Dynamic range enhancing technique for form, waviness and roughness measurements using fringe projection

Optical techniques are used for non contact, high precision measurement tools. The most common optical technique is classical laser interferometry. Although laser interferometers offer high resolution, they suffer from limited dynamic range since the range is related to the wavelength of light. Other optical techniques like scanning white light interferometry and holography overcome this limitation. In this paper we propose a technique to enhance the vertical measurement range of a fringe projection system without reduction in its vertical resolution. It is based on the principle of inverse fringe projection, where the surface form is first measured by projecting a low frequency straight grating, and then used to create high frequency fringes with the proper inverse profile to project back on the surface and measure the surface finish without the impact of the form. The proposed technique is modeled, simulated and tested to measure the form, waviness and roughness of surfaces.