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Browse Prior Art Database

Angular Velocity Control System for Magnetic Disks

IP.com Disclosure Number: IPCOM000042806D
Original Publication Date: 1984-Jun-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 2 page(s) / 44K

Publishing Venue

IBM

Related People

Collins, DW: AUTHOR

Abstract

This angular velocity control system uses magnetic recording heads 1 and 2, located on the same track 3 of magnetic disk 4, and a magnetic recording head 5, positioned above track 7 having an index mark 8. Head 1 is driven with a signal derived from oscillator 9 to write a signal with a constant frequency on track 3. Head 2 is positioned above track 3 15Πdownstream to read the signal written by head 1. The phase of the signal read by head 2 is proportional to the time required for a point on track 3 of disk 4 to move from head 1 to a position under head 2. A phase detector 10 measures the phase difference between the signal from oscillator 9 and the signal from head 2 and develops a signal to control the torque of motor 11 through motor drive unit 12.

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Angular Velocity Control System for Magnetic Disks

This angular velocity control system uses magnetic recording heads 1 and 2, located on the same track 3 of magnetic disk 4, and a magnetic recording head 5, positioned above track 7 having an index mark 8. Head 1 is driven with a signal derived from oscillator 9 to write a signal with a constant frequency on track 3. Head 2 is positioned above track 3 15OE downstream to read the signal written by head 1. The phase of the signal read by head 2 is proportional to the time required for a point on track 3 of disk 4 to move from head 1 to a position under head 2. A phase detector 10 measures the phase difference between the signal from oscillator 9 and the signal from head 2 and develops a signal to control the torque of motor 11 through motor drive unit 12. Because the oscillator 9 runs at a relatively high frequency, there are many cycles of the signal between the heads 1 and 2, for example, 1000. This means that the velocity can be controlled with great precision. Since the phase detector can be made to respond to a phase shift of approximately one-third of a degree, the velocity can be controlled to one part per million. Because the phase detector 10 and oscillator 9 do not actually measure the number of cycles, the control system can hold velocity constant with great precision but cannot attain a given velocity without some absolute speed reference. Head 5 is used to produce a measure of absolute speed. Index mar...