Browse Prior Art Database

Disk File Servo for Rotary Actuator

IP.com Disclosure Number: IPCOM000052049D
Original Publication Date: 1981-Apr-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 3 page(s) / 59K

Publishing Venue

IBM

Related People

Day, RC: AUTHOR

Abstract

Use of a dedicated servo surface within a disk pack runs into limitations as recording track density is increased due to uneven thermal expansion between disks and mechanical tolerances within the stack. As a result, techniques like sector (sampled) servoing and buried layer servos have been used to move the servo information directly to the data disk without using large areas of surface which could be used for data. The present technique provides continuous dedicated servo information with a minimum use of recording area and can use existing dedicated servo circuits for track counting and servo-controlled track following.

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Disk File Servo for Rotary Actuator

Use of a dedicated servo surface within a disk pack runs into limitations as recording track density is increased due to uneven thermal expansion between disks and mechanical tolerances within the stack. As a result, techniques like sector (sampled) servoing and buried layer servos have been used to move the servo information directly to the data disk without using large areas of surface which could be used for data. The present technique provides continuous dedicated servo information with a minimum use of recording area and can use existing dedicated servo circuits for track counting and servo-controlled track following.

This technique makes use of a rotary actuator with a dedicated servo head and servo area to provide continuous on-disk servoing. As shown in Figs. 1 and 2, one or more data heads per surface are mounted on a pivoted arm with a servo head mounted on a radius which is a fraction of data head radius. The fraction is determined by the number of servo tracks contained in the width of one data track so the servo head is mounted on a radius one-third of the data head radius.

The percentage of recording area real estate needed for servo information depends upon how many data heads are used per disk and whether a spare area, like guard bands, can be used to contain the servo tracks. If it is found that starting and stopping the read heads in the guard band does not harm the servo information or introduces only small errors which can be skipped over and still provide reliable servoing, then no recording area will be lost. If, on the other hand, only one data head per surface is used and the servo information must be taken from the recording area, then a maximum of 16.7% of recording area will be lost for a three-servo-track implementation. In Fig. 1, two read heads are used per surface so 8.3% would be used if spare areas could not be used for servo information.

The pivoted arm is shown mounted outside the disk circumference which limits the servo head to the outside area of the recording surface. Pivoting can be done within the recording surface by using a more complex arm structure. The servo head can then be positioned anywhere within the recording area if tolerances so require.

Referring to Fig. 2, it can be seen that the servo head width spans three tracks of se...