Flexible joint control: Robustness analysis of the collocated and non-collocated feedbacks

The robustness and performance properties of a proportional-derivative controller applied to a very flexible joint are discussed. Because of a flexible mode due to in-joint compliance, the classical collocated control does yield good rigid mode dynamics with a correct phase margin in low and high frequency, and noncollocated control does not allow correct damping of the rotor mode. The simultaneous analysis of discrete root loci and Nicholas plots leads to a phase control law with a derivative term built from both input and output velocities. Simulations taking into account various real nonlinearities and measurement imperfections are proposed to validate this improved control design.