“Binary Stiffness Compliant Mechanism EXPLAINED” - Binary Stiffness (Part 1)

This video depicts a translational binary stiffness compliant mechanism that achieves two different states of stiffness by being triggered using a simple switch. One state is very compliant while the other state is very stiff.

Details about this video are published in the journal, Extreme Mechanics Letters, and can be found at this link:

A raw video of this mechanism was previously uploaded to my student, Reinier Kuppen’s, YouTube channel,
but this video is intended to explain the mechanical principles behind how the mechanism works.

The part files to 3D print this mechanism can be downloaded on Thingiverse at the following link:

This video is the first part of a five-part mini-series about binary-stiffness compliant mechanisms. Be sure to watch the other parts to learn more about how they work and for what applications they could be used.

Also, to understand more about compliant mechanisms in general, be sure to watch the other videos in my Compliant Mechanism Design series on this channel.

Acknowledgements:
This video would not have been possible without the brilliance of Reinier Kuppens, who designed the mechanism, so a huge thanks to him for the great work he did in my lab at UCLA! And although we jointly own the copyright on this material, I’m grateful to him for giving me permission to publish about the content.

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Disclaimer:
Responsibility for the content of this video is my own. The University of California, Los Angeles is not involved with this channel nor does it endorse its content.

[Sleepyy_Manikin]

Honestly this series doesn't get enough credit for how awesome it is. This is very educational and interesting that it explains a popular trend going on right now. Thanks for the hard work, keep it up guys!

[sukumarankannan]

You mentioned Part C of episode 3 on this channel, however your latest video prior to this one was Part B. Do you have another channel, or are your videos available anywhere else?

[billj]

Additioinal comment: The "negative stiffness" wasn't immediately intuitive so I had to think about it a little bit. Once triggered and then deflected laterally, there are 4 elements involved in bending and/or compression/tension. The 2 vertical elements are strictly in bending and fairly linear, with stiffness of 12EI/L^3. The 2 "truss" elements are the key to the negative stiffness. When the meachanism is "set" the 2 truss elements are buckled and in compression to hold the deflected position. As the mechanism deflects to one side one truss element lengthens and the other shortens. Elements in a buckled shape are not linear when they shorten or lengthen, requiring less force to shorten than the amount of force they gain when they lengthen. This change in force of one vs. the other is what provides the negative stiffness. IOW if the vertical elements were removed, or made longer/thinner so they offer less resistance, I believe the mechanism would actually be laterally unstable meaning when it was set it would want to also deflect left or right and hold that position. (Actually I think "negative stiffness" is somewhat the definition of unstable.) The mechanism as pictured is somewhat balanced so that the straight vertical elements have just enough stiffness to brace the 2 bucked truss elements that want to make the mechanism buckle laterally.

[shirleysycamore]

This series is so fascinating and educational. Thank you for posting it! Keep the video’s coming.

[MrGoulien]

I just stumbled upon your series and it is amazing! Thank you very much for all the hard work you (and your students) have put into this!

[TimothyKNetherlands]

Stumbled on this video!
I know this guy from my old university (TU Delft, the Netherlands), used to get lectures from here when he did his PhD. Cool!

[Grabus]

Great and inspiring video! Your videos inspired me to order 3D printer and to start working with compliant mechanisms on my own :) Thank You!

[liggerstuxin]

What a great idea! This seems like a solution without a problem but I can guarantee we can find many purposes for this invention. The comments alone in here have a plethora.

[billj]

It is interesting that the mechanism can trigger itself. Of course in the untriggered state where the restraint is primarily due to truss action, the truss can't deform significantly unti lone of the elements buckles, and as that element buckles the tension in the other element pulls on the switch to trigger it. This type of behavior can happen in buildings with steel braces during seismic loads where one brace will buckle and lose its stiffness while the brace in tension maintains its strength and starts pulling on something else. (I'm a structural engineer and I understand completely how this is behaving, but it is still very interesting to watch.)

[satibel]

so with a well calculated lever you can use that as a resettable overstrain/out of bounds flag, though that can trivially be done with strain gauges and software, the fact that it becomes loose is useful compared to a stiffer mechanism, and it doesn't require energy.

I can see it used as resettable a pressure safety valve for example, where the arm is connected to a plunger, and if the pressure is too high or too low it triggers, allowing the pressure to equalize

[gordonstull]

Totally awesome!!! Those two critical forces that pulls-straight & pushes & bends are well explained. After watching your videos I am beginning to realize that there maybe a way to categorize those complex-degrees of freedom of motion concerning the RNA and DNA molecules volumetric displacements, sorta like mapping the "mechanical codes" of both the RA and DNA molecules!

[Barnaclebeard]

It's amazing to be witnessing a whole new science. It's like microcomputers in the 80s in that it's accessible to almost everyone and the floor is littered with innovations just waiting for someone to pick it up and run with it.

[UNgineering]

Thank you for providing the paper without a paywall!

[sanjuansteve]

You had me at “Binary Stiffness Compliant Mechanism EXPLAINED”... jeje

[MNbenMN]

I would have said that the tension of the angled blade flexures (one or the other depending on direction) is the primary limiting condition resulting in stiffness when the bistable switch is in the "stiff" position. The animation showing strain curves of the "truss" arrangement appears to ignore the possibility that the material may not have enough elasticity to stretch as depicted.

[butcher]

wow, inventing the cricle all over again is very impressive

[ThevenimX]

I saw it and immediately knew how it worked but the terminology was completely new to me

[abodg]

Everything was created in beautiful and most effective way. Why!
Because the creator is The Affectionate and have the knowledge of all things.
He gave us physics to show us how hard and beautiful his creation is, So we love him for giving us all of it.

[leowic]

This would be great for a "hidden lock" button. The shuttle i.e. the router of the lock, could be locked/ fixed until the "button" is pressed freeing the lock.

[liveuk]

Varying degrees of on and offness at last, love it. Look at the J banned suspension from f1 you will like it.