Visual servoing schemes for automatic nanopositioning under scanning electron microscope

This paper presents two visual servoing approaches for nanopositioning in a scanning electron microscope (SEM). The first approach uses the total pixel intensities of an image as visual measurements for designing the control law. The positioning error and the platform control are directly linked with the intensity variations. The second approach is a frequency domain method that uses Fourier transform to compute the relative motion between images. In this case, the control law is designed to minimize the error i.e. the 2D motion between current and desired images by controlling the positioning platform movement. Both methods are validated at different experimental conditions for a task of positioning silicon microparts using a piezo-positioning platform. The obtained results demonstrate the efficiency and robustness of the developed methods.