US3647196A

US3647196A - Dryer control system

Info

Publication number: US3647196A
Application number: US46332A
Authority: US
Inventors: Curran D Cotton
Original assignee: Maytag Corp
Current assignee: Maytag Corp
Priority date: 1970-06-15
Filing date: 1970-06-15
Publication date: 1972-03-07
Anticipated expiration: 1989-03-07
Also published as: CA935537A

Abstract

A control system for a fabric-drying apparatus comprising an actuation circuit including an SCR operable for initiating termination of operation of the apparatus responsive to one of a plurality of condition-responsive trigger circuits. The SCR is effectively responsive to a preselected dryness condition of the fabrics, to an absence of flame at the fuel burner, or to a malfunction of the apparatus, for example, to initiate a shutting down of the apparatus.

Description

United States Patent otton [45] Mar. 7, 1972 [54] DRYER CONTROL SYSTEM [72] Inventor: Curran 1). Cotton, Newton, Iowa [73] Assignee: The Maytag Company, Newton, Iowa [22] Filed: June 15, 1970 [211 Appl. No.: 46,332

[52] U.S. Cl. ....263/33 B, 34/45 [51] Int. Cl ....F27b 7/00, F26b 19/00 [58] Field of Search ..263/33 B; 34/45 [56] References Cited UNITED STATES PATENTS 3,558,110 1/1971 Kushner ..263/33 B 3,521,376 9/1967 Beller ..34/45 Pnmary Examiner-John .l. Carnby Attorney-William G. Landwier and Richard L. Ward ABSTRACT A control system for a fabric-drying apparatus comprising an actuation circuit including an SCR operable for initiating termination of operation of the apparatus responsive to one of a plurality of condition-responsive trigger circuits. The SCR is effectively responsive to a preselected dryness condition of the fabrics, to an absence of flame at the fuel burner, or to a malfunction of the apparatus, for example, to initiate a shutting down of the apparatus.

15 C ,5 Drawing Figures FUEL \GNlTlON PAIENTEDHAR 71912 3, 647, 196

sum 1 0F 3 PAIENIEnm 1 I972 SHEEI 3 0F 3 mXXXXO m x xxo mooxoo moooox mxxxoo muouuo mxxxxe mxxxoo llv m n H T F m mmww WANDLO. SLA F" UMP... wmmmm vaugro lee SWITCH SWITCH SWITCH XCLOSED QOPEN DMOIENTMILY CLOSED v /NVEA/7'0? Comm/v Q 60 rrw/ 8v DRYER CONTROL SYSTEM BACKGROUND OF THE INVENTION 1. Field of the Invention This invention is related to a drying apparatus and more particularly to a control system for initiating termination of operation of the drying apparatus responsive to one of a plurality of predetermined normal or abnormal conditions.

2. Description of the Prior Art Prior art has shown a moisture-sensing control system operable in a drying apparatus for initiating termination of operation thereof responsive to a particular dryness condition of the fabrics. Other prior art has shown separate control systems for independently terminating operation of the apparatus responsive to other conditions of the drying apparatus.

These separate systems have included, however, duplication of components resulting in increased original cost and greater complexity and chance of malfunction.

SUMMARY OF THE INVENTION It is an object of the instant invention to provide an improved drying apparatus control system including means responsive to a plurality of condition-responsive trigger circuits for initiating termination of operation of the apparatus.

It is a further object of the instant invention to provide an improved drying apparatus control system having a single solid-state switching device responsive to a plurality of trigger circuit signals for initiating termination of the apparatus.

It is a further object of the instant invention to provide an improved drying apparatus control system responsive to a preselected dryness condition of the fabrics and to one of a plurality of other conditions of the apparatus.

It is a still further object of the instant invention to provide an improved drying apparatus control system for initiating termination of operation of the apparatus and including a gatecontrolled solid-state switching device responsive to a plurality of trigger circuits that are independently actuatable for triggering the solid-state switch to a conductive condition.

The instant invention achieves these objects in a control system for a fabric-drying apparatus through use of a solidstate switching device operable for initiating termination of operation of the apparatus responsive to a signal from one of a plurality of condition-responsive trigger circuits.

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 sheets of drawings.

BRIEF 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 fabric-drying apparatus partially broken away and sectioned and incorporating the control system of the instant invention;

FIG. 2 is an electrical schematic diagram showing an improved control circuit for a fabric-drying apparatus and comprising a preferred embodiment of the instant invention;

FIG. 3 is a fragmentary view showing a portion of a fuel burner nozzle and further showing a portion of flame-sensing means included in one embodiment of the instant invention;

FIG. 4 is a chart indicating the operation of various switches of the circuit of FIG. 2; and

FIG. 5 is a sectional view of one of the fabric-engaging electrodes included in the control system of the instant invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1 of the accompanying drawings is shown a fabricdrying apparatus having a base that serves as a support for upwardly extending

channel members

11 and 12 that join with crosspiece 14 to support the hollow blower housing 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 which 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 supporting webs 22.

Journaled within bearing retainer 23 is a drum drive shaft 31 projecting 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, 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 shaft 31 is rigidly connected to the drum spider member 46 which has radiating spokes 51 that support a rim 52.

A horizontally mounted fabric-tumbling drum 60 has a rear wall 61 secured to rim 52 for support and rotation of the drum 60 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 elevating vanes or baffles 66 for tumbling fabrics within the drum 60 during rotation thereof. Cylindrical sidewall 65 is connected to the front drum wall 67. The front wall 67 has a centrally located access opening defined by the annular flange 68 and an annular perforate portion 69 located concentrically around the access opening. This perforate portion 69, including several concentric rows of holes, serves as the air intake to drum 60.

Cabinet 70 is fastened to the base 10 and substantially encloses the entire drying apparatus. The cabinet 70 has an access opening defined by the cabinet flange 71 and aligned with the drum access opening to receive a rearwardly extending portion of the door gasket 72. The door 73 is hinged on the cabinet 70 and forms a substantially airtight seal with the gasket 72. Also fastened to the cabinet 70 is a shroud or cowling member 74 generally spaced from the annular front wall 67 0f the drum 60.

Located below the cowling or shroud member 74 and mounted on the base 10 is an air-mixing chamber 75 through which air is drawn and in which the air is heated and then redirected into the annular space between the front wall 67 of the drum and the shroud member 74. A heater, such as the fuel burner apparatus 84 shown in fragmentary form in FIG. 3, is located generally in the entry portion of the mixing chamber 75 for raising the temperature of the air passing through the mixing chamber 75. The air is drawn into and through the mixing chamber 75, through the space between the drum front wall 67 and shroud member 74, and then through the perforate portion 69 into the interior of the fabric drum 60. A felt seal 76 bridges the space between the shroud member 74 and the drum 60 to prevent air from being drawn inwardly through the space and thereby bypassing the mixing chamber 75 and the heater therein. If an electric heater is used in the dryer apparatus, the heating element may be disposed annularly about the drum front in the space between the drum front 67 and shroud member '74.

Airflow into drum 60 through perforate area 69 is produced by rotation of the revoluble impeller member 77 located in the blower housing 17. The fan pulley 78 formed on the rear end of the impeller 77 is driven directly by the motor 34 and main drive belt 37. A felt air-sealing member 79 encircles the gap between the front periphery of blower housing 17 and the rear periphery of circular shoulder 55 to prevent air from being drawn in at the junction and thus bypassing the air mixing chamber 75 and drum 60.

The blower housing 17 supports at least one thermostat 82 connected in series with the heating means to maintain the inlimit thermostat 83 which is mounted on an upper part of the shroud member 74 and operable to turn off the heater in case the temperature near the front of the drum should rise above a predetermined selected temperature during operation of the clothes dryer. Such a temperature rise might accompany reduced airflow through the drum 60.

Electrodes or

probes

80 and 81 are mounted within the drum to sense the electrical conductivity or resistance of the fabrics within the drum 60 as a measure of the condition of dryness of the fabrics. 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.

Referring to FIG. 5, the baffle 66, on which the

electrodes

80 and 81 are mounted, is formed as a substantially hollow member open at the bottom and attachable to the peripheral wall of the fabric container 60 oriented with respect to the axis of rotation of the fabric container for broadside engagement with the fabrics to lift them for tumbling. The baffle 66 is formed to receive a pair of electrode members and 81 separated by an intermediate ridge 85 so that the major portion of each electrode is positioned for contact by the tumbling fabrics within the rotating container 60. The ridge 85 between the

electrodes

80 and 81 prevents simultaneous contact of both electrodes by rigid objects such as metal buttons or buckles. The

electrodes

80 and 81 include downwardly turned end legs 86 insertable into openings formed in the baffle 66 for positioning and retaining the electrodes on the baffle and for receiving terminals to connect the

electrodes

80 and 81 into the control circuit.

The baffles 66 are formed of an electrically nonconductive material in order to insulate the

electrodes

80, 81 from each other. The electrodes, however, may be electrically shorted by the contact of wet materials during tumbling of the fabric container. A plurality of baffles 66 may be mounted within the drum and provided with the electrodes similar to 80 and 81.

Referring to FIG. 1, electrical energy is supplied to electrode 80, for example, by a lead 88 that is connected to a brush 89 that rotates with the drum 60 and slidingly engages the stationary slip ring 90 while the drum 60 is rotating. The slip ring 90 is mounted on the electrically insulative band.79 and is electrically connected by lead 91 to the control unit 92. The electrode 81 is connected by lead 93 to the rotatable drum and in turn is electrically connected to earth ground through the drum 60, the spider 46, the drive shaft 31, blower housing 17, and the chassis including the base 10. The chassis is connected to earth ground through a conductor 94 electrically connected with the base, for example. The automatic control unit 92 may be secured within a control housing 95 on the cabinet structure 70. The lead 91 is connected to the control unit to be described hereinafter.

Referring now to FIG. 2, illustrating the control circuitry for the fabric-drying apparatus, there is shown diagrammatically a plurality of control components including a manually operable preselection means having a plurality of switches 101 through 108 actuatable between open and closed positions, according to the chart of FIG. 4, under control of push rods or a plurality of manually actuatable pushbuttons 110 through 113 for selectable cycles of operation corresponding to Regular, Permanent Press, Damp Dry, and Air Fluff," respectively.

The switches 101 through 108 are shown collectively with the pushbuttons 110 through 113 in the upper right-hand comer of the diagram and are shown schematically in the circuit for controlling initiation and termination of the fabricdrying apparatus as will I be more fully shown hereinafter. Operation of the group of switches 101 through 108 between open and closed positions is also under the control of a selectively energizable solenoid 115 to terminate operation of the drying apparatus.

The control circuitry of FIG. 2 includes a pair of conductors 118 and .119 that are selectively connectable with a conventional two-wire single-phase alternating current supply. For the explanation of the circuitry of FIG. 2, it will be assumed that the first conductor 118 is connectedwith the powerline and that the second conductor 119 is connected to the neutral line of the two-wire supply and grounded through resistor 120. It is also assumed that the Regular cycle has been selected by the operator.

As previously indicated, the chart of FIG. 4 shows the electrical posture of the preselection switches 101-108 for the various selectable cycles. It is noted, for example, that the preselection switch 101 in the first conductor is closed for each of the Regular, Permanent Press, and .Damp Dry cycles;

Thus in the following explanation of the circuit of FIG. 2, with a Regular cycle assumed, selection switches 101, 102, 104, 107 and 108 are closed, preselection switches 105 and 106 are open, and preselection switch 103 is momentarily closed for initially energizing the machine.

The cycling thermostat 82 and high-limit thermostat 83 are connected in the powerline 118 for effective clothes-drying operation. The normally closed cycling thermostat 82 controls the temperature to a preselected range while the high-limit thermostat 83, also normally closed, deenergizes the circuit upon reaching a safe maximum high temperature level. In the preferred embodiment of FIG. 2 a conventional double-solenoid fuel valve control is connected between the two

lines

118, 119 and is energizable for opening the fuel valve 121. Electrically operable fuel ignition means 124, such as a glow coil or spark ignition means, may be provided between th pair of

lines

118, 119.

Also connected between the lines is the motor 34 including start windings 125, run windings 126 and centrifugal switch 128. Door switch 129, cool-down thermostat 130 and

switches

102 and 103 are in the motor circuit.

The foregoing portion of the circuit of FIG. 2 is operable upon initiation of a Regular cycle as follows: Operation of one of the pushbuttons, such as 110, will close

switches

101, 102, 104, 107 and 108 and momentarily close switch 103. The motor 34 will be energized by a circuit including the closed door switch 129, the conductor 131, and switches 102 and 103. Initially both the run and start

windings

125, 126 will be energized through contacts and 136 of the centrifugal switch 128 but, upon the motor reaching a predetermined speed, centrifugal switch 128 will operate contact 136 to com tact 138 and, assuming that momentary switch 103 is open,

deenergize the start winding 125 while maintaining the run winding 126 energized through the conductor 139.

Also, upon the motor 34 reaching the predetermined speed the centrifugal switch 140 in line 119 will be closed. The fuel valve 121 and the fuel ignition means 124 will then be energized to initiate the drying operation.

Other major portions of the circuit of FIG. 2 are set off by broken lines and will be referred to as the solenoid actuation circuit 144, fabric-dryness-sensing control 145, flame-sensing circuit 146, flame rod shunt detector circuit 148, and a DC power supply circuit 149. As previously indicated, the instant invention is directed to the triggering of the actuation means by one of a plurality of trigger means, such as the drynesssensing control 145, flame-sensing circuit 146, and the flame rod shunt detector circuit 148. These major portions of the control circuit of FIG. 2 will be described in greater detail hereinafter.

The selectively energizable solenoid 115 is mechanically linked to the preselection means 100 and is operable upon energization for resetting the switch members 101 through 108 to the posture corresponding to the off condition of the drying apparatus and effectively terminating operation of the apparatus.

The solenoid 115 is under control of the actuation circuit 144 that includes a normally nonconductive gate-controlled solid-state switch in the form of an SCR having an anode 154 and a cathode 155 in series with solenoid 115. The actuation circuit 144 also includes a seriesconnected resistor 156 and capacitor 157 in a parallel circuit across the anode 154 and cathode 155 of the SCR 150. This parallel-connected snubber network is effective to prevent erratic triggering of the SCR 150 from stray current spikes. There is also a filter capacitor 160 connected across the gate 161 and cathode 155 of the SCR 150 to prevent erratic triggering due to transient current flow within the circuit. A gate resistor 162 is also connected across the gate 161 and cathode 155 of the SCR 150.

Upon the impression of sufficient voltage and current at the gate 161 of the SCR 150, the SCR is triggered to a conductive condition between the anode 154 and cathode 155 for energizing the solenoid 115. The energizing circuit for the solenoid 115 extends between the

powerlines

118, 119 and includes the door switch 129, the conductor 131, switch 108, the solenoid 115, and the conductor 163 to the anode 154 of the SCR 150. The circuit continues from the cathode 155 of the SCR 150 to the neutral powerline 1 19 through the conductor 164.

This operation of the solenoid 115 resets the switches 101-108, in a manner shown in FIG. 4, to effectively initiate termination of operation of the apparatus. More specifically, switch 101 will be opened for deenergizing the fuel valve 121 to interrupt the heat. In addition, switches 102 and 107 will be operated to the open condition for interrupting energization of the fabric-dryness-sensing control 145. Deenergization of the motor 34 will be delayed, through the use of cool-down thermostat 130, until the temperature within the drum 60 decreases to a predetermined temperature; however, the interruption of the heating means and the deenergization of the sensing control comprise a generally irreversible shut-down sequence and may be considered as interruption of the drying apparatus or as initiation of termination thereof.

The first of the trigger means for actuating the SCR 150 to the conductive condition is the fabric-dryness-sensing control 145. The dryness-sensing control 145 for a Regular cycle is energized across

lines

118, 119 by a circuit including closed door switch 129, conductor 131, switch 102, switch 107 and the conductor 165. A low-current branch circuit is also completed from conductor 131 through switch 108, the coil of solenoid 115 and resistor 166 to conductor 165. The current flow in this branch circuit is insufficient to energize solenoid 115. The fabric-dryness-sensing control 145 comprises an RC

circuit including resistors

168, 169 and 170. Resistor 171 is also in the circuit for a Damp Dry cycle. The sensing circuit also includes a rectifier 174, a capacitor 175, and a neon tube discharge device 176.

The circuit of FIG. 2 shows a series connection of the rectifier 174, resistor 168, resistor 169, and capacitor 175. The series connection is effectively connected across the

powerlines

118, 119 for charging the capacitor 175; however, it is noted that a conductor 178, switch 104, resistor 170,

conductors

91, 93, and 94, and the chassis, indicated generally by numeral 179, effectively connect the electrodes in parallel with the capacitor 175. Thus as long as wet fabrics are in contact with the

electrodes

80, 81, the current for charging the capacitor 175 is conducted through the

electrodes

80, 81 and the fabrics so that the capacitor 175 is maintained discharged. As the fabrics become dry, however, less current passes through the fabrics and the charge on the capacitor 175 builds to a point sufficient to cause the neon tube 176 to become conductive.

The breakdown of the neon tube 176 permits the capacitor 175 to discharge for effecting current flow through the conductor 180 and junction 181 to the gate 161 of the SCR 150 in the actuation circuit 144. The current is suflicient to trigger the SCR to a conductive condition and thereby establish a current path across the anode 154 and cathode 155 for energizing the solenoid 115.

Closure of switch 105 in the fabric-dryness-sensing control 145 upon the reset of the preselection means 100 is operable for completely deenergizing capacitor 175 to insure consistent fabric-dryness sensing during the next operation of the drying apparatus.

A second trigger means, in the form of a flame-sensing circuit 146, is responsive to a timed absence of flame at the burner 84 for actuating the SCR 150 and thereby initiating termination of the drying apparatus. The flame-sensing circuit 146 is connected to a DC power supply circuit portion 149 that includes a current-rectifying diode 184, a resistor 185, and a capacitor 186 connected in series between lines 118 and l 19.

The flame-sensing circuit includes an electrode or flame rod 188 juxtaposed to the burner 84 for contact by the flame and also includes an RC circuit portion connected to the DC power supply 149 by conductor 189. The RC circuit portion is also connected to the flame rod 188. The RC circuit portion comprises a resistor 190 and capacitor 191 connected in series between junction 194 and line 119. A second resistor 195 is connected to the resistor 190 and capacitor 191 atone terminal and to the flame rod' 188 at the other terminal. A discharge device in the form of a neon tube 196 is connected to the capacitor 191 and through the gate 161 and cathode 155 of the SCR to line 119 for discharge of the capacitor 191 upon the capacitor charging to a predetermined voltage. The discharge of the capacitor 191 is sufficient to trigger the SCR 150 to a conductive condition.

The third trigger means is in the form of a flame rod shunt detector circuit 148. The shunt detector circuit 148 is associated with the flame-sensing circuit 146 by connections through the junction 194 and conductor 198 and includes a resistor 199, neon tube 200, capacitor 201, and diode 202. The neon tube 200 is connected to the diode 202 that is in turn connected by conductor 204 and the junction 181 to the gate 161 of the SCR 150. The capacitor 201 is connected by conductor 198 to the flame rod 188 and resistor 195.1n order to distinguish from other capacitors in the circuit of FIG. 1, the capacitor 201 will be referred to as a shunt capacitor 201. It does not operate as a shunt but is used in the shunt detector circuit 148.

The components of the flame-sensing circuit 146 and the flame rod shunt detector circuit 148 are cooperable to provide a plurality of circuit means operable for effecting selective actuation of the SCR 150 to a conductive condition depending upon predetermined conditions at the fuel burner 84. A first circuit means, operable for conducting actuation current to the SCR 150 at a level below that sufficient to effect a change in the SCR from the nonconductive to the conductive condition, includes the actuation capacitor 191, resistor 195, conductor 198, shunt capacitor 201, neon tube 200, diode 202,

conductor 204, junction 181, and the gate 161 and cathode of the SCR 150. This circuit is initially made, after closing of centrifugal switch 140, and indicates an absence of a short of the flame rod 188 to the burner 84.

A second circuit means is operable for conducting a higher current to the SCR 150 when the flame rod 188 is shunted to substantially ground potential by being shorted acres the flame gap to the grounded burner 84. The second circuit means includes a conductive path from the grounded burner 84 through the flame rod 188, conductor 198, shunt capacitor 201, neon tube 200, diode 202, conductor 204, junction 181, the gate 161 and cathode 155 of the SCR 150 to the neutral line 119 through conductor 164 which is a substantially ground potential. The second circuit means thus forms a closed loop through the grounded burner 84. This circuit effects a discharge of the shunt capacitor 201 when the flame rod 188 is shorted to the burner 84 and thereby conducts sufficient current to the gate 161 of the SCR 150 to actuate it to a conductive condition. The increased current is possible since the current-limiting resistor is excluded from the circuit by conduction across the effectively eliminated flame gap.

A third circuit means comprises the actuation capacitor 191, the neon tube 196, junction 181, the gate 161 and cathode 155 of the SCR 150 and is operable for conducting suflicient current to the gate 161 of the SCR for effecting a change in the SCR from a nonconductive to the conductive condition after a predetermined time delay, such as 10 seconds, following the sensing of the absence of flame at the burner 84 and the absence of a shunt of said flame rod 188 to said burner 84. The operation of these circuits therefore provides fail-safe operation of the fuel burner.

Referring to FIG. 3, there is shown a preferred embodiment of the fuel burner 84 and the flame rod 188 adjacent thereto. The flame rod 188 is positioned for envelopment by the flame as the burning of the fuel takes place. The end of the flame rod is within approximately one-fourth inch to three-sixteenths inch of the closest part of the grounded burner 84 and is fonned of stainless steel mounted in a ceramic holder 206 with a wire 207 extending from the back end of the holder 206 and being connected to the circuitry as shown in FIG. 2.

By way of example, and not for purposes of limitation, a specific reduction to practice of the preferred embodiment shown in FIG. 1 included resistors and capacitors having specific values as shown in the following table:

Resistors (in ohms) Figure 2 Numeral ohms Capacitors (in microfarads with voltage rating) Figure 1 Numeral Microfarads 0.l (400 volts) 7.0-10.9 (l volts) 0.22 (I50 volts) 0.47 (100 volts) (u 100 volts) 0.] (150 volts) Further circuit details and operation explanation of the flame-sensing circuit 146 and the flame rod shunt detector circuit 148 are included in application Ser. No. 731,907 filed May 24, 1968, by C. D. Cotton et al. and assigned to the assignee of the instant application.

It is thus clear that the instant application describes a novel combination of electrical components and circuit portions comprising an improved control circuit for a fabric-drying apparatus. The circuit is one in which a single actuation means, in the form of an SCR, is responsive to a plurality of potential conditions within the fabric-drying apparatus for initiating termination of operation of the fabric-drying apparatus. In a preferred embodiment, described herein, the SCR is responsive to either the sensing of a desired dryness condition of the fabrics, to the absence of flame at the fuel burner, or to an inoperative condition of the flame rod. In each of these circumstances, it is desirable to tenninate operation of the fabric-drying apparatus.

Other conditions of the apparatus which might necessitate a termination of operation of the machine for which sensing circuits could be provided and connected to the gate of the SCR include: excessive high temperature, insufficient airflow, excessive vibration, or inoperability of dryness-sensing control.

It is sufficiently clear that this combination provides a complete control system for a fabric-drying apparatus while achieving elimination of a number of components. This permits a reduction in manufacturing costs and an improvement in reliability and serviceability of the machine.

In the foregoing 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 defined in the following claims.

1 claim: 1

1. A fabric-drying apparatus comprising: means operable for effecting drying of fabrics in said apparatus; means for energizing and controlling operation of said means for effecting drying to achieve said drying of fabrics; means including a solid-state switch actuatable from a first condition to a second condition for initiating termination of operation of the means for effecting drying; means for sensing fabric dryness and including first trigger means responsive to a predetermined condition of fabric dryness for actuating said solid-state switch to said second condition; and second trigger means responsive to a secondary condition of said fabric-drying apparatus for actuating said solid-state switch to said second condition whereby operation of said drying apparatus is terminated responsive to said predetermined fabric dryness or to the presence of said secondary condition.

2. in a fabric-drying apparatus as defined in claim 1 and further including means for effecting a cooldown operation subsequent to initiating termination of operation of said drying apparatus.

3. In a fabric-drying apparatus as defined in claim 2 wherein said first and second trigger means each include a normally nonconductive discharge device operable at a predetermined voltage for actuating saidsolid-state switch from said first condition to said second condition.

4. In a fabric-drying apparatus as defined in claim 3 wherein each of said first and second trigger means includes an RC circuit for effecting operation of said discharge device at said predetermined voltage after a time delay.

5. In a fabric-drying apparatus as defined in claim 3 wherein said solid-state switch includes a gate portion connected to each of said discharge devices and responsive to operation of said discharge devices for actuating from said first condition to said second condition.

6. A fabric-drying apparatus comprising: means operable for effecting drying of fabrics in said apparatus including a fuel burner; means for energizing and controlling operation of said means for effecting drying to achieve said drying of fabrics; means including a solid-state switching device actuatable from a first condition to a second condition for initiating tennination of operation of said means for effecting drying including shutting down said fuel burner; means for sensing fabric dryness and including first trigger means responsive to a predetermined condition of fabric dryness for actuating said solid-state switching device to said second condition; and safety trigger means responsive to a malfunction associated with said fuel burner for actuating said solid-state switching device to said second condition whereby operation of said drying apparatus is terminated responsive to said predetermined fabric dryness or to the occurrence of said malfunction.

7. in a fabric-drying apparatus as defined in claim 6 wherein said safety trigger means includes means for sensing the absence of flame at said fuel burner and is operable for actuating said solid-state switching device from said first condition to said second condition.

8. In a fabric-drying apparatus as defined in claim 6 wherein said safety trigger means includes flame rod means adjacent said fuel burner for sensing the absence of flame at said fuel burner and actuating said solid-state switching device to said second condition after a predetermined period of absence of flame and wherein said safety trigger means further includes circuit means for sensing a shunting of said flame rod for actuating said solid-state switching device to said second condition whereby operation of said drying apparatus is terminated responsive to the absence of flame at said fuel burner or to a condition of flame rod shunting.

9. A fabric-drying apparatus comprising: means operable for effecting drying of fabrics in said apparatus; means for energizing and controlling operation of said means for effecting drying to achieve said drying of fabrics; circuit means including a solid-state switching device having a gate portion for actuating said solid-state switching device from a first condition to a second condition for initiating termination of operation of said means for effecting drying; means for sensing fabric dryness and including first trigger means responsive to a predetermined condition of fabric dryness and connected to said gate portion for actuating said solid-state switching device to said second condition; and second trigger means responsive to a secondary condition of said fabric-drying apparatus and connected to said gate portion for actuating said solid-state switching device to said second condition whereby operation of said drying apparatus is terminated responsive to said predetermined fabric dryness or to the presence of said secondary condition.

10. In a fabric-drying apparatus as defined in claim 9 wherein each of said first and second trigger means include a normally nonconductive discharge device connected to said gate portion and operable at a predetermined voltage for actuating said solid-state switching device from said first condition to said second condition.

11. In a fabric-drying apparatus as defined in claim 9 wherein said means for energizing and controlling include manually operable preselection means operable to an off condition for terminating operation of said fabric-drying apparatus.

12. In a fabric-drying apparatus as defined in claim' 11 and further including solenoid means operable for resetting said preselection means to said off condition responsive to actuation of said gate-controlled solid-state switching means to said second condition.

13. In a fabric-drying apparatus as defined in claim 12 and further including means operable with said preselection means in said off condition for effecting a cooldown operation of said fabric-drying apparatus.

14. In a fabric-drying apparatus as defined in claim 13 wherein said gate-controlled solid-state switching device is in the form of an SCR having a normally nonconductive anodeto-cathode path connected to said solenoid for effecting operation of said solenoid to reset said preselection means to said off condition for initiating termination of the fabric-drying apparatus. 7

15. A fabric-drying apparatus comprising: means operable for effecting drying of fabrics in said apparatus and including a rotatable fabric container, heating means, and drive means for rotating said fabric container; preselection means manually operable for energizing said motor means and said heating means and initiating and controlling operation of said means for effecting drying; solenoid means operably connected to said preselection means and selectively actuatable for efiecting a resetting of said preselection means to an off condition; means including a solid-state switching device actuatable from a first condition to a second condition for actuating said solenoid means; means for sensing fabric dryness and including first trigger means responsive to a predetermined condition of fabric dryness for actuating said solid-state switching device to said second condition; second trigger means responsive to a secondary condition of said fabric-drying apparatus for actuating said solid-state switching device to said second condition, said preselection means being responsive to actuation of said solenoid for effecting deenergization of said heating means; and means operable for maintaining said motor means energized independently of said preselection means after deenergization of said heater means for effecting a cooldown operation.

Claims

3. In a fabric-drying apparatus as defined in claim 2 wherein said first and second trigger means each include a normally nonconductive discharge device operable at a predetermined voltage for actuating said solid-state switch from said first condition to said second condition.

6. A fabric-drying apparatus comprising: means operable for effecting drying of fabrics in said apparatus including a fuel burner; means for energizing and controlling operation of said means for effecting drying to achieve said drying of fabrics; means including a solid-state switching device actuatable from a first condition to a second condition for initiating terMination of operation of said means for effecting drying including shutting down said fuel burner; means for sensing fabric dryness and including first trigger means responsive to a predetermined condition of fabric dryness for actuating said solid-state switching device to said second condition; and safety trigger means responsive to a malfunction associated with said fuel burner for actuating said solid-state switching device to said second condition whereby operation of said drying apparatus is terminated responsive to said predetermined fabric dryness or to the occurrence of said malfunction.

12. In a fabric-drying apparatus as defined in claim 11 and further including solenoid means operable for resetting said preselection means to said off condition responsive to actuation of said gate-controlled solid-state switching means to said second condition.

14. In a fabric-drying apparatus as defined in claim 13 wherein said gate-controlled solid-state switching device is in the form of an SCR having a normally nonconductive anode-to-cathode path connected to said solenoid for effecting operation of said solenoid to reset said preselection means to said off condition for initiating termination of the fabric-drying apparatus.

15. A fabric-drying apparaTus comprising: means operable for effecting drying of fabrics in said apparatus and including a rotatable fabric container, heating means, and drive means for rotating said fabric container; preselection means manually operable for energizing said motor means and said heating means and initiating and controlling operation of said means for effecting drying; solenoid means operably connected to said preselection means and selectively actuatable for effecting a resetting of said preselection means to an off condition; means including a solid-state switching device actuatable from a first condition to a second condition for actuating said solenoid means; means for sensing fabric dryness and including first trigger means responsive to a predetermined condition of fabric dryness for actuating said solid-state switching device to said second condition; second trigger means responsive to a secondary condition of said fabric-drying apparatus for actuating said solid-state switching device to said second condition, said preselection means being responsive to actuation of said solenoid for effecting deenergization of said heating means; and means operable for maintaining said motor means energized independently of said preselection means after deenergization of said heater means for effecting a cooldown operation.