Patent Publication Number: US-6903321-B2

Title: High-frequency heating apparatus with illumination device

Description:
This application claims the benefit of International Application Number PCT/JP02/11800, which was published in English on May 22, 2003. 

   TECHNICAL FIELD 
   The present invention relates to the structure of an air guide for guiding air to a heating chamber in a radio-frequency heating apparatus. 
   BACKGROUND OF THE ART 
   Among conventional radio-frequency heating apparatuses of a type concerned are ones that are provided with an air guide for guiding air to a heating chamber to prevent dew condensation there and clouding of a door inner surface. The air guide is produced by shaping a metal plate-like material or a resin material into a generally U-shaped form. An illumination device is fixed to the inside of the air guide.  FIG. 5  shows the configuration of a conventional radio-frequency heating apparatus. 
   In  FIG. 5 , reference numeral  1  denotes a heating chamber for housing a cooking object;  2 , a door for inputting and outputting the cooking object;  3 , a magnetron for supplying radio-frequency waves to the heating chamber;  4 , a high-voltage transformer for supplying power to the magnetron  3 ;  5 , a cooling fan for cooling electric parts;  6 , an air guide for guiding air to the heating chamber  1 ; a waveguide for holding the magnetron  3  and guiding the generated radio-frequency waves to the heating chamber  1 ; and  8 , an illumination device for illuminating the cooking object in the heating chamber  1 . 
   In the above conventional configuration, if the air guide  6  is made of a resin material, when the illumination device  8  is attached to the air guide  6 , the illumination device  8  can easily be held by the air guide  6  by using fixing nails that were formed by molding. However, if the air guide  6  is made of a metal plate, it is insufficient to hook the illumination device  8  on a bent metal portion; fixing with a vis is indispensable. However, fixing the illumination device  8  with a vis causes a problem that when the door  2  of the radio-frequency heating apparatus is opened or closed, vibration is transmitted to the filament or the like and a disconnection may occur there. This makes it necessary to use a special, stepped vis or sandwiching a buffer member between the vis and the illumination apparatus  8 . 
   Further, the temperature tends to vary to a larger extent in metal plates than in resin materials. This results in a problem that after completion of cooking, steam that goes back from the heating chamber  1  likely condenses into dew, whereby water droplets may drop onto electric parts that are disposed under the air guide  6  to deteriorate their insulation performance. 
   DISCLOSURE OF INVENTION 
   The present invention has been made to solve the above problems in the art and an object of the invention is therefore to provide a radio-frequency heating apparatus that is provided with an air guide to which an illumination device can be fixed without using a vis and from which water droplets hardly drop, though it is made of a metal plate. 
   To solve the above problems, in a radio-frequency heating device according to the invention, an air guide made of a metal plate material has a top plate that is provided with at least two inverted-L-shaped nails. One nail is inserted in a hole of the illumination device and another nail holds a peripheral portion of the illumination device. When the air guide is attached to a radio-frequency wave generating device, the peripheral portion of the illumination device contacts the waveguide. Each of a central plate and a bottom plate of the air guide is provided with a guide for guiding water droplets. 
   With the above configuration, the illumination device is held by the nails of the air guide with slight play. Since the peripheral portion of the illumination device is in contact with the waveguide, the illumination device is prevented from disengaging from the nails. The illumination device can thus be fixed without using a vis. Further, the guides that are provided in the central plate and the bottom plate of the air guide can guide water droplets so that they do not drop onto electric parts that are disposed under the air guide. 
   According to the invention, there are provided a heating chamber for housing a cooking object, a door that is attached to an opening portion of the heating chamber so as to be able to be opened and closed to thereby allow input and output of the cooking object, an illumination device for illuminating the cooking object in the heating chamber, a radio-frequency wave generating device for generating radio-frequency waves, a waveguide for guiding the generated radio-frequency waves to the heating chamber, a fan for cooling electric parts including a magnetron that is part of the radio-frequency wave generating device, and an air guide for guiding a wind generated by the fan from the magnetron to the heating chamber, and the air guide is made of a metal plate material and has a top plate that is provided with at least one inverted-L-shaped nail. With this configuration, the illumination device is held with slight play, which prevents the problem that when the door of the radio-frequency heating apparatus is opened or closed, vibration is transmitted to the filament or the like and a disconnection may occur there. 
   According to the invention, the air guide is made of a metal plate material and has a top plate that is provided with at least two inverted-L-shaped nails, and one nail is inserted in a hole of the illumination device and another nail holds a peripheral portion of the illumination device. With this configuration, the illumination device is held with slight play, which prevents the problem that when the door of the radio-frequency heating apparatus is opened or closed, vibration is transmitted to the filament or the like and a disconnection may occur there. 
   According to the invention, the illumination device is attached at such a position that one peripheral portion thereof comes close to an end of the air guide, and when the air guide is attached to the radio-frequency wave generating device the peripheral portion of the illumination device contacts the waveguide. This prevents the illumination device from disengaging from the nails of the air guide. 
   According to the invention, the air guide has a central plate that is provided with a projected surface that is inclined so as to decrease in height in a direction from the outside to the heating chamber. With this configuration, when steam goes back from the heating chamber and condenses into dew on the central plate of the air guide and water droplets drop down its inner surface, the water droplets reach the projected surface and are guided by the projected surface to the wall surface of the heating chamber. This prevents the problem that water droplets drop from the air guide onto electric parts to deteriorate their insulation performance. This prevents the problem that water droplets drop from the air guide onto underlying electric parts to deteriorate their insulation performance. 
   According to the invention, the air guide has a bottom plate that is provided with an inclined surface that is inclined so as to decrease in height in a direction from the outside to the heating chamber. With this configuration, even if steam goes back from the heating chamber and condenses into dew on the bottom plate of the air guide, water droplets are guided by the inclined surface to the wall surface of the heating chamber. This prevents the problem that water droplets drop from the air guide onto underlying electric parts to deteriorate their insulation performance. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a perspective view showing the appearance of an air guide of a radio-frequency heating apparatus according to a first embodiment of the present invention; 
       FIG. 2  is a plan view showing the air guide as viewed from above when an illumination device is attached to it in the first embodiment of the invention; 
       FIG. 3  is a main-part-enlarged view showing the air guide as viewed from above in a state that it is attached to a radio-frequency wave generating device in the first embodiment of the invention; 
       FIG. 4  is a main-part-enlarged view showing the structures of internal surfaces of the air guide according to the first embodiment of the invention; and 
       FIG. 5  is a perspective view showing the appearance of a conventional radio-frequency heating apparatus. 
   

   BEST MODE FOR CARRYING OUT THE INVENTION 
   An embodiment of the present invention will be hereinafter described with reference to the drawings. 
   Embodiment 1 
     FIG. 1  shows the appearance of an air guide of a radio-frequency heating apparatus according to a first embodiment of the invention. 
     FIG. 2  shows the air guide as viewed from above when an illumination device is attached to it in the radio-frequency heating apparatus according to the first embodiment of the invention. 
   In  FIGS. 1 and 2 , reference symbols  9   a ,  9   b , and  9   c  denote a central plate, a top plate, and a bottom plate (not shown) of the air guide, respectively. Slit-like holes  10  are formed at the boundaries between the central plate  9   a  and the top plate  9   b  and between the central plate  9   a  and the bottom plate  9   c . The air guide is given a generally U-shaped form by bending the top plate  9   b  and the bottom plate  9   c . The top plate  9   b  has a lamp hole  11  for fixing a lamp  12  as an illumination device for illuminating a cooking object in the heating chamber. Inverted-L-shaped nails  15   a  and  15   b  are provided adjacent to the hole  11 . The lamp  12  is provided with a holding portion  13  that is formed by molding a resin and has two holding holes  14   a  and  14   b.    
     FIG. 3  shows the air guide as viewed from above in a state that it is attached to a radio-frequency wave generating device of the radio-frequency heating apparatus according to the first embodiment of the invention. 
   As shown in  FIG. 3 , the air guide is fixed to a magnetron  17  by inserting a vis or the like into a hole  16  that is formed in the top plate  9   b . The magnetron  17  is fixed, with vises or the like, to a waveguide holding plate  19  that is fixed to a waveguide  18  by welding or the like. In this state, part of the periphery of the top plate  9   b  of the air guide is close to the holding plate  19 . 
     FIG. 4  shows the structures of internal surfaces of the air guide of the radio-frequency heating apparatus according to the first embodiment of the invention. 
   As shown in  FIG. 4 , the central plate  9   a  of the air guide has a projected surface  20  that is convex inward and is inclined so as to decrease in height in the direction from the outside to the heating chamber. The bottom plate  9   c  of the air guide has an inclined surface  21  that is inclined so as to decrease in height in the direction from the outside to the heating chamber. 
   How the above-configured radio-frequency heating apparatus operates and functions will be described below. 
   First, the top plate  9   b  of the air guide has the lamp hole  11  for fixing the lamp  12  as the illumination device for illuminating a cooking object in the heating chamber, and the inverted-L-shaped nails  15   a  and  15   b  are provided adjacent to the hole  11 . The one nail  15   a  is bent toward the center of the lamp hole  11  so as to assume the inverted-L shape. The other nail  15   b , which is provided adjacent to that position on the periphery of the lamp hole  11  which is opposed to the one nail  15   a , and is bent in a direction that forms a certain angle with the direction passing through the center of the hole  11  so as to assume the inverted-L shape. The lamp  12  has the holding portion  13  that is formed by molding a resin and has the two holding holes  14   a  and  14   b . To attach the lamp  12 , the lamp  12  is inserted into the lamp hole  11  and the nail  15   a  is fitted into the one holding hole  14   a . At this time, deviating the lamp  12  from the center of the lamp hole  11  to the side opposite to the nail  15   b  allows the lamp  12  to be inserted into the lamp hole  11  without causing interference between the nail  15   b  and the holding portion  13 . Then, the holding portion  13  is slid toward the nail  15   b , whereby the centers of the lamp  12  and the lamp hole  11  coincide with each other and a peripheral portion of the holding portion  13  fits into the nail  15   b . At this time, the lamp  12  can be fixed with some play if the height dimension of the nails  15   a  and  15   b  is set slightly greater than the thickness dimension of the holding portion  13 . 
   When the lamp  12  is attached in such a manner that the centers of the lamp  12  and the lamp hole  11  coincide with each other, the peripheral portion of the holding portion  13  that is opposed to the nail  15   b  is fixed so as to be close to part of the periphery of the top plate  9   b  of the air guide. When the air guide is fixed to the magnetron  17  with vises or the like, the waveguide holding plate  19  is set close to the above part of the periphery of the top plate  9   b  of the air guide and, as a result, contacts the above peripheral portion of the holding portion  13 . 
   The central plate  9   a  of the air guide is formed with the projected surface  20  that is convex inward and is inclined so as to decrease in height in the direction from the outside to the heating chamber. Therefore, when steam goes back from the heating chamber and condenses into dew on the central plate  9   a  of the air guide and water droplets  22  drop down the central plate  9   a , the water droplets  22  reach the projected surface  20  and are guided by the projected surface  20  to the heating chamber side. 
   Further, the bottom plate  9   c  of the air guide is formed with the inclined surface  21  that is inclined so as to decrease in height in the direction from the outside to the heating chamber. Therefore, even if steam goes back from the heating chamber and condenses into dew on the bottom plate  9   c  of the air guide, water droplets  23  are guided by the inclined surface  21  to the heating chamber side. 
   As described above, according to this embodiment, the top plate of the air guide is formed with the two inverted-L-shaped nails. One nail is inserted into the hole of the illumination device and the other nail holds the peripheral portion of the illumination device. In this manner, the illumination device is held with slight play without the need for using a vis. This solves, at a low cost without impairing the workability, the problem that when the door of the radio-frequency heating apparatus is opened or closed, vibration is transmitted to the filament or the like and a disconnection may occur there. 
   Whereas the width of the nail to be inserted into the hole of the illumination device is restricted by the size of the hole, the width of the nail to hold the peripheral portion of the illumination device is not restricted at all. Therefore, the illumination device can be fixed stably by making the latter nail large. 
   The illumination device is attached at such a position that its one peripheral portion comes close to an end of the air guide. Therefore, when the air guide is attached to the radio-frequency wave generating device, the peripheral portion of the illumination device contacts the waveguide. This prevents the illumination device from disengaging from the nails of the air guide. 
   The central plate of the air guide is formed with the projected surface is inclined so as to decrease in height in the direction from the outside to the heating chamber. Therefore, when steam goes back from the heating chamber and condenses into dew on the central plate of the air guide and water droplets drop down its surface, the water droplets reach the projected surface and are guided by the projected surface to the heating chamber side. This prevents the problem that water droplets drop from the air guide onto underlying electric parts to deteriorate their insulation performance. 
   Although in the embodiment the projected surface has a circular cross-section, a projected surface having a triangular or like cross-section can provide the same advantage. 
   Although the embodiment employs the single projected surface, employment of a plurality of projected surfaces can enhance the advantage. 
   The bottom plate of the air guide is formed with the inclined surface that is inclined so as to decrease in height in the direction from the outside to the heating chamber. Therefore, even if steam goes back from the heating chamber and condenses into dew on the bottom plate of the air guide, water droplets are guided by the inclined surface to the heating chamber side. This prevents the problem that water droplets drop from the air guide onto underlying electric parts to deteriorate their insulation performance. 
   INDUSTRIAL APPLICABILITY 
   As described above, the present invention makes it possible to construct a radio-frequency heating apparatus that is provided with an inexpensive air guide to which an illumination device can be fixed without using a vis and from which water droplets hardly drop, though it is made of a metal plate.