  Grounding of kinesthetic feedback against a user's hand can increase the
portability and wearability of a haptic device. However, the effects of
different hand-grounding locations on haptic perception of a user are unknown.
In this letter, we investigate the effects of three different hand-grounding
locations-back of the hand, proximal phalanx of the index finger, and middle
phalanx of the index finger-on haptic perception using a newly designed
wearable haptic device. The novel device can provide kinesthetic feedback to
the user's index finger in two directions: along the finger-axis and in the
finger's flexion-extension movement direction. We measure users' haptic
perception for each grounding location through a psychophysical experiment for
each of the two feedback directions. Results show that among the studied
locations, grounding at proximal phalanx has a smaller average just noticeable
difference for both feedback directions, indicating a more sensitive haptic
perception. The realism of the haptic feedback, based on user ratings, was the
highest with grounding at the middle phalanx for feedback along the finger
axis, and at the proximal phalanx for feedback in the flexion-extension
direction. Users identified the haptic feedback as most comfortable with
grounding at the back of the hand for feedback along the finger axis and at the
proximal phalanx for feedback in the flexion-extension direction. These
findings show that the choice of grounding location has a significant impact on
the user's haptic perception and qualitative experience. The results provide
insights for designing next-generation wearable hand-grounded kinesthetic
devices to achieve better haptic performance and user experience in virtual
reality and teleoperated robotic applications.
