An assistive upper-limb exoskeleton controlled by multi-modal interfaces for severely impaired patients: development and experimental assessment

Abstract

Active exoskeletons can help adults with muscular dystrophy regain independence and self-esteem, which have been limited due to their severe and progressive muscular weakness. A four degrees-of-freedom fully actuated upper limb exoskeleton, equipped with a spring-based anti-gravity system, has been designed, prototyped, and tested on end-users. While wearing the exoskeleton, the user directly controls the system by actively driving the end-effector position (i.e., the hand) using a joystick or vocal control. The exoskeleton’s kinematic model has been determined so that, given a desired user’s position in the task-space, a differential inverse kinematics algorithm computes the desired joint-space motion trajectories. The dynamic model was investigated in the vertical plane, demonstrating that gravity torques were considerably higher than velocity-induced and inertia torques, which have been therefore neglected. A pilot study on 14 Muscular Dystrophy patients was conducted. Outcome measures included: (i) externally-assessed functional benefit evaluated through the Performance of Upper Limbs module, (ii) self-perceived functional benefit assessed through the ABILHAND questionnaire, and (iii) usability of the system assessed through the System Usability Scale. All participants strongly increased their range of motion, and they were able to perform activities that were not possible without the exoskeleton, such as feeding. The externally-assessed and self-perceived functional improvements were statistically improved when wearing the exoskeleton (PUL p-value=0.001, ABILHAND p-value=0.005). System usability was evaluated to be excellent. Patients’ feedbacks were encouraging and outlined future development steps.