Abstract
Absolute distance measurement is a field of research with a large variety of applications. Laser triangulation is a well-tested and developed technique using geometric relations to calculate the absolute distance to an object. The advantages of laser triangulation include its simple and cost-effective setup with yet a high achievable accuracy and resolution in short distances. A main problem of the technology is that even small changes of the optomechanical setup, e.g., due to thermal expansion, lead to significant measurement errors. Therefore, in this work, we introduce an optical setup containing only a beam splitter and a mirror, which splits the laser into a measurement beam and a reference beam. The reference beam can then be used to compensate for different error sources, such as laser beam dithering or shifts of the measurement setup due to the thermal expansion of the components. The effectiveness of this setup is proven by extensive simulations and measurements. The compensation setup improves the deviation in static measurements by up to 75%, whereas the measurement uncertainty at a distance of 1 m can be reduced to 85 μm. Consequently, this compensation setup can improve the accuracy of classical laser triangulation devices and make them more robust against changes in environmental conditions.
Highlights
Absolute distance measurement (ADM) has been an essential research field in the past and present [1,2]
With the base distance of 130 mm and the assumption, that the components are mounted on an aluminum base, a temperature change of 1 ◦C would result in an increase of the base distance by μm, leading to an error in the distance measurement of around μm
It is important that the laser output, the beam splitter and the mirror stay in a fixed relation to one another, as a change in their geometrical relation would result in a deviation of only the reference beam, leading to an error in the compensated distance measurement
Summary
Absolute distance measurement (ADM) has been an essential research field in the past and present [1,2]. Li et al [27] used a digital optical phase conjugation system in a straightness measurement setup to compensate for the influence of beam bending due to an air refractive index gradient and turbulences in the measurement path, strongly decreasing the measurement deviation As this setup is complex, using active components like a spatial light modulator, it is not suitable for a simple triangulation setup. The error introduced due to the laser spot center calculation can be decreased by improved image processing algorithms and by averaging over time or several laser spot positions The latter can be done through the projection of several laser spot images onto the detector by using multiple lasers in a setup to increase the achievable sensor accuracy and avoid occlusions [36,37,38].
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