Vibrating mirror for tracking on optically recorded disc - includes metallic body with flexible blade which oscillates in flexing mode

摘要

Information recorded along tracks (930) on a disc (93) is read by the radiating beam from a laser (90). A read head comprises a mirror (91) which pivots about an axis and also a focussing lens (92) is bringing the beam onto the required track. Under the disc is an optoelectronic detector (95) comprising photoelectric cells in four quadrants. This assembly converts the intensity variations from the beam passing through the recorded information into an electrical signal (VS1). A second signal (VS2) is obtained which gives radial tracking error. This is applied to a synchronous detector (97) with a signal (VS) derived from an oscillatory piezoelectric blade mirror (3) in the laser beam path. This blade is excited by an oscillater (8) which produces a reference signal for the electronic circuit (96) providing the oscillator drive. The electronic circuit provides the signal (VS) for the synchronous detector. The error is applied to a pivoting mirror (3) to provide tracking correction.