An underactuated wearable arm-swing rehabilitator for gait training

This paper presents the design concept and fabricated prototype of a device that swings the arms for use in gait rehabilitation. The device is designed to be used in conjunction with a body-weight-support treadmill. The device is backdrivable, wearable, capable of assisting the user´s arm swing in the sagittal plane, and has unhindered kinematics in the remaining unactuated degrees of freedom. Tests are performed to validate the shoulder-angle prediction equations based on the non-collocated motor-angle sensor measurements, to validate the device´s ability to provide adequate torque to induce arm-swing in a passive user, and to investigate whether or not the user´s active involvement can be determined by examining sensor data. The results show that the device does provide sufficient torque to move the arms with a factor of safety, but that the model-based shoulder-angle estimates obtained from the motor measurements have non-negligible error with the current prototype. It is shown that the controlled device generates low RMS tracking error and is able to diagnose user-assistance level (i.e., if the user is passive or actively assisting arm swing) online by observing shoulder-angle amplitudes and peak motor torques.