Improvement of loading/unloading performance using control input position and considering disk vibration characteristics

Loading/unloading (L/UL) dynamic characteristics are affected by various operating parameters, such as L/UL speed, disk speed, disk vibration, and so on. The effects of these parameters on L/UL performance are investigated experimentally using an acoustic emission (AE) sensor, an in-plane laser Doppler vibrometer (LDV), and a vertical LDV. The experimental data shows that during the loading of the slider, the contact probability is lower for low L/UL speeds. The frequencies of slider-disk contact are lower for low disk rpm during the loading process, whereas in the unloading process the contact probability is lower for high disk rpm. The effects of disk vibration on the L/UL process are also studied, and we have found that the relative gap and slider-disk velocity between the disk and ramp affect the contact events in the L/UL process. During 1000 unloading cycles, most noncontact events occurred near the region of the maximum ramp gap during the loading process. During unloading, most of the contacts between the slider and disk occurred at the minimum relative speed. Slider-disk contact rarely occurred at the maximum relative unloading speed. The noncontact region tends to expand with higher disk speeds during the unloading process. This paper proposes a method to control the unloading input position to improve L/UL performance. By controlling the unloading instant based on the disk vibration characteristics, we can significantly reduce the number of slider-disk contacts.