High frequency heating apparatus

[57] ABSTRACT

In a high frequency heating apparatus including a cubiform cavity or oven of conductive material having an opening, a supply source for supplying high frequency energy into the cavity and a door for providing access to the cavity mounted so as to close the opening; a periphery of the door has a sash with a groove thereon extending along the periphery and a periphery surrounding the opening of the cavity has a sensing member with a protrusion for fitting in the groove when the door is closed.

The sensing member is urged away from the peripherel surface of the cavity by virtue of a spring and when the door is closed the protrusion of the member is fitted in the groove. However, if a door is inadvertently closed with an obstacle such as a dishcloth sandwiched between both peripheries of the door and cavity, the obstacle depresses the protrusion and the sensing member is forced toward the peripheral surface of the cavity.

A safety switch is provided in engagement with the sensing member for turning off the supply source in response to the depression of the member caused by the obstacle. Therefore, leakage of the high frequency energy caused by the sandwiched obstacle is prevented.

Claims, 10 Drawing Figures

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PATENTED APR 171973

3,728,512

SHEET 1 OF 5

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PATENTED APR 171973

3,728,512

SHEET 2 OF 5

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PATENTED APR 171973

3,728,512

SHEET 3 OF 5

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PATENTED APR 1 71973

3,728,512

SHEET U OF 5

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FIG. 8

PATENTED APR 171973

SHEET 5 OF 5

3,728,512

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FIG. 10

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3,728,512

HIGH FREQUENCY HEATING APPARATUS

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a high frequency heating apparatus and more specifically to such an apparatus as to effectively prevent leakage of high frequency electromagnetic energy through a gap with respect to such energy caused by an obstacle undesirably sandwiched between a periphery of a closed door and a periphery of an oven enclosure of such apparatus.

2. Description of the Prior Art

In a high frequency heating apparatus, which has now found wide use, materials are heated or cooked by applying high frequency energy to the materials. The heating or cooking is achieved due to the dielectric loss presented by the materials to the high frequency energy, as is well known. The heating apparatus of this type includes a cubiform cavity or oven of conductive, typically metallic, material, and a supply source for supplying high frequency energy into the cavity. One of the walls of the oven defining the cubic cavity is constructed as a door providing access to the cavity and which, when shut, effects a suitable seal of the cavity.

As well known, one of the greatest problems in high frequency heating apparatus is the leakage of high frequency electromagnetic energy radiated through a gap between the oven enclosure and the door of such apparatus. However, in view of the fact that such leaking energy is absorbed by a body of a person near such apparatus, resulting in troubles, such leakage must be prevented as much as possible. Typical conventional seal means for preventing leakage of radiation are metallic spring contact means, conductive rubber, magnetic rubber, etc. provided either on the door of the heating apparatus or on the front of the oven enclosure.

Another one of the greatest problems in high frequency heating apparatus is leakage of the high 40 frequency electromagnetic energy through a gap with respect to such energy caused by an obstacle undesirably sandwiched between a periphery of the door and a periphery of an oven enclosure of such heating apparatus when the door is closed and the apparatus is 45 put into operation. More specifically, when the door is inadvertently closed with pieces of food attached to or a dishcloth hanged over the periphery of the door, sealing between the door and the oven enclosure is not perfect due to the presence of dielectric material or a gap with respect to the high frequency electromagnetic energy arises therebetween, resulting in leakage of such energy therethrough. Such leakage of the energy should be avoided absolutely.

SUMMARY OF THE INVENTION

In accordance with the present invention, either the periphery of the door or the periphery of the opening of the oven enclosure or cavity of the high frequency heating apparatus has a sensing strip provided extending along the periphery thereof and movably toward the surface of the periphery thereof in response to an obstacle undesirably sandwiched between both peripheries of the door and the opening of the oven enclosure and a safety switch is provided in engagement with said sensing strip for turning off the power source for high frequency energy source. Preferably said sensing member is positioned adjacent the seal member for sealing the high frequency energy provided on both or either of the peripheries of the door and the opening of the oven enclosure.

When the door is inadvertently closed with an obstacle sandwiched between both peripheries, a gap could arise therebetween with respect to the high frequency energy, resulting in leakage of the energy. In such case, however, the safety switch is turned off to deenergize ¹⁰ the high frequency energy source. Thus, the leakage of the energy is prevented.

Therefore, an object of the present invention is to provide an apparatus for preventing the leakage of the high frequency energy through a gap with respect to the high frequency energy caused by an obstacle undesirably sandwiched between both peripheries of the door and the opening of the oven enclosure of the high frequency heating apparatus when the door is closed.

2θ Another object of the present invention is to turn off the safety switch of the high frequency heating apparatus in response to an obstacle sandwiched between both peripheries of the door and the opening of the cavity when the door is closed.

Other object of the present invention is to turn off the safety switch of the high frequency heating apparatus in response to an obstacle sandwitched between both peripheries of the closed door and the opening of the cavity, wherever along the peripheries of the obstacle may be located.

These objects and other objects and features of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of the high frequency heating apparatus with the door closed in accordance with the present invention,

FIG. 2 is a front view of the apparatus of FIG. 1 with the door removed,

FIG. 3 is a perspective view from the backside of the door in an opened state,

FIG. 4 is an enlarged sectional view of a portion shown in a dotted line circle in FIG. 1,

FIG. 5 is an enlarged sectional view along line V—V in FIG. 2 but in a state of the door being closed,

FIG. 6 is an enlarged sectional view similar to FIG. 4 50 but in case of the door being closed with an obstacle sandwiched between the door and the cavity,

FIG. 7 is an enlarged sectional view similar to FIG. 4 but of another embodiment in accordance with the present invention,

FIG. 8 is an enlarged sectional view similar to FIG. 5 but of the same embodiment as FIG. 7,

FIG. 9 is an enlarged sectional view similar to FIG. 6 but of the same embodiment as FIG. 7, and

FIG. 10 is a schematic diagram of a control circuit ⁶⁰ for the embodiment of a control circuit for the embodiment shown in FIGS. 7 through 9.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1 and 2, there are shown a side view of the high frequency heating apparatus with the door closed in accordance with the present invention

3,728,512 and a front view of the apparatus of FIG. 1 with the door removed, respectively. The high frequency heating apparatus as shown comprises an oven enclosure or cavity 1 which is housed in a housing 2 and defined by a conductive, typically metallic, wall and a high frequency supply source 4, typically a magnetron, which supplys high frequency energy into the cavity 1. One portion of the wall of an oven defining the cavity 1 forms an opening 3. One side (bottom side in an illustrated embodiment) of the periphery encompassing the opening is rotatably provided with a conductive door 10 by means of a hinge 31 and when the door 10 is closed, the said opening 3 is shut, providing a closed heating chamber. On the occasion of operation, high frequency energy is supplied from the high frequency energy supply source 4 through a waveguide 5 into the cavity 1. Though not shown, stirring blades, if desired, are provided in order to make even the distribution mode of high frequency energy in the cavity 1, thereby heating evenly materials being heated. A time period for energizing the source 4 is controlled e.g. by a timer 8 provided on the control panel 6. The time set by the timer 8, is indicated by means of a scale 9 provided on the panel 6. A main switch 7 is also provided on the panel 6 for energizing the high frequency heating apparatus.

Referring to FIG. 3, there is shown a perspective view from the backside of the door 10 in an opened state. The door 10 comprises in a given central area thereof a plurality of small apertures 11 so that materials being heated placed inside the cavity 1 may be observed from the outside. Sashes 14, preferably of metal, with grooves 13 thereon are secured by means of screws 15 along the periphery of the door 10 opposite the periphery 12 encompassing the opening 3 of the cavity 1.

Referring now to FIGS. 4 and 5, there are shown an enlarged sectional view of a portion shown in a dotted line circle in FIG. 1 and an enlarged sectional view along line V — V in FIG. 2 but in a state of the door being closed. A metal flat spring strip 16 of an inverted V in section is provided extending along the whole periphery 12 encompassing the opening 3 by securing one side of the strip 16 by means of screws 17 on the periphery 12, whereby the other side of the strip 16 is urged away from the peripheral surface 12 due to the elasticity of the strip 16. Therefore, when the door 10 is closed, as shown in FIGS. 4 and 5, the protruded portion of the strip 16 comes in contact with the periphery of the door 10 under a certain value of pressure as determined by the elasticity of the strip 16. As seen from these figures, the metal strip 16 effects the sealing between both peripheries of the door 10 and the cavity 1 to prevent leakage of high frequency energy through therebetween.

Extending along the periphery 12 encompassing the opening 3 in parallel with the metal strip 16 is also provided metal flat spring strip 18 by securing one side of the strip 18 on the periphery 12 of the cavity 1 with the screws 17, whereby the other side of the strip 18 is urged away from the peripheral surface of the cavity 1. A protrusion 19 formed at the other side of the strip 18 is so adapted that it may be fitted in the groove 13 of the sash 14, when the door 10 is closed. A plurality of microswitches 20 are provided spaced apart from each other and arranged along with the periphery 12 surrounding the opening 3 of the cavity 1, as shown as at P in FIG. 2, so that each switch 20 is mounted in a space between a housing wall and a cavity wall and an actuator 22 of the switch 20 is protruded from the peripheral surface 12 through an aperture thereof to be opposite to the rear side depressing portion 22 of the metal strip 18. All these switches 20 are connected in series with each other and with a power source for the high frequency energy source 4, so that actuation of any one of the switches 20 deenergizes the high frequency source 4.

In operation, materials being heated is placed inside the cavity 1 and the door 10 is closed, in which case the strip 16 of the cavity 1 comes in contact with the periphery of the door 10 to prevent leakage of the high frequency energy through therebetween. The protrusion 19 of the strip 18 is fitted in the groove 13 of the sash 14 of the door 10, so that the side depressing portion 22 does not depress the actuator 21 of the switch 20, leaving all switches 20 in a closed state. In this connection it is to be pointed out that the strip 18 also comes into contact with the sash 14 at the bottom of the groove 13, resulting in additional prevention of leakage of the high frequency energy through between both peripheries. Upon turning on the main switch 7 and setting the timer 8, the high frequency source 4 is energized and the high frequency energy is supplied into the cavity 1, making the materials be heated.

Now let it be assumed that through inadvertence the door 10 is closed with an obstacle 23 such as a dishcloth hung over the periphery thereof, as shown in FIG. 6. As seen from FIG. 6, the obstacle 23 is sandwiched between the periphery of the door 10 and the strip 16, so that both of the door 10 and the strip 16 are out of contact with each other. This would have caused leakage of the high frequency energy through therebetween, if the present invention had not been employed.

In accordance with the present invention, such obstacle 23 is also sandwiched between the sash 14 and the strip 18, in view of the fact that the sash 14 and the strip 18 are positioned adjacent the strip 16. Thus, the obstacle 23 interrupts the protrusion 19 fitting in the groove 14. In other words, the protrusion side of the strip 18 is depressed by the obstacle 23 toward the peripheral surface 12 of the cavity 1. Accordingly, the rear side depressing portion 22 depresses the actuator 21 to turn off the switch 20. The high frequency source 4 is deenergized and the high frequency energy is not supplied into the cavity 1. Thus, the leakage of the energy caused by the obstacle 23 sandwiched between both peripheries of the door 10 and the cavity 1 is perfectly prevented.

FIGS. 7 through 10 shows another embodiment of the present invention, which merely comprises a modified switching means responsive to the obstacle. FIGS. 7, 8 and 9 correspond to FIGS. 4, 5 and 6, respectively, referred to in connection with the first embodiment. Therefore, in these figures, like numerals designate like part.

Referring now to FIGS. 7 through 10, only a modified portions will be described. In the second embodiment, the strip 18 is, as to be more fully described later, connected to the ground or held in the same

3,728,512 potential as the cavity 1. A contact layer 20' is provided on an insulation plate 21' extending along the periphery 12 surrounding the opening 3 of the cavity 1. The contact portion 22' of the strip 18 and the contact layer 20' are so adapted that in a normal state both are spaced apart from or are out of contact with each other, because the strip 18 urged away from the peripheral surface 12, but when the strip 18 is depressed by an obstacle, both come in contact with each other. Thus it is seen that in the second embodiment the strip 18 or the contact portion 22' and the contact layer 20' constitute a switch, which corresponds to the microswitch 20 in the first embodiment.

Referring to FIG. 10, there is shown a control circuit operating in response to a switch formed by the contact 22' and 20'. A drive circuit D for driving the magnetron 4 includes a relay contact 27 as well as the main switch 7 and the timer 8 connected in series with each other. A relay coil 24 for the relay contact 27 is connected in series with a thyristor 25, a gate of which is connected to a transistor 26, a base of which is connected to the switch formed by the contacts 22' and 20'.

In operation, the protrusion 19 of the strip 18 is fitted in the groove 13 of the sash 14 of the door 10, assuming that no obstacle has been sandwiched between the peripheries of the door 10 and the cavity opening 3. Since the contact 20' and 22' are out of contact, the transistor 26 and, accordingly, the thyristor 25 remain off, which keeps the contact 27 closed. By setting the switch 7 and timer 8, the magnetron 4 is energized for heating the material placed inside the cavity 1.

Assuming that the obstacle be inadvertently sandwiched between both peripheries of the door 10 and the cavity 1 when the door 10 is closed, the protrusion 19 of the strip 18 is depressed by the obstacle 23, the contact 20' and 22' come in contact and the transistor 26 and, accordingly, the thyristor 25 are turned on, as shown in FIGS. 9 and 10. The relay coil 24 is energized to turn the contact 27 off. Thus, the driving circuit D is turned off and the leakage of the high frequency energy is prevented.

While specific preferred embodiment of the invention have been described, it will be apparent that obvious variations and modifications of the inventions will occur to those of ordinary skill in the art from a consideration of the foregoing description. It is therefore desired that the present invention be limited only by the appended claims.