Note: Descriptions are shown in the official language in which they were submitted.
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FIELD OF THE INVENTION
This invention relates to new and useful improvements
in microwave treating mechanisms and pertains particularly
to such a treating mechanism as applied in association with
a hollow drum which is rotatably driven on substantially a
horizontal axis and which is arranged to receive and tumble
articles to be dried.
SUMMARY OF THE INVENTION
According to the present invention and forming a primary
objective thereof, a microwave treating mechanism is provided
that employs a novel concept of using microwave power as a
drying and heating medium.
A more particular object of the invention is to provide
a mechanism of the type described that utilizes a hollow
drum which is rotatably supported on substantially a hori-
zontal axis and which is arranged to tumble articles there-
around while being treated with the microwave power.
Another object is to provide a novel output for the
microwave power means which is arranged to protect such
power means from tumbling articles æ well as from abnormal
reflected power.
Another object of the invention is to provide a micro-
wave treating mechanism having a hollow tumbler-type drum
arranged to receive articles from which moisture is to be
removed. The drum has an unobstructed end opening and is
supported on substantially a horizontal axis. Drive means
rotates the drum whereby articles being treated tumble across
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ne interior of the drum, and microwave power means on the
support means are disposed with the output thereof pointed
in an axial direction directly into the drum through the end
opening for engaging articles tumbling across the drum. The
support means includes a housing for the drum and a door on
the housing disposed adjacent to one end of the drum, the
drum having an opening facing the door and the door having
means coupling the energy from the microwave power means to
a cavity formed by the drum. An electric circuit is provided
for the power means and includes control means therein. The
mechanism has forced air means moving heated air through the
drum for carrying away moisture within the drum, and a dome-
like shield transparent to microwaves is mounted on the door
and covers the coupling means, said shield being of a size
and shape to keep the tumbling articles out of the near
field of the coupling means.
Other objects of the invention are to provide
circuit elements in the circuit to the power means arranged
to protect the power means from excessive average reflected
or peak VSWR; to provide humidity sensing means arranged
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to turn off the power means at a selected dried condition
of the articles being -treated; and to provide other safety
features which include a foolproof mac3netically operated
door switch that turns off the power to the microwave .
5 power means when the door is opened, and means arranged
to turn off such power rneans if the article receiving drum l'
should accidentally be subjected to an abnormal weight ~I,
The irvention will be better understood and additional
objects and advantages will become apparent from the follow- j
10 ing description taken in connection with the accompanying ¦
drawinys.
Figure 1 is a front elevational view of apparatus with
which the present invention may be employed;
Figure 2 is an enlarged vertical sectional view of the
15 apparatus taken on the line 2-2 of Figure l;
Figure 3 is a fragmentary el.evational view, partly
broken away, taken on the line 3-3 of Figure 2;
Figure 4 is a vertical fragrnentary sectional view taken
on the line 4-4 of Figure 3;
Figure 5 is a fragmentary end elevational view taken
on the line 5-5 of Figure 4;
Figure 6 is an enlarged fragmentary sectional view taken
on the line 6-6 of Figure 3;
Figure 7 is an enlarged fragmentary sectional view
25 taken on the line 7-7 of Figure 3;
Figure 8 is a schematic view of electrical circuitry
associated with the present mechanism; and
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Yigure 9 is a schematic of a modified circuit which
may be associated with the present mechanism.
- DETAILED DESCRIPTION GF PREYERRED EMBODIMENTS
With particular reference to the drawings, and first
5 to Figures 1-7, one particular application of the present
microwave treating mechanism is illustrated. One such
application comprises the association of microwave power
means for heating and drying articles being tumbled in a
rotating drum, such as in association with clothes dryer
10 mechanism using a tumbler as in present day use. The
mechanism comprises a housing 10 or other support means
having a hollow drum or tumbler 12 supported therein on
substantially a horizontal axis. As best seen in Figure 2,
such drum is supported for rotation on a rear bearing
15 assembly 14 supported in the housing. The drum is driven
by a belt and pulley assembly 16 associated with a drive
motor 18. A feature of the invention is a spring suspension
support for the bearing means 14, such as by one or more
equally spaced tension or compression springs 20, secured
20 to support brackets22 on the housing, as well as a pivot
support 24 at one end of the motor and a tension spring
support 26 at the other end. Motor 18 has a switch housing
28 secured thereto having a spring held contact assembly 30
connected at its other end to the housing 10. The spring
suspension of the bearing 14 and the motor 18, as well as
the spring contact assembly 30, is arranged such that if
an abnormal load should be present in the drum 12, such as
an overload of articles or if a child should crawl into
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the drum, switch 28 will open the circuit to power means to
be described. The front of the drum has suitable rotatable
support in the housing such as by a plurality of bearing
mounted rollers 31.
The rear of the drum 12 has an opening 32 through
which air used to ventilate articles within the drum can
flow out and be discharged through a rear outlet 34. Rear
opening 32 is covered by a screen 36 to prevent or reduce
leakage of microwave power from the drum to the door housing,
Housing 10 has a loading door 40 supported by hinges
41. Such door has a substantial thickness between its
front panel 42 and its rear panel 44 so as to enclose micro-
wave power means 46, such as a magnetron, supported on a
base plate 48 disposed above ,the bottom of the door and-
15 contained within an enclosure 50 forming an enclosed area
for the magnetron in combination with the front and rear
panels of the door as well as w-ith one side of the door
A blower 54 having an inlet 56 is mounted adjacent to
the bottom of the housing 10 and has an outlet 58 communi-
20 cating with the enclosure 50 when the door 40 of themechanism is closed. Rear panel 44 of the door has an out-
let opening 60 within the enclosure 50 communicating with
the open end of the drum 12. By operation of the blower
54, air is arranged to be circulated through the housing 50,
into the drum 12, and out the outlets 32 and 34. Opening
60 preferably is covered by a screen material 62 to prevent
or reduce leakage of microwave power from the drum to the
door housing, Magnetron g6 preferably has cooling fins
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;
64 to achieve maximum coo]ing from the air flowing through
the enclosure 50. Since the forced air system for venti- ! !
lating the drum 12 also rnoves past the magnetron 46 for I ¦
cooling the latter, such forced air serves a dual purpose.
Magnetron 46 has an output dome 70, and according to !
the present invention, such output dome is associated with
a transition section 72 of coaxial line which in turn leads
to a directional coupler 74 in turn connected to a three
stub coaxial tuner 76 which acts as a matching section between 1,
the coaxial line portion of the system and a cylindrical
wave guide 78 to the rearward end of which, Figure 5, is
provided with a horseshoe shaped slot 80. Slot 80 acts as
a slot-type antenna and serves as a coupler between the wave
guide 78 and the cavity or space formed by the drum. One
feature of the wave path 72, 74 and 76 is that such path is
elongated so as to get good wave distribution as well as to
lessen the possibility of reflected wave damage to the magnetron
46.
With reference to Figure 4, a feature of the invention also
resides in the provision of a dome-like shield 84 of dielectric
material secured on the rear panel 44 of the door over the end
of the cylindrical wave guide 78. This shiela serves to pro-
tect the end of the wave guide physically from tumbling arti-
cles in the drum and also serves to space tumbling articles
from such wave guide so as to keep objects a minirnum wave length
distance away from the mi.crowave co,upler and thus out of the
coupler's near field. Such prevents perturbations of the near
field by articles in the dryer from providing increases in the
average reflected power or voltage standing wave ratio which
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may be damaging to the rnagnetron. The shi eld 84 can be
of any shape, it being preferred that the shape used provide
a minimum spacing from articles in the drum to the coupler
of at least one half to one wave length. It is preferred
5 that the shield 84 have a sea]ed fit with the wall 44 so
as to protect the coupler from dirt and moisture.
With reference to Figure 6, the inner panel 44 of the
door has inwardly facing edge sockets 86 for receiving first
- a rubber gasket 88 or the like to provide a tight seal with
10 the housing 10 at the door opening 40a of the housing and
second an RF gasket 90 which serves to prevent the outflow
of power from the tumbler. A further choke for the out-
flow of power is provided by an air space 92 formed between
an annular baffle 94 secured to the inner surface of the
15 housing 10 and extending parallel with the drum surface. -
In addition to known interlocks, it is desired that a
substantially foolproof interlock be provided so that the
power will not likely be on at any time that the door is
open. For this purpose, and with reference to Figures 3 -
20 and 7, a switch housing 100 is mounted on the rear door panel
44 and encloses a reed switch 102 in the main circuit to -the
magnetron. Disposed adjacent to the reed switch 102 within
the switch housing 100 is a socket 104 that opens through
the panel 44. Associated with the socket 104 is a magnet
25 106 secured on the front wall of the housing 10 whereby with
the reed switch 102 being constructed of magnetically
actuatable material, and in an arrangement wherein such
switch will normally be open but will close upon entrance
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of the magnet in the socket 104, the main cireuit to the
power means will open as soon as the door is opened. In
order to provide a foolproof arrangement, it is preferred
that the socket 104 and the projecting magnet 106 have a
5 substantially exclusive interfitting relation such as a
triangular cross section or other shape which would be
difficult to match. In addition, this arrangement of
door interloek ean also have a magnetie power relation sueh
that the magnet must be of a seleeted power to aetuate the
10 reed switeh. This would add even a greater foolproof arrange-
ment for the power circuit.
Reference is now made to Figure 8 which shows eircuitry
for the dryer. Such eireuitry ineludes infeed lines 110 and
112 providing power to an auto/isolation transformer 114 in
15 turn supplying power to a transformer 116 for the filament
118 of the magnetron 46. Infeed line 110 ineludes a main
switeh 120, a eontrol panel interlock switch 122, and a timer
switeh 124. A power indieating lamp 126 is eonneeted in
parallel aeross the infeed lines. Blower motor 54 and drum
20 motor 18 are in eircuit with a start switch 130 also in-
eluding a time delay switeh 132 the eontrol deviee 134 of
whieh is eonneeted across the primary of transformer 114.
A latching relay 138 is conneeted in series with the
start switeh 130. The energization of relay 138 eloses
25 a contact 140 thereof whieh latehes said relay and continues
the supply of power to a drive motor 124a for the timer 124.
An indieating lamp 142 is eonneeted in the timer eireuit.
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In the operation Gf the circuit thus far described,
the timer 124 is first set to the desired drying time, and .
assuming that switches 120 and 122 are cl.osed, the start ~
button 130 is pressed. Such latches relay 138 to supply .
5 power to the blower motor 54 and drum rnotor 18 as well as .
the ti.mer motor 124a. The timer motor then proceeds to run
until the desired drying time is up at which time the switch
124 is opened to remove the power from the transformer 1~14
and thus power to the magnetron 46. The time delay 134
10 maintains the switch 132 closed for a shcrt while after the .
power to the magnetron is turned off so that the blower
motor 54 and the drum motor 18 continue~ to operate for a
specified time to insure that the magnetron is cooled.
Filament transformer 116 is connected across the input
to the magnetron power supply derived from the auto/isolation
transformer 114. A time delay device 146 is connected across
the primary of transformer 116 and a pair of contacts 148
of such time delay are connected in series with the output
of the transformer 114. Upon supplying power to the trans-
former 114 and thus to time delay 146, the latter providesa pre-set time delay to allow the magnetron filament 118
sufficient time to warm up before contacts 148 close allow-
ing voltage to be supplied to the magnetron 46.
The power supply to magnetron 46 includes a bridge
rectifier 150 connected in the output circuit of the trans-
former 114. The.output of the rectifier is connected to a
capacitorl52 and bleeder resistor 154 for generating a DC
voltage at the top end of a~pulse transformer 156 supplying
1175495
pulsed power between the cathode 158 and the anode 159
of the magnetron. Conventional regulating means 160
ror supplying DC power of the required value to control
circuitry now to be described is included in the magnetron
5 circuit.
The present invention inc]udes protective circuits for
the magnetron which operate through the use of pulse modu-
lation of the magnetron. The magnetron is pulse modulated
through the action of an electronic switch 164 connected
10 to the primary of pulse transformer 156 (whose secondary
is connected between the cathode 158 and the anode 159 of
the magnetron) and arranged to rapidly open and close the
circuit formed by the DC power supply and pulse transformer
and a variable pulse width multivibrator 165 acting through
15 AND gate 166 associated with other inputs to be described.
In normal operation, the other inputs to the AND gate 166
are such that upon a pulse from multivibrator 165 switch
164 is closed thus providing through the transformer action
and design of the pulse transformer 156 a pulse of power
20 (of proper voltage, polarity, and current) to the anode
of the magnetron and of the same duration as the pulse from
multivibrator 165. With zero input to multivibrator 165
the pulse duration is such that the average power from the
magnetron when operating into a matched load is the desired
25 yalue; thus any decrease in pulse width will be reflected
as a dec-ease in average output power. The switch 164 may
be a switch which is electrically controllable and fast
enough operating. Examples are Hex Fet and VMOSFet switches.
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A first protective circuit for the magnetron,
designated generally by the numeral 170 includes a
magnetron thermal protector switch 172 of conventional
construction and various interlock switches such as the ¦
5 door interlock switch 102 shown in Figure 7, door panel ¦-
interloc~ switch 174, and other interlock switches 176.
Circuit 170 also includes a contact 179 operated by
the relay 138 and acting as a control to the pulse modu]ator
switch 164 along with the other switches in series there-
10 with. Contact 179 serves as a direct turn-off for the
magnetron as soon as the relay 138 is deenergized.
Also in the circuit 170 is h~midity sensor means
arranged to control operation of the switch 164 through the
gate 166. Such sensor means comprises a first humidity
15 sensor 180 located in the path of the inlet air to the
clothes dryer, such as in the portion 58 or 60 shown in
Figure 3, and a second humidity sensor 182 located in the
path of the outlet air of the dryer such as adjacent to the
outlet 34 shown in Figure 2. The outputs of the humidity
20 sensors 180 and 182 are fed to the two lnputs of a difference
amplifier 184, and the output of such amplifier is fed to
a comparator 186 which compares such output to a reference
input 188. The system can be arranged such that when the
output of the two humidity sensors becomes equal or differ
25 by a specified amount, the output of the difference amplifier
goes below the reference voltage and the comparator's OUI-
put of the comparator 186 to an AND gate 190 whose other
input is connected to a logic generator 192 and whose output
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is connected to the series chain of interlocks in the
circuit 170 and can shut the magnetron off at the AND gate
166 associated with pulse modu]ator switch 164, the hu~idity
sensing means in the circuit 170 serves to prevent artic]es
5 in the drum from being overdried or at least dried to a
specified amount.
In addition to the circuitry described, the pulse
modulated magnetron as controlled through the pulse modulator
electronic switch 164 allows the use of additional protective
10 circuits to prevent the magnetron from being subjected to
excessive reflected power. Such additional circuits can
be operated through the AND gate 166 along with the circuit
170.
A first of such protective circuits comprises a circuit
15 194 arranged to sample the average reflected power in the
transmission line or wave guide connected to the magnetron.
Such circuit comprises a sensor 196 of conventional design
- and located in the directional coupler 74, for example, Figure
3, and arranged to sample the reflected power in such coupler.
20 Such sensor provides a signal proportional to the reflected
power and such signal is in turn averaged over a number of
pulses by an integrator 198. The averaged signal from the
integrator is then fed to one input of a difference ampli-
fier 200 whose other input 202 is connected to a reference
25 voltage. The output of amplifier 200 feeds into the variable
pulse width multivibrator 165 connected to the AND gate 166.
When the average reflected power signal exceeds a value
determined by the reference, a signal is produced which is
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proportional to the amount that the average reflected -
power exceeds the reference level determined by the
reference. The gain of the difference amplifier is -
sufficient enough that a small increase in the average
reflected power above the reference will provide enough
signal at the width control input to the pulse width
multivibrator 165 so as to reduce the pulse width from
its maximum value to a value such as to keep the average
forward and hence the reflected power below its maximum
allowable value. If the average reflected power should
exceed a preset level as determined by reference voltage
202 and a regulating band determined by the gain of
amplifier 200 and the voltage input required to reduce
the pulse width of multivibrator 165 to zero, the pulse
width of the pulse output of multivibrator 165 will become
zero, thus turning completely off AND gate 166 and hence
switch 164. This in turn deenergizes the magnetron.
Another protective circuit for the magnetron which
operates through the AND gate 166 comprises a circuit 210
for protecting the magnetron from peak voltage standing
wave ratios in excess of the source capabilities. Circuit
210 comprises a sensor assembly 212 in the transmission line
such as in the directional coupler 74, Figure 3, containing
structure to sample and detect a signal which is proportional
to the forward power. This signal along with the reflected
power signal derived from sensor 196 is-fed to an operational
amplifier 214 hooked up so that its output is proportional
to the ratio of the reflected power signal to the forward
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power signal and thus a measure of the voltage standing
wave ratio in the transrnission line connected to the
magnetron. The output signal of the amplifier is fed to
a comparator 216 whose other input 218 is connected to a l,
5 reference voltage. When the signal from the ratio ampli- j
fier exceeds the reference voltaye, the comparator's out-
put opens the A~D gate 166.
Circuit 210 as well as circuit 194 causes the magnetron
to be turned off partially or completely only during the
10 undesirable periods which if temporary will only amount
to a momentary shut down. These circuits were designed
to protect the magnetron from voltage standing wave ratios
which may be in excess of the source capabilities such as
may happen in the event that a metal object, for example,
15 is in a load to the dryer. Although circuits 194 and 210
are shown herein in conjunction with a dryer mechanism
employing a tumbler which presents articles to be dried
to the output power of the magnetron, such circuits could
as well be applied to other mechanisms such as conventional
20 microwave ovens forprctecting the magnetron from excessive
average reflected or peak standing wave ratios.
Sensors 196 and 212 may comprise suitable and con-
ventional sensing devices such as a diode rectifier which
converts the RF energy provided by the directional coupler
to a DC voltage.
Figure 9 shows an alternative form of circuit 194' for
controlling the average and peak reflected powers to the
magnetron. In this circuit, the output from the pulse
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transformer 156 is connected to a rectifier filter so as
to become a switching power supply. The integrator is
eliminated and its function is solved by an inductor
connected to a capacitor 222 and bleeder resistor 224.
5 In this circuit a diode 225 acts as a rectifier whose
output is connected to an LC filter comprised of inductor
220 and capacitor 222. Diode 226 acts as a commutating
diode. In the circuit of Figure 9, the magnetron power
~ output is now controlled by ànode voltage which decreases
10 as the pulse width decreases. -
It is to be understood that the form,of our inventionherein shown and described are to be taken as preferred
examples of the same and that various other changes in ¦
the shape, size and arrangement of parts may be resorted ¦
to without departing from the spirit of our invention, or
the scope of the subjoined claims. For exarnple,it is
within the concept of the invention to mount the magnetron ¦
in the housing 10 rather than in the door, it merely being
necessary as one example that an RF connection which is
supplied by a flexible coaxial line extend from the magnetron
in the housing to a suitably mounted wave guide.
Having thus described our invention, we claim:
