Note: Descriptions are shown in the official language in which they were submitted.
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SAFETY DEVICE FOR LADDER CL:[M~ERS
BACKGROUND OF THE INVENTI()N
Safety clamp devices adapted to be attached to a work-
man's belt and having a friction plate or shoe which is moved
into gripping engagement with a safety line if the workman falls
have been known and in use for many years. See, for example,
U.S. Patent No. 3,317,971 issued to R. E. Meyer on May 9, 1967
and U.S. Patent No. 3,492~702 issued to L. R. Staord on
February 3, 1970. Such prior safety clamps have had a number of
disadvantages and shortcomings. A primary problem has been the
ina~ility of prior safety clamps to satisfactorily meet the dual
requirements of being freely slidable on a saety cable as a
workman goes up and down a ladder, and yet quickly and positive-
ly shiftable into clamping engagement with a safety line or
cable when the workman falls. Moreover, known safety clamps
have not been readily mountable on a safety cable at various
vertical positions of desired use.
The safety clamp of this invention incorporates a
combination of features which overcome the a~oresaid difficul-
ties encountered with previously known safety clamps. Foremost
among such features are a camming system which instantly urges a
wedge plate through a cable clearance space into uniform engage-
ment with a safety cable over the entire length of the wedge
plate under free fall conditions, and the mounting and actuation
of the wedge plate so as to permit the friction force of a
safety cable acting on it to draw it into very tight, gripping
engagement with the cable.
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B~IEF SUMMARY OF THE IN~NTION
The safety clamp of this invention is particularly
characterized by a wedge pla-~e and actuating arm assembly
mounted on a clamping bracket so as to provide ~ree, unimpaired
sliding movement of the clamping device along a safety cable or
rod during normal vertical movement of a workman on a ladder,
and to ensure the instantaneous, positive gripping of a safety
cable between the wedge plate and an elongated clamping surface
on the clamping bracket if the workman falls, without unduly
damaging the safety cable.
These basic objects and advantages have been realized
by shiftably supporting an elongated wedge plate on a clamping
bracket on one end of the pivotal actuating arm with an elonga-
ted clamping side of the wedge plate disposed in spaced apart
relation to an elongated clamping surface on one end of the
clamping bracket for the extension of an elongated safety carr-
ier therebetween. A cam follower surface on one end of the
wedge plate is disposed in ooacting engagement with a camming
member secured to the clamping bracket, with the cam follower
surface extending generally upwardly and inwardly towards the
aforesaid bracket clamping surace. The outer, free end of the
actuating arm is provided with means for attachment to the
safety belt of a workman; and, if a workman falls, a tension
spring connected between the actuating arm and the wedge plate
will pivot the actuating arm outwardly and downwardly with the
result that the inner end of the actuating arm will carry the
wedge plate upwardly against the camming member. The engagement
of a sharply inwardly contoured upper segment of the wedge plate
cam follower surface with the camming member instantly urges the
wedge plate upwardly and inwardly to a clamping position in
engagement with a safety carrier in response to the very
slightest pivotal movement of the outer end of the actuating
arm in a downward direction.
--2--
The aforesaid camming member preferably takes the form
of a pin extending horizontally across the clamping bracket, and
positioned between the wedge plate camming surface and a guide
finger afixed to the wedge plate in paral:Lel, spaced apart
relation to the camming surface. The guide finger assists in
keeping the wedge plate in a uniformly upright position, para-
llel to the safety cable, both during normal vertical movement
of the clamp on the cable, and in the course of clamping move-
ment against the cable.
The pivotal mounting of the actuating arm on the
clamping bracket and the driving association of the inner end of
the actuating arm with the wedge plate in such a way that:the
actuating arm imparts an upward, closing movement to the wedge
plate is particularly advantageous. The upward, frictional
drag of a safety carrier on the wedge plate under free fall con-
ditions tends to draw the wedge plate towards its clamping or
closing position. Thus, with the wedge plate's cam follower
surface positioned between the camming member and the bracket
clamping surface, the frictional force of the safety carrier
will act to pull the wedge ~late tightly between the camming
member and the safety carrier, thereby resulting in more holding
power of the safety clamp on the safety carrier.
To facilitate free, sliding movement of the safety
clamp on a safety carrier such as a cable or rod, a substantial
cleaxance space is provided between the clamping side of the
wedge plate and the safety carrier, when the clamping bracket
is mounted in its position of use on a carrier. Roller assem-
blies on the top and bottom ends of the wedge plate ensure the
free movement of the wedge plate and clamping bracket assembly
up and down a safety cable during normal vertical movement of a
workman.
A particularly advantageous aspect of my improved
safety clamp resides in the provision of an inclined cam guide
--3--
surface on the wedge plate which angles upwardly and outwardly
in a direction away from the clamping side of the wedge plate.
The actuating arm is arranged so that a camminy surface on its
inner end normally bears against the bottom end of -the inclined
cam guide surface. As the outer end of the actuating arm pivots
downwardly under free falling conditions, its inner end will
pivot upwardly and revolve against the wedge plate's inclined
cam guide surface and thereby assist in urging the wedge plate
upwardly and inwardly towards its clamping position in gripping
engagement with a safety carrier.
With the aforesaid upwardly and inwardly extending cam
follower surface formed on the upper end of the wedge plate, the
provision of this latter, inclined cam guide surface on the low-
er end of the wedge plate ensures that the wedge plate will be
maintained in a straight, upright position with its clamping
side parallel to the bracket clamping surface and to a safety
carrier, as the wedge plate is moved to its clamping position.
This mode of operation is further enhanced by the provision of a
contact or camming element in the form of a laterally projecting
pin on the inner end of the actuating arm. This pin normally
bears against the outside edge of the bottom end oE the wedge
plate. As the actuating arm swings downwardly for clamping,
this pin forces the bottom end of the wedge plate inwardly
against the safety cable.
These and other objects and advantages of my invention
will become readily apparent as the following description is
read in conjunction with the accompanying drawings, wherein like
reference numerals have been used to designate like elements
throughout the several views.
30BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a top, plan view of the safety clamp struc-
ture;
--4--
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Fig. 2 is a vertical, section view of the safety
clamp taken along lines 2-2 of Fig. l;
Fig. 3 is a vertical, section view of the safety
clamp, similar to Fig. 3, but with additional portions cut away
and showing the wedge plate of the safety clamp actuated to its
clamping position; and
Fig. 4 is a ve~tical, section view of the safety
clamp taken along lines 4-4 of Fig. 2
DESCRIPTION OF THE PREF_RRED EMBODIMENT
The safety clamp of this invention has been developed
for use by workmen working on ladders, fixed or removable, in
any kind of servicing or work environment at an eleva~ed level.
I anticipate that my improved safety clamp will find particular-
ly widespread application with respect to fixed ladders such as
those mounted on smokestacks, water tanks~ storage tanks, grain
elevators and towers and poles of various kinds. In Fig. 2,
reference numeral 1 designates an upright portion of such a
stack, tank or tower strùcture to which a fixed ladder 2 is
rigidly secured. The vertically spaced ladder rungs are desig-
nated by reference numeral 3. An elongated, vertically extend-
ing safety carrier 4 is positioned adjacent to the ladder, pre-
ferably centrally of the ladder in front of it. Various types
of safety carriers such as ropes, cables and rods may be util-
ized, and such safety carriers are preferably secured at their
bottom ends, as well as at their top ends to serve as a safety
line on which a clamping device affixed to the belt of a workman
may be slidably mounted. In the drawings, safety carrier 4 is
illustrated as a steel cable.
As is shown in Figs. 1, 2 and 4, the safety clamp is
comprised of a clamping bracket generally indicated by reference
numeral 6. Clamping bracket 6 preferably takes the form of an
elongated, U-shaped member as shown having opposedl spaced apart
--5--
side walls ~ and 9 join~d together at one end by an upright/ end
wall segment 10, and open along their opposite endsO The inside
vertically extending surface lOa of end wall segment 10 serves
as an elongated clamping surface which is constructed and
arranged to bear against one side of safety cable 4 with clamp-
ing bracket 6 slidably mounted thereon in an upright position of
use. With clamping bracket 6 so mounted on carrier 4, clamping
surface lOa wi].l extend generally parallel to safety cable 4.
Shiftably supported on clamping bracket 6 between opposed side
walls 8 and 9 is a wedge plate 12. When assembled in its posi-
tion of use as shown, wedge plate 12 will be contained between
clamping bracket side walls 8 and 9 parallel thereto, in an up-
right position. Wedge plate 12 is so mounted on clamping
bracket 6 that the inner, elongated clamping side 14 of wedge
plate 12 extends parallel to clamping surface lOa of bracket 6
in spaced apart relation thereto ao as to accommodate the exten-
sion of safety cable 4 therebetween. A cam follower surface gen-
erally indicated by reference numeral 16 formed on the upper end
of wedge plate 12 is positioned in coacting engagement with a
stationary cam member 18 when wedge plate 12 is mounted in its
normal position of use on bracket 6. For purposes hereinafter
explained, cam follower surface 16 is comprised of a lower,
inclined cam follower surface 16a, and an upper, more sharply
contoured surface segment 16b. Cam follower surface 16 extends
generally upwardly and inwardly from its lower end towards
bracket clamping surface lOa and is disposed between camming
member 18 and bracket clamping surface lOa in the manner shown.
A guide finger 17 is affixed to wedge plate 12 in spaced apart
relation to cam follower surface 16. The base end 17a of finger
17 is attached to wedge plate 12 as an extension thereof as
shown in Figs. 2 and 3. The parallel position and con:Eiguration
of the inner surface of finger 17 with respect to cam follower
surface 16 permits the desired movement of wedge plate 12
--6--
towards safety cable 4 in a manner hereinafter explained.
Camming member 18 preerably takes the form of a cylin-
drical pin mounted transversely on clamping bracket 6 across its
side walls 8 and 9 so as to extend generally horizontally in its
position of use as shown. Camming pin 18 is positioned between
camming surface 16 and guide finger 17, with sufficient clear-
ance space being provided between pin 18 and the inner surface
of finger 17 to avoid interference with the desired clamping
movement of wedge plate 12 against cable 4. For ease of instal-
lation of the entire safety clamp on a safety cable, camming pin18 is removably inserted through apertures in bracket side walls
8 and 9. Pin 18 may be a commercially available holding pin
having a spring loaded detent 18a at one end and an enlarged
head on its opposite end, by means of which it is held in place
on bracket 6. For the purposes of cooperative coaction between
camming member 18 and cam follower surface 16, upper cam follow-
er surface segment 16b is of arcuate shape and conforms to the
shape of cylindrical camming pin 18. With wedge plate 12 in its
rest or release position shown in Fig. 2, upper cam foll~e~r
surface 16b will be positioned in engagement with camming pin
18. Arcuate camming surface 16b is contoured upwardly and
sharply inwardly in a direction towards bracket clamping surface
lOa in the manner shown most clearly in Fig. 3 to provide an
initial, rapid thrust of wedge plate 12 towards cable 4 and
bracket clamping surface lOa as explained below with respect to
the operation of the safety clamp. Lower, inclined cam follower
surface segment 16a also is directed upwardly and inwardly
towards bracket clamping surface lOa, but is contoured less
sharply inwardly towards clamping surface lOa from the vertical
than arcuate surface segment 16b.
Wedge plate 12 is supported on the inner end of an
actuating arm 20 which is removably attached to clamping bracket
6 by means of a pivot pin 22 extending t~ansversely through
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bracket side walls 8 and 9 in a direction parallel ~ camming
pin 18. Like camming pin 18, pivot pin 22 is removable, and is
held in place by a spring loaded detent 22a on one end thereof.
As appears most clearly in Fig. 4, the botlom end of wedge plate
12 is bifurcated to form a pair of spaced apart, downwardly
extending plate segments 12a and 12b. The inner end 24 of
actuating arm 20 is of reduced thickness, and is received
between plate segments 12a and 12b of wedge plate 12, thereby
serving to support wedge plate 12 between pivot pin 22 and
bracket clamping surface lOa.
To ensure positive, driving association between the
inner end of actuating arm 20 and wedge plate 12, these parts
are mechanica.ly linked together by means of a circular aperture
and pin connection 26, 28. Aperture 26 extends through the
inner end 24 of actuating arm 20; and pin 28 extends transverse-
ly through aperture 26, as well as through plate segments 12a
and 12b of wedge plate 12, and is affixed thereto, as appears
most clearly in Fig. 4.
A tension spring 30 is connected between actuating arm
20 and the bottom end of wedge plate 12 as shown in Fig. 3, so
as to normally exert a downward, biasing force on the outer end
of actuating arm 20. Spring 30 is connected between an attach-
ment eye 32 on the bottom of arm 20, outwardly from its pivot
pin connection 22 to wedge plate 12, and a pin 34 secured
between the bottom ends of wedge plate segments 12a and 12b as
shown in Figs. 2 and 4. Spring 34 is sufficiently strong that
under free fall conditions of the entire clamping bracket assem~
bly on cable 4, it will pivot the outer end of actuating arm 20
downwardly about horizontally extending pivot pin 22, with the
result that the inner end 24 of arm 20 will drive wedge plate 12
upwardly towards its closing or clamping position against cable
4 The attachment of actuating arm 20 to pivot pln 22 at a
location between the outer, free end of arm 20 and the location
--8--
of driving association of its inner end 24 with wedge plate 12
through connecting pin 28 ensures that wedge plate 12 will be
driven upwardly in its closing movement towards cable 4, as the
outer end of actuating arm 20 pivots downwardly.
For purposes hereinafter explained, a camming surface
36 is formed on the top edge of inner end 24 of actuating arm
20 and normally bears against the bottom end of an inclined
guide surface 38 formed on wedge plate 12. Inclined guide sur-
face 38 is located at the juncture of the upper ends of wedge
plate bottom segments 12a and 12b at a location below cam
follower surface 16. The upper edge of the inner end 24 of
actuating arm 20 is angled as shown in Fig. 3 to conform to the
slope of inclined cam guide surface 38, and will be disposed
directly thereunder with actuating arm inner end 24 extending
between wedge plate bottom segments 12a and 12b.
A further camming element is provided in the form of a
laterally projecting pin 29 on the inner end of actuating arm
20. Pin 29 extends transversely through arm 20 and is aEfixed
thereto as shown in Figs. 2 and 4. The ~ojecting ends of pin 29
normally bear against the outside edges of the lower ends of
wedge plate bottom segments 12a and 12b. As illustrated in
Figs. 1 and 2, the outer, free end of actuating arm 20 has an
aperture 40 extending therethrough, within which a removable pin
42 is received. The outer end of arm 20 projects outwardly away
from clamping bracket 6 a sufficient distance that it may be
readily received between the spaced apart side walls of a bifur-
cated buckle bracket or clip 44. Connecting pin 42 extends
through the side walls of buckle bracket 44, as well as through
aperture 40 in actuating arm 20 and is held in place to secure
ihese two elements together by means of a spring loacled detent
42a. A belt 46 worn by a workman is extended through aligned
slots 48 in buckle bracket 44, whereby bracket 44 serves as a
means for connecting actuating arm 20, and the entire safety
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clamp assembly to a workman.
In order to ensure uniformly free movemen-t of the
clamp assembly up and down a cable during normal vertical move-
ment by a worXman, a pair of roller assemblies are provided at
the top and bottom ends of wedge plate 12. As is shown most
clearly in Fig. 4, wed~e plate top roller 50 is rotatably
supported on a roller pin 52 extending between laterally spaced,
upper extensions 54 and 56 on wedge plate 12. Lower roller 58
is similarly supported on a pin 60 positioned between spaced
apart plate segments 12a and 12b on the bottom end of wedge
plate 12~ Rollers 50 and 58 are positioned so that they will be
in a direct alignment with safety cable 4. If either end of
wedge plate 12 is canted into contact with cable 4 during normal
vertical movement of the clamp assembly, free and unimpaired
movement of the clamp assembly on ~e cable is ensured by rollers
50 and 58. The use of such rollers is particularly beneficial
in allowing the clamp assembly to move freely up and down
corroded cables, and different types of cables. It is to be
noted that fixed pins can be used in place of removable pins 18
and 22 to provide a fixed rather than a portable safety clamp
assembly. With such a fixed clamp, rollers as described above
could be provided on the clamp bracket 6 between side walls 8
and 9, rather than on wedge plate 12.
Undesired lateral movement of the wedge plate within
the clamping bracket is limited by laterally projecti.ng protru-
sions on the opposite sides of the wedge plate. These protru-
sions preferably take the form of spherical segments 62 and 64
which bear lightly against the opposed inside faces of clamping
bracket side walls 8 and 9. The tendency of the wedge ~late to
shift or cant laterally within the clamping bracket due to inter-
action of the wedge plate with cable 4/ and resultant bind.ing
between the wedge plate 12 and clamping bracket 6, is precluded
by projections 62 and 64. The spherically rounded outer ends of
--10--
these projections ensure minimum frictional contact with bracket
side walls 8 and 9 and smooth, unrestricted clamping movement of
wedge plate 12 in response to actuation by arm 20.
In operation, clamping bracket 6 is slidably mounted on
safety carrier 4 at a desired vertical location of use, by slip-
ping the U-shaped bracket 6 over safety cable 4 with cable 4
extending between bracket side walls 8 and 9. The wedge plate
and actuating arm assembly 12~ 20 is then inserted between the
bracket side walls 8 and 9, these parts being held together by
connecting pin 28. Wedge plate 12 and actuating arm 20 are held
in place in their release or open positions shown in Fig. 2 by
inserting camming pin 18 and pivot pin 22 in place through the
hracket side walls. In this release position, wedge plate 12
will be spaced outwardly from safety cable 4 to provide a clear-
ance space therebetween as shown in Fig. 2. With actuating arm
20 attached to the belt 46 of a workman through pin 42 and
buckle 44, clamping bracket 6 will be free to slide up and down
on cable 4 as the workman moves up and down on a ladder. When
the workman is climbingj the upward movement of his body tends
to pivot the outer end of actuating arm 20, through its connec-
tion with buckle 44 and the workman's belt 46, thereby holding
arm 20 in its horizontal, release position against the downward
bias of tension spring 30. As the workman descends the ladder,
the entire clamping bracket assembly, including actuating arm
20, will drop together along safety cable 4; and the attachment
of actuating arm 20 to the workman's belt will resist the force
of spring 30 tending to pivot arm 20 downwardly towards its
closing or clamping position. Finger 17 and camming pin 29 com-
bine to prevent any pivotal movement of the top and bottom ends
of wedge plate 12 away from vertical alignment with cable 4
during normal movement of the clamp assembly up and down the
cable~ Finger 17 resists the tendency of wedge plate 12 to
shift or swing inwardly towards cable 4, and pin 29 prevents
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outward movement of wedge plate 12 away from cable 4 during
such normal use. This wedge plate restraining and guiding
function of finger 17 and pin 29, in cooperation with rollers
50 and 58, ensures free movement of the clamp assembly up and
down cable 4.
If, however, the workman should fall or ~herwise lose
control, the safety clamp will instantly lock onto safety cable
4, thus supporting the workman and preventing a fall. The rota-
tion of the outer end of actuating arm 20 downwardly is caused
by the weight of the workman being applied at the outer end of
arm 20 through his safety belt 46 and belt clip or buckle 44
In the case of a free fall, during which all of the components
of the safety clamp assembly would normally fall together under
the force of gravity, tension spring 30 imparts an unbalanced
force to the outer end of arm 20 in a downward direction. As
the outer end of arm 20 pivots downwardly about pivot pin 22,
the inner end 24 of arm 20 pivots upwardly, thereby driving
wedge plate 12 upwardly between camming pin 18 and safety cable
4. Because of the fact that upper cam follower surface segment
16b is contoured sharply inwardly towards cable 4, the slightest
upward motion of wedge plate 12 in response to the pivotal move-
ment of actuating arm 20 in its closing direction, will cause
wedge plate 12 to instantly move across the clearance space
between its clamping side 14 and carrier 4 into secure, clamping
engagement with safety cable 4. As wedge plate 12 continues to
move upwardly under the impetus of actuating arm 20, the engage-
ment of upwardly and inwardly inclined cam follower surface seg-
ment 16a with camming pin 18 will force wedge plate 12 tightly
against safety carrier 4 As a result, carrier 4 is tightly
clamped between clamping surface lOa of clamping bracket 6 and
clamping side 14 of wedge plate 12 along the length of these two
clamping sur~aces. Moreover, since wedge plate 12 moves in an
upward direction during its closing motion, the frictional drag
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of safety cable 4 on wedge plate 12 will tend to pull it even
more tightly into clamping engagement with cable 4. This
achieves particularly strong holding power for the saety clamp
on cable 4.
It is to be noted that cam follower surface 16 is
formed along the upper end o~ wedge plate 12, and thus tends to
move the upper end of wedge plate 12 upwardly and inwardly
towards safety carrier 4 by engagement with camming pin 18. The
coaction of camming surface 36 on the inner end 24 of actuating
arm 20 with inclined cam guide surface 38 during the closing
movement of wedge plate 12, ensures that its lower end will move
upwardly and inwardly uniformly with its upper end. As the
inner end 24 of actuating arm 20 pivots upwardly under free fall
conditions, its camming surface 36 will revolve against inclined
guide surface 38. Since cam guide surface 38 inclines upwardly
and outwardly as shown, the engagement of camming surface 36
therewith will assist in urging wedge plate 12 upwardly and in
wardly along its entire length in a uniform manner, in combina-
tion with the coaction between camming surface 16 and camming
pin 18. Moreover, camming pin 29 on the inner end of arm 20
will be urged against the bottom end of wedge plate 12 as the
inner end 24 of arm 20 swings upwardly. This provides a fur-
ther, positive driving force urging the lower end of wedge
plate 12 against cable 4. As a result, wedge plate 12 is main-
tained in the upright position shown with its clamping side 14
parallel to bracket clamping surface lOa at all times as it
moves from its release position of Fig. 3 to its clamping posi-
tion shown in Fig 4.
It is also to be noted that aperture 26 in inner end
24 of actuating arm 20 provides sufficient clearance space with
connecting pin 28 extending there-through to permit the necessary
shifting movement of wedge plate 12 towards cable 4 and bracket
clamping surface lOa. This particular manner of mechanically
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linking actuating arm 20 and wedge plate 12 further ensures
that wedge plate 12 wlll be able to move upwardly and inwardly
in a uniform manner over its entire length and thereby remain in
an upright position parallel to cable 4 ancl clamping surface
lOa as actuating arm 20 drives it into its clamping position.
As this actuating pivotal movement of arm 20 takes place, the
relatively large clearance space between arm aperture 29 and
wedge pin 28 allows the camming nose 36 of arm 20 to maintain
contact with inclined surface 38 on wedge plate 12,
Those skilled in the art will appreciate tha-t the safe-
ty clamp described and shown herein provides a particularly
rapid response and very strong clamping action in frictional
engagement with a safety carrier under free fall conditions
which might be encountered by a workman falling from a ladder.
Rollers 50 and 58 improve the ability of the clamp assembly to
move freely up and down a safety cable. It is contemplated
that these rollers could be provided with a radiused, concave
surface conforming generally to the shape of the safety cable or
rod. This would permit the rollers to directly track on the
safety cable to further ensure that neither the wedge plate 12
or the clamping bracke-t 6 deviate from an upright position in
alignment with the cable during normal use. Although I have
described my improved safety clamp with respect to a particular,
preferred embodiment thereof, I anticipate that various changes
may be made in the size, shape and operation of the various
components of the safety clamp without departing from the spirit
and scope of my invention as defined by the following claimsO
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