haptic interfaces for virtual reality and teleoperation

Haptic Interfaces for Virtual Reality and

Teleoperation

Haptics

‘The sensibility of the world adjacent to the body by use of

the body’

(Gibson, 1966)

Terminology

Proprioceptive Relating to sensory information about the state of the body (including cutaneous,kinesthetic and vestibular sensations).

Vestibular Pertaining to the perception of head position, acceleration and deceleration.Kinesthetic The feeling of motion. Relating to sensations originating in muscles, tendons and

joints.Cutaneous Pertaining to the skin itself as a sense organ. Includes sensations of pressure,

temperature and pain.Force Feedback The mechanical production of information sensed by the human kinesthetic

system.

Kinesthetic Feedback

• Golgi tendon organs (force)

• Muscle Spindles (position and velocity)

• Experimental data ambiguous

• Bandwidth estimates 20-30 Hz. (Brooks, 1990)

The Cutaneous Sense

Receptor Type Field

Diameter(mm)

Frequency at which

most easily

excited(Hz)

Amplitude

Threshold (m)

Probable Sensed

Correlate

RAI 3-4 8-64 30 Tickle, Vibration,

Tap

SAI 3-4 2-32 15 Pressure

RAII >20 >64 1 Vibration, Tickle

SAII >10 <8 60 Stretch, Tension

Haptic Interfaces

• Constrained Motion Devices

• Tactile Displays

Constrained Motion Devices

• Force Feedback

• DOF constrained to portray contract.

•‘Virtual free space’

• ‘Virtual constraint’

Device Limitations

• Sampling Period

• Device Dynamics

• Power Limitations

Ideal Equivalent Performance

|Z|, dBVirtual Constraint

Virtual Free Space

Max Impedance for Free Space

Min. Impedance For Hard Contact

FORBIDDEN REGION

Freq.

Low Inherent Impedance

• Nominally displays Virtual free space.

• Position feedback increases impedance.

• High gain servos constrain motion.

• Limitations:

• Stability & power

The PHANToM

High Inherent Impedance

• Nominally displays Virtual Constraint.

• Impedance reduced by force feedback.

• Framework conveys stiffness.

• Limitations:

• Dynamics & Stability

The HapticMASTER

TextureShape

High FrequencyLow Frequency

Region of Ambiguity

Bandwidth & The Haptic Spectrum

Temporal & Spatial Relationships

t = s v

• t = Temporal frequency (Hz.)• s = Spatial Frequency (Cycles/m.)• v = Exploration velocity (m/s).

Vibrotactile Display

Bonded Neodymium Magnets, Radially Polarised Magnetic Field

LVDT

Spring

Retaining Plate

200 Turns of 0.6mm Diameter Copper Wire

37mm

20mm

110mm

15mm

Multi Modal Interaction

• HCI Occurs Using:

• Haptic

• Visual

• Auditory

• Smell ?!?

• Overcome limitations using other modes.