Agnelo Denis Vieira

A Model for PLC Implementation of Supervisory Control of Discrete Event Systems

This paper deals with the implementation of supervisory control of discrete events systems in programmable logic controllers. A modular approach of the supervisory control theory is applied for performing the formal synthesis of supervisors. Some problems that arise in the implementation of supervisory control are reviewed from the literature. The main contribution of this paper is the introduction of conceptual aspects of a systematic procedure to structure and to detail the program to be implemented in a programmable logical controller. The program resulting from the application of this procedure is in conformity with the international standard IEC 61131-3.

Modeling Business Rules for Supervisory Control of Process-Aware Information Systems

Companies are demanding more flexibility from their Process Aware Information Systems (PAIS). However, regulations and standards that impose limits to process executions are becoming increasingly important for business process management. The need for a compliance agenda and the security requisites for PAIS are pushing companies to search and to acquire new systems and technics for control and audit business processes. The aim is to avoid process execution that violates some business rules. In order to build an approach that support companies in auditing and controlling their business processes, there is a need for a formal and systematic modeling of business rules. In the present paper we have two objectives. The first one is to propose a set of business rules related to the ordering of tasks and to the involvement of a role or agent in cases. The second one is to build a supervisory control of PAIS that ensures compliance of business rules. To evaluate the correctness of our approach we applied it in two different business processes.

Dealing with routing in an automated manufacturing cell: a supervisory control theory application

Automated manufacturing cells are capable of producing different products using the same set of resources. This characteristic allows a more efficient use of resources, but makes the control of these systems more difficult and susceptible to errors. This article addresses the problem of routing control in an automated manufacturing cell that consists of three workstations, a transportation system, a feeding conveyor and a retrieving conveyor. In the modelling step, this article employs a systematisation of system and behavioural specifications modelling. This systematisation aims to minimise the impact caused by changes on system constitution and production specifications. In the synthesis step, the local modular control approach of the supervisory control theory is used to obtain the supervisors that match the specifications. In the implementation step, the systematic translation of the results obtained with the application of this theory into the application program to be implemented in the programmable logic controller that controls the cell occurs. The proposed approach in this study was tested and validated in a real manufacturing cell and the experimental results show the viability and success of this project.

A Method for PLC Implementation of Supervisory Control of Discrete Event Systems

This paper faces the problem of coordinating equipment operation in a flexible manufacturing system consisting of several subsystems including robots, assembling machines, CNC lathes, and mills. There are two main problems in such a system. The first is controlling each individual subsystem considering its own sensors, actuators, and specialized controller to perform a certain sequence of activities. Due to their expertise and/or application of formal methods, programmable logic controller (PLC) practitioners and equipment manufacturers develop efficient and safe solutions to address this problem. The second problem is coordinating the concurrent operation of these subsystems with the goal of producing what is requested as efficiently as possible and guaranteeing the integrity and safety of the system. Supervisory control theory (SCT) is particularly suited to this problem. This paper presents a method that allows a designer to systematically convert SCTs results into a PLC application program. The resulting program conforms to IEC 61131-3 and preserves the natural modularity of the system to be controlled and control specifications. An extension of this method allows a designer to reuse existing PLC hardware and application programs designed for the control of equipment by easily integrating with the code corresponding to the SCT solution. A major portion of this code may even be automatically generated, reducing development time and minimizing editing errors.

Application of the supervisory control theory in the project of a robot-centered, variable routed system controller

This paper aims to present the development of the controller of a manufacturing system based on the application of the Supervisory Control Theory, in particular an extension of such theory named Local Modular Control approach. The foundations of this work are a Supervisory Control Architecture and a Programmable Logic Controller (PLC) method of implementation of such architecture, both of these found in the literature. The manufacturing system is constituted by an industrial robot that plays the role of a transport system and three workstations. We show that applying formal methods of controller synthesis, as well as applying the referred PLC method of implementation makes easier to express the control specifications, to check out the systempsilas controlled behavior, and specially, to make the necessary modifications when the system has to be reconfigured.

Application of the supervisory control theory to automated systems of multi-product manufacturing

This paper presents an approach for modeling a physical system and its required specifications for a multi-product manufacturing system applying Supervisory Control Theory (SCT). The analyzed systems have the capacity of simultaneously processing various types of products, always following their specified production sequences. The systematization of the modeling aims at facilitating physical system and control logic reconfiguration, common and necessary aspects in these types of systems. To validate the proposed approach, modeling, synthesis and implementation of the control logics are developed for a real manufacturing system.

Dealing with Constraint-Based Processes: Declare and Supervisory Control Theory

The constraint-based processes are those that do not require a procedural model that explicitly specify the execution procedure. Declarative languages are more suitable for modeling and implementing this type of process. This paper aims to present and analyze two approaches that deal with the modeling and execution of constraint-based processes. The first approach makes use of Linear Temporal Logic and software Declare as a tool for modeling constraints. The second approach is based on the Supervisory Control Theory (SCT). Both approaches presented in this paper aims to monitor and restrict execution sequences of tasks such that constraints are not violated. Despite the control logic is built based on constraints, it does not limit the user by imposing rigid control-flow structures. A discussion of the results, advantages and the main drawbacks of the two approaches are presented in this paper.

A computational control implementation environment for automated manufacturing systems

This paper presents a computational environment as a tool for supporting the implementation of control coding of an automated manufacturing system. The proposed environment considers a cyclic three-stage control development – modelling, synthesis and implementation – until the real system accomplishes the required specification, resulting in the automated and integrated manufacturing system. The research details the three stages and describes the steps executed for each one. The mathematical formalism used in this work is also presented, as a basis for control implementation. The implementation environment is proposed in order to validate the control structure of this formalism and to allow a progressive integration of control hardware and software. To submit to a test and validate the proposal environment, two experiments are performed, in two different manufacturing systems. Thus, it is demanded that the control system can be reconfigurable in a fast and reliable way.

Supervision of Constraint-Based Processes: A Declarative Perspective

Constraint-based processes require a set of rules that limit their behavior to certain boundaries. Declarative languages are better suited to modeling these processes precisely because they facilitate the declaration of little or no business rules.These languages define the activities that must be performed to produce the expected results but not define exactly how these activities should be performed. The present paper proposes a new approach to deal with constraint-based processes. The proposed approach is based on supervisory control theory, a formal foundation for building controllers for discrete-event systems.The controller proposed in this paper monitors and restricts execution sequences of tasks such that constraints are always obeyed. We demonstrate that our approach can be used as a declarative language for constraint-based processes.

Control synthesis and implementation for an integrated manufacturing system based on Supervisory Control Theory

This paper presents the implementation of a controller to an integrated manufacturing system, made through the application of the Supervisory Control Theory (SCT). The work explores the modeling of subsystems and the specifications of a real manufacturing system. A supervisor, which fulfills the specifications, is synthesized. Based on these SCT implementation aspects presented on the text, the synthesized supervisor is accomplished in the manufacturing execution system. A physical implementation topology, which accomplishes the control proposal, is also discussed.