Length-measured method for virtual coordinate measurement by laser tracking system

The main methods for measuring geometric parameters used to be static or quasi-static. At present, former static measurement methods with sliding guide have met with great difficulty when measuring the outline and profile of large-scale workpiece or coordinates of objects moving in large dimension. Thus we established the laser tracking system for high precision, large range, non-contact, dynamic measurement. Laser tracking system involves in interdisciplinary knowledge and it can be made up into a new type of computer integral system with both measuring and controlling capacity. With common static coordinate measurement system, such as CMM, the probe must move along the three orthogonal guides equipped with standard rulers, while the laser tracking system has no such objective reference coordinate system. So we put forward the notion of 'Virtual Coordinate System,' that means during the measurement, the coordinate frame is not fixed. On the primary stage of our research, we established practical system for 2D moving target measurement in real-time. In order to measure the coordinate of the target, three tracking stations are used, which only measure length changes between the target and stations each, with no angles are measured. By solving non- linear least-square equations, the target and the tracking stations' coordinate can be attained respectively. We also present the optical design and the tracking controlling system based on the PID controlling principle. At the end of this paper, we will give the experiment result of the system.