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Browse Prior Art Database

Disk File Actuator Equalization

IP.com Disclosure Number: IPCOM000083628D
Original Publication Date: 1975-Jun-01
Included in the Prior Art Database: 2005-Mar-01
Document File: 3 page(s) / 51K

Publishing Venue

IBM

Related People

Betts, AJ: AUTHOR [+2]

Abstract

The velocity of a servo controlled recording and playback head during a track access operation over a recording disk can be derived from two sources. One is by differentiation of the track crossing signal obtained from the servo information on the disk, and the other is by integration of the current through the actuator motor producing the movement of the head.

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Disk File Actuator Equalization

The velocity of a servo controlled recording and playback head during a track access operation over a recording disk can be derived from two sources. One is by differentiation of the track crossing signal obtained from the servo information on the disk, and the other is by integration of the current through the actuator motor producing the movement of the head.

In practice, the signal representing actual velocity Va is generated by mixing these two signals, so that the low-frequency components are provided by the differentiated track crossing signal and the high-frequency components by the integrated motor current. If the scaling factors of these two signals differ from one another, errors in velocity determination occur during acceleration and deceleration of the head. This problem is overcome by a tuning adjustment to make the mix ratio of the two velocities equal to unity.

Fig. 1 shows a block diagram of the velocity and position loop electronics of a servo controlled disk file. A portion of a disk 1 is shown with a servo head 2 located over a guide path 3, which is the boundary between two adjacent servo tracks 4 and 5. The head 2 is supported at the end of actuator arm 6, driven about a pivot 7 by a current Im supplied to motor 8 at the other end of the arm 6.

During track following operations, a voltage is generated in servo head winding 9 indicating the magnitude and direction of deviations of the head 2 from a particular guide path. This voltage is supplied to position detect circuit 10 and a position error signal is produced on output line 11. The position error signal is represented by the expression K1. Wt/Wh delta theta, where K1 is the scaling factor of the position detect circuit 10 Wt is the width of a servo track, Wh is the head width, and delta theta is the small angular error of the arm 6. A tuning resistor Rt forming part of the network of position detect circuit 10 determines the value of the scaling factor K1.

During a track following operation, this signal is passed through a phase lead/lag compensator 12 and used to produce motor drive current Im of a magnitude and polarity, to drive the head 2 in a direction so as to reduce the position error delta theta. The function of the compensator 12 is represented by the expression f1 (S). K2, where f1 (S) is the transfer function and K2 is the scaling factor of the compensator 12.

During a track access operation, the actuator motor 8 is controlled to move the head 2 so that its actual velocity Va at all times is equal to or closely follows a predetermined desired velocity Vd. The position error signal varies periodically as tracks are crossed and provides the track crossing signal during an access operation. This track crossing signal on line 11 is supplied to differentiator 13 to produce one component of the velocity V1 on output line 14. The component V1 is represented by the equation: - V1= theta. K1.K3.Wt/Wh 1 where K3 is the scal...