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High Track Density Servo Position Error Signal Processing

IP.com Disclosure Number: IPCOM000041392D
Original Publication Date: 1984-Jan-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 3 page(s) / 43K

Publishing Venue

IBM

Related People

Liu, CC: AUTHOR

Abstract

Described here is a novel method for processing servo position error signals (PES) in disk file applications. It is applicable to certain classes of PES systems having two separated and yet related PES output signals. Their output vs. head displacement characteristics must be identical, except one is shifted from the other by an amount of one track pitch. An electronic linear operation of 'summing' and 'difference' is applied to the PES outputs. As a result of the operation, new signals are generated such that they exhibit the following unique properties: (1) higher track density, (2) quadrature PES, and (3) larger PES gain linear range. Fig. 1 shows a pair of the PES outputs (A,B) from a servo system employing a tetra-orthogonal servo encodement.

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High Track Density Servo Position Error Signal Processing

Described here is a novel method for processing servo position error signals (PES) in disk file applications. It is applicable to certain classes of PES systems having two separated and yet related PES output signals. Their output vs. head displacement characteristics must be identical, except one is shifted from the other by an amount of one track pitch. An electronic linear operation of 'summing' and 'difference' is applied to the PES outputs. As a result of the operation, new signals are generated such that they exhibit the following unique properties: (1) higher track density,
(2) quadrature PES, and (3) larger PES gain linear range. Fig. 1 shows a pair of the PES outputs (A,B) from a servo system employing a tetra-orthogonal servo encodement. PES output A yields zero potential at every data track center designated by 'even' track numbers; output B yields zero potential at every 'odd' data track center. The PES gain linear range of (A,B) is one track width. By the application of the linear operation, new PES signals are generated. They can be expressed as follows: S = A+B ( 1.a ) D = A-B ( 1.b )

The linear operation and the plots of Expressions (1.a) and (1.b) are shown in Fig. 2. It can be shown that the signals (S,D) yield zero potentials alternately at every half-track distance. Because of this property, they can be used as a pair of quadrature PES components. Conventionally, servo quadrature PES is obtained by using complicated servo patterns, and consequently more servo pack write time is required. Here, the quadrature PES is realized by electronic means and is added to an existing PES system; therefore, the pack write time is the same. The signals (S,D) can be used together with the signals (A,B) in the same way, and they have doubled the track density. The signals (S,D) have the same PES gain as that of the signals (A,B), but the PES gain linear range is extended from one track width to two track widths of the original track density, or is extended from two track widths to four track widths according to the new track density which is doubled. This is desirable for track-seeking operation. The servo head is moving at a maximum velocity during a long seek. The envelope of the PES is usually drooped under this mode of operation, mainly due to the low-pass PES channel bandwidth constraint. For servo system control purposes, the envelope droop is tightly specified. The range extension property obtained will assist in achieving it more readily. Fig. 3 shows another form of PES outputs with which the present technique can be employed. The PES outputs P and Q are again assumed to...