Rotation control apparatus for constant linear velocity system information recording disc

Claim 1

A rotation control apparatus for a constant linear velocity system information recording disc which is rotated by a motor, said information recording disc being pre-recorded with an address signal indicative of a position of said information recording disc within a predetermined region thereof, said rotation control apparatus comprising: rotation detecting means for detecting a rotation of said information recording disc and for generating rotation detection pulses having a period inversely proportional to a rotation frequency of said information recording disc; a pickup device for recording and reproducing an information signal on and from said information recording disc by scanning said information recording disc; a moving mechanism for moving said pickup device in a radial direction of said information recording disc; control means responsive to a signal reproduced from said information recording disc by said pickup device for supplying to said moving mechanism a signal for moving said pickup device to an arbitrary position within said predetermined region and for moving said pickup device at a normal speed after reproducing the address signal in a stop reproduction mode in which one track turn on said information recording disc is scanned repeatedly; address signal detecting means for detecting a reproduced address signal within the reproduced signal from said pickup device; operation circuit means for calculating from the reproduced address signal an initial value in accordance with a regular rotation frequency of said information recording disc at said arbitrary position; an oscillator for generating a signal having a constant frequency; frequency dividing means for counting said rotation detection pulses by starting from said initial value and for frequency-dividing the output signal of said oscillator by a frequency dividing ratio which successively increases with a counted value; and comparator means for comparing phases of said rotation detection pulses and an output signal of said frequency dividing means and for producing a phase error signal, said phase error signal being supplied to said motor to control the rotation thereof, so that a relative linear velocity between said pickup device and said information recording disc is maintained substantially constant.