Multiple-sensor integration for rapid and high-precision coordinate metrology

In this paper, the development of a multiple-sensor coordinate measuring system is introduced and its applications to automated part localization and rapid surface digitization are experimentally demonstrated. The developed multiple-sensor coordinate measuring machine (CMM) is characterized by an integrated use of a high-precision CMM equipped with a motorized touch probe, and a three-dimensional (3-D) active vision system, advanced computational software, and the associated electronics. The 3-D active vision system consists of three components: a charge-coupled device camera, a digital light professing (DLP) projector, and a personal computer with an image processing board. The DLP projector is based on the innovative digital micro-mirror device, which can be controlled by the personal computer to project various structured light patterns. With the flexibility of the DLP projector, the orientation, range, density, and colors of the structured light patterns are programmable and adaptable to different needs. Consequently, the active vision system is capable of digitizing surface coordinates of objects having multiple features. With the coordinate data acquired using the 3-D active vision system, intelligent feature recognition algorithms can be applied to extract the global surface information of the object. The obtained information can be subsequently used to automatically guide the touch probe for rapid coordinate data acquisition and to strategically control the coordinate measuring machine for high precision sampling of critical surface area. In this paper, the information automation for the multiple-sensor integrated system is demonstrated in part localization when computer-aided design models are available, and rapid and high-precision surface digitization in reverse engineering. By integrating the developed technology with the state of the art equipment, a highly automated high-speed high-precision 3-D coordinate acquisition system can be developed. It has potential applications in a whole spectrum of manufacturing problems with a major impact on metrology, inspection, and reverse engineering.