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Gait asymmetry is an important clinical characteristic of the hemiplegic gait most stroke survivors suffered, leading to restricted functional mobility and long-term negative impact on their quality of life. In recent years, robot assistance has been proven able to improve stroke patients' functional walking, but few studies have been conducted to specifically correct gait asymmetry of stroke patients during the whole gait cycle. In this work, an adaptive oscillator-based assistive torque control was developed and implemented on a unilateral hip exoskeleton driven by a novel nonlinear series elastic actuator (nSEA), aiming at correcting gait asymmetry at hip joints during the whole gait cycle. The adaptive oscillator-based gait asymmetry detection method extracted continuous gait phase and gait asymmetry seamlessly, and then the proposed assistive control attempted to correct gait asymmetry by delivering precise assistive torques synchronized with the continuous gait phase of the patients' gait. An initial experimental study was conducted to evaluate the proposed assistive control on seven healthy subjects with artificial impairment. The participants walked on a treadmill with assistance from the hip exoskeleton, while artificial impairment was added to mimic the hemiplegic gait with both spacial and temporal asymmetry (such as reduced hip flexion in the impaired side and reduced hip extension in the healthy side). Experimental results suggested the effectiveness of the proposed assistive control in restoring gait symmetry to levels comparable to a normal gait of the participants (p < 0.05).

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