Design and implementation of a general main axis controller for the ESO telescopes

2012 
Most of the real-time control systems at the existing ESO telescopes were developed with "traditional" methods, using general purpose VMEbus electronics, and running applications that were coded by hand, mostly using the C programming language under VxWorks. As we are moving towards more modern design methods, we have explored a model-based design approach for real-time applications in the telescope area, and used the control algorithm of a standard telescope main axis as a first example. We wanted to have a clear work-flow that follows the "correct-by-construction" paradigm, where the implementation is testable in simulation on the development host, and where the testing time spent by debugging on target is minimized. It should respect the domains of control, electronics, and software engineers in the choice of tools. It should be a targetindependent approach so that the result could be deployed on various platforms. We have selected the Mathworks tools Simulink, Stateflow, and Embedded Coder for design and implementation, and LabVIEW with NI hardware for hardware-in-the-loop testing, all of which are widely used in industry. We describe how these tools have been used in order to model, simulate, and test the application. We also evaluate the benefits of this approach compared to the traditional method with respect to testing effort and maintainability. For a specific axis controller application we have successfully integrated the result into the legacy platform of the existing VLT software, as well as demonstrated how to use the same design for a new development with a completely different environment.
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