Utility of contact detection reflexes in prosthetic hand control

Tactile sensations make grasping fragile objects a simple and unchallenging task for the human hand. Prosthetic hands lack these sensory capabilities and their users frequently struggle with such tasks. To address this problem, the benefits of compliant fingertips with contact-detection reflexes were assessed in one prosthesis user when grasping fragile objects (eggshells, foam packing peanuts, crackers, and soft clay). A commercially available myoelectric prosthetic hand was modified to include the compliant BioTac® tactile sensors (SynTouch, LLC), which have previously been demonstrated to be more sensitive to contact than the human fingertip. Upon sensing contact during hand closure on an object, the gain of the operator's EMG command signals to the prosthesis' motor was reduced to prevent excessive closing forces, a behavior similar to an inhibitory reflex. This allowed the prosthetic hand to quickly react to the presence of the object and permitted the operator to handle fragile objects with ease and without the usual dependency on visual feedback. The time required to grasp and move a set of fragile objects with this modified prosthesis was compared to the subject's usual prosthetic hand. The contact detection method demonstrated both utility and reliability through faster completion times and reduced variance in the times to complete these trials.