Browse Prior Art Database

Access Control System With Reduced Velocity Error

IP.com Disclosure Number: IPCOM000086776D
Original Publication Date: 1976-Oct-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 18K

Publishing Venue

IBM

Related People

Reed, JW: AUTHOR

Abstract

An access control system for a disk file comprises a track crossing pulse generator 1, a difference counter 2 and a digital-to-analog converter 3 which cooperate to generate a reference velocity profile chi ref. The reference velocity is compared with a measured velocity in a summing junction 4 to generate a velocity error. Conventionally, the velocity error signal is amplified in amplifier 5/chi/ with gain K(vo) and applied to a power driver 6 of gain K(I) to produce current I. Current I drives a voice coil motor 7 of motor constant K(m)/m, where m is the moving mass. Integration of motor current in a tachometer circuit provides a measured velocity chi, which is scaled by a factor K(T) and fed back for comparison with chi ref.

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Access Control System With Reduced Velocity Error

An access control system for a disk file comprises a track crossing pulse generator 1, a difference counter 2 and a digital-to-analog converter 3 which cooperate to generate a reference velocity profile chi ref. The reference velocity is compared with a measured velocity in a summing junction 4 to generate a velocity error. Conventionally, the velocity error signal is amplified in amplifier 5/chi/ with gain K(vo) and applied to a power driver 6 of gain K(I) to produce current I. Current I drives a voice coil motor 7 of motor constant K(m)/m, where m is the moving mass. Integration of motor current in a tachometer circuit provides a measured velocity chi, which is scaled by a factor K(T) and fed back for comparison with chi ref.

The steady-state velocity error of the system thus far described can be shown to be

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By the addition of a positive current feedback loop of gain K(FI) during the deceleration phase of the access motion, the expression for steady-state velocity error becomes: Thus, by selecting the desired value of K(FI), the steady-state velocity can be made as small as Possible as long as K(vo)K(I)K(FI) does not approach 1. This method of adjustment offers independence from Physical limitations which may affect K(vo) and K(I).

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