High precision laser tracker system for contactless position measurement

This paper presents the development of a multi laser tracker system (MLTS) used as position feedback sensor, which can track a retro-reflector mounted on the moving kinematic. Four laser trackers build up the MLTS. In the first part of the study, we present the required algorithms that enable the MLTS to measure the position of the retro-reflector. The algorithms include the localization of the retro-reflector, the communication between the laser trackers as well as the tracking control of the laser beam. The localization algorithm is designed to find the retro-reflector within an initialization phase, which is based on an Archimedean spiral derived in polar coordinates. Furthermore, the proposed algorithm allows the single laser tracker to search the retro-reflector in the complete working range. To accelerate the initialization phase a communication channel between the laser trackers of the MTLS is designed. In the case that two laser trackers at least hit the target, the position information is utilized to support the residual laser trackers of the MLTS to localize the retro-reflector. In the second part of this study we present the tracking control to follow the retro-reflector. After the initialization phase is finished the tracking control algorithm is activated to follow the retro-reflector. The model-based control consists of a PID controller in combination with disturbance compensation.