| 摘要 |
PURPOSE:To enable detection of both to be performed with an optical means by utilizing an information reading luminous flux for detection of the focal position of an optical lens for focusing the luminous flux for information reading on a video disc and the detection of a beam spot position. CONSTITUTION:The luminous flux which is made to an approximately parrallel luminous flux in one of the two mutually perpendicularly inersecting sections parallel to the advancing direction and is made to a divergent or convergent luminous flux in other section is used as a luminous flux 11 for information reading. Such luminous flux 11 passes through a light transmittable plate form body 12 such as galss or the like which oscillates about the axis on the plane approximately perpendicular to the advancing direction of said luminous flux 11 and is condensed onto a light reflecting face 17 by an optical lens 16. The reflected luminous flux from the light reflecting face 17 is led to photo detectors 19, 21. The output of the phot detector 19 is led to a focal position gradual adjusting mechanism 20, whereby the focal position is matched to the light reflecting face 17. The reference position of the oscillation of the plate form body 12 is controlled so that the signal component in the output of the photo detector 21 becomes maximum, whereby the beam spot is always maintained on the track. |
