A two-step heuristic algorithm for layout design of unequal-sized facilities with input/output points

The facility layout problem (FLP) is to arrange facilities within a given area so as to minimise the total material-handling cost. An efficient arrangement of facilities plays an important part in the achievement of high productivity in a manufacturing system. This paper focuses on the layout design of unequal-sized facilities with fixed shapes and input/output (I/O) points. A mixed-integer programming (MIP) model is developed to obtain optimal solutions. Since the MIP model is not applicable to large-sized problems, a two-step heuristic algorithm is developed to solve the FLPs. In the first step, a layout solution with moderate quality is generated by using an interconnected zone algorithm and a simulated annealing (SA) algorithm. The zone algorithm is a newly developed layout construction technique which places facilities successively within designated zones according to a placing sequence. The zone concept is introduced to reduce the solution space such that the computational effort is decreased, while SA is used to search for the placing sequences. The second step improves that solution further using the reduced MIP by employing the relative position information obtained from the first step. Computational experiments indicate that the algorithm in the first step can yield on average a 1.048% improvement on the best solutions obtained by the existing algorithms. The second step can further improve the solutions obtained in the first step by 0.484% on average. Compared to the commercial software VIP-PLANOPT 2006 (Engineering Optimization Software 2005 Engineering Optimization Software. 2005. PLANOPT User’s Manual, Florida: Deltona.  [Google Scholar]), the proposed two-step algorithm improves the solutions by 9.113% on average.     

A three-phase heuristic algorithm for fixed-charge capacitated material flow network design with input/output points location

In this paper, we consider the material flow network design problem in which locations of input and output points of departments and flow paths are determined concurrently on a given block layout. The objective of the problem is to minimize the sum of transportation cost, flow paths construction cost and penalty cost for non-smooth material flows, i.e., flows with turns. A mixed integer programming model is given for the problem and a three-phase heuristic algorithm is developed to solve the problem. In the suggested algorithm, we generate an initial flow network by determining locations of input/output points and flow paths sequentially in the first and second phases, respectively, and then improve it by changing locations of input/output points and flow paths iteratively in the third phase. To evaluate the performance of the suggested algorithms, a series of computational experiments are performed on well-known problem instances as well as randomly generated test problems. Results of computational experiments show that the suggested algorithm gives good solutions in a short computation time.     

Routing problem under the shared storage policy for unit-load automated storage and retrieval systems with separate input and output points

In this study the routing problem for unit-load automated storage and retrieval systems (AS/RSs) with separate input and output points is considered under the shared storage policy. The problem is to find an optimal travel route of a S/R (storage and retrieval) machine to process given storage and retrieval requests so that the total travel time is minimised, where the input and output points are possibly separate and the shared storage policy is assumed. We first give two types of formulations as 0–1 integer linear programming problems corresponding to two types of dwell point settings: the dwell point is the input point and the output point. Next, we propose a simple but efficient exact solution algorithm based on the formulations that utilises a general MILP (Mixed Integer Linear Programming) solver. Its efficiency is then demonstrated by numerical experiments. Instances with 400 items (200 for each storage and retrieval) are solved within 100 s.     

Rectangular characteristic gratings for waveguide input and output coupling

Normal-incidence planar-optical waveguide-imbedded phase gratings of finite aperture width and length are analyzed with Svidzinskii's (Sov. J. Quantum Electron. 10, 1103 (1980)] two-dimensional Braggdiffraction theory. Svidzinskii's characteristic-grating equations are adapted for the rectangulargrating case, and an overlap integral is used to extend the theory to account for the mode structure of the waveguide. The combined theory is used to optimize the throughput of a system composed of an input grating coupler, a waveguide, and an output grating coupler for both the highly multimode (thickwaveguide) and the few-mode (thin-waveguide) cases.     

A scale model for fitting object shapes from fixed location data

In this paper we present a scale model for fitting an ideal shape to an object. The measurements of the object are taken corresponding to a fixed coordinate system at a set of well-defined locations on the surface of the object. We propose an algorithm to estimate the model parameters and hypothesis tests to make statistical inferences about several possible special cases of the general model. The model is tested with an example that analyzes data on the feet of people in Hong Kong.     

A construction algorithm for the machine layout problem with fixed pick-up and drop-off points

A construction algorithm which considers some practical aspects of the machine layout problem is presented. The methodology considers machine dimensions and their input and output locations with flow data. The layout is generated on a continuum, considering the best configuration and orientation of input and output locations of machines to minimize the material flow cost. The location procedure searches along the boundary of existing machines. A bi-criterion optimization approach is proposed to overcome one of the weaknesses inherited by construction procedures. The suggested construction procedure is implemented on a microcomputer and applied to solve some test problems with encouraging results.     

Systems analysis for planning of air fleets and maintenance facilities

The high cost and extraordinary demands made on sophisticated air defence systems, pose hard challenges to the managers and engineers who plan the operation and maintenance of such systems. This paper presents a study aimed at developing simulation and systems analysis techniques for the effective planning and efficient operation of small fleets of aircraft, typical of the air force of a developing country. We consider an important aspect of fleet management: the problem of resource allocation for achieving prescribed operational effectiveness of the fleet. At this stage, we consider a single flying-base, where the operationally ready aircraft are stationed, and a repair-depot, where the planes are overhauled. An important measure of operational effectiveness is ‘ availability ’, which may be defined as the expected fraction of the fleet fit for use at a given instant. The tour of aircraft in a flying-base, repair-depot system through a cycle of ‘ operationally ready ’ and ‘ scheduled overhaul ’ phases is represented first by a deterministic flow process and then by a cyclic queuing process. Initially the steady-state availability at the flying-base is computed under the assumptions of Poisson arrivals, exponential service times and an equivalent singleserver repair-depot. This analysis also brings out the effect of fleet size on availability. It defines a ‘ small ’ fleet essentially in terms of the important ‘ traffic ’ parameter of service rate/maximum arrival rate. A simulation model of the system has been developed using GPSS to study sensitivity to distributional assumptions, to validate the principal assumptions of the analytical model such as the single-server assumption and to obtain confidence intervals for the statistical parameters of interest.     

An expert system for planning/replanning programmable facilities

New requirements for facility planning/replanning in programmable production are presented. A computer aided facility planning (CAFP) methodology is reviewed and revised to satisfy the new requirements by expert system's capabilities, and a prototype of facility planning expert system is specified and illustrated.     

Low-loss ultrabroadband 90 degree optical rotator with collinear input and output beams

An achromatic device to rotate optical polarization by 90 degrees is described. This is based on a series of reflecting surfaces that rotates incoming light about the optical axis and translates it such that the exiting light is collinear. Polarization rotation is achieved by rotation of the optical beam, as opposed to the more common approach of phase retardation by use of birefringent elements. For broadband operation from the UV to the near infrared, the device was constructed by use of total internal reflection in three fused-silica glass components. Losses are minimized with interstitial surfaces designed to be angled close to Brewster's angle.     

Interdisciplinary information input and output of a nano-technology project

The input and output information of a national project of Japan for nano-technology will be analysed. In 1996 Japanese government stipulated a guideline to evaluate national technology projects on economic criteria as well as technological ones. In addition to the criteria intrinsic to economy but extrinsic to technology and unfriendly to technologists, however, another view more intrinsic to technology may be useful as well. This study will attempt to complement the governmentally stipulated evaluation method with a bibliometric one. Considering the interdisciplinary approach as a merit of national projects, this study will analyse how interdisciplinary information was used as input and was published as output by the project. Focussing on the publication behaviours of the project, information flow from technology to science or a development pattern of science pulled by technology will be discussed. Finally, the matching of the evaluation criteria to technology development and the friendliness of evaluation methods to technologists will be discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Optimal scheduling for sequentially connected cluster tools with dual-armed robots and a single input and output module

We examine a cyclic scheduling problem of sequentially connected cluster tools with a single input and output module, which includes multi-cluster tools and linear cluster tools. Every component tool has a dual-armed robot, and chambers are parallelised for a long process step. An intermediate buffer between each pair of adjacent component tools has a limited capacity, and all processed wafers should return to the input and output module. To examine the scheduling problem, we first compute workloads of the process steps and robots to obtain a lower bound on the tool cycle time. We then identify a rule of assigning the chambers to the process steps that makes the tool cycle time independent of the order of using the parallel chambers. We also propose a simple robot task sequence which is modified from the well-known swap sequence for each component tool. We prove that the modified swap sequence is optimal when one of the process steps, not a robot, is the bottleneck. We also present a scheduling strategy which controls robot task timings to deal with interference of wafer flows between each pair of adjacent component tools. Finally, we perform numerical experiments to show the performance of the proposed sequence.     

Multi-criteria location planning for public facilities in tsunami-prone coastal areas

We present a model for multi-objective decision analysis with respect to the location of public facilities as schools in areas near to coasts, taking risks of inundation by tsunamis into account. A mathematical programming formulation with three objective functions is given. The first objective function is a weighted mean of a minisum and a maximum coverage criterion. The second objective function expresses risk by possible tsunami events; for quantifying this risk, a statistical model for tsunami occurrences by Kaistrenko and Pinegina is applied. The third criterion represents costs. For the solution of the multi-objective optimization problem, we propose a heuristic approach based on the NSGA-II algorithm and compare it with a decomposition technique where the region under consideration is partitioned into smaller sub-regions, and the problem is solved for each separate subregion either exactly or heuristically. Both approaches are tested on two real-life instances from southern Sri Lanka.     

Simultaneous order-lot pegging and wafer release planning for semiconductor wafer fabrication facilities

In semiconductor wafer fabrication facilities, order-lot pegging is the process of assigning wafer lots to orders and meeting the due dates of orders is considered one of the most important operational issues. In many cases of order-lot pegging, some orders cannot be fulfilled with the current wafers in the lots being processed, necessitating the release of additional new wafer lots into the wafer fabrication facility. In this paper, we propose a simultaneous decision model for order-lot pegging and wafer release planning in semiconductor wafer fabrication facilities, and develop a Lagrangian heuristic for solving the model. The results of computational experiments conducted using randomly generated problem instances that mimic actual field data from a Korea semiconductor wafer fabrication facility indicate that the performance of the Lagrangian heuristic is superior to that of a practical greedy algorithm for practical-sized problem instances. The results also point to how sensitivity analysis can be used to answer important managerial questions for effective management of the semiconductor wafer fabrication process.     

Peak factor minimization of input and output signals of linearsystems

An overview is given of existing analytical and numerical methods for the comparison of the peaks of discrete, finite sum of sines. A novel method that compresses the signals optimally or almost optimally is presented. The algorithm is extended to the simultaneous compression of the input and output signals of a linear system. The implications of strong signal compression for the signal-to-noise ratio lead to the formulation of a two-step optimal experimental setup for system identification and parameter estimation of linear systems     

Polarization changes at Lyot depolarizer output for different types of input beams

Lyot depolarizers are optical devices made of birefringent materials used for producing unpolarized beams from totally polarized incident light. The depolarization is produced for polychromatic input beams due to the different phase introduced by the Lyot depolarizer for each wavelength. The effect of this device on other types of incident fields is investigated. In particular two cases are analyzed: (i) monochromatic and nonuniformly polarized incident beams and (ii) incident light synthesized by superposition of two monochromatic orthogonally polarized beams with different wavelengths. In the last case, it is theoretically and experimentally shown that the Lyot depolarizer increases the degree of polarization instead of depolarizes.     

Tool procurement planning for wafer fabrication facilities: a scenario-based approach

The rate of change in technology in the semiconductor industry has made the demand supply planning process extremely challenging for manufacturers. This problem is further exacerbated for tool procurement because the tools are made to order, very expensive and have a long lead time for delivery. In this paper, we present a scenario-based stochastic planning approach for tool procurement under uncertainty in demand and formulate the problem as a mixed integer program. Our results based on the data from a manufacturing line indicate that the heuristics for stochastic planning can significantly outperform deterministic planning.