Microwave oven for heating the contents of a cup

Abstract: The present invention relates to a microwave oven and more particularly to an apparatus and a method of heating a cup in a microwave oven by judging quantity of food in the cup on the basis of variation degree of an initial temperature and compensating a cooking temperature. The method of heating the cup according to the present invention comprises the steps of detecting variation degree of the temperature for initial uniform time period, judging the quantity of the subject matter on the basis of the detected variation degree of the temperature, estimating the raised temperature on the basis of quantity of the subject matter, comparing the estimated temperature with the temperature detected by sensor to determine the higher temperature as a current temperature, and executing the cooking mode until the current temperature is raised to the set cooking temperature.

Description: BACKGROUND OF THE INVENTION The present invention relates to an apparatus and a method of heating a cup in a microwave oven by judging the quantity of subject matter in the cup on the basis of a variation degree of an initial temperature and compensating a cooking temperature. In the general cooking method for heating the cup in the microwave oven, the cup is heated until the temperature detected by an infrared sensor is raised to the prescribed temperature, after the heating mode is started. FIG. 1 is a block diagram showing the structure of the conventional microwave oven. In the conventional microwave oven, as shown in the figure, the cooking chamber has an opening 4 formed at the upper portion of its side wall and an infrared sensor 5 sensing the temperature of the object set therein through the opening 4. Further, the microwave oven includes a heating unit 3 generating the microwave on the basis of the temperature detected by the infrared sensor 5 and a judging unit 6 controlling the operation of the heating unit 3. In the lower portion of the cooking chamber, a motor 8 is mounted to drive a turntable 2 with a control signal from the judging unit 6. The turntable to be rotatably mounted within the cooking chamber 1 is provided at the upper portion of the shaft of the motor 8. On the turntable, the object containing the food to be cooked is located. The judging unit 6 is controlling the heating unit 3 and the motor 8 after operating the heat starting key. The judging unit 6 includes the structure indicated in FIG. 2. This structure is described in detail as follows. The judging unit 6 comprises a key input unit 6a for setting the cooking temperature corresponding to the selected food or inputting the heat starting signal, a set temperature storing unit 6b for storing the set cooking temperature, a current temperature storing unit 6c for temporarily storing the current temperature detected by the infrared sensor 5, a display unit 6d including the liquid crystal display to indicate the set and current temperature, and an output controlling unit 6e for comparing the set temperature with the current temperature to control the output. With the signal detected by the sensor 5, the current temperature is judged by the judging unit 6. In case where the detected current temperature is lower than the set temperature, the judging unit 6 controls the heating unit 3 until the current temperature is identified to correspond with the set temperature for completion of the cooking. The object 7 within the cooking chamber 1 is heated by the microwave generated by the heating unit 3. When starting the heating operation, the turntable is rotated to apply the microwave to the object 7. Hereinafter, the operation of the conventional microwave oven is described in detail accompanying the drawings. FIG. 3 is a flow chart for the cooking operation of the conventional microwave oven. By the user, the object 7 is first put on the turntable 2 in the cooking chamber 1 and the key input unit 6a is operated to set the appropriate cooking temperate and to select the cooking start key. The set cooking temperature is memorized in the set temperature storing unit 6b. When the cooking start key is selected, the heating unit 3 is driven according to the controlling signal from the output controlling unit 6e. As a result, the microwave is generated by the heating unit 3 so that the object 7 is heated. By the heating operation of the heating unit 3, the temperature of the object 7 is gradually increased. On the other hand, the temperature of the object 7 is detected by the infrared sensor 5 through the opening 4. The output controlling unit 6e reads the temperature stored in the current temperature storing unit 6c and the cooking temperature stored in the set temperature storing unit to compare them (step 110). Thereafter, when the detected current temperature is determined to be lower than the cooking temperature, the heating unit 3 is continuously driven by the output controlling unit 6e to heat the object 7. When the current temperature is raised to the cooking temperature, the output controlling unit 6e stops the operation of the heating unit 3 for completion of the cooking (step 120). The object located in the cooking chamber 1 includes a cup containing a subject matter such as water and milk. Since the cup is heated by the microwave generated by the drive of the heating unit 3, the practical temperature of the subject matter 9 in the cup can be higher than the cooking temperature and the current temperature detected by the infrared sensor 5. Specially, if the amount of subject matter 9 in the cup is small, the difference between the practical temperature of the subject matter 9 and the set cooking temperature is larger. This difference is caused by the heat conduction. That is, the heat of the subject matter is transmitted to the cup so that the subject matter 9 has the higher temperature than the cup. Further, the temperature deviation between the various parts of the cup and the subject matter causes the temperature difference between the cup and the subject matter according to quantity of the subject matter. In case where the cup is heated to a set cooking temperature of 50°C, for example, if the subject matter in the cup is 100ml, the temperature is 73°C; if the subject matter in the cup is 150ml, the temperature is 69°C; if the subject matter in the cup is 200ml, the temperature is 63°C; if the subject matter in the cup is 250ml, the temperature is 55°C; if the subject matter in the cup is 300ml, the temperature is 51°C; and if the subject matter in the cup is 350ml, the temperature is 43°C. In the conventional method of heating the cup in the microwave oven using the infrared sensor 5 to sense the temperature, that is, the subject matter of a small quantity is blocked from the sensing region of the infrared sensor 5 by the cup, since the infrared sensor 5 is mounted at the upper portion of the side wall (as shown in FIG. 4). In the conventional microwave oven, therefore, the practical subject matter in the cup has a great difference in temperature from the set cooking temperature. As a result, there are some inconveniences for user. SUMMARY OF THE INVENTION An object of the present invention is to provide an apparatus and a method of heating a subject matter in a cup in the microwave oven in which the difference between the temperature of the subject matter within the cup and the set cooking temperature can be minimized. In order to achieve this object, the method of heating a subject matter in a cup according to the present invention comprises the steps defined in claim 1. Further, the apparatus for heating a subject matter in a cup in the microwave oven comprises the features of claims 4. In the apparatus and the method of heating the cup according to the present invention, the detected temperature of the subject matter is compensated, because the infrared sensor cannot detect the temperature of the subject matter in the cup for small quantity of the subject. For a large variation degree of the initial temperature, that is, for a large quantity of the subject matter, the variation degree of the temperature for the subject matter is directly detected by the infrared sensor so that the current temperature is raised with certain low gradient. For a small variation degree of the initial temperature, that is, for a small quantity of the subject matter, the variation degree of the temperature for the subject matter cannot be measured by the infrared sensor so that the current temperature is raised with prescribed high gradient. Thus, the detected temperature is compensated according to the quantity of the subject matter in the cup and the temperature deviation for the quantity of the subject matter can be minimized by comparing the highest of the compensated current temperature and the temperature detected by the sensor with the set cooking temperature. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view showing the conventional microwave oven. FIG. 2 is a block diagram showing the judging unit of FIG. 1. FIG. 3 is a flow chart showing the method of heating the cup in the conventional microwave oven. FIG. 4 is a view showing the sensing state of the temperature by the sensor in case of a small quantity of the subject matter according to the present invention. FIG. 5 is block diagram showing the judging unit for the temperature compensation control according to the present invention. FIG. 6 is a flow chart showing the method of heating the cup according to the present invention. FIG. 7 and FIG. 8 are graphs showing the characteristics of the temperature compensation according to the present invention. DETAILED DESCRIPTION OF THE INVENTION Hereinafter, the present invention is described in detail accompanying the drawings. The entire structure of the microwave oven is described in FIG. 4 and the judging unit is described in FIG. 5. The microwave oven comprises the turntable 2 to be rotated at the center of the cooking chamber 1, the heating unit 3 generating the microwave to heat the cup 7, the temperature sensor 5 of thermopile type for detecting the temperature of the cup 7 in the cooking chamber 1 in noncontact manner through the opening 4 formed at the upper portion of the side wall in the cooking chamber 1, and the judging unit 6 for determining the operation of the circuit unit including the heating unit by the detected temperature. The judging unit 6 comprises the key input unit 6A for setting the cooking temperature of the selected food at an appropriate temperature and inputting the heat starting key, the set temperature storing unit 6B for storing the set cooking temperature, a first current temperature storing unit 6C for storing the current temperature detected by the sensor 5, and a display unit 6D for displaying the cooking temperature, the current temperature, and the time. Further, the judging unit 6 includes the output controlling unit 6E for controlling the output by comparing the current temperature with the set cooking temperature, a timer 6F for counting the cooking time, a storing unit 6G for storing the gradient for the variation degree of the initial temperature of cup 7, and a second current temperature storing unit 6H for estimating and storing the estimated current temperature of the subject matter 9 in the cup 7. In the above structure, when the user operates the key input to heat the cup 7, the heating unit 3 heats the cup for the initial set time period under the control of the output controlling unit 6E. When the cup is heated for this set time period, the temperature variation over time, i.e. the gradient is detected. At this time, the detected gradient of the temperature variation is stored in the storing unit 6G. The output controlling unit 6E judges the quantity of the subject matter in the cup 7 by the gradient and estimates the temperature thereof according to this quantity. At this time, the initial time is set as a part time for the total heat time. If the variation degree of the detected temperature is large for the initial time period, this means that the temperature is directly detected by the infrared sensor 5, as shown in FIG. 1. In this case, the subject matter, the water, in the cup 7 is more than the appropriate quantity. That is, the temperature of the subject matter is rapidly raised at the initial state of the heating. Thus, the variation degree of the temperature detected by the infrared sensor 5 becomes large. If the variation degree of the detected temperature is small for the initial time period, this means that the temperature is not directly detected by the infrared sensor 5, as shown in FIG. 4. In this case, the heat is transmitted to the cup 7 after the subjected matter in the cup 7 is heated. Thus, the temperature of the initial heating state is merely different from that before heating. As a result, since the temperature of the cup is held at a low temperature during the initial time period, the variation degree of the temperature detected by the infrared sensor 5 for the initial time period is small. As described above, when the variation degree of the temperature detected by the infrared sensor 5 for the initial time period is small, the infrared sensor 5 does not directly detect the temperature of the subject matter so that the subject matter is judged as a small quantity. By the above method, the output controlling unit 6E judges the quantity of the subject matter in the cup 7 and estimates the temperature of the subject matter on the basis of its quantity. Further, the output controlling unit 6E compares the estimated temperature with the set cooking temperature to execute the cooking mode until the estimated temperature is raised to the cooking temperature. Hereinafter, the operation of the present invention is described in detail accompanying FIG.6. FIGs.7 and 8 are graphs showing the characteristics of the temperature compensation in the heating method. First, the user puts the cup 7 containing the water or milk on the turntable 2 and selects the heat starting key through the key input unit 6A. When the heat starting key is selected, then the turntable driving motor 8 and the heating unit 3 are driven by the output controlling unit 6E. The microwave is generated by the heating unit 3 so that the temperature of the cup 7 in the cooking chamber 1 is raised. At this time, the turntable on which the cup is located is rotated by the motor 8. On the other hand, the cooking temperature is set by the user through the key input unit 6A before inputting the heat starting key and this set cooking temperature is stored in the set temperature storing unit 6B. This means that the cooking temperature is set by the user according to the kind of the food to be cooked. For some food, however, the cooking temperature is previously stored in the set temperature storing unit 6B so that the output controlling unit 6E reads the stored cooking temperature to drive the motor 8 and the heating unit 3. In other words, the output controlling unit 6E recognizes the stored cooking temperature. Similarly, the cooking time is also set by the user through the key input unit 6A before inputting the heat starting key. Further, the previously set cooking time can be recognized by the output controlling unit 6E by selecting the automatic cooking mode. As described above, the output controlling unit 6E recognizes the cooking temperature and the cooking time to control the oscillation of the heating unit 3. The timer 6F counts the cooking time when the heating unit 3 starts to oscillate. When the heating unit 3 is oscillating, the time counted by the timer 6F is continuously inputted to the output controlling unit 6E so that the output controlling unit 6E judges that the cooking time expires 30 seconds after start of the heating (step 201). In the step 201, that is, the variation degree of the temperature is detected for an initial constant time period. Therefore, it is not necessary for the initial constant time period to be limited to 30 seconds. According to the kind of the food, the initial constant time periods can be set as long or short time period in each case of the long or short cooking time so as to detect the variation degree of the temperature. Thus, the output controlling unit 6E executes the gradient detecting process from starting the heating operation of the heating unit 3 to expiry of the initial constant time period (about 30 seconds) by the step 201. The current temperature detected by the infrared sensor 5 is temporarily stored in the current temperature storing unit 6C. This stored current temperature is repeatedly compared with the previously detected temperature to detect the gradient according to the variation degree of the temperature for the constant time period (step 203). In the step 203, the gradient is differently detected in the following two cases. The first case is that the variation degree of the cooking temperature for 30 seconds after starting the heating process is large as shown in FIG. 7. The second case is that the variation degree of the cooking temperature for the initial constant time period is small as shown in FIG.8. If the gradient of the temperature for the initial constant time period (about 30 seconds which should be determined as multiple of the rotating period to correctly detect the variation degree of the temperature) is steep as shown in FIG. 7, the infrared sensor 5 directly detects the temperature of the subject matter 9 in the cup 7 as shown in FIG. 1. In this case, the cup contains a large quantity, so that the output controlling unit 6E estimates the temperature which is in proportion to the cooking time and in inverse proportion to the gradient detected in the step 203. After the initial constant time period, the output controlling unit 6E estimates the detected temperature with the following equation (1). estimated temperature = a / b (current time - 30 seconds) + c where a is a certain constant. On the basis of the highest temperature ( c ) of the detected temperatures for 30 seconds, the output controlling unit 6E obtains the estimated temperature which is in inverse proportion to the gradient of the variation degree of the initial temperature obtained in the step 203 ( a / b ) and in proportion to the cooking time (current time - 30 seconds). At this time, since the estimated temperature is calculated by the lower gradient than the gradient obtained in the step 203, the raising degree of the estimated temperature is small. Thus, the estimated temperature is less steep than the temperature shown in FIG. 8 (step 205). As shown in FIG. 8, when the gradient of the temperature for initial constant time period (about 30 seconds which should be determined as multiple of the rotating period to detect correctly the variation degree of the temperature) is less steep than the gradient shown in FIG. 7, the infrared sensor 5 cannot detect directly the temperature of the subject matter 9 in the cup 7. In this case, the cup contains a small quantity, so that the output controlling unit 6E estimates the temperature which is in proportion to the cooking time and in inverse proportion to the detected gradient. In this time, also, the current temperature is estimated with equation 1. The variation degree of the temperature to be estimated is raised with the larger gradient than the previously calculated gradient. In this case, therefore, the gradient is steeper compared with the gradient shown in FIG.7 (step 205). When the current temperature is estimated in the step 205, the output controlling unit 6E compares the estimated temperature dependent upon the cooking time with the temperature detected by the sensor 5 (step 207). If the detected temperature is higher than the estimated temperature, the output controlling unit 6E determines the detected temperature as the current temperature (step 213). If the detected temperature is lower than the estimated temperature, the output controlling unit 6E determines the estimated temperature as the current temperature (step 209). That is, the output controlling unit 6E determines the higher temperature of the detected temperature and the estimated temperature as the current temperature. As shown above, since the higher temperature of the two is determined as the current temperature of the subject matter 9 in the cup 7, the temperature deviation dependent upon the quantity of the subject matter may be decreased. Further, the determined current temperature and the set cooking temperature are compared with each other (step 211). Until the determined current temperature is raised to the cooking temperature, the heating unit 3 is driven. When the current temperature is raised to cooking temperature, the heating unit 3 is stopped by the output controlling unit 6E (step 215). In the present invention, as described above, it is judged that the cup contains the subject matter of a large quantity, when the variation degree of the initial temperature is large. Thus, the current temperature is raised with small gradient. In case of the small variation degree of the initial temperature, however, it is judged that the cup contains the subject matter of a small quantity, so that the current temperature is raised with the large gradient. By comparing the calculated temperature with the set cooking temperature, the temperature deviation dependent upon the quantity of the subject matter in the cup can be minimized. As shown above, the present invention estimates the detected temperature by judging the quantity of the subject matter in the cup and this estimated temperature is compared with the set cooking temperature for cooking. Therefore, the cooking temperature may be controlled precisely, so that the user is able to obtain the well-cooked food.

Claims: A method of heating a subject matter in a cup in a microwave oven, the method comprising the steps of: detecting a variation degree of a temperature for an initial constant time period of heating (201,203); judging the quantity of the subject matter in the cup on the basis of the detected variation degree of the temperature; estimating a temperature of the subject matter on the basis of the judged quantity of the subject matter (205); comparing the estimated temperature with a detected temperature detected directly by a sensor to determine the current temperature of said subject matter as the highest of both temperatures (207,209,213); and executing a cooking mode until said determined current temperature is raised to a set cooking temperature (211). The method according to claim 1, wherein the quantity of the subject matter is judged as a large quantity in case of a large variation degree of the detected temperature for the initial constant time period of heating and as a small quantity in case of a small variation degree of the detected temperature for the initial constant time period of heating. The method according to claim 1 or 2, wherein the temperature of the subject matter is estimated on the basis of the highest temperature (c) detected during the initial constant time period set in inverse proportion to the gradient of the detected variation degree of the temperature during the initial constant time period of heating and in proportion to the cooking time after the initial constant time period of heating. The method according to claim 1, 2 or 3, wherein the initial constant time period of heating for detecting the variation degree of the temperature is set depending on the length of a set cooking time. An apparatus for heating a subject matter in a cup (7) in a microwave oven, comprising: means (6G) for storing a gradient determined based upon a variation degree of a temperature detected by a sensor (5) for an initial constant time period of heating; first storing means (6C) for storing a detected temperature detected by the sensor (5); second storing means (6H) for storing an estimated temperature, the estimated temperature being in inverse proportion to the gradient stored in the gradient storing means (6G) and in proportion to the cooking time; means (6) for comparing the temperatures stored in the first and second storing means (6C,6H) to determine the current temperature of said subject matter as the highest of both temperatures; and means (3,6E) for heating the subject matter until said determined current temperature is raised to a set cooking temperature.

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