Evaluación Mecánica y Funcional de una Prótesis de Mano Basada en Soft-Robotics

Abstract

In Colombia, around 1'486,213 people have some type of disability, 19% of them have difficulty carrying, moving, and/or using objects with their hands. Within this group are hand amputations, where the main causes are traumatisms, congenital and vascular causes. Prostheses arise from the need to replace the function of the missing limb and their main development has been with rigid materials. However, factors such as weight, cost, physical appearance, among others, make users not completely satisfied with the device. Prostheses based on soft-robotics are those that for their structure use materials with elasticity modules similar to the human body or those that have elastic joints and their actuation mechanism is by cables. This project aims to mechanically and functionally evaluate a hand prosthesis based on soft-robotics. The prosthesis was developed under the framework of the PrExHand project, and its main objective is that in addition to being functional, it is low cost. The PrExHand prosthesis is an electro-pneumatic device. The flexion and extension of the fingers are done with tendons that go to a motor and the abduction and adduction of the fingers are done with air-controlled silicone actuators. Two designs have been proposed within the project, which will be evaluated within the framework of this degree work. Design A (PrExHand A) links the tendons that actuate the fingers to the motor using an inelastic element and some parts of the fingers are covered with silicone. Design B (PrExHand B) links the tendons to the motor using a sliding mechanism located in the palm of the prosthetic hand, and the fingers are completely covered with silicone. The objective of this thesis is to determine the pros and cons of the designs and propose the final version that will be evaluated with patients. For this purpose, mechanical and functional tests are used to characterize the prostheses. The literature review provided information on the mechanical and functional tests generally used in prostheses. From the state of the art, 3 mechanical tests were defined: grip force, energy, and tensile force. The Anthropomorphic Hand Assessment Protocol (AHAP) was also found, to be applied to the two designs proposed for the PrExHand prosthesis. The results of the mechanical tests showed that design A has a maximum grip force of 22.07 ± 2.03 N, requires the energy of 0.76 ± 2.03 J to close, dissipates the energy of 0.21 ± 0.17 J, and withstands a tensile force of 173.31 ± 5.66 N. On the other hand, design B has a maximum grip force of 33.68 ± 1.34 N, to close requires the energy of 1.28 ± 0.13 J, dissipates the energy of 0.96 ± 0.12 J, and withstands a tensile force of 78.48 ± 0 N. In functional testing, in addition to testing the two designs of the PrExHand prosthesis, the robotic prosthesis from Prótesis Avanzadas was tested. This test showed as a result that the commercial prosthesis had a higher score what it means that its functionality is similar to the hand in 79.31%, followed by PrExHand A with 73.33% and PrExHand B with 69.17%. In conclusion, mechanically PrExHand A had results closer to the expected in energy and in the tensile force that supports. The difference between the results related to energy and traction force is related to two characteristics of PrExHand B. On the one hand, the fingers have a full silicone coating and on the other hand, the sliding mechanism caused the motor to have to generate more force on the tendons to close the prosthesis. The grip force of PrExHand B performed better than design A. This was a consequence of the fact that the silicones allowed the motor to generate more force on the tendons to close the prosthesis. This was a consequence of the silicones allowing the prosthesis to grip the dynamometer better and have higher results. Finally, although functionally the commercial prosthesis performed better overall than the two PrExHand prosthesis designs, in some types of grips it was seen that the latter had higher scores. This opens the possibility of applying some of the concepts used in the grips where the scores for the PrExHand prostheses were higher than the commercial prosthesis of Advanced Prosthetics.