Robust 6-DOF motion sensing for an arbitrary rigid body by multi-view laser Doppler measurements

We propose a novel method for the robust, non-contact, and six degrees of freedom (6-DOF) motion sensing of an arbitrary rigid body using multi-view laser Doppler measurements. The proposed method reconstructs the 6-DOF motion from fragmentary velocities on the surface of the target. It is unique compared to conventional contactless motion sensing methods since it is robust against lack-of-feature objects and environments. By discussing the formulation of motion reconstruction by fragmentary velocities, we show that at least three viewpoints are essential for 6-DOF motion reconstruction. Further, we claim that the condition number of the measurement matrix can be a measure of system accuracy, and numerical simulation is performed to find an appropriate system configuration. The proposed method was implemented using a laser Doppler velocimeter, a galvanometer scanner, and some mirrors. We introduce the methods for calibration, coordinate system selection, and the calculation pipeline, all of which contribute to the accuracy of the proposed system. For evaluation, the proposed system is compared with an offline chessboard-tracking scheme of a 500 fps camera. Experiments of measuring six different motion patterns are demonstrated to show the robustness of the proposed method against different kinds of motion. We also conduct evaluations with different distances and velocities. The mean value error is less than 1.3 deg/s in rotation and 3.2 mm/s in translation, and is robust against changes in distance and velocity. For speed evaluation, the throughput of the proposed method is approximately 250 Hz and the latency is approximately 20 ms.