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Haptics and Virtual Reality

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This lecture delves into the critical components of haptic systems, focusing on sensors and actuators vital for immersive virtual reality experiences. It covers various sensor types, such as magnetic, optical, and inertial sensors, alongside examples of these technologies. The session highlights the importance of optical encoders and Hall-effect sensors, their working principles, and how they impact haptic feedback. Additionally, different actuator types, including DC motors and pneumatic actuators, are discussed, emphasizing their roles in creating realistic sensations in VR applications.

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Haptics and Virtual Reality

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  1. Haptics and Virtual Reality Lecture 3: • Sensors & Actuators-1 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 • Outside-Looking-In • Inside-Looking-Out

  22. Optical Tracker

  23. Data gloves

  24. Data gloves

  25. ActuatorTypes Electricmotors  • DC(direct current) • Brushed & Brushless • PM(permanent magnet) • Stepper Motors Pneumatic Actuators  Hydraulic Actuators 

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

  27. DCmotorcomponents

  28. DCmotorcomponents

  29. MotorEquations Torqueconstant,K Dynamicequation  

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

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

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

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

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

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

  36. 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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