<title>Simple, robust digital controller for the Onsala 20-m radio telescope</title>

Abstract

As part of a general upgrade of the 20 m radio telescope at Onsala Space Observatory a new digital control loop has been implemented using discrete time state space control theory. The model of the telescope is reduced to second order. The controller has been designed for two different modes, corresponding to small (tracking) and large (slewing) reference position changes. For the tracking mode the control includes position error integration and reference value feedforward. For the slewing mode the velocity is controlled with regard to maximum allowed acceleration and control voltage. Incremental encoders on both axes are the only inputs to the system, consequently the velocity is reconstructed via a current estimator. The main objective was to create a robust controller, given the uncertainties in the parameters and non-linearities of the telescope system. The control loop runs on a standard VMEbus CPU- board in parallel with astronomical coordinate transformation routines, display, and watchdog programs. The result is a stand-alone telescope unit which is controlled through high level commands using ethernet or serial communication lines.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.