Optical focus position control in an optical memory system

Claim 1

An optical focus and positioning control device for controlling the optical focus and position of an optical beam such as a laser beam in an optical disc apparatus, the optical focus position control device comprising: an objective lens; lens support means for supporting said objective lens; a stationary holder; tracking control means for shifting said lens support means in the radial direction of the optical disc, said tracking control means including, a movable intermediate holder, tracking parallel spring means for connecting said lens support means to said intermediate holder in a manner to allow said lens support means to move in with respect to said intermediate holder in the radial direction of the optical disc, and electromagnetic tracking drive means, having a closed magnetic circuit mounted for movement with said intermediate holder, for shifting said lens support means in said radial direction within said intermediate holder, said closed magnetic circuit minimizing flux leakage therefrom; and focus control means for shifting said tracking control means in the direction of the optical axis of said optical beam, said focus control means including, focusing parallel spring means for connecting said intermediate holder to said stationary holder in a manner to allow said intermediate holder to move with respect to said stationary holder in said optical axis direction and electromagnetic focus drive means for shifting said intermediate holder in said optical axis direction within said stationary holder, said electromagnetic focus drive means including a closed magnetic circuit to minimize flux leakage therefrom said electromagnetic focus drive means comprising, a focusing permanent magnet creating said closed magnetic circuit, a focusing yoke plate supporting said focusing permanent magnet, a focusing yoke mounted on said stationary holder and supporting said focusing yoke plate, a focusing magnetic space formed between said focusing yoke plate and said focusing yoke, and a focusing drive coil disposed in said focusing magnetic space so as to cross said focusing magnetic space, wherein said focusing magnetic space is located close to an optical disc when installed in said optical disc apparatus, and wherein said focusing parallel spring means includes, a parallel metal spring and a latexed acrylic-ethylene rubber attached to the surface of said parallel metal spring.