High-resolution absolute range sensors based on the combination of frequency modulation and laser triangulation for heavy industry application

Feedback control of metal strip rolling processes requires inline-capable, fast and robust thickness gauges. An optical thickness gauge is developed which measures the distance to the top and bottom of the strip with two optical sensors. They combine triangulation and multi-wavelength interferometry for a robust absolute high-resolution range measurement. Sinusoidal modulation interferometry is used to realize a very compact Fizeau-type multi-wavelength interferometer. The performance of the thickness gauge is studied in the laboratory under dynamic conditions that are close to production environment. The expanded measurement uncertainty of 0.48 μm of the system is thereby consistent with the observed deviation of the measurement values from a tactile reference sensor

Two multi-wavelength interferometers for large-scale surveying

[EN] Deformation monitoring requires the detection of smallest changes, always at the limits of technical feasibility. Trying to push these limits further, we have realised two terrestrial ranging instruments: a long-range 1D electro-optic distance meter and a 3D multilateration-capable sensor system of 50 m range. The former one is intended as primary standard for the calibration of geodetic instrumentation with low uncertainty to the SI definition of the metre. The latter one is intended for monitoring larger monuments like VLBI antennas. In this contribution, we describe the technical challenges and our solutions for such instrumentation. We use the two-colour method for inline refractive index compensation. As common optical source, we developed a versatile multi-wavelength generator based on two Nd:YAG lasers stabilised by a phase-locked loop realised by Field Programmable Gate Arrays (FPGA). The 1D interferometer uses custom-designed achromatic optics and a mechanical frame optimised for form stability under field conditions. The phase demodulation system allows for maximum range flexibility from several meters up to several kilometres. The base ranging unit of the 3D multilateration system adheres to a different demodulation technique, which allows a relatively simple interferometer head design. This approach requires a sophisticated source modulation scheme limiting the applicability to distances over 15 m up to approximately 50 m in our case.This project 18SIB01 GeoMetre has received funding from the EMPIR programme co-financed by the Participating States and from the European Union’s Horizon 2020 research and innovation programme. We would like to thank P. Knigge, D. Fiala, M. Wedde, and M. Peglow for technical assistance.Sauthoff, A.; Köchert, P.; Prellinger, G.; Meyer, T.; Pilarski, F.; Weinrich, S.; Schmaljohann, F.... (2023). Two multi-wavelength interferometers for large-scale surveying. Editorial Universitat Politècnica de València. 31-39. https://doi.org/10.4995/JISDM2022.2022.13635313

The European GeoMetre project : developing enhanced large-scale dimensional metrology for geodesy

We provide a survey on the joint European research project “GeoMetre”, which explores novel technologies and their inclusion to existing surveying strategies to improve the traceability of geodetic reference frames to the SI definition of the metre. This work includes the development of novel distance meters with a range of up to 5 km, the realisation of optical multilateration systems for large structure monitoring at an operation distance of 50 m and beyond, and a novel strategy for GNSS-based distance determination. Different methods for refractivity compensation, based on classical sensors, on dispersion, on spectroscopic thermometry, and on the speed of sound to reduce the meteorological uncertainties in precise distance measurements, are developed further and characterised. These systems are validated at and applied to the novel European standard baseline EURO5000 at the Pieniny Kippen Belt, Poland, which was completely refurbished and intensely studied in this project. We use our novel instruments for a reduced uncertainty of the scale in the surveillance networks solutions for local tie measurements at space-geodetic co-location stations. We also investigate novel approaches like close-range photogrammetry to reference point determination of space-geodetic telescopes. Finally, we also investigate the inclusion of the local gravity field to consider the deviations of the vertical in the data analysis and to reduce the uncertainty of coordinate transformations in this complex problem