Patent Publication Number: US-2010117039-A1

Title: Inflatable structure for use in an inflatable lifting device and an inflatable lifting device incorporating two or more such structures

Description:
TECHNICAL FIELD OF THE INVENTION 
     This patent application relates to an inflatable structure for use in an inflatable lifting device of the type made up of a series of such stacked inflatable structures that can be sequentially inflated to elevate a load. The application also relates to an inflatable lifting device comprising two or more such structures. 
     Inflatable lifting devices of the type to which the present invention is directed must be capable of stably supporting a load, such as a disabled or infirm person, as the structures are inflated and/or deflated in order to dynamically raise and lower the load. The requirements of a dynamic inflatable lifting device, and the structures which make up the device, are very different from static inflatable supports such as inflatable mattresses, lilos and the like. Static inflatable supports of this type are generally designed to support a load only when fully inflated and are not considered suitable for use in dynamically raising or lowering a load in a safe and controlled manner. 
     BACKGROUND TO THE INVENTION 
     It is known, for example from GB 2 296 941 A and WO 2005/058222 A2, to produce inflatable lifting devices comprising a stack of generally rectangular inflatable structures. The upper and lower surfaces of each structure are interconnected by vertically aligned internal webs to create nominally horizontal upper and lower surfaces. The surfaces are in fact corrugated as the material is restrained by the webs but bulges outwardly in between the webs to form ridges. When identical structures are stacked one on the other, point contact is made by the ridges in the lower surface of an upper structure resting on the ridges in the upper surface of a lower structure. When the stack is loaded, the ridges are depressed until, at a given internal pressure, there is sufficient contact area to transmit the load from the upper to the lower structure. When multiple structures are stacked on top of each other to make a lifting device, the cumulative effect of these depressions can lead to a deflection of the upper surface of the stack, when loaded, which is unacceptable. 
     It is also known to form a lifting device comprising tubular ring-like inflatable structures. Such an arrangement is shown for example in the applicant&#39;s co-pending application GB2428564 A. In this arrangement, there is point contact between each tube in the stack and its neighbour which gives rise to similar problems to those discussed above as the tubes are depressed when the device is loaded.  FIG. 8   a  of the accompanying drawings illustrates this problem and shows in cross section two inflated tubular structures  1 ,  2  one on top of the other. If the assembly is loaded, the tubes deflect by a distance d until a contact area A sufficient to transmit the load from the upper to the lower tube is achieved. In a stack of n structures, the total deflection D will be d(n−1). 
     A method of joining tubular structures in a stack to overcome this problem is disclosed in GB2428564 A and is illustrated in  FIG. 8   b  of the accompanying drawings. In this method, the tubular structures  3 ,  4 , are welded together to create a membrane  5  that is common to both the upper and lower structures. The area A of this common membrane is large enough that, once inflated to a given a given pressure, the desired load can be supported with a minimum of deflection. The drawback to this method is that all the structures need to be permanently joined to each other such that if one is damaged the complete assembly must be scrapped. 
     There is a need therefore for an improved inflatable lifting device which overcomes or at least mitigates some or all of the drawbacks of the prior art. There is also a need for an improved inflatable structure which can be used together with other similar structures to form such an improved lifting device. 
     SUMMARY OF THE INVENTION 
     In accordance with a first aspect of the invention, there is provided an inflatable structure for use in a lifting device comprising a plurality of stacked structures, the structure having at least two internal webs extending between an upper and lower surface, in which the webs are configured so as to create a different profile on the upper surface from that of the lower surface when the structure is inflated. 
     When structures in accordance with the invention are stacked together to form a lifting device, the upper surface of a lower structure nests within the profile of the lower surface of a structure positioned above it in the stack. This increases the surface area over which adjacent structures contact one another, enabling the device to carry a load with a reduced deflection when compared with the prior art arrangements at a given internal pressure. 
     The webs may be arranged so that when the structure is inflated, at least one ridge is formed in one of the upper and lower surfaces and at least one trough is formed in the other of the upper and lower surfaces opposite the ridge. 
     At least two of the internal webs may be arranged so as to extend between the upper and lower surfaces at an angle to one another. The at least two of the internal webs may be arranged so as to diverge from one another across the structure when it is inflated such that a ridge is produced in one of the upper and lower surfaces between the webs at their widest end whilst a trough is produced in the other of the upper and lower surfaces opposite from the ridge. The webs may be spaced apart at their narrowest end such that a smaller ridge is produced at the base of the trough when the structure is inflated. 
     The structure may comprise one or more generally tubular sections and there may be two internal webs arranged to extend divergently between the upper and lower surfaces of at least one of the sections when the structure is inflated. 
     The structure may be generally rectangular in shape having a depth which is less than its length and its width, the structure having three or more internal webs arranged such that when inflated, two or more ridges are produced in one of the upper and lower surfaces with a corresponding number of troughs being produced in the other of the upper and lower surfaces, each trough being aligned opposite a respective ridges. 
     There may be an even number of internal webs arranged in divergent pairs. 
     The structure may comprise a number of interconnected inflatable sections in which at least one of the sections comprises at least two internal webs extending between an upper and lower surface, the webs being configured so as to create a different profile on the upper surface of the section from that of the lower surface of the section when the structure is inflated. 
     The structure may comprise two elongate sections aligned generally parallel to one another in spaced relation, the two elongate sections being interconnected at or close to either end by an inflatable cross member to form a generally rectilinear ring-like structure, in which each of the elongate sections comprises at least two internal webs extending between an upper and lower surface, the webs being configured so as to create a different profile on the upper surface of the elongate section from that of the lower surface when the structure is inflated. The two elongate sections may also be interconnected by means of a further inflatable cross member at a position between their ends to form a generally rectilinear figure of 8. 
     In accordance with a second aspect of the invention there is provided an inflatable lifting device comprising at least two structures in accordance with the first aspect of the invention stacked one on top of another, the arrangement being such that at least one region of the upper surface of a lower one of the structures nests within a corresponding region of the lower surface of another of the structures when the device is inflated. 
     Each of the structures may have internal webs arranged so that when the structure is inflated, at least one ridge is formed in an upper surface and at least one trough is formed in a lower surface opposite the ridge. 
     The structures may be arranged in the stack so that the, or each, ridge formed in the upper surface of each of the structures below the uppermost structure engages in a trough in the lower surface of a structure positioned above it in the stack. 
    
    
     
       DETAILED DESCRIPTION OF THE INVENTION 
       Several embodiments of the invention will now be described, by way of example only, with reference to the remaining drawings in which: 
         FIG. 1  is a perspective view of an inflatable lifting device comprising a number of inflatable structures in accordance with the invention stacked one upon another; 
         FIG. 2  is a plan view of the lifting device of  FIG. 1 ; 
         FIG. 3  is a cross sectional view through the lifting device of  FIGS. 1 and 2  taken on line A-A of  FIG. 2 ; 
         FIG. 4  is a cut-away perspective view the lifting device of  FIGS. 1 to 3 ; 
         FIG. 5  is a cross-sectional view through one of the structures forming the lifting device of  FIG. 1  on an enlarged scale; 
         FIG. 6  is a perspective view of an inflatable structure for use in an inflatable lifting device in accordance with a second embodiment of the invention; 
         FIG. 7  is a view similar to that of  FIG. 6  but with part of the outer casing material removed to show the internal webs; 
         FIG. 8   c  is a cross-sectioned perspective view of part of a lifting device in accordance with a third embodiment of the invention; and 
         FIG. 9  is a perspective view of a further embodiment of an inflatable lifting device in accordance with the invention. 
     
    
    
     With reference to  FIGS. 1 to 5 , a first embodiment of a lifting device  10  in accordance with the invention comprises a plurality of inflatable structures  12  stacked one on top of another. In the present embodiment, there are four structures in the stack but the number of structures  12  can be varied as required to give the desired range of lift. Each structure  12  is separable from the others in the stack and can be inflated independently using a pressurised fluid such as air. 
     In use, a required number of un-inflated structures  12  are formed into a stack  10  and inflated sequentially, starting with the lowest structure and working towards the uppermost structure. Although not shown in the drawings, the structures  12  will usually be secured together in the stack using mechanical fasteners in a manner known in the art. 
     Each of the structures  12  in the present embodiment are generally rectangular in shape, though with rounded corners, and have a depth that is significantly less that its width and length. The outer casing  14  is formed by means of two sheets of material that are joined together by means of a fin seal  16 . However, the outer casing can be produced in any suitable way. Although not shown in the drawings, each structure  12  has a valve arrangement through which a pressurised fluid can be admitted into the interior to inflate the structure. Means for releasing the pressurised fluid from the structure will also be provided. This may be integral with the inlet valve or separate. 
     Each structure  12  has a number of internal webs  18  that extend longitudinally over the majority of the length of the structure and which interconnect the upper  20  and lower  22  surfaces of the structure. The internal webs  18  restrain outward movement of the upper and lower surfaces as the structure is inflated so that the upper and lower surfaces remain nominally horizontal (that is to say nominally parallel to a surface on which the device is placed). 
     In accordance with the invention, the internal webs  18  are arranged so that the profile of the upper surface  20  is different from that of the lower surface such that regions of the upper surface of one structure are able to nest within corresponding regions of the lower surface of another structure  12 . This increases the surface contact area between the structures, enabling the device  10  to carry a desired load with minimal, or at least acceptable, deflection. A further advantage of this nesting is that it gives an initial locating means for one structure relative to its neighbour. 
     The differing profiles of the upper and lower surfaces  20 ,  22  is achieved by offsetting the position at which each web  18  is connected with the upper surface  20  relative to the position at which it is connected with the lower surface  22 . As a result, when the structure  12  is inflated, the webs  18  do not extend perpendicularly between the upper and lower surfaces but are angled relative to a plane (indicated by dashed line X in  FIG. 3 ) taken perpendicularly to the nominal horizontal planes of the upper and lower surfaces. This results in a series of longitudinal ridges  24  and troughs  26  being produced on the upper and lower surfaces  20 ,  22 , with the ridges  24  on the upper surface being offset from the ridges  24  on the lower surface. By appropriate positioning of the webs  18 , it can be arranged that the ridges  24  formed in the upper surface  20  of one structure  12  align with and nest in the troughs  26  formed in the lower surface of another one of the structures when the outer peripheries of the structures are aligned. 
     In the present embodiment, there are four internal webs  18  arranged in two pairs  18   a ,  18   b  and  18   c ,  18   d , with the webs in each pair diverging in a direction from the lower surface  22  towards the upper surface  20 . This results in a ridge  24  being formed in the upper surface  20  between the webs  18  in each pair where they are at their widest and a trough  26  being formed in the lower surface  22  opposite the ridge  24  where the webs in each pair are at their narrowest. In the present embodiment, the webs  18   a ,  18   b  and  18   c ,  18   d  in each pair are spaced apart slightly at there narrowest where they connect with the lower surface  22 . This allows the material of the lower surface between the webs to bulge outwardly when the structure is inflated to produce a small ridge  28  at the base of each of the troughs  26 . By careful positioning, it can be arranged that the tops of the ridges  24  in the upper surface of one structure  12  contact the smaller ridges  28  in the lower surfaces of a further structure  12  placed on top of it to further increase the contact area between the structures. However, the webs in each pair need not be spaced at their narrowest point or need only be spaced by a small amount if desired. 
       FIGS. 6 and 7  show a second embodiment of a structure  12 ′ in accordance with the invention and which can be combined with other similar structures to form an inflatable lifting device  10 . The structure  12 ′ is similar to the structure  12  described above in relation to the first embodiment except that it is wider and has eight internal webs  18  arranged in four divergent pairs. This provides four ridges  24  on the upper surface  20  and a corresponding number of troughs in the lower surface. 
     The generally rectangular nesting shapes described above may form part or parts of a more complicated structure. Not all elements of the complex structure need be constructed in accordance with the present invention to provided nesting upper and lower surfaces. For example,  FIG. 8   c  shows part of a third embodiment of an inflatable lifting device  110  in accordance with the invention. In this embodiment, each structure  112  has a number of generally tubular sections linked to form a rectangular, ring-like shape, similar to the structures shown in GB 2 428 564 A. At least one of the tubular sections in each structure has two internal webs  118   a ,  118   b  that diverge from lower surface  122  towards the upper surface  120 . This produces a single ridge  124  in the upper surface and a single trough  126  in the lower surface opposite the ridge. When two or more structures  112  are stacked, the ridge  124  in the upper surface of a lower structure nests within the trough  126  in the lower surface of a structure  112  positioned above it in the stack. If desired, more than two internal webs can be provided any one section such that more than one ridge and more than one trough is formed on the upper and lower surfaces. Furthermore, the webs could be reversed so as to provide a ridge on the lower surface and corresponding trough on the upper surface if desired. 
       FIG. 9  illustrates a further embodiment of a lifting device  210  comprising a stack of complex inflatable structures  212 . Each structure  212  is made up of a number of generally tubular sections connected together form a generally rectangular “figure of 8” shape. 
     Each of the structures  212  comprises two generally tubular, elongate longitudinal sections  230  aligned parallel to one another but spaced apart. The two longitudinal sections  230  are interconnected at either end by an inflatable cross member  232 ,  234  to form a rectilinear ring-like structure. A third inflatable cross member  236  interconnects the two longitudinal sections  230  at a position between their ends so that the resulting structure has a rectilinear figure of 8 shape. In an alternative embodiment, the third cross member  236  could be omitted so that the structure has a ring-like shape similar to that discussed above in relation to  FIG. 8   c.    
     The longitudinal sections  230  and the cross members  232 ,  234 ,  236  are interconnected internally by means of ports (not shown) to allow air (or other pressurised fluid) to flow through the whole structure from a single inflation point. As shown in  FIG. 9 , a number of the structures  212  can be stacked one on top of another to provide a lifting device  210  having the desired range of lift. As with the previous embodiments, the structures  212  are inflated sequentially to effect lift. 
     Each of the longitudinal sections  230  are constructed in a similar manner to the tubular sections  112  described above with reference to  FIG. 8   c , with divergent longitudinal internal webs  118   a ,  118   b  arranged so that when the structure  212  is inflated, a ridge  224  is formed along the upper surface of the longitudinal sections  230  and a corresponding trough  226  is produced in the lower surface opposite the ridge. When the structures  212  are formed into a stack and inflated, the ridges  224  on the upper surfaces of the longitudinal sections  230  in each of the structures  212  below the uppermost structure engage in the troughs  226  in the lower surface of the corresponding longitudinal sections of the structure  212  positioned above it in the stack. 
     In the present embodiment, only the longitudinal sections  230  are provided with internal webs arranged to produce a ridge  224  on the upper surface and a corresponding trough  226  in the lower surface. In practice this has been found to be sufficient to enable the device  210  to take a given load with an acceptable amount of deflection. However, if desired, some or all of the cross members  232 - 236  could also be provided with internal webs  118   a ,  118   b  so that they also have corresponding ridges  224  and troughs  226  on their upper and lower surfaces when inflated. It should also be noted that the web arrangement can be reversed so that ridges are formed in the lower surfaces of the sections and corresponding troughs in the upper surfaces. 
     As illustrated in the embodiment shown in  FIG. 9 , where an inflatable structure comprises a number sections, not all the sections need have differing upper and lower surface profiles to allow nesting, provided that the total surface area over which adjacent structures in the stack contact one another is sufficient to enable the device to carry a desired load with an acceptable deflection at a given internal pressure. 
     Where an inflatable structure in accordance with the invention is made up of two or more sections, the sections can be of any shape and need not be tubular. For example, two or more generally rectangular sections, each being similar to the structures  12 ,  12 ′ described above, can be combined together to form a single inflatable structure for use in a lifting device. Furthermore, whilst structures having a rectilinear ring-like or figure of 8 form have been found to be particularly useful, inflatable structures in accordance with the invention can have any suitable shape. 
     In order to produce a ridge  24 ,  124 ,  224  on one surface of an inflatable structure opposite a corresponding trough  26 ,  126 ,  226  on an opposing surface, it is generally necessary to have at least two internal webs  18 ,  118  which extend divergently between the surfaces. However, there is no upper limit to the number of internal webs that can be used. Furthermore, whilst it is convenient to have the internal webs arranged in pairs to provide a stable bottom surface, this is not essential. 
     Because the structures  12 ,  12 ′,  112 ,  230  in accordance with the invention are not permanently joined together when stacked to form a lifting device, the device can be configured to give a desired range of lift by adding or subtracting structures as required. In addition, damage to one structure can be remedied by changing that structure only rather than scrapping the whole assembly. 
     The foregoing embodiments are not intended to limit the scope of protection afforded by the claims, but rather to describe examples as to how the invention may be put into practice. For example, whilst the webs in the present embodiments have been configured to produce corresponding ridges and troughs in the upper and lower surfaces, other nesting profiles could also be produced.