CA1148618A - Induction heating apparatus for cooking - Google Patents
Induction heating apparatus for cookingInfo
- Publication number
- CA1148618A CA1148618A CA000361451A CA361451A CA1148618A CA 1148618 A CA1148618 A CA 1148618A CA 000361451 A CA000361451 A CA 000361451A CA 361451 A CA361451 A CA 361451A CA 1148618 A CA1148618 A CA 1148618A
- Authority
- CA
- Canada
- Prior art keywords
- signal
- load
- detecting
- generating
- induction heating
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B6/00—Heating by electric, magnetic or electromagnetic fields
- H05B6/02—Induction heating
- H05B6/06—Control, e.g. of temperature, of power
- H05B6/062—Control, e.g. of temperature, of power for cooking plates or the like
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- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Induction Heating Cooking Devices (AREA)
- Cookers (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
An induction heating apparatus for cooking use is disclosed, which has a flat supporting plate made of non-magnetic material on which an object such as a pan to be heated is placed, an induction heat-ing coil located underneath the supporting plate which will generate magnetic flux when it is energized to heat the pan by eddy current loss generated in the pan,a signal generator having a switching device for switching a recti-fied DC signal from an AC signal and for generating a signal supplied to the induction heating coil, a drive signal generator for generating a drive signal for the switching device, a gating circuit connected between the drive signal generator and the switching device for gating the drive signal, a detecting circuit for detecting whether the object placed on the supporting plate is made of magnetic material or not and for generating an output, a search pulse generator controlled by the output of the detecting circuit and for generating a search pulse controlling the gating circuit, a load detecting circuit for detecting the load for the signal generator and gene-rating an output controlling the gating circuit together with the search pulse, and a periodic signal generator controlled by the output of the load detecting circuit and for generating a periodic signal supplied to the search pulse generator, whereby the search pulse generator generates the search pulse at the rate corresponding to the frequency of the periodic signal.
An induction heating apparatus for cooking use is disclosed, which has a flat supporting plate made of non-magnetic material on which an object such as a pan to be heated is placed, an induction heat-ing coil located underneath the supporting plate which will generate magnetic flux when it is energized to heat the pan by eddy current loss generated in the pan,a signal generator having a switching device for switching a recti-fied DC signal from an AC signal and for generating a signal supplied to the induction heating coil, a drive signal generator for generating a drive signal for the switching device, a gating circuit connected between the drive signal generator and the switching device for gating the drive signal, a detecting circuit for detecting whether the object placed on the supporting plate is made of magnetic material or not and for generating an output, a search pulse generator controlled by the output of the detecting circuit and for generating a search pulse controlling the gating circuit, a load detecting circuit for detecting the load for the signal generator and gene-rating an output controlling the gating circuit together with the search pulse, and a periodic signal generator controlled by the output of the load detecting circuit and for generating a periodic signal supplied to the search pulse generator, whereby the search pulse generator generates the search pulse at the rate corresponding to the frequency of the periodic signal.
Description
- ` BACKGROUND OF T~IE INVFNTION_ Field of the Invention The present invention relates generally to an induc-tion heating apparatus for cooking, and is directed more particularly to an induc~ion heating apparatus for cooking easy to be used.
Description o~ the Prior Art Recently, an induction heating apparatus ~or cooking has been proposed. According to this induction heating apparatus, an object such as a pan and so o~ made of magnetic material to be heated is placed in the magnetic flux generated from a coil to which an AC current is supplied, so that eddy current loss is generated in the object whereby the object is heated by this eddy current loss. In this cooking apparatus, the object such as pan or the like to be heated is placed on a so-called top plate made of non-magnetic material and then heated by the above theory. With such a cooking apparatus, the top plate itself is not heated and hence does not become hot, so that it is less in risk and hence good for the health.
With the above induction heating apparatus for cooking, if a pan, for example, made of non-magnetic material such as aluminum is placed on the top plate, no eddy current loss is generated in the pan and hence the pan is not heated any even though the AC current is supplied to the coil. That is, in such a case/ the current is consumed uselassly. Further, there is caused such a danger by the cooking apparatus thàt when a spoon made of magnetic material a clock or the like, which is not to be heated, is placed on the top plate erroneously, it is ..
~
. .
.. :
,, ' '~
, ~ heated and hence damaged. In order to avoid the above danger and so on, a magnetic material detecting circuit and a load detecting circuit are provided in the prior art in~
duction heating apparatus for cooking. This magnetic material detecting circuit is made by, for example, locating a magnet beneath the top plate which then detects whether the substance placed on the top plate is made of magnetic material or not, then controls such that no current is supplied to the coil when the substance is detected as made of non-magnetic material, but it generates a search signal once based upon the detected output and the current is supplied to the coil in a short period of time when the substance is detected as made of magnetic material. While, the load detecting circuit detects the size of the load or object placed on the top plate during the above period of time by, for example, aetecting the magnitude , duty or the like of the current flowing through a switching element in an inverter which will provide the ~C current to be fed to the coil. When the load or object on the top plate is detected or judged as a light load i.e. a small load such as a spoon, clock or the like as set forth above, the inverter is made inoperative nOt-tQ supply current to the coil.
By the provision of the magnetic material detecting circuit and the load detecting circuit in the cooking apparatus, the above-mentioned defects are avoided.
However, when the pan made of magnetic material and to be heated is placed on the top plate on a corner position deviat-ed from a normal or central position thereof, the magnetic material detecting circuit detects, of course, the pan as made of magneti.c material and generates the search signal once.
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Then, the load detecting circuit cletects the size of -the load.
At this time, however, the load detectin~ circui-t performs such a judgement that the load is small or liyht and hence the pan is not heated. In this case, however, a user can not ascertain whether or not the pan is heated. Even when it is noted later that the pan is not heated due to the fact that the pan is not placed on the top plate at the normal position and then the pan is moved on the top plate to its nor-mal position, the magnetic material detecting circuit no longer generates the search signal and hence the load detection is not performed. Therefore, even though the position of the pan on the top plate is corrected, the pan is not heated still.
Further, since the load detection is carried out in short period of time, there may occur such a fear that even if the normal pan or pan made of magnetic material and having the normal size is placed on the top plate at the normal position, it is not detected as the normal substance or judged erroneously and hence the pan is not heated.
OBJECTS AND SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a novel induction heating apparatus for cooking.
Another object of the invention is to provide an induction heating apparatus for-cooking free from the defects inheren-t to the prior art.
A further object of the present invention is to provide an induction heating apparatus for cooking which can positively heat a normal object to be heated.
A still further object of the invention is to provide an induction heating apparatus for cooking which .. . . .
. . .
has provided wi-th an arrangement for generating an alarm when an object which should not be heated is placed on a top plate of the apparatus.
According to an aspect of the present invention, an induction heating apparatus for cooking is provided which comprises:
a) a flat supporting plate on which an object to be heated is placed, b) an induction heating coiL located underneath said supporting plate and for generating magnetic flux by which said object is heated, c) a signal generator having a switching device for switching a rectified DC~ signal.from an -AC~
signal and for generating a signal supplied to said induction heating coil, d) a drive signal generator for generating a drive signal for said switching device, e) gating means connected between said drive signal generator and said switching device and ~or gating said drive signal, f) detecting means for detecting whether said object on said supporting plate is made of magnetic material or not and for generating an output, g) a search pulse generator controlled by said output of said detecting means and for generating a search pulse controlling said gating means, h) load detecting means for detecting the load for said signal generator and generating an output cont-rolling said gating means together with said search pulse, and .. -- 6 ~L ~ L~
i) a periodic signal generator controlled by said output of said load detecting means and for generating a periodic signal supplied to said search pulse genrator whereby said search pulse ~enerator generates the search pulse at the rate corresponding to the frequency of said periodic signal.
The other objects, features and advantages of the present invention will become apparent from the following description taken in conjunction with the accom-panying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a block diagram showing an example of the induction heating apparatus for cooking according to the present invention, and Figs. 2 and 3 are respectively waveform diagrams used for explaining the example of the invention shown in Fig. l.
DESCRIPTION OF THE PREFERRED EMBODIMENT
An example of the inductlon heating apparatus according to the present invention will be hereinafter des-cribed with reference to the attached drawings.
Turning to Fig. 1 which shows an example of the induction heating apparatus for cooking according to the invention in block, 1 designates a plug which will be connected to a commercial power source when it is used.
This plug l is connected through a fuse 2 and switches 3a, 3b to the input side of a rectifier circuit 4 whose positive voltage output terminal 4a is connected to a negative voltage output terminal 4b thereof through the series connection of a choke coil 5 for blocking a high frequency, an induction .. ..
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, heating or work coil 6 and a capacitor 7 for resonance.
The connection poin-t between the choke coil 5 and the work coil 6 is connected to the cathode of a damper diode 8, whose anode is in turn connected to the negative voltage output terminal 4b, and also to the anode of a GCS (gate controlled switc~ 9 serving as a switching element for generating high frequency AC current to be supplied to the induction heating coil 6. The cathode of the GCS 9 is in turn connected to the negative voltage outpu-t ter-minal 4b.
Above the wor~ coil 6, arranged is a flat supporting or top plate 10 made of non-magnetic material.
An object 11 such as a pan made of magnetic material and to be heated is located on the top plate 10. When the AC current is applied through the GCS 9 to the work coil 6, it generates magnetic flux. Thus, if the pan 11 made of magnetic material is placed on the top plate 10 at a normal or correct position, eddy current loss appears in the pan 11 and hence it is heated as in the prior art.
In Fig. 1, 12 denotes an oscillator which generates a rectangular waveform signal with the frequency of, for example, 25 KHz and the duty of 50~. The oscillation signal therefrom is fed to one of the input terminals of an AND circuit 13, whose output signal is applied through a drive circuit 14 to the gate of the GCS
9 to make it ON and OFF at high frequency.
A magnet switch 15 is provided which will detect whether a substance or object disposed on the top plate 10 is made of magnetic material or not. This magnet switch 15 is so constructed that it will produce a high level signal "1" when the substance located on the .- :
top plate 10 is made of magnetic material while a low level signal "0" when the same substance is ma~e of non-magnetic material. The output signal from the mag-net switch 15 is fed to one of the input terminals of an AND circuit 16.
An alarm oscillator 17 is provided which will generate a rectangular waveform signal with the period of, for example, 1.45 seconas and the duty of 50%.
The output signal therefrom is applied to the other input terminal of the AND circuit 16 through a 2 frequency diviaer 18. In this case, the alarm oscillator 17 is so constructed that it always oscillates except that when the power source is applied and a load detecting circuit 19, which will be described later, produces a high level signal "1" at the output side thereof i.e. normal object such as pan 11 and so on to be heated is located on the top plate 10. The output signal from the alarm oseil-lator 17 is also fed to an alarm light generating device 20 in which a light emission dioae or the like is flashed in synchronism with the oscillation signal from the alarm oscillator 17. The oscillation signal from the alarm oscillator 17 is further supplied to one of the input terminals of an AND eircuit 21 which is also supplied at its other input terminal with the output signal from the AND circuit 16 through an inverter 22. The output sig-nal from the AND eircuit 21 is fed to an alarm sound generating device 23 whieh is, for example, a buzzer and generates a s~una only when the output signal from the ~ND circuit 21 is the high level signal "1". In this case, the sound volume of the alarm can be adjusted by 9 _ ~f~
means of a variable resistor 24 connected to the device 23.
The output signal from the AND circuit 16 is also supplied to the trigger terminal of a monostable multivibrator 25 which then will produce a search signal.
The output signal therefrom is supplied to one of the input terminals of an OR circuit 26 whose output terminal is connected to a D-terminal of a D-type flip-flop circuit 27 whose Q-terminal is connected to the other input terminal of the AND circuit 13. In this case, the time constant of the monostable multivibrator 25 is selected, for example, 120 m sec. (milli seconds) and the output signal therefrom is used as the search signal.
A power source synchronizing pulse generator ~8 is provided which is connected to the plug 1 through the switch 3a and will generate a pulse signal in synchronism with the commercial power source. This pulse signal is applied to a clock input terminal C of the D-type flip-flop circuit 27.
The connection point between the choke coil 5 and the work coil 6 is also connected to the input side of the load detecting circuit 19 which will detect the time period within which the damper diode 8 is in ON-state and then detect whether the substance placed on the top plate 10 is a light load i.e. small body such as a spoon, fork and the like not to be heated or a normal load such as pan 11 to be heated. The load detecting circuit 19 delivers a high level signal "1" when the normal load such as the pan 11 is placed on the top plate 10, while a low level signal "0" when the other objects not to be heated are 30 placed on the top plate 10. The output signal from the .
load detec-tin~ circuit 19 is supplied to the other input terminal of the OR circuit 26 and also to the osciIation control terminal of the alarm oscillator 17 through an in-verter 29. In this case, the alarm oscillator 17 is so formed that it is not oscillated when the output signal from the load detecting circuit 19 is the high level signal "1".
Since the present invention is constructed as described above, when the normal pan 11 made of magnetic material and to be heated as set forth above is placed on the top plate 10, the output signal from the magnet switch 15 is the high level signal "1" and the output signal from the load detecting circuit 19 is the low level signal "0"
at the instant when the power supply switches 3a and 3b are made ON. Therefore, at this time, the alarm oscillator 17 oscillates to generate at the output side thereof an oseillation signal as sho~m in Fig. 2A. Since this oseillation signal is fed to the 12 frequency divider 18, this 12 frequency divider 18 produces at its output side a signal 18a with the period of, for example, 2.9 sec. as shown in Fig. 2~. This signal 18a is fed to the other input terminal of the AND eircuit 16, so that this AND
eircuit 16 delivers the signal shown in Fig. 2B to its output side. This signal from the AND cireuit 16 is fed to the monostable multivibrator 25 so that this multi-vibrator 25 is triggered to produce at its output side a pulse signal 25a with the width of, for example, 120 ms ¦mul-li second) shown in Fig. 3A. The pulse signal 25a is fed through the OR cireuit 26 to the D-terminal of the D-type flip-flop cireuit 27 so that it produces at its Q-terminal the high level signal "1" whieh is fed to the . . .
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:
, - o-ther input terminal oE the AND circuit 13. Thus, the outpu-t signal ~rom -the oscillator 12 is supplied through the AND circui-t 13 and the drive circuit 14 to the gate of the GCS 9 to make the work coil 6 carry out the induction heating operation or generate the magnetic flux. At this time, since the normal pan 11 to be heated is located on the top plate 10, the load detecting circuit 19 produces at its output side the high level signal "1" shown in Fig. 3C
which is fed throush the inverter 29 to the alarm oscillator 17 to stop its oscillation. At the same time, the high level signal "1" from the load detecting circuit 19 is sup-plied through the OR circuit 26 to the D-terminal of the D-type flip-flop circuit 27, so that a signal, which is the added signal of those shown in Figs. 3A and 3C as shown in Fig. 3D, is applied to the D-terminal of the D-type flip-flop circuit 27 whose outpu-t signal at its Q-terminal is sup-plied to the other input terminal of the AND circuit 13.
Thus, the oscillation output signal from the oscillator 12 is fed through the AND circuit 13 and the drive circuit 14 to the gate of the GCS ~ continuously, whereby the work coil 6 continues its induction heating operation or the eddy current loss is generated in the pan 11 by the magnetic flux from the coil 6 and the pan 11 is heated. Since the pulse synchronized with the commercial power source r for example, 50 Hz as shown in Fig. 3B is applied to the C - (clock) terminal of the D-type flip-flop circuit 27 from the generator 28, its output at the Q-terminal becomes the low level signal "0" in synchronism with the commercial power source.
While, when a small body or light load such .
as a spoon, fork or -the like, which is made of ma~netic material but small in size as compared with the normal pan 11 and should not be heated, is placed on the top plate 10, the magne-t switch 15 delivers the high level signal "1"
similar to the case of the normal pan 11. At this time, since the alarm oscillator 17 oscillates, the search signal 25a shown in Fig. 3A is derived at the output side of the monostable multivibrator 25 and then fed through the OR
circuit 26 to the D-terminal of the D-type flip-flop circuit 27. Thus, at its Q-terminal appears the high level sig-nal "1" which is fed to the other input terminal of the AND circuit 13 and hence the oscillation signal from the oscillator 12 is applied through the AND circuit 13 and the drive circuit 14 to the gate of the GCS 9. At this time, the load detecting circuit 19 produces at its output side the low level signal 1l 0 " since the small substance not to be heated is placed on the top plate 10. As a result, the alarm oscillator 17 continues its oscillation.
Therefore, the oscillation output signal therefrom is fed to the other input terminal of the AND circuit 16. Thus, since the output signal from the AND circuit 16 becomes the high level signal "1" again after, for example, 2.9 sec., the monostable multivibrator 25 again delivers the search signal 25a as shown in Fig. 3E, whereby the load detecting ~5 is carried out as set forth above. Thereafter, the above operation will be repeated.
At this time, the output signal from the alarm oscillator 17 is applied to the alarm light generating device 20, so that the latter is flashed in synchronism with the output signal from the alarm oscillator 17.
: . ' . , . ' . . ' .: , ' At the same time, a-t the output side of the AND circuit 16 derived is the signal shown in Fi~. 2B, so that the signal applied to the other input terminal o~ the AND circuit ~l is the sign~l which is the inverted signal of that at the output side of the AND circuit 16 as shown in Fig. 2C due to the existence of the inverter 22. Since the output signal from the alarm oscillator 17 shown in Fig. 2A is applied to one input terminal of the AND circuit 21, this AND circuit 21 passes therethrough a half of the output or pulse signal from the alarm oscillator 17 as shown in Fig. 2D. The pulse signal from the AND circuit 21 is fed to the alarm sound generating device 23 so that this device 23 repeatedly emits a given sound with the period twice as that of the alarm oscillator 17. In other words, when a light load of a small size such as a spoon, fork or the like which should not be heated, is placed on the top plate 10, the light is flashed and at the same ti~e the;given sound is emitted with the period twice as that of the flash-ing light.
Further, when the first detection by the load detecting circuit l9 is erroneous, it carries out the operation by the second, third, --- search signals similar to the case where the normal pan is placed. Thus, the erroneous operation can be also corrected. Further, when the load detecting circuit l9 makes an erroneous detection or judgement due to the fact that the normal pan is not placed on the top plate at the correct position, even though the pan is moved on the top plate to the correct position, the search signal 25a is sequentially generated with the given period. Thus, the erroneous operation can be corrected at once.
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: . - : : . . : -,. ~ . -: ~ . :
. , . -, ~, ~ ' : ' ~n this case, the period of the search signal is determined by the oscillation frequency of the alarm oscillator 17. However, the period and time interval of the search signal are so selected that the small substance such as the spoon, fork and the like is not heated during that period and time interval.
When a pan and so on, each being made of non-magnetic material, are placed on the top plate 10 or no substance or load: is placed on the top plate 10, the magnet switch 15 produces the low level signal "0".
Therefore, the output from the AND circuit 16 is the low level signal "0" and hence at this time no search signal is delivered. As a result, the output signal from -the load detecting circuit 19 is always the low level signal "0" and hence the alarm oscillator 17 continues its oscil~
lation. Also, the other input terminal of the AND cir-cuit 21 is kept to be supplied with the high level signal "1" while one input terminal of the AND circuit 21 is supplied with the output signal from the alarm oscillator 17. Therefore, while the alarm light generating device 20 emits the flashing light, the alarm sound generating device 23 emlts the given repeating sound in synchronism with the .lashing light, Thus, such a condition can be detected that no load and a substance made of non-magnetic material are placed on the top plate 10 or a substance made of magnetic material but small in size as compared ~ith the normal substance (which should not be heated) is placed on the top plate 10, In the above example of the presen-t inVention~ the D-t~pe flip-flop clrcu~t 27 is clocked .
-: ': ' - , in synchronism with the AC powe~ source so that when the voltage of the AC power source is ~ero, the signal supply to the GCS 9 can be stopped. Hence, there occurs no such a trouble that an abnormal voltage increases at the stop of the signal supply.
As described above, according to the invention, even when the search signal for detecting the load is delivered once and the load detection is erroneously performed by some reasons, the search signal is again delivered after a predetermined time period.
Therefore, no problem occurs in view of practical use.
Further, according to the above example of the invention, it is detected or discriminated whether the load is small in size or made of non-magnetic materia~, so that it is convenient in practical use.
In the above example of the invention, the volume of the alarm sound can be adjusted desirably by operating the variable resistor 24 as described above, so that it is convenient when it is used by a person who is hard of hearing or used in a quiet room since the volume of the alarm sound can be set in accordance with the request of the user.
It will be apparent that many modi~ications and variations could be effected by one skilled in the art without departing from the spirits or scope of the novel concepts of the present invention, so that the spirits or scope o~ the invention should be determined by the appended claims only.
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Description o~ the Prior Art Recently, an induction heating apparatus ~or cooking has been proposed. According to this induction heating apparatus, an object such as a pan and so o~ made of magnetic material to be heated is placed in the magnetic flux generated from a coil to which an AC current is supplied, so that eddy current loss is generated in the object whereby the object is heated by this eddy current loss. In this cooking apparatus, the object such as pan or the like to be heated is placed on a so-called top plate made of non-magnetic material and then heated by the above theory. With such a cooking apparatus, the top plate itself is not heated and hence does not become hot, so that it is less in risk and hence good for the health.
With the above induction heating apparatus for cooking, if a pan, for example, made of non-magnetic material such as aluminum is placed on the top plate, no eddy current loss is generated in the pan and hence the pan is not heated any even though the AC current is supplied to the coil. That is, in such a case/ the current is consumed uselassly. Further, there is caused such a danger by the cooking apparatus thàt when a spoon made of magnetic material a clock or the like, which is not to be heated, is placed on the top plate erroneously, it is ..
~
. .
.. :
,, ' '~
, ~ heated and hence damaged. In order to avoid the above danger and so on, a magnetic material detecting circuit and a load detecting circuit are provided in the prior art in~
duction heating apparatus for cooking. This magnetic material detecting circuit is made by, for example, locating a magnet beneath the top plate which then detects whether the substance placed on the top plate is made of magnetic material or not, then controls such that no current is supplied to the coil when the substance is detected as made of non-magnetic material, but it generates a search signal once based upon the detected output and the current is supplied to the coil in a short period of time when the substance is detected as made of magnetic material. While, the load detecting circuit detects the size of the load or object placed on the top plate during the above period of time by, for example, aetecting the magnitude , duty or the like of the current flowing through a switching element in an inverter which will provide the ~C current to be fed to the coil. When the load or object on the top plate is detected or judged as a light load i.e. a small load such as a spoon, clock or the like as set forth above, the inverter is made inoperative nOt-tQ supply current to the coil.
By the provision of the magnetic material detecting circuit and the load detecting circuit in the cooking apparatus, the above-mentioned defects are avoided.
However, when the pan made of magnetic material and to be heated is placed on the top plate on a corner position deviat-ed from a normal or central position thereof, the magnetic material detecting circuit detects, of course, the pan as made of magneti.c material and generates the search signal once.
::
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Then, the load detecting circuit cletects the size of -the load.
At this time, however, the load detectin~ circui-t performs such a judgement that the load is small or liyht and hence the pan is not heated. In this case, however, a user can not ascertain whether or not the pan is heated. Even when it is noted later that the pan is not heated due to the fact that the pan is not placed on the top plate at the normal position and then the pan is moved on the top plate to its nor-mal position, the magnetic material detecting circuit no longer generates the search signal and hence the load detection is not performed. Therefore, even though the position of the pan on the top plate is corrected, the pan is not heated still.
Further, since the load detection is carried out in short period of time, there may occur such a fear that even if the normal pan or pan made of magnetic material and having the normal size is placed on the top plate at the normal position, it is not detected as the normal substance or judged erroneously and hence the pan is not heated.
OBJECTS AND SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a novel induction heating apparatus for cooking.
Another object of the invention is to provide an induction heating apparatus for-cooking free from the defects inheren-t to the prior art.
A further object of the present invention is to provide an induction heating apparatus for cooking which can positively heat a normal object to be heated.
A still further object of the invention is to provide an induction heating apparatus for cooking which .. . . .
. . .
has provided wi-th an arrangement for generating an alarm when an object which should not be heated is placed on a top plate of the apparatus.
According to an aspect of the present invention, an induction heating apparatus for cooking is provided which comprises:
a) a flat supporting plate on which an object to be heated is placed, b) an induction heating coiL located underneath said supporting plate and for generating magnetic flux by which said object is heated, c) a signal generator having a switching device for switching a rectified DC~ signal.from an -AC~
signal and for generating a signal supplied to said induction heating coil, d) a drive signal generator for generating a drive signal for said switching device, e) gating means connected between said drive signal generator and said switching device and ~or gating said drive signal, f) detecting means for detecting whether said object on said supporting plate is made of magnetic material or not and for generating an output, g) a search pulse generator controlled by said output of said detecting means and for generating a search pulse controlling said gating means, h) load detecting means for detecting the load for said signal generator and generating an output cont-rolling said gating means together with said search pulse, and .. -- 6 ~L ~ L~
i) a periodic signal generator controlled by said output of said load detecting means and for generating a periodic signal supplied to said search pulse genrator whereby said search pulse ~enerator generates the search pulse at the rate corresponding to the frequency of said periodic signal.
The other objects, features and advantages of the present invention will become apparent from the following description taken in conjunction with the accom-panying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a block diagram showing an example of the induction heating apparatus for cooking according to the present invention, and Figs. 2 and 3 are respectively waveform diagrams used for explaining the example of the invention shown in Fig. l.
DESCRIPTION OF THE PREFERRED EMBODIMENT
An example of the inductlon heating apparatus according to the present invention will be hereinafter des-cribed with reference to the attached drawings.
Turning to Fig. 1 which shows an example of the induction heating apparatus for cooking according to the invention in block, 1 designates a plug which will be connected to a commercial power source when it is used.
This plug l is connected through a fuse 2 and switches 3a, 3b to the input side of a rectifier circuit 4 whose positive voltage output terminal 4a is connected to a negative voltage output terminal 4b thereof through the series connection of a choke coil 5 for blocking a high frequency, an induction .. ..
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, heating or work coil 6 and a capacitor 7 for resonance.
The connection poin-t between the choke coil 5 and the work coil 6 is connected to the cathode of a damper diode 8, whose anode is in turn connected to the negative voltage output terminal 4b, and also to the anode of a GCS (gate controlled switc~ 9 serving as a switching element for generating high frequency AC current to be supplied to the induction heating coil 6. The cathode of the GCS 9 is in turn connected to the negative voltage outpu-t ter-minal 4b.
Above the wor~ coil 6, arranged is a flat supporting or top plate 10 made of non-magnetic material.
An object 11 such as a pan made of magnetic material and to be heated is located on the top plate 10. When the AC current is applied through the GCS 9 to the work coil 6, it generates magnetic flux. Thus, if the pan 11 made of magnetic material is placed on the top plate 10 at a normal or correct position, eddy current loss appears in the pan 11 and hence it is heated as in the prior art.
In Fig. 1, 12 denotes an oscillator which generates a rectangular waveform signal with the frequency of, for example, 25 KHz and the duty of 50~. The oscillation signal therefrom is fed to one of the input terminals of an AND circuit 13, whose output signal is applied through a drive circuit 14 to the gate of the GCS
9 to make it ON and OFF at high frequency.
A magnet switch 15 is provided which will detect whether a substance or object disposed on the top plate 10 is made of magnetic material or not. This magnet switch 15 is so constructed that it will produce a high level signal "1" when the substance located on the .- :
top plate 10 is made of magnetic material while a low level signal "0" when the same substance is ma~e of non-magnetic material. The output signal from the mag-net switch 15 is fed to one of the input terminals of an AND circuit 16.
An alarm oscillator 17 is provided which will generate a rectangular waveform signal with the period of, for example, 1.45 seconas and the duty of 50%.
The output signal therefrom is applied to the other input terminal of the AND circuit 16 through a 2 frequency diviaer 18. In this case, the alarm oscillator 17 is so constructed that it always oscillates except that when the power source is applied and a load detecting circuit 19, which will be described later, produces a high level signal "1" at the output side thereof i.e. normal object such as pan 11 and so on to be heated is located on the top plate 10. The output signal from the alarm oseil-lator 17 is also fed to an alarm light generating device 20 in which a light emission dioae or the like is flashed in synchronism with the oscillation signal from the alarm oscillator 17. The oscillation signal from the alarm oscillator 17 is further supplied to one of the input terminals of an AND eircuit 21 which is also supplied at its other input terminal with the output signal from the AND circuit 16 through an inverter 22. The output sig-nal from the AND eircuit 21 is fed to an alarm sound generating device 23 whieh is, for example, a buzzer and generates a s~una only when the output signal from the ~ND circuit 21 is the high level signal "1". In this case, the sound volume of the alarm can be adjusted by 9 _ ~f~
means of a variable resistor 24 connected to the device 23.
The output signal from the AND circuit 16 is also supplied to the trigger terminal of a monostable multivibrator 25 which then will produce a search signal.
The output signal therefrom is supplied to one of the input terminals of an OR circuit 26 whose output terminal is connected to a D-terminal of a D-type flip-flop circuit 27 whose Q-terminal is connected to the other input terminal of the AND circuit 13. In this case, the time constant of the monostable multivibrator 25 is selected, for example, 120 m sec. (milli seconds) and the output signal therefrom is used as the search signal.
A power source synchronizing pulse generator ~8 is provided which is connected to the plug 1 through the switch 3a and will generate a pulse signal in synchronism with the commercial power source. This pulse signal is applied to a clock input terminal C of the D-type flip-flop circuit 27.
The connection point between the choke coil 5 and the work coil 6 is also connected to the input side of the load detecting circuit 19 which will detect the time period within which the damper diode 8 is in ON-state and then detect whether the substance placed on the top plate 10 is a light load i.e. small body such as a spoon, fork and the like not to be heated or a normal load such as pan 11 to be heated. The load detecting circuit 19 delivers a high level signal "1" when the normal load such as the pan 11 is placed on the top plate 10, while a low level signal "0" when the other objects not to be heated are 30 placed on the top plate 10. The output signal from the .
load detec-tin~ circuit 19 is supplied to the other input terminal of the OR circuit 26 and also to the osciIation control terminal of the alarm oscillator 17 through an in-verter 29. In this case, the alarm oscillator 17 is so formed that it is not oscillated when the output signal from the load detecting circuit 19 is the high level signal "1".
Since the present invention is constructed as described above, when the normal pan 11 made of magnetic material and to be heated as set forth above is placed on the top plate 10, the output signal from the magnet switch 15 is the high level signal "1" and the output signal from the load detecting circuit 19 is the low level signal "0"
at the instant when the power supply switches 3a and 3b are made ON. Therefore, at this time, the alarm oscillator 17 oscillates to generate at the output side thereof an oseillation signal as sho~m in Fig. 2A. Since this oseillation signal is fed to the 12 frequency divider 18, this 12 frequency divider 18 produces at its output side a signal 18a with the period of, for example, 2.9 sec. as shown in Fig. 2~. This signal 18a is fed to the other input terminal of the AND eircuit 16, so that this AND
eircuit 16 delivers the signal shown in Fig. 2B to its output side. This signal from the AND cireuit 16 is fed to the monostable multivibrator 25 so that this multi-vibrator 25 is triggered to produce at its output side a pulse signal 25a with the width of, for example, 120 ms ¦mul-li second) shown in Fig. 3A. The pulse signal 25a is fed through the OR cireuit 26 to the D-terminal of the D-type flip-flop cireuit 27 so that it produces at its Q-terminal the high level signal "1" whieh is fed to the . . .
.
:
, - o-ther input terminal oE the AND circuit 13. Thus, the outpu-t signal ~rom -the oscillator 12 is supplied through the AND circui-t 13 and the drive circuit 14 to the gate of the GCS 9 to make the work coil 6 carry out the induction heating operation or generate the magnetic flux. At this time, since the normal pan 11 to be heated is located on the top plate 10, the load detecting circuit 19 produces at its output side the high level signal "1" shown in Fig. 3C
which is fed throush the inverter 29 to the alarm oscillator 17 to stop its oscillation. At the same time, the high level signal "1" from the load detecting circuit 19 is sup-plied through the OR circuit 26 to the D-terminal of the D-type flip-flop circuit 27, so that a signal, which is the added signal of those shown in Figs. 3A and 3C as shown in Fig. 3D, is applied to the D-terminal of the D-type flip-flop circuit 27 whose outpu-t signal at its Q-terminal is sup-plied to the other input terminal of the AND circuit 13.
Thus, the oscillation output signal from the oscillator 12 is fed through the AND circuit 13 and the drive circuit 14 to the gate of the GCS ~ continuously, whereby the work coil 6 continues its induction heating operation or the eddy current loss is generated in the pan 11 by the magnetic flux from the coil 6 and the pan 11 is heated. Since the pulse synchronized with the commercial power source r for example, 50 Hz as shown in Fig. 3B is applied to the C - (clock) terminal of the D-type flip-flop circuit 27 from the generator 28, its output at the Q-terminal becomes the low level signal "0" in synchronism with the commercial power source.
While, when a small body or light load such .
as a spoon, fork or -the like, which is made of ma~netic material but small in size as compared with the normal pan 11 and should not be heated, is placed on the top plate 10, the magne-t switch 15 delivers the high level signal "1"
similar to the case of the normal pan 11. At this time, since the alarm oscillator 17 oscillates, the search signal 25a shown in Fig. 3A is derived at the output side of the monostable multivibrator 25 and then fed through the OR
circuit 26 to the D-terminal of the D-type flip-flop circuit 27. Thus, at its Q-terminal appears the high level sig-nal "1" which is fed to the other input terminal of the AND circuit 13 and hence the oscillation signal from the oscillator 12 is applied through the AND circuit 13 and the drive circuit 14 to the gate of the GCS 9. At this time, the load detecting circuit 19 produces at its output side the low level signal 1l 0 " since the small substance not to be heated is placed on the top plate 10. As a result, the alarm oscillator 17 continues its oscillation.
Therefore, the oscillation output signal therefrom is fed to the other input terminal of the AND circuit 16. Thus, since the output signal from the AND circuit 16 becomes the high level signal "1" again after, for example, 2.9 sec., the monostable multivibrator 25 again delivers the search signal 25a as shown in Fig. 3E, whereby the load detecting ~5 is carried out as set forth above. Thereafter, the above operation will be repeated.
At this time, the output signal from the alarm oscillator 17 is applied to the alarm light generating device 20, so that the latter is flashed in synchronism with the output signal from the alarm oscillator 17.
: . ' . , . ' . . ' .: , ' At the same time, a-t the output side of the AND circuit 16 derived is the signal shown in Fi~. 2B, so that the signal applied to the other input terminal o~ the AND circuit ~l is the sign~l which is the inverted signal of that at the output side of the AND circuit 16 as shown in Fig. 2C due to the existence of the inverter 22. Since the output signal from the alarm oscillator 17 shown in Fig. 2A is applied to one input terminal of the AND circuit 21, this AND circuit 21 passes therethrough a half of the output or pulse signal from the alarm oscillator 17 as shown in Fig. 2D. The pulse signal from the AND circuit 21 is fed to the alarm sound generating device 23 so that this device 23 repeatedly emits a given sound with the period twice as that of the alarm oscillator 17. In other words, when a light load of a small size such as a spoon, fork or the like which should not be heated, is placed on the top plate 10, the light is flashed and at the same ti~e the;given sound is emitted with the period twice as that of the flash-ing light.
Further, when the first detection by the load detecting circuit l9 is erroneous, it carries out the operation by the second, third, --- search signals similar to the case where the normal pan is placed. Thus, the erroneous operation can be also corrected. Further, when the load detecting circuit l9 makes an erroneous detection or judgement due to the fact that the normal pan is not placed on the top plate at the correct position, even though the pan is moved on the top plate to the correct position, the search signal 25a is sequentially generated with the given period. Thus, the erroneous operation can be corrected at once.
, ..
: . . ' . :
' ': ~ ' ' . ' ' ~
.
.. . . . . ~
: . - : : . . : -,. ~ . -: ~ . :
. , . -, ~, ~ ' : ' ~n this case, the period of the search signal is determined by the oscillation frequency of the alarm oscillator 17. However, the period and time interval of the search signal are so selected that the small substance such as the spoon, fork and the like is not heated during that period and time interval.
When a pan and so on, each being made of non-magnetic material, are placed on the top plate 10 or no substance or load: is placed on the top plate 10, the magnet switch 15 produces the low level signal "0".
Therefore, the output from the AND circuit 16 is the low level signal "0" and hence at this time no search signal is delivered. As a result, the output signal from -the load detecting circuit 19 is always the low level signal "0" and hence the alarm oscillator 17 continues its oscil~
lation. Also, the other input terminal of the AND cir-cuit 21 is kept to be supplied with the high level signal "1" while one input terminal of the AND circuit 21 is supplied with the output signal from the alarm oscillator 17. Therefore, while the alarm light generating device 20 emits the flashing light, the alarm sound generating device 23 emlts the given repeating sound in synchronism with the .lashing light, Thus, such a condition can be detected that no load and a substance made of non-magnetic material are placed on the top plate 10 or a substance made of magnetic material but small in size as compared ~ith the normal substance (which should not be heated) is placed on the top plate 10, In the above example of the presen-t inVention~ the D-t~pe flip-flop clrcu~t 27 is clocked .
-: ': ' - , in synchronism with the AC powe~ source so that when the voltage of the AC power source is ~ero, the signal supply to the GCS 9 can be stopped. Hence, there occurs no such a trouble that an abnormal voltage increases at the stop of the signal supply.
As described above, according to the invention, even when the search signal for detecting the load is delivered once and the load detection is erroneously performed by some reasons, the search signal is again delivered after a predetermined time period.
Therefore, no problem occurs in view of practical use.
Further, according to the above example of the invention, it is detected or discriminated whether the load is small in size or made of non-magnetic materia~, so that it is convenient in practical use.
In the above example of the invention, the volume of the alarm sound can be adjusted desirably by operating the variable resistor 24 as described above, so that it is convenient when it is used by a person who is hard of hearing or used in a quiet room since the volume of the alarm sound can be set in accordance with the request of the user.
It will be apparent that many modi~ications and variations could be effected by one skilled in the art without departing from the spirits or scope of the novel concepts of the present invention, so that the spirits or scope o~ the invention should be determined by the appended claims only.
. .
.- , ~ . , .
.' , , - - ' '. :, . `: . . : ' ' ' . ~ . --
Claims (3)
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. Induction heating apparatus comprising:
a flat supporting plate for supporting an object to be heated;
an induction heating coil located in the vicinity of said supporting plate for generating magnetic flux by which said object is heated;
signal generator means having a switching device for switching a rectified DC signal for generating an AC signal supplied to said induction heating coil;
magnetic detecting means for detecting whether said object supported by said supporting plate is made of a magnetic material and for generating a magnetic detecting output in response thereto;
load detecting means for detecting the load of said object and for generating a load detecting output in response thereto;
search pulse generator means controlled by said magnetic detecting output for generating a search pulse signal;
periodic signal generator means controlled by said load detecting output for generating a periodic signal supplied to said search pulse generator means so that said search pulse generator means generates the search pulse signal at a rate corresponding to the frequency of said periodic signal; and drive signal generator means for generating a drive signal for said switching device and being controlled by said load detecting output to cause said signal generator means to continuously supply said AC signal to said induction heating coil only when said load detecting means detects that said object has a predetermined load and said magnetic detecting means detects that said object is made of a magnetic material, and being controlled by said search pulse signal to cause said signal generator means to periodically supply said AC signal to said induction heating coil when said load detecting means detects that said object does not have said predetermined load and said magnetic detecting means detects that said object is made of a magnetic material.
a flat supporting plate for supporting an object to be heated;
an induction heating coil located in the vicinity of said supporting plate for generating magnetic flux by which said object is heated;
signal generator means having a switching device for switching a rectified DC signal for generating an AC signal supplied to said induction heating coil;
magnetic detecting means for detecting whether said object supported by said supporting plate is made of a magnetic material and for generating a magnetic detecting output in response thereto;
load detecting means for detecting the load of said object and for generating a load detecting output in response thereto;
search pulse generator means controlled by said magnetic detecting output for generating a search pulse signal;
periodic signal generator means controlled by said load detecting output for generating a periodic signal supplied to said search pulse generator means so that said search pulse generator means generates the search pulse signal at a rate corresponding to the frequency of said periodic signal; and drive signal generator means for generating a drive signal for said switching device and being controlled by said load detecting output to cause said signal generator means to continuously supply said AC signal to said induction heating coil only when said load detecting means detects that said object has a predetermined load and said magnetic detecting means detects that said object is made of a magnetic material, and being controlled by said search pulse signal to cause said signal generator means to periodically supply said AC signal to said induction heating coil when said load detecting means detects that said object does not have said predetermined load and said magnetic detecting means detects that said object is made of a magnetic material.
2. Induction heating apparatus comprising:
support means for supporting an object to be heated;
induction heating coil means positioned in the vicinity of said support means for generating magnetic flux so as to heat said object;
supply means for supplying an AC control signal to said induction heating coil means so as to generate said mag-netic flux;
magnetic detecting means for detecting whether said object is made of a magnetic material and for producing a magnetic detecting output in response thereto;
load detecting means for detecting whether said object has a predetermined load and for producing a load de-tecting output in response thereto; and means for controlling said supply means in response to said magnetic detecting output and said load detecting out-put so that said AC control signal is supplied continuously to said induction heating coil means only when said object has said predetermined load and is made of a magnetic material and said AC control signal is supplied periodically to said induc-tion heating coil means when said object is made of a magnetic material but does not have said predetermined load.
support means for supporting an object to be heated;
induction heating coil means positioned in the vicinity of said support means for generating magnetic flux so as to heat said object;
supply means for supplying an AC control signal to said induction heating coil means so as to generate said mag-netic flux;
magnetic detecting means for detecting whether said object is made of a magnetic material and for producing a magnetic detecting output in response thereto;
load detecting means for detecting whether said object has a predetermined load and for producing a load de-tecting output in response thereto; and means for controlling said supply means in response to said magnetic detecting output and said load detecting out-put so that said AC control signal is supplied continuously to said induction heating coil means only when said object has said predetermined load and is made of a magnetic material and said AC control signal is supplied periodically to said induc-tion heating coil means when said object is made of a magnetic material but does not have said predetermined load.
3. Induction heating apparatus comprising:
support means for supporting an object to be heated;
induction heating coil means positioned in the vicinity of said support means for generating magnetic flux so as to heat said object;
supply means for supplying an AC control signal to said induction heating coil means so as to generate said mag-netic flux;
magnetic detecting means for detecting whether said object is made of a magnetic material and for producing a magnetic detecting output in response thereto;
load detecting means for detecting whether said object has a predetermined load and for producing a load detecting output in response thereto; and means for controlling said supply means in response to said magnetic detecting output and said load detecting out-put so that said AC control signal is supplied continuously to said induction heating coil means only when said object has said predetermined load and is made of a magnetic material and said AC control signal is supplied periodically to said induc-tion heating coil means when said object is made of a magnetic material but does not have said predetermined load, said means for controlling including drive signal generator means for generating a drive signal to control said supply means, search pulse generator means for generating a search pulse signal in response to said magnetic detecting output to control said drive signal generator means so that said heating coil means is periodically supplied With said AC signal, and periodic signal generating means controlled by said load detecting means for producing a periodic signal for controlling the rate at which said search pulse signal is generated.
support means for supporting an object to be heated;
induction heating coil means positioned in the vicinity of said support means for generating magnetic flux so as to heat said object;
supply means for supplying an AC control signal to said induction heating coil means so as to generate said mag-netic flux;
magnetic detecting means for detecting whether said object is made of a magnetic material and for producing a magnetic detecting output in response thereto;
load detecting means for detecting whether said object has a predetermined load and for producing a load detecting output in response thereto; and means for controlling said supply means in response to said magnetic detecting output and said load detecting out-put so that said AC control signal is supplied continuously to said induction heating coil means only when said object has said predetermined load and is made of a magnetic material and said AC control signal is supplied periodically to said induc-tion heating coil means when said object is made of a magnetic material but does not have said predetermined load, said means for controlling including drive signal generator means for generating a drive signal to control said supply means, search pulse generator means for generating a search pulse signal in response to said magnetic detecting output to control said drive signal generator means so that said heating coil means is periodically supplied With said AC signal, and periodic signal generating means controlled by said load detecting means for producing a periodic signal for controlling the rate at which said search pulse signal is generated.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP12667979A JPS5652890A (en) | 1979-10-01 | 1979-10-01 | Electromagnetic induction heating cooking device |
| JP126679/79 | 1979-10-01 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1148618A true CA1148618A (en) | 1983-06-21 |
Family
ID=14941165
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000361451A Expired CA1148618A (en) | 1979-10-01 | 1980-09-30 | Induction heating apparatus for cooking |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPS5652890A (en) |
| CA (1) | CA1148618A (en) |
| DE (1) | DE3036900A1 (en) |
| FR (1) | FR2466932A1 (en) |
| GB (1) | GB2061640B (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS58142789A (en) * | 1982-02-19 | 1983-08-24 | 三洋電機株式会社 | Induction heating cooking device |
| GB2197999B (en) * | 1986-11-25 | 1991-01-09 | Ti Creda Ltd | Improvements in or relating to induction heating circuits for cooking appliances |
| EP2461105B1 (en) * | 2010-12-01 | 2016-06-29 | Coprecitec, S.L. | Cooking appliance |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5441143B2 (en) * | 1974-02-04 | 1979-12-06 | ||
| BE844219A (en) * | 1976-07-16 | 1976-11-16 | INDUCTION HEATING DEVICE | |
| DE2633741A1 (en) * | 1976-07-27 | 1978-02-02 | Bosch Siemens Hausgeraete | COOKING EQUIPMENT FOR INDUCTIVE HEATING OF A COOKING APPLIANCE |
| GB1529114A (en) * | 1977-03-31 | 1978-10-18 | Diamond Controls Ltd H | Power supply circuits |
-
1979
- 1979-10-01 JP JP12667979A patent/JPS5652890A/en active Pending
-
1980
- 1980-09-30 DE DE19803036900 patent/DE3036900A1/en not_active Withdrawn
- 1980-09-30 GB GB8031431A patent/GB2061640B/en not_active Expired
- 1980-09-30 CA CA000361451A patent/CA1148618A/en not_active Expired
- 1980-10-01 FR FR8021061A patent/FR2466932A1/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| FR2466932A1 (en) | 1981-04-10 |
| JPS5652890A (en) | 1981-05-12 |
| FR2466932B1 (en) | 1984-11-23 |
| GB2061640A (en) | 1981-05-13 |
| DE3036900A1 (en) | 1981-04-16 |
| GB2061640B (en) | 1984-01-04 |
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