Laser RangeFinders - saba.kntu.ac.irsaba.kntu.ac.ir/eecd/ecourses/instrumentation/.../LaserRangefinder.pdf · averaged together for a range measurement. 5. Turbulence in the air through

Laser Laser RangeFindersRangeFinders

Hamed Hamed LotfizadLotfizad....…………………………………………..791210122..791210122MehdiMehdi ModaresiModaresi……………………………………………….791210125.791210125

Professor Professor ………………....…………………….Dr .Dr H.TagiradH.Tagirad

The Invention of the LaserThe Invention of the Laser

The Invention of the LaserThe Invention of the Laser

•• Invented in 1958 by Charles Townes and Invented in 1958 by Charles Townes and Arthur Schawlow of Bell LaboratoriesArthur Schawlow of Bell Laboratories

•• Was based on EinsteinWas based on Einstein’’s idea of the s idea of the ““particleparticle--wave dualitywave duality”” of light, more than 30 years of light, more than 30 years earlierearlier

History of Laser Ranging

• In 1840’s, First remotesensing used withpigeons• 1969, the first lunarlaser ranging done byusing reflectors placedon the moon by Apollo11

Theory

There are 3 types of laser distance measurements

1)Pulsed2)Continuous wave3)Interferometer MethodLaser ranging is called LIDAR which stands

for Light Detection and Ranging

DefinitionsDefinitions

•• TargetTarget•• Cooperative TargetCooperative Target•• Uncooperative TargetUncooperative Target•• RetroreflectionRetroreflection•• Diffuse ReflectionDiffuse Reflection•• ReflectanceReflectance•• Response TimeResponse Time•• Depth of FieldDepth of Field

Cooperative Targets

Non-cooperative Targets

Pulsed Laser Ranging

Short duration and high power1)Transmit pulse2)Detect reflection3)Measure time difference4)Compute distance from speed of light

Pulsed Laser System

How to Compute the Distance

• 2R = C*Tr• R = distance• C = speed of light• Tr = total travel time• 30 cm over kilometers precision

Continuous Wave

Frequency modulated laser rangingWe know that:1)Light travels in straight lines2)Laser light is coherent3)The speed of light is knownTherefore we can compute the exact distancethat the light has traveled

Beam-modulation Telemetry

How to Compute the RoundtripTime

• Phi(r) was obtained from last diagram

• Now Tr calculates with this formula

• Then …

ϕϕϕ

Tr = roundtrip timePhi r = phase

How to Compute the Distance

2R = C*TrR = distanceC = speed of lightTr = total travel time1 cm over kilometers precision

Factors affecting accuracy

1. Frequency of the tone or modulation.2. Accuracy of the phase-measurement loop. This depends

on signal strength, noise, and so on.3. Stability of the modulation oscillator.4. Number of cycles (or measurements) that can be

averaged together for a range measurement.5. Turbulence in the air through which the. measurement ismade.6. Variations in the index of refraction of the air.

Triangulation

1 Triangulation is amethod of determiningdistance by usingangles andtrigonometry.

2.There are manydifferent types oftriangulation.

Some of Applications of LIDAR

• Satellite Systems (SLR)• Sensing of Surface Elevations

Satellite Systems (SLR)

• Determine position ofEarth’s satellites

• Topography• Oceanography• Gravity Waves• Plate Tectonics

Sensing of Surface Elevations

Rangefinders

• Uses pulses of infraredlight

• Based on time differencefrom transmission toreception

Many Uses for Rangefinders

Golf

Hunting

Architecture

GPS(Global Positioning System)

• GPS uses severalsatellites and the conceptof triangulation.

• For this example there are

satellites that are usedto pinpoint the location ofthe transmitting vehicleon earth

Step 1

• The vehicle determines how far away the first satellite is from it. Either pulsed or CWtechniques can beused.

Step 2

• The vehicle determines how far away a second satellite isfrom it.

Step 3

• The vehicle determines how far away a third satellite is from it. Then it can combine all of the information anddetermine where on Earth it is located.

The Future of LIDAR

• In the future laserranging willbecome moreprecise andcheaper, and manynew applicationswill beimplemented

Corporations and manufacturesCorporations and manufactures

•• Acuity ResearchAcuity Research•• Freedom TechnologiesFreedom Technologies•• SequenceSequence•• VydasVydas

AccuRange 200™ laser displacement sensors

AccuRange 4000™ laser rangefinder

AccuRange600™ laser displacement sensors

AR200 SensorsAR200 SensorsPrinciples of OperationThe AR200 sensors project a beam of visible laser light that creates a spot on a target surface. Reflectedlight from the surface is viewed from an angle by a line scan camera inside the AR200 sensor. Thetarget’s distance is computed from the image pixel data. The AR200 can not be overloaded and measuresaccurately even when a mirror reflects the entire light beam back to the detector. Likewise, on surfacesof polished glass or water, almost the entire beam passes through or is reflected away. The AR200sensors can measure distance from the small remaining scattered light.

AccuRange600 laser displacement sensors

Principles of OperationThe AR600 sensors project a beam of visible laser light that creates a spot on a target surface. Reflectedlight from the surface is viewed from an angle by a line scan camera inside the AR600 sensor. Thetarget’s distance is computed from the image pixel data. The AR600 can not be overloaded and measuresaccurately even when a mirror reflects the entire light beam back to the detector. Likewise, on polishedsurfaces, almost the entire beam is reflected away. The AR600 sensors can measure distance from thesmall remaining scattered light.a

AccuRange 4000™ laser rangefinder

This sensor opeartes on "Time of flight" Principle.

Freedom Technologies PreciCura SeriesPreciCura sensor opeartes on “Triangulation" Principle.

Different Types of applicationsDifferent Types of applications

Sequence Technologies, Inc.

Tightly collimated output beam for small spot sizeLightweight, compact, low power design Fast response time – 50KHz maximum rate

0.1 in (2.5mm) accuracy, 0.02 in (0.5mm) short- term repeatability

Zero to 50 feet operating range for most surfaces

ST263 DistoGAGE Laser Sensor

Comparison Between Different types of Comparison Between Different types of distance sensorsdistance sensors

1.Inductive sensors

2.UltraSonic 2.UltraSonic SensorsSensors

3.Laser Distance Sensors3.Laser Distance Sensors

مطالعه در بازار ايران مطالعه در بازار ايران

•• Searching for Searching for ““laser range sensorlaser range sensor”” in in GomhoryGomhory street : street : ““NOT FOUND !!NOT FOUND !!””

•• Searching For Searching For ““laser rangefinderlaser rangefinder”” in in lalehzarlalehzar street :street :

•• 15 m with 1cm accuracy 15 m with 1cm accuracy 96,000 96,000 tomanstomans•• Some Device with Some Device with

accuracy in mm accuracy in mm --> 650,000 > 650,000 tomanstomans

Thanks.Thanks.

•• References:References:•• 1. 1. AcuityResearchAcuityResearch CorporationCorporation

at at www.AcuityResearch.comwww.AcuityResearch.com•• 2. Sam2. Sam’’s Laser FAQs Laser FAQ•• 3. Sequence Technologies.3. Sequence Technologies.•• 3. 3. VydasVydas Corp Corp www.vydas.comwww.vydas.com