Patent Publication Number: US-11649968-B2

Title: Cooking appliance

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/586,738 filed on Sep. 27, 2019, which is based on and claims priority under 35 U.S.C. § 119 to Korean Patent Application No. 10-2018-0114916 filed on Sep. 27, 2018 in the Korean Intellectual Property Office, the disclosures of which are herein incorporated by reference in their entirety. 
    
    
     BACKGROUND 
     1. Field 
     The disclosure relates to a cooking appliance including a knob assembly used for operating the cooking appliance. 
     2. Description of the Related Art 
     In general, a cooking appliance is a home appliance including a cooking room, a heating apparatus for applying heat to the cooking room, and a circulating apparatus for circulating heat generated by the heating apparatus inside the cooking room to cook food. 
     The cooking appliance is an appliance for cooking food by sealing and heating the food. Cooking appliances are generally classified into an electric type, a gas type, and an electronic type according to their heat sources. 
     For example, an electric oven uses an electric heater as a heating source, and a gas oven and a microwave use heat generated by gas and frictional heat of water molecules caused by high frequency as heating sources, respectively. 
     The cooking appliance includes a control panel on any one of the front and top surfaces of the main body. In the control panel, a plurality of buttons, a key pad, a knob assembly, etc. configured to set a user&#39;s desired cooking mode or various conditions required for cooking are provided. 
     Particularly, when a knob assembly is provided on the control panel, a user turns the knob assembly to control an operation of the main body. 
     Generally, the knob assembly operates by a push to turn method due to the property of a valve that drives a heating source. 
     The user controls the operation of the main body through the knob assembly by a two-step mechanism of pushing the knob assembly to push the valve shaft of the valve and then turning the knob assembly. 
     However, when the user unintentionally pushes the knob assembly to turn it, a fire/burn may be caused. Accordingly, the cooking appliance needs to include a knob stopper for preventing an unintended operation of the knob assembly or a knob cap for opening and closing the knob assembly. 
     However, for a user to use the knob assembly, he/she needs to remove the knob stopper or open the knob cap. Therefore, the two-step mechanism changes to a three-step mechanism. 
     Furthermore, the knob stopper and the knob cap may deteriorate the entire design of the cooking appliance, and also, the knob stopper and the knob cap may be deformed by heat generated when the cooking appliance is used. 
     SUMMARY 
     Therefore, it is an aspect of the disclosure to provide a cooking appliance capable of preventing a user&#39;s unintended rotation of a knob assembly. 
     It is another aspect of the disclosure to provide a cooking appliance that increases a push distance of a knob to prevent a user&#39;s unintended rotation of a knob assembly. 
     It is another aspect of the disclosure to provide a cooking appliance including a knob assembly configured to rotate when an inner knob is pushed. 
     Additional aspects of the disclosure will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the disclosure. 
     In accordance with an aspect of the disclosure, a cooking appliance includes: a main body including a control panel; a valve positioned inside the main body, and including a valve shaft being pushable and rotatable; and a knob assembly including an inner knob coupled with the valve shaft, and an outer knob being movable in a first direction in which the outer knob approaches the inner knob, wherein, when the outer knob moves by a first push distance in the first direction, the valve shaft and the inner knob are prevented from rotating. 
     When the outer knob moves in the first direction by a second push distance that is longer than the first push distance, the valve shaft and the inner knob may be rotatable. 
     The first direction may be parallel to a direction in which the valve shaft extends. 
     The knob assembly may further include an elastic member positioned between the outer knob and the inner knob, 
     When the outer knob moves in the first direction, the elastic member may provide an elastic force to move the outer knob in a second direction that is opposite to the first direction. 
     The elastic force of the elastic member may be smaller than a force required when the valve shaft is pushed in the first direction. 
     The outer knob may include a boss portion protruding toward the inner knob, wherein a screw thread may be formed in an inner surface of the boss portion. 
     The inner knob may include a hole being opposite to the boss portion, and a support surface positioned around the hole. 
     The knob assembly may further include a coupling member passed through the hole and screwed with the screw thread of the boss portion. 
     One end of the elastic member may be in contact with the boss portion, and the other end of the elastic member may be in contact with the support surface. 
     The coupling member may include a head portion having a diameter that is larger than a diameter of the hole. 
     The head portion may prevent the outer knob from being separated from the inner knob in the second direction that is opposite to the first direction. 
     In accordance with another aspect of the disclosure, a cooking appliance includes: a main body comprising a control panel; a valve positioned inside the main body, and including a valve shaft being pushable and rotatable; and a knob assembly including a knob coupled with the valve shaft and configured to push and rotate the valve shaft, and a cover knob covering the knob to prevent the knob from being pushed. 
     When the knob is pushed, the cover knob, the knob, and the valve shaft may be rotatable. 
     When the cover knob is pushed, the cover knob, the knob, and the valve shaft may be prevented from rotating. 
     The cover knob may include a boss protruding toward the knob, wherein a screw thread may be formed in an inner surface of the boss. 
     The knob may include a boss hole through which the boss passes. 
     The knob assembly may further include a coupling member screwed with the boss. 
     The coupling member may include a head portion having a diameter that is larger than a diameter of the boss hole. 
     The knob assembly may further include an elastic member positioned between the boss and the head portion. 
     When the knob is pushed in a first direction to push and rotate the valve shaft, the elastic member may provide an elastic force to move the knob in a second direction that is opposite to the first direction. 
     The cover knob may be pushable by a first distance, and the knob may be pushable by a second distance that is longer than the first distance. 
     When the cover knob is pushed by the first distance, the valve shaft may be prevented from rotating. 
     When the knob is pushed by the second distance, the valve shaft may be rotatable. 
     In accordance with another aspect of the disclosure, a cooking appliance includes: a valve body; a valve shaft being insertable in the valve body, and being rotatable with respect to the valve body when being inserted in the valve body; and a knob assembly coupled with the valve shaft and configured to insert the valve shaft in the valve body and rotate the valve shaft with respect to the valve body. 
     The knob assembly may include: an inner knob coupled with the valve shaft; and an outer knob being movable relative to the inner knob by a predetermined distance, wherein, when the outer knob moves by the predetermined distance in a direction in which the outer knob approaches the inner knob, the outer knob does not push the inner knob. 
     Before undertaking the DETAILED DESCRIPTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like. 
     Definitions for certain words and phrases are provided throughout this patent document. Those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts: 
         FIG.  1    illustrates a perspective view of a cooking appliance according to an embodiment of the disclosure; 
         FIG.  2    shows a cooking appliance according to an embodiment of the disclosure when a door of the cooking appliance opens; 
         FIG.  3    illustrates a side cross-sectional view of a cooking appliance according to an embodiment of the disclosure; 
         FIG.  4    illustrates a perspective view of a knob assembly positioned in a control panel in a cooking appliance according to an embodiment of the disclosure; 
         FIG.  5    illustrates an exploded perspective view of a knob assembly positioned in a control panel in a cooking appliance according to an embodiment of the disclosure; 
         FIG.  6    illustrates a side cross-sectional view of a knob assembly and a control panel, cut along line A-A′ of  FIG.  4   ; 
         FIG.  7    illustrates a side cross-sectional view of a knob assembly and a control panel when an outer knob is pushed by a first push distance; 
         FIG.  8    illustrates a side cross-sectional view of a knob assembly and a control panel when an outer knob is pushed by a second push distance; 
         FIG.  9    illustrates a perspective view of a knob assembly positioned in a control panel in a cooking appliance according to another embodiment of the disclosure; 
         FIG.  10    illustrates an exploded perspective view of a knob assembly positioned in a control panel in a cooking appliance according to another embodiment of the disclosure; 
         FIG.  11    illustrates a side cross-sectional view of a knob assembly and a control panel, cut along line B-B′ of  FIG.  9   ; 
         FIG.  12    illustrates a side cross-sectional view of a knob assembly and a control panel when an inner knob is pushed; and 
         FIGS.  13  and  14    show an operation of a knob assembly in a cooking appliance according to another embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS.  1  through  14   , discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged system or device. 
     Configurations illustrated in the embodiments and the drawings described in the present specification are only the illustrative embodiments of the disclosure, and thus it is to be understood that various modified examples, which may replace the embodiments and the drawings described in the present specification, are possible when filing the present application. 
     The terms used in the present specification are merely used to describe embodiments, and are not intended to limit the disclosure. An expression used in the singular encompasses the expression of the plural, unless it has a clearly different meaning in the context. 
     In the present specification, it is to be understood that the terms such as “comprising”, “including” or “having”, etc., are intended to indicate the existence of the features, numbers, operations, components, parts, or combinations thereof disclosed in the specification, and are not intended to preclude the possibility that one or more other features, numbers, operations, components, parts, or combinations thereof may exist or may be added. 
     It will be understood that, although the terms “first”, “second”, etc., may be used herein to describe various elements, these elements should not be limited by these terms. The above terms are used only to distinguish one component from another. For example, a first component discussed below could be termed a second component, and similarly, a second component may be termed a first component without departing from the teachings of this disclosure. 
     In the following description, the terms “front direction”, “rear direction”, “upper portion” and “lower portion” are defined based on the drawings, and the shapes and positions of the corresponding components are not limited by the terms. 
     Hereinafter, the embodiments of the disclosure will be described in detail with reference to the accompanying drawings. Hereinafter, a cooking appliance according to an embodiment of the disclosure is an oven range including an oven, however, the embodiments of the disclosure may be applied to a cooking appliance including no oven. 
       FIG.  1    illustrates a perspective view of a cooking appliance according to an embodiment of the disclosure.  FIG.  2    shows a cooking appliance according to an embodiment of the disclosure when a door of the cooking appliance opens.  FIG.  3    illustrates a side cross-sectional view of a cooking appliance according to an embodiment of the disclosure. 
     As shown in  FIGS.  1 ,  2 , and  3   , a cooking appliance  1  may include a main body  10  including an inner case  11  in which a cooking room  20  is formed and an outer case  12  coupled with an outer portion of the inner case  11  and forming an outer appearance of the cooking appliance  1 . 
     The inner case  11  and the outer case  12  may be substantially in the shape of a box whose front side opens. 
     The cooking appliance  1  may include a cooktop  30  which is positioned on a top of the cooking appliance  1  and on which a container with food is put and heated. The cooktop  30  may include at least one heating portion  31 . A container with food may be placed on the heating portion  31  to be heated directly. 
     The cooking appliance  1  may include a door  50  positioned on a front side of the main body  10  to open and close the cooking room  20 . 
     The outer case  12  may include a front panel  13  forming the front side of the main body  10 , side panels  14  forming lateral sides of the main body  10 , and a rear panel  15  forming a rear side of the main body  10 . 
     In the front panel  13 , an opening may be formed, and by the opening, a front side of the cooking room  20  formed in the inside of the main body  10  may open. At an upper portion of a front surface of the front panel  13 , a control panel  41  may be provided to cover a front side of a machine room  40 . In the control panel  41 , a display module  60  may be installed. 
     The control panel  41  may be positioned at at least one portion of the main body  10 . According to an embodiment of the disclosure, the control panel  41  may be positioned at a side of the front surface of the main body  10 , although not limited thereto. However, the control panel  41  may be positioned on a top surface of the main body  10  or form one side of the main body  10 . 
     In the rear panel  15 , an inlet  15   a  may be provided to inhale air into the machine room  40 . Air inhaled in the machine room  40  through the inlet  15   a  may flow inside the machine room  40  to cool electrical components, although not limited thereto. 
     However, the inlet  15   a  may be located at any other position as long as the inlet  15   a  guides outside air to be inhaled into the machine room  40 . 
     The cooking room  20  may be defined by a upper plate  21 , a bottom plate  22 , both side plates  23 , and a rear plate  24 . The cooking room  20  may be a cooking space, wherein the front side of the cooking room  20  opens through the opening of the front panel  13  to enable a user to put food in the cooking room  20  or take food out of the cooking room  20 . 
     On inner surfaces of the side plates  23 , a plurality of support bars  25  may be positioned. On the support bars  25 , at least one removable rack  26  may be placed to put food thereon. 
     On the support bars  25 , a rail (not shown) along which the rack  26  slides to move may be provided. The user may move the rack  26  through the rail (not shown) to take food from the rack  26  or put food on the rack  26 . 
     On the support bars  25 , a divider (not shown) for dividing the cooking room  20  into a plurality of cooking rooms  20  may be placed. The plurality of cooking rooms  20  divided by the divider may have not necessarily the same size. That is, the plurality of cooking rooms  20  may have different sizes. 
     Therefore, the user may use spaces of the cooking rooms  20  divided according to his/her intention in various ways. The divider may be formed of an insulating material to insulate the individual cooking rooms  20 . 
     In the cooking room  20 , a heater  27  for heating food may be provided, and the heater  27  may be an electric heater including an electric resistance element, although not limited thereto. However, the heater  27  may be a gas heater for burning gas to generate heat. Accordingly, the cooking appliance  1  may include an electric oven and a gas oven. 
     In the rear plate  24  of the cooking room  20 , a circulating fan  28  for circulating air of the cooking room  20  to uniformly heat food and a circulating motor  29  for driving the circulating fan  28  may be installed. 
     A fan cover  28   a  may be positioned in front of the circulating fan  28  to cover the circulating fan  28 . In the fan cover  28   a , a discharge hole  28   b  may be formed to cause air to flow. 
     The open front side of the cooking room  20  may be opened or closed by the door  50 , and the door  50  may be rotatably coupled with the main body  10  by a hinge  51  installed in a lower portion of the main body  10 . 
     In a front upper portion of the door  50 , a handle  52  may be provided which is gripped by the user for the door  50  to open or close the cooking room  20 . 
     The display module  60  for displaying various operation information of the cooking appliance  1  and enabling the user to input an operation command may be positioned in the control panel  41  provided in the front upper portion of the front panel  13 . 
     The display module  60  may include a liquid crystal display (LCD), and the LCD may display electrical information being a change of liquid crystal transmittance according to an applied voltage as visual information. 
     The LCD may include a liquid crystal module for displaying images and a light source unit for radiating light to the liquid crystal module. The light source unit may be a LED. 
     The display module  60  may include a cover panel  61  positioned on a front surface of the LCD. The cover panel  61  may be a protective panel for protecting the LCD or a touch panel capable of receiving a user&#39;s touch commands. 
     In the control panel  41 , a knob assembly  100  for operating the cooking appliance  1  may be provided. According to an embodiment of the disclosure, four knob assemblies  100  may be provided, although not limited thereto. The knob assembly  100  will be described in detail, later. 
     An insulating material  20   a  for insulating the machine room  40  and the cooking room  20  may be positioned between the machine room  40  and the cooking room  20  to prevent hot air of the cooking room  20  from being transferred to the machine room  40 . 
     The insulating material  20   a  may surround the entire of the cooking room  20 , as well as between the machine room  40  and the cooking room  20 , to prevent hot air of the cooking room  20  from being transferred to outside of the cooking appliance  1 . 
     Because an inside temperature of the machine room  40  may rise by heat from various electrical components, a blow apparatus  70  for circulating air around the machine room  40  to cool the machine room  40  may be provided in the cooking appliance  1 . 
     The blow apparatus  70  may include a blow fan  71  for blowing air, and a discharge flow path  72  for discharging air inhaled by the blow fan  71  toward a front side of the cooking appliance  1 . 
     The blow fan  71  may inhale air in an axial direction and then discharge the air in a radial direction. That is, the blow fan  71  according to the disclosure may be a centrifugal fan. However, the blow fan  71  may be an axial flow fan. 
     Outside air may be inhaled into the machine room  40  through the inlet  15   a  positioned in the rear panel  15 , and air inhaled in the machine room  40  may flow inside the machine room  40  to cool the electrical components and then flow along the discharge flow path  72  to be discharged in a front direction from the cooking appliance  1  through an outlet  80 . 
     The outlet  80  may include a space between the front panel  13  and the control panel  41 , although not limited thereto. However, the outlet  80  may be located at various positions and have various shapes, as long as the outlet  80  allows air inhaled through the inlet  15   a  to be discharged to the outside of the main body  10 . 
     A part of inside air of the cooking room  20  may be inhaled in the discharge flow path  72  through a cooking room flow path  73  and discharged to the front side of the cooking appliance  1 . 
     In the discharge flow path  72 , a bypass hole  74  for allowing a part of air flowing from the discharge flow path  72  to the outlet  80  to flow to the cooking room flow path  73  may be formed. The bypass hole  74  may be opened or closed by an opening and closing device  75 . 
     When the bypass hole  74  is opened and closed by the opening and closing device  75 , an amount of air entering the cooking room flow path  73  among air flowing from the discharge flow path  72  to the outlet  80  may be adjusted. Therefore, an emission amount of air that is discharged from the cooking room  20  to the cooking room flow path  73  may be adjusted. 
     The door  50  rotatably coupled with the front side of the main body  10  to open or close the cooking room  20  may be a plurality of doors. The door  50  may be configured with a plurality of glass plates. 
       FIG.  4    illustrates a perspective view of a knob assembly positioned in a control panel in a cooking appliance according to an embodiment of the disclosure.  FIG.  5    illustrates an exploded perspective view of a knob assembly positioned in a control panel in a cooking appliance according to an embodiment of the disclosure. 
     As shown in  FIGS.  4  and  5   , the cooking appliance  1  according to an embodiment of the disclosure may include a valve  90  installed inside the main body  10 . The valve  90  may include a control module  92 , and a valve shaft  91  that is able to be inserted in the control module  92 . In other words, the valve shaft  91  may be coupled with the control module  92  in such a way to be able to be pushed into the control module  92 . 
     The control module  92  may control a heating source (not shown) of the cooking appliance  1 . The valve shaft  91  may be coupled with the control module  92  in such a way to be able to be pushed into the control module  92  and rotate with respect to the control module  92 . The valve shaft  91  may be coupled with the control module  92  in such a way to be rotatable with respect to the control module  92 . However, when the valve shaft  91  is not pushed into the control module  92 , the valve shaft  91  may be prevented from rotating. When the valve shaft  91  is pushed into the control module  92  and rotates with respect to the control module  92 , the control module  92  may control an operation of the heating source (not shown). 
     The control module  92  may receive signal about a degree of rotation of the valve shaft  91  to control the heating source. For example, the control module  92  may control an on/off operation, a temperature, etc. of the heating portion  31  (see  FIG.  1   ) of the cooktop  30  (see  FIG.  1   ), and control an on/off operation, a temperature, a cooking time, a cooking mode, etc. of the heater  27  (see  FIG.  2   ). 
     The cooking appliance  1  may include the knob assembly  100  positioned in the control panel  41  to adjust an amount of opening and closing of the valve  90 . The knob assembly  100  may push and rotate the valve shaft  91  to open the valve  90 . An interior of the control panel  41  can include a receiving portion  43  to receive the valve shaft  91 . 
     The knob assembly  100  may include an outer knob  110  and an inner knob  120 . The outer knob  110  may be spaced a first push distance d 1  from the inner knob  120 . The outer knob  110  may cover the inner knob  120 . However, the outer knob  110  may include an opening so that a portion of the inner knob  120  is exposed to outside. An exterior of the control panel  41  can include a raised enclosure  42  to surround the outer knob  110 . 
     The outer knob  110  may include an outer knob body  111  being substantially in the shape of a donut, a grip portion  112  spaced a predetermined distance from the outer knob body  111 , and a connecting portion  113  connecting the outer knob body  111  with the grip portion  112 . Also, the outer knob  110  may include a light emitting portion  116 . The light emitting portion  116  may irradiate light according to whether or not the valve  90  opens. The light emitting portion  116  may be positioned over the grip portion  112  and the connecting portion  113 . 
     The knob assembly  100  may include a first elastic member  130  positioned between the outer knob  110  and the inner knob  120  to provide an elastic force, and a first coupling member  140  locating the first elastic member  130  between the outer knob  110  and the inner knob  120 . Also, the knob assembly  100  may include a shaft coupling portion  150  coupled with the inner knob  120  and the valve shaft  91 , and a knob base  160  including a washer  164  that covers a bottom surface of the knob assembly  100 . 
     The inner knob  120  may include an inner knob body  121  being substantially in the shape of a cylinder, and a protrusion  122  protruding toward the outer knob  110  from the inner knob body  121  and having a smaller diameter than the inner knob body  121 . A side surface of the protrusion  122  may be processed to increase a friction force. The processing of the side surface of the protrusion  122  may be to prevent slipping when a user grips the protrusion  122  and rotates the knob assembly  100 , although not limited thereto. However, the side surface of the protrusion  122  may be a smooth surface. 
     In an upper surface of the protrusion  122 , a resting portion  123  on which the first elastic member  130  is rested may be formed. The upper surface of the protrusion  122  may be one surface of the protrusion  122  being opposite to the outer knob  110 . In the resting portion  123 , a coupling hole  124  (see  FIG.  6   ) through which the first coupling member  140  passes may be formed. 
     The shaft coupling portion  150  may include a shaft insertion portion  151  in which the valve shaft  91  is inserted, and a knob coupling portion  154  coupled with the inner knob  120 . The shaft insertion portion  151  may be formed at one end of the shaft coupling portion  150 , and the knob coupling portion  154  may be formed at the other end of the shaft coupling portion  150 . Also, the shaft coupling portion  150  may include a base coupling portion  152  coupled with the knob base  160  and a base coupling hole  153  formed in the base coupling portion  152 . 
     The knob base  160  may include a shaft hole  161  through which the valve shaft  91  passes, a base hole  162  formed at a location corresponding to the base coupling hole  153 , and a base rib  163  formed around the base hole  162 . 
       FIG.  6    illustrates a side cross-sectional view of a knob assembly and a control panel, cut along line A-A′ of  FIG.  4   .  FIG.  7    illustrates a side cross-sectional view of a knob assembly and a control panel when an outer knob is pushed by a first push distance.  FIG.  8    illustrates a side cross-sectional view of a knob assembly and a control panel when an outer knob is pushed by a second push distance. 
     Hereinafter, an operation of the knob assembly  100  according to an embodiment of the disclosure will be described in detail with reference to  FIGS.  6 ,  7 , and  8   . Also, an internal coupling structure of the knob assembly  100  will be described in detail. 
     As shown in  FIGS.  4  and  6   , the outer knob  110  may be spaced the first push distance d 1  from the inner knob  120 . 
     The outer knob  110  may include a boss portion  114  protruding toward the inner knob  120 . In an inner surface of the boss portion  114 , a screw thread  115  may be formed. The inner knob  120  may include the coupling hole  124  in which the first coupling member  140  is inserted. The coupling hole  124  may be opposite to the boss portion  114 . 
     The first coupling member  140  may include a body portion having a screw thread  141  formed on the outer surface and having a smaller diameter than that of the coupling hole  124  such that the body portion passes through the coupling hole  124 , and a head portion  142  having a larger diameter than that of the coupling hole  124 . A portion of the body portion may be screwed with the boss portion  114 . The first elastic member  130  may be positioned between the boss portion  114  and the resting portion  123 . One end of the first elastic member  130  may be in contact with the boss portion  114 , and the other end of the first elastic member  130  may be in contact with the resting portion  123 . The first elastic member  130  may be a compression spring. 
     Because the diameter of the head portion  142  is larger than that of the coupling hole  124  and the body portion of the coupling member  140  is screwed with the boss portion  114 , the outer knob  110  may be not separated from the inner knob  120 . Also, the elastic member  130  may be not separated from the boss portion  114  and the resting portion  123 . 
     The elastic member  130  may provide an elastic force in a direction in which the outer knob  110  moves away from the inner knob  120 . The elastic member  130  may elastically bias the outer knob  110  in a direction in which the outer knob  110  moves away from the inner knob  120 . By the elastic force of the elastic member  130 , the outer knob  110  may be spaced the predetermined distance d 1  from the inner knob  120 . 
     The inner knob  120  may include ribs  125  and  126  coupled with the knob coupling portion  154 . The ribs  125  and  126  may include a first rib  125  and a second rib  126  positioned inside the first rib  125 . The knob coupling portion  154  may be inserted between the first rib  125  and the second rib  126 . 
     Referring to  FIG.  7   , when a user pushes the outer knob  110 , the outer knob  110  may be pushed by the first push distance d 1 . 
     The elastic force of the elastic member  130  may be smaller than a force required when the valve shaft  91  is inserted into the control module  92 . Accordingly, although the elastic member  130  is compressed, the valve shaft  91  may be not inserted into the control module  92 . When the outer knob  110  is pushed by the first push distance d 1 , the valve shaft  91  may be not inserted into the control module  92 , and the valve shaft  91  and the inner knob  120  may be prevented from rotating. 
     According to a concept of the disclosure, although the outer knob  110  is pushed by the first push distance d 1 , the inner knob  120  and the valve shaft  91  may be not inserted in the control module, and the inner knob  120  and the valve shaft  91  may be prevented from rotating. The first push distance d 1  may function as a preliminary push distance. Accordingly, when the user accidentally pushes the outer knob  110  by a predetermined distance, for example, by the first push distance d 1 , the knob assembly  100  may be prevented from rotating. Accordingly, accidents in which a fire or a user&#39;s burn occurs due to the user&#39;s unintended rotation of the knob assembly  100  causing an operation of the heating source may be prevented in advance. In other words, the knob assembly  100  according to an embodiment of the disclosure may increase a push distance of the knob for operating the heating source to thereby prevent a user&#39;s unintended rotation of the knob. 
     Referring to  FIG.  8   , after the outer knob  110  is pushed by the first push distance d 1 , the outer knob  110  may be further pushed by a second push distance d 2 . 
     When the outer knob  110  is pushed by the first push distance d 1  and the second push distance d 2 , the inner knob  120  and the valve shaft  91  may be pushed by the second push distance d 2  together with the outer knob  110 . 
     When the inner knob  120  and the valve shaft  91  are pushed by the second push distance d 2 , the inner knob  120  and the valve shaft  91  may be rotatable to open the valve  90  and operate the heating source. 
     As described above, the knob assembly  100  according to an embodiment of the disclosure may increase the push distance of the knob to prevent a user&#39;s unintended rotation of the knob. More specifically, by increasing the push distance by the first push distance d 1  which is a preliminary push distance, safety accidents such as a fire/burn may be prevented in advance. 
       FIG.  9    illustrates a perspective view of a knob assembly positioned in a control panel in a cooking appliance according to another embodiment of the disclosure.  FIG.  10    illustrates an exploded perspective view of a knob assembly positioned in a control panel in a cooking appliance according to another embodiment of the disclosure. 
     Referring to  FIGS.  9  and  10   , a cooking appliance according to another embodiment of the disclosure may include a knob assembly  200  positioned in the control panel  41 . 
     The knob assembly  200  may include a cover knob  210 , and a knob  220  positioned inside the cover knob  210  and coupled with the valve shaft  91 . Also, the knob assembly  200  may include a second elastic member  230  and a second coupling member  240 . 
     The cover knob  210  may include a cover knob body  211  formed in the shape of a cylinder whose top and bottom sides open, a cover portion  212  spaced from the cover knob body  211 , and a cover connecting portion  213  connecting the cover knob body  211  with the cover portion  212 . The cover portion  212  may have a smaller area than that of the top side of the cover knob  210 , and therefore, the cover knob  210  may include an open area. 
     The knob  220  may be coupled with an inner portion of the cover knob  210 . The knob  220  may include grip surfaces  221  and  222  which a user grips. The grip surfaces  221  and  222  may include a first grip surface  221  and a second grip surface  222  that are perpendicular to each other. A top surface  224  of the knob  220  may protrude from the second grip surface  222  toward the cover knob  210 . The top surface  224  of the knob  220  may be opposite to the cover portion  212  of the cover knob  210 . In the top surface  224  of the knob  220 , a boss hole  223  may be formed. 
       FIG.  11    illustrates a side cross-sectional view of a knob assembly and a control panel, cut along line B-B′ of  FIG.  9   .  FIG.  12    illustrates a side cross-sectional view of a knob assembly and a control panel when an inner knob is pushed. 
     Hereinafter, a structure of the knob assembly  200  according to another embodiment of the disclosure will be described in detail with reference to  FIGS.  11  and  12   . Also, an operation of the knob assembly  200  according to another embodiment of the disclosure will be described in detail. 
     The cover knob  210  may include a boss  214  protruding toward the knob  220 . In an inner surface of the boss  214 , a screw thread  215  may be formed. 
     The knob  220  may include a boss hole  223  into which the boss  214  is inserted. The boss  214  may move relative to the boss hole  223 . 
     A second coupling member  240  may be screwed with the boss  214 . The second coupling member  240  may include a body portion on which a screw thread  241  is formed, and a head portion  242  having a larger diameter than that of the boss hole  223 . 
     The second elastic member  230  may be positioned between an outer circumference of the boss hole  223  and the head portion  242 . The second elastic member  230  may provide an elastic force for causing the knob  220  to be in contact with the cover knob  210 . The second elastic member  230  may provide an elastic force for causing the knob  220  to approach the cover knob  210 . The second elastic member  230  may be a compression spring. 
     The knob  220  may include a valve boss  226  coupled with the valve shaft  91 . The valve shaft  91  may be inserted in a boss groove  227  formed in the valve boss  226  at an opposite end of the valve boss  226  from a head portion  225 . 
     Referring to  FIGS.  11  and  12   , the knob  220  may be in contact with the cover knob  210 . The second elastic member  230  may provide an elastic force for causing the knob  220  to be in contact with the cover knob  210 . 
     When a user pushes the cover knob  210 , the cover knob  210  may be pushed by a first distance g 1 . When the cover knob  210  is pushed by the first distance g 1 , the knob  220  and the valve shaft  91  may be prevented from rotating. In other words, although the cover knob  210  is pushed by the first distance g 1 , the knob  210  and the valve shaft  91  may be not pushed until the valve  90  opens. Accordingly, although the user pushes the cover knob  210 , the knob assembly  200  may be prevented from rotating. 
     The knob assembly  200  according to another embodiment of the disclosure may include the cover knob  210 , and may not operate the heating source although the user pushes the cover knob  210 . Accordingly, when the user pushes the cover knob  210  by mistake, the knob assembly  200  may be prevented from rotating, so that a fire and burn that may be caused by an unintended rotation of the knob assembly  200  may be prevented. 
     As shown in  FIG.  12   , when the user pushes the knob  220  by a second distance g 2 , the knob  220  and the valve shaft  91  may be rotatable. When the user pushes the knob  220  by the second distance g 2 , the valve shaft  91  coupled with the knob  220  may be inserted in the control module  92 , so that the valve  90  may open. Accordingly, the knob assembly  200  may become a rotatable state. 
     According to another embodiment of the disclosure, when the cover knob  210  is pushed, the knob assembly  200  may be prevented from rotating, whereas, when the knob  220  is pushed, the knob assembly  200  may be allowed to rotate. Because pushing the knob  220  is safely determined as a user&#39;s intention to operate the heating source, the knob assembly  200  may be rotatable when the knob  220  is pushed. 
     The second elastic member  230  may provide an elastic force for causing the knob  220  to be in contact with the cover knob  210  when a user does not push the knob  220 . The second elastic member  230  may provide an elastic force to move the knob  220  to its original position. 
       FIGS.  13  and  14    show an operation of a knob assembly in a cooking appliance according to another embodiment of the disclosure. 
     Referring to  FIGS.  13  and  14   , the knob assembly  200  according to another embodiment of the disclosure may be rotatable when the knob  220  is pushed. Although not shown in the drawings, when the cover knob  210  is pushed, the knob assembly  200  may be prevented from rotating. Accordingly, safety accidents in which a fire or a user&#39;s burn occurs due to the user&#39;s unintended rotation of the knob assembly  100  causing an operation of the heating source may be prevented in advance. 
     According to a concept of the disclosure, the cooking appliance capable of preventing a user&#39;s unintended rotation of the knob assembly may be provided. 
     According to another concept of the disclosure, the cooking appliance that increases a push distance of the knob to prevent a user&#39;s unintended rotation of the knob assembly may be provided. 
     According to another concept of the disclosure, the cooking appliance including the knob assembly being rotatable when the inner knob is pushed may be provided. 
     Although the present disclosure has been described with various embodiments, various changes and modifications may be suggested to one skilled in the art. It is intended that the present disclosure encompass such changes and modifications as fall within the scope of the appended claims.