Gel-filled fingertips could give prosthetic hands greater sensitivity, even allowing them to react 鈥渋nstinctively鈥� to objects slipping from their grasp.
Human hands automatically estimate the minimum force needed to hold on to an object, using a built-in reflex that responds to tiny vibrations in the skin as an object starts to slip through our fingers.
Existing artificial hands do not have this reflex mechanism, so their operators have to consciously estimate the required force. 鈥淚t鈥檚 very mentally taxing,鈥� says Jeremy Fishel, one of a team that built the new fingertip at the University of Southern California, Los Angeles. The tip consists of a rubber skin, filled with thick silicon gel. When an object begins to slip, the vibrations in the finger鈥檚 elastic skin transmit through the silicon gel to acoustic sensors attached to a central acrylic 鈥渂one鈥�. This provides instant feedback, telling the motors in the hand to tighten their grip until the vibrations stop.
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The finger鈥檚 bone is also covered with tiny electrodes, across which a small voltage is applied. Deformations in the elastic skin caused by holding an object alter the distribution of gel in the fingertip, changing the amount of electricity that is conducted between the electrodes. This information could be transmitted to a pressure device worn on a patch of the hand-operator鈥檚 healthy skin, helping them to 鈥渇eel鈥� what their prosthetic hand is touching. The team will present a prototype of the finger at the BioRob conference in Scottsdale, Arizona, next month.
