Fire escape – ladder – or scaffold – Single stile – strand or pole – Flexible
Reexamination Certificate
2002-02-07
2004-03-30
Chin-Shue, Alvin (Department: 3634)
Fire escape, ladder, or scaffold
Single stile, strand or pole
Flexible
C182S005000
Reexamination Certificate
active
06712181
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a safety device which is carried by a lifeline or tether line and which will hold fast when weighted, but which is slidable along the lifeline or tether line when unweighted.
BACKGROUND OF THE INVENTION
FIG. 1
illustrates a form of Prusik knot
10
, also known as a triple sliding hitch or “monkey fist.” Such a knot can be used in fall arrest safety systems which include a lifeline or tether line
12
having one end portion
14
adapted for connection to an anchoring device. For example, one end of the lifeline
12
can be formed with a sturdy eye
16
for receiving a carabiner
18
which, in turn, is secured to the eye of a roof anchor. The lifeline hangs from the anchor. The Prusik knot, when unweighted, can be slid along the lifeline as desired. A termination knot
20
can be provided to limit the extent of sliding movement of the Prusik knot along the lifeline.
In general, the Prusik knot can be formed of a single stretch of rope having several wraps
22
around the lifeline
12
. The free end portions
24
of the rope are tucked through the longitudinally extending portion of a loop
26
. In the embodiment illustrated in
FIG. 1
, the free ends of the rope are threaded through rings
28
of a thimble
30
which forms a central eye
32
, and then are hand tied to form the end knot
33
. A carabiner
34
is carried in the eye
32
and can be connected by a lanyard to a worker's harness. In normal use, with little or no weight applied to the eye portion of the Prusik knot, the wraps
22
can be slid along the lifeline to a desired position. If substantial weight is applied to the eye, such as by way of the carabiner
34
, the knot holds fast on the lifeline.
There are a myriad of regulations and specifications for fall arrest safety equipment. For the design shown in
FIG. 1
, the Prusik knot should contain at least six wraps
22
. However, sometimes the knot will be unfastened by sliding the thimble
30
and rope ends
24
through the loop
26
, resulting in fewer wraps
22
on the lifeline
12
. The entire knot can be unfastened in this manner. Also, there can be concerns with respect to the type of connection from a user's harness and/or lanyard to the eye
32
. It is generally preferred that a large loop carabiner
34
be used, but sometimes a snap hook having a smaller opening will be connected to the thimble. In that case, a twisting force of the snap hook in the thimble eye may disengage the hook by damaging the swinging clasp of the snap hook. Also, in the construction of
FIG. 1
, some protection is formed for the inside portion of the rope loop around the thimble, but the exterior portion is exposed and may become frayed. Further, in fall arrest systems it is desirable for an integral component such as a the Prusik knot to be replaced if it has been subjected to the substantial force of a fall, but whether or not the knot has been subjected to such a force is not immediately ascertainable. Finally, it is possible for the hand tied knot
33
to become loosened over time, requiring frequent and careful inspection if the safety system utilizing the knot is to be reliable.
SUMMARY OF THE INVENTION
The present invention provides an improved rope grab device operating on the principles of a Prusik knot. In a preferred embodiment, a casing or cover is provided for the free end portions of the stretch of rope forming the knot. The cover can be formed of complimentary halves defining an internal cavity receiving the free end portions of the knot. One free end portion is much longer than the other and is looped in an internal channel to form a bight. This end portion can be secured to the other end portion, such as by a swage. The cover can completely encase the end portions of the knot so that they are not subjected to cutting or fraying, and can assist in reliably securing the free end portions of the knot without hand tying. In other aspects of the invention, the cover permits convenient and reliable interconnection with other components without compatibility problems such as can occur with certain snap hooks. The cover can be formed to provide a reliable indication of a strong force having been exerted on the safety device, and to lessen the likelihood of the knot unraveling.
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International Search Report dated May 29, 2002, Application No. PCT/US02/03563, filed Feb. 7, 2002 ( Applicant: Steve Nichols).
Chin-Shue Alvin
Christensen O'Connor Johnson & Kindness PLLC
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