Abstract:
A mattress corner lifter that includes a base and a lifting mechanism supported by the base. Also, a platform is rotatably supported at the top of the lifting mechanism. The lifting has a compressed state, an extended state and an intermediate state between the compressed and extended states. In the compressed state the mattress lifter pushes up with a force of less than 25 lbs, but in its intermediate state the force with which the mattress lifter presses up increases as the mattress lifter extends, until it reaches a maximum of at least 40 lbs, and wherein at the extended state the mattress lifter resists compression with a force of at least 40 lbs.

Description:
BACKGROUND 
     Those tasked with changing sheets on a bed typically must lift up the corner of a mattress to take out the old fitted sheet and replace it with a new one. This can be difficult, particularly for people who are old or infirm or both. Although some devices have been introduced to ease this task, none has truly filled the human need. 
     SUMMARY 
     The following embodiments and aspects thereof are described and illustrated in conjunction with systems, tools and methods which are meant to be exemplary and illustrative, not limiting in scope. In various embodiments, one or more of the above-described problems have been reduced or eliminated, while other embodiments are directed to other improvements. 
     In a first separate aspect, the present invention may take the form of a method of lifting up and then pressing down, an end portion of a mattress that is generally supported on a supporting surface. The method utilizes a lifting device having an expanded position that is between 15 cm and 45 cm high, and a compressed position that is up to 6 cm high, and which in the expanded position resists compression sufficiently so that the weight of the mattress does not compress the device, but in the compressed position is urged toward its expanded position by a force small enough so that the weight of the mattress maintains the device in its compressed position and which is urged toward its expanded position by a force that is greater than the weight of the mattress, after the device has been released from the compressed position, but before reaching its extended position, the device being in its compressed state and underneath an end portion of the mattress, and being supported by the supporting surface, before subsequent steps of the method are performed. The mattress end portion is lifted up, thereby reducing the force exerted by the weight of the mattress to a level below the force urging the device toward its expanded position, and thereby permitting the device to expand into its expanded position, so that the device lifts the mattress end portion and supports it in an elevated position. Later, the mattress end portion is pushed down with sufficient force that together with force exerted by the weight of the mattress, the device is compressed into its compressed state. 
     In a second separate aspect, the present invention may take the form of a bed, having a base, having a rectangular top surface, defining two mattress-wide end portions, each including two interior corners of said base and a mattress having two mattress-wide end portions each including two interior corners of said mattress, supported by the rectangular top surface. Further, a mattress end portion lifter is supported by the base at an end portion, beneath a first mattress end portion. The lifter has a compressed state, in which the lifter exerts an upward force that is less than the weight of the mattress pushing down on the lifter and an intermediate, partially-extended state, in which the lifter exerts an upward force that is greater than the weight of the mattress pushing down on the lifter and further has an extended state, in which the lifter resists compression by a force great enough to resist being compressed by the downward force of the weight of the mattress. Accordingly, a user may release the lifter from its compressed state by lifting up on the first mattress end portion and may place the lifter into its compressed state by pushing down on the first mattress corner. 
     In a third separate aspect, the present invention may take the form of a mattress corner lifter that includes a base and a lifting mechanism supported by the base. Also, a platform is rotatably supported at the top of the lifting mechanism. The lifting has a compressed state, an extended state and an intermediate state between the compressed and extended states. In the compressed state the mattress lifter pushes up with a force of less than 25 lbs, but in its intermediate state the force with which the mattress lifter presses up increases as the mattress lifter extends, until it reaches a maximum of at least 40 lbs, and wherein at the extended state the mattress lifter resists compression with a force of at least 40 lbs. 
     In addition to the exemplary aspects and embodiments described above, further aspects and embodiments will become apparent by reference to the drawings and by study of the following detailed descriptions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments are illustrated in referenced drawings. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than restrictive. 
         FIG. 1  shows a top-side-front isometric view of a mattress lifting device according to the present invention. 
         FIG. 2  is a perspective view of the device of  FIG. 1  in its compressed state, underneath a mattress corner. 
         FIG. 3  is a perspective view of the device of  FIG. 1  in its extended state, underneath a mattress corner. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In a preferred embodiment of the invention, as shown in  FIG. 1 , a lifting device  10  is comprised of a base platform  12 , which is joined to a top platform  14  through a series of eight interconnected bars, comprising two parallel sets of four interconnected bars. In the first set, the first end of a first bar  16  is joined to a base platform  12  through a first hinge point  18 A mounted on intermediate element  20 . A second hinge point  22  is located at the midpoint of a first bar  16 , and joins said first bar  16  with a second bar  36 , such that the bars may appear to intersect one another at a variety of angles, depending on the expansion or compression of the lifting device  10 . The second end of a first bar  16  is hinged to the first end of a third bar  24  at a hinge point  26 ; likewise, the second end of a second bar  36  is hinged to the first end of a fourth bar  28  at a hinge point  32 . The second ends of a third bar  24  and a fourth bar  28  are then hinged together at a hinge point  30 . The top platform  14  is rotatably attached to a hinge point  30  by a second intermediate element  34 . 
     In the second set of four interconnected bars, the first end of a fifth bar  38  is joined to a base platform  12  through a first hinge point  18 B mounted on intermediate element  20 . A second hinge point  40  is located at the midpoint of the fifth bar  38 , and joins said fifth bar  38  with a sixth bar  42 , such that the bars may appear to intersect one another at a variety of angles, depending on the expansion or compression of the lifting device  10 . The second end of a fifth bar  38  is hinged to the first end of a seventh bar  48  at a hinge point  52 ; likewise, the second end of a sixth bar  42  is hinged to the first end of an eighth bar  46  at a hinge point  44 . The second ends of the seventh bar  48  and an eighth bar  46  are then hinged together at a hinge point  50 . The platform  14 , in addition to being hinged at point  30 , as noted above, is rotatably attached to hinge point  50 . 
     Notably, bars  24 ,  28 ,  46 , and  48  are of identical proportions, and bars  16 ,  36 ,  38 , and  42  are also of identical proportions, such that device  10  may expand between 15 and 45 centimeters, and compress to 6 centimeters. Cross-members  54  join the hinge points  32  and  44 ,  26  and  52 , and  30  and  50 , thus allowing the lifting device  10  to expand and compress. A spring  56  is fastened to a cross-member  54  between hinge points  32  and  44  and a second cross-member  54  between hinge points  26  and  52 , and tensions the device  10 . The first ends of bars  36  and  42  may feature wheels  58  as shown in  FIG. 1 , or, alternatively, smooth, blunt ends (not shown) that can slide on base platform  12 , allowing a user to expand or compress the device  10  more easily. In another preferred embodiment, the lifting device  10  may include only one set of four interconnected bars. In one embodiment one or more of the bars might have a forked end or forded ends, for greater transverse stability. In another embodiment, the platform  14  may be attached to at a single one of hinge point  34  or  50  with a ball and socket joint, permitting a greater range of pivoting motion, thus permitting the device  10  to adapt to a greater range of mattress configurations. 
     In this embodiment, the expansion of the spring  56  is positively related to the degree of compression of the device  10 . This relationship may be explained mathematically using Equation 1, where k is the stiffness constant of the spring  56 , θ is the angle formed between the bar  24  and spring  56 , F is the upward force exerted by superior platform  14  (or the force resisting compression, when device  10  is in its extended state), L S  is the length of the compressed spring  56 , and L B  is the length of any one of bars  24 ,  28 ,  46  or  48  and F I  is the initial resistance against extension of spring  56 .
 
( F   I +2 k ( L   B  Cos θ−0.5 L   S ))(sin θ)= F   Equation 1
 
     Skilled persons will recognize that the upward force F will initially grow as θ is reduced and the spring  56  is stretched, exerting a greater force. But a maximum is reached when the value of sin θ, which decreases with decreasing θ, begins to decrease faster than the spring force is increasing. Put into familiar physical terms, the spring is exerting more force, but a smaller proportion of that force is directed upwardly, as an upward force. 
     The lifting device  10  may lift up an end portion, which could more specifically by a corner, of a mattress that is generally supported on a supporting surface. After the end portion has been lifted, for example to change a fitted sheet, it may be returned to its initial resting position by pressing down upon it, so that the downward force exerted by a user, plus the mattress weight returns device  10  to its compressed position, as shown in  FIG. 2 . As used in this application, the term “end portion” may refer to a mattress-wide end portion or to a mattress corner. The lifting device  10  may be an integral component of a bed, which may be manufactured such that there is one at each mattress-wide end portion (two in all) or one for each corner (four in all) beneath the mattress. Alternatively a set of lifting devices  10  may be added to an existing bed beneath the mattress. Lifting devices  10 , adapted to be added to an existing bed, may have some engagement features on the bottom of base platform  12  or at the top of top platform  14 , or both, to engage the surface upon which device  10  rests, and/or engage the mattress  60 . Such engagement features could include adhesives, short spikes or a “grippy” rubberized material. Alternatively, device  10  could be affirmatively fastened to the surface upon which it rests. 
     When a user lifts up on a mattress end portion  60 , the downward force exerted by the weight of the mattress is reduced to a level below that of the upward force F exerted by the platform  14 . Consequently, the device  10  begins to expand vertically with increasing force for at least a first portion of its expansion, until it reaches its extended state. However, when the user presses down on the mattress end portion  60 , the combined downward forces from the user-applied pressure and the weight of the mattress surpass the upward force, thereby urging the device towards its compressed position, causing the spring  56  to expand and the device  10  to compress.  FIG. 2  shows the device in its compressed state as a result of these overwhelming downward forces, where it will stay from the mattress weight, as the upward force in the compressed position is much smaller than the upward force in the expanded or intermediate position. 
     In one preferred embodiment, 62 lbs of force is required to begin to compress device  10 , and after achieving its compressed position, 20 lbs of force is required to keep it in that position. Further, in this embodiment top platform  14  measures 18 cm×13 cm (7″×5″) and the base platform measures 25 cm×13 cm (10″×5″). Finally, in a preferred embodiment the device expands from a compressed height of 3.8 cm (1.5″) to an expanded height of 28 cm (11″). Device  10  may be made of steel. Alternatively, the bars  24 ,  28 ,  46 , and  48  and bars  16 ,  36 ,  38 , and  42  may be made of wood, as well as can be platforms  12  and  14 . In general, any material having the requisite strength may be used. 
     While a number of exemplary aspects and embodiments have been discussed above, those possessed of skill in the art will recognize certain modifications, permutations, additions and sub-combinations thereof. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions and sub-combinations as are within their true spirit and scope.