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Phase-Sensitive Track Following Tape Servo with V-SHAPED Tracks

IP.com Disclosure Number: IPCOM000112442D
Original Publication Date: 1994-May-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 4 page(s) / 96K

Publishing Venue

IBM

Related People

Dovek, MM: AUTHOR [+2]

Abstract

A dual MR-read element servo in conjunction with specially patterned servo tracks can be used for a phase sensitive servo positioning scheme. The servo is intended for mechanical track positioning in digital tape recording. Conventional amplitude base servo schemes maintain an equal amplitude at two frequency components of the signal read back by a wide servo head. The problems with this scheme originate from defects such as scratches or smears or sensitivity asymmetries of the head that result in higher amplitude from one side of the head compared to the other side. Conventional phase or timing sensitive servos, on the other hand, determine phase or timing by comparing two servo bursts.

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Phase-Sensitive Track Following Tape Servo with V-SHAPED Tracks

      A dual MR-read element servo in conjunction with specially
patterned servo tracks can be used for a phase sensitive servo
positioning scheme.  The servo is intended for mechanical track
positioning in digital tape recording.  Conventional amplitude base
servo schemes maintain an equal amplitude at two frequency components
of the signal read back by a wide servo head.  The problems with this
scheme originate from defects such as scratches or smears or
sensitivity asymmetries of the head that result in higher amplitude
from one side of the head compared to the other side.  Conventional
phase or timing sensitive servos, on the other hand, determine phase
or timing by comparing two servo bursts.  We propose establishing
timing or phase differences by the simultaneous readback of two
independent head elements for less computation and higher bandwidth.

The primary advantages of this scheme include:

o   Simple electronics to realize a PES.

o   Phase detection from a tape written with inductive write heads.

o   PES can be made velocity independent over a broad range.

o   Some implementations allow for concomitant track identication.

o   Extendability to higher track density in future drives woud
    require no change in tape formatting scheme.

BASIC CONCEPT - In Fig. 1 is the proposed basic servo track
transition pattern which consists of a single frequency track written
in the shape of a V.  This pattern is two dimensional and cannnot be
written by a conventional write head but can be deposited by a
magnetic drum technique.  However, due to its repetitive structure,
alternative write techniques such as grooved write-head substrate or
crossed write-head pairs can be used.

      The basic servo-read head has two MR elements which ride on
independent branches of the V as shown in Fig. 1a.  Each head is
sufficiently narrow that asymmetries in the head will translate into
negligibly small displacements of the head cereline.  The two heads
typically share a common lead.

      The Position Error Signal (PES) is proportional to the phase
difference between the two heads and will zero when the servo heads
symmetrically straddle the V.  The electronics to generate the PES
consist of a pulse to square wave convertor at the output of each of
...