Suppressing Laser Triangulation Sensors Optical Aberrations by Replacing the Lens with a Slit

This paper presents a new capture method for laser triangulation sensors consisting in replacing the lens with a slit—effectively making it a pinhole camera—and exploiting diffraction effects. This new method circumvents optical aberrations such as spherical, defocusing, coma, field curvature, and lens distortion, as well as lens flare to a point where it can be virtually ignored. Moreover, using a slit reduces the number of optical parts and simplifies the modeling of the laser spot to find its center. To test our proposed method, we generated data sets taking pictures with both a lens and a slit on different materials placed on a worm gear with its position controlled by a high-precision step motor. With this data, we extracted the center of the laser spot with different image processing algorithms. It was then possible to assess the goodness of fit of the triangulation curve using the sets of captured points by both methods. We show that not only we circumvent the adverse effects of optical aberrations and lens flares, we obtain a more accurate estimation of the actual known distance of the target.