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This paper introduces a control framework for self-balancing lower limb exoskeletons (SBLLE) that enables stable turning motions without external assistive devices. The framework includes a turn-specific gait planner and an adaptive variable impedance controller (AVIC) that adjusts the center of mass in real-time, ensuring balance during walking across a range of users with varying mobility impairments. Validation through simulations and human-subject experiments shows that the approach maintains the Zero Moment Point within the support polygon, demonstrating robust performance in stable turning.
Stable turning in self-balancing exoskeletons is achievable without external aids, thanks to a novel adaptive control framework that adapts to user needs in real-time.
Self-balancing lower limb exoskeletons (SBLLE) hold the promise of helping individuals with diverse mobility impairments regain their ability to walk. Equipping exoskeletons with stable turning capabilities is crucial for their real-world application. This paper presents an effective control framework that enables stable turning motions in SBLLE without relying on external assistive devices. A turn-specific gait planner has been designed to generate stable reference gaits. Moreover, an adaptive variable impedance controller (AVIC) is introduced, which adjusts the center of mass (CoM) motion in real time to maintain balance during walking, even when carrying different patients. The proposed approach is validated through simulations, comparative studies, and multi-stage human-subject experiments with ten participants, ranging from healthy users to individuals with severe lower-limb motor impairment. Results consistently demonstrate stable turning performance, with the Zero Moment Point (ZMP) remaining within the support polygon during the entire walking process. Note to Practitioners—This paper proposes a control framework to achieve stable turning gait for a self-balancing lower limb exoskeleton (SBLLE). The framework involves offline gait planning and online stability control. We first established a centroid dynamics model for the SBLLE, based on which two gait planning methods for curved walking and turning in place were designed. Then, a novel adaptive variable impedance controller (AVIC) was developed. It demonstrates strong robustness against user physical characteristics and turning-induced disturbances, while incorporating active impedance into the exoskeleton system. Finally, the framework has been implemented on a full-scale exoskeleton prototype and evaluated through simulation, comparative controller studies, and multi-stage human experiments involving ten participants with diverse physical conditions, including users with severe lower-limb motor impairment. The consistent stability observed in these tests suggests that the proposed approach provides a practical and deployable solution for self-balancing turning in wearable exoskeleton systems, offering a solid foundation for further clinical-oriented development.