Patent ID: 6798607
Filing Date: 2004-09-28
Classification: G11B

Abstract:
A servo system for calibrating servo index positions of a magnetic tape for track following, said magnetic tape having at least one set of parallel linear servo edges, each said servo edge comprising an interface between two dissimilar recorded servo signals, each said set of servo edges comprising one of said servo edges on each of opposite lateral sides of a middle said recorded servo signal, at least a plurality of said servo index positions laterally offset from said linear servo edges, said servo system comprising:at least one servo sensor of a tape head, said tape head movable laterally of said magnetic tape, said at least one servo sensor sensing said recorded servo signals of said magnetic tape comprising at least one said servo edge of said dissimilar recorded servo signals; a servo detector coupled to said at least one servo sensor for determining a ratio of said servo signals sensed by said servo sensor and providing digital servo signals at a predetermined sample rate; an independent position sensor to sense lateral position of said magnetic tape with respect to said tape head servo sensor; a servo loop for positioning said tape head laterally with respect to said magnetic tape to track follow said sensed servo signals at specific position error signals representing displacements from said at least one linear servo edge as determined from ratios of said sensed servo signals as determined by said servo detector; and logic coupled to said servo detector, said independent position sensor, and said servo loop, said logic: operating said servo loop to laterally position said at least one servo sensor to sense said servo signals at continually altered digital set points of said ratios of said sensed servo signals, said set points altered at said sample rate of said servo loop, said set points altered to inject a predetermined sinusoidal pattern single frequency positioning signal, whereby said servo loop track follows said at least one linear servo edge with said servo loop at said continually altered digital set points; digitally determining, from said independent position sensor at said sample rate, said lateral position of said tape head servo sensor with respect to said servo edge locations of said magnetic tape; digitally determining, from said servo detector at said sample rate, said ratios of said servo signals sensed by said servo sensor; converting said digitally determined independent position sensor lateral positions to frequency components; converting said digitally determined ratios of said servo signals to frequency components; selecting from said frequency components of said independent position sensor lateral positions, said predetermined sinusoidal pattern single frequency and at least one harmonic thereof; selecting from said frequency components of said servo signal, said predetermined sinusoidal pattern single frequency and at least one harmonic thereof; converting said independent position sensor selected frequency components to independent position sensor lateral positions; converting said servo signal selected frequency components to ratios of said servo signals; and fitting a curve to said converted independent position sensor lateral positions of said selected frequency components with respect to said converted ratios of said servo signals of said selected frequency components, to calibrate expected said position error signals for said servo loop at said laterally offset servo index positions with respect to said at least one sensed servo edge.