Use of the relative position signal for microactuators in hard disk drives

A practical technique for measuring the relative position of a secondary actuator in a hard disk drive is described. Experimental results verify that it is able to measure and compensate for the first microactuator resonance. Many different techniques for introducing secondary actuators into hard disk drives to improve performance have been proposed in the past, but the majority of these have relied on the standard position signal for controlling both actuators. Alternative control loops that use the relative position signal are also described. A comparison of these configurations and the effects of noise on the relative position signal are presented.