Novel three dimensional shape measurement technique for fast rotating objects
Final Report Abstract
Absolute shape and vibration measurements of rotating workpieces and cutting tools in CNC machines are significant for machine operation optimizations and thereby for improving the machining accuracy. Simultaneous position and velocity measurements enable absolute 3D shape measurements of fast rotating workpieces for instance for monitoring the cutting process in a lathe. Laser Doppler distance sensors (P-LDD sensors) enable simultaneous position and velocity measurements with a single sensor head by evaluating the scattered light signals. However, superposed speckle signals, temperature drifts or mechanical scanning result in an increased velocity, distance and shape uncertainty. To overcome above drawbacks, the MST developed novel camera based P-LDD sensors and signal processing algorithms. Thus, the Doppler frequency from each speckle can be evaluated separately and the velocity and distance uncertainty decreases with the increase of the speckle number. An in-situ fringe spacing calibration method is realized to eliminate the fringe spacing uncertainty resulting from temperature drifts. Coherent fiber bundles were employed for the first time to forward the scattered light towards the cameras. This removes the cameras from the sensor head and therefore enables a compact and passive sensor head with keyhole access. A reduction of the shape uncertainty by the order of one magnitude was verified by the numerical simulations and experimental results, respectively. Furthermore, the lateral measurement range of the sensor was extended. This enables 4D shape measurement without feed motion and therefore completely avoids the measurement uncertainty and position deviation due to mechanical scanning. Moreover, a measurement system for investigating the tip vibration inside of a CNC milling machine under different rotational speeds was developed. A signal processing algorithm was proposed, which enables simultaneously bi-directional vibration measurements at non-continuous surface of tool tip. Depending on the measured vibration, the dynamic behavior parameters including the natural frequency and damping ratio of the tool were estimated in force direction and its vertical direction. This is particularly significant for machine modelling, error prone state identification and thereby optimizing machine operation. Lastly, the sensor was applied to validate a model-based approach for separating roundness deviations and spindle errors, successfully. Currently the application of the camera based P-LDD sensor is mainly limited by the frame rate of the camera and the speed of big data evaluations. The possibility to employ high speed cameras with several ten MHz for high speed moving object of several 100m/s is expected. Meanwhile, FPGA techniques can be used for processing the measurement data captured by the high speed cameras in real time in the further. The used coherent fiber bundle consists of multimode fibers. The present investigation shows that in CFBs fiber speckles caused by the multimode lead to an additional uncertainty on the shape measurement. This issue can be solved by using single mode fibers. Therefore, the possibility to employ single mode fiber bundles will be investigated.
Publications
- “Camera-based speckle noise reduction for 3-d absolute shape measurements,” Optics express, vol. 24, no. 11, pp. 12130–12141, 2016
H. Zhang, R. Kuschmierz, J. Czarske, and A. Fischer
(See online at https://doi.org/10.1364/OE.24.012130) - “Miniaturized interferometric 3-d shape sensor using coherent fiber bundles,” Optics and Lasers in Engineering, vol. 107, pp. 364–369, 2018
H. Zhang, R. Kuschmierz, and J. Czarske
(See online at https://doi.org/10.1016/j.optlaseng.2018.04.011) - “Measurement uncertainty propagation in spindle error separation techniques-investigation by means of stochastic spectral method,” International Journal of Machine Tools and Manufacture, vol. 141, pp. 36–45, 2019
S. Shi, H. Zhang, J. Qu, G. Jin, R. Kuschmierz, and J. Czarske
(See online at https://doi.org/10.1016/j.ijmachtools.2019.03.006) - “Modeling, quantification, and mitigation of uncertainty propagation in two-step roundness measurements”, Measurement, vol 155, 107530, 2020
S. Shi, R. Kuschmierz, G. Zhang, J. Lin, J. Czarske, J. Qu
(See online at https://doi.org/10.1016/j.measurement.2020.107530) - “Non-contact, bi-directional tool tip vibration measurement in CNC milling machines with a single optical sensor,” Mechanical Systems and Signal Processing, vol 139, 106647, 2020
H. Zhang, D. Anders, M. Löser, S. Ihlenfeldt, J. Czarske, and R. Kuschmierz
(See online at https://doi.org/10.1016/j.ymssp.2020.106647)
