\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{shapes,positioning}
\usetikzlibrary{narrow}

\tikzset{block/.style={draw, rectangle, line width=2pt,
     minimum height=3em, minimum width=3em, outer sep=0pt}}
\tikzset{sumcircle/.style={draw, circle, outer sep=0pt, 
     label=center:{{$\sum$}}, minimum width=2em}}
\tikzset{every picture/.style={auto, line width=1pt,
          >=narrow,font=\small}}

\begin{document}
  \begin{tikzpicture}
      \node[block](G1){$G_1$};
      \node[sumcircle,right=10mm of G1](sum2){};
      \node[block,right=10mm of sum2](G2){$G_2$};
      \node[block,above=7 mm of G2](G5){$G_5$};
      \node[sumcircle,right=10mm of G2](sum3){};
      \node[block,right=10mm of sum3](G3){$G_3$};
      \node[block,below=9mm of G2](G4){$G_4$};
      \node[sumcircle,left=12mm of G1](sum){};
      \node[coordinate, left=15mm of sum](ref){};

      \draw[->](ref)--node[xshift=-4mm](){$r$}(sum);
      \draw[->](sum)--node[xshift=-1mm](){$e$}(G1);
      \draw[->](G1)--(sum2);
      \draw[->](sum2)--(G2);
      \draw[->](G2)--(sum3);
      \draw[->](sum3)--(G3);
      \node[coordinate, right=12mm of G3](output){};
      \draw[->](G3)--node[xshift=-1mm](Y){$y$}(output);
      \draw[->](Y)|-(G4);
      \draw[->](G4)-|(sum);
      \node[coordinate, above=18mm of sum3](disturbance){};
      \draw[->](disturbance)node[right](){$v$}--(sum3);
      \draw[->](disturbance)|-(G5);
      \draw[->](G5)-|node[above]{$u_{FF}$}(sum2);
  \end{tikzpicture}
\end{document}



