rehrauer@apollo.HP.COM (Steve Rehrauer) (11/30/89)
This sort of thing may've been discussed here before, but since I
don't normally read this group...
For awhile now, I've been kicking around an idea for a project. Most
of it I either know how to do now, or can feel comfortable about hand-
waving at for now. The only part I'm really stumped on involves a
distance sensor. Without trying to be coy, I'll just describe what
characteristics I'd like the sensor to have, rather than describe the
whole project.
Basically, the sensor
- must be able to measure distances of about 0 - 6", with an accuracy
of about 1/8" or better;
- must be non-contact (well, perhaps I should say "ideally won't
depend on contact");
- will be pointed at surfaces which aren't very reflective, are
of a range of colors, are somewhat uneven (say, a variance of
1" or less in height), aren't metallic, and cannot be marked in
any manner beforehand (i.e.: with a tracking grid of some sort);
- needn't worry about rapid movement (i.e.: the target will be
stationary, and the sensor movement well-defined);
- must be fairly cheap (say, less than $200, including the sensor
itself and drive electronics).
I guess Polaroid sells a "hacker's kit" with the sonar gizmo they use
on their autofocus cameras, and I think for under $200. But I seem to
recall reading that the range was more like 12" - dozens of feet, with
an accuracy of 1" or worse. Does anyone know if that's a fundamental
limit on the sensor itself, or only the way the electronics were
designed in the kit? (Be gentle; I'm mostly a software person. I
know enough about electronics to think I know what I'm doing until
it's too late. ;-)
Also, I'd guess that the surface characteristics of the targets probably
rule out an infrared design?
Anyone have any ideas for me? Am I asking for the moon with that list?
Thanks in advance!
--
>>"Aaiiyeeee! Death from above!"<< | Steve Rehrauer, rehrauer@apollo.hp.com
"Flee, lest we be trod upon!" | The Apollo System Division of H.P.peg@psuecl.bitnet (PAUL E. GANTER) (11/30/89)
> I guess Polaroid sells a "hacker's kit" with the sonar gizmo they use > on their autofocus cameras, and I think for under $200. But I seem to > recall reading that the range was more like 12" - dozens of feet, with > an accuracy of 1" or worse. Does anyone know if that's a fundamental > limit on the sensor itself, or only the way the electronics were > designed in the kit? (Be gentle; I'm mostly a software person. I Recently my robotics class was discussing distance sensing, and one of the methods we covered was acoustics (my prof is doing research on them). One large problem with acoustic transceivers involves the air they travel through: the speed of sound in air varies quite a bit with temperature, humidity, barometric pressure, etc. I don't have quantitative figures on the variation; I will ask my prof. Try playing with the formula for speed of sound in most physics texts. I see that speed of sound varies about 10% from 0C to 100C. Add the effects of humidity and pressure and you are probably much higher. Maybe you could build timing circuits to measure transit time of light (if you do, I'll buy them for $1000 cash !! :) Good luck! Paul
strong@tc.fluke.COM (Norm Strong) (12/02/89)
In article <69060@psuecl.bitnet> peg@psuecl.bitnet (PAUL E. GANTER) writes: }> I guess Polaroid sells a "hacker's kit" with the sonar gizmo they use }> on their autofocus cameras, and I think for under $200. But I seem to }> recall reading that the range was more like 12" - dozens of feet, with }> an accuracy of 1" or worse. Does anyone know if that's a fundamental }> limit on the sensor itself, or only the way the electronics were }> designed in the kit? (Be gentle; I'm mostly a software person. I } }Recently my robotics class was discussing distance sensing, and one }of the methods we covered was acoustics (my prof is doing research }on them). One large problem with acoustic transceivers involves the }air they travel through: the speed of sound in air varies quite a bit }with temperature, humidity, barometric pressure, etc. I don't have }quantitative figures on the variation; I will ask my prof. Try playing }with the formula for speed of sound in most physics texts. I see that }speed of sound varies about 10% from 0C to 100C. Add the effects of }humidity and pressure and you are probably much higher. The tempco of sound in air is about +0.18%/deg C at 20 deg. It's easy to temperature compensate an ultrasonic distance measuring circuit to cancel this factor. Changes due to humidity and barometric pressure are slight and can be safely ignored. -- Norm (strong@tc.fluke.com)
Nagle@cup.portal.com (John - Nagle) (12/02/89)
Ultrasonic sonar ranging is difficult for short distances. The
Polaroid sensor system has a minimum range of about two feet, imposed by
the use of the same transducer for sending and receiving. You can
improve on this slighty by using active damping of the transducer, I'm
told, but this can't take the minimum distance down to much more than
a few inches. You can use separate transducers for sending and receiving,
and Cybermation, the mobile robotics firm, has built such devices. This
gets the minimum range down to an inch or so. Below that, leakage
between the sending and receiving transducer overpowers reflections.
There are short-range distance sensors that work on IR reflectance.
The concept is clever; you have one light source and two receivers, set
up as a reflectance system with the two receivers at different distances.
Thus, a nearby object reflects light onto both sensors, but since the
reflected light falls off with the inverse square of the distance to the
object, the levels sensed at the two sensors are different. Thus, from
the ratio of the values at the two sensors, you can calculate distance.
This works for most diffuse target objects, and was used in a now-defunct
robotics project at Stanford as part of a robot hand to sense the presence
of nearby objects. Usually, you use a modulated light source and filters
on the sensor outputs to eliminate interference from other light sources.
This works reasonably well. If you have three receivers, you can do a
consistency check and determine if your data is reliable.kelly@uts.amdahl.com (Kelly Goen) (12/08/89)
does anyone know of an address or fax number for the
division of poloroid that sells this hacker kit???
I would be highly interested in knowing!!
thanx in advance
kelly
--
Kelly Goen
CSS Inc.
DISCLAIMER: I Dont represent Amdahl Corp or Onsite consulting. Any statements ,opinions or additional data are solely my opinion and mine alone...
Seen in alt.sex recently "SEX is FUN , Thats why there are so many of us!!"
My Opinion: Sex between Consenting Computers leads to Social Data Diseases!sic@ritcsh.cs.rit.edu (Eric A. Neulight) (12/10/89)
In article <51u602a472kn01@amdahl.uts.amdahl.com> you write: > >does anyone know of an address or fax number for the >division of poloroid that sells this hacker kit??? I am assuming you are referring to the Polaroid "Ultra-Sonic Ranging System" "hacker's kit". I've tinkered with it before when I was playing with robotics. I happen to have the old manual with specs in my library. Here's what it says: Ultra-Sonic Ranging System (Polaroid) Comes with: (1) 1 Polaroid Instrument Grade Electrostatic Transducer. Part # 604142 (2) 1 Polaroid Ultra-Sonic Ranging Board (modified) either 4-freq Part # 606745 or 1-freq Part # 607089 (3) 1 Experimental Demo Board (4) 1 Polaroid Circular Polarizer (5) 2 Polaroid Polapulse Batteries Part # 604152 (6) 1 Polapulse Battery Holder Part # 604145 (7) 1 Cable Assembly Part # 604789 (8) Assorted Connectors and Wires If I remember correctly the whole kit fell within the $100-$150 range. Keep in mind that the info I have is circa 1985. It's a nice kit though and gets you started pretty well. The manual supplies full schematics, data sheets, and theory. All of the above parts are also available separately. Here's the info you asked for: Polaroid Corporation Commercial/Battery Division 575 Technology Square - 3 Cambridge, MA 02139 Phone# (617) 577-4681 I have no affiliation with Polaroid other than being the standard, satisfied customer. ============================================================================== CLAIMER: Well -- I wrote it! Eric Alan Neulight "Nothing is Impossible -- Just Impractical." Electrical Engineering "For every Lock, there is a Key." Computer Science House "INSANITY is just a state of mine." Rochester Institute of Technology BITNET: EAN4762@RITVAX IP: sic@ritcsh.cs.rit.edu ==============================================================================