Key points are not available for this paper at this time.
Pure motion-control at the speed and precision required for disk drives is difficult by itself, but the problems become even worse when it comes to emergency conditions like the loss of supply voltages. To prevent the head from crashing into or sticking on the media in this case, it has to be moved to a park position-still with broken power supply. This and many other functions are integrated in the motion-control circuit, covering the range from power/analog to digital circuitry.
W. Sereinig (Wed,) studied this question.