Elastic member for a timepiece mechanism

Abstract

The present invention relates to an elastic member (1) intended to equip a timepiece mechanism and comprising at least two elastic blades (2, 3) arranged parallel to each other, secured at least at one of their ends (21, 22, 31, 32) and shaped to exert a force or a moment during bending or compression or buckling of the blades (2, 3). The elastic blades (2, 3) are separated by a slot (6) extending along an axis parallel to the longitudinal axes of the elastic blades (2, 3) and whereof the dimension perpendicular to said axis is strictly greater than 0 and less than or equal to 10 µm, preferably less than 5 µm, even more preferably less than or equal to 1 µm.

Description

[0001] Elastic organ for clockwork mechanism

[0002] The present invention relates to an elastic member intended to equip a clockwork mechanism and comprising at least two elastic blades arranged parallel to each other, secured at at least one of their ends and shaped to exert a force or a torque during the bending or compression or buckling of the blades.

[0003] In watchmaking, there are several types of elastic organ such as those above called leaf springs formed of at least one elastic leaf. In most arrangements, one end of the leaf - the heel - is fixed while the other end, free, rests on a component of the watch mechanism to exert a force or torque following the bending of the leaf. Such springs are notably used as return springs or jumper springs. In another configuration, the leaf spring can be arranged to work in buckling and provide its force or torque during the compression of the leaf in a direction parallel to its longitudinal axis.

[0004] The force of an elastic member of the leaf spring type is the force required to achieve a certain deformation of the elastic leaf (deflection), within the elastic limit of the material. This force will correspond to the torque that the leaf spring exerts on the component on which it acts. The properties of the material of the elastic leaf are essential since the elastic limit must not be exceeded. In particular, the stresses (tension, shear, compression) in the leaf during its deformation must be taken into account. The ratio between the force and the deformation is called stiffness.

[0005] Figure 1 schematically illustrates a leaf spring 10 of the prior art intended to equip a clockwork mechanism. This leaf spring 10 comprises an elastic leaf 100 whose ends 110 and 120 are fixed for example on the frame 130 of a clockwork mechanism. The actuator of the leaf spring 10 (not illustrated) is located symmetrically with respect to the leaf 100 and is arranged to exert a force P on the leaf 100 which will flex said leaf 100. This actuator is the component on which the leaf spring 1 acts.

[0006] The blade 100 is characterized by its length L, its thickness e (dimension in the axis of the force P) and its height or depth h (dimension perpendicular to the force P). We also consider E, the Young's modulus of the material constituting the blade 10.

[0007] We determine the maximum deflection f at the center of the blade 100 and the corresponding force P:

[0008] The quadratic moment I with respect to the blade reference 100 for a rectangular section is given by:

[0009] We therefore obtain:

[0010] In continuous media mechanics, and in the strength of materials in general, mechanical stress describes the forces that the elementary particles of a medium exert on each other per unit area. Stress goes hand in hand with a deformation of the material in which it is exerted. The stress in the blade 10 is given by the following relationship: where M is the maximum moment of force at the center of the blade 100 and where y is the distance between the upper or lower surface of the blade 100 and its neutral fiber. The above equations clearly establish the relationship between thickness, length, modulus of elasticity and stress.

[0011] A thin blade generates less stress during deformation. This can be advantageous depending on the yield strength of the blade material. However, a thin blade exerts little stress, which may not be sufficient depending on the application. In addition, a thin blade can be difficult to manufacture depending on the material.

[0012] To increase the torque, it is possible to increase the length and / or thickness of the blade. The stresses also increase and care must then be taken to remain within the elastic range of the blade material. In this case, the size of the elastic member also increases, which is not always desirable in a watch mechanism.

[0013] By changing the material, the elastic limit changes and it is then possible to find another balance between force and constraints to produce a leaf spring of the same size but with greater force.

[0014] Finally, it is also known to add one or more additional elastic blades in parallel. The blades are secured at at least one of their ends and are separated by a space essentially equivalent to the space of a blade. In this case, the forces are additive: the torque generated by the leaf spring as a whole is the addition of the torques of each of the blades. The stresses, however, are not additive and the stress of the entire spring is equivalent to that of a blade, provided that the blades are essentially equivalent. This solution can still be cumbersome. Moreover, in this case, the necessary pre-tensioning is greater since the blades must first be brought to bear on each other to allow the spring to exert the total force on another component.

[0015] The aim of the present invention is to provide an elastic member intended to equip a clockwork mechanism comprising at least two elastic blades arranged parallel to each other, secured at at least one of their ends and arranged to provide a force during bending, compression or buckling of the blades which makes it possible to offer a significant force for the lowest possible stress or stiffness, all in a compact and preferably aesthetic arrangement.

[0016] The present invention relates to an elastic member intended to equip a clockwork mechanism according to claim 1. The present invention also relates to a clockwork movement according to claim 5 and a timepiece according to claim 6.

[0017] Other characteristics and advantages of the present invention will appear on reading the description which follows, given solely by way of non-limiting example, and made with reference to the appended drawings in which:

[0018] Figure 1, discussed in the introduction, schematically illustrates an elastic member of the prior art comprising an elastic blade whose ends are fixed and which is arranged to work in flexion.

[0019] Figure 2 schematically illustrates an embodiment of an elastic member according to the invention.

[0020] In the embodiment of Figure 2, the elastic member 1 comprises at least two elastic blades 2, 3, arranged in parallel, that is to say parallel to each other as illustrated in Figure 2, and secured to each other at each of their ends 21, 22, 31, 32. The ends 21, 31 of the elastic blades 2, 3 form the first heel 20 of the elastic member 1 while the ends 22, 32 form a second heel 30. In the illustrated embodiment, the first and second heels 20, 30 of the elastic member 1 are intended to be fixed or at least supported on two fixed parts 4, 5 of the frame of a clockwork movement.

[0021] According to the invention, the two elastic blades 2, 3 are separated by a non-zero space or slot 6 extending over the entire height of the blades 2, 3 (height being the dimension of the blades perpendicular to the bending plane of the blades). In the illustrated embodiment, the slot 6 is closed at its ends 61, 62. The slot 6 therefore extends longitudinally between the first and second heels 20, 30 of the elastic member 1. In addition, the slot 6 is a through slot since it extends over the entire height of the elastic blades 2, 3. By slot, we mean a narrow and long opening. Thus, at the level of the slot 6, when the elastic member 1 is at rest, there is a contactless space between the elastic blades 2, 3 parallel to each other.

[0022] According to the invention, the slit has a width strictly greater than 0 pm and less than or equal to 10 pm, preferably less than 5 pm, even more favorably 1 pm. For example, the slit could have a width essentially equal to approximately 4, 3.5, 3, 2.5, 2, 1.5, 1 or even 0.5 pm. These measurements are of course understood when the elastic member and the elastic blades are at rest.

[0023] In the illustrated embodiment, the elastic member 1 is arranged to work in flexion.

[0024] It is considered that the elastic member 1 according to the invention illustrated in Figure 2 is characterized by the same parameters as the elastic member 10 according to the prior art illustrated in Figure 1. It is also considered that the two elastic blades 2, 3 are essentially identical and that their thickness is equal to e / 2 for each. For the same maximum deflection fi_ / 2 at the center of the spring member 1 according to the invention, the corresponding force Pi is determined:

[0025] As for the constraint, since the elastic blades 2, 3 are considered identical, the constraint 01 on each of the blades is identical and is worth: Since the moment of force Mi at the center of the elastic member 1 is equal to 1 / 8 of the moment of force ML / 2 at the center of the elastic member 10 in figure 1, we obtain:

[0026] 1. , i — — 2t J

[0027] Thus, with an elastic blade 10 split into two equal elastic blades 2, 3, the force of the elastic member 1 is divided by 4 while its stress is divided by 2.

[0028] The elastic member 1 as illustrated in Figure 2 is arranged to work in bending between two support points 4, 5 and a central actuation point (location of force Pi). Alternatively, the invention applies to an elastic member such as that of Figure 2 arranged to work in buckling, by compression of one or the other or both of the heels 20, 30 along the longitudinal axis of the blades 2, 3. Alternatively, the invention applies to an elastic member whose blades are arranged parallel to each other and secured to each other at only one of their ends, the other end being free. In this case, the slot between the blades is open at the free end of said blades. The same calculations as above with adapted formulas apply for both variants.

[0029] Generally speaking, the elastic member according to the invention is intended to equip a clockwork mechanism and comprises at least two elastic blades arranged parallel to each other, and secured to each other at at least one of their ends. The elastic member is arranged to work in bending or buckling. The elastic blades (at rest) are separated by a slot whose width (dimension parallel to the direction of the force exerted by the spring) is less than or equal to 10 μm, preferably less than or equal to 5 μm, even more preferably less than or equal to 1 μm. For example, the slot could have a width essentially equal to approximately 4, 3.5, 3, 2.5, 2, 1.5, 1 or even 0.5 μm.In other words, the elastic blades extend parallel to each other and, at rest, are separated by a slot which extends along an axis essentially parallel to the longitudinal axes of the elastic blades, the width of the slot, that is to say its dimension along an axis perpendicular to its longitudinal axis, is strictly greater than 0 and less than or equal to 10 pm, preferably less than or equal to 5 pm, even more preferably less than or equal to 1 pm.

[0030] Preferably, the elastic blades are essentially identical as in the illustrated embodiment. Alternatively, the elastic blades could be different and in particular have different thicknesses. Similarly, the elastic blade directly in contact with the component on which the elastic member acts could have a particular shape (inclined planes of a jumper spring).

[0031] In all cases, the total force of the elastic member is obtained by adding the force of each of the blades that compose it while the stress of the elastic member is the stress of the thickest elastic blade.

[0032] It is also noted that with the elastic member according to the invention, the total stiffness in the operating plane (bending or buckling plane) is equal to the stiffness of an elastic blade which would have as thickness the summed thickness of all the elastic blades and as height the summed height of all the elastic blades of the elastic member according to the invention, while the stiffness outside the operating plane (plane perpendicular to the bending or buckling plane) will decrease since the height of each of the blades is a fraction of the total height of the elastic member.

[0033] Thanks to the present invention, it is possible to find for a certain application an optimum between effort, constraint and bulk. For example, if in a control mechanism subjected to the action of an elastic member of the single-leaf leaf spring type, a higher repositioning torque is required to more clearly mark the positions of the control mechanism (haptic feedback of a pusher or position of a time-setting or winding crown) but without changing the material, it is possible to add to the leaf spring elastic blades separated by slots of width less than or equal to 10 μm. The forces of these blades are added together, while the constraint does not increase. In addition, given the smallness of the slots separating the blades, the bulk due to the addition of one or more blades is reduced compared to a known multi-leaf spring.The fineness of the slots also has the advantage that pre-arming is minimal since the blades, although separated by the slot in the rest position, will touch at the slightest deformation. Finally, a slot smaller than 10 pm is almost invisible to the naked eye, which can be an aesthetic advantage if you are not looking for the comb or harp shape of the elastic organ.

[0034] The elastic member according to the invention can be made of any suitable material such as steel or NiP. Preferably, the elastic member according to the invention is made of a material without plastic deformation such as silicon, ceramic, quartz, glass or silicon carbide. The elastic member can be manufactured according to well-known micromachining methods. In particular, despite the fineness of the slot(s) between the blades, these can be produced by known DRIE methods since their length generally allows good renewal of the gases during the manufacture of the slot.

[0035] In the following, a preferred method of manufacturing a spring member according to the invention is described in a material without plastic deformation and in particular in silicon.

[0036] In a first step, for example, a silicon wafer is prepared, preferably having a thickness equivalent to that of the elastic member to be manufactured. Alternatively, the wafer could not be entirely made of silicon or could be made of doped silicon. The wafer could also be a silicon-on-insulator (SOI) wafer. Alternatively, the wafer could be made of a layer of silicon applied to another type of base, such as metal. The silicon can be monocrystalline or polycrystalline.

[0037] In a second step, the plate is oxidized to form a layer of silicon oxide. This step can be carried out in particular by a surface treatment such as a thermal oxidation treatment, chemical vapor deposition (CVD) or physical vapor deposition (PVD), in order to obtain a layer of silicon dioxide of a thickness greater than the layer of so-called "native" silicon dioxide forming naturally in the presence of air.

[0038] On this silicon oxide layer, a metallic layer is applied in a third step. Preferably, the metallic layer is a layer of chromium sputtered or evaporated by a physical vapor deposition (PVD) method. Alternatively, the metallic layer could be a layer of titanium or tantalum deposited directly on the silicon oxide layer without a prior primer layer or a layer of nickel, aluminum, indium or tungsten deposited on a primer layer previously deposited on the silicon oxide layer.

[0039] In a fourth step, a layer of photosensitive resin (hereinafter simply resin) is deposited on the metal layer.

[0040] The fifth step is a photolithography step during which the resin layer is exposed to radiation (typically UV) through an exposure mask or reticle. Preferably, this photolithography step is done using a stepper. This system, short for step-and-repeat camera or step-and-scan camera for the most recent versions, works like a slide projector. The elastic member to be manufactured - its elastic blades and the slit(s) separating them - is reproduced on a large scale on a reticle (the slide). The reticle is robust and faithfully reproduces all the dimensions and structures forming the elastic member to be manufactured. The reticle is positioned relative to the plate and the resin layer, a light source insolates the resin layer through the reticle and a system of lenses that reduce the projected image (generally, between 4 and 10 times).The stepper then moves the reticle relative to the plate and repeats the process. This results in a first etching mask in the resin layer, which is repeated many times and contains the precise image of the pattern on the reticle. Using a stepper allows for very high definition, resolution and precision in the creation of the first etching mask.

[0041] The following steps in the process are etching steps.

[0042] In the sixth step, the metal layer is etched through the first etching mask formed in the resist layer. The technique used is, for example, a reactive ion etching (RIE) technique. This produces a second etching mask in the metal layer, into which the precise and repeated images of the first etching mask are transferred with very high precision and resolution. During this step, at least part of the resist layer is consumed.

[0043] In the seventh step, the second etching mask in the metal layer is used to etch the silicon oxide layer to form a third etching mask in the silicon oxide layer. A plasma etching process can be used, for example. During this step, the remainder of the resin layer is usually completely consumed, as well as some or all of the metal layer.

[0044] Finally, in an eighth step, the third etching mask allows the etching of the silicon wafer by deep reactive ion etching (DRIE). This forms the desired elastic member or a set of desired elastic members in the wafer. During this step, part or all of the oxide layer is consumed.

[0045] An additional step may be provided consisting of coating the micromechanical components with a layer of silicon dioxide over their entire outer surface to increase their mechanical strength. This step is carried out by a surface treatment such as a thermal oxidation treatment, chemical vapor deposition (CVD) or physical vapor deposition (PVD), in order to obtain a layer of silicon dioxide of a thickness greater than the layer of so-called "native" silicon dioxide forming naturally in the presence of air. The thickness of this final layer of silicon dioxide is preferably at least equal to 0.5 micrometers. In this case, care will have been taken to produce during the manufacture of the elastic member slots of a width such that after the thermal oxidation treatment, said slots still have a sufficient width.

[0046] Considering the manufacturing process above, it is understood that each of the oxide, metal and resin layers must have sufficient thickness to be able to serve as an etching mask and therefore to resist until the lower layer is opened or etched. In particular, the thickness of the plate (and therefore in general the thickness of the micromechanical component to be manufactured) will determine the necessary thickness for the oxide layer. The thickness of the metal layer is then chosen according to the thickness of the oxide layer and the thickness of the resin layer according to the thickness of the metal layer. Since the oxide layer is generally significantly thinner than the thickness of the plate, the chromium and resin layers can also be very thin compared to the thickness of the plate.

[0047] For example, for a plate 1 of 120 pm (i.e. for a micromechanical component to be manufactured of the same thickness), the oxide layer may have a thickness preferably between 0.4 and 3 pm. The metal layer 3 deposited on the oxide layer may then have a thickness of a few hundred nanometers, between 100 and 500 nanometers, preferably 100 nanometers. Finally, the resin layer 4 may be as thin as possible, with a thickness between 0.1 and 5 pm, more favorably between 0.2 and 3 pm and even more favorably between 0.4 and 0.8 pm.

[0048] It is understood that the thickness of the silicon oxide, metal oxide, and resin layers depends on the thickness of the plate and / or the depth of the desired final etching. Generally, the thickness of the plate 1 can vary and can in particular go up to 300 μm or more.

[0049] Thus, the above method makes it possible to produce precise and high-definition fine structures using a succession of layers to guarantee sufficient selectivity at each etching step and ultimately obtain an etching on the silicon plate that is sufficiently deep, forming very fine structures whose aspect ratio is greater than 20, 50 or 100, which corresponds to the dimensions of the slot of the elastic member according to the invention.

[0050] This produces a multi-blade elastic member offering a wide variety of applications in a watch mechanism, making it possible to balance force, stress and stiffness in and out of the deformation plane. In addition, the elastic member according to the invention allows the use of modern materials such as materials without plastic deformation, in particular silicon, and offers a compact and aesthetic solution for producing elastic members with high force, a very important criterion in watchmaking.

Claims

Claims 1. Elastic member (1) intended to equip a clockwork mechanism and comprising at least two elastic blades (2, 3) arranged parallel to each other, secured at at least one of their ends (21, 31, 22, 32) and shaped to exert a force or a torque during the bending or compression or buckling of the blades (2, 3), characterized in that the elastic blades (2, 3) are separated by a slot (6) extending along an axis parallel to the longitudinal axes of the elastic blades (2, 3) and the dimension of which perpendicular to this axis is strictly greater than 0 and less than or equal to 10 pm, preferably less than 5 pm, even more preferably less than or equal to 1 pm.

2. Elastic member according to claim 1, characterized in that said at least two elastic blades (2, 3) are essentially identical.

3. Elastic members according to one of the preceding claims, characterized in that said at least two elastic blades (2, 3) are integral at each of their ends (21, 31, 22, 32).

4. Elastic members according to one of the preceding claims, characterized in that it is made of steel, NiP or a material without plastic deformation, in particular silicon.

5. Clockwork movement comprising an elastic member according to one of the preceding claims.

6. Timepiece comprising a movement according to the preceding claim.

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