Development of photoelectric edge sensors for closed-loop active reflectors

With increasing demands on large-area deep surveys of submillimeter galaxies, a 60-meter single dish submillimeter telescope has been recently proposed [1]. In order to maintain a high level of surface accuracy for the 60-meter main reflector under the high-altitude site conditions, a high-performance closed-loop active surface control technology based on optoelectronic edge sensors has been developed. Two sensor types have been proposed. The first sensor is composed of a laser diode(LD) and a position sensing sensor (PSD), and the sensor error after nonlinear calibration is less than 0.6µm. The second sensor is composed of a LED and a CMOS with position accuracy and repeatability error better than 0.02 pixel completely(0.13µm), By placing the edge sensors across the gaps between adjacent composite panels, six-DOF panel position parameters can be determined with 2 edge sensors installed on each gap. Numerical simulation results show that such a sensor network achieves an overall surface measurement accuracy of 15µm with single sensor noise of 0.5µm, showing good application potential in real-time monitoring and maintenance of surface figure for large submillimeter telescopes.