Novel three dimensional shape measurement technique for fast rotating objects

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The measurement of shape und position of fast rotating workpieces with sub-micron precision enables important advances in process technology. During the first funding period a novel laser Doppler distance sensor (P-LDD Sensor) was investigated systemically. The P-LDD sensor system employs the simultaneous measurement of the lateral surface velocity and the axial surface distance, in order to measure the absolute shape and position of rotation axis with keyhole access. A scientific breakthrough was accomplished. The measurement uncertainty has been reduced by more than one magnitude by observing the scattered light under different angles and employing novel signal evaluation. Furthermore, the P-LDD sensor system was integrated into a lathe (cooperation with PTB in Braunschweig) and the shape of a workpiece was measured with a standard deviation of 300 nm also at high lateral surface velocities. However, the total measurement uncertainty for this novel system is currently limited by speckle noise and thermal drifts of the calibration functions. Additionally, the lateral resolution is limiting the application of the sensor to measurements of macro geometric features.Therefore, the aim of the proposed second funding period is to reduce the measurement uncertainty due to the speckle effect and due to drifts of the calibration functions (systematic uncertainties) as well as to increase the lateral resolution. This will enable macro- and micro-geometric shape measurements with sub-micron uncertainty at rotating objects. For this purpose cameras will be introduced to the system instead of single detectors and novel image processing for moving speckle pattern will be applied and fundamentally investigated. The image processing will enable an evaluation of single speckles. Therefore phase jumps, which currently occur in the detector signal will be eliminated. Preliminary, numerical experiments show a reduction of the speckle induced measurement deviations. Using a matrix camera and an extended image processing enables an in-situ calibration additionally, which will be applied and characterized to reduce systematic deviations. Furthermore, the extension of the P-LDD sensor system by a camera enables an increased lateral resolution. Thus, micro-geometric features of free form parts can be resolved additionally to the shape in-situ.