Abstract:
A heating pad system comprises a pad formed of layers of flexible material, a heating element applied to or embedded within a layer of the pad and including conductive yarn, a temperature sensor associated with the pad to generate a temperature signal indicative of a temperature of the pad, and a battery-powered control module removably connected to the heating element and the temperature sensor. The control module is operable to supply current to the heating element to generate heat, wherein the current supplied to the heating element is regulated in response to the temperature signal from the temperature sensor to maintain the pad at a substantially constant temperature. The pad layers, heating element, and temperature sensor are machine-washable as a unit. The pad may be worn under an orthopedic or athletic brace.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to heating pads for applying heat to muscles and joints to relieve pain and promote healing, and more particularly to heating pads usable with orthopedic braces and similar devices. 
       BACKGROUND OF THE INVENTION 
       [0002]    It is known to relieve pain and/or promote healing by localized application of heat to an effected area of the body, such as a joint or muscle group. Chemical or microwavable gel pads are available which provide heat to an application area, however the heat generation and transfer dissipates quickly. 
         [0003]    Electric heating pads are available which provide constant heat for a more extended period of time. Typically, such electric heating pads plug into a standard AC outlet power source and include a removable cover that is machine-washable separately from the rest of the pad. Thus, the user must remain near a power outlet during treatment, and internal portions of the pad which may be exposed to perspiration or other contaminants are not machine-washable. Moreover, conventional electric heating pads are not intended to be used with an orthopedic or athletic brace that may be recommended for treatment, and thus the brace must be removed while heat is applied. 
       SUMMARY OF THE INVENTION 
       [0004]    It is therefore the object of the present invention to provide a heating pad system that maintains constant heat transfer, is readily transportable, and has a machine-washable pad. 
         [0005]    It is another object of the present invention to provide a heating pad system that may be used while the user is wearing an orthopedic or athletic brace. 
         [0006]    It is yet another object of the present invention to provide a heating element suitable for incorporation into a machine-washable heating pad. 
         [0007]    In furtherance of these and other objects, a heating pad system is described that comprises a pad including a plurality of layers formed of flexible material; a heating element applied to or embedded within one of the layers, the heating element including conductive yarn; a temperature sensor associated with the pad, the temperature sensor generating a temperature signal indicative of a temperature of the pad; a control module removably connected to the heating element and the temperature sensor, the control module being operable to supply current to the heating element to generate heat, wherein the current supplied to the heating element is regulated in response to the temperature signal to maintain the pad at a substantially constant temperature; wherein the pad, heating element, and temperature sensor are machine-washable as a unit. 
         [0008]    The invention also provides a machine-washable electric heating pad comprising an inner layer, an outer layer, and a middle layer between the inner and outer layers; and a heating element fixed to the middle layer, the heating element including conductive yarn. 
         [0009]    As a further aspect of the present invention, a heating element for a machine-washable heating pad is described. The heating element comprises a plurality of parallel nonconductive warp threads; a nonconductive weft thread interlaced with the plurality of warp threads; and at least one conductive weft thread interlaced about one of the plurality of nonconductive warp threads. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The nature and mode of operation of the present invention will now be more fully described in the following detailed description of the invention taken with the accompanying drawing figures, in which: 
           [0011]      FIG. 1  is a perspective view of a heating pad system formed in accordance with an embodiment of the present invention; 
           [0012]      FIG. 2  is an exploded isometric view of a heating pad of the heating pad system shown in  FIG. 1 ; 
           [0013]      FIG. 3  is an enlarged plan view showing a woven tape heating element of the heating pad shown in  FIG. 2 ; and 
           [0014]      FIG. 4  is a schematic block diagram showing electrical circuitry of the heating pad system of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    Reference is made initially to  FIG. 1 , wherein a heating pad system formed in accordance with an embodiment of the present invention is shown and designated generally by reference numeral  10 . Heating pad system  10  is intended for use with an orthopedic brace (not shown) to apply heat to a joint or other area of a user&#39;s body to ease pain, promote healing, and improve flexibility. Heating pad system  10  generally comprises a heating pad  12  adapted to be worn against the skin and held in place by a surrounding orthopedic brace, for example a knee brace or an elbow brace, and a control module  14  connected to heating pad  12  by an electrical cord  16  for energizing heating pad  12 . Electrical cord  16  may be provided with a plug connection element  17  at one or both ends thereof, with a mating receptacle being provided in control module  14  and/or at pad  12 . The size and shape of heating pad  12  are open to variation depending upon the size of the user and the intended area of application on the user&#39;s body. Pad  12  depicted in  FIG. 1  is shaped to be a knee pad, and includes a patella hole  18 . 
         [0016]    As shown in  FIG. 2 , heating pad  12  includes an outer fabric layer  20  for removable attachment to a brace, an inner fabric layer  22  for contacting the skin of a user, and a middle fabric layer  24  situated between outer layer  20  and inner layer  22 . 
         [0017]    Outer layer  20  may be made from polyester felt or other suitable fabric, and may be adapted for releasable attachment to an overlying brace by the provision of a plurality of micro-hook (i.e. VELCRO®) strips  26  sewn on an outwardly facing surface of outer layer  20  for engaging fabric on the brace. Outer layer  20  acts as an insulating layer to inhibit heat loss through the brace and keep most of the heat transfer in the direction of the user. A 100% polyester felt fabric is effective for this purpose, however other fabrics may be used. 
         [0018]    Inner layer  22  contacts the user&#39;s skin. Therefore, the material for inner layer  22  may be selected to wick moisture away from the skin to prevent build up of perspiration and help keep the skin dry and comfortable. A nylon-LYCRA® blend fabric is suitable for this purpose, however other fabric materials may be substituted. 
         [0019]    Pad  12  further includes a conductive heating element  28 , described below. Middle layer  24  serves as a substrate for conductive heating element  28 . Polyester woven fabric is suitable for making middle layer  24 , however other fabrics may be used. 
         [0020]    Heating element  28  of the present embodiment is shown in detail in  FIG. 3 . Heating element  24  may be formed as a flexible tape woven from polyester filament yarn and conductive yarn. In the depicted embodiment, the tape is about twelve millimeters wide and includes eleven nonconductive, generally-parallel warp threads  30  and one nonconductive weft thread  32  interlaced back and forth across all eleven warp threads  30 . As mentioned, the nonconductive threads may be made of polyester filament yarn. A suitable linear mass density of the polyester filament yarn is 150 Denier, however yarns of other densities may also be suitable. Heating element  28  also includes at least one conductive thread for generating resistive heat when current is applied. As shown in the embodiment of  FIG. 3 , two conductive yarn weft threads  34  are interlaced about the fourth and eighth nonconductive warp threads, respectively, to run the length of heating element  28 . A suitable conductive yarn for forming conductive threads  34  is BEKINOX® continuous stainless steel filament yarn, Type VN 14/1x90/200Z/316 L/HT, sold by NV Bekaert SA. By forming heating element  28  in this manner, the conductive threads  34  are supported so that they will be less apt to break or splinter, and heating element  28  may be sewn onto middle layer  24  by an attachment thread that engages only nonconductive threads of the heating element. Sewing is a preferred method of fixing heating element  28  to middle layer  24 , however other methods may be used, including adhesives, staples, and the like. 
         [0021]    In the present embodiment, heating element  28  is arranged in spiral fashion around patella hole  18  on the side of middle layer  24  facing inner layer  22 , and a terminal end of the heating element is wrapped around onto the opposite side of middle layer  24 . Terminal ends of conductive threads  34  are crimped and connected by electrical cord  16  to control module  14 . A lead opening  36  may be provided through outer layer  20  via which electrical cord  16  may be connected to the conductive threads  34  of heating element  28 . 
         [0022]    Pad  12  also includes a temperature sensor  38  attached, such as by sewing, onto heating element  28  and/or middle layer  24 . The DS18S20 High-Precision 1-WIRE® digital thermometer from Dallas Semiconductor/Maxim is suitable as temperature sensor  38 . A conformal coating, such as HUMISEAL® or CRC Acryform, is applied to temperature sensor  38  to protect it from moisture. An electrical lead (not shown) to temperature sensor  38  may be bundled in electrical cord  16 . 
         [0023]    Reference is also made now to  FIG. 4 , which provides a schematic diagram of the electrical components of heating pad system  10 . A DC power source  40  supplies power to control module  14 , heating element  28 , and temperature sensor  38 . For sake of the present embodiment, power source  40  may be a 6 Volt/4.2 Amp-Hour battery pack, for example a POWERIZER® 6V4200 mAh Ni-MH rechargeable battery, available from www.batteryspace.com under number RA-H43AF5R1TB. A 6V to 30V DC-DC converter  42  connected to power source  40  provides sufficient voltage to energize heating element  28  via a switch/relay  44 . A 6V to 5V voltage regulator  46  connected to power source  40  provides operating power to a microcontroller  48 , switch/relay  44 , and temperature sensor  38 . A Philips Semiconductor P89C669 eight-bit microcontroller with extended memory may be used as microcontroller  48 , however other microcontrollers may be substituted without straying from the invention. A control panel  50  on control module  14  provides an on/off switch and temperature selector, and may also include an LED indicator  51 , preferably a red LED, for signaling that power source  40  is low on charge and in need of recharging. Another LED indicator (not shown), such as a green LED, may be provided to indicate that module  14  is powered on. In the embodiment described at present, the temperature selector is a three-position selector providing low, medium, and high temperature settings. Those skilled in the art will realize that fewer or more than three discrete temperature settings may be provided, or a continuously variable temperature selector (for example a dial or slider) may be provided. Microcontroller  48  receives a temperature setting from control panel  50  and a temperature reading from temperature sensor  38 , and operates switch/relay  44  as needed to maintain a predetermined temperature corresponding to the selected temperature setting. By way of example, a low temperature setting may correspond to 40° C., a medium temperature setting may correspond to 42° C., and a high temperature setting may correspond to 45° C. 
         [0024]    In the present embodiment, heating element  28  should impose a resistance of at least ninety ohms to produce sufficient heat. Also, it is advantageous (but not a strict requirement) that the conductive threads  34  be spaced within five to seven millimeters of one another to provide a uniform heat distribution. Consequently, a heating element length of 2.4 meters may be used with two conductive threads  34  in parallel in the disclosed embodiment. 
         [0025]    Heating pad system  10  may be fabricated and assembled in the following manner. Outer layer  20 , inner layer  22 , and middle layer  24  are cut to size. The coated temperature sensor  38  is sewn onto heating element  28 , and the heating element  28  is arranged on middle layer  24  in a spiral pattern about patella hole  18  and sewn to the middle layer (a terminal end of the heating element is left unattached and is wrapped around to the opposite side of the middle layer as shown in  FIG. 2 ). The terminal end of heating element  28  is crimped, and conductive threads  34  and temperature sensor  38  are connected to lead wires extending through electrical cord  16 . Inner layer  22  is arranged to cover heating element  28 , thereby ensuring that the conductive threads  34  face inward toward the user&#39;s skin. The outer layer is placed on the opposite side of middle layer  24  with micro-hook strips  26  facing away from middle layer  24 , and the wiring is passed through lead opening  36  in outer layer  20 . The layers  20 ,  22 , and  24  are then sewn to one another by embroidery stitches  21  and  23  along the peripheral edges of pad  12  and patella hole  18 , respectively. Electrical cord  16  may then be connected to control module  14 . 
         [0026]    Heating pad system  10  is used by placing heating pad  12  in contact with the body area to be treated, and donning a brace over the pad such that micro-hook strips  26  affix to fabric on the brace, whereby heating pad  12  is held in place. Control panel  50  is used to turn control module  14  on and select a temperature setting. It is contemplated to provide braces designed to hold control module  14 , such as by hook-and-loop fastening strips or a fitted pocket, while heating pad system  10  is in use. As mentioned above, pad  12  is machine-washable between uses. Electrical cord  16  is disconnected from control module  14  prior to washing heating pad  12 , and may be left connected to the pad during washing or may be disconnected from the pad if a plug connection is provided at the pad. 
         [0027]    While the invention has been described in connection with an exemplary embodiment, the detailed description is not intended to limit the scope of the invention to the particular forms set forth. The invention is intended to cover such alternatives, modifications, and equivalents of the described embodiment as may be included within the spirit and scope of the invention.