Browse Prior Art Database

AGC System for Dual Element Magnetic Head Servo System

IP.com Disclosure Number: IPCOM000087630D
Original Publication Date: 1977-Feb-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 44K

Publishing Venue

IBM

Related People

Granata, PJ: AUTHOR [+2]

Abstract

In one possible method of causing a magnetic read/write head to follow data tracks on a magnetic disk without the use of specially recorded servo patterns, dual servo head elements, each of half the data track width, are associated with each read/write head. The dual elements cover respective halves of the data track of interest. The rectified mean amplitude values of the dual head element signals, E(1) and E(2), stay constant as long as the elements are correctly positioned. If the elements should deviate from the track, one of the signals will fall while the other remains constant. The position error magnitude and direction is given by the algebraic difference signal E(1)- E(2). The variation of E(1), E(2) and the position error signal (E(1) - E(2)) with head movement is shown in Fig. 1.

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AGC System for Dual Element Magnetic Head Servo System

In one possible method of causing a magnetic read/write head to follow data tracks on a magnetic disk without the use of specially recorded servo patterns, dual servo head elements, each of half the data track width, are associated with each read/write head. The dual elements cover respective halves of the data track of interest. The rectified mean amplitude values of the dual head element signals, E(1) and E(2), stay constant as long as the elements are correctly positioned. If the elements should deviate from the track, one of the signals will fall while the other remains constant.

The position error magnitude and direction is given by the algebraic difference signal E(1)- E(2). The variation of E(1), E(2) and the position error signal (E(1) - E(2)) with head movement is shown in Fig. 1. Track centers are illustrated by dashed lines.

In the circuit shown in Fig. 2, signals from dual servo head elements 1 and 2 are preamplified at 3 and further amplified by variable gain amplifiers 4. After further amplification at 5 the head signals E(1) and E(2) are rectified and smoothed in amplitude detectors 6 to remove their data content. The mean amplitudes E(1) and E(2) from each element are then subtracted in difference amplifier 7 to produce the position error signal (PES) which is fed back by means (not shown) to control a mechanism (not shown) for positioning the heads.

Prior to being fed to the amplitude detecto...