U.S. patent number 3,830,991 [Application Number 05/382,138] was granted by the patent office on 1974-08-20 for pressure sensitive mat switch construction.
This patent grant is currently assigned to Essex International Inc.. Invention is credited to Gideon A. Durocher.
United States Patent |
3,830,991 |
Durocher |
August 20, 1974 |
PRESSURE SENSITIVE MAT SWITCH CONSTRUCTION
Abstract
A pressure sensitive switch useful in a mat of the kind adapted
to operate a door in response to a person's stepping on the mat
comprises a switch assembly composed of a pair of sheet-like
electrical conductors between which is interposed a sheet of
resiliently compressible and expansible non-conductive material
such as foamed rubber or plastic having a plurality of openings
therethrough in each of which is accommodated a bridging member
operable to establish a conductive path between the two conductors
when the latter are moved relatively toward one another in response
to the application to the mat of a compressive force. The switch
assembly is enclosed within a non-conductive rubber or plastic
sheath. Conductive wires connected to the two conductors of the
switch assembly extend through the sheath for connection to a
source of energy and to the actuating mechanism for the door to be
operated. Means are provided for limiting the compressive force to
which said bridging member may be subjected.
Inventors: |
Durocher; Gideon A. (Mt.
Clemens, MI) |
Assignee: |
Essex International Inc. (Fort
Wayne, IN)
|
Family
ID: |
23507674 |
Appl.
No.: |
05/382,138 |
Filed: |
July 24, 1973 |
Current U.S.
Class: |
200/86R |
Current CPC
Class: |
H01H
3/141 (20130101); H01H 1/029 (20130101) |
Current International
Class: |
H01H
1/029 (20060101); H01H 3/02 (20060101); H01H
1/02 (20060101); H01H 3/14 (20060101); H01h
013/16 () |
Field of
Search: |
;200/86R,85R
;340/272,278 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Smith, Jr.; David
Attorney, Agent or Firm: Learman & McCulloch
Claims
I claim:
1. A pressure sensitive switch assembly comprising a resilient,
compressible, non-conductive member having an opening therethrough;
electrical conductors spaced apart by said non-conductive member,
the compressibility of said non-conductive member enabling relative
movement of said conductors toward one another; bridging means
accommodated in said opening and operable in response to relative
movement of said conductors toward one another to establish a
conductive path between said conductors; and means for limiting the
compressive force to which said bridging means may be subjected
irrespective of the extent to which said non-conductive member may
be compressed.
2. An assembly according to claim 1 wherein said bridging means
normally is non-conductive and is rendered conductive in response
to compression thereof.
3. An assembly according to claim 1 wherein said bridging means
normally is conductive and has a height less than the spacing
between said conductors when said non-conductive member is in its
uncompressed condition.
4. An assembly according to claim 1 wherein said limiting means
comprises a relatively incompressible member encircling said
bridging member.
5. An assembly according to claim 4 wherein said relatively
incompressible member is interposed between said non-conductive
member and one of said conductors.
6. An assembly according to claim 1 including a non-conductive
sheath enclosing said assembly.
7. An assembly according to claim 6 wherein said sheath is composed
of resilient material.
8. An assembly according to claim 1 including means for connecting
at least one of said conductors to a source of electrical
energy.
9. An assembly according to claim 1 wherein at least one of said
conductors comprises a metallic screen.
10. An assembly according to claim 9 wherein said screen is
adhesively secured to said non-conductive member.
11. An assembly according to claim 1 wherein said bridging member
comprises an elastomer throughout which is dispersed a plurality of
electrically conductive particles.
12. An assembly according to claim 11 wherein the quantity of said
particles is such that a sufficient number thereof are in
engagement to establish a conductive path through said elastomer
without the application of external compressive force to said
elastomer.
13. An assembly according to claim 11 wherein the quantity of said
particles is such that a conductive path may be established through
said elastomer only upon the application of an external compressive
force to said elastomer.
14. A pressure sensitive switch assembly comprising a pair of
spaced apart sheet-like conductors; a sheet-like, non-conductive,
resilient, relatively compressible and expansible member interposed
between said conductors and having a plurality of spaced apart
openings therethrough, the compressibility of said non-conductive
member enabling relative movement of said conductors toward one
another; a bridging member accommodated in each of said openings
and operable in response to relative movement of said conductors
toward one another to establish an electrically conductive path
between said conductors; and relatively incompressible limit means
interposed between said conductors adjacent each of said bridging
members for limiting the extent of movement of said conductors
toward one another and consequently limiting the compressive force
to which said bridging members may be subjected.
15. An assembly according to claim 14 wherein each of said limit
means comprises an annulus encircling a bridging member.
16. An assembly according to claim 15 wherein each of said annuli
is interposed between said non-conductive member and one of said
conductors.
17. An assembly according to claim 14 including a resilient,
non-conductive sheath enclosing said assembly.
Description
The invention disclosed herein relates to a pressure sensitive
switch construction adapted to be incorporated in a mat which, when
stepped upon by a person, will effect operation of mechanism for
opening a normally closed door or the like. Mat switches of the
kind referred to conventionally are located adjacent doors leading
into and out of supermarkets, airports, and other public places so
as to lie in the path of pedestrians approaching such doors. As a
pedestrian approaches such a door he steps upon the mat, thereby
compressing the latter and closing a normally open switch contained
in the mat so as to actuate a mechanism for opening the door
automatically.
Conventional mat switches have many problems associated therewith.
For example, most of the mat switches currently in use employ a
switch mechanism comprising a pair of conductive, metal plates held
in spaced apart relation by a plurality of insulators. When a
compressive force is applied to the upper plate it is deformed to
engage the lower plate, thereby closing a circuit. If the
compressive force is applied directly over one of the insulators,
however, the insulator prevents engagement of the plates. Moreover,
the force required to effect closing of the switch varies in
accordance with the distance from an insulator that the force is
applied. Other problems are created by this construction upon the
installation of a mat switch on an uneven surface, by the
entrapment of stones between the mat and its foundation, and the
bending or warping of one or both of the steel plates.
Additional problems associated with metal plate mat switches of the
kind referred to are those resulting from the sheer weight of the
plates themselves and from the necessity of degreasing and cleaning
the plates. Once the plates have been cleaned, they must be
incorporated rather quickly in the switch assembly so as to prevent
corrosion of the surfaces of the plates with consequent adverse
effects on the electrical integrity of the switch assembly.
An object of this invention is to provide a mat switch construction
which overcomes the disadvantages referred to above of previously
known mat switches.
Another object of the invention is to provide a mat switch
construction which enables operation of the switch at any part of
the mat under a uniform force.
A further object of the invention is to provide a mat switch of the
character described and in which the switch assembly incorporates
means for automatically protecting the switch assembly against
damage due to the application of excessive forces.
Other objects and advantages of the invention will be pointed out
specifically or will become apparent from the following description
when it is considered in conjunction with the appended claims and
the accompanying drawings in which:
Fig. 1 is a plan view of a mat switch constructed in accordance
with the invention with parts being broken away;
FIG. 2 is a sectional view taken on the line 2--2 of FIG. 1 and
illustrating the switch in its open or non-conductive
condition;
FIG. 3 is a view similar to FIG. 2, but illustrating the mat switch
in its conductive condition; and
FIG. 4 is a vertical section view taken on the line 4--4 of FIG. 1
and illustrating the means for connecting the mat switch to a
source of energy and to apparatus to be operated by the switch.
A switch assembly constructed in accordance with the invention
comprises a flat sheet 1 of resiliently compressible and
expansible, non-conductive material such as foamed rubber,
polyurethane, or the like having a plurality of rows of spaced
openings 2 extending therethrough. The openings in each row are
uniformly spaced apart at about 2-inch intervals and adjacent rows
are spaced about one inch apart, with the openings in adjacent rows
staggered. Adhesively secured to the lower surface of the sheet 1
is a plurality of washers 3, each of which has a bore 4. The
washers may be formed of any suitable phenolic or other
non-conductive, rigid, relatively incompressible material. The
washers 3 are so arranged that one washer is associated with one of
the openings 2 and is so oriented with respect to its associated
opening that the opening 2 and the bore 4 are coaxial. The washers
constitute force limiting means as will be explained more fully
hereinafter.
On opposite sides of the non-conductive sheet 1 are flexible,
electrically conductive sheets 5 and 6 which preferably comprise
copper screens. The screen 5 may be adhered to the sheet 1 by an
adhesive 7, if desired. The adhesive 7 preferably is electrically
conductive, of which there are many known kinds, but if the
adhesive 7 is not conductive, then such adhesive will be omitted at
the openings 2. The conductive screen 6 may have applied thereto a
layer of adhesive 8 similar to the adhesive 7. Again, the adhesive
may be electrically conductive or non-conductive. In the latter
case, the adhesive will be omitted at the openings 2.
Accommodated in each opening 2 and in the bore of the companion
washer 3 is a resiliently compressible and expansible switching or
bridging member 9, each of which preferably comprises a cylindrical
module composed of an elastomeric, non-conductive material, such as
silicone rubber, throughout which is dispersed a large quantity of
electrically conductive, preferably spherical particles. Each
bridging member may be electrically conductive in the absence of an
external compressive force or, if desired, each bridging member may
be non-conductive until it is subjected to a compressive force of
predetermined magnitude. In either case, any one of the bridging
members is capable of establishing an electrically conductive path
between the conductive screens 5 and 6.
The initial condition of conductivity of the bridging members 9 is
determined in general by the concentration of the conductive
particles and by the state of the elastomer. If the elastomer resin
contains a relatively large number of particles and is molded under
pressure, the bridging member may be normally conductive. If the
number of particles contained in the resin is less, or if the resin
is molded in the absence of pressure, the bridging member may be
normally non-conductive. In this case, the application of a
compressive force on the bridging member effects relative movement
of the particles so that a sufficient number thereof move into
engagement and establish a conductive path through the elastomer.
Upon removal of the compressive force the elastomer expands,
thereby enabling the engaged particles to move out of engagement
and break the conductive path.
The size of the conductive particles is so selected as to enable
them to accommodate currents up to a predetermined value, and to
decompose or be consumed by the heat of a current in excess of the
predetermined value, thereby enabling each bridging member to
function as a fuse or circuit breaker. Not all of the particles in
a bridging member will be consumed by an overload current, however,
thereby enabling such member to function as a switching member when
it again is subjected to compressive force.
The compressive force to which a given bridging member must be
subjected to render it conductive depends upon several factors,
such as the size and concentration of the particles, the hardness
of the elastomer, and the dimensions of the bridging member. These
factors are described in detail in pending application Ser. No.
857,941 filed Sept. 15, 1969, and to which reference may be had for
a more detailed disclosure. Such factors also may be determined
empirically.
Following assembly of the members 1, 3, 5, 6, and 9 in the manner
illustrated in FIG. 2, the assembly may be enclosed in a molded,
non-conductive sheath 10 composed of two mating halves 11 and 12 of
a resiliently compressible plastisol such as polyvinylchloride. The
two halves of the sheath then may be secured to one another by
ultrasonic welding or the like so as to provide an air- and
moisture-tight enclosure for the switch assembly.
When the switch assembly is enclosed within the sheath 10 the sheet
1 will be compressed adjacent each washer 3, as is shown clearly in
FIG. 2, due to the presence of such washer. The height of each
bridging member 9, however, is less than the spacing between the
conductive screens 5 and 6 so as to preclude any possibility of
establishing a current path between the screens. The relative
diameters of the openings 2, the bore 4, and the members 9 are such
that clearance exists around each member 9 when the latter is in
its normal, uncompressed condition.
Any suitable means may be utilized to connect the conductors 5 and
6 to a source of energy and to apparatus to be operated. FIG. 4
discloses suitable connection means comprising an annular,
resiliently compressible and expansible contact member 13, similar
to the bridging members 9 except for its annular configuration, in
engagement with the conductor 5 and in engagement with a conductive
terminal 14 which extends through the sheath 10 for connection to a
mechanism 15 to be operated electrically. A contact member 16 like
the contact 13 engages the conductor 6 and a terminal 17 which is
adapted for connection to a source of electrical energy. Between
the terminals 14 and 17 is an annular insulator 18. Insulating
grommets 19 and 20 overlie the screens 5 and 6, respectively. A
rivet 21 maintains the grommets in axial alignment so as to subject
the members 13 and 16 to sufficient compressive force to maintain
them conductive. The terminals 14 and 15 are enclosed within an
insulating sheath 22.
To condition a mat switch constructed according to the invention
for operation, the sheath-enclosed switch assembly may be
positioned on a suitable foundation adjacent a door (not shown)
with the terminal 14 connected to the door actuating mechanism 15
and the terminal 17 connected to an energy source. When a person
steps on the upper surface of the sheath 10 a compressive force F
is applied on the upper half 11 of the sheath so as to deform the
latter and effect downward movement of the conductive screen 6
toward the conductive screen 5. Downward movement of the conductor
6 is accompanied by compression of the insulating sheet 1 so as to
enable the conductor 6 to bear against the upper surface of at
least one of the bridging members 9 and axially compress the latter
between the conductors 5 and 6, thereby establishing a conductive
path from the energy source through the conductor 6, through the
bridging member 9, and through the conductor 6 to the mechanism 15.
The larger diameters of the opening 2 and the washer bore 4 enable
the member 9 to be expanded radially as it is compressed axially.
Upon removal of the compressive force F, the resilience of the
sheet 1 and the bridging members will restore the parts to the
positions shown in FIG. 2.
A switch assembly adapted to be actuated by pedestrians must be
capable of functioning under greatly varying forces. For example,
such a switch should be operable by the weight of a child, as well
as by the weight of a much heavier adult. Further, such a switch
must be capable of accommodating an extermely high concentration of
force, such as that imposed by the relatively small area of a
woman's shoe heel. A switch assembly according to the invention is
capable of functioning under the greatly differing load factors
referred to inasmuch as the sheath 10, the member 7, and the
bridging members 9 are all resiliently compressible and the
conductors 5 and 6 are flexible.
The switch assembly can withstand greatly excessive compressive
forces inasmuch as the washers 3 protect the bridging members 9
against excessive compression due to the incompressibility of the
washers themselves. Thus, when the switch assembly is in the
condition shown in FIG. 3, an increase in the force F does not
cause a corresponding increase in the compressive force applied to
the adjacent bridging member 9 inasmuch as the latter cannot be
compressed to a thickness less than that of the force limiting
washer 3. The bridging members, therefore, are protected by the
washers against destruction or deterioration due to excessive
compression, irrespective of the force applied on the switch
assembly.
The disclosed embodiment is representative of a presently preferred
form of the invention, but is intended to be illustrative rather
than definitive thereof. The invention is defined in the
claims.
* * * * *