Opto-electronic apparatus for writing and/or reading recording tracks by means of a radiation beam

Claim 1

An opto-electronic apparatus for writing and/or reading recording tracks in a recording surface of a record carrier by means of a radiation beam, such as the scanning by means of a light beam of video and/or audio recording tracks or digital data recording tracks in a reflecting recording surface of a rotating video or audio disc or a data disc respectively, which apparatus comprises: - a frame, - an objective holder provided with an objective having an optical axis and having a lens system for concentrating the radiation beam so as to form a radiation spot in a focussing plane, - a bearing arrangement for supporting the objective holder for movement relative to the frame in accordance with a desired number of degrees of freedom out of six theoretically possible, independent degrees of freedom, said bearing arrangement including counteracting means for counteracting those movements of the objective holder relative to the frame which are in accordance with other, undesired degrees of freedom, and - actuator means comprising parts which are connected to the frame and to the objective holder respectively and which cooperate magnetically with each other via an air gap, for driving the objective holder relative to the frame with electromagnetic actuator forces in accordance with the said desired degrees of freedom, which actuator means comprise at least one actuator coil for the desired degree of freedom, characterized in that: - the apparatus comprises an objective-position measuring device for continuously measuring the position of the objective holder (94; 114; 139) relative to the frame (96; 115; 141) in accordance with at least one of the said undesired degrees of freedom and generating a positional-error signal, - said counteracting means comprises at least one levitation coil secured to one of said frame and objective holder and magnetic means arranged on the other of said frame and objective holder, said magnetic means cooperating with said levitation coil via an air gap so as to produce an electromagnetic levitation force which counteracts undesired movement of the objective holder in accordance with at least one of said undesired degrees of freedom, - the bearing arrangement only permits movements of the objective holder relative to the frame in accordance with two desired degrees of freedom in a single plane of movement, one of the desired degrees of freedom being along a first translation axis (Z) which coincides with the optical axis of the objective, and the second degree of freedom being along a second translation axis (X) which is perpendicular to the first translational axis, - for electromagnetically driving the objective holder along the second translational axis and for electromagnetically counteracting movements of the objective holder in accordance with a third, undesired, degree of freedom about an axis of rotation (Y) which is perpendicular to the first and second translation axes said actuator means and said counteracting means comprise at least a first and a second combination coil (103A, 104A; 118A, 127A; 142, 143A) which function both as actuator coils and levitation coils, which two combination coils are spaced from each other, viewed along the second translation axis (X), and - a levitation control circuit is provided which compares the positional-error signal from the objective-position measuring device with a reference signal of specific value and which comprises at least one output for applying an electric levitation current whose value depends on the error signal to a levitation coil for maintaining substantially constant the position of the objective relative to the frame in accordance with an undesired degree of freedom.