Paulo E. Miyagi

Modeling and analysis of fault-tolerant systems for machining operations based on Petri nets

This paper introduces a methodology for modeling and analyzing fault-tolerant manufacturing systems that not only optimizes normal productive processes, but also performs detection and treatment of faults. This approach is based on the hierarchical and modular integration of Petri nets. The modularity provides the integration of three types of processes: those representing the productive process, fault detection, and fault treatment. The hierarchical aspect of the approach allows us to consider processes on different levels of detail (i.e., factory, manufacturing cell, or machine). Case studies considering detection and treatment of faults are presented, and a simulation tool is applied to verify the models.

On Resource Arc for Petri Net Modelling of Complex Resource Sharing System

PFS-R – Production Flow Schema with Resources – is a novel graphical representation for complex resource sharing discrete production systems proposed in this paper. The PFS-R is an augmented version of the PFS (Production Flow Schema, previously proposed by the authors) which includes correspondences of system resources at each production step. The PFS-R is able to model system structures as well as system behaviours in a more simplified and transparent manner than ordinary Petri net representations. That is, the PFS-R solves an important drawback when actually adopting Petri nets as a design technique for intelligent manufacturing systems. First, the paper introduces the basic elements of PFS-R, and the equivalent transformations of PFS-R model into hybrid nets and Petri nets, taking into account the net conservativeness. Next, examples of discrete production systems to illustrate the effectiveness of PFS-R are presented. In addition, it is shown, using an example, that the correspondence between resources and production steps in the process flow has a tree structure, which is an effective way to evaluate whether or not the objects designed have a well-defined structure.

Detection and treatment of faults in manufacturing systems based on Petri Nets

This paper introduces a methodology for modeling and analyzing fault-tolerant manufacturing systems that not only optimizes normal productive processes, but also performs detection and treatment of faults. This approach is based on the hierarchical and modular integration of Petri Nets. The modularity provides the integration of three types of processes: those representing the productive process, fault detection, and fault treatment. The hierarchical aspect of the approach permits us to consider processes on different levels of detail (i.e. factory, manufacturing cell, or machine). Case studies considering detection and treatment of faults are presented, and a simulation tool is applied for verifying the models.

Bayesian Network Supervision on Fault Tolerant Fuel Cells

In this paper, a supervisor system, able to diagnose different types of faults during the operation of a proton exchange membrane fuel cell (PEMFC) is introduced. The diagnosis is developed by applying Bayesian networks, which qualify and quantify the cause-effect relationship among the variables of the process. The fault diagnosis is based on the online monitoring of variables easy to measure in the machine such as voltage, electric current, and temperature. The fault effects are based on experiments on a fault tolerant fuel cell, which are reproduced in a fuel cell model. A database of fault records is constructed from the fuel cell model, improving the generation time and avoiding permanent damage to the equipment

A procedure for modeling and analysis of service-oriented and distributed productive systems

Geographic dispersion and distribution of productive activities in relatively autonomous systems are viable due to the advances in mechatronics, communication and information technologies. These productive systems are then composed of several components (sub-systems) with some degree of autonomy, and these must present a collaborative relationship to assure the overall performance of the system. Therefore, the challenge is to implement a collaborative distributed architecture that assures effective interactions among the services, in special for tele-operation and remote monitoring operations. Thus, new modeling techniques that guarantee verification and validation of the collaborative systems specifications are necessary. In this context, this paper proposes a procedure for modeling and analysis of service-oriented and distributed productive systems based on the characterization of the distributed productive system as a discrete event dynamic system. This procedure uses techniques derived from interpreted Petri net in order to perform the system modeling. Different levels of abstraction are considered to model the systems: the conceptual description is obtained through the production flow schema (PFS) technique and a refinement into functional models through the Petri net technique. Then, a procedure to detail the workflow process in the distributed productive system is described with emphasis on the integration of the component models.

Petri Net approach for modelling system integration in intelligent buildings

In this paper, a Petri Net approach is introduced for modelling and simulation of control strategies in Intelligent Building. In this context, it is claimed that integration with other building systems can be achieved in a more systematic way considering a mechatronic approach (i.e. multidisciplinary concepts applied to the development of systems). The case study is the Ambulatory Building of Medical School Hospital of University of Sao Paulo. Particularly, the developed methodology is applied to the elevator system and to the HVAC (Heating, Ventilation and Air Conditioning) system. It is shown that using this approach, the control systems could be integrated, improving performance.

Modelagem e simulação distribuída de sistema produtivo baseados em rede de Petri

Based on the existing computational capability and disperse infrastructure of some productive systems, there are interest for distributed modeling and simulation of these systems. These techniques are considered fundamental for design, implementation and performance improvement of productive systems. The approach is the simulation through the use of computers physically dispersed but integrated via a communication network to evaluate the behavior of systems still in conception level and also to improve the performance of existing plants. This work proposes a procedure for modeling of productive systems in distributed environment. This procedure was applied to case studies to confirm it effectiveness. The work includes an algorithm for the management of the distributed simulation. With the modeling method and the management algorithm we have the main elements for the practical implementation of the disperse productive system simulator.

Modeling of Programs and Its Verification for Programmable Logic Controllers

Abstract Programmable logic controller is still the main device used for control of productive systems, which can be approached as discrete event dynamic systems. For programming these controllers, five languages were standardized by IEC 61131, and the LD (ladder diagram) language is distinguished among the others, i.e., it has been widely applied in productive systems, even with studies that confirm the restrictions and problems regarding the use of this language, such as the difficulties for errors identification in developed control programs. Therefore, this work presents a proposal for the modeling of extended finite state machines from control programs written in LD. These models are verified through a computational tool, aiming the identification of possible errors in the control program.

Landing system verification based on petri nets and a hybrid approach

One of the most important activities of control system design is its verification. Verification ensures that the controlled system will behave as expected under any circumstances it may operate. In this context, the purpose of this paper is to introduce a new method for the verification of aircraft control systems. The focus of this method is on aircraft systems that are characterized as hybrid, i.e., that merge continuous and discrete dynamics. The method proposed is divided into two main parts: the system modeling and the verification of behavioral properties. In the first part, Petri net, differential equation systems, and object oriented concepts are used concurrently in order to model complex hybrid systems. In the second part, the distributed nature of the model is explored in order to decompose a complex verification problem into series of simple local problems. Linear logic is used as a basis of a theorem-proving approach for the verification from the discrete-event point of view. The verification method has been applied to a number of case studies. Among them is the landing system of a military aircraft, which is described in this paper

Fault detection in Flexible Assembly Systems using Petri net

A significant part of the activities in a manufacturing system involve assembly tasks. Nowadays, these tasks are object of automation due to the market increasing demand for quality, productivity and variety of the products. Consequently, the automation of assembly systems should consider flexibility to face product diversification, functionalities, delivery times, and volumes involved. However, these systems are vulnerable to faults due to the characteristic of their mechanism and the complex interaction among their control devices. In this context, the present work is focused on the modeling design of flexible assembly systems control, including the occurrence of faults. The proposed method structures a sequence of steps for the models construction of assembly processes and their fault detection, based on the theory of discrete events systems and Petri net. This work use in special, production flow schema/mark flow graph (PFS/MFG) technique to describe and model the flexible assembly systems control through a rational and systematic procedure, as well as, the processes data record based on quantitative techniques for fault detection. This approach is applied to a flexible assembly systems installed and in operation to compare the effectiveness of the developed procedure.