Abstract:
An inflatable mat includes a compressible inner mat and an airtight shell. One or more heating elements are embedded within the compressible inner mat. Embedding the heating elements within the mat includes removing sections of the inner mat, splitting the sections into upper and lower pieces, inserting the heating elements between the pieces, replacing the section and heating elements to the inner mat, and bonding the airtight shell to the inner mat. Wires embedded in the inner mat conduct electricity from an external power source to the heating elements. The wires may extend primarily around the edges of the inner mat and penetrate into the inner portions of the mat proximate the heating elements. A thermostatic switch and a timer may be interposed between the heating elements and the external power source to control current passing through the heating elements.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates generally to inflatable sleeping mats and, more specifically, to apparatus and methods for heating inflatable sleeping mats. 
       BACKGROUND OF THE INVENTION 
       [0002]    Sleeping mats are critical to the comfort of any backpacker or camper. A sleeping mat provides the user both padding and insulation from the ground. One popular form of sleeping mat includes a foam pad surrounded by an inflatable, wear-resistant outer shell. The foam pad is compressible, enabling air to be driven out of the outer shell and foam to minimize the volume occupied by the mat when packed. Upon inflation, the foam elastically expands the outer shell, drawing in air to facilitate inflation of the mat. 
         [0003]    However, during use of such mats, the shoulders and upper back of the user often create pressure points on the mat, compressing the foam pad into a very thin layer. Accordingly, the insulating properties of the mat at such pressure points are very much reduced. Heat from the user&#39;s body will therefore tend to escape through these pressure points, resulting in discomfort in these areas. Furthermore, the torso, including the shoulders and upper back, stores much of the thermal energy of the body and supplies thermal energy to the extremities. Accordingly, loss of heat from such areas is likely to result in discomfort at the extremities as well. 
         [0004]    Furthermore, the mats are typically made very thin. Backpackers who use such mats typically wish to minimize weight and are willing to sacrifice some of the thickness of the mat to do so. However, reducing the thickness further reduces the insulative properties of the mat. 
         [0005]    In view of the foregoing, it would be an advancement in the art to provide an apparatus maintaining the comfort of an user of inflatable foam-core sleeping mats near such pressure points at the upper back and shoulders and at the extremities. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention comprises a system for heating an inflatable sleeping mat. The mat includes a compressible inner mat and an airtight shell bonded to the inner mat. One or more heating elements embed within the inner mat in the torso or foot regions of the inner mat. One method for embedding heating elements within the mat includes removing a section of the inner mat slightly larger than the heating element. The section is split horizontally into upper and lower pieces. The heating element is placed between the upper and lower pieces and then the upper and lower pieces are returned to the inner mat. The shell is then bonded to the inner mat and retains the section in place. 
         [0007]    Wires conduct electricity from an internal or external power source to the heating elements. The wires extend primarily around the edges of the inner mat and penetrate into the inner portions of the mat proximate the heating elements. A horizontal slit may be formed at the edges of the inner mat to receive the wires. Where the wires penetrate the inner portions of the mat, they may pass through holes drilled or otherwise formed in the inner mat. 
         [0008]    A thermostatic switch is interposed between the external power source and the heating elements. The thermostatic switch is configured to close when the ambient temperature is below a low threshold and to open when it is above a high threshold. A timer may also be interposed between the external power source and the heating elements. The timer alternately opens and closes in a periodic manner allowing current to pass to the heating elements in short pulses. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Preferred and alternative embodiments of the present invention are described in detail below with reference to the following drawings. 
           [0010]      FIG. 1  is top view of a heated sleeping mat, in accordance with the present invention; 
           [0011]      FIG. 2  is a side sectional view of a wire path formed at the edge of the inner mat, in accordance with the present invention; 
           [0012]      FIG. 3  is a side sectional view of a wire path through a foam inner mat, in accordance with the present invention; 
           [0013]      FIG. 4  is an exploded view of a portion of the heated sleeping mat, in accordance with the present invention; 
           [0014]      FIG. 5  is a perspective view of a jack for a plug secured to a heated sleeping mat, in accordance with the present invention; 
           [0015]      FIG. 6  is a perspective view of the jack and an integrated thermostat prior to insertion into the heated sleeping mat, in accordance with the present invention; 
           [0016]      FIG. 7  is a top view of a heating element, in accordance with the present invention; 
           [0017]      FIG. 8  is a top view of a heating element packaged for insertion into a heated sleeping mat, in accordance with the present invention; and 
           [0018]      FIG. 9  is a schematic representation of the electrical components of a heated sleeping mat, in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0019]    Referring to  FIG. 1 , a sleeping mat  10  may include an inner mat  12  and a shell  14 . The inner mat  12  is typically formed of a readily compressible foam material. Typically, an open cell foam will be used to permit air to be driven out of the inner mat  12 . The inner mat  12  may include a head region  16 , torso region  18 , and a foot region  20  corresponding approximately to the location of the head, torso, and feet, respectively, of a user reclining on the mat  10 . In some embodiments, the inner mat  12  may have meshed regions  22 . Meshed regions may be formed at the time the material constituting the mat  12  was formed into sheets, or may be the result of a cutting operation. Meshed regions  22  serve to reduce the weight of the inner mat  12 , while still providing an elastic structure for inflating the sleeping mat  10  as discussed below. 
         [0020]    The shell  14  typically conforms to the shape of the inner mat  12  and may be bonded to the outer surfaces of the inner mat  12 . The shell  14  is typically formed of an airtight material and has an outermost surface that is wear resistant. In some embodiments, the shell  14  is formed of multiple layers, such as an airtight inner layer and a wear resistant outer layer. In the illustrated embodiment, the wear resistant outer layer is formed of nylon, such as a rip-stop nylon commonly used in products made for outdoor use. 
         [0021]    A valve  24  secures to the shell  14 , typically near the head region  16 , and is openable and closable by a user in order to inflate and deflate the sleeping mat  10 . In operation, as a user opens the valve  24  the foam forming the inner mat  12  expands, drawing air into the shell  14 . A user may further inflate the shell  14  by use of the lungs or a pump. When the proper degree of inflation is reached the user then closes the valve  24 . To deflate the sleeping mat  10 , the user opens the valve  24  and compresses the inner mat  12  by rolling it tightly, thus forcing the air out of the valve  24 . When the sleeping mat  10  is sufficiently deflated, the valve  24  is closed. 
         [0022]    In one embodiment of the present invention, one or more heating elements  26   a - 26   c  are positioned within the shell  14 . Heating elements  26   a ,  26   b  are typically positioned in the torso region  18 . Positioning in the torso region  18  may be advantageous due to the role of the torso in regulating body temperature. Warm blood from the torso is carried to extremities and cooler blood from the extremities return to the torso to be heated. Accordingly, locating the heating elements  26   a ,  26   b  in the torso region  18  permits them to indirectly warm the extremities. Furthermore, pressure points from the back and upper shoulders typically occur within the torso region  18 , compressing the inner mat  12  and reducing its insulating properties. Accordingly, positioning the heating elements  26   a ,  26   b  within the torso region  18  serves to counteract this effect. 
         [0023]    In some embodiments, a heating element  26   c  may also be positioned in the foot region  20 . Inasmuch as the feet are a large distance from the torso, they are susceptible to becoming cold. Accordingly, many users may benefit from positioning the heating element  26   c  proximate the feet. 
         [0024]    In some embodiments, the inner mat  12  is meshed to reduce its weight. However, in the illustrated embodiment, unmeshed regions  28   a - 28   c  surround the heating elements  26   a - 26   c . The unmeshed regions  28   a - 28   c  may serve as a sturdy substructure, which the heating elements  26   a - 26   c  may mount in or on. Unmeshed portions may also be more resistant to compression and therefore provide increased support at pressure points. An additional unmeshed region  30  may be provided in the torso region  18 . The unmeshed region  30  may provide material through which cables carrying power to the heating elements  26   a ,  26   b  may pass. The unmeshed region  30  may also serve to resist compression of the inner mat  12 . 
         [0025]    Cables  32   a - 32   c  connect the heating elements  26   a - 26   c  to an interface  34 . The interface  34  pierces the shell  14  and provides a connection point for an exterior power source, such as a battery to connect to the heating elements  26   a -  26   c . The interface  34  may be a socket receiving a plug or a plug for insertion into a socket. In the illustrated embodiment, the interface  34  is flush with, or extends only slightly, from the shell  14 . In others, the interface  34  is a wire that extends a substantial distance from the shell  14  and has a plug or socket secured to the end thereof. 
         [0026]    In some embodiments, the power source may be an internal battery. Accordingly, the interface  34  may provide an electrical connection for charging the internal battery. In some embodiments, the internal battery is charged by a flexible solar cell secured to the shell  14  or forming part of the shell  14 . Accordingly, in such embodiments, an interface  34  may be unnecessary. 
         [0027]    Each cable  32   a - 32   c  typically includes at least a positive and a negative wire. The cables  32   a - 32   c  extend around the edge of the sleeping mat  10  and extend into the more central portions of the sleeping mat  10  near the heating elements  26   a - 26   c . The illustrated arrangement of the cables  32   a - 32   c  and wires  58  within the inner mat  12  is exemplary. Various other arrangements are possible. For example, the cables  32   a - 32   c  may extend down the same edge of the inner mat  12  or opposite edges. The wires forming the cables  32   a - 32   c  may be bound in a common sheath or be separate but follow the same path. Inasmuch as the manufacture of the sleeping mat  10  may expose the cables  32   a - 32   c  to high temperatures, the sheathing of the wires constituting the cables  32   a - 32   c  may be made of silicone or other heat resistant materials. 
         [0028]    Referring to  FIG. 2 , the cables  32   a - 32   c  may extend through slits  36  formed at the edges of the inner mat  12 . In some embodiments, the inner mat  12  has meshed regions to reduce the weight of the sleeping mat  10 . However, the inner mat  12  may have unmeshed regions proximate the edges. Unmeshed edge regions may facilitate formation of a slit  36  therein to receive the cables  28   a - 28   c.    
         [0029]    Referring to  FIG. 3 , the cables  32   a - 32   c  may extend from near the edges of the inner mat  12  toward the heating elements  26   a - 26   c  through apertures  38  extending through the inner mat  12 . The apertures  38  may be formed by drilling or like means. Alternatively, the apertures  38  may be embodied as slits  38  cut through the inner mat  12 . The slits  38  may extend through the inner mat  12  without breaking the upper or lower surface of the inner mat  12  or may be formed by cutting the upper or lower surface of the inner mat  12 . The portions of the inner mat  12  in which the apertures  38 , or slits  38 , are formed may be unmeshed, such as unmeshed regions  28   a ,  28   b , and  30 . 
         [0030]    Referring to  FIG. 4 , while still referring to  FIG. 3 , the heating elements  26   a - 26   c  may be embedded within the inner mat  12 . In the illustrated embodiment, a section of the inner mat  12  having a size somewhat larger than one of the heating elements  26   a - 26   c  is removed from the inner mat  12  for each heating element  26   a - 26   c , leaving an aperture  40  in the inner mat  12 . The removed sections are divided in the horizontal plane into two pieces  42 ,  44 . The pieces  42 ,  44  may have different thicknesses  46 ,  48 . The piece  42  may have a thinner thickness  46  to promote conduction of heat therethrough to a user. The piece  44  may have a greater thickness  48  to discourage heat loss to the ground. 
         [0031]    In an alternative embodiment, the pieces  42 ,  44  may be formed of a different material cut to fit within the aperture  40  in the inner mat  12 . For example, the piece  42  may be made of a material that is readily compressible or that readily conducts heat, promoting conduction of heat from the heating element  26   a - 26   c  to the user. The piece  44  may be made of a material that does not conduct heat readily or that is not readily compressible to discourage heat loss to the ground. In some embodiments, additional layers may be positioned between the piece  44  and the shell  14  or between the heating element  26   a - 26   c  and the piece  44  to discourage heat loss. For example, a layer of reflective material may be used to discourage radiated heat loss to the ground. 
         [0032]    The heating element  26   a - 26   c  may be positioned between the pieces  42 ,  44 , which are then placed within the aperture  40 . A cable  32   a - 32   c  may be passed through an aperture  38  formed in the inner mat  12  to the heating element  26   a - 26   c  and secured thereto. Alternatively, a cable  32   a - 32   c  may be first secured to the heating element  26   a - 26   c  and then passed through the aperture  38 , or slit  38 . 
         [0033]    The shell  14  may then be bonded to the inner mat  12 . In some embodiments, bonding the shell  14  to the inner mat  12  requires the application of heat. The application of heat may cause the pieces  42 ,  44  to bond to the surrounding mat  12  as well as to the shell  14 . In other embodiments, the pieces  42 ,  44  may be adhered to the surrounding inner mat  12  by means of adhesive or heat applied directly to the pieces  42 ,  44  and inner mat  12 . In still other embodiments, the bonding of the shell  14  to the inner mat  12  serves to retain the pieces  42 ,  44  within the aperture  40 . 
         [0034]    Referring to  FIGS. 5 and 6 , the interface  34  may be embodied as a socket  50  having an aperture  52  for receiving a plug electrically coupled to a battery. The socket  50  may be sized to insert into an aperture  54  formed near the head region  16 . The aperture  54  may be formed in a rigid block  56  secured to the shell  14 . In the illustrated embodiment, the block  56  is formed of molded urethane. The socket  50  has wires  58  extending therefrom, which couple to the cables  32   a - 32   c . Alternatively, the cables  32   a - 32   c  may couple directly to the socket  50 . The wires  58  or cables  32   a - 32   c  may secure to the socket  50  before or after the socket  50  is inserted within the aperture  54 . In one method of making the sleeping mat  10 , the socket  50  secures to the block  56  and wires  58  or cables  32   a - 32   c  before the shell  14  is bonded to the inner mat  12 . In another method, wires  58  or cables  32   a - 32   c  are accessible through the aperture  54  and secure to the socket  50  after the shell  14  has been bonded to the inner mat  12 . 
         [0035]    In some embodiments, a thermostatic switch  60  is secured to the socket  50 . For example, the thermostatic switch  60  may be surrounded by molded plastic, which also surrounds portions of the socket  50 . Alternatively, the thermostatic switch  60  may be interposed in the conducting path of one of the wires  58  and not secure directly to the socket  50 . The thermostatic switch may be designed to close when the ambient temperature is below a certain threshold and to open when the ambient temperature is above a certain threshold. In one embodiment, the low threshold is 20 degrees centigrade and the upper threshold is 25 degrees centigrade. 
         [0036]    Referring to  FIG. 7 , the heating elements  26   a - 26   c  may be embodied as one or more metallic strips  62  having a positive end  64  and a negative end  66  secured to the positive wire  68  and negative wire  70  of one of the cables  32   a - 32   c  by means of solder or other fastening means providing electrical conductivity between the ends  64 ,  66  and the wires  68 ,  70 . The denotation as positive or negative applied to the ends  64 ,  66  and wires  68 ,  70  is exemplary; the positive and negative ends  64 ,  66  may be reversed without altering the function of the heating element  26   a - 26   c . The strips  62  may have alternating narrow portions  72  and wide portions  74  along their lengths. The narrow portions  72  have greater resistance and therefore generate heat as current is passed through the strips  62 . The wide portions  74  may serve to provide a large area radiating heat away from the heating element  26   a - 26   c . In the illustrated embodiment, the two metallic strips  62  constituting the heating elements  26   a ,  26   b  are designed to consume approximately 2.2 Watts, whereas the heating element  26   c  is designed to consume approximately one Watt. 
         [0037]    Referring to  FIG. 8 , the positive end  64  and negative end  66  of the metallic strips  62  may be bound by nonconductive material such as electrical tape  76 , or the like, to avoid electrical shock to a user. In some embodiments, the electrical tape  76  secures additional nonconductive material, such as rigid plastic plates over the point of attachment of the cables  32   a - 32   c  to the metallic strips  62 . Additional bands of material, such as electrical tape  72 , may surround the metallic strips  62  and wires  68 ,  70  at a location between the positive end  64  and negative end  66  to maintain the wires  68 ,  70  and metallic strips  62  in a parallel arrangement. Part or all of the metallic strips  62  may be covered by a sheath  78  formed of plastic or another nonconductive material. The electrical tape  76  may secure the sheath  78  to the metallic strips  62 . The wires  68  may also pass through the sheath  78 . 
         [0038]    Referring to  FIG. 9 , in the illustrated embodiment, the heating elements  26   a - 26   c  connect in parallel to a battery  80 . In some embodiments, a timer  82  is electrically interposed between the battery  80  and the heating elements  26   a - 26   c . The timer  82  may open and close a conduction path between the battery  80  and heating elements  26   a - 26   c  in periodic intervals of short duration when a voltage is applied thereto. For example, the timer  82  may repeatedly close for two seconds and then open for two seconds. The timer may be disposed near the battery  80 , thermostatic switch  60 , or at other points in the electrical paths from the battery  80  to the heating elements  26   a - 26   c . In the illustrated embodiment, the timer  82  secures to the battery  80  and is embodied as a bimetallic snap switch. 
         [0039]    The manner of connecting the heating elements  26   a - 26   c , thermostatic switch  60 , and timer  82  are exemplary. Many alternative arrangements of the heating elements  26   a - 26   c , thermostatic switch  60 , timer  82 , and connecting cables  32   a - 32   c  and wires  58  are possible. For example, the heating elements  26   a - 26   c , or two of the heating elements  26   a - 26   c  may connect in series. Separate thermostatic switches  60  may control current flowing to each heating element  26   a - 26   c . Likewise, separate timers  82  may also control current flowing to each heating element  26   a - 26   c.    
         [0040]    While the preferred embodiment of the invention has been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. Accordingly, the scope of the invention is not limited by the disclosure of the preferred embodiment. Instead, the invention should be determined entirely by reference to the claims that follow.