High-Precision 3-D Measurements on Moving Objects

This article presents a six degree of freedom dual stage sample-tracking system for compensating relative motion and enabling high precision 3-D surface measurements on moving objects. The system comprises a 3-D measurement module for fine positioning, which is mounted as end effector to an industrial robot being used for coarse positioning. The embedded free-floating measurement platform actively tracks a sample to locally establish lab-like conditions for the integrated 3-D measurement tool. A dual stage position control scheme is designed to dynamically reposition the long-range actuator for tracking a moving sample, such that the measurement platform is kept within its actuation range. Experiments on a moving sample demonstrate a residual tracking error of 490 nm rms in sample-motion direction, corresponding to a performance increase by factor 32, as compared to the state-of-the-art approach. The analysis of the performed measurements shows an uncertainty reduction by one order of magnitude to 610 nm rms, enabling 3-D measurements on a moving sample with submicrometer precision.