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 a control module for mode decision and control modules for station logic controllers. Each station control module is represented by connecting 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: operation causality condition. Using the modular structure of a logic controller, the control logic can be easily reconfigured and automatic code generation is possible.