Ultrahigh-Precision Rotational Positioning under a Microscope: Nanorobotic System, Modeling, Control, and Applications

High-precision positioning is an essential requirement for sample operation at a small scale. At the current stage, although nanometer-scale accuracy has been achieved for the linear positioning, the rotational positioning (attitude control) is still very challenging and rarely addressed. This paper presents a rotatable nanorobotic system with rotational degrees of freedom first. Then, the system error, i.e., nonaxisymmetrical eccentricity error of the mechanism, is investigated dynamically and its fault model is established. After that, a double-loop servo repetitive controller is accordingly designed based on the circle interpolation strategy. The theoretical analysis and experimental results verify that the rotational positioning accuracy can be controlled up to submicrometers stably, which improves at least one order of magnitude than the current static method. Finally, two application cases are given to highlight the significance of this approach, i.e., surface defect detection from 360° and in situ twisting characterization of 1-D micro/nanomaterial. This research paves a new avenue for the ultrahigh rotational positioning at microscopy environment, which is expected to generate a long-term impact on the micro/nanofields, such as microscopy imaging, material characterization, and so on.