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Processing System for Position Error Signal From Quadrature Servo Pattern in Disk Files

IP.com Disclosure Number: IPCOM000039005D
Original Publication Date: 1987-Apr-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 3 page(s) / 50K

Publishing Venue

IBM

Related People

Jones, DM: AUTHOR

Abstract

In magnetic recording disk files, the read/write head attached to the actuator is positioned to the desired data track and maintained over the track through the use of a servo control system. The servo information for positioning the head is obtained from a dedicated servo disk located among the stack of disks in the disk file or from sectors of servo data interspersed around the surface of the data disk. The specific pattern of servo information located in the servo tracks on the servo disk or in the servo track sectors of the data disk can be a conventional type of quadrature pattern, such as is described in the IBM Technical Disclosure Bulletin 21, 804-805 (July 1978).

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Processing System for Position Error Signal From Quadrature Servo Pattern in Disk Files

In magnetic recording disk files, the read/write head attached to the actuator is positioned to the desired data track and maintained over the track through the use of a servo control system. The servo information for positioning the head is obtained from a dedicated servo disk located among the stack of disks in the disk file or from sectors of servo data interspersed around the surface of the data disk. The specific pattern of servo information located in the servo tracks on the servo disk or in the servo track sectors of the data disk can be a conventional type of quadrature pattern, such as is described in the IBM Technical Disclosure Bulletin 21, 804-805 (July 1978). In the signal processing system described herein, a single logic implementation receives the digital position error signal (PES) input and provides all the necessary outputs required for the processing of PES signals from the quadrature servo pattern. In a quadrature servo pattern, the PES channel provides two output signals which have a 90o phase difference. The typical normal and quadrature waveforms are depicted in Fig. 1. As shown, the radial position of the head is determined from the value of one or the other normal (N) or quadrature (Q) signals. In order to provide the PES signal into the servo control system the slope of the selected N or Q waveform, which can be either positive or negative, must be determined so that negative feedback can be maintained in the servo control loop. In addition, the PES slope is important as it is a factor in the overall servo loop gain. Also as shown in Fig. 1, the sum of magnitudes of the normal and quadrature signals ( N + Q ) provides a value that is

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proportional to the track scale factor, i.e., the PES gain. In a sampled sector servo disk file, the cylinder pulse which represents track crossings of the head cannot be provided because a track crossing only rarely occurs when the sampling instant takes place. By reference to Fig. 1, however, it is noted that one of the four track types can be determined by determining which of the N or Q PES signals was selected and the sign of the unselected N or Q PES signal. The invention, as shown by block diagram in Fig. 2, is a hardware structure which analyzes the output of a 12-bit digitized quadrature PES channel and provides ramp select, sum of magnitudes ( N + Q ), PES slope, and track-type information. The same hardware performs all...