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.     

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.     

A genetic algorithm and queuing theory based methodology for facilities layout problem

Facilities layout, being a significant contributor to manufacturing performance, has been studied many times over the past few decades. Existing studies are mainly based on material handling cost and have neglected several critical variations inherent in a manufacturing system. The static nature of available models has reduced the quality of the estimates of performance and led to not achieving an optimal layout. Using a queuing network model, an established tool to quantify the variations of a system and operational performance factors including work-in-process (WIP) and utilisation, can significantly help decision makers in solving a facilities layout problem. The queuing model utilised in this paper is our extension to the existing models through incorporating concurrently several operational features: availability of raw material, alternate routing of parts, effectiveness of a maintenance facility, quality of products, availability of processing tools and material handling equipment. On the other hand, a queuing model is not an optimisation tool in itself. A genetic algorithm, an effective search process for exploring a large search space, has been selected and implemented to solve the layout problem modelled with queuing theory. This combination provides a unique opportunity to consider the stochastic variations while achieving a good layout. A layout problem with unequal area facilities is considered in this paper. A good layout solution is the one which minimises the following four parameters: WIP cost, material handling cost, deviation cost, and relocation cost. Observations from experimental analysis are also reported in this paper. Our proposed methodology demonstrates that it has a potential to integrate several related decision-making problems in a unified framework.     

A machine-to-loop assignment and layout design methodology for tandem AGV systems with multiple-load vehicles

In this paper, we propose a design methodology for tandem Automated Guided Vehicle (AGV) systems with multiple-load vehicles. Our goal is to devise a design methodology that can achieve the following objectives in multiple-load tandem AGV designs. The first objective is to achieve the workload-balance between vehicles of different loops. The second objective is to minimize the inter-loop flow. The final objective is to minimize the flow distance. To achieve these objectives, the following problems are studied. First, we conduct simulations to study the relationship between a vehicle's load-carrying capacity and work capacity. This relationship is then considered in the second problem, i.e. the problem of determining the machine content of each loop. A two-stage machine-to-loop assignment method is proposed for solving this problem. At the first stage, an initial machine-to-loop assignment is generated. This initial assignment is then improved at the second stage using Simulated Annealing (SA). The third problem is the problem of determining the layout of machines in each loop. A flow-line design method and SA are adopted for solving this problem. The fourth problem is the layout problem of guide-path loops. To solve this problem, a famous layout method found in the literature is adopted. The last problem includes the problem of determining the best orientation of each loop and the problem of finding the best places to set up transfer stations between adjacent loops. A mathematical programming model that can solve them simultaneously is proposed. Simulations are then conducted to verify the design, and to show that the proposed design methodology is indeed capable of producing good and satisfactory tandem AGV designs with multiple-load AGVs. Finally, it is our hope that the knowledge learned from this study can help us have a better understanding of multiple-load AGV systems and allow us to have successful implementations of similar systems in practice.     

A machine-to-loop assignment and layout design methodology for tandem AGV systems with single-load vehicles

In this paper, we propose a method for design of tandem automated guided vehicle (AGV) systems with single-load vehicles. We consider the concurrent design of machines layout and AGV guide paths for a tandem system. Our goal is to devise a method that can achieve the following objectives: (1) maximise the workload balance between loops; (2) minimise the inter-loop flow; and (3) minimise the total flow distance. Our method solves the problem in four stages, considering the machines layout and the tandem paths at the same time. It assigns machines to loops, determines the layout of each loop, arranges loops on the floor, and finally designs a transportation centre to link the loops. We compare the performance of our method with a sequential design method that first determines the layout and then assigns the machines to loops. We solve a number of randomly generated problems for both methods. Results indicate that the proposed algorithm performs faster and achieves lower values of inter-loop flows and inter-loop flow distances.     

Facilities layout planning based on Fuzzy multiple criteria decision-making methodology

Space requirements for facilities and the activity relationships among these facilities are important factors in determining the design of a facility layout. A facility layout problem is an unstructured decision problem. One of the real difficulties in developing and using models for layout design is the natural vagueness associated with the inputs to the models. The personnel flow rate between different departments should be viewed as vague inputs. The analyst is typically uncertain about what this input should be, yet the formulation requires exact inputs. Similarly, arbitrary numerical ratings are assigned for the relationship chart. This paper presents a distinct methodology for the facility layout process using a fuzzy decision-making system for handling inexact, vague data. The selection routine for the placement of facilities (departments) in an open continual plane is developed by using a multifactor fuzzy inference system. It considers both qualitative and quantitative factors that influence the layout structure. A two-tier fuzzy inference system is proposed to compare the proposed layout methodology with that of a conventional selection routine with respect to personnel flow cost, dead space and the minimum required area of the layout. The suggested distinct methodology is coded in C⁺⁺ language and implemented in a personal computer. The experimental results for a test problem with six departments, 30 activities (moves) and four influencing factors are illustrated with encouraging results under a fuzzy multicriteria environment.     

A methodology for solving the unequal area facility layout problem using distance and shape-based measures

This paper presents a methodology for solving the unequal area facility layout problem commonly encountered in industry practice. A mixed-binary nonlinear-programming model is formulated to capture the operational issues encountered on the shop floor. In particular, in addition to the distance measure that is typically used to quantify the material handling costs, the impact of geometry or the shape of the departments is quantified in the formulation of the model. A higher-level heuristic solution algorithm, based on a concept known as ‘tabu search’, is proposed to efficiently solve industry-relevant problems. The methodology not only considers the impact of both distance and shape-based measures simultaneously in the proposed initial solution finding mechanism, but also in the evaluation of the objective function during the entire search procedure, in the hope that it will lead to identifying a better final solution. Taking into consideration fixed and variable tabu list sizes, along with long-term memory with maximum and minimum frequencies, has led to developing six different heuristics for the solution algorithm. A single factor experiment based on randomized block design has been used to compare the performances of the six different heuristics on three different problem structures—small, medium, and large—using the total cost as the criterion. Based on this experiment, the characterizations of search procedures have been recommended to facilitate identifying the best solution for each problem structure. The proposed method is also compared with those in the published literature by solving fairly well known unequal area facility layout problems. When an improvement is observed, the comparison has led to identifying a percentage improvement in total cost of approximately 2.8% to 11.8%, thus demonstrating the effectiveness of the model and the algorithm.     

A multi-factor Rasch scale for artistic judgment

Measurement properties are reported for a combined scale of abstract and figurative artistic judgment aptitude items. Abstract items are synthetic, rule-based images from Visual Designs Test which implements a statistical algorithm to control design complexity and redundancy, and figurative items are canvas paintings in five styles, Fauvism, Post-Impressionism, Surrealism, Renaissance, and Baroque especially created for this research. The paintings integrate syntactic structure from VDT Abstract designs with thematic content for each style at four levels of complexity while controlling redundancy. Trained test administrators collected preference for synthetic abstract designs and authentic figurative art from 462 examinees in Johnson O'Connor Research Foundation testing offices in Boston, New York, Chicago, and Dallas. The Rasch model replicated measurement properties for VDT Abstract items and identified an item hierarchy that was statistically invariant between genders and generally stable across age for new, authentic figurative items. Further examination of the figurative item hierarchy revealed that complexity interacts with style and meaning. Sound measurement properties for a combined VDT Abstract and Figurative scale shows promise for a comprehensive artistic judgment construct.     

Numerical taxonomy applied to group technology and plant layout

This paper identifies the need for a technique which can assess whether a functional or n group cell system of production is most appropriate in a specific case as well as develop the appropriate system. The paper describes the technique of numerical taxonomy and shows how it may be applied to both group technology and plant layout. A computer programme for production flow analysis is presented. The component-machine matrix method of production flow analysis, as presented by Burbridge, is shown to be of limited value in practical cases and an improved method is proposed. The use of numerical taxonomy in developing functional-type layout is also described.     

An integrated methodology for automating the determination of layout and materials handling system

There is a severe scanty of models and solution techniques for the determination of layout and the materials handling system when neither are fixed. This is a complex problem for which this paper proposes a new integrated methodology using a knowledge-based/optimisation approach to the problem. The knowledge-base consists of facts and rules to determine the feasibility of using a materials handling equipment type for a given move. The optimisation part determines the layout of machines minimising the materials handling costs and the dead space in the layout using a multi-criteria optimisation model. The methodology aims to minimise materials handling costs, aisle space usage and dead-space in the resulting layout. It is particularly applicable to heavy manufacturing environments. The system outputs the optimum location, configuration and orientation of machines, and the material handling equipment types, their design capacities, utilisations and the assignment of moves to each item of materials handling equipment. The results of a successful application to an example problem are given.     

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.     

Integrating occupational health and safety in facility layout planning,part I: methodology

An influential factor affecting the efficiency of a manufacturing facility is its layout. In a production facility, measure for efficiency can be based on the total cost of transporting the items between different departments and throughout the facility. However, other factors may influence efficiency of the manufacturing facility too. As such are: supporting the organisation's vision through improved material handling, material flow and control; effectively assigning people, equipment, space and energy; minimising capital investment; adaptability and ease of maintenance; as well as providing for employee safety and job satisfaction. By incorporating health and safety measures in the initial design of a facility layout, the organisation may avoid money and manpower loss resulting from industrial accidents. This paper proposes a facility layout planning methodology which integrates the occupational health and safety (OHS) features in the early design of a facility layout. The model considers transportation cost in the facility as well as safety concerns. By this means, the OHS issues are reflected prior to the construction of a facility.     

A model for warehouse layout

This paper describes an approach to determine a layout for the order picking area in warehouses, so that the average travel distance for the order pickers is minimized. We give analytical formulas that can be used to calculate the average length of an order picking route under two different routing policies. The optimal layout can be determined by using these formulas as the objective function in a nonlinear programming model. The optimal number of aisles in an order picking area appears to depend strongly on the required storage space and the pick list size.     

Genetic algorithms for layout optimization in crossdocking operations of a manufacturing plant

In this study, we use genetic algorithms to optimize the lane layout associated with the crossdocking operation at the Toyota Motor Manufacturing plant in Georgetown, Kentucky, USA. A genetic algorithm solution can be obtained within seconds, whereas an exhaustive search would require a computing time of over five days on a 1?GHz Intel Pentium III. The results of this study show that a simple rearrangement of the lanes will lead to a decrease in workload of nearly 34% in the crossdocking area and ultimately result in an overall reduced lead time.     

A genetic algorithm for facility layout

Facility layout is an important aspect of designing any manufacturing setup. However, the problem of finding optimal layouts is hard and deterministic techniques are not computationally feasible. In this work a genetic algorithm is presented for obtaining efficient layouts. The different aspects involved in the design of efficient genetic algorithms are discussed in detail. It is shown that the population maintained by the genetic algorithm for facility layout should consist of feasible solutions only. A new efficient crossover operator is developed. Experimental results obtained with the proposed algorithm on test problems taken from the literature are promising.     

二氧化碳风险控制及空分工厂布置优化

周围大气环境对安装在工业区的空分设备的运行可靠性与安全性有较大的影响。大气中二氧化碳含量随工业化进程在世界范围内逐年增高,它对空分设备而言是一种有害的堵塞气体。介绍二氧化碳的性质和危害以及空分设备所采取的风险控制。阐述为优化空分工厂布置应进行的二氧化碳定量风险分析和扩散计算,从而控制二氧化碳的影响和相应风险。     

A reexamination of the distance-based facility layout problem

In this paper we qualitatively and numerically compare basic modeling approaches to the distance-based facility layout problem and the types of result obtained from them. In the process we observe that when the facility layout problem is modeled as a QAP, one will not necessarily obtain an optimal solution to the layout problem even if the QAP is solved to optimality. We also propose an alternative distance measure, namely, EDIST, which is based on the expected distance between two departments. We illustrate how the EDIST measure addresses some of the well-known shortcomings associated with the centroid-to-centroid distance measure.     

A risk-based sensor placement methodology

A risk-based sensor placement methodology is proposed to solve the problem of optimal location of sensors to protect population against the exposure to, and effects of, known and/or postulated chemical, biological, and/or radiological threats. Risk is calculated as a quantitative value representing population at risk from exposure at standard exposure levels. Historical meteorological data are used to characterize weather conditions as the frequency of wind speed and direction pairs. The meteorological data drive atmospheric transport and dispersion modeling of the threats, the results of which are used to calculate risk values. Sensor locations are determined via an iterative dynamic programming algorithm whereby threats detected by sensors placed in prior iterations are removed from consideration in subsequent iterations. In addition to the risk-based placement algorithm, the proposed methodology provides a quantification of the marginal utility of each additional sensor. This is the fraction of the total risk accounted for by placement of the sensor. Thus, the criteria for halting the iterative process can be the number of sensors available, a threshold marginal utility value, and/or a minimum cumulative utility achieved with all sensors.     

A new approach to the block layout problem

The main problem concerned with applying graph theory to facilities layout is the conversion of the dual graph to a block layout. This paper presents a new method of producing a planar orthogonal layout or floorplan of a set of facilities subject to adjacency and area constraints. It improves upon previous approaches by accepting any maximal planar graph representing the adjacencies as input. Simple selection criteria for choosing the next facility to be inserted into the floorplan are used. Further, any sensible orthogonal shape for the facilities in the resulting floorplan can be generated.     

影响电压暂降问题的多源属性排序方法

对电压暂降的多源属性进行分析,不仅能为供电工程的规划设计、设备选型、运行维护等环节提供全过程技术支撑,还可以有效评估电能质量事件的风险及其严重程度。该文提出电压暂降的多源属性贡献度排序方法。首先,列举电压暂降的多源属性,将其分为内源属性和外源属性;然后,采用设备兼容度指标,计算多源属性下设备的暂降兼容度,并建立基于层次分析法的三层致因体系,针对多源致因属性的权重进行计算;最后,利用蒙特卡洛法进行仿真,结合实际工程数据,分析多源致因属性下发生电压暂降的严重性程度,评估结果验证该方法可行。