Linear drive device

Abstract

The invention relates to a linear drive (2) comprising a linear unit (4) for effecting a linear movement, an engine (10) for driving the linear unit (4) with an engine, and a drive connection (12) from the engine (10) to the linear unit (4). In order to ensure safe operation in the event of a power failure, it is proposed that the linear drive (2) has a centrifugal brake device (32) which is rotationally coupled to the drive connection (12).

Description

[0001] This application is a divisional application of the application filed on March 4, 2020, with application number "202010144921.0" and invention title "Linear Drive Device". Technical Field

[0002] The present invention relates to a linear drive device comprising: a linear unit for realizing linear motion; an engine for driving the linear unit; and a drive connection from the engine to the linear unit. Background Technology

[0003] A linear drive is a drive system used to generate translational motion. Normally, this motion is linear (movement along a straight line), however, it can also follow other predetermined motion sequences.

[0004] When using a rotary engine (which serves as the drive unit for the engine, typically an electric motor), the rotary drive motion of the engine is converted into linear efficient motion, as is the case in drive units for beds, medical technology equipment, or industrial applications. For this purpose, a linear drive unit includes a linear unit that converts the rotary motion of the engine or an intermediate transmission into linear motion.

[0005] In most cases, the linear unit has a threaded spindle with a nut mounted on it, which is rotatable relative to the spindle and thus moves longitudinally. The translational motion of the nut relative to the spindle is transmitted to a schubrohr (universal joint tube) operably connected to the nut. Such linear drives have a connecting portion (e.g., a fork) on or connected to the schubrohr, where a load to be moved can be secured. The longitudinal movement of the schubrohr is used to move the load. Summary of the Invention

[0006] If a linear drive is used to lift a large load, the reduction of the load can result in a large back torque on the engine. To reduce this back torque, the linear drive can have a braking device that converts the potential energy of the downward motion into heat.

[0007] The objective of this invention is to provide a linear drive device that has high safety.

[0008] This task is accomplished by a linear drive device according to the invention, which has a centrifugal braking device that is rotatably coupled to the drive connection portion.

[0009] This invention is based on the consideration that existing braking devices—in the event of motor failure—must maintain a linear drive under load. In this case, further load reduction can only be achieved by manually releasing the brake. However, there is a high risk associated with manually releasing the brake, as the load drops very rapidly through the non-locking spindle because the linear drive cannot adequately brake due to its low friction. This drop can lead to damage to the engine and transmission, partly due to the exceptionally high speeds within the linear drive and partly due to the sudden stop when the load reaches the ground.

[0010] A centrifugal brake—rotatably coupled to the drive connection—can brake unexpected load drops, thereby preventing excessive rotational speed of the linear drive. The centrifugal brake, through its braking action, limits the rotational speed in the drive connection to a predetermined maximum speed or range, ensuring that even under high loads, this maximum speed or range is not exceeded. The rotational speed range—for the centrifugal brake, this maximum speed depends on the driving force acting upon it, even to a very small extent—is conveniently set through the design of the centrifugal brake, allowing the linear drive to ensure rotation within this range without damage. The linear drive is protected, and the surrounding environment is protected from the effects of rapidly decreasing loads.

[0011] The linear unit mechanically converts rotary motion into linear motion and vice versa. To this end, the linear unit has a threaded spindle and a nut rotating thereon, the nut being arranged to move longitudinally relative to the spindle by rotational motion. The linear drive is connected to a rotary engine (e.g., an electric motor) via a drive connection. The drive connection may include a transmission that converts the higher engine-side rotational speed into a lower linear unit-side rotational speed.

[0012] Regardless of the arrangement of the centrifugal brake on the drive connection, rotation of the drive connection will cause rotation of the centrifugal brake. The centrifugal brake remains unbraked until a predetermined number of revolutions is reached, and braking begins when the predetermined number of revolutions is exceeded. The force of the centrifugal brake increases with increasing speed.

[0013] To generate a braking effect, a centrifugal braking device advantageously includes at least one friction element, which is pressed against a preferably stationary mating element by a centrifugal force above a predetermined number of revolutions and friction occurs on the mating element, thereby converting rotational energy into heat through friction. Hereinafter, the mating element is also referred to as a friction element. There are at least two or more friction elements that are pressed together by a centrifugal force above a predetermined number of revolutions and thus dissipate energy through friction. For this purpose, the friction elements are configured to be movable relative to each other, so that they can move relative to each other under the action of centrifugal force. Hereinafter, only two friction elements are described for simplicity, but the number of friction elements should not be limited to two.

[0014] In an advantageous embodiment of the invention, the linear drive unit includes a transmission device in the drive connection. The centrifugal braking device is advantageously rigidly coupled to a component of the drive connection located between the engine and the transmission device. Compared to the linear element side of the transmission device, the centrifugal braking device is easier to actuate and smaller in size due to the generally higher rotational speed in the connection region.

[0015] When the centrifugal braking device is rigidly connected to the engine shaft, a simple and compact implementation of the linear drive device can be achieved.

[0016] To reliably prevent unintentional triggering of the centrifugal braking device, the device advantageously includes a spring that holds the friction element in its unconstrained position, and the friction element must be moved to its braking position by centrifugal force against the spring force. The spring and the two friction elements are suitably positioned relative to each other such that the friction elements can be spaced apart in a stationary state, and that braking can be achieved by pressing the friction elements together by the centrifugal force of rotation.

[0017] Linear drive units may have engine-controlled braking devices, such as electromechanically driven braking devices. Advantageously, this braking device is used to brake a descending load, or it can function as a handbrake. Such braking devices have: a brake drive, typically electrically driven; and friction elements that are pressed together by the brake drive and thereby achieve their frictional action. When an electromechanically driven braking device with friction elements is available, it is advantageous if these friction elements are also those of a centrifugal braking device. This saves on friction elements and allows for the compact and cost-effective manufacture of linear drive units.

[0018] To reliably brake the linear drive unit in the event of a power failure, it is advantageous that the electromechanical braking device includes a spring and a braking drive, and is configured such that the spring presses the friction unit into its braking position when the braking drive is de-energized. Alternatively or supplementarily to the spring, a permanent magnet may be present, which presses the friction unit into its braking position when the braking drive is de-energized. For simplicity, only the case of a spring is described below, while the inclusion of a magnet should be considered as an alternative.

[0019] Depending on the implementation of the spring, the friction element can also be pulled to its braking position. For simplicity, the terms "pull" and "press" can be used semi-synonymous here so that the spring can be described regardless of the direction of its action.

[0020] The friction element of an electromechanically driven braking device is advantageously a radial friction element, which is drawn outward to its braking position by radial movement and moved inward from the braking position by radial movement. In such embodiments, the friction element can be particularly easily actuated by centrifugal force and used as the friction element of a centrifugal braking device. It is advantageous in this respect that braking is achieved if at least one of the friction elements is radially movable in its unconstrained position, thereby being pressed against another friction element by a centrifugal force exceeding a threshold.

[0021] In cases where the friction element serves the dual function of both an additional braking device and a centrifugal braking device, it is advantageous to have two—and possibly more—springs acting against each other. When the braking drive is de-energized, the brake spring presses or pulls the friction element to its braking position. Furthermore, the release spring presses or pulls the braking element to its release position. In this configuration, these springs are advantageously arranged such that the brake spring presses down on the release spring, ensuring that the friction element is reliably pressed to its braking position both when the braking drive is stationary and when the power is off.

[0022] Regardless of the operation of the braking drive, the centrifugal braking device should be designed to brake upon reaching a predetermined number of revolutions. This can be achieved if at least one of the friction elements is radially movable in its unconstrained position, thereby being pressed against the other friction element by a centrifugal force exceeding a threshold, thus achieving braking.

[0023] To release the electromechanically driven brake, an alternative drive mechanism may be available, such as a manual drive mechanism (e.g., a mechanical lever), which can be operated by an operator. Therefore, the brake can be released even when the brake is de-energized, and the linear drive mechanism can be moved. To keep the centrifugal brake operational, it is necessary that at least one of the friction elements be radially movable in its released position. Even when the alternative drive mechanism is actuated, the friction element can be moved to its braking position by centrifugal force and brake the linear drive mechanism.

[0024] This invention can be particularly advantageously applied to scissor lifts equipped with the linear drive mechanism described above. It is also advantageous to use it on a mobile work platform, such as a forklift cable drive, a scissor lift, or a bagger. The following description uses only a scissor lift as an example; however, it can be alternatively replaced by the other devices described above.

[0025] To raise and lower a scissor lift, a linear drive typically actuates the lift via a large lever, allowing a small movement of the linear drive to result in a large movement of the scissor lift. When lowering the scissor lift, a large force acts on the linear drive due to the transmission conditions. To prevent the linear drive from rotating too quickly, the centrifugal braking device according to the invention is particularly advantageous.

[0026] The present invention also relates to a method for braking a linear drive, wherein an external, particularly linear, force is applied to a linear unit of the linear drive, which converts the force into rotation, and the rotation is at least partially transmitted to the engine via a drive connection.

[0027] To ensure the safe operation of the linear drive, a rotary actuated centrifugal braking device is proposed, which limits the rotation to a predetermined range of revolutions. Once this range of revolutions is reached, the centrifugal braking device can initiate braking, which also ensures that the maximum achievable revolutions remain within the predetermined range, because the braking force increases with increasing revolutions and counteracts any further increase in revolutions.

[0028] The description of advantageous implementations of the invention given so far includes several technical features, which are summarized in several dependent claims. However, these technical features can also be advantageously considered individually and (particularly when referring back to the claims) combined into other meaningful combinations, such that individual technical features in the dependent claims can be combined with individual, multiple, or all technical features in other dependent claims. Furthermore, these technical features can be combined individually and in any suitable combination with the method and apparatus according to the invention as described in the dependent claims. Therefore, method technical features can also be objectively regarded in form as attributes of the corresponding device unit, and functional technical features of the device unit can also be objectively regarded in form as corresponding method technical features. Attached Figure Description

[0029] The aforementioned attributes, features, and advantages of the present invention, as well as the ways and methods by which they are achieved, will be more clearly and explicitly understood in conjunction with the following description of embodiments, which will be described in detail with reference to the accompanying drawings. These embodiments are illustrative of the invention and are not intended to limit the invention to the combinations of technical features given therein, nor to functional technical features. Furthermore, suitable technical features of each embodiment may be considered explicitly in isolation and in any combination according to the claims.

[0030] What is shown is: Figure 1 A linear drive device is shown, comprising: a linear unit with a main shaft; an engine; and a drive connection between the engine and the linear unit, which includes a transmission device and a centrifugal braking device. Figure 2 A scissor lift with a linear drive is shown. Figure 3 The diagram shows two friction elements of a centrifugal braking device coupled by springs; and Figure 4 An illustrative cross-sectional view of the centrifugal braking device is shown.

[0031] List of reference numerals 2 Linear drive device 4 Linear Units 6 spindles 8 nuts 10 engines 12 Drive Connection Part 14 engine shafts 16 Transmission Devices 18 Universal Joint Tube 20 casings 22. Slip knot 24 Scissor lifts 26 load 28 Braking System 30 Braking System 32 Centrifugal Braking Device 34 friction elements 36 Spring Components 38 brake pads 40 supports 42 brake drum 44 supports 45 engine shaft 46 springs 48 Electromechanical drive units 50 electric motor 52 Mechanical devices 54 drive unit 56 Leverage 58 Mechanical Devices Detailed Implementation Figure 1 A linear drive unit 2 with a linear unit 4 is shown. The linear unit 4 includes a spindle 6 with external threads and a nut 8 with internal threads, which runs on the spindle 6. The linear unit 4 is driven by a motor 10 in the form of an electric motor. Figure 1 The diagram is shown only schematically. The engine 10 and the linear unit 4 are connected to each other via a drive connection 12. This drive connection 12 extends from the engine shaft 14 via (in...) Figure 1 (As shown only in schematic form) The transmission 16 extends to the main shaft 6 of the linear unit 4, thereby enabling the engine 10 to drive the main shaft 6 via the transmission 16. Thus, the transmission 16 converts the higher speed of the engine 10 into the lower speed of the main shaft 6.

[0032] Nut 8 is connected to universal joint tube 18 and is anti-rotatably connected to sleeve 20, or otherwise anti-rotatably positioned, for example, by a fork-shaped head or a slipknot head 22 on a platform. Therefore, as the spindle 6 rotates, nut 8 moves linearly or translationally along sleeve 20, allowing universal joint tube 18 to retract and extend from sleeve 20. Both spindle 6 and nut 8 are arranged concentrically with the longitudinal motion axis of linear unit 4, which is also the rotation axis of spindle 6. The longitudinal movement of universal joint tube 18 is attributed to the rotational movement of spindle 6, which is converted into translational movement of nut 8.

[0033] A slipknot 22 is fixed at the front end of the universal joint tube 18, by means of which the linear drive device 2 can be form-fitted with the system to be moved. Such a system may be a hospital bed, operating table, crane, or other device. In the following text, it will be referred to as... Figure 2 The scissor lift 24 shown in the illustration is used to describe this application.

[0034] Figure 2 A scissor lift 24 is schematically shown in a side view, carrying a load 26, which in this embodiment is a vehicle. The scissor lift 24 can be raised or lowered via a linear drive 2—which is also only schematically shown in this figure. To raise the load 26, the universal joint tube 18 extends from the sleeve 20, and to lower the load 26, the universal joint tube 18 retracts back into the sleeve 20.

[0035] When raising and lowering the scissor lift 24, depending on the configuration, the linear motion of the linear drive unit 2 is converted into the load 26 or the raising or lowering of the scissor lift 24. Smaller linear motions of the linear drive unit 2 are converted into larger raising or lowering motions of the scissor lift 24. Due to this conversion and the fact that the scissor lift 24 may bear a very large load 26, the force exerted by the scissor lift 24 on the linear drive unit 2 is large. For the non-self-locking threaded connection between the main shaft 6 and the nut 8, the torque applied to the engine 10 by the scissor lift 24 or the load 26 is also large.

[0036] Therefore, a malfunction of the engine 10—such as a malfunction caused by a power supply failure—can cause problems. Specifically, the reaction force generated by the engine 10 collapses, the scissor lift 24 breaks down, and the load 26 falls. To maintain the scissor lift 24 even when the engine is powered off, the linear drive 2 includes a braking system 28 with a releasable, engine-driven brake 30. This brake 30 is designed to be in its braking state during a power outage. The friction elements of the brake 30 press against each other and brake the rotation of the engine 10, thereby braking the rotation of the main shaft 6. Therefore, in the event of a power outage or other malfunction, the universal joint tube 18 is prevented from retracting into the sleeve 20 due to external pressure.

[0037] Furthermore, in the event of such a safety hazard, it is necessary to lower the scissor lift 24 to remove the load 26 from it. Due to the lack of power supply, the release of the electromechanical drive of the brake 30 and the operation of the engine 10 will be impossible. To enable manual control of this state, the brake 30 includes a manual drive mechanism by which it can be released. An operator can operate this manual drive mechanism, and the universal joint tube 18 can retract into the sleeve 20—actuated by the load 26.

[0038] However, a problem exists here: the linear drive unit 2 has only a relatively small reaction force to resist the descent of the scissor lift 24 or the load 26, and the descent of the load 26 is only subject to minor braking. That is, the manual drive of the braking device 30 is implemented such that the braking device 30 can only be manually and slightly released to brake the retraction of the universal joint tube 18. This poses a risk that the load 26 may fall in the event of an operational error, a situation that should be avoided.

[0039] To address this issue, the braking system 28 includes a centrifugal braking device 32. This centrifugal braking device 32 is forcibly coupled to the rotating portion of the drive connection 12, and in the illustrated embodiment, rigidly coupled to the engine shaft 14. Therefore, the universal joint tube 18 retracts into the sleeve 20 due to pressure, inevitably causing the centrifugal braking device 32 to rotate. If a predetermined rotational speed range is reached, the centrifugal braking device 32 initiates braking and maintains the rotational speed of the drive connection 12 (in this case, the engine shaft 14) within the predetermined rotational speed range regardless of the load. For this purpose, the centrifugal braking device 32 includes a friction element 34 (… Figure 2 ), which is activated by rotation.

[0040] Figure 3 Two such friction elements 34 are shown in perspective. These friction elements 34 are connected to each other by spring elements 36, each carrying one or more springs. Figure 3 The spring element 36 is shown in a relaxed or pre-tensioned state, and the friction element 34 is in its unconstrained state, in which the centrifugal brake 32 has no braking effect. The friction elements 34 are respectively included in the brake pads 38 on the support 40, which is rigidly connected to the drive connection 12 (engine shaft 14 in the case shown) by a connection not shown.

[0041] When the drive connection 12 rotates, the friction element 34 also rotates, and the spring element 36 is pulled away due to centrifugal force. The friction element 34 is pressed outward in the radial direction and contacts the brake drum 42 when a predetermined number of revolutions is reached. Figure 3 The brake drum 42 is indicated by dashed lines and is shown schematically only. The brake drum 42 can also be understood as friction element 42. The interaction of friction elements 34 and 42 generates a braking force that increases as the rotational speed of the centrifugal brake 32 increases, thus maintaining the rotation of the centrifugal brake 32 within a predetermined range. This predetermined range is not exceeded, and the load 26 is reduced at a desired speed when the linear drive 2 is de-energized and when the engine-driven brake 30 is fully released.

[0042] Figure 4 A schematic cross-sectional view through a braking system 28 is shown, which includes an electromechanically driven braking device 30 and a centrifugal braking device 32. Shown are a brake drum 42 with a fixed housing, a non-rotating friction element 34, and a support 44, which is connected to... Figure 4 The engine shaft 45 is rigidly connected only schematically. A spring 46 exists between the support 44 and the friction element 34, with its spring force directed radially outward. When the braking system 28 is de-energized, the spring 46 presses the friction element 34 against the friction element 42 or the brake drum 42, thereby braking the rotation of the engine shaft 14 or the drive connection 12.

[0043] Driven by an engine-driven device 48—which includes an electric motor 50 and a mechanical device 52 shown only schematically—the spring 46 is capable of radially inward contraction and releasing the friction element 34 from the outer friction element 42. This state is... Figure 4 As shown in the diagram, the centrifugal brake 32 is in its unrestrained position, and the linear drive 2 is functioning normally. Since the engine-driven drive 48 releases the constraint of the spring 46 when the power is off, thereby causing the brake 30 to engage, an alternative, manually operated drive 54 (e.g., with a lever 56) may also be present. Figure 4 The diagram is shown only schematically. With the aid of this alternative drive unit 54 and other mechanical devices 58, the spring 46 can be tensioned and the brake device 30 released by manual operation.

[0044] In the aforementioned released state, the rotatable portion of the braking system 28 rotates, and the friction element 34 is subjected to centrifugal force, which pulls the friction element 34 radially outward. As... Figure 3As described, in this state, the friction element 34 resists the action of the spring element 36 and moves radially outward, thereby initiating braking of the centrifugal braking device 32 upon reaching a predetermined range of revolutions. For this purpose, the friction element 34 is arranged so that it can be released radially from the support 44 and / or the spring 46, thereby causing it to approach the outer friction element 42 due to centrifugal force and initiate braking. The spring element 36 counteracts the radial centrifugal movement and, in the stationary state of the centrifugal braking device 32, presses the friction element 34 radially inward against the spring 46, the support 44, or other retaining elements not shown.

[0045] Friction element 34 serves not only as the friction element 34 of centrifugal braking device 32 but also as the friction element 34 of engine-driven braking device 30. Therefore, it is endowed with dual functions, and it can initiate braking of braking device 30 or centrifugal braking device 32 by both spring actuation and centrifugal force actuation. Thus, even in the absence of power, linear drive device 2 can not only be safely braked but also safely retracted, thereby enabling the safe driving of a system to be moved, such as a scissor lift 24, using linear drive device 2.

Claims

1. A linear drive device (2), comprising: A linear unit (4) for achieving linear motion, an engine (10) for driving the linear unit (4) by an engine, a drive connection (12) from the engine (10) to the linear unit (4), a transmission device (16) in the drive connection (12), and a centrifugal braking device (32) rotatably coupled to the drive connection (12), wherein the centrifugal braking device can limit the number of revolutions in the drive connection (12) to a predetermined maximum number of revolutions or a maximum number of revolutions range by its braking action, wherein the centrifugal braking device (32) is rigidly coupled to a component of the drive connection (12) disposed between the engine (10) and the transmission device (16), and is rigidly connected to the engine shaft (45) of the engine (10).

2. The linear drive device (2) as described in claim 1. Its features are, The centrifugal braking device (32) has at least one spring (36) and at least two friction elements (34, 42), which are arranged relative to each other such that the friction elements (34, 42) are spaced apart from each other in a stationary state, and that the friction elements (34, 42) are pressed together by the centrifugal force of rotation to perform braking.

3. The linear drive device (2) as described in any of the preceding claims. Its features are, The friction element (34) is held in its unconstrained position by a spring (36).

4. The linear drive device (2) as described in any of the preceding claims. Its features are, The engine-driven braking device (30) includes friction elements (34, 42), which are also the friction elements (34, 42) of the centrifugal braking device (32).

5. The linear drive device (2) as described in claim 4. Its features are, The engine-driven braking device (30) includes a spring (46) and a braking drive device (48), and is configured such that the spring (46) presses the friction element (34) to its braking position when the braking drive device (48) is de-energized.

6. The linear drive device (2) as described in claim 4 or 5. Its features are, At least one of the friction elements (34) is able to move radially in its unconstrained position, thereby being pressed against another friction element (42) by a centrifugal force above a threshold, thereby braking.

7. The linear drive device (2) as described in any one of claims 4 to 6. Its features are, The friction element (34) can be led to its unconstrained position by an alternative drive device (54) when the brake drive device (48) is de-energized, wherein at least one of the friction elements (34) can move radially in its unconstrained position.

8. A scissor lift (24) having a linear drive (2) as described in any of the preceding claims.

9. A method for braking a linear drive device (2), wherein, An external force, especially a linear force, acts on the linear unit (4) of the linear drive device (2), which converts the force into rotation, and the rotation is at least partially transmitted to the engine (10) via the drive connection (12) and by means of the transmission device (16), wherein the rotation actuates the centrifugal brake device (32), which is rigidly coupled to the component of the drive connection (12) disposed between the engine (10) and the transmission device (16), and is rigidly connected to the engine shaft (45) of the engine (10), and the centrifugal brake device (32) limits the rotation to a predetermined number of revolutions by its braking action.

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