Patent Application
20160011567
This application claims priority from European Patent Application No. 14176919.0 filed Jul. 14, 2014, the entire disclosure of which is incorporated herein by reference.
The present invention relates to flexible timepiece guidance, in particular a device for elastic guidance in rotation allowing pivoting of an element of a watch movement about an axis of rotation.
In timepiece movements, there are several components which pivot about an axis of rotation, such as the pallets, or the balance wheel of an escapement device. Some of these pivoting elements are coupled to a spring, amongst other oscillating elements, such as the balance wheel of the escapement device. In mechanical watches, it is advantageous to have a high-output movement in order to increase the power reserve. The loss of energy due to friction in the bearings of the pivoting parts is one of the greatest sources of energy loss. The quality factor of the parts is also an important consideration for mechanical watches.
In order to reduce these losses, it is known to propose flexible guidance in rotation oscillating about a pivot without bearings, such as described in the patent application EP 2 273 323. This flexible guidance comprises silicon components etched in a silicon wafer in order to produce a monolithic structure comprising a frame, elastic blades and a central attachment body. In order to obtain a sufficiently robust frame and a sufficiently high amplitude of rotation for the oscillator function, a plurality of these monolithic structures are stacked one on the other. One of the disadvantages of this structure is that the manufacturing cost of the three-dimensional monolithic elements is high. Furthermore, the spring blades extending in the radial direction are delicate and do not have an optimum shape for the desired function, i.e. great flexibility in the plane orthogonal to the axis of rotation and great rigidity in the direction of the axis of rotation. In fact, since the blades are etched in a silicon wafer in the direction orthogonal to the surface of the wafer, control of the thickness of the blade is difficult to control with precision, which has a negative influence on performance and in particular well-determined properties of flexibility, robustness and elasticity parameters.
One object of the invention is to provide a device for elastic guidance in rotation which is compact and economical to manufacture and has good performance in use.
It is advantageous, for certain functions, to provide a device for elastic guidance which allows a large angle of rotation.
It is advantageous to provide a method for manufacturing a device for elastic guidance in rotation which makes it possible to produce complex structures, according to the application, but which is economical to implement.
It is advantageous to provide a device for elastic guidance with very low consumption of energy in use.
It is advantageous to provide a robust device for elastic guidance.
The objects of the invention are achieved by a device for elastic guidance in rotation for a timepiece mechanism according to claim 1. The dependent claims describe advantageous aspects of the invention.
In the present case, a device for elastic guidance in rotation for a timepiece mechanism is described, which allows rotation of one element relative to another element about an axis of rotation defining an axial direction.
The device comprises construction blades, each construction blade comprises an assembly fixing part comprising a body and a functional part extending from the body as far as one end, the assembly fixing part and the functional part being separated by at least one slot in at least two extensions which are elastically connected and extend in a radial direction, said radial direction being transverse to the axial direction, the device comprising furthermore anchorage zones which are disposed at opposite axial ends of the flexible guidance device, and configured to be fixed to said elements. The assembly fixing part of each of the construction blades comprises a cavity or an assembly recess and an assembly extension which intersect and which fit together in a radial direction in order to be locked together.
In one embodiment, the construction blades are formed from a wafer of material, for example from a crystalline material, defining a main plane, the construction blades being orientated such that the axis of rotation of the flexible guidance is parallel to the main plane of the construction blades.
In one embodiment, the thin wafer comprises two layers of equal or different thicknesses, welded or glued together, the construction blade having parts with a thickness corresponding to the thickness of one of the layers and parts with a thickness corresponding to the thickness of the two layers.
In one embodiment, the body represents a central part of the device encompassing an axis of rotation of the device.
In one embodiment, one of the construction blades includes a slot forming the assembly cavity, the functional part of the other blade being inserted in the slot until the body of the latter abuts against the body of the former.
Advantageously, each construction blade can be formed by deposition and/or etching processes according to an essentially bi-dimensional process.
In some embodiments, the construction blades can be formed by an electroforming process of the LIGA type.
In some embodiments, the construction blades are made of a material based on silicon.
In some embodiments, the construction blades can be manufactured by an “SOI”—silicon on insulator—process. In this variant, the structure is formed from a stack of a layer of silicon on a layer of insulator. This insulator can be for example sapphire or preferably silicon dioxide (SiO2).
In some embodiments, the construction blades can be made of Ni, NiP or of amorphous metal.
The construction blades can also comprise sacrificial structures which assist assembly.
In one embodiment, each construction blade comprises a functional part extending in a radial direction on both sides of the body, this body forming a central part for rotation relative to the ends of the blades.
In one embodiment, the ends of the blades are free and floating.
In one embodiment, the device can advantageously be configured as a spring, and simultaneously as a support, for an oscillator or an element pivoting about the axis of rotation, without requiring another pivot or support for the pivoting element.
In one embodiment, each of the construction blades comprises only one functional part which extends from the assembly fixing part, forming for example a configuration essentially in a “V”.
In one embodiment, the construction blades include a plurality of slots spaced in the axial direction in order to form a plurality of functional extensions which have elastic portions.
In one embodiment, each construction blade forms a monolithic structure.
In one embodiment, the device comprises only two monolithic construction blades.
Other aims and advantageous aspects of the invention will appear upon reading the claims and also the detailed description of embodiments hereafter, and annexed drawings, in which:
a is a schematic perspective view of a device for elastic guidance in rotation for a timepiece mechanism, according to an embodiment of the invention;
b is a view of the embodiment of
c is a schematic drawing illustrating a function of the guidance device in a mechanism;
a, 2b are schematic exploded perspective views of a device for elastic guidance in rotation for a timepiece mechanism, according to a second embodiment of the invention;
c is a perspective view of the assembled device of
a is an exploded perspective view of a device for elastic guidance in rotation for a timepiece mechanism, according to a fourth embodiment of the invention;
b and 4c are perspective views of the fourth embodiment in neutral and pivoted positions respectively.
Referring to the Figures, a device for elastic guidance in rotation 2 comprises construction blades 4a, 4b configured to be assembled and fixed together in order to form the device for elastic guidance in rotation. Each construction blade includes at least one slot 12 separating the construction blade into at least two parts which are coupled elastically and moveable. The device for elastic guidance allows rotation about an axis of rotation Z, of an element 1 (for example a balance wheel or the pallets) relative to another element 3 (for example a frame), the elements fixed to the device for elastic guidance at the anchorage zones 9, 11 respectively. The anchorage zones 9, 11 are disposed at opposite axial ends of the device for flexible guidance, the axial direction being defined by the axis of rotation Z.
The construction blades 4a, 4b comprise an assembly fixing part 6, and a functional part 10 extending from the assembly fixing part as far as a free end 8, the assembly fixing part 6 and the functional part 10 being separated by at least one slot 12 in at least two extensions 17 which are elastically connected and extend in a radial direction X, Y transverse to the axial direction Z.
The device can have construction blades with functional parts on both sides of the assembly fixing part 6 as illustrated in
In the Figures, the axial direction is represented by the axis Z which is parallel to the axis of rotation of the device for elastic guidance in rotation. The radial direction is illustrated by the axes X and Y situated in a plane orthogonal to the orthogonal direction Z. In flexible guidance applications, having great rigidity in the axial direction and great flexibility in rotation is sought.
The assembly fixing part comprises a body 13a, 13b, the body 13b of at least one of the construction blades 4b including a cavity or an assembly recess 14, configured for insertion in a radial direction of one part of the other construction blade 4a so that, in the assembly fixing part 6, the construction blades 4a, 4b intersect. This intersection of the assembly fixing parts of the two construction blades 4a, 4b is very advantageous since it makes it possible to manufacture the construction blades independently in an optimum manner in order to define the thicknesses of the blade whilst having, once assembled, a device for elastic guidance in rotation with great rigidity in the axial direction Z. In fact, each construction blade 4a, 4b can be formed by known processes of deposition or etching, for example through a photolithographic mask, of silicon or of other materials in an essentially bi-dimensional process. A bi-dimensional process makes it possible to obtain precise thicknesses over the length of the blade and shapes represented by various thicknesses over the length of the blade which are easy to manufacture with great precision via masks defined by simple photolithographic processes. The direction of increase or reduction of the blades can be effected solely according to an elastic displacement direction Tx, Ty orthogonal to the radial direction X, Y, such a process being simple, economical and allowing easy control of the thicknesses in order to obtain blades which are rigid in the axial direction Z but have elasticity which is precise and well controlled with a uniform, robust structure.
According to an advantageous embodiment of the invention, the construction blades are formed from a sheet cut out in a block of material, in particular a crystalline material, the sheet being commonly termed “wafer”. The block of material can in fact be a block of monocrystalline silicon or a block of another material used in the wafers for integrated circuits or micromechanics industry. Etching of the construction blades is effected in a direction orthogonal to the main plane of the wafer (which is parallel to the cut surface of the wafer). The construction blades are orientated such that the axis of rotation of the flexible guidance, which extends in the axial direction Z, is parallel to the main plane of the construction blades. The properties and elastic characteristics of the construction blades in their elastic displacement direction Tx, Ty are consequently dependent upon the thicknesses in the direction orthogonal to the main plane, these thicknesses being able to be well controlled in economic manufacturing processes.
In one embodiment, the wafer can comprise two layers of equal or different thicknesses, welded or glued together, this making it possible, in an etching process, to obtain precise thicknesses corresponding to the thicknesses of one or other of the layers. In fact, the interface between the two layers defines a threshold which makes it possible to stop precisely the reduction of material at the level of the interface during the etching process. The precision in formation of the thicknesses is an advantage for controlling well the elastic properties and the resistance of the construction blades. In this embodiment, it is possible to manufacture, economically and with precision, construction blades with two levels, having parts with a thickness corresponding to the thickness of one or other of the layers and parts with a thickness corresponding to the thickness of the two layers.
The construction blades can also comprise sacrificial structures which assist assembly.
In the embodiment illustrated in
The body 13a, 13b is fixed in the anchorage zones 9, 11 on both sides of the slot 12 to two elements, one being moveable relative to the other. For example, one of the anchorage zones 9 can be fixed to a frame, and the other of the anchorage zones to an element which pivots relative to the frame. In this embodiment, the device can serve as spring and support for an oscillator or element pivoting about the axis of rotation Z, without requiring another pivot or support for the pivoting element. The device can however be used in other configurations, for example the central body 13 can be fixed to two moveable elements at the anchorage zones 9, 11, the ends 8 of the blades being coupled to a frame.
Referring to the embodiment illustrated in
The construction blades can have complex shapes whilst being easy to manufacture with precision, by varying the thickness in the etching, respectively deposition, direction (direction T), for example as illustrated in
The elasticity in the direction of rotation (direction T) of the construction blades can be controlled by varying the length of the rigid portions 18, respectively the length of the elastic portions 16, and also by varying the number of radial extensions, respectively of slots, stacked in the axial direction. This likewise makes it possible to control the distribution of the masses and finally not only the spring constant but likewise the resonance frequencies, in particular of the first order of the elastic system.
One advantage of the invention is that the construction blades can be manufactured as structured pieces and in two levels: a first level which can be very fine, for example of the order of 10 μm in order to fashion the flexible blades, and a thicker level, for example of the order of magnitude of 400 μm, making it possible to produce rigid mountings, this giving essentially a planar part structured at two levels with slots. The assembly of two blades by intersection and fitting together is also very simple to effect.
Flexible guidance according to the invention can be used for various applications, for example as guidance of the pallets in a watch, or as guidance of the balance wheel in a watch, the balance wheel no longer having a pivoting frictional axis nor a spiral, these two elements being replaced by the flexible guidance.
| Number | Date | Country | Kind |
|---|---|---|---|
| 14176919.0 | Jul 2014 | EP | regional |
