Mechanism for operating a flexible indicator pointer moved by a clockwork mechanism

Description

Technical field of the invention

[0001] The present invention relates to a mechanism for actuation of a flexible pointer driven by a clockwork mechanism and arranged to display information in an analog manner. The present invention particularly relates to a simplified mechanism for actuation of a flexible display pointer. Technological background

[0002] We already know of flexible hands which, by changing their length and shape as desired, can closely follow with their tip the periphery of a dial which deviates from a circular shape, for example an ovoid shape, to display information in an analog way, for example the current time.

[0003] Such a flexible needle, an example of which is disclosed in European patent application EP 2 863 274 A1 in the name of the Applicant, is visible on the figure 1attached to this patent application. This flexible needle 1 comprises a first drive barrel 2 connected to a first end of a first flexible arm 4, and a second drive barrel 6 connected to a first end of a second flexible arm 8. At their second end, the first and second flexible arms 4, 8 are connected to each other by a tip 10. In a free, unconstrained state of the flexible needle 1, the first and second drive barrels 2, 6 are spaced apart from each other. Conversely, a service position in which the flexible needle 1 has a defined shape and length is a constrained position in which the first drive barrel 2 and the second drive barrel 6 are arranged coaxially around the same output axis DIn this constrained position, the first drive barrel 2 is mounted with a first defined preload angle, and the second drive barrel 6 is mounted with a second defined preload angle in the opposite direction to that of the first drive barrel 2. The flexible needle 1 is arranged so as to change its shape and length as desired when the angular position of the second drive barrel 6 varies relative to the angular position of the first drive barrel 2 by pivoting around the output axis. D. To this end, each of the first and second flexible arms 4, 8 of the flexible hand 1 performs an angular rotation θ1 which is applied by a clockwork movement to the flexible hand 1 to display the information, the angular rotation θ1 applied by the clockwork movement to the flexible hand 1 being further modulated by an angle of rotation ϕ by an actuation mechanism 12, this angle of rotation ϕ, applied in opposite directions to the first and second flexible arms 4, 8 of the flexible hand 1, determining the change in shape and length of the flexible hand 1.

[0004] An embodiment of a flexible needle actuation mechanism of the type described above is disclosed in European patent application EP 3 764 170 A1 in the name of the Applicant.

[0005] This example is given for illustrative purposes only and is in no way exhaustive in connection with the figure 1attached to this patent application. Designated as a whole by the general numerical reference 12, this actuation mechanism comprises first driving means 14 of the first drive barrel 2 around the output axis D , and second drive means 16 of the second drive barrel 6 around the same output axis D The first drive means 14 and the second drive means 16 are arranged to deform the first and second flexible arms 4 and 8 by varying the angular position of the second drive barrel 6 relative to the angular position of the first drive barrel 2 around the output axis. D , and to vary the radial position of the tip 10 relative to this output axis D .

[0006] More specifically, the actuation mechanism 12 comprises a planet carrier frame 18 which is provided with a first pivot 20 on which a planet wheel 22 is mounted for free rotation. This planet wheel 22 is equipped with a cam follower finger 24 arranged to follow the profile 26 of a cam 28, against which it is held by the elasticity of the flexible needle 1. The cam 28 is the only fixed element of the actuation mechanism 12. The planet carrier frame 18 is also provided with a tube 30 on which a first and second driving bearing 32 and 34 are mounted for free rotation concentrically.The first drive shaft 2 of the flexible needle 1 is driven onto the second drive wheel 34 with a defined preload angle, then the second drive shaft 6 of this same flexible needle 1 is driven onto the first drive wheel 32 with an identical preload angle but in the opposite direction to that of the first drive shaft 2. Finally, the actuation mechanism 12 is completed by a first sun gear 36 formed by teeth carried by the first drive wheel 32, and by a second sun gear 38 formed by teeth carried by the second drive wheel 34. When the planet carrier frame 18 is driven in rotation by the clockwork movement, for example clockwise, it drives with it the planet wheel 22 which rotates on its own axis by tracing the profile 26 of the cam 28 with its cam follower finger 24.The first driving wheel 32, in direct contact with this satellite wheel 22, therefore rotates on itself relative to the satellite carrier frame 18. As for the second driving wheel 34, it rotates relative to the satellite carrier frame 18 at the same speed as the first driving wheel 32, but in the opposite direction, because the rotation of the satellite wheel 22 is transmitted to it via a return wheel 40 mounted freely in rotation on a second pivot 42.

[0007] To move the flexible needle 1 from a first to a second position, the actuation mechanism 12 applies, in addition to the rotation θ1, an identical rotation of angle ϕ but in the opposite direction to each of the first and second drive shafts 2, 6 of the flexible needle 1. To accomplish this, the actuation mechanism 12 is driven by the clockwork mechanism which applies a rotation of angle θ1 to the input of the planet carrier frame 18. As illustrated in the figure 2annexed to this patent application, this rotation of angle θ1 is converted by the actuation mechanism 12 into a rotation of angle α(θ1) of the first drive barrel 2 of the flexible needle 1, and into a rotation of angle β(θ1) of the second drive barrel 6. The output angles α(θ1) and β(θ1) of the actuation mechanism thus follow the following relationships: α θ 1 = θ 1 + φ θ 1 β θ 1 = θ 1 − φ θ 1

[0008] Assuming that the flexible needle 1 is symmetrical, the angular position θ2 of the tip 10 of the flexible needle 1 is defined as the bisector of the first and second flexible arms 4 and 8, i.e. the average of the angles α(θ1) and β(θ1) according to the relation: θ 2 = α θ 1 + β θ 1 2 = θ 1

[0009] From the above, it is understood that in order to allow the flexible hand 1 to change shape and length as desired, the clockwork movement applies, via the actuation mechanism 12, a rotation of angle θ1 modulated by an identical rotation of angle ϕ but in the opposite direction on each of the first and second drive spars 2, 6 of the flexible hand 1.

[0010] The present invention aims to provide a new actuation mechanism for a flexible needle that is of a simpler design. Summary of the invention

[0011] The invention relates to a simplified mechanism for actuation of a flexible needle driven by a clockwork movement.

[0012] To this end, the present invention relates to a mechanism for actuation of a flexible needle to which a clockwork movement applies a first angular rotation, the flexible needle comprising a first drive barrel and a second drive barrel connected to a tip of the flexible needle by means of a first flexible arm, respectively a second flexible arm, the first drive barrel being provided with a first set of teeth and the second drive barrel being provided with a second set of teeth, the first and second drive barrels being spaced apart when the flexible needle is in a free, unconstrained state, a service position in which the flexible needle has a defined shape and length being a constrained position in which the first drive barrel is mounted with a first defined preload angle,and the second drive barrel is mounted with a second preload angle defined in the opposite direction to that of the first drive barrel, the first drive barrel and the second drive barrel being arranged so that the first toothing of the first drive barrel meshes with the second toothing of the second drive barrel in the constrained position of the flexible needle, the flexible needle being arranged to change shape and length in a desired manner when the angular position of the second drive barrel varies by pivoting relative to the first drive barrel, the angular rotation applied by the clockwork movement to the actuation mechanism being modulated by an angle of rotation by the actuation mechanism, this angle of rotation,applied with an opposite direction to the first and second flexible arms of the flexible needle by meshing the first toothing of the first drive barrel with the second toothing of the second drive barrel determining the change in shape and length of the flexible needle.,

[0013] According to a special embodiment of the invention, the actuation mechanism comprises a planet carrier frame to which the clockwork movement applies the first angular rotation, this planet carrier frame being provided with a first and a second fixedly mounted tube on which a first, respectively a second driving wheel pivots, the actuation mechanism also comprising a cam follower finger arranged to travel along the profile of a cam against which this cam follower finger is held by the elasticity of the flexible hand, this cam being a fixed element of the actuation mechanism,the cam follower finger being arranged to travel along the profile of the cam so that the first angular rotation applied by the clockwork movement to the planet carrier frame is further modulated by an angle of rotation applied in a direction opposite to the second flexible arm by the first flexible arm by meshing of the first toothing with the second toothing, this angle modulation determining the change in shape and length of the flexible needle.,

[0014] According to another embodiment of the invention, one of the driving carriages is equipped with the cam follower finger.

[0015] According to yet another embodiment of the invention, one of the first or second arms is equipped with the cam follower finger.

[0016] The present invention also relates to a mechanism for actuation of a flexible needle to which a clockwork movement applies a first angular rotation, the flexible needle comprising a first drive barrel and a second drive barrel connected to a tip of the flexible needle by means of a first flexible arm, respectively a second flexible arm, the first drive barrel being provided with a first set of teeth and the second drive barrel being provided with a second set of teeth, the first and second drive barrels being spaced apart when the flexible needle is in a free, unconstrained state, a service position in which the flexible needle has a defined shape and length being a constrained position in which the first drive barrel is mounted with a first defined preload angle,and the second drive barrel is mounted with a second preload angle defined in the opposite direction to that of the first drive barrel, the first drive barrel and the second drive barrel being arranged so that the first tooth of the first drive barrel is in contact with the second tooth of the second drive barrel in the constrained position of the flexible needle, the flexible needle being arranged so as to change shape and length in a desired manner when the angular position of the second drive barrel varies by pivoting relative to the first drive barrel, the clockwork movement applying the first angular rotation to a cam against which a feeler is supported, the feeler pivoting under the effect of the rotation of the cam by an angle which is a function of the first angular rotation applied by the clockwork movement to the cam,When the pivoting of the probe is applied to one of the first or second drive barrels, the first or second drive barrel to which the pivoting of the probe is applied applies this pivoting in the opposite direction to the other drive barrel, causing the flexible needle to deform lengthwise.

[0017] According to yet another embodiment of the invention, the actuation mechanism comprises tubes fixedly mounted on a support and on which the first and second drive carriages are mounted freely in rotation, the first drive carriage of the flexible needle being driven onto the first drive carriage with a defined preload angle, and the second drive carriage of this same flexible needle being driven onto the second drive carriage with an identical preload angle but in the opposite direction to that of the first drive carriage, one of the first and second drive carriages carrying the feeler in support against the rotating cam.

[0018] The present invention also relates to a flexible needle comprising a first drive barrel and a second drive barrel connected to a tip of the flexible needle by means of a first flexible arm, respectively a second flexible arm, the first drive barrel being provided with a first set of teeth and the second drive barrel being provided with a second set of teeth, the first and second drive barrels being spaced apart when the flexible needle is in a free, unconstrained state, a service position in which the flexible needle has a defined shape and length being a constrained position in which the first drive barrel is mounted with a first defined preload angle, and the second drive barrel is mounted with a second defined preload angle in the opposite direction to that of the first drive barrel.the first drive barrel and the second drive barrel being arranged so that the first toothing of the first drive barrel engages with the second toothing of the second drive barrel in the constrained position of the flexible needle, the flexible needle being arranged so as to change shape and length in a desired manner when the angular position of the second drive barrel varies by pivoting relative to the first drive barrel.

[0019] Thanks to these features, the present invention provides an actuation mechanism for a flexible needle with a simplified structure. By applying a phase shift to one of the drive shafts, the other drive shaft is actuated via the teeth in the opposite direction, allowing the needle's length to be changed without the needle rotating. Another embodiment of the invention allows the needle's length to be changed while simultaneously rotating it, using a simplified mechanism. Brief description of the figures

[0020] Other features and advantages of the present invention will become clearer from the following detailed description of an embodiment of the flexible needle according to the invention, this example being given purely for illustrative purposes and not as a limitation, only in connection with the accompanying drawing in which: there figure 1The already cited illustration is a perspective and exploded view of one embodiment of a prior art flexible switch actuation mechanism, this actuation mechanism comprising a differential-type device carried by a satellite-carrying frame, the first and second drive shafts of the flexible switch being coaxial around a first and second driving track; figure 2 The previously mentioned angle represents the rotation angles of the cannons and the flexible needle so that the tip of this flexible needle travels through an angle θ1 which corresponds to the rotation applied by the clockwork movement to the input of the actuation mechanism; figure 3 is a perspective and exploded view of one embodiment of a flexible needle actuation mechanism according to the invention; the figure 4 is a perspective and exploded view of a special embodiment of the actuation mechanism of the figure 3in which the cam follower finger is fixed to one of the arms of the flexible needle; the Figure 5 is a perspective and exploded view of a special embodiment of the flexible needle actuating mechanism in which the clockwork movement applies an angular rotation θ1 to the cam; the Figure 6A is a plan view of a flexible needle according to the invention in a free, unstressed state, this view being accompanied by an enlargement in the region of the first and second drive barrels; figures 6B to 6D are plan views, each accompanied by an enlargement of the flexible needle of the Figure 6Ain service position in which the flexible needle has a defined shape and length which are conditioned by the preload angle with which the first and second drive tubes are mounted, the first and second tubes each being equipped with teeth by which they mesh with each other so that the flexible needle gradually changes shape and length in the desired way when the angular position of the second drive tube varies with respect to the first drive tube by pivoting. Detailed description of the invention

[0021] The present invention proceeds from the general inventive idea of ​​providing a simplified actuation mechanism for transmitting angular rotation applied by a clockwork movement to a flexible hand. To this end, the present invention teaches that the first and second drive shafts of the flexible hand are each equipped with teeth, so that the angular rotation applied by the clockwork movement to the first drive shaft is transmitted to the second drive shaft by meshing the teeth of the first drive shaft with the teeth of the second drive shaft. By avoiding the need to apply the angular rotation supplied by the clockwork movement to the first and second drive shafts separately via the actuation mechanism, the actuation mechanism is thus simplified.

[0022] There figure 3is a perspective and exploded view of one embodiment of a flexible needle actuation mechanism according to the invention. Designated as a whole by the general reference numeral 44, this flexible needle comprises a first drive barrel 46 connected to a first end of a first flexible arm 48, and a second drive barrel 50 connected to a first end of a second flexible arm 52. At their second ends, the first and second flexible arms 48, 52 are connected to each other by a tip 54. Finally, the flexible needle 44 is completed by the addition, on each of the first and second drive barrels 46, 50, of a first, and respectively a second set of teeth 56, 58. As can be seen in the Figure 6AIn a free, unconstrained state of the flexible needle 44, the first and second drive bushings 46, 50 are separated from each other, the first and second teeth 56, 58 not being engaged with each other. Conversely, when the flexible needle 44 is in a service position as illustrated in the Figure 6B , it has a defined shape and length in which the first drive barrel 46 is mounted with a first defined preload angle, and the second drive barrel 50 is mounted with a second defined preload angle opposite that of the first drive barrel 46, the first drive barrel 46 and the second drive barrel 50 being arranged so that the first toothing 56 of the first drive barrel 46 is in engagement with the second toothing 58 of the second drive barrel 50.

[0023] As regards the actuation mechanism, this, designated as a whole by the general numerical reference 60, includes a satellite carrier chassis 62 to which the clockwork movement applies a first angular rotation θ1.

[0024] The satellite carrier chassis 62 is also provided with a first and a second tube 64, 66 on which a first, respectively a second driving roadway 68, 70 are pivotally mounted. The first drive bushing 46 of the flexible needle 44 is driven onto the first drive track 68 with a defined preload angle, then the second drive bushing 50 of this same flexible needle 44 is driven onto the second drive track 70 with an identical preload angle but in the opposite direction to that of the first drive bushing 46. One of the drive tracks 68, 70, for example the first, is equipped with a cam follower finger 72 arranged to travel along the profile 74 of a cam 76 against which this cam follower finger 72 is held by the elasticity of the flexible needle 44. This cam 76 is a fixed element of the actuation mechanism 60.The first and second drive shafts 46, 50 are arranged so that the first and second gear teeth 56, 58 mesh with each other. As it rotates, the first drive shaft 68 drives the first drive shaft 46 in rotation, this first drive shaft 46 in turn driving the second drive shaft 50 in rotation by meshing the first and second gear teeth 56, 58 with each other.

[0025] It is understood that when the clockwork mechanism applies an angular rotation θ1 to the planet carrier frame 62, this planet carrier frame 62 drives the first and second driving wheels 68 and 70 with it, and the first driving wheel 68 rotates with the planet carrier frame 62, tracing the profile 74 of the cam 76 with its cam follower finger 72, so that the angular rotation θ1 applied by the clockwork mechanism to the planet carrier 62 and the flexible hand 44 is further modulated by an angle of rotation ϕ by the action of the cam follower finger 72. This angle of rotation ϕ, applied in the opposite direction to the second flexible arm 52 by the first flexible arm 48 through the meshing of the first toothed wheel 56 with the second toothed wheel 58, determines the change in shape and length of the flexible hand 44. In addition to rotating, this flexible needle 44 deforms radially along a radius Rwhich passes between the two drive barrels 46, 50 and through the tip 54 of the flexible needle 44..

[0026] According to a special form of execution illustrated in the figure 4 , the cam follower finger 72 is fixed, not on one of the first or second bearings 68 or 70, but on one of the first or second flexible arms 48 or 52, for example the first, of the flexible needle 44. For the rest, the actuation mechanism 60 remains unchanged.

[0027] It is understood that the present invention is not limited to the embodiments just described, and that various simple modifications and variations can be envisaged by a person skilled in the art without departing from the scope of the invention as defined by the appended claims. In particular, according to a special embodiment of the invention illustrated in the Figure 5The actuation mechanism 60 includes a cam 76 to which the clockwork movement applies the angular rotation θ1. The tubes 64, 66 are fixedly mounted on a support such as a plate or bridge 78, and on these tubes 64, 66, the first and second drive bearings 68, 70 are mounted freely for rotation. The first drive bushing 46 of the flexible needle 44 is driven onto the first drive bearing 68 with a defined preload angle, and then the second drive bushing 50 of this same flexible needle 44 is driven onto the second drive bearing 70 with the same preload angle but in the opposite direction to that of the first drive bushing 46. One of the first and second drive bearings 68, 70, for example the first, is equipped with a feeler 80 bearing against the rotating cam 76.Under the effect of the rotation of the cam 76, the first driving wheel 68 pivots by an angle of rotation ϕ, which causes the radial deformation along the radius. R of the flexible needle 44 without it rotating on its own axis. This is illustrated on the figures 6B-6D on which we can see that the flexible needle 44 changes shape and length but does not rotate on itself. Nomenclature

[0028] 1. Flexible needle 2. First drive barrel 4. First flexible arm 6. Second drive barrel 8. Second flexible arm 10. Tip D.Output axis θ1. Angular rotation ϕ. Rotation angle 12. Actuating mechanism 14. First drive means 16. Second drive means 18. Planet carrier frame 20. First pivot 22. Planet wheel 24. Cam follower 26. Profile 28. Cam 30. Tube 32. First drive cannon 34. Second drive cannon 36. First sun gear 38. Second sun gear 40. Idler wheel 42. Second pivot 44. Flexible needle 46. First drive barrel 48. First flexible arm 50. Second drive barrel 52. Second flexible arm 54. Point 56. First toothing 58. Second toothing 60. Actuating mechanism 62. Planet carrier frame 64. First tube 66. Second tube 68. First drive cannon 70. Second drive wheel 72. Cam follower finger 74. Profile 76. Cam 78. Plate 80. Feeler R Radius

Claims

1. Actuation mechanism (60) of a flexible hand (44) to which a clockwork movement applies a first angular rotation (θ1), the flexible hand (44) comprising a first drive cannon (46) and a second drive cannon (50) connected to a point (54) of the flexible hand (44) by means of a first flexible arm (48) and a second flexible arm (52) respectively, the first drive cannon (46) being provided with a first toothing (56) and the second drive cannon (50) being provided with a second toothing (58), the first and second drive cannons (46, 50) being spaced apart from one another when the flexible hand (44) is in a free, unstressed state, an operating position in which the flexible hand (44) has a defined shape and length being a stressed position in which the first drive cannon (46) is mounted at a defined first pre-stressing angle, and the second drive cannon (50) is mounted at a defined second prestressing angle in opposite direction to the first drive cannon (46), the first drive cannon (46) and the second drive cannon (50) being arranged such that the first toothing (56) of the first drive cannon (46) are engaged with the second toothing (58) of the second drive cannon (50) in the stressed position of the flexible hand (44), the flexible hand (44) being arranged so as to change the shape and length in a desired manner when the angular position of the second drive cannon (50) is varied by pivoting relative to the first drive cannon (46), the angular rotation (θ1) applied by the clockwork movement to the actuation mechanism (60) being modulated by an angle of rotation (ϕ) by the actuation mechanism (60), this angle of rotation (ϕ), applied in opposite direction to the first and second flexible arms (48, 52) of the flexible hand (44) by meshing the first toothing (56) of the first drive cannon (46) with the second toothing (58) of the second drive cannon (50) determining the change in shape and length of the flexible hand (44).

2. Actuation mechanism (60) according to claim 1, characterised in that it comprises a planetary wheel-holding frame (62) to which the clockwork movement applies the first angular rotation (θ1), this planetary wheel-holding frame (62) being provided with a first and a second tube (64, 66) on which a first and a second driving cannon-pinion (68, 70) respectively are mounted to be freely rotatable, the actuation mechanism (60) also comprising a cam follower finger (72) arranged to run along the profile (74) of a cam (76) against which this cam follower finger (72) is held by the resilience of the flexible hand (44), this cam (76) being a fixed element of the actuation mechanism (60), the cam follower finger (72) being arranged to traverse the profile (74) of the cam (76) so that the first angular rotation (θ1) applied by the clockwork movement to the planetary wheel-holding frame (62) is further modulated by an angle of rotation (ϕ) applied in a direction opposite the second flexible arm (52) by the first flexible arm (48) by meshing the first toothing (56) with the second toothing (58), this angle modulation (ϕ) determining the change in shape and length of the flexible hand (44).

3. Actuation mechanism according to claim 2, characterised in that one of the driving cannon-pinions (68, 70) is equipped with the cam follower finger (72).

4. Actuation mechanism according to claim 2, characterised in that one of the first or second flexible arms (48, 52) is equipped with the cam follower finger (72).

5. Actuation mechanism (60) of a flexible hand (44) to which a clockwork movement applies a first angular rotation (θ1), the flexible hand (44) comprising a first drive cannon (46) and a second drive cannon (50) connected to a point (54) of the flexible hand (44) by means of a first flexible arm (48) and a second flexible arm (52) respectively, the first drive cannon (46) being provided with a first toothing (56) and the second drive cannon (50) being provided with a second toothing (58), the first and second drive cannons (46, 50) being spaced apart from one another when the flexible hand (44) is in an unstressed free state, an operating position in which the flexible hand (44) has a defined shape and length being a stressed position in which the first drive cannon (46) is mounted at a defined first prestressed angle, and the second drive cannon (50) is mounted at a defined second prestressed angle in opposite direction to the first drive cannon (46), the first drive cannon (46) and the second drive cannon (50) being arranged such that the first toothing (56) of the first drive cannon (46) is engaged with the second toothing (58) of the second drive cannon (50) in the stressed position of the flexible hand (44), the flexible hand (44) being arranged so as to change the shape and length in a desired manner, when the angular position of the second drive cannon (50) is varied by pivoting relative to the first drive cannon (46), the clockwork movement applying the first angular rotation (θ1) to a cam (76) against which a feeler-spindle (80) bears, the feeler-spindle (80) pivoting by an angle of rotation (ϕ) from the effect of the first angular rotation (θ1) applied by the clockwork movement to the cam (76), the pivoting of the feeler-spindle (80) being applied to one of the first or second drive cannons (46, 50), whichever of the first or second drive cannons (46, 50) to which the pivoting of the feeler-spindle (80) is applied applying this pivoting in opposite direction to the other drive cannon, which causes the radial deformation of the flexible hand (44).

6. Actuation mechanism according to claim 5, characterised in that it comprises first and second tubes (64, 66) fixed onto a support and on which the first and second driving cannon-pinions (68, 70) are mounted to freely rotate, the first drive cannon (46) of the flexible hand (44) being driven onto the first driving cannon-pinion (68) at a defined prestressed angle, and the second drive cannon (50) of this same flexible hand (44) being driven onto the second driving cannon-pinion (70) at an identical prestressed angle but in opposite direction to that of the first drive cannon (46), one of the first and second driving cannon-pinions (68, 70) supporting the feeler-spindle (80) bearing against the rotary cam (76).

7. Flexible hand (44) comprising a first drive cannon (46) and a second drive cannon (50) connected to a point (54) of the flexible hand (44) by means of a first flexible arm (48) and a second flexible arm (52) respectively, the first drive cannon (46) being equipped with a first toothing (56) and the second drive cannon (50) being provided by a second toothing (58), the first and second drive cannons (46, 50) being spaced apart from one another when the flexible hand (44) is in an unstressed free state, an operating position in which the flexible hand (44) has a defined shape and length being a stressed position in which the first drive cannon (46) is mounted at a first defined prestressed angle, and the second drive cannon (50) is mounted at a second defined prestressed angle in opposite direction to the first drive cannon (46), the first drive cannon (46) and the second drive cannon (50) being arranged such that the first toothing (56) of the first drive cannon (46) is in engagement with the second toothing (58) of the second drive cannon (50) in the stressed position of the flexible hand (44), the flexible hand (44) being arranged so as to change shape and length in a desired manner when the angular position of the second drive cannon (50) varies pivotally relative to the first drive cannon (46).