Heating time control means for a heating appliance

By intermittently starting and stopping a timer motor of a timer which is a heating time setting device by means of an intermittent switch to turn on and off the power source, two speeds are obtained, and one timer may be used to set both a long time and a short time, and moreover when the timer is set for a long time, the input of heating means is also connected and disconnected so as to obtain a heating output which makes possible simmering or stewing.

FIELD OF THE INVENTION 
This invention relates to improvement of the means to control the heating 
time setting device and heating source in heating appliances for cooking 
such as electric oven and microwave ovens. 
BACKGROUND OF THE INVENTION 
For example, conventional high frequency heating appliances for cooking are 
very convenient cooking appliances capable of heating efficiently and 
rapidly because only the object to be heated, e.g. food, is heated by 
induction. Or, depending on the menu of cooking, it is also possible to 
heat for a long time at low output by controlling the high frequency 
output for thawing, egg dishes, or long and slow cooking food such as 
stew, and high frequency heating appliances with an output selector have 
been conventionally used and provide expected effects. In particular, 
since stewing requires a very long heating time at low output, the heating 
time setting is naturally very long. For instance, while a setting of 15 
minutes or 20 minutes may be sufficient for the usual high frequency 
output induction heating at about 500 W or 600 W, a setting of about an 
hour is necessary for stewing because of heating at a high frequency 
output of about 1/3 of the usual heating, and it is very inconvenient if 
the conventional appliance permits a time setting of only 15 or 20 
minutes. 
In one of the conventional examples, as shown in FIG. 1, the object e.g. 
food, to be heated (not shown) is put on a turntable 2 in a heating 
compartment 1, the door 3 is closed, and a timer 4 for high output is set 
to a proper heating time according to a menu table 5 depending on the kind 
and size (weight) of the food, and the cooking start button 6 is pressed, 
and when the timer 4 expired, the cooking ends. In this arrangement, 
however, two timers are required, one for usual heating and the other for 
long-time setting for stewing. 
One of such examples is shown in FIG. 2. There is a selector for high 
frequency output, and a timer 4 for high output and a timer 7 for low 
output are used. The heating time is set by the timer 4 where high output 
was needed, and by the timer 7 where low output is needed for stewing or 
the like. 
Its circuit is shown in FIG. 3, in which a time switch 8 is turned on when 
the low output timer 7 is actuated, and the timer motor 9 for low output 
begins to rotate at the same time. In this operation, the time switch 8 
remains closed until expiration. 
As an attempt to solve this problem, a two-speed timer 10 has been used for 
setting both long time and short time. That is, as shown in FIG. 4, the 
time setting is divided at about 20 minutes, and a heating time of up to 
20 minutes can be easily set on large graduations, and a longer time is 
set on small timer graduations which are operating time display 
graduations, so that the timer operating speed may be varied by an output 
selector button 13 in order to set a long time. 
In the heating appliance for cooking having such design, however, when the 
operating speed of the timer motor is varied, a time lag occurs 
structurally, and a discrepancy of about two or five minutes occurs 
relative to the setting graduation due to the error between the angle of 
inducator 11 of the time switch for varying the operating speed and 
graduations 12 of two-speed timer 10, which results in poor finishing of 
the cooking due to the discrepancy of heating time as described above. 
Yet, since the structure is extremely complicated as compared with that of 
one-speed timers, and the cost of parts is as high as for two timers and 
the quality is inferior because of the complicated structure. The only 
merit is saving of space in designing. 
DISCLOSURE OF THE INVENTION 
This invention makes it possible to heat and cook either in a short time or 
in a long time by means of only one timer, by varying the operating speed 
of the timer for setting the heating time and controlling the heating 
source by supplying the power to the timer motor either intermittently or 
continuously, and also by varying the heating output. 
According to the present invention, the time graduations may be designed 
freely as compared with the conventional timer having a fixed constant 
speed timer motor, and the precision of setting time is enhanced by the 
electric control of the timer motor, so that heating and cooking with a 
particularly high precision can be achieved in high frequency heating 
appliances or the like.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In the following description, the object to be heated is described for 
purposes of illustration as food, and the heating is described in terms of 
cooking the food. The invention is not limited to heating of food for 
cooking, but extends to heating of any object to be heated. 
A heating appliance for cooking according to a first embodiment of the 
present invention is shown in FIGS. 5 to 11. In this embodiment, a cam 15 
is attached to a timer shaft 14 of a timer 10 which changes the operating 
speed in between two modes, and a microswitch 16 is mounted on to a plate 
on which the timer 10 is mounted. 
Referring first to FIG. 5, an operation panel 17 is located in the vicinity 
of a door 3 which closes the front side of the heating compartment in the 
main body being supported axially to open and close freely. This operation 
panel 17 accommodates a menu table 5 indicating the cooking time according 
to the dishes and cooking hints, a timer knob 10a for setting the cooking 
time, graduations 12 around the knob, an output selector 13 for selecting 
high frequency output, a cooking start button 6, a display lamp 18 to show 
that the cooking is in progress, and other conventional devices. 
In this ordinary two-speed one-timer high frequency heating appliance (a 
microwave oven), the food F is put on a turntable 2 in a heating 
compartment 1, the door 3 is closed, the timer 10 is set to a proper 
heating time depending on the kind, size and weight of the food after 
selecting the output by the output selector 13, and the cooking start 
button 6 is pressed to start cooking, and when the timer 10 expires, the 
cooking ends. 
Referring now to the graduations 12 of the timer 10, in FIG. 6, if the full 
scale of the operating angle of the timer 10 for the high frequency 
heating appliance is 300.degree., the range from angle 0.degree. to 
200.degree. corresponds to 20 minutes, and one minute is equal to 
10.degree., while the range from angle 200.degree. to 300.degree. 
corresponds to 100 minutes, and one minute is equal to 1.degree.. That is, 
the scale is 1/10 of graduations per minute in the range from 0.degree. to 
200.degree. (or ten times that from 0.degree. to 200.degree.). 
Referring to the timer shaft 14, in FIG. 7, in the one timer 10 
corresponding to the conventional high output timer, the power to the 
timer motor 20 is supplied continuously, as is conventional, in the range 
from angle 0.degree. to 200.degree., and is supplied intermittently in the 
range from angle 200.degree. to 300.degree.. When the user turns the timer 
knob 10a and sets a time limit, the microswitch 16 is turned off by the 
cam 15 and lever 19 attached to the timer shaft 14. In the control circuit 
diagram shown in FIG. 8, the power is supplied to the contact a side of 
the microswitch 16, so that the timer motor 20 remains in ON state. That 
is, this is the range from "OFF" to "20" (angle 0.degree. to 200.degree.) 
in FIG. 6. 
On the other hand, when the user further turns the timer knob 10a and sets 
a time limit, the microswitch 16 is turned on by the cam 15 and lever 19 
attached to the timer shaft 14. 
In FIG. 8, the power is supplied to the contact b side of the microswitch 
16, and the timer motor 20 is operated intermittently by the connection 
and disconnection of an intermittent switch 22 which is turned on and off 
intermittently by the rotation of a fan motor 21. That is, this is the 
range from graduation "20" to "120" (angle 200.degree. to 300.degree.) in 
FIG. 6. 
Describing now the control circuit according to FIG. 8, one of the lines of 
a power plug 23 is connected in series with a first latch switch 26 which 
is interlocked with an abnormal temperature rise preventive device 24 of 
the heating compartment 1, overcurrent preventive device (fuse) 25, and 
also serves as the switch to generate high frequency when the cooking 
start button 6 is pressed, and a door switch 28 which serves as the door 
switch to be interlocked with the opening and closing of the door 3 and as 
the switch for forming a short circuit to turn off the fuse 25 by 
monitoring an abnormal state (melting) of the first latch switch 26 and a 
second latch switch 27, and is also connected in parallel with the timer 
motor 20, display lamp 18 to indicate that cooking is in progress, fan 
motor 21 for cooling the magnetron, and transformer 29 for high frequency 
generation. 
On the other hand, the other line of the plug is connected in series with 
the second latch switch 27, time switch 8 interlocked with timer motor 20, 
and contact c of output selector 13 for selecting the amount of high 
frequency output. The other line of the timer 20 is connected to the 
microswitch 16 for two speed selection. This microswitch 16 is connected 
parallel to the intermittent switch 22 which connects and disconnects the 
high frequency output (the primary input into transformer 29 for high 
frequency generation), and its contact b is connected with contact d of 
the output selector switch 30 which selects the output in response to 
pressing the output selector 13. 
Concerning next the high frequency output selection (primary selection of 
transformer 29 for high frequency generation), when one line of the plug 
23 is connected with the second latch switch 27, time switch 8, contact c 
of output selector switch 30, and transformer 29, the output is changed to 
the high side. And the high frequency output becomes low when one line of 
the plug 23 is connected with the second latch switch 27, time switch 8, 
intermittent switch 22, contact d of output selector switch 30, and 
transformer 29 for high frequency generation. 
Thus, the speed selection of the timer 10 is not related with the output 
selector switch 30 for high frequency output, and two speeds of the timer 
10 may be achieved by using the intermittent switch 22 for low high 
frequency output. 
An example of this construction is shown in FIG. 9, in which pulleys 34, 35 
are fitted respectively on shafts 32, 33 of the worm gear 31 for 
converting the rotating force of the fan motor 21 for cooling the 
magnetron by 90.degree.. A belt 36 is connected between these pulleys 34 
and 35 the pulley 34 being mounted on the motor 21. Another belt 40 is 
applied between a pulley 38 provided on a transmission rod 37 and a 
rotating body 39 in order to transmit the rotating force of the motor 21 
to the rotating body 39. When the rotating body 39 carrying a driving 
magnet 41 is put into rotation, a turntable 43 carrying a permanent magnet 
42 follows the rotation of magnet 41. The intermittent switch 22 is 
provided in a gear box 44 in which a worm gear 31 is housed, and it is 
turned on and off by a cam (not shown) rotating in this box. 
Referring now to FIGS. 7 and 10, the relation between the cam 15, lever 19, 
and the microswitch 16 is explained hereunder. In these figures, the cam 
15 is set and fixed at a specified position, height and angle on the timer 
shaft 14. In particular, the cam part 15a (radius l.sub.1 part) is 
situated at the side (angle 200.degree. to 300.degree. in FIG. 7) for 
turning on and off the power source of the timer motor 20. That is, from 
angle 0.degree. to 200.degree., the cam 15 has a smaller radius l.sub.2, 
and at this time on force is applied to the cam in the relation between 
the cam 15 and lever 19, and lever spring 45 of lever 19. 
At the same time, the configuration of fulcrum shaft 46 of lever 19, 
microswitch 17 for two speed selection, and timer shaft 14 is designed as 
follows. 
The angle .alpha. formed by the fulcrum shaft 46 of lever 19, operating 
point 47 of lever 19 and cam 15, and timer shaft 14 of timer 10 is set to 
be 90.degree. or wider. 
Therefore, the vector when the lever 19 rides over the operating point 47 
is A&gt;B&gt;C as shown in FIG. 10, where A is the vector in the tangential 
direction of radius l.sub.1, B is the vector of lever fulcrum and 
operating point direction, and C is the vector in the centrifugal 
direction of radius l.sub.1, so that if the lever 19 rides over the cam 15 
part it is smooth and the feel of operation is smooth. 
Occurrence of fire due to overheating in the heating compartment may be 
almost completely prevented. 
FIG. 11 shows the method of setting the timer graduations for using 
one-speed timer in two speeds, in which the maximum rotating angle of the 
timer knob is point B and the speed change point of the timer motor 9 is 
point A. Supposing 
.alpha.: rotating angle from zero to point A of timer knob 
.beta.: maximum rotating angle from zero to point B of timer knob 
(300.degree.) 
H.sub.A : set time of point A (20 minutes) 
H.sub.B : set time of point B (120 minutes) 
V.sub.A : timer speed from point A to zero 
V.sub.B : timer speed from point B to zero (1/10 V.sub.A), 
the graduation .alpha. of the timer knob for setting the high output is 
EQU .alpha.=[H.sub.A ].times.[V.sub.A ]. . . (1) 
and the graduation of the timer knob for low output is 
EQU .beta.-.alpha.=[H.sub.B ].times.[V.sub.B ]. . . (2) 
Therefore, once the maximum rotating angle of the timer knob 
(.beta.=300.degree.) is set, since .alpha.+(.beta.-.alpha.)=.beta., eqs. 
(1) (2) may be rewritten as 
##EQU1## 
By multiplying eq. (3) by [H.sub.A ]=20, the value of .alpha. is obtained 
##EQU2## 
Thus, if one timer is used in two speeds, the graduations corresponding to 
low output timer and high output timer can be easily determined. 
By this embodiment, the following effects will be obtained. When setting 
the heating means for a long time, that is when the speed of the timer 
motor 20 is slow, the power to the timer motor 20 is supplied 
intermittently, so that the timer graduations 12 may be freely designed, 
while a heating appliance for cooking excelling in timer precision is 
obtained at the same time. 
Besides, regardless of the timer speed, the heating time of high output or 
low output is easy to set, and the ease of use is further improved. In 
addition, since the lever 19 is provided between the cam 15 and 
microswitch 16, the following effects are achieved as compared with the 
conventional construction in which the microswitch 16 was pressed only by 
the cam 15 without use of the lever 19. 
(1) The operating direction of the lever 19 can be set so as to exert an 
operating force always in a specified actuator moving direction to the 
actuator of the microswitch 16, so that the durability of the microswitch 
16 may be greatly increased, together with the enhancement of the 
reliability of the mechanism. 
(2) Since the length of arm (m.sub.1, m.sub.2) of the lever 19 may be 
freely set, it is possible to ignore the force applied from the side on 
the timer shaft 14 of the timer 10, so that the incidence of fire due to 
interruption of the timer 10 may be assumed in the designing stage. 
(3) The intermittent switch 22 for output selection of high frequency 
output may be used to slow down or quicken the speed of the timer motor 20 
during rotation of the timer 10 regardless of the high frequency output, 
so that the timer 10 may be designed freely according to the cooking 
software, and since the speed of the timer motor 20 is changed over by the 
intermittent switch without using a special speed selector, it is 
economical and the mass production effect is great. 
(4) Since the degree of freedom is very ample, such as the diameter of cam 
15, position of the lever, length of the arm, position of the engagement 
point, and the angle, the number of types of timers 10 can be reduced, 
which also contributes to the mass producibility, and the cost of the 
timer 10 can be reduced, while its reliability is increased. 
Furthermore, by using a one-speed timer 10 as a two-speed timer depending 
on the purpose of use in a simple structure, an easy-to-use heating 
appliance for cooking which is stable in both quality and performance can 
be provided at a low price. 
Also by using a one-speed timer as a two-speed one, the mounting space and 
the assembling processes can be reduced, and since the power source of the 
timer motor 20 is designed to be turned on and off by the intermittent 
switch 22 which is operated by the cam 15 provided on the motor shaft 14 
and the cam of the motor for driving the turntable, the graduations 12 of 
the timer may be arbitrarily designed. 
Moreover, by the correspondence of one minute to 10.degree. in the range of 
0 to 20 minutes on the timer graduations 12, it is easy to set the cooking 
time, and the following cooking methods are possible by use of the 
intermittent switch 22, and it is very convenient. 
______________________________________ 
Reheating Cooking Thawing Simmering 
______________________________________ 
Heating 
High High Low Low 
output 
Timer 0.about.15 0.about.15 
0.about.15 
30 min 
range min min min & over 
______________________________________ 
A second embodiment is described below with reference to FIG. 12. The timer 
10 for high output continuously supplies power to the timer motor 50 shown 
in FIG. 12 by means of the timer selector switch 49 in FIG. 12 which is 
turned on by the cam 15 provided on the timer shaft 14 in FIG. 7, at the 
time of high output of high frequency waves as shown in FIG. 5, that is, 
when the timer knob 10a is turned and the high output side button 13 is 
pressed to close the contact A 48 in FIG. 12. Or when a low output of the 
high frequency is desired, that is, when the timer knob 10a is turned and 
the low output side button 13 in FIG. 5 is pressed, the timer selector 
switch 49 in FIG. 12 is turned off, and the intermittent switch 52 
provided between the timer selector switch 49 and the primary side of the 
transformer 51 for high frequency generation is turned on and off, so that 
setting of a long time is made possible. Therefore, by setting the on/off 
cycle of the timer selector switch 49 and intermittent switch 52 as 
desired, any timer suited to a specific application may be set up. To 
control the operation of the timer selector switch 49 to turn on and off 
the power source of the timer motor 50, a cam is provided in a motor 53 
which rotates and drives the turntable incorporated in the heating 
compartment 1, and the timer selector switch 49 and the intermittent 
switch 52 is turned on and off by this cam. 
A third embodiment is described below with reference to FIGS. 13 and 14, in 
which a cam is mounted on a steplessly variable motor 54 which can change 
the output of the high frequency generation unit freely from low output to 
high output, and the timer selector switch 49 and intermittent switch 52 
are turned on and off by this cam. Numeral 8 denotes a time switch which 
is interlocked with the timer setting operation, and 55, 56 are door 
switches interlocked with the opening and closing of the door 3. 
According to the heating appliance for cooking of this embodiment, the 
following effects are obtained. 
(1) Since a timer 10 of one speed can be used as a two-speed timer 
depending on the purpose of use by a simple construction, the timer 10 is 
mass producible, and heating appliance for cooking with stable quality can 
obtained. 
(2) By use of a one-speed timer 10 as a two-speed one, it is simple to 
handle, easy to use, and advantageous in enhancement of assembling 
efficiency. 
(3) By arbitrarily varying the rotating speed of the timer motor 50, the 
setting of timer gradiations may be freely designed. 
(4) By changing over the rotating speed of the timer motor by means of 
intermittent switch 52, the output operation of the heating means can be 
adjusted from low output to high output, so that cooking and heating 
according to the menu is possible. 
POSSIBILITIES OF INDUSTRIAL USES 
By using the heating appliance for cooking of this invention, as described 
above, an inexpensive one-speed timer may be used as a two-speed timer 
depending on the purpose of a use by a simple structure of cam and 
intermittent switch, so that the enhancement of mass producibility of 
timers and stability of quality can be achieved, thereby providing heating 
appliances for cooking which require a reduced mounting space and which 
are easy to handle. 
It is evident, needless to say, that it may be widely expanded and 
developed in appliances having similar timers.