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\title{
Industrial solutions trends for the control of HiRes spectrograph@E-ELT
}

   \subtitle{}

\author{
P. \,Di Marcantonio\inst{},
V. \,Baldini\inst{},
G. \,Calderone\inst{},
R. \,Cirami\inst{},
I. \, Coretti\inst{}
\and S. \, Cristiani\inst{}
          }

  \offprints{P. Di Marcantonio}
 

\institute{
Istituto Nazionale di Astrofisica --
Osservatorio Astronomico di Trieste, Via Tiepolo 11,
I-34131 Trieste, Italy;
\email{dimarcan@oats.inaf.it}
}

\authorrunning{Di Marcantonio}


\titlerunning{Industrial solutions trends for E-ELT}

\abstract{
Starting a few years ago, ESO initiated a number of projects aiming to explore 
the possible adoption of industrial standards and commercial off-the-shelf
components (COTS) for the control of future VLT and E-ELT instrumentations. In this context, 
ESPRESSO, the next generation high-stability spectrograph for the VLT and to a certain extent, 
a precursor of HiRes, has adopted since the preliminary design phase those solutions.
Based on the ESPRESSO experience and taking into account the requirements inferred from the 
preli\-mi\-nary Hi-Res studies in terms of both high-level operations as well as low-level control, 
I will present in this paper the current proposal for the HiRes hardware architecture.
\keywords{E-ELT instruments: control electronics -- E-ELT instruments: control software -- COTS -- Industrial standards}
}
\maketitle{}

\section{Introduction}

In the past, due to limited industrial solutions that could fit
astronomical requirements in terms of devices control, there was no
other choice as to develop, ad-hoc, custom
solutions for most of the hardware/software control related aspects. 
This was the case for the ESO VLT Observatory and
in the literature a lot of examples could be found that report   
the same happening for other Observatories \citep{tng}.

Even though requirements were in this way fulfilled, this approach 
has inherently se\-ve\-ral drawbacks: custom solutions are expensive both to 
develop and implement as well as to maintain (especially on a long term).
Engineers that contribute to the initial development not always remain 
in the same working place and in course of the time the ``painful'' process
of know-how transfer could become an issue.
Moreover, for more hardware related aspects, it is well known that technology 
is advancing very fast, and the core components chosen
in the early design days may soon become obsolete yielding 
problems for system maintainability. 

For all these reasons and looking ahead towards the E-ELT era, 
ESO, with the contribution of INAF-OATs, started to investigate
the possible adoption of widely accepted COTS industrial standards
components with the aim of lowering the system procurement and maintenance
costs as well as of mitigating obsolescence by improving components 
interoperability.

In this paper, after describing the outcome of these studies, I'll present the results
applied to the control of the forthcoming HiRes spectrograph for the E-ELT.
As a real, working example, I will also introduce
the ESPRESSO case, the new high-resolution spectrograph for the VLT
\citep{espresso} which could be seen as a test bed for the future HiRes instrument.

\section{The VLT case}

The current VLT standard dedicated to the control of hardware sub-systems
of all the instruments, including telescopes
in Paranal, is hea\-vi\-ly based on the concept of a 
\emph{VME-based Local Control Unit} (shortly, LCU). The VME bus 
(which is, by the way, an industrial international standards) 
interconnects (specific) CPU board with  others dedicated
to perform particular tasks such as motion control, analog/digital signal I/Os etc.
composing what is known as ``the VME crate''.
The actual limitation is that there is a strong software/hardware coupling
in the way ESO has implemented this architecture which prevents to easily change 
the obsolete boards without significant changes in  
the associated software. Several limits in terms of deployment 
and distribution also came out 
when trying to adapt this architecture to the ESPRESSO case 
(and in perspective to the HiRes) which is inherently distributed due to
its capability to use any of the 4 UTs.

The VME-based real-time control architecture concept has been used by ESO
also to control the technical CCDs (shortly, TCCDs) needed for stabilization or
for secondary guiding purposes at the instrument level. The ESO compliant TCCDs, 
although fulfilling the astronomical requirements, are however expensive in terms of costs, 
manufacturing, integration and maintenance especially if compared to 
available COTS devices
one can find on the market which led to seek for other solutions
already for the ESPRESSO case. 

To overcome all these issues, ESO and INAF-OATs
initiated several projects aiming at modernize the VLT
hardware/software control system. The eventually identified technologies 
are currently adopted in ESPRESSO and will very likely constitute the core for the control 
of future E-ELT instruments.

\begin{figure}[b!]
  \resizebox{\hsize}{!}
            {\includegraphics[clip=true]{PLCmodules.eps}}
  \caption{
    \footnotesize
    Example of Beckhoff Automation PLC CPU and modules  
  }
\label{bckplc}
\end{figure}


\section{Industrial trends}

The key point when analyzing industrial trends for the future E-ELT
is the level of ``standardization''. Only components adhering
to wide spread accepted standard (possibly, IEEE certified) 
could overcome or mitigate the obsolescence guaranteeing interoperability
and inter-changeability
considering the long foreseen time span for the E-ELT instrumentation
(at least 10 years from now for first operations, followed by 20-30
years of lifetime).
Based on this, the proposed control of the future HiRes spectrograph,
follows \textbf{standard} industrial trends (where applicable) in the following areas:
\begin{itemize}
\item fieldbus distribution;
\item time synchronization;
\item high performance camera communication;
\item unified architecture;
\item device control.
\end{itemize}
The proposed solutions are not only ``paper-work'', but are currently being applied 
(for the first time at the VLT for a permanent instrument) to the ESPRESSO 
control case; additional information could be found in \citep{cots} 
and references therein.
  
\subsection{Fieldbus distribution}

The current trend in control paradigm departs slightly from the VLT adopted one
by superseding the centralized vision and
by putting more emphasis on distributed architectures interconnecting intelligent nodes
(like PLCs, see Fig. \ref{bckplc}). The interconnections could be achieved by dedicated
networks on which proprietary (or open) protocols run, as well as by dedicated networks 
based on standard Ethernet infrastructure. For our applications, the latter seems 
the most appropriate choice since this will allow to fully reuse future
infrastructure that will be certainly available at the E-ELT not imposing 
additional requirements. 
Example of real-time protocols that could 
run on such Ethernet-based fieldbus systems are EtherCAT (standardized in IEC 61158) 
invented (and used by COTS provided) by Beckhoff Automation or PROFINET used by Siemens.

\subsection{Time synchronization}

Even though at the time of writing this paper no definitive requirements
are imposed by E-ELT to external consortia involved in the
feasibility studies for the instrumentation, the time synchronization
protocol is an exception in this context. Several tests have been made in the past years 
and the final choice is to rely, for time synchronization, 
on the Precision Time Protocol (PTP, standardized as IEEE 1588), which allows to
reach accuracy in the sub-microsecond range. Due to very positive results,
also VLT (and consequently ESPRESSO) is going to adopt the same protocol 
(superseding the current custom solution available at Paranal). Both Siemens
and Beckhoff Automation offer COTS components based on this protocol 
(as well as other vendors) which guarantees interoperability and long lifetime
also looking ahead towards E-ELT instruments.

\subsection{High performance camera communication}

Triggered by the ESPRESSO requirements a market survey was conducted 
to analyze current trends in CCD cameras communication. Again gigabit-Ethernet
based communication has been an imposed initial strict requirement
(as opposed to USB or Camera Link connections) due to limits in cabling scheme 
and possible re-use of existing network infrastructure. Among the very wide
palette of pro\-ducts found, the cameras supporting the 
GigE Vision\textsuperscript{\textregistered} 
protocol introduced in 2006 by (and supported by) the European Machine Vision
Association presented a promising answer to cope both with high performance 
communication needs, as well as interoperability and inter-changeability issues 
and thus could be seen as a valuable candidates for future E-ELT applications;
further details could be found in \citep{cots}.


\begin{figure*}[t!]
  \resizebox{\hsize}{!}
            {\includegraphics[clip=true]{espresso.eps}}
  \caption{
    \footnotesize
    ESPRESSO distributed control architecture based on fieldbus interconnecting Beckhoff Automation COTS components
  }
\label{espr}
\end{figure*}

\subsection{Unified architecture}

OPC Unified architecture (OPC UA) is an industrial (standard) communication protocol
developed by the OPC foundation aimed to connect various kind of systems 
and devices over TCP networks.
The interoperability is achieved through a server-client approach: the server is
(usually) supplied by the hardware manufacturer and represents the interface 
between internal proprietary protocols and OPC UA standard. Through the ``server'', 
control nodes are exposed to outside world in a standardized way which could
be than accessed by dedicated ``clients''. The client implements the OPC UA
communication by means of APIs and allows the user application to access
the exposed nodes. By properly separating the client logic from the 
communication protocol, this approach guarantees
full interoperability:
devices from different vendors could be seamlessly exchanged without affecting
high level software and, vice-versa, high level software could be
improved and/or changed without the need to maintain the initial chosen hardware.
This represent a big achievement if compared to the existing Paranal VME world and
it is at the base of the chosen ESPRESSO control architecture \citep{cots}. 

\subsection{Device control}

Among all the industrial trends analyzed in this paper the control of
the devices will eventually depends on the technological choices imposed by the
E-ELT. Therefore it is still premature to foresee or propose a definitive choice
for the control of the vital parts of an instruments (like motorized 
functions, lamps, sensors) considering also that a design
of HiRes does not exist yet. Nowadays however, PLCs (Programmable Logic Controllers),
are an example of wide spread devices used in this field and represent a valid
choice also looking ahead. They are essentially a hard real-time
systems where outputs are produced based in response of input 
conditions. The way outputs are done is fully programmable and this offer
a huge flexibility allowing with the same PLC to control almost
any functionality the system will require.
PLC programming languages are standardized in IEC61131-3 
open international standard; their usage coupled with the PLCOpen
motion control standard specifications allows to write efficient and
flexible PLC code that is vendor and product-independent as has been
proved in ESPRESSO case (see Fig. \ref{espr}).
   

\section{From ESPRESSO to HiRes}

All the technologies presented in this paper are currently in use in
ESPRESSO which could be reasonable seen as a precursor and test bed 
of HiRes@E-ELT. The main difference is that in HiRes several 
spectrograph modules (instead of one) are foreseen, but for the rest 
the overall conceptual design is quite similar: no movable parts 
inside the modules to guarantee
ultra-stability and complex front-end for properly feeding the light. 
The ultimate lesson learned from ESPRESSO is that relying on COTS solutions
adhering to widespread industrial standards lowers procurement
and maintenance costs and seems the correct way to minimize obsolescence 
by guaranteeing product interoperability and inter-changeability.


\bibliographystyle{aa}
\begin{thebibliography}{}

\bibitem[Baldini et al.(2014)]{cots} Baldini, V.~et al.\ 
2014, Proc. SPIE 9152, 915228 

\bibitem[Duhoux et al.(2014)]{tccd} Duhoux, P.~et al.\ 
2014, Proc. SPIE 9152, 91520I

\bibitem[Ghedina et al.(2014)]{tng} Ghedina, A.~et al.\ 
2014, Proc. SPIE 9145, 914553 

\bibitem[M{\' e}gevand et al.(2014)]{espresso} M{\' e}gevand, D.~et al.\ 
2014, Proc. SPIE 9147, 91471H 

\end{thebibliography}


\end{document}

