kjb@cs.brown.edu (Ken Basye) (06/08/91)
We're looking for a way of getting a single range measurement in a
particular direction. We have sonar, but the beam is far too wide.
I don't think that simple active IR will not have enough range.
Ideally, we'd like something that has low power consumption, a 5-10
degree cone (or less) and a range up to at least 4 meters, although it
need not be very accurate (even +/- 10 cm would be OK).
We've thought about trying to narrow our sonar with some sort of cone,
and also of trying to retroengineer an electronic tape measure. We're
also looking into structured light as a solution. If anyone out there
has any other ideas, or any helpful hints about the ideas above, I'd
appreciate hearing about them. Please respond by mail; I'll summarize
if there's enough interest.
Thanks,
Ken
Internet/CSnet kjb@cs.brown.edu U.S. MAIL Ken Basye
UUCP uunet!brunix!kjb Box 1910
Dept. of Computer Science
Brown University
Providence, RI 02912smith@sndpit.enet.dec.com (Willie Smith) (06/08/91)
In article <77904@brunix.UUCP>, kjb@cs.brown.edu (Ken Basye) writes... >We're looking for a way of getting a single range measurement in a >particular direction. We have sonar, but the beam is far too wide. [...] >Ideally, we'd like something that has low power consumption, a 5-10 >degree cone (or less) and a range up to at least 4 meters, although it >need not be very accurate (even +/- 10 cm would be OK). What's wrong with sonar again? The Polaroid sensors have a beam width of something like 12 degrees.... I called Polaroid the other day and they mentioned that the beamwidth is approximately inversely proportional to transducer size, and one way to get narrow beamwidths is to use arrays of transducers. Willie Smith smith@sndpit.enet.dec.com smith%sndpit.enet.dec.com@decwrl.dec.com {Usenet!Backbone}!decwrl!sndpit.enet.dec.com!smith
kilian@cray.com (Alan Kilian) (06/08/91)
In article <1290@sousa.ltn.dec.com>, smith@sndpit.enet.dec.com (Willie Smith) writes: > I called Polaroid the other day and they mentioned that the beamwidth is > approximately inversely proportional to transducer size, and one way to get > narrow beamwidths is to use arrays of transducers. > Willie Smith I can understand that the beam divergence could be proportional to the transducer width but I don't see how a larger transducer can produce a narrower beam. Is this really true? Also how does an array of transducers produce a narrow beam? Truth is really stranger than fiction. -Alan -- -Alan Kilian kilian@cray.com 612.683.5499 Cray Research, Inc. | "If the human brain was so simple that we 655 F Lone Oak Drive | could understand it, we would be so simple Eagan MN, 55121 | that we couldn't". -Pugh (Whoever that is)
smith@sndpit.enet.dec.com (Willie Smith) (06/08/91)
In article <160412.13057@timbuk.cray.com>, kilian@cray.com (Alan Kilian) writes... > I can understand that the beam divergence could be proportional to the >transducer width but I don't see how a larger transducer can produce a narrower >beam. Is this really true? > Also how does an array of transducers produce a narrow beam? Correction, the beam width is _inversely proportional_ to transducer size. As the transducer size increases, the beam gets smaller. An array of transducers acts just like a single larger one when you drive them right. Don't ask me for details, I don't have any, try Polaroid, they suggested it to me... Willie Smith smith@sndpit.enet.dec.com smith%sndpit.enet.dec.com@decwrl.dec.com {Usenet!Backbone}!decwrl!sndpit.enet.dec.com!smith
jpexg@gaak.lcs.mit.edu (John Purbrick) (06/09/91)
>In article <160412.13057@timbuk.cray.com>, > kilian@cray.com (Alan Kilian) writes... >> I can understand that the beam divergence could be proportional to the >> transducer width but I don't see how a larger transducer can produce a >> narrower beam. Is this really true? >> Also how does an array of transducers produce a narrow beam? Alright, here's a rough & ready explanation: If you have a single transducer, at some distance it is essentially a point source. Sound will radiate and be returned in all directions, hence your transducer is geometrically omnidirectional, with only the characteristics of the transducer to give you limited directionality. If you have a large transducer, or a lot of small ones in parallel, you generate a nearly flat wavefront advancing into space (like those physics problems involving flat capacitors "big enough that we can ignore edge effects"). Essentially, if the transducer is large compared with the distance to the target, you will get the desired parallel wavefronts; if not, you get waves on a circular pattern. A team at the University of Nottingham, England, invented a phased-array sonar system; once the target was located they would "steer" their beam across its surface by firing the transducers at the right times so that at the desired point on the target all the beams would be in phase, while at all other points the beams would cancel at least partly. John Purbrick
nagle@well.sf.ca.us (John Nagle) (06/10/91)
>In article <77904@brunix.UUCP>, kjb@cs.brown.edu (Ken Basye) writes... >>We're looking for a way of getting a single range measurement in a >>particular direction. We have sonar, but the beam is far too wide. >[...] >>Ideally, we'd like something that has low power consumption, a 5-10 >>degree cone (or less) and a range up to at least 4 meters, although it >>need not be very accurate (even +/- 10 cm would be OK). Cybermation makes a megahertz-range sonar system with a narrow beam only 3-4 degrees wide, which they offer with their mobile bases or separately. They're at 5457 Joe Valley Road, Roanoke, VA 24014, phone 703-982-2641. Cybermation has a whole line of mobile robot components, but they are not cheap. Theirs are industrial-strength systems. John Nagle
jm59@prism.gatech.EDU (MILLS,JOHN M.) (06/10/91)
In article <1290@sousa.ltn.dec.com> smith@sndpit.enet.dec.com (Willie Smith) writes: > >In article <77904@brunix.UUCP>, kjb@cs.brown.edu (Ken Basye) writes... >>We're looking for a way of getting a single range measurement in a >>particular direction. We have sonar, but the beam is far too wide. >[...] [objectives, questions, and suggestions deleted] There are three ways to get better range: (1) more power (may fry transducer, but you could try to reduce the pulse or burst length, or otherwise limit duty cycle), (2) preprocessing or gain added to echo detector (but this is usually a "high tech" approach), or (3) narrow the beam, which it sounds like you also want for a more selective measurement. Going with (3), two possibilities: (1) several transducers, spaced out into an array and driven in phase [another BUT] (but Polaroid may depend on the transducer's resonance to both form and resonate with the burst), or (2) use a parabolic reflector. The other arguments were really "straw men." I think a reflector is the way to go. For a spot beam, try a round reflector: maybe you can find one of those "spy microphone" toys once sold by Radio Shack and other sub-MIL vendors, or the fire/cigarette lighter mirrors from Edmund, et al. For a "fan" (narrow one way, wide the other), a long curved strip should work. Use parabolic shapes, and use a slide projector to illuminate them for focus adjustment. (a few "points of light" in the form of shiny metal tape may help on a dull-surfaced reflector.) You benefit from the increased aperture on transmission and reception, which is important, since you are fighting a 1/R^2 relation. Once you have built the thing, build a [fairly small] corner reflector, and map it out (unless you have a microphone that can "see" the ultrasound). Remember the fan beam will be wide across the _narrow_ dimension of the reflector, and vice-versa. The mirror needn't be much larger than the transducer's beamwidth, and far enough away that the transducer and its supports don't block too much of the view. This sets the ratio of focal distance to reflector diameter. (You will have to use a big enough reflector of long enough focal length.) This implies you need a reasonable idea of the original beamwidth, but you seem to have that. If you want to get tricky, you can illuminate the reflector obliquely. You might get even get a product design out of this. Consult books on antenna theory for more info. Let me know how it works, since these comments are in the "ideas are cheap" category: I haven't actually built one! >>Ideally, we'd like something that has low power consumption, a 5-10 >>degree cone (or less) and a range up to at least 4 meters, although it >>need not be very accurate (even +/- 10 cm would be OK). >What's wrong with sonar again? The Polaroid sensors have a beam width of >something like 12 degrees.... Regards -- happy hunting. --jmm-- -- MILLS,JOHN M. Georgia Institute of Technology, Atlanta Georgia, 30332 uucp: ...!{decvax,hplabs,ncar,purdue,rutgers}!gatech!prism!jm59 Internet: jm59@prism.gatech.edu
vdputten@ravel.inria.fr (Frits Van Der Putten) (06/12/91)
In article <1991Jun9.051512.29194@mintaka.lcs.mit.edu>, jpexg@gaak.lcs.mit.edu (John Purbrick) writes: > >In article <160412.13057@timbuk.cray.com>, > > kilian@cray.com (Alan Kilian) writes... > >> I can understand that the beam divergence could be proportional to the > >> transducer width but I don't see how a larger transducer can produce a > >> narrower beam. Is this really true? > >> Also how does an array of transducers produce a narrow beam? > -- skipped a part -- > A team at the University of Nottingham, England, invented a phased-array > sonar system; once the target was located they would "steer" their beam > across its surface by firing the transducers at the right times so that at the > desired point on the target all the beams would be in phase, while at all other > points the beams would cancel at least partly. > > John Purbrick At our instrumentation department we have quite a lot of experience using ultrasound for underwater, air or seismic applications. One of the devices we develloped a few years agoo was a phased array of 32x32 ultrasonic transduces for underwater acoustics. By means of using phase shifts in firing the transducers the beam could be pointed at any location hence acting as an directional acoustic antenna. Please contact mr. G. Boersma (phone: +31.15.69.23.31) at our department in Delft for more details. The same techniques can also be applied in air. I agree completely with the rough explanation by John Purbick that small devices will act as point sources and larger devices will spread plane waves. However, we used a parallel set of six polaroid transduces and did not use any sophisticated phase shifting in steering those devices. Thus we obtained a beamwith of approximately 6 degrees and an accuracy of 0.4 mm in axial direction. This development was done by my collegue mr. R. Breeuwer (also in Delft, phone: +31.15.69.22.20) -- Frits van der Putten TNO, Institute of Applied Physics INRIA Stieltjesweg 1 2004 Route des Lucioles Delft 06561 Valbonne, Cedex The Netherlands France Tel: + 31.15.69.20.00 Tel: + 33.93.65.78.57 Fax: + 31.15.69.21.11 Fax: + 33.93.65.78.58 e-mail: vdputten@tpdsun.tno.nl e-mail: vdputten@mirsa.inria.fr
bleck@ai.mit.edu (Olaf Bleck) (06/13/91)
I have this thing made by a company called Calculated Industries, the Dimension Master Plus (TM) Tapeless Measure/Calculator that's designed for architects I think. It has a phased array of three sonar actuators (they're 1inch diameter), and it advertises roughly a 3deg. beamwidth, which is believable based on playing with it. Good resolution too--it gives millimeters...not that anyone would care. I don't know how we got it or where, so don't ask, but it probably cost a few hundred $$$. Dimensions are about 3"x6"x1", weighs less than a pound with batteries. Tear Here: ----------------------------------------------------------------- _________________________________________________________________ Olaf Bleck bleck@ai.mit.edu Research Scientist 617-253-0997 MIT Artificial Intelligence Lab Mobile Robotics Group