This paper presents the mechanical design and evaluation of a knee-ankle-foot robot, which is compact, modular, and portable for stroke patients to carry out overground gait training at outpatient and home settings. The robot is driven by a novel series elastic actuator (SEA) for safe human-robot interaction. The SEA employs one soft translational spring in series with a stiff torsion spring to achieve high intrinsic compliance and the capacity of providing peak force. The robotic joint mechanism and the selection of the actuator springs are optimized based on gait biomechanics to achieve portability and capability. The robot demonstrated stable and accuracy force control in experiments conducted on healthy subjects with overground walking. Major leg muscles of the subjects showed reduced level of activations (Electromyography, EMG) while maintaining normal gait patterns with robotic assistances, indicating the robot's capability of providing effective gait assistance.
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