frerichs@ux1.cso.uiuc.edu (David J Frerichs) (11/27/90)
does anyone know of a supplier of optical gyroscopes...??? -or- any sort of lightweight gyro...??? I think the net has finnaly stumbled onto the solution of the simple detection of lateral movements (turning the head)... 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... -dfRERICHS Univ of IL/CU Dept of CompEng
jdunn@polyslo.CalPoly.EDU (Jeff Dunn) (11/28/90)
ichs@ux1.cso.uiuc.edu (David J Frerichs) writes: > >does anyone know of a supplier of optical gyroscopes...??? >-or- >any sort of lightweight gyro...??? > >I think the net has finnaly stumbled onto the solution of the simple detection >of lateral movements (turning the head)... This may be a solution, but not a simple one. As someone else mentioned, drift will be a major problem. Getting a small system to work reliably may take years of r & d. >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... You don't have to "whip" your head around to register an acceleration. Accelerometers were available a couple of years ago that could detect forces as small as 10E-6 g. I believe this can detect rotational motion less than 1 RPM (depending on the radius of the object, of course). >-dfRERICHS >Univ of IL/CU >Dept of CompEng -jd jdunn@polyslo.calpoly.edu -- TALK HARD
brucec%phoebus.labs.tek.com@RELAY.CS.NET (Bruce Cohen;;50-662;LP=A;) (11/28/90)
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
23r@sage.cc.purdue.edu (John Dormer) (11/28/90)
I recall from a couple years back, when I was very interested in laser
devices, that Hughes Aircraft had made optical (laser-ring) gyroscopes. The
ones for military aircraft could detect >extremely< small rotations...measured
in degrees per minute, and they were decimal numbers to boot.
I don't know if anyone has made smaller versions of this technology, but it
should be feasable. The Hughes ring was about $200k I think...a bit expensive,
but I remember reading somewhere about a company who had sucessfully made a
solid version of the ring-gyroscope (Hughes used mirrors on a stout frame
about 10" across [from the photos]), which used beveled, mirrored faces on
the outside of some kind of crystal material (optical glass probably). The
availability of IR laser diodes should bring the price down quite a bit. And
because these devices use phase to tell which direction (combination of
directions) the ring has moved, you need only one to detect any twisiting
motion. I don't know how well they fare as acceleratometors, but they should
do allright. The most expensive part of this would still be the detector
optics, and I don't know enough about that part to make an educated guess on
how much it would cost. The whole package should cost less than the original
Hughes device (I'd hope! 8), but more than $10,000 most likely (at first).
Holographic lenses could shave the cost of the detector again, but this is
also something beyond me. These lenses could be produced cheaply in quantity
with decent quality control. Maybe we're talking $2000 for this device in
production quantities of 1000 per lot, who knows.
another brilliant idea?
John Dormer
dormer@medusa.cs.purdue.eduxanthian@zorch.SF-Bay.ORG (Kent Paul Dolan) (11/28/90)
The way to get past the drift problem with optical gyros is to use some other system to give you a ground truth, perhaps a system whose location accuracy or stability is better but whose sampling rate is too slow. That way, the optical gyro gives you excellent short term sensitivity and accuracy, while the ground truth from, say, an infrared triangulation system, is averaged and fed back as an error correction for the long term drift of the optical gyro. Lots of military navigation hardware is designed along similar lines. Kent, the man from xanth. <xanthian@Zorch.SF-Bay.ORG> <xanthian@well.sf.ca.us>
frerichs@ux1.cso.uiuc.edu (David J Frerichs) (11/28/90)
I give up... Is there such a thing as a lightweight gyroscope that is CHEAP? -or- Are silicon accellerometers inexpensive enough to use in a garage VR system? someone out there must know the answers to one of these questions... BTW Tim Leary and G.G. Liddy were at the Univ of IL/ CU last night giving their canned debate on individuality vs. collectivism... and the subject actually touched on VR a little, not that any lay person would know it. Leary kept brushing off the topic when asked directly about his involvement and spouted about a "global audio-visual 3d iconic language" at inappropriate times. This all added up to people thinking that the idea of VR is nonsense... oh well, lets see what they say in five years when they jack in and actually "reach out and touch someone." -dfRERICHS Univ of IL/CU Dept of CompEng
brucec%phoebus.labs.tek.com@RELAY.CS.NET (Bruce Cohen;;50-662;LP=A;) (11/29/90)
In article <11836@milton.u.washington.edu> 23r@sage.cc.purdue.edu (John Dormer) writes: > > I recall from a couple years back, when I was very interested in laser > devices, that Hughes Aircraft had made optical (laser-ring) gyroscopes. The > ones for military aircraft could detect >extremely< small rotations...measured > in degrees per minute, and they were decimal numbers to boot. > I don't know if anyone has made smaller versions of this technology, but it > should be feasable. The Hughes ring was about $200k I think...a bit expensive, > but I remember reading somewhere about a company who had sucessfully made a > solid version of the ring-gyroscope (Hughes used mirrors on a stout frame > about 10" across [from the photos]), which used beveled, mirrored faces on > the outside of some kind of crystal material (optical glass probably). The > availability of IR laser diodes should bring the price down quite a bit. A smaller, more rugged, and potentially cheaper design is to use an optical fiber as a light path for the gyro. I don't know about commercial sources for such things, but I've seen photos of lab units whose sensitivity is dependent on the length of the fiber. The fibers are quite thin, so lots of meters of fiber can be coiled neatly into a small volume. -- ------------------------------------------------------------------------ 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
gt4115a@prism.gatech.edu (HARDIE,PETER THOMAS) (12/03/90)
In article <11836@milton.u.washington.edu> 23r@sage.cc.purdue.edu (John Dormer) writes: > I recall from a couple years back, when I was very interested in laser >devices, that Hughes Aircraft had made optical (laser-ring) gyroscopes. The >ones for military aircraft could detect >extremely< small rotations...measured >in degrees per minute, and they were decimal numbers to boot. One caveat about using aircraft gyros. I have been told that all of these devices made for commercial (non-US military) use have built-in 15 minute 'alignment' times - to prevent non-US military from buying a bunch of DC-9's with the gyro's and moving them to fighter aircraft. I would doubt that VR is sufficient reason for the govt to change the design of the aircraft gyros at this point. > John Dormer > dormer@medusa.cs.purdue.edu -- Pete Hardie Georgia Institute of Technology, Atlanta Georgia, 30332 uucp: ...!{decvax,hplabs,ncar,purdue,rutgers}!gatech!prism!gt4115a Internet: gt4115a@prism.gatech.edu