GPI observer based linear control of the Stewart-Gough platform

This work proposes an ADRC (Active Disturbance Rejection Control) for parallel robotic platform, namely the Stewart-Gough configuration. The platform is intended for CNC machining processes where repeatability and accuracy requirements of the robot´s motion are of utmost importance. The proposed approach makes use of linear high gain disturbance observation, where model uncertainties and external disturbances are lumped together into a general additive disturbance input that is estimated by Generalized Proportional Integral (GPI) observers and rejected on-line. The GPI control strategy replaces the more common PID controller in the joint control framework, and is used in order to better reject disturbances and non-linearities related with the robot configuration. Simulation results obtained by a co-simulation between Matlab and NX software, where the interaction dynamics and actuator non-linearities of the platform (i.e. saturation and headbands) were taking into account, closely approximate real robot operation and shows that the GPI observer-based linear control presents a better performance tracking trajectories compared with other control schemes, i.e. mixed sensitivity H∞ control.