Visually servoed 3-D alignment of multiple objects with subnanometer precision

This paper presents a visual measurement technique and the associated visual servo control method that enable 3-D alignment of multiple objects with subnanometer precision. Such high precision is achieved through eliminating the bias error caused by spatial sampling in the in-plane motion estimation, using a highly sensitive measurement technique based on interference for the out-of-plane motion, and continuously compensating for time varying uncertainties induced by mechanical forces and thermal drifts. The developed measurement technique is integrated with a motion stage to experiment-ally demonstrate visually servoed alignment, in which two microcantilevers are aligned in the 3-D space with alignment errors below 1 nm (rms) in all axes. Nanostepping of 0.5 nm magnitude along the out-of-plane z-axis is also performed between the two microcantilevers to illustrate the super precision of the visually served 3-D alignment.