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Interferometer Cosine Error Alignment With Video Feedback

IP.com Disclosure Number: IPCOM000100817D
Original Publication Date: 1990-Jun-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 3 page(s) / 107K

Publishing Venue

IBM

Related People

Pack, TJ: AUTHOR [+2]

Abstract

This article describes an error alignment system which utilizes a video image processing system to measure alignment error.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Interferometer Cosine Error Alignment With Video Feedback

       This article describes an error alignment system which
utilizes a video image processing system to measure alignment error.

      High accuracy motion measurements are easily obtained by
utilizing a laser interferometer.  However, if the axis of motion is
not precisely aligned with the axis of the interferometer, a
measurement error occurs.  This error is proportional to the cosine
of the misalignment angle and is referred to as a cosine error, as
illustrated in Fig. 1.  In addition, the misalignment results in the
measurement laser beam being laterally displaced on the
interferometer detector as the object moves.  This results in a loss
of signal amplitude, thus decreasing the signal-to-noise ratio.

      In the absence of precise reference surfaces on the motion
device, the cosine error can be minimized by iteratively aligning the
laser beam to the axis of travel while watching the return beam on
the detector aperture.  As the misalignment angle decreases, the
lateral displacement of the return beam also decreases.  The best
alignment occurs when there is no perceived motion of the beam.  This
type of alignment is based on the operator's qualitative assessment
of laser beam motion.  It also requires the operator to stare at the
diffuse reflection of the laser beam for extended periods of time.
The system described herein utilizes a solid-state charge-coupled
device (CCD) camera to image the return beam and an image processing
system to measure the beam displacement.  It provides a quantitative
measurement of beam displacement.

      The video alignment system of this disclosure is shown in block
diagram (Fig. 2) combined with the interferometer system which
consists of a laser 1, an interferometer head 2, a moving
retroreflector 3, and a receiver 4.  The laser beam is split into two
paths at the in...