HK1218445B - Device and method for fixing a movement in a case - Google Patents

Description

Device and method for fixing movement in case

Technical Field

The present invention relates to a device and a method for securing a movement in a watch case, in particular in a diving watch case.

Background

In the field of horology, the plate on which the movement is arranged generally comprises a thread, i.e. an upper edge provided for attaching the movement to the case. In this way, the threads can be fixed by means of a clip and a screw inserted into the threaded hole and thus pressed against the shoulder of the middle part of the watch case. Despite the advantages of this type of attachment, which are reliable and reversible, it has the drawback of being relatively complex to implement, due to the various operations required for the screws and the clamps, which seriously affect the productivity and make the method unsuitable for watch making intended for mass production.

The applicant's patent application US2002/0131332 describes an alternative method for attaching a movement which does not require the use of threads or clamps, but still uses set screws. A first set of screws is inserted in through holes arranged on the periphery of the movement in order to assemble the movement to the bezel, and then a second set of screws is used to assemble the back cover to the same bezel. Thus, although the centre piece for this type of attachment is no longer the middle part of the case but the bezel of the watch, the same drawback still exists in terms of productivity and is even greater due to the increased number of operations of the threaded connection required during the assembly of the movement.

Because of this, one sometimes prefers a press-fit attachment method, usually by means of an intermediate piece such as a casing ring, which also allows fixing a small calibration movement in a larger casing.

The solution described in patent EP1046967 of the applicant relates, for example, to such a method for attaching a movement by means of a casing ring made of a plastically deformable material intended to allow radial or axial adjustment of the movement in a determined position with respect to the casing.

Whatever the attachment method chosen, the lower edge of the screw is always made to abut against a portion of the middle part of the case, while the shape of the back of the case, which may or may not be integral with the middle part of the case, matches the shape of the lower part of the movement, within machining tolerances. Patent US4558955 describes a solution for attaching a movement in which the movement is housed directly in a recess of the middle part-back of the case in one piece and is held axially between the bottom of this recess, on which the movement rests, and the dial, which is held by the watch mirror. A disadvantage of this type of mode of attachment is that any deformation of the back cover, particularly during underwater use, is directly reproduced on the deck, and the deck is particularly sensitive.

In order to prevent any accidental deformation of the constituent parts of the watch, an alternative consists, in particular for plastic watches, in reinforcing the case using a reinforcing structure, for example comprising a skeleton made of metal or other type of material. However, this alternative cannot be envisaged if it is desired to maintain the attractive features of the watch case, in particular if it is desired that the watch case remains at least partially transparent.

In addition, for watches that house other internal modules in addition to the movement, a structure with a double back cover is also known. For example, patent EP0670532 relates to a watch provided with a pressure sensor and describes the assembly of the movement to the middle part of the case in a conventional manner by means of a casing ring, the inner back cover housing the pressure sensor being covered by the back cover of the case. However, this construction has the disadvantage of considerably increasing the thickness of the watch case and also slowing down the production times, since each back cover assembly operation is doubled.

Therefore, there is a need for a method and a device for attaching a movement in a watch case that do not present these known limitations.

Disclosure of Invention

To this end, the invention relates to a timepiece comprising a case housing a movement including a lower peripheral bearing surface, said case comprising a case middle part to which a back cover and a mirror are respectively assembled. Said timepiece being characterized in that it further comprises a clamping element provided with a lower retaining surface, said movement comprising an upper peripheral bearing surface, said lower retaining surface and said upper peripheral bearing surface of said clamping element being in contact with each other, said back cover comprising a peripheral annular shoulder against which said lower peripheral bearing surface of said movement rests, said movement being pressed between said lower peripheral bearing surface of said movement and said upper peripheral bearing surface of said movement by said peripheral annular shoulder of said back cover and said lower retaining surface of said clamping element, respectively.

The invention also concerns a separately removable back cover for such a timepiece, characterized in that it comprises a central depression of varying thickness and a peripheral annular shoulder of constant thickness.

Finally, the invention also relates to a preferred assembly method for obtaining such a timepiece. The method is characterized in that the assembly of the movement in the case comprises the following steps:

-inserting the movement into the case from the dial side;

-resting the lower peripheral bearing surface of the cartridge on the peripheral annular shoulder of the back cover, and then

-clamping the movement on the back cover by means of a clamping element bearing against an upper peripheral bearing surface of the movement, so that the movement is pressed between the lower peripheral bearing surface of the movement and the upper peripheral bearing surface of the movement by the peripheral annular shoulder of the back cover and a lower retaining surface of the clamping element, respectively.

One advantage of the invention is that, since the inner surface of the back cover is completely separated from the movement, it allows to better absorb any deformations of the back cover, for example when the pressure or temperature varies considerably. This therefore avoids any harmful torsional stresses being exerted on the plate and therefore on all the elements of the movement, in particular on the arbour and bridge.

According to this preferred assembly method, the movement is inserted from the top of the case at the dial side, which avoids turning the case over during assembly, thus advantageously increasing the production rate.

Drawings

Further characteristics and advantages of the invention can be found from the detailed description given by way of non-limiting example and the accompanying drawings, in which:

figure 1 shows a schematic cross-section of a movement according to a preferred embodiment of the invention assembled in a watch case;

figures 2A and 2B show respectively a top view and a cross-section of a diving watch using an assembly method according to a preferred embodiment.

Detailed Description

Fig. 1 shows a cross-section of a timepiece according to a preferred embodiment of the invention in an assembled position, in which movement 3 is assembled in case 2 by a method corresponding to a preferred embodiment of the invention, lever 7 is attached to movement 3, and movement 3 drives hands 30 above dial 8. According to this preferred embodiment, the case comprises a back cover-case middle part in one piece, i.e. the back cover part 4 is made in one piece with the case middle part 20 forming the central part of the case 2. This one-piece component simplifies the assembly process of the movement 3 by eliminating one assembly step; in this case, the movement 3 can be inserted directly from the upper part of the case 2, i.e. the dial side, without requiring subsequent assembly of the back cover or turning over of the case 2 to insert the movement. It will be appreciated, however, that the assembly method of the invention is equally applicable to back cover 4 assembled on middle part 20 of the watch case by snapping, screwing or gluing or any other common attachment method. Nevertheless, the step of assembling back cover 4 to case middle part 20 is preferably performed before inserting movement 3 into the case, so that movement 3 is always inserted from the dial side.

The back cover 4 comprises, at the edge of its inner surface, a peripheral annular shoulder 41 of a first width (L), against which the movement 3 rests, the back cover 4 also comprising a central recess 40 of depth (d). The lower peripheral bearing surface 31 of the movement 3 at least partially overlaps (superposer) the upper peripheral bearing surface 32 of this movement 3, having the second width (I), this upper peripheral bearing surface 32 being clamped by the lower retaining surface of a clamping element, here formed by a portion 52 of a base 51 of the watch mirror 5, having the third width (T), the lower surface of this portion 52 resting on the upper peripheral bearing surface 32 of the movement 3.

According to a preferred embodiment, the first width L of the lower peripheral bearing surface 31 of the movement 3 is chosen to be greater than the second width I of the upper bearing surface 32, but this is compensated by the third width T of the base 51, chosen to be greater than the first width L of the lower peripheral bearing surface 31 of the movement 3, so as to obtain a grip and a symmetrical compression of the movement 3 at its periphery, which generates a minimum torque.

The thickness of the back cover at the peripheral annular shoulder 41 is constant and equal to (E), whereas the thickness varies throughout the central depression 40 and is minimal and has the value (E) at the centre of the back cover 4. As can be seen from fig. 1, there is the equation E + d ═ E. When a force due to the pressing represented by arrow (P) is exerted on watch case 2, for example during a dive to a depth of more than about ten metres or a pressure greater than an additional 1 bar, corresponding to twice the ambient pressure, is exerted on the entire outer surface of the watch case, central depression 40 allows back cover 4 to be slightly deformed, in particular at its centre, without thereby affecting the movement, which is clamped between its lower and upper peripheral bearing surfaces 31 and 32, but without contacting back cover 4 at its central depression 40. In this way, case 2 is strong at the pressure value so that the curvature of the back cover does not reverse to such an extent that central recess 40 of back cover 4 comes into contact with movement 3 again. The shape of the central depression 40 of the back cover 4 is preferably chosen to be parabolic in order to facilitate torsional deformation of the back cover 4 and to prevent stresses from being transmitted at the peripheral gripping area of the movement 3.

Within the scope of the invention, the diameter of movement 3 is preferably between 25 and 40 mm, in which case the first width L of peripheral annular shoulder 41 of back cover 4 is preferably chosen to be between 2 and 5 mm. More generally, the first width L of the peripheral shoulder 41 of the back cover is chosen to be between 1/4 and 1/10 of the value of the diameter of the movement 3, in order to improve the grip effect at its periphery, while also allowing the back cover 4 to deform more easily under the action of external stresses. With a maximum thickness E of back cover 4 of between 3 mm and 5 mm and a minimum thickness E of said back cover of between 2.5 and 4 mm, watch case 2 can therefore withstand a pressure of at least about 35 bar.

It can be seen in fig. 1 that, on the extension of the portion 52 abutting against the upper peripheral bearing surface 32 of the movement 3, the base 51 of the mirror 5 is in contact with the shoulder 21 of the case middle part 20. According to this preferred embodiment, the step of clamping movement 3 between its lower and upper peripheral portions 31 and 32 is carried out together with the step of mounting the watch mirror 5 on the case middle 20, preferably by ultrasonic welding. The resulting assembly structure has the advantages of: the torsional stresses on the welds are reduced, since the upper peripheral bearing surface 32 of the movement 3 extends axially over the shoulder 21 of the middle part of the case and therefore improves the robustness and durability of the connection between the welds.

The fact that, according to the preferred embodiment illustrated, lower bearing surface 31 and upper bearing surface 32 partially overlap also allows to maintain the integrity of movement 3 by avoiding the application of torsional stresses which tend to deform the movement due to opposite stresses of similar magnitude applied on regions of very different distances from the centre.

The protection of the movement from deformations of the watch case is further enhanced by the fact that: in the preferred embodiment shown, the base 51 of the watch mirror, whose third width T is preferably between 4 and 8 mm, completely overlaps the peripheral annular shoulder 41 to further improve the clamping effect. For reasons of symmetry and therefore of optimal stress distribution intended to minimize the generation of torque, the third width T of the base 51 will also preferably be chosen at most equal to twice the first width L of the peripheral annular shoulder 41.

It should be noted that movement 3 of figure 1 is shown without threads, since, unlike conventional movements, no threads are used to provide a stop or snap-fit surface during assembly of the movement in case 2.

3 fig. 3 2A 3 and 32 3 B 3 show 3 a 3 top 3 view 3 and 3 a 3 cross 3- 3 sectional 3 view 3 along 3 axis 3 a 3- 3 a 3, 3 respectively 3, 3 of 3 a 3 preferred 3 embodiment 3 of 3 an 3 assembly 3 method 3 according 3 to 3 the 3 invention 3 for 3 assembling 3 a 3 movement 33 3 in 3 a 3 watch 3 case 32 3 for 3 a 3 timepiece 31 3 corresponding 3 to 3 a 3 diving 3 watch 3. 3

Fig. 2A is a top view of the diving watch, showing the watch case 2 and the mirror 5 covered by the bezel 8. Fig. 2B shows the components inside watch case 2, in particular movement 3 provided with a thread 33 on its upper part in a conventional manner. However, this thread 33 is not provided to ensure the axial retention of the movement 3 in the case 2, this function being performed by the peripheral annular shoulder 41 of the back cover 4 and the portion 52 of the base 51 of the mirror 5, said peripheral annular shoulder 41 and said portion 52 sandwiching between them the lower peripheral bearing surface 31 and the upper peripheral bearing surface 32, respectively, of the movement 3 when the mirror 5 is welded to the shoulder 21 of the case middle part 20 at the thermal welding zone 22 represented by the small beak downwards from the periphery of the base 51, to clamp the movement. Thus, the movement 3 is clamped between the portion 52 of the base 51 of the watch mirror 5 and the peripheral annular shoulder 41 of the back cover 4, while the watch mirror is heat welded to the case middle 20. The bezel 8 can then be snapped onto the watch mirror 5.

As can be seen in fig. 2B, according to this preferred embodiment, a movement is used having a diameter of about 33 mm, the lower peripheral bearing surface 31 of which has a first width L equal to 4 mm, the second width I of the upper peripheral bearing surface 32 of which is equal to 2.5 mm, just like the width of the peripheral annular shoulder 41 of the back cover 4 pressing said lower peripheral bearing surface 31 via the back cover 4, the lower peripheral bearing surface 31 and the upper peripheral bearing surface 32 of which are completely overlapped, just like the width of the portion 52 of the base 51 of the mirror 5 pressing the upper peripheral bearing surface 32 from above, so that the clamping action thus formed generates a minimum torque at the periphery of the movement. Also, for the same reason of minimizing the torsional deformation stresses on the movement 3, the base 51 has a third width T of 7 to 8 mm and completely overlaps the peripheral annular shoulder 41. For reasons of symmetry and in order to relieve the stresses exerted on the thermowelded zone 22, the base 51 will comprise, on the opposite side of the thermowelded zone 22, a portion extending inwards with respect to the portion 52 that clamps the movement on the upper bearing surface 32 of the movement.

According to the preferred embodiment, the thickness E of the rear cover is about 3 mm and its minimum thickness E is 2.5 mm, so that a recess with a depth of about 0.5 mm appears in the center. Central depression 40 of back cover 4 preferably has a parabolic shape to facilitate deformation of back cover 4 and to optimize the distribution of stresses exerted on the back cover of watch case 2. Also for reasons of symmetry and of optimal distribution of the stresses generated by the pressing, the watch mirror 5 preferably has a shape and thickness similar to those of the back cover 4.

In the preferred embodiment of the invention, after the operation of directly clamping movement 3 between its lower and upper peripheral bearing surfaces 31 and 32, a preferred assembly structure is obtained involving a portion 52 of base 51 of watch crystal 5 as the lower retaining surface of the clamping element and a laser welding operation which not only allows the removal of the parts dedicated to axially retaining movement 3, movement 3 being pressed against peripheral annular shoulder 41 of back cover 4 by watch crystal 5 acting as a clamping element, but also eliminates the dedicated operation for attaching movement 3, since movement 3 is fixed to the back cover while watch crystal 5 is welded to case middle part 20. Therefore, the reduction in the number of parts and assembly operations required to attach the movement not only reduces the production cost but also improves the productivity. Instead of laser welding, other attachment methods can be envisaged, such as brazing, gluing or pressing, without departing from the scope of the invention, and furthermore, according to alternative embodiments not shown, it is also possible to envisage interposing an intermediate piece, such as a ring, between the watch crystal 5 and the movement 3, or assembling another piece for clamping directly onto the middle part 20 of the case, without involving the watch crystal 5, for example a piece with an L-shaped section, in which the first side comprising the lower clamping surface is placed over the thread of the movement 3 and the second side is pressed into a circular rib of the middle part 20 of the case.

It should furthermore be pointed out that the components assembled within the scope of the invention, in particular the rear cover 4, are preferably made of a plastic material. However, the invention also comprises a watch case 2, in particular for a diving watch, comprising a back cover 4 made of steel or metal, which, despite the greater rigidity of the back cover 4, cannot be freed from any deformation at very high pressures.

List of reference numerals

1	Clock and watch
		2	Watch case
20	Middle part of watch case
		21	Shoulder of middle part of watch case

22	Heat-welded zone of middle part/mirror of watch case
		3	Movement
30	Watch hand of movement
		31	Lower annular bearing surface for movement
32	Upper annular bearing surface of movement
		33	Screw thread of movement
4	Back cover
		40	Concave part of rear cover
41	Annular shoulder of rear cover
		5	Watch mirror
51	Base of watch mirror
		52	Part of the base of the watch mirror resting on surface 32 of the movement
6	Dial plate
		7	Control rod
8	Watch ring
		E	(maximum) thickness of rear cover
e	(minimum) thickness of rear cover
		d	Depth of central depression 40
L	First width of lower bearing surface
		l	Second width of upper bearing surface
T	Third width of base 51 of watch mirror
		A-A	Sectional axis of FIG. 2A

Claims (10)

1. Timepiece (1) comprising a case (2) housing a movement (3) including a lower peripheral bearing surface (31), said case (2) including a case middle part (20), a back cover (4) and a mirror (5) being assembled respectively onto said case middle part (20), characterized in that said timepiece (1) further includes a clamping element provided with a lower retaining surface, said movement (3) including an upper peripheral bearing surface (32), said lower retaining surface and said upper peripheral bearing surface (32) of said clamping element being in contact with each other, said back cover (4) including a peripheral annular shoulder (41) having a constant thickness and a central recess (40) having a variable thickness, said lower peripheral bearing surface (31) of said movement (3) resting on said peripheral annular shoulder (41), said movement (3) passing through said peripheral annular shoulder (41) and said peripheral annular shoulder (41) of said back cover (4), respectively The lower retaining surface of the clamping element is squeezed between the lower peripheral bearing surface (31) and the upper peripheral bearing surface (32) of the movement (3), wherein the lower peripheral bearing surface (31) and the upper peripheral bearing surface (32) at least partially overlap.

2. Timepiece (1) according to claim 1, characterised in that the lower retaining surface of the clamping element is formed by a portion (52) of a base (51) of the mirror (5).

3. Timepiece (1) according to claim 2, characterised in that the back cover (4) and the case middle part (20) form a one-piece part.

4. Timepiece (1) according to claim 2, characterised in that the base (51) of the mirror (5) completely overlaps the peripheral annular shoulder (41) of the back cover (4).

5. Timepiece (1) according to claim 2, wherein the movement (3) has a diameter between 25 mm and 40 mm, the peripheral annular shoulder (41) of the back cover (4) extending over a first width (L) of at most 5 mm, the base (51) of the mirror (5) extending over a third width (T) of at most 8 mm, the portion (52) of the base (51) extending over a second width (I) of at most 4 mm.

6. A back cover (4) for a timepiece (1) according to claim 1, characterized in that it comprises a peripheral annular shoulder (41) with a constant thickness and a central recess (40) with a variable thickness, and in that the minimum thickness of the back cover is at the centre of the back cover.

7. The back cover according to claim 6, wherein the maximum thickness (E) of the back cover is between 3 mm and 5 mm and the minimum thickness (E) of the back cover is between 2.5 mm and 4 mm.

8. Rear cover according to claim 6, characterized in that the width of said peripheral annular shoulder (41) is between a quarter and a tenth of the value of the diameter of said movement.

9. An assembly method for a timepiece (1) according to claim 1, characterised in that the assembly of the movement (3) in the case (2) comprises the following steps:

-inserting the movement (3) into the case (2) from the dial side;

-resting the lower peripheral bearing surface (31) of the movement (3) on a peripheral annular shoulder (41) of constant thickness of the back cover (4), the back cover (4) also comprising a central depression (40) of variable thickness and parabolic shape, then

-clamping the movement (3) on the back cover (4) by means of a clamping element bearing against an upper peripheral bearing surface (32) of the movement (3), so that the movement is pressed between the lower peripheral bearing surface (31) of the movement (3) and the upper peripheral bearing surface (32) of the movement (3) by the peripheral annular shoulder (41) of the back cover (4) and a lower retaining surface of the clamping element, respectively, wherein the lower peripheral bearing surface (31) and the upper peripheral bearing surface (32) at least partially overlap.

10. Method of assembly according to claim 9, characterized in that the back cover (4) and the middle part (20) of the case form a one-piece part, the lower retaining surface of the clamping element being formed by a portion (52) of a base (51) of the watch mirror (50), the clamping step being carried out together with the step of assembling the watch mirror (5) onto the middle part (20) of the case.