U.S. patent number 3,857,397 [Application Number 05/309,867] was granted by the patent office on 1974-12-31 for electrically conductive wrist strap.
This patent grant is currently assigned to Custom Materials, Inc.. Invention is credited to Alfred J. Brosseau.
United States Patent |
3,857,397 |
Brosseau |
December 31, 1974 |
ELECTRICALLY CONDUCTIVE WRIST STRAP
Abstract
An electrically conductive wrist strap comprises a strip of
conductive plastic material having an opening spaced from one end,
outwardly of which is a pad of Velcro hooks. Intermediate its ends,
there is a pad of Velcro loops of conductive material. The other
end of the strap passes through the opening to form an adjustable
loop, and a conductive terminal is carried by the other end for
connection with a grounding conductor having a cooperating fastener
at one end and a bull-dog clamp at the opposite end. The strap has
a breaking strength permitting it to be broken by a strong pull, as
in an emergency. A laminated electrically conductive material of
predetermined tensile strength comprising an intermediate layer of
Nylon scrim between and bonded to two outer layers of conductive
polyolefin.
Inventors: |
Brosseau; Alfred J. (Natick,
MA) |
Assignee: |
Custom Materials, Inc.
(Chelmsford, MA)
|
Family
ID: |
23200017 |
Appl.
No.: |
05/309,867 |
Filed: |
November 27, 1972 |
Current U.S.
Class: |
607/149; 174/5SB;
361/220; 128/DIG.15; 428/100 |
Current CPC
Class: |
A61N
1/14 (20130101); A61N 1/04 (20130101); Y10S
128/15 (20130101); Y10T 428/24017 (20150115) |
Current International
Class: |
A61N
1/04 (20060101); A61N 1/14 (20060101); A61N
1/00 (20060101); A61n 001/04 () |
Field of
Search: |
;128/384,379,402,404,410-411,416,418,303.1,82.1,172.1,362,DIG.15
;174/5SB,36,117FF ;317/2B ;2/162,120,311-312,318,321
;24/26A,22,17AP,DIG.118,265WS,265AL |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Gaudet; Richard A.
Assistant Examiner: Cohen; Lee S.
Attorney, Agent or Firm: Lavine; Irvin A.
Claims
I claim:
1. An electrically conductive wrist strap comprising:
a. an electrically conductive flexible strip having first and
second ends,
b. means comprising an opening in said strip spaced from and
adjacent to the first end for permitting passage therethrough of
the second end of said strip;
c. first cooperating fastening means on said strip between said
opening and said first end and second cooperating fastening means
on said strip between said opening and said second end for
adjustably fastening an intermediate portion of said strip to said
strip at the first end thereof, and
d. conductive terminal means on said strip, whereby a person
wearing said strap may be connected to ground.
2. The electrically conductive wrist strap of claim 1, said
cooperating fastening means each comprising a sheet of Velcro-type
material.
3. The electrically conductive wrist strap of claim 2, wherein only
one of said sheets of Velcro-type material is electrically
conductive.
4. The electrically conductive wrist strap of claim 3, wherein a
said Velcro-type sheet containing loop elements is electrically
conductive.
5. The electrically conductive wrist strap of claim 2, wherein said
second sheet is of greater length along said strip than said first
sheet.
6. The electrically conductive wrist strap of claim 1, wherein only
one of said adjustable fastening means is electrically
conductive.
7. The electrically conductive wrist strap of claim 1, said strip
comprising means having a breaking strength permitting breaking of
said strap by manual force.
8. The electrically conductive wrist strap of claim 7, said strip
having a tensile strength between about 4,000 and 5,000 pounds per
square inch and a cross-sectional area of about 0.0084 square
inches.
9. The structure of claim 1, and further comprising a linearly
extending conductor having structure engaging means at one end and
means at the other end engaging said terminal.
10. The structure of claim 9, said last mentioned means comprising
means releasably and rotatably engaging said terminal.
11. The electrically conductive wrist strap of claim 1, wherein
said strip is a laminated material comprising an intermediate layer
of scrim between two outer layers of conductive polyolefin
material, said layers being in adjacent bonded relationship.
12. The electrically conductive wrist strap of claim 11, said
intermediate layer being nylon scrim.
Description
BACKGROUND OF THE INVENTION
The present invention relates to an electrically conductive strap
to be worn on the body, for grounding a human body to prevent the
build up of static electricity.
It has been recognized that in a number of occupations, it is
highly desirable to connect the workmen to ground. One such
occupation in particular is the assembly of or working on devices
which are sensitive to static electricity charges, and in such
operations, the assembly workers must be electrically connected to
earth, i.e., grounded, so that static electricity charges which may
be built up by movement of the workmen, such as hand movements, are
quickly discharged through the electrical connection to earth or
ground. This is necessary in order that there be no build up of
static electricity charges on the workmen which could be
transferred to the products being worked upon, to their detriment.
Further, electrically conductive body-worn grounding devices have
proven useful in other occupations, such as where there is danger
where the workman is in an electrostatic field, or in an explosive
atmosphere.
A number of prior art devices are known which are intended to be
placed upon one part or another of a workman, and which are
electrically connected to earth or ground in order to drain off
electrostatic charges. One such device, commonly used where workmen
are assembling devices which are sensitive to static electricity
charges comprises a wrist strap made of electrically conductive
plastic material having secured to it at one end a strip of Velcro
hook material facing in one direction, and at the other end a strip
of Velcro loop material facing in the opposite direction. A
terminal clip is provided of spring construction for engaging a pin
which is at one end of a linearly extending conductor, the other
end of the conductor having a suitable connector such as a
releasable clamp for engaging a structure connected to earth or
ground; this may be, for example, a water pipe.
While the prior art wrist strap above described was entirely
suitable for conducting charges of static electricity from the body
of an assembly worker, it suffered from certain deficiencies. One
deficiency was the inconvenience of the device, since one wrist had
to be placed on the strap, and the other hand used to bring the two
Velcro strips into engagement, so as to secure the strap about the
wrist. The Velcro strips being of conducting material, could
generate a spark discharged between them when being separated to
remove the strap, and this is an undesirable characteristic.
Further, should an emergency arise requiring the worker to leave
the work station without delay, an impediment was provided to such
action in that the strap was securely engaged about the wrist of
the worker and was connected to a structure connected to earth or
ground, thus inhibiting the rapid departure of the worker from the
work station.
In another prior art device of this type, there is provided a coil
spring having its ends secured to an insulator block, with a cord
threaded through the coil spring. Thus, an endless loop or band was
provided which was expanded to be passed over, for example, the
foot of a worker, thereafter resting upon the ankle of the worker.
While this construction was convenient to put on, if the coil
spring was made sufficiently strong to provide good engagement with
the skin at the ankle of the workman, it would tend to grip so
strongly so as to be uncomfortable, due to the fact that there was
at each point of engagement of the wire coil with the skin a very
small area of contact, so that the workman could be somewhat
discomforted. If the coil spring was not as strong, then there
would be less contact and therefore less effective conducting of
electricity. Further, since the sizes of various workmen vary
significantly, the noted construction, in order to be comfortable,
would likely be provided in different sizes, so as to provide a
reasonable degree of comfort.
Another suggestion was the provision of a structure similar to a
bicycle clip, being a metallic band of spring material, such as
spring steel, open at one end and of generally circular formation,
so as to be placed upon the leg of a wearer by spreading apart the
ends of the clip. This construction suffers from many of the same
defects noted above in connection with the device made of a coil
spring.
Yet another construction known in the prior art was in the form of
a conventional garter, made electrically conductive, and fastened
by conventional hook members. This construction, like those noted
above, could not readily be disconnected in an emergency, so that a
rapid departure from a work-site would be prevented or inhibited,
and like the first-mentioned prior art, was not convenient to put
on because of the necessity for fastening the hook members placed
at either end of the garter-like device.
Among the objects of the present invention are to provide a body
encircling strap, such as a wrist strap, which is electrically
conductive and convenient to put on. Another object of the present
invention is the provision of an electrically conductive wrist
strap which is conveniently formed, and which is adjustable in
size. A further object of the present invention is to provide an
electrically conductive wrist strap which will remain in loop form,
and which can be worn with effective electrical contact and with
comfort by workmen of various sizes.
A further object of the present invention is to provide an
electrically conductive wrist strap which will not inhibit the
rapid departure from the work-site of a workman, as in an
emergency. A further object of the present invention is the
provision of an electrically conductive wrist strap having a
breaking strength permitting it to be broken in an emergency by
manual strength, while at the same time being sturdy enough for
conventional usage over an extended period of time.
Yet another object of the present invention is to provide an
electrically conductive wrist strap which is convenient, adjustable
in size, and which is not subject to discharging a spark when
fastener elements of this strap are separated.
SUMMARY OF THE INVENTION
The electrically conductive wrist strap comprises a strip of
electrically conductive material of a length in excess of the
normal circumference of a human wrist, or ankle. An opening is
provided in the conductive strip adjacent to but spaced from one
end thereof, the opening being sufficiently large to permit passage
of the opposite end of the strip through it, and the strip is
further provided with two cooperating sheets of Velcro material.
One sheet is adjacent the opening, between the opening and the
adjacent end of the conductive strip, so that it thereby not only
serves as a fastening element, but also strengthens the end of the
conductive strip. At an intermediate portion of the strip, there is
a second Velcro sheet, the first Velcro sheet preferably having
hooks and the second mentioned sheet having loops, and only one of
the Velcro sheets is conductive. When the strap is in the flat
condition, before passage of one end through the opening, both of
the Velcro sheets are on the same side. At its opposite end, the
electrically conductive strip forming the wrist strap is provided
with a conductive terminal, preferably in the form of a snap
fastener, and a conductor is provided having a cooperating snap
fastener portion, so that it may be connected to the strap in a
releasable manner, and yet there is flexibility of the connection
between the conductor and the wrist strap, the construction thereby
providing for both electrical conductivity and flexibility of the
fastening. At its opposite end, the conductor is provided with a
connector device, preferably in the form of a spring-urged clamp,
for connection to a structure which is in turn connected to earth
or ground, such as a pipe or the like. The conductive strip of
which the strap is made has a breaking strength yieldable to a
strong or sudden force within the strength range of even the
weakest workers, so that in an emergency the strap may be broken,
the workman not being required to disengage connections or the
like. The electrically conductive strip is made of a laminated
material having outer layers of electrically conductive olefin, and
an inner layer of nylon scrim. There is also disclosed a sheet
material having an intermediate layer of nylon scrim and outer
layers of electrically conductive olefin, the three layers being
bonded together.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a perspective view of a wrist strap and conductor in
position on a wrist.
FIG. 2 is an exploded, elevational view, with parts broken away, of
the wrist strap of the present invention and conductor.
FIG. 3 is plan view of the wrist strap shown in FIG. 2, with parts
broken away.
FIG. 4 is an enlarged perspective view of the wrist strap, in
endless band or loop form.
FIG. 5 is an exploded perspective view showing the laminated
construction of the material of which the wrist strap is made.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings, wherein like or corresponding parts
are designated by like or corresponding reference numerals
throughout the several views, there is shown in FIG. 1 a portion of
a human arm, including the wrist W and the hand H. Encircling the
wrist W is an electrically conductive wrist strap 10 in accordance
with the present invention, having a linearly extending conductor
50 connected to it. As will be understood, the conductor 50 is of
convenient linear extent, and in practice this is preferably about
4 feet.
Referring now to FIGS. 2 and 3, the wrist strap 10 comprises an
electrically conductive strip 12 having ends 14 and 16. Adjacent to
and spaced from the end 14 is an opening 18 which is of adequate
size so as to readily receive therethrough the end 16. Preferably,
the conductive strip 12 is of a relatively large width from the end
14, past the location of the opening 18, and to a necked down
portion 20, and from the portion 20 to end 16, the strip 12 is
relatively narrow. Hence, the end 16 is narrow in comparison to the
end 14.
Two sheets of Velcro material are provided for adjustable fastening
of the wrist strip 10. A first sheet 22 is adhered to the
conductive strip 12, on the bottom face thereof as shown in FIG. 2,
and has a large number of hook elements 24 of flexible resilient
material projecting therefrom. A second sheet 26 is secured to the
same face of the conductive strip 12, having a substantial linear
extent as shown in FIGS. 2 and 3, which is greater than the linear
extent of the sheet 22, and has a large number of loop elements 28
of flexible resilient material projecting therefrom. As will be
understood, when placed in face-to-face relationship, the two
sheets 22 and 26 cooperate by action of the hooks 24 interlocking
with the loops 28, the hooks 24 hooking into some of the loops 28,
so as to bind the sheets 22 and 26 securely together. A pulling
action separating the sheets 22 and 26 will effect the release of
this engagement.
The sheet 26 and loop elements 28 are conductive, and are in
electrically conducting relationship to the strip 12, while the
sheet 22 and hook elements 24 are non-conductive. As will be
understood, the sheet 26 and loop elements 28 may be made
non-conductive, and the sheet 22 and hook elements 24 may be made
conductive.
Adjacent the end 16 of conductive strip 12 is a terminal 30,
preferably in the form of a post-element of a snap fastener,
secured to the strip 12, terminal 30 being electrically conductive,
and electrically connected to strip 12.
The conductor 50 is provided adjacent one end 52 with a
female-element 54, of a size to cooperate in conventional
snap-fastener manner with the terminal 30, so as to provide for
connection of the conductor 50 with the wrist strap 10. This
connection is electrically conductive, is releasable, and provides
for rotational movement of the conductor 50 relative to the wrist
strap 10. At its opposite end, the conductor 50 is provided with a
spring-urged clamp 56 having jaws 58 and 60, the clamp 56 being
partially within a flexible shroud 62 of suitable material. Hence,
by grasping the shroud between the thumb and finger, the jaws 58
and 60 of the clamp 56 may be opened, against the force of the
spring therein (not shown) and caused to engage a structure
connected to earth or ground, such as a water pipe or the like. The
conductor 50 may be made of the same material as the strip 10,
having a suitable width.
The conductive strip 12 is made of a material, and has dimensions,
which together provide it with a breaking strength which will
permit to be broken by manual force, so that in an emergency, a
workman wearing the wrist strap 10, having the conductor 50 secured
to it, will be able to leave the work area rapidly and without
hindrance, by moving his arm with sufficient force so as to break
the strip 12, even if the other hand of the workman cannot be used
for disconnecting clamp 56, or for separating the conductor 50 from
the wrist strap 10, or for manipulating the strap so as to separate
the Velcro sheets. This is achieved by providing the conductive
strip, in the preferred embodiment, with a tensile strength of
between 4,000 and 5,000 pounds per square inch, and a
cross-sectional area at the smallest dimension of the conductive
strip 12 of about 0.0084 square inches, the strap being 0.015
inches thick and 0.526 inches wide, in practice.
Referring now to FIG. 5, there is shown in exploded perspective a
sheet 70 of the material from which the strip 12, and also the
conductor 50, is made. There are provided two outer layers 72 and
74 of conductive polyolefin film, having a thickness of 0.006
inches each. An intermediate layer 76 is of nylon scrim, and has a
thickness of 0.005 inches. These layers are pressed together in
known fashion, so that they become bonded and form a unitary sheet
of material, which then may be cut into strips of the desired sizes
and configurations. This material can therefore be closely
controlled as to its width and thickness dimensions, therefore the
above noted cross-sectional area of the smallest part of the wrist
strap conductive strip 12 can be obtained, with consequent
obtaining of the desired tensile strength of the material and
breaking the strength of the completed wrist strap.
In use, and referring to FIG. 4, there is shown the wrist strap 10,
with the end 16 of the conductive strip 12 having been passed
through the opening 18, with the Velcro sheet 26 in facing
relationship to the Velcro sheet 22, and ready to be placed in
face-to-face contact for securement of the wrist strap 10 about the
wrist of a person. The wrist strap 10 can remain, over many uses of
it, in the convenient loop form shown in FIG. 4. To place the wrist
strap 10 upon the wrist, the person simply passes his hand through
the loop formed by the wrist strap 10, and grasps the conductive
strip 12, as between the end 16 and the Velcro sheet 26, drawing
the wrist strap 10 into snug but comfortable engagement with his
wrist, and then moving the free hand so as to place the Velcro
sheets in face-to-face cooperative, interlocking engagement. Due to
the positioning of the sheet 22, with its edge adjacent the opening
18, the sheet 22 will serve as a bearing for the intermediate
portion of the conductive strip 12 inwardly of the end 16 to slide
it over, and the sheet 22 will also provide stiffness for the
portion of the conductive strip 12 inwardly of the end 14. Due to
the linear extent of the sheet 26, it is not necessary to provide
different sizes of the wrist strap 10 for individuals of different
sizes since the length of the sheet 26 will permit engagement of
the wrist strap 10 in secure, comfortable fashion about the wrists
of both large and small workmen.
As will be understood, due to the above reference breaking strength
of the wrist strap 10, in an emergency, it may be broken as
hereinabove mentioned, so as to permit the rapid departure of the
workman from the work station. The conductor 50 while being in
secure, electrically conductive relationship to a structure
connected to earth or ground, provides for flexibility between the
conductor 50 and wrist strap 10 by the snap fastener arrangement
including the elements 30 and 54, thereby providing for
satisfactory maneuverability of the hand of the workman wearing the
wrist strap 10. When the wrist strap 10 is to be removed, it is
only necessary to separate the Velcro sheets 22 and 26 in normal
manner, as by "peeling" action, and due to the fact that one of the
Velcro sheets is conductive and the other is non-conductive, there
will be no danger of a spark discharge during or immediately after
this separation of the Velcro sheets.
The material 70 will be understood to have good conductive
properties, together with not only desirable strength
characteristics, but strength characteristics which can be
predetermined to lie within desired limits.
There has been provided an electrically conductive wrist strap
which is extremely convenient to use, which can be used with
safety, and which can be used by workmen of different sizes. The
wrist strap may be connected and disconnected without danger of
spark discharge from the fastening elements used, specifically
Velcro sheets, and the construction of the wrist strap is
sufficiently sturdy for normal use, while permitting breaking of
the wrist strap when desired, as during an emergency.
There has also been provided a material having controllable tensile
strength properties, while being electrically conductive, and
economical to manufacture.
It will be obvious to those skilled in the art that various changes
may be made without departing from the spirit of the invention and
therefore the invention is not limited to what is shown in the
drawings and described in the specification but only as indicated
in the appended claims.
* * * * *