CANopen control for NAOMI in the auxiliary telescopes of the VLTI

NAOMI, the New Adaptive Optics Module for Interferometry is one of the latest additions to the Auxiliary Telescopes of the VLTI system in the Paranal observatory. The changeling task to bring new advanced features was given by the reduced space and wiring restrictions of the current telescope's infrastructure . New cables could not be installed and the exiting ones had slightly different pin-outs for each of the four Auxiliary Telescopes. These complications were overcome by using the CANopen protocol which offers low complexity with minimal wiring and robust noise immunity. Only two wires for data transfer and capable of very low baud-rates (250 k-bit/sec), allowing to use the low-frequency exiting cables. Additionally CANopen brought valuable simplicity to the integration process, like motor control for optical alignment without a PLC, multi-point access to the control bus, transmission quality tests and straightforward Beckhoff PLC integration.