LINEAR DRIVE

Abstract

The invention is based on a linear drive comprising a linear unit for carrying out a linear movement, a motor for the motorized driving of the linear unit and a drive connection which extends from the motor as far as the linear unit. In order to ensure reliable operation even in the event of a power failure, it is proposed that the linear drive have a centrifugal brake which is rotationally coupled to the drive connection.

Claims

1. A linear drive comprising a linear unit for carrying out a linear movement, a motor for the motorized driving of the linear unit and a drive connection which extends from the motor as far as the linear unit, characterized by a centrifugal brake which is rotationally coupled to the drive connection.

2. The linear drive as claimed in claim 1, characterized by a gear mechanism in the drive connection, wherein the centrifugal brake is rigidly coupled to the portion of the drive connection arranged between the motor and gear mechanism.

3. The linear drive as claimed in claim 1, characterized in that the centrifugal brake is rigidly connected to a motor shaft of the motor.

4. The linear drive as claimed in claim 1, characterized in that the centrifugal brake has at least one spring and at least two friction elements, which are arranged with respect to each other in such a manner that the friction elements are spaced apart from each other in the idle state and are pressed on each other by means of centrifugal forces of a rotation in a braking manner.

5. The linear drive as claimed in claim 4, characterized in that the friction elements in their release position are retained in their release position by means of a spring.

6. The linear drive as claimed in claim 1, characterized by a motorized brake containing friction elements, which are also the friction elements of the centrifugal brake.

7. The linear drive as claimed in claim 6, characterized in that the motorized brake contains a spring and a brake drive and is constructed in such a manner that the spring presses the friction elements into their braking position in a powerless state of the brake drive.

8. The linear drive as claimed in claim 6, characterized in that at least one of the friction elements is radially movable in the release position thereof so that, as a result of centrifugal forces above a threshold value, it is pressed in a braking manner on the other friction element.

9. The linear drive as claimed in claim 7, characterized in that the friction elements in the powerless state of the brake drive can be moved by means of an alternative drive into their release position, wherein at least one of the friction elements is radially movable in the release position thereof.

10. A scissor lift having a linear drive as claimed in claim 1.

11. A method for braking a linear drive, wherein an external, in particular linear force acts on a linear unit of the linear drive, this linear unit converts the force into a rotation and the rotation is at least partially transmitted to a motor by means of a drive connection, characterized in that the rotation activates a centrifugal brake which limits the rotation to a predetermined speed range.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0030] FIG. 1 shows a linear drive comprising a linear unit having a spindle, a motor and a drive connection between the motor and linear unit having a gear mechanism and a centrifugal brake,

[0031] FIG. 2 shows a scissor lift having a linear drive,

[0032] FIG. 3 shows two friction elements of the centrifugal brake which are coupled by means of springs, and

[0033] FIG. 4 is a schematic section through the centrifugal brake.

DETAILED DESCRIPTION OF THE INVENTION

[0034] FIG. 1 shows a linear drive 2 having a linear unit 4, which has a spindle 6 with an outer thread and a threaded nut 8 which has an inner thread and which runs on the spindle 6. The linear unit 4 is driven by means of a motor 10 in the form of an electric motor which is illustrated only schematically in FIG. 1. The motor 10 and linear unit 4 are connected to each other by means of a drive connection 12. The drive connection 12 extends from the motor shaft 14 via a gear mechanism 16 which is also illustrated only schematically in FIG. 1 as far as the spindle 6 of the linear unit 4 so that the motor 10 drives the spindle 6 via the gear mechanism 16. The gear mechanism 16 in this instance converts a higher speed of the motor 10 into a lower speed of the spindle 6.

[0035] The threaded nut 8 is connected to a thrust pipe 18 and connected to a covering pipe 20 in a rotationally secure manner or supported in some other rotationally secure manner, for example, on a table via a fork head or articulated head 22. In the event of a rotational movement of the spindle 6, the threaded nut 8 therefore carries out a linear movement or a translational movement along the covering pipe 20 so that the thrust pipe 18 can be moved in and out of the covering pipe 20. Both the spindle 6 and the threaded nut 8 are arranged concentrically relative to the longitudinal movement axis of the linear unit 4 which is also the rotation axis of the spindle 6. The longitudinal movement of the thrust pipe 18 is carried out as a result of the rotational movement of the spindle 6 which is converted into a translational movement of the threaded nut 8.

[0036] At the front end of the thrust pipe 18 there is fixed an articulated head 22, by means of which the linear drive 2 can be connected in a positive-locking manner to a system which is intended to be moved. Such a system may be a patient's bed, an operating table, a lifter or another arrangement. The use on a scissor lift 24 which is illustrated schematically in FIG. 2 is described below by way of example.

[0037] FIG. 2 is a schematic side view of a scissor lift 24 which carries a load 26, in this embodiment a car. The scissor lift 24 can be raised or lowered by means of the linear drive 2 which is also indicated only schematically in this Figure. For lifting, the thrust pipe 18 is moved out of the covering pipe 20 and it is retracted again in order to lower the load 26.

[0038] When the scissor lift 24 is raised and lowered, the construction type of the scissor lift 24 results in a translation of the linear movement of the linear drive 2 into raising or lowering of the load 26 or the scissor lift 24. A smaller linear movement of the linear drive 2 is converted into a larger lifting or lowering movement of the scissor lift 24. As a result of this translation and also the fact that a scissor lift 24 under some circumstances carries a very large load 26, the force with which the scissor lift 24 presses on the linear drive 2 is great. In the case of a non-self-locking threaded connection between the spindle 6 and threaded nut 8, the torque which the scissor lift 24 or the load 26 applies to the motor 10 is also great.

[0039] It is therefore problematic when the motor 10 fails, for example, as a result of a defect in the power supply. The counter-force produced by the motor 10 fails, the scissor table 24 collapses and the load 26 falls down. In order also to retain the scissor lift 24 in the powerless state of the motor, the linear drive 2 comprises a brake system 28 having a motor-releasable brake 30. The brake 30 is constructed in such a manner that it is in the braking state thereof in the powerless state. Friction elements of the brake 30 are pressed against each other and block a rotation of the motor 10 and consequently also the spindle 6. In the event of a power failure or other defect, therefore, a retraction of the thrust pipe 18 into the covering pipe 20 brought about by external pressure is blocked.

[0040] In the event of such a safety blockage, it may also be advantageous to lower the scissor lift 24 in order to retrieve the load 26 from the scissor lift 24. In this instance, an electromechanical release of the brake 30 and an operation of the motor 10 are not possible where applicable as a result of a failure of the power supply. In order to be able to manually control this state, the brake 30 comprises a manual drive by means of which the brake 30 can be released. An operator operates this manual drive and the thrust pipe 18 canin a manner driven by the load 26be retracted into the covering pipe 20.

[0041] In this instance, however, there is the problem that the linear drive 2 counteracts a lowering of the scissor lift 24 or the load 26 with only a small counter-force and the load 26 is lowered with only little braking. Although the manual drive of the brake 30 may be constructed in such a manner that the brake 30 can only be slightly released manually so that the retraction of the thrust pipe 18 is braked, there is still the risk of the load 26 falling down in the event of an operator error, which should be avoided.

[0042] In order to solve this problem, the brake system 28 comprises a centrifugal brake 32. This brake is necessarily coupled to the rotation of the drive connection 12, in the embodiment shown rigidly to the motor shaft 14. A retraction of the thrust pipe 18 into the covering pipe 20 as a result of pressure therefore necessarily leads to a rotation of the centrifugal brake 32. If a predetermined speed range of the centrifugal brake 32 is reached, the centrifugal brake 32 activates a braking operation and keeps the rotation speed of the drive connection 12, in this instance of the motor shaft 14, in a predetermined speed range irrespective of the load. To this end, the centrifugal brake 32 comprises friction elements 34 (FIG. 2) which are activated by means of rotation.

[0043] FIG. 3 is a perspective view of two such friction elements 34. The friction elements 34 are connected to each other by means of resilient elements 36 with one or more springs respectively. FIG. 3 shows the resilient elements 36 in the relaxed state or a pretensioned state and the friction elements 34 in their release state in which the centrifugal brake 32 has no braking action. The friction elements 34 each contain a brake liner 38 on a caliper 40 which is rigidly connected by means of a connection which is not illustrated to the drive connection 12, in this instance the motor shaft 14.

[0044] When the drive connection 12 rotates, the friction elements 34 also rotate and pull the resilient elements 36 apart as a result of centrifugal force. The friction elements 34 are pressed radially outward and contact when the predetermined speed range is reached a brake drum 42 which is illustrated with dashed lines and only schematically in FIG. 3. The brake drum 42 can also be understood to be friction elements 42. The interaction of the friction elements 34, 42 produces a braking force which increases as the speed of the centrifugal brake 32 increases and consequently keeps the rotation of the centrifugal brake 32 in the predetermined speed range. The predetermined speed range is not exceeded and the load 26 is also lowered at a desired speed in the powerless state of the linear drive 2 and when the motorized brake 30 is completely released.

[0045] FIG. 4 is a schematic cross-section through the brake system 28 with the electromechanical brake 30 and the centrifugal brake 32. There is illustrated the brake drum 42 which is secured to the outer housing, the rotation-free friction elements 34 and a caliper 44 which is rigidly connected to the motor shaft 45 which is illustrated only schematically in FIG. 4. Between the caliper 44 and friction elements 34, there is provided a spring 46 whose resilient force is directed radially outward. In the powerless state of the brake system 28, the spring 46 presses the friction elements 34 against the friction element 42 or the brake drum 42 and thus blocks a rotation of the motor shaft 14 or the drive connection 12.

[0046] Via a motorized drive 48 having an electric motor 50 and a mechanism 52 which is illustrated only schematically, the spring 46 can be tensioned inward in a radial direction and the friction elements 34 can be released from the outer friction element 42. This state is illustrated in FIG. 4. The centrifugal brake 32 is in the release position thereof and the linear drive 2 can operate in a regular manner. Since the motorized drive 48 releases the spring 46 in the powerless state so that the brake 30 blocks, an alternative and manual drive 54 having, for example, a lever 56 is provided and is also illustrated only schematically in FIG. 4. Using this alternative drive 54 and another mechanism 58, the spring 46 can be tensioned by manual operation and the brake 30 can be released.

[0047] If, in this released state, the rotatable portion of the brake system 28 is caused to carry out a rotational movement, the friction elements 34 are subjected to the centrifugal force, which pulls them radially outward. As described in relation to FIG. 3, in such a state the friction elements 34 operate counter to the resilient elements 36 and move radially outward in order when the predetermined speed range is reached to initiate a braking of the centrifugal brake 32. To this end, the friction elements 34 are arranged so as to be able to be radially released from the caliper 44 and/or the spring 46 so that, as a result of centrifugal force, they move closer to the outer friction element 42 and initiate the braking operation. The resilient elements 36 counteract this radial centrifugal movement and press the friction elements 34 in the idle state of the centrifugal brake 32 radially inward counter to the spring 46, the caliper 44 or another retention element which is not illustrated.

[0048] The friction elements 34 are friction elements 34 both of the centrifugal brake 32 and of the motorized brake 30. A dual function is therefore associated with them and, in a state driven by a spring and driven by centrifugal force, they can activate the braking action of the brake 30 or the centrifugal brake 32. The linear drive 2 can thereby also be blocked in an operationally reliable manner in the powerless state and retracted in an operationally reliable manner so that with the linear drive 2 a system which is intended to be moved, such as, for example, the scissor lift 24, can always be operated in a reliable manner.

[0049] The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention:

LIST OF REFERENCE NUMERALS

[0050] 2 Linear drive [0051] 4 Linear unit [0052] 6 Spindle [0053] 8 Threaded nut [0054] 10 Motor [0055] 12 Drive connection [0056] 14 Motor shaft [0057] 16 Gear mechanism [0058] 18 Thrust pipe [0059] 20 Covering pipe [0060] 22 Articulated head [0061] 24 Scissor lift [0062] 26 Load [0063] 28 Brake system [0064] 30 Brake [0065] 32 Centrifugal brake [0066] 34 Friction element [0067] 36 Resilient element [0068] 38 Brake liner [0069] 40 Caliper [0070] 42 Brake drum [0071] 44 Caliper [0072] 45 Motor shaft [0073] 46 Spring [0074] 48 Electromechanical drive [0075] 50 Electric motor [0076] 52 Mechanism [0077] 54 Drive [0078] 56 Lever [0079] 58 Mechanism