Disk storage drive

Claim 1

In a digital information-storage apparatus of the type having a read and/or write head which inscribes information bits onto, and/or reads them from, at least one data storage disk which is rotated at high speed relative to such head by means of a rotary disk-holding structure configured to be accommodated in the large central aperture of such disk and transmit rotation thereto, the combination with said rotary disk-holding structure of a brushless d.c. reluctance-torque motor, said brushless d.c. reluctance-torque motor comprising a stator, a rotor, said rotor being coupled to said rotary disk-holding structure to transmit rotation thereto, said rotor being a permanent-magnet rotor, said stator having a stator winding which when energized by d.c. current establishes a stator field which in cooperation with said rotor produces an electromagnetic-torque component having a magnitude which is a variable function of rotor angular position and which, at predetermined angular positions of said rotor, is of zero magnitude, and thus incapable of starting the rotor from said predetermined positions, whereby if, when the motor is shut off, the rotor were to come to a complete stop in said predetermined positions, it could not thereafter be restarted by mere application of current to the stator winding, said rotor and stator being separated from each other by an air gap and together forming a magnetic circuit whose reluctance is a function of the angular position of said rotor thereby producing a reluctance-torque component, the reluctance-torque component varying as a function of rotor angular position and having a magnitude which is of non-zero value at said predetermined rotor angular positions at which the electromagnetic-torque component is of zero value, said non-zero value of said reluctance-torque component at said predetermined angular positions precluding the rotor from becoming stuck at said predetermined positions during start-up of the motor, an angular position detector detecting the angular position of said rotor, and means controlling flow of current through said stator winding in dependence upon the operation of said angular position detector to cause said stator field to alternate, in dependence upon rotor angular position, between two stator-field orientations which are 180 electrical degrees opposite to each other.