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Browse Prior Art Database

Head-Disk Spacing Controller for Magnetic Recording

IP.com Disclosure Number: IPCOM000034769D
Original Publication Date: 1989-Apr-01
Included in the Prior Art Database: 2005-Jan-27
Document File: 2 page(s) / 43K

Publishing Venue

IBM

Related People

Jefferson, CM: AUTHOR [+2]

Abstract

The invention, described herein, allows a magnetic recording read/write element to be positioned at arbitrary heights above a magnetic disk spinning at an arbitrary rotational velocity. No air-bearing slider is used. Capacitive sensing of head height is used in an adaptive control system to maintain the head-disk spacing essentially constant. The head spacing controller uses a head-disk spacing actuator, as shown in the figure. The spacing actuator may be any transducer whose extension is controlled by an applied voltage and whose dynamic range is sufficient to exceed the head-disk spacing runout which is to be removed. A piezoelectric stack is the preferred spacing actuator. One end of the spacing actuator is fixed to the radial actuator used for track access in the disk file.

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Head-Disk Spacing Controller for Magnetic Recording

The invention, described herein, allows a magnetic recording read/write element to be positioned at arbitrary heights above a magnetic disk spinning at an arbitrary rotational velocity. No air-bearing slider is used. Capacitive sensing of head height is used in an adaptive control system to maintain the head-disk spacing essentially constant. The head spacing controller uses a head-disk spacing actuator, as shown in the figure. The spacing actuator may be any transducer whose extension is controlled by an applied voltage and whose dynamic range is sufficient to exceed the head-disk spacing runout which is to be removed. A piezoelectric stack is the preferred spacing actuator. One end of the spacing actuator is fixed to the radial actuator used for track access in the disk file. This may be a conventional voice coil motor (VCM). The other end of the spacing actuator serves as a platform upon which is mounted a small, conducting substrate which holds the read/write head. The spacing between the substrate and the disk is measured dynamically by means of the capacitance between the substrate and the disk. This capacitance is inversely proportional to the head- disk spacing. The capacitance signal is input to control circuitry which processes it and outputs a voltage to the spacing actuator such that the spacing between the substrate and the disk is held constant, regardless of the motion of the disk. The frequency spectrum and amplitude of the runout of disks in a direction perpendicular to the plane of the disks are sufficiently severe that a simple closed-loop control system is incapable of providing enough gain to reduce the errors in the servo to the required levels. As a result, a special...