Illumination of rotating surface with laser beam and examination of interference patterns resulting from diffused reflections determines position of axis and direction of motion. Interference patterns are viewed through a lens or recorded on film as circular streaking patterns

Massey, G. A.

English

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December 1970	 Brief 70-10439 
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Laser Method for Finding Axis of Rotation 
of a viewing lens, the interference patterns in two 
different planes can be examined. 
The interference pattern at any distance from the 
surface rotates with the surface. For rotation angles 
greater than a few degrees, the circular streaking 
is clearly visible. Since all streaks are concentric 
with the axis, the axis position is that point in 
the interference pattern where the streaking reduces 
to zero. If two interference planes at different dis-
La se 
The problem: 
To determine remotely the axis of rotation of a 
moving body. 
The solution: 
Illuminate the rotating surface with a laser beam 
and examine the interference patterns resulting from 
diffused reflections to determine the position of the 
axis and the direction of motion. 
rp
Spinning 
Object
Axis of Rotation
A 
Viewing Lens 
Two Planes for Viewing 
Interference Patterns
	
I 
Experimental Setup 
How it's done: 
A laser beam is directed toward a diffuse reflect-
ing surface on the rotating object. Light is reflected 
from the surface as random phase waves which 
overlap in the region of space in front of the surface 
and form random ("sparkle") interference patterns 
that rotate as the object rotates. The interference 
patterns can be viewed through a lens or recorded 
on film as circular streaking patterns. With the aid
tances from the surface are examined, the position 
of the rotational axis can be determined in each 
plane within an error equal to the width of one 
bright point in the interference pattern. The accuracy 
of the axial direction measurement is limited (by 
diffraction) to an angular error approximately equal 
to the wavelength divided by the illuminated diameter 
of the beam at the reflecting surface. A value of 
iO radian for a beam diameter of 10 millimeters 
can be obtained. (continued ovedeal) 
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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.
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The following documentation may be obtained 
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Springfield, Virginia 22151 
Single document price $3.00 
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Reference: 
NASA-CR-985 (N68-14070), Study of Vibra -
tion Measurement by Laser Methods
Patent status: 
No patent action is contemplated by NASA. 
Source: G. A. Massey 
Sylvania Electronic Systems 
under contract to 
Ames Research Center 
(ARC-10388)
Owl
0 
Brief 70-10439	 Category 03


Laser method for finding axis of rotation

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