement results shows which level of vertical integration can be reasonably allowed, taking into account the required response times.

Toward a Theory of Integrated Modelling

Abstract For many years, complex systems designers have been able to use modelling techniques which are steady and proven. Today, most of these modelling techniques are used in «integrated methods». These methods provide analysts with a framework to design increased-complexity systems. In this paper, we propose an approach which makes integrated-methods formal by modelling them. Two examples are given to illustrate these concepts.

Designing operational control architectures of critical systems by reachability analysis

This paper presents a method that eases the design of the operational architecture of a control system by providing, from the knowledge of some characteristics of the functions that the control system must ensure and a generic model of controller, an assignment solution of these functions that satisfies capabilities and distribution constraints. This method relies on the verification of a reachability property on a network of communicating automata that models the assignment process. The benefit of this proposal is illustrated by a non-trivial case study from industry.

Eco-Problem Solving for the Adaptive Control of Production Systems: The Casper Project

Abstract For many years, multi-agents have been successfully used in different domains of the design and exploitation of manufacturing systems. ☺This paper presents an original experience of multi-agents in the field of manufacturing control. The benefit of this approach is to increase the flexibility of the control system without increasing its complexity. An example is given - on a milling cell - to illustrate the concepts and techniques used.

Measures vs. analytic evaluation of response time of Networked Automation Systems

In this paper, we present a study that deals with response time of Networked Automation Systems (NAS). The main aim is to verify experimentally the validity of an analytic formulation of NAS response time, obtained in our past investigations [12]. To that purpose, we carried out, under different conditions, a lot of measurements on a laboratory facility. Each time, we compared the observed measures to the predicted values. Overall, the study reveals clear agreement between the real observations and the theoretic predictions of our formula. It therefore promotes the formula to be used confidently for NAS response time evaluation while avoiding tedious and onerous experiments.

Using a meta-model to build operational architectures of automation systems for critical processes

This paper addresses the design of the operational architecture of a critical system control. This design results from the allocation of control functions onto physical devices by taking into account numerous constraints such as capability, safety, time performance or reliability constraints. This paper focuses on the two first ones, capability and safety constraints by proposing a method based on reachability analysis in a network of communicating automata. The link with complementary studies about time performance or reliability constraints is established using an UML architecture meta-model that captures and shares information about control architectures. Automata models and their parameters used for reachability analysis are derived from this meta-model and, conversely, generated operational architectures give rise to a set of meta-model instances that can be used as input for complementary evaluation.

PERFORMANCE VERIFICATION OF DISCRETE EVENT SYSTEMS USING HYBRID MODEL-CHECKING

The results generated over the past few years on the formal verification of both Discrete Event Systems (DES) and Hybrid Dynamic Systems (HDS) are quite substantial, especially as regards the controllers properties of liveness and safety. In this paper, we will study the range of possibilities offered using the model-checking techniques in order to evaluate DES performances (in terms of quality of service provided by the automated system). This task calls for proceeding with a model-based approach that couples a hybrid model of the plant with a timed discrete model of the controller. We will also show, using a basic example, that by parameterizing the hybrid process model, the model-checker may then be employed to evaluate the robustness of the discrete control to perturbations encountered by the plant.

Comparison of Different Modeling Approaches in Simulation of Programmable Logic Controller

Abstract To design the control of automated systems, the designer must evaluate the performances of various solutions. Our research deals with the evaluation of distributed control architecture. We have chosen Colored Timed Petri Nets (CTPN) models for describe behaviors of each equipment of control and we use design/CPN simulation tool to assess response times performance. The aims of this paper are to build various Programmable Logic Controller (PLC) behavior models and to select the best according to our needs in performance evaluations. Various approaches for the creation of CTPN models are discussed. Some of them are based on synthesis techniques and some of them are based on an identification technique. Finally, a comparison method is presented. It will allow the designer to choose the right model for the simulation in the evaluation stage.