On the integration of input and output control : Workload Control order release

Workload Control is a production planning and control concept developed for high-variety job shops. It integrates two control mechanisms: (i) input control, to regulate the inflow of work to the system; and (ii) output control, which uses capacity adjustments to regulate the outflow of work from the system. Much Workload Control research has focused on input control, while output control has been largely neglected. Only recently has research emerged that uses Workload Control theory to guide capacity adjustments. Yet this literature focuses on capacity adjustments (output control) only – it fails to integrate it with Workload Control’s input control element. In response, this study explores the performance impact of Workload Control when input control (controlled order release) and output control (capacity adjustments) are combined. Job shop simulation results demonstrate that input and output control can and should play complementary roles. Both elements significantly enhance performance in isolation, and performance effects appear to complement each other. Further, results indicate that the choice of the workload threshold that triggers capacity adjustments has a stronger impact on performance than the actual size of the adjustment. The measure of workload used to guide the load-based order release decision is also used to determine the workload threshold that triggers the capacity adjustment. This facilitates implementation in practice. Finally, although our study is on Workload Control, the findings have important implications for other production planning and control concepts.