Mechanical timepiece movement comprising a magnetic pivoting balance

Abstract

An organ comprises a rotating element (22) and a magnetic device for rotationally guiding the rotating element, the magnetic device being arranged to exert a radial magnetic biasing force on the rotating element when a central axis (26) of the rotating element undergoes a radial displacement with respect to a given rotation axis (28). The magnetic device comprises a pair of annular magnets, a first annular magnet (32) of the pair of annular magnets being carried by the rotating element and a second annular magnet (34) being carried by a structure of the organ. When the central axis of the rotating element coincides with the rotation axis, the second annular magnet is parallel and axially superposed to the first annular magnet, the first and second annular magnets being in a magnetic attraction arrangement so as to exert a first axial magnetic force on each other and a first radial magnetic force substantially as soon as the central axis of the rotating element is radially displaced from the rotation axis. In particular, the organ is a timepiece movement and the rotating element is a balance.

Description

Technical Field

[0001] This invention relates to the field of pivoting and rotating elements in micromechanical applications, particularly in watchmaking. Specifically, this invention relates to mechanical watch movements comprising a mechanical resonator, wherein the balance wheel of the mechanical resonator is magnetically pivoted, i.e., it is essentially guided by a magnetic mechanism. Background Technology

[0002] A method for pivotally guiding a watch component (particularly a balance wheel) is known from document WO 2012 / 062524, as well as a device for pivotally guiding such a watch component. This document proposes using a magnetic pivot guiding device to guide the balance wheel according to a given axis of rotation, the magnetic pivot guiding device being formed by a pair of magnetic pivots. Figure 1 The diagram shows a mechanical resonator 2 formed by a balance wheel 4 associated with a hairspring 3. The balance wheel is formed by an inertial mass 4a and a shaft 6, which provides two magnetic pivots 6a and 6b to rotatably guide the balance wheel. These two magnetic pivots are rotatably guided by two magnetic bearings, each formed by two permanent magnets 10 and 12. For example, these magnets are formed of rare-earth alloys, particularly SmCo or NdFeB. Specifically, they are made of materials known under reference number VAC677_HR. The shaft 6 of the balance wheel is made of a material with high permeability, such as steel. Advantageously, carbon steel known under reference number 20_AP can be used. One of the two magnets should be stronger than the other, such that one of the two pivots 6a, 6b of axis 6 is in contact with the strongest magnet 10 (or with the intermediate support stone, such as a disc made of a polished hard material like synthetic ruby), while the other pivot is kept at a shorter distance from the weakest magnet 12 (or from the intermediate protective disc of that magnet, especially a common support stone), and thus remains in normal non-contact with the corresponding magnetic bearing. This arrangement for magnetically guiding the balance wheel-hairspring rotation has a major advantage, particularly in reducing friction compared to two ordinary mechanical bearings.

[0003] Figure 2 The theoretical curve of the magnetic bias force FM as a function of the radial displacement X of the balance wheel 4 from its axis of rotation 8 is shown. The balance wheel 4 is used for... Figure 1 The magnetic guiding device of the type shown is illustrated. The axis of rotation of the balance wheel is defined by a geometric axis passing through the middle of the two magnets 10 and 12. The function F can be observed. M(X) is substantially linear for small movements. Thus, by virtue of such an arrangement, the magnetic biasing force increases proportionally with a given radial movement of the balance from its axis of rotation. This poses a problem of centering of the balance 2, since the biasing force is low for small movements of the balance from its intended axis of rotation. Moreover, the fact that ordinary magnets often have a non-uniformity of the order of a millimeter makes this problem of centering of the balance even more serious. And the diameters of the magnets 10, 12 are in the range of one millimeter. This problem of centering poses a problem of interaction of the balance with the escapement associated with the balance. SUMMARY

[0004] The object of the present invention is to solve the problem of centering of a magnetic bearing rotating guiding a small rotating element, in particular in the watchmaking industry, and more particularly to solve the problem of centering of a rotating / pivotable magnetic guide of a balance of a mechanical resonator included in a mechanical timepiece movement.

[0005] To this end, the invention relates to a mechanism comprising a rotating element and a magnetic device for rotating guiding the rotating element, the magnetic device being arranged to exert a radial magnetic biasing force on the rotating element when a central axis of the rotating element undergoes a radial movement with respect to a rotation axis, the rotation axis being predefined in the mechanism for the rotating element. According to the invention, the magnetic device comprises a pair of annular magnets, a first annular magnet of the pair of annular magnets being carried by the rotating element so that a center of the first annular magnet remains coincident with said central axis, and a second annular magnet being carried by a structure of the mechanism so that a center of the second annular magnet remains coincident with said rotation axis. When the central axis of the rotating element coincides with the rotation axis, the second annular magnet is parallel and at least partially axially superposed to the first annular magnet, these first and second annular magnets being in a magnetic attraction arrangement so as to exert a first axial magnetic force on each other and a first radial magnetic force substantially as soon as the central axis of the rotating element is radially offset from the rotation axis.

[0006] Thanks to the features of the invention, the magnetic guiding device allows an efficient way of centering the rotating element radially so as to limit in normal operation any radial movement of the central axis of the rotating element with respect to the rotation axis. Indeed, the superposition of the two annular magnets and the arrangement in magnetic attraction allow to obtain a relatively high radial biasing force from small radial movements of the rotating element with respect to the rotation axis provided in the mechanism for the rotating element.

[0007] According to an advantageous embodiment, the magnetic device further comprises at least one first end magnet, which is arranged axially opposite to a first end of the shaft of the rotating element, which shaft is at least partially formed of soft ferromagnetic or magnetic material, such that the first end magnet exerts a second axial magnetic force of magnetic attraction on the shaft, and such that the first end magnet further exerts a second radial magnetic force on the shaft when the central axis of the rotating element is radially away from the rotation axis, the second axial magnetic force having the same direction as the first axial magnetic force.

[0008] According to a preferred embodiment, on the second annular magnet side, the first annular magnet has a plurality of first annular regions having alternating polarity, and on the first annular magnet side, the second annular magnet has a plurality of second annular regions having alternating polarity, at least two annular regions of the plurality of first annular regions substantially completely axially overlap and are of magnetic attraction with a respective two annular regions of the plurality of second annular regions when the central axis of the rotating element coincides with the rotation axis. BRIEF DESCRIPTION OF DRAWINGS

[0009] The application will be described in greater detail below, with the aid of the drawings provided by way of non-limiting example, in which:

[0010] - already described Figure 1 is a side view showing a magnetic device for guiding a balance-spring according to the prior art;

[0011] - already described Figure 2 is Figure 1 a graph of the radial magnetic biasing force exerted by the magnetic device of

[0012] - Figure 3 is a partial perspective view of a first embodiment of the mechanism according to the application;

[0013] - Figure 4 is Figure 3 a side view of the mechanism of

[0014] - Figure 5 is a partial perspective view of a second preferred embodiment of the mechanism according to the application;

[0015] - Figure 6 shows a plan view of the first and second magnets forming a pair of annular magnets of a magnetic device for rotatingly guiding a balance-spring in a first variant of the second embodiment;

[0016] - Figure 7A and Figure 7Bis a graph of the first radial magnetic biasing force exerted by the pair of annular magnets on the balance as a function of the radial displacement of the balance in each of the first and second embodiments, and which is respectively with respect to two separate distances between the first and second annular magnets;

[0017] - Figure 8 a plan view showing the first and second magnets forming the pair of annular magnets of the magnetic device for the rotationally guiding balance-spring in the second variant of the second embodiment is shown; and

[0018] - Figure 9 a plan view showing the first and second magnets forming the pair of annular magnets of the magnetic device for the rotationally guiding balance-spring in the third variant of the second embodiment is shown. DETAILED DESCRIPTION

[0019] Reference will be made to Figure 3 and 4 , a first embodiment of a timepiece movement according to the present application will be described, which is partially shown.

[0020] The timepiece movement 20 comprises a mechanical resonator formed by a balance 22 having a shaft 24 defining a central axis 26 of the balance, and a magnetic device for rotationally / pivotally guiding the balance, which comprises a pair of annular magnets consisting of a first annular magnet 32 arranged on a support 30 carried by the shaft 24, and a second annular magnet 34 arranged on a support 36 made of soft ferromagnetic or non-magnetic material, which is engaged on a cylindrical tube 38 which is fitted or otherwise fastened into an opening of a main clamping plate 40 of the timepiece movement. It should be noted that the inertial mass of the balance and the spring of the mechanical resonator are not shown in Figure 3 and Figure 4 (for these elements, see Figure 1 ). It should be noted that a gap is left between the flange supporting the inertial mass of the balance and the support 30, which is for the arrangement of a device 72 for coupling the balance with the escapement, in particular a plate 74 carrying a pin 76 intended to interact in a conventional manner with the pallet fork (not shown) of the escapement.

[0021] Generally, the first annular magnet 32 is carried by the balance 22 so that its center remains coincident with the central axis 26; and the second annular magnet 34 is carried by the structure of the timepiece movement so that its center remains coincident with the rotation axis 28, which is predefined in the timepiece movement for the balance. In the variant shown, the support 30 is an annular support made of a material having a low magnetic permeability, in particular made of paramagnetic or diamagnetic material, which is fixedly mounted on the shaft 24. In one variant, the support 30 comprises a thin annular plate made of soft ferromagnetic material arranged directly under the first annular magnet 32. In another variant, the support 30 is made of a material having a high magnetic permeability, in particular made of ferromagnetic material, which is fixedly mounted on the shaft 24. In this case, the first annular magnet 32 is arranged on a support 32' made of a material having a low magnetic permeability, in particular made of paramagnetic or diamagnetic material, which is arranged directly under the first annular magnet 32.Figure 4 In the figure, it can be noted that the shaft 24, the support 30 and the first annular magnet 32 are shown in uncut side view, while the other elements are shown in cut view according to a cut plane including the rotation axis 28. The balance wheel 22 is shown in a centered position as expected in normal operation, whereby the central axis 26 of the shaft 24 coincides with the rotation axis 28.

[0022] The magnetic device for the rotational guiding of the balance wheel is arranged to exert a radial magnetic biasing force F R (X) on the balance wheel when its central axis 26 experiences a radial displacement X with respect to the rotation axis 28. In the first embodiment, the second annular magnet 34 is parallel and substantially completely axially overlapping the first annular magnet 32 when the central axis 26 of the rotating element coincides with the rotation axis 28. The first and second annular magnets are arranged in magnetic attraction in order to exert a first axial magnetic force on each other and subsequently a first radial magnetic force F R (X) as soon as the balance wheel's central axis 26 exhibits a feature of radial deviation from the rotation axis 28. To this end, the inner and outer diameters of the first and second annular magnets are substantially identical, preferably identical. For example, the inner diameter of both annular magnets is between 0.8 mm and 1.1 mm and their outer diameter is between 1.5 mm and 2.2 mm.

[0023] In the first embodiment, the first and second annular magnets are each bipolar magnets, the two annular bipolar magnets having the same polarity (axially magnetized in the same direction) to attract each other. These two bipolar magnets should be relatively thin, for example between 50 and 150 microns. Nevertheless, in other specific embodiments, they can be thicker to increase the magnetic force. In particular, these magnets can be laser cut into plates magnetized perpendicularly to the general plane of the main clamping plate or deposited in thin layers. The first axial force and the first radial force are in particular dependent on the gap / distance G between the two annular magnets. Next, we will see a graph comparing the first radial force F R (X) as a function of the first and second embodiments and two different spacings, this first radial force F R (X) serving as a magnetic centering of the shaft 24 of the balance wheel 22.

[0024] Thereafter, in a manner similar to the prior art embodiment described in the technical background, the magnetic means further comprises a first end magnet 42 and a second end magnet 44, which are respectively arranged axially opposite to a first end (first pivot) and to a second end (second pivot) of the shaft 24 of the balance 22. The first end magnet 42 is arranged inside a cylindrical tube 38 which carries the second annular magnet 34 (the annular magnet being fixed relative to the structure carrying the first and second end magnets). Inside the cylindrical tube 38 is also arranged a perforated stone 54 which forms a first radial safety stop for the shaft 24 so as to limit the radial movement of this shaft (more particularly of its first end) in the event of a shock. It should be noted that the first end magnet is covered with a plate 46 made of hard material, which is a protective end stone enabling pivoting with less friction and relatively low wear. The second end magnet 44 is also arranged inside a cylindrical tube 50 which fits or is otherwise fastened into an opening of the bridge 52 (in particular the balance bridge). Inside the cylindrical tube 50 is also arranged a perforated stone 56 which forms a second radial safety stop for the shaft 24 so as to limit the radial movement of this shaft (more particularly of its second end) in the event of a shock. The second end magnet is also covered with a plate 48 made of hard material. By way of example, the diameter of the two end magnets is comprised between 0.8 mm and 1.0 mm and their height is comprised between 0.4 mm and 0.6 mm.

[0025] The shaft 24 is formed of a soft ferromagnetic material, so that the first end magnet 42 exerts on the shaft a second axial magnetic force which is magnetically attractive and has the same direction as the first axial magnetic force; and, when the central axis 26 of the balance is radially far from the rotation axis 28, the first end magnet 42 also exerts on the shaft a second radial magnetic force. The second end magnet 44 exerts on the shaft a third axial magnetic force which is magnetically attractive and has a direction opposite to that of the second axial magnetic force; and, when the central axis 26 of the balance is radially far from the rotation axis 28, the second end magnet 44 also exerts on the shaft a third radial magnetic force. The magnitude of the third axial magnetic force is provided to be lower than the total magnitude of the first axial magnetic force and of the second axial magnetic force. As shown by the curve of figure Figure 2 The total magnitude of the second radial force and of the third radial magnetic force is characterized by a substantially linear dependence on the distance between the central axis 26 and the rotation axis 28. The end magnets 42 and 44 have respective central axes which are aligned and define the rotation axis 28 of the balance 22, which is thus predefined in the timepiece movement 20. The rotation axis is maintained in a given fixed position relative to the carrying structure of the balance 22, i.e. the main clamping plate 40 and the bridge 52.

[0026] It should be noted that, according to the provision of the pair of annular magnets, it is possible to significantly reduce the size of the first end magnet and of the second end magnet, and more particularly the size of the first end magnet, which in the prior art should have a greater size than the second end magnet (in the prior art, the first end magnet exerts on the shaft a greater axial magnetic force than the second end magnet exerts on the shaft). Indeed, in view of the presence of the first axial magnetic force generated by the pair of annular magnets, which exerts in the same direction as the second axial magnetic force, the latter no longer needs to have a greater size than the size of the third axial magnetic force. Moreover, as will be seen again later, the arrangement of the pair of annular magnets according to the application also allows to mainly reduce the second radial magnetic force, and, taking into account the distancing of the second end magnet 44 from the pair of annular magnets, also preferably to a lesser extent, while the third radial magnetic force has a better magnetic centering of the mechanical resonator (balance wheel - hairspring).

[0027] The preceding description also allows to consider two particular embodiments, which are not illustrated in the attached drawings. In a first particular embodiment, only one end magnet is provided in addition to the pair of annular magnets 32 and 34. In a first variant, the only end magnet is the one which is located on the same side of the inertial mass as the pair of annular magnets, and it generates an axial magnetic force in the same direction as the pair of annular magnets. In a second variant, the only end magnet is the one which is located on the opposite side of the inertial mass from the side on which the pair of annular magnets is located, and it generates an axial magnetic force having a direction opposite to the direction of the axial magnetic force generated by the pair of annular magnets. In this second variant, the axial magnetic force of the pair of annular magnets should be higher than in the first variant. In a second particular embodiment, the magnetic means for the rotational guiding of the mechanical resonator included in the mechanical movement are composed only of the pair of annular magnets 32 and 34. Advantageously, variants of this second particular embodiment include a pair of annular magnets according to the second embodiment, which will be described hereinafter. In the second particular embodiment, the pivot of the shaft of the balance has a small horn-shaped dome against which it is supported, for retaining the pivot in a substantially central position, i.e. substantially on the axis of rotation provided for the balance. It should be noted that such a small horn-shaped dome can advantageously be provided in all the embodiments of the application.

[0028] Reference Figure 5 , 6 , 8 and 9, a second embodiment of the mechanism 60 according to the application will be described hereinafter. The relevant parts already described previously will not be described in detail again. In this second embodiment, the pair of annular magnets 32 and 34 is arranged in such a way that the first axial magnetic force generated by the pair of annular magnets is greater than the second axial magnetic force generated by the pair of annular magnets. In this second embodiment, the pair of annular magnets 32 and 34 is arranged in such a way that the third axial magnetic force generated by the pair of annular magnets is greater than the second axial magnetic force generated by the pair of annular magnets. In this second embodiment, the pair of annular magnets 32 and 34 is arranged in such a way that the third axial magnetic force generated by the pair of annular magnets is greater than the first axial magnetic force generated by the pair of annular magnets. Figure 5 and 6In a first variant shown in Figs. 2 and 3, the second embodiment differs from the first embodiment mainly in that, on the side of the second annular magnet 64, the first annular magnet 62 has a plurality of first annular magnetization regions 62a, 62b and 62c having alternating polarity (N, S, N); and on the side of the first annular magnet 62, the second annular magnet 64 has a plurality of second annular magnetization regions 64a, 64b and 64c having alternating polarity (S, N, S). Overall, when the central axis 26 of the balance wheel 22A coincides with the rotation axis 28, at least two annular magnetization regions of the plurality of first annular magnetization regions substantially completely axially overlap with a respective two annular magnetization regions of the plurality of second annular magnetization regions and are magnetically attracted to the respective two annular regions. In the first variant, the plurality of first annular magnetization regions comprises three annular magnetization regions which completely overlap with three annular magnetization regions of the plurality of second annular magnetization regions, respectively. In the second embodiment, the first annular magnet 62 has a plurality of first annular magnetization regions 62a, 62b and 62c having alternating polarity (N, S, N) and the second annular magnet 64 has a plurality of second annular magnetization regions 64a, 64b and 64c having alternating polarity (S, N, S). In the first variant, the plurality of first annular magnetization regions comprises three annular magnetization regions which completely overlap with three annular magnetization regions of the plurality of second annular magnetization regions, respectively. Figure 5 In a partial perspective view of Fig. 4, the second annular magnet 64 is shown without its support so that the outer face of this magnet is visible. Conversely, in Fig. 5, the two annular magnets 62 and 64 are shown separately, viewed from the intermediate gap between these two annular magnets. The second embodiment is also characterized by differences at the two end magnets 42 and 44. While in the first embodiment these two end magnets are provided substantially with the same size and the same magnetic force; in the second embodiment, the first end magnet 42 is provided with a smaller size which is smaller than the size of the second end magnet 44, the second end magnet 44 being much further from the pair of annular magnets than the first end magnet which is located relatively close to this pair of annular magnets. Figure 6

[0029] Advantageously, the two annular magnets 62 and 64 are made by a gas phase deposition process of a rare earth material alloy in a vacuum envelope, in particular by sputtering. For example, the thickness of the two multipole annular magnets can be provided in the range of 10 to 50 microns, in particular between 15 microns and 30 microns. The permanent magnetization of each layer of rare earth material alloy deposited on the support can be carried out in a facility arranged to be able to generate a strong magnetic field which crosses the deposited layer orthogonally, with the vector of this magnetic field mainly in one direction or in the opposite direction according to the different regions of the deposited layer, to obtain magnetized annular regions with alternating polarity. Thus, bipolar annular magnetization regions with axial magnetization are obtained.

[0030] As presented in Figs. 6 and 7, the second embodiment allows to significantly increase the magnetic centering force exerted by the pair of annular magnets. Figure 7A 7B Figure 7A is a graph showing the radial magnetic biasing force F R ​​​(X) is a graph representing the radial displacement X of the central axis 26 of the balance wheel relative to the rotation axis 28, where the distance G between the pair of annular magnets is equal to 0.2 mm (200 micrometers). Curve 80 illustrates this function for the second embodiment, while curve 82 illustrates it for the first embodiment (where the annular magnets are the same size). It can be noted that the force F... R (X) and force F E (X) added together, force F E (X) is the radial magnetic bias force generated by the two end magnets (see...). Figure 2 Nevertheless, it should be noted that the slope of the linear function depends on the magnetic power of the end magnet, and in particular on its size.

[0031] It can be observed that the toroidal magnet according to the invention rapidly applies a relatively large bias force F toward the axis of rotation. R (X), the initial slopes of curves 80 and 82 are relatively steep in the first 50 micrometers, which is consistent with the linear function F. E (X) forms a contrast. Furthermore, it can be observed that the slope in the second embodiment is steeper than that in the first embodiment (more than twice as steep), which is highly advantageous for obtaining effective and accurate magnetic centering.

[0032] Figure 7B It is similar to Figure 7A The graphs show the second embodiment, but the distance G between the two toroidal magnets is equal to 0.1 mm (100 micrometers). Curve 84 relates to the second embodiment, while curve 86 relates to the first embodiment. First, it can be observed that the maximum value of the radial magnetic bias force FR(X) (approximately X = 100 micrometers) is much larger (almost 6 times larger) at a distance G = 0.1 mm than at a distance G = 0.2 mm. This makes the gradients of curves 84 and 86 higher than those of curves 80 and 82, respectively, in the first 50 micrometers, and the gradient in curve 84 is much higher (almost 5 times higher) than in curve 86. This shows that the second embodiment is particularly effective and advantageous with the smaller distance between the two toroidal magnets, which are arranged parallel to each other when the central axis 26 is parallel to the axis of rotation 28.

[0033] exist Figure 8 and Figure 9 In, similar to Figure 6 Two other variations of the second embodiment are shown. Figure 8In the second variation, the first annular magnet 62 generally includes N annular magnetized regions (62a, 62b, 62c), where N is greater than 1; and the second annular magnet 66 includes N+1 annular magnetized regions (64a, 64b, 64c, 64d); when the central axis 26 of the balance wheel coincides with the rotation axis 28, the N annular magnetized regions of the first annular magnet 62 axially overlap with the N annular magnetized regions of the second annular magnet 64, including the inner region (64a); the multiple second annular magnetized regions include an outer region (64d) extending radially beyond the first annular magnet 62. Figure 8 In the specific example shown, the natural number N is equal to three, i.e., N = 3. Regarding the same first annular magnet 62 embedded in the rotating movable element (i.e., the balance wheel 22A), this second variant allows for an increase in the radial magnetic bias force F compared to the first variant. R (X).

[0034] exist Figure 9 In the third variation, the first annular magnet 68 generally comprises N annular magnetized regions (62a, 62b), where N is greater than 1; and the second annular magnet 66 comprises N+2 annular magnetized regions (64a, 64b, 64c, 64d); when the central axis 26 of the rotating element (especially the balance wheel) coincides with the rotation axis 28, the N annular magnetized regions of the first annular magnet 68 axially overlap with the N inner annular magnetized regions (64b, 64c) of the second annular magnet 66 located between the outer region (64d) and the inner region (64a); these inner and outer regions extend radially from both sides of the first annular magnet 68. Figure 9 In the specific example shown, the natural number N is equal to two, i.e., N = 2. Regarding the first ring magnet embedded in the balance wheel, this second variation allows for a relatively high radial magnetic bias force FR(X), the first ring magnet having a small size, and therefore a lighter weight due to the small size of the support for the first ring magnet. Thus, very efficient magnetic centering is achieved while adding almost no increase to the inertia of the rotating elements (especially the balance wheel).

Claims

1. A mechanism (20; 60) comprising a rotating element (22; 22A) and a magnetic device for rotatably guiding the rotating element, the magnetic device being arranged to apply a radial magnetic bias force (F) on the rotating element when the central axis (26) of the rotating element undergoes a radial movement (X) relative to a rotation axis (28). R The rotation axis (28) is predefined for the rotating element in the mechanism, characterized in that... The magnetic device includes a pair of annular magnets, a first annular magnet of which is carried by the rotating element such that the center of the first annular magnet coincides with the central axis, and a second annular magnet is carried by a structure (40) of the mechanism such that the center of the second annular magnet coincides with the axis of rotation, wherein, when the central axis of the rotating element coincides with the axis of rotation, the second annular magnet is parallel to and at least partially axially overlaps the first annular magnet, the first and second annular magnets are arranged with magnetic attraction to apply a first axial magnetic force to each other and a first radial magnetic force (F) is applied once the central axis of the rotating element deviates radially from the axis of rotation. R (X)).

2. The mechanism according to claim 1, characterized in that, The magnetic device further includes at least one first end magnet (42) axially arranged opposite to a first end of the shaft (24) of the rotating element (22; 22A), the shaft being at least partially formed of a soft ferromagnetic material or a magnetic material, such that the first end magnet applies a second axial magnetic force, the second axial magnetic force being magnetically attractive and having the same direction as the first axial magnetic force, and the first end magnet also applies a second radial magnetic force on the shaft when the central axis of the rotating element is radially moved away from the axis of rotation.

3. The mechanism according to claim 2, characterized in that, The magnetic device includes a second end magnet (44) arranged opposite to the second end of the shaft (24), the shaft (24) being formed of a soft ferromagnetic material, the second end magnet applying a third axial magnetic force on the shaft, the third axial magnetic force being magnetically attractive and having a direction opposite to that of the second axial magnetic force, and the second end magnet also applying a third radial magnetic force on the shaft when the central axis of the rotating element is radially moved away from the axis of rotation, the magnitude of the third axial magnetic force being less than the total magnitude of the first axial magnetic force and the second axial magnetic force.

4. The mechanism according to claim 2 or 3, characterized in that, The first annular magnet is arranged on an annular support (30) made of a material with low magnetic permeability, the annular support being fixedly mounted on the shaft (24).

5. The mechanism according to any one of claims 1-3, characterized in that, On the side of the second annular magnet, the first annular magnet has a plurality of first annular magnetization regions with alternating polarities, and on the side of the first annular magnet, the second annular magnet has a plurality of second annular magnetization regions with alternating polarities. When the central axis (26) of the rotating element (22; 22A) coincides with the rotation axis (28), at least two annular magnetization regions of the plurality of first annular magnetization regions completely overlap axially with corresponding two annular magnetization regions of the plurality of second annular magnetization regions and are magnetically attracted to the corresponding two annular regions.

6. The mechanism according to claim 5, characterized in that, Each of the plurality of first annular magnetization regions and the plurality of second annular magnetization regions includes three annular magnetization regions.

7. The mechanism according to claim 5, characterized in that, The first annular magnet includes N annular magnetization regions, where N is greater than 1, and the second annular magnet includes N+1 annular magnetization regions; when the central axis (26) of the rotating element coincides with the rotation axis (28), the N annular magnetization regions of the first annular magnet and the N annular magnetization regions of the second annular magnet, including the inner region, respectively overlap axially, and the plurality of second annular magnetization regions include the outer region (64d) that extends radially beyond the first annular magnet.

8. The mechanism according to claim 5, characterized in that, The first annular magnet includes N annular magnetization regions, where N is greater than 1, and the second annular magnet includes N+2 annular magnetization regions. When the central axis (26) of the rotating element coincides with the rotation axis (28), the N annular magnetization regions of the first annular magnet and the N inner annular magnetization regions of the second annular magnet located between the outer region (64d) and the inner region (64a) of the plurality of second annular magnetization regions respectively overlap axially. The inner region and the outer region extend radially from both sides of the first annular magnet respectively.

9. The mechanism according to claim 2 or 3, characterized in that, The first annular magnet is arranged on an annular support (30) made of paramagnetic or diamagnetic material.

Images