Evaluation of A Haptic Interface

Three criteria for effective interface: (J.K. Salisbury)
 a. free space must feel free
 b. solid object must feel sniff
 c. virtual constraint must not be easily saturated

These descriptions above can be illustrated by five indicators which are mainly considered for designing a general haptic device:
  1. DOF (degree of freedom)
  2. workspace
     a comfortable  angular workspace was estimated to be of the order of 90 degrees of pitch, and yaw combined with a roll of 120 degrees.
  3. resolution
     average position just-noticable-difference (JND) for wrist and elbow are both 2 degrees.
  4. maximum output force
  5. back-drivability
      transparency: how realistic the feeling of touch is when user is touching the virtual object via haptic device. 
      => improving the transparency of haptic interaction is a goal. 
      a haptic device has to transmit force sensation as realistic as possible to user through well-controlled actuators. when detecting in free space, there will be a strength power which can be felt in contacting with stiff surface, ex. mass, inertia, and friction of the move part, which affect the back-drivability of haptic device and the inertia is the leading factor in this device.      

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