Surface profile measuring system based on fringe projection and sinusoidal phase modulation

A fiber-optic interferometer based on fringe projection and sinusoidal phase modulation(SPM)for three-dimensional surface profile measurement was presented. It made use of Young's double pinhole interference principle to achieve fringe projection. And sinusoidal phase modulation was accomplished by driving piezoelectric transducer using a cosine voltage single. To eliminate the external disturbances such as mechanical vibration and temperature fluctuation, a phase control system was proposed by detecting the phase drift and giving real-time compensation. The phase error was reduced to 6.8 mrad after compensating. A high phase stability of the interference fringe can be achieved. By measuring the surface profile of a glass plate for two times over an interval of 10 min, the repeatability is about 0.05 wave. Experimental results show that the proposed interferometer can be used for surface profile measurement with a high precision.