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Disk File Track Access Control

IP.com Disclosure Number: IPCOM000081384D
Original Publication Date: 1974-May-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 3 page(s) / 33K

Publishing Venue

IBM

Related People

Commander, RD: AUTHOR [+2]

Abstract

Data heads in a servo-controlled magnetic disk file are moved from one track position to another, according to a predetermined velocity profile. Curve 1 in Fig. 1 is a plot of actual velocity v of a head during a track access operation, plotted against the number of tracks to be crossed. Curve 2 is a plot of the desired head velocity which should be followed at least over the final stages of the access operation. Clearly, during the initial stages of the access operation, the actual velocity of the head is considerably less than the desired velocity and remains less until the two curves intersect at point P. From this point the velocity of the head is controlled to substantially follow the desired velocity profile, until it comes to rest over the destination track.

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Disk File Track Access Control

Data heads in a servo-controlled magnetic disk file are moved from one track position to another, according to a predetermined velocity profile. Curve 1 in Fig. 1 is a plot of actual velocity v of a head during a track access operation, plotted against the number of tracks to be crossed. Curve 2 is a plot of the desired head velocity which should be followed at least over the final stages of the access operation. Clearly, during the initial stages of the access operation, the actual velocity of the head is considerably less than the desired velocity and remains less until the two curves intersect at point P. From this point the velocity of the head is controlled to substantially follow the desired velocity profile, until it comes to rest over the destination track.

A block diagram of the control circuit is shown in Fig. 2. A magnetic head assembly 1 is moved across a rotating magnetic disk 2 from one track location to another by an actuator mechanism 3. The movement of the assembly is depicted simply by the double-headed arrow 4. Signals representing the actual velocity of the head 1 during access operations are supplied from actuator 3 to compare unit 5, where they are compared with signals representing desired velocity supplied from a velocity profile generator 6. Error signals resulting from the comparison are used to control the actuator 3 in such a way, as to reduce the differences between the actual and desired velocity signals. In practice, the actuator is accelerated at a maximum until the point P is reached.

The velocity profile generator consists of a read-only store 7 which stores the desired velocity profile in digital form. Digital signals representing the number of remaining tracks in an access are supplied from a control unit 9 to the store 7 where they are decoded, to provide a digital value representing the desired velocity of the head at that particular point in the access. The input to the store 7 is decremented by unity, in response to...