Component especially for horology with surface topology and method for manufacturing the same

This application claims priority to European Patent Application No. 18188355.4 filed on Aug. 9, 2018, the entire disclosure of which is hereby incorporated herein by reference.

The present invention relates to a micromechanical component, used, in particular, in the field of horology, intended to be subjected during use to friction contact with another component. It also relates to the method for manufacturing the component.

Numerous timepiece components, such as escapement components, jumpers, springs, etc., are subjected to friction during use. Conventionally, to be well made, such components must have a contact/friction surface that is perfectly smooth. However, friction between two bodies generally causes the formation of wear particles forming a third body. Far from having a proven positive effect, this third body may cause accelerated wear of the component with a detrimental effect on its function. To prevent such wear and reduce the friction forces that result in losses for certain functions, lubrication is applied to the surfaces of the components that come into friction contact. However, in the configuration where two perfectly smooth contact surfaces rub against each other, the lubricant gradually drains away from the contact/friction areas, resulting in medium and long term degradation of the friction contact conditions.

It is an object of the present invention to overcome the aforecited drawbacks by proposing a system with two components in friction contact wherein at least one component has a topology, in the area intended to be subjected to friction, which, on the one hand, facilitates the removal of particles produced by friction, and on the other, forms a reservoir for the lubricant.

To this end, the component has a scalloping structure in said area. This structure defines a set of troughs extending in the direction of friction and forming as many channels for the evacuation of debris generated by friction and for the flow of lubricant. The system of the invention is defined by claim 1 .

According to the invention, the scalloping structure is created during the step of machining the component. The manufacturing method used is the DRIE process (deep reactive ion etching). This process causes the formation of scallops or undulations on the etched wall of the component. This scalloping is an inherent defect of the process that those skilled in the art, according to the state of the art, wish to eliminate. To this end, the DRIE process is generally followed by an oxidation and deoxidation step intended to smooth out the scalloped profile. By contrast, according to the invention, this step is at least partially obviated to maintain the scalloped profile which allows for the evacuation of wear debris and serves as lubricant reservoir.

The manufacturing method according to the invention thus makes it possible, in a single step, to machine the component and texture the surface. Further, the advantage of the method according to the invention is that the scalloped texturing is naturally aligned in the direction of friction on the etched wall. The method of the invention is defined by claim 12 .

The invention also relates to a mould machined using the DRIE process to form a scalloped structure on the etched sidewalls of the mould. These moulds with the scalloped texture form a pattern for subsequent production of electroformed components. The electroformed components thus also have a texture of complementary shape to the scalloping, with troughs serving as debris evacuation channels and as lubricant reservoir in the area where friction occurs. The mould is defined in claim 9 .

According to other advantageous variants of the invention:

the troughs are longitudinal and parallel to each other. said troughs have a depth P which is greater than or equal to 100 nm and less than or equal to 500 nm, and preferably, less than or equal to 300 nm. the series of peaks and troughs or bumps and hollows form a periodic structure. the texture is present on one side of said at least one component machined by deep reactive ion etching. each of the two components includes said texture on a surface in the functional area, said troughs being disposed facing each other. only said at least one component has said texture on its surface, the other component of the system having a smooth surface in the functional area. said at least one component is made from silicon or metal. both components are timepiece components

Other features and advantages of the present invention will appear in the following description of preferred embodiments, given by way of non-limiting example, with reference to the annexed drawings.

FIGS. 1A and 1B schematically represent a system with two components, wherein one of the two components, on the friction surface thereof intended to be partially in contact with the other component, has a texture in the form of a series of scallops parallel to each other according to the invention. Friction occurs along a longitudinal direction parallel to the longitudinal direction of the troughs receiving the third body ( FIG. 1A ) and the lubricant ( FIG. 1B ).

FIGS. 2A and 2B represent a variant of the system with two components wherein one of the two components has a texture of complementary shape to that represented in FIGS. 1A and 1B .

FIG. 3A is a representation of a timepiece system comprising two components (escapement wheel/pallet lever) which, on the edge of the teeth and/or of the pallets, have a texture according to the invention. FIG. 3B schematically represents the texture on the etched wall.

FIG. 4 schematically illustrates, in a known manner, the various steps of the DRIE deep reactive ion etching process.

The present invention relates to components made from metal or from silicon comprising surfaces intended to be subjected to friction during use. The present invention thus relates more specifically to a system including two components having surfaces subjected to friction in a so-called ‘functional’ area. In the field of horology, this may be, for example, a system of the following type: escape wheel/pallets, cam/sensor, click/toothed wheel, jumper/disc, coupling disc/spring, brake disc/brake lever, etc. The present invention also relates to the moulds that make it possible to produce these components by electroforming. It also relates to the method for manufacturing the components or moulds.

As represented schematically in FIGS. 1A-2B , at least one of the two components 2 of system 1 has, in the functional area of its friction surface, a surface topology that, on the one hand, facilitates the evacuation of third-body particles and, on the other hand, forms a reservoir for the lubricant.

Referring to FIGS. 1A and 1B , the surface topology is formed of periodic scallops parallel to each other with troughs 3 a , also called hollows, of rounded shape separated by peaks 3 b . According to this variant, the contact between the two components 2 occurs on peaks 3 b of the structure. The longitudinal dimension of troughs 3 a extends parallel to the direction of friction in the functional area and the troughs serve as reservoirs for lubricant 5 and channels for evacuation of friction debris 4 . According to the invention, depth P of the troughs which is the distance between the low point of the trough and the top of the peak is typically greater than or equal to 100 nm and less than or equal to 500 nm ( FIG. 3B ).

In FIGS. 2A and 2B , the structure has a series of rounded bumps 3 c separated by troughs 3 a . This structure is obtained by electroforming metal components in moulds having the scalloped structure of FIGS. 1A and 1B . Depth P of the hollows thus corresponds here to the distance between the low point of the trough and the top of the bump and is of course equal to the aforementioned depth P. According to this other variant, the contact between the two components 2 occurs at the top of bumps 3 c of the texture.

In the variants presented in FIGS. 1A-2B , only one of the two components includes troughs, the other component having a substantially smooth friction surface in the functional area. According to another variant that is not represented, the two components can have troughs in this area which face each other and together form debris evacuation channels and lubricant reservoirs.

By way of illustration, FIG. 3A represents a timepiece system 1 : escape wheel 6 /pallet lever 7 wherein one or both components 6 , 7 have, at least on the sidewall 8 a , 9 a of teeth 8 and/or pallets 9 that is subjected to friction, a texture according to the invention ( FIG. 36 ).

This surface texture is obtained during machining of the component or of the mould by the DRIE process which is a plasma etching process that includes two different cycles that succeed one another, namely an etching cycle and a passivation cycle. The method is schematically represented in FIG. 4 . In a known manner, a silicon blank 10 is provided. A perforated mask 11 defining the trench to be machined is formed on the surface of blank 10 ( FIG. 4 a ). The method then consists in the series of steps of etching ( FIG. 4 b ) in fluorinated gas (e.g. SF 6 ) and of passivation (layer 12 ) using fluorocarbon gas (e.g. C 4 F 8 ), wherein the alternate etching and passivation steps produce the scalloped structure on the etched sidewall. The periodicity and depth of the troughs can, in a known manner, be adjusted by changing, amongst other things, the etching and passivation sequence times. (for example, 6 of etching—2 of passivation, or 3 of etching—1 of passivation). Preferably, the etching phase durations are greater than the passivation phase durations. Typically, these troughs have a depth P comprised between 100 and 1000 nm and preferably on the order of a few hundred nanometres with a trough periodicity comprised between 1.5 and 6 μm and preferably on the order of 3 μm.

Optionally, to reduce the depth of the troughs, without thereby removing surface roughness, an oxidation step followed by a deoxidation step can be envisaged (not represented). This step consists in performing thermal oxidation at temperatures typically comprised between 900 and 1200° C. followed by chemical deoxidation typically in hydrofluoric acid. By way of example, trough depth P can thus be reduced from 300 nm to 100-200 nm during this step.

Then, when the aforementioned method is used to manufacture a mould, the method further includes a deposition step by electroforming a metal alloy on the textured surface of the mould to produce the component with a series of bumps and troughs on its surface.

( 1 ) System of components

( 2 ) Component

( 3 ) Scalloped structure

a) Trough or hollow b) Peak c) Bump

( 4 ) Debris

( 5 ) Lubricant

( 6 ) Escape wheel

( 7 ) Pallet-lever

( 8 ) Escape wheel tooth

a. Edge or sidewall

( 9 ) Pallets

a. Edge or sidewall

( 10 ) Blank

( 11 ) Mask

( 12 ) Passivation layer