Lifting mechanism for a bed

Abstract

The lifting mechanism for a bed comprises: a support frame 12; a leg 40 having a first end rotatably and slidably connected to the support frame and a second end connected to a foot; a leg linkage 60

Description

FIELD OF THE INVENTION The present invention relates to the field of lifting mechanisms for beds, and beds incorporating such lifting mechanisms. The lifting mechanisms are particularly suited to use in beds in the healthcare industry. The lifting mechanisms allow a bed to be lowered close to the floor to reduce injuries from falls and to be raised to a suitable height to enable easy access to a person lying on the bed. BACKGROUND TO THE INVENTION It is known to provide lifting mechanisms in beds in hospitals and other healthcare facilities. The lifting mechanisms are used to raise and lower the height of the bed, i.e. increase or decrease a distance between the mattress and the floor. This has the advantage of allowing the bed to be raised to a height at which a healthcare worker, such as a doctor or nurse, has easy access to the patient without bending. In some situations the lifting mechanisms may also allow the bed to be lowered such that the mattress is close to the floor on which the bed is standing. This has the advantage that, if a patient rolls out of the bed, they will not fall a large distance to the floor. There is, therefore, a lower risk of injury to the patient than if the bed was at a greater height. A number of prior art lifting systems are known; however, these known systems have a number of disadvantages. Some of these systems can be expensive to manufacture due to the large number of components and the complexity of the lifting mechanism. Other systems are bulky, taking up a lot of space at the end of the bed. These bulky systems not only significantly increase the size and weight of the bed, but also restrict access to the patient. If the lifting mechanism is located in a headboard or footboard of the bed, then this prevents the headboard or footboard being removed from the bed when, for example, emergency access is needed to the patient for cardiopulmonary resuscitation (CPR). If a bulky lifting mechanism is located under the frame of the bed, this restricts how low the bed can go, i.e. how close the mattress can be positioned relative to the floor. Against this background it is desirable to provide an improved bed lifting mechanism that overcomes at least one of the disadvantages of prior art systems, whether referred to herein or otherwise. SUMMARY OF THE INVENTION A first aspect of the invention provides a lifting mechanism for a bed, comprising: a support frame; a leg assembly having a first end rotatably and slidably connected to the support frame and a second end connected to a foot assembly; a leg linkage assembly pivotally connected to the support frame and pivotally connected to the leg assembly between its first and second ends; a drive lever pivotally connected to the leg linkage assembly at a drive pivot; and an actuator arranged to apply a force to the drive lever to change a distance between the second end of the leg assembly and the support frame, wherein, during a lower range of movement of the actuator the drive lever is in contact with and directly applies a force to the support frame, and during an upper range of movement of the actuator the drive lever only applies a force directly to the leg linkage assembly. The lifting mechanism of the present invention is designed to move the support frame between a fully raised position and a fully lowered position relative to the foot assembly. The lifting mechanism is arranged to move the support frame from the fully lowered position, through the lower range of movement, through the upper range of movement and to the fully raised position. Similarly, the lifting mechanism is arranged to move the support frame from the fully raised position, through the upper range of movement, through the lower range of movement and to the fully lowered position. The lifting mechanism may be configured to hold and retain the support frame at any position between the fully lowered and fully raised positions. In the following description of a preferred embodiment of the invention, the lower range of movement includes a first range of movement and a second range of movement, and the upper range of movement includes a third range of movement. In other embodiments the lower range of movement may only include the second range of movement. In preferred embodiments the leg assembly comprises a leg member and a slider is connected to the first end of the leg member. A guide rail is preferably connected to the support frame. The slider is preferably engaged with the guide rail. The slider may be in the form of a wheel that rolls along the guide rail. In some embodiments an axis of the guide rail is at a non-zero angle to a plane of the support frame. In some embodiments a first end of the guide rail is adjacent the support frame and a second end of the guide rail is offset from and lower than the support plane. In preferred embodiments the drive lever includes a drive bearing and the support frame includes a contact surface. In these embodiments the drive bearing is preferably in contact with the contact surface during the lower range of movement of the actuator. The contact surface may be curved. Preferably the contact surface has a concave curvature and faces in a generally downwards direction towards a surface on which the foot assembly is standing in use. In some embodiments the lower range of movement comprises a first range of movement and a second range of movement. During the first range of movement the drive bearing may move from a first end of the contact surface towards a midpoint of the contact surface and during the second range of movement the drive bearing may move from the mid-point of the contact surface to a second end of the contact surface. In some embodiments the leg assembly comprises a pivot member and the drive lever includes a pivot surface, and the pivot surface is in contact with the pivot member during the first range of movement of the actuator. The pivot member may be a bracing member of the leg assembly. The pivot surface may be a cupped surface of the drive lever. In preferred embodiments the pivot surface comprises a concave surface of the drive lever. In embodiments in which the drive lever includes a drive bearing, the pivot surface may be disposed between the drive bearing and the connection between the actuator and the drive lever. In preferred embodiments the leg linkage assembly comprises a bearing member and the drive lever includes a cradle, and the bearing member is in contact with the cradle during the upper range of movement of the actuator. The cradle may comprise a concave surface of the drive lever. In embodiments in which the drive lever includes a drive bearing, the cradle may be disposed between the drive bearing and the drive pivot. In preferred embodiments the leg linkage assembly comprises a leg linkage member pivotally connected at a first end to the support frame and pivotally connected at a second end to the leg. The pivotal connection between the leg linkage member and the support frame is preferably spaced from the first end of the leg and is preferably disposed between the first end of the leg and an end of the support frame. The leg linkage member may not be straight and may include at least one bend region between its first and second ends. In embodiments in which the drive lever includes a drive bearing, the drive lever may be in the form of a generally triangular plate with the drive bearing disposed at a first vertex, the drive pivot disposed at a second vertex, and the connection between the actuator and the drive lever disposed at a third vertex of the plate. In preferred embodiments the actuator is a linear actuator pivotally connected to the drive lever. In embodiments in which the drive lever includes a drive bearing, the actuator is preferably connected to the drive lever at an actuator connection point, the leg assembly comprises a pivot member and the drive lever includes a pivot surface arranged to engage with the pivot member. The leg linkage assembly preferably comprises a bearing member and the drive lever preferably includes a cradle arranged to engage with the bearing member. In these embodiments (i) during the first range of movement of the actuator contact between the pivot surface and the pivot member forms a fulcrum, an effort arm of the drive lever is defined between the actuator connection point and the pivot surface and a load arm of the drive lever is defined between the drive bearing and the pivot surface, (ii) during a second range of movement of the actuator the drive pivot forms a fulcrum, an effort arm of the drive lever is defined between the actuator connection point and the drive pivot and a load arm of the drive lever is defined between the drive bearing and the drive pivot, and (iii) during a third range of movement of the actuator the drive pivot forms a fulcrum, an effort arm of the drive lever is defined between the actuator connection point and the drive pivot and a load arm of the drive lever is defined between the drive pivot and the cradle. In preferred embodiments, during the lower and upper ranges of movement of the actuator, the drive lever continuously rotates about the drive pivot. A second aspect of the invention provides a bed comprising: a support frame for supporting a mattress; a first leg assembly having a first end rotatably and slidably connected to the support frame and a second end connected to a first foot assembly, the first foot assembly being disposed proximate a first end of the support frame; a second leg assembly having a first end rotatably and slidably connected to the support frame and a second end connected to a second foot assembly, the second foot assembly being disposed proximate a second end of the support frame; a first leg linkage assembly pivotally connected to the support frame and pivotally connected to the first leg assembly; a second leg linkage assembly pivotally connected to the support frame and pivotally connected to the first leg assembly; a first drive lever pivotally connected to the first leg linkage assembly at a first drive pivot; a second drive lever pivotally connected to the second leg linkage assembly at a second drive pivot; a first actuator arranged to apply a force to the first drive lever to change a distance between the first foot assembly and the support frame; and a second actuator arranged to apply a force to the second drive lever to change a distance between the second foot assembly and the support frame, wherein, during a lower range of movement of the first and second actuators the first and second drive levers are in contact with and directly apply a force to the support frame, and during an upper range of movement of the first and second actuators the first and second drive levers only apply a force directly to the respective leg linkage assembly. Preferably the first and second actuators are operable independently of each other. Preferred and / or optional features of each aspect and embodiment described above may also be used, alone or in appropriate combination, in the other aspects and embodiments also. BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be further described by way of example only and with reference to the accompanying drawings, in which like reference signs are used for like features, and in which: Figures 1, 2 and 3 are perspective views of a bed frame including a lifting mechanism according to the present invention in fully lowered, raised and fully raised configurations respectively; Figure 4 is a perspective view of a part of the bed frame of Figure 1 in the fully lowered configuration, with a mattress support frame and feet assemblies removed, to more clearly show the lifting mechanism; Figure 5 is a side view of the bed frame of Figure 4; Figures 6 and 7 are sectional views, showing the same section in two different orientations, of one of two lifting mechanisms included in the bed frame of Figure 4; Figure 8 is a perspective view of a part of the bed frame of Figure 2 in the raised configuration, with a mattress support frame and feet assemblies removed, to more clearly show the lifting mechanism; Figure 9 is a side view of the bed frame of Figure 8; Figures 10 and 11 are sectional views, showing the same section in two different orientations, of one of two lifting mechanisms included in the bed frame of Figure 8; Figure 12 is a perspective view of a part of the bed frame of Figure 3 in the fully raised configuration, with a mattress support frame and feet assemblies removed to more clearly show the lifting mechanism; Figure 13 is a side view of the bed frame of Figure 12; and Figures 14 and 15 are sectional views, showing the same section in two different orientations, of one of two lifting mechanisms included in the bed frame of Figure 12. DESCRIPTION OF THE PREFERRED EMBODIMENTS A bed frame 10 according to a preferred embodiment of the present invention is shown in Figures 1 to 3. The bed frame 10 comprises a main support frame 12. The main support frame 12 extends in a length direction between first and second ends 14a, 14b (shown most clearly in Figures 5, 9 and 13). The main support frame 12 is preferably generally rectangular. The main support frame 12 defines a support plane of the bed frame 10. A longitudinal axis or length of the bed frame 10 extends between the first and second ends 14a, 14b. A lateral axis or width of the bed frame 10 extends perpendicular to the longitudinal axis and is defined between first and second sides 16a, 16b of the main support frame 12 (shown most clearly in Figures 4, 8 and 12). A mattress support frame 18 is connected to and supported by the main support frame 12. The mattress support frame 18 may be in contact with an upper surface of the main support frame 12. In use, the mattress support frame 18 supports a mattress on its upper surfaces. The mattress support frame 18 may, as illustrated and as known in the art, include a plurality of mattress panels, each panel providing support for a different section of the mattress. In this embodiment, headboard support brackets 20a are attached at and extend from the first end 14a of the main support frame 12, and footboard support brackets 20b are attached at and extend from the second end 14b of the main support frame 12. A headboard (not shown) is attachable to the headboard support brackets 20a and a footboard (not shown) is attachable to the footboard support brackets 20b. The bed frame 10 comprises four feet 22. In this embodiment each foot 22 includes a trolley 24 to which two wheels or casters 26 are attached, as shown most clearly in Figure 3. Two feet 22 of a first pair of feet are connected by an elongate shaft or axle 28 to form a first foot assembly 30a. Similarly, two feet 22 of a second pair of feet are connected by an elongate shaft or axle 28 to form a second foot assembly 30b. Each foot assembly 30a, 30b is attached to the main support frame 12 by a respective leg assembly 32. The first foot assembly 30a is attached to the main support frame 12 by a first leg assembly 32 so that the first foot assembly 30a is disposed at or proximate the first end 14a of the main support frame 12. The second foot assembly 30b is attached to the main support frame 12 by a second leg assembly 32 so that the second foot assembly 30b is disposed at or proximate the second end 14b of the main support frame 12. Furthermore, the feet 22 of each pair of feet are spaced apart and disposed at first and second ends of the respective axle 28 so that a first foot 22 of each foot assembly 30 is disposed proximate the first side 16a of the of the main support frame 12 and a second foot 22 of each foot assembly 30 is disposed proximate the second side 16b of the of the main support The leg assemblies 32 are configured to allow the support frame 12 to move with respect to the feet 22 between a fully raised position, illustrated in Figure 3, and a fully lowered position, illustrated in Figure 1. A lifting mechanism or linkage arrangement associated with each of the leg assemblies 32 allows the support frame 12 to be positioned at any point between the fully lowered and fully raised position. Figure 2 illustrates the bed frame 10 with the support frame 12 in a position between the fully raised and fully lowered positions. This position may be referred to as a partially raised or partially lowered position of the main support frame 12 with respect to the feet 22. Preferably, each leg assembly 32 is both pivotally attached to the support frame 12 and pivotally attached to the respective foot assembly 30. In this embodiment the connection between each leg assembly 32 and the main support frame 12 permits movement of the leg assembly 32 with respect to the main support frame 12 such that the main support frame 12 can be moved between the fully raised and fully lowered positions without a distance between the first and second foot assemblies 30a, 30b changing. In other words, the bed frame 10 may be raised and lowered without the feet 22 moving. In other embodiments the feet may move as the bed is raised and lowered. Preferably movement of the feet is limited so as not to destabilise the bed. It will be appreciated that references to upper and lower are with respect to the bed frame 10 standing on its feet 22 on a surface such as a floor in a normal orientation in use. Upper refers to an element facing in a direction away from the surface and / or disposed furthest from the surface, and lower refers to an element facing in a direction towards the surface and / or disposed closest to the surface. Similarly, the term raised refers to an upward direction away from that surface, and the term lowered refers to a downward direction towards the surface. As shown most clearly in Figure 3, each foot trolley 24 preferably comprises an upper plate 34, to which the two casters 26 are attached, and an axle support 36 which extends from the upper plate 34 between the two casters 26. An end of an axle 28 is connected to the axle support 36 such that an axis of the axle 28 lies in substantially the same plane as the rotational axes of the casters 26. As will be described further below, this has the advantage that the bed frame 10 may be lowered very close to the floor, as shown most clearly in Figure 1. In this embodiment the axis of each of the axles 28 extends parallel to the lateral axis of the bed frame 10. A distance between the first and second ends of each of the axles 28 is preferably greater than a distance between the first and second sides 16a, 16b of the main support frame 12, at least proximate the first and second ends 14a, 14b of the main support frame 12, so that the feet 22 of each foot assembly 30 lie outside of the main support frame 12, in particular when the bed frame 10 is fully lowered. In this embodiment, each of the first and second leg assemblies 32 are identical. Accordingly, the configuration of one of the leg assemblies 32 will now be described. Referring additionally to Figures 4 to 15, the leg assembly 32 comprises two elongate leg members 40. Each leg member 40 extends between a first end 42 and a second end 44. The second ends 44 of the leg members 40 are attached to one of the axles 28 of a foot assembly 30. In this embodiment the axle 28 is rigidly attached to the second ends 44 of the leg members 40, and the first and second ends of the axle 28 are rotationally connected to the axle supports 36 of the feet 22. In other embodiments the axle may be rotationally connected to the second ends of the leg members. The first ends 42 of the leg members 40 are pivotally and slidably connected to the main support frame 12. In this embodiment, the first end 42 of each leg member 40 is connected to a respective side member or side beam 46 of the main support frame 12. Outer surfaces of the side beams 46 define the first and second sides 16a, 16b of the main support frame 12. First and second ends of the side beams 46 define the first and second ends 14a, 14b of the main support frame 12. Referring to Figures 10 and 14, each side beam 46 includes a guide rail 48. The guide rail 48 extends longitudinally along the side beam 46 from a first end 50 to a second end 52. The guide rail 48, in this example, is provided on an inner surface or inner side of the side beam 46. The first end of the guide rail 48 is disposed proximate a mid-point of the side beam 46 between the first and second ends 14a, 14b. The second end 52 of the guide rail 48 is disposed closer to the respective first or second end 14a, 14b. It will be appreciated that, because the bed frame 10 includes first and second leg assemblies 32, each side beam 46 has two guide rails 48 extending in opposite directions towards opposite first and second ends of the side beam 46. There is a non-zero angle between a plane or axis of the guide rail 48 and the support plane of the bed frame 10. The angle between the axis of the guide rail 48 and the support plane of the bed frame 10 is preferably between 10 and 20°. The guide rail 48 is sloped with respect to the side beam 46 such that the second end 52 of the guide rail 48 is lower than the first end 50 of the guide rail 48. In this embodiment the guide rail 48 comprises a channel having a base and side walls, and an angle between the base of the channel and the support plane of the bed frame 10 is preferably between 1° and 20°. In this example the base of the channel at the first end 50 of the guide rail 48 is adjacent or congruent with a lower surface of the side beam 46, and the base of the channel at the second end 52 of the guide rail 48 is below the lower surface. A slider 54 is connected to the first end 42 of each of the leg members 40. The slider 54 is engaged with the guide rail 48 to slide along the guide rail 48 between its first and second ends 50, 52. In this embodiment the slider 54 comprises a wheel seated in the channel, and the wheel is rigidly connected to the leg member by a spindle. As well as sliding along the channel, the wheel is able to rotate with respect to the channel, thereby providing a rotational connection between the guide rail 48 and the leg member 40. In other embodiments the slider may not comprise a wheel, and pivotal movement of the slider relative to the leg member may provide the rotational connection between the guide rail 48 and the leg member 40. It will therefore be appreciated that the term slider refers to an element connected to the first end of the leg member that ‘slides’ or moves along guide rail, between the first and second ends of the guide rail. The slider may, in some embodiments, be considered to roll along the guide rail, for example when the slider is in the form of a wheel. The leg assembly 32 further comprises a bracing member 56 that extends between the leg members 40. An axis of the bracing member 56 is parallel to the axis of the axle 28. The bracing member 56 is rigidly attached, at each of its ends, to each of the leg members 40. The bracing member 56 is disposed between the first and second ends 50, 52 of the leg members 40, and in this embodiment a distance between the bracing member 56 and the second ends 52 of the leg members 40 is smaller than a distance between the bracing member 56 and the first ends 50 of the leg members 40. A leg linkage assembly 60 is connected to the main support frame 12 and the leg assembly 32. The leg linkage assembly 60 comprises a pair of leg linkage arms 62. A first end 64 of each of the leg linkage arms 62 is pivotally attached to a respective one of the side beams 46 of the main support frame 12. A second end 66 of each of the leg linkage arms 62 is pivotally attached to a respective one of the leg members 40 between its first and second ends 50, 52. In this embodiment the second end 66 of the leg linkage arm 62 is pivotally attached to the leg member 40 at a point between the first end 50 of the leg member 40 and the pivot member 56. Each of the first ends 64 of the leg linkage arms 62 is pivotally attached to the side beam 46 at a distance from the slider 54, and between the second end 52 of the guide rail 48 and the first or second end 14a, 14b of the main support frame 12. Also, each of the first ends 64 of the leg linkage arms 62 is attached to the side beam 46 proximate the respective first or second end 14a, 14b of the main support frame 12. The leg linkage assembly 60 further comprises a bearing cross member 68 and a support cross member 70. Because the leg linkage arms 62 are disposed adjacent a respective side beam 46, the leg linkage arms 62 are spaced laterally across the main support frame 12. Each of the bearing cross member 68 and support cross member 70 extends between and rigidly connects the leg linkage arms 62 at points between their first and second ends 64, 66. In this embodiment the bearing cross member 68 is attached to the leg linkage arms 62 closer to the second ends 66 than to the first ends 64 and the support cross member 70 is attached to the leg linkage arms 62 closer to the first ends 64 than to the second ends 66. In this embodiment the leg linkage arms 62 are not straight. Each linkage arm 62 includes three generally straight sections joined by two bend regions, so that the linkage arm 62 has a zig zag or lightning bolt shape. A first straight section extends from the first end 64 to a first bend. A second straight section extends from the first bend to a second bend. A third straight section extends from the second bend to the second end 66 of the linkage arm 62. The support cross member 70 extends from the first straight section, and the bearing cross member 68 extends from the second bend. The leg linkage arms 62 preferably have this shape to accommodate the positions of other parts of the bed frame 10 when the bed frame 10 is in its fully lowered position, as well as to provide the necessary leverage during movement of the leg linkage assembly 60. The leg linkage assembly 60 further comprises a pair of support brackets 72 that are rigidly connected to both the bearing cross member 68 and the support cross member 70. In this example, a first end of each of the support brackets 72 is connected to the support cross member 70 and the support brackets 72 extend in a direction towards the bearing cross member 68, with a second end of each of the support brackets 72 extending beyond the bearing cross member 68. In this way, the bearing cross member 68 is disposed between the first and second ends of the support brackets 72. The support brackets 72 extend in a direction generally parallel to the leg linkage arms 62 and are disposed approximately midway between the leg linkage arms 62. In this embodiment there is a gap between the support brackets 72 for receiving a drive element 74, and the second ends of the support brackets 72 provide a pivotal connection between the drive element 74 and the leg linkage assembly 60, described further below. The drive element 74 comprises a pair of drive levers 76 joined by and spaced apart by a spacer element 78. Each drive lever 76, as shown most clearly in Figure 10, includes a drive pivot 86. The drive pivot 86 provides the pivotal connection between each drive lever 76 and a respective one of the second ends of the support brackets 72. An actuator 92 is connected between the main support frame 12 and the drive element 74. In this embodiment, the actuator 92 is a linear actuator. A first end 94 of the actuator 92 is pivotally connected to the main support frame 12. The first end 94 of the actuator 92 is preferably pivotally connected to the main support frame 12 approximately halfway along the length of the main support frame 12 between its first and second ends 14a, 14b. A second end 96 of the actuator 92 is pivotally connected to the drive element 74. In this embodiment the second end 96 of the actuator 92 is pivotally connected to each of the pair of drive levers 76. The second end 96 of the actuator 92 is received in a gap between the drive levers 76 defined by the spacer element 78. As such, one actuator 92 is connected to two drive levers 76 which are each, in turn, connected to a respective one of the support brackets 72 spaced apart laterally along the support cross member 70. This allows the force from the actuator 92 to be applied evenly to each of the leg linkage arms 62 and therefore to each of the leg members 40. The connection between a single drive lever 76 and the associated leg linkage arm 62 and leg member 40 will now be further described with particular reference to Figures 6, 7, 10, 11, 14 and 15. The drive lever 76 further comprises a drive bearing 80, a cradle 82 and a cupped or concave surface 84. The drive bearing 80 is arranged to contact and apply a force to a part of the main support frame 12. In particular, the drive bearing 80 contacts a curved contact surface 88 of the main support frame 12. In this embodiment, the curved contact surface 88 is provided by a bearing plate 90 attached to a cross member of the main support frame 12. The curved contact surface 88 is a concave curved surface facing in a generally downwards direction towards a surface on which the bed frame 10 is standing. In this example, the drive bearing 80 is in the form of a drive bearing wheel 80 rotatably connected to the drive lever 76. In use, a circumferential surface of the drive bearing wheel contacts and moves along the curved contact surface 88. The cradle 82 is arranged to contact and apply a force to a part of the leg linkage assembly 60. The cradle 82 is preferably in the form of a recess or concavity configured to engage with the bearing cross member 68 of the leg linkage assembly 60. The cupped surface 84 may also be in the form of a recess or concavity, and is positioned and configured to provide clearance for the bracing member 56 of the leg assembly 32 when the main support frame 12 is in the fully lowered position. In this embodiment each of the drive levers 76 has the form of a generally triangular plate. Each of the drive pivot 86, drive bearing 80 and pivotal connection with the actuator 92 is disposed at or proximate a respective vertex of the triangular plate. The cradle 82 is in the form of a concave surface disposed along a side of the triangular plate between the drive pivot 86 and the drive bearing 80. In this embodiment the cradle 82 is disposed closer to the drive pivot 86 than to the drive bearing 80. The cupped surface 84 is in the form of a concave surface disposed along a side of the triangular plate between the drive bearing 80 and the pivotal connection with the actuator 92. In this embodiment the cupped surface 84 is disposed closer to the drive bearing 80 than to the pivotal connection with the actuator 92. The main support frame 12, leg assembly 32, leg linkage assembly 60, and drive element 74, together with an actuator 92, form a lifting mechanism of the bed frame 10. To operate the lifting mechanism to raise the main support frame 12 from a fully lowered position to a fully raised position, the actuator 92 is operated to apply a force to the drive levers 76. During a first range of movement of the actuator 92, illustrated in Figures 4 to 7, the drive bearing 80 is in contact with the contact surface 88 of the main support frame 12, such that the driver lever 76 applies a force directly to the main support frame 12. During this first range of movement the drive bearing 80 is in contact with a first portion of the contact surface 88. This first portion of the contact surface 88 is sloped such that, as the main support frame 12 is raised, movement of the drive bearing 80 along the contact surface 88 is in a generally upwards direction. In this embodiment the drive bearing 80 moves from a first end towards a mid-point of a downward-facing concave contact surface 88. During a second range of movement of the actuator 92, illustrated in Figures 8 to 11, the drive bearing 80 remains in contact with the contact surface 88 of the main support frame 12, such that the driver lever 76 continues to apply a force directly to the main support frame 12. During this second range of movement the drive bearing 80 is in contact with a second portion of the contact surface 88. This second portion of the contact surface 88 is sloped such that, as the main support frame 12 is raised, movement of the drive bearing 80 along the contact surface 88 is in a generally downwards direction. In this embodiment the drive bearing 80 moves from the midpoint of the downward-facing concave contact surface 88 towards a second end. During a third range of movement of the actuator 92, illustrated in Figures 12 to 15, the cradle 82 is in contact with the bearing cross member 68 of the leg linkage assembly 60, and contact between the drive bearing 80 and the contact surface 88 of the main support frame 12 is lost, such that the drive lever 76 only applies a force directly to the leg linkage assembly 60. Figures 4 to 7 show the bed frame 10 of the present embodiment in the fully lowered configuration. In this position, the leg members 40 extend substantially parallel to the plane of the main support frame 12. Furthermore, in this example, the axle 28 of the foot assembly 30 is in contact with a lower surface of the main support frame 12. The slider 54 connected to the first end 42 of the leg member 40 is disposed proximate the first end 50 of the guide rail 48. In this way, a distance between the first end 64 of the leg linkage arm 62 and the slider 54, along the side beam 46 of the main support frame 12, is at its greatest. In the fully lowered configuration the linear actuator 92 is at its shortest length. The drive bearing 80 is in contact with the main support frame 12 proximate a first end of the curved contact surface 88. The cupped surface 84 provides clearance for the bracing member 56. In this position, the drive lever 76 acts primarily as a first class lever. The drive pivot 86 acts as a fulcrum, with the effort being applied to the drive lever 76 by the actuator 92 on a first side of the fulcrum (at the pivotal connection between the drive lever 76 and the actuator 92) and the load in the form of the main support frame 12 contacting the drive lever 76 on a second side of the fulcrum (at the drive bearing 80). As the actuator 92 extends and applies a force to the drive lever 76, the drive lever 76 rotates about the drive pivot 86 and the drive bearing 80 pushes on the curved contact surface 88 to move the main support frame 12 in an upward direction away from the bracing member 56. This causes the leg member 40 to rotate about the slider 54, so that a gap between the axle 28 and the main support frame 12 increases, and an angle between the leg member 40 and the plane of the main support frame 12 increases. During this movement, there is also relative rotation between the drive lever 76 and the leg linkage assembly 60 about the drive pivot 86, and relative rotation between the leg linkage arm 62 and both the main support frame 12 and the leg member 40. Now referring to Figures 8 to 11, as the actuator 92 continues to increase in length, the angle between the leg member 40 and the plane of the main support frame 12 increases, and the drive bearing 80 moves along a length of the curved contact surface 88. The geometrical arrangement of the drive lever 76, curved contact surface 88 and leg linkage assembly 60 means that continued lengthening of the actuator 92 causes (i) the drive lever 76 to rotate about the drive pivot 86 and the drive bearing 80 to apply a force to the main support frame 12 in a generally upwards direction, and (ii) the drive lever 76 to rotate about the drive bearing 80 and the drive lever 76 to apply a force to the support bracket 72 of the leg linkage assembly 60 in a generally downwards direction. Accordingly, the drive lever 76 acts primarily as a first class lever. The drive pivot 86 acts as a fulcrum, with the effort being applied to the drive lever 76 by the actuator 92 on a first side of the fulcrum (at the pivotal connection between the drive lever 76 and the actuator 92) and the load in the form of the main support frame 12 contacting the drive lever 76 on a second side of the fulcrum (at the drive bearing 80). As the components of the mechanism are moving with respect to each other it may also be considered that the contact between the drive bearing 80 and the contact surface 88 acts as a fulcrum, with the effort being applied to the drive lever 76 by the actuator 92 on a first side of the fulcrum (at the pivotal connection between the drive lever 76 and the actuator 92) and the load in the form of the leg linkage assembly 60 being connected to the drive lever 76 at the drive pivot 86. During this second range of movement of the actuator 92 and drive lever 76, an angle between the leg member 40 and the main support frame increases, an angle between the leg linkage arm 62 and the main support frame 12 increases, and an angle between the leg linkage arm 62 and the leg member 40 increases. Because the pivotal connection between the first end 64 of the leg linkage arm 62 and the slider 54, and the pivotal connection between the second end 66 of the leg linkage arm 62 and the leg member 40, are both fixed, the movement of the drive lever 76 causes the slider 54 to move along the guide rail 48 such that the distance between the first end 64 of the leg linkage arm 62 and the slider 54 decreases. At a transition position, contact between the drive bearing 80 and the curved contact surface 88 is lost, and the cradle 82 comes into contact with the bearing cross member 68 of the leg linkage assembly 60. Now referring to Figures 12 to 15, as the actuator 92 continues to increase in length past the transition position, the drive lever 76 rotates about the drive pivot 86 and the cradle 82 applies a force to the bearing cross member 68 in a generally downwards direction. Alternatively, it may be considered that the drive lever 76 rotates about the contact between the cradle 82 and the bearing cross member 68, and the drive lever 76 applies a force to the support bracket 72 in a generally downwards direction. Accordingly, the drive lever 76 acts primarily as a first class lever. The drive pivot 86 acts as a fulcrum, with the effort being applied to the drive lever 76 by the actuator 92 on a first side of the fulcrum (at the pivotal connection between the drive lever 76 and the actuator 92) and the load in the form of the leg linkage assembly 60 being connected to the drive lever 76 at the cradle 82. As the components of the mechanism are moving with respect to each other it may also be considered that the contact between the cradle 82 and the bearing cross member 68 acts as a fulcrum, with the effort being applied to the drive lever 76 by the actuator 92 on a first side of the fulcrum (at the pivotal connection between the drive lever 76 and the actuator 92) and the load in the form of the leg linkage assembly 60 being connected to the drive lever 76 at the drive pivot 86. The result is that the angle between the leg member 40 and the main support frame continues to increase, the angle between the leg linkage arm 62 and the main support frame 12 continues to increase, and the angle between the leg linkage arm 62 and the leg member 40 continues to increase. The slider 54 moves along the guide rail 48 towards the second end 52 of the guide rail 48 such that the distance between the first end 64 of the leg linkage arm 62 and the slider 54 decreases. It will be appreciated from the above that as the actuator 92 extends, the drive lever 76 continuously rotates about the drive pivot 86. The fully raised configuration may be reached at a point when further rotation of the drive lever 76 about the drive pivot 86 is prevented. The fully raised configuration may be reached at the maximum extension of the actuator 92. On movement of the bed frame 10 from the fully raised to the fully lowered position it will be understood that the relative movement of the components of the bed frame 10 are reversed. Starting from the fully raised position (Figures 12 to 15), as the actuator 92 retracts, the bearing cross member 68 is seated in and supported by the cradle 82. Upon further retraction of the actuator 92 (Figures 8 to 11), the curved contact surface 88 contacts the drive bearing 80. The drive lever 76 is configured so that, once this contact with the drive bearing 80 has been made, contact between the cradle 82 and the bearing cross member 68 is lost. Contact between the drive bearing 80 and contact surface 88 is maintained until the bed frame 10 reaches the fully lowered position (Figures 4 to 7). A bed frame 10 will, preferably, have two leg assemblies 32, two leg linkage assemblies 60 (one connected to each of the leg assemblies 32), two drive elements 74 and two actuators 92, as described above. In this embodiment the two actuators may be linked to be operated together, or the two actuators may be operable independently of each other. Providing the ability to operate the actuators independently allows first and second ends of the bed frame to be raised to different heights such that the support frame may be tilted. In some embodiments a bed frame 10 may have only a single leg assembly 32, linkage assembly 60, drive element 74 and actuator 92 as described above. Such a bed frame may have a second leg assembly having a different configuration to that described. This may be the case, for example, if a bed frame is only required to tilt (i.e. one end only being raised and lowered), in contrast to the complete support frame being raised and lowered. In some embodiments the actuator 92 may not be a linear actuator. In preferred embodiments the actuator is arranged to apply a force to the drive levers to rotate the drive levers about their respective drive pivots. Although in the above example the drive lever had a generally triangular shape, in other embodiments the drive lever may have a different shape and / or configuration, dependent on the specific arrangement and relative positions of the leg linkage assembly and leg assembly. The shape of the drive lever may also be dependent on the type of actuator and its position relative to the drive lever. Importantly, the drive lever is configured so that during first and second ranges of movement of the actuator the drive lever is in contact with and directly applies a force to the support frame, and during a third range of movement of the actuator the drive lever only applies a force directly to the leg linkage assembly. In some embodiments the guide rail may not form part of the side beam of the main support frame. The guide rail may be in the form of a separate guide rail that is connected or attached to the main support frame. The guide rail may be spaced from the side beam of the main support frame. In the above example, the drive bearing is in the form of a drive bearing wheel rotatably connected to the drive lever that contacts and moves along the curved contact surface. In other embodiments the drive bearing may not rotate with respect to the drive lever. The drive bearing may, for example, be in the form of a rod or bar fixed to the drive lever. The non-rotating drive bearing may slide against or along the contact surface fixed to the support frame. In one embodiment the drive bearing may comprise a steel bar and the contact surface may be provided by a polymeric bearing surface. In other embodiments, during the first range of movement of the actuator, the cupped surface 84 may be arranged to contact and apply a force to the leg assembly 32. In particular, during this alternate first range of movement, the cupped surface 84 may be positioned and configured to engage with the bracing member 56 of the leg assembly 32. During the first range of movement of the actuator 92, the drive bearing 80 may be in contact with the contact surface 88 of the main support frame 12 and the cupped surface 84 is in contact with the bracing member 56 of the leg assembly 32, such that the driver lever 76 applies a force directly to both the main support frame 12 and the leg assembly 32. In this embodiment, in the fully lowered configuration, drive lever 76 is seated on the leg assembly 32 so that the pivot surface 84 is in contact with the pivot member 56. In this position, the drive lever 76 acts primarily as a first class lever. The bracing member 56 acts as a fulcrum, with the effort being applied to the drive lever 76 by the actuator 92 on a first side of the fulcrum (at the pivotal connection between the drive lever 76 and the actuator 92) and the load in the form of the main support frame 12 contacting the drive lever 76 on a second side of the fulcrum (at the drive bearing 80). At a transition position, between the first and second ranges of movement of the actuator, contact between the cupped surface 84 and the bracing member 56 is lost. At this transition position, the drive bearing 80 is still in contact with the curved contact surface 88. In embodiments in which the actuator 92 is a linear actuator, the fully raised configuration may be reached at a point when an axis of the linear actuator 92 (extending between first and second ends 94, 96 of the actuator 92) is aligned with a line connecting the drive pivot 86 and the pivotal connection between the second end 96 of the actuator 92 and the drive lever 76. In other words, when the drive pivot 5 lies on or crosses over the axis of the actuator 92. In these embodiments, there may be an optional fourth range of movement of the actuator 92 during which the contact between the cradle 82 and the bearing cross member 68 is lost. During this fourth range of movement the weight of the main support frame 12 results in a tensile force in the drive lever 76. This tensile force is located, primarily, between the drive pivot 10 86 and the pivotal connection between the second end 96 of the actuator 92 and the drive lever 76. Other modifications and variations not explicitly disclosed above may also be contemplated without departing from the scope of the invention as defined in the 15 appended claims.

Claims

1. A lifting mechanism for a bed, comprising:a support frame;a leg assembly having a first end rotatably and slidably connected to the support frame and a second end connected to a foot assembly;a leg linkage assembly pivotally connected to the support frame and pivotally connected to the leg assembly between its first and second ends;a drive lever pivotally connected to the leg linkage assembly at a drive pivot; andan actuator arranged to apply a force to the drive lever to change a distance between the second end of the leg assembly and the support frame,wherein, during a lower range of movement of the actuator the drive lever is in contact with and directly applies a force to the support frame, and during an upper range of movement of the actuator the drive lever only applies a force directly to the leg linkage assembly.

2. A lifting mechanism according to Claim 1, in which the leg assembly comprises a leg member, a slider is connected to the first end of the leg member, a guide rail is connected to the support frame, and the slider is engaged with the guide rail.

3. A lifting mechanism according to Claim 2, in which an axis of the guide rail is at a non-zero angle to a plane of the support frame, such that a first end of the guide rail is adjacent the support frame and a second end of the guide rail is offset from and lower than the support plane.

4. A lifting mechanism according to any preceding claim, in which the drive lever includes a drive bearing and the support frame includes a contact surface, and the drive bearing is in contact with the contact surface during the lower range of movement of the actuator.

5. A lifting mechanism according to Claim 4, in which the contact surface iscurved.

6. A lifting mechanism according to Claim 5, in which the contact surface has a concave curvature and faces in a generally downwards direction towards a surface on which the foot assembly is standing in use.

7. A lifting mechanism according to any one of Claims 4 to 6, in which the lower range of movement comprises a first range of movement and a second range of movement, and in which during the first range of movement the drive bearing moves from a first end of the contact surface towards a mid-point of the contact surface and during the second range of movement the drive bearing moves from the midpoint of the contact surface to a second end of the contact surface.

8. A lifting mechanism according to Claim 7, in which the leg assembly comprises a pivot member and the drive lever includes a pivot surface, and the pivot surface is in contact with the pivot member during the first range of movement of the actuator.

9. A lifting mechanism according to Claim 8, in which the pivot surface comprises a concave surface of the drive lever.

10. A lifting mechanism according to Claim 8 or Claim 9, when dependent on Claim 4, in which the pivot surface is disposed between the drive bearing and the connection between the actuator and the drive lever.

11. A lifting mechanism according to any preceding claim, in which the leg linkage assembly comprises a bearing member and the drive lever includes a cradle, and the bearing member is in contact with the cradle during the upper range of movement of the actuator.

12. A lifting mechanism according to Claim 11, in which the cradle comprises a concave surface of the drive lever.

13. A lifting mechanism according to Claim 11 or Claim 12, when dependent on Claim 4, in which the cradle is disposed between the drive bearing and the drive pivot.

14. A lifting mechanism according to any preceding claim, in which the leg linkage assembly comprises a leg linkage member pivotally connected at a first end to the support frame and pivotally connected at a second end to the leg, and the pivotal connection between the leg linkage member and the support frame is spaced from the first end of the leg and is disposed between the first end of the leg and an end of the support frame.

15. A lifting mechanism according to Claim 14, in which the leg linkage member is not straight and includes at least one bend region between its first and second ends.

16. A lifting mechanism according to any preceding claim, when dependent on Claim 4, in which the drive lever is in the form of a generally triangular plate and the drive bearing is disposed at a first vertex, the drive pivot is disposed at a second vertex, and the connection between the actuator and the drive lever is disposed at a third vertex.

17. A lifting mechanism according to any preceding claim, in which the actuator is a linear actuator pivotally connected to the drive lever.

18. A lifting mechanism according to Claim 4, in which the actuator is connected to the drive lever at an actuator connection point, the leg assembly comprises a pivot member and the drive lever includes a pivot surface arranged to engage with the pivot member, and the leg linkage assembly comprises a bearing member and the drive lever includes a cradle arranged to engage with the bearing member, and wherein(i) during the first range of movement of the actuator contact between the pivot surface and the pivot member forms a fulcrum, an effort arm of the drive lever is defined between the actuator connection point and the pivot surface and a load armof the drive lever is defined between the drive bearing and the pivot surface,(ii) during a second range of movement of the actuator the drive pivot forms a fulcrum, an effort arm of the drive lever is defined between the actuator connection point and the drive pivot and a load arm of the drive lever is defined between the drive bearing and the drive pivot, and(iii) during a third range of movement of the actuator the drive pivot forms a fulcrum, an effort arm of the drive lever is defined between the actuator connection point and the drive pivot and a load arm of the drive lever is defined between the drive pivot and the cradle.

19. A lifting mechanism according to any preceding claim, in which during the lower and upper ranges of movement of the actuator, the drive lever continuously rotates about the drive pivot.

20. A bed comprising:a support frame for supporting a mattress;a first leg assembly having a first end rotatably and slidably connected to the support frame and a second end connected to a first foot assembly, the first foot assembly being disposed proximate a first end of the support frame;a second leg assembly having a first end rotatably and slidably connected to the support frame and a second end connected to a second foot assembly, the second foot assembly being disposed proximate a second end of the support frame;a first leg linkage assembly pivotally connected to the support frame and pivotally connected to the first leg assembly;a second leg linkage assembly pivotally connected to the support frame and pivotally connected to the first leg assembly;a first drive lever pivotally connected to the first leg linkage assembly at a first drive pivot;a second drive lever pivotally connected to the second leg linkage assembly at a second drive pivot;a first actuator arranged to apply a force to the first drive lever to change a distance between the first foot assembly and the support frame; anda second actuator arranged to apply a force to the second drive lever tochange a distance between the second foot assembly and the support frame, wherein, during a lower range of movement of the first and second actuatorsthe first and second drive levers are in contact with and directly apply a force to the support frame, and during an upper range of movement of the first and second5 actuators the first and second drive levers only apply a force directly to the respective leg linkage assembly.

21. A bed according to Claim 20, in which the first and second actuators are operable independently of each other.10

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