SMART: the closed-loop control system for LAMOST

In multi-target telescopes, the back-illuminated method is commonly used to correct the position of optical fibers. A design named Special-shaped Micro-lens Aimer for Real-time Targeting (SMART) is presented to correct the position of the science fiber during astronomical observation. The characters are chosen based on the requirement of LAMOST. When the science fiber is offset from the image the target star, the offset direction and the relative offset distance can be identified by the signals in the feedback fiber. Based on the dual rotary fiber positioning structure of LAMOST, a set of position correction algorithms suitable for SMART is designed. The offset direction and the relative offset distance are decomposed into several θ and φ. The position of the science fiber is corrected by stepping movement. The experimental results show that the average farthest distance that the method could correct is 600μm, and 75.9% positioning accuracy under our closed control method can reach 10μm, 94.8% positioning accuracy can reach 20μm, 100% positioning accuracy can reach 30μm. For corrections within the 500μm offset distance, 97.5 % of the correction time is within one minute.