Study on the activation speed and the energy consumption of “federica” prosthetic hand

Important features of a hand prosthesis are certainly the comfort in wearing it, the ease of use, the activation speed, the low energy consumption and no less important the anthropomorphic aspect. This study focused on the activation speed and the energy consumption of an under-actuated, low-cost, active hand prosthesis named “Federica”. The prosthesis is moved by a single servomotor able to rotate 180 degrees. Video acquisitions of complete rotations of the servomotor, when it works freely or fixed to the mechanical components of the prosthesis, were used to compare the different kinematic behaviors of the servomotor. A current sensor was used to measure the absorbed current, i.e. the energy absorption, by the servomotor under different uses of the prosthesis (at rest, grasping objects, raising water bottles, etc.). The comparison between the kinematic behaviors of the servomotor alone or connected to the prosthesis, showed the mechanical efficiency of the prosthesis with very low latencies and small variations in velocity and acceleration profiles. The prosthesis took about half a second from the muscle sensor trigger to the complete closure of the hand, showing a significant speed. Finally, tests on current absorption of the servomotor in various conditions resembling prosthesis daily usage, revealed the capacity to guarantee an autonomy of at least one day when powered by 7.4 V, 3000 mAh battery pack.