fig1 - 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 fig1 ). as noted an alternative construction ( useful in production embodiments ) is a ball and socket arrangement . this is shown in fig1 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 ( fig1 c ) 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 . fig1 d 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 . fig5 & 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 fig5 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 fig7 and 8 . in the arrangement shown in fig7 - 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 fig8 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 fig8 a and is similar to the configuration shown in fig1 . 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 fig8 a 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 fig1 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 fig1 c , an air cell cushion is shown . in fig4 a foam cylinder with a flat top is shown . fig6 b shows a domed top . fig6 c shows a square top surface 30 a . fig9 shows a further embodiment in which a coil spring tissue interface is shown . the assembly 55 shown in fig9 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 . fig9 a & 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 fig9 a & 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 . fig1 a 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 . fig1 , 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 .
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 .