Method of and device for scanning a radiation-sensitive surface of a

Abstract

A method and apparatus for scanning a rotating optical disc record carrier with a radiation beam which forms a scanning spot on the carrier and which is moved radially relative thereto. Pulses are generated at a frequency proportional to the angular velocity of the carrier, and clock pulses are generated at a constant frequency differing from and preferably higher than that of the velocity pulses. In response to each velocity pulse an accumulator is incremented by a first correction value (INC) and in response to each clock pulse the accumulator is decremented by a second correction value (DEC). The angular velocity of the record carrier is controlled to maintain a constant value of the average of the sum output of the accumulator over the intervals between successive velocity pulses, and the correction values are adjusted so that the ratio thereof is maintained proportional to the radial distance between the scanning spot and the axis of rotation of the carrier. Scanning is thereby accurately maintained at a constant linear scanning velocity.