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.