Philippe Saey

UAF: a generic OPC unified architecture framework

As an emerging Service Oriented Architecture (SOA) specically designed for industrial automation and process control, the OPC Unied Architecture specication should be regarded as an attractive candidate for controlling scientic instrumentation. Even though an industry-backed standard such as OPC UA can oer substantial added value to these projects, its inherent complexity poses an important obstacle for adopting the technology. Building OPC UA applications requires considerable eort, even when taking advantage of a COTS Software Development Kit (SDK). The OPC Unied Architecture Framework (UAF) attempts to reduce this burden by introducing an abstraction layer between the SDK and the application code in order to achieve a better separation of the technical and the functional concerns. True to its industrial origin, the primary requirement of the framework is to maintain interoperability by staying close to the standard specications, and by expecting the minimum compliance from other OPC UA servers and clients. UAF can therefore be regarded as a software framework to quickly and comfortably develop and deploy OPC UA-based applications, while remaining compatible to third party OPC UA-compliant toolkits, servers (such as PLCs) and clients (such as SCADA software). In the rst phase, as covered by this paper, only the client-side of UAF has been tackled in order to transparently handle discovery, session management, subscriptions, monitored items etc. We describe the design principles and internal architecture of our open-source software project, the rst results of the framework running at the Mercator Telescope, and we give a preview of the planned server-side implementation.

Towards a new Mercator Observatory Control System

A new control system is currently being developed for the 1.2-meter Mercator Telescope at the Roque de Los Muchachos Observatory (La Palma, Spain). Formerly based on transputers, the new Mercator Observatory Control System (MOCS) consists of a small network of Linux computers complemented by a central industrial controller and an industrial real-time data communication network. Python is chosen as the high-level language to develop flexible yet powerful supervisory control and data acquisition (SCADA) software for the Linux computers. Specialized applications such as detector control, auto-guiding and middleware management are also integrated in the same Python software package. The industrial controller, on the other hand, is connected to the majority of the field devices and is targeted to run various control loops, some of which are real-time critical. Independently of the Linux distributed control system (DCS), this controller makes sure that high priority tasks such as the telescope motion, mirror support and hydrostatic bearing control are carried out in a reliable and safe way. A comparison is made between different controller technologies including a LabVIEW embedded system, a PROFINET Programmable Logic Controller (PLC) and motion controller, and an EtherCAT embedded PC (soft-PLC). As the latter is chosen as the primary platform for the lower level control, a substantial part of the software is being ported to the IEC 61131-3 standard programming languages. Additionally, obsolete hardware is gradually being replaced by standard industrial alternatives with fast EtherCAT communication. The use of Python as a scripting language allows a smooth migration to the final MOCS: finished parts of the new control system can readily be commissioned to replace the corresponding transputer units of the old control system with minimal downtime. In this contribution, we give an overview of the systems design, implementation details and the current status of the project.

A professional project based learning method in mobile robotics

Due to its high potential and encouraging results, project-based learning emerges as a highly interesting paradigm in the education systems worldwide. Moreover, robotics is an interdisciplinary field where students could learn and apply their skills in mechanics, electronics, computer science, mathematics and control engineering. This paper presents a robotics project-based learning methodology which focuses on collaborating with the industry to design, develop, evaluate, integrate and manage projects designated to be used in real-life applications. This learning method emphasizes and enables the students to apprehend the importance of fulfilling client requirements and the interactions with the client, the suppliers and with the other members of the team. The students, coached by a partner from industry, have the opportunity to apply and to improve their project management skills under a large-scale, highly complex project. This method is being applied since 2008 at ISEN Lille, France, with good results and significant impact.

Using an industrial hardware target for Matlab generated real-time code to control a torsional drive system

Recent developments enable easier transfer of Matlab/Simulink based controller design into real-time code for standard industrial hardware targets. This paper evaluates this design method using state of the art industrial components - embedded controller, high speed remote I/O, Ethernet based industrial network - in a torsional drive system.

Guided independent learning package for advanced topics in electrical engineering, automation and control systems

Ever more students start their master programme with a bachelor degree which does not provide the ideal background for their study. Such students benefit from dedicated help when they have to master advanced topics in automation, control and electrical engineering. Because individual help is adequate but too labour-intensive, a self-study package has been developed by which individual students can select an optimal path to update their required knowledge -depending on their foregoing trajectory- and acquire the required competencies. Topics cover electrical systems (medium and high voltage, power protection, power quality), power electronics (prototyping, electromagnetic compatibility), automation (drive control, drive efficiency, industrial networks and diagnosis). The guided self-study approach consists of a handbook and a digital learning platform; practical hands-on laboratories take place, distributed over several university colleges. A final assessment checks whether students obtained the required competencies. Approximately 12 groups of students, from 9 programmes in 7 institutions, cover 25 topics and laboratory visits yearly.

Developing a PLC-friendly state machine model: lessons learned

Modern Programmable Logic Controllers (PLCs) have become an attractive platform for controlling real-time aspects of astronomical telescopes and instruments due to their increased versatility, performance and standardization. Likewise, vendor-neutral middleware technologies such as OPC Unified Architecture (OPC UA) have recently demonstrated that they can greatly facilitate the integration of these industrial platforms into the overall control system. Many practical questions arise, however, when building multi-tiered control systems that consist of PLCs for low level control, and conventional software and platforms for higher level control. How should the PLC software be structured, so that it can rely on well-known programming paradigms on the one hand, and be mapped to a well-organized OPC UA interface on the other hand? Which programming languages of the IEC 61131-3 standard closely match the problem domains of the abstraction levels within this structure? How can the recent additions to the standard (such as the support for namespaces and object-oriented extensions) facilitate a model based development approach? To what degree can our applications already take advantage of the more advanced parts of the OPC UA standard, such as the high expressiveness of the semantic modeling language that it defines, or the support for events, aggregation of data, automatic discovery, ... ? What are the timing and concurrency problems to be expected for the higher level tiers of the control system due to the cyclic execution of control and communication tasks by the PLCs? We try to answer these questions by demonstrating a semantic state machine model that can readily be implemented using IEC 61131 and OPC UA. One that does not aim to capture all possible states of a system, but rather one that attempts to organize the course-grained structure and behaviour of a system. In this paper we focus on the intricacies of this seemingly simple task, and on the lessons that we’ve learned during the development process of such a “PLC-friendly” state machine model.

Design and first commissioning results of PLC-based control systems for the Mercator telescope

The 1.2m optical Mercator Telescope (based at the Roque de Los Muchachos Observatory at La Palma) is currently in the commissioning phase of a third permanently installed instrument called MAIA (Mercator Advanced Imager for Asteroseismology), a three-channel frame-transfer imager optimized for rapid photometry. Despite having three cryostats, MAIA is designed as a highly compact and portable instrument by using small Stirling-type cryocoolers, and a single PLC in charge of all temperature control loops, cryocooler interaction, telemetry acquisition and other instrument control related tasks. To accommodate MAIA at the Nasmyth B focal station of the telescope, a new mechanism for the tertiary mirror had to be built since the former mechanism only allowed motor controlled access to the Cassegrain and Nasmyth A focal stations. A second PLC has been installed in order to control the two degrees of freedom of this mirror mechanism by interfacing with its motor controllers, high-precision optical encoders, and limit switches. This PLC is not dedicated to the tertiary mirror control but will serve as a general purpose controller for various tasks related to the telescope and the observatory, as part of a new Telescope Control System primarily based on PLCs and OPC UA communication technology. Due to the central location of the PLC inside the observatory, the position control loops of the mirror mechanism are distributed using EtherCAT as the communication fieldbus. In this paper we present the design and the first commissioning results of both the MAIA instrument control and the tertiary mirror control.

Low-cost PROFIBUS DP Slave Shield for embedded controllers

The presented PROFIBUS DP Slave Shield creates a link between a PROFIBUS DP network and a microcontroller or embedded controller. The hardware can be used as an extension module for different embedded controllers with sufficiently fast IO. The system opens possibilities to connect virtual systems or Hardware-In-the-Loop systems running real-time MATLAB models to a PROFIBUS DP network running up to 12 Mbps. Measurement of signal timing and latency shows that the shield itself does not introduce significant latency.

Knowledge-based engineering of a PLC controlled telescope

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.

Design of an Arduino based low-cost error generator for PROFIBUS DP

This paper briefly discusses the design of a low-cost, versatile and configurable error generator for PROFIBUS DP. Using a PROFICORE ULTRA oscilloscope trigger pulse, a small circuit designed around an Arduino MEGA 2560 disrupts messages on the industrial network, without adding an extra slave.