Active damping in HDD actuator

A non-traditional mechanical modification technique to take care of the major servo bandwidth limited resonance mode (butterfly mode) is developed, analyzed, and validated. With an additional sensor on the actuator and an external feedback loop, the butterfly mode can be damped and stiffened such that the gain of the head mechanical transfer function is close to 1/s/sup 2/. Servo improvement is also studied comparing to notch filter approach. It shows that the butterfly mode notch filter can be removed, and the phase margin can be improved by 7 degrees.