Soft transfemoral prosthetic socket with EMG sensing and augmenting feedback: a case study

In lower limb prostheses, the physical interface constituted by the socket is a crucial component for the device success. This work proposes a new design based on a rigid frame integrated into a silicone structure which allows for a more comfortable biomechanical coupling with the residual limb and facilitates the integration of smart technologies. In particular, four surface EMG sensors and three vibrotactile units have been integrated to enable a bidirectional interface able to decode the user’s motor intention and provide augmenting feedback, respectively. The new socket was tested on a transfemoral amputee. The sEMG signals were registered during five different locomotion tasks in a circuit training and the classification median accuracy of an intention decoding algorithm was found always higher than 73%. The user’s perception of vibrotactile feedback was assessed through a psychophysical experiment of localization of single, couple or triple of stimuli. It revealed that vibrations from singularly activated units were the best perceived. Questionnaire results confirmed a high satisfaction level. However, tests on temperature and humidity within the socket suggest that more efforts are still required in terms of skin perspiration. The proposed socket paves the way to smart physical interfaces for robotic prostheses.