Patent Grant
10260755
The present subject matter relates generally to a cooking appliance and methods for operating a cooking appliance. More particularly, the present subject matter relates to cooking appliances and methods for operating cooking appliances to limit the temperature of a cooking utensil positioned on a heating source of the cooking appliance.
Cooking appliances, such as, e.g., cooktops (also known as hobs) or ranges (also known as stoves), generally include one or more heated portions for heating or cooking food items within a cooking utensil placed on the heated portion. The heated portions utilize one or more heating sources to output heat, which is transferred to the cooking utensil and thereby to any food item or items within the cooking utensil. Typically, an electronic controller or other control mechanism, such as a thermo-mechanical electrical switch (also known as an infinite switch), regulates the heat output of the heating source selected by a user of the cooking appliance, e.g., by turning a knob or interacting with a touch-sensitive control panel. For example, the control mechanism may cycle the heating source between an activated or on state and a substantially deactivated or off state such that the average heat output approximates the user-selected heat output. This cycling action may have a period of several seconds, as is typically the case when relays are employed, or might take place on each half-cycle of an AC waveform, which is possible with semiconductor switching devices.
However, the transfer of heat to the cooking utensil and/or food items may cause the food items or cooking utensil to overheat or otherwise cause unwanted and/or unsafe conditions on the cooktop. Although the cooking appliance usually has features for regulating the heat output of the heating source as described above, setting the heat output to a high level can cause the cooking utensil, and its contents, to reach excessively high temperatures. As an example, a high heat output setting may cause a frying pan or skillet containing only a thin layer of cooking oil to quickly rise in temperature because the thermal mass of the cooking utensil and cooking oil is small. In some cases, the temperature may rise such that the cooking oil self-ignites. On the other hand, a high heat output setting typically does not lead to dangerous conditions for large food loads, e.g., a pot filled with water, because the large thermal mass slows the rate at which the cooking utensil and food heat up and, in this particular example, because water is a self-temperature-regulating compound and is not a self-igniting chemical compound. Therefore, cooking performance of the cooking appliance may be negatively impacted if the appliance regulates every use of a high heat output setting regardless of the temperature reached by the cooking utensil and/or its contents.
Accordingly, a cooking appliance with features for selectively limiting a maximum temperature reached by a cooking utensil placed on a heating source of the cooking appliance without impacting the performance of the cooking appliance during other cooking operations would be useful. Methods for operating a cooking appliance to selectively limit a maximum temperature reached by a cooking utensil placed on a heating source of the cooking appliance without impacting the performance of the cooking appliance during other cooking operations also would be beneficial. In particular, an appliance and its associated methods that limits a maximum temperature reached by a lightly-loaded cooking utensil containing highly combustible foods (e.g., cooking oil, grease, and bacon) but does not limit the heat output to a heavily-loaded cooking utensil containing non-combustible foods (e.g., water or a water-based sauce) would be advantageous.
Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.
In one exemplary embodiment of the present subject matter, a method for operating a cooking appliance is provided. The method includes providing power to the heating source according to a first control mode; determining whether to transition from the first control mode to a second control mode and, if so, then providing power to the heating source according to the second control mode. The method further includes determining whether to transition from the second control mode to a third control mode and, if so, then providing power to the heating source according to the third control mode.
In a further exemplary embodiment of the present subject matter, a cooking appliance is provided. The cooking appliance includes a heating source; a temperature sensor; an energy control device for modulating the power provided to the heating source; and a controller. The temperature sensor is positioned to sense the temperature of a bottom surface of a cooking utensil when the cooking utensil is placed on or adjacent to the heating source. The controller is in operative communication with the temperature sensor and the energy control device. The controller is configured for providing power to the heating source according to a first control mode; determining whether to transition from the first control mode to a second control mode and, if so, then providing power to the heating source according to the second control mode. The controller also is configured for determining whether to transition from the second control mode to a third control mode and, if so, then providing power to the heating source according to the third control mode.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which:
Reference will now be made in detail to present embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. The detailed description uses numerical and letter designations to refer to features in the drawings. Like or similar designations in the drawings and description have been used to refer to like or similar parts of the invention. Further, each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.
Referring now to the drawings, wherein identical numerals indicate the same elements throughout the figures,
Cooking surface 20 of cooking appliance 10 includes heating source assemblies 22 having heating sources 24 (
As shown in
Referring still to
The operation of cooking appliance 10, including heating sources 24, may be controlled by a processing device such as a controller 30, which may include a microprocessor or other device that is in operative communication with components of appliance 10. Controller 30 may include a memory and microprocessor, such as a general or special purpose microprocessor operable to execute programming instructions or micro-control code associated with a cleaning cycle. The memory may represent random access memory such as DRAM, and/or read only memory such as ROM or FLASH. In one embodiment, the processor executes programming instructions stored in memory. The memory may be a separate component from the processor or may be included onboard within the processor. Alternatively, controller 30 may be constructed without using a microprocessor, e.g., using a combination of discrete analog and/or digital logic circuitry (such as switches, amplifiers, integrators, comparators, flip-flops, AND gates, and the like) to perform control functionality instead of relying upon software. Controls 18 and other components of cooking appliance 10 may be in communication with controller 30 via one or more signal lines or shared communication busses.
In some embodiments, one or more components of cooking appliance 10 may be controlled independent of controller 30. For example, the heat output of heating source 24 may be controlled by a mechanical, electromechanical, or thermo-electro-mechanical control mechanism, such as, e.g., an infinite switch. In other embodiments, a combination of controller 30 and one or more other control mechanisms may be used to control the features of cooking appliance 10. As an example, controller 30 may control the heat output of heating source 24 during one or more operating modes of appliance 10 and another control mechanism, such as the infinite switch, may control the heat output during other operating modes of appliance 10.
In the depicted embodiment, temperature sensor 26 is positioned such that sensor 26 contacts a bottom surface 11 of cooking utensil 12 (
Preferably, temperature sensor 26 is a spring-loaded sensor as depicted in
Referring now to
In some embodiments, as shown in
Because they are wired in series with the heat source 24, mechanical device 31 and energy control device 32 may each cause a pulse width modulation (“PWM”) of the power provided to heating source 24 to regulate the heat output of the heating source. In general, heating source 24 is fully controlled via the mechanical device 31, which regulates the output heat level of heating source 24 according to a user's input via user control 18. As such, heating source 24 usually is controlled via energy control device 32 only in the case of an unsafe cooking condition; that is, when an unsafe condition is detected, PWM by the mechanical device 31 is overridden by the temperature limiting algorithm described below such that the energy control device 32 causes the PWM of power provided to heating source 24.
In other embodiments, as shown in
Accordingly, unlike embodiments having a mechanical device 31 as illustrated in
As further described below, one or more methods may be used to limit a maximum temperature of cooking utensil 12 to prevent unsafe conditions of cooking appliance 10. In such methods, if cooking utensil 12 approaches a potentially unsafe temperature, controller 30 may be configured to utilize energy control device 32 to regulate or modulate the duty cycle of heating source 24 such that the average heat output over the duty cycle is a fraction of the user's selected heat output level. In an example embodiment, such a temperature limiting system may include three operating modes—a first control mode, a second control mode, and a third control mode. In the first control mode, a power level of heating source 24 may be regulated such that the power level approximates a user-selected power level. However, in the first control mode, a control device such as controller 30 may also monitor the temperature and/or rate of temperature change of a cooking utensil 12 positioned on the heating source 24 to determine whether to regulate the power level according to the second control mode. That is, if the control device determines heating of utensil 12 is approaching an unsafe condition, the control device may transition to the second control mode. In the second control mode, the power level of heating source 24 may go to essentially zero to allow dissipation of the thermal energy of the cooking utensil 12 and any food items therein, as well as to allow the temperature of the utensil and its contents to stabilize. After the power level has been essentially zero for a period of time, the power level of heating source 24 may be regulated in the third control mode, which controls the temperature of utensil 12 to a predetermined temperature limit. Of course, when operating in the second or third control modes, the temperature limiting system also include features for determining whether to transition back to the first control mode rather than continuing to operate in the current control mode or transitioning to the next control mode.
At step 502, heating source 24 is activated at a user selected heat output level. For example, controller 30 may detect a touch input to a touch-type control 18 or the user may manipulate of a knob, button, or other mechanical control 18 to input a power or heat level for heating source 24. Typical heat output levels of cooking appliances range from “LOW,” e.g., the lowest or least heat output of a heating source 24, to “HIGH,” e.g., the highest or greatest heat output of heating source 24. Other heat output levels, e.g., medium-low (“MED-LOW”), medium (“MED”), medium-high (“MED-HI”), and the like between the lowest and the highest levels also may be selectable. Thus, at step 502, heating source 24 may be activated according to a user input (LOW, MED, HIGH, etc.), i.e., according to a heat output level selected by the user, such that power (e.g., electric current or gas) is provided to heating source 24 to enable heating source 24 to provide heat at the selected heat output level.
Next, at step 504, power is provided to heating source 24 according to a first control mode M1. That is, for the particular heating source 24 activated at the user selected power level at step 502, a power level PHS is provided to the heating source to produce a heat output based on the power level input, i.e., based on the user selected power level. In an exemplary embodiment in which the user manipulates a touch-type control 18 to select a power level, controller 30 controls the duty cycle of heating source 24, as described above, to provide power at the power level PHS established by a first control mode M1. The first control mode M1 establishes the power level PHS as a power level determined by a formula or look-up table that corresponds to the user setting or user selected power level. That is, the first control mode M1 essentially regulates the power PHS of heating source 24 according to traditional methods for operating electronically-controlled heat sources in an electric cooktop. For example, in some embodiments, the power level PHS in the first control mode M1 is regulated through PWM of energy control device 32 at some predetermined rate (e.g., a period of 20 seconds). In another exemplary embodiment in which mechanical device 31 responds to manipulation of user control(s) 18 to regulate the power level of heating source 24, mechanical device 31 controls the duty cycle of heating source 24, as described above, to provide power at the power level PHS established by the first control mode M1. In such embodiments, controller 30 deactivates energy control device 32 and allows mechanical device 31 to control the power level PHS of heating source 24. An exemplary embodiment of the first control mode M1 is shown in
A cooking utensil 12 may be positioned on heating source 24, and as heating source 24 outputs heat, the cooking utensil 12 and any food items therein begin to warm. Controller 30 may monitor a temperature Tsensed of cooking utensil 12, e.g., by using temperature sensor 26 as described above. If the cooking temperature Tsensed begins to rise at a rapid rate, such that controller 30 calculates the cooking utensil temperature Tsensed will reach a target temperature limit Tlimit within a certain time period, controller 30 may determine that the power PHS provided to heating source 24 should be modulated differently than the power PHS is modulated in the first control mode M1. As such, method 500 may further include step 506 of determining whether to transition from the first control mode M1 to a second control mode M2. If so, then controller 30 provides power PHS to heating source 24 according to the second control mode M2, as shown at step 508. However, if at step 506 controller 30 determines not to transition to the second control mode M2, then controller 30 continues to provide power PHS to heating source 24 according to the first control mode M1.
The second control mode M2 may include reducing the power PHS provided to heating source 24 to a minimum power level Pmin, i.e., essentially disabling heating source 24 for a period of time to halt the input or delivery of heat to cooking utensil 12. Thus, the second control mode M2 essentially deactivates heating source 24 such that the residual thermal energy (i.e., heat) within the heating source may be dissipated into cooking utensil 12, allowing the heating of the utensil (and any food therein) to diminish and the temperature to stabilize; ideally, the temperature stabilizes at or below the target temperature limit Tlimit. An exemplary embodiment of the second control mode M2 is shown in
Next, as shown at step 510 in
As shown as step 514, if controller 30 determines to transition to the third control mode M3, power PHS is provided to heating source 24 according to the third control mode M3. In the third control mode, the power level PHS of heating source 24 is modulated as follows to help prevent cooking utensil 12 and/or any food items therein from overheating:
I=I+(Ki*Terr)
PHS=(Kp*Terr)+1
where
Terr=Tlimit−Tsensed
In the third control mode M3, controller 30 may use energy control device 32 to control the duty cycle of heating source 24 and thereby control the power PHS provided to heating source 24.
As shown, the third control mode M3 may utilize a proportional-integral (PI) or proportional-integral-derivative (PID) control algorithm; a PI control implementation is detailed herein. The PI control algorithm utilizes a temperature error Terr to determine the power PHS provided to heating source 24. The temperature error Terr is the difference between the cooking utensil temperature Tsensed measured or sensed by temperature sensor 26, which preferably is contact with bottom surface 11 of cooking utensil 12 as described above, and the target temperature limit Tlimit. The target temperature limit Tlimit is a predetermined temperature to which controller 30, using method 500, regulates the temperature of cooking utensil 12 to help prevent undesirable conditions that may occur as heat is provided to cooking utensil 12 and any food items within utensil 12. In some embodiments, the measured or sensed temperature Tsensed may be noise filtered to reduce the effects of spikes or irregularities in the measured values. Any appropriate noise filter may be used, such as, e.g., a moving average filter, a lag filter, or the like.
Further, the PI control utilizes a proportional gain factor Kp, an integral gain factor Ki, and an integrated temperature error term I to determine the power PHS provided to heating source 24. The proportional gain factor Kp and integral gain factor Ki may be predetermined and programmed into controller 30. For example, the proportional gain factor Kp and the integral gain factor Ki may be determined based on a specific system, e.g., based on a mass and power density of heating source 24 and/or a diameter, mass, and specific heat of cooking utensils 12 likely to be used with a particular cooking appliance 10. As such, the proportional gain factor Kp and the integral gain factor Ki used in the above PI control algorithm may vary from one embodiment to another of method 500. The integral term I may be established as a typical PI control integral term would be established, i.e., its value during each execution loop may be increased or decreased based on the calculated temperature error Terr.
Next, as shown at step 516, controller 30 may determine whether to transition from the third control mode M3 to the first control mode M1. If so, method 500 returns to step 504, and controller 30 provides power PHS to heating source 24 according to the first control mode M1. If controller 30 determines not to transition back to the first control mode, controller 30 continues to provide power to heating source 24 according to the third control mode M3. An exemplary embodiment of the third control mode M3 is shown in
As previously stated,
where Tsensed(0) is the current temperature and Tsensed(X) is the temperature measured or sensed X seconds ago. It will be appreciated that either or both of the temperature Tsensed and rate of change ΔT may be noise filtered as described above, e.g., using a moving average, lag, or other appropriate filter. Also, it will be appreciated that an electrically-heated cooking system (e.g., an electric coil or electric radiant cooking appliance 10) may have a relatively large thermal inertia because cooking utensil 12 and any food therein, as well as heating element 24, must be heated. As such, the rate of change ΔT of the cooking utensil temperature Tsensed will be relatively slow. Thus, in embodiments in which heating assembly 22 is an electric heating assembly, the time interval X should be fairly long or large, i.e., to accurately calculate the rate of temperature change ΔT, the temperature Tsensed should sampled over a fairly long time interval X, e.g., 10 seconds. Conversely, in embodiments in which heating assembly 22 is a gas-heated or induction heating assembly, where the heating source 24 typically does not have to heat up to provide heat to cooking utensil 12, the thermal inertia is relatively small such that the time interval X can be shorter, e.g., 3 seconds. Of course, other values of the time interval X may be used as well.
The first control mode M1 illustrated in
As with the cooking utensil temperature Tsensed and the rate of change ΔT of the temperature Tsensed, the time interval tlimit optionally may be noise filtered to prevent an unnecessary transition from the first control mode M1 to the second control mode M2, where the power provided to heating source 24 is reduced such that the power level PHS is zero or near zero. Stated differently, noise filtering the time interval tlimit may help prevent false reductions of the power PHS provided to heating source 24.
After calculating the time to target, controller 30 determines if the time interval tlimit to reach target temperature limit Tlimit is less than or equal to a predetermined time interval limit tturn_off, as shown at step 506c. If so, method 500 transitions to the second control mode M2 and power is provided to heating source 24 according to the second control mode M2, as illustrated at step 508. However, if the time interval tlimit is greater than the predetermined time interval limit tturn_off, controller 30 determines whether the cooking utensil temperature Tsensed is at least equal to the target temperature limit Tlimit, as shown at step 506d. If so, method 500 proceeds to step 508 and controller 30 provides power PHS to heating source 24 according to the second control mode M2. If not, controller 30 continues to provide power PHS to heating source 24 according to the first control mode M1. Optionally, method 500 also may include a check, whereby if the time interval tlimit is less than or equal to the predetermined time interval limit tturn_off, controller 30 determines if the cooking utensil temperature Tsensed is at least equal to an enabling threshold temperature Tthr before transitioning to the second control mode M2 and step 508. The enabling threshold temperature Tthr may be somewhat less than the target temperature limit Tlimit but close enough to the temperature limit Tlimit that it may be desirable to regulate the power PHS according to the second control mode M2.
Thus, in the first control mode M1, controller 30 evaluates how quickly cooking utensil 12 is expected to reach the target temperature limit Tlimit. The predetermined time interval limit tturn_off is selected as a threshold value; if controller 30 calculates it should take time interval tturn_off, or less than the time interval tturn_off, to reach the target temperature limit Tlimit, then it is likely that cooking utensil 12 will soon reach the target temperature limit Tlimit. If so, controller 30 may determine that the power to heating source 24 should be substantially reduced, i.e., the power to heating source 24 should be regulated according to the second control mode M2, to avoid cooking utensil 12 reaching undesirably high temperatures, which can lead to unsafe conditions of cooking appliance 10. As such, the predetermined time interval limit tturn_off preferably is selected such that the power to heating source 24 may be reduced to a minimum power level Pmin before cooking utensil 12 reaches an undesirably high temperature but is not reduced during routine cooking operations, such as boiling a pot of water. Prematurely reducing the power level PHS to the minimum power level Pmin, when there is a minimal or no threat to the safety of the user, cooking appliance 10, and the user's surroundings, could be a nuisance to the user. Typical values of time interval limit tturn_off may be between 70 and 100 seconds, but other values may be used as well. The value of tturn_off may be determined by experimental testing of heating source 24 and a variety of empty utensils 12 to determine how long the temperature of the utensil Tsensed will continue to rise after a power reduction, such that time interval tturn_off may be set to a value whereby the worst-case scenario (i.e., the longest continuation of temperature rise) will not over-shoot the target temperature limit when the power PHS is reduced.
Referring now to
Because of the thermal inertia of heating source 24, the cooking utensil temperature Tsensed will continue to rise after controller 30 reduces the power level PHS to the minimum power level Pmin. Method 500 includes waiting a period of time toff, but not longer than a threshold time interval tthr, for the thermal inertia of heating source 24 to dissipate. As shown at step 510b, controller 30 increments a timer, which is monitoring the time interval toff the power PHS provided to heating source 24 has been reduced to the minimum power level Pmin. Incrementing the timer generally may be represented as
toff=toff+1
such that the current value of toff is incrementally increased at a fixed rate over the previous value of time interval toff. Of course, in other embodiments, the time interval toff may be incremented in a non-linear or at a non-fixed rate.
After the timer is incremented, controller 30 determines at step 510c if the time interval toff has surpassed the threshold time interval tthr. If so, method 500 proceeds to step 514, where controller 30 provides power to heating source 24 according to the third control mode M3. Optionally, method 500 may include determining if the cooking utensil temperature Tsensed is at least equal to the target temperature limit Tlimit before transitioning to the third control mode M3 at step 514.
However, if at step 510c the time interval toff is not greater than the threshold time tthr, method 500 proceeds to step 512, and controller 30 determines whether to transition back to the first control mode M1. Controller 30 may determine whether to transition back to the first control mode M1 by comparing the temperature Tsensed of cooking utensil 12 to a disabling threshold temperature Tresume. If the cooking utensil temperature Tsensed is at or below the disabling threshold temperature Tresume, controller 30 may determine to transition back to step 504 and provide power to heating source 24 according to the first control mode M1. Transitioning back to providing power according to the first control mode M1 also may include resetting the time interval toff of the timer, i.e., setting timer toff to zero such that the timer is initialized at zero for any future iterations of the second control mode M2. However, if the cooking utensil temperature Tsensed is greater than the disabling threshold temperature Tresume, controller 30 may determine not to transition to the first control mode M1 such that controller 30 continues to provide power PHS to heating source 24 according to the second control mode M2.
PHS=(Kp*Terr)+1
At any point after heating source 24 has been activated, the user may select to turn off the heating source, e.g., when a cooking operation is complete or for any other reason. Thus, controller 30 also may determine whether heating source 24 should be deactivated, i.e., if the user has selected to deactivate or turn off heating source 24. More particularly, controller 30 may determine heating source 24 should be deactivated based on an input by a user of cooking appliance 10, e.g., the user may manipulate a user control 18 that signals to controller 30 that heating source 24 should be deactivated. If controller 30 determines the user has selected to deactivate the heating source, controller 30 deactivates heating source 24. As stated, a user may select to deactivate heating source 24 at any point after the heating source is activated, such that controller 30 may determine at any point in method 500 after step 502 that heating source 24 should be deactivated. That is, method 500 may include a step of determining whether heating source 24 should be deactivated at or between any appropriate step or steps within the method and is not limited to providing the step of determining whether heating source 24 should be deactivated at any particular point(s) within method 500.
It will be appreciated that method 500 may be utilized with one or more heating sources 24 of cooking appliance 10. That is, controller 30 may control the heat output of one or more heating sources 24 of appliance 10 according to method 500. In some embodiments, the power PHS provided to every heating source 24 may be regulated according to method 500, but in other embodiments, only one or only a portion of the heating sources 24 of appliance 10 may be regulated using method 500. That is, not all of the heating sources 24 of appliance 10 may utilize the foregoing algorithm; some of the heating sources 24 might not have a temperature limiting system or might utilize an alternative temperature limiting system than as described with respect to method 500. However, where the temperature limiting system of method 500 is utilized, each heating source 24 preferably has its own unique temperature sensor 26 and a corresponding energy control device 32 modulated by a uniquely-calculated PHS value.
As illustrated in
As depicted in
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.
| Number | Name | Date | Kind |
|---|---|---|---|
| 4620083 | Andre | Oct 1986 | A |
| 4692597 | Tsuda | Sep 1987 | A |
| 4913038 | Burkett | Apr 1990 | A |
| 5398597 | Jones | Mar 1995 | A |
| 5990454 | Westerberg | Nov 1999 | A |
| 6933477 | Becker | Aug 2005 | B2 |
| 7022949 | Shukla | Apr 2006 | B2 |
| 9131537 | Broders et al. | Sep 2015 | B2 |
| 9132302 | Luongo et al. | Sep 2015 | B2 |
| 20040149736 | Clothier | Aug 2004 | A1 |
| 20160076775 | Luongo et al. | Mar 2016 | A1 |
| 20160294219 | Van Wageningen | Oct 2016 | A1 |
| Number | Date | Country | |
|---|---|---|---|
| 20180010805 A1 | Jan 2018 | US |
