EP2175328A2 - Balance-spring resonator spiral and its method of fabrication - Google Patents

Abstract

The movement has a balance-hairspring resonator comprising a hairspring (10) formed of a plate with a succession of turns. An end of an inner curve (11) is fixed to an axle (9) of a balance. An end of an outer curve (14) is fixed to a balance-coq or to a piece of the balance-coq. The turns are formed by a single band from the inner curve to the outer curve, where the inner curve presents Grossmann type geometry. A portion of the outer curve presents a section larger than that of a plate forming other turns. The turns are made of metal, metal alloy or monocrystalline/polycrystalline silicon.

Description

The present invention relates to a spiral spring-balance spiral spring obtained by a manufacturing method for improving the isochronism by acting on the one hand on the construction parameters of the spiral as such, on the other hand on a method of attachment on the balance shaft to reduce the geometric difference inherent in the usual fastening modes between the point of origin of the Archimedes spiral and the axis of rotation of the balance. In the following description, isochronism is understood to mean the gait variations as a function of the oscillation amplitude variations of the balance wheel, as well as the gait deviations between the horizontal position and the vertical positions of the watch.

In a known manner a spiral, having turns of uniform section and pitch, allows, by a particular conformation of the curve inside and the curve outside in the plane of the spiral or, more often, in different planes. , to obtain a concentric development of the hairspring and to have a displacement of the center of mass of the hairspring and a variation of the spiral inertia during the development, minimizing the gait disturbances as a function of the amplitude and the positions of the hairspring compared to the gravity vector. In addition to the fact that the realization of such a spiral requires great skill, height congestion is a drawback for its use in wristwatches should have, for obvious reasons of aesthetics, as small a thickness as possible.

For this reason, it is still preferred to use a flat hairspring, such as that represented in FIG. figure 1 . Such a hairspring is manufactured in known manner by strapping from a wire or a metal strip of constant section over its entire length, and has at rest a constant pitch between the turns. As we see on the figure 1 , the curve inside is fixed, for example by laser welding, on a shell 20, driven on the axis 9 of a balance 8.

Compared to this state of the art, as regards the pitch between the turns, it is nevertheless necessary to mention the patent CH 465 537, filed in 1966 , in which is described a method for producing from a strip or wire of constant section, wound in the groove of a matrix, then annealed and quenched, spirals having any configuration, particularly with a variable step. To the best knowledge of the applicant, no product of this type has been placed on the market, which suggests that the manufacturing process was technically or economically unsatisfactory.

With regard to the variation of the thickness of a coiled metal strip, mention may be made of the patent GB 1020 456 which describes the manufacture of a barrel spring by butt welds of blades having increasing sections from the center to the periphery. Such a spring is designed, with equal space, to increase the power reserve, but it is obvious that by applying this manufacturing method to a hairspring, the presence of welds would not allow to have a concentric development and obtain reproducible isochronism from one spiral to the other.

This same principle had already been proposed in a patent US 209,642 of 1878 to improve the isochronism of a spiral built with a turn inside of smaller section. As will be seen in the detailed description, the experiment contradicts this statement.

The subject of the invention is therefore a flat hairspring and processes for manufacturing by micro-machining or galvanic growth, making it possible to conveniently choose the most favorable construction parameters in order to improve the isochronism by the shape of the hairspring as well as than by the fastening means.

For this purpose the invention relates to a flat spiral, formed of a blade composed of a succession of turns having between them a pitch "p", for a balance adjusting mechanism, said spring being obtained by a manufacturing method which allows to get closer to a perfect isochronism. The turns of rectangular section are formed in a single continuous material from the curve inside to the curve outside, but have, on certain portions between the fastener in the center and the fastener outside. , a non-uniform section "s" and / or have one or more shaped portions outside the pattern of a perfect spiral. The term "non-uniform section" means that for a blade having a constant height "h", the thickness "e" of a selected portion may be either greater than or less than the thickness of the remainder of the blade constituting the spiral.

As will be explained later in the detailed description, the manufacturing process uses micro-techniques, such as photolithography and electroplating of a metal or an alloy, or the micromachining of a wafer. "thickness" h "made of an amorphous or crystalline material such as silicon in monocrystalline or polycrystalline form.

According to a first embodiment, the section "s" of the turns increases progressively from the curve outside to the curve inside.

According to a second embodiment, which can be combined with the first embodiment, the pitch "p" between the turns decreases steadily from the outside curve to the curve inside.

According to yet another embodiment, it is possible to select a determined turn portion and locally vary the blade width to act on other parameters favorable to isochronism. This increase can be made for example on the curve inside, on the curve outside or at the same time on the two curves, or in many other places on other portions of the spiral.

It is also possible to obtain a hairspring having a turn portion deviating from the curve of a perfect spiral, for example having a Grossmann-type inside curve.

The invention also offers the advantage of being able to manufacture, at the same time as the hairspring itself, the fixing means on the balance shaft, this fastening means being formed by a self-locking washer having in the center, by for example, a star-shaped contour and having recesses in its periphery to give it sufficient elasticity to mount and avoid a gap between the point of origin of the Archimedes spiral and the axis of rotation of the balance.

For a metal or alloy spiral, the manufacturing process basically consists of applying the LIGA technique to form a mold corresponding to the profile desired by the spiral. Given the properties of photoresists currently available on the market, it is possible to adjust the thickness of the photoresist layer to obtain the full range of spirals with blade heights of up to a few tenths of a millimeter.

For a hairspring made of an amorphous or crystalline material, the method basically consists in etching a wafer of said material through masks.

• la figure 1 représente un balancier-spiral de l'art antérieur;
• la figure 2 est une représentation agrandie du spiral de la figure 1 ;
• la figure 3A correspond à un diagramme d'isochronisme obtenu avec le spiral représenté à la figure 2;
• la figure 3B correspond à un diagramme d'isochronisme obtenu avec un autre spiral de l'art antérieur;
• la figure 4 représente un premier mode de réalisation d'un spiral selon l'invention;
• la figure 5 correspond à un diagramme d'isochronisme obtenu avec le spiral de la figure 4;
• la figure 6 représente un deuxième mode de réalisation d'un spiral selon l'invention;
• la figure 7 correspond à un diagramme d'isochronisme obtenu avec le spiral de la figure 6;
• la figure 8 représente un troisième mode de réalisation d'un spiral selon l'invention;
• la figure 9 correspond à un diagramme d'isochronisme obtenu avec le spiral de la figure 8;
• la figure 10 représente un mode de fixation d'un spiral selon l'invention, et
• les figures 10A à 10E représentent d'autres formes de fixation au centre.

Other characteristics and advantages of the present invention will become apparent in the description of various exemplary embodiments given by way of nonlimiting illustration with reference to the appended drawings in which:

• the figure 1 represents a sprung balance of the prior art;
• the figure 2 is an enlarged representation of the spiral of the figure 1 ;
• the figure 3A corresponds to an isochronism diagram obtained with the spiral represented at figure 2 ;
• the figure 3B corresponds to an isochronism diagram obtained with another spiral of the prior art;
• the figure 4 represents a first embodiment of a spiral according to the invention;
• the figure 5 corresponds to an isochronism diagram obtained with the spiral of the figure 4 ;
• the figure 6 represents a second embodiment of a spiral according to the invention;
• the figure 7 corresponds to an isochronism diagram obtained with the spiral of the figure 6 ;
• the figure 8 represents a third embodiment of a spiral according to the invention;
• the figure 9 corresponds to an isochronism diagram obtained with the spiral of the figure 8 ;
• the figure 10 represents a method of fixing a hairspring according to the invention, and
• the Figures 10A to 10E represent other forms of fixation in the center.

The figure 1 , partially broken away, represents a sprung balance of the prior art mentioned in the preamble. Its characteristics will serve as a reference to show the significant progress made by the invention at the level of isochronism. The hairspring 10 has the end of its curve in the center 11 fixed in a conventional manner on a shell 20 driven on the axis 9 of the balance 8 pivoted between the plate 7 and the cock 6. The regulating device further comprises, in a known manner, a stud carrier 5 for fixing the curve to the outside 14 of the hairspring 10 and possibly a racket 4 provided with pins 3 and a racket tail 2 opposite a graduation 1. On the figure 2 , which is an enlarged representation of the hairspring 10 alone, it is seen that said hairspring is formed of 14 turns having a uniform rectangular cross-section, for example 0.05 x 0.30 mm from the curve at the center 11 to the curve at the outside 14, and that the turns have between them a constant pitch p . The point of attachment of the curve to the center 11 is situated at a distance r from the center of pivoting of the spiral, and that of the curve to the outside 14, at a distance R, before the bend 16. In this example, r and R are respectively 0.57 mm and 2.46 mm. These values of r and R, as well as number of turns, will be the same in the remainder of the description, unless otherwise indicated.

Referring now to the figure 3A the isochronism diagram of a spiral having the above-mentioned characteristics is shown. The amplitude of oscillation of the pendulum expressed in degrees with respect to its equilibrium position has been plotted on the abscissa. On the ordinate, the difference in walking expressed in seconds per day has been reported. This diagram has five curves corresponding to the usual positions of measurements with the spiral balance, horizontal (curve 1), then vertical (curves 2 to 5, by rotation of 90 ° from one curve to another). The dotted line corresponds to the envelope of all the most unfavorable positions. The appreciation of the deviation is carried out traditionally taking into consideration the maximum deviation of the envelope for an amplitude of between 200 ° and 300 °. On the diagram of the figure 3A it is observed that this maximum difference, with this reference spiral of the prior art, is 4.7 s / d for an amplitude of 236 °.

To the figure 3B the diagram obtained is represented with a spiral (not shown) having the characteristics mentioned in the patent US 209,642 cited in the preamble, namely with a blade thickness varying between 0.046 mm for the outside curve 14 and 0.036 mm for the curve inside 11. Contrary to what can be expected from the teaching of said patent it will be observed that the maximum deviation has increased to 7.7 s / d for an amplitude of 230 °.

Referring now to Figures 4 and 5 a first embodiment of a spiral, the manufacture of which by micromachining (photolithography and galvanic growth, or etching of an amorphous or crystalline material makes it possible to obtain a geometry favorable to isochronism, is described below. As can be seen, the pitch p between one turn and the next decreases as one approaches the center of the hairspring.Inversely, the section increases from the curve to the outside 14 to the curve at the Since the manufacturing processes give the blade a constant height, the section variation corresponds in fact to a variant of the thickness which passes from 0.036 mm for the outside curve 14 to 0.046 mm for the curve inside 11.

On the diagram shown in figure 5 it can be seen that the maximum deviation is lowered to 2.8 s / d for an amplitude of 242 °. One would still obtain a favorable result on this maximum deviation by acting solely, either on the pitch p , or on the thickness e of the blade.

• une portion 12 de la courbe à l'intérieur 11 sur un secteur angulaire d'environ 80° dont la partie médiane se trouve sensiblement à - 110° d'un axe de référence Ox, et
• une portion 15 de la courbe à l'extérieur 14 sur un secteur angulaire d'environ 20° dont la partie médiane se trouve sensiblement à + 115° de l'axe de référence Ox.

The Figures 6 and 7 correspond to a second embodiment of type "Michel" for the curve outside 14 and for the curve inside 11. The turns have between them a constant pitch and a constant section corresponding to a constant thickness of 0.042 mm , with the exception of two portions of turns for which the thickness is increased to 0,056 mm:

• a portion 12 of the curve inside 11 on an angular sector of about 80 °, the median portion of which is substantially at -110 ° of a reference axis Ox, and
• a portion 15 of the curve outside 14 on an angular sector of about 20 °, the middle portion is substantially + 115 ° of the reference axis Ox.

On the diagram shown in figure 7 we can see that the maximum difference is only 1.8 s / d. The value of the overthickness and the positions on the turns are given above for illustrative purposes, and it is obvious that the skilled person can choose to have a greater number of zones of extra thickness in different places. .

The Figures 8 and 9 correspond to a third embodiment in which the curve inside 11 is Grossmann type 13, that is to say having a geometry such as that described in the book "General Theory of Watchmaking" of L. Defose. Such a geometry is very delicate to obtain by deformation of a metal blade. The manufacturing method according to the invention makes it possible to very easily obtain such a configuration without the intervention of highly qualified personnel. The diagram shown in figure 9 shows that the maximum deviation at 300 ° is only 2.1 s / d.

Of course, given the freedom of configuration that give the manufacturing methods according to the invention, it is possible to combine the embodiments described above to obtain a spiral according to the invention having improved isochronism.

To the figure 10 a spiral corresponding to the first embodiment is shown ( figure 4 ) in which the shell 20 is replaced by a self-locking washer 17 formed at the same time as the hairspring 10. This washer 17 has at its center a contour 19 such that it allows to block without play the axis 9 of the balance 8 having a certain elasticity provided by lights 18 distributed around the blocking contour 19 shown in a star at the figure 10 . The Figures 10A to 10E show other possible conformations of the self-locking washer 17 with a blocking contour 19 triangle, square, hexagonal, circular or ogive. When the self-locking spiral washer is produced by photolithography and galvanic growth, it is advantageous, by means of an additional step, to make said self-locking washer 17 with a thickness greater than the height of the blade to obtain a better holding of the hairspring. 10 on the axis 9 of the balance.

• appliquer une plaquette de silicium sur un substrat en créant une interface en SiO₂ isolante;
• amincir la plaquette jusqu'à la hauteur "h" de lame désirée selon la méthode décrite par C. Harendt et al. ("Wafer bonding and its application to silicon-on-insulator fabrication" Technical Digest MNE'90, 2nd Workshop, Berlin, November 90, p. 81-86 );
• former par photolithographie un masquage correspondant au contour de spiral désiré;
• effectuer la gravure de la plaquette de silicium jusqu'au substrat, selon des procédés connus, telle qu'une attaque chimique par voie humide, un usinage à sec par plasma, ou une combinaison des deux; et
• séparer le spiral du substrat.

A hairspring according to the invention made of an amorphous or crystalline material such as silicon may be manufactured by adapting the micro-machining processes already used for example for the manufacture of integrated circuits or accelerometers from a silicon wafer. In particular, it is possible to refer to the processes described in the patents US 4,571,661 and US 5,576,250 concerning accelerometers. The process basically consists of the following steps:

• applying a silicon wafer to a substrate by creating an insulating SiO ₂ interface;
• thin the wafer to the desired blade height "h" according to the method described by C. Harendt et al. ("Wafer bonding and its application to silicon-on-insulator manufacturing" Technical Digest MNE'90, 2nd Workshop, Berlin, November 90, pp. 81-86 );
• forming by photolithography a masking corresponding to the desired spiral contour;
• etching the silicon wafer to the substrate, according to known methods, such as wet chemical etching, plasma dry machining, or a combination of both; and
• separate the hairspring from the substrate.

Given the very small dimensions of a spiral, it is obviously possible and advantageous to batch them from a single silicon wafer.

To manufacture a spiral according to the invention made of metal or alloy, use is made of the known LIGA technique since the mid-1970s. In a first step, the method basically consists in spreading on a substrate previously coated with a sacrificial layer a positive or negative photoresist on a thickness corresponding to the desired "h" height of the blade and forming by means of a mask by photolithography and etching a hollow structure corresponding to the desired contour for the hairspring. In a second step, said hollow structure is filled with a metal or a metal alloy either by electrodeposition as indicated for example in the patent US 4,661,212 or by compression and sintering nanoparticles, as indicated for example in the patent application US 2001/0038803 .

In a final step, the hairspring is released from the substrate by elimination of the sacrificial layer.

Claims (5)

Watch movement comprising a balance-spring resonator whose spiral is mounted on a balance shaft (9) pivoting between a plate (7) and a cock (6), said spiral (10) being formed of a composite blade a succession of turns having between them a pitch "p", the end of the curve inside (11) being secured to the axis (9) balance (8) and the end of the curve on the outside (14) being fixed to the cock (6) or to an integral part thereof, the turns being formed of a single band from the curve inside (11) to the curve at the outside part (14) characterized in that a portion of the outside curve (14) has a larger cross-section than the blade forming all the other turns and in that the curve inside has a conformation Grossmann type. Movement according to claim 1, characterized in that the curve inside (11) is extended by a self-locking washer (17) formed in one and the same piece as the blade and acting as a ferrule for positioning said spiral on the axis ( 9) of the balance (8), thus allowing to control the distance and the orientation of the point of origin of the Archimedes spiral with respect to the axis of rotation of the balance (8) Movement according to one of the preceding claims, characterized in that the spiral is formed of silicon in monocrystalline or polycrystalline form. Movement according to one of claims 1 to 4, characterized in that the spiral is formed of a metallic material or a metal alloy. Movement according to claim 4 dependent on claim 2, characterized in that the self-locking washer (17) has a thickness greater than the height "h" of the blade.

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