Design of flexible plant layouts

In this paper, we present an approach for the design of plant layouts in stochastic environments. We consider systems where the, product mix and product demand are subject to variability and where duplicates of the same department type may exist in the same facility. In contrast to a job shop layout, we allow these duplicates to be placed in non-adjacent locations on the plant floor and for flow allocation between pairs of individual departments to be made as a function of the layout and the product demand realization. We present a scenario-based procedure that iteratively solves for layout and flow allocation. We show that having duplicates of the same departments, which can be strategically located in different areas of the plant floor, can significantly reduce material handling cost while effectively hedging against fluctuations in flow patterns and volumes. We show that the effect of duplication is of the diminishing kind, with most of the cost reduction occurring with relatively few duplicates. We also show that the quality of the obtained layouts can be quite insensitive to inaccuracies in estimating demand scenario probabilities.     

An interactive approach to computer aided facility layout

In all manufacturing and service industries the layout of facilities is an important determinant of operating efficiency and costs. Whenever the flow of materials or people is complex, computerized procedures offer the only feasible means of developing and evaluating alternative arrangements.

This paper describes an interactive approach to construction and improvement procedures which utilizes a refresh graphics terminal (IMLAC)linked to a PRIME 400 computer. Input includes projected materials flow, estimates of material handling costs, 2-D templates of machines, etc., and an initial layout which can be either existing, proposed, or constructed using the procedure INLAYT. A heuristic procedure, S-ZAKY, utilizes multi-pairwise facility exchange to develop improved layouts based upon an analysis of materials flow. The improved layout is displayed in detail alongside the initial layout at the graphics terminal together with relevant material handling costs. The user may then accept, reject or modify the improved layout using the light-pen attached to the terminal before proceeding to successive iterations until satisfied. An economic evaluation of the projected savings in material handling costs against costs of relayout may be displayed at each iteration. On completion, a fully documented record including drawings may be obtained for every stage in the. procedure.     

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%.     

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.     

Bi-objective facility expansion and relayout considering monuments

In this paper, the unequal area facility expansion and relayout problem is studied. The facility relayout problem is important since both manufacturing and service entities must modify their layouts over time when their operational characteristics change. A bi-objective approach is proposed to solve the relayout problem for cases of both a fixed facility area and an expanded facility area. Material handling costs and relayout costs are minimized using a tabu search meta-heuristic optimizer. This heuristic randomly alternates the objective function between the two objectives of the problem in each step and, by doing so, eliminates the difficulty of weighting and scaling the two objectives. The approach is flexible in handling various aspects of the problem such as stationary portions of departments (i.e., monuments), addition of new departments, and changes in existing department and facility areas. Computational experiments show that the bi-objective tabu search approach is effective and tractable. The use of the Pareto front of designs is demonstrated by showing a few approaches to analyzing the trade-offs between initial costs (relayout cost) and ongoing expenses (material handling costs).     

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.     

基于VRML模型的协同装配工艺规划仿真方法

在研究了虚拟现实建模语言(VRML)模型特点以及协同装配工艺规划过程的基础上,将以VRML三维模型为设计信息载体的协同装配工艺规划仿真分为无约束的规划仿真和基于约束的规划仿真,并提出了相应的实现方法.所提方法使网络化的同步协同装配规划操作成为可能,通过实时交流,使产品装配工艺规划能够在集合多方设计经验的基础上方便快捷地实现.应用实例的应用结果表明,所提方法可快速发现设计缺陷并显著地缩短产品工艺规划周期.     

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.     

Using distributed search methods for balancing mixed-model assembly lines in the automotive industry

Currently, modern companywide PC networks usually possess significant unused calculation capacity. Since the connected personal computers are mainly used for office applications, considerable off-peak times occur. Consequently, in order to solve planning problems more efficiently, it is promising to apply distributed search procedures that make use of those available off-peak times. This applies in particular to complex problems where insights into the structure of the solution space are lacking. The paper at hand illustrates the application of distributed search methods to automotive assembly line balancing. Modern mass customization programs in the automotive industry frequently comprise more than a billion theoretical variants. Since this causes an oscillating capacity demand at the line, deliberately designing the layout of a mixed-model assembly line is of significant importance. The paper at hand provides a new mixed-model assembly line balancing approach that integrates specific aspects relevant for the automotive industry. However, by integrating several -hard subproblems like a detailed personnel planning or a flexible process planning of each task, the resulting model has significant complexity. Consequently, in order to find appropriate line layouts in reasonable time, specifically designed distributed solution approaches are provided and evaluated. Among these approaches, particularly the use of a specific clustered Tabu Search algorithm attains promising results. By making use of an adaptive dynamic load balancer, substantial improvements of the solution quality can be obtained even under unfavorable circumstances like oscillating background loads in the PC network.     

Developing a method to generate semi-distributed layouts by genetic algorithm

Recent research in industries shows that existing layout configurations do not satisfy the needs of multi-product enterprises in turbulent environments but within new layout strategies, distributed layouts have deserved more attention in most manufacturing environments and have a promising potential to cope with demand disturbances. This study is an attempt to design weighted distributed layouts via considering machine independent capabilities by a resource elements (REs) approach, which has caused generation of a new type of distributed layout named semi-distributed layout. REs are used to define processing requirements of parts and processing capabilities of machines. Another contribution of this paper is applying genetic algorithms (GAs) to distribute REs to find the optimal assignment of machines to available locations in such a way the travelled distances of parts are minimised and the accessibility of them to the required machines are maximised. The methodology of this paper is illustrated using a two-phase procedure. First, all machining facilities are divided into a set of REs based on their capabilities and second, the weighted connections among REs are considered to distribute them over the floor through implementing the developed GA. To evaluate the methodology, the proposed algorithm is tested with three illustrative examples obtained from the literature, in which two of them are comparable with outputs of simulated annealing (SA). The comparison between the outputs of the GA and the SA on the same cases presents that for large size problems, the GA significantly outperforms the SA.     

Heuristics for the N-product,M-stage,economic lot sizing and scheduling problem with dynamic demand

This paper presents a new composite heuristics approach for solving the N-product, M-stage lot sizing and scheduling problem with dynamic demands and limited production capacity. The first phase of these composite heuristics aims at finding a feasible solution. This solution is such that for each period and for each product, the lot size equals the net demand of the considered period plus the demand of a number of upcoming periods. If capacity does not satisfy all demands of a given period, we try to find earlier periods where we can produce the missing units. The second phase is an improvement procedure which recursively attempts to move back each lot, provided that it is both more economical to do so and capacity feasible. We also provide two variants of this heuristic to handle the case where production capacity can be increased by using overtime. Overtime is a usual practice in real life which, in many cases, allows a reduction of the overall cost. The first variant constructs the initial solution without recourse to overtime and introduces overtime only during the solution improvement phase. The second one considers overtime during both the first and second phases. The performance of the proposed heuristics is numerically assessed and the most efficient ones are identified.     

Capability-based distributed layout approach for virtual manufacturing cells

It is shown in the literature that in highly volatile manufacturing environments functional job shops and classical cellular manufacturing systems do not perform well. Classical cellular manufacturing systems are very sensitive to changing production requirements due to their limited flexibility. In order to adapt cellular manufacturing systems to volatile manufacturing environments, the virtual cellular manufacturing concept was proposed in the 1980s by the National Bureau of Standards in USA. This concept is similar to group technology where job families are processed in manufacturing cells. The main difference between a virtual cell and the classic cell is in the dynamic nature of the virtual manufacturing cell; whereas the physical location and identity of classic cell is fixed, the virtual cell is not fixed and will vary with changing production requirements. The virtual manufacturing cell concept allows the flexible reconfiguration of shop floors in response to changing requirements. In the literature, the formation and scheduling process of virtual cells are clearly explained and researched in detail. However, the layout issue is not addressed entirely. Virtual cells are generally formed over functionally divided job shops. Forming virtual cells over a functional layout may adversely affect the performance of a virtual cellular manufacturing system. There is a need to search for different layout strategies in order to enhance the performance. The distributed layout approach may be a better alternative for virtual cellular manufacturing applications. In this research paper, a novel capability-based approach is proposed for the design of distributed layouts. A simulated annealing based heuristic algorithm is developed from the distributed layout. The proposed approach is tested with a problem with real data. An example is also shown in order to give an idea about the superiority of a capability-based distributed layout over the functional layouts in forming virtual manufacturing cells.     

Unidirectional circular layout for overhead material handling systems

The reentrant flow type of the semiconductor wafer manufacturing process creates a large amount of overhead material flows in the interbay system. This paper proposes unidirectional circular layout for overhead multi-carrier systems. The layout configuration can potentially reduce the control complexity of heavy traffic flow, streamline the empty carrier supply, and meet the delivery requirements. The layout contains a central loop to reach every stocker at high speed and supply empty carriers, provide prompt delivery service to each loop addition in a dynamic and responsive manner. It is preferred to other track architectures, as minimal traffic control is required for the large amount of wafer flows in semiconductor fabs. The proposed construction procedure proceeds in two stages. In the first stage, four quantitative measures are provided to select good candidates of main loop layouts in order to minimize the total flow times distances, construction costs and service response time. Once the main loop is chosen, minimum carrier flow requirement and the critical segments can be identified. The required carrier flows depend on the minimum flow requirement on the critical segments. In the second stage, forward and backtrack reducible loops are found as loop additions to connect to exterior stockers (stockers outside the main loop) as well as to eliminate the flows on critical segments. A dynamic programming procedure is presented to minimize the total construction and operating costs in the hybrid loop addition process. This two-stage procedure identifies a number of good and feasible layouts in which multiple layouts are maintained throughout the execution process.     

Analysis on high throughput layout of container yards

The operational efficiency of handling resources plays an important role in promoting container flows at a container terminal. As these handling resources operate on specific yard layouts, a well-designed layout will promote the performance of the handling activities. This study aims to discuss a design process to maximise the throughput capacity, as well as minimise the resource configuration when designing the yard layout. Various experiments were conducted and analysed to demonstrate the effects on the layout structure and the resource configuration for the two types of parallel yard layouts: the double-lane yard layout where vehicles can access the block at both side and the single-lane yard layout where two adjacent blocks in a row are grouped together and vehicles can access each block at only one side. According to the findings, the container flows by vehicles exert greater influence on the design of a container yard compared to the time taken for container processing by quay cranes and yard cranes. It is also found that the single-lane yard layout is preferable when high throughput capacity is required, whereas the double-lane yard layout is superior in favour of high efficiency of vehicle flows.     

The constraints satisfaction problem approach in the design of an architectural functional layout

A design support system with a new strategy for finding the optimal functional configurations of rooms for architectural layouts is presented. A set of configurations satisfying given constraints is generated and ranked according to multiple objectives. The method can be applied to problems in architectural practice, urban or graphic design—wherever allocation of related geometrical elements of known shape is optimized. Although the methodology is shown using simplified examples—a single story residential building with two apartments each having two rooms—the results resemble realistic functional layouts. One example of a practical size problem of a layout of three apartments with a total of 20 rooms is demonstrated, where the generated solution can be used as a base for a realistic architectural blueprint. The discretization of design space is discussed, followed by application of a backtrack search algorithm used for generating a set of potentially ‘good’ room configurations. Next the solutions are classified by a machine learning method (FFN) as ‘proper’ or ‘improper’ according to the internal communication criteria. Examples of interactive ranking of the ‘proper’ configurations according to multiple criteria and choosing ‘the best’ ones are presented. The proposed framework is general and universal—the criteria, parameters and weights can be individually defined by a user and the search algorithm can be adjusted to a specific problem.     

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.     

Flexible guidepath design for automated guided vehicle systems

We address the problem of unidirectional guidepath layout design for automated guided vehicle systems- A two-step layout design method to consider both loaded and empty vehicle movements is developed to guarantee a complete layout design. First, the flow path selection (FPS) problem is formulated to design guidepath layout with the objective of minimizing loaded vehicle movements. Both a mathematical model and a heuristic algorithm for FPS are presented. Since AGV guidepath layouts are used by both loaded and empty vehicles, the FPS does not guarantee a closed or complete layout design. For the case when an incomplete or unclosed layout is produced from the first step, a complementary layout design (CLD) approach to convert the incomplete layout into complete one with the consideration of empty vehicle movements is considered in the second step. A heuristic for the CLD problem is developed. An example problem is used to illustrate the whole design approach.     

Incorporating heterogeneous distance metrics within block layout design

This paper focuses on optimal design of block layouts when using more than one distance metric within a single facility. Previous work in block layout has assumed a single distance metric, usually the shortest rectilinear distance between department centroids, during the design step. However, most facilities have more than one method of material handling and alternative material handling systems can imply alternative distance metrics and cost structures. Specifically, up to three distance metrics within a single facility are considered--the shortest rectilinear distance between centroids (appropriate for automated guided vehicles and forklift trucks), the Tchebychev (maximum) distance (appropriate for overhead cranes) and the shortest Euclidean distance between centroids (appropriate for conveyor lines). Optimal block layouts using each of these distance metrics individually and then collectively are compared and contrasted. This approach can also be used to compare layouts when the choice of material handling system is not clear. It is argued that incorporating the distance metric that best reflects the planned material handling device is more realistic than previous formulations, avoids block layouts that are sub-optimal for the material handling systems installed, and is quite workable within a heuristic optimization framework.     

利用集成计算方法迈向虚拟产品开发的道路

 满足功效需求的计算机辅助产品开发过程使得提供新的集成软件产品成为必需.然而,由于对产品开发来说不可少的CAE工具缺乏兼容性和集成度,因此出现了很大的问题.利用虚拟产品开发的概念启发了新的思路,可以消除现今CAE应用中普遍存在的缺陷.以一个汽车制造和机械制造配件供应公司里“技术计算”参与部门的开发过程为例,描述了用以优化开发过程且改善与用户之间数字通信的一种方式.     

Designing self-storage warehouses with customer choice

Self-storage warehousing is a rapidly growing industry where consumers or companies can rent storage space for personal or company use, over a certain horizon. This paper addresses the question of how to design the facilities so that revenue can be maximised over a finite horizon, considering multiple demand requirements with respect to size, pricing, location within the facility, climate control, security or outside access, among others. Using a customer choice model to specify the probability of purchase for each fare product as a function of the set of fare products offered, we propose methods to design self-storage warehouses while allowing different customer choice behaviours. We model the problem as a mixed-integer program and solve it using column generation and branch-and-price algorithms. In addition, we study the impact of re-layout and methods to modify facility layout, since self-storage facilities are relatively flexible in layout and individual storage compartments can be adapted to changes in demand. We validate our model using the data of four self-storage warehouses, and show our method can improve the expected revenue by nearly 11% on average for these cases.