Load smoothing with feedback in a bottleneck job shop

Most of the past research on job shop scheduling has assumed the shop environment where the load-smoothing function in the production planning and control system is ignored and consequently no visibility is provided to the shop. In practice, some kind of load-smoothing is used to smooth the work load level of the shop across the periods, by pulling jobs forward or pushing jobs back. In this study three load-smoothing approaches with two levels of control for each approach are proposed and tested with two order review/release decisions in a bottleneck job shop. No smoothing becomes a benchmark. Also, the effectiveness of a feedback loop between load-smoothing and the shop floor is investigated. Experiments were conducted in a six-machine job shop simulation model. Results showed that the employment of load-smoothing is important, and pulling jobs forward in a valley period is better than pushing back jobs in a peak period. Controlling the release of jobs to the shop floor in the order review/release phase, given the amount of jobs to be processed during the planning period, is not effective. Also, the feedback system between the planning phase and shop floor to maintain the minimum shop load becomes much more important than simply controlling job release time.