The Combination of Speckle Correlation and Fringe Projection for the Measurement of Dynamic 3-D Deformations of Airbag Caps

Abstract

Highly dynamic 3-D deformations of airbag caps in the time interval from the ignition of the airbag to the fracture of the covers have been studied optically. The large out-of-plane displacement compared to the in-plane displacements afforded that the measurement problem was solved by combining white light speckle correlation with fringe projection. In order to record the speckle patterns and the fringe patterns simultaneously by two high speed CCD cameras they had to be separated spectrally. The in-plane displacements yield from the speckle patterns by pattern recognition methods. The out-of-plane displacements can be calculated from the contour of the caps. They yield from the phase maps which are calculated from the fringe patterns. For each time instant only one image is available so that phase shifting procedures to evaluate the fringe patterns could not be applied. In this paper we present a method which is based on the simulation of a phase locked loop (PLL). This results in continuous phase maps without phase unwrapping.