Moving system for a videodisk reader-recorder

Claim 1

A moving system for a videodisk reader-recorder of the type comprising an objective which serves to focus a light beam on a track carried by a videodisk along a first axis substantially perpendicular to the disk, a carriage adapted to support said objective and means for displacing said carriage radially with respect to said disk along a second axis so as to follow the track, wherein said moving system further comprises: a frame for supporting the objective, means for joining said frame to said carriage whereby said frame is permitted to carry out a first longitudinal movement with respect to the carriage along the first axis in order to maintain focusing of the light beam on the disk and to carry out a second movement of rotation with respect to said carriage about a third axis perpendicular to the first two axes in order to maintain the focal point of the light beam on the track of the disk, magnetic field generation means having at least one magnet with two pole-pieces and one armature providing two air-gaps extending parallel to the direction of said second axis, one air-gap above the other air-gap with respect to said first axis, in which uniform magnetic fields are developed, in one direction for the upper pole-piece and in the other direction for the lower pole-piece and at least one first pair of flat coils attached to the frame in a plane at right angles to the third axis and symmetrical with respect to the first axis, said at least one first pair of flat coils circulating within said air-gaps in order, for each coil, to force current to flow parallel to the direction of said second axis and in one direction in a portion of said coil which is located within one of said air-gaps and in the other direction in a portion of said coil which is located within the other of said air-gaps, said coils developing forces which initiate said first and said second movement when said coils carry electric currents and are placed in said magnetic fields.