HK1232965B - Fastening of a timepiece spring by adhesive bonding - Google Patents

Description

Fastening of watch springs by adhesive bonding

Technical Field

The present invention relates to a timepiece subassembly.

The invention also relates to an oscillator comprising at least one such subassembly.

The invention also relates to an escapement comprising at least one such subassembly.

The invention also relates to a watch comprising such an escapement and/or comprising at least one such subassembly.

The present invention relates to the field of mechanical oscillators for timepieces comprising at least one elastic return means formed by a balance spring, and more particularly to the case where this balance spring is made of silicon or silicon oxide or DLC or other similar micromechanical materials manufactured according to MEMS or similar methods.

The invention more particularly relates to the securing of the exterior of a balance spring.

Background Art

Said balance spring, in conventional timepiece oscillators, in particular with a sprung balance, is usually fastened to a balance spring stud which in turn is fastened to the balance bridge.

The outer portion of the hairspring is typically bonded to the stud with adhesive. Due to the difficult-to-reproduce shrinkage of the adhesive, the bond position is often difficult to reproducibly determine. Once the bond is formed, its quality is difficult to test, except through destructive testing of samples. However, due to the poor reproducibility of the bond, even with a fixed operation (one with strictly controlled parameters), there is no guarantee that the sample is representative of the entire batch. The risk is that once the adhesive has set/cured, the hairspring will separate from the stud.

The use of a balance spring including an end plate offers a relative improvement in bonding, thanks to the fact that the use of an end plate, larger in size than the balance spring's coils, provides a larger bonding contact surface. Indeed, the strength of an adhesive bond deteriorates if the cross-section and dimensions of the component to be bonded—in this case, the balance spring—are too low. This end plate is necessary to ensure a certain contact surface for the adhesive layer, thus ensuring mechanical strength, an absolute necessity, as chemical strength alone is insufficient to reliably hold the components to be assembled.

Patent application DE 2333 446 A1 in the name of JUNGHANS GmbH discloses a balance spring in which the outer end of the balance spring is arranged on a protrusion of an end plate made of plastic material and is held in place by melting the plastic material. The end of the balance spring can be arranged in a groove provided in the protrusion, the shoulder of which can be melted by ultrasonic welding. The fastening is improved by cutting a groove in the edge of the end of the balance spring in the fastening area. The weld is reversible and can be removed during maintenance, so conventional adhesive bonding methods are still possible.

Summary of the Invention

The present invention proposes to ensure improved handling properties of the connection between the stud and the balance spring end plate assembled by adhesive bonding.

In order to achieve this, it is necessary to ensure sufficient space between the end plate and its reception in the stud, thereby ensuring a proper flow of adhesive into the reception and thus achieving improved strength of the joined assembly.

The present invention gives preference to the use of "profiled" endplates, i.e. endplates with a specific shape optimized to ensure better mechanical strength of the combined assembly, in particular better mechanical strength against traction. Thus, if it is necessary to reduce the size of the endplates, the insertion of an appropriately shaped endplate ensures good strength, even if the adhesive contact surface is significantly reduced.

To this end, the invention relates to a timepiece subassembly comprising a hairspring stud arranged to be fastened to a balance bridge of a timepiece movement, the subassembly comprising a hairspring comprising, in order: a spiral winding, an outer ring, a connection region and an end plate having a cross-section larger than that of the outer ring, the end plate terminating at a distal end opposite the spiral winding, the hairspring stud comprising, between an inlet and an outlet, a housing arranged to loosely accommodate the end plate of the hairspring in a first free state of the subassembly, wherein the end plate of the hairspring has a tangential direction relative to the outer ring at the connection region. tangential mobility, and in a second fixed state of the subassembly, the end plate connected to the housing is fixed by an adhesive layer, and the adhesive layer fixes the end plate and the housing to each other, wherein in the second fixed state, the adhesive layer covers at least one cross-sectionally changing shoulder of the end plate, and wherein, in the second fixed state, the adhesive layer forms a mechanical seal for the hairspring at least in a longitudinal direction of the housing that is substantially parallel to the tangential direction of the hairspring, wherein the end plate includes at least one eyelet that communicates with the adhesive layer in the second fixed state.

The invention also relates to an oscillator comprising at least one such subassembly.

The invention also relates to an escapement comprising at least one such subassembly.

The invention also relates to a watch comprising such an escapement and/or comprising at least one such subassembly.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present invention will become apparent upon reading the following detailed description with reference to the accompanying drawings, in which:

FIG1 shows a schematic cross-section of a timepiece subassembly according to the present invention, comprising a hairspring stud secured to a balance bridge, the stud housing an end plate of a hairspring within a receptacle therein. The cross-section is shown in a plane approximately midway between the end plate and the last coil of the hairspring adjacent to the end plate. The end plate includes an eyelet. An adhesive layer fills the receptacle in the stud, completely filling the eyelet. The end meniscus formed by the adhesive layer extends, on the inner side of the hairspring, beyond a shoulder formed at the connection area between the end plate and the last coil of the hairspring, and, on the outermost side of the hairspring, tangentially relative to the coil at the connection area, beyond the distal end of the hairspring, so that the end plate is completely surrounded by the adhesive layer in all directions. The portion of the adhesive layer within the eyelet forms a blocking pin that is difficult to remove.

Figures 2 to 7 each show, in a section similar to that of Figure 1 , the end of a balance spring comprising end plates of different geometries, all developed to offer optimal mechanical resistance to removal by extraction, in particular in the tangential direction:

- the end plate of FIG. 2 comprises two shoulders facing each other and jointly delimiting a stop of maximum cross-section of the end plate, forming the transverse arm of a cross whose longitudinal arms lie within the extension of the outer coil of the balance spring;

- the end plate of FIG. 3 being L-shaped comprises a shoulder opposite its distal end, which shoulder in turn defines a transverse arm projecting laterally on one side relative to the longitudinal arm of the end plate, said longitudinal arm being within the extension of the outer coil of the balance spring,

- the end plate of FIG. 4 comprises, at its distal end, a substantially cylindrical portion projecting laterally on both sides relative to the longitudinal arms of the end plate, said longitudinal arms being within the extension of the outer coil of the balance spring;

- the T-shaped end plate of FIG. 5 comprises a shoulder opposite its distal end, which shoulder in turn defines transverse arms projecting laterally on both sides relative to the longitudinal arms of the end plate, said longitudinal arms being within the extension of the outer coil of the balance spring,

- the end plate of FIG. 6 is a variant of that of FIG. 2 , in which the transverse blocking arm is located directly on the outer coil side of the balance spring and is inclined on the opposite side to form a slope;

- the end plate of FIG. 7 comprises, on either side of the trailing arm within the extension of the outer coil of the balance spring, two recessed profiles, which here in this particular but non-limiting embodiment are not directly opposite each other, each recessed profile being arranged to receive a layer of adhesive in a manner similar to the eyelet of FIG. 1 ;

- Figure 8 shows a section through a balance spring in which the outer coil ends in a loop forming an eyelet to block the adhesive layer, this loop then being housed in a stud housing;

FIG. 9 shows a variant of FIG. 1 of further reduced dimensions, in which the balance spring comprises an outer shoulder between the bezel and the end plate, not surrounded by the adhesive layer, and in which the distal end of the end plate is also not surrounded by the adhesive layer, the adhesive layer passing directly through an eyelet in the end plate to secure the end plate. This outer shoulder serves to adjust the optical or mechanical guide markings, or to display or mark the effective length of the balance spring when said length is determined by contact between the bezel area and a pin or the like, the outer shoulder then allowing a better understanding of the position of the contact zone and, if necessary, calculation of the precise effective length;

- Figure 10 is a cross section of a hollow outer pile receiving portion;

- Figure 11 is a block diagram showing a watch comprising a movement incorporating a sprung-balance oscillator comprising a subassembly according to the invention.

DETAILED DESCRIPTION

The invention ensures improved handling properties of the connection between the balance spring stud and the balance spring end plate, assembled by adhesive bonding, based on good mechanical strength, which compensates for the lack of chemical strength alone, which is insufficient to reliably hold the assembled components together, in particular with regard to resistance to removal by pulling tangentially to the outer coil of the balance spring subjected to a restoring torque. Once the adhesive layer has been shaped in the stud housing, the specific geometry of the end plate is essential to ensure this mechanical strength and prevent the end plate from being removed from the shaped adhesive mass.

To this end, the invention relates to a timepiece subassembly 100 comprising a balance spring stud 20 arranged to be fastened to a balance bridge 40 of a timepiece movement 300. This subassembly 100 comprises a balance spring 1 .

This balance spring 1 comprises, in order, a spiral winding, a bezel 2 , a connecting zone 11 and an end plate 10 of larger cross-section than the bezel 2 , the end plate 10 terminating in a distal end 12 opposite the spiral winding, and the connecting zone 11 comprising a change in cross-section between the bezel 2 and the end plate 10 .

Balance spring stud 2 comprises, between inlet 23 and outlet 24, a housing 21 designed to loosely house end plate 10 of balance spring 1 in a first, free state of subassembly 100, wherein end plate 10 of balance spring 1 has tangential mobility relative to bezel 2 in a tangential direction T at a connection region 11, while in a second, fixed state of subassembly 100, end plate 10 connected to housing 21 is fixed by means of an adhesive layer 30 which secures housing 21 and end plate 10 to one another.

According to the present invention, in the second fixed state, the adhesive layer 30 covers at least the variable-section shoulder 5 of the end plate 10 .

1 , adhesive layer 30 also covers connection zone 11 . This arrangement only concerns applications in which the effective length definition point of the balance spring is located in an area of bezel 2 different from connection zone 11 .

For many common applications where connecting zone 11 defines the effective length of the balance spring, the variant of FIG9 is preferred. In fact, if adhesive were deposited on connecting zone 11, the effective length of the balance spring and, consequently, its frequency and daily rate would be modified, which is undesirable, and therefore no adhesive should be present on connecting zone 11.

In this second fixed state, adhesive layer 30 forms a mechanical seal for balance spring 1 , at least in a longitudinal direction L of housing 21 , substantially parallel to a tangential direction T of the balance spring.

More specifically, as seen in the variant of FIG. 1 , in the second fixed state, adhesive layer 30 covers connection region 11 and forms a mechanical seal for balance spring 1 at least in a longitudinal direction L of housing 21 substantially parallel to a tangential direction T of balance spring 1 .

FIG1 shows the stud positioned horizontally in the movement; of course, the stud could be in a conventional vertical position with the same benefits offered by the invention.

Preferably, housing 21 is large enough for adhesive layer 32 to completely surround at least a portion of end plate 10, which portion comprises one or more shoulders 5, 11 or at least one eyelet 6 in the particular case of FIG. 1 and not in the more general case of FIG. 9 , with sufficient play between housing 21 and this particular portion of end plate 10 in the unbonded free state to ensure that adhesive layer 30, once deposited, surrounds this portion of the end plate on all sides, so that adhesive layer 30 then forms a mechanical seal in housing 21 for balance spring 1 in all degrees of freedom.

Advantageously, the housing 21 comprises at least one protruding or recessed volume arranged to form at least one barrier for the adhesive layer 30 , or comprises corrugated grooves or recesses on its inner walls 25 , 26 , or is made to have a roughened surface state with a roughness R of above 12 microns to ensure mechanical retention of the adhesive layer 30 .

In the variant of FIGS. 2 to 7 , the end plate 10 comprises a varying cross-section perpendicular to the longitudinal direction L. In the variant of FIGS.

In the variant of Figures 1 and 9, where the end plate 10 comprises an eyelet 6, and where the outer contour of the end plate 10 is of substantially constant cross-section, the cavity of the eyelet 6 determines the smaller resulting cross-section of the end plate 10 outside the area of the eyelet 6.

In a particular variant, and as can be seen in particular in FIGS. 3 and 5 , the cross-section of the end plate 10 decreases continuously and/or stepwise from its outer distal end 12 towards the outer ring 2 .

More specifically, as can be seen in FIG9 , the end plate 10 comprises at least one shoulder 5 , wherein the cross-section of the end plate 10 varies, said shoulder 5 being distinct from the connection region 11 between the outer ring 2 and the end plate 10 , and in the second fixed state, the adhesive layer 30 covers this shoulder 5 , while the connection region 11 remains outside the adhesive layer 30 .

In the variant of Figures 2 and 6, the end plate 10 includes at least a first shoulder 5A and a second shoulder 5B, wherein the cross-section of the end plate 10 varies, and the first shoulder 5A and the second shoulder 5B jointly define a blocking portion 13 of the end plate 10 with the largest cross-section, and the first shoulder 5A and the second shoulder 5B are completely different from the connection area 11.

More specifically, in the same variant of FIGS. 2 and 6 , the first shoulder 5A and the second shoulder 5B are distinct from the distal end 10 of the end plate 10 .

In a particular variant, and as can be seen in particular in Figures 1, 8 and 9, the end plate 10 comprises at least one eyelet 6, 8 communicating with the adhesive layer 30 in the second fixed state.

More specifically, when the bottom plate 10 comprises the blocking portion 13 , the holes 6 , 8 are housed within the thickness of the blocking portion 13 of the largest section of the end plate 10 .

In the particular variant of Figures 1 and 9, the end plate 10 forms a ring 4 comprising at least one eyelet 6, wherein the layer 30 penetrates only along an anchoring direction A substantially perpendicular to the tangential direction T in the second fixed state.

In the particular variant of FIG. 8 , the end plate 10 forms a hook 7 comprising at least one eye 8 open on the side of the outer ring 2 and comprising a bend 9 at its end furthest from the outer ring 2 .

Figures 2 to 7 show different geometries of end plate 10 that are very suitable for embodiments of the present invention: they either have a protruding cross shape, an L-shape, a shape with a cylindrical end, a T-shaped profile, as in Figures 2 to 6, with shoulder 5 forming a perpendicular surface relative to the tangential direction and arranged to provide the greatest resistance to the pull of the spiral portion of balance spring 1 in this direction; or they have a concave profile, as seen in Figure 7, not necessarily directly opposite, so as to avoid that end plate 10 is weakened too much due to a too small cross-section.

The invention is particularly well suited to the fastening of a balance spring 1 made of silicon and/or silicon oxide, or DLC, or other similar micromechanical materials produced via MEMS or similar methods.

The present invention also relates to an oscillator 200 comprising at least one of the subassemblies 100 .

The invention also relates to an escapement mechanism 300 comprising at least one such assembly 100 .

The invention also relates to a watch 400 comprising the escapement 200 and/or comprising at least one of the subassemblies 100 .

Claims (16)

1. A watch subassembly (100) comprising a hairspring stud (20) configured to be fastened to a balance bridge (40) of a watch movement, and the subassembly (100) comprising a hairspring (1) comprising, in sequence: a spiral winding portion, an outer ring (2), a connecting region (11), and an end plate (10) having a cross-section larger than that of the outer ring (2), the end plate (10) terminating at a distal end (12) opposite to the spiral winding portion, the hairspring stud (20) comprising a receiving portion (21) between an inlet (23) and an outlet (24), the receiving portion (21) being configured to loosely receive the end plate (10) of the hairspring (1) in a first free state of the subassembly (100), wherein the end plate (10) of the hairspring (1) has a portion at the connecting region (11) relative to the outer ring (2) The end plate (10) connected to the receiving portion (21) is fixed by an adhesive layer (30) in the second fixed state of the sub-assembly (100), the adhesive layer fixing the end plate and the receiving portion to each other, wherein, in the second fixed state, the adhesive layer (30) covers at least one cross-sectional change shoulder (5) of the end plate (10), and wherein, in the second fixed state, the adhesive layer (30) forms a mechanical seal for the hairspring (1) at least in the longitudinal direction (L) of the receiving portion (21) substantially parallel to the tangential direction (T) of the hairspring (1), characterized in that the end plate (10) includes at least one eyelet (6; 8) communicating with the adhesive layer (30) in the second fixed state. 2. The watch sub-assembly (100) according to claim 1, wherein the adhesive layer (30) covers at least one variable cross-section shoulder (5) of the end plate (10) and does not cover the connection area (11). 3. The watch sub-assembly (100) according to claim 1, characterized in that, in the second fixed state, the adhesive layer (30) covers the connection area (11). 4. The watch sub-assembly (100) according to claim 1, characterized in that the adhesive layer (30) forms a mechanical seal for the hairspring (1) in all degrees of freedom in the receiving portion (21). 5. The watch sub-assembly (100) according to claim 1, wherein the end plate (10) comprises a variable cross-section perpendicular to the longitudinal direction (L). 6. The clock sub-assembly (100) according to claim 5, characterized in that the variable cross section of the end plate (10) decreases continuously and/or progressively from the outer distal end (12) toward the outer ring (2). 7. The watch sub-assembly (100) according to claim 6, characterized in that the end plate (10) includes at least one of the cross-section changing shoulders (5), the cross-section of the end plate (10) changing at the cross-section changing shoulders, the cross-section changing shoulders (5) being different from the connecting region (11), wherein, in the second fixed state, the adhesive layer (30) covers the cross-section changing shoulders (5), while the connecting region (11) remains outside the adhesive layer (30). 8. The watch sub-assembly (100) according to claim 5, characterized in that the end plate (10) includes at least a first shoulder (5A) and a second shoulder (5B), the cross section of the end plate (10) changes at the first shoulder (5A) and the second shoulder (5B), the first shoulder (5A) and the second shoulder (5B) together define the blocking portion (13) of the end plate (10) having the largest cross section, the first shoulder (5A) and the second shoulder (5B) being different from the connecting region (11). 9. The watch sub-assembly (100) according to claim 8, characterized in that the first shoulder (5A) and the second shoulder (5B) are different from the distal end (12) of the connecting plate (10). 10. The clock sub-assembly (100) according to claim 8, wherein the eyelet (6; 8) is accommodated in the blocking portion (13) of the end plate (10) having the largest cross-section. 11. The watch sub-assembly (100) according to claim 1, characterized in that the end plate (10) forms an annulus (4) including at least one eyelet (6), wherein the adhesive layer (30) penetrates only in the second fixed state along the anchoring direction (A) which is substantially perpendicular to the tangential direction (T). 12. The watch sub-assembly (100) according to claim 1, characterized in that the end plate (10) forms a hook portion (7) including at least one eyelet (8) opening on the side of the outer ring (2), and includes a bend (9) at the end furthest from the outer ring (2). 13. The watch sub-assembly (100) according to claim 1, wherein the hairspring (1) is made of silicon and/or silicon oxide. 14. An oscillator mechanism (200) comprising at least one clock sub-assembly (100) according to claim 1. 15. An escapement mechanism (300) comprising at least one clock sub-assembly (100) according to claim 1. 16. A wristwatch, comprising the escapement (300) according to claim 15 and/or comprising at least one watch sub-assembly (100) according to claim 1.