Patent Application
20180253061
This application claims priority from European Patent Application No. 17159361.9 filed on Mar. 6, 2017; the entire disclosure of which is incorporated herein by reference.
The present invention concerns a timepiece provided with a device for positioning a movable element in a plurality of discrete positions. In particular, the invention concerns a device for positioning a date ring in a plurality of display positions.
Conventionally, discs or rings used for the display of calendar data (date, day of the week, month, etc.) are held in any one of a plurality of display positions by a jumper (also called a jumper-spring). This jumper constantly presses against a toothing of the disc or ring in question. When changing from one display position to another, the jumper moves away from the toothing, undergoing a rotational motion in an opposite direction to the return force exerted by the spring of the jumper. Thus, the toothing is configured such that torque exerted on the jumper by its spring is minimal in the display positions and, when the disc or ring are driven, the jumper goes through a peak in torque. If it is desired to ensure positioning in the event of shocks, the toothing and the jumper must be designed, in particular the stiffness of the spring, such that the aforementioned peak in torque (maximum torque to be overcome to change the display) is relatively high. It is therefore difficult to dimension calendar discs or rings, in particular date rings, in timepiece movements, since a compromise must be found between guaranteeing the positioning function and minimising the energy consumption of the system when changing from one display position to another. Indeed, the spring cannot be too flexible, because it is necessary to ensure the immobilization of the disc or the ring, but it cannot be excessively stiff, because this would require a very high torque to be provided by a mechanism of the timepiece movement. In this latter case, the disc or ring drive mechanism may be bulky and there is a significant energy loss for the energy source incorporated in the timepiece movement during the driving of the disc or the ring.
It is an object of the present invention to overcome the problems associated with conventional jumpers and to propose a device for positioning a movable element, capable of occupying successively a plurality of discrete stable positions, which is reliable, relatively compact and which requires relatively little energy from the timepiece movement to change from one discrete stable position to another.
To this end, the present invention concerns a timepiece movement, comprising a movable element, which is capable of being driven along an axis of displacement and of being momentarily immobilised along said axis of displacement successively in a plurality of discrete stable positions, and a device for positioning this movable element in any one of the plurality of discrete stable positions. The positioning device comprises a lever and a magnetic system formed of a first magnet, a second magnet integral with the lever and a magnetic structure integral with the movable element, this magnetic structure being formed of a highly magnetically permeable material and having, relative to the axis of displacement, a transverse dimension that varies periodically to define a plurality of periods which respectively correspond, for the movable element, to the distances to be covered between the positions of the plurality of discrete stable positions. The first and second magnets are arranged such that their magnetic axes are in opposite directions, in projection onto a reference axis substantially passing through the respective centres of these first and second magnets, and respectively on either side of the magnetic structure so that, when the movable element is driven along its displacement axis from any one stable position to the next stable position, the magnetic structure moves between the first and second magnets. The magnetic system is also arranged such that, when the movable element is driven along its axis of displacement from any one stable position to the next stable position, a first magnetic torque exerted on the lever carrying the second magnet has a first direction over a first section and a second direction, opposite to the first direction, over a second section of the corresponding distance, the first direction corresponding to a return torque towards the movable element for a contact portion of said lever, whereas the second direction tends to move this contact portion away from the movable element. The magnetic structure is arranged along the axis of displacement such that, in each position of the plurality of discrete stable positions, the first magnetic torque is applied in the aforementioned first direction.
The magnetic system produces a second magnetic torque that is exerted directly on the magnetic structure and thus on the movable element. In a main variant, this second magnetic torque has a zero value, corresponding to a stable magnetic equilibrium position for the movable element, while the first magnetic torque is applied to the lever in the first direction.
In an advantageous variant, the lever is associated with a spring that exerts an elastic force on the lever so as to produce a mechanical torque that pushes the contact portion of the lever towards a toothing comprised in the movable element and which the contact portion penetrates to mechanically position the movable element.
In a main application, the movable element forms a display support for calendar information. In particular, the movable element is a date ring.
The invention will be described in detail below with reference to the annexed drawings, given by way of non-limiting example, and in which:
Referring to
Magnetic system 2 includes a first fixed magnet 4, a highly magnetically permeable element 6 and a second magnet 8 which is movable, along a displacement axis coincident here with the axis of alignment 10 of these three magnetic elements, with respect to the assembly formed by first magnet 4 and element 6. Element 6 is arranged between the first magnet and the second magnet, close to the first magnet and in a determined position relative to the latter. In a particular variant, the distance between element 6 and magnet 4 is less than or substantially equal to one tenth of the length of this magnet along its axis of magnetization. Element 6 consists, for example, of a carbon steel, tungsten carbide, nickel, FeSi or FeNi, or other alloys with cobalt such as Vacozet® (CoFeNi) or Vacoflux® (CoFe). In an advantageous variant, this highly magnetically permeable element consists of an iron or cobalt-based metallic glass. Element 6 is characterized by a saturation field BS and a permeability μ. Magnets 4 and 8 are, for example, made of ferrite, of FeCo or PtCo, of rare earths such as NdFeB or SmCo. These magnets are characterized by their remanent field Br1 and Br2.
Highly magnetically permeable element 6 has a central axis which is preferably substantially coincident with the axis of magnetization of first magnet 4 and also with the axis of magnetization of second magnet 8, this central axis being coincident here with axis of alignment 10. The respective directions of magnetization of magnets 4 and 8 are opposite. These first and second magnets thus have opposite polarities and are capable of undergoing a relative motion between them over a certain relative distance. The distance D between element 6 and moving magnet 8 indicates the distance of separation between this moving magnet and the other two elements of the magnetic system. It will be noted that axis 10 is arranged here to be linear, but this is a non-limiting variant. Indeed, the axis of displacement may also be curved, as in the embodiments that will be described hereinafter. In this latter case, the central axis of element 6 is preferably approximately tangent to the curved axis of displacement of the moving magnet and thus the behaviour of such a magnetic system is, at first glance, similar to that of the magnetic system described here. This is particularly so if the radius of curvature is large relative to the maximum possible distance between element 6 and moving magnet 8. In a preferred variant, as represented in
The two magnets 4 and 8 are arranged to repel each other so that, in the absence of highly magnetically permeable element 6, a force of magnetic repulsion tends to move these two magnets away from each other. However, surprisingly, the arrangement between these two magnets of element 6 reverses the direction of the magnetic force exerted on the moving magnet when the distance between this moving magnet and element 6 is sufficiently small, so that the moving magnet is then subjected to a force of magnetic attraction. Curve 12 of
The magnetic force exerted on the moving magnet is a continuous function of distance D and thus has a value of zero at distance Dinv at which the magnetic force reversal occurs (
Referring to
Timepiece movement 20 comprises a date ring 22 which is capable of being driven in rotation in the clockwise direction, along a circular axis of displacement 24, and of being momentarily immobilised along this axis of displacement successively in a plurality of discrete stable positions. The timepiece movement comprises a device for positioning the date ring in any one angular position of the plurality of discrete stable positions, this positioning device being formed of two complementary systems that are associated, namely a mechanical system, formed by a lever 30 associated with a spring 32, and by a toothing 26 comprising a plurality of hollows or notches 28, in which is successively inserted an end portion 31 of the lever (which defines a contact portion of the toothing) when the ring is successively positioned in the angular positions of said plurality of discrete stable positions, and a magnetic system formed of a first fixed magnet 34, a second magnet 36 integral with the lever and a magnetic structure 38 integral with ring 22.
Magnetic structure 38 is formed of a highly magnetically permeable material and, relative to the axis of displacement of ring 22, has a transverse dimension that varies periodically, defining a plurality of angular periods e which correspond, for the movable ring, to the angular distances that it has to cover between its display positions (plurality of discrete stable positions). More particularly, in the variant described in
First magnet 34 and second magnet 36 are respectively arranged on either side of magnetic structure 38 with their magnetic axes substantially aligned on a reference axis AREF that they define (this axis passes substantially through their respective centres). The magnetic axes of the two magnets have opposite directions (magnets with opposite polarities). Next, these first and second magnets, and consequently lever 30, are arranged such that, when the date ring is driven along its axis of displacement 24, the magnetic structure moves between the two magnets. The physical phenomenon of the magnetic system described in
Further, the magnetic system of the positioning device of the invention further produces a second magnetic torque on ring 22 by means of a magnetic force exerted by the magnetic system directly on magnetic structure 38, this second magnetic torque strengthens the first magnetic torque since the magnetic structure (the magnetic toothing) is arranged such that the second magnetic torque is relatively low, preferably almost zero, when the ring is in any one of its angular display positions, and it increases relatively quickly on either side of each display position to resist, firstly, any movement of the ring out of the display position that it occupies, by returning the ring towards this display position. The evolution of the second magnetic torque is represented in
The graph of
a first curve 50 showing the magnetic torque exerted on the lever when the latter is in an open position (corresponding to a position in which end portion 31 is located outside toothing 26) and the ring is driven over an angular period θP between two successive display positions (i.e. from any one display position to the next display position);
a second curve 52 showing the magnetic torque exerted on the lever when the latter is in a closed position (corresponding to a position in which end portion 31 is located at the bottom of toothing 26, i.e. in a notch 28); and
a third curve 54 approximately representing the operating magnetic torque applied to the lever over each angular period, this operating magnetic torque defining the first magnetic torque.
It will be noted that curve 52 is theoretical, since the lever cannot be held in a closed position during an angular movement of the ring over a distance corresponding to an angular period in the presence of the ring with its toothing 26. However, such a curve can be observed by taking a test ring with a profile in its general plane that corresponds to that of the magnetic structure. Operating torque curve 54 is an approximation of actual behaviour since the position of the lever depends not only on the first magnetic torque, but also on the profile of toothing 26, the profile of end portion 31 of the lever and the mechanical torque produced by the spring (it will be noted that the operating torque represented corresponds in fact to an embodiment without a spring and without a toothing). In the variant represented in
The first magnetic torque exerted by the first magnet and the magnetic structure on lever 30 carrying the second magnet, as a function of the angular position of ring 22 (and thus of magnetic structure 38) over an angular period between two display positions of the ring, has a first direction (negative direction in
It is observed that first part TR1a of the first section of a given period directly follows second part TR1b of the first section of the period that precedes this given period. Thus, between the two sections TR2, the first magnetic torque is applied in the first direction over continuous sections each formed of a first part TR1a and a second part TR1b respectively located on either side of a stable position Pn. Preferably, the first magnetic torque (operating torque 54) has a maximum negative value (i.e. maximum in absolute value) for an angular position PCM close to each discrete stable position Pn. In an advantageous variant, this maximum negative value is substantially attained in each discrete stable position Pn.
It will be noted that end portion 31 of the lever which presses against the toothing here includes the second magnet 36. In the represented variant, the non-magnetic support forming this end portion and carrying the second magnet is arranged to abut against toothing 26 such that said second magnet can approach magnetic teeth 40 without, however, entering into contact with the ring. In a variant, the second magnet has a surface in contact with the toothing, this contact surface being hardened by a suitable treatment. In another variant, the portion of the second magnet located on the toothing side is protected by a protective layer deposited on the second magnet, this protective layer being in contact with the toothing.
The graph of
a first curve 56 showing the magnetic torque applied to the magnetic structure, and thus directly to the ring when the lever is in an open position and the ring is driven over an angular period θP;
a second curve 58 showing the magnetic torque applied to the magnetic structure when the lever is in a closed position; and
a third curve 60 approximately representing the operating magnetic torque applied to the magnetic structure over each angular period, this operating magnetic torque defining a second magnetic torque occurring in the positioning device of the invention.
It will be noted again that curve 58 is a theoretical curve, since the lever cannot be held in a closed position when the ring is being driven over an entire angular period because of toothing 26, and operating torque curve 60 is an approximation of real behaviour since the position of the lever depends, in particular, on the profile of toothing 26 and the profile of end portion 31 of the lever.
The second magnetic torque has a substantially zero value in position Pn defining the start of an angular period between two display positions. In each position Pn (where n is a natural number), the magnetic structure and consequently ring 22 are in a stable magnetic position, since the negative slope of curve 60 in this position Pn indicates that the second magnetic torque tends to return the ring to this position when it moves away therefrom (positive direction of the angle of rotation is the clockwise direction). Preferably, the ring and the lever are arranged so that each position Pn of the plurality of discrete stable positions corresponds to a stable magnetic position, as is the case in the first embodiment. The first magnetic torque is applied to the lever in the first direction when the ring is in any stable magnetic equilibrium position. In an advantageous variant represented in
The second magnetic torque 60 has, in each angular period, a negative value over a first section TR3 and a positive value over a second section TR4. These two sections each extend substantially over a half-period. It will be noted that this second magnetic torque has a zero value between these two sections, this position corresponding to an unstable magnetic equilibrium position. In this position, reference axis AREF moves substantially between two magnetic teeth 40 and consequently between two notches or hollows 28 of toothing 26, these notches or hollows being radially aligned with magnetic teeth 40.
The pressure from spring 32 on the lever produces a mechanical torque applied by the lever to ring 22. It will be noted that this mechanical torque can be relatively low, given the first and second magnetic torques produced by the magnetic system that are exerted on the ring in the same direction as the mechanical torque when the ring is in any one of the plurality of display positions. It will also be noted that the mechanical torque can be greater than the first magnetic torque applied in the second direction, i.e. than its maximum positive value on second section TR2, such that lever portion 31 remains continuously bearing against lever toothing 26. However, in another variant, the mechanical torque is lower than this maximum positive value over a certain angular pivoting distance of the lever. However, in this latter case, the spring stiffness is advantageously selected such that said spring limits, in second section TR2, the distance separating magnet 36, carried by lever end portion 31, from magnetic structure 38. It this is not the case, then an element of the timepiece movement must have a stop function for the lever when portion 31 moves away from the toothing, so as to limit the distance separating it from the toothing in second section TR2 of each period.
It will be noted that the two magnetic forces, which are exerted respectively on the lever, via the magnet carried thereby, and on the ring, via the magnetic structure carried thereby or of which it is formed, are vectors that each have a certain amount of variable intensity and also a variable direction in the general plane of the ring and of the lever. These two parameters (intensity and direction) are involved in the first magnetic torque and in the second magnetic torque. The first magnetic torque is defined relative to the axis of pivoting of the lever, while the second magnetic torque is defined relative to the geometric axis of rotation of the ring.
In a variant embodiment, with a lever arranged symmetrically to the lever represented in
In
A second embodiment of the invention is represented in
As in the first embodiment, the first and second magnetic torques act in concert with the mechanical torque produced by spring 32 to position the ring in any one of the plurality of display positions and to hold it in this position when the ring is not driven by its drive mechanism arranged in the timepiece movement (mechanism known to those skilled in the art). It will be noted that the drive mechanism must overcome the first and second magnetic torques and the mechanical torque to drive the ring from one stable display position to the next stable display position. However, as already stated, the second magnetic torque is substantially conservative. Likewise, the first magnetic torque and the mechanical torque can return a certain amount of energy to the ring in the second half of the movement between two stable display positions. This also depends on the toothing profile and, of course, on the friction force of the lever on the ring toothing.
Apart from the two magnetic torques that act in concert on the ring to position and stabilise it, the positioning device according to the invention is remarkable in that the first magnetic torque that is exerted on the lever decreases quickly once the end portion 31 of the lever starts to leave one of notches 28 and then changes sign when the ring is driven further forward to change from one display position to another. In other words, the magnetic torque decreases as soon as the lever is moved away from the ring via its toothing, which thus quickly decreases the magnetic positioning torque immediately on drawing away from a discrete stable position. Indeed, when the lever moves away from the toothing, the first magnetic torque decreases quickly and is even reversed, which greatly facilitates passage over a tooth and therefore requires little energy. It will be noted that this behaviour is the reverse of the mechanical torque exerted by the spring on the lever, since the mechanical return force towards the ring increases when the end portion of the lever leaves a notch, or, more generally, when it draws away to allow passage over a tooth of the positioning toothing (which may also serve to drive the ring).
The magnetic elements 86 have an oblong shape with two truncated ends. In a variant, these magnetic elements simply have a rectangular shape. Referring to
Finally, a third embodiment of a timepiece movement 90 according to the invention is shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 17159361.9 | Mar 2017 | EP | regional |
