COMPENSATION METHOD TO CORRECT THERMALLY INDUCED OFF-TRACK ERRORS IN DISC DRIVES

摘要

ABSTRACT OF THE DISCLOSUREA thermal test tract is provided outside the user-accessible area on the disc. A tack complete of a knownfrequency is then written on either side of this thermaltest track, preferably half the usual track separatedistance away. To develop a thermal compensation con-stant, the transducer is moved to the thermal test trackwith no compensation applied. This way, any thermallyinduced off-track error, which would affect seeks touser-accessible data tracks, will be reflected in theoff-track from the nominal position of the thermal testtrack. The transducer is now moved in a series ofdefined increments smaller than normal track-to-tracksteps, or "micro-steps," away from the uncompensatedposition of the thermal track toward one of the trackswritten with the known frequency. When the data on thewritten track to the side of the thermal test track isdetected, a note is made of the number of micro-stepsthe transducer has been moved. The transducer is thenmicro-stepped incrementally in the opposite directionuntil the data written on the other side of the thermaltest track is detected. A simple comparison of thesetwo micro-step counts will yield the existing thermalshift, which can be converted into a thermal compensa-tion constant for the transducer positioning mechanismby means of a simple look-up table.