Tactile Feedback Interfaces

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Tactile Feedback Interfaces

• Five main approaches for surface texture and
  geometry feedback at fingertips
• Visual
• Pneumatic
• Vibro-tactile
• Electro-tactile (risky)
• Neuromuscular stimulation (risky)
• Provide electric pulses to the skin
• Provide the signal directly to the users
  primary cortex

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Pneumatic Ring Actuator System
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Pneumatic Ring Actuator System

• The actuator consists of a small rubber balloon
  (8 mm diameter) which is pressed against the
  users fingertip by a small plastic cuff.
• A strain gauge interposed between the inflatable
  balloon and the fingertip measures the actual
  force exerted on the finger.
• The air is pressurized by a compressor and
  regulated by a custom electric-pneumatic
  converter.

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Pneumatic Touch Feedback

• Provide touch feedback by placing micro air
  pockets in a double-layered glove worn by the
  user
• Not only fingertips, but also upper hand and palm
  have air pocket
• Air pressure necessary for feedback is obtained
  with a small compressor placed in the control
  interface

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Pneumatic Touch Feedback Commander

• This is a gloveless touch feedback device with
  a hand grip that houses a 3D tracker and 3 to 5
  small air pockets
• To reduce the total cost, the compressor was
  replaced with simple solenoid-actuated pistons

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Vibrotactile Feedback

• Use of vibrotactile display (voice coils)
• The voice coil was driven at 250 Hz
• A function generator produces a sinusoidal base
  signal C
• The signal C is then transmitted to a two-channel
  amplifier

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Voice Coils Control Circuit
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Vibrotactile Feedback (Voice Coils)
This system is called The Touch Master has 6 to
10 voice coils at a fixed frequency of 210
Hz. Optional control is available for varying
the frequency and amplitude of the feedback
signal.
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Micro-Pin Actuators

• An alternative to voice coils for vibrotactile
  stimulation is the use of micro-pin actuators
  either individually or in an array configuration
• Compared to voice coils, micro-pin actuators have
  higher power requirements, have higher
  noise-to-signal ratios and may produce some pain
  to users if used inappropriately

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Multimodal Mouse

• A single micro-pin tactile actuator
• designed to improve graphic-user interface
• a regular mouse is modified by adding a
  solenoid-actuated aluminum pin that protrudes
  through a hole in one of the buttons
• a rubber film fixed on the backside of the mouse
  button returns the pin to its zero position once
  the solenoid is deenergized

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Multimodal Mouse

• By synchronizing the haptic feedback with the
  image on the screen, it is possible to give the
  user a feel of touching a graphics window or
  button.
• The multimodal mouse has the capability of
  surface texture feedback.

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SMM Micro-pin Array

• Named Programmable Tactile Simulator
• Use light shape memory metal (SMM) actuators to
  obtain the necessary reduction in weight.
• The micro-pins are arranged in a matrix array as
  shown.

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SMM Micro-pin Array

• The figure illustrate a virtual finger
  translating over the edge of a virtual object

Alternatively, it is possible to vibrate a single
or group of actuators to convey surface texture
information, similar to the example given
previously for the multimodal mouse.
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SMM Micro-pin Array

• When a current is passed through the SMM wire, it
  is heated.
• The alloy will then shrink and bend the
  cantilever beam upwards by the angle as shown.

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SMM Micro-pin Array

• Each of the SMM actuators are controlled
  independently through pulse-width modulation
  with a duty cycle of 50 (controlling the current
  on for about the same amount of time it is
  off)
• Frequency about 20 Hz (prevents overheating and
  permanent damage to the SMMs)

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Surface Slip Feedback

• Why need it?
• Surface slip feedback together with force
  feedback are required whenever the grasping of a
  virtual object must be modeled realistically.
• When no slippage feedback is presented in the
  simulation, users are required to apply large
  force to maintain stable grasp, resulting in
  fatigue and discomfort.
• When slippage feedback is present, users reduce
  the grasping force to much smaller level.

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Surface Slip Feedback

• A motor A velcro strip

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Surface Temperature Feedback

• Thermal feedback is required
• When navigating in very cold (or very warm)
  virtual world
• When grasping cold or hot virtual object
• Helps identify objects based on their thermal
  signature
• It is especially needed when direct tactile
  exploration is impossible.

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Surface Temperature Feedback
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Surface Temperature Feedback

• A dc source is connected to the semiconductors
  through copper electrodes, so that the two
  junctions are electrically in series and
  thermally in parallel.
• Ceramic plates places between the heat pump and
  the cold or hot end plates serve as thermal
  conductors and provide high mechanical strength.
• When current is applied, the P or N charges in
  the semiconductors are accelerated to the copper
  connectors, and transfer heat to the hear sink.
• The more current is applied, the more charges are
  attracted and more heat is removed from the hear
  source.

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Surface Temperature Feedback

• The heat pumps are integrated into a multimodal
  sensing and feedback glove