Richard C.M. Yam

Wavelet Analysis and Envelope Detection For Rolling Element Bearing Fault Diagnosis—Their Effectiveness and Flexibilities

The components which often fail in a rolling element bearing are the outer-race, the inner-race, the rollers, and the cage. Such failures generate a series of impact vibrations in short time intervals, which occur at Bearing Characteristic Frequencies (BCF). Since BCF contain very little energy, and are usually overwhelmed by noise and higher levels of macro-structural vibrations, they are difficult to find in their frequency spectra when using the common technique of Fast Fourier Transforms (FFT). Therefore, Envelope Detection (ED) is always used with FFT to identify faults occurring at the BCF. However, the computation of ED is complicated, and requires expensive equipment and experienced operators to process. This, coupled with the incapacity of FFT to detect nonstationary signals, makes wavelet analysis a popular alternative for machine fault diagnosis. Wavelet analysis provides multi-resolution in time-frequency distribution for easier detection of abnormal vibration signals. From the results of extensive experiments performed in a series of motor-pump driven systems, the methods of wavelet analysis and FFT with ED are proven to be efficient in detecting some types of bearing faults. Since wavelet analysis can detect both periodic and nonperiodic signals, it allows the machine operator to more easily detect the remaining types of bearing faults which are impossible by the method of FFT with ED. Hence, wavelet analysis is a better fault diagnostic tool for the practice in maintenance.

A study of the relationship between competitiveness and technological innovation capability based on DEA models

Researchers and managers have been searching for appropriate methods to explore the relationship between technological innovation capability and competitiveness in recent years. This study attempts to find a systematic quantitative methodology to tackle this problem. In a recent survey covering 182 industrial innovative firms in China, the traditional data envelopment analysis (DEA) model was employed to analyze the data collected. The research results show that only 16% of the enterprises operate on the best-practice frontier and there are some inconsistencies between organizational innovation capability and competitiveness in many enterprises. Decreasing returns to scale were found among about 70% of the inefficient enterprises and increasing returns to scale were found among the remaining 30% of the inefficient enterprises. Thus the internal innovation harmonizing process in these enterprises is considerably inefficient. Based on the restricted ranges of the input/output factors, a multi-objective DEA projection model has also been developed in this study to provide a benchmark for auditing competitiveness. Research results further indicate that there is still much room for enterprises to improve competitiveness in situations of confining score ranges of technological innovation capability and competitiveness.

GENERAL SEQUENTIAL IMPERFECT PREVENTIVE MAINTENANCE MODELS

This paper presents new sequential imperfect preventive maintenance (PM) models incorporating adjustment/improvement factors in hazard rate and effective age. The models are hybrid in the sense that they are combinations of the age reduction PM model and the hazard rate adjustment PM model. It is assumed that PM is imperfect: It not only reduces the effective age but also changes the hazard rate, while the hazard rate increases with the number of PMs. PM is performed in a sequence of intervals. The objective is to determine the optimal PM schedule to minimize the mean cost rate. Numerical examples for a Weibull distribution are given.

Supply chain integration and product modularity: An empirical study of product performance for selected Hong Kong manufacturing industries

Purpose – While the beneficial impact of supply chain integration (SCI) and modular product design are generally acknowledged, few empirical studies have examined how an organization can achieve better performance through SCI with modular product design. The purpose of this paper is to examine the relationship between SCI and modular product design, as well as their impact on product performance.Design/methodology/approach – By surveying 251 manufacturers in Hong Kong, structural equation modelling is used to test the research constructs and the hypothesized model.Findings – The results confirm that information sharing, product co‐development and organizational coordination are crucial organizational processes within SCI. Companies that have high levels of product modularity appear to be good at product co‐development and organizational coordination directly and at information sharing indirectly. Furthermore, companies that have high levels of product co‐development or product modularity appear to have be...

Sequential imperfect preventive maintenance models with two categories of failure modes

In this paper, we introduce the concept of two categories of failure modes: maintain- ablefailuremodesandnonmaintainablefailuremodesintothemodelingofpreventivemaintenance (PM) activities. The hybrid model proposed by Lin et al. is used to model the effect of a PM activ- ity on the failure rate function of maintainable failure modes. However, PM does not change the hazardratefunctionofnonmaintainablefailuremodes.PMisperformedatasequenceofintervals. The objective is to determine the optimal PM schedules to minimize the mean cost rate. Numerical examples for Weibull hazard rates are given. c 2001 John Wiley & Sons, Inc. Naval Research Logistics 48: 172{183, 2001

Collaboration between industry and research institutes/universities on industrial innovation in Beijing, China

Abstract Most R&D resources in China were allocated to public research institutes/universities until the economic transition of the mid 1990s. To maximize the return from these resources, it is important to have a healthy collaboration between industry and research institutes/universities on industrial innovation. This paper examines that relationship and discusses some empirical evidence on its efficiency with particular reference to industry in Beijing. Following a survey of 950 industrial enterprises, the influences of the collaboration relationship on industrial innovation were analyzed. The main findings indicate that the technology novelty of industrial innovation is positively related to that relationship, i.e. the more the collaboration, the higher the technology novelty of the innovation. However, the collaboration relationship is less efficient in terms of economic performance indicators such as innovation sales and profit ratios, to measure innovation. Moreover, the collaboration relationship is still far from efficient in stimulating industrial innovation in China. The major barriers to successful collaboration have also been addressed in this paper with the aim of devising policies and suggesting possible improvements to collaboration efficiency.

Supply chain product co‐development, product modularity and product performance: Empirical evidence from Hong Kong manufacturers

Purpose – This paper aims to examine how an organization can achieve higher performance through integrating supply chain product co‐development (SCPC) and modular product design.Design/methodology/approach – Based on a comprehensive review of literature on product development, supply chain management and system theory, the four proposed hypotheses concerning the relationships among SCPC, product modularity (PM), manufacturing capabilities and product performance (PP) were tested empirically through a sample of 251 Hong Kong manufacturers.Findings – SCPC is found to have a direct and positive relationship with PM and PP. PM improves flexibility and customer service and in turn PP.Research limitations/implications – Given the cross‐sectional nature of the study and the focus on manufacturing industry, future research should replicate this study in different industries with more longitudinal studies.Practical implications – The study provides solid evidence that managers should involve their suppliers, inter...

Optimal replacement policy for a multistate repairable system

In this paper, a deteriorating simple repairable system with k + 1 states, including k failure states and one working state, is studied. The system after repair is not ‘as good as new’ and the deterioration of the system is stochastic. Under these assumptions, we study a replacement policy, called policy N, based on the failure number of the system. The objective is to maximize the long-run expected profit per unit time. The explicit expression of the long-run expected profit per unit time is derived and the corresponding optimal solution may be determined analytically or numerically. Furthermore, we prove that the model for the multistate system in this paper forms a general monotone process model which includes the geometric process repair model as a special case. A numerical example is given to illustrate the theoretical results.

A comprehensive reliability allocation method for design of CNC lathes

Abstract In the design and development of computerized numerical control lathes, an effective reliability allocation method is needed to allocate system level reliability requirements into subsystem and component levels. During the allocation process, many factors have to be considered. Some of these factors can be measured quantitatively while others have to be assessed qualitatively. In this paper, we consider seven criteria for conducting reliability allocation. A comprehensive failure rate allocation method is proposed for conducting the task of reliability allocation. Example data from field studies are used to illustrate the proposed method.

A method for evaluation of reliability indices for repairable circular consecutive-k-out-of-n:F systems

Abstract In this paper, a repairable circular consecutive- k -out-of- n : F system with one repairman is studied. It is assumed that the working time and the repair time of each component are both exponentially distributed and every component after repair is ‘as good as new’. Each component is classified as either a key component or an ordinary component. Key components have priority in repair when failed. By using the definition of generalized transition probability, the state transition probabilities of the system are derived. Important reliability indices are evaluated for an example.