Patent Application
20200319597
The present invention concerns an antishock device with rigid stop and a timepiece mechanical oscillator with flexure guiding having such an antishock device. The present invention also concerns a timepiece mechanical oscillator comprising said antishock device.
In the field of high-precision micromechanics and that of horology in particular, the use of so-called antishock devices to protect components, for example those of a watch, is well known.
The document EP3076245 describes a shock and/or vibration damping device comprising a flexible element adapted to be deformed by the effect of a stress and a so-called dissipative layer produced from a material having a shear modulus lower than the shear modulus of the flexible element at least partly secured to said flexible element.
The document EP3324246 describes rigid axial stop means suitable for the protection of the blade resonator mechanism against axial shocks in the direction of the shaft.
In the case of the antishock devices described in EP3076245 and EP3324246, the antishock device cooperates with a pivot shaft related to the centre of the oscillator. The part of the shaft that comes into contact with the antishock device is always the same whatever the intensity of the shock, namely the end of the shaft for axial shocks and the bearing surface at the end of the shaft for radial shocks. The diameter of the bearing surface at the end of the shaft must therefore be sufficiently large for no shock, whatever its intensity, to be able to damage it. This implies a large shaft diameter or a long lever arm that generates a high friction torque on the balance in the event of a shock.
Wearing shocks (<500 G NIHS) can easily occur and repeat at a high frequency. Thus a high friction torque associates with wearing shocks (<500 G NIHS) repeated at a high frequency may lead to a severe loss of amplitude of the balance or even to stopping or jamming of the mechanism. This is all the more critical for oscillators with flexure guiding that generally operate with a low nominal amplitude.
An object of the present invention is to minimize the friction between an oscillator with flexure guiding and its antishock device and therefore to reduce the loss of amplitude of the oscillator following wearing shocks, which is particularly critical for oscillators with flexure guiding that generally have on the one hand a low nominal amplitude and on the other hand an escapement that is not self-starting and may jam if the amplitude of the oscillator is too low
The present invention integrates a visco-elastic spring and associates it with a rigid stop so that the wearing shocks are absorbed by the visco-elastic antishock device and accidental shocks by the rigid stop.
Wearing shocks are defined by the standard NIHS 91-30, “Definition of linear accelerations encountered by a wristwatch on sudden gestures and wearing shocks”. Accidental shocks are defined by the standard NIHS 91-20, “Definition of linear shock types for wristwatch components”. The standard NIHS 91-10 specifies the minimum requirement applicable to shock-resistant watches and describes the corresponding test method.
According to the invention, these objects are achieved in particular by means of an antishock device comprising a visco-elastic element and a rigid stop, each being configured in such a manner as to cooperate with a portion of the oscillator; in which the visco-elastic element is configured in such a manner as to be deformed elastically if the oscillator is subjected, in the event of a shock, to an acceleration between 20 G and 1000 G NIHS, preferably between 50 G and 500 G NIHS; in which said portion cooperates with the rigid stop if the portion is subjected to an acceleration beyond at least 1000 G NIHS, preferably at least 500 G NIHS; and in which there is no contact between said portion of the oscillator and the antishock device for an acceleration less than 50 G NIHS.
The present invention also concerns a timepiece mechanical oscillator comprising a balance, a suspension with flexure guiding guiding and elastically restoring the balance into an oscillation plane and provided with shock protection, the oscillator comprising at least one antishock device according to the invention.
In this context and in contrast to the antishock devices described in EP3076245 and EP3324246, the antishock device of the present invention interacts with a shaft having two different bearing surfaces each characterized by a specific diameter. Accordingly, the shaft bearing surface characterized by the smaller diameter cooperates with the visco-elastic spring for wearing shocks whereas the shaft bearing surface characterized by the greater diameter cooperates with the rigid stop for accidental shocks. This enables minimization of friction and therefore of the loss of amplitude of the balance following wearing shocks by guaranteeing that the shaft is not damaged for accidental shocks of high intensity (>500 G NIHS).
The operation of the antishock device of the present invention is similar to that of the Incabloc® antishock device for wearing shocks in the range 20 G to 1000 G NIHS (or 50 G to 500 G NIHS) and for accidental shocks from 1000 G to 5000 G NIHS, except for the difference that the antishock device of the invention dissipates the energy of the wearing shocks from 20 G to 1000 G NIHS (or 50 G to 500 G NIHS) through the viscosity of the spring whatever the direction of the shock whereas the Incabloc® dissipates only the energy of radial shocks by dry friction and does not dissipate any of the energy of axial shocks. Dissipating the energy of the shock is important because the more rebounds there are following the shock between the oscillator and the antishock device the longer the oscillator will rub against the antishock device and the greater will be the resulting loss of amplitude of the oscillator. For wearing shocks in the range 0 G to 50 G NIHS the operation of the present invention is completely different from that of the Incabloc®. Indeed, the Incabloc® must simultaneously provide the function of guidance of the shaft of the balance and the antishock function. This implies that the spring of the Incabloc® is preloaded so that the bearing guiding the balance is not moved by very low wearing shocks (<50 G NIHS). This enables guidance of the balance except in the case of strong disturbance (>50 G NIHS).
For the oscillator of the present invention, guidance is provided by the flexible pivot. There is therefore no contact between the attached shaft and the antishock device for low wearing shocks (<50 G NIHS). Because of this, it is on the one hand not necessary to preload the visco-elastic spring and on the other hand the balance is less disturbed by this type of shock than in the case of the Incabloc®.
Embodiments of the invention are indicated in the description illustrated by the appended figures, in which:
The oscillator comprises a balance 10, a suspension 11 with flexure guiding guiding and elastically restoring the balance 10 into an oscillation plane. The suspension 11 with flexure guiding connects the balance 10 to a fixed base 5 of the oscillator 1. The base 5 is intended to be fixed to a fixed part of the timepiece movement. The oscillator 1 comprises a shaft 3 rigidly connected to the balance 10 by a rigid connection 4 that attaches this shaft 3 at the centre of rotation of the balance 10. In the example shown, the suspension with flexure guiding includes elastic blades 11 connecting the base 5 to the balance 10 via a rigid ring 6 secured to the rigid connection 4.
The stiffness of the visco-elastic element 20 is more particularly adjusted in such a manner that said portion of the oscillator (for example the shaft 3) cooperates with the visco-elastic element 20 when the oscillator is subjected to an acceleration between 50 G and 500 G NIHS and cooperates with the rigid stop 21 if the oscillator is subjected to an acceleration beyond at least 500 G NIHS.
According to the embodiment shown in
Still in accordance with the configuration shown in
In this configuration, if the oscillator is subjected to an acceleration between 50 G and 500 G NIHS, the visco-elastic element 20 damps the shock through the deformation of the visco-elastic material 202 of the flexible blades 201. If the oscillator is subjected to an acceleration beyond at least 500 g, the flexible blades 201 are sufficiently deflected for contact to occur between the portion (the shaft 3) of the oscillator at the rigid stop 21.
If the oscillator is subjected to an acceleration between 50 G and 500 G NIHS, the flexible blades 201 may more particularly be deflected radially and axially (for example relative to the central shaft 26). In this configuration the visco-elastic element 20 damps a shock suffered by the oscillator in the axial direction and in the radial direction, that is to say in the plane in which the flexible blades 201 extend, a plane perpendicular to the central shaft 26.
To this end, the flexible blades 201 may have an axial stiffness and a radial stiffness that are adjusted so that the portion of the oscillator (the shaft 3) cooperates with the visco-elastic element 20 if the oscillator is subjected to an acceleration, respectively axial and radially, between 50 G and 500 G NIHS, and cooperates with the rigid stop 21 if the oscillator is subjected to an acceleration, respectively axial and radial, beyond at least 500 G NIHS.
Still in accordance with the configuration shown in
In accordance with one embodiment the first housing 24 is blind. A stone 23 may be positioned in the bottom of the first housing 24.
The flexible blades 201 may be made of silicon. The visco-elastic material 202 may then be contained between the flexible blades 201 or in the flexible blades 201. For example, the visco-elastic material 202 may be deposited in a cavity formed in the flexible blade 201. Let us note that, as silicon withstands little local plastic deformation, the intermediate part 22 (and the stone 23) that is called upon to be in direct contact with the portion of the oscillator may be made from a material other than silicon, more resilient than silicon. The visco-elastic material 202 advantageously has a low shear modulus, i.e. a shear modulus preferably less than 10 GPa, a loss factor of at least 0.1. The visco-elastic material 202 preferably has a shear modulus at least ten times lower than the shear modulus of the flexible blade or blades 201. To this end, the visco-elastic material 202 may comprise a polymer, preferably an elastomer.
Alternatively, the flexible blades 201 may be made from a metal or metal alloy, for example with the aid of an LIGA (Lithography, Electroplating, and Moulding) type method or by laser cutting.
The role of the flexible blades 201 is to enable movement of the visco-elastic element 202 if the oscillator 1 is subjected, in the event of a shock, to an acceleration between 20 G and 1000 G (typically between 50 G and 500 G), which enables damping of the shock (dissipation of all or part of the energy of the shock) without jamming and/or braking the principal mode of oscillation of the oscillator 1.
In accordance with one embodiment each shaft 3 comprises at least a shaft end 30, a bearing surface 31 at the end having a small diameter and connected to the shaft end 30, a proximal bearing surface 32 of greater diameter than the bearing surface 31 at the end and a shoulder 33 connecting the proximal bearing surface 32 to the base 34 of the shaft 3.
If the oscillator 1 suffers a shock in the radial direction with a radial acceleration between 50 G and 500 G NIHS, the bearing surface 31 at the end cooperates with the visco-elastic element 20. The proximal bearing surface 32 cooperates with the rigid stop 21 if the radial acceleration is beyond at least 500 G NIHS. For example, the bearing surface 31 at the end cooperates with the lateral edges of the first housing 24 and the proximal bearing surface 32 cooperates with the lateral edges 21′ of the second housing 25.
If the oscillator 1 suffers a shock in the axial direction with an axial acceleration between 50 G and 500 G NIHS, the shaft end 30 cooperates with the visco-elastic element 20. The shoulder 33 cooperates with the rigid stop 21 if the radial acceleration is beyond at least 500 G NIHS. For example, the shaft end 30 cooperates with the bottom (the stone 23) of the first housing 24 and the shoulder 33 cooperates with a lower plane 21″ of the rigid stop 21.
Let us note that for shocks of very low intensity (<50 G NIHS), the shaft 3 does not come into contact with the antishock device 2. It is the mass and stiffness properties of the oscillator 1 and likewise the clearances between the shaft 3 and the intermediate part 22 (and the stone 23) that determines this level of shock for a first contact between the oscillator 1 and the antishock device 2.
It is the mass and stiffness properties of the oscillator 1, the clearances between the shaft 3 and the rigid stop 21 and finally the axial and radial stiffnesses of the visco-elastic element 20 that determine this level of shock for a first contact between the oscillator 1 and the rigid stop 21. Thus the visco-elastic element 20 serves above all to prevent the shaft 3 coming into contact with the rigid stop 21 for wearing shocks at least less than 500 G NIHS.
The antishock device 2 can deform and damp post-shock vibrations radially and axially; it also enables dissipation of the tip/tilt rotation movements that may occur (and even be superimposed on the radial and axial movements) following shocks of the oscillator on the stop. The behaviour of the anti-shock device 2 may be similar for axial and radial shocks.
Compared to the known antishock devices, the oscillator 1 of the invention comprising two antishock devices 2 enables reduction of the diameter of the bearing surface 31 at the end collaborating with the antishock device in order to minimize friction for shocks at least less than 500 G NIHS. There is also better dissipation of the energy of tip/tilt axial, radial shocks at least less than 500 G NIHS compared to known antishock devices.
Other possible configurations of the visco-elastic element 20 enabling the function of flexure guiding of the flexible blades 201 to be achieved can also be envisaged. For example,
In a further embodiment shown in
In the variants of the antishock device 2 shown in
The reservoirs 203 may have dimensions such as, as in the spiral configuration of the visco-elastic element 20, to enable the deposition of a visco-elastic polymer, for example by capillarity, between the two facing faces of the elastic blades 201, thus producing a sandwich structure of which the visco-elastic material 202 constitutes the core.
| Number | Date | Country | Kind |
|---|---|---|---|
| 00461/19 | Apr 2019 | CH | national |
