Measurements of slider-disk contacts during dynamic load-unload

The laser Doppler vibrometer (LDV) and acoustic emission (AE) have been used to investigate the slider dynamics and to detect possible slider-disk contacts during dynamic load-unload. One of the puzzling aspects of previous work has been the AE indication of contacts at an LDV measured spacing of about 8 mu m. The procedure of LDV spacing measurement for load-unload is investigated, and three sources of possible error are found and verified by experiment. First is the deviation between single shot and average measurements. Second is the disk motion that occurs during loading. Third is the elevation difference at the measured point and the closest point during loading, which depends on the unloaded pitch and roll angles. It is found that the jump in the velocity signal of single shot LDV measurement gives a good indicator of contacts. The electrical resistance method is applied to the detection of contacts during dynamic load-unload and compared with the results obtained by the LDV and AE. Its contact signal is in good agreement with the jump in the LDV velocity signal and more distinguishable than the AE signal.<
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