Hajime Yamashina

A heuristic algorithm for the assembly line model-mix sequencing problem to minimize the risk of stopping the conveyor

SUMMARY The purpose of this paper is to describe a new formulation of the mixed-model sequencing model in such a way as to minimize the risk of stopping the conveyor under the circumstances of system variability and to develop an efficient heuristic method for large-scale, mixed-model assembly lines. The proposed method always produced optimal solutions for. randomly constructed small-scale, mixed-model sequencing problems for which the optimal solutions were available through the application of the improved branch and bound method. The method should produce excellent (and almost always optimal) results for actual large-scale, mixedi-model sequencing problems.

Analysis of the Effect of Buffer Storage Capacity in Transfer Line Systems

Abstract The purpose of this paper is to gain insight into the effect of buffer storage capacity in two-stage transfer lines by presenting results of a theoretical study of the problem. A Markov model of the problem is proposed to analyze the effect of in-process inventory banks on the production rate and the mean number of units in the storage area. Based on the model developed, the effect of internal storage is evaluated, and the question of how much buffer storage capacity should be provided is discussed.

Japanese manufacturing strategy and the role of total productive maintenance

Discusses the strategies used by Japan in the past to become a leading economic power. Examines the problems of the 1990s including the impact of the appreciation of the Yen, cost structures and offshore production. Presents strategies currently being implemented by Japanese manufacturing firms and the role of total productive maintenance (TPM) to help maintain and strengthen Japan’s competitive edge. The strategies include just‐in‐time product development and cost reduction with the help of TPM.

An inspection policy for a deteriorating single-unit system characterized by a delay-time model

This paper develops a method for determining the discrete time points of inspection for a deteriorating system which is under condition-based maintenance. The system is regarded as a single component unit, and it has the following states: a normal state, a symptom state and a failed state. A delay-time model is utilized in order to describe the transition of the states. The transition time from a normal state to a symptom state and the transition time from a symptom state to a failed state are assumed to obey independent and identically distributed probability density functions respectively. Two types of probabilities with respect to inspections are considered: failed-dangerous (FD) probability or type I error that a system is wrongly diagnosed as in a normal state when the system is actually in a symptom state and failed-safe (FS) probability or type II error that a system is wrongly diagnosed as in a symptom state when the system is actually in a normal state. The determination method is formulated to m...

Analysis of in-process buffers for multi-stage transfer line systems

Abstract The paper deals with the role of buffer stock in multi-stage transfer lines by presenting computer simulation results. It is shown that an n-stage line should be designed such that the lowest stage production rate occurs in the nth stage, the second lowest in the first stage, the third lowest in the (n - 1 )st stage, the fourth lowest in the second stage and so on, to maximize line production rate. The paper also demonstrates that the total buffer capacity should be allocated such that (a) the difference between the production rates of the stages on either side of a storage point is minimized, and (b) the production rate of the stages before the storage point is slightly greater than that of the stages following the storage point

Justification for Installing Buffer Stocks in Unbalanced Two Stage Automatic Transfer Lines

Abstract This paper deals with the role of inventory banks in balanced and unbalanced flow-line production systems by presenting results of a theoretical study of the problem and numerical experiments by computer simulation. It is shown that if the costs of both storage capacity and division of the line for a buffer are high, and therefore installing a buffer is not possible, then the line should be designed to have the same cycle times over all stages. When installing a buffer is possible, the line should be designed in such a way that the stage production rates are the same. Provision of a buffer in this case will improve line output.

Cost‐optimized maintenance of the elevator – single unit case

Elevator manufacturers are responsible for securing the safety and maintaining the performance, cleanliness and cosmetic appearance of the elevators which they sell.The purpose of this paper is to develop a cost‐optimized after‐sales strategy for the maintenance of an elevator part. First, in order to find an optimum maintenance method, the replacement probability and the inspection probability of the part are theoretically derived using each of the three maintenance methods: Time Based Maintenance (TBM), Condition Based Maintenance (CBM), and Breakdown Maintenance (BM). Then, the approach to plan a cost‐optimized maintenance method is presented and the relationship between the failure characteristics of the part and the cost‐optimized maintenance method is discussed.The results of using the proposed approach are compared with those obtained by Online Quality Engineering (Taguchi methods). Finally, from numerical experiments, it is shown that this approach can provide a more cost‐effective and better maintenance method than the method provided by Online Quality Engineering.

Optimal preventive maintenance planning for multiple elevators

The purpose of this paper is to properly plan the preventive maintenance schedule for multiple elevators and optimize the number of maintenance workers.The total amount of the maintenance cost consisting of the labor cost, the part cost, and the quality cost (the loss evaluated in terms of cost, to be incurred when an elevator breaks down) is to be minimized.The method is presented of setting up the optimal preventive maintenance schedule on a long‐term basis by rescheduling the contents of schedule dynamically and flexibly in accordance with the ever‐changing maintenance conditions, taking the possibility of the future occurrence of failure into consideration. From numerical experiments, the validity of the proposal procedure for planning the preventive maintenance schedule and the effectiveness of considering the possibility of the future occurrence of failure in planning the schedule are shown, and the optimal number of maintenance workers can be decided.

CAD for free-form surfaces

Recently, consumer products with complex idiosyncratic curved surfaces are becoming increasingly common in the market. It is now usual for designers of products such as cars and consumer electronic goods to use free-form surfaces that cannot be adequately represented in two-dimensional drawings. As a result, computers, especially three-dimensional CAD systems, have become essential design tools. Unfortunately, 3D CAD systems are still regarded as impossibly complicated by many designers. To address this problem, we have developed a 3D CAD system that makes it easy for designers to interactively create and modify the shapes that they have in mind. This system features high-quality modelling functions, can also produce rendered views of the models it generates, and incorporates a user-friendly interface that allows the designer to operate the system unaided. Compared to conventional design processes based on 2D drawings and fabrication of the mock-up products, this system provides an environment that can make great contributions to design work. This paper describes the functions and features of the system.

Failure diagnosis of a servovalve by neural networks with new learning algorithm and structure analysis

SUMMARY This paper considers a failure diagnosis of a pneumatic servovalve used in automated production systems. The valve is monitored by an accelerometer. Six parameters characterizing the vibration data are extracted, and fed into neural networks to solve four types of diagnosis problems. A conjugate gradient followed by a variable metric method is demonstrated as an effective learning algorithm. Neural network structures are analysed through Boolean expressions summarizing network simulation results for given learning patterns. The neural networks are found to utilize majority voting mechanisms. Irrelevant neurons can be identified and removed without degrading the diagnosis performance.