Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SPECIFICATION
TITLE OF Tile INVENTION
Heating Appliances
TECHNICAL FIELD
This invention relates to an automatic cooking
appliance and more particularly to a cooking appliance
capable of automatic control of cooking with the aid
of a sensor responsive to a steam emanating from a
heating load.
BRIEF DESCRIPTION OF TIE DRAWINGS
Fig. 1 is a side elevation view, in section,
showing a cooking appliance as an embodiment of this
invention;
Fig. 2 is an enlarged perspective exterior view
showing a sensor segment in the same appliance;
Fig. pa e are characteristic curves representing
changes in relative humidity and heating patterns of
the conventional cooking appliances;
Fig. pa is a characteristic curve representing
the change in the amount of steam in a cooking
appliance which is an embodiment of this invention;
Fig. 4b is a characteristic curve representing
the heating pattern of the same appliance;
Fig. 4c is a characteristic curve representing
the heating pattern of a second embodiment of this
invention;
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Fig. Ed is a characteristic curve showing the
heating pattern of a third embodiment of this
invention;
Fig. 5 is an electric circuit diagram for the
first embodiment of this invention;
Fig. 6 is another circuit diagram for said first
embodiment,
Fig. 7 is an electric circuit diagram for said
second embodiment;
Fig. pa, b are side-elevation views, in section,
showing a cooking appliance of a fourth embodiment of
this invention; and
Fig pa, b, c are characteristic curves showing
the heating pattern and the changes in the amount of
steam and in relative humidity in the same cooking
appliance.
BACKGROUND ART
The conventional microwave range is generally
such that as shown in Fig. a relative humidity
sensor 12 responsive to a steam emanating from a
heating load 2 is disposed in a heating chamber or an
exhaust air duct 12, with the result that in prolonged
use of the appliance the sensor 12 is gradually fouled
with liquid splashes, vapors, oily fumes, etc. from
the heating load, and, as a consequence, loses its
initial performance characteristics and sensitivity.
To solve this problem, there was proposed a cleaning
system in which a coil heater 14 disposed in the
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vicinity of a sensor element 13 as shown in Fig. 2 is
energized immediately after the start ox cooking to
heat the sensor element 13 to a temperature of a-t
least 400C and to thereby burn out the fouling matter
deposited thereon and preserve the performance an
sensitivity characteristics of the sensor.
However, aster cleaning ox the sensor 12 and
suspension of the current supply to the coil heater
14, the sensor 12 does not immediately resume a
satisfactory and stable detection performance. The
reason will be explained with reference to Fig. pa.
Fig. pa is a characteristic graph obtained by plotting
time on the horizontal axis and relative humidity on
the vertical axis, showing changes in relative
humidity within the exhaust air duct 11 after the
start of heating at point A. At this start point A,
cleaning of the sensor 12 also begins so that the
ambient temperature of the sensor undergoes a sharp
increase due to heating by the coil heater 14 and
accordingly the relative humidity decreases
progressively toward point B. The point B is a point
where the sensor 12 has reached a predetermined
temperature and gone through cleaning. Since the
current supply to the coil heater 14 is suspended at
point B, despite a small overshoot, the sensor 12 is
cooled by the exhaust air current and gradually
returns to the normal temperature, so that the
relative humidity increases toward point C. after the
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sensor 12 has returned to issue normal state at point C,
as the temperature of -the exhaust air increases,
though gradually, with the progress of heating, -the
relative humidity decreases toward point D. This
point D is a time point where the increment of
relative humidity due to the steam generated from the
heating load 2 overcomes the decrement of relative
humidity due to a temperature increase of the exhaust
air, and as the amount of steam generated from the
heating load 2 continues to increase thereafter, the
relative humidity keeps increasing to point E and to
point F.
It is general practice to detect the amount of
change in relative humidity ASH at point D and onwards
to automatically control the output of a magnetron 3
and, therefore, heating. From Fig. 3 it is apparent
that such a change of relative humidity RHO occurs
also in the interval between point B and point C '-
during which the sensor after completion of cleaning
returns to the normal state but since the change in
relative humidity in this interval is not the one
caused by steam emanating in a large quantity from the
heating load 2, it cannot be utilized for the
detection of heating. It follows that there must be a
waiting time of lo before the sensor 12 becomes fully
responsive. Now, let it be assumed that heating was
started at a high outplay lo of. when a small load 2
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is heated, -the relative humidity would have reached
100% by the time whelp the sensor 1.2 would have
returned to its normal state, i.e. time-point lo, so
that when lo has arrived, the change in relative
humidity RHO would no longer be detected. T~lercfore,
there was proposed a system in which, as shown in Fig.
3b, a zero output is maintained up to time-point lo
after start of cooking and, then, switched to a high
output.
In such system, however, there is actually no
heating at all during the time after the start of
cooking till time-point lo, so that the time required
for heating is prolonged by lo and, therefore, the
time efficiency of the appliance is adversely
affected. Therefore, it was proposed, as illustrated
in Fig. 3c, to start heating at a high output level at
if which precedes lo so as to improve the time
efficiency by (lo - to However, the time point if
must be determined with utmost care so that there will
not be a large output of steam from the heating load
2/ etc. due to high-output heating during the time (lo
- to). It was found that about I seconds is a
maximum time period that can be alloyed to (lo - if).
Although this is conducive to some improvement of time
efficiency, Kit does not result in a practically useful
improvement.
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still another known system is shown in Fix. clue.
This system is such that heating is effected at a low
output level PLY up to a pretermined time point to'
and, thereafter, at a high output level.
There is also known a still another system as
illustrated inlFig. ye. This system consists of an
intermittent operation phase of ON for time To and OFF
for time To during a predetermined time period if"
and, after to", a continuous operation phase at a high
output level. As it is true of the foregoing systems,
the factor of low output Pi and the time elements if',
to To and To must all be determined and set in
relation to the heating load 2. In other words,
output must be determined so that no large amount of
steam will be liberated from the heating load.
However t if the energy absorbed by the heating load 2
up to the time lo after the beginning of cooking
exceeds a given level, a large amount of steam is
generated, with the result that any improvement of
time efficiency realized is not greater than that
achieved by the earlier system illustrated in Fig. 3c.
DISCLOSURE OF TIRE INVENTION
This invention relates to a cooking appliance
wherein a means of heating and cleaning a humidity
sensor element is operative only for a predetermined
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time within the time period after inputting of an
input signal representing a start of cooking till a
humidity sensor means returns to its responsive state,
the heat output of said heating means being switched ..
to a low output or suspended immediately before said
humidity sensor means returns to its responsive state,
the exhaust air containing the steam or gas emanating
from a heating load is temporarily decreased by forced
exhaustion or bypassing via a passageway in which said
sensor means is disposed, and the heating output is
increased after the humidity sensor has regained its
sensing performance.
In the above construction, even if a large amount
of steam or gas is evolved on sufficient heating of
the heating load before the sensor means regains its
sensing performance, the heat output has already been
switched to a low level or stopped before the sensor
means becomes sensitive again, with the result that
the amount of steam or gas generated is decreased to a
level approximating that prevailing immediately after
the beginning of heating and after the sensor means
has become sensitive again, it functions as if there
had been no heating at all before so that the heating
state of the load can be accurately detected.
Therefore, whereas it was formerly impossible to
effect heating only sparingly before the sensor means
regains its sensing perforr.lance in order to prevent
generation of a large amount of steam or gas, it is
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now possible to detect the cooking state with accuracy
and hence to effect sufficient heating so that there
can be implemented a cooking appliance having a
remarkably improved time efficiency.
BEST MODE FOR CARRYING OUT TIE INVENTION
(First Embodiment)
Referring to Fix. 1, the reference numeral 1
denotes a heating chamber in which a heating load 2 is
heated by high frequency energy generated from a
magnetron 3. Designated by the numeral 4 is a fan
motor which not only cools the magnetron 3 and other
elements but also forces a ventilation air current 7
into the heating chamber through an air duct 5 and air
apertures 6. An exhaust air current 9 containing
steam 8 as emanating from the heating load 2 is
discharged into an exhaust duct 11 through exhaust air
apertures 10. There is also provided a sensor means
12 which senses the relative humidity of the exhaust
air current 3. In Fig. 2 is shown an enlarged view of
the sensor means 12 (hereillafter referred to briefly
as sensor). Indicated at 13 is a sensor element,
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while a coil heater 14 is disposed in the vicinity of
the sensor element 13. The numeral 15 denotes a
ceramic support.
The heating output control as a distinct feature
of this invention will be explained with reference to
Fig. pa, b.
Referring to Fig. 4, heating is commenced at a
high output immediately at the start of cooking and
continued up to a predetermined time point to and,
then, heating is suspended till time point lo when the
humidity sensor 12 will have regained its normal
sensing performance. When lo has been reached,
heating at said high output level is restarter.
he change in the amount of steam in the heating
chamber 1 is shown in Fig. pa. The amount of steam at
the beginning of cooking depends on the environment in
which the electronic range is located. By the heating
at a high output level during the time from the start
of cooking till time t , the amount of steam is caused
to increase to x2. however, since the heat output is
zero during the time from to to time lo when the
sensor 12 will have become sensitive again, there is
no evolution of steam in this period and the steam in
the heating chamber is discharged from the chamber 1
by the fan motor 4, with the result that the amount of
steam in the heating chamber 1 returns to the initial
amount Jo. Thus, heating during the period from the
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start of cooking till to does not exert any influence
on the detection of relative humidity. Furthermore,
even if a large amount of steam is generated by
heating during this time after the start of cooking
till time to, substantially the initial environment
can be reestablished during the time from to through
lo so that a sufficient energy can be applied to the
heating load during the time after the start of
cooking till time to. Therefore, heating time can be
decreased by time to, with a consequent improvement of
time efficiency.
Fig, 5 shows an exemplary electric circuit
diagram for this arrangement. The reference numeral
16 denotes a commercial line source and the numeral 17
denotes a contact interposed in a main circuit, said
contact 17 being brought into ON position at the start
of costing to apply a voltage to the fan motor 4.
There also are provided a high voltage transformer 19,
a high voltage capacitor 20 and a stack diode 21 which
is a positive pole power supply for the magnetron 3.
Indicated at 23 is a high voltage lead relay contact
which turns on and off a supply of positive pole
voltage to the magnetron 3. Indicated by the numeral
22 is a coil thereof which is controlled by a control
section 18 including a microcomputer.
Another embodiment of the above electric circuit
is shown in Fig. 6. The reference numeral 25 is a
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relay and its coil I is controlled by a control
section 18. The relay 25 an coil 24 may be
implemented with a trial.
With the circuit constructions shown in Fig 4
and Fig. 5, the high voltage lead relay 23 in Fig. 4
or the relay 25 in Fig. 5 is switched on to excite the
magnetron 3 during the period after the start of
cooking till time to, switched off after time to and
switched on again after time lo to excite the
magnetron 3. In this manner, heating can be
accomplished at a high output level. In the circuit
of Fig. S where the relay 25 is on the low voltage
side which is the primary side of the high voltage
transformer lo the construction does not require a
special relay switch and, therefore, is economical.
(Second Embodiment)
Another embodiment of this invention is shown in
Fig. 4c. In this embodiment, heating is effected at a
high output level up to a predetermined time point
to', then at a low output PLY up to time point lo when
the sensor will have regained its normal sensing
performance, and again at said high output after time
lo. The amount of steam generated from the heating
load 2 depends on the amount of heat applied to the
load 2. Therefore, provided that said low output PLY '
is set at a level where the generation of steam is
negligible, it is possible to regain, at lo, a state
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almost similar to the state prevailing immediately
after the star-t of cooking as explained for the
embodiment ox Ego. 4b. Fig. 7 shows an electric
circuit for implementing this embodiment. The
reference numeral 28 denotes a output switch relay
contact and when it is ON, a large composite capacity
is obtained from a first high voltage capacitor 20 and
a second capacitor 26 connected in parallel therewith
so that the high frequency energy output of the
magnetron 3 is at a high level while it is at a low
level when the contact is off. The reference numeral
27 represents a coil of the output switch relay, which
is driven by signals from a control section.
(Third Embodiment
Fig. Ed shows a still another embodiment.
Simultaneously with the start of cooking, heating is
started at a high output level and continued at that
level up to a predetermined time point to" and,
therefore, it is off during period To up to time point
lo and on again during period To. Thus, the output is
switched to the high level at lo. The energy output
during the period from to" to lo is substantially low,
and in the determination of times To and To it must
be similar to the low output PLY mentioned earlier
with reference to the embodiment shown in Fig. 4c.
This embodiment may be implemented with the electric
circuits shown in Figs. 5 and 6.
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It will be apparent from the above description
of First through Third Embodiments that a still
further improvement of cooking time efficiency can be
accomplished my heating the load at a substantially
low output during the period of to' to lo and during
the period of to" to lo.
(Fourth embodiment)
A still another embodiment of this invention is
shown in Fig. pa, b.
referring to Fig. pa, the reference numeral l
denotes a heating chamber in which a load 2 is heated
by a high frequency energy generated from a magnetron
3. The numeral 4 represents a fan motor which not
only cools the magnetron 3 but also ventilates the
heating chamber l via an air duct 5 and air current
apertures 6, the exhaust air being discharged into an
exhaust air duct 11. The other flow is directed to
the exhaust air duct if via the duct 5. The exhaust
air duct 11 is partially divided into an upper portion
and a lower portion by means of a partitioning plate
29. sensor 12 is mounted in the upper one of these
portion. The exhaust air duct is communicating with
the air duct 5. Formed in the exhaust air duct is a
valve 30 which is operated by a solenoid 31. The air
forced against the sensor 12 by the valve 30 is
switched between the air from the air duct 5 and the
exhaust air from the heating chamber.
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The operation of the system having the above
construction will be explained below.
At the start of cooking, the valve 30 is set in
the position shown in Fig. pa, so that only a cooling
air for the magnetron 3 is sent to the sensor 12, and
after the sensor 12 has become sensitive again, the
valve 30 is shifted to the position shown in Fig. 8b,
whereby only the exhaust air from the heating chamber
is supplied to the sensor 12. At this time, the high
frequency energy is applied as shown in Fig. pa. The
state of steam generation and the change of relative
humidity in the vicinity of the sensor 12 are shown in
Fig. 9b and ~ig.9c, respectively. By the heating
during the time period from the start of cooking to
time point lo, the amount of steam is caused to
increase from x0 to xc. On the other hand, the
relative humidity changes from the initial level Rho
toward a low humity side once due to cleaning of the
sensor 12 but as the sensor 12 is cooled by the air
from the air duct 5, returns to substantially the
initial level Run at time point lo. Thereafter, the
valve 30 is switched so that the sensor 12 is supplied
with the exhaust air from the heating chamber 1.
Therefore, due to the steam XC which had been
generated by the time lo, the relative humidity
increases to RHO. If (RHO - Rho has reached a
predetermined amount of change in relative humidity
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aurora it is presumed that the heating load 2 has
reached a given cooked state and the heating is
automatically controlled. If it remains yet to reach
said predetermined amount of change, the relative
humidity drops, though gradually, due to the
temperature increase of the exhaust air as illustrated
in Fig. 9c. With the relative humidity RHmin at the
point when the increment of relative humidity due to
steam exceeds the temperature increase as a threshold
level, the subsequent sharp increase of steam results
in an increase of relative humidity RHO The increase
of RHO is detected from RHmin and the heating is
automatically controlled. In this manner, the sensor
lo is exposed to the exhaust air after returning to
its responsive state and, up to that time, exposed to
an atmosphere almost similar to the initial condition,
so that even if a large amount of steam is generated
prior to lo, the sensor 12 always detects the initial
environment at lo and, then, detects the exhaust air,
with the result that the generation ox steam prior to
lo can be detected. Moreover, even if a large amount
of steam is generated after lo, the relative humidity
can be sensed as in the First embodiment. In this
manner, heating can be continuously effected from the
start of cooking to lo and further thereafter, so that
the time efficiency is not adversely affected at all.
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INDUSTRIAL APPLICABILITY
In accordance with this invention, the following
results can be expected in electronic ranges,
electronic ovens, etc.
I Since, in accordance with this invention, the
sensor element is cleaned up at the start of
cooking, a stable detection performance is
ensured at all times. Moreover, as heating is
effected without waiting for the sensor to become
responsive, a satisfactory time efficiency is
realized.
I Since an environment substantially identical with
the one immediately after the start of cooking is
assured immediately before the sensor returns to
its responsive state, the sensing performance of
the sensor after becoming responsive is as exact
as the sensing described for the conventional
systems and, in addition, a large energy can be
applied before the sensor returns to its
responsive state, the cooking time can be reduced
in a significant measure.
