Abstrict
A combined microwave and electric heater oven includes a fan system
for cooling a magnetron, and a damper for selectively introducing
a forced air flow generated by the fan system into an oven cavity.
A damper cam is secured to a drive shaft of a damper motor, and
a damper link is disposed between the damper cam and the damper
to drive the damper. A microswitch is disposed near the damper cam
so that the microswitch develops a first detection signal when the
damper is tightly closed. In response to the first detection signal,
the rotation of the damper motor is terminated to hold the damper
in the tightly closed state. The microswitch develops a second detection
signal when the damper is placed in the full-open state. In response
to the second detection signal, the rotation of the damper motor
is terminated to hold the damper in the full-open state.
Claims
What is claimed is:
1. A cooking apparatus comprising:
an oven cavity defined by an oven wall, said oven wall having an
aperture formed therein;
fan means for creating a forced air flow along an outer surface
of said oven wall in such a manner that a portion of said forced
air flow is introduced into said oven cavity through said aperture;
damper means for selectively closing said aperture formed in said
oven wall for precluding the introduction of said forced air flow
into said oven cavity; and
a damper drive system for selectively placing said damper means
in a closed condition and an open state, said damper drive system
including:
a damper motor having a drive shaft; means for rotating said drive
shaft of said damper motor;
transfer means for transferring the rotation of said drive shaft
of said damper motor to said damper means;
switch means operatively connected to said transfer means for selectively
being turned off and on;
detection means for sensing a voltage indicative of said switch
means being in said on position and developing a first detection
signal when said damper means is in the closed condition, and for
sensing a voltage indicative of said switch means being in said
off position and developing a second detection signal when said
damper means is in the open state; and
a motor drive unit for terminating the rotation of said drive shaft
of said damper motor when said first detection signal or said second
detection signal is developed.
2. The cooking apparatus of claim 1, said transfer means comprising:
a damper cam secured to said drive shaft of said damper motor;
and
a damper link disposed between said damper cam and said damper
means.
3. The cooking apparatus of claim 2, wherein said damper cam includes:
a large diameter semicircular portion; and
a small diameter semicircular portion.
4. The cooking apparatus of claim 3, said switch means comprising
a normally close microswitch disposed near said damper cam, said
normally close microswitch being switched off when said large diameter
semicircular portion faces said normally close microswitch.
5. The cooking apparatus of claim 4, wherein said first detection
signal is developed in response to a leading edge of a switching
operation of said normally close microswitch from the OFF state
to the ON state, and said detection signal is developed in response
to a trailing edge of a switching operation of said normally close
microswitch from the ON state to the OFF state.
6. A damper drive system for selectively placing a damper in the
closed condition and the open state, comprising:
a damper motor having a drive shaft; means for rotating said drive
shaft of said damper motor;
transfer means for transferring the rotation of said drive shaft
of said damper motor to said damper;
switching means associated with said transfer means, said switching
means being placed in a first condition when said damper is tightly
closed and in a second condition when said damper is placed in the
full-open state;
detection means for sensing a voltage indicative of said switching
means being in an on position or an off position and for detecting
the switching operation of said switching means from said first
condition to said second condition or from said second condition
to said first condition; and
motor drive control means for terminating the rotation of said
drive shaft said damper motor when said detection means detects
said switching operation of said switching means.
7. The damper drive system of claim 6, said transfer means comprising:
a damper cam secured to said drive shaft of said damper motor;
and
a damper link disposed between the damper and said damper cam.
8. The damper drive system of claim 7, said switching means comprising
a normally close microswitch disposed near said damper cam so that
said normally close microswitch is switched off when a preselected
portion of said damper cam faces said normally close microswitch,
wherein said detection means detects the trailing edge or the leading
edge of an output signal derived from said normally close microswitch.
Description BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to a damper drive system in a combined
microwave and electric heater oven for controlling the direction
of the forced air flow created by a fan system.
In a combined microwave and electric heater oven, a fan system
is provided for cooling a magnetron disposed in a space formed between
an oven wall and a housing of the combined microwave and electric
heater oven. The forced air flow created by the fan system is introduced
into the oven cavity for discharging the gas generated in the oven
cavity during the microwave cooking operation. The air flow must
not be introduced into the oven cavity during the electric heater
cooking operation, because the interior of the oven cavity must
be maintained at a high temperature during the electric heater cooking
operation. However, even during the electric heater cooking operation,
the fan system is continuously operated in order to protect the
magnetron from the high temperature generated by the electric heater.
Therefore, a damper mechanism is normally provided in the combined
microwave and electric heater oven for selectively introducing the
forced air flow into the oven cavity. A typical construction of
the combined microwave and electric heater oven including a damper
mechansim is described in copending application Ser. No. 138,749,
"DAMPER ACTIVATION IN A COMBINED MICROWAVE AND ELECTRIC HEATING
OVEN", filed on Apr. 9, 1980 by Yasuo Shin now U.S. Pat. No.
4,369,347, patented Jan. 18, 1983 and assigned to the same assignee
as the present invention.
Accordingly, an object of the present invention is to provide a
novel damper drive system in a combined microwave and electric heater
oven.
Another object of the present invention is to simplify a damper
drive mechanism in a combined microwave and electric heater oven.
Other objects and further scope of applicability of the present
invention will become apparent from the detailed description given
hereinafter. It should be understood, however, that the detailed
description and specific examples, while indicating preferred embodiments
of the invention, are given by way of illustration only, since various
changes and modifications within the spirit and scope of the invention
will become apparent to those skilled in the art from this detailed
description.
To achieve the above objects, pursuant to an embodiment of the
present invention, a motor is provided to open or close the damper.
A relay switch mechanism is provided for energizing the motor at
a desired time. A detection system is associated with the damper,
which develops a detection signal when the damper is completely
opened or when the damper is completely closed. In response to the
thus developed detection signal, the relay switch mechanism is turned
off, thereby deenergizing the motor.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be better understood from the detailed
description given hereinbelow and the accompanying drawings which
are given by way of illustration only, and thus are not limitative
of the present invention and wherein:
FIG. 1 is a block diagram of a combined microwave and electric
heater oven employing an embodiment of a damper drive system of
the present invention; and
FIGS. 2 and 3 are schematic plan views showing an operation mode
of the damper drive system of the present invention, wherein FIG.
2 shows an opened condition, and FIG. 3 shows a closed condition.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As illustrated in FIG. 1, a combined microwave and electric heater
oven generally comprises a magnetron 10 for conducting the microwave
cooking operation. The magnetron 10 is disposed in a space provided
between the oven cavity wall and the housing of the combined microwave
and electric heater oven. In addition, an electric heater 12 is
disposed in an oven cavity 14 for conducting the electric heater
cooking. A fan motor 16 is associated with a cooling fan 18 in order
to create a forced air flow 20 in the above-mentioned space, thereby
cooling the magnetron 10. A damper 22 is provided for selectively
introducing the forced air flow 20 into the oven cavity 14. More
specifically, in the microwave cooking operation mode wherein the
magnetron 10 is energized, the damper 22 is opened in order to introduce
the forced air flow 20 into the oven cavity 14. In the electric
heater cooking operation mode, the damper 22 is closed in order
not to introduce the forced air flow 20 into the oven cavity 14.
The damper 22 is driven to open or close an aperture 24 by means
of a damper motor 26. A control unit 28 controls the activation
of the damper motor 26. The control unit 28 further controls the
energization of the magnetron 10, the electric heater 12 and the
fan motor 16.
As illustrated in FIGS. 2 and 3, a damper cam 30 is secured to
a shaft of the damper motor 26. The damper cam 30 has a large diameter
semicircular portion 300 and a small diameter semicircular portion
302. A normally closed microswitch 32 is disposed near the damper
cam 30 in such a manner that the actuator of the microswitch 32
is depressed by the large diameter semicircular portion 300, whereby
the microswitch 32 is switched off when the large diameter semicircular
portion 300 faces the microswitch 32. A damper link 34 is connected
between the free end of the damper 22 and the damper cam 30 for
transferring the rotation of the damper motor 26 to the damper 22.
The operation mode of the combined microwave and electric heater
oven of the present invention is as follows:
To perform the microwave cooking operation, the microwave cooking
mode switch is actuated to introduce the microwave mode signal into
the control unit 28. The control unit 28 develops a control signal
to activate a first relay 36, thereby closing a relay contact 38.
In response thereto, the damper motor 26 is supplied with power
to open the damper 22. The rotation of the damper motor 26 is transferred
to the damper 22 via the damper cam 30 and the damper link 34. When
the damper 22 is placed in the full-opened condition, the large
diameter semicircular portion 300 contacts the actuator of the normally
closed microswitch 32 as shown in FIG. 2. The microswitch 32 is
switched off. The trailing edge of the switching operation of the
microswitch 32 is detected by the control unit 28 which develops
a control signal to deenergize the first relay 36. Accordingly,
the power supply to the damper motor 26 is terminated for holding
the damper 22 at the open state.
Under these conditions, when the cook start switch is actuated,
a second relay 40 is energized to close a relay contact 42 for activating
the fan motor 16. The forced air flow 20 is created by the cooling
fan 18. Since the damper 22 is held in the open state, a portion
of the forced air flow 20 is introduced into the oven cavity 14.
Further, a third relay 44 is energized in order to activate the
magnetron 10 via a relay contact 46 and a transformer 48.
To perform the electric heater cooking operation, the electric
heater cooking mode switch is actuated to introduce the electric
heater mode signal into the control unit 28. The control unit 28
develops a control signal to activate the first relay 36, thereby
closing the relay contact 38. The damper motor 26 rotates to close
the damper 22. The rotation of the damper motor 26 is transferred
to the damper 22 via the damper cam 30 and the damper link 34. When
the damper 22 is placed in the tight-close condition, the small
diameter semicircular portion 302 faces the normally closed microswitch
32 as shown in FIG. 3. The microswitch 32 is switched on, and the
leading edge of the switching operation of the microswitch 32 is
detected by the control unit 28. The control unit 28 develops the
control signal to deenergize the first relay 36, whereby the relay
contact 38 is switched off. The rotation of the damper motor 26
is terminated so that the damper 22 is held at the closed condition.
Under these conditions, when the cook start switch is actuated,
the second relay 40 is activated to close the relay contact 42.
The fan motor 16 is energized to generate the forced air flow 20
through the use of the cooling fan 18. The thus created forced air
flow 20 is not introduced into the oven cavity 14 because the damper
22 is closed. Further, a fourth relay 50 is energized to supply
power to the electric heater 12 through a relay contact 52.
The control unit 28 is preferably implemented with an LSI model
No. M58841-024SP manufactured by Mitsubishi Denki Kabushiki Kaisha.
The invention being thus described, it will be obvious that the
same may be varied in many ways. Such variations are not to be regarded
as a departure from the spirit and scope of the invention, and all
such modifications are intended to be included within the scope
of the following claims. |