U.S. patent number 3,824,476 [Application Number 05/405,203] was granted by the patent office on 1974-07-16 for grounded control circuit.
This patent grant is currently assigned to The Maytag Company. Invention is credited to Curran D. Cotton.
United States Patent |
3,824,476 |
Cotton |
July 16, 1974 |
GROUNDED CONTROL CIRCUIT
Abstract
A material moisture sensing control includes a circuit
connectable to a two-wire alternating current supply in either of
two polarity postures. The circuit includes an earth grounding of
one electrode and is operable for providing the desired consistent
sensing and safe operation with either polarity posture while
eliminating the need for either an isolation transformer or an
auxiliary isolation resistor at the earth ground electrode.
Inventors: |
Cotton; Curran D. (Newton,
IA) |
Assignee: |
The Maytag Company (Newton,
IA)
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Family
ID: |
26821168 |
Appl.
No.: |
05/405,203 |
Filed: |
October 10, 1973 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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123046 |
Mar 10, 1971 |
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803637 |
Mar 3, 1969 |
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Current U.S.
Class: |
327/509; 327/493;
327/507; 34/528 |
Current CPC
Class: |
G01N
27/048 (20130101) |
Current International
Class: |
G01N
27/04 (20060101); G06n 027/00 () |
Field of
Search: |
;328/4 ;307/308
;34/45,48 ;317/5 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Rolinec; Rudolph V.
Assistant Examiner: Davis; B. P.
Attorney, Agent or Firm: Landwier; William G. Ward; Richard
L.
Parent Case Text
This is a continuation of application Ser. No. 123,046, filed Mar.
10, 1971 which in turn is a continuation of application Ser. No.
803,637 filed Mar. 3, 1969, now abandoned.
Claims
I claim:
1. A control for an apparatus and including a control circuit
connectable to an electrical supply where one wire of said supply
is a power line and another wire is an earth-grounded neutral line,
the combination comprising: a first circuit portion; means for
connecting said control circuit to said power supply including a
first conductor connectable between one side of said first circuit
portion and said power line and including a second conductor
connectable between the other side of said first circuit portion
and said earth-grounded neutral line; means connected in circuit
with said first circuit portion and responsive to a predetermined
electrical condition of said first circuit portion for initiating a
control function; a second circuit portion including a first
terminal connected to said first circuit portion and a second
terminal effectively electrically disconnected from said first
circuit portion and from said second conductor within said control
circuit; chassis grounding means for connecting said second
terminal to earth ground through a relatively low resistance
chassis path whereby a circuit may be completed from said second
terminal to the other side of said first circuit portion through an
earth ground path exterior to said control circuit, said second
circuit portion being operable when incomplete through said chassis
path and said earth ground path to said second conductor for
effectively controlling said first circuit portion to produce said
predetermined electrical condition whereby initiation of said
control function is dependent on the presence of an earth grounding
of said apparatus.
2. A control as defined in claim 1 wherein said first circuit
portion includes a capacitor connected between said first and
second conductors and wherein said means responsive to a
predetermined electrical condition is responsive to a predetermined
voltage on said capacitor for interrupting operation of said
apparatus and wherein further said second circuit portion is
operable as a discharging path for said capacitor to effectively
maintain said capacitor discharged and said apparatus operable
whereby an earth grounding of said apparatus is essential to
operation of said apparatus.
3. A control for an apparatus and including a control circuit
connectable to an electrical power supply where one wire of said
supply is a power line and another wire is an earth-grounded
neutral line, the combination comprising: means for connecting said
control circuit to said power supply including first and second
conductors; a first circuit portion effectively connected on one
side to said first conductor and on the other side to said second
conductor; means connected in circuit to said first circuit portion
and responsive to a predetermined electrical condition of said
first circuit portion for initiating a control function; and a
second circuit portion including a first terminal connected to said
first circuit portion and a second terminal effectively
electrically disconnected from the other side of said first circuit
portion and from said second conductor within said control circuit
and connected to a relatively low resistance chassis path to earth
ground, said second conductor being disconnected within said
control circuit from said low resistance chassis path whereby
completion of a circuit through said second circuit portion
includes the chassis path and an earth ground path external to said
control circuit, said second circuit portion when incomplete being
operable for effectively controlling said first circuit portion to
produce said predetermined electrical condition.
4. A control as defined in claim 3 wherein said means responsive to
a predetermined electrical condition for initiating a control
function comprises means for interrupting operation of said
apparatus whereby a proper earth grounding of said apparatus is
essential to operation of said apparatus.
5. A control as defined in claim 4 wherein said first circuit
portion includes a capacitor operable at a predetermined charge for
producing said predetermined condition and wherein said second
circuit portion is operable for maintaining said capacitor below
said predetermined charge when said second circuit portion is
connected to earth ground through said conductive chassis path.
6. A control as defined in claim 4 wherein said second circuit
portion includes means for sensing a condition within a properly
grounded apparatus and initiating termination thereof upon a
predetermined condition.
7. A control for an apparatus and including a control circuit
connectable to an electrical power supply where one wire of said
supply is a power line and another wire is an earth-grounded
neutral line, the combination comprising: means for connecting said
control circuit to said power supply including first and second
conductors; a first circuit portion including a capacitor connected
between said first and second conductors; means responsive to a
predetermined voltage on said capacitor for interrupting operation
of said apparatus; and a series circuit portion including a first
terminal connected to one side of said capacitor and a second
terminal effectively electrically disconnected from the other side
of said capacitor within said control circuit and connected to a
relatively low resistance chassis path to earth ground, said second
conductor being effectively electrically disconnected from said low
resistance chassis path within said control circuit whereby
completion of a circuit through said series circuit portion
includes the chassis path and an earth ground path external to said
control circuit, said series circuit portion being operable as a
discharging path for said capacitor to effectively maintain said
apparatus operable whereby an earth grounding of said apparatus is
essential to operation of said apparatus.
8. A control as defined in claim 7 and further including sensing
means responsive to a predetermined condition in said apparatus for
initiating termination thereof and comprising a pair of electrodes
in said series circuit portion normally shunted by low resistance
material during operation of said apparatus whereby existence of
one of the conditions including the absence of a proper earth
ground path and the absence of a low resistance shunt across said
electrodes will effect interruption of operation of said
apparatus.
9. A material moisture sensing control circuit connectable to an
alternating current supply where one wire of said supply is a power
line and another wire is an earth grounded neutral line, the
combination comprising: means for connecting said moisture sensing
control circuit to said alternating current supply including first
and second conductors; a resistance-capacitance circuit portion
including a capacitor connected between said first and second
conductors; trigger means connected in circuit to said capacitor
and responsive to a predetermined voltage on said capacitor for
initiating termination of operation of a controlled apparatus;
electrode means engageable with materials being treated and
comprising a first electrode electrically connected to one side of
said capacitor and a second electrode spaced from said first
electrode and effectively electrically disconnected from the other
side of said capacitor and from said second conductor within said
control circuit, said materials bridging said electrodes and
forming a series circuit portion including said first and second
electrodes and said materials bridging therebetween; and grounding
means including a conductive chassis grounding path and connecting
said second electrode to earth ground, said second conductor being
effectively electrically disconnected from said low resistance
chassis path within said control circuit and being effectively
connected to earth ground for completing a circuit to the other
side of said capacitor through said series circuit portion and
including said chassis path and an earth ground path exterior to
said control circuit, said series circuit portion being operable as
a discharging path for said capacitor to effectively maintain said
apparatus operable while said materials are wet whereby an earth
grounding of said apparatus is essential to operation of said
apparatus.
10. A moisture sensing control circuit as defined in claim 9
wherein said pair of conductors are reversibly connectable to said
two wires in first and second polarity postures whereby each of
said conductors is potentially connectable to the power line and
wherein said capacitor is alternately charged and discharged at
relative rates dependent upon the moisture content of said
materials during successive half cycles of the alternating current
supply in each of said polarity postures whereby the said control
circuit is operable in either of said polarity postures.
11. A non-polarity sensitive material moisture sensing control
circuit controlling an auxiliary circuit and connectable to a
single phase alternating current supply where one wire of said
supply is a power line and another wire is an earth-grounded
neutral line, the combination comprising: means for connecting said
moisture sensing control circuit to said alternating current supply
including a pair of conductors reversibly connectable to said two
wires in first and second polarity postures whereby each of said
conductors is potentially connectable to the power line; a
rectifier electrically connected to a first of said conductors; a
resistance-capacitance circuit portion including a capacitor
connected between said first and second conductors in series with
said rectifier; trigger means connected in circuit to said
capacitor and responsive to a predetermined voltage on said
capacitor for initiating actuation of said auxiliary circuit; and
electrode means engageable with materials and comprising a first
electrode electrically connected to the rectifier side of said
capacitor and a second electrode effectively electrically
disconnected from the other side of said capacitor within said
control circuit and electrically connected through a low resistance
chassis grounding path to earth ground, the other of said
conductors being effectively electrically disconnected from said
chassis grounding path and separately connected to earth ground
when said first conductor is connected to said power line, said
materials bridging said electrodes and forming a series circuit
portion including said first and second electrodes, said materials,
said chassis grounding path and said earth ground to said other
conductor whereby said series circuit portion is effectively
connected in parallel with said capacitor through an earth ground
path external to said control circuit, said capacitor being
chargeable to said predetermined voltage as said materials assume a
predetermined moisture content with said pair of conductors
selectively connected to said alternating current supply in said
first and second postures.
12. A non-polarity sensitive material moisture sensing circuit as
defined in claim 11 wherein said trigger means includes a normally
non-conductive discharge device in parallel to said capacitor and
operable to a conductive condition at said predetermined voltage
for effecting discharge of said capacitor through said discharge
device and for actuating said auxiliary circuit.
13. A non-polarity sensitive material moisture sensing circuit as
described in claim 11 and including resistance means in series with
said capacitor wherein said capacitor is alternately charged and
discharged during successive half cycles of the alternating current
supply with the discharging of said capacitor being effected
through the series circuit portion including the materials and the
earth ground path whereby the rate of discharging decreases as the
materials across said electrode means become dry and whereby said
capacitor is gradually charged to said predetermined voltage.
14. A non-polarity sensitive material moisture sensing circuit as
defined in claim 13 wherein current-limiting resistance means is
connected in the circuit to said first electrode.
15. A non-polarity sensitive material moisture sensing control
circuit controlling an auxiliary circuit and connectable to a
single phase alternating current supply where one wire of said
supply is a power line and another wire is an earth-grounded
neutral line, the combination comprising: means for connecting said
moisture sensing control circuit to said alternating current supply
including a pair of conductors reversibly connectable to said two
wires in first and second postures whereby each of said conductors
is potentially connectable to the power line with the other
conductor being connected to the earth-grounded neutral line; a
rectifier electrically connected at a first side to a first of said
conductors; and R-C circuit portion including series-connected
resistance means and capacitance means, said R-C circuit portion
being connected at one side to a second side of said rectifier and
at the other side to the second of said conductors; trigger means
connected in circuit to said capacitance means and responsive to a
predetermined voltage on said capacitance means for actuating said
auxiliary circuit; and electrode means engageable with materials
and comprising a first electrode connected in circuit to the
rectifier side of said R-C circuit portion and a second electrode
effectively electrically disconnected from the other side of said
capacitor and said other conductor within said control circuit and
electrically connected to earth ground through a low resistance
chassis grounding path, said other conductor being effectively
electrically disconnected from said chassis grounding path and
separately connected to earth ground, said materials bridging said
electrodes and forming a series circuit portion including said
first electrode, said materials, said second electrode, and said
chassis grounding path whereby said series circuit is effectively
connected in parallel with said R-C circuit portion only through an
earth ground path external to said control circuit, said
capacitance means being chargeable to said predetermined voltage as
said materials assume a predetermined moisture content with said
pair of conductors selectively connected to said alternating
current supply in said first and second postures.
16. A non-polarity sensitive material moisture sensing circuit as
defined in claim 15 wherein said trigger means includes a normally
non-conductive discharge device in parallel connection to said
capacitance means and said series circuit portion and operable to a
conductive condition at said predetermined voltage and wherein said
capacitance means is alternately charged and discharged during
successive half cycles of the alternating current supply with the
discharging of said capacitance means being effected through the
series circuit portion including the materials and the earth ground
path when the charge on said capacitance means is below said
predetermined voltage and wherein said capacitance means is at
least partially discharged through said discharge device at said
predetermined voltage.
17. A material drying apparatus operable through a drying operation
and connectable to a single phase alternating current supply where
one wire of said supply is a power line and another wire is an
earth-grounded neutral line and having a material dryness sensing
control circuit operable for initiating termination of said drying
operation, the combination comprising: means for connecting said
material drying apparatus to said two wires comprising a pair of
conductors reversibly connectable to said two wires in a first
posture with a first conductor connected to said power line and in
a second reversed posture with a second conductor connected to said
power line; a rectifier electrically connected on one side to one
of said conductors; an R-C circuit portion including
series-connected resistance means and a capacitor, said R-C circuit
portion being electrically connected at one side to a second side
of said rectifier and at the other side to the other of said
conductors; trigger means connected in circuit to said capacitor
and responsive to a predetermined voltage on said capacitor for
initiating termination of said drying operation; electrode means
including a pair of electrodes engageable with materials for
completing an electrical current path therethrough, one of said
electrodes being connected through current limiting resistance
means to said R-C circuit portion between said rectifier and said
capacitor, the other of said electrodes being effectively
electrically disconnected from the other side of said R-C circuit
portion and from said other conductor within said control circuit;
and earth ground conductor means electrically connected to said
other electrode and including a low resistance chassis grounding
path, said other conductor being effectively electrically
disconnected from said earth ground conductor means and separately
connected to earth ground, said materials bridging said pair of
electrodes and forming a series circuit portion including said pair
of electrodes, said materials, and said earth ground conductor
whereby said series circuit is effectively in parallel with said
capacitor only through an earth ground path external to said
control circuit, said capacitor being alternately charged and
discharged during successive half cycles of the alternating current
supply with the discharging of said capacitor being effected
through the series circuit portion including the materials whereby
the rate of discharging decreases as the materials become dry and
whereby said capacitor is gradually charged to said predetermined
voltage when said pair of conductors is selectively connected to
said alternating current supply in either of said first or second
postures.
18. A material drying apparatus as defined in claim 17 wherein said
trigger means includes a normally non-conductive discharge device
in parallel to said capacitor and operable to a conductive
condition at said predetermined voltage on said capacitor.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a control system in a machine for
treating materials and more particularly to a non-polarity
sensitive moisture sensing control for initiating termination of an
operation after the materials have reached a predetermined moisture
content.
2. Description of the Prior Art
One type of control system becoming increasingly used for effecting
automatic termination of the drying operation in a fabric drying
apparatus includes sensing the electrical conductivity of the
fabrics by means of a pair of electrodes 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 for terminating the
dryer operation at a preselected dryness condition. It is essential
that charging of the capacitor to a predetermined voltage be
consistently achieved under numerous operating conditions. One
condition, that of reverse polarity of the circuit, however, is
ignored or sidestepped in the prior art patents. If a proper
circuit is not provided, a reverse polarity hookup can result in
inoperability of the sensing circuit, inconsistent dryness sensing,
or even more important, can result in a dead short to the
electrodes and create an unsafe electrical conditon of the dryer
apparatus.
Most prior art patents show the dryer sensing circuit in
association with a 220 volt three-wire system. Many of the prior
art sensing systems shown in a three-wire arrangement would result
in improper or unsafe operating conditions if the polarity of the
circuit were reversed. There is little opportunity, however, that
the polarity of the circuit may be reversed because of the nature
of a three-wire system and its installation.
Other prior art patents show use of an isolation transformer to
avoid having to overcome the polarity sensitivity problem.
The polarity sensitivity problem becomes most acute in a drying
apparatus designed to operate on 110 volts across a two-wire
system. These 110 volt machines include most gas models and the
electric models in which the heat input is substantially less than
that for the electric model operating on 220 volts. In each of
these 110 volt drying devices, it is possible that the machine may
be improperly installed or that the two-prong connector may be
reversibly inserted into the electrical outlet.
Thus, it becomes clear that there is need for a dryness sensing
circuit operable in a non-polarity sensitive manner to provide
consistent dryness sensing and safe operating conditions in either
of the two polarity postures.
SUMMARY OF THE INVENTION
It is an object of the instant invention to provide an improved
material moisture sensing circuit having non-polarity sensitive
operation.
It is a further object of the instant invention to provide an
improved material moisture sensing circuit having electrically safe
electrodes and being operable to provide uniform moisture sensing
in either of two alternate polarity postures.
It is a further object of the instant invention to provide an
improved material moisture sensing circuit operable across a power
line and a neutral line in either posture of connection and
including an earth ground connection with one electrode.
It is a still further object of the instant invention to provide an
improved material moisture sensing circuit operable in a safe
non-polarity sensitive manner and including an electrode connected
at one end into the control circuit through an earth ground path
only.
These objects are achieved in a material moisture sensing control
reversibly connectable to a two-wire alternating current supply in
either of two polarity postures and including a
resistance-capacitance circuit portion. One of the pair of
electrodes is connected with an earth ground. The circuit for the
charging and discharging of the capacitor includes a closed loop
path including an earth ground path.
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 fabric 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 principles of the instant invention;
FIG. 3 is a chart indicating the operation of various switches of
the circuit of FIG. 2;
FIG. 4 is a fragmentary portion of a circuit that may be
substituted into the circuit of FIG. 2 to provide an alternate
circuit embodying the instant invention;
FIG. 5 is a simplified diagrammatic electrical circuit portion
showing a specific alternating current half cycle operation of the
circuit of FIG. 2;
FIG. 6 is a simplified diagrammatic electrical circuit similar to
FIG. 5 and showing an opposite half cycle alternating current
operation;
FIG. 7 is a simplified diagrammatic electrical circuit similar to
that shown in FIG. 5 with the circuit reversed to show an opposite
polarity hookup;
FIG. 8 is a simplified diagrammatic electrical circuit similar to
that shown in FIG. 7 and showing the opposite alternating current
half cycle operation; and
FIG. 9 is a simplified diagrammatic electrical circuit similar to
those shown in FIGS. 5 through 8 but depicting a circuit similar to
the polarity sensitive prior art fabric dryness control
systems.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In FIG. 1 of the accompanying drawings is shown a clothes dryer
apparatus having a base 10 that serves as a support for upwardly
extending channel members 11 and 12 that join with crosspiece 14 to
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 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 web 22.
Journalled within member 23 is a revoluble 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, 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 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
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
cabinet 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 on the rear end of the impeller 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
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.
In this embodiment, 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 band 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 spider 46, 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 non-conductive
material in order to insulate the electrodes 80, 81 from each
other. The electrodes, however, are electrically shorted by the
contact of web 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 including a plurality of
switches 101 through 108 actuatable between open and closed
positions, according to the chart of FIG. 3, under control of push
rods or a plurality of manually actuatable push buttons 110 through
113 indicated at "Regular," "Permanent Press," "Damp Dry," and "Air
Fluff," respectively. The switches 101 through 108 are shown
collectively at the right side of the diagram under control of the
push buttons 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 control of a selectively energizable
solenoid 116, as indicated in FIG. 3, to terminate the drying
cycle.
The control circuitry of FIG. 2 includes a pair of conductors 119
and 120 that are selectively connectable with a conventional
two-wire single phase alternating current supply through a
conventional plug and receptacle arrangement including the plug
121. For the explanation of the circuitry of FIG. 2, it will be
assumed that the first conductor 119 is connected with the power
line and that the second conductor 120 is connected to the neutral
line of the two-wire supply.
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 push buttons 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 following explanation of the circuit of FIG. 2, it
will be assumed that a Regular cycle has been selected by the
operator and thus selection switches 101, 102, 104, 107, and 108
are closed and preselection switches 105 and 106 are open while
preselection switch 103 is momentarily closed during the
preselection and machine energization process.
The heater 75 is connected between the first and second conductors
119 and 120 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
first conductor 119 through a door switch 124, closed preselection
switch 102, a conductor 125, and momentarily closed preselection
switch 103 to one side of the motor 34. The other side of the motor
34 is connected to the second 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 first conductor 119 through
the door switch 124, preselection switch 102, and conductors 125,
130, 131 to the motor 34.
A cool-down 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
heat on, the cool-down thermostat 133 will close and maintain the
motor 34 energized until the temperature within the drum 60 is
reduced to the 135.degree. F. This cool-down thermostat 133,
therefore, provides a fabric cool-down operation following a
heat-on drying operation.
The fabric dryness sensing circuit is energized from the first
conductor 119, through the door switch 124, selector switch 102,
selector switch 107, and conductor 134 to one side of a half-wave
rectifier 135. The other side of the rectifier 135 is connected to
a pair of parallel related resistors 139 and 140 with a first
resistor 139 being in the circuit normally and a second resistor
140 being in parallel with the first resistor 139 upon the closing
of selector switch 106 by selection of Damp Dry cycle. The parallel
related resistors 139, 140 are then in turn connected to a junction
point 141. Extending from the junction point 141 is one circuit
portion including a selector switch 104 and 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 at 144 in FIG. 2, and to an earth
ground through the earth ground conductor 87. Connected to the
junction point 141 is a resistor 146 in series with a capacitor 145
that is in turn connected to the second conductor 120.
Also connected to the junction point 141 is one side of a selector
switch 105 that is connected at its other side to the second
conductor 120 to provide a shunt circuit across the capacitor 145.
It will be noted that the capacitor 145 may be charged, as the
fabrics across the electrodes 80, 81 become dry, by the d.c.
circuit extending through the rectifier 135 and resistor 146. The
circuit portion including selector switch 105 provides a closed
loop path for selectively discharging the capacitor 145 at the end
of each cycle. Beginning each cycle with a shorted capacitor
insures 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 neom lamp 149, is connected
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 within the
tube is ionized and a circuit is conducted therethrough. In series
with the neon tube 145 is a reed relay coil 150 responsive to
completion of a circuit through the neon tube 145 for closing the
juxtaposed reed switch 151. The reed switch 151 completes an
energizing circuit to 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
first conductor 119 through the door switch 124, a conductor 153,
and selector switch 108 to one side of the solenoid 116. The other
side of the solenoid 116 is connected by a conductor 154 to the
reed switch 151. The other side of the reed switch 151 is connected
to the second conductor 120.
It will be seen from a further analysis of FIGS. 2 and 3 that upon
actuation of the solenoid 116 the heating operation will be
terminated but that the motor 34 will remain energized to effect
continued tumbling of the fabrics within the drum 60 for a
cool-down operation under operation of the cool-down thermostat
133. Upon the temperature of the air within the drum reaching a
predetermined lower temperature, the thermostat 133 will open for
de-energizing the motor 34 to terminate the cycle of operation.
Referring to FIG. 4, there is shown an alternate means for
actuating the solenoid. The circuit includes a neon tube 149 in
series with a current-limiting resistor and responsive to a
predetermined voltage on a capacitor as in FIG. 2. Upon the firing
of the neon tube 149, a circuit is completed to the gate 156 of an
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. The SCR circuit portion, or the reed relay circuit
portion in the case of the circuit of FIG. 2, and the solenoid
circuit portion may be considered as an auxiliary circuit
responsive to the dryness sensing circuit.
Referring now to FIGS. 5 through 8, the charging of the capacitor
during the drying operation will be more specifically
discussed.
Each of FIGS. 5 through 8 show a simplified circuit having a
two-prong plug 121 engageable with a two-wire single phase
alternating current input 163. There is shown a coil 164 in each of
the figures representing the secondary winding of the step-down
transformer in the electrical distribution system. There is also
shown an earth ground 165 as would be included in the electrical
distribution system. It will be noted that FIGS. 5 and 6 are
substantially identical except for broken lines 168 and 169
indicating electron flow during each of the two half cycles of the
alternating current input. Likewise, FIGS. 7 and 8 are identical
except for the broken lines 170 and 171 indicating electron flow
during the half cycles of the alternating current input. It is
noted that the polarity of FIGS. 7 and 8 is reversed as compared to
FIGS. 5 and 6 and represents the situation in which the plug 21 is
turned over and inserted into the receptacle, for example. Such a
reverse polarity might also result from improper installation of
the dryer or by improper installation of the household wiring.
Furthermore, the safety provided by three-prong plugs presently
provided with electrical apparatus could be bypassed by removing
the grounding prong on the plug or by improperly using an adaptor
to permit the operator to unknowingly reverse the plug in the
receptacle.
It will be seen that the circuits of FIGS. 5 through 8 include a
simplified version of the circuit of FIG. 2 and comprising the
rectifier 135, resistors 139, 143, and 146, the electrodes and
fabrics across the electrodes as represented by a variable resistor
174, capacitor 145, neon tube 149, the reed relay coil 150, and
earth ground conductor 87.
By way of an example of an operative circuit to achieve the
intended drying sensitivity, the resistors 139, 143 and 146 shown
in FIGS. 5 through 8 may be of the values 30 megohms, 560,000 ohms,
and 100,000 ohms respectively. The capacitor 145 will have a value
of approximately 9 microfarads and the neon tube 149 is operable
for becoming conductive at approximately 70 volts.
The connection of the two-prong plug 121 with the two-wire system
163 as shown in FIG. 5 makes the upper conductor 175 the power or
"hot" line. FIG. 5 is intended to show that part of a full wave in
which the upper conductor 175 is positive with respect to the lower
conductor 176. Under these conditions, the positive potential at
the upper conductor 175 causes electron flow from the earth ground
conductor 87 through the electrodes and wet clothes, as shown by
the variable resistor symbol 174, the resistor 143, and through the
timing resistor 139 and the rectifier 135 to the upper conductor
175. Electrons also flow from the top plate of the capacitor 145
leaving the top plate positively charged with respect to the bottom
plate. This electron flow is shown by the broken line 168 in FIG. 5
and includes a closed loop extending from the broken line as shown,
through the upper prong of the connector 121 to the upper wire of
the two-wire supply 163, and through the coil 164 to a junction
179. From the junction point 179, one portion of the closed loop
extends to earth ground connection 165 and through the earth ground
to the earth ground connection 87 at one of the electrodes. The
other branch of the closed loop extends from junction 179 through
the lower of the two-wire supply, and through the lower prong of
the plug 121 and the lower conductor 176 to the lower plate of the
capacitor 145. FIG. 5 thus shows the electron flow with a normal
polarity connection during the positive half cycle.
The circuit of FIG. 6 also shows normal polarity with the upper
conductor 175 being the "hot" line. The broken line 169 in this
figure, however, indicates electron flow during the negative half
cycle. Because of the alternating current input, the upper
conductor 175 is now negative with respect to the lower conductor
176 and the biasing of the rectifier 135 prevents electron flow
from the upper conductor 175. Thus there will be no electron flow
through the timing resistor 139 or the rectifier 135. At the
beginning of this negative half cycle, the top plate of the
capacitor 145 is positively charged with respect to earth ground
and therefore electrons will flow from the earth ground connection
87 through the electrodes and fabrics 174 toward the top plate of
the capacitor in an attempt to equalize the charge on the capacitor
145. As the fabrics within the dryer become more dry and therefore
less conductive, however, the electron flow away from the top
plate, as shown in FIG. 5, will exceed the equalizing flow of
electrons as shown in FIG. 6. The difference between the flow of
electrons from the top plate and the flow of electrons to the top
plate will become greater as the fabrics become more dry and the
capacitor 145 will gradually build a more positive charge. It is
thus seen that at some preselected dryness condition, the capacitor
145 will achieve a predetermined voltage for firing the neon tube
149 connected in parallel across the capacitor.
Referring now to FIG. 7, the circuitry is shown reversed to
indicate that the two-prong plug 121 has been reversed to give an
opposite polarity to the control circuitry. What was the lower
conductor 176 or the neutral line in FIG. 5 is now the "hot" line
in FIG. 7. When the conductor 176 is negative with respect to
conductor 175 as during the negative half cycle, the rectifier 135
is forwardly biased and electrons flow away from the bottom of the
capacitor 145 through the discharge resistor 146 and then branch
through the parallel paths including one path comprising the
electrode resistor 143 and the variable resistance 174 of the
electrodes and fabrics to the earth ground connection 87. The other
electron flow path includes the timing resistor 139 and the
rectifier 135. The balance of the closed loop path will include the
two-wire supply 163 and earth ground as explained in conjunction
with FIG. 5. With this electron flow, the bottom plate of the
capacitor 145 will become positively charged with respect to the
upper plate as shown in FIG. 7. During the positive half cycle, as
shown in FIG. 8, conductor 176 is positive with respect to
conductor 175 and the rectifier 135 prevents the flow of electrons
through the rectifier 135 and the timing resistor 139. During the
positive half cycle, the top plate of the capacitor 145 is now
highly positive with respect to ground because of being connected
directly to conductor 176 and electrons will flow from the earth
ground connection 87 through the electrodes and fabrics 174 and
through the electrode resistor 143 and discharge resistor 146 to
the bottom plate of the capacitor 145 tending to impart to it a
negative charge.
The negative flow in FIG. 8 is greater in magnitude than the
negative flow of FIG. 6 because of the relative electromotive
forces causing the flow in each of the circuits. The flow in FIG. 6
is caused by the slightly positive charge on the capacitor 145 as
the result of the flow in FIG. 5, whereas the negative flow of FIG.
8 is the result of the high positive potential on the top plate of
the capacitor 145. The increased electron flow through the parallel
paths of FIG. 7 offsets the high opposite electron flow of FIG. 8
and causes both line polarities to permit the control to sense the
same moisture retention of the clothes. As the clothes become more
dry, the electron flow through the clothes in each of the FIGS. 5
through 8 become smaller and smaller until it is negligible and the
timing circuit effects a positive charging of the capacitor 145.
Upon the capacitor 145 reaching a predetermined charge, the neon
tube 139 is actuated.
It will be seen in FIGS. 7 and 8 that an alternating current flows
through the clothes when conductor 176 is the "hot" side of the
line. In this condition, the value of the electrode resistor 143
and the discharge resistor 146 become important from a safety
standpoint so that the operator upon touching the electrodes 80, 81
and ground will not be subject to an unsafe current flow. Such a
current flow should not exceed 0.2 milliamps.
Referring to FIG. 9, there is shown a simplified electrical diagram
similar in part to the diagrams shown in FIGS. 5 through 8. The
diagram of FIG. 9, however, shows a prior art circuit portion that
is polarity sensitive and thus not operable for achieving
satisfactory sensing and safety requirements in both of the two
polarity postures. A brief consideration of the polarity sensitive
circuit of FIG. 9 will make the advantages of the instant invention
more meaningful. In FIG. 9, with the upper conductor 183 connected
to the "hot" line 184, the top plate of the capacitor 185 will
become positively charged during the positive half cycle and then
will be neutralized during the negative half cycle by the flow of
electrons through the resistor 186, the dryer chassis 189, and
through the variable resistance 190 of the electrodes and fabrics.
As the fabrics become dry, this neutralizing flow of electrons will
be decreased and the capacitor 185 will become positively charged.
If, however, polarity of the system is changed so that the upper
conductor 183 becomes the neutral side of the line, there will be a
circuit completed, during the positive half cycle, through the
lower conductor 191, which would now be connected to "hot" line
184, and through the pair of isolation resistors 193, and 186
directly to the earth ground connection 194 through the cabinet or
chassis 189 and no charging of the capacitor 185 will result. It is
therefore clear that the circuit of FIG. 9, characteristic of prior
art devices, is polarity sensitive and thus not as desirable for
use in a fabric dryness sensing control circuit subject to a
reversed polarity relationship.
It is therefore clear from the above description that the improved
non-polarity sensitive fabric dryness sensing circuit as described
hereinabove offers distinct advantages for use in a dryer apparatus
in an installation where there is a potential reversal of polarity.
This is particularly true in two-wire 110 volt installations as
versus the 220 volt three-wire installations where proper grounding
is more assured. The circuit of the instant invention eliminates
the closed loop discharge path through the dryer cabinet and
chassis and substitutes a closed loop through earth ground to
achieve non-polarity operation without an isolation transformer.
Furthermore, the circuit provides consistent sensing of preselected
dryness conditions in either polarity posture. Still further, the
use of the earth ground path provides a system which is inoperable
without an earth ground of the cabinet to assure, in the interest
of safety, that the cabinet is properly earth grounded. More
specifically, the dryer will shut off after a short period of time,
as if no clothes were in the drum, if there is no earth ground
connection to the dryer.
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 expendient
without departing from the spirit or scope of this invention as
further defined in the following claims.
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