François Gellot

Remote Control of Automation Systems for DES Courses

The objective of technical courses is the transfer of knowledge and know-how to students. In the case of discrete event system courses, it is important for a learner to locally or remotely control real systems (or plants) that are composed of many sensors and actuators. The use of these devices poses several problems. First, it is difficult to adapt them to the students level (from beginner to expert). Second, these systems are generally designed with industrial components. An error on the control-command design can involve safety problems and breakdowns. In this paper, the authors propose an original solution to solve these two problems. To guarantee the safety of the operators and the equipment, an approach using a validation filter is proposed. It is based on the definition of logical constraints, which should in no case be violated. To adapt the difficulty level, it is proposed to modify the level of automation. For that, the functional dimension of the automation system is modified to adapt the students level of autonomy. The level of automation is defined by the teacher by means of a functional analysis of the system. To validate the approach, it is applied to an original project with ten-year-old children on a packaging system. The aim of the project is to enable ldquoyoung novice control engineersrdquo to perform their first programmable logic controller program to control the whole system.

Prevention of human control errors by robust filter for manufacturing system

Abstract In this paper, we are interested at the errors that can commit by a human operator in the control program. When a command error is made, the presence of a product in the system can cause damage. In this paper, we design a robust filter placed inside the PLC which authorizes or forbids outputs from the PLC. The filter is composed of several logical constraints which have to be respected at each PLC cycle. In order to guarantee the filter quality, it is necessary to check that all constraints have been well defined. For that, in order to validate the filter, an original formal method has been proposed. This one is based on a modular modelling approach of the manufacturing system by using different timed automata models (actuators, sensors, items, and PLC), and by considering the most permissive PLC program. UPPAAL checker is used to verify that the filter is sufficient to avoid the manufacturing system to reach dangerous forbidden states. If it is the case, the filter guarantees the safety whatever the PLC program. Hence, the filter still remains active even if there are changes in the PLC program during the lifecycle of the production system.

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.

Human-Machine Systems concepts applied to Control Engineering Education

In this paper, we interest us to Human-Machine Systems (HMS) concepts applied to Education. It is shown how the HMS framework enables to propose original solution in matter of education in the field of control engineering. We focus on practical courses on control of manufacturing systems. The proposed solution is based on an original use of real and large-scale systems instead of simulation. The main idea is to enable the student, whatever his/her level to control the whole system, from novice to expert, in a safety mode. The teacher is responsible for sharing the control design tasks between the student and the automatic system. Different teachers and students have tested this approach, on different manufacturing systems. By an experiment with a class of “10-year-old novice control engineer”, we have shown the interest and the power of the proposed solution. We have proposed at the children to realize their first control program of a packaging process. This experiment encountered a big success.

Robust filtering of PLC program for automated systems of production

Abstract The proposed methodology enables to secure the control program of automated production systems. The principle is to place a robust filter inside the PLC of the automated production system to inhibit or authorize actions in the event of detection of errors in the control program. The proposed methodology rests on the one hand, on a rigorous analysis of the automated production system in order to formally build the set of constraints which constitute the filter using temporal and boolean logic. And on the other hand, a phase of modeling by finite-state automata which is necessary to validate the sufficiency of the constraints and to check the robustness of the filter as well as the safety properties using Model-Checking tools.

REQUIREMENT AND USE FOR REMOTE TEACHING OF DISCRETE EVENTS SYSTEMS

Today, Internet makes possible remote access to PLC (Programmable Logic Controllers) remote maintenance, monitoring, supervision and follow-up of plants. In this article, we are interested in the possibilities that Internet offers for the D.E.S (Discrete Events System) teaching. The concept of distributed practical work room is proposed in order to facilitate the technical know-how transmission. The idea consists for students, on the one hand to use a real PLC and specialized software via Internet and on the other hand, to check their controller program by the mean of a plant simulation. In addition, the controller program verification problem is proposed. Indeed, as well within the framework of the real as simulated plant use, it is necessary to develop controller verification tools able to cooperate with the teacher and students and having explanatory capacities.

Control validation of D.E.S systems: Application to remote laboratories

Objectives of Automation courses are knowledge and know-how transfer to students. It is important for learner to control locally or remotely real systems composed of many sensors and actuators. The use of these devices poses several problems. Firstly, it is difficult to adapt them to the student’s level (from beginner to expert). Secondly, these systems are generally designed with industrial components. An error on the control-command design can involve safety problems and breakdowns. Technologies today allow remote use of plant. That makes it possible to improve the availability of the work practice rooms but ask pedagogy and safety questions. In this paper, we propose an original solution to solve these 2 problems. In order to guarantee the safety of the operators and the equipment, an approach using a validation filter is proposed. It is based on the logical constraints which should in no case to be violated. In order to adapt the difficulty level, it is proposed to modify the level of automation. For that, the functional dimension of the automation system is modified to adapt the student’s level of autonomy. In order to validate the approach, we applied it to an original project with 10 year old children on a packaging system.

Safe control synthesis based on Boolean constraints for manufacturing systems

Abstract This paper presents an original approach of safe control synthesis of manufacturing systems. This is an extension of the work that CReSTIC has led for several years on the definition and design of a logic filter (placed into a Programmable Logic Controller (PLC)) robust to control errors, and formally verified using a model checker. The proposed approach, which separates the functional control part from the safety control part, is simple to implement and ensures that the designed controller is safe. The methodology is based on the use of safety constraints coming from the filter in order to get the most permissive safe controller. This controller is then constrained by functional constraints. The approach is illustrated by using an example of sorting boxes simulated using the ITS PLC software from the Real Games company ( www.realgames.pt ). The control algorithm is presented and allows to result in a safe control, may be simpler than a conventional approach based on a specification in GRAFCET (IEC 60848), that does not distinguish the functional aspect from the safety aspect. This approach presents interesting perspectives like the management of several operating modes.

Control synthesis based on logical constraints for safe manufacturing systems

Abstract This paper presents an original approach of safe control synthesis of manufacturing systems. This approach is based on the use of a logic filter (placed at the end of PLC (Programmable Logic Controller)) robust to control errors, and formally validated using a model checker. The proposed approach, which separates the functional control part from the safety control part, is simple to implement and ensures that the designed controller is safe. The methodology is based on the use of safety constraints coming from the filter in order to get the most permissive safe controller. This controller is then constrained by functional constraints. The approach is illustrated by using an example of sorting boxes simulated using the ITS PLC software from the Real Games company ( www.realgames.pt ). The control algorithm is presented and allows to result in a safe control, may be simpler than a conventional approach based on a specification in GRAFCET (IEC 60848), that does not distinguish the functional aspect from the safety aspect. This approach involves a new way to see the control of manufacturing systems and presents interesting perspectives like the management of several operating modes.

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.