U.S. Philips Corporation

Johannes L Van Velthoven

Antonius H Akkermans

Theodorus A Koopmanschap

Scanning apparatus for a disc-shaped record carrier having a spiral track, the apparatus including a scanning head arranged on a slide which is radially displaceable with respect to the record carrier. The scanning point produced by the scanning head is maintained on the track by a tracking control system which includes a fine positioning device secured to the slide and which radially displaces the scanning point within a predetermined limited range of displacement determined by the positioning of the fine-positioning device with respect to the slide. A position-indication signal (PS) indicative of such position is generated, and a control unit detects when such signal exceeds a predetermined limit value. In that event, the control unit energizes a driving motor of the radial displacement device by supplying an energizing pulse pattern thereto which causes displacement of the slide to a position at which the position-indication signal returns to a value below the limit value. The energizing pulse pattern is adjusted by the control unit so that the displacement of the fine-positioning device in response thereto remains within predetermined limits and/or is symmetrical about a central position of such device relative to the slide.

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Middelburg, Netherlands

Johannes L Van Velthoven