Performance evaluation of material handling vehicles operating in a closed-loop path.

摘要

Loop-based material handling systems provide simplicity and flexibility in a variety of applications, and have been the subject of past studies. In this study, we present two papers to evaluate the performance of trip-based material handling vehicles serving intermixed loading and unloading stations that are located around a unidirectional closed-loop path. We present analytical and simulation results to evaluate the throughput performance of the system, and the expected waiting times at the loading stations.; In chapter 2, given the location of the stations as well as the flow and routing data for the loads, assuming sufficient buffer capacities, we derive stability conditions for the material handling system to meet throughput when it consists of: (1) One uni-load vehicle; (2) Two uni-load vehicles (with blocking); (3) One multi-load vehicle; and (4) Two multi-load vehicles (with negligible blocking). Using simulation, we show that adding uni-load vehicles to a closed-loop of finite length reduces the number of loads moved per hour per vehicle, and may eventually reduce the overall throughput performance of the system. We also show that a system that consists of uni-load vehicles provides better throughput performance than a system with one multi-load vehicle with an equivalent load capacity.; In chapter 3, again assuming sufficient buffer capacities, we present analytical models to approximate the expected waiting times at the loading stations for a system with: (1) One uni-load vehicle; and (2) Two uni-load vehicles. Using simulation, we also show that a system that consists of uni-load vehicles results in lower expected waiting times than a system that consists of one multi-load vehicle with an equivalent load capacity. In chapter 4, we state our conclusions and present possible directions for future research.