US3599342A

US3599342A - Dryer control

Info

Publication number: US3599342A
Application number: US803687A
Authority: US
Inventors: Curran D Cotton
Original assignee: Maytag Corp
Current assignee: Maytag Corp
Priority date: 1969-03-03
Filing date: 1969-03-03
Publication date: 1971-08-17
Anticipated expiration: 1988-08-17

Abstract

This control system for a clothes dryer includes a fabric dryness sensing circuit comprising a resistance-capacitance circuit portion, a neon tube, and a thyristor in the form of SCR operable for initiating termination of the dryness sensing operation. A chime indicating the end of the drying or sensing operation is operable during the cooldown operation in a repeating manner under control of the resistance-capacitance timing circuit.

Description

United States Patent inventor Curran D. Cotton Newton, Iowa App]. No. 803,687 Filed Mar. 3, 1969 Patented Aug. 17, 1971 Assignee The Maytag Company Newton, Iowa DRYER CONTROL 16 Claims, 4 Drawing Figs.

US. Cl. 34/45, 34/48 Int. Cl F26!) iii/Ll} Field of Search 34/43, 44, 45, 48 5 3 [56] References Cited UNITED STATES PATENTS 3,398,460 8/1968 Elders 34/45 3,399,461 9/1968 Doty 34/45 Primq ry Examiner-Carroll B. Don'ty, Jr. Att0rneyWilliam G. Landwier ABSTRACT: This control system for a clothes dryer includes a fabric dryness sensing circuit comprising a resistancecapacitance circuit portion, a neon tube, and a thyristor in the form of SCR operable for initiating termination of the dryness sensing operation. A chime indicating the end of the drying or sensing operation is operr hle during the cooldown operation in a repeating manner under control of the resistancecapacitance timing circuit.

PATENTEDAUBI'HS?! I 3,599,342

SHEET 3 OF 3 SWITCH 10/ 102 /03/04 05 /06 /07 m3 REGULAR- x x [II x o 0 D x PERMANENT PRESS x 'x D o o O U x DAMP'DRY x x U x x 0 1:! x

AIR FLuFF o x u x o o n x SLIDE PULLED o o 0 0 o v o o Xc'oNTAc'T CLOSED DMOMENTARY-CLOSED WHEN PUSH ROD FULLY DEPRESSED VCONTACT CLOSED ONLY FOLLOWING PERM. PRESS 0 CONTACT OPE N DRYER CONTROL BACKGROUND OF THE INVENTION l. Field of the Invention This invention relates to a dryer control system and more particularly to a circuit for terminating the drying operation.

2. Description of the Prior Art One type of dryer control becoming more frequently used for effecting automatic termination of the drying operation of a fabric-drying apparatus includes a pair of electrodes for sensing the electrical conductivity of the fabrics in the fabrictumbling container. The prior art patents show a number of specific control circuits for determining fabric dryness by means of a sensing circuit including a resistance-capacitance circuit portion responsive to the resistance of the fabrics across the electrodes and operable for terminating the drying operation at a preselected dryness condition. These moisturesensing systems must be operable with a wide variety of fabric types including the synthetic fabrics, or treated fabrics, sometimes referred to as having permanent press" characteristics. Furthermore, it is necessary to remove the permanent press fabrics from the drying apparatus immediately upon completion of the tumbling to prevent the setting of new wrinkles in the fabrics. It is therefore desirable and advantageous to provide an audible or visual indicator means observable by the operator upon completion of the cycle so that the fabrics may be immediately removed from the dryer.

SUMMARY OF THE INVENTION It is an object of the instant invention to provide an improved fabric dryness sensing circuit operable for terminating the dryness sensing operation at a desired fabric dryness condition.

It is a further object of the instant invention to provide an improved fabric dryness sensing circuit comprising a thyristor uniquely adaptable for energizing actuation means to terminate the dryness sensing operation.

It is a further object of the instant invention to provide an improved fabric dryness sensing circuit and to provide indicator means associated with the dryness sensing circuit operable on completion of the sensing operation for signalling the termination thereof. I

It is a still further object of the instant invention to provide a combined dryness sensing circuit and repeating end-of-cycle indicator means utilizing common components to achieve the sensing of dryness and the timing of the repeating indicator means.

It is yet a further object of the instant invention to provide an improved dryer control including a solenoid responsive to operation of a dryness sensing'circuit at a selected fabric dryness condition for terminating the dryness sensing operation and also operable responsive to a timing circuit for actuating an indicator means to signal completion of the drying operation.

These objects are achieved in a fabric-drying apparatus having a dryness sensing circuit comprising a resistancecapacitance circuit portion operable for sensing the moisture of the fabrics and initiating termination of the drying operation. The resistance-capacitance circuit portion is also operable for timing a repeating indicator operable upon completion of the dryness sensing operation. The dryness sensing circuit and the indicator timing circuit are each operable for energizing an actuation means for terminating the dryness sensing operation and energizing the indicator means.

Operation of the device and further objects and advantages thereof will become evident as the description proceeds and from an examination of the accompanying three pages of drawings.

DESCRIPTION OF THE DRAWINGS The drawings illustrate a preferred embodiment of the invention with similar numerals referring to similar parts throughout the several views, wherein:

FIG. 1 is a view of a dryer partially broken away and sectioned and incorporating the control system of the instant invention;

FIG. 2 is an electrical schematic diagram of a preferred circuit embodying the dryness sensing circuit portion and the indicator circuit portion of the instant invention;

FIG. 3 is a chart indicating the operation of various switches of the circuit of FIG. 2; and

FIG. 4 is a view of a portion of the control components of the circuit of FIG. 2 including the preselectionswitch, the solenoid, and the indicator chime.

In FIG. 1 of the accompanying drawings is shown a clothes dryer apparatus having a base 10 that serves as a support for upstanding channel members 11 and 12 which together with crosspiece 14 support the hollow blower housing casting 17. The housing 17 includes a tubular portion 21, a divider wall 20 having a rearwardly flared inner portion defining an intake into an impeller chamber, and radially directed longitudinal webs 22 that converge toward a central axis and join with a cylindrical bearing retainer member 23. A plurality of segmental passageways are therefore defined by the tubular member 21, the bearing retainer member 23, and the support' ing webs 22.

Journaled within member 23 is a revolvable drum drive shaft 31 which projects from both ends of the housing 17. Fixed to the drum drive shaft 31 adjacent the rear of the dryer is a large pulley 33 which is driven by motor 34 through a motor pulley 36, main drive belt 37, a speed reduction system (not shown) driven by the main drive belt 37, and belt 40 driven in turn by the speed reduction system.

The forward end of the drum drive shaft 31 is rigidly connected to the drum spider member 46 which has radiating spokes 51 that support a rim 52. I

A horizontally mounted fabric-tumbling drum 60 has a rear wall 61 which is secured to rim 52 for support and rotation by shaft 31. Rear drum wall 61 is imperforate except for a central exhaust opening defined by the circular shoulder 55 that is aligned with the blower tubular member 21. The outer periphery of the rear wall 61 is flanged to form a supporting shoulder for the imperforate cylindrical sidewall 65 which carries the clothes elevating'vanes or baffles 66 for tumbling clothing within the drum 60 during rotation thereof. Cylindrical sidewall 65 is also connected to the front drum wall 67.

The front wall 67 has a centrally located access opening defined by flange 68 and an annular perforate portion 69 located concentrically around the annular flange 68. This perforate portion 69 formed by several concentric rows of holes serves as the air intake to drum 60.

Cabinet 70 is fastened to the base 10 and encloses the entire drying machine. The cabinet has an access opening defined by flange '71 and aligned with the drum access opening thereby allowing both of the flanges 68 and 71 to receive a rearwardly extending portion of the door gasket 72. The door 73 is hinged and forms a substantially airtight seal with the gasket 72.

Fastened to the cabinet 70 is a shroud or cowling member 74. Located between the shroud 74 and the front drum wall 67 is an open coil electric heating element 75 which extends around the inside of the cowling member 74 to raise the temperature of the air passing through the perforate portion 69 into the drum 60. A gas heater may be used in place of the electrical heating element 75.

Airflow into drum 60 through the perforate area 69 and into the blower housing 17 is produced by rotation of the revoluble impeller member 76 located in the blower housing 17. The fan pulley 77 formed integrally with the impeller 76 is driven directly by the driving motor 34 through the main drive belt 37. A felt air-sealing member 78 encircles the front periphery of blower housing 17 and the circular shoulder 55 to prevent air from being drawn in at the junction and thus bypassing the heater 75 and drum 60.

The blower housing casting 17 supports at least one thermostat 82 which is connected in series with the heating element 75 to maintain the interior drum 60 at the proper selected drying temperature. Also connected in series with the heating element 75 is the high limit thermostat 79 which is mounted on an upper part of the shroud member 74 so as to disconnect heating element 75 from its source of power in case the temperature near the front of the drum should rise above a predetermined selected temperature during the operation of the clothes dryer, for instance, in the event of reduced airflow through the drum 60.

In order to measure the electrical conductivity or resistance of the fabrics within the drum 60, as a measure of the condition of dryness of the fabrics, electrodes or

probes

80 and 81 are mounted within the drum 60. In a preferred embodiment, the electrodes are in the form of a pair of elongated conductor members mounted on the crown of each of the baffle members 66 to provide a contacting surface engageable by the fabrics tumbling within the drum. It will be realized that different forms of electrodes, or probes, may be used, although the type disclosed herein is a preferred construction.

Electrical energy is supplied to electrode 80, for example, by lead 84 that is connected to a brush 85 that engages the stationary slip ring 86 while the drum 60 is rotating. The slip ring 86 is mounted on the electrically insulative air sealing member 78. The slip ring 86 is in turn connected to a lead 90 which runs to the control unit 92. The electrode 81 is connected by lead 83 to the rotatable drum 60 and through the drum 60, the drive shaft 31, and blower housing 17 to the chassis including the base 10. The chassis is then connected to earth ground through a conductor 87 electrically connected with the base 10, for example. Electrode 81 is thus connected to earth ground.

The automatic control unit 92 may be secured to an upper portion of the cabinet. The lead 90 enters the control unit and is connected to the control unit to be described hereinafter.

The baffles 66 are formed of an electrically nonconductive material in order to insulate the electrodes. The electrodes, however, are electrically shorted by the contact of wet fabrics during tumbling. A plurality of baffles may be mounted within the drum and each may be provided with

electrodes

80 and 81 with the electrode pairs being connected in parallel for achieving a greater sensitivity of control. Referring now to FIG. 2 which illustrates the control circuitry for the fabric drying apparatus, there is shown diagrammatically a manually operable preselection means 100, which is also shown in outline form in FIG. 4. The preselection means 100 includes a plurality of switches 101 through 108 actuatable between open and closed positions, according to the chart of FIG. 3, under control of a plurality of manually actuatable pushbuttons 110 through 113 indicated as Regular, Permanent Press, Damp Dry, and Air Fluff," respectively. The switches 101 through 108 are shown collectively at the right side of the diagram of FIG. 2 under control of the pushbuttons 110 through 113 and are shown schematically in the circuit for controlling initiation and termination of the fabric-drying apparatus as will be more fully shown hereinafter. Operation of the group of switch members 101 108 between open and closed positions is also under the control of a selectively energizable solenoid 116, shown in FIG. 4 and indicated schematically in FIG. 2, to terminate the drying cycle.

The control circuitry of FIG. 2 includes three

conductors

118, 119, and 120 that are selectively connectable with a conventional three-wire 220 volt, alternating current supply. For the explanation of the circuitry of FIG. 2, it will be assumed that the conductors 118 and 119 are connected with the power lines and that the other conductor 120 is connected to the neutral line.

The chart of FIG. 3 indicates the electrical posture of the preselection switches 101-108 upon selection of each of the selectable cycles corresponding to the pushbuttons -113 and upon operation of the resetting solenoid 116. It is noted, for example, that the preselection switch 101 in the heater circuit is closed for each of the Regular, Permanent Press, and Damp Dry cycles. In the explanation of the circuit of FIG. 2, it will be assumed that a Permanent Press cycle has been selected by the operator and thus selection switches 101, 102, and 108 are closed and

preselection switches

104, 105 and 106 are open while preselection switches 103 and 107 are momentarily closed during the preselection and machine energization process.

The heater 75 is connected between the first and second conductors 1 18 and 119 by a circuit portion including the preselection switch 101, a cycling thennostat 82, a high limit thermostat 79, and a centrifugal switch 123 in the motor 34. The centrifugal switch 123 is normally open but is operable to a closed position upon energization of the motor 34.

The drive motor 34 is energized by a circuit extending from the conductor 1 18 through a door switch l24, closed preselection switch 102, a conductor 125, and momentarily closed preselection switch 103 to junction 127 at one side of the motor 34. The other side of the motor 34 is connnected to neutral conductor 120. Subsequent to initial energization of the motor 34, centrifugal switch 126 within the motor 34 will operate and a circuit for maintaining operation of the motor will be completed from the conductor 118 through the door switch 124, preselection switch 102, and

conductors

125, 130, and 131 to the motor 34.

A cooldown thermostat 133 is also provided in the circuit to the motor 34 and is operable to a closed position at a predetermined temperature within the drum 60 of, for example, 135 F. After the dryer apparatus has operated for a period of time with the heat on, the cooldown thermostat 133 will close and maintain the motor 34 energized until the temperature within the drum 60 is reduced to 135 F. This cooldown thermostat 133, therefore, provides a fabric cooldown operation following a heat-on drying operation.

The fabric dryness sensing circuit is energized from the conductor 118, throughthe door switch 124, selector switch 102, conductor 125, and momentary switch 103 to junction 127 and then through conductor 134 to the junction point 132. After the momentary switch 103 opens, a bypass circuit around switch 103 includes conductors and 131, and motor switch 126. The junction point 132 connects with a resistance

network including resistors

136 and 137 and selection switches 104, 105, and 106. The circuit continues through the junction 138 to one side of a rectifier 135. The other side of the rectifier is connected to a resistor 139 which is in turn connected to a junction point 141. Extending from the junction point 141 is one circuit portion including a resistor 143 in series with the electrode 80. The other electrode 81 is connected to the drum 60 and through various electrically conductive portions of the apparatus, indicated as 144 in FIG. 2, and to an earth ground through the earth ground conductor 87. Also connected to the junction point 141 is a resistor that is in turn connected to a junction 142.

Connected to the junction point 142 is a resistor 146 and a selector switch 107 that is connected at its other side to the neutral conductor 120 to provide a shunt circuit across the capacitor 145. The capacitor 145 is connected to junction 142 on one side and to the neutral conductor 120 on the other side. It will be noted that during the Permanent Press cycle the capacitor 145 may be charged, as the fabrics across the

electrodes

80, 81 become dry, by the DC circuit extending through

resistors

136 and 137, and through the rectifier 135 and

resistors

139 and 140. The rate of charging of the capacitor is selected to give the desired dryness condition of the fabrics and is determined, in this embodiment, by the amount of resistance in series with the capacitor 145. The circuit portion including selector switch 107 provides a closed loop path for selectively discharging the capacitor 145 at the beginning of a cycle through the momentarily closed switch 107 toinsure a consistent relationship of the charge on capacitor 145 to the dryness of the fabrics across the

electrodes

80, 81.

A gaseous discharge tube, such as a neon lamp 149, is connected in series with

resistors

155 and 157 and in turn across the capacitor 145. The neon tube 149 normally has an effectively infinite resistance; however, when the charge on the capacitor 145 reaches a predetermined value, the gas is ionized and a circuit is conducted therethrough. A thyristor, in the form of silicon controlled rectifier, or SCR 159, includes a gate portion electrically connected to one side of the neon lamp 149. The gate may be directly connected as in FIG. 2 or alternately through a resistor. Upon the firing of the neon lamp, a circuit is completed to the gate of SCR 159, which in turn becomes conductive and completes a circuit between the anode 160 and cathode 161 to effect energization of the solenoid 116 for resetting the selector switches 101--108 and thereby initiating termination of the drying operation.'The solenoid energizing circuit is completed from the conductor 1 18 through the door switch 124, selection switch 102, a conductor 163, and selector switch 108 to one side of the solenoid 116. The other side of the solenoid 116 is connected by

conductors

164 and 165 to the anode 160 of the SCR 159. The cathode 161 of the SCR 159 is connected to the neutral conductor 120. A filter capacitor 169 and resistor 170 is connected in parallel to the SCR 159.

Energization of the solenoid 116 resets the preselection means 100. The resetting effects opening of the selection switches 101, 102, and 108, to terminate the sensing operation for the Permanent Press cycle and to deenergize the heater 75. It will be seen from a further analysis of FIGS. 2 and 3 that even after actuation of the solenoid 116 the motor 34 will remain energized through an auxiliary circuit to effect continued tumbling of the fabrics within the drum 60 for a cooldown operation under control of the cooldown thermostat 133. Upon the temperature of the air within the drum reaching a predetermined lower temperature, the thermostate 133 will open for deenergizing the motor 34 to terminate the cycle of operation.

it will also be seen that upon the firing of the neon tube 149 responsive to a predetermined dry condition, actuation of the solenoid 116 will effect operation of the chime 174 which is shown schematically in FIG. 2 and in outline form in FIG. 4. This one-time operation of the chime will occur at the end of each cycle of operation. Subsequent to the completion of the sensing operation and during the cooldown operation for a Permanent Press cycle of operations, however, the solenoid 116 will be periodically reenergized for effecting a repeating chime under control of a timing circuit operable during the cooldown operation as will be more fully explained hereinafter. This repeating chime during the cooldown portion of the Permanent Press cycle of operations in this embodiment signals the operator so that the fabrics may be immediately removed following the end of the tumbling to prevent the forming of wrinkles in the fabrics.

Referring to FIG. 4, the structure and interrelationship of the solenoid 116, preselection means 100, and chime 174 will now be more fully described. The preselection means 100, the solenoid 116, and the chime 174 are mounted to a panel 175 of the dryer apparatus through a bracket 176 attached to the panel 175 with a plurality of screws 179. The preselection means 100 is mounted to the bracket 176 so that the pushbuttons 1101l3 are accessible to the operator and selectively operable for initiating a desired cycle of operations. The solenoid 116 is mounted to the bracket 176 and is linked to a switch-actuating member 180 through the linkage 181. The chime 174 includes a bell member 183 engageable by a hammer 184 that is attached through a spring member 185 to the mounting bracket I76. Actuation of the solenoid 6 will move the switch-actuating member 180 toward the solenoid for resetting the switches within the preselection means 110. The actuation of the solenoid 116 will also move the chime hammer 184 for effecting engagement thereof with the chime bell 183.

During the cooldown operation a timing circuit is completed to the resistance-capacitance portion of the circuit of FIG. 2 and an actuation circuit is periodically completed to the solenoid 116 through the current-limiting resistor 189 connected in parallel with the selector switch 108. More specifically, a timing circuit is completed to the junction 127 through the door switch 124, cooldown thermostat 133, conductor 131, and switch 126. From junction 127, the circuit is completed to junction 132 through conductor 134. It will be seen from FIG. 3 that selection switch 106 is closed during the cooldown operation of a Permanent Press cycle only, so that a circuit is completed from the junction 132 to the resistancecapacitance portion of the circuit including rectifier 135.

Thus during the cooldown operation of a Permanent Press cycle, and with the fabrics substantially dry as sensed by the dryness sensing control, there will be a charging of the capacitor 145 in a manner as previously described except that less resistance is in series with the capacitor 145, since

resistors

136 and 137 are bypassed. The capacitor 145 will therefore charge over a relatively short predetermined time period for actuating the neon tube 149 and gating the SCR 159. The gating of the SCR 159 will complete a circuit to the solenoid 116 for energizing the solenoid at a reduced power level, however, because of the open switch 108 resulting in the completion of the circuit through the current limiting resistor 189. The circuit extends from the conductor 118 through the door switch 124, the cooldown thermostat 133, the

conductors

130, 125, and 163 and the resistor 189 to one side of the solenoid 116. The other side of the solenoid is connected to the neutral conductor through the anode-cathode path of the SCR 159. The charging of the capacitor and the firing of the SCR 159 for energizing the solenoid 116 will continue during the cooldown operation in the Permanent Press cycle for repeatedly energizing the solenoid with a frequency of energization determined by the R-C constant of the resistancecapacitance circuit portion.

As previously indicated, the solenoid 116 is periodically actuated at the lower power level during the cooldown operation under timing control of the resistance-capacitance circuit portion. Since the switches 101-108 are already in the reset position, the lower power output of the solenoid 116 is sufficient for overcoming the spring pressure on the chime hammer 184 and effecting actuation of the chime 174 for issuing an audible signal.

Thus it is seen that a repeating chime indicating the end of a Permanent Press cycle of operations, for example, is achieved with substantially no addition of components. Solenoid 116 is operable for achieving the dual operation of terminating the operation by resetting the preselection means 100 while also being operable at a reduced power level for actuating the repeating chime 174 during the cooldown operation. Furthermore, the use of the resistance-capacitance portion of the sensing circuit provides timing of the chime and thus eliminates the need for an auxiliary timer. Still further, the use of the SCR permits an energization of the solenoid at the completion of the sensing operation and also a cyclic energization for operating the repeating chime, and thus the need for an auxiliary circuit for cyclically energizing the solenoid is eliminated.

In the drawings and specification, there has been set forth a preferred embodiment of the invention and although specific terms are employed these are used in a generic and descriptive sense only and not for purposes of limitation. Changes in form and the proportion of parts as well as the substitution of equivalents are contemplated as circumstances may suggest or render expedient without departing from the spirit or scope of this invention as further defined in the following claims.

I claim:

1. A control system for a fabric-drying apparatus having means for effecting drying of fabrics in said apparatus and operable through a drying operation, the combination comprising: means for sensing the dryness condition of said fabrics including first resistance-capacitance circuit means and operable at a preselected dryness condition for producing an electrical signal; actuation means responsive to said electrical signal for initiating termination of operation of said apparatus;

indicator means responsive to said electrical signal for indicating the end of said drying operation; and second resistancecapacitance circuit means for periodically producing said electrical signal and reenergizing said indicator means to effect a repeating indication of termination of the drying operation.

2. In a control system for a fabric-drying apparatus as defined in claim 1 wherein said indicator means is in the form of an audible device responsive to the electrical signals produced by said first and second resistance-capacitance circuit means.

3. In a control system for a fabric-drying apparatus as defined in claim I wherein said second resistance-capacitance circuit means includes at least a portion of said first resistancecapacitance circuit means.

4. In a control system for a fabric-drying apparatus as defined in claim I wherein said actuation means includes a selectively energizable solenoid responsive to the electrical signal produced by said dryness sensing means for initiating termination of operation of said apparatus.

5. In a control system for a fabricdrying apparatus as defined in claim 4 wherein said indicator means is in the form of an audible device actuatable by said solenoid and wherein said solenoid is energized responsive to the electrical signals produced by said first and second resistance-capacitance circuit means.

6. In a fabric-drying apparatus including a heater and further including a motor for rotating a fabric container during a drying operation and a cooldown operation, the combination comprising: means for sensing thedryness condition of fabrics including a resistance-capacitance circuit and operable at a preselected dryness condition for producing an electrical signal to initiate termination of the drying operation; actuation means responsive to said electrical signal for deenergizing said heater; auxiliary circuit means for maintaining the motor energized during said cooldown operation; indicator means responsive to said electrical signal for indicating the end of said drying operation; and timing circuit means for periodically reenergizing said indicator means following termination of said drying operation to produce a repeating indication during the cooldown operation.

7. In a fabric-drying apparatus as defined in claim 6 wherein said indicator means is periodically energized through said auxiliary circuit means under control of said timing circuit means during said cooldown operation.

8. In a fabric-drying apparatus operable through a drying operation and a cooldown operation, the combination comprising: means for sensing the dryness condition of fabrics including a resistance-capacitance circuit and operable at a preselected dryness condition for producing an electrical signal to initiate termination of the drying operation; a normally nonconductive solid state switch operable to a conductive condition responsive to said electrical signal; actuation means controlled by said solid state switch and operable for terminating said drying operation; indicator means controlled by said solid state switch and operable for indicating the end of said drying operation; and timing circuit means for periodically operating said solid state switch to a conductive condition for reenergizing said indicator means following termination of said drying operation to produce a repeating indication of termination of the drying operation.

9. In a fabric-drying apparatus as defined in claim 8 wherein said timing circuit means includes at least a portion of said resistance-capacitance circuit and is operable for momentarily changing said solid state switch to the conductive condition with a predetermined frequency during said cooldown operation.

10. In a fabric-drying apparatus as defined in claim 8 wherein said actuation means includes a solenoid having a coil in series with said solid state switch and wherein said solenoid is operable for actuating said indicator means responsive to operation of said solid state switch to the conductive condition at the end of said drying operation and during said cooldown operation.

11. In a fabric-drying apparatus as defined in claim 10 wherein said indicator means is in the form of a chime actuatable by said solenoid at a repeating frequency controlled by said timing circuit means.

12. In a fabric-drying apparatus operable through a drying operation, the combination comprising: means for sensing the dryness condition of fabrics including a resistancecapacitance circuit and operable at a preselected dryness condition for producing an electrical signal to initiate termination of the drying operation; a normally nonconductive solid state switch operable to a conductive condition responsive to said electrical signal; solenoid means controlled by said solid state switch and operable at a first power level for terminating said drying operation; means for indicating the end of said drying operation, said solenoid means being operable at a second lower power level for operating said indicating means; and timing circuit means for periodically operating said solid state switch to a conductive condition for reenergizing said solenoid means at said lower power level following termination of said drying operation to produce a repeating indication of termination of the drying operation.

13. In a fabric-drying apparatus as defined in claim 12 wherein said timing circuit means is electronic and includes at least a portion of said resistance-capacitance circuit.

14. In a fabric-drying apparatus having means for effecting drying of fabrics in said apparatus and operable through a drying operation, the combination comprising: indicator means for indicating the end of said drying operation; means for initiating termination of operation of said apparatus and effecting actuation of said indicator means; and resistancecapacitance circuit means for periodically producing an electrical signal and effecting reactuation of said indicator means to provide a repeating indication of termination of the drying operation.

15. In a fabric-drying apparatus as defined in claim 14 wherein said means for initiating termination of operation includes means for sensing the dryness condition of said fabrics that in turn comprises a resistance-capacitance circuit portion associated with said resistance-capacitance circuit means.

16. In a fabric-drying apparatus as defined in claim 15 and further including solid state switch means responsive to said resistance-capacitance circuit portion for initiating termination of said drying operation and actuating said indicator means and responsive to said resistance-capacitance circuit means for effecting reactuation of said indicator means.

Claims

1. A control system for a fabric-drying apparatus having means for effecting drying of fabrics in said apparatus and operable through a drying operation, the combination comprising: means for sensing the dryness condition of said fabrics including first resistance-capacitance circuit means and operable at a preselected dryness condition for producing an electrical signal; actuation means responsive to said electrical signal for initiating termination of operation of said apparatus; indicator means responsive to said electrical signal for indicating the end of said drying operation; and second resistance-capacitance circuit means for periodically producing said electrical signal and reenergizing said indicator means to effect a repeating indication of termination of the drying operation.

3. In a control system for a fabric-drying apparatus as defined in claim 1 wherein said second resistance-capacitance circuit means includes at least a portion of said first resistance-capacitance circuit means.

4. In a control system for a fabric-drying apparatus as defined in claim 1 wherein said actuation means includes a selectively energizable solenoid responsive to the electrical signal produced by said dryness sensing means for initiating termination of operation of said apparatus.

5. In a control system for a fabric-drying apparatus as defined in claim 4 wherein said indicator means is in the form of an audible device actuatable by said solenoid and wherein said solenoid is energized responsive to the electrical signals produced by said first and second resistance-capacitance circuit means.

6. In a fabric-drying apparatus including a heater and further including a motor for rotating a fabric container during a drying operation and a cooldown operation, the combination comprising: means for sensing the dryness condition of fabrics including a resistance-capacitance circuit and operable at a preselected dryness condition for producing an electrical signal to initiate termination of the drying operation; actuation means responsive to said electrical signal for deenergizing said heater; auxiliary circuit means for maintaining the motor energized during said cooldown operation; indicator means responsive to said electrical signal for indicating the end of said drying operation; and timing circuit means for periodically reenergizing said indicator means following termination of said drying operation to produce a repeating indication during the cooldown operation.

12. In a fabric-drying apparatus operable through a drying operation, the combination comprising: means for sensing the dryness condition of fabrics including a resistance-capacitance circuit and operable at a preselected dryness condition for producing an electrical signal to initiate termination of the drying operation; a normally nonconductive solid state switch operable to a conductive condition responsive to said electrical signal; solenoid means controlled by said solid state switch and operable at a first power level for terminating said drying operation; means for indicating the end of said drying operation, said solenoid means being operable at a second lower power level for operating said indicating means; and timing circuit means for periodically operating said solid state switch to a conductive condition for reenergizing said solenoid means at said lower power level following termination of said drying operation to produce a repeating indication of termination of the drying operation.

14. In a fabric-drying apparatus having means for effecting drying of fabrics in said apparatus and operable through a drying operation, the combination comprising: indicator means for indicating the end of said drying operation; means for initiating termination of operation of said apparatus and effecting actuation of said indicator means; and resistance-capacitance circuit means for periodically producing an electrical signal and effecting reactuation of said indicator means to provide a repeating indication of termination of the drying operation.