Switching proportional EMG control of a 3D endpoint arm support for people with duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a disease resulting in progressive muscle degeneration. Active arm supports can improve the quality of life for people with DMD by augmenting the residual motor capabilities of their arm. As an extension of our previous study, this research aims at developing a EMG-based control interface to detect the user´s movement intention required to control more than 1-DOF. The interface switches between two horizontal and one vertical translations. Translations are proportionally controlled by EMG. The passive interaction torques measured between the arm and the active arm support, are used to make the robot´s endpoint resemble a gimbal mechanism. Hence decreasing the endpoint´s DOF from six to three by actively reducing the impedance of the rotational DOF. A preliminary evaluation of the control method has been carried out with one healthy subject, within a series of 2-D horizontal tracing and 3-D horizontal-vertical reaching tasks. A pilot study was also conducted with a boy with DMD controlling the device in a 2-D horizontal tracing task. Performance was evaluated in terms of path efficiency, smoothness, task completion rate and time. The results indicate that the control method is able to successfully detect the intention of the user and translate it into the intended movement. Furthermore, the reduction of the endpoint´s DOF, results in a simple yet functional controller able to support natural movements of the arm.