Pure torque, limited displacement transducer

Claim 1

A brushless, bidirectional, pure torque generating, electromechanical rotary actuator for random access, rapid positioning, along an arc of less than 90 degrees of a data transducer assembly among preselected ones of concentric data tracks of a rotating data storage disk, said actuator comprising: a base plate, a lower flux return plate secured to said base plate, permanent magnet means secured to said lower flux return plate for providing an even number plurality of adjacently opposed field magnetic field segments in which the north and south poles alternate at the major surfaces thereof, a stationary shaft connected to said base plate and extending vertically perpendicular to said base plate through the center of said lower flux return plate and said permanent magnet means, a hub rotatably mounted to said shaft, a coil assembly secured to said rotatable hub and closely spaced from said permanent magnet means, said coil assembly containing the same even number plurality of coils as there are magnet segments in said permanent magnet means, said coils being aligned adjacent to said magnetic segments at at least one position of rotation of said assembly, said coils being connected into two series of opposed windings equidistantly and symmetrically located about said assembly, an upper flux return plate secured to said base plate parallel to said permanent magnet means defining therebetween an annular space for said coil assembly and closely spaced to said coil assembly, a data transducer carriage connected to said hub and having a data transducer secured to its distal end, and a counterweight secured to said hub on the opposite side of said data transducer carriage to balance the weight thereof, whereby energizing said coils causes pure torque to be applied to said hub rotating said rotor arm and positioning said data transducer relative to said rotating data storage disk.