HK1200927B - Shock-proof bearing for a timepiece - Google Patents

Description

Shock-resistant bearing for a timepiece

Technical Field

The present invention relates to the field of anti-seismic bearings for timepieces (bearings with shock-absorbing means) and methods for manufacturing said anti-seismic bearings. In particular, the invention relates to a shock-resistant bearing for receiving the pivot of the balance staff of a mechanical watch movement.

Background

Patent CH700496 describes a shock-resistant bearing formed of single-crystal silicon comprising a central portion and radially resilient arms connecting the central portion to an outer peripheral ring portion. The central portion includes a flared aperture having a tetrahedral pyramid/tetrahedral shape. First, it should be noted that the bottom of the tetrahedral orifice is not optimal for supporting the pivot. With respect to the fabrication of holes of the type described, the above-mentioned patent provides an anisotropic wet chemical etching process. For this purpose, it is mentioned here that the silicon substrate must be oriented appropriately to be able to machine the pyramid-shaped holes. Next, in order to machine the rest of the integral silicon part, in particular the spring arms, the patent proposes to use another machining technique, namely Deep Reactive Ion Etching (DRIE). The latter technique requires the use of complex and expensive equipment, different from the equipment used for anisotropic wet chemical etching. Therefore, the anti-vibration bearing according to the above patent is relatively expensive to manufacture. It should be noted that the use of two different techniques for machining silicon parts in different devices to unnecessarily complicate the method of manufacturing silicon anti-seismic bearings is not intended by the authors of patent CH 700496. In fact, it is due to the requirements caused by the properties of monocrystalline silicon. In fact, the orientation of the silicon substrate required to obtain the flared hole of the pyramidal shape does not provide a resilient structure with arms having substantially vertical side walls, or an outer peripheral annular portion.

In general, the inventors of the present invention have found that silicon does not allow machining structures with substantially vertical walls and does not allow to exhibit a curvature by means of etching in an acidic bath. Furthermore, in order to obtain an aperture with vertical walls in a monocrystalline silicon wafer, only a specific silicon crystal orientation in the wafer (incompatible with the orientation of the holes used to obtain the pyramid shape) is possible. The possible directions for such a vertical wall are limited and the vertical wall is formed by a flat surface only.

Patent application WO2009/060074 describes a shock-resistant bearing comprising a one-piece silicon part and a perforated jewel associated therewith. The integral component defines a resilient structure and a back-off bit. Which are formed in a silicon wafer by well-known photolithography and etching techniques. This patent document mentions that the unitary component may be made of silicon or other single crystal material that preferably can be easily machined by photolithographic and chemical etching techniques. But no other examples than silicon are given. With respect to silicon, as described above, although a groove or orifice having a vertical wall is available, the design is limited. In particular, it is not possible to obtain all the designs shown in the figures of the above-mentioned patent documents by chemical etching of silicon crystal wafers. The technique of the above patent relating to the manufacturing method of the anti-vibration bearing made of a single crystal material is unclear. Only the case of silicon is explicitly mentioned. Limitations and defects of silicon crystal embodiments are described in the discussion of patent CH 700496. Furthermore, the meaning given herein for chemical etching is unclear. In any case, it can be concluded that elastic structures such as those shown in the figures are not made in an acidic bath, but by deep reactive ion etching as in patent CH 700496.

The applicant of patent application WO2009/060074 also filed patent application EP2015147 (same priority date). The latter document discloses an anti-seismic bearing formed from a single crystal material sheet; the blade defines a resilient structure and a central portion having a blind hole for receiving a balance pivot. In a variant, the elastic structure defines three spirals arranged in a staggered/overlapping manner. The blind holes have a flat-bottomed cylindrical shape, as shown in the figures. It should be noted that a flat-bottomed cylindrical shape is not optimal, since the pivot moves and rubs against the cylindrical portion in an irregular manner, since the hole is wider than the portion of the pivot introduced therein. According to the main embodiment proposed in this patent document, a single-crystal silicon wafer body or wafer is used, which is machined by means of known photolithographic techniques (also called chemical processes).

Disclosure of Invention

The object of the present invention is to solve the problem of complex and expensive machining of single-piece single-crystal components and to provide a shock-resistant bearing which is formed from a single-piece component which defines a resilient structure and a central portion in which a hole for receiving a pivot shaft of a rotating element/rotating wheel set is machined, which shock-resistant bearing can be machined industrially with high quality at relatively low cost.

Another object of the present invention is to provide an anti-seismic bearing of the aforementioned type having a blind hole whose shape is advantageous for properly centering the shaft of the rotating element pivoting in said blind hole and minimizing friction.

It is another object of the present invention to provide a shock-resistant bearing that has an attractive and particularly discernible appearance.

The invention relates to an anti-seismic bearing for a timepiece, comprising an elastic structure and a central portion carried by the elastic structure, the central portion having a blind hole for receiving a pivot of a rotating element of the timepiece. The resilient structure and the central portion are formed from one unitary component formed from single crystal quartz, the blind bore having three inclined planes that collectively define a truncated or non-truncated triangular pyramid.

In a preferred variant, the one-piece component is a perforated wafer, the axis of which perpendicular to its two main surfaces is almost parallel to the optical axis of the monocrystalline quartz.

The invention also relates to two main implementation methods for manufacturing a shock-resistant bearing, wherein the elastic structure and the central part carried by the elastic structure and having the blind hole are made of monocrystalline quartz.

The manufacturing method according to the invention makes it possible to obtain high-quality, transparent, shock-resistant bearings by a relatively inexpensive method which requires only machining in a chemical bath. Furthermore, the method makes it possible to machine a blind hole for a bearing, the bottom of which is at least partially defined by a triangular pyramid, against the plane of which the pivot of the rotating element abuts. The blind hole ensures an improved centering of the shaft of the rotating element and minimizes friction. Transparent bearings also have the technical advantage of easier inspection for the presence of oil in the bore.

Other specific features and advantages of the invention will be set forth in the following detailed description of the invention.

Drawings

The invention will be described below with reference to the attached drawings, given by way of non-limiting example, in which:

figure 1 is a cross-sectional view of an embodiment of the anti-seismic bearing according to the invention.

Figure 2 is a top view of the perforated single-crystal quartz plate forming the anti-seismic bearing in figure 1.

Fig. 3 is a schematic perspective view of a crystal of monocrystalline quartz, in which the wafer to be cut off for producing the perforated sheet of fig. 2 is shown.

FIG. 4A is a cross-sectional view of a quartz wafer covered on both main surfaces with masks chosen to withstand a quartz etching bath.

Fig. 4B is a schematic cross-sectional view of the wafer of fig. 4A after machining in a chemical bath configured for anisotropic etching of quartz.

Fig. 5 is a plan view of a blind hole obtained in a quartz wafer machined according to the method of the invention.

Fig. 6 is a plan view of a second variant of the blind hole obtained in a quartz wafer machined according to the method of the invention.

Fig. 7 is a sectional view along the line VII-VII of fig. 6 for a variant which differs from the embodiment in fig. 6 only in that the initial portion of the blind hole does not have a vertical wall but rather a steep slope.

Fig. 8A and 8B are cross-sectional views corresponding to fig. 4A and 4B of a quartz wafer with a thicker thickness and of a blind hole with a larger diameter, the shape of which is similar to that shown in fig. 6 and 7.

Detailed Description

The anti-vibration bearing 2 according to the invention will be described below with reference to fig. 1, 2, 3 and 5. The shock-resistant bearing is arranged in a bridge or base plate 4 of a timepiece and is constituted by a monocrystalline quartz wafer 6 (the wafer defining a plate of disc or circular shape) and a base 8 having a cavity/housing for the wafer 6. The wafer includes: a resilient structure 10 formed by a substantially circular groove 12 machined in the wafer; and a central portion 14 carried by said elastic structure and having a blind hole 16 for receiving a pivot of a rotating element/wheel set (not shown) of the timepiece movement. The grooves, substantially in the shape of circular arcs, define between them elastic helical arms connecting the central portion to the outer peripheral zone of the wafer 6. The resilient structure and the central portion are thus formed by a one-piece component made of monocrystalline silicon quartz.

Since the elastic structure is provided at the outer periphery of the central portion 14, the latter may experience movements in the plane of the wafer 6, and also vertical movements to some extent. For this purpose, a groove is preferably provided between the elastic structure 10 and the bottom of the cavity of the base 8. The bearing 2 defines a suspension-type anti-seismic bearing. It will be understood that the base comprises a hole for the passage of the spindle of the rotating element and acts as a stop member in the event of severe axial and/or vertical vibrations. It will be understood that the stop member may be provided in a number of ways, in a variant the wafer 6 is provided directly in the clamping or main plate 4 without the use of an intermediate element.

The spring structure may have a number of design variations in the plane of the wafer 6. The central portion 14 is connected to the outer peripheral portion of the base 8 in an elastic manner. However, the provision of a staggered/shingled arrangement of helical arms of the type shown in fig. 2 is advantageous because the length of the resilient arms is increased relative to configurations having radial arms. For this reason, the choice of quartz wafers is excellent, since this type of design can be obtained by an etching process in a bath, as will be explained below.

In accordance with the present invention, the blind hole 16 machined in the bottom surface of the central portion 14 has three inclined planes 40A, 40B, 40C which together at least partially define a triangular pyramid (see fig. 5). According to a variant, each of the three planes defines an angle of about 40 ° with respect to the central axis Z of the blind hole, i.e. the central straight line 42 of each of these planes defines an angle of about 40 ° with respect to the central axis of the blind hole. The bottom of the blind hole may have other flat surfaces, especially when the diameter of the hole becomes larger (see fig. 6). These different planes result from the quartz etching provided by the manufacturing method according to the invention described below.

In a preferred variant, the blind hole also has, in its initial part, substantially vertical side walls (see fig. 7). Thus, the three planes do not extend to the outer surface of the one-piece component where the blind holes open to the outside, and the steepness/inclination or steepnesses of the side surface of the blind hole between the outer surface and the three planes is/are greater than the steepness of the three planes. According to a particular variant, the inclination/steepness (or inclinations) defined by the lateral surface of the blind hole with respect to the central axis of the blind hole is less than 20 degrees (20 °).

According to a preferred embodiment, the monocrystalline quartz wafer 6 is chosen such that the axis Z perpendicular to its two main surfaces is approximately the optical axis of the monocrystalline quartz. Fig. 3 schematically shows a quartz crystal 18 and a cut sheet 6A cut out of the quartz crystal for producing a plate in which a wafer 6 according to the invention is subsequently machined.

According to a first embodiment or first implementation of the method for manufacturing a shock-resistant bearing of this type, comprising a resilient structure and a central portion carried by said resilient structure and having a blind hole for receiving a pivot of a rotating element of a timepiece, said resilient structure and said central portion are formed by one integral part, the following steps are provided:

A) producing a single crystal quartz wafer having two major surfaces, first and second surfaces, respectively, oriented substantially perpendicular to an optical axis of a crystal structure of the single crystal quartz;

B) forming a first mask on a first surface of a single crystal quartz wafer, the first mask being structured by lithography so as to define on the first surface contours of elastomeric structures and blind holes provided in the wafer;

C) elastomeric structures and blind holes are machined in a single crystal quartz wafer by inserting the wafer into a chemical etching bath adapted to anisotropically etch the single crystal quartz very advantageously along the optical axis, the first mask being selected to withstand etching by the etching bath.

It is noted that in case of relatively small hole diameters, in particular smaller than about 120 micrometer (120 μm), the speed of forming the hole along the central axis of the hole is slower than the speed of machining the resilient structure in the direction of the (optical) axis, so that the blind hole and the resilient structure can be obtained simultaneously by simply etching from the first surface.

According to a preferred variant, the elastic structure being machined has a design comprising curved slots and/or apertures, the edges of which have at least partially curved lines; this optimizes the spring structure as described above.

In a preferred variant of the first embodiment, as shown in fig. 4A and 4B, the following steps are provided:

A) producing a single crystal quartz wafer 6A whose two main surfaces, respectively the first and second surfaces, are oriented substantially perpendicular to the optical axis Z of the crystal structure of the single crystal quartz;

B) forming a first mask 20 on a first surface of a single-crystal quartz wafer, forming a second mask 26 on a second surface of said wafer, said first and second masks being structured by lithography so as to define, respectively, on said first and second surfaces, the outline of the elastic structure 10, the first mask 20 also defining the outline of a blind hole 16A provided in the wafer 6;

C) the elastomeric structures 10 and blind holes 16A are machined in a single crystal quartz wafer by inserting the wafer into a chemical etching bath adapted to anisotropically etch the single crystal quartz very advantageously along the optical axis, the first and second masks being selected to withstand the etching of the chemical etching bath.

Thus, the quartz wafer is etched on both sides of the quartz wafer simultaneously to form the spring structure. This makes it possible, firstly, to reduce the machining time in the etching bath and also to obtain orifices with vertical walls. This variant is particularly suitable in the case of blind holes having a relatively large diameter, in particular greater than 150 micrometers (150 μm). In this way, it is easy to machine the elastomeric structure and to produce blind holes simultaneously in the same chemical etching bath. It should be noted, however, that this variant is advantageous even for the manufacture of elastic structures when the blind holes have a small diameter.

In a specific modification, the normals to the two main surfaces of the quartz wafer form an angle (birefringence angle) of about 2 degrees (2 °) with respect to the optical axis of the crystal structure of the single crystal quartz. The quartz etching bath contains, inter alia, hydrofluoric acid (HF). In a variation, the quartz etching bath further contains ammonium fluoride (NH 4F).

The lithographic method used to fabricate the two masks is standard. Photosensitive layers 22, 28 are deposited on metal layers 20, 26, respectively, such as a chromium-gold layer (Cr-Au). Each photosensitive layer is then selectively irradiated and developed to obtain apertures corresponding to the formed mask. In this way, the photosensitive layer 22 has an aperture 24A for the elastic structure and an aperture 25 for the blind hole; while the photosensitive layer 28 only has apertures 24B for the elastic structure 10. After the photosensitive layers 22 and 28 have been structured, the wafer 6A is placed in a chemical bath suitable for etching the metal layers 20 and 26, thereby defining two corresponding masks (numbered the same as the metal layers) for the subsequent partial quartz etching

Finally, the wafer 6A formed with the two masks is placed in a chemical bath chosen to perform a strongly anisotropic etching of the monocrystalline quartz by favouring the etching substantially on the optical axis Z. After a determined time has elapsed in the chemical bath, which varies in particular with the thickness of the wafer and with the required depth of the blind hole, a perforated wafer 6 is obtained with circular grooves 12 having substantially vertical walls. Furthermore, a blind hole 16A is obtained whose bottom has an inclined plane as described above (the symmetrical V-shaped profile in the section of fig. 4B is schematic, since in transverse section the two planes of the pyramid are not traversed in general with the same degree of inclination). In the variant shown in fig. 4B, the bottom of the hole is formed by a triangular pyramid only. By way of example, the wafer 6 has a thickness of about 200 microns, the diameter of the blind holes being 100 or 200 microns.

According to a second example or embodiment of a method of manufacturing a shock-resistant bearing of the above-mentioned type, the method comprises the following steps:

A) producing a single crystal quartz wafer having two major surfaces, first and second surfaces, respectively, oriented substantially perpendicular to an optical axis of a crystal structure of the single crystal quartz;

B) forming a first initial mask on a first surface of the single crystal quartz wafer, the first initial mask being structured lithographically so as to define on the first surface the contour of the elastic structure but not the contour of the blind hole for receiving the pivot of the rotating element;

C) machining in part in a single crystal quartz wafer, by placing said wafer in a chemical etching bath suitable for anisotropic etching of single crystal quartz with a very favourable etching along the optical axis of said single crystal quartz, an elastic structure defined by a first initial mask obtained in said step B), said first initial mask being selected to be resistant to etching by said chemical etching bath;

D) constructing the first initial mask so as to define the outline of the blind holes and obtain a first final mask;

E) final machining of the elastomeric structure by placing the wafer again in the chemical etching bath, while machining blind holes defined by the first final mask structured in step D).

A preferred variant of the second embodiment of the method of the invention is schematically shown in fig. 8A and 8B. In this preferred variant, before step C), a second mask is formed on the second surface of the monocrystalline quartz wafer, the second mask being structured by photolithography so as to define on the second surface a profile of the elastic structure. This variation allows etching on both sides of the wafer 36A, as shown in fig. 8A. Fig. 8A schematically shows a cross-section of a single crystal quartz wafer 36A after having undergone step C) of the method according to the variant described herein and after irradiation and development of the photosensitive layer 23 to obtain apertures 25A in said layer for enabling holes 25 (fig. 8B) to be made in the initial mask 21A, so as to obtain the final mask 21. The final mask makes it possible to machine blind holes 16B in the final machining stage of the elastic structure 10, in order to obtain the perforated wafer 36 shown in fig. 8B. A second mask 27 is constructed using the photosensitive layer 29. In order to etch the masks 21A and 27, the photosensitive layers 23 and 29 are respectively structured by photo-etching, and then the apertures 24A and 24B corresponding to the desired elastic structures 10 are respectively obtained. Prior to etching the apertures 25 in the mask 21A, i.e., prior to step D) of the method described herein, the wafer 36A is placed in an anisotropic quartz etch bath for a first stage or period of time. After the wafer has been removed from the bath, the spring structure is partially machined as shown in FIG. 8A. Recesses 32 and 33 are obtained on both sides of the wafer 36A.

According to a preferred variant, between the aforementioned steps B) and C), the photosensitive layer 23 is irradiated, which was once used for the partial configuration of the first initial mask 21A to define the elastic structure, to form in the photosensitive layer the apertures 25A corresponding to the desired blind holes (fig. 8A). It should be noted that the development of the photosensitive layer 23 to obtain the apertures 25A may take place before or after step C). The structuring of the first mask is thus effected here in two stages in an etching bath which is selected for etching a metal layer deposited on a monocrystalline quartz wafer and forming the first mask.

The second embodiment of the method according to the invention makes it possible to determine two different time periods for machining the elastic structure and the blind hole in the anisotropic etching bath for monocrystalline quartz. This optimizes the etching time for the spring structure and for the blind holes. Thus, by way of example, a single crystal quartz wafer has a thickness of 300 microns, with a diameter of the blind hole equal to about 200 microns. The period of the first etching phase of the elastomeric structures lasts, for example, about two hours (2h), and the period of the second etching phase of the elastomeric structures and the blind holes lasts, for example, about two hours. The depth of the blind holes is for example between 100 and 150 micrometers.

As shown in fig. 6 and 7, in particular when the diameter of the blind hole is greater than 150 microns, in addition to the corresponding planes 40A, 40B, 40C of the substantially triangular pyramid as described in fig. 5, a plane 42 is also present in the central region of the bottom of the blind hole 16B, each plane defining a relatively large angle (in particular about 60 °) with respect to the vertical axis Z. Thus, the basic triangular pyramid is truncated, i.e. the area of its top is cut into planes, each having a smaller inclination than the three planes of the triangular pyramid. Preferably, the blind hole 1B has a substantially vertical wall 44 in its initial portion. The pivot 50 of the spindle of the wheel set introduced into the blind hole is preferably configured so that the abutment point of said pivot against the bottom of the blind hole is located in the three-plane regions 46 of the main triangular pyramid, these regions 46 forming an angle of substantially 40 ° with respect to the axis of rotation Z of the pivot 50.

Claims (9)

1. A method of manufacturing an anti-seismic bearing comprising an elastic structure (10) and a central portion (14) carried by the elastic structure, the central portion having a blind hole (16; 16A; 16B) for receiving a pivot of a rotating element of a timepiece, the elastic structure and the central portion being formed by one integral part (6), the method being characterized by the steps of:

A) producing a single crystal quartz wafer (6A) whose two main surfaces, respectively a first surface and a second surface, are oriented substantially perpendicularly to an optical axis (Z) of the crystal structure of the single crystal quartz;

B) forming a first mask (20) on a first surface of the single crystal quartz wafer, the first mask being structured by lithography so as to define on the first surface the contours of the elastic structure and the blind holes;

C) the elastomeric structures and blind holes are machined in a single crystal quartz wafer by placing the single crystal quartz wafer into a chemical etching bath adapted to anisotropically etch the single crystal quartz very advantageously along the optical axis, the first mask being selected to withstand etching by the chemical etching bath.

2. A method of manufacturing an anti-seismic bearing comprising a resilient structure (10) and a central portion (14) carried by the resilient structure, the central portion having a blind hole (16; 16A; 16B) for receiving a pivot of a rotating element of a timepiece, the resilient structure and the central portion being formed from one integral part (36), the method being characterized by the steps of:

A) producing a single crystal quartz wafer (36A) whose two main surfaces, respectively a first surface and a second surface, are oriented substantially perpendicular to an optical axis (Z) of a crystal structure of the single crystal quartz;

B) forming a first initial mask (21A) on a first surface of the single-crystal quartz wafer, said first initial mask being structured by lithography so as to define on the first surface the outline of said elastic structure but not of said blind holes;

C) machining the resilient structure defined by the first initial mask partially in a single crystal quartz wafer by placing the single crystal quartz wafer into a chemical etching bath adapted to anisotropically etch the single crystal quartz very advantageously along the optical axis, the first initial mask being selected to withstand etching by the chemical etching bath;

D) -structuring said first initial mask so as to define the profile of said blind holes and obtain a first final mask (21);

E) the final machining of the elastic structure and the simultaneous machining of the blind holes are carried out by placing the monocrystalline quartz wafer again in the chemical etching bath.

3. Method according to claim 2, characterized in that, between said steps B) and C), a photosensitive layer (23) deposited on said first initial mask and used for structuring said first initial mask is irradiated to subsequently form apertures (25A) in said photosensitive layer corresponding to said blind holes.

4. Method according to claim 1, characterized in that, before step C), a single crystal quartz wafer (6A; 36A) is formed on the second surface of the substrate (26; 27) said second mask being structured by photo-etching so as to define a profile of said elastic structure on the second surface.

5. Method according to claim 2, characterized in that, before step C), a single crystal quartz wafer (6A; 36A) is formed on the second surface of the substrate (26; 27) said second mask being structured by photo-etching so as to define a profile of said elastic structure on the second surface.

6. The method of claim 1, wherein the machined resilient structure has a design comprising curved slots and/or apertures, edges of the slots or apertures at least partially defining curved lines.

7. A method according to claim 2, wherein the machined resilient structure has a design comprising curved grooves and/or apertures, the edges of which at least partially define curved lines.

8. The method according to claim 1, characterized in that the blind hole has three inclined planes (40A; 40B; 40C) which together define a truncated or non-truncated triangular pyramid.

9. The method according to claim 2, characterized in that the blind hole has three inclined planes (40A; 40B; 40C) which together define a truncated or non-truncated triangular pyramid.