The impact of free goods on the performance of drum-buffer-rope scheduling systems

The scheduling system theory of constraints (TOC) uses is often referred to as drum-buffer-rope (DBR). DBR systems operate by developing a schedule for the system's primary resource constraint. In TOC, any product that is not processed at the system's primary resource constraint is referred to as a free good. Because free goods do not use capacity at the primary resource constraint, very little attention is given to them under TOC literature. Based on simulation of a job shop operation, this study finds that the performance of DBR is very sensitive to changes in the levels of free goods released into the operation. Therefore, contrary to the way free goods have been treated in the past, schedulers using DBR need to be cognizant of how orders of these items are accepted and scheduled.