10m-10cm distance measurement with 1cm accuracy at a rate of 50Hz

Yugo wrote:

No, but I guess they excist. You could use RADAR, simply send out sound,
and see how long time it takes for it to return (knowing sound travels
more or less 300m/s. This would make it dependent on the altitude, but
it'd be easier to make with a microcontroller than light/radio based
RADAR, since light would require really really good timing...


--
MVH,
Vidar

www.bitsex.net

What about the samll commercial distance measuring units they sell at builders
shops?  Cheap and easy to get,  But I dont know about the specs

David

Vidar Løkken wrote:


   Use of light or radio pulses (as in RADAR) is just as easy as use of
sound pulses; timing is easy.
   Been around since the 1940's.

Robert Baer wrote:


Ranging radar is very much more difficult than dopler radar. Dopler radar is
fairly easy to do, $100 bucks or so -- hell you can buy dopler radar off
the net to measure your pitching speed.

Ranging radar has to emit a pulse and measure the time delay from transmit
and recieve. With SONAR, this is dist = (340/2)/T (we divide by two because
echo is a two way trip), well in the millisecond range. With RADAR this is
dist = (300000000/2)/T. If you are measuing meters you are in the nano
second range. If you are trying to measure centimeters you are in the pico
second range.

This is not to say it can't be done, but it would be very expensive.

You can't meet the 50Hz requirement at maximum range with sound in air, the
best you could get would be about 16Hz.
(assuming 330 metres/second)

Deep.

Deep Reset wrote:

No, you can get higher, ...
... why wait until a pulse is received ?
Ok next thing to do is "modulate" the pulses,
for example,
   send a puls
   send a second puls 10 msec later
   next puls 15 msec later
   next puls 12 msec later
By now combining the results of multiple measurements,
you can avoid the ambiguity.

A more diffcult way is to use continuous wave (of course modulated)
ultrasound.

Stef Mientki

Stef Mientki wrote:


How do you differentiate between pulses? What about echos from multiple
surfaces at different distences?

<Yugo> wrote:


Speed of sound is about 340 meters per second, if you want a range of 10
meters, that is a round trip of 20 meters. 340 meters per second / 20
meters round trip, that means a theoretical maximum of about 17 readings
per second, and a practical max of about 10.

Unless you can alter your specifications, SONAR is out of the question and
you'll have to use rangning RADAR.

Ranging RADAR is expensive because, unlike police speed traps which use
dopler frequency shift on the bounced return signal, a ranging radar
system, like a ranging sonar system, needs to measure between send and
recieve. Where sound travels at a pokey 240 meters per second and can be
easily measered, light travels a little less than 300,000,000 meters per
second, and requires some real precision to measure. Especially at the cm
to 10 meter range.

Yugo wrote:

Check into the SICK laser rangers. Not cheap, though.

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<Yugo> wrote in message

Yugo - I don't know if the range or all other constraints are satisfied, but
you may want to have a look at the Sharp ranging modules, IR based IIRC.
Have a look on the Manuco website.
rob
http://www.manuco.com.au/

Leica has a few hand-held laser distance devices that seem close to
your specs.
http://www.leica-geosystems.com/cpd/en/products/laser_distancemeter

Below is some data about their higher end system.  But they also have a
cheaper version that has the similar measurement abilities.
=3D=3D=3D=3D=3D=
The Leica DISTO™ plus is the only device in the world that offers the
highest accuracy, attractive design and wireless data transfer by means
of BLUETOOTH® in one package. Even if you are currently still working
with paper and pencil, integrated BLUETOOTH®  technology allows you to
make the change at any time and to record your values electronically.
The data can be transferred on site wireless to a PDA (Pocket PC) or
directly to a laptop and easily used for other purposes.

 Range of measurement: 0.2 up to 200 m
 (0.7 up to 650ft). Accuracy:  ±1.5mm
 (0.06in)
=3D=3D=3D=3D=3D=

Regarding price; I looked at a similar system by another vendor a few
years back and it was around $800 at the time.


Joe Dunfee

===========
The Leica DISTOT plus is the only device in the world that offers the
highest accuracy, attractive design and wireless data transfer by means
of BLUETOOTH® in one package. Even if you are currently still working
with paper and pencil, integrated BLUETOOTH®  technology allows you to
make the change at any time and to record your values electronically.
The data can be transferred on site wireless to a PDA (Pocket PC) or
directly to a laptop and easily used for other purposes.

 Range of measurement: 0.2 up to 200 m
 (0.7 up to 650ft). Accuracy:  ±1.5mm
 (0.06in)
===========


What is the theory behind laser ranging?

Thanks.

Time of flight.  Just like sonar, but MUCH faster.

--TE

Not always. A cheaper approach is to modulate the light beam, and then
compare the phase of the return beam with an internal reference beam (or
clock). Sometimes referred to as tone ranging. Yet another type, more
suitable for shorter distances (say, up to 50-60 feet), uses
interferometric methods, and are accurate to a quarter wavelength.

Leica's DISTO transits use phase measurement. They'd be much more
expensive if they used time-of-flight.

File this under the "FWIW" and "who the heck cares?" departments! <g>

-- Gordon

I thought the DISTO was time of flight.  When using the phase technique or
the interferometric method, is it still possible to use a servo mounted
45degree mirror to "pan" the beam around or does it mess up the measurement?
I have been planning to use a DISTO on a future robot project.

--TE

Leica has a FAQ where they answer some of the common technical
questions. From the wording of the FAQ it sounds like the DISTO units
sample the sub beam that comes from the opposite side of the diode. This
is often more accurate than sampling the signal that is used to modulate
the beam.

I don't think a turret mount would work for most interferometric laser
systems as the optics have to be held to very tight tolerances during
the measurement.

SICK has some scanning laser measurement and detection systems that I've
seen on some robots, but these are fairly pricey.

-- Gordon

So how much is the Leica device?

Mitch

I've seen the entry-level DISTO at about $500 on some online stores.
Never pulled out my wallet to get one, though.

-- Gordon

I've used a SICK LMS-291 which is a laser ranging device.  It runs
around $6K and is superb.  It can be configured to scan continuously
and report the object distances for a 180 degree field of view at 0.5
degree increments - good out to about 40 meters, and as close as a few
centimeters, with very good precision - millimeter accuracy.

It is a very, very, nice sensor, though somewhat heavy and power
hungry.  You need a beefy 'bot to carry it.

-Brian
--
Brian Dean
BDMICRO - ATmega128 Based MAVRIC Controllers
http://www.bdmicro.com/