This study proposes a composite control framework for upper-limb rehabilitation exoskeletons integrating fractional-order impedance control, computed-torque compensation, and a momentum-based nonlinear disturbance observer. By combining Jacobian-transpose force mapping, fractional-order impedance shaping, and observer-based compensation, the framework enhances compliant yielding and tracking robustness under non-ideal dynamics. Simulation results show that, under severe spasticity-like impact, interaction force remains within 45 N. Under 30% mass mismatch and strong friction, tracking accuracy improves without reaching the 60 N·m torque limit. Under tremor-like disturbance, 4-8 Hz oscillations are attenuated while low-frequency voluntary motion is preserved, improving compliance, disturbance rejection, and torque smoothness.
Chun Liu, Xinrong Liu, Yuhang Xue· Computer Methods in Biomecha...· 0 citations
Offshore wind turbine blade repair requires stable material removal and precise force regulation under curved‐surface contact and environmental disturbance. To address these challenges, this paper proposes an integrated constant‐force grinding method that combines a passive compliant end‐effector, a particle swarm optimization‐backpropagation neural network (PSO‐BP), and an improved active disturbance rejection control (ADRC) strategy. First, a passive compliant end‐effector with variable stiffness is designed to improve contact adaptability and reduce grinding impact on curved blade surfaces. Second, a PSO‐BP model is established to predict the material removal rate (MRR) and surface roughness (Ra) under different grinding conditions, thereby providing data‐driven support for process‐state evaluation and parameter scheduling. Third, based on a controller‐oriented force‐dynamics model, an improved ADRC framework integrating a tracking differentiator, nonlinear extended state observer, nonlinear state error feedback, and PSO‐BP‐assisted gain scheduling is developed for constant‐force grinding. A Lyapunov‐based analysis shows that the closed‐loop system is uniformly ultimately bounded under bounded disturbances and bounded scheduling error. Simulation and experimental results demonstrate that, compared with PID and standard ADRC, the proposed method achieves higher force‐tracking accuracy, stronger disturbance rejection, and better grinding quality. Under equivalent initial damage conditions, it produces the lowest post‐grinding surface roughness, indicating that the proposed method provides an effective solution for offshore blade grinding repair.
Yuhang Xue, Xinrong Liu, Tianhao Wang· Journal of Field Robotics· 0 citations
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