Cushioning system with parallel sheets having opposing indentions for linear deflection under load

[0001] This application claims priority under 60/641,412, filed Jan. 5, 2005, which is incorporated herein by reference in its entirety.

[0002] 1. Field of the Invention

[0003] This invention relates to cushioning systems, materials and methods. The cushioning system of the invention may be used for any comfort-related cushioning application including, but not limited to, mattresses, furniture cushioning, body padding, footwear and packaging. One exemplary embodiment is a portable seat cushion designed to be easily moved from one seating surface to another by the user.

[0004] 2. Description of the Related Art

[0005] In the past, portable seat cushions have commonly been constructed using one or more pieces of foam contained within a plastic or fabric enclosure. These products typically use a low-density foam that, after several hours of operation, provide little or no comfort layer for the user because the foam has compressed too much and will not return to its original shape.

[0006] More recently, a novel plastic cushioning material developed by Skydex Technologies, Inc. (Centennial, Colo.) has come into use for footwear and body protective gear. This material and its method of fabrication are disclosed in the following U.S. patents: U.S. Pat. No. 6,098,313 “Shoe sole component and shoe sole component construction method” U.S. Pat. No. 6,029,962 “Shock absorbing component and construction method” U.S. Pat. No. 5,976,451 “Construction method for cushioning component” and U.S. Pat. No. 5,572,804 “Shoe sole component and shoe sole component construction method.”

[0007] The invention provides for a cushioning system that combines a SKYDEX flexible plastic cushioning material layer and a visco-elastic foam layer. In one preferred embodiment, both layers are enclosed in a moisture resistant bag. The SKYDEX plastic cushioning material layer provides a nearly linear force-deflection curve which allows for maximum comfort throughout the compression and shock cycle. The foam layer, which may be the top layer and closest to the user, acts as the comfort layer between the user and the SKYDEX layer. For a seating application, the foam may be contoured to match the user's buttocks area, which provides for proper positioning when using the product. In other applications, the foam may be shaped in other ways so as to spread the contact surface as greatly as possible. The invention is portable, and handles may be provided on one or more sides of the bag, for the user to move the product with them in and out of each system they are using the product in, which could be, but not limited to, a vehicle, an aircraft, an office seat, a boat, etc. The bag may be made from a heavy-duty upholstery fabric such as Cordura® fabric that can be expected to withstand many hours of use, as well as providing for a moisture resistant layer to keep moisture away from the foam and SKYDEX. The bag of Cordura fabric is also resistant to tears or punctures. The SKYDEX layer of the combination allows for air and moisture flow through the layer and is generally easier to clean than foam.

[0026] Referring to FIG. 1, one preferred embodiment of the invention is shown wherein a lower layer of SKYDEX® linear-response plastic cushioning material and an upper layer of formed visco-elastic foam are encased in a fabric bag.

[0027] The upper surface of the foam layer is molded to conform to an adult human's buttocks when in a seated position. The lower surface of the foam layer is molded to mate with the upper surface of the SKYDEX linear-response plastic cushioning material.

[0028] The bag or enclosure may be formed of any suitable material including vinyl plastic, fabric reinforced plastic, and upholstery fabric. One particularly preferred upholstery material is CORDURA® fabric developed by E. I. du Pont de Nemours and Company (Wilmington, Del.) and available from Invista North America S.A.R.L. Corporation (Wilmington, Del.). The bag may be provided with one or more openings having a closure device such as a zipper or VELCRO hook-and-loop type fasteners to facilitate the insertion and removal of the cushioning materials. Moisture-resistant materials are particularly preferred for the bag so as to prevent water from infiltrating the cushioning layers.

[0029] A particularly preferred cushioning material comprises two thermoformed sheets of plastic that, when formed with a cavity of a particular geometry, mimic a linear spring when compressed. The seat cushioning material has square cavities on the top and bottom of two sheets of plastic that are joined at the middle of the product (see FIGS. 1-7). The square depressions are rounded on the bottom while the sides are straight. The seat cushioning material has a contoured shape to better fit the user and the seat. The square cavities allow for compression to occur in a linear force/deflection environment when a user sits on the cushion. The straight walls of the square indentations compress evenly on both sides of the plastic, providing for this linear curve. The preferred method of construction is to twin-sheet thermoform the plastic material because of speed and cost. This method will form and adhere the two pieces together in one operation.

[0030] This invention allows for a linear force-deflection curve for the majority of the deflection that is seen when a person compresses the product. FIG. 8 shows a square shaped SKYDEX material geometry (dark blue line) and a twin-hemi shaped SKYDEX material geometry (pink line). The Linear line (black) is on the chart to represent the linear curve that the square geometry follows. What is shown is that the square indentation follows the linear curve more closely than the SKYDEX material using hemispheres, which provides a greater comfort feel than the non-linear twin-hemi curve. The other two curves on the chart represent two different types of foam that were tested, that both have an exponential force-deflection curve. Having a product with a linear force deflection curve minimizes the pressure points that are felt by the subject when using the product and allows for greater comfort. Another way to think of comfort is in terms of a mattress, which uses coil springs in its internal system. Coil springs typically have a linear force-deflection curve.

[0031] Other products (like different types of foams) provide for an exponential force-deflection curve during compression. This can place pressure points on areas of the buttocks that cause discomfort when sitting on the cushion for long periods of time. A seat cushion with a linear force-deflection curve can minimize this discomfort and reduce pressure points.

[0032] Alternative forms of SKYDEX cushioning technology can also work in this invention for example by providing an internal hemisphere at the bottom of the square depression. The added hemisphere supports the square cavity at the same point that this buckling occurs, thereby increasing the steepness of the curve and producing a more nearly linear response curve.

[0033] Alternative methods of construction include vacuum forming or single sheet thermoforming. Both of these methods may require the two sheets of plastic to be secured via a secondary operation such as, but not limited to: sonic welding or hot gun welding.

[0034] FIG. 9B is a plot of force (in pounds) versus deflection (in inches) for two different SKYDEX hemi-ellipsoidal springs. Curve #1 (shown in red) is for a shallow profile hemi-ellipse spring. Curve #2 is for a steep profile hemi-ellipse spring. It will noted that both of these springs have a non-linear force-deflection curve due to “buckling” of the plastic which, in the examples illustrated, begins at about 0.3 inch of deflection.

[0035] FIG. 10B illustrates the more nearly linear response obtained with a square type SKYDEX spring (as shown in FIG. bA). Curve #1 (black line) is for square SKYDEX material fabricated using a first elastomer. Curve #2 (shown in yellow) is for square SKYDEX material fabricated using a second elastomer. For comparison purposes, the linear force versus displacement curve of a coil spring is shown as Curve #3 (shown in red). It will be noted that the force versus deflection curve of the square SKYDEX material fabricated from elastomer material 2 closely approximates the linear response of a coil spring.

[0036] FIG. 11 is a comparison of force versus deflection curves for two different hemi-ellipse SKYDEX materials and a square type SKYDEX spring. It is apparent from FIG. 11 that the square profile SKYDEX spring more nearly approximates a linear force vs. displacement response than does a hemi-ellipse profile SKYDEX spring.

[0037] FIG. 12 illustrates some engineering variables that may be selected for tuning square profile SKYDEX material to provide a desired response. The variables include: the material type; the thickness of the material; the size of the square projections; the height of the projections; the radius of the mating surfaces of the projections; the radii on the [side] corners of the projections; and, the optional presence of an imbedded hemi-ellipsoid projection at or near the center of the square projections for added stiffness.

[0038] FIG. 13 shows the various dimensions of a sample of square-type SKYDEX material whose values may be varied to affect the response of the material to deflection. In certain embodiments, it may be desired to adjust these variables so as to achieve a nearly linear force versus displacement response.

[0039] FIG. 14 shows the force versus displacement curves for four different samples of square-type SKYDEX material having differing values of wall height and joining radius R (as shown in FIG. 13). In each sample, the dimension W (FIG. 13) was held constant at 1.00 inch. As is apparent from the graph, the response of the Square 2 sample was the most nearly linear of the group. The dimensions for Square 2 were increased proportionately to a larger square shape having dimension W=2.0 inches. The force versus displacement of the 2-inch square-type SKYDEX material for two different material thickness values is shown in FIG. 15. As may be seen in FIG. 15, film thickness is another variable that should be taken into consideration when tuning the material for the desired force versus displacement response.

[0040] FIG. 16 illustrates the force versus deflection response of a third embodiment of the square-type SKYDEX material having the dimensions: W=1.25 inches; H=0.47 inch; and, R=0.28 inch (as illustrated in FIG. 13). The response of two different embodiments having different material thickness values is shown. Both nearly approximate a linear response curve.

[0041] While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.