% ---------------------------------------------------------------
% Sistema de controle em malha aberta.
% ---------------------------------------------------------------
\begin{tikzpicture}[>=Latex, line width=0.9pt, node distance=1.4cm,
  bloco/.style={draw, minimum width=2.2cm, minimum height=1.1cm, fill=blue!8},
  seta/.style={->}]

  \node (r) at (0,0) {$r(t)$};
  \node[bloco, right=of r]   (c) {Controlador};
  \node[bloco, right=of c]   (g) {Planta};
  \node[right=of g] (y) {$y(t)$};

  \draw[seta] (r) -- (c);
  \draw[seta] (c) -- node[above, font=\small]{$u(t)$} (g);
  \draw[seta] (g) -- (y);

\end{tikzpicture}