Design, implementation and control of a self-aligning full arm exoskeleton for physical rehabilitation

We present kinematics, design, control, characterization and user evaluation of AssistOn-Arm, a novel, powered, self-aligning exoskeleton for robot-assisted upper extremity rehabilitation that allows for movements of the shoulder girdle as well as shoulder rotations. AssistOn-Arm can both actively and passively enable translational movements of the center of glenohumeral joint, while also passively compensating for the translational movements at elbow and wrist. Automatically aligning all its joint axes, AssistOn-Arm provides an ideal match between human joint axes and the exoskeleton axes, guaranteeing ergonomy and comfort throughout the therapy, and extending the usable range of motion for upper extremity movement therapies. Furthermore, self-aligning feature of AssistOn-Arm significantly shortens the setup time required to attach the patient to the exoskeleton. In addition to the typical shoulder rotation exercises, AssistOn-Arm can deliver glenohumeral mobilization (scapular elevation/depression and protraction/retraction) and scapular stabilization exercises, extending the type of therapies that can be administered using the upper-arm exoskeletons. To ensure safety and gentle interactions with the patient, AssistOn-Arm is designed to be passively backdriveable, thanks to its capstan-based multi-level transmission and spring-based passive gravity compensation mechanism. Open and closed-loop impedance controllers have been implemented to safely regulate interactions of AssistOn-Arm with patients and performance of the device has been experimentally characterized. Ergonomy and useability of the device has also been demonstrated through human subject experiments