http://repub.eur.nl/res/aut/2452/ List of Publications en http://repub.eur.nl/static-eur/img/logo.png http://repub.eur.nl http://repub.eur.nl/res/pub/20308/ 2010-02-01T00:00:00Z is paper studies the performance of static and dynamic scheduling approaches in vehicle-based internal transport (VBIT) systems and is one of the first to systematically investigate under which circumstances, which scheduling method helps in improving performance. In practice, usually myopic dispatching heuristics are used, often using look-ahead information. We argue more advanced scheduling methods can help, depending on circumstances. We introduce three basic scheduling approaches (insertion, combined and column generation) for the static problem. We then extend these to a dynamic, real-time setting with rolling horizons. We propose two further real-time scheduling approaches: dynamic assignment with and without look-ahead. The performances of the above five scheduling approaches are compared with two of the best performing look-ahead dispatching rules known from the literature. The performance of the various approaches depends on the facility layout and work distribution. However, column generation, the combined heuristic, and the assignment approach with look-ahead consistently outperform dispatching rules. Column generation can require substantial calculation time but delivers very good performance if sufficient look-ahead information is available. For large scale systems, the combined heuristic and the dynamic assignment approach with look ahead are recommended and have acceptable calculation times. http://repub.eur.nl/res/pub/8129/ 2006-11-28T00:00:00Z This paper studies the performance of static and real-time scheduling approaches in vehicle-based internal transport (VBIT) systems, which can be found in manufacturing and warehouse facilities. We propose three heuristic approaches for static VBIT problems (insertion, combined and column generation), extend them to a dynamic, real-time setting and compare their performance over a rolling time horizon. This time horizon can be seen either as a fixed-time interval in which advance information about loads’ arrivals is available, or as a fixed number of loads which are known to become available in the near future. We also propose two dynamic assignment approaches: with and without look-ahead, respectively. Performance (primarily average load waiting time) of the above five dynamic scheduling approaches is compared with two nearest-vehicle-first rules (with and without look-ahead), which are the best vehicle dispatching rules known from literature and which are commonly used in practice. Experimental results show that, if sufficient prior information is available, our dynamic scheduling approaches consistently outperform vehicle dispatching rules. Results also reveal that guide-path layout, load arrival rate and variance, and amount of load pre-arrival information have strong impacts on the performance of vehicle control approaches. Column generation or the combined heuristics are recommended in small or medium-scale VBIT systems, whereas for large scale VBIT systems, both the combined heuristic and the dynamic assignment approach with look ahead perform best. http://repub.eur.nl/res/pub/11875/ 2006-05-16T00:00:00Z This paper presents a review on design and control of automated guided vehicle systems. We address most key related issues including guide-path design, determining vehicle requirements, vehicle scheduling, idle-vehicle positioning, battery management, vehicle routing and deadlock resolution. We discuss and classify important models and results from key publications in literature, including often-neglected areas, such as idle-vehicle positioning and battery management. In addition, we propose a new dispatching-rule classification, a framework for design and control of automated guided vehicle systems, and suggest some fruitful research directions. http://repub.eur.nl/res/pub/6554/ 2005-04-21T00:00:00Z Tuan Le Anh was born in Hanoi, Vietnam (1973). He studied electrical engineering at the Hanoi University of Technology and received his bachelor and master degrees in electrical engineering in 1995 and 1997. In 1998, he got his postgraduate diploma in industrial engineering from the Asian Institute of Technology. In 2000, he received his master degree (with great distinction) in industrial management at the Catholic University of Leuven with the thesis on applying heuristics to solve multi-item single-level capacitated lot-sizing problems. From 2001, he started his Ph.D research at the RSM Erasmus University(formerly Rotterdam School of Management/ Erasmus University Rotterdam). His Ph.D research focuses on the operational control of vehicle-based internal transport systems, which has resulted in a number of published (or forthcoming) articles in international scientific journals such as Journal of Operations Management, International Journal of Production Research and European Journal of Operational Research. He has also given presentations on his research in several international conferences in both Europe and North America. http://repub.eur.nl/res/pub/11872/ 2005-04-15T00:00:00Z On-line vehicle dispatching rules are widely used in many facilities such as warehouses and manufacturing facilities to control vehicles' movements. Single-attribute dispatching rules, which dispatch vehicles based on only one parameter, are usually used. However, multi-attribute dispatching rules prove to be better in general. In this paper, we study the impact of reassigning moving vehicles on some good dispatching rules, both single- and multi-attribute, in the literature. Results suggest that reassigning moving-to-park vehicles has a significant positive effect on reducing the average load waiting time. We evaluate the dispatching rules' performance using the experimental design of a real-life case study. The performance criteria are: minimizing the average load waiting time, keeping the maximum load waiting time as short as possible and utilizing better vehicles. The results show that the combined dispatching rules which integrates multi-attribute dispatching and vehicle reassignment yields the best performance overall. http://repub.eur.nl/res/pub/1809/ 2004-11-19T00:00:00Z Internal transport systems using automated guided vehicles (AGVs) are widely used in many facilities such as warehouses, distribution centers and transshipment terminals. Most AGV systems use online dispatching rules to control vehicle movements. In literature, there are many types of dispatching rules such as single- and multi-attribute dispatching rules. However, a dispatching rule that is good for all cases does not exist. In this research, we study a specific type of AGV environments which has not received much attention from researchers - AGV systems with many vehicles as can be seen in airport baggage handling systems. We propose two new multi-attribute dispatching rules for this type of environment and compare their performance with that of two of the best dispatching rules in literature. Using simulation we show that the new multi-attribute dispatching rules are robust and perform very well. http://repub.eur.nl/res/pub/1452/ 2004-08-06T00:00:00Z In this paper, we study the problem of scheduling and dispatching vehicles in vehicle-based internal transport systems within warehouses and production facilities. We develop and use two rolling horizon policies to solve real-time vehicle scheduling problems. To solve static instances of scheduling problems, we propose two new heuristics: combined and column-generation heuristics. We solve a real-time scheduling problem by applying a heuristic to dynamically solve a series of static instances under a rolling horizon policy. A rolling horizon can be seen either as a fixed-time interval in which advance information about loads’ arrivals is available, or as a fixed number of loads which are known to become available in the near future. We also propose a new look-ahead dynamic assignment algorithm, a different dynamic vehicle-scheduling approach. We evaluate these dynamic scheduling strategies by comparing their performance with that of two of the best online vehicle dispatching rules mentioned in the literature. Experimental results show that the new look-ahead dynamic assignment algorithm and dynamic scheduling approaches consistently outperform vehicle dispatching rules. http://repub.eur.nl/res/pub/11871/ 2004-08-01T00:00:00Z Guided vehicles (GVs) are commonly used for the internal transportation of loads in warehouses, production plants and terminals. These guided vehicles can be routed with a variety of vehicle dispatching rules in an attempt to meet performance criteria such as minimizing the average load waiting times. In this research, we use simulation models of three companies to evaluate the performance of several real-time vehicle dispatching rules, in part described in the literature. It appears that there is a clear difference in average load waiting time between the different dispatching rules in the different environments. Simple rules, based on load and vehicle proximity (distance-based) perform best for all cases. The penalty for this is a relatively high maximum load waiting time. A distance-based rule with time truncation, giving more priority to loads that have to wait longer than a time threshold, appears to yield the best possible overall performance. A rule that particularly considers load-waiting time performs poor overall. We also show that using little pre-arrival information of loads leads to a significant improvement in the performance of the dispatching rules without changing their performance ranking. http://repub.eur.nl/res/pub/1323/ 2004-06-21T00:00:00Z This paper presents a review on design and control of automated guided vehicle systems. We address most key related issues including guide-path design, estimating the number of vehicles, vehicle scheduling, idle-vehicle positioning, battery management, vehicle routing, and conflict resolution. We discuss and classify important models and results from key publications in literature on automated guided vehicle systems, including often-neglected areas, such as idle-vehicle positioning and battery management. In addition, we propose a decision framework for design and implementation of automated guided vehicle systems, and suggest some fruitful research directions. http://repub.eur.nl/res/pub/1324/ 2004-06-21T00:00:00Z On-line vehicles dispatching rules are widely used in many facilities such as warehouses to control vehicles' movements. Single-attribute dispatching rules, which dispatch vehicles based on only one parameter, are used commonly. However, multi-attribute dispatching rules prove to be better in general. In this study, we introduce new dispatching rules and evaluate their performance compared to several good dispatching rules in literature, using the experimental design of a real case study. The performance criteria are minimizing the average load waiting time while keeping the maximum load waiting time as small as possible and better utilize vehicles. The experiments show that newly introduced hybrid dispatching rule yields the best performance overall.