US3266167A

US3266167A - Dryer control

Info

Publication number: US3266167A
Application number: US270901A
Authority: US
Inventors: Finnegan Francis
Original assignee: Texas Instruments Inc
Current assignee: Texas Instruments Inc
Priority date: 1963-04-05
Filing date: 1963-04-05
Publication date: 1966-08-16
Anticipated expiration: 1983-08-16
Also published as: FR1415973A

Description

Aug. 16, 1966 F. FINNEGAN 3,266,167

DRYER CONTROL Filed April 5, 1963 3 Sheets-Sheet 1 29u/ Z9 U3 P- LL/o H5476? Lj L2 :29h /LLZ-o Moro@ AA/ a 014/51? i t; L I CJ D, D2 1 L3 l pB 29C R3 Mo/srz/Rf 35 m 1|; sfws/A/G\ R ,5- U

I 7 TL FIG. 2.

'Filed April 5, 1963 Aug. 16, 1966 F. FlNNl-:GAN

DRYER CONTROL FIGB.

5 Sheets-Sheet 2 Aug. 16, 1,966 F. FINNEGAN 3,256,167

DRYER CONTROL Filed April 5, 1965 5 Sheets-Sheet 3 HG. 5. *y $13 l ro HEATER U. 29a LL/ 29. --C Jr I| LL 29o I United States Patent O 3,266,167 DRYER CUNTROL Francis Finnegan, Brockton, Mass., assigner to Texas Instruments Incorporated, Dallas, Tex., a corporation of Delaware Filed Apr. 5, 1963, Ser. No. 270,901 7 Claims. (Cl. 34--45) This invention relates to a dryer control, and more particularly to methods and apparatus for measuring the moisture content in items to be dried and for terminating a drying cycle of a dryer at a preselected level of moisture content.

Among the `several objects of this invention may be noted the provision of a control for accurately determining the moisture content in items or a load being dried; the provision of such a control which is independent of drying temperature and which therefore may be employed to control the drying of very delicate fabric Where there is little or no heat applied; the provision of a control of the class described which does not employ costly or elaborate moisture sensing apparatus; the provision of a control for a dryer which terminates a drying cycle when the moisture content of items being dried is reduced to a preselected level, and wherein this level may be readily and accurately selected; the provision of a control of the class described which can respond to the wettest piece in a load including items which exhibit nonuniform drying rates; the provision of a control for a dryer in which the system characteristics can be readily and continuously varied from a wettest piece response to an average wetness piece response; the provision of a method for measuring the moisture content of a load being dried, and for terminating a drying cycle at a preselected level of moisture content; and the provision of a control for a dryer which employs a reduced number of complex components and which is therefore relatively inexpensive and highly reliable in operation. Other objects and features will be in part apparent and in part pointed out hereinafter.

Brieiiy, the present invention relates to a control for a dryer having a drum in which a load to be dried is tumbled or agitated. This 4control comprises a pick-up assembly having first and second terminals and a pair of pickup elements electrically connected to a respective one of these terminals. These pickup elements have conductive portions in electrical contact with the load or items within the drum so that this load establishes or completes a current path between the irst and second terminals. The resistivity of the items being dried is a function of the amount of moisture present in the items. As the items become dry, their ability to conduct decreases and as a result, the resistance of the circuit or current path between the two terminals of the pickup assembly is a function of the moisture content of the load or items being dried. The control of this invention further includes switching means adapted when actuated to terminate a drying cycle of the dryer, and an electrical circuit interconnected with the terminals of the pickup assembly for actuating this switching means when the resistance of the current path between the terminals of the pickup assembly indicates that the moisture content of the items within the drum is at or below a preselected level. The electrical circuit includes means for accurately and in `some forms for also continuously, varying this preselected level thereby to control the moisture content of the items at which the drying cycle is terminated. In one preferred embodiment disclosed herein, the electrical circuit also includes means which insures that the Wettest items in a load having nonuniform drying rates have reached the above-mentioned preselected level. Accordice ing to another embodimenL-the electrical circuit includes means for determining whether the system responds to the average moisture content of the items in the drum or to the wettest items within this drum.

The invention accordingly comprises the constructions and methods hereinafter described, the scope of the invention being indicated in the following claims.

In the accompanying drawings in which several of Various possible embodiments of the invention are illustrated,

FIG. l is a perspective phantom view of a clothes dryer illustrating generally the physical details of one exemplary embodiment of the present invention;

FIG. 2 is a circ-uit diagram illustrating the electrical components of one embodiment of this invention and their interconnection;

FIG. 3 is a circuit diagram illustrating a second ernbodiment of this invention;

FIG. 4 is a circuit diagram of another embodiment of this invention;

FIG. 5 illustrates the circuitry of a fourth embodiment of this invention;

FIG. 6 is a trimetricview of a drum for a clothes dryer illustrating details of a preferred embodiment of the present invention;

FIG. 7 is a cross section of this drum taken on the plane of line 7 7 in FIG. 6; and

FIG. 8 is a developed view of the sensing elements of the FIG. 6 embodiment.

Corresponding reference characters indicate corresponding parts throughout the drawings.

Referring now to the drawings, and more particularly to FIG. 1, a domestic clothes dryer incorporating one embodiment of the present invention is illustrated in its er1- tirety by reference numeral 11. This dryer includes a console or cabinet 13 in which is mounted a container or drum 15. This drum receives the items or load being dried through a door in the cabinet, outlined at 17. The drum is mounted for rotation about a horizontal axis to tumble or agitate the items being dried during a drying cycle. An electric motor, indicated at M, is adapted through a mechanical drive (not shown) to rotate drum 15 about a substantially horizontal axis. A heat source 19, which is illustrated as including an electric heating element 21 and a high-limit temperature-responsive switchl or thermostat 23, is located within the console. The heating element 21 is positioned in heat exchange relationship or thermal communication with the drum. Console 13 has an upwardly extending portion 25 which constitutes a control panel and in which is provided an electronic control module 27 and a switching relay 29 electrically interconnected with the various electrical components of the dryer.

Positioned within drum 15 is a pickup assembly which includes two sensing `or

pickup electrodes

31 and 33. These elements or electrodes are connected respectively to a pair of terminals (indicated by leads 35 and 37). Each electrode includes a conductive portion, indicated at 31a and 33a, electrically insulated -by a layer of insulation 3111, 33b from drum 1S. Each conductive portion is adapted to contact the items or load wit-hin the dryer so that these items complete or establish a current path or electrical circuit between

leads

35 and 37. Lea-

ds

35 and 37 are connected to the electronic control module 27 as explained in detail hereinafter.

The present invention makes -use of the fact that the electrical resistance of wet cloth increases as this cloth dries. On removal from a washing machine, for example, wet cloth exhibits an electrical resistance on the order of a kilohrn or so; as the cloth dries, this resistance increases to values in the order o-f well over megohms. The resistance between

leads

35 and 37 thus provides a clear indication of the moisture content of the clothes or item-s within the drum. FIGS. 2-5 illustrate four electronic systems or circuits which respond to this resistance change thereby to control a drying cycle of an automatic dryer. For the most part, the various electronic components of these circuits are located within electronic module 27, with appropriate controls being presented on the face of panel for convenient manipulation by the user of the dryer.

Referring now to FIG. 2, one embodiment of a dryer control system is illustrated as comprising three input conductors L1, L2 and L3 which supply power from a -threeswlire single-phase, 230-volt power source. Lines L1 and L2 may be connected to the two hot lines of a typical single-phase service, while line L3 may be connected to the neutral line of this service. Preferably line Y L3 is connected to ground as indicated to constitute a common ground for the dryer control. Connected in lines L1 and L2 are the contacts of relay 29, indicated at 29a and 29b. Relay 29 also includes a solenoid coil 29C which controls the position or condition of contacts 29a and 29h. (The connection of coil 29C will be descri-bed hereinafter.) A pair of conductors LL1 and LLZ are connected to

contacts

29a and 29b, respectively, and in turn to the various electrical components of dryer 11; for example, heating element 21, motor M, and a blower if one is provided.

Connected in parallel with contacts 2% is a momentary-contact, push button PB. A rectifying diode D1 is connected between line LL2 and a conductor LL3 which supplies halt-wave rectified or pulsating D.C. power to the remaining portion of the FIG. 2 control. A voltagedividing network which includes a pair of serially connected resistors R1 and R2, and the resistance (indicated by a resistance R) of the current path established by the load or items in drum 15 between

leads

35 and 37 is connected between the cathode of a rectifying diode D2 and -line L3. The anode of diode D2 is connected to line LL3. Lead 35 constitutes one output terminal of this voltage-dividing network, while lead 37 constitutes the second terminal thereof. Resistor R1 is a variable resistance, and preferably a continuously variable type which has a relatively high maximum resistance setting, eg., on the order of megohms. As explained hereinafter, the setting of resistor R1 selects or deterrnines thermoisture content of the items being dried at which a drying cycle is terminated.

Connected in shunt across output terminals and 37 is a sizable capacitor C1, e.g., 4 microfarads, the ungrounded terminal of which is connected by a resistance R3 to one terminal or electrode of a voltage breakdown dev-ice constituted by a neon bulb N1. Connected across lines LL3 and L6 is the emitter-collector circuit of a transistor Q1 and a resistor R4. The base or control electrode of transistor Q1 is connected to a terminal of neon bulb N1, while the output or collect-or electrode is connected to the gate electrode of a silicon controlled rectitier (SCR) Q2. The anode-cathode circuit of this SCR is interconnected with coil 29e of `relay `29 across lines LL3 and D3. As explained hereinafter, relay 29 and SOR Q2 comprise a switching means which controls both the initiation and termination of a drying cycle.

Operation of the FIG. 2 embodiment is as follows: To initiate a drying cycle, push button PB is closed momentarily. Transistor Q1 is initially non-conducting and hence the potential appearing at the gate electrode of SCR Q2 is initially at a relatively high level. This conditions SCR Q2 to conduct and accordingly, the closing of switch PB causes current to flow through coil 29C and the anode-cathode circuit of SCR Q2. This energizes relay 29, causing contacts 29a and 29h to close. This in turn energizes lines LLI and LL2 `which are connected to motor M and heating element 21. Motor M rotates drum 15 to tumble or agitate the items or load to be dried, while the heating element provides the proper heating of this load.

Since at the beginning of a drying cycle the items within the dryer have a relatively high moisture content, the resistance of these items, i.e., the resistance of the current path between leads 35 and 37, is at a relatively low level and hence the potential at lead 35 (the voltage across capacitor C1) is a small fraction of the voltage across lines LL3 and L3. As the moisture within the clothes or items decreases, the resistance thereof increases. This in turn 'increases the voltage across capacitor C1. Because of this capacitor, the system has a relatively long time constant and therefore does not respond to transient variations in the resistance of the items within the drum which could, if capacitor C1 were not provided, cause premature termination of the drying cycle. Neon bulb N1 exhibits avalanche type operating characteristics and accordingly, when the voltage across capacitor C1 reaches a point sufficient to tire neon bulb N1, this bulb ionizes and applies the energy vstored on capacitor C1 to the base of transistor Q1 in the form of a positive pulse.V This causes this transistor to conduct in the saturation region and in turn considerably lowers the potential at the gate electrode of SCR Q2. This decreases the gate current of this control rectitier to a point at which this device is cut oif. As a result, current iioW through coil 29C is cut oif, causing relay 29 to be deenergized.

Contacts

29a and 29b thus return to their normally open conditions, thereby disconnect'ing lines LLI and LL2 from the power source, and terminating a drying cycle.

The resistance of the load being dried (and hence the moisture content of this l-oad) at which a drying cycle is terminated is controlled by the setting or adjustment of variable resistance R1 which controls or determines the voltage across leads 35 and 37. Increasing resistance R1, for example, generally decreases the voltage across resistance R and thereby insures that the items to be dried must reach a condition of less retained moisture (i.e., greater electrical resistance) before the potential across the load is suiicient to cause neon bulb N1 to break down and thereby terminate a drying cycle.

In addition to causing the system to have a long time constant so that it does not respond to transient or incipient variations in the voltage across leads 35, 37 (which could cause premature termination of a fdrying cycle), capac'itor C1 also causes the system to respond somewhat to the wetter cloth or items in a mixed load of clothes or items exhibiting nonuniform drying rates. Additionally, this capacitor provides a means of storing energy -so that when the neon bulb i'on'izes, there is a substantial amount of energy for driving transistor Q2 into saturation quickly.

Because the FIG. 2 control system actually senses the moisture content of the items being dried, no timer is necessary to control a `drying cycle. Moreover, because a continuously variable resistor is employed to select the level of moisture content in the items at which a drying cycle is terminated, this level may be varied or adjusted over a continuous range between preselected upper and lower limits. The system thus possesses substantial advantages over prior art systems wherein only one or two moisture levels may be selected.

A second embodiment of this invention is illustrated in FIG. 3. This embodiment is similar, for the most part, to the FIG. 2 embodiment and like elements are indicated by corresponding reference numerals. In this embodiment, instead of connecting capacitor C1 directly across resistance R, a nonlinear resistance network which. includes a Idiode D3 and a yresistance R5 connected in parallel is provided between terminal 3S of the voltagedividing network and the ungrounded terminal of capacitor C1.

In many instances, it is desirable that the dryer control system respond to the wettest pieces in a load of clothes lof various configuration and fabric which exhibit nonuniform drying rates. A common failure of prior art control systems of this type is that an average dryness measurement is employed to determine the termination of a drying cycle. When a mixed load is being dried, i.e., when the various 'items in the dryer exhibit substantially different drying rates, resistance R will vary erratically between high and low values in its increasing trend as the moisture content of the load diminishes. Some pieces might remain quite wet Iif termination of a drying cycle is based on average dryness. The provision of the nonlinear network D3, R5 in FIG. 3 causes this control system to respond to the low values of resistance R and to terminate a `drying cycle in response to the wettest piece of cloth within the dryer reaching the level of dryness determined by the setting of resistor R1.

Operation of the FIG. 3 system is as follows: A drying cycle is initiated, as before, by the closing of push button PB. As the clothes or items in the drum become dry, the voltage impressed across these items increases and charging current ows to capacitor C1 through resistor R5. As wetter parts of the load occasionally bridge or interconnect the electrodes of the pickup assembly in the drum, a relatively low-resistance discharge path is presented to the capacitor through di-ode D4 and resistance R. Accordingly, capacitor C1 charges slowly in response to average decreasing retained moisture in the clothes or items, but `discharges rapidly through diode D3 in response to intermittent indications of high retained moisture. The system therefore tends to respond to the wettest parts in the load within the dryer. This tendency remains effective until the low value of resistance R becomes large enough to render the time constant of the capacitor discharge path through D3 and R suiciently large relative to the time constant of the capacitor charge path through D1, D2, R1, R2 and R5 so that the voltage across capacitor C1 is permitted to build up to a level sufficient to ionize neon bulb N1 and thereby terminate the drying cycle.

Since the magnitude of R1 and R2 determine the preset terminating dryness level, and since the magnitude of R5 does not affect this adjustment, the magnitude of R5 can be selected to provide the desired amount of response to high-retained moisture items of the load. The larger the value Iof R5, the greater will be the tendency of the system to maintain the dryer in operation until the very last part of the load reaches the preset retained moisture level. In a design of the c-ontrol system, this is an important feature, i.e., to be able to control this tendency, since in many instances it is undesirable to excessively bake some parts of the load if a single stubborn item remains damp for a long time.

A third embodiment of the present invention is illustrated in FIG. 4. Tests have indicated that for a bone dry operation or cycle, i.e., a cycle wherein the load being dried is thoroughly dried, performance is enhanced by measuring the wettest piece or item in a load exhibiting nonuniform drying rates. The system of FIG. 3 is therefore particularly adapted for this type of operation. For damp dry operation, on the other hand, i.e., to condition clothes forironing, tests show that best performance is obtained by measuring the average wetness of the load. The Vembodiment of FIG. 4 provides the advantages of both types of operations by providing a system wherein an operator is able to vary the characteristics of the system from a wettest cloth response for bone dry operation to an average cloth response for damp dry operation. Additionally, with the FIG. 4 system an operator may select an air-fluff cycle wherein the load is tumbled or agitated for a preselected period of time without the application of heat.

Referring now to FIG. 4, three conductors which supply power from a 230-volt, single-phase power source are indicated at L11, L12 and L13. A first set of contacts of relay 29, indicated at 29a, are connected between line L12 and a conductor L14. A normally open, cool-down thermostat, e.g., a snap acting disc type thermostat T1 is connected in shunt across contacts 29a. A second set of contacts 29h is connected between line L12 and an anode of a rectifying diode D11. The cathode of diode D11 is connected to a conductor L15. A momentary-contact push button PB is connected in shunt with contacts 29b. Whenreither push button PB or contacts 29b are closed, conductor L15 supplies half-wave rectified or pulsating D.C. to the control portion of the FIG. 4 circuit. Interconnected between conductors L15 and L13 is a series circuit which includes a diode D12, a pair of resistors R12 and R15, a switch S1, and leads 35 and 37 of the pickup assembly within the drum 15. Again the resistance of the load within the drum is indicated by a resistor R. Switch S1 constitutes one switch of a ganged three-switch assembly which also includes switches S2 and S3. Switch S2 is a single-pole, double-throw switch which in one position connects the anode of a diode D13 to the ungrounded terminal of a capacitor C11 and in a second position connects a terminal of an air-fluff resistor R16 to this capacitor. When S2 closes the circuit between D13 and R13, switches S1 and S3 are also closed through the interlocking mechanism; conversely, switches' S1 and S3 are opened when S2 is moved to close the circuit between R13 and R16. The other terminal of resistor R16 is connected to the cathode of diode D12. A variable control resistor R11, preferably a continuously variable type which has a relatively high maximum resistance setting, e.g., on the order of 30 megohms, is connected in shunt across resistance R15 and diode 13. Interconnected between the base or control electrode of a transistor Q11 is a series circuit which includes a resistor R13 and a neon lamp or bulb N11. The emitter of transistor Q11 is connected to line L13, while the collector of this transistor is connected to the gate -or control electrode of a silicon controlled rectifier Q12. A resistor R14 is connected across the anode-gate circuit of this SCR. The coil 29e of relay 29 is connected in series with the anode-cathode circuit of SCR Q12 and in parallel with a series circuit which comprises the heating element 30a of a thermal relay and switch S3. This thermal relay controls a set of contacts 3012 connected in line L12 which contacts are actuated by a thermally responsive device positioned in thermal communication or heat exchange relationship with the heating element 30a. Contacts 30b are normally open, i.e., they close when heating element 30a is energized.

The electrical heating element of the dryer being con- -trolled is illustrated as comprising two resistance heaters H1 and H2 connected by a high-limit thermostat T2 (corresponding to thermostat 23 in FIG. 1) to contacts 30h. An exhaust or heat-modulation-contr-ol thermostat T3 is interconnected between heater H2 and thermostat T2 to control the energization of heater H2.

The run winding of motor M (FIG. 1), indicated at RW in FIG. 4, is interconnected between lines L13 and L14. A centrifugal starting switch S4 selectively connects the start winding SW of motor M in parallel `with winding RW across lines L13 and L14. After motor M is energized to rotate drum 15, centrifugal switch S4 is actuated by the rotating shaft of motor M to the dotted line position in FIG. 4 to deenergize the start winding and connect heaters H1 and H2 across lines L13 and L14.

There are generally two modes of operation of the FIG. 4 control: a drying mode wherein items within the drum are dried either to a damp dry or a bone dry condition, and an air-fluff mode wherein the items in the drum are agitated or uifed for a preselected period of time without the application of heat, i.e., while heaters H1 and H2 are deenergized. The positions of switches S1, S2 and S3 determine or control the mode of operation. With switches S1 and S3 closed and switch S2 interconnecting diode D13 with resistance R13, the circuit is set u-p for a drying mode. The opening of switches S1 and S3, and the actuation of switch SZto interconnect resistances R13 and R16, establishes the air-fluff mode. In the drying mode, the setting or adjustment of variable resistance R11 concurrently determines or controls (1) the moisture content of the items or load being dried at which a drying cycle is terminated and (2) whether the system exhibits a wettest piece response or an average wetness piece response. In the 1) situation, the FIG. 4 system response is similar to that described for the FIG. 2 system. In the (2) situation, for wettest piece response, the FIG. 4 system responds to the low values of R as described above in connection with the FIG. 3 system. For the faverage wetness piece response, the FIG. 4 system responds to a value of R above the low values of R.

As noted above, when damp dry operation is selected it is desirable for the system to respond to average wetness of the load, whereas for bone dry operation, best results are obtained when the system exhibits a wettest cloth response. By increasing resistance R11, the systems characteristics are varied gradually or continuously from a damp dry (and average wetness piece response) operation to'a bone dry (and wettest piece response) operation.

Operation of the FIG. 4 circuit is as follows: It will be assumed that switches Sil-S3 are set for a drying cycle and that resistance R11 is set or adjusted for a damp dry operation. To initiate a drying cycle, push button PB isI closed momentarily. Initially, transistor Q11 is not conducting and as a result the potential at its collector is at a relatively high level. This causes conduction of SCR Q12, resulting in energization of coil 29C of relay 29 and heating element of 30a of the thermal relay. Energization of the latter causes contacts 3tlb to close, While energization of coil 29c causes contacts 29a and 29h to close. This energizes windings RW and SW of motor M, the latter through centrifugal switch S4. As the motor rotates drum 15 to agitate or tumble the items to be dried, switch S4 is actuated to its dotted line position, thereby deenergizing :start winding SW and connecting heaters H1 and H2 across lines L11 and L14. The provision of switch S4 insures that the heaters may not be energized unless motor M is rotating drum 15, The exhaust temperature is sensed by thermostat T3 which functions to selectively control energization of heater H2 to maintain the applied heat within predetermined upper and lower limits.` High-limit thermostat T2 prevents the heat within' the drum from exceeding a preselected maximum level. Cool-down thermostat T1 closes when the temperature within the drum goes above a predetermined level and thereby functions to prevent deenergization of winding RW ofmotor M so long as the drum temperature is above this level.

Since at the beginning of a drying cycle the items within the dryer have` an appreciable moisture content, the resistance of these items, i.e., the resistance of the current path between leads 35 and 37 of the pickup assembly, is at a relatively low level. Under these conditions, the voltage across resistance R11 and capacitor C11 is at a low level. As the moisture content of the items being dried decreases, the resistance thereof increases, thereby increasing the potential applied across resistance R11 and capacitor C11. This charges this capacitor at a rate determined by the setting of resistance R11. As the wettest items of the load occasionally bridgeor interconnect the electro-des of the pickup assembly, a relatively low-resistance discharge pathkfor capacitor C11 is provided by diode D13 and resistance R. The tendency of the control system to maintain the dryer in operati-on until the very last part of a load reaches a preselected retained moisture level is determined by the size of the resistance in the charging path compared to the resistance in the discharge path and thus is determined by the setting of resistance R11 in the charging path. Because resistance R11 is included in the voltage-dividing network, the setting of R11 will determine the particular resistance of the load being dried (and hence the moisture content of this load), at which the drying cycle will .be terminated. When the resistance of the load reaches this preselected level, the voltage across capacitor C1 reaches a level sufficient to lire or ionize neon bulb N11. The energy stored on capacitor C11 is appliedto the base or control elect-rode of Hansisand H2, and also deenergizes the control portion of the circuit. When the temperature within the drum cools down to a level wherein thermostat T1 returns to its normally open condition, the run winding RW of motor M is -deenergized, thereby terminating the drying cycle.

In order to select a -bone dry operation in a drying'cycle, resistance R11 is increased. This does two things: first, it increases the time constant of the charging path for capacitor C11 as compared to the time constant of the discharge path for this capacitor thereby increasing the tendency of the control to exhibit a wettest piece response; and secondly, it increases the resistance level which the clothes or load withinv the drum must exhibit before a drying cycle is terminated. An important feature of the FIG. 4 system is that no matter what condition or degree lof dryness is selected by the operator, the proper bias of the system (between wettest cloth response and average cloth response) is automatically selected, since the Ysame element, resistance R11, provides both controls or serves -both lfunctions.

To :select a fluff-dry cycle, `switches S1 and S3 are opened and switch S2 actuated to interconnect resistance R16 in` series with capacitor C11. Closing of push button PB causes coil 29e to be energized as before, but, because S3 is open, does not cause energization of heating ele# ment 30a. Accordingly,

contacts

29a and 29b close, but contacts 30h remain open thereby preventing energization of heating elements H1 and H2. Closing of contacts 29a energizes the windings RW and SW of motor M and causes the drum to agitate or yfluff the items therewithin. The closing of contact 29h completes a charging path for capacitor `C11 through diodes D11, D12, and resistance R16. When the'voltage across capacitor C11 builds up to a value suicient to lire or ionize neon bulb N1, the cycle is terminated as outline above. The time it takes for the voltage across C11 to reach this terminating level is dependent upon the RC time constant of'resistance R16 and capacitor C11. Selection of the parameters of resistor R16 therefore controls the iluf mode operating time. In one specific application of the FIG. 4 control, for example, the vparameters of C11 and R16 were chosen to provide a seven minute fluff-dry cycle. Again no timer, such, is necessary to control the operation of the dryer.

A` fourth embodiment of this invention is illustrated in FIG. 5. This embodiment is similar for the most part to the FIG. 2 system and like elements or components are designated by corresponding reference characters. In FIG. 5, instead of connecting capacitor C1 directly across the terminals or leads 35, 37 of the pickup assembly, this capacitor is connected in series with a resistance R21 and the resulting series RC circuit is switchably connected across the terminals ofthe pickup assembly by a pair of ganged cycle or mode selector switches S11 and S12. A rheostat R23 having a sizeable fixed resistance and a movable wiper arm or slider is included in the FIG. 5l

the slider of R23 is switchably connected by switch S11` with lead 35 of the pickup assembly. Rheostat R23 is a special resistor constructed to present a resistance between resistor R25 and switch S11 which is continuously variable from nearly zero to approximately 30 megohms and then to an open circuit in the last few degrees of control shaft or slider rotation. It is preferred that there be no apparent step or transistion between the upper resistance values and the open circuit condition. An airflul resistance R27 having a very high resistance value,- eg., on the order of 120 megohms, interconnects the cornmon junctionof R23 and R25 with resistor R21.4 A resistance R4 is provided, interconnected between the anode and gate electrodes of SCR Q2.

In addition to performing functions analogous to those outlined above in connection with FIG. 2, the FIG. circuit provides for an air-fluit mode similar to that of the FIG. 4 system. To provide an air-llufrt mode, an additional switch S13, ganged with selector switches S11 and S12, is included in the FIG. 5 system to maintain the heating elements of the dryer deenergized when switches S11 and S12 are in their respective open positions.

Operation of the FIG. 5 circuit is as follows: To establish the drying mode, cycle selector switches S11 and S12 are closed, thereby connecting lead 35 of the pickup assembly to resistor R21. The system in this mode functions in a manner analogous to that of FIG. 2 described above, except that resistance R1 is replaced by the parallel combination of R23 and R27. In view of the special construction of rheostat R23, this arrangement permits the control resistance, i.e., R23 and R27, to be varied continuously from nearly zero to a very high value, greater than 25 megs. As the slider of R23 is advanced beyond the maximum resistance value to the open circuit position, this control resistance changes abruptly to the value of resistor R27, for example, 120 megs. Because of the parallel combination of resistances R23 and R27, rheostat R23 can be considerably less expensive than variable resistances R1 or R11 in FIGS. 2-4, and yet the composite control resistance can be set to a resistance value considerably greater than is possible in FIGS. 2-4. This permits the retained moisture level of the load at which a drying cycle is terminated to be set somewhat lower than is possible in the FIGS. 2-4 systems. The nonlinear resistance characteristics of the items being dried, i.e. resistance R, permits the control of FIG. 5 to appear as continuously variable to the operator of the dryer. That is, the nonlinear characteristics of the control resistance are, for all practical purposes, offset by the nonlinear resistance characteristics of the load being dried.

To establish the air-fluff mode, selector switches S11, S12 and S13 are opened. Capacitor C1 charges through a network which includes resistances R25, R27 and R21 and, as explained above in connection with FIG. 4, terminates the air-fluff cycle a predetermined time after the actuation thereof; this time being a function of the size of resistors R25, R27 and R21 and the capacitance of capacitor C1. It will be appreciated that, instead of employing a separate air-fluff resistor as in FIG. 4, resistor R27 is employed both as a portion of the control resistance during a drying cycle and as the air-fluff resistance during an air-lluff mode of operation.

A modilied and preferred form lof pickup assembly for use in the various systems of this invention is illustrated in FIGS. 6-8. The drum or container of the dryer under control is indicated at reference numeral 115. This drum is formed from a cylindrical portion 117- closed at one end by la circular plate 119. Drum 115 receives the items to be dried and is rotated by any conventional driving mechanism to tumble or agitate these items. A hollow shaft 121 bolted to drum 115 may, for example, carry a gear or pulley (not shown) mechanically interconnected with motor M. Preferably shaft 121 and drum 115 are connected to ground as indicated.

The pickup assembly of FIGS. 6-8 includes two cylindrical belts or

bands

123 and 125 vof electrical insulating material secured by a plurality of

pins

127 and 129 to the inner surface of portion 117. Each of these bands carries two separated and electrically insulated printed circuit conductors; the conductors carried by band 123 being indicated at 131 and 133, and those carried by band 125 being shown at 135 and 137. Each of these conductors forms a tortuous conductive path on its respective band; the paths of the conductors on each band being offset with respect to each other as indicated. A pair of conductive bolts or pins 139 and 141 serves to electrically interconnect conductors-131 and 135 to drum 115 which is grounded. A pair of

pins

143 and 145, insulated from drum 115, electrically interconnects

conductors

133 and 137 to a lead 147. The latter is carried on the outside of the drum, through a hole 149 in shaft 121, and connected with a terminal or stud 151 projecting out of the end of shaft 121. A spring-biased wiper member 153 bears against stud 151 making electrical contact therewith. In the arrangement illustrated in FIGS. 6-8, one of the terminals of the pickup assembly (corresponding to terminal 37) is the common chassis ground of the dryer, while the other terminal (corresponding to terminal 35) consists of wiper member 153.

The spacing between the conductors 1311, 133, and 13H is such that the items or load to be dnied normally bridge or interconnect a portion of one of these conductors with portion-s of the others.A A current path or circuit is thus normally completed or established from tenmina-l 153, through stud 151 and lead 147 to conductors 133 and/or 1.37, through the items or-load within the drum toconductors 1131 and/or 135, and then to ground which constitutes the second terminal orf the assembly. An adL vantage of the FIGS. 6-8 pickup assembly is that no matter how small the load within the dryer, a circuit is noirmally completed between the two terminals of the pickup assembly. This reduces or eliminates transient variations in the resistance of the current path between the terminals of the pickup assembly which could occur if the load only intenmittently bridged or interconnected fthe conductive portions of the pickup electrodes. Moreover, because four conductors are employed, two 'sepanate panallel conductive paths' through the load are normally provided; one from conductor' 1-31 to conductor 133, and a second from 135 to 1137. This lolwers the effective resistance between

terminals

35 and 37, thereby increasing to some degree the sensitivity of the control. It will be understood that the assembly illustrated in FIGS. 6-8 coul-d be employed with any of the control circuits illustrated in FIGS. 2-5.

In addition to the componen-ts illustrated in-FIGS'. l-8, a typ-ical dryer may include other control devices. For example, in many dryer-s a door-.operated safety switch would be provided to interrupt a drying cycle when the door of the dryer is opened. Since such controls form no part of this invention, they have not been specilically illustrated. f

Also, Within the purview of this invention `the dryer could also be set to openate as a control for a 11o-heat dry-ing cycle :for delicate fabric items by opening switch S3 and by maintaining switches S1 and S2 in the closed position sholwn in FIG. 4. VIt will be seen that with this arrangement heaters H1 and H2 remain deenergized because relay contacts 30h remain open since hea-ter 30a is deenergized.

While the present invention is illustrated as controlling the operation of an electric clothes dryer which employs electric heat-ing elements, it will be understood that it is equally applicable to the control of other types of dryers as well, for example, gas dryers. Further, while the FIGS. 2-5 embodiments have been illustrated and described as used with a three-wire single-phase 230-volt power source, it will be understood that the various ernbodirnents of this invention can also be used with two Wire power sources, ei-ther grounded orungrounded, and of diierent voltages, etg. 120 volts, and can also be used 'with three-phase power sources.

`be employed to perform these functions.

Also, while the invention is illustrated as employing transistors and controlled rectifiers to perform the various co-ntrol functions, other electronic transducers or ampli- -fying devices, for example, vacuum tubes or thyratrons, lwhich exhibit analogous operating characteristics could And while the controlled rectiifiers employed in the systems of FIGS. 2-5 are disclosed as silicon controlled rectie'rs, these transducers could be made of semiconductor material other than silicon so long as they exhibit proper operating characteristics. Moreover, other electronic devices which exhibit avalanche type operating characteristics, for example, avalanche diodes, could be employed in place of neon bulbs N1 and N11. Regarding the pickup assembly, if the interior ot the drum (or at least a portion of the interior of the drum) presents a conductive surface to the items in the drum, the pickup assembly could employ this portion of the drum as one of the pickup electrodes.

In view orf the above, it will be seen that the several objects oft' the invention are achieved and other advantageous results attained.

As various changes could be made in the above constructions and methods Without departing from the scope ot the invention, it is intended that all matter contained in the abo-ve description and shown in the accompanying drawings he interpreted as illustrative and not in a limiting sense.`y i

What i-s claimed is:

.1. A control for a dryer having means for agitating items ot a'load to be dried and electrode means adapted to Contact items of the load to establish a current path therethrough', the resistance of said path being a function orf the moisture contents ot the items of the load contactingl said electrodes; said control comprising a source of unidirectional current, a voltage divider which is connected across said source and includes said path for providing a voltage which is' a tunctionof the resistance of said path, a capacitor, a nonlinear resistance network which connects said divide-r to said capacitor and through which said voltage is applied to said capacitor, said network permitting said capacitor to discharge m-ore rapidly than to charge, switching means adapted when actuated to terminate the drying `cycle ot said dryer, an electrical circuit interconnecting said capacitor withV said switching means thereby to terminate said drying cycle when the charge on said capacitor reaches a predetermined level whereby said control is biased to respond tothe .wettest items in a load exhibiting nonfunito'rm Vdrying rates and where-by said switching'means is not actuated until these lwettest item-s reach a predetermined dryness.

2. A control as set forth in claim 1 in which said voltageprolviding means includes means for varying the level of predetermined dryness over a range between preselected upper and lower limits. y

A control as set forth in claim 1 in which the switching means includes a silicon controlled rectier.

4. Ar control as set forth in claim, 1f in which the electrical circuit includes an electronic element which exhihi-ts avalanche-type operating characteristics, said element causing operation of said switching means'wh'en the charge on said capacitor rises above a predetermined level.

5. A control asset forth in claim 1 wherein said nonlinear network includes a diodeland a resistor connected .12 in parallel between one terminal of said capacitor and said electrode means.

6. A control for a dryer having means 'for agitating items of a load to be dried and electrode means adapted to contact items ot the load to establish a current path therethrough, the resistance off the path being a function of the moisture contents of the items ot the load, said control comprising:

a relay which is normally energized during a drying cycle an-d which upon deenergization initiates tenmina-tion of a drying cycle;

an SCR having a gate electrode and an anode-cathode circuit .which is serially connected with said relay for controlling the ilolw of current thereto;

means for applying pulsating current to said serially connected relay and SCR;

means for applying triggering current to the gate electrode oi said SCR;

a transistor having an emitter-collector circuit which is connected across the gate-cathode circuit of said SCR for selectively shunting sai-d triggering current away rom the gate electrode of said SCR thereby to prevent tiring of said SCR;

voltage divider means including said path for providing a voltage which varies as a .function of the resistance of said path;

a capacitor for integrating s-aid voltage;

and a voltage .breakdown device connecting said capacitor to the base electrode of said transistor whereby, when said load reaches a preselected level of dryness, the ltered voltage reaches the breakdown voltage of said device which then conducts thereby causing the emit-ter-collector circuit of said transistor to shunt said triggering current away from the gate electrode oi said SCR whereupon said relay is deenergized to initiate termination of the drying cycle.

7. A control as set forth in claim 6 wherein said voltage breakdown device is a gaseous discharge device which exhibits avalanche type operating charac-teristics.

References Cited by the Examiner UNITED STATES PATENTS 2,045,381 6/1936i Elberty 34-54 2,807,889' 10/1957 Dunkelman 34-45 2,885,789 5/1959 Conkling f 34-45 2,980,827 4/1961 Hill S17-148.55 3,038,106 6/1962 Cutsogeorge S17-148.55 3,122,426 2/ 19614 Horecky 34-45 3,180,038 4/'1965 Cha'fee 34-45 3,197,884 8/1965` Smith 34-45 3,198,903' y8/ 1965 Chafe'e v 34-45 X 3,210,863 10/1965 Nye et al 34-45 FOREIGN PATENTS 877,553 9/ 1961 Great Britain.

OTHER REFERENCES Radio-Electronics, vol. XXXI, No. 12, pp. 28 and 29, December 1960. l FREDERICK L. MATTESON, JR., Primary Examiner.

NORMAN YUDKOFF, WILLIAM F. ODEA,

Examiners.

D. A. TAMBURRO, Assistant Examiner.

Claims

1. A CONTROL FOR A DRYER HAVING MEANS FOR AGITATING ITEMS OF A LOAD TO BE DRIED AND ELECTRODE MEANS ADAPTED TO CONTACT ITEMS OF THE LOAD TO ESTABLISH A CURRENT PATH THERETHROUGH, THE RESISTANCE OF SAID PATH BEING A FUNCTION OF THE MOISTURE CONTENTS OF THE ITEMS OF THE LOAD CONTACTING SAID ELECTRODES; SAID CONTROL COMPRISING A SOURCE OF UNIDIRECTIONAL CURRENT, A VOLTAGE DIVIDER WHICH IS CONNECTED ACROSS SAID SOURCE AND INCLUDES SAID PATH FOR PROVIDING A VOLTAGE WHICH IS A FUNCTION OF THE RESISTANCE OF SAID PATH, A CAPACITOR, A NONLINEAR RESISTANCE NETWORK WHICH CONNECTS SAID DIVIDER TO SAID CAPACITOR AND THROUGH WHICH SAID VOLTAGE IS APPLIED TO SAID CAPACITOR, SAID NETWORK PERMITTING SAID CAPACITOR TO DISCHARGE MORE RAPIDLY THAN TO CHARGE, SWITCHING MEAND ADAPTED WHEN ACTUATED TO TERMINATE THE DRYING CYCLE OF SAID DRYER, AN ELECTRICAL CIRCUIT INTERCONNECTING SAID CAPACITOR WITH SAID SWITCHING MEANS THEREBY TO TERMINATE SAID DRYING CYCLE WHEN THE CHARGE ON SAID CAPACITOR REACHES A PREDETERMINED LEVEL WHEREBY SAID CONTROL IS BIASED TO RESPOND TO THE WETTEST ITEMS IN A LOAD EXHIBITING NONUNIFORM DRYING RATES AND WHEREBY SAID SWITCHING MEANS IS NOT ACTUATED UNTIL THESE WETTEST ITEMS REACHES A PREDETERMINED DRYNESS.