Bearing provides continuous, smooth movement of the cat's-eye mirror, eliminating wear and deterioration of bearing surface and resulting oscillation effects in servo system. Design features self-aligning configuration; single-point, pivotal pad mounting, having air passage through it; and design of pads that allows for precise control of discharge path of air from pads

Mayall, S. D.

English

NASA Technical Reports Server

Interferometer Servo Drive
March 1974	 B73-10456 
NASA TECH BRIEF 
NASA Pasadena Office 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Linear Kinematic Air Bearing 
The problem: 
Servo driven precision optical systems require con-
tinuous and very smooth servo action to maintain 
optimum optical performance. Sometimes this is difficult 
to develop. In one practical example, an interferometer, 
in which a servo drive is used for a cat's-eye mirror, 
incorporates a bearing consisting of precision-made 
rollers moving on a glass surface. Microconchoidal 
fractures may develop on this surface and cause rough 
servo action and oscillation. 
The solution: 
A linear kinematic air bearing provides a contin-
uous, smooth movement of the cat's-eye mirror, elimi-
nating the wear and deterioration of the bearing surface 
and the resulting oscillation effects in the servo system. 
How it's done: 
In the design shown in the figure, a self-aligning 
carriage is mounted on two rails by means of five air-
bearing pads. The four pads pivotally mounted on the
inside of a right-angular extrusion align the carriage 
with the right-angular rail. The fifth pad engages a flat 
rail to support the end of the carriage opposite the 
right-angular rail. 
The carriage is essentially a triangularly mounted, 
self-aligning, floating support having negligible friction. 
It should be noted that the gap between the pads and 
the rails is 0.0001 inch (0.0025 mm) in normal 
operation. This would appear to put a severe constraint 
on the machining of the rails, particularly on the 
orthogonality of the right-angle rail. However, this is 
obviated by the fact that each pad is pivotally mounted 
at its center by a single screw, having a hemispherical 
superfimshed end which mates to a conical super-
finished bore in the body of each pad. Each screw has a 
central bore which serves as a conduit for pressurized 
air to the pad. A plenum chamber is mounted under-
neath the carriage baseplate. The chamber, as in all 
pneumatic devices, absorbs elastic shocks originating 
anywhere in the fluid system. 
(continued overleaf) 
This document was prepared under the sponsorship of the National
	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States
	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States
	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19730000456 2020-03-17T07:32:53+00:00Z
The design features the following: 
1. The self-aligning configuration, including the tri-
angular structure traveling on the right-angular and 
flat rails; 
2. The single-point, pivotal pad mounting, having the 
air passage through it; and 
3. The design of the pads that allows for the precise 
control of the discharge path of air from the pads.
Note: 
Requests for further information may be directed to: 
Technology Utilization Officer 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Reference: TSP73-10456 
Patent status: 
NASA has decided not to apply for a patent. 
Source: Sherwood D. Mayall of
Caltech/JPL
under contract to
NASA Pasadena Office 
(NPO-13 15 1) 
B73-10456
	 Category 06,03


Linear kinematic air bearing

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