TRACKING CHECK DEVICE OF OPTICAL HEAD APPARATUS FOR DISTRIBUTING COOLING GAS UNDER A RETAINING SLEEVE AT ONE END OF A TURBO-ALTERNATOR ROTOR EXCITATION WINDING

摘要

PCT No. PCT/JP85/00391 Sec. 371 Date Mar. 12, 1986 Sec. 102(e) Date Mar. 12, 1986 PCT Filed Jul. 11, 1985 PCT Pub. No. WO86/00742 PCT Pub. Date Jan. 30, 1986.The present invention is, in an optical head tracking error detecting apparatus in which a laser beam from a semiconductor laser element (1) is introduced into a diffraction grating (3), a 0-order beam and +/-1st-order beams emitted from the diffraction grating (3) are introduced through a beam splitter (4) to an objective lens (5), a 0-order beam and +/-1st-order beams of converged beams which are introduced into an optical recording medium (6) and reflected on the optical recording medium (6) are passed through the objective lens (5), reflected on the reflection surface of the beam splitter (4), and then introduced into a photodetector (7), a pair of photo-detection outputs corresponding to said +/-1st order beams are obtained from the photodetector (7) and on the basis of the difference between the pair of photo-detection outputs, there is generated a tracking error signal corresponding to the tracking state of the 0-order beam on the optical recording medium (6), to provide a pair of positive lenses (9) and (10) between the semiconductor laser element (1) and the diffraction grating (3) and a light shielding member (11) between the pair of positive lenses (9) and (10) to pass therethrough a central beam of the central beam and both side beams which are reflected on the optical recording medium (6), passed through the objective lens (5), the beam splitter (4) and the diffration grating (3) and directed to the semiconductor laser element (1) but to shield the both side beams, whereby to generate a tracking error signal which is not changed by the change of a tangential skew angle of the 0-order beam of an optical head OH relative to the optical recording medium (6).