Abstract: A servo system moving a transducer between tracks in a sector servo disk drive generates a velocity profile representing the variation of the desired velocity of the head in moving from a first track to a second track. The velocity profile has an acceleration phase and deceleration phase, with the transition from acceleration phase to deceleration phase identified as a switch point.The velocity of movement of the head is periodically sampled from the sector servo pattern in a sequence of sample periods during movement of the head. The energization of the head moving element is controlled so that the switch point occurs during one of the sample periods, thereby resulting in improved performance in positioning the head at the desired track. The system accommodates itself to variations, such as mechanical or electrical disturbances, which would otherwise affect the system.

Abstract: A system for controlling the operation of a polyphase DC motor having a rotor and a plurality of phase windings with separate outer terminals and a common center tap terminal supplies electrical energy sequentially to the phase windings to produce rotation of the rotor relative to the phase windings. The voltage between the outer terminal of one of the phase windings and the center tap terminal is sensed during periods when that one phase winding is not energized to control the sequential supplying of electrical energy to the phase windings.