US3192642A

US3192642A - Automatic fabric drying machine and control means

Info

Publication number: US3192642A
Application number: US150578A
Authority: US
Inventors: Philip G Hughes
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1961-11-06
Filing date: 1961-11-06
Publication date: 1965-07-06
Anticipated expiration: 1982-07-06
Also published as: GB989906A

Description

y 6, 1965 P. G. HUGHE S 3,192,642

AUTOMATIC FABRIC DRYING MACHINE AND CONTROL MEANS Filed Nov. 6, 1961 3 Sheets-Sheet 1 INVENTOR. PH\LI P e. HUGHES H as ATTORNEY July 6, 1965 P. e. HUGHES 3,192,642

AUTOMATIC FABRIC DRYING MACHINE AND CONTROL MEANS Filed NOV. 6, 1961 3 sheetsrsheet 2 MPLIFIER 6 (,4, 5| .5 4 l AvA'A 58 s4 s9 56 53 S! II I k r17 s LLEI sucnaAL REFLECTED 5 DRY FAIRICS I00 1 1 5 l 5 l o w 29 3o 40 5'0 60 7o DRYtNG TIMI. m M\NUI'I.5

'4 or WATER RETENHON F l G 4 ENVELOPE oi VOLTAGE STANDING WAVES INVENTOR.

PHILIP G. HUGHES .40 MINUTES BY w P j f H \5 ATTORNEY AUTOMATIC FABRIC DRYING MACHINE AND CONTROL MEANS Filed Nov. 6. 1961 P. G. HUGHES 'July 6, 1965 3 Sheets-Sheet 3 FlG.7

Fias

INVENTOR. PHHJP G. HUGHES BY Q2 M H \S ATTORNEY United States Patent This invention relates to an automatic fabric drying machine, and more particularly to an improved system in such machines for sensing when the fabrics therewithin are substantially dry and for accordingly terminating further drying operations within the machine.

Many commercially produced fabric drying machines are provided with means for automatically terminating a drying cycle when the clothes are substantially dry, as opposed to the earlier approach of requiring that the operator estimates the drying time of the clothes and set a timer accordingly. While a number of systems have been evolved for determining when the clothes are dry and shutting oi the machine, a substantial difiiculty in virtually all of them has been in the achievement of a high degree of sensitivity and accuracy as the clothes approach dryness so that the machine will be accurate in its determination and will tend neither to overdry nor to underdry clothes.

For this reason, it is an object of my invention to provide an improved control system for a fabric drying machine wherein the drying operation is automatically terminated in response to the elimination of substantially all moisture from the fabrics in the machine.

A more specific object of my invention is to achieve the aforementioned goal by the use of high frequency electromagnetic waves emitted into the fabric container.

Yet a more specific object of my invention is to achieve the desired goal of terminating the operation when the fabrics are dry by matching the wave length of the high frequency waves to the dimensions of the clothes container so that the container will reflect a predetermined part of the emitted waves when the clothes reach the desired condition of dryness.

In one aspect of my invention I provide a fabric drying machine which has, in the usual manner, a substantially closed fabric container of conductive material. This may, for instance, be a rotating tumbler or drum formed of sheet metal. Suitable means are provided for drying the fabrics contained in the drum, and While these may assume any desired form, the usual typical structure involves the application of heat to the fabrics in the drum to evaporate the moisture in the fabrics, and then some means for carrying off the evaporated moisture. I further provide means for generating an electric current having a high frequency, and I couple this generating means to a suitable structure positioned so that it emits electromagnetic waves of high frequency into the container.

The container is so proportioned to the frequency of the waves that the reflection of the waves from the container changes toward a predetermined pattern as the amount of moisture in the fabrics within the container decreases toward substantial dryness. Stated differently, wet fabrics, by the absorption and reflection of power by the moisture in the fabrics, modify the pattern of wave reflection from that which exists when substantially all the power inflection is provided by the container. As the fabrics dry, the modification of the wave pattern becomes less and less, approaching more closely to the predetermined dryness pattern as the moisture content of the fabrics decreases. Measuring means are provided to determine the pattern of reflection of the emitted waves, and when the measuring means determines that the reflection of the waves has assumed a predetermined $392,642 Patented July 6, 1965 pattern it causes the drying means to be shut off to terminate drying within the machine. With this structure, a drying operation is automatically terminated as a direct function of the amount of moisture within the drum regardless of the type of fabric involved, and regardless of whether the moisture is deep within the fabrics or at the surface of the fabrics.

The subject matter which I regard as my invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. My invention, however, both as to organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings.

In the drawings,

FIGURE 1 is a side elevational view of a clothes dryer incorporating my improved dryness control arrangement, the View being partly broken away and partly sectionalized in order to illustrate details;

FIGURE 2 is a schematic illustration of my improved control system as used in the machine of FIGURE 1;

FIGURE 3 is a graph showing actual experimental results in a machine of the type described in FIGURES l and 2 for different types of clothes loads;

FIGURE 4 is another graph showing experimental results in a machine of the type described in FIGURES l and 2 for a typical clothes load;

FIGURE 5 is a fragmentary side elevational view of a clothes dryer of the general type shown in FIGURE 1 but which incorporates a second embodiment of my improved dryness control arrangement;

FIGURE 6 is a fragmentary side elevational view of a clothes dryer of the general type shown in FIGURE 1 in which a third embodiment of my invention is shown; and

FIGURE 7 is a fragmentary side elevational view of the front part of a clothes dryer of the general type shown in FIGURE 1 illustrating a fourth embodiment of my invention.

Referring now to FIGURE 1, I have shown therein a domestic clothes dryer 1 including a clothes tumbling con tainer or drum 2 and provided with a suitable outer casing or cabinet 3 which completely encloses the drum on all sides. The drum is mounted for rotation within cabinet 3 on a substantially horizontal axis, and is generally cylindrical in shape, having a first outer cylindrical wall portion 4, second and third cylindrical outlet wall portions 5 and 6 located respectively adjacent the ends of the drum, a back wall '7, and a front wall 8. The drum is formed of sheet metal; outer wall portions 4, 5 and 6 are formed of imperforate sheet metal over their entire length, so that the entire outer shell of the basket is imperforate; on the interior surface of central portion 4 there is provided a plurality of clothes tumbling ribs 9 for causing the basket, when it rotates to move the clothes upwardly and then drop them thereby continually to change the exposed surfaces of the fabric. Ribs g are preferably formed of non-conductive material, in this particular embodiment, although appropriate design of the various components has been found to permit the use of a drum with ribs of conductive material.

The front of drum 2 is rotatably supported within the outer casing 3 by means of a pair of idler roller wheels, one of which is shown by the numeral 10, which are rotatably secured to the top of an upwardly extending member 11. Member 11 is mounted at its bottom to the base 12 of the machine. Rollers 10 are disposed beneath the drum on each side thereof in contact with portion 6. The rear end of the drum receives its support from a roller wheel 13 which is positioned beneath porsasaeee tion of the drum in supporting and frictionally driving engagement therewith.

Roller 13 is secured on a. shaft 14 supported in bearings 15. Shaft 14 is secured to a pulley 16 which is driven from a belt 17 in turn powered by a pulley 18 mounted on the end of a shaft 19 of an electric motor 2d. The motor, pulleys, and roller 13 are so proportioned to drum 2 and to each other that drum 2 is rotated by roller 13 at the appropriate speed to provide tumbling action for mticles of clothing placed therein.

In order that a stream of drying air may be introduced into and passed through the clothes drum, the drum is provided with a central aperture 21 in its front wall 8 and with a plurality of perforations 22 extending in an annulus around back wall 7. Rigidly secured to the rear wall 23 of easing 5 by any desired means such as, for instance, welding at points 24, is a bafile member 25 which has secured thereto heating means such as an electric heater 25 appropriately insulated from the baffle member. Heating elements 26 may be annular in shape so as to be generally coextensive with perforations 22 and drum 2. A baille member 27 is rigidly secured to the back wall 7 of the drum outside the ring of perforations 22 and within the stationary baffle 25 so that an annular air inlet 28 is in effect formed by the baffles 25 and 27. Battle 27 is further provided with an annular series of spaced openings 29. In this manner, a passage is formed for air to enter annular opening 26 between the bafiles, pass over the eating elements 26, and through openings 29 and perforations 22 into the interior of the drum 2.

In addition to the air guiding function, the baffles 25 and 2'7 help rollers it} and 13 to support the drum 2. Secured to the central portion 3% of battle 27 is a bracket 31 to which in turn is secured a stub shaft 32 substantially coaxially positioned relative to drum 2. The central portion of battle 25 has a slot-like opening 34 formed therein. The slot is suitably formed (as is more fully described in copending application Serial No. 789,869

filed lanuary 29, 1959, now Patent No. 3,009,259, by I William F. Simpson and assigned to the same assignee as this invention) so as to permit stub shaft 32 a limited amount of movement in the vertical direction but virtually no movement in the horizontal direction. Thus, the slight vertical motion of the drum which results from the tumbling of the clothes can be accommodated while at the same time undesirable horizontal motion is afiirmatively prevented by engagement of stub shaft 32 in slot The front opening 21 of the drum is substantially closed by means of a stationary bulkhead generally indicated by the numeral 35. Bulkhead 35 is made up of a number of adjacent members including the inner surface 36 of an access door 37 mounted on the dryer cabinet, stationary frame 38 for the door, the inner surface 39 of an exhaust duct 4d, and an annular flange 41 mounted on the frame 35 and on the duct wall. It will be noted that a suitable clearance is provided between the inner edge of the drum opening 21 and the edge of bulkhead 35 so that there is no rubbing between the drum and the bulkhead during rotation of the drum. In order to prevent any substantial air leakage through opening 21 between the interior and the exterior of the drum a suitable ring seal 32, preferably formed of felt-like material, is secured to flange 41 in sealing relationship with the exterior surface of drum wall 8.

Front opening 21, in addition to serving as part of the air flow path through the drum, also serves as a means whereby clothes may be loaded into and unloaded from the drum. The door 37, whose inner surface forms part of the bulkhead closing the opening, is movably mounted on cabinet 3 for movement between its closed and open positions; when the door is open, the clothes may be insorted into or removed from the drum through the door Cil frame 38. It will be noted that the door includes an outer flat imperforate section t3, and an inwardly extending hollow section 44 mounted on the fiat outer section. Hollow section 44 extends into the door frame 38 when the door is closed, and the door surface 36 which comprises part of the combination bulkhead is actually the inner wall of the hollow section. Surface 36, while it is preferably made up primarly of sheet metal, includes a section 45 formed of some dielectric material which is substantially rigid and formed to withstand the heat within the dryer. in this connection, the polypropylenes are one typical class of substances which may be used. Directly behind the sheet of dielectric material there is provided a metallic sheet-metal box-like member 46 which is substantially enclosed on all sides except at its front where it abuts sheet 45. This member 46, positioned in the door 37, forms an important part of my invention and will be further explained herebelow in connection with the system of FIGURE 2.

The air opening from the basket is provided by a perforated opening 47 which may be formed in the inner wall 36 of the hollow door section 44. The bottom wall section of door section 4-4 and the adjacent wall of door frame 38 are provided with aligned openings &8 and 49, opening 49 providing the entrance to duct 46. As shown, a lint trap 50 which may comprise a fine mesh bag is preferably positioned in duct 46 at opening 49, the bag being supported by the door frame. Duct 4% leads to suitable air moving means which may, as shown, comprise a centrifiugal blower 51 mounted on the shaft of motor 2% and thus driven directly by this motor. The outlet of blower 49 communicates with a suitable outlet duct (not shown) which is formed in the usual manner so as to permit passage of air out of the machine 1. During operation of motor 20, the rotation of blower 51 causes air to be drawn into cabinet 3 through any suitable opening such as that shown by the numeral 52 provided at the front of the machine. The air then passes through annular opening 28, over heater elements 26, through openings 29 and perforations 22 into drum 2, and across the drum, through perforated opening 47 and aligned

openings

48 and 49 into duct 40, and then through the blower 51 to the aforementioned outlet duct.

It will be understood at this point that a conventional timing mechanism, which is schematically shown by numeral 53 in FIGURE 2 but is not otherwise shown, may be provided. Timer 53, through a suitable manual control such as that shown at 54 in FIGURE 1, may be caused to initiate the operation of motor 28 and the heating element 26 so that air is drawn into the machine over the heater so as to be heated, and then into the basket where it heats the clothes and thus causes evaporation of moisture from the clothes. The air is then exhausted through the aforementioned path, carrying off with it the evaporated moisture.

As one important component of my invention, I provide, as shown in FIGURE 2, a circuit generally indicated by the numeral 55 for generating a high frequency current power output. A relatively typical circuit is shown for achieving this purpose. It will be understood that the term high frequency is used in a non-technical sense, and includes frequencies in both the VHF and UHF zones as they are technically defined (30 megacycles to 300 megacycles for Vl-IF and 300 megacycles to 3000 megacycles for UHF). The circuit includes a suitable transistor 56 having a base 57, an emitter 5S, and a collector 59. A feed back capacitor 60 is connected across the emitter and the collector so as to provide capacitive feed back from the collector to the emitter. The collector 59 of transistor 56 is connected to a resonant circuit 61 which includes an inductive loop 62, and a tuning capacitor 63 connected across the inductive loop. Power input to the emitter may be provided from any source of DC. power which, in the present case, is shown schematically for the sake of simplicity in the form of a battery 63a. The circuit further includes suitable dropping

resistors

64 and 65, a bias resistor 66 and bypass capacitors 67 and 68 having one side connected to ground 69.

For the particular conventional circuit shown, it has been found that a germanium mesa transistor such as Model No. 2Nl405 manufactured by Texas Instruments, Inc., may be used for transistor 56 in connection with a 12 volt source of DC. power as typified by battery 63a. In this circuit, suitable values for resistors 64-, 65 and 66 are 1,000 ohrns, 2,000 ohms and 10,000 ohms respectively. The two bypass capacitors 6'7 and 68 may be on the order of 100 picofarads, and the feed back ca pacitor 60 may be on the order of 1 picofarad. The tuning capacitor 63 may be variable between values of 1 to picofarads thereby to provide output wave frequencies on the order of 250 megacycles to 1,000 megacycies.

The generating circuit 55 described hereabove may be coupledto a suitable transmission line member 70 by any suitable means. In the present case, the coupling means is shown as a tap 71 on the loop 62, but it will be understood that any other type of coupling, such as inductive or capacitive, may be used.

A downwardly extending probe portion 75 of structure 70 is provided extending through a small opening 76 into sheet metal member 46. The box member 46 is so formed that its back surface 77 is spaced as closely as opssible to one quarter wave length from the probe 75. It is well known that the wave length (X) may readily be found by dividing the speed of light by the frequency (f), i.e., the formula This formula shows that at frequencies below 900 megacycles, the wave length exceeds 33 centimeters, and in the particular structure shown the door will not normally have a thickness suitable to provide the M4 spacing. Therefore, as can be seen in FIGURE 1, probe 75 is located as far forward toward the sheet 45 as possible so as to leave the maximum distance between probe 75 and the back wall 77 of member 46. With this arrangement, member 46 in effect forms a guide for the waves which emanate from the probe 75, propagating them into the drum 2. The wave guide 46 further has its side walls 73 each preferably spaced laterally at least one quarter wave length from the downwardly extending probe 75 for the purpose of avoiding excessive attentuation of the electromagnetic wave emission from the probe 75.

The equipment thus far described in connected with FIGURE 2 is provided for the purpose of causing power in the form of high frequency electromagnetic waves to emanate from probe 75 and be guided by the wave guide 46 into the drum 2 which, in the terminology of microwave technology, forms, cavity in that it is a dielectric region of arbitrary form entirely enclosed by conducting walls. In this connection, it will be understood that the small openings which are provided within the drum 2 to permit air circuation into and out of the drum may in effect be ignored for the purpose of considering the drum to be entirely enclosed by conductive walls.

When a cavity is excited by electromagnetic waves whose length is short compared to the dimensions of the cavity, resonance may be found in the vicinity of many frequencies due to reflections from the walls of the cavity which cause standing waves to be produced in the electromagnetic fields inside the cavity. Also, standing waves of voltage andcurrent will be found in the transmission line that feeds the cavity resonator (or probe).

This resonance effect is obtained when the space within drum 2 is fully occupied by substantially low loss dielectric material such as air or dry fabrics. However, when wet fabrics are being tumbled in the drum 2, they represent a poor insulator, that is, rather than being a high grade dielectric they represent a lossy dielectric. The

meter per sec.

presence of wet fabrics therefore results in absorption and reflection of a very substantial part of the emitted power by the water; when this occurs, the waves do not reflect off the surfaces of the drum so as to have the anticipated effect on the emitted waves. the presence of wet fabrics within the cavity provides a substantial difference in the reflective action on the emitted waves from that which might normally be expected from the reflected waves.

It will be seen from the foregoing that, when the pat tern of wave reflection for dry clothes within drum 2 has been determined, it is then only necessary to provide suitable means which, in response to attainment of that pattern of reflection, will then cause termination of the drying operation. While this may be done in several ways, I prefer to measure the fluctuations of the voltage standing wave in the transmission line 70 coupling the generator circuit 55 to the probe 75. This may be measured by suitable connection of a crystal diode 79 to member 70 at a suitable location experimentally determined. A signal is then passed by diode 79, as shown, to an amplifier which may be entirely conventional and is therefore shown simply by the box 80. Amplifier 80 has a pair of

output terminals

81 and 82 across which a relay coil 83 is connected. When the signal output passed by rectifier 79 reaches a predetermined level, the relay 33 is energized, closing its associated switch 84 and thereby energizing the aforementioned timer motor 53. The timer motor may then provide a few more minutes of heating to insure bone dryness if such is desired, or may provide a cool-down period during-which the motor 20 operates and the heaters do not. These are conventional aspects of automatic drying machines and, being well known in the art, are therefore not further described herewithin. Of course, in the event appropriate sensitivity or time delays are incorporated in the system, the predetermined pattern of reflection which shows that the clothes are dry may cause termination of the heating operation immediately without any further operation of the machine 1.

By using a system substantially in accordance with the above description, excellent control of fabric dryness has been achieved using, experimentally, mc., 375 mc., 500 mc., 780 mc. and 915 mc. These frequencies thus represent typical values which may be used, although it will be understood that my invention is not limited by these frequencies, and that other frequencies, including both higher and lower ones, may be found appropriate in particular instances.

To illustrate one example of my invention, there are shown in FIGURE 3, in graph form, the results of drying different clothes loads in a drum 18 inches deep and 25% inches in diameter, wherein a 9-15 mc. signal was being emitted and suitable equipment was being used to measure the degree, or level, of reflection of the signal.

7 Curve A reprsents a 3% pound load of synthetic fabrics,

Curve B is a 6 pound stuffer load (uniformly sized pieces of thin cotton fabric), Curve C is a 6 pound standard AHLMA load (a mixed load of cottons including a sheet, towels, shirts, etc. representing a typical family load), and Curve D is a 13 /2 pound bath mat load. It can be seen that, for the three loads which were fully dried (Curves A, B and D), virtually the same percent reflection indicated bone dryness, and that, for a lesser percentage reflection, a slight degree of dampness (Curve C) is present. Thus, with the knowledge that in this particular system about 80% reflection means dryness, conventional controls may be provided to give either dryness or any desired limited degree of dampness at the end of a cycle.

A further understanding of the operation of my inven tion can be attained by reference to FIGURE 4, which represents test results obtained in the complete drying of a 6 pound AHLMA load in a drum of the dimensions described and again with a field of 915 mc. As has been stated, it is not necessary to use the level of reflection In other words,

as the criterion, as was done in connection with the test runs illustrated in FIGURE 3. Rather, as shown in FIG- URE 4, other reflection patterns such as the magnitude of the standing wave, which represents the voltage fluctuation during drum rotation, may be measured with the knowledge that the magnitude of the fluctuations decreases to a predetermined level when the clothes are dry. This type of measurement is easily made with the connections shown in FIGURES 1 and 2 and also represents an accurate reflection of the condition of the clothes as to dryness. In this respect it will be noted that two separate functions are plotted along the ordinate; the abscissa represents time in minutes, while both (1) percent Water retention by the fabrics, and (2) the voltage standing wave envelope, or magniture of voltage fluctuation, are plotted along the ordinate.

It can been seen that the voltage fluctuation remains at a high level as long as a substantial amount of liquid is retained in the clothes. Then, when the liquid retention decreases to 15 percent, the voltage fluctuation starts to decrease, and this decrease continues until a water retention of 5% is reached. Thus, as the clothes approach dryness, the system actually increases in sensitivity over that which it had when there was a substantial amount of water in the clothes. in other words, the fluctuations remain substantially constant throughout the wide range when the clothes are quite wet, but decrease quite steeply as dryness is approached so that in the area of dryness and minor dampness there is high sensitivity. This is most desirable in a system intended to measure the dryness of fabrics and shut off a machine in response thereto.

While the level of reflection in the drum and the magnitude of the voltage standing wave have been shown as two useful reflection patterns serving as measuring sticks, it will be understood that the invention encompasses any of the conventional means of measuring the pattern of the standing waves or the modification of power requirements. Thus, for instance, rather than measuring the voltage standing wave in the transmission line, as has been done in the present case, the ratio of input to output, or the amount of power being required by the generator also serve as indications of Whether and to what degree the waves are being absorbed and reflected by water rather than reflected by the drum walls. Thus, the power requirements of the circuit 55 could be measured and also provide the intelligence as to the wave reflection pattern. Another system that could be used is to match the impedance of the dry clothes load so that with dry clothes there is very little reflection, and with wet clothes 2. larger reflection. In other words, what is provided, in the board sense, is a change that is indicative of the water content of the clothes in the region near dryness.

All of these phenomena, or indicia of phenomena, could be used .to provide a signal which in turn could be amplified to achieve a control function. Also, of course, any desired wave generating arrangement could be used rather than the one specifically shown to illustrate the invention.

It will further be understood that, while as described the introduction of the electromagnetic field into the drum cavity has been effected by means of a probe positioned in the door of the machine together with a wave guide for sending the field into the cavity, it will readily occur to those skilled in the art that a probe may be insorted into the cavity itself; this would eliminate the need for a particular structure such as box or guide 46 to guide the field into the cavity.

In this connection, in FIGURE 5 there is shown in enlarged form a drum structure wherein the back wall '7 of a typical drum, like that of FIGURE 1, includes the supporting bracket 31 and the stub shaft 32 extending through opening 34. In this case, the stub shaft is made hollow with an opening 89 extending therethrough to permit the entrance of a probe 81. It will be understood that while it is not shown, the probe 81 is coupled to a w suitable generating circuit in the same manner as discussed in connection with the structure of FIGURES 1 and 2. With the probe extending directly into the cavity formed by the drum, the need for a wave guide in order to direct the electromagnetic field into the drum is obviated.

Of course, in order to prevent the fabrics within the drum from becoming tangled on the extending probe, a suitable cover 82 of dielectric material may be provided, which extends smoothly from wall 7 so as to entirely enclose the probe 81, it being understood that clothes will slide off part 82 Without any problem. With part 32 made of a suitable dielectric material, it will be understood that the probe 81 is within the drum cavity in the true sense of the word, and that the member 82 merely becomes another factor to be dealth with in providing the level at which the signal used will cause the drying cycle to be ended.

Yet another means of introducing the field so as to excite the cavity formed by the drum is shown in FIG- URE 6, wherein it is shown that the tumbling ribs 9 are formed of plastic or non-conductive material, with a conductive loop 83 being positioned within at least one of the ribs so as to excite the cavity. In this case, of course, some suitable slip ring arrangement would be desirable in order to provide the necessary power to the generating circuit, but the details of such an arrangement will readily be apparent to those skilled in the art.

Yet a further structure, shown in FIGURE 7 and high ly suitable in those cases Where the dryer door is of limited thickness, is the provision of a probe 84 suitably covered by a smooth member 85 of dielectric material secured to the inside surface of the door. This structure is very similar to that discussed in connection with FIG- URE 5, in that a straight sationary probe provides the necessary excitation within the cavity to effect a dryness measurement.

It can be seen from the foreging that my invention provides a control system for a drying machine wherein the dryness of the fabric within the container is measured directly by virtue of the changing dielectric and energy absorbing qualities of the fabrics as they become dried.

While in accordance with the patent statutes I have described what at present is considered to be the preferred embodiment of my invention, it will be obvious to those skilled in the art that various changes and modifications, including but not limited to those specifically mentioned above, may be made therein without departing from the invention, and it is therefore aimed in the appended claims to cover all such equivalent variations as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A fabric drying machine comprising: a substantially closed fabric container of conductive material; means for drying fabric in said container; means for generating an electric current having a high frequency; means coupled to said generating means and positioned to emit electromagnetic waves of said high frequency into said container; means for measuring the extent to which the emitted waves are reflected from said container, said container being proportioned to said high frequency so that the reflection of said waves changes toward a predetermined pattern as the amount of moisture in the fabrics in said container decrease toward substantial dryness of the fabrics; and means connected to said measuring means and responsive to said predetermined pattern of reflection to shut oil said drying means,

2. The apparatus defined in claim 1 wherein said means coupled to said generating means includes a conductive probe member extending into said container, said measuring means also being coupled to said probe member so as to measure the standing waves in said probe member.

3. A fabric drying machine comprising: a substantially closed fabric container of conductive material; means for drying fabrics in said container; means for generating an electric current having a high frequenc; at least part of said container being formed as a wave guide for electromagnetic waves of said high frequency; means coupled to said generating means for emitting electromagnetic waves of said high frequency through said wave guide into said container; means for measuring the extent to which the emitted waves are reflected from said container, said container being proportioned to said high frequency so that the reflection of said Waves changes toward a predetermined pattern as the amount of moisture in the fabrics in said container decreases toward substantial dryness of the fabrics; and means connected to said measuring means and responsive to said predetermined pattern of reflection to shut 01f said drying means.

4. The apparatus defined in claim 3 wherein said means coupled to said generating means includes a metallic probe member extending into said wave guide, said measuring means also being coupled to said probe member so as to measure the standing waves in said probe member and wave guide.

5. The apparatus defined in claim 1 wherein said container is in the form of a substantially cylindrical metallic drum rotatably mounted for rotation on a non-vertical axis thereby to effect tumbling of fabrics within the drum.

6. A fabric drying machine comprising: a substantially closed fabric container of conductive material comprising a substantially cylindrical metallic drum having one open end for access purposes and mounted for rotation on a non-vertical axis; a cabinet enclosing said drum; and a metallic door in said cabinet arranged to engage said open end of said drum thereby to complete an enclosure therewith; means for drying fabrics in said enclosure; means for generating an electric current having a high frequency; said door having a portion thereof formed as a wave guide for electromagnetic waves of said high frequency; means coupled to said generating means for emitting electromagnetic waves of said high frequency through said wave guide into said enclosure; means for measuring the extent to which the emitted waves are reflected from said enclosure, said enclosure being proportioned to said high frequency so that the reflection of said waves changes toward a predetermined pattern as the amount of moisture in the fabrics in said enclosure decreases toward substantial dryness of the fabrics; and means connected to said measuring means and responsive to said predetermined pattern of reflection to shut off said drying means.

7. The apparatus defined in claim 1 wherein said means for drying fabrics includes heating means positioned to heat the fabrics in said container, and means for removing the moisture evaporated from the fabrics, said means responsive to said predetermined pattern of reflection being effective to cause said drying means to be shut off in response to said predetermined level of reflection.

8. The apparatus defined in claim 3 wherein said wave guide is substantially rectangular in form, and said coupled means includes a member extending through a wall of said Wave guide thereinto.

9. The apparatus defined in claim 8 wherein said means for measuring the extent to Which the emitted waves are reflected includes a diode positioned to measure the standing wave of the electromagnetic field within said container.

14 The apparatus defined in claim 1 including a timer mechanism effective when started to toll a predetermined operation of said drying means and thereupon stop operation of said drying means, said timer being started in response to said predetermined pattern of reflection.

11. A fabric drying machine comprising: a substantially closed fabric container of conductive material comprising a substantially cylindrical metallic drum having one open end for access purposes and mounted for rotation on a non-vertical axis; a cabinet enclosing said drum; and a metallic door in said cabinet arranged to engage said open end of said drum thereby to complete an enclosure therewith; means for drying fabrics in said enclosure; means for generating an electric current having a frequency; means coupled to said generating means and extending into said enclosure for emitting electromagnetic waves of said high frequency into said enclosure; smooth means formed of dielectric material covering said coupled means within said enclosure; means for measuring the extent to which the emitted waves are reflected from said enclosure, said enclosure being proportioned to said high frequency so that the reflection of said waves changes toward a predetermined pattern as the amount of moisture in the fabrics in said enclosure decreases toward substantial dryness of the fabric; and means connected to said measuring means and responsive to said predetermined pattern of reflection to shut off said drying means.

12. The apparatus defined in claim 11 wherein said coupled-means extends into said enclosure through said door.

13. The apparatus defined in claim 11 wherein said coupled means extends into said enclosure through the end thereof opposite said open end.

14. The apparatus defined in claim 11 wherein said drum has clothes tumbling ribs of non-conductive material formed therein and said coupled means extends into said drum within at least one of said ribs.

References titted by the Examiner UNITED STATES PATENTS 2,045,381 6/36 Elberty 34-55 2,611,804 9/52 Zaleski 32458.5 2,729,786 1/56 Wild 32458.5 2,792,548 11/57 Hershberger 32458.5 2,882,610 4/59 Hughes 3445 3,034,046 4/62 Sasaki 32458.5 3,079,552 2/63 Walker 32458.5

PERCY L. PATRICK, Primary Examiner.

NORMAN YUDKOFF, Examiner.

Claims

1. A FABRIC DRIVING MACHINE COMPRISING: A SUBSTANTIALLY CLOSED FABRIC CONTAINER OF CONDUCTIVE MATERIAL; MEANS FOR DRYING FABRIC IN SAID CONTAINER; MEANS FOR GENERATING AN ELECTRIC CURRENT HAVING A HIGH FREQUENCY; MEANS COUPLED TO SAID GENERATING MEANS AND POSITIONED TO EMIT ELECTROMAGNETIC WAVES OF SAID HIGH FREQUENCY INTO SAID CONTAINER; MEANS FOR MEASURING THE EXTENT TO WHICH THE EMITTED WAVES ARE REFLECTED FROM SAID CONTAINER, SAID CONTAINER BEING PROPORTIONED TO SAID HIGH FREQUENCY SO THAT THE REFLECTION OF SAID WAVES CHANGES TOWARD A PREDETERMINED PATTERN AS THE AMOUNT OF MOISTURE IN THE FABRICS IN SAID CONTAINER DECREASE TOWARD SUBSTANTIAL DRYNESS OF THE FABRICS; AND MEANS CONNECTED TO SAID MEASURING MEANS AND RESPONSIVE TO SAID PREDETERMINED PATTERN OF REFLECTION TO SHUT OFF SAID DRYING MEANS.