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 (PN s). A modular logic controller structure is introduced and formalized for h igh-volume transfer lines. The modular logic controller consists of a contr ol module for mode decision and control modules for station logic controlle rs. Each station control module is represented by connecting operation modu les which are designed with respect to the fault recovery processes of oper ations; their connection algorithm is also provided. In our formal represen tation, each control module is represented by a live, safe, and reversible PN. A condition for the modular logic controller to generate a correct cont rol logic is provided: operation causality condition. Using the modular str ucture of a logic controller, the control logic can be easily reconfigured and automatic code generation is possible.