Sensory Feedback for Smart Prosthetics

Though mechanical aspects of upper-limb prosthesis technology is rapidly advancing, these devices lack a sense of touch required for dexterous manipulation and exploring environments. We aim to address this concern by developing non-invasive technology to provide missing touch sensations in prosthetic limbs via sensory substitution with modular add-on devices separate from the prosthesis.
 

The Rice Haptic Rocker (Rocker) is a single degree of freedom skin-stretch device used to convey the hand aperture of a prosthetic hand, or how open or closed it is. Experiments in collaboration with the University of Pisa and the Italian Institute of Technology were done to test the efficacy of the (Rocker) to convey the aperture of the Pisa/IIT SoftHand, an under-actuated compliant robotic hand, in three cases:

1) A visually occluded and grasp-controlled experiment as an initial proof of concept

2) A second controlled experiment with an unrelated task as a distraction between the onset of the cue and the participant’s decision to assess steady-state perception

3) A partially occluded task with free grasping, to assess size discrimination with uncontrolled grasping positions

The results of the above experiments showed promise in the application of haptic devices for prosthetic applications. However, the results also showed improvement could be made in the perceptual resolution of the Rocker. Three experiments were done to assess the impact of design decisions on the perceptual resolution of skin stretch:

1) The impact of varying the arc length for each degree of motion, by varying the radius of curvature as a function of angular displacements, compared to implementing a s-curve mapping to create a similar effect

2) Comparing stretch across the arm in the lateral direction to stretch along the arm in the longitudinal direction

3) Comparing the perceptual resolution of given angular displacement when approached at varying angular velocities