Multiple-line full-field laser-camera range sensor

摘要

Optical methods based on structured-light projection are typically used for three-dimensional (3D) surface-geometry measurement as the methods are non-contacting. Single-line projection techniques are most commonly used; however, they require a translation or rotation stage to scan the range-sensor head across the object surface. Phase-shifting fringe projection full-field methods have been commonly used with projection of two to four fringe patterns during measurement. Simultaneous projection of multiple structured-light lines is a practical alternative full-field method as it offers the advantage of range image capture using a single image or simultaneously captured image pair. This paper presents a multiple-line full-field laser-camera range sensor, calibrated using a novel 2-D image-plane to 3D-object-space mapping. The sensor employs a 31 laser-line projector and two CCD cameras. To calibrate the system, 31 laser lines were simultaneously projected onto a black plate with horizontal line markings of known spacing. Images were acquired with the plate at 6 known depths over a 200 mm range of depth. After conical diffraction correction was applied to the object-space coordinates for all points, a mapping of 2D image coordinates to the known 3D object-space coordinates was carried out for each of the 31 laser projections using closed-form Bezier surface fitting. The mean of the absolute value of the calibration errors were 0.010 mm and 0.010 mm in X, 0.598 and 0.465 mm in Y (vertical), and 0.190 mm and 0.189 mm in Z (depth), for the two cameras, respectively. The method has the advantage that no knowledge of the geometry of the laser-camera setup is required and accurate alignment of the laser and camera is not necessary. The calibration technique also accounts for any lens distortion from the low cost cameras.