Measurements of absolute long distances

摘要

The production of large components, e. g. in aerospace industries, requires flexible and yet highly precise measurement techniques to determine absolute lengths of up to one hundred metres. Two different approaches are presented in this paper. One is based on a time-of-flight measurement, using a femtosecond frequency comb as an advanced modulator. By the combined phase analysis of lines of different distinct frequencies in the Mega- and Gigahertz frequency range, a measurement distance of one hundred metres with a relative measurement uncertainty of 1 X 10~(-7) was achieved in laboratory conditions. In a second approach to long distance measurements, two standard interferometric measurement techniques, i.e. variable synthetic and fixed synthetic wavelength interferometry, were combined. The two interferometry techniques were realised within a single set-up, using two external cavity diode lasers as sources. Experimentally, lengths of up to twenty metres could thus be determined with relative uncertainties below 1 X 10~(-6), in good agreement with theoretical analysis. Both techniques, femtosecond fibre laser-based time-of-flight and diode laser-based multi-wavelength interferometry, are therefore capable of absolute, guidance-free long distance measurements and have achieved demonstrated relative measurement uncertainties below 1 X 10~(-6) for distances over ten metres.