05/370863

12/17/1974

06/18/1973

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General Electric Company (Louisville, KY)

34/265

219/752

D06F58/02; D06F58/26; F26B3/34; D06F58/20; F26B3/32; F26B3/34

34/1,17,48,55,68,133 219/10.55

3440385	ELECTRONIC OVENS	April 1969	Smith
3446929	MICROWAVE APPARATUS	May 1969	Smith
3458755	CROSSED-FIELD DISCHARGE DEVICE AND MICROWAVE CIRCUITS INCORPORATING THE SAME	July 1969	Staats
3546783	ELECTROSTATIC APPARATUS	December 1970	Candor et al.
3605272		September 1971	Boucher

Myhre, Charles J.

Devinsky, Paul

Weidner, Frederick Boos Francis P. H.

What is claimed is

1. An electronic fabric dryer comprising:

2. The invention of claim 1 wherein said heat source comprises an electric resistance heating element.

3. An electronic clothes dryer comprising:

4. The invention of claim 3 further including a microwave reflector disposed in said conduit between said blower and said antenna means to prevent the transmission of microwave energy to said blower.

5. The invention of claim 3 wherein:

6. The invention of claim 5 wherein said microwave window comprises a generally cross-shaped opening in said door, the microwave window having a cover associated therewith overlying the cross-shaped opening, the cover being transparent to microwave energy while preventing the passage of fabric through the opening into the hollow interior of said door.

7. The invention of claim 6 wherein said drying chamber comprises a generally cylindrical metallic drum mounted for rotation about a substantially horizontal axis, the drum having an air ingress and an access aperture at spaced-apart points thereof, said air ingress being impermeable to microwave energy but allowing the free flow of air therethrough.

8. The invention of claim 7 further including an electrically conductive door seat mounted adjacent said access aperture such that the door seat overlaps said door in the closed position thereof a distance corresponding to one-fourth of the wave length of said predetermined ultrahigh frequency thereby providing a choke joint to prevent the escape of microwave energy from said cabinet.

9. The invention of claim 3 wherein said control means comprises a power supply, a relay having a pair of contacts coupled in series with an input of the power supply and a coil winding coupled in series between an output of the power supply and an input of said magnetron, the relay being responsive to the current through the input of said magnetron for opening the contacts and de-energizing the power supply and said magnetron and said heat source when the current through the input of said magnetron reaches a predetermined value as the result of the drying of the wet fabric to a predetermined degree of dryness.

BACKGROUND OF THE INVENTION

This invention relates generally to drying machines. More specifically, it relates to machines for drying wet material utilizing microwave radiation as a source of energy for causing evaporation, and a preheated air flow for removing the evaporated moisture.

The use of ultrahigh frequency electromagnetic energy, such as microwave energy, for heating is, of course, well known in the art. Devices producing microwave energy have found utility in industrial heating processes for some years and more recently have been utilized for cooking on commercial and home usage bases. The industrial uses of microwave energy have included the utilization of microwave devices for drying such things as painted articles or articles which have been glued or caused to adhere to each other by the use of some kind of adhesive. Typically, in drying applications the microwave energy has been supplied by providing a radiator in the form of a coil which is excited by a microwave source and radiates energy to wet articles caused to pass within the turns of the coil. Such applications have, of necessity, involved some means for feeding the article to the area encompassed by the coil, such means usually including some kind of conveyor or article transport device.

There are, however, numerous situations where it is desired to dry objects, yet, it is uneconomical or impracticable to utilize conveyors for transporting the articles to and from an area encompassed by a microwave coil radiator. Consequently, the drying of articles in a chamber becomes desirable. In order to permit drying to proceed rapidly and efficiently when a chamber is used, it is desirable to provide means for removing from the chamber the moisture evaporated from the articles.

There are, of course, other applications of microwave energy for heating articles in a chamber, as for instance, cooking. The article to be heated is placed within the chamber, an oven, and the energy is coupled to the interior of the chamber. In this kind of application, of course, drying of the food is the last thing that is desired for the removal of water from cooked foods generally adversely affects their taste and texture.

Therefore, it is an object of this invention to provide a novel drying machine wherein microwave energy is utilized within a chamber to evaporate moisture from wet materials therein, and a preheated air stream is utilized to remove the evaporated moisture from the chamber.

It is a further object of this invention to provide a novel drying machine which utilizes heated moving air to remove moisture evaporated from wet objects by the microwave energy and which utilizes a single conduit functioning as part of the microwave energy transmitting means and as part of the air moving means so as to provide a relatively economical and compact arrangement which at the same time is efficient in its operation.

A particular application wherein drying apparatus in accordance with the invention may find utility is a clothes drying machine such as is used in the home or commercial operations. Such machines have rotating clothes tumbling drums mounted within a protective cabinet. Included in the space between the tumbling drum and the protective cabinet are the means for mounting the drum for rotation, a motor for rotating the drum and a blower to blow dry, heated air over and through the clothes as they are tumbled within the drum. A door is provided to give access through the cabinet to the drum interior to permit the user to place wet clothes within the drum and to remove the dry clothes therefrom. It is believed that a considerable advantage in performance and the economics of manufacture can be achieved by the utilization of apparatus in accordance with this invention in such a dryer, and particularly where the clothes tumbling drum and the conduit or duct for directing airflow through the drum are advantageously formed in the customary manner from sheet metal.

It is another object of this invention to provide a clothes dryer which utilizes microwave energy as a drying medium and which does not require a substantial reconstruction of a conventional clothes dryer.

It is still another object of this invention to provide a clothes dryer utilizing microwave energy as a drying medium which is safe for use by relatively unskilled operators as simple but effective means is provided to prevent microwave radiation from entering the atmosphere or any place where a user could inadvertently place his hands or any other part of his body.

It is a still further object of this invention to provide a means for automatically interrupting the transmission of microwave energy to a drying chamber when all of the wet material therein has been dried to a predetermined degree of dryness.

It is still another object of this invention to provide a dryer utilizing microwave energy wherein automatic control of the source of microwave energy is effected without the necessity of any sensing or timing devices so as to interrupt the transmission of microwave energy to the drying chamber when all of the wet material has been dried to a predetermined degree of dryness.

SUMMARY OF THE INVENTION

In accordance with the present invention there is provided an electronic dryer comprising a casing within which is mounted a drying chamber for accommodating items to be dried. Also included is air circulating means and a conduit associated with the drying chamber for circulating a stream of air therethrough and generating means is provided which is adapted to produce ultrahigh frequency electromagnetic energy at a predetermined frequency. Means are provided for coupling the generating means with the conduit for transmitting energy from the generating means to the conduit, the conduit serving both as an air duct and as a waveguide for the electro-magnetic energy. The moisture evaporated from wet articles placed in the drying chamber is carried from the drying chamber by the air stream and is exhausted through the conduit to the exterior of the cabinet.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of apparatus embodying the invention;

FIG. 2 is a side elevational view partially broken away and partially in section illustrating a preferred embodiment of the invention in a clothes drying machine;

FIG. 3 is a partial side elevational view of the clothes drying machine shown in FIG. 2, partially broken away and partially in section, illustrating the blower apparatus and drive machinery;

FIG. 4 is a front elevational view in partial section taken generally along the lines 4--4 in FIG. 2 illustrating the flow path for air and microwave energy; and

FIG. 5 is a schematic diagram of a control circuit embodying an aspect of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring first to FIG. 1, there is shown an electronic dryer in accordance with the present invention. The apparatus includes an outer casing or cabinet 42 preferably of sheet metal construction. The cabinet 42 is provided with air inlet means 12 and air egress means such as exhaust 140 whereby air may enter the cabinet enclosure from the atmosphere, flow through the interior thereof and be thereafter exhausted to the atmosphere. Air inlet 12 is covered by a screen 80 which prevents the undesirable entrance of large particles of foreign matter into the enclosure. Air is drawn into and exhausted from the cabinet 42 by air circulation means such as a blower 128 mounted therein and driven by a motor 74. Mounted within the cabinet 42 is a microwave impermeable drying chamber 56 into which is placed the item or items to be dried. Drying chamber 56 is provided with an air ingress 82 and air outlet means, such as a plurality of perforations 126, in a spaced-apart relationship, whereby air flowing through chamber 56 will readily remove moisture evaporated from the articles being dried therein. As can be readily seen, air ingress 82 and outlet means 126 are depicted in FIG. 1 as perforations in opposing sides of the drying chamber 56. A conduit 130 connects the air outlet means or perforations 126 through the input of the blower 128. By virtue of the arrangement illustrated, when the blower 128 is operating, air is drawn into cabinet 42 through air inlet 12 and flows along the path indicated by the air shown in solid lines, into the drying chamber 56 through the air ingress 82 and out through the perforations 126 to the conduit 130, to blower 128 which vents to atmosphere.

In accordance with one embodiment of this invention, a heat source 88 may be positioned within the cabinet 42 so as to be in the path of the air flow into the drying chamber 56 through air ingress 82. The heat source is shown as being of the electrical resistance type; however, in another embodiment of this invention, heat source 80 may be a gas burner, the flame of which heats the air flowing into drying chamber 56.

Mounted within the cabinet 42 adjacent the air inlet 12 is generating means 150 for producing ultrahigh frequency electromagnetic energy such as microwave energy. Generating means 150 may be any of several well known types, but is preferably a cross-field discharge device, or a magnetron of the type disclosed in U.S. Pat. No. 3,458,755-Staats, issued July 29, 1969 and assigned to the same assignee as the present invention. Coupled to the output terminals of the generating means 150 is a coaxial transmission line 152, transmission line 152 terminating in a section of conduit 130. The termination of line 152 is provided by antenna means such as antenna 158 coupled to the inner conductor of the coaxial line 152.

Antenna 158 is adapted to radiate microwave energy into conduit 130 which serves as a waveguide for propagating the microwave energy toward drying chamber 56. Disposed in the center of the air outlet means 126 is a microwave window 162 which is closed by a sheet or cover of microwave transparent material. More particularly, the microwave energy radiated by antenna 158 into conduit 130 is propagated upwardly therealong, as shown by the dashed arrows, entering the drying chamber 56 through microwave window 162. Window 162 has a perimeter which is greater than one wavelength of the frequency of operation of the magnetron 150 such that it may function for its intended purpose as is well known to those skilled in the art.

To prevent transmission of the microwave energy through the conduit 130 toward the blower 128, a microwave reflector such as wire mesh screen 138 is provided. Wire mesh screen 138 serves to reflect the microwave energy and confine it to the conduit 130 while at the same time permitting passage of air drawn through conduit 130 by blower 128. Likewise, the perforations forming air ingress 82 will not permit the passage of microwave energy therethrough, such that the microwave energy is confined within the microwave impermeable drying chamber 56.

In operation, the items to be dried are inserted into the drying chamber 56 by suitable means (not shown in this FIGURE but shown and described later in connection with a clothes dryer embodying the invention) and the motor 74 is energized to cause the blower 128 to operate. The operation of the blower 128 drawing air through the air outlet perforations 126 and conduit 130 creates an area of reduced pressure in drying chamber 56 and thereby generates a stream of air through the drying apparatus. This stream of air is drawn into the cabinet and through the air inlet 12. As shown by the solid line arrows, the air flow sweeps over the generating means or magnetron 150 to cool the magnetron and heat the air to a small extent, being then drawn upwardly through the air ingress 82 into the drying chamber 56. Prior to entering the drying chamber, the air is further heated by heat source 88 to a predetermined temperature range, the upper limit of which is less than that temperature which would cause damage to the items being dried, such as by physical deterioration or scorching or burning. The elevated temperature of the air flowing through the drying chamber 56 is of course desirable, as the moisture carrying capacity of the air is increased with elevated temperature. Upon entering the drying chamber 56, the air is swept over the articles to be dried, picking up moisture therefrom, then flowing out of the drying chamber 56 through air outlet 126 to be exhausted to atmosphere by a conduit 130 and blower 128.

At or about the same time that the blower motor 74 is energized, magnetron 150 is energized to begin producing microwave energy at the output terminals thereof at a predetermined ultrahigh frequency, preferably in this embodiment at 915 MHz. This microwave energy is transmitted along the transmission line 152 and is radiated by the antenna 158 into conduit 130. Conduit 130 is dimensioned to act as a waveguide at the frequency of operation of the generating means 150 and propagates the microwave energy toward microwave window 162. As previously pointed out, mesh screen 138 serves to reflect the microwave energy impinging thereupon to confine it such that it may not reach blower 128, while at the same time permitting air to be drawn through conduit 130 toward blower 18. Microwave energy is transmitted from conduit 28 through microwave window 162 into the interior of drying chamber 56.

In the drying chamber, the microwave energy is selectively absorbed by the wettest portions of the items to be dried, serving to heat and vaporize the moisture or water content of the items in a manner well known in the art. As the water content of the wet items is vaporized by the microwave energy, it is freed from the items and is carried from the drying chamber 56 by the air stream passing therethrough as described above. In this manner, the wet articles are quickly and efficiently dried to any desired degree of dryness. It is a quality of microwave drying that the wettest articles absorb the most microwave energy whereby the drying of such articles is speeded considerably while at the same time articles which are not quite so wet are prevented from being scorched. Thus, there is achieved a rapid and uniform drying of a load of items of varying degree of wetness.

It will also be noted that the heating and vaporizing of the moisture in the articles to be dried is facilitated by the fact that the stream of air can be heated before it passes through the drying chamber 56 to effect conventional convection drying of the wet articles. As previously set forth, this heating of the air stream is accomplished by its passage over heat source 88. Some additional preliminary heating of the air stream is effected by the passage of the air stream over generating means 150 as the air stream enters the cabinet 42 through the air inlet 12. Thus while the air stream serves to cool the generating means 150, the heat drawn therefrom is utilized to provide additional warming of the air stream to enhance its drying affect on the wet articles in the drying chamber 56. Similarly, the air flow may serve to cool the power supply (not shown in FIG. 1) for the generating means, by positioning the power supply in the air flow path in the same manner as the generator or generating means 150.

As previously stated, a particular embodiment of this invention, wherein its objects and advantages are readily employed, is a domestic clothes dryer. FIG. 2 illustrates such a clothes dryer generally designated by reference numeral 41. A dryer, in accordance with this invention, may utilize a mechanical structure which is similar to that disclosed in U.S. Pat. No. 3,009,259 - Simpson, assigned to the same assignee as the present invention, the disclosure of which is incorporated herein by reference.

The dryer includes an outer casing or cabinet 42 comprising a top wall 44, a bottom wall 46, a pair of opposite side walls 48, a front wall 50 and a rear wall 52, all preferably of sheet metal construction. Mounted at the rear end of top wall 44 is a panel 54 on which are mounted the controls of the dryer. A drum 56 having a generally cylindrical side wall 58, a generally circular rear end wall 60 and an annular front wall 62, is preferably of sheet metal construction and is mounted within the cabinet 42 for rotation about a substantially horizontal axis. The cylindrical side wall 58 of drum 56 is provided on the inner surface thereof with a plurality of tumbling ribs 64 for engaging the fabric or clothing as the drum rotates to cause tumbling of the clothing in a well known manner. The drum 56 thus defines a microwave impermeable drying chamber for accommodating wet clothing to be dried.

In order to support and rotate the drum 56, recessed cylindrical wall 66 and 68 are disposed at the rear and front ends respectively of the cylindrical side wall 58. The front recessed portion 68 of the drum side wall 58 is rotatably supported within the cabinet 42 by means of a pair of idler roller wheels 70, one of which is shown in FIG. 3.

As also seen in FIG. 3, the rear recessed wall portion 66 of the cylindrical side wall 58 is supported by a drive roller wheel 72 driven by an electric motor 74 which also drives the blower as will be subsequently described. The idler roller wheels 70 and the drive roller wheel 72 constitute elements of a known home dryer as shown in the patent to Simpson, mentioned above. Referring again to FIG. 2, the axis of rotation of the drum 56 is maintained in vertical alignment of the drive roller wheel 72 by the inner action of a stub shaft 76 secured at the center of circular rear end wall 60 and an elongated slot 78 formed in a member to be hereinafter described which is supported from the rear wall 52 of the cabinet 42. The slot 78 has a relatively large vertical dimension and a relatively small horizontal dimension only slightly greater than the diameter of the shaft 76, whereby the slot 78 prevents sidewise motion of the shaft 76 therein but accommodates a small degree of vertical motion of the shaft 76 and the drum 56 resulting from the driving motion imparted thereto by the driving roller wheel 72. The details of construction of the shaft 76 and its cooperation with the slot 78 are disclosed in the aforementioned U.S. Pat. No. 3,009,259.

Having described the dryer drum 56 and the means for supporting it for rotation in the cabinet 42, the means for providing an air flow through the cabinet and drum will now be described. Air enters the cabinet 42 through an air inlet formed by air inlet screen 80 disposed at the bottom of rear wall 52, and thereafter enters the drying drum 56 through air ingress means formed as an annular array of perforations 82 in the rear end wall 60 of drum 56.

Rigidly secured to the rear wall 52 of cabinet 42 by suitable means, such as welding at points 84, is an outer baffle member 86 having secured on the inner surface thereof a plurality of heating elements 88 comprising a heat source. The heating elements 88 may be of the electrical resistance type and may be generally annular in shape so as to be substantially coextensive with the annular array of perforations 82 in the rear wall 60 of the drum 56. An inner baffle member 90 is rigidly secured about the periphery thereof to the rear wall 60 of the drum 56 and is disposed within the outer baffle member 86. The inner baffle member 90 is slightly smaller than the outer baffle member 86 and is disposed a slight distance inwardly therefrom and cooperates therewith to form an annular air inlet passage 92 therebetween. The inner baffle member 90 is further provided with an annular series of openings 94 opening into the rear wall 60 of drum 56. Thus, a path for air flow is provided through the air inlet passage 92 between the baffle members over the heating elements 88 through the openings 94 and perforations 82 into the drum 56. It will be noted that the inner baffle member 90 has a depressed central portion 96 to which is secured a bracket 98 supporting shaft 76 set forth above.

Access means for placing articles to be dried in the drum 56 and for removal therefrom are provided by a substantially circular access aperture or opening 100 formed in front wall 62 of drum 56 and by a hollow microwave impermeable door 102 preferably of sheet metal construction provided in front wall 50 of cabinet 42 in alignment with the access opening 100. The upper portion of the front wall 50 of the cabinet 42 is provided with a doorway defined therein by a door frame or electrically conductive door seat 104 which comprises a part-cylindrical wall sloping inwardly from the drum 56 and having a substantially flat horizontal bottom portion 106, which effectively truncates the upper portion of the part-cylindrical door seat 104 and slopes inwardly toward the drum. The door seat 104 is disposed substantially in axial alignment to the access opening 100 of drum 56 with its cylindrical portion being substantially concentric with access opening 100 and the inner edge of the door seat 104 being received within a cylindrical flange 108 integrally formed with front wall 62 and spaced radially inward a slight distance therefrom to provide clearance to permit free rotation of the drum 56.

Mounted on the outer surface of the door seat 104 around the periphery thereof is a flange 110 having secured thereto a ring seal 112 preferably formed of feltlike material and extending rearwardly therefrom and engaging the front wall 62 of the drum 56 in a sealing relationship so as to prevent leakage of air from the drum 56 between the flange 110 and the door seat 104. The door 102 is hingedly mounted on the front wall 50 of the cabinet 42 and includes an outer imperforate section 114 generally rectangular in shape, and a hollow inwardly extending portion 116 which is shaped complementary to the door seat 104 and is closed at its inner end by the inner wall 118. The door 102 is movable between an open position extending outwardly from the front wall 50 substantially normal thereto and a closed position wherein the hollow inwardly extending portion 116 is received within the door seat 104 and closes the access opening 100. The inwardly extending portion 116 of the door 102 has a flat bottom portion 120 provided with a generally rectangular opening 122 therein spaced complementary to an opening 124 in the flat horizontal bottom portion 106 of door seat 104 and disposed in registry therewith when the door is in its closed position. The inner wall 118 of the door 102 is provided with a plurality of microwave impermeable perforations or openings 126 therethrough communicating with the hollow interior of the door 102 whereby air may flow from the drum 56 through openings 126 and the hollow interior of door 102 to openings 122 and 124.

Referring now to FIGS. 2, 3 and 4, the means by which air flows from the drum 56 through perforations 126 and inner wall 118 of the door 102 to be exhausted from the cabinet 42 will be described. The intake of a centrifugal blower 128 driven by electric motor 74 is connected to a conduit such as duct 130 which includes a front section 132 and a rear section 134. The front section 132 is substantially rectangular in crosssection and extends upwardly along the front wall 50 of the cabinet 42 from the lower end thereof and then terminates in an open upper end connected to the flat bottom section 106 of the door seat 104 in registry with the opening 124 therein. The rearward extending portion 136 of the front section 132 is connected to the rear section 134 as best shown in FIG. 3. Spanning the joint between the front and rear sections of the duct 130 is a wire mesh screen 138 which serves as a reflector of microwave energy as will be hereinafter described. The exhaust of centrifugal blower 128 is directed to an outlet or exhaust opening 140.

Carried by the flat bottom portion 106 of door seat 104 in the opening 124 therein is a lint trap generally designated by the numerals 141 and which is provided with a mounting collar 142 and a filter screen 143. The mounting collar 142 is substantially rectangular in shape and is provided with a screen supporting flange 144 shaped complementary to the opening 124 and extending downwardly into the open upper end of the front duct section 132. Integral with the upper end of the screen supporting flange 144 and extending outwardly therefrom is a mounting flange 146 which overlies the bottom 120 of the door seat 104 about the periphery of the opening 124 therein for supporting the lint trap 141 thereon.

The screen 143 is preferably formed of a fine wire mesh and defines a bag or basket having an open upper end embedded in a screen supporting flange 148 on the mounting collar 142 and having a closed lower end extending downwardly into the upper end of the front duct section 132. The screen is shaped complementary to the front duct section and is spaced a slight distance inwardly therefrom so as to provide a clearance between the screen and the inner surface of the front duct section around the entire periphery thereof. In particular, the upper end of the screen is embedded in the mounting collar 142 a slight distance inwardly of the inner surface of the duct section 132 so as to be spaced therefrom by the thickness of the screen supporting flange 148, the perimeter of which is dimensioned so as to be greater than the wavelength of the frequency of operation of the microwave generator provided. The mounting collar 142 is preferably formed of plastic or other microwave transparent material as will be explained more fully hereinafter. Disposed in the bottom of the cabinet 42 adjacent the air inlet screen 80 is a magnetron 150 for producing microwave energy of a predetermined high frequency, and may be of the type disclosed in U.S. Pat. No. 3,458,755, as mentioned above.

Coupled to the output terminals of the magnetron 150 is a coaxial transmission line 152 which includes a hollow outer conductor 154 and insulated therefrom by suitable means, an inner conductor 156. The transmission line 152 terminates at the front section 132 of the duct 130, the outer conductor 154 being connected to the duct section 132 and the inner conductor 156 terminating in antenna means such as an antenna 158. The antenna 158 extends into the duct section and both the inner conductor 156 and the antenna 158 are insulated from the duct section and the outer structure by an insulating spacer 160. The antenna 158 is adapted to radiate microwave energy into the front section 132, this front section serving as a waveguide for propagating microwave energy toward the drum 56 as will be described in detail below.

There is provided in the inner wall 118 of the door 102 a microwave window generally designated by the numeral 162 and including a generally cross-shaped opening 164 covered by a plastic sheet or cover 166 which is formed of suitable microwave transparent material. The perimeter of the opening 164 is greater than one wavelength of the frequency of operation of the magnetron 150 whereby the opening serves as a microwave aperture or window as is well known to those skilled in the art.

Thus the door 102 and the duct section 132 cooperate to form a waveguide for transmitting microwave energy from the transmission line 152 into the drying chamber of the drum 56. More particularly, the microwave energy is radiated by the antenna 158 into the front section 132 which then functions as a waveguide to propagate the microwave energy upwardly therealong to the open upper end thereof. At this point, the wire mesh screen 143 of lint trap 141 is opaque to the microwave energy but the mounting collar 142 is formed of a material which is transparent to that energy and as the perimeter of the screen supporting flange 144 is greater than the wavelength of the frequency of operation of the generating means, the flange 148 thereof serves as a microwave aperture for the microwave energy. The microwave energy then passes through the opening 124 in the door seat 104 which also has a perimeter greater than one wavelength of the frequency of operation of the generator, and thence into the hollow interior of the door 102. From the door 102 the microwave energy passes through the microwave window 162 into the drying chamber of the drum 56. It will be noted that the window 162 is necessary to permit the transmission of microwave energy through the inner wall 118 of the door since the perforations 126 therein are too small to permit the transmission of such energy therethrough. Similarly, the perforations 82 in the rear wall 60 of the drum 56 will not permit the passage of microwave energy therethrough whereby the energy is confined within the drum 56.

In order to further insure that no microwave energy escapes from drum 56, the door seat 104 and the inner portion 116 of the door 102 overlap a distance corresponding to approximately 1/4 of the wavelength of the frequency of operation of magnetron 150 whereby the inner portion of the door 102 cooperates with the door seat 104 to form a quarter-wave choke joint to block the passage of microwave energy therebetween.

In operation, wet clothes to be dried are placed in the drum 56 through the access opening 100, when the door 102 is in its open position. After the door 102 is closed, the drive motor 74 is energized to begin rotation of the drum 56 and the tumbling of the clothes therein. At the same time the blower 128 is rotated to create an area of reduced pressure in the drying chamber and thereby create a stream of air through the dryer 41. This air stream is drawn into the cabinet 42 through the air inlet opening in screen 80, sweeps over the magnetron generator 150 and is drawn upwardly through the opening 92 between baffle members 86 and 90, over the heating elements 88 and through the perforations 82 of the drum 56 into the drying chamber thereof. The air stream is then swept over the clothing in the drum 56 and outwardly through the perforations 126 in the door 102 into the hollow portion thereof, through the aligned openings 122 and 124 in the door 102 and the door seat 104, respectively, through the lint screen 143, the front duct section 132, the wire mesh screen 138 and the rear duct section 134 to the blower 128. From the blower the air stream is exhausted through the exhaust outlet 140 to the atmosphere.

At this time the magnetron 150 is also energized to produce microwave energy at a predetermined high frequency, preferably in this embodiment at 915 MHz. The microwave energy is transmitted along transmission line 152 and is radiated by the antenna 158 into the duct front section 132. Duct section 132 propagates the microwave energy toward the lint trap 141. It will be noted that transmission of microwave energy through the duct 130 toward the blower 128 is prevented by the wiremesh screen 138 which serves to reflect the radiated energy thereby to confine it to the duct portion 132. The microwave energy is then transmitted through the aperture provided around the filter screen 143, through the opening 122 into the interior of the door 102 and then through the microwave window 162 into the drying chamber of the drum 56.

In the drying chamber of the drum 56, the microwave energy is selectively absorbed by the wettest portions of the clothes, serving to heat and vaporize the moisture of water content of the clothing in a well known manner. As the water in the wet clothing is vaporized by means of microwave energy, it is carried from the drying chamber of the drum 56 by the air stream passing therethrough as described above. In this manner the wet clothes are quickly and efficiently dried to any desired degree of dryness. It is an important factor of microwave drying that the wettest clothing absorbs the most microwave energy whereby the drying of heavy materials such as towels which hold a great deal of moisture is accelerated considerably while at the same time the lighter clothing which is already dried is prevented from being scorched. Thus, there is achieved a rapid and uniform drying of each load even though the load may comprise many different weights and textures of materials.

It will also be noted that the heating and vaporizing of the moisture in the clothing is accelerated by the fact that the air stream is heated before it passes through the drying chamber of the drum 56 so that it effects conventional air convection drying of the wet clothing while being able to hold more moisture. This is accomplished by the passage of the air stream over the heating elements 88 located between the baffle elements 86 and 90. Additional preliminary heating of the air is effected by the passage of the air stream over the magnetron 150 as the air stream enters the cabinet 42 through the intake screen 80. Thus, the air stream serves to cool the magnetron and the heat drawn therefrom is utilized to provide additional warming of the air to enhance its drying effect on the wet clothing.

Referring now to FIG. 5 of the drawings, there is illustrated a circuit diagram for the control means for the dryer 41 and the magnetron 150, the circuit being designated generally by the numeral 170. Circuit 170 includes the magnetron 150 and a power supply 172 therefor. Circuit 170 is coupled through a three wire Edison network which, in a typical household installation, may provide 236 volts single phase 60 HzAC and includes ungrounded conductors L1 and L2 and a grounded neutral conductor N. The three conductors terminate in an electrically insulating terminal block 174. The power supply 172 is provided with a pair of input terminals 176 and 178 coupled respectively to the line conductors L1 and L2. A first pair of output terminals 180 and 182 supply a rectified and filtered DC voltage which constitutes the DC voltage which constitutes the DC operating potential for the magnetron 150. A second pair of output terminals 184 and 186 supply relatively low voltage AC power for energizing the magnetron heater.

The output terminal 180 is connected to an input terminal 188 of the magnetron 150 through one coil 190 of a latching relay 192 via conductors 194 and 196. The latching relay 192 includes a movable contact 198, a fixed contact 200, a closing coil 202 and the coil 190 which functions as an opening coil. The contacts 198 and 200 are connected in series between the line conductor L1 and the input terminal 176 of the power supply 172. The line conductor L1 is also connected to one terminal of the closing coil 202 by means of a conductor 204 and a momentary switch 206. The other terminal of the coil 202 is connected by a conductor 208 to the neutral line N. In addition to the input terminal 188, the magnetron 150 is provided with an input terminal 210 which is connected via a conductor 212 to the output terminal 182 of the power supply 172. A third input terminal 214 is provided for the magnetron 150 and it in turn is connected via conductor 216 to the output terminal 184 of power supply 172 while the conductor 218 connects the output terminal 186 of power supply 172 to the magnetron input terminal 210.

The anode of the magnetron 150 is represented by a terminal 220 and is connected to one end of the outer conductor 154 of the transmission line 152 as at 222, the inner conductor 156 of the transmission line 152 being connected to the input terminal 210. The other end of the inner conductor 156 is connected to the antenna 158 while the other end of the outer conductor 154 is connected to the duct front section 132 which in turn is connected to the cabinet 42 as described above and is grounded as at N for safety purposes. However, since the output of the magnetron 150 may not be grounded there is provided a capacitive coupling 224 in the outer conductor 154 and a capacitive coupling 226 in the inner conductor 156 to provide DC isolation between the duct section 132 and the magnetron 150.

In operation, when it is desired to energize the magnetron 150 after the wet clothing has been loaded into the drying chamber of the drum 56 and the door 102 has been closed, the momentary switch 206 is closed thereby energizing the closing coil 202 of relay 192. Upon energization of the coil 202 the movable contact 198 is moved into engagement with the fixed contact 200 to complete an energizing circuit to the input terminals 176 and 178 of the power supply 172. The power supply when energized provides the DC and AC operationg potentials for the magnetron 150.

In accordance with the present invention, it has been found that the anode current drawn by the magnetron 150 from the power supply 172 is a function of the load impedance reflected to the magnetron 150 by the wet clothing in the drum 56. Thus, when a dryer in accordance with the invention begins to operate, the impedance reflected to the magnetron 150 by the relatively high water content of the very wet clothing in the drum 56 is such that the magnetron anode 220 draws a relatively low current. However, as the clothes in the drum 56 are dried and the moisture content thereof reduced, the impedance reflected to the magnetron 150 is such that the anode current drawn thereby correspondingly increases. Accordingly, the current through the opening coil 190 of the relay 192 also increases. The operating parameters of the relay 192 are chosen so that when the clothing has been dried to a predetermined degree of dryness, the anode current of the magnetron 150 will be sufficient to energize the coil 190 to open the contacts 198 and 200. In this manner, the power supply 172 is disconnected from the power line L1 and accordingly de-energizes when the clothing has been sufficiently dried, thereby de-energizing the magnetron 150 and interrupting the flow of microwave energy therefrom.

It will, of course, be recognized that suitable control apparatus for the control and cycling of the drive motor 74 and the heating elements 88 will also typically be provided in a dryer in accordance with the invention, such control apparatus being well known in the art. In addition, as is well known in the art, interlock switches may be provided to prevent energization of the magnetron 150 unless the door 102 is in its closed position. Further, microwave filters may be provided in the transmission line 152 to limit propagation therefrom of harmonics of the frequency of operation of the magnetron 150.

From the foregoing, it will be seen that there has been provided an improved drying machine wherein uniform drying is obtained for materials of varying weight and absorbency. In addition, there has been provided an electronic or microwave clothes dryer which efficiently utilizes the space available and existing structure of a conventional home dryer.

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be understood that various modifications may be made therein and it is intended to cover in the appended claims all such modifications which fall within the true spirit and scope of the invention.