Linear actuator

1. A linear actuator comprising:

a reversible electric motor ( 19 ),

a transmission ( 20 ), and

a non-self-locking spindle ( 21 ),

wherein the electric motor ( 19 ), through the transmission ( 20 ), drives the non-self-locking spindle ( 21 ), and

wherein the linear actuator comprises a spindle nut ( 22 ) on the spindle ( 21 ) and an adjustment element ( 23 ) secured against rotation, and

wherein the adjustment element ( 23 ) can be moved axially, in that the adjustment element ( 23 ) is connected to or integral with the spindle nut ( 22 ) on the spindle ( 21 ), and

wherein the linear actuator further comprises a quick release ( 27 ) for disengagement of the adjustment element ( 23 ) from the reversible electric motor ( 19 ) and the part of the transmission ( 20 ) extending from the reversible electric motor ( 19 ) to the quick release ( 27 ), such that the spindle ( 21 ) is rotated under the load on the adjustment element ( 23 ), and

wherein the linear actuator comprises brake means ( 28 ) connected to the spindle for controlling the speed of the adjustment element ( 23 ) under the external load when the quick release is activated,

characterized in that the linear actuator comprises a coupling ( 34 ; 52 , 53 , 54 ) connected to the brake means ( 28 ),

wherein the brake means ( 28 ) is configured to be in either

1) an active state, wherein the rotation of the spindle ( 21 ) is braked, or

2) An inactive state, wherein the rotation of the spindle ( 21 ) is not braked,

and wherein the coupling is ( 34 ; 52 , 53 , 54 ) configured to be in a state of either

3) engaged, or

4) slipping or disengaged,

and wherein the coupling ( 34 ; 52 , 53 , 54 ) is configured to set the brake means ( 28 ) in

1) the active state, when the coupling ( 34 ; 52 , 53 , 54 ) is 3) engaged, or

2) the inactive state, when the coupling ( 34 ; 52 , 53 , 54 ) is 4) slipping or disengaged.

2. The linear actuator according to claim 1 , further comprising:

a rear mounting ( 26 ) for mounting of the linear actuator, characterized in that the rear mounting ( 26 ) comprises a cavity ( 44 ) adapted to receive at least a part of the coupling,

wherein a side wall ( 45 ) of the cavity has an approximately circular cross section, and wherein a circular arc of the side wall ( 45 ) is displaced radially outwards, and wherein the circular arc comprises a stop ( 49 ).

3. The linear actuator according to claim 1 , characterized in that the brake means is a rotary damper ( 28 ).

4. The linear actuator according to claim 1 , characterized in that the brake means is a wrap spring.

5. The linear actuator according to claim 1 , characterized in that the coupling is a manual coupling ( 52 , 53 , 54 ).

6. The linear actuator according to claim 5 , further comprising a rear mounting ( 26 ) for mounting of the linear actuator, characterized in that the manual coupling ( 52 , 53 , 54 ) comprises a damper holder ( 52 ) with a protrusion ( 53 ) extending out from a side of the damper holder ( 52 ), and wherein the rear mounting ( 26 ) comprises a cavity ( 51 ) for receiving at least a part of the manual coupling, and further comprises a stop element ( 54 ), which can be moved in and out of the cavity ( 51 ) by a manual operation,

wherein the manual coupling ( 52 , 53 , 54 ) is in the engaged state when the stop element ( 54 ) extends into the cavity ( 51 ), such that the protrusion ( 53 ) engages the stop element ( 54 ), whereby the damper holder ( 52 ) cannot rotate, and wherein the manual coupling ( 52 , 53 , 54 ) is in the slipping or disengaged state when the stop element ( 54 ) is fully or almost fully retracted from the cavity ( 51 ), such that the damper holder ( 52 ) can rotate.

7. A bed comprising an adjustable carrying surface for a mattress, wherein the carrying surface comprises an adjustable section ( 5 , 6 ),

characterized in that the

bed comprises at least one linear actuator according to claim 1 , wherein the linear actuator is configured to adjust the adjustable section of the bed.

8. The bed according to claim 7 ,

characterized in that the adjustable section is a back-rest section ( 5 ).

9. The bed according to claim 7 ,

characterized in that the bed is a hospital or care bed ( 1 ).

10. The linear actuator according to claim 1 , characterized in that the coupling is a centrifugal coupling ( 34 ).

11. The linear actuator according to claim 10 , characterized in that the centrifugal coupling ( 34 ) comprises a damper holder ( 35 ), a spring ( 36 ), and a sliding element ( 37 ),

wherein the damper holder ( 35 ) comprises a cavity ( 39 ) for receiving the sliding element ( 37 ),

and wherein the cavity ( 39 ) comprises an opening ( 41 ) through which at least a part of the sliding element ( 37 ) can be displaced,

wherein the spring ( 36 ) is arranged between the sliding element ( 37 ) and the damper holder ( 35 ) such that the sliding element ( 37 ) is spring-loaded relative to the damper holder ( 35 ),

wherein the linear actuator comprises a stop ( 49 ) prepared for engagement with the part of the spring-loaded sliding element ( 37 ) extending out of the opening of the damper holder ( 35 ),

wherein the coupling is in

3) the engaged state, when the part of the spring-loaded sliding element ( 37 ) extending out of the opening ( 41 ) of the damper holder ( 35 ) fully engages the stop ( 49 ), and

4) the slipping or disengaged state, when the part of the spring-loaded sliding element ( 37 ) extending out of the opening of the damper holder ( 35 ) is slipping or disengaged from the stop ( 49 ).

12. The linear actuator according to claim 11 , characterized in that the spring is a compression spring ( 36 ).

13. The linear actuator according to claim 11 , characterized in that the spring is an extension spring.