Note: Descriptions are shown in the official language in which they were submitted.
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Description.
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STRAIN RELIEF DEVICE AND METHOD OF USE ~ ~
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Technical Field
The present invention relates to devices for relieving the strain on
an electrical wire cable.
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10 ~ackgroundofthelnvent~n
Wire cables are often used to connect electrical equipment
together. A power cord is a common electrical wire cable providing electrical
power to a housing for an electrical device. A data cable connecting a pointing
device to a computer is another example of a wire cable.
All electrical wire cables, whether they carry electrical power or
data signals, should have some form of strain ~relief to prevent the wire cable
from breaking or tearing loose from the housing to which it is attached. As
~i~ shown in Figure 1, prior art strain relief devices 2 generally secure a wire
cable 4 at a point of entry 6 into a housing 8. The wire cable 4 is solidly secured
20 at a point of entry. The sheathing enclosing the wire conductors is typically bonded to the strain relief 2.
The drawback to this approach is that when a pulling force is
applied to the wire cable 4, the sheathing will not move because it is bonded tothe strain relief 2. However, the wire conductors inside the wire cable 4 stretch
~; 25 at a different rate than the sheathing, and tend to move when the pulling force is
applied to the wire cable 4.
Therefore it can be appreciated that there is a significant need for a
strain relief device that will secure a wire cable without causing it to break if a
pulling force is applied.
: Surnmary of the lnvention
The invention is embodied in a strain relief device for a wire cable
eomprising a housing into which the wire cable is routed. The wire cable enters
the housing through an nperture size to permit the entry of the wire cable. First
i- 35 and second posts secured within the housing are spaced such that the wire cable
passes on one side of the first post and loops around the second post so that the
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wire cable presses against itself in an area near the first post. When strain isapplied to the wire cable, the wire cable cinches itself around the posts.
In one embodiment the posts contain vertical ridges in the area
where the wire cable contacts the posts. The ridges prevent slippage of the wire5 cable. A guide tunnel may be used to guide the wire cable into the aperture. Apair of guide posts may be used to route the wire cable from the first and second
posts to circuitry within the housing.
Brief Description of the l)rawings
Figure 1 is a prior art device used to relieve strain on a wire cable.
Figure 2 is a bottom plan view of a computer pointing device
housing in which a strain relief device of the present invention is mounted.
Figure 3 is a top plan view of a housing bottom cover for the
housing of Figure 2 with the bottom cover removed from the housing to show the
15 inventive strain relief device.
Figure 4 is a perspective view of the bottom cover of the housing
of Figure 2 showing the inventive strain relief from one side.
Figure 5 is a perspective view of the bottorn cover of the housing
of Figure 2 showing the inventive strain relief from another side.
[2etailed Description of the Invention
As shown in Figures2 and 3 for purposes of illustration, the
present invention embodied in a strain relief device 18 mounted within a
housing 20 for relieving strain on a wire cable 22. The inventive device prevents
25 the wire cable 22 from breaking if a pulling force is applied to the wire cable.
As shown in Figure 2, a wire cable 22 is attached to the housing 20
which contains therewithin the device 18. The wire cable 22 enters the
housing 20 through an aperture 24 in a bottom housing cover 23 sized to permit
free passage of the wire cable. The size of the aperture 24 is such that the
30 aperture itself does not provide strain relief.
As shown in Figure3, the devicel8 includes first and second
posts 26 and 28, respectively, positioned within the housing and securely
fastened to an inward side of the bottom housing 20. The posts 26 and 28 are
integrally formed with and rigidly attached to the bottom housing cover 23 which~` 35 is made of a plastic material. The posts 26 and 28 may alternatively be attached
to the housing 20 by adhesives, screws or other well known fastening means.
Alternatively, the posts 26 and 28 could be mounted on an intermediate platform,, ,~
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such as a printed circuit board, which in turn is securely fastened to the
housing 20. The present invention is not limited by the manner in which the
posts 26 and 28 are secured within the housing 20.
The posts 26 and28 each have a retainer member32 that is
S attached to the top of the post and projects outward beyond the posts to define a
lip extending partially about the post. As will be described in more detail below,
the wire cable22 is wrapped about the posts 26 and 28. The member32
prevents the wire cable 22 from slipping upward oE the posts 26 and 28. In the
presently preferred embodiment, the retainer member 32 only projects outward
10 from the posts 26 and 28 on their one side to perrnit the wire cable 22 to be more
easily installed around the posts 26 and 28. As shown in Figure 4, posts 26
and 28 have a height, indicated by the reference numeral 30, which is greater
than the diameter of the wire cable 22. Alternatively, the height 30 could be
slightly less than the diameter of the wire cable 22 to provide a snug fit and help
15 retain the wire cable 22 in position around the posts 26 and 28. If the wire
cable 22 is a flat cable, the flat side of the wire cable fits under the retainer
member32 and Elat againstthe posts 26 and28. Accordingto the principles of
the present invention, the overall size of the strain relief 18 is approximately the
size of the wire cable 22. The strain relief 18 may be used in situations where
20 space is limited and there is a need for a iow profile strain relief.
The posts 26 and 28 are positioned apart within the housing 20 so -
that there is sufficient space between the posts for the wire cable 22 to pass
therebetween. The wire cable22 has a free end34 which is connectable to
electronic circuitry (not shown) within the housing20. The wire cable 22,
25 starting from its free end 34, follows a path passing by (and in contact with a first
side 26a of the first post 26. The path of the wire cable 22 then loops around the
second post 28 so that the wire cable passes back on itself to form a loop with the
wire cable contacting itself at a position 36 adjacent to the first side 26a of the
first post 26. The wire cable 22 then passes straight from the second post 28 to30 and through the aperture 24 to the exterior of the housing 20. A cable tunnel 38
in the bottom housing cover 23 guides the wire cable 22 through the aperture 24.The first and second posts 26 and 28 are positioned relative to the aperture 24 so
that the wire cable22 will have a straight lengthwise portion22a extending
between the second post and the aperture and a bent lengthwise portion 22b bent
35 toward the straight portion as a result of it passing around the first side 26a of the
, first post. The first side26a of the first post 26 faces toward the straight
~I portion 22a of the wire cable 22. As strain is applied to the wire cable 22 by
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applying a pulling force on the portion of the wire cable exterior of the
housing 2~, the first post 26 is positioned close enough to the straight portion 22a
of the wire cable22 that the straight portion will press against the bent
portion 22b of the wire cable at the position area 36, and press the bent portion of
S the wire cable against the first side 26a of the first post 26, with a cinching force.
Thereby, a self-tightening strain relief is provided. The greater the pulling force
applied to the wire cable 22, the greater the cinching force that results. The wire
cable 22 is strain relieved in a manner that does not require the wire cable to be
solidly secured at the aperture where the wire cable enters the housing 20 as is10 typically done in the prior art such as shown in Figure 1.
The first post 26 is generally circular in cross-sectional shape, with
its retainer member 32 projecting outward on the side of the first side 26a where
the wire cable 22 contacts the first post 26 and extends over the wire cable to
hold it in place. ~Iternatively, the retainer member 32 of the first post 26 could
15 circumferentially fully about the first post 26. As best shown in ~igure 4, the
first post 26 has a plurality of ridges 40 on its first side 26a under its retainer
member 32 to help prevent slippage of the wire cable 22 relative to the first post.
The first side 26a of the first post 26 has an arcuate surface when viewed in
perpendicular cross section. The ridges 40 are axially oriented with respect to
20 the first post 26 so that the wire cable 22 extends substantially perpendicular to
the ridges. As the pulling force is applied to the portion of the wire cable 22
exterior of the housing20, the straight portion22a presses against the bent
portion 22b which, in turn, is pressed against the vertical ridges 40 to inhibitslippage. The greater the pulling force, the more the bent portion 22b is pressed
25 against the vertical ridges. Alternatively, the ridges 40 could be replaced by
teeth-like protrusions to inhibit slippage.
The second post 28 has a first side 28a with an arcuate surface in
cross section as seen in Figure S. The retainer member 32 for the second post 28projects outward on the side of the first side 28a where the wire cable 22 contacts
30 the second post and extends over the wire cable to holcl it in place. As with the
first post 26, the retainer member 32 of the second post 28 could extend
circumferentially fully about the second post 28. The second post 28 also has a
pair of generally flat second and third sides 28b and 28c, respectively, oriented
with respect to each other to ~orm a "V" shape. The thircl side 28c of the second
35 post 28 is oriented with its flat s~lrface in alignment with a side of the aperture 24
and the cable tunnel 38 so that the straight portion 22a of the wire cable 22
passes in a generally straight line path between the first sicle 28a of the second
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post and the aperture. The second side 28b of the second post 28 is angled to
permit the wire cable 22 to bend more sharply around the second post 28 as it
passes between the first post 26 and around the ~Irst side 28a of the second
post 28. In addition, the V shape provides greater strength to inhibit breaking the
5 post 28 when a pulling force is applied to the wire cable 22. The second post 28
also has a plurality of vertical ridges 40 on its first side 28a under its retainer
member 32 to prevent slippage of the wire cable 22 by the second post.
First and second guide posts44 and 46, respectively, are also
integrally formed with housing cover 23. The guide posts 44 and 46 serve to
10 guide the wire cable22 as it passes from the first post2~ to the electronic
circuitry (not shown) to which the free end 34 of the wire cable is connected
within the housing 20. The first guide post 44 is located near one side of the
cable tunnel 38 and positioned to define the path of the bent portion 22b so that it
bends about the first surface 26a of the ~Irst post 26 in a direction away from the
15 straight portion 22a. The second guide post 46 is spaced apart from the firstguide post 44 at a distance to permit the wire cable 22 to pass therebetween.
It is noted that the first and second posts 26 and 28, and the first
and second guide posts 44 and 46, may have shapes other than illustrated and
described. Preferably, the first and second posts 26 and 28 have a shaped that
20 minimizes sharp corners where the posts contact the wire cable 22 to avoid
cutting the wire cable. The invention may also be practiced with more than the
first and second posts 26 and 28 to provide a cinching force on the wire cable 22.
~ For example, three posts may be spaced apart to accomplish the same purpose.
-;~ ~ ~ Also, the guide posts 44 and 46 could be eliminated.
-~ 25 With the present invention, the wire cable 22 is securely fastened
to the housing 20 in a manner that inhibits breakage of the wire cable at the point
of retention by the housing as is common in the prior art. The inventive strain
relief device 18 may be manufactured, and may be sized for different types and
~ sizes of wire cables.
l ! 30 1 It is to be understood that even though a specific embodiment of
the present invention has been set forth in the foregoing description, the abovedisclosure is illustrative only, and changes may be made in detail, yet remain
within the broad principles of the invention. Therefore, the present invention is
to be limited only by the appended claims,
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