Fringe pattern projection method combined with digital holography

摘要

Optical measurement methods based on digital holography are highly effective for shape and deformation investigation of microcomponents. One of the most commonly discussed methods is digital holographic contouring connected with digital holographic interferometry. Unfortunately, this approach requires much time and it is difficult to apply to real time measurements. In the paper a novel, simple and inexpensive setup for shape and deformation measurements is proposed. The method uses fringe projection combined with digital holography. First a fringe image projected onto the surface under the test is registered using digital holography without any optical system. Next, the fringe image is reconstructed from the hologram what allows the determination of the surface shape. Small displacements are measured with digital holographic interferometry and larger ones by comparing the shapes for two object states. Because only one hologram for the shape and two for the displacement investigation are needed, quite fast measurements are possible. However, the CCD camera used in the arrangement restricts the measurement time. The comparison of both methods, particularly related to the measurement precision, will be given. The results obtained by experimental means are presented together with a discussion of the limitations and further possibilities of this method.