A data recording disk drive has a plurality of capacitive sensors, each sensor
facing a surface of an associated disk, a capacitance sensing circuit for converting
the sensed capacitance to a voltage representative of the distance between the
sensor and the disk surface, and a feedforward controller that receives the voltage
signal. The feedforward controller has a transfer function with gain and phase
characteristics designed to match the transfer function from the out-of-plane disk
vibration to the position of the read/write head while accounting for the effects
of the sensor dynamics and the dynamics of the actuator. The output from the feedforward
controller is combined with the output from the disk drive's servo feedback controller
so that the effects of disk vibration on track misregistration of the head are
removed from the control signal to the actuator.