Control systems of the large millimeter telescope

This paper presents the analysis results (in terms of settling time, bandwidth, and servo error in wind disturbances) of four control systems designed for the Large Millimeter Telescope (LMT). The first system, called PP, consists of the proportional and integral (PI) controllers in the rate and position loops, and is widely used in the antenna and radio telescope industry. The analysis shows that the PP control system's performance is remarkably good when compared to similar control systems applied to typical antennas. This performance is achieved because the LMT structure is exceptionally rigid; however, it does not meet the stringent LMT pointing requirements. The second system, called PL, consists of the PI controller in the rate loop, and the linear-quadratic-Gaussian (LQG) controller in the position loop. This type of controller is implemented in the NASA Deep Space Network antennas, where pointing accuracy is twice that of the PP control system. The third system, called LP, consists of the LQG controller in the rate loop, and the proportional-integral-derivative (PID) controller in the position loop. This type of loop has not been yet implemented at known antennas or radio telescopes, but the analysis shows that its pointing accuracy is the ten times better than the PP control system. The fourth system, called LL, consists of the LQG controller in both the rate loop and the position loop. It is the best of the four, with accuracy 250 times better than the PP system. It is thus worth further investigation to identify implementation challenges for telescopes with high pointing requirements.