International Business Machines Corporation

Francis Edward Mueller

Chung Chuan Liu

Wayne Leung Cheung

Martin H Dost

Edward F Bradley

A digital servo control system for a disk drive provides asynchronous servo information signal demodulation. The system includes a digital demodulator having a digital squarer that removes any phase component of the digitized servo information signal and includes a burst signal accumulator that accumulates the squared terms according to respective burst timing intervals to produce a digital, quadrature position error signal (PES). The demodulator also can include a filter comprising a harmonic notch filter preferably implemented as a Hilbert Transform filter. Alternatively, the demodulator does not include a filter and squarer and, instead, the squarer comprises a sum-and-squarer that sums the squares of odd and even digitized samples. A split burst servo pattern for the servo control system is comprised of half-width transitions that can be written in a single pass of a recording head and therefore has no phase misalignment between adjacent flux patterns.

Quadrature servo pattern disk providing asynchronous digital PES

Asynchronous digital PES demodulation disk drive servo control system

A track-seeking and track-following servo encodement and detection system employs a servo pattern using a reference signal and control signals, the control signals having an orthogonal phase relationship to each other by cyclically revolving in phase by 90.degree., 180.degree., 270.degree., and repeating this pattern every four tracks.

Servo encodement and detection system using tetra-orthogonal servo

An improved electronic velocity measurement device for an accessing type disk drive combines a differentiated cyclically discontinuous displacement (position error) signal (PES) with integrated motor current signals to produce an accurate continuous velocity signal over the entire range of displacements of a linear actuator. Differentiation of the displacement signal is achieved by low bandwidth differentiator circuitry that is corrected for periodic reversal of the displacement signal by a unique fill-in signal derived from integrated motor current. In a specific embodiment, the fill-in signal is derived by the use of a second differentiator using a second displacement signal in space quadrature with the primary displacement signal.

Growing community of inventors

San Jose, CA, United States of America

Francis Edward Mueller