An apparatus capable of detecting a displacement of a probe from a track of a recording medium caused by track fluctuations and vibrations at a recording/reproducing period. For example, a probe is maintained to vibrate at a frequency and in the direction perpendicular to a data train at a amplitude...http://www.google.com.au/patents/US5404349?utm_source=gb-gplus-sharePatent US5404349 - Position displacement detecting apparatus
