Closed-loop simulation of workload control: Integrating input-output regulation with feedback

When responsiveness to demand fluctuations is a key performance factor, continuous dynamic models can advantageously replace discrete event simulation, often employed in Workload Control (WLC) studies. Nonetheless, dynamic modelling tools and feedback control are scarcely applied to WLC or other shop floor control systems. To fill this gap, this paper presents a closed-loop model of WLC incorporating feedback control and shop floor input-output control. The bond graphs’ dynamic modelling technique is employed. The model is implemented in Simulink® and its behaviour in face of disturbances is analysed. The load of the machines and of the job pool of WLC is considered to adjust order release (input control). The capacity of each machine (output control) is altered in function of the level of its preceding buffer. The machines’ processing rates stabilize and the reference levels for the buffers are reached when a step disturbance in order entry is simulated. Also, the system responded with a maximum capacity increment of 15 % when cyclic demand is simulated. This novel approach of a smart production control system can help managers to better control shop floor load in response to disturbances.