LINEAR ACTUATOR

Abstract

Linear actuator, where a reversible electric motor (20) through a transmission (21) drives a non-self-locking spindle (22), by means of which an adjustment element (24) secured against rotation can be moved axially for adjusting an element connected thereto such as a backrest section in a bed. The actuator further comprises a quick release (27) for disengagement of the adjustment element (24) from the electric motor (20) and the part of the transmission (21) extending from the electric motor (20) to the quick release (27), such that the spindle (22) is rotated under the load on the adjustment element (24). Further, the actuator comprises brake means for controlling the speed of the adjustment element (24), when the quick release (27) is activated. The brake means are constituted by a rotary damper (45) of the fluid type comprising an internal body located in a liquid-filled hollow in an outer body, where one body is in driving connection with the spindle (22) or the part of the transmission extending from the spindle (22) to the quick release (27), and where a dampening effect, which dampens the speed of the spindle (22) and thus the adjustment element (24), is generated when this body is rotated relative to the other body as a result of activation of the quick release (27). It is thus possible to provide a construction where the lowering speed is self-controlling when the quick release is activated.

Claims

1. A linear actuator comprising a reversible electric motors, a transmission and a non-self-locking spindle, where the electric motor through the transmission drives the non-self-locking spindle, and where the linear actuator comprises a spindle nut on the spindle and an adjustment element secured against rotation, and where the adjustment element can be moved axially, in that it is connected to or integral with the spindle nut on the spindle, and where the linear actuator further comprises a quick release for disengagement of the adjustment element from the reversible electric motor and the part of the transmission extending from the reversible electric motor to the quick release, such that the spindle is rotated under the load on the adjustment element, and where the linear actuator comprises brake means for controlling the speed of the adjustment element under the external load when the quick release is activated, wherein the brake means are constituted by a rotary damper of the fluid type comprising an internal body located in a liquid-filled hollow in an outer body, where one body is in driving connection with the spindle or the part of the transmission, which extends from the spindle to the quick release, and where a viscous dampening effect, which dampens the speed of the spindle and thus the adjustment element, is generated when this body is rotated relative to the other body as a result of activation of the quick release.

2. A linear actuator comprising a reversible electric motor, a transmission and a spindle, where the reversible electric motor through the transmission drives the spindle, and where the linear actuator comprises a spindle nut on the spindle and a tubular adjustment element, which can be moved axially, in that it with a rear end is connected to the spindle nut on the spindle, and where the linear actuator comprises a front mounting connected to an outer end of the tubular adjustment element and a quick release arranged between the outer end of the tubular adjustment element and the front mounting for disengagement of the tubular adjustment element from the front mounting, such that the tubular adjustment element is rotated under the load thereon, and where the linear actuator further comprises brake means for controlling the speed of the tubular adjustment element under the outer load, when the quick release is activated, wherein the brake means are constituted by a rotary damper comprising an internal body placed in a liquid-filled hollow in an outer body, where one body is in driving connection with the tubular adjustment element, and where a viscous dampening effect, which dampens the speed of the tubular adjustment element, is generated when this body is rotated relative to the other body as a result of activation of the quick release.

3. The linear actuator according to of claim 1, further comprising a free wheel bearing arranged such that the body, which is in driving connection with the spindle or the part of the transmission, which extends from the spindle to the quick release, stands still when the adjustment element is moved against the load.

4. The linear actuator of claim 2, further comprising a free wheel bearing arranged such that the body, which is in driving connection with the adjustment element, stands still when the adjustment element is moved against the load.

5. The linear actuator of claim 3, wherein the free wheel bearing is incorporated in the rotary damper.

6. A linear actuator of claim 4, wherein the free wheel bearing is incorporated in the rotary damper.

Description

[0014] A linear actuator according to the invention will be described more fully below under reference to the accompanying drawing. The drawing shows:

[0015] FIG. 1, an outline of a hospital bed,

[0016] FIG. 2, a perspective view of a linear actuator with quick release and rotary damper,

[0017] FIG. 3, a linear actuator with quick release and rotary damper seen from above,

[0018] FIG. 4, a longitudinal section through the actuator shown in FIG. 2,

[0019] FIG. 5, a detailed section of the longitudinal section shown in FIG. 4,

[0020] FIG. 6, parts of the quick release unit in its initial position seen from the side,

[0021] FIG. 7, parts of the quick release unit in a disengaged position seen from the side,

[0022] FIGS. 8a and 8b, the inner coupling part seen from each end, respectively,

[0023] FIGS. 9a and 9b, the outer coupling part seen from each end, respectively,

[0024] FIG. 10, an exploded view of a release mechanism,

[0025] FIG. 11, the release mechanism seen from above and into the housing of the quick release unit, and

[0026] FIG. 12, a schematic construction of a linear actuator.

[0027] The hospital bed 1 shown in FIG. 1 of the drawing comprises a lower frame 3 equipped with drive wheels 2 and an upper frame 4. An adjustable carrying surface for the matrass is mounted to the upper frame 4. The carrying surface comprises a back rest section 6, an articulated leg rest section 7 and a fixed middle section 8 between these. The back rest and leg rest section 6,7 can be adjusted with a linear actuator 9,10 each, such that the carrying surface can assume various contours, indicated by the arrow 5. The upper frame 4 is connected to the lower frame 3 with an articulation 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 articulations 11,12. The actuators 9,10;13,14 are connected to a control box 15 containing a power supply for connection to mains, a rechargeable battery pack as well as a controller. Operating units such as hand controls 16, fixed control panels in guard rails 17 and possibly other periphery equipment such as underbed light 18 is connected to the control box 15.

[0028] As it appears from FIGS. 2-11 of the drawing, the linear actuator 9, which moved the back rest section 6, comprises a housing 19 with a reversible electric motor 20, which through a worm gear 21 drives a spindle 22 with a spindle nut 23, to which a tubular adjustment element 24, also called an inner tube, surrounded by an outer tube 25, is secured. A front mounting 26 is located at the end of the tubular adjustment element 24 for mounting of the linear actuator. The actuator concerned is equipped with a quick release unit 27 with a release mechanism 28.

[0029] The quick release unit 27 comprises two coupling parts 29,30, where the inner coupling part 29 is mounted on a shaft end 22a of the spindle 22, while the outer coupling part 30 has a hollow 31 (partial cylindrical track) in which a protrusion 32 on the inner coupling part 29 can be received in a torque-transferring connection. The outer side of the outer coupling part 30 further comprises a groove 33 for engagement with a corresponding tongue on the inner side of the through-going hole of the worm wheel 21, such that a torque-transferring connection is also formed here. Thus, the reversible rotation of the electric motor 20 through the worm gear (including the worm wheel 21) and further through the connection between the outer and inner coupling part 29,30 can drive the spindle 22. The spindle nut 24, which is secured against rotation, can thus move back and forth on the spindle 22 depending on the direction of rotation of the electric motor 20.

[0030] The quick release unit 27 further comprises a housing 34 with a cover 35, in which the release mechanism 28 is arranged. The housing 34 has two entries 34a,34b for a not shown cable leading to a lever, not shown either. The release mechanism 28 comprises a tubular activation element 36, which partially is led through a hole in the bottom of the housing 34 and thus extends partially into the housing 19 of the linear actuator. The upper end of the activation element 36, which is placed in the housing 34 comprises an arm 37, which extends in a radial direction from the rotation and central axis (see FIGS. 6 and 11) of the activation element 36. The arm 37 of the activation element is connected to a cable holder 38 with two holes 38a, 38b in which a cable, e.g. in the shape of a wire, can be secured. Each of the cables can be guided in the two entrances 34a, 34b, respectively in the housing 34. The upper end of the activation element 36 has a hollow cylindrical part, in which a return spring 39 is arranged. A free end of the winding of the return spring is fixed in a track in the housing 34. Under reference to FIGS. 6, 7 and 11, the activation element 36 will be rotated in a clockwise direction, when a cable is pulled via the arm 37. Concurrently with the pull force in the cable being reduced, the return spring 39 will cause the activation element 36 to rotate in a counter clockwise direction to an initial position.

[0031] The lower end of the tubular activation element 36 is partially shortened with a notch, which has a first plane surface perpendicular to the rotation and central axis of the activation element and a second plane surface 40 parallel to the rotation and central axis of the activation element. Seen from the end of the lower end of the activation element 36 the second plane surface 40 forms a chord in the circular section of the activation element.

[0032] When the activation element 36 is in its initial position the second plane surface 40 rests against a collar 41 on the outer coupling part 30. In this initial position the outer coupling part 30 is in engagement with the inner coupling part 29. This torque-transferring connection between the two coupling parts 29, 30 is achieved by spring-loading the outer coupling part 30. Thus, the outer coupling part 30 is displaceably arranged on a bushing 42, which further comprises a compression spring 43 placed between an end wall 44 on the bushing 42 and the outer coupling part 30. In this embodiment, the bushing 42 sits across the threads of the spindle 22 in continuation of the shaft end 22a of the spindle, such that the end wall 44 is located farthest away from the shaft end 22a of the spindle.

[0033] When the activation element 36 is rotated as a result of a pull in a cable, the second plane surface 40 will displace the outer coupling part 30 in the direction towards the end wall 44 of the bushing and thus compress the compression spring 43. After a given rotation of the activation element 36 the outer coupling part 30 will be displaced so much that the torque-transferring connection is interrupted.

[0034] Hereby, the spindle 22 can rotate freely independent of transmission 21 and electric motor 20. The spindle 22, spindle nut 23 and the tubular adjustment element 24 of the actuator will thus be disengaged and the back rest section 6 of the bed will under its load move downwards into its horizontal position.

[0035] A rotary damper 45 of the fluid type is connected to the free end of the shaft end 22a of the spindle, which is embedded with a bearing in the housing 19. The rotary damper 45 is mounted in a hollow in a rear mounting 46 on the rear end of the linear actuator. The rotary damper 45 comprises an inner body in the shape of a cylinder placed in a liquid-filled hollow in an outer body, which is also constituted by an outer body. The liquid used in the hollow of the rotary damper 45 is a silicone oil. The inner body is through a shaft end in driving connection with the shaft end 22a of the spindle. When the quick release unit 27 through the release mechanism 28 is activated and the spindle thus is disengaged, this rotates the inner body relative to the outer body. Hereby, a dampening effect is generated, which dampens the speed of the spindle and thus the adjustment element. Based on the maximum load on the actuator, the maximum dampening with which the rotary damper should dampen the speed of the adjustment element 24 can be determined and thus determine a maximum lowering speed. Dampening can be determined based on choice of liquid and its viscosity, as well as the design and size of the inner and outer bodies. An example of a rotary damper is provided in EP 0 763 671 A2 to Illinois Tool Works Inc.

[0036] The rotary damper has a built-in free wheel bearing such that the rotary damper is disengaged under normal operation and thus does not interrupt this or require extra energy.

[0037] FIG. 12 of the drawing shows a schematic view of a linear actuator 47 according to the invention, which consists of a reversible electric motor, a transmission, a spindle with a spindle nut and a tubular adjustment element (inner tube) 48. At the outer end of the tubular adjustment element 48 is a front mounting 49 for securing of the actuator 47. Between the front mounting 49 and the tubular adjustment element 48 is a quick release 50 connected to a rotary damper 51 of the fluid type. During normal operation of the actuator 47 the front mounting will be fixed relative to the tubular adjustment element 48. By activation of the quick release 49 the tubular adjustment element 48 is disengaged from the front mounting 49, by which the tubular adjustment element 48, e.g. through a bearing connection (not shown), can rotate freely relative to the front mounting 49. A compression force on the front mounting 49 will thus be transferred to the tubular adjustment element 48 and result in this being rotated in an inwards direction. It is noted that the spindle of the actuator is fixed during the rotation of the tubular adjustment element 48. The rotary damper 51 generates a dampening effect, which dampens the rotation and thus the speed, at which the tubular element 48 is moved in the inwards direction.