Body support system

[0002] This invention relates to a body support system such as may be used for a seat cushion. More particularly, this invention relates to a body support system such as may be used for a seat cushion and having improved mechanical response characteristics and improved thermal interaction with a user.

[0003] The comfort provided to a user by a body support system such as a seat cushion will depend on a variety of factors. One such factor is the mechanical response of the body support system to the compressive and shear forces applied by a user seated on the body support system. Another such factor is the ability of the body support system to provide thermal regulation in the form of heat exchange with a user. If the body support system is to be used in conjunction with a moving device such as a wheelchair, a farm implement such as a tractor or riding mower, or as a seating element for public transportation, then the ability of the body support system to provide dynamic response to reduce transmission of impact to a user is another factor.

[0004] Conventional contemporary office seats are usually made of either upholstered padding or synthetic mesh in a frame assembly. Each of these types of seats has its own characteristic thermal properties. Padded upholstery seating provides heat exchange with the user through conduction and sweat evaporation processes. Upholstered padding is better suited for lower workspace temperatures on the order of 16-25° C. (61-77° F.) and shorter sitting times. Mesh seating provides heat exchange with the user with radiation and convection. Mesh chairs are better suited for higher workspace temperatures on the order of 25-35° C. (77-95° F.) and longer sitting times. Neither of these prior art seating designs provides for thermal regulation in a wide variety of office temperature environments.

[0005] Thermal properties are major ergonomic features that should be considered in the design of an office chair. The human body always works to retain its core temperature near 37° C. (98.6° F.), by means such as postural adjustments, varying skin temperatures such as by perspiration, regulation of cardiovascular and pulminary activity such as pulse and breath rates to affect blood flow and vessel sizes especially in skin areas close to an interface with a seat cushion. A chair that prompts sweating after a relatively short period of sitting and which requires the human body to engage in such thermal regulation processes will be uncomfortable and may affect work efficiency. For example, with conventional upholstered padding, heat can build up at the user/seat interface causing the user to limit muscular activity to reduce heat generation. The user may also begin sweating to expedite the thermal transfer across the user/seat interface. When the user/seat interface inhibits sweat evaporation due to low cushion vapor permeability under even small pressures, heat is not dissipated at the interface leading to even greater discomfort for the user. On the other hand, mesh chairs have high vapor permeability and heat dissipation and do not allow for any heat build up at the seat user interface. It has been postulated that a limited heat build up that would not reach a level of discomfort to the user would be favorable. Thus, with open mesh seats the thermal comfort of the user becomes significantly dependent on the ambient temperature of the work environment.

[0006] Further, conventional seating designs do not provide for variations in the size and comfort levels of different users. Different individuals will have different thermal generation rates and different comfort levels.

[0007] It is thus one object of the invention to provide a body support system such as a seat cushion having improved thermal regulation properties.

[0008] It is yet another object of the invention to provide a body support system such as a seat cushion having improved mechanical response properties including low intensity pressure distribution.

[0009] It is still another object of the invention to provide a body support system such as a seat cushion in which the thermal regulation properties and/or the mechanical characteristics can be varied to the needs or preferences of a particular user or group of users.

[0010] A body support system is provided having improved static support characteristics and improved thermal interaction with a user. The improved static support is provided by means for distributing the weight of a user in response to applied compressive and shear forces at the user-support system interface. The means for distributing the weight of the user comprises a plurality of vertical columns disposed substantially centrally in said body support system. The columns are capable of deflecting substantially independently of one another in response to the compressive forces applied by a user. The improved thermal interaction is provided by structures that provide enhanced air flow through and about said body support system, thereby providing convective thermal regulation, and dry and evaporative heat exchange. An elastomeric member disposed above said columns also serves to facilitate heat exchange with a user, and cooperates with the columns in the distribution of the user's weight for improved static support.

[0011] The body support system comprises a foam body. In one embodiment, the vertical columns can be configured as upwardly extending risers, formed integrally with said foam body. In an alternative embodiment, the columns can extend downwardly from the elastomeric member. The columns can be formed of a material having density and mechanical response characteristics either the same as or different from the density and mechanical response characteristics of the foam body. This feature permits the inventive body support system to be customized to the needs of different users.

[0012] The spaces between the vertical columns define an air reservoir within the interior of the body support system. The body support system further comprises means for directing the flow of air from the air reservoir to the periphery of the body support system, and then toward the upper surface thereof, for heat exchange processes with the user, thereby increasing the comfort of the user when using the body support system for long periods of time. The means for directing the flow of air from the air reservoir to the periphery can comprise a plurality of channels formed within the foam body and extending from the air reservoir to the foam body periphery. When compressive forces are applied by a user, air within the reservoir will be displaced and directed through the channels toward the periphery and upwards. Advantageously, air flow through the body support system is achieved without the need for active airflow circulation devices such as fans, valves, or pumping devices. Air deflecting means disposed about the periphery of the foam body function to deflect the air received at the periphery from the reservoir to a region above the foam body for heat exchange with the user. This thermal regulation function is further enhanced by the aforementioned elastomeric member, which functions as a large capacity heat sink to remove heat from the user.

[0013] The body support system of the instant invention can further comprise an air-permeable viscoelastic layer disposed above the elastomeric member and the foam body. The viscoelastic layer can reduce the transmission of both compressive and shear forces to the elastomeric member. The air-permeable viscoelastic layer can also facilitate the flow of displaced air at the periphery of the cushion to enhance thermal regulation. The airflow achieved with the body support system of the instant invention also contributes to mechanical function of the body support system by providing recoverable dissipation of applied shear and compressive forces

[0014] The body support system of the instant invention can be used in a wide variety of seating applications. The body support system can be configured as a seat cushion such as for use in office seating, in which case the seat cushion can be mounted onto a chair frame including a pre-formed seat pan. The seat pan acts as a rigid support for the cushion. The body support system can also be used in rehabilitative seating and other support, such as in wheelchairs, hospital beds, and the like, where improved responsiveness to compressive and shear forces can help in the prevention of decubitus ulcers. The inventive body support system can also be used in dynamic situations such as motor vehicles, particularly vehicles driven for long periods of time such as trucks, and even more particularly vehicles driven for long periods of time over uneven surfaces, such as snowplows and farm implements, which vehicles are subject to motion-induced vibration and in which the vehicle driver can benefit from the damping of such motion-induced vibration as can be provided by the inventive body support system disclosed herein.

[0015] FIG. 1 is an exploded view of an embodiment of a seat cushion made in accordance with the instant invention and a seat pan with which it can be used.

[0016] FIG. 2 is a top plan view of the foam body used in the embodiment of the seat cushion of FIG. 1.

[0017] FIG. 3 is a cross-section view through line 3—3 of the foam body illustrated in FIG. 2.

[0018] FIG. 4 is an exploded view of a second embodiment of a seat cushion made in accordance with the instant invention.

[0019] FIG. 5 is an exploded view of a third embodiment of a seat cushion made in accordance with the instant invention.

[0020] The figures herein illustrate various embodiments of the invention wherein the body support system is in the form of a seat cushion such as for use with an office chair. It will be understood that these embodiments are presented herein for illustrative purposes only, and that the inventive body support member can be used in other embodiments and for other purposes, as discussed below.

[0021] FIG. 1 is an exploded view of a first embodiment of a seat cushion body support member 10 of the instant invention. Seat cushion 10 comprises foam body 12, illustrated in FIGS. 1-3. Foam body 12 can be formed of materials typically used in such seat cushions, such as open-celled or closed-celled polyurethane foam. Foam body 12 has an upper surface 13 and a plurality of vertical columns 15 disposed substantially centrally in said foam body 12. In the illustrated embodiment, the columns 15 extend upwardly such that the top surface of said columns 15 define a curved surface substantially parallel to upper surface 13. In the embodiment illustrated in FIGS. 1-3, the columns 15 are formed integrally with foam body 12. The foam material of which foam body 12 and columns 15 are made will be resiliently deformable to some extent. The columns 15 are structured such that, in the absence of other structural elements of the body support member 10, each column 15 is capable of deflecting substantially independently of the other columns 15 in response to compressive forces applied by a user.

[0022] Vertical columns 15 are structured so as to define a plurality of air spaces 16 therebetween, which together define a plenum or air reservoir 18. A plurality of channels 20 disposed within foam body 12 extend from air reservoir 18 toward the periphery of foam body 12. In the illustrated preferred embodiment of a seat cushion, the channels 20 are directed to the front and lateral sides of the foam body 12.

[0023] Design parameters of vertical columns 15 include their number, planar spacing, depth, aspect ratios, and material density and stiffness. Depending on their size and shape, the number of vertical columns can be in the range of about 5-180 columns, more preferably in the range of about 30-90 columns, and even more preferably about 40-80 columns. The columns can have a diameter at their lower end in the range of about 0.5-4.0 inches, more preferably in the range of about 0.75-3.0 inches, and most preferably in the range of about 1.0-2.0 inches. The columns can have a diameter at their upper end in the range of about 0.5-4.0 inches, more preferably in the range of about 0.75-3.0 inches, and most preferably in the range of about 0.9-2.0 inches. The height of the columns can range up to about 4 inches, more preferably will be in the range of about 0.5-3.0 inches, and most preferably will be in the range of about 0.5-1.5 inches. The columns 15 in a seat cushion 10 can be of different sizes and shapes.

[0024] The number of air channels 20 will depend upon their size. For example, in the illustrated embodiment, the channels 20 directed toward the front edge of the chair are of different sizes with one large channel in the center and three smaller channels on either side of the large channel. Similarly, the channels 20 directed toward the sides of the chair can be of pre-determined size and number. The total volume capacity of channels 20 will be a function of the volume capacity of air reservoir 18.

[0025] The seat cushion 10 further comprises an elastomeric layer 30 that overlays the upwardly extending risers 15. In the illustrated embodiment, the periphery 31 of elastomeric layer 30 is seated within fitting edge 14 at the upper surface 13 of foam body 12. Elastomeric layer 30 comprises a top surface 32 and a bottom surface 34. Bottom surface 34 of elastomeric layer 30 defines the top surface of air reservoir 18. Elastomeric layer 30 comprises a material having significant resilience and flow properties. Suitable materials for elastomeric layer 30 include, for example, a gelatinous sheet and a polymeric membrane, or other gelatinous materials with variable viscoelastic properties. One suitable material includes a gel sold under the trademark LEVAGEL® by Royal Medica of Italy. Information about this material is available at www.royalmedica.it. Elastomeric layer 30 and upwardly extending risers are each characterized by both an elastic stiffness value and a dissipative stiffness value In a preferred embodiment of the invention, the ratio of elastic stiffness to dissipative stiffness of the vertical columns 15 is greater than the ratio of elastic stiffness to dissipative stiffness of the elastomeric layer 30.

[0026] Depending on the material selected and the properties of the seat cushion desired, elastomeric layer 30 can have a thickness in the range o about 0.1-1.5 inches, more preferably in the range of about 0.1-0.5 inches, and most preferably in the range of about 0.2-0.4 inches. As illustrated in FIG. 1, the area of elastomeric layer 30 can be less than the area of top surface 13. The relative area of elastomeric layer 30 to top surface 13 can be in the range of about 20-95%, more preferably in the range of about 25-60%, and most preferably in the range of about 30-55%. In one embodiment, elastomeric layer 30 is about 0.25 inches thick, and has an area of 210 sq. in., relative to a total area of top surface 13 of 392 sq. in.

[0027] In use, the foam body 12 of seat cushion 10 is supported by a stiff seat pan 25 rigidly fixed on a seating system (not shown). In the illustrated embodiment, seat pan 25 comprises an inner pan 26 bolted to pan support 27. Pan support 27 can be made of glass-filled nylon, for example, and preferably includes a plurality of support ribs 28. When a user is seated on a seat cushion of the instant invention, the user's weight is transmitted as vertical compressive forces and transverse shear forces to the user/seat cushion interface. These forces are transmitted through elastomeric layer 30 to vertical columns 15. Elastomeric layer 30 and vertical columns 15 function cooperatively with one another to achieve a self-limiting mechanical response to obtain desired mechanical qualities. As a result of the ratios of elastic stiffness to dissipative stiffness of the columns 15 and elastomeric layer 30, each column 15 responds substantially in the manner of an elastic spring with weak dissipation, analogous to various engineering models of springs and dashpots. Further, the columns 15 will respond to localized forces substantially independently of one another. Highly localized compressive forces at the seat/user interface would result in undesirable pressure peaks, resulting in greater deformation of the columns 15 in that particular location, i.e., each column is expected to deform in direct proportion to the applied forces to that column. The elastomeric layer 30 mitigates these ergonomically undesirable effects by deforming in response to the applied forces, partially dissipating the applied forces and causing elastic transfer of excess applied force to neighboring or remote columns 15. The applied forces are distributed to neighboring or remote columns 15 to obtain a more even pressure distribution. Thus, elastomeric layer 30 creates interdependence of the column deflections by transmitting stresses resulting from differential column deflections, be elastic and dissipative means, thereby limiting individual column deflections, and the corresponding column reaction on the user's body, in a predetermined manner. In accordance with the invention, the materials of the elastomeric layer 30 and columns 15 may be selected to produce the level of applied force redistribution desired for a particular user or a particular type of seating application.

[0028] The redistribution of applied forces can be further enhanced by air-permeable layer 35, disposed above elastomeric layer 30. Air-permeable layer 35 may comprise an open-cell or nonwoven viscoelastic material having specified thickness and viscoelastic properties, which air-permeable layer 35 can function to further dissipate applied forces before such forces reach elastomeric layer 30. Optionally, an intermediate foam layer 37 can be placed between air-permeable layer 35 and elastomeric layer 30. A cover fabric, not shown, can overlie the entire seating structure. The layers 12, 30, 37, 35, and the cover fabric can be pre-bonded to one another such as with adhesives. Alternatively, the layers can simply be stacked on top of each other, in which case there should be a sufficient amount of friction between the layers to prevent slippage of the layers with respect to one another in response to shear forces applied during use.

[0029] The structure of the instant invention will transmit shear forces emanating at the user/seat interface across the interfaces between each of the layers until elastomeric layer 30. Elastomeric layer 30 will deform viscously in response to applied shear forces, thereby counteracting the shear component of the user's weight by dissipative means, such that the user's skin will not experience the shear component. As a result, the user's tissues will experience substantially only compressive stresses in the normal direction. This reduction in shear stress can reduce the potential for the development of pressure ulcers, and reduce undesirable interference with blood vessel activity in the vicinity of these tissues.

[0030] When the user leaves the seat cushion of the instant invention, the resiliency of the foam body 12, vertical columns 15 and the elastomeric layer 30 allows full recovery of both shear and compression deformational mechanisms of the cushion. The passive air pump depressurizes, allowing outside air to pass through the outside cover, the air permeable layer, and optional intermediate foam layer to enter the air reservoir and channels, and open cells in the foam body 12 if open-celled foam is used. The elastomeric layer 30 will also return to its original shape prior to the application of compression and shear forces by a user.

[0031] The body support system of the instant invention provides both dynamic and static support. User discomfort in dynamic seating situations arises when vibrations are transmitted through a seating system to the user, such as in vehicle or public transportation seating systems. The multi-layer structure of the inventive body support system provides enhanced dynamic support by filtering out harmful higher frequency components in the compressive and shear vibration modes. Each of the body support system elements, namely, the foam body, the vertical columns, the elastomeric layer, and the air permeable layer, can contribute to the vibration filtering process. The materials for these elements, and the size and shape of these elements, can be selected to provide dynamic support characteristics for a particular environment in which the body support system will be used. Static support will be a function of the stiffness of the components, and particularly the stiffness of the vertical columns.

[0032] The inventive body support system also provides improved thermal interaction with a user. This is achieved through several means. The inventive body support system promotes thermal exchange between the user as a heat source and the body support system as a heat conduit and heat sink. This heat exchange is achieved partially through convection, facilitated by air exchange. When the seat cushion is not in use, air reservoir 18 and air channels 20 are filled with air, as are the cells of foam body 12. When a user occupies the seat and applies compressive and shear forces to seat cushion 10, air is forced from air reservoir 18 through air channels 20 from which it is reflected back to the region between elastomeric layer 30 and air-permeable layer 35. Some air may also permeate directly from air channels 20 through air-permeable layer 35. Air-permeable layer 35 serves to diffuse the air toward the user to facilitate heat exchange and promote user comfort. Air permeable layer 35 also allows air permeation from the user to the seat cushion, where air and heat can pass through air-permeable layer 35 to elastomeric layer 30, which then acts as a heat sink This airflow at the user/seat interface also allows for evaporation which enhances the cooling effects and further promotes user comfort.

[0033] To facilitate heat exchange, the air-permeable layer 35 will have pre-selected fiber directionality and anisotropic air-permeability, depending on the particular application of seat cushion 10. In addition, air-permeable layer 35 can be treated with phase changing materials to further regulate heat exchange processes at the user/seat interface. Such phase change materials, generally in the form of tiny capsules, will be such size and packed in such a way that the mricroporosity of air-permeable layer 35 will not be affected. Suitable phase change materials include those commercially available from Outlast Technologies, Inc. of Boulder, Colo., and those described in U.S. Pat. No. 6,207,738 assigned to Outlast Technologies, Inc. Air-permeable layer 35 also may be formed from multiple layers of material.

[0034] Generally, in each of the embodiments disclosed herein, thermal regulation can be enhanced by 1) the cellular construction of the foam body; 2) the airflow circulation generated by the structures of the components of the body support system; 3) the large heat capacity of the elastomeric layer; 4) the thermal conductive properties of the materials selected; and 5) the use of phase-change materials.

[0035] The body support system of the instant invention thus allows convective heat transfer to occur along with, or in lieu of, conductive, evaporative, and radiative heat transfer processes such as occur with prior art devices. The favorable thermal properties are further achieved by pressure air circulation mechanisms as a result of deformation of vertical columns 15. Advantageously, this air circulation is achieved without air flow valves or fans, and without externally powered air pumps.

[0036] FIG. 4 illustrates an alternative embodiment of a seat cushion of the instant invention. Seat cushion 110 comprises foam body 112. Foam body 112 can be formed of materials typically used in such seat cushions, such as open-celled or closed-celled polyurethane foam. Foam body 112 has an upper surface 113 and a plurality of vertical columns 115 disposed substantially centrally in said foam body 112 such that the top surface of said columns 115 define a curved surface substantially parallel to that of upper surface 113. In the embodiment illustrated in FIG. 4, the columns 115 are formed integrally with foam body 112. The foam material of which foam body 112 is made will be resiliently deformable to some extent. The columns 115 are structured such that each column 115 is capable of deflecting substantially independently of the other columns 115 in response to compressive forces applied by a user.

[0037] Vertical columns 115 are structured so as to define a plurality of air spaces 116 therebetween, which together define a plenum or air reservoir 118. A plurality of channels 120 are disposed within foam body 112, and extend from air reservoir 118 toward the periphery of foam body 112.

[0038] The seat cushion 110 further comprises an elastomeric layer 130 that overlays the vertical columns 115. In the illustrated embodiment, the periphery 131 of elastomeric layer 130 is seated within fitting edge 114 at the upper surface 113 of foam body 112. Elastomeric layer 130 comprises a top surface 132 and a bottom surface 134. Bottom surface 134 of elastomeric layer 130 defines the top surface of air reservoir 118. Elastomeric layer 130 comprises a material having significant resilience and flow properties. Suitable materials for elastomeric layer 130 include, for example, a gelatinous sheet and a polymeric membrane, or other gelatinous materials with variable viscoelastic properties. Elastomeric layer 130 and vertical columns 115 are each characterized by both an elastic stiffness value and a dissipative stiffness value. In a preferred embodiment of the invention, the ratio of elastic stiffness to dissipative stiffness of the columns 115 is greater than the ratio of elastic stiffness to dissipative stiffness of the elastomeric layer 130. Elastomeric layer 130 will function in a manner analogous to that of elastomeric layer 30 in the embodiment of FIGS. 1-3.

[0039] The embodiment of FIG. 4 further comprises seat pan 125 and air-permeable layer 135, the structures and functions of which are analogous to those of seat pan 25 and air-permeable layer 35 in the embodiment illustrated in FIGS. 1-3.

[0040] The embodiment of FIG. 4 is characterized by modular insert 142 having vertical columns 145. Modular insert 142 has a perimeter 141 that will be sized and shaped to fit within a seating edge 144 formed in foam body 112. Modular insert 142 can be made of the same material as foam body 112, or modular insert 142 can be made of a material wherein the ratio of elastic stiffness to dissipative stiffness is greater than or less than that of the material of which foam body 112 is made. Further, the size and shape of columns 145 can be the same as or different from the size and shape of columns 115. The choice of materials to be used in the manufacture of modular insert 142, and the design of the size and shape of columns 145, permit the seating designer to select from a variety of mechanical and thermal properties for the seat cushion 110 of the instant invention.

[0041] FIG. 5 illustrates yet another embodiment of a seat cushion made in accordance with the instant invention. Seat cushion 210 comprises foam body 212. Foam body 212 can be formed of materials typically used in such seat cushions, such as open-celled or closed-celled polyurethane foam. Foam body 212 has an upper surface 213 and a plurality of vertical columns 2115 disposed substantially centrally in said foam body 212 such that the top surface of said columns 215 define a curved surface substantially parallel to upper surface 213. In the embodiment illustrated in FIG. 5, the columns 215 are formed integrally with foam body 212. The foam material of which foam body 212 is made will be resiliently deformable to some extent. The columns 215 are structured such that each column 215 is capable of deflecting substantially independently of the other columns 215 in response to compressive forces applied by a user.

[0042] Vertical columns 215 are structured so as to define a plurality of air spaces 216 therebetween, which together define a plenum or air reservoir 218. A plurality of channels 220 disposed within top surface 213 of foam body 212 extend from air reservoir 218 toward the periphery of foam body 212.

[0043] The seat cushion 210 further comprises an elastomeric layer 230 that overlays the vertical columns 215. Elastomeric layer 230 comprises a top surface 232 and a bottom surface 234. Bottom surface 234 of elastomeric layer 230 defines the top surface of air reservoir 218. Elastomeric layer 230 comprises a material having significant resilience and flow properties. Suitable materials for elastomeric layer 230 include, for example, a gelatinous sheet and a polymeric membrane, or other gelatinous materials with variable viscoelastic properties. Elastomeric layer 230 and upwardly extending risers are each characterized by both an elastic stiffness value and a dissipative stiffness value. In a preferred embodiment of the invention, the ratio of elastic stiffness to dissipative stiffness of the columns 215 is greater than the ratio of elastic stiffness to dissipative stiffness of the elastomeric layer 230.

[0044] The embodiment of FIG. 5 further includes periphery edge component 250 designed to fit within fitting edge 214 of foam body 212, which edge surrounds the region of foam body 212 where vertical columns 215 are formed. In this embodiment, elastomeric layer 230 is also sized and shaped to fit within periphery edge component 250. Periphery edge component 250 thus serves to securely locate elastomeric layer 230 directly over vertical columns 215, thereby assuring that compressive and shear forces transmitted by a user through elastomeric layer 230 will be transmitted to upwardly extending risers 215. In addition, periphery edge component 250 helps to define air reservoir 218, and can function as an airflow diffuser. Periphery edge component 250 can be made of materials such as open-cell polyurethane or non-woven synthetic material. Periphery edge component 250 can also be used in those embodiments of the invention that employ modular insert 142 illustrated in FIG. 4.

[0045] In each of the embodiments of the instant invention described above, the airflow resulting from the structural design and choices of materials for each of the component parts results in two important effects. First, the airflow contributes to the thermal regulation function at the user/seat cushion interface through convection. Second, the airflow provides important mechanical effects, in that the airflow pumping generates a delay in the cushion responses of deformation and recovery due to loading and unloading of the user's weight. The modular construction of the seat cushion allows the seating designer to choose materials and designs for each of the component parts that will provide both the thermal properties and the mechanical properties desired for a particular application. Thus the seat cushion of the instant invention is adaptable to a wide variety of uses. For example, the seat cushion can be designed for static uses, such as office seating, or for rehabilitative seating such as wheelchairs, or for dynamic uses in which damping of vibrations is an important feature, such as trucks, public transportation seating, farm implements, construction trucks, forklifts, and snowplows.

[0046] In yet another embodiment, the fluid in reservoir 18 and channels 20 need not be air, but can be some other fluid such as electrically induce polymer gels, or electro-rheological fluids that change between solid and liquid phase and/or change colors in response to a stress-generated electric field in the fluid. Electric fields in the fluid also can be generated by piezo electric elements at the vertical columns.

[0047] There have been disclosed several embodiments of a body support system having improved mechanical response characteristics and improved thermal regulation. Those skilled in the art will recognize that other embodiments can be made using obvious variations of the disclosed embodiments, and such variations are intended to be within the scope of the claims appended hereto.