Distributed simulation approach for enabling cooperation between entities in heterarchical manufacturing systems

In this paper, a method for performing time-scaled distributed simulation is described for control of heterarchical manufacturing systems, where it is used as a mechanism by which highly autonomous entities in these systems can cooperate implicitly and to adapt to disturbance events in real-time. A replica of the system software, executing at a speed that is several orders of magnitude faster than real time, serves as an accurate, detailed, distributed simulation model that can be developed at low cost. Performance estimates obtained from simulations are used as feedback by entities in the system to iteratively improve global coherence. The time-scaled approach eliminates the need for explicitly synchronizing events and thereby eliminates the complexity associated with discrete event distributed simulation approaches. The method is applied in the paper to a manufacturing control system in which control laws with a continuous feedback structure are embedded in the autonomous workpiece entities and used to adjust the timing of events required to produce workpieces. The control laws ensure the stability and convergence of the system, while allowing it to be effectively controlled with minimal global information.