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Haptics and Virtual Reality

Haptics and Virtual Reality. Lecture 3: Sensors & Actuators. M. Zareinejad. Outline. # Sensors. Sensor types Sensor examples. – –. #Actuators. Actuator types Actuator examples. – –. The Haptic System. Human. Passive & Active joint. Sensor Applications. Eye tracking

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Haptics and Virtual Reality

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  1. Haptics and Virtual Reality Lecture 3: • Sensors & Actuators M. Zareinejad

  2. Outline # Sensors Sensortypes Sensorexamples – – #Actuators Actuatortypes Actuatorexamples – –

  3. TheHapticSystem Human

  4. Passive & Active joint

  5. SensorApplications Eyetracking Headtracking Bodytracking Handtracking     Mostimportantfortypicalhapticinterfaces –

  6. Sensortypes Magnetic Optical Acoustic Inertial Mechanical      Mostimportantfortypicalhapticinterfaces –

  7. MechanicalTrackers Ground-basedlinkagesmostcommonlyused PositionSensors   digital:opticalencoders analog:Hall-effect(magnetic) – –

  8. OpticalEncoders Emitter Howdotheywork? Detector  Afocusedbeamoflightaimedatamatched photodetectorisinterruptedperiodicallybyacoded patternonadisk Producesanumberofpulsesperrevolution(Lotsof pulses=highcost) – – Quantizationproblemsatlowspeeds Absolutevs.Incremental  

  9. OpticalEncoders Absolutevs. Incremental  Resolution?

  10. OpticalEncoders Phase-quadratureencoder 2channels,90°outofphase   allowssensingofdirectionofrotation –

  11. Encoder States & Decoding

  12. Hall-EffectSensors Howdotheywork?  – Asmalltransversevoltageisgeneratedacrossa current-carryingconductorinthepresenceofa magneticfield (Discoverymadein 1879,butnotuseful untiltheadventof semiconductor technology.)

  13. Hall-Effect Sensors Vh=Hallvoltage Rh=Hall coefficient RhIB t I=Current B=Magnetic fluxdensity t=Elementthickness Vh= Amountofvoltageoutputrelatedtothe strengthofmagneticfieldpassingthrough. Linearoversmallrangeofmotion   Needtobecalibrated – Affectedbytemperature,othermagnetic objectsintheenvironments 

  14. Hall-Effect Sensors Vh=Hallvoltage Rh=Hall coefficient I=Current B=Magnetic fluxdensity t=Elementthickness RhIB t Vh= • The voltage varies sinusoidally with rotation angle Resolution?

  15. Potentiometers

  16. Potentiometers Resolution?

  17. Acoustic Tracker Speaker Microphone

  18. Acoustic Tracker

  19. Magnetic Tracker

  20. Magnetic Tracker

  21. Optical Tracker • Inside-Looking-Out • Outside-Looking-In

  22. Optical Tracker

  23. Data gloves

  24. Data gloves

  25. MeasuringVelocity Differentiateposition  advantage:usesamesensoraspositionsensor disadvantage:getnoisesignal – – Alternative  forencoders,measuretimebetweenticks –

  26. Digitaldifferentiation P1-P2 t Manydifferentmethods SimpleExample:   V= Average20readings=P1 Averagenext20readings=P2 wheretisthetheperiodoftheservoloop – – – Differentiation Increases noise 

  27. Time-between-ticks Time per ticks rather than ticks per time  useaspecialchipthatmeasurestime betweenticks  Especially good to do at slow speeds – Farespoorlyathighvelocities – p t v=

  28. ActuatorTypes Electricmotors  • DC(direct current) • Brushed • PM(permanent magnet) Pneumatic Actuators 

  29. PMDCbrushedmotors Howdothey work?  Rotatingarmature withcoilwindings iscausedtorotate relativetoa permanentmagnet currentistransmittedthroughbrushesto armature,andisconstantlyswitchedsothatthe armaturemagneticfieldremainsfixed. – –

  30. DCmotorcomponents

  31. DCmotorcomponents

  32. DCmotorterms Cogging  Tendencyfortorqueoutputtorippleasthebrushes transferpower – Friction/damping  Causedbybearingsandeddycurrents – Stalltorque  Maxtorquedeliveredbymotorwhenoperated continuouslywithoutcooling –

  33. MotorEquations Torqueconstant,KT T=KT I Dynamicequation   dI dt V=L +RI+E

  34. PneumaticActuators Howdotheywork?  Compressedairpressureisusedtotransferenergy fromthepowersourcetohapticinterface. – Manydifferenttypes Concernsarefrictionandbandwidth  

  35. SomeTerms AD/DA  analogtodigital digitaltoanalog – – Interruptroutine ServoLoop Servorate    Usuallyneedstobe>500Hz –

  36. D/AandA/D Convertsbetween voltagesandcounts Computerstores informationdigitally, andcommunicates withtheoutside worldusing+/-5V signals 101010101    LSB MSB

  37. D/AandA/D Convertsvoltagestocountsandviceversa A12-bitcard:   212decimalnumbers(4096) – 2994 Decimal(base10): Binary(base2): 1 0 1 1 1 0 1 1 0 0 1 0 Hexadecimal(base16): 1 0 1 1 1 0 1 1 0 0 1 0 B B 2 = BB2

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