International Business Machines Corporation

David W Collins

Joel Scott Johnson

Michael Charles Stich

Michael M Siverling

Laurence J Schmidt

Michael J Burke

John J Neesz

Michael Allen Weed

William S Wentink

Frederick E Axmear

Phase difference demodulator for measuring the phase difference between two signals of the same frequency, time multiplexed onto a single analog input, and providing a precision digital output signal representing the phase difference. The most significant part of the signal, the upper bits, is determined by digital processes while analog-to-digital processes determines the lower bits. The analog-to-digital processes utilize an integrating capacitor and current sources for demodulating servo bursts for obtaining phase difference. The current sources are a coarse current and a fine current 1/16 in value of the coarse current source. The capacitor is switched in a differential scheme by the integrator to determine error during the digital approximation of the upper bits in analog to digital conversion. The same capacitor and current sources are utilized in the error acquired in analog form and then during the analog-to-digital conversion.

Phase difference demodulator

An optical tool is disclosed which permits a sequence of aligned transducer gaps to be positioned parallel to the axis of a disk file. The tool is surfaced with transparent material, has a thickness the same as the disk or disks of a disk stack being simulated and presents an etched alignment grid at the interface surface between transducer and tool. The virtually common plane of the transducer gap and etched grid substantially eliminates parallax and the unfilled etched grid permits the gap to be seen, whether aligned with the transparent unetched surface or the translucent etched surface portion. The use of inclined mirrored surfaces underlying the grid permits alignment to be effected using a bright field microscope and observing from a direction rotated 90 degrees from a line perpendicular to the grid to enable alignment of transducer gaps confronting one another at opposite sides of the disk.

Optical tool for aligning transducer head assemblies

In parallel track data storage systems, such as disk files, servo information is recorded using a plurality of constant frequency fields each having a phase shift between tracks. Servo information is thus encoded in the phase of the servo pattern instead of the amplitude of the servo signal lobes. Multiple phase shifts per track are used to make the signal constantly varying with transducer head displacement. Phase is measured modulo 360.degree. such that the phase of a given field will go through 360.degree. every M tracks. By using several fields having different values of M, coarse, medium and fine position resolution can be obtained with the same servo pattern and demodulation scheme. Further, using two fields, one field may be split and positioned at either side of the other field to provide a common center for both fields and eliminate error conditions due to factors such as speed variation.

Phase modulated servo system

A three level motor speed control for a device such as a magnetic disk drive requiring a closely regulated running speed provides for acceleration, deceleration, obtaining close speed regulation and maintaining speed regulation of a rotating device during operation. The first level control provides acceleration or deceleration while checking velocity each eighth revolution and the second level control uses single revolutions to measure speed over an accurate rotational distance to obtain close speed regulation. Both level one and level two are controlled by the device controller. During run conditions with no error signal, a third level of control of the closely regulated velocity is maintained by separate hardware circuits which frees the processor for other uses. An error condition forces control to level one for re-establishment of the regulated running speed and a command to stop the drive forces control to level one for deceleration and stop procedures.

Multi-level disk drive motor speed control

A brushless D. C. motor is disclosed having two bifilar winding wire pairs with each bifilar pair forming alternate windings. Each winding is switched by a transistor which has a back poled diode connected in parallel therewith. The control circuit sequences energization of single windings with each winding energized being in a different bifilar pair than the next preceding energized winding whereby when a transistor is switched off the other winding of the bifilar pair and the associated back poled diode protect the transistor and provide an energy conserving/heat eliminating path for the induced current. Each winding is further formed of a pair of subwindings having an angle of separation therebetween approximately half the angular separation between adjacent windings.

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Rochester, MN, United States of America

David W Collins