Matsushita Electric Industrial Co., Ltd.

Kyokuto Electric Company, Limited

Keizo Amagami

Mitsuyuki Kiuchi

Takumi Mizukawa

Hideyuki Kominami

Takao Kobayashi

Tadao Toyooka

Hirokazu Yoshida

Yoshio Ogino

Yukio Hirai

Masatatsu Nakamura

Tatsuo Saka

Shigeru Kusunoki

Hiroshi Fujieda

Shigeru Maeda

Shinichi Matsumoto

Kouji Funakoshi

Shigeharu Saegusa

Hazime Mori

Induction cooking apparatus having cooling arrangement therefor

A plurality of magnetic field sensors are mounted adjacent the periphery of an induction heating coil of flat, spiral configuration which is energized by ultrasonic frequency energy to generate a time-varying magnetic field. The magnetic field sensors are connected in a ciruit to produce an output signal when a magnetic utensil load is placed asymmetrically with respect to the center of the induction heating coil. In response to sensor output exceeding a predetermined value a warning indication is provided. The ultrasonic energy level is reduced in response to the warning indication to minimize radio interference which would otherwise occur due to leakage magnetic flux.

Circuit for detecting a utensil load placed asymmetrically relative to

An induction heating cooking apparatus includes a pan supporting plate made of a flat sheet of a heat-resistant dielectric material, a heating coil for induction heating disposed below the pan supporting plate, and touch pads each constituting a capacitor-pair formed by first, second and third electrodes. The touch pads when including three pads respectively serves for turning on a power supply, for turning off the power supply, and for setting a power level to a predetermined level. The induction heating or the supply of the power is permitted to take place only when the touch pad is first touched and followed by touching the touch pad. The first electrodes of the touch pads are provided on the upper surface of the pan supporting plate, and are enclosed by guard rings of a conductive material to prevent erroneous operation.

Induction heating cooking apparatus

Induction heating apparatus using gate-controlled switching devices includes a zero crossing point detector for detecting the occurrence of each zero crossing point of high frequency energization current, and a timing circuit which provides timing action in response to the detected zero crossing point. The timing action is controlled by a power control circuit which detects the level of energy delivered to a load within a range from the inherent turn-off time of the gate-controlled switching devices to a desired value.

Induction heating apparatus with means for detecting zero crossing point

In an induction heating cooking apparatus, the frequency of electromagnetic energy is varied in response to a desired power setting level within an allowable range and the duty cycle of the energy is varied in response to the setting level while the frequency is set at the lower limit of the allowable range. The combined effects of frequency and duty cycle controls permit the power to vary from as low as 50 watts to as high as 2 kilowatts.

Power adjustment with variable frequency and duty-cycle control for

A plurality of switches each is provided in the vicinity of each of a plurality of heater coils of an induction heating apparatus, and responsive to removel of a cooking implement from a corresponding heater coil for being rendered open. A plurality of timers each is connected to each of the switches and causes the heater coil to be de-energized when the cooking implement is kept away from the heater coil for more than a predetermined time period.

Induction heating apparatus having timing means responsive to temporary

A switching and heat control mechanism for induction heating cooking apparatus having a plurality of induction heating work coils comprises a single control shaft provided with a plurality of contact operating members. A plurality of switch contact units operable by the corresponding contact operating members provide different combinations of open and closed circuit conditions for various points of the apparatus in sequence as the control shaft is rotated. An elevating mechanism, carrying an associated work coil, moves the coil up and down in response to the angle of rotation of the control shaft to form a variable, power level controlling gap between the coil and a load placed on a nonmagnetic cook top.

Switching and heat control mechanism for induction heating cooking

A multiple-load induction heating cooking apparatus comprises two or more induction heating commutation circuits each having the junction between its commutating inductor and capacitor manually selectively connected by corresponding one of a plurality of interconnecting switches equal in number to the commutation circuits to form a series-connected LC circuit to a high frequency energy source. The potential at the common point of connection is compared with a reference potential to produce an error signal which is used to control the frequency of the energy source so that the potential at the common point is maintained constant regardless of the magnitude of induction heating loads.

Multiple-load induction heating cooking apparatus with means for

An induction heating apparatus comprising a pair of inversely parallel-connected gate-controlled switching devices connected to an alternating current source, a resonant circuit including an induction heating coil and a variable frequency gating circuit for firing the switching devices to generate oscillations through the conducting device and the induction heating coil. The switching devices are gated into conduction in succession in a first order during the positive half cycle of the alternating current and in a reversed order during the negative half cycle. A zero crosspoint detector is provided to inhibit gating when the source voltage is near zero crosspoint level and to control the gating frequency in accordance with the instantaneous value of the source voltage to increase the turn-off time of the switching devices for lower input source voltage.

Induction heating apparatus using a pair of inversely parallel connected

An induction heating apparatus includes a saturable reactor having a pair of rectangular ferrite cores. An air gap is provided in each ferrite core to provide a gradually increasing saturation characteristic on the magnetization curve of the cores. A pair of series-connected load windings is coiled around each core and a control winding is coiled around a common magnetic path of the cores. A power control circuit produces a DC control current that passes through the control winding. The high frequency energization current is passed through the load windings. Means are provided to control the DC control current at a desired setting. Preferably, the actual power level is detected to control the DC current through a feedback loop.

Induction heating apparatus using a saturable reactor for power control

An induction heating apparatus is provided with protective circuit arrangements which ensure against surge currents caused by inappropriately timed gating-on of a gate controlled rectifier or by erroneous use of a load material such as non-magnetic or ferromagnetic material. The timed gating of the gate-controlled rectifier is accomplished by means of a delay circuit which serves to count timing after a rectified excitation potential drops to the zero voltage point. A coincidence circuit is provided to detect coincidence of two signals, one is a pulse having a predetermined width and the other is a signal derived when the periodic cycle of the energization currents departs from the predetermined cycle period.

Induction heating apparatus with protective circuit arrangement

Electromagnetic coupling between a pan or utensil load to be heated by magnetic induction and a source of high frequency magnetic flux is sensed by detecting a current which is indicative of the electromagnetic coupling by means of a current transformer. The detected current is compared with a reference level. Intermittent generation of the magnetic flux is commenced when, for example, a small magnetic metal object is inadvertently placed as a load with the result that the detected current becomes lower than the reference level. This allows intermittent check for the presence and absence of the inadvertently placed load for subsequent cooking operations and minimization of the heat generated therein.

Pan detector for induction heating apparatus

A high frequency heating apparatus in which a combination of a microwave oven for heating food through dielectric heating and a cooking device for heating metallic vessel through electrical induction is incorporated to effect efficient cooking and simultaneous formation of brown scorching on the surface of food. In the heating apparatus, power required for the magnetron of the microwave oven and also for the heating coil of the cooking device is supplied through one inverter unit, by which arrangement, an efficient cooking apparatus of compact size is presented.

High frequency heating apparatus

A pan detector for an induction heating apparatus of the type having an induction heating coil adapted to electromagnetically couple to a cooking vessel comprises a first, vertically movable magnet and a second, fixed magnet spaced therefrom and a reed switch disposed between the first and second magnets. Upon the placement of a cooking vessel of magnetic metal in overlying relation to the heating coil, the first magnet moves upwardy by attraction between the bottom wall of the cooking vessel and the first magnet to result in a change in magnetic flux level in the neighborhood of the reed switch. The reed switch operates in response to the change in magnetic flux level to permit and prevent, respectively, energization of the heating coil. The first and second magnets have their poles oriented in opposition to each other to provide repulsion therebetwen to increase the attraction.

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Kadoma, Japan

Keizo Amagami