Machine integrated health models for condition-based maintenance

Strojevi su podložni degradaciji zbog tehničkih kao i ne-tehničkih faktora koji im povećavaju mogućnost kvarova i pogoršavaju njihovo stanje zdravlja. Zbog toga raste zanimanje za nove metode procjenjivanja zdravstvenog stanja. Sada se inherentno zdravlje stroja procjenjuje praćenjem podataka koje pružaju senzori. Drugim riječima, razvoj inherentnog zdravlja ovisi jedino o razvoju tehničkih čimbenika te stoga ne daje sveobuhvatnu informaciju o stanju stroja. Ovaj rad uvodi koncepte "inherentnog zdravlja" i "integriranog zdravlja" kao i njihovu povezanost. Na osnovu procjene inherentnog zdravlja, integrirano zdravlje uzima u obzir ne-tehničke faktore koji se odnose na starost, radne uvjete i održavanje stroja. Učinkovitost održavanja se također razmatra integrirajući sekvencijalnu nesavršenu politiku održavanja u strategiju održavanja koja se zasniva na integriranim zdravstvenim uvjetima. Sveobuhvatnom procjenom i otkrivanjem u stvarnom vremenu stanja integriranog zdravlja, ovaj se model može koristiti kao podrška upravljanju zdravljem stroja i donošenju odluke o održavanju. U analizi pojedinih slučajeva, očekuje se da će se očite razlike između inherentnog zdravlja i integriranog zdravlja pojaviti u određenim uvjetima.Machines undergo degradation as a result of both technical factors and non-technical factors that increase the potential for failures and deteriorate their health condition, and there is growing interest in new methods for health condition assessment. Currently, the inherent health of a machine is evaluated by monitoring of the data acquired by sensors. In other words, the evolution of the inherent health depends only on the evolution of technical factors, and therefore does not comprehensively represent the overall condition of the machine. This study introduces the concepts of "inherent health" and "integrated health" as well as their relationship. On the basis of inherent health assessment, the integrated health considers the non-technical factors related to the age, working conditions, and maintenance of a machine. By integrating a sequential imperfect maintenance policy into the maintenance strategy based on the integrated health conditions, the maintenance effectiveness is also considered. Through comprehensive assessment and real-time detection of the integrated health condition, this model may be used to support machine health management and maintenance decision-making. In case studies, the obvious differences between inherent health and integrated health are expected to appear under certain circumstances

Evaluating maintenance policies by quantitative modeling and analysis

International audienceThe growing importance of maintenance in the evolving industrial scenario and the technological advancements of the recent years have yielded the development of modern maintenance strategies such as the condition-based maintenance (CBM) and the predictive maintenance (PrM). In practice, assessing whether these strategies really improve the maintenance performance becomes a funda-mental issue. In the present work, this is addressed with reference to an example concerning the stochastic crack growth of a generic mechanical component subject to fatigue degradation. It is shown that modeling and analysis provide information useful for setting a maintenance policy

Integrated production quality and condition-based maintenance optimisation for a stochastically deteriorating manufacturing system

This paper investigates the problem of optimally integrating production quality and condition-based maintenance in a stochastically deteriorating single- product, single-machine production system. Inspections are periodically performed on the system to assess its actual degradation status. The system is considered to be in ‘fail mode’ whenever its degradation level exceeds a predetermined threshold. The proportion of non-conforming items, those that are produced during the time interval where the degradation is beyond the specification threshold, are replaced either via overtime production or spot market purchases. To optimise preventive maintenance costs and at the same time reduce production of non-conforming items, the degradation of the system must be optimally monitored so that preventive maintenance is carried out at appropriate time intervals. In this paper, an integrated optimisation model is developed to determine the optimal inspection cycle and the degradation threshold level, beyond which preventive maintenance should be carried out, while minimising the sum of inspection and maintenance costs, in addition to the production of non-conforming items and inventory costs. An expression for the total expected cost rate over an infinite time horizon is developed and solution method for the resulting model is discussed. Numerical experiments are provided to illustrate the proposed approach

Evaluation of proactive maintenance policies on a stochastically dependent hidden multi-component system using DBNs

In complex systems with stochastically dependent components which are not observed directly, determining an effective maintenance policy is a difficult task. In this paper, a dynamic Bayesian network based maintenance decision framework is proposed to evaluate proactive maintenance policies for such systems. Two preventive and one predictive maintenance strategies from a cost perspective are designed for multi-component dependable systems which aim to reduce maintenance cost while increasing system reliability at the same time. Tabu procedure is employed to avoid repetitive similar actions. The performances of the policies are compared with a reactive maintenance strategy and also with each other using different strategy parameters on a real life system confronted in thermal power plants for six different scenarios. The scenarios are designed considering different structures of system dependability and reactive cost. The results show that the threshold based maintenance which is the predictive strategy gives the minimum cost and maintenance number in almost all scenarios.This research is supported by the Scientific and Technological Research Council of Turkey (TUBITAK) under grant: 117M587.Publisher's Versio

Análise Multivariada do Sistema de Medição de um Processo de Solda a Ponto por Resistência Elétrica utilizando Componentes Principais Ponderados.

O processo de soldagem a ponto por resistência elétrica (RSW) apresenta ampla aplicabilidade na indústria, principalmente no setor automotivo, devido à sua rápida execução, não utilização de consumíveis e adequação a operações automáticas. Sendo um processo de grande destaque, a busca pela melhoria da qualidade do produto é incessante e em um processo já capaz, não deve haver erro de medição. O RSW apresenta diversas características da qualidade e a análise de múltiplas grandezas correlacionadas pode ser melhor abordada utilizando-se técnicas multivariadas. Assim, esta dissertação busca aplicar o estudo de repetitividade e reprodutibilidade de caráter multivariado (GR&Rm) com o objetivo de analisar o sistema de medição de um processo de soldagem a ponto por resistência elétrica fazendo uso de uma estratégia por componentes principais ponderados, que se caracteriza por um método que trabalha com o escores dos componentes principais, ponderando-os pelo seus autovalores, a partir de grandezas correlacionadas. Para o estudo fora selecionado sete características da qualidade, duas respostas para ensaios mecânicos destrutivos e cinco para caracterização geométrica do ponto soldado. Para complementar as análises, realizou-se a comparação com os instrumentos convencionais de metrologia para duas características da qualidade distintas. No que diz respeito aos resultados, os ensaios destrutivos identificaram uma falta de repetitividade nas medições de uma das máquinas, favorecendo à realização de possíveis melhorias neste sistema. Para a caracterização geométrica do ponto soldado, o ndcm apresentou-se como aceitável, porém o estudo GR&Rm se classificou como marginal, podendo variar para um valor até 6,94, mostrando que este SM tem capacidade de apresentar melhorias e ter classificação aceitável, diante ao intervalo de confiança estabelecido. Na análise comparativa com instrumentos convencionais de metrologia, verificou-se que a coerência das medições através do analisador de imagens se apresentou superior em ambos os casos avaliados

A study of new and advanced control charts for two categories of time related processes

Ph.DDOCTOR OF PHILOSOPH