I need a good source of Unobtainium. It is really hard to find these days, 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. 🙂
Of course, I jest. "Unobtainium" is a made-up word that sounds official. It would really come in handy for dealing with conflicting constraints on a recent project, however. You have likely been there too.
Today we have an engineering case study where we had to get creative to make a machine base which started with several conflicting constraints. The design is simple in concept, but that is where the simple ends.
The customer originally approached me with a few quick questions about cutting steel and welding. As we got into it, I realized it was a lot more. While the project definitely needs cutting, it also needed some creative thinking about how to accomplish the broader goals. Since the big picture sets the stage, projects that start with simple questions can easily turn into full blown design innovation.
The Big Picture First
Remember the Triangle of Achievable Engineering? Yeah, the one where we talk about hitting objectives. The triangle is all about managing conflicting constraints, so take a minute to read that article. Here is the triangle image again.
It is a useful tool when thinking about engineering goals. And, we can modify it to fit the objectives when they are not as generic as the image shows. 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 machine heads 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. Vibration is the enemy.
Now the hiccup, the assembly must be light enough to carry by hand. (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! And expensive.
- 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 for accuracy.
You get the picture. This is all about managing conflicting constraints – or, in this case, 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 Conflicting Constraints Into Focus
Well, if I can't have the infinitely stiff, infinitely strong, Unobtainium that weights virtually nothing, then we will have to settle for another method. Innovation is my "Go-To" technique in situations like this, because innovating can shift the paradigm. What is yours?
For 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 "box" per se, but maybe that is just me.
This customer came asking about cutting structural steel bars like angle, tube and flat stock. He wanted to cut and weld to build the machine platform. Sounds reasonable.
My first reaction was one of accommodation – until I understood more about what he is doing. Accuracy in alignment is hard to get when welding steel bars like that, so that brought on some new thinking.
As the higher level goals came into focus, it became clear that the best solution is not down a traditional path. Yes, it is a machine pedestal, and welding the structure can certainly work, but when we add in the other requirements for vibration and accuracy, the conflicting constraints come into focus.
I think a different approach will come much closer to reaching all of the big picture engineering goals.
The Creative Engineering 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 cannot be the alignment. For good alignment, we need fixed datums that are datums by definition. Puzzle pieces can interlock, and that will give great structural strength, but water 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 is is complete. The plates will then form a super rigid structure, as the interlocking bits all become one.
Some internal pieces (the cool tid-bits, not shown in the photos) create the accurate datums to assure a square, aligned fit. (The datum bars internal are really the magic for success with this project. This is a design innovation which reflects one primary reason to hire Synthesis.)
The broad plates crisscrossing within will carry all the forces, and give a 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 fills the need for weight and stability. When the sand is dumped out, the reduction in weight allows the desired portability.
That gives this pedestal a reasonable balance with respect to the conflicting constraints. It is both light to carry (without the sand), and heavy for stability, plus, sand is excellent 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 he needs more vibration damping.
Did We Balance The Conflicting Constraints?
Looking at the above Triangle again – Weight, Vibration, Accuracy – how did we do? We did not compromise Accuracy, and we found a good strategy for both weight and vibration (function). While handling sand is definitely an inconvenience, the result redirects the initial target. All of that to meet our engineering goals.
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. So, as noted in the article about the engineering triangle, we sacrificed Convenience to fully achieve the other legs.
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. Things that seem to conflict at first, can change to things that benefit if we creatively design the solutions with a different paradigm. And still, we can achieve our engineering goals.
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, 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 super innovative about the solution in this example. It is simply applying differently some things we have already done elsewhere. A new problem, with several old solutions mashed together for something that looks and feel 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. This is a proven method of changing the paradigms of conflicting constraints.
So, 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 or parallel.)
Starting with the initial concept, 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, another 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 above: Yes, it can feel innovative when it all comes together and delights the customer in ways that they are not expecting. And this is not so different from the discussion on Prototyping the Impossible.
So, the twin pedestal, 3D puzzle box is light enough for people 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 paradigm shift. Convenience to move the sand aspect, but that change also gave us amazing vibration absorption. Yes, we hit the goals for accuracy and vibration. Those were most 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.
When 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 an excellent tool.
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. Focus on the engineering goals, but 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.)