US 3715553 A
A high-frequency heating equipment in which a high-frequency generator is stopped when the handle of a door of a heating chamber is touched or grasped upon opening the door, thereby avoiding high-frequency waves from leaking out through a port of the heating chamber, thus preventing any accident imparting an impediment to the human body and simultaneously preventing any interference to other communication appliances.
Description (OCR text may contain errors)
O Unlted States atent 1 91 1 11 3,715,553 ()gawa et al. 1 Feb. 6, 1973 [541 HIGH-FREQUENCY HEATING 3,281,567 10/1966 Meissner et a1. ..219 10.55 EQUIPMENT 2,595,748 5/1952 Andrews ..2l9/10.55 2,896,131 7/1959 Schumann... .....200/D[G. l  Invemms? 03a; 2,320,462 6/1943 Nawells ..200/1510. 2 of Nara Japan 1,657,459 1/1928 Davis ..200/1310. 2  Assignee: Matsushita Electric Industrial Co.
Ltd., Oaza Kadoma, Kadoma-shi, Primary Examiner-R. F. Staubly \Osaka, Japan Assistant Examiner-Hugh D. Jaeger  Filed: June 25, 1970 Att0rney-Stevens, Davis, Miller & Mosher  Appl. No.: 49,624  ABSTRACT A high-frequency heating equipment in which a highl l Foreign Application Prlomy Data frequency generator is stopped when the handle of a July 3, 1969 Japan ..44/53623 door of a heating chamber is touched or grasped "P opening the door, thereby avoiding high-frequency  U.S. Cl ..219/10.55, ZOO/DIG. 1 waves from leaking u through a port of the heating  Int. Cl ..l-l05b 9/06 chamber, h p n ing any accident imparting an  Field of Search....219/10.55;200/6l.85,D1G. l, impediment to the human body and simultaneously 2 0O/D1G.2 preventing any interference to other communication appliances.  References Cited 6 Claims, 9 Drawing Figures UNITED STATES PATENTS 3,619,537 11/1971 Nara et a1 ..219/10.55
7 2\ POWER SOURCE j DETECVUR PATENTEDFEB "6 I975 3.715.553 sum 10F 2 2 POWER SOURCE j FIG. 2a
K oA/a 1 NV E NTOR ATTORNEY 1 HIGH-FREQUENCY HEATING EQUIPMENT This invention relates to a high-frequency heating equipment, and more particularly to a safety device for high-frequency heating equipments wherein a detecting section is provided at the handle of a door for a heating chamber and freely opened and shut, whereby when the handle is grasped this will be detected in the form of an electrical, physical or magnetic signal by the detecting section, which signal is caused to stop the high-frequency generator thus to prevent any accident imparting an impediment to the human body as due to an external leakage of high-frequency waves through a port of the heating chamber.
The principal object of the invention is to provide a high-frequency heating equipment which causes the high-frequency generator to stop immediately when a hand touches-the handle of the door of the heating chamber, thereby assuring safety of the human body upon opening the door and simultaneously preventing any interference to other communication appliances.
Another object is to provide a high-frequency heating equipment wherein a pair or more of electrodes for detection are disposed at the door handle made of an electrical insulator, whereby generator is stopped through detection of a change in electrical resistance which occurs when a short-circuit is provided across the detecting electrodes by a part of the human body.
Still another object is to provide a high-frequency heating equipment wherein at least one electrode for detection is disposed at the door handle made of an electrical insulator, whereby generator isv stopped through detection of a current which is produced when a part of the human body touches the detecting electrode.
A further object is to provide a high-frequency heating equipment wherein atleast a pair of or more magnetic poles for detection are disposed at the door handle made of a magnetic insulator, whereby the highfrequency generator is stopped through the detection of a change in magnetic reluctance which occurs when 'a short-circuit is provided across the detecting magnetic poles by a part of the human body.
' A yet further object is to provide a high-frequency heating equipment wherein a movablepiece moved,
the high-frequency the high-frequency upon grasping the door handle, by a grasping power at that time and a pressure exerted upon the movable piece is transmitted to a pressure-sensitive element, whereby the high-frequency generator is stopped by a signal'from the element.
A still further object isto provide a high-frequency heating equipment wherein a movable piece moved; upon grasping the door handle, by a grasping power at that time, whereby the high-frequency generator is stopped by effecting the make-and-break of a switch contact with a pressure exerted upon the movable piece.
Furtherobjects and features of the invention will be apparent from the following descriptiontaken in conjunction with the accompanying drawings, in which:
FIG. 1 is a block diagram ofa safety device for a high-frequency heating equipment, showing an embodiment of thepresent invention; I
FIGS. 2 to 6 show modifications of door handles:
wherein FIGS. 2a and 3a are plan views whileFIGS. 2b
and 3b sectional views, and FIGS. 4 to 6 are sectional views of the essential parts of the modifications; and
FIG. 7 is a diagram of an example of circuit arrangement embodying the safety device shown in block in FIG. 1.
Referring to FIG. 1 of the accompanying drawings which'shows a preferred embodiment of the invention, a high-frequency generator 1 has a power source circuit 2 thereof connected to a control circuit 3. This control circuit is connected between a series circuit consisting of current fuses 4 and a power switch 5 and the power circuit 2. A signal detecting section 6 is disposed at a handle 7 of a freely-openable-and-closable door closing a port of a heating chamber into which are radiated electric waves from the high-frequency oscillator l. A detector 8 detects a signal at the signal detecting section 6 in the form of either an electrical or magnetic signal, which is amplified by an amplifier 9 and is supplied to the control circuit 3.
More specifically, in the embodiment, when the handle 7 is grasped for opening the door by hand, this will be detected in the form of an electrical or magnetic signal by means of the detector 8 inclusive of the signal detecting section 6. The electrical or magnetic signal detected is amplified by the amplifier 9 and is fed to the control circuit 3. Then, this circuit is opened, whereby power supply to the power circuit 2 of the highfrequency generator 1 is interrupted thereby to stop the generator 1 from radiating electric waves.
Accordingly, upon grasping the handle 7 by hand, the oscillation from the high-frequency generator 1 is ceased. Hence even when the handle 7 is successively. drawn to open the lid of the heating chamber, there will be eliminated the fear of leakage of the electric waves.
FIGS. 2 to 6 are views of concrete constructions for the signal detecting section 6 which is equipped at the handle 7 in the above embodiment. In the construction of FIGS. 2a and 2b, the handle 7a formed of an electrically insulating material is provided with an electrode 10 for detection which is made of metal. A current produced when a hand touches the detecting electrode 10 is detected in the form of an electrical signal by the detector 8, and'is amplifiedby the amplifier 9 to be fed to the control circuit 3, thereby interrupting the power supply to the power circuit 2 of the high-frequency oscillator 1-. v
In FIGS. 3a and 3b, the handle 7b made of metal is provided with a movable pressing piece 12 through a partition wall member 1 l formed of an insulator. In the partition wall member ll, a pressure-sensitive element 14 is disposed upon which a pressure is exerted by the movable pressing piece 12 which moves against the bias of a spring 13 upon grasping the handle 7b.
. More specifically, when the handle 7b is grasped by hand, the movable pressing member 12 will be pressed against the spring 13 to impart a pressure to the pressure-sensitive element 14. Then, the element 14 has its electrical constant changed, and the detectorB in FIG. 1 is causedto sense this change in the form of an electrical signal.
Referring to FIG. 4, the handle 7chas two conductive electrodes 16 and 17, along with an intermediate member 15 disposed therebetween and made of an introdes l6 and 17 of this handle 7c, the resistance across these electrodes will vary. The variation is detected in the form of an electrical signal, and operation is effected by the circuit arrangement shown in FIG. 1.
The handle 7d in FIG. is provided with magnetic poles and 21 for detection which have an electromagnetic coil 19 disposed in a magnetically insulating material 18, and with a moving iron piece 22 which can get into a space between the two magnetic poles.
When a hand touches this handle 7d the moving iron piece 22 will be brought against the bias of a spring (not shown) into the space between the magnetic poles 20 and 21 to change the magnetic reluctance. This is detected by the detector 8 in FIG. 1, and is used as a signal.
FIG. 6 refers to the case in which the metal-made handle 7 is per se made an electrode 23 for detection More'specifically, with the stabilized power source, a
constant-voltage circuit consisting of resistors R,, R and a varistor Vr is connected to an AC power source, and an output amplified and smoothed by a rectifier unit D, and a capacitor C, appears across terminals a I and b. These terminals a and b are connected to B- power supply circuits ofthe detector 8, the control circuit 3 and the amplifier 9. The detector 8 has the values of its resistor R resistor R and capacitor C determined such that an electrical signal appearing at the detecting electrode 10 of the handle 7 may be detected as a change in the current or voltage across the terminals a and c. Namely, in case the electrode 10 for detection is disposed at the handle 7 as in FIG. 2, the elements are set at constants at which there is efficiently detected the current produced when a hand touches the detecting electrode 10. In this case, the resistor R, is adjusted in value so as to establish a current value to the extent that no danger exists upon touching the detecting electrode 10 by hand.
In the case of the handle 7 shown in FIG. 3, the circuit constants of the detector may be set such that an electrical signal sensed by the pressure-sensitive element 14 or a spring switch may be efficiently induced in the form of a change in the current or voltage across the terminals a and c.
The amplifier 9 amplifies the change in the current or. voltage occurring across the terminals a and c, by means of transistors Q, and Q and causes the amplified current to flow across the terminals b and c. The transistor 0, is connected through a resistor R, to the B-power supply.
The current or voltage detected across the terminals a and c renders the transistor Q, conductive, so voltages across a capacitor C and a resistor R drop, and a voltage across terminals d and a also drops through a rectifier D Accordingly the base-emitter potential difference of the transistor 0 is reduced resulting in the conduction of the transistor 0,, whereby this transistor amplifies the detected current or voltage across the terminals a and c.
The control circuit 3 has an operating circuit which consists of a control switch S, and a variable resistor R The control switch S, is connected in series with a timer switch S for cooking which is attached to the electronic heating equipment, with a door switch S, which is opened and closed in interlocking relation to the opening and closure of the door of the heating chamber, and with the like, and is connected to an operating coil of an electromagnetic switch S, which in turn is connected to the power circuit 2 of the highfrequency generator 1.
When a change in potential occurs across the terminals d and a, the transistor 0 becomes conductive and the control switch S, is brought into the open state, with the result that current will be prevented from flowing through the operating coil of the electromagnetic switch S, connected to the power circuit 2 of the highfrequency oscillator I, thus opening the electromagnetic switch 8,. Consequently, the high-frequency generator 1 stops oscillation.
In addition to the preferred example shown in FIG. 7, there may be considered the combination of the detector 8, amplifier 9 and control circuit 3; the combination of the circuits 8 and 3; a case in which the detector 8 self-contains a switch thereby per se constituting the control circuit 3; and so on, where it is intended to cease the oscillation of the high-frequency generator 1 by means of an electrical or magnetic signal occurring at the handle 7 of the door of the high-frequency heating apparatus and using the stabilized power circuit 25, detector 8, amplifier 9 and control circuit 3.
For example, if a Darlington circuit is employed for the detector 8 and a Schmitt circuit for the amplifier 9, then stabilized accuracy will be obtained.
Furthermore, there is considered a method wherein the control circuit is integrally provided with the control switch S, and the electromagnetic switch S, which is connected to the power circuit 2 of the high-frequency generator 1, thereby operating by means of the amplified current across the terminals d and a the electromagnetic switch which is directly connected to the power source of the high-frequency generator 1. Yet furthermore, it is possible to use for the control circuit 3 a switching element other than the electromagnetic switch 8,, e.g. a unidirectional three-terminal thyristor or the like. It is also possible to employ a spring switch as the operating switch for the power supply of the high-frequency generator 1.
In addition, numeral 26 in FIG. 7 designates an actuating switch of the heater. When the actuating switch 26 is pressed to be closed under the open door state, then current will be caused to flow through the circuits of the operating coils of the switches 8,, S S and the electromagnetic switch S Thereafter, even if the pressing force is removed from the actuating switch 26, the electromagnetic switch S, will operate. The switch 26 may be dispensed with, and at that time a lead wire 27 connecting one end of the operating coil to one end of the power circuit 2 shall be removed.
1. A high-frequency heating equipment comprising a high-frequency generator, a heating chamber for heating materials to be cooked by means of high-frequency waves produced by said high-frequency generator, a door disposed at a front port of said heating chamber so as to be freely opened and shut, a handle provided with a detecting section for detecting as an external signal a contact thereon of the human body, and a control circuit to amplify the signal detected by said handle and to control the make-and-break of a power circuit of said high-frequency generator, whereby the contact of the human body onto said handle causes said control circuit to operate through said detecting section prior to opening said door.
2. A high-frequency heating equipment according to claim 1, wherein said detecting section comprises an electrode for receiving a very small current therethrough from said human body to ground due to electricity induced in said body, said small current being amplified by said control circuit for controlling the make-and-break of said power circuit.
3. A high-frequency heating equipment according to claim 1, wherein said handle of said door is provided with at least one pair of electrodes for detection connected to a detector circuit, said pair of electrodes being adapted to cause said detector circuit to produce a signal due to variations in the resistance between them when short-circuited by the human body, said signal being amplified by said control circuit for controlling the make-and-break of said power circuit.
4. A high-frequency heating equipment according to claim 1, wherein said handle of said door is provided with at least one pair of magnetic poles and with a movable member of a magnetic substance disposed between these magnetic poles for detection, whereby a change in magnetic reluctance is detefted which is produced when said movable member is located between said magnetic poles by a part of the human body.
5. A high-frequency heating equipment according to claim 1, wherein said handle of said door is provided with a movable piece which moves by means of a grasping power when said handle is grasped and with a pressure-sensitive element, whereby a pressure exerted on said movable piece is detected by said pressure-sensitive element.
6. A high-frequency heating equipment comprising a high-frequency generator, a heating chamber for heating materials to be cooked by means of high-frequency waves produced by said high-frequency generator, a door disposed at a front port of said heating chamber so as to be freely opened and shut, a handle self-containing a make-and-break contact, and a control circuit to control the make-and-break of a power circuit of said high-frequency generator through the operation of said make-and-break contact, whereby the action of grasping said handle upon opening said door causes said control circuit to operate.