Design and experimental characterization of a shoulder-elbow exoskeleton with compliant joints for post-stroke rehabilitation

This paper presents the design and experimental characterization of a 4-degree-of-freedom shoulder-elbow exoskeleton, NeuroExos Shoulder-elbow Module (NESM), for upper-limb neurorehabilitation and treatment of spasticity. The NESM employs a self-aligning mechanism based on passive rotational joints to smoothly self-align the robot's rotational axes to the user's ones. Compliant yet high-torque series-elastic actuators allow the NESM to safely interact with the user, particularly in response to sudden unpredicted movements, such as those caused by spastic contractions. The NESM control system provides a variety of rehabilitation exercises, enabling the customization of therapy to patients exhibiting a range of movement capabilities. Available exercises include passive mobilization, active-assisted, active-resisted, and active-disturbed training modes. The experimental characterization of two NESM actuation units demonstrated position and torque control performance suitable for use in neurorehabilitation applications, including up to 7 Hz of bandwidth in torque control. An algorithm for online detection of spastic contractions or sudden object collisions has been implemented and tested as well, with results suggesting that the current system can ensure safe interaction with patients.