Disturbance Rejection Improvement in Robust Motion Control of Series Elastic Actuator

Contact safety and high control performance are important for human assistive collaborative robots and wearable technology. A series elastic actuator (SEA) has a spring inserted between the motor and the load, which has high compliance. A motor/load-side encoder that acquires motor and load angles enables precise control. SEA with a motor/load-side encoder is appropriate for a human assistive system. However, resonant poles due to the low stiffness of SEA cause resonant vibration and low robustness. Human assistive systems need to achieve control that is precise and robust to disturbances from humans and the environment. This paper proposes a novel control system design that achieves vibration suppression and high robustness. The proposed method consists of torsion torque control and an inverse system filter. By dividing the suppression of resonant pole effects and improving robustness into different controllers, the proposed method makes it easier to design appropriate gains for human assistive systems than conventional methods. The validity of the proposed method and the effect of stiffness error were verified by simulations of position and force control.