Omega Co-axial escapement - What is it and how does it work?

[andrema]

I know quite a few of you have an Omega with the co-axial movement, so I wanted to pull something together to provide a baseline to explain what it is and how it works.

Overview


Co-axial escapement is a type of modern watch escapement mechanism invented by English watchmaker George Daniels. Considered by many to be one of the most significant horological advancements since the invention of the lever escapement, the co-axial escapement functions with virtually no lubrication thereby eliminating one of the shortcomings of the traditional lever escapement.

How it works

For most people who wear an OMEGA wristwatch equipped with a Co-Axial calibre, the important things will be the timekeeping performance and the long service intervals. But the radical Co-Axial technology deserves a closer look.


The functioning of OMEGA’s exclusive Co-Axial calibres differs considerably from that of a conventional lever escapement with index. The mechanics of this design must be considered in order to fully appreciate the benefits the OMEGA Co-Axial escapement offers in terms of reduced friction and greater stability of the watch’s rate over time.

The OMEGA Co-Axial escapement consists of an intermediary wheel, a double coaxial wheel consisting of an escapement pinion and an escapement wheel, a lever with three ruby pallet-stones and a roller carrying a ruby impulse stone and a ruby impulse pin.




In any modern watch escapement, energy must be transmitted to the oscillator in both clockwise and anti-clockwise vibrations. In the OMEGA Co-Axial escapement, the clockwise impulse is provided by the teeth on escape wheel directly engaging the ruby impulse stone. The anti-clockwise impulse is provided by the teeth of escape pinion engaging the lever impulse stone. After each impulse, the escape wheel is made stationary by the locking pallets, allowing the balance to complete its vibration.

The main benefit of this new design becomes clear when it is compared with the lever escapement. The impulse in a lever escapement involves the wheel tooth sliding along the inclined surface of the pallet. This sliding movement generates considerable friction, making optimal lubrication vital if the escapement is to function correctly. However, lubricants are highly sensitive to ageing, as well as changes in their environment (temperature, humidity etc.) and therefore compromise the stability of the watch’s rate over time.

In contrast, the Co-Axial Escapement transmits energy using tangential forces provided by the components’ radial movements. Its very short sliding movement considerably reduces the contact surfaces and, therefore, the friction in the escapement. As a result, the escapement function is similar to that of a gear wheel meshing with a tooth, which means that it is unaffected by lubrication (a mere protective film on the tip of the escapement wheel teeth is sufficient to preclude wear and tear) and thus ensures a stable rate over the long term.

The OMEGA Co-Axial escapement is used in conjunction with a free sprung-balance without index. The watch’s rate can be adjusted by modifying the moment of inertia of the balance by means of two gold regulating micro screws embedded in the circular balance. This design avoids the disturbing effects of contact between the balance-spring and the index pins and therefore ensures that the stability of rate offered by the Co-Axial Escapement is maintained over long periods of use.


Escapement sequence:


1/. The balance is towards the limit of its excursion, towards the right.The octagonal escape-wheel is retained by the upper detent.





2/. An elliptical pin on the balance roller enters the fork in the detent lever and begins to disengage the upper detent.





3/.The co-axial star wheel leads the detent lever across, ready to engage the lower detent. This also provides security - one or other of the detents must always block the escapement - for a 'run-away' 'scape wheel will invariably be wrecked...



4/. The lower detent is engaged, and the balance continues its excursion freely.





5/. As the balance returns the detent lever is led to the left, releasing the lower detent...



6/. ...allowing the escape-wheel proper to give an impulsion to the balance.




7/. As the impulse pallet leaves the wheel, the upper detent re-engages - the cycle begins again.



Coaxial Escapement in Motion







Sources -

http://www.omegawatches.com/spirit/watchmaking/co-axial/technology

http://sites.google.com/site/simeonlapinbleu/co-axial

http://www.abbeyclock.com/coaxial.html