Video disc head tracking apparatus

An improved tracking system for an optical disc playback apparatus adapted to recover information from a plurality of information tracks recorded on a reflective optical disc, said improved tracking system including:

• an optical system for directing a beam of radiant energy to impinge upon the reflective optical disc and for directing radiant energy reflected by the disc to a photocell detector configured to ouptut a first signal proportional to the amount of said reflected radiant energy actually received by said photocell detector;
• beam steering means for moving said beam of radiant energy in a radial direction relative to the disc to follow a selected one of said information tracks;
• servo control means, operatively associated with said beam steering means, for controlling said beam steering means to cause said beam to impinge upon a predetermined edge portion of said selected one of said information tracks being followed by said beam, said servo control means including:
• said photocell detector;
• bias means for outputting a second signal;
• a comparator having a pair of inputs and a single output, a first one of said inputs being said first signal and the second one of said inputs being said second signal, said single output of said comparator being an error signal representing the difference between said first signal and said second signal,said error signal causing said beam steering means to move said beam in a first direction when said first signal indicates that said beam is impinging upon more than said predetermined edge portion, and to move said beam in a second direction when said first signal indicates that said beam is impinging upon less than said predetermined portion.