50 Robotics: Rangefinding Devices part1
Description
This article is from the Robotics FAQ, by Kevin Dowling nivek@cs.cmu.edu with numerous contributions by others.
50 Robotics: Rangefinding Devices part1
"Principles" There are four basic techniques for distance measurement
using electro magnetic radiation. These are:
1. Pulse Timing
2. Phase Comparison
3. Doppler Methods
4. Interferometry
All are used in practice for distance measurement depending on the
particular application.
Pulse timing, as the name suggests, involves measuring the round time
for a signal to be transmitted to a reflective surface and return.
This is the principle used in Radar, DME for aircraft, LORAN,
Satellite Altimetry, Airborne RADAR Altimetry, Lunar Laser Ranging
etc. Some of the newer EDM instruments used by surveyor are also using
pulse timing and accuracies of +/- 5mm are possible. Most of the
military range finders also use pulse timing. The GPS system uses
pulse timing for coarse distance measurement. Very Long Base
Interferometry (VLBI) is also a pulse timing technique where signals
>from pulsars are timed from two or more radio telescopes and the
difference in times of arrival are converted to intercontinental
distances with a precision of a few centimetres.
Phase difference involves the use of a carrier wave which may be
modulated at different wavelengths. By measuring the difference in
phase between the transmitted signal and the received signal after it
has been reflected from the other end of the target, the distance can
be determined as an integer number (unknown) of wavelengths plus a
fraction of a wavelength which is known from the phase comparison. By
using a range of modulation frequencies the ambiguity can be resolved.
There are many applications of this technique. A wide range of carrier
frequencies are used ranging from visible through infra red to
microwave and right down to VLF. Typical instruments used by surveyors
have accuracies of +/-(1to2 mm +1to3 parts per million) and use infra
red as the carrier. Precise positioning using GPS can be achieved by
phase comparison of the carrier wave signals of the various
satellites. Accuracies in position of better than 1 part per million
can be achieved.
Doppler techniques were used in the earlier satellite positioning
systems. The received frequency of a low orbit satellite is compared
with the actual transmitted signal as a function of time. The rate of
change of frequency gives the slant range between the satellite and
the observer while the instant when the two freqencies are the same
gives the point of closest approach. By knowing the orbital parameters
of the satellite which are transmitted, the observers position can be
determined.
Interferometric methods are the same as those used in the original
Michelson Interferometer. It is used for metrology, high precision
distance measurement over short distances (up to 60 metres) and in the
definition of the metre.
There are a variety of laser rangefinding devices that have been built
and used over the past decade for robotics use. The 3D devices are
still large, power hungry and heavy but give very nice images suitable
for fast map building and navigation work. Expect to pay over $50K for
these time-of-flight devices. Most AM Lidars measure phase shift
between outgoing and reflected beams. A mirror system rasters the beam
forming a video-camera-like image. Some devices supply the reflectance
image as well as range which is nice for corresponding the two.
Comprehensive references include:
* Electronic Distance Measurement by JM Rueger, Springer-Verlag
* P. Besl, ``Active, Optical Range Imaging Sensors'', Machine Vision
and Applications, v. 1, p. 127-152, 1988.
A longer version of Besl's paper appears in ``Advances in Machine
Vision: Architectures and Applications'', J. Sanz (ed.),
Springer-Verlag, 1988.
* Other good surveys are Ray Jarvis' article in IEEE TPAMI v5n2 and
Nitzan's article in IEEE PAMI v10n2.
A good report on the characterization of a particular scanner is:
* Experimental Characterization of the Perceptron Laser Rangefinder,
In So Kweon, Regis Hoffman, and Eric Krotkov. Carnegie Mellon
University Technical Report, CMU-RI-TR-91-1. 1991.
* M. Hebert and E. Krotkov. 3-D Measurements from Imaging Laser
Radars: How Good Are They? Int. Journal of Image and Vision
Computing, 10(3):170-178, April 1992
* International Journal of Robotics Research, Vol. 13, No. 4, Aug.
1994, pp 305-314. {get title}
A number of laboratory works have also demonstrated FM or chirp
systems which can be highly accurate (e.g. high resolution elevation
maps of coins) but these are very specialized and I don`t know of
commercial devices currently.
"Acuity Research"
20863 Stevens Creek Blvd. #200
Cupertino, Ca. 95014
tel: 408-252-9639
fax: 408-725-1580
net: contact@acuity.com or Bob Clark, rrc@acuity.com
The AccuRange 400 is an optical distance measurement sensor with a
range of 0 to 16m for most diffuse reflective surfaces. It operates by
emitting a collimated laser beam that is reflected from the target
surface and collected by the sensor. 0.5mm short-term repeatability,
RS-232 output and optional 4-20mA current loop. Also PW and analog
indication of range available. Visible or IR output available. (670nm
and 780nm respectively) Around $2500. 5VDC@300mA. 50KHz sampling rate.
"Atomic Energy of Canada Ltd. (AECL)"
contact: Narinder Bains (nbains@bart.candu.aecl.ca)
net: 905.823.9040 x6120
Laser Eye ranging system. It consists of a robotic head with a
combined vision / range sensor. The sensor provides colour images and
distance to an object in the centre of the camera field of view. There
is of course software to process images from the camera and detect a
target, to control the head, communication, nice GUIs, etc. Is being
used for vehicle navigation.
From the head position you get the bearing to the target and the
rangefinder provides you with the distance. Angular resolution is
better than 0.05 degree, the distance can be measured up to 100m with
accuracy of ~5 cm. Note that the range measurement is 1D along the
camera axis.
The cost of the vision system and complexity of the software depends
on your specific application: how difficult is it to detect and track
your vehicle, how fast is it moving, is it possible to use special
markers, is illumination constant, etc.
"BCT GmbH "
Martin-Schmeisser-Weg 9
D-44227 Dortmund
BCT in Germany makes laser-3D-scanners with a CAD-interface
"ERIM (Environmental Research Institute of Michigan) "
ERIM has built a number of custom AM laser rangefinders including
those used in the ALV (Autonomous Land Vehicle) program. CMU and
Martin Marietta have both used this systems in extensive work. Basic
system was a 128x64 2fps 20m (ambiguity interval) system.
"Erwin Sick GmbH. "
UK:
Erwin Sick
Optic-Electronic Ltd.
Waldrich House
39 Hedley Road
St. Albans
Herfordshire AL1 5BN
tel: 0727/831121
fax: 0727/856767
in US:
Sick Optic-Electronic, Inc.
7694 Golden Triangle Drive
P.O.-Box 444-240
Eden Prairie, MN 55344
tel: 612.941.6780
fax: 612.941.9287
PLS-100: This device measures distance by TOF from 4 cm up to 80 m,
guaranteed range of 4 m (at a black lether target), is eye-safe (IEC
Class 1), takes a 180 degree scan in 20 ms, total 25 scans a second,
angle resolution 0.5 degree (361 scan points in a scan). This device
is build in a industrial IP65 case. And it is rather cheap (6.900,- DM
+ VAT, in Germany).
"ESP Technologies "
21 LeParc Drive
Lawrenceville, NJ 08648
tel: 609.275.0356
fax: 609.275.0356
$15K LED based IR ranging system. 15cm diameter rotating scanning
device with collimated LED light beam that uses phase differences to
calculate distance. Range 0.6 to 6m. 2.5cm resolution, 15cm accuracy.
1Khz update rate
"Hammamatsu Corp. "
New Jersey
tel: 908.231.0960
fax: 908.231.1539
Hamamatsu S4282 Light Modulation Photo IC The size of a normal
transistor (approx 1/4" square). It has 4 leads, Vcc, Gnd, Vout, LED.
All you do is attach an IR LED to the LED lead to give you an instant
IR proximity detector (the photo diode detector is built into the
part). Two can be aimed at each other and they won't interfere since
they'll be out of phase. They have another model with a lens over the
photo diode that is claimed could be used up to 30 feet! Hammamatsu
also sells a number of photo sensors like color sensors, position
sensitive detectors, pyroelectric sensors.
* S4282-11 short range $7.75 single unit
* S4282-72 long range $19.00 single unit
"Hymarc"
5-38 Auriga Drive
Ottawa, ON, Canada K2E 8A5
tel: 613.727.1584
fax: 613.727.0441
net: [36]info@hymarc.com
Hyscan laser digitizing systems. High speed 3D surface mapping. Hyscan
probe retrofits to any CMM, CNC, or any other translation device.
10,000 points/sec.
Model 25 Model 50
Accuracy +/-0.025mm +/-0.050mm
Resolution (Z) 0.003mm 0.003mm
Depth of field 40mm 80mm
Scan width 70mm 80mm
Stand-off 100mm 100mm
Size 260x110x65mm
Weight 2.2kg
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