High Frequency Heating Apparatus

Abstract

In a high frequency heating apparatus of the class comprising a cabinet defining a heating chamber having an access opening at one side thereof, a door mounted on the cabinet for closing the access opening, a high frequency oscillator mounted on the cabinet for radiating high frequency electromagnetic wave in the heating chamber and a locking mechanism for holding the door in the closed position, there are provided a door operating handle connected to the locking mechanism for operating the same and a switch mounted on the cabinet, the switch being interlocked with the locking mechanism for controlling the operation of the high frequency oscillator when the door is locked and unlocked by the locking mechanism.

Description

This invention relates to high frequency heating apparatus and more particularly to improved high frequency heating apparatus such as an electronic oven provided with a locking mechanism for controlling the operation of a high frequency oscillator in response to opening and closing operations of the door of the oven.

The electronic oven utilized to cook various foodstuffs is usually provided with a high frequency oscillator operating at a frequency of about 2,450 MHz. If there is a gap between the periphery of the door and the cabinet, the high frequency electromagnetic wave leaks to the outside through this gap during the operation of the oven, thereby adversely affecting nearby communication apparatus, such as a television receiving set as well as the operator of the oven. For this reason, it is highly desirable that the high frequency oscillator is positively deenergized when the door of the oven is opened.

In the prior electronic oven it is usual to provide an electric switch interlocked with the door such that the high frequency oscillator energizing the oven is deenergized whenever the door is opened during the cooking operation. However, owing to the construction of the operating mechanism of the switch and the mechanical play between the switch and the door it is inevitable to have a certain time delay between the instant at which the door is begun to be opened inadvertently and the instant at which the switch is actually opened to deenergize the high frequency oscillator. During this time delay there is a risk of leaking the high frequency electromagnetic wave. Further, where the switch does not operate normally, due to the welding of its contacts for example, the damage to the operator and nearby apparatus becomes more serious.

It is therefore an object of this invention to provide an extremely safe high frequency heating apparatus provided with an improved door locking mechanism which can positively control the operation of the high frequency oscillator in response to the operation of the door of the high frequency heating apparatus.

A more specific object of this invention is to provide a new and improved electronic oven whereby the leakage of the high frequency electromagnetic wave can be positively prevented when the door of the cabinet is inadvertently opened during the operation of the oven.

SUMMARY OF THE INVENTION

According to this invention, in a high frequency apparatus of the class comprising a cabinet defining a heating chamber having an access opening at one side thereof, a door mounted on the cabinet for closing the access opening, a high frequency oscillator mounted on the cabinet for radiating high frequency electromagnetic waves in the heating chamber and a locking mechanism for holding the door in the closed position, there are provided a door operating handle connected to the locking mechanism for operating the same and a switch mounted on the cabinet, the switch being interlocked with the handle operated locking mechanism for controlling the operation of the high frequency oscillator when the door is locked and unlocked by the locking mechanism.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a side view of an electronic oven embodying the invention;

FIG. 2 is a sectional view showing the locking mechanism and components associated therewith which are utilized in the embodiment shown in FIG. 1;

FIG. 3 is a schematic connection diagram of the high frequency oven shown in FIG. 1;

FIG. 4 shows a modified door locking mechanism;

FIG. 5 shows a still further modification of the door locking mechanism;

FIG. 6 shows another modification of the door locking mechanism;

FIG. 7 shows a modification of the embodiment shown in FIG. 6;

FIG. 8 shows yet another embodiment of the door locking mechanism; and

FIG. 9 shows a modification of the embodiment shown in FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Throughout the drawings and the following description like parts are designated by the same reference numerals.

The electronic oven shown in FIG. 1 comprises a cabinet 1 including a heating or cooking chamber 2 defined by a metal casing having an access opening at one side thereof. On the upper wall of the cooking chamber are mounted a magnetron oscillator 3 and a stirrer fan 4 to distribute the high frequency electromagnetic waves radiated in the cooking chamber by magnetron 3 by the action of the stirrer fan, whereby to uniformly heat and cook the foodstuff loaded in the cabinet. The high frequency electromagnetic waves may be radiated through a wave guide from the magnetron oscillator into the cooking chamber. A door 5 is pivotally mounted as at 6 on the lower edge of the access opening for opening and closing the cooking chamber. First and second door switches 7a and 7b for controlling the operation of the magnetron in response to the opening and closing operations of the door are provided in the spaces between both side walls of the cabinet 1 and the casing of the cooking chamber 2. To this end, there are provided first and second levers 8a and 8b extending through slots (not shown) formed through the front wall 1a of the cabinet, the outer ends of these levers being pivotally connected to door 5. The inner ends of levers 8a and 8b are normally biased in the clockwise direction as viewed in FIG. 1 by means of springs 9a and 9b each having one end secured to the cabinet. Thus, when the door is closed, the inner ends of levers 8a and 8b urge upwardly the operating levers of switches 7a and 7b to open them. As the door is opened, levers 8a and 8b are pulled out by being guided by said slots to release the operating levers of the switches 7a and 7b thus opening the same. A panel board 10 carrying a timer and the like is mounted on the cabinet above the access opening.

As best shown in FIG. 2, a handle 11 is mounted on the upper front portion of door 5 for operating the same. The handle extends through perforations 15 and is provided with a hook 14 at its inner end, and an arm 13 pivotally mounted on a supporting plate 12 secured to the inner surface of the front wall of the door. The perforations 15 have a height sufficient to permit the desired rotary motion for arm 13. A spring 16 is connected between arm 13 and the inner surface of the front wall of the door for biasing the arm in the counterclockwise direction so as to cause the hook 14 to engage a locking member or latch 18 secured to the front wall 1a of the cabinet. Thus, the locking mechanism is comprised by arm 13 having hook 14, spring 16 and locking member 18. Near the locking member 18 is provided a micro-switch 19 for controlling the operation of magnetron 3, the operating lever 19a of micro-switch 19 being arranged to be engaged by hook 14 when it is caught by locking member 18 for operating the micro-switch. A metal strip 20 is secured to the rear wall of the door which is urged against the periphery of the access opening of the heating chamber 2 in order to prevent a gap from being formed between the door and the cabinet when the door is closed. To open the door, the arm 13 is rotated in the clockwise direction against the action of spring 16 so as to disengage the hook from the locking member concurrently with the opening of micro-switch 19.

FIG. 3 shows a connection diagram of the electronic oven. A series circuit including a fuse 22a, normally opened contacts 23a of an electromagnetic contactor 23, the second door switch 7b, the primary winding 24a of a high voltage transformer 24, other normally opened contacts 23b of the electromagnetic contactor 23, and a fuse 22b is connected across an a-c power source 21. The secondary winding 24b of the high voltage transformer 24 is connected to the anode electrodes of magnetron 3 through a rectifier circuit 25 including a diode D and a capacitor C.sub.1. The juncture between fuse 22a and normally opened contacts 23a and that between fuse 22b and normally opened contacts 23b are grounded through capacitors C.sub.2 and C.sub.3, respectively. The primary winding 27a of a low voltage transformer 27 is connected across said two junctures through a source switch 26 and the secondary winding 27b of low voltage transformer 27 is connected to the cathode heater of magnetron 3. One terminal of the secondary winding 27b is connected to the juncture between the diode D and capacitor C.sub.1 of the rectifier circuit 25. Connected in parallel with the primary winding 27a are a fan motor 28, a lamp 29 mounted in the cabinet, and a series circuit including a thermal switch 30 responsive to an excessive temperature rise of magnetron 3, the driving motor 31M of a timer 31, the normally opened contact 31a of the timer, the above described micro-switch 19 and said first door switch 7a. Furthermore, a motor 4M for driving the stirrer fan 4 and the operating coil of electromagnetic switch 23 are connected in parallel with timer motor 31M. A buzzer 32 which operates when the cooking operation is completed is connected across a series circuit including timer motor 31M and its normally opened contact 31a via a normally closed contact 31b of the timer.

The operation of the electronic oven will be described below with reference to FIGS. 1 to 3. After loading a foodstuff in the heating or cooking chamber 2, the door 5 is closed. Then, door switches 7a and 7b are closed and the door is locked in the closed position by the locking mechanism described above. At the same time, micro-switch 19 is closed by the engagement of its operating lever 19a with hook 14. Then source switch 26 is closed to preheat the cathode electrode of magnetron 3. When timer 31 is preset to a desired cooking time, its normally opened contact 31a is closed to energize timer motor 31M and electromagnetic contactor 23. Closure of contacts 23a and 23b supplies a high DC voltage to the anode electrodes of magnetron 3 through high voltage transformer 24 and rectifier 25 whereby magnetron 3 begins to oscillate to radiate high frequency electromagnetic waves in cooking chamber 2 to commence the cooking operation. After the predetermined interval preset by the timer 31, its normally opened contact 31a is opened to deenergize timer motor 31M and the electromagnetic contactor 23, whereupon its contacts 23a and 23b are opened to stop oscillation of the magnetron.

FIG. 4 shows a modified embodiment of the locking mechanism. In this example, the locking member 18 is in the form of a letter U having a recess 18a for receiving the operating lever 19a of micro-switch 19. Thus, the vertical movement of the operating lever 19a is limited so that damage of the operating lever caused by hook 14 when it is inserted into the operating position through perforation 17 can be precluded.

In another modification shown in FIG. 5, arm 13 is comprised by a first lever 40 having an outer end connected to handle 11 and an inner end pivotally mounted on a supporting plate 12 and a second lever having an outer end pivotally mounted on supporting plate 12 and an inner end carrying hook 14. The first lever 40 is provided with a shoulder 42 near the pivot while the second lever 41 is provided with a projection or pin 43 cooperating with shoulder 42. With this construction when handle 11 is rotated in the clockwise direction, shoulder 42 engages pin 43 to rotate lever 41 in the clockwise direction against the force of spring 16, thus unlocking the door. On the other hand, when handle 11 is rotated in the counterclockwise direction, shoulder 42 does not engage pin 43 so that hook 14 is not released. In this manner, lever 41 and hence hook 14 are operated only when the lever 40 is rotated in the clockwise direction so that even when the handle is rotated in the counterclockwise direction with a strong force for closing the door the engaging surfaces between hook 14 and locking member 18 and those between hook 14 and operating lever 19a which require a high degree of precision are not damaged.

In the embodiment shown in FIG. 6, a handle 60 with two legs 60a and 60b is slidably mounted on the door 5. On the inner end of leg 60a is secured a rod 61a extending through the slots 62a and 63a formed through the front and rear walls 5a and 5b of the door and carrying a hook 66a on the inner end. Similarly a rod 61b is connected to leg 60b, which extends through slots 62b and 63b formed through the front and rear walls of the door and carries a hook 66b at its inner end. Rods 61a and 61b are provided with flanges or cross-pins 64a and 64b, respectively, for limiting the outward movement of the handle. The door is normally biased toward the right as viewed in FIG. 6 by a spring 65 connected between rod 61a and the front wall of the door. On the front wall 1a of the cabinet are secured locking members or catches 68a and 68b which constitute the locking mechanism together with rods 61a, 61b and spring 65 for locking hooks 66a and 66b, thus firmly holding the door in the closed position. As described before, the operating lever 69a of micro-switch 69 is engaged by hook 66a for closing the micro-switch.

To open the door, handle 60 is operated in the direction of arrow a. This movement disengages hooks 66a and 66b from locking members 68a and 68b thus unlocking the door, while at the same time the operating lever 69a is released to open the micro-switch 69 for deenergizing the magnetron.

FIG. 7 shows a modification of the embodiment shown in FIG. 6. Again, handle 70 is slidably mounted on door 5 but is provided with a single rod 71 secured to one leg 70b. It is to be understood that two rods may be provided when desired as in the case shown in FIG. 6. A switch casing 72 containing a micro-switch 79 is secured inside of the cabinet 1. The casing 72 is provided with an opening aligned with an opening 76 formed through the front wall 1a of the cabinet and adapted to receive a hook 77 of the rod 71 and a locking member or catch 72a adapted to be engaged with the hook. The locking member 72a may be formed by bending a portion of the side wall of the casing 72 which is secured to the front wall 1a of the cabinet. When the door is closed, the pointed end of hook 77 which is now caught by the locking member 72a against the lower end of the operating lever 73 that is pivotally mounted on an arm 74. An adjusting screw 78 secured to the upper end of lever 73 against the operating button 79b of micro-switch 79, thus closing the same. A spring 75 is interposed between lever 73 and casing 72 so that the hook 77 is disengaged from locking member 72a by moving handle 70 in the direction of arrow a. The spring 75 rotates lever 73 in the clockwise direction to release push button 79b, thus closing micro-switch 79.

In another embodiment shown in FIG. 8, a handle 80 is provided with an integral lever 82 extending through a perforation 81 in the front wall 5a of the door and pivotally mounted on a supporting plate 83 secured on the inner surface of front wall 5a. The outer end of lever 84 extending through perforations 85 and 87 formed through the rear wall 5b of the door and the front wall of the cabinet is also pivotally mounted on supporting plate 83. The lever 84 is provided with a hook 84a at its inner end which is caught by locking member 88 secured to the front wall 1a of the cabinet. Hook 84a, locking member 88 and spring 86 comprise the locking mechanism. On the outer end of the lever 84 is provided a pin 84b cooperating with the lower side of the inner end of lever 82. The lever 82 is provided with a depending arm 82a at its inner end and a pin 89 is pivotally connected to the lower end of depending arm 82a to extend into the cabinet through an opening 85a in the rear wall 5b of the door and an opening 87a through the front wall 1a of the cabinet. When the door is closed, the hook 84a is caught by the locking member 88 thus locking the door in the closed position while at the same time the pin 89 pushes the operating lever 90a of micro-switch 90 secured in the cabinet whereby the switch is closed to energize the magnetron. To open the door, handle 80 is rotated in the counterclockwise direction as shown by arrow a thus releasing pin 84b. As a result, spring 86 causes hook 84a to disengage from locking member 88 to unlock the door. At the same time, pin 89 is moved to the right thus opening the micro-switch 90 to deenergize the magnetron.

In the modification shown in FIG. 9 the depending arm 82a shown in FIG. 8 is omitted while pin 89 is connected to the lower end of handle 80.

Claims

What we claim is:

1. In a high frequency heating apparatus comprising a cabinet defining a heating chamber having an access opening at one side thereof, a door mounted on said cabinet for closing said access opening, a high frequency oscillator for radiating high frequency electromagnetic waves in said heating chamber and a locking mechanism for holding said door in the closed position,

the improvement which comprises:

a door operating handle mechanism including a lever arm extending from said door outwardly of said cabinet, and a handle member connected to an end of said lever arm, said lever arm being pivotally connected to said door at substantially the middle portion of said lever arm for pivotal movement in a substantially vertical plane and being connected to said locking mechanism for operating the same, the portion of said lever arm extending outside said door being upwardly curved relative to the pivot point of said lever arm;

a switch coupled to said high frequency oscillator, said switch being mounted on said cabinet; and

means interlocking said switch with said locking mechanism for controlling the operation of said high frequency oscillator by operation of said locking mechanism when said door is locked and unlocked by said locking mechanism.

2. A high frequency heating apparatus according to claim 1 wherein said locking mechanism comprises a locking member secured to said cabinet, the end of said lever arm remote from said handle being formed with a hook adapted to engage said locking member, and a spring connected between said lever arm and said door for biasing said lever arm so as to cause said hook to engage said locking member; and wherein said switch is provided with an operating lever actuated by said hook when it is engaged with said locking member for locking said door in the closed position so as to close said switch and energize said high frequency oscillator, said operating lever being released when said hook disengages said locking member so as to open said switch and deenergize said high frequency oscillator.

3. A high frequency heating apparatus according to claim 2 wherein said locking member is recessed to receive said operating lever of said switch to thereby define the limits of movement of said operating lever.

4. A high frequency heating apparatus according to claim 2 wherein said arm comprises a first lever and a second lever, the outer end of said first lever being connected to said handle and the inner end of said first lever being pivotally connected to said door, the outer end of said second lever being pivotally mounted on said door and the inner end of said second door being provided with said hook, and means for operatively interconnecting said first and second levers such that said second lever is rotated only when said first lever is rotated in a predetermined direction.

5. A high frequency heating apparatus according to claim 1 wherein said handle includes legs mounted on said door and adapted to be slidable in parallel with the front surface thereof; said locking member comprises a locking member secured to said cabinet, a locking rod, one end of said locking rod being secured to said leg and the other end being provided with a hook adapted to engage said locking member, and a spring connected between said locking rod and said door for causing said hook to engage said locking member when said door is closed; and said switch includes an operating lever disposed to be operated by said hook when it is engaged by said locking member so as to close said switch, said operating lever being released when said hook disengages said locking member for opening said switch, thus deenergizing said high frequency oscillator.

6. A high frequency heating apparatus according to claim 5 wherein said switch is contained in a casing secured to said cabinet, said locking member is formed by a portion of said casing and said switch operating member is pivotally supported by said casing for actuating said switch through an adjusting screw.

7. A high frequency heating apparatus according to claim 1 wherein said handle comprises a lever with its inner end pivotally mounted on said door, an arm formed on said inner end of said lever, and a pin connected to said arm and extending into said cabinet; said locking mechanism comprises a locking member secured to said cabinet, a locking lever having at its inner end a hook adapted to be engaged by said locking member and pivotally mounted on said door, means for operatively interconnecting said handle and said locking lever such that said locking lever is operated only when said handle is rotated in a predetermined direction, and a spring connected between said locking lever and said door for urging said hook to engage said locking member when said door is closed; and and switch is coupled to and closed by said pin carried by said arm when said hook engages said locking member and is opened when said hook disengages said locking member for deenergizing said high frequency oscillator.

8. A high frequency heating apparatus according to claim 7 wherein said pin for operating said switch is connected to the outer end of said handle.

9. A high frequency heating apparatus according to claim 1 wherein said door operating handle mechanism includes a pair of said lever arms extending from said door and connected to said handle.

10. A high frequency heating apparatus according to claim 1 wherein said operating lever of said switch is interposed between said hook and said locking member when said door is locked in the closed position.