1.
Comparison of Deterministic and Stochatic Dispatching Policies in the Design
Phase of a Material Handling Network
Ardavan Asef-Vaziri
We compare the effectiveness and efficiency of alternative operational dispatching
policies that are integrated into the design phase of a circular material handling
network. Exact formulations describe the problem of optimal concurrent design of the
unidirectional loop track layout along with the locations of the pickup and drop-off
stations. The objective is to minimize the total loaded and empty vehicle trip distances,
which is the main driver of the fleet size of the vehicles. The two alternative operational
dispatching policies of first-come-first-served and shortest-trip-distance-first are
incorporated into optimization models. A primary interest of our work is to illustrate the
superiority of the deterministic shortest-trip-distance-first over the stochastic first-comefirst-
served when integrated into the design phase. We also show that optimization
under shortest-trip-distance-first in the design phase produces the best solution for the
first-encountered-first-served in the operation phase. The findings of the optimization
models in the design phase are supported by the outcomes of the simulation model in
the operation phase.
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2. Probabilistic Modeling and Alleviation of Congestion in a Facility Layout
Min Zhang, Rajan Batta, and Rakesh Nagi
Traditional facility layout research ignores workflow congestion and tends to focus on
distance-based transportation cost. Recently many authors have identified workflow
congestion as a major concern in a facility layout, yet few analytical models have been
proposed. This paper attempts to address this concern in the following way. First, we
formalize the concept of workflow congestion, which incorporates a variety of workflow
interruptions. We establish a probabilistic model for workflow interruptions and develop
a method for evaluating the expected travel time through an aisle. We then formulate
the facility layout problem as one for minimizing the total expected travel time, i.e., we
focus on alleviating workflow congestion. A solution approach based on “sliding
bottleneck paths” is presented along with an example and computational results.
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3. Optimizing Inbound and Outbound Door Assignments in Crossdocks
Yavuz A. Bozer and Hector J. Carlo
Crossdocks play a critical role in contemporary supply networks; they are used by many
transportation service providers and a number of manufacturing companies (or their
logistics providers) as a consolidation or re-distribution point. In this paper, assuming
that the assignment of inbound trailers to doors is optimized on a nightly basis, and that
the outbound trailers have permanent door assignments over a user-specified time
period (such as 60 days), we develop a simulated annealing-based heuristic procedure
to determine both inbound and outbound trailer-to-door assignments in order to
minimize the material handling effort expressed in flows times rectilinear distances. The
proposed heuristic addresses forklift congestion as well as the robustness of the
solutions in a “worst case” sense. The latter concern comes into play since all work at
the crossdock must be completed overnight. The heuristic is tested using three
internally generated sets of flow data for a 32-door rectangular crossdock with
alternative shapes in order to examine the relationship between crossdock shape and
the material handling effort. The study was conducted in collaboration with Con-Way
Transportation Services, Inc. and a major crossdock the company operates.
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4. Integration of Flow-Based Department Formation into Facility Layout Design
Junjae Chae and Brett A. Peters
The design of facility layout takes into account a number of issues including the
formation of departments, the layout of these, the determination of the material handling
methods to be used, etc. To achieve an efficient layout, these issues should be
examined simultaneously. However, in practice, these problems are generally
formulated and solved sequentially due to the complicated nature of the integrated
problem. Specially, there is close interaction between the formation of departments and
layout of these departments. These problems are treated as separate problems that are
solved sequentially. This procedure is mainly due to the complexity of each problem
and the interrelationships between them. In this paper, we integrate flowbased
department formation and layout into a comprehensive mathematical model intended to
determine assignment of manufacturing components to departments, number and
dimension of departments, and location of departments within the floor space, and
develop appropriate solution procedure. Complicating department area constraints are
linearized to allow solution with general purpose optimization software.
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5.
A Consistent Approach for Vehicle Planning and Control in Large Unified
Automated Material Handling Systems
Jairo R. Montoya-Torres, Stéphane Dauzère-Pérès and Leon Vermariën
This paper focuses on the analysis of transport strategies in Automated Material
Handling Systems (AMHS) for the semiconductor industry. A difference against
previous work is that our approach takes into account the unified nature of inter-bay and
intra-bay load transport operations that limits the practical usefulness of former
research results. Since, in a unified AMHS, vehicles can travel along the whole network
path to deliver loads directly from one machine to another without passing by
intermediate storage, we propose a strategy that divides the network into zones and
assigns a fleet of vehicles to each zone in order to decrease the time needed to serve a
transportation request. The problem is addressed by means of a hierarchical tacticaloperational
decision making framework. This paper focuses on the analyzing the
consistency between the tactical level, for which the problem of vehicle distribution is
addressed using integer linear programming, and the operational level, where
discreteevent simulation is used.
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6. Makespan Minimization at Aalsmeer Flower Auction
René de Koster and Mengfei Yu
Teamwork has been demonstrated as an effective tool to improve productivity in
industrial environments. However, few distribution centers in Western Europe apply the
concept. No flower auction uses teamwork. At Bloemenveiling Aalsmeer (VBA), about
19 million flowers have to be distributed daily to customer trolleys in a building of 1
million m2 within a few hours. With the increasing daily number of customer orders, the
distributor congestion in the main distribution area increases, leading to decreasing
worker productivity, more work stress, and higher laborer turnover. As a consequence,
the makespan exceeds the available time and flowers arrive too late in the customer
aisles. This paper investigates a teamwork concept based on warehouse zoning, in
which distributors work as a team for a fixed group of customers. Customers are
assigned to aisles to minimize congestion. We show by simulation that zoning with
teamwork indeed reduces congestion and leads to considerable improvements in both
makespan and transaction lead time.
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7. Earliest Completion Rule: An Alternative Order Sortation Strategy
Fahrettin Eldemir and Charles J. Malmborg
One of the most important operational issues in Order Accumulation and Sortation
Systems is the assignment of orders to the accumulation lanes that is also called
sortation strategy. There are several sortation strategies available. Sortation strategies
can be grouped into two families, fixed priority rules and dynamic assignment rules. In
this research an alternative sortation strategy in the dynamic assignment category and
a sortation time model for this rule are developed. The new rule called Earliest
Completion Rule. Earliest Completion Rule is compared with the existing sortation
strategies for different sortation scenarios. It has been observed that great savings can
be achieved in total sortation time by using Earliest Completion Rule.
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8. Availability Modeling of Powered Roller Conveyors
John R. English, John Usher, G. Don Taylor and Ed Pohl
This paper provides an analysis of the reliability and availability of two common designs
of the line-shaft roller conveyor. The first is a standard design in which each roller is
belted directly to a spinning line shaft under the conveyor. The second is a new design
in which only one top roller is belted to the line shaft, and all other rollers are belted to
the one powered roller in a series arrangement. The main reason for this design is that
the upper belts are faster to replace than belts connected to the line shaft, thus
increasing system availability. However, the latter design is less reliable in that the
failure of a single belt may lead to multiple roller failures. In this paper we expand upon
previous work of English, Usher, and Mendoza [4] that focused on the inherent
reliability differences in the two designs, and analyze the availability aspects by
considering failure and repair rates. Our analysis results in specific design
recommendations for a variety of operational parameters.
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9. On Inventory Control with Inventory Supermarket
Liam Cahalane and Bill Ferrell
This research focuses on control of the push-pull boundary that is commonly found in
modern production facilities. In this case, there are three stages: 1) a large, off-site
warehouse that is supplied raw materials using a classic push system, 2) a small area
within the building that houses the production operation that is supplied by the large
warehouse and supplies the production operation, and 3) the production operation that
is supplied from the small storage area using a pull system. A mathematical model of
this supply chain is modeled using mixed integer programming and the model is solved
for a number of scenarios in an effort to glean practical insights into efficient ways for
moving inventory thought this system.
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10.
Effects of a Decentral Control on the Performance of Part-To-Picker Order-
Picking Systems
Dr. Thorsten Schmidt and Guido Follert
Developments in the field of decentralized control are inducted through enhancements
of semiconductors as well as powered through demand of industry. Rapidly changing
requirements of the distribution industry and other users of material handling
equipment are worth developing adaptable systems for changing order or process
situations. As proven in an existing test field application at Dortmund University the
concept of decentralized control using RFID is ready to become reality. This paper
highlights the influences of decentralized control on a part-to-picker order picking
system with several miniload-aisles serving picking locations arranged in parallel. To
quantify the change in performance measures a discrete simulation is used.
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