HK1120872B - Assembly element including fork shaped elastic structures and timepiece including the same - Google Patents

Description

Assembly comprising a fork-shaped elastic structure and timepiece comprising such an assembly

Technical Field

The invention relates to an assembly and a timepiece comprising such an assembly.

The invention relates more particularly to an assembly, particularly suitable for a timepiece, formed in a plate of brittle material, such as silicon, comprising a hole provided for the axial insertion of a spindle, the inner wall of the hole comprising elastic structures etched in the plate and each of which comprises at least one support surface for radially clamping or pressing the spindle, so as to fix the assembly with respect to the spindle.

Background

In timepieces, in general, the components such as the hands of the timepiece and the gear are fixed by being driven on their rotating arbors, i.e. the hollow cylinder is pressed on a pin whose diameter is slightly greater than the internal diameter of the cylinder. The elastic and plastic properties of the employed materials, usually metals, are used to drive into the elements. For parts made of brittle materials such as silicon, which do not have a usable range of elasticity, it is not possible to drive hollow cylinders onto conventional rotating spindles with a diameter tolerance of +/-5 microns, like those used in mechanical watches.

Furthermore, the solution for fixing components such as pointers must provide sufficient force to keep the elements in place in the event of a shock. The force that must be applied to a conventional timepiece hand is, for example, of the order of one newton.

To overcome these problems, it has been proposed to manufacture in an assembly such as a silicon balance spring collet a flexible strip-like elastic structure arranged at the periphery of the hole, to secure the collet on the spindle by a drive-in arrangement using elastic deformation of the strip, to grip the spindle and to retain the collet on the spindle. An example of this type of fixing method is specifically disclosed in EP patent No. 1655642.

This solution is not entirely satisfactory, in particular because of the significant stiffness of these flexible strips, which causes assembly problems. Moreover, this method cannot be used to fix a rotating element to its rotating spindle, which may result in relative sliding between the two parts.

Disclosure of Invention

The object of the present invention is to overcome these problems by providing an improved elastic structure, in particular allowing the use of the assembly as a rotating element in a timepiece mechanism, in particular as a timepiece hand.

The invention thus proposes an assembly of the aforementioned type, characterized in that: each elastic structure is formed by a fork, connected to the inner wall of the hole by a bridge of material, and comprising two branches extending on either side of the bridge of material, generally towards the mandrel; and each branch comprises a support surface adjacent to its free end.

The assembly according to the invention improves the clamping force against the spindle, allowing a better distribution of the stresses associated with elastic deformations in the material forming the assembly and a better control of the clamping force obtained on the spindle, while maintaining the elimination of material breakage ranges.

Furthermore, the elastic structure according to the invention provides, after its elastic deformation, a radial clearance sufficient to compensate for the manufacturing tolerances applied to the diameter of the arbour, such as those used for chronographs, for driving the hands.

According to other features of the invention:

each branch of the elastic structure has a substantially parabolic shape, one fixed end of which is arranged on the bridge of the relevant material and a second free end of which faces the free end of the other end of the elastic structure, the support surface of each branch being arranged on the inner surface of the free end portion thereof;

each elastic structure comprises a main portion extending on either side of the bridge of material, from one end of the main portion opposite the bridge of material, along an inclined rectilinear direction towards the relative branch, each branch extending with respect to a radial direction and being provided at its free end with a support surface of each branch;

-the main portion extends substantially in a circumferential direction;

the inner wall of the bore comprises at least three elastic structures regularly distributed around the mandrel;

-a timer hand forming component.

The invention also provides a timer, which is characterized in that: comprising at least one assembly according to any of the preceding features.

Other characteristics and advantages of the invention will appear more clearly on reading the following detailed description, given by way of non-limiting example with reference to the accompanying drawings, in which:

drawings

Figure 1 is an axial section schematically showing a timepiece fitted with an assembly formed by the hands of a timepiece made according to the teachings of the present invention;

figures 2 to 4 are top views which respectively schematically show the hour, minute and second hands assembled to the timepiece of figure 1 and which are equipped with elastic structures in a C-shaped embodiment;

FIG. 5 is an enlarged view of one of the parts of FIG. 2, showing the hour hand mounting ring;

figures 6 to 8 are similar views to figures 2 to 4, schematically showing the hour, minute and second hands, respectively, when they are equipped with elastic structures according to the second L-shaped embodiment.

Detailed Description

In the following description, identical or similar elements are denoted by the same reference signs.

Figure 1 schematically illustrates a timepiece 10 made in accordance with the teachings of the present invention.

Timepiece 10 includes a movement 12 mounted in a case 14 closed by a crystal 16. Movement 12 drives in rotation, about axis a1, an analogue display device, here formed by an hour hand 18, a minute hand 20 and a second hand 22, which extend over a dial 24. The hands 18, 20, 22 are fixed in a drive-in arrangement by being resiliently clamped to coaxial cylindrical rotating spindles 26, 28, 30, as seen hereinafter.

Preferably, spindles 26, 28, 30 are conventional spindles commonly used in timepiece movements, such as metal or plastic spindles.

In the following description, we will use, in a non-limiting manner, an axial orientation along the axis of rotation a1 of the hands 18, 20, 22 and a radial orientation with respect to the axis a 1. Furthermore, the elements will be referred to as being inner or outer, according to their radial orientation relative to axis a 1.

The fingers 18, 20, 22 form an assembly, each finger 18, 20, 22 being formed in a plate of brittle material, preferably a silicon-based crystalline material, and being mounted on its mandrel 26, 28, 30.

Figures 2, 3 and 4 show a first embodiment of the invention, to which an hour hand 18, a minute hand 20 and a second hand 22 are applied, respectively. Each pointer 18, 20, 22 here comprises a mounting ring 31, which mounting ring 31 defines a hole 32, which hole is provided for fixing the pointer 18, 20, 22 to the associated spindle 26, 28, 30 by inserting the hole 32 axially. The inner wall 33 of the hole 32 comprises elastic structures 34, which are etched in the plate forming the mounting ring 31 and which each comprise a support surface 36, 38 for radially gripping the associated spindle 26, 28, 30 in order to axially and radially retain the pointer 18, 20, 22 on the spindle 26, 28, 30 and rotationally fix the spindle and the associated pointer to each other.

According to the teachings of the present invention, each elastic structure 34 is constituted by a fork connected to the inner wall 33 of the hole 32 by a bridge 40 of material and which comprises two branches 42, 44 extending on either side of the bridge 40 of material generally towards the spindles 26, 28, 30. In addition, each branch 42, 44 includes a support surface 36, 38 adjacent a free end 46, 48 thereof.

According to a first embodiment of the invention, which is described by means of fig. 2 to 5, the two branches 42, 44 of each elastic structure 34 are bent in a mutually facing manner, forming an almost closed "C".

As shown in fig. 2 and in an enlarged manner in fig. 5, a first embodiment of the elastic structure 34 according to the invention is now described by examining the hour hand 18. Note that the elastic structure 34 is shown here in a rest state, i.e. before deformation by insertion of the relative spindle 26, 28, 30.

Each branch 42, 44 of each elastic structure 34 has a substantially parabolic shape, with a first fixed end 50, 52 thereof arranged on the bridge 40 of the relative material and a second free end 46, 48 thereof facing the free end 46, 48 of the other branch 42, 44 of the elastic structure 34.

Preferably, the free ends 46, 48 of the branches 42, 44 of each elastic structure 34 are sufficiently close that the inner surface of each branch 42, 44 is substantially tangential to the axial surface of the mandrel 26, near the free ends 46, 48, the support surface 36, 38 of each branch 42, 44 thus being positioned on the inner surface of its free end portion, opposite the mandrel 26.

When the spindle 26 is inserted into the bore 32, the radial force exerted on the support surfaces 36, 38 causes elastic deformation of the two branches 42, 44 of the elastic structure 34, thereby causing the free ends 46, 48 of the branches 42, 44 to move radially outwards. This elastic deformation produces a radial clamping of the spindle 26, similar to the drive-in arrangement.

Preferably, the elastic structures 34 are evenly distributed about the axis a 1.

Advantageously, for each cursor 18, 20, 22, the number of elastic structures 34 arranged around the hole 32 is chosen as a function of the diameter of the relative arbour 26, 28, 30 and as a function of the radial space available between the inner wall 33 of the hole 32 and the outer wall 54 of the mounting ring 31 of the cursor 18, 20, 22. Thus, the larger the diameter of the mandrels 26, 28, 30 and the smaller the radial spacing described above, the greater the number of resilient structures 34.

Thus, in this embodiment, since the diameter of the arbour 26 associated with the hour hand 18 is much greater than the diameter of the arbour 30 associated with the second hand 22, and since the outer diameter of the mounting ring 31 does not vary proportionally, we have chosen a number of elastic structures 34 equal to 12 for the hour hand 18 and a number of elastic structures 34 equal to 3 for the second hand 22. In an intermediate manner, the number of elastic structures 34 in the minute hand 20 is here equal to 6.

It is noted that having the fixing system with at least three elastic structures 34 helps to center the mounting ring 31 with respect to the associated spindle 26, 28, 30.

A second embodiment of elastic structure 34 is shown in fig. 6 to 8, which show mounting rings 31 fixed to hour hand 18, minute hand 20 and second hand 22, respectively. According to this second embodiment, each elastic structure 34 comprises a main portion 56 which extends on either side of the bridge 40 of material. Each branch 42, 44 extends in a rectilinear direction from the end of the main portion 56 of the bridge 40 opposite the material. Each branch 42, 44 is inclined with respect to the radial direction towards the associated branch 42, 44. The support surface 36, 38 of each branch 42, 44 is provided at a free end 46, 48 of the branch 42, 44.

Preferably, the main portion 56 of each elastic structure 34 extends substantially parallel to the inner cylindrical wall 33 of the hole 32 in a circumferential direction, which maximizes the length of the main portion 56 and of the rectilinear branches 42, 44, so as to distribute the stresses associated with the elastic deformation of the branches 42, 44 over a greater volume.

The second embodiment has the advantage of creating a self-locking effect when the spindles 26, 28, 30 and associated hands 18, 20, 22 are assembled together. In fact, the inclination of the branches 42, 44 allows a dynamic reaction to the rotational acceleration, which makes the present embodiment particularly suitable for fixing assemblies experiencing high angular accelerations or in the case of rotating elements with a significant imbalance in the weight distribution, as is the case with the hands of a timepiece.

In the second embodiment, the two branches 42, 44 of each elastic structure 34 exert thrust forces in opposite directions, so that each branch 42, 44 prevents the relative rotation of the hands 18, 20, 22 with respect to the associated arbour 26, 28, 30 in a preferred direction of rotation. In the example shown in fig. 6, first branch 42 of each elastic structure 34 prevents relative rotation of pointer 18 in a counterclockwise direction, and second branch 44 of each elastic structure 34 prevents relative rotation of pointer 18 in a clockwise direction. The resilient structure 34 of the second embodiment thus provides a particularly effective securing means for rotation between the hands 18, 20, 22 and the associated arbour 26, 28, 30.

The elastic structure 34 is made in the form of a fork comprising a tangentially or circumferentially oriented portion (portion 56) and a rectilinear portion (branches 42, 44) oriented towards the relative arbour 26, 28, 30, reducing the stiffness of the elastic structure 34, which allows a sufficient amount of radial clearance to allow fixing of said structure to the arbour 26, 28, 30, in particular to compensate for the diametral tolerances of the arbour. Each elastic structure 34 must be sufficiently flexible to be fixed both to mandrels with a diameter smaller than the nominal value and to mandrels with a diameter greater than the nominal value.

The advantages mentioned here with reference to the second embodiment will be applied in part to the first embodiment, since the formation of the elastic structure comprising the two branches 42, 44 provides the advantage of a dynamic reaction to angular acceleration. Furthermore, the curvilinear branches 42 of the first embodiment also allow obtaining a reduction in the stiffness of the elastic structure 34 and create a sufficient radial clearance to be fixed to the mandrel.

Note that in the first and second embodiments, each elastic structure 34 has an axial symmetry plane P extending along a radius through the middle of the bridge 40 of material.

Although the invention has been described with respect to the assembly formed by the hands 18, 20, 22, it is not limited to these embodiments. Thus, the assembly may be formed by another type of rotating element, such as a gear used in a timepiece movement. The assembly may also be formed by a non-rotating element, such as a sheet of brittle material mounted on another element including a metal stationary mandrel or stud.

The invention is applicable to fingers 18, 20, 22 formed in silicon plates comprising a single silicon layer and in silicon plates of the SOI (silicon on insulator) type comprising a top layer and a bottom layer of silicon separated by an intermediate layer of silicon oxide.

Claims (9)

1. Assembly (18, 20, 22) for a timepiece (10) formed in a plate of brittle material, comprising a hole (32) provided for the axial insertion of a spindle (26, 28, 30), the inner wall (33) of the hole (32) comprising elastic structures (34) etched in the plate and each comprising at least one support surface (36, 38) for radially clamping the spindle (26, 28, 30) so as to fix the assembly (18, 20, 22) with respect to the spindle (26, 28, 30), characterized in that: each elastic structure (34) is formed by a fork which is connected to the inner wall (33) of the hole by a bridge (40) of material and which comprises two branches (42, 44) which extend on either side of the bridge (40) of material, generally towards the spindle (26, 28, 30), and each branch (42, 44) comprises a support surface (36, 38) adjacent to its free end (46, 48).

2. The assembly (18, 20, 22) of claim 1, wherein: each branch (42, 44) of the elastic structure (34) has a substantially parabolic shape, one fixed end (50, 52) of which is arranged on the bridge (40) of the relevant material, a second free end (46, 48) of which faces the free end (46, 48) of the other branch (42, 44) of the elastic structure (34), and a support surface (36, 38) of each branch (42, 44) is arranged on the inner surface of the free end portion thereof.

3. The assembly (18, 20, 22) of claim 1, wherein: each elastic structure (34) comprises a main portion (56) extending on either side of the bridge (40) of material, each branch (42, 44) extending from the end of the main portion (56) opposite the bridge (40) of material, along a slanted straight line towards the associated branch (42, 44), with respect to the radial direction, and the support surface (36, 38) of each branch (42, 44) is arranged at its free end (46, 48).

4. The assembly (18, 20, 22) of claim 3, wherein: the main portion (56) extends in a substantially circumferential direction.

5. The assembly (18, 20, 22) of claim 1, wherein: the inner wall (33) of the bore (32) comprises at least three elastic structures (34) regularly distributed around the mandrel (26, 28, 30).

6. The assembly (18, 20, 22) of claim 1, wherein: formed by a rotating element (18, 20, 22) rotatably mounted on a spindle (26, 28, 30).

7. The assembly (18, 20, 22) of claim 6, wherein: formed by timer hands (18, 20, 22).

8. The assembly (18, 20, 22) of any one of claims 1 to 7, wherein: the brittle material is silicon.

9. Timepiece (10), characterized in that: comprising an assembly according to any of the preceding claims.