A laser tracking interferometer system (LTS), which is capable of measuring 3-D coordinate, has been developed at AIST. The LTS makes use of the principle of laser trilateration i.e. the position of the target is determined by three lengths from three base points. Recently, we developed a compact and accurate laser tracker. The key component of the tracker is a hemispherical mirror; a hemisphere and a small sphere are connected with a rod. The plane surface of the hemisphere is mirror coated and the laser beam is reflected on the mirror. By moving the small sphere by an X-Y stage, the angle of the mirror can be changed; hence the direction of the laser beam is also changed. The hemisphere sits on three small balls, so that the center position of the hemisphere does not shift. In experiments, the mechanical error of the laser tracker is smaller than 0.5 mm. The measurement accuracy of the LTS was assessed by comparing it to a high precision coordinate measuring machine (CMM). The accuracy of our LTS was about 2~3 mm, which is much better than other commercial LTSs.

We will apply this system for calibrating CMMs (large scale or low cost) and evaluating dynamic characteristics of industrial robots.

AIST Today Vol. 1, No. 7 (2001) 12