Mechanical assessment of novel compliant mechanisms for underactuated prosthetic hands

This paper proposes novel compliant mechanisms for constructing hand prostheses based on soft robotics. Two models of prosthetic hands are developed in this work. Three mechanical evaluations are performed to determine the suitability of the two designs for carrying out activities of daily living (ADLs). The first test measures the grip force that the prosthesis can generate on objects. The second determines the energy required and dissipated from the prosthesis to operate. The third test identifies the maximum traction force that the prosthesis can support. The tests showed that the PrHand1 prosthesis has a maximum grip force of 23.38 +/- 1.5 N, the required energy is 0.76 +/- 0.13 J, and the dissipated energy is 0.21 +/- 0.17 J. It supports a traction force of 173.31 +/- 5.7 N. The PrHand2 prosthesis has a maximum grip force of 36.13 +/- 2.3 N, the required energy is 1.28 +/- 0.13 J, the dissipated energy is 0.96 +/- 0.12 J, and it supports a traction force of 78.48 +/- 0 N. In conclusion, the PrHand1 prosthesis has a better performance in terms of energy and tensile force supported. The difference between the energy and traction force results is related to two design features of the PrHand2: fully silicone-coated fingers and a unifying mechanism that requires more force on the tendons to close the prosthesis. The grip force of the PrHand2 prosthesis was more robust than the PrHand1 due to its silicone coating, which allowed for an improved grip.