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.
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