EP4662425A1 - Screw-nut transmission system - Google Patents

Abstract

The present invention relates to a screw-nut transmission system, comprising: - a first element (10; 20); - a second element (20; 10) arranged to rotate about an axis (X) and engaging with the first element (10; 20) such that the first element (10; 20) moves with a translational motion along this axis (X) when the second element (20; 10) rotates, the first element (10; 20) being a nut or a screw, and the second element (20; 10) being the screw or the nut, respectively; - a fixed shell (60) at least partially surrounding the first element (10; 20) and the second element (20; 10) and comprising a groove (90) defined by sides; - the first element (10; 20) comprising a portion arranged to move with a translational motion inside the groove (90), characterised in that the system comprises: - a first magnet (40) connected to this portion and to the fixed shell (60); and - a contact surface (51) made of ferromagnetic material and/or a second magnet, connected to the fixed shell (60) and to this portion, this contact surface (51) and/or the second magnet engaging with the first magnet (40), so as to block any rotation of the first element (10; 20).

Description

Screw-nut transmission system

Technical field

[0001] The present invention relates to a screw-nut transmission system, in particular a screw-nut transmission system intended for high-precision positioning applications, namely for applications in which the positioning accuracy is less than or equal to 50 pm, in particular less than or equal to 10 pm, for example less than or equal to 1 pm. The present invention relates more specifically to a screw-nut transmission system which exploits a magnetic force to cancel an angular play.

State of the art

[0002] One of the conventional solutions for transforming a rotary motion into a translational (or linear) motion and vice versa is the screw-nut transmission system.

[0003] Typically, a screw-nut transmission system includes:

- a first element,

- a second element arranged to rotate about an axis and cooperating with the first element such that the first element moves with a translational motion along that axis when the second element rotates.

[0004] In the case where the first element is a nut and the second element a screw, the nut moves by translation along the rotating screw. [0005] In the case where the first element is a screw and the second element a nut, it is the screw which moves by translation along its main axis when the nut rotates around the screw.

[0006] By adding balls between the first and second elements, the screw-nut system is called a "ball screw system". The balls allow the transmission to be carried out by rolling and not by sliding or friction, which is the case with a screw-nut system.

[0007] To ensure the transformation of the rotary motion into a translational (or linear) motion in a screw-nut transmission system and thus obtain, for example, a linear actuation along a direction, for example along the X direction, it is desirable or even necessary to reduce or block the degree of freedom of rotation d0X around the X axis of the element which moves with a translational motion.

[0008] Indeed, this anti-rotation condition of the element which moves with a translational movement has an impact on the positioning precision of this element. For an angular tolerance range d0X, the positioning deviation is equal to:

P d0X/36O° (1)

P being the pitch (of the screw and/or the nut).

[0009] Therefore, for an application requiring high positioning accuracy, it is necessary to limit d0X or even eliminate it.

[0010] Solutions exist to limit or even eliminate d0X.

[0011] In one of these solutions, the nut is the first element, which moves with a translational motion along the screw when the screw rotates around its main axis. In this solution, the transmission system comprises a fixed envelope surrounding the nut and the screw, this envelope comprising a groove defined by sides.

[0012] At least a portion of the nut moves with a translational motion in the groove.

[0013] In this solution, the screw-nut transmission system uses as an anti-rotation member a pin generally fixed on the nut. In order for the pin to reduce or prevent rotation of the nut, a clearance must be present between the pin and the groove.

[0014] A conventional solution for taking up the play between the pin and the groove involves applying an angular preload using, for example, a torsion spring between the nut and the casing.

[0015] This stress ensures that there is always contact between the pin and one side of the groove. If there is no play compensation in the groove, when the second element rotates in the opposite direction and therefore the first element translates in the opposite direction, the pin can rest on the other side of the groove and this generates an error called "hysteresis".

[0016] In the case where there are balls between the screw and the nut, the transmission system also comprises a rolling body guide device such as a ball bearing, to guide the movement of the nut in the groove. This makes it possible to have rolling of the nut on one side of the groove rather than friction, which makes it possible to reduce or eliminate the phenomena known as "stick-slip", in particular to achieve precision positioning.

[0017] The presence of a torsion spring for taking up angular play causes certain disadvantages, in particular the volume used by the spring which can be critical if this solution is used in very compact devices, such as for example and in a non-limiting way implanted devices.

[0018] The presence of a torsion spring also causes risks of uncontrolled friction of the coils of the spring on the various components of the system: coils can overlap during folding, which can cause uncontrolled friction.

[0019] In addition, the preload force may vary during the travel of the nut. In the case of a tension spring, the force difference is equal to the product of the spring stiffness and its elongation. This variation may affect the positioning accuracy because of the difference in load state.

[0020] Finally, the use of a torsion spring involves a significant force to ensure play compensation over the entire travel of the nut. This has an impact on the sizing of an actuator (e.g. a linear actuator) connected to the screw-nut transmission system, on the necessary drive torque, on the energy consumption of the system and/or on the volume used.

[0021] Document US9273766 discloses an electric actuator comprising a ball screw mechanism for converting the rotational motion of the electric motor, into an axial linear motion of a drive shaft. The system may comprise a magnet on a pin and cooperating with a sensor, for example a Hall effect sensor, for the purpose of detecting the position of the shaft from the rotation angle of the pin.

[0022] Document JP2004182063 describes a screw-nut system for an automobile, which exploits a magnetic force to prevent rotation of the nut. [0023] Document JP2021035311 relates to a screw-nut system. Rotation of the nut and an associated piston is avoided by exploiting a magnetic interaction between internal magnets and external magnets.

Brief summary of the invention

[0024] An object of the present invention is to provide a screw-nut transmission system free from the limitations of known screw-nut transmission systems.

[0025] Another object of the present invention is to provide a screw-nut transmission system suitable for high-precision positioning applications.

[0026] Another object of the present invention is to propose a screw-nut transmission system which has a reduced volume compared to known systems.

[0027] Another aim of the present invention is to propose a screw-nut transmission system which has a volume suitable for use in very compact devices, such as, for example and in a non-limiting manner, implanted devices.

[0028] Another aim of the present invention is to propose a screw-nut transmission system in which friction is better controllable compared to known systems.

[0029] Another aim of the invention is to propose a screw-nut transmission system which makes it possible to take up the angular play of the element which moves by translation while minimizing the energy requirement, by guaranteeing a constant state of load over the entire travel of the element which moves by translation, by ensuring a state of isostatic stress and/or having minimal impact on the volume of the system.

[0030] According to the invention, these aims are achieved in particular by means of the screw-nut transmission system according to claim 1.

[0031] The screw-nut transmission system comprises:

- a first element,

- a second element arranged to rotate about an axis and cooperating with the first element so that the first element moves with a translational movement along this axis when the second element rotates, the first element being a nut respectively a screw, the second element being the screw respectively the nut,

- a fixed envelope at least partially surrounding the first element and the second element and comprising a groove defined by sides,

- the first element comprising a portion arranged to move with a translational movement in the groove.

[0032] According to the invention, the system also comprises a first magnet connected (directly or indirectly) to this portion respectively to the fixed envelope.

[0033] According to the invention, a contact surface made of ferromagnetic material and/or a second magnet is (are) connected to the fixed envelope respectively to this portion, this surface and/or this second magnet cooperating with the first magnet, so as to block any rotation of the first element.

[0034] This solution has in particular the advantage over the prior art of a screw-nut transmission system adapted to these high-precision positioning applications. [0035] This solution also has the advantage over the prior art of having a reduced volume compared to known systems, in particular a volume suitable for use in very compact devices, such as, for example and in a non-limiting manner, implanted devices.

[0036] The embodiment in which the first magnet is connected to the portion of the first element and the contact surface made of ferromagnetic material and/or the second magnet is (are) connected to the fixed casing has the advantage of having an even smaller volume compared to the embodiment in which the first magnet is connected to the fixed casing and the contact surface made of ferromagnetic material and/or the second magnet is (are) connected to the portion of the first element. Indeed, in this second embodiment, the first magnet may have larger dimensions compared to the first embodiment, however this has an impact on the total diameter of the screw-nut transmission system.

[0037] Furthermore, in both embodiments, the presence of the first magnet and a surface made of ferromagnetic material and/or a second magnet makes it possible to better control friction compared to known systems.

[0038] The screw-nut transmission system according to the invention makes it possible in all cases to compensate for the angular play of the element which moves by translation while minimizing the energy requirement, by guaranteeing a constant load state over the entire travel of the element which moves by translation, while ensuring a state of isostatic stress and/or having a minimal impact on the volume of the system.

[0039] In one embodiment, the screw-nut transmission system comprises a guide device for guiding the movement of the element which moves with a translational movement. [0040] In one embodiment, the guide device is a rolling body guide device (rolling transmission). In this embodiment, there are balls between the screw and the nut.

[0041] In one embodiment, the rolling bodies are non-magnetic, for example and in a non-limiting manner they are made of ceramic.

[0042] In one embodiment, the rolling bodies are made of a magnetizable material, for example magnetizable steel.

[0043] In one embodiment, the rolling body guide device is a ball bearing.

[0044] In one embodiment, the rolling body guide device comprises an outer ring, at least a portion of which is arranged to roll on the contact surface made of ferromagnetic material and/or on the second magnet, or it comprises a sleeve connected to the outer ring and at least a portion of which is arranged to roll on the contact surface made of ferromagnetic material and/or on the second magnet.

[0045] In one embodiment, the first magnet is connected to the outer ring or the sleeve. In this embodiment, the first magnet is therefore a rotating magnet, namely a magnet arranged to rotate about the axis of the rod during operation of the screw-nut transmission system.

[0046] In one embodiment, the portion arranged to move with a translational motion in the groove is connected to a rod (e.g. a pin, a stud, etc.) arranged to move by translation in the groove and to carry the first magnet. [0047] In one embodiment, the rolling body guide device is carried by this rod.

[0048] In one embodiment, the guide device is a plain bearing, which is fixed and at least partially surrounds the screw and the nut (sliding transmission). In this case, the plain bearing may comprise the contact surface and/or the second magnet.

[0049] In this case, in one embodiment the contact surface and/or the second magnet must have a low coefficient of friction, for example a coefficient of friction less than 0.15, preferably equal to 0.05.

[0050] In one embodiment, the groove belongs to a plane and the contact surface made of ferromagnetic material and/or the second magnet is substantially perpendicular to this plane.

[0051] In one embodiment, the contact surface made of ferromagnetic material and/or the second magnet has the dimension parallel to the translation direction of the first element less than 15 |im, preferably less than 10 |im, for example equal to 1 |im.

[0052] In one embodiment, the contact surface made of ferromagnetic material and/or the second magnet has a roughness (Ra) of less than 1 |im, preferably less than 0.8 |im, for example equal to 0.2 |im.

[0053] In one embodiment, the fixed casing comprises a plate, the plate comprising the ferromagnetic material contact surface and/or the second magnet, and a fixing surface for fixing the plate to the fixed casing.

[0054] In one embodiment, the plate is made of ferromagnetic material. [0055] In one embodiment, the contact surface and/or the second magnet is perpendicular to the attachment surface.

[0056] In an alternative embodiment to the embodiment in which the first magnet is connected to the fixed casing and the contact surface made of ferromagnetic material and/or the second magnet is (are) connected to the portion of the first element, the first magnet is located on the casing, for example near a rolling plate which is not necessarily ferromagnetic, and a portion of the first element and/or a portion of the guide device (for example an outer ring and/or a bushing if the guide device is a ball bearing) is made of ferromagnetic material.

[0057] The present invention also relates to a rotary stroke bearing guiding device, comprising:

- the transmission system according to the invention,

- a part (for example a lens) connected to the first element and therefore arranged to move with a translational movement, the contact surface made of ferromagnetic material and/or the second magnet cooperating with the first magnet, in order to block any rotation of the first element and therefore any rotation of the part.

Brief description of the figures

[0058] Examples of implementation of the invention are indicated in the description illustrated by the appended figures in which:

Figure 1 illustrates a perspective view of a linear actuator comprising a screw-nut transmission system according to one embodiment of the invention, with a nut which moves with a translational movement, a rotating screw, a ball bearing and a first rotating magnet. Figure 2 illustrates a longitudinal section of the linear actuator of Figure 1.

Figure 3 illustrates a detail of Figure 2.

Figure 4 illustrates a cross-section of Figure 1.

Figure 5 illustrates a bottom view of another linear actuator comprising a screw-nut transmission system according to another embodiment of the invention, with a nut which moves with a translational movement, a rotating screw, a ball bearing and a first non-rotating magnet.

Figure 6 illustrates a side view of the linear actuator of Figure 5.

Figure 7 illustrates a longitudinal section of the linear actuator of Figure 6.

Figure 8 illustrates a cross-section of the linear actuator of Figure 7, along the A-A axis.

Figure 9 illustrates a longitudinal section of a perspective view of another linear actuator comprising a screw-nut transmission system according to another embodiment of the invention, with a nut which moves with a translational movement, a rotating screw, a plain bearing and a first magnet which moves with a translational movement.

Figure 10 illustrates a longitudinal section of the linear actuator of Figure 9. Figure 11 illustrates a longitudinal section of a perspective view of another linear actuator comprising a screw-nut transmission system according to another embodiment of the invention, with a rotating nut, a screw which moves with a translational movement, a plain bearing and a first magnet which moves with a translational movement.

Example(s) of embodiment of the invention

[0059] In the following description, reference will be made, for the sake of simplicity, to a magnetic force between a (first) magnet and a ferromagnetic support. It should be understood, however, that the invention is not limited to such a magnetic force, but also comprises (in addition or alternatively) a magnetic force between the first magnet and a second magnet.

[0060] In the following description provided by way of example, reference will be made, for simplicity, to a screw-nut system in which the first magnet is connected to the portion of the first element (the one which moves with a translational movement) and the contact surface made of ferromagnetic material is connected to the fixed casing.

[0061] It should however be understood that the invention is not limited to such an embodiment, but also includes all screw-nut transmission systems covered by the claims.

[0062] For example, in another embodiment, not illustrated in the figures, the first magnet is connected to the fixed casing and the contact surface made of ferromagnetic material is connected to the portion of the first element. In this other embodiment, the first magnet may be located near a rolling plate which is not necessarily ferromagnetic, and a portion of the first element and/or a portion of the guide device (for example an outer ring and/or a bushing if the guide device is a ball bearing) is made of ferromagnetic material.

[0063] In this other embodiment, the first magnet may have larger dimensions compared to the first embodiment, however this has an impact on the total diameter of the screw-nut transmission system.

[0064] Figure 1 illustrates a perspective view of a linear actuator 1 comprising a screw-nut transmission system according to one embodiment of the invention. Figure 2 illustrates a longitudinal section of the linear actuator 1 of Figure 1. Figure 3 illustrates a detail of Figure 2. Figure 4 illustrates a cross section of Figure 1.

[0065] In the embodiment of Figures 1 to 4, the screw-nut transmission system comprises a nut 10 which moves with a translational movement along a main axis X (visible for example in Figure 2) of a screw 20 which rotates around this axis X with a rotational speed given by a motor M, possibly reduced by a reducer R. The nut 10 is connected to a head T, which therefore also moves by translation.

[0066] The linear actuator 1 may for example be used in a device such as for example and in a non-limiting manner an implantable device. Other examples include a linear actuator that can be assembled in parallel to constitute a tripod or a hexapod for positioning components such as mirrors, lenses or semiconductor wafers, or for guiding surgical tools for operations requiring high precision.

[0067] In the embodiment of Figures 1 to 4, the transmission system comprises a fixed casing 60 surrounding the nut 10 and the screw 20. In this embodiment, there are balls between the screw 20 and the nut 10. In this embodiment, the casing 60 is not a single piece, namely made monolithically, but it comprises several parts, including an internal part 61. In the embodiment of Figures 1 to 4, the casing also comprises a radial force take-up part 62, the presence of which is optional. In the embodiment of Figures 1 to 4, this part 62 is a ball cage (balls are for example visible in Figure 4) arranged to move half of the nut in the rotating screw configuration.

[0068] The casing 60, and in particular its internal part 61, comprises a groove 90 defined by sides. A portion of the nut 10 is arranged to move with a translational movement along the axis X in this groove 90.

[0069] In the embodiment of Figures 1 to 4, the transmission system comprises a rod 30 (for example a pin or a stud) essentially perpendicular to the axis X. This rod 30 is integral with the nut 10, so it also moves with a translational movement along the axis X in this groove 90. In the embodiment of Figures 1 to 4, this rod 30 is inserted into a cavity of the nut 10.

[0070] This rod 30 makes it possible in the embodiment of figures 1 to 4 to carry the first magnet 40 and also the guide device, which in this case is a ball bearing 80.

[0071] However, in other embodiments, the first magnet 40 and/or the guide device is (are) carried directly by the portion of the nut 10 which moves in the groove 90.

[0072] The guide device makes it possible to guide the movement of the portion of the nut 10 (and in the embodiment of FIGS. 1 to 4, of the rod 30 as well) in the groove 90. [0073] As best seen in FIG. 4, the ball bearing 80 comprises an inner ring 82 (which in this embodiment is static), an outer ring 83 (which in this embodiment is dynamic and in particular rotates about the Y axis, and rolling bodies 81 (balls in FIGS. 1 to 4) held between the outer ring 83 and the inner ring 82. In one embodiment, the static ring comprises two separate and interconnected parts, in particular a core and a cone, which is generally driven onto the core and which determines the desired clearance in the bearing. In another embodiment, the static ring comprises a single part, namely a core (without a cone): advantageously, the bearing may have clearance, since this is taken up by the system according to the invention.

[0074] A cage may in certain cases be used in a known manner in order to space the rolling bodies 81 between the rings.

[0075] The number of contact points (for example in the case where the rolling bodies are balls) or contact lines (for example in the case where the rolling bodies are rollers) of the rolling bodies with the rings may vary depending on the type of bearing. In the embodiment of FIGS. 1 to 4, the bearing 80 is a deep groove bearing. In another embodiment (not shown), the bearing 80 is a ball bearing with four contact points: in this case, the system according to the invention makes it possible to have a ball bearing with reduced play.

[0076] In one embodiment of FIGS. 1 to 4, the rolling bodies are non-magnetic or with low magnetic permeability, for example and in a non-limiting manner they are made of ceramic, which also avoids lubricating the bearing 80. The use of non-magnetic rolling bodies or with low magnetic permeability makes it possible to prevent any magnetization of the rolling bodies from disturbing the operation of the system according to the invention. However, the system according to the invention also operates with magnetizable rolling bodies, for example rolling bodies made of magnetizable steel. [0077] As best seen in Figure 4, the ball bearing 80 comprises in this embodiment an (external) sleeve 84 connected to the outer ring 83 and therefore also rotating around the Y axis.

[0078] In the embodiment of Figures 1 to 4, the screw-nut transmission system comprises a first magnet 40 connected via the rod 30 to the portion of the nut 10 which moves in the groove 90. In this embodiment, the first magnet 40 is integral with the dynamic part of the bearing 80, in particular the sleeve 84, and therefore it is also arranged to roll around the Y axis.

[0079] In one embodiment, the first magnet and/or the second magnet is a permanent magnet. In one embodiment, the first magnet and/or the second magnet is magnetized along the X-axis. In one embodiment, the first magnet and/or the second magnet has a substantially cylindrical shape.

[0080] According to the invention, the transmission system comprises a contact surface 51 made of ferromagnetic material (for example and in a non-limiting manner made of iron, iron alloy or magnetizable steel) connected to the fixed casing 60. In the embodiment of FIGS. 1 to 4, this contact surface 51 belongs to a plate 50 which is connected to the fixed casing 60, for example via one or more screws V. In another embodiment not illustrated, this contact surface 51 belongs directly to the fixed casing 60. In another embodiment, the plate 50 and the fixed casing 60 form a single-piece part.

[0081] According to the invention, this contact surface 51 cooperates with the first magnet 40, so as to block any rotation of the nut 10.

[0082] In the embodiment of Figures 1 to 4, the contact between the portion of the nut 10 which moves by translation in the groove 90 and one side of the groove 90 is an indirect contact, for example via the rod 30 and/or the guide device 80. In the embodiment of Figures 1 at 4, the bushing 84 of the guide device 80 touches the plate 50. In the absence of the bushing 84, it is the ring 83 which can roll on the plate 50. In this embodiment, the groove 90 is a clearance and is not intended to serve as a support for rolling. In the case of the plain bearing (figures 9 to 11), one side of the groove can be considered as a contact surface.

[0083] In one embodiment, at least one dynamic portion of the guide device (the outer sleeve 84 in the embodiment of FIGS. 1 to 4) comes into direct contact C with a portion of the contact surface 51, as for example visible in FIG. 4. The outer sleeve 84 therefore rolls on this contact surface 51.

[0084] In one embodiment, there is a distance d (air gap) between the first magnet 40 and the contact surface 51, visible for example in FIG. 4.

[0085] The magnetic attraction between the first magnet 40 and the contact surface 51 makes it possible to ensure the contact C, visible in FIG. 4, between a dynamic portion of the guide device (the outer sleeve 84 in the embodiment of FIGS. 1 to 4) and a portion of the contact surface 51.

[0086] In one embodiment, the adhesion force is sized to ensure this contact C under the extreme conditions required by the application of the system according to the invention (maximum load and acceleration). The adhesion force depends in particular on the magnetization power of the first magnet 40, the distance d and the material of the plate 51, etc.

[0087] As a non-limiting example, with a first cylindrical magnet 40 with a diameter of 4 mm and a height of 2 mm in neodymium N45 with a holding force of 4.1 N, a plate 50 in pure iron and a distance d of 0.3 mm, the adhesive force is 2.1 N. This force multiplied by the distance separating it from the X axis of the screw 20 must be greater than the transmissible torque during the extreme operating conditions of the system according to the invention (maximum load and acceleration).

[0088] In one embodiment, the contact surface made of ferromagnetic material 51 has the dimension parallel to the direction of translation of the nut 10 (therefore parallel to the axis X) less than 15 pm, preferably less than 10 pm, for example equal to 1 pm.

[0089] In one embodiment, the contact surface made of ferromagnetic material has a roughness (Ra) of less than 1 pm, preferably less than 0.8 pm, for example equal to 0.2 pm. In one embodiment, quenching and/or grinding is (are) used to obtain this roughness.

[0090] In the embodiment of FIGS. 1 to 4, the plate 50 comprises not only the contact surface 51 made of ferromagnetic material but also a fixing surface 52 (visible for example in FIG. 4) for fixing the plate 50 to the fixed casing 60.

[0091] In one embodiment, the entire plate 50 is made of ferromagnetic material.

[0092] In one embodiment, the contact surface 51 is substantially perpendicular to the fixing surface 52, as visible for example in FIG. 4. In the absence of this perpendicularity, a calibration of the system according to the invention can be carried out before its use.

[0093] Figure 5 illustrates a bottom view of another linear actuator 1 comprising a screw-nut transmission system according to another embodiment of the invention. Figure 6 illustrates a side view of the linear actuator 1 of Figure 5. Figure 7 illustrates a section longitudinal of the linear actuator 1 of figure 6. Figure 8 illustrates a cross-section of the linear actuator of figure 7, along the AA axis.

[0094] In the embodiment of Figures 5 to 8, the screw-nut transmission system comprises a screw 20 rotating about a main axis X of the screw (visible for example in Figure 7), with a rotation speed given by a motor M, possibly reduced by a reducer R. This rotation causes a translational movement of the nut 10 along the axis X. In the embodiment of Figures 5 to 8, there are balls between the screw 20 and the nut 10. This is a system similar to that of Figures 1 to 4, with the difference that in the embodiment of Figures 5 to 8, the first magnet 40 is non-rotating.

[0095] In the embodiment of Figures 5 to 8, the screw 20 rotates in a cavity of an intermediate part 70, which serves as a rolling surface for the ball bushing 61, 62 which takes up the radial forces and the bending force moment.

[0096] As in the embodiment of Figures 1 to 4, the transmission system of Figures 5 to 8 comprises a fixed casing 60 surrounding the nut 10 and the screw 20.

[0097] In the embodiment of FIGS. 5 to 8, the transmission system comprises a rod 30 (for example a pin or a stud) essentially perpendicular to the screw 20 and integral with the nut 10, therefore which also moves with a translational movement along the axis X in the groove 90. In the embodiment of FIGS. 5 to 8, this rod 30 is inserted into a cavity of the intermediate part 70 which is connected to the screw 20.

[0098] This rod 30 allows in the embodiment of figures 5 to 8 to carry the first magnet 40 and also the guide device, which is in this case also a ball bearing 80. [0099] The guide device makes it possible to guide the movement of the portion of the nut 10 (and in the embodiment of FIGS. 5 to 8, of the rod 30 as well) in the groove 90.

[00100] In the embodiment of Figures 5 to 8, the bearing 80 is also a deep groove ball bearing.

[00101] As best seen in Figure 8, the ball bearing 80 comprises in this embodiment an (external) sleeve 84 connected to the outer ring 83 and therefore also rotating around the Y axis.

[00102] However, in the embodiment of FIGS. 5 to 8, the first magnet 40 is carried by the rod 30 but it is not connected to the dynamic part of the bearing. Therefore in this embodiment, the first magnet 40 is non-rotating.

[00103] According to the invention, the transmission system comprises a contact surface 51 made of ferromagnetic material (for example and in a non-limiting manner made of iron, iron alloy or magnetizable steel) connected to the fixed casing 60. In the embodiment of FIGS. 5 to 8, this contact surface 51 belongs to a plate 50 which is connected to the fixed casing 60, for example via one or more screws V.

[00104] According to the invention, this contact surface 51 cooperates with the first magnet 40, so as to block any rotation of the nut 10.

[00105] In the embodiment of FIGS. 5 to 8, the contact between the portion of the nut 10 which moves by translation in the groove 90 and one side of the groove is an indirect contact, namely via the rod 30 and/or the guide device 80. [00106] In one embodiment, at least one dynamic portion of the guide device (the outer sleeve 84 in the embodiment of FIGS. 1 to 4) comes into direct contact C with a portion of the contact surface 51, as for example visible in FIG. 8.

[00107] In one embodiment, there is a distance d (air gap) between the first magnet 40 and the contact surface 51, visible for example in FIG. 8.

[00108] The magnetic attraction between the first magnet 40 and the contact surface 51 makes it possible to ensure contact C between a dynamic portion of the guide device (the outer sleeve 84 in the embodiment of FIGS. 1 to 4) and a portion of the contact surface 51.

[00109] As for the embodiment of figures 1 to 4, the adhesion force is dimensioned to ensure this contact C under the extreme conditions required by the application of the system according to the invention (maximum load and acceleration).

[00110] Of course, the presence of a first non-rotating magnet 40 is not linked to the presence of a nut 10 which moves by translation. The first magnet, rotating or not, can be placed either on the element which translates or on the casing. Generally, the aim is to minimize the mass of the element which translates. In the embodiments of FIGS. 1 to 4 and 5 to 8 and of FIG. 11, the first magnet is placed on the part which translates (on the nut subassembly for FIGS. 1 to 4 and 5 to 8; on the screw subassembly for FIG. 11).

[00111] In the embodiments of Figures 9 to 11, the guide device is a plain bearing 80'. In the embodiment of Figures 9 to 10 it is the nut that moves with a translational movement, on the other hand in the embodiment of Figure 11 it is the screw that moves with a translational movement. A linear actuator configuration 1 with a rotating nut (like the one in Figure 11) is commonly referred to as a “non-captive screw actuator.”

[00112] As regards the embodiment of FIGS. 9 and 10, the nut 10 which moves with a translational movement along a main axis X (visible for example in FIG. 9) is integral with an intermediate part 70, defining a cavity which receives at least a portion of the rotating screw 20.

[00113] In the embodiment of Figures 9 to 10, the transmission system comprises a fixed casing 60 surrounding the nut 10 and the screw 20.

[00114] The fixed casing 60 also comprises a plain bearing 80'. This plain bearing 80' comprises a groove 90 defined by sides. A portion of the intermediate piece 70 (or - in the absence of the intermediate piece 70 - a portion of the nut 10) is arranged to move with a translational movement along the X axis in this groove 90.

[00115] In the embodiment of FIGS. 9 to 10, the transmission system comprises a rod 30 (for example a pin or a stud) essentially perpendicular to the intermediate part 70 and secured to the intermediate part 70, and therefore to the nut 10, therefore which also moves with a translational movement along the axis X in this groove 90. In the embodiment of FIGS. 9 to 10, this rod 30 is inserted into a cavity of the intermediate part 70.

[00116] This rod 30 makes it possible, in the embodiment of FIGS. 9 to 10, to carry the first magnet 40.

[00117] In the embodiment of Figures 9 to 10, the guide device makes it possible to guide the movement of the rod 30 in the groove 90. In particular, at least a portion of the rod 30 comes into frictional contact with one side of the groove 90.

[00118] In the embodiment of Figures 9 to 10, the screw-nut transmission system comprises a first magnet 40 connected via the rod 30 to the portion of the intermediate piece 70 which moves in the groove 90. In this embodiment, the first magnet 40 is non-rotatable.

[00119] According to the invention, the transmission system comprises a contact surface 51 made of ferromagnetic material connected to the fixed casing 60. As for the embodiments of FIGS. 1 to 8, in the embodiment of FIGS. 9 to 10, this contact surface 51 belongs to a plate 50 which is connected to the fixed casing 60, for example via one or more screws V. In another embodiment not illustrated, this contact surface 51 is located directly on the fixed casing 60. In another embodiment, the plate 50 and the fixed casing 60 form a single piece.

[00120] According to the invention, this contact surface 51 cooperates with the first magnet 40, so as to ensure contact between the rod 30 and one side of the groove, which makes it possible to block any rotation of the nut 10.

[00121] In one embodiment, there is a distance d (air gap) between the first magnet 40 and the contact surface 51, visible for example in FIG. 10.

[00122] The magnetic attraction between the first magnet 40 and the contact surface 51 makes it possible to ensure contact C' between a portion of the smooth bearing 80' and a portion of the rod 30, as visible in FIG. 10.

[00123] As for the embodiments of figures 1 to 8, the adhesion force is dimensioned to ensure this contact C' under the extreme conditions required by the application of the system according to the invention (load and maximum acceleration). The adhesive force depends in particular on the magnetizing power of the first magnet 40, the distance d and the material of the plate 51, etc.

[00124] Figure 11 illustrates a longitudinal section of a perspective view of another linear actuator comprising a screw-nut transmission system according to another embodiment of the invention.

[00125] In the embodiment of Figure 11, the screw-nut transmission system comprises a nut 10 which moves with a rotational movement around a main axis X with a rotational speed given by a motor M, possibly reduced by a reducer R. (visible for example in Figure 9). The screw 20 moves by translation along this axis X.

[00126] In the embodiment of FIG. 11, the screw 20 is secured to an intermediate part 70, defining a cavity which receives at least a portion of the screw 20.

[00127] In the embodiment of Figure 11, the transmission system comprises a fixed casing 60 surrounding the nut 10 and the screw 20.

[00128] The casing 60 comprises a plain bearing 80' which comprises a groove 90 defined by sides. A portion of the intermediate piece 70 (or - in the absence of the intermediate piece 70 - a portion of the screw 20) is arranged to move with a translational movement along the X axis in this groove 90.

[00129] In the embodiment of Figure 11, the transmission system comprises a rod 30 as for the embodiments of Figures 9 to 10. This rod 30 makes it possible in the embodiment of Figure 11 to carry the first magnet 40. [00130] In the embodiment of FIG. 11, the guide device makes it possible to guide the movement of the rod 30 in the groove 90. In particular, at least a portion of the rod 30 comes into contact by friction with one side of the groove 90.

[00131] In the embodiment of Figure 11, the screw-nut transmission system comprises a first magnet 40 connected via the rod 30 to the portion of the intermediate piece 70 which moves in the groove 90. In this embodiment, the first magnet 40 is non-rotatable.

[00132] According to the invention, the transmission system comprises a contact surface 51 made of ferromagnetic material (for example and in a non-limiting manner made of iron, iron alloy or magnetizable steel) connected to the fixed casing 60. As for the embodiments of FIGS. 1 to 10, this contact surface 51 belongs to a plate 50 which is connected to the fixed casing 60, for example via one or more screws V. In another embodiment not illustrated, this contact surface 51 directly to the fixed casing 60. In another embodiment, the plate 50 and the fixed casing 60 form a single piece.

[00133] According to the invention, this contact surface 51 cooperates with the first magnet 40, so as to block any rotation of the screw 20.

[00134] In one embodiment, there is a distance d (air gap) between the first magnet 40 and the contact surface 51. The magnetic attraction between the first magnet 40 and the contact surface 51 makes it possible to ensure direct contact between a portion of the plain bearing 80' (in this case one side of the groove 90) and a portion of the rod 30.

[00135] In this case too, the adhesive force is dimensioned to ensure this contact under the extreme conditions required by the application of the system according to the invention (maximum load and acceleration). The adhesive force depends in particular on the magnetization power of the first magnet 40, the distance d and the material of the plate 51, etc. [00136] The invention relates to a rotary stroke bearing guiding device comprising:

- the transmission system according to the invention,

- a part (for example a lens) connected to the first element and therefore arranged to move with a translational movement, the contact surface made of ferromagnetic material cooperating with the first magnet, in order to block any rotation of the first element and therefore any rotation of the part.

[00137] In one embodiment, the lens must be moved linearly, but must not rotate (risk of changing the optical parameters of the lens composition). In this case, a magnetic play compensation according to the invention in this connection can be applied.

Tl

Reference numbers used in the figures

1 Linear actuator 10 Nut 20 Screw 30 Rod 40 First magnet 50 Plate 51 Contact surface 52 Fixing surface 60 Fixed casing 61 Internal part of the fixed casing 62 Radial force absorption part

70 Intermediate piece 80 Ball bearing 80' Plain bearing 81 Rolling bodies 82 Inner ring 83 Outer ring 84 Ball bearing sleeve 90 Groove A-A Axis for cross section C Contact between the bearing and the contact surface C' Contact between the bearing and the rod d Distance first magnet - contact surface M Motor MR Gearbox T Head V Screw X Main screw axis Y Axis of rotation of the bearing 80

Claims

Claims 1. Screw-nut transmission system, comprising: - a first element (10; 20), - a second element (20; 10) arranged to rotate about an axis (X) and cooperating with the first element (10; 20) so that the first element (10; 20) moves with a translational movement along this axis (X) when the second element rotates (20; 10), the first element (10; 20) being a nut respectively a screw, the second element (20; 10) being the screw respectively the nut, - a fixed envelope (60) at least partially surrounding the first element (10; 20) and the second element (20; 10) and comprising a groove (90) defined by sides, - the first element (10; 20) comprising a portion arranged to move with a translational movement in the groove (90), characterized in that the system comprises: - a first magnet (40) connected to this portion respectively to the fixed envelope (60), and in that - a contact surface (51) made of ferromagnetic material and/or a second magnet, the contact surface (51) and/or the second magnet being connected to the casing (60) fixed respectively to this portion, this contact surface (51) and/or the second magnet cooperating with the first magnet (40), so as to block any rotation of the first element (10; 20). 2. System according to claim 1, comprising a guide device (80; 80') for guiding the movement of the portion of the first element (10; 20). 3. System according to one of claims 1 or 2, the guide device being a rolling body guide device (80). 4. System according to claim 3, the rolling body guide device (80) being a ball bearing. 5. System according to one of claims 3 to 4, the rolling body guide device (80) comprising an outer ring (83) of which at least one portion is arranged to roll on the contact surface (51) made of ferromagnetic material and/or on the second magnet, or comprising a sleeve (84) connected to the outer ring (83) and of which at least one portion is arranged to roll on the contact surface (51) made of ferromagnetic material and/or on the second magnet. 6. System according to claim 5, the first magnet (40) being connected to the outer ring (83) or to the sleeve (84). 7. System according to one of claims 3 to 6, the rolling bodies being non-magnetic. 8. System according to one of claims 1 to 7, the portion of the first element (10; 20) being connected to a rod (30) arranged to move by translation in the groove and to carry the first magnet (40). 9. System according to claim 8, the rolling body guide device (80) being carried by the rod (30). 10. System according to one of claims 1 or 2, the guide device being a plain bearing (80'), the plain bearing (80') comprising said groove (90). 11. System according to one of claims 1 to 10, the contact surface (51) made of ferromagnetic material and/or on the second magnet having the dimension parallel to the translation direction (X) of the first element less than 15 |im. 12. System according to one of claims 1 to 11, the contact surface (51) made of ferromagnetic material and/or on the second magnet having a roughness (Ra) less than 1 |im. 13. System according to one of claims 1 to 12, in which the fixed casing (60) comprises a plate (50), the plate (50) comprising the contact surface (51) made of ferromagnetic material and/or on the second magnet, and a fixing surface (52) for fixing the plate (50) to the fixed casing (60). 14. System according to claim 13, the plate (50) being made of ferromagnetic material. 15. System according to one of claims 13 or 14, the contact surface (51) and/or on the second magnet being perpendicular to the fixing surface (52).