Robust Position Control of Series Elastic Actuator via Load Port Control and Novel Acceleration Estimation

Abstract

Precise position control of Series Elastic Actuator (SEA) is crucial yet challenging. Conventional methods like Load Feedback Control (LFC) compromise stability due to inherent phase lag, while Motor Feedback Control (MFC) can ensure stability but may introduce load-side vibrations during transients. This paper presents Load Port Control (LPC) as an alternative approach to achieve both stability and high-performance position tracking for SEA. Implementing LPC requires accurate load acceleration estimation, which is complicated by the limitations of existing methods; differentiation with low-pass filtering introduces phase delay, and simplified dynamics models are sensitive to external torques. To overcome this, we propose a novel acceleration estimation method that fuses low-pass filtered position information with high-pass filtered dynamics model data. This approach mitigates phase lag while enhancing robustness against external torque. The effectiveness of the LPC strategy is evaluated through theoretical analysis and experiments on a two-mass testbed. Under the evaluated conditions, the proposed method showed improved stability, tracking performance, and disturbance robustness relative to the compared methods.