Note: Descriptions are shown in the official language in which they were submitted.
1301258
Automatic heating apparatus
The present invention relates to an automatic heating
apparatus that is designed Eor automation of cooking by
employing a gas sensor and a weight sensor to detect the
condition of an object being cooked.
Such apparatus for automatically controlling the
heating time of a food ha.s been widely used. An automatic
electronic oven is one example of such apparatus that has
been highly appreciated in terms of convenience of use,
and accordingly has occupied a large share of the oven
market. Such apparatus has been developed in various
types, such as one equipped with a gas sensor that reacts
to steam or various kinds of gases generated during heating
of the food, or an infrared ray sensor for detecting the
surface temperature of the food, or a thermistor Eor
detecting the temperature of air El.owing in and out of the
heating chamber. The manner of heating depends on the
kind and condition of the food in any one of the above-
described types. A representative example is USP Re.
31,094 issued January 25, 1980.
To enable the prior art to be described with the aid
of diagrams, the figures of tke drawings will first be
listed.
Fig. 1 is a perspective view of a main body of an
~k
1~30~258
automatic heatlng apparatus:
Fig. 2 ls an enlarged front view of an operating panel
of a conventional automatic heating apparatus:
Fig. 3 iS a graph showing the relationship of the
detection and the control of a reheat key of the apparatus
of Fig. 2;
Fig. 4 is a front elevational view of an operating
panel, on an enlarged scale, of a conventional heating
apparatus;
Fig. 5 is a graph showing the relationship of the
detection and the control of a reheat key of conventional
automatic heating apparatus;
Fig. 6 is a graph showing the control of a weight
sensor of the conventional apparatus of Fig. 5
Figs. 7(a) and 7(b) are graphs showing the detection
and the control of a reheat key in conventional automatic
heating apparatus:
Fig. 8 is a front elevational view, on an enlarged
scale, of an operating panel of an automatic heating
apparatus according to one preferred embodiment of the
present invention
Figs. 9(a) and 9(b) are graphs showing the relationship
of the detection and control of a reheat key of the
apparatus of Fig. 8;
Figs. lO(a) and lO(b) are graphs for judging the food
group to be reheated in the apparatus of Fig. 8;
Fig. 11 is a diagram showing the structure of the
apparatus of Fig. 8;
Fig. 12 is a circuit diagram of the apparatus of Fig.
8 and
Figs. 13 and 14 are flow-charts of the control program
of the apparatus of Fig. 8.
Fig. 1 is a perspective view of the prior art referred
to above, Fig. 2 being a front view of the operating panel
of the apparatus of Fig. 1. In Fig. 1, a door 2 can be
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freely opened or closed in the front face of a main body
1. The apparatus has many select keys 4 arranged on an
operating panel 3 located in the front face of the main
body 1 to select the manner of heating depending on the
temperature, condition and kind of food. In the category
of food for reheating, five select keys, namely, for "cold
boiled rice", "soup", "curry/stew", "frozen boiled rice"
and "frozen curry" are arranged for suitahle selection.
The reason Eor these five select keys resides in the fact
that, if the heating operation is stopped when steam or
gas is generated from the food or when the surface tempera-
ture of the food reaches a predetermined temperature, some
kinds of foods may not yet be sufficiently heated at the
center, thus requiring further heating, the time for which,
however, varies for each Eood. E'ig. 3 shows the relation-
ship of heating time to the amount of steam generated from
the food and detected by the gas sensor. In the graph of
Fig. 3, Tl is the time spent before the first detection
point when a predetermined amount of steam is detected by
the gas sensor. When cold boiled rice is reheated, it is
good to stop heating when the generation of steam is
detected. In the case of reheating soup, it is still
lukewarm, and requires to be heated for an additional time
KlxTl, K1 heing constant and selected from experience to
be 0.1-0.5. In the case of a ~elly-like curry or stew, it
is necessary to apply further heat for a t;me K2xT], in
addition to the time T1, K2 being 0.3-0.8. For frozen
rice with ]ittle moisture that has been obtained by
freezing cold boiled rice, it is necessary to reduce the
caloric value of the heating from the time Tl when steam
is detected, and to heat for a further time K3xT2 beyond
the time T2 which is a second detection point when a
predetermined amount of steam is detected from the food
after the entirety of the frozen food has been defrosted,
13(~1258
~ 4 --
K3 being 0.01-0.5. Also, for frozen curry with m~ch
moisture, which has been obtained by freezing cold curry,
it can be heated to a suitable temperature if the curry is
fully defrosted, with the heating caloric value reduced
5 from time Tl, and further heated for a time K4xT2 after
time T2 when the predetermined amount of steam is detected
to be generated, K4 being 0.3-2Ø The reason why the
value of K is different for each food is that the steam is
generated in a different way by each food, and the reason
10 why the caloric va]ue is reduced or not during heating is
that the initial temperature condition is different for
each food, depending upon whether it is frozen or not.
Since the heat conductivity and the convection properties
are different for each food, and steam generation starts
locally in some foods, the value of K is different for
almost every food.
In consequence, a user of the prior art heating
apparatus has been obliged to select from several select
keys one key that is most suitable for the food to be
heated. However, since only 5-6 menus can be indicated at
most on the keyboard of the apparatus, the user is required
to consult a cookbook or the like to ascertain whether a
food that is not indicated on the keyboard is able to be
cooked automatically. For example, if there is a wish to
reheat macaroni, an inexperienced user does not know which
key to select. Market surveys reveal that the automatic
heating function is not highly utilized, although much
reheating is done. This is because it is a burden for the
user to find out which key to select.
Accordinq to the above-described apparatus of one
type, reheating is performed by selection of a key from
among many select keys that are arranged in accordance
with the kind and the initial temperature of the food to
be heated. On the other hand, according to apparatus of
another type, foods are classified into two groups, i.e.
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frozen foods and cold foods, and two select keys are
arranged Eor respectively reheating frozen foods and cold
foods. The operation of reheating in this latter apparatus
will be described with reference to the operating panel
shown in Fig. 4.
Heating apparatus of the latter type is provided with
a gas sensor and a weight sensor which detects the weight
of the food to be heated, such as disclosed in USP
4,590,350. For heating the group of cold foods, the thres-
hold value for detection of the gas sensor is set high,and the heating time is calculated by the weight sensor in
accordance with the total weight of the food (including
the packing). The apparatus is so arranged that both the
gas sensor and the weight sensor are controlled in a
parallel relation. Accordingly, food having a small K
value is heated on the basis of the weight detected by the
weight sensor, whi]e food having a large K value is heated
on the basis of time and the amount of moisture detected
by the gas sensor. For heating the group of frozen foods,
the caloric value is changed from the first detection
point when steam is detected as being generated by the
food, and then heating is continued. Thereafter, the
ratio of the time before the second detection point when
it is detected that the generated amount of steam reaches
a predetermined amount with respect to the time lag
between the Eirst detection point and the second detection
point is obtained. Thus an additional heating factor K
corresponding to the calculated time ratio is obtained.
When the value of K is small, the food is determined to
have less moisture and to be easy to warm, and therefore
the additional heating time KxT is made short. On the
contrary, when the value of K is large, the food to be
heated is regarded to be full of moisture and hard to
warm, with a long additional heating time KxT.
~O~Z58
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~ ow heating of the cold food group is carried out in
the prior art apparatus wil~ be explained with reference
to the graph of Fig. 5 which shows the change of the steam
detection points by the gas sensor in accordance with the
lapse of the heating time. Three points marked * are the
conventional detection points of Fig. 3, while the "reheat"
point is a new detection point disclosed in USP 4,590,350.
The new detection point has a considerably higher threshold
value, as compared with the conventional ones, and is
positioned approximately at the center of the conventional
finishing points for "soup" and "curry/stew". "Soup" is
finished a little hotter at the new detection point, and
"curry/stew" which is in a jellied state is still a little
lukewarm at the new detection point, which is no in-
convenience in practice use. On the contrary, however,"cold boiled rice" is considerably overheated at the new
detection point and would be turned solid into a rubber-
like material. Therefore, the weight sensor is employed
to prevent col~ boiled rice or some kinds of soups from
being overheated. Detection points of the gas sensor by
the new threshold value are plotted in Fig. 6 for each
menu. In this arrangement of the apparatus, cold boiled
rice and consomme soup are overheated, while curry and
noodles are finished in an almost favorahle condition.
Therefore, overheating oE the cold boiled rice and consomme
soup is arranged to be solved in the following manner. The
total weight (including the weight of a container) of the
food is measured by the weight sensor, and the necessary
cooking time for the food is calculated on the basis of
the detected total weight of the food. The measurement by
the weight sensor is controlled in parallel (by OR logic)
with the detection by the gas sensor. At this time, if
the calculation formula is suitably selected,
only such menus as cold boiled rice, consomme or milk that
would be overheated if based on the detection by the gas
1~0~;~58
-- 7
sensor can he heated on the basis of measurement of the
weight sensor. This is because, slnce cold boiled rice,
consomme soup or milk is generally put in, for example, a
rice bowl or a teacup having a large capacity (150-~00 cc)
in comparison with its own weight (7n-200 g), the weight
of the Eood with respect to the total weight is large.
Accordingly, the detection hy the gas sensor in the case
of the cold boiled rice, consomme soup or milk is delayed
as compared with the case of noodles or curry/stew, if they
have the same total weight, and therefore cold boiled rice,
consomme soup or milk is located at the upper limit as
shown in Fig. 6. Thus, cold boiled rice, consomme soup or
milk can be automatically cooked on the basis of detection
by the weight sensor.
From experiments, it is found that the above-mentioned
calculation formula can be expressed by a linear expression
To=AWo, wherein the constant A is most preferably 0.3 or so
(To (second) and Wo(g)). Cold boiled rice, consomme soup
or milk is heated well after the weight time as expressed
above. Moreover, when curry, noodles or a small amount of
cooked vegetables (1/2 cup) is heated for the weight time,
the result is better than when it is heated on the basis
of detection bv the gas sensor. That is, the weight sen.sor
is effective to improve a poor correspondence to the volume
of the food of the gas sen.sor (to avold too late a stopping
of heating).
Hereinafter, how the group of frozen foods is heated
in the prior art devices will be described.
The food is started to be heated by a high output, as
shown in Fig. 7. As heating of the food proceeds, the
power is s~7itched to a low output, as shown in Fig. 7(a).
When the gas sensor detects the generation of a small
amount of steam or gas from the food, that is, at the
first detection point, the power is switched to low. The
reason why the heating power is switched from high to low
~A0~ 258
is that, since the food is vigorously heated in the
beginning hy the high output, most of the heating takes
place in only a limited part of the food which suddenly
discharges a great amount of steam. Therefore, a large
part of the food is sufficiently heated when the second
detection point comes, i.e. heating is interrupted earlier.
Accordingly, by changing the heating power from high to
low, the heat in the limited part of the food where the
heating is advanced can be transmitted to other parts of
the food. Thus, while heating continues, the temperature
of the entire body of food is raised to suddenly increase
the amount of steam or gas per unit time at the time
detection time point. When the signal level of the gas
sensor reaches the second detection point in accordance
with an increase in the amount of steam generated from the
food, an additional heating time KxT2 after the second
detection point is obtained based on the ratio of the time
from the start of heating to the second detection point
with respect to the time lag between the first detection
point and the second detection point. Heating is further
continued for the additional heating time and then stopped.
During the time lag between the first detection point and
the second detection point, the food which has been partly
heated is entirely warmed, and accordingly, the time lag
between the first detection point and the second detection
point expresses the conduction speed of the heat in the
material of the food. On the other hand, the time from
the start of heating to the second detection point indi-
cates the volume of the food. Therefore, the food can be
expressed with a genera1 characteristic value identifying
the material and the volume of the food by the above-
mentioned time ratio. If heating is continued after the
second detection point for an additional heating time
corresponding to the product KxT2 of the additional heating
time factor K which is obtained on the basis of the
~30~2S8
characteristic value and the time period T2 from the start
of heating to the second detection point, the food can be
heated in a manner suitable for its kind and volume.
The foregoing description is related to the reheating
of the cold food group and the frozen food group in heating
apparatus of the first and second types. As shown in Fig.
4, two select keys are allotted in the prior art heating
apparatus for reheating the cold foods and the froæen foods
respectively. However, since there are among the frozen
foods some that can be eaten raw if they are only
defrosted, the select keys may be divided into a "defrost"
key and the "defrost-reheat" key. However, this brings
about dangerous possibilities for an erroneous operation
by the user. From the above viewpoint, it is desired to
provide one select key for reheating of all groups of foods
in the best condition.
Accordingly, an essential object of the present
invention is to provide automatic heating apparatus having
a single select key assigned for the reheating operation,
which has been classified into reheating of the cold food
group and reheating of the frozen food group in the con-
ventional heating apparatus, thereby to enhance convenience
for use.
To this end, the invention consists of an automatic
heating apparatus comprising a heating means for heating
an object to be heated; a control means for controlling
said heating means; a first sensor means for detecting
the weight of said object to be heated; a second sensor
means for detecting gas or steams generated from said
object to be heated; and an input means for selecting a
heating sequence, wherein said control means lncludes a
detection means for detecting the weight of said object to
be heated by said first sensor means, a calculation means
for calculating an identification time period to judge the
kind of object to be heated on the basis of the detected
~:~0~2S8
- 10 -
weight, a timer means for indicating that heating is
performed for said identification time period, a
comparison means for comparing the change value of the
signal level detec~ed by said second sensor means with a
predetermined identification value when said identification
time has passed, an identification means for identifying
the kind of said object to be heated on the basis oE the
comparison result, and a changing means for changing the
heating sequence depending on the identified kind of object
to be heated.
The invention also consists of an automatic heating
method comprising the steps of: (1) operating a heating
sequence select key and an input key for starting heating,
with an object to be heated placed in a heating chamber;
(2) starting heating of the object to be heated, while the
weight of the object to be heated (including the packing)
is measured, and the initial state of the food to be heated
in the gas sensor section is watched; (3) calculating the
indentification time for judging the kind of the food to
~e heated on the basis of said watched welght value; (4)
comparing the difference amount (change amount) between
the state in the gas sensor section when the time passed
from the start of heating reaches said identification time
period and in the initial state, with a predetermined
value; and (5) selecting a heating sequence from among
many heating sequences based on the comparison result of
the difference arnount with the predetermined value.
With reference to Fig. 8, showing an operating panel
of automatic heating apparatus of the present invention,
various select keys 4 are arranged on the operating panel
3. It is arranged that every reheating operation is per-
formed ~y depression of a single "mighty reheat" key 5.
Although two reheat keys are provided in the prior art
devices, respectively for the cold food group and the
frozen food group (referring to Fig. 4), a single
1301258
"already-cooked reheat~ key 5 is enough for both the cold
food group and the frozen food group according to the
present invention. The reason for this will be made clear
hereinbelow.
The apparatus is provided with two sensors. A first
sensor is a weight sensor which detects the total weight
of the food (including the packing). One example of such
a weight sensor as above is a weight sensor manufactured
by the assignee of the present application, Matsushita
Electric Industrial Co., Ltd., which is in the form of an
air condenser having two ceramic base plates with metallic
films attached so that the metallic films are opposite
each other through an air layer. In the Matsushita weight
sensor, the capacity of the condenser is changed in
accordance with the scale of the weight load. Thus, the
total weight of the food to be heated is detected by the
first sensor means when the food is started to be heated,
and the time value Tw is calculated on the basis of the
detected weight. On the other hand, a second sensor means
is a gas sensor which detects gas or steam generated from
the food. The gas sensor is, for example, a specific
humidity sensor ~Neo-humi-SERAM~, manufactured by
Matsushita Electric Industrial Co., Ltd., or a gas sensor
manufactured by Le Figaro.
Fig. 9 shows detection points by the gas sensor and
the detection time of the food by the weight sensor, etc.
Specifically, Fig. 9(a) shows the case where the cold food
group is heated, and Fig. 9(b) shows the case where the
frozen food group is heated. The operation common to both
cases is that the total weight of the food is detected
when the food is started to be heated, and it is watched
se~uentially whether the amount of steam generated from
the Eood before the time point Tw calculated on the basis
of the detected total weight of the food is changed, such
watching taking the form of the signal level of the gas
* Trade Mark
,~ .
,i~
13~258
sensor changing from the initial value V by the level ~g
or hy the level ah. Wlth a change by the level ah observed
at the time point Tw, the food to be heated is judged to
be the cold food group, and the food is continuously heated
as it is. On the other hand, without the change by the
level h observed at the time point Tw, the food to be
heated is determined to be the frozen food group, and the
heating caloric value is switched while the food is con-
tinuously heated. By noting the time period Tw determined
by the total weight of the food, the food can be classified
into the group of cold foods or the group of frozen foods,
because it has been made clear from experiments that, as
shown in Fig. 10(a), the cold food group displays the
change ~h earlier than the calculated time point Tw=AxW+~,
while the frozen food group shows the change ~h later than
the time point Tw=AxW+~. Logically explaining the above-
described phenomenon, even when a cold food and a frozen
food having the same weight are heated by the same heating
caloric value, the initial temperature of the food is
different, that is, the initial temperature of the frozen
food is below the freezing point, whereas that of the cold
food is above 0C. Even if the cold food had been placed
in a refrigerator, the initial temperature thereof is about
5C. Consequently, the accumulative heating caloric value
necessary for raising the initial temperature of the food
to the boiling temperature at which steam is generated
from the food is different, and the time period
representing the difference of the accumulative heating
caloric value is longer in the frozen food than in the
cold food. In the manner as above, according to the
present invention, the food to be heated can be classified
into the cold food group or the frozen food group in the
same single heating sequence, and therefore a single
select key can perform automatic reheating of various
~3~2513
- 13 -
kinds of foods such as "cold boiled rice", "soup",
"curry/stew", "frozen rice" or "frozen curry".
It has been found by experiment that the formula for
identifying the food to be heated on the basis of its
5 weight can be expressed by a linear expression: Tw=AxW+B
wherein constant A is optimum at about 0.25, and constant
B is optimum at about 30, with Tw being seconds, W being
grams, and B being seconds. Even when the total weight of
the cold food is different +200g from that of the frozen
lO food, because of the weight difference of the packing, the
identification of the food is done correctly. Therefore,
by this linear expression, the food can be heated in a
manner suitab]e to its nature.
The construction of the apparatus will now be
15 described.
Referring to Fig. 11, various commands inputted
through depression of the selected key 4 on the operating
panel 3 are read in a control section 6 and displayed in a
predetermined manner, thus control]ing the progress of the
20 heating. Reference numeral 5 indicates a "reheat" key.
Food 8 to be heated is placed in a chamber 7 and heated
by a magnetron 9 which is a high-frequency generating
means. The supply of power to the magnetron 9 is
contro]led by the control section 6 through a driver 10.
25 A fan 11 is provided to coo] the magnetron 9 and at the
same time to venti]ate the chamber 7. In a guide 12 for
discharging the exhaust out of the apparatus there is
provided a second sensor means, namely, a gas sensor ]3
which detects gas or steam generated from the food, thereby
30 giving information on the heating condition to the control
section 6 through a detector circuit 14.
The apparatus is also provided with a first sensor
means, i.e., a weight sensor 15 which detects the total
weight of the food 8 on a platform 16. The control section
35 6 is formed of microcomputers. The gas sensor 13, which
1301258
- ~4 -
makes use of the fact that an electric characteristic such
as the resistance value of a sensor element or capacity of
a condenser is changed as the density or the amount of the
liquid component of the steam and an aromatic organic gas
5 or an aromatic inorganic gas, etc. in the air is changed,
is served by a specific humidity sensor manufactured by
Matsushita Electric Industrial Co., Ltd. or Tokyo Shibaura
Co., Ltd., or a gas sensor produced by Le Figaro. A
pressure gauge of an air condenser system manufactured by
10 Matsushita Electric Industrial Co., Ltd. may be employed
for the weight sensor 15.
Although the formula for ohtaining the detection time
of the food by the weight sensor is a linear expression
T2=AxW+B (A and B are constants) in the present embodiment,
15 an expression of a higher degree can be selected. Needless
to say the value of the level ~h is peculiar to the
apparatus, and the most suitable value can be selected for
each apparatus.
Fig 12 is a circuit diagram showing the construction
of the circuit controlled by a micro-computer 17. A
command inputted from the select key 4 to input terminals
I0-I3 of the microcomputer 17 is decoded in the micro-
computer 17, to generate a predetermined output. For
example, when the "reheat" key is depressed, the micro-
computer 17 makes the display "Al" in a display section18. The display section 18 is driven to be dynamically
turned on in order to decrease the s:ignal lines. Lighting
data is outputted to data outputs D0-D7 and a digital
control signal is outputted to digital outputs S0-S4. The
digital control signal is also used for sweeping of the
key matrix 4. An output of the gas sensor 13 is inputted
to an A/D conversion input terminal A/D of the micro-
computer 17 in which the change of the resistance value as
a result of the change of the steam amount is measured.
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An output of the weight sensor 15 is inputted to the
input terminal T~ of the microcomputer 17 through a
detection circuit 19. The detector circuit 19 is formed
by an oscillation circuit and a bridge circuit, etc.
Upon starting of heating, relay control outputs R0 and
Rl are outputted from the microcomputer 17 through a
driver 20. A relay switch 21 controls outputting of the
microwave through intermittent operatlon thereof, and a
relay switch 22 controls the supply of electricity to the
heating apparatus. The magnetron 9 serves to supply the
microwave energy to the heating chamber. The apparatus
also has a motor 23 for the cooling fan, etc., a light 24
inside the apparatus, a door switch 25 operated con-
currently with opening or closlng of the door, and a
bu%zer 26 for notifying the user of the end of the heating
process.
Figs. 13 and 14 are flow-charts of the control program.
First, the microcomputer 17 and the control circuit are
initialiæed by initial setting. Then, the display decoder
is controlled in the manner as explained with reference to
Fig. 12. Thereafter, it is judged whether cooking is being
carried out. If cooking is not being performed, an
inputted key is read. When the "reheat" key is selected,
with the food to be heated inside the heating chamber, and
the "heating start" key is depressed, then heating is
started. Simultaneously with this, the weight (Wg) and
the initial humidity condition (V0 level) of the food to
be heated are detected by the weight sensor and the gas
sensor, respectively. Then, three heating stop time
periods, TLl, TL2 and TL3, together with an identification
time period Tw for stopping heating in accordance with the
condition of the food, are calculated (a). Meanwhile,
upon start of heating, the humidity condition (V) is kept
watched, and also the passed time (T) is continuously
1:~0~258
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observed (b). In order to stop heating of food among the
cold food group, such as cold boiled rice that is easy to
warm and fast to generate steam in the heating stop time
period TLl calculated on the basis of the Eood weight, it
is arranged to watch whether the amount of steam generated
from the food is changed by the g level corresponding to
the change of the signal level of the gas sensor. When
the humidity change by the g level is noticed, with the
time period TLl passed, heating is immediately stopped
(c). At this time, if either one of the above conditions
is not satisfied, that is, the humidity change of the g
level is not observed or the time TLl is not passed,
heating is not stopped, but it is determined whether the
passed time T is the time period Tw which is obtained on
the basis of the food weight (d) (1-3 levels are designated
for g). When the passed time T is over the time T2, it is
compared and detected whether the food is heated so much
that the steam generated from the food changes the signal
level of the gas sensor by the h level, or whether the
amount of the generated steam is too small to cause a
change by the h level. As a result, one of the first
heating processes for the cold food group and the second
heating process Eor the frozen Eood group is selected for
the heating sequence (e) (5-12 levels are assigned for
h). In this manner, the food is classified by the presence
or absence of a change over the h level of the signal
level of the gas sensor in comparison with the lnitial
value in the time period Tw determined on the basis of the
food weight.
According to the second heating process for the frozen
food group, heating by the microwave energy is inter-
mittently done as shown in Fig. 14(f). The humidity
condition (V), the passed time (T), etc. are watched (g).
It is determined whether or not the passed time (T) is
beyond the heating stop time TL2 which is calculated on
~l301258
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the basis of the Eood weight W (h). The value of f is so
determined that there is no ~ood that has been heated over
the time TL2 and is reheated, and which generates too
small an amount of steam to bring about the change of the
f level. In other words, the value of f is so set as to
prevent the dangerous state that food that is too dry or
unfit for reheating is continuously heated and scorched or
set on fire. In the case where the signal level of the
gas sensor is changed hy the f level, heating is continued.
However, if the signal level of the gas sensor is not
changed by the f level, the food is regarded as being in a
dangerous condition and heating is stopped (i) (2-5 levels
are selected for f). Even for heating of the frozen food
group, the time when the h level change in the signal
level of the gas sensor is observed as the food is heated
to become warm is memorized as the first detection time
point Tl (j), with the aim that when the passed time is
beyond the TL3 calculated on the basis of the food weight,
it can be detected either that the food is fully heated
for automatic heating and cooking, or that the food is in
such a condition that not enough steam is generated from
the food to make the heating condition ready for automatic
heating and cooking in spite of the h level change observed
in the signal level of the gas sensor. If insufficient
steam is generated from the food, heating is stopped to
prevent the food being heated too much and scorched or set
on fire (k). Thereafter, the food is heated enough before
the second detection point when the signal level of the
gas sensor is a times the initial value V0, with the
generated steam filling the heating chamber (Q). The time
period passed before the second detection point is
memorized as T2. The time factor K for setting an
additional heating time is calculated on the basis of the
ratio of the time lag (T2-Tl) between the first detection
~:301258
point T1 and the second detection point T2 with respect to
the passed time period T2, so that the additional heating
time is obtained by the product of the passed time period
T2 and the factor K (m). Thus, heating is continued for
the additional time KxT2, to complete heating of the frozen
food in the second heating process.
Although heating is carried out slowly by the inter-
mittent supply of electromagnetic energy in such second
heating process, it goes without saying that the food to
be heated can be supplied with small heat, such as the
heat of an electric heater or of gas combustion, thereby
to realize heating of the whole frozen food in a moderate
manner.
Moreover, also in the case of reheating of cold food
in the first heating process, for identifying the kind of
food to be heated, an additional heating time factor K is
calculated based on the ratio of the time lag (T2-Tl)
between the first detection point Tl when the h level
change in the signal level of the gas sensor due to the
steam generated from the food is observed and the second
detection point T2 when the change of the signal level of
the gas sensor due to the generation of steam from the
food becomes ~ times the initial value V, with respect to
the time period T2 passed before the second detection
point. The additional heating time KxT2 is then obtained
by the product of the calculated additional heating time
factor K and the passed time T2. After heating Eor the
additional heating time, heating is EinalLy stopped.
Since the additional heating time KxT2 is calculated
based on the time lag between the first detection point
and the second detection point, which time lag changes
depending on the material and the amount of food and the
condition of the container of the food, the additional
heating time KxT2 can be determined to correspond to the
condition of the food, whether it is cold food or frozen
i3~)~258
- 19 -
food.
The additional heating time factor K ca]culated on the
basis of the ratio (T2-Tl )/T2 reflects the condition of
the food as follows. The time lag between the first
detection point and the second detection point reflects
the difference of the food, namely, that the food to be
heated has low heat conductivity and needs a long time to
be totally heated or that the food can be heated fast in a
short time. Further, when the food is covered with a
wrapping made of a transparent resinous film, time is
necessary beEore the steam is generated from the food and
gathered in the food so much as to break the wrapping
after the food gets warm, and a large amount of steam is
generated all at once after the wrapping is broken.
Accor~ingly, the time lag between the first detection
point and the second detection point becomes small. On
the contrary, without wrapping, steam is generated
gradually in accordance with the temperature rise of the
food, and therefore the first detection point comes soon
in a short heating time, resulting in a larger time lag
between the first detection point and the second detection
point. As described above, the time lag differs depending
on whether the food is wrapped or not, or by the
characteristic of the heat conductivity of the food, etc.
Moreover, when the total weight of the Eood is large, the
time before generation of steam from the whole of the food
becomes long. Therefore, if only the time lag between the
first detection point and the second detection point is
taken into consideration, it is difficult to determine
what the time lag results from, namely, the difference of
the kind of the food, whether the food is easy to generate
steam per unit weight, or whether the food is easy to
warm. Beca~se of this fact, the time period T2 passed
before the second detection point is employed for
representing the total weight of the food, and the ratio
13012S8
- 20 -
of the time lag hetween the fiest detection point and the
second detection point with respect to the passed time
before the second detection point are calculated.
Accordingly, the ratio can be regarded as a characteristic
value of the food, in consideration of the material,
condition, and total weight of the food.
As is made clear from the foregoing description, the
automatic heating apparatus described herein has the
following effects and merits.
(l) The apparatus employs both a gas sensor and a
weight sensor, so that it watches how much the signal
level of the gas sensor is changed as compared with the
initial value thereof at the start of heating in the time
calculated on the basis of the weight of the food
(including the packing), thereby to detect the presence of
a large change of the signal level over the predetermined
value. Reheating can thus be performed by depression of a
signal "mighty reheat" key. Accordingly, the user of the
apparatus need not be concerned with which key to select,
and therefore the operating efficiency is remarkably
improved. Nevertheless, the finished menus are as good as
in the conventional heating apparatus having 4-5 select
keys.
(2) The poor correspondence of the gas sensor to the
weight of food is improved by the weight sensor. There-
fore, the heating can be so controlled as to be stopped
even when a small increase of the amount of steam generated
from the food is detected in the time calculated on the
basis of the total weight of the food detected by the
weight sensor, thus preventing overheating of foods that
generates little steam.
(3) Even when the amount of steam generated from the
food is not so much as to change the signal level of the
gas sensor to a predetermined level, although the weight
of the food is enough, or the signal level of the gas
~301~58
- 21 -
sensor is not chanqed due to hreakage of the gas sensor,
i.e., even under particular conditions for automatic
heating, it can be prevented that the precious food is
heated too much and scorched. Moreover, even if the
5 apparatus is operated without any food in the heating
chamber, since it will happen that no change is brought
about in the slgnal level of the gas sensor correspondinq
to a predetermined amount before the heating time detected
on the basis of the detection of the weight sensor, heating
10 is safely stopped in quite a short time.
(4) Even when the food weight is enough, and the
signal level of the gas sensor is changed by the generated
steam to a predetermined first level change, but not to a
second level change, namely, even when dry food is heated
15 or a frozen meat bun contained in a large heavy container
is heated, under particular conditions for automatic
heating, such an accident that the food is overheated and
scorched can be prevented, since it is arranged to stop
heating by the time calculated on the basis of the food
20 weight. Further, even if noises from outside, such as the
microwaves of the heating apparatus, discharging noises of
a relay contact or induction surge noises of the trans-
former or motor arrive at the control section during
heating, and consequently the normal change of the signal
level of the gas sensor is not transmitted to the control
section, heating is stopped by the time calculated on the
basis of the food weight, without keeping heating until
the signal level of the gas sensor reaches the level at
the second detection point (impossible level). The
apparatus of the present invention is thus safe.
As has been described hereinabove, the present
invention enables the operating keys to be simplified,
with the heating apparatus provided with a gas sensor and
a weight sensor, such as an electronic oven, an electric
oven, a combination oven, or a gas oven. Moreover the
13~ 5l!3
- 22 -
heating apparatus according to the present invention is
provided with sensors, not a single sensor, so as to
detect the condition of the food to be heated time after
time~ so that the heating time can be controlled properly
to prevent overheating of the food. As a result, the
heating apparatus of the present invention enjoys a great
improvement in safety.
Although the present invention has been fully described
in connection with the preferred embodiments thereof with
reference to the accompanying drawings, it is to be noted
that various changes and modifications are apparent to
those skilled in the art. Such changes and modifications
are to be understood as included within the scope of the
present invention as defined by the appended claims unless
they depart therefrom.
