Micro wave leakage preventing apparatus for micro wave oven
FIELD OF THE INVENTION 
     The present invention relates to a micro wave leakage preventing apparatus for a micro wave oven, in which micro waves in a heating room are shielded so as not to be leaked to the outside, so that adverse influences should not be given to the surrounding portions of the motor and to humans. 
     BACKGROUND OF THE INVENTION 
     In the conventional micro wave ovens, a motor shaft resolves by receiving a driving power from a motor which is installed below and outside the bottom of a heating room, and this motor shaft passes through the bottom wall of the heating room in order to rotate a turn table which is installed concentrically within the heating room and at a proper height. Therefore, the micro wave which are introduced into the heating room are leaked through the through-hole formed on the bottom of the heating room, with the result that the surrounding portions of the motor are heated by the leaked micro waves, thereby causing over-heatings and malfunctions on them. Further, the micro waves which are leaked to the outside can harm humans. 
     In an attempt to overcome the above described problems, there has been proposed a micro wave leakage preventing apparatus which is constituted as shown in FIG. 3, and as described below. That is, a turn table 11, which is to be rotated and to mount foods within the heating room 10 (into which micro waves are supplied), receives a driving power from a motor 12 which is installed concentrically with the turn table at the outside of the heating room 10. The turn table 11 revolves by being driven by a motor shaft 12a which passes through a through-hole 10b formed on a bottom 10a of the heating room 10. A motor supporting member 13 is fitted to the motor shaft 10a and between the motor 12 and the bottom wall 10a of the heating room 10 enabling the member 13 to be disposed on the top of the motor 12. A first shielding member 14 having the shape of a funnel is disposed on the motor supporting member 13, and the lower end portion of the first shielding member 14 is fitted to the motor shaft 12a, while a dish shaped second shielding member 15 with a through-hole formed thereon is weld-fixed to the leading end of the first shielding member 13. Meanwhile the top of the second shielding member 15 is weld-fixed to the bottom 10a of the heating room 10. 
     In the apparatus as described above, the first shielding member 14 is installed in contact with the motor shaft 12a, and the second shielding member 15 is weld-fixed under the through-hole 10b which is formed on the bottom wall 10a of the heating room 10, as well as being weld-fixed to the first shielding member 14. Thus it becomes possible to shield up the micro waves which are leaked through the through-hole 10b of the heating room 10. However, it is impossible to suppress in a natural manner the reflection of micro waves from the first and second shielding members 14, 15, even though the heating room is sealed up. Therefore, the heat which is accumulated as the result of the reflections of the micro waves elevates the temperatures of the surrounding portions of the motor 12, thereby leaving the problem of malfunctions as before. 
     Meanwhile, in an attempt to overcome the conventional problems, there is proposed another micro wave leakage preventing apparatus which is disclosed in Japanese Utility Model, Laid-Open Publication No. 60-118894. In this apparatus, the turn table which mounts foods and rotates the foods within the heating room is interlocked with a motor shaft which transfers a driving power from a motor which is concentrically installed with the shaft. Further, a roller supporting member is formed on the bottom of the heating room in such a manner that the roller supporting member should be able to movably support in the radial direction a supporting roller which moves around the revolution axis of the turn table to movably support the turn table. Further, a reflecting member which moves together with the supporting roller in the radial direction in order to reflect the micro waves is fixedly secured to the supporting shaft of the supporting roller. 
     However, in the apparatus as described above, the supporting roller moves to the left and right by being guided by the roller supporting member which has a concavely recessed portion and a rectangular trace on the bottom of the heating room. In accordance with the movements of the supporting roller, the reflecting member moves in an interlocked manner in order to reflect micro waves, and therefore, the micro waves which are concentrated to the lower portion of the turn table can be dispersed. However, a part of micro waves is leaked through the clearance of the through-hole through which the motor shaft is inserted. Thus, the portions surrounding the motor are elavated in their temperatures, thereby causing malfunctions of the surrounding portions and fatal harms to human bodies. 
     SUMMARY OF THE INVENTION 
     The present invention is intended to overcome the above described disadvantages of the conventional techniques. 
     Therefore it is the object of the present invention to provide a micro wave leakage preventing apparatus for the micro wave oven, in which the micro waves are prevented from being leaked through the motor driving portion from the heating room to enable the micro waves to naturally disappear, thereby preventing the malfunctions caused by the temperature elevation, and also preventing harmful effects given to human bodies. 
     In achieving the above object, the micro wave leakage preventing apparatus for a micro wave oven according to the present invention includes: a heating room for receiving micro waves in order to heat up foods; a turn table for mounting foods within the heating room; a motor having a motor shaft, with the motor shaft being concentrically installed below the heating room to rotate the turn table after pasing through a through-hole of the bottom wall of the heating room; a shielding member installed between the motor and the bottom wall of the heating room in such a manner as to shield the micro waves leaked through the through-hole. 
     The micro wave leakage preventing apparatus according to the present invention is further characterized in that: the shielding member is provided with a flange on the upper edge thereof, with a through-hole being formed at the center of the bottom of the shielding member, and with a bent portion being formed along an edge of the through-hole so as for the motor shaft to be wrapped by the bent portion; a plurality of shielding protuberances are disposed around the through-hole in a circular form with a proper height and at a proper radial distance; slots are formed at positions radially outwardly from the shielding protuberances, with the slots being formed during the press-forming of the shielding protuberances; and the micro waves leaked through the through-hole are randomly reflected from the shielding member so as for the randomly reflected waves to be naturally suppressed. Thus the malfunctions which are liable to occur due to the temperature elevation caused by the leaked waves can be prevented, because micro waves are not leaked to the outside. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above object and other advantages of the present invention will become more apparent by describing in detail the preferred embodiment of the present invention with reference to the attached drawings in which: 
     FIG. 1 is a sectional view of a lower portion of a micro wave oven showing a shielding mechanism according to the present invention; 
     FIG. 2 is a perspective view of the shielding member according to the present invention; and 
     FIG. 3 is a sectional view through a conventional shielding member. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1 and 2, reference numeral 1 indicates a heating room in which foods are heated by means of micro waves supplied from a magnetron (not shown). At the bottom 1a of the heat room 1, there is provided a recess 1c which is formed by pressing, and, above the recess 1c, there is installed a turn table 2 for mounting foods at a proper height. A through-hole 1b is formed at the center of the recess 1c, and a motor shaft 3a passes through the through-hole 1b, while the motor shaft 3a is connected concentrically to a motor 3 which is installed below and at the outside of the heating room. 
     Below and at the outside of the recess 1c, there is installed a shielding member 4 which has a cylindrical or rectangular shape, and this shielding member 4 is secured between the top of the motor 3 and the bottom of the recess 1c (which is formed on the bottom of the heating room 1), in such a manner that the member 4 should be able to shield off or naturally suppress the micro waves which are leaked through the through-hole 1b of the recess 1c. 
     The shielding member 4 includes a generally horizontal wall portion 6 and an upwardly extending flange portion 8. The latter provided with a flange 4c in an outwardly bent form at its upper edge, and a through-hole 4a is formed at the center of the horizontal wall portion 6, with a bent portion 4e being formed along the edge of the through-hole 4a in order to wrap the motor shaft 3a. Around the through-hole 4a and at a proper radial distance from the hole 4a, there are formed in the horizontal wall portion 6 a plurality of upstanding shielding protuberances or reflectors 4b. The protuberances have a height which is less than the vertical spacing between the floor and the horizontal wall portion 6. The protuberances are spaced circumferentially about the hole 4a in a circular pattern. At outer positions from the shielding protuberances 4b, there are formed slots 4d as many as the shielding protuberances 4b, these slots being produced during the blanking of the shielding protuberances by a press. These slots 4d serve as the heat releasing holes when heat is produced in the space between the bottom 4a and the shielding member 4 by the micro waves which are leaked through the through-hole 1b. 
     Further, under the shielding member 4, there is fixedly secured a motor supporting member 5 which supports the motor 3, and which is provided with a plurality of ventilation holes 5a on the circumferential surface of it. 
     The apparatus of the present invention constituted as above will now be described as to its operation and effects. 
     As shown in FIGS. 1 and 2, if the user pushes a selecting button (not shown) of a control section (not shown) in order to use the micro wave oven, then a control signal is supplied to the motor 3 to activate the motor 3. Then a driving power is transmitted from the motor through the motor shaft to the turn table 2 to drive the turn table 2, and, under this condition, the food mounted upon the turn table is cooked by being heated by the micro waves emitted from a micro wave supplying device (not shown) which is installed on the ceiling or side wall of the heating room. 
     The motor shaft 3a which passes through the through-hole 1b and rotates the turn table 2 has a diameter smaller than that of the through-hole 1b so as for the shaft 3a to revolve without being contacted with the side of the through-hole 1b. Therefore, the micro waves which are introduced into the heating room 1 are leaked through between the motor shaft 3a and the through-hole 1b to the outside of the heating room 1. 
     Under this condition, the micro waves which are leaked through between the motor shaft 3a and the through-hole 1b are suppressed in a natural manner after being shielded by the shielding member 4 which is fixedly secured under the bottom 1a of the heating room 1. That is, the micro waves which are leaked in the above described manner are reflected after being collided with a the shielding protuberances 4b which are formed around the through-hole 4a of the shielding member 4 in a circular form. Then the reflected waves are reflected again at the bottom 1a of the heating room 1, and this cycle is repeated, so that the waves should be damped and suppressed in a natural manner. The heat which is accumulated during this process is released through the slots 4d of the shielding member 4 and through ventilating holes 5a of the motor supporting member 5 to the outside. Thus the temperature elevations on the portions surrounding the motor 3 can be prevented, and the micro waves can be prevented from being leaked to the outside in a sure manner. 
     According to the micro wave leakage preventing apparatus of the present invention as described above, the micro waves which are leaked through between the motor shaft and the through-hole are repeatedly reflected to and fro between the shielding protuberances of the shielding member and the bottom of the heating room, with the result that the leaked micro waves are damped to be suppressed in a natural manner through the repeated collisions. Therefore, the temperature elevations on the portions surrounding the motor, as well as their malfunctions, can be prevented, and the possibility that humans can be affected by the harmful effects of the waves can also be prevented.