Bridging the Gap Between Design and Implementation of Discrete-Event Controllers

Abstract

Extended labeled Petri nets (ELPNs), i.e., labeled Petri nets with inhibitor arcs, are usually used to model the desired closed-loop behavior of a controlled discrete-event system, and, as such, their states are formed with both the controller and the plant states. However, the control logic is based on the controller states only and the interaction between controller and plant is carried out through sensor readings from the plant and control actions (forced events) from the controller. This makes ELPN not suitable for modeling the controller. Control interpreted Petri nets (CIPNs), on the other hand, include control actions in the places and sensor readings in the transitions as part of their formal structure, and so provide a better formalism for controller modeling. In this paper, we propose a two-step approach to discrete-event controller implementation, as follows: (i) we first propose a set of transformation rules to convert the initial ELPN to an equivalent CIPN, therefore extracting the control logic from the desired closed-loop behavior and (ii) we present a straightforward systematic way to translate the CIPN into a ladder diagram. We apply the results presented here to the implementation of the automation system of a plastic molding machine.Note to Practitioners-The usual approach to the design of manufacturing systems is to model the desired closed-loop system behavior using, for example, Petri nets, and in the sequel to extract the discrete-event controller from this model with the view to implementing the control logic on a Programmable Logic Controller (PLC). So far, the controller extraction is carried out in an ad hoc and intuitive way. In order to overcome the lack of formal methods to deal with controller extraction and implementation, we propose here a set of rules to construct, in a systematic way, the ladder diagram that implements the discrete-event controller. We illustrate the conversion technique proposed here by applying it to the implementation of the automation system of a plastic molding machine.Index Terms-Discrete-event systems (DESs), ladder diagram, manufacturing systems, Petri nets, programmable logic controller (PLC).

Controlling Supervised Industry 4.0 Processes through Logic Rules and Tensor Deformation Functions

“…Other supervisory control solutions for future industrial scenarios based on autonomous agents have been described. These mechanisms are typically defined as Discrete event systems (Wonham et al, 2018) and are focused on autonomous robots (Gonzalez et al, 2018) and similar mobile machines (Roszkowska, 2002), although other applications to real-time solutions (Sampath et al, 1995) and fault diagnosis (Moreira and Basilio, 2014) may be found. Logic rules have been also employed to implement robot navigation frameworks (Kloetzer and Mahulea, 2016) and different mechanisms to optimal (Fabre and Jezequel, 2009) or clean paths (Iqbal et al, 2012) in robotized Industry 4.0 have been also reported.…”

AUTOMAÇÃO DE UM SISTEMA PICK & PLACE BASEADO EM SISTEMAS A EVENTOS DISCRETOS

“…Apesar do Diagrama Ladder ser de fácil implementação para sistemas simples, ele se torna mais complicado para sistemas mais complexos, precisando assim de um método sistemático para implementá-lo. Alguns trabalhos mostram a implementação em Ladder utilizando sistemas mo-delados em Sistemas a Eventos Discretos (Liu and Darabi, 2002;S.Peng and Zhou, 2004;Music et al, 2005;Moreira and Basilio, 2014).…”

“…os autores apresentam um algoritmo para converter modelos em autômato para Diagrama Ladder. Em (S. Peng and Zhou, 2004) e (Moreira and Basilio, 2014) os autores apresentam métodos para transformar modelos em Redes de Petri em Ladder. No entanto, estes trabalhos não apresentam uma implementação em um PLC real.…”

Sincronização de Sistemas a Eventos Discretos com Compartilhamento de Recursos

“…O projeto do controlador de SEDsé geralmente realizado de duas formas: (i) modela-se o comportamento nãocontrolado do sistema e, após isso, controladores são sintetizados a partir da teoria de controle supervisório, (Vieira et al, 2017) e; (ii) projeto do controlador a partir do comportamento desejado do sistema, usando por exemplo, RPICs (Moreira & Basilio, 2014). O uso de modelos como RPICs e sua composição para o controle de uma planta pode resultar em uma explosão do espaço de estados para sistemas complexos que envolvem muitos componentes (Iordache et al, 2008).…”

“…Dois tipos diferentes de abordagens para a sincronização serão apresentados, assim como dois algoritmos para sua implementação. Por fim, o métodoé implementado em um sistema real por meio de CLPs programados em linguagem Ladder, cuja programaçãoé obtida por meio da conversão de RPIC para Ladder desenvolvida em (Moreira & Basilio, 2014).…”