Browse Prior Art Database

Tri Bit Servo Pattern

IP.com Disclosure Number: IPCOM000081233D
Original Publication Date: 1974-Apr-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 3 page(s) / 67K

Publishing Venue

IBM

Related People

Wallis, CN: AUTHOR

Abstract

Fig. 1 represents a portion of a magnetic disk surface 1 encoded with magnetic patterns which, in conjunction with a servo head 2, supplies position information pulses, Fig. 2, to disk file control electronics. A plurality of `odd' tracks 3, 5, 7, 9 and `even' tracks 4, 6, 8 are shown extending in concentric circles around the disk surface. The direction of magnetization of the various portions of the tracks is represented in the figure by arrows.

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Tri Bit Servo Pattern

Fig. 1 represents a portion of a magnetic disk surface 1 encoded with magnetic patterns which, in conjunction with a servo head 2, supplies position information pulses, Fig. 2, to disk file control electronics. A plurality of `odd' tracks 3, 5, 7, 9 and `even' tracks 4, 6, 8 are shown extending in concentric circles around the disk surface. The direction of magnetization of the various portions of the tracks is represented in the figure by arrows.

The servo tracks are written with no gaps between them and magnetic flux reversals in one of the two directions (negative say) are aligned from one track to the next, thus providing continuous transitions of the same polarity radially across the disk surface. The flux reversals in the opposite direction (positive) on alternate tracks are staggered, either both early or both late about the midpoint or the aligned radial transitions. A servo transducer positioned over the tracks experiences flux reversals, as each junction between different magnetic regions passes the transducer gap. The polarity and amplitude of the resulting pulses are proportional to the magnitude and polarity of the flux reversal producing it.

Fig. 2a shows the pulses produced by the servo transducer position as shown in Fig. 1, symmetrically displaced above the boundary between the two tracks 3 and 4. The resulting pulse pattern consists of negative clock pulses 11, and positive position pulses 12 from the odd track 3 and positive position pulses 13 from the even track 4 as the tracks pass the transducer gap. The position pulses 12 and 13 are of equal magnitude, each being half the magnitude of a clock pulse 11, provided the transducer 2 is accurately positioned over the boundary between the two tracks. Such boundaries between tracks are called `guide' paths. The boundaries between tracks 3 and 4, 5 and 6, 7 and 8, etc. are called `odd' guide paths and those between tracks 4 and 5, 6 and 7, 8 and 9, etc. are called `even' guide paths.

Should the servo transducer 2 move out of the position shown over the guide path towards odd track 3, then position pulses 13 will increase in magnitude with a corresponding decrease in magnitude of the position pulses 12. The difference in amplitude between the two position pulses is a measure of the position error of the transducer 2 from the...