Tracking control apparatus for controlling the tracking of a target track

A tracking control apparatus comprising:

• an information recording and reproducing medium having tracks on or from which information is recorded and reproduced,
• a pickup system radiating a light beam on said information recording and reproducing medium for reproducing the information from said medium as an output signal,
• error detecting means for detecting a displacing error between one of said tracks and a spot of said light beam on said medium in an orthogonal direction to said tracks,
• on-track detecting means for detecting on the basis of the output signal from said pickup system that said spot is positioned on one of said tracks and for outputting an on-track signal,
• traveling-direction detecting means for outputting a traveling direction signal representing a detected traveling direction in which said spot is moved relative to said tracks on the basis of the displacing error from said error detecting means and the on-track signal from said on-track detecting means,
• track slippage detecting means for detecting a track-slippage on the basis of the output signal from said pickup system and the traveling direction signal from said traveling-direction detecting means and for outputting a target track on-signal representing that said spot is positioned on a target track when said spot is positioned on said target track, and for outputting a track-slippage signal representing the direction of said spot being slipped out of said target track when said spot is slipped out of said target track,
• control signal output means responsive to said target track-on signal for outputting the output signal of said error detecting means as a control signal when said spot is positioned on said target track and for outputting the track-slippage signal of said track slippage detecting means as a control signal when said spot is not positioned on said target track, and
• tracking control means for driving said pickup system in a manner to allow said spot to follow said target track based on the control signal from said control signal output means.