Modular Logic Controllers Research Articles

Verification of Fault Tolerance of Discrete-Event Object-Oriented Models using Model Checking

Abstract The Object-Oriented (O-O) approach has been recently used in the industrial automation to design logic control systems, thanks to the features of specification languages (e.g. UML) that can help to describe event-based behavioral requirements. In this paper, we aim to formalise an O-O framework for the design of modular logic controllers, in which faults occurring in the plant can alter the behavior of closed-loop system. Given the formal model of the system in terms of Kripke structures, it is possible to verify with model checking that even in case of faults the system do not violate given safety and liveness properties. Moreover, we will consider the case in which an O-O logic controller is refined applying the so-called “design-by-extension” mechanism, in which case it is important to verify that the fault tolerance property is inherited by the refined system.

RECONFIGURABLE LOGIC CONTROLLER FOR EMBEDDED APPLICATIONS

The design methodology of modular Logic Controllers, which are realised in reconfigurable array logic, is presented. Sequential Function Chart is considered as an initial behavioural specification of Concurrent State Machine with Data Path. SFC is supplemented with textual explanation of its guards and actions, written in Structured Text. Before a final design, it is transformed into a particular kind of modular control interpreted Petri net and described in VHDL on Register Transfer Level. The dedicated Data Path is formed from previously designed Function Blocks. Refined, structured and verified description of Reconfigurable Logic Controller is mapped directly into FPGA by means of using dedicated and commercial synthesis tools.

A modeling and analysis methodology for modular logic controllers of machining systems using Petri net formalism

Logic controllers for machining systems typically have three control modes: auto, hand and manual. In this paper, a unified formal representation of logic controllers with three control modes is provided using Petri nets (PNs). A modular logic controller structure is introduced and formalized for high-volume transfer lines. The modular logic controller consists of one control module for the mode decision and other control modules for station logic controllers. Each station control module is represented by connecting together operation modules, which are designed with respect to the fault recovery processes of operations; their connection algorithm is also provided. In our formal representation, each control module is represented by a live, safe and reversible PN. A condition for the modular logic controller to generate a correct control logic is provided: the operation causality condition. Using the modular structure of a logic controller, the control logic can be easily reconfigured and automatic code generation is possible.

Modular logic controllers for machining systems: formal representation and performance analysis using Petri nets

The machining systems considered are high volume transfer lines which are widely used in automotive manufacturing. In these machining systems, several machines linked together provide complete processing of a part. A logic controller is a discrete event supervisory system which controls parallel and synchronized sequences of elementary operations of each machine to achieve the goal of the machining system. Normal operation is governed by the auto-cycle function of a logic controller. A modular logic controller is introduced and formalized for high volume transfer lines. Its event-based functional properties are verified and its reconfigurability is considered. A live and safe marked graph can be directly transformed into a sequential function chart (which is one of the IEC 1131-3 languages) and, using this SFC representation, a modular logic controller can be implemented. The performance analysis of the modular logic controller is also introduced. The cycle time during normal operation is used as the performance metric of a transfer line. By adding time specifications to the model, a timed modular logic controller is generated. The time-based cyclic behavior of high volume transfer lines is thus characterized using timed Petri nets. Two efficient algorithms to compute the cycle time and critical operations are developed.