Voice coil motor with linearized force constant

Claim 1

Tracking actuator apparatus for an optical beam addressable information storage disk drive system adapted to move a read/write head rapidly along a stroke path parallel with a planar surface of a recording medium and generally parallel with a line normal to a plurality of closely spaced parallel data tracks formed on said planar surface thereby to position a focused optical beam generated within the head on one of said data tracks, said apparatus comprising: elongated head means for generating said optical beam, said head means having first and second end portions with said optical beam emanating from one of said end portions; flexure means for suspending said head means with smooth, friction-free translation motion along said stroke path between extremes thereof; a plurality of magnetic circuit means for establishing mutually isolated magnetic fields across a plurality of elongated air gaps individually disposed on opposite sides of the head means intermediate the end portions thereof, the elongated dimensions of each of said air gaps being parallel with the elongated dimension of said head means and longitudinally centered with respect to the center of said stroke path, each of said magnetic circuit means including an elongated permanent magnet and an elongated flux return pole spaced in parallel from the magnet to form said air gaps, each of said magnets having an air gap face area shaped to have a reduced width at the center relative to the widths of the face at the ends of the magnet to maintain a substantially constant force constant throughout the length of said stroke path; electromagnetic coil means having a plurality of turns formed coaxially about the longitudinal center line of said head means and secured to the head means intermediate the end portions thereof, said coil means having end turn segments spaced symmetrically away from said head means and disposed in said air gaps, said flexure means suspending said head means with said turn segments centered between the extremes of said stroke path; and means for supplying tracking actuator signals to said coil means to cause said coil and head means to move longitudinally along said stroke path with a substantially uniform force constant through the full length of said stroke path.