Active optical primary mirror segmented technology is one of the most critical core technologies for ground-based large optical infrared telescopes. The co-phase segment of mirror surfaces is the fundamental guarantee for giving full play to the optical performance of large primary mirrors. To achieve this goal, the performance of the position actuators presents a huge challenge. Considering the two key indicators of control accuracy and power consumption, we developed a new compound position actuator, which consists of a fine-tuning mechanism and an active offloading mechanism. For this new type of actuator, we have developed a high-performance control system based on the active disturbance rejection control algorithm. The experimental results show that the position actuator system we developed can achieve high-precision position tracking and position control, can meet the index requirements.
The Multi-channel Photometric Survey Telescope (Mephisto) is a wide-field ground based telescope with a 1.6m primary mirror and 2° field of view, proposed by Yunnan University. The telescope will be capable of imaging the northern sky in three colors simultaneously and deliver a colored movie of the universe. The R-C system with lens corrector was adopted as the optical system considering of the image quality requirement, light obscuration and camera arrangement, in which three cubic splitters were adopted for the three channel beams in order to get satisfied image quality over the whole field of view. Dichroic coating on the cubic will lead to nonuniform efficiency on the focal plane due to the polarization problem and wide incident angle, which need calibration. The image quality represented in 80% encircled light energy is around 0.6arcsec. In order to keep the optimal image quality in any operational conditions, a 5-DOF mechanism was designed to actively adjust M2 mirror positions according to the wavefront sensors or by direct star psf. Now the telescope are under developing in Nanjing, expected to be installed at Lijiang observatory before the end of 2021.
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