Application of the active disturbance rejection control structure to improve the controller performance of uncertain pneumatic actuators

In many robotic applications, pneumatic actuators are not adequate for tracking control tasks given the poor performance obtained with traditional control techniques like PID controllers. In this paper we show that the so-called Active Disturbance Rejection Control Structure (ADRCS), combined with a discontinuous observer and standard or robust algorithms in the controller block, provides a good solution to regulation and tracking control problems of pneumatic actuators. The discontinuous observer estimates the velocity, and whose discontinuous nature permits to estimate also the disturbances affecting the system, allowing to use a very simple model of the actuator and avoiding an off-line parameter identification. To analyze the observer ability to estimate the disturbances, we test three different algorithms in the controller block, the standard PD and two discontinuous controllers proposed elsewhere. The performance of the closed loop system is evaluated through experimental results using a performance index based on an. 2 norm, for constants and sinusoidal references. Also, we compare the performance of the proposed algorithms with the controllers with those using the same control algorithm but not including the disturbance compensation, showing the important effect of the disturbance estimation included in the ADRCS on the overall controller performance.