Adaptive Patient-Cooperative Control of an Omnidirectional Mobile Exoskeleton Robot for Lower Limb Rehabilitation

Abstract This paper presents an adaptive patient-cooperative control strategy and implements it on an originally designed lower limb rehabilitation robot. The robot structure comprises a lower limb exoskeleton and an omnidirectional mobile platform, and this design enables it to provide omnidirectional overground gait training for hemiplegic patients. The kinematic models of the lower limb exoskeleton, the omnidirectional mobile platform, and their movement coordination that can be used for robot control are established. To enhance patients' active participation during rehabilitation training, a patient-cooperative control strategy consisting of an outer-loop with admittance controller and an inner-loop with velocity controller is proposed, and an adaptive law is designed to adjust admittance parameters based on the exoskeleton joint angle and human-robot interaction force. Experiments involving five healthy subjects are conducted, and the results demonstrate that the proposed control strategy exhibits excellent trajectory tracking performance and can adaptively adjust the robot gait speed according to the subject's motion state and intention, which indicates significant potential in improving rehabilitation effect.