Calibration of a laser range-finding coordinate-measuring machine

Abstract

An automated, self-calibrating, active-laser-triangulation 3-D surface-measuring system has been designed and built for the acquisition of surface coordinate information. The system is driven by a 50-MHz 80486-based PC/AT computer controlling a laser, a CCD camera, a frame-grabber card, and an encoded motor-driven positioning system. A novel self-calibration procedure is executed in a matter of seconds with the use of a standard sphere and a flat plane. Data acquisition rates of 750 points/s are obtained with an overall system accuracy of ± 0.12 mm using a 75-mm compound lens. Resolutions for the system, using the 75-mm lens, are 480 parts per image width of field in the x axis, 0.6 im in the y axis, and 4096 parts per depth of field in the z axis. The system operates at a standoff of 30 cm, a depth of view of 7 cm, and a width of field of view of 4.5 cm in the close plane and 6 cm in the far plane. The theory and design of the system are presented along with the derivation and implementation of the calibration equations, followed by results of the system's application, and a brief discussion on ways of improving accuracy, resolution, and data acquisition rates.