Laser Range FinderMech 207 – Advanced Mechatronics

I

TJ Leising

October 23, 2009

Introduction Laser light basics

– Propagates dominantly in one direction in the form of a beam

– Beam can maintain integrity for very long distances

Lasers are ideal to measure distances– Different methods used to measure different lengths– i.e. Triangulation and Time of Flight

All photos courtesy Acuity

Introduction (cont.) Time of Flight

– Measures the time the laser take to travel the distance and back

– Short pulse fired out and time measured for a reflected portion to come back

– Longer time = farther away– temporal accuracy must be very high – e.g. 1 ns for a

spatial accuracy of 15 cm

Triangulation– Have sensors offset to measure angle of reflectance– Based on geometry, distance can be determined

Courtesy: Sensorland.com

Courtesy: Physorg.com

Laser Physics Laser Light is:

– Monochromatic: it contains one specific wavelength of photons

– Coherent: All the photons have wave fronts that are in unison

– Directional: Propagates generally in one direction in a concentrated

beam

Atoms are excited and release photons that travel down the tube reflecting off mirrors and exciting more atoms untilthey leave the tube through a lens in a concentrated laser beam.

Implementation Laser is installed to additional sensing

circuitry A photo sensor receives the reflected signal

– Triggers “timer stopping” circuitry or “angle valve” input

Data from the time of flight or the angle of impact is used to determine the distance to target

Courtesy: philohome.com

Applications Recreation

– Golf and Hunting

Production Control– Keep a level surface

3-D mapping– For robotics or scouting

High Precision Guidance– Missiles, Targeting Computers

Courtesy: binocularsdirect.com

Courtesy: seattlerobotics.org

Courtesy: foxnews.com

Challenges Issues with lasers

– Tend to be expensive– Dependent on line-of-sight (wall vs. chair)– Can involve complicated circuitry that might not be

necessary– Laser pointing fluctuations– Laser noise issues

Courtesy: Encyclopedia of Laser Physics

References Encyclopedia of Laser Physics and Technology

– http://www.rp-photonics.com/

Acroname Robotics – http://www.acroname.com/

Acuity Laser Measurements– http://www.acuitylaser.com/products.shtml

Sensorland.com– http://www.sensorland.com/HowPage056.html

Encoder: The Newsletter of the Seattle Robotics Society– http://www.seattlerobotics.org/encoder/200110/vision.htm

How Stuff Works– http://www.howstuffworks.com/