| The purpose of this dissertation is to compare the performance of the pull release mechanisms employed in a mixed/multi model flow line, where the line has a shifting bottleneck depending on the product mix. Only pull release mechanisms that have a single-control loop are evaluated. Specifically, there are three release mechanisms evaluated in this study. One mechanism that is incorporated in the study is CONWIP, which maintains a constant WIP level throughout the line by having the pulling point located at the last station of the line. The other two release mechanisms are adapted from the concept of drum-buffer-rope (DBR) and is applicable to a line with a shifting bottleneck. These latter two mechanisms are labeled pull-from-bottleneck (PFB) and pull-from-last-bottleneck (PFLB). PFB dynamically adjusts the pulling point according to the current bottleneck, while PFLB has the pulling point at the bottleneck closest to the end of the line. The performance measure used in the study is the average cycle time required to process a given number of units of multiple products. The dissertation examines the relative performance of release mechanisms under various possible environments, including variations in the amount of control WIP in the pull loop, the amount of protective capacity, variation in processing time, and variation of the frequencies of machine breakdowns. In order to provide valid and unbiased comparisons, the study compared the average cycle time of the release mechanisms at the same level of average WIP in the system.;The dissertation shows that generally PFB is the best release mechanism, PFLB is the second best release mechanism and CONWIP is the lease effective release mechanism. The study also illustrated that the extent to which the performance of a given release mechanism differs from the others is affected by the structure of the production line. Specifically, the performance of the mechanism differs depending on the amount of protective capacity and the amount of control WIP in the pull loop. |
