Change LaTeX journal files => IOP

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% sage_latex_guidelines.tex V1.20, 14 January 2017
\documentclass[Afour,sageh,times]{sagej}
\usepackage{moreverb,url}
\usepackage[colorlinks,bookmarksopen,bookmarksnumbered,citecolor=red,urlcolor=red]{hyperref}
\newcommand\BibTeX{{\rmfamily B\kern-.05em \textsc{i\kern-.025em b}\kern-.08em
T\kern-.1667em\lower.7ex\hbox{E}\kern-.125emX}}
\def\volumeyear{2016}
\begin{document}
\runninghead{Smith and Wittkopf}
\title{A demonstration of the \LaTeXe\ class file for
\itshape{SAGE Publications}}
\author{Alistair Smith\affilnum{1} and Hendrik Wittkopf\affilnum{2}}
\affiliation{\affilnum{1}Sunrise Setting Ltd, UK\\
\affilnum{2}SAGE Publications Ltd, UK}
\corrauth{Alistair Smith, Sunrise Setting Ltd
Brixham Laboratory,
Freshwater Quarry,
Brixham, Devon,
TQ5~8BA, UK.}
\email{alistair.smith@sunrise-setting.co.uk}
\begin{abstract}
This paper describes the use of the \LaTeXe\
\textsf{\journalclass} class file for setting papers to be
submitted to a \textit{SAGE Publications} journal.
The template can be downloaded \href{http://www.uk.sagepub.com/repository/binaries/SAGE LaTeX template.zip}{here}.
\end{abstract}
\keywords{Class file, \LaTeXe, \textit{SAGE Publications}}
\maketitle
\section{Introduction}
Many authors submitting to research journals use \LaTeXe\ to
prepare their papers. This paper describes the
\textsf{\journalclass} class file which can be used to convert
articles produced with other \LaTeXe\ class files into the correct
form for submission to \textit{SAGE Publications}.
The \textsf{\journalclass} class file preserves much of the
standard \LaTeXe\ interface so that any document which was
produced using the standard \LaTeXe\ \textsf{article} style can
easily be converted to work with the \textsf{\journalclassshort}
style. However, the width of text and typesize will vary from that
of \textsf{article.cls}; therefore, \textit{line breaks will change}
and it is likely that displayed mathematics and tabular material
will need re-setting.
In the following sections we describe how to lay out your code to
use \textsf{\journalclass} to reproduce much of the typographical look of
the \textit{SAGE} journal that you wish to submit to. However, this paper is not a guide to
using \LaTeXe\ and we would refer you to any of the many books
available (see, for example, \cite{R1}, \cite{R2} and \cite{R3}).
\section{The three golden rules}
Before we proceed, we would like to stress \textit{three golden
rules} that need to be followed to enable the most efficient use
of your code at the typesetting stage:
\begin{enumerate}
\item[(i)] keep your own macros to an absolute minimum;
\item[(ii)] as \TeX\ is designed to make sensible spacing
decisions by itself, do \textit{not} use explicit horizontal or
vertical spacing commands, except in a few accepted (mostly
mathematical) situations, such as \verb"\," before a
differential~d, or \verb"\quad" to separate an equation from its
qualifier;
\item[(iii)] follow the journal reference style.
\end{enumerate}
\section{Getting started} The \textsf{\journalclassshort} class file should run
on any standard \LaTeXe\ installation. If any of the fonts, style
files or packages it requires are missing from your installation,
they can be found on the \textit{\TeX\ Collection} DVDs or downloaded from
CTAN.
\begin{figure*}
\setlength{\fboxsep}{0pt}%
\setlength{\fboxrule}{0pt}%
\begin{center}
\begin{boxedverbatim}
\documentclass[<options>]{sagej}
\begin{document}
\runninghead{<Author surnames>}
\title{<Initial capital only>}
\author{<An Author\affilnum{1},
Someone Else\affilnum{2} and
Perhaps Another\affilnum{1}>}
\affiliation{<\affilnum{1}First and third authors' affiliation\\
\affilnum{2}Second author affiliation>}
\corrauth{<Corresponding author's name and full postal address>}
\email{<Corresponding author's email address>}
\begin{abstract}
<Text>
\end{abstract}
\keywords{<List keywords>}
\maketitle
\section{Introduction}
.
.
.
\end{boxedverbatim}
\end{center}
\caption{Example header text.\label{F1}}
\end{figure*}
\section{The article header information}
The heading for any file using \textsf{\journalclass} is shown in
Figure~\ref{F1}. You must select options for the trim/text area and
the reference style of the journal you are submitting to.
The choice of \verb+options+ are listed in Table~\ref{T1}.
\begin{table}[h]
\small\sf\centering
\caption{The choice of options.\label{T1}}
\begin{tabular}{lll}
\toprule
Option&Trim and font size&Columns\\
\midrule
\texttt{shortAfour}& 210 $\times$ 280 mm, 10pt& Double column\\
\texttt{Afour} &210 $\times$ 297 mm, 10pt& Double column\\
\texttt{MCfour} &189 $\times$ 246 mm, 10pt& Double column\\
\texttt{PCfour} &170 $\times$ 242 mm, 10pt& Double column\\
\texttt{Royal} &156 $\times$ 234 mm, 10pt& Single column\\
\texttt{Crown} &7.25 $\times$ 9.5 in, 10pt&Single column\\
\texttt{Review} & 156 $\times$ 234 mm, 12pt & Single column\\
\bottomrule
\end{tabular}\\[10pt]
\begin{tabular}{ll}
\toprule
Option&Reference style\\
\midrule
\texttt{sageh}&SAGE Harvard style (author-year)\\
\texttt{sagev}&SAGE Vancouver style (superscript numbers)\\
\texttt{sageapa}&APA style (author-year)\\
\bottomrule
\end{tabular}
\end{table}
For example, if your journal is short A4 sized, uses Times fonts and has Harvard style references then you would need\\
{\small\verb+\documentclass[ShortAfour,times,sageh]{sagej}+}
Most \textit{SAGE} journals are published using Times fonts but if for any reason you have a problem using Times you can
easily resort to Computer Modern fonts by removing the
\verb"times" option.
\subsection{`Review' option}
Some journals (for example, \emph{Journal of the Society for Clinical Trials}) require that
papers are set single column and with a larger font size to help with the review process.
If this is a requirement for the journal that you are submitting to, just add the \verb+Review+ option to the \verb+\documenclass[]{sagej}+ line.
\subsection{Remarks}
\begin{enumerate}
\item[(i)] In \verb"\runninghead" use `\textit{et~al.}' if there
are three or more authors.
\item[(ii)] For multiple author papers please note the use of \verb"\affilnum" to
link names and affiliations. The corresponding author details need to be included using the
\verb+\corrauth+ and \verb+\email+ commands.
\item[(iii)] For submitting a double-spaced manuscript, add
\verb"doublespace" as an option to the documentclass line.
\item[(iv)] The abstract should be capable of standing by itself,
in the absence of the body of the article and of the bibliography.
Therefore, it must not contain any reference citations.
\item[(v)] Keywords are separated by commas.
\item[(vi)] If you are submitting to a \textit{SAGE} journal that requires numbered sections (for example, IJRR), please add the command
\verb+\setcounter{secnumdepth}{3}+ just above the \verb+\begin{document}+ line.
\end{enumerate}
\section{The body of the article}
\subsection{Mathematics} \textsf{\journalclass} makes the full
functionality of \AmS\/\TeX\ available. We encourage the use of
the \verb"align", \verb"gather" and \verb"multline" environments
for displayed mathematics. \textsf{amsthm} is used for setting
theorem-like and proof environments. The usual \verb"\newtheorem"
command needs to be used to set up the environments for your
particular document.
\subsection{Figures and tables} \textsf{\journalclass} includes the
\textsf{graphicx} package for handling figures.
Figures are called in as follows:
\begin{verbatim}
\begin{figure}
\centering
\includegraphics{<figure name>}
\caption{<Figure caption>}
\end{figure}
\end{verbatim}
For further details on how to size figures, etc., with the
\textsf{graphicx} package see, for example, \cite{R1}
or \cite{R3}.
The standard coding for a table is shown in Figure~\ref{F2}.
\begin{figure}
\setlength{\fboxsep}{0pt}%
\setlength{\fboxrule}{0pt}%
\begin{center}
\begin{boxedverbatim}
\begin{table}
\small\sf\centering
\caption{<Table caption.>}
\begin{tabular}{<table alignment>}
\toprule
<column headings>\\
\midrule
<table entries
(separated by & as usual)>\\
<table entries>\\
.
.
.\\
\bottomrule
\end{tabular}
\end{table}
\end{boxedverbatim}
\end{center}
\caption{Example table layout.\label{F2}}
\end{figure}
\subsection{Cross-referencing}
The use of the \LaTeX\ cross-reference system
for figures, tables, equations, etc., is encouraged
(using \verb"\ref{<name>}" and \verb"\label{<name>}").
\subsection{End of paper special sections}
Depending on the requirements of the journal that you are submitting to,
there are macros defined to typeset various special sections.
The commands available are:
\begin{verbatim}
\begin{acks}
To typeset an
"Acknowledgements" section.
\end{acks}
\end{verbatim}
\begin{verbatim}
\begin{biog}
To typeset an
"Author biography" section.
\end{biog}
\end{verbatim}
\begin{verbatim}
\begin{biogs}
To typeset an
"Author Biographies" section.
\end{biogs}
\end{verbatim}
%\newpage
\begin{verbatim}
\begin{dci}
To typeset a "Declaration of
conflicting interests" section.
\end{dci}
\end{verbatim}
\begin{verbatim}
\begin{funding}
To typeset a "Funding" section.
\end{funding}
\end{verbatim}
\begin{verbatim}
\begin{sm}
To typeset a
"Supplemental material" section.
\end{sm}
\end{verbatim}
\subsection{Endnotes}
Most \textit{SAGE} journals use endnotes rather than footnotes, so any notes should be coded as \verb+\endnote{<Text>}+.
Place the command \verb+\theendnotes+ just above the Reference section to typeset the endnotes.
To avoid any confusion for papers that use Vancouver style references, footnotes/endnotes should be edited into the text.
\subsection{References}
Please note that the files \textsf{SageH.bst} and \textsf{SageV.bst} are included with the class file
for those authors using \BibTeX.
The files work in a completely standard way, and you just need to uncomment one of the lines in the below example depending on what style you require:
\begin{verbatim}
%%Harvard (name/date)
%\bibliographystyle{SageH}
%%Vancouver (numbered)
%\bibliographystyle{SageV}
\bibliography{<YourBibfile.bib>}
\end{verbatim}
and remember to add the relevant option to the \verb+\documentclass[]{sagej}+ line as listed in Table~\ref{T1}.
%\section{Support for \textsf{\journalclass}}
%We offer on-line support to participating authors. Please contact
%us via e-mail at \dots
%
%We would welcome any feedback, positive or otherwise, on your
%experiences of using \textsf{\journalclass}.
\section{Copyright statement}
Please be aware that the use of this \LaTeXe\ class file is
governed by the following conditions.
\subsection{Copyright}
Copyright \copyright\ \volumeyear\ SAGE Publications Ltd,
1 Oliver's Yard, 55 City Road, London, EC1Y~1SP, UK. All
rights reserved.
\subsection{Rules of use}
This class file is made available for use by authors who wish to
prepare an article for publication in a \textit{SAGE Publications} journal.
The user may not exploit any
part of the class file commercially.
This class file is provided on an \textit{as is} basis, without
warranties of any kind, either express or implied, including but
not limited to warranties of title, or implied warranties of
merchantablility or fitness for a particular purpose. There will
be no duty on the author[s] of the software or SAGE Publications Ltd
to correct any errors or defects in the software. Any
statutory rights you may have remain unaffected by your
acceptance of these rules of use.
\begin{acks}
This class file was developed by Sunrise Setting Ltd,
Brixham, Devon, UK.\\
Website: \url{http://www.sunrise-setting.co.uk}
\end{acks}
\begin{thebibliography}{99}
\bibitem[Kopka and Daly(2003)]{R1}
Kopka~H and Daly~PW (2003) \textit{A Guide to \LaTeX}, 4th~edn.
Addison-Wesley.
\bibitem[Lamport(1994)]{R2}
Lamport~L (1994) \textit{\LaTeX: a Document Preparation System},
2nd~edn. Addison-Wesley.
\bibitem[Mittelbach and Goossens(2004)]{R3}
Mittelbach~F and Goossens~M (2004) \textit{The \LaTeX\ Companion},
2nd~edn. Addison-Wesley.
\end{thebibliography}
\end{document}

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%% %% This is file `iopams.sty' %% File to include AMS fonts and extra definitions for bold greek %% characters for use with iopart.cls %% \NeedsTeXFormat{LaTeX2e} \ProvidesPackage{iopams}[1997/02/13 v1.0] \RequirePackage{amsgen}[1995/01/01] \RequirePackage{amsfonts}[1995/01/01] \RequirePackage{amssymb}[1995/01/01] \RequirePackage{amsbsy}[1995/01/01] % \iopamstrue % \newif\ifiopams in iopart.cls & iopbk2e.cls % % allows optional text to be in author guidelines % % Bold lower case Greek letters % \newcommand{\balpha}{\boldsymbol{\alpha}} \newcommand{\bbeta}{\boldsymbol{\beta}} \newcommand{\bgamma}{\boldsymbol{\gamma}} \newcommand{\bdelta}{\boldsymbol{\delta}} \newcommand{\bepsilon}{\boldsymbol{\epsilon}} \newcommand{\bzeta}{\boldsymbol{\zeta}} \newcommand{\bfeta}{\boldsymbol{\eta}} \newcommand{\btheta}{\boldsymbol{\theta}} \newcommand{\biota}{\boldsymbol{\iota}} \newcommand{\bkappa}{\boldsymbol{\kappa}} \newcommand{\blambda}{\boldsymbol{\lambda}} \newcommand{\bmu}{\boldsymbol{\mu}} \newcommand{\bnu}{\boldsymbol{\nu}} \newcommand{\bxi}{\boldsymbol{\xi}} \newcommand{\bpi}{\boldsymbol{\pi}} \newcommand{\brho}{\boldsymbol{\rho}} \newcommand{\bsigma}{\boldsymbol{\sigma}} \newcommand{\btau}{\boldsymbol{\tau}} \newcommand{\bupsilon}{\boldsymbol{\upsilon}} \newcommand{\bphi}{\boldsymbol{\phi}} \newcommand{\bchi}{\boldsymbol{\chi}} \newcommand{\bpsi}{\boldsymbol{\psi}} \newcommand{\bomega}{\boldsymbol{\omega}} \newcommand{\bvarepsilon}{\boldsymbol{\varepsilon}} \newcommand{\bvartheta}{\boldsymbol{\vartheta}} \newcommand{\bvaromega}{\boldsymbol{\varomega}} \newcommand{\bvarrho}{\boldsymbol{\varrho}} \newcommand{\bvarzeta}{\boldsymbol{\varsigma}} %NB really sigma \newcommand{\bvarsigma}{\boldsymbol{\varsigma}} \newcommand{\bvarphi}{\boldsymbol{\varphi}} % % Bold upright capital Greek letters % \newcommand{\bGamma}{\boldsymbol{\Gamma}} \newcommand{\bDelta}{\boldsymbol{\Delta}} \newcommand{\bTheta}{\boldsymbol{\Theta}} \newcommand{\bLambda}{\boldsymbol{\Lambda}} \newcommand{\bXi}{\boldsymbol{\Xi}} \newcommand{\bPi}{\boldsymbol{\Pi}} \newcommand{\bSigma}{\boldsymbol{\Sigma}} \newcommand{\bUpsilon}{\boldsymbol{\Upsilon}} \newcommand{\bPhi}{\boldsymbol{\Phi}} \newcommand{\bPsi}{\boldsymbol{\Psi}} \newcommand{\bOmega}{\boldsymbol{\Omega}} % % Bold versions of miscellaneous symbols % \newcommand{\bpartial}{\boldsymbol{\partial}} \newcommand{\bell}{\boldsymbol{\ell}} \newcommand{\bimath}{\boldsymbol{\imath}} \newcommand{\bjmath}{\boldsymbol{\jmath}} \newcommand{\binfty}{\boldsymbol{\infty}} \newcommand{\bnabla}{\boldsymbol{\nabla}} \newcommand{\bdot}{\boldsymbol{\cdot}} % % Symbols for caption % \renewcommand{\opensquare}{\mbox{$\square$}} \renewcommand{\opentriangle}{\mbox{$\vartriangle$}} \renewcommand{\opentriangledown}{\mbox{$\triangledown$}} \renewcommand{\opendiamond}{\mbox{$\lozenge$}} \renewcommand{\fullsquare}{\mbox{$\blacksquare$}} \newcommand{\fulldiamond}{\mbox{$\blacklozenge$}} \newcommand{\fullstar}{\mbox{$\bigstar$}} \newcommand{\fulltriangle}{\mbox{$\blacktriangle$}} \newcommand{\fulltriangledown}{\mbox{$\blacktriangledown$}} \endinput %% %% End of file `iopams.sty'.

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%% %% This is file `iopart10.clo' %% %% This file is distributed in the hope that it will be useful, %% but WITHOUT ANY WARRANTY; without even the implied warranty of %% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. %% %% \CharacterTable %% {Upper-case \A\B\C\D\E\F\G\H\I\J\K\L\M\N\O\P\Q\R\S\T\U\V\W\X\Y\Z %% Lower-case \a\b\c\d\e\f\g\h\i\j\k\l\m\n\o\p\q\r\s\t\u\v\w\x\y\z %% Digits \0\1\2\3\4\5\6\7\8\9 %% Exclamation \! Double quote \" Hash (number) \# %% Dollar \$ Percent \% Ampersand \& %% Acute accent \' Left paren \( Right paren \) %% Asterisk \* Plus \+ Comma \, %% Minus \- Point \. Solidus \/ %% Colon \: Semicolon \; Less than \< %% Equals \= Greater than \> Question mark \? %% Commercial at \@ Left bracket \[ Backslash \\ %% Right bracket \] Circumflex \^ Underscore \_ %% Grave accent \` Left brace \{ Vertical bar \| %% Right brace \} Tilde \~} \ProvidesFile{iopart10.clo}[1997/01/13 v1.0 IOP Book file (size option)] \renewcommand\normalsize{% \@setfontsize\normalsize\@xpt\@xiipt \abovedisplayskip 10\p@ \@plus2\p@ \@minus5\p@ \abovedisplayshortskip \z@ \@plus3\p@ \belowdisplayshortskip 6\p@ \@plus3\p@ \@minus3\p@ \belowdisplayskip \abovedisplayskip \let\@listi\@listI} \normalsize \newcommand\small{% \@setfontsize\small\@ixpt{11}% \abovedisplayskip 8.5\p@ \@plus3\p@ \@minus4\p@ \abovedisplayshortskip \z@ \@plus2\p@ \belowdisplayshortskip 4\p@ \@plus2\p@ \@minus2\p@ \def\@listi{\leftmargin\leftmargini \topsep 4\p@ \@plus2\p@ \@minus2\p@ \parsep 2\p@ \@plus\p@ \@minus\p@ \itemsep \parsep}% \belowdisplayskip \abovedisplayskip } \newcommand\footnotesize{% \@setfontsize\footnotesize\@viiipt{9.5}% \abovedisplayskip 6\p@ \@plus2\p@ \@minus4\p@ \abovedisplayshortskip \z@ \@plus\p@ \belowdisplayshortskip 3\p@ \@plus\p@ \@minus2\p@ \def\@listi{\leftmargin\leftmargini \topsep 3\p@ \@plus\p@ \@minus\p@ \parsep 2\p@ \@plus\p@ \@minus\p@ \itemsep \parsep}% \belowdisplayskip \abovedisplayskip } \newcommand\scriptsize{\@setfontsize\scriptsize\@viipt\@viiipt} \newcommand\tiny{\@setfontsize\tiny\@vpt\@vipt} \newcommand\large{\@setfontsize\large\@xiipt{14}} \newcommand\Large{\@setfontsize\Large\@xivpt{18}} \newcommand\LARGE{\@setfontsize\LARGE\@xviipt{22}} \newcommand\huge{\@setfontsize\huge\@xxpt{25}} \newcommand\Huge{\@setfontsize\Huge\@xxvpt{30}} \if@twocolumn \setlength\parindent{12\p@} \else \setlength\parindent{15\p@} \fi \setlength\headheight{12\p@} \setlength\headsep {12\p@} \setlength\topskip {10\p@} \setlength\footskip{20\p@} \setlength\maxdepth{.5\topskip} \setlength\@maxdepth\maxdepth \setlength\textwidth{31pc} \setlength\textheight{49pc} \setlength\oddsidemargin {24\p@} \setlength\evensidemargin {24\p@} \setlength\marginparwidth {72\p@} \setlength\marginparsep {10\p@} \setlength\marginparpush{5\p@} \setlength\topmargin{\z@} \setlength\footnotesep{6.65\p@} \setlength{\skip\footins} {9\p@ \@plus 4\p@ \@minus 2\p@} \setlength\floatsep {12\p@ \@plus 2\p@ \@minus 2\p@} \setlength\textfloatsep {20\p@ \@plus 2\p@ \@minus 4\p@} \setlength\intextsep {12\p@ \@plus 2\p@ \@minus 2\p@} \setlength\dblfloatsep {12\p@ \@plus 2\p@ \@minus 2\p@} \setlength\dbltextfloatsep{20\p@ \@plus 2\p@ \@minus 4\p@} \setlength\@fptop{0\p@} \setlength\@fpsep{8\p@ \@plus 2fil} \setlength\@fpbot{0\p@} \setlength\@dblfptop{0\p@} \setlength\@dblfpsep{8\p@ \@plus 2fil} \setlength\@dblfpbot{0\p@} \setlength\partopsep{2\p@ \@plus 1\p@ \@minus 1\p@} \def\@listI{\leftmargin\leftmargini \parsep=\z@ \topsep=5\p@ \@plus3\p@ \@minus3\p@ \itemsep=3\p@ \@plus2\p@ \@minus\p@} \let\@listi\@listI \@listi \def\@listii {\leftmargin\leftmarginii \labelwidth\leftmarginii \advance\labelwidth-\labelsep \topsep=2\p@ \@plus2\p@ \@minus\p@ \parsep=\z@ \itemsep=\parsep} \def\@listiii{\leftmargin\leftmarginiii \labelwidth\leftmarginiii \advance\labelwidth-\labelsep \topsep=\z@ \parsep=\z@ \partopsep=\z@ \itemsep=\z@} \def\@listiv {\leftmargin\leftmarginiv \labelwidth\leftmarginiv \advance\labelwidth-\labelsep} \def\@listv {\leftmargin\leftmarginv \labelwidth\leftmarginv \advance\labelwidth-\labelsep} \def\@listvi {\leftmargin\leftmarginvi \labelwidth\leftmarginvi \advance\labelwidth-\labelsep} \endinput %% %% End of file `iopart.clo'.

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* Title Page :ignore:
#+begin_export latex
\title{Active Damping of Rotating Platforms using Integral Force Feedback}
\author{Thomas Dehaeze$^{1,3}$ and Christophe Collette$^{1,2}$}
\address{$^1$ Precision Mechatronics Laboratory, University of Liege, Belgium}
\address{$^2$ BEAMS Department, Free University of Brussels, Belgium}
\address{$^3$ European Synchrotron Radiation Facility, Grenoble, France}
\ead{dehaeze.thomas@gmail.com}
\vspace{10pt}
\begin{indented}
\item[]November 2020
\end{indented}
#+end_export
#+begin_export latex
\begin{abstract}
This paper investigates the use of Integral Force Feedback (IFF) for the active damping of rotating mechanical systems.
Guaranteed stability, typical benefit of IFF, is lost as soon as the system is rotating due to gyroscopic effects.
To overcome this issue, two modifications of the classical IFF control scheme are proposed.
The first consists of slightly modifying the control law while the second consists of adding springs in parallel with the force sensors.
Conditions for stability and optimal parameters are derived.
The results reveal that, despite their different implementations, both modified IFF control scheme have almost identical damping authority on suspension modes.
\end{abstract}
\vspace{2pc}
\noindent{\it Keywords}: Active Damping, IFF
\ioptwocol
#+end_export
* Introduction
<<sec:introduction>>
There is an increasing need to reduce the undesirable vibration of many sensitive equipment.
A common method to reduce vibration is to mount the sensitive equipment on a suspended platform which attenuates the vibrations above the frequency of the suspension modes.
In order to further decrease the residual vibrations, active damping can be used for reducing the magnification of the response in the vicinity of the resonances.
In cite:preumont92_activ_dampin_by_local_force, the Integral Force Feedback (IFF) control scheme has been proposed, where a force sensor, a force actuator and an integral controller are used to directly augment the damping of a mechanical system.
When the force sensor is collocated with the actuator, the open-loop transfer function has alternating poles and zeros which facilitate to guarantee the stability of the closed loop system cite:preumont02_force_feedb_versus_accel_feedb.
However, when the platform is rotating, gyroscopic effects alter the system dynamics and IFF cannot be applied as is.
The purpose of this paper is to study how the IFF strategy can be adapted to deal with these Gyroscopic effects.
The paper is structured as follows.
Section ref:sec:dynamics presents a simple model of a rotating suspended platform that will be used throughout this study.
Section ref:sec:iff explains how the unconditional stability of IFF is lost due to Gyroscopic effects induced by the rotation.
Section ref:sec:iff_hpf suggests a simple modification of the control law such that damping can be added to the suspension modes in a robust way.
Section ref:sec:iff_kp proposes to add springs in parallel with the force sensors to regain the unconditional stability of IFF.
Section ref:sec:comparison compares both proposed modifications to the classical IFF in terms of damping authority and closed-loop system behavior.
* Dynamics of Rotating Platforms
<<sec:dynamics>>
** Model of a Rotating Platform :ignore:
In order to study how the rotation does affect the use of IFF, a model of a suspended platform on top of a rotating stage is used.
Figure ref:fig:system represents the model schematically which is the simplest in which gyroscopic forces can be studied.
#+name: fig:system
#+caption: Schematic of the studied System
#+attr_latex: :width \linewidth
[[file:figs/system.pdf]]
The rotating stage is supposed to be ideal, meaning it induces a perfect rotation $\theta(t) = \Omega t$ where $\Omega$ is the rotational speed in $\si{\radian\per\second}$.
The suspended platform consists of two orthogonal actuators represented by three elements in parallel: a spring with a stiffness $k$ in $\si{\newton\per\meter}$, a dashpot with a damping coefficient $c$ in $\si{\newton\per\meter\second}$ and an ideal force source $F_u, F_v$.
A payload with a mass $m$ in $\si{\kilo\gram}$, representing the sensitive equipment, is mounted on the (rotating) suspended platform.
Two reference frames are used: an inertial frame $(\vec{i}_x, \vec{i}_y, \vec{i}_z)$ and a uniform rotating frame $(\vec{i}_u, \vec{i}_v, \vec{i}_w)$ rigidly fixed on top of the rotating stage with $\vec{i}_w$ aligned with the rotation axis.
The position of the payload is represented by $(d_u, d_v, 0)$ expressed in the rotating frame.
#+latex: \par
** Equations of Motion :ignore:
To obtain the equations of motion for the system represented in Figure ref:fig:system, the Lagrangian equations are used:
#+name: eq:lagrangian_equations
\begin{equation}
\frac{d}{dt} \left( \frac{\partial L}{\partial \dot{q}_i} \right) + \frac{\partial D}{\partial \dot{q}_i} - \frac{\partial L}{\partial q_i} = Q_i
\end{equation}
with $L = T - V$ the Lagrangian, $T$ the kinetic coenergy, $V$ the potential energy, $D$ the dissipation function, and $Q_i$ the generalized force associated with the generalized variable $\begin{bmatrix}q_1 & q_2\end{bmatrix} = \begin{bmatrix}d_u & d_v\end{bmatrix}$.
The equation of motion corresponding to the constant rotation in the $(\vec{i}_x, \vec{i}_y)$ plane is disregarded as the motion is considered to be imposed by the rotation stage.
#+name: eq:energy_functions_lagrange
\begin{equation}
\begin{aligned}
T &= \frac{1}{2} m \left( ( \dot{d}_u - \Omega d_v )^2 + ( \dot{d}_v + \Omega d_u )^2 \right), \\
V &= \frac{1}{2} k \big( {d_u}^2 + {d_v}^2 \big), \ Q_1 = F_u, \\
D &= \frac{1}{2} c \big( \dot{d}_u{}^2 + \dot{d}_v{}^2 \big), \ Q_2 = F_v
\end{aligned}
\end{equation}
Substituting equations eqref:eq:energy_functions_lagrange into eqref:eq:lagrangian_equations for both generalized coordinates gives two coupled differential equations
#+name: eq:eom_coupled
\begin{subequations}
\begin{align}
m \ddot{d}_u + c \dot{d}_u + ( k - m \Omega^2 ) d_u &= F_u + 2 m \Omega \dot{d}_v \\
m \ddot{d}_v + c \dot{d}_v + ( k \underbrace{-\,m \Omega^2}_{\text{Centrif.}} ) d_v &= F_v \underbrace{-\,2 m \Omega \dot{d}_u}_{\text{Coriolis}}
\end{align}
\end{subequations}
The uniform rotation of the system induces two Gyroscopic effects as shown in eqref:eq:eom_coupled:
- Centrifugal forces: that can been seen as added negative stiffness $- m \Omega^2$ along $\vec{i}_u$ and $\vec{i}_v$
- Coriolis Forces: that couples the motion in the two orthogonal directions
One can verify that without rotation ($\Omega = 0$) the system becomes equivalent to two uncoupled one degree of freedom mass-spring-damper systems:
#+name: eq:oem_no_rotation
\begin{subequations}
\begin{align}
m \ddot{d}_u + c \dot{d}_u + k d_u &= F_u \\
m \ddot{d}_v + c \dot{d}_v + k d_v &= F_v
\end{align}
\end{subequations}
#+latex: \par
** Transfer Functions in the Laplace domain :ignore:
To study the dynamics of the system, the differential equations of motions eqref:eq:eom_coupled are transformed in the Laplace domain and the $2 \times 2$ transfer function matrix $\bm{G}_d$ from $\begin{bmatrix}F_u & F_v\end{bmatrix}$ to $\begin{bmatrix}d_u & d_v\end{bmatrix}$ is obtained.
#+name: eq:Gd_mimo_tf
\begin{equation}
\begin{bmatrix} d_u \\ d_v \end{bmatrix} = \bm{G}_d \begin{bmatrix} F_u \\ F_v \end{bmatrix}
\end{equation}
\begin{subequations}
\begin{align}
\bm{G}_{d}(1,1) &= {\frac{ms^2 + cs + k - m \Omega^2}{\left( m s^2 + cs + k - m \Omega^2 \right)^2 + \left( 2 m \Omega s \right)^2}} \\
&= \bm{G}_{d}(2,2) \nonumber \\
\bm{G}_{d}(1,2) &= {\frac{2 m \Omega s}{\left( m s^2 + cs + k - m \Omega^2 \right)^2 + \left( 2 m \Omega s \right)^2}} \\
&= -\bm{G}_{d}(1,2) \nonumber
\end{align}
\end{subequations}
To simplify the analysis, the undamped natural frequency $\omega_0$ and the damping ratio $\xi$ are used
\begin{equation}
\omega_0 = \sqrt{\frac{k}{m}} \text{ in } \si{\radian\per\second}, \quad \xi = \frac{c}{2 \sqrt{k m}}
\end{equation}
The transfer function matrix $\bm{G}_d$ becomes equal to
#+name: eq:Gd_w0_xi_k
\begin{subequations}
\begin{align}
\bm{G}_{d}(1,1) &= {\scriptstyle \frac{\frac{1}{k} \left( \frac{s^2}{{\omega_0}^2} + 2 \xi \frac{s}{\omega_0} + 1 - \frac{{\Omega}^2}{{\omega_0}^2} \right)}{\left( \frac{s^2}{{\omega_0}^2} + 2 \xi \frac{s}{\omega_0} + 1 - \frac{{\Omega}^2}{{\omega_0}^2} \right)^2 + \left( 2 \frac{\Omega}{\omega_0} \frac{s}{\omega_0} \right)^2} } \\
\bm{G}_{d}(1,2) &= {\scriptstyle \frac{\frac{1}{k} \left( 2 \frac{\Omega}{\omega_0} \frac{s}{\omega_0} \right)}{\left( \frac{s^2}{{\omega_0}^2} + 2 \xi \frac{s}{\omega_0} + 1 - \frac{{\Omega}^2}{{\omega_0}^2} \right)^2 + \left( 2 \frac{\Omega}{\omega_0} \frac{s}{\omega_0} \right)^2} }
\end{align}
\end{subequations}
For all further numerical analysis in this study, we consider $\omega_0 = \SI{1}{\radian\per\second}$, $k = \SI{1}{\newton\per\meter}$ and $\xi = 0.025 = \SI{2.5}{\percent}$.
Even though no system with such parameters will be encountered in practice, conclusions can be drawn relative to these parameters such that they can be generalized to any other set of parameters.
#+latex: \par
** System Dynamics and Campbell Diagram :ignore:
The poles of $\bm{G}_d$ are the complex solutions $p$ of eqref:eq:poles.
#+name: eq:poles
\begin{equation}
\left( \frac{p^2}{{\omega_0}^2} + 2 \xi \frac{p}{\omega_0} + 1 - \frac{{\Omega}^2}{{\omega_0}^2} \right)^2 + \left( 2 \frac{\Omega}{\omega_0} \frac{p}{\omega_0} \right)^2 = 0
\end{equation}
Supposing small damping ($\xi \ll 1$), two pairs of complex conjugate poles are obtained eqref:eq:pole_values.
#+name: eq:pole_values
\begin{subequations}
\begin{align}
p_{+} &= - \xi \omega_0 \left( 1 + \frac{\Omega}{\omega_0} \right) \pm j \omega_0 \left( 1 + \frac{\Omega}{\omega_0} \right) \\
p_{-} &= - \xi \omega_0 \left( 1 - \frac{\Omega}{\omega_0} \right) \pm j \omega_0 \left( 1 - \frac{\Omega}{\omega_0} \right)
\end{align}
\end{subequations}
The real part and complex part of these two pairs of complex conjugate poles are represented in Figure ref:fig:campbell_diagram as a function of the rotational speed $\Omega$.
As the rotational speed increases, $p_{+}$ goes to higher frequencies and $p_{-}$ to lower frequencies.
The system becomes unstable for $\Omega > \omega_0$ as the real part of $p_{-}$ is positive.
Physically, the negative stiffness term $-m\Omega^2$ induced by centrifugal forces exceeds the spring stiffness $k$.
In the rest of this study, rotational speeds smaller than the undamped natural frequency of the system are assumed ($\Omega < \omega_0$).
#+name: fig:campbell_diagram
#+caption: Campbell Diagram : Evolution of the complex and real parts of the system's poles as a function of the rotational speed $\Omega$
#+attr_latex: :environment subfigure :width 0.48\linewidth :align c
| file:figs/campbell_diagram_real.pdf | file:figs/campbell_diagram_imag.pdf |
| <<fig:campbell_diagram_real>> Real Part | <<fig:campbell_diagram_imag>> Imaginary Part |
Looking at the transfer function matrix $\bm{G}_d$ in Eq. eqref:eq:Gd_w0_xi_k, one can see that the two diagonal (direct) terms are equal and the two off-diagonal (coupling) terms are opposite.
The bode plot of these two terms are shown in Figure ref:fig:plant_compare_rotating_speed for several rotational speeds $\Omega$.
These plots confirm the expected behavior: the frequency of the two pairs of complex conjugate poles are further separated as $\Omega$ increases.
For $\Omega > \omega_0$, the low frequency pair of complex conjugate poles $p_{-}$ becomes unstable.
#+name: fig:plant_compare_rotating_speed
#+caption: Bode Plots for $\bm{G}_d$ for several rotational speed $\Omega$
#+attr_latex: :environment subfigure :width 0.48\linewidth :align c
| file:figs/plant_compare_rotating_speed_direct.pdf | file:figs/plant_compare_rotating_speed_coupling.pdf |
| <<fig:plant_compare_rotating_speed_direct>> Direct Terms | <<fig:plant_compare_rotating_speed_coupling>> Coupling Terms |
* Decentralized Integral Force Feedback
<<sec:iff>>
** Force Sensors and Control Architecture :ignore:
In order to apply IFF to the system, force sensors are added in series with the two actuators (Figure ref:fig:system_iff).
As this study focuses on decentralized control, two identical controllers $K_F$ are used to feedback each of the sensed force to its associated actuator and no attempt is made to counteract the interactions in the system.
The control diagram is schematically shown in Figure ref:fig:control_diagram_iff.
#+name: fig:system_iff
#+caption: System with added Force Sensor in series with the actuators
#+attr_latex: :width \linewidth
[[file:figs/system_iff.pdf]]
#+name: fig:control_diagram_iff
#+caption: Control Diagram for decentralized IFF
#+attr_latex: :scale 1
[[file:figs/control_diagram_iff.pdf]]
#+latex: \par
** Plant Dynamics :ignore:
The forces $\begin{bmatrix}f_u & f_v\end{bmatrix}$ measured by the two force sensors represented in Figure ref:fig:system_iff are equal to
#+name: eq:measured_force
\begin{equation}
\begin{bmatrix} f_{u} \\ f_{v} \end{bmatrix} =
\begin{bmatrix} F_u \\ F_v \end{bmatrix} - (c s + k)
\begin{bmatrix} d_u \\ d_v \end{bmatrix}
\end{equation}
Inserting eqref:eq:Gd_w0_xi_k into eqref:eq:measured_force yields
#+name: eq:Gf_mimo_tf
\begin{equation}
\begin{bmatrix} f_{u} \\ f_{v} \end{bmatrix} = \bm{G}_{f} \begin{bmatrix} F_u \\ F_v \end{bmatrix}
\end{equation}
\begin{subequations}
\label{eq:Gf}
\begin{align}
\bm{G}_{f}(1,1) &= {\scriptstyle \frac{\left( \frac{s^2}{{\omega_0}^2} - \frac{\Omega^2}{{\omega_0}^2} \right) \left( \frac{s^2}{{\omega_0}^2} + 2 \xi \frac{s}{\omega_0} + 1 - \frac{{\Omega}^2}{{\omega_0}^2} \right) + \left( 2 \frac{\Omega}{\omega_0} \frac{s}{\omega_0} \right)^2}{\left( \frac{s^2}{{\omega_0}^2} + 2 \xi \frac{s}{\omega_0} + 1 - \frac{{\Omega}^2}{{\omega_0}^2} \right)^2 + \left( 2 \frac{\Omega}{\omega_0} \frac{s}{\omega_0} \right)^2} } \\
\bm{G}_{f}(1,2) &= {\scriptstyle \frac{- \left( 2 \xi \frac{s}{\omega_0} + 1 \right) \left( 2 \frac{\Omega}{\omega_0} \frac{s}{\omega_0} \right)}{\left( \frac{s^2}{{\omega_0}^2} + 2 \xi \frac{s}{\omega_0} + 1 - \frac{{\Omega}^2}{{\omega_0}^2} \right)^2 + \left( 2 \frac{\Omega}{\omega_0} \frac{s}{\omega_0} \right)^2} }
\end{align}
\end{subequations}
The zeros of the diagonal terms of $\bm{G}_f$ are equal to (neglecting the damping for simplicity)
\begin{subequations}
\begin{align}
z_c &= \pm j \omega_0 \sqrt{\frac{1}{2} \sqrt{8 \frac{\Omega^2}{{\omega_0}^2} + 1} + \frac{\Omega^2}{{\omega_0}^2} + \frac{1}{2} } \label{eq:iff_zero_cc} \\
z_r &= \pm \omega_0 \sqrt{\frac{1}{2} \sqrt{8 \frac{\Omega^2}{{\omega_0}^2} + 1} - \frac{\Omega^2}{{\omega_0}^2} - \frac{1}{2} } \label{eq:iff_zero_real}
\end{align}
\end{subequations}
The frequency of the pair of complex conjugate zeros $z_c$ eqref:eq:iff_zero_cc always lies between the frequency of the two pairs of complex conjugate poles $p_{-}$ and $p_{+}$ eqref:eq:pole_values.
For non-null rotational speeds, two real zeros $z_r$ eqref:eq:iff_zero_real appear in the diagonal terms inducing a non-minimum phase behavior.
This can be seen in the Bode plot of the diagonal terms (Figure ref:fig:plant_iff_compare_rotating_speed) where the low frequency gain is no longer zero while the phase stays at $\SI{180}{\degree}$.
The low frequency gain of $\bm{G}_f$ increases with the rotational speed $\Omega$
#+name: eq:low_freq_gain_iff_plan
\begin{equation}
\lim_{\omega \to 0} \left| \bm{G}_f (j\omega) \right| = \begin{bmatrix}
\frac{\Omega^2}{{\omega_0}^2 - \Omega^2} & 0 \\
0 & \frac{\Omega^2}{{\omega_0}^2 - \Omega^2}
\end{bmatrix}
\end{equation}
This can be explained as follows: a constant force $F_u$ induces a small displacement of the mass $d_u = \frac{F_u}{k - m\Omega^2}$, which increases the centrifugal force $m\Omega^2d_u = \frac{\Omega^2}{{\omega_0}^2 - \Omega^2} F_u$ which is then measured by the force sensors.
#+name: fig:plant_iff_compare_rotating_speed
#+caption: Bode plot of the dynamics from a force actuator to its collocated force sensor ($f_u/F_u$, $f_v/F_v$) for several rotational speeds $\Omega$
#+attr_latex: :width \linewidth
[[file:figs/plant_iff_compare_rotating_speed.pdf]]
#+latex: \par
** Decentralized Integral Force Feedback with Pure Integrators :ignore:
<<sec:iff_pure_int>>
The two IFF controllers $K_F$ consist of a pure integrator
#+name: eq:Kf_pure_int
\begin{equation}
\begin{aligned}
\bm{K}_F(s) &= \begin{bmatrix} K_F(s) & 0 \\ 0 & K_F(s) \end{bmatrix} \\
K_F(s) &= g \cdot \frac{1}{s}
\end{aligned}
\end{equation}
where $g$ is a scalar representing the gain of the controller.
In order to see how the IFF affects the poles of the closed loop system, a Root Locus plot (Figure ref:fig:root_locus_pure_iff) is constructed as follows: the poles of the closed-loop system are drawn in the complex plane as the controller gain $g$ varies from $0$ to $\infty$ for the two controllers $K_F$ simultaneously.
As explained in cite:preumont08_trans_zeros_struc_contr_with,skogestad07_multiv_feedb_contr, the closed-loop poles start at the open-loop poles (shown by $\tikz[baseline=-0.6ex] \node[cross out, draw=black, minimum size=1ex, line width=2pt, inner sep=0pt, outer sep=0pt] at (0, 0){};$) for $g = 0$ and coincide with the transmission zeros (shown by $\tikz[baseline=-0.6ex] \draw[line width=2pt, inner sep=0pt, outer sep=0pt] (0,0) circle[radius=3pt];$) as $g \to \infty$.
The direction of increasing gain is indicated by arrows $\tikz[baseline=-0.6ex] \draw[-{Stealth[round]},line width=2pt] (0,0) -- (0.3,0);$.
#+name: fig:root_locus_pure_iff
#+caption: Root Locus: evolution of the closed-loop poles with increasing controller gains $g$
#+attr_latex: :scale 1
[[file:figs/root_locus_pure_iff.pdf]]
Whereas collocated IFF is usually associated with unconditional stability cite:preumont91_activ, this property is lost as soon as the rotational speed in non-null due to gyroscopic effects.
This can be seen in the Root Locus plot (Figure ref:fig:root_locus_pure_iff) where the poles corresponding to the controller are bound to the right half plane implying closed-loop system instability.
Physically, this can be explain like so: at low frequency, the loop gain is very large due to the pure integrators in $K_F$.
The control system is thus canceling the spring forces which makes the suspended platform no able to hold the payload against centrifugal forces, hence the instability.
In order to apply decentralized IFF on rotating platforms, two solutions are proposed to deal with this instability problem.
The first one consists of slightly modifying the control law (Section ref:sec:iff_hpf) while the second one consists of adding springs in parallel with the force sensors (Section ref:sec:iff_kp).
* Integral Force Feedback with High Pass Filter
<<sec:iff_hpf>>
** Modification of the Control Law :ignore:
As was explained in the previous section, the instability comes in part from the high gain at low frequency caused by the pure integrators.
In order to limit this low frequency controller gain, an high pass filter (HPF) can be added to the controller
#+name: eq:IFF_LHF
\begin{equation}
K_{F}(s) = g \cdot \frac{1}{s} \cdot \underbrace{\frac{s/\omega_i}{1 + s/\omega_i}}_{\text{HPF}} = g \cdot \frac{1}{s + \omega_i}
\end{equation}
This is equivalent to slightly shifting the controller pole to the left along the real axis.
This modification of the IFF controller is typically done to avoid saturation associated with the pure integrator cite:preumont91_activ.
This is however not the case in this study as it will become clear in the next section.
#+latex: \par
** Feedback Analysis :ignore:
The loop gains, $K_F(s)$ times the direct dynamics $f_u/F_u$, with and without the added HPF are shown in Figure ref:fig:loop_gain_modified_iff.
The effect of the added HPF limits the low frequency gain as expected.
The Root Loci for the decentralized IFF with and without the HPF are displayed in Figure ref:fig:root_locus_modified_iff.
With the added HPF, the poles of the closed loop system are shown to be stable up to some value of the gain $g_\text{max}$
#+name: eq:gmax_iff_hpf
\begin{equation}
g_{\text{max}} = \omega_i \left( \frac{{\omega_0}^2}{\Omega^2} - 1 \right)
\end{equation}
It is interesting to note that $g_{\text{max}}$ also corresponds to the gain where the low frequency loop gain (Figure ref:fig:loop_gain_modified_iff) reaches one.
#+name: fig:loop_gain_modified_iff
#+caption: Modification of the loop gain with the added HFP, $g = 2$, $\omega_i = 0.1 \omega_0$ and $\Omega = 0.1 \omega_0$
#+attr_latex: :width \linewidth
[[file:figs/loop_gain_modified_iff.pdf]]
#+name: fig:root_locus_modified_iff
#+caption: Modification of the Root Locus with the added HPF, $\omega_i = 0.1 \omega_0$ and $\Omega = 0.1 \omega_0$
#+attr_latex: :scale 1
[[file:figs/root_locus_modified_iff.pdf]]
#+latex: \par
** Optimal Control Parameters :ignore:
Two parameters can be tuned for the modified controller eqref:eq:IFF_LHF: the gain $g$ and the pole's location $\omega_i$.
The optimal values of $\omega_i$ and $g$ are here considered as the values for which the damping of all the closed-loop poles are simultaneously maximized.
In order to visualize how $\omega_i$ does affect the attainable damping, the Root Loci for several $\omega_i$ are displayed in Figure ref:fig:root_locus_wi_modified_iff.
It is shown that even though small $\omega_i$ seem to allow more damping to be added to the suspension modes, the control gain $g$ may be limited to small values due to eqref:eq:gmax_iff_hpf.
#+name: fig:root_locus_wi_modified_iff
#+caption: Root Locus for several HPF cut-off frequencies $\omega_i$, $\Omega = 0.1 \omega_0$
#+attr_latex: :width \linewidth
[[file:figs/root_locus_wi_modified_iff.pdf]]
In order to study this trade off, the attainable closed-loop damping ratio $\xi_{\text{cl}}$ is computed as a function of $\omega_i/\omega_0$.
The gain $g_{\text{opt}}$ at which this maximum damping is obtained is also displayed and compared with the gain $g_{\text{max}}$ at which the system becomes unstable (Figure ref:fig:mod_iff_damping_wi).
#+name: fig:mod_iff_damping_wi
#+caption: Attainable damping ratio $\xi_\text{cl}$ as a function of $\omega_i/\omega_0$. Corresponding control gain $g_\text{opt}$ and $g_\text{max}$ are also shown
#+attr_latex: :width \linewidth
[[file:figs/mod_iff_damping_wi.pdf]]
Three regions can be observed:
- $\omega_i/\omega_0 < 0.02$: the added damping is limited by the maximum allowed control gain $g_{\text{max}}$
- $0.02 < \omega_i/\omega_0 < 0.2$: the attainable damping ratio is maximized and is reached for $g \approx 2$
- $0.2 < \omega_i/\omega_0$: the added damping decreases as $\omega_i/\omega_0$ increases
* Integral Force Feedback with Parallel Springs
<<sec:iff_kp>>
** Stiffness in Parallel with the Force Sensor :ignore:
In this section additional springs in parallel with the force sensors are added to counteract the negative stiffness induced by the rotation.
Such springs are schematically shown in Figure ref:fig:system_parallel_springs where $k_a$ is the stiffness of the actuator and $k_p$ the stiffness in parallel with the actuator and force sensor.
Amplified piezoelectric stack actuators can also be used for such purpose where a part of the piezoelectric stack is used as an actuator while the rest is used as a force sensor cite:souleille18_concep_activ_mount_space_applic.
The parallel stiffness $k_p$ then corresponds to the amplification structure.
An example of such system is shown in Figure ref:fig:cedrat_xy25xs.
#+name: fig:system_parallel_springs
#+caption: Studied system with additional springs in parallel with the actuators and force sensors
#+attr_latex: :width \linewidth
[[file:figs/system_parallel_springs.pdf]]
#+name: fig:cedrat_xy25xs
#+caption: XY Piezoelectric Stage (XY25XS from Cedrat Technology)
#+attr_latex: :width 0.8\linewidth
[[file:figs/cedrat_xy25xs.png]]
#+latex: \par
** Effect of the Parallel Stiffness on the Plant Dynamics :ignore:
The forces $\begin{bmatrix}f_u & f_v\end{bmatrix}$ measured by the two force sensors represented in Figure ref:fig:system_parallel_springs are equal to
#+name: eq:measured_force_kp
\begin{equation}
\begin{bmatrix} f_{u} \\ f_{v} \end{bmatrix} =
\begin{bmatrix} F_u \\ F_v \end{bmatrix} - (c s + k_a)
\begin{bmatrix} d_u \\ d_v \end{bmatrix}
\end{equation}
In order to keep the overall stiffness $k = k_a + k_p$ constant, thus not modifying the open-loop poles as $k_p$ is changed, a scalar parameter $\alpha$ ($0 \le \alpha < 1$) is defined to describe the fraction of the total stiffness in parallel with the actuator and force sensor
\begin{equation}
k_p = \alpha k, \quad k_a = (1 - \alpha) k
\end{equation}
The equations of motion are derived and transformed in the Laplace domain
#+name: eq:Gk_mimo_tf
\begin{equation}
\begin{bmatrix} f_u \\ f_v \end{bmatrix} =
\bm{G}_k
\begin{bmatrix} F_u \\ F_v \end{bmatrix}
\end{equation}
#+name: eq:Gk
\begin{subequations}
\begin{align}
& \bm{G}_{k}(1,1) = \dots \nonumber \\
& {\scriptstyle \frac{\big( \frac{s^2}{{\omega_0}^2} - \frac{\Omega^2}{{\omega_0}^2} + \alpha \big) \big( \frac{s^2}{{\omega_0}^2} + 2 \xi \frac{s}{\omega_0} + 1 - \frac{{\Omega}^2}{{\omega_0}^2} \big) + \big( 2 \frac{\Omega}{\omega_0} \frac{s}{\omega_0} \big)^2}{\big( \frac{s^2}{{\omega_0}^2} + 2 \xi \frac{s}{\omega_0} + 1 - \frac{{\Omega}^2}{{\omega_0}^2} \big)^2 + \big( 2 \frac{\Omega}{\omega_0} \frac{s}{\omega_0} \big)^2} } \\
& \bm{G}_{k}(1,2) = {\scriptscriptstyle \frac{- \left( 2 \xi \frac{s}{\omega_0} + 1 - \alpha \right) \left( 2 \frac{\Omega}{\omega_0} \frac{s}{\omega_0} \right)}{\left( \frac{s^2}{{\omega_0}^2} + 2 \xi \frac{s}{\omega_0} + 1 - \frac{{\Omega}^2}{{\omega_0}^2} \right)^2 + \left( 2 \frac{\Omega}{\omega_0} \frac{s}{\omega_0} \right)^2} }
\end{align}
\end{subequations}
Comparing $\bm{G}_k$ eqref:eq:Gk with $\bm{G}_f$ eqref:eq:Gf shows that while the poles of the system are kept the same, the zeros of the diagonal terms have changed.
The two real zeros $z_r$ eqref:eq:iff_zero_real that were inducing non-minimum phase behavior are transformed into complex conjugate zeros if the following condition hold
#+name: eq:kp_cond_cc_zeros
\begin{equation}
\alpha > \frac{\Omega^2}{{\omega_0}^2} \quad \Leftrightarrow \quad k_p > m \Omega^2
\end{equation}
Thus, if the added parallel stiffness $k_p$ is higher than the negative stiffness induced by centrifugal forces $m \Omega^2$, the direct dynamics from actuator to force sensor will show minimum phase behavior.
This is confirmed by the Bode plot of the direct dynamics in Figure ref:fig:plant_iff_kp.
Figure ref:fig:root_locus_iff_kp shows Root Loci plots for $k_p = 0$, $k_p < m \Omega^2$ and $k_p > m \Omega^2$ when $K_F$ is a pure integrator eqref:eq:Kf_pure_int.
It is shown that if the added stiffness is higher than the maximum negative stiffness, the poles of the closed-loop system stay in the (stable) right half-plane, and hence the unconditional stability of IFF is recovered.
#+name: fig:plant_iff_kp
#+caption: Bode plot of $f_u/F_u$ without parallel spring, with parallel springs with stiffness $k_p < m \Omega^2$ and $k_p > m \Omega^2$, $\Omega = 0.1 \omega_0$
#+attr_latex: :width \linewidth
[[file:figs/plant_iff_kp.pdf]]
#+name: fig:root_locus_iff_kp
#+caption: Root Locus for IFF without parallel spring, with parallel springs with stiffness $k_p < m \Omega^2$ and $k_p > m \Omega^2$, $\Omega = 0.1 \omega_0$
#+attr_latex: :width \linewidth
[[file:figs/root_locus_iff_kp.pdf]]
#+latex: \par
** Optimal Parallel Stiffness :ignore:
Even though the parallel stiffness $k_p$ has no impact on the open-loop poles (as the overall stiffness $k$ stays constant), it has a large impact on the transmission zeros.
Moreover, as the attainable damping is generally proportional to the distance between poles and zeros cite:preumont18_vibrat_contr_activ_struc_fourt_edition, the parallel stiffness $k_p$ is foreseen to have a large impact on the attainable damping.
To study this effect, Root Locus plots for several parallel stiffnesses $k_p > m \Omega^2$ are shown in Figure ref:fig:root_locus_iff_kps.
The frequencies of the transmission zeros of the system are increasing with the parallel stiffness $k_p$ and the associated attainable damping is reduced.
Therefore, even though the parallel stiffness $k_p$ should be larger than $m \Omega^2$ for stability reasons, it should not be taken too high as this would limit the attainable bandwidth.
This is confirmed in Figure ref:fig:opt_damp_alpha where the attainable closed-loop damping ratio $\xi_{\text{cl}}$ and the associated control gain $g_\text{opt}$ are computed as a function of $\alpha$.
#+name: fig:root_locus_iff_kps
#+caption: Comparison the Root Locus for three parallel stiffnessses $k_p$
#+attr_latex: :scale 1
[[file:figs/root_locus_iff_kps.pdf]]
#+name: fig:opt_damp_alpha
#+caption: Optimal Damping Ratio $\xi_\text{opt}$ and the corresponding optimal gain $g_\text{opt}$ as a function of $\alpha$
#+attr_latex: :width \linewidth
[[file:figs/opt_damp_alpha.pdf]]
* Comparison and Discussion
<<sec:comparison>>
** Introduction :ignore:
Two modifications to adapt the IFF control strategy to rotating platforms have been proposed in Sections ref:sec:iff_hpf and ref:sec:iff_kp.
These two methods are now compared in terms of added damping, closed-loop compliance and transmissibility.
For the following comparisons, the cut-off frequency for the HPF is set to $\omega_i = 0.1 \omega_0$ and the stiffness of the parallel springs is set to $k_p = 5 m \Omega^2$.
#+latex: \par
** Comparison of the Attainable Damping :ignore:
Figure ref:fig:comp_root_locus shows the Root Loci for the two proposed IFF modifications.
While the two pairs of complex conjugate open-loop poles are identical for both techniques, the transmission zeros are not.
This means that the closed-loop behavior of both systems will differ when large control gains are used.
One can observe that the closed loop poles of the system with added springs (in red) are bounded to the left half plane implying unconditional stability.
This is not the case for the system where the controller is augmented with an HPF (in blue).
It is interesting to note that the maximum added damping is very similar for both techniques and is reached for the same control gain $g_\text{opt} \approx 2 \omega_0$.
#+name: fig:comp_root_locus
#+caption: Root Locus for the two proposed modifications of decentralized IFF, $\Omega = 0.1 \omega_0$
#+attr_latex: :scale 1
[[file:figs/comp_root_locus.pdf]]
#+latex: \par
** Comparison Transmissibility and Compliance :ignore:
The two proposed techniques are now compared in terms of closed-loop transmissibility and compliance.
The transmissibility is defined as the transfer function from the displacement of the rotating stage to the displacement of the payload.
It is used to characterize how much vibration is transmitted through the suspended platform to the payload.
The compliance describes the displacement response of the payload to external forces applied to it.
This is a useful metric when disturbances are directly applied to the payload.
The two techniques are also compared with passive damping (Figure ref:fig:system) where the damping coefficient $c$ is tuned to critically damp the resonance when the rotating speed is null.
\begin{equation}
c_\text{crit} = 2 \sqrt{k m}
\end{equation}
Very similar results are obtained for the two proposed IFF modifications in terms of transmissibility (Figure ref:fig:comp_transmissibility) and compliance (Figure ref:fig:comp_compliance).
It is also confirmed that these two techniques can significantly damp the suspension modes.
#+name: fig:comp_transmissibility
#+caption: Comparison of the two proposed Active Damping Techniques - Transmissibility
#+attr_latex: :scale 1
[[file:figs/comp_transmissibility.pdf]]
#+name: fig:comp_compliance
#+caption: Comparison of the two proposed Active Damping Techniques - Compliance
#+attr_latex: :scale 1
[[file:figs/comp_compliance.pdf]]
On can see in Figure ref:fig:comp_transmissibility that the problem of the degradation of the transmissibility at high frequency when using passive damping techniques is overcome by the use of IFF.
The addition of the HPF or the use of the parallel stiffness permit to limit the degradation of the compliance as compared with classical IFF (Figure ref:fig:comp_compliance).
* Conclusion
<<sec:conclusion>>
Due to gyroscopic effects, decentralized IFF with pure integrators was shown to be unstable when applied to rotating platforms.
Two modifications of the classical IFF control have been proposed to overcome this issue.
The first modification concerns the controller and consists of adding an high pass filter to the pure integrators.
This is equivalent as to moving the controller pole to the left along the real axis.
This renders the closed loop system stable up to some value of the controller gain $g_\text{max}$.
The second proposed modification concerns the mechanical system.
Additional springs are added in parallel with the actuators and force sensors.
It was shown that if the stiffness $k_p$ of the additional springs is larger than the negative stiffness $m \Omega^2$ induced by centrifugal forces, the classical decentralized IFF regains its unconditional stability property.
While having very different implementations, both proposed modifications are very similar when it comes to the attainable damping and the obtained closed loop system behavior.
Future work will focus on the experimental validation of the proposed active damping techniques.
The Matlab code that was used for this study is available under a MIT License and archived in Zenodo cite:dehaeze20_activ_dampin_rotat_posit_platf.
* Acknowledgments
:PROPERTIES:
:UNNUMBERED: t
:END:
This research benefited from a FRIA grant from the French Community of Belgium.
* References
:PROPERTIES:
:UNNUMBERED: t
:END:
\bibliographystyle{iopart-num}
\bibliography{ref.bib}

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% Created 2020-10-29 jeu. 12:36
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\begin{document}
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\title{Active Damping of Rotating Platforms using Integral Force Feedback}
\author{Thomas Dehaeze$^{1,3}$ and Christophe Collette$^{1,2}$}
\address{$^1$ Precision Mechatronics Laboratory, University of Liege, Belgium}
\address{$^2$ BEAMS Department, Free University of Brussels, Belgium}
\address{$^3$ European Synchrotron Radiation Facility, Grenoble, France}
\ead{dehaeze.thomas@gmail.com}
\newcommand\BibTeX{{\rmfamily B\kern-.05em \textsc{i\kern-.025em b}\kern-.08em
T\kern-.1667em\lower.7ex\hbox{E}\kern-.125emX}}
\vspace{10pt}
\begin{indented}
\item[]November 2020
\end{indented}
\hypersetup{colorlinks,bookmarksopen,bookmarksnumbered,citecolor=red,urlcolor=red}
\author{Dehaeze Thomas\affilnum{1,3} and Collette Christophe\affilnum{1,2}}
\affiliation{\affilnum{1}Precision Mechatronics Laboratory, University of Liege, Belgium\\
\affilnum{2}BEAMS Department, Free University of Brussels, Belgium\\
\affilnum{3}European Synchrotron Radiation Facility, Grenoble, France}
\email{dehaeze.thomas@gmail.com}
\begin{abstract}
This paper investigates the use of Integral Force Feedback (IFF) for the active damping of rotating mechanical systems.
Guaranteed stability, typical benefit of IFF, is lost as soon as the system is rotating due to gyroscopic effects.
@ -35,15 +43,14 @@ The first consists of slightly modifying the control law while the second consis
Conditions for stability and optimal parameters are derived.
The results reveal that, despite their different implementations, both modified IFF control scheme have almost identical damping authority on suspension modes.
\end{abstract}
\keywords{Active damping, IFF, Rotating platform}
\date{}
\title{Active Damping of Rotating Platforms using Integral Force Feedback}
\begin{document}
\maketitle
\vspace{2pc}
\noindent{\it Keywords}: Active Damping, IFF
\ioptwocol
\section{Introduction}
\label{sec:org6f081c2}
\label{sec:orgcbd1527}
\label{sec:introduction}
There is an increasing need to reduce the undesirable vibration of many sensitive equipment.
A common method to reduce vibration is to mount the sensitive equipment on a suspended platform which attenuates the vibrations above the frequency of the suspension modes.
@ -63,21 +70,21 @@ Section \ref{sec:iff_kp} proposes to add springs in parallel with the force sens
Section \ref{sec:comparison} compares both proposed modifications to the classical IFF in terms of damping authority and closed-loop system behavior.
\section{Dynamics of Rotating Platforms}
\label{sec:org42fff77}
\label{sec:org90939ec}
\label{sec:dynamics}
In order to study how the rotation does affect the use of IFF, a model of a suspended platform on top of a rotating stage is used.
Figure \ref{fig:system} represents the model schematically which is the simplest in which gyroscopic forces can be studied.
\begin{figure}[htbp]
\centering
\includegraphics[width=0.8\linewidth]{system.pdf}
\includegraphics[width=\linewidth]{figs/system.pdf}
\caption{\label{fig:system}Schematic of the studied System}
\end{figure}
The rotating stage is supposed to be ideal, meaning it induces a perfect rotation \(\theta(t) = \Omega t\) where \(\Omega\) is the rotational speed in rad/s.
The rotating stage is supposed to be ideal, meaning it induces a perfect rotation \(\theta(t) = \Omega t\) where \(\Omega\) is the rotational speed in \(\si{\radian\per\second}\).
The suspended platform consists of two orthogonal actuators represented by three elements in parallel: a spring with a stiffness \(k\) in N/m, a dashpot with a damping coefficient \(c\) in N/(m/s) and an ideal force source \(F_u, F_v\).
A payload with a mass \(m\) in kg, representing the sensitive equipment, is mounted on the (rotating) suspended platform.
The suspended platform consists of two orthogonal actuators represented by three elements in parallel: a spring with a stiffness \(k\) in \(\si{\newton\per\meter}\), a dashpot with a damping coefficient \(c\) in \(\si{\newton\per\meter\second}\) and an ideal force source \(F_u, F_v\).
A payload with a mass \(m\) in \(\si{\kilo\gram}\), representing the sensitive equipment, is mounted on the (rotating) suspended platform.
Two reference frames are used: an inertial frame \((\vec{i}_x, \vec{i}_y, \vec{i}_z)\) and a uniform rotating frame \((\vec{i}_u, \vec{i}_v, \vec{i}_w)\) rigidly fixed on top of the rotating stage with \(\vec{i}_w\) aligned with the rotation axis.
The position of the payload is represented by \((d_u, d_v, 0)\) expressed in the rotating frame.
@ -93,9 +100,9 @@ The equation of motion corresponding to the constant rotation in the \((\vec{i}_
\begin{equation}
\label{eq:energy_functions_lagrange}
\begin{aligned}
T &= \frac{1}{2} m \left( \left( \dot{d}_u - \Omega d_v \right)^2 + \left( \dot{d}_v + \Omega d_u \right)^2 \right), \\
V &= \frac{1}{2} k \left( {d_u}^2 + {d_v}^2 \right), \\
D &= \frac{1}{2} c \left( \dot{d}_u{}^2 + \dot{d}_v{}^2 \right), \quad Q_1 = F_u, \quad Q_2 = F_v
T &= \frac{1}{2} m \left( ( \dot{d}_u - \Omega d_v )^2 + ( \dot{d}_v + \Omega d_u )^2 \right), \\
V &= \frac{1}{2} k \big( {d_u}^2 + {d_v}^2 \big), \ Q_1 = F_u, \\
D &= \frac{1}{2} c \big( \dot{d}_u{}^2 + \dot{d}_v{}^2 \big), \ Q_2 = F_v
\end{aligned}
\end{equation}
@ -124,27 +131,29 @@ One can verify that without rotation (\(\Omega = 0\)) the system becomes equival
\end{subequations}
\par
To study the dynamics of the system, the differential equations of motions \eqref{eq:eom_coupled} are transformed in the Laplace domain and the \(2 \times 2\) transfer function matrix \(\bm{G}_d\) from \(\begin{bmatrix}F_u & F_v\end{bmatrix}\) to \(\begin{bmatrix}d_u & d_v\end{bmatrix}\) is obtained
To study the dynamics of the system, the differential equations of motions \eqref{eq:eom_coupled} are transformed in the Laplace domain and the \(2 \times 2\) transfer function matrix \(\bm{G}_d\) from \(\begin{bmatrix}F_u & F_v\end{bmatrix}\) to \(\begin{bmatrix}d_u & d_v\end{bmatrix}\) is obtained.
\begin{equation}
\label{eq:Gd_mimo_tf}
\begin{bmatrix} d_u \\ d_v \end{bmatrix} = \bm{G}_d \begin{bmatrix} F_u \\ F_v \end{bmatrix}
\end{equation}
\begin{subequations}
\begin{align}
\bm{G}_{d}(1,1) &= \frac{ms^2 + cs + k - m \Omega^2}{\left( m s^2 + cs + k - m \Omega^2 \right)^2 + \left( 2 m \Omega s \right)^2} \\
&= \bm{G}_{d}(2,2) \nonumber \\
\bm{G}_{d}(1,2) &= \frac{2 m \Omega s}{\left( m s^2 + cs + k - m \Omega^2 \right)^2 + \left( 2 m \Omega s \right)^2} \\
&= -\bm{G}_{d}(1,2) \nonumber
\end{align}
\begin{align}
\bm{G}_{d}(1,1) &= {\frac{ms^2 + cs + k - m \Omega^2}{\left( m s^2 + cs + k - m \Omega^2 \right)^2 + \left( 2 m \Omega s \right)^2}} \\
&= \bm{G}_{d}(2,2) \nonumber \\
\bm{G}_{d}(1,2) &= {\frac{2 m \Omega s}{\left( m s^2 + cs + k - m \Omega^2 \right)^2 + \left( 2 m \Omega s \right)^2}} \\
&= -\bm{G}_{d}(1,2) \nonumber
\end{align}
\end{subequations}
To simplify the analysis, the undamped natural frequency \(\omega_0\) and the damping ratio \(\xi\) are used
\begin{equation}
\omega_0 = \sqrt{\frac{k}{m}} \text{ in rad/s}, \quad \xi = \frac{c}{2 \sqrt{k m}}
\omega_0 = \sqrt{\frac{k}{m}} \text{ in } \si{\radian\per\second}, \quad \xi = \frac{c}{2 \sqrt{k m}}
\end{equation}
The elements of the transfer function matrix \(\bm{G}_d\) become equal to
The transfer function matrix \(\bm{G}_d\) becomes equal to
\begin{subequations}
\label{eq:Gd_w0_xi_k}
\begin{align}
@ -153,16 +162,19 @@ The elements of the transfer function matrix \(\bm{G}_d\) become equal to
\end{align}
\end{subequations}
For all further numerical analysis in this study, we consider \(\omega_0 = 1\,\text{rad}/s\), \(k = 1\,N/m\) and \(\xi = 0.025 = 2.5\,\%\).
For all further numerical analysis in this study, we consider \(\omega_0 = \SI{1}{\radian\per\second}\), \(k = \SI{1}{\newton\per\meter}\) and \(\xi = 0.025 = \SI{2.5}{\percent}\).
Even though no system with such parameters will be encountered in practice, conclusions can be drawn relative to these parameters such that they can be generalized to any other set of parameters.
\par
The poles of \(\bm{G}_d\) are the complex solutions \(p\) of
The poles of \(\bm{G}_d\) are the complex solutions \(p\) of \eqref{eq:poles}.
\begin{equation}
\label{eq:poles}
\left( \frac{p^2}{{\omega_0}^2} + 2 \xi \frac{p}{\omega_0} + 1 - \frac{{\Omega}^2}{{\omega_0}^2} \right)^2 + \left( 2 \frac{\Omega}{\omega_0} \frac{p}{\omega_0} \right)^2 = 0
\end{equation}
Supposing small damping (\(\xi \ll 1\)), two pairs of complex conjugate poles are obtained:
Supposing small damping (\(\xi \ll 1\)), two pairs of complex conjugate poles are obtained \eqref{eq:pole_values}.
\begin{subequations}
\label{eq:pole_values}
\begin{align}
@ -179,13 +191,13 @@ Physically, the negative stiffness term \(-m\Omega^2\) induced by centrifugal fo
In the rest of this study, rotational speeds smaller than the undamped natural frequency of the system are assumed (\(\Omega < \omega_0\)).
\begin{figure}[htbp]
\begin{subfigure}[c]{0.45\linewidth}
\includegraphics[width=\linewidth]{campbell_diagram_real.pdf}
\begin{subfigure}[c]{0.48\linewidth}
\includegraphics[width=\linewidth]{figs/campbell_diagram_real.pdf}
\caption{\label{fig:campbell_diagram_real} Real Part}
\end{subfigure}
\hfill
\begin{subfigure}[c]{0.45\linewidth}
\includegraphics[width=\linewidth]{campbell_diagram_imag.pdf}
\begin{subfigure}[c]{0.48\linewidth}
\includegraphics[width=\linewidth]{figs/campbell_diagram_imag.pdf}
\caption{\label{fig:campbell_diagram_imag} Imaginary Part}
\end{subfigure}
\hfill
@ -199,14 +211,14 @@ These plots confirm the expected behavior: the frequency of the two pairs of com
For \(\Omega > \omega_0\), the low frequency pair of complex conjugate poles \(p_{-}\) becomes unstable.
\begin{figure}[htbp]
\begin{subfigure}[c]{0.49\linewidth}
\includegraphics[width=\linewidth]{plant_compare_rotating_speed_direct.pdf}
\caption{\label{fig:plant_compare_rotating_speed_direct} Direct Terms \(d_u/F_u\) and \(d_v/F_v\)}
\begin{subfigure}[c]{0.48\linewidth}
\includegraphics[width=\linewidth]{figs/plant_compare_rotating_speed_direct.pdf}
\caption{\label{fig:plant_compare_rotating_speed_direct} Direct Terms}
\end{subfigure}
\hfill
\begin{subfigure}[c]{0.49\linewidth}
\includegraphics[width=\linewidth]{plant_compare_rotating_speed_coupling.pdf}
\caption{\label{fig:plant_compare_rotating_speed_coupling} Coupling Terms \(d_v/F_u\) and -\(d_u/F_v\)}
\begin{subfigure}[c]{0.48\linewidth}
\includegraphics[width=\linewidth]{figs/plant_compare_rotating_speed_coupling.pdf}
\caption{\label{fig:plant_compare_rotating_speed_coupling} Coupling Terms}
\end{subfigure}
\hfill
\caption{\label{fig:plant_compare_rotating_speed}Bode Plots for \(\bm{G}_d\) for several rotational speed \(\Omega\)}
@ -214,7 +226,7 @@ For \(\Omega > \omega_0\), the low frequency pair of complex conjugate poles \(p
\end{figure}
\section{Decentralized Integral Force Feedback}
\label{sec:org955ee19}
\label{sec:orgabd3121}
\label{sec:iff}
In order to apply IFF to the system, force sensors are added in series with the two actuators (Figure \ref{fig:system_iff}).
As this study focuses on decentralized control, two identical controllers \(K_F\) are used to feedback each of the sensed force to its associated actuator and no attempt is made to counteract the interactions in the system.
@ -222,13 +234,13 @@ The control diagram is schematically shown in Figure \ref{fig:control_diagram_if
\begin{figure}[htbp]
\centering
\includegraphics[width=0.8\linewidth]{system_iff.pdf}
\includegraphics[width=\linewidth]{figs/system_iff.pdf}
\caption{\label{fig:system_iff}System with added Force Sensor in series with the actuators}
\end{figure}
\begin{figure}[htbp]
\centering
\includegraphics[scale=1]{control_diagram_iff.pdf}
\includegraphics[scale=1]{figs/control_diagram_iff.pdf}
\caption{\label{fig:control_diagram_iff}Control Diagram for decentralized IFF}
\end{figure}
@ -266,7 +278,7 @@ The zeros of the diagonal terms of \(\bm{G}_f\) are equal to (neglecting the dam
The frequency of the pair of complex conjugate zeros \(z_c\) \eqref{eq:iff_zero_cc} always lies between the frequency of the two pairs of complex conjugate poles \(p_{-}\) and \(p_{+}\) \eqref{eq:pole_values}.
For non-null rotational speeds, two real zeros \(z_r\) \eqref{eq:iff_zero_real} appear in the diagonal terms inducing a non-minimum phase behavior.
This can be seen in the Bode plot of the diagonal terms (Figure \ref{fig:plant_iff_compare_rotating_speed}) where the low frequency gain is no longer zero while the phase stays at \(180\,\text{deg}\).
This can be seen in the Bode plot of the diagonal terms (Figure \ref{fig:plant_iff_compare_rotating_speed}) where the low frequency gain is no longer zero while the phase stays at \(\SI{180}{\degree}\).
The low frequency gain of \(\bm{G}_f\) increases with the rotational speed \(\Omega\)
\begin{equation}
@ -281,7 +293,7 @@ This can be explained as follows: a constant force \(F_u\) induces a small displ
\begin{figure}[htbp]
\centering
\includegraphics[scale=1]{plant_iff_compare_rotating_speed.pdf}
\includegraphics[width=\linewidth]{figs/plant_iff_compare_rotating_speed.pdf}
\caption{\label{fig:plant_iff_compare_rotating_speed}Bode plot of the dynamics from a force actuator to its collocated force sensor (\(f_u/F_u\), \(f_v/F_v\)) for several rotational speeds \(\Omega\)}
\end{figure}
@ -290,17 +302,20 @@ This can be explained as follows: a constant force \(F_u\) induces a small displ
The two IFF controllers \(K_F\) consist of a pure integrator
\begin{equation}
\label{eq:Kf_pure_int}
\bm{K}_F(s) = \begin{bmatrix} K_F(s) & 0 \\ 0 & K_F(s) \end{bmatrix}, \quad K_F(s) = g \cdot \frac{1}{s}
\begin{aligned}
\bm{K}_F(s) &= \begin{bmatrix} K_F(s) & 0 \\ 0 & K_F(s) \end{bmatrix} \\
K_F(s) &= g \cdot \frac{1}{s}
\end{aligned}
\end{equation}
where \(g\) is a scalar representing the gain of the controller.
In order to see how the IFF affects the poles of the closed loop system, a Root Locus plot (Figure \ref{fig:root_locus_pure_iff}) is constructed as follows: the poles of the closed-loop system are drawn in the complex plane as the controller gain \(g\) varies from \(0\) to \(\infty\) for the two controllers \(K_F\) simultaneously.
As explained in \cite{preumont08_trans_zeros_struc_contr_with,skogestad07_multiv_feedb_contr}, the closed-loop poles start at the open-loop poles (shown by crosses) for \(g = 0\) and coincide with the transmission zeros (shown by circles) as \(g \to \infty\).
The direction of increasing gain is indicated by arrows.
As explained in \cite{preumont08_trans_zeros_struc_contr_with,skogestad07_multiv_feedb_contr}, the closed-loop poles start at the open-loop poles (shown by \(\tikz[baseline=-0.6ex] \node[cross out, draw=black, minimum size=1ex, line width=2pt, inner sep=0pt, outer sep=0pt] at (0, 0){};\)) for \(g = 0\) and coincide with the transmission zeros (shown by \(\tikz[baseline=-0.6ex] \draw[line width=2pt, inner sep=0pt, outer sep=0pt] (0,0) circle[radius=3pt];\)) as \(g \to \infty\).
The direction of increasing gain is indicated by arrows \(\tikz[baseline=-0.6ex] \draw[-{Stealth[round]},line width=2pt] (0,0) -- (0.3,0);\).
\begin{figure}[htbp]
\centering
\includegraphics[scale=1]{root_locus_pure_iff.pdf}
\includegraphics[scale=1]{figs/root_locus_pure_iff.pdf}
\caption{\label{fig:root_locus_pure_iff}Root Locus: evolution of the closed-loop poles with increasing controller gains \(g\)}
\end{figure}
@ -314,7 +329,7 @@ In order to apply decentralized IFF on rotating platforms, two solutions are pro
The first one consists of slightly modifying the control law (Section \ref{sec:iff_hpf}) while the second one consists of adding springs in parallel with the force sensors (Section \ref{sec:iff_kp}).
\section{Integral Force Feedback with High Pass Filter}
\label{sec:orgeb779c5}
\label{sec:orgb936693}
\label{sec:iff_hpf}
As was explained in the previous section, the instability comes in part from the high gain at low frequency caused by the pure integrators.
@ -343,13 +358,13 @@ It is interesting to note that \(g_{\text{max}}\) also corresponds to the gain w
\begin{figure}[htbp]
\centering
\includegraphics[scale=1]{loop_gain_modified_iff.pdf}
\includegraphics[width=\linewidth]{figs/loop_gain_modified_iff.pdf}
\caption{\label{fig:loop_gain_modified_iff}Modification of the loop gain with the added HFP, \(g = 2\), \(\omega_i = 0.1 \omega_0\) and \(\Omega = 0.1 \omega_0\)}
\end{figure}
\begin{figure}[htbp]
\centering
\includegraphics[scale=1]{root_locus_modified_iff.pdf}
\includegraphics[scale=1]{figs/root_locus_modified_iff.pdf}
\caption{\label{fig:root_locus_modified_iff}Modification of the Root Locus with the added HPF, \(\omega_i = 0.1 \omega_0\) and \(\Omega = 0.1 \omega_0\)}
\end{figure}
@ -362,7 +377,7 @@ It is shown that even though small \(\omega_i\) seem to allow more damping to be
\begin{figure}[htbp]
\centering
\includegraphics[scale=1]{root_locus_wi_modified_iff.pdf}
\includegraphics[width=\linewidth]{figs/root_locus_wi_modified_iff.pdf}
\caption{\label{fig:root_locus_wi_modified_iff}Root Locus for several HPF cut-off frequencies \(\omega_i\), \(\Omega = 0.1 \omega_0\)}
\end{figure}
@ -371,7 +386,7 @@ The gain \(g_{\text{opt}}\) at which this maximum damping is obtained is also di
\begin{figure}[htbp]
\centering
\includegraphics[scale=1]{mod_iff_damping_wi.pdf}
\includegraphics[width=\linewidth]{figs/mod_iff_damping_wi.pdf}
\caption{\label{fig:mod_iff_damping_wi}Attainable damping ratio \(\xi_\text{cl}\) as a function of \(\omega_i/\omega_0\). Corresponding control gain \(g_\text{opt}\) and \(g_\text{max}\) are also shown}
\end{figure}
@ -383,7 +398,7 @@ Three regions can be observed:
\end{itemize}
\section{Integral Force Feedback with Parallel Springs}
\label{sec:org41af864}
\label{sec:org9c04fb0}
\label{sec:iff_kp}
In this section additional springs in parallel with the force sensors are added to counteract the negative stiffness induced by the rotation.
Such springs are schematically shown in Figure \ref{fig:system_parallel_springs} where \(k_a\) is the stiffness of the actuator and \(k_p\) the stiffness in parallel with the actuator and force sensor.
@ -394,14 +409,14 @@ An example of such system is shown in Figure \ref{fig:cedrat_xy25xs}.
\begin{figure}[htbp]
\centering
\includegraphics[width=0.8\linewidth]{system_parallel_springs.pdf}
\includegraphics[width=\linewidth]{figs/system_parallel_springs.pdf}
\caption{\label{fig:system_parallel_springs}Studied system with additional springs in parallel with the actuators and force sensors}
\end{figure}
\begin{figure}[htbp]
\centering
\includegraphics[width=0.8\linewidth]{cedrat_xy25xs.pdf}
\includegraphics[width=0.8\linewidth]{figs/cedrat_xy25xs.png}
\caption{\label{fig:cedrat_xy25xs}XY Piezoelectric Stage (XY25XS from Cedrat Technology)}
\end{figure}
@ -430,8 +445,9 @@ The equations of motion are derived and transformed in the Laplace domain
\begin{subequations}
\label{eq:Gk}
\begin{align}
\bm{G}_{k}(1,1) &= {\scriptstyle \frac{\left( \frac{s^2}{{\omega_0}^2} - \frac{\Omega^2}{{\omega_0}^2} + \alpha \right) \left( \frac{s^2}{{\omega_0}^2} + 2 \xi \frac{s}{\omega_0} + 1 - \frac{{\Omega}^2}{{\omega_0}^2} \right) + \left( 2 \frac{\Omega}{\omega_0} \frac{s}{\omega_0} \right)^2}{\left( \frac{s^2}{{\omega_0}^2} + 2 \xi \frac{s}{\omega_0} + 1 - \frac{{\Omega}^2}{{\omega_0}^2} \right)^2 + \left( 2 \frac{\Omega}{\omega_0} \frac{s}{\omega_0} \right)^2} } \\
\bm{G}_{k}(1,2) &= {\scriptstyle \frac{- \left( 2 \xi \frac{s}{\omega_0} + 1 - \alpha \right) \left( 2 \frac{\Omega}{\omega_0} \frac{s}{\omega_0} \right)}{\left( \frac{s^2}{{\omega_0}^2} + 2 \xi \frac{s}{\omega_0} + 1 - \frac{{\Omega}^2}{{\omega_0}^2} \right)^2 + \left( 2 \frac{\Omega}{\omega_0} \frac{s}{\omega_0} \right)^2} }
& \bm{G}_{k}(1,1) = \dots \nonumber \\
& {\scriptstyle \frac{\big( \frac{s^2}{{\omega_0}^2} - \frac{\Omega^2}{{\omega_0}^2} + \alpha \big) \big( \frac{s^2}{{\omega_0}^2} + 2 \xi \frac{s}{\omega_0} + 1 - \frac{{\Omega}^2}{{\omega_0}^2} \big) + \big( 2 \frac{\Omega}{\omega_0} \frac{s}{\omega_0} \big)^2}{\big( \frac{s^2}{{\omega_0}^2} + 2 \xi \frac{s}{\omega_0} + 1 - \frac{{\Omega}^2}{{\omega_0}^2} \big)^2 + \big( 2 \frac{\Omega}{\omega_0} \frac{s}{\omega_0} \big)^2} } \\
& \bm{G}_{k}(1,2) = {\scriptscriptstyle \frac{- \left( 2 \xi \frac{s}{\omega_0} + 1 - \alpha \right) \left( 2 \frac{\Omega}{\omega_0} \frac{s}{\omega_0} \right)}{\left( \frac{s^2}{{\omega_0}^2} + 2 \xi \frac{s}{\omega_0} + 1 - \frac{{\Omega}^2}{{\omega_0}^2} \right)^2 + \left( 2 \frac{\Omega}{\omega_0} \frac{s}{\omega_0} \right)^2} }
\end{align}
\end{subequations}
@ -450,13 +466,13 @@ It is shown that if the added stiffness is higher than the maximum negative stif
\begin{figure}[htbp]
\centering
\includegraphics[scale=1]{plant_iff_kp.pdf}
\caption{\label{fig:plant_iff_kp}Bode Plot of \(f_u/F_u\) without parallel spring, with parallel springs with stiffness \(k_p < m \Omega^2\) and \(k_p > m \Omega^2\), \(\Omega = 0.1 \omega_0\)}
\includegraphics[width=\linewidth]{figs/plant_iff_kp.pdf}
\caption{\label{fig:plant_iff_kp}Bode plot of \(f_u/F_u\) without parallel spring, with parallel springs with stiffness \(k_p < m \Omega^2\) and \(k_p > m \Omega^2\), \(\Omega = 0.1 \omega_0\)}
\end{figure}
\begin{figure}[htbp]
\centering
\includegraphics[scale=1]{root_locus_iff_kp.pdf}
\includegraphics[width=\linewidth]{figs/root_locus_iff_kp.pdf}
\caption{\label{fig:root_locus_iff_kp}Root Locus for IFF without parallel spring, with parallel springs with stiffness \(k_p < m \Omega^2\) and \(k_p > m \Omega^2\), \(\Omega = 0.1 \omega_0\)}
\end{figure}
@ -472,19 +488,19 @@ This is confirmed in Figure \ref{fig:opt_damp_alpha} where the attainable closed
\begin{figure}[htbp]
\centering
\includegraphics[scale=1]{root_locus_iff_kps.pdf}
\includegraphics[scale=1]{figs/root_locus_iff_kps.pdf}
\caption{\label{fig:root_locus_iff_kps}Comparison the Root Locus for three parallel stiffnessses \(k_p\)}
\end{figure}
\begin{figure}[htbp]
\centering
\includegraphics[scale=1]{opt_damp_alpha.pdf}
\includegraphics[width=\linewidth]{figs/opt_damp_alpha.pdf}
\caption{\label{fig:opt_damp_alpha}Optimal Damping Ratio \(\xi_\text{opt}\) and the corresponding optimal gain \(g_\text{opt}\) as a function of \(\alpha\)}
\end{figure}
\section{Comparison and Discussion}
\label{sec:org2279161}
\label{sec:org6e6cf51}
\label{sec:comparison}
Two modifications to adapt the IFF control strategy to rotating platforms have been proposed in Sections \ref{sec:iff_hpf} and \ref{sec:iff_kp}.
These two methods are now compared in terms of added damping, closed-loop compliance and transmissibility.
@ -503,7 +519,7 @@ It is interesting to note that the maximum added damping is very similar for bot
\begin{figure}[htbp]
\centering
\includegraphics[scale=1]{comp_root_locus.pdf}
\includegraphics[scale=1]{figs/comp_root_locus.pdf}
\caption{\label{fig:comp_root_locus}Root Locus for the two proposed modifications of decentralized IFF, \(\Omega = 0.1 \omega_0\)}
\end{figure}
@ -526,14 +542,14 @@ It is also confirmed that these two techniques can significantly damp the suspen
\begin{figure}[htbp]
\centering
\includegraphics[scale=1]{comp_transmissibility.pdf}
\includegraphics[scale=1]{figs/comp_transmissibility.pdf}
\caption{\label{fig:comp_transmissibility}Comparison of the two proposed Active Damping Techniques - Transmissibility}
\end{figure}
\begin{figure}[htbp]
\centering
\includegraphics[scale=1]{comp_compliance.pdf}
\includegraphics[scale=1]{figs/comp_compliance.pdf}
\caption{\label{fig:comp_compliance}Comparison of the two proposed Active Damping Techniques - Compliance}
\end{figure}
@ -542,7 +558,7 @@ On can see in Figure \ref{fig:comp_transmissibility} that the problem of the deg
The addition of the HPF or the use of the parallel stiffness permit to limit the degradation of the compliance as compared with classical IFF (Figure \ref{fig:comp_compliance}).
\section{Conclusion}
\label{sec:org40ed087}
\label{sec:org0fc9335}
\label{sec:conclusion}
Due to gyroscopic effects, decentralized IFF with pure integrators was shown to be unstable when applied to rotating platforms.
@ -562,9 +578,12 @@ Future work will focus on the experimental validation of the proposed active dam
The Matlab code that was used for this study is available under a MIT License and archived in Zenodo \cite{dehaeze20_activ_dampin_rotat_posit_platf}.
\section*{Acknowledgment}
\label{sec:org7ba6f08}
This research benefited from a FRIA grant (grant number: FC 31597) from the French Community of Belgium.
\section*{Acknowledgments}
\label{sec:org45730f8}
This research benefited from a FRIA grant from the French Community of Belgium.
\section*{References}
\label{sec:org676de81}
\bibliographystyle{iopart-num}
\bibliography{ref.bib}
\end{document}

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@ -1,584 +0,0 @@
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\gdef\@email{%
\footnotetext[0]{\sagesf Email: #1}}}
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\def\corrauth#1{\gdef\@corrauth{%
\footnotetext[0]{\par\vskip-3pt\sagesf\noindent\textbf{Corresponding author:}\\ #1}}}
\let\@corrauth\@empty
\def\affiliation#1{%
\gdef\@affiliation{%
\footnotetext[0]{\sagesf #1}}}
\let\@affiliation\@empty
\def\affilnum#1{${}^{\text{{#1}}}$}
\renewcommand\maketitle{\par
\begingroup
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\ifnum \col@number=\@ne
\@maketitle
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\@maketitle
\fi
\thispagestyle{title}\label{FirstPage}\@affiliation\@corrauth\@email%
\endgroup
%\setcounter{footnote}{0}%
\global\let\affiliation\relax
\global\let\thanks\relax
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\global\let\title\relax
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\begin{center}
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\begin{sf}
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\begin{minipage}[t]{\textwidth-57.625mm}
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\end{minipage}\hspace{15mm}\begin{minipage}[t]{42.625mm}
\hbox{}\scriptsize\journalname\\
\hbox{}\volumenumber(\issuenumber):\startpage--\endpage\\
\hbox{}\copyright The Author(s) \volumeyear\\
\hbox{}Reprints and permission:\\
\hbox{}sagepub.co.uk/journalsPermissions.nav\\
\hbox{}DOI: 10.1177/ToBeAssigned\\
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%\hbox{}\includegraphics[height=4mm]{SAGE_Logo}
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{\noindent\usebox\absbox\par}
{\vspace{20pt}%
%
{\noindent\normalsize\@keywords}\par}
\if@PCfour
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\def\endpage{\pageref{LastPage}}
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\def\journalname{Journal Title}
\def\runninghead#1{\markboth{{#1}}{}}
\def\ps@title{%
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\noindent\rule{\textwidth}{0.5pt}%
}}%
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{\scriptsize{\it Prepared using \textsf{\journalclass} [Version: \update]}}}}
\let\@evenfoot\@oddfoot}
\def\ps@sagepage{%
\let\@mkboth\@gobbletwo
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\noindent\rule{\textwidth}{0.25pt}}}
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\def\@evenfoot{\parbox[t]{\textwidth}{%
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\def\@oddfoot{\@evenfoot}
}
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\@bls=\baselineskip
\renewcommand\section{\@startsection {section}{1}{\z@}%
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{5pt\@afterindentfalse}%
{\sagesf\large\bfseries\raggedright}}
\renewcommand\subsection{\@startsection{subsection}{2}{\z@}%
{0.9\@bls plus .3\@bls minus .1\@bls}%
{4pt\@afterindentfalse}%
{\sagesf\large\itshape\raggedright}}
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{0.5\@bls plus .3\@bls minus .1\@bls}%
{-0.5em\@afterindentfalse}%
{\sagesf\normalsize\itshape}}
\renewcommand\paragraph{\@startsection{paragraph}{4}{1em}%
{0.3\@bls plus .3\@bls minus .1\@bls}%
{-0.5em\@afterindentfalse}%
{\sagesf\normalsize\itshape}}
\def\enumerate{\ifnum \@enumdepth >3 \@toodeep\else
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\edef\@enumctr{enum\romannumeral\the\@enumdepth}\list
{\csname label\@enumctr\endcsname}{\usecounter
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\def\makelabel##1{\hss\llap{##1}}}\fi}
\let\endenumerate =\endlist
\def\itemize{\ifnum \@itemdepth >3 \@toodeep\else \advance\@itemdepth \@ne
\edef\@itemitem{labelitem\romannumeral\the\@itemdepth}%
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\def\makelabel##1{\hss\llap{##1}}}\fi}
\let\enditemize =\endlist
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\@ifempty{#3}{\let\thmnote\@gobble}{\let\thmnote\@iden}%
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%\the\thm@headpunct
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}%
\ignorespaces}
\def\thmhead@plain#1#2#3{%
\thmname{#1}\thmnumber{\@ifnotempty{#1}{ }{#2}}%
\thmnote{ {\the\thm@notefont #3. }}}
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{\subsection*{\normalsize\sagesf\bfseries Acknowledgements}\begin{refsize}\noindent #1}%
{\end{refsize}}
\newenvironment{funding}[1]%
{\subsection*{\normalsize\sagesf\bfseries Funding}\begin{refsize}\noindent #1}%
{\end{refsize}}
\newenvironment{sm}[1]%
{\subsection*{\normalsize\sagesf\bfseries Supplemental material}\begin{refsize}\noindent #1}%
{\end{refsize}}
\newenvironment{dci}[1]%
{\subsection*{\normalsize\sagesf\bfseries Declaration of conflicting interests}\begin{refsize}\noindent #1}%
{\end{refsize}}
\newenvironment{biog}[1]%
{\subsection*{\normalsize\sagesf\bfseries Author biography}\begin{refsize}\noindent #1}%
{\end{refsize}}
\newenvironment{biogs}[1]%
{\subsection*{\normalsize\sagesf\bfseries Author Biographies}\begin{refsize}\noindent #1}%
{\end{refsize}}
%Endnotes
\def\enotesize{\refsize}
\def\enoteheading{\subsection*{\normalsize\sagesf\bfseries\notesname}%
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%\renewcommand\makeenmark{\theenmark.\hspace{0.75em}}
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\leavevmode{\makebox[0cm][r]{%
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{\bfseries}% Theorem head font
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%AS\pushQED{\qed}%
\normalfont \topsep6\p@\@plus6\p@\relax
\trivlist
\item[\hskip\labelsep
\bfseries
#1\@addpunct{.}]\ignorespaces
}{%
%AS\popQED
\endtrivlist\@endpefalse
}
%\renewenvironment{thebibliography}{%
%\section*{\normalsize\refname}
%\list{}{\topsep=0\p@\parsep=0\p@
%\partopsep=0\p@\itemsep=1\p@\labelsep=0\p@\itemindent=-20\p@
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%}\refsize\rm
%\def\newblock{\ }
%\sloppy\clubpenalty4000\widowpenalty4000
%\sfcode`\.=1000\relax}{\endlist}
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\renewcommand{\bibfont}{\refsize}
\renewcommand\refname{{\normalsize References}}
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\usepackage[super,sort&compress,comma]{natbib}
%\bibpunct{(}{)}{;}{}{}{,}
\renewcommand{\bibnumfmt}[1]{#1.}
\setlength{\bibsep}{0pt}
%\setlength{\bibhang}{20pt}
\renewcommand{\bibfont}{\refsize}
\renewcommand\refname{{\normalsize References}}
\fi
\if@sageapa
%\usepackage{apalike}
\usepackage{mslapa}
\setlength{\bibhang}{16pt}
\@ifundefined{chapter}{\def\thebibliography#1{\section*{\refname}\list
{\relax}{\setlength{\labelsep}{0em}
\setlength{\itemindent}{-\bibhang}
\setlength{\leftmargin}{\bibhang}
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\parsep 0pt}%AS
\def\newblock{\hskip .11em plus .33em minus .07em}
\sloppy\clubpenalty4000\widowpenalty4000
\sfcode`\.=1000\relax}}%
\fi
\AtEndDocument{%
\label{LastPage}}
\pagestyle{sagepage}
\if@shortAfour
\twocolumn
\fi
\if@Afour
\twocolumn
\fi
\if@MCfour
\twocolumn
\fi
\if@PCfour
\twocolumn
\fi
\normalsize
\sloppy