Newsgroups: comp.robotics
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From: zins@netcom.com (Steven Zins)
Subject: Re: WANTED: Electronic compasses and gyros.
Message-ID: <zinsCFKIyw.9HL@netcom.com>
Organization: NETCOM On-line Communication Services (408 241-9760 guest)
References: <DULIMART.93Oct25205508@pacific.cps.msu.edu> <af.2062.33.0NAF5F03@mecheng.fullfeed.com>
Date: Wed, 27 Oct 1993 18:20:56 GMT
Lines: 36

greg.jackson@mecheng.fullfeed.com (Greg Jackson) writes:

>There are also people that make laser ring gyros which use
>interferometer techniques and relativistic principles to check out
>acceleration.  Those devices work wherever relativity applies (most
>places I can think of) and are pretty accurate.  I think they are core
>devices for aircraft navagation.  The light goes around a circle (hence
>the term "laser ring") in both directions.  When the ring accelerates
>forward, the light on one side of the ring is phase shifted from the
>light that is currently on the other side of the ring.  The phase shift
>is measured from shifts in the interference pattern as the two light
>paths collide. While the shift is pretty small for non-relativistic
>speeds, the light wavelength is smaller still and the system provides
>good sensitivity to acceleration.  A double integral of acceleration
>will yield position but watch out for integrator drift.

(i hope i have the attrribution correct)

Anyway, I believe that laser ring gyros detect only angular velocity.
It is not linear motion, as implied by your use of the word *forward*.
It is not acceleration but (angular) velocity which is the signal put
out directly from the gyro and is derived from the phase difference
between the two counterpropagating light rays.
The physical effect is called the Sagnac effect, which is not usually
considered a relativistic effect but is consistent with relativity theory.
Integration errors can be problematic, but the error is in orientation,
not position.

I think Thomas's Register of industrial companies (i forget what it is
called), which is available in many libraries, has subject headings for
these categories.

Good Luck   :)

Steve Zins    zins@netcom.com

