VR Gadgets part 1

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VR - Gadgets(part 1)

• Jyun-Ming Chen
• Fall 1999

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Contents

• Part 1
• 3D position sensors
• Trackballs
• 3D probes
• Sensing gloves

• Part 2
• Stereo viewing
• 3D sound
• Force feedback
• Other sensors

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VR System

• reality engine
• generate desired output from the cues of input
  sensors
• for example
• input pos/orient of head
• output scene to HMD

4
Position Sensors

• 6DOF (x,y,z, r,p,y)
• contact vs. non-contact
• potentiometer
• magnetic, ultrasound, radar
• absolute vs. relative

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Sensor Parameters

• update rate
• measurement per sec.
• latency
• time delay between action result
• accuracy
• difference between actual measured
• resolution
• minimal detectable change

• modes of operation
• streaming sensor send data continuously
• one-shot data sent when requested
• working envelope
• data property
• noise, interference, limitations, ...

6
Magnetic Sensors

• 3 stationary orthogonal antenna, producing a low
  freq. field
• receiver another set of ortho. antennas
• signals of receiver to determine pos/orient
• hook up receiver to moving objects

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Magnetic Sensors (cont)

• Sensor noise
• conditioning circuitry
• increase near the limit of envelope
• accuracy degrades near metallic objects
• calibration method

• Multiple receiver/transmitter
• large envelope
• moving objectS
• data transmission speed up
• Demo Bird

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Ascension The Bird
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Ascension Film
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Ultrasound Sensors

• from 9 distance between speaker-microphone,
  compute the pos/orient
• c (167.6 0.6T)m/s
• each speaker activates in cycles

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Ultrasound (cont)

• pros
• cheaper
• not subject to metallic interference
• cons
• line-of-sight constraint
• lower update rate (than magnetic ones)
• background noise (bounced off surfaces)
• multiple spkr/mic possible

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Logitech Product
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Trackballs

• relative sensor
• drawbacks
• sensor coupling (may be resolved by s/w)
• openloop modes
• small work envelope
• suitable for CAD systems !?
• Demo Spaceball

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Trackballs
Spaceball 2003
Logitech Magellan
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3D Probe

• 6 joint angles to specify 6 DOF
• direct kinematic calculation based on angle and
  link length
• mode navigate or move objects
• not affected by magnetic field
• high update rate

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Data Glove

• most intuitive way to interface with virtual
  world
• gesture human hands has a much richer vocabulary
  (than the 6 DOF)

• original goal
• Zimmerman, interested in computer music, wondered
  whether theres a way to make music by playing
  air guitar
• 1987 optical fiber Lycra glove Polhemus
  Isotrack

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Hand DOF

• most gloves handle angle flexion only

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Joint-Angle Measurement

• technology determines the price and accuracy
• optical fiber
• strain gauge
• conductive ink sensor
• mechanical devices

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Glove Calibration

• apply least square on the following model
• q a br c ln(r)
• homework
• before operation, each user need to calibrate
• impossible to predict a priori how the glove
  suits a particular user

• other issues
• adduction/abduction sensor
• extrapolating distal joint
• q3 a - bq2 cq22
• ergonomics (cyberglove)
• palm finger removed for better ventilation,
  typing, writing

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Commercial Gloves
General Reality
CyberGlove
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Commercial Gloves
Pinch Glove (Fakespace)
PowerGlove (Nintendo, 1989) homework
DataGlove (JPL)
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Glove Films
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Review Questions

• ex Bird on 9600 line given data format,
  compute update rate
• principles of magnetic sensors pos/orient
• Bird calibration importance and how
• principles of ultrasound sensors power gloves
• simple questions on kinematic computation (on
  probes)
• on glove calibration model computation and
  whats the motivation of ln(r )? Why make a fist
  to calibrate?