%&tex
\documentclass{standalone}
\usepackage{tikz}
\usepackage{siltex}
\usetikzlibrary{calc,positioning,patterns,math}
% Compliant PDF
\usepackage[a-3u]{pdfx}

\begin{document}
\begin{tikzpicture}[x=0.75cm, y=0.75cm]
    \tikzstyle{arrow} = [-latex,ultra thick]

    % draw roof
    \fill[pattern = north east lines] ($ (0,0) + (-1,0) $) rectangle ($ (0,0) + (1,0.5) $);
    \draw[thick] ($ (0,0.5) + (-1,0) $) -- ($ (0,0.5) + (1,0) $);

    %draw arm and joints
    \pgfmathsetmacro{\alphahoek}{120};
    \pgfmathsetmacro{\a}{4};
    \pgfmathsetmacro{\betahoek}{-105};
    \pgfmathsetmacro{\b}{4};
    \pgfmathsetmacro{\radius}{0.8};
    \begin{scope}[shift={(0,0.5)}]
        \draw (\radius,0) arc [start angle=0, end angle=\alphahoek, radius=\radius] node[above,midway] {$\alpha$};
        \begin{scope}[rotate=\alphahoek]
            \fill (0,0) circle (0.2);  
            \draw[thick] (0,0) to node[midway,right,draw=none] {$a$} (\a,0);  
            \begin{scope}[shift={(\a,0)}]
                \draw (-\radius,0) arc [start angle=-180, end angle=\betahoek, radius=\radius] node[right,midway] {$\beta$};
                \begin{scope}[rotate=\betahoek]
                    \fill (0,0) circle (0.2);  
                    \draw[thick] (0,0) to node[midway,below,draw=none] {$b$} (\b,0);  
                    \begin{scope}[shift={(\b,0)}]
                        \draw[fill=white] (0,0) circle (0.3) node {$m$};
                    \end{scope}
                \end{scope}
            \end{scope}
        \end{scope}
    \end{scope}
\end{tikzpicture}
\end{document}