High-frequency Heating Device

Abstract

A high-frequency heating device in which an electromagnetic contactor for controlling a high-voltage circuit of a high-frequency wave oscillator is provided with a touch switch circuit which is energized by detecting an electric variation caused when brought into contact with a human body, and said electromagnetic contactor is controlled when a human body touches and leaves contact electrodes provided in said touch switch circuit.

Description

The present invention relates to a high-frequency heating device, and its primary object is to provide a high-frequency heating device which, provided with a contact switch in an electromagnetic contactor circuit for detecting an electric variation caused when brought into contact with a human body, stops the output of a high-frequency oscillator controlled by said electromagnetic contactor as soon as a human body touches the contact electrodes of the touch switch, for example, in opening or closing a door, thereby to protect the human body as well as communications equipment.

Another object of the present invention is to provide a contact switch which is energized without fail at a slight touch through two contact electrodes, the contact of the human body with said contact electrodes being detected and a corresponding voltage being amplified by a Darlington pair and further amplified by a Schmitt circuit to open the exciting circuit of the electromagnetic contactor.

Another object of the present invention is to control variations in source voltage and to provide a common circuit consisting of one of said contact electrodes and the grounded side of the power circuit in the above-described touch switch.

Still another object of the present invention is to provide a touch switch in which an erroneous response to the dust or vapor attached on the contact electrodes is eliminated for stable operation and in which the dirt and dust are easily cleaned off the electrodes.

Still another object of the present invention is to provide a touch switch which controls the exciting circuit of the electromagnetic contactor by amplifying a slight current flowing from the earth through the human body to the electrodes.

Still another object of the invention is to obtain the same electrical characteristics regardless of a grounded power supply concerning the touch switch mentioned in the foregoing paragraph.

Still another object of the present invention is to provide a self-maintaining circuit which saves the trouble of depressing a starting switch after carelessly touching the touch switch.

The above and other objects, features and advantages will be made apparent by the detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 shows a diagram of a main circuit of a high-frequency heating device embodying the present invention;

FIG. 2 shows an electric circuit diagram of an embodiment of the touch switch circuit according to the present invention;

FIG. 3 is an electric circuit diagram showing another embodiment of the above-mentioned touch switch circuit;

FIG. 4a shows a side view of a handle of an oven door provided with the contact electrodes shown in FIGS. 2 and 3;

FIG. 4b shows a plan of the handle as shown in FIG. 4a;

FIG. 4c is a cross-sectional view of the handle in the plane B--B' as shown in FIG. 4a;

FIG. 5 is an electric circuit diagram of a high-frequency heating device showing another embodiment of the present invention;

FIG. 6 is an electric circuit diagram showing another embodiment of the touch switch as shown in FIG. 5; and

FIG. 7 is an electric circuit diagram showing still another embodiment of the high-frequency heating device according to the present invention.

The basic circuit of the high-frequency heating device according to the invention is shown in FIG. 1, in which the main circuit consists of a closed circuit including the power supply terminal 1, contact 2, contact piece 3, contact 4, the primary winding of the transformer 5, terminal 6, contact 7, contact piece 8, contact 9, terminal 10, door switch 11 and the power supply terminal 12. Numeral 5 shows a boosting transformer, the secondary voltage of which is applied to the load 14 or a high-frequency oscillator. Numeral 13 shows a normally open switch used as a starting switch. Numeral 15 shows a touch switch circuit which is energized by detecting contact with a human body. Numeral 16 shows an exciting coil of an electromagnetic contactor consisting of the contacts 2, 4, 7 and 9 and the contact pieces 3 and 8. Numeral 11 shows a door switch which is opened as the door is opened.

Referring now to the operation of the circuit of the above construction, the starting switch 13 is closed after closing the door and short circuiting the door switch 11. Then a closed circuit is formed which consists of the power terminal 1, contact 2, exciting coil 16, touch switch 15, contact 7, terminal 6, starting switch 13, terminal 10, door switch 11 and power supply terminal 12, thereby energizing the electromagnetic contactor and closing the main circuit. Under these condition, even if the starting switch 13 is opened, the main circuit is maintained closed as a closed circuit has been formed which consists of the power supply terminal 1, contact 2, exciting coil 16, touch switch 15, contact 7, contact piece 8, contact 9, terminal 10, door switch 11 and power supply terminal 12. However, the main circuit is opened when the touch switch circuit 15 is energized by being brought into contact with a human body. After that, the main circuit is closed again if the starting switch is depressed.

An embodiment of the touch switch circuit shown in FIG. 1 by a block is illustrated in FIG. 2. This touch switch is energized by a light touch on two adjacent contact pieces. An AC power supply is connected with the diode 17, the capacitor 18, the Schmitt circuit 33 consisting of the resistors 19, 20, 22 and 23, relay 25, transistors 21, and 24, and the Darlington pair consisting of the transistors 27 and 28. The base of the transistor 28 is connected with the contact electrode 32, and the collector thereof with the contact electrode 31 through the resistor 29. The contact of the relay 25, incidentally, is connected, as required, with the exciting coil 16 of the electromagnetic contactor for the high-frequency oscillator.

The source voltage is rectified and smoothed by the diode 17 and capacitor 18, and applied to the well-known Schmitt circuit 33. The transistor 24 in the Schmitt circuit is in an "off" state as long as no signal is applied to it. Even in such a condition, however, the transistor 21 is maintained conducting as a base current flows in the closed circuit consisting of the power supply, relay 25, resistor 20, the emitter and base of the transistor 21 and resistor 23. When the electrodes 31 and 32 are bridged by a finger or hand, the source voltage is also applied to the resistor 29, the resistance of the finger or hand and the resistor 30, and therefore the small current flowing between the electrodes 31 and 32 is amplified by the transistors 27 and 28, smoothed by the capacitor 26 and applied to the transistor 24, thereby energizing the transistor 24. As a result, the voltage between the base and emitter of the transistor 21 becomes almost zero, which cuts off the transistors 21. In this way, one of the two transistors in the Schmitt circuit is normally maintained on while the other is off, and this state is rapidly reversed, namely, the former transistor is turned off and the latter on when a signal is applied. It follows therefore that, by inserting a relay coil 25 as a load of the transistor 24, a switching operation of the electromagnetic contactor circuit can be accomplished.

Although the surface resistance of a hand touching the electrodes varies according to the race and the manner in which the hand is touched, there is no problem if the circuit constant is set so as to trigger the circuit at the maximum value of the variations. The touch switch of the above construction is applicable to any electrical equipment including a television set and fan as well as a high-frequency heater, whenever required by the use of such a device.

Another embodiment of the touch switch circuit 15 as shown in FIG. 1 is illustrated in FIG. 3. The electric circuit of this touch switch starts a controlling operation by bridging the two contact electrodes at a light touch. This embodiment features a stabilizing operation despite variations in the source voltage and the direct connection of one of the contact electrodes with the grounded side of the power supply.

In FIG. 3, numeral 34 shows an insulating transformer for voltage reduction, numeral 35 a diode, numeral 36 a smoothing capacitor, numeral 37 a constant voltage element, numeral 38 relay coil, numeral 39 a transistor, numerals 40 and 41 contact electrodes, numeral 42 a biasing resistor and numeral 43 an AC power supply. The primary of the insulating transformer 34 is connected across the AC power supply 43, the secondary thereof being connected through the diode 35 with a parallel circuit consisting of the capacitor 36, constant voltage element 37 and the series-connected relay coil 38 and transistor 39. The junction point between the diode 35 and the relay coil 38 is grounded. The contact electrode 40 is connected to the grounded side of the circuit, while the contact electrode 41 is inserted between the base and emitter of the transistor 39.

When the electrodes 40 and 41 are bridged by a finger or hand, a current flows in the closed circuit of the secondary side of the transformer 34 which consists of the diode 35, contact electrode 40, surface of the finger or hand, contact electrode 41 and the base and emitter of the transistor 39, and thereby the transistor 39 is made to conduct, causing a working current to flow in the relay coil 38. As a consequence, the on-off control of the electromagnetic contactor is made possible if its exciting circuit is connected with the contact of the relay.

Further, since the positive side of the secondary is grounded, the potential of the contact electrode 40 can be made equal to that of the earth and therefore it is enough to insulate the other contact electrode from the earth. This makes it possible to simplify the construction of the contact electrodes of such an appliance as an electronic range whose main body is grounded.

Also, since the voltage across the series circuit of the relay 38 and the transistor 39 is always maintained at a fixed level by the constant voltage element 37, stabilized operation result regardless of variations in the source voltage. Furthermore, the use of the insulating transformer eliminates danger to the human body. The arrangement of the contact electrodes as shown in FIGS. 2 and 3 is exemplified in FIGS. 4a, 4b and 4c. In this arrangement, false energization due to dirt and dust or vapor adhering to the electrodes is eliminated thereby stabilizing their operation, and it is also easy to clean off the dirt and dust from the electrodes. Numeral 44 shows a handle which consists of the grips 45 and 45'. Between the grips 45 and 45' is formed the space 46. Numerals 47 and 47' show electrodes used as those shown by numerals 31 and 32 in FIG. 2 and numerals 40 and 41 in FIG. 3, which are disposed on the lower side of the grips 45 and 45'. It is desirable that the grips 45 and 45' be made of an insulating material such as resin, but they may be made of a metal if they are insulated to be utilized as the electrodes.

Another embodiment of the high-frequency heating device equipped with a touch switch circuit is shown in FIG. 5. Contacts of an electromagnetic contactor in series with the primary of a high-voltage transformer constitute a main circuit, and a coil for energizing the electromagnetic contactor in series with the relay contacts of a touch switch constitute a touch switch circuit. The feature of this embodiment is that when a finger or hand touches a plate provided at a door handle or other part of the main body of the high-frequency heating device, said relay contacts are opened to stop the generation of a high-frequency electric wave. In this way, the leakage of the high-frequency electric wave is prevented at the time of opening the door, improving the safety of the high-frequency heating device. In FIG. 5, numeral 48 shows a power switch, numeral 49 an electromagnetic contactor, numeral 50 a high voltage transformer, numeral 51 a coil for the electromagnetic contactor, numeral 52 a cooking switch, numeral 53 a door switch, numeral 54 a time switch and numeral 55 a self-maintaining relay. The symbol A shows a touch switch control section which consists of current-limiting resistors 56 and 58, full-rectifying diode 57, constant-voltage varistor 59, smoothing capacitor 60, relay 61 with the normally closed contact 61a for the touch switch, transistors 62 and 63 making up a Darlington pair, safety resistor 64 for protecting the human body, and the touch plate 65 provided on the door handle of the high-frequency heating device.

Assume now that, after shutting the door, the cooking switch 52 is depressed with the door switch 53, power switch 48 and time switch 54 closed. Then, the self-maintaining relay 55 is energized and the contact 55a is closed to achieve self-maintenance. At the same time, the coil 51 of the electromagnetic contactor is energized and the contacts 49a and 49b are closed. As a result, a current flows in the high-voltage transformer 50, thereby generating a high-frequency wave through the high-frequency wave oscillator inserted in the secondary of the high-voltage transformer 50. At this time, if the door handle is touched to open the door, a small current flows through the grounded power supply, human body, plate 65, safety resistor 64, the base and emitter of transistors 62 and 63, diode 57 and the other power supply. This current is amplified by the Darlington pair of transistors 62 and 63, causing a current to flow through the relay 61 and open the contact 61a. As a consequence, the coil 51 of the electromagnetic contactor is deenergized and the contacts 49a and 49b of the electromagnetic contactor 49 are opened, thereby stopping the generation of the high-frequency wave. Therefore, it never happens that electric waves leak out so long as the door remains open. In addition, when the door is opened, the door switch 53 is opened and therefore the current stops flowing through the self-maintaining relay 55. As a result, the contact 55a is opened to release the self-maintained circuit. Therefore, the high-frequency power supply cannot be switched on unless the cooking switch 52 is depressed after closing the door again.

As can be seen from the above description, the coil for energizing the electromagnetic contactor which constitutes a part of the touch switch circuit is provided independently of the main circuit which consists of the contacts of the electromagnetic contactor in series with the primary winding of the high-voltage transformer. Therefore, no large current flows in the cooking switch. Also, when the touch plate 65 located on the handle of the high-frequency heating device is brought into contact with a finger or hand, said relay contact is opened in such a manner as to stop the generation of high-frequency electric waves. As a consequence, the opening of the door always causes the power supply to be cut off, which completely eliminates the leakage of electric waves, greatly contributing to the safety of the device.

Another embodiment of the contact switch as shown in FIG. 5 is illustrated in FIG. 6. This embodiment relates to a contact switch in which, when a human body touches the electrodes, a small current flowing from the earth through the human body to the electrodes is amplified to energize a relay for a switching operation. With a simple circuit arrangement, the touch switch circuit according to this embodiment maintains the same characteristics regardless of a grounded power supply. The primary of the insulating transformer 67 is connected between the terminals 66 and 66' of an AC power supply, the secondary thereof being connected with a series circuit consisting of the diode 69, relay 70 and transistor 71. The terminal 68 of the secondary is grounded. Numeral 72 shows an electrode connected with the base of the transistor 71. Since either side of a pole transformer for the house-service power supply is grounded, the problem of polarity arises for those appliances which require frequent plug-inserting and -pulling out operations. However, no such problem arises in the present embodiment because it employs the insulating transformer 67 for the power supply and also the terminal 68 is grounded. If the power supply terminal 66 is grounded, a closed circuit is formed which consists of a terminal 68, human body, electrode 72, base and emitter of the transistor 71 and the terminal 68', and thereby the transistor is turned on energizing the relay. Also, if the power supply terminal 66' is grounded, a closed circuit is formed which consists of the terminal 68, a human body, electrode 72, the base and emitter of the transistor 71 and terminal 68', thereby making the transistor conductive. Therefore, a low-cost, high-precision touch switch free from the problem of polarity can be obtained.

An electrical circuit diagram of still another embodiment of the high-frequency heating device according to the invention is shown in FIG. 7. In a circuit arrangement which provides a touch switch in addition to a circuit for opening and closing a load by means of an electromagnetic contactor, the main circuit is cut off when a hand or finger touches the handle for purposes other than opening the door, and therefore a starting switch has to be inconveniently depressed each time a continued heating operation is desired. The present embodiment is aimed at obviating this disadvantage by combining the starting switch with a self-maintaining relay contact.

In FIG. 7, the main circuit consists of the power supply terminal 73, contact 74, contact piece 75, contact 76, the primary of the transformer 77, contact 78, contact piece 79, contact 80, terminal 81, door switch 82 and power supply terminal 83. Numeral 86 shows an exciting coil of the electromagnetic contactor, numeral 89 a touch switch, numeral 87 a relay coil and numeral 85 a normally open contact of said relay, the relay coil 87 and the normally open contact 85 being interlocked with each other. Numeral 84 shows a starting switch. Assume now that, in the above construction, the power supply is switched on and the door is closed. Then the door switch 82 is closed. After that, by depressing the starting switch 84, a closed circuit is formed which consists of the power supply terminal 73, contact 74, exciting coil 86, touch switch 89, starting switch 84, terminal 81, door switch 82 and power supply terminal 83, whereby the electromagnetic contactor is energized, thereby to switch on the main circuit. At this time, a voltage is applied also to the relay coil 87 and as a result the normally open relay contact 85 is closed. Under this condition, the main circuit remains closed if the starting switch 84 is opened. If, however, a hand or finger touches the door handle, the touch switch provided on the handle is opened and the electromagnetic contactor is deenergized, thereby opening the main circuit. But as soon as the hand is detached from the handle to close the touch switch 89, the main circuit is closed. In this way, this embodiment saves the trouble of depressing the starting switch 84 again after touching the door handle for purposes other than opening the door. This condition continues until the door switch 82 is cut off by opening the door, contributing to the more convenient use of a high-frequency heating device.

The present invention is not limited to the above-described embodiments but covers all the high-frequency heating devices which stop oscillation of a high-frequency wave by detecting an electrical variation caused when brought into contact with a human body.

Claims

What is claimed is:

1. A high-frequency heating device comprising a door, a handle on said door, a high-frequency wave oscillator, an electromagnetic contactor for controlling a high-voltage circuit of said high-frequency-wave oscillator, and a touch switch provided on said handle and in an exciting circuit of said electromagnetic contactor which is controlled by said touch switch as a human body touches and leaves said touch switch whereby said high-voltage circuit is deactuated upon contact of the human body with said handle and actuated upon the human body leaving contact with said handle.

2. A high-frequency heating device according to claim 1, in which said touch switch consists of a Darlington pair having at least two transistors; a plurality of contact electrodes with one terminal connected to the terminals of the same polarity of said Darlington pair and the other to the bases of the transistors constituting said Darlington pair; a capacitor for smoothing the current detected by said contact electrodes and amplified by said Darlington pair; a Schmitt circuit having at least two transistors and which reverses the on-off state of said transistors when a voltage is applied to it; and a relay which is energized by the current amplified by said Schmitt circuit; said Darlington pair and Schmitt circuit amplifying electrical variations caused when a human body is brought into contact with said contact electrodes, thereby to energize said relay and to cut off the exciting circuit of said electromagnetic contactor.

3. A high-frequency heating device according to claim 1, in which said touch switch consists of a smoothing circuit comprising a diode and capacitor inserted in the secondary of an insulating transformer; a constant voltage element and a series circuit including a relay coil and a transistor, connected in parallel with said capacitor; and contact electrodes connected respectively with the collector and base of said transistor; said contact electrode connected to the collector of said transistor being grounded.

4. A high-frequency heating device according to claims 2 and 3, in which each of said electrodes is disposed on each of the grips of a door handle, said electrodes being separated from each other by a space interposed therebetween.

5. A high-frequency heating device according to claim 1, in which said touch switch is connected with a DC power supply comprising a current-limiting resistor, full-wave-rectifying diodes, constant-voltage element and smoothing capacitor which are in turn connected with a relay in series with a Darlington pair, the base of the forward transistor of said Darlington pair being provided with contact electrodes.

6. A high-frequency heating device according to claim 1, in which said touch switch consists of an AC power supply connected with the primary winding of an insulating transformer, and a series circuit comprising variable-impedance elements including a diode, relay and transistor connected with the secondary winding thereof, the side of said series circuit from which a DC current flows in being grounded and the base of said transistor being connected with contact electrodes.

7. A high-frequency heating device in which the exciting coil of an electromagnetic contactor in series with a touch switch on a door handle is connected with the power supply side of said electromagnetic contactor for controlling a high-voltage circuit of high-frequency oscillator; a relay coil is connected in parallel with said series circuit; said parallel circuit is connected in series with a second parallel circuit consisting of a normally open contact for said relay coil and a starting switch; and the second parallel circuit is connected through a door switch to the power supply whereby said high-voltage circuit is deactuated upon contact of the human body with said handle and actuated upon the human body leaving contact with said handle.