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.     

The facilities layout problem: a multi-goal approach

This paper presents a combined quantitative and qualitative (subjective) approach to the plant layout problem. The two objectives, which may be conflicting, are minimizing the material handling cost and maximizing a closeness rating measure. A heuristic algorithm is developed which results in a discrete efficient frontier set, including only 'efficient layouts’. By specifying the different weights, or range of weights, for these goals, the 'best’ solution (layout) is generated.     

An integrated approach to the facilities and material handling system design

The facility layout problem involves the optimal location of manufacturing facilities into a workshop. The classical approach to the layout design is carried out in two separate steps: the first step is the construction of the block layout, i.e. the location of the departments into the workshop, and the second step is the design of the material handling system. The separate optimization of these two aspects of the problem leads to solutions that can be far from the total optimum. In this paper, an integrated approach to the facilities and material handling system design is proposed. Referring to a physical model, named the bay structure , and to a unidirectional AGV system, a genetic approach is proposed to individuate the locations of the departments, the positions of the pickup/delivery stations and the direction of the flow-path. The minimization of material handling cost is adopted as optimality criterion.     

A Monte Carlo simulation based heuristic procedure for solving dynamic line layout problems for facilities using conventional material handling devices

A simple procedure is proposed to identify line layout solutions when a production facility with work centres of unequal size uses conventional material handling devices and operates under stochastic demand scenarios. The procedure uses Monte Carlo simulation (MCS) to empirically search for robust solutions defined as those that simultaneously meet minimum material handling cost performance levels across all demand scenarios. The results reported in this study suggest that ‘robust’ line layout solutions can be identified using a modest volume of random sampling. The procedure and results are demonstrated through a series of sample problems.     

Two graph-theoretic procedures for an improved solution to the facilities layout problem

A new operation, referred to as the T-operation, for replacing edges of the maximal planar graph is presented. Cases of this operation are discussed. It is then used to develop two graph-theoretic improvement procedures for solving facilities layout problems. Both procedures can be employed to improve solutions of any existing graph-theoretic construction heuristic. A computational experiment is reported for a series of test problems which indicates that both procedures can considerably improve the initial solutions in a cost-effective manner. Since they are simple and effective, realistically sized facilities layout problems can be solved efficiently by their use.     

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.     

Quadratic assignment problem QAP with adaptable material handling devices

The traditional quadratic assignment problem (QAP) assumes handling costs between two facilities are directly proportional to the distance between them. This linearity assumption is, in general, untrue in actual industrial settings due to changing equipment requirements as the distance between facilities changes. Therefore, this paper presents a model that reflects actual industrial practice in the design of layouts, assignment of departments to sites, and the selection of proper mode of handling between departments in response to the distances between department pairs. The paper discusses how data can be represented to make it easier to develop such a model and shows the methodology to solve the model. The paper concludes with an analysis of modelling error as a way to illustrate the cost associated with applying the wrong model as seems to be reflected in the traditional applications of the model.     

An efficient local search heuristic for the double row layout problem with asymmetric material flow

The double row layout problem (DRLP) consists of arranging a number of rectangular machines of varying widths on either side of a corridor to minimize the total cost of material handling for products that move between these machines. This problem arises in the context of many production environments, most notably semiconductor manufacturing. Because the DRLP contains both combinatorial and continuous aspects, traditional solution approaches are not well suited to obtain solutions within a reasonable time. Moreover, previous approaches to this problem did not consider asymmetric flows. In this paper, an effective local search procedure featuring linear programming is proposed for solving the DRLP with asymmetric flows (symmetric flows being a special case). This approach is compared against several constructive heuristics and solutions obtained by a commercial mixed integer linear programming solver to evaluate its performance. Computational results show that the proposed heuristic is an effective approach, both in terms of solution quality and computational effort.     

Extended range tactility in material handling

Optical fibres sensitized to their geometric curvature are arranged in loops around an autonomous guided vehicle (AGV) in order to extend the vehicle's tactile sensing range and allow larger speeds that require larger stopping distances. When the AGV approaches other objects (obstacles) within this range, fibre optic loops deform and sense the gradual change in their curvature. No intermediate mechanical elements are used to either transfer the impact loads onto the sensitive element or to provide compliance to it. Optical fibres themselves achieve these two functions simultaneously. As a result, tactility is achieved within a comparatively large position range extending over 15 cm. Throughout this range, virtually no reaction forces are generated with the impacting body. The range mentioned is on top of the one provided by the more traditional elastic bumper on which the optical fibres are mounted. Obstacle avoidance and wall-following AGV guidance can readily be achieved with such loops of optical fibre. A high degree of reactive capability and safety is hence provided in the system. With similar advantages, the method can likewise be applied to fixed or mobile material-handling robots.     

The machine layout problem in robot cells

This paper addresses the machine layout problem in a flexible manufacturing cell served by a robot. The objective of the proposed approach is to obtain the optimum values of the locations and orientations of machines and the corresponding feasible configurations of the robot at each input/output location. Two optimization criteria have been considered, the travel time and the total joint displacement for all possible sequences of operations required by the robot at a given period of time. Non-linear optimization models are proposed which can be applied not only to a planar robot but also to an industrial one. The optimization problems were solved by a sequential quadratic programming algorithm.     

The integrated machine allocation and layout problem

Cellular manufacturing has received a considerable amount of attention in the research literature as an approach for improving the performance of manufacturing facilities. However, recent studies have shown that cellular layouts are not always superior to the traditional functional machine layout. We propose a model that does not require the machines to be placed in a functional layout or in a cellular arrangement, but allows the material flow requirements to dictate the machine placement. The model is formulated as an aggregation of the quadratic assignment problem and several network flow problems coupled with linear side constraints. A mixed integer program is presented to find the optimal solution for small problems, and heuristics are developed to solve larger problems. Computational results evaluating the quality of the solution methodologies are also presented.     

Advances in discrete material handling system design

The paper presents an outline of the research done in the area of facility layout and discrete material handling system design. The objective of this paper is to observe the trend in the literature in the area of manufacturing system design and predict the direction of future research in this area. The paper attempts to link the areas of facility layout design and material flow network design. A methodology for solving the integrated design problem is presented. An algorithm which aids in solving the combined pick-up/drop-off point location and material handling flowpath problem is outlined.     

Managing lean manufacturing in material handling operations

The problem addressed by this research is to implement lean manufacturing in a material handling system of a petroleum drill bit manufacturing company. Lean manufacturing has been mandated by higher level management as a tool to be used in waste reduction. Operational group must define the objectives of lean manufacturing and deploy the tools to specific work cells. A methodology that provides operational group with a tool to assist in defining the objectives of lean manufacturing is developed. A case study is used to demonstrate the lean implementation in material handling operations.     

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.     

A graph-theoretic heuristic for minimizing total transport cost in facilities layout

Existing graph-theoretic heuristics for block plan design attempt to maximize the sum of the REL chart seores of adjacent pairs of facilities. A new graph-theoretic heuristic is presented which has the aim of minimizing total transport ation cost instead. This has the advantage of giving credit in the objective function to pairs of facilities which are somewhat near but not actually adjacent. Reported computational experience with the method is encouraging.     

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.     

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.     

An integrated materials handling model for machine location in existing facilities

A machine location criterion is proposed for situations where machines must be located in existing facilities to manufacture new products. The location criterion is based on a measure of materials handling service. It is applicable when an existing, automated materials handling system is fully integrated within an existing manufacturing facility. The service level is measured by the expected rate of unsuccessful load transfers associated with a fixed production schedule, handling system, and assignment of machines to locations in a facility. An analytical model focused on the interfaces of automated materials handling systems is formulated to predict the corresponding service level associated with alternative machine locations in an existing facility. The model is illustrated through a sample problem which demonstrates how the specific operating characteristics of a typical automated materials handling system can be modelled to predict handling performance for alternative machine locations.     

A reallocation-based heuristic to solve a machine loading problem with material handling constraint in a flexible manufacturing system

In this research, a comprehensive heuristic solution is evolved to include all the three segments of a machine loading problem of flexible manufacturing systems. These are part type sequence determination, operation allocation on machines and reallocation of part types. The machine loading problem has been formulated keeping in view two well-known objective functions, namely minimization of system unbalance and maximization of throughput. In addition to constraints related to machine time and tool slots availability, this research considers one more constraint related to material handling, i.e. number of AGVs available in the system. The part type sequence determination has been carried out by evaluating the contribution of part type to characteristics such as batch size, total processing time, and the AGV movement. Decisions pertaining to operation allocation are taken based on the enumeration of priority index. An iterative reallocation procedure has been devised to ensure minimum positive system unbalance and maximum throughput. A test problem is simulated to represent the real shop floor environment and the same has been solved using various steps of the proposed algorithm. Extensive computational experiments have been carried out to assess the performance of the proposed heuristic and validate its relevance to solve the real shop floor problems.     

Optimising material handling costs in an assembly workshop

The intense competition imposed by the current global market, forces companies to implement lean manufacturing techniques. Major progress has already been made in this field and factories continue to reduce costs and lead times. Within this context, the crucial impact of logistics on production efficiency renders the design and planning of the supply chain a key factor in the reduction of costs and the maximisation of product availability. The logistics of an assembly workshop are usually specified empirically, which often generates an overestimation of its needs. Therefore, the current study focuses on these needs and introduces the ACW (assignment of components in warehouses) method for optimising the assignment of components to storage areas. This original method is based on a successive resolution of cost assessments, shortest path problems and generalised assignment problems. It takes into account congestions in the network of aisles that appear during the loading/unloading stages of material handling. A case study of Renault's Flins factory is detailed to validate the proposed method.