Robustness to Friction Estimation for Nonlinear Position Control of an Electrohydraulic Actuator

A near input-output (IO) linearizing position tracking controller is a nonlinear controller based on a nonlinear model of an electrohydraulic actuator. It uses feedback of piston friction force. In this paper, a friction model is identified from offline experiments and is subsequently approximated with differentiable functions. The effects of altering the friction estimate and even of ignoring it altogether, are investigated. For the test system considered, the near IO linearizing controller is moderately robust to this uncertainty in friction.