HERMES travels by CAN bus

Lewis G. Waller; Keith Shortridge; Tony J. Farrell; Minh Vuong; Rolf Muller; Andrew I. Sheinis

doi:10.1117/12.2055022

18 July 2014 HERMES travels by CAN bus

Lewis G. Waller, Keith Shortridge, Tony J. Farrell, Minh Vuong, Rolf Muller, Andrew I. Sheinis

Proceedings Volume 9152, Software and Cyberinfrastructure for Astronomy III; 91522A (2014) https://doi.org/10.1117/12.2055022
Event: SPIE Astronomical Telescopes + Instrumentation, 2014, Montréal, Quebec, Canada

Abstract

The new HERMES spectrograph represents the first foray by AAO into the use of commercial off-the-shelf industrial field bus technology for instrument control, and we regard the final system, with its relatively simple wiring requirements, as a great success. However, both software and hardware teams had to work together to solve a number of problems integrating the chosen CANopen/CAN bus system into our normal observing systems. A Linux system running in an industrial PC chassis ran the HERMES control software, using a PCI CAN bus interface connected to a number of distributed CANopen/CAN bus I/O devices and servo amplifiers. In the main, the servo amplifiers performed impressively, although some experimentation with homing algorithms was required, and we hit a significant hurdle when we discovered that we needed to disable some of the encoders used during observations; we learned a lot about how servo amplifiers respond when their encoders are turned off, and about how encoders react to losing power. The software was based around a commercial CANopen library from Copley Controls. Early worries about how this heavily multithreaded library would work with our standard data acquisition system led to the development of a very low-level CANopen software simulator to verify the design. This also enabled the software group to develop and test almost all the control software well in advance of the construction of the hardware. In the end, the instrument went from initial installation at the telescope to successful commissioning remarkably smoothly.

Citation Download Citation

Lewis G. Waller, Keith Shortridge, Tony J. Farrell, Minh Vuong, Rolf Muller, and Andrew I. Sheinis "HERMES travels by CAN bus", Proc. SPIE 9152, Software and Cyberinfrastructure for Astronomy III, 91522A (18 July 2014); https://doi.org/10.1117/12.2055022

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KEYWORDS

Spectrographs

Amplifiers

Computer programming

Servomechanisms

Control systems

Cameras

Device simulation

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