Visual Tracking of Six-Axis Motion Rendering Ultraprecise Visual Servoing of Microscopic Objects

This paper presents visual tracking of six-axis motion that renders ultraprecise visual servoing of microscopic objects. The principle of three-axis out-of-plane motion tracking is based on three-degree-of-freedom laterally sampled white light interferometry and real-time unbiased nonlinear parameter estimation of orientation-dependent interference fringes. A continuously shifting model of the warped shadow projection image of the object is derived and employed to achieve unbiased real-time image registration for three-axis in-plane motion tracking. Processing of images and parameter estimation are synchronized with real-time image acquisition to realize six-axis motion tracking. The ability of the proposed approach to eliminate measurement bias associated with previous approaches is validated through computer simulations. The visual motion tracking system is integrated with a six-axis compliant piezo stage to establish a six-axis visual servo control system. Experimental results are presented and used to examine positioning resolution and to demonstrate superior precision achieved for long-range motion tracking.