1.
Workload Balancing Based Warehouse Management In a Central European Distribution Center
Jalal. Ashyeri & R.C. de Booy
This paper describes the potential effects of workload balancing based warehouse
management in a central European Distribution Center (EDC) located in the
Netherlands by considering the warehouse as a multiple shop manufacturing system.
The paper studies the effect of different storage allocation, picking capacity provision,
and order release decisions on the responsiveness of the EDC. The objective is to
speed up workflow by reducing the order picking time and cutting on major cost
components of order fulfillment, while balancing the workload among different sections
of the EDC, and across all working shifts. The paper applies workload balancing
optimization concepts used in manufacturing environments to measure the operational
performance of a distribution center. A framework is proposed that tests and evaluates
several policies to determine how the greatest savings can be achieved relative to the
current policies. Sensitivity analyses are completed to examine the effect of storage
space and order picking manpower allocations on the performance of the EDC. Results
show great workforce savings and improvement in responsiveness. This case study
adds to the available literature by illustrating that the use of simple workload balancing
methodologies can be effective in warehouse operations management and have great
potentials to be included in the Warehouse Management Systems (WMS).
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2.
Increasing Rack Feeder Performance
Mathias Bachmayer, Michael Schipplick, Willibald A. Günthner and Heinz Ulbrich
Elasticity in industrial machinery has become more and more important for control
design, especially since achieving higher machine dynamics at constant or even better
precision and energetic efficiency has become essential for the manufacturers’ success
on the market. Therefore numerical optimization approaches as well as an analytical
feed forward control for linearly actuated robots like placement machines or rack
feeders is presented. These methods help to reduce the time required for positioning in
dynamic automation scenarios where the structure’s elasticity is essential for achieving
high positioning precision in a minimum of time.
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3. Optimizing a Dynamic Order-Picking Process
Yossi Bukchin, Eugene Khmelnitsky, Pini Yakuel
This research studies the problem of batching orders in a dynamic, finite-horizon
environment to minimize tardiness & overtime costs. The problem introduces the
following trade-off: at every period, the picker has to decide whether to go on a tour and
supply the orders accumulated so far, or to wait for more orders to arrive. By waiting,
the picker risks higher tardiness of existing orders for the potential lower tardiness of
future orders. We use a Markov Decision Process (MDP) based approach to set an
optimal decision making policy. In order to evaluate the potential improvement of the
proposed approach in practice, we compare the optimal policy with two naive heuristics:
1) “Go on tour immediately after an order arrives”, and, 2) “Wait as long as the current
orders can be picked and supplied on time”. The optimal policy shows a considerable
improvement, ranging from 1%-1300%, depending on the picking process parameters.
Moreover, we discover that one measure, the slack percentage of the picking process,
associated with the difference between the promised lead time and the single item
picking time, predicts quite accurately the cost reduction generated by the optimal
policy. Results indicate that the difference between the optimal solution and the best
naive heuristic increases with the value of the slack. Since a large slack is associated
with a low cost environment, we suggest that the proposed approach is mostly effective
in a medium slack size.
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4. Routing New Types of Stacking Crane Configurations at Container Terminals
Hector J. Carlo and Iris F.A. Vis
The containerized trade market is growing rapidly with the uprising of the Far East.
Container ports worldwide should be responsive by developing tools to handle these
massive volumes of containers in order to retain their level of competitiveness. One of
the areas in a container terminal that is highly affected by the increase in the demand of
containers is the storage yard or stack. The stack is used to temporarily store
containers upon further transport to their destination. This study is concerned with
scheduling sea and land-side storages and retrievals in a stack with two ASCs working
in a single block. We examine different types of two-ASC technologies. Heuristics can
be applied to route the ASCs through the stack to handle all requests. In this paper, we
compare the performance of both concepts to single ASC. As main performance
measure we use the total time required to handle all storage and retrieval requests at
both the sea and land-side of the stack.
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5.
An Algorithm for Integrated Facility Layout and Material Handling System Design in
Semiconductor Fabrication Facilities
Junjae Chae and Moonsu Lee
Semiconductor manufacturing has drawn the attention of global manufacturing
industries and it will continue to increase in importance as the demand for integrated
circuits (ICs) increases. Many fabrication facilities (fabs) have been built and more are
planned throughout the world. Facility design and material handling system design are
two major design issues for the efficient operation of a fab. The interactions between
the material handling system and facility layout are widely known. Integration of facility
layout design with material handling system design hopes to achieve an effective fab
that reduces material handling costs, improves system performance, and justifies a
costly long-term investment.
In this study, an algorithm with a shortcut design procedure is proposed to solve the
layout and material handling system design integration problem. The number of
shortcuts is one of the decision variables to be determined during layout configuration.
The algorithm generates a favorable layout with an efficient shortcut design for fabs that
have a bay layout arrangement with a central spine-based material handling system.
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6.
The Applicability of Data Envelopment Analysis to the Benchmarking of Container
Terminals
Rene de Koster, B.M. Balk and W. Van Nus
Many papers have appeared recently on container terminal benchmarking, based on
public data, using Data Envelopment Analysis. This paper compares some of the recent
benchmarking studies, compares them with own results based on primary data of large
terminals obtained from APM and PSA and shows that results differ strongly. There are
several causes for these differences: (1) inaccuracy of the public data used, (2) studies
in literature compare different terminal types, (3) terminals of different scale are
compared, and (4) terminals are mixed with orts. In practice, companies use mainly
ratio scales as DEA studies exclude some vital variables influencing performance. It
therefore only leads to partial insight and does not really help to improve performance.
We conclude that DEA may be appropriate for container terminal benchmarking, but
only if better quality and additional input and output data can be obtained. In its
application, the analysis should be controlled for terminal types.
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7. Effective Material Flow for Assembly Operations
Kimberly P. Ellis, Russell D. Meller, Joseph H. Wilck, IV, Pratik J. Parikh and
Franky Marchand
Effective material flow in an assembly facility leads to reduced material handling costs
and increased productivity. This research focuses on improving the flow of materials for
an assembly facility that receives supplied parts through receiving docks and transfers
the parts to material storage locations and then to part usage locations. The locations of
the receiving docks, storage locations, and line locations are predetermined, but the
assignment of parts to dock locations and storage locations and the material flow paths
through the facility are decision variables. Furthermore, design decisions like the dock
strategy employed and the configuration of the storage areas lead to additional decision
variables. The goal is to reduce overall material handling costs by effectively receiving,
storing and transferring the material from loading docks to line locations. To accomplish
this goal, material flow decision models and solution approaches are developed and
used to analyze material flow for a Volvo truck assembly facility in Dublin, VA. The
contribution of our research is in applying multi-commodity network flow models that
integrate many of the subproblems that are assumed to be solved a priori in many
existing models. This integrated approach was used to evaluate configuration changes
for the facility. One of the scenarios analyzed showed an improvement in the material
handling costs of nearly 10% as compared to current practices.
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8. A Statistical Process Control Approach to Monitoring Inventory Accuracy
John English, Long Yu, Manuel Rossetti, Nebil Buyurgan
when on-hand inventories don’t match recorded inventories, time is spent rectifying
observed problems. Even though the activities, which span corrections to the data base
to expedited replenishment, demand resources to rectify human error, they are
necessary to satisfy customer expectations. If the inventory accuracy is poor, tangible
costs (e.g., the loss of customer good-will) are realized. Cycle counting is a proven
methodology used to monitor inventory accuracy on a continuous basis. It requires that
items kept in inventory be counted periodically to ensure an accurate inventory. This
approach requires 100% inspection of all stock keeping units maintained in inventory on
a periodic basis. This work demonstrates the effectiveness of a statistical process
control (SPC) approach to monitoring inventory accuracy as an alternative to cycle
counting. The benefit of such an approach is that random samples are utilized in lieu of
100% inspection. In this research, we document the unique statistical properties of
inventory scenarios found in large retail/warehousing environments. The robustness of
SPC, specifically the p chart, in these environments is measured through computer
simulation and resulting probabilities of Type I and II errors are presented.
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9. Increasing Profits Through Superior Distribution Decisions
Bill Ferrell, Jr. and Priyantha Devapriya
Distribution costs are frequently a very large component in the overall cost of a product.
Many companies that supply products to retail facilities own and operate distribution
centers as well as make the decisions on the mode of transportation for all deliveries. In
the very common case where demand is random and lead times are short, the shipping
decision is quite often to have all but the largest orders shipped by less than truckload
carriers. While this decision is very sound relative to meeting promised delivery dates, it
is also rather expensive and can be a significant contributor to the overall distribution
costs. In this research, we investigate some alternative strategies that can reduce costs
a meaningful amount and that can be easily implemented within the current federal
regulations and operating policies of many trucking companies.
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10.
Evaluation of Routing Strategies for Decentralized Self-Organization in Large Scale
Conveyor Systems
Guido Follert and Moritz Roidl
Decentralized self-organization of dynamic activities in the field of materials handling
raises another level of complexity in the material flow control mechanisms. It is
essential to provide a systematic approach to those new control mechanisms by means
of modeling and deduction. We present an approach for modeling the routing problem
in material flow networks with a graph based model. Moreover the elementary algorithm
of Dijkstra for finding shortest paths is subsequently adapted to the requirements of
decentralized routing. Several of those strategies deduced from Dijkstra are applicable
to various problems in decentralized routing. Additionally, the graph model is integrated
into a material flow simulation suite. This enables the direct comparison between
classical centralized material flow control and the decentralized multiagent-based
control.
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