Papers by Author: L.W. Tang

Abstract: Silver dispersed lead titanate films were prepared with different Pb/Ti ratio precursors. The influence of lead excess in precursor on the formation and dielectric properties of silver-dispersed lead titanate film was investigated. Firstly, Pb excess in precursor will eliminate the formation of pyrochlore PbTi3O7 and increase c/a ratio of perovskite PbTiO3. Secondly, excessive Pb will react with silver, and they can produce volatile product, which evaporate during heat treatment process. The volatility of the reaction product varies with the increase in lead excess. When lead excess is low (Pb/Ti=1.1), volatility of reaction product is high. At this time, only small amount of silver remain in the film. The remanent silver aggregate to form small silver particles. When lead excess is high (Pb/Ti=1.2 and Pb/Ti=1.3), volatility of reaction product gradually becomes poor. At this time, the content of remanent silver in the film increase with the increase in lead excess. Compared with the film prepared with low Pb/Ti ratio, the dispersive degree of silver in film prepared with high Pb/Ti ratio is higher. Due to the decrease of remanent silver content in the film, dielectric constant and dissipation factor both decrease when Pb/Ti initially increase from 1 to 1.1. And after that, dielectric constant and dissipation factor both increase with the addition of excessive Pb in precursor, due to the increase in the content and dispersion degree of silver, and increase in c/a ratio of PbTiO3 lattice with the addition of excess Pb. The film prepared with appropriate excessive lead (Pb/Ti=1.3) precursor expresses higher dielectric constant and lower dissipation factor than the film prepared with stoichiometric Pb/Ti ratio.

Abstract: Time-frequency and transient analysis have been widely used in signal processing and faults diagnosis. These methods represent important characteristics of a signal in both time and frequency domain. In this way, essential features of the signal can be viewed and analyzed in order to understand or model the faults characteristics. Historically, Fourier spectral analyses have provided a general approach for monitoring the global energy/frequency distribution. However, an assumption inherent to this method is the stationary and linear of the signal. As a result, Fourier methods are not generally an appropriate approach in the investigation of faults signals with transient components. This work presents the application of a new signal processing technique, empirical mode decomposition and the Hilbert spectrum, in analysis of vibration signals and gear faults diagnosis for a machine tool. The results show that this method may provide not only an increase in the spectral resolution but also reliability for the gear faults diagnosis.

Abstract: A novel scheme for ball bearing faults detection is presented based on Hilbert-Huang transformation and its energy spectrum. The basic method is introduced in detail. The energy spectrum is applied in the research of the faults diagnosis for the ball bearing of machine tool. Firstly, the analyzed vibration signals are separated into a series of intrinsic mode function using the empirical mode decomposition. Then, the energy spectrum is applied to the intrinsic mode function. The experimental results show that this method based on Hilbert-Huang transformation and energy spectrum can effectively diagnosis the faults of the ball bearing.