Integrated method for 3-D rigid-body displacement measurement using fringe projection

A novel method using a charge-coupled device (CCD) camera is developed to measure 3-D rigid-body displacement of an object. This method combines fringe projection and digital image correlation (DIC) methods into one optical system. In this method, sinusoidal fringes are projected on an object using a liquid crystal display (LCD) fringe projector. Images of the object's surface are captured by a CCD camera and stored for further processing. With the aid of the Fourier transform, the fringes in the images are removed while the background intensity variation is preserved. DIC is subsequently used to obtain in-plane displacement using the fringe-free images. The original images are also processed by fast Fourier transform (FFT) to obtain information on the shape of the object. Based on the in-plane displacement obtained by DIC, the reference and measured profiles are compared to obtain out-of-plane displacement. Experiments are conducted on a small coin, and the results demonstrate that both in-plane and out-of-plane displacements can be accurately measured using the proposed method.