PDF not generated but I see no error!

Question

I am having a lot of trouble adding png images and also with hyphenations, All of a suddent I was adding the following tkiz scheme and when I add the lattest part I started getting a bunch of Underfull vbox and Overfull xbox/hbox, I worked around it (or I thingk) but then as I said when I added the second half of the scheme my pdf is not generated anymore.. I have tried splitting the tikz pictures into to figures and force a \pagebreak in between and other stuff but so far nothing... I am adding both the tikz scheme which seems to be the problem and the output I get at the very end.

CODE:

\begin{figure}
\centering
\begin{tikzpicture}
\node [fill=white, draw=black, name=force_operator, shape=rectangle, text width=1.5cm,text centered, minimum width = 1.5cm, font=\footnotesize] at (0,0) {Operator's Force};
\node [fill=black!20, draw=black, name=sum1, shape=circle, inner sep=2pt, right=0.75cm of force_operator, minimum size= 0.5cm, font=\footnotesize] {+};
\node [fill=blue!20, draw=black, name=model_master, shape=rectangle, text width=2cm, text centered, font=\footnotesize, right=0.5 of sum1] {$\frac{1}{m\cdot{s} + b}$};
\node [fill=blue!20, draw=black, name=delay1, shape=rectangle, text width=1cm, text centered, font=\footnotesize, right=1.5cm of model_master] {$e^{-2s\tau}$};
\node [fill=blue!20, draw=black, name=simplification_slave, shape=rectangle, text width=4cm, text centered, font=\footnotesize, right=0.5cm of delay1] {$\frac{B\cdot{s} + K {m\cdot{s^2} + (B+b)\cdot{s} + K}$};
\node [fill=white, draw=white, name=a, right=0.5cm of simplification_slave]{};
\node [fill=blue!20, draw=black, name=master_controller, shape=rectangle, text width=2cm, text centered, font=\footnotesize, below=1cm of model_master]  {$\frac{B\cdot{s} + K}{s}$};
\node [fill=black!20, draw=black, name=sum4, shape=circle, inner sep=2pt, right=0.5cm of master_controller, minimum size= 0.5cm, font=\footnotesize] {$+$};

\draw[->] (force_operator) -- node[above, font=\footnotesize]{$F_h$}(sum1);
\draw[->] (sum1) -- node[above, font=\footnotesize]{}(model_master);
\draw[->] (model_master) -- node[above, font=\footnotesize, name=c]{$V_m$}(delay1);
\draw[->] (delay1)  -- node[above, font=\footnotesize]{}(simplification_slave);
\draw[-] (simplification_slave) -- node[above, font=\footnotesize]{}(a.center);
\draw[-] (a.center)     |- node[above, font=\footnotesize]{}(sum4);
\draw[->] (sum4)    -- node[above, font=\footnotesize]{}(master_controller);
\draw[->] (master_controller) -| node[left, pos=0.95] {\footnotesize{$-$}} node[left, font=\footnotesize]{$F_m$}(sum1);
\draw[->] (c) -- (sum4);
\end{tikzpicture}
\end{figure}

\pagebreak[4]

\begin{figure}
\centering
\begin{tikzpicture}
\node [fill=white, draw=black, name=force_operator, shape=rectangle, text width=1.5cm, text centered, minimum width = 1.5cm, font=\footnotesize] at (0,0) {Operator's Force};
\node [fill=black!20, draw=black, name=sum1, shape=circle, inner sep=2pt, right=0.75cm of force_operator, minimum size= 0.5cm, font=\footnotesize] {+};
\node [fill=blue!20, draw=black, name=model_master, shape=rectangle, text width=2cm, text centered, font=\footnotesize, right=0.5 of sum1] {$\frac{1}{m\cdot{s} + b}$};
\node [fill=blue!20, draw=black, name=simplification, shape=rectangle, text width=2cm, text centered, font=\footnotesize, right=1cm of model_master] {};%$\frac{m\cdot{s^2} + (B+b)\cdot{s} + K + (B\cdot{s} +K)\cdot{\exp{-2s\tau}}}{m\cdot{s^2} + (B+b)\cdot{s} + K}$};
\node [fill=white, draw=white, name=a, right=0.5cm of simplification{};
\node [fill=blue!20, draw=black, name=master_controller, shape=rectangle, text width=2cm, text centered, font=\footnotesize, below=1cm of model_master]  {$\frac{B\cdot{s} + K}{s}$};

\draw[->] (force_operator)  -- node[above, font=\footnotesize]{$F_h$}(sum1);
\draw[->] (sum1)        -- node[above, font=\footnotesize]{}(model_master);
\draw[->] (model_master)    -- (simplification);
\draw[-] (simplification)   -- (a.center);
\draw[->] (a.center) |- node[above, font=\footnotesize]{}(master_controller);
\draw[->] (master_controller)   -| node[left, font=\footnotesize]{$F_m$}(sum1);
\end{tikzpicture}
\end{figure}

AND THE OUTPUT:

(...)

LaTeX Warning: Reference `eq:B_for_critically_damped_no_delay' on page 28 undef ined on input line 223.

LaTeX Warning: Reference `eq:B_for_critically_damped_no_delay' on page 28 undef ined on input line 223.

Overfull \hbox (103.13486pt too wide) in paragraph at lines 230--232 [] [] [28] [29]) (./chapters/Related_Work/2.1.3.The_Effect_of_Delay.tex

LaTeX Warning: Reference `fig:pos_pos_sym_delay' on page 30 undefined on input line 5.

LaTeX Warning: Reference `fig:pos_force_delay' on page 30 undefined on input li ne 5.

Overfull \hbox (2.18416pt too wide) in paragraph at lines 40--41 [][]

LaTeX Warning: Reference `' on page 30 undefined on input line 77.

LaTeX Warning: Reference `' on page 30 undefined on input line 77.

Underfull \vbox (badness 10000) has occurred while \output is active [30]

Answer 1

Is this what you want?

 \documentclass{article}
 \usepackage{tikz}
 \begin{document}
 \begin{center}
 \begin{tikzpicture}[auto, node distance=3cm]
 \tikzstyle{block}=[draw, rectangle, text width=1.5cm, text centered, minimum width =  
 1.5cm, font=\footnotesize, minimum height=2em, minimum width=4em]
 \tikzstyle{sum}=[draw, circle, inner sep=2pt, right of= force_operator, minimum 
 size=0.5cm, font=\footnotesize]
 \node [block, name=force_operator ] at (0,0) {Operator's Force};
 \node [sum,fill=black!20, draw=black, name=sum1]   {+};
 \node [block, fill=blue!20, name=model_master, right  of = sum1] {$\frac{1} 
 {m\cdot{s} + b}$};
 \node [block, fill=blue!20, name=delay1, shape=rectangle, text width=1cm, text
 centered, font=\footnotesize, right of= model_master] {$e^{-2s\tau}$};
 \node [fill=blue!20, draw=black, name=simplification_slave, shape=rectangle, text
 width=3cm, text centered, font=\footnotesize, right of =delay1]
 {$\frac{B\cdot{s} + K {m\cdot{s^2} + (B+b)\cdot{s} + K}}{x}$};
 \node [fill=white, draw=white, name=a, right of = simplification_slave]{};
 \node [block, fill=blue!20, name=master_controller, below of = model_master]   
 {$\frac{B\cdot{s} + K}{s}$};
 \node [sum,fill=black!20, draw=black, name=sum4, right of = master_controller, node 
 distance=0.79cm] {$+$};
 \draw[->] (force_operator) -- node[above, font=\footnotesize]{$F_h$}(sum1);
 \draw[->] (sum1) -- node[above, font=\footnotesize]{}(model_master);
 \draw[->] (model_master) -- node[above, font=\footnotesize, name=c]{$V_m$}(delay1);
 \draw[->] (delay1)  -- node[above, font=\footnotesize]{}(simplification_slave);
 \draw[-] (simplification_slave) -- node[above, font=\footnotesize]{}(a.center);
 \draw[-] (a.center)  |- node[above, font=\footnotesize]{}(sum4);
 \draw[->] (sum4) -- node[above, font=\footnotesize]{}(master_controller);
 \draw[->] (master_controller) -| node[left, pos=0.95] {\footnotesize{$-$}}
  node[left, font=\footnotesize]{$F_m$}(sum1);
 \draw[->] (c) -- (sum4);
 \end{tikzpicture}
 \end{center}

 \begin{center}
 \begin{tikzpicture}[auto, node distance=3cm]
 \tikzstyle{block}=[draw, rectangle, text width=1.5cm, text centered, minimum width =    
 1.5cm, font=\footnotesize, minimum height=2em, minimum width=4em]
 \tikzstyle{sum}=[circle, inner sep=2pt, right of= force_operator, minimum size= 
 0.5cm, font=\footnotesize]
 \node [block, fill=white, name=force_operator, ] at (0,0) {Operator's Force};
 \node [sum, fill=black!20, draw=black, name=sum1] {+};
 \node [block, fill=blue!20, name=model_master,  right of = sum1] {$\frac{1}
 {m\cdot{s} + b}$};
 \node [fill=blue!20, draw=black, name=simplification, shape=rectangle, text
 width=4.5cm, node distance=5cm, text centered, font=\footnotesize, right of = 
 model_master] {$\frac{m\cdot{s^2} + (B+b)\cdot{s} + K + (B\cdot{s}  
 +K)\cdot{\exp{-2s\tau}}}{m\cdot{s^2} + (B+b)\cdot{s} + K}$};
 \node [fill=white, name=a, right of= simplification{};
 \node [block, fill=blue!20,  name=master_controller, below of = model_master]  
 {$\frac{B\cdot{s} + K}{s}$};
 \draw[->] (force_operator)  -- node[above, font=\footnotesize]{$F_h$}(sum1);
 \draw[->] (sum1) -- node[above, font=\footnotesize]{}(model_master);
 \draw[->] (model_master)  -- (simplification);
 \draw[-] (simplification) -- (a.center);
 \draw[->] (a.center) |- node[above, font=\footnotesize]{}(master_controller);
 \draw[->] (master_controller) -| node[left, font=\footnotesize]{$F_m$}(sum1);
 \end{tikzpicture}
 \end{center}
 \end{document}

Comments:

1. The main errors occur at syntax "right of = some block", but you used right = xxcm of some block.

2. Since the the blocks are all similar/alike you could use \tikzstyle={...} to define it as shown by the defined "block" and "sum". However, if the actual block is larger than the defined block then add the needed dimensions in the option. (I leave one line there for you to check.)

3. In the first diagram, I guess a denominator is missing, where an x is used instead.

4. Once you understand the syntax, you can modify them to suit your need.

5. It is not necessary putting them in figure environment.

An image is attached