Peter Schuur

ON A MEDIUM TERM PRODUCT RECOVERY AND DISPOSAL STRATEGY FOR DURABLE ASSEMBLY PRODUCTS

The introduction of extended producer responsibility makes original equipment manufacturers formally responsible for take-back, recovery and reuse of discarded products. One of their key problems is to determine to what extent return products must be disassembled and which recovery and disposal options should be applied. On a tactical management level, this involves anticipating problems like meeting (legislative) recovery targets, limited secondary end markets and investments in recycling infrastructure. In this paper, a comprehensive model is presented, which determines an optimal product recovery and disposal strategy for one product type. The objective function takes into account technical, commercial and ecological criteria as well as uncertainty on these criteria due to lack of information, in particular regarding the quality level. Optimization is done on overall net profit and occurs using a two-phased DPalgorithm. The applicability of the model is shown in a case study.

Mathematical model for warehouse design and product allocation

The two primary functions of a warehouse include (1) temporary storage and protection of goods and (2) providing value added services such as fulfilment of individual customer orders, packaging of goods, after sales services, repairs, testing, inspection and assembly. To perform the above functions, the warehouse is divided into several functional areas such as reserve storage area, forward (order collation) area and cross-docking. The paper presents a mathematical model and a heuristic algorithm that jointly determine product allocation to the functional areas in the warehouse as well as the size of each area using data readily available to a warehouse manager.

Generic planning and control of automated material handling systems

This paper discusses the problem to design a generic planning and control architecture for automated material handling systems (AMHSs). We illustrate the relevance of this research direction, and then address three different market sectors where AMHSs are used, i.e., baggage handling, distribution, and parcel & postal. The research in this paper is heavily motivated by a collaboration between the authors and a major global company supplying AMHSs. We analyze requirements from practice for a generic control architecture, and then review the literature to investigate whether these practical requirements have been met. From this confrontation of theory with practice, we conclude that many practical issues are not yet covered in the current literature. We take the initiative to define a research direction in concrete terms, pinpoint problems to work on, and propose an agenda for future research. Moreover, we take a step to propose a concept control architecture.

On-line scheduling of multi-server batch operations

The batching of jobs in a manufacturing system is a very common policy in many industries. The main reasons for batching are the avoidance of setups and/or facilitation of material handling. Good examples of batch-wise production systems are the ovens that are found in the aircraft industry and in the manufacture of semiconductors. These systems often consist of multiple machines of different types for the range and volumes of products that have to be handled. Building on earlier research in the aircraft industry, where the process of hardening synthetic aircraft parts was studied, we propose a new heuristic for the dynamic scheduling of these types of systems. Our so-called look-ahead strategy bases its decision to schedule a job on a certain machine on the availability of information on a limited number of near future arrivals. The new control strategy distinguishes itself from existing heuristics by an integrated approach that involves all machines in the scheduling decision, instead of only considering idle machines. It is shown by an extensive series of simulation experiments that the new heuristic outperforms existing heuristics for most system configurations. Especially in the case of complex systems, where multiple products have to be handled by non-identical machines, the new heuristic proves its value as a practical scheduling tool. Important insight is obtained with regard to the relation between the system is configuration and its performance.

Dynamic job assignment heuristics for multi-server batch operations - A cost-based approach

In many industries production facilities are used which process products in a batch-wise manner. Guided by research in the aircraft industry, where the process of hardening synthetic aircraft parts was studied, we propose a new control strategy for these types of systems. Given the availability of information on a few near future arrivals the strategy decides on when to schedule a job in order to minimize logistical costs. The fact that different cost structures can be incorporated, makes it a valuable tool for use in practical situations in business. The potential of the new strategy is demonstrated by an extensive series of simulation experiments, in which its response for various system configurations was tested in comparison with existing heuristics.

Network Design in Reverse Logistics: A Quantitative Model

The introduction of (extended) producer responsibility forces Original Equipment Manufacturers to solve entirely new managerial problems. One of the issues concerns the physical design of the reverse logistic network, which is a problem that fits into the class of facility-location problems. Since handling return flows involves a lot of different processing steps, the physical system might consist of two or more echelons. In this paper, a MILP-model is presented that gives decision support in designing the physical network structure of a multi-echelon reverse logistic system. The model is applied to a case from the automotive industry. The general applicability of the model in logistic network design is discussed. Finally, subjects for further research are pointed out.

Covering a rectangle with six and seven circles

In a recent article (Heppes and Melissen, Period. Math. Hungar. 34 (1997) 63–79), Heppes and Melissen have determined the thinnest coverings of a rectangle with up to five equal circles and also for seven circles if the aspect ratio of the rectangle is either between 1 and 1.34457…, or larger than 3.43017… . In this paper we extend these results. For the gap in the seven circles case we present thin coverings that we conjecture to be optimal. For six circles we determine the thinnest possible covering if the aspect ratio is larger than 3.11803… . Furthermore, for six and seven circles, we give thin coverings for the remaining range of values, thereby extending our previous conjecture for the square (Melissen and Schuur, Electron. J. Combin. 3 (1996) R32). [6].

Design and evaluation of a simulation game to introduce a Multi-Agent system for barge handling in a seaport

Multi-Agent systems have been studied extensively, but only a few of these systems are deployed in practice. Essential to get a system implemented is acceptance. In a distributed setting this is challenging, especially when one deals with multiple independent and competing companies. We share our experiences with the use of a real-time multi-player simulation game that we developed to illustrate a Multi-Agent system for the barge handling problem in the Port of Rotterdam. We experienced that the game has many advantages over a more passive approach, such as vocal presentations. We conclude that the game has considerably contributed to the acceptance of the illustrated Multi-Agent system.

Look-ahead strategies for dynamic pickup and delivery problems

In this paper we consider a dynamic full truckload pickup and delivery problem with time-windows. Jobs arrive over time and are offered in a second-price auction. Individual vehicles bid on these jobs and maintain a schedule of the jobs they have won. We propose a pricing and scheduling strategy based on dynamic programming where not only the direct costs of a job insertion are taken into account, but also the impact on future opportunities. Simulation is used to evaluate the benefits of pricing opportunities compared to simple pricing strategies in various market settings. Numerical results show that the proposed approach provides high quality solutions, in terms of profits, capacity utilization, and delivery reliability.

Order oriented slotting: a new assignment strategy for warehouses

This paper deals with a new strategy for the assignment of Stock Keeping Units (SKUs) to storage locations in a warehouse, called Order Oriented Slotting (OOS). Given an empty warehouse, a set of orders to be picked and a routing policy, OOS stores the SKUs in such a way that the total time needed to pick all the orders is minimised. Unlike the Cube per Order Index (COI) slotting strategy which stores an item based on how frequently it is picked without regard to picking sequences, OOS aims to store items, that appear together in orders, close to each other. OOS can be formulated as an Integer Linear Programming model when the routing is S-shaped and when a Vertical Lift Module (VLM) is adopted. Given the computational complexity of the problem, we present several heuristics. Their performance is compared through a set of VLM test problems with different order characteristics. [Received 7 November 2006; Revised 17 March 2007; Accepted 18 May 2007]