Title: Knowledge-based engineering of a PLC controlled telescope
Authors: Pessemier, Wim
Raskin, Gert
Saey, Philippe
Van Winckel, Hans
Deconinck, Geert
Issue Date: Jun-2016
Host Document: pages:1-11
Conference: SPIE edition:2016 location:Edinburgh date:26/06/2016 - 01/07/2016
Abstract: As the new control system of the Mercator Telescope is being finalized, we can review some technologies and design
methodologies that are advantageous, despite their relative uncommonness in astronomical instrumentation.
Particular for the Mercator Telescope is that it is controlled by a single high-end soft-PLC (Programmable Logic
Controller). Using off-the-shelf components only, our distributed embedded system controls all subsystems of the
telescope such as the pneumatic primary mirror support, the hydrostatic bearing, the telescope axes, the dome,
the safety system, and so on. We show how real-time application logic can be written conveniently in typical
PLC languages (IEC 61131-3) and in C++ (to implement the pointing kernel) using the commercial TwinCAT 3
programming environment. This software processes the inputs and outputs of the distributed system in real-time
via an observatory-wide EtherCAT network, which is synchronized with high precision to an IEEE 1588 (PTP,
Precision Time Protocol) time reference clock. Taking full advantage of the ability of soft-PLCs to run both
real-time and non real-time software, the same device also hosts the most important user interfaces (HMIs or
Human Machine Interfaces) and communication servers (OPC UA for process data, FTP for XML configuration
data, and VNC for remote control). To manage the complexity of the system and to streamline the development
process, we show how most of the software, electronics and systems engineering aspects of the control system
have been modeled as a set of scripts written in a Domain Specific Language (DSL). When executed, these scripts
populate a Knowledge Base (KB) which can be queried to retrieve specific information. By feeding the results of
those queries to a template system, we were able to generate very detailed “browsable” web-based documentation
about the system, but also PLC software code, Python client code, model verification reports, etc. The aim of
this paper is to demonstrate the added value that technologies such as soft-PLCs and DSL-scripts and design
methodologies such as knowledge-based engineering can bring to astronomical instrumentation.
Publication status: published
KU Leuven publication type: IC
Appears in Collections:Electrical Engineering (ESAT) TC, Technology Campuses Ghent and Aalst
Institute of Astronomy
Physics and Astronomy - miscellaneous
Technologiecluster ESAT Elektrotechnische Engineering
ESAT - ELECTA, Electrical Energy Computer Architectures

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