Disturbance observer design with Bode’s ideal cut-off filter in hard-disc-drive servo system

In order to improve the disturbance compensation performance under vibrations in hard-disc-drive servo system, Bode’s ideal cut-off (BICO) filter is applied for the disturbance observer (DOB) design. New DOB is designed with BICO low pass filter (LPF) substituting the normal LPF in the original DOB design. With this BICO LPF, the new DOB can achieve strengthened attenuation of error sensitivity in disturbance frequency range to obtain better disturbance compensation performance while maintaining the robust specifications. This benefit comes from the less phase loss property of the BICO filter. Meanwhile, the BICO filter with the property of sharp roll-off magnitude is applied for the disturbance frequency range detection filter design. Using this BICO identification filter, multiple-DOB control can be used for the disturbance compensation based on the switching according to the disturbance detection. Industrial drive level experimental results are included to validate the proposed new DOB scheme under vibration.