Research projects by Kees Jan Roodbergen

Kees Jan Roodbergen: "The focus of my research has been aimed mainly at logistic processes within the nodes of a supply chain, such as warehouses, container terminals and cross docking facilities. Several papers on these topics have been published in or accepted by international journals such as Operations Research, IIE Transactions and the European Journal of Operational Research. A recent new research interest concerns human factors in Operations Management and Logistics. Typically, humans are treated in logistics models as if they were replaceable equipment with a pre-determined performance. It is, however, generally understood that humans interact with the production system and have a major influence on system performance. A certain level of decision latitude may be highly appreciated by employees. Furthermore, there is variability between and within humans. It seems, therefore, vital to incorporate more human characteristics and behaviours in logistics models."

Order picking in warehouses

This topic has been one of my favorite themes. Order picking is the most crucial process in warehouses since it involves the retrieval of products to satisfy orders of customers. Any delays or errors in this process therefore directly impact the downstream supply chain and customer satisfaction. It is, however, a very complex problem to solve. Numerous aspects play a role such as (1) the layout of the order picking area, (2) determining good routes to visit all locations where a product must be picked, (3) determining the best storage location for each product, (4) possibilities to combine two or more customer orders into a single route, and (5) dividing the order picking area into smaller segments to distribute the work load over the available employees. My research has focused on the first three aspects. Most of my papers try to optimise or improve one of the aspects while keeping the other factors at a predetermined setting. Techniques used include dynamic programming, statistical performance estimation, and design of heuristics. New papers on this topic can be expected.

Scheduling of container storage and retrieval

We analyse the scheduling of jobs at a container terminal. Several containers need to be retrieved from the storage area to be loaded onto a ship or onto trucks. Other containers have just arrived and must be stored to wait for further transportation. Typically, there is a vehicle available in each section of the storage area to transport the containers to their destination. An algorithm is developed that finds the optimal solution in polynomial time for the sequencing of all transport requests. Accepted for publication in Operations Research.

Determining a layout for the order picking area in warehouses

The objective of this research is to minimise the average travel distance needed to pick an order or batch of orders by optimising the layout of the order picking area. We developed an analytical formula by which the average length of an order picking route can be calculated. This analytical formula is based on statistical properties of a commonly used routing method. Using the analytical formula for average travel distance as an objective function in a non-linear programming model, we can determine the optimal layout for a given situation. The model assumes that the required storage space, the probability distribution of the number of picks per route and the properties of the equipment are known. Equipment properties include for example centre-to-centre distance between aisles and the speed of the picking vehicle. Using these inputs we can determine the number of aisles, the number of cross aisles and the aisle length that minimise average travel distance. Accepted for publication in IIE Transactions.

Human aspects in operations management

Human aspects in operations management have long time been ignored by operation management decision making models either by assuming machine-like characteristics for humans and/or by neglecting "human welfare" objectives. Bourdreau et al. (2003) specify the commonly unrealistic assumptions found in Operations Management models: (1) people are not a major factor, (2) people are deterministic and predictable, (3) people are independent of other people, (4), people are stationary, (5) people are emotionless. The three main research themes of this project are: (a) Short-term economic goals versus ergonomic goals in order picking, (b) Incorporating safety and fatigue in work schedule design (rostering), (c) Optimising worker productivity and motivation through target setting. This project is carried out by José Larco.