BACKUP CHAIR WITH IMPROVED SUPPORT AND ELASTICITY CROSS REFERENCE TO RELATED APPLICATIONS This patent application refers to patent applications with the title "Chair with Backward and Forward Passive Tilt Capabilities", Serial No. E.U.A. 10 / 749,008, file of agent number 087522-785-323; "Horizontally Adjustable Chair Arm Rest", Serial No. E.U.A. 10 / 748,537, file of agent number 087522-785-329; "Vertically Adjustable Chair Arm Rest," U.S. Series No. 10 / 749,010, agent file number 087522-785-347; "Chair with Adjustable Seat Depth," U.S. Series No. 10 / 748,079, agent file number 087522-785-349; and "Chair with Tilt Lock Mechanism," Serial No. E.U.A. 10 / 749,009, file of agent number 087522-785-350; All of these applications were submitted on December 30, 2003 and are incorporated herein by reference in full. PREVIOUS TECHNIQUE This invention relates to a chair having a seat portion and a backrest portion, wherein the backrest includes means for providing improved resilience and support. In particular, the invention relates to a chair for office use, wherein the backrest includes means for providing improved support and resilience, which means that it automatically self-adjusts as the backrest portion reclines. It is known in the office seating design technique to provide an office chair with a backrest portion that reclines in an adjustable manner in response to the pressure exerted by the wearer's back and then returns to its original position. as the user's back moves forward. These chairs or chairs are typically designed to provide support for the back of the user when the backrest portion is in the fully upright position. The lumbar support can either be fixed or manually adjustable. One difficulty with these prior art chairs is that a fixed lumbar support, or even one that is manually adjustable, may not satisfy and sustainably support the lumbar regions of users with different heights. Another difficulty with these chairs of the prior art is that as the user reclines backwards, the position of the user's lumbar region changes with respect to the position of the fixed lumbar support in the backrest portion. In this way, as the backrest portion is reclined, the user's lumbar region may not receive optimal support in the range of movement of the backrest. Thus, an object of the invention is to provide a backrest portion for a chair, which includes means for automatically providing resiliency and support for a user's back. Another object of the invention is to provide a backrest portion for a chair that includes means for providing self-adjusting lumbar support, to comfortably support users of different heights. Still another object of the invention is to provide a backrest portion for a chair, including means for providing adjustable support elasticity, which automatically adjusts itself to comfortably hold users as the user changes positions against the backrest, and as the backrest portion reclines at different inclination angles in response to the pressure exerted by the user's back. DESCRIPTION OF THE INVENTION These and other objects of the invention are met by a chair or chair having a seat portion and a backrest portion, the backrest portion being able to recline in response to the pressure exerted by a user's back. , the backing portion includes in its interior means for providing self-adjusting support elasticity, the seals comprise a cushion containing fluid. The cushion is substantially coextensive with at least that region of the surface of the back portion that engages with the lumbar region of the user. The cushion provides automatically varying pressure, in response to the variable pressure exerted by different regions of the user's lumbar region, or other regions of the user's back superimposed on the cushion. The cushion automatically accommodates users of different heights and automatically adjusts to variations in applied pressures as the backrest portion reclines through a range of angles. In a preferred embodiment, the cushion comprises two sheets of flexible plastic film,
"air impermeable, sealed together to define a volume having a lower region and an upper region." The cushion preferably has seams that define a plurality of channels that generally extend from the lower region to the upper region, when the cushion It is installed in a backrest portion of a chair.Each channel is partially filled with fluid.As the user leans their back against the backrest, more pressure will be exerted against the cushion by the upper part of the back and shoulders of the user than by the user's lumbar region.This will bring more fluid from the upper region of the cushion down to the inner region, to provide increased lumbar support for the user.The precise location of the increased lumbar support may vary over the length of the channels, to provide improved lumbar support as an individual user changes position in the chair, and for users of Even more, as the individual user reclines the backrest, the location of the increased lumbar support may change in response to varying pressures exerted by different regions of the user's back, such that the improved backrest automatically provides optimal back support elastic to the user at any angle of inclination. BRIEF DESCRIPTION OF THE DRAWINGS The present invention is easier to understand by reference to the Figures, wherein: Figure 1 is a cross-sectional view of a chair having a backrest of the invention;
Figure 2 is a front section view of an embodiment of a chair backrest of the invention; Figure 3 is an end view of the cushion of Figure 2; and Figure 4 is a front elevation view of another embodiment of a cushion for use in the present invention. BEST MODE FOR CARRYING OUT THE INVENTION As illustrated in Figure 1, a chair 10 includes a back 12 having one side facing forward 14 and one side facing back 16. The back 12 comprises a substantially supportive member rigid, covered at least on its side facing forward 14 with a cover type 20 upholstery, such as cloth, vinyl or leather. Optionally, a cushion 22 of foam or other elastic material such as is known in the art is placed on the surface with forward facing of the substantially rigid support member 18. According to the invention, a means for providing elasticity and support for the back of a user, comprises a cushion containing fluid 30 placed between the substantially rigid support member 18 and the upholstery cover 20. An optional cushion 23 of foam or other elastic material can be placed between the cushion 30 and the upholstery cover 20. The cushion 30 comprises a first layer 32 and a second layer 34, each of the layers is made of an air impermeable plastic, the layer is hermetically sealed with respect to its respective peripheries, to form a peripheral seal 36. The cushion 30 preferably is sized to be substantially coextensive with at least that region of the back 12 that will experience the pressure exerted by the backing of a user of chair 10, extending from the upper back and shoulders to and including the lumbar region. For ease of reference, the structure of the invention will be discussed in terms of a lower region 40 and an upper region 42, although it will be appreciated that the current proportions of the cushion of the invention serving as lumbar support region and support region of the Upper back respectively, will depend on the size and height of the individual user. In a preferred embodiment, the two layers 32 and 34 of the cushion 30 are additionally joined by a plurality of seams 37. The seams 37 together with the peripheral seal 36 define a plurality of channels 38, which generally extend from the lower region 40 to the upper region 42. The channels can be substantially vertical, as illustrated in the Figures, or can be oriented at different angles. Each channel 38 contains a fluid. In the illustrated embodiments of the invention, the channels are in fluid communication with each other through a plurality of plurality of openings 39 in each of the seams 37. The sizes and locations of the openings 39 can be varied to achieve a desired response. Alternatively, the openings 39 can be omitted, and each channel 38 will seal itself completely. The fluid in the cushion can be air, gas or mixtures of gas, liquid or a fluid gel. The cushion should only be partially filled with fluid, so that fluid can move from one region of the cushion to another, or from one region in one channel to another. In response to variations in the applied pressure caused by user movements. In use, when a user of the chair rests against the back 12, the user's back will be in contact with the front surface 14 and exert pressure. The upper part of the user's back and shoulders will cause some compression of partially filled channels 38, primarily in the upper region 42, causing fluid to move to the lower lumbar region 40, where it provides additional support to the user's lumbar region. , where this support is most often required. It can be seen that the exact location of the additional lumbar support over the length of the channels 38 will be determined automatically by the physical dimensions of each individual user. It is not necessary for an individual user to make manual adjustments to the chair in order to obtain optimal support in the lumbar region. In this way, the fluid support system of the present invention provides an automatic passive adjustable support of the lumbar region, in response to each individual user. The system of the invention advantageously applies pressure compensated along the back of the user. Still further, when a user reclines the back 12 of the chair 10, the curvature of the individual's spine will change, with the shape and amount of changes depending on the physical dimensions of the individual and the angle of inclination of the backrest. The lumbar region 19 of the rigid support member 18 is curved to generally adapt to the lumbar region of a user. In general, the radius of curvature of a user's back will be smaller than the radius of curvature of the lumbar region 19 of a rigid support member 18. The space between the lumbar region of a user and the lumbar region 19 of the member of rigid support 18, defines a relatively small volume to be filled with fluid. As the seatback is reclined, the curvature of a user's spine changes and in particular the arch of the user's lower back and upper back. The pressure areas exerted by the back of the user when reclined will vary over the length of the channels 38. Fluid within the partially filled channels will move from the areas where the pressure is greatest, such as the region 42 contacted by the upper part of the back and shoulders of the user, towards the areas where the pressure is minimal, such as the region 40 in the lumbar area of the user. Typically, it is the lumbar region where more support is required. The displacement of fluid within the channels 38 will happen automatically as the user alternately reclines and straightens the backrest. At the same time, there will be less volume of fluid in the cushion in the upper region of the back '42, so that there will be greater stability in the upper part of the user's back, without unwanted side-to-side rolling motion. . In this way, the fluid-containing cushion of the present invention automatically adjusts to the needs of different individual users and to different needs of a single individual, as that user acquires different inclination angles and different positions during the course of ordinary use of the device. chair. Advantageously, the user will not feel any discontinuity of pressure or support in the lumbar region, regardless of the angle of inclination; that is, there is no "wedge" where the lumbar support ends, as can be experienced with systems employing a discrete mechanical lumbar support member. It will be appreciated that the channels 38 are preferably not filled to their highest capacity. If the pressure of the channels 38 were very high, then the cushion 30 will not yield in response to pressures applied unevenly; that is, the fluid will not be able to move from a region of higher applied pressure such as the region of the shoulders and upper part of the back 42, to a region of lower applied pressure such as the lumbar region 40. The cushion of the The present invention can be made of fluid impervious plastic films which can be sealed together to form airtight seals. These plastic films may include, for example, vinyls, polyurethanes, polyvinyl chlorides, ethylene vinyl acetates, urethane-coated membranes, polyolefins, saran and multilayer engineering films. The plastic film selected for the cushion will be practically impermeable to air, with an air transmissibility rate as measured by ASTM D1434 (standard test method for determining gas permeability characteristics of films and plastic sheets) of less than about 100cm3 / m / day / atm; preferably less than about 10 cm3 / m2 / day / atm; and more preferably less than about 5 cm3 / m2 / day / atm. The thickness of the plastic film may be in the range of about .00508-.0508 cm (2-20 mils) more preferably .01016-.0254 cm (4-10 mils) and optionally in approximately .01016 cm (4 mils). A particularly preferred material for an air-containing cushion is Saranex 15 of .01016 cm (4.0 mil), a multilayer film available from Dow Medical Films and comprising a "Saran *" barrier resin co-extruded between outer layers of polyolefins . The films can be sealed together to form the peripheral seal 36 and the seams 37 by known seal means, such as adhesives, heat sealing, ultrasonic sealing and RF sealing. Those skilled in the art will be able to choose an appropriate seal means for the particular film material that is employed. A desired amount of air is injected into the various chambers of the cushion during the sealing process by methods known in the art of making air-filled bladders. The dimensions of the cushion, and the size, number and angular orientation of the cushion channel 88, may be varied to conform to (1) the different needs of users; (2) the design of the chair as a whole, including whether any optional foam pads and other elastic materials are employed on the front and / or back of the pad, and the characteristics of the optional pads; and (3) the different applications for which the chair will be used. The size and number of openings 39 can also be varied to achieve a desired fluid response. In addition, additional cushioning such as a foam layer or a gel layer can be sandwiched between the cushion 30 and the upholstery layer 20. Figure 4 illustrates a preferred embodiment of a back cushion generally indicated with the reference numeral 130. The cushion 130 comprises two sheets of plastic film sealed in conjunction with a peripheral seal 136. Extending along the length of the cushion 130 are two seams 134, 135 that divide the interior of the cushion 130 into a central chamber 139 and two side chambers 138. In this embodiment, each central chamber 139 and side chamber 138 is partially inflated with air. The partial seams 137 in each side chamber 138 extend from approximately the top of each side chamber 138 downward approximately the vertical midpoint. These partial seams 137 prevent the side chambers 138 from bulking too much at the upper end and maintaining a more uniform pressure level across the length of the cushion. It will be understood that the partial seams 137 may be in the form of spot welds, that is to say discrete points where the two layers of cushion 130 are joined together. These points can be arranged in lines or over an area, as long as they serve to moderate the expansion of the side chambers 138. In the illustrated embodiment, the partial seam 137 terminates in a teardrop-shaped element, which relieves tensions located in the leaves. of plastic. In the illustrated embodiment, the cushion 130 has an approximate height of 45.72 cm (18") and an approximate width of 35.56 cm (14") on its upper horizontal edge 150. The sides taper inwardly slightly beginning at approximately 15.24 cm ( 6") from the bottom edge, such that the width of the bottom edge 152 is approximately 25.4 cm (10"). The central chamber 139 is pressurized with 100 cm 3 of air and the side chambers 138 each pressurized with approximately 300 cm 3 of air. Alternatively, an external pump may be provided such that the user can adjust the amount of air in the cushion, according to individual preferences. The present invention provides a significant improvement over the backing supports of the prior art. Unlike foam cushions, which simply compress in response to applied pressure, the fluid support of the present invention redistributes the pressure, so that as one part of the cushion is compressed, another part expands, to provide additional support where more is required. While the novel features of the present invention have been described with respect to particular embodiments, it will be appreciated by those skilled in the art that substitutions of materials and modifications in structure and details can be made without departing from the spirit of the invention.