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New AP escapement - some more info....

March 29 2006 at 10:02 AM

SuitbertW  (Login wsw_de)
Belles Lettres Discussion Group

The new AP escapement





Hi all,
sorry for beeing so late with this - but finally here's a bit more info about the new escapement.
As already said it's a single impulse design based on the Robin escapement created in 18th. century. "Single impulse" in this context meaning that the balance wheel receives only one impulse through an entire oscillation. Or differently said it's impulsed only at one half beat, the other half beat is without an impulse. This principle was and is considered to have positive influence on the oscillators performance and precision, as an impulse also means "disturbation" at the same time (as is the unlocking).
So, "single impulse" in the physical sense means less disturbations for the oscillator. The traditional swiss lever escapement performs with double impulse - and of course the former inventors also had good reasons. As nothing is really ideal in real world, the obviously great advantages of the single impulse designs (among those also the famous detent and pivoted detent escapements) had their share of problems when carried and moved around. At the end all those escapements were considered less than ideal for all watches underlying more or less strong movements (such as pocket watches, wrist watches were considered almost impossible).

That's where AP and AP R&P started more than 6 years ago, inspired by the ingenious invention of Rober Robin, a single impulse escapement with a sort of anchor element:



Just to show the difference, here's a classical spring detent chronometer escapement:




I'll try to describe the main difference between those two escapements. Both are single and direct impulse, direct in this context describing the fact that the impulse is delivered directly from escape wheel to balance (without any connecting element, like with other lever escapements).
The spring detent (as the pivoted detent as well) is unlocked, the escape wheel delivers impulse to the balance wheel impulse jewel and than directly returns to its locking position. Therefore it always needs a returning force, mostly a spring (it should be noted here that there are some more exotic detent escapements sourcing the return force by the escape wheel as well).
The Robin escapement unlocks, the impulse is delivered the same way as with a detent escapement, but, as the anchor has two locking jewels it remains in the same position where it went after unlocking (i.e. it doesn't return to the initial position before unlocking like the detent). Now, on it's way back the balance wheel unlocks again, but no impulse is given! It may appear as potentially less efficient, but apparently there are good reasons for it as well.

Here's a drawing shówing the important parts of the new AP escapement:



As you may see through comparison with the original Robin design above, the AP escapement is quite different. The anchor is extremely compact (a similar developement can be observed with almost all lever escapements over the time) and the guard pin design is completely different - a point which well can be considered as major!

Here's a detail view of the AP safety guard pin - not really a "pin", more an adjustable "hook". The former "safety roller"now is a "cup shaped" piece with a small cut out allowing the guard pin to enter/pass for unlocking.





I'll have to continue later now - but maybe even this is at least of some interest

Best regards
Suitbert


p.s.: Please forgive any errors, typos... I'm writing this out of the top of my head and under less than ideal conditions -






 
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Fol de Dol
(Login foldedol)
AP Discussion Group

Nice !

March 29 2006, 12:12 PM 

Very nice article !!!

Hope we'll have an animation to really see how it works :p

One question :
Considering that the best actual anchor escapements are able to keep within +/- 1 second a day...
Can we imagine that the new escapements design like this one will go further ? like maybe +/- 1 second a week or something ?

 
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ei8htohms
(Login ei8htohms)
AP Discussion Group

the best Swiss lever escapements are not capable of keeping time to +/- 1 seconds a day

March 29 2006, 12:25 PM 

Hi Fol de Dol,

You might occasionally find an exceptionally well adjusted or exceptionally lucky Swiss lever escapement equipped movement that will keep time to +/- 1 second a day for a period of time, but certainly the majority don't and noone is capable of producing them with that level of accuracy with anything approaching repeatability, much less consistency. I think the often misquoted COSC specs of -4/+6 seconds per day are a pretty good generalization of what a finely made Swiss lever escapement is capable of in the real world in series production. I have no idea what we might expect to see from this escapement or any of the other novel escapements coming out recently though.

_john

 
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Fol de Dol
(Login foldedol)
AP Discussion Group

Re: the best Swiss lever escapements are not capable of keeping time to +/- 1 seconds a day

March 29 2006, 5:02 PM 

Ok, thanks for the precision

 
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Valentin Blank
(Login vblank)
AP Discussion Group

Thanks Suitbert! Your info is much appreciated...

March 29 2006, 1:33 PM 


... I hope to catch sight of one of this miraculouos new Cabinet pieces somewhere along the way. It's always nice to know that AP keeps commiting itself to such "useful" and highly interesting contributions.

Thanks, Valentin

 
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MichaelC
(Login MichaelC1000m)
AP Discussion Group

Thanks Suitbert!! Even though...

March 29 2006, 2:51 PM 

I don't understand as much about movements as I should/would like too, I am learning. Thanks for the post

 
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Allen
(Login acs540)
AP Discussion Group

Thanks Suitbert! So the ticking that we'll hear from this watch

March 29 2006, 10:07 PM 

will sound slower, right?


 
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SuitbertW
(Login wsw_de)
Belles Lettres Discussion Group

Very good point. Allen....

March 30 2006, 7:36 AM 

....and in fact the sound is different. This also causes some trouble using the traditional timing machines, in fact they don`t really work well with this new escapement.
But, the ticking isn`t slower (as it is with a single impulse chronometer detent), it`s just that the first tick (with delivering impulse) is well distinguishable louder than the second (which only unlocks/locks without impulse).
The timing machines recognize the louder of both only, and so count the half rate... if at all.
For that reason AP uses an optical device for testing as well (a laser beam beeing triggered by the balance arms)-

Best
Suitbert

 
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Allen
(Login acs540)
AP Discussion Group

Wow, a laser timing machine. Thanks for the explanation.

March 30 2006, 9:33 AM 

I think this is one watch that has to be seen in person.

 
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Jack Forster
(Login JackForster)
Belles Lettres Discussion Group

Hi Suitbert, a very interesting feature of the escapement which. . .

March 30 2006, 6:17 AM 

. . .I hadn't appreciated at first. So essentially the guard pin passes through the cutout in the safety roller during unlocking of the lever? It seems to me that this means that the lever is prevented from moving off the banking pins unless it's actually being unlocked by the balance? I'm not sure I understand why this would be necessary; it looks from the drawings as if there ought to be some draw between the entry and exit stones and the escape wheel teeth; is there not enough to ensure that the lever won't unlock accidentally (say if the watch is given a hard knock)?

Jack

 
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SuitbertW
(Login wsw_de)
Belles Lettres Discussion Group

The new designed guard pin....

March 30 2006, 7:42 AM 

Hi Jack,
in fact it's exactly this guard pin design which finally made this escapement work reliably (at least that's what the developers explained to me). And you may imagine that it is superior to the formerly used guard pin/safety roller as known from the swiss lever escapement in several regards.
And yes the locking stones/pallets do have a draw angle which is sufficient for normal running conditions. But to make it work really reliably and shock resistant for a wrist watch this wouldn't be enough alone.

Best
Suitbert

 
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