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T H E   U N C O N D I T I O N A L L Y   S T A B L E   C A G E 


The cage instability phenomenon has caused numerous malfunctions, sometimes dramatic, in various space applications (gyroscopes, reaction wheels, turbopumps, ...) but also in other industrial sectors (machine tool spindles, turbomolecular pumps, ...). For over 50 years, the issue has nearly remained a mechanical enigma, eluding COMPREHENSIVE characterization and resolution.

We dit it with the Butterfly Cage.

Patent is pending.
























Videos Courtesy of ESA/ESTL (ESR Technology, UK)

The peculiar nature of cage instability is its tendency to arise unexpectedly. Counterintuitively, there is no need for the bearing's operating conditions to deteriorate, nor is it necessary to await possible advanced wear: cage instability occurs without warning, at any moment.

Contrary to popular belief, the phenomenon does not only occur at high speeds and is definitely far from rare. Its manifestations can also be erroneously confused with other causes, such as resonance, for example.

The BUTTERFLY cage offers a concrete and immediately applicable solution that completely PREVENTS cage instability.

APO-GEE performed extensive experimental validations that delved deep into the mechanisms governing cage instability. Notably, for the first time ever, cage instabilities were recreated on demand, demonstrating perfect control over the phenomenon.



cage instability is a chaotic phenomenon



























We are frequently asked why our unconditionally stable cage is called the BUTTERFLY cage

This is because cage instability is a chaotic phenomenon. Chaos theory suggests that small changes in the starting state of a system can lead to significantly different outcomes over time. The butterfly analogy, often referred to as the butterfly effect, illustrates this sensitivity. It suggests that the flap of a butterfly's wings in one location could potentially set off a chain of events that, under intricate and interconnected conditions, might lead to significant consequences elsewhere, such as causing or preventing a storm on the other side of the world.

A dynamical system can be considered chaotic if it meets two criteria. The first one is a particularly high sensitivity to the initial conditions. The second criterion is a lack of periodicity in the evolution of the system’s variables over time, which gives the impression of a random process. 

The motion of a ball bearing cage is chaotic. Indeed, it is not possible to predict where the cage will be located within the bearing, even a few tenths of a second after the start of the bearing rotation. In the same way that it is not possible to predict the weather in the medium or long term with a mathematical model, however good it may be, computing the trajectory of the cage is pretty much impossible. That's also why cage instability cannot be fully solved by purely computational methods or by AI.

APO-GEE has identified the elements necessary for the onset of dynamic cage instability. The goal is not to predict where and when cage instability will appear but to explain why it will. We do understand the mechanisms that govern the instability. With that key knowledge, we have been about to efficiently act on bearing design to prevent the deleterious phenomenon. Any kind of prediction then becomes useless: the cage will be stable in every circumstance.

And this is very good news for many space and industrial applications.


Innovation in ball bearings has witnessed some strides, thanks to the invaluable contributions of intelligent individuals within various organizations.


However, what truly sets apart a groundbreaking innovation in this field is often the rare opportunity to delve deep into a single subject for an extended period. A real extended one. This makes it possible to understand the phenomena, to ask the right questions, to open doors, to close others, without any other constraint than to precisely and truly understand ball bearing physics.


We had the opportunity to study the kinematics of the balls for over a decade. It is an exceptional occurrence, as in most organizational settings, the constraints of time and resource allocation often prevent prolonged focus on a single research and development project.


This is this extended commitment to exploring the intricacies of bearing physics that paved the way for the remarkable advancement of the BUTTERFY cage. 

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