Starting point of arrows in tikzpicture

I am new to drawing a block diagram using tikzpicture. The following MWE

\documentclass[a4paper,11pt]{article}

\usepackage{amsmath}
\usepackage{tikz} %http://www.texample.net/tikz/examples/control-system-principles/
\usetikzlibrary{shapes,arrows}
\tikzstyle{block} = [draw, fill=blue!20, rectangle,
minimum height=3em, minimum width=6em]
\tikzstyle{sum} = [draw, fill=blue!20, circle, node distance=1cm]
\tikzstyle{input} = [coordinate]
\tikzstyle{output} = [coordinate]
\tikzstyle{pinstyle} = [pin edge={to-,thin,black}]

\begin{document}
\begin{tikzpicture}[auto, node distance=2cm,>=latex']
% We start by placing the blocks
\node [input, name=input] {};
\node [sum, right of=input, name=sum] (sum) {};
\node [block, right of=sum,label=below:controller] (controller) {?};
\node [sum, right of=controller,node distance=2cm,pin={[pinstyle]above:$D(s)$}] (sum2) {};
\node [block, right of=sum2,node distance=2cm,label=below:process dynamics] (system) {$\dfrac{32}{s(s+4)(s+16)}$};
% We draw an edge between the controller and system block to
% calculate the coordinate u. We need it to place the measurement block.
\draw [->] (controller) -- node[name=u] {} (system);
\node [output, right of=system] (output) {};
\node [block, below of=u,label=below:sensor] (measurements) {1};
% Once the nodes are placed, connecting them is easy.
\draw [draw,->] (input) -- node {$\varphi_d$} (sum);
\draw [->] (sum) -- node {} (controller);
\draw [->] (controller) -- node {} (sum2);
\draw [->] (sum2) -- node {} (system);
\draw [->] (system) -- node [name=y] {$\varphi$}(output);
\draw [->] (y) |- (measurements);
\draw [->] (measurements) -| node[pos=0.99] {\tiny $-$}
node [near end] {} (sum);
\end{tikzpicture}
\end{document}


yields

How can I let the arrow connecting the second sum to the block 'process dynamics' start on the right side of the sum, rather than on the left side (see orange arrow)?

-
There are two arrows. Use \draw [->,red] (sum2.north) -- node {} (system); and you'll see that the right arrow has the correct size. The problem is the other one. –  Sigur Mar 29 '14 at 15:31

You can use (sum2.east) to connect at the right.

\draw [->] (controller) -- node {} (sum2.west);            %% used west
\draw [->] (sum2.east) -- node {} (system);                %% used east


Further, I have changed the \draw to \path in

\path [->] (controller) -- node[name=u] {} (system);      %% changed \draw to \path


Full code:

\documentclass[a4paper,11pt]{article}

\usepackage{amsmath}
\usepackage{tikz} %http://www.texample.net/tikz/examples/control-system-principles/
\usetikzlibrary{shapes,arrows,positioning}
\tikzset{block/.style = {draw, fill=blue!20, rectangle,
minimum height=3em, minimum width=6em},
sum/.style = {draw, fill=blue!20, circle, node distance=1cm},
input/.style = {coordinate},
output/.style = {coordinate},
pinstyle/.style = {pin edge={to-,thin,black}}
}

\begin{document}
\begin{tikzpicture}[auto, >=latex']
% We start by placing the blocks
\node [input, name=input] {};
\node [sum, right =of input, name=sum] (sum) {};
\node [block, right = of sum,label=below:controller] (controller) {?};
\node [sum, right =of controller,pin={[pinstyle]above:$D(s)$}] (sum2) {};
\node [block, right = of sum2,label=below:process dynamics] (system) {$\dfrac{32}{s(s+4)(s+16)}$};
% We draw an edge between the controller and system block to
% calculate the coordinate u. We need it to place the measurement block.
\path [->] (controller) -- node[name=u] {} (system);      %% changed \draw to \path
\node [output, right = of system] (output) {};
\node [block, below =of u,label=below:sensor] (measurements) {1};
% Once the nodes are placed, connecting them is easy.
\draw [draw,->] (input) -- node {$\varphi_d$} (sum);
\draw [->] (sum) -- node {} (controller);
\draw [->] (controller) -- node {} (sum2.west);            %% used west
\draw [->] (sum2.east) -- node {} (system);                %% used east
\draw [->] (system) -- node [name=y] {$\varphi$}(output);
\draw [->] (y) |- (measurements);
\draw [->] (measurements) -| node[pos=0.99] {\tiny $-$}
node [near end] {} (sum);
\end{tikzpicture}
\end{document}


-
Nice! We can not remove the line with superfluous arrow since it is being used to calculate u. So we have to use path instead draw. Great. –  Sigur Mar 29 '14 at 15:38
Why the node sum2 is not on the middle point between the two rectangles? It looks like its west anchor is there. –  Sigur Mar 29 '14 at 15:46
@Sigur Now it is at the center. Culprit was the of= syntax. I used positioning library and right =of. Also removed the spurious node distance=2cm –  Harish Kumar Mar 29 '14 at 16:04
Nice! Now the horizontal space between controller and process is exactly the width of sensor. Looks beautiful. –  Sigur Mar 29 '14 at 16:07
@MWijnand Accepting and upvoting are the conventional ways of thanking in this site. For details, please refer: How do you accept an answer –  Harish Kumar Mar 30 '14 at 0:35