Visual servoing of a mobile microrobot inside a scanning electron microscope

Mobile microrobots with piezo slip-stick actuation and more than one degree of freedom mostly do not have internal pose sensors. One possibility for fast pose estimation with high accuracy is the application of external visual sensors like a video camera in combination with a light microscope or a scanning electron microscope (SEM). In particular, the use of a SEM makes high demands on the image processing. High update rates of the pose data enforce a short image acquisition time of the SEM images. Hence, the image noise increases, because frame averaging or averaging of the detector signal is time consuming. This paper presents a method to calculate the x, y position and the orientation of a micro gripper in a strongly noised SEM image stream with cross-correlation in real-time. To make real-time pose estimation possible, only a region-of-interest (ROI) is correlated with the target pattern. The SEM is almost predestined to work with ROI´s, because the scan area of the electron beam can be chosen arbitrarily. At the beginning of the paper, the setup of the used mobile microrobot based nanohandling station was described briefly.