Improved linear actuator comprising a centrifugal clutch and associated method

Abstract

The invention relates to a linear actuator (1) comprising: - a linear unit (2) able to generate a linear movement, - a motor (3) for a motorized drive of the linear unit (2), comprising a drive shaft (4), - a drive connection (5) extending from the motor (3) to said linear unit (2), - a centrifugal brake (6), connected to the drive shaft (4) or to the drive connection (5) via a one-way clutch device (7). The one-way clutch device (7) is configured such that: - when the drive shaft (4) or the drive connection (5) is driven in a first direction of rotation, the centrifugal brake (6) is not rotated by said drive shaft (4) or said drive connection (5), and then does not produce any braking torque, - when the drive shaft (4) or the drive connection (5) is driven in a second direction of rotation, opposite to the first direction of rotation, the centrifugal brake (6) is rotated by said drive shaft (4) or said drive connection (5) and can therefore produce, upward of a predetermined rotational speed, a braking torque acting on the drive shaft (4) or on the drive connection (5).

Description

IMPROVED LINEAR ACTUATOR INCLUDING A CENTRIFUGAL CLUTCH AND ASSOCIATED METHOD TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to the field of linear actuators usable for generating linear movement.

[0002] A linear actuator is known comprising: - a linear unit capable of generating linear movement, - a motor for a motorized drive of the linear unit, comprising a motor shaft, - a drive connection extending from the motor to said linear unit.

[0003] For maximum efficiency in driving the linear unit by the motor, the drive connection and the linear unit are generally designed to have the least possible friction. The linear actuator therefore most often has an easily reversible character.

[0004] This can be particularly critical when the linear actuator is used to lift a load (which may be people): in the event of a motor failure or a power failure to the motor, gravity can cause reverse and uncontrolled drive in terms of speed or torque, which can damage the motor and / or the drive connection and / or the linear unit. This poses a significant risk of accident to the load (people, for example) carried via the linear actuator or to people in the immediate vicinity, due to a lowering speed that is too fast and / or an excessively intense shock at the end of the lowering stroke.

[0005] To solve this drawback, documents JP H08-26620 A and DE 10 2019 105 560 A1 provide for a centrifugal brake rigidly and permanently coupled to the motor shaft or drive connection. When the linear actuator operates above a predetermined speed, especially in reverse, the centrifugal brake produces a braking torque of the motor shaft or drive connection.

[0006] A first disadvantage is that the centrifugal brake permanently limits the speed of the motor shaft or drive connection, and therefore of the linear actuator. A second disadvantage is that it adds rotating elements that increase inertia and decrease the efficiency of the linear actuator. STATEMENT OF THE INVENTION

[0007] A problem addressed by the present invention is to provide a linear actuator having other means limiting the risks of damage to the motor and / or the drive connection and / or the linear unit, and limiting the risks to loads (e.g. individuals).

[0008] At the same time, the present invention aims to provide such a linear actuator with a wider operating speed range and improved efficiency.

[0009] To achieve these and other objects, the invention provides a linear actuator comprising: - a linear unit capable of generating linear movement, - a motor for a motorized drive of the linear unit, comprising a motor shaft, - a drive connection extending from the motor to said linear unit, - a centrifugal brake, connected to the motor shaft or the drive connection via a one-way clutch device configured so that: a. when the motor shaft or the drive connection is driven in a first direction of rotation, the centrifugal brake is not rotated by said motor shaft or said drive connection, and then does not produce any braking torque, b. when the motor shaft or the drive connection is driven in a second direction of rotation, opposite to the first direction of rotation, the centrifugal brake is rotated by said motor shaft or said drive connection and can then produce, above a predetermined rotational speed, a braking torque of the motor shaft or the drive connection.

[0010] The centrifugal brake is thus not rigidly and permanently coupled to the motor shaft or the drive connection. When the motor rotates in the first direction, the centrifugal brake which is not driven in rotation does not limit the operating speed of the linear actuator, and does not reduce its efficiency.

[0011] The operating speed of the linear actuator is only limited when the motor rotates in the second direction (corresponding to a reverse operation of the linear actuator such as lowering a load and / or individuals). In the event of a reverse operation (following a failure of the motor or its electrical power supply), the centrifugal brake produces, beyond a predetermined rotation speed, a braking torque of the motor shaft or the connection This effectively limits the risk of damage to the motor and / or the drive connection and / or the linear unit, as well as the risk of accidents to the load (possibly people) carried via the linear actuator or to people in the immediate vicinity.

[0012] In a particular embodiment, it can be provided that: - the drive connection comprises at least one rotation speed reduction device, preferably with gears, - the one-way clutch device is directly coupled to a section of the drive connection which is arranged between the motor and the reduction device.

[0013] The centrifugal brake is thus driven with the fastest rotation speed available in the linear actuator, which makes its operation more reliable and responsive.

[0014] The location of the centrifugal brake may however be different due to space or accessibility constraints. Thus, in another particular embodiment, it can be provided that: - the drive connection comprises at least one rotation speed reduction device, preferably with gears, - the one-way clutch device is coupled to a section of the drive connection which is arranged between said reduction device and said linear unit, - the one-way clutch device is coupled to said section of the drive connection by means of a rotational speed multiplication device, preferably with gears, arranged to give the centrifugal brake a rotational speed greater than that of said section of the drive connection.

[0015] The multiplication device allows the centrifugal brake to be driven at a rotation speed high enough to ensure its reliable operation and responsiveness.

[0016] In one embodiment, the one-way clutch device may comprise a ratchet mechanism.

[0017] In another embodiment, the one-way clutch device may comprise a roller freewheel.

[0018] Advantageously, the centrifugal brake can include: - a brake drum having an engagement surface, - at least one friction element having a friction surface, rotatable relative to the brake drum and radially movable between a rest position, in which the friction surface is located away from the surface engagement, and a braking position, in which the friction surface is in contact with the engagement surface, - elastic means permanently returning said at least one friction element to its rest position, and in which, beyond a predetermined rotational speed, said at least one friction element is moved by the effect of centrifugal force into its braking position by being pressed according to its friction surface against the engagement surface.

[0019] Preferably, to limit friction and improve the efficiency of the linear actuator, the linear unit may comprise a ball screw whose rod is driven in rotation by the drive connection and whose nut is movable bidirectionally in translation in a longitudinal direction by rotation of said ball screw rod.

[0020] Advantageously, the linear actuator may comprise: - an electromagnetic brake which, when the motor is no longer electrically powered, brakes the rotating motor shaft, - means for releasing the electromagnetic brake, manually actuated by a user to interrupt the braking of the motor shaft by the electromagnetic brake.

[0021] Such an electromagnetic brake makes it possible to effectively immobilize the linear actuator in the event of a failure of the motor or its power supply, while allowing voluntary release by a user if necessary (for example to lower a load, or even individuals, carried via the linear actuator).

[0022] According to another aspect, the present invention provides a device for lifting a load comprising a linear actuator as previously described.

[0023] Said device for lifting a load may preferably be of the scissor lift type.

[0024] According to another aspect, the present invention provides a method for braking a linear actuator comprising: - a linear unit capable of generating a linear movement, - a motor for a motorized drive of the linear unit, comprising a motor shaft, - a drive connection extending from the motor to said linear unit, - a centrifugal brake, wherein: - when the linear actuator is driven by the motor rotating in a first direction of rotation, the centrifugal brake is not rotated and therefore produces no braking torque, - when the linear actuator is subjected to an external force causing rotation of the motor or drive connection in a second direction of rotation, opposite to the first direction of rotation, the centrifugal brake is rotated and can then produce, above a predetermined rotational speed, a braking torque of the motor shaft or drive connection. SUMMARY DESCRIPTION OF THE DRAWINGS

[0025] Other objects, characteristics and advantages of the present invention will emerge from the following description of particular embodiments, made in relation to the attached figures, among which:

[0026] [Fig.1] Figure 1 is a schematic longitudinal sectional view of a first variant of a first embodiment of a linear actuator according to the present invention, with an actuator rod in a retracted position;

[0027] [Fig.2] Figure 2 is a schematic longitudinal sectional view of the linear actuator of Figure 1, with the actuator rod in an extended position;

[0028] [Fig.3] Figure 3 is a schematic detail view in longitudinal section of a centrifugal brake used in the linear actuator of Figures 1 and 2;

[0029] [Fig.4] Figure 4 is a schematic detail view in cross-section, in a first section plane, of the centrifugal brake of Figure 3;

[0030] [Fig.5] Figure 5 is a schematic cross-sectional detail view, in a second section plane parallel and offset from the first section plane, of the centrifugal brake of Figure 3;

[0031] [Fig.6] Figure 6 is a schematic detail view in longitudinal section of an electromagnetic brake used in the linear actuator of Figures 1 and 2;

[0032] [Fig.7] Figure 7 is a schematic longitudinal sectional view of a second variant of the first linear actuator embodiment of Figures 1 and 2;

[0033] [Fig.8] Figure 8 is a schematic longitudinal sectional view of a third variant of the first linear actuator embodiment of Figures 1 and 2;

[0034] [Fig.9] Figure 9 is a schematic longitudinal sectional view of a first variant of a second embodiment of a linear actuator according to the present invention;

[0035] [Fig.10] Figure 10 is a schematic detail view in longitudinal section of a centrifugal brake used in the linear actuator of Figure 9;

[0036] [Fig.11] Figure 11 is a schematic cross-sectional detail view of the centrifugal brake of Figure 9;

[0037] [Fig.12] Figure 12 is a schematic longitudinal sectional view of a second variant of the second linear actuator embodiment of Figure 9;

[0038] [Fig.13] Figure 13 is a schematic longitudinal sectional view of a third variant of the second linear actuator embodiment of Figure 9;

[0039] [Fig.14] Figure 14 is a schematic longitudinal sectional view of a fourth variant of the second linear actuator embodiment of Figure 9;

[0040] [Fig.15] Figure 15 is a schematic side view of a scissor lift type load lifting device using a linear actuator according to the present invention. DESCRIPTION OF PREFERRED EMBODIMENTS

[0041] When identical reference numerals are used in several figures, embodiments or variations of the invention, these reference numerals designate identical or similar elements in each of the figures, embodiments or variations.

[0042] In Figures 1 and 2 is illustrated a first variant of a first embodiment of linear actuator 1 according to the present invention.

[0043] Linear actuator 1 comprises: - a linear unit 2 capable of generating a linear movement illustrated by the double arrow ML, - a motor 3 for motorized driving of the linear unit 2, comprising a motor shaft 4, - a drive connection 5 extending from the motor 3 to said linear unit 2, - a centrifugal brake 6, connected to the drive shaft 4 via a one-way clutch device 7.

[0044] More precisely, the linear unit 2 comprises a rod 8 which can be moved linearly in a longitudinal direction 11 between a retracted position (figure 1) and at least one extended position (figure 2). In figure 2, the rod 8 is in an intermediate position between the retracted position (figure 1) and a position maximum extension. The rod 8 is arranged telescopically in an external tube 9.

[0045] The longitudinal movement of the rod 8 is caused by a ball screw 10. The ball screw 10 comprises a threaded rod 11 driven in rotation by the drive connection 5 and a nut 12 movable bidirectionally in translation in the longitudinal direction 11 by rotation of said threaded rod 11 of the ball screw 10.

[0046] The nut 12 is arranged to slide in the external tube 9, without the possibility of rotation around the longitudinal direction 11. To do this, the nut 12 is secured to an indexing member 13 provided with two radial protuberances 13a and 13b inserted into two internal longitudinal grooves 9a and 9b of the external tube 9.

[0047] The threaded rod 11 extends between a proximal end 11a coupled to the drive connection 5 via a coupling shaft 14 and a distal end 11b arranged to slide relative to the rod 8.

[0048] The motor shaft 4 is provided with an output pinion 15 which meshes with a first toothed wheel 16. The first toothed wheel 16 itself meshes with a second toothed wheel 17. The first 16 and second 17 toothed wheels constitute a reduction device 18 for the rotation speed. The role of the reduction device 18 is to drive the threaded rod 11 of the ball screw 10 at a lower rotation speed (for example 10 times lower) than that of the motor shaft 4.

[0049] When the motor 3 drives the motor shaft 4 in a first direction of rotation, the rod 8 is moved in the longitudinal direction 11 to its extended position (figure 2). When the motor 3 drives the motor shaft 4 in a second direction of rotation, opposite to the first direction of rotation, the rod 8 is moved in the longitudinal direction 11 to its retracted position (figure 1).

[0050] The linear actuator also includes: - an electromagnetic brake 19 which, when the motor 3 is no longer electrically powered (or experiences a fault), brakes the rotation of the motor shaft 4, - means 20 for releasing the electromagnetic brake 19, manually actuated (handle 21) by a user to interrupt the braking of the motor shaft 4 by the electromagnetic brake 19.

[0051] The electromagnetic brake 19 is a safety device intended to act in the event of a power failure or fault in the motor. The electromagnetic brake 19 is dimensioned so as to be able to apply sufficient braking torque to the motor shaft 4 to brake the motor shaft 4 to a standstill, in particular when a fault in the motor 3 or its power supply causes a reverse operation of the linear actuator by a force applied to the rod 8 and tending to retract it. An example of an electromagnetic brake for an electric motor is for example illustrated in document DE 199 35 196 C1.

[0052] An electromagnetic brake 19 is more particularly illustrated schematically in Figure 6. This electromagnetic brake 19 comprises a friction disc 22 slidably mounted on the motor shaft 4 in the longitudinal direction 11-11 of said motor shaft 4 (the motor shaft 4 is not shown in Figure 6) and is indexed in rotation on the motor shaft 4 (by a key or splines for example). On either side of the friction disc 22 are provided two friction linings 23 and 24, immobile in rotation relative to the frame 19a of the electromagnetic brake 19. When the motor 3 is electrically powered, a first system of springs and an electromagnet also electrically powered (not shown) keep the friction disc 22 away in the longitudinal direction 11-11 from the friction linings 23 and 24.When the motor 3 is no longer electrically powered, a second spring system (not shown) is released by the simultaneous interruption of the power supply to the electromagnet. This second spring system moves (in the longitudinal direction II-II) and presses the friction lining 24 towards the friction lining 23 until it sandwiches the friction disc 22 with a pressing force making it possible to brake and stop the rotation of the friction disc 22.

[0053] To interrupt the braking of the motor shaft 4 by the electromagnetic brake 19, a user can manually move the handle 21 by applying a pulling force thereto illustrated by the arrow 25. Moving the handle 25 in a movement parallel to the longitudinal direction 11-11 allows the friction lining 24 to be moved away from the friction lining 23 and against the second spring system, which has the effect of releasing the friction disc 22 and the motor shaft 4 which can then rotate again. If the user releases the force applied to the handle 25, the second spring system returns and presses the friction lining 24 towards the friction lining 23 until it sandwiches the friction disc 22 to restore the braking of the motor shaft 4.

[0054] The one-way clutch device 7 (Figures 1 and 2) is configured so that: - when the motor shaft 4 or the drive connection 5 is driven in a first direction of rotation, the centrifugal brake 6 is not driven in rotation by said motor shaft 4 or said drive connection 5, and then does not produce any braking torque, - when the motor shaft 4 or the drive connection 5 is driven in a second direction of rotation, opposite to the first direction of rotation, the centrifugal brake 6 is rotated by said motor shaft 4 or said drive connection 5 and can then produce, beyond a predetermined rotational speed, a braking torque of the motor shaft 4 or of the drive connection 5.

[0055] When motor 3 rotates in the first direction of rotation, the centrifugal brake 6 is not driven in rotation and does not limit the operating speed of the linear actuator 1.

[0056] The operating speed of the linear actuator 1 is, however, limited when the motor 3 rotates in the second direction (corresponding to a reverse operation of the linear actuator 1 such as the lowering of a load and / or individuals). In the event of a reverse operation (following a failure of the motor 3 or its electrical power supply), the centrifugal brake 6 produces, above a predetermined rotation speed, a braking torque of the motor shaft 4 or the drive connection 5. This effectively limits the risks of damage to the motor 3 and / or the drive connection 5 and / or the linear unit 2, but also the risks of accidents for the load (possibly individuals) carried via the linear actuator 1 or for individuals located in the immediate vicinity.

[0057] If there is a power failure of the motor 3 or a failure of the motor 3 when the linear unit 2 is in the at least partial extension position of its rod 8 (or even completely as in Figure 2), the load carried via the linear actuator 1 induces on the rod 8 a force F (Figure 2) tending to move it towards its retracted position (Figure 1). The low friction in the linear unit 2 (ball screw 10 in particular) and in the drive connection 5 then allows an uncontrolled reverse operation of the linear actuator 1 which may present: - a risk of damage to the motor 3, the drive connection 5 and / or the linear unit 2, and / or - a risk to individuals located in the immediate vicinity of the linear actuator 1.

[0058] The interruption of the electrical power supply to the motor 3 or failure of the motor 3 causes an interruption of the power supply to the electromagnet of the electromagnetic brake 19, which immediately applies to the motor shaft 4 a braking torque sufficient to brake the motor shaft 4 until it stops. The rod 8 is then held in its position in the first longitudinal direction 11.

[0059] It may however be necessary to maneuver the rod 8 towards its retracted position, for example to lower the load (possibly individuals) which is blocked. To do this, a user can interrupt the braking of the motor shaft 4 by the electromagnetic brake 19, by manually moving the handle 21 by applying a pulling force illustrated by the arrow 25.

[0060] The force F then causes a reverse operation of the linear actuator 1 with a rotation of the motor 3 or of the drive connection in the second direction of rotation: the centrifugal brake 6 is rotated by said motor shaft 4 or said drive connection 5 and can then produce, beyond the predetermined rotation speed, a braking torque of the motor shaft 4 or of the drive connection 5. The predetermined rotation speed is naturally chosen so as to limit the risks, whether for the motor 3, the drive connection 5, the linear unit 2, the individuals located in the immediate vicinity of the linear actuator 1 as well as for the load (possibly individuals) carried via the linear actuator.

[0061] In other words, a method of braking a linear actuator 1 is implemented comprising: - a linear unit 2 capable of generating a linear movement, - a motor 3 for a motorized drive of the linear unit 2, comprising a motor shaft 4, - a drive connection 5 extending from the motor 3 to said linear unit 2, - a centrifugal brake 6, in which process: - when the linear actuator 1 is driven by the motor 3 rotating in a first direction of rotation, the centrifugal brake 6 is not driven in rotation and therefore does not produce any braking torque, - when the linear actuator 1 is subjected to an external force causing rotation of the motor 3 or the drive connection 5 in a second direction of rotation, opposite to the first direction of rotation, the centrifugal brake 6 is driven into rotation and can then produce, above a predetermined rotation speed, a braking torque of the motor shaft 4 or the drive connection 5.

[0062] The centrifugal brake 6 and one-way clutch device 7 used in the first embodiment illustrated in Figures 1 to 8 are more particularly illustrated in Figures 3 to 5. Figure 4 is a sectional view taken along a section plane P1 while Figure 5 is a sectional view taken along a section plane P2.

[0063] The one-way clutch device 7 comprises a roller freewheel 26. An example of a one-way clutch of the roller freewheel type is for example illustrated in document US 5,664,653 A.

[0064] When the motor shaft 4 rotates in the first direction of rotation S1, the rollers 26a slide on the outer surface of an inner ring 27a (keyed to the motor shaft 4) of the freewheel so that the centrifugal brake 6 is not driven in rotation by said motor shaft 4. When the motor shaft 4 rotates in the second direction of rotation S2, the rollers 26a are braced between the outer surface of the inner ring 27a (keyed to the motor shaft 4) and an outer ring 27b of the freewheel which drives the centrifugal brake 6 in rotation.

[0065] Centrifugal brake 6 includes: - a braking drum 28 comprising an engagement surface 29, - three friction elements 30a to 30c comprising a respective friction surface 31a to 31c, radially movable between a rest position (figure 5), in which the friction surfaces 31a to 31c are located away from the engagement surface 29, and a braking position, in which the friction surfaces 31a to 31c are in contact with the engagement surface 29, - elastic means 32 (two helical springs 32a and 32b) permanently returning the friction elements 30a to 30c to their rest position.

[0066] Beyond said predetermined speed, the friction elements 30a to 30c are moved by the effect of centrifugal force into their braking position by being pressed according to their respective friction surfaces 31a to 31c against the engagement surface 29.

[0067] In the variants of the first embodiment, respectively illustrated in figures 1 and 2, 7 and 8: - the drive connection 5 comprises at least one device 18 for reducing the rotation speed (with gears), - the one-way clutch device 7 is directly coupled to a section of the drive connection 5 which is arranged between the motor 3 and the reduction device 18.

[0068] More precisely: - in the first variant of the first embodiment, illustrated in Figures 1 and 2, the one-way clutch device 7 is directly coupled to the output end of the drive shaft 4, just after the output pinion 15, - in the second variant of the first embodiment, illustrated in Figure 7, the one-way clutch device 7 is directly coupled to the drive shaft 4 just before the output pinion 15, - in the third variant of the first embodiment, illustrated in Figure 8, the one-way clutch device 7 is directly coupled to the rear end of the drive shaft 4 protruding beyond the electromagnetic brake 19.

[0069] In all these variants, such an arrangement makes it possible to drive the centrifugal brake 6 according to the fastest rotation speed available in the linear actuator 1, which makes the operation of the centrifugal brake 6 more reliable and makes it more responsive.

[0070] The centrifugal brake 6 and one-way clutch device 7 used in the second embodiment illustrated in Figures 9 to 14 are more particularly illustrated in Figures 10 and 11. The centrifugal brake 6 is similar to that illustrated in Figures 3 to 5 previously explained.

[0071] Figure 11 is a sectional view taken along a section plane P3, and shows that the one-way clutch device 7 comprises a ratchet mechanism 33a to 33d.

[0072] The pawls 33a to 33d are carried by an internal cage 34 of the one-way clutch device 7 made integral in rotation with the drive shaft 4 by means of a key 35. The centrifugal brake 6 is coupled to the drive shaft 4 by a ball bearing 36 and is integral with an external cage 37 of the one-way clutch device 7. The external cage 37 of the one-way clutch device 7 comprises a plurality of housings 38 capable of receiving and cooperating with the pawls 33a to 33d to couple in rotation the internal cage 34 and the external cage 37.

[0073] When the motor shaft 4 rotates in the first direction of rotation S1, the pawls 33a to 33d slide on the surface of the outer cage 37 so that the centrifugal brake 6 is not rotated by said motor shaft 4. When the motor shaft 4 rotates in the second direction of rotation S2, the pawls 33a to 33d engage in the housings 38 of the outer cage 37 and couple in rotation the inner cage 34 and the outer freewheel cage 37 which rotates the centrifugal brake 6.

[0074] In the first, second and third variants of the second embodiment, respectively illustrated in Figures 9, 12 and 13: - the drive connection 5 comprises at least one device 18 for reducing the rotation speed (with gears), - the one-way clutch device 7 is directly coupled to a section of the drive connection 5 which is arranged between the motor 3 and the reduction device 18.

[0075] More precisely: - in the first variant of the second embodiment, illustrated in Figure 9, the one-way clutch device 7 is directly coupled to the output end of the drive shaft 4, just after the output pinion 15, - in the second variant of the second embodiment, illustrated in Figure 12, the one-way clutch device 7 is directly coupled to the drive shaft 4, just before the output gear 15, - in the third variant of the second embodiment, illustrated in the figure 13, the one-way clutch device 7 is directly coupled to the rear end of the drive shaft 4 protruding beyond the electromagnetic brake 19.

[0076] In all these variants, such an arrangement makes it possible to drive the centrifugal brake 6 according to the fastest rotation speed available in the linear actuator 1, which makes the operation of the centrifugal brake 6 more reliable and makes it more responsive.

[0077] In the fourth variant of the second embodiment, illustrated in Figure 14, the centrifugal brake 6 is connected to the drive connection 5 via the one-way clutch device 7.

[0078] More precisely: - the drive connection 5 comprises at least one device 18 for reducing the rotation speed (with gears), - the one-way clutch device 7 is coupled to a section of the drive connection 5 which is arranged between said reduction device 18 and said linear unit 2, - the one-way clutch device 7 is coupled to said section of the drive connection 5 via a rotation speed multiplication device 39.

[0079] Here, the internal structure of the multiplication device 39 is not explained, but it may for example comprise gears. Functionally, the multiplication device 39 is interposed between the proximal end 11a of the rod 11 of the ball screw 10 and the one-way clutch device 7. The multiplication device 39 makes it possible to maintain a drive of the centrifugal brake 6 at a rotation speed that is sufficiently high to make its operation and responsiveness reliable.

[0080] It should be noted that an arrangement of the centrifugal brake 6 with a multiplication device 39 as illustrated in the fourth variant of the second embodiment (figure 14) is also possible in the first embodiment of figures 1 to 8.

[0081] In Figure 15 is illustrated an example of use of a linear actuator 1 according to the present invention. In this case, the linear actuator 1 is used in a device 40 for lifting a load (here the load comprises individuals 41). The lifting device 40 is more particularly of the scissor lift type driven by the linear actuator 1: when the rod 8 of the linear actuator is moved to its extension position, the scissor structure is unfolded to raise the individuals, and when the rod 8 of the linear actuator is moved to its retracted position, the scissor structure is folded to lower the individuals.

[0082] The present invention is not limited to the embodiments which have been explicitly described, but it includes the various variations and generalizations contained within the scope of the following claims.

Claims

CLAIMS

1. Linear actuator (1) comprising: - a linear unit (2) capable of generating a linear movement, - a motor (3) for a motorized drive of the linear unit (2), comprising a motor shaft (4), - a drive connection (5) extending from the motor (3) to said linear unit (2), - a centrifugal brake (6), connected to the motor shaft (4) or to the drive connection (5), characterized in that the centrifugal brake (6) is connected to the motor shaft (4) or to the drive connection (5) via a one-way clutch device (7) configured so that: a. when the motor shaft (4) or the drive connection (5) is driven in a first direction of rotation, the centrifugal brake (6) is not rotated by said motor shaft (4) or said drive connection (5), and then does not produce any braking torque, b.when the motor shaft (4) or the drive connection (5) is driven in a second direction of rotation, opposite to the first direction of rotation, the centrifugal brake (6) is rotated by said motor shaft (4) or said drive connection (5) and can then produce, above a predetermined rotational speed, a braking torque of the motor shaft (4) or the drive connection (5).

2. Linear actuator (1) according to claim 1, characterized in that: - the drive connection (5) comprises at least one device (18) for reducing the rotation speed, preferably with gears, - the one-way clutch device (7) is directly coupled to a section of the drive connection (5) which is arranged between the motor (3) and the reduction device (18).

3. Linear actuator (1) according to claim 1, characterized in that: - the drive connection (5) comprises at least one device (18) for reducing the rotation speed, preferably with gears, - the one-way clutch device (7) is coupled to a section of the drive connection (5) which is arranged between said reduction device (18) and said linear unit (2), - the one-way clutch device (7) is coupled to said section of the drive connection (5) by means of a rotational speed multiplication device (39), preferably with gears, arranged to give the centrifugal brake (6) a rotational speed higher than that of said section of the drive connection (5) which is arranged between said reduction device (18) and said linear unit (2).

4. Linear actuator (1) according to any one of the claims 1 to 3, characterized in that the one-way clutch device (7) comprises a ratchet mechanism (33a-33d).

5. Linear actuator (1) according to any one of claims 1 to 3, characterized in that the one-way clutch device (7) comprises a roller freewheel (26).

6. Linear actuator (1) according to any one of claims 1 to 5, characterized in that the centrifugal brake (6) comprises: - a brake drum (28) comprising an engagement surface (29), - at least one friction element (30a-30c) comprising a friction surface (31a-31c), radially movable between a rest position, in which the friction surface (31a-31c) is located away from the engagement surface (29), and a braking position, in which the friction surface (31a-31c) is in contact with the engagement surface (29), - elastic means (32) permanently returning said at least one friction element (30a-30c) to its rest position, and in which, above a predetermined speed, said at least one friction element (30a-30c) is moved by the effect of centrifugal force into its braking position by being pressed according to its friction surface (31a-31c) against the engagement surface (29).

7. Linear actuator (1) according to any one of claims 1 to 6, characterized in that the linear unit (2) comprises a ball screw (10) whose rod (11) is driven in rotation by the drive connection (5) and whose nut (12) is movable bidirectionally in translation in a longitudinal direction (ll) by rotation of said rod (11) of the ball screw (10).

8. Linear actuator (1) according to any one of claims 1 to 7, characterized in that it comprises: - an electromagnetic brake (19) which, when the motor (3) is no longer electrically powered, brakes the rotating motor shaft (4), - means (20) for releasing the electromagnetic brake (19), manually actuated by a user to interrupt the braking of the motor shaft (4) by the electromagnetic brake (19).

9. A load lifting device (40) comprising a linear actuator (1) according to any one of claims 1 to 8, said load lifting device (40) preferably being of the scissor lift type.

10. Method for braking a linear actuator (1) comprising: - a linear unit (2) capable of generating a linear movement, - a motor (3) for a motorized drive of the linear unit (2), comprising a motor shaft (4), - a drive connection (5) extending from the motor (3) to said linear unit (2), - a centrifugal brake (6), in which method: - when the linear actuator (1) is driven by the motor (3) rotating in a first direction of rotation (S1), the centrifugal brake (6) is not driven in rotation and therefore does not produce any braking torque, - when the linear actuator (1) is subjected to an external force causing rotation of the motor (3) or the drive connection (5) in a second direction of rotation (S2), opposite to the first direction of rotation, the centrifugal brake (6) is rotated and can then produce, above a predetermined rotational speed, a braking torque of the motor shaft (4) or the drive connection (5).

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