Note: Descriptions are shown in the official language in which they were submitted.
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9D-H~-13669
~AC~GROUND DISCUSSIOM
This invention concerns saf~ty arrangemen~s for
appliances and more particularly safety arrangements which
insure that the line voltage to the appliance circuitry is
caused to be disapplied in the eYent of signi~icant damage
to th~ con~rol panel. That is, such damage as occurs due
to fire or Lmpacts with the control panel.
In r~ce~t years, ~he use o so-called membrane
switches ~or ~he operator con~rol inpu~ to the appliance
con~rol circuitry hav~ been employedO Such membra~e switches
present a relatively smooth uninterrup~ed ~urface for th~
control panel and are conveniently manipulated by the appli-
ance operator.
Such appliance membrane swi~ch~s co~si~t of a
pair o circuit bearing sheets of thin material such as
polyester ~ilm upon which is deposited conductor ~racks on
the opposing faces of the circuit layers. In addition,
certain areas bear a solid conductox material which corr~s-
ponds to the switching location arranged in an array at cor-
responding location~ on either circuit layer.
Interposed between the circuit layer is an insu-
lator shield having cutouts in the same corresponding loca-
tions.
A graphic electrostatic shield bearing the appro-
priate legends o~erlays thP topmost circuit layer. By pres-
sing the outer conductive areas, the operator causes the
corresponding conductive areas in the lower circuit layer
to be contacted and a circuit established. According to ~he
nature of the control circuitry, this causes various func-
tions or selections in the control cycles to be made. ~or
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9D-HL-13669
example, in the case o~ a dry~r, high and low heat ~ettings,
~abric types, etc., i~ a mannex well know~ in the art.
In ~he e~en~ of damag~ to the appliance such as
caused by fire, it may be advantageous to cause the line
5 voltag~ applied to the appliance ~o be di~continu~d in or-
der to reduce shock and ~ire hazards which may be present
du~ to the damage tQ the machi~e, particularly to the more
vulnerable areas such as the membra~e switch region of the
con~rol panel.
Accordingly~ it i~ an o~ject of ~he present inven-
tion ~o pro~ide an appliance safety arrangem~nt whih cau~e~
the power supply to the appliance to be interrupted in ~h~
event of physical damaye to the control panel of an appli-
ance such as a clothes dryer.
It is a further ob j ec~ of the present inven~ion
to provide ~uch a safety arrangem~nt for an appliance in-
corporating a membrane type switch which particularly re-
sponds to damage absorbed by such membrane switch to dis-
con~inue application of line voltage to the appliance cir-
2 0 cuitry,
S~RY OF THE ~NVENTION
.. . . . .. . ~ .
These and o~her objécts o the present inven~ion,
which will become apparent upon a reading of the following
spe~ification and claims, are achieved by the provision on
the outermos~ circuit layer o~ ~he membrane switch of a con-
ductive trac~ pat~ern which pattern forms a series circuit
loop, which circuit loop form~ a frangible interrupter
circui~. This circuit controls th~ application of line
voltage to the appliance circuitry so that upon the develop-
men~ of a discontinuity in the conductive ~rack pattern,
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as will occur with physical damaye to the membrane switch,
a power shutoff to the appliance is effected to reduce the
resultant hazards which could occur due to such damage to
the appliance control panel.
The conductive track pattern is formed on the
topmost or outermost circuit layer in the membrane switch
to maximize the probability of such continuity interruption
in the event of such damage.
DESCRIPTION OF THE DRAWINGS
FIGURE 1 is a perspective view of a clothes dryer
incorporating a membrane switch mounted on the control panel.
FIGURE 2 is an exploded perspective view of the
major components of the membrane switch illustrating the
conductive pattern forming a part of the present invention
on the outer of the circuit layers.
FIGURE 3 is a block diagrammatic representation
of a safety protection arrangement according to the present
invention.
FIGURE 4 is a circuit diagram of a representaiive
safety interrupter circuit.
DETAILED DESCRIPTION
. _ _
In the following detailed description, certain
specific terminology will be employed for the sake of clarity
and a particular embodiment described in accordance with the
requirements of 36(1) of the Patent Act, but it is to be under-
stood that the same is not intended to he limiting and should
not be so construed inasmuch as the invention is capable of
taking many forms and variations within the scope of the appended
claims.
Referring to the drawings, particularly FIGURE 1,
the safety power interrupter arrangement according to the
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HL-13
present invention will be described in conjunction with
Co h~ r ~ cr~
the use of a clothes dryer 10 of a tvpical _
with a cabinet housing 12, a rotatable drum (not shown~
and other functional components into which clothlng items
may be placed through a frontal acce5s door 14. A control
panel 16 is provided having a front face 18 on which is
visible an array of switching areas 20 which are pressure
sensitive such that an operator may set in various cycle
parameters and can control the cycling of the machine, i.e.,
such as to set in ~he heat levels, etc.
The switching functi,on is carried out by rneans
of a touch panel array of switch preferably of the so-called
memhrane switch type which consists basically of the
components depicted in FIGURE 2. This includes a
top circuit layer 22, an intermediate insulator layer 24,
a bottom circuit layer 26, and an adhesive layer 28, also
provided with release paper for assembly of the membrane
switch to the remaining switch hardware (not shown).
Each of the top circuit layer 22, intermediate
insulator layer 24 and bottom circuit layer 26 may be com-
prised of a suitable dielectric film such as a polyester
film on the order of .005 inch thickness.
The top circuit layer 22 is assembled to be
immediately adjacent the front face 18 of the dryer control
panel 16 with a graphic overlay provided with the various
indicia corresponding to the switching areas 20. The top
circuit layer 22 is provided with conductive switch contacts
30 which are in corresponding locations to the switching
areas 20 on the front face 18.
Also provided are cutouts 32 in order to provide
transmission of light developed by lamps which corresponds
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to the various switch states, i.e., when the switch is
activated, lamps are provided which are illuminated upon
activation of the switch in a manner well known in the
art.
The intermediate insulator layer 24 is provided
with cutouts 34 corresponding to each of the conductive
switch contacts 30 in the top layer 22 and also is provided
with cutouts 36 corresponding to the cutouts 32 in the top
circuit layer 22.
The bottom circuit layer 26 is provided with
conductive switch contacts 38 in corresponding locations to
the conductive switch contacts 30 in the top ~ircuit layer
22 and the switch cutouts 34 on the intermediate insulator
layer 24, and also similarly is provided with window cutouts
40.
The switch conductor circuitry (not shown) is
associated with the undersurface of top circuit layer 22
and the top surface of the bottom circuit layer 26 as
viewed in FIGURRE 2. This is associated with the various
conductive switch contacts 30 and 38 such as to provide
various switching combinations which are read out on pin
conductive tracks (not shown) on the corresponding surfaces
of the projecting portions 42 and 44 of the top circuit
layer 22 and bottom circuit layer 26 in a manner well known
in the art.
Such switching results in various control functions
being activated by means of solid state circuitry of the
type well known in the art. Since all of the details do
not comprise part of the present invention, a description
hereof is not disclosed.
The switching function is basically achieved
by pressure on the switching regions 20 causing the conductive
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switch contacts 30 and 38 to be brought into electrical
contact by a sl.ight distension of the conductive switch
contact 30 of the top circuit layer 22 through the contact
switch cutouts 34 of the insulator and into contact with the
conductive switch contact 38 on the bottom circuit layer 26.
According to the concept of the present invention,
one of the layers, shown here as the top circuit layer 22, is
provided on its upper or outermost surface 46 with a serpentine
conductive track pattern 48 consisting of a thin conductive
strip, which serpentine pattern forms a series circuit between
input and output conductors or tracks 50 and 52, respectively,
contained on the projecting portion 42 of the top circuit
layer 22.
The serpentine conductive track pattern 48 is such
as to substantially cover the entire upper surface of the top
circuit layer 22 and is readily frangible so that significant
physical damage to the top circuit layer 22 on any area
thereof will result in disruption or discontinuity being
developed in the serpentine conductive track pattern 48 so as
to open the series circuit between input and output tracks 50
and 52.
If an electrostatic shield is employed, overlaying
the top circuit layer 22, an insulating la~er must be interposed
to maintain isolation of the loops in the track pattern 48.
48
The series circuit~ is incorpora-ted into the inter-
rupter circuit as indicated in FIGURE 3. Interrupter circuit
54 includes means for interrupting the supply of power from the
external power supper 56 to the appl:iance operat.ing circuitry
58 upon the development of an electrical d.iscontinuity in
conductive track pattern 43 such as may be caused by physical
damage to the control panel 16.
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Such an int~rrupter circuit coulcl be pro~ided by
many methods known to those skilled in the art, as by the
use of relays, etc.
A typical such arrangement is shown in diagrammatic
form in FIGURE 4 and includes the application of input voltage,
either AC or DC, as per the particular design requirements,
across the terminals 56a and 56b which is thereby applied
across the serpentine conductive track pattern 48 and
relay hold-in coil 62 of relay 60. Relay 60 is a normally
closed relay having switching contacts 64 which are open
when relay hold-in coil 62 is energized and closed when coil
62 is de-energized. Contacts 64 are arranged to shunt operating
circuitry 70 through shunt line 76 when closed. Relay 60
is placed in series with the serpentine conductive track pattern
48, in such a manner that the hold-in coil 62 is energized
through the serpentine conductive track pattern 48 as long as
track pattern 48 remains intact. The line voltage from the
external power supply is applied across terminals 66 and 68
and is normally applied to the appliance circuitry 70 via
lines 7~ and 74.
A high amperage fuse 78 is placed in line 72
for serially connecting the external power supply to the
appliance circuitry 70 and relay contacts 6~. Fuse
78 is operative to interrupt the flow of current
2~ therethrough when the current level exceeds its pre-
determlned rated limit. If the switching contact 64
closes due to interruption of the serpentine conductive
track pattern 48, then line or power supp:Ly voltage applied
across terminals Ll and N is shorted through shunt line 76
causing the current through fuse 78 to exceed its ra-ted limit,
whereupon fuse 78 prevents further current flow to the appliance
circuitry thereby effectively disconnecting the operating
circuitry from the power supply.
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9D-HL-136~i9
It will be appreciated by those skilled in the
art ~hat this arrangement is generally referred to as a
"crow~ar" circuit, and this results in the disapplication
of line voltage to the appliance circuitry 70.
Accordingly, it can be seen that this arrange-
ment provides a highly reliable method o~ ~hutting o~f
power to th~ appliance in the e~en~ualities noted to ~hereby
redu~e the hazards associa~ed with ~he application of line
vol~age ~o the applianc~ circui~ry iA ~his situation.
A~ the same ~ime, it can be appreciated that
the arrangem2~t can ~e pxovidea a~ very modes~ co~t such
as to no~ add substantially to the manufacturing cost~ of
appliances incorporating ~his feature.
