Adaptive Oscillator-Based Assistive Torque Control for Gait Asymmetry Correction With a nSEA-Driven Hip Exoskeleton

Abstract

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).

A Robotic Assistance Personalization Control Approach of Hip Exoskeletons for Gait Symmetry Improvement

“…The results of gait symmetry improvement in this study are comparable to or even better than the performance of existing lower-limb exoskeletons studies, such as from 21.5%±3.3% in artificially impaired condition to 3.4%±0.5% in assisted condition [21], from 11.1%±0.7% in artificially impaired condition to 3.9%±0.6% in assisted condition [48], and from 12.7% in artificially impaired condition to 7.4% in assisted condition [48]. More importantly, this study provides an adaptive optimal control framework to automatically tune control parameters for a hip exoskeleton to provide personalized optimal assistance that reproduces the desired gait symmetry.…”

“…Many recent research studies have addressed gait symmetry improvement by using hip exoskeletons and three main approaches, including joint trajectory-tracking control [14], [15], finite-state-machine (FSM)-based assistive control [16], [17], and adaptive frequency oscillators (AFO)-based assistive control [18]- [21]. However, the trajectory-tracking position control may cause discomfort or even injuries to patient wearers who still have voluntary motor functions although it is more appropriate for patient wearers with full paraplegia, which potentially discourages active engagement of the patients.…”

Discernment on assistive technology for the care and support requirements of older adults and differently-abled individuals

“…The knee exoskeleton included a waist belt, shank support frame, loadcell, actuator, thigh support frame, elastic straps, hinge, linkage, and control electronics. The beginning and finishing of the kneeling gait were identified by a threshold-dependent kneeling gait recognition process ( 19 ). Comfort and fit on wearing the device had to be taken care of.…”

Gait Adaptation to Asymmetric Hip Stiffness Applied by a Robotic Exoskeleton

“…Recent studies have highlighted the potential of lower limb exoskeletons in compensating for asymmetries and improving walking performance in individuals post-stroke [ 18 ], [ 19 ]. However, the primary focus of compensation or assistance paradigms is to restore or attain a desired motor behavior while the wearable exoskeleton is actively being used.…”