Patent Application
20190324401
The invention concerns a timepiece resonator mechanism comprising a structure and an anchor unit to which is suspended at least one inertia element arranged to oscillate with a first rotational degree of freedom RZ about a pivot axis extending in a first direction Z, said inertia element being subjected to return forces exerted by a flexure pivot comprising a plurality of first elastic strips, each fixed, at a first end to said anchor unit, and at a second end to said inertia element, each said elastic strip being deformable essentially in a plane XY perpendicular to said first direction Z, said resonator mechanism comprising axial stop means including at least a first axial stop and/or a second axial stop to limit the translational travel of said inertia element at least in said first direction Z, said axial stop means being arranged to abuttingly engage with said inertia element in order to protect said first strips at least against axial impacts in said first direction Z.
The invention also concerns a timepiece oscillator including at least one such resonator mechanism.
The invention also concerns a timepiece movement including at least one such oscillator and/or one such resonator mechanism.
The invention also concerns a watch including such a timepiece movement and/or such an oscillator and/or such a resonator mechanism.
The invention concerns the field of timepiece resonators and more particularly those that include elastic strips acting as return means for operation of the oscillator.
Shock resistance is a difficult issue for most timepiece oscillators, and in particular for crossed strip resonators. Indeed, during out-of-plane impact, the stress experienced by the strips rapidly reaches very high values, which, accordingly, reduces the travel that the part can make before yielding.
Shock absorbers for timepieces are available in many variants. However, their function, essentially, is to protect the fragile pivots of the arbor, and not the elastic elements, such as, conventionally, the balance spring.
European Patent Application No. EPEP3054357A1 in the name of ETA Manufacture Horlogère Suisse discloses a timepiece oscillator including a structure and distinct primary resonators, which are temporally and geometrically offset, each comprising a weight returned towards the structure by an elastic return means. This oscillator includes coupling means for the interaction between the primary resonators, including driving means for driving motion of a wheel set which includes driving and guiding means arranged to drive and guide a control means articulated to transmission means, each articulated, at a distance from the control means, to a weight of a primary resonator. The primary resonators and wheel set are arranged such that the articulation axes of any two primary resonators and the articulation axis of the control means are never coplanar.
European Patent Application No. EP3035127A1 in the name of SWATCH GROUP RESEARCH & DEVELOPMENT Ltd discloses a timepiece oscillator including a resonator formed by a tuning fork which includes at least two oscillating moving parts, fixed to a connection element by flexible elements whose geometry determines a virtual pivot axis of determined position with respect to a plate, and about which oscillates the respective moving part, whose centre of mass coincides in the rest position with the respective virtual pivot axis.
For at least one moving part, the flexible elements are formed of crossed elastic strips at a distance from each other in two parallel planes, and whose directions, in projection onto one of the parallel planes, intersect at said virtual pivot axis of the moving part.
New mechanism structures make it possible to maximise resonator quality factor, through the use of a flexure bearing with the use of a lever escapement having a very small angle of lift, according to Swiss Patent Application No CH713150 in the name of ETA Manufacture Horlogère Suisse and derivative patents, whose teaching can be directly used in the present invention, and whose resonator can be further improved as regards its shock sensitivity, in certain particular directions. It is thus a matter of protecting the strips from breakage in the event of impact. It is clear that the anti shock systems so far proposed for resonators with flexure bearings only protect the strips from impact in certain directions, but not in all directions, or that they have the drawback of letting the point of attachment of the flexure pivot move slightly during its oscillatory rotation, which should be avoided as far as possible.
It is thus a matter of protecting the strips from breakage in the event of impact. In other words, to make a good rotating resonator with a flexure bearing, the latter, which forms a flexure pivot and defines a virtual pivot axis, must be both very flexible for oscillatory rotation in a first rotational degree of freedom RZ, but it must be very stiff in the other degrees of freedom (X, Y, Z, RX, RY) in order to avoid undesired motions of the centre of mass of the resonator. Indeed, such undesired motions can cause errors of run, if the orientation of the resonator changes in the field of gravity (referred to as ‘error in the positions’). Very stiff suspension of the attachment point of the pivot is necessary according to the degree of freedom of the oscillation, to avoid disturbing the isochronism of the resonator, and to avoid dissipating energy in motions due to reaction forces.
The invention proposes to limit the out-of-plane displacements of the strips of a strip resonator, and thus to ensure improved resistance of the system,
To this end, the invention concerns a strip resonator mechanism according to claim 1.
The invention also concerns a timepiece oscillator including at least one such resonator mechanism.
The invention also concerns a timepiece movement including at least one such resonator mechanism.
The invention further concerns a watch including such a timepiece movement and/or a such a resonator mechanism.
Other features and advantages of the invention will appear upon reading the following detailed description, with reference to the annexed drawings, in which:
The idea here, is to suspend a flexure pivot 200 of a timepiece resonator 100 to a suspension system that is flexible in 5 degrees of freedom but stiff in the only degree of freedom in which said pivot works and which is that of the oscillation of at least one inertia element 2, comprised in this resonator 100. The 5 flexible degrees of freedom, which correspond to the directions in which impacts could damage the pivot strips, have a travel limited by stops, against which the inertia element of the resonator comes to rest in the event of impact.
The present description more particularly illustrates the case of a mechanical watch movement, provided with a resonator 100 with a rotary flexure bearing, which forms a flexure pivot 200 defining a virtual pivot axis D in a first direction Z. This flexure pivot 200 is, in this particular case, made from flexible strips 3, which, according to the invention, are protected from breakage in the event of impact by an anti shock system comprising a flexible suspension system, which connects the anchor point of flexure pivot 200 to a structure 1, especially the plate of the movement, in combination with a set of stops which are arranged to limit the travel of the inertia element of the resonator via bearing surfaces.
According to the invention, this anti shock system is flexible in 5 degrees of freedom and stiff in the degree of freedom corresponding to oscillation of the resonator, which is first direction Z here. The stops allow inertia element 3 to move freely in the oscillatory degree of freedom of the resonator but limit its travel in the other 5 degrees of freedom.
The invention therefore concerns a timepiece resonator mechanism 100, comprising a structure 1 and an anchor unit 30, to which at least one inertia element 2 is suspended. Each inertia element 2 is arranged to oscillate in a first rotational degree of freedom RZ about a pivot axis D extending in a first direction Z. The centre of inertia resulting from all the inertia elements 2 is aligned on pivot axis D.
The invention is illustrated in the Figures, in non-limiting manner, with a single inertia element 2; those skilled in the art will know how to apply the teaching of the present Application to the case of a plurality of inertia elements, particularly superposed elements.
Inertia element 2 is subjected to return forces exerted by a flexure pivot 200 comprising a plurality of first elastic strips 3, each fixed, at a first end to anchor unit 30, and at a second end to inertia element 2. Each elastic strip 3 is deformable essentially in a plane XY perpendicular to first direction Z.
Resonator mechanism 100 includes axial stop means, which include at least a first axial stop 7 and/or a second axial stop 8 to limit the translational travel of inertia element 2, at least in first direction Z. These axial stop means are arranged to abuttingly engage with inertia element 2 in order to protect first strips 3, at least against axial impacts in first direction Z.
According to the invention, anchor unit 30 is suspended to structure 1 by a flexible suspension system 300, which is arranged to allow anchor unit 30 mobility in five flexible degrees of freedom of the suspension system.
These five flexible degrees of freedom of the suspension system are:
a first translational degree of freedom in first direction Z;
a second translational degree of freedom in a second direction X orthogonal to first direction Z;
a third translational degree of freedom in a third direction Y orthogonal to the second direction X and to first direction Z;
a second rotational degree of freedom RX about an axis extending in second direction X;
and a third rotational degree of freedom RY about an axis extending in third direction Y.
In short, anchor unit 30 is suspended to structure 1 by flexible suspension system 300, in a manner that allows it some mobility in all degrees of freedom other than first rotational degree of freedom RZ in which only inertia element 2 must be able to move, to avoid any disturbance to its oscillation, which is essential for the invention. Anchor unit 30 carries flexure pivot 200 to which inertia element 2 is suspended, and the stiffness of suspension system 300 in first rotational degree of freedom RZ must be very considerably higher than the stiffness of flexure pivot 200 in this same rotational degree of freedom RZ.
In each of the other five flexible degrees of freedom of the suspension system listed above, the condition is reversed: the stiffness of the suspension system in each of these five flexible degrees of freedom of the suspension system must be much lower than that of flexure pivot 200 in the same degree of freedom considered.
Stiffness is defined here, for a degree of freedom T as:
in rotation C, =dMoment/dAngle;
in translation K1=dForce/dDisplacement.
The matrix below sets out the relative conditions between the stiffness of the suspension system and that of the pivot for each degree of freedom:
The essential degree of freedom of the pivot:
And the five flexible degrees of freedom of the suspension system:
Value N is preferably chosen to be higher than or equal to 10, and in particular higher than or equal to 100 or to 1000.
Value M is preferably chosen to be higher than or equal to 10, and in particular higher than or equal 50.
Thus, in first rotational degree of rotation RZ, flexible suspension system 300 is at least N times, in particular 10 times, stiffer than flexure pivot 200 in first rotational degree of freedom RZ.
Further, in the first translational degree of rotation, second translational degree of rotation, third translational degree of rotation, second rotational degree of freedom RX and third rotational degree of freedom RY, flexible suspension system 300 is at least M times, in particular 10 times, less stiff than flexure pivot 200 in said first translational degree of freedom, said second translational degree of freedom, said third translational degree of freedom, said second rotational degree of freedom RX and said third rotational degree of freedom RY.
Consequently, in the first translational degree of freedom, second translational degree of freedom, third translational degree of freedom, second rotational degree of freedom RX and third rotational degree of freedom RY, flexible suspension system 300 is at least N·M times, in particular 100 times, less stiff than it is in first rotational degree of freedom RZ.
More particularly, in first rotational degree of rotation RZ, flexible suspension system 300 is at least 100 times stiffer than flexure pivot 200 in first rotational degree of freedom RZ. In other words, the stiffness in the stiffest degree of freedom of the suspension system is at least 100 times greater than the stiffness of the flexure pivot of the resonator.
More particularly still, in first rotational degree of rotation RZ, flexible suspension system 300 is at least 1000 times stiffer than flexure pivot 200 in first rotational degree of freedom RZ.
More particularly, in the first translational degree of rotation, second translational degree of rotation, third translational degree of rotation, second rotational degree of freedom RX and third rotational degree of freedom RY, flexible suspension system 300 is at least 50 times less stiff than flexure pivot 200 in said first translational degree of freedom, said second translational degree of freedom, said third translational degree of freedom, said second rotational degree of freedom RX and said third rotational degree of freedom RY.
The stiffness of each of the 5 flexible degrees of freedom can be calculated using the relation:
Ki=fs*mi*ari/xi
where:
fs is a safety factor less than 1;
mi is the mass or inertia for the degree of freedom i;
ari is the acceleration in the degree of freedom i, which would cause breakage of the flexure pivot, in ‘direction’ i;
xi is the distance between the stop and said bearing surface of the resonator, in other words, the travel of the resonator in degree of freedom i up to the stop.
In a variant, flexible suspension system 300 includes a first elastic connection, which is arranged to allow it mobility in the first translational degree of freedom in first direction Z, and/or a second elastic connection arranged to allow it mobility in the second translational degree of freedom in second direction X, and/or a third elastic connection to allows it mobility in the third translational degree of freedom in third direction Y, and/or a fourth elastic connection to allow it mobility in rotation in second rotational degree of freedom RX, and/or a fifth elastic connection arranged to allow it rotational mobility in third rotational degree of freedom RY.
Advantageously, the axial stop means are also arranged to abuttingly engage with inertia element 2 in order to protect first strips 3 in second direction X, in third direction Y, in second rotational degree of freedom RX and in third rotational degree of freedom RY. These axial stop means include first radial bearing surfaces 79, 89, which are arranged to cooperate with complementary first bearing surfaces 279, 289, comprised in inertia element 2, and second bearing surfaces 78, 88, which are arranged to cooperate with complementary second bearing surfaces 278, 288, comprised in inertia element 2. More particularly, these stop means are carried by structure 1. The teaching of Swiss Patent Application No CH713137 in the name of Swatch Group Research & Development Ltd can be used for the present invention.
As seen in
Advantageously, the flexibility of the elastic means of the flexible suspension system in the five flexible degrees of freedom of the suspension system, is such that the frequencies of the natural vibration modes of the flexible suspension system in these five degrees of freedom are at least 10 times higher than the main oscillation frequency of the resonator during oscillation of inertia weight 2. More particularly, they are at least 50 times higher than the main oscillation frequency of the resonator during oscillation of inertia weight 2. Advantageously, this main oscillation frequency of the resonator is high, higher than 10 Hz, especially close to 20 Hz.
It is understood that numerous alternative arrangements are possible for bending and/or twisting some of these elastic connections, particularly by decoupling or coupling the degrees of freedom, which can result in five different elastic connections, and four intermediate weights between structure 1 and anchor unit 30. However, to save space which is always scarce inside a watch, it is advantageous to couple several degrees of freedom on certain connections.
In a variant, a plate, which includes at least two parallel and coplanar flexible strips, provides the first elastic connection with mobility in the first translational degree of freedom in first direction Z, the fourth elastic connection with rotational mobility in second rotational degree of freedom RX, and the fifth elastic connection with rotational mobility in the third rotational degree of freedom RY: it controls flexibility in degrees of freedom Z, RX and RY.
In another variant, mobility in the second translational degree of freedom in second direction X is provided by a set of flexible strips comprising at least two parallel and non coplanar flexible strips, and/or mobility in the third translational degree of freedom in third direction Y is provided by a set of flexible strips comprising at least two parallel and non coplanar flexible strips.
In yet another variant, mobility in the second translational degree of freedom in second direction X and in second rotational degree of freedom RX, is provided by a single flexible strip essentially deformable in a plane XY perpendicular to first direction Z and arranged to withstand a twist of +/−10° with respect to its longitudinal direction.
In a similar manner in another variant, mobility in the third translational degree of freedom in third direction Y and in third rotational degree of freedom RY, is provided by a single flexible strip essentially deformable in a plane XY perpendicular to first direction Z and arranged to withstand twisting by +/−10° with respect to its longitudinal direction.
Naturally, a lower number of elastic connections can be employed, if conditions as to the inequalities to be respected between stiffnesses are satisfied.
More particularly, elastic strips 3 of elastic pivot 200 are straight and the directions in which elastic strips 3 extend, in projection onto a plane perpendicular to this pivot axis D, intersect at pivot axis D. More particularly, these elastic strips are arranged according to the teaching of Swiss Patent Application Nos. CH712068 in the name of ETA Manufacture Horlogère Suisse and CH710524 in the name of Swatch Group Research & Development Ltd.
More particularly, the pivot is of the type having a large angular travel, in accordance with Swiss Patent Application No. CH00980/17 in the name of Swatch Group Research & Development Ltd.
In a non-illustrated variant, the mechanical interaction between the axial stop means and surfaces of inertia element 2 is supplemented by magnetic interaction between these axial stop means and these surfaces.
More particularly, inertia element 2 includes at least one inertia block 29 which is adjustable in position and/or orientation to adjust the position setting of its centre of mass and of its inertia.
Advantageously, mass MA of anchor unit 30, like the mass of every intermediate unit, such as first intermediate weight 303 or second intermediate weight mass 305, which is placed in the flexible suspension system between anchor unit 30 and structure 1, is less than a tenth of mass MO of inertia element 2.
The invention also concerns a timepiece oscillator mechanism 500 including such a timepiece resonator mechanism 100 and an escapement mechanism 400, arranged to cooperate with one another. Inertial element 2 includes here a pin 28 for this purpose.
The invention also concerns a timepiece movement 1000 including at least one such oscillator mechanism 500, and/or at least one such resonator mechanism 100. This movement 1000 carries, on structure 1, an energy source 1100 such as a barrel, powering a train 1200 providing the display and coupled to escapement mechanism 400.
In a variant, this movement is provided with a Swiss lever escapement.
In another variant, this movement is provided with a frictional rest escapement.
In yet another variant, this movement is provided with a magnetic rest escapement.
Advantageously, the flexure pivot is made of silicon and temperature compensated by a layer of silicon dioxide.
In a particular embodiment, flexible suspension system 300 and anchor unit 30 form a one-piece assembly.
In another particular embodiment, flexible suspension system 300 and flexure pivot 200 form a one-piece assembly.
Advantageously, at least one of the components of escapement mechanism 400 is made of silicon, or suchlike, to minimise its inertia, and notably is a pierced component, such as the escape wheel of
Advantageously, the inertia element is an at least locally latticework structure in order to minimise its mass/inertia ratio.
The invention also concerns a watch 2000 including at least one such movement 1000, and/or at least one such timepiece oscillator 500, and/or at least one such resonator mechanism 100.
The invention makes it possible to uncouple the useful degree of freedom of the flexure pivot from the degrees of freedom of the suspension system. In this manner, the suspension system protects the pivot from breakage in the event of impact in five degrees of freedom, without affecting the stiffness of the pivot which is useful in the degree of freedom that it defines. If the degrees of freedom were not uncoupled, the suspension system would allow the point of attachment of the strips to move, which would result in a significant decrease in the resonator quality factor. If the suspension system were extremely stiff, this would result in breakage of the pivot strips in the event of accidental impacts. Thus, the invention makes it possible to protect the flexure pivot from breakage without impairing the qualities of the resonator.
| Number | Date | Country | Kind |
|---|---|---|---|
| 18168765.8 | Apr 2018 | EP | regional |
