1,721,094 research outputs found
An integrated approach to dynamic plant location and capacity planning
No full textWe consider a dynamic capacitated plant location problem in which capacities of opened plants are determined by acquisition and/or disposal of multiple types of facilities. We determine the opening schedule of plants, allocations of customers' demands and plans for acquisition and/or disposal of plant capacities that minimise the sum of discounted fixed costs for opening plants, delivery costs of products, and acquisition and operation costs of facilities. The dynamic capacitated plant location problem is formulated as a mixed integer linear program and solved by a heuristic algorithm based on Lagrangian relaxation and a cut and branch algorithm which uses Gomory cuts. Several solution properties of the relaxed problem are found and used to develop efficient solution procedures for the relaxed problem. A subgradient optimisation method is employed to obtain better lower bounds. The heuristic algorithm is tested on randomly generated test problems and results show that the algorithm finds good solutions in a reasonable amount of computation time
Capacity planning for phased implementation of flexible manufacturing systems under budget restrictions
No full textWe consider a problem of gradually replacing conventional dedicated machines with flexible manufacturing modules (FMMs) under budget restrictions over a finite planning horizon assuming that dedicated machines cannot be purchased during the planning horizon and acquired FMMs are kept until the end of the horizon. In the problem, a replacement schedule is to be determined and operations are to be assigned to the FMMs or the dedicated machines with the objective of minimizing the sum of discounted costs of acquisition and operation of FMMs and operation costs of conventional dedicated machines. In this research, the problem is formulated as a mixed integer linear program and solved by a Lagrangean relaxation approach. A subgradient optimization method is employed to obtain lower bounds of solutions and a multiplier adjustment method is devised to improve the lower bounds. We develop a linear programming-based Lagrangean heuristic algorithm to find a good feasible solution of the original problem in a reasonable amount of computation time. The algorithm is tested on randomly generated test problems and the results are reported. (C) 1998 Elsevier Science B.V
Plant location and procurement planning in knockdown production systems
No full textWe consider an integrated problem of plant location and capacity planning for components procurement in knockdown production systems. The problem is that of determining the schedule of opening components manufacturing plants, plans for acquisition of capacities in opened components manufacturing plants, and plans for components procurement in final assembly plants with the objective of minimizing the sum of fixed costs for opening plants; acquisition and operation costs of facilities, and delivery and subcontracting costs of components. The problem is formulated as a mixed integer linear program and solved by a two-stage solution procedure. In the solution procedure, the problem is decomposed into two tractable subproblems and these subproblems are solved sequentially. In the first stage, a dynamic plant location problem is solved using a cut and branch algorithm based on Gomory cuts, while a multiperiod capacity planning problem is solved in the second stage by a heuristic algorithm that uses a cut and branch algorithm and a variable reduction scheme. The solution procedure is tested on problems of a practical size and results show that the procedure gives reasonably good solutions
A new driving mechanism to allow a rescue robot to climb stairs
No full textThere have been numerous studies directed toward the development of driving mechanisms for off-road mobility and rescue robots. To achieve surveillance, reconnaissance, and rescue, it is necessary for robots to have a driving mechanism that can handle off-road environments. We propose a new type of single-track driving mechanism with a variable geometry for a rescue robot. This mechanism has a symmetric configuration so that the robot can advance in two directions and also remain operable when overturned. By transforming its geometry, the robot can reduce energy consumption in steering and rotating as well as maximize its ability to climb obstacles such as stairs. The robot is also designed to have a compact size and low center of gravity to facilitate driving when on a set of stairs. In this paper, we analyzed the design parameters of the robot for the four phases of climbing stairs and determined the specifications needed to enhance its adaptability
A due-date-based algorithm for lot-order assignment in a semiconductor wafer fabrication facility
No full textThis paper focuses on a lot-order assignment problem, called the pegging problem, in a semiconductor wafer fabrication facility. Pegging is a process of assigning wafer lots to orders for wafers. We consider two types of pegging strategies: hard pegging strategy, under which the lot-order assignment is not changed once lots are assigned to orders; and soft pegging strategy, under which the lot-order assignment can be changed during the production period. For the soft pegging strategy, we develop three operational policies and three algorithms for the pegging problem of assigning lots to orders with the objective of minimizing total tardiness of the orders. To evaluate performance of the suggested policies and algorithms, we perform simulation experiments using real factory data as well as randomly generated data sets. Results of the simulation tests show that the repegging policies and the algorithms operated under the soft pegging strategy give better results than the hard pegging strategy
Due-date based scheduling and control policies in a multiproduct semiconductor wafer fabrication facility
No full textThis paper focuses on lot release control and scheduling problems in a semiconductor wafer fab producing multiple products that have different due dates and different process flows, For lot release control, it is necessary to determine the type of a wafer lot and the time to release wafers into the wafer fab, while it is necessary to determine sequences of processing waiting lots in front of workstations for lot scheduling. New dispatching rules are developed for lot release control and scheduling considering special features of the wafer fabrication process. Simulation experiments are carried out to test the dispatching rules, Results show that lot release control and lot scheduling at photolithography workstations are more important than scheduling at other workstations, Also, it is shown that new dispatching rules work better in terms of tardiness of orders than existing rules such as the EDD (earliest due date) rule and other well-known dispatching rules for multimachine scheduling
Tool requirements planning in a flexible manufacturing system with an automatic tool transporter
No full textWe consider a tool requirements planning problem in a flexible manufacturing system with an automatic tool transporter. The problem considered here is that of determining the number of tool copies of each tool type with the objective of minimizing total tardiness of orders with distinct due dates for a given budget for tool purchase. For the problem, several heuristic algorithms are developed using greedy search methods and simulation. In the heuristic algorithms, the numbers of tool copies for certain tool types are increased until they cannot be increased any more because of the budget limit. Simulation results are used to determine search directions or to select tool types of which the numbers of copies are to be increased. Computational experiments are performed on randomly generated test problems and results show that a good tool requirements plan can be obtained with the heuristic algorithms in a reasonable amount of computation time
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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