Timepiece micromechanical part

Abstract

The micro-mechanical horology component comprises contact surfaces designed to slide against corresponding contact zones of another micro-mechanical component in a timepiece; – the micro-mechanical component being manufactured from a fragile material; – the said contact surfaces of the micro-mechanical component being grooved, the grooves being rectilinear and parallel to the direction of sliding; – the said grooves being separated by solid lands of a width of between 0.5 and 50 microns; and – the surface area occupied by the solid lands, referred to as the effective contact area, being comprised between 2 and 70% of the total area of the contact surface.

Description

[0001] A first embodiment of the present invention relates to a watchmaking micromechanical part arranged to interact mechanically with another micromechanical part in a watchmaking part, the two micromechanical parts comprising respective contact areas which are arranged to slide against each other during mechanical interactions between the watchmaking micromechanical part and the other micromechanical part.A second embodiment of the present invention relates to a mechanical timepiece comprising a first and a second micromechanical component arranged to interact mechanically. The first and second micromechanical components each have respective contact areas arranged to slide against each other during mechanical interactions between them. At least the first micromechanical component is constituted by a watch micromechanical part according to the first embodiment of the invention. The invention relates in particular to a watch micromechanical part conforming to the above definition and forming part of a lever escapement. In this regard, it should be noted that the escapement is the mechanism that provides the interface between the gear train and the regulating organ (the balance wheel or pendulum) of a timepiece.The escapement's function is, in particular, to maintain the oscillations of the regulating organ. EARLIER ART

[0002] The known escapement mechanisms are diverse and numerous; see JP2010077528 and EP2579104. However, currently, the escapement mechanisms equipping the vast majority of mechanical watches are of the Swiss lever escapement type. Escapements of this type include an anchor whose two arms each end in a pallet. The anchor is arranged to pivot alternately in one direction and then the other so that the pallets successively lock and then release one of the teeth of the escape wheel. When one of the pallets releases a tooth it was previously locking, the escape wheel rotates briefly before the next tooth falls against the other pallet.The escape wheel thus advances in fits and starts, and it can be noted that the successive impacts of the teeth of this wheel (alternately against the outside of the inlet pallet, and the other times against the inside of the outlet pallet) are responsible for the "tick-tock" of the watch. It is clear from the above that the pallets are constantly subjected to shocks and friction. This is why the pallets are most often made of rubies.

[0003] The movement of the escapement during each half-cycle of the balance wheel can be broken down into three phases. These three phases are: the release phase, during which the anchor pivots to disengage one of its pallets from the tooth of the escape wheel with which it was engaged. As the anchor pivots, the pallet slides free against the front flank of the tooth, moving slightly away from the escape wheel. Once the pallet is free from the front flank of the tooth, the escape wheel is no longer completely locked, and the movement then enters the impulse phase, during which the impulse plane of the tooth pushes diagonally against the impulse plane of the pallet.Because the force exerted by the tooth on the pallet is oriented at an angle, the tangential component of this force causes the impulse plane of the tooth to slide against that of the pallet, and simultaneously, the normal component of this force propels the anchor, causing it to pivot and briefly drive the balance wheel. The anchor pivots until the pallet is finally outside the tooth's path, ending the impulse phase. The escape wheel is then completely free to rotate until the next tooth falls onto the other pallet, causing the escape wheel to stop again. This third phase is called the fall phase.

[0004] The sliding of the pallets against the teeth of the escape wheel inevitably generates frictional forces. Thus, during the release phase, a frictional force opposes the sliding of the pallet's resting surface against the leading edge of the escape wheel tooth. The pallet fork must perform some work to overcome this force. Similarly, during the subsequent impulse phase, a frictional force opposes the sliding of the pallet's impulse plane against the impulse plane of the tooth. The escape wheel must perform some work to overcome this force. The existence of these relatively intense frictional forces between the pallets of the escapement and the teeth of the escape wheel leads to a reduction in both the accuracy and the lifespan of the watch movement.In particular, the energy lost by the balance wheel as friction during the release phase must then be compensated by the escapement during the impulse phase. Furthermore, the escapement must also compensate for the energy lost as friction during the impulse phase itself, and the amount of energy expended for this purpose reduces the amount of energy the escapement can actually deliver to the balance wheel. Another problem is that friction accelerates wear on the contact surfaces between the escapement components. The components eventually become deformed and therefore require more frequent replacement.

[0005] According to a well-known relationship, the friction force that must be overcome for a solid to slide on a surface at a constant speed is given by the following formula: F d = μ ⋅ F N Or F d is the dynamic friction force; µis the coefficient of dynamic friction; F N is the normal component of the applied force.

[0006] In most real-world situations, the force of application and its normal component F N are more akin to given parameters of the problem than to parameters that can be manipulated. Thus, in order to reduce friction, the focus has been on decreasing the coefficient of friction. µWe know that this coefficient depends on several factors, such as the matching of the materials in contact, the roughness of the contact surfaces, surface treatments, lubrication, etc. In particular, the use of oil as a lubricant is very common in watchmaking. However, the use of lubrication presents a number of problems. It notably requires regular servicing of the watch, particularly to allow for re-oiling or cleaning of the gears. It would therefore be advantageous to have watch micromechanical components conforming to the definition given in the introduction and which do not require the use of a lubricant. BRIEF SUMMARY OF THE INVENTION

[0007] One object of the present invention is to overcome the drawbacks of the prior art which have just been explained. The present invention achieves this object and others by providing, on the one hand, a micromechanical watch component according to the attached claim 1, and on the other hand, a mechanical watch component according to the attached claim 7.

[0008] It will be understood that the expression "contact zone" can refer to both a planar contact zone (in other words a contact surface) and a linear contact zone (in other words an edge formed by the meeting of two surfaces).

[0009] According to the invention, the contact surfaces of the micromechanical component have straight, parallel grooves. A primary effect of the presence of grooves on a contact surface is to reduce the area of ​​the contact surface that is actually in contact when the contact surface slides against a contact area of ​​another component. In this regard, it is worth noting that the contact area does not appear in the formula for the dynamic friction force (given above). Indeed, it is generally accepted that the friction force is independent of the contact area. However, tests carried out by the applicant show that the presence of grooves on the contact surface leads to a reduction in friction forces even in the case of a relatively large contact surface (component height of 130 micrometers).

[0010] According to the invention, the watchmaking micromechanical component is made of a brittle material. It will be understood that in this text, the expression "brittle material" refers to materials which, in the context of watchmaking micromechanics, are characterized by brittle fracture, that is, fracture without prior plastic deformation, during elastic loading, as soon as the stress locally reaches the critical threshold. A brittle material is therefore, by definition, a material that breaks easily due to its very nature. A brittle material may exhibit a certain degree of elasticity. However, when subjected to stresses of a certain intensity, it breaks without prior plastic deformation.Examples of brittle materials that can be used with the invention include glasses, ceramics, silicon, and polymers, particularly quartz, sapphire, and monocrystalline or polycrystalline silicon, as well as amorphous quartz. Examples of glasses include vitreous silica, soda-lime glasses, borosilicates, non-alkaline glasses, vitreous silica, aluminosilicates, and fluorinated glasses. Three families of ceramics can also be identified: oxides, non-oxides, and composites. These three families of ceramics include silicon dioxide, zirconium oxide, alumina, silicon carbides or nitrides, and Silinvar® for composites. Finally, among polymers, examples include high-performance polymers such as PEEK or polyamides.

[0011] Generally speaking, the impact resistance of fragile materials is also not very high. This is probably why, to the applicant's knowledge, it has never been proposed to manufacture components for an escapement mechanism as monolithic parts, each made from a single piece of glass. Those skilled in the art know that glass designed to withstand impacts is usually laminated glass. That is to say, laminated glass made up of multiple sheets of glass bonded together by interlayer films that exhibit plastic properties.

[0012] According to the second embodiment of the invention, the mechanical timepiece comprises a first and a second micromechanical component, each having respective contact areas arranged to slide against one another during mechanical interactions between the first and second micromechanical components. At least the first micromechanical component is a watchmaking micromechanical part conforming to the first embodiment of the invention.

[0013] According to a particular embodiment of the second version of the invention, only the first component conforms to the first version of the invention; the straight and parallel grooves of the contact areas of the second component are inclined or perpendicular to the sliding direction. An advantage of this embodiment is that it reduces the risk of the respective contact areas catching on each other. BRIEF DESCRIPTION OF THE FIGURES

[0014] Other features and advantages of the present invention will become apparent from the following description, given solely by way of non-limiting example, and made with reference to the accompanying drawings in which: there figure 1 is a schematic plan view representing an earlier Swiss lever escapement; the figure 2 is a schematic perspective view of an escape wheel corresponding to a first exemplary embodiment of the micromechanical part of the invention; the figure 3A is a schematic plan view representing the impulse plane of one of the teeth of the escape wheel of the figure 2 ; there figure 3B is a cross-sectional view according to BB of the figure 3A ; there figure 4 is a perspective view of an anchor corresponding to a second exemplary embodiment of the micromechanical part of the invention; the figure 5 is a close-up showing in more detail the impulse plane of the anchor's input palette figure 4 ; there figure 6 is a schematic plan view representing an impulse plane which may belong to one of the pallets of an anchor according to a third embodiment of the invention, or alternatively, belong to one of the teeth of an escape wheel according to a fourth embodiment of the invention; the figure 7 is a schematic plan view of an embodiment of a contact zone of the second micromechanical component of a timepiece, said contact zone being arranged to slide against a contact zone of the first micromechanical component of the timepiece, and the first component being constituted by a micromechanical timepiece conforming to an embodiment of the invention. DETAILED DESCRIPTION OF IMPLEMENTATION METHODS

[0015] The invention will be described below in the context of a Swiss lever escapement. It will be understood, however, that the invention is not limited to this restricted field of application, but that it concerns, on the contrary, all escapement mechanisms, and more generally, all horological micromechanical devices in which two components are brought to rub against each other.

[0016] There figure 1 This is a schematic plan view representing a Swiss lever escapement of the prior art. The mechanism shown includes, in particular, an escape wheel 3, an anchor 5, and a large plate 7 through the center of which passes the balance staff 9. The two arms of the anchor each terminate in a pallet 11, 13. The pallets are arranged to cooperate with the teeth 15 of the escape wheel 3. Conventionally, the escape wheel is connected to the mainspring barrel (not shown) via a gear train (not shown) which meshes with the escape pinion (referenced 17). The escape wheel is thus constantly driven forward (that is, clockwise as shown in the diagram). figure 1 Note that at the moment shown, one of the teeth 15 of the escape wheel 3 is held against the resting surface of the pallet fork 11 of the anchor 5. Driven by the balance wheel, the anchor 5 begins a pivoting motion around the axis 19 in a clockwise direction. The clockwise pivoting of the anchor causes the pallet fork to slide upwards (in the drawing) against the front face of the tooth 15. This disengagement phase will end the instant the pallet fork's resting surface ceases to obstruct the advance of the tooth's front face. Then, the flattened top of the tooth 15 (called the tooth's impulse plane) will slide against the underside of the pallet 11 (the pallet's impulse plane). The angled contact between the two impulse planes will also have the effect of pushing the input paddle 11 upwards, so that the pivoting movement of the anchor 5 in the clockwise direction will be accentuated.This impulse phase will end when the inlet pallet 11 has been pushed back far enough to offer a completely clear passage to the tooth 15. The two successive phases just described during which a tooth 15 of the escape wheel 3 slides against the surfaces of one of the pallets 11, 13 of the anchor 5, are each generators of considerable friction.

[0017] There figure 2 Figure 53 is a schematic perspective view of an escape wheel corresponding to a first particular embodiment of the invention. The escape wheel in this example is a monolithic piece made from a single piece of glass. It will be understood, however, that according to other variants of the invention, the escape wheel might not be made of glass, but of another fragile material. Furthermore, the escape wheel might not be monolithic, but be formed from several assembled pieces. figures 3A et 3B are schematic plan and cross-sectional views, respectively, of the impulse plane 67 of one of the teeth 65 of the escape wheel 53. According to the invention, the escape wheel 53 differs from prior art escape wheels in that the impulse planes 67 of each of the teeth 65 have straight grooves (or slots) parallel to the sliding direction. With particular reference to figures 3A et 3B As can be seen, the surface of each of the impulse planes 67 has seven parallel ribs (or crenellations) (each represented by a thick white line), and each rib is separated from its neighbors by a groove (represented by a thick black line). In the example shown, the ribs and grooves are each 10 microns wide, so the total width of the impulse plane 67 is 130 microns. It should be noted that the escape wheel 53 has a constant thickness and is therefore equal to the width of the impulse planes; that is, 130 microns. It can also be calculated that the effective contact area during the impulse phase is reduced by 46.2% compared to an escape wheel of the same dimensions with smooth impulse planes.As previously mentioned, the applicant has conducted tests demonstrating that using a grooved escape wheel like the one in this example can significantly reduce the proportion of energy dissipated due to friction. Furthermore, the distinctive angular shape of the crenellations and bevels is easily produced by laser. This allows for a highly precise cut and control of the crenellation depth using a simple parameterization tool. This shape also facilitates easy monitoring of the wear on the watch micromechanical component. Like a wear indicator, the crenellations and bevels reveal at a glance whether or not friction has altered the mechanical properties of the micromechanical component by deteriorating the shape of the contact area.

[0018] There figure 4 is a perspective view of an anchor 105 which corresponds to a second particular embodiment of the invention. The figure 5 Figure 105, for its part, is a close-up showing in more detail the impulse plane 121 of the entry paddle 111 of the anchor 105. The anchor shown is a monolithic piece made from a single piece of glass. It will be understood, however, that according to other embodiments of the invention, the anchor might not be made of glass, but of another fragile material. Furthermore, the anchor might not be monolithic, but be formed from several assembled pieces. According to the invention, the anchor 105 is distinguished from prior art anchors in that the impulse planes 121, 123 of its two paddles 111, 113 have straight striations parallel to the sliding direction. With particular reference to the figure 5 As can be seen, the surface of impulse plane 121 has seven parallel ridges (or crenellations), and each ridge is separated from its neighbors by a groove (or striation). In the illustrated example, the ridges are 12 microns wide, while the grooves are 8 microns wide, so the total width of impulse plane 121 is 132 microns. Similar to the escape wheel in the previous example, the illustrated anchor has a constant thickness. Its thickness is therefore approximately 132 microns. It can also be calculated that the effective contact area during the impulse phase is reduced by 36.4% compared to an anchor of the same dimensions with smooth impulse planes.

[0019] There figure 6 is a schematic plan view similar to the figure 3A The impulse plane it represents can be that of one of the pallets of an anchor according to a third embodiment of the invention, or alternatively, that of one of the teeth of an escape wheel according to a fourth embodiment of the invention. In the example shown, the impulse plane comprises five parallel rows of eleven lugs each. It will be understood that these five rows are separated from each other by four first grooves oriented parallel to the sliding direction. It can also be observed that the impulse plane also comprises two lateral grooves (or shoulders) parallel to the first grooves, and ten second grooves separating the eleven lugs of each row from each other.The second set of grooves is oriented perpendicular to the sliding direction, so that it intersects the first four grooves and the two lateral grooves at right angles, forming a rectangular grid with them. In the illustrated example, the grooves are all 13 microns wide, and the lugs are squares with sides of 10 microns, so the total width of the impulse plane is 128 microns and its length is slightly greater than 240 microns.

[0020] The micromechanical watch component of the invention can be manufactured using any process that a person skilled in the art would deem suitable. However, advantageously, the component can be produced by 3D machining a piece of silica glass (amorphous quartz). Preferably, the component is manufactured from a piece of transparent silica glass using a femtosecond laser machining process. This process consists of using a laser that produces pulses with a duration on the order of a femtosecond; focusing the laser beam so as to selectively expose the volume of a piece of transparent glass according to a desired pattern; and finally, chemically etching the exposed piece of glass with hydrofluoric acid.

[0021] We have seen that a second embodiment of the invention relates to a mechanical timepiece comprising a first and a second micromechanical component arranged to interact mechanically. The first and second micromechanical components each have contact areas arranged to slide against each other during mechanical interactions between them, and at least the first micromechanical component is a watchmaking micromechanical part according to the first embodiment of the invention. According to an exemplary embodiment of this second embodiment of the invention, only the first component conforms to the first embodiment. The second component comprises contact areas with straight, parallel grooves inclined or perpendicular to the direction of sliding.

[0022] There figure 7 is a schematic plan view of an exemplary embodiment of a contact zone of the second micromechanical component of a timepiece, said contact zone being arranged to slide against a contact zone of the first micromechanical component of the timepiece, and the first component being a watch micromechanical part conforming to an embodiment of the invention. It can be seen that the contact zone shown in the figure 7 is very similar to that of the figure 6 However, it can be seen that the rows of lugs in the contact area of ​​the second micromechanical component are inclined at 30° relative to the sliding direction. The inclination can vary from 10° to 45°, which advantageously reduces friction.

[0023] It will also be understood that various modifications and / or improvements, obvious to a person skilled in the art, can be made to the embodiments described herein without departing from the scope of the present invention as defined by the appended claims. In particular, although the invention has been described in relation to an escape wheel and an anchor, it is clear that the invention does not relate solely to escapement components, but rather, quite generally, to all micromechanical parts of watches.

Claims

1. Micro-mechanical timepiece part, namely escape wheel (3, 53) or escapement anchor (1, 105), comprising impulse planes (67, 121) provided to slide against corresponding contact zones of another micro-mechanical part, namely an escapement anchor or an escape wheel respectively, in a timepiece, characterised in that - the micro-mechanical part is produced from a fragile material; - said impulse planes of the micro-mechanical part are striated, the striations being straight and parallel to the sliding direction; - the striations are separated by solid intervals having a width between 0.5 and 50 micrometres; preferably between 0.5 and 25 micrometres; - in cross section, the striations have the angular shape of crenellations and the solid intervals have the angular shape of merlons; - the impulse planes each have an effective contact area corresponding to the area of the portion of the impulse plane that is occupied by the solid intervals; - the effective contact area is between 2 and 70% of the total area of the impulse plane.

2. Micro-mechanical timepiece part as claimed in claim 1, characterised in that it is a one-piece part produced from a single piece of a fragile material.

3. Micro-mechanical timepiece part as claimed in claim 2, characterised in that the fragile material is selected from glasses, silicon, ceramics and polymers.

4. Micro-mechanical timepiece part as claimed in claim 2, characterised in that the fragile material is silica glass.

5. Micro-mechanical timepiece part as claimed in any one of the preceding claims, characterised in that said impulse planes of the micro-mechanical part have first striations parallel to the sliding direction, and second striations of orientations different from those of the first striations, the first and the second striations together forming a lattice.

6. Micro-mechanical timepiece part as claimed in claim 5, characterised in that the second striations are orientated perpendicularly to the sliding direction.

7. Mechanical timepiece comprising a first and a second micro-mechanical component which are arranged to interact mechanically, the first and second micro-mechanical components comprising respective contact zones arranged to slide one against the other during the mechanical interactions between the first and the second micro-mechanical component; characterised in that - at least the first micro-mechanical component is produced from a fragile material; - the contact zones of the first micro-mechanical component are striated surfaces, the striations being straight and parallel to the sliding direction; - said striations are separated by solid intervals having a width between 0.5 and 50 micrometres; preferably between 0.5 and 25 micrometres; - in cross section, the striations have the angular shape of crenellations and the solid intervals have the angular shape of merlons; - the contact zones of the first micro-mechanical component each have an effective contact area corresponding to the area of the portion of the contact zone that is occupied by the solid intervals; - the effective contact area is between 2 and 70% of the total area of the contact zone.

8. Mechanical timepiece as claimed in claim 7, characterised in that the contact zones of the second micro-mechanical component are striated, the striations being straight and forming an angle with the sliding direction.

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