Motion estimation of a levitation mechanisms using piezoelectric element

We are studying a friction force control mechanism using levitation mechanism. We usually measure levitation height of the levitation mechanisms by the use of a displacement sensor. An inchworm using the levitation mechanisms was proposed, and realized micron order precise displacement over large horizontal working range. An optical fiber displacement sensor used in this research can measure the vertical levitation height but cannot follow the horizontal displacement. Therefore, it is difficult for the displacement sensor to measure the levitation height since the levitation mechanism moves horizontally even though the levitation height is in the vertical direction. We estimate the levitation height by measuring the capacitance between the levitation mechanism and the substrate, which realizes sensorless levitation estimation. The circuit which detects the electric capacitance is a series RC circuit. We apply sine wave AC voltage to the series RC circuit and measure the terminal voltage of the resistance. The estimation method proposed can extend the working range. This paper describes the comparison of the levitation height estimated by the method proposed and one measured by the optical fiber displacement sensor.