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.

The logic controller for a machining system is a discrete event supervisory system. In high volume transfer lines, it consists of three control modes: auto, hand, and manual. A logic controller can achieve the goal of a machining system by its control logic. The paper addresses a formal Petri net representation of the control logic and its implementation. The control logic is represented by two Petri net models: one for the mode decision control logic and the other for the sequence control logic. Because the Petri net models are live, safe, and reversible, the actual logic control program can be generated directly from the Petri net models by using IEC1131-3 programming languages.

The machining systems considered are high volume transfer lines. The cycle time during normal operation is used as the performance metric. Normal operation is governed by the auto-cycle function of a logic controller. A modular logic controller is introduced and formalized for event-based functional properties analysis of transfer line. By adding time specifications, a timed modular logic controller is generated. The time-based cyclic behavior of high volume transfer lines is characterized using timed Petri nets. Two efficient algorithms to compute the cycle time and critical operations are developed. A method for improving the performance of a transfer line is introduced.

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.