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Servo Demodulation on Double-Sided Flexible Disk Using Single Demodulator

IP.com Disclosure Number: IPCOM000060447D
Original Publication Date: 1986-Apr-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 2 page(s) / 31K

Publishing Venue

IBM

Related People

Farran, J: AUTHOR

Abstract

A disk file track-following servo system uses servo information recorded on both surfaces of the disk by time sharing the servo demodulation circuitry. On a double-sided file where only one read head is used at a time, there arises the problem of what to do with the unused head/arm; i.e., should it be detented where it is with some type of magnetic clamp, or, should it be returned to the guard band while the other head is in use. Both of these methods pose problems of recovery to a controlled state when that head is needed, thus using up time in getting access to data under that head. One solution is to have two servo loops in operation all the time controlling each head/arm. The main disadvantage with this method is the unnecessary duplication of hardware.

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Servo Demodulation on Double-Sided Flexible Disk Using Single Demodulator

A disk file track-following servo system uses servo information recorded on both surfaces of the disk by time sharing the servo demodulation circuitry. On a double-sided file where only one read head is used at a time, there arises the problem of what to do with the unused head/arm; i.e., should it be detented where it is with some type of magnetic clamp, or, should it be returned to the guard band while the other head is in use. Both of these methods pose problems of recovery to a controlled state when that head is needed, thus using up time in getting access to data under that head. One solution is to have two servo loops in operation all the time controlling each head/arm. The main disadvantage with this method is the unnecessary duplication of hardware. The present technique involves time sharing the demodulation function and possibly the actuator driver function. This can be done by writing the disks at servowriter time with a 50 percent overlap of the sectors on the two sides of the disk, as shown in Fig. 1. With such a disk, the servo loop, when controlling each arm, can switch the demodulation function from one side of the disk to the other, as shown in Fig. 2. Once a Position Error Signal (PES) has been produced by the demodulator, and A-D converted, the demodulator is then free to produce a new value of PES from the other side of the disk.

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