Patent Publication Number: US-2019170364-A1

Title: Cooking device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of U.S. Patent Application No. 62/594,230, filed on Dec. 4, 2017, and Korean Patent Application No. 10-2018-0154011, filed on Dec. 3, 2018, the disclosures of which are incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     1. Field of the Disclosure 
     The present disclosure relates to a cooking device which allows a user to set a heating power level and a cooking time quickly and easily. 
     2. Discussion of Related Art 
     Cooking devices are one of household devices for cooking food and may be classified into various types of cooking device according to a heating source, a cooking type, a fuel type, or the like to be used. 
     Cooking devices may be classified into an open-type and a sealed-type depending on a shape of a space where foods are placed. 
     Sealed-type cooking device are types of cooking device that shields a space where food is placed and cooks food by heating the shielded space. The sealed-type cooking devices include an oven, a microwave oven, and the like. 
     Open-type cooking devices are types of cooking device that cooks food by heating a container containing food or food placed in an open space. The open-type cooking devices include a gas stove, an induction range, and the like. 
     In recent years, combination type cooking devices having both the sealed-type cooking device and the open-type cooking device and capable of cooking food in various ways are used. In the combination type cooking device, the open-type cooking device is mainly disposed on an upper portion thereof, and the sealed-type cooking device is mainly disposed on a lower portion thereof. The combination type cooking device may include a plurality of open-type cooking devices of different types and sealed-type cooking devices of different types. Thus, a user may cook food using the combination type cooking device at the same time in different ways. 
     The user needs to adjust an amount of heat energy supplied by a heating source provided in the cooking device in order to use the cooking device. The amount of the heat energy supplied by the heating source of the cooking device may be displayed as a cooking temperature and a heating power level depending on the type of the cooking device. That is, the user may adjust the amount of the heat energy supplied to the food or containers by adjusting the cooking temperature and the heating power level displayed on the cooking device. Further, the user may set a time at which the food is cooked, i.e., the cooking time in addition to the adjustment of the amount of the heat energy 
     An operation method for adjusting the amount of the heat energy and the cooking time for the cooking differs according to the type of the cooking device. Korean Patent Publication No. 10-2011-0079007 discloses a structure and an operation method of a combination cooking device according to the related art. 
       FIG. 1  illustrates a structure of a combination cooking device according to the related art. 
     Referring to  FIG. 1 , a combination cooking device  10  according to the related art includes a cooktop unit  21  configured to heat food or a container containing the food placed thereon to cook the food, an oven unit  30  configured to heat an inner space thereof in which the food or the container containing the food is placed to cook the food, a drawer unit  40  configured to store the food placed in an inner space thereof in a warm state or worm up the food, and a control unit  51  configured to control the cooktop unit  21 , the oven unit  30 , the drawer unit  40 . 
     The cooktop unit  21  includes a plurality of cooktop heaters  22  which provide heat energy to heat the food or the container. The oven unit  30  includes a cooking chamber (not shown), which is the inner space of the oven unit  30  in which the food or the container containing the food is placed, and a door  32  configured to open and close the cooking chamber. The door  32  is provided with a handle  33  for gripping when the user opens or closes the door  32 . Further, the drawer unit  40  includes a handle  41  for gripping when the user moves the drawer unit  40  forward or backward. 
     A control panel  51  is disposed on a front surface of the cooktop unit  21 , i.e., above the door  32 . The control panel  51  is formed in a hexahedral shape having a certain inner space. A knob-type input unit  52  is provided on a front surface of the control panel  51  for the user to input operational signals for operating the cooktop unit  21 , the oven unit  30 , and the drawer unit  40 . 
     As shown in  FIG. 1 , conventionally, an amount of heat energy supplied by a heating source provided in the cooking device or a cooking time is adjusted mainly by rotating the knob-type input unit  52 . 
     However, according to the related art, since the user has to adjust the amount of the heat energy or the cooking time depending on only scales marked on the knob-type input unit, the user may not accurately and precisely adjust the amount of the heat energy or the cooking time. 
     Further, according to the related art, it is difficult for the user to easily and accurately grasp the amount of the heat energy supplied by the cooking device and a remaining cooking time in the cooking process. 
     SUMMARY OF THE INVENTION 
     The present disclosure is directed to providing a cooking device which enables a user to easily and quickly adjust a level of heat energy supplied by the cooking device and the cooking time of the food. 
     The present disclosure is also directed to providing a cooking device capable of easily and quickly recognizing a variety of information such as a level of heat energy supplied by a heating module, a remaining cooking time, an operation mode of the heating module, or an operation status of the heating module 
     The present disclosure is also directed to providing a cooking device having a control means for allowing the user to control the cooking process more conveniently and accurately and to promptly check the information required for cooking. 
     The present disclosure is also directed to providing a cooking device which does not require replacement of the control means even if the heating module is replaced, by providing a single type of control means capable of controlling different type of heating modules. 
     The present disclosure is also directed to providing a cooking device having a simple and unified design by providing a single type of control means that is arranged independent of the heating module and can control different type of heating modules. 
     Aspects of the present disclosure are not limited to the above-described aspects, and other aspects and advantages of the present disclosure will be understood by the following description and will be more definitely understood through the embodiments of the present disclosure. Also, it will be easily appreciated that the aspects and advantages of the present disclosure may be implemented by means shown in the claims and a combination thereof. 
     The cooking device according to the present disclosure includes a new form of control device configured to control cooking processes using the cooking device. The new form of control device, i.e., a knob module, includes a knob which operates in a push-and-turn manner and a knob ring which is coupled to the knob and operates in a click or hold manner, and a display unit formed integrally with the knob ring and capable of displaying a temperature, a heating power level, a time, or other information set according to an operation of the knob or the knob ring. 
     A user may accurately and conveniently set an amount of heat energy supplied by various heating sources included in the cooking device, that is, a heating module, or an operation time of the heating module, that is, a cooking time, using the knob module provided in the cooking device according to the present disclosure. 
     For example, when the user intends to set a heating power level of the heating module provided in the cooking device using the knob module, the user rotates the knob in a first direction or a second direction. The heating power level, which is assigned according to a rotational position of each knob by the rotational movement of the knob, is set to the heating power level of the heating module. 
     Further, the user may operate the knob ring provided on the knob module to set a desired cooking time precisely. 
     The knob ring according to the present disclosure has a structure of returning to its initial position after moving within a predetermined angle in the first direction or the second direction. In the present disclosure, an operation of the knob ring is classified into a click operation or a holding operation according to a time for which a state in which the knob ring is moved in the first direction or the second direction is maintained. 
     In the present disclosure, an operation, in which the knob ring returns to its initial position before a preset reference time (for example, 2 seconds) passes after the user moves the knob ring in any direction within the predetermined angle, is defined as the click operation of the knob ring. An operation, in which a state in which the knob ring is moved is maintained over the preset reference time (for example, 2 seconds) after the user moves the knob ring in any direction within the predetermined angle, is defined as the holding operation of the knob ring. 
     In this manner, in the present disclosure, it is possible to easily and precisely set the amount of the heat energy supplied by the heating module provided in the cooking device and the cooking time using the knob which operates in a push-and-turn manner and the knob ring which operates in a click or hold manner. 
     Values (for example, heating power level) set by the user using the knob module are immediately displayed on the display unit formed integrally with the knob ring whenever the user operates the knob or knob ring. In the process of cooking the food using the cooking device, various information such as the cooking temperature and the heating power level of the heating module set by the user, a remaining cooking time, whether the cooking is completed, and an operation mode are displayed on the display unit. 
     Thus, the user may more easily and accurately set the amount of the heat energy supplied by the heating module and the cooking time on the basis of information displayed on the display unit. Further, various information related to the cooking may be quickly and conveniently confirmed through the display unit even in the cooking process. 
     Since the cooking device according to the present disclosure includes a plurality of different heating modules, various information regarding each heating module must be provided to the user during the cooking process. In the case of displaying such various information through a single display disposed at a position different from the control means of each heating module, the user has to check the display every time the control operation for each heating module is performed. This inconvenience increases as the size of the cooking device increases or as the type of the heating module increases. 
     Also, if information regarding a plurality of heating modules is displayed on a single display, the screen configuration of the display becomes complicated and it is difficult for the user to check desired information. 
     However, according to the present disclosure, each of the knob modules for controlling the respective heating modules includes a display unit, and information about corresponding heating modules is displayed on each of the display units simultaneously with the operation of the knob module. Therefore, the user can quickly and intuitively check information about each heating module whenever performing a control operation for each heating module. 
     Particularly, the display unit of the knob module according to the present disclosure is integrally formed with the knob ring. Information that is set or changed each time the user rotates the knob or moves the knob ring by touching the body (e.g., a finger) to the knob ring or the display unit is immediately displayed on the display unit. Thus, user&#39;s convenience is improved and information can be checked easily. 
     The display unit of the knob module according to the present disclosure is integrally formed with the knob ring in a protruding form on the knob ring surface. Due to such a structure, when the user operates the knob or the knob ring, the display unit is not blocked by the user&#39;s body (e.g., a hand), so that the visibility of the information displayed on the display unit is very high. 
     Also, according to the present disclosure, the heating operation for different types of heating modules can be controlled using the single type of knob module. According to the present disclosure, different knob modules corresponding to different types of heating modules are arranged on a single control panel. Thus, a simple and unified design for different types of heating modules is possible. As a result, the aesthetics of the product can be enhanced. 
     Also, according to the present disclosure, even if the type of the heating module included in the cooking device is changed, a single type of knob module can be applied. Further, the control panel in which the knob module is disposed in the cooking device is formed separately from the heating module. Thus, it is possible to produce various types of cooking devices having various combinations of heating modules by simply replacing the heating modules without replacing the knob modules. Accordingly, the manufacturing process can be simplified while lowering the designing difficulty and cost required for producing various types of cooking devices. 
     For example, if a new model of a cooking device including only a low-temperature heating module and a gas heating module is to be produced based on a model of a cooking device including a low-temperature heating module, a gas heating module, and an induction heating module, At the same time, the design and production of the new model can be easily completed simply by connecting the existing knob module to the newly placed heating module. 
     The cooking device according to the present disclosure has an advantage that the user can easily and quickly adjust the size of the heat energy supplied through the cooking device and the cooking time of the food. 
     Further, according to the present disclosure, the user may easily and quickly check various information such as a level of heat energy supplied by a heating module, a remaining cooking time, an operation mode of the heating module, or an operation status of the heating module. 
     Further, the cooking device according to the present disclosure has an advantage that the user can more conveniently and accurately control the cooking process and promptly check the information required for cooking. 
     Further, the cooking device according to the present disclosure includes a single type of control means capable of controlling different heating modules. Therefore, even if the heating module constituting the cooking appliance is replaced, it is not necessary to replace the control means. 
     Also, the cooking device according to the present disclosure has a simple and unified design by providing a single type of control means that is independent of the heating module and can control different types of heating modules. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features, and advantages of the present disclosure will become more apparent to those of ordinary skill in the art by describing in detail exemplary embodiments thereof with reference to the accompanying drawings, in which: 
         FIG. 1  illustrates a structure of a combination cooking device according to the related art; 
         FIG. 2  is a perspective view of a cooking device according to one embodiment of the present disclosure; 
         FIG. 3  illustrates a configuration of an induction heating module included in the cooking device according to one embodiment of the present disclosure; 
         FIG. 4  illustrates an initialized state of the knob module included in the cooking device according to one embodiment of the present disclosure; 
         FIG. 5  illustrates a state in which the knob of the knob module according to one embodiment of the present disclosure is pushed; 
         FIG. 6  illustrates a state in which the knob of the knob module according to one embodiment of the present disclosure is rotated; 
         FIGS. 7 and 8  illustrate a state in which a knob ring of the knob module according to one embodiment of the present disclosure is moved in a first direction; 
         FIG. 9  illustrates a state in which the knob ring of the knob module according to one embodiment of the present disclosure is moved in a second direction; 
         FIG. 10  is an exploded view of the knob module according to one embodiment of the present disclosure; 
         FIG. 11  is a perspective view of a heating power adjustment unit according to another embodiment of the present disclosure; 
         FIG. 12  is an exploded view of the heating power adjustment unit according to another embodiment of the present disclosure; 
         FIGS. 13 and 14  are cross-sectional views illustrating an operation of the heating power adjustment unit according to another embodiment of the present disclosure; 
         FIGS. 15 and 16  are cross-sectional views illustrating an operation of a knob ring according to another embodiment of the present disclosure; 
         FIG. 17  is a block diagram illustrating a configuration of the cooking device according to one embodiment of the present disclosure; 
         FIG. 18  illustrates a seventh knob module, an eighth knob module, and a flexible button configured to control a heating operation of the induction heating module included in the cooking device according to one embodiment of the present disclosure; 
         FIG. 19  illustrates a container which is seated on the induction heating module and a heating area of the induction heating module when the induction heating module operates in a normal mode in one embodiment of the present disclosure; 
         FIG. 20  illustrates a method of setting a heating power level of a first heating area to 3 using the knob module when the induction heating module operates in the normal mode in one embodiment of the present disclosure; 
         FIG. 21  illustrates a method of operating the first heating area in a boost mode using the knob module when the induction heating module operates in the normal mode in one embodiment of the present disclosure; 
         FIG. 22  illustrates a state in which the container is not recognized in the heating area when the induction heating module operates in the normal mode in one embodiment of the present disclosure; 
         FIG. 23  illustrates a method of setting a cooking time of the heating area using the knob module when the induction heating module operates in the normal mode in one embodiment of the present disclosure; 
         FIG. 24  illustrates the container which is seated on the induction heating module and a heating area of the induction heating module when the induction heating module operates in a flexible mode in one embodiment of the present disclosure; 
         FIG. 25  illustrates a method of setting the induction heating module to the flexible mode in one embodiment of the present disclosure; 
         FIG. 26  illustrates a method of setting a heating power level of the heating area to 4 using the knob module when the induction heating module operates in the flexible mode in one embodiment of the present disclosure; 
         FIG. 27  illustrates a state in which the container is not recognized in the heating area when the induction heating module operates in the flexible mode in one embodiment of the present disclosure; 
         FIG. 28  illustrates a method of setting the cooking time of the heating area using the knob module when the induction heating module operates in the flexible mode in one embodiment of the present disclosure; and 
         FIG. 29  is a flowchart illustrating operation processes of the cooking device according to one embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     The above-described objects, features, and advantages will be described below in detail with reference to the attached drawings to allow one of ordinary skill in the art to execute the technical concept of the present disclosure easily. In the description of the embodiments of the present disclosure, a certainly detailed explanation of a well-known function or component of the related art will be omitted when it is deemed to unnecessarily obscure the essence of the present disclosure. Hereinafter, exemplary embodiments of the present disclosure will be described in detail with reference to the attached drawings. Throughout the drawings, like reference numerals refer to like or similar elements. 
       FIG. 2  is a perspective view of a cooking device according to one embodiment of the present disclosure. 
     Referring to  FIG. 2 , a cooking device 1 according to one embodiment of the present disclosure is a combination type cooking device and includes a plurality of heating modules. For example, as illustrated in the drawings, the cooking device 1 includes a low-temperature heating module  202 , a gas heating module  220 , and an induction heating module  222  which are disposed on an upper portion of a main body  20 . 
     Further, a first oven, which is opened and closed by a first door  240  disposed on a front surface of the main body  20 , and a second oven, which is opened and closed by a second door  242  disposed on the front surface of the main body  20 , are disposed in a lower portion of the main body  20 . 
     As a reference, types of the heating modules included in the cooking device 1 shown in  FIG. 2  and a position and a disposition order of each of the heating modules are only one example and may vary according to embodiments. 
     A control panel  230  configured to control the heating operation of each of the heating modules is disposed above the first door  240  and the second door  242  of the front surface of the main body  20 . 
     The control panel  230  includes a plurality of knob modules  231  to  238  configured to adjust at least one of a cooking temperature, a heating power level, and a cooking time of the low-temperature heating module  202 , the gas heating module  220 , and the induction heating module  222 . As described below, each of the knob modules  231  to  238  includes a knob, a knob ring, and a display unit. 
     Further, the control panel  230  includes a touch panel  270 . The touch panel  270  recognizes commands input by a user&#39;s touch operation or displays various information related to the cooking. 
     For example, the user may set the cooking temperature and/or the cooking time of the first oven or the second oven using the touch panel  270 , or control the heating operation of the first oven or the second oven by inputting a heating operation start command or a heating operation end command through the touch operation. Further, the touch panel  270  may display various information related to the cooking of the food or the operation of the cooking device 1 such as the cooking temperature and/or the cooking time of the first oven or the second oven, or an operation mode of the first oven or the second oven. 
     Referring again to  FIG. 2 , the user may perform a low-temperature vacuum cooking using the low-temperature heating module  202 . 
     The low-temperature vacuum cooking method, which is also referred to as sous vide, is a cooking method in which food is vacuum packaged with a packaging material (for example, vinyl), and the vacuum-packaged food is heated in low-temperature water for a long time. By using the low-temperature vacuum cooking method, the original taste of a material may be utilized as it is, and texture, flavor, and nutrients of the material may be kept to the maximum. Especially, food cooked by the low-temperature vacuum cooking method is prevented from being toughed by the deformation of protein, so that the food is kept in a soft and moist state and the inside and outside of the food is heated uniformly. 
     In one embodiment of the present disclosure, the low-temperature heating module  202  includes an accommodation space  204  configured to accommodate a water container  206  and a cover  210  configured to open and close the accommodation space  204 . 
     The accommodation space  204  is a space having a hexahedral shape for accommodating the water container  206  and may have a shape similar to the water container  206 . A heating device (for example, an electric heater) for supplying the heat energy to the water container  206  accommodated in the accommodation space  204  is disposed on a bottom surface of the accommodation space  204 . When the user puts the water container  206  into the accommodation space  204  and then closes the cover  210  and inputs a start of the heating operation, power is supplied to the heating device in a lower portion the accommodation space  204 , and the heating device heats the water container  206 . 
     In order to use the low-temperature heating module  202 , the user fills the water container  206  with water according to a marker line marked inside the water container  206 . The user may place a rack  208  inside the water container  206  as necessary. When the rack  208  is used, it is possible to prevent a phenomenon in which the food placed in the water container  206  sinks on a bottom surface of the water container  206  so that the food is not boiled evenly. The user puts the water container  206  filled with the water into the accommodation space  204 . 
     When the user uses the low-temperature heating module  202  to cook the food, the user may preheat the water in the water container  206  as needed. 
     When the user intends to preheat the water in the water container  206  in a state in which the heating operation of the low-temperature heating module  202  is not started, the user puts the water container  206  filled with the water into the accommodation space  204  and closes the cover  210  without putting food into the water container  206 . Thereafter, the user sets a preheating temperature and/or the cooking time of the low-temperature heating module  202  using a first knob module  231  and/or a second knob module  232  to issue the heating operation start command to the low-temperature heating module  202 . 
     When a temperature of the water container  206  or water in the water container  206  reaches the preheating temperature set by the user by the heating operation, the low-temperature heating module  202  informs the user that the preheating is completed through a preheating end notification operation. The user opens the cover  210  in a state in which the preheating is completed, puts a vacuum-packed food into the water container  206 , and closes the cover  210 . Thereafter, the user sets the preheating temperature and/or the cooking time using the first knob module  231  and/or the second knob module  232  of the low-temperature heating module  202  to issue the heating operation start command to the low-temperature heating module  202 . Accordingly, the low-temperature cooking of the food is performed after the preheating. 
     Thereafter, when the cooking time set by the user or a preset time limit is reached, the low-temperature heating module  202  ends the heating operation and informs the user that the cooking of the food is completed through a cooking end notification operation. 
     When the user intends to perform the low-temperature cooking immediately without preheating the water inside the water container  206  in a state in which the heating operation of the low-temperature heating module  202  is not started, the user puts the water container  206  filled with the water into the accommodation space  204 , puts the vacuum-packed food into the water container  206 , and closes the cover  210 . Thereafter, the user sets the cooking temperature and/or the cooking time of the low-temperature heating module  202  using the first knob module  231  and/or the second knob module  232  to issue the heating operation start command to the low-temperature heating module  202 . 
     When the temperature of the water container  206  or the water in the water container  206  reaches the cooking temperature set by the user by the heating operation, the low-temperature heating module  202  informs the user that the preheating is completed through a preheating end notification operation. Thereafter, when the user does not take any action until a predetermined waiting time passes, the low-temperature heating module  202  maintains the heating operation according to the cooking temperature previously set by the user until the cooking time set by the user or the preset time limit is reached. 
     Thereafter, when the cooking time set by the user or a preset time limit is reached, the low-temperature heating module  202  ends the heating operation and informs the user that the cooking of the food is completed through a cooking end notification operation. 
     In one embodiment of the present disclosure, the user may set the cooking temperature of the low-temperature heating module  202  using the first knob module  231  provided on the control panel  230 . Further, the user may set the cooking time of the low-temperature heating module  202  using the second knob module  232  provided on the control panel  230 . 
     Referring again to  FIG. 2 , the gas heating module  220  or a gas stove is disposed at one side of the low-temperature heating module  202 . 
     The gas heating module  220  uses gas as the heating source to supply the heat energy to the food or the container containing the food. In the embodiment of  FIG. 2 , the gas heating module  220  includes a first gas heating module  212 , a second gas heating module  214 , a third gas heating module  216 , and a fourth gas heating module  218 . However, the number of individual modules constituting the gas heating module  220  may vary according to the embodiments. 
     The user may use a third knob module  233 , a fourth knob module  234 , a fifth knob module  235 , and a sixth knob module  236 , which are included in the control panel  230  and respectively correspond to the first gas heating module  212 , the second gas heating module  214 , the third gas heating module  216 , and the fourth gas heating module  218 , to adjust the heating power level and/or the cooking time of each of the gas heating modules. 
     For example, the user who intends to cook the food using the first gas heating module  212  of the gas heating module  220  rotates a knob of the third knob module  233  to an ignition position. Accordingly, a spark is generated by an ignition module of the first gas heating module  212 , and simultaneously a gas valve is open, and gas is supplied to ignite the flame. 
     When the ignition is completed, the user rotates the knob of the third knob module  233  to adjust a heating power level of the first gas heating module  212 . The amount of gas supplied through the gas valve is adjusted according to the heating power level set by the user using the knob of the third knob module  233 . 
     Further, the user may also set a duration time of the heating operation performed by the first gas heating module  212 , i.e., the cooking time using a knob ring of the third knob module  233 . When the user sets the cooking time using the knob ring of the third knob module  233 , a start of the countdown of the cooking time set by the user is displayed through a display unit of the third knob module  233 . When the cooking time set by the user is reached, an end of the countdown may be displayed through the display unit of the third knob module  233 . Further, when the cooking time set by the user is reached, a audio indicating the end of the countdown may be output through the audio output unit provided in the cooking device 1. The operation of notifying that the countdown has been completed through the display unit or the audio output unit is referred to as a countdown end notification operation. 
     In another embodiment, when the cooking time set by the user is reached, the control unit (not shown) may close the gas valve to shut off the gas supply, thereby terminating the heating operation. 
     When the user does not set the cooking time, the control unit (not shown) may end the heating operation according to the heating operation end command of the user or end the heating operation after the predetermined time limit passes. 
     Referring again to  FIG. 2 , the induction heating module  222  or an induction range is disposed at one side of the gas heating module  220 . The induction heating module  222  heats the container placed on heating areas  224  and  226  using working coils disposed therein. 
       FIG. 3  illustrates a configuration of an induction heating module included in the cooking device according to one embodiment of the present disclosure. 
     Referring to  FIG. 3 , the induction heating module  222  provided in the cooking device according to one embodiment of the present disclosure includes a case  250  and a cover plate  260  coupled to the case  250  to seal the case  250 . 
     A bottom surface of the cover plate  260  is coupled to an upper surface of the case  250  to seal a space formed inside the case  250  from the outside. An upper surface of the cover plate  260  is formed with an upper plate  262  on which an object to be heated, that is, a container for cooking food may be placed. The upper plate  262  may be made of various materials, such as tempered glass, for example, ceramic glass. 
     Working coils  254  and  256  configured to heat the container are disposed in an inner space of the case  250 , which is formed by coupling the cover plate  260  to the case  250 . Heating areas  224  and  226  corresponding to positions of the working coils  254  and  256  disposed at the inner space of the case  250  are formed on the upper plate  262  of the cover plate  260 . 
     A power supply unit (not shown) configured to supply power to the working coils  254  and  256  and an interface unit  114  is disposed at the inner space of the case  250 . The power supply unit (not shown) is electrically connected to the working coils  254  and  256 , and converts power applied from an external power supply into power suitable for driving the working coils  254  and  256  according to the control of the control unit (not shown), and supplies the power to the working coils  254  and  256 . 
     The control unit (not shown) controls the power supply unit (not shown) according to heating power levels and/or cooking time of the heating areas  224  and  226  set by the user using a seventh knob module  237  or an eighth knob module  238  of  FIG. 2  to adjust a supply of the power and an amount of the power of each of the working coils  254  and  256  respectably corresponding the heating areas  224  and  226 . 
     As a reference, although an embodiment in which two working coils  254  and  256  are disposed at the inner space of the case  250  is shown in  FIG. 3 , depending on the embodiments, either one working coil or two or more working coils may also be disposed at the inner space of the case  250 . 
     When a high-frequency alternating current supplied by the power supply unit (not shown) is applied to the working coils  254  and  256 , an induction magnetic field is formed on a periphery of the working coils  254  and  256 . When magnetic force lines of the induction magnetic field generated as described above, pass through the bottom of the container including a metal component, which is placed on the heating areas  224  and  226 , an eddy current is generated inside the bottom of the container. When the eddy current generated as described above flows through the bottom of the container, the container itself is heated. 
     In one embodiment of the present disclosure, the control unit (not shown) may sense whether or not a heatable container is present on the heating areas  224  and  226  using a container sensing function. When it is determined that the container is not present on the heating areas  224  and  226  as a result of the container sensing, the control unit (not shown) may display a symbol indicating that the container is not present through a display unit included in the seventh knob module  237  or the eighth knob module  238 . 
     Further, the control unit (not shown) may control the power supply unit (not shown) to supply the power to the working coils  254  and  256  only when the heatable container is present on the heating areas  224  and  226  as a result of the container sensing, and otherwise control the power supply unit (not shown) so that the power is not supplied to the working coils  254  and  256  even when the user requests the start of the heating operation. 
     Also, in one embodiment of the present disclosure, the induction heating module  222  may operate in either a normal mode or a flexible mode. 
     The normal mode refers to a mode in which each of the working coils  254  and  256  included in the induction heating module  222  operates as a separate heating source. That is, when the induction heating module  222  is set to the normal mode, the user may heat two different containers, each of which corresponds to the size of each of a first heating area  224  and a second heating area  226 . The user may separately control the heating operations of the first heating area  224  and the second heating area  226  using the seventh knob module  237  and the eighth knob module  238  in the normal mode. 
     The flexible mode refers to a mode in which the working coils  254  and  256  included in the induction heating module  222  operate as a single heating source. That is, when the induction heating module  222  is set to the flexible mode, the first heating area  224  and the second heating area  226  operate as if they are a single heating area. Accordingly, the user may perform the cooking using a large-sized container covering both the first heating area  224  and the second heating area  226 . The user may control the heating operations of the heating areas  224  and  226  using only one knob module of the seventh knob module  237  and the eighth knob module  238  in the flexible mode. 
     The user may set the duration time of the heating operation performed in the heating areas  224  and  226 , i.e., the cooking time, using a knob ring of the seventh knob module  237  or the eighth knob module  238 . When the user sets the cooking time using the knob ring of the seventh knob module  237  or the eighth knob module  238 , a start of the countdown of the cooking time set by the user is displayed through the display unit of the seventh knob module  237  or the eighth knob module  238 . When the cooking time set by the user is reached, an end of the countdown may be displayed through the display unit of the seventh knob module  237  or the eighth knob module  238 . Further, when the cooking time set by the user is reached, a audio indicating the end of the countdown may be output through the audio output unit provided in the cooking device 1. 
     The operation of notifying that the countdown has been completed through the display unit or the audio output unit is referred to as a countdown end notification operation. 
     In another embodiment, when the cooking time set by the user is reached, the control unit (not shown) may cut off the supply of the power from the power supply unit (not shown) to the working coils  254  and  256 , thereby completing the heating operation. 
     When the user does not set the cooking time, the control unit (not shown) may end the heating operation according to the heating operation end command of the user or end the heating operation after the predetermined time limit has passed. 
     Further, when it is sensed that the container is removed while the heating operation is being performed as it is confirmed that the container is present on the heating areas  224  and  226 , the control unit (not shown) may terminate immediately the heating operation and inform the user that the container is not present on the heating areas  224  and  226  through the display unit or the audio output unit (not shown) included in the knob module. 
     Hereinafter, a method of operating the seventh knob module  237  and the eighth knob module  238  to control the induction heating module  222  included in the cooking device 1 according to one embodiment of the present disclosure will be described. 
       FIG. 4  illustrates an initialized state of a knob module included in the cooking device according to one embodiment of the present disclosure.  FIG. 5  illustrates a state in which a knob of the knob module according to one embodiment of the present disclosure is pushed.  FIG. 6  illustrates a state in which the knob of the knob module according to one embodiment of the present disclosure is rotated.  FIGS. 7 and 8  illustrate a state in which a knob ring of the knob module according to one embodiment of the present disclosure is moved in a first direction.  FIG. 9  illustrates a state in which the knob ring of the knob module according to one embodiment of the present disclosure is moved in a second direction. 
     As a reference, although a method of operating the seventh knob module  237  for setting a heating power level and a cooking time of the first heating area  224  of the induction heating module  222  is shown in  FIGS. 4 to 9 , the eighth knob module  238  for setting a heating power level and a cooking time of the second heating area  226  of the induction heating module  222  may also be operated in the same manner as the seventh knob module  237 . 
     As shown in  FIGS. 4 to 9 , the seventh knob module  237  is coupled to the control panel  230  and disposed to protrude in a front surface direction of the control panel  230 . The seventh knob module  237  includes a first knob  302 , a first knob ring  304 , and a first display unit  306 . 
     In one embodiment of the present disclosure, the first knob  302  operates in a push-and-turn manner. That is, when the user intends to set the heating power level using the first knob  302 , the user has to rotate the first knob  302  in a state in which the first knob  302  is pressed in a direction toward the control panel  230  (pushed state). Depending on the embodiment, heating power level setting may be possible by simply rotating the first knob  302  without pushing first knob  302 . 
     The first knob  302  may be infinitely rotated in a first direction (for example, counterclockwise) or in a second direction (for example, clockwise). As shown in  FIGS. 4 to 9 , a plurality of heating power levels (1, 2, 3, . . . , 9, OFF) which are corresponding to the respective rotational positions of the first knob  302  and set to have preset intervals (for example, 1) are marked on a surface of the first knob  302 . 
     The higher the heating power level marked on the surface of the first knob  302 , the higher the heating power. Further, “OFF” refers to an end of the heating operation for the first heating area  224 . 
     In the embodiment of  FIGS. 4 to 9 , the heating power level (1, 2, 3, . . . , 9, OFF) assigned to the first knob  302  is set such that it increases or decreases by “1” whenever the first knob  302  rotates 36°. However, this is merely an example, and the value of each heating power level or a rotation angle of the first knob  302  corresponding to each heating power level may be set differently according to the embodiment. 
     The first knob ring  304  is a ring-shaped member surrounding the first knob  302  and rotates only by a predetermined angle in the first direction (for example, counterclockwise) or the second direction (for example, clockwise). That is, the user applies the pressure to a first knob ring through an outer surface of the first knob ring  304  or the first display unit  306  to move the first knob ring  304  in the first direction or the second direction only within the predetermined angle. When the pressure applied to the first knob ring  304  by the user disappears, the first knob ring  304  returns to its initial position again. 
     In the present disclosure, an operation, in which the first knob ring  304  returns to its initial position before a preset reference time (for example, 2 seconds) passes after the user moves the first knob ring  304  in any direction within the predetermined angle, is defined as a click operation of the first knob ring  304 . An operation, in which a state in which the first knob ring  304  is moved is maintained over the preset reference time (for example, 2 seconds) after the user moves the first knob ring  304  in any direction within the predetermined angle, is defined as a holding operation of the knob ring. 
     When the first knob ring  304  is moved within the predetermined angle in the first direction or the second direction in a state in which the cooking time or a timer is not set, a cooking time setting mode is started. When the cooking time setting mode is started, the first display unit  306  displays a numeral (for example, “5”) indicating a preset initial time (for example, 5 minutes). 
     When the first knob ring  304  is moved within the predetermined angle in the first direction or the second direction after the cooking time setting mode is started, the cooking time displayed on the first display unit  306  increases or decreases by a preset adjustment unit (for example, 1 minute), For example, when the user clicks the first knob ring  304  in the first direction (for example, counterclockwise), the cooking time set by the user decreases by 1 minute. Further, when the user clicks the first knob ring  304  in the second direction (for example, clockwise), the cooking temperature set by the user increases by 1 minute. 
     As another example, when the user holds the first knob ring  304  in the first direction (for example, counterclockwise), the cooking time set by the user continuously decreases by the preset adjustment unit (for example, 1 minute) according to a preset speed until the holding state of the first knob ring  304  is released. Further, when the user holds the first knob ring  304  in the second direction (for example, clockwise), the cooking time set by the user continuously increases by the preset adjustment unit (for example, 1 minute) according to a preset speed until the holding state of the first knob ring  304  is released. 
     When the pressure applied to the first knob ring  304  by the user is released and the first knob ring  304  returns to its initial position, the holding state of the first knob ring  304  is released, and the increase or decrease of the cooking time is also terminated. When the cooking time is not changed for a certain time (for example, 1 second) after the cooking time is changed, the control unit (not shown) may determine that the cooking time setting is completed. 
     Thus, the user may operate the first knob ring  304  to adjust the cooking temperature or the cooking time precisely. 
     The heating power level or cooking time set or adjusted according to the operation of the first knob  302  or the first knob ring  304  by the user is displayed in letters or in numerals on the first display unit  306 . Further, various types of letters, numerals, or symbols indicating the operation state or operation mode of the induction heating module  222  may be displayed on the first display unit  306 . 
     A process in which the user sets the heating power level and the cooking time for the first heating area  224  of the induction heating module  222  using the seventh knob module  237  will be described below. 
     First, as shown in  FIG. 4 , when the power of the cooking device 1 is in an off state, or the power of the cooking device 1 is in an on state but the induction heating module  222  does not start the heating operation, the seventh knob module  237  may be maintained in the initialized state. In the initialized state, nothing is displayed on the first display unit  306 . 
     When the user pushes the first knob  302  by applying the pressure in a direction toward the control panel  230  in the initialized state, as shown in  FIG. 5 , the first knob  302  is pushed by a certain distance toward the control panel  230 . 
     In a state in which the first knob  302  is pushed, the user rotates the first knob  302  with reference to the heating power level (1, 2, 3, . . . , 9, OFF) marked on the surface of the first knob  302 . As shown in  FIG. 6 , the user rotates the first knob  302  such that the marked position of the heating power level to be set among the heating power levels (1, 2, 3, . . . , 9, OFF) marked on the surface of the first knob  302  matches with a position of a reference point  308 . 
     When the user rotates the first knob  302  such that the heating power level 1 is positioned at the reference point  308  and releases the pressure applied to the first knob  302  as in the embodiment of  FIG. 6 , the heating power level of the low-temperature heating module  202  is set to “1” Here, “1”, which is the heating power level set by the user, is displayed on the first display unit  306 . 
     The user may set the cooking time by operating the first knob ring  304  in a state in which the user sets a heating power level of the first heating area  224  to “1” using the first knob  302 . 
     When the first knob ring  304  is clicked in the first direction (for example, counterclockwise) or in the second direction (for example, clockwise) in a state in which the cooking time or timer is not set for the first heating area  224 , the cooking time setting mode is started. 
     For example, as in the embodiment of  FIG. 7 , when the user clicks the first knob ring  304  in the first direction in a state in which the user does not set the cooking time or the timer for the first heating area  224 , the cooking time setting mode is started. When the cooking time setting mode is started, a numeral indicating the preset initial time (for example, 5 minutes) is displayed on the first display unit  306  as shown in  FIG. 7 . Depending on the embodiment, a audio may be output to notify the start of the cooking time setting mode with the start of the cooking time setting mode. 
     In a state in which the cooking time setting mode is started, the user may adjust the cooking time displayed on the first display unit  306  as desired by clicking or holding the first knob ring  304  in the first direction or the second direction. 
     For example, when the user clicks once the first knob ring  304  in the first direction in a state in which “5”, which is the initial time is displayed on the first display unit  306  as shown in  FIG. 8 , the cooking time displayed on the first display unit  306  is decreased by “1”. Accordingly, “4” is displayed on the first display unit  306 . 
     As another example, when the user clicks once the first knob ring  304  in the second direction in a state in which “5”, which is the initial time, is displayed on the first display unit  306  as shown in  FIG. 9 , the cooking time displayed on the first display unit  306  is increased by “1”. Accordingly, “6” is displayed on the first display unit  306 . 
     Further, when the user holds the first knob ring  304  in the first direction or the second direction, the numeral displayed on the first display unit  306  increases or decreases by the preset adjustment unit in proportion to the time at which the first knob ring  304  is held. 
     In one embodiment of the present disclosure, a displaying unit and an adjustment unit of an adjustment time displayed on the first display unit  306  may vary depending on the size of the adjustment time set. 
     For example, when the adjustment time set by the user is less than 180 minutes, the displaying unit of the adjustment time displayed on the first display unit  306  is “minute”. Accordingly, when the adjustment time set by the user is 8 minutes, “8” is displayed on the first display unit  306 , and when the adjustment time set by the user is 167 minutes, “167” is displayed on the first display unit  306 . 
     Further, when the adjustment time set by the user is less than 180 minutes, the adjustment unit of the cooking time according to the operation of the first knob ring  304  may be set to 1 minute. Accordingly, when the user clicks or holds the first knob ring  304  in a state in which the adjustment time set by the user is less than 180 minutes, the cooking time displayed on the first display unit  306  increases or decreases by one. 
     Further, when the adjustment time set by the user is equal to or more than 180 minutes, the displaying unit of the adjustment time displayed on the first display unit  306  is “hour”. Accordingly, when the adjustment time set by the user is 180 minutes, the first display unit  306  displays “3H” indicating 3 hours. 
     Further, when the adjustment time set by the user is equal to or more than 180 minutes, the adjustment unit of the cooking time according to the operation of the first knob ring  304  may be set to 1 hour. Accordingly, when the user increases the adjustment time by clicking or holding the first knob ring  304  in a state in which the adjustment time set by the user is 3H, the cooking time displayed on the first display unit  306  increases by one hour. However, when the user decreases the adjustment time by clicking or holding the first knob ring  304  in a state in which the adjustment time set by the user is 3H, the cooking time displayed on the first display unit  306  decreases by one minute while being displayed again in minutes. 
     Meanwhile, when the user intends to cancel the cooking time setting after the cooking time setting mode is started, the user operates the first knob ring  304  to reduce the cooking time to a preset minimum value (for example, 0) in a state in which the cooking time is displayed on the first display unit  306 . 
     For example, when the user clicks the first knob ring  304  in the first direction five times in a state in which “5” is displayed on the first display unit  306 , a symbol (for example, “---”) indicating cancellation of the cooking time setting mode is displayed on the first display unit  306 , and the cooking time setting mode is canceled. Depending on the embodiment, a audio may be output to notify the cancellation of the cooking time setting mode with the cancellation of the cooking time setting mode. 
     When the preset waiting time passes after the cooking time setting mode is canceled, the first display unit  306  displays the current heating power level set for the first heating area  224 . 
     As described above, the user may operate the first knob  302  and the first knob ring  304 , which are included in the seventh knob module  237 , to set the heating power level and/or the cooking time for the first heating area  224  quickly and easily. In the same manner as above, the user may operate the second knob and the second knob ring, which are included in the eighth knob module  238 , to set the heating power level and/or the cooking time for the second heating area  226  quickly and easily. 
       FIG. 10  is an exploded view of the knob module according to one embodiment of the present disclosure. As a reference, although an exploded view of the seventh knob module  237  is shown in  FIG. 10 , the eighth knob module  238  may also have the same structure as that of  FIG. 10 . 
     A knob  302  is formed with a handle formed on an upper portion of a body thereof having a circular shape and a knob shaft connected to an adjustment shaft  325  of a heating power adjustment unit  324 . Although the handle has a shape protruding in a bar shape in the illustrated embodiment, the shape of the handle may be variously changed. 
     The knob  302  may be infinitely rotated in a first direction (for example, counterclockwise) or in a second direction (for example, clockwise). When the user rotates the knob  302 , the knob  302  maintains the position where the user moved as it is without returning to its initial position. In one embodiment of the present disclosure, the knob  302  may be configured as a non-return type rotary switch. 
     When the heating module controlled by the knob module is a gas heating module or a gas stove, the heating power adjustment unit  324  becomes a valve assembly. Further, when the heating module controlled by the knob module is an induction heating module or an induction range, the heating power adjustment unit  324  becomes a heating power level adjusting device (for example, a variable resistor) configured to adjust the heating power level. 
     The knob  302  may be made of a synthetic resin injection material or may be manufactured by processing a metal material. The material and shape of the knob  302  may be variously modified. 
     When the knob  302  is rotated, a rotation direction and/or a rotation amount of the knob  302  is detected by a knob sensor E 1  connected through the knob shaft and the adjustment shaft  325 . When the knob  302  rotates, a gear G 1  coupled to the adjustment shaft  325  and a gear G 4  engaged with the gear G 1  are rotated. The knob sensor E 1  senses the rotation direction and/or the rotation amount of the knob  302  on the basis of the rotation amount of the gear G 4  and transmits the sensed rotation direction and/or rotation amount to the control unit (not shown). The control unit (not shown) may calculate a current position of the knob  302  on the basis of the rotation direction and/or the rotation amount sensed by the knob sensor E 1 . 
     The knob ring  304  has a circular ring shape and is disposed on an outer peripheral surface of the knob  302 . The knob ring  304  supports the knob  302  and finishes an exterior of a periphery of the knob  302  to improve the quality of the exterior of the knob module. 
     The knob ring  304  may rotate independently of the knob  302 . The knob ring  304  may not rotate indefinitely unlike the knob  302  and moves only within the predetermined angle in the first direction (for example, counterclockwise) or the second direction (for example, clockwise). 
     When the knob ring  304  is rotated by the user, the rotation direction and/or the rotation amount of the knob ring  304  is sensed by a knob ring sensor E 2 . When the knob ring  304  is rotated, a gear G 2  provided in a support ring  320  connected to the knob ring  304  and a gear G 3  engaged with the gear G 2  are rotated. The knob ring sensor E 2  senses the rotation direction and/or the rotation amount of the knob ring  304  on the basis of the rotation direction and/or the rotation amount of the gear G 3 , and transmits the sensed rotation direction and/or rotation amount to the control unit (not shown). The control unit (not shown) may confirm the rotation direction of the knob ring  304  and whether the knob ring  304  is rotated on the basis of the rotation direction and/or the rotation amount sensed by the knob ring sensor E 2 . 
     A display unit  123  is formed on an outer peripheral surface of the knob ring  304 . Values (for example, the cooking temperature or the cooking time) changing by the movement of the knob  302  or the knob ring  304  are displayed on the display unit  123 . Further, various information related to an operation state and the operation mode of the heating module may be displayed on the display unit  123 . 
     Letters or numerals displayed on the display unit  123  may be displayed in different colors according to the type of the heating module controlled by the knob module or the type of letters or numerals displayed on the display unit  123 . For example, the cooking temperature and the heating power level are displayed in a red color, and the cooking time may be displayed in a white color or a blue color. 
     The knob  302  and the knob ring  304  are exposed in a front surface direction of the control panel  230  in a coupled state. 
     A bearing shell  311  includes a body part  315  having a cylindrical shape and a circular plate part  313  which is bent in the body part  315  and protrudes in a radial direction. The body part  315  is inserted into a space between an outer peripheral surface of the support ring  320  coupled with the knob ring  304  and an inner peripheral surface of a fixing frame  322  to reduce friction between the support ring  320  and the fixing frame  322 . 
     The circular plate part  313  is inserted into a space between the control panel  230  and the knob ring  304  to reduce friction between the knob ring  304  and the control panel  230 . The circular plate part  313  allows the knob ring  304  to be spaced apart from the control panel  230  by a certain distance, thereby reducing scratch or abrasion of the control panel  230  due to the friction generated between the knob ring  304  and the control panel  230  when the knob ring  304  rotates. 
     A support frame  319  is coupled to a rear surface of the control panel  230  to support the knob ring  304 . Further, the support frame  319  surrounds the outer peripheral surface of the support ring  320  and supports the support ring  320  so that the support ring  320  may rotate around a certain axis. 
     The support ring  320  is coupled to a rear surface of the knob ring  304  and rotates integrally with the knob ring  304 . Accordingly, a rotation amount of the support ring  320  is the same as a rotation amount of the knob ring  304 . Thus, when the rotation amount of the support ring  320  is sensed, the rotation amount of the knob ring  304  may be sensed. The support ring  320  may be provided with the gear G 2  to sense the rotation amount of the support ring  320 . 
     The fixing frame  322  is fixed to the support frame  319  by fastening components such as a screw and prevents the support ring  320  from being separated from the support frame  319 . 
     Further, the fixing frame  322  constrains a rotation range of the support ring  320  such that the support ring  320  and the knob ring  304  rotates in leftward and rightward directions only within the predetermined angle. 
     As illustrated in the drawings, the fixing frame  322  is formed to have a shape like a bow tie. A portion corresponding to a wing of the fixing frame  322  restricts the support ring  320  to rotate within the predetermined angle. Further, a portion connecting both wings of the fixing frame  322  fixes the support ring  320  to prevent the support ring  320  from being separated. 
     Meanwhile, the knob ring  304  according to the present disclosure has a return type operation structure. In other words, the knob ring  304  returns to its initial position when the pressure applied by the user is released in a state in which the user applies the pressure and the knob ring  304  moves in the first direction or the second direction. 
     Return springs S 1  and S 2  provide a restoring force which causes the knob ring  304  to return to the original position thereof. A first return spring S 1  provides a restoring force in a clockwise direction, and a second return spring S 2  provides a restoring force in a counterclockwise direction. Elastic forces of the first return spring S 1  and the second return spring  52  are balanced with respect to each other so that the knob ring  304  maintains its initial position unless pressure is applied to the knob ring  304  from the outside. 
     Both ends of the return springs S 1  and S 2  may be respectively fixed to the support ring  320  and the support frame  319 . Since the support ring  320  and the knob ring  304  integrally rotate, the knob ring  304  maintains its initial position by the elastic forces of the return springs S 1  and S 2 , and the knob ring  304  may rotate in the clockwise or counterclockwise direction within the predetermined angle. 
       FIG. 11  is a perspective view of a heating power adjustment unit according to another embodiment of the present disclosure.  FIG. 12  is an exploded view of the heating power adjustment unit according to another embodiment of the present disclosure. 
     As shown in the drawings, the heating power adjustment unit  324  includes a valve  370  combined with a gas pipe  31  and a gas pipe frame  35 , an ignition switch  360  fitting on a valve shaft  325  of the valve  370 , and a knob sensor  400 . 
     The knob sensor  400  may detect a rotation angle of a valve shaft  330  by sensing a position of a knob sensor magnet  460  included in a rotating plate  450  through a plurality of hall sensors  444  arranged radially on a knob sensor substrate  440 . 
     As shown in  FIG. 12 , the plurality of hall sensors  444  are arranged at equidistance radially on the knob sensor substrate  440 . Hereinafter, a rightmost hall sensor is referred to as a first hall sensor, and other hall sensors will be sequentially referred to as second to seventh hall sensors. 
     The knob sensor  400  forms absolute coordinates by generating a different signal for each of the hall sensors  444  and detects a position of the knob sensor magnet  460  using the absolute coordinates. 
     That is, regardless of an immediately preceding position of the knob sensor magnet  460 , when a finally received signal is a signal generated by an nth hall sensor, the knob sensor  400  determines a position of the knob sensor magnet  460  is a position corresponding to an nth hall sensor area. 
     Accordingly, even when a knob is rapidly operated, it is possible to precisely sense a final position of the knob sensor magnet  460  in a state in which rotation of a knob handle is grasped. Accordingly, a set value may be accurately detected. 
     The knob sensor  400  includes a knob sensor plate  410  fastened to the valve  370 , a knob sensor housing  430  combined with the knob sensor plate  410  to be movable in an axial direction, a sensor spring  420  providing an elastic force between the knob sensor housing  430  and the knob sensor plate  410 , the knob sensor substrate  440  which includes the hall sensors  444  and is fastened to the knob sensor housing  430 , and the rotating plate  450  which is combined with the valve shaft, rotates integrally with the valve shaft, and is combined with the knob sensor magnet  460  sensed by the hall sensors  444 . 
     The ignition switch  360  includes a valve shaft combination hole  362  having a D-shaped cross section. Accordingly, the ignition switch  360  receives a rotation force of the valve shaft such that an on/off state of the ignition switch  360  may be converted according to a rotation angle of the valve shaft. The ignition switch  360  changes to an on state when the valve shaft rotates by a certain angle and generates sparks at a fuel intake. 
       FIGS. 13 and 14  are cross-sectional views illustrating an operation of the heating power adjustment unit according to another embodiment of the present disclosure. 
     Referring to  FIGS. 13 and 14 , as a pressure is applied to the knob, a universal joint  200  moves in a direction of compressing the sensor spring  420 . The sensor spring  420  and a valve spring  340  are compressed by movement of the universal joint  200 , and the knob sensor housing  430 , to which a rotating plate  50  and the knob sensor substrate  440  are fastened, and the valve shaft  325  move in a direction in which the sensor spring  420  is compressed. 
     When the pressure applied to the knob is removed, due to restoring forces of the valve spring  340  and the sensor spring  420 , the knob sensor housing  430 , to which the valve shaft  325  and the knob sensor substrate  440  are fastened, and the rotating plate  450  return to initial positions. 
     The knob sensor plate  410  is fastened to a valve cap  384 , and the sensor spring  420  provides an elastic force in a direction in which the knob sensor housing  430  is pressed against the rotating plate  450 . Accordingly, the rotating plate  450  comes into contact with a first shaft combination pipe  227  of the universal joint  200 , and a supporting protrusion  435  of the knob sensor housing  430  comes into contact with the rotating plate  450 . 
     A state in which the supporting protrusion  435  of the knob sensor housing  430  is in contact with the rotating plate  450  is always maintained when the knob is not pressed as shown in  FIG. 6  or when the knob is pressed as shown in  FIG. 7 . 
     Accordingly, since the rotating plate  450  and the knob sensor plate  410  of the knob sensor may constantly maintain a uniform distance therebetween despite axial movement of the valve shaft, a distance between the knob sensor magnet  460  disposed on the rotating plate  450  and the hall sensors  444  arranged on the knob sensor plate  410  may be uniformly maintained. This structure increases operational reliability of the knob sensor  400 . 
       FIGS. 15 and 16  are cross-sectional views illustrating an operation of a knob ring according to another embodiment of the present disclosure. 
     Operating of a knob ring  120  may be recognized by rotation of an operational ring  170  rotated in cooperation with rotation of the knob ring  120 . A knob ring sensor  500  is installed near the operational ring  170  and may sense the rotation of the knob ring  120  by sensing the rotation of the operational ring  170 . 
     The operational ring  170  is combined with a pair of such return springs S 1  and S 2  which provide elastic forces for returning the operational ring  170  rotated to a position spaced apart from an initial position to the initial position. 
     Since the operational ring  170  and the knob ring  120  rotate integrally, the knob ring  120  remains in an initial position due to the elastic forces of the return springs S 1  and S 2  connected to the operational ring  170 . Also, when a pressure is applied to the knob ring  120  which remains in the initial position as described above, the knob ring  120  may rotate within the predetermined angle clockwise or counterclockwise and may return to the initial position again due to the restoring forces provided by the return springs S 1  and S 2  when the pressure is related in a rotated state. 
     A position of a knob ring sensor magnet  530  is changed according to the rotation of the operational ring  170 . The knob ring sensor  500  senses the rotation of the operational ring  170  by sensing a change in position of the knob ring sensor magnet  530  and senses the rotation of the knob ring  120  connected to the operational ring  170  therethrough. 
     The knob ring sensor magnet  530  is a component to be sensed by the knob ring sensor  500  and is installed on the operational ring  170 . In the embodiment, it is exemplified that the knob ring sensor magnet  530  is installed on a circular plate part  172  of the operational ring  170 . In the drawing, since the knob ring sensor magnet  530  is located on a rear surface of a knob ring sensor substrate  520 , it is shown as a dotted line. 
     The knob ring sensor magnet  530  is installed on the circular plate part  172  to be disposed on one side surface of the circular plate part  172  facing the knob ring sensor  500 . The knob ring sensor magnet  530  installed as described above is rotated with the operational ring  170  when the operational ring  170  rotates. 
     In the embodiment, it is exemplified that the knob ring sensor magnet  530  is disposed in a position adjacent to an outer circumferential surface of the circular plate part  172 . The knob ring sensor magnet  530  disposed in the above-described position draws a track similar to a shape of an outer circumferential surface of the circular plate part  172  having a circular shape during the rotation of the operational ring  170  such that a position of the knob ring sensor magnet  530  may change. 
     The knob ring sensor  500  is provided to sense the change in position of the knob ring sensor magnet  530  and is fastened to a support frame  150  on a rear surface of the operational ring  170 . 
     The knob ring sensor  500  includes a knob ring sensor housing  510 , the knob ring sensor substrate  520 , and hall sensors  522   a  and  522   b.    
     The knob ring sensor housing  510  is fixedly installed on the support frame  150 , that is, in more detail, on a bottom part of a frame body part  141 , The knob ring sensor substrate  520  connected to the control unit of the cooking device is installed on the knob ring sensor housing  510 . 
     In the embodiment, it is exemplified that the knob ring sensor substrate  520  is installed on the knob ring sensor housing  510  to be installed on a side facing the frame body part  141  and the knob ring sensor magnet  530 . Also, a sensor for sensing the change in position of the knob ring sensor magnet  530  is installed on the knob ring sensor substrate  520 . 
     The knob ring sensor  500  having the above components senses a position of the knob ring sensor magnet  530  in a non-contact manner like the knob sensor  400 . To this end, the knob ring sensor magnet  530  may include a magnetic member which generates a magnetic force, and the knob ring sensor  500  may include a hall sensor  522  which senses the magnetic force of the magnetic member which approaches within a certain distance. 
     The hall sensor  522  is installed on the knob ring sensor substrate  520 , senses the magnetic force of the knob ring sensor magnet  530  when the knob ring sensor magnet  530  approaches the hall sensor  522  within a certain distance, and generates a signal corresponding thereto. 
     The knob ring sensor  500  includes a plurality of such hall sensors  522 , and the plurality of hall sensors  522  are arranged to be spaced at certain intervals apart along a rotational path of the knob ring sensor magnet  530 . 
     That is, when the knob ring sensor magnet  530  rotates while drawing a circular track similar to the shape of the outer circumferential surface of the circular plate part  172  during the rotation of the operational ring  170 , the plurality of hall sensors  522  are arranged on the knob ring sensor  500  to be located on an arc corresponding to a rotational track of the knob ring sensor magnet  530 . 
     In the embodiment, arrangements of the hall sensors  522   a  and  522   b  and the knob ring sensor magnet  530  are exemplified that the pair of hall sensors  522   a  and  522   b  are arranged on the knob ring sensor  500 , and the knob ring sensor magnet  530  is located between the pair of hall sensors  522  when the knob ring  120  and the operational ring  170  are in the initial positions. 
     Accordingly, when the knob ring  120  rotates in one direction, the knob ring sensor magnet  530  approaches any one of the pair of hall sensors  522  (hereinafter, referred to as a left hall sensor) within a certain distance such that the corresponding hall sensor  522   a  senses the knob ring sensor magnet  530 . When the knob ring  120  rotates in the other direction, the knob ring sensor magnet  530  approaches the other of the pair of hall sensors  522  (hereinafter, referred to as a right hall sensor) within a certain distance such that the corresponding hall sensor  522   b  senses the knob ring sensor magnet  530 . 
     To provide a cooking time setting function or timer function, when the knob ring  120  rotates in one direction, the knob ring sensor magnet  530  approaches the left hall sensor  522   a  within a certain distance such that the left hall sensor  522   a  senses the knob ring sensor magnet  530 . Accordingly, operating of the knob ring  120  for initiating a cooking time setting mode is sensed by the knob ring sensor  500  such that the cooking time setting mode may be started. 
     Also, when the knob ring  120  is rotated in the other direction, the knob ring sensor magnet  530  approaches the right hall sensor  522   b  within a certain distance such that the right hall sensor  522   b  senses the knob ring sensor magnet  530 . Accordingly, operating of the knob ring  120  for initiating the cooking time setting mode is sensed by the knob ring sensor  500  such that the cooking time setting mode may be started. 
     In the embodiment, it is exemplified that the hall sensors  522  generate different types of signals. That is, a signal generated by the left hall sensor  522   a  differs from a signal generated by the right hall sensor  522   b.    
     Utilizing this, the knob ring  120  may be configured to have a function of setting a cooking time to be different according to a rotation direction of the knob ring  120  or a function of providing a different function according to the rotation direction of the knob ring  120 . 
       FIG. 17  is a block diagram illustrating a configuration of the cooking device according to one embodiment of the present disclosure; 
     Referring to  FIG. 17 , the seventh knob module  237  includes a first knob  302 , a knob sensor E 1 , a first knob ring  304 , a knob ring sensor E 2 , and a first display unit  306 . Further, the eighth knob module  238  includes a second knob  312 , a knob sensor E 3 , a second knob ring  314 , a knob ring sensor E 4 , and a second display unit  316 . 
     For example, when the user pushes the first knob  302  or the second knob  312  and applies the pressure in the first direction or the second direction, the first knob  302  or the second knob  312  rotates. The rotation direction and/or the rotation amount of the first knob  302  or the second knob  312  is detected by the knob sensor E 1  or the knob sensor E 3 , and the knob sensor E 1  or the knob sensor E 3  transmits the detected rotation direction and/or rotation amount of the first knob  302  or the second knob  312  to the control unit  406 . 
     The control unit  406  calculates a current position of the first knob  302  or the second knob  312  on the basis of the rotation direction and/or the rotation amount of the first knob  302  or the second knob  312  transmitted from the knob sensor E 1  or the knob sensor E 3 , and determines the heating power level set by the user by rotating the first knob  302  or the second knob  312  on the basis of the calculated position. For example, when it is determined that the first knob  302  or the second knob  312  is rotated by 72° in the second direction, that is, the clockwise direction from its initial position, the control unit  406  sets “2”, which is the heating power level assigned to the position rotated by 72° in the clockwise direction, to a heating power level of the first heating area  224  or the second heating area  226 . 
     Further, when the user applies pressure in the first direction or the second direction, in a state in which the user touches the first knob ring  304  or the second knob ring  314 , or the first display unit  306  or the second display unit  316  with a part of her or his body (e.g., a finger), the first knob ring  304  or the second knob ring  314  rotates. 
     The rotation direction and/or the rotation amount by the rotation of the first knob ring  304  or the second knob ring  314  is detected by the knob ring sensor E 2  or the knob ring sensor E 4 , and the knob ring sensor E 2  or the knob ring sensor E 4  transmits the detected rotation direction and/or rotation amount of the first knob ring  304  or the second knob ring  314  to the control unit  406 . 
     The control unit  406  determines the rotation direction of the first knob ring  304  or the second knob ring  314  and whether the first knob ring  304  or the second knob ring  314  is rotated on the basis of the rotation direction and/or rotation amount of the first knob ring  304  or the second knob ring  314  transmitted from the knob ring sensor E 2  or the knob ring sensor E 4 . The control unit  406  determines that the first knob ring  304  or the second knob ring  314  is rotated only when the first knob ring  304  or the second knob ring  314  is rotated by the predetermined reference angle. 
     Further, the control unit  406  compares the time, at which the first knob ring  304  or the second knob ring  314  is maintained in the rotated state after being rotated by the predetermined reference angle, with a predetermined reference time to determine the operation state of the first knob ring  304  or the second knob ring  314 . When the first knob ring  304  or the second knob ring  314  maintains the rotation state thereof over the reference time, the operation of the first knob ring  304  or the second knob ring  314  is determined as the holding operation, and when the first knob ring  304  or the second knob ring  314  maintains the rotation state thereof below the reference time and returns to its initial position, the operation of the first knob ring  304  or the second knob ring  314  is determined as the click operation. 
     The control unit  406  increases or decreases the cooking time set by the user according to the rotation direction and the operation state of the first knob ring  304  or the second knob ring  314  by the preset adjustment unit. For example, when the first knob ring  304  or the second knob ring  314  is clicked twice in the first direction, that is, in the counterclockwise direction, the control unit  406  decreases twice the cooking time set by the user by the preset adjustment unit (for example, 1 minute). As another example, when the first knob ring  304  or the second knob ring  314  maintains the holding state thereof in the second direction, that is, the clockwise direction, the control unit  406  continuously increases the cooking time set by the user in proportion to the time at which the first knob ring  304  or the second knob ring  314  is held by the preset adjustment unit (for example, 1 minute). 
     Whenever the user sets or changes the heating power level or the cooking time using the first knob  302  or the second knob  312 , or the first knob ring  304  or the second knob ring  314 , the control unit  406  displays the heating power level or cooking time set or changed by the user through the first display unit  306  or the second display unit  316  provided on an outer peripheral surface of the first knob ring  304  or the second knob ring  314 . In one embodiment of the present disclosure, when the user sets the heating power level or cooking time, the control unit  406  may output a preset setting notification audio through a audio output unit  412 . 
     Further, the cooking device 1 includes a first working coil  254  corresponding to the first heating area  224  and a second working coil  256  corresponding to the second heating area  226 , The first working coil  254  is driven by the power supplied from a first power supply unit  408  to supply the heat energy to the container seated on the first heating area  224 . The second working coil  256  is driven by the power supplied from a second power supply unit  410  to supply the heat energy to the container seated on the second heating area  226 . 
     The control unit  406  applies a control signal to the first power supply unit  408  or the second power supply unit  410  so that the power having the magnitude corresponding to the heating power level set by the operation of the seventh knob module  237  or the eighth knob module  238  is supplied to the first working coil  254  or the second working coil  256 , respectively. Further, the control unit  406  displays the heating power level set by the operation of the seventh knob module  237  or the eighth knob module  238  on the first display unit  306  or the second display unit  316 , respectively. 
     Further, the control unit  406  performs the measurement or countdown operation of the cooking time on the basis of the cooking time or the timer set in accordance with the operations of the seventh knob module  237  and the eighth knob module  238 . 
     The control unit  406  measures the cooking time, at which the heating operation of each heating area is performed from the time when the cooking time is set by the user, and compares the measured cooking time with the cooking time set by the user. As another example, when the user sets the cooking time, the control unit  406  may perform the countdown operation until the cooking time becomes zero. The countdown operation may be performed according to a preset countdown unit time (for example, 1 second). The control unit  406  displays the measured cooking time or a time being counted down on the first display unit  306  or the second display unit  316 . 
     Further, the control unit  406  may display information related to the operation state and the operation mode of the induction heating module  222  through the display unit  306  and output a audio related to the operation state and the operation mode of the heating module  408  through the audio output unit  412 . For example, when the cooking time set by the user is reached, the control unit  406  displays letters (for example, “---”) indicating the end of the timer on the display unit  306 , and outputs a audio notifying an end of the timer through the audio output unit  412 . The user may intuitively recognize that the timer has been terminated through such a notification operation. 
     Further, the control unit  406  may sense whether the heatable container is present on the heating areas  224  and  226  through the container sensing function. When it is determined that the container is not present on the heating areas  224  and  226  as a result of performing the container sensing, the control unit  406  may display a symbol indicating that the container is not present through the first display unit  306  or the second display unit  316  or may output a audio indicating that there is no container through the audio output unit  412 . 
     Further, the control unit  406  may control the first power supply unit  408  or the second power supply unit  410  to supply the power to the first working coil  254  or the second working coil  256  only when the heatable container is present on the heating areas  224  and  226  as a result of the container sensing, and otherwise, control the first power supply unit  408  or the second power supply unit  410  not to supply the power to the first working coil  254  or the second working coil  256  even when the user requests the start of the heating operation. 
     Hereinafter, a heating operation control process of the induction heating module  222  using the seventh knob module  237  and the eighth knob module  238  will be described with reference to  FIGS. 18 to 28 . 
       FIG. 18  illustrates a seventh knob module, an eighth knob module, and a flexible button configured to control a heating operation of the induction heating module included in the cooking device according to one embodiment of the present disclosure; 
     As shown in  FIG. 18 , both the seventh knob module  237  configured to control the heating operation of the first heating area  224  of the induction heating module  222  and the eighth knob module  238  configured to control the heating operation of the second heating area  226  of the induction heating module  222  are disposed on the control panel  230 . 
     Further, a flexible button  380  configured to change the operation mode (the normal mode or the flexible mode) of the induction heating module  222  is disposed between the seventh knob module  237  and the eighth knob module  238 . Whenever the user touches the flexible button  380 , the operation mode of the induction heating module  222  is alternately changed to the normal mode or the flexible mode. 
     The normal mode refers to the mode in which each of the working coils  254  and  256  included in the induction heating module  222  operates as the separate heating source. That is, when the induction heating module  222  is set to the normal mode, the user may heat two different containers, each of which corresponds to the size of each of the first heating area  224  and the second heating area  226 . In the normal mode, the user may separately control the heating operations of the first heating area  224  and the second heating area  226  using the seventh knob module  237  and the eighth knob module  238   
     The flexible mode refers to the mode in which the working coils  254  and  256  included in the induction heating module  222  operate as the single heating source. That is, when the induction heating module  222  is set to the flexible mode, the first heating area  224  and the second heating area  226  operate as if they are the single heating area. Accordingly, the user may perform the cooking using the large-sized container covering both the first heating area  224  and the second heating area  226 . In the flexible mode, the user may control the heating operations of the heating areas  224  and  226  using only one knob module of the seventh knob module  237  and the eighth knob module  238   
     Although the flexible button  380  is described as an electronic touch button having a built-in touch sensor in the embodiment described below, the type of the flexible button  380  may vary according to the embodiments. Further, the position of the flexible button  380  may vary depending on the embodiments. 
     Further, a lamp which is turned on or off according to the operation mode of the induction heating module  222  may be built in the flexible button  380 . For example, when the induction heating module  222  is set to the flexible mode as the flexible button  380  is touched, the lamp built in the flexible button  380  is turned on. Further, the induction heating module  222  is set to the normal mode as the flexible button  380  is touched, the lamp built in the flexible button  380  is turned off 
     The seventh knob module  237  includes the first knob  302  configured to set the heating power level of the first heating area  224 , the first knob ring  304  configured to set the cooking time of the first heating area  224 , and the first display unit  306  formed on an outer peripheral surface of the first knob ring  304  and configured to display the heating power level of the first heating area  224 , the cooking time, whether the container is present, or the like. 
     The eighth knob module  238  includes the second knob  312  configured to set a heating power level of the second heating area  226 , the second knob ring  314  configured to set the cooking time of the second heating area  226 , and the second display unit  316  formed on an outer peripheral surface of the second knob ring  314  and configured to display the heating power level of the second heating area  226 , the cooking time, whether the container is present, or the like. 
     Hereinafter, a method of controlling the heating operation of the heating area using the knob module when the induction heating module  222  operates in the normal mode will be described with reference to  FIGS. 19 to 23 . 
       FIG. 19  illustrates a container which is seated on the induction heating module and a heating area of the induction heating module when the induction heating module operates in a normal mode in one embodiment of the present disclosure.  FIG. 20  illustrates a method of setting a heating power level of a first heating area to “3” using the knob module when the induction heating module operates in the normal mode in one embodiment of the present disclosure.  FIG. 21  illustrates a method of operating the first heating area in a boost mode using the knob module when the induction heating module operates in the normal mode in one embodiment of the present disclosure.  FIG. 22  illustrates a state in which the container is not recognized in the heating area when the induction heating module operates in the normal mode in one embodiment of the present disclosure.  FIG. 23  illustrates a method of setting a cooking time of the heating area using the knob module when the induction heating module operates in the normal mode in one embodiment of the present disclosure; 
     When the operation mode of the induction heating module  222  is set to the normal mode, the lamp built in the flexible button  380  is turned off as shown in  FIG. 18 . In the normal mode, each of the first heating area  224  and the second heating area  226  operates as a separate heating area. Accordingly, the user has to use a container having a size corresponding to the size of each of the first heating area  224  and the second heating area  226 . 
     For example, when the operation mode of the induction heating module  222  is the normal mode, the user places a container P 1  having the size corresponding to the size of the first heating area  224  on the first heating area  224  as shown in  FIG. 19 . 
     After placing the container P 1  on the first heating area  224 , the user operates the first knob  302  of the seventh knob module  237 , which corresponds to the first heating area  224 , to set the heating power level of the first heating area  224 . For example, as shown in  FIG. 20 , the user may rotate the first knob  302  by 108° in the second direction (the clockwise direction) so that the heating power level “3” matches with the reference point  308 . 
     Thereafter, when the user does not change the heating power level for a certain time (for example, 1 second), the heating power level of the first heating area  224  is set to “3”. When the heating power level is set, a audio notifying the setting of the heating power level may be output through the audio output unit  412 . 
     When the setting of the heating power level is completed, the control unit  406  applies a control signal to the first power supply unit  408  so that the first power supply unit  408  is driven in a driving frequency corresponding to the heating power level set by the user. When the first power supply unit  408  is driven by the control signal, the power is supplied to the first working coil  254 , and the heating operation for the container P 1  is performed. 
     Meanwhile, the induction heating module  222  according to the present disclosure may operate in a boost mode according to the setting of the heating power level. For example, as shown in  FIG. 21 , the user rotates the first knob  302  in the first direction (counterclockwise direction) in a state in which the first knob  302  is in its initial position, that is, in a state in which “OFF” matches with the reference point  308 , to match a maximum level, that is, the heating power level “9”, with the reference point  308 , thereby setting the operation mode of the first heating area  224  to the boost mode. When the operation mode of the first heating area  224  is set to the boost mode, letters or a symbol (for example, “bst”) indicating that the operation mode of the first heating area  224  is the boost mode is displayed on the first display unit  306 . 
     As a reference, when the user rotates the first knob  302  in the second direction (clockwise direction) to match the heating power level “9” with the reference point  308 , the heating power level of the first heating area  224  is set to “9”. 
     In the boost mode, each working coil operates at an output greater than the maximum heating power level (for example, 9) of the heating area. For example, when the output of the first working coil  254  is set to 1800 kW in a state in which the heating power level of the first heating area  224  is “9”, in the boost mode, the output of the first working coil  254  may be set to 2000 kW which is greater than 1800 kW. 
     In one embodiment of the present disclosure, when the induction heating module  222  operates in the boost mode, the output of each working coil may be set the same as the maximum output of each working coil. 
     Further, in one embodiment of the present disclosure, the heating area set in the boost mode operates in the boost mode only for a preset boosting time (for example, 5 minutes). When the boosting time has passed, the heating power level of the heating area set in the boost mode is set to a preset return level (for example, “9”). 
     For example, when the user sets the operation mode of the first heating area  224  to the boost mode, as shown in  FIG. 21 , the letters or the symbol (for example, “bst”) indicating that the operation mode of the first heating area  224  is the boost mode is displayed on the first display unit  306 , and the first working coil  254  is driven at the maximum output (2000 kW) for 5 minutes. Thereafter, when 5 minutes have passed, the heating power level of the first heating area  224  is automatically set to “9” and “9” is displayed on the first display unit  306 . 
     Meanwhile, the control unit  406  of the cooking device 1 according to the present disclosure may sense whether the heatable container is present on the heating areas  224  and  226  through the container sensing function, and inform the user of the sensing result. 
     For example, when it is determined that the container is not present on the first heating area  224  as a result of performing the container sensing for the first heating area  224 , the control unit  406  may display a symbol (for example, “ ”) indicating that the container is not present through the first display unit  306  of the seventh knob module  237 . According to the embodiments, the control unit  406  may control the audio output unit  412  to output a audio indicating that the container is not present. 
     The operation of notifying that the container is not present on the heating area is referred to as a container absence notification operation. 
     In one embodiment of the present disclosure, the container sensing and container sensing result displaying by the control unit  406  may be performed when the user operates the knob module to set the heating power level or during the heating operation of the heating area. 
     For example, when the user sets the heating power level for the first heating area  224  in a state in which the heating operation for the first heating area  224  is not started, the control unit  406  may perform the container sensing for the first heating area  224 . When the container is not present on the first heating area  224  as a result of the container sensing, the control unit  406  controls the first display unit  306  to display the symbol (for example, “ ”) indicating that the container is not present other than the heating power level set by the user. 
     As another example, the control unit  406  may perform the container sensing for the first heating area  224  when the heating operation of the first heating area  224  is in progress as the heating power level for the first heating area  224  is set. When the container is not present on the first heating area  224  as a result of the container sensing, the control unit  406  controls the first power supply unit  408  to terminate power supply to the first working coil  254 . Further, the control unit  406  performs the container absence notification operation in which the symbol (for example, “ ”) indicating that the container is not present other than the heating power level set by the user is displayed on the first display unit  306  or the audio is output. 
     Further, the user may set the cooking time of the first heating area  224  before or after the setting of the heating power level for the first heating area  224 . When the user clicks or holds the first knob ring  304  in the first direction or the second direction in a state in which the cooking time is not set, the cooking time setting mode is started. 
     For example, as shown in  FIG. 23 , when the user clicks the first knob ring  304  in the second direction in a state in which the user does not set the cooking time or the timer for the first heating area  224 , the cooking time setting mode is started. When the cooking time setting mode is started, a numeral indicating the preset initial time (for example, 5 minutes) is displayed on the first display unit  306  as shown in  FIG. 23 . Depending on the embodiment, a audio may be output to notify the start of the cooking time setting mode with the start of the cooking time setting mode. 
     In a state in which the cooking time setting mode is started, the user may adjust the cooking time displayed on the first display unit  306  by clicking or holding the first knob ring  304  in the first direction or the second direction. 
     For example, when the user clicks once the first knob ring  304  in the first direction in a state in which “5”, which is the initial time is displayed on the first display unit  306 , the cooking time displayed on the first display unit  306  is decreased by “1”. Accordingly, “4” is displayed on the first display unit  306 . 
     As another example, when the user clicks once the first knob ring  304  in the second direction in a state in which “5”, which is the initial time, is displayed on the first display unit  306 , the cooking time displayed on the first display unit  306  is increased by “1”. Accordingly, “6” is displayed on the first display unit  306 . 
     Further, when the user holds the first knob ring  304  in the first direction or the second direction for a certain time, the numeral displayed on the first display unit  306  increases or decreases by the preset adjustment unit in proportion to the time for which the first knob ring  304  maintains the holding state. 
     When the cooking time is not changed for a certain time (for example, 1 second) after the cooking time is changed, the control unit  406  may determine that the cooking time setting is completed. When the cooking time setting is completed, the control unit  406  starts the cooking time measurement or the countdown operation. When the user operates the first knob ring  304  to reset the cooking time during the cooking time measurement or countdown operation, the cooking time is reset. 
     When the user sets the cooking time using the first knob ring  304 , the countdown of the cooking time set by the user through the first display unit  306  is started. When the cooking time set by the user is reached, an end of the countdown may be displayed through the first display unit  306 . Further, when the cooking time set by the user is reached, a audio indicating the end of the countdown may be output through the audio output unit  412 . 
     In another embodiment, when the cooking time set by the user is reached, the control unit  406  may terminate the supply of the power from the power supply unit to the working coils  254  and  256 , thereby completing the heating operation. 
     When the user does not set the cooking time, the control unit  406  may end the heating operation according to the heating operation end command of the user or end the heating operation after the predetermined time limit passes. 
     In one embodiment of the present disclosure, a displaying unit and an adjustment unit of the cooking time displayed on the first display unit  306  may vary depending on the size of the set cooking time. 
     For example, when the cooking time set by the user is less than 180 minutes, the displaying unit of the cooking time displayed on the first display unit  306  is “minute”. Accordingly, when the cooking time set by the user is 8 minutes, “8” is displayed on the first display unit  306 , and when the cooking time set by the user is 167 minutes, “167” is displayed on the first display unit  306 . 
     Further, when the cooking time set by the user is less than 180 minutes, the adjustment unit of the cooking time according to the operation of the first knob ring  304  may be set to 1 minute. Accordingly, when the user clicks or holds the first knob ring  304  in a state in which the cooking time set by the user is less than 180 minutes, the cooking time displayed on the first display unit  306  increases or decreases by “1”. 
     Further, when the cooking time set by the user is equal to or more than 180 minutes, the displaying unit of the cooking time displayed on the first display unit  306  is “hour”. Accordingly, when the cooking time set by the user is 180 minutes, the first display unit  306  displays “3H” indicating 3 hours. 
     Further, when the cooking time set by the user is equal to or more than 180 minutes, the adjustment unit of the cooking time according to the operation of the first knob ring  304  may be set to 1 hour. Accordingly, when the user increases the cooking time by clicking or holding the first knob ring  304  in a state in which the cooking time set by the user is 3H, the cooking time displayed on the first display unit  306  increases by one hour. However, when the user decreases the cooking time by clicking or holding the first knob ring  304  in a state in which the cooking time set by the user is 3H, the cooking time displayed on the first display unit  306  decreases by one minute while being displayed again in minutes. 
     Meanwhile, when the user intends to cancel the cooking time setting after the cooking time setting mode is started, the user operates the first knob ring  304  to reduce the cooking time to a preset minimum value (for example, 0) in a state in which the cooking time is displayed on the first display unit  306 . 
     For example, when the user clicks the first knob ring  304  in the first direction five times in a state in which “5” is displayed on the first display unit  306 , a symbol (for example, “---”) indicating cancellation of the cooking time setting mode is displayed on the first display unit  306 , and the cooking time setting mode is canceled. Depending on the embodiment, a audio may be output to notify the cancellation of the cooking time setting mode with the cancellation of the cooking time setting mode. 
     When the preset waiting time passes after the cooking time setting mode is canceled, the first display unit  306  displays again the current heating power level set for the first heating area  224 . 
     Although the method of controlling the heating operation for the first heating area  224  using the seventh knob module  237  when the induction heating module  222  operates in the normal mode has been described above, the heating operation for the second heating area  226  may be controlled using the eighth knob module  238  in the same manner. 
     Next, a method of controlling the heating operation of the heating area using the knob module when the induction heating module  222  operates in the flexible mode will be described with reference to  FIGS. 24 to 28 . 
       FIG. 24  illustrates the container which is seated on the induction heating module and a heating area of the induction heating module when the induction heating module operates in a flexible mode in one embodiment of the present disclosure, and  FIG. 25  illustrates a method of setting the induction heating module to the flexible mode in one embodiment of the present disclosure.  FIG. 26  illustrates a method of setting a heating power level of the heating area to 4 using the knob module when the induction heating module operates in the flexible mode in one embodiment of the present disclosure.  FIG. 27  illustrates a state in which the container is not recognized in the heating area when the induction heating module operates in the flexible mode in one embodiment of the present disclosure.  FIG. 28  illustrates a method of setting the cooking time of the heating area using the knob module when the induction heating module operates in the flexible mode in one embodiment of the present disclosure. 
     When the user intends to operate the induction heating module  222  in the flexible mode, as shown in  FIG. 24 , the user places a container P 2  having a size capable of covering both the first heating area  224  and the second heating area  226  on the first heating area  224  and the second heating area  226 . In the flexible mode, the first heating area  224  and the second heating area  226  operate as a single heating area. 
     As shown in  FIG. 25 , the user pushes or touches the flexible button  380  to change the operation mode of the induction heating module  222  from the normal mode to the flexible mode. When the operation mode of the induction heating module  222  is set to the flexible mode, the lamp built in the flexible button  380  is turned on as shown in  FIG. 25 . 
     When the user changes the operation mode of the induction heating module  222  to the flexible mode, any one knob module of the seventh knob module  237  and the eighth knob module  238  is set as a control device for the heating areas  224  and  226 . For example, in the embodiment of  FIG. 25 , the eighth knob module  238  is set as the control device for the heating areas  224  and  226 . 
     When the operation mode of the induction heating module  222  is changed to the flexible mode, as shown in  FIG. 25 , letters (for example “FLE”) indicating the flexible mode setting is displayed on the second display unit  316  of the control device for the heating areas  224  and  226 , that is, the eighth knob module  238 . Accordingly, the user may recognize that the heating areas  224  and  226  can be controlled using the eighth knob module  238  in addition to that the induction heating module  222  is set to the flexible mode. 
     The user places the container P 2  over the heating areas  224  and  226  and then operates the second knob  312  of the eighth knob module  238  to set the heating power level of the heating areas  224  and  226 . For example, as shown in  FIG. 26 , the user may rotate the second knob  312  by 144° in the second direction (the clockwise direction) so that the heating power level “4” matches with the reference point  308 . 
     Thereafter, when the user does not change the heating power level for a certain time (for example, 1 second), the heating power level of the heating areas  224  and  226  is set to “4”. When the heating power level is set, a audio notifying the setting of the heating power level may be output through the audio output unit  412 . 
     When the setting of the heating power level is completed, the control unit  406  applies a control signal to the first power supply unit  408  and the second power supply unit  410  so that the first power supply unit  408  and the second power supply unit  410  are driven in a driving frequency corresponding to the heating power level set by the user. When the first power supply unit  408  and the second power supply unit  410  are driven by the control signal, the power is supplied to each of the first working coil  254  and the second working coil  256 , respectively, and the heating operation for the container P 2  is performed. 
     Further, although not shown in the drawings, the user may set the operation mode of the heating areas  224  and  226  to the boost mode by rotating the second knob  312  in the first direction (the counterclockwise direction) to match the heating power level “9”, which is the maximum level, with the reference point  308  in a state in which the second knob  312  is in its initial position (“OFF”). When the operation mode of the heating areas  224  and  226  is set to the boost mode, letters or a symbol (for example, “bst”) indicating that the operation mode of the heating areas  224  and  226  is the boost mode is displayed on the second display unit  316 . The induction heating module  222  set to the boost mode operates in the same manner as in the normal mode. 
     Further, the control unit  406  may sense whether the heatable container is present on the heating areas  224  and  226  through the container sensing function, and inform the user of the sensing result. 
     For example, as shown in  FIG. 27 , when it is confirmed that the container is not present on at least one of the first heating area  224  and the second heating area  226  as a result of performing the container sensing for the first heating area  224  and the second heating area  226 , the control unit  406  may display a symbol (for example, “ ”) indicating that the container is not present through the second display unit  316  of the eighth knob module  238 . According to the embodiments, the control unit  406  may control the audio output unit  412  to output a audio indicating that the container is not present. 
     The operation of notifying that the container is not present on the heating area is referred to as the container absence notification operation. 
     Like the normal mode, even in the flexible mode, the container sensing and container sensing result displaying by the control unit  406  may be performed when the user operates the knob module to set the heating power level or during the heating operation of the heating area. 
     Further, the user may set the cooking time of the heating areas  224  and  226  before or after the setting of the heating power level for the heating areas  224  and  226 . When the user clicks or holds the second knob ring  314  in the first direction or the second direction in a state in which the cooking time is not set, the cooking time setting mode is started. 
     For example, as shown in  FIG. 28 , when the user clicks the second knob ring  314  in the first direction in a state in which the user does not set the cooking time or the timer for the heating areas  224  and  226 , the cooking time setting mode is started. When the cooking time setting mode is started, a numeral indicating the preset initial time (for example, 5 minutes) is displayed on the second display unit  316  as shown in  FIG. 28 . Depending on the embodiment, a audio may be output to notify the start of the cooking time setting mode with the start of the cooking time setting mode. 
     In a state in which the cooking time setting mode is started, the user may adjust the cooking time displayed on the second display unit  316  by clicking or holding the second knob ring  314  in the first direction or the second direction. 
     When the user sets the cooking time, the countdown of the cooking time set by the user through the second display unit  316  is started. When the cooking time set by the user is reached, an end of the countdown may be displayed through the second display unit  316 . Further, when the cooking time set by the user is reached, a audio indicating the end of the countdown may be output through the audio output unit  412 . 
     In another embodiment, when the cooking time set by the user is reached, the control unit  406  may terminate the power supply from the power supply unit to the working coils  254  and  256 , thereby completing the heating operation. 
     When the user does not set the cooking time, the control unit  406  may end the heating operation according to the heating operation end command of the user or end the heating operation after the predetermined time limit passes. 
     Meanwhile, when the user intends to cancel the cooking time setting after the cooking time setting mode is started, the user operates the second knob ring  314  to reduce the cooking time to a preset minimum value (for example, 0) in a state in which the cooking time is displayed on the second display unit  316 . Accordingly, the cooking time setting is canceled. 
     In the above, the embodiment in which the induction heating module includes two heating areas and two working coils corresponding to two heating areas has been described. However, the induction heating module of the cooking device according to the present disclosure may include one or three more heating areas and working coils. Further, even when the number of heating areas and working coils included in the induction heating module is changed, the control method using the knob module and the knob module described above may be similarly applied. 
       FIG. 29  is a flowchart illustrating operation processes of the cooking device according to one embodiment of the present disclosure. 
     After the power is applied to the cooking device 1, the control unit  406  sets the operation mode of the induction heating module  222  to the normal mode or the flexible mode depending on whether the flexible button  380  is touched or pushed by the user ( 602 ). An initial operation mode of the induction heating module  222  may be set to the normal mode, and when the user touches or pushes the flexible button  380 , the operation mode of the induction heating module  222  is changed to the flexible mode. 
     Next, the user sets the heating power level of the heating area to be used by using the knob module. As described above, When the operation mode of the induction heating module  222  is the normal mode, the user may selectively set the heating power level of the first heating area  224  or the second heating area  226  using the seventh knob module  237  or the eighth knob module  238 . When the operation mode of the induction heating module  222  is the flexible mode, the user may set the heating power level of the heating areas  224  and  226  using the eighth knob module  238 . 
     The control unit  406  sets the heating power level of the heating area on the basis of the type of the knob module and the heating power level operated by the user ( 604 ). 
     Although not shown in the drawings, when the user sets the heating power level, the control unit  406  performs the container sensing to confirm whether the container is present on the heating area, and when the container is not present as a result of the confirmation, the control unit  406  may notify the user that the container is not present on the heating area. 
     When the setting of the heating power level is completed, the control unit  406  controls the working coil to be driven so as to start the heating operation of the heating area so that the heat energy corresponding to the set heating power level may be supplied to the container ( 606 ). 
     Although not shown in the drawings, the control unit  406  may perform the container sensing to confirm whether the container is present on the heating area even when the heating operation of the heating area is being performed. As a result of the confirmation, when the container is not present on the heating area, the control unit  406  may notify the user that the container is not present on the heating area. Further, the control unit  406  may terminate the heating operation of the heating area when the container is not present on the heating area. 
     When the heating operation of the heating area is being performed, the control unit  406  confirms whether the cooking time or the timer is set by the user ( 608 ). 
     As a result of the confirmation in operation  608 , when the timer is set by the user, the control unit  406  starts the countdown operation according to a preset unit time (for example, 1 second) ( 610 ). The control unit  406  confirms whether the countdown is completed ( 612 ), and continuously performs the countdown until the countdown is completed. 
     When it is confirmed that the countdown is completed as a result of the confirmation in operation  612 , the control unit  406  notifies the user that the countdown is completed ( 614 ). 
     Although not shown in the drawings, when the user commands the end of the heating operation by operating the knob of the knob module to be an OFF state while performing operation  608  of confirming the timer setting or operations  610  to  614  of performing the countdown, the heating operation of the heating area is immediately terminated. 
     After operation  608  of confirming the timer setting or operations  610  to  614  of performing the countdown, the control unit  406  confirms whether a heating end command is input by the user ( 616 ). As a result of confirmation in operation  616 , when the heating end command is not input, the control unit  406  maintains the heating operation. As a result of confirmation in operation  616 , when the heating end command is input, the control unit  406  terminates the heating operation of the heating area ( 618 ). 
     As described above, the cooking device according to the present disclosure includes the knob which operates in a push-and-turn manner and the knob ring which operates in a click or hold manner. The user may easily and quickly set the amount of the heat energy supplied by the heating module provided in the cooking device and the cooking time using the knob or the knob ring. 
     Further, since the user may operate the knob or the knob ring while confirming information displayed on the display unit in real time, the amount of the heat energy supplied by the heating module and the cooking time may be set more easily and accurately. 
     Further, various information related to the cooking may be quickly and conveniently confirmed through the display unit even in the process of being cooked by the cooking device. 
     A cooking device according to the present disclosure has an advantage in that an amount of heat energy supplied through the cooking device and a cooking time of the food can be easily and quickly adjusted. 
     Further, a cooking device according to the present disclosure has an advantage in that a user can easily and accurately grasp an amount of heat energy supplied from the cooking device and a remaining cooking time during a cooking process. 
     Further, a cooking device according to the present disclosure has an advantage in that a user can more conveniently and accurately control cooking processes and immediately confirm information required for cooking. 
     Although the present disclosure has been described with reference to the drawings, it is obvious that the present disclosure is not limited by the embodiments and drawings disclosed in this specification, and various modifications may be made by those skilled in the art within the scope of the technical idea of the present disclosure. Further, although the operating effects according to the configuration of the present disclosure are not explicitly described while describing an embodiment of the present disclosure, it should be appreciated that predictable effects are also to be recognized by the configuration.