Note: Descriptions are shown in the official language in which they were submitted.
- ` 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
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~ 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
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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
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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
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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
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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
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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
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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.
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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
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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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