Error-compensation for temperature detection in a microwave oven

Abstract: The present invention relates to a temperature compensation method for a microwave oven, and more particularly to the method capable of compensating for the detected temperature error of food caused by electromagnetic wave noise when heating operation of microwave oven is controlled by an infrared sensor. The present invention comprises the first step of comparing a detected temperature with a predetermined cooking temperature, the second step of stopping heating operation as the detected temperature is higher than the cooking temperature, the third step of comparing a real detected temperature of food with the cooking temperature as heating operation is stopped, and the fourth step of compensating the real temperature of food by resuming heating operation when the real temperature of food is lower than the cooking temperature.

Description: The present invention relates to a cooking temperature compensation method for a microwave oven, and more particularly to the method capable of compensating for the detected temperature error of food caused by electromagnetic wave noise when heating operation of microwave oven is controlled by an infrared sensor. A conventional microwave oven (hereinafter "MWO") finishes cooking by stopping heating operation when a detected temperature from an infrared sensor reaches cooking temperature after heating operation starts. As a result, it is difficult to discriminate whether the temperature detected from the infrared sensor is real temperature of food or the temperature caused by electromagnetic wave noise. Namely, at the moment the temperature detected from the infrared sensor reaches cooking temperature, cooking is stopped immediately. Accordingly, the problem that cooking is half done occurs. Fig. 1 illustrates a block diagram showing a hardware system of a MWO in general. The MWO comprises an opening 4 at the upper part of a cooking chamber 1 and an infrared sensor 5 for detecting the temperature of the food 7 placed in the cooking chamber 1 through the opening. Also, the MWO comprises a heating part 3 for generating microwave based on the temperature detected from the infrared sensor 5 and a controlling part 6 for controlling all the operation of the system. Moreover, a turntable driving motor 8 being driven under control of the controlling part 6 is installed at the lower part of the cooking chamber 1. A turntable 2 is installed inside of the cooking chamber 1 and the turntable 2 turned by the rotation of the motor is mounted at the upper part of the motor 8 axis. Cooking stuff is placed thereon. The controlling part 6 controls the heating part 3 and the driving of motor 8 after a heating start key is operated. As shown in Fig.2, the controlling part 6 comprises: A key inputting part 6a for predetermining the cooking temperature suitable for desired food, or inputting the heating start signal; a predetermined temperature storing part 6b for storing the predetermined cooking temperature; a detected temperature storing part 6c for temporarily storing the temperature detected from the infrared sensor 5; a displaying part 6d for displaying simple message like the predetermined temperature and the detected temperature with liquid crystal display; and a output controlling part 6e for controlling the output by comparing the predetermined temperature with the detected temperature. That is, the controlling part 6 discriminates the detected temperature by a signal detected from the sensor 5, and then operates the heating part 3 to the extent that the detected temperature comes up to the predetermined temperature and controls the heating part 3 until cooking is completed. Food 7 is heated by microwave emitted from the heating part 3. The turntable 2 rotates to have the microwave emit widely to the food 7 when the heating part is operated. The control operation of the conventional MWO including the above system is described in detail as follows. The user puts food 7 on the turntable 2, predetermines proper cooking temperature through the key inputting part 6a and inputs the heating start key. The predetermined cooking temperature is stored in the predetermined temperature storing part 6b. The output controlling part 6e, as the heating start key is inputted, operates the heating part 3 and the turntable driving motor 8. In this way, microwave is emitted from the heating part 3, and the microwave heats food 7. As the heating part 3 is operated continually, the temperature of food 7 rises. On the other hand, the infrared sensor 5 detects through an opening 4 the food temperature placed in the cooking chamber 1. The detected temperature is temporarily stored in the detected temperature storing part 6c. The output controlling part 6e reads the temperatures stored in the detected temperature storing part 6c and the cooking temperature stored in the predetermined temperature storing part 6b, and compares both of them. Then, the output controlling part 6e heats food 7 by continuously operating the heating part 3 to the degree that the detected temperature comes up to the cooking temperature. And, as the temperature detected from the sensor 5 reaches the cooking temperature, the output controlling part 6e stops the operation of the heating part 3 and cooking is finished therein. Therefore, the automatic cooking controlling method for a conventional MWO completed cooking operation when the predetermined cooking temperature is detected through the sensor 5. According to the temperature controlling method for conventional the MWO, there was a slight difference between the detected temperature value of food detected from the sensor 5 and the real temperature value of food caused by high frequency while the heating part oscillates. That is, the detected value of the infrared sensor 5 does not coincide with the value of the predetermined cooking temperature due to high frequency, which is generated by the oscillation of the heating part 3, even if the real temperature of food 7 does not reach the predetermined cooking temperature. A prior art method for compensating a cooking temperature in a microwave oven with the steps recited in the preamble portion of claim 1 is disclosed in US-4 553 011 A. In this prior art method the oscillations in the microwave oven are repeatedly started and stopped to determine the temperature of the food stuff via the infrared sensor during a non-operation state and these temperature sensing cycles are repeated until a desired temperature is reached. SUMMARY OF THE INVENTION The object of the present invention is to provide a method for compensating a cooking temperature in a microwave oven which can compensate for the detected temperature error of food stuff caused by electromagnetic wave noise when the heating operation of the microwave oven is controlled by an infrared sensor. To achieve this object the present invention provides a method for compensating a cooking temperature in a microwave oven as recited in claim 1. This method comprises the steps of: heating a food stuff in a cooking chamber of a microwave oven; comparing a temperature of said food stuff detected by an infrared sensor with a predetermined cooking temperature; detecting another temperature of said food stuff during a non-heating operation of the microwave oven when said detected temperature is higher than said predetermined cooking temperature; comparing said another temperature of said food stuff with said predetermined cooking temperature; and compensating for said another temperature of said food stuff by resuming a heating operation of said microwave oven when said another temperature of said food stuff is lower than said predetermined cooking temperature; recalculating said another temperature and using said recalculated temperature for comparing with said predetermined temperature of said food stuff when it is determined that said another temperature has reached said predetermined cooking temperature due to an electromagnetic wave noise. Preferred embodiments of this method are defined in the dependent claims. The method of the present invention provides advantages in that it reduces the error in a detected temperature that can be caused by electromagnetic wave noise and which is likely to occur when a small quantity of food is to be cooked. Thereby, the method prevents that the cooking process is terminated due to this error before the food stuff has actually reached the desired, i.e. a predetermined temperature. The characteristics and advantage of the present invention will become more apparent by describing the preferred embodiments thereof with reference to the accompanying drawings, in which: Fig.1 illustrates a hardware block diagram for whole system of conventional MWO, Fig.2 illustrates a detailed block diagram of controlling part in Fig.1 for conventional automatic cooking control. Fig.3 illustrates a detailed block diagram of controlling part in Fig.1 for compensating cooking temperature according to the present invention. Fig.4 illustrates a flowchart showing the method for compensating cooking temperature according to the present invention. Fig.5 illustrates a waveform mixed with oscillating noise of magnetron according to the present invention. Referring to Fig.1 and 3, the whole system and the controlling part 6 in the present invention is described in detail as follows. According to Fig.1, the device to which the present invention is applicable comprises a turntable 2 located in the center of a cooking chamber 1, a heating part 3 for generating microwave to heat food 7, a temperature sensor 5 of a kind of noncontacting type such as thermopile sensor for detecting temperature of food 7 through an opening 4 placed in the upper part of the cooking chamber 1 and a controlling part 6 for controlling all the operations of each part. According to Fig.3, the controlling part 6 comprises a key inputting part 6A for predetermining cooking temperature appropriate for desired cooking and inputting a heating start key, a predetermined cooking temperature storing part 6B for storing a predetermined cooking temperature, a detected temperature storing part 6C for storing the temperature detected from said sensor 5, and a displaying part 6D for displaying the predetermined cooking temperature or the detected temperature, etc. Also, the controlling part 6 comprises a output controlling part 6E for controlling the operation of the heating part 3 by comparing the cooking temperature with the detected temperature, a first timer 6F for counting cooking time, and a second timer 6G for counting a rotational cycle of the turntable 2. That is, the temperature control of the present invention discriminates whether the temperature detected from a sensor 5 reaches the real temperature of food or not. In case the temperature detected from the sensor 5 reaches the predetermined cooking temperature even when the real temperature of food 7 does not come to the cooking temperature, the detected temperature is re-calculated. In other words, the detected temperature is re-calculated by adding a value being a product of a predetermined variable and the re-heating time TI of the heating part 3 to the maximum value CMAX of real temperature of food 7 and discriminates whether the re-calculated temperature reaches the predetermined cooking temperature or not. Related to Fig. 4, the temperature compensation method of the present invention is described below. The user puts food 7 on the turntable 2 in the cooking chamber 1 and selects the heating start key through the key inputting part 6A. The output controlling part 6E, when the heating start key is input, operates the driving motor 8 for the turntable and the heating part 3. The heating part 3 generates microwave and increases temperature of food in the cooking chamber 1. The turntable 2 is rotated by motor 8. On the other hand, the predetermined cooking temperature CS is set through the key inputting part 6A by the user before the heating start key is inputted. The predetermined cooking temperature CS is stored in the predetermined cooking temperature storing part 6B. The predetermined cooking temperature CS can be set directly by the user or the cooking temperature CS already stored in the predetermined cooking temperature storing part 6B may be read by the output control part 6E by selecting an auto cooking mode. In any case, the output controlling part 6E recognizes the predetermined cooking temperature CS. Likewise, cooking time TS can be set directly by the user through the key inputting part 6A before the heating start key is inputted or the predetermined cooking time TS may be read by the output controlling part 6E by selecting an auto cooking mode. In this way, the output controlling part 6E recognizes the cooking temperature CS and the cooking time TS, and controls the operation of the heating part 3. And the first timer 6F counts the cooking time under the control of the output controlling part 6E since the start of operation of the heating part 3. After that, temperature of food 7 is increased gradually, as time goes by, in relation to the oscillating operation of the heating part 3. The infrared sensor 5 detects the temperature of food 7 through the opening 4 and this detected temperature is temporarily stored in the detected temperature storing part 6C. The output controlling part 6E continually reads the detected temperature CC, which is stored in the detected temperature storing part 6C. And the heating part 3 continues to oscillate until the detected temperature reaches the cooking temperature comparing the detected temperature CC with the predetermined cooking temperature CS(The 101 step). In the 101 step, when the detected temperature CC detected from the sensor 5 is equal to or higher than the predetermined cooking temperature CS, the output controlling part 6E discriminates whether the detected temperature CC detected from the sensor 5 has reached the predetermined cooking temperature CS during the predetermined cooking time TS or not (The 103 step). If 'no' in the 103 step, the output controlling part 6E reads a counted present time TC since the first timer 6F started and compares the counted present time TC with the predetermined cooking time TS (The 113 step). In the 113 step, when the output controlling part 6E discriminates that the real temperature of food 7 reaches the predetermined cooking temperature when the value of the counted present time TC is greater than the value of the cooking time TS and then stops the cooking operation (The 115 step). That is, the finishing of cooking means that the heating operation of the heating part 3 and the rotation of turntable driving motor 8 stop. However, when the output controlling part 6E discriminates, in the 113 step, that the value of the counted present time TC is not greater than the value of the cooking time TS, it is recognized that there are the temperature errors, which is detected from said sensor, caused by electromagnetic wave noise. And the output controlling part 6E temporarily stops the heating operation of the heating part 3 and substitutes the present time TC for a time variable TN. Also, it sets flagl as logical "1" in order to express that the detected temperature CC has come to the predetermined cooking temperature CS within the cooking time TS (The 117 step). Again, operating process returns to the 101 step and performs the 101 step and the 103 step repeatedly. And, in the 103 step, the controlling part 6E discriminates that the detected temperature CC has ever reached the predetermined cooking temperature CS within the cooking time TS according to the value (Flag=1) resulting from the 117 step. Next, the output controlling part 6E discriminates whether the detected temperature CC caused by electromagnetic wave noise and detected from the sensor 5 has reached the predetermined cooking temperature CS (The 105 step). At this time, a decision in the 105 step is made in the state of stopping the heating operation of the heating part 3 under the control of the output controlling part 6E. So, the error of detected temperature caused by electromagnetic wave noise generated from heating part 3 is eliminated. In this state, the output controlling part 6E discriminates that there is no influence by noise when the cooking temperature CS hardly differs from the real temperature of food 7 detected from the sensor 5 during a revolution of the turntable 2. To carry out the above decision operation, the output controlling part 6E continually counts the revolution time of the turntable 2 by means of the second timer 6G. At the same time, the output controlling part 6E continuously recognizes the value counted by the first timer 6F while the turntable 2 rotates. That is, the output controlling part 6E discriminates that if the present time TC which is counted by the first timer 6F is greater than the time (TN + 1 second), which adds 1 second to the time variable TN gained from the 117 step, and if it is within the value [TN + TT + 1 second], which adds the revolution cycle TT of the turntable which is counted by the second timer 6G plus 1 second to the time variable TN (The 119 step). And, after the present time TC counted by the first timer 6F exists within the range be. set in the 119 step, the temperature detected from the sensor 5 becomes the real temperature of food 7. That is, the output controlling part 6E substitutes higher value for a maximum temperature CMAX of food 7, by continually comparing the present detected temperature with previous detected temperature (The 121 step and the 123 step). The present time TC is counted until a revolution of turntable 2 terminates for detecting of the maximum temperature CMAX of food 7(The 125 step). Therefore, when the operation of the 125 step ends, the present time TC becomes the value (TN+TT+1second) which adds the revolution cycle TT of the turntable 2 and 1 second to the time variable TN set in the 117 step. Then, the output controlling part 6E discriminates whether the error of temperature detection caused by noise or the termination of normal cooking operation by comparing the maximum temperature CMAX of food with the cooking temperature CS. To carry out the above decision operation, the output controlling part 6E allocates a certain of the error temperature CM to the cooking temperature CS in consideration of an error occurred in cooking actually. The error temperature is given as follows. CM=(0.5×CS-15) (The 127 step) The error temperature can be set differently depending on MWO and food that is to be cooked. And, the output controlling part 6E completes cooking by discriminating if the real temperature of food 7 has reached the cooking temperature, in case that the maximum temperature CMAX of food gained from carrying out up to the 125 step is greater than the value (CS-CM) subtracted the error temperature CM from the cooking temperature CS (The 133 step). Yet, in case that the maximum temperature CMAX of food gained from carrying out up to the 125 step is smaller than the value (CS-CM) subtracted the error temperature CM from the cooking temperature CS, the output controlling part 6E discriminates if the present detected temperature has reached the cooking temperature by noise and sets Flag2 as logical "1" (The 131 step). And again, the output controlling part 6E enables the process to return to the first step 101. The output controlling part 6E performs the 103 step if the detected temperature CC is greater than the cooking temperature CS in the 101 step and performs the 105 step if the detected temperature (the result gained after carrying out the 117 step) ever reaches the cooking temperature within the cooking time TS in the 103 step. And, the output controlling part 6E recognizes that the detected temperature has reached the cooking temperature by noise in the 105 step (the result gained from carrying out up to the 131 step) and re-operates the heating part 3. And, regardless of temperature detected from the sensor 5, by adding the temperature (0.05 × re-operation time TI of the heating part3) gained in proportion to the heating time to the maximum temperature CMAX of food gained in the 125 step, the output controlling part 6E calculates the detected temperature CC (The 107 step). Then, if the detected temperature resulted in the 107 step is greater than the cooking temperature (the 109 step), the output controlling part 6E recognizes that the food temperature has reached the cooking temperature, and stops the operation of the heating part 3 (The 111 step). As described above, the present invention compares the detected temperature CC of food detected from sensor 5 in cooking with the predetermined cooking temperature CS and stops the operation of the heating part 3 when the detected temperature has reached the cooking temperature, and measures the maximum temperature CMAX of food 7 by the sensor 5 during one or more revolution cycle of the turntable 2 and discriminates that the real temperature of food has reached the cooking temperature when the measured temperature is approximately the same as the cooking temperature. If the real temperature of food 7 does not reach an approximate value of the cooking temperature, the present invention discriminates that the detected temperature has reached the cooking temperature due to noise and re-operates the heating part 3. And regardless of the temperature detected from the sensor 5, the present invention compares the re-calculated temperature, which is the sum of the temperature (0.05 × re-operation time TI of the heating part3) gained in proportion to the heating time and the maximum temperature CMAX of food, with the cooking temperatures and discriminates whether the real temperature of food 7 has reached the cooking temperature and stops cooking. In this way, the real temperature of food appears to reach the cooking temperature even if the one does not reach the other. It is because the oscillating noise of magnetron influences detecting of a signal of the sensor and the error of detected temperature occurs when the heating part operates, as shown in fig. 5. Therefore, the present invention has advantages to reduce the error temperature value caused by electromagnetic wave noise which is likely to occur in cooking a small quantity of food especially, so that it can be prevented from finishing earlier.

Claims: A method for compensating a cooking temperature in a microwave oven, the method comprising the steps of: heating a food stuff (7) in a cooking chamber (1) of a microwave oven; comparing a temperature (CC) of said food stuff detected by an infrared sensor (5) with a predetermined cooking temperature (CS); detecting another temperature of said food stuff (7) during a non-heating operation of the microwave oven when said detected temperature (CC) is higher than said predetermined cooking temperature (CS); comparing said another temperature of said food stuff with said predetermined cooking temperature (CS); and compensating for said another temperature of said food stuff by resuming a heating operation of said microwave oven when said another temperature of said food stuff is lower than said predetermined cooking temperature (CS); characterized by the step of recalculating said another temperature and using said recalculated temperature for comparing with said predetermined temperature of said food stuff when it is determined said another temperature has reached said predetermined cooking temperature (CS) due to an electromagnetic wave noise. The method for compensating a cooking temperature in a microwave oven according to claim 1, wherein said non-heating operation is performed when an accumulated present cooking time (TC) is shorter than a preset time duration (TS) for reaching said predetermined cooking temperature (CS). The method for compensating a cooking temperature in a microwave oven according to claim 1 or 2, wherein the said detecting of said another temperature of said food stuff is performed during a rotational period of a turntable (2). The method for compensation a cooking temperature in a microwave oven according to any one of claims 1 to 3, further comprising the step of setting said another temperature of said food stuff to a maximum value (CMAX) of said temperature. The method for compensating a cooking temperature in a microwave oven according to any one of claims 1 to 4, wherein said step of recalculating includes the step of calculating the said temperature of said food stuff as a sum of a maximum of said temperature (CMAX) and a product of a predetermined variable and a time of re-operation (TI) of a heating part (3) of said microwave oven. The method for compensating a cooking temperature in a microwave oven according to any one of claims 1 to 5, further comprising the step of determining if said temperature obtains a temperature level of said predetermined cooking temperature within a predetermined time. The method for compensating a cooking temperature in a microwave oven according to claim 6, wherein the step of determining includes the step of rectifying if an accumulated present time is greater than said predetermined time, whereby if said accumulated present time is greater than said predetermined time, it is determined said another temperature has been reached and an operation of the microwave is terminated. The method for compensating a cooking temperature in a microwave oven according to claim 7, wherein in the step of rectifying, if it is determined said accumulated present time is less than said predetermined time, then an operation of a heating part (3) is at least temporarily caused to turn off.

Inventors: PARK WON KYUNG, PARK, WON KYUNG
Applicants: LG ELECTRONICS INC, LG ELECTRONICS INC.
Application year: 1998
Main classification: H05B6
IPC codes: H05B6