Browse Prior Art Database

Disk Accessing System

IP.com Disclosure Number: IPCOM000086361D
Original Publication Date: 1976-Aug-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 3 page(s) / 43K

Publishing Venue

IBM

Related People

Fraser, GB: AUTHOR

Abstract

The accessing system being considered includes a head-arm assembly driven by a voice coil actuator over a disk surface to perform transducing operations. Ideally, the actuator accelerates the head-arm assembly band to some intermediate point in the access and decelerates the remainder of the way. The maximum possible deceleration is fixed by the actuator parameters and the minimum access time is achieved by starting to decelerate as late as possible and using maximum available deceleration.

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Disk Accessing System

The accessing system being considered includes a head-arm assembly driven by a voice coil actuator over a disk surface to perform transducing operations. Ideally, the actuator accelerates the head-arm assembly band to some intermediate point in the access and decelerates the remainder of the way. The maximum possible deceleration is fixed by the actuator parameters and the minimum access time is achieved by starting to decelerate as late as possible and using maximum available deceleration.

Since it is impossible to select such a reversal point with sufficient accuracy to stop the access at the center of a target track, practical systems use a velocity following servo following a velocity profile for the deceleration generated as a function of the remaining distance to go. Such a velocity profile is required to perform two not entirely compatible functions. First, it is required to determine when the voice coil driver should change from applying full accelerate drive to the actuator to a decelerate drive, which will enable it to reach the target track at the desired velocity. Second, it is required to determine the velocity profile of the actuator during deceleration. If the voice coil current were to follow the applied voltage directly the same profile would fulfill both functions. This is not the case in practice.

Fig. 1 shows a velocity profile as curve 1 which is ideal from the point of view of the second requirement, in that it demands maximum possible deceleration down to the target track. In practice, an actuator attempting to follow this profile will overshoot to a point in the phase plane above the velocity profile and will miss the target track. The actual velocity of the actuator is shown as curve 2 in Fig. 1.

Fig. 2 shows a velocity profile as curve 1 which is ideal from the point of view of the first requirement. Here the maximum velocity from which the actuator can slow down in the requisite distance with full deceleration applied is computed for ...