Adaptive dual-mode active control for lower limb exoskeleton robot with variable stiffness

Purpose This paper aims to enhance the versatility and adaptability of lower limb exoskeleton robot (LLER) across diverse scenarios by proposing a novel adaptive dual-mode active control framework that dynamically couples joint stiffness adjustment with motion control. Design/methodology/approach A dual-mode control strategy is designed: a torque-priority active assistive control mode for rehabilitation, combining enhanced PID trajectory tracking with human–robot interaction (HRI) force compensation, and a stiffness-priority motion-following control mode for daily locomotion, using gait phase impedance control. A HRI force-threshold triggered mechanism synchronizes real-time stiffness adjustment with motion intent. Findings Prototype experiments demonstrate that both control modes effectively assist human movement. The system successfully adapts to interaction forces, maintaining stable tracking performance and improving overall human–robot coordination. Originality/value This study introduces a HRI force-based coordination mechanism that overcomes the conventional decoupling of stiffness and motion control, enabling context-aware, synchronous adjustment of assistance torque and joint compliance. This framework offers a practical solution for enhancing LLER adaptability in both rehabilitation and daily locomotion.