Abstract:
A cooking appliance is disclosed. The cooking appliance includes an electric heater for heating an object to be cooked, a mechanical manipulation unit connected to the electric heater for allowing a user to input primary ON/OFF of the electric heater and power of the electric heater, a normal open type DC relay connected to the manipulation unit, and a controller for controlling the DC relay to control secondary ON/OFF of the electric heater based on sensing of a primary ON state of the electric heater by the manipulation unit (a state in which the manipulation unit is operated).

Description:
[0001]    This application claims the benefit of Korean Patent Application No. 10-2015-0033977, filed on Mar. 11, 2015, which is hereby incorporated by reference as if fully set forth herein. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a cooking appliance, and more particularly to a cooking appliance that is capable of safely controlling a heater. 
         [0004]    2. Discussion of the Related Art 
         [0005]    Cooking appliances are products that cook food using electricity or other kinds of energy at home. Among cooking appliances, there are a gas stove, a gas oven, and a gas oven/stove, which use gas. In the gas stove, the gas oven, and the gas oven/stove, food is cooked using the combustion of gas. In addition, there are an electric cooktop, an electric stove, an electric oven, and an electric oven/stove, which use electricity. In the electric cooktop, the electric stove, the electric oven, and the electric oven/stove, food is cooked using an electric heater. Of course, a single cooking appliance may use both electricity and gas. 
         [0006]      FIG. 1  is a side view showing a general oven/stove, which is an example of such a cooking appliance. Of course, the cooking appliance shown in  FIG. 1  may be a cooking appliance according to an embodiment of the present invention. That is,  FIG. 1  is merely an illustration for describing the construction of a general cooking appliance. 
         [0007]    As shown in  FIG. 1 , a cooking appliance  10  or an oven/stove includes a cabinet  20  defining the external appearance of the cooking appliance. In the cabinet  20  may be defined a chamber  25  for receiving food to be cooked. Of course, the chamber  25  may be omitted from the cooking appliance  10 . 
         [0008]    A cooktop  26 , on which cooking containers are placed, may be provided at the upper side of the cabinet  20 . That is, cooking containers, such as pots, may be located on the cooktop  26  such that cooking is performed using heat generated from gas, supplied underneath the cooktop, or using heat generated by an electric heater. 
         [0009]    The chamber  25  or the cooktop  26  may be a cooking unit, in which cooking is performed using heat. Based on the kind of cooking appliance, various cooking units may be provided. For example, the cooking unit may be configured such that cooking is performed through the direct use of heat generated by the electric heater or through the radiation or conduction of the heat generated by the electric heater. In a case in which electricity is used, the cooktop  26  may be an example of a cooking unit using conduction of heat, and the chamber  25  maybe an example of a cooking unit using radiation or convention of air. 
         [0010]    The cabinet  20  may be provided at the front thereof with a door  50  for opening and closing the chamber  25 . A handle  60  may be provided at the door  50 . A user may open and close the door  50  while holding the handle  60 . 
         [0011]    The cooking appliance may include a panel  30 , which may be integrally formed with the cabinet  20  or may be coupled to the cabinet  20 . The panel  30  may be provided with a user interface including a manipulation unit  40  for allowing a user to control the cooking appliance. 
         [0012]    The manipulation unit  40  may be configured to turn the electric heater ON or OFF and to adjust the power of the electric heater. Higher power of the electric heater may mean a larger amount of heat that is generated. The manipulation unit may include a timer. In addition, the manipulation unit may further include a display part for informing the user of cooking information or a current state of the cooking appliance. 
         [0013]    In a case in which the electric heater is used in the cooking appliance, the manipulation unit  40  may be provided at the panel  30  in the shape of a knob. The user may manipulate the manipulation unit  40  in order to drive the electric heater, which is located at a specific position in the cooking appliance. 
         [0014]    For example, the user may manipulate the manipulation unit  40  in order to drive an electric heater located in the chamber or to drive an electric heater connected to a specific one selected from among a plurality of cooktops. 
         [0015]    An electronic manipulation unit or a mechanical manipulation unit may be used as the manipulation unit  40 . 
         [0016]    A controller may recognize a value input by a user through the electronic manipulation unit  40 , and may control ON/OFF and power of the electric heater. To this end, it is necessary to provide a complex circuit and an electronic device. That is, it is necessary to provide a circuit and an electronic device that calculate and supply power of the electric heater using a value input by the user. In the cooking appliance having the electronic manipulation unit, therefore, the controller substantially control ON/OFF and power of the electric heater. However, the manufacturing cost of the cooking appliance having the electronic manipulation uni may be increased, and the cooking appliance may malfunction, by the provision of the circuit and the electronic device. 
         [0017]    The mechanical manipulation unit solves the problems caused by the electronic manipulation unit. 
         [0018]    The mechanical manipulation unit is a kind of rotary switch. The mechanical manipulation unit may have a bimetal provided therein. That is, an ON/OFF duty ratio of the electric heater is mechanically decided based on an angle by which the user rotates the mechanical manipulation unit. In the cooking appliance having the mechanical manipulation unit, therefore, the mechanical manipulation unit controls ON/OFF and power of the electric heater in place of the controller. Consequently, the cooking appliance may have a simple structure, whereby manufacturing cost of the cooking appliance may be decreased, and a possibility that the cooking appliance will malfunction is relatively low. 
         [0019]    Since the cooking appliance is an apparatus that uses heat, safety is critical. In particular, it is necessary to prevent malfunction of the cooking appliance by children. For example, the cooking appliance includes a child lock input unit for preventing the cooking appliance from being operated according to child&#39;s manipulation performed through the manipulation unit. 
         [0020]    When the user selects the child lock input unit, the electric heater may not be driven even though the manipulation unit is manipulated. The child lock input unit is mainly used for cooking appliances having the electronic manipulation unit. 
         [0021]    However, the child lock input unit is not used for cooking appliances having the mechanical manipulation unit since manufacturing cost is considerably increased. Nevertheless, cooking appliances in which the child lock input unit is applied to the mechanical manipulation unit for safety has been provided. 
         [0022]    Hereinafter, a conventional cooking appliance having a mechanical manipulation unit and a child lock input unit will be described with reference to  FIG. 2 . 
         [0023]    An alternating current (AC) voltage of, for example, 240 V may be applied between live terminals L 1  and L 2 . A mechanical manipulation unit  60  and a heater  61  may be connected between the live terminals L 1  and L 2 . In addition, an AC relay  62  may be connected between the mechanical manipulation unit  60  and the live terminal L 2 . The mechanical manipulation unit  60  is provided for primary ON/OFF of the heater  61 , and the AC relay  62  is provided for secondary ON/OFF of the heater  61 . That is, the heater is driven in a state in which both the mechanical manipulation unit  60  and AC relay  62  are ON. 
         [0024]    First, when a user manipulates the mechanical manipulation unit  60  to primarily turn the heater  61  ON, the heater is driven since the AC relay  62  is in a normally closed state. That is, since a normal close (NC) type AC relay  62  is used, the heater  61  is driven when the user rotates the mechanical manipulation unit  60 . 
         [0025]    Meanwhile, a child lock input unit  80  may be selected in order to prevent user&#39;s incorrect manipulation. That is, when the child lock input unit  80  is selected, the heater must not be driven even though the heater  61  is primarily turned ON through the mechanical manipulation unit  60 . When the child lock input unit  80  is selected, therefore, the AC relay  62  must be open. That is, the AC relay  62  is driven such that the state of the AC relay  62  is switched from a closed state to an open state. To this end, a normal open (NO) type DC relay  63  may be connected to the AC relay  62 . 
         [0026]    The DC relay  63  is driven through the controller  70 . That is, the DC relay  63  is controlled according to a DC signal applied from the controller  70 . When the controller  70  applies a DC signal to the DC relay  63 , the DC relay  63  is switched to a closed state. When the controller  70  does not apply a DC signal to the DC relay  63 , the DC relay  63  may be maintained in an open state. 
         [0027]    The controller  79  applies a DC signal to the DC relay  63  in a state in which the child lock input unit  80  is selected. That is, the controller  70  applies a DC signal to the DC relay  63  to turn the DC relay  63  ON. Of course, the controller  70  may not apply a DC signal to the DC relay  6  in a state in which the child lock input unit  80  is not selected, which may be referred to as application of an OFF signal, which is distinguished from an ON signal. 
         [0028]    In a state in which the DC relay  63  is closed, the DC relay  63  applies an AC signal to the AC relay  62 . The AC relay  62  is an NC type AC relay  62 . When an AC signal is applied to the AC relay  62 , therefore, the AC relay  62  is switched to an open state. Of course, when no AC signal is applied to the AC relay  62 , the AC relay  62  is maintained in a closed state. 
         [0029]    When the cooking appliance has the conventional mechanical manipulation unit  60  and the child lock input unit  80 , therefore, the NC type AC relay  62  and the NO type DC relay  63  must be provided. The AC relay is a relay that is driven according to an AC signal, and the DC relay is a relay that is driven according to a DC signal. 
         [0030]    Since the conventional cooking appliance uses the NC type AC relay  62  and the NO type DC relay  63 , points to be wired are increased with the result that a manufacturing process is complicated. In addition, the NC type AC relay  62  is expensive. As a result, manufacturing cost of the cooking appliance is increased. For these reasons, the child lock input unit  80  may not be applied to inexpensive cooking appliances. 
         [0031]    In a case in which there is no input through the child lock input unit  80 , the relay connected to the mechanical manipulation unit  60  must be configured to drive the heater  61 . That is, the relay must be an NC type relay. Electric current used for the NC type relay is fixed, and only the AC relay is applied in consideration of electric current used in the cooking appliance. This is because the maximum current for the NC type DC relay is remarkably lower than the maximum current for the NO type DC relay. For example, the maximum current for the NC type DC relay may be 15 A, and the maximum current for the NO type DC relay may be 30 A. However, both the NO type AC relay and the NC type AC relay may have a maximum current of 30 A. When considering the number of heaters in the cooking appliance and margins of the cooking appliance, the NC type AC relay is used in place of the NC type DC relay. 
         [0032]    As a result, the manufacturing cost of the conventional cooking appliance is increased by the provision of the AC relay, and the manufacturing process of the cooking appliance is complicated due to the increase in number of points to be wired. 
       SUMMARY OF THE INVENTION 
       [0033]    Accordingly, the present invention is directed to a cooking appliance and a control method of the same that substantially obviate one or more problems due to limitations and disadvantages of the related art. 
         [0034]    An object of the present invention is to provide a cooking appliance that can be manufactured with low cost and improved workability and a control method of the same. 
         [0035]    Another object of the present invention is to provide a cooking appliance that is capable of safely driving an electric heater and a control method of the same. 
         [0036]    Another object of the present invention is to provide a cooking appliance that enables a user to easily control an electric heater and a control method of the same. 
         [0037]    Another object of the present invention is to provide a cooking appliance that is capable of preventing user&#39;s incorrect manipulation, particularly child&#39;s incorrect manipulation, by the provision of a child lock input unit and a control method of the same. 
         [0038]    A further object of the present invention is to provide a cooking appliance that is capable of maintaining the driving of an electric heater even though a child lock input unit is selected a state in which the electric heater is driven, thereby improving convenience in use, and a control method of the same. 
         [0039]    Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
         [0040]    To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a cooking appliance includes an electric heater for heating an object to be cooked, a mechanical manipulation unit connected to the electric heater for allowing a user to input primary ON/OFF of the electric heater and power of the electric heater, a normal open type DC relay connected to the manipulation unit, and a controller for controlling the DC relay to control secondary ON/OFF of the electric heater based on sensing of a primary ON state of the electric heater by the manipulation unit (a state in which the manipulation unit is operated). 
         [0041]    The DC relay may be connected in series to the electric heater. 
         [0042]    Specifically, in a case in which AC voltage is applied between a live terminal L 1  (positive) and a live terminal L 2  (negative), wiring may be achieved in order of the live terminal L 1 , the mechanical manipulation unit (positive), the electric heater, the mechanical manipulation unit (negative), the DC relay, and the live terminal L 2 . That is, electric current may flow in order as described above. In a case in which electric current flows in order as described above, therefore, the electric heater is driven. In a case in which the flow of electric current is interrupted at any one of the above-mentioned elements, the electric heater is not driven. Elements at which the flow of electric current is interrupted may be the mechanical manipulation unit and the DC relay. For this reason, the mechanical manipulation unit may have a double switch structure. 
         [0043]    The mechanical manipulation unit may be a mechanical switch configured to be rotated in order to perform the primary ON/OFF of the electric heater. In addition, the mechanical manipulation unit may control the power of the electric heater in a state in which the electric heater is ON. 
         [0044]    An ON/OFF duty ratio of the electric heater may be increased with the increase of a rotational angle of the mechanical manipulation unit. That is, the duty ratio of the electric heater may be increased with increase of a rotational angle of the mechanical manipulation unit rotated by the user. 
         [0045]    Consequently, the mechanical manipulation unit may directly control the power of the electric heater. 
         [0046]    Meanwhile, since the NO type DC relay is applied, the electric heater is not driven when the user primarily operate the mechanical manipulation unit. For this reason, it is necessary to provide an element for switching the DC relay to a closed state or it is necessary to control the DC relay to be switched to a closed state. This means that the electric heater may be more safely used. 
         [0047]    The cooking appliance may further include a child lock input unit for preventing user&#39;s incorrect input or incorrect manipulation. The child lock input unit may be configured to restrict a specific user, such as a child who is not accustomed to using the cooking appliance, from using the cooking appliance. The child lock input unit may be configured to be selected by the user. In a case in which the user selects the child lock input unit, child lock may be set. This lock may be lock of the entire cooking appliance, particularly lock of the electric heater. That is, the electric heater may not be driven even through the mechanical manipulation unit is manipulated. 
         [0048]    The controller may control the secondary ON/OFF of the electric heater based on whether child lock has been set through the child lock input unit. That is, in a case in which the child lock has been set, the controller may turn the electric heater OFF. Consequently, the electric heater is not driven even though the electric heater has been primarily turned ON by the manipulation unit. On the other hand, in a case in which the child lock has been released, the controller may turn the electric heater ON. Consequently, the electric heater is driven according to primary heater ON by the mechanical manipulation unit and secondary heater ON through the DC relay. In other words, the electric heater may be operated only when both a state in which the manipulation unit is operated and a state in which the DC relay is closed are satisfied. 
         [0049]    When the child lock has been set through the child lock input unit, the controller may control the DC relay to be maintained in a normal open state even in a state in which the manipulation is operated. 
         [0050]    When the child lock has not been set through the child lock input unit, the controller may control the DC relay to be switched to a closed state. 
         [0051]    The cooking appliance may further include a photo coupler for sensing a state in which the manipulation unit is operated. The controller may control the child lock input unit to be disabled in a state in which the manipulation unit is operated. That is, the controller may determine whether the mechanical manipulation unit is operated using the photo coupler. Upon determining that the mechanical manipulation unit is operated, therefore, the controller may disable the child lock input unit. Disabling may be not reflecting of an input signal even though input is performed through the child lock input unit or interrupting the reception of an input signal. 
         [0052]    By disabling the child lock input unit, it is possible to prevent driving of the electric heater from being stopped by the child lock input unit in a state in which the mechanical manipulation unit is operated, e.g. in a state in which the electric heater is driven. In a case in which incorrect input is performed through the child lock input unit during driving of the electric heater, therefore, it is possible to prevent driving of the electric heater to be stopped. As a result, it is possible to prevent user&#39;s confusion. 
         [0053]    The cooking appliance may further include a light emitting unit connected to the manipulation unit, and the light emitting unit may be operated when the manipulation unit is operated. Consequently, it is possible for the user to easily recognize through the light emitting unit that the mechanical manipulation unit is operated. The light emitting unit is an element that generates light when electricity is applied thereto. For example, the light emitting unit may be a lamp or a light emitting diode (LED). 
         [0054]    In another aspect of the present invention, a cooking appliance includes an electric heater for heating an object to be cooked, a mechanical manipulation unit connected to the electric heater and configured to be manipulated by a user in order to drive the electric heater, a normal open type DC relay connected to the manipulation unit, a sensor for sensing a state in which the manipulation unit is operated, a child lock input unit for preventing user&#39;s incorrect input, and a controller for controlling the DC relay to be closed in order to drive the electric heater only when both a state in which the mechanical manipulation unit is operated and a state in which child lock has been released through the child lock input unit are satisfied. 
         [0055]    The mechanical manipulation unit may control power of the electric heater, and the controller may control only ON/OFF of the electric heater. 
         [0056]    The cooking appliance may further include a light emitting unit connected to the mechanical manipulation unit for emitting light in a state in which the mechanical manipulation unit is operated. 
         [0057]    The sensor may be a photo coupler provided between the light emitting unit and the controller. 
         [0058]    In a further aspect of the present invention, a control method of a cooking appliance, including an electric heater for heating an object to be cooked, a mechanical manipulation unit configured to be manipulated by a user in order to drive the electric heater, and a child lock input unit, includes determining whether the mechanical manipulation unit is operated (a first step), upon determining at the first step that the mechanical manipulation unit is operated, determining whether child lock has been set through the child lock input unit (a second step), and upon determining at the second step that the child lock has been set through the child lock input unit, maintaining an open state of a normal open type DC relay to prevent driving of the electric heater (a third step). 
         [0059]    Specifically, a controller may determine whether the mechanical manipulation unit is operated using a sensor or a photo coupler. In addition, the controller may determine whether child lock has been set through the child lock input unit. Upon determining that the child lock has been set through the child lock input unit, the controller may control the open state of the normal open type DC relay to be maintained. Consequently, the controller may prevent driving of the electric heater even in a state in which the mechanical manipulation unit is operated. 
         [0060]    The control method may further include, upon determining at the second step that the child lock has been released through the child lock input unit, closing the normal open type DC relay to drive the electric heater (a fourth step). The controller may determine that the mechanical manipulation unit is operated and that the child lock has been released or not set through the child lock input unit, and may control the normal open type DC relay to be closed. As a result, the electric heater may be finally driven. 
         [0061]    Setting of the child lock through the child lock input unit may be prevented during the fourth step. The fourth step may be maintained even though setting of the child lock through the child lock input unit is input during the fourth step. That is, the controller may disable the child lock input unit when the electric heater is finally driven. Consequently, it is possible to prevent driving of the electric heater to be stopped by input through the child lock input unit. 
         [0062]    It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0063]    The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings: 
           [0064]      FIG. 1  is a side view showing an example of a general cooking appliance; 
           [0065]      FIG. 2  is a schematic block diagram showing a conventional cooking appliance having a child lock input unit; 
           [0066]      FIG. 3  is a schematic block diagram showing a cooking appliance according to an embodiment of the present invention; and 
           [0067]      FIGS. 4 to 6  are wiring diagrams of the cooking appliance shown in  FIG. 3 , wherein 
           [0068]      FIG. 4  is a wiring diagram showing an OFF state of a mechanical manipulation unit; 
           [0069]      FIG. 5  is a wiring diagram showing an ON state of the mechanical manipulation unit; and 
           [0070]      FIG. 6  is a wiring diagram in a case in which child lock is not set in a state shown in  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0071]    Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
         [0072]    First, control components of a cooking appliance according to an embodiment of the present invention will be described in detail with reference to  FIG. 3 . 
         [0073]    The cooking appliance according to this embodiment may include a mechanical manipulation unit  100  and an electric heater  110 . The electric heater  110  is configured to emit heat when electric current flows in the electric heater  110 . Consequently, the electric heater  110  operates (emits heat) when electric current is supplied to the electric heater  110 , and the electric heater  110  does not operate when the supply of electric current to the electric heater  110  is interrupted. 
         [0074]    The mechanical manipulation unit  100  may be formed in the shape of a rotary switch or a rotary knob. The mechanical manipulation unit  100  may have a switch structure therein. When mechanical manipulation unit  100  is operated, therefore, electric current may flow in the switch structure. In an initial state or an OFF state, the switch structure is open with the result that the supply of electric current is interrupted. Consequently, the mechanical manipulation unit  100  may be a mean for primarily supplying electric current to the electric heater  110  or interrupting the supply of electric current to the electric heater  110 . 
         [0075]    Meanwhile, the mechanical manipulation unit  100  may be a regulator for controlling the temperature of the electric heater in addition to turning the electric heater  110  ON or OFF. A bimetal is provided in the mechanical manipulation unit  100  such that the supply of electric current is automatically interrupted to control the temperature of the electric heater  110  when a predetermined amount of electric current flows in the bimetal. As a rotational angle of the mechanical manipulation unit  100  is increased, an electric current interruption cycle may be increased to adjust the temperature of the electric heater  110 . 
         [0076]    In other words, the mechanical manipulation unit  100  may be a means for controlling the amount of heat generated by the electric heater  110 , i.e. the power of the electric heater  110 , in addition to turning the electric heater  110  ON or OFF. The mechanical regulator is well known in the art to which the present invention pertains, and therefore a detailed description thereof will be omitted. 
         [0077]    In this embodiment, the cooking appliance may include a child lock input unit  140  in order to provide a child lock function. In the conventional cooking appliance, as described with reference to  FIG. 2 , the NC type relay must be used in order to provide the child lock function. This is because the cooking appliance is basically in a state in which child lock is not set, and the electric heater must be driven when the mechanical manipulation unit  100  is operated in the basic state. That is, in the basic state, the NC type relay must be used in order to drive the electric heater. 
         [0078]    Meanwhile, an NC type DC relay cannot be used for high current, as previously described. For this reason, an NC type AC relay is used in the conventional art. 
         [0079]    In this embodiment, the cooking appliance uses an NO type DC relay  120  instead of using an NC type AC relay. That is, an NO mode is primarily used instead of an NC mode, and a DC mode is secondarily used instead of an AC mode, to provide a cooking appliance that is capable of more safely performing child lock with low cost and a control method of the same. 
         [0080]    The NO type DC relay  120  is connected in series to the electric heater  110 . Consequently, the mechanical manipulation unit  100 , the electric heater  110 , and the NO type DC relay  120  are sequentially connected between live terminals L 1  (positive) and L 2  (negative), to which commercial AC power is supplied. In order to operate the electric heater  110 , therefore, the mechanical manipulation unit  100  may be primarily turned ON, and the NO type DC relay  120  may be secondarily closed. The DC relay is a relay for selectively interrupting or allowing the supply of AC current. DC means that the relay is operated according to a DC signal. 
         [0081]    In this embodiment, therefore, the NO type DC relay  120 , which is connected in series to the electric heater  110 , is used in order to secondarily operate the electric heater  110 . As a result, child lock may be performed even for high current. 
         [0082]    A controller  130  may be provided to control the NO type DC relay  120 . The controller  130  may be a main printed circuit board (PCB). The main PCB selectively applies a control signal to the DC relay  120  to control the DC relay  120 . The main PCB applies a DC signal as a control signal. Since the main PCB applies a DC signal very satisfactorily due to the characteristics of the main PCB, no additional conversion device is needed. For example, an additional DC relay, which is a middle medium for controlling the AC relay, as shown in  FIG. 2 , is not needed. 
         [0083]    According to this embodiment, therefore, the number of components constituting the cooking appliance is reduced, whereby wiring is simplified. In addition, manufacturing cost of the cooking appliance is reduced. Of course, simpler control may result in higher safety. 
         [0084]    The controller  300  may determine whether child lock has been set through the child lock input unit  140 . The child lock input unit  140  may be provided at the control panel  30  shown in  FIG. 1  in a button shape. A plurality of buttons may be input simultaneously to set child lock. 
         [0085]    That is, child lock may be set and released through the child lock input unit  140 . Setting and release of child lock may be recognized by the controller  130 . 
         [0086]    First, upon determining that child lock has been set through the child lock input unit  140 , the controller  130  may apply an OFF signal to the DC relay  120 . The OFF signal is a signal for disabling the operation of the DC relay. Of course, no signal may be applied not to operate the DC relay. The OFF signal is distinguished from an ON signal. Since the DC relay  120  is not operated, therefore, the DC relay remains open. 
         [0087]    Consequently, the electric heater is not driven due to the open state of the DC relay even though the electric heater is primarily turned ON by the mechanical manipulation unit  100 . That is, the electric heater is not operated even though the mechanical manipulation unit  100  is manipulated in a state in which child lock is input. 
         [0088]    On the other hand, upon determining that child lock has not been set or has been released through the lock input unit  140 , the controller  130  may apply an ON signal to the DC relay  120 . The ON signal is a signal for enabling the operation of the DC relay. Consequently, the DC relay is operated, and is switched to a closed state. Consequently, the electric heater  110  is finally driven according to primary heater ON by the mechanical manipulation unit  100  and secondary heater ON through the DC relay. 
         [0089]    The controller may determine whether the mechanical manipulation unit  100  is being operated or not through a sensor or a photo coupler. That is, the mechanical manipulation unit  100  being operated means that electric current flows in the mechanical manipulation unit  100 , and the mechanical manipulation unit  100  not being operated means that the flow of electric current in the mechanical manipulation unit  100  is interrupted. When the electric current flows in the mechanical manipulation unit  100  or when the flow of electric current in the mechanical manipulation unit  100  is interrupted, therefore, the controller  130  may sense potential difference between opposite ends of the sensor or the photo coupler to easily determine whether the mechanical manipulation unit  100  is being operated or not, which may be easily embodied using a lamp  150 , which will hereinafter be described. 
         [0090]    The relay, connected in series to the electric heater, is converted from an AC relay to a DC relay and from an NC relay to an NO relay to more safely and conveniently perform child lock with low cost. 
         [0091]    Hereinafter, wiring and controlling of the cooking appliance according to this embodiment for respective states will be described in detail with reference to  FIGS. 4 to 6 . 
         [0092]    A dashed dotted line indicates wiring between a live terminal L 1  (positive) and control elements, a broken line indicates wiring between a live terminal L 2  (negative) and control elements, a solid line indicates wiring between control elements. A dotted line indicates a control line. Consequently, the broken line between the control elements means a state in which electric current is flowing. The control elements include a mechanical manipulation unit  100 , a lamp  150 , a DC relay  120 , a main PCB  130 , and an electric heater  110 . 
         [0093]      FIG. 4  is a view showing the flow of electric current in an initial state, i.e. a state in which the mechanical manipulation unit  100  is OFF. 
         [0094]    The mechanical manipulation unit  100  is a kind of switch. In an OFF state, therefore, the flow of electric current between the mechanical manipulation unit  100  and the electric heater  110  is interrupted. Meanwhile, the lamp  150 , connected in series to the mechanical manipulation unit  100  between the live terminal L 1  and the live terminal L 2 , is also in an OFF state. That is, in a state in which the mechanical manipulation unit is OFF, the lamp  150  is also OFF. Consequently, the lamp  150  may visually inform a user of an operation state of the mechanical manipulation unit  100 , i.e. an ON/OFF state of the mechanical manipulation unit  100 . In this state, as shown in  FIG. 4 , the lamp  150  does not emit light, and the electric heater  110  is not driven. 
         [0095]      FIG. 5  is a view showing the flow of electric current in a state in which the mechanical manipulation unit  100  is ON. 
         [0096]    In a state in which the mechanical manipulation unit  100  is ON, electric current may flow among the live terminal L 1 , the mechanical manipulation unit  100 , and the electric heater  110 . In addition, electric current may flow among the live terminal L 1 , the lamp  150 , and the live terminal L 2 . Consequently, the lamp  150  is switched to an ON state. As a result, a user may recognize from light emitted from the lamp  150  that the mechanical manipulation unit  100  is in an ON state irrespective of driving of the electric heater. 
         [0097]    That is, when the mechanical manipulation unit  100  is switched from an OFF state to an ON state, the lamp  150  emits light, whereby the user may easily recognize that the mechanical manipulation unit  100  is in the ON state. 
         [0098]    At this time, the flow of electric current among the electric heater  110 , the mechanical manipulation unit  100 , and the live terminal L 2  is interrupted even though the mechanical manipulation unit  100  has been switched to the ON state, since the DC relay is an NO type relay. This is because the DC relay  120  is in an open state. 
         [0099]    Meanwhile, when the lamp  150  is switched to an ON state, electric current also flows between the lamp  150  and the controller  130 . That is, electric current flows among the live terminal L 1 , the mechanical manipulation unit  100 , the lamp  150 , the controller  130 , and the live terminal L 2 .  FIG. 5  shows a state in which the lamp  150  has emitted light, and the electric heater  110  has not yet been driven. That is, electric power has primarily been supplied to the electric heater, but electric power has not finally (secondarily) supplied to the electric heater. 
         [0100]    In a state shown in  FIG. 5 , the controller  130  may determine based on the flow of electric current as described above whether the mechanical manipulation unit  100  is in an ON state. In other words, the controller  130  may determine based on an ON/OFF state of the lamp  150  whether the mechanical manipulation unit  100  is in an ON/OFF state. 
         [0101]    First, upon determining that the lamp  150  is in an ON state, the controller  130  determines whether child lock has been set through the child lock input unit. That is, the controller  130  determines whether child lock has been set on the premise that the lamp  150  is in an ON state or the mechanical manipulation unit  100  is in an ON state. Upon determining that child lock has not been set or child lock has been released, the controller  130  applies an operation signal to the DC relay. That is, the controller  130  applies a DC signal for closing the DC relay to the DC relay  120 . When the DC relay is closed, the electric heater  110  is driven. 
         [0102]    That is, upon the controller  130  determining that there is no child lock in a state shown in  FIG. 5 , the state shown in  FIG. 5  is switched to a state shown in  FIG. 6 . Consequently, a predetermined time may be required for determination of the controller  130 , application of an operation signal to the DC relay, and driving of the electric heater. For example, 1 second may be required. In other words, when the mechanical manipulation unit  100  is switched to an ON state even in a case in which there is no child lock, the electric heater is driven after the lapse of a predetermined time. Of course, when the mechanical manipulation unit  100  is switched to an ON state, the lamp  150  is also immediately switched to an ON state. 
         [0103]    The predetermined time is required since it is not possible for the user to easily perceive an initial driving state of the electric heater  110 . That is, driving of the electric heater after a short time, e.g. about 1 second, is desirable due to the characteristics of the electric heater  110 . This is because users repeatedly rotate the mechanical manipulation unit  100  in alternating directions in order to drive the mechanical manipulation unit  100 . When visually informed that the lamp has been turned ON, the user intuitively recognizes that the mechanical manipulation unit  100  has been properly manipulated. 
         [0104]    Meanwhile, upon the controller  130  determining that child lock has been set in a state shown in  FIG. 5 , the state shown in  FIG. 5  is maintained. That is, the controller  130  controls the DC relay  120  to remain open. To this end, a DC signal may be applied to open the DC relay  120 , or no DC signal may be applied to the DC relay  120 . Basically, no DC signal is applied to the DC relay  120  such that the DC relay  120  remains open. 
         [0105]    When the child lock has been set on the premise that the mechanical manipulation unit  100  is in an ON state, therefore, the controller  130  controls the supply of electric power to the electric heater  110  to be interrupted. That is, the controller  130  interrupts the supply of electric power to the electric heater  110  through the NO type DC relay  120 . That is, even when the mechanical manipulation unit  100  is switched to an ON state, the state shown in  FIG. 5  is maintained in a state in which child lock has been set. 
         [0106]    In a state in which child lock has been set, therefore, the electric heater  110  is not driven even though a specific user manipulates the mechanical manipulation unit  100 . Consequently, it is possible to prevent a specific user, such as a child, from operating the cooking appliance. 
         [0107]    The controller  130  may control the DC relay  120  as follows. 
         [0108]    First, the controller  130  determines whether the state of the mechanical manipulation unit  100  has been switched from an OFF state to an ON state. At this time, the controller  130  may determine based on light emitted from the lamp  150  or a signal from the sensor or the photo coupler connected to the lamp whether the state of the mechanical manipulation unit  100  has been switched. 
         [0109]    Subsequently, the controller  130  determines whether child lock has been set. That is, upon determining that there is no child lock after the state of the mechanical manipulation unit  100  has been switched, the controller  130  switches the DC relay  120  to an On state. On the other hand, upon determining that there is child lock, the controller  130  maintains the DC relay  120  in an OFF state. 
         [0110]      FIG. 6  shows a state in which the electric heater  110  is driven as a result of the mechanical manipulation unit  100  being operated in a state in which child lock has not been set. At this time, the user may manipulate the child lock input unit  140  (see  FIG. 3 ). That is, the user may input or release child lock through the child lock input unit  140 . 
         [0111]    Since the controller  130  has already known a state in which the electric heater  110  is driven, the controller  130  may disable the child lock input unit  140  in a state in which the heater  110  is driven. That is, the controller  130  may control child lock not to be set in a state in which the heater  110  is driven. Since the heater  110  is driven on the premise that child lock has been set, release of child lock does not occur in a state in which the heater  110  is driven. 
         [0112]    Conventionally, when child lock is set in a state in which the electric heater  110  is driven, the controller may turn the NC type AC relay OFF. As a result, driving of the electric heater is stopped even though the mechanical manipulation unit is operated. That is, driving of the electric heater is stopped even though a user has not turned the mechanical manipulation unit OFF. As a result, the user may incorrectly determine that the cooking appliance has trouble. 
         [0113]    In this embodiment, setting of child lock may be restricted when the electric heater  110  is driven. That is, the controller  130  may disregard a user&#39;s input of child lock. Of course, it may not be possible to input child lock. Consequently, it is possible to prevent the operation of the electric heater  110  from being stopped due to user&#39;s incorrect input of child lock through the child lock input unit in a state in which the electric heater  110  is driven. 
         [0114]    According to this embodiment as described above, it is possible for the controller, i.e. the main PCB, to directly apply a DC signal to the DC relay  120  without additional conversion of the signal. The DC relay  120  may be connected in series to the electric heater  110  such that electric power is directly supplied to the electric heater  110  or the supply of electric power to the electric heater  110  is interrupted. Since an AC relay may be omitted, very simple wiring may be achieved. In addition, since an inexpensive DC relay may be used, total manufacturing cost may be considerably reduced. 
         [0115]    Furthermore, since a NO type relay is used, it is possible to secure a short delay time, e.g. about 1 second, between the operations of the mechanical manipulation unit  100  and the electric heater  110 . As a result, it is possible to prevent the electric heater  110  from being operated immediately in response to unnecessary manipulation of the mechanical manipulation unit  100 . Consequently, it is possible to reduce energy consumption. 
         [0116]    As is apparent from the above description, according to an embodiment of the present invention, it is possible to provide a cooking appliance that can be manufactured with low cost and improved workability and a control method of the same. 
         [0117]    According to an embodiment of the present invention, it is possible to provide a cooking appliance that is capable of safely driving an electric heater and a control method of the same. 
         [0118]    According to an embodiment of the present invention, it is possible to provide a cooking appliance that enables a user to easily control an electric heater and a control method of the same. 
         [0119]    According to an embodiment of the present invention, it is possible to provide a cooking appliance that is capable of preventing user&#39;s incorrect manipulation, particularly child&#39;s incorrect manipulation, by the provision of a child lock input unit and a control method of the same. 
         [0120]    According to an embodiment of the present invention, it is possible to provide a cooking appliance that is capable of maintaining the driving of an electric heater even though a child lock input unit is selected a state in which the electric heater is driven, thereby improving convenience in use, and a control method of the same. 
         [0121]    It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the inventions. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.