BACKGROUND OF THE INVENTION 
     This application is a continuation-in-part of U.S. application Ser. No. 335,508 filed Apr. 10, 1989 now U.S. Pat. No. 5,027,459. 
     This invention relates generally to mattresses, and more particularly to easily operable means to increase the &#34;firmness&#34; of mattresses. It can be applied to any structure or mechanism which supports the body, i.e., seats, sofas, etc. 
     There is need for mattress constructions in which the firmness or hardness of the mattress is determined by means other than the strength or number of coil springs used. While it is known to provide a wire mesh overlying the coil springs of the mattress, no way was known to employ a sub-frame and to tension it by interaction with the periphery of the mattress, and in the simple, easily adjustable manner provided by the present invention. Also, no way was known to enable ready detachment of a mattress stiffening wire mesh from the main mattress. 
     SUMMARY OF THE INVENTION 
     It is a major object of the invention to provide an improved mattress construction meeting the above need. 
     It is another object to provide an adjustably tensionable grid or sheet mechanism for application to a mattress, the grid or sheet being easily attachable to the mattress. 
     The invention is incorporated in a mattress construction including upper and lower structures defining generally parallel planes, and coil springs operatively connected to the structures and located between the planes, and includes: 
     a) at least one of the upper and lower structures defining a first tensionable sheet, 
     b) first means extending at the periphery of the mattress and connected with the first tensionable sheet to interact with it and to transmit force for tensioning the tensionable sheet, 
     c) and means for adjusting the tension exerted by the first means. 
     As will appear, an adjustable crank/ratchet mechanism may be used to control firmness, lift, stretch, rebound, and decompression of the person&#39;s spine and associated anatomy. In this regard, there is a need for patients with spinal compression to have a variable adjustable mattress surface to reduce or increase surface lift, tension or rebound on the surface, trampoline, grid or surface structure to decompress the patient&#39;s spine and associated anatomy, to reduce spinal compression and alleviate pain resulting from spinal disc, nerve, vascular, and associated anatomical compression. Burn victims and patients who must lie in bed due to illness or other reason often suffer from vascular, neurological and soft tissue injury, including decubitis ulcers and other such compression syndromes due to the pressure of their mattress. This can be alleviated, controlled or altered to improve proper physiological response, including increased circulation and neuromuscular reeducation and homeostasis, through the use of a mechanically altering and adjustable surface tension made possible by the crank/ratchet mechanism associated with a mattress. 
     Further, the principles of the invention are particularly applicable to hospital beds which must bend at varied locations of the mattress. By using a hand crank/ratchet, electrical, or pneumatic/hydraulic system, pressure upon the surface top/bottom of the mattress can be altered, bent or positioned to create firmness, tensioning, or lift, and can be controlled for the physiological benefits of the patient. 
     It is a further object of the invention to provide an improved grid which incorporates a looping sub-frame to which grid wires are attached, the sub-frame then being easily attachable to the main outer frame of a mattress. In this regard, non-metallic band means may be employed for securing such attachment in an easy, load distributing manner for tensioning the grid and its sub-frame. This also facilitates ease of removal of the grid by ready detachment of the band means. 
     As will appear, the band means may include multiple bands which are spaced apart and extend to different locations of support at the periphery of the mattress; the bands may consist of flat, flexible fabric of high tensile strength or metal band or other materials to produce greater rigidity; and they may easily be secured to the main frame by looping connection about a frame member. 
     It is a further object to provide band connection configurations that interact with both upper and lower outer frames of the mattress; and a third such frame may be employed between the upper and lower outer frames to interact with the bands, as during imposition of loading on the mattress to tension the grid and its sub-frame. 
     Both upper and lower grids, and sub-frames, may be provided, and the bands may interconnect them in a tensioning mode, with band interaction via the main frame members of the mattress, as will be seen. 
     These and other objects and advantages of the invention, as well as the details of an illustrative embodiment, will be more fully understood from the following specification and drawings, in which: 
    
    
     DRAWING DESCRIPTION 
     FIG. 1 is a perspective view of a mattress embodying the invention; 
     FIG. 1a is a plan view of a plastic grid; 
     FIG. 2 is a top plan view of a corner portion of the mattress; and 
     FIGS. 3-6 are schematic, fragmentary elevations showing tensioning of grids by various band arrangements, FIG. 3 taken on lines 3--3 of FIG. 2; 
     FIGS. 7 is a perspective view showing adjustability of a grid or sheet on a mattress; 
     FIG. 8 is an enlarged perspective view showing, in exploded form, elements of mechanism to relieve such adjustability; 
     FIG. 9 is a side elevation showing, in section, elements of the adjusting mechanism; 
     FIG. 10 is a section taken on lines 10--10 of FIG. 9; 
     FIG. 11 is an enlarged perspective view of a rotor shown in FIGS. 9 and 10; 
     FIGS. 12 &amp; 13 are schematics showing how tensioning is achieved; FIG. 13a is a modification; 
     FIG. 14 is a perspective view of a sectioned mattress, adjustably tensionable; and 
     FIG. 15 is an elevation showing actuator operation of rod means. 
    
    
     DETAILED DESCRIPTION 
     In FIGS. 1-3, a mattress construction 10 includes upper and lower structures 11 and 12 defining generally parallel planes 11a and 12a. Metallic coil springs 20 are positioned between 11 and 12 in lateral and longitudinal rows as is clear from FIG. 2 and the tops and bottoms of the springs are attached to such structures 11 and 12. For example, structure 11 includes an upper mesh 13 integrated with heavy metal looping upper frame 14, the latter including longitudinal horizontal lengths 14a and 14b, and lateral horizontal lengths 14c and 14d. Mesh 13 includes elongated longitudinal strands 13a and elongated lateral strands 13b. Those strands 13a and 13b typically define tight, small coils along their lengths. The ends of coiled strands 13a are connected to frame lengths 14c and 14d; and the ends of coiled strands 13b are connected to frame lengths 14a and 14b. 
     Similarly, structure 12 includes a lower mesh 15 integrated with heavy metal looping lower frame 16, the latter including longitudinal horizontal lengths 16a and 16b, and lateral horizontal lengths 16c and 16d. Mesh 15 includes elongated longitudinal strands 15a and elongated lateral strands 15b. Those strands 15a and 15b typically define tight coils along their lengths. 
     In accordance with one aspect of the invention, the upper structure 11 includes a first grid 22, seen in FIG. 2, as overlying the mesh 13. That grid includes a sub-frame 23 extending in a loop and having heavy sub-frame longitudinal lengths 23a and 23b, and lateral lengths 23c and 23d. The latter are respectively spaced inwardly from frame lengths 14a-14d, as shown. The first grid 22 also includes mesh strands 24a and 24b, the strands 24a consisting of wires that extend longitudinally with their ends connected to 23a and 23b; and the strands 24b consisting of wires that extend laterally with their ends connected to 23a and 23b. Wires 24a are preferably of heavier gage than wires 24b, or 24b may be of heavier gage than 24a. 
     Further, in accordance with the invention, means is provided to extend at the periphery of the mattress and to be connected with the first grid, to interact with same and transmit force for tensioning the first grid, i.e., laterally and/or longitudinal for example. This enables the first grid and to resist deflection vertically under loading imposed vertically (see arrow 25 in FIG. 1), thereby adding materially to the &#34;hardness&#34; of the mattress, as desired by many persons. According, an existing &#34;soft&#34; mattress, as in FIG. 1, can easily be converted to a harder mattress by use of the first grid 22. 
     Such means attaching the grid 22 to the mattress typically includes band means extending from the frame lengths 23a-23d of the first grid to different portions of the mattress periphery. As shown in FIG. 2, the band means is seen to include multiple flat bands or straps 26 which are spaced apart to extend at different locations (27a-27d for example) of support at the periphery of the mattress. Each band typically and preferably consists of strong, flexible, flat fabric, one good example being TEFLON, or metal band or other materials to produce greater rigidity, the band being between 1/2 and 1 inch in width, and having its opposite ends wrapped about and attached to frame and sub-frame lengths. The flatness of the bands prevents snagging with bedding, such as padding placed upon the mattress. Also, the bands 26 position as well as tension the grid 22 in use. The bands may be stapled, crimped or looped to frame lengths 23c and 14c for example. The bands remain tensioned during mattress deflection. 
     In FIG. 3, the band 26 wraps partly about 14c and 16c, and then also extends at 16d toward a lower grid 32, i.e., toward frame length 32c for attachment thereto. Thus, both grids 32 and 22 interact with one another, and with the frame lengths 14c and 16c, under imposed loading to tension the grids. Lower grid 32, which is part of 12, has the same construction as the upper grid 22, with corresponding elements as follows (multiple bands connect the upper and lower frames): 
     
         ______________________________________Upper Grid    Lower Grid______________________________________22            3223            3323a           33a23b           33b23c           33c23d           33d______________________________________ 
    
     In FIG. 4, the band 26 is attached at 26a to grid frame length 23c; it extends toward and wraps partly about frame length 14c, and then extends downward at 26c for wrapping about and attachment to lower frame member 16c. This causes interaction between both frame members 14c and 16c and the grid 22, under imposed loading, for tensioning the grid. Also, the bands hold the frames 14 and 16 in predetermined spaced relation in the absence of loading but tensioned toward one another. In FIG. 5, separate upper and lower bands 26 are provided, upper band 26 connecting 14c and 23c, and lower band 26 connecting 16c and 33c. Multiple of such bands 26 are spaced adjacent the mattress on all four sides. 
     In FIG. 6, the construction is the same as in FIG. 3, but an additional or third frame 42 forms a loop with four lengths 42a-42d, each spaced inwardly of the mattress periphery, as by distance &#34;d&#34;, and spaced between planes 11a and 12a. The band lengths 26c loop partly about the length 42a-42d, at their inward facing sides, tending to pull those lengths outwardly at all times, since the bands are tensioned at all times. In this way, the two grids 22 and 32 both interact with and are tensioned by all these frames 22, 32 and 42, under imposed loading, and the bands position the frames. 
     Finally, an additional unitary grid consisting of longitudinal and lateral strands of plastic, may be provided as at 50 in FIG. 1a. The strands 51 and 52 are fused together at their interconnections, and the grid 50 is not peripherally connected to the mattress but merely meshes with or underlies the grid 22 to cushion same. Grid 50 is retained in position by tensioned grid 22. Grid 50 extends in superimposed relation to grid 22 and is retained between the grid 22 and the coil springs. The invention may be considered to relate generally to rehabilitation equipment and to apparatus usable in conjunction with a mattress to aid or achieve therapeutic decompression of the spine. The problem of decreasing pressure on the spine, discs, nerve roots, and associated anatomy to relieve pain is a continuing one. There is abundant need for effective apparatus and techniques to achieve and/or facilitate such pain relieving spinal decompression, which the present invention meets. 
     Referring now to FIGS. 12 and 13, mattress (or trampoline) 110 may have the same general side construction of FIGS. 3-6, including upper and lower structures 111 and 112 defining generally parallel planes. Structure 111 includes an upper mesh 113 (corresponding to mesh 13) integral with heavy metal looping upper frame 114 (corresponding to frame 14). Mesh 113 includes elongated strands, such as indicated at 13a and 13b above. Similarly, lower structure 112 includes a lower mesh 115 (corresponding to mesh 15). Mesh 115 includes elongated strands, such as indicated at 15a and 15b above, and integral with heavy metal looping lower frame member 116. 
     Upper structure 111 includes a first controllably tensionable sheet member 122 (a continuous sheet or a grid) seen as overlying mesh 113; and lower structure 112 includes a second controllably tensionable sheet member 132 (a continuous sheet or grid) seen as underlying mesh 115. Such controllable tensioning of upper and lower sheets 122 and 132 achieves variable &#34;hardness&#34; of these mattresses, i.e., provide a means to achieve therapeutic decompression of the spine of a person lying on the mattress. 
     The means to adjust sheet tension is shown at 120 in the form of two elongated rods 123 and 124 extending parallel with the side of the mattress generally between frame members 114 and 116, together with upper sheet extension 126a and lower sheet extension 126b, extending adjacent the rods 123 and 124 to wrap about them as the rods are rotated, as indicated by arrows 127 in FIG. 12. Note that the sheet extensions may be interconnected by sheet portions or bands at 126c and 126d and confine rod 124 therebetween. The resultant wrap is seen in FIG. 13, and may be regarded as floating between 114 and 116, in the sense that the up-tension indicated by arrow 128 is equal to the down tension indicated at 129. As will be seen, a lock means is provided to lock the adjustably rotated rods in any selected wrap position to produce the desired sheet tension at the top and/or bottom of the mattress. The rod lock means is schematically indicated at 180 in FIG. 13. 
     Referring now to FIG. 7, elements the same as those in FIGS. 12 and 13 are given the same identifying numerals. Mechanism 160 to rotate and lock the rods is located at one end of the two-rod combination, and the opposite ends of the rods may be joined together as indicated at 124a. Such ends extend along the length of the mattress 170 at one side thereof. A similar apparatus 163 includes two rods extending along one end of the mattress 170, and rod rotating and locking mechanism 166 integral with the same housing 167 as is mechanism 160. Either or both mechanisms can be hand cranked using the same crank means 168. Thus, the end of the crank pin 168a can be inserted into either socket 172 (associated with mechanism 160) or a similar socket (associated with mechanism 163). 
     Apparatus 163 is employed to controllably tension the upper and lower sheets 181 and 182 running lengthwise of the mattress beneath sheets 122 and 132, respectively. Sheets 181 and 122 have extensions 181a 182a that wrap about the rods of apparatus 163, in the same way that extensions 122a and 132a wrap about rods 123 and 124. Housing 167, and the two sets of rods &#34;float&#34;, as described above. 
     Referring now to FIGS. 8-11, the ends of rods 123 and 124 fit into bores 200 and 201 formed on a clutch rotor 202 received within a bore 203 in the housing. A flange 205 on the rotor engages housing shoulder 206 to position the rotor axially in the housing in one direction. A cap 207 is attached to the opposite end of the rotor as by a fastener o fasteners 208, and engages housing shoulder 209 to position the rotor axially in the housing in the opposite direction. 
     The clutch rotor has a series of circumferentially spaced, outwardly presented clutch shoulders or teeth 211 which are engageable by teeth 212 on a latch dog 212a carried by the housing. A handle 213 on the latch dog may be pulled (retracted) radially outwardly to move the dog teeth clear of the clutch teeth (to allow release of the rotor so that the rotor may rotate to relieve the tensioning of the rods and sheet); alternately, the handle 213 may be pushed radially inwardly to move the dog teeth into position engaging teeth 211 to join or lock the rotor in the housing (thereby to clutch the rotor for holding the rods and sheets in a locked position corresponding to selected tension achieved by rotating the crank). Note that dog 212a is received between housing shoulders 214 and 215 that block rotation of the dog about the clutch rotor axis 218. 
     Referring to FIG. 14, it shows the upper sheet (or grid) 122 in two sections--122&#39; and 122&#39;--each of which is independently tensioned in the same manner as described above as for example in FIGS. 12 and 13. The lower sheet or grid 132 is also in two sections, 132&#39; and 132&#34;, independently tensionable. Thus, sections 122&#39; and 132&#39; are tensioned by rotatable rod means 123&#39; and 124&#39; about which sheet extensions 122a&#39; and 132a&#39; are wrappable; and sections 122&#34; and 132&#34; are independently tensioned by rotatable rod means 123&#34; and 124&#34; about which sheet extensions 122a&#39; and 132a&#39; are wrappable. Mechanisms to rotate the rods are indicated generally at 220 and 220&#39;, each corresponding to that described above in FIGS. 9-11. This construction, as applied to a mattress, allows one sleeping portion of a mattress proximate 122&#39; to be made adjustably &#34;harder&#34; than another sleeping portion proximate 122&#34; to accommodate to two users, as desired. 
     FIG. 15 shows an actuator 300 for tensioning the sheet extensions 122a and 132a. The actuator may be either hydraulic, electrical or pneumatic (or mechanical, as described above). Hydraulic or pneumatic fluid under pressure from a source 301 is admitted by a control valve 302 to operate the rotary motor 303 that rotates the two rods 123 and 124, about axis 400. The motor output rotor 304 corresponds to element 202 above. 
     FIG. 13a is like FIG. 13 but shows an adjustable means 320, generally, which exerts controllable tension on 126a and 126b; and 320 may be mechanical, pneumatic, electrical, or hydraulic. Controllable force or pressure is thus exerted on the top and bottom border wires creating surface tension, to modify the distribution of weight and load, as well as assist in creation of controlled muscular stretch, to decompress the body spine, disc areas, vertebrae, and associated musculature.
A mattress construction includes upper and lower structures defining generally parallel planes, and coil springs operatively connected to such structures and located between those lanes, and with at least one of the upper and lower structures including a first tensionable sheet; a member or members extending at the periphery of the mattress and connected with the first tensionable sheet to interact therewith and transmit force for tensioning the tensionable sheet; and a device for adjusting the tension exerted by said member or members. The mattress construction also enables treating of a patient having a spinal condition for which traction is recommended by suspending the patient's body to extend generally horizontally on a "trampoline" grid mattress surface which interacts with the mattress border perimeter structure to create a surface lift and therefore stretch reflex on the patient's body. This surface lift is transmitted vertically in a rebound proportional to the weight and movement of the body or bodies on it to further transmit forces horizontally to the perimeter border surface and substructures creating an elongation and decompression of the patient's spine.