Binary torsional stiffness compliant mechanism

A demonstration is given of a fully compliant mechanism with binary torsional stiffness. More details can be found in the research paper that is found at
1. https://doi.org/10.1016/j.eml.2020.101120
2. https://www.researchgate.net/profile/Reinier_Kuppens

EDIT: Check out an explanation in these videos:
https://youtu.be/CV-zewG3lBY
https://youtu.be/R_-KHQVmjMM
More videos coming soon!

EDIT: The research paper is now open access and can be freely downloaded by anyone at the doi link above.

EDIT: TLDR: It's a spring with close to zero stiffness that can be easily made on the small scale. Applications are for example sensors, surgical tools, energy harvesters, haptic devices, inertial threshold devices, mechanical logic and microrobots.

There have been a lot of comments on and questions about what it is that we are seeing here. So let me try to explain :)

This is a compliant mechanism. A compliant mechanism works by elastic deformation of slender segment, plate springs, instead pin-joints that you find for example in the suspension mechanism of your car. Compliant mechanisms are awesome, because they can be made to have no overlap and no relative motion between components. This is nice, because it reduces friction, thus wear, no need to lubricate, less noise, less vibrations. It reduces assembly, thus cost, no backlash, simplifies manufacturing. This makes them perfect for applications that need to be extremely precise (like super precise positioning), super clean (like cleanroom clean) and makes it relatively simple to make them very very small (like accelerometer sensors in your phone small).

The downside is that they always push back, after all, they are basically springs. This elastic restoring force can mess up energy efficiency, make them oscillate very fast (especially on small scales things start to vibrate fast) and limit how far they can move.

The idea of this mechanism was to make a spring without stiffness that can be made very small! One can get rid of the stiffness by preloading, which is done here with the mechanical switch at the bottom. It preloads the v-shaped plate spring that compensates the stiffness of the rotational stage. It is a torsional stiffness (or rotational stiffness), because the stage rotates around a virtual rotation point where the plate springs intersect.

Why?

Well, it enables us to make sensor that can measure extremely low frequency phenomena very small. Think of measuring the earth tides, variations in local gravity, small accelerations. To make small mechanical energy harvesters. Make micro robots more efficient. Make meta materials. Improved haptic feedback in for example compliant laparoscopic surgical tools and haptic devices. It can be considered a mechanical transistor or and-gate and thus could be used for mechanical computing (this can only be done if they can be made small :) ). You can give sensitive equipment (in the soft mode) a robust transportation mode (in the stiff mode). Think of the forces involved in launching something to space! You can use it as an inertial threshold detector.

And I have seen many more excellent applications in other comments!

I have also designed one that has linear motion: https://youtu.be/X2tRcEME14w
EDIT: wow, this has gotten way more attention that I ever expected. Thank all of you for your interest. I see from the comments quite some requests for STL files. So I've uploaded them to thingiverse: https://www.thingiverse.com/thing:4759853

As for references on the design of compliant mechanisms I can highly recommend the youtube channel by UCLA Professor Jonathan Hopkins, called The Facts of Mechanical design (https://www.youtube.com/channel/UC5Jz6SBlu2Sv61kfssv4DOw), which discusses theory and applications in much more detail!

Relevant literature is for example the book "Compliant Mechanisms" by Larry Howell and "Design Principles for precision mechanisms" by Herman Soemers is a great reference.

Видео Binary torsional stiffness compliant mechanism канала Reinier Kuppens