A stretchable, conductive rubber sensor to detect muscle contraction for prosthetic hand control

Recently, many type of prosthetic hands have been proposed. Nonetheless, any active prosthesis needs patient's physiological signals to be controlled. Electromyography is one of the most used signals to control prostheses. However, EMG needs electrodes in contact with patient's skin. This study aims to test an alternative, easy to wear sensor able to detect muscle contraction and to control hand prosthesis as well. The new sensor consists of a conductive rubber cord that changes its electrical resistance when stretched. The rubber cord was enclosed in a soft fabric cuff that can be easily worn by the patient. No electrical contact between the cord and the patient is needed. Simultaneous recordings of EMG and the correspondent rubber cord resistance were carried out in order to test the relationship between the two signals and to assess the effectiveness of proportional control of the prosthesis motor. A simple 3D printed, under-actuated prosthetic hand was connected to the new sensor. Results show that the new sensor offers a control signal very similar to the EMG envelope and it is able to provide both on-off and proportional control of the prosthesis.