Design and Control of a Flexible Actuator Joint for Lower Limb Exoskeleton Robot

Lower limb exoskeleton robots provide assistance to the wearer through a human-robot interaction device. However, the joint actuators are unable to adjust their stiffness according to the wearer's load, walking speed, or other factors, limiting the adaptability of the exoskeleton to different scenarios and compromising safety during human-robot interaction. This paper explores the design and control methods of flexible actuator joints in lower limb exoskeleton robots. A variable stiffness joint, based on the principle of leaf spring adjustment, is designed. A stiffness model of the variable stiffness mechanism is established using deformation screw theory, and the influence of the effective length of the leaf spring on joint stiffness is analyzed. For the designed flexible actuator joint, a torque controller and impedance control strategy, based on gain scheduling and a disturbance observer, are proposed. Controller simulation analysis is performed to achieve compliant joint motion control.