Abstract:
An apparatus is provided for detecting movement of a vessel positioned on a cooktop surface. The apparatus includes a resonant circuit that has at least an inductive loop positioned proximate to the cooktop surface. A signal conditioner is connected to the resonant circuit for conditioning signals received from the resonant circuit. A processor is connected to the signal conditioner and compares the conditioned signals received from the signal conditioner to a reference signal whereby detecting movement of the vessel.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an apparatus and method for detecting movement of a vessel on a cooktop surface and more particularly to the detection of movement by measuring signals produced by an inductive loop positioned below the cooktop surface. 
     A popular trend in electronically controlled cooktops and/or ranges, typically, includes a cooktop surface composed of a glass-ceramic material that is positioned above one or more radiant heating elements. The cooktop includes various user controls that can be used by an operator to adjust the amount of power supplied to the radiant heating elements and, therefore, the heat desired for cooking. The radiant heating elements can be powered by, for example, electricity, natural gas, propane or iso-butane. The radiant heating elements and the controls are connected to a controller that user controls the amount of energy supplied to the cooktop. The cooktop can also includes temperature sensors and/or other sensor that are connected to the controller to aid in controlling the energy supplied to the radiant heating element and ultimately the heat supplied to the cooktop. The temperature sensors and other sensors are also used in conjunction with the controller and/or other processors to detect certain detrimental conditions that can arise during operation of the cooktop. 
     For example, the temperature sensors in conjunction with the controller and/or other processors can detect a boil dry condition. Typically, a boil dry condition occurs when the liquid contents of a vessel positioned on the cooktop is caused to boil by heat from the radiant heating source such that all the liquid contents are boiled from the vessel. Specifically, a boil drying condition is predicted when a relatively rapid increase in the temperature of the cooktop surface occurs while constant energy is being supplied to the radiant heating element. When all the liquid contents have been evaporated and/or converted to gas from the vessel being heated on the cooktop, the radiant heating source will continue to supply heat to the cooktop causing the cooktop surface and/or the vessel to overheat and possibly become damaged. To prevent such damage, the temperature sensors and/or other sensors provide information to the controller and/or other processors that predicts the boil dry condition based on specific sensor characteristics, and when a boil dry condition is detected, energy is no longer supplied to the radiant heating element. 
     In addition, the controller is programmed with a maximum temperature that should not be exceeded to ensure a long service life for the glass ceramic cooktop surface. When the temperature sensors and controller determine that the temperature of the cooktop and/or the vessel is approaching the maximum temperature, the controller instructs the radiant heating source to reduce the heat being applied to the cooktop such that a constant temperature is maintained. The controller also ensures that the constant temperature is at or below the maximum temperature. When the controller holds the radiant heating element at a constant temperature, the controller enters a condition known as thermal limiter mode. While in thermal limiter mode, the temperature of the cooking surface and/or the vessel cannot be used to determine if a boil dry condition has occurred because the cooktop and/or range is being held at a constant temperature. Therefore when the controller is in thermal limiter mode, a boil dry condition is determined by monitoring the energy being applied to the radiant heating source. During thermal limiter mode, a rapid decrease in energy applied to the radiant heating source to maintain the maximum temperature will be interpreted as a boil dry condition by the controller, and energy will no longer be applied to the radiant heating element. 
     When the controller is in thermal limiter mode, conditions may occur that make the controller predict a false boil dry condition. If the bottom of the vessel has areas that are warped, dirty or imperfect, the thermal characteristics of the vessel can change as the vessel is, for example, moved on the cooktop surface. These thermal characteristics can cause changes in the temperature sensed by the temperature sensor when the vessel is moved or rotated on the cooktop, when the vessel is heated or cooled, or when cold or hot contents are added to the vessel. For example, the temperature sensor may be located near an area where the bottom of the vessel has good thermal contact, and then the vessel is moved or rotated such that an area having poor thermal contact is located near the temperature sensor. Under these conditions, the temperature sensed by the temperature sensor may increase simply because the vessel has been moved or rotated. Due to the increase in temperature sensed by the temperature sensor, the controller may instruct that less energy should be applied to the radiant heating element to maintain the constant temperature. Thus, since less energy is being applied to the radiant heating source to maintain the temperature, the controller may detect a false boil dry condition during thermal limiter mode. However, under the condition where the change in temperature is caused by a warped vessel, a boil dry condition may not necessarily exist because the poor thermal characteristics of the vessel caused the change in temperature rather than an actual boil dry condition. The false boil dry condition can cause dissatisfaction to an operator of the cooktop because when a boil dry condition is detected the power to the radiant heating element is turned off. Therefore, a desire exists to eliminate or reduce false detection of boil dry conditions resulting from vessels having poor thermal qualities in an electronically controlled cooktop. 
     BRIEF SUMMARY OF THE INVENTION 
     In one exemplary embodiment, an apparatus is provided for detecting movement of a vessel positioned on a cooktop surface. The apparatus comprises a radiant heating element positioned below the cooktop surface for heating at least the vessel. A controller is provided and is connected to the radiant heating element. The controller controls power supplied to the radiant heating element. A temperature sensor is connected to the controller and measures the temperature near the cooktop surface. An inductive loop is positioned proximate to the cooktop surface. A detection circuit is connected to the controller and the inductive loop. The detection circuit detects movement of the vessel on the cooktop surface using signals produced by at least the inductive loop. 
     In even another exemplary embodiment, a method is provided for detecting movement of a vessel on a cooktop surface. The movement is detected using a resonant circuit including an inductive loop. The method comprising supplying an energy signal to the inductive loop. At least a resultant signal produced by the inductive loop is measured. At least a magnitude and phase of angle of the resultant signal are determined. An instantaneous inductance of the inductive loop is calculated from at least the magnitude and the phase angle of the resultant signal. A reference inductance is determined. The reference inductance is determined by tabulating a predetermined number of instantaneous inductances over a predetermined amount of time, and calculating the reference inductance from the tabulated instantaneous inductances. Movement of the vessel is detected by comparing the instantaneous inductance to the reference inductance. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view and block diagram of one exemplary embodiment of an electronically controlled cooktop; 
     FIG. 2 is a top view and block diagram of another exemplary embodiment of an electronically controlled cooktop; 
     FIG. 3 is a block diagram of one exemplary embodiment of a detection circuit; and 
     FIG. 4 a graphic representation of various signals measured by an exemplary embodiment of the detection circuit. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in FIG. 1 and 2, one representative embodiment of an electronically controlled cooktop  100  is provided that comprises at least an inductive loop  160  and a detection circuit  170 . When a vessel  120  is moved or rotated on a cooktop surface  110 , the inductive loop  160  and the detection circuit  170  detects the movement of the vessel  120 . The detection of the vessel  120  movement is communicated to a controller  140  such that, for example, a false determination of a boil dry condition, among other conditions, is reduced and/or eliminated. 
     As shown in FIG. 1, the electronically controlled cooktop  100  comprises a radiant heating element  130  positioned below a cooktop surface  110 . It should be appreciated that, in other representative embodiments, that the radiant heating element  130  can be positioned on, above, proximate or within the cooktop surface  110 . In addition, the radiant heating element  130  produces heat and can be powered by, for example, electrical energy, natural gas, propane, etc. It should also be appreciated that, in another representative embodiment, the cooktop surface  110  comprises a glass ceramic material. A vessel  120  contains contents  122  and is positioned on the cooktop surface  110 . An inductive loop  160  is positioned below the cooktop surface  110  and is connected to a detection circuit  170 . It should be appreciated that the induction loop  160  can, in other representative embodiments, comprise various shapes and sizes, such as, for example, a rectangular shape, a circular shape, a straight rod shape and a triangular shape. In addition, it should also be appreciated that the inductive loop  160  can be positioned, for example, on, near, within, above, and proximate to the cooktop surface  110  and/or proximate to the vessel  120 . Additionally, it should also be appreciated that the mechanical design of the inductive loop  160  can also comprise other forms. 
     A temperature sensor  150  is positioned below the cooktop surface  110  to detect the temperature near the cooktop surface  110 . In one embodiment, the temperature near the cooktop surface  110  comprises the temperature of the area between the heating element  130  and the cooktop surface  110 . In another embodiment, the temperature near the cooktop surface  110  comprises the temperature of the cooktop surface  110 . A controller  140  is connected to the radiant heating element  130  to supply a controlled energy output via output  132 . Additionally, the controller  140  is connected to the temperature sensor  150  and the detection circuit  170 . It should be appreciated that, in other representative embodiments, the detection circuit  170  can be comprised within the controller  140 , and therefore, the inductive loop  160  can, in these other representative embodiments, be connected to the controller  140 . A user input interface  180  is also connected to the controller  140  to allow a user to select a desired power level to heat the cooktop surface  110  and thus the contents  122  of the vessel  120 . 
     As shown in FIG. 2, one representative embodiment of the detection circuit  170  includes a capacitive circuit  206  having a capacitor  204  connected in parallel to an amplifier  202 . The capacitive circuit  206  is connected to the inductive loop  160 . The combination of the capacitive circuit  206  and the inductive loop  160  comprises an electronic oscillator  200 . Also shown in FIG. 2, the detection circuit  170  also comprises a signal processor  210  connected to the capacitive circuit  206  and a processor  220  connected to the signal processor  210  and the controller  140 . 
     In FIG. 3, in another representative embodiment, the signal processor  210  of the detection circuit  170  further comprises a square wave generator  312  connected to the electronic oscillator  200  and a divider  314  connected to the processor  220  and the square wave generator  312 . The processor  220  is connected to the divider  314  via output  316 . In addition, the processor  220  is also connected to the controller  140 . The combination of the capacitor  204  and the inductive loop  160  comprises resonant circuit  208 . In the resonant circuit  208 , the inductive (L) component comprises the inductive loop  160  and the capacitive (C) component comprises the capacitor  204 . Therefore, the resonant circuit  200  comprises a tuned L-C circuit that can be tuned to detect a desired resonant frequency based on the choice of the inductive loop  160  (inductance L) and the capacitor  204  (capacitance C). 
     When the vessel  120  is moved or rotated on the cooktop surface  110 , the effective inductance of the inductive loop  160  changes and therefore, the resonant frequency of the resonant circuit  208  also changes. As such, in one representative embodiment, an energy signal is supplied to the inductive loop  160 . The movement of the vessel  120  can be determined by measuring the inductance of the inductive loop  160  over a predetermined amount of time and comparing the measured inductance to a reference inductance. The absolute value of the difference between the measured inductance and the reference inductance determines if the vessel  120  has been moved or rotated if the difference is greater than a predetermined value. In one representative embodiment, the predetermined value comprises a value that is, for example, about zero. In another representative embodiment, the predetermined value comprises a value that is, for example, greater than about zero. It should be appreciated that the energy signal supplied to the inductive loop  160  can comprise, for example, a fixed excitation energy signal or a variable excitation energy signal. 
     In even another representative embodiment, an energy signal is supplied to the inductive loop  160 . The movement of the vessel  120  is determined by measuring the frequency of the resonant circuit  208  over a predetermined amount of time and comparing the measured frequency to a reference frequency. In one representative embodiment, the absolute value of the difference between the measured frequency and the reference frequency determines if the vessel  120  has been moved or rotated when the difference is greater than a predetermined value. In one representative embodiment, the predetermined value comprises a value that is, for example, about zero. In another representative embodiment, the predetermined value comprises a value that is, for example, greater than about zero. It should be appreciated that the energy signal supplied to the inductive loop  160  can comprise, for example, a fixed excitation energy signal or a variable excitation energy signal. 
     In yet another representative embodiment, an energy signal is supplied to the inductive loop  160 . The magnitude and the phase angle of a resultant signal from the inductive loop  160  are measured. In one embodiment the resultant signal from the inductive loop  160  comprises, for example, the voltage and/or current of the inductive loop  160 . The instantaneous inductance of the inductive loop  160  is calculated from at least the magnitude and the phase angle. The instantaneous inductance of the inductive loop  160  is compared to a reference inductance to determine movement of the vessel  120 . In one embodiment, the absolute value of the difference between the instantaneous inductance and the reference inductance determines if the vessel  120  has been moved or rotated when the difference is greater than a predetermined value. In one representative embodiment, the predetermined value comprises a value that is, for example, about zero. In another representative embodiment, the predetermined value comprises a value that is, for example, greater than about zero. It should be appreciated that the energy signal supplied to the inductive loop  160  can comprise, for example, a fixed excitation energy signal or a variable excitation energy signal. 
     In one embodiment, a reference inductance is determined by tabulating a predetermined number of instantaneous inductances of the inductance loop  160  over a predetermined amount of time. The tabulated instantaneous inductances are used to calculate the reference inductance, such as, for example, taking an average of the predetermined number of tabulated instantaneous inductances over the predetermined amount of time. It should be appreciated that other methods of determining a reference inductance can be used, such as, for example, calculating a reference inductance before each use. 
     As shown in FIG. 3, the square wave generator  312  receives signals from the electronic oscillator  200 . As described above, the signals can comprise, for example, frequency, magnitude, phase angle, voltage and current. The square wave generator  312  generates a square wave in response to the signals received from the electronic oscillator  312 . The square wave from the square wave generator  312  is supplied to the divider  314  output  316 . The divider  314  divides the square wave signal into a predetermined number of pulses per second to allow easier calculation by the processor  220 . It should be appreciated that the divider  314  is used to assist the processor  220  during calculation of the frequency. In another embodiment, the divider  314  is not required and the processor  220  can be connected directly to the square wave generator  312 . In even another embodiment, the divider  314  and the square wave generator  312  are not required and the processor  220  can be directly connected to the electronic oscillator  200 . The divided square wave signal from the divider  314  is measured and recorded by the processor  220 . In one representative embodiment, the processor  220  is used to count the pulses produced by the divider  314  in response over a predetermined amount of time and measures the frequency or other properties of the square wave signal. Typically, a stable signal (frequency, inductance, current or voltage) is generated when the vessel  120  is stationary, as shown in FIG. 4 at time period A. Also shown in FIG. 4, the signal will include variations when the vessel  120  is moved or rotated, such as, for example, rotation of the vessel (time periods B and E), rocking the vessel  120  (time period D) and small discreet movements (time period C). 
     Any movement of the vessel  120  that changes the amount of metal and/or the gap length between the vessel  120  and the field of the inductive loop  160  will have the effect of changing the inductance of the inductive loop  160 . Accordingly, the frequency of the oscillations of the electronic oscillator  200  and/or the resonant circuit  208  will also change. Therefore, the processor  220  determines the movement of the vessel  120  by comparing the reference inductance and instantaneous inductance. In one representative embodiment, the reference signal comprises, for example, a value measured earlier in time and/or an average of prior tabulated instantaneous inductances. In another representative embodiment, when movement of the vessel  120  is detected, the processor  220  provides a signal and/or data to the controller  140  and the controller  140  executes a predetermined function in response to the received signal. It should be appreciated that, in other representative embodiments, the second processor  324  supplies the data from the divider  314  to the controller  140 , and the controller  140  performs the analysis of the divided square wave signal. 
     When the controller  140  has determined that the vessel  120  has been moved, the controller  140  can reduce or eliminate the false detection of various conditions involved with using a radiant heating element  130  to heat the contents  122  of a vessel  120  positioned on a cooktop surface  110 . In one representative embodiment, a boil dry condition that is detected immediately after movement or rotation of the vessel  120  can be ignored to eliminate a false boil dry detection. In addition, the determination of vessel  120  movement can also be used in temperature control, boil detection and other conditions to reject disturbances caused by movement of the vessel  120  and make the detection of these conditions more robust. 
     The foregoing discussion of the invention has been presented for purposes of illustration and description. Further, the description is not intended to limit the invention to the form disclosed herein. Consequently, variations and modifications commensurate with the above teachings and with the skill and knowledge of the relevant art are within the scope of the present invention. The embodiment described herein above is further intended to explain the best mode presently known of practicing the invention and to enable others skilled in the art to utilize the invention as such, or in other embodiments, and with the various modifications required by their particular application or uses of the invention. It is intended that the appended claims be construed to include alternative embodiments to the extent permitted by the prior art.