Abstract: An electric motor, which is preferably a disk drive spindle motor, contains a multi-phase stator driven by switching the phases of drive current at corresponding commutation angles of the rotor. Small semi-random offsets are introduced into the commutation angles at which the drive current is switched, spreading the frequency of excitation over a wider range, and reducing the peak harmonic excitation at the switching frequency. Preferably, a table of offsets is maintained, and an offset from the table is added to each commutation point. The table preferably has more entries than the number of commutation points, the entries being cycled on a round-robin or other basis.

Abstract: A capacitor discharge retract system is provided for small disk drives wherein the small spindle size is incapable of generating enough electrical energy to enable conventional actuator retraction and the form factor is too small to accommodate capacitors of sufficient size to enable a conventional capacitive discharge system. A capacitive discharge retract technique is enabled using an elevated voltage, significantly above the disk drive supply voltage, to allow smaller capacitive storage elements to perform the function. The effectiveness of the system is further enhanced in those environments where a source of the required elevated voltage can be found already resident in the device circuitry where it was generated to support another function.

Abstract: Rotary actuator arc compensation correction method and apparatus are provided for a direct access storage device (DASD). A reference feedforward correction signal is generated at each of a plurality of sectors around a predetermined track on a disk surface. A specific selected track is identified, and both magnitude and phase of the generated reference feedforward correction signal are modified to correct for the arced trajectory caused by the rotary actuator at the specific selected track. Improved actuator servo control is provided by using pseudo sector compensation to interpolate the feedforward correction signal between servo sectors.

Abstract: Rotary actuator arc compensation correction method and apparatus are provided for a direct access storage device (DASD). A reference feedforward correction signal is generated at each of a plurality of sectors around a predetermined track on a disk surface. A specific selected track is identified, and both magnitude and phase of the generated reference feedforward correction signal are modified to correct for the arced trajectory caused by the rotary actuator at the specific selected track. Improved actuator servo control is provided by using pseudo sector compensation to interpolate the feedforward correction signal between servo sectors.

Abstract: A demodulator system for identifying the position of a transducer assembly over a disk of a direct access memory device. The demodulator identifies alias cases and uses information placed in the boundary between tracks to generates a more robust indication of the location of the transducer assembly.

Abstract: An apparatus and method for correcting for track misregistration when a slider or head assembly contains a separate read element and write element. The offset is determined at a first position and at a second position of the actuator arm assembly. From these offsets a constant and a multiplier are determined for determining an offset as a function of the cylinder location. Also disclosed is a method and apparatus for minimizing distance traveled to prevent misregistration when repositioning between the read element and a write element. The read element is intentionally offset from the write element at an angle so as to minimize the distance traveled across the disk.

Abstract: A reduced size brushless DC motor preferably for use as a disk drive spindle motor includes a rotor having two sets of permanent magnets, and a stator having separate portions corresponding to the two sets. An upper set of permanent magnets and the corresponding portion of the stator are located within the upper portion of the hub, which fits within the holes of the disks of a disk drive. A lower set of permanent magnets and corresponding portion of stator are located in the flange of the motor hub which supports the disks from below. In one embodiment, the stator core has an L-shaped cross-sectional area in the plane of the motor axis, one leg of the L driving the upper set of magnets in the rotor and the other leg driving the flange magnets. In a second embodiment, the stator core includes two separate pieces, one corresponding to each set of permanent magnets.