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From: frerichs@ux1.cso.uiuc.edu
Newsgroups: sci.virtual-worlds
Subject: rambling on motion
Message-ID: <10924@milton.u.washington.edu>
Date: 9 Nov 90 22:32:00 GMT
Sender: hlab@milton.u.washington.edu
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motion sensing...
A very sticky problem.

there are various ways to sense the movement (rotation, etc. not gestures) in
the head and hand.
VPL uses a polhemus sensor (built by Rockwell I think) that works by magnetic
induction.  3 small coils are mounted on the head at right angles to each other
(as a set of coodinate axis), another set is mounted on a stationary object,
and another is mounted on the hand.  Interacting magnetic fields produce
currents in each other that are proportional to their rotational alignment.
(induction).  As the head or hand moves or twists in relation to the reference
coil, the voltage fluxuates.  This variance is measured and translated to 
motion data.  So far so good, but...
there is a problem...
NOISE...
the system is so noise sensitive that the machine always thinks you are
jittering.  Even with software compensation, it still jiggles a bit.
maybe this problem can be solved, maybe not...

another way is to use mercury switches.  A small bead on mercury rolls around
inside a container with sensors at various angles.  A couple of these together
at strategic angles could detect most rotational and leverage movements, but
not lateral (at least I can't see it being able to).
cheap, sturdy solution...but slightly limiting.

does anyone else have any comments on any mistakes in logic or tech I have
made
-or-
does anyone have other solutions to the motion sensing problem?

we could use sensor arrays, but who want's to limit themselves to VR that
takes up a whole room...???

-dfRERICHS
Dept of CompEng,
Univ of Illinois, CU