In recent years, the efficiency of material handling systems has been recognized as a key factor in the success of automated manufacturing systems(AMSs) or CIM factories. As a result, manufacturing system designers are increasingly interested in having simulation tools and mathematical tools to aid automated material handling system design. A sorting and buffering system(SBS) is a well-defined automated material handling system in which incoming items of different part types are automatically sorted and buffered in lots of the same part type so that the processing machines can process the parts in lots.
Proposed in the thesis are 1) a structured two-phase approach to event graph modeling of SBS and AMSs based on the concept of supervisory control model which is easily obtained once the dynamic behavior of the system is understood, 2) analysis tools such as an SBS simulator and a mathematical model for calculating the cell buffering capacity, and 3) an empirical approach to generate ladder diagram based on event graph model.
The procedure at the first phase of the proposed event graph modeling, supervisory control modeling, is 1) classifying the AMS components into stations by the modular and hierarchical structure of AMSs, 2) closed-loop control sequence generation for activity control and decision control of AMS with 5 nodes and 2 arcs, and 3) link the interaction between control cycles with information flow arc. The procedure at the second phase, event graph generation, is 1) event identification from supervisory control model, 2) definition of system variables for representing system state changes and conditions, 3) event graph construction with identified events, system variables and supervisory control model, and 4) event graph reduction. A proposed supervisory control model serves as a modeling aid for both the FA design engineer and the simulation practitioner: the design engineer may use the control model in verifying his design logic as well as in developing control programs, while the simulation expert uses the control model in developing a formal model for computer simulation. It should serve as a communication tool between the design engineer and the simulation expert.
A SIMAN-based SBS simulator is implemented for the SBS generic event graph model. Because the simulation language SIMAN is designed based on a process view, the implementing procedure from event graph is showed. The process of a part entity is represented as the sequence of events associated with part flow.
The empirical procedure for ladder diagram generation from event graph model is 1) classification of defined events according to types of being influenced by generated events, 2) mapping the system variables into the registers of programmable logic controller, 3) conversion of the initial system status into ladder diagram, 4) conversion of the state changes by events into ladder diagram and 5) represent the output load for actuator control at the last section of ladder diagram.
