CA1175495A - Microwave treating mechanism - Google Patents

Abstract

MICROWAVE TREATING MECHANISM

ABSTRACT OF THE DISCLOSURE

A housing rotatably supports a hollow drum on sub-stantially a horizontal axis whereby articles to be treated tumble around the interior of the drum when the latter is rotated. A microwave power mechanism, such as a magnetron, is provided in a door for the housing and has an output portion thereof directed into the drum for heating and dry-ing articles tumbling in the drum. An output portion of the microwave power mechanism has a dielectric dome-like shield mounted over it for deflecting tumbling articles away from such output. A forced air system is provided for ventilat-ing the interior of the drum, and such system includes a passageway extending adjacent to the power mechanism so that such ventilating air also cools the power means. The present mechanism is associated with an electrical circuit having door interlocks, door panel interlocks, and other interlocks, as well as a magnetically operated door inter-lock that is substantially foolproof so that power from the microwave power mechanism is positively deenergized when the door is open. Circuitry is provided for the microwave power mechanism to protect it from excess average and peak reflected power. The circuitry also includes a humidity sensor to prevent excessive drying.

Description

~ 175 4g5 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 -3a- ~17~g5 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 ~ 1754g5 -4- .

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 _5_ ~ 175495 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 l 175~9~

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 -7- ~ 17549~
;
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 ~ 17549~ 1 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 _9_ 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.

-lo- ~.75~9~ 1~

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 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.

~175495 ~

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 -13- i~

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 -14- ~17549~

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 ~ 1~54g~ , 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 -16- ~ 175495 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:

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
1.
Microwave treating mechanism for removing moisture from articles comprising (a) a hollow tumbler-type drum arranged to receive articles from which moisture is to be removed, (b) said drum having an unobstructed end opening, (c) support means supporting said drum on sub-stantially a horizontal axis, (d) drive means arranged to rotate said drum whereby articles being treated tumble across the interior of said drum, (e) microwave power means on said support means dis-posed with the output thereof pointed in an axial direction directly into said drum through said end opening for engaging articles tumbling across said rotating drum for removing moisture therefrom, (f) said support means including a housing for said drum and a door on said housing disposed adjacent to one end of said drum, (g) said drum having an opening facing said door, (h) said door having means coupling the energy from said microwave power means to a cavity formed by said drum, (i) an electric circuit for said power means, (j) control means in said circuit for said power means, (k) forced air means in said mechanism moving heated air through said drum for carrying away moisture within said drum, (l) and a dome-like shield transparent to microwaves mounted on said door and covering said coupling means, (m) said shield being of a size and shape to keep the tumbling articles being dried out of the near field of said coupling means.
2.
The microwave treating mechanism of claim 1 wherein said power means is supported on said door.
3.
The microwave treating mechanism of claim 1 including an RF gasket between said door and said housing arranged to choke off power from said microwave power means leaking through the joint between said housing and door, and a separate gasket of resilient material between said door and said housing to seal off the leakage of air through the joint between said housing and door.
4.
The microwave treating mechanism of claim 1 wherein said power means is supported on said door, and in-cluding choke means between said drum and housing arranged to choke off power from said microwave power means leaking through the joint between said drum and housing and then through the exterior of said support means.

5.
The microwave treating mechanism of claim 1 wherein said forced air means includes air inlets into said support means and drum, and air outlet from said drum, and a passageway between said inlet and outlet, said passageway extending adjacent to said power means in an arrangement such that forced air that removes moisture from said drum cools said power means and said power means in being cooled causes said forced air to be heated before its entry into said drum to increase the vapor carrying capabilities of said forced air.
6.
The microwave treating mechanism of claim 1 wherein said power means comprises a magnetron, said magnetron having outwardly projecting fins for cooling by said forced air.