LINEAR ACTUATOR

Abstract

Linear actuator (8) comprising a quick release (27) for disengagement of an adjustment element (23) from an electric motor (19) and the part of a transmission (20) extending from the electric motor (19) to the quick release (27), such that the spindle (21) of the linear actuator is rotated under the load on the adjustment element (23). Further, the linear actuator comprises brake means (28) connected to the spindle (21) for controlling the speed of the adjustment element (23), when the quick release (27) is activated. A coupling (34;52,53,54) connected the brake means (28) is configured to set the brake means (28) in an active state, when the coupling (34; 52,53,54) is engaged, or in an inactive state, when the coupling (34;52,53,54) is slipping or disengaged.

Claims

1. Linear actuator comprising a reversible electric motor (19), a transmission (20) and a non-self-locking spindle (21), where the electric motor (19) through the transmission (20) drives the non-self-locking spindle (21), and where the linear actuator comprises a spindle nut (22) on the spindle (21) and an adjustment element (23) secured against rotation, and where the adjustment element (23) can be moved axially, in that it is connected to or integral with the spindle nut (22) on the spindle (21), and where 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 where 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), where the brake means (28) is configured to be in either 1) an active state, where the rotation of the spindle (21) is braked, or 2) an inactive state, where the rotation of the spindle (21) is not braked, and where the coupling (34; 52,53,54) being configured to be in a state of either 3) engaged, or 4) slipping or disengaged, and where the coupling (34; 52,53,54) will 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. Linear actuator according to claim 1, characterized in that the coupling is a centrifugal coupling (34).

3. Linear actuator according to claim 2, characterized in that the centrifugal coupling (34) comprises a damper holder (35), a spring (36), and a sliding element (37), where the damper holder (35) comprises a cavity (39) for receiving the sliding element (37), and where the cavity (39) comprises an opening (41) through which at least a part of the sliding element (37) can be displaced, where 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), where 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), where 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),

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

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

6. Linear actuator according to claim 1, characterized in that the brake means is a wrap spring.

7. Linear actuator according to claim 3, characterized in that the spring is a compression spring (36).

8. Linear actuator according to claim 3, characterized in that the spring is an extension spring.

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

10. Linear actuator according to claim 9, 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 the side of the damper holder (52), and where 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, where 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 where 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.

11. A bed comprising an adjustable carrying surface for a mattress, where the carrying surface comprises an adjustable section (5, 6), characterized in that the bed comprises at least one linear actuator according to claim 1, where the linear actuator is configured to adjust the adjustable section of the bed.

12. A bed according to claim 11, characterized in that the adjustable section is a back-rest section (5).

13. A bed according to claim 11, characterized in that the bed is a hospital or care bed (1).

Description

[0016] A linear actuator according to the invention will be described more fully below under reference to the accompanying drawing. The drawing shows:

[0017] FIG. 1, an outline of a hospital or care bed,

[0018] FIG. 2, a perspective view of a linear actuator with quick release, brake means and a coupling for activating the brake means,

[0019] FIG. 3, a longitudinal cross section of the linear actuator in FIG. 2,

[0020] FIG. 4, an exploded perspective of a rear mounting, centrifugal coupling, and brake means,

[0021] FIG. 5a-d, different views of a damper holder of the centrifugal coupling,

[0022] FIG. 6a-b, two perspectives of a sliding element of the centrifugal coupling,

[0023] FIG. 7a-b, a top view and a perspective of the rear mounting,

[0024] FIG. 8, a cross section of the linear actuator through the rear mounting, where the centrifugal coupling is in a slipping or disengaged state,

[0025] FIG. 9, a cross section of the linear actuator through the rear mounting, where the centrifugal coupling is in an engaged state,

[0026] FIG. 10a-b, a side view and perspective of the centrifugal coupling and rotary damper, where the centrifugal coupling is in a slipping or disengaged state,

[0027] FIG. 11a-b, a side view and perspective of the centrifugal coupling and rotary damper, where the centrifugal coupling is in an engaged state, and

[0028] FIG. 12a-b, a schematic cross section of second embodiment of the coupling.

[0029] The hospital or care bed 1 shown in FIG. 1 of the drawing comprises a lower frame 2 equipped with drive wheels 3 and an upper frame 4. An adjustable carrying surface for the mattress is mounted to the upper frame 4. The carrying surface comprises a back-rest section 5, an articulated leg-rest section 6 and a fixed middle section 7 between these two sections 5,6. The back-rest and leg-rest sections 5,6 can be adjusted with a linear actuator 8,9 each, such that the carrying surface can assume various contours, indicated by the arrow 10. The upper frame 4 is connected to the lower frame 2 with a lever mechanism 11,12 at each end. The upper frame 4 can be raised and lowered by means of a pair of actuators 13,14 connected to the lever mechanism 11,12. The actuators 8,9;13,14 are connected to a control box 15 containing a power supply for connection to mains, optionally a rechargeable battery pack as well as a controller. Operating units such as hand controls 16 and fixed control panels in guard rails 17 are connected to the control box 15.

[0030] FIG. 2 shows a linear actuator 8 which is arranged to move the back-rest section 5 of the hospital or care bed 1. The linear actuator comprises a housing 18 with a reversible electric motor 19, which through a worm gear 20 drives a spindle 21 with a spindle nut 22, to which a tubular adjustment element 23, also called an inner tube, surrounded by an outer tube 24, is secured. A front mounting 25 is located at the end of the tubular adjustment element 23, and a rear mounting 26 for mounting of the linear actuator 8 is located at the rear end of the linear actuator. The linear actuator 8 is equipped with a quick release unit 27 with a release mechanism.

[0031] Referring to FIGS. 3-11, the linear actuator 8 comprises a rotary damper 28 which is connected to the lower/rear end of the spindle 21, i.e. the end closest to the rear mounting 26. The rotary damper 28 comprises an inner body in the shape of a cylinder placed in a liquid-filled hollow in an outer body 29. The liquid used in the hollow of the rotary damper 28 is preferably a silicone oil. The inner body is through a shaft end 30 in driving connection with the shaft end of the spindle 21.

[0032] The rotary damper 28 can be connected directly to the spindle 21 or via one or more parts depending on the specific construction of a linear actuator. In the present embodiment (FIGS. 2-11), the shaft end 30 of the rotary damper 28 is connected to a gear wheel 31, which engages a position wheel 32. The rear end of the spindle 21 is connected to an end nut 33, which engages the position wheel 32.

[0033] The outer body 29 of the rotary damper 28 is fixed to a centrifugal coupling 34, which comprises a damper holder 35, a spring 36, and a sliding element 37. The damper holder 35 is a circular element with two circular segments cut off.

[0034] Collars 38a-c for rotationally fixing the rotary damper 28 to the damper holder 35 extends from an upper side thereof. The damper holder 35 has a cavity 39 with two openings 40,41. The opening 40 is open towards the upper end and the opening 41 is open to the side of the damper holder 35. The cavity 39 is adapted to receive the sliding element 37, which is shaped as an oblong rectangular block with a protrusion 42 at one end extending to the side of the sliding element 37. The end of the sliding element 37 placed at the opening 41 is curved such that it levels with the circular outer surface of the damper holder 35. A small part of the cavity 39 is adapted to receive a spring 36, here a compression coil spring. One end of the spring 36 engages a wall piece 43 of the cavity 39. The other end of the spring 36 engages the protrusion 42 of the sliding element 37. To fit in the space between the wall piece 43 and the protrusion 42, the spring 36 is compressed and therefore in a pre-stressed state. Hence, the sliding element 37 is spring-loaded.

[0035] The rear mounting 26 comprises a cavity 44 having a wall 45 with an approximately circular cross section. The cavity 44 is adapted to receive at least a part of the coupling 34 with a small distance of play between the coupling 34 and the wall 45. A circular arc of the circumference of the wall 45 is displaced radially outwards, creating a small arc shaped track 46 relative to the circular cross section of the cavity 44. The cavity 44 has a small hole 47 at its bottom adapted to receive a pin 48 extending from the underside of the damper holder 35 with a small distance or play between the two. In this embodiment, the underside of the damper holder 35 engages a part of the bottom of the cavity 44. This serves among other things to keep the rotary damper 28 in place along the longitudinal axis of the spindle 21.

[0036] Since the damper 28 and the coupling 34 (35,36,37) are directly and/or indirectly connected to the spindle 21, both will rotate together with the spindle 21. If the rotational speed of the spindle 21 passes a certain threshold, the centrifugal force exerted on the sliding element 37 will cause it to be displaced out of the opening 41 of the cavity 39. This threshold can only be reached if the quick release unit 27 is activated. Hence, during normal operation, the linear actuator 8 will not reach such a high rotational speed.

[0037] Passing the threshold will cause the curved end of the sliding element 37 to engage the wall 45 of the cavity 44 of the rear mounting 26. When the sliding element 37 reaches the circular arc of the circumference of the wall 45, it will displace into the arc shaped track 46. Once here, a side of the sliding element 37 will engage the end 49 of the track 46, which functions as a stop. In this embodiment, the track end 49 is constituted by a hollow cylindric tube 50 with a longitudinal slit, in which a protrusion of the wall 45 is received.

[0038] The relation between the size of the centrifugal force and the impact of the engagement between the sliding element 37 and the track end 49, determines whether the sliding element 37 remains in engagement with the track end 49 or is forced back into the cavity 39. The latter constitutes a slipping state of the coupling 34, which will cause the spindle 21, the damper 28 and the coupling 34 to continue its rotation. The former constitutes an engaged state of the coupling 34, which causes an activation of the rotary damper 28. More precisely, the damper holder 35 and thereby the outer body 29 of the rotary damper 28 will be kept in a fixed non-rotating position. Only the shaft end 30 of the inner body of the rotary damper 28 will continue to rotate with the spindle 21. Consequently, the rotary damper 28 will dampen the rotational speed of spindle 21. Upon reduction of the rotational speed of the spindle 21, the centrifugal force exerted on the sliding element 37 reduces, causing it to retract into the cavity 39. This again will cause the complete rotary damper 35, the coupling 34, and the spindle 21 to rotate together.

[0039] The coupling 34 will normally be in a slipping state a number of times, before the rotational speed reaches the threshold causing the coupling 34 to be in an engaged state. For the sake of clarity, a disengaged and slipping state of the coupling will be regarded as one single state. The threshold can be set to a determined level depending on the bed or other construction in which the linear actuator is used. A range number of parameters can be used to reach the threshold. These could be, but are not limited to, the following, namely the thread pitch of the spindle 21, geometry and material of the damper holder 35 and sliding element 37, and the spring force of the spring 36. The coupling 34 could also be embodied such that the spring 36 could be an extension spring rather than a compression spring.

[0040] In the present embodiment, the rotary damper 28 is rotationally fixed by the collars 38a-c and fixed along the longitudinal axis of the spindle by the engagement between the underside of the damper holder 35 and a part of the bottom of the cavity 44 of the rear mounting 26. In an alternative embodiment, the collars 38a-c could be embodied as snap locks and thus extend along the full height of the outer body 29 and engage the top surface thereof. This would fix the rotary damper 28 both rotationally and in the longitudinal direction. Engagement between the underside of the damper holder 35 and the bottom of the cavity 44 would therefore not be needed.

[0041] Instead of a rotary damper, other types of brake means or dampers could be used, e.g. a wrap spring brake.

[0042] FIG. 12a-b shows schematic cross sections of a second embodiment of the invention, where the coupling is a manual coupling. In FIGS. 12a-b, the rear mounting 50 of the linear actuator has a circular side wall forming a cavity 51 adapted for receiving at least a part of the manual coupling. The damper holder 52 comprises a protrusion 53 extending out from the side of damper holder 52. The rear mounting 50 comprises a stop element 54, which can be moved in and out of the cavity 51. Collars 55a-c for rotationally fixing a brake means to the damper holder 52 extends from an upper side thereof. The brake means is connected to the spindle of the linear actuator in the same way as described in the first embodiment. At least the damper holder 52 and the stop element 54 constitutes the manual coupling of this embodiment. The manual coupling can be in either of two states as the centrifugal coupling 34 of the first embodiment. A slipping or disengaged state where the stop element 54 is fully or almost fully retracted from the cavity 51, such that the damper holder 52 can rotate freely, or an engaged state where the stop element 54 is extended into the cavity 51, such that the protrusion 53 engages the stop element 54, whereby the damper holder 52 cannot rotate. In the latter situation, the brake means will be in an active state and thus dampen the rotational speed of the spindle. In the former situation, slipping or disengaged state, the brake means will be in an inactive state and thus not dampen the rotational speed of the spindle.