Abstract:
An all mechanical support surface that tracks the flotation properties of a true fluid and utilizes a series of constant restoring force springs connecting reciprocating pistons which have supporting surfaces with multiple degrees of freedom to define a user supporting surface that assumes the shape of the user and minimizes the force differential on different areas of the user&#39;s skin.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     This invention relates to an all mechanical support surface which synthesizes the flotation properties of a true fluid. Specifically, this invention relates to a non-pneumatic support surface that has the capability of assuming the shape of the person lying or sitting on it to minimize the force differential on different areas of the skin of such person. This characteristic of the support surface is particularly critical to facilitate blood flow particularly where the user is handicapped, bedridden or disabled. 
     The present invention provides the flotation properties of a true fluid as follows: (1) Low surface tension caused by providing a highly displaceable support surface. (2) Buoyancy caused by providing suspension forces that have a constant restoring force which is independent of immersion depth. (3) Wetted surface equivalence is provided by shape compliance, where the application of suspension forces at the tissue-surface interface has multiple degrees of freedom to align with and envelope the shape of the person at the contacted surface areas. (4) Low friction to maintain the constant restoring force properties of the moving elements (piston) throughout the immersion depth of the device. (5) Low friction at the tissue interface, using dry lubricant techniques, e.g., teflon-coated fabrics, to permit some sliding as the shape fitting is occurring. (6) Viscosity control with dash-pot techniques, to maintain the feel of a true fluid and to provide slow changes when a floating body moves. Motion control is of great importance when serving the safety needs of the disabled person. High viscosity, however, does not provide positional stability to the supported object. Stability is defined as: when an object moves after receiving a disturbing force it will return to its initial position after the disturbing force is removed. 
     A support surface having the foregoing characteristics is especially important when used by persons prone to decubitus ulcers which occur when deformation occurs on areas of the body inducing interference with the flow of blood at the contacted site. 
     One solution to this problem is the use of cellular air filled cushions and the inventor of this application has numerous patents which are directed to air inflatable cushions which have upstanding soft flexible cells, many of which have finned sides, known as ROHO DRY FLOTATION cushions and mattresses. Among these are patent numbers 3605145, 3870450, 4005236, and 4541136, all issued to Robert H. Graebe. These cushions are made from neoprene rubber or plastic films to create a highly displaceable high resolution surface. The cells also are interconnected pneumatically in what are known as “feedback pathways.” The cells in a particular cushion may all be interconnected or sets of said cells can be isolated from other sets in the same cushion with the cells in each set interconnected to allow for positioning of the user in a desired stable position on the cushion. Among patents with such configurations are 5052068, 5163196, and 5461741. These cellular air-filled cushions can be constructed to fit on the mechanical piston of this invention. 
     In the ROHO cushions, each air cell acts as a piston to develop constant restoring forces as a function of its internal air pressure and because of the feedback pathways they all have the same restoring force to buoy up the person being supported. The use of feedback pathways causes a catastrophic failure mode, when an aircell develops a leak, and the support surface goes flat. By design each air cell has the same effective piston size to assure uniformity of forces across the support surface. Having different sized pistons and therefore non-uniform forces produces a change in wetted surface area and shape compliance but the total summation of all the suspension forces contributing to buoyancy still must equal the weight of the person being supported. Uniform cell (piston) size and/or cell shape facilitates production and inventory issues more than suspension performance results. These air filled cushions or mattresses with slow air flow feedback paths create a high viscosity effect and permit selecting immersion depth for each individual by adjusting the internal working pressure of the cushion. 
     The soft flexible cells provide multiple (6) degrees of freedom at the tissue interface by deforming to align with the contours of the supported object to enhance its wetting equivalence to a true fluid. The multiple fin design is employed to create gluing surfaces between individual cells and may have some effect on suspension performance which cannot be measured when compared to a more simple non-finned cell. 
     It is a principal object of the present invention is to provide a mechanical device which emulates the effect of the aforementioned ROHO air cell cushions and mattresses. Another object is to provide a cushion and mattress constructed from rigid materials which still will provide the flotation properties of a true fluid. Still another object is to provide a cushion and mattress which has a series of reciprocal piston heads which are controlled by constant restoring force springs whereby the force exerted by the piston head is constant regardless of its travel within its movement limits. 
     A further object of this invention is to provide a cellular cushion and mattress construction in which the cells (pistons) are mechanical and are easily replaceable to adjust the restoring force of the cells to accommodate users of various body weights and contact areas. A further object is to provide a means to dampen piston movement rates to create viscosity control. A further object is to provide a support surface that does not have a catastrophic failure mode. 
     Still another object is to provide a mechanical cushioned mattress using reciprocal piston rods operated by constant restoring force springs which can be located inside or outside the piston to change the surface area and density of the pistons. Another object is to provide mechanical piston operated cushions and mattress in which the end of the piston rod has multiple degrees of freedom. These and other objects and advantages will become apparent hereinafter. 
     The present invention comprises mechanically operated mattresses and cushions which are controlled by constant restoring force springs and the arrangements and combination of parts simulate the flotation properties of a true fluid. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     In the accompanying drawings which form part of the specification and wherein like numerals and letters refer to like parts wherever they occur; 
     FIG. 1 is a side elevational view of a single constant restoring force piston; 
     FIG. 1A is a fragmentary sectional view taken along line  1 A— 1 A of FIG. 1; 
     FIG. 1B is a fragmentary sectional view taken along line  1 B— 1 B of FIG. 1; 
     FIG. 1C is a view similar to FIG. 1B, but showing an air cell cushion topping the piston head; 
     FIG. 1D is a view similar to FIG. 1B but showing a spring between the piston head and the cap; 
     FIG. 1E is a view similar to FIG. 1B but showing a ball and socket connection between the piston head and cap; 
     FIG. 2 is a sectional view taken along line  2 — 2  of FIG. 1; 
     FIG. 3 is a sectional view taken along line  3 — 3  of FIG. 1; 
     FIG. 4 is a sectional view taken along line  4 — 4  of FIG. 1; 
     FIG. 5 is a top plan view of an array of pistons formed into a support surface; 
     FIG. 5A is a fragmentary plan view of a portion of the top member of the support surface of FIG. 5; 
     FIG. 6 is a vertical sectional view taken along line  6 — 6  of FIG. 5; 
     FIG. 6A is an end elevational view of a modification of the invention; 
     FIG. 6B is an end elevational view of another modification of the invention; 
     FIG. 6C is a top plan view of another modification of the invention; 
     FIG. 7 is an end elevational view of another modification of the invention; 
     FIG. 8 is a vertical sectional view taken along line  8 — 8  of FIG. 7; 
     FIG. 8A is a fragmentary vertical sectional view of a modification of the invention; 
     FIG. 9 is a vertical sectional view of another modification of the invention; 
     FIG. 9A is a vertical sectional view of another modification of the invention; 
     FIG. 10 is a fragmentary sectional view taken along line  10 — 10  of FIG. 9A; 
     FIG. 10A is a fragmentary view partly in section showing a modification of the invention; 
     FIG. 11 is a fragmentary diagrammatic side view showing a person sitting on a cushion of this invention; 
     FIG. 11A is a view similar to FIG. 11 taken along line  11 A— 11 A of FIG. 11; 
     FIG. 11B is a view similar to FIG. 11 taken along line  11 B— 11 B of FIG. 11; and 
     FIG. 12 is a fragmentary diagrammatic side view showing a person lying on a mattress of this invention. 
    
    
     The invention also consists in the parts and in the arrangements and combinations of parts hereinafter described and claimed. 
     DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1-4 show a constant restoring force member or piston  10  which comprises a second tubular member  11  positioned on a base  12  and a first tubular member  13  slidable in and guided by the second tubular member  11 . A constant restoring force return spring  14  interconnects the members  11  and  13 . The spring  14  is mounted on a rod  15  which is anchored to the second tubular member  11  and slides through longitudinal slots  16  in the first tubular member  13 . One end of the spring  14  is anchored to a rod  17  positioned in the first tubular member  13 . The constant restoring force spring  14  can be any commercially available spring such as the SPEC® BRAND spring sold by ASSOCIATED SPRING RAYMOND BARNES GROUP of Cory, Pa. 16407. The characteristic of the spring  14  is that its rating determines the force necessary for relative movement between the cylinders  11  and  13  and the restoring force on the first member  13  is constant within its limits of travel regardless of the depth of its immersion in the second member  11 . 
     The constant restoring force spring  14  is located inside the first member  13  to provide a force component that is acting along the centerline of the member  13  to minimize side loading which can cause friction between the member  13  and the member  11 . 
     A preferred embodiment of the invention includes a bottom member  13   a  on the first tubular member  13 . The bottom member  13   a  has a groove  18  in which is positioned an O-ring seal  18   a . The seal  18   a  engages the inside wall  11  a of the second tubular member  11  and tends to prevent escape of air past it as the first tubular member  13  moves into the second tubular member  11 . An opening  19  is located through the bottom member  13   a  to provide controlled escape of air past the bottom member  13   a  as the first member  13  moves into the; second member  11 . This provides a damper on the rate of movement of the first member  13  and creates an effect similar to a controlled viscosity fluid. This provides a smooth controlled feel for the person sitting on the piston assembly. 
     Positioned on the free or outer end of the first cylinder  13  is a top structure  20  which includes a base cap  21  which can be frictionally mounted on the end of the first cylinder  13 . The cap  21  has a central aperture  22  in which a rivet  23  (or a ball and socket joint) is loosely positioned. The rivet  23  is slidable and tiltable in the aperture  22 . The outer end of the rivet  23  is fixed to a rigid disc  24 . Thus, the disc  24  is tiltable with respect to the cap  21 . A resilient compressible buffer  25  is positioned around the rivet  23  between the cap  21  and the bottom side of the disc  24 , to act as a spring to align an unloaded disk. The combination of the rivet  23 , the enlarged cap opening  22 , and the resilient washer  25  allows the disc  24  to have a universal type movement with multiple degrees of freedom with respect to the tubular member  13  (indicated by the arrows A in FIG.  1 ). 
     As noted an alternative construction (useful in production embodiments) is a ball and socket arrangement. This is shown in FIG.  1 E. The ball  35  is attached to a stem  36  which is fixed to the disc  24 . A socket  37  is formed in the cap  21  to allow movement of the disc  24  with respect to the cap  21 . 
     To enhance a soft surface feel, a foam top member  26  may be positioned on the outer surface of the disc  24 . 
     If desired, a sealed cell or interconnected cell air-filled cushion  27  (FIG. 1C) can be positioned on top of the foam paid  26 . The air-filled cellular cushion  27  also can be attached directly to the rigid disc  24  omitting the foam pad. These air cushions are shown in the aforementioned Graebe patents. 
     FIG. 1D shows another modification in which a coil spring  28  is used in place of the compressible buffer  25 . 
     When considering the effect moderate external forces have on the soft tissues of the body, when applied for extended periods of time, two things may happen. If the forces induce a shape change, deformation, the flow of blood in those affected tissues will be reduced. This reduction, known as ischemia, can create pain and if the reduction is enough for a long enough time the local tissue cells will die, a condition called necrosis. 
     These external forces also compress those tissues and will force the local fluids to move elsewhere in the body. This condition only occurs when a portion of the tissues are involved. When a person is totally immersed in a fluid and all of that person&#39;s tissues are being effected equally, excess fluids stay uniformly distributed or may exit the body as urine. 
     FIGS. 5 &amp; 6 show an array of the pistons  10  assembled to define a support surface  30 . The plurality of pistons  10  sitting on the surface  30  act to buoy up a person and minimize changing the person&#39;s shape. Depending on the weight of the person and the number of pistons, a spring force can be determined which will literally float the person without having the person touch bottom (or ‘bottom out’) which would induce high forces in a concentrated area to cause deformation of the soft tissues and ischemia. Bottoming out occurs when one or more of the pistons reaches its maximum length of travel or the second member  13  is moved as far as it can go into the first member  11 . 
     The support surface  30  comprises a base member  31 , side and end members  32  and a top member  33  which is provided with a plurality of openings  34  (FIG. SA) located in a predetermined arrangement to accommodate the pistons  10 . 
     Since there is a need to accommodate various body weights and contact areas a means to adjust this assembly is desirable. To adjust this type of support surface  30 , the spring force can be changed, the density of pistons changed or the travel deflection distance of the second piston member  13  changed. To facilitate adjustment of the surface  30  shown in FIG. 5, pistons  10  in the support base are removable which allows an individual piston assembly  10  to be easily inserted in the openings  34 . Cell density is controlled by the design of the openings  34 . Spring force levels are a function of the design of the spring  14 . However, several springs  14  can be layered together to increase the total level of force. The location of the drum type of spring inside a tube limits how small a piston  10  can be constructed. When the spring or several springs are placed outside the piston, ignoring the risk of friction from side loads, a smaller sized piston and constant restoring force spring can be used and therefore a higher density of pistons can be used to construct a high density support surface as illustrated in FIGS. 7 and 8. 
     In the arrangement shown in FIGS. 7-8A, each restoring force member  40  comprises a singular rod  41  (preferably hollow) positioned and slidable in an opening  42  formed in a connecting horizontal member  43  of an inverted U-shaped bracket  44 . The bracket  44  includes spaced vertical legs  45  connected by the horizontal member  43  and end members  46  for installing the bracket  44  in a base  47  to form a composite support surface. A series of the brackets  44  are positioned in the base  47  to form the desired support surface  48  from the ends of the rods  41 . Constant restoring force springs  49  are anchored to the legs  45  by pins  50  and to the rods  41  at  51 . An additional bearing member  52  having openings  52   a  to stabilize the lower end of the slidable rod  41  may be employed and is illustrated in FIG.  8 A. The arrangement provides space and purchase points to add a separate dash-pot to control the velocity rate of the slidable rod. This too is shown in FIG.  8 A and is similar to the configuration shown in FIG.  1 . In this form, a cylinder  53  is aligned with and holds the hollow rod  41 . The lower end of the rod  41  has an opening  54  and an annular groove  54   a  which holds an O-ring seal  54   b . The air in the cylinder  53  escapes slowly through the opening  54  and a second opening  54   c  in the rod  41  to dampen and control movement of the rod  41 . The arrangement of FIG. 8A can be modified to use only the cylinders  53  and not the bearing  52  or it may only use the bearing  52  and not the cylinder  53 . 
     To provide multiple degrees of freedom at the top of the piston several mechanical arrangements can be supplied. In FIG. 1, a tilting plate with a thin foam top  26  is shown. The foam top  26  is not required and the disc  24  can be used alone. In FIG. 1C, an air cell cushion is shown. In FIG. 4, a foam cylinder with a flat top is shown. FIG. 6B shows a domed top. FIG. 6C shows a square top surface  30   a.    
     FIG. 9 shows a further embodiment in which a coil spring tissue interface is shown. The assembly  55  shown in FIG. 9 includes a housing having side and end walls  56  and a floor  57 . Inside the housing is a bracket  58  which supports the pistons  10 . On the caps  21  of each piston  10  are coil springs  59 . 
     Since it is desirable to have the top of these pistons close together to create a reasonably continuous surface, mechanical interference can occur. This interference acts as a friction component of force and causes the constant restoring force to become not constant and this condition needs to be avoided. When using coil springs  59  on the cap  21 , retainers  60  which extend below the top coils of the coil springs  59  are dropped over each spring  59  to prevent the coils from inter locking. The retainer  60  is fabricated from rigid plastic and has a highly slippery low friction surface. 
     FIGS. 9A &amp; 10 show still another modification of the cushion  65 . In this arrangement piston density is reduced to increase the distance between the tops of the pistons. To present a smooth surface to the person being supported, a pad  66  is placed on top of the pistons  10 . The addition of any interface padding on top of a displaceable surface reduces its capability to assume the shape of the person being supported. However, this compromise is acceptable when comfort is the objective. The pad  66  can be expanded foam or any other suitable material. 
     The arrangement of FIGS. 9A &amp; 10 is shown with coil springs  59  interposed between the pad  66  and the caps  21 , but any of the illustrated tops can be used with a pad  66 . For example, a pad  66  can be placed over an array of discs  24 . 
     FIG. 10A shows another modification of the present invention in which a socket  70  is mounted on the housing floor  57  and the piston  10  is set in the socket  70 . 
     FIGS. 11,  11 A,  11 B &amp;  12  show diagrammatic representations of the deflection of the pistons  10  and the relative positions of the disc  24  and any interface member attached thereto when a person is seated or is lying on the cushion or mattress embodying this invention. 
     Thus it is seen that the present invention achieves all of the objects and advantages sought therefor and this invention is intended to cover all changes and modifications of the example of the invention herein chosen for purposes of the disclosure which do not constitute departures from the spirit and scope of the invention. 
     
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 Parts List 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 10 
                 restoring force member or piston 
               
               
                   
                 11 
                 second tubular member 
               
               
                   
                 12 
                 base 
               
               
                   
                 13 
                 first tubular member 
               
               
                   
                 13a 
                 base of 13 
               
               
                   
                 14 
                 constant restoring force spring 
               
               
                   
                 15 
                 rod 
               
               
                   
                 16 
                 slots 
               
               
                   
                 17 
                 rod 
               
               
                   
                 18 
                 groove in 13a 
               
               
                   
                 18a 
                 O-ring seal 
               
               
                   
                 19 
                 opening through 13a 
               
               
                   
                 20 
                 top structure 
               
               
                   
                 21 
                 cap 
               
               
                   
                 22 
                 hole in cap 
               
               
                   
                 23 
                 rivet 
               
               
                   
                 24 
                 disc 
               
               
                   
                 25 
                 buffer 
               
               
                   
                 26 
                 foam top 
               
               
                   
                 27 
                 air cell cushion 
               
               
                   
                 28 
                 coil spring 
               
               
                   
                 29 
               
               
                   
                 30 
                 support surface 
               
               
                   
                 30a 
                 square top 
               
               
                   
                 31 
                 base member 
               
               
                   
                 32 
                 side and end members 
               
               
                   
                 33 
                 top member 
               
               
                   
                 34 
                 openings 
               
               
                   
                 35 
                 ball 
               
               
                   
                 36 
                 stem 
               
               
                   
                 37 
                 socket 
               
               
                   
                 38 
               
               
                   
                 39 
               
               
                   
                 40 
                 restoring force member 
               
               
                   
                 41 
                 rod 
               
               
                   
                 42 
                 opening in 43 
               
               
                   
                 43 
                 horizontal member 
               
               
                   
                 44 
                 U-shaped bracket 
               
               
                   
                 45 
                 legs 
               
               
                   
                 46 
                 end member 
               
               
                   
                 47 
                 base 
               
               
                   
                 48 
                 support surface 
               
               
                   
                 49 
                 CF spring 
               
               
                   
                 50 
                 pin 
               
               
                   
                 51 
                 anchor point 
               
               
                   
                 52 
                 bearing opening 
               
               
                   
                 53 
                 cylinder 
               
               
                   
                 54 
                 opening 
               
               
                   
                 54a 
                 groove 
               
               
                   
                 54b 
                 o-ring 
               
               
                   
                 54c 
                 second opening 
               
               
                   
                 55 
                 assembly 
               
               
                   
                 56 
                 side &amp; end walls of housing 
               
               
                   
                 57 
                 floor 
               
               
                   
                 58 
                 bracket 
               
               
                   
                 59 
                 coil spring 
               
               
                   
                 60 
                 retainer 
               
               
                   
                 61 
               
               
                   
                 62 
               
               
                   
                 63 
               
               
                   
                 64 
               
               
                   
                 65 
                 cushion 
               
               
                   
                 66 
                 foam top 
               
               
                   
                 67 
               
               
                   
                 68 
               
               
                   
                 69 
               
               
                   
                 70 
                 socket