Portable Force Feedback

1
Portable Force Feedback

• Advantage of non-portable haptic interface
• Off-load the actuator weight from users
• Disadvantage of non-portable haptic interface
• Reduction in the users freedom of motion
• Portable Haptic Interface
• An interface where actuating or sensing
  structures are grounded on the users body.
• More difficult to design because there are
  limitations in overall weight and volume.

2
Classification of Portable Force-Feedback
Interface

• According to their mechanical grounding
• Arm exoskeletons (also called External Force
  Feedback (EFF)) usually grounded to a back
  plate
• Hand masters (also called Hand Force Feedback
  (HFF)) usually grounded to the users wrist or
  to the palm
• The discussion in the section starts with Arm
  exoskeleton, followed by hand masters.

3
Arm Exoskeletons

• Portable arm skeletons are structures that
  measure the users arm motion and apply forces as
  required by the simulation.
• The human arm has 7 DOF

4
GLAD-IN-ART Arm Exoskeleton
5
GLAD-IN-ART Arm Exoskeleton

• DC servo motors that provide torques to five
  joints through a tendon-based transmission
  system.
• The user controls the exoskeleton through a
  handle attached to the end of the last rigid
  link.
• Each joint has position sensors and torque
  sensors that measure the differences between
  current position and desired position.
• The total structure weight is approximately
  10kg!!!

6
The Univ of Salford Arm Master

• This is a lightweight arm master.
• Why light?
• Due to the use of very light pneumatic muscle
  actuators 15cm long and weigh only 15 grams
  with their contractile force can exceed 150 N.
• The design uses actuators acting in opposition
  for each skeleton joint.

7
The Univ of Salford Arm Master

• Constructed of a combination of steel and
  aluminum with only 2kg weight
• Its geometry allows the user to reach over 90 of
  his normal work volume.

8
Hand Masters

• Portable hand masters differ from the
  non-portable ones (e.g., Tokyo Sensing Glove) -
  the masters are grounded on the users forearm or
  palm.
• The entire weight is sustained by the user and
  may easily lead to user fatigue if the interface
  is heavy.
• Therefore, most of todays designs place
  actuators remote from the hand (either on the
  forearm, or on the users back)
• The more DOF are active (up to 20 for the hand
  alone), the more actuators needed, and more
  surface is required for them.

9
Univ. of Tsukuba Hand Master

• A String-based Haptic Interface
• To keep the structure light, the device provides
  feedback to only two fingers (thumb and index)

10
Univ. of Tsukuba Hand Master

• The haptic interface uses a string and pulley
  transmission to actuators placed on the dorsal
  side of the hand
• This design permit maximum freedom of motion for
  the fingers and allows the grasping of real
  object while the user is wearing the interface,
  because the palm area is free.
• A rotary encoder measures string displacement
• The fingertip position is obtained
  based on the string length S (Here a calibration
  is needed)

11
LRP Hand Master

• Another string-based hand master
• This haptic interface provides feedback to all
  fingers as 14 hand locations
• All motors, power supply, and VME bus interface
  are placed in a separate control box that
  communicates with the host computer running the
  graphics simulation over an Ethernet

12
The ARTS Hand Master
Developed by the GLAD-IN-ART European consortium
13
The ARTS Hand Master

• The hand master consists of a metacarpal plate
  and a glove-attached exoskeleton
• The metacarpal plate has 2 DOF providing force
  feedback at users wrist
• The hand exoskeleton attaches to the back of the
  users hand wearing a glove
• The palm area is left free
• Position-sensing resolution for all degrees of
  freedom is very good (0.1 degree)

14
The EXOS SAFIRE Master

• Similar to ARTS hand master
• Use dc motors and cables to apply forces on the
  thumb, index, and middle fingers
• Each actuator has its own position encoder and
  torque sensor for improved force-feedback control.

15
The Virtex CyberForce Glove

• Use a double-layered glove with Kevlar tendon on
  the back of the hand
• The master is significantly lighter by
  eliminating the metallic exoskeleton.
• This is a combination of force and touch feedback

16
Rutgers Master I
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The Rutgers Master I

• This is a direct-drive design
• The cable transmission is eliminated by placing
  the actuators directly in the users palm
• The structure consists of four metallic
  micro-cylinders place on a small L-shaped
  platform
• The base of the piston is with small spherical
  joints that allow the passage of small air tubes
• Thus, each actuator has a conical work envelope
• Like any other portable hand masters that has no
  wrist feedback, cannot simulate the virtual
  objects weight, or large collision forces with
  the environment

18
The Rutgers Master II

• In Rutgers Master I, the master reliance on a
  commercial sensing glove for position sensing
• In Rutgers Master II, all sensing had been
  integrated in the force-feedback structure

19
The IBM V-Flexor

• Do not have any actuators
• Users feel passive force feedback by squeezing
  a sensorized handle in hand
• The handle has five air chambers and
  corresponding pressure sensors that measure the
  grasping force.
• Also include a triple thumb and a
  three-dimensional tracker
• The advantage is its simple and robust
  construction, which eliminates the need for
  complex calibration

20
Conclusion

• The vase majority of the interfaces described
  here place actuators remotely from the desired
  force application points
• This is because of the poor power-to-weight and
  power-to-volume ratios of todays actuator
  technology.
• The tactile feedback allows the simulation of
  contact geometry, surface texture, temperature,
  slippage, and so on, which supplements
  force-feedback information.