Showing papers in "Iie Transactions in 1987"

Solving Quadratic Assignment Problems by ‘Simulated Annealing’

Abstract: Recently, an interesting analogy between problems in combinatorial optimization and statistical mechanics has been developed and has proven useful in solving certain traditional optimization problems such as computer design, partitioning, component placement, wiring, and traveling salesman problems. The analogy has resulted in a methodology, termed “simulated annealing,” which, in the process of iterating to an optimum, uses Monte Carlo sampling to occasionally accept solutions to discrete optimization problems which increase rather than decrease the objective function value. This process is counter to the normal ‘steepest-descent’ algorithmic approach. However, it is argued in the analogy that by taking such controlled uphill steps, the optimizing algorithm need not get “stuck” on inferior solutions. This paper presents an application of the simulated annealing method to solve the quadratic assignment problem (QAP). Performance is tested on a set of “standard” problems, as well as some newly gen...

On Sequencing Retrievals In An Automated Storage/Retrieval System

Abstract: This paper addresses throughput improvement by retrieval sequencing in conventional unit load automated storage/retrieval systems when several retrieval requests are available and dual command cycles are performed. Taking first-come-first-served as the reference sequencing rule, the potential for improvement is identified. A “nearest-neighbor” sequencing rule is proposed as an alternative, an analytic model for its expected performance is developed, and Monte Carlo simulation is used for evaluation. In addition, a lower bound on dual command cycle times is developed, and the dynamic behavior of two heuristic sequencing rules is discussed.

Dynamically Adjusting the Number of Kanbans in a Just-in-Time Production System Using Estimated Values of Leadtime

Abstract: In a Just-in-Time (JIT) production system with Kanbans, as used by the Japanese, the number of Kanbans employed at each workcenter remains relatively constant from month to month even though demand may change, This occurs because of the unique (and stable) conditions inherent in the production environment of Japanese firms. However, a number of American firms have considered or attempted the implementation of a JIT system without a similar production environment, thus, necessitating that the number of Kanbans at each workcenter be adjusted periodically. In this paper, a procedure for dynamically adjusting the number of Kanbans at workcenters in an unstable production environment is presented and analyzed. The adjustment methodology is presented in a step-by-step manner. This is followed by three examples presented within the context of a simulation model of a hypothetical shop. The first example will illustrate the methodology while the last two examples will demonstrate how well the methodology ...

Stochastic Leadtimes in Two-Level Assembly Systems

Abstract: Shortages of assembly parts often arise from late arrivals of one or more batches of components. We address the problem of determining planned leadtimes in two-level assembly systems with stochastic leadtimes, with the objective of minimizing the sum of inventory holding costs and tardiness costs. An algorithm is developed which exploits properties of the objective function to find optimal solutions. Computational results indicate that optimal solutions often have negative safety times for at least one of the components, as well as substantial safety times for the assembly stage.

A decomposition method for the approximate evaluation of capacitated transfer lines with unreliable machines and random processing times

Abstract: This paper presents a decomposition method to evaluate the performance measures of a capacitated transfer line with unreliable machines and random processing times. The decomposition is based on approximating the k - 1-buffer system by k - 1 single-buffer systems. Numerical examples indicate that the approach is accurate as long as the probability that a machine is starved and blocked at the same time is small.

Minimizing Weighted Absolute Deviation in Single Machine Scheduling

Abstract: This paper presents a procedure to minimize the total penalty when jobs are scheduled on a single machine subject to earliness and tardiness penalties This performance criterion has been shown to be non-regular thus, requiring a search among schedules with inserted machine idle time to find a solution A procedure to optimally insert idle time is also presented

Two-Parameter Approximations For Multi-Echelon Repairable Inventory Models With Batch Ordering Policy

Abstract: In this paper we present a model for multi-echelon repairable systems with batch ordering policy at the bases. Such an ordering policy is desirable when demand rates and/or the set up cost for ordering are relatively high. Operating characteristics of such a system are analyzed. A two-parameter approximation scheme for the distribution of the number of orders outstanding and consequently backorders is developed, and its performance evaluated. It is found that, under a variety of scenarios including both finite and infinite servers at the repair facility, the approximation scheme is very effective in providing a relatively simple means to determine the stocking levels at both the depot and the bases to minimize the cost of inventory holding and backorders. For the special case when the batch size is one, we confirm the effectiveness of the use of the negative binomial distribution as an approximation for the distribution of orders outstanding, as suggested by recent studies, under a much more gene...

Evaluating Flexible Manufacturing Systems

Abstract: Many firms are considering Flexible Manufacturing Systems (FMS) as a means for increasing productivity, quality and profitability. In this paper a methodology for properly comparing and evaluating FMS's is presented, The appropriate financial criteria are presented. Mathematical models of different FMS's are presented. The important stochastic variables are determined. The principles of stochastic dominance, risk preference and the value of information; and a decision analysis cycle are used to evaluate the FMSY

Production Learning and Quality Control

Abstract: The purpose of this paper is to establish a linkage between quality control, the production learning process and the firm's propensity to use quality control under various conditions. A stochastic dynamic programming approach together with a numerical example are used to compute quality control policies and justify the intensive use of quality control in manufacturing.

A General Model of a Production Line with Intermediate Buffer and Station Breakdown

Abstract: A general model for a class of production lines with two unreliable stations, a finite capacity interstation buffer, discrete items, constant cycle time, and synchronous transfer is presented. The model is applicable to a broad range of production lines with various item service mechanisms, item transfer mechanisms, station breakdown mechanisms, and station repair mechanisms. The model provides insights into the general properties of production lines and gives rise to a general recursive solution for the steady-state probabilities. Sufficient conditions are given for the two special cases, the matrix geometric case and the scalar geometric case, which permit the efficient computation of the production rate.

Performance of a Manufacturing Cell with Increased Product Mix

Abstract: We investigate the impact of increasing the number of items made in a cell on its performance. The optimal lotsizes of production and queuing delays are both shown to increase with increased product mix. However, these adverse effects diminish as more items are assigned to the cell. We also examine a strategy of sequencing which attempts to minimize the number of setups by looking ahead in the queue and processing all items for which the machine is already setup. In the case of similar items, it is found that this sequencing policy results in little savings in setup time.

Matching Based Interactive Facility Layout

Abstract: This paper is concerned with the development of an interactive block layout system which utilizes b-matching as the optimization component. The objective function utilized by the b-matching is to maximize a weighted sum of adjacent departments. The b-matching model is a relaxation of the layout problem, hence human interaction is critical to overcome the factors not captured by the model.

A Study of Work-Time Distributions on Unpaced Tasks

Abstract: Recent investigations into the work-time distributions of light assembly tasks indicate that some reserve must be used when applying the generalized relationships which are traditionally believed to hold Video recordings were made of industrial operations and, in subsequent analysis, any process controlled or nonproductive elements were excluded The elements studied were all analyzed using MTM-1 so that the nature of the element and the method used to perform it could be defined closely The work time distributions obtained show the general pattern expected in regard to positive skewness and gross measures of dispersion However, measures of skewness and the coefficient of variation show wide differences throughout the overall sample Analysis of the nature of the individual work elements and their statistical characteristics failed to reveal any clear explanation for the differences encountered The need for further research in this area is, therefore, underlined where the prediction of the na

Selection of a Threshold Value Based on Material Handling Cost in Machine-Component Grouping

Abstract: Machine-component grouping is a basic step in the application of group technology to manufacturing. It is the process of finding families of similar parts (part-families) and forming the associated machine cells such that one or more part-families can be processed within a single cell. Among the algorithms used to form the machine cells, those based on the Similarity Coefficient Method (SCM) are more flexible in incorporating the manufacturing data into the machine-component grouping process. SCM is the application of clustering techniques in forming the machine cells. One of the major problems with SCM is that it generates a set of alternative solutions rather than a unique solution. The number and size of machine cells in a given solution depends upon the similarity coefficient (threshold value) at which machine cells/machines are joined. This paper discusses the problem of selecting a proper threshold value and presents a solution to it.

Priority assignment procedures in multi-level assembly job shops

Abstract: This paper deals with the design of priority rules for job shops that process multi-level assembly jobs. Specifically, it explores the means by which the structural complexity of jobs can be incorporated explicitly into priority rules to reduce job lead times. The job lead time is viewed as consisting of two components: flow time and job staging delays. The primary focus of the paper is on the development of a class of priority rules that is aimed at reducing the staging delay. The class of priority rules that is developed is then used in combination with rules that are effective for the flow time component. The combined rule results in the improvement of the lead time performance. The paper also includes experimental results on sets of jobs of varying degrees of complexity. These results provide a comparative perspective on the performance of priority rules that have been examined in the earlier research literature as well as the rules specifically developed in this paper.

Planned Leadtimes For Serial Production Systems

Abstract: We investigate the problem of setting planned leadtimes in serial production systems when the actual leadtimes are stochastic. The objective is to minimize the sum of inventory holding costs, rescheduling costs arising from tardiness at intermediate stages of production, and tardiness of delivery to the customer. A single-pass algorithm is developed which finds optimal solutions. The analytical models underlying the algorithm and extensive computational experience indicate that it is never optimal to have planned leadtimes of zero when there are rescheduling costs at intermediate stages of production. This also implies that unconditional immediate dispatching is not optimal under these conditions.

Optimal Project Scheduling with Materials Ordering

Abstract: A mixed integer 0–1 programming formulation of a Project Scheduling-Materials Ordering Problem (PSMOP) is presented that provides an optimal schedule of project activities and materials orders. It is proven that an optimal solution may be found by decomposing the problem into the derivation of the project schedule and the subsequent derivation of materials lot sizes.

Matrix-geometric and Recursive Algorithm Solution of a Two-stage Unreliable How Line

Abstract: A two stage flow line finite inventory bank and stages that can fail on completion of a task is equivalent to a C2/C2/1/N queueing model in which the arrival process is switched off once N customers wait for service. After transformation of the state equations, two alternative solution procedures are developed, one based on the matrix geometric algorithm and the other based on a recursive algorithm. A comparison of the two algorithms shows that there is no difference in the bank size at which numerical instability occurs, but the recursive algorithm is about eight times faster.

The Effects of Inspection Error on a Complete Inspection Plan

Abstract: In a complete inspection plan, every incoming item is subject to variable inspection. If the inspection result indicates that an item fails to meet predetermined specification limits, the item is reworked so that its quality characteristic is exactly equal to the target value. The specification limits are determined by the tradeoff among the cost incurred by imperfect quality, cost of rework and cost of inspection. The economic and statistical effects of inspection error on the complete inspection plan are investigated. Two models with considerations of inspection error are developed under different rework schemes, then compared with the model without inspection error consideration.

Strategic allocation of inspection effort in a serial, multi-product production system

Abstract: For a multi-stage production system, optimal location of inspection activities is an important consideration in minimizing the inspection-related and salvage costs. Set-up and inventory carrying costs also become important factors when several products are produced on the same line due to the product changeovers involved. In this paper we discuss the effect of these additional costs (set-up and inventory carrying) on the inspection strategy, i.e., “all or none” versus partial inspection. We suggest a shortest path heuristic to determine the strategic location of inspection activities and the production lot sizes.

A Parallel Heuristic Algorithm for Lot-Sizing in Multistage Production Systems

Abstract: Existing studies on heuristic lot-sizing techniques for multistage production systems concentrate on optimizing the production operations of the individual stages. This approach induces a family of heuristics, in which the production plans for the individual stages are computed sequentially starting from the final stage. In this paper we introduce a parallel heuristic for the problem. The method, which may be considered as the generalization of the single stage Wagner-Whitin algorithm, attempts to optimize over all stages simultaneously, while building the production plans in a forward manner. In computational experiments the new algorithm performed extremely well.

An Approximate Model of Multistage Automatic Transfer Lines with Possible Scrapping Of Workpieces

Abstract: We consider multistage automatic transfer lines with unreliable stages, finite interstage buffer storages, and possible scrapping of workpieces. It is assumed that the first stage never idles and the last stage never becomes blocked. Assuming that uptimes and downtimes of a stage are geometrically distributed, an approximate model is developed to compute different performance measures of the transfer line. The results obtained through the approximate model are compared to the exact results for three-stage transfer lines and to simulation results for longer transfer lines. It is observed that the approximate results are good in almost all cases considered.

A Dual-Cost Heuristic For The Capacitated Lot Sizing Problem

Abstract: This paper examines a mathematical programming method of accounting for capacity costs for the deterministic, multi-item, single operation lot sizing problem. With the capacity constraints of CLSP removed with Lagrangian relaxation, the problem decomposes into a set of uncapacitated single product lot sizing problems which are solved with dynamic programming. The Lagrangian dual costs are updated by subgradient optimization. Feasible solutions (production plans within the capacity limitations) are constructed with a heuristic smoothing procedure. The dual-cost heuristic gave solutions which were better on average than the other algorithms tested (and was faster than some comparable algorithms).

Effects of Correlated Sub-Samples in Statistical Process Control

Abstract: This paper considers the effects of correlated data within subgroups that have been defined for the purposes of statistical process control. Such correlation may arise if the grouping is accomplished because of simplicity in data collection, such as multiple but similar measurements on a single product or multiple station machines. The effect of correlated measurements within the subgroup is shown to increase the Type I error rate for the X chart. Variance charts are shown not to be affected in the same fashion when equality of covariances of the measurements is assumed. Monte Carlo simulation is used to show similarity of the effects on the range chart when the number of measurements in the subgroup exceeds two. Several examples are given.

An Input/Output Control System For The Dynamic Job Shop

Abstract: A combined input/output control system is presented for periodically determining the set of jobs to be released (input variables) and the capacities of processing centers (output variables) in the dynamic job shop, so that a composite cost function is minimized. An interactive heuristic optimizing algorithm incorporating a 0–1 linear mixed integer program is formulated. The resulting control system is compared by simulation with an alternate system for which only input is subject to control. Significant improvements are obtained for most performance measures evaluated.

Exact and Approximate Solutions to Two-Stage Transfer Lines with General Uptime and Downtime Distributions

Abstract: We consider a transfer line with two unreliable stages and an intermediate buffer storage of a finite capacity. It is assumed that the distribution of uptimes and downtimes of each stage are of phase type. It is also assumed that a part may be scrapped with a certain probability when the stage processing it breaks down. Using the phase structure of the underlying distributions, the system is modelled as a Markov chain. This model is used to study the behavior of the system. It is also used to find out whether a two moment approximation to the uptime and downtime distributions is adequate. A simple approximation to the production rate that involves only the first two moments of the uptime and downtime distributions is also developed. It is shown that this approximation is quite reasonable.

An Exploratory Study on Stopping a Paced Line When Incompletions Occur

Abstract: This is an exploratory study of “hybrid” lines, i.e., “paced” lines whose cycle time can be extended (something like an “unpaced” line) when some task incompletions occur. Such a line should have its tasks classified into two categories; only the tasks in the first category have sufficiently high incompletion costs to justify extending the cycle time to ensure their completion. A heuristic procedure is developed to perform this classification, and we found that such hybrid lines may have a lower total cost (i.e. sum of labor and incompletion costs) than standard paced lines.

Production Scheduling with Sequence Dependent Setup Costs

Abstract: The problem of scheduling products, with constant demand rates, on a single facility is difficult. This difficulty is compounded if the setup costs are not constant for each product but depend on the sequence in which the products are made. A heuristic that iterates between solving the scheduling problem with constant setup costs and solving a “traveling salesman” formulation with sequence dependent setup costs is presented. The heuristic works well in practice and always provides a feasible solution if one exists. Some computational experience is also given.

On The Validity of an Isometric Biomechanical Model of Worker Strengths

Abstract: Over the last 18 years the Center for Ergonomics at The University of Michigan has worked to develop a computerized, biomechanically based model to predict worker muscle strengths in various tasks. During the last few years new input strength data has been acquired from published works of others. Worker isometric strength testing also has been performed by the Center in various industries to determine gross lifting, pushing and pulling capabilities of a heterogeneous group of men and women. These data, acquired from 1577 men and women are compared to the strength predictions of the biomechanically based model. For prediction of mean strength capabilities of both men and women performing varied types of symmetric sagittal plane exertions, the model results were relatively unbiased and were well correlated with r 2 between 0.85 and 0.88 with the population data. The results were not as good for predicting the mean strengths of two-handed assymetric exertions (r 2 between 0.54 and 0.74), and for one...

A Successful Application of Job Enlargement/Enrichment at Toyota

Abstract: When designing a production system to meet the company desires, the desire of the workers should also be considered. A survey at the Toyota Tsutsumi plant indicated that workers wanted enlarged/enriched jobs. The jobs were enlarged/enriched through a system of cross-training and job rotation. Productivity and quality were improved.