Innovation with Conflicting Constraints

Case Study: Managing Conflicting Constraints

I am looking for a good source of Unobtainium.  With the pandemic in full swing, it's really hard to find.  Yet, the demand keeps growing.  I have a few customer projects that need it to solve conflicting constraints, so if you know a good source, please pass it along.

Unobtainium would really come in handy on this recent project in dealing with conflicting constraints.  You have likely been there too.

Today we have an example of a simple structure.  The customer originally approached me with a few quick questions about cutting steel and welding.  As we got into it, I realized is was a lot more.  While the project definitely needs cutting, it also needs a little more thinking about how to accomplish the broader picture goals.  Since the big picture sets the stage, things that start with simple questions can easily turn into a full blown project.

The Big Picture First

Remember the Triangle of Achievable Engineering?  Yeah, that one where we talk about hitting objectives.  The triangle is all about conflicting constraints, so take a minute and read that article.  Here is the triangle image again.

Achievable Engineering FocusIt is a useful tool when we think about other goals too.  For this project, we can relabel the sides with the goals of Weight (lighter is better) / Vibration (minimize it) / Accuracy (for positional interaction).

For this project, the customer has two small machines that need to mount on two different height pedestals.  Both machines create some vibration, yet the two machines must interact solidly, and accurately, with respect to each other.  Now the hiccup, the assembly must be light enough to hand carry.  (2 people.)

Looking At The Triangle . . .
  • It is easy to get Low Weight and High Accuracy if we drop the Vibration requirement.  Accuracy can be great statically, but enter the vibration on a lightweight platform and accuracy goes out the window.
  • It is also pretty easy to make it rock solid even with vibration if we don't care about weight.  A huge solid chunk of machined steel would certainly do the job, but much to heavy!
  • The combination of low Weight with well damped Vibration is also pretty easy if we don't care about accuracy.  Rubber mounting does that, but it would move around and fail to achieve the necessary requirements with accuracy.

You get the picture.  This is all about managing conflicting constraints - or shifting the paradigm.

A friend once described engineering as The Science of Balance.  That statement is true in physical ways, human ways, mental ways, financial ways, and so many more.  No wonder we reach so often for the holy grail of something we can't have.  Like my favorite material, Unobtainium.

Bringing Things Into Focus

Well, if I can't have the infinitely stiff, infinitely strong, Unobtainium that weights virtually nothing, then I'll have to settle for another method.  Innovation is certainly my "Go-To".  What is yours?

3D Puzzle in SteelFor me, the Elegant Solution usually comes as I shift paradigms.  Some people call it thinking outside the box, but I don't really recognize a thinking "box" per se, but maybe that is just me.

Interlocking PiecesThis customer came asking about cutting steel (angle, tube and flat), then welding to build the platform.  My first reaction was one of accommodation - until I understood what he is doing and thought about getting the alignment right.

As the higher level goals came into focus, it became clear the solution is not down a traditional path.  Yes, it is a machine pedestal, and welding the structure can work, but a different approach will come closer to reaching all of the big picture goals.

The Solution

Let's ditch the structural steel, and instead, make a 3D puzzle.  A bunch of interlocking plates will make assembly easy.  It will also achieve a fairly close alignment — almost by default.

However, the 3D puzzle pieces can't be the alignment.  For good alignment, we need fixed datums that are datums by definition.  Puzzle pieces can interlock, and provide the end strength, but cut edges do not make good datums.  That will end up as a mess.

Welding will join all the pieces and solidify the assembly once the assembly is complete.  The plates will then for a super rigid structure, and the interlocking bits all become one.

Some internal pieces (the cool tid-bits, not shown) create the datums and all but assure a square, aligned fit.  (That is really the magic for success with this project, and it reflects one primary reason to hire Synthesis.)

The broad plates will carry all the forces crisscrossing within, and give great surface area for the internal damping material — sand.  (Loose sand is an awesome damper for vibration.)  Finally, if the damping material (sand) is put in and taken out separate, then it becomes modular (in a different way), yet has the need weight for stability - and when dumped out, a weight loss to allow portability.

That gives a pedestal with a reasonable balance of the conflicting constraints.  It is both light to carry (without the sand), and heavy (plus) for damping the machine vibration.  It also achieves a very stiff and accurate pedestal for both machines.

Truth be told, because of the inconvenience in handling sand, he will try it without the sand first.  Then, use the sand if we find the vibration objectionable.

Did We Balance The Conflicting Constraints?

Looking at the above Triangle again — Weight, Vibration, Accuracy — how did we do?  We did not compromise much on Accuracy, and we found a good strategy for weight and vibration (function), by increasing cost and inconvenience.  (Handling sand is definitely an inconvenience.)

So, really our paradigm shift changed the triangle with respect to the conflicting constraints.  We end up with triangle legs of Accuracy / Weight & Vibration Balance / Convenience & Cost.

Of course, there are a lot of ways to think about the triangle, and maybe you see it different.  The point here is a change in what we first think can lead to solutions that are quite different from the original vision.

As a side note, I do not believe a simple table made from welding angle can even compare to the stability and vibration damping / resistance of this final pedestal.

Achievement:  We were able to set the two plates for mounting the machines at about 0.002" parallelism.  The machine (without sand) did show just a tiny bit of vibration issue, but it was more felt than seen.  We stiffened some parts of the one machine, then filled the base with sand to eliminate the effects of vibration.  The hand carry requirement was to navigate stairs and corners.  That was easy, and if it needs to move in the future, it will not be hard.

When Is Innovation Innovative?

Is that a silly question?

There is nothing very innovative about the solution in this example.  It is just applying differently some things we have already done elsewhere.  A new problem, with several old solutions mashed together for something that looks kind-of new.  Is that really innovation?  Well, I have a lot of patents that are basically just that.  Cross-pollination from industry to industry has been powerful for me - well, really for my customers - a method of changing the paradigms of conflicting constraints.

Internals Solve Conflicting ConstraintsSo, for this project, you can see the images.  By applying principles of care from the design, to the parts, to the build, we came very close to parallel and perpendicular just in the weldment.  (And, welding is not known for being flat and parallel.)

Starting in the engineering, we applied good sense in what we could expect for part tolerance in ways that gave dependable datums for building.  We also thought carefully about the manufacturing processes to bias the design for methods we knew are easy to make right.  It is one thing to envision something perfect, and quite another to make it that way.  Again, a different kind of conflicting constraints, because you have to build it.  That includes leaving appropriate access - in this case to weld on the inside.

To answer the question, it can feel innovative when it all comes together and delights the customer in ways that they are not expecting.  Which is not so different from the discussion on Prototyping the Impossible.

So, the twin pedestal, 3D puzzle box is light enough to lift, and amazingly stiff.  Plus, it has all the needed adjustment (with shims and screws) so high accuracy is achievable.  So, in managing the conflicting constraints, we did sacrifice some on weight which is the convenience to move it, but we hit the goals for accuracy and vibration.  Those were more important for the customer anyway.

The Elegant Solution from Conflicting Constraints

This photo shows the final result (minus the old cart it is sitting on.)  Of course, it looks better after powdercoat, but that is not part of this discussion.

Solution for Conflicting ConstraintsWhen it comes right down to it, there is not a fixed path for achieving engineering balance.  Every project brings new challenges and new conflicting constraints.  Getting out of a thought groove definitely helps.  Changing the paradigms of conflicting constraints (whatever they are) is also a big help.

Seriously, creative thinking is usually better than wishing for the elusive Unobtainium - and certainly more available.

But, I think the most useful piece is a willingness to go back to the big picture and look at the world different.  Challenge what you think are the conflicting constraints, and never settle for the first solution.

Yes, and a big one is staying stay out of the weeds until you know the furrow.  (Sorry, I'm just an old farm boy.)

Good Luck With Your Projects!

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