How to draw control-systems block diagrams?

[bcbeckman (Brian Beckman)]

In the documentation ClosedLoopResponsesWithAPIDController, There is a very nice block diagram. I want to create my own block diagrams similar to this. I clicked on the diagram and pressed “command-shift-E” to show the underlying expression. I found the expression below. While this is explicit and reasonably easy to modify and extend, For really big graphs (which I have) it will rapidly become too difficult to manage by hand. I wonder if there is an easier way to produce such graphics? Is there a tool I just don’t know about for drawing and / or automatically laying out such things?

Graph[{1, 2, 3, 4, 5, 6, 7, 8, 
        9}, {{{1, 2}, {2, 3}, {3, 4}, {4, 5}, {5, 6}, {6, 7}, {6, 
    2}, {8, 4}, {9, 6}}, Null}, {
        EdgeLabels -> {DirectedEdge[8, 4] -> Placed[
                 Style["+", {FontFamily -> "Helvetica", 
                     GrayLevel[0, 1], 12}], {1, {-0.8, 0.2}}], 
    DirectedEdge[3, 4] -> Placed[
                 Style["+", {FontFamily -> "Helvetica", 
                     GrayLevel[0, 1], 12}], 0.9], 
    DirectedEdge[9, 6] -> Placed[
                 Style["+", {FontFamily -> "Helvetica", 
                     GrayLevel[0, 1], 12}], {1, {-0.8, 0.2}}], 
    DirectedEdge[5, 6] -> Placed[
                 Style["+", {FontFamily -> "Helvetica", 
                     GrayLevel[0, 1], 12}], 0.9], 
    DirectedEdge[6, 2] -> Placed[
                 Style["-", {FontFamily -> "Helvetica", 
                     GrayLevel[0, 1], 12}], {0.965, {-0.7, 0}}], 
    DirectedEdge[1, 2] -> Placed[
                 Style["+", {FontFamily -> "Helvetica", 
                     GrayLevel[0, 1], 12}], 0.9]}, 
         EdgeShapeFunction -> {}, 
         EdgeStyle -> {
             GrayLevel[0, 1]}, Epilog -> {
             Text[
               Style["u", {FontFamily -> "Helvetica", 
                   GrayLevel[0, 1], 12}], {2.5, 0.1}]}, 
  ImageSize -> 500, 
         VertexCoordinates -> {{0., 0.}, {0.7, 0.}, {1.8, 0.}, {2.9, 
     0.}, {3.9, 0.}, {5., 0.}, {5.6, 0.}, {
             2.9, 0.66}, {5., 0.66}}, VertexLabels -> {1 -> Placed[
                 Style["r", {FontFamily -> "Helvetica", 
                     GrayLevel[0, 1], 12}], Center], 6 -> Placed[
                 Style["", {FontFamily -> "Helvetica", 
                     GrayLevel[0, 1], 12}], Center], 9 -> Placed[
                 Style["m", {FontFamily -> "Helvetica", 
                     GrayLevel[0, 1], 12}], Center], 2 -> Placed[
                 Style["", {FontFamily -> "Helvetica", 
                     GrayLevel[0, 1], 12}], Center], 8 -> Placed[
                 Style["d", {FontFamily -> "Helvetica", 
                     GrayLevel[0, 1], 12}], Center], 7 -> Placed[
                 Style["y", {FontFamily -> "Helvetica", 
                     GrayLevel[0, 1], 12}], Center], 3 -> Placed[
                 Style["PID controller", {FontFamily -> "Helvetica", 
                     GrayLevel[0, 1], 12}], Center], 4 -> Placed[
                 Style["", {FontFamily -> "Helvetica", 
                     GrayLevel[0, 1], 12}], Center], 5 -> Placed[
                 Style["linear system", {FontFamily -> "Helvetica", 
                     GrayLevel[0, 1], 12}], Center]}, 
         VertexShapeFunction -> {
            3 -> "Square", 4 -> "Circle", 7 -> "Square", 
    5 -> "Square", 9 -> "Square", 1 -> "Square", 6 ->
              "Circle", 8 -> "Square", 2 -> "Circle"}, 
         VertexSize -> {8 -> {0.1, 0.1}, 3 -> {0.6, 0.2}, 
    2 -> {0.125, 0.125}, 1 -> {0.1, 0.1}, 9 -> {0.1, 0.1}, 
             4 -> {0.125, 0.125}, 6 -> {0.125, 0.125}, 
    5 -> {0.6, 0.2}, 7 -> {0.1, 0.1}}, 
         VertexStyle ->
   {2 -> Directive[GrayLevel[1], 
      EdgeForm[{GrayLevel[0], AbsoluteThickness[1]}]], 
    1 -> Directive[Opacity[0], EdgeForm[{}]],
    8 -> Directive[Opacity[0], EdgeForm[{}]],
    7 -> Directive[Opacity[0], EdgeForm[{}]],
    5 -> Directive[GrayLevel[1], 
      EdgeForm[{GrayLevel[0], AbsoluteThickness[1]}]],
    6 -> Directive[GrayLevel[1], 
      EdgeForm[{GrayLevel[0], AbsoluteThickness[1]}]],
    4 -> Directive[GrayLevel[1], 
      EdgeForm[{GrayLevel[0], AbsoluteThickness[1]}]],
    9 -> Directive[Opacity[0], EdgeForm[{}]],
    3 -> Directive[GrayLevel[1], 
      EdgeForm[{GrayLevel[0], AbsoluteThickness[1]}]]
    }}]

[johanr (Johan Rhodin)]

One way to get technical diagrams into Mathematica is to construct them in SystemModeler and then use the function WSMModelData to get the diagram.

Here I’ve constructed a simple control system in SystemModeler:

Next, I fetch the diagram into Mathematica:

WSMModelData["controlSystem", "Diagram"]

I know that the icons in this library (Modelica.Blocks) doesn’t looks like the typical textbook example you mentioned. If you are going to draw and use a large number of diagrams like this, it might be worthwhile to create custom components in SystemModeler that looks exactly like you want them to. (It’s easy, there are drawing tools and everything you need)