Optical head assembly with a minimum of inertia and feasible for high high-speed access

Claim 1

An optical head assembly for use with an optical disk apparatus for focusing a light beam issuing in a track traversing direction which is substantially parallel to a radial direction of an optical disk onto a recording medium surface of said optical disk from a focusing direction which is substantially perpendicular to said recording medium surface, and guiding a reflection from said recording medium surface along a same path as but in the opposite direction to the light beam to record and/or reproduce information out of said optical disk, said assembly comprising: magnetic circuit means comprising permanent magnets each being elongate in the track traversing direction and a yoke for forming a magnetic circuit which conducts a magnetic field generated by said permanent magnets, said yoke being provided with a first through hole extending throughout said yoke in the focusing direction, magnetic gaps located at opposite sides of said first through hole in the track traversing direction and each accommodating respective one of said permanent magnets, and a second through hole for admitting the light beam issuing in the track traversing direction to guide the light beam to said first through hole, said first through hole and said magnetic gaps each having a cross-section which is relatively long in the track traversing direction; beam deflecting means loosely fitted in said first through hole for deflecting in the focusing direction the light beam which is incident to said beam deflecting means via said second through hole; a carriage supporting said beam deflecting means; an objective lens for focusing the light beam deflected by said beam deflecting means in the focusing direction onto said recording medium surface; a lens holder holding said objective lens and mounted on said carriage movably in the focusing direction; guide members supporting said magnetic circuit means and said carriage movably in the track traversing direction along said recording medium surface; a focusing coil wound around said lens holder and partly contained in said magnetic gaps for, when a current is fed through said focusing coil, transporting said lens holder in the focusing direction in cooperation with the magnetic field which is developed by said permanent magnets; tracking coils wound around said lens holder and partly contained in said magnetic gaps for, when a current is fed through said tracking coils, transporting said lens holder in the track traversing direction in cooperation with the magnetic field which is developed by said permanent magnets; and drive means connected to said magnetic circuit means for transporting said magnetic circuit means in the track traversing direction along said recording medium surface with said magnetic circuit means being guided by said guide means.