| 摘要 |
1533888 Automatic control of focus and position PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 25 Feb 1976 [28 Feb 1975] 07415/76 Heading G3R In optical playback apparatus, parallel tracks are read by at least two detectors disposed on the same side of a plane passing through the optical axis of the apparatus and the track to be read, and within the "far field" of the track i.e. disposed so that different diffraction orders can be distinguished. The apparatus also includes tracking and focus error corrections for the optical system. In the embodiment, for optically reading video data points 3 (e.g. pits) in a spiral or concentric track of a disc 1, a laser beam passes via mirror 9 and objective lens 11 to the disc. After transmission through, or reflection from, the data point 3, the beam which is modulated according to the information on the disc passes via lens 11, mirrors 8 and 9 to detectors 12, 13 and 14. The detector 12 is used to extract the video signal Si, and the detectors 13, 14 are used to sense interference lines of the modulated beam, the data points 3 acting as a diffraction grating. The period of the interference lines is determined by the focusing of the beam on data points 3, and the phase determined by the position of the beam relative to the data track i.e. centering of the beam. The outputs of detectors 13, 14 are summed to form a centering control signal Sr that varies the movement of mirror 9, and the outputs are differenced to form a focusing control signal Sf that varies the position of lens 11. The mirror 9 and lens 11 are moved until their respective control signals Sr, Sf are zero, preferably utilizing the centering control first. Up to four rectangular or triangular detectors may be used in the focusing and centering controls and these detectors are placed remote from the information detector 12. |
