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Navigation problemDefine internal navigation sensors for a ground robot with car type kinematics (4 wheels + ackerman steering + rear wheel drive)Sensors?Where?Why?~ 15-20 min.Describe your system shortly.

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Navigation (internal) Sensors

To sense robot’s own stateMagnetic compass (absolute heading)Gyro (angular speed => change of heading)Acceleration sensors (acceleration)tako, encoder (speed, distance)syncro, resolver (speed, position)

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Magnetic CompassesBased on the detection of earth’s magnetic field~60μTAbsolute heading, coarse accuracyAvailable magnetic compasses:

Mechanical magnetic compassesFluxgate compassesMagnetoinductive compassesHall-effect compassesMagnetoresistive compassesMagnetoelastic compasses

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Magnetic Compasses

Magnetic field ~ 60μT About from south to northDeclination = the angle between true and magnetic northDeviation = the angle between the indicated and actual bearing to magnetic northInclination = the vertical component of the magnetic field (magnetic dip)Variation = local errors

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Mechanical Magnetic Compasses

Marine navigation device (the first writtenreference: China 2634BCE, commonly in use 1300)

Fluid damping and gimbal mounting is adequate for marine applicationsproblems in rough terrain

‘Starguide’ miniatyre compasspermanent-magnet rotorlow-friction jeweled bearinginternal damping8 led display or analog output

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Fluxgate-CompassFluxgate = trade name of the first commercial saturable-core magnetometerHigh permeability core non-saturated (A) and saturated (B) controls the magnetic flux Saturation is controlled with sinusoidal or quadratic wave in the drive-coilThe expanding and collapsing magnetic flux induces to the sense coil an emf. relative to the existing magnetic field

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Fluxgate-CompassIn rod type structure the field of caused by the drive coilaffects to the sense coil

undesired phenomenaa rod is replaced with two rods where drive coils are wound oppositely ⇒opposite magnetic fluxescompensate each other

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Fluxgate-CompassTo measure the direction of the (earth’s)magnetic field two perpendicular sense coils are neededToroidal structure is suitable because

magnetic fluxes (by drive coils) compensate each otherdemagnetization effects are smaller than in the rod-type structure

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Fluxgate-CompassAn other popular design is three-legged spider configuration

Three horizontal sense coils (120° apart each others)Common vertical drive coil

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ZEMCO Fluxgate-Compass

Two perpendicular sense coils on a toroidal drive coilUsed in ROBART IIElectrical cabling of the robot and metal object near by caused errorsRelatively high power consumption (250 mA, 12V)

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ZEMCO Fluxgate-CompassAnalog compass was later replaced with digital one by same manufacturerSmaller power consumption (94 mA)Typical accuracy ± 6º

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WATSON Fluxgate – Gyro –Compass

Fluxgate-Compass and gyro data is fused with microprocessor ⇒

More stableless sensitive to enviromental noise

Toroidal ring-core fluxgate sensor internally gimbal mountedPiezoelectric tuning-fork gyro (next chapter)Analog output and serial 12-bit digital outputAccuracy ± 2º (with ModBot on flat storage floor)

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WATSON Fluxgate – Gyro –Compass

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KVH Fluxgate-CompassesDifferent type of fluxgate-compasses from inexpensive tosophisticated systems intended for military applicationsExample: C100 Compass Engine developers kit• Micro processor controlled toroidal ring-core fluxgate

sensor• Different type of internal mountings for different tilt

angles• Resolution ± 0,1º, accuracy ± 0,5º, repeatability ± 0,2º• System damping is user selectable• Automatic compensation algorithm (SW) to correct the

magnetic anomalities associated with the host vehicle• Analog/digital output

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Miniatyre Orientation sensor

Applied Physics SystemsThree axis (pitch, roll, yaw) orientation sensorThe combination of three axis acceleration sensor and non-gimballed three axis fluxgate-sensorInterface: RS-232 portOutput: either angles (pitch, roll, yaw) or individual acceleration values and magnetic field valuesAccuracy ± 0,5º

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Magnetoinductive Compass

One sense coil for each axixSense coil serves as an inductive element in low-power LR-oscillatorThe relative permeability of the coil core material varies as a function of the magnetizing force=> output signal is relative to the existing magnetic field = orientation in the earth’s fieldpower consumption is smaller than with fluxgate-sensors

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Magnetoinductive TCM-CompassThree axis magneto-inductive sensor for the X-, Y- ja Z- components of the magnetic fieldTwo axis inclinometer fortilt and roll measurementMicroprocessor corrects theerror from inclinationsAutomatic distortion detection algorithm raise warning when disturbances (metallic objects, cables)are detected

Accuracy ± 1º5...25 VDC, 6...12 mAFor mobile robots like(ROBART III, MDARS)

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Hall-effect Compasses

A voltage is generated in Hall-sensor by the presence of external magnetic field (Chapter 3)Experimental compasses have been builtProblems with sensitivityBoth chips and compasses available

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Magnetoresistive CompassThe resistivity of magnetoresistive material changes as the function of the external magnetic fieldMagnetoresistive AMR (anisotropic magnetoresistive) ja GMR (giant magnetoresistive) - sensors are discussed in chapter 3Magnetoresistive compasses are perfect for mobile robots:

Excellent sensitivitySmall power consumptionSmall sizeDecreasing price=> future technology!

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Magnetoresistive CompassEverett represents three magnetoresistive options:

Philips AMR-compassRestricted sensitivity

Space Electronics AMR-kompassiMicro-Mag-sensor with Wheatstone-bridge

Honeywell digital intelligent HMR-magnetometerThree perpendicular sensorsAccuracy ± 1% from full scaleDevelopment Kit available

Honeywell has a wide variety of magnetoresistive sensors:http://www.ssec.honeywell.com/magnetic/products.html

And Philips:http://www.nxp.com/pip/KMZ51.html#description

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Magnetoelastic Compass

Based on magnetoelastic (= magnetostrictive) material as sensor elementMagnetostriction = all ferromagnetic materialsshrink or expand in the direction of magnetizationVery accurate displacement sensor needed

Interferometric measurementTunneling-tip sensing (tunneling microscopy)

Prototypes manufactured

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Magnetoinductive TCM2 –Compass (demonstrated)

Basic structure like in TCM1Better sensitivityMore advanced compensation algorithmAccuracy +/- 0,2 degResolution +/- 0,1degRepeatibility +/- 0,1 deghttp://www.pnicorp.com/