Closed-Loop Workload Input-Output Control of Production Systems: A Hybrid Simulation Study

Workload Control (WLC) is a method of adjusting the overall workload in the production system by controlling the input of production orders and the output of produced items. It contributes to the predictability of lead times and more accurate delivery date commitments in make-to-order manufacturing. Input control relates to order release and output control to capacity adjustment. Recently, a novel approach to simultaneous and integrated input-output control has been proposed: a dynamic closed-loop model where automatic feedback control is added and where order release and capacity decisions are based on the observed shop floor state. The control was applied to an abstracted continuous dynamic model of a shop with unidirectional flow and three control rules were tested in scenarios with unbalanced work in process (WIP) and demand fluctuations. In this paper, the approach was further investigated in a more realistic hybrid simulation setting, combining discrete-time controllers and a discrete-event model of a manufacturing shop. The results show that simultaneous input-output control is effective and enables the system to maintain WIP balance, absorb demand fluctuations and effectively reject disturbances, especially when global information is provided to the controller.