Diffractive optical element based sensor for roughness measurement

A roughness sensing system, based on the fringe projection technique, is introduced. Roughness parameters are estimated from the fringe pattern projected on the target. The system employs a new projection unit in which light, coming from a laser diode, is coupled to a fiber optic and then impinges on a diffractive optical element (DOE) to produce sinusoidal fringes. The proposed sensor is simple, small and cheap and its sensitivity is easily adjustable. Fringes generated by the DOE are analyzed by a fast fourier transform (FFT) based algorithm, which can work also on curved surfaces.

Experimental results, obtained on varying spark erosion surface roughness standards, showed the capability of the system to perform roughness measurements with a resolution of about 0.5 μm.