Position control of a linear ultrasonic motor: An active disturbance rejection approach

This paper presents a general overview of the theory and operation of Linear Ultrasonic Motors (LUMs). A nominal linear model of the LUM is used to perform the parametric estimation. Subsequently, with the estimated parameters, two controllers are designed to carry out the nano-positioning using a Proportional-Derivative (PD) controller plus a Generalized Proportional Integral (GPI) Observer and a PD controller plus a Disturbance Observer (DOB), then the performance of both are compared. External and internal perturbations are assumed to be a lumped bounded disturbance and its estimate is used in the design of the controller to compensate its effects. Experiments with a laboratory prototype allow evaluating the good performance of both control schemes obtaining steady-state position errors of 50 nm using both disturbance estimators.