Scissor lift

Abstract

The present invention relates to a scissor lift (1) having: a base (2); a platform (4); a scissor mechanism (6), which is arranged between the base and the platform, for raising and lowering the platform (4) relative to the base (2); and a linear drive (8) for actuating the scissor mechanism (6). The linear drive (8) comprises: i) a motor (12) having a motor shaft (12a); ii) a linear unit (40) having a rotatably mounted spindle (42), which is operatively connected to the motor shaft (12a), and a nut (44), which is operatively connected to the spindle (42) and can be translated along the spindle (42), for converting a rotational movement of the motor shaft (12a) into a translational movement of the nut (44); iii) a push rod (14) for coupling a scissor movement of the scissor mechanism (6) to a translational movement of the nut (44); and iv) an inertia brake (30), which is operatively connected to the spindle (42), for limiting an acceleration of the platform (4).

Description

[0001] Scissor lift

[0002] The present invention relates to a scissor lift.

[0003] Electric linear actuators are commonly used to move machine parts or to actuate positioning mechanisms. These linear actuators feature an electric motor whose rotary output motion is converted into a translational motion by means of a linear unit consisting of a spindle and a connected nut. These linear actuators, also known as electric cylinders, are used, among other things, in scissor lifts, where they actuate a scissor mechanism to raise and lower a platform relative to a base. Compared to hydraulic solutions, such as hydraulic cylinders, these linear actuators allow for more precise positioning and eliminate the need for a hydraulic system. In particular, no hydraulic system needs to be integrated into such a scissor lift, thus saving installation space.

[0004] In such scissor lifts, the motor of the respective linear drive can not only position the platform as desired, but also stabilize its position once set. In particular, the motors can counteract the restoring torque caused by the weight of a load supported by the platform. This is because the linear units of such linear drives are typically not self-locking in order to improve power transmission.

[0005] Since a motor malfunction, such as a power outage, can prevent the platform from remaining in the desired position, additional safety systems are often provided to prevent the platform from lowering unintentionally and / or uncontrollably. For example, motorized locking systems can be used to lock the scissor mechanism in the desired position. However, such locking systems have the disadvantage that the scissor mechanism must remain locked until the motor is functioning again. Therefore, for example, German patent application DE 10 2019 105 560 proposes a braking system for a scissor lift that allows for controlled lowering of the platform in the event of a motor failure.

[0006] Against this background, it is an object of the invention to further improve the operational safety of a scissor lift, in particular to provide a scissor lift with a multi-stage safety concept.

[0007] This task is solved by a scissor lift according to the independent claim.

[0008] Preferred embodiments of the invention are the subject of the dependent claims and the following description.

[0009] According to a first aspect of the invention, a scissor lift comprises a base, a platform, a scissor mechanism arranged between the base and the platform for raising and lowering the platform relative to the base, and a linear drive for actuating the scissor mechanism. The linear drive includes i) a motor with a motor shaft, ii) a linear unit with a rotatably mounted spindle operatively connected to the motor shaft and a nut operatively connected to the spindle and translatable along the spindle for converting a rotational movement of the motor shaft into a translational movement of the nut, iii) a push rod for coupling a scissor movement of the scissor mechanism to a translational movement of the nut, and iv) an inertial brake operatively connected to the spindle for limiting the acceleration of the platform.

[0010] One aspect of the invention is based on the approach of equipping a scissor lift with an inertial brake. The inertial brake is advantageously directly operatively connected to the spindle of the linear drive, which is used to actuate the scissor mechanism of the scissor lift. In particular, the inertial brake can be integrated into the linear drive in such a way that it is triggered by a high rotational acceleration, e.g., when a predetermined rotational acceleration threshold of the spindle is reached or exceeded, and thus prevents further rotation of the spindle—and therefore a lowering of the platform supported by the scissor mechanism. The inertial brake can be located directly on the spindle or be constructed entirely around the spindle. In particular, the spindle can form part of the inertial brake. In this way, the inertial brake can be used to effectively prevent malfunctions or failures in the drive train, e.g.,to safeguard the motor used to drive the linear unit or a gearbox connected between the motor and the linear unit. This prevents, for example, an uncontrolled "fall," i.e., an unbraked or at least only frictionally slowed descent of the platform, as could occur if the motor or gearbox fails.

[0011] The inertial brake is preferably a device in which the inertia of a component integrated into or coupled to the drive train of the linear drive is utilized to generate a braking force or braking torque. The inertial brake expediently comprises an inertial element that, during normal operation of the linear drive, rotates together with an inertial brake input shaft due to at least one constraint force. The inertial element is operatively connected to the inertial brake input shaft, for example via a suitable thread or ball bearing, such that, during rotation relative to the inertial brake input shaft, the inertial element can perform an axial, translational movement relative to this shaft.If the rotational speed of the inertial brake input shaft changes such that an inertial force acting on the inertial element exceeds the constraint force, the inertial element can come into contact with a stationary brake block. Consequently, the inertial brake can limit the rotational acceleration of the inertial brake input shaft and, therefore, also the acceleration of the platform, provided the inertial brake input shaft is integrated into the linear drive train. In particular, the operative connection between the inertial brake input shaft and the inertial element can, in this case, also prevent further rotation of the inertial brake input shaft relative to the inertial element (and thus further lowering of the platform). For this purpose, the inertial brake input shaft can, for example, correspond to the spindle of the linear drive unit.Preferred embodiments of the invention and their further developments are described below. These embodiments can be combined with each other and with the aspects of the invention described below, unless expressly excluded.

[0012] The linear drive additionally includes a centrifugal brake operatively connected to the spindle for limiting the platform's descent speed. Preferably, the centrifugal brake is coordinated with the inertial brake, or vice versa, for example with regard to the release speed or acceleration.

[0013] Another aspect of the invention is based on the approach of combining an inertial brake with a centrifugal brake and integrating them into a drive train of the linear actuator for actuating the scissor mechanism. Advantageously, both the inertial brake and the centrifugal brake are operatively connected to the spindle of a linear unit of the linear actuator. The centrifugal brake can thus be coupled to the inertial brake via the spindle, and vice versa. This allows the centrifugal brake to be secured by the inertial brake and / or vice versa.

[0014] The interaction of the inertial brake and the centrifugal brake goes beyond simple redundancy. Rather, the functions of the inertial brake and the centrifugal brake complement each other advantageously, ensuring that a user of the scissor lift or a load on the platform is reliably protected in the event of a wide range of possible malfunctions. In particular, it is possible to protect the platform against both excessively rapid descent and excessive acceleration.

[0015] The centrifugal brake is preferably a device in which the centrifugal force of at least one component, integrated into or coupled to the drive train of the linear actuator, is used to generate a braking force or braking torque. The centrifugal brake expediently comprises at least one brake caliper, which can be coupled to a centrifugal brake input shaft by at least one spring-loaded retaining element. The retaining element expediently counteracts the centrifugal force acting on the brake caliper during its rotation together with the centrifugal brake input shaft. The brake caliper is preferably arranged within a brake drum, with which the brake caliper can come into contact when the centrifugal force exceeds a predetermined restoring force of the spring-loaded retaining element.Consequently, the centrifugal brake can be used to limit the rotational speed of the centrifugal brake input shaft and, therefore, also the descent speed of the platform, if the centrifugal brake input shaft is integrated into the drive train of the linear drive. For this purpose, the centrifugal brake input shaft can, for example, correspond to a motor shaft of a linear drive motor.

[0016] In a preferred embodiment, the linear drive comprises a gearbox that operatively connects the motor shaft to the spindle. The gearbox is preferably a reduction gearbox that converts the rotational speed of the motor shaft into a lower rotational speed of the spindle. The motor, gearbox, and linear unit expediently form a drive train for the scissor lift, particularly the linear drive. The centrifugal brake is preferably integrated on the motor side of the gearbox, and the inertial brake on the spindle side of the gearbox, into the drive train thus formed. The linear drive is advantageously configured such that the centrifugal brake can engage in the event of motor failure, allowing the platform to descend slowly. The centrifugal brake can therefore engage, for example, when the motor is de-energized and thus cannot exert any braking effect. This is because, as the platform descends, the nut is forced by the platform or...The load being carried is pressed along the spindle, setting the spindle into rotation. This rotational movement is transmitted through the gearbox to the motor. The centrifugal brake located on the motor side of the gearbox prevents, in particular, the motor from over-rotating and the resulting damage.

[0017] However, since a high torque applied to the gearbox on the spindle side, such as can occur when the linear unit is actuated by an external force acting on the nut, poses a risk of gearbox failure, for example, due to a gearbox breakage, and thus a decoupling of the motor shaft from the linear unit, the arrangement of the inertial brake on the spindle side of the gearbox is advantageous. This allows the inertial brake to engage even in the event of such a gearbox failure and prevent the platform from lowering uncontrollably. Likewise, the inertial brake can effectively engage in the event of a failure of the centrifugal brake.

[0018] Furthermore, by placing the inertial brake on one spindle side of the gearbox, it is conceivable to reduce the safety requirements for the gearbox. As a result, production effort and the associated costs can be reduced.

[0019] In another preferred embodiment, the centrifugal brake is directly operatively connected to the motor shaft. For example, the centrifugal brake can be mounted directly on the motor shaft, meaning the motor shaft can act as the centrifugal brake input shaft. Alternatively, the centrifugal brake can be mounted on a motor-side transmission input shaft, which is coupled to the motor shaft and effectively acts as an extension of the motor shaft. This allows the centrifugal brake to remain directly operatively connected to the motor shaft, without any reduction or gearing. The centrifugal brake can thus be positioned in the drivetrain immediately upstream of the assembly, i.e., the motor, whose failure it protects against. This results in a particularly short causal chain in the event of motor failure (motor failure triggering the centrifugal brake). Consequently, even stringent safety requirements can be met, and operational reliability can be further enhanced.

[0020] In a further preferred embodiment, the inertial brake comprises a lock nut operatively connected to the spindle and at least one, in particular axial, stop surface. The stop surface is advantageously axially fixed, e.g., mounted to the housing. The lock nut advantageously forms an inertial element. The inertial brake is preferably designed such that, during normal operation, the lock nut rotates with the spindle and, upon exceeding an angular acceleration threshold, undergoes a translational movement along the spindle due to its inertia until the lock nut, in particular an (axial) braking surface of the lock nut, comes into contact with the stop surface. The stop surface is advantageously designed to be complementary to the braking surface of the lock nut.

[0021] The stop surface is preferably provided by a stop, for example a brake component fixed in a housing of the linear drive. Alternatively, the stop surface can also be provided by the housing itself.

[0022] While the nut is secured against rotation, i.e., prevented from rotating (together with the spindle), the locknut is expediently not secured against rotation, i.e., it is essentially free to rotate in the circumferential direction. The nut may, for example, have a radial projection that engages in an axially extending groove in the housing, thus preventing rotation of the nut relative to the housing. The locknut, on the other hand, expediently does not have such a guide.

[0023] Consequently, the locknut can be "carried along" by the rotating spindle during normal operation due to constraint forces. Such a constraint force can, for example, be caused by friction between the spindle and the locknut mounted on it. This constraint force can be generated, in particular, by a shallow thread guide or a shallow ball guide, i.e., threads or ball guide grooves with a low pitch on both the spindle and the locknut. Only when the inertial force acting on the locknut at high angular acceleration exceeds these constraint forces, meaning the locknut is no longer rotating as fast as the spindle, can the locknut translate along the spindle—preferably by means of the (shallow) threads or ball guide grooves—and come into contact with the stop surface.

[0024] By designing the inertial brake as a locknut operatively connected to the spindle, the inertial brake can be positioned directly upstream of the gearbox, whose failure it protects against. Consequently, the causal chain in the event of gearbox failure (activation of the inertial brake) is particularly short. This allows for compliance with increased safety requirements and further enhances operational reliability.

[0025] In a further preferred embodiment, the linear actuator has a housing in which the linear unit and the inertial brake are arranged. The inertial brake preferably comprises two housing-mounted stops, each with an at least substantially axial stop surface. The lock nut is advantageously arranged (axially) between the two stops, particularly the stop surfaces. The spindle advantageously passes through the stops. For this purpose, the stops can have a bore, particularly a central one, through which the spindle passes. The two stops allow the inertial brake to act on both sides, i.e., to be triggered by both tension and compression of the push rod. Consequently, the linear actuator can be mounted independently of its orientation relative to the platform.

[0026] In a further preferred embodiment, the inertial brake includes a spiral spring-like stabilizing element. This stabilizing element advantageously serves to stabilize the lock nut in a position spaced away from the at least one stop surface. By means of the stabilizing element, it is possible to prevent the lock nut from unintentionally coming into contact with the at least one stop surface. In particular, the lock nut can only come into contact with the at least one stop surface and thus prevent further rotation of the spindle when the inertial force acting on the lock nut, during a (high) angular acceleration of the spindle, overcomes a spring force exerted by the stabilizing element. The stabilizing element can therefore generate, or at least contribute to, a constraint force that causes the lock nut to rotate together with the spindle during normal operation.

[0027] To enable space-saving installation of the spiral spring-like stabilizing element, the lock nut preferably has an annular gap. The stabilizing element is advantageously arranged at least partially within this annular gap. The annular gap can extend, for example, from an axial end face of the lock nut, particularly from the axial braking surface, in the axial direction deep into the lock nut.

[0028] In another preferred embodiment, the inertial brake is designed, i.e., set or configured, such that it triggers when the rotational acceleration of the spindle reaches or exceeds a predetermined threshold value that is greater, for example, by a factor of 1.5, than the spindle's rotational acceleration that occurs when the platform descends with a delay caused by the inertia of the motor or its rotor, which is coupled to the scissor mechanism via the linear unit. Such a delayed descent of the platform, caused by the coupling to the motor, corresponds to the normal state. If the coupling to the motor fails, for example, due to a failure of the gearbox between the motor and the linear unit, the platform's acceleration is significantly higher, so that the rotational acceleration threshold can be reached or exceeded.The inertial brake is particularly preferably configured, and especially designed, such that a predetermined acceleration threshold of g / 4 is not exceeded when the platform accelerates. Here, g is ≈ 9.81 m / s². 2 the acceleration due to gravity. Therefore, the inertial brake can engage and block the system as soon as a free fall of the platform is imminent, for example in the event of a thread failure.

[0029] In a further preferred embodiment, the centrifugal brake is configured, in particular designed, such that a predetermined speed threshold of 800 mm / s, preferably 500 mm / s, and even more preferably 300 mm / s, is not exceeded when the platform is lowered. This allows the platform to be lowered in a controlled manner, particularly at a speed at which there is no risk of injury to personnel on the platform. At the same time, this prevents the motor and / or transmission from over-revving.

[0030] The invention will now be explained in more detail with reference to the figures. Where expedient, equivalent elements are designated with the same reference numerals. The invention is not limited to the embodiments shown in the figures – not even with regard to functional features. The preceding description, as well as the subsequent description of the figures, contains numerous features, some of which are summarized in the dependent claims. However, those skilled in the art will also consider these features, as well as all other features disclosed above and in the subsequent description of the figures, individually and combine them into meaningful further combinations. In particular, all the aforementioned features can be combined individually and in any suitable combination with the lifting platform according to the first aspect of the invention and the working robot according to the second aspect of the invention. The figures show, at least partially schematically:

[0031] Figure 1 shows an example of a scissor lift;

[0032] Figure 2 shows an example of a centrifugal brake; and

[0033] Figure 3 shows an example of an inertial brake.

[0034] Figure 1 shows an example of a scissor lift 1 with a base 2, a platform 4, a scissor mechanism 6 arranged between the base 2 and the platform 4 for raising and lowering the platform 4 relative to the base 2, and a linear actuator 8 for actuating the scissor mechanism 6, so that the platform 4 can be raised or lowered relative to the base 2 by means of the linear actuator 8. For this purpose, a housing 10 of the linear actuator 8 is advantageously mounted in a first mounting section 16a on a linkage 16 of the scissor mechanism 6, while a push rod 14, which can be extended out of or into the housing 10, is mounted on the linkage 16 in a second mounting section 16b. The second mounting section 16b is movable relative to the first mounting section 16a. In principle, however, the linear actuator 8 can also be integrated into the scissor lift 1 in other ways. For example, the housing 10 or the push rod 14 can be mounted on the linkage 16 in a second mounting section 16b.the push rod 14 is mounted on the base 2.

[0035] In the present example, the base 2 is designed as a chassis and includes wheels 2a. A motor 2b is expediently integrated into the chassis to drive the wheels 2a. This makes the scissor lift 1 mobile.

[0036] Platform 4 can be used to place objects for vertical transport. Alternatively or additionally, platform 4 can also transport people vertically. Platform 4 can be equipped to secure such objects or people, for example by providing a railing or similar device (not shown in Figure 1).

[0037] The housing 10 expediently accommodates a linear unit 40, described in more detail in connection with Figure 3, for converting a rotational motion generated by a motor 12 into a translational motion of the push rod 14. The linear unit 40 is coupled to the motor 12 via a gearbox 18, which is arranged in a gearbox housing 18a mounted at one end of the housing 10. The gearbox 18, linear unit 40, and push rod 14 thus form a drive train for driving the scissor mechanism 6. The platform 4 is coupled to the motor via the scissor mechanism 6, the push rod 14, the linear unit 40, and the gearbox 18.

[0038] For efficiency reasons, the linear unit 40 is expediently designed not to be self-locking. This means that the direction of action of the linear unit 40 can reverse. Under a compressive or tensile load on the push rod 14, the resulting translation can also be converted into a rotational movement, which is then transmitted to the motor 12 via the gearbox 18.

[0039] To safeguard against malfunctions of the motor 12 and / or the gearbox 18, and to protect these components, the linear drive 8 preferably comprises an inertial brake 30, expediently arranged together with the linear unit 40 in the housing 10, and a centrifugal brake 20. The centrifugal brake 20 is configured to limit the descent rate of the platform 4, in particular to prevent it from exceeding a predetermined descent rate threshold. The inertial brake 30 is configured to limit the acceleration of the platform 4, in particular to lock the platform 4 when a predetermined acceleration threshold is reached or exceeded.

[0040] The inertial brake 30 is arranged on the output side of the gearbox 18 located in the gearbox housing 18a. This allows the inertial brake 30 to prevent the platform 4 from falling, which would be associated with strong acceleration of the platform 4, e.g., in the event of a gearbox failure. The centrifugal brake 20, on the other hand, is arranged on the input side of the gearbox 18. The centrifugal brake 20 can, in particular, be mounted directly on a motor shaft 12a or at least on an extension of the motor shaft 12a, which serves as the gearbox input shaft of the gearbox 18. As shown in Figure 1, the centrifugal brake 20 can, for example, be mounted on a side of the gearbox housing 18a facing away from the motor 12. The motor shaft 12a or its extension passes through the gearbox housing 18a essentially completely in the axial direction. The centrifugal brake 20 can thus prevent the motor from overspeeding. B. prevent this in the event of a lowering of platform 4.

[0041] Figure 2 shows an example of a centrifugal brake 20 for a linear drive, as used in a scissor lift 1 shown in Figure 1. The centrifugal brake 20 has two brake calipers 22, which are coupled to each other via spring-elastic retaining elements 24. The retaining elements 24 counteract the centrifugal forces acting on the brake calipers 22 during rotation. The brake calipers 22 are coupled to a centrifugal brake input shaft M (not shown) so that they rotate synchronously with the centrifugal brake input shaft M.

[0042] The brake calipers 22 are provided with brake linings 26 on their outer surface and are arranged in a brake drum 28. If the centrifugal brake input shaft M, for example the motor shaft 12a shown in Figure 1, reaches or exceeds a predetermined rotational speed, the centrifugal force acting on the brake calipers 22 exceeds the retaining force exerted by the retaining elements 24. The brake calipers 22 therefore move radially outwards, so that the brake linings 26 come into contact with the brake drum 28 and the rotational speed of the brake calipers 22 – and thus also of the centrifugal brake input shaft M – can no longer increase.

[0043] The example shown in Figure 2 is only one of several possible embodiments of a centrifugal brake 20 suitable for use in the scissor lift 1 shown in Figure 1. Other embodiments are also possible. For example, an embodiment is conceivable in which each of the brake calipers 22 is coupled separately to the centrifugal brake input shaft M via the spring-elastic retaining elements 24.

[0044] Figure 3 shows an example of an inertial brake 30 for a linear drive 8, as used in a scissor lift 1 shown in Figure 1 and partially depicted in Figure 3. The linear drive 8 comprises a housing 10 and a linear unit 40 arranged therein, formed by a spindle 42 and a nut 44 operatively connected to it, so that a rotation of the spindle 42 can be converted into a translation of the nut 44 along the spindle 42. In this example, the linear unit 40 is designed as a ball screw drive, in which the spindle 42 is operatively connected to the nut 44 via rolling elements 46. The spindle 42 has at least one guide groove 42a extending like a helical guide for guiding the rolling elements 46; however, other configurations of the linear unit 40 are also conceivable, for example as a simple (trapezoidal) lead screw drive or planetary roller screw drive.To prevent the nut 44 from rotating with the spindle 42, the nut 44 is expediently secured against rotation relative to the housing 10.

[0045] The inertial brake 30 is advantageously operatively connected to the spindle 42. That is, the inertial brake 30 can be activated by a rotation, in particular a highly accelerated rotation, of the spindle 42.

[0046] For this purpose, the inertial brake 30 has a lock nut 32 that cooperates with the spindle 42. The lock nut 32 can have an internal thread 32a which engages in at least one guide groove 42a that runs around the spindle 42 in a spiral pattern. However, unlike the nut 44, the lock nut 32 is not secured against rotation relative to the housing 10. The lock nut 32 can therefore follow the rotation of the spindle 42. The lock nut 32 is driven along by the spindle 42, for example, by the frictional forces acting on the lock nut 32, such as those acting between the spindle and the lock nut 32. In normal operation of the linear drive 8, the lock nut 32 and the spindle 42 thus advantageously rotate synchronously.

[0047] The inertial brake 30 also comprises two spaced-apart stops 34. The lock nut 32 is arranged axially between the stops 34. On the sides facing the lock nut 32, the stops 34 each provide an axial stop surface 34a with which the lock nut 32 can come into contact during translation along the spindle 42, i.e., during axial movement. The stops 34 have through bores 34b through which the spindle 42 passes.

[0048] The lock nut 32 is advantageously stabilized in a position between the two stops 34 by means of a spiral spring-like stabilizing element 36. The stabilizing element 36 can thus contribute to the constraint forces that cause the lock nut 32 to rotate together with the spindle 42 during normal operation. If the lock nut 32 is deflected axially from this position, the restoring force of the stabilizing element 36 pushes or pulls the flanks of the internal thread 32a axially against the opposite flank of the guide groove 42a. This increases the friction between the lock nut 32 and the spindle 42, causing the lock nut 32 to be driven along by the spindle 42.

[0049] To save installation space, a ring-shaped gap 32b is advantageously provided in the lock nut 32 for the spiral spring-like stabilizing element 36, into which the stabilizing element 36 engages. Within the gap 32b, one end of the stabilizing element 36 can be freely suspended circumferentially, i.e., fixed only axially, to the lock nut 32. The other end of the stabilizing element 36 is advantageously attached to the stop 34 opposite the opening of the gap 32b.

[0050] If the spindle 42 is subjected to angular acceleration, for example by a tensile or compressive load on a thrust tube coupled to the nut 44, an inertial force acts on the locknut 32. If this inertial force, with sufficiently strong acceleration of the spindle 42, exceeds the constraint forces responsible for driving the locknut 32, the operative connection between the spindle 42 and the locknut 32 leads to a translation of the locknut 32 along the spindle 42. The locknut 32 can therefore move axially along the spindle 42 if it no longer rotates synchronously with the spindle 42. This axial movement of the locknut 32 is stopped as soon as the locknut 32 comes into contact with one of the stop surfaces 34a. This contact also prevents further rotation of the locknut 32 and thus also further rotation of the spindle 42.Reference list Scissor lift base a Wheel b Motor Platform Scissor mechanism Linear drive 0 Housing 2 Motor 2a Motor shaft 4 Push rod 6 Linkage 6a First mounting section 6b Second mounting section 8 Gearbox 8a Gearbox housing 0 Centrifugal brake 2 Brake caliper 4 Retaining element 6 Brake lining 8 Brake drum 0 Inertial brake 2 Lock nut 2a Internal thread 2b Gap 4 Stop 4a Stop surface 4b Through hole 6 Stabilizing element 0 Linear unit 2 Spindle 42a Guide groove.

[0051] 44 Mother

[0052] 46 rolling elements

[0053] M centrifugal brake input shaft

Claims

Patent claims 1. Scissor lift (1) comprising a base (2), a platform (4), a scissor mechanism (6) arranged between the base (2) and the platform (4) for raising and lowering the platform (4) relative to the base (2), and a linear drive (8) for actuating the scissor mechanism (6), wherein the linear drive (8) comprises: - a motor (12) with a motor shaft (12a), - a linear unit (40) with a rotatably mounted spindle (42) operatively connected to the motor shaft (12a) and a nut (44) operatively connected to the spindle (42) and translatable along the spindle (42) for converting a rotational movement of the motor shaft (12a) into a translational movement of the nut (44) and - a push rod (14) for coupling a scissor movement of the scissor mechanism (6) to a translational movement of the nut (44), - a centrifugal brake (20) operatively connected to the spindle (42) for limiting a sinking speed of the platform (4), characterized in that the linear drive (8) comprises an inertial brake (30) operatively connected to the spindle (42) for limiting an acceleration of the platform (4).

2. Scissor lift (1) according to claim 1, wherein the linear drive (8) has a gearbox (18) which operatively connects the motor shaft (12a) to the spindle (42), and the centrifugal brake (20) on the motor side of the gearbox (18) and the inertial brake (30) on the spindle side of the gearbox (18) are integrated into the drive train formed.

3. Scissor lift (1 ) according to claim 1 or 2, wherein the centrifugal brake (20) is directly operatively connected to the motor shaft (12a).

4. Scissor lift (1) according to one of the preceding claims, wherein the inertial brake (30) comprises a lock nut (32) operatively connected to the spindle (42) and at least one stop surface (34a) and is designed such that the lock nut (32) rotates with the spindle (42) during normal operation and, when an angular acceleration threshold is exceeded, a translational deceleration occurs due to its inertia. movement along the spindle (42) until the lock nut (32) comes into contact with the stop surface (34a).

5. Scissor lift (1 ) according to claim 4, wherein the linear actuator (8) has a housing (10) in which the linear unit (40) and the inertial brake (30) are arranged and the inertial brake (30) comprises two housing-fixed stops (34) each with an axial stop surface (34a) between which the lock nut (32) is arranged.

6. Scissor lift (1 ) according to one of claims 4 or 5, wherein the inertial brake (30) has a spiral spring-like stabilizing element (36) for stabilizing the lock nut (32) in a position that is spaced away from the at least one stop surface (34a) and the lock nut (32) has an annular gap (32b) on an end face in which the spiral spring-like stabilizing element (36) is at least partially arranged.

7. Scissor lift (1) according to one of the preceding claims, wherein the inertial brake (30) is configured to ensure that a predetermined acceleration threshold of g / 4 is not exceeded when the platform (4) is accelerated.

8. Scissor lift (1) according to one of the preceding claims, wherein the centrifugal brake (20) is configured to ensure that a predetermined speed threshold of 4 m / s is not exceeded when the platform (4) is lowered.

Images