Abstract:
A method for preventing overheating of a microwave oven including a controller for controlling an output level of a magnetron is disclosed. The method includes: a) receiving information of cooking conditions and a cooking start command input by a user, the cooking conditions including an output level of the magnetron for subsequent cooking, b) detecting a pausing period of time from a time of finishing preceding cooking to a time of starting the subsequent cooking if it is determined that the output level of the magnetron is greater than a preset output level thereof, and c) operating the microwave oven at the preset output level after changing the output level to the preset output level according to the detected pausing period. According to this method, components of the microwave oven are effectively prevented from being overheated while maintaining cooking efficiency.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a method for preventing overheating of a microwave oven. 
   2. Description of the Related Art 
   A microwave oven is a kitchen appliance based on a principle that generates heat via molecular motion of the food itself by passing microwave radiation at a frequency of about 2,450 MHz through the food within a metallic case. 
   In the microwave oven, when microwave radiation at the frequency of about 2,450 MHz is oscillated from a magnetron, and passes through the food in a cooking chamber, molecules constituting the food are charged to have a positive charge and a negative charge arranged at opposite sides thereof by the microwave radiation. At this time, the molecules have the positive charge at one side near a negative polarity of electric field created by the microwave beam, and the negative charge at the other side near a positive polarity of the electric field. 
   In this regard, polarity of electric field is changed two thousand four hundred and fifty million times per second, and causes severe collisions between the molecules, so that the food is cooked by heat created by the collision of the molecules of the food. 
     FIG. 1  is a constructional view illustrating a conventional microwave oven. 
   As shown in  FIG. 1 , the conventional microwave oven comprises a power terminal through which commercial alternating current power is supplied, a fan motor  50  connected with the power terminal to drive a cooling fan for cooling various electric components, a tray motor  60  connected in parallel with the fan motor  50  to rotate a tray of a cooling chamber, a high voltage transformer  70  connected with the power source to supply high voltage power to a magnetron. 
   In addition, a fuse  80  and a door switch  90  are connected in series between the power terminal and the fan motor  50  in which the door switch  90  is switched on and off according to opening and closing of a door of the microwave oven. A sub relay  30  is connected between the power terminal and the fan motor  50 , and a main relay  40  is connected between the fan motor  50  and a primary coil of the high voltage transformer  70 . 
   The microwave oven further comprises a controller  20  which outputs a control signal in order to control the main relay  40  and the sub relay  30  to be switched on/off according to a key signal input from a key input part  10 . The sub relay  30  is switched on/off according to the control signal from the controller  20 , and serves to supply or cut off the commercial AC power through the power terminal to or from the fan motor  50 , the tray motor  60 , and the high voltage transformer  70 . The main relay  40  is switched on or off according to the control signal from the controller  20 , and serves to supply or cut off the commercial AC power through the power terminal to or from the high voltage transformer  70 . 
   In the conventional microwave oven, when the magnetron is continuously operated for a long period of time by supplying power to the high voltage transformer  70 , various electric components of the microwave oven including the high voltage transformer  70  are liable to be overheated, and thus it is necessary to control an output level according to a cooking period of time. 
   However, the conventional microwave oven has a problem in that, since the output level is determined depending on the cooking period of time, the electric components can be damaged due to overheating of the microwave oven which can occur when an internal temperature of the microwave oven before or after cooking is not considered in the case where the microwave oven is continuously operated without a pause or with intervals of short pauses. 
   SUMMARY OF THE INVENTION 
   The present invention has been made to solve the above problems, and it is an object of the present invention to provide a method for preventing overheating of a microwave oven, by which an output of a magnetron can be automatically controlled according to an operating time and a pausing period of the microwave oven, thereby preventing the microwave oven from being overheated. 
   In accordance with one aspect of the present invention, the above and other objects can be accomplished by the provision of a method for preventing overheating of a microwave oven including a controller for controlling an output level of a magnetron, the method comprising the steps of: receiving information of cooking conditions and a cooking start command input by a user, the cooking conditions comprising an output level of the magnetron for subsequent cooking; detecting a pausing period of time from a time of finishing preceding cooking to a time of starting the subsequent cooking if it is determined that the output level of the magnetron is greater than a preset output level thereof; and operating the microwave oven at the preset output level after changing the output level to the preset output level according to the detected pausing period. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other objects and features of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a circuit diagram illustrating a conventional microwave oven; and 
       FIG. 2  is a flow diagram illustrating a method for preventing overheating of a microwave oven in accordance with one embodiment of the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings along with description of terms and reference characters. 
   T: a cooking period of time preset by a user. 
   td: a period of time during which a microwave oven is not operated before start of current cooking. That is, it means a pausing period of time between preceding cooking and current cooking. 
   Specifically, it further comprises an elapsed period from a time of stopping the microwave oven by opening a door of the microwave oven or by pushing buttons to temporarily pause, stop or cancel during operation of the microwave oven as well as a time of finishing of preceding cooking, i.e., an end of cooking period, to a time of pushing a button for starting current cooking. 
   T 1 : an operating period of time for preceding cooking. That is, it means an operating period of the microwave oven during which the microwave oven is operated for the preceding cooking. 
   Here, if the pausing period of time td is 5 minutes or less between previous cooking periods of time, T 1  means a cooking period of time obtained by adding the previous cooking periods of time before and after the pausing period of time. For example, if the microwave oven is operated in the sequence of 10 minutes cooking+25 minutes or less pausing+current cooking, T 1  required for changing an output level of a magnetron for the current cooking is 10 minutes which is the preceding cooking period of time. If the microwave oven is operated in the sequence of 10 minutes cooking+2 minutes pausing+10 minutes cooking+2 minutes pausing+current cooking, T 1  required for changing the output level of the magnetron for the current cooking is 20 minutes which is obtained by adding 10 minutes and 10 minutes. 
   T 2 : a reference period of time for changing the output level. Specifically, it means a period of time for changing the output level during cooking, and is set to T 2 =T 1 +t 2 +a weighted value. 
   The weighted value is determined by T 1  and td, and is provided as 0, 5, 10 and the like. 
   t 2 : an elapsed period of current cooking. That is, it means an elapsed period of subsequent cooking. 
   A: a basic level output value, which is provided as a value to operate the microwave oven at an output level preset by the user for a predetermined period of time prior to operation in any other conditions related to change of an output level when the microwave oven starts cooking. 
   That, when the microwave oven starts cooking, it operates at an output level predetermined by the user for A minutes so long as an output level changing event is not generated. 
   According to the present invention, A is provided as 0, 5, and 13 according to the range of td. 
   Z: a counter value for changing an output level. It means a value increasing by 1 when the pausing period of time “td” between preceding cooking and subsequent cooking is 25 minutes or less. If Z is 4 or more, that is, if the preceding cooking is continuously performed 4 or more times, followed by the subsequent cooking within 25 minutes or less, the microwave oven is forced to operate directly at an output level of 70% instead of an initial output level for A minutes according to the range of the pausing period of time even if the output level is set to 80% or more by a user. 
   Final operating condition: a condition wherein a pausing period of time “td” between preceding cooking and subsequent cooking exceeds 25 minutes. At this time, Z is converted to 1. 
   A method for preventing overheating of a microwave oven according to the invention will hereinafter be described with reference to  FIG. 2 . 
   As shown in  FIG. 2 , a process of preventing overheating of the microwave oven according to the invention is executed as soon as a user inputs a cooking start command to the microwave oven after setting a cooking period of time and an output level of a magnetron for cooking a predetermined food. First, at S 11 , T 1  and Z are initialized, and then, at S 13 , it is determined whether or not a power level, i.e., an output level of the magnetron is 70% or less. 
   As a result of determination at step S 13 , if it is determined that the power level is 70% or less, the microwave oven operates according to the preset conditions input by the user. If it is determined that the power level is greater than 70%, the process moves to S 15 , wherein it is determined whether or not td is 5 or less. 
   If it is determined at step S 15  that td is greater than 5, the process moves to S 61  to determine whether or not td is in the range of 5&lt;td≦15 (S 61 ). If it is determined at S 15  that td is 5 or less, the process moves to S 17  wherein t 2  is initialized to 0, and then at S 19 , Z is set to Z+1. 
   Then, at S 21 , it is determined whether or not Z is 4 or more. If it is determined that Z is 4 or more, the process moves to S 45  wherein A is set to 0. If it is determined that Z is less than 4, the process moves to S 23  wherein the microwave oven starts cooking after setting A to 5. 
   At S 25 , T 1  is set to t 2 +t 2 , and at S 27 , t 2  is timed. Then, at S 29 , the microwave oven is operated at a preset output level for A minutes. 
   At S 31 , the microwave oven is operated at the preset output level for (T 2 −A) minutes, and at S 33 , it is determined whether or not A+(T 2 −A), that is, T 2 , is 30 minutes or more. 
   As a result of determination at S 27 , if it is determined that T 2  is less than 30 minutes, the process returns to S 27 . If it is determined that T 2  is 30 minutes or more, the process moves to S 35  wherein the power level is converted to 70%. Then, at S 37 , it is determined whether or not T is t 2 . 
   As a result of determination at S 37 , if it is determined that T is not t 2 , step S 37  is repeated until T becomes t 2 . If it is determined that T is t 2 , the process moves to S 39  wherein operation of the microwave oven is stopped. 
   Then, at S 41 , T 1  is set to T 2 , and at S 43 , timing of td is started, and continued until operation command is input by the user. 
   That is, if td is 5 minutes or less, T 1  at subsequent cooking is obtained by T 2 (T 1 +t 2 ) which is achieved by adding the period of time for preceding cooking and current cooking, instead of t 2  which is the elapsed period for current cooking. 
   Meanwhile, after step S 45 , the process moves to S 47  wherein the power level is converted to 70%. Then, at S 49 , it is determined whether or not T is t 2 . 
   If it is determined that T is not t 2 , step S 49  is repeated until T becomes t 2 . If it is determined that T is t 2 , the process moves to S 51  wherein operation of the microwave oven is stopped. 
   Then, at S 53 , T 1  is set to t 2 , and the process moves to S 43 . 
   Meanwhile, as a result of determination at S 61 , if it is determined that td is not in the range of 5&lt;td≦15, the process moves to S 63  wherein t 2  is initialized to 0, and at S 65 , Z is set to Z+1. 
   Then, at S 67 , it is determined whether or not Z is 4 or more. If it is determined that Z is 4 or more, the process moves to S 45  wherein A is set to 0. If it is determined that Z is less than 4, the process moves to S 69  wherein the microwave oven starts cooking after setting A to 5. 
   Then, at S 71 , it is determined whether or not T 1  is 10 or less. If it is determined that T 1  is more than 10, the process moves to S 93  wherein it is determined whether T 1  is in the range of 10&lt;T 1  ≦15. If it is determined that T 1  is 10 or less, the process moves to S 73  wherein T 1  is set to t 2 +t 2 +10. Then, at S 75 , t 2  is timed, and at S 77 , the microwave oven is operated at the preset output level for A minutes. 
   At S 79 , the microwave oven is operated at the preset output level for (T 2 −A) minutes, and at S 81 , it is determined whether or not A+(T 2 −A), that is, T 2 , is 30 minutes or more. 
   As a result of determination at S 81 , if it is determined that T 2  is less than 30 minutes, the process returns to S 75 . If it is determined that T 2  is 30 minutes or more, the process moves to S 83  wherein the power level is converted to 70%. Then, at S 85 , it is determined whether or not T is t 2 . 
   As a result of determination at S 85 , if it is determined that T is not t 2 , step S 37  is repeated until T becomes t 2 , and if it is determined that T is t 2 , the process moves to S 87  wherein operation of the microwave oven is stopped. 
   Then, at S 89 , T 1  is set to t 2 , and at S 91 , timing of td is started, and continued until operation command is input by the user. 
   Meanwhile, as a result of determination at S 93 , if it is determined that T 1  is not in the range of 10&lt;td≦15, that is, if it is determined that T 1  is greater than 15, the process moves to S 115  wherein T 1  is set to t 2 +t 2 . On the contrary, if it is determined that T 1  is in the range of 10&lt;td≦15, the process moves to S 95  wherein T 1  is set to t 2 +t 2 +5, and at S 97 , t 2  is timed. Then, at S 99 , the microwave oven is operated at the preset output level for A minutes. 
   At the next step S 101 , the microwave oven is operated at the preset output level for (T 2 −A) minutes, and at S 103 , it is determined whether or not A+(T 2 −A), that is, T 2 , is 30 minutes or more. 
   As a result of determination at S 103 , if it is determined that T 2  is less than 30 minutes, the process returns to S 97 . If it is determined that T 2  is 30 minutes or more, the process moves to S 105  wherein the power level is converted to 70%. Then, at S 107 , it is determined whether or not T is t 2 . 
   As a result of determination at S 107 , if it is determined that T is not t 2 , step S 107  is repeated until T becomes t 2 , and if it is determined that T is t 2 , the process moves to S 109  wherein operation of the microwave oven is stopped. 
   Then, at S 111 , T 1  is set to t 2 , and at S 113 , timing of td is started, and continued until operation command is input by the user. 
   Then, after step S 115 , t 2  is timed at S 117 , and at S 119 , the microwave oven is operated at the preset output level for A minutes. 
   At S 121 , the microwave oven is operated at the preset output level for (T 2 −A) minutes, and at S 123 , it is determined whether or not A+(T 2 −A), that is, T 2 , is 30 minutes or more. 
   As a result of determination at S 123 , if it is determined that T 2  is less than 30 minutes, the process returns to S 117 . If it is determined that T 2  is 30 minutes or more, the process moves to S 125  wherein the power level is converted to 70%. Then, at S 127 , it is determined whether or not T is t 2 . 
   As a result of determination at S 127 , if it is determined that T is not t 2 , step S 127  is repeated until T becomes t 2 . If it is determined that T is t 2 , the process moves to S 129  wherein operation of the microwave oven is stopped. 
   Then, at S 131 , T 1  is set to t 2 , and at S 133 , timing of td is started, and continued until operation command is input by the user. 
   Meanwhile, as a result of determination at S 135 , if it is determined that td is not in the range of 15&lt;td≦25, the process moves to S 165  wherein t 2  is initialized to 0. If it is determined that td is in the range of 15&lt;td≦25, the process moves to S 137  wherein t 2  is initialized to 0, and at S 139 , Z is set to Z+1. 
   Then, at S 141 , it is determined whether or not Z is 4 or more. If it is determined that Z is 4 or more, the process moves to S 45  wherein A is set to 0. If it is determined that Z is less than 4, the process moves to S 143  wherein the microwave oven starts cooking after setting A to 13. 
   Then, at S 145 , T 2  is set to T 1 +t 2 , and at S 147 , t 2  is timed. Next, at S 149 , the microwave oven is operated at the preset output level for A minutes. 
   At S 151 , the microwave oven is operated at the preset output level for (T 2 −A) minutes, and at S 81 , it is determined whether or not A+(T 2 −A), that is, T 2 , is 30 minutes or more. 
   As a result of determination at S 135 , if it is determined that T 2  is less than 30 minutes, the process returns to S 147 . If it is determined that T 2  is 30 minutes or more, the process moves to S 155  wherein the power level is converted to 70%. Then, at S 157 , it is determined whether or not T is t 2 . 
   As a result of determination at S 157 , if it is determined that T is not t 2 , step S 157  is repeated until T becomes t 2 . If it is determined that T is t 2 , the process moves to S 159  wherein operation of the microwave oven is stopped. 
   Then, at S 161 , T 1  is set to t 2 , and at S 163 , timing of td is started, and continued until operation command is input by the user (S 165 ). 
   Meanwhile, after 1 is added to Z at S 167  and A is set to 0 at S 196 , the microwave oven starts cooking. 
   Then, at S 171 , T 1  is set to t 2 , and at S 173 , timing of td is started, and continued until operation command is input by the user at S 175 . 
   At S 171 , T 2  is set to t 2 , and at S 173 , t 2  is timed. At S 175 , the microwave oven is operated at the preset output level for A minutes. 
   At S 177 , the microwave oven is operated at the preset output level for (T 2 −A) minutes, and at S 179 , it is determined whether or not A+(T 2 −A), that is, T 2 , is 25 minutes or more. 
   As a result of determination at S 179 , if it is determined that T 2  is less than 25 minutes, the process returns to S 173 . If it is determined that T 2  is 25 minutes or more, the process moves to S 181  wherein the power level is converted to 70%. Then, at S 183 , it is determined whether or not T is t 2 . 
   As a result of determination at S 183 , if it is determined that T is not t 2 , step S 183  is repeated until T becomes t 2 . If it is determined that T is t 2 , the process moves to S 185  wherein operation of the microwave oven is stopped. 
   Then, at S 187 , T 1  is set to t 2 , and at S 189 , timing of td is started, and continued until operation command is input by the user. 
   Accordingly, if the microwave oven is continuously operated with a pausing period of time within 5 minutes or less, it is possible to prevent overheating of the microwave oven by adding a preceding cooking period of time to a current cooking period of time. If a pausing period of time is in the range of 5 to 15 minutes, T 1  is divided into an operating period of 10 minutes or less, an operating period in the range of 10 minutes&lt;T 1 &lt;15 minutes and an operating period of 15 minutes or more, and a weight value of +10, +5 or +0 is added to T 1 , thereby solving the problem upon continuous cooking of 3 times or more. 
   In particular, the reason of setting A to 13 minutes at step S 143 , and of setting A to 0 at step S 169  is that these pausing periods are considered to be sufficient to cool the components of the microwave oven, and prevent damage of the microwave oven. In addition, the reason of determining at step S 179  whether T 2  is 25 minutes or more is that A is O which is different from the other conditions. 
   Meanwhile, it is desirable that the value of Z be set to 0 when the microcomputer is reset at an initial operation, that Z be increased by 1 when the microwave oven is continuously used, and that Z be set to 1 when td is 25 minutes or more. 
   As apparent from the above description, with the method for preventing overheating of the microwave oven according to the invention, if a user controls the microwave oven to operate at a magnetron output level of 70% or less, it is operated according to conditions input by the user, but if the user controls the microwave oven to operate at an output level above 70%, the output level of the magnetron is automatically changed according to a preceding cooking period and a pausing period, so that the components of the microwave oven are effectively prevented from being overheated while maintaining cooking efficiency even when a short period of time is required for cooking. 
   It should be understood that the embodiments and the accompanying drawings have been described for illustrative purposes and the present invention is limited by the following claims. Further, those skilled in the art will appreciate that various modifications, additions and substitutions are allowed without departing from the scope and spirit of the invention as set forth in the accompanying claims.