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From: brucec%phoebus.labs.tek.com@RELAY.CS.NET (Bruce Cohen;;50-662;LP=A;)
Newsgroups: sci.virtual-worlds
Subject: Re: optical gyros
Message-ID: <11765@milton.u.washington.edu>
Date: 27 Nov 90 17:44:33 GMT
References: <11727@milton.u.washington.edu>
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In article <11727@milton.u.washington.edu> frerichs@ux1.cso.uiuc.edu (David J Fr
erichs) writes:
> 
> The accelerometer idea is a bit flaky though... who wants to whip their head
> around just to get the movement to register... for vertical and twisting
> motion, I think mercury switches is still the best idea...

I don't think you are aware of the state of the art in accelerometers these
days; it's way beyond what you need to detect slow head motions.  In fact,
a common technique in circulatory system research about 15 years ago (the
last time I had any direct contact with the field) was something called
"ballistocardiography" in which a subject lies on a table and the
accelerations induced in the table by the force of the heart muscle exerted
through the body to the table are recorded.

Mercury switches have two main drawbacks:
    a) they are essentially digital (yes they have a small linear domain as
       they switch over, but it will cover perhaps a degree or two of the
       total tilt, and commercial units that I have seen don't make it easy
       to use that domain).

    b) they have considerable hysteresis.  The units I have used switched
       at a known tilt with a reproducible accuracy of ~1 degree, but with
       better than 3 degrees of hysteresis between directions of swing.
--
------------------------------------------------------------------------
Speaker-to-managers, aka
Bruce Cohen, Computer Research Lab        email: brucec@tekchips.labs.tek.com
Tektronix Laboratories, Tektronix, Inc.                phone: (503)627-5241
M/S 50-662, P.O. Box 500, Beaverton, OR  97077