Manufacturing flow line systems: a review of models and analytical results

The most important models and results of the manufacturing flow line literature are described. These include the major classes of models (asynchronous, synchronous, and continuous); the major features (blocking, processing times, failures and repairs); the major properties (conservation of flow, flow rate-idle time, reversibility, and others); and the relationships among different models. Exact and approximate methods for obtaining quantitative measures of performance are also reviewed. The exact methods are appropriate for small systems. The approximate methods, which are the only means available for large systems, are generally based on decomposition, and make use of the exact methods for small systems. Extensions are briefly discussed. Directions for future research are suggested.National Science Foundation (U.S.) (Grant DDM-8914277

Factory Models for Manufacturing Systems Engineering

We review MIT research in manufacturing systems engineering, and we describe current and possible future research activities in this area. This includes advances in decomposition techniques, optimization, token-based control systems analysis, multiple part types, inspection location, data collection and several other topics.Singapore-MIT Alliance (SMA

Analysis and design of manufacturing systems with multiple-loop structures

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (p. 281-284).Kanban means card or token. A kanban-controlled production system is one where the flow of material is controlled by the presence or absence of a kanban, and where kanbans travel in the system according to certain rules. The study of kanban-controlled production systems can be traced back to the Toyota Production System in the 1950s. The classic kanban-controlled system was designed to realize Just-In-Time (JIT) production. Kanban-controlled production systems, though pervasively used in industry and studied for decades, are not well understood quantitatively yet. The essence of kanban-controlled production systems is to use single or multiple closed loops to provide information flow feedback using kanbans. By doing this, the systems keep tight controls over inventory levels, while providing satisfactory production rates. The goal of this research is to study the behavior of the class of manufacturing systems with multiple closed loop structures and explore the applications in design and operational control of production systems using multiple-kanban loops. To do so, stochastic mathematical models and effcient analytical methods for evaluating the performance of systems with complex structures are required.(cont.) In this thesis, we present an assembly/disassembly network model which integrates the control information flows with material flows. Blocking and starvation properties due to machine failures in a system are analyzed by establishing an effcient underlying graph model of the system. Based on the mathematical model and blocking and starvation properties, effcient and accurate algorithms are developed for evaluating the performance of systems with arbitrary multiple-loop structures. We study the behavior of multiple-loop structures and develop intuition for optimal design and operational control using multiple-kanban loops. Some practical guidelines for the design and control of production systems using multiple-kanban loops are provided at the end.by Zhenyu Zhang.Ph.D

The impact of unequal processing time variability on reliable and unreliable merging line performance

Research on merging lines is expanding as their use grows significantly in the contexts of remanufacturing, reverse logistics and developing economies. This article is the first to study the behavior of unpaced, reliable, and unreliable merging assembly lines that are deliberately unbalanced with respect to their coefficients of variation (CV). Conducting a series of simulation runs with varying line lengths, buffer storage capacities and unbalanced CV patterns delivers intriguing results. For both reliable and unreliable lines, the best pattern for generating higher throughput is found to be a balanced configuration (equal CVs along both parallel lines), except for unreliable lines with a station buffer capacity of six. In that case, the highest throughput results from the descending configuration, i.e. concentrating the variable stations close to the beginning of both parallel lines and the steady stations towards the end of the line. Ordering from the least to most steady station also provides the best average buffer level. By exploring the experimental Pareto Frontier, this study shows the combined performance of unbalanced CV patterns for throughput and average buffer level. Study results suggest that caution should be exercised when assuming equivalent behavior from reliable and unreliable lines, or single serial lines and merging lines, since the relative throughput performance of some CV patterns changed between the different configurations

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

Title from cover.Bibliography: p. 19.by Yong F. Choong, Stanley B. Gershwin

Performance of merging lines with uneven buffer capacity allocation: the effects of unreliability under different inventory-related costs

This simulation study investigates whether machine efficiency, mean time to failure (MTTF) and mean time to repair (MTTR) significantly affect the performance of uneven buffer capacity allocation patterns for merging lines. Also studied is the trade-off between increasing throughput via bigger buffers and their associated inventory-related costs, since previous studies have shown that higher overall buffer capacity and higher average inventory content result in higher throughput. Results suggest that an ascending buffer allocation pattern (concentrating buffer capacity towards the end of the line) produces higher throughput in shorter, more unreliable lines; whereas the balanced pattern shows better performance in longer, more reliable lines. Increasing average buffer capacity per station and/or having higher average buffer content was found to be more cost-effective in lines with lower machine inefficiency, shorter MTTF and MTTR, and longer lines. Results differed between reliable and unreliable lines since reliable lines were particularly penalised by buffer capacity investiment/maintenance costs due to a relatively low increase in throughput resulting from the addition of extra buffer capacity

An efficient decomposition method for the approximate evaluation of tandem queues with finite storage space and blocking

"December, 1983"Bibliography: p. 36-37."DAAK11-82-K-0018"Stanley B. Gershwin

Hierarchical Control of Production Flow based on Capacity Allocation for Real-Time Scheduling of Manufacturing System

8International audienceThis paper considers the modelling and simulation of a hierarchical production-flow control system. It uses a continuous control approach for machine capacity allocation at the design level and real time scheduling at the shop-floor level. Particularly, at the design level, the control of machine throughput has been addressed by a set of distributed and supervised fuzzy controllers. The objective is to adjust the machine's production rates in such a way that satisfies the demand while maintaining the overall performances within acceptable limits. At the shop-floor level, the problem of scheduling of jobs is considered. In this case, the priority of jobs (actual dispatching times) is determined from the continuous production rates through a discretization procedure. A case study demonstrates the efficiency of the proposed methodology through a simulation case study

Analytical Methods for Performance Enhancement in Unreliable Multistage Manufacturing Systems with Imperfect Production

Ph.DDOCTOR OF PHILOSOPH

The two-machine one-buffer continuous time model with restart policy

This paper deals with the performance evaluation of production lines in which well defined machine start/stop control policies are applied. A modeling approach has been developed in order to reduce the complexity of a two-machine one-buffer line where a specific control policy, called “restart policy”, is adopted. The restart policy exercises control over the start/stop condition of the first machine: when the buffer gets full and, as a consequence, the first machine is forced to stop production (i.e., it is blocked), the control policy keeps the first machine in an idle state until the buffer becomes empty again. The rationale behind this policy is to reduce the blocking frequency of the first machine, i.e. the probability that a blockage occurs on the first machine due to the buffer filling up. Such a control policy is adopted in practice when outage costs (e.g., waste production) are related to each restart of the machine. The two-machine one-buffer line with restart policy (RP line) is here modeled as a continuous time Markov process so as to consider machines having different capacities and working in an asynchronous manner. The mathematical RP model is described along with its analytical solution. Then, the most critical line performance measures are derived and, finally, some numerical examples are reported to show the effects of such a policy on the blocking frequency of the first machine