In this study, we develop a 3D coordinate measurement system based on a multilateration technique and an absolute distance metrology for a mobile machine platform. Since the multilateration only uses distance values without angle measurements, it is possible to make 3D coordinate measurements with high accuracy in a large area. In addition, absolute distance is suitable for industrial application because of enabling real-time continuous measurement after the obstruction. The system is composed of four laser tracking stations and a four channel absolute distance meter which is a fs pulse laser based high accuracy absolute distance measurement. In order to measure 3D coordinate of targets, each tracker measures a distance value with real time tracking, and multilateration algorithm is applied to derive 3D coordinate values using the measured distance values. This paper introduces the multiple absolute distances based 3D coordinate measurement system and discusses in detail.
We have developed an absolute distance measurement system for the three-dimensional (3D) coordinate measurement. The final project goal is to develop a multilateration based coordinate measuring system for precise 3D positioning. This coordinate measuring system consists of an absolute distance measuring system and four laser tracking stations. Accurate positioning become possible by determining coordinates using only four distance values instead of angular measurements that cause major errors in the coordinate measurement. In each station, distance is measured by the absolute distance measurement system. There are several advantages to using absolute distance measurement instead of an incremental-type laser interferometer for 3D positioning. If the beam is accidentally broken, incremental-type devices must measure again from the beginning. However, in the absolute distance measurement, the distance of an object can be measured continuously without such a problem. The other is to improve coordinate measurement precision by reducing the number of variables in the multilateration algorithm. In order to measure high precision 3D position in a large area, we have developed a femtosecond laser based absolute distance measurement system. Two-femtosecond lasers and optical cross-correlation technique are applied to improve precision in the distance measurement. This method enables several micrometer-level distance measurement at distances of a few tens of meters.