HK1194157B - Clock movement having a balance-wheel and hairspring - Google Patents

Description

The present invention relates to a watch movement, in particular a movement comprising a coil-swing regulator and an exhaust.

During the oscillations of the swing of a traditional spiral-swing regulator, the spiral expands eccentrically due to the fact that its center of gravity is not on the axis of the regulator and moves. This eccentric development generates significant pull forces between the pivots of the regulator shaft and the bearings in which they rotate, forces which further vary depending on the amplitude of the swing. These pull forces disrupt the oscillations of the swing and affect the isochronism of the movement, i.e. increase the variations in the walking in the amplitude of the swing.

However, it is known that the concentricity of the development of a spiral is not the only factor that influences isochronism. Mounted in a movement, the regulator is disturbed by the exhaust, which induces a running delay. Indeed, during the release phase, the regulator undergoes a resistant torque before the center line, which causes a running delay. During the impulse phase, the regulator undergoes a driving torque first before the center line, which causes a running advance, and then after the center line, which causes a running delay.

The present invention aims to further improve the isochronism of a coil-wheel balancer and proposes a clock movement according to claim 1.

It was found with surprise that by playing on the arrangement of the stiffened portion of the outer spiral, e.g. its position, extent or thickness, the overall isochronism of the movement, taking into account both the disturbance due to the non-concentricity of the spiral and the disturbance due to the exhaust, could be significantly improved compared to the regulator described in EP 1473604.

The rigid portion is preferably arranged to produce a speed advance of at least 2 s/d, or at least 4 s/d, or at least 6 s/d, or at least 8 s/d, at an amplitude of 150° compared with 300°, compensating at least partially for the said speed change due to the exhaust.

According to a first embodiment, the rigidised section is closer to the outer end of the coil than a theoretical rigidised section which would make the development of the coil considerably perfectly concentric, the thickness and extent of the rigidised section being substantially identical to those of the said theoretical rigidised section.

According to a second embodiment, the rigidised portion is less thick than a theoretical rigidised portion which would make the development of the spiral appreciably perfectly concentric, the position and extent of the rigidised portion being substantially identical to those of the said theoretical rigidised portion.

A third embodiment is that the rigid portion is less extensive than a theoretical rigid portion which would make the development of the spiral considerably perfectly concentric, the position and thickness of the rigid portion being substantially identical to that of the theoretical rigid portion.

Further features and advantages of the present invention will be apparent from the following detailed description made by reference to the attached drawings in which: Figure 1 shows a spiral with a portion of the outer spiral stiffened according to the previous technique, a virole associated with this spiral being shown schematically by a dotted line;Figure 2 shows an isochronism curve obtained by numerical simulation of the displacements of the geometric center of the spiral shown in Figure 1, the regulator or oscillator of which this spiral is part being considered free, i.e. not subject to the action of an exhaust;Figure 3 shows global isochronism measurement results obtained on a real movement with a spiral behaviour as shown in Figure 1;Figure 4 shows a spiral portion of the outer spiral stiffened according to a method of implementation of the invention;Figure 5 shows a numerical isochronism curve obtained by simulation of the displacements of the geometric center of the spiral shown in Figure 4.the control or oscillator of which this spiral is a part is considered free, i.e. not subject to the action of an exhaust;Figure 6 shows results of measurements of overall isochronism obtained on a real motion with a spiral as shown in Figure 4;Figure 7 shows a spiral with a portion of the outer spiral rigidised according to a second embodiment of the invention;Figure 8 shows an isochronism curve obtained by numerical simulation of the displacements of the geometric centre of the spiral as shown in Figure 7;the control or oscillator of which this spiral is a part is considered free,This means that the control or oscillator is not subject to the action of an exhaust; Figure 9 shows a spiral with a portion of the outer spiral stiffened according to a third embodiment of the invention; Figure 10 shows an isochronism curve obtained by numerical simulation of the movements of the geometric centre of the spiral shown in Figure 9, the regulator or oscillator of which this spiral is part being considered free, i.e. not subject to the action of an exhaust.

Figure 1 shows a plane spiral of the type described in patent EP 1473604, for a swing-spiral regulator of a watch movement. This spiral, designated by the reference 1, is in the shape of an Archimedean spiral and is fixed by its inner end 2 to a virole 3 mounted on the swing shaft and by its outer end 4 to a python (not represented) mounted on a fixed part of the movement such as the cock.The outer spire 5 of the spiral 1 has locally a portion 6 which is thicker e than the rest of the blade forming the spiral. This thickness e, which can be variable along the portion 6 as depicted, stiffens the portion 6 and thus makes it noticeably inactive during the development of the spiral. The position and extent of the stiffened portion 6 are chosen so that the center of deformation of the spiral, which corresponds significantly to the center of gravity of the part of the spiral other than the stiffened portion 6, is significantly confused with the geometric center O of the spiral,This outer end 4, more precisely a terminal part 7 of the outer spiral 5 including the stiffened portion 6, is radially deflected outwards from the Archimedean spiral path to ensure that the penultimate spiral 8 remains radially free, i.e. does not touch any element such as the piton, outer spiral or a racket pin, during the operation of the movement.The gap between terminal part 7 and the front-end of spire 8 must be greater than that of a traditional spiral, because due to the concentric development of the spiral, the front-end of spire 8 moves radially more towards the python when the spiral expands. The front-end of spire 8 is shaped like a circle arc with center C. The angular extent θ of the rigid portion 6 and its angular position α (defined for example by the angular position of the center of the rigid portion 6 relative to the angular position of the outer end 4) are defined from this center C. The thickness is measured along a radius starting from C.In the example shown, the values θ and α are respectively 85,9° and 72° and the maximum thickness e is 88,7 μm. The thickness e0 of the blade forming the spiral (measured by a radius from the geometric centre O of the spiral), excluding the stiffened portion 6, is 32,2 μm.

Figure 2 is an isochronism diagram obtained with the spiral illustrated in Figure 1 by numerical simulation. Specifically, the diagram in Figure 2 is obtained by considering the fixed outer end 4 and the shaft on which the 3 and the free balance are fixed (i.e. not mounted in bearings), by calculating in finite elements the displacement of the geometric center O of the spiral during the oscillations of the balance, then by interpolating and integrating the displacement curve in terms of the amplitude of oscillation.

Measurements were made on twenty movements of identical design, equipped with the spiral as shown in Figure 1 and a traditional exhaust. For each movement, in each of six different positions (VH: upper vertical, VG: left vertical, VB: lower vertical, VD: upper vertical, HB: lower horizontal and HH: upper horizontal), the movement speed was measured during the discharge of its motor spring and the measurements were carried over to a graph.The speed of the motor spring is reduced by the decrease in the spring force, which gradually decreases between the fully up and the drifted state of the motor spring. As can be seen, the speed gradually decreases as the oscillation amplitude decreases. For each position of each motion a curve was interpolated and the gait difference between the 150° oscillation amplitude and the 300° oscillation amplitude was determined. The average gait differences for all positions and all movements was about 6.7 s/d between these amplitudes.This decrease in speed, or delay at low amplitudes compared with high amplitudes, is mainly due to the exhaust.

The present inventors have observed that the decrease in gait due to the exhaust can be at least partially compensated by changing the arrangement of the stiffened portion 6, i.e. its position α and/or its extent θ and/or its thickness e, in relation to the arrangement in Figure 1 which gives the spiral spires perfect or near-perfect concentricity.

In particular, it was found that a parameter of the rigid section 6 which has a particular influence on isochronism is its position α. Moving the rigid section 6 to the outer end 4 of the spiral creates a gauge advantage at small amplitudes relative to the large oscillation amplitudes of the pendulum.The change in gait due to the exhaust can thus be substantially fully compensated. Figure 4 shows the new spiral obtained, with its portion of rigid outer spiral designated by the reference 6. The displacement of the rigid portion 6 naturally changes the development of the spiral, which is no longer as concentric.The increase in the speed between the 300° and 150° amplitude is noticeably linear and is inversely proportional to the slope of the change in the speed due to the exhaust. The isochronism curve I1 of the spiral shown in Figure 1 has also been carried over to Figure 5 for comparison.These results show that the variation in gait was significantly reduced by moving the rigid portion to the α' position, particularly in the 180° to 300° amplitude range where the overall shape of the graph is flat.

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In some variants, the above methods of production can of course be combined, i.e. at least two of the parameters α, e and θ can be changed.

Claims (7)

1. Timepiece movement comprising a balance-and-hairspring regulator and an escapement co-operating with the regulator, the outer turn (5) of the hairspring comprising a stiffened portion (6'; 6"; 6"') arranged to make the development of the hairspring more concentric, characterised in that the stiffened portion (6'; 6"; 6"') is also arranged to produce a rate gain of at least 2 s/d at an amplitude of 150° with respect to an amplitude of 300°, at least partially compensating for the variation in the rate of the movement in dependence upon the oscillation amplitude of the balance caused by the escapement, the gain value being obtained by digital simulation by considering the outer end of the hairspring as being fixed and the shaft on which the collet and the balance are fixed as being free, and by calculating by finite elements the displacement of the geometric centre of the hairspring as the balance oscillates, then by interpolating and integrating the displacement curve as a function of the oscillation amplitude.
2. Timepiece movement as claimed in claim 1, characterised in that the stiffened portion (6'; 6"; 6"') is arranged to produce a rate gain of at least 4 s/d at an amplitude of 150° with respect to an amplitude of 300°, at least partially compensating for said rate variation caused by the escapement, the gain value being obtained by digital simulation by considering the outer end of the hairspring as being fixed and the shaft on which the collet and the balance are fixed as being free, and by calculating by finite elements the displacement of the geometric centre of the hairspring as the balance oscillates, then by interpolating and integrating the displacement curve as a function of the oscillation amplitude.
3. Timepiece movement as claimed in claim 2, characterised in that the stiffened portion (6'; 6"; 6"') is arranged to produce a rate gain of at least 6 s/d at an amplitude of 150° with respect to an amplitude of 300°, at least partially compensating for said rate variation caused by the escapement, the gain value being obtained by digital simulation by considering the outer end of the hairspring as being fixed and the shaft on which the collet and the balance are fixed as being free, and by calculating by finite elements the displacement of the geometric centre of the hairspring as the balance oscillates, then by interpolating and integrating the displacement curve as a function of the oscillation amplitude.
4. Timepiece movement as claimed in claim 3, characterised in that the stiffened portion (6'; 6"; 6"') is arranged to produce a rate gain of at least 8 s/d at an amplitude of 150° with respect to an amplitude of 300°, at least partially compensating for said rate variation caused by the escapement, the gain value being obtained by digital simulation by considering the outer end of the hairspring as being fixed and the shaft on which the collet and the balance are fixed as being free, and by calculating by finite elements the displacement of the geometric centre of the hairspring as the balance oscillates, then by interpolating and integrating the displacement curve as a function of the oscillation amplitude.
5. Timepiece movement as claimed in any one of claims 1 to 4, characterised in that the stiffened portion (6') is closer to the outer end (4) of the hairspring than a theoretical stiffened portion (6) which would have the same thickness (e) and the same extent (θ) as said stiffened portion (6') and which would make the development of the hairspring substantially perfectly concentric.
6. Timepiece movement as claimed in any one of claims 1 to 4, characterised in that the stiffened portion (6") is thinner than a theoretical stiffened portion (6) which would have the same position (α) and the same extent (θ) as said stiffened portion (6") and which would make the development of the hairspring substantially perfectly concentric.
7. Timepiece movement as claimed in any one of claims 1 to 4, characterised in that the stiffened portion (6"') is less extended than a theoretical stiffened portion (6) which would have the same position (α) and the same thickness (e) as said stiffened portion (6"') and which would make the development of the hairspring substantially perfectly concentric.