Communication of the multi laser tracker system used as position feedback sensor

Abstract

This paper presents a communication as well as localization algorithm of a multi laser tracker system (MLTS). The proposed localization algorithm enables the possibility to find a retro-reflector, which is mounted on the Tool Center Point (TCP) of a positioning stage. The MLTS consists of four laser trackers and is used as a high precision feedback sensor in order to provide a contactless measurement of the position. A single laser tracker is build up out of a homodyne laser interferometer as well as a galvanometer scanner and tracks the retro-reflector by utilization of a model-based PID controller. Using the Archimedean spiral a mathematical localization algorithm of the retro-reflector is designed. This approach was chosen due to the fact, that it allows the laser beam to search the retro-reflector in the complete working range of the tracker. The algorithm is derived in polar coordinates and is afterwards transformed into angle coordinates of the galvanometer scanner. In the second part of the presented study, a communication channel between the laser trackers is designed. This enables the possibility to speed up the localization of the retro-reflector significantly, because the position of the TCP is determined using the triangulation. Hence only two laser trackers are required in the first localization step. In the case, that the TCP was found, the information is utilized to support the residual laser trackers of the MLTS to localize the retro-reflector. At the end it is shown by experimental results, that the communication between the laser trackers is effective in order to localize the retro-reflector as fast as possible.