Le fonctionnement de l’échappement à ancre suisse peut être divisé en quatre phases qui se déroulent immuablement selon le même cycle à chaque alternance de l’organe régulateur. Ces quatre phases sont :

1. Le repos
2. Le dégagement
3. L’impulsion
4. Les sécurités

Détaillons ci-dessous l’action de chacun des composants durant chacune des quatre phases:

1. Le repos

Durant cette phase, l’ensemble du rouage de finissage est à l’arrêt, bloqué par l’échappement.

Double plateau:

C’est le seul élément de l’échappement alors en mouvement.

Durant la phase de repos, le double plateau effectue librement son arc supplémentaire ascendant α puis son arc supplémentaire descendant β (ci-dessous Figure 1, point 1). Il s’agit de l’angle que parcoure le double plateau (et donc le balancier) durant la période d’arrêt de la roue d’échappement et de l’ancre.

Ancre:

L’ancre est à l’arrêt. La baguette de l’ancre est maintenue en appui contre la goupille de limitation (ci-dessous Figure 1, point 2) par la dent de la roue d’échappement sous l’effet du tirage (cf onglet Le tirage).

Roue d’échappement:

Comme l’ancre, la roue est à l’arrêt. L’une de ses dents est en appui sur le plan de repos de la palette de l’ancre (ci-dessous Figure 1, point 3).

Figure 1

repos

2. Le dégagement

Durant cette phase, la roue d’échappement et le rouage de finissage reviennent très légèrement en arrière.

Double plateau:

La phase du dégagement débute lorsque la cheville de plateau entre au contact de la fourchette (Figure 2, point 4). La phase de dégagement du double plateau correspond à l’angle α qu’il parcoure, alors que la cheville de plateau pousse la fourchette de l’ancre (Figure 3).

Ancre:

La phase de dégagement de l’ancre correspond à l’angle β qu’elle parcoure durant l’action de la dent de la roue d’échappement sur le plan de repos de la palette (Figure 3). La phase de dégagement se termine lorsque la dent de la roue se trouve théoriquement sur le bec de repos de la palette (Figure 4, point 5).

Roue d’échappement:

Par le levier que constitue l’ancre et sa géométrie, la roue d’échappement recul légèrement durant la phase de dégagement (recul géométrique, env. 0.15-0.25°) puis poursuit son mouvement en se détachant brièvement du plan de repos de la palette (recul dynamique, env. 0.04°). La somme du recul géométrique et du recul dynamique constitue l’angle γ (Figure 3). Enfin, la roue d’échappement reprend son sens de rotation normal sous la force de l’énergie motrice. Comme pour l’ancre, on considère que la phase de dégagement se termine alors que la dent de la roue se trouve théoriquement sur le bec de repos de la palette (Figure 4, point 5)

Figure 2

début du dégagement

Figure 3

phase du dégagement

Figure 4

fin du dégagement

3. L’impulsion

C’est durant cette phase que l’échappement transmet l’énergie reçue du barillet via le rouage de finissage à l’organe régulateur.

Double plateau:

Le début de l’impulsion à lieu lorsque la fourchette rattrape la cheville de plateau (Figure 5, point 6). La phase d’impulsion du double plateau correspond à l’angle δ qu’il parcoure alors que la fourchette pousse la cheville de plateau (Figure 6).  La phase d’impulsion débute avant le point mort et se termine après le point mort (Figure 7).

Ancre:

La phase d’impulsion de l’ancre correspond à l’angle ε (Figure 6) qu’elle parcoure pendant que le bec d’impulsion de la dent de la roue parcoure le plan d’impulsion de la palette. La phase d’impulsion se termine lorsque le bec d’impulsion de la dent de la roue se trouve sur le bec d’impulsion de la palette (Figure 8).

Roue d’échappement:

La phase d’impulsion de la roue d’échappement correspond à l’angle qu’elle parcoure durant l’action du plan d’impulsion de sa dent sur le plan d’impulsion de la palette. L’impulsion commence lorsque le bec de repos de la palette entre en contact du plan d’impulsion de la palette (Figure 5, point 7) et se termine lorsque le bec d’impulsion de la dent atteint le bec d’impulsion de la palette (Figure 8, point 8).

Figure 5

début de l’impulsion

Figure 6

phase d’impulsion

 

 

 

Figure 7

point mort (impulsion)

 

 

 

Figure 8

fin de l’impulsion

 

 

4. Les sécurités

Les sécurités sont des angles parcourus par la roue d’échappement et l’ancre en pure perte juste après la phase d’impulsion.

Double plateau:

Au début de la phase des sécurités, la cheville de plateau perd le contact avec la fourchette de l’ancre (Figure 9, point 9). Le double plateau entame alors librement son arc supplémentaire ascendant α’ puis son arc supplémentaire descendant β’ (Figure 9).

Ancre:

L’angle de sécurité de l’ancre s’appelle le chemin perdu. C’est l’angle que parcoure la baguette de l’ancre dès lors que la dent de la roue d’échappement entre en contact avec le plan de repos de la palette (Figure 10, point 11) et l’instant où la baguette de l’ancre entre en contact avec la goupille de limitation sous l’effet du tirage (Figure 11, point 12).

Roue d’échappement:

L’angle de sécurité de la roue d’échappement s’appelle la chute. La chute correspond à l’angle parcouru par la roue dès lors qu’une de ces dents quitte le plan d’impulsion de la palette (Figure 9, point 10) et qu’une autre dent entre en contact avec le plan de repos de l’autre palette (Figure 10, point 11).

Figure 9

début de la chute (sécurités)

Figure 10

fin de la chute et début du chemin perdu (sécurités)

 

 

 

Figure 11

fin du chemin perdu (sécurités)

Note:

Pour une vision complète du fonctionnement de l’échappement à ancre suisse, se référer aux deux animations figurant en tête de cette page.

1. The double roller (de facto the Balance)

Description of the different angles of the double roller (and therefore of the Balance) during two Vibration (one Oscillation).

 

 

 

(*) Important:

When the Escape wheel performs its dynamic recoil (see operation tab), the Pallets (lever) continues its movement while being driven by the Impulse pin (roller jewel). When the escape wheel resumes its forward motion, the wheel’s tooth regains contact with the impulse plane of the Pallets (lever) pallet stone and the Impulse phase transmitted to the Balance begins. During this period, contact between the Impulse pin (roller jewel) and the Fork of the Pallets (lever) has been briefly interrupted and the double roller (and therefore the Balance) freely travels through a small angle between the end of Unlocking (drop angle) and the beginning of Impulse (angles described above as the Balance’s free travel).

 

 

2. The Pallets (lever)

2.1 Total lift angle (Figure 3)

The total Lift angle of the Pallets (lever) corresponds to the displacement of the Rod (baguette shape) of the Pallets (lever) between the two banking pins (or banking studs). It corresponds to the sum of the unlocking, impulse and Backlash angles and its value is generally between 12° and 20°.

 

2.2 Virtual engagement angle (Figure 4)

This is the angle between the resting tip of the Pallet stone (see the Pallets (lever)) and the point where the tooth of the Escape wheel falls onto the resting plane of the Pallets (lever)’s Pallet stone.

 

2.3 Backlash angle (Figure 4)

This is the angle traveled by the Pallets (lever) between the end of the Impulse and the Fork resting against the banking pin (or the banking stud) (see the operation tab)

 

 

2.4 Total depth angle (Figure 5)

The total depth angle corresponds to the sum of the virtual depth angle (Figure 4 – ) and the Backlash (Figure 4 – )

 

While the Balance travels through its supplementary arc (rising or falling), the Pallets (lever) rests against one or the other of the banking pins (or the banking studs) due to the effect of draw (see draw tab). If a shock overcomes the draw torque, the pallets swing against the other banking pin. At the end of the falling supplementary arc of the balance, the Impulse pin (roller jewel) then comes to strike against the back of the Horn (lug), thus causing the watch to stop immediately. (Figure 1).

In order to prevent Overbanking, the Swiss lever escapement has four organs:

• The Dart (safety pin)
• The small roller
• The Horns (lugs)
• The Impulse pin (roller jewel)

When the Balance travels through its supplementary arc, the Dart (safety pin) rests against the edge of the small roller preventing thePallets (lever) to tip against the other Banking pin and therefore the Overbanking (Figure 2).

The small roller has a notch aligned with the Impulse pin (roller jewel). During the Unlocking (drop angle) and Impulse phases (see the operation tab), this notch allows the Dart (safety pin) to pass and the Pallets (lever) to tip normally from one pin to the other. During these phases, it is the inside of the Horns (lugs) that comes to rest against the Impulse pin (roller jewel), thus preventing Overbanking (Figure 3).

 

 

 

 

The various shocks of the Swiss lever escapement are perceptible to the ear. This is the “tick-tock” of mechanical watches. But when the human ear perceives a tick or a tock, the escapement has actually emitted five sounds due to five shocks. These sounds are so close together that the ear hears only one (a tick or a tock).

Analyzing these sounds, by the intensity of each and the spacing between them, makes it possible to detect malfunctions or poor adjustments of the escapement. Similarly, the graphs from a Timing machine make it possible to identify problems related to the escapement. For each Vibration, these five shocks are as follows:

1. Unlocking (drop angle)
2. The start of the Impulse of the Escape wheel
3. The start of the Impulse of the Balance
4. The end of the Drop (impact)
5. The end of the Backlash

1. Unlocking (drop angle)

The first shock of a Vibration occurs when the impulse pin comes into contact with the inside of the fork (Figure 1).

2. Start of the escape wheel impulse

Shortly after the unlocking, the resting tooth tip of the escape wheel drops onto the impulse plane of the pallet stone. This is the second impact (Figure 2).

 

 

3. Start of the balance impulse

The fork catches up with the impulse pin and transmits its impulse to the balance via the double roller. This is the third impact (Figure 3).

 

 

4. End of the Drop (impact)

A tooth of the Escape wheel comes into contact with the resting plane of a pallet stone of the Pallets (lever) (Figure 4).

 

 

5. End of the Backlash

Finally, at the end of its Backlash, the Rod (baguette shape) of the Pallets (lever) comes into contact with one of the Banking pins (or a limiting stud) (Figure 5).

 

 

 

Watch rate testing devices (timing machines) provide a lot of information such as the instantaneous daily rate, the Amplitude and the guide mark value. However, a good reading of the diagrams delivered by timing machines makes it possible to identify many problems arising from the finishing train, the escapement and the regulating organ.

Thus, during defect-free operation of a perfectly regulated watch, the diagram shows a single horizontal line (Figure 1).

 

When the guide mark is too large, two parallel lines appear on the diagram (Figure 2). The correction consists in adjusting the guide mark (via the movable stud holder or the collet) and then readjusting the rate.

 

 

When the line on the diagram is ascending, the watch is running fast (Figure 3a). Conversely, when it is descending, the watch is running slow (Figure 3b). This then requires adjusting the rate (by modifying the active length of the hairspring or the moment of inertia of the balance).

 

 

In some cases, a variation in the rate will be observed during measurements of the Movement in the horizontal position and vertical positions (Figure 4). In this case, the correction consists in tightening the Banking pins.

 

 

When the diagram shows a regular sinusoidal line, it is useful to measure the time interval between each peak of the sinusoid. If the frequency corresponds to the rotation speed of the Fourth wheel (seconds wheel) (60 sec if the movement has a seconds Hand), an Out-of-flat (hairspring defect) or Out-of-round (hairspring defect) defect exists on the seconds wheel (Figure 5). The correction then consists of checking and correcting the riveting of the seconds wheel on its pinion or replacing the Fourth wheel (seconds wheel).

 

 

The diagram sometimes shows an irregular and random line. In such cases, Amplitude is often too low or shows numerous variations (Figure 6). In such a case, it is recommended to carry out a complete overhaul of the Movement.

 

 

If the diagram occasionally shows almost vertical lines, the sounds of the Escapement race and become irregular, and there is a sharp increase in Amplitude (or the total loss of amplitude information), this means that the amplitude is momentarily too high and that the Balance knocks (Figure 7). One can then replace the Mainspring with a spring developing less torque or modify the value of the total depth of the pallets’ pallet stones.

 

Multiple and irregular lines indicate that the Balance knocks continuously (Amplitude too high) (Figure 8). Here again, the defect will be corrected by replacing the mainspring with a lower torque spring where the total depth of the pallet stones will be modified.

 

 

A diagram showing a sinusoidal curve with a tight frequency (a few seconds) indicates an out-of-round (hairspring defect) problem of the escape wheel (Figure 9). It is then recommended to replace the escape wheel.

 

 

If the diagram shows a random line superimposed on a straight line, this means that the entry pallet stone of the pallets (lever) is catching or is dirty (Figure 10). It is then recommended to carefully clean Pallets (lever) and the escape wheel and, if necessary, replace the pallets (lever) or the entry pallet stone.

 

 

Vertical lines marking a normal rate trace indicate that the hairspring (balance spring) occasionally touches the regulator pins or the stud (hairspring stud) (Figure 11). This defect can be corrected by checking the geometry and centering of the hairspring (balance spring).

 

 

A stabilization of the rate and amplitude too slow between two measurement positions indicates a problem of Lubrication of the pivots of the Balance or of the finishing train (Figure 12).

 

The draw is a safety feature that keeps the rod of the Pallets (lever) resting against the banking pins when the Balance performs its supplementary arc. This prevents the Dart (safety pin) comes into contact with the periphery of the roller table and disturbs the period of the Regulating organ.

The mechanical action of the draw results from the pressure of a tooth of the Escape wheel on the resting surface of one or the other of the pallet stones of the pallets.

Thus, the force F1 exerted by the wheel tooth acts perpendicularly to the resting surface of the pallet stone and creates a moment of force through the lever arm of the distance d1 with the pivot point of the pallets. This moment of force results in the pallets’ rod being pressed against the banking pin with a force F2 and the lever arm d2, corresponding to the distance between the pivot point of the Pallets (lever) and the center of the Banking pin (Figure 1).

 

The Pallets (lever) is thus held in contact against the Banking pin. If a shock manages to overcome the force of the draw, the Pallets (lever) will move and the Dart (safety pin) may briefly come into contact with the edge of the small roller, but the force of the draw will immediately bring it back to its resting position.

Value of the draw’s moment of force

The moment of force of the draw can be defined by the following calculations:

 

 

The distance d1 varies according to the value of the angle α measured at the rest point B1. A variation of the angle α thus causes an increase or a decrease in the moment of force M of the draw (Figure 2).

 

 

The draw angle β is the value between a perpendicular raised at the rest point B on the line joining this point to the pivot point of the Pallets (lever) and the rest plane of the Pallet stone BP (Figure 3).

 

 

As we have just seen, the draw angle β is defined at the resting tip B of the pallet stone. It can also be defined at the resting point B1 of the pallet stone. In this case, the draw angle is then named: α (Figure 4). We thus understand that during unlocking (see functioning tab), the draw angle varies from β to α.

 

 

The draw angle is defined during the construction of the Escapement (ideally, it is 9° for the Steel wheel – Ruby / Jewel pallet stone combination). But a draw angle that is too small decreases the draw force and thus reduces its safety. It also increases the coefficient of friction. Conversely, an angle that is too large increases the moment of force required for Unlocking (drop angle) and increases the recoil value of the Escape wheel (loss of Impulse value). Thus, a draw angle that is too small or too large disturbs the regulating qualities of the Regulating organ. In this way, an ideal draw angle can be defined (for a Steel Escape wheel and Ruby / Jewel pallet stones) within a range generally between 13° and 16°.

Finally, it should be noted that during Unlocking (drop angle) the draw angle increases on the Entry pallet stone by the value of the angle ε (β = α + ε) (Figure 4).

Whereas it decreases on the exit pallet stone by this same value ε (β = α – ε) (Figure 5).

1. Stop on the rest plane

We observe the stop on the rest plane when the Movement is fully wound. We then manually position the Balance so that the Impulse pin (roller jewel) is at the start of the Unlocking (drop angle) phase (see “Operation” tab) (Figure 1).

 

If the Balance fails to release the Escape wheel from the rest plane of the pallet stone by the sole force of the Hairspring (balance spring), the movement is considered to have stop on the resting surface.

The stop on the resting surface is most pronounced when the movement is at maximum winding, because the force exerted by the tooth of the escape wheel on the resting surface of the pallet stone (and therefore the draw) is then at its maximum. As we describe in the “draw” tab, the draw increases during unlocking on the entry pallet stone and decreases during unlocking on the exit pallet stone.

Movements with a diameter greater than 24mm must under no circumstances show a stop on the resting surface. However, a stop on the resting surface cannot be prevented when it comes to a movement with a diameter of less than 24mm. Indeed, when the size of the movement is reduced, the moment of inertia and the torque of the hairspring decrease more rapidly than the torque of the Mainspring.

In movements with a diameter smaller than 24mm, it is not tolerated to have a stop on the resting plane after 24 hours of running, since the difficulty in performing the unlocking significantly disturbs the Isochronism of the Regulating organ.

1a. Causes of the stop on the resting plane

The causes of a stop on the resting plane can be as follows:

• A lack of freedom or poor Lubrication of the escapement wheels. (noticeable by a too low Amplitude)
• A defective surface condition of the resting plane of either pallet stone, or poor lubrication between the escape wheel and the pallet stones.
• A defective profile or surface condition of the resting plane of the escape wheel teeth.
• A drop angle that is too strong.
• A lack of shake of the impulse pin in the fork of the pallets.
• Fork entry sides that are too short, causing a shake of the dart that is too large at the beginning of the supplementary arc of the balance.
• An incorrect guide mark setting

To avoid or limit stopping on the resting plane (depending on the diameter of the movement), it is necessary to determine the position of the balance when the stop on the resting plane occurs. It is then possible to reduce the total depth of each pallet stone in order to angularly shift the end of the unlocking so that it occurs before the stopping position on the resting plane. This solution, however, involves a reduction in the value of the backlash.

Another solution, more complicated to implement, consists of increasing the inclination of the impulse planes of the pallet stones. This will decrease the value of the total depth without reducing the angle of the backlash. Care should then be taken to maintain a sufficient value for the virtual depths.

When developing small-diameter movements, one can minimize the stop on the resting plane by increasing the ratio between the lift angles of the pallets and the balance (see table below). This implies reducing the diameter of the rollers and lengthening the fork of the pallets. Thus, the balance begins its unlocking with a larger angle relative to the dead point, which increases its torque and limits the stop on the resting plane. However, a high lift angle of the balance increases the disruptive influence of the escapement on the isochronism of the regulating organ.

2. Stop on the impulse plane

We observe the stop on the Impulse plane by winding the Mainspring by two teeth of Ratchet wheel. We then manually position the Balance so that one of the teeth of the Escape wheel is at the beginning of the Impulse plane of the Pallet stone (Figure 2). If the Impulse is not fully given by this weak driving force, the Movement is then considered to have a stop on the Impulse plane.

 

 

All Movements have a stop on the Impulse plane. To check whether this is acceptable, the Mainspring is wound very gradually until the Movement starts spontaneously, taking care to observe the rotation of the Ratchet wheel. The accepted values for overcoming the stop on the Impulse plane are as follows:

Small-diameter Movements: Starts after 4 to 5 teeth of Winding of the Ratchet wheel.

Medium diameter Movements: Starts after 1/2 turn of Winding of the Ratchet wheel.

Large diameter Movements: Starts after 1 to 2 turns of Winding of the Ratchet wheel.

 

2.a Causes of stopping on the Impulse plane

The causes of stopping on the Impulse plane can be as follows:

• A lack of driving force (Mainspring too weak, lack of freedom of the finishing Train, gearing defects, poor Lubrication).
• A lack of freedom of the Pallets (lever) or the Balance.
• A defective surface finish or profile of the Impulse plane of the Pallet stone.
• A defective surface finish or profile of the Impulse plane of the Escape wheel teeth.
• Poor Lubrication between the Escape wheel and the Pallets (lever).
• A lack of shake (play) of the impulse pin (roller jewel) in the fork of the pallets (lever).
• A defective surface finish or profile of the entry of the fork of the pallets (lever).
• Poor guide mark setting.

Important

The stop on the impulse plane increases in proportion to the diameter of the movement. This is not really a defect, as it does not affect the precision of the movement or the isochronism of the regulating organ.However, when it is too great, it does not allow the movement to start spontaneously under the sole influence of the mainspring force, and requires manually giving a first impulse to the balance (by rapid rotation of the movement, of the watch for example).

To obtain the best regulation/adjustment and the best isochronism possible, it is preferable to have the balance lift angle as small as possible.

Accepted values & ratios of lift angles