Miniaturized interferometric 3-D shape sensor using coherent fiber bundles

Mach-Zehnder interferometer based sensors for simultaneous distance and velocity measurement allow for absolute 3-D shape measurements of rotating workpieces for instance in cutting lathes. The achievable shape uncertainty is limited to around one micron due to the speckle effect and temperature drifts, however. In this paper, a laser Doppler distance sensor with phase evaluation (P-LDD sensor) with a camera based scattered light detection is investigated. A novel speckle separation technique and in-situ fringe distance calibration method are realized to reduce the measurement uncertainty. A coherent fiber bundle is employed to forward the scattered light towards the camera. This enables a compact and passive sensor head with keyhole access. Compared with a photo detector based sensor, the camera based setup allows to decrease the measurement uncertainty by the order of one magnitude. As a result, the total shape uncertainty of absolute 3-D shape measurements can be reduced to about 100 nm.