A New Controller for the Acquisition and Guiding Unit for the Gemini South Telescope : New architecture and control schemes to use Power PMAC

Abstract: When the Gemini Telescopes were built 20 years ago, the control architecture for the high precision requirements was the same for all systems. It consisted of VME cards, Programmable Multi Axis Con-trollers (PMAC) with specific amplifiers and a central computer. It was the state of the art. Nevertheless such an infrastructure takes up a lot of space. It is also difficult to maintain mainly because of obsoles-cence and the lack of support of the engineers who do not consider this system adapted to the control.The code, documentation and wiring were complex and not fully understood. Thus, it led the Gemini Observatory to consider the acquisition of a new controller for one of the most critical unit: the Acquisition and Guidance (A&G). To address these issues, I propose an alternative control system which will not only solve the current issues but also improve the performance. The new generation of controller from Delta Tau is more efficient, more reliable and with a high level of integration. The main concern of compatibility with the current motors and encoders of the Acquisition and Guidance has been solved by testing 27 motors out of the 29 present in the unit. Results were obtained using a test bench and mechanical systems built during the internship. A fully functional test bench has been delivered. Furthermore, a new control scheme for the backlash compensation is proposed. It consumes half the energy of the current one, is nearly two times faster and without oscillations. This will reduce the frequency of maintenance and the reliability of the unit. A cross gantry control for the skew compensation of the Science fold leads to a smarter control of the differences between the motors to prevent the mirror from breaking. Finally, an identification technique for the tilt mechanism provides more robustness and takes into account the ageing of the equipment.