Abstract:
The invention provides a mattress  5  comprising an array of air springs  30 , each in communication with a supply of air  65  for selectively varying the air pressure within said spring, so as to provide a resilient body  30  against which a user may recline; an aperture in an upper surface of each air spring, providing access to a cavity  50  within said spring, said cavity open to ambient pressure and sealed from the air supply  65.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to systems and assemblies for bedding structures including mattress arrangement and bed frame structures in which to encase said mattresses. 
         [0003]    2. The Prior Art 
         [0004]    Key determinants for the function of a mattress include comfort, aesthetics, and stability. Furthermore these determinants are measured not on an initial basis, but over an extended period of years of use. 
         [0005]    Traditional forms of mattresses, including sleeping mats filled with natural materials, were subsequently replaced by more comfortable resilient materials used, such as polyurethane foam, foam latex, air and even water, in order to provide a homogeneous material which will provide long time stability and comfort to the user. 
         [0006]    The difficulty with these homogeneous materials is the lack of resilient behavior, with these materials tending to absorb the load and so sacrificing comfort for long term stability. In any event, the polymer materials, such as latex and polyurethane, still lack long term effectiveness as the material is eventually broken down, to deform into set shapes, such as the user&#39;s body shape, or flattening down and otherwise diminishing in comfort. 
         [0007]    Whilst involving a higher degree of assembly, alternative construction using springs represents the higher end of the mattress market. This premium is due to the cumulative benefits of distributing load to the individual spring units, which provides greater resilience and prevents deformed shapes. The springs, therefore, provide a mattress with longer term comfort and stability. 
         [0008]    The drawback of a spring mattress, however, is its load carrying capacity. Because the springs are of metal construction, if a user is too heavy, the springs in the preferred sleeping position will eventually fatigue and deform. Alternatively, if a bed having stiffer springs is used and the user is underweight, the mattress will lack comfort through being too hard. Thus, conventional spring construction requires a balance between the stiffness of the springs and the weight of the user. 
         [0009]    A mattress having multiple foam layers instead of springs is shown in U.S. Pat. No. 6,701,556. The patent places above foam base  10 ,  50 , one or more indented fiber layers or other such three dimensional engineered material layers having a plurality of resilient members  76  over the base  10 ,  50 . Such engineered materials may include three dimensioned fiber layer networks made from textile fibers that have projections and optional depressions, or other such structures, for example, spring or spring-like protrusions may be used. Typically, two to four such layers  60  are provided as illustrated in  FIGS. 2 and 2A . The foam base  10 ,  50  and the plurality of layers  60  are then encased in a cover  62  as shown in  FIG. 2 . 
         [0010]    Further, encapsulating the mattress will typically be some form of structure to retain the mattress in place. The function of such a structure will vary widely and include aesthetics, the ability to retain the mattress in a single location, a support for bedroom furniture and other such uses. 
         [0011]    A mattress having an air/foam mattress matrix assembly is described in U.S. Pat. No. 5,836,027. The mattress includes an air mattress with a plurality of compressible and expandable members extending upwardly from the base. The expandable members have a cylindrical shape with a flat top that can be adjusted vertically by increasing the pressure therein. The expandable members are contained within a foam restraining member. However, the mattress does not include a bed frame to contain the mattress. 
         [0012]    The side walls used to construct the bed frame structure are typically wooden and sometimes coated in a polyurethane foam. Given the desired longevity of the mattress, the structure encapsulating the mattress is expected to maintain its structural and aesthetic function for at least as long. 
         [0013]    However, typical construction of the bed frame structure will exhibit damage through wear and tear. Further, it is susceptible to damage from insect infestation, such as termites and borers, not to mention warping of the side walls, particularly in humid conditions. Thus, the longevity of the bed frame structure is often diminished functionally and frequently diminished aesthetically. 
       SUMMARY OF THE INVENTION 
       [0014]    It is therefore an object of the present invention to provide air springs with increased comfort. 
         [0015]    It is another object to create a cavity within the air springs to hold an insert of various types to enhance the sleeping experience. 
         [0016]    It is a further object to provide a frame which supports the air mattress and is easily manufactured from a polymer material. 
         [0017]    It is yet another object to provide a vibration free support for a compressor that is suspended from the frame platform. 
         [0018]    Therefore, in a first aspect of the present invention, the use of air springs achieves the benefit of conventional metal springs through providing an array of support to the user. However, unlike metal springs, the use of air as the supporting material does not suffer fatigue or defamation and so the long term benefit is enhanced. Further, the addition of a cavity in the spring provides further resilient behavior under load from the individual spring and may further provide advantage in adding extrinsic material to the spring, such as perfume, magnets, anti-bacterial material, etc., without affecting performance. 
         [0019]    In one embodiment, the cavity may be used to support a soft material such as foam, rubber, or polyurethane foam to add further comfort to the user. 
         [0020]    By providing this cavity, the mattress construction is not limited on the quantity or size of the materials placed in the cavity, as would be the case were the cavity not present. 
         [0021]    The mattress may include an airbag in communication with the underside of the air spring in order to selectively apply pressure to one or more groups of air springs via a compressor. Accordingly, a system according to the present embodiment may provide better stability and reduce shock impulses arising from a change of position of the user during sleep. 
         [0022]    With regard to the second aspect, reinforcing the side wall members of the bed frame structure may allow extra materials to be used purely for aesthetic purposes, with the metal reinforcement acting as the major structural component of the bed frame structure. In one embodiment, the side walls of the bed frame structure may include an outer polymer layer. In a further embodiment, the polymer layer may be a relatively soft and resilient material, for instance, polyurethane, foam latex. 
         [0023]    In a further embodiment, the inter connector located between adjacent side walls may be connectable to the metal reinforcement within each side wall. 
         [0024]    In a further aspect, the bed frame structure may be constructed according to the method of preparing supporting frame work for the side walls; arranging the supporting framework using a bracket; installing the connector to each adjacent side wall at said corner; arranging the frame work at 90 degrees at each corner; and bolting the inter connector so as to fix the side walls in place. 
         [0025]    In a further embodiment, the side walls may be integrally formed about the steel reinforcement. For instance, the side walls may be molded so as to encapsulate the steel reinforcement. Said metal reinforcement may include projections or other elements to facilitate bonding with the molded material to form the side wall. Still further, the metal reinforcement may include members projecting from the side wall following the encapsulating process, so as to facilitate connection with the interconnecting members. Thus, the encapsulation may not be a complete encapsulation, but instead sufficient to allow projections at distal ends of said side walls. 
         [0026]    It will be noted that through a bolted connection with the inter connector, the bed frame structure may be assembled and disassembled for transport and storage. 
         [0027]    In a further embodiment, the bed frame structure may include a platform mounted within the assembled side walls for supporting a mattress to be placed thereon. In a further embodiment, the platform may provide stability for the assembled side walls, so as to maintain shape. 
         [0028]    In a further embodiment, the side walls may include projections or recesses, such that placement of the platform fits onto said projections or into said recesses to form an interconnected assembly. 
         [0029]    In a further embodiment, the cavity may be arranged to receive an insert of a material softer than the air spring, the cumulative effect of said inserts within the array of air springs increasing the relative softness of the mattress. 
         [0030]    The air springs may be connected to an air supply and valve arrangement. If the user wishes more support, more air can be added by opening the valve; and if less support, then air can be vented. This threshold pressure will depend on the design of the mattress, including thickness of the air spring material, number of air springs, etc. 
         [0031]    The bed frame structure further includes an array of air springs and an air bladder in communication with said array of air springs for providing varying levels of air pressure to said array of air springs. A foam layer having a plurality of through cut-outs is in registration with said air springs. The array of air springs are disposed within said frame, with said foam layer being placed on top of said array with each air spring occupying a corresponding through cut-out. Each air spring includes an outer cylindrical surface formed with accordion folds, wherein said accordion folds, said foam layer and said side wall members collectively restrict the air springs from outward radial expansion when subject to increased internal pressure. 
         [0032]    The mattress assembly further includes a foam bullet disposed within the aperture of the air springs. The foam layer comprises a first fixed density component, with said air spring comprising a variable density component. The foam bullet comprises a second fixed density component completely encircled by said variable density component; wherein the first, second and third density components all reside within the same plane. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0033]    The advantages, nature, and various additional features of the invention will appear more fully upon consideration of the illustrative embodiments now to be described in detail in connection with accompanying drawings. In the drawings wherein like reference numerals denote similar components throughout the views: 
           [0034]      FIG. 1A  is an exploded isometric view of a mattress assembly according to one embodiment of the present invention. 
           [0035]      FIG. 1B  is a further exploded isometric view showing the components with respect to the frame. 
           [0036]      FIGS. 2A and 2B  are sectional views of an air spring according to a further embodiment of the present invention. 
           [0037]      FIGS. 3A to 3D  are various views of an air spring according to a further embodiment of the present invention. 
           [0038]      FIG. 4  is a plan view of a bed frame structure according to one embodiment of the present invention. 
           [0039]      FIG. 5  is a detailed view of a corner assembly of the bed frame structure according to a further embodiment of the present invention. 
           [0040]      FIG. 6  is a sectional view of a side wall of a bed frame structure according to a further embodiment of the present invention. 
           [0041]      FIG. 7  is a sectional elevation view of the side wall of  FIG. 6 . 
           [0042]      FIGS. 8A and 8B  are isometric views of a compressor attachment according to a further embodiment of the present invention. 
           [0043]      FIG. 9  is an isometric view of the compressor attachment according to a further embodiment of the present invention. 
           [0044]      FIG. 10  is a cross-sectional view of the air springs showing multiple density components residing within one plane. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0045]    Referring now in detail to the drawings,  FIGS. 1A and 1B  shows the mattress assembly  5  according to one aspect of the present invention. The components of  FIG. 1A  will be described from the top layer down. Here the exploded view of the mattress assembly shows an upper mattress portion  10 . In one embodiment, the upper mattress portion includes three layers including an upper cover  12  with a latex layer  15  directly beneath it. The third and lowest layer may be a polyurethane foam layer  20 . 
         [0046]    Upper cover  12  may be made from a natural or synthetic fabric. In a practical embodiment, the cover was made from a fabric containing 0.14% intense polyamide, 4% polyamide, 80% polyester and 16% viscose. The fabric had a weight of 340 grams/m 2 . The fabric contained finishing comprising silver which functions as an antimicrobial treatment. The process involves reducing metallic silver to ultra-fine particles which are attached to the textile fibers. An example of a commercially available product is Silpure®, which is a Registered trademark of Thomson Research Associates of Toronto, Canada. 
         [0047]    Layer  15 , which is referred to as a “latex” layer for the purposes of identification, may be made from natural latex, heat sensitive foam, memory foam or polyurethane foam. In a practical embodiment, layer  15  and layer  20  were made from a polyurethane foam having a density in the range from about 22 to about 70 kg/m 3 . Layer  15  could alternatively be made from memory foam, heat sensitive foam or natural latex having a density in the range from about 75 to about 80 kg/m 3 . 
         [0048]    Next is an ethylene-vinyl acetate (EVA) foam layer  25  having a plurality of apertures  25   a  arranged therein. The EVA foam layer  25  overlies an air bladder  30  having a plurality of air springs  45 . The air springs  45  and apertures  25   a  are disposed in registration with each other so that the air springs will extend up into the apertures  25   a  when the EVA foam layer  25  is placed onto air bladder  30 . The above described components are mounted within a bed frame structure  92  and supported by a platform  100 . Platform  100  may be provided with a cushion layer, for example a lower foam layer  47  enclosed within a lower cover  46 . Lower foam layer  47  may be the same material as foam layer  20 . Lower cover  46  may be the same material as upper cover  12 . 
         [0049]    The EVA foam layer  25  may have a density in a range of about 40 to about 70 kg/m 3 . In comparison to layer  15  with the 22-70 kg/m 3  density, the density of the EVA  25  to layer  15  may be in a ratio (EVA  25 :layer  15 ) from about 3.2:1 through 1:1.75. In comparison to layer  15  with the 75-80 kg/m 3  density, the density of the EVA to layer  15  may be in a ratio (EVA  25 :layer  15 ) from about 1:1 through 1:2. In comparison to layer  20 , the density of the EVA to layer  20  may be in a ratio (EVA  25 :layer  20 ) from about 3.2:1 through 1:1.75. 
         [0050]    As will be described more fully below, EVA layer  25  functions to contain air springs  45  and to provide support for the spaces in between the air springs. A suitable material for layer  25  will possess the following material properties. A Tensile Strength within a range of about 450 to about 800 kPa, according to ASTM D 412-87, Die A. The Tensile Strength can be nominally 600 kPa. A Tear Strength within a range of about 2.5 to about 4.5 kN/m, according to ASTM D 624-86, Die C. The Tear Strength can be nominally 3.5 kN/m. An Elongation at Break of 200-250% or 250-300%, according to ASTM D 412-87, Die A. A Compressive Strength in the range of about 30 to about 90 kPa, according to ASTM D 3575-91, Suffix D. The Compressive Strength can be nominally 45 kPa. 
         [0051]    A description of  FIG. 1B  will be provided from the bottom layer up. Bed frame structure  92  and platform  100  will be described in further detail below. Air bladder  30  communicates with air springs  45 . Air bladder  30  may comprise a single chamber which communicates will all air springs  45 . Alternatively, air bladder  30  may be divided into two or more chambers, each of which communicates with a selected group of air springs  45 . For example, air bladder could be divided into a left, middle and right chamber, each of which communicates with approximately one-third of the air springs. Air bladder  30  and air springs  45  may be made from a soft and flexible plastic material, such as polyurethane (PU), polyvinyl chloride (PVC), a synthetic/natural rubber, a plastic, a rubberized plastic or a rubber/plastic blend. Generally, the air bladder and springs can be made from any suitable air impermeable material that allows the air springs to expand and contract vertically as the air pressure within the air bladder increases and decreases. 
         [0052]    A single bed  30  typically has 150 or more air springs  45 . The firmness of the entire bed is controlled through the air pressure that is delivered to the air bladder which then communicates to the air springs. The user can vary the pressure in the air bladder. The ability to vary the pressure, and consistently change between different pressure settings is a major advantage of the air mattress of the invention over mattresses of the prior art. A compressor  32  is connected to air bladder  31  via hose  32   a . Compressor  32  is equipped with a pressure sensor  32   b . A controller  34  is operatively connected to compressor  32  by either wired or wireless means. Controller  34  permits the user to operate compressor  32  to increase or decrease the pressure within air bladder  30 . A pressure meter  34   a  may be provided on controller  34  so that the user can read pressure values. 
         [0053]      FIGS. 2A and 2B  show a series of cross-sectional views of an air spring  45  according to one embodiment of the present invention. In cross-section the air spring has an M-shaped envelope which creates a U-shaped internal void  55 . The pressurized air can be supplied from the compressor, through the air bladder into the envelopes of the air springs. The air spring includes an annulus  57  which surrounds and defines a cavity  50  in an upper portion of the air spring  45 . In other words, the air spring  45  forms the shape of a cup, mug or a hollow cylindrical tube. At the base of the cavity is a concave bowl  60  which may be used to receive liquid or gel, such as perfume or other aromatic material. It should be noted that the cavity  50  may be shaped to receive a range of articles, including magnets or extra foam inserts, so as to change the nature of the mattress assembly. In the case of the foam inserts, the inserts may be softer than the air spring and so enhance the overall softness of the mattress as compared to the mattress without the inserts. A small amount of adhesive may be provided to secure the article within the cavity, for example, double-sided tape or Velcro. 
         [0054]    The outer lower edge of cylinder  57  terminates in a skirt  57   a  which forms a flat ring. The air bladder  30  may be manufactured in a manner similar to conventional air mattresses for sleeping or outdoor recreational applications. The top surface of air bladder  30  has a series of holes cut therein, for example by a cutting die. An air spring  45  is placed over each hole, with skirt  57   a  ultrasonically welded to the air bladder. The weld line  57   b  is formed as a complete circle to seal internal void  55  to the interior of air bladder  30 . Within the internal void of 55 of the air spring  45 , air pressure  65  may be selectively introduced into the air spring, which may bear  70  upon the underside of the bowl  60  and may bear  75  on the external walls of annulus  57 . 
         [0055]    In a practical embodiment, air bladder  30  has been constructed from polyvinyl chloride (PVC) having an elasticity of 55 phr. Other suitable materials may be used which have an elasticity within a range of about 45 to about 65 phr. 
         [0056]    The accordion folds along the side of hollow cylinder  57  may be molded at various angulations representing differing degrees of folding. The angulations will allow air spring  45  to maintain a partially expanded configuration, even at low or no internal pressure. The accordion folds thereby provide a degree of pre-load in relation to the fully-expanded height of annulus  57 . The accordion folds are then expanded as a function of pressure within internal void  55 . As will be understood by those skilled in the art, the density and thickness of material used will also contribute to the degree of pre-load. In a practical embodiment, air springs  45  have been constructed from polyvinyl chloride (PVC), for example PVC 120A which is 90% transparent. The PVC may be dyed with a coloring agent in an amount of about 0.5% by weight, for example Blue P 6283 
         [0057]      FIG. 2A  illustrates air spring  45  inflated to a moderate pressure level. Depending on their construction, the accordion folds may be slightly expanded from their resting state. A top flat surface  58   a  is shown at the upper side of air spring  45 . In this configuration, top flat surface  58   a  may be generally in the same plane as the upper surface of EVA foam layer  25  and the lower layer of upper mattress portion  10 . At lower pressure levels, top flat surface  58   a  may reside below the plane of EVA foam layer  25  or below the plane of the lower layer of upper mattress portion  10 . 
         [0058]      FIG. 2B  illustrates hollow cylinder  57  inflated to a higher pressure level. The accordion folds would be slightly more expanded than in the illustration of  FIG. 2A . The most apparent change is the top curved surface  58   b . Mathematically, top curved surface  58   b  may be described as having a frusto-toroidol shape, i.e. the shape of the upper portion of a toroid. In this configuration, top curved surface  58   b  may be generally extending above the plane of the upper surface of EVA foam layer  25 . The top curved surfaces collectively press upward on the lower surface of upper mattress portion  10 . In other words, polyurethane foam layer  20  may experience slight upward pressure from one or more banks of air springs. As the pressure increases, the top surface  58   b  becomes more rounded, and the contact patch pressing upwardly against PU foam layer  20  decreases. Cumulatively, these circular contact patches provides slight separation between PU foam layer  20  and EVA foam layer  25 , to simulate floating of upper mattress portion  10 . 
         [0059]      FIGS. 3A to 3D  show various views of a further embodiment of the air springs according to the present invention. More particularly,  FIG. 3A  is a bottom plan view of air spring  80  and  FIG. 3D  is a bottom perspective view, both showing reinforcing ribs  90 . Here an air spring  80  has a different structure from that of  FIGS. 2A and 2B .  FIG. 3B  shows a side elevational view of air spring  80  with the internal structure of cavity  85  shown in dotted line. Functionally the two air springs  45 ,  80  will work in much the same way.  FIG. 3C  shows a perspective view of air spring  80 . The air spring  80  of  FIGS. 3A to 3D  includes ribbing  90  to strengthen concave bowl  60  and so create a more rigid cavity  85 . 
         [0060]      FIG. 4  shows a plan view of the bed frame structure  92  according to one embodiment of the present invention. Here a platform  100  is supported within an assembly of top and bottom side frames  95   a  and  95   b , and left and right side frames  110   a  and  110   b , generally referred to as side frames  95 ,  110 . The side frames are supported at each corner by an interconnecting member  105 .  FIG. 5  shows a detailed view of the corner assembly of the bed frame structure  92 . 
         [0061]    As can be seen in more detail in the partial cut-away view of  FIG. 5 , side frames  95 ,  100  are connected to together at each corner by an interconnecting member  105 , which are securely coupled to reinforcing members  120 ,  121  which are parts of the side wall members  95 ,  110 . The interconnecting member  105  may be screwed to members  120 ,  121 , for example with wood screws, machine screws or sheet metal screws, however, the connection may be bolted or otherwise connected, to provide a removable connection. By providing a removable connection, the side walls can be separated from each other for ease of storage or moving. Reinforcing member  105  is configured as a connecting bracket, having, for example, a first side connection panel  105   a , a central panel  105   b  set at 45 degrees to the first panel, and a second side connection panel  105   c  set at 45 degrees to the central panel. Each connection panel  105   a ,  105   c  may be provided with two or more non-threaded screw holes. Members  120 ,  121  are then provided with threaded screw holes. Machine screws will then pass through the screw holes and be threaded into members  120 ,  121 . By appropriate tightening, the screw heads will apply a significant clamping force on panels  105   a ,  105   c  against members  120 ,  121 . 
         [0062]      FIG. 6  shows a partial cut away view of a side wall member  95 ,  110  where it can be shown a reinforcing member  130  is encapsulated by a material  135 . In this case, the reinforcing member  130  is a metal rectangular hollow section, encased within a synthetic polymer molded member  135 . In one embodiment, the polyurethane may be molded over a high-strength steel reinforcing member  130 , so ensuring good contact between the reinforcing member  130  and the polyurethane  135 . Reinforcing members  130  may be provided with slits or holes, into which the polymer can seep to increase its holding strength on the reinforcing members. From a manufacturing point of view, the reinforcing member is suspended in place within a mold. The foam is cast in place around the reinforcing member. End portions of the reinforcing member may extend outside of the mold to provide an exposed connecting end. Alternatively, a portion of the cast foam may be cut away to expose the connecting end of the reinforcing member. 
         [0063]    In a practical embodiment, reinforcing members  130  have been constructed from steel tubes, for example square hollow bars having a width of about 20 mm and a height of 40 mm with a wall thickness of 1.2 mm. Polymer molded member  135  is formed from molded polyurethane foam. 
         [0064]    In an alternative embodiment, as shown in  FIG. 7 , the reinforcing member  130  may fit within a channel  140  of members  135 . Thus, the side wall member  125  may comprise an assembly of a pre-molded polyurethane member  135  into which the rectangle hollow section  130  is fit later. Member  135  may be formed by injection molding, extrusion or other suitable industrial process. Channel  140  may be pre-formed in member  135 , or may be cut from the members in a separate processing step. The lower portion of member  135  may be provided with a fillet section  145 . Fillet section  45  provides a wider base to improve the stability of bed frame structure  92  when installed upon platform  100 . Suitable wood screws may be installed through fillet section  145  to removably secure bed frame structure  92  to platform  100 . 
         [0065]      FIGS. 8A ,  8 B, and  9  show a further embodiment of platform  150  which includes an aperture  160 . A base support  155  is suspended below aperture  160 . The base support  155  includes connecting legs  165  with press fit elements  175  at the distal end of the legs  165 . The press fit element  175  fit into recesses  170  on the platform  150 . When installed as shown in  FIG. 8B , base support  155  can act as a shelf  157  upon which articles can be placed whilst connected to the mattress assembly. 
         [0066]    For instance as shown in  FIG. 9 , the support assembly  155  is used to support the compressor  32 , which maintains and varies pressure in the air spring according to a further embodiment of the present invention. Aperture  160  may be cut with a recessed forming a lip that supports a closing panel  180 . When installed, base support  155  lies flush with the upper surface of platform  100  to provide a consistent support across its surface for the mattress components. 
         [0067]    A cross-sectional view of the completed mattress assembly is shown in  FIG. 10 . The platform  100  and frame  92  provides a rigid support on the bottom and sides for the mattress components. The optional lower foam layer  47  and lower cover  46  are shown directly placed onto platform  100 . Compressor provides pressurized air to bladder  30  which communicates with air springs  300   a  and  300   b . Two air springs are shown for the sake of clarity, however, an actual mattress will have a plurality of air springs arranged in multiple columns and rows. The EVA foam layer  200  is shown in cross-section, cut across two of the apertures, with the air springs currently occupying those apertures. When viewing across the plane  202 , the mattress assembly includes fixed density components in range  210 . In planes of foam layer  200  that are in between the air-spring receiving apertures (not shown), the mattress comprises a fixed density component  210  contained on opposite sides thereof by a rigid frame  92 . 
         [0068]    In planes of foam layer  200  that include the apertures, like plane  204 , fixed density components  210  alternate with variable density components in range  310 . These alternating sections are labeled across the bottom of  FIG. 10 . If there are 8 air springs across, then 9 fixed density components  210  would alternate with 8 variable density components  310 . Air spring  300   a  is shown with a moderate amount of air pressure, analogous to the air bladder shown in  FIG. 2A . At low pressure levels a slight gap may be formed between the top of air spring  300   a  and the bottom of upper mattress portion  10 . Air spring  300   a  may be further pressurized thereby increasing its height, for example where it is raised to the height of the top of foam layer  200 . As pressure increases, air spring  300   a  will gradually contact upper mattress portion  10  and subsequently begin to exert upward pressure thereagainst. 
         [0069]    At high pressure the top portion of air spring  300   b  will begin to form a donut shape, analogous to the air spring shown in  FIG. 2B . As can be seen in the left hand portion of  FIG. 10 , upper mattress portion is raised slightly off of foam layer  200 . The air springs are restricted from expanding laterally or expanding radially outwardly due to their accordion or bellows shaped side walls. These bellows-shaped, outer side walls are formed in a corrugated cylindrical shape. Cylindrical expanding bodies formed from non-expandable material will typically resist increasing in diametrical size, since the air pressure exerted in an outwardly direction is equal in all radial directions. However, when substantial body weight is placed on the mattress, some lateral expansion may occur. To guard against this expansion, the air springs  300   a  and  300   b  are surrounded by foam layer  200  which is contained within rigid frame  92 . Air springs  300   a  and  300   b  are collectively referred to as air springs  300 . 
         [0070]    The cavity  500  inside each air spring  300   b  may be filled with a foam bullet  250  to further adjust the softness or firmness of the mattress at varying pressure levels. The foam bullet  250  provides a further region  260  of fixed density, referred to as a second fixed density component. Foam bullet  250  may be made from the same material as foam layer  200 . If using the same material, the density of foam bullet  250  may be greater or less than the density of foam layer  200 . Alternatively, foam bullet  250  may be made from a different material than foam layer  200 . The second fixed density component  260  (foam bullet  250 ) is completed encircled by the variable density component  310  (air spring  300   a ). The variable density component  310  is completely encircled by the first fixed density component  210  (foam layer  200 ). The first, second and third density components are contained within the same plane  204 . 
         [0071]    Accordingly, the mattress assembly includes a first fixed density components  210 , alternating with variable density components  310  and optional second fixed density component  260 , all contained within a fixed frame. The fixed frame comprises a rigid reinforcing bar surrounded by a polymer. The variable density components comprise air springs, which can be selectively inflated to provide a frusto-toroidal contact area which exerts upward pressure on the upper mattress portion. The frusto-toroidal, or donut shaped contact area, allows the upper mattress portion to float above the first fixed density component. The frusto-toroidal contact area provides a more evenly distributed upward force, than a circular contact area that would be present if the air spring was a solid cylinder. In other words, the donut contact area provides an equivalent upward force with reduced contact area, making the mattress feel softer. The variable density components being cup-shaped can further contain a second fixed density component inside. 
         [0072]    Having described preferred materials, configurations and methods (which are intended to be illustrative and non-limiting) it is noted that modifications and variations can be made by persons skilled in the art in light of the above teachings. This specification provides an exemplary listing of materials and mechanical properties that can be utilized to construct a mattress assembly. Other materials having the same mechanical properties may be used in connection with the invention to achieve similar results. It is therefore to be understood that changes may be made in particular embodiments of the invention disclosed which are within the scope and spirit of the invention as defined by the claims. Having thus described the invention with the details and particularity required by the patent laws, what is claimed and desired to be protected by Letters Patent is set forth in the appended claims.