ESO's ELT M4 dynamic control and computational performance

The ESO's ELT M4 adaptive mirror is based on the large, contactless voice-coil adaptive mirror technology, with 5352 actuators controlling the shape of the six mirror segments [1]. The control concept is still based on a closed loop control with co-located capacitive sensors that measure in real time the gap between the controlled thin mirror and the reference body; feedforward terms are implemented to improve the command response bandwidth. Several control features, in particular related to the feedforward terms, have been improved in the past years and deployed on the M4. The co-located control, and also the global control terms together with saturation control and feedback to the Real Time Reconstructor, are executed by the hardware processors (FPGAs) that are embedded in each control subsystem, called brick. The highly parallel computational scheme allows achieving a very remarkable computational throughput exploiting the available processing power. We present here the control architecture and the dynamic performances measured on the 222 actuators Demonstration Prototype, together with the processing latency and jitter achieved on a significant test setup that has been assembled for testing before starting final system integration.