U.S. patent number 3,599,342 [Application Number 04/803,687] was granted by the patent office on 1971-08-17 for dryer control.
This patent grant is currently assigned to The Maytag Company. Invention is credited to Curran D. Cotton.
United States Patent |
3,599,342 |
Cotton |
August 17, 1971 |
DRYER CONTROL
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.
Inventors: |
Cotton; Curran D. (Newton,
IA) |
Assignee: |
The Maytag Company (Newton,
IA)
|
Family
ID: |
25187181 |
Appl.
No.: |
04/803,687 |
Filed: |
March 3, 1969 |
Current U.S.
Class: |
34/393;
34/446 |
Current CPC
Class: |
F26B
25/22 (20130101); D06F 34/06 (20200201); D06F
2101/20 (20200201); D06F 2105/28 (20200201); D06F
2105/60 (20200201); D06F 2105/46 (20200201); D06F
58/38 (20200201); D06F 2103/10 (20200201); D06F
2103/38 (20200201) |
Current International
Class: |
D06F
58/28 (20060101); F26B 25/22 (20060101); F26b
013/10 () |
Field of
Search: |
;34/43,44,45,48,53 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Dority, Jr.; Carroll B.
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 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.
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 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.
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 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.
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 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.
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.
Description
BACKGROUND OF THE INVENTION
1. 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 fabric-tumbling
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 moisture-sensing 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.
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 resistance-capacitance 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 preselection switch, 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
supporting 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.
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 110--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
118 and 119 by a circuit portion including the preselection switch
101, a cycling thermostat 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 118 through a door switch 124, 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.degree. 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.degree. 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, through the 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
130 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 135 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 140 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 to insure 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 118 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 110--113 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 176. Actuation of the solenoid 116 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 resistance-capacitance 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 120 through the anode-cathode path of the SCR
159. The charging of the capacitor 145 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 resistance-capacitance 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.
* * * * *