Robustness of state-dependent queues and material handling systems

This article may be used for research, teaching and private study purposes. Any substantial or systematic reproduction, redistribution , reselling , loan or sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material. In many factory settings, performance modeling and optimisation of material handling systems (MHS) is a complex problem. State-dependent queueing models are effective and robust tools to capture this traffic congestion. The integration of state-dependent models of the material handling elements and finite queueing models of work stations is demonstrated. An important property of the state-dependent models when used to model the material handling elements is that they appear to be insensitive to the input distribution. Numerous topological network design (TND) problems and experiments are presented to show the effectiveness of state-dependent queueing models for TND/MHS design. 1. Introduction In many factory settings as well as service situations, individual workstations (machines i) are interconnected with a material handling system (e.g., accumulating conveyors, people, carts, lift trucks, etc.) in order to buffer the machines and accommodate the transfer or travel time of products and materials between machines and workstations. How one should capture these time delays and congestion and at the same time develop performance measures for throughput, work-in-process, cycle time, as well as utilisation, is the focus of this paper.