Citation
Abstract
The article describes the existing 70-m antenna control system, the master equatorial (ME) control system, and their "master-slave" interaction through the autocollimator coupling. The analysis describes the open-loop models of the antenna and ME, obtained through field tests and system identification. Next, the performances of closed-loop systems of the antenna and ME are evaluated. The closedloop performance indicates that a single control algorithm can replace three existing algorithms and that the mode-switching algorithm is no longer required. This new single control algorithm provides significant performance improvement at minimal cost, using primarily existing equipment. Difierent configurations of the antenna and ME are proposed and evaluated. In the existing configuration, the ME is a master: it follows a target, and the antenna is a slave, following the ME. This arrangement causes occasional problems. Since antenna drives were designed for rates smaller than 0.25 deg/s and for accelerations smaller than 0.2 deg/s2, tracking at high rates (e.g., near the keyhole) may leave the antenna outside the autocollimator acquisition range. It causes the breakdown of the ME-antenna optical link and termination of the track. Here we analyze two new ME-antenna configurations. Configuration A is a modification of the existing configuration with new control algorithms and a command preprocessor added, where the antenna follows the ME. Configuration B also includes new control algorithms and a command preprocessor, but unlike Configuration A, the ME is a slave and follows the antenna. It serves, in efiect, as an antenna position sensor. Analysis shows that both configurations are feasible for high-rate tracking using the existing autocollimator. Configuration B, however, is superior as it has much smaller autocollimator errors. Finally, for the existing configuration and for Configurations A, there is no provision for ME wrap direction, while Configuration B would simplify identification of wrong ME wrap and make it easier to derive a recovery scheme. There are two tracking modes: the autocollimator and encoder modes. Switching between the two is necessary when the autocollimator link is terminated. Switching is a concern because it creates jerks and antenna oscillations. Since the switching in the existing configuration causes excessive jerks, a special filter is implemented to suppress them. Analysis shows that switching jerks in Configurations A and B are small; thus, the switching does not need a dedicated algorithm for jerk reduction. A comparison of the characteristics of the existing configuration and Configurations A and B is given.
Keywords
Details
- Volume
- 42-144
- Published
- February 15, 2001
- Pages
- 1–22
- File Size
- 813.0 KB