IMPROVED LINEAR ACTUATOR

Abstract

IMPROVED LINEAR ACTUATOR Linear actuator (1) comprising: - a linear unit (2) capable of generating linear motion, - a motor (3) for 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 driven in rotation by said drive shaft (4) or said drive connection (5), and therefore produces no 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 driven in rotation by said drive shaft (4) or said drive connection (5) and can then produce, beyond a predetermined rotational speed, a braking torque on the drive shaft (4) or the drive connection (5). Figure to be published with the abbreviation: Fig. 1.

Description

Title of the invention: IMPROVED LINEAR ACTUATOR TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to the field of linear actuators usable to generate linear motion.

[0002] A linear actuator is known comprising: - a linear unit capable of generating linear motion, - a motor for 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 as little friction as possible. The linear actuator thus most often exhibits easily reversible characteristics.

[0004] This can be particularly critical when the linear actuator is used to lift a load (which may be people): in the event of motor failure or power supply failure, gravity can cause an uncontrolled reverse drive in terms of speed or torque, potentially damaging the motor and / or the drive connection and / or the linear unit. This poses a significant risk of injury to the load (people, for example) being lifted by the linear actuator, or to people in the immediate vicinity, due to an excessively rapid lowering speed and / or an excessively strong shock at the end of the lowering stroke.

[0005] To overcome 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 beyond a predetermined speed, particularly in reverse, the centrifugal brake produces a braking torque on 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. Description of the invention

[0007] One 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 linear unit, and limiting the risks to loads (e.g. individuals).

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

[0009] To reach these objects and others, the invention proposes a linear actuator comprising: - a linear unit capable of generating linear motion, - a motor for motorized drive of the linear unit, comprising a drive shaft, - a drive connection extending from the motor to said linear unit, - a centrifugal brake, connected to the drive shaft or drive connection via a one-way clutch device configured such that: a. when the drive shaft or drive connection is driven in a first direction of rotation, the centrifugal brake is not driven in rotation by said drive shaft or drive connection, and therefore produces no braking torque, b. when the drive shaft or drive connection is driven in a second direction of rotation, opposite to the first direction of rotation, the centrifugal brake is driven in rotation by said drive shaft or drive connection and can then produce, beyond a predetermined rotational speed, a braking torque of the drive shaft or drive connection.

[0010] The centrifugal brake is therefore 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, nor does it reduce its efficiency.

[0011] The operating speed of the linear actuator is limited only when the motor rotates in the second direction (corresponding to a reverse operation of the linear actuator, such as lowering a load and / or people). In the event of a reverse operation (following a failure of the motor or its power supply), the centrifugal brake, beyond a predetermined rotational speed, produces a braking torque on the motor shaft or the drive 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 by the linear actuator or to people in the immediate vicinity.

[0012] In a particular embodiment, it can be provided that: - the drive connection includes at least one speed reduction device, preferably geared, - 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 rotational speed available in the linear actuator, which makes its operation more reliable and more responsive.

[0014] The location of the centrifugal brake may, however, be different due to space or accessibility constraints. Thus, in another particular embodiment, it may be provided that: - the drive connection includes at least one speed reduction device, preferably geared, - the one-way clutch device is coupled to a section of the drive connection which is disposed 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 speed multiplication device, preferably geared, arranged to give the centrifugal brake a rotational speed greater than that of said section of the drive connection.

[0015] The multiplication device makes it possible to maintain a drive of the centrifugal brake at a rotational speed high enough to ensure the reliability of its operation and its responsiveness.

[0016] In one embodiment, the unidirectional clutch device may include a ratchet mechanism.

[0017] In another embodiment, the unidirectional clutch device may include a roller freewheel.

[0018] Advantageously, the centrifugal brake may comprise: - a brake drum comprising an engagement surface, - at least one friction element comprising a friction surface, rotatable relative to the brake drum and radially movable between a rest position, in which the friction surface is away from the engagement surface, and a braking position, in which the friction surface is in contact with the engagement surface, - elastic means that continuously return 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 displaced by the effect of centrifugal force into its braking position by being pressed along its friction surface against the engagement surface.

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

[0020] Advantageously, the linear actuator may include: - an electromagnetic brake which, when the motor is no longer electrically powered, brakes the rotating motor shaft, - means of releasing the electromagnetic brake, which can be manually operated 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 failure of the motor or its power supply, while allowing voluntary release by a user if needed (for example to lower a load, or even individuals, carried via the linear actuator).

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

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

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

[0025] Other objects, features and advantages of the present invention will become apparent from the following description of particular embodiments, made in relation to the accompanying figures, among which:

[0026] [Fig-1] Fig. 1 is a schematic longitudinal cross-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] The [Fig.2] is a schematic longitudinal sectional view of the linear actuator of the [Fig.1], with the actuator rod in an extended position;

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

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

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

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

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

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

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

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

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

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

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

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

[0040] [Fig. 15] The [Fig. 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 IMPLEMENTATION METHODS

[0041] When identical numerical references are used in several figures, embodiments or variants of the invention, these numerical references designate identical or similar elements in each of the figures, embodiments or variants.

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

[0043] The linear actuator 1 comprises: - a linear unit 2 capable of generating linear motion, illustrated by the double arrow ML, - a motor 3 for 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 drive shaft 4 via a one-way clutch device 7.

[0044] More precisely, the linear unit 2 comprises a rod 8 that can be moved linearly along a longitudinal direction II between a retracted position ([Fig. 1]) and at least one extended position ([Fig. 2]). In [Fig. 2], the rod 8 is in an intermediate position between the retracted position ([Fig. 1]) and a maximum extended position. The rod 8 is arranged telescopically within 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 along the longitudinal direction II by rotation of said threaded rod 11 of ball screw 10.

[0046] The nut 12 is arranged to slide in the outer tube 9, without the possibility of rotation around the longitudinal direction II. To achieve this, the nut 12 is fixed to an indexing member 13 having two radial protrusions 13a and 13b inserted into two internal longitudinal grooves 9a and 9b of the outer tube 9.

[0047] The threaded rod 11 extends between a proximal end 1 coupled to the drive connection 5 via a coupling shaft 14 and a distal end 11b arranged to slide relative in the rod 8.

[0048] The drive shaft 4 is equipped with an output pinion 15 which meshes with a first gear 16. The first gear 16 meshes with a second gear 17. The first 16 and second 17 gears together form a speed reduction device 18. The role of the speed reduction device 18 is to drive the threaded rod 11 of the ball screw 10 at a lower rotational speed (for example, 10 times lower) than that of the drive shaft 4.

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

[0050] The linear actuator also includes: - an electromagnetic brake 19 which, when the motor 3 is no longer electrically supplied (or has a fault), brakes the rotation of the motor shaft 4, - means of releasing the electromagnetic brake 19 20, which can be manually operated (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 designed to act in the event of a power failure or motor malfunction. The electromagnetic brake 19 is dimensioned to be able to apply sufficient braking torque to the motor shaft 4 to bring it to a standstill, particularly when a fault in the motor 3 or its power supply causes the linear actuator to reverse direction by applying force to the rod 8, tending to retract it. An example of an electromagnetic brake for an electric motor is illustrated, for instance, in document DE 199 35 196 CL

[0052] An electromagnetic brake 19 is illustrated schematically in particular in [Fig. 6]. This electromagnetic brake 19 comprises a friction disc 22 slidably mounted on the drive shaft 4 in the longitudinal direction II-II of said drive shaft 4 (the drive shaft 4 is not shown in [Fig. 6]) and is indexed against rotation on the drive shaft 4 (by a key or splines, for example). On either side of the friction disc 22 are two friction linings 23 and 24, which are fixed against 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), hold the friction disc 22 away from the friction linings 23 and 24 in the longitudinal direction II-II.When the motor 3 is no longer electrically powered, a second spring system (not shown) is released by the simultaneous interruption of the electromagnet's power supply. This second spring system displaces (along 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 that brakes and stops the friction disc 22 from rotating.

[0053] To interrupt the braking of the drive shaft 4 by the electromagnetic brake 19, a user can manually move the handle 21 by applying a pulling force as illustrated by the arrow 25. The movement of the handle 25 along a A movement parallel to the longitudinal direction II-II allows the friction lining 24 to move away from the friction lining 23 and against the second spring system, thereby releasing the friction disc 22 and the drive 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, thus re-establishing the braking of the drive shaft 4.

[0054] The one-way clutch device 7 (Figures 1 and 2) 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 driven in rotation by said drive shaft 4 or said drive connection 5, and therefore produces no 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 driven in rotation by said drive shaft 4 or said drive connection 5 and can then produce, beyond a predetermined rotational speed, a braking torque of the drive shaft 4 or the drive connection 5.

[0055] When the 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 limited when the motor 3 rotates in the second direction (corresponding to a reverse operation of the linear actuator 1, such as lowering a load and / or people). In the event of a reverse operation (following a failure of the motor 3 or its power supply), the centrifugal brake 6, beyond a predetermined rotational speed, produces a braking torque on the motor shaft 4 or the drive connection 5. This effectively limits the risk of damage to the motor 3 and / or the drive connection 5 and / or the linear unit 2, as well as the risk of accidents for the load (possibly people) carried via the linear actuator 1 or for people in the immediate vicinity.

[0057] If there is a power failure to the motor 3 or a failure of the motor 3 occurs when the linear unit 2 is in the position of at least partial extension of its rod 8 (or even fully extended as in [Fig. 2]), the load carried via the linear actuator 1 induces a force F on the rod 8 ([Fig. 2]) tending to move it towards its retracted position ([Fig. 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 movement of the linear actuator 1 which may result in: - 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 linear actuator 1.

[0058] A power failure to motor 3 or a motor 3 malfunction causes a power failure to the electromagnet of the electromagnetic brake 19, which immediately applies a braking torque to the motor shaft 4 sufficient to brake the motor shaft 4 until it comes to a stop. The rod 8 is then held in its position along the first longitudinal direction II.

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

[0060] The force F then causes a reverse movement of the linear actuator 1 with a rotation of the motor 3 or the drive connection in the second direction of rotation: the centrifugal brake 6 is driven in rotation by said motor shaft 4 or said drive connection 5 and can then produce, beyond the predetermined rotational speed, a braking torque of the motor shaft 4 or the drive connection 5. The predetermined rotational 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 braking method for a linear actuator 1 is implemented, comprising: - a linear unit 2 capable of generating linear motion, - a motor 3 for 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 produces no braking torque, - when the linear actuator 1 is subjected to an external force causing the motor 3 or the drive connection 5 to rotate 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, beyond a predetermined rotational speed, a braking torque of the motor shaft 4 or of the drive connection 5.

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

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

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

[0065] The centrifugal brake 6 comprises: - a brake drum 28 having an engagement surface 29, - three friction elements 30a to 30c having respective friction surfaces 31a to 31c, movable radially between a rest position ([Fig.5]), in which the friction surfaces 31a to 31c are 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 the said predetermined speed, the friction elements 30a to 30c are displaced 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 includes at least one speed reduction device 18 (gear-type), - 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 motor shaft 4, just after the output pinion 15, - in the second variant of the first embodiment, illustrated in [Fig.7], the one-way clutch device 7 is directly coupled to the motor shaft 4 just before the output pinion 15, - in the third variant of the first embodiment, illustrated in [Fig.8], the unidirectional 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 allows the centrifugal brake 6 to be driven according to the fastest rotational speed available in the linear actuator 1, which makes the operation of the centrifugal brake 6 more reliable and responsive.

[0070] The centrifugal brake 6 and unidirectional 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] Fig. 11 is a sectional view taken along a section plane P3, and shows that the unidirectional clutch device 7 comprises a ratchet mechanism 33a to 33d.

[0072] The pawls 33a to 33d are carried by an inner cage 34 of a one-way clutch device 7 which is rotationally fixed to 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 fixed to an outer cage 37 of a one-way clutch device 7. The outer cage 37 of the one-way clutch device 7 has a plurality of housings 38 adapted to receive and cooperate with the pawls 33a to 33d to rotationally couple the inner cage 34 and the outer cage 37.

[0073] When the drive shaft 4 rotates in the first direction of rotation SI, the pawls 33a to 33d slide on the surface of the outer cage 37 so that the centrifugal brake 6 is not driven in rotation by said drive shaft 4. When the drive 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 drives in rotation 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 includes at least one speed reduction device 18 (gear-type), - 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 [Fig.9], the one-way clutch device 7 is directly coupled to the output end of the motor shaft 4, just after the output pinion 15, - in the second variant of the second embodiment, illustrated in [Fig. 12], 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 second embodiment, illustrated in [Fig. 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 allows the centrifugal brake 6 to be driven according to the fastest rotational speed available in the linear actuator 1, which makes the operation of the centrifugal brake 6 more reliable and responsive.

[0077] In the fourth variant of the second embodiment, illustrated in [Fig. 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 includes at least one speed reduction device 18 (gear-type), - the one-way clutch device 7 is coupled to a section of the drive connection 5 which is disposed between said reduction device 18 and said linear unit 2, - the unidirectional clutch device 7 is coupled to said section of the drive connection 5 via a speed multiplication device 39.

[0079] Here, the internal structure of the multiplication device 39 is not explicitly described, but it may, for example, include gears. Functionally, the multiplication device 39 is interposed between the proximal end 1 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 rotational speed sufficiently high to ensure its reliable operation and responsiveness.

[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 ([Fig. 14]) is also possible in the first embodiment of Figures 1 to 8.

[0081] Figure 15 illustrates an example of the use of a linear actuator 1 according to the present invention. In this case, the linear actuator 1 is used in a device lifting device 40 of a load (here the load includes 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 towards its extension position the scissor structure is unfolded to raise the individuals, and when the rod 8 of the linear actuator is moved towards its retraction position the scissor structure is folded to lower the individuals.

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

Claims

Demands

1. Linear actuator (1) comprising: - a linear unit (2) capable of generating linear motion, - a motor (3) for 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 drive shaft (4) or to the drive connection (5) via a one-way clutch device (7) configured such that: a. when the drive 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 drive shaft (4) or said drive connection (5), and therefore does not produce any braking torque, b. 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 driven in rotation by said drive shaft (4) or said drive connection (5) and can then produce, beyond a predetermined rotational speed, a braking torque of the drive shaft (4) or the drive connection (5).

2. Linear actuator (1) according to claim 1, characterized in that that: - the drive connection (5) includes at least one speed reduction device (18), preferably geared, - 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 speed reduction device (18), preferably geared, - the one-way clutch device (7) is coupled to a section of the drive connection (5) which is disposed 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 speed multiplication device (39), preferably geared, arranged to give the centrifugal brake (6) a rotational speed greater than that of said section of the drive connection (5) which is disposed between said reduction device (18) and said linear unit (2).

4. Linear actuator (1) according to any one of 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. A linear actuator (1) according to any one of claims 1 to 5, characterized in that the centrifugal brake (6) comprises: - a brake drum (28) having an engagement surface (29), - at least one friction element (30a-30c) having a friction surface (31a-31c), radially movable between a rest position, in which the friction surface (31a-31c) is separated 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) continuously returning said at least one friction element (30a-30c) to its rest position, and in which, beyond a predetermined speed, said at least one friction element (30a-30c) is displaced by the effect of centrifugal force into its braking position. pressed along 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 in a bidirectional translation along a longitudinal direction (II) by rotation of said rod (11) of 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 supplied, brakes the rotating motor shaft (4), - means for releasing the electromagnetic brake (19) (20), which can be manually operated by a user to interrupt the braking of the motor shaft (4) by the electromagnetic brake (19).

9. 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. A method for braking a linear actuator (1) comprising: - a linear unit (2) capable of generating linear motion, - a motor (3) for 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), wherein the 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 produces no 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 driven in rotation and can then produce, beyond a predetermined rotational speed,a braking torque of the motor shaft (4) or the drive connection (5).

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