Sensorsless Electrostatic Suspension System Based on Observer Controller

Abstract

This paper introduces a new type of active electrostatic suspension system without using position sensors. The concept is to design a feedback controller without using position signals of the object instead using the voltage signals. In the working process of the electrostatic suspension system, the capacitance formed between the electrode and the suspended object is treated as a capacitor of two parallel plates, and if the gap length between them is changed the capacitance is then changed. This causes to change the voltage across the capacitance formed between the electrode and suspended object. This voltage is measured, and it then is used to estimate all variables of the system that are the displacement, velocity of the suspended object, and voltage across the capacitance formed. These estimated values are employed in the feedback schema instead of actual states values. The design of the controller follows the classical observer state-space approach. First, a state feedback controller is constructed with the assumption that all the state variables of the suspension system that are displacement, velocity of the suspended object, and voltage across the capacitance formed by the electrodes and the suspended object, are available for feedback. Second, a full observer is designed for estimating all the states from the measured voltage across the capacitance. Finally, the estimated signals produced by the full observer are used in the feedback controller instead of the actual states, and the self-sensing electrostatic suspension without using position sensors is achieved. The experimental and simulation results show that the suspended object successfully levitated at reference gap without using position sensors.