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Sensors used in navigation• Dead Reckoning

– Encoders

– Potentiometer

– LVDT

– Tachometer

– Gyroscopes

– Accelerometer

– Doppler

• External Sensors– Ultrasonic

– Laser range sensors

– Bearing lasers

– Radar

– Global Positioning System

– Vision

VehicleModel

InternalSensor

External Sensor

StateEstimate

Navigation Architecture

External sensors. ( Absolute sensors )

Low Frequency sensors.

The Error is bounded.

Ultrasonic

Radar

GPS

Beacon and Range/Bearing/Intensity laser

VisionThese sensors include distance measurements based on different principles:

TOF: measure time-of-flight of a signal after reflecting a surface

Phase shift measurements ( phase difference between direct andreflecting signal

FM: The signal is frequency modulated to detect range with the returnecho frequency

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Time of flight sensors

The measured pulses typically come formultrasonic, RF and optical energy sources.

D = v * t

D = round-trip distance

v = speed of wave propagation

t = elapsed time

Sound = 0.3 meters / msec

RF/light = 0.3 meters / ns (Very difficult to measureshort distances 1-100 meters)

Ultrasonic Sensors. Polaroid

It was developed for an automatic camera focusing system.

The transducer and electronic circuits cost is less than 50 $US

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Hardware operation

The Electronic board supplied has the following I/0

INIT: trigger the sensor, ( 16 pulses are transmitted )

BLANKING: Goes high to avoid detection of own signal

ECHO : Echo was detected.

BLNK : to be generated if multiple echo is required

time

Ultrasonic Information

-5 (dB) 0-5-10-15

0°

90°

45°

Beam Angle

Beam Angle

Sensor Arc ofUncertainity

Sensor Specification Sensor Model, angle = 15 degrees

Range is very accurate but bearing has a 30 degree uncertainty. The objectcan be located anywhere in the arc.

Typical ranges are of the order of cm to 30 meters.

Another problem is the propagation time (340 m/s). The signal will take200 msec to travel 60 meters. ( 30 meters roundtrip )

Maximum bandwidth with 30 meter range is 5 Hz.

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Pumps

High-speedfluid flow

Motors

Environmentalultrasonic noise

Environmentalultrasonic noise

Ultrasonicsensors on other

mobile robots

Ultrasonicsensors on other

mobile robots

Crosstalkpath

Wall

Mobilerobot

Mobilerobot

Crosstalkpath

Wall

Crosstalkpath

Wall

Mobilerobot

Mobilerobot

Crosstalkpath

Wall

Crosstalk fromonboard

ultrasonicsensors

Crosstalk fromonboard

ultrasonicsensors

Other problems with Ultrasonic sensors

Other Problem: Specular Reflections

• Specular reflection occur when the wave-front from a sensor hits a smooth surfacethat is tilted relative to the incoming "beam" at an angle αααα > 20 - 40 deg.

• The wave-front is reflectedaway from the sensor,and no echo is received.

Incomingwave-front

Smoothwalls

Specularreflection

ααA Corner will

look fartheraway

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Laser Range finder based on TOF

Schwartz Electro-Optics Laser RangefindersMaximum of 100 meters (328 ft). The system uses a pulsedInGaAs laser diode in conjunction with an avalanchephotodiode detector

SEO Scanning Helicopter Interference Envelope Laser Detector(SHIELD)This system was developed for the U.S. Army as an onboard pilotalert to the presence of surrounding obstructions in a 60-meterradius hemispherical envelope below the helicopter.

Phase Shift measurements

The phase-shift measurement (or phase-detection) ranging techniqueinvolves continuous wave transmission as opposed to the short pulsedoutputs used in TOF systems.A beam of amplitude-modulated laser, RF, or acoustical energy is directedtowards the target. A small portion of this wave is reflected by the object'ssurface back to the detector along a direct pathThe returned energy is compared to a simultaneously generated referencethat has been split off from the original signal, and the relative phase shiftbetween the two is measured

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Infrared Range finderA low-cost near-infrared range-finder, for use in autonomous robot navigation infactories and similar environments is manufactured by ESP Technologies using eye-safe 2 mW, 820-nanometer LED is used

The Optical Ranging System (ORS-1) provides three outputs: range and bearing ofthe target, and an automatic gain control (AGC)

Range resolution at 6.1 meters is approximately 6 centimeters, while angularresolution is about 2.5 centimeters at a range of 1.5 meters.

Sick laser Range Sensor.Maximum range : 80 meters

Resolution : 10 mm

Field of view : 100 - 180 degrees

Angular resolution : 0.25 degrees

Scan time : 13 - 40 msec.

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Laser Profiles

0 200 400 600 800 1000 1200 1400 1600 1800-600

-500

-400

-300

-200

-100

0

HD

Infrastructure

ore /coal carBack wall

Front wall

Laser

Last Pulse Return

These lasers are moreimmune to Dust andFog.

Range 2-500 meters

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Bearing Laser

This sensor is commonly used for navigation of industrial autonomous guidedvehicle (AGV) systems.

A pencil laser beam is mechanically scanned in azimuth around the environment.Passive reflectors, occasionally bar codes, are placed around the environment atknown surveyed locations.

When a scanner mounted on a vehicle moves through the environment it detects thepresence of these reflectors or beacons. An encoder mounted on the scanner is usedto record the azimuth angle which a reflector is detected. In some cases it can alsoreturn the width of the target making range measurements also possible.

As the vehicle moves through the environment, a sequence of bearing measurements,to a number of fixed and known landmarks are made and its position is updated

γ

z k r( ) ( , )= θx k x y( ) ( , , )= φ

φ

0,0 x

y

B3

θ

B2

B1

Denning LaserNav Position SensorThis is laser-based scanning beacon system that computesvehicle position and headingThe fan-shaped beam is spread 4 degrees vertically to ensuretarget detection at long range while traversing irregular floorsurfaces, with horizontal divergence limited to 0.017 degrees.Each target can be uniquely coded so that the sensor candistinguish between up to 32 separate active or passive targetsduring a single scan.

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Attenuation

Lasers are muchmore affected byfog than MMWR

This radar operates in the 77 GHZ band frequency.

The device has a rotor which rotates a deflector to obtain 360 degree-azimuth rangeinformation. A control unit maintains a constant rotational velocity of the deflector platepositioned above the aperture and reads azimuth of each radar sweep.

The beam angle in the horizontal direction is 1 degree and the vertical angle is 6 degreesto make the radar insensitive with respect to roll and pitch of the vehicle. (Spoiler)

MMWR. ( University of Sydney)

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This radar is designed for beacon detection and for obstacle avoidance tasks. The radar isdesigned to enable the beacons to be identified from all other object reflections. This isachieved though appropriate design of the beacons and polarization of the radartransmitted signal

MMWR. ( University of Sydney)

Frequency ModulationThis technique involves transmission of a continuous electro-magnetic wave modulated by a periodic triangular signal that adjuststhe carrier frequency above and below the mean frequency fThe transmitter emits a signal that varies in frequency as a linearfunction of time:

f t f at( ) = +0

Tdc

= 2

F f t f T t atb = − + =( ) ( )

Signal generated by the sensor

The reflection from thetarget arrives at t + T

d=target distance

The frequency difference is proportionalto the target distance

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Imaging results

• Signal Power over 360o to 50m

• Test site

Container stack image

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Detection

Airborne radar image

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Orepass radar

Radar Level 1

CrusherStation

Stop Pulling

Level 3

Stop Tipping

Level 2

Orepass and Orepass Echo Profile Obtained using a FMCW Radar 0 50 100 150 200 250 300 350 400-20

-15

-10

-5

0

5

10

15

20Meas ured Echo: 300m Orepas s ; Fins ch Mine

DEPTH m

Sig

nalL

evel

dB

Stereo VisionDisparity between a Stereo Pair

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Stereo Vision

A pair of cameras separated at adistance “baseline” produce apair of images that can be used todetermine range

Panoramic Vision

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Panoramic Vision

Inclinometers

This are absolute sensors that measure the inclination of aplatform with respect to a plane tangential to the earth.

They are all based on detection of gravity. Any additionalacceleration will perturb the measurement.

A set of perpendicular accelerometers can be used as aninclinometer.

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Inclinometers

Pendulum gyros

These sensors use the property that a pendulum with alength of the radios of the earth will always be in verticalposition.

This can be approximated with electronic compensationachieving good rejection of translational acceleration.

Watson pendulum gyros Rate Gyro

0.02 Hz 0.02 Hzfreq freq

Inclinometers

This sensor consist of a capacitor divided in fourquadrants.

A fluid with a high dielectric constant is sealed inside. Ifthe sensor is tilted the bubble will change the positionand the capacitance measured in each quadrant.

With appropriate capacitor shapes the output can bemade linear to the orientation of the sensor