Design of distributed layouts

Distributed layouts are layouts where multiple copies of the same department type may exist and may be placed in non-adjoining locations. In this paper, we present a procedure for the design of distributed layouts in settings with multiple periods where product demand and product mix may vary from period to period and where a relayout may be undertaken at the beginning of each period. Our objective is to design layouts for each period that balance relayout costs between periods with material flow efficiency in each period. We present a multi-period model for jointly determining layout and flow allocation and offer exact and heuristic solution procedures. We use our solution procedures to examine the value of distributed layouts for varying assumptions about system parameters and to draw several managerial insights. In particular, we show that distributed layouts are most valuable when demand variability is high or product variety is low. We also show that department duplication (e.g., through the disaggregation of existing functional departments) exhibits strong diminishing returns, with most of the benefits of a fully distributed layout realized with relatively few duplicates of each department type.     

Mitigation of risk in facility layout design for single and multi-period problems

The most desirable characteristic of a facility layout is its ability to maintain its efficiency over time while coping with the uncertainty in product demand. In the traditional facility layout design method, the facility layout is governed by the flow intensity between departments, which is the product flow quantity between departments. Hence, an error in the product demand assessment can render the layout inefficient with respect to material handling costs. Most of the research integrates uncertainty in the form of probability of occurrence of different from-to charts. In an environment where the variability of each product demand is independent, the derivation of ‘probabilistic from-to chart’ based scenario cannot be used to address uncertainty of individual demands. This paper presents an FLP (facility layout problem) approach to deal with the uncertainty of each product demand in the design of a facility layout. Two procedures are presented: the first procedure is utilised to assess the risk associated with the layout, while the second procedure is used to develop the layout that minimises the risk. Results from case studies have shown that the procedure produces a reduction of risk as high as 68%.     

Unequal-area stochastic facility layout problems: solutions using improved covariance matrix adaptation evolution strategy,particle swarm optimisation,and genetic algorithm

Determining the locations of departments or machines in a shop floor is classified as a facility layout problem. This article studies unequal-area stochastic facility layout problems where the shapes of departments are fixed during the iteration of an algorithm and the product demands are stochastic with a known variance and expected value. These problems are non-deterministic polynomial-time hard and very complex, thus meta-heuristic algorithms and evolution strategies are needed to solve them. In this paper, an improved covariance matrix adaptation evolution strategy (CMA ES) was developed and its results were compared with those of two improved meta-heuristic algorithms (i.e. improved particle swarm optimisation [PSO] and genetic algorithm [GA]). In the three proposed algorithms, the swapping method and two local search techniques which altered the positions of departments were used to avoid local optima and to improve the quality of solutions for the problems. A real case and two problem instances were introduced to test the proposed algorithms. The results showed that the proposed CMA ES has found better layouts in contrast to the proposed PSO and GA.     

Layout design in fractal organizations

Today's complex, unpredictable and unstable marketplace requires flexible manufacturing systems capable of cost-effective high variety–low volume production in frequently changing product demand and mix. In fractal organizations, system flexibility and responsiveness are achieved by allocating all manufacturing resources into multifunctional cells that are capable of processing a wide variety of products. In this paper, various fractal cell configuration methods for different system design objectives and constraints are proposed. These parameters determine the level of interaction between the cells, the distribution of different product types among the cells and the similarity of cell capabilities. A tabu-search-based method is proposed to optimize the product distribution to the cells and the arrangement of machines and cells on the shop floor. This optimization is performed for different fractal cell configuration methods and cell quantities. The quality of the resulting shop floor layouts is measured in terms of resource requirements and material movements. The results indicate that in fractal layouts, a trade-off is required between machine quantities and material travelling distance. It was generally possible to reduce travelling distances by increasing the degree of optimization on machine layout and product distribution for a specific product demand and mix.     

Multiple objective facility layout: a heuristic to generate efficient alternatives

Most multiple-objective approaches to solving the facility layout problem generate different layouts by varying the weights of the objectives using heuristic methods. It is possible, however, to generate the same layout using different weights. It is also possible that many efficient layouts will not be generated because it is not clear which weights would generate them. Furthermore, there may be some efficient layouts that cannot be generated regardless of what weights are used. In this paper we propose a heuristic algorithm for generating efficient layouts through pairwise interchange of departments. We show that if the decision maker's preferences for the selection of the best layout cannot be expressed as a linear utility function, it is essential to use other techniques such as the one developed in this paper, rather than weighting techniques, to generate efficient layouts. An example and some experiments are discussed.     

A hybrid approach for concurrent layout design of cells and their flow paths in a tree configuration

The layout design of multiple-cell automated manufacturing systems includes cell layout design and flow path layout design. Traditional layout methods often treat these two as separate problems and the sequence for solving them is usually cell layout first and flow path layout later. However, approaches of these kinds have one major drawback, that is, they may produce cell layouts that are awkward or difficult for designers to conduct flow path layouts, or cell layouts that do not turn out to be as good as expected after flow path layouts have been performed. Other drawbacks of traditional layout methods include irregular shapes of cells, inaccurate calculations of flow distances, etc. This paper addresses the layout problem of cells and their connecting flow paths in a tree configuration. The proposed layout procedure is designed to avoid the aforementioned drawbacks of traditional layout methods by emphasizing concurrent layout design of cells and flow paths. It combines a search algorithm and mathematical programming models. The search algorithm has a backtracking procedure that allows one to explore alternative layouts, while the mathematical programming models help one obtain accurate layouts of cells and flow paths. The proposed layout procedure also interacts with designers and allows designers to include their qualitative consideration into the layout design. As a result, one can obtain more accurate and good-quality layouts with the proposed layout procedure.     

Sharing clearances to improve machine layout

This paper considers a double-row layout problem with shared clearances in the context of semiconductor manufacturing. By sharing some clearances, reductions in both layout area and material handling cost of approximately 7–10% are achieved. Along with minimal clearances for separating adjacent machines, clearances that can be shared by adjacent machines are considered. The shared clearances may be located on either or both sides of machines. A mixed integer linear programming formulation of this problem is established, with the objective to minimise both material flow cost and layout area. A hybrid approach combining multi-objective tabu search and heuristic rules is proposed to solve it. Computational results show that the hybrid approach is very effective for this problem and finds machine layouts with reduced areas and handling costs by exploiting shared clearances.     

A design methodology for fractal layout organization

This paper proposes a methodology for designing job shops under the fractal layout organization that has been introduced as an alternative to the more traditional function and product organizations. We first begin with an illustration of how a fractal job shop is constituted from individual fractal cells. We then consider joint assignment of products and their processing requirements to fractal cells, the layout of workstation replicates in a fractal cell and the layout of cells with respect to each other. The main challenge in assigning flow to workstation replicates is that flow assignment is in itself a layout dependent decision problem. We confront this dilemma by proposing an iterative algorithm that updates layouts depending on flow assignments, and flow assignments based on layout. The proposed heuristic is computationally feasible as evidenced by our experience with test problems taken from the literature. We conclude by showing how the methodologies developed in this paper have helped us evaluate fractal job shop designs through specification of fractal cells, assignment of processing requirements to workstation replicates, and development of processor level layouts. This step has had the far-reaching consequence of demonstrating the viability and the validity of the fractal layout organization.     

ELEMENTS OF WAREHOUSE LAYOUT

The work summarised in this paper has been directed to examine the basic requirements of warehouse layouts. Two simple types of layout have been examined and equations derived for the dimensioning of these, given such information as total volume of stock and number of stock lines. A sketch of the layouts is given.

Ten factors have been considered in arriving at the theoretical layouts and it is shown that different types of layout are affected by different factors, some layouts being independent of factors to which others are sensitive.

Dimensions of a layout can be calculated to minimise handling distance, handling time or space utilisation. Where cost functions are available for these parameters, total cost can also be minimised. The formulae lend themselves readily to computer manipulation, enabling an optimum layout to be determined given only the number of stock lines and volumes stored.     

Linear sequencing for machine layouts by a modified simulated annealing

Machine sequencing is an essential step towards the physical layout of machines as it determines the relative positions of machines in a layout. Linear machine sequencing is most popular due to its efficient flow structure and its ability to arrange machines in various flow layouts. For example, in a conveyor or an AGV system, the layout can be a straight line, a U-shape line, a serpentine line, or a loop. This paper addresses the problem of determining a common linear machine sequence (also known as a linear flowline) for multi-products with different operation sequences. Each machine type has a limited number of duplicates available for use. The objective is to minimize the total flow distance travelled by the products on this linear flowline. The flows of products are allowed in the forward direction, either in-sequence or by-pass (i.e. no backtrack movements are allowed). To solve this problem, we first construct a feasible flow network that satisfies all operation sequences and then transform it into a linear machine sequence. To improve the solution, a modified simulated annealing is utilized. The new algorithm was tested on several examples in the literature.     

Designing multi-product lines: job routing in cellular manufacturing systems

An operation sequence-based method which integrates intra-cell layout cost with cell formation to minimize the total cost of the materials flow and machine investment is developed here for designing a cellular manufacturing system. The method comprises three distinct approaches: part-family formation, cell-formation, and layout configuration. In the first phase, an operation sequence-based similarity coefficient is applied in a p-median model to group the parts to form part families with similar operation sequences. In the second phase, machine assignment to part families is determined where a trade-off between potential inter-cell movement cost due to the. bottleneck machine and the potential benefit of assigning bottleneck machines to certain part-family is considered. In the third phase, intra-cell layout is determined for each cell so as to refine the initial layout of the cell further. Numerical examples are employed to demonstrate the mechanism of the procedure throughout all phases. A comparative study is also performed to support the present method     

An improved pair-wise exchange heuristic for the dynamic plant layout problem

Much of the research in facility layout has focused on static layouts where the material handling flow is assumed to be constant during the planning horizon. But in today's market-based, dynamic environment, layout rearrangement may be required during the planning horizon to maintain layout effectiveness. A few algorithms have been proposed to solve this problem. They include dynamic programming and pair-wise exchange. In this paper we propose an improved dynamic pair-wise exchange heuristic based on a previous method published in this journal. Tests show that the proposed method is effective and efficient.     

基于SLP的钢铁厂总体布局设计

以钢铁厂总生产工艺流程为基础,按主要作业单元的总体设计要求,对钢铁厂主要作业场地的总体布置关系予以确定。依据生产车间、辅助车间、动力车间、交通运输设施、职能部门、附属生产和生活服务等部门之间的内外关联、物料进出状况,进行系统优化布置设计。再由各个作业单位的面积大小、位置关系,适当参考其他限制条件和常识惯例,做出钢铁厂总体布局设计,达到布局科学、节约资源、产能提升的效果。     

Fuzzy approach to the robust facility layout in uncertain production environments

The proposed method approaches the problem of the optimal facility layout using fuzzy theory. The optimal layout is a robust layout that minimizes the total material handling cost, when the product market demands are uncertain variables, which are defined as fuzzy numbers. Since each department has a limited production capacity, not all possible combinations, deriving from each product's market demand, are taken into account because some combination could exceed the overall department's productivity. Therefore, the optimal solution results by solving a 'constrained' fuzzy optimization problem, in which the fuzzy material handling costs corresponding to the layouts are evaluated, and a ranking method, which considers the grade of pessimism of the decision maker, is established to determine the optimal layout.     

A design methodology for fractal layout organization

Venkatadri el a.(HE Transactions, 29, 911-924, 1997) have proposed a new methodology for shop floor layout that involves the use of fractal cells and have compared the performance of their new layout with those obtained using the function, group and holographic layouts. A few inconsistencies are present in their results, expressed as flow scores. This note points out these inconsistencies through the use of appropriate examples.     

用二叉树遍历展开凸多面体外表面

在工程实践中，同一种凸多面体其外表面不同的展开方式将影响生产与施工的可行性与经济性。借助改进的二叉树遍历算法并引入随机数，可以生成凸多面体外表面的各种不同的展开方式，为从中筛选最优方案，指导生产施工提供了帮助。在此，将介绍以最简单的正凸多面体为研究对象编制出的试验程序，从而证明该算法应用于凸多面体外表面展开的可行性。     

Pricing and capacity planning for product-line expansion and reduction

We investigate optimal pricing and capacity planning decisions for product-line settings such as introducing a new product or dropping an existing one. We consider a two-product, two-period model with stochastic demands, where price and capacity decisions are made at the outset. Investment in capacity must be traded-off against the possibility of buying at higher spot market prices due to shortage in capacity or charging a higher price to manage the demand. Prior studies argue that introducing an additional product to the product-line strains capacity, resulting in an increase in the price of an existing product. In contrast, we find that introducing a new product can also result in a drop in price of an existing product, enabling strategic pricing by firms. The necessary condition for this to occur is that the demand uncertainties for the products are of similar magnitude and negatively correlated. Similar insights are obtained for the setting where an existing product is dropped from the product-line. Hence, product-market decisions and contextual factors play a role in capacity planning, capacity cost allocation and pricing.     

MULTI-HOPE: A tool for multiple floor layout problems

The objective of most facility layout problems is to minimize material handling cost, which is directly proportional to both the distance between the machines and the mix, as well as the volume of products handled. The mix and volume of products are dependent on the demand patterns, and the distance is dependent on the layout plan used for the facility. Because it is relatively difficult to change the demand patterns, and hence the mix and volume of products, the primary focus of most designers has been to deal with the distance attribute of the material handling costs. The limitations of available horizontal space create a need to explore vertical expansion of facilities. This brings up new aspects of vertical material handling and flow that need to be considered in the facility design problem. In this paper, we present a genetic algorithm-based heuristic for generating block layouts for multiple-floor layout problems. This approach produces better solutions than existing simulated annealing-based heuristics for all but one of five multiplefloor test problems available in the literature.     

Facility layout objective functions and robust layouts

In this paper we examine the adjacency-based, distance-based, and weighted-criteria facility layout objective functions in an attempt to relate them to actual layout costs, which are typically dependent on material handling costs. As a result of this examination, we develop an objective function based on a basic material handling cost structure. We then show that this objective function is a generalization of the traditional weighted objective. Since specifying weights may not be an exact process, we explore the impact of imperfect weighting-value information on solution quality. In the process, we illustrate with test problems from the literature that robust solutions—good solutions as measured by more than one set of weights—can be found with a simple procedure we call the robust layout method. This leads us to our general conclusion that using imperfect weighting-value information while we generate the layouts is better than using complete weighting-value information only after we generate the layouts.     

An extended distance-based facility layout problem

The distance-based facility layout problem with unequal-area departments has been studied by many researchers for over 30 years. Still, current approaches require certain assumptions that limit the type of solutions obtained. In this paper, we consider manufacturing systems in which replicates of the same machine type may exist in the facility, and propose an extended distance-based facility layout problem that concurrently determines the number and shape of the departments, the assignment of machines to departments, and the allocation of part flow volume to individual machines. A non-linear mixed-integer program that accurately captures the extended facility layout and part flow allocation problem, a decomposition approach that exploits the structure of the formulation using a heuristic solution procedure, as well as computational results that evaluate the proposed approach, are presented.