Shape measurements of rotating objects using mutually tilted interference fringe systems

In the field of process control the shape measurement of rotating objects is important. For this task the laser Doppler distance sensor technique has been introduced by the TU Dresden some years ago. The technique is based by two mutual tilted interference fringe systems, where the distance is coded in the phase offset between both interference signals. However, due to the speckle effect, the envelopes and phase jumps of the interference signals are different. This results in the reduction of the signal correlation degree with increasing tilting angle of the interference fringe systems. By a matching of the illumination and the receiving optic a high correlation degree have been persisted also for large tilting angles [P. Günther et al., Opt. Lett., 37/ 22, pp. 4702, 2012]. This novel method enabled the reduction of the distance measurement uncertainty by more than one magnitude. Since the lateral velocity of the moving surface is measured additionally, the diameter, the ellipticity and generally the shape of rough objects can be determined.