A variable head to disk spacing controller for magnetic recording on rigid disks

Abstract

This paper presents an apparatus which allows the spacing dependence of magnetic recording devices to be studied by positioning the head at arbitrary (and continuously variable) heights ahove a rigid magnetic disk operating at a high and constant linear velocity. The spacing between the head and the disk is sensed electronically and deviations from the desired height arc removed by a sophisticated electro-mechanical control system. No air bearing is used. This control system utilizes an adaptive “learning machine” to build a model for the topography of the disk and then uses this model to anticipate repeatable runout. As much as a 40 dB reduction in residual spacing error relative to that possible with a conventional control system may be achieved by this means. The head to disk spacing may be varied in seconds over the range 0.05 microns to as much as 2.5 microns without changing either head or disk. Results using standard 5 1/4 inch thin film disks and thin film heads which demonstrate the large increase in linear density possible when the head to disk spacing is reduced to near-contact will be presented. © 1988 IEEE