Active disturbance rejection control for the joint driven by PMAs

The system of a joint driven by PMAs (pneumatic muscle actuators) is a strong nonlinear time-varying self-balanced second-order system. Traditional control methods are difficult to overcome the conflict between the control accuracy, the regulating speed and the stability. A second-order active disturbance rejection control (ADRC) is designed, in which a third-order ESO (extended states observer) is adopted to estimate the non-modeling part and external disturbance in real time and to make the linear compensation for system. Meanwhile, the control efficiency is improved by a nonlinear feedback. On the premise of ensuring the stability, the adjusting speed and control accuracy is enhanced. The system's steady-state accuracy is less than 0.1± and the tracking accuracy is less than 0.5±. Even in the case of the unknown or partly known system model, the system using ADRC can still achieve a satisfactory control result.