A laser rangefinder with the ability to identify surface roughness and detect the 3-D shape of metal parts

This paper describes a method of identifying the surface roughness and three-dimensional shape of a metal part with a laser rangefinder. Our rangefinder is equipped with an optical position sensor that can simultaneously detect the position of a light and its incident angle with respect to the sensor. Moreover, the sensor has an autonomous exposure time control function with a microcomputer. Therefore, the laser rangefinder can detect the three-dimensional (3-D) shape of an object with unknown reflectance. We constructed a prototype system and performed experiments with measured objects made of thermally sprayed materials. First, we inspected the surface reflection of each element in the thermally sprayed materials and established the measurement procedure using our rangefinder, which can identify surface roughness based on the optical properties of a surface. Next, we measured the thermally sprayed materials with several kinds of delaminations. From the measurement results, we found the error of the 3-D shape measurement to be Deltaz / z = 0.7%, which was independent of the surface reflection of the measured objects. Regarding the detection of the surface roughness, we could identify four types of delamination conditions with accuracy. The proposed method has great potential for use in a wide range of industrial inspections.