Nodes and text in block diagram (Tikz)

\documentclass[border=3.141592]{standalone} \usepackage{tikz} \usetikzlibrary{arrows.meta, calc, chains, positioning, quotes} \usepackage{bm} \begin{document} \begin{tikzpicture}[ node distance = 11mm and 7mm, start chain = A going right, arr/.style = {-Stealth, semithick}, box/.style = {draw, text width=22mm, minimum height=11mm, align=center}, dot/.style = {circle, fill, inner sep=1.2pt, node contents={}}, sum/.style = {circle, draw, minimum size=6mm, node contents={}}, every edge/.style = {draw, arr} ] \begin{scope}[nodes={on chain=A}] \coordinate (in); % A-1 \node [sum]; % A-2 \node [box] {A-3}; \node [box] {A-4}; \node [box] {A-5}; \node [box] {A-6}; \node [dot]; % A-7 \coordinate (out); % A-8 \end{scope} \node [box, above=of A-5] (A-9) {A-9: o}; \node [box, below=of {$(A-4.south east)!0.5!(A-5.south west)$}] (A-10) {A-10: f}; % \path (in) edge ["$\bm{r}$"] (A-2) (A-2) edge (A-3) (A-3) edge ["$\bm{v}$"] (A-4) (A-4) edge ["$\bm{v}$"] (A-5) (A-5) edge ["$\bm{u}$"] (A-6) (A-6) edge [pos=0.25,"$\bm{x}$"] (out) % <--- red x label ([xshift=-2mm] A-9.south) edge ["$t$" '] ([xshift=-2mm] A-5.north) % <--- red lines in your MWE (A-9) edge (A-5) ([xshift=+2mm] A-9.south) edge ["$t$"] ([xshift=+2mm] A-5.north) % <--- red lines in your MWE ; \begin{scope}[every path/.style ={arr}] \draw (A-7) |- (A-9); \draw (A-9) -| node[pos=0.25,above] {$t$} (A-4); % <--- red lines from observer \draw (A-7) |- (A-10); \draw (A-10) -| (A-2.south) node[pos=0.98,left] {$-$}; % \draw ([xshift=-2mm] A-10.north) -- ++ (0,5mm) -| (A-4); % <--- red lines from feedback \draw ([xshift=+2mm] A-10.north) -- ++ (0,5mm) -| (A-5); % <--- red lines from feedback \end{scope} \end{tikzpicture} \end{document} 

Edit: Added are variables t at red lines and comments to code, which define red lines in your sketch.

In proposed solution I do the following editing steps (code I wrote before you edited question)

• at all nodes use defined style box, i.e. block in your code and than delete all local definition of nodes style. By this code become far more shorter and clearer. Beside this, image has now uniform style of nodes (real content od nodes, which can influence on this decision, is still unknown)
• Since nodes with exception for observer (does top nodes present it?) are in chain, for their positions I suggest to use chains library and by this remove repeating of right=of <node name> and make code further shorter
• Because chain is named as A, the nodes in it are numbered as A-1, A-2 etc. This enable to remove nodes names needed for drawing arrows, however, you still can gives them names as you have (for example I preserve name of for first and last node (now replaced by coordinates).
• In drawing arrows between nodes I prefer to use edge quotes. Code is a bit shorter, but require to ad quotes library in document preamble
• that writing of arrows between nodes are used edges. Their style is also defined in tikzpicture options. By its use code for drawing arrows is further shortened.

That is all.

Changes in MWE should be evident from comparison of both MWE. Yes, in editing of your code fragment are done a lot of changes. If after this descriptions something is still not clear, don0t hesitate ask for explanation.

Changes, which added red lines in your images are now marked by % <--- <description>

Also is corrected proposed MWE, now contain variables, which you write at red arrows, too.

Edit (2): Added is lost output arrows with label x, labels u and v are moved to the same place as they are in the your sketch, and \boldsymbolis replaced with\bm` which is defined in the package of the same name.

In boxes are added their names. This may help you to identify coordinates of arrows.

It may happen, that in MWE are still some errors, for example wrong labels (be aware that you have two v what is -- to my opinion -- wrong), which now should be able to correct yourself ;-)