Watch movement and watch

Abstract

The utility model relates to a watch movement and a watch. The watch movement comprises a mechanical resonator composed of a balance wheel and a balance spring; means for setting the oscillation frequency of the mechanical resonator; and a mechanism for setting a guide mark on the mechanical resonator. The moving member of the setting device includes a mechanism for attaching the outer end portion of the hairspring and a mechanism for defining the effective length of the hairspring. The mechanism for varying the effective length includes a first gear carried by the moving member and a first tooth arranged along the outer end portion of the hairspring, the first gear meshing with the first tooth. The fastening mechanism retains the outer end portion by friction so that the first gear can drive the outer end portion via the first teeth and thus change the effective length of the hairspring. The first gear is in meshing relationship with a second gear that is integral with the resonator support such that when the outer end portion undergoes angular displacement in a selected direction relative to the moving member, the moving member is simultaneously angularly displaced by a corresponding angular distance in an opposite direction.

Description

TECHNICAL FIELD

[0001] The utility model relates to a kind of watch movement, the watch movement includes mechanical resonator and the device for setting the frequency of this resonator.The utility model further relates to a kind of device for setting the guide mark of escapement associated with mechanical resonator.

[0002] Particularly, the utility model relates to a kind of device for setting the frequency of mechanical watch resonator, which does not affect the guide mark of prior setting of the "balance wheel and anchor" system. BACKGROUND

[0003] Patent application BE 483992A describes various embodiments of a device for setting the frequency of a balance-spring forming a mechanical watch resonator. With reference to Figures 50 to 54, this document describes a setting device having the advantage of being able to set the resonator frequency from the outside of the watch case, which is arranged so that the user can set the frequency in this way. The setting device comprises a complex system for correcting the frequency of the mechanical resonator while maintaining the "balance wheel and anchor" system on the guide mark. The setting device is complex. First, the setting device comprises a clamp that holds the outer coil of the spring firmly at a given angular position of a support, called "sector", which rotates around the rotation axis of the balance wheel, this clamping of the outer coil defining the effective length of the spring and thus the oscillation frequency of the balance-spring. The terminal coil is clamped by a slide bar arranged in the watch case, which comprises a protruding internal part arranged to act on a resilient arm of the clamp. The slide bar can be actuated substantially tangentially with respect to the rotation axis of the balance wheel by an actuation member accessible from the outside of the watch case on this slide bar. The resilient arm is configured so that, in a first angular position of the slide bar, the slide bar presses laterally against the resilient arm in order to clamp the outer coil and close the access opening to a setting wheel machined in the watch case, and so that, in a second angular position, the slide bar releases the access opening while stopping the lateral force exerted on the resilient arm so that the outer coil is no longer held by the clamp. The setting device also comprises a post mounted on a second resilient arm of the support and two mutually meshing wheels, each having a helical cam. The cam of the first wheel presses against the second resilient arm so that it defines the angular position of the post and the angular distance from the clamp. The cam of the second wheel presses against a third helical cam, which is fixed but the angular position of which can be set by the watchmaker when setting the initial guide mark, the cam of the second wheel being held against the fixed cam by a resilient mechanism for actuating the rotation of the support.

[0004] To set the resonator frequency, when the slide bar is in its second angular position and the clamp has released the outer coil of the hairspring, the second wheel can be actuated by means of a tool. This actuation causes the first wheel and its cam to rotate, so that the second elastic arm moves, thereby changing the angular position of the stud and, consequently, the angular distance between this stud and the clamp. As a result, once the clamp is closed, the effective distance changes, and therefore the effective length of the hairspring, and consequently the oscillation frequency, also changes. The following are the features of interest of this complex setting device: turning the second wheel not only changes the angular position of the stud and, consequently, the effective length of the hairspring, but also causes said support to be angularly displaced towards said stud in the opposite direction, by a substantially identical angular distance, so that the guide marks of the initial setting are not affected and remain unchanged.

[0005] The setting device described above is complex and has many drawbacks. First, the setting device is composed of a large number of components that must be adjusted. Machining certain components is complex, as is assembling the setting device. Furthermore, a significant problem is that the oscillation frequency cannot be set once the watch movement has been completed, but only when this watch movement has been installed in the watch case, and then only through an access opening provided in the side portion of the watch case. A major problem is that the setting device includes a component that is mounted on the watch case and is necessary whenever it is necessary to set said frequency. Furthermore, this setting device requires a plurality of elastic components, i.e. the hairspring and the two elastically deformable arms, which must be correctly dimensioned and can exhibit some fatigue damage over time. Finally, the end of the outer coil of the hairspring is usually held in the stud by a lateral screw or more often by adhesive bonding; these fastening mechanisms create stresses on the end of the hairspring, which affect the accuracy of the frequency setting. SUMMARY

[0006] The object of the present invention is to solve the problems of the prior art mentioned in the technical background by providing a watch movement equipped with a mechanical resonator and a device for setting the frequency of this mechanical resonator, which is less complex, reliable and independent with respect to the watch case, and which makes it possible to effectively set the frequency without changing the initial setting of the guide marks.

[0007] To this end, the present invention relates to a watch movement comprising:

[0008] - a mechanical resonator composed of a balance wheel rotatably mounted in a support and a hairspring,

[0009] - an escapement comprising an anchor arranged to oscillate in synchronism with the balance wheel, and

[0010] - a device for setting the oscillation frequency of the mechanical resonator, referred to as a setting device,

[0011] The setting device comprises a mobile part, called mobile part, rotating around an axis of rotation of the balance, comprising a mechanism, called fastening mechanism, for attaching the outer end portion of the balance spring, and a mechanism, called defining mechanism, for defining the effective length of the balance spring, said defining mechanism defining the end point of the effective part of the balance spring at a fixed point on the mobile part once the balance spring has been attached to the mobile part by the fastening mechanism. The setting device also comprises a mechanism, called changing mechanism, for changing the effective length of the balance spring, making it possible to set the oscillation frequency by angular displacement of the outer end portion with respect to the mobile part, and therefore with respect to said fixed point on the mobile part, in a selected direction with respect to said axis of rotation, the setting of the oscillation frequency being combined with the rotation of the mobile part over an angular distance substantially corresponding to said angular displacement and in a direction opposite to the selected direction.

[0012] The watch movement also comprises a mechanism, called guide mark setting mechanism, for setting the guide mark of the mechanical resonator with respect to the anchor. Said changing mechanism comprises a first toothed wheel carried by the mobile part and a first tooth arranged along the outer end portion of the balance spring, the first tooth being in meshing engagement with the first toothed wheel which can be rotated to perform the angular displacement, said fastening mechanism retaining the outer end portion by friction so as to enable the first toothed wheel to drive the outer end portion via the first tooth, so as to angularly displace the outer end portion with respect to the mobile part and said defining mechanism, so as to change the effective length of the balance spring. Finally, the first toothed wheel is in meshing relationship with a second tooth which is integral with the resonator support, so that when the outer end portion undergoes said angular displacement in the selected direction with respect to the mobile part, the mobile part simultaneously angularly displaces said angular distance in the opposite direction. Thus, the outer end portion does not undergo any angular displacement and the guide mark set beforehand is unchanged.

[0013] The setting device does not require a hairspring. Furthermore, it is sufficient to provide a mechanism that actuates the first gear or the mobile part to set the resonator frequency without misaligning the guide mark set beforehand. Although this setting device, which is able to set the oscillation frequency while automatically maintaining the guide mark set in the preliminary step, can be provided for a watch, once the watch has been fully installed, said setting device enables such a setting, but it is independent with respect to the watch case, so that such a watch movement can also be installed in a watch case that cannot be set from the outside of the watch case. The device can appear complex in practice in terms of the outer end portion of the hairspring comprising a tooth. Such a tooth can be formed in a portion that is initially separate from the hairspring and is joined or welded or fastened by any other means to the end of the outer coil of the conventional hairspring. Since today's hairsprings are increasingly made of silicon and use micro-machining techniques borrowed from the micro-technology field, implementing the outer end portion of the hairspring with a lateral tooth, in other words the cut profile of the hairspring with a tooth, does not pose particular problems. The same applies to hairsprings made of glass or similar materials. It should be noted that the guide mark can simply be set by the initial positioning of the first tooth with respect to the first gear in the case where the mobile part is in a given initial position. BRIEF DESCRIPTION OF DRAWINGS

[0014] The utility model will be described in more detail below with reference to the attached drawings, which are given by way of non-limiting example, in which:

[0015] - Figure 1 is a perspective top view of an embodiment of a watch movement according to the utility model, the Figure 1 shows a watch movement assembly comprising a setting device and an outer end portion of a hairspring.

[0016] - Figure 2 is Figure 1 a top view of the watch movement assembly shown in

[0017] - Figure 3 is Figure 1 a perspective top view of the watch movement assembly in

[0018] - Figure 4 is Figure 1 a partial perspective view from below of the assembly shown in

[0019] - Figure 5A and 5B is Figure 1partial view from below of the assembly shown in the middle and of the outer end portion of the balance spring, with the mobile member in two different positions corresponding to two different effective lengths of the balance spring. DETAILED DESCRIPTION

[0020] With reference to the drawings, the following is a description of a watch movement according to the present application.

[0021] The watch movement 2 comprises:

[0022] - a mechanical resonator consisting of a balance (only the balance staff 14 forming the support of the balance is shown in the figures) rotatably mounted in the support and a balance spring 6 (only a portion of the outer coil 7 and the outer end portion 8 of the balance spring are shown in the figures),

[0023] - an escapement comprising an anchor arranged to oscillate in synchronism with the balance (the escapement is not shown in the figures, in particular a traditional watch escapement with a Swiss-type anchor), and

[0024] - means 4 for setting the frequency of the mechanical resonator, referred to as "setting means".

[0025] In particular, the balance is a typical balance with a clapper having a pin that acts as a periodic coupling member between the anchor and the oscillating balance, causing a reciprocating motion of the anchor, which thus oscillates in synchronism with the balance. The setting means 4 comprise a mobile member 16, referred to as "mobile member", rotating around the rotation axis 50 of the balance, the function of which is to fasten the outer end portion 8 of the balance spring 6 and to define the effective length of the balance spring. Furthermore, the mobile member 16 and the outer end portion 8 are arranged so that the mechanical resonator guide mark can be set with respect to the escapement anchor. Furthermore, as will be understood more clearly in what follows, the mobile member 16 is arranged so that, once the resonator and the setting means 4 have been mounted in the watch movement 2, a variation of the effective length of the balance spring is obtained in order to set the oscillation frequency of the mechanical resonator, while maintaining the angular position of the outer end portion as determined at the time of its fastening, and thereby maintaining the stable angular position of the balance-balance spring at rest, so as not to lose the previously set guide mark. Thus, in particular, the effective length of the balance spring is varied while maintaining the correct alignment of the balance pin at rest, i.e. the radial alignment on the rotation axis of the balance and on the rotation axis of the anchor.

[0026] Thus, in general, the mobile member 16 comprises: a mechanism for attaching the outer end portion 8 of the balance spring 6, referred to as "fastening mechanism"; and a mechanism for defining the effective length of the balance spring 6, referred to as "defining mechanism", which defines the end point P F on the effective part of the balance spring 6 on a fixed point P EThe setting device 4 also comprises a mechanism for varying the effective length of the hairspring, called "variation mechanism", making it possible to set the oscillation frequency by P an angular displacement in a selected direction with respect to the axis of rotation 50, in combination with a rotation of the mobile part around said axis of rotation at an angular distance substantially corresponding to said angular displacement and in the opposite direction to the selected direction (see Figure 5A and 5B ). The watch movement also comprises a mechanism for setting the guide mark of the mechanical resonator with respect to the escapement anchor in a preliminary step, called "guide mark setting mechanism". This preliminary step is a step that occurs when the resonator is installed in the watch movement, or a step that occurs when the watch movement is serviced by a watchmaker.

[0027] According to the invention, the variation mechanism consists of a first toothed wheel 22 carried by the clamping plate 18 on the mobile part 16 and a first tooth 10 arranged along the outer end portion 8 of the hairspring, the first tooth being in meshing engagement with the first toothed wheel, which is able to rotate to perform the angular displacement mentioned above. Preferably, the hairspring is made of silicon or glass and is obtained using micro-machining techniques. Thus, when the hairspring 6 is manufactured, the first tooth can be easily obtained.

[0028] According to the invention, the fastening mechanism retains said outer end portion 8 by friction, so as to allow the first toothed wheel 22 to drive this outer end portion via the first tooth 10 and thus to angularly displace the outer end portion with respect to the mobile part 16 and to said limiting mechanism, so as to vary the effective length of the hairspring 6. The first toothed wheel 22 is in meshing engagement with a fixed tooth 30 comprising an upper clamping plate 28 fastened to the resonator support, more generally, to the resonator support to which the second tooth 30 is integral, so that when the outer end portion undergoes said angular displacement in a selected direction with respect to the mobile part 16, the mobile part is simultaneously angularly displaced in the opposite direction by said angular distance.

[0029] In the advantageous variant illustrated in the figures, the fastening mechanism also comprises a first eccentric 32 and a second eccentric 33 arranged on either side of the outer end portion 8 of the hairspring 6. These first and second eccentrics can each be turned by a tool, so that, when the hairspring is mounted in the movement 2, when the hairspring 6 is in the unconstrained state and thus in its rest position in itself, the first and second eccentrics respectively contact the first and second lateral faces of the outer end portion 8, so that, for any frequency of oscillation in the useful range, the portion of the outer end portion located between the first eccentric 32 and the second eccentric 33 has a spatial positioning corresponding to that of the rest position in itself of the hairspring, and this portion can retain this spatial positioning after fastening of the outer end portion, when the mechanical resonator oscillates. This feature is very advantageous for ensuring that the swing of the hairspring when the watch movement ticks is properly centred on the axis of rotation 50. This increases the accuracy of the watch movement. The second eccentric 33 is positioned facing the wheel 22 located on the other side of the second eccentric with respect to the outer end portion 8. The second eccentric 33 also holds the first tooth in the first toothed wheel 22, thereby ensuring that they are in meshing engagement. The radial positioning of the outer end portion of the hairspring 6, the radial positioning of the first toothed wheel and the various components involved in the first toothed wheel are preferably machined with sufficiently low tolerances, so that, in the rest position in itself of the hairspring (the hairspring is in the unconstrained state), the first tooth 10 is in meshing relationship with the first toothed wheel 22 with a certain amount of play. Indeed, if this were not the case, it would not be possible to have meshing between the first toothed wheel and the first tooth of the hairspring, while maintaining the portion of the outer end portion 8 located between the first eccentric 32 and the second eccentric 33 in a spatial position corresponding to that of the rest position in itself of the hairspring. It should be noted that the first and second eccentrics advantageously have a circular recess in which the outer end portion 8 is placed. Such a recess makes it possible to axially position this outer end portion.

[0030] The mechanism for defining the effective length of the hairspring 6 comprises a first eccentric 32 against which the first portion 9a of the outer end portion 8 is pressed. The point of contact at which this first portion 9a is pressed against the first eccentric defines the end of the effective portion of the hairspring and thus the end point P E of its effective length. This end point is located at a contact point which is fixed with respect to the mobile component, so that this end point is always located at a particular fixed point P F , i.e. at an invariant point on the mobile component.

[0031] The guide mark setting mechanism consists of a first tooth 10 on the hairspring 6, which is arranged along the middle portion of the outer end portion 8 of the hairspring, and a first toothed wheel 22, the initial angular positioning of the guide mark with respect to the first toothed wheel by the first tooth being set when the mobile member 16 is in a given initial angular position, which can be any position in the angular travel of the mobile member, but is preferably substantially in the middle of the angular travel.

[0032] In the variant described, the fastening mechanism comprises a third eccentric 34, which is arranged on the same side of the outer end portion of the hairspring as the first eccentric 32, the second eccentric 33 being located between the first and third eccentrics along the outer end portion, the first eccentric 32 being positioned with respect to the second eccentric towards the outer coil 7 of the hairspring 6. The third eccentric is arranged so that it can be turned by a tool to exert a third transverse force F3 on the outer end portion 8, so that the first and second eccentrics react by exerting respectively a first transverse force Fl and a second transverse force F2 on the outer end portion 8, thereby retaining the outer end portion in place by the friction forces between the outer end portion and the first, second and third eccentrics without the first toothed wheel 22 rotating.

[0033] According to an advantageous feature, the first transverse force Fl can be of such a magnitude and the first portion 9a of the outer end portion 8 facing the positioning of the first eccentric 32 can have a selected stiffness, so that it can remain in contact with the first eccentric when the mechanical resonator is oscillating. Thus, once set, the effective length of the hairspring remains constant when the resonator is oscillating, independently of the fact that the first portion 9a is in contact on one side only with the mechanism for defining the effective length of the hairspring, which consists only of the first eccentric 32. In particular, the stiffness of the first portion 9a is chosen so that the oscillation frequency can be set accurately.

[0034] According to a particular feature of the fastening mechanism, the outer end portion 8 has a terminal portion 9b located behind the first tooth 10, which occupies the middle portion of the outer end portion, the terminal portion 9b being more flexible than the first portion 9a and facing the positioning of the third eccentric 34, which can exert a third transverse force F3 on the terminal portion. Preferably, the width of the terminal portion 9b increases towards its free end, so that the third transverse force F3 remains substantially constant for any frequency setting, and thus for any effective length in the range of expected settings.

[0035] In the embodiment described, the mobile member 16 comprises a second toothed wheel 24 mounted coaxially with the first toothed wheel 22, these first and second toothed wheels being fastened to the same mandrel 20 so that they rotate together. The second toothed wheel 24 is engaged with the fixed teeth 30 of the upper clamping plate 28, which is attached to the balance lever 14 forming part of the mechanical resonator support.

[0036] According to a particular variant, the mobile component 16 comprises a third tooth 38 carried by the arm 18a of the clamping plate 18 and the mechanical movement 2 comprises means for rotating the mobile component about said axis of rotation 50 via the third tooth. The clamping plate 18 further comprises two elastic arms 18b and 18c which form a split ring around the support of the anti-shock bearing 46 which thus guides the rotation of the mobile component 16. The drive means are arranged so that they can be actuated from the lateral periphery of the movement to rotate the mobile component 16 so as to produce a variation in the effective length of the hairspring 6 from this lateral periphery via the first and second pinions 22 and 24. The drive means comprise a third pinion 40 meshing with an Archimedes screw 42 having an end 42a accessible from the lateral periphery of the mechanical movement and having a non-cylindrical coupling portion designed to allow the Archimedes screw to be coupled to a member for actuating the Archimedes screw. It should be noted that the upper clamping plate 28 has a protrusion 28a which holds the Archimedes screw in a constant longitudinal position so that when the Archimedes screw is rotated, the pinion 40 is driven to rotate even in the absence of any longitudinal pressure exerted on the Archimedes screw.

[0037] The utility model still relates to a kind of watch comprising the mechanical movement according to the utility model. The watch includes the shell (not shown) containing mechanical movement 2, and it is arranged so that the drive means of mobile component can be actuated by the aforementioned actuating member (not shown), and the actuating member can be operated from the outside of watch.

Claims

1. A watch movement (2) comprising: - a mechanical resonator consisting of a balance spring (6) and a balance wheel rotatably mounted in a support; - an escapement comprising an anchor arranged to oscillate in synchronism with the balance wheel; and - means (4) for setting the oscillation frequency of the mechanical resonator, called setting means; The setting device (4) comprises a mobile element (16) called mobile element rotating about the rotation axis (50) of the balance, comprising a mechanism called fastening mechanism for attaching the outer end portion (8) of the hairspring and a mechanism called defining mechanism for defining the effective length of the hairspring, the defining mechanism defining the end point (P E ) of the effective portion of the hairspring at a fixed point (P F ) on the mobile element (16) once the hairspring has been attached to the mobile element by the fastening mechanism, the setting device further comprising a mechanism called changing mechanism for changing the effective length of the hairspring (6) so that the oscillation frequency can be set by an angular displacement of the outer end portion (8) relative to the mobile element, and therefore relative to the fixed point on the mobile element, relative to the rotation axis and in a selected direction, the setting of the oscillation frequency being combined with a rotation of the mobile element (16) in the angular distance corresponding to the angular displacement and in the opposite direction to the selected direction; the watch movement further comprising a mechanism for setting the mechanical resonator guide marker relative to the anchor, called guide marker setting mechanism; characterized in that the changing mechanism comprises a first gearwheel (22) carried by the mobile element and a first tooth (10) arranged along the outer end portion of the hairspring, the first gearwheel being in meshing with the first tooth and the first tooth being rotatable to perform the angular displacement, the fastening mechanism retaining the outer end portion (8) by friction so as to enable the first gearwheel to drive the outer end portion via the first tooth and therefore angularly displace the outer end portion relative to the mobile element and the defining mechanism so as to change the effective length of the hairspring; and in that the first gearwheel (22) is in meshing relationship with a second tooth (30) integral with the resonator support, so that when the outer end portion undergoes the angular displacement in the selected direction relative to the mobile element, the mobile element is simultaneously angularly displaced in the opposite direction by the angular distance.

2. A watch movement according to claim 1, characterised in that the balance spring (6) being made of silicon or glass and obtained by micro-machining techniques.

3. A watch movement according to claim 1 or 2, characterised in that, the fastening mechanism comprising a first eccentric (32) and a second eccentric (33) arranged on either side of an outer end portion (8) of the balance spring and able to be turned by a tool, such that when the balance spring (6) is mounted in the watch movement, the first and second eccentric respectively come into contact with a first and second side of the outer end portion (8) while the balance spring is in a non-constrained and thus in its own rest position, such that for any setting of the oscillation frequency in the useful range, the portion of the outer end portion between the first eccentric (32) and the second eccentric (33) has a spatial positioning corresponding to that of the balance spring's own rest position, the fastening mechanism retaining this spatial positioning to the portion of the outer end portion once it is fastened, the first eccentric (32) constituting the delimiting mechanism.

4. A watch movement according to claim 3, characterised in that the fastening mechanism comprising a third eccentric (34) arranged on the same side of the outer end portion (8) of the balance spring as the first eccentric (32), the second eccentric (33) being located between the first and third eccentric along the outer end portion, the first eccentric being located towards the outer rim (7) of the balance spring relative to the second eccentric, and the third eccentric (34) being arranged such that it can be turned by a tool to exert a third transverse force on the outer end portion (8), such that the first and second eccentric react by exerting a first and second transverse force respectively on the outer end portion, the outer end portion thus remaining in place by friction between the outer end portion and the first, second and third eccentric without the first toothed wheel rotating.

5. A watch movement according to claim 4, characterised in that the first transverse force can have a magnitude and the first portion of the outer end portion facing the location of the first eccentric can have a selected stiffness, such that the first portion can remain in contact with the first eccentric when the mechanical resonator oscillates.

6. A watch movement according to claim 5, characterised in that the stiffness is selected such that the oscillation frequency can be set precisely.

7. A watch movement according to claim 5 or 6, characterised in that, the outer end portion has a terminal portion located after the first tooth, the terminal portion being more flexible than the first portion and facing the location of the third eccentric, the third eccentric being able to exert the third transverse force on the terminal portion.

8. A watch movement according to any one of claims 1, 2 and 4 to 6, characterized in that, the guide mark setting mechanism consists of the first tooth of the balance spring and the first toothed wheel, the guide mark being set by the initial positioning of the first tooth relative to the first toothed wheel when the mobile part is in a given angular position. the first toothed wheel is able to rotate by a tool, such that when the balance spring is mounted in the watch movement, the first tooth comes into contact with a first side of the first toothed wheel while the balance spring is in a non-constrained and thus in its own rest position, such that for any setting of the oscillation frequency in the useful range, the first tooth has a spatial positioning corresponding to that of the balance spring's own rest position, the first toothed wheel retaining this spatial positioning to the first tooth once it is turned, the first toothed wheel constituting the delimiting mechanism. the first toothed wheel is able to rotate by a tool, such that when the balance spring is mounted in the watch movement, the first tooth comes into contact with a first side of the first toothed wheel while the balance spring is in a non-constrained and thus in its own rest position, such that for any setting of the oscillation frequency in the useful range, the first tooth has a spatial positioning corresponding to that of the balance spring's own rest position, the first toothed wheel retaining this spatial positioning to the first tooth once it is turned, the first toothed wheel constituting the delimiting mechanism.

9. A watch movement according to any one of claims 1, 2 and 4 to 6, characterised in that, The mobile member (16) comprises a second toothed wheel (24) mounted coaxially with a first toothed wheel (22), the first and second toothed wheels being arranged on a same arbor (20) so that they rotate together, the second toothed wheel (24) being in engagement with the second teeth (30).

10. A watch movement according to claim 9, characterised in that The mobile member (16) comprises third teeth (38) and the watch movement comprises means for rotating the mobile member about the axis of rotation (50) via the second teeth (30); and the drive means are arranged so that they can be actuated from the lateral periphery of the watch movement by an actuation member to rotate the mobile member (16) to produce a variation in the effective length of the hairspring from the lateral periphery via the first and second toothed wheels.

11. A watch movement according to claim 10, characterised in that, The drive means comprise an Archimedes screw (42) one end of which is accessible from the lateral periphery of the watch movement and which has a non-cylindrical coupling portion to enable the Archimedes screw to be coupled to the actuation member for actuating the Archimedes screw.

12. A watch comprising a watch movement according to claim 10 or 11, characterized in that, The watch comprises a case containing the watch movement (2) and is arranged so that the drive means of the mobile member (16) can be actuated by the actuation member, the actuation member being operable from outside the watch.

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