This application claims priority from European Patent Application No 14199040.8 filed on Dec. 18, 2014; the entire disclosure of which is incorporated herein by reference.
The invention concerns a timepiece oscillator comprising a time base with at least one resonator formed by a tuning fork, which includes at least two mobile oscillating parts, said mobile parts being fixed to a connection element, comprised in said oscillator, by flexible elements whose geometry determines a virtual pivot axis having a determined position with respect to said connection element, said respective mobile part oscillates about said virtual pivot axis and the centre of mass of said mobile part coincides in the rest position with said respective virtual pivot axis.
The invention also concerns a timepiece movement including a structure to which one such oscillator is fixed.
The invention also concerns a timepiece or watch including at least one such movement.
Timepiece time bases are always a compromise between good operating precision, acceptable efficiency, sufficient compactness and resistance for use in a watch, and economic production.
Sprung balance resonators are sensitive to external phenomena, the production and development thereof also requires highly qualified personnel, and it is difficult to achieve manufacturing reproducibility.
The invention proposes to make a high quality factor time base for mechanical timepiece movements, in order to ensure a high level of autonomy, and good operating precision, while satisfying quality standards, particularly in terms of behaviour with regard to shocks, temperature, and magnetism.
The invention also proposes to provide a simple and economic alternative to the sprung balance.
To this end, the invention concerns a timepiece oscillator comprising a time base with at least one resonator formed by a tuning fork, which includes at least two mobile oscillating parts, said mobile parts being secured to a connection element, comprised in said oscillator, by flexible elements whose geometry determines a virtual pivot axis having a determined position relative to said connection element, said respective mobile part oscillates about said virtual pivot axis, the centre of mass of the mobile part coincides in the rest position with said respective virtual pivot axis, characterized in that, for at least one said mobile part, said flexible elements are formed of intersecting resilient strips extending at a distance from each other in two parallel planes, and whose directions, in projection on one of said parallel planes, intersect at said virtual pivot axis of said mobile part concerned.
According to a feature of the invention, said resonator includes two said mobile parts whose centres of mass correspond to virtual pivot axes aligned with a main centre of said connection element.
According to a feature of the invention, said two mobile parts are symmetrical with respect to an axis of symmetry passing through a main centre of said connection element.
According to a feature of the invention, said connection element couples the motions of said two mobile parts by elastic forces.
According to a feature of the invention, said connection element is suspended by at least one resilient connection from a support arranged to be fixed on a structure of a timepiece movement.
According to a feature of the invention, said resilient connection is formed by resilient strips whose directions converge towards said main centre of said connection element.
According to a feature of the invention, at least one said mobile part includes a substantially circular arc about its said virtual pivot axis, said arc comprising an inertia block at each end thereof, and said flexible elements cooperating with said arc.
According to a feature of the invention, at least one said resonator is a one-piece assembly comprising said connection element, at least one said mobile oscillating part and said resilient strips which connect said mobile part to said connection element.
According to a feature of the invention, at least one said resonator is a one-piece assembly comprising said connection element, and a plurality of said mobile oscillating parts each including said resilient strips which connect the parts to said connection element.
According to a feature of the invention, said oscillator is one-piece assembly comprising said connection element and a plurality of said resonators.
According to a feature of the invention, said oscillator is one-piece assembly further comprising a support integral with the structure of a timepiece movement, and a resilient connection connecting said support to said connection element.
According to a feature of the invention, said one-piece assembly is made of silicon and/or a silicon oxide, or diamond-like-carbon (DLC), or quartz.
According to a feature of the invention, said resilient strips forming said flexible elements comprise an oxidation layer providing heat compensation.
According to a feature of the invention, said oscillator includes stop surfaces limiting the motion of each said mobile part.
The invention also concerns a timepiece movement comprising a structure to which one such oscillator is fixed, either directly by its connection element, or by a support to which said connection element is connected by a resilient connection.
The invention also concerns a timepiece or watch including at least one movement.
Other features and advantages of the invention will appear upon reading the following detailed description, with reference to the annexed drawings, in which:
The present invention refers to “centres of mass” which can also be understood to mean “centres of inertia”.
The invention concerns a timepiece oscillator 200 including a time base with at least one resonator 100 formed by a tuning fork which comprises at least two mobile oscillating parts 11, 12.
These mobile parts 11, 12, are fixed to a connection element 2, comprised in oscillator 200, by flexible elements 31, 41 or respectively 32, 42, whose geometry determines a virtual pivot axis O1, O2, having a determined position with respect to connection element 2.
The mobile part 11, 12, whose centre of mass coincides in the rest position with said respective virtual pivot axis O1; O2, oscillates about the respective virtual pivot axis O1, O2.
According to the invention, for at least one of the two mobile parts 11, 12, flexible elements 31, 41, or 32, 42, are formed of intersecting resilient strips extending at a distance from each other in two parallel planes, and whose directions, in projection on one of the parallel planes, intersect at the virtual pivot axis O1, O2 of the mobile part 11, 12 concerned. These intersecting strips allow the weights to rotate, and substantially prevent translation of the weights in the three X, Y, Z directions and also provide good resistance to small shocks.
In a particular advantageous variant, illustrated by
The design of this resonator thus makes it possible to obtain a mean of the oscillations of each of the two mobile parts 11, 12: one oscillates more quickly if the other oscillates more slowly, the two centres of mass move, by a very small value, in the same direction X, but in different ways, which compensates for defects in the centres of mass.
The use of a tuning fork according to the invention can adjust the timing defect to a very low value, of a few seconds per day, since moving the centres of mass perpendicularly to the connection direction X does not affect chronometry.
The case of an symmetrical tuning fork is merely a particular case, and the invention also functions with an asymmetrical tuning fork.
The resulting movement relative to the plate of a movement on which such an oscillator 200 is fixed, is virtually zero. No loss on the support guarantees a high quality factor, much higher than that of a sprung balance.
In a particular embodiment, as seen in
More specifically, these two mobile parts 11, 12 are symmetrical with respect to main centre O.
Even more specifically, these two mobile parts 11, 12, are identical.
In an advantageous manner specific to the invention, connection element 2 couples the motions of the two mobile parts 11, 12, by elastic forces. Element 2 is arranged to couple the two mobile parts 11, 12, to ensure a symmetrical motion of said parts with respect to main centre O, preferably by means of a symmetrical arrangement of the attachments of flexible elements 31, 41, 32, 42, to said connection element 2.
In an advantageous embodiment, and as seen in a non-limiting manner in
In a variant, as seen in
In another variant, as seen in
In an advantageous embodiment of the invention, as seen in
It is understood that excitation of the resonator can be achieved either on an arc, or an inertia block, this latter alternative being the most convenient to achieve.
In a particular non-limiting embodiment, the resilient strips which form flexible elements 31, 41, 32, 42, are less stiff than the respective arc 110; 120, which is in turn less stiff than the respective inertia blocks 111, 112, 121, 122. The latter are preferably infinitely stiff. In another variant, arcs 110, 120 and inertia blocks 111, 112, 121, 122, are of equal stiffness, and only resilient strips 31, 41, 32, 42, are less stiff than the arcs and inertia blocks.
In another advantageous embodiment, as seen in
Preferably, the resilient strips forming flexible elements 31, 41, 32, 42 are in symmetrical pairs in projection with respect to an axis passing through the virtual pivot axis concerned O1, O2, and through a main centre O on connection element 2.
In a preferred embodiment, when resonator 100 includes two mobile parts 11 and 12, the virtual pivot axes O1, O2 and main centre O are aligned.
In an advantageous embodiment, as seen in all the Figures, at least one such resonator 100 is a one-piece assembly comprising connection element 2, at least two mobile oscillating parts 11, 12 and resilient strips 31, 41, 32, 42 which connect the mobile part to connection element 2.
More specifically, at least one such resonator 100 is a one-piece assembly comprising connection element 2, and a plurality of mobile oscillating parts 11, 12, each comprising resilient strips 31, 41, 32, 42, which connect the mobile part to connection element 2.
Even more specifically, oscillator 200 is a one-piece assembly comprising connection element 2 and a plurality of such resonators 100.
In particular, oscillator 200 is a one-piece assembly further comprising a support 5 arranged to be fixedly secured to the structure of a timepiece movement 300, and a resilient connection 60 connecting support 5 to connection element 2.
Preferably, such a one-piece assembly is made of silicon and/or a silicon oxide, or DLC, or quartz, or any micro-material made in “MEMS” or “LIGA” technologies.
The use of such technologies makes it easier to provide adjustment means, for example notched areas on two opposing surfaces of the same one-piece component, to modify their relative position, and thereby the position of the centre of mass of a mobile part. In order to make an adjustment it is also possible to use usual means for making an adjustment to a timepiece balance, such as additional weights to increase inertia and lower frequency, and/or additional adjustment weights (adjustment screw, off-centre inertia blocks) to finely adjust the frequency or position of the centre of mass, or similar means.
To obtain a lower frequency of the oscillator, it is possible to add inertia, particularly by metal weights, pivoting on the inertia blocks or the arcs, or similar, of the mobile parts, or guided in translation with respect to these elements. For example, and in a non-limiting manner, a metal weight extending in direction Y may be guided, or even simply fixed, to two inertia blocks of the mobile part that are symmetrical with respect to axis X.
Creating such a tuning fork in a silicon part or similar, allows for high precision, and excellent relative adjustment of the centre of mass of each mobile part with the virtual pivot axis concerned. Each mobile part 11, 12 is therefore guided by means of intersecting strips, which are manufactured using double side silicon wafer technology. The space separating the intersecting strips may also have a very low value, which ensures maximum compactness. For example, the removal of an oxide layer formed between two layers is equivalent to 4 micrometres of play, which is sufficient to ensure proper operation with no friction between the strips.
This technology permits the manufacture of very thin strips, which can lower the oscillation frequency to a very low value, of around 40 Hz. In a specific embodiment, the resilient strips forming said flexible elements 31, 41, 32, 42, include an oxidation layer providing heat compensation.
The lever effect of mobile parts 11, 12, can produce a sufficiently large movement of the end inertia blocks 111, 112, 121, 122 to allow such an oscillator 200 or at least such an oscillator 100, to be associated with a mechanical escapement mechanism, as seen in
In a preferred, entirely symmetrical construction, the symmetrical motion of the inertia blocks, and of the centres of mass of the two mobile parts 11, 12, at the same point, or at least in immediate proximity to the same point, as the intersection of the strips, limits to a maximum the motion of the overall centre of mass of the complete system, and thus reactions on the support.
In a particular embodiment, oscillator 200 includes stop surfaces 80, 91, 92, limiting the motion of each mobile part 11, 12, comprised in said oscillator 200. This ensures resistance against the greatest shocks.
The invention also concerns a timepiece movement 300 comprising a structure to which is fixed an oscillator 200, either directly by its connection element 2, or by means of a support 5 to which the connection element 2 is connected by a resilient connection 60.
The invention also concerns a timepiece 400, particularly a watch, including at least one such timepiece movement 300.
The Figures detail certain specific, non-limiting embodiments.
Other variants are also possible, for example with a mobile part suspended by an RCC Remote Center Compliance type connection with four necks or similar.
This resilient connection between connection element 2 and support 5 ensures good shock absorption
The Figures are very schematic and illustrate a general case where the intersecting strips are embedded obliquely in the connection element that carries them. An advantageous configuration consists in embedding the strips in a surface that is orthogonal to the end of each strip where it is embedded in the connection element.
The invention makes it possible to obtain a one-piece mechanism that is easy to install, reliable, very reproducible, with a high quality factor, low energy consumption, and ensuring a high level of autonomy of the movement.
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