[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

In the accident prevention countermeasure for industrial machinary, the quantitative evaluation of residual risk may be carried out based on existing probability and statistical theories. however, the indeterminateness which is included in risk evaluation is sometimes larger than the estimate of the accident occurrence rate. Therefore, the method for eradicating the indeterminateness which is encluded in risk evaluation is proposed in this study. The method of giving 1 at asymmetric error rate of the safety confirmation system was proposed. It considers the uncertain condition as the hazardous condition. It was proved that the triple diversity and redundancy composition with self-checking was required when this technique was applied to safety confirmation system composed of programable electric control systems, in order to achieve the desired value of the accident occurrence rate.

View full abstract

This paper discusses on techniques and the electronic interlocking system (PRIME) software which was developed in conformance with safety-related international standards and practical evaluated result, by a comparison of quality data with a former electronic interlocking system (SMILE). PRIME has been developed based on the draft of IEC61508 "Functional safety of electrical/electronic/programmable electronic safety-related systems." As a result of these developments, the quality (a number of bugs) and testing time of PRIME is improved efficiently as compared with SMILE. This paper reports on the effect by achieving conformance of standards.

View full abstract

The paper considers a single-machine production-inventory system where the machine is subject to random failure and at most two failures are allowed to occur in a production cycle. After first failure if shortages occur due to longer repair time, they are backlogged partially. While backlogging if failure occurs again, the machine is repaired towards the termination of the production process and all the accumulated shortages are lost. The expected average cost function is derived for general failure and repair time distributions. Some properties of the proposed model are studied under exponentially distributed failure and repair times. The optimal lot sizing decision is obtained and sensitivity analysis is carried out with the help of a numerical example.

View full abstract

The article considers an estimation problem of repairable units. We consider two types of data: (i) field data which is collected from the failure of field units and (ii) experimental data which is collected from the experiments in laboratories. Field units are assumed to be repairable. The lifetimes of field units follow a mixed Weibull distribution and the units are imperfectly repaired on failures. The Malik's model is used for describing repair effects. The parameters of a mixed Weilbull distribution and maintenance effects are estimated by maximum likelihood method. Simulation is used to illustrate the accuracy of the proposed method.

View full abstract

This paper considers a software reliability model which allows for two types of imperfect debuggings at each failure of the software system. For one type of imperfect debugging, the fault that causes the failure is imperfectly debugged without changing the fault contents of the software system. For the other type of imperfect debugging, the fault is not only imperfectly debugged, but also a new fault is generated and introduced to the system. The probability of perfect debugging assumed to be an increasing function of the number of repairs performed prior to the failure of the system. Based on the software reliability model presented, we develop a profit model, assuming the truncated expected software profit. The optimal values of release time are shown to be finite and unique. Numerical examples are provided for illustrative purposes.

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

The problem of trend change in the failure rate is great interest in the reliability and survival analysis. In this paper we develop a test statistic for testing whether or not the failure rate changes its trend. We do not assume that the turning point or the proportion before the turning point is known. We establish the asymptotic null distribution of test statistic and obtain asymptotic critical values of the asymptotic null distribution. Example is used to illustrate the application of our test.

View full abstract

[in Japanese]

View full abstract

A failure probability model based on Von-Mises failure criterion and the standard normal probability function is proposed. The effects of varying boundary conditions such as internal fluid pressure, external soil, traffic loads, temperature change and corrosion on failure probability of the buried pipes are systematically investigated. To allow for the uncertainties of the design variables, a reliability analysis technique has been adopted; this also allows calculation of the relative contribution of the random variables and the sensitivity of the failure probability.

View full abstract

The major failure in the field was that several keys were operated simultaneously on the keyboard of a personal computer. Based upon detail failure analyses, we found that the malfunction was result from an Ag ion migration in a membrane since the pattern of the membrane on the keyboard was composed of Ag paste. From the simulated tests, we noticed that the Ag ion migration was happened by moisture penetration into the membrane when the board is exposed to high temperature and high humidity for a long time. In this study, we developed a semi-waterproof membrane not only can prevent happening of a migration but also does not increase a manufacturing cost. It was verified that the mean lifetime of the newly-designed membrane can be assured minimum 5 years at the condition of (40℃, 90%RH). In addition, an accelerated test was developed to induct an ion migration and to validate reliability in a relatively short time. We found that the value of the acceleration factor was 17 at the stress (85℃, 85%RH) compared to the condition of (40℃, 90%RH)

View full abstract

[in Japanese]

View full abstract

The Formal Safety Assessment (FSA) is one of the emerging issues in the International Maritime Organization (IMO). FSA, in which reliability analysis technique is vital, is anticipated to be a systematic and efficient tool for the safety of ships. The object of this paper is to introduce and attract experts of reliability analysis, whose collaboration with naval architects and mariners should give rise to contributing results for better ship safety. Furthermore, maintenance policy to reduce machinery failure is examined for application. It is also suggested that possible and constructive communication can be established between researchers in various sectors and neighboring countries.

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

This paper presents a model for process quality assurance when the fraction nonconforming is very small. We design an acceptance control chart based on variable quality characteristic and time-censored accelerated testing. The distribution of the characteristics is assumed to be normal or lognormal with a location parameter of the distribution that is a linear function of a stress. The design parameters are sample size, control limits and sample proportions allocated to low stress level. These parameters are obtained under minimization of the relative variance of the MLE of location parameter subject to APL and RPL constraints.

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract