Dismiss
InnovationQ will be updated on Sunday, Oct. 22, from 10am ET - noon. You may experience brief service interruptions during that time.
Browse Prior Art Database

Air Bearing Gap Servo

IP.com Disclosure Number: IPCOM000101113D
Original Publication Date: 1990-Jun-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 2 page(s) / 58K

Publishing Venue

IBM

Related People

Kulesza, JD: AUTHOR

Abstract

Disclosed is a means of controlling the air gap of granite-based air bearings to maintain a specific fly height through varying loads or to statically vary the height of a work piece. The method detects the change in capacitance brought on by a change in air gap and adjusts air flow to the bearing in a servo control loop.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 69% of the total text.

Air Bearing Gap Servo

       Disclosed is a means of controlling the air gap of
granite-based air bearings to maintain a specific fly height through
varying loads or to statically vary the height of a work piece.  The
method detects the change in capacitance brought on by a change in
air gap and adjusts air flow to the bearing in a servo control loop.

      Fig. 1 shows an air bearing which serves as one plate of a
capacitor, the granite surface which serves as the other plate, and
the air itself is the dielectric.  The granite surface must be clad
with a conductive material, such as gold leaf or aluminum epoxy,
which will not also degrade the granite flatness.  The air flow
control valve is a piezoelectric air servo valve, which has a
bandwidth of 1000 Hz.  The valve is mounted near the bearing to
minimize losses due to air compression.

      The granite side of the capacitor is held at ground potential
and the air bearing side is charged.  The air bearing is made of
aluminum and must be electrically isolated from the bearing supports.
A gap width detector circuit uses the air gap capacitance to modulate
a fre quency which is then demodulated to produce an analog voltage
relative to the air gap.  A sinusoid frequency is used in conjunction
with an inductor and resistor to augment the effect of the change in
capacitance in an RLC circuit.

      The detector circuit is in the feedback loop (block #3) of the
servo control block diagram shown in Fig....