Abstract:
An apparatus, system and method for warming food by controlled heating of heat retention objects such as cookware items or pellets located on a trivet positioned on a countertop, using heating control units, such as induction heating units, remotely located beneath the countertop. The preferred trivet insulates the countertop against damages, and also includes circuitry enabling the indication or display of its proper positioning on the countertop, and also indicating whether the heating unit is heating the heat retention object.

Description:
BACKGROUND OF THE INVENTION 
     U.S. Ser. No. 11/750,571, filed May 18, 2007, titled “Detachable Tag-Based Temperature Sensor For Use In Heating Of Food And Cookware,” assigned to the present assignee, is hereby incorporated by reference in its entirety into this patent application. 
     The present invention generally relates to devices used to heat the contents of cookware such as dishes, buffet trays and the like. More particularly, the invention relates to a heating device and system, such as for induction heating of objects such as cookware or food containers through stone or other materials on which cookware may be placed. 
     Various methods are known for heating cookware and food containers. As one example, radio-frequency identification (RFID) tagging systems have been used to activate and control magnetic induction heating systems for use in heating foods and associated food containers, cookware and warming/heat retention objects. Use of such systems allows objects not physically connected to a magnetic induction heater to be heated and temperature-regulated using RFID technology. In such systems, an RFID tag having a temperature sensor are mounted within the item to be heated, such as cookware; an RFID reader is located within the magnetic induction heater unit. When the tagged object comes within the reading field of the RFID reader, the tag may be used to transmit information such as temperature and the class of object being heated, so that the heater control circuitry may use the information to commence an appropriate heating cycle for heating and temperature-regulating the object. Various such systems are available, including those disclosed in U.S. Pat. Nos. 6,025,725 to Gershenfeld et al., and 6,320,169 and 6,953,919 to Clothier, the entire disclosures of each of these three patents hereby being incorporated by reference herein. Use of this technology enables relatively precise heating and temperature regulation. 
     Other non-contact/indirect, remote control methods are known or may be devised. As non-limiting examples, remote controller devices used with televisions typically operate based on optical (infrared) communication. Non-contact modes of communication other than RFID may be used, likewise, for measuring the temperature of cookware and food containers, such as those involving communication via optical means, ultrasound, infrared, or other communication modes. 
     Induction heating of cookware may be accomplished by mounting the cookware on a range or countertop. Often, it may be desirable to hide the induction heating unit beneath a countertop made of stone (e.g., granite, man-made composites such as silestone, etc.) or other materials (e.g., formica, glass, wood, etc.), which may be typically about 3 centimeters thick, as a rough exemplary range of thickness. The countertop carries the cookware, which may be induction-heated by conveyance of magnetic field waves passing through the stone. Due to its combustive nature, the use of wood may not be desirable. Stone and composites present problems in this application, as market experience and the inventors&#39; own testing have shown that the substantial temperature variations involved in warming or heating of food containers or cookware tends to crack the stone or generate surface damage (mechanical and/or visual). 
     For warming food or liquid items held for serving, the U.S.D.A. sets 145° F. as a minimum holding temperature. Typically, because it is not desired to boil the food or liquid item, 180° F.-190° F. is the top range. The resulting temperature variations have proved problematic when using countertops made of stone or other materials due to cracking or surface damage issues. 
     Another problem encountered when using a stone, composite or other countertop covering an induction heating unit has been how to locate the cookware on the countertop so that it is properly positioned for heating activation within the radio tagging transmission area of the induction heating unit, as well as being optimally positioned for the induction heating process. Two factors complicate this problem. First, it may be desirable to have a “clean” countertop, devoid of markings, logos, designs, etc. Second, it may be desirable to have induction heater (e.g., buffet) units, for example, slidably mounted on tracks beneath the countertop, so that their location can change beneath the countertop. Accordingly, it would be advantageous to provide a way of indicating to the user when the cookware is properly located over the induction heating unit, and also to indicate whether the heating unit is currently heating the heat retention object. 
     Still another problem encountered in the industry of warming food items using cookware is how to control the temperature of the cookware remotely, using indirect heating. 
     It would also be advantageous to provide a cookware-warming device that may be used with any cookware, such that it need not be specially designed to have induction heating apparatus (e.g., an RFID tag) attached to it. 
     Accordingly, it would be advantageous to provide a cookware heating device and system that solves the problems recited above, while providing new advantages not currently available. 
     DEFINITION OF CLAIM TERMS 
     The following terms are used in the claims of the patent as filed and are intended to have their broadest meaning consistent with the requirements of law. Where alternative meanings are possible, the broadest meaning is intended. All words used in the claims are intended to be used in the normal, customary usage of grammar and the English language. 
     “Cookware” means cooking, serving or delivery containers for warming or heating food, including but not limited to dishes, pots, trays including buffet trays and warming trays, etc. 
     “Food” means any item or material which may be normally ingested by humans, including solid or liquid matter. 
     “Food container” means any container for warming food or for maintaining food in a warmed condition, such as but not limited to pizza delivery trays, food bags, etc. 
     “Heat retention object” means any object, such as cookware, pellets, or other objects, which may function to receive heat from indirect heating methods such as induction heating, and which may be used to heat or warm food or to maintain food in a generally heated or warmed condition. 
     “Indirect heater” or “indirect heating” or “indirect heating system” means a heater or method of heating, or system involving such heating, respectively, in which food contained by an item of cookware or other cooking, serving or delivery food container, is heated through conduction of heat from the cookware or container to the food. 
     “Reader” means a device capable of receiving information from a tag relevant to the heating of cookware of other cooking-, serving-, or delivery-related food containers, and of transmitting this information to heating controls associated with an indirect heater. 
     “RFID technology” means a tagging system including but not limited to a tag having information regarding an object, such as its temperature, humidity, volume or weight, and a reader in communication with the tag and with an appliance such as an induction heater separated by some distance from the tag. 
     “Tag” means a device possessing information relevant to the heating of cookware or other cooking-, serving- or delivery-related food containers, that is capable of transmitting sensor information such as but not limited to temperature, humidity, volume or weight to a reader associated with heating controls of an indirect heater, which communication may occur through the mode of RFID, optical, ultrasound, or other modes. 
     “Trivet” means an object located between cookware used to warm or heat food, on the one hand, and a countertop, range, table or other surface for supporting the cookware, on the other, and which is used as an insulator to protect the supporting surface from heat damage. A “trivet” within the meaning of this invention may but does not necessarily include an induction heating, sensing and/or communications device such as an RFID tag attached to it; alternatively, such a device may be attached to the cookware. In addition, a “trivet” within the meaning of this invention may but does not necessarily include circuitry communicating with the heater unit and/or user to indicate whether the trivet is properly positioned and whether the heater unit is currently heating the heat retention object. 
     SUMMARY OF THE INVENTION 
     The objects mentioned above, as well as other objects, are solved by the present invention, which overcomes disadvantages of prior tagging objects and systems used with heating devices for cooking and/or warming applications, while providing new advantages not previously obtainable with such tagging objects and systems. 
     In a preferred embodiment, an apparatus is provided for measuring and controlling the temperature of a heat retention object such as a food container, an item of cookware, a heat-retentive pellet, or another heat retention object, which may be used to warm or keep warm a food item. A trivet is provided in contact with the heat retention object. The trivet rests on a countertop, which may be made from one or more of the following materials: stone; composites; formica; glass; ceramic; or wood. The trivet acts as an insulator to limit the amount of heat transferring from the heat retention object through the trivet to the countertop. A tag may be associated with the heat retention object or, alternatively, with the trivet. The tag is capable of communication with a reader associated with a heating control unit located below the countertop, enabling controlled heating of the heat retention object or, alternatively, the trivet. Preferably, the trivet indicates when it is properly positioned on the countertop so as to allow proper heating of an object by the heating control unit; this may be accomplished using electronic circuitry powering a display such as an LED, which may also indicate whether the heating control unit is currently heating the heat retention unit. If the heating control unit is an induction heater, then RFID tags and RFID readers may be employed, and proper positioning of the trivet may entail locating the trivet within the magnetic field of the induction heater located beneath the countertop. 
     In order for the trivet to limit conducted and radiated heat from damaging the countertop, the trivet is preferably made of appropriate insulating materials and/or has a limited footprint in contact with the countertop and/or the heatable object. For this purpose, a preferred trivet may include channels or cavities on its lower portion in contact with the countertop; legs may also be employed. Pick-up and associated electronic circuitry may be located within these channels or cavities, as may tags and readers, for example. 
     In a preferred embodiment, a coupler mechanism may carry the tag. The coupler mechanism may be removably magnetically attached to the heat retention object. Alternatively, the coupler may be magnetically attached to the trivet; in this event, the trivet may be constructed of an upper, magnetic portion to which the coupler is removably attached, and a lower, insulating, non-magnetic portion. Alternatively, if the coupler is to be removably attached to a non-metallic portion of the heat retention object or trivet, double-sided adhesive tape may be used, for example. The preferred magnetic coupler may include a housing in which the tag is located, and a tongue portion having a temperature sensor. The tongue portion may be in abutting contact with the heat retention object when the magnetic coupler is magnetically coupled to it. An antenna may be used with the heating unit to facilitate communication between the tag and the reader; preferably, the coupler housing has a length sufficient to allow positioning of the tag within the housing at a location which is within a reception area of the antenna. 
     A system for measuring and controlling temperatures of heat retention objects, such as food containers, items of cookware, heat retentive pellets, or other heat retention objects, used to warm or to keep warm food also forms part of the present invention. A preferred embodiment of such a system includes a trivet supporting the heat retention object and resting on a countertop. The trivet insulates the countertop from heat generated in the heat retention object which may travel from the heat-generating source to the countertop. A tag may be associated with either the trivet or the heat retention object. A heater control unit is also provided, such as an induction heater, in communication with a reader capable of receiving information from the tag. This enables directly controlled heating of either the trivet or the heat retention object, depending on which is associated with the tag. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The novel features which are characteristic of the invention are set forth in the appended claims. The invention itself, however, together with further objects and attendant advantages thereof, will be best understood by reference to the following description taken in connection with the accompanying drawings, in which: 
         FIG. 1  is a side and top perspective view of a dish placed on a trivet, supported by stone covering an induction heating unit with a front display; 
         FIG. 2  is a side and top perspective view of a trivet according to the present invention; 
         FIG. 3  is a rear view of the trivet shown in  FIG. 2 ; 
         FIG. 4  is a schematic view of electrical components located in the trivet in one preferred embodiment of the invention; 
         FIG. 5  is a schematic view similar to  FIG. 4 , showing more detailed electrical circuitry in a preferred embodiment of the invention; 
         FIG. 6  is a schematic view of components present in a preferred embodiment of the invention; 
         FIGS. 7 and 8  are alternative embodiments of a trivet according to the present invention; and 
         FIG. 9  is a perspective view of one embodiment of a magnetic coupler, shown attached to a serving dish, for use in induction heating applications. 
     
    
    
     The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present invention. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Set forth below is a description of what are believed to be the preferred embodiments and/or best examples of the invention claimed. Future and present alternatives and modifications to this preferred embodiment are contemplated. Any alternatives or modifications which make insubstantial changes in function, in purpose, in structure, or in result are intended to be covered by the claims of this patent. 
     Referring to  FIG. 1 , in a preferred embodiment of the present invention, a suitable heater, such as magnetic induction heater unit  10 , may be employed to heat various heat retention objects, such as cookware, pellets, or other objects, which may function to receive heat from indirect heating methods such as induction heating, and which may be used to heat or warm food or to maintain food in a generally heated or warmed condition. In a preferred embodiment, a cookware item such as serving dish  25 , used for warming food within the dish, whether for delivery or to be served, may be used and may be located on a countertop  20 . Alternatively, a food container (not shown) may be used. Alternatively, a heat retentive pellet of the type disclosed in U.S. Pat. No. 6,232,585 titled “Temperature Self-Regulating Food Delivery System” (see “pellet 86,” for example), incorporated herein by reference, may be used with or instead of a cookware item. Alternatively, a pellet or other heat retention object may be employed with other food delivery or food transportation items (e.g., pizza delivery bags, etc.) for use with the present invention. 
     Magnetic induction heater  10  may be of the type described in pending U.S. Ser. No. 11/750,571, as well as U.S. Pat. Nos. 6,025,725 to Gershenfeld et al., and 6,320,169 and 6,953,919 to Clothier, each of which are incorporated herein by reference. Of course, it will be understood that forms of non-contact or indirect heating other than induction heating (e.g., radiant heating, etc.), or other modes of communication between a tag and a reader (e.g., optical, infrared, ultrasound, etc.) may be used in conjunction with the principles of the present invention. 
     Referring to  FIGS. 2-3 , trivet  40 , designed according to one embodiment of the present invention, is shown. Trivet  40  preferably is designed not to interfere with indirect heating, such as using the magnetic waves of induction heating, of cookware that it supports, while insulating against conducted and radiated heat that may attempt to move from the cookware and through the trivet to the countertop. Preferred trivet  40  may include a RFID temperature sensor  42  ( FIG. 3 ), which communicates via radio waves with induction unit  10  as is well known, allowing programming of unit  10  to remotely control the temperature of the cookware. 
     To protect the countertop from conducted heat, trivet  40  may be designed with a relatively small vertical cross-section and/or sufficient insulating properties so that heat does not conduct from serving dish  25  back down to the countertop. The overall trivet thickness may be about ¼ inch, for example, and U-shaped channels may be designed into it, as shown. 
     Trivet  40  may be made of a variety of insulating materials such as wood, polycarbonate or another high temperature plastic capable of being molded. Preferably, the trivet is non-metallic so as to be transparent to the magnetic field created by induction heating. 
     Alternative trivet designs, also designed to substantially prevent heat conduction back from the cookware to the countertop, are shown in  FIGS. 7 and 8 . These designs include legs  58  for limiting heat conduction from the cookware back through the trivet to the countertop. Trivets according to the present invention may have different shapes and sizes to accommodate dish sizes, or to create a custom look for a hotel logo. 
     It was found experimentally that using a trivet design according to  FIG. 3 , heat variations on stone countertops were about 100° F. less than those encountered when not using a trivet. In other words, the trivet of the present invention provides roughly about 100 degrees of an insulation factor, which is a safe operating range for countertop materials. 
     Still referring to  FIG. 3 , energy pick-up coil  46  and associated electronics  47  may be located within the U-shaped channels  41  of trivet  40 . Pick-up coil  46  may be used to drive an LED  49  located on trivet  40  which may function as a locator light showing when the trivet is properly positioned over induction unit  10  (e.g., LED  49  may flash, for example, when trivet  40  is properly positioned within the magnetic field of induction heating unit  10 ). This may be accomplished by thresholding the energy and/or field strength from the coil to provide physical locating information, such as determining the position of the induction coil. Pick-up coil and associated electronics  46  may also be used to sense, transmit and display on the induction unit or elsewhere other user information, including whether the induction unit is currently heating the heat retention object (e.g., to show that heating is taking place, LED  49  may present a steady light). For example, this coil-originating energy may be used to power a processor which in turn may intelligently determine trivet position, power to the load, temperature detection, the content of the food dish, how long it has been warming, its humidity, or other parameters, and provide a suitable display as to any of these factors. 
     Because trivet  40  may include the RFID temperature sensor, the cookware need not be outfitted with any special induction-heating-related sensors, tags or controls. Alternatively, rather than attaching the RFID temperature sensor to the trivet, the cookware may have the sensor attached to it, in any convenient manner, such as through a magnetic, removable attachment or coupler  30  as disclosed in pending U.S. Ser. No. 11/750,571, and shown in  FIG. 9 . Coupler  30  includes housing  31  and tongue  34 , positioned below serving dish  25 . Coupler  30  communicates with an induction heating unit, as disclosed in U.S. Ser. No. 11/750,571, enabling heating control over cookware item  25 . 
     Alternatively, coupler  30  may be attached to trivet  40 , which in this case may be fabricated of an insulator on its lower portion, and a metal plate portion on its upper portion to which coupler  30  may be attached, for example. This would enable heating of cookware items such as glass or ceramic dishes, for example, that cannot be heated directly with induction methods; in this case, the RFID temperature sensor contained in coupler  30  would measure the trivet temperature. 
     Referring to  FIG. 4 , the electronics  47  may include electronic objects to rectify, filter and regulate the power from the coil  46  to operate LED  49 . Referring to  FIG. 5 , circuitry for providing the rectifying, filtering and regulation functions is shown, as well as the locating circuitry for positioning the trivet and powering the LED, including “TC” or the thresholding circuit and “TS” or the transistor switch. Referring to  FIG. 6 , a schematic diagram is shown indicating how the induction power supply may be used to power a processor to perform a variety of functions, such as coil voltage sensing, temperature sensing, etc., and then, in turn, provide various displays such as LEDs, numerical displays, etc. 
     The above description is not intended to limit the meaning of the words used in the following claims that define the invention. For example, while preferred embodiments involving power induction principles applied to heating cookware have been described above, persons of ordinary skill in the art will understand that a variety of other designs still falling within the scope of the following claims may be envisioned and used. It is contemplated that future modifications in structure, function or result will exist that are not substantial changes and that all such insubstantial changes in what is claimed are intended to be covered by the claims.