An Introduction to Robotic Navigation

ECE 450

Introduction to Robotics

Navigational Methods

• Dead-Reckoning

• Landmark-Based Navigation

• Map-Based Navigation

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A Matter of Scale

• Global – Getting between end-points

• Local– The immediate area about the robot

• Personal– Monitoring the robot and anything in contact

3http://www.doc.ic.ac.uk/~nd/surprise_97/journal/vol4/jmd/

Frame of Reference

• Absolute– Reference is to a fixed stationary point that

whose position is known

• Relative– Reference is to a stationary point whose

absolute position is not known

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Global Positioning System (GPS)

• 24 operating satellites that transmit one-way signals that give the current GPS satellite position and time.

• The control segment consists of worldwide monitor and control

• The user segment consists of the GPS receiver equipment to calculate the user’s three-dimensional position and time.

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USGlobalSat 20 Channel EM-406a SiRFIII GPS Engine Board with Patch Antenna

From http://en.wikipedia.org/wiki/GPS

Rotary Shaft Encoders• Mechanical

– Low Cost, Low Resolution– Generate output by making / breaking a circuit– Example: volume control on a car radio

• Optical– Low to High Cost, Low to High Resolution– Generate output using infrared light and phototransistor– Example: Panel control in precision applications

• Magnetic– Medium to High Cost, Medium Resolution– Generate output by detecting changes in magnetic flux fields– Example: used most often in adverse environments

• Fiber Optic– High Cost, Medium to High Resolution– Generate output via a laser and phototransistor– Example: Where extremely flammable gasses are present

• Capacitive– Low Cost, Low to High Resolution– Generates output via changes in capacitance using high frequency

reference signal– Example: Digital calipers

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Rotary Shaft EncodersOptical Encoders

• Incremental– Tachometer encoder– Phase-quadrature encoder

• Absolute

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Rotary Shaft EncodersCapacitive Encoder on Expansion Board

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Linear & Rotational Speed Sensors

• Doppler Sensor– Based on Doppler shift in frequency– Lower frequencies easier to detect– Usually pointed 45º to ground to sense movement

• Accelerometer– Provide velocity rate– Poor signal-to-noise ratio at lower accelerations– One, Two and Three axis accelerometers

• Gyroscope– Provide angular rates– Need to be mounted on a very stable platform

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HiTec's HG-R01 Robot Gyro $50

Active Beacons(Line-of-Sight)

• Radio

• Ultrasonic

• Reflective

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Hagisonic StarGazer Robot Localization System

Ranging Sensors

• Types– Sonar– Laser– Light

• Methods for Determining Range– Time-Of-Flight– Phase-Shift Measurements– Triangulation

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• Measures distance in range from 20 to 80cm.

• Designed to interface to small micro-controllers.

• It’s relatively insensitive to the color and texture of the object at which it is pointed.

• Low current consumption at stand-by mode (Approximately 3 A).

Actual Sensor Size

Triangulation Range SensorGP2D02 SENSORGP2D02 SENSOR

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• IR LED Transmits a bundled beam to the object plane.

• Reflected beam is receive by the photo detector.

• The angle of the received beam depends on distance of the object plane.

Two Different Object Planes

Distance Measurement by Triangulation

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• N-conductive substrate layer is an isolation layer

• P-conductive layer is embedded in isolation layer from IR irradiated

• Contact of the p-layer is made on left and right side

Structure of a position sensitive photo diode(PSD)

Structure of Photo Diode

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• Diodes in the Op-Amp’s feedback give a logarithmic behavior to the I-to-V conversion circuit.

• Collector current, Ic, in each Op-amp is identical to the I1 and I2.

• Third Op-Amp processes the difference of the two output voltages from previous Op-Amps.

• Vo =VT. ln(I1/I2)

Circuit for position sensitiveCurrent-to-voltage conversion

Circuit Diagram of a PSD

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• Spot irradiation in the center of the p-layer, both currents I1, I2 will have same value.

• Spot irradiation goes to the right, the I1 will decrease and I2 will increase by the same amount.

• The difference between the I1 and I2 will give the location of a spot irradiation on PSD.

How Does A PSD Measures Distance?

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Distance vs. irRange Value

0

50

100

150

200

250

300

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Distance (inches)

irRan

ge V

alue (

int)

Distance Chart

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• When interfacing with any type of hardware, timing is an issue.

• Vin and Vout are control measurements.

• Vin drops to low for minimum 70ms.

• IR LED transmits 16 pulses towards the object.

• Mean value of 16 measurements reduces possible errors.

Timing Diagram for Measurement and

data handling

TimingTiming

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NavigationDead Reckoning

• Two typical methodologies– Odometers

• Advantages:– Good short-term accuracy

– Inexpensive

– High sampling rates

• Disadvantages– Systemic Errors

» Unequal Wheel Diameters

» Misalignment of wheels

» Finite encoder resolution

– Non-systemic Errors

» Uneven floors

» Bumps

» Wheel slippage

– Inertial Navigation• Requires gyroscopically stabilized sensor platform

• Uses 3-axis accelerometer and integrates for velocity & position

• INS on aircraft cost from about $5,000 to $200,000.20

NavigationLandmark-Based

• Natural Landmarks– Typically uses a vision system

– Matches observed features to known landmarks

• Artificial Landmarks– Vision system can more easily detect

• Known pattern

• High contrast with background

• Line Navigation– Can use many types of sensors

• Electromagnetism, reflections, optical sensing…

– Used for many years in buildings, restricts movement

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NavigationMap Based

• Map Building– Feature extraction from raw data– Fusion of data from various sensors– Auto generation of an abstract model of the environment

• Map Matching– Most challenging due to different angles of observation– Feature extraction– Determining correspondence to model features

• Advantages– Uses existing structures to derive position– Can generate an updated map for other uses– Allows robot to learn about new environment

• Disadvantages– Must have enough stationary & distinguishable features– Sensor map must be accurate– Significant amount of sensing and processing

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