Design and control of the A-Arm: An active planar arm support for adults with Duchenne muscular dystrophy

Adults with Duchenne muscular dystrophy (DMD), due to their severe muscular weakness, cannot benefit from passive arm supports that only compensate for the weight of their arms. Active arm supports can potentially enable adults with DMD to perform activities of daily living, improving their independence, and increasing their participation in social activities. In this paper we present the A-Arm, an inconspicuous and simple planar active arm support for adults with DMD that can be controlled with force- or EMG-based interfaces. The A-Arm is intended to replace the arm rest of the wheelchair and assist during table top tasks such as computer, tablet, or smartphone use, writing and drawing, and the use of the wheelchair's joystick. In the force-based control interface we have implemented active compensation of the joint-stiffness forces using a measurement-based method to obtain an estimation of the voluntary forces of the user. A pilot evaluation with an adult with DMD (24 years-old, Brooke 5) has shown that the A-Arm was able to increase the functional workspace of the arm (from 100 cm2 to 190-200 cm2). We found that while force-based control was experienced by the participant as more fatiguing than EMG-based control, the movements with EMG-based control were less accurate. These preliminary results give promising perspectives for the use of simple active arm supports to increase the independence of people with DMD.