A sinusoidal signal is added to the notch filtered micro-actuator control signal
stimulating the micro-actuator. The voice coil control signal is notch filtered
to remove the frequency component of the sinusoidal signal before it stimulates
the voice coil motor. The micro-actuator control signal is notch filtered to remove
the frequency component of the sinusoidal signal before it stimulates the micro-actuator.
The response of the system is measured as the Position Error Signal (PES), for
the magnetic head moved by the micro-actuator. The measured PES is then demodulated
at the frequency of the sinusoidal signal to create a measured amplitude. The stroke
sensitivity is then calculated from the measured amplitude and amplitude of the
sinusoidal stimulus. The frequency of the sinusoidal signal and notch filters is
essentially the same, chosen away from significant excitation frequencies and outside
the bandwidth of the servo system. The invention includes using multiple frequencies,
as well as various formulas for the stroke sensitivity. The invention may be applied
to more than one micro-actuator within the hard disk drive to create a stroke sensitivity
for each micro-actuator, a combination, or for all micro-actuators. The invention
includes the method implemented using a servo-controller, as well as the program
system for the servo-controller, at least partly implementing the method.