“Open-Loop” Tracking Interferometer Measurement Using Rotary Axes of a Five-Axis Machine Tool

The tracking interferometer, or the laser tracker, is a laser interferometer with a steering mechanism to change the laser beam direction to automatically follow a retroreflector. Many researchers have studied its application to the multilateration to measure the retroreflector's three-dimensional position. This paper shows that the multilateration measurement can be done by regulating the laser beam toward the command retroreflector position, assuming that the machine tool's positioning error is reasonably small. The machine's rotary axes are used to regulate the laser beam direction. The proposed scheme enables a user to perform the multilateration measurement by using a laser interferometer and the machine's rotary axes only, without requiring any specialized tracking mechanism. An experiment is presented to investigate its measurement performance. The paper's emphasis is on the assessment of its measurement uncertainty, introduced by the elimination of automated tracking mechanism.