Charge Feedback Hysteresis Disturbance Observer Design of a Multi-axis Piezo-actuated Stage

Piezo-actuated stage has excellent dynamic response and high resolution, and is widely used in micro- or nanoscale precision positioning systems. However, the nonlinearities such as hysteresis and creep make its control very difficult.
In this thesis, the hysteresis nonlinearity is considered as an extra disturbance over a linear system. A novel approach using the parasitic capacitance charge feedback in conjunction with a Preisach model to estimate the hysteresis disturbance is proposed. The charge over the parasite capacitance is measured through a serially connected capacitance. The hysteresis disturbance is calculated on-line using the Preisach model and is added to the control input. Under this architecture, the hysteresis nonlinearity is compensated by the hysteresis observer and the digital controller deals only with the linear electro-mechanical system. The setup dramatically reduces the complexity of controller design. In contrast to the inverse-model-based control, this approach is more robust and easier to implement. The proposed approach requires no complex charge amplifier circuit and has little limitations on the bandwidth. The thesis provides detailed analysis and parameter identification of the piezo actuator, the building process of the Preisach model, and the dynamic response analysis of the stage. Low pass filter and feed forward compensator are also employed to improve the tracking performance. Tracking control results under sinusoidal reference at different frequencies and stair-case reference tracking confirms the effectiveness of this approach.