Development of a room laser based real-time alignment monitoring system using an array of photodiodes.

PURPOSE To develop a real-time alignment monitoring system (RAMS) to compensate for the limitations of the conventional room-laser-based alignment system. To verify the feasibility of the RAMS, reproducibility and accuracy tests were conducted. METHODS RAMS was composed of a room laser sensing array (RLSA), an electric circuit, an analog-to-digital converter (ADC), and a control PC. The RLSA was designed to arrange photodiodes in a pattern that results in the RAMS having a resolution of 1mm. The photodiodes were used for quantitative assessment of the alignment condition. To verify the usability of the developed system, we conducted tests of temporal reproducibility, repeatability, and accuracy. RESULTS The results of the temporal reproducibility test suggested that the signal of the RAMS was stable with respect to time. Further, the repeatability test resulted in a maximum coefficient of variance of 1.14%, suggesting that the signal of the RAMS was stable over repeated set-ups. The accuracy test confirmed that the "on" and "off" signals could be distinguished by signal intensity, considering that the "off" signal was below 75% of the "on" signal in every case. In addition, we confirmed that the system can detect 1mm of movement by monitoring the pattern of the "on" and "off" signals. CONCLUSION We developed a room laser based alignment monitoring system. The feasibility test verified that the system is capable of quantitative alignment monitoring in real time. We expect that the RAMS can propose the potential of the room laser based alignment monitoring method.