US3210863A

US3210863A - Clothes drier control apparatus

Info

Publication number: US3210863A
Application number: US455148A
Authority: US
Inventors: Jr Dudley D Nye; Phillip M Connaught
Original assignee: Robertshaw Controls Co
Current assignee: Robertshaw Controls Co
Priority date: 1965-05-12
Filing date: 1965-05-12
Publication date: 1965-10-12
Anticipated expiration: 1982-10-12

Description

Oct 1 ,19 D. D. NYE, JR.. ETAL 3,210,363

CLOTHES DRIER CONTROL APPARATUS Original Filed Dec. 21, 1960 2 Sheets-Sheet 1 I DRYING CYCLE TERMINATION RELAY Ac. SOURCE IOO I @1 so I I -I N 40 MAXIMUM VARIATION OF TUBE FIRING POINT I --I N g I I I I O I *1 '"DRY I00 80 6O 40 I 20 7 3 0 ZMoIsTuRE INVENTORS 12 /n 9 6 & /%///p% [5???(524/ ATTORNEY 1965 D. p. NYE, JR.. ETAL 3,210,863

CLOTHES DRIER CONTROL APPARATUS Original Filed Dec. '21, 1960 2 Sheets-Sheet 2 TO TERMINALS 9 8 IO OF FIG. I

TO TERMINALS TO TERMINALS III/ 11 by y 9 8 IO 0F FIG I II11111111111111111111111111I INVENTORS dawz na 4: P/J/X p fidiz agw? Wmm ATTORNEY aired tates This application is a continuation application of our pending application Serial No, 77,363 filed December 21, 1960.

The invention presented herein relates to control apparatus which utilizes the change in the electrical conductivity of fabrics being dried in a clothes drier to provide an electrical signal for use in terminating a drying process and more particularly to such electrical apparatus which can be so used where the fabrics areimoved' about in a random manner.

A number'of clothes drier termination control circuits utilize indirect sensing of the moisture content if the fabrics being dried. Such devices do not measure the moisture content of the fabric directly, but rather the effect of the moisture on another medium. In general, this is accomplished by sensing the temeprature of the air in the exhaust duct of a drying apparatus or by sensing the relative humidity in the exhaust duct. It has been found that such drier termination controls provide reasonable accuracy only so long as each load dried is relatively the same size. The entrained or internal moisture of the fabrics-also has a bearing on the accuracy of the termination. In the case of the system which terminates the drying process by sensing the relative humidity of the exhaust air, the accuracy of the system is also effected by the ambient humidity level of the air supply.

. It is an object of this invention to provide apparatus which is responsive to direct sensing of the moisture of the fabrics being dried to provide an electrical signal for use in controlling the termination of a clothes drier.

Another object of this invention is to provide a circuit for use in'controllin'g the termination of a clothes drier which operates independently of any normal changes in the supply voltage, ambient atmospheric variations, load size, type of fabrics being dried, temperature of the air supply, and time.

A further object of this invention is to provide a drier termination control apparatus using one or more sampling electrodes positioned within the drying chamber of the clothes drier to provide 1 pair of electrical terminals which are contacted by the fabrics'being dried as they are tossed about in the drying chamber.

Briefly, the above and further objects of this invention are achieved by providing a control apparatuscomprising a source of direct voltage for charging a capacitor via a resistance network including the resistance presented by the fabrics being dried. The fabrics are tossed about during the drying process into contact with one or more sensing electrodes connected to the resistance network and positioned within the drying chamber of the drier. The resistance presented by the fabrics thus forms a part of the resistance network each-time the fabrics contact a sensing electrode. The resistance of the fabrics being dried increases as the drying'proce'ss continues, causing the voltage presented by the capacitor to be reduced in magnitude as the fabrics are dried. The capacitor is connected across a portion of the resistance network to provide a known rate of discharge for the capacitor.

The capacitor voltage is used to provide the control voltage "for a voltage responsive electronic switch used i atent to control the tlow of current to a control device arranged to terminate the drying process.

The apparatus also includes means for charging the capacitor prior to the start of the drying period in the event a sensing electrode is not contacting the fabrics to be dried at the start of the period and thus prevent the electronic switch from conducting prematurely. In order that the operator can select the degree of dryness desired for the fabrics, the source of adjustable biasing voltage is provided which opposes the voltage presented by the capacitor to vary the magnitude of the capacitor voltage at which the electronic switch conducts.

The arrangement of the resistance network is such that the ratio of the incremental decrease in voltage appearing across the capacitor versus a given incremental decrease is percent of moisture contained in the fabrics increases sufiiciently as the drying process continues to provide a control voltage versus percent of moisture relationship that permits the'use of voltage responsive electronic switches which may operate anywhere within a range of control voltages without causing the drying process to be terminated outside the desired band of dryness for the various fabrics.

For a better understanding of the invention, attention is now directed to the following description taken in connection with the accompanying drawing in which:

FIG. 1 is an electrical schematic of the control apparatus;

FIG. 2 is a graph showing the effect of normal tube parameter variations in the firing point of the thyratron shown in FIG. 1 on the percent charge of the capacitor for the degree of dryness desired for the fabrics to be dried;

. FIG. 3 is a perspective view, partially in section, of one form of sampling electrode that can be mounted within the drying chamber of a clothes drier;

FIG. 4 is a perspective view, partially in section, of another form of sampling electrode; and

FIG. 5 is a diagrammatic view of an arrangement for mounting and wiring the sampling electrodes shown in either FIG. 3 or FIG. 4 within the drying compartment of a clothes drier.

Referring now to the drawings and more particularly to FIG. 1, there is shown a transformer 1 having a primary winding 2 for connection to an alternating current source (not shown) and a secondary winding 3 which provides the electrical power for the circuit. A capacitor 4 and a series connected rectifier 5 are connected to the secondary winding 3 to provide a source of direct voltage. For descriptive convenience, it will be assumed that the rectifier 5 isconductive when the anode, designated by the arrowhead portion of the symbol, is positive with respect to the cathode. The cathode of rectifier 5 is connected to the upper portion of secondary winding 3 causing the polarity of the side of capacitor 4 connected to the rectifier 5 to be negative with respect to the other side of the capacitor.

The direct voltage available across capacitor 4 is used to charge a capacitor 6 via a resistive network 7. The resistive network 7 includes a first and second resistance branch connected in series. The first resistance branch includes a resistor 8 and the resistance presented by the fabrics electrically connected to the

terminals

9 and 10 provided by one or more sampling electrodes mounted in the drying compartment of the drier. The resistor 8 is connected to the negative side of capacitor 4. The resistance presented by the fabrics being dried in the drying compartment of a drier is represented by the variable resistor 11. The second resistance branch includes a resistor 12 connected to the resistor 11 and in series with a portion of the resistance of a potentiometer 13 via adjustable contact 14 of the potentiometer. The capacitor V the control element 16 of an electronic switch 17, such as a grid-controlled hot cathode are tube of the thyratron type. A 2D2l type thyratron tube, for example, is suitable. The thyratron tube 17 has a plate 18 and a cathode 19. The cathode 19 is connected to the same end of secondary winding 3 as resistor 13 while the plate 18 is connected to a source of electrical power via a current responsive control device indicated by the relay winding 20. The alternating voltage available from the secondary winding 3 provides a suitable source of electrical power for the thyratron 17. The connection for the plate circuit is made at the end of the secondary winding adjacent the rectifier 5. The heater element 21 of thyratron 17 may be energized in any number of conventional ways. In the circuit shown, an additional secondary winding 22 is used to provide the necessary electrical energy for the heater element 21.

A switch 23 is used to provide a short-circuit across terminals 9, prior to the start of a drying process and is removed when the drying process is started. Thus, switch 23 is closed prior to the start of the drying process and is opened when the drying process is started. One manner of accomplishing this is by mounting the switch 23 so it is actuated by the door of the drier and arranged to close when the door is open and open upon closure of the drier door. This arrangement causes capacitor 6 to have an initial charge that is sutficient to bias thyratron 17 to cut off at the start of the drying process. In addition, switch 23 provides a safety feature in that the operator will receive no current should he short out the

terminals

9, 10 while loading the fabrics in the drier. Should switch 23 become defective, the operator is protected by the resistor 8 which limits current flow via terminals9, 10 to a safe value.

The operation of the circuit is as follows: With the rectifier Sconnectcd in the manner described, the voltage appearing across the capacitor 6 is such that the side of capacitor 6 connected to the control element 16 via resistor is negative. The voltage applied between the control element 16 and the cathode 19 at any instant of time is the sum of the DC. voltage V across the capacitor 6 and the voltage V across that portion of potentiometer 13 connected between capacitor 6 and cathode 19. During one-half of each cycle of the alternating voltage supplied from secondary winding 3, the voltage V will oppose the voltage V This occurs when the upper end of secondary winding 3 is positive with respect to the lower end of the secondary winding so that the firing voltage for the thyratron is the difference between the absolute value of V. and V The potentiometer 13 connected to the secondary winding 3 thus provides a variable source of biasing voltage for altering the effect of the voltage developed across capacitor 6 on the thyratron 17. This method of biasing insures proper phasing of plate voltage and bias voltage. This is necessary since tube 17 can fire only when 18 is Neglecting the resistance presented by that portion of potentiometer 13 which carries direct current, it can be seen that the voltage V may be determined by the equation where E is the direct voltage appearing across capacitor 4. During theloading of fabrics, switch 23 is closed. R in the above equation is then zero causing V at the beginning of the drying process to be much greater than the biasing voltage V available from potentiometer 13 making the control element 16 negative with respect to the cathode 19 to bias the thyratron 17 oil. The resistance ll, representing the resistance of the fabrics being dried, increases as the drying process continues and with the capacitor 6 in parallel with resistor 12 to provide a discharge path for capacitor 6, the voltage V across capacitor 6 decreases. The control element voltage V V will be reduced in magnitude at the time the plate 18 is positive until the firing potential for thyratron 17 is reached, causing it to conduct, energizing the relay winding 20. Energizing of winding 20 is effective to terminate the drier. This can be accomplished, for example, by the opening of switch contacts (not shown) in response to energization of the winding 20 which control the flow of electrical power to the drier in the case of an electric drier. In the case of a gas drier, the output current of the thyratron 17 can be used to terminate the flow of gas to the drier. In addition, should the drier be connected to permit drying at room temperature, the energization of the winding 20 can also be used to actuate switch contacts for controlling the current to the blower motor. Other obvious ways for utilizing the output current of the thyratron 17 to terminate the drying action of a gas or electric drier will be apparent to those skilled in the art.

The degree to which the fabrics are dried before the thyratron 17 fires can be varied by the adjustment of potentiometer 13 since the alternating voltage V developed across that portion of the resistance of potentiometer 13 connected between the adjustable contact 14 and the cathode l9 alters the effect of the voltage developed across capacitor 6v Adjustment of the variable contact 14 of potentiometer 13 is made available to the operator in the form of a control knob (not shown) which controls the position of the adjustable contact 14. Appropriate dial indications are provided adjacent the control knob for the capacitors use in selecting the desired settings, e.g., dry, damp dry."

The particular resistive network for charging the condenser 6 permits the establishment of a percent charge versus percent moisture relationship which is especially desirable in view of the variation in the firing point of a gas tube such as a thyratron. FIG. 2 shows two curves. Curve A shows the percent charge versus percent moisture relationship that is obtained with the circuit described when resistance 8 is much larger than the effective resistance, while cure B shows a percent charge versus percent moisture relationship when resistance 8 is approximately equal to resistance 11. The two horizontal dotted lines show the maximum variation of'the thyratron firing point that can be expected. Such a variation results in a termination of the drying cycle when the moisture content of the fabrics of curve A is between 3% and 7%,which is the percent of moisture content of fabrics which drier manufacturers consider dry. The slope of curve A remains substantially the same between 0% and 2.0% moisture content so that the variation in the termination point for a given setting within this range will remain about 4%. Curve B is used to .show how a curve having a slope which is less than that of curve A will allow the thyratron to operate outside the desired band of dryness. Thus, for the same variation in the thyratron firing point, curve B shows that the thyratron would fire when the fabrics have a 52% to 17% moisture content which is well outside the dry range of 3% to 7% moisture content.

FIGS. 3 and 4 illustrate two types of sampling electrodes which are suitable for mounting within the drying compartment of a drier to provide the

contacts

9, 10 needed to electrically connect the resistance of the fabrics being dried in the circuit shown in FIG. 1.

The temperature of the drier during the drying process is approximately to which rules out the use of a number of materials which might otherwise be suitable. Moisture absorption of otherwise suitable insulating materials, as well as ionization of, the air caused by the static charge certain fabrics generate when in rubbing contact with some insulating materials which results in a decrease in the resistance of the fabrics presented across the sampling electrode contacts, had to be considered in the construction of the sampling electrodes.

The base 24 of the sampling electrode shown in FIG. 3 is formed from a plastic material, such as tetrafiuorethylene available under the trademark Teflon. It is, of course, necessary that the sampling electrode present a smooth surface to the fabrics. The cylindrical shape for base 24 presents such a surface and is a convenient shape for use, since Teflon is available in rod form. Metal strips 25 are secured to the base 24 by bolts 26 which extend through the strips 25 and the base 24. The metal strips 25 are spaced lengthwise on the base in parallel grooves formed in the outer surface of the base and are mounted flush with the outer surface of the base to present a smooth surface to fabrics being dried.

Though two metal strips are sutficient, the sampling electrode shown in FIG. 3 uses three metal strips which increases the possibility of obtaining good contact with the fabrics. The center metal strip is used as either one of the

contacts

9 or 10, indicated in FIG 1, while the two outside metal strips are electrically connected to provide the other contact. The side of the base 24 mounted adjacent the surface to which the sampling electrode is connected is formed to conform with the mounting surface presented to the drying compartment of a drier. The bolts 26 serve as electrical conductors in addition to providing a means for securing the sampling electrode to the mounting surface. Therefore, the bolts securing strips connected to 9 should not be connected electrically to strip connected to 10.

FIG. 4 shows a sampling electrode for contacting the fabrics to be dried which is formed using printed circuit techniques. The base 27, which is generally rectangular in shape, is formed by the thin base material used in copper-clad printed circuit material. A material suitable for use as the insulating material for a sampling electrode is sold under the trademark Textolite, which 6 in the drier drum 31, it is possible to use more than one sampling electrode to obtain better sensing of the fabrics being dried. When more than one'sarnpling electrode is used, they are connected in parallel in the circuit shown in FIG. 5.

The invention described herein is not limited to the details shown but may assume numerous forms. The scope of the invention is to be defined solely by the following claims.

What is claimed is:

1. Control apparatus operable in response to the electrical resistance of fabrics which are tossed about in a random manner while being dried in the drum of a clothes drier, comprising load circuit means including a voltage source, a load, a voltage-responsive bistable device and means connecting said source, load and bistable device in series, control voltage means including a capacitor connected with said bistable device for controlling the state of operation thereof and the state of energization of said load circuit means, means charging said capacitor to a potential that is a function of the instantaneous electrical resistance of the fabrics at a given time, said charging means including a source of charging voltage connected with said capacitor, means for discharging said capacitor at a constant predetermined rate, means mounted on said drum in intermittent contact with said fabrics for connecting at random the resistance presented by said fabrics in series intermediate said source of charging voltage and said capacitor, whereby the said capacitor is charged at random at a rate determined by said resistance presented by said fabrics, said means for discharging said capacitor including a first resistor connected in parallel with said capacitor to define a parallel branch a first terminal of which is connected with a first .terminal of said charging voltage source via said means nals of said parallel branch and said charging voltage is a woven glass fabric epoxy laminate, and is used as the 7 base material for copper-clad printed circuit material. The surface of the base 27 has two

separate metal surfaces

28, 29 formed on it. Surface 28 is a narrow strip running lengthwise of the base 27 and is centrally located on the base. The other conducting surface 29 is a closed narrow strip which surrounds the conducting surface 28. Mounting holes 30, which extend through the conducting

portions

28, 29, and the base 27, are used to secure the sampling electrode to a mounting surface with suitable metal fasteners which also serve as electric conductors. The base 27 is pliable in order that the sampling electrode can be readily secured to an irregular surface.

Choice of location and the number of sampling electrodes to use is dependent upon the drier design. FIG. 5 is a diagrammatic-drawing showing of how the necessary electrical connections are made in the case of a drier having a rotating drum 31 as the drying compartment. The sampling electrode 32, of the type shown in FIG. 3, is mounted along the edge of ribs 33 secured to the inner surface of the drum 31. The two parallel lines 34,-35, shown on the sampling electrode 32, represent the metal strips forming the

contacts

9, 10 of the circuit shown in FIG. 1. 'The drum 31 is fitted or formed with a shaft 36 which is positioned for rotation in the drier frame 37.

The metal strip 34 is electrically connected to a metal contact button 38'extending downwardly from the end of shaft36 and is insulated therefrom. A spring-loaded contact 39 is used to provide continuous contact'with contact button 38. The exterior connection from the metal strip '35 is accomplished by connecting the strip 35 to the drum 31. An electrical path is then. available from i the drumvia shaft 36 to the'frame 37.

Although one sampling electrode is shown mounted 1 source, said bistable device being responsive to the voltage across said first terminal of said parallel branch and that end of said second resistor which is connected with said charging voltage source.

2. Apparatus as defined in claim 1 wherein said second resistor is adjustable.

3. Apparatus as defined in claim 1 and further includ ing means for charging said capacitor prior to the start of the drying process comprising a short-circuiting switch connected in parallel across said means intermittently in contact with said fabrics, said switch being arranged to be closed prior to the start of the drying process and to be opened at the start of said drying process.

4. Apparatus as defined in claim 1 wherein said'load circuit voltage source is an alternating current voltage source which serves also as said charging voltage source, wherein said bistable device includes a pair of power circuit electrodes connected with opposite terminals, respectively, of said alternating current voltage source, said bistable device including a control electrode connected with said first terminal of said parallel branch, and further including a diode rectifier connected in series intermediate said means in intermittent contact with said fabrics and one terminal of said source, and another capacitor connected at one end intermediate said diode and said means in intermittent contact with said fabrics and at the other end with the other terminal of said voltage source- References Cited by the Examiner UNITED STATES PATENTS 2,045,381 6/36 Elberty 34-55 2,812,976 11/57 Haxenkamp 324-65 WILLIAM F. ODEA, Primary Examiner.

Claims

1. CONTROL APPARATUS OPERABLE IN RESPONSE TO THE ELECTRICAL RESISTANCE OF FABRICS WHICH ARE TOSSED ABOUT IN A RANDOM MANNER WHILE BEING DRIED IN THE DRUM OF A CLOTHES DRIER, COMPRISING LOAD CIRCUIT MEANS INCLUDING A VOLTAGE SOURCE, A LOAD, A VOLTAGE-RESPONSIVE BISTABLE DEVICE AND MEANS CONNECTING SAID SOURCE, LOAD AND BISTABLE DEVICES IN SERIES, CONTROL VOLTAGE MEANS INCLUDING A CAPACITOR CONNECTED WITH SAID BISTABLE DEVICE FOR CONTROLLING THE STATE OF OPERATION THEREOF AND THE STATE OF ENERGIZATION OF SAID LOAD CIRCUIT MEANS, MEANS CHARGING SAID CAPACITOR TO A POTENTIAL THAT IS A FUNCTION OF THE INSTANTANEOUS ELECTRICAL RESISTANCE OF THE FABRICS AT A GIVEN TIME, SAID CHARGING MEANS INCLUDING A SOURCE OF CHARGING VOLTAGE CONNECTED WITH SAID CAPACITOR, MEANS FOR DISCHARGING SAID CAPACITOR AT A CONSTANT PREDETERMINED RATE, MEANS MOUNTED ON SAID DRUM IN INTERMITTENT CONTACT WITH SAID FABRICS FOR CONNECTING AT RANDOM THE RESISTANCE PRESENTED BY SAID FABRICS IN SERIES INTERMEDIATE SAID SOURCE OF CHARING VOLTAGE AND SAID CAPACITOR, WHEREBY THE SAID CAPACITOR IS CHARGED AT RANDOM AT A RATE DETERMINED BY SAID RESISTANCE PRESENTED BY SAID FABRICS, SAID MEANS FOR DISCHARGING SAID CAPACITOR INCLUDING A FIRST RESISTOR CONNECTED IN PARALLEL WITH SAID CAPACITOR TO DEFINE A PARALLEL BRANCH A FIRST TERMINAL OF WHICH IS CONNECTED WITH A FIRST TERMINAL OF SAID CHARGING VOLTAGE SOURCE VIA SAID MEANS IN TERMITTENT CONTACT WITH SAID FABRICS, AND A SECOND RESISTOR CONNECTED IN SERIES INTERMEDIATE THE OTHER TERMINALS OF SAID PARALLEL BRANCH AND SAID CHARGING VOLTAGE SOURCE, SAID BISTABLE DEVICE BEING RESPONSIVE TO THE VOLTAGE ACROSS SAID FIRST TERMINAL OF SAID PARALLEL BRANCH AND THAT END OF SAID SECOND RESISTOR WHICH IS CONNECTED WITH SAID CHARGING VOLTAGE SOURCE.