Diameter Measurement of Spherical Objects by Laser Triangulation in an Ambulatory Context

A new method for robust noncontact diameter determination of spherical objects is studied. Applications can be found in the grinding and in the robotic inspection fields. The principle is based on laser triangulation under structured lighting, where laser planes create lines on the object under test, which are observed by a charge-coupled device camera. Two methods are proposed for radius calculation. The first one is an extension of what we call the "three-tangent method," which is developed in the context of a previous study consisting of the measurement of the diameter of cylinders. The second one is the gradient-descent method, which is a statistical optimization technique. Experimental results obtained on a preprototype setup with both methods are given and compared, showing slightly better performances for the "three-tangent method." A general accuracy of about 1% for spherical objects of 10-30 cm in diameter is claimed for distances ( a priori not known) up to 2.5 m