Automatic scan tracking servo system

Abstract

An improved automatic scan tracking servo for use in a magnetic recording and reproducing apparatus is disclosed. The automatic scan tracking servo operates generally in the digital domain. The apparatus has a movable element which is transversely moved relative to the longitudinal direction of a recorded track so that the transducing head can be made to accurately follow the track during special motion reproducing modes. The RF video signal is sampled a predetermined number of times during each rotation of the scanning drum carrying the transducing head. The phase of the oscillatory motion or dither that is applied to the movable element carrying the head, the operation of a synchronous detector and the sampling are all totally synchronized to obtain an accurate error signal so that an accurate error correcting signal can be generated to have the transducing head accurately follow a track during such reproducing. The servo utilizes the longitudinal tape speed to provide a predicted value of the slope of the ramp that is required to have the head follow the track and the error correcting signal merely modifies the ramp in accordance with the actual error that is detected. The combination of the synchronism and the predicted value of the slope enables a reduced dither amplitude to be used to obtain an accurate error signal.