| Three essays are presented concerned with device dispatching within the framework provided by trip-based material handling systems, which represent a wide range of systems such as lift trucks and unit load automated guided vehicles in industrial applications and patient movement systems in healthcare applications. The move requests (MRs) arrive according to a Poisson process, and each MR is served, one at a time, by one of the devices, according to the dispatching rule. In the first essay, a new analytic model is developed to estimate empty device travel with multiple devices operating under the modified first-come-first-served (Mod-FCFS) dispatching rule. The analytic technique used in the first essay is extended in the second essay to develop a new analytic model to estimate empty device travel with multiple devices operating under the shortest-travel-time-first (STTF) rule, which is a simple, well-known, and efficient rule but difficult to model analytically. To our knowledge, the analytic model in the second essay is the first model to explicitly estimate empty device travel under STTF. Using simulation, we show that both models perform well in estimating empty device travel and the expected device utilization. We also investigate the MR wait times under STTF, and propose a new rule, namely B-STTF, to avoid excessive wait times which are known to occur under STTF. The results show that B-STTF is as efficient as STTF while successfully avoiding excessive MR wait times.;In the third essay, we model intra-facility patient movement systems as a trip-based material handling system, where a "device" represents a patient mover (PM), and each "MR" represents a patient. Using simulation, we study the performance of the patient movement system as a function of the dispatching rule and the number/location of the equipment marshalling areas (that is, wheelchairs, gurneys, and closets). System performance is measured in terms of efficiency (i.e., reducing empty travel for the PMs and the expected MR wait times) and effectiveness (i.e., avoiding excessive wait times for the MRs). We observe that the FCFS dispatching rule is less efficient but it avoids excessive patient wait times since the MRs are served according to their order of arrival. In contrast, the STTF rule is efficient but some patients experience excessive wait times, which is detrimental. We thus present a new rule that strikes a balance between efficiency and effectiveness. We also analyze the impact of the number and location of the equipment marshalling areas. We observe that carefully planning the number and location of the marshalling areas based on usage by the PMs can improve the performance of the system as much as, if not more than, a more efficient dispatching rule. |
