Measurement of surface topography of transparent objects by using digital phase-shifting shadow moiré method without painting

Abstract

Light guide plate (LGP) is one of the essential components of a back light module (BLM). Warpage may be produced during the manufacturing process due to the lower structural strength of the LGP in a thinner thin film transistor liquid crystal display (TFT-LCD) as required by the market. Basically, the fringe pattern produced by the digital phase-shifting shadow moiré (DPSSM) method is generated from interference between the reference grating and its projected grating on the test surface. For a transparent object such as a LGP, reflective painting is generally sprayed on the object's surface to make the projected grating sufficiently visible. However, the LGP may no longer be re-used or may be damaged during the process of painting or de-painting. To investigate the feasibility of obtaining the surface topography of a transparent object by employing the DPSSM method without painting, fringe patterns generated from different capture angles with the same incident angle were examined. With the help of the image correction program, it was found that skewed images obtained from different capture angles can be successfully recovered. The surface topography of a LGP can then be correctly determined. © The Society for Experimental Mechanics, Inc. 2014.