Adaptive Fractional Hybrid Impedance Control of Rotary Series Elastic Actuator in Flat Terrains

This study presents a novel control approach, called adaptive fractional hybrid impedance control (AFH-IC), for rotary series elastic actuators (RSEAs) operating in flat terrains, such as solid floors (hard), carpet (medium), and grass (soft). The main objective is to develop a high-sensitivity torque and position control system capable of handling various motion trajectories, including sudden hard changes. Unlike traditional impedance control methods, AFH-IC, which is enhanced with fractional-order control and an adaptive fuzzy algorithm, is designed to eliminate torque errors in time-varying stiffness environments. The fractional parameters of the AFH-IC are optimized using particle swarm optimization for each terrain under different constraints. A custom-designed RSEA is utilized in both simulations and experiments. The proposed control structure demonstrates superior performance compared to conventional methods such as fractional hybrid impedance control and hybrid impedance control. The results confirm that AFH-IC significantly enhances force-tracking accuracy and robustness in real-world applications.