Machine selection (dispatching) rule for on-line production control

Dispatching rules for on-line production control consist of the machine selection rule for job and the operation sequence rule for each machine. In this paper, the machine selection rule is focused on. It is reported in previous researches that 2 machine selection rules; the ECT (Earliest Completion Time) rule and the BWL (Balanced Work Load) rule perform well for high production efficiency. ECT is a rule to assign jobs to the machines which can complete their operations in the earliest time. BWL is a rule to assign jobs to machines with the aim of balancing machines' workloads. We analyze the difference between ECT and BWL in production efficiency by using the queuing theory. As a result, BWL is proved to be more efficient than ECT when the production workload is high and the difference of processing speeds among machines is large. Moreover, we propose a function to switch the machine selection rules by considering the machine workload and the processing speed difference among machines. It is confirmed that the function is effective on shortening jebs' lead-lime (LT).