Importance

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Abstract

An automatic focusing device includes an optical head which comprises a focusing lens system and an optical sensor. The focusing lens system focuses a reading laser beam or a recording laser beam on an optical disk. The optical sensor generates photoelectric signals which correspond to the sections of a beam spot formed by a laser beam reflected from the optical disk. Record signal components corresponding to a recording laser beam are removed from the photoelectric signals by switch circuits. The photoelectric signals no longer containing record signal components are supplied to envelope detectors. The envelope detectors generate envelope signals each formed of signal components which correspond to a laser beam reflected from the surface of the optical disk. According to the difference between the envelope signals the focusing lens system is driven to thereby focus a laser beam on the optical disk.

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First Claim