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

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...

Interesting criteria

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.

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

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.

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.

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

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

Leica has a few hand-held laser distance devices that seem close to your specs.

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=3D=3D=3D=3D=3D=3D The Leica DISTO=99 plus is the only device in the world that offers the highest accuracy, attractive design and wireless data transfer by means of BLUETOOTH=AE in one package. Even if you are currently still working with paper and pencil, integrated BLUETOOTH=AE 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: =B11.5mm (0.06in) =3D=3D=3D=3D=3D=3D=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

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

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

Try the Sharp GP2D12 sensors.

Steve

schreef in bericht news:4242a351$0$29448$ snipped-for-privacy@news.optusnet.com.au...

=========== 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!

-- Gordon

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