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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ejor.2009.10.004 Byline: Marco Bijvank (a), Ger Koole (a), Iris F.A. Vis (b) Keywords: Inventory; Repair kit problem; Multi-period; Multi-item; Closed-form expression Abstract: Field services are a particular type of after-sales service performed at the customer's location where technicians repair malfunctioning machines. The inventory decisions about which spare part types to take to the repair site and in what quantities is called the repair kit problem. This problem is characterized by an order-based performance measure since a customer is only satisfied when all required spare parts are available to fix the machine. As a result, the service level in the decision making process is defined as a job fill rate. In this paper we derive a closed-form expression for the expected service level and total costs for the repair kit problem in a general setting, where multiple units of each part type can be used in a multi-period problem. Such an all-or-nothing strategy is a new characteristic to investigate, but commonly used in practice. Namely, items are only taken from the inventory when all items to perform the repair are available in the right quantity. We develop a new algorithm to determine the contents of the repair kit both for a service and cost model while incorporating this new expression for the job fill rate. We show that the algorithm finds solutions which differ on average 0.2% from optimal costs. We perform a case study to test the performance of the algorithm in practice. Our approach results in service level improvements of more than 30% against similar holding costs. Author Affiliation: (a) VU University Amsterdam, Faculty of Exact Sciences, Department of Mathematics, De Boelelaan 1081a, 1081 HV Amsterdam, The Netherlands (b) VU University Amsterdam, Faculty of Economics and Business Administration, Department of Information Systems and Logistics, De Boelelaan 1105, Room 3A-31, 1081 HV Amsterdam, The Netherlands Article History: Received 11 August 2006; Accepted 10 October 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ejor.2005.01.030 Byline: Ger Koole, Auke Pot Keywords: Dynamic programming; Re-entrant lines; Power series algorithm; Curse of dimensionality Abstract: This paper is concerned with workload minimization in re-entrant lines with exponential service times and pre-emptive control policies. Using a numerical algorithm called the power series algorithm we obtain nearly optimal policies for systems with up to 8 queues. We also improve considerably the implementation of the power series algorithm. Author Affiliation: Vrije Universiteit, De Boelelaan 1081a, 1081 HV Amsterdam, The Netherlands Article History: Received 11 June 2003; Accepted 14 January 2005

The problem of scheduling repairs of faulty components is addressed using two maintenance models, a warm standby model and a cold one. Both have the same number of parallel groups of identical parts with exponentially distributed times to failure. To obtain optimal repairman assignment, it is demonstrated that the repairman should be assigned to the faulty component in the group with the least number of functioning parts.