Cooking system for sensing the status of a food item

[0001] 1. Technical Field

[0002] The invention relates to cooking appliances, and more particularly, to a food cooking system having a sensor for determining information about the food being cooked.

[0003] 2. Related Art

[0004] Conventional cooking appliances such as ovens, griddles, and waffle irons, use thermostats to control the cooking temperature of the appliance. Thermostats control cooking temperatures by turning heating elements on or off to maintain a constant temperature at a particular location such as, for example, in the cavity of an oven, at the surface of a griddle, or in or near the food.

[0005] Some prior efforts have been made to use thermostats to determine the status of a food item. For example, some prior art waffle irons illuminate a ready light (or sound a ready tone), indicating that the waffle being cooked is done. In these prior approaches, the appliance's fixed temperature thermostat energizes the heating element in response to a cold batter being poured onto the waffle iron. When the thermostat detects that a fixed predetermined temperature has been reached by the heating element, the thermostat deenergizes the heating element, and illuminates the ready light. Operating based on a fixed predetermined temperature (set by the calibration of the thermostat) has certain disadvantages. For instance, under this prior approach, the ready light or tone is triggered at this predetermined temperature, even if the waffle is not yet done, or is over done. Furthermore, since the prior art waffle iron operates only based on a fixed, predetermined temperature, it does not adapt well to particular situations such as differences in waffle recipes that may require a higher or a lower temperature, or to differing food types altogether. In addition, with the prior art waffle irons, at the particular moment when batter is added to the cooking surface, the fixed temperature thermostat may be below the fixed temperature setting, in which case the appliance cannot detect when the food is added. In other words, since the fixed temperature thermostat, under such circumstances, already requires additional heating, the need for additional heating can not change in response to the addition of a food load. This prevents the appliance from having the capability of timing the cooking cycle, and it can only rely on a fixed temperature threshold to indicate when a food might be done. This is a less reliable method of determining the status or doneness of a food item. Thus, there is a need in the cooking art for a cooking system that is able to determine the status of a food item (e.g., when a food item is added to a cooking apparatus or flipped), to automatically determine the beginning of a cooking cycle, or when a food item is done. There is a further need in the art to provide appliances that can control the cooking of various foods based on such determination.

[0006] These and other advances in the art are provided by the disclosed system. The system may be embodied in various methods and apparatuses for determining the status of a food item. The system examines the time-temperature curve at either the food item or the cooking medium toward determining, for example, when a user has added a food item to a cooking medium, when a food item has been flipped, or when a food item is done (i.e. finished cooking). In particular, the system may sense a number of temperatures, and/or compare data related to the sensed temperatures with predetermined temperature data (for example, delta setpoints as described in detail below), toward determining the status of the food item. The system may also heat the food item, and may further cause some predetermined action based on the status of the food item.

[0007] The system may involve inputting user information corresponding to the food item being cooked. This user information may include what type of food the food item is, or the desired level of doneness of the food item. Also, the system may identify a delta value from a plurality of delta values, determine from the currently determined delta values that a food item has been introduced to the heating medium, and heat the food item for a predetermined period of time. Alternatively, the system may heat the food item until it reaches a predetermined temperature value, regardless of heating time. In addition, the system may also automatically shut off the heating medium in certain circumstances after a predetermined period of time, such as a period of nonuse.

[0008] Other systems, methods, features and advantages of the invention will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims.

[0009] The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principals of the invention. Moreover, in the figures, like reference numerals designate corresponding parts throughout the different views.

[0010] FIG. 1A is a block diagram showing a control means for use with this invention.

[0011] FIG. 1B is a top schematic view of one cooking apparatus that may incorporate this invention.

[0012] FIG. 1C is a side elevational schematic view of the cooking apparatus of FIG. 1B.

[0013] FIG. 2 illustrates one potential approach to a user interface for use with this invention in association with a cooking apparatus such as that shown in FIGS. 1B and 1C.

[0014] FIG. 3 is a block diagram of the electronics that may be utilized in implementing one approach to this invention for use in association with a cooking apparatus, such as that shown in FIGS. 1B and 1C, and user interface of FIG. 2.

[0015] FIG. 4A is an example of a main state-variable diagram generally illustrating the various cooking states achieved in accordance with one embodiment of the invention.

[0016] FIG. 4B is an example of a cookmode state diagram generally illustrating the various cookmode states achieved in accordance with one embodiment of the invention.

[0017] FIG. 5 is a flow chart illustrating a method for determining the status of a food item during a cooking event in accordance with this invention.

[0018] FIG. 6 is a flow chart illustrating one potential approach to the determining cycle of FIG. 5.

[0019] FIG. 7 is a flow chart illustrating another potential approach to the determining cycle of FIG. 5.

[0020] FIG. 8 illustrates a time-temperature curve of the cooking of an egg on the cooking apparatus illustrated in FIGS. 1B and 1C.

[0021] FIG. 9 illustrates an auto shutoff feature that may be utilized as part of this invention.

[0022] FIG. 1A illustrates a general block diagram showing a control means for an appliance in accordance with this invention. The control means generally includes a sensor means 101, a means for determining the status and/or doneness of a food item 103, and an indicator means 107. Certain specific embodiments of each of these means are described in detail with respect to FIGS. 11B, 1C, 2 and 3.

[0023] The sensor means 101 may be, for example, one or more heat sensors for sensing temperatures. In accordance with the invention, all or part of the sensor means 101 is put into thermal relationship with a food item or items. The sensor means 101 senses one or more successive temperatures over time. The sensed temperatures are generally sent to a means for determining the status or doneness of the food item or items 103, and the determining means 103 generates a status signal 105 which is sent to an indicator means 107.

[0024] The determining means 103 may include, for example, a microprocessor, an arithmetic logic unit (ALU), an analog circuit, or an application-specific integrated circuit (ASIC). As explained below, the status is determined based on successively sensed temperatures over time. Based on the status signal 105, the indicator means 107, which is operably associated with the determining means 103, operates to indicate the status of the food item to a user.

[0025] FIGS. 1B and 1C illustrate one potential cooking apparatus 100 incorporating the invention. Specifically, the cooking apparatus 100 may include a heating medium 102, a temperature control unit 104, a food temperature sensor 106 and a control temperature sensor 108. The heating medium 102 may be, for example, a griddle, a grill, an oven, a deep fryer, a rotisserie oven, or a sandwich-type dual-surface griddle. In the presently illustrated embodiment, the heating medium 102 is an aluminum griddle casting surface.

[0026] In a griddle, the temperature control unit 104 may include a temperature probe 110 via which the heating medium 102 is heated. In such an embodiment, the temperature probe 110 is connected to a power source (not shown) which provides the energy used to heat the heating medium 102. The temperature control unit 104 may also include a temperature control interface, such as a dial 112, by which a user may manually adjust the temperature set point of the heating medium 102.

[0027] The food temperature sensor 106 is physically placed in association with the heating medium 102 such that it will be in thermal relationship with a food item to be observed. In a griddle, for instance, the food temperature sensor 106 would preferably be embedded within the heating medium 102, as shown in FIGS. 1B and 1C. In a preferred embodiment, there may be visual indicia identifying the location of the food temperature sensor 106 in association with the heating medium 102 such that a user may place the food item appropriately. For example, the location of the food temperature sensor may be indicated by a raised outline or symbol, by a metal insert with a different appearance or color, an anodized coating of a different color, or a nonstick teflon type coating of a different color, so as to assist a user in placing the food item to be cooked in an appropriate location to better ensure thermal relationship with the food temperature sensor 106.

[0028] The control temperature sensor 108 is placed such that it will be in thermal relationship with the surrounding environment of the heating medium and not in thermal relationship with the food item itself. As explained below, the control temperature sensor 108 may be optional. In an electric griddle, the control temperature sensor 108 is preferably embedded in the probe 110 of the temperature control unit 104. Both the food temperature sensor 106 and the control temperature sensor 108 may be conventional negative temperature coefficient (NTC) thermistors such as a Fenwall ESX8206 glass encapsulated thermistors rated 470 KOhms at 25 C. Of course, other elements that sense temperature such as positive temperature coefficient (PTC) thermistors, thermocouples, resistance temperature devices (RTDs) or solid state temperature sensors may also be used.

[0029] The food temperature sensor 106 senses a plurality of temperatures of the food item (or items) over time. The control temperature sensor 108 senses a plurality of temperatures of the environment surrounding the food item over time. Thus, if the food temperature sensor 106 indicates a drop (or increase) in temperature, while the control temperature sensor 108 does not indicate a similar drop (or increase), then the drop (or increase) at the food temperature sensor 106 is likely due to a change in temperature at the food item. On the other hand, if both the food and control temperature sensors indicate a similar drop in temperature, then the temperature drop is more likely due to a temperature drop in the surrounding environment of the heating medium, as might be caused by a breeze from a person walking by the apparatus or from an open window.

[0030] Although the system of FIGS. 1B and 1C suggests the use of a single food temperature sensor 106 and a single control temperature sensor 108, in an alternative embodiment of this invention, multiple food and/or control temperature sensors 106, 108 may be used. For instance, the multiple food sensors may be arranged to sense temperatures associated with a single food item. In another example, the multiple food sensors may be arranged to sense temperatures for multiple food items (e.g., separate pancakes in a griddle). Similarly, control temperature sensors may be placed in multiple and/or alternative locations associated with the cooking apparatus 100 such as, for example, on the temperature control unit 104, or on one of the legs 114 of the heating medium 102.

[0031] With multiple food temperature sensors 106, the food temperature values sensed may, in certain embodiments, be averaged together for a more accurate reading. Similarly, with multiple control temperature sensors 108, the control temperature values sensed may be averaged together. Alternatively, the system may be designed to provide a doneness indicator with respect to each sensor 106, individually.

[0032] In one embodiment of the invention, a user interface 116 may be operably associated with the cooking apparatus 102. One such association may be accomplished via hard-wired connection to the temperature control unit 104. In another approach, the user interface 116 may be integral to the temperature control unit 104 itself. FIG. 2 illustrates one embodiment of the user interface 116 for use with the invention. As shown, the user interface 116 may include light, medium and dark selection keys, 202-206, a power indicator light 208, a ready indicator light 210, a cancel key 212, a select key 214, and a display 216. The light, medium and dark keys 202-206 allow an end user to input the desired level of doneness of the food item (e.g., light, medium or dark) to be cooked by pressing one of the light, medium or dark keys 202-206. Various types of switches may be used to implement the keys including various momentary contact switches. It is also contemplated that a single slider switch could be used to implement a plurality of variations or settings between light and dark. Another possible approach would involve a textual or numeric interface or keyboard, where various words or numbers may be associated with corresponding light or dark settings.

[0033] When the power indicator light 208 is illuminated, this indicates that the cooking apparatus is powered-on. Similarly, when the ready indicator light 210 is illuminated, this indicates that the heating medium 102 is pre-heated or that the food item presently being cooked is ready to be flipped, or is done cooking. There may also be separate indicator lights for each of these states, each of which would be physically associated with appropriate textual legends (i.e., pre-heated, ready to flip, and done cooking). In another approach, the status of the apparatus and any food items could be displayed via a single display. In addition (or alternatively) to the ready indicator light(s) 210, the user interface 116 may include a speaker for sounding a tone when, for example, the heating medium is pre-heated, the food is ready to be flipped, and/or the food is done cooking.

[0034] The cancel key 212, as described further with respect to FIG. 4B, may be provided to allow a user to cancel a present state of the cooking apparatus such as, for example, a Cook Start State or a Cook Flip State (as described below with respect to FIG. 4B). It may also be used to clear an entry into the user interface.

[0035] In some embodiments, a select key 214 may be provided to allow a user to, for example, select the type of food to be cooked, or a cookmode, such as, for example, a manual cooking mode with fewer or no automatic food sensing features. For example, the cooking apparatus 102 may be pre-programmed to cook Eggs, French Toast, Hamburgers, Sandwiches, Pancakes, or Texas Toast. If, for example, the user desires to cook Pancakes, then the select key 214 may be pressed a number of times to scroll through the menu of known foods, until Pancakes appears on the display 216. Display 216 may be, for example, an LCD or CRT type display. Further, it would be possible to include the indicators (e.g., 208, 210) with this display 216.

[0036] In the embodiment of FIG. 2, the function of the keys shown in this FIG. 2 (e.g., 202-206, 212, 214) may also be accomplished by a series of menus on, for example, a LCD or interactive screen. Thus, for example, instead of the select key 214 as described above, the display may include one or more pull-down menus comprising various lists of options (e.g., type of food, desired level of doneness, temperature), which may be selected by a user via, for example, a touch-screen, a stylus-pen operated screen, a mouse device, or a set of multipurpose keys associated with the screen.

[0037] In an embodiment where, for example, a menu display option is available, if the menu of known foods is very long, the user may first choose from a shorter menu of categories of foods (e.g. Breakfast, Meat, Sandwiches). Then, once the broader category is selected, a more specific menu of foods within the category (e.g., under Breakfast, the known foods may include Eggs, Pancakes, Texas Toast, French Toast, Sausage Patties, etc.) would appear from which the user may select the specific food item to be cooked. In an alternative embodiment, when the food is first placed on or in the heating medium, the system may detect the category of foods to which the current food item being cooked belongs (e.g., a food having eggs as a major component) from certain characteristics of the food item (e.g., mass, minimum temperatures, and/or magnitude and slope or rate of initial drop in temperature). Then, in this embodiment, to assist the user once the particular food category is determined, the user may be provided with a shorter menu having fewer food items from which to select the particular item being cooked.

[0038] FIG. 3 illustrates an electronic block diagram of the electronics that may be used to implement this inventive system. As shown, the electronics may include a microprocessor 302 which interfaces with and controls the various components of the system, including the user interface 116, the control temperature sensor 108, the food temperature sensor 106, the speaker 304, a heating element relay 306, and a memory unit 308.

[0039] Microprocessor 302 may be a conventional microprocessor such as a Microchip PIC 16C73A microprocessor. As explained further below, the microprocessor 302 may be used to accomplish various functions to determine the status of a food item, including, but not limited to, performing simple arithmetic functions, including incrementing counters and/or indices, calculating delta values, or performing various value comparisons. While a microprocessor is the preferred means for performing the various functions to determine the status of the food item, other means may be used as well. For example, one of skill in the art would understand that an arithmetic logic unit (ALU), or an application-specific integrated circuit (ASIC) may be used to perform the desired calculations. Similarly, a hard-wired digital circuit or analog circuit may be used as well to perform the calculations. With respect to the methods described below, the microprocessor will be more generally referred to as a controller.

[0040] The various indicator lights (208, 210) may be standard high efficiency light-emitting diodes (LEDs). The heating element relay 306 may be a conventional SPST DC coil relay such as an Aromat JS1A24 or a solid state switch such as a Triac.

[0041] FIG. 4A illustrates an example of a main state-variable diagram generally identifying the various cooking states achieved in accordance with an embodiment of the invention. In this example state diagram, there are illustrated ten (10) example states as set forth in Table 1 below.

TABLE 1
	DESCRIPTION
		food	delta	time (sec):
STATE	display	sensing	setpoint	min/med/dark
Start State (402)	Smart Grille	Disabled	N/A	N/A
initialize	and/or Press a
variables	Key
Default State	Smart Grille	Disabled	N/A	N/A
(404)	and/or Press a
	Key
Egg State (406)	Eggs	Enabled	7	95/110/130
French Toast	French Toast	Enabled	7	130/145/175
State (408)
Hamburger State	Hamburger	Enabled	7	360/400/580
(410)
Sandwich State	Sandwiches	Enabled	7	105/145/175
(412)
Pancake State	Pancakes	Enabled	7	105/120/150
(414)
Texas Toast	Texas Toast	Enabled	7	130/175/200
State (416)
325 C. State	Other Foods -	Disabled	N/A	N/A
(418)	325 C.
350 C. State	Other Foods -	Disabled	N/A	N/A
(420)	350 C.
375 C. State	Other Foods -	Disabled	N/A	N/A
(422)	375 C.

[0042] While in the start state 402, all cooking state-variables are initialized. Each state-variable is associated with a different state. For example, the Egg State 406 may have an egg_state variable such that if egg_state1, the cooking apparatus is in the Egg State (i.e., in a state to cook an egg) and if egg_state0 the cooking apparatus is not in the Egg State. In each state, the present cooking method and apparatus may have various predetermined settings. For example, in the Egg State (e.g., when egg_state1), the display may read Eggs, the delta setpoint (as described in detail below) may be equal to 7, and the cooking time for each side may be set to 95 sec., 110 sec., or 130 sec. (for light, medium or dark selections, respectively). Also as illustrated in FIG. 4A, a user may press the select button in order to toggle between the different states.

[0043] In addition to various food specific states (e.g., Egg State, French Toast State, Hamburger State, etc.), the present cooking method and apparatus may have temperature specific states (e.g., 350 C. State, 375 C. State). In such temperature specific states, the user may desire to cook a food at a specific temperature without using the sensing feature of the cooking apparatus. In such a case, the user may select, for example, 350 C. at which to cook a particular food. In such a 350 C. State, the 350 C._state variable may be equal to 1 when this state is selected, and 0 when this state is not selected. In this example, in the 350 C. State, the display may read Other Foods 350 C., and the food sensing function is disabled.

[0044] FIG. 4B illustrates an example of a cookmode state diagram generally identifying the various cookmode states achieved in accordance with an embodiment of the invention. In this example cookmode state diagram, there are illustrated five (5) example states as set forth in Table 2a below.

TABLE 2a
	DESCRIPTION
STATE	display	Food sensing/cooking
Cook Default	current food	set delta setpoint to 7.
State (424)	(based on
	cooking-state-
	variable of FIG.
	4A)
Cook Start	Cooking and	Initiate timer (based on cooking state-
State (426)	progress bar	variable and based on auto-shutoff)
Cook Flip	Flip Now and	set delta setpoint to 3
State (428)	erase progress bar
Cook Flipped	Cooking and	initiate timer (based on main state-
State (430)	progress bar	variable and based on auto-shutoff)
Cook Done	Done and erase	initiate timer to return to Cook
State (432)	progress bar	Default State and based on
		auto-shutoff

[0045] As explained with respect to FIG. 4A, while in the start state 402, all cookmode variables are initialized. Each cookmode state is associated with one or more different cookmode variables. For example, the Cook Flip State (428) may have a cookflip_state variable where cookflipstate1 means that the food item being cooked is ready to be flipped, and cookflip_state0 means that the food item being cooked is not ready to be flipped. An example of the values for other potential cookmode variables associated with the cookmode states of FIG. 4B is illustrated in Table 2b below.

TABLE 2b
Cook Default State	cookdefault_state 1 (in default mode)
(424)	cookdefault_state 0 (not in default mode)
Cook Start State (426)	cookstart_state 1 (in cook start modetimed
	cooking)
	cookstart_state 0 (not in cook start mode)
Cook Flip State (428)	cookflip_state 1 (in cook flip modeready
	to flip)
	cookflip_state 0 (not in cook flip mode)
Cook Flipped State	cookflipped_state 1 (in cook flipped
(430)	modefood flipped; timed cooking)
	cookflipped_state 0 (not in cook flipped mode)
Cook Done State (432)	cookdone_state 1 (in cook done
	modefood done)
	cookdone_state 0 (not
	in cook done modefood not done)

[0046] In each cookmode state, the present cooking method and apparatus would have various predetermined settings. For example, when cookflip_state1, the display may read Flip Now indicating that the food is ready to be flipped, and the delta setpoint (described below) may be set to 3.

[0047] Also as illustrated in FIG. 4B, a user may press the cancel button while the apparatus is in various cookmode states. For example, the user may press cancel while the apparatus is in the Cook Flip State 428 (i.e., cookflip_state1) in order to bypass flipping of the food. Similarly, the user may press cancel while the apparatus is in the Cook Start State 426 if the user wants to cancel cooking altogether. Pressing the cancel button during any of the cookmode states generally resets the particular cookmode variable in progress to zero.

[0048] FIG. 5 is a flow chart illustrating a possible method for determining the status of a food item during a cooking event in accordance with the present invention. A cooking event is the complete cooking or heating of a food item in accordance with the invention. A timing period is a period either during which timed cooking or heating is occurring, or during which a predetermined temperature is being achieved (e.g., pre-heating). Timed cooking may be based on a predetermined period of time, or may vary depending on the minimum or maximum delta value set by the microprocessor 302. For example, a larger food item having greater mass tends to have a steeper negative temperature slope than a smaller food item (i.e., the temperature decreases more quickly when the food item is placed on or in the heating medium). Thus, the predetermined cooking time in those situations may vary so that if a larger food item is detected, the cooking time may be automatically increased by the microprocessor 302. This would tend to compensate for differences in, for example, the mass of the food items. A cooking cycle is an entire cycle of sensing, timed cooking, and alerting the user (e.g., sensing a food item has been added to the heating medium, timed cooking on the first side of the food item, and alerting the user that the food item is ready to be flipped). After the cooking apparatus 100 is turned on, the heating medium preheats (step 502). In certain embodiments, this pre-heating step may occur upon the actuation of a key or button. Alternatively, the pre-heating step 506 may occur when the apparatus 100 is plugged into a power outlet and/or turned on.

[0049] After the heating medium is pre-heated, step 502, the controller drives a ready signal (e.g., a status signal 105, as described in FIG. 1A) to the ready indicator light 210 and/or the speaker 304, wherein the light 210 illuminates and/or the speaker 304 sounds a tone, alerting the user that the cooking apparatus 100 is preheated, step 504.

[0050] Next, the user may input data into the apparatus (step 506) via, for example, the user interface 116. For example, if the user desires to cook pancakes that are very well done, the user would enter Pancakes via the select key and select the dark key 206 (as opposed to light key 202 or medium key 204).

[0051] In certain embodiments, no user data is entered at all. This may occur, for example, where the apparatus is designed especially for cooking one particular type of food (e.g., a waffle iron). With such an embodiment, there is no need to input a type of food to be cooked because the type of food (e.g., a waffle) is assumed. As another example where no user data is entered at all, the apparatus may be designed only for sensing doneness, such as an electronic turkey timer. In such an embodiment, there is no need for a user to input any data.

[0052] Generally, after the user selects the type of food to be cooked 506, the food item is placed in operable association with the heating medium, step 508, and then the determining cycle occurs (step 510). During the determining cycle, as described in detail with respect to FIGS. 6 and 7, the microprocessor periodically senses and compares temperatures until the food item is ready to be flipped or is done (see FIGS. 6 and 7). Depending upon the food item and/or heating medium, there may be only one determination (e.g., where the food is not flipped at all) per cooking event, or there may be more than one determining cycle (e.g., the food is flipped one or more times, and/or there is more than one side of a food item to be cooked) per cooking event.

[0053] In general, a record of temperatures measured at the food sensor(s), and optionally at the control sensor(s), is kept in an array of locations in the memory unit (referred to as a temperature array and more specifically, as a food temperature array and a control temperature array, respectively). Each temperature array has at least N_MAX memory locations. Based on the inventor's research, N_MAX has been set equal to 7 in a preferred embodiment. Also in this preferred embodiment, one new temperature is sensed and then stored in this temperature array every period. In a preferred embodiment, a period is equal to one second. However, the period may differ in different embodiments. Further, although other methods may be used, in a preferred embodiment, the temperatures (referred to collectively as temperature data) are stored in first-in first-out (FIFO) order. Thus, the oldest temperature data in the temperature array is discarded, every other temperature data is moved up in the order by one position, and the newest data is inserted at the first position in the temperature array.

[0054] FIG. 6 is a flow chart illustrating one potential approach to the determining cycle (i.e., step 510) of FIG. 5, for use in an embodiment where a control temperature sensor is not provided and/or used. Although this determining cycle appears in FIG. 5 to only occur once (e.g., after the food item to be cooked is placed on (or in) the cooking medium), the determining cycle is preferably continually occurring in the background while the cooking apparatus is powered on. However, it is after the food item is placed on or in the heating medium or flipped when a complete determining cycle occurs.

[0055] During the determining cycle, an interrupt occurs every period (preferably 1 second), step 602. During the interrupt, the food temperature data in a food temperature array shifts in FIFO order so that the oldest food temperature is discarded leaving room for a new food temperature to be stored in the food temperature array, step 604. Accordingly, the food temperature stored at memory location J of the food temperature array would be shifted to food memory location J1, and the food memory location J0 would be cleared. Then, a new food temperature is sensed, step 608, and stored in food memory location J0, step 610.

[0056] Next, the microcontroller 302 may perform a series of calculations to determine the current status of the food item. The controller calculates one or more food delta values based on the currently stored food temperature data, step 612. A delta value is generally a value indicating a change in temperature between two temperatures. Thus, a food delta value specifically is a change in temperature between two food temperatures. In a preferred approach, a food delta value may be calculated by taking the current food temperature (i.e., the food temperature most recently sensed, which is stored in memory location J0) and subtracting from that temperature the value of each other sensed food temperature stored in the food temperature array. This approach is illustrated in Table 3 below. Optionally, the controller may divide these food delta values by the appropriate time difference to obtain conventional slope values.

[0057] Table 3 shows a sample temperature array where T_N refers to the temperature stored in the Nth location of the temperature array. In the temperature array shown in Table 3, a food item (e.g., an egg) is placed on the pre-heated heating medium:

	TABLE 3
	T0	145
	T1	100
	T2	90
	T3	86
	T4	85.3
	T5	84.9
	T6	84.7

[0058] Based on the example sensed food temperatures of Table 3, the food delta values calculated from this data would be as follows:

	TABLE 4
	M6-0	60.3 C.
	M6-1	15.3 C.
	M6-2	5.3 C.
	M6-3	1.3 C.
	M6-4	0.6 C.
	M6-5	0.2 C.

[0059] The maximum calculated food delta value may then be compared to predetermined delta data (referred to as delta setpoints) to determine the status of the food item (e.g., whether a food item has been introduced to the heating medium or flipped), steps 614-616. In a preferred embodiment, the delta setpoints are 7 C. to determine when the food has originally been placed on the heating medium (the start-cook setpoint), and 3 C. to determine when the food is flipped (the flip setpoint).

[0060] If the maximum food delta value is greater than some delta setpoint as described above, step 616, then the microprocessor 302 determines whether the current cookmode state of the apparatus is, for example, either Cook Start State or Cook Flipped State, 618. If the maximum food delta value is greater than the start-cook setpoint, this indicates that the food item has been placed on or in the pre-heated heating medium, and thus the apparatus enters the Cook Start State (i.e., cookstart-state1). In this case, this is the start of a new timing period, and thus the timer is reset and begins timing, step 620, whereupon timed cooking proceeds 622. Similarly, if the maximum delta value is between the cook-start setpoint and the flip setpoint, this indicates that the food item has been flipped, and thus the apparatus should enter the Cook Flipped State (i.e., cookflipped-state1). In this case, this is the start of the next, or flipped timing period, and the timer is reset and begins timing, step 628, whereupon timed cooking of the second side proceeds, 630.

[0061] As explained above, timed cooking may be based on a predetermined period of time, or may vary depending on the minimum or maximum delta value determined by the processor. For example, a larger food item having greater mass tends to have a steeper negative temperature slope than a smaller food item (i.e., the temperature decreases more quickly when the item is placed on or in the heating medium). Thus, the predetermined cooking time in the situation may vary so that if a larger food item is detected, the cooking time may be automatically increased by the microprocessor 302. This would tend to compensate for differences in, for example, the mass of the food items. In an alternative embodiment, rather than timed cooking (i.e., cooking for a predetermined period of time), heating of the food item may be controlled based on an absolute food temperature. After timed cooking is complete, a light illuminates and/or the speaker sounds a tone 624, alerting the user of the occurrence of an event (e.g., first side is done, or second side is done).

[0062] Next, the microprocessor determines if a timing period is complete 634. If a timing period is not complete then timed cooking continues 638, and any other background tasks (e.g., temperature control, user interface functions, etc.) continue 640. If a timing period is completed, 634, then a light illuminates and/or the speaker sounds a tone 636, alerting the user as such, and other background tasks continue, step 640.

[0063] If, after the microprocessor determines that the maximum food delta value is greater than a delta setpoint (e.g., the start-cook or flip setpoints), step 616, it is determined that the current cookmode of the apparatus is neither Cook Start State nor Cook Flipped State, step 618, then the microprocessor determines whether the timing period for the first side of the food item (first side timing period) is complete, step 626. If the first side timing period is not complete, then timed cooking continues, step 638, and other background tasks continue, step 640. If the first side timing period is complete, then the apparatus goes into the Cook Flip Mode, and the timing period for the second side of the food item (flip side timing period) begins, step 630. The user may then be alerted that the cooking of the second side has begun. At the end of this new flip side timing period, a light illuminates and/or the speaker sounds a tone, step 636, alerting the user that the current timed cooking is complete, and other background tasks continue, step 640.

[0064] If, the maximum food delta value is not greater than any of the delta setpoints (step 616), the microprocessor determines if a timing period is complete 634. If a timing period is not complete then timed cooking continues 638, and other background tasks described herein continue 640. If a timing period is completed, then a light illuminates and/or the speaker sounds a tone, step 636, alerting the user as such, and other background tasks continue, step 640.

[0065] FIG. 7 illustrates another potential approach for a modified determining cycle (i.e., steps 510) of FIG. 5, for use in an embodiment where a control temperature sensor is provided in addition to a food temperature sensor. As explained above, although the determining cycle appears in FIG. 5 to only occur once (e.g., after the food item to be cooked is placed on (or in) the cooking medium), the determining cycle is preferably continually occurring in the background while the cooking apparatus is powered on.

[0066] However, it is after the food item is placed on or in the heating medium when a complete determining cycle occurs.

[0067] During the modified determining cycle, an interrupt occurs every period (preferably equal to 1 second), step 702. During the interrupt, the food temperature data in the food temperature array shifts in FIFO order so that the oldest food temperature is discarded leaving room for the newly sensed food temperature to be stored in the food temperature array, step 704. Accordingly, the food temperature stored at food memory location J is shifted to food memory location J1, and the food memory location J0 is cleared. Then, a new food temperature is sensed, step 706, and stored in food memory location J0, step 708.

[0068] The modified determining cycle of FIG. 7 also utilizes control temperature data which is sensed by the control temperature sensor and stored in a control temperature array. Thus, during each interrupt, the control temperature data in the control temperature array shifts in FIFO order so that the oldest control temperature is discarded leaving room for a newly sensed control temperature to be stored in the control temperature array, step 710. Accordingly, the control temperature stored at control memory location K is shifted to control memory location K1, and the control memory location K0 is cleared. Then, a new control temperature is sensed, step 712, and stored in control memory location K0, step 714.

[0069] The microcontroller 302 may then perform a series of calculations to determine the current status of the food item. The microcontroller 302 calculates one or more food delta values (as discussed with respect to FIG. 6) based on the currently stored food temperature data, step 716. Similarly, the microcontroller 302 calculates one or more control delta values based on the currently stored control temperature data, step 716. (As explained with respect to FIG. 6, a delta value is a value indicating a change in temperature between two temperatures.) Thus, a control delta value specifically is a change in temperature between two control temperatures. In a preferred approach, the control delta values may be calculated by taking the current control temperature (i.e., the control temperature most recently sensed, which is stored in memory location K0) and subtracting from that temperature the value of each other sensed control temperature stored in the control temperature array. Optionally, the controller may divide these control delta values by the appropriate time difference to obtain conventional slope values. When the control delta values and food delta values are calculated, normalized delta values may be determined be subtracting each control delta value from a respective food delta value, step 720. An example of the foregoing is illustrated in Tables 5 and 6 below.

	TABLE 5
	Food	Control
T0	97.3	80.1
T1	97.5	80.3
T2	98	80.2
T3	98.5	80.2
T4	93.7	74.9
T5	99.5	80.1
T6	100	80.2

[0070] Based on the example sensed temperatures of Table 5, the food delta values, control delta values and normalized delta values calculated from this data would be as follows:

	TABLE 7
	Food Delta	Control	Normalized
	Values	Delta Values	(food-control)
	M6-0	2.7 C.	0.1 C.	2.6 C.
	M6-1	2.5 C.	0.1 C.	2.6 C.
	M6-2	2.0 C.	0 C.	2.0 C.
	M6-3	1.5 C.	0 C.	1.5 C.
	M6-4	6.3 C.	5.3 C.	1.0 C.
	M6-5	0.5 C.	0.1 C.	0.4 C.

[0071] After the normalized delta values are determined, 720, the maximum calculated normalized delta value may then be compared to predetermined delta data (e.g., the delta setpoints) to determine the status of the food item (e.g., whether a food item has been introduced to the heating medium or flipped) or a stage of doneness of the food item, steps 722-724. As explained, in a preferred embodiment, the start-cook setpoint is 7 C., and the flip setpoint is 3 C.

[0072] If the maximum normalized delta value is greater than a delta setpoint as described above, step 724, then the microprocessor determines whether the current cookmode state of the apparatus is, for example, either Cook Start State or Cook Flipped State, step 726. If the maximum normalized delta value is greater than the start-cook setpoint, this indicates that the food item has been placed on or in the pre-heated heating medium, and thus the apparatus enters the Cook Start State. In this case, this is the start of a new timing period, and thus the timer is reset and begins timing, step 728, whereupon timed cooking proceeds, 730. Similarly, if the maximum normalized delta value is between the cook-start setpoint and the flip setpoint, this indicates that the food item has been flipped, and thus the apparatus enters the Cook Flipped State. In this case, this is the start of the next or flipped timing period, and the timer is reset and begins timing, step 736, whereupon timed cooking of the second side proceeds, 738.

[0073] As explained above, timed cooking may be based on a predetermined period of time, or may vary depending on the minimum or maximum delta value determined by the processor. For example, a larger food item having greater mass tends to have a steeper negative temperature slope than a smaller food item (i.e., the temperature decreases more quickly when the item is place on or in the heating medium). Thus, the predetermined cooking time in the situation may vary so that if a larger food item is detected, the cooking time may be correspondingly increased. This adjustment would tend to compensate for differences in, for example, the mass of the food items. In an alternative embodiment, rather than timed cooking (i.e., cooking for a predetermined period of time), heating of the food item may be controlled based on an absolute food temperature. After timed cooking is complete, a light illuminates and/or the speaker sounds a tone, step 732, alerting the user of the occurrence of an event (e.g., first side is done, or second side is done).

[0074] Next, the microprocessor determines if a timing period is complete, step 742. If a timing period is not complete then timed cooking continues, step 746, and other background tasks continue, step 748. If a timing period is completed, step 742, then a light illuminates and/or the speaker sounds a tone, step 744, alerting the user as such, and other background tasks continue, step 748.

[0075] If after the microprocessor determines that the maximum normalized delta value is greater than a delta setpoint, step 724, it is determined that the current cookmode of the apparatus is neither Cook Start State nor Cook Flipped State, step 726, then the microprocessor determines whether the timing period for the first side of the food item (first side timing period) is complete, step 734. If the first side timing period is not complete, then timed cooking continues, step 746, and other background tasks continue. step 748. If the first side timing period is complete, then the apparatus goes into the Cook Flip Mode, and the timing period for the second side of the food item (flip side timing period) begins, step 738. The user is then alerted that the cooking of the second side has begun. At the end of this new flip side timing period, a light illuminates and/or the speaker sounds a tone, step 744, alerting the user that the current timed cooking is complete, and other background tasks continue, step 748.

[0076] If, the maximum normalized delta value is not greater than any of the delta setpoints (step 724), the microprocessor determines if a timing period is complete, step 742. If a timing period is not complete then timed cooking continues, step 746, and other background tasks described herein continue, step 748. If a timing period is completed, then a light illuminates and/or the speaker sounds a tone, step 744, alerting the user as such, and other background tasks continue, step 748.

[0077] In the example shown in Tables 5 and 6, according to the method illustrated by FIG. 6, the system would indicate that the food item has been flipped (since the maximum food delta value is 6.3 C. which is greater than the flip setpoint, 3 C.), thus triggering a new flip side timing period. However, as explained below, in accordance with the method illustrated by FIG. 7, the food delta values would be modified by subtracting the control delta values from the food delta values to calculate normalized delta values. The control delta values act as a control variable to account for possible environmental anomalies in the temperature measurements and delta value calculations. Then, in this approach, the normalized delta values (rather than the actual food delta values) are compared with the delta setpoints, step 716.

[0078] Thus, as in the example of Tables 5 and 6, it appears that a substantial dip in temperature (i.e., T₄) occurred, perhaps due to a breeze from an open window or some other drop in room temperature. Thus, by modifying the food delta values to determine normalized food delta values, step 714, the method of FIG. 7 better avoids false triggering of a new timing period. Thus, the timing period will only begin when the food temperature sensor experiences a steep drop in temperature, but the control temperature sensor does not.

[0079] An example showing the status or stage of doneness of a particular food item at different periods of time is illustrated in FIG. 8, which shows a time-temperature profile produced by cooking one large egg on a particular heating surface. Using this easily obtained data, the time-temperature profiles illustrate the status of the food item including introducing a food item to the heating medium 802, cooking the first side of the food item for a predetermined period of time 804, flipping the food item 806, and cooking the second side of the food item for a predetermined period of time 808. Thus, by conducting simple experiments for any cooking event for each desired type of food, a database of time-temperature data may be created and stored within the memory unit 308. As would be understood, memory unit 308 may be discrete or integral to microcontroller 302.

[0080] FIG. 9 illustrates an auto shutoff routine 900 for use with the present invention. With this auto shutoff feature, if no new timing periods are detected, and no keys on the user interface 116 are pressed, within a predetermined period of time (e.g., 16 minutes), then the apparatus automatically shuts itself off, and waits until a key is pressed before heating back up again.

[0081] As shown in the approach of FIG. 9, first, a clock timer, t, is reset to zero (0) at the end of a previous timing period, or when a key has been pressed, step 902 (e.g., when cookmode is set to 0). The clock timer (t) keeps track of the time that has passed since the beginning of the current timing period. The value of t is continually compared to a predetermined maximum, t_Max, step 904, during the current period when a timing period is not in progress, to determine if the time that has passed since the end of the previous timing period has exceeded t_Max. If t is not greater than t_Max, the controller checks for a timing period, 906. If there is no timing period in progress, it checks whether any keys have been pressed, 908. If no keys have been pressed, the controller again checks whether t has exceeded t_Max, 904, and steps 906 and 908 are repeated, accordingly. If, during this loop (steps 902-908), a timing period is detected, step 906, the clock timer, t, is reset to zero, and the loop (902-908) continues to repeat. Similarly, if the controller detects that a key has been pressed, 908, the clock timer, t, is reset to zero, and the loop (902-908) also continues to repeat.

[0082] If, during the comparison, step 904, t exceeds t_Max, indicating that the time that has passed since the end of the previous timing period, or since a key was pressed, exceeds t_Max, the temperature control of the heating medium automatically shuts off, step 910. In one embodiment of the invention, although the temperature shuts off, the apparatus remains powered on so that the controller may detect whether a key has been pressed, step 912. Once a key has been pressed after automatic shut off, the heating medium again begins to pre-heat, step 914, and operation may continue. Alternatively, when t exceeds t_Max, the entire device may shut off and remain powered off until turned on again by a user.

[0083] While various embodiments of the application have been described, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible that are within the scope of this invention. Accordingly, the invention is not to be restricted except in light of the attached claims and their equivalents.