Synthesis of flatness control for a multi-axis robot manipulator: An experimental approach

This paper reports the results of research conducted on designing, modelling and controlling an electro-mechanical robot manipulator that serves as a sensing and motion system for hybrid testing. The conceptual design was inspired by the Stewart Platform mechanism for a two-degree-of-freedom (2DoF) moving platform. This design resulted in non-linear kinematics, coupled dynamics and an inertial moving platform that attracted model-based control strategies. A novel control technique based on differential geometric flatness was successfully implemented on this manipulator to simultaneously achieve linearisation, decoupling and asymptotic tracking. Simulation results demonstrated the validity of the proposed approach that established a robust control formulation resulting in perfect trajectory tracking at different excitation conditions. For the experimental implementation, the actuator time-delays was compensated for using forward prediction algorithms based on a fourth-order polynomial extrapolation. This compensation demonstrated a well synchronised control signal at varying frequencies.