Abstract:
A design and method of manufacture for a conforming air cell device to be used for seating, vibration and shock isolation, custom fitting and other applications. Interconnected air cells are formed from two thin sheets of highly resilient thermoformed plastic, so that once inflated, the air cells readily conform to the shape of the user while equalizing pressure from cell to cell. The manufacturing method simultaneously thermoforms both halves of the cell structure, followed immediately by joining these halves while still at the material&#39;s forming temperature. The result is a relatively complex matrix of air cells, interconnecting passages and one or more inflation features in a single manufacturing process, greatly simplifying the manufacturing process over previous methods. The design and method of manufacture result in an extremely lightweight, flexible and compactable system that quickly inflates and deflates, and can easily be taken and used anywhere it is needed.

Description:
[0001]    This document contains the non-provisional submittal for provisional application 60/811,641, which had a filing date of Jun. 6, 2006. The provisional application was entitled “Conforming Air Cell Design and Method of Manufacture” authored by Mark Massmann. 
     
     TECHNICAL FIELD OF THE INVENTION 
       [0002]    The present invention relates to supporting devices which provide a surface to support at least a portion of a user&#39;s body. Specifically, this invention relates to air-filled supporting devices which readily conform to a user&#39;s body, equalizing pressure against the user to provide long-term comfort. 
       BACKGROUND OF THE INVENTION 
       [0003]    The field of conforming materials and products is very broad and diverse. However all of these products strive for the same goal, which is to equalize pressure required to support the user so as to reduce or eliminate high pressure points as much as possible. On the human body, these high pressure points inevitably cause discomfort and pain through the restriction of blood-flow to neighboring tissue. Many different approaches have been used and proposed to try and solve this problem, including contoured hard surfaces, various foams, and products filled with gel, liquid and air. In reality, very few of these products have provided effective long-term comfort, and those that do typically utilize expensive manufacturing processes which result in products too high in cost for the average consumer. The more effective products are therefore typically marketed to the medical field, where they are mainly used for patients recovering from illness and injury as well as those suffering from various levels of paralysis. In addition to high cost, current medical products tend to retain heat from the user and therefore become uncomfortably hot when used for long periods. An example of this would be products made of rubber or foam materials, whose insulating properties “trap” body heat when formed against the user. The materials used in these products also tend to make them relatively bulky and heavy, not easily carried for use in car and air travel, entertainment events and sporting activities. 
         [0004]    As our society becomes more and more reliant on prolonged sitting for work, travel and entertainment, there is an increasing need for supportive surfaces that perform as well as the best medical grade devices, but are less costly to own and are more portable. Prolonged periods of sitting in our society not only causes discomfort and loss of enjoyment, but can also lead to more serious medical conditions such as blood clots and bed sores. In addition, as an increasing number of jobs require extended hours sitting to perform daily tasks, the discomfort caused by inadequately supportive seating results in significantly lost productivity by causing difficulty concentrating and the need to frequently stand in order to alleviate pain. 
       Description of Prior Art 
       [0005]    For the purposes of comparison with the present invention, it is widely recognized that certain air-filled cushioning devices provide superior support to the user when compared to non-air filled devices such as foams, gels or liquids. This is demonstrated by the fact that cushioning devices sold in the medical field are almost exclusively air-filled. For example, patients confined to a wheelchair and/or bedridden, whose tissue is most likely to develop pressure sores, almost universally employ specially designed air-filled cushions because they are best able to spread the load supporting the user and to maintain blood-flow at peak pressure points. The term “specially designed” is employed here to describe cushions that are not only air-filled (such as an ordinary beach ball), but also have many air-filled cells that are interconnected and separately cradle the user. The specialized designs work by minimizing surface tension at the user interface, while ordinary air-filled devices create tension at their surface and therefore create higher peak pressures. 
         [0006]    It is for this reason that the present invention is best compared to the prior art for other specially designed air-filled devices which strive to minimize surface tension. U.S. Pat. No. 3,870,450 discloses one such device which has been widely used in the medical field. Its manufacturing approach begins with a mandrel that is used to create a plurality of open-ended air cells. The mandrel is repeatedly dipped into a vat of heated rubber material so that once cured and removed from the mandrel, it forms into a multi-celled structure of air cells that are open at the bottom end. This structure is then glued to a flat base of similar material to become an air-filled structure. An inflation valve is then added by gluing an additional interface which mates to both the base material and valve. 
         [0007]    This approach has a number of challenges. First, it is very time-consuming and therefore very expensive. Dipping of mandrels in a vat of rubber, allowing it to cure, then having to glue both a backing and valve interface to this requires excessive manual labor. Secondly, the design tries to provide a continuous surface against the user. This, along with the use of rubber material serves to retain excessive heat against the user, making it uncomfortable over time. Third, the rubber material is prone to forming leaks, since thickness of the material in any specific location is very hard to control with the dipping process. U.S. Pat. No. 6,623,080 also discloses a device that uses this same mandrel-dipping process. 
         [0008]    U.S. Pat. Nos. 5,596,781 and 5,839,140 both disclose air-filled devices that use a vacuum thermoforming process in the place of mandrel-dipping, and an RF (radio frequency) welding process in the place of adhesive glue. For these approaches, a plurality of open-ended air cells is created by pulling a heated sheet of thin plastic against a vacuum-type mold. Once formed, this part is mated to a flat base material by the use of RF welding, a method that flows electricity through the plastic to heat it, so that the resulting structure can retain air. Typically, an inflation valve is added by RF welding an additional interface to both the air-filled structure and valve. Though the manufacturing approach used in these disclosures eliminates the mandrel-dipping process, significant problems remain. The open-ended air cell matrix created from thermoforming still must be attached to a base in order to create an air-filled structure. First, it must be trimmed of flash material used to hold the plastic for thermoforming, which can damage it by exposing the thin formed part to a cutting device. Then it must be held in place (again without damage) and a special RF welding tool must be used to locally heat it to the base material along very specific weld lines. 
         [0009]    As can be imagined, both the number and close-spacing of the weld lines can become very difficult to execute, resulting in either missed welds or damage to parts that cause additional leaks. The RF welding process itself is inherently difficult to control and repeat. Putting enough heat into the weld areas can often result in plastic around the welds being over-heated and melting, or in burning all of the way through on the weld lines. Not putting enough heat into the welds can result in weak welds, causing leaks after delivery of the product to the user. Many other factors can render the RF welding process to be defective, such as relative air temperature changes, temperature of the plastic before welding, thickness of plastic before welding, over heating and burn-out of RF tooling electrodes, pressure of the electrodes against the plastic, operator error and the like. Finally, an inflation valve feature also must be added with a similar but separate RF welding process. Once successful welds are achieved, final trimming of excess material must be accomplished, which as noted previously can by itself result in damaged parts. 
         [0010]    As can be seen from this discussion, the manufacturing process used for U.S. Pat. Nos. 5,596,781 and 5,839,140 still requires much human labor and leaves many opportunities for the air-filled structure to be damaged. In addition, the design which can be created from this process is very limited. In both patents, an open air cell design is mated to a flat base material, requiring the air cells themselves to extend the full thickness of the device. Plastic must be drawn to that thickness, which thins more of the plastic out in the process (especially in corners). As corners thin down, parts become more susceptible to leaks, which can be caused even by small imperfections in the plastic sheet. Tall air cells also tend to more easily fold over on themselves instead of supporting the user. Finally, the use of RF welding limits both the number of welds and how closely they can be spaced apart, limiting how complex the air flow passages can be and therefore limiting functional complexity of the device. 
         [0011]    There remains, then, a large need for an air-filled cushioning device that provides a maximum level of comfort, but that is also manufactured in a way which is more efficient than prior approaches. In addition, there is a need for a technology which is very lightweight, well-vented so as to avoid heat build-up and that quickly collapses into a small package for portability. 
       SUMMARY OF THE PRESENT INVENTION 
       [0012]    The present invention is an air-filled device made up of interconnected air cells which, once filled with air, creates a readily conforming supportive surface that equalizes pressure against the user. This device is formed from thin sheets of highly resilient material, in which both halves of a complex air cell matrix are formed and joined concurrently in a single manufacturing process. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    It is to be understood that while certain forms of the present invention are illustrated, it is not to be limited to the specific forms described and shown. The illustrated application is for an air-filled seat cushion, though other applications would include products such as bedding, air-casts, air inserts for footwear, cushioning for sensitive electronics and the like. It will be apparent to those skilled in the art that various applications can be made from this technology without departing from the scope of the invention. 
           [0014]      FIG. 1  is a perspective view of a seating application for the invention; 
           [0015]      FIG. 2  is a top view of same seating application; 
           [0016]      FIG. 3  is a partial top view showing air cell shape and interconnectivity; 
           [0017]      FIG. 4  is a cross section showing air cell shape and interconnectivity; 
           [0018]      FIG. 5  is a close-up view of the airflow channel design; 
           [0019]      FIG. 6  is a perspective of mold sides A and B in preparation for thermoforming; 
           [0020]      FIG. 7  is a flow-chart describing the twin-sheet thermoforming process. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0021]    Referring now to  FIG. 1 , a perspective view is shown of a preferred embodiment of the invention, in applying the concept for an improved seat cushion. Two thin sheets of highly resilient plastic (approximately 0.010″ thick to 0.040″ thick) are used to form a top half  10  and bottom half  12  in opposing protrusions which when joined, create a multiplicity of individual air cells  14 . Plastic types that have the resilient properties desired for the present invention include thermoplastic polyurethanes, highly flexible polypropylenes, soft vinyls, flexible polyethylenes and the like. The intent of the plastic is to create soft, very pliable air cells while being adequately robust to support internal pressures and resist puncture. The plastic could be colored for improved aesthetics, to result in a translucent gray or opaque blue for example. This device could be inserted into a fabric cover to give it a softer feel, customize the look of the seating system, and protect it against damage. It could also be incorporated directly into a seating system such as an office chair or automotive seat. The overall dimensions of the preferred embodiment are approximately 1.5 inches thick, 20 inches wide and 16 inches deep. 
         [0022]    In the manufacturing process of the present invention, a cylindrical port  16  is formed to mate with a shut-off valve that allows inflation of the air cell matrix, adjustment of pressure based on user preference, and deflation for easy transport from place to place. Additional ports can also be formed to provide further control of air flow. In one embodiment, ports  18  and  20  are created similar to port  16 , to allow shutoff of flow between right and left sides of the air cell matrix. This could provide the added benefit of stabilizing the user from side to side, especially useful for maintaining proper sitting posture or preventing excessive body lean in activities where a stable upright position is desired, such as flying aircraft or racing automobiles 
         [0023]      FIG. 2  shows a top view of the same seating application, with references to  FIGS. 3 and 4  for further detail. In this preferred embodiment, the air cells on the left side of the air matrix are isolated from air cells on the right, so that air must flow through the dashed tubing shown from port  18  into port  20  and back. This flow can also be blocked with the addition of a simple clamping device or additional valve, which would completely stabilize the cushion from side to side. Allowing a restricted amount of flow through this tube would serve to partially stabilize the user, providing a delayed response as air takes more time to move out of the cells being pressed upon. This feature provided a surprise benefit of creating a “breathing” sound, making the cushion feel and sound alive and responsive to adjustments in user posture. 
         [0024]      FIG. 3  shows a close-up of one corner of the seating application. When joined, material from both halves creates a thin web  22  between all air cells of approximately 0.020″ to 0.040″ thick. The air cells are interconnected by small passages  24  which serve to equalize pressure in all cells while allowing rapid inflation and deflation and maintaining flexibility between cells. Spacing of the air cells  26  is designed to allow flexibility of the system as well allowing air to flow freely between the exterior walls of the cells and away from the user. With proper spacing and air cell shape, the present invention leaves pathways of air between compressed air cells, down along the webbing, and out the sides of the air matrix. When a user shifts his or her weight on the device, air is pushed through these passages and recycled to help remove heat. 
         [0025]    Referring now to  FIGS. 4 and 5 , a cross-section of the air cell matrix is shown to elaborate on further details. These views show the opposing protrusion design of the air cell&#39;s top half  10  and bottom half  12  more clearly. This opposing protrusion design makes the air cell matrix more stable and less susceptible to “shearing” over, compared to a design that had tall cells extending up from a flat base. Thin web  22  is shown here and which holds the entire air matrix together. At specific locations of this webbing, small air passages  24  are formed to allow air to flow from one air cell to another. These passages have a special cross section as shown more clearly in  FIG. 5 . This narrow eye shape allows more flexibility than other shapes such as cylindrical or U-shaped passages, by allowing the material to flex more closed or open, depending on stresses applied. In addition, this shape helps to avoid “hard spots” that would be created by a other designs, and is significantly easier for the plastic to form into, maintaining a more even plastic distribution. 
         [0026]    In the preferred embodiment of the invention, some air passages are larger in size to allow for more rapid inflation and deflation to occur. These passages are strategically placed along the air flow route from the inflation valve, through air passages to ports  18  and  20  and into the left side of the air matrix. The larger passages effectively “spread” the flow of air, exposing more of the small air passages  24  to maximum flow during inflation and deflation. Flow in and out of an inlet valve attached to port  16  is therefore more closely matched to the sum of what the internal passages can accommodate. The result is a faster inflation and deflation of the entire matrix, making this process much more convenient, which is especially useful for travel purposes. 
         [0027]    It should be noted that the parting line  28  between the upper and lower air cell halves can be altered to further tailor the design. In other words, the air cell halves do not need to be equal in thickness. For example, a shallow bottom half with taller top half could be used to create thicker plastic on the bottom and thinner plastic on the top, providing more robustness on the bottom with more comfort on the top half. The depth of cells can therefore be used to control the amount of thinning that occurs when the plastic forms into the cells for a specific function. At its extreme, the air cells could have a fully formed top half mated to a flat bottom. This however would create a tendency for the cells to shear over as discussed previously and would cause other detrimental effects. 
         [0028]    In another embodiment of the invention, holes or slots could be added in the webbing area between air cells, so that air could flow from the top half of the air matrix through to the bottom and visa versa. This increased in air flow could be used to keep the user cooler than without holes. 
         [0029]    In yet another embodiment, ports in the air cell matrix could be configured so as to link multiple parts together, creating a larger supporting surface as needed. This could be used, for example, to create a bedding surface from multiple smaller parts. This would have the advantage of being able to further tailor the system based on need, while also avoiding the cost of building a much larger mold for production (a significant cost). 
         [0030]    For any of these embodiments, a control system could be added to control pressure automatically, by used of an electric air pump and electronic control box. This could be used, for example, to cycle the air pressure through separate quadrants, or to maintain pressure in multiple sections at different levels. 
       Method of Manufacture 
       [0031]    The preferred method of manufacture of the present invention is twin-sheet thermoforming. This process has large advantages over prior approaches in the manufacture air-filled seating devices. The following section helps to summarize this process from beginning with plastic selection to ending with finished parts. 
         [0032]    The twin-sheet thermoforming process begins with extrusion of the chosen plastic to a desired film thickness. Exact thickness of plastic should be determined before production by forming parts from various plastic thicknesses first (for example, targeting 0.020″ thick film). This is because some amount of sagging occurs when the plastic is heated and before it is vacuum formed against the molds. This sagging thins the material slightly, so that the resulting thickness for finished parts is lessened to some degree. Since extrusion companies have minimum orders, and larger runs reduce overall cost per pound of film, it is important to take the time to determine what the right thickness is based on the actual forming process. This will avoid purchasing plastic that is either too thin or too thick. 
         [0033]    Plastic is then extruded based on the width necessary to envelope the mold and be clamped into “clamp frames” outside the edges of the mold. Typically, about one half inch in extra width is needed on each side of the mold to permit this. As discussed previously, a number of plastic types could be used for the present invention, including but not limited to urethanes, vinyls, polypropylenes, polyethylenes and special formulations that combine some of these together (for example vinyl with urethane to minimize cost). 
         [0034]    The extruded plastic is then delivered to a company capable of twin-sheet thermoforming thin plastic film. As mentioned earlier, this process involves simultaneous thermoforming of top and bottom halves of a plastic part, then quickly joining these halves together while at the plastic&#39;s forming temperature. In the case of the present invention this would result in a complex matrix of air cells, interconnecting passages and one or more inflation features in a single manufacturing process, greatly reducing manufacturing costs over previous methods. Also as mentioned earlier, one major benefit of this method over prior approaches is in the elimination of RF welding. By forming both sides at the same time and mating both halves together in the same operation, many subsequent problems with RF welding can be eliminated. Weld lines can be much more tightly controlled, handling damage from RF welding can be avoided, and final trimming can be accomplished before the thermoformed parts are ejected from the vacuum molds. The production rate with twin-sheet thermoforming can be accomplished much faster than single sheeting and RF welding, minimizing machine time and therefore cost. 
         [0035]    Twin-sheet thermoforming offers a number of other benefits which may not be apparent to those skilled in the art of thermoforming. First, twin-sheet thermoforming allows much more elaborate designs to be manufactured as detailed above, enabling the creation of the present invention and variations within its scope. Second, twin-sheet thermoforming allows creation of interfacing ports for the attachment of air valves and the like, as opposed to previous methods which require additional processes for this. 
         [0036]    Third, twin-sheet thermoforming allows interconnecting air channels of multiple designs to easily be designed in and formed, as well as features to avoid excess thinning of plastic for the present invention. Fourth, twin-sheet thermoforming is very repeatable, ensuring high-quality parts can be consistently made, unlike other manufacturing methods. Fifth, when parts are joined in this process, heated material pushes inwards at the weld seam, forming a “bead” of material along all welds for extra strength. This is especially important when starting with a thin film of plastic as with the present invention. RF welding, in contrast, relies on the width of the weld, or “weld margin” for sealing strength. Sixth, the twin-sheet thermoforming process results in slightly thicker plastic closer to the parting line  28 , because it cools when it first touches this area, then stretches into the depth of the forming cavities. This material distribution allows the vertical air cell walls to maintain a tube-like shape while under the load of the user, allowing air to flow more freely in a horizontal direction and out the perimeter of the air cell device. Finally, twin-sheet thermoforming allows parts to be trimmed as part of the forming process, by designing the molds to cut through the forming material as they are pressed together, removing the “flash” (waste material) used to hold the plastic in clamp frames described earlier. 
         [0037]    Twin-sheet thermoforming has some additional benefits as well. It allows the function and/or look of the product to be changed by simply using a different thickness, type, or color of plastic. The same tooling can support manufacturing with all of these options, greatly reducing manufacturing cost to make these changes. If a change in design needs to be made, a new set of forming plates can be machined and attached to the mold bases (which interface with the manufacturer&#39;s vacuum and cooling systems) used with the initial forming plates. The cost of a new set of forming plates for the size of the present invention is very reasonable (less than $3,000 depending on complexity). 
         [0038]      FIG. 6  shows the thermoforming molds A (number  30 ) and B (number  32 ) in perspectives for clarity, to help illustrate the twin-sheet thermoforming process. The forming plates are the exact shape for each half of the air cell matrix of the present invention, and include many small vacuum holes that allow the heated plastic film to be vacuum formed against this shape. The vacuum holes are sized so that they avoid pulling plastic into them in the forming process, so for example using 0.020″ thick film as a rule of thumb would require no larger than 0.020″ dia holes (very small). These forming plates are each mounted to a mold base  34  that interfaces with the manufacturer&#39;s twin-sheet machine, and includes mounting provisions, plumbing for vacuum and cooling tubes to control the temperature of the forming plates during manufacture. This temperature is very important, as it effects how the plastic thins out when it is vacuum formed against the forming plates. The mold base/forming plate assemblies (collectively called molds) are then mounted into the twin-sheet thermoforming machine, where they are aligned so as to mate together properly and provide a desired gap, or end thickness of material, where the forming plates come together. This gap is controlled by stops which are set to ensure that the forming plates come together the same distance every time. Once this is accomplished, clamp frames are installed to hold “blanks” of plastic film (one for the top and one for the bottom). The forming process can then begin. 
         [0039]    For the forming process, two “blanks” (pre-cut sheets) of plastic  36  are loaded into their respective clamp frames, and then moved into a large oven that provides even heating of the blanks. This oven is usually computer controlled, and has an infrared eye that records temperature across the blanks when they exit the oven to ensure proper temperature control. The heated blanks are moved between molds A ( 30 ) and B ( 32 ), where one blank is vacuum formed against the mold A and one is vacuum formed against the mold B. Immediately following this, both molds are brought together so that the top half of the part is fused to the bottom half at the parting line. It is crucial that the forming and joining process happens very quickly, as heat is quickly lost from thin plastic. If timing from the oven to joining of halves is excessive, proper fusing of the materials will not occur. 
         [0040]    The formed part is then ejected from the mold, die-cut on the perimeter (if not already trimmed in the mold), and ready for installation of pneumatic fittings to complete the system. Because of the weld bead, it may be necessary to smooth out the inner bore of the interfacing ports so that they properly seal tightly against their respective pneumatic fittings.  FIG. 7  shows a flow-chart of the twin-sheeting process for further clarification. 
         [0041]    Utilizing the twin-sheet thermoforming process to create the present invention has valuable benefits over methods to create prior air-filled devices. The benefits of this manufacturing approach make the present invention feasible in terms of design and cost, allowing its unique function and performance to be manufactured as efficiently as possible. 
         [0042]    It is to be understood that while certain forms of the present invention have been illustrated, it is not to be limited to the specific forms described herein. It will be apparent to those skilled in the art that various changes may be made without departing from the scope of the invention or its potential applications.