Time–frequency characterization of hand-transmitted, impulsive vibrations using analytic wavelet transform

Current guidelines to assess health risk of hand–arm vibration are based on the frequency-weighted rms acceleration level, therefore do not fully consider the effect of temporal variations of the spectral energy. Time averaging effect involved with the frequency analysis may severely underestimate the risk of impact tools. A time–frequency (T–F) analysis is necessary to characterize a highly transient signal whose spectral characteristics change rapidly in time. The analytic wavelet transform (AWT) is an ideal T–F analysis tool as it possesses the advantages of both the Fourier and wavelet transforms. The AWT is applied to acceleration signals measured from six tools, five impact type tools and one relatively steady-type tool, to explore possible improvements of the current risk assessment method of hand–arm vibration exposure. Based on the unique capability of the AWT, several new concepts including frequency-weighted time history, cumulative injury function, and cumulative injury index are defined in this study. Possible applications of these new concepts to hand–arm vibration research are described. Based on the results from this study, needs for future research are discussed.