Is the tourbillon balance wheel affected by the unidirectional rotation of the cage?

Hey everyone,

After browsing the forum for a few hours on my free sunday I ran into Shing's discussion on Toubillons somewhere else on this forum. It relighted my drive to understand the inner workings of a mechanical timepiece of which I now understand the basics.

However, the working of a tourbillon, even after some research eludes me. On a "normal" balance wheel the "zero" position of the balance wheel does not change i.e. the mounting cage of the balance wheel does not move around its own axis. On every two beats the balance wheel gets a push from the excapement, once passing the zero position in the clockwise and once in the anti-clockwise direction. This cancels out any non symmetrical effects.

In a tourbillon however, the cage in which the balance wheel is mounted is itself moving. This causes the zero or equilibrium position of the balance wheel to rotate in one direction. Doesn't this movement affect the movement of the balancewheel asymmetrically, in that, on every oscillation it needs to move a certain amount to "catch up" namely the distance over which the equilibrium position has moved? Is this effect adjusted for in any way?

Regards,

Waimar

EDIT: maybe the animation on this link makes my point more clear:
www.tp178.com/jd/uber-comp/artikel_4_4.html
One can see the equilibrium position of the balance wheel shifting with every beat...

The rotation of the cage obviously affects the isochronism of the balance wheel. The only way to avoid this perturbation is to put the balance wheel outside the cage of the tourbillon.

Regarding the behaviour of a normal balance wheel, we have non-symmetrical perturbations due to the gravity effect and the position of the watch (along with his concerns to avoid problems related to lubrication, that's why Breguet thought of the tourbillon) but I guess you're already aware of that.

Roberto,

Thanks for your response. But if you look at the URL I posted you see the balance wheel's equilibrium position rotate. In this I assume the pin which is actuating the escapement (in the animation it is shaped as a red/pink half circle) is rigidly attached to the balancewheel. If this holds, then the position exactly between the two extreme positions of the pin is the balance wheel equilibrium point, which is moving around the circle thus affecting isochronism. If the pin is not rigidly attached to the balance wheel I do not see how the balance wheel movement in transferred to the escapement..

Regards,

Waimar

Waimar,

I probably didn't understand your question, you're describing the action of the impulse jewel, within the pallet fork, inside an ordinary swiss lever escapement (not really ordinary in the animation whose link you've posted).

To my cheap knowledge, a tourbillon doesn't differ for that to a watch that's not a tourbillon; what makes a tourbillon different, is the cage, normally, it contains the escapement wheel.

Here's a link to an explanatory illustration on how a normal tourbillon is designed: worldwide.espacenet.com/publicationDetails/originalDocument?FT=D&date=20101029&DB=EPODOC&locale=fr_EP&CC=CH&NR=700862A1&KC=A1

I don't know if this information may turn useful to you or is the answer you were looking for, at least I'm trying :)