Abstract:
The invention provides an adjustable bed frame having a main support including head and foot ends. The support is movable between raised and lowered positions and independent first and second elevating mechanisms are coupled to the main support. The mechanisms are spaced from one another on the main support to carry the bed frame on a support surface. An electrical supply system provides power to actuate the mechanisms to change the height of the main support above the support surface and a controller is coupled to the supply system to selectively activate the first and second elevating mechanisms to move the main support between raised and lowered positions. DC motors and worm drives are used independently to drive the elevating mechanisms and stops are provided at the raised and lowered positions to ensure that the main support is horizontal in the raised and lowered positions.

Description:
FIELD OF THE INVENTION 
     This invention relates to adjustable beds and more particularly to bed frames used in such beds. The bed frames are of the type which provide for elevation of a main support between raised and lowered positions and are particularly suitable for use by patients who require that the bed be lowered into a minimal height position. 
     BACKGROUND OF THE INVENTION 
     Adjustable bed frames are available in many forms. Mechanisms used to elevate and lower the bed frames include electro-mechanical, pneumatic, cable and pulley, and various devices involving a variety of mechanical linkages. In general, the structures include a main support and a pair of mechanisms located at the respective head and foot ends of the main support. The mechanisms are operable to change the elevation of the main support and in some cases to change the longitudinal orientation of the main support relative to horizontal. Such structures are often complicated require mechanical interconnection between the mechanisms to ensure that during elevation the main support is maintained in a fixed relationship to the horizontal. 
     The present invention is intended to provide an adjustable bed frame capable of being lowered as close to a support surface as possible while providing access under the bed frame for the feet of a patient lifting device and also maintaining the option of elevating the bed fame into a normal position for use. 
     SUMMARY OF THE INVENTION 
     In one of its aspects the invention provides an adjustable bed frame having a main support including head and foot ends. The support is movable between raised and lowered positions and independent first and second elevating mechanisms are coupled to the main support. The mechanisms are spaced from one another on the main support to carry the bed frame on a support surface. An electrical supply system provides power to actuate the mechanisms to change the height of the main support above the support surface and a controller is coupled to the supply system to selectively activate the first and second elevating mechanisms to move the main support between raised and lowered positions. 
     Preferably each of the first and second elevating mechanisms includes a DC motor and a worm drive coupled to the DC motor. The worm drive has stops corresponding to the raised and lowered positions so that on using the controller to move the independent first and second elevating mechanisms to bring the main support into said raised or lowered positions, the worm drives will meet the corresponding stops to ensure the main support is horizontal in the raised and lowered positions. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partially exploded isometric view of a bed frame according to the invention and ready to receive a mattress support structure, the bed frame being shown in a raised position; 
     FIG. 2 is a side view of the bed frame showing the mattress support structure in ghost outline and indicating movement of parts of the bed frame when moving from the raised position (as shown) towards a lowered position; and 
     FIG. 3 is a view similar to FIG.  2  and showing the bed in the lowered position. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference is first made to FIG. 1 to describe a bed frame designated generally by the numeral  20 . The bed frame is shown in a raised position about to receive a headboard  22  and footboard  24  and consists essentially of an elongate main support  22  carried by a pair of first and second independent elevating mechanisms  24 ,  26  powered by an electrical supply system  28 . A controller is connected to the supply system  28  to permit a user to elevate and lower the bed. The independent elevating mechanisms  24 ,  26  are similar but differ in detail as will be explained. The movements of the mechanisms  24 ,  26  are independent in the sense that they are not mechanically connected but are driven simultaneously by the electrical supply system  28  when directed to do so by the controller  30 . They independently meet raised and lowered positions so that if one of the mechanisms  24 ,  26  lags behind the other sightly, the mechanisms will reset on meeting either the raised or the lowered positions. This will be more fully explained later. 
     Returning to the structure of the bed frame, it will be seen that the main support  22  consist of inverted L-shaped side members  32 ,  34  extending longitudinally and arranged in parallel and defining the length of the bed frame. The side members  32 ,  34  have respective head and foot ends meeting corresponding channel-sectioned head and foot members  36 ,  38  which define respective slots  40 ,  42 . Brackets  44 ,  46  on the respective head and footboards  22 ,  24  are made to slide vertically into the respective slots  40 ,  42  so that the head and footboards can be dropped into place by engagement of the brackets  44 ,  46  in the slots  40 ,  42 , and removed by reversing the procedure. 
     Reference is next made to FIGS. 1 and 2 to describe the elevating mechanism  24  which is similar to the elevating mechanism  26  but, as mentioned previously, differs in detail. Once the mechanism  24  has been described, the differences between that mechanism and mechanism  26  will be explained. 
     The mechanism  24  has a parallel linkage which is attached to the side members  32 ,  34  at respective trunnions  48 ,  50  mounted above the side members  32 ,  34  and at a pair of bearing blocks  52 ,  54  mounted below the trunnions  48 ,  50  on the underside of the side members  32 ,  34 . The elevating mechanism  24  is also attached at a pivot block  56  which can be better seen in FIG.  2 . This block is attached to the head member  36 . 
     The mechanism  24  includes parallel outer links  58 ,  60  connected by a transversely extending shaft  62  which is fixed to the outer links  58 ,  60  and passes through the trunnions  48 ,  50  to permit rotation of the assembly relative to the axis of the shaft  62 . Similarly, a pair of inner links  64 ,  66  are independently pivotally attached to the respective pivot bearing blocks  52 ,  54  and the inner links  64 ,  66  are fixed in relation to one another by a transverse member  68  welded to the links. Unlike the outer links  58 ,  60 , the inner links  64 ,  66  are not straight. The links  64 ,  66  are cranked outwardly below the transverse member  68  in order to bring the lower ends (as drawn) of the inner links  64 ,  66  into alignment with the corresponding ends of the outer links  58 ,  60  to facilitate pivotal attachment to upright elements  70 ,  72 . These elements carry respective wheels  74 ,  76  mounted on a transverse axis and a bumper rail  78  is provided to locate the bed against a wall when the bed is in the lowered position as will be described with reference to FIG.  3 . 
     The outer links  58 ,  60  and inner links  64 ,  66  are rotatable about respective transverse first and second parallel axes  80 ,  82  positioned one above the other. The axes  80 ,  82  are arranged so that the upright elements  70 ,  72  are maintained in a vertical orientation as the outer and inner links rotate about the respective axes  80 ,  82 . Consequently the wheels  74 ,  76  are continuously in contact with the support surface regardless of the orientation of the outer and inner links  58 ,  60  and  64 ,  66 . 
     The elevating mechanism  24  also includes an electrically driven actuator  84  connected to the pivot block  56  and to a pair of cranks  86  attached to the shaft  62 . The actuator  84  is pivotally connected between the cranks  86  so that operation of the actuator  84  will create a turning force around the axis  80  and this will drive the mechanism  24  to either raise or lower the main support  22 . The actuator  84  includes a DC motor  88  which receives DC power from the supply system  28  which has a connection lead  90  to receive AC power. The system  28  converts AC input to DC output to supply the motor  88 . In turn, the motor powers a worm drive  92  which causes a rod  94  to move linearly outwardly and inwardly thereby rotating the cranks  86 . It will now be evident from FIG. 2 particularly, that operation of the actuator  84  can cause the outer links  58 ,  60  to rotate about the axis  80 . The inner links  64 ,  66  act as slave links in that they simply maintain the relationship of the upright elements  70 ,  72  as the links  58 ,  60  are driven to move angularly. 
     The actuators  84  are preferably made by Linak A/S of Denmark, Model No. LA31. 
     The actuator  84  has a high mechanical advantage so that it is capable of lifting heavy loads which could be found for instance when a patient or visitor sits on the end of a bed. This extreme situation will not normally exist when changing the elevation of the main support, but nevertheless, the actuator  84  is designed to change the elevation of the bed in such conditions. Before discussing this in detail, the mechanism  26  will be described. 
     Those parts in mechanism  26  which are similar to those described with reference to mechanism  24  will be indicated with numerals which are similar to those in mechanism  24  but increased by  100 . For instance, outer link  60  in mechanism  24  has a corresponding link  160  in mechanism  26 . The differences between mechanisms  24  and  26  lie in the slightly different purpose given to the mechanism  26 . Whereas the mechanism  24  always has the wheels  74 ,  76  on the support surface, mechanism  26  includes a pair of upright elements  96  (one of which can be seen) which terminate in padded feet  98  which are shown resting on the support surface to locate this mechanism on the support surface. Consequently, when the bed is moved vertically, the resulting change in length between the wheels  74 ,  76  and the padded feet  98  is accommodated by the wheels  74 ,  76  rolling on the support surface (as indicated in FIG. 2) while the padded feet  98  remain stationary on the support surface. This will be more fully explained with reference to FIG.  3 . 
     The mechanism  26  does not include wheels but a castor assembly  100  is provided attached to the main support  22  and including castors  102 ,  104  which will only come into contact with the support surface when the bed frame is in the lowered position as shown in FIG.  3 . 
     FIG. 2 also illustrates in ghost outline how a mattress support  106  is assembled on the main support  22  and includes the usual adjustments for Trendelenburg positions. 
     Reference is next made to FIGS. 2 and 3 to describe how the bed frame is adjusted to change the height of the main support. It will be seen in FIG. 2 that the main support  22  is in an elevated condition in which the mechanisms  24 ,  26  have been activated by rotating the respective cranks  86 ,  186  about respective axes  80 ,  180  thereby rotating the outer links  58 ,  60  and  158 ,  160 . The first upright elements  70 ,  72  and second upright elements  96  are maintained in a vertical orientation as was described previously by the combination of the associated links. The bed frame is supported on the wheels  74 ,  76  and on the padded feet  98  which engage the floor to limit the likelihood of accidental movement. 
     When it is desired to lower the main support  22 , the controller  30  is actuated which in turn causes power to be provided through the supply system  28  to the DC motors  88 ,  188 . The result is that the worm drives  92 ,  192  operate to withdraw the shafts  94 ,  194  thereby turning the cranks  86 ,  186  so that the wheels  74 ,  76  will move to the left as shown in FIG.  2  and the main support  22  of the bed frame  20  will be lowered as this happens. The movement will continue until the actuators  84 ,  184  reach the ends of their travels, which may be exactly at the same moment, or there could be a slight lag one after the other. This possible lag is immaterial because the actuators will continue independently to meet their individual limits to travel resulting in the main support reaching the position shown in FIG.  3 . In this position, the movement of the actuator  26  is such that the padded feet  98  are raised slightly off the support surface as the castors  102 ,  104  come into play. The bed is then supported on these castors and on the permanently supporting wheels  74 ,  76  in the mechanism  24 . The bed can now be moved in any direction because the castors  102 ,  104  can rotate about respective vertical axes as they roll on the support surface. 
     FIG. 3 illustrates an important aspect of the invention. As seen in this figure, links  60  and  160  are in horizontal alignment and positioned slightly above a plane containing the upper surface of the side member  34 . Similarly, the inner links  66  and  166  are also in horizontal alignment and positioned below the side member  34 . It will be appreciated that it is necessary to have a significant separation between the parallel axes  80 ,  82  and similarly between axes  180 ,  182  in order to provide stability. If these axes are too close, there will be limited stability in the parallel linkage provided by the outer and inner links  60 ,  66  and  160 ,  166 . Consequently, in order to provide a compact and very low bed frame in the lowered position, it is necessary to accommodate the separation between these axes while at the same time maintaining a very compact arrangement. This has been achieved as can be seen in FIG. 3 while providing space under the main support  22  between the mechanisms  24 ,  26 . This space results in part because the mechanisms  24 ,  26  are independent and not connected by mechanical hardware which would likely take up some of the space. As a result, there is adequate clearance space to receive the feet of lifting equipment used to move patients, and the location of the space is such that the equipment can be located above the patient in the ideal position for lifting. 
     Upon elevating the main support  22 , the cranks  86 ,  186  will be rotated back towards the position shown in FIG.  2 . As this happens, the padded feet  98  will come into contact with the support surface to stabilize the position of the bed and the wheels  74 ,  76  will roll to allow the change in length as the wheels  74 ,  76  move towards the padded feet  98 . 
     Although not shown in the drawings, it will be evident that because the mechanisms  24 ,  26  are independent, the electrical supply system can be arranged to drive one or the other of the motors  88 ,  188  thereby tilting the main support either with the head down or the foot down. The bed can then be brought back to horizontal using the controller and judging the position of the main support with reference to horizontal, or by driving the main support into either the lowered or the raised positions, thereby causing the individual actuators to meet the ends of their travels. If one actuator reaches the end of its travel first and the other is continued to be driven to the end of its travel, then the main support  22  will automatically come into a horizontal position. Similarly, if there is a slight variation in travel due to the weight differences at the ends of the main frame  24 , although the frame may tilt very marginally in travelling, it will meet the horizontal position at the end of its travel. It has been found that with a suitable mechanical advantage in the actuators, this is not a problem. 
     As seen in FIG. 3, when the bed frame is moved on the support surface, it will normally be moved in the lowered position with the castors  102 ,  104  (FIG. 1) on the surface. The bumper rail  78  can then be used to meet a wall to locate the bed frame relative to the wall. As the main support  24  is raised, the feet  98  will remain in place and the wheels  74 ,  76  (FIG. 1) will move towards the feet taking the bumper rail  78  away from the wall. 
     In the preferred embodiment, the wheels  76  and castors  104  have diameters of 7.6 cm; the outer links  60  and  160  have a length of 48.3 cm between axes of rotation; the overall height of the bed frame  20  in the lowered position (without mattress frame  106 ) is 16.2 cm with a clearance above the support surface between castors and wheels of 5.4 cm. 
     It will be evident that variations can be made to the described embodiments and such variations are within the scope of the invention as claimed.