Sit-to-Stand Assistance for Patients with Parkinson's Disease Using a Lower-Limb Exoskeleton Robot

Sit-to-stand (STS) transfer is fundamental to many activities of daily living, but it is difficult for individuals with motor dysfunction or impairment. This study presents an observer-based impedance-control framework for a lower-limb exoskeleton robot to assist STS transfer. To account for external disturbances, including the wearer's joint torques and model uncertainties, a nonlinear disturbance observer (NDO) is used to estimate the lumped disturbance. An impedance-control strategy based on adaptive fuzzy sliding mode control (AFSMC) is then used to regulate the human exoskeleton system by compensating for these unknown terms. STS trials were conducted in one healthy participant and three participants with Parkinson's disease (PD), with and without exoskeleton assistance, to evaluate the proposed system. Across ten trials in the healthy participant, O-AFSMC had the lowest mean hip/knee RMSE (2.1247°/2.9375°). In PD participants, assistance reduced CoP and CoM excursion at the 3-s STS condition in each individual; in the H-Y stage-2 participant, CoP excursion decreased from 25.39 to 15.18 cm and CoM excursion from 17.83 to 14.21 cm. These pilot findings support the feasibility of STS assistance with a lower-limb exoskeleton robot.